Tin-based nanomaterials for electrochemical energy storage

Abstract

Electrochemical energy storage has received a lot of attention due to the common recognition of sustainable development. Nanomaterials are ideal candidates as electrode materials in different fields of energy storage devices, offering favorable transport features, high surface to volume ratio and excellent physicochemical properties. This review is focused on the recent progress in nanostructured Sn-based electrode materials, including Sn, Sn alloys, Sn oxides (SnO_x, x = 1, 2), dichalcogenides (SnS_x, x = 1, 2) and oxysalts for lithium/sodium-ion batteries and supercapacitors. Sn-based compounds, including SnO, SnO₂, MSn_xO_y (M = Co, Ca, Zn, Mo; x = 1, y = 3), SnS, SnS₂, Sn₃P₄, SnC₂O₄, SnP₂O₇, etc., and their composites, possess various valence states and exhibit rich chemistry. They are very attractive candidates for efficient electrochemical energy storage systems because of their unique physicochemical properties, such as conductivity, mechanical and thermal stability, and cyclability. In this review, we aim to provide a systematic summary of the synthesis, modification, and electrochemical performance of nanostructured Sn-based compounds, as well as their energy storage applications in lithium/sodium-ion batteries (LIB/SIB), and supercapacitors. The relationship between nanoarchitectures and electrochemical performances, as well as the related charge-storage mechanism is discussed. Moreover, remarks on the challenges and perspectives of Sn-containing compounds for further development in electrochemical energy storage applications are proposed. This review sheds light on the sustainable development of advanced rechargeable batteries and supercapacitors, with a focus on Sn-based nanomaterials.

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Mingming Zhao

Mingming Zhao is a student at Yangzhou University, under supervision by Professor Huan Pang. She focuses on nanomaterials for energy storage, like supercapacitors.

Qunxing Zhao

Qunxing Zhao is currently a graduate student under supervision by Professor Huan Pang at Yangzhou University, and Professor Wen-Yong Lai at the Institute of Advanced Materials (IAM), Nanjing University of Posts and Telecommunications. His current research focuses on one dimensional silver nanomaterials and their composite and flexible thin film electrodes for energy-storage devices, like supercapacitors.

Jiaqing Qiu

Jiaqing Qiu is a student at Yangzhou University under supervision by Professor Huan Pang. She focuses on nanomaterials for energy storage, like supercapacitors.

Huaiguo Xue

Huaiguo Xue received his Ph.D. degree in polymer chemistry from Zhejiang University in 2002. He is currently a professor of physical chemistry and the dean of the College of Chemistry and Chemical Engineering at Yangzhou University. His research interests focus on electrochemistry, functional polymers and biosensors.

Huan Pang

Huan Pang received his Ph.D. degree from Nanjing University in 2011. He then founded his research group in Anyang Normal University, where he was appointed as a distinguished professor in 2013. He has now joined Yangzhou University as a university distinguished professor. He has published more than 90 papers in peer-reviewed journals, including Chemical Society Reviews, Advanced Materials, Energy Environ. Sci., with 3500 citations (H-index = 31). His research interests include the development of inorganic nanostructures and their applications in flexible electronics, with a focus on energy devices.

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1. Introduction

Nowadays, the increasing environmental problems, such as global warming and pollution, provide great impetus for the reduction of the society's dependence on fossil fuels; it is preferable to produce energy from renewable and sustainable resources. The utilization of electricity generated from intermittent renewable sources requires efficient energy storage systems (ESSs). Among clean energy technologies, electrochemical ESSs are considered the most feasible, environmentally friendly, and sustainable. Electrochemical ESSs such as rechargeable batteries (LIB/SIB) and supercapacitors have been widely used in portable electronics, electric vehicles, and smart electrical grids.

Nanomaterials, with attractive chemical and physical properties, are being explored for their potential in energy storage applications. The design and creation of new materials and substances that are chemically modified from the molecular and atomic level, to sizes on the nanoscale, would offer significantly enhanced functions for energy storage applications. During the past decades, much effort has been particularly devoted to fabricating a great number of nanostructured materials as electrodes in a range of LIBs, SIBs and supercapacitors. This research trend has been evidenced by many important pioneering studies published during the past decades. As expected, a notable improvement in performance has been achieved through recent advances in the development of advanced nanostructured materials and understanding of charge storage mechanisms. In batteries and supercapacitors, the nanostructuring of electrode materials may reduce diffusion/transport lengths for both ions and electrons, increase active sites, and relieve the volume expansion/contraction, thus leading to improved capacity, and higher power/energy density, and a longer cycle life. In some cases, new thermodynamics and/or kinetics allow enhanced phase transitions and rate capabilities during Li⁺ intercalation–deintercalation. It is believed that new developments in the field of nanomaterial chemistry hold the key to further breakthroughs in ESSs.^155,254

Recent progress has demonstrated that Sn-based nanomaterials are very promising candidates for ESSs because of their unique physical and chemical properties, such as conductivity, mechanical and thermal stability. Sn is also inexpensive (roughly 20 dollars per kilogram), relatively safe to work with as a powder (not extremely pyrophoric), nontoxic, and highly abundant. The use of Sn@C, SnO₂@C nanocomposites has been primarily investigated as an effective strategy. The carbonaceous materials are used not only as effective buffer zones to minimize the volume changes, but also as conductive phases to alleviate the low electrical conductivity and poor electrochemical stabilities of pure Sn based materials, resulting in enhanced cycle stability and rate capability. In this review, we present a summary on the synthesis, modification, and electrochemical performance of Sn-based nanomaterials. Also, their energy storage applications in the fields of LIBs, SIBs and supercapacitors are emphasized. The relationship between nanoarchitectures and electrochemical performances, as well as related charge-storage mechanisms is discussed. This review ends with an outlook on Sn-containing compounds for further progress in electrochemical energy storage applications.

2. Li-ion batteries

2.1 Sn

2.1.1 Pure Sn. New anode materials with higher theoretical capacities have been exploited, such as Sn-based materials (∼992 mA h g⁻¹), Si-based materials (∼4200 mA h g⁻¹), Co₃O₄ (890 mA h g⁻¹), and Fe₃O₄ (928 mA h g⁻¹). Among them, metallic tin (Sn) receives considerable attention for its advantageous properties, such as high theoretical capacity, high tap density, and safe thermodynamic potential. Sn is a promising option for high-capacity anode materials upon undergoing the Li-alloying/de-alloying reaction, due to its high theoretical gravimetric and volumetric capacities, according to the Li_4.4Sn stoichiometry in the fully lithiated state.¹ To date, various Sn nanostructures, such as nanoparticles, nanowires and nanosheets have been developed.^2–4 Nevertheless, the practical application of Sn anode materials in Li-ion batteries (LIBs) is still restricted because of the low intrinsic electrical conductivity of Sn and the huge volumetric expansion and aggregation of Sn nanoparticles (NPs) during lithium alloying and dealloying processes, which lead to severe degradation of the electrodes upon cycling and dramatically shorten the cycle life of the Sn electrode. Besides, the mechanical stress induced by the severe volume variation (>300%) that occurs upon full lithiation and de-lithiation of Sn ultimately leads to a loss of Sn as a malleable, ductile, and highly crystalline metal.^5,6 Generally, lithiation and de-lithiation occur reversibly, according to the following eqn (1):

xLi + xe⁻ + ySn ↔ Li_xSn (1)

2.1.2 Sn@C. Sn undergoes large volume changes upon lithium alloying and de-alloying.⁷ This well-known phenomenon leads to pulverization of the active material and loss of contact with the current collector, eventually resulting in rapid capacity fading upon cycling. In order to address this challenge, there are several approaches involving the generation of not only porous nanostructures of Sn, but also Sn@C, such as Sn@CNFs, Sn@graphene, Sn@C/graphene, Sn/CNTs/graphene.^8–15

Among the various structures of Sn/C nanocomposites, the most attention is paid to one dimensional (1D) core–shell nanomaterials consisting of Sn nanomaterials as core and carbon layers as shell.^16–19 The roles of carbon in the unique core–shell structure have been proposed as follows: (1) limiting the volume expansion and stabilizing the structure; (2) increasing the electrical conductivity; (3) protecting the nanomaterials from damage in various working environments. These core–shell nanomaterials can be produced via in situ methods. Li et al. reported the in situ synthesis of Sn nanowires encapsulated in amorphous carbon nanotubes. Deng and Lee also presented the fabrication of rambutan-like tin–carbon nanocomposites, via an ex situ method. The optimized thickness of carbon layers can help to approach the better performance of the anodes. Therefore, combining Sn that has a high capacity, with carbon having a good cycling behavior, can yield synergetic results. Another effective way to enhance the performance is by decorating Sn nanoparticles in the 2D or 3D nanomaterials using various methods, such as electroless plating, ball milling, fluidized-bed chemical vapor deposition (CVD), spray pyrolysis, solid-state reaction, and microwave-plasma CVD (MPCVD). These composite nanostructures suppress the volume expansion of the Sn nanoparticles during the charge/discharge cycles with the unique property of the 2D network of favoring both the electronic and ionic charge transport during the cell operation. The composite anode has shown outstanding electrochemical performance in terms of reversible capacity (and of a relatively low irreversible capacity), rate capability and cycle life, which have been evaluated in very demanding charge/discharge conditions.^20–27

2.1.3 Sn@others. Sn can composite with other materials, including titanium dioxide and conducting polymers, not only to prevent the aggregation of Sn but to also serve as a buffer scaffold.^28–36 TiO₂ has a small volume expansion ratio (3%) upon intercalation/extraction of Li-ions, exhibiting good cyclic stability.^28,245,248 Li et al. scrupulously designed a robust, porous 1D TiO_2−x–carbon (TiO_2−x–C) substrate to encapsulate Sn nanoparticles, as shown in Fig. 1a, in which the firm TiO_2−x–C substrate can fully absorb the volume expansion of the Sn nanoparticles in the TiO_2−x–C substrate during the charging–discharging processes, as shown in Fig. 1a. The porous TiO_2−x–C–Sn nanofibers exhibit a high capacity of 957 mA h g⁻¹ after 200 cycles at 0.1 A g⁻¹ and can cycle over 10 000 times at 3 A g⁻¹ while retaining 82.3% of their capacity, which represents the longest cycling life of Sn-based anodes for LIBs so far.²⁹

Fig. 1 (a) Schematic illustration of the formation of highly stable porous TiO_2−x–C–Sn composite nanofibers and insertion of Sn nanoparticles. (b) SEM images of 3D Sn/PPy composite network. (c) TEM images of Sn nanoparticles highly dispersed and embedded in PPy nanosheets. (d) Electrochemical cycling performance and (e) coulombic efficiency of the 3D Sn/PPy electrode, Sn@PPy/PVDF electrode, and Sn/PVDF electrode at a charge–discharge current of 200 mA g⁻¹. Reproduced with permission ref. 29. Copyright 2014 American Chemical Society (a). Reproduced with permission ref. 37. Copyright 2014 Springer (b–e).

In order to optimize the electrode system of lithium-ion batteries for problems such as lithium ion diffusion, electron transportation, and large volume changes during cycling processes, judicious combinations of conducting polymers, such as polyaniline,¹⁵⁴ polypyrrole (PPy), with selected metals with tailored structures as anode materials are fascinating, due to their underlying synergistic effects and simple fabrication procedures.^30–34 Fan et al. designed and synthesized a novel anode material composed of ultrafine Sn nanoparticles (5 nm) anchored inside a well-connected three-dimensional (3D) PPy nanosheet network through a simple microemulsion-based preparation of tin nanoparticles with organic crystal surface-induced PPy polymerization, as shown in Fig. 1b–e. The PPy network acts as both binder and conductive matrix for the dispersion of Sn nanoparticles. It is capable of forming a conformal coating that tightly binds Sn nanoparticles with the current collector, and can serve as a geometrical coating to insure the structural and interfacial stability of tin nanoparticles during cycling. Furthermore, the distinct 3D ultrathin PPy nanosheet network with large surface area can provide a stable support for the high dispersion of Sn nanoparticles, as well as the highway for electron/Li⁺ transport. Using the designed 3D Sn/PPy electrode, outstanding electrochemical performance has been achieved, such as stable reversible capacity, high coulomb efficiency, and superior rate capacities upon increased currents, as shown in Fig. 1b–e.^35–37

2.2 Sn–M (M = Co, Ni, Cd, Zn, Fe)

Sn-alloys possess high theoretical capacities and fast charge/discharge rates, making them very promising, high specific energy anode materials for LIBs. Advanced alloy anodes have been developed with a long cycle life of over 300 cycles and a reversible capacity of 500–700 mA h g⁻¹. The capacity fade rates of these alloy materials are as low as 0.07% per cycle. Simultaneously, the first-cycle irreversible capacity loss of alloy anodes can be reduced to 50–100 mA h g⁻¹, corresponding to a high initial coulombic efficiency of ∼90%. The cause of first cycle capacity loss has been attributed to (a) a loss of active material, (b) SEI formation, (c) Li trapping in the host alloy, (d) reaction with oxide impurities and (e) the aggregation of active particles. The approaches used for improving the cycling performance of alloy anodes include (a) multiphase composites, (b) porous anode structures, (c) reducing active particle size, (d) intermetallic phases, (e) thin-film and amorphous alloys, (f) hollow nanoparticles.^38–48 Qin synthesized a 3D hybrid Sn–Ni@PEO nanotube array as a high performance anode for a lithium-ion battery, through a simple one-step electrodeposition method, for the first time. As shown in Fig. 2a, the electrode morphology is well preserved after repeated Li⁺ insertion and extraction, indicating that the positive synergistic effect of the alloy nanotube array and 3D ultrathin PEO coating could authentically optimize the current volume-expansion electrode system. As shown in Fig. 2c, the electrochemistry results confirm that the superiority of the Sn–Ni@PEO nanotube array electrode could largely boost durable high reversible capacities and superior rate performances, compared to the Sn–Ni nanowire array.^49,50 Hou embedded Sn@Ni₃Sn₄ into nanocable-like carbon hybrids through a novel gas-phase route. The introduced Ni₃Sn₄ layer not only suppresses the tin-induced volume expansion, but also provides more voids and vacancies in the interior of the nanocables. The hybrids exhibit a long cycle life (360 mA h g⁻¹ at 1 A g⁻¹ after 1500 cycles).^51–54 Leibowitz synthesized FeSn₂–TiC nanocomposite alloy anodes by a mechanochemical process. The FeSn₂–TiC alloy shows an initial gravimetric capacity of 511 mA h g⁻¹ (1073 mA h cm⁻³) with a first-cycle coulombic efficiency of 77%, as shown in Fig. 2b. The TiC buffer matrix in the nanocomposite anode accommodates the large volume change occurring during the charge–discharge process and leads to good cyclability, compared to similar Sn-based anodes.^55–58

Fig. 2 (a) Schematic illustration of the formation of the Sn–Ni@PEO nanotube array. (b) HRTEM images of the as-synthesized FeSn₂–TiC electrode powder, showing a lower magnification image of a ∼100 nm agglomerate, with the inset showing the diffraction pattern. (c) Cycle performance of the Sn–Ni@PEO nanotube array and Sn–Ni nanowire array in the electrode potential range of 0.01–2.0 V (vs. Li/Li⁺) at 0.2 A g⁻¹. Reproduced with permission ref. 50. Copyright 2014 Royal Society of Chemistry (a and c). Reproduced with permission ref. 55. Copyright 2015 Elsevier (b).

2.3 SnO₂

2.3.1 Pure SnO₂. Nanostructured SnO₂ with a high theoretical gravimetric lithium storage capacity of 782 mA h g⁻¹ and low potential of Li-ion intercalation has been considered as an attractive replacement for the graphite anodes. However, the SnO₂ anode electrode suffers severe mechanical disintegration, due to the drastic volumetric changes during lithium ion insertion and extraction, and therefore leads to the rapid deterioration in capacity. Large improvement attempts have been focused on controlling the volumetric change by using nano-sized SnO₂ particles with various morphologies, such as hollow nanospheres, nanowires, nanocolloids, mesoporous structures and nanobelts. These materials have been proven to exhibit better electrochemical performance, suggesting that structure modification could be an effective solution to enhance the electrochemical performance.^59–70

2.3.2 MSnO₃ (M = Co, Ca, Cd, Na, Zn). MSnO₃ are synthesized with different structures, such as nanoboxes, yolk–shell hollow microcubes and nanotubes.^71–77 Lou developed a new type of hybrid nanostructure, a carbon coated hollow nanostructure of amorphous complex metal oxides, for highly reversible lithium storage, as shown in Fig. 3a and b. This unique structure well integrates three main design principles and is anticipated to manifest excellent lithium storage performance because of the superior structural advantages, as shown in Fig. 3c and d.^71,72 Amorphous ZnSnO₃ double-shell and yolk–shell hollow microcubes were synthesized by the calcination of their corresponding ZnSn(OH)₆ precursors, pre-prepared through a facile chemical solution method in argon. The as-prepared amorphous ZnSnO₃ double-shell hollow microcubes have an average edge length of 1.6 μm.^73–77

Fig. 3 (a) FESEM images of CoSnO₃@C nanoboxes; (b) a uniform carbon coating layer on the surface of CoSnO₃ nanoboxes; (c) comparative cycling performance of CoSnO₃ nanoboxes with and without carbon coating, CoSnO₃ nanocubes, crystalline Co–Sn–O nanoboxes and commercial SnO₂ particles; (d) rate capability of CoSnO₃ nanoboxes, with and without carbon coating, obtained between 0.01 and 1.5 V at various current densities. Reproduced with permission ref. 71. Copyright 2013 Royal Society of Chemistry (a–d).

2.3.3 M-doped SnO₂ (M = Mo, Fe, Cu). Dopants favor the reversible formation of lithium oxide, thus, enabling the beneficial combination of lithium storage by alloying and conversion. This value is slightly higher than that obtainable by the alloying process of Sn present in the material. Compared to SnO₂, Mo-doped SnO₂ showed a lower first cycle reversible capacity, but improved capacity retention when cycled in a rather narrow voltage range (0.0–1.0 V), which was assigned to decreased crystallite growth upon synthesis and a favored dispersion of the electrochemically active metallic Sn, formed upon the first lithiation.⁸³ Doping SnO₂ with Fe leads to a significantly enhanced specific capacity, cycling stability, and coulombic efficiency. After ten cycles, SFO-C exhibits a reversible specific capacity of 1519 mA h g⁻¹, which is about twice that of pure SnO₂.⁸⁴

2.3.4 SnO₂@M (Ni, Mo, Fe). The SnO₂/metal composites exhibit a high reversible capacity, stable cycling performance and superior rate capability, benefiting from high electron transport and fast ion diffusion. Jiang developed a porous Ni/SnO₂ composite electrode composed of homogeneously distributed SnO₂ and Ni nanoparticles; the reaction kinetics of SnO₂ is greatly enhanced, leading to a full conversion reaction, superior cycling stability and improved rate capability. The uniformly distributed Ni nanoparticles provide a fast charge transport pathway for electrochemical reactions, and restrict the direct contact and aggregation of SnO₂ nanoparticles during cycling. In the meantime, the void space among the nanoclusters increases the contact area between the electrolyte and active materials, and accommodates the huge volume change during cycling as well. The Ni/SnO₂ composite electrode possesses a high reversible capacity of 820.5 mA h g⁻¹ at 1 A g⁻¹ up to 100 cycles.^84,85 Tin titanate nanowires, coupled with SnO₂ nanoparticles have been prepared by combining the hydrolysis of the Sn(II) precursor with tin-to-hydrogen ion exchange using layered hydrogen titanate nanowires as conformal templates under hydrothermal conditions. This synthetic strategy allows for the incorporation of electrochemically active Sn into the layered titanate and simultaneous deposition of SnO₂ nanoparticles on the as-prepared tin titanate nanowires. The tin titanate nanowires coupled with SnO₂ nanoparticles showed improved cycle performance and increased lithium storage capacity, as compared to mesoporous SnO₂ nanoparticle aggregates and hydrogen titanate nanowires. The SnO₂ nanoparticles supported on tin titanate can buffer the large volume changes during the Li–Sn alloying and dealloying process in flexible layered titanate nanostructures with large interlayer distances.⁸⁶

2.3.5 SnO₂@M_xO_y (Fe, Ni, Mn). Hybridizing tin oxide with transition metal oxide can effectively activate the irreversible capacity because the transition metal nanoparticles in the composites can reversibly convert extra Li₂O to Li⁺.^87,88 Yu et al. prepared SnO₂–CuO–Li₂O film with multideck-cage porous morphology, which showed a high reversible capacity (1158.5 mA h g⁻¹) and only an initial capacity loss of 17.6% at 0.5C. Du et al. demonstrated that Fe₂O₃ (ref. 255 and 256) @SnO₂@C porous core–shell nanorods showed high initial coulombic efficiency (73%), high reversible capacity (995.4 mA h g⁻¹ at 0.2 A g⁻¹), and good cycling performance.⁸⁹ Yuan designed and synthesized a quaternary hierarchical nanocomposite (rGO-Fe₃O₄–SnO₂–C); Fe₃O₄ and SnO₂ nanoparticles were uniformly dispersed on the rGO nanosheets and fully encapsulated by the outmost carbon layers, forming a sandwich-like buffering structure for excellent dimensional integrity. It exhibited a reversible capacity of 868.6 mA h g⁻¹ after 100 cycles at a current density of 200 mA g⁻¹.⁹⁰ For CoO-in-CoSnO₃, Co₂(OH)₂CO₃ nanowires were first obtained by a hydrothermal method and then deposited with ALD SnO₂. The CoO wire-void-CoSnO₃ tube was formed with the decomposition of Co₂(OH)₂CO₃ and its simultaneous reaction with the outer SnO₂ layer. In this unique wire-in-tube structure, both CoO and CoSnO₃ are promising materials for lithium ion battery anodes with high theoretical capacities, and the porous and hollow feature is essential for better electrode/electrolyte contact, shorter ion diffusion path and better structure stability. Enhanced rate capability and cycling stability have been demonstrated with the structure, showing its promising application for the anode material of lithium ion battery.^78–82

2.3.6 SnO₂@non-metal. A variety of nanostructured tin oxides/carbon composites with peculiar morphologies, such as yolk–shell, nanochains, nanorods/GS and NSs/graphene structures have been synthesized.^{73,74,78–81} They all exhibited better lithium storage and cycling performance as anode materials for LIBs, which can be attributed to the fully synergistic effects of nanostructured tin oxides and the highly flexible and good conductive carbon. The carbon component of tin oxides/carbon composites can partly accommodate the volume change of tin oxides, prevent tin oxides from aggregation and pulverization, prevent continual formation of the SEI film, ensure the electrode integrity during prolonged cycling processes, enhance the electronic conductivity of the overall electrode and further facilitate electron and ion transport throughout the electrode.^93–100 For example, Zhang et al. reported that chemically anchored SnO₂ nanoparticles on both sides of rGO, retained a specific capacity of 558 mA h g⁻¹ after 50 cycles at a current density of 264 mA g⁻¹, indicating a capacity loss of 0.6% per C–D cycle.^101–103 The SnO₂/CNTs hybrid has been prepared by several groups with different kinds of methods.^104–107 Fairly scattered tin dioxide nanocrystals serve as highly active sites for lithiation and delithiation, while the CNTs provide a flexible support for loading tin dioxide nanocrystals and highways for lithium ion and electron transport. These composites exhibit similarly decreasing cycling performance, with no more than 200 cycles. Although Lee et al., Zhang et al., and Kim et al. accomplished stable cycling by complex electrode design, those so-called elaborate nanostructures still exhibit deficiencies in achieving recoverable initial reversible capacity, suffering from large rates.^99,108–110 Conducting polymers have been introduced to improve the anode performance in LIBs.^111–113 In addition to improving electron conductivity, the soft polymer matrix can also relax the internal stress of solid particle anodes that suffer from severe volume change during charge–discharge cycles.^114–116 SnO₂ particles covered by PPy demonstrated improved cycling performance, compared to the standalone SnO₂ nanoparticles.^116–118 The SnO₂-PPy hybrid nanowires were synthesized in a one-step process by a simple electrochemical method. Over 200 cycles, the hybrid nanowires showed superior cyclic performance and a charge capacity higher than 0.307 mA h cm⁻², because the polypyrrole matrix effectively prevented agglomeration of the SnO₂ nanoparticles and acted as an elastic buffer to mitigate volumetric changes in the nanoparticles.^117,118

To improve the cycling characteristics of the pure SnO_x (such as SnO₂) thin film anodes, an efficient method was carried out by adding P₂O₅ to increase the number of spectator atoms to constitute the matrix. The high specific capacity of 136 mA h cm⁻² was maintained after 300 cycles, and they showed cycle stability for 300 cycles with a very high current. In the case of Sn₂P₂O₇, the amorphous solid had better performance than the crystalloids. It showed lower initial irreversible discharge capacity and higher reversible capacity.^91,92 Zhang synthesized core–shell nanostructured composite material consisting of nano-Si as the core and SnO₂ as the shell by a sol–gel method. The partial reversible reaction between Li and SnO₂ during the first cycle was identified, and the reactivity of the Si core was investigated by ex situ analyses. The nano-Si/SnO₂ core–shell nanostructured electrode showed a reversible capacity of 1000 mA h g⁻¹ and good cycle retention, close to 80% of the first charge capacity over 50 cycles.^119,120

2.4 SnS₂

2.4.1 Pure SnS₂. SnS₂ is a promising material, due to a high surface area (which can increase ion uptake and lead to higher capacities) and a crystal structure conducive to repeated Li-ion insertion and de-insertion, without a significant loss of capacity. In the crystal structure, octahedral coordinated Sn atoms are sandwiched between two layers of sulfur atoms, hexagonally close packed through strong Sn–S covalent bonds to form triple layers. The adjacent triple layers of SnS₂ are attached via weak van der Waals interactions. During charge/discharge, Li-ions can easily undergo insertion/deinsertion between these layers, which are stacked together through the van der Waals gap. Thus, the layered material can minimize the volume change during the charge/discharge process and facilitate the transport of lithium ions. The electrochemical reactions of SnS₂ with lithium are expressed in the following two step reactions (2) and (3).

SnS₂ + 4Li⁺ + 4e⁻ → Sn + 2Li₂S (2)

Sn + xLi⁺ + xe⁻ ↔ Li_xSn (0 ≦ x ≦ 4.4) (3)

During the initial discharge process, SnS₂ reacts with Li⁺ ions and converts to active Sn and Li₂S, and metallic Sn is embedded within the inert matrix of Li₂S. In the subsequent step, metallic Sn further reacts with Li⁺ ions to form the Li_4.4Sn alloy, which can be reversibly converted into Sn and Li⁺ during charging (dealloying). It is the second step that involves a large volume expansion of about 300%. At the same time, it is stipulated that Li₂S serves as the buffering domain during Li–Sn alloying/dealloying, thereby reducing the volume variation and capacity fading by maintaining electrode integrity. It provides an ion-conducting medium for Li-ion migration and prevents the aggregation of the nanosized Sn metal particles formed in the first step. However, during repetitive cycling, the buffering effect of Li₂S becomes inefficient, due to the enormous volume variation, and therefore the Sn particle aggregation is no longer contained and this manifests in fast capacity fading. Different strategies have been employed to minimize this volume variation. One strategy involves controlling the morphology of the compound by forming porous structures; so far, various nanostructured morphologies, such as nanorods, nanobelts, nanosheets and 3D nanoflowers have been reported.^121–139 The main advantages of porous nanostructured materials are large surface area and large pore sizes, which can easily accommodate the volume expansion. Further, short diffusion path lengths and large contact areas between the electrode and the electrolyte can increase the rate capability of the active material.

Among the various nanostructured morphologies, the 3D hierarchical structures formed by self-assembly offer a large surface area and high porosity and are ideal for minimizing the pulverization of the electrode. Jana et al. reported an ionothermal synthesis method, where hierarchical flower-like assemblies composed of 2D nanosheets of SnS₂ were obtained;^140,142 the nanostructure showed an average discharge capacity of 458 mA h g⁻¹ after 50 cycles. Wu et al. prepared layer-stacked hexagonal tin disulfide (SnS₂) nanorods by using tetragonal tin (Sn) nanorods as sacrificial templates and silica (SiO₂) as nano-reactors.¹⁴¹ The SnS₂–SiO₂ nanorod electrode retained a capacity of 536 mA h g⁻¹ after 25 cycles in the potential range of 0.01–1.15 V at a current density of 200 mA g⁻¹. Zhai et al. prepared ultrathin hexagonal SnS₂ nanosheets by a hydrothermal method using tin(IV) chloride and thioacetamide.¹⁴³ The SnS₂ nanosheets exhibited a high discharge capacity of 513 mA h g⁻¹ after 50 cycles at a current density of 100 mA g⁻¹. A solvothermal synthesis of 1D layered SnS₂ ultralong nanobelts was carried out by Wang et al., using SnCl₄, CS₂ and ammonia reagents; the nanobelts showed a capacity of 560 mA h g⁻¹ at a 0.1C rate between 0.01 to 2 V.¹⁴⁴ Sun et al. prepared 2D SnS₂ nanoplates and this material showed a very high capacity and even after 30 cycles, it retained a capacity of 583 mA h g⁻¹ at a current density of 323 mA g⁻¹ between 0.001 to 1.1 V.¹⁴⁵ Jiao et al. synthesized a 3D flower-like SnS₂ hierarchical architecture by a simple solvothermal method using SnCl₄ and CS₂ in ethanol.¹⁴⁶ The electrode exhibited a specific capacity of 549.5 mA h g⁻¹ at a current density of 100 mA g⁻¹ after 100 cycles. The above-described literature survey on some notable research outcomes in SnS₂ nanostructures and their application to LIBs, shows that a variety of methods, such as ionic liquid assisted, templating and thermal decomposition have been used in the past for preparing these nanostructures.

2.4.2 SnS₂@C. These SnS₂-based anodes suffer from rapid capacity decay caused by pulverization of the electrode materials, due to the large volume changes during extended discharge/charge processes. The same vacillations, which reduce cyclability in SnS₂, plague other anode materials such as silicon and numerous metal oxides. Two effective strategies have been developed to solve this problem. The first strategy is to reduce the size of the electrode materials in order to relax the strain during the volume expansion and contraction. The other is to prepare them as composites using a carbon matrix, such as mesoporous carbon, N-doped microporous carbon nanospheres, graphene, and carbon nanotubes (CNTs).^147,148,244 These matrices can buffer the volume variation and accelerate ion and electron transport during the discharge/charge processes. The combination of these two approaches could potentially offer a viable way to mitigate the volume changes and further improve the electrochemical performance of LIBs. Gao developed a kind of nanocomposite material made of layered SnS₂ nanoplates vertically grown on reduced graphene oxide nanoribbons (rGONRs) as an anode in lithium ion batteries. At a rate of 0.4 A g⁻¹, the material exhibits a high discharge capacity of 823 mA h g⁻¹, even after 800 cycles. It shows a high capacity of 642 mA h g⁻¹ at 0.2 A g⁻¹, superior rate and cycling stability after long-term cycling. Moreover, the full cell has a high output working voltage of 3.4 V. These excellent lithium storage performances can be mainly attributed to the synergistic effect between the highly conductive network of rGONRs and the high lithium-ion storage capability of layered SnS₂ nanoplates.¹⁴⁹ Tang developed a three-dimensional (3D) interconnected graphene network embedded with uniformly distributed SnS₂ nanoplates by a facile two-step method. The as-prepared SSG exhibits excellent cycling performance with a capacity of 1060 mA h g⁻¹, retained after 200 charge/discharge cycles at a current density of 100 mA g⁻¹, and also a superior rate capability of 670 mA h g⁻¹, even at such a high current density of 2000 mA g⁻¹. This favorable performance can be attributed to the unique 3D interconnected architecture with great electro-conductivity and its intimate contact with SnS₂.¹⁵⁰

2.5 Sn₄P_3, SnF₂

Tin phosphide (Sn₄P₃) has a high theoretical capacity and forms Li₃P with Li ion conductivity in the initial lithium insertion. Li₃P acts as a matrix, suppressing the volume change and giving lithium ion conduction paths.¹⁵¹ Liu synthesized Sn₄P₃ nanoparticles with different sizes via a facile solvothermal method at 180 °C for 10 h. The as-prepared Sn₄P₃ nanoparticles have an average size of about 15 nm. Sn₄P₃ nanoparticles with the smallest size give the best cycling and rate performances. They deliver a discharge capacity of 612 mA h g⁻¹ after 10 cycles and could still maintain 442 mA h g⁻¹ after 320 cycles at the current density of 100 mA g⁻¹ within a voltage limit of 0.01–3.0 V. Even after 200 cycles at a current density of 200 mA g⁻¹, the specific capacity could still remain at 315 mA h g⁻¹.¹⁵² Tin(II) fluoride (SnF₂) has a high Li-storage capacity because it stores lithium first by a conversion reaction and then by a Li/Sn alloying/dealloying reaction. A polyacrylonitrile (PAN)-bound SnF₂ electrode was heat-treated to enhance the integral electrical contact and the mechanical strength through its cross-linked framework. The heat-treated SnF₂ electrode showed reversible capacities of 1047 mA h g⁻¹ in the first cycle and 902 mA h g⁻¹ after 100 cycles. Part of the excess capacity is due to lithium storage at the Sn/LiF interface, and the other part is assumed to correspond to the presence of reduced SnF₂ with protons released during the thermal cross-linking of PAN.¹⁵³

3. Na-ion batteries

3.1 Sn

3.1.1 Pure Sn. Tin can be used as an efficient negative electrode material for Na-ion batteries.^156–163 Similar to Li, it was reported that Na can also alloy with a number of metals, such as Sn, Sb, Pb, and Ge, and that these alloys have relatively high theoretical capacities by forming Na-rich intermetallic compounds, such as Na₁₅Sn₄, Na₃Sb, Na₁₅Pb₄, and Na₃Ge, respectively. Among these metals, Sn is one of the most attractive anode materials because of its high theoretical capacity and low reaction potential.^162–165 To understand and improve the electrochemical properties of the Sn anode for Na-ion batteries, the alloying/dealloying of Sn with Na has been investigated. Chevrier et al. investigated a voltage profile for the electrochemical reaction of Sn with Na, based on density functional theory (DFT) calculations of the Na–Sn binary phases with crystal structures. According to their calculations, the voltage curve has four plateaus corresponding to NaSn₅, NaSn, Na₉Sn₄, and Na₁₅Sn₄, which is almost identical to the experimental results of Huggins, with the exception of the NaSn₅ phase. On the basis of these studies, Ellis et al. examined the electrochemical insertion of Na into Sn using in situ X-ray diffraction at ambient temperatures. XRD analysis clearly confirmed the formation of four different Na–Sn alloy phases in two-phase regions. Nevertheless, only the Na₁₅Sn₄ phase formed at full sodiation was identically matched with the reference data, and the three other intermediate Na–Sn phases did not correspond to any of the reported Na–Sn phases. Baggetto et al. investigated the Na-ion reaction mechanism of Sn using various analyses and reported a new metastable phase of Na₅Sn₂ in the Na–Sn system, which remained an unknown phase in the work of Ellis et al. In addition, they suggested that at least two more plateaus are present during charging above 0.7 V, which had not been reported in previous studies. According to their mechanism, the insertion of Na into Sn progressed via a series of four steps: an unidentified phase (Na_0.6Sn), an amorphous phase (Na_1.2Sn), a hexagonal R3̄m phase (Na₅Sn₂), and a fully sodiated I4̄3d phase (Na₁₅Sn₄). This mechanism was confirmed by the theoretical voltages calculated from existing crystal structures using DFT calculations and constant current and quasiequilibrium measurements (GITT). However, Wang et al. proposed a different mechanism for the reaction of Sn with Na based on in situ transmission electron microscopy (TEM) studies. In their mechanism, the sodiation of Sn nanoparticles proceeded via a two-step reaction: the first step is the phase transition of Sn to amorphous NaSn₂, and amorphous Na₉Sn₄, Na₃Sn and crystalline Na₁₅Sn₄ are formed sequentially in the second step. They suggested that the first step is a two-phase reaction with a migrating phase boundary to form an amorphous Na_xSn alloy (x = 0.5) and that the second step is a single-phase reaction without the formation of a phase boundary. These single-phase sodiation reactions are not consistent with the two-phase mechanism proposed by other groups. Because the phase behaviors are significantly affected by kinetic factors, such as the experimental configuration and sample conditions, the Sn nanoparticles may take a different reaction pathway compared with the Sn electrode prepared by magnetron sputtering. Nam et al. found that two Sn electrodes having completely different morphologies and crystallographic orientations prepared by electrodeposition, and their electrochemical properties for Na-ion battery applications were examined, with an emphasis on the effects of the morphology and the phase structure of Sn on the cyclability of the electrodes. Finally, the feasibility of the pure Sn electrode, which is prepared by a binder- and conductive agent-free process, would be verified.¹⁷⁰

Hou et al. reported Sn hollow nanospheres, which maintained much better reversible capacity than solid Sn nanospheres, indicating a close connection between this alloy anode nanostructure and its electrochemical properties. However, similar works with reported precise structural control in NIBs are still in rapid expansion when further exploring the performance of Sn anodes.^166–170 Liu et al. developed Sn nanoparticle-coated, viral nanoforests to achieve long cycling stability with high performance in a Na-ion battery.¹⁶⁶ However, the use of vapor deposition (CVD and PVD) and electrodeposition techniques during the preparation may also increase the processing cost of the Na-ion battery, hindering its development in industrial applications.^{166,167,169,171,172} Nam demonstrated a novel electrochemical approach to synthesize single-crystalline 1D Sn nanofibers using an organic compound as a growth modifier. This process is low-cost, one-step, extremely fast and performed at room temperature using a nontoxic bath preparation. Specifically, no additional processes are needed for preparing and removing the templates. Moreover, this process is suitable for mass production on large-area substrates because of the high uniformity of the nanofibers over the entire substrate.¹⁷³

3.1.2 Sn@C. Sodium can reversibly alloy with tin at high theoretical capacities.¹⁷⁴ However, these compounds still suffer from rapid capacity degradation as a result of large changes in volume and the resultant pulverization and loss of electrical connectivity. To address this issue, nanocomposites with different carbonaceous materials have been widely synthesized.¹⁷⁵ Liu et al. reported the fabrication of Sn nanodots finely encapsulated in porous N-doped carbon (designated as PNC) nanofibers by an electrospinning technique and subsequent thermal treatment, as shown in Fig. 4a and b. The as-prepared Sn NDs@PNC nanofibers with flexible free-standing membranes can be directly used as binder- and current collector-free anodes, demonstrating promising electrochemical performance in Na-ion batteries.¹⁷⁶ Xie et al. reported the preparation of core-sheath structured Sn@carbon nanotube (Sn@CNT) nanopillars, grown vertically on carbon paper (Sn@CNT-CP) through a novel and facile soaking-chemical vapour deposition (S-CVD) technique, as shown in Fig. 4c and d. The electrode achieved a reversible capacity of 887 mA h cm⁻² in the first cycle and good cyclability extending to 100 cycles.¹⁷⁷ As a high-capacity, high-rate, and long-cycle life anode for sodium ion batteries, ultra-small Sn nanoparticles (≈8 nm) homogeneously embedded in a spherical carbon network (denoted as 8-Sn@C) was prepared using an aerosol spray pyrolysis method, as shown in Fig. 4e and f. The remarkable electrochemical performance of 8-Sn@C is due to the synergetic effects between the well-dispersed ultra-small Sn nanoparticles and the conductive carbon network. This unique structure of very-fine Sn nanoparticles embedded in the porous carbon network can effectively suppress the volume fluctuation and particle aggregation of tin during the prolonged sodiation/desodiation process, thus solving the major problems of pulverization, loss of electrical contact and low utilization rate facing the Sn anode.¹⁷⁸

Fig. 4 (a) SEM and (b) TEM of Sn NDs@PNC nanofibers. (c) Medium-magnification SEM images of Sn@CNT-CP. (d) TEM image of a single Sn@CNT nanopillar. (e and f) SEM and TEM images of 8-Sn@C. Reproduced with permission ref. 176. Copyright 2015 Wiley (a and b). Reproduced with permission ref. 177. Copyright 2015 Elsevier (c and d). Reproduced with permission ref. 178. Copyright 2015 Wiley (e and f).

3.1.3 Sn@others. Apart from the above materials, other well-functioning materials have been synthesized for this application, such as polymers, natural wood fiber, and Sn_4+xP₃@(Sn–P). A pure Sn nanoparticle electrode with conductive binder was prepared showing higher specific capacity and higher cycling stability without any carbon black, compared to Sn/CMC (carboxymethylated cellulose) and Sn/PVDF (polyvinylidene fluoride) electrodes. The Sn in the Sn/PFM electrode delivered 806 mA h g⁻¹ at C/50 and 610 mA h g⁻¹ at C/10. After 10 cycles at C/10, the capacity of Sn had no decay.¹⁷⁹ Zhu et al. reported an electrodeposited Sn film on conductive wood fiber to achieve 339 mA h g⁻¹ for a stable cycling performance of 400 cycles. The soft nature of the wood fibers effectively releases the mechanical stresses associated with the sodiation process, and the mesoporous structure functions as an electrolyte reservoir that allows for ion transport through the outer and inner surfaces of the fiber.¹⁸⁰ Li et al. prepared a novel tin phosphide and amorphous Sn and P (Sn_4+xP₃@(Sn–P)) composite in large amounts by a simple low-energy ball-milling method that can meet the demand for large-scale applications. The as-obtained Sn_4+xP₃@(Sn–P) composite was investigated as the anode for SIBs in half-cells and showed high capacity and high rate capability.¹⁸¹

3.2 Sn–M (M = Sb, Co, Cu, Ge)

3.2.1 Sn–M. Amorphous bimetallic nanoalloys with good conductivity, strain tolerance, and large sites for the insertion of Na⁺ ions are desirable electrode materials for superior SIBs.^182–186 The bare Sn electrode suffers from a severe pulverization issue, due to volumetric expansion and disintegration, leading to poor cycling performance. The benefits of amorphous bimetallic nanoalloys are that the uniform distribution of the electrically conducting M1 (e.g., Co) nanoparticles in close proximity to the high-capacity M2 (e.g., Sn) storage compound could contribute to electrical integration in the electrodes.¹⁸⁶ Tin-based alloys are considered as necessary electrode materials for sodium ion batteries (Sn–Sb, Sn–Ni, Sn–Co, Sn–Cu, Sn–Ge, Sn–Ge–Sb). The mechanism of Sn alloys is not a simple combination of Sn and other transition metal reactions. To easily explain the process, we take the Sn and SnSb anode with Na as an example. The reversible reaction occurs during the majority of the charge process. A large proportion of Na exists at the charge anode material, showing that the crystalline Sb is lacking in the process of recrystallization. The reaction of SnSb yields Na₃Sb at full discharge at higher temperatures, while the RT reaction yields amorphous compounds, indicating that the Na reaction with SnSb may not be simply written as SnSb + Na → Na₃Sb + Sn.¹⁸⁶ Liu et al. synthesized highly porous Ni₃Sn₂ microcages, composed of tiny nanoparticles, by a facile, template-free, solvothermal method for use as anode materials for high capacity and high-rate-capability Na-ion batteries. A reversible capacity of approximately 270 mA h g⁻¹ was stably maintained at 1C during the first 300 cycles.¹⁸⁵ Farbod et al. reported the electrochemical charge/discharge cycling behavior of Sn–Ge–Sb, Sn–Ge, and Sb–Ge alloy thin films for use as sodium ion battery anodes. Sn₅₀Ge₂₅Sb₂₅ demonstrates the best overall cycling performance, with 662 mA h g⁻¹ of capacity remaining after 50 cycles. The alloy also offers an exquisite rate capability, delivering a stable cycling capacity of 658 and 381 mA h g⁻¹ at 850 and 8500 mA g⁻¹, respectively.¹⁸⁶

3.2.2 Sn–M@C. Sn alloys suffer from poor electrochemical properties, mainly attributed to the large volume change during cycling, the relatively low conductivity and aggregation of the alloy particles. To circumvent these obstacles and achieve improved electrochemical properties, a variety of nanostructures or carbon-based nanocomposites have been investigated. At present, carbon-based@Sn alloys nanocomposites are mainly carbon and graphene; Sn–Cu–C, SnSe/C, Cu₆Sn₅–TiC–C, SnSb–TiC–C, SnSb–CNF, and C/Sn/Ni/TMV have been widely synthesized.^187–191 Kim et al. studied porous CNF-supported SnSb nanocomposites as anodes for rechargeable NIBs, using electrospinning and a subsequent thermal treatment processes to get good performance, high rate capability, high reversibility, and long-term stability.¹⁹² Ji synthesized rGO-SnSb nanocomposites where SnSb alloy particles can tightly combine with the surfaces of rGO sheets, which can not only effectively suppress the agglomeration of SnSb particles, but also maintain excellent electronic conduction, as shown in Fig. 5a and b. Furthermore, the mechanical flexibility of the rGO phase can accommodate the volume expansion and contraction of SnSb particles during the prolonged cycling and therefore improve the electrode integrity mechanically and electronically, as shown in Fig. 5c.¹⁹³ Yang et al. prepared SnSe/rGO by a facile ball milling method, and its electrochemical performance was significantly enhanced, as reflected by a high specific capacity of 590 mA h g⁻¹ at 0.050 A g⁻¹, a rate capability of 260 mA h g⁻¹ at 10 A g⁻¹, and long-term stability over 120 cycles. This improvement may be attributed to the high electronic conductivity of rGO, which also serves as a matrix to buffer changes in volume and maintain the mechanical integrity of the electrode during (de)sodiation processes.¹⁹⁴

Fig. 5 (a) Schematic illustration of the fabrication processes of rGO-SnSb nanocomposites for rechargeable Na-ion batteries, (b) TEM images of rGO-SnSb nanocomposites, (c) the cycling performance of rGO-SnSb electrodes in the voltage window of 0.001–2.5 V at a cycling rate of 0.2C. Reproduced with permission ref. 193. Copyright 2014 Wiley (a–c).

3.3 SnO₂

3.3.1 Pure SnO₂. SnO₂ can exhibit a theoretical capacity of 667 mA h g⁻¹ based on the reaction of 3.75 Na and one Sn (Na₁₅Sn₄), except for Na₂O formation. Park et al. investigated the electrochemical properties of the SnO₂ electrode for sodium-ion batteries, as shown in Fig. 6a. The Na/SnO₂ cell delivered initial discharge and charge capacities of 747 and 150 mA h g⁻¹, respectively. In-plane cracks caused the loss of electrical contact of the active material and hence, the capacities decreased gradually.¹⁹⁵ Lu et al. reported SnO, and SnO₂ prepared by hydrothermal reactions, as shown in Fig. 6b and c. Although SnO had larger particles, more uneven particle size, and particle distribution, it outperformed both SnO₂ and SnO₂/C. The material demonstrated high reversible capacity, low polarization, and low irreversible capacity loss. Shimizu et al. prepared the SnO thick-film electrodes using a gas-deposition method. The SnO electrode showed a high-rate performance with the capacity of 200 mA h g⁻¹ at the high current density of 500 mA g⁻¹.¹⁹⁶

Fig. 6 (a) Schematic drawing of SnO₂ electrochemical reactions during discharge. The lightning bolt represents in-plane crack propagation. (b) Medium magnification images of flower-like SnO₂. (c) Discharge and charge voltage profiles of the Na/SnO₂ cell cycled at a current density of 100 mA h g⁻¹. Reproduced with permission ref. 195. Copyright 2014 Elsevier (a). Reproduced with permission ref. 196. Copyright 2015 Elsevier (b and c).

3.3.2 SnO₂@C. SnO₂ can deliver a high theoretical sodium storage capacity of 1378 mA h g⁻¹, but with the same volume variation problem as Sn metal; hence, further surface treatment or a matrix scaffold is needed to stabilize the SnO₂ anode and improve the electronic conductivity.^197,198 Zhang et al. synthesized a nanohybrid anode consisting of ultrafine SnO₂ anchored on few-layered rGO by a facile hydrothermal route, as shown in Fig. 7a and b. The hybrid can sustain a stable cycling with a charge capacity of 369 mA h g⁻¹ retained after 100 cycles at 100 mA g⁻¹. SnO₂@graphene nanocomposites have improved cycling performance, but this method lacks the process ability and rate capability because of the high cost of graphene;^199,200 therefore, many other carbon materials, such as multiwalled carbon nanotubes, carbon cloth, and porous carbon nanofiber have been applied. Wang et al. Reported a SnO₂@multiwalled carbon nanotubes (MWCNTs) nanocomposite, synthesized by a solvothermal method, exhibiting a high reversible sodium storage capacity and a good cycling performance.²⁰¹ Liu et al. demonstrated an anode consisting of a SnO₂ nanocrystal layer grown on hierarchical microfibers of carbon cloth (CC) with extra surface coating, to addresses the above challenges associated with SnO₂ anodes by the hydrothermal and ALD method, as shown in Fig. 7c and d. The soft nature of CC and the nanocrystal structure of SnO₂ layers can effectively accommodate the volume change associated with the sodiation process.²⁰² Dirican et al. introduced a new amorphous carbon-coated SnO₂-electrodeposited porous carbon nanofiber (PCNF@SnO₂@C) composite that not only has high sodium storage capability, but also maintains its structural integrity with ongoing repetitive cycles, as shown in Fig. 7e and f.²⁰³

Fig. 7 (a and b) SEM, TEM images of SnO₂/rGO. (c and d) SEM and TEM images of SnO₂/CC. (e and f) SEM images and TEM images of PCNF@SnO₂@C composite. Reproduced with permission ref. 200. Copyright 2015 Elsevier (a and b). Reproduced with permission ref. 202. Copyright 2015 Elsevier (c and d). Reproduced with permission ref. 203. Copyright 2015 American Chemical Society (e and f).

3.4 SnS₂

Considering the additional capacity contribution from the conversion reaction, tin sulfides possess higher theoretical capacities compared to metallic tin. Moreover, tin sulfide appears to be more promising, due to the large interlayer spacing in its layered structure, which facilitates the insertion and extraction of sodium ions. 2D SnS₂ nanosheets (34 nm in thickness) with high specific capacity, good rate capability, and cycling stability were synthesized via a facile refluxing process. The SnS₂ nanosheets delivered a high reversible specific capacity of 733 and 435 mA h g⁻¹ at 0.1 and 2 A g⁻¹, respectively, and still exhibited a high capacity retention of 647 mA h g⁻¹ during the 50th cycle at 0.1 A g⁻¹.²⁰⁴ Dutta et al. Synthesized tin monosulphide by a simple wet chemical synthesis approach. The as-prepared tin monosulphide has been used as the anode in Na-ion batteries without any in situ conductive carbon or graphene coating, and the electrode exhibits a high reversible sodium reversible capacity of ∼500 mA h g⁻¹ at a discharge rate of 125 mA g⁻¹.^205–208 However, because of severe pulverization due to great volume expansion (420%) and poor kinetics caused by slow electron transport, SnS₂ cracks and gradually loses contact with the current collector, resulting in poor cycle ability and low rate capability.^209–211 A general approach to enhancing its electrochemical performance is to fabricate SnS₂ based nano-composite architectures.^212–216 Qu et al. came up with a novel SnS₂-rGO nanocomposite, produced by a facile hydrothermal route from a mixture of tin(IV) chloride, thioacetamide (TAA) and GO, exhibiting high-capacity, high-rate, and long-cycle life, as shown in Fig. 8.²¹⁷ Wang et al. developed a simple solid–state reaction method, in which the carbon-coated SnS₂ (SnS₂/C) anode materials were synthesized by annealing metallic Sn, sulfur powder, and polyacrylonitrile in a sealed vacuum glass tube. The SnS₂/C nanospheres with unique layered structure exhibited a high reversible capacity of 660 mA h g⁻¹ at a current density of 50 mA g⁻¹ and maintained 570 mA h g⁻¹ for 100 cycles with a degradation rate of 0.14% per cycle. The superior cycling stability of the SnS₂/C electrode is attributed to the stable nanosphere morphology and structural integrity during charge/discharge cycles, as evidenced by ex situ characterization.²¹⁸

Fig. 8 (a) Representative FESEM image of the SnS₂-rGO composite. (b) HRTEM image of the SnS₂-rGO composite. (c) Cycling performance of SnS₂-rGO, SnS₂ and graphene electrodes at 0.2 A g⁻¹ for 100 cycles. (d) Rate performance of SnS₂-rGO and SnS₂ electrodes. Reproduced with permission ref. 217. Copyright 2014 Wiley (a–d).

3.5 Sn₄P₃

The long cycle stability and rate performance of the as-obtained Sn₄P₃ nanoparticles have been tested as anode material for lithium ion batteries for the first time. Sn₄P₃ nanoparticles, with the smallest size give the best cycling and rate performances. The improved electrochemical performances of the Sn₄P₃ electrode might be largely attributed to their small-size. Liu et al. developed a facile approach to the synthesis of Sn₄P₃ nanoparticles by a solvothermal reaction.²¹⁹ An intermetallic compound of Sn₄P₃ was obtained by facile high-energy mechanical ball milling in an Ar atmosphere for an hour. Sn₄P₃ delivered a high reversible capacity of 718 mA h g⁻¹, and showed very stable cycle performance with negligible capacity fading over 100 cycles; the cycle performance of Sn₄P₃ was better than those of previously reported Sn-based materials and phosphorus/carbon composites.²²⁰ Phosphorus/carbon composite materials have shown excellent electrochemical performance, including the highest specific capacity (1890 mA h g⁻¹) among all reported anode materials.^221,222 However, phosphorus has poor electrical conductivity, and thus, a large amount of carbon (30 wt%) has to be used in the phosphorus/carbon composites to enhance their electrical conductivity, which decreases their gravimetric and volumetric energy densities.²²³ Uniform yolk–shell Sn₄P₃@C nanospheres were facilely synthesized via a top-down phosphorized route with yolk–shell Sn@C nanospheres as the precursor. As anode materials for Na-ion batteries, they exhibit a very high reversible capacity (790 mA h g⁻¹), superior rate capability and stable cycling performance (a high capacity of 360 mA h g⁻¹ at 1.5C after long 400 cycles). Qian et al. described a green approach to the synthesis of the Sn₄P₃/C nanocomposite and demonstrated its excellent Na-storage performance as a novel anode of Na-ion batteries. This Sn₄P₃/C anode can deliver a very high reversible capacity of 850 mA h g⁻¹ with a remarkable rate capability with 50% capacity output at 500 mA g⁻¹ and can also be cycled with 86% capacity retention over 150 cycles.²²⁴

3.6 Others

Other tin based materials like tin–phosphate glass, multiphase tin and tin sulfide@other transition metal sulfide also exhibit high performance. The tin–phosphate glass is a promising candidate for new anode active material that realizes high energy density sodium ion batteries. During the first charge process, sodium ions diffused into the tin–phosphate glass matrix and due to the reduction of Sn²⁺ to the SnO state, sodiated tin metal nano-sized particles were formed in the oxide glass matrix. After the second cycle, Honma et al. confirmed the steady reversible reaction of ∼320 mA h g⁻¹ at 0–1 V cutoff voltage conditions, by the alloying process in Na_xSn₄.²²⁵ Kim et al. successfully synthesized multiphase SnSb nanoparticles-on SnO₂/Sn/C nanofibers by electrospinning, followed by heat treatment under Ar atmosphere. The nanocomposite fibers were observed to be multiphase single crystalline SnSb particles on SnO₂/Sn/C nanofibers. These fiber electrodes exhibited high capacity in both lithium and sodium tests, due to the synergistic effects of 1D and 0D hybrid nanostructures, offering large surface area, good electric conductivity, and buffer volume variation.²²⁶ Tin-molybdenum oxide yolk–shell microspheres prepared by a one-pot spray pyrolysis process transformed into yolk–shell SnS–MoS₂ composite microspheres. The yolk–shell SnS–MoS₂ composite microspheres with high structural stability during repeated sodium insertion and desertion processes have low charge-transfer resistance, even after long-term cycling, as shown in Fig. 9. This resulted from the synergetic effect of the yolk–shell structure and uniform mixing of the SnS and MoS₂ nanocrystals.²²⁷

Fig. 9 (a and b) FE-SEM image, TEM image of the yolk–shell SnS–MoS₂ composite microspheres, (c) initial charge/discharge curves at a constant current density of 0.5 A g⁻¹, (d) cycling performances of all samples at a constant current density of 0.5 A g⁻¹. Reproduced with permission ref. 227. Copyright 2014 American Chemical Society (a–d).

4. Supercapacitors

4.1 SnO₂

4.1.1 Pure SnO₂. The hydrous RuO₂ electrode with its extraordinary capacitance properties is the most suitable electrode material for supercapacitors. However, due to its rarity and high cost, wide usage of RuO₂ in supercapacitor applications is limited. Therefore, efforts have been made to find inexpensive materials, such as MnO₂, NiO, SnO₂ and Co₃O₄ for supercapacitor applications. Due to the non-toxic nature and low cost, SnO₂ is attracting much attention in the field of supercapacitors. SnO₂ is noted as co-material for RuO₂, due to its chemical stability and high electrical conductivity. Generally, two different mechanisms have been proposed for the charge storage mechanisms.²³⁰ For the pseudocapacitors, it is the intercalation/deintercalation of protons or alkaline metal cations that leads to the full utilization of the electrode material. This may be the reason for obtaining a higher specific capacitance at a lower scan rate. There are redox peaks in the cyclic voltammetric (CV) curves of pseudocapacitors. For electric double-layer capacitors (EDLC), the explanation of mechanism relates to the surface adsorption process for a higher scan rate. This is based on the diffusion effect of the proton within the electrode materials. Hence, it is believed that part of the surface of electrode materials contributed at a high charging/discharging rate, which decreased the specific capacitance. EDLC depends mainly on the accumulation of charges at the interface of the electrode/electrolyte. Moreover, supercapacitor performance is morphology dependent and improved performance is observed with porous morphology, due to better insertion of the electrolyte within the pores of the electrode material. As a result, Sn based materials with porous morphology have been widely studied. The shapes of the CV curves of EDLC are rectangular (more or less). The excellent performances of the supercapacitor were attributed to the morphology and structure of the materials. Several examples of Sn-based nanomaterials and their electrochemical properties are given in Table 1. Meng et al. have synthesized 3D SnO₂ nanoflowers on Ti substrate by a one-step and surfactant-free hydrothermal method. This is a very simple and cost-effective technique for the industrial production of SnO₂ nanostructures. 3D SnO₂ nanoflowers grown on Ti substrate not only offer a direct path for electrons toward the current collector, but can also alleviate the volume change during the charge/discharge process, due to the unique hierarchical structure. Moreover, it has an accessible surface for electrochemical reactions. Ni nanoparticles on SnO₂ nanoflowers have also been developed.²²⁸ SnO₂ aggregation nanostructures with uniform pores were synthesized through a gas–liquid interfacial reaction driven by solvothermal means. This architecture exhibits excellent cycling stability as an electrode for supercapacitors (97% capacity retention over 1000 cycles at 1 A g⁻¹ after the first 80 cycles decay).²²⁹ Nanocrystalline SnO₂ thin films were deposited by a simple and inexpensive chemical route. The deposited films were nanocrystalline with the tetragonal rutile structure of SnO₂. The SnO₂ showed a maximum specific capacitance of 66 F g⁻¹ in 0.5 Na₂SO₄ electrolyte at 10 mV s⁻¹ scan rate. The enhanced specific capacitance observed in our case may be due to its highly porous morphology.²³⁰

Table 1 Summary of the state-of-the-art Sn and Sn compound based electrode materials for supercapacitor applications

Category	Selected examples	Electrochemical properties	Ref.
Sn	Sn@graphene	320 F g^−1 at 10 mV s^−1, 96%, 800 cycles	261
SnO2	Ni–SnO2	410 mF cm^−2, ∼93.6%, 2500 cycles	228
	SnO2 thin films	66 F g^−1 at 10 mV s^−1	230
	SnO2 aggregations	50.3 F g^−1, 1 A g^−1, 1000 cycles	229
SnO2@C	SnO2@C	37.8 F g^−1 at 5 mV s^−1	243
	SnO2/rGO	347.3 F g^−1 at 5 mV s^−1, 90%, 3000 cycles	239
	PtRu/SnO2 on G	99.7 F g^−1 at 50 mV s^−1	242
	PANI/SnO2	173 F g^−1 at 25 mV s^−1	247
	G-SnO2-PANI	913.4 F g^−1 at 5 mV s^−1, 90.8%, 1000 cycles	249
	SnO2/carbon aerogel	62.5–66.6 F g^−1	241
Others	Ru–Sn oxides	714 F g^−1 at 25 mV s^−1	256
	Sb–SnO2–MnO2	319.0 F g^−1 at 0.2 A g^−1	259
	SnO2@MoO3	295 F g^−1 at 5 mV s^−1, 97%, 1000 cycles	258
	Ni/Co/SnOx	328 F g^−1 at 1 mV s^−1, 86%, 600 cycles	244
	Sn doped PEDOT	181.41 F g^−1 at 10 mV s^−1, 92%, 1000 cycles	262
	LiSn2(PO4)3	19.4 F g^−1, 0.05 A g^−1	266

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4.1.2 SnO₂@C. Materials that could be used as supercapacitor electrode materials include metal oxides, carbon materials, and conducting polymers.²³¹ Of particular interest are carbon-based electrode materials because of their low cost and potential to realize both high specific capacitance and high power density as a result of their high surface areas. Carbon-based materials have usually been added with the active materials for improving the electrical, electrochemical, and electrocatalytic properties, especially in energy devices. This inhomogeneous mechanical dispersion reduces the performance of the active materials.²³² However, the limited charge accumulation in the electrical double layer restricts the specific capacitance of EDLCs to a range of relatively small values between 90 and 250 F g⁻¹. Meanwhile, pseudocapacitors based on metal oxides such as RuO₂, CoO_x, and MnO₂ or conducting polymers including polypyrrole and polyaniline usually show less cycling stability than EDLCs, but have high specific capacitance values.²³³ Graphene, a novel and unique EDLC-based carbon material with a one-atom thick layer has been used as a supercapacitor electrode material, due to its high surface area, excellent stability, and good conductivity.^234–237 Wang and co-workers reported on the microwave-assisted, one-pot synthesis of SnO₂/graphene, which gave rise to the specific capacitance of 99.7 F g⁻¹.²³⁸ Zhang adopted a simple and fast colloid electrostatic self-assembly method to prepare the SnO₂/graphene nanocomposite (SGNC). As shown in Fig. 10, the SGNC has the specific capacitance of 347.3 F g⁻¹. Furthermore, this material also showed excellent cycling stability, and the specific capacitance was 90% retained after 3000 cycles.²³⁹ Li et al. prepared SnO₂/graphene using a one-pot synthesis approach, which showed a specific capacitance of 34.6 F g⁻¹.²⁴⁰ SnO₂/graphene nanocomposite hydrogel was synthesized using a solvothermal processing route. This one-pot synthesis strategy is facile and does not require any reducing or oxidizing agent. The in situ growth of SnO₂ led to uniformly decorated nanoparticles on the surface of graphene. The SnO₂/graphene nanocomposite possessed a pronounced enhancement of electrochemical properties, allowing the nanocomposite to be used as a supercapacitor.^241,242 To realize a suitable pseudocapacitor nanomaterial, the recently developed technique of reaction under autogenic pressure at elevated temperature has been employed to synthesize SnO₂@C nanocomposites. The synthesized SnO₂@C nanomaterials are highly crystalline with hexagonal shape. The nanocomposite has a maximum specific capacitance of 37.8 F g⁻¹ at a scan rate of 5 mV s⁻¹.²⁴³

Fig. 10 (a) Schematic illustration of the preparation of SGNC, (b) capacitance values of SGNC, rGO, and SnO₂ against scan rates calculated by CV curves, (c) cycling performance of SGNC at a current density of 100 mA g⁻¹; the inset gives the initial and the last 10 cycles of SGNC. Reproduced with permission ref. 239. Copyright 2015 Springer (a–c).

Polyaniline (PANI) has attracted significant attention, due to its environmental stability and controllable electrical conductivity. However, the conductance of these polymers is low in the dedoped state, which would result in high ohmic polarization of supercapacitors, reducing their reversibility and stability.²⁴⁶ To solve these problems and explore any potential synergistic effects, Hu et al. proposed polyaniline–tin oxide composites (PANI/SnO₂) as electrode materials for supercapacitors. The results indicate that the PANI/SnO₂ has a synergistic effect on the complementary properties of both components.²⁴⁷ Jin synthesized a nanostructured graphene–SnO₂–polyaniline (GSP) ternary composite via a one-pot method, including the reduction of GO by Sn²⁺, and tiny SnO₂ nanoparticles were homogeneously distributed on the graphene sheets. PANI was synthesized in situ on the surface of the graphene–SnO₂ composite in order to obtain the GSP ternary composite. The GSP ternary composite achieved a maximum capacitance of 913.4 F g⁻¹ after 1000 cycles.²⁴⁹

4.1.3 SnO₂@M_xO_y (M = Ru, Ti, Ta, Mo). Due to the high cost of ruthenium precursors and the possible synergistic effects occurring among RuO₂, SnO₂, TiO₂, and Ta₂O₅, binary (Ru–Sn, Ru–Ti, Ru–Ta) and ternary (Ru–Sn–Ti, Ru–Sn–Ta) mixed oxides have been developed. For example, the utilization of RuO₂ was promoted by introducing Sn into RuO₂·xH₂O via a modified sol–gel method.^250–253 Since the total specific capacitance of mixed Ru–Sn oxides is highly composition-dependent and a precise composition control for this series of oxides is complicated, a simple process for preparing Ru–Sn mixed oxides with very high-power characteristics, acceptable specific capacitance, and long service-life is practically desirable.^256,257 Tin oxide coated molybdenum oxide nanowires (SnO₂/MoO₃) were synthesized by a combination of hydrothermal and wet chemical routes. The specific capacitance of SnO₂/MoO₃ core–shell composite nanowires is 295 F g⁻¹, which is much higher than the specific capacitance of pure individual MoO₃ (69 F g⁻¹) and SnO₂ (96.6 F g⁻¹), as shown in Fig. 11. Moreover, the synthesized core shell composite nanowires have also exhibited excellent long-term cycling stability.²⁵⁸ To enhance the specific capacity and cycling stability of manganese oxides (MnO₂) for supercapacitors, Sb doped SnO₂ (SS) were coated on MnO₂ through a sol–gel method to prepare MnO₂ electrodes. SS-MnO₂ electrodes hold the porous structure, displaying superior cycling stability at large current work conditions in charge–discharge tests and good capacity performance at high scanning rates in CV tests.²⁵⁹ Ferreira synthesized ternary oxides by the Pechini method, with subsequent deposition onto a titanium substrate in a thin-film form. It exhibited a maximum specific capacitance of 328 F g⁻¹. Specific power and specific energy were 345.7 W kg⁻¹ and 18.92 W h kg⁻¹, respectively, and the capacitance retention was kept at 86% of its initial value after 600 cycles.²⁶⁰

Fig. 11 (a) FE-SEM image of MoO₃ nanowires synthesized at 180 °C for 10 h. (b) FE-SEM image of 5 nm SnO₂ deposited MoO₃ nanowires. (c) Specific capacitance variation of MoO₃ and 5 nm SnO₂ coated MoO₃ nanowires at different current densities. (d) Galvanostatic charge–discharge curves of MoO₃ and 5 nm SnO₂ coated MoO₃ nanowires at a charge discharge current density of 0.5 A g⁻¹. Reproduced with permission ref. 258. Copyright 2012 Elsevier (a–d).

4.2 Others

Other tin based nanomaterials have been widely researched in recent years. Sn nanoparticle decorated graphene (Sn–Gr) materials were prepared by adding tin powder to the reaction of graphite oxide during thermal reduction. The Sn nanoparticles were uniformly distributed on the surface of Gr sheets, in which Sn nanoparticles acted as a spacer to effectively to prevent the restacking of Gr sheets. The Sn–Gr electrodes exhibited a high specific capacitance of 320 F g⁻¹ at a scan rate of 10 mV s⁻¹ in 2 M KNO₃ aqueous solution.²⁶¹ Electrochemically synthesized tin ion (Sn²⁺) doped poly(3-methylthiophene) and poly(3,4-ethylenedioxythiophene) on pencil graphite electrode (PGE) were prepared to be utilized as the electrode materials for supercapacitor applications.²⁶² In contrast to carbon-based materials and metal oxides, conducting polymers have good electrical conductivity and large capacitance.^263–265 Among conducting polymers, polythiophene and its derivatives have received much interest, due to their several advantages: (i) compatibility in both aqueous and organic electrolytes, (ii) ability to work in a wide potential range, (iii) environmental stability, (iv) high electrical conductivity, (v) large pseudocapacitance, (vi) fast electrochemical charge/discharge process.^266–268

5. Conclusion and outlook

In this review, we have attempted to chart the significant progress in nanostructured Sn, Sn oxides, dichalcogenides (SnS_x, x = 1, 2), Sn alloys, oxysalts and their nanocomposites for rechargeable LIBs/SIBs and supercapacitors. The rational and creative design of unique nanoarchitectures helps to address the significant issues encountered during the electrochemical reactions, thus dramatically enhancing the capacity, rate capability, and cycle life of Sn-based electrodes. These developments greatly enrich Sn based chemistry and represent promising steps towards viable energy storage devices. Compared to other new anode materials with higher theoretical capacities, such as Si-based materials, Ge-based materials and transition metal oxides like Co₃O₄ and Fe₃O₄, the Sn-based materials have received considerable attention for their advantageous properties, such as high theoretical capacity, high tap density, and safe thermodynamic potential in LIBs and SIBs. In supercapacitors, different oxide materials such as RuO₂, MnO₂, CoO, NiO, Bi₂O₃, Fe₃O₄, SnO₂, SnO have been studied widely, however, Sn based nanomaterials have attracted more attention because of their low cost, chemical stability and high electrical conductivity.

Despite the various structural forms, based on our comprehensive study, the Sn-based anode materials must enable the relief of the Sn volume variation during cycling, promotion of the ion/electron transfer and inhibition of the SEI formation. In addition to these three design principles, the Sn-based anodes should afford high tap/packing density to increase the areal/volumetric capacities for their viable applications in next-generation batteries. Future research should be focused on developing novel processes capable of preparing high tap/packing density Sn-based anodes, which is also the key to removing the threat from Si-based materials to their potential implementation in future LIBs and SIBs. What is more, by virtue of the modern analytical techniques on the atomic or molecular level, the investigation on increasing the initial coulombic efficiency of nanostructured electrode materials needs to be emphasized, since it is important for the commercialization of nanostructured materials for rechargeable LIBs/SIBs and supercapacitors. Although the road to viable energy storage devices based on nanostructured Sn-based materials is still significantly challenging, great strides have been achieved over the past decade. For the realization of wide industrial applications of nanostructured Sn-based electrode materials in the energy-storage fields, more work is required to achieve large-scale preparation, improve volumetric energy density (i.e., increase the tap density), and maintain high compatibility between electrodes with electrolytes, as well as device systems.

Acknowledgements

This work was supported by the Program for New Century Excellent Talents of the University in China (grant no. NCET-13-0645) and the National Natural Science Foundation of China (NSFC-21201010, ​21673203, 21671170, 21673203, 21505118 and 51202106), Innovation Scientists and Technicians Troop Construction Projects of Henan Province-164200150018, Plan for Scientific Innovation Talent of Henan Province, Program for Innovative Research Team (in Science and Technology) in University of Henan Province (14IRTSTHN004, 16IRTSTHN003), the Science & Technology Foundation of Henan Province (122102210253 and 13A150019), the Science & Technology Foundation of Jiangsu Province (BK20150438), the Six Talent Plan (2015-XCL-030), Innovation and Entrepreneurship Training Program for College Students in Jiangsu province (No. 201611117047Y) and the China Postdoctoral Science Foundation (2012M521115). We also acknowledge the Priority Academic Program Development of Jiangsu Higher Education Institutions.

References

1. Y. Yu, L. Gu, P. A. V. Aken and J. Maier, J. Am. Chem. Soc., 2009, 131, 15984–15987.
2. B. C. Duan, W. K. Wang and Y. S. Yang, Rare Met. Mater. Eng., 2012, 41, 93–100.
3. Y. J. Hsu and S. Y. Lu, J. Phys. Chem. B, 2005, 109, 4398–4403.
4. T. L. Tan, O. I. Malyi and S. Manzhos, Solid State Ionics, 2014, 268, 273–276.
5. Y. Zou and Y. Wang, ACS Nano, 2011, 5, 8108–8114.
6. H. S. Im, Y. J. Cho, C. S. Jung, D. M. Jang, J. Park, F. Shojaei and H. S. Kang, ACS Nano, 2013, 7, 11103–11105.
7. N. Li, H. W. Song, G. W. Yang and C. X. Wang, J. Mater. Chem. A, 2014, 2, 2526–2529.
8. F. Nobili, I. Meschini, F. Croce, R. Tossici and R. Marassi, Electrochim. Acta, 2013, 107, 85–92.
9. I. Meschini, F. Nobili, R. Marassi, R. Tossici, A. Savoini, M. L. Focarete and F. Croce, J. Power Sources, 2013, 226, 241–248.
10. Y. J. Hong and Y. C. Kang, Small, 2015, 11, 2157–2163.
11. K. Shiva, K. Jayaramulu and A. J. Bhattacharyya, Z. Anorg. Allg. Chem., 2014, 5, 1115–1118.
12. J. Z. Chen, L. Yang, Z. X. Zhang, A. Deb and S.-I. Hirano, Electrochim. Acta, 2014, 127, 390–396.
13. G. H. Zhang, J. Zhu, S. C. Hou, F. L. Gong, F. Li, C. C. Li and H. G. Duan, Nano Energy, 2014, 9, 61–70.
14. F. Cheng, W.-C. Li, W.-P. Zhang and A.-H. Lu, Nano Energy, 2016, 19, 486–494.
15. Z. Q. Zhu, S. W. Wang, Q. Jin, T. R. Zhang, F. Y. Cheng and J. Chen, Nano Lett., 2014, 14, 153–157.
16. Y. Zhong, X. F. Li, R. Y. Li, M. Cai and X. L. Sun, Appl. Surf. Sci., 2015, 332, 192–197.
17. K.-C. Hsu, C.-E. Liu, C.-Y. Lee and H.-T. Chiu, J. Mater. Chem., 2012, 22, 21533–21535.
18. M.-J. Deng, D.-C. Tsai, C.-F. Li and F.-S. Shieu, Appl. Surf. Sci., 2013, 285P, 180–184.
19. W. Ni, J. L. Cheng, X. D. Li, B. Wang, Q. Guan, L. Huang, G. F. Gu and H. Li, J. Mater. Chem. A, 2014, 2, 19122–19124.
20. D.-H. Nam, J. W. Kim, S.-Y. Lee, H.-A.-S. Shin, S.-H. Lee and Y.-C. Joo, J. Mater. Chem. A, 2015, 3, 11021–11023.
21. H. Y. Wang, H. Q. Huang, C. G. Wang, B. Yan, Y. T. Yu, Y. Yang and G. Yang, ACS Sustainable Chem. Eng., 2014, 2, 2310–2317.
22. F. R. Beck, R. Epur, A. Manivannan and P. N. Kumta, Electrochim. Acta, 2014, 127, 299–306.
23. X. Y. Zhou, Y. L. Zou and J. Yang, J. Power Sources, 2014, 253, 287–293.
24. C. D. Wang, Y. Li, Q.-H. Wu, X. F. Chen and W. J. Zhang, Nanoscale, 2013, 5, 10599–10602.
25. X. S. Zhou, J. C. Bao, Z. H. Dai and Y.-G. Guo, J. Phys. Chem. C, 2013, 117, 25367–25373.
26. P. C. Lian, J. Y. Wang, G. X. Liu, Y. Y. Wang and H. H. Wang, J. Alloys Compd., 2014, 604, 188–195.
27. J. C. Guo, Z. C. Yang and L. A. Archer, J. Mater. Chem. A, 2013, 1, 8710–8713.
28. X. Y. Li, Y. M. Chen, H. T. Wang, H. M. Yao, H. T. Huang, Y. W. Mai, N. Hu and L. M. Zhou, Adv. Funct. Mater., 2016, 26, 376–383.
29. Z. F. Li, H. Y. Zhang, Q. Liu, Y. D. Liu, L. Stanciu and J. Xie, ACS Appl. Mater. Interfaces, 2014, 6, 5996–6001.
30. D. L. Ma, Z. Y. Cao, H. G. Wang, X. L. Huang, L. M. Wang and X. B. Zhang, Energy Environ. Sci., 2012, 5, 8538–8542.
31. F. Han, D. Li, W. C. Li, C. Lei, Q. Sun and A. H. Lu, Adv. Funct. Mater., 2013, 23, 1692.
32. H. J. Ding, B. Yao, J. K. Feng and J. X. Zhang, J. Mater. Chem. A, 2013, 1, 11200–11203.
33. P. J. Zhang, L. B. Wang, J. Xie, L. W. Su and C. A. Ma, J. Mater. Chem. A, 2014, 2, 3776–3781.
34. H. Yu, L. J. Pan, N. Liu, M. T. McDowell, Z. N. Bao and Y. Cui, Nat. Commun., 2013, 4, 1943–1947.
35. M. Sindoro, Y. H. Feng, S. X. Xing, H. Li, J. Xu, H. L. Hu, C. C. Liu, Y. W. Wang, H. Zhang, Z. X. Shen and H. Y. Chen, Angew. Chem., Int. Ed., 2011, 50, 9898–9901.
36. J. X. Zhu, D. Yang, X. H. Rui, D. Sim, H. Yu, H. H. Hng, H. E. Hoster, P. M. Ajayan and Q. Y. Yan, Small, 2013, 9, 3390–3393.
37. X. Fan, X. N. Tang, D. Q. Ma, D. Q. Maa and X. H. Xu, J. Solid State Electrochem., 2014, 18, 1137–1145.
38. D. B. Polat, J. Lu and K. Amine, ACS Appl. Mater. Interfaces, 2014, 6, 10877–10885.
39. M. Uysal, T. Cetinkaya, A. Alp and H. Akbulut, Thin Solid Films, 2014, 572, 216–223.
40. H. X. Dang, K. C. Klavetter, M. L. Meyerson, A. Hellera and C. B. Mullins, J. Mater. Chem. A, 2015, 3, 13500.
41. H. Gul, M. Uysal, T. C. Etinkaya, M. O. Guler, A. Alp and H. Akbulut, Int. J. Hydrogen Energy, 2014, 39, 21414–21419.
42. X. Liu, J. Y. Xie, P. P. Lv, K. Wang, Z. H. Feng and K. Swierczek, Solid State Ionics, 2015, 269, 86–92.
43. H. G. Zhang, T. Shi, D. J. Wetzel, R. G. Nuzzo and P. V. Braun, Adv. Mater., 2016, 28, 742–747.
44. J. Liu, Y. R. Wen, P. A. V. Aken, J. Maier and Y. Yu, Nano Lett., 2014, 14, 6387–6392.
45. M. Uysal, H. Gul, A. Alp and H. Akbulut, Int. J. Hydrogen Energy, 2014, 39, 21391–21398.
46. D. S. Guan, J. Y. Li, X. F. Gao and C. Yuan, J. Alloys Compd., 2014, 617, 464–471.
47. Z. Edfouf, M. T. Sougrati and F. Cuevas, J. Power Sources, 2013, 238, 210–217.
48. K. Zhuo, M. G. Jeong and C. H. Chung, J. Power Sources, 2013, 244, 601–605.
49. X. Fan, P. Dou, D. Q. Ma, P. Bi, A. N. Jiang, J. Zhu and X. H. Xu, ACS Appl. Mater. Interfaces, 2014, 6, 22282–22288.
50. J. Qin, X. Zhang, N. Q. Zhao, C. S. Shi, E. Z. Liu, J. J. Lia and C. N. He, RSC Adv., 2014, 4, 49247–49251.
51. X. Y. Hou, Y. J. Hu, H. Jiang, Y. F. Li, X. F. Niu and C. Z. Li, Chem. Commun., 2015, 51, 16373–16376.
52. Q. L. Jiang, D. Z. Hu, M. Q. Jia and R. S. Xue, Appl. Surf. Sci., 2014, 321, 109–115.
53. A. Birrozzi, F. Maroni and R. Raccichini, J. Power Sources, 2015, 294, 248–253.
54. P. X. Zhang, Y. Y. Wang and J. W. Wang, Electrochim. Acta, 2014, 137, 121–130.
55. J. Leibowitz, E. Allcorn and A. Manthiram, J. Power Sources, 2015, 295, 125–130.
56. B. Liu, A. Abouimrane, D. E. Brown, X. F. Zhang, Y. Ren, Z. Z. Fang and K. Amine, J. Mater. Chem. A, 2013, 1, 4376–4380.
57. Y. Ye, P. Wu, X. Zhang, T. Zhou, Y. W. Tang, Y. M. Zhou and T. H. Lu, RSC Adv., 2014, 4, 17401–17405.
58. B. Liu, A. Abouimrane, Y. Ren, M. Balasubramanian, D. P. Wang, Z. gang, Z. Fang and K. Amine, Chem. Mater., 2012, 24, 4653–4661.
59. J. P. Liu, Y. Y. Li, X. T. Huang, R. M. Ding, Y. Y. Hu, J. Jiang and L. Liao, J. Mater. Chem., 2009, 19, 1859–1862.
60. P. Meduri, C. Pendyala, V. Kumar, G. U. Sumanasekera and M. K. Sunkara, Nano Lett., 2009, 9, 612–617.
61. M. S. Park, Y. M. Kang, G. X. Wang, S. X. Dou and H. K. Liu, Adv. Funct. Mater., 2008, 18, 455–460.
62. J. Z. Wang, N. Du, H. Zhang, J. X. Yu and D. R. Yang, J. Phys. Chem. C, 2011, 115, 11302–11307.
63. Y. Wang, J. Y. Lee and H. C. Zeng, Chem. Mater., 2005, 17, 3899–3903.
64. Z. X. Yang, G. D. Du, C. Q. Feng, S. A. Li, Z. X. Chen, P. Zhang, Z. P. Guo, X. B. Yu, G. N. Chen, S. Z. Huang and H. K. Liu, Electrochim. Acta, 2010, 55, 5485–5488.
65. J. F. Ye, H. J. Zhang, R. Yang, X. G. Li and L. M. Qi, Small, 2010, 6, 296–302.
66. F. Cheng, Z. Tao, J. Liang and J. Chen, Chem. Mater., 2008, 20, 667–671.
67. C. Wang, G. H. Du, K. Stahl, H. X. Huang, Y. J. Zhong and J. Z. Jiang, J. Phys. Chem. C, 2012, 116, 4000–4007.
68. C. Wang, Q. Wu, H. L. Ge, T. Shang and J. Z. Jiang, Nanotechnology, 2012, 23, 075704.
69. R. Yang, Y. G. Gu, Y. Q. Li, J. Zheng and X. G. Li, Acta Mater., 2010, 58, 866–869.
70. S. J. Ding and X. W. Lou, Nanoscale, 2011, 3, 3586–3589.
71. Z. Y. Wang, Z. C. Wang, W. T. Liu, W. Xiao and X. W. Lou, Energy Environ. Sci., 2013, 6, 87–91.
72. X. F. Chen, Y. Huang and H. J. Huang, Mater. Lett., 2015, 149, 33–36.
73. Y. K. Wang, D. Li and J. M. Zhang, Mater. Lett., 2016, 167, 222–225.
74. Q. S. Xie, Y. T. Ma, X. Q. Zhang, H. Z. Guo, A. L. Lu, L. S. Wang, G. H. Yue and D. L. Peng, Electrochim. Acta, 2014, 141, 374–383.
75. Y. T. Ma, Q. S. Xie, X. Liu, Y. C. Zhao, D. Q. Zeng, L. S. Wang, Y. Zheng and D. L. Peng, Electrochim. Acta, 2015, 182, 327–333.
76. S. Zhao, Y. Bai and W.-F. Zhang, Electrochim. Acta, 2010, 55, 3891–3896.
77. Y. Sharma, N. Sharma, G. V. S. Rao and B. V. R. Chowdari, J. Power Sources, 2009, 192, 627–635.
78. K. Wang, Y. Huang, T. Z. Han, Y. Zhao, H. J. Huang and L. L. Xue, Ceram. Int., 2014, 40, 2359–2364.
79. Y. Q. Cao, L. Zhang and K. P. Su, Electrochim. Acta, 2014, 132, 483–489.
80. G. Q. Fang, S. Kaneko, W. W. Liu, B. B. Xia, H. D. Sun, R. X. Zhang, J. W. Zheng and D. C. Li, Appl. Surf. Sci., 2013, 283, 963–967.
81. F. Q. Fan, G. Q. Fang, R. X. Zhang, Y. H. Xu, J. W. Zheng and D. C. Li, Appl. Surf. Sci., 2014, 311, 484–489.
82. C. Guan, X. L. Li, H. Yu, L. Mao, L. H. Wong, Q. Y. Yanc and J. Wang, Nanoscale, 2014, 6, 13824–13830.
83. L. L. Li, S. J. Peng, J. Wang, Y. L. Cheah, P. F. Teh, Y. Ko, C. L. Wong and M. Srinivasan, ACS Appl. Mater. Interfaces, 2012, 4, 6005–6012.
84. Y. Z. Jiang, Y. Li, P. Zhou, S. L. Yu, W. P. Sun and S. X. Dou, ACS Appl. Mater. Interfaces, 2015, 7, 26367–26373.
85. Y. Hwa, W.-S. Kim, B.-C. Yu, H. S. Kim, S.-H. Honga and H.-J. Sohn, J. Mater. Chem. A, 2013, 1, 3733–3736.
86. H. K. Wang, M. Wang, B. B. Li, X. Yang, K. Safarova, R. Zboril, A. L. Rogachc and M. K. H. Leung, CrystEngComm, 2014, 16, 7529–7534.
87. C. X. Hua, X. P. Fang, Z. X. Wang and L. Q. Chen, Chem.–Eur. J., 2014, 20, 5487–5491.
88. M. Chen, P. P. Liu, C. J. Wang, W. J. Ren and G. W. Diao, New J. Chem., 2014, 38, 4566–4573.
89. G. E. Luo, Y. H. Lu, S. S. Zeng, S. B. Zhong, X. Y. Yua, Y. P. Fang and L. Y. Sun, Electrochim. Acta, 2015, 182, 715–722.
90. T. Z. Yuan, Y. Z. Jiang and M. Yan, Electrochim. Acta, 2014, 136, 27–32.
91. S. H. Lee, S. H. Jee and Y. S. Yoon, Electrochim. Acta, 2013, 87, 905–911.
92. W.-J. Cui, J. Yi, L. Chen, C.-X. Wang and Y.-Y. Xia, J. Power Sources, 2012, 217, 77–84.
93. J. X. Wang, W. Li and F. Wang, Nanoscale, 2014, 6, 3217–3222.
94. X. Y. Yu, S. Y. Yang, B. H. Zhang, D. Shao, X. M. Dong and Y. P. Fang, J. Mater. Chem., 2011, 21, 12295–12302.
95. P. Wu, N. Du, H. Zhang, J. X. Yu and D. R. Yang, J. Phys. Chem. C, 2010, 114, 22535–22538.
96. Y. Zhao, J. Li, N. Wang, C. X. Wu, G. F. Dong and L. H. Guan, J. Phys. Chem. C, 2012, 116, 18612–18617.
97. C. H. Xu, J. Sun and L. Gao, J. Mater. Chem., 2012, 22, 975–979.
98. J. F. Liang, W. Wei, D. Zhong, Q. L. Yang, L. D. Li and L. Guo, ACS Appl. Mater. Interfaces, 2012, 4, 454–459.
99. Z.-S. Wu, G. Zhou, L.-C. Yin, W. Ren, F. Li and H.-M. Cheng, Nano Energy, 2012, 1, 107–131.
100. X. Wang, X. Cao, L. Bourgeois, H. Guan, S. Chen, Y. Zhong, D.-M. Tang, H. Li, T. Zhai, L. Li, Y. Bando and D. Golberg, Adv. Funct. Mater., 2012, 22, 2682–2690.
101. J. Yao, X. Shen, B. Wang, H. Liu and G. Wang, Electrochem. Commun., 2009, 11, 1849–1852.
102. S.-M. Paek, E. Yoo and I. Honma, Nano Lett., 2009, 9, 72–75.
103. L.-S. Zhang, L.-Y. Jiang, H.-J. Yan, W. D. Wang, W. Wang, W.-G. Song, Y.-G. Guo and L.-J. Wan, J. Mater. Chem., 2010, 20, 5462–5467.
104. G. Chen, Z. Wang and D. Xia, Chem. Mater., 2008, 20, 6951–6956.
105. P. Wu, N. Du, H. Zhang, J. Yu and D. Yang, J. Phys. Chem. C, 2010, 114, 22535–22538.
106. D. Ahn, X. Xiao, Y. Li, A. K. Sachdev, H. W. Park, A. Yu and Z. Chen, J. Power Sources, 2012, 212, 66–72.
107. L. Noerochim, J. Z. Wang, S. L. Chou, D. Wexler and H. K. Liu, Carbon, 2012, 50, 1289–1297.
108. H. X. Zhang, C. Feng, Y. C. Zhai, K. L. Jiang, Q. Q. Li and S. S. Fan, Adv. Mater., 2009, 21, 2299–2304.
109. K. J. Chan, H. I. Sung, S. S. Deok, L. G. Hee, S. H. Woo, P. K. Soo and K. D. Wan, Nanotechnology, 2012, 23, 465402.
110. H. W. Song, N. Li and C. X. Wang, Electrochim. Acta, 2014, 120, 46–51.
111. I. Boyano, M. Bengoechea, I. Meatza, O. Miguel, I. Cantero, E. Ochoteco and J. Rodriguez, J. Power Sources, 2007, 166, 471–477.
112. S. Y. Chew, C. Feng and H. Liu, J. Electrochem. Soc., 2007, 154, A633–A637.
113. M. Sun, S. Zhang, T. Jiang and J. Yu, Electrochem. Commun., 2008, 10, 1819–1822.
114. B. Veeraraghavan, J. Paul and B. Popov, J. Power Sources, 2002, 109, 377–387.
115. G. X. Wang, L. Yang, Y. Chen, J. Z. Wang, S. Bewlay and H. K. Liu, Electrochim. Acta, 2005, 50, 4649–4654.
116. L. Cui, J. Shen, F. Cheng, Z. Tao and J. Chen, J. Power Sources, 2011, 196, 2195–2201.
117. L. Yuan, J. Wang, S. Y. Chew, J. Chen, Z. P. Guo, L. Zhao and H. K. Liu, J. Power Sources, 2007, 174, 1183–1187.
118. D.-H. Nam, S.-J. Lim, M.-J. Kim and H.-S. Kwon, RSC Adv., 2013, 3, 16102–16108.
119. L. P. Zhang, Y. F. Wang, S. Q. Gou and J. H. Zeng, J. Phys. Chem. C, 2015, 119, 28721–28727.
120. Y. Hwa, W.-S. Kim, B.-C. Yu, H. S. Kim, S.-H. Honga and H.-J. Sohn, J. Mater. Chem. A, 2013, 1, 3733–3737.
121. S. Liu, X. Yin, Q. Hao, M. Zhang, L. Li, L. Chen, Q. Li, Y. Wang and T. Wang, Mater. Lett., 2010, 64, 2350–2353.
122. P. Wu, N. Du, H. Zhang, J. Liu, L. Chang, L. Wang, D. Yang and J. Z. Jiang, Nanoscale, 2012, 4, 4002–4006.
123. J. Lu, C. Nan, L. Li, Q. Peng and Y. Li, Nano Res., 2013, 6, 55–64.
124. H. Mukaibo, A. Yoshizawa, T. Momma and T. Osakaa, J. Power Sources, 2003, 12, 119–121.
125. S. Liu, X. Yin, L. Chen, Q. Li and T. Wang, Solid State Sci., 2010, 12, 712–718.
126. C. Zhai, N. Du and H. Z. D. Yang, Chem. Commun., 2011, 47, 1270–1272.
127. J. Wang, J. Liu, H. Xu, S. Ji, J. Wang, Y. Zhou, P. Hodgson and Y. Li, J. Mater. Chem. A, 2013, 1, 1117–1122.
128. J. Ma, D. Lei, L. Mei, X. Duan, Q. Li, T. Wang and W. Zheng, CrystEngComm, 2012, 14, 832–836.
129. J. W. Seo, J. T. Jang, S. W. Park, C. Kim, B. Park and J. Cheon, Adv. Mater., 2008, 20, 4269–4273.
130. H. Zhong, G. Yang, H. Song, Q. Liao, H. Cui, P. Shen and C. X. Wang, J. Phys. Chem. C, 2012, 116, 9319–9326.
131. T. J. Kim, C. Kim, D. Son, M. Choi and B. Park, J. Power Sources, 2007, 167, 529–535.
132. J. Ma, D. Lei, X. Duan, Q. Li, T. Wang, A. Cao, Y. Maod and W. Zheng, RSC Adv., 2012, 2, 3615–3617.
133. J. Zai, K. Wang, Y. Su, X. Qian and J. Chen, J. Power Sources, 2011, 196, 3650–3654.
134. J. Zai, X. Qian, K. Wang, C. Yu, L. Tao, Y. Xiao and J. Chen, CrystEngComm, 2012, 14, 1364–1375.
135. Y. Du, Z. Yin, X. Rui, Z. Zeng, X. J. Wu, J. Liu, Y. Zhu, J. Zhu, X. Huang, Q. Yan and H. Zhang, Nanoscale, 2013, 5, 1456–1459.
136. X. Y. Yu, H. Hu, Y. Wang, H. Chen and X. W. Lou, Angew. Chem., Int. Ed., 2015, 54, 7395–7398.
137. Q. Wu, L. Jiao, J. Du, J. Yang, L. Guo, Y. Liu, Y. Wang and H. Yuan, J. Power Sources, 2013, 239, 89–93.
138. Y. Liu, H. Kang, L. Jiao, C. Chen, K. Cao, Y. Wang and H. Yuan, Nanoscale, 2015, 7, 1325–1332.
139. L. Zhang, H. B. Wu, Y. Yan, X. Wang and X. W. Lou, Energy Environ. Sci., 2014, 7, 3302–3306.
140. C. K. Chan, H. Peng, G. Liu, X. F. Zhang, R. A. Huggins and Y. Cui, Nat. Nanotechnol., 2008, 3, 31–35.
141. X. Su and J. Li, Adv. Energy Mater., 2014, 4, 31–35.
142. J. Cai, Z. Li and P. K. Shen, ACS Appl. Mater. Interfaces, 2012, 4, 4093–4098.
143. M. Sathish, S. Mitani and I. Honma, J. Phys. Chem. C, 2012, 116, 12475–12481.
144. Z.-Y. Sui, C. Wang, K. Shu, Q.-S. Yang, Y. Ge, G. G. Wallace and B.-H. Han, J. Mater. Chem. A, 2015, 3, 10403–10412.
145. C. Sun, Y. Deng, L. Wan, X. Qin and G. Chen, ACS Appl. Mater. Interfaces, 2014, 6, 11277–11285.
146. M. Zheng, D. Qiu, B. Zhao, L. Ma, X. Wang, Z. Lin, L. Pan, Y. Zheng and Y. Shi, RSC Adv., 2013, 3, 699–703.
147. S. Liu, X. Lu, J. Xie, G. Cao, T. Zhu and X. Zhao, ACS Appl. Mater. Interfaces, 2013, 5, 1588–1595.
148. J.-G. Kang and G.-H. Lee, J. Mater. Chem., 2012, 22, 9330.
149. C. T. Gao and L. Li, ACS Appl. Mater. Interfaces, 2015, 7, 26549–26556.
150. H. L. Tang, X. Qi, W. J. Han, L. Ren, Y. D. Liu, X. Y. Wang and J. X. Zhong, Appl. Surf. Sci., 2015, 355, 7–13.
151. A. Ueda, M. Nagao, A. Inoue, A. Hayashi, Y. Seino, T. Ota and M. Tatsumisago, J. Power Sources, 2013, 244, 597–600.
152. S. L. Liu, H. Z. Zhang, L. Q. Xu, L. B. Ma and X. X. Chen, J. Power Sources, 2016, 304, 346–353.
153. L. Shen, L. Shen, Z. Wang and L. Q. Chen, Chem.–Eur. J., 2015, 21, 8491–8496.
154. H. Tang, J. Wang, H. Yin, H. Zhao, D. Wan and Z. Tang, Adv. Mater., 2015, 27, 1117–1123.
155. X. H. Zhang, H. Y. Xu, L. L. Ge and R. Guo, Acta Phys-Chim Sin, 2016, 32, 356–364.
156. S. Komaba, Y. Matsuura, T. Ishikawa, N. Yabuuchi, W. Murata and S. Kuze, Electrochem. Commun., 2012, 21, 65–71.
157. L. D. Ellis, T. D. Hatchard and M. N. Obrovac, J. Electrochem. Soc., 2012, 159, A1801–A1806.
158. J. W. Wang, X. H. Liu, S. X. Mao and J. Y. Huang, Nano Lett., 2012, 12, 5897–5902.
159. M.-F. Ng, J. Zheng and P. Wu, J. Phys. Chem. C, 2010, 114, 8542–8547.
160. Y. Wang, M. Wu, Z. Jiao and J. Y. Lee, Chem. Mater., 2009, 21, 3210–3214.
161. J. W. Zheng, S. M. L. Nai, M. Gupta, P. Saha, K. Kadakia, S. K. Park and P. N. Kumta, J. Phys. Chem. C, 2009, 113, 14015–14019.
162. W.-J. Zhang, M. F. Ng, P. Wu, J. Wei and M. Gupta, J. Power Sources, 2011, 196, 13–17.
163. M. K. Datta, R. Epur, P. Saha, K. Kadakia, S. K. Park and P. N. Kumta, J. Power Sources, 2013, 225, 316–321.
164. M. N. Obrovac, L. Christensen, D. B. Le and J. R. Dahnb, J. Electrochem. Soc., 2007, 154, A849–A853.
165. V. L. Chevrier and G. Ceder, J. Electrochem. Soc., 2011, 158, A1011.
166. Y. H. Liu, Y. H. Xu, Y. J. Zhu, J. N. Culver, C. A. Lundgren, K. Xu and C. S. Wang, ACS Nano, 2013, 7, 3627–3634.
167. X. Q. Xie, K. Kretschmer and J. Zhang, Nano Energy, 2015, 13, 208–217.
168. H. S. Hou, X. N. Tang and M. Q. Guo, Mater. Lett., 2014, 128, 408–411.
169. P. R. Abel, Y.-M. Lin and T. D. Souza, J. Phys. Chem. C, 2013, 117, 18885–18890.
170. D.-H. Nam, K.-S. Hong, S.-J. Lim, T.-H. Kim and H.-S. Kwon, J. Phys. Chem. C, 2014, 118, 20086–20093.
171. Y. Y. Cheng, J. F. Huang, R. Z. Li, Z. W. Xu, L. Y. Cao, H. B. Ouyang, J. Y. Li, H. Qi and C. W. Wang, Electrochim. Acta, 2015, 180, 227–233.
172. W. Chen, Z. L. Fan and C. L. Wang, Chem. Commun., 2010, 46, 3905–3911.
173. D.-H. Nam, T.-H. Kim and H.-S. Kwon, ACS Nano, 2014, 8, 11824–11835.
174. Y. Kim, K.-H. Ha and K. T. Lee, Chem.–Eur. J., 2014, 20, 11980–11992.
175. X. Yang, R. Y. Zhang and N. Chen, Chem.–Eur. J., 2016, 22, 1445–1451.
176. Y. C. Liu, N. Zhang and J. Chen, Adv. Mater., 2015, 27, 6702–6707.
177. X. Q. Xie, K. Kretschmer and B. Sun, Nano Energy, 2015, 13, 208–217.
178. Y. C. Liu, N. Zhang and J. Chen, Adv. Funct. Mater., 2015, 25, 214–220.
179. K. H. Dai, H. Zhao, Z. H. Wang, X. Y. Song, V. Battaglia and G. Liu, J. Power Sources, 2014, 263, 276–279.
180. H. L. Zhu, Z. Jia, Y. C. Chen, N. Weadock, J. Y. Wan, O. Vaaland, X. G. Han, T. Li and L. B. Hu, Nano Lett., 2013, 13, 3093–3100.
181. W. J. Li, S.-L. Chou, J.-Z. Wang, J. H. Kim, H.-K. Liu and S.-X. Dou, Adv. Mater., 2014, 26, 4037–4042.
182. J. Zhu and D. Deng, J. Phys. Chem. C, 2015, 119, 21323–21328.
183. P. R. Abel, M. G. Fields, A. Heller and C. B. Mullins, ACS Appl. Mater. Interfaces, 2014, 6, 15860–15867.
184. M. G. Wang, J. Han, H. X. Xiong and R. Guo, Langmuir, 2015, 31, 6220–6228.
185. J. Liu, Y. R. Wen, J. Maier and Y. Yu, Nano Lett., 2014, 14, 6387–6392.
186. M. Dahbi, N. Yabuuchi, K. Kubota, K. Tokiwa and S. Komaba, Phys. Chem. Chem. Phys., 2014, 16, 15007–15028.
187. A. Darwiche, M. T. Sougrati, B. Fraisse, L. Stievano and L. Monconduit, J. Am. Chem. Soc., 2012, 134, 20805–20811.
188. M. He, K. Kravchyk and M. Walter, Nano Lett., 2014, 14, 1255–1262.
189. Y. Zhu, X. Han, Y. Xu, Y. Liu and S. Zheng, ACS Nano, 2013, 7, 6378–6386.
190. Z. A. Zhang, X. X. Zhao and J. Li, Electrochim. Acta, 2015, 176, 1296–1301.
191. I. T. Kim, E. Allcorn and A. Manthiram, J. Power Sources, 2015, 281, 11–17.
192. I. T. Kim, S.-O. Kim and A. Manthiram, J. Power Sources, 2014, 269, 848–854.
193. L. W. Ji, M. Gu, Y. Y. Shao, X. L. Li, M. H. Engelhard, B. W. Arey, W. Wang, Z. M. Nie, J. Xiao, C. M. Wang, J.-G. Zhang and J. Liu, Adv. Mater., 2014, 26, 2901–2908.
194. L. W. Ji, W. D. Zhou, V. Chabot, A. P. Yu and X. C. Xiao, ACS Appl. Mater. Interfaces, 2015, 7, 24895–24901.
195. J. Park, J.-W. Park, J.-H. Han, S.-W. Lee, K.-Y. Lee, H.-S. Ryu, K.-W. Kim, G. X. Wang and J.-H. Ahn, Mater. Res. Bull., 2014, 58, 186–189.
196. Y. C. Lu, C. Ma, T. Kidera, J. Alvarado, T. Kidera, N. Dimov, Y. S. Meng and S. Okada, J. Power Sources, 2015, 284, 287–295.
197. M. D. Slater, D. Kim, E. Lee and C. S. Johnson, Adv. Funct. Mater., 2012, 8, 947–958.
198. Y. Wang, D. Su, C. Wang and G. Wang, Electrochem. Commun., 2013, 29, 8–11.
199. D. Su, H.-J. Ahn and G. Wang, Chem. Commun., 2013, 49, 3131–3133.
200. Y. D. Zhang, J. Xie, S. C. Zhang, P. Y. Zhu, G. S. Cao and X. B. Zhao, Electrochim. Acta, 2015, 151, 8–15.
201. Y. Wang, D. W. Su, C. Y. Wang and G. X. Wang, Electrochem. Commun., 2013, 29, 298–311.
202. Y. H. Liu, X. Fang, M. Y. Ge, J. P. Rong, C. F. Shen, A. Y. Zhang, H. A. Enaya and C. W. Zhou, Nano Energy, 2015, 16, 399–407.
203. M. Dirican, Y. Lu, Y. Q. Ge, O. Yildiz and X. W. Zhang, ACS Appl. Mater. Interfaces, 2015, 7, 18387–18396.
204. W. P. Sun, X. H. Rui, D. Yang, Z. Q. Sun, B. Li, W. Y. Zhang, Y. Zong, S. Madhavi, S. X. Dou and Q. Y. Yan, ACS Nano, 2015, 4, 11371–11381.
205. P. K. Dutta, U. K. Sen and S. Mitra, RSC Adv., 2014, 4, 43155–43159.
206. Y. D. Zhang, P. Y. Zhu, L. L. Huang, J. Xie, S. C. Zhang, G. S. Cao and X. B. Zhao, Adv. Funct. Mater., 2014, 25, 481–489.
207. B. H. Qu, C. Z. Ma, G. Ji, C. H. Xu, J. Xu, Y. S. Meng, T. H. Wang and J. Y. Lee, Adv. Mater., 2014, 26, 3854–3859.
208. T. F. Zhou, W. K. Pang, C. F. Zhang, J. P. Yang, Z. X. Chen, H. K. Liu and Z. P. Guo, ACS Nano, 2014, 8, 8323–8333.
209. Z. F. Jiang, C. Wang, G. H. Du, Y. J. Zhong and J. Z. Jiang, J. Mater. Chem., 2012, 22, 9494–9496.
210. X. Q. Xie, D. W. Su, S. Q. Chen, J. Q. Zhang, S. X. Dou and G. X. Wang, Chem.–Asian J., 2014, 9, 1611–1619.
211. J. W. Wang, X. H. Liu, S. X. Mao and J. Y. Huang, Nano Lett., 2012, 12, 5897–5902.
212. Y. J. Hong, J. W. Yoon, J. H. Lee and Y. C. Kang, Chem.–Eur. J., 2015, 21, 371–376.
213. Y. C. Liu, H. Y. Kang, L. F. Jiao, C. C. Chen, K. Z. Cao, Y. J. Wang and H. T. Yuan, Nanoscale, 2015, 7, 1325–1332.
214. W. W. Xu, K. N. Zhao, L. Zhang, Z. Q. Xie, Z. Y. Cai and Y. Wang, J. Alloys Compd., 2016, 654, 357–362.
215. C. Ma, J. Xu, J. Alvarado, B. H. Qu, J. Somerville, J. Y. Lee and Y. S. Meng, Chem. Mater., 2015, 27, 5633–5640.
216. Y. D. Zhang, P. Y. Zhu, L. L. Huang, J. Xie, S. C. Zhang, G. S. Cao and X. B. Zhao, Adv. Funct. Mater., 2015, 25, 481–489.
217. B. H. Qu, C. Ma, G. Ji, C. H. Xu, J. Xu, Y. S. Meng, T. H. Wang and J. Y. Lee, Adv. Mater., 2014, 26, 3854–3859.
218. J. J. Wang, C. Luo, J. F. Mao, Y. J. Zhu, X. L. Fan, A. C. Mignerey and C. S. Wang, ACS Appl. Mater. Interfaces, 2015, 7, 11476–11481.
219. S. L. Liu, H. Z. Zhang, L. Q. Xu, L. B. Ma and X. X. Chen, J. Power Sources, 2016, 304, 346–353.
220. Y. J. Kim, Y. Kim, A. Choi, S. Woo, D. Mok, N.-S. Choi, Y. S. Jung, J. H. Ryu, S. M. Oh and K. T. Lee, Adv. Mater., 2014, 26, 4139–4144.
221. Y. Kim, Y. Park, A. Choi, N.-S. Choi, J. Kim, J. Lee, J. H. Ryu, S. M. Oh and K. T. Lee, Adv. Mater., 2013, 25, 3045–3050.
222. J. Qian, X. Wu, Y. Cao, X. Ai and H. Yang, Angew. Chem., Int. Ed., 2013, 52, 4633–4638.
223. Y. J. Kim, Y. Kim, A. Choi, S. Woo, D. Mok, N.-S. Choi, Y. S. Jung, J. H. Ryu, S. M. Oh and K. T. Lee, Adv. Mater., 2014, 26, 4139–4144.
224. J. F. Qian, Y. Xiong, Y. L. Cao, X. P. Ai and H. X. Yang, Nano Lett., 2014, 14, 1865–1869.
225. T. Honma, T. Togashi, H. Kondo, T. Komatsu, H. Yamauchi, A. Sakamoto and T. Sakai, APL Mater., 2013, 052101–052103.
226. J.-C. Kim and D.-W. Kim, Electrochem. Commun., 2014, 46, 124–127.
227. J. F. Qian, Y. Xiong and Y. L. Cao, Nano Lett., 2014, 14, 1865–1869.
228. X. Q. Meng, M. Zhou, X. L. Li, J. Y. Yao, F. L. Liu, H. C. He, P. Xiao and Y. H. Zhang, Electrochim. Acta, 2013, 109, 20–26.
229. X. Q. Meng, M. Zhou and X. L. Li, Electrochim. Acta, 2013, 109, 20–26.
230. S. N. Pusawale, P. R. Deshmukh and C. D. Lokhande, Appl. Surf. Sci., 2011, 257, 9498–9502.
231. S. Y. Wang, S. P. Jiang and X. Wang, Electrochim. Acta, 2011, 56, 3338–3344.
232. R. K. Selvan, I. Perelshtein, N. Perkas and A. Gedanken, J. Phys. Chem. C, 2008, 112, 1825–1830.
233. S. P. Lim, N. M. Huang and H. N. Limb, Ceram. Int., 2013, 39, 6647–6655.
234. Y. Wang, Z. Shi, Y. Huang, Y. Ma, C. Wang, M. Chen and Y. Chen, J. Phy. Chem. C, 2009, 113, 13103–13107.
235. C. Liu, Z. Yu, D. Neff, A. Zhamu and B. Z. Jang, Nano Lett., 2010, 10, 4863–4868.
236. T. Y. Kim, H. W. Lee, M. Stoller, D. R. Dreyer, C. W. Bielawski, R. S. Ruoff and K. S. Suh, ACS Nano, 2011, 5, 436–442.
237. M. D. Stoller, S. Park, Y. Zhu, J. An and R. S. Ruoff, Nano Lett., 2008, 8, 3498–3502.
238. S. Wang, S. P. Jiang and X. Wang, Electrochim. Acta, 2011, 56, 3338–3344.
239. Y. K. Wang, Y. S. Liu and J. M. Zhang, J. Nanopart. Res., 2015, 17, 420–424.
240. F. Li, J. Song, S. Gan, S. Gan, Q. Zhang, D. Han and L. N. A. Ivaska, Nanotechnology, 2009, 20, 455602.
241. S. P. Lim, N. M. Huang and H. N. Limb, Ceram. Int., 2013, 39, 6647–6655.
242. S. Y. Wang, S. P. Jiang and X. Wang, Electrochim. Acta, 2011, 56, 3338–3344.
243. R. K. Selvan, I. Perelshtein and A. Gedanken, J. Phys. Chem. C, 2008, 112, 1825–1830.
244. F. Su, C. K. Poh, J. S. Chen, G. Xu, D. Wang, Q. Li, J. y. Lin and X. W. Lou, Energy Environ. Sci., 2011, 4, 717–724.
245. H. Ren, J. j. Sun, R. b. Yu, M. Yang, L. Gu, P. Liu, H. j. Zhao, D. Kisailuse and D. Wang, Chem. Sci., 2016, 7, 793–798.
246. P. Manivel, S. Ramakrishnan, N. K. Kothurkar, A. Balamurugan, N. Ponpandian, D. Mangalaraj and C. Viswanathan, Mater. Res. Bull., 2013, 48, 640–645.
247. Z.-A. Hu, Y.-L. Xie, Y.-X. Wang, L.-P. Mo, Y.-Y. Yang and Z.-Y. Zhang, Mater. Chem. Phys., 2009, 114, 990–995.
248. J. Du, X. y. Lai, N. l. Yang, J. Zhai, D. Kisailus, F. B. Su, D. Wang and L. Jiang, ACS Nano, 2011, 5, 590–596.
249. Y. H. Jin and M. Q. Jia, Colloids Surf., A, 2015, 464, 17–25.
250. S. Trasatti, Parts A & B, Elsevier, 1980.
251. S.-M. Lin and T.-C. Wen, J. Appl. Electrochem., 1993, 23, 487–492.
252. S. Ferro and A. D. Battisti, J. Phys. Chem. B, 2002, 106, 2249–2252.
253. C.-C. Wang and C.-C. Hu, J. Electrochem. Soc., 2005, 152, A370–A375.
254. J. Han, M. G. Wang, R. Chen, N. Han and R. Guo, Chem Commun, 2014, 50, 8295–8298.
255. X. Y. Lai, J. Li, B. A. Korgel, Z. H. Dong, Z. m. Li, F. b. Su, J. Du and D. Wang, Angew. Chem., Int. Ed., 2011, 50, 2738–2741.
256. D. Mao, J. Yao, X. Y. Lai, M. Yang, J. Du and D. Wang, Small, 2011, 5, 578–582.
257. C.-C. Wang and C.-C. Hu, Electrochim. Acta, 2005, 50, 2573–2581.
258. I. Shakir, M. Shahid and D. J. Kang, Electrochim. Acta, 2012, 72, 134–137.
259. Y. Q. Zhang and Y. Mo, Electrochim. Acta, 2014, 142, 76–83.
260. C. S. Ferreira, R. R. Passos and L. A. Pocrifka, J. Power Sources, 2014, 271, 104–107.
261. Z. Qin, Z. J. Li and R. A. Outlaw, J. Power Sources, 2012, 3, 303–308.
262. D. P. Dubal, S. V. Patil and C. D. Lokhande, J. Alloys Compd., 2012, 552, 240–247.
263. F. Cao, Y. Liu and J. Yuan, Electrochim. Acta, 2012, 81, 1–7.
264. H. Liu, Y. Wang and Y. Ding, Mater. Sci. Eng., B, 2013, 178, 293–298.
265. C. Fu, H. Zhou and Y. Kuang, Mater. Chem. Phys., 2012, 132, 596–600.
266. F. C. Cebeci, E. Sezer and A. S. Sarac, Electrochim. Acta, 2009, 54, 6354–6360.
267. J. E. Benedetti, S. C. Canobre and S. Neves, Electrochim. Acta, 2007, 52, 4734–4741.
268. G. P. Pandey and A. C. Rastogi, Electrochim. Acta, 2013, 87, 158–168.

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