Layer-by-layer anodes with an orientation-arranged structure induced by magnetic field for high-performance lithium ion batteries

Abstract

Fe₃O₄/carbon fibers (CFs) in a novel layer-by-layer (LBL) alignment as anodes for lithium ion batteries (LIBs) were successfully prepared through the assistance of a magnetic field. In this approach, Fe₃O₄ nanoparticles were deposited on carbon fibers by the sol–gel approach. Induced by a magnetic field, the alignment of Fe₃O₄/CFs was formed, and the LBL structure was fabricated by alternately dropping the hydrous and organic slurries of active materials. Due to the change in the orientation of the magnetic field, each subsequent prepared Fe₃O₄/CF alignment layer was vertical to the last one, and the electrical conductivity of Fe₃O₄/CFs, spaces for Li⁺ storage and channels for the diffusion of Li⁺ all sharply increased. Thus, a high electrochemical performance was achieved: specific capacities of 1671.3 and 504.6 mA h g⁻¹ at current densities of 0.1 A g⁻¹ and 3 A g⁻¹, respectively; capacity retention of 83.8% and specific capacity > 420 mA h g⁻¹ at 3 A g⁻¹ after 2000 cycles for LIBs.

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1 Introduction

With the rapid promotion and popularization of portable electronics, the development of high-performance Li ion batteries (LIBs) is inevitable.^1–5 One strategy is the design of novel electrodes for the batteries by improving the specific capacity of active materials or modifying the structure of electrodes.^5–10 Transition metal oxides and sulfides are promising anode materials for LIBs and sodium ion batteries (SIBs) due to their high theoretical specific capacity (e.g., 926 mA h g⁻¹ for Fe₃O₄).^11–14 However, some challenges must be overcome before the commercial applications of transition metal oxide or sulfide-based electrodes can be achieved; for example, excessive volume effect, suffered a lot by the electrode materials, is caused by the active material layer and current collector in the repeated extraction-insertion of Li⁺/Na⁺.^13,14 Moreover, the poor intrinsic conductivity of transition metal oxides or sulfides also limits the performance of anodes.^15,16 In recent years, many studies have investigated methods to overcome the above defects: one strategy is loading these active materials on a conductive framework (such as graphene, porous carbon, amorphous carbon) to enhance the transfer of electrodes;^17–21 the preparation of an active materials@shell structure is another strategy to buffer the excessive volume effect as the strong skeleton of shells limits the volume change of active materials in charge/discharge processes.^8,22–27 Additionally, modifying the structure of electrodes is also an efficient strategy to conquer the above challenges.^28–32 Fe₃O₄/Cu nanorod anodes were fabricated by a two-step approach: Cu nanorods were grown using a electrochemically assisted template method and then Fe₃O₄ nanoparticles were electrodeposited.³³ A carbon cloth was also employed as general scaffolds to develop novel electrodes without the usage of binders.^34,35 Notably, the electrodes were also modified by the assistance of a magnetic field that served as the driving force for the self-assembly of materials.^36–39 For example, graphitic anodes were modified by ferromagnetic nanoparticles, and the current collector could be vertically distributed so as to reduce the tortuosity under the induction of the magnetic field.^36,37 Single layer orientation-arranged electrodes were also induced by a magnetic field because they were made from Fe₃O₄ composites. Such a layered electrode structure built an efficient conductive network and reduced the electrode resistance, further enhancing the rate capacity and cycle performance of LIBs.^38,39

In the present work, Fe₃O₄/carbon fibers (CFs) in a novel layer-by-layer (LBL) alignment have been successfully prepared through the assistance of a magnetic field as anodes for LIBs. In this approach, Fe₃O₄ nanoparticles were deposited on carbon fibers by the sol–gel approach. Induced by a magnetic field, the alignment of the Fe₃O₄/CFs was formed and the LBL structure was fabricated by alternately dropping the hydrous and organic slurries of active materials. Due to the change in the orientation of the magnetic field, the prepared Fe₃O₄/CF alignment layer was vertical to the last one. These LBL Fe₃O₄/CF alignments might be superb anode materials for LIBs and SIBs, exhibiting superior electrochemical properties.

2 Experiment

2.1 Preparation of Fe₃O₄/CFs

To synthesize a Fe₃O₄/CF composite, in N₂ atmosphere, 0.01 mol Fe²⁺ and 0.02 mol Fe³⁺ ions were dissolved into 100 mL deionized water and then 2.52 g carbon fibers were dispersed in deionized water stirred at 60 °C; Fe₃O₄ nanoparticles were deposited on carbon fibers by adding NaOH into the solution to maintain pH > 10. Finally, Fe₃O₄/CFs was obtained after filtering and drying.

2.2 Preparation of the layer-by-layer Fe₃O₄/CF alignment-anode

In this work, arboxyl methylated cellulose (CMC) and N-methyl pyrrolidinone (NMP) were employed as binders. Fe₃O₄/CFs, super-p and PVDF were dispersed in N-methyl pyrrolidinone (NMP) to get a slurry with a mass ratio of 8 : 1 : 1. The organic slurry was dropped on the copper foil, and then the Fe₃O₄/CF coating was placed in the magnetic field for 1 h to form the first Fe₃O₄/CF alignment-layer. To form the second layer, Fe₃O₄/CF, super-p and CMC were dispersed in distilled water at a weight ratio of 8 : 1 : 1. The hydrous slurry was dropped on the first Fe₃O₄/CF alignment layer and then was placed in the magnetic field for 1 h, which was vertical to the alignment of the first layer. Thus, the layer-by-layer Fe₃O₄/CF alignment-anode was formed by alternately dropping the hydrous and organic mixing slurries in the magnetic field (Fig. 1). For comparison, 2-layer, 4-layer and 6-layer anodes were assembled. Unfortunately, the 6-layer anode was too thick and cracked. The 2-LBL and 4-LBL Fe₃O₄/CF alignment anodes were marked by 2L and 4L Fe₃O₄/CFs, respectively. Fe₃O₄/CF-based anode prepared by traditional methods without the LBL alignment was marked by R-Fe₃O₄/CFs. To observe the cross-section of the layer-by-layer Fe₃O₄/CF alignment structure, a 5-LBL structure was prepared on the glass slide, which was easier broken than the structure prepared on the copper foil.

Fig. 1 Scheme of the pathway for the synthesis of an LBL Fe₃O₄/CF alignment-anode.

2.3 Characterization

Samples were characterized and analyzed by a X-ray diffractometer (XRD, Bruker AXS), vibrating sample magnetometer (VSM, MLVSM9 MagLab 9 T, Oxford Instrument), high resolution transmission electron microscopy (TEM: JEOL, JEM-2100F) and field emitted scanning electron microscopy (FESEM, JEOL: JSM-6700F).

2.4 Electrochemical measurements

Coin cells (2016-type) were assembled by using the as-prepared LBL alignment structure as a working electrode and a lithium metal disk as the counter. Porous polypropylene film (Celgard 2400) and 1 M LiPF6 dissolved in a solution with 1 : 1 : 1 (volume ratio) ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) were used as the separator and electrolyte, respectively. After assembly, the cyclic voltammetry (CV) profiles were scanned at a rate of 0.1 mV s⁻¹ in the voltage range of 0.01–3 V (electrochemical workstation: CHI 760E). The cycling stability and galvanostatic charge–discharge (GCD) measurements of the cells were carried out at between 0.001 and 3 V (vs. Li⁺/Li, for LIBs) with a battery test system (LAND CT-2001A tester). An electrochemical workstation (Autolab Pgstat302n) was employed to measure the impedance spectrum and simulate the circuit of batteries. The frequency range was 0.01 Hz to 100 kHz, with a 5 mV amplitude.

3 Results and discussion

The XRD pattern of Fe₃O₄/CFs prepared by the sol–gel approach is shown in Fig. 2a and the peaks are consistent with the XRD patterns of Fe₃O₄ (JCPDS: 19-0629), of which 2θ = 30.07°, 35.42°, 43.05°, 53.41°, 56.93° and 63.48° correspond to the (220), (311), (400), (422), (511) and (440) crystal planes of Fe₃O₄, respectively; and no characteristic peaks of impurities (e.g., Fe₂O₃ and other ferrous oxides) have been found in the XRD pattern of Fe₃O₄/CFs. The diffraction peak (2θ = 26.6°) is in the (002) crystal plane of the carbon fiber, which is very strong, indicating that the carbon fiber has superior crystallinity. When being dispersed in an aqueous solution, all prepared Fe₃O₄/CF composites can respond to the added magnetic field (Fig. S1 in ESI†). According to the results of the VSM, the saturation magnetization (M_s) and coercivity values (H_c) of Fe₃O₄/CFs are 62 emu g⁻¹ and 135 Oe, respectively (Fig. 2b). Thus, the magnetic property of the prepared Fe₃O₄/CFs can be aligned by being induced with magnets.

Fig. 2 (a) XRD pattern, (b) VSM hysteresis loops (the central part of the loop was inserted) and (c) SEM image of Fe₃O₄/CFs, and (d) high resolution TEM images of Fe₃O₄ nanoparticles.

The morphology and microstructure of the Fe₃O₄/CF sample and the 4L-Fe₃O₄/CF anode are shown in Fig. 2 and 3. The SEM image of Fe₃O₄/CFs is shown in Fig. 2c and Fe₃O₄ nanoparticles are distributed on the surface of carbon fiber (their average diameter is ∼6.5 μm). The average size of the prepared Fe₃O₄ nanoparticles is ∼20 nm and the (220) lattice of Fe₃O₄ nanoparticles can be easily found in the HRTEM image (Fig. 2d). Because of magnetic Fe₃O₄ nanoparticles, the majority of Fe₃O₄/CFs is moved to form the alignment; as shown in Fig. 3a, the nanofibers are regularly interleaved and form the support skeleton network of the anode. Due to the alignment layer being very thin, the next Fe₃O₄/CF layer is exposed, which causes the orientation-arranged structure to look ambiguous (Fig. 3a). Thus, an optical microscope is employed to further observe the orientation-arranged anodes (Fig. S2†), suggesting the orientation of the Fe₃O₄/CFs is well arranged. Alternately dropping the hydrous and organic mixing slurries causes the LBL Fe₃O₄/CFs alignment anode and the Fe₃O₄/CFs alignment layer to be vertical to the next layer due to the changing orientation of the magnetic field (Fig. 3b and c). The fibers are overlapped regularly to form a continuous electronic conductive network in the anode. It is worth mentioning that the interleaving gap formed by the regular alignment of fibers in the anode structure may provide sufficient space for the volume change of Fe₃O₄ particles during charge and discharge and higher Li⁺ storage space, which might enhance the stability and specific capacity accordingly. Additionally, there are such interleaving gaps in the longitudinal distribution of the whole anode and these form a layered continuous conductive network, which further optimizes the anode. Therefore, under the same anode load, the layered alignment anode has more advantages than the traditionally assembled anode (R-Fe₃O₄/CFs).

Fig. 3 SEM images of (a) Fe₃O₄/CF alignment (because the alignment layer is very thin, the next Fe₃O₄/CFs layer is exposed, which is marked by yellow circles) and (b) and (c) cross section of layer-by-layer structure.

Fig. 4a shows the cyclic voltammetry curve of the prepared Fe₃O₄/CF anodes measured at room temperature at a scanning rate of 0.1 mV s⁻¹ and voltage of 0.01–3 V (vs. Li/Li⁺). In the first cycle, the reduction peak at 0.55 V is caused by the reduction of Fe³⁺ and Fe²⁺ to Fe⁰ and the irreversible reaction of the electrolyte to form a solid electrolyte interface (SEI) layer.^40–45 The reduction peak at 0.902 V can be attributed to the insertion of Li⁺ to form the Li_xFe₃O₄ intermediate.²¹ During charging, the wide peak at 1.73 V is mainly due to the oxidation of Fe⁰ to Fe²⁺ and Fe³⁺. Furthermore, the anodic peak at about 0.25 V represents the intercalation processes of lithium in the carbon phase (C + xLi⁺ + xe⁻ → Li_xC).⁴⁰ After the first cycle, the redox peaks shift to a higher potential. The redox peaks in the second and third cycles correspond to the mutual transformation between Fe⁰ and Fe₃O₄, and the reaction is 3Fe + 4Li₂O ↔ Fe₃O₄ + 8Li⁺ + 8e⁻.^21,41,42 The two reduction peaks at 0.6 V and 0.905 V merge into one reduction peak in the second and third cycles, and the peak intensity is weakened, indicating that there is an irreversible capacity loss in the initial intercalation process.

Fig. 4 Electrochemical performance of the prepared anodes for LIBs: CV profile (a) at a scan rate of 0.1 mV s⁻¹ between 0.01 and 3 V vs. Li⁺/Li for the 1st–3rd charge/discharge cycles of 4L-Fe₃O₄/CFs; (b) the galvanostatic charge–discharge profiles of 4L-Fe₃O₄/CFs; (c) charge–discharge cycling performance of 4L-Fe₃O₄/CFs and 2L-Fe₃O₄/CFs, and R-Fe₃O₄/CFs at different current densities from 0.1 to 3 A g⁻¹; (d) specific capacity retention rate of 4L-Fe₃O₄/CFs at 3 A g⁻¹.

Fig. 4b shows the discharge–charge profiles of the 4L-Fe₃O₄/CF anode at a current density of 0.1 A g⁻¹. It can be observed that the specific discharge/charge capacity of the first cycle is 1983.3 mA h g⁻¹ and 1558.4 mA h g⁻¹, respectively, with initial coulombic efficiency (ICE) is 78.6%. The irreversible capacity mainly comes from the formation of the SEI membrane. The discharge voltage platforms of the first cycle are located at ∼1 and ∼0.75 V (Fig. 4b), which correspond to the two reduction peaks in Fig. 4a.

The curves of the second and third cycles basically coincide, indicating that the formation of the SEI film has been basically completed in the first cycle, and the anodic active material tends to be stable. In the period of 2–5 cycles, CE is significantly increased to nearly 100%, and the curves overlap, demonstrating significant stability.

All Fe₃O₄/CF anodes' rate performances have been tested at gradually increased current densities ranging from 0.1 to 3 A g⁻¹ (Fig. 4c). The reversible specific capacities of the 4L-Fe₃O₄/CF anode are 1671.3, 1360.1, 1022.5 and 504.6 mA h g⁻¹ at current densities of 0.1, 0.5, 1 and 3 A g⁻¹, respectively. In contrast, 2L-Fe₃O₄/CFs (1428.6, 1091.7, 584.1 and 220.2 mA h g⁻¹, respectively) and R-Fe₃O₄/CFs (1299.3, 908.7, 448.1 and 106.7 mA h g⁻¹, respectively) exhibit poor rate performance. When the current density is returned to 0.1 A g⁻¹, the capacity is 1670.6 mA h g⁻¹, which is equivalent to 99.96% of the first reversible specific capacity. It is worth noting that the high discharge capacity of the 4L-Fe₃O₄/CF anode should be attributed to the orientation-arranged and layered structure of the anode.

In order to further examine the superior electrochemical performance of the 4L-Fe₃O₄/CF anode, the cyclic performance of the 4L-Fe₃O₄/CF anode was investigated (Fig. 4d). At a high current density of 3 A g⁻¹, the capacity of the 4L-Fe₃O₄/CF anode decays slowly in the first 100 cycles, and it is still able to maintain the reversible capacity of 421.1 mA h g⁻¹. The stablity of the 4L-Fe₃O₄/CFs is one time more than that of the 2L-Fe₃O₄/CFs and the R-Fe₃O₄/CFs, after 2000 cycles. After 20 cycles, CEs of all Fe₃O₄/CF anodes reach 100%. The cycle stability and capacity are greatly enhanced compared with 2L-Fe₃O₄/CFs and R-Fe₃O₄/CFs, and the coulomb efficiency is close to 100%. It shows that the 4L-Fe₃O₄/CF anode has superior cycle stability, and the reversibility of specific capacity is still very good under high current charge and discharge. This outstanding high-rate stability performance is due to the alignment and layered structure of the anode that prevent the crushing and loss of active substances in the process of circulation.

To gain a comprehensive understanding of the lithium ion storage mechanism of the 4L-Fe₃O₄/CF anode, a series of CV measurements were conducted at various scanning rates. The type of Li⁺ storage can be qualitatively distinguished based on the CV curve at various scan rates (Fig. 5a). The peak current (i) and scan rate (v) have a relationship shown in the following equations:

i = av^b (1)

log(i) = log(a) + b log(v) (2)

where a and b are constants; the value of b can be determined by the slope of formula (2). When b is 0.5, diffusion control contributes to the peak current; when b is 1, capacitance contributes to the peak current.⁴¹ According to the data presented in Fig. 5b, the two representative peak b values of the CV curve are 0.78 and 0.88, with an average of 0.83, indicating that capacitance cannot be ignored and plays a leading role.

Fig. 5 (a) CV curves of 4L-Fe₃O₄/CFs at scan rates from 0.1 to 1 mV s⁻¹; (b) relationship between log(peak current) and log(scan rate) plots for anodic and cathodic sweeps of CV; (c) fitted pseudo capacitance contribution of 4L-Fe₃O₄/CFs at 0.5 mV s⁻¹ and (d) contribution ratio of capacitance-controlled and diffusion-controlled capacities at various scan rates for LIBs.

The peak current value consists of the capacitive contribution (k₁v) and the diffusion control contribution (k₂v^1/2). In order to distinguish quantitatively between two types of Li⁺ storage, eqn (2) can be transformed into eqn (3):

i = k₁v + k₂v^1/2 (3)

k₁ and k₂ have different values at different voltage positions.⁴⁰ Therefore, the percentage of lithium storage capacity can be determined by calculating k₁ and k₂. For instance, when the scan rate is 0.5 mV s⁻¹, the capacitive contribution in Fig. 5c corresponds to the blue region, while the diffusive contribution corresponds to the red one. At various scan rates, the percentage of diffusion control and capacitance to total capacity is shown in Fig. 5d. As the sweep speed increases, the proportion of capacitive contribution increases proportionally: when the sweep speed is 0.1, 0.3, 0.5, and 1.0 mV s⁻¹, the proportion of capacitive contribution is 44%, 55%, 58%, and 72%, respectively. Such a high capacitance explains further why the Fe₃O₄/CFs anode's specific capacity exceeds the theoretical capacity. The capacitance is a result of the novel alignment structure between the layers of anode, which enables faster lithium ion and electron transfer and transmission.

The electrochemical impedance spectroscopy (EIS) of 4L-Fe₃O₄/CFs and R-Fe₃O₄/CFs has been tested (Fig. 6a) to better examine the mechanism of the superior electrochemical performance of 4L-Fe₃O₄/CFs. The equivalent circuit diagram obtained by simulation has been inserted, as shown in Fig. 6a. The semicircle in the high frequency region represents charge transfer, whereas the linearity in the low frequency region represents diffusion. The charge transfer resistance (R_ct) of 4L-Fe₃O₄/CFs is much lower (158 Ω) than that of R-Fe₃O₄/CFs (583 Ω), indicating that the LBL structure of 4L-Fe₃O₄/CFs sharply improves the electrical conductivity of Fe₃O₄/CFs. CNT/fibers have come under the spotlight because of the possibility that they can be arranged in a controlled way.⁴³ Therefore, it is necessary to construct orientation-arranged composite structures for improving the properties of composites. For example, in research investigating the effect of aligning CNTs in composite material structures, a remarkable improvement in the electrical properties of CNT composites was observed, as compared to their random placements.⁴⁴ In recent research reported by Lee et al., two factors, the CNT length and their arrangement, were introduced as important characteristics affecting electron transport properties in the matrix of composite materials.⁴⁵ Additionally, the linear fitting of Z′–ω^−1/2 in the low-frequency region is showed in Fig. 6b, from which a slope of σ can be obtained. The lithium-ion diffusion coefficient can be computed from the formulae as follows:

D = R²T²/(2A²n⁴F⁴C²σ²) (4)

Z′ = R_s + R_ct + σ²ω^−1/2 (5)

where R and T represent gas constant and room temperature, respectively. A, n, F and C correspond to the surface area of the anode, the number of electrons per molecule participating in the electron transfer reaction, the Faraday constant, and the concentration of lithium ions in the anode, respectively. In addition, σ is the slope of the line Z′–ω^−1/2, which can be obtained from the line of Z′–ω^−1/2 (shown in Fig. 6b). The only variable that influences the calculation result in this formula is σ. The lithium ion diffusion coefficient D_Li⁺ (cm² s⁻¹) of the 4L-Fe₃O₄/CF anode is 5.195 × 10⁻¹⁵ cm² s⁻¹, which is a bit greater than that of R-Fe₃O₄/CFs (3.448 × 10⁻¹⁵ cm² s⁻¹), according to the calculations, which suggests the LBL structure enhances Fe₃O₄/CFs mainly by improving their electrical conductivity.

Fig. 6 (a) Nyquist plots and Randles equivalent circuit of the prepared 4L-Fe₃O₄/CFs, R-Fe₃O₄/CFs anodes and the common equivalent circuit, and (b) the relationship between Z′ and ω^−1/2 of 4L-Fe₃O₄/CFs and R-Fe₃O₄/CFs anodes (vs. Li/Li⁺).

It should be noted that the layer-by-layer structure of the anode improves the electrochemical performance of Fe₃O₄/CFs due to the novelty of the structure. The present LBL structure of the anodes sharply improves the electrical conductivity of Fe₃O₄/CFs. In the 4L-Fe₃O₄/CF anode, each alignment layer is vertical to the next layer, which increases the contact between two layers. Thus, a regular and continuous conductive network has been built, which gives 4L-Fe₃O₄/CFs higher conductivity, significantly reduces the R_ct (Fig. 6a), leading to its superior rate performance (Fig. 4c). Additionally, the ordered structure could create many nanopores in the LBL anode, which provides more spaces for Li⁺ storage (Fig. 4c) or channels for the diffusion of Li⁺ (Fig. 6b). Finally, the novel structure can preserve the mechanical integrity of the anode by buffering the volume change, and further preventing the pulverization of Fe₃O₄ during the charge–discharge process; with the same loading of Fe₃O₄/CFs, 4L-Fe₃O₄/CFs has higher retention of specific capacity than 2L-Fe₃O₄/CFs in the cycle performance test (Fig. 4d). The 4L-Fe₃O₄/CF anode performs better (1671.3 mA h g⁻¹ at a current density of 0.1 A g⁻¹; 504.6 mA h g⁻¹ at 3 A g⁻¹) than many reported Fe₃O₄-based anodes for LIBs (at 0.1 A g⁻¹): ∼600 (Fe₃O₄/Fe₃C/CF),¹⁶ ∼732 (C/Fe₃O_4/rGO),²⁰ <772 (Fe₃O₄/rGO),¹⁹ 973 (Fe₃O₄/rGO),⁴² 1084 (porous Fe₃O₄/carbon microspheres (PFCMs)),⁴⁶ 1101.4 (Fe₃O₄@C2e),⁴⁷ 1334 (Fe₃O₄@C/rGO),¹⁷ 1411.8 (Fe₃O₄/C),⁴⁸ ∼1500 (hollow Fe₃O₄/graphene),⁴⁹ 903 (at 0.2C, magnetic field-induced orientation-arranged Fe₃O₄/graphene nanocomposites)³⁸ and 1140 (at 0.2C, magnetic field assisted orientation-arranged Fe₃O₄ nanocrystal/rGO paper)³⁹ mA h g⁻¹; at 3 A g⁻¹: <250 (α-Fe₂O₃@Fe₃O₄ heterostructure (CFH)),²¹ 335.8 (Fe₃O₄/rGO),¹⁹ <400 (Fe₃O₄/Fe₃C/CF),¹⁶ <400 (N-doped carbon nanofibers (Fe₃O₄/NCNFs)),⁵⁰ 240 (at 5C, magnetic field-induced orientation-arranged Fe₃O₄/graphene nanocomposites),³⁸ <500 (Fe₃O₄@C/rGO)⁵¹ and ∼500 (porous Fe₃O₄/carbon microspheres (PFCMs)⁴⁶ mA h g⁻¹). Hence, such a layer-by-layer Fe₃O₄/CF alignment provides a novel method for advanced electrodes, which might be widely used in areas as supercapacitors, catalysis, adsorbents and fuel cells.^52–60

4 Conclusions

In summary, Fe₃O₄/carbon fibers in a layer-by-layer alignment have been successfully prepared through a facile approach as anodes for LIBs. Each alignment layer is vertical to the one before it, which increases contact between two layers, leading to the sharp increase of the electrical conductivity of Fe₃O₄/CFs, as well as more spaces for Li⁺ storage and channels for the diffusion of Li⁺. Thus, a high electrochemical performance is achieved, with specific capacities of 1671.3 and 504.6 mA h g⁻¹ at current densities of 0.1 A g⁻¹ and 3 A g⁻¹, respectively; capacity retention of 83.8% and specific capacity >420 mA h g⁻¹ at 3 A g⁻¹ after 2000 cycles for LIBs.

Conflicts of interest

The authors declare no conflicts of interest.

Acknowledgements

This research was supported by funds from Shanghai Institute of Technology (YJ2010-50-1), Pujiang Talent Project (13PJ1407400) and funds (14520503100, 15520503400) from science and technology commission of Shanghai municipality, and research fund (project #21306113) from the National Natural Science Foundation of China.

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Footnotes

† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d2se01291j

‡ Q. M. X. and Z. M. S. contributed equally to this work.

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