A multifunctional ionic liquid additive providing a solvation structure and electrostatic shielding layer for highly stable aqueous zinc ion batteries

Abstract

The growth of dendrites and water-induced side reactions on the zinc (Zn) metal anode surface present significant challenges to the practical application of aqueous zinc ion batteries (AZIBs). To address these challenges, 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF₆) was employed as a multifunctional ionic liquid additive. First-principles calculations and molecular dynamics simulations reveal that [BMIM]⁺ cations preferentially adsorb onto the protrusions of the Zn metal anode surface due to its high adsorption energy, promoting homogeneous Zn²⁺ ion deposition and effectively mitigating the “tip effect”. Simultaneously, the PF₆⁻ anions participate in the solvation structure of hydrated Zn²⁺ ions to minimize the solvation effect by reducing the number of surrounding water (H₂O) molecules. This suppresses unexpected side reactions caused by active H₂O molecules entering the Helmholtz Plane (HP), thereby optimizing the diffusion and nucleation behaviour of Zn²⁺ ions. Therefore, the Zn//Zn symmetric cell achieved an extended cycle lifetime of over 1000 h at a high current density of 4 mA cm⁻² and a capacity of 0.5 mA h cm⁻². Meanwhile, even after 3000 cycles at a high current density of 10 A g⁻¹, the Zn//NH₄V₄O₁₀ full cell exhibited an impressive capacity retention of 92.7%. The practical application of flexibility further demonstrates that the designed AZIBs exhibit promising potential for large-scale energy storage and provide valuable insights for future studies.

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Introduction

In recent years, due to the continuous advancement of industrialization, the global demand for energy storage has grown rapidly. Due to its high theoretical specific capacity (820 mA h g⁻¹, 5855 mA h cm⁻³), low redox potential (−0.76 V vs. standard hydrogen electrode (SHE)), environmental friendliness, and crustal abundance, aqueous zinc ion batteries (AZIBs) have emerged as a promising alternative to lithium-ion batteries (LIBs) for large-scale energy storage systems.^1,2 However, despite the several advantages of AZIBs, they also face challenges, including intrinsic Zn dendrite growth,³ hydrogen evolution reaction (HER),⁴ Zn passivation and corrosion,⁵ and dissolution of cathode materials,⁶ which lead to lower reversibility in AZIBs, ultimately affecting their electrochemical performance. Addressing these significant challenges is essential for AZIBs as a meaningful and valuable alternative for large-scale energy storage.

Significant efforts have been devoted to addressing the challenges in recent years, focusing on electrode structure construction, electrolyte engineering and so on.^7–10 For example, surface regulation, as a normal optimization strategy, can provide a stable solid electrolyte interphase (SEI) layer on the surface of the Zn electrode with high Zn²⁺ ion conductivity, chemical stability, and mechanical strength. For example, Dong et al.¹¹ introduced an anionic polyelectrolyte alginate acid (SA) to initiate the in situ formation of the high-performance SEI layer on the Zn anode. Owing to the anionic groups of –COO⁻, the affinity of Zn²⁺ ions to alginate acid induces a well-aligned accelerating channel for uniform plating. In addition, electrolyte engineering is considered an effective strategy for enhancing the cycling stability, energy density, and safety of AZIBs by regulating interfacial reactions, solvation structures, and the overall electrochemical environment. Typically, electrolyte engineering focuses on the introduction of additives into the electrolyte¹² and the use of “water-in-salt” electrolytes (WiSE).¹³ Among these, the use of additives is particularly promising due to its ability to prevent dendrite-free formation and extend the lifespan conveniently and cost-effectively.¹⁴ Researchers have proposed several optimization strategies for electrolyte additives in AZIBs, including: (1) organic additives with nucleophilic functional groups (–COO⁻, –SO₃⁻etc.), such as sodium tartaric acid (TA-Na),¹⁵ oleic acid (OA),¹⁶ and sodium 3-mercapto-1-propanesulfonate (MPS),¹⁷ which adsorb onto the Zn anode surface, promoting uniform electric field distribution and smooth deposition; (2) electrostatic shielding layers, such as tetrabutylammonium sulfate (TBA₂SO₄)¹⁸ and tetramethylammonium sulfate (TMA₂SO₄),¹⁹ to reduce local electric field enhancement and regulate Zn²⁺ ion deposition; (3) specific additives, like 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)amide ([BMIM]FSI),²⁰ 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([BMIM]OTF),²¹ and 2-methyl imidazole (Hmim),²² can form an ideal stable SEI which is zincophilic and hydrophobic, thereby decreasing the nucleation overpotential of Zn plating, enhancing the interfacial charge transfer kinetics, homogenizing the Zn deposition behavior, and inhibiting parasitic side reactions; (4) solvent-based additives, including methanol,²³ ethylene glycol,²⁴ and acetonitrile (AN),²⁵ to modify Zn²⁺ ions' solvation structures and optimize ion migration and deposition, improving battery efficiency and cycle life.

However, due to the limitations of single additives, such as organic additives which may reduce H₂O activity but struggle with maintaining high ionic conductivity, as well as the overall cost and complexity compared to conventional surface engineering techniques, combining multiple additives has proven to be a more effective approach.¹⁹ For example, Yang et al.²⁶ introduced xylitol (XY) and graphene oxide (GO) into the basic electrolyte, where XY molecules solvate hydrated Zn²⁺ ions and the GO layer accelerates reaction kinetics. The formed SEI layer effectively ensures uniform Zn deposition and prevents Zn dendrite growth. Similarly, Chen et al.²⁷ developed an interfacial dual modulation strategy using D-mannose and sodium lignosulfonate, where the D-mannose and lignosulfonate species are alternately adsorbed on the Zn anode, accelerate Zn²⁺ ion transportation and reduce side reactions. However, mixing multiple additives may lead to interference, complicating electrolyte design and optimization. Additives may interact, causing unintended reactions that alter their effectiveness, such as reduced ion mobility or the formation of byproducts that degrade performance. These interactions can destabilize the electrolyte, posing challenges for reproducibility and scalability. In practical applications, balancing additive synergy becomes even more difficult under varying environmental conditions, leading to long-term performance degradation and reduced electrochemical efficiency.^19,28

Room-temperature ionic liquids (ILs) are well-known for their numerous advantages, including high ionic conductivity, superior thermal stability, nonvolatility, nonflammability, and a wide electrochemical window. Consequently, several ILs have been effectively introduced into AZIBs, demonstrating their capacity to stabilize the Zn anode. For instance, Chen and Yu et al.^20,21 employed [BMIM]OTF and 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)amide (EmimFSI) as additives. These ILs effectively regulate the solvation structure of Zn²⁺ ions and facilitate in situ SEI film formation, thereby mitigating hydrogen evolution reactions (HER) and preventing the growth of Zn dendrites. Similarly, Su et al. added N,N-dimethylpyrrolidinium tetrafluoroborate ([DMP]BF₄) into ZnSO₄ to electrolytes to suppress Zn dendrites and side reactions.²⁹ Building on these seminal studies, a multifunctional IL additive, 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF₆), aims to develop multifunctional IL additives that not only modulate the solvation structure of Zn²⁺ ions but also preferentially adsorb on the Zn anode surface, creating an electrostatic shielding layer and generating SEI layers in situ. The introduction of [BMIM]PF₆ additive significantly enhanced the stability of the Zn//Zn symmetric cell, achieving an impressive cycling lifespan of over 1000 h at 4 mA cm⁻²/0.5 mA h cm⁻² with a high coulombic efficiency (CE). Furthermore, the full cell assembled with the NH₄V₄O₁₀ cathode showed excellent cycling performance, achieving a stabilized capacity of 162.5 mA h g⁻¹ at 5 A g⁻¹ with 90.2% capacity retention after 4000 cycles, and a stabilized capacity of 90 mA h g⁻¹ with 92.7% capacity retention even at a current density of 10 A g⁻¹ after 3000 cycles. The use of [BMIM]PF₆ additives in flexible batteries further illustrates their great potential for application in flexible energy storage.

Results and discussion

The intrinsic growth of Zn dendrites, HER, zinc passivation, and corrosion lead to an irreversible Zn anode when using a blank electrolyte (BE, 2 M ZnSO₄), as illustrated in Fig. 1a. This is primarily due to the significant preference of hydrophilic sulfate ions (–SO₄²⁻) and free H₂O molecules to penetrate the Helmholtz Plane (HP).³⁰ Unresolved structures and enhanced diffusion rates lead to the non-uniform deposition of Zn²⁺ ions, resulting in the “dendritic tip effect”,³¹ which, as deposition continues, severely exacerbates Zn dendrite formation. Concurrently, water-induced side reactions generate hydrogen gas and the byproduct Zn₄SO₄(OH)₆·xH₂O (ZSH), increasing the risk of battery rupture and electrolyte leakage. In contrast, by introducing the [BMIM]PF₆ as an electrolyte additive, the observed problems can be effectively resolved, as illustrated in Fig. 1b. After the addition of [BMIM]PF₆ to the electrolyte, the additive [BMIM]PF₆ dissociates into [BMIM]⁺ cations and PF₆⁻ anions. On one hand, [BMIM]⁺ cations, with longer molecular chains and imidazole groups, play a part in shielding during the Zn deposition process. Due to their tendency to accumulate at sites of localized high current density under electric fields,³² [BMIM]⁺ cations are drawn to the surface of the Zn foil, limiting further growth of protrusions. On the other hand, the PF₆⁻ anion modifies the solvation structure of Zn²⁺ ions. The PF₆⁻ anion replaces the typical active water molecules in the solvation shell of Zn²⁺ ions, effectively inhibiting water-driven side reactions and thereby stabilizing the interface of the Zn anode.

Fig. 1 Mechanism schematic and performance comparison of different electrolytes: schematic diagram of Zn plating in (a) the BE system and (b) [BMIM]PF₆/BE system. SEM images and optical images of zinc foil after 7 days of immersion in (c) the BE system and (d) [BMIM]PF₆/BE system. (e) XRD patterns of the Zn foil after 7 days in the BE and [BMIM]PF₆/BE systems. (f) The electrochemical stability window of different electrolytes tested on Ti electrodes by scanning at a rate of 1 mV s⁻¹. (g) Linear polarization curves for the Zn foil in the BE and [BMIM]PF₆/BE systems, recorded at a scan rate of 1 mV s⁻¹. (h) Time–voltage profiles of Zn//Zn symmetric cells containing blank electrolytes and electrolytes with different contents at 10 mA cm⁻² and 0.5 mA h cm⁻².

It is well known that the electric double layer (EDL) structure plays a crucial role in the stability of the electrode–electrolyte interface. Therefore, electric double layer capacitance (EDLC) was employed to investigate the adsorption behavior of the [BMIM]PF₆ additive on the Zn anode. Cyclic voltammetry (CV) tests were carried out at various scan rates to determine the EDLC of Zn//Zn cells in both BE and [BMIM]PF₆/BE systems (Fig. S1a and b†). The EDLC values were calculated using the equation C = i_c/V, where i_c and V represent the corresponding current density at voltage 0 V and the scan rate, respectively.³³ The capacitance measurements of various Zn//Zn symmetric cells are summarized in Fig. S1c and d.† In the BE system, the Zn anodes show EDLC values of 63.1 μF cm⁻², which increased to 109.7 μF cm⁻² in the [BMIM]PF₆/BE system. The increased EDLC values suggest preferential adsorption of [BMIM]⁺ cations on the Zn anode surface, which is in agreement with the theoretical calculations. The preferential adsorption of [BMIM]⁺ cations on the zinc surface enhances the interaction with Zn²⁺ ions, which leads to a decrease in the thickness of the Zn²⁺ ion diffusion layer near the Zn anode.^9,34,35 Furthermore, these forces prompt the IHP to undergo a reconfiguration, which serves to impede the corrosion of free H₂O molecules on the Zn negative surface while simultaneously facilitating the desolvation process.

To preliminarily assess the protective effects of [BMIM]PF₆ additive, the corrosion behavior of Zn foil was examined by immersing it in the electrolyte. As shown in the inset of Fig. 1c, after 7 days, the Zn foil in the BE system exhibited significant surface roughness due to severe interfacial side reactions. In contrast, the Zn foil immersed in the [BMIM]PF₆/BE system maintained a smooth surface with minimal morphological alterations, as shown in the inset of Fig. 1d. Scanning electron microscopy (SEM) images, exhibited in the inset of Fig. 1c and d, confirm that the Zn foil in the BE system developed irregular, flaky by-products, whereas the surface of the Zn foil in the [BMIM]PF₆/BE system remained relatively smooth. X-ray diffraction (XRD) measurements (Fig. 1e) corroborate these results, displaying clear diffraction peaks for Zn₄SO₄(OH)₆·5H₂O on the Zn foil in the BE system, which were scarcely detectable in the presence of [BMIM]PF₆ additive. All these results indicate that [BMIM]PF₆ additive effectively prevents the formation of undesired by-products and significantly mitigates corrosion on the surface of the Zn anode.

The additive concentration is a key factor in determining the overall performance of the battery. When the amount of [BMIM]PF₆ additive in the Zn²⁺ ion solvation sheath increases, the solvation sheath expands accordingly. Consequently, the distance between Zn²⁺ ions and the Zn anode increases, leading to a higher energy requirement for zinc deposition and resulting in an increased overpotential. The significantly high overpotential indicates a considerable energy requirement for Zn deposition, potentially leading to cell failure due to mass transfer issues during extended cycling. Therefore, optimizing the overpotential by adjusting the [BMIM]PF₆ concentration is essential to improve the reversibility of the Zn anode. Various characterizations were conducted to illustrate the influence of [BMIM]PF₆ additive within the BE system. The ability of the [BMIM]PF₆ to curb the HER and prevent corrosion-induced side reactions was evaluated using linear scanning voltammetry (LSV) and the Tafel test. The electrochemical stability window of the electrolyte with various doping concentrations of [BMIM]PF₆ under the same conditions was measured using LSV, as exhibited in Fig. S2.† Due to the introduction of [BMIM]PF₆, the electrochemical stability window has been enlarged obviously and the optimum concentration of [BMIM]PF₆ was confirmed to be 1%. As exhibited in Fig. 1f, the BE system displays a current response of −1.103 V versus SCE, corresponding to a low potential and indicating notable HER. In comparison, the current response in the 1% [BMIM]PF₆ electrolyte is shifted negatively by 106 mV, highlighting the effective suppression of the HER by [BMIM]PF₆. The chemical stability of the Zn anode in the electrolyte was assessed using linear polarization measurements (Fig. 1g). Meanwhile, the introduction of 1% [BMIM]PF₆ additive notably reduced the corrosion current density of the Zn anode from 0.287 mA cm⁻² to 0.184 mA cm⁻², while also raising the corrosion potential from −1.084 V to −1.004 V, confirming that the [BMIM]PF₆ additive effectively reduced the corrosion rate of the Zn anode.³⁶ In addition, the linear polarization curves of various [BMIM]PF₆ electrolyte concentrations were examined, as exhibited in Fig. S3.† The low concentrations of [BMIM]PF₆ led to the formation of an inconsistent protective layer on the surface of the anode, which significantly impacted the optimized performance. Conversely, having too much [BMIM]PF₆ as an electrolyte can hinder the optimization of the system. This phenomenon arises due to its limitation on the adsorption capacity of the Zn surface, amplification of polarization effects, and hindrance of the kinetics of both diffusion and redox reactions (Fig. S4†). The time–voltage curves of electrolytes with different [BMIM]PF₆ contents were also measured, and the electrolyte containing 1% [BMIM]PF₆ showed the lowest polarization voltage and the optimum cycling stability at 10 mA cm⁻²/0.5 mA h cm⁻² (Fig. 1h). Therefore, the 1% [BMIM]PF₆ added to the blank electrolyte system ([BMIM]PF₆/BE) was selected as the electrolyte for further investigation.

To confirm the working mechanism of [BMIM]PF₆ as described above, that [BMIM]PF₆ acted as a multifunctional IL additive which enables electrolyte solvation structure and electrostatic shielding for AZIBs, several characterizations and theoretical calculations have been conducted. Fourier transform infrared (FTIR) spectroscopy was employed to evaluate the influence of [BMIM]PF₆ on the solvation structure of Zn²⁺ ions in the electrolyte. The observed shifts in O–H stretching vibrational signals from 3172.2 to 3116.7 cm⁻¹ with increasing [BMIM]PF₆ concentration indicate the penetration of PF₆⁻ anion molecules into the Zn²⁺ ion solvation sheath, displacing bound H₂O molecules and enhancing the hydrogen-bond network, as shown in Fig. 2a. Notably, the electrophilic ((CH₃)₃N⁺–) groups in [BMIM]⁺ cations also contribute to the regulation of the solvated structure, as demonstrated by Raman spectroscopy, which shows a red shift in the –SO₄²⁻ band from 1022 cm⁻¹ to 1026 cm⁻¹ with the introduction of [BMIM]PF₆ (Fig. 2b). Theoretical calculations confirm stronger binding between [BMIM]⁺ cations and –SO₄²⁻ compared to H₂O. As shown in Fig. 2c, the binding energy of [BMIM]⁺ cations with –SO₄²⁻ (−117.85 kcal mol⁻¹) is significantly lower than that of –SO₄²⁻ to a H₂O molecule (−7.07 kcal mol⁻¹) and the [BMIM]⁺ cation to a H₂O molecule (−8.52 kcal mol⁻¹), indicating that –SO₄²⁻ preferentially coordinates with [BMIM]⁺ cations over H₂O molecules, further confirming the binding effect on –SO₄²⁻ after the addition of [BMIM]PF₆. All results indicate that the introduction of [BMIM]PF₆ additive not only reduces the reactivity between H₂O molecules and Zn metal anodes but also inhibits the interaction between [BMIM]PF₆ and the sulfate anion to prevent the formation of ZSH as a by-product.

Fig. 2 Experimental and theoretical analysis of the solvation structure of electrolytes. (a) FTIR spectra of BE systems and electrolytes with different doping concentrations of [BMIM]PF₆ additive. (b) Raman spectra of the BE system and [BMIM]PF₆/BE system. (c) The comparison of binding energies between Zn²⁺&H₂O, H₂O&–SO₄²⁻, [BMIM]⁺&H₂O and [BMIM]⁺&–SO₄²⁻. 3D snapshot of MD simulation cells in the (d) BE and (f) [BMIM]PF₆/BE system. (e) Radial distribution functions (RDFs) of Zn²⁺–O (H₂O) and radius-dependent coordination numbers in the BE system. (g) RDFs of Zn²⁺–O (H₂O), Zn²⁺–P (PF₆⁻), and the radius-dependent coordination numbers in the [BMIM]PF₆/BE system.

To better understand the mechanics of [BMIM]PF₆ on Zn deposition, molecular dynamics (MD) simulations were conducted. The coordination distribution function (Fig. 2d and e) and radial distribution functions (RDFs) revealed that approximately 5.46 H₂O molecules typically coordinate with each Zn²⁺ ion within a distance of 2.98 Å, which is consistent with the typical formation of [Zn(H₂O)₆]²⁺ in the BE system. In the [BMIM]PF₆/BE system, PF₆⁻ anions participate in the solvation structure by substituting one of the H₂O molecules around Zn²⁺ ions (Fig. 2f and g), resulting in new coordination numbers of 5.16 for Zn²⁺–O (H₂O) and 0.12 for Zn²⁺–P (PF₆⁻). The substitution not only reduces the solvation effect by diminishing the H₂O molecules around Zn²⁺ ions but also alters the coordination environment, minimizing undesirable side reactions and enhancing Zn²⁺ ion diffusion and nucleation.³⁷ In summary, the substitution of an H₂O molecule by PF₆⁻ anions in the Zn²⁺ ions' solvation structure reduces electrostatic repulsion around Zn²⁺ ions, promoting faster ion migration and stabilizing the deposition process.

The formation of the solvent sheath structure has been carried out. It is crucial to confirm the electrostatic shielding layer formed by the [BMIM]⁺ cations, which plays a pivotal role in enhancing battery performance by reducing charge accumulation at the electrode interface. The decomposition of [BMIM]PF₆ is expected to create a hydrophobic and zincophilic stable electrostatic shielding layer, enhancing the even dispersion of Zn deposits and mitigating adverse outcomes. To confirm the formation of the electrostatic shielding layer on the Zn anode, a detailed investigation involved measuring the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies of both H₂O molecules and [BMIM]PF₆ additive, as shown in Fig. S5.† Accordingly, the molecules with lower LUMO energies exhibit higher electron affinity and are more predisposed to reduction.³⁸ [BMIM]PF₆ displays a lower LUMO energy (−0.108 eV) than H₂O molecules (0.029 eV), indicating a preference for reduction to form a stable electrostatic shielding layer. The preferential adsorption of [BMIM]⁺ cations on the Zn anode also can be substantiated by adsorption energy calculations and charge density differences. Fig. 3a illustrates first-principles calculations of the adsorption energies for H₂O molecules and the [BMIM]⁺ cations on the Zn (002) crystal plane. Compared to H₂O molecules, the [BMIM]⁺ cations exhibit a significantly more negative adsorption energy (−1.07 eV), suggesting a stronger affinity for [BMIM]⁺ cations on the Zn surface. The [BMIM]⁺ cation adsorption results in a locally hydrophobic electrode/electrolyte interface, as it displaces the water dipoles typically absorbed at the interface in aqueous solutions.³⁹ A contact angle test was further conducted to detect the affinity at the electrolyte/electrode interfaces, and as shown in Fig. 3b, the contact angle for the polished bare Zn electrode in the BE system is 86.72°, and decreases to 70.04° with the introduction of [BMIM]PF₆, indicates a higher affinity of [BMIM]PF₆ for the Zn surface. The enhanced compatibility between bare Zn and the [BMIM]PF₆/BE system can be attributed to the presence of zincophilic groups in [BMIM]PF₆. The adsorption of [BMIM]⁺ cations on the Zn anode surface prevents direct H₂O–Zn interactions, thereby efficiently suppressing water-induced side reactions.¹⁶Fig. 3c illustrates the variation in charge density when [BMIM]⁺ cations are absorbed onto the Zn (002) crystal plane, with significant electron transfer underscoring the strong interaction between [BMIM]⁺ cations and the Zn metal.

Fig. 3 Experimental and theoretical analysis of the adsorption behaviour of [BMIM]PF₆/BE and BE systems on zinc surfaces. (a) The adsorption energies of H₂O molecules and [BMIM]PF₆ additive on the Zn (002) crystal plane. (b) Contact angles of BE and [BMIM]PF₆/BE on the Zn metal anode surface. (c) Differential charge density plot of [BMIM]⁺ cations adsorbed on the Zn (002) crystal plane. (d) High-resolution XPS spectra of the Zn anodes after 50 cycles with the BE system (upper panel) and [BMIM]PF₆/BE system (lower panel) at 1 mA cm⁻²/1 mA h cm⁻². High-resolution XPS spectra of the Zn anodes after 50 cycles with the [BMIM]PF₆ electrolyte at 1 mA cm⁻²/1 mA h cm⁻²: (e) S 2p. Investigations of Zn deposition behaviour. (f) Current–time profiles for the Zn//Zn symmetric cell in BE and [BMIM]PF₆/BE systems. (g) CV curves of Zn//Ti cells with various electrolytes. (h) The initial Zn nucleation overpotentials using Zn//Cu half cells at 5 mA cm⁻² in different electrolytes. (i) Arrhenius plots and activation energies for BE and [BMIM]PF₆/BE systems.

The preferential adsorption of [BMIM]⁺ cations on the Zn anode surface is further confirmed by the X-ray photoelectron spectroscopy (XPS) analysis of the Zn anode after cycling, as exhibited in Fig. 3d and S6,† confirming the interfacial composition resulting from [BMIM]PF₆ modification. After 50 cycles, nitrogen (N) is detectable on the surface of cleaned and dried Zn electrodes only when [BMIM]PF₆ is present. As illustrated in Fig. 3d (lower panel), high-resolution analysis of the N 1s spectrum reveals two distinct peaks: the one at 401.8 eV is associated with nitrogen atoms within the [BMIM]⁺ cations, indicating adsorption of the cation, while the other at 399.2 eV is associated with nitrogen atoms in the C–N bonds of the stable electrostatic shielding layer,^21,40 suggesting the chemisorption between the N-containing molecules and Zn anode. The adsorbed molecules could isolate H₂O adsorption, further restricting the side reactions such as corrosion and the HER.^41,42 In addition, sulfur (S), in the form of C–S and Zn-containing inorganic salt (ZnS), –SO₄²⁻, is present only with the introduction of [BMIM]PF₆ (Fig. 3e and S6†). It is reported that the formation of ZnS would not only block the contact of the inner Zn metal with water and suppress side reactions, but also provide Zn²⁺ ion diffusion paths and homogenize Zn²⁺ ion flux,⁴³ which can be further confirmed by a higher ion transfer coefficient in the [BMIM]PF₆/BE system (0.66) compared to the BE system (0.36), as illustrated in Fig. S7.† These results further confirmed that the introduction of [BMIM]PF₆ additive significantly contributes to forming the stable electrostatic shielding layer on the Zn anode surface, which effectively suppresses the growth of Zn dendrites, the formation of inert by-products, and hydrogen evolution.

To systematically explore the role of the electrostatic shielding layer on the Zn surface, deposition behaviour electrochemical measurements for the nucleation of Zn²⁺ ions were carried out. Hydrogen precipitation occurs on the electrode surface when the Zn metal anode interacts with the aqueous electrolyte due to its higher redox potential compared to Zn deposition.⁴⁴ To further explore the modulation of the formed stable electrostatic shielding layer, chronoamperometry (CA) tests were conducted. Time–current curves were measured at an overpotential of −150 mV to assess diffusion kinetics and surface changes during deposition.⁴⁵ As exhibited in Fig. 3f, the Zn//Zn symmetric battery with BE exhibited a continuous increase in current density over 400 s, indicating a prolonged 2D diffusion process that leads to Zn accumulation and dendrite formation.⁴⁶ This is due to the fact that a larger nucleus can easily develop dendritic structures with random 2D diffusion. During 2D diffusion, adsorbed ions migrate across the surface in search of an optimal charge transfer point.³¹ In contrast, the symmetric battery with [BMIM]PF₆/BE transitioned from a 2D to a 3D diffusion process after 80 s, resulting in a steady-state current density and promoting more uniform Zn deposition.⁴⁷ This can be attributed to the constrained effect of adsorbed [BMIM]⁺ cations on Zn²⁺ diffusion. The interaction behavior among Zn²⁺ ions, H₂O molecules, and [BMIM]⁺ cations was studied by DFT calculations. It appears from the binding energy results that Zn²⁺ ions tend to combine with [BMIM]⁺ cations rather than H₂O molecules (Fig. S8†). The amino group is involved in the Zn²⁺–[BMIM]⁺ interaction through the lone pair electrons of the nitrogen atom. In short, homogeneous and fast Zn deposition can be easily achieved by the introduction of [BMIM]PF₆ additive. Electrochemical impedance spectroscopy (EIS) analysis was used to evaluate ion transport kinetics. The ionic conductivities of the SS//SS (stainless steel) symmetric cells in the BE and [BMIM]PF₆/BE systems were calculated to be 18.5 and 22.6 mS cm⁻¹, respectively, as exhibited in Fig. S9.† The enhanced ionic mobility indicates that the inclusion of [BMIM]PF₆ additive does not negatively impact ion movement, thus maintaining system efficiency. CV tests of the Zn//Ti battery in both BE and [BMIM]PF₆/BE systems, as shown in Fig. 3g, indicated that after the introduction of [BMIM]PF₆ additive, the response current increased as the nucleation overpotential increased. The Zn nucleation overpotential increased by 40 mV (from B to B′), indicating that the deposited Zn particles were smaller.⁴⁸ This increase also indicates that [BMIM]PF₆ effectively regulates Zn²⁺ ion diffusion and galvanic kinetics, leading to more uniform Zn deposition.⁴⁹ The voltage distribution in Zn//Cu half-cells further supported these findings, with the nucleation overpotential increasing from 73.06 to 90.64 mV with [BMIM]PF₆, as depicted in Fig. 3h. These results confirm that [BMIM]PF₆ additive plays a significant role in promoting smooth and uniform Zn nucleation while preventing Zn dendrite formation. It has been observed that the solvation of hydrated Zn²⁺ ions at the electrode–electrolyte interface significantly hinders charge migration during Zn deposition.⁴⁴ The solvation structure limits the mobility of Zn²⁺ ions in the electrolyte and influences the plating and stripping processes at the electrode surface. It also impacts the rate at which Zn²⁺ ions are removed and incorporated, and can modify the properties of the formation and structure of the expected stable electrostatic shielding layer. In general, a lower desolvation energy barrier for hydrated Zn²⁺ ions accelerates the migration of Zn²⁺ ions.⁵⁰ To quantitatively compare the desolvation energy barriers during Zn²⁺ ion deposition, the activation energy (E_a) can be calculated using the EIS measurements at various temperatures, based on the Arrhenius equation:^51,52

1/R_ct = A exp(−E_a/RT) (1)

where R_ct denotes the charge-transfer resistance, T represents the absolute temperature, and R represents the gas constant. Both R_ct and E_a are key parameters influencing the energy required for Zn²⁺ ion diffusion through the stable electrostatic shielding layer.⁵³ Nyquist plots for Zn//Zn symmetric cells in various electrolytes are presented in Fig. S10.† The experimental data were fitted using the equivalent circuits shown in the insets of Fig. S10,† with the fitting results summarized in Table S1.† The E_a for the Zn anode in the [BMIM]PF₆/BE system and the BE system was 41.15 kJ mol⁻¹ and 43.37 kJ mol⁻¹ (Fig. 3i), respectively, indicating that the formation of the electrostatic shielding layer facilitated the desolvation of hydrated Zn²⁺ ions. Furthermore, it's worth noting that the omission of the data point for the BE system at 70 °C was due to the inability of the battery in the BE system to suffer from high temperature conditions. Specifically, at 70 °C, the batteries under the BE system conditions failed and, in some instances, ruptured, as exhibited in the inset of Fig. S10.† In contrast, in the [BMIM]PF₆/BE system, the thermal stability of the Zn//Zn symmetric cell is significantly enhanced, which can be attributed to the use of the introduction of [BMIM]PF₆ additive, as an ionic liquid known for its high thermal stability.^20,54 The E_a for the Zn anode in the [BMIM]PF₆/BE system and the BE system was 41.15 kJ mol⁻¹ and 43.37 kJ mol⁻¹ (Fig. 3i), respectively, indicating that the formation of the electrostatic shielding layer facilitated the desolvation of hydrated Zn²⁺ ions.

The EIS measurements further confirm the importance of the stable electrostatic shielding layer on the anode surface. An equivalent circuit model was employed to fit the impedance data (Fig. S11†), with the corresponding electrochemical parameters detailed in Table S2.† Initially, the [BMIM]PF₆/BE system exhibits higher R_ct and R_f values than the BE system, due to the adsorption of [BMIM]PF₆ additive on the Zn anode, as demonstrated by first-principles calculations, leading to 3D Zn²⁺ ion deposition. As plating and stripping proceeded, R_ct and R_f significantly decreased in both electrolytes. However, values in the electrolyte without [BMIM]PF₆ increased continuously during cycles due to persistent side reactions and unstable interfaces. In contrast, the electrolyte with [BMIM]PF₆ exhibited relatively stable interfacial impedance. The formation of a stable electrostatic shielding layer not only minimizes side reactions between the Zn anode and the electrolyte but also controls the deposition behavior of Zn²⁺ ions.^55,56

The effective inhibition of Zn dendrite growth, inert by-products, and hydrogen precipitation, resulting from the formation of a stable electrostatic shielding layer, can be directly visualized through in situ optical microscopy. In the BE system (Fig. 4a), the Zn anode surface showed significant dendritic protrusions after a 5 minute deposition process, evolving into irregular prismatic and tree-like structures by 10 minutes. These protrusions led to severe inhomogeneous Zn deposition, with moss-like dendrites forming after 15 minutes, ultimately causing internal short circuits and degrading battery performance. In contrast, the electrolyte with [BMIM]PF₆ additive (Fig. 4b) maintained a smooth and uniform Zn anode surface throughout the deposition process. No dendrite formation can be observed even after 15 minutes of cycling, demonstrating a significant enhancement of the stability of Zn anodes by promoting balanced Zn²⁺ ion deposition and improving performance over extended cycling. The corresponding SEM images further confirmed the morphologies of the Zn anode surface modified by various electrolytes during cycling, providing evidence of the impact of [BMIM]PF₆ additive on Zn²⁺ ion deposition. In the BE system, the Zn anode surface exhibited roughness with unevenly distributed lamellar dendrites (Fig. 4c), indicating inhomogeneous deposition during electroplating. With continued cycling, the coverage and size of layered dendrites increased (Fig. 4d), reflecting uncontrolled dendrite aggregation and by-product formation. In contrast, the [BMIM]PF₆/BE system displayed a smoother, flatter Zn anode surface (Fig. 4e and f) with no parasitic by-products. This uniform deposition morphology suggests that [BMIM]PF₆ promotes a consistent Zn²⁺ ion flux and evenly distributed nucleation sites.

Fig. 4 In situ optical microscopy images of Zn deposition in (a) BE and (b) [BMIM]PF₆/BE systems at various deposition durations at 10 mA cm⁻². SEM images of the Zn anode after (c) 10 and (d) 20 cycles in the BE system. SEM images of the Zn anode after (e) 10 cycles and (f) 20 cycles in the [BMIM]PF₆/BE system. (g) XRD patterns of Zn anodes after cycling in different electrolytes. (h) AFM images of cycled Zn anodes in the BE system and (i) [BMIM]PF₆/BE system.

In order to confirm the significant role of [BMIM]PF₆ ions in stabilizing the structure of the deposited layer during the reconfiguration process, the Zn anode after 20 cycles was analysed by XRD measurement, as shown in Fig. 4g. The diffraction peaks located at 2θ = 8.06° in the BE system can be attributed to the unexpected byproduct Zn₄SO₄(OH)₆·xH₂O (ZSH) (PDF #39-0688). In contrast, no characteristic peak corresponding to ZSH can be detected in the [BMIM]PF₆/BE system. Moreover, the relative intensity of the (002) plane of the Zn anode in the [BMIM]PF₆/BE system was significantly enhanced after 20 cycles compared to the BE system. This observation suggests that the [BMIM]⁺ cations are preferentially adsorbed on the Zn (002) surface, promoting the flat growth of Zn nucleation on the anode surface.^57,58 The atomic force microscopy (AFM) images (Fig. 4h and i) clearly show the homogeneous surface morphology regulated by [BMIM]PF₆. The surface roughness of the Zn anode after 20 cycles at 1 mA cm⁻² and 1 mA h cm⁻² was examined using AFM. 3D AFM images clearly demonstrate the significant difference in Zn deposition between the two electrolytes (Fig. 4h and i). The root-mean-square roughness (R_q) is a quantitative indicator of the evolution of electrode surface morphology. In the BE system, the R_q value of the Zn anode is 442 nm, indicating that the surface morphology of the Zn anode after cycling is very rough, the deposition of Zn²⁺ ions is inhomogeneous and severe Zn (100) and (101) crystalline surfaces are observed, which will lead to severe growth of Zn dendrites. In contrast, the R_q value in the [BMIM]PF₆/BE system is only 57.4 nm, which indicates that the deposition of Zn²⁺ ions in the [BMIM]PF₆/BE system is much more homogeneous and organized.⁵⁹ The AFM and XRD results are in agreement with the SEM images obtained after 20 cycles at 1 mA cm⁻² and 1 mA h cm⁻². These results clearly demonstrate that the Zn anode maintains a uniform surface, which is significantly influenced by the introduction of the [BMIM]PF₆ additive.

The cycling performance and electrochemical stability of the [BMIM]PF₆ additive were investigated through cycling tests on symmetric cells under different constant-current conditions for an extended period. The Zn//Zn symmetric cells were evaluated using both [BMIM]PF₆/BE and BE systems at 1 mA cm⁻²/1 mA h cm⁻² to assess the stability of the Zn anode, as shown in Fig. 5a. The BE system showed a polarization voltage of 54 mV. However, after only 80 h of cycling, it suddenly short-circuited and exhibited poor cycling stability, likely caused by Zn dendrite growth from uneven deposition during the cycling process.³² In contrast, the symmetric cell in the [BMIM]PF₆/BE system maintained a cycle life of over 800 h under the same conditions and showed a slightly higher polarization voltage of 70 mV, with no short circuits (as illustration in Fig. 5a). The larger transfer resistance is what causes the larger polarization voltage. However, the polarization voltage of [BMIM]PF₆/BE increases significantly more slowly than that of BE, which implies faster Zn²⁺ ion migration and lower Zn²⁺ ion desolvation barriers.⁴¹ The charge/discharge curves demonstrate that the Zn//Zn symmetric cells with [BMIM]PF₆/BE exhibit stable voltage plateaus over long-term cycling, indicating reliable performance. The effectiveness of [BMIM]PF₆ as an additive was further evaluated under specific conditions of 4 mA cm⁻²/0.5 mA h cm⁻², as exhibited in Fig. 5b. Cells without [BMIM]PF₆ additive experienced a circuit failure within 22 h whereas those with [BMIM]PF₆ additive operated continuously for over 1000 h without short circuits. Furthermore, the [BMIM]PF₆ additive containing cells maintained stable cycling performance for 400 h at 4 mA cm⁻²/4 mA h cm⁻² without short circuits (Fig. S12 and S13†), whereas the BE system cells lasted only 46 h.

Fig. 5 Stability of Zn//Zn cells with [BMIM]PF₆ and without [BMIM]PF₆ electrolyte additive at (a) 1 mA cm⁻² and (b) 4 mA cm⁻² conditions. (c) Comparison of the rate capability of Zn//Zn cells with [BMIM]PF₆ and without [BMIM]PF₆ electrolyte. (d) CE values of Zn//Cu cells evaluated with [BMIM]PF₆ and without [BMIM]PF₆ electrolyte additive. (e) Comparison of the cycling lifespan between this study and previously published research, focusing on the impact of electrolyte addition. The specific citations relating to each point number are presented in Table S3.†

Comparisons at different current densities revealed that cells with [BMIM]PF₆ additive maintained stable stripping/deposition and efficient operation even at 8 mA cm⁻². In addition, these cells demonstrated excellent reversibility when the current density was reduced to 1 mA cm⁻². In contrast, the Zn//Zn symmetric cells in the BE system failed at 8 mA cm⁻², indicating the limited rate performance of the Zn anode (Fig. 5c). Zn//Zn symmetric cells with varying concentrations (0.5% and 1.5%) of [BMIM]PF₆ additive were also measured, as presented in Fig. S14 and S15,† indicating that the cells with 1% [BMIM]PF₆ additive exhibited superior cycling stability with smaller polarization voltage. Furthermore, a Zn//Cu cell was used to evaluate the CE, as exhibited in Fig. 5d, in BE and [BMIM]PF₆/BE systems. The Zn//Cu cell in the [BMIM]PF₆/BE system demonstrated consistent performance over 500 cycles, maintaining an average CE of 99.8% at 1 mA cm⁻². In contrast, the BE system exhibited a fluctuating voltage profile with an average CE of 99.2% and failed after 102 cycles due to local short circuits from Zn dendrite growth. Notably, the introduction of [BMIM]PF₆ additive resulted in a more stable nucleation potential (Fig. S16†), effectively reducing side reactions and Zn dendrite formation.^60,61 These results can be corroborated by SEM and XRD data, as illustrated in Fig. S17 and S18,† which were obtained from the surface of the Zn anode of a Zn//Cu half-cell after 20 cycles at a current density of 5 A g⁻¹. The SEM images (Fig. S17†) reveal the morphological changes on the Zn anode surface. In the BE system, continuous uneven Zn deposition led to significant 2D diffusion, resulting in the growth of Zn dendrites. These dendrites eventually aggregate and pierce through the separator, causing a short circuit within the battery.⁵⁹ In contrast, the Zn anode in the [BMIM]PF₆/BE system exhibited a smooth and flat surface without obvious dendrites, indicating that the [BMIM]PF₆ additive induced uniform deposition of Zn²⁺ ions and inhibited the growth of dendrites. The above results were also confirmed by XRD plots (Fig. S18†), and there was no obvious dendrite growth in the zinc anode introduced with [BMIM]PF₆ additive after cycling. All these results confirm the role of [BMIM]PF₆ additive in improving the reversibility and stability of the Zn anode. For comparison, the cycling lifespan of previously reported aqueous Zn//Zn symmetric cells and the cumulative plating capacity are summarized in Fig. 5e and Table S3.† The cumulative capacity, which reflects the total amount of Zn plated across all cycles, was significantly high, with the Zn anode in the [BMIM]PF₆/BE system achieving a maximum cumulative capacity of 4.2 Ah cm⁻² at 4 mA cm⁻²/4 mA h cm⁻², demonstrating outstanding electrochemical stability.

To determine the practicality of using [BMIM]PF₆ additive, Zn//NH₄V₄O₁₀ full cells were tested to evaluate their impact on electrochemical performance. SEM images of the synthesized cathode NH₄V₄O₁₀, corresponding elemental mapping, and XRD patterns of the NH₄V₄O₁₀ cathode are provided in Fig. S19 and S20.† Fig. S21† presents the CV plots of the cells using the BE and the [BMIM]PF₆/BE systems at 0.1 mV s⁻¹. The shape of the CV curves for the full cell remained almost the same, indicating that the introduction of [BMIM]PF₆ additive shows a negligible effect on the redox reaction of the NH₄V₄O₁₀ cathode. As shown in Fig. 6a and S22,† the rate performance of the Zn//NH₄V₄O₁₀ full cell was evaluated. The full cell using an electrolyte with [BMIM]PF₆ additive maintained a reversible capacity of 85.7 mA h g⁻¹ even at a high current density of 10 A g⁻¹. In contrast, the full cell with the BE system retained only 54.8 mA h g⁻¹ at the same current density, indicating a poor rate performance. Moreover, when the current density was reduced back to 0.5 A g⁻¹, the cell with [BMIM]PF₆ additive exhibited a stable capacity recovery to 278.2 mA h g⁻¹. The improved performance of the battery with the introduction of [BMIM]PF₆ additive further confirms the advantages of [BMIM]PF₆ additive in enhancing Zn²⁺ ion plating/stripping and reaction kinetics in the Zn//NH₄V₄O₁₀ battery.⁶² These results provide strong evidence that the [BMIM]PF₆ additive improves the stability and reversibility of the full cell. As shown in Fig. 6b and c, the full cells of both BE and [BMIM]PF₆/BE systems exhibited similar discharge-specific capacities on the 10th cycle at 0.5 A g⁻¹. However, the specific capacity of the full cell with the BE system declined from 221.7 mA h g⁻¹ at the 10th cycle to 101.2 mA h g⁻¹ by the 200th cycle, achieving a retention of only 45.6%. The degradation is mainly attributed to the uncontrolled formation of Zn dendrites and side reactions.⁶³ In contrast, due to the introduction of [BMIM]PF₆ additive, the full cell exhibited outstanding stability, retaining 97.2% of its capacity over 200 cycles and maintaining an average CE of 99.8%. Even after 500 cycles, it still retained a specific capacity of 222.6 mA h g⁻¹.

Fig. 6 Electrochemical performance of NH₄V₄O₁₀//Zn cells with and without [BMIM]PF₆ electrolyte: (a) rate performance in different electrolytes. (b) Electrostatic charge/discharge curves for different cycles at 0.5 A g⁻¹ current density. The corresponding cycle performance of NH₄V₄O₁₀//Zn cells at (c) 0.5 A g⁻¹, (d) 5 A g⁻¹, and (e) 10 A g⁻¹. (f) Structural diagram of a flexible battery. (g) The PAM–[BMIM]PF₆ flexible full cell powering a lamp.

The performance of full cells under high current densities is crucial because it provides insights into the battery's ability to deliver large amounts of power quickly. This is particularly important for applications requiring rapid discharge rates, such as electric vehicles and portable electronic devices. The proficiency of the Zn//NH₄V₄O₁₀ full cell in rapid plating and stripping processes under high current density was evaluated and is illustrated in Fig. 6d. The experimental findings indicate that the Zn//NH₄V₄O₁₀ full cell, when supplemented with [BMIM]PF₆ additive, exhibits a significant increase in capacity when operating at 5 A g⁻¹. After undergoing 4000 cycles, the cell consistently maintains a constant capacity of 162.5 mA h g⁻¹. Furthermore, even after 4000 cycles, it retains an impressive 90.2% of its initial capacity. This demonstrates how well [BMIM]PF₆ addition works to improve the efficiency and stability of the cell in challenging situations. The marked enhancement in both the rate capability and the cycling stability is primarily due to the incorporation of [BMIM]PF₆ additive into the BE system. This addition facilitates an even distribution of Zn²⁺ ions during deposition and effectively prevents the formation of zinc dendrites. Fig. 6e illustrates the long-term cycling performance of the NH₄V₄O₁₀//Zn cell at 10 A g⁻¹. The integration of [BMIM]PF₆ into the system resulted in a capacity retention rate of 92.7% after a substantial 3000 cycles. This remarkable stability during extended cycling is credited to the suppression of side reactions and dendrite growth, facilitated by the adsorptive properties of [BMIM]PF₆. These results indicate that the [BMIM]PF₆ additive can form a specific planar deposition layer and exhibit excellent Zn plating/stripping efficiency even under high current density testing. Consequently, by forming uniform Zn deposition through the co-conditioning effect of anions and cations, the [BMIM]PF₆ electrolyte additive plays a crucial role in safeguarding the Zn anode and preventing the formation of dendrites, further optimizing the kinetic performance of the Zn//NH₄V₄O₁₀ full cell. It also exhibits superior fast electrochemical response and excellent long-term cycling stability.

The flexible Zn//NH₄V₄O₁₀ cells were fabricated, as shown in Fig. 6f, with the electrolyte prepared by the introduction of [BMIM]PF₆ and PAM (PAM–[BMIM]PF₆). The cathode and anode were coated on a rectangular stainless-steel mesh with dimensions of 75 × 25 mm, thus constructing a flexible ZIB (FZIB). The fabricated flexible Zn//NH₄V₄O₁₀ cell, shown in Fig. S23,† provided a voltage of 0.94 V. To simulate practical applications in various situations, the FZIB cell was used to power the “NTU” consisting of LED lights, as shown in Fig. 6g. The performance of the FZIB under flat, bent, twisted, and sheared conditions is shown in Fig. S19.† It is noteworthy that a strong power supply is retained by the battery in all deformation states, indicating the resilience of its mechanical components. In addition, as shown in Fig. S24,† the flexible cell maintains its normal operation after 200 cycles (with a capacity retention of 95.1%), demonstrating good cycling performance.

Conclusions

In this work, a functional electrolyte additive ([BMIM]PF₆) for highly stabilized Zn metal anodes was developed. Various test results, such as Raman, FTIR, and DFT calculations, were utilized to analyze the entire electrolyte system. The electrochemical deposition behavior of Zn²⁺ ions can be significantly improved due to the introduction of [BMIM]PF₆ by generating an electrostatic shield at the Zn protrusions and tuning the solvation structure of Zn²⁺ ions. In addition, a zincophilic–microhydrophobic interphase was formed on the Zn anode surface, which not only established a smooth and flat Zn surface but also inhibited the generation of HER and by-products. Therefore, the Zn//Zn symmetric cell and the Zn//NH₄V₄O₁₀ full cell exhibit excellent electrochemical performance. The Zn//Zn symmetric cells with [BMIM]PF₆ additive exhibit a stable cycle life of more than 800 h at 1 mA cm⁻²/1 mA h cm⁻² and more than 1000 h at 4 mA cm⁻²/0.5 mA h cm⁻² under rapid charge/discharge conditions. More importantly, the Zn//NH₄V₄O₁₀ full cell with [BMIM]PF₆ additive was cycled for more than 3000 cycles (10 A g⁻¹) with a capacity retention of 92.7%. All results reveal that the ionic liquid [BMIM]PF₆ plays a crucial role in modulating the solvation structure of the electrolyte through anions and establishing a bifunctional strategy of electrostatic shielding through cations, providing a new strategy for the development of AZIBs with high long-cycle stability and efficiency.

Data availability

The authors declare that all data supporting the findings of this study are available within the paper and its ESI.†

Conflicts of interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was supported in part by the Key Program of Jiangsu Provincial Department of Education of China (23KJA510006, 22KJA510005) and Large Instruments Open Foundation of Nantong University (KFJN2322).

References

1. L. Ma, M. A. Schroeder, O. Borodin, T. P. Pollard, M. S. Ding, C. Wang and K. Xu, Nat. Energy, 2020, 5, 743–749.
2. V. Viswanathan, A. H. Epstein, Y.-M. Chiang, E. Takeuchi, M. Bradley, J. Langford and M. Winter, Nature, 2022, 601, 519–525.
3. Z. Hao, Y. Dai, X. Xu, X. Zhao, Y. Cong, X. Wu and W. Zhou, J. Mater. Chem. A, 2023, 11, 11031–11047.
4. Y. Yang, H. Lyu, Q. Wang, F. Mushtaq, X. Xie, F. Liu, X. Bo, W. Li and W. A. Daoud, J. Mater. Chem. A, 2023, 11, 12373–12383.
5. Z. Yang, C. Hu, Q. Zhang, T. Wu, C. Xie, H. Wang, Y. Tang, X. Ji and H. Wang, Angew. Chem., Int. Ed., 2023, 62, e202308017.
6. Z. Yan, Q.-H. Yang and C. Yang, J. Mater. Chem. A, 2024, 12, 24746–24760.
7. J. Luo, L. Xu, Y. Zhou, T. Yan, Y. Shao, D. Yang, L. Zhang, Z. Xia, T. Wang, L. Zhang, T. Cheng and Y. Shao, Angew. Chem., Int. Ed., 2023, 62, e202302302.
8. B. Liu, S. Wang, Z. Wang, H. Lei, Z. Chen and W. Mai, Small, 2020, 16, 2001323.
9. M. Yan, N. Dong, X. Zhao, Y. Sun and H. Pan, ACS Energy Lett., 2021, 6, 3236–3243.
10. Q. Wang, S. Wang, T. Lu, L. Guan, L. Hou, H. Du, H. Wei, X. Liu, Y. Wei and H. Zhou, Adv. Sci., 2023, 10, 2205233.
11. H. Dong, X. Hu, R. Liu, M. Ouyang, H. He, T. Wang, X. Gao, Y. Dai, W. Zhang, Y. Liu, Y. Zhou, D. J. L. Brett, I. P. Parkin, P. R. Shearing and G. He, Angew. Chem., Int. Ed., 2023, 62, e202311268.
12. M. Du, Z. Miao, H. Li, Y. Sang, H. Liu and S. Wang, J. Mater. Chem. A, 2021, 9, 19245–19281.
13. Y. Zhu, J. Yin, X. Zheng, A.-H. Emwas, Y. Lei, O. F. Mohammed, Y. Cui and H. N. Alshareef, Energy Environ. Sci., 2021, 14, 4463–4473.
14. P. Wang, X. Xie, Z. Xing, X. Chen, G. Fang, B. Lu, J. Zhou, S. Liang and H. J. Fan, Adv. Energy Mater., 2021, 11, 2101158.
15. J. Wan, R. Wang, Z. Liu, L. Zhang, F. Liang, T. Zhou, S. Zhang, L. Zhang, Q. Lu, C. Zhang and Z. Guo, ACS Nano, 2023, 17, 1610–1621.
16. M. Wang, X. Wu, D. Yang, H. Zhao, L. He, J. Su, X. Zhang, X. Yin, K. Zhao, Y. Wang and Y. Wei, Chem. Eng. J., 2023, 451, 138589.
17. Y. Lin, Y. Li, Z. Mai, G. Yang and C. Wang, Adv. Energy Mater., 2023, 13, 2301999.
18. A. Bayaguud, X. Luo, Y. Fu and C. Zhu, ACS Energy Lett., 2020, 5, 3012–3020.
19. Y. Cui, R. Zhang, S. Yang, L. Liu and S. Chen, Mater. Futures, 2024, 3, 012101.
20. L. Yu, J. Huang, S. Wang, L. Qi, S. Wang and C. Chen, Adv. Mater., 2023, 35, 2210789.
21. J. Chen, W. Zhou, Y. Quan, B. Liu, M. Yang, M. Chen, X. Han, X. Xu, P. Zhang and S. Shi, Energy Storage Mater., 2022, 53, 629–637.
22. C. Wu, C. Sun, K. Ren, F. Yang, Y. Du, X. Gu, Q. Wang and C. Lai, Chem. Eng. J., 2023, 452, 139465.
23. P. Zou, R. Lin, T. P. Pollard, L. Yao, E. Hu, R. Zhang, Y. He, C. Wang, W. C. West, L. Ma, O. Borodin, K. Xu, X.-Q. Yang and H. L. Xin, Nano Lett., 2022, 22, 7535–7544.
24. J. Hao, L. Yuan, C. Ye, D. Chao, K. Davey, Z. Guo and S.-Z. Qiao, Angew. Chem., Int. Ed., 2021, 60, 7366–7375.
25. X. Song, H. He, M. H. Aboonasr Shiraz, H. Zhu, A. Khosrozadeh and J. Liu, Chem. Commun., 2021, 57, 1246–1249.
26. X. Yang, W. Li, Z. Chen, M. Tian, J. Peng, J. Luo, Y. Su, Y. Zou, G. Weng, Y. Shao, S. Dou and J. Sun, Angew. Chem., Int. Ed., 2023, 62, e202218454.
27. H. B. Chen, H. Meng, T. R. Zhang, Q. Ran, J. Liu, H. Shi, G. F. Han, T. H. Wang, Z. Wen, X. Y. Lang and Q. Jiang, Angew. Chem., Int. Ed., 2024, 63, e202402327.
28. H. Tang, N. Hu, L. Ma, H. Weng, D. Huang, J. Zhu, H. Yang, Z. Chen, X. Yin, J. Xu and H. He, Adv. Funct. Mater., 2024, 29, 2402484.
29. K. Su, H. Zhang, Y. Wang, X. Zhang, Y. Mu, Z. Lu, Y. Han, S. Wan and J. Lang, Chem. Eng. J., 2024, 496, 153927.
30. T. C. Li, C. Lin, M. Luo, P. Wang, D.-S. Li, S. Li, J. Zhou and H. Y. Yang, ACS Energy Lett., 2023, 8, 3258–3268.
31. M. Zhou, S. Guo, J. Li, X. Luo, Z. Liu, T. Zhang, X. Cao, M. Long, B. Lu, A. Pan, G. Fang, J. Zhou and S. Liang, Adv. Mater., 2021, 33, 2100187.
32. S. Xu, J. Huang, G. Wang, Y. Dou, D. Yuan, L. Lin, K. Qin, K. Wu, H. K. Liu, S.-X. Dou and C. Wu, Small Methods, 2023, 98, 2300268.
33. M. Zhou, Z. Tong, H. Li, X. Zhou, X. Li, Z. Hou, S. Liang and G. Fang, Adv. Funct. Mater., 2024, 33, 2412092.
34. Y. Lv, M. Zhao, Y. Du, Y. Kang, Y. Xiao and S. Chen, Energy Environ. Sci., 2022, 15, 4748–4760.
35. Z. Zha, T. Sun, D. Li, T. Ma, W. Zhang and Z. Tao, Energy Storage Mater., 2024, 64, 103059.
36. Y. Zhong, Z. Cheng, H. Zhang, J. Li, D. Liu, Y. Liao, J. Meng, Y. Shen and Y. Huang, Nano Energy, 2022, 98, 107220.
37. T. Huang, K. Xu, N. Jia, L. Yang, H. Liu, J. Zhu and Q. Yan, Adv. Mater., 2023, 35, 2205206.
38. Y. Xia, P. Zhou, X. Kong, J. Tian, W. Zhang, S. Yan, W.-h. Hou, H.-Y. Zhou, H. Dong, X. Chen, P. Wang, Z. Xu, L. Wan, B. Wang and K. Liu, Nat. Energy, 2023, 8, 934–945.
39. X. Ma, H. Yu, C. Yan, Q. Chen, Z. Wang, Y. Chen, G. Chen and C. Lv, J. Colloid Interface Sci., 2024, 664, 539–548.
40. L. Cao, D. Li, T. Pollard, T. Deng, B. Zhang, C. Yang, L. Chen, J. Vatamanu, E. Hu, M. J. Hourwitz, L. Ma, M. Ding, Q. Li, S. Hou, K. Gaskell, J. T. Fourkas, X.-Q. Yang, K. Xu, O. Borodin and C. Wang, Nat. Nanotechnol., 2021, 16, 902–910.
41. H. Yu, D. Chen, Q. Li, C. Yan, Z. Jiang, L. Zhou, W. Wei, J. Ma, X. Ji, Y. Chen and L. Chen, Adv. Energy Mater., 2023, 13, 2300550.
42. J. Cao, Y. Sun, D. Zhang, D. Luo, L. Zhang, R. Chanajaree, J. Qin, X. Yang and J. Lu, Adv. Energy Mater., 2024, 14, 2302770.
43. C. Huang, X. Zhao, S. Liu, Y. Hao, Q. Tang, A. Hu, Z. Liu and X. Chen, Adv. Mater., 2021, 33, 2100445.
44. Y. Wang, R. Zhao, M. Liu, J. Yang, A. Zhang, J. Yue, C. Wu and Y. Bai, Adv. Energy Mater., 2023, 13, 2302707.
45. L. Hu, Y. Han, L. Yan, C. Zhu, Z. Xu, X. Zou, Y. Zhou and B. Xiang, Energy Storage Mater., 2024, 65, 103114.
46. J. Hao, B. Li, X. Li, X. Zeng, S. Zhang, F. Yang, S. Liu, D. Li, C. Wu and Z. Guo, Adv. Mater., 2020, 32, 138175.
47. L. Luo, C. Zhu, L. Yan, L. Guo, Y. Zhou and B. Xiang, Chem. Eng. J., 2022, 450, 138175.
48. A. Pei, G. Zheng, F. Shi, Y. Li and Y. Cui, Nano Lett., 2017, 17, 1132–1139.
49. Y. Feng, Y. Wang, L. Sun, K. Zhang, J. Liang, M. Zhu, Z. Tie and Z. Jin, Small, 2023, 19, 2302650.
50. C. Wang, Z. Pei, Q. Meng, C. Zhang, X. Sui, Z. Yuan, S. Wang and Y. Chen, Angew. Chem., Int. Ed., 2020, 60, 990–997.
51. D. Han, C. Cui, K. Zhang, Z. Wang, J. Gao, Y. Guo, Z. Zhang, S. Wu, L. Yin, Z. Weng, F. Kang and Q.-H. Yang, Nat. Sustainability, 2021, 5, 205–213.
52. X. Zhang, J. Li, D. Liu, M. Liu, T. Zhou, K. Qi, L. Shi, Y. Zhu and Y. Qian, Energy Environ. Sci., 2021, 14, 3120–3129.
53. D. Xie, Y. Sang, D. H. Wang, W. Y. Diao, F. Y. Tao, C. Liu, J. W. Wang, H. Z. Sun, J. P. Zhang and X. L. Wu, Angew. Chem., Int. Ed., 2022, 62, 2003699.
54. J. Sun, Z. Xiu, L. Li, K. Lv, X. Zhang, Z. Wang, Z. Dai, Z. Xu, N. Huang and J. Liu, Petroleum, 2024, 10, 11–18.
55. T. Li, J. Sun, S. Gao, B. Xiao, J. Cheng, Y. Zhou, X. Sun, F. Jiang, Z. Yan and S. Xiong, Adv. Energy Mater., 2021, 11, 2003699.
56. K. Wang, F. Liu, Q. Li, J. Zhu, T. Qiu, X.-X. Liu and X. Sun, Chem. Eng. J., 2023, 452, 139577.
57. J. Zhang, Y. Liu, Y. Wang, Z. Zhu and Z. Yang, Adv. Funct. Mater., 2024, 34, 2401889.
58. H. Zhang, Y. Zhong, J. Li, Y. Liao, J. Zeng, Y. Shen, L. Yuan, Z. Li and Y. Huang, Adv. Energy Mater., 2023, 13, 2203254.
59. Y. Li, L. Liu, H. Zhang, H. Wang, Z. Sun, Z. Zhang, W. Pang, S. Omanovic, S. Sun, X. Chen and H. Song, Adv. Funct. Mater., 2024, 34, 2410855.
60. J. Abdulla, J. Cao, D. Zhang, X. Zhang, C. Sriprachuabwong, S. Kheawhom, P. Wangyao and J. Qin, ACS Appl. Energy Mater., 2021, 4, 4602–4609.
61. M. Yan, K. Singh, S. Rajput, E. Dozois, P. Rose, N. V. Tran, J. Martinez-Jorge, I. A. Petersen and A. Vijayasekaran, Plast. Reconstr. Surg. Global Open, 2021, 9, 82–83.
62. W. Xu, K. Zhao, W. Huo, Y. Wang, G. Yao, X. Gu, H. Cheng, L. Mai, C. Hu and X. Wang, Nano Energy, 2019, 62, 275–281.
63. H. Lu, X. Zhang, M. Luo, K. Cao, Y. Lu, B. B. Xu, H. Pan, K. Tao and Y. Jiang, Adv. Funct. Mater., 2021, 31, 2103514.

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Footnote

† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d4ta07230h

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