Electrolytes for Aqueous Zn-Ion Batteries Working in Wide-Temperature Range: Progress and Perspective

: Aqueous Zn-ion Batteries (AZIBs) have garnered signiﬁcant interest in recent years, owing to their inherent safety, affordability, and eco-friendliness. Recently, substantial research has been conducted to broaden the application scenarios of AZIBs by regulating the electrode and electrolyte materials. In this review, we provide a comprehensive analysis of the challenges and solutions associated with AZIBs to meet extreme conditions, such as low temperatures, high temperatures, and wide temperature ranges. We also discuss electrolyte optimization strategies for each of these conditions. Finally, we outline potential avenues for further advancements and offer insights into the future of this burgeoning ﬁeld of AZIBs.


Introduction
In today's society, with the continuous expansion at social and economic scales, people's demand for energy and resources is growing [1][2][3][4][5][6][7].Countries and regions around the world have prioritized new energy storage technologies to effectively utilize the green, low-carbon, and environmentally friendly renewable energy sources [8].In recent years, batteries based on electrochemical energy storage are one of the most efficient, simple, and reliable devices available, and they have become the focus of research to improve their electrochemical performance and to broaden their application scenarios [2,[9][10][11][12][13].
The aqueous Zn-based batteries are one of the most promising battery systems for large-scale storage due to their intrinsic safety and low cost by applying the H 2 O-based electrolyte.More importantly, the Zn metal anode could accommodate high theoretical gravimetric capacity and the volumetric capacity at 820 mAh/g and 5855 mAh/cm 3 , respectively, enabling it to deliver high energy and power at full cell level (Figure 1a) [14][15][16][17][18][19].Therefore, aqueous Zn-ion batteries (AZIBs) have sparked a lot of enthusiasm in the energy storage field due to their inherent safety, low cost, and environmental friendliness [20][21][22][23][24].
The demand for energy storage and conversion has become diversified such that the AZIBs need to operate over a wide temperature range as global temperature extremes intensify to wide ranges [25][26][27][28].The publication of papers on the topic of wide-temperature AZIBs in the Web of Science database since the last three years was counted (Figure 1b).The results show that the number of relevant papers published on this topic has increased year by year since the last three years, and the total number of papers published exceeded more than 2200 until the preparation of this manuscript, especially from 2020 to 2021.The growth rate of papers published has reached as much as 81.51%, indicating that many research workers in this research area have emerged in the fields of energy batteries and material preparation.However, AZIBs face significant challenges in Zn electrode and electrolyte performance under wide-temperature operating conditions, resulting in poor battery stability and inferior electrochemical performance for a wide temperature range [29][30][31].Specifically, the solidification of the aqueous electrolytes at sub-zero temperatures would result in a large decrease in the ionic conductivity of the electrolyte, thus deteriorating the poor rate capability and the large over-potentials of the working voltages for the AZIBs.In addition, the intensified protons' activity of the aqueous electrolyte would trigger severe side reactions, such as the hydrogen evolution, and accelerate the dendrite/by-products formation at high temperatures, thus deteriorating the cycling stability of the AZIBs.Consequently, developing AZIBs capable of operating under wide temperature conditions holds significant scientific and practical importance.Nevertheless, realizing excellent electrochemical performance for AZIBs under wide temperature conditions remains a considerable challenge both theoretically and technologically.The demand for energy storage and conversion has become diversified such that the AZIBs need to operate over a wide temperature range as global temperature extremes intensify to wide ranges [25][26][27][28].The publication of papers on the topic of widetemperature AZIBs in the Web of Science database since the last three years was counted (Figure 1b).The results show that the number of relevant papers published on this topic has increased year by year since the last three years, and the total number of papers published exceeded more than 2200 until the preparation of this manuscript, especially from 2020 to 2021.The growth rate of papers published has reached as much as 81.51%, indicating that many research workers in this research area have emerged in the fields of energy batteries and material preparation.However, AZIBs face significant challenges in Zn electrode and electrolyte performance under wide-temperature operating conditions, resulting in poor battery stability and inferior electrochemical performance for a wide temperature range [29][30][31].Specifically, the solidification of the aqueous electrolytes at sub-zero temperatures would result in a large decrease in the ionic conductivity of the electrolyte, thus deteriorating the poor rate capability and the large over-potentials of the working voltages for the AZIBs.In addition, the intensified protons' activity of the aqueous electrolyte would trigger severe side reactions, such as the hydrogen evolution, and accelerate the dendrite/by-products formation at high temperatures, thus deteriorating the cycling stability of the AZIBs.Consequently, developing AZIBs capable of operating under wide temperature conditions holds significant scientific and practical importance.Nevertheless, realizing excellent electrochemical performance for AZIBs under wide temperature conditions remains a considerable challenge both theoretically and technologically.
Current studies focus on the failure mechanism and performance optimization of AZIBs to enhance their practical application under wide temperature conditions [31][32][33][34][35][36][37][38].Current studies focus on the failure mechanism and performance optimization of AZIBs to enhance their practical application under wide temperature conditions [31][32][33][34][35][36][37][38].At present, according to the division of the working temperature range, AZIB research is mainly divided into "low temperature condition" and "high temperature condition" branches [3,[39][40][41][42][43].Unfortunately, few review articles have been published thus far focusing on the detailed analysis and systematic summary of electrolytes used in AZIBs operating at wide temperatures.Examining the latest progress and potential guidance to improve the wide-temperature performance of AZIBs is a compelling and necessary research frontier.

Low Temperature Condition
Energy storage batteries in certain activities, such as high latitude and polar areas, often face harsh low temperature operating environments.The solvent of AZIBs' electrolyte is based on water as H 2 O; however, the physicochemical properties of H 2 O solvent at temperatures below 0 • C would pose numerous challenges to the stable operation of AZIBs, including electrolyte solidification, reduced ionic conductivity, and poor electrolyteto-electrode wettability.It would inhibit the desolvation and diffusion of Zn 2+ at the electrode/electrolyte phase interface.Preventing electrolyte solidification at subzero conditions and constructing low-temperature AZIBs is a priority [44][45][46][47][48].
Hydrogen bonding is the basic structural and energy storage unit of H 2 O solvent.The hydrogen bonding constantly breaks and reorganizes between water molecules, forming a unique "hydrogen bonding network" structure [49][50][51].The freezing process involves a complex rearrangement of the hydrogen bonding network from disordered water molecules to ordered ice, driven by the formation of additional thermodynamic driving force.When the ambient temperature drops to 0 • C, the aqueous solution eventually forms solid ice, and the electrolyte viscosity increases until it solidifies.The freezing of the electrolyte not only decreases ionic conductivity but also reduces electrolyte-to-electrode wettability, hindering desolvation and the diffusion of Zn 2+ at the electrode/electrolyte phase interface.Reducing the freezing point of the electrolyte and inhibiting ice crystal formation are generally accepted as prerequisites to ensuring AZIB operation at low temperatures [25,26].The dominant research has focused on reconstructing the hydrogen bonding network of the aqueous electrolyte by introducing effective additives.

Optimizing Aqueous Electrolytes
Aqueous electrolytes could serve as a medium for ionic conduction and facilitating electrochemical reactions.The properties of the electrolyte could determine the migration rate of Zn 2+ ions, solvation structure, electrode/electrolyte interface stability, safety, and electrochemical performance of the battery.Various strategies have been employed to design anti-freeze electrolytes, thereby enhancing AZIBs' performance at subzero temperatures, including highly concentrated electrolytes, water/organic hybrid electrolytes, and antifreeze hydrogels.These approaches have proven to be both feasible and effective.Table 1 shows the summary of the electrochemical performance in AZIBs at low temperature.

Water-in-Salt Electrolyte
Thermodynamically, pure water freezes at 0 • C at standard atmospheric pressure.Highly concentrated (or saturated) salt solutions, e.g., the salt-in-water electrolytes, can effectively reduce the freezing point by weakening hydrogen bonding between water molecules [25,60].Zhang et al. [52] reported that aqueous ZnCl 2 electrolyte with a high concentration of 7.5 mol/L has a high ionic conductivity (1.79 mS cm −1 at −60 • C) and good compatibility with the Zn anode under low temperature conditions.The solid-liquid transition temperature of the aqueous electrolyte is suppressed from 0 • C to −114 • C by disrupting the initial hydrogen bonding network in the ZnCl 2 solution.Based on the ZnCl 2 electrolyte, they created a polyaniline||Zn cell that can function in an extremely low temperature range.The specific capacity is near 85 mAh/g under the current 0.2 A/g and the long cycling performance of ~2000 cycles at −70 • C (Figure 2a).The interactions between the ions and the water molecules causes the initial hydrogen bond structure to be reconstructed, as seen in Figure 2b, and Zn 2+ solvation configurations appear.This electrolyte is mostly made up of Zn(H 2 O) 2 Cl 4 2− , ZnCl + , and Zn(H 2 O) 6 2+ , as well as water molecules with weak hydrogen bond interactions.The electrolyte's freezing point is reduced by the high-concentrated ions to weaken the hydrogen bond among the H 2 O molecules [52].
temperature range.The specific capacity is near 85 mAh/g under the current 0.2 A/g and the long cycling performance of ~2000 cycles at −70 °C (Figure 2a).The interactions between the ions and the water molecules causes the initial hydrogen bond structure to be reconstructed, as seen in Figure 2b, and Zn 2+ solvation configurations appear.This electrolyte is mostly made up of Zn(H2O)2Cl4 2− , ZnCl + , and Zn(H2O)6 2+ , as well as water molecules with weak hydrogen bond interactions.The electrolyte's freezing point is reduced by the high-concentrated ions to weaken the hydrogen bond among the H2O molecules [52].Original water network linked by H-bonding can easily transform to ice network at 0 °C.After adding ZnCl2, the H-bond network is broken by the strong interaction between ions and water, while the ion interactions are enhanced.By balancing the H-bonding and ion interactions for modulating Tt, the electrolyte at critical C can be operated at extremely low temperature.© Copyright 2020, The Author(s) [52].
It is worth mentioning that Sun et al. [40] introduced the BF4 − anions to break the original hydrogen bonding network between H2O molecules by forming O-H⋅⋅⋅F hydrogen bonding and developed a Zn(BF4)2 electrolyte with a low freezing point (−122 °C) and high ionic conductivity.The Zn||tetrachlorobenzoquinone (TCBQ) cell based on the 4 mol/L Zn(BF4)2 electrolyte exhibited excellent electrochemical performance over a low temperature range from −60 °C to −95 °C.The Zn/TCBQ battery achieves a high discharge specific capacity of 86.1 mAh/g, 71.8 mAh/g, and 63.5 mAh/g at −60 °C, −80 °C, and −95 °C, respectively, at an average voltage of 1.2 V.It has been shown that adding BF4 − anions could damage the hydrogen bond (HB) network in water molecules and reduce the freezing point even further.To study the development of HBs in this system from a basic perspective, molecular dynamics (MD) simulations were used.The pictures in Figure 3a,b [40] clearly show that following the addition of 4 M Zn(BF4)2 salt, the HBs of water molecules have rapidly diminished, and a large number of O-H•••F HBs among BF4 − ions and water molecules are generated.Four different forms of HBs among water molecules and the BF4 -anion have been identified from the outcomes of MD simulations, and they are shown in Figure 3c-f.The mean number of hydrogen bonding between BF4 − ions and water molecules is shown in Figure 3g.In Figure 3h, the ratio of the various kinds The schematic of the structure evolutions of water and electrolyte, and the design of low-T t solution.Original water network linked by H-bonding can easily transform to ice network at 0 • C.After adding ZnCl 2 , the H-bond network is broken by the strong interaction between ions and water, while the ion interactions are enhanced.By balancing the H-bonding and ion interactions for modulating T t , the electrolyte at critical C ZnCl 2 can be operated at extremely low temperature.© Copyright 2020, The Author(s) [52].
It is worth mentioning that Sun et al. [40]  anions could damage the hydrogen bond (HB) network in water molecules and reduce the freezing point even further.To study the development of HBs in this system from a basic perspective, molecular dynamics (MD) simulations were used.The pictures in Figure 3a,b [40] clearly show that following the addition of 4 M Zn(BF 4 ) 2 salt, the HBs of water molecules have rapidly diminished, and a large number of O-H•••F HBs among BF 4 − ions and water molecules are generated.Four different forms of HBs among water molecules and the BF 4 -anion have been identified from the outcomes of MD simulations, and they are shown in Figure 3c-f.The mean number of hydrogen bonding between BF 4 − ions and water molecules is shown in Figure 3g.In Figure 3h, the ratio of the various kinds of HBs is shown.With an increase in Zn(BF 4 ) 2 quantity, the ratio of O-H•••O HBs steadily declines.In contrast, all HB ratios show a trend to decline, and the proportion of O-H•••F HBs gradually rises, demonstrating that the addition of BF 4 − ions not only disrupts the HB network but also decreases the amount of HBs present in the initial water molecules [40].
of HBs is shown.With an increase in Zn(BF4)2 quantity, the ratio of O-H•••O HBs steadily declines.In contrast, all HB ratios show a trend to decline, and the proportion of O-H•••F HBs gradually rises, demonstrating that the addition of BF4 − ions not only disrupts the HB network but also decreases the amount of HBs present in the initial water molecules [40].The reports above greatly provide an effective strategy to promote low-temperature AZIBs by adjusting the electrolyte structure with highly concentrated solutions of salt.Although "water-in-salt" electrolytes have significant advantages, such as lower electrolyte freezing point and improved electrode materials, it is still a fundamental challenge to overcome the inherent limitations of "water-in-salt" electrolytes in the future, including high viscosity caused by strong cation-anion coupling, high cost, and salt precipitation at low temperature.Therefore, excessive salt concentrations might be optimized when designing anti-freezing electrolytes, and the development of low-cost salt for highly concentrated electrolyte is essential to improve market competitiveness.

Organic Additives
Introducing organic additives into the aqueous electrolytes is a key strategy to realize the low freezing points of the electrolyte.The effectiveness of additives to expand the lowtemperature range of AZIBs largely relies on the capabilities to disturb and reconstruct the hydrogen bond network to inhibit the regular formation of ice crystals, and thus reduce the freezing point of the electrolyte.At present, a large number of organic solvents The reports above greatly provide an effective strategy to promote low-temperature AZIBs by adjusting the electrolyte structure with highly concentrated solutions of salt.Although "water-in-salt" electrolytes have significant advantages, such as lower electrolyte freezing point and improved electrode materials, it is still a fundamental challenge to overcome the inherent limitations of "water-in-salt" electrolytes in the future, including high viscosity caused by strong cation-anion coupling, high cost, and salt precipitation at low temperature.Therefore, excessive salt concentrations might be optimized when designing anti-freezing electrolytes, and the development of low-cost salt for highly concentrated electrolyte is essential to improve market competitiveness.

Organic Additives
Introducing organic additives into the aqueous electrolytes is a key strategy to realize the low freezing points of the electrolyte.The effectiveness of additives to expand the lowtemperature range of AZIBs largely relies on the capabilities to disturb and reconstruct the hydrogen bond network to inhibit the regular formation of ice crystals, and thus reduce the freezing point of the electrolyte.At present, a large number of organic solvents have been applied to reduce the freezing point of the electrolytes for AZIBs, such as 1,3-Dioxolane (DOL)) [55], ethylene glycol (EG) [61][62][63][64], ethanol [65], and glycerol [66,67].
1,3-Dioxolane (DOL), an organic solvent with a low freezing point and a high dielectric constant, is an exemplified solvent as an additive in aqueous electrolytes.Du et al. [55] reported a "Zn trifluoromethanesulfonate (Zn(OTf) 2 )-DOL-H 2 O" electrolyte to reduce the freezing point of the electrolyte to −51.2 • C, which enabled the Zn||V 2 O 5 cell to maintain 131 mA/g −1 at a low temperature of −30 • C.This enables the Zn||V 2 O 5 cell to maintain a stable average capacity of 131 mAh/g for 300 cycles at 0.1 A/g current density at a low temperature of −30 • C (Figure 4a).To further study the interaction between the components in the mixed electrolyte, the solvation structure of the aqueous electrolyte and the 1:1 electrolyte was studied by MD simulation.For the 1:1 electrolyte, the snapshot of the simulated electrolyte structure shows that the DOL molecule is combined with the have been applied to reduce the freezing point of the electrolytes for AZIBs, such as 1,3-Dioxolane (DOL)) [55], ethylene glycol (EG) [61][62][63][64], ethanol [65], and glycerol [66,67].
1,3-Dioxolane (DOL), an organic solvent with a low freezing point and a high dielectric constant, is an exemplified solvent as an additive in aqueous electrolytes.Du et al. [55] reported a "Zn trifluoromethanesulfonate (Zn(OTf)2)-DOL-H2O" electrolyte to reduce the freezing point of the electrolyte to −51.2 °C, which enabled the Zn||V2O5 cell to maintain 131 mA/g −1 at a low temperature of −30 °C.This enables the Zn||V2O5 cell to maintain a stable average capacity of 131 mAh/g for 300 cycles at 0.1 A/g current density at a low temperature of −30 °C (Figure 4a).To further study the interaction between the components in the mixed electrolyte, the solvation structure of the aqueous electrolyte and the 1:1 electrolyte was studied by MD simulation.For the 1:1 electrolyte, the snapshot of the simulated electrolyte structure shows that the DOL molecule is combined with the H2O molecule by hydrogen bonding (Figure 4b,c).There are two forms of binding between DOL and H2O.Most DOL interacts with only one H2O molecule, and some DOL binds to two H2O molecules.The probabilities of DOL-H2O, DOL-2H2O, and H2O-H2O were calculated by the Density Function Theory (DFT).As shown in Figure 4d, the binding energies of DOL-H2O and DOL-2H2O are 2.662 kcal/mol and 5.278 kcal/mol, respectively, and the binding energies of H2O-H2O are 2.542 kcal/mol, respectively.The theoretical calculation results further prove that H2O is more inclined to combine with DOL than H2O [55].The "Zn sulfate (ZnSO4)-EG-H2O" electrolyte designed by Chang et al. has high ionic conductivity at low temperature.The research [56] shows that the Zn 2+ -EG solvation effectively reduces the freezing point of the mixed electrolyte, improves the reversibility of Zn deposition/stripping, and improves the deposition morphology of the Zn anode.Therefore, the Zn//PANI-V2O5 battery with EG40 (volume ratio of EG to water is 40%) exhibits high discharge capacity of 100 mAh/g at 0.2 A/g current density and long cycle life (250 cycles) at −20 °C (Figure 5a).To further study the solvation structure of a mixed electrolyte, MD simulation and DFT calculation were carried out.The snapshots of the The "Zn sulfate (ZnSO 4 )-EG-H 2 O" electrolyte designed by Chang et al. has high ionic conductivity at low temperature.The research [56] shows that the Zn 2+ -EG solvation effectively reduces the freezing point of the mixed electrolyte, improves the reversibility of Zn deposition/stripping, and improves the deposition morphology of the Zn anode.Therefore, the Zn//PANI-V 2 O 5 battery with EG40 (volume ratio of EG to water is 40%) exhibits high discharge capacity of 100 mAh/g at 0.2 A/g current density and long cycle life (250 cycles) at −20 • C (Figure 5a).To further study the solvation structure of a mixed electrolyte, MD simulation and DFT calculation were carried out.The snapshots of the simulated electrolyte structure (Figure 5b,c) show that there are ionic solvation clusters of Zn 2+ coordinated with SO 4 2− , H 2 O, and EG in the electrolyte with EG addition.The coordination number (CN) analysis of H 2 O, EG, and SO 4 2− around Zn 2+ in a series of hybrid electrolytes is shown in Figure 5d.With the increasing EG-to-water ratio, the CN of SO 4 2− anions around Zn 2+ increased slightly.The CN of H 2 O molecules in the first hydration layer gradually decreased, while the CN of EG molecules gradually increased, indicating that the introduction of EG greatly destroyed the solvation structure of Zn 2+ and H 2 O.With the increasing EG content, the diffusion coefficient of Zn 2+ increased first and then decreased (Figure 5e).When the ratio of EG-to-water is less than 60%, the diffusion coefficient of the mixed electrolyte is still higher than that of EG0.This indicates that the solvation structure of Zn 2+ coordinated with EG and H 2 O contributes to the rapid transport of Zn 2+ .Nevertheless, when the solvation effect of EG and Zn 2+ is more prominent, the Zn 2+ in the mixed electrolyte achieved rapid transport at low temperature.In addition, the relative binding energies of Zn 2+ cations with anions and solvents are in the order of Zn 2+ -SO 4 2− > Zn 2+ -EG > Zn 2+ -H 2 O.The results show that Zn 2+ is preferentially coordinated with EG rather than H 2 O, resulting in the rapid exchange of EG around Zn 2+ , so that Zn 2+ is rapidly conductive in the electrolyte added with EG.In addition, after the introduction of EG molecules in the system, the electrostatic potential of the solvation state of Zn 2+ -5H 2 O (Figure 5f,g) was significantly reduced.Therefore, the electrostatic repulsion between Zn 2+ cations can be reduced.simulated electrolyte structure (Figure 5b,c) show that there are ionic solvation clusters of Zn 2+ coordinated with SO4 2− , H2O, and EG in the electrolyte with EG addition.The coordination number (CN) analysis of H2O, EG, and SO4 2− around Zn 2+ in a series of hybrid electrolytes is shown in Figure 5d.With the increasing EG-to-water ratio, the CN of SO4 2− anions around Zn 2+ increased slightly.The CN of H2O molecules in the first hydration layer gradually decreased, while the CN of EG molecules gradually increased, indicating that the introduction of EG greatly destroyed the solvation structure of Zn 2+ and H2O.With the increasing EG content, the diffusion coefficient of Zn 2+ increased first and then decreased (Figure 5e).When the ratio of EG-to-water is less than 60%, the diffusion coefficient of the mixed electrolyte is still higher than that of EG0.This indicates that the solvation structure of Zn 2+ coordinated with EG and H2O contributes to the rapid transport of Zn 2+ .Nevertheless, when the solvation effect of EG and Zn 2+ is more prominent, the Zn 2+ in the mixed electrolyte achieved rapid transport at low temperature.In addition, the relative binding energies of Zn 2+ cations with anions and solvents are in the order of Zn 2+ -SO4 2− > Zn 2+ -EG > Zn 2+ -H2O.The results show that Zn 2+ is preferentially coordinated with EG rather than H2O, resulting in the rapid exchange of EG around Zn 2+ , so that Zn 2+ is rapidly conductive in the electrolyte added with EG.In addition, after the introduction of EG molecules in the system, the electrostatic potential of the solvation state of Zn 2+ -5H2O (Figure 5f,g) was significantly reduced.Therefore, the electrostatic repulsion between Zn 2+ cations can be reduced.In general, organic solvents possessing certain attributes, such as low melting points, reduced viscosity, and elevated polarity, can effectively decrease electrolyte freezing points and suppress water-induced side reactions.Although implementing organic electrolyte systems enhances electrochemical stability at subzero temperatures, capacity or voltage may be compromised [68,69].Notably, the majority of the organic solvents exhibit flammability and toxicity, which may pose safety concerns when present in excess within hybrid electrolytes.Consequently, the design of water/organic hybrid electrolytes for low-temperature applications should judiciously minimize the incorporation of superfluous organic solvents.

Hydrogel Electrolyte
The hydrogels emerge as a promising solution to enable the working capability for AZIBs to work at sub-zero temperatures.Hydrogels are cross-linked hydrated polymer chains rich in hydrophilic functional groups, such as -OH, -COOH, -SO 3 , and -NH 2 .The formation of intra-or intermolecular hydrogen bonding within hydrogels, as well as the competition between water molecules across different chemical functional groups, regulates their anti-freeze properties.
Hydrogel electrolytes offer enhanced electrode interface stabilization compared to liquid electrolytes [70] and are frequently utilized in conjunction with co-solvents, additives, or highly concentrated salts to extend their low-temperature performance [71].Chen et al. [57] developed a frost-resistant borax cross-linked polyvinyl alcohol (PVA)/glycerol gel electrolyte capable of withstanding temperatures below −60 • C. Employing this antifreeze gel electrolyte, they constructed a stretchable quasi-solid-state Zn-MnO 2 battery with an energy density of 46.8 mWh/cm 3 (1330 Wh/cm 2 ) at 25 • C and a power density of 96 mW/cm 3 (2.7 mW/cm 2 ), surpassing nearly all reported AZIBs (Figure 6a,b).More importantly, even at −35 • C, it can still reach a relatively high energy density (25.8 mWh/cm 3 , 732 Wh/cm 2 ).When the power density increases by about 10 times, it can maintain 53.3% of the energy density.
reduced viscosity, and elevated polarity, can effectively decrease electrolyte freezing points and suppress water-induced side reactions.Although implementing organic electrolyte systems enhances electrochemical stability at subzero temperatures, capacity or voltage may be compromised [68,69].Notably, the majority of the organic solvents exhibit flammability and toxicity, which may pose safety concerns when present in excess within hybrid electrolytes.Consequently, the design of water/organic hybrid electrolytes for low-temperature applications should judiciously minimize the incorporation of superfluous organic solvents.

Hydrogel Electrolyte
The hydrogels emerge as a promising solution to enable the working capability for AZIBs to work at sub-zero temperatures.Hydrogels are cross-linked hydrated polymer chains rich in hydrophilic functional groups, such as -OH, -COOH, -SO3, and -NH2.The formation of intra-or intermolecular hydrogen bonding within hydrogels, as well as the competition between water molecules across different chemical functional groups, regulates their anti-freeze properties.
Hydrogel electrolytes offer enhanced electrode interface stabilization compared to liquid electrolytes [70] and are frequently utilized in conjunction with co-solvents, additives, or highly concentrated salts to extend their low-temperature performance [71].Chen et al. [57] developed a frost-resistant borax cross-linked polyvinyl alcohol (PVA)/glycerol gel electrolyte capable of withstanding temperatures below −60 °C.Employing this anti-freeze gel electrolyte, they constructed a stretchable quasi-solid-state Zn-MnO2 battery with an energy density of 46.8 mWh/cm 3 (1330 Wh/cm 2 ) at 25 °C and a power density of 96 mW/cm 3 (2.7 mW/cm 2 ), surpassing nearly all reported AZIBs (Figure 6a,b).More importantly, even at −35 °C, it can still reach a relatively high energy density (25.8 mWh/cm 3 , 732 Wh/cm 2 ).When the power density increases by about 10 times, it can maintain 53.3% of the energy density.content reaches a certain threshold.The optimized hydrogel retains an ionic conductivity of 14.6 mS/cm and exhibits robust mechanical properties at −20 °C.Furthermore, the Zn-MnO2 battery assembled with this gel electrolyte demonstrates exceptional lowtemperature performance, retaining over 80% of its capacity when transitioning from room temperature to −20 °C.No significant capacity degradation was observed after several alternating cycles between high and low temperatures (Figure 7c) [59].Huang et al. [53] form ternary and weak hydrogen bonding by introducing the chaotropic ClO4 − polymer chains into the H2O molecule network, which can reduce the freezing point of the electrolyte.Firstly, density functional theory (DFT) was used to examine how the chaotropic ClO4 − anions, water, and polymer chains interacted.The strong retaining capacity of the hydrogel is confirmed by Figure 8a, which shows that the binding energy of PAM to water is significantly greater than that of water to water.To test the effectiveness of the Zn(ClO4)2 salts on gel electrolyte anti-freezing, a dual-network hydrogel (designated as CSAM) composed of modified polysaccharides carboxymethyl chitosan (CMCS) and polyacrylamide (PAM) was created and used as an example system.It proves that the ClO4 − anion has a potent interaction with PAM chains, allowing it to enter the polymer chains, break the HB in PAM-PAM and PAM-CSAM, and control the hydrogel's mechanical flexibility.This increases the hydrophilic property of the hydrogel − anions, water, and polymer chains interacted.The strong retaining capacity of the hydrogel is confirmed by Figure 8a, which shows that the binding energy of PAM to water is significantly greater than that of water to water.To test the effectiveness of the Zn(ClO 4 ) 2 salts on gel electrolyte anti-freezing, a dual-network hydrogel (designated as CSAM) composed of modified polysaccharides carboxymethyl chitosan (CMCS) and polyacrylamide (PAM) was created and used as an example system.It proves that the ClO 4 − anion has a potent interaction with PAM chains, allowing it to enter the polymer chains, break the HB in PAM-PAM and PAM-CSAM, and control the hydrogel's mechanical flexibility.This increases the hydrophilic property of the hydrogel and improves its mechanical characteristics by forming a ternary HB reciprocity between the ClO 4 − anion, water, and polymer chains, as shown in Figure 8b.Ref. [53] At −30 • C, the Zn//polyaniline battery is composed of the electrolyte with an ionic conductivity of 7.8 mS/cm and a reversible capacity of 70 mAh/g after 2500 cycles at a current density of 5 A/g (Figure 8c).and improves its mechanical characteristics by forming a ternary HB reciprocity between the ClO4 − anion, water, and polymer chains, as shown in Figure 8b.Ref. [53] At −30 °C, the Zn//polyaniline battery is composed of the electrolyte with an ionic conductivity of 7.8 mS/cm and a reversible capacity of 70 mAh/g after 2500 cycles at a current density of 5 A/g (Figure 8c).The performance of AZIBs at low temperatures significantly impacts their practical applications.Currently, research in this area remains in its nascent stages.Efforts to enhance the subzero temperature performance of AZIBs predominantly focus on the meticulous design of electrolytes.It is crucial to recognize that both electrode and nonactive materials influence the low-temperature performance of AZIBs.Consequently, the development of anti-freezing electrolytes must consider the electrochemical stability window and ensure compatibility with both electrode and non-active materials.Additionally, the enhancement of electrolytes would generally necessitate the utilization of high-concentration salt solutions and organic electrolytes.To maintain the competitiveness of AZIBs in the market, it is essential to prioritize their cost effectiveness and their safety advantages.

High Temperature Condition
In addition to low-temperature conditions, AZIBs often encounter elevated temperatures exceeding 40 °C in various applications, such as geological exploration and deployment in tropical regions.Current research indicates that high-temperature environments can accelerate the internal chemical reaction rates, enhancing the charge transfer kinetics to a degree.At these elevated internal temperatures, solvent evaporation and solute precipitation from the electrolyte may occur, subsequently degrading the hightemperature electrochemical performance of AZIBs and potentially resulting in battery failure [72].The issues are located at the Zn anode side corresponding to irreversible dendrites and the hydrogen evolution at high temperatures, which could be ascribed to the enhanced proton/H2O activity in the aqueous electrolyte.It would not only promote the hydrogen evolution but also accelerate the Zn dendrite formation.Furthermore, the cathode material may exhibit substantial dissolution phenomena under high-temperature conditions, leading to rapid battery capacity degradation [73].Considering the boiling point of the aqueous solution, current research posits that increasing the electrolyte's The performance of AZIBs at low temperatures significantly impacts their practical applications.Currently, research in this area remains in its nascent stages.Efforts to enhance the subzero temperature performance of AZIBs predominantly focus on the meticulous design of electrolytes.It is crucial to recognize that both electrode and non-active materials influence the low-temperature performance of AZIBs.Consequently, the development of anti-freezing electrolytes must consider the electrochemical stability window and ensure compatibility with both electrode and non-active materials.Additionally, the enhancement of electrolytes would generally necessitate the utilization of high-concentration salt solutions and organic electrolytes.To maintain the competitiveness of AZIBs in the market, it is essential to prioritize their cost effectiveness and their safety advantages.

High Temperature Condition
In addition to low-temperature conditions, AZIBs often encounter elevated temperatures exceeding 40 • C in various applications, such as geological exploration and deployment in tropical regions.Current research indicates that high-temperature environments can accelerate the internal chemical reaction rates, enhancing the charge transfer kinetics to a degree.At these elevated internal temperatures, solvent evaporation and solute precipitation from the electrolyte may occur, subsequently degrading the high-temperature electrochemical performance of AZIBs and potentially resulting in battery failure [72].The issues are located at the Zn anode side corresponding to irreversible dendrites and the hydrogen evolution at high temperatures, which could be ascribed to the enhanced proton/H 2 O activity in the aqueous electrolyte.It would not only promote the hydrogen evolution but also accelerate the Zn dendrite formation.Furthermore, the cathode material may exhibit substantial dissolution phenomena under high-temperature conditions, leading to rapid battery capacity degradation [73].Considering the boiling point of the aqueous solution, current research posits that increasing the electrolyte's boiling point and developing high-temperature-resistant cathode materials are fundamental requirements to ensure AZIBs' operational stability under high-temperature conditions.In this review, we specifically emphasize optimization strategies for electrolytes in AZIBs to improve their performance at elevated temperatures.Table 2 shows the summary of electrochemical performance in AZIBs at high temperature.

Optimizing Aqueous Electrolytes
The current AZIBs encounter various side reactions caused by water on the anode side, such as hydrogen evolution reaction, Zn corrosion, and dissolution of cathode materials, which could be ascribed to the enhanced activity of H + and H 2 O at high temperatures [79][80][81][82][83]. Consequently, inhibiting the H 2 O activity at high temperature could enable the stable performance of AZIBs.Recent studies have demonstrated that employing polymer and cosolvent electrolytes can suppress these undesirable side reactions [84][85][86][87][88][89].However, to satisfy more stringent application demands, it is essential to explore further possibilities for AZIBs at elevated temperatures, potentially reaching the boiling point of water.

Cosolvent Electrolytes
Introducing a crowding agent into the electrolyte can enhance the battery stability by suppressing parasitic reactions of the Zn metal anode at high temperatures.Wang et al. [43] achieved uniform Zn deposition at elevated temperatures using an eco-friendly crowding agent, 1,5-pentanediol (PD), which effectively reduced water reactivity and diminished H 2 O content in the Zn 2+ dissolution sheath, thereby significantly inhibiting water-induced parasitic reactions.After 100 cycles at 100 • C, the Zn//Te battery retained a discharge capacity of 195.7 mAh/g Te at 2 C (850 mA/g Te ), exhibiting remarkable cycling stability under exceptionally high temperatures (Figure 9a).MD simulation can provide a more in-depth understanding of the solvation structure and intermolecular interactions of electrolytes.The basis distribution functions (RDF) of different electrolytes at 25 • C (Figure 9b,c) show that PD emits a large amount of H 2 O in the Zn 2+ solvation sheath of the Zn(OTf) 2 -H 2 O/PD electrolyte, and the Zn-O (H 2 O) coordination number of the Zn(OTf) 2 -H 2 O electrolyte is significantly reduced from 5.0 (83.7%) to 1.8 (29.2%) (Figure 9d), which is beneficial to suppress the parasitic side reactions caused by H 2 O molecules in the Zn 2+ solvation sheath.In addition, the change of RDF at 100 • C (Figure 9e,f) is consistent with that at 25 • C. In addition, the hydroxyl distribution of the PD isomer 1,2-pentanediol (1,2-PD) on the carbon chain is completely different (Figure 10a,b), and its application potential in high-temperature ZMBs is also studied.The H 2 O/1,2-PD cosolvent electrolyte was simulated by MD (Figure 10c,d).The results show that in H 2 O/1,2-PD, the amount of H 2 O in the Zn 2+ solvation shell is larger than that in H 2 O/PD, which may be due to the larger steric hindrance of the coordination between the hydroxyl group and Zn 2+ , thus hindering the inhibition of side reactions on the Zn anode.In addition, at 100 • C, the coulombic efficiency (CE) of the Zn/Ti battery based on H 2 O/1,2-PD is lower than that of the similar battery based on H 2 O/PD (Figure 10e), which is consistent with the MD simulation results, indicating the importance of the solvent molecular structure to the electrolyte performance.
steric hindrance of the coordination between the hydroxyl group and Zn 2+ , thus hindering the inhibition of side reactions on the Zn anode.In addition, at 100 °C, the coulombic efficiency (CE) of the Zn/Ti battery based on H2O/1,2-PD is lower than that of the similar battery based on H2O/PD (Figure 10e), which is consistent with the MD simulation results, indicating the importance of the solvent molecular structure to the electrolyte performance.Wang et al. reported a Zn-organic battery with ZnSO4/H2O-50% EG as the electr and phenanthrenequinone macrocyclic trimer (PQ-MCT) as the cathode, which sh that the discharge capacities at 0.2 A/g still maintained 88 mAh/g after 900 cycles at 6 In Ref. [77], Qiu et al. also reported a Zn//polytriphenylamine composite (PTPAn) ba using Zn trifluoromethanesulfonate (Zn-TFMS) salt-mixed solvent of propylene carb (PC) and triethyl phosphate (TEP) as the electrolyte, which maintained 300 cycles at at the same temperature, 60 °C.In Ref. [78], the rate performance of the PTPAn catho a high temperature of 60 °C and the cyclic stability of Zn//PTPAn cells at 60 °C are sh Wang et al. reported a Zn-organic battery with ZnSO 4 /H 2 O-50% EG as the electrolyte and phenanthrenequinone macrocyclic trimer (PQ-MCT) as the cathode, which showed that the discharge capacities at 0.2 A/g still maintained 88 mAh/g after 900 cycles at 60 • C. In Ref. [77], Qiu et al. also reported a Zn//polytriphenylamine composite (PTPAn) battery using Zn trifluoromethanesulfonate (Zn-TFMS) salt-mixed solvent of propylene carbonate (PC) and triethyl phosphate (TEP) as the electrolyte, which maintained 300 cycles at 2 A/g at the same temperature, 60 • C. In Ref. [78], the rate performance of the PTPAn cathode at a high temperature of 60 • C and the cyclic stability of Zn//PTPAn cells at 60 • C are shown in Figure 11a,b.According to the scheme (Figure 11c), during the charging process, one of the TPA units (containing a C-N bond) at first gives up one p-electron of the C=N bond and then becomes positively charged, producing the corresponding radical cation (C=N + ) and anion TDMS -and attracting p-electrons from the benzene ring under the connection of intermolecular forces, while the second adjacent TPA loses another electron of C=N bond at higher potential.Therefore, the reaction at the PTPAn cathode includes the oxidation/reduction of the TPA units (i.e., C-N C=N + ) and is accompanied by the combination/release of the TFMS into the polymer chains.

Colloidal Electrolytes
Colloidal electrolytes have been reported to enhance the high-temperature electrochemical performance of AZIBs positively.Xie et al. [74] proposed a hightemperature-resistant "Ben-colloid" colloidal electrolyte, prepared by mixing liquid electrolyte (2 M ZnSO4 and 0.1 M MnSO4) with bentonite.AZIBs assembled using this colloidal electrolyte maintained a capacity of 114.9 mAh/g after 300 cycles at a current density of 2 A g −1 at 55 °C (Figure 12a).Yang et al. reported that a cotton-like LVO-250 battery using ZnSO4 electrolyte showed excellent electrochemical performance with 232 mAh/g after 500 cycles at 5 A/g, and 192 mAh/g after 1000 cycles at 10 A/gat 50 °C [75].

Colloidal Electrolytes
Colloidal electrolytes have been reported to enhance the high-temperature electrochemical performance of AZIBs positively.Xie et al. [74] proposed a high-temperatureresistant "Ben-colloid" colloidal electrolyte, prepared by mixing liquid electrolyte (2 M ZnSO 4 and 0.1 M MnSO 4 ) with bentonite.AZIBs assembled using this colloidal electrolyte maintained a capacity of 114.9 mAh/g after 300 cycles at a current density of 2 A g −1 at 55 • C (Figure 12a).Yang et al. reported that a cotton-like LVO-250 battery using ZnSO 4 electrolyte showed excellent electrochemical performance with 232 mAh/g after 500 cycles at 5 A/g, and 192 mAh/g after 1000 cycles at 10 A/gat 50  .This electrolyte displayed excellent mechanical properties, high sulfur conductivity, thermochemical cycling stability, and exceptional electrochemical performance.The battery utilizing this electrolyte demonstrated outstanding cycling stability at 25 °C, 40 °C, and 60 °C after 120 charge/discharge cycles, with capacity retention of 99%, 97%, and 96%, respectively.Moreover, the long-term cycling capacity retention of Zn//CuVO exceeded 200 mAh/g after 1200 cycles under high-temperature conditions (60 °C), and the corresponding coulombic efficiency of the Zn//CuVO-code cell remained close to 99% at 5A/g current (Figure 12b).
The aforementioned electrolyte strategies can enhance the electrochemical performance of AZIBs under specific temperature conditions (high or low temperature).However, to meet practical requirements, it is crucial to develop a wide-temperaturerange electrolyte that can accommodate both high and low temperatures.• C after 120 charge/discharge cycles, with capacity retention of 99%, 97%, and 96%, respectively.Moreover, the long-term cycling capacity retention of Zn//CuVO exceeded 200 mAh/g after 1200 cycles under high-temperature conditions (60 • C), and the corresponding coulombic efficiency of the Zn//CuVO-code cell remained close to 99% at 5A/g current (Figure 12b).

Wide Temperature Condition
The aforementioned electrolyte strategies can enhance the electrochemical performance of AZIBs under specific temperature conditions (high or low temperature).However, to meet practical requirements, it is crucial to develop a wide-temperature-range electrolyte that can accommodate both high and low temperatures.

Wide Temperature Condition
AZIBs encounter significant Zn cathode and electrolyte challenges at wide temperature operating conditions, leading to poor battery operability and suboptimal electrochemical performance.Consequently, understanding the failure mechanisms of AZIBs at various operating temperatures and developing AZIBs with stable operation under widetemperature conditions are essential.In recent years, numerous studies have addressed wide-temperature AZIBs to advance both theoretical research and practical applications, where the major efforts have been devoted to regulating the hydrogen bonding network, simultaneously enabling the anti-freezing for low temperature and the inhibited H 2 O activity for high temperature.Table 3 shows the summary of electrochemical performance in AZIBs at wide temperature.) with large interlayer spacing using a pre-intercalation strategy and assembled a quasi-solid-state battery by pairing Zn//δ-MgVO as a cathode with a polyvinyl alcohol/glycerol gel electrolyte.This quasi-solid-state battery demonstrates satisfactory performance across a wide temperature range of −30 • C to 60 • C, making it suitable for environmentally adaptive aqueous energy storage devices.High capacities of 308.7, 269.7, 227, and 153 mAh/g are sustained at 60, 25, 0, and −30 • C, from high temperature to low temperature, respectively, after a cycle life test of 5000 cycles at 2 A/g (Figure 13a).The PVA/G battery can nevertheless offer high reversible capacities of 246.3, 226.4,204.9, 176.1, and 136.7 mAh/g at current densities of 0.2, 0.5, 1, 2, and 5 A/g, respectively, even at a relatively low temperature of −30 • C (Figure 13b).Lu et al. [98] suggested that a multi-component cross-linked hydrogel electrolyte could suppress Zn dendrites and enable low-temperature environmental adaptation of ZIBs.Leveraging the inhibitory effect of polyacrylamide and dimethyl sulfoxide (DMSO) on Zn dendrites, the completed full-cell exhibits a large specific capacity of 265.2 mAh/g at current densities of 0.2 A/g and remarkable cyclic stability with a capacity retention of 95.27% after 3000 cycles.More importantly, the galvanostatic charge-discharge (GCD) curves measured at temperatures ranging from −40 • C to 60 • C indicate that the twostep charge storage mechanism of the charge/discharge process remains unchanged with temperature (Figure 13c,d).

Organic Additives
By reducing the water content in the aqueous electrolyte and increasing the organic solvent, the hybrid aqueous-organic electrolyte is prepared with suppressed water activity, which also exhibits good performance over a wide temperature range.Han et al.
[99] used EG as a solvent and added it into the water-containing organic electrolyte based on Zn(BF4)2, which has accommodated flame retardancy.Due to the strong hydrogen bonding between various components, the electrolyte can not only effectively inhibit the dendrite reaction, corrosion, and hydrogen evolution reaction of the Zn anode in a wide operating temperature range, but it can also promote the formation of a favorable ZnF2 passivation layer and form a certain protection mechanism.The electrochemical performance of Zn/Cu cells across a wide temperature range from 40 °C to −30 °C was examined to determine the viability of the 4 M Zn(BF4)2/EG electrolyte in challenging circumstances.The Zn‖Cu battery using this electrolyte displayed a high CE of 97.3%, 96.9%, and 95.7% with good cycling stability (over 135, 100, and 100 cycles) at 40 °C, −15 °C, and −30 °C, respectively (Figure 14a-c).In contrast, the electrochemical performance of the cell using the reference ZnSO4 electrolyte exhibited poor CE properties for 95.8% and 47.1% along with a short term of sixty cycles, and only one cycle under the conditions of 40 °C and −15 °C.In addition, the battery showed the worst performance, which was frozen, so that it could not work at −30 °C.These results demonstrate the Zn(BF4)2/EG electrolyte's exceptional wide temperature performance.The interaction inside the electrolyte and the solvation structure of Zn 2+ were verified by DFT calculations and MD simulations.DFT calculations show that the relative binding energy between any two components obeys the order of magnitude of Zn 2+ -BF4 − > Zn 2+ -EG > Zn 2+ -H2O > BF4 − -EG > BF4 − -H2O > EG-H2O in 4 M Zn(BF4)2/EG electrolyte (Figure 15a).MD simulations show that in 4 MZn(BF4)2/EG, three components (EG, H2O, and BF4 − ) are involved in the solvation sheath of Zn 2+ ions (Figure 15b,c).

Organic Additives
By reducing the water content in the aqueous electrolyte and increasing the organic solvent, the hybrid aqueous-organic electrolyte is prepared with suppressed water activity, which also exhibits good performance over a wide temperature range.Han et al. [99] used EG as a solvent and added it into the water-containing organic electrolyte based on Zn(BF 4 ) 2 , which has accommodated flame retardancy.Due to the strong hydrogen bonding between various components, the electrolyte can not only effectively inhibit the dendrite reaction, corrosion, and hydrogen evolution reaction of the Zn anode in a wide operating temperature range, but it can also promote the formation of a favorable ZnF 2 passivation layer and form a certain protection mechanism.The electrochemical performance of Zn/Cu cells across a wide temperature range from 40 • C to −30 • C was examined to determine the viability of the 4 M Zn(BF 4 ) 2 /EG electrolyte in challenging circumstances.The Zn Cu battery using this electrolyte displayed a high CE of 97.3%, 96.9%, and 95.7% with good cycling stability (over 135, 100, and 100 cycles) at 40 • C, −15 • C, and −30 • C, respectively (Figure 14a-c).In contrast, the electrochemical performance of the cell using the reference ZnSO 4 electrolyte exhibited poor CE properties for 95.8% and 47.1% along with a short term of sixty cycles, and only one cycle under the conditions of 40 • C and −15 • C. In addition, the battery showed the worst performance, which was frozen, so that it could not work at −30 • C.These results demonstrate the Zn(BF 4 ) 2 /EG electrolyte's exceptional wide temperature performance.The interaction inside the electrolyte and the solvation structure of Zn 2+ were verified by DFT calculations and MD simulations.DFT calculations show that the relative binding energy between any two components obeys the order of magnitude of Zn 2+       Mo et al. proposed a biomimetic organohydrogel (BM-gel) electrolyte, which can effectively and efficiently block water evaporation and seclude hydrogel from external surroundings.This BM-gel electrolyte kept up excellent electrochemical performance even at excessive temperatures (from 80 • C to −20 • C) in the Zn-MnO 2 battery, which exhibited a stable specific capacity of 105 mAh/g after 150 cycles at 2.0 A/g current density at 80 • C and a high specific capacity of 165 mAh/g at 0.2 A/g current density at subzero temperature -20 • C [21].
It can be seen that the electrolytes of AZIBs are modified by the above method, and quasi-solid electrolytes are the main means to achieve wide temperature range.The electrolytes need satisfy the characteristics of the high-temperature domain and the lowtemperature domain, which greatly expands the application range of the AZIBs in various environments.

Summary and Outlook
The wide-temperature performance of AZIBs significantly impacts their practical applications.This review discussed the challenges and strategies associated with AZIBs under extreme conditions, such as low temperatures, high temperatures, and wide temperature ranges, where regulating the hydrogen bonding network and H 2 O activity is the effective strategy.Despite advancements in the field of wide-temperature AZIB electrolytes over the past three years, several obstacles remain.Based on the authors' knowledge and understanding, future research should focus on addressing the following challenges: 1.
In addition to the development of wide-temperature electrolytes, self-protection represents another approach to enhance the wide-temperature performance of AZ-IBs [100,101].Efficient thermal self-protection strategies for Zn-ion batteries using smart hygroscopic hydrogel electrolytes have been reported [97,102].The reversible water evaporation and regeneration processes within the hydrogel are closely associated with temperature fluctuations, which can modulate ion migration in AZIB hydrogels.These findings present novel opportunities for creating environmentally adaptive aqueous energy storage devices with improved wide-temperature performance, driving future practical applications.2.
While AZIBs' operation at wide temperatures through intricate electrolyte design has been documented, the mechanisms underlying the entire battery system warrant a more comprehensive and systematic examination to better inform the practical application of AZIBs.Additionally, much of the current research on AZIBs remains confined to laboratory settings, with a considerable gap between these investigations and practical implementation.As such, achieving the real-world application of AZIBs necessitates the collective efforts of researchers worldwide.

Batteries 2023, 9 , 23 Figure 1 .
Figure 1.(a) Comparison of the properties of common metals used as ion batteries.(b) Statistics of papers published on the topic of wide-temperature aqueous Zn-ion batteries in the past three years.

Figure 1 .
Figure 1.(a) Comparison of the properties of common metals used as ion batteries.(b) Statistics of papers published on the topic of wide-temperature aqueous Zn-ion batteries in the past three years.

Figure 2 .
Figure 2. (a) Cycling performance of PANI|LTE|Zn batteries at −70 °C at 0.2 A/g.LTE = lowtemperature electrolyte.(b) The schematic of the structure evolutions of water and electrolyte, and the design of low-Tt solution.Original water network linked by H-bonding can easily transform to ice network at 0 °C.After adding ZnCl2, the H-bond network is broken by the strong interaction between ions and water, while the ion interactions are enhanced.By balancing the H-bonding and ion interactions for modulating Tt, the electrolyte at critical C can be operated at extremely low temperature.© Copyright 2020, The Author(s)[52].

Figure 2 .
Figure 2. (a) Cycling performance of PANI|LTE|Zn batteries at −70 • C at 0.2 A/g.LTE = lowtemperature electrolyte.(b) The schematic of the structure evolutions of water and electrolyte, and the design of low-T t solution.Original water network linked by H-bonding can easily transform to ice network at 0 • C.After adding ZnCl 2, the H-bond network is broken by the strong interaction between ions and water, while the ion interactions are enhanced.By balancing the H-bonding and ion interactions for modulating T t , the electrolyte at critical C ZnCl 2 can be operated at extremely low temperature.© Copyright 2020, The Author(s)[52].
introduced the BF 4 − anions to break the original hydrogen bonding network between H 2 O molecules by forming O-H•••F hydrogen bonding and developed a Zn(BF 4 ) 2 electrolyte with a low freezing point (−122 • C) and high ionic conductivity.The Zn||tetrachlorobenzoquinone (TCBQ) cell based on the 4 mol/L Zn(BF 4 ) 2 electrolyte exhibited excellent electrochemical performance over a low temperature range from −60 • C to −95 • C. The Zn/TCBQ battery achieves a high discharge specific capacity of 86.1 mAh/g, 71.8 mAh/g, and 63.5 mAh/g at −60 • C, −80 • C, and −95 • C, respectively, at an average voltage of 1.2 V.It has been shown that adding BF 4 −
H 2 O molecule by hydrogen bonding (Figure 4b,c).There are two forms of binding between DOL and H 2 O.Most DOL interacts with only one H 2 O molecule, and some DOL binds to two H 2 O molecules.The probabilities of DOL-H 2 O, DOL-2H 2 O, and H 2 O-H 2 O were calculated by the Density Function Theory (DFT).As shown in Figure 4d, the binding energies of DOL-H 2 O and DOL-2H 2 O are 2.662 kcal/mol and 5.278 kcal/mol, respectively, and the binding energies of H 2 O-H 2 O are 2.542 kcal/mol, respectively.The theoretical calculation results further prove that H 2 O is more inclined to combine with DOL than H 2 O [55].

Figure 4 .
Figure 4. (a) Cycling stability of ZnV2O5 cell based on the hybrid electrolyte at −30 °C with a current density of 0.1 A/g.(b) Snapshot of the MD simulation cell for the 1:1 electrolyte.(c) The solvation structure of Zn 2+ obtained by MD simulation.(d) Relative binding energy for DOL with H2O molecules obtained from DFT calculations.© Copyright 2021, Elsevier B.V [55].

Figure 4 .
Figure 4. (a) Cycling stability of ZnV 2 O 5 cell based on the hybrid electrolyte at −30 • C with a current density of 0.1 A/g.(b) Snapshot of the MD simulation cell for the 1:1 electrolyte.(c) The solvation structure of Zn 2+ obtained by MD simulation.(d) Relative binding energy for DOL with H 2 O molecules obtained from DFT calculations.© Copyright 2021, Elsevier B.V [55].

Figure 5 .Figure 5 .
Figure 5. (a) Low-temperature performance of ZnPANI-V2O5 batteries based on EG40 at −20 °C with a current density of 0.2 A/g.(b-g) Optimized structure for the hybrid electrolytes from MD simulations and DFT calculations.Snapshots of (b) EG0 and (c) EG40 during MD simulations.(d) Coordinated numbers of H2O, EG, and SO4 2− around Zn 2+ and the diffusion coefficient of Zn 2+indifferent electrolytes calculated from MD simulations.(e) Relative binding energy for Zn 2+ with Figure 5. (a) Low-temperature performance of ZnPANI-V 2 O 5 batteries based on EG40 at −20 • C with a current density of 0.2 A/g.(b-g) Optimized structure for the hybrid electrolytes from MD simulations and DFT calculations.Snapshots of (b) EG0 and (c) EG40 during MD simulations.(d) Coordinated numbers of H 2 O, EG, and SO 4 2− around Zn 2+ and the diffusion coefficient of Zn 2+indifferent electrolytes calculated from MD simulations.(e) Relative binding energy for Zn 2+ with different species obtained from DFT calculations.Electrostatic potential maps of (f) the original Zn 2+ -H 2 O system and (g) the EG-added system.© Copyright 2020, The Royal Society of Chemistry [56].

Figure 6 .
Figure 6.AZIB performance using hydrogel electrolyte.(a) Areal and (b) volumetric Ragone plots of our PVA-B-G battery, in comparison with previously reported energy storage devices.© Copyright 2020, The Royal Society of Chemistry [57].

Figure 6 .
Figure 6.AZIB performance using hydrogel electrolyte.(a) Areal and (b) volumetric Ragone plots of our PVA-B-G battery, in comparison with previously reported energy storage devices.© Copyright 2020, The Royal Society of Chemistry [57].Wang et al. [58] devised a concentrated hydrogel electrolyte by combining xanthan gum with a ZnCl 2 aqueous solution, forming a hydrogel electrolyte.At −20 • C and −40• C, the discharge-specific capacities were 201 mAh/g and 83 mAh/g, respectively, when the current density was 0.2 A/g (Figure7a,b).An ethylene glycol (EG)-based aqueous anionic polyurethane acrylate (EG-waPUA) hydrogel electrolyte was employed in a flexible Zn/MnO 2 battery.H 2 O molecules are confined through effective hydrogen bond interactions with EG and polymer molecules, enabling the freezing point to be controlled by adjusting the EG content.The hydrogel remains unfrozen at −20 • C when the EG content reaches a certain threshold.The optimized hydrogel retains an ionic conductivity of 14.6 mS/cm and exhibits robust mechanical properties at −20 • C. Furthermore, the Zn-MnO 2 battery assembled with this gel electrolyte demonstrates exceptional lowtemperature performance, retaining over 80% of its capacity when transitioning from room temperature to −20 • C. No significant capacity degradation was observed after several alternating cycles between high and low temperatures (Figure7c)[59].

Figure 7 .
Figure 7. (a) Rate of electrochemical performance of the batteries based on the electrolytes prepared using 0.8 g, 1.2 g, and 1.6 g of xanthan gum combined with 4 m ZnCl 2 at −20 • C. © Copyright 2021, Elsevier Ltd. [58].(b) Rate performance of the battery with the optimized electrolyte at −40 • C. © Copyright 2021, Elsevier Ltd. [58].(c) Cyclic testing of PAM-battery and AF-battery under 20, 0, −20 • C at 0.3 A/g.PAM = polyacrylamide; AF = anti-freezing.© Copyright 2019, The Royal Society of Chemistry [59].Huang et al. [53] form ternary and weak hydrogen bonding by introducing the chaotropic ClO 4 − polymer chains into the H 2 O molecule network, which can reduce the freezing point of the electrolyte.Firstly, density functional theory (DFT) was used to examine how the chaotropic ClO 4− anions, water, and polymer chains interacted.The strong retaining capacity of the hydrogel is confirmed by Figure8a, which shows that the binding energy of PAM to water is significantly greater than that of water to water.To test the effectiveness of the Zn(ClO 4 ) 2 salts on gel electrolyte anti-freezing, a dual-network hydrogel (designated as CSAM) composed of modified polysaccharides carboxymethyl chitosan (CMCS) and polyacrylamide (PAM) was created and used as an example system.It proves that the ClO 4 − anion has a potent interaction with PAM chains, allowing it to enter the polymer chains, break the HB in PAM-PAM and PAM-CSAM, and control the hydrogel's mechanical flexibility.This increases the hydrophilic property of the hydrogel and improves its mechanical characteristics by forming a ternary HB reciprocity between the ClO 4 − anion, water, and polymer chains, as shown in Figure8b.Ref.[53]At −30 • C, the Zn//polyaniline battery is composed of the electrolyte with an ionic conductivity of 7.8 mS/cm and a reversible capacity of 70 mAh/g after 2500 cycles at a current density of 5 A/g (Figure8c).

Figure 11 .
Figure 11.(a) The rate performance of PTPAn cathode at high temperature of 60 • C and (b) cyclic stability of Zn//PTPAn cells at 60 • C was shown.(c) Scheme showing the reactions at the PTPAn cathode.© Copyright 2021, Wiley-VCH GmbH [78].

Figure 12 .
Figure 12.AZIB performance at high temperature condition.(a) The function of ben-colloid electrolyte and electrochemical performance at 55 and 80 • C. © Copyright 2021, Wiley-VCH GmbH [74].(b) Long-term cycling capacity retention and corresponding coulombic efficiency of Zn//CuVO yarn battery at 5 A g −1 at 60 • C. © Copyright 2022, American Chemical Society [76].3.1.3.Hydrogel Electrolytes For flexible energy storage systems, a gel electrolyte is particularly appealing compared to liquid electrolytes because of the following benefits [84]: (1) A gel electrolyte can stop liquid electrolytes from escaping (Ref.[90]); (2) A gel electrolyte may function as a separator by itself, making the construction of zinc-ion batteries simpler; (3) The sticky interface of the gel electrolyte may improve the electrodes' interfacial suitability and guarantee steady electrochemical performances; gel electrolytes with smart flexibility, self-healing properties, and stretchability might provide devices additional cuttingedge features (Ref.[91]); (4) A gel electrolyte might inhibit the creation of zinc dendrites (Ref.[92]); and (5) Gel electrolytes with smart responsiveness, a self-healing nature, and stretchability could give devices more innovative functions (Refs.[93-95]).To stabilize the H 2 O molecular network in the electrolyte, Liu et al. [76] developed a hydrogel electrolyte PNMT with a semi-interpenetrating cross-linked network structure based on polyacrylamide (PAM), cotton cellulose nanofibers (CNF), and carboxymethyl cellulose IV (CMC).This electrolyte displayed excellent mechanical properties, high sulfur conductivity, thermochemical cycling stability, and exceptional electrochemical performance.The battery utilizing this electrolyte demonstrated outstanding cycling stability at 25 • C, 40 • C, and 60 • C after 120 charge/discharge cycles, with capacity retention of 99%, 97%, and 96%, respectively.Moreover, the long-term cycling capacity retention of Zn//CuVO exceeded 200 mAh/g after 1200 cycles under high-temperature conditions (60 • C), and the corresponding coulombic efficiency of the Zn//CuVO-code cell remained close to 99% at 5A/g current (Figure12b).The aforementioned electrolyte strategies can enhance the electrochemical performance of AZIBs under specific temperature conditions (high or low temperature).However, to meet practical requirements, it is crucial to develop a wide-temperature-range electrolyte that can accommodate both high and low temperatures.

Figure 15 .
Figure 15.(a) Relative binding energies between any two ingredients in the Zn(BF 4 ) 2 /EG electrolyte obtained from DFT calculations.(b) Snapshot of a typical MD-simulated cell for the 4 m Zn(BF 4 ) 2 /EG electrolyte.(c) Representative Zn 2+ solvation structure in the 4 m Zn(BF 4 ) 2 /EG electrolyte obtained from the MD simulation in (b).© Copyright 2021, The Author(s), Springer Nature Limited [99].

Author Contributions:Funding:
Conceptualization, G.L.; methodology, F.M. and H.H.; software, Z.S.; validation, L.S.; formal analysis, L.S.; investigation, L.S.; resources, C.D. and Q.W.; data curation, L.S.; writing-original draft preparation, L.S.; writing-review and editing, L.S. and Z.S.; visualization, Z.S.; supervision, G.L.; project administration, G.L.; funding acquisition, L.S., Z.S. and G.L. All authors have read and agreed to the published version of the manuscript.This work was supported by the National Natural Science Foundation of China (No. 51972151 and 52171212).The authors gratefully acknowledge the financial support provided by the Shenzhen Municipality under the Stability Support Program of Shenzhen Colleges and Universities (GXWD20220817150352006) and the Project of Scientific Research Foundation for Returned Scholars (Grant No. DD11409018).

Table 1 .
The summary of electrochemical performance in AZIBs at low temperature (anode: Zn).

Table 2 .
The summary of electrochemical performance in AZIBs at high temperature (anode: Zn).

Table 3 .
The summary of electrochemical performance in AZIBs at wide temperature (anode: Zn).