HYBRID ELECTROLYTE SOLUTIONS FOR ELECTROCHEMICAL DEVICES WITH A WIDE OPERATING TEMPERATURE RANGE AND PREPARATION METHOD THEREOF

PRIORITY DOCUMENT

[0001] The present application claims priority from Australian Provisional Patent Application No. 2022902879 titled “HYBRID ELECTROLYTE SOLUTIONS FOR ELECTROCHEMICAL DEVICES WITH A WIDE OPERATING TEMPERATURE RANGE AND PREPARATION METHOD THEREOF” and filed on 4 October 2022, the content of which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

[0002] The present disclosure relates generally to electrolyte solutions for an electrochemical device and preparation methods thereof. In particular, the present disclosure relates to hybrid electrolyte solutions for an electrochemical device with a wide operating temperature range and methods for their preparation.

BACKGROUND

[0003] Energy storage will dramatically transform the way the world uses energy. Although organic electrolyte-based batteries show high energy densities which are, in principle, suitable for large scale energy storage, they suffer from inherent instability and safety issues caused by the use of expensive yet highly volatile and flammable organic solvents (for example, dimethyl carbonate and diethyl carbonate) and of chemically unstable and toxic salts (for example, lithium hexafluorophosphate (LiPFe)) in the electrolyte solution. To reduce flammability of an electrolyte solution, various strategies have been employed: (i) the use of low vapour pressure ionic liquids, (ii) the use of halogenated solvents (such as fluorinated carbonates), and (iii) the use of flame-retardant additives (FRAs). In some circumstances, a battery pack (for example for an electrical vehicle) may need to be equipped with a thermal management system (BTMS) that enables the battery to operate within the safest temperature range, normally 10 °C to 40 °C. Organic electrolytes may also encounter a high charge transfer impedance and a high desolvation penalty at the electrode/electrolyte interface, which prevent the cathode from delivering its full capacity [1].

[0004] Aqueous batteries such as aqueous zinc ion batteries (ZIBs) are promising to resolve these issues and provide a new candidate for energy storage applications given their cost effectiveness, high ionic conductivity and much improved safety. However, the increased viscosity, the decreased ionic conductivity as well as the liquid to solid phase transformation of the aqueous electrolytes at low temperatures hinder their practical application [2] . It is important to address the high freezing point and the low ionic conductivity at subzero temperature conditions associated with water-based electrolytes. Attempts have been made to extend the operating temperature range of an aqueous electrolyte, for example through (i) formulating an organic electrolyte solution to form a eutectic or an anti-freezing hydrogel; (ii) formulating a concentrated electrolyte solution with a high ratio of salt to water (such as “water in salt” strategy) [2-4]. Although the highly concentrated “water in salt” electrolyte solution could significantly lower the freezing point of an aqueous electrolyte, disadvantages like high viscosity, low conductivity as well as increasing costs occur. In comparison, an organic solvent can be used at a dilute concentration without sacrificing the intrinsic physical properties of an aqueous electrolyte [5,6].

[0005] ZIBs are regarded as one of the most promising candidates because of their inherent merits including safety, attractive gravimetric energy density, affordable cost, high abundance of Zn, and environmental friendliness [7]. ZIBs are generally composed of a metallic Zn anode, a Zn salt-containing electrolyte, and a Zn ²⁺ ion host cathode. Compared with other metallic metal anodes such as lithium, sodium and potassium, the low reactivity and the acceptable redox potential ( -0.76 V vs standard hydrogen electrode) of metallic Zn enable ZIBs to be relatively safe [8]. An aqueous electrolyte solution containing, for example, ZnSCh or zinc trifluoromethanesulfonate (Zn(OTf)2) is inherently safe, inexpensive and environmentally-friendly, which make it particularly attractive. Nevertheless, aqueous ZIBs are still facing challenges like narrow electrochemical stability window (ESW, 1.23 V), corrosion of Zn anode, dendrite growth, poor temperature adaptability, and dissolution of cathode materials [9]. The operating voltage of an aqueous battery is determined by the potential of the cathode and anode materials, and it should be within the ESW of an aqueous electrolyte (around 1.23 V), otherwise hydrogen or oxygen evolution reactions occur, which result in increases in battery internal pressure [10]. Gas generation could also derive from self-corrosion of Zn anodes since a certain amount of H3O ⁺ exists in a mild acidic electrolyte and could withdraw electrons from metallic Zn. Accompanied by hydrogen evolution, the accumulated OH ions would aggregate with Zn ²⁺ and anions to form passivation species, such as zinc hydroxysulfate [Zn^OH^SOrnlEO]. These passivation species could prevent diffusion of Zn ²⁺ ions and electron transmission, which further causes uneven Zn deposition and dendrite growth. Furthermore, the majority of aqueous ZIBs cannot work in sub-zero and hot (>40 °C) environments due to the high freezing point (0 °C) and low boiling point (100 °C) of water. Another potential issue with an aqueous electrolyte solution is the dissolution of active cathode material, which will lead to rapid capacity fading.

[0006] Suggestions to mitigate the above issues include constructing an artificial protection layer [11], adding functional additives [12], and regulating Zn ²⁺ ion deposition behaviours [13]. However, the issues have not been entirely addressed, especially challenges arising from the water solvent. It is well- acknowledged that self-ionisation of H2O would occur in pure water to form OH and H ;O ⁺ (2H2O H ₃ O ⁺ + OH ). Zn ²⁺ generated through dissolution of zinc salts such as ZnSO4 and Zn(OTf)2 would interact with water molecules and cause more water molecules to spontaneously ionise, which makes the pH value reduce from near 7 for pure water to around 5 for a 1 M ZnSC>4/Zn(OTf)2 aqueous solution. Furthermore, the electric field of Zn ²⁺ would exert a force on water molecules, inducing the electron transfer from coordinated H2O to the empty orbitals of Zn ²⁺ , which significantly weakens the O-H bonds of water molecules and promotes hydrogen evolution reaction [14,15]. In theory, self-ionisation of water molecules cannot be effectively suppressed by a small amount of additive. Highly concentrated “water-in- salt” electrolyte has been suggested as a solution, in which the dissolved salts enormously outnumber the water molecules and confine all the water molecules in the ion solvation shells. By suppressing interaction between Zn ²⁺ and H2O, hydrolysis of zinc salt is eliminated and the pH value of “water-in- salt” electrolytes stays at around 7. In this case, water shows less activity and the ESW of the electrolyte can be expanded to around 3.0 V [14]. However, it is definitely not a cost-effective strategy. Researchers thereby set their sights on organic electrolytes to fundamentally eliminate H3O ⁺ . Organic electrolytes possess overwhelming superiority in ESW, operating temperature range, and thermodynamic stability with metallic Zn anode, however, most of them are ignitable, posing a safety threat to ZIBs.

[0007] Accordingly, there remains a need for an electrochemical device which solves or alleviates one or more of the above problems and may particularly be used over a wide operating temperate range, for example, at sub-zero temperatures.

SUMMARY

[0008] In a first aspect, provided herein is a hybrid solvent for a hybrid electrolyte solution of an electrochemical device, wherein the hybrid solvent comprises water and at least one organic co-solvent, the electrochemical device being operable in a temperature range of about -80 °C to about 70 °C.

[0009] In a second aspect, provided herein is a hybrid electrolyte solution for an electrochemical device comprising an electrolyte and a hybrid solvent, wherein the hybrid solvent comprises water and at least one organic co-solvent, the electrochemical device being operable in a temperature range of about - 80 °C to about 70 °C.

[0010] In a third aspect, provided herein is an electrochemical device comprising a positive electrode, a negative electrode, and the hybrid electrolyte solution of the second aspect.

[0011] In certain embodiments of the first, second or third aspect, the hybrid solvent further comprises a hydrophobic solvent to allow the electrochemical device to be operable in a temperature range of about -80 °C to about 70 °C.

[0012] In certain embodiments of the first, second or third aspect, the at least one organic co-solvent has a donor number higher than about 18 kcal/mol, for example higher than about 23 kcal/mol. In some embodiments, the at least one organic co-solvent is selected from the group consisting of triethyl phosphate (TEP), trimethyl phosphate (TMP), tributyl phosphate (TBP), dimethyl methylphosphonate (DMMP), dimethylacetamide (DM AC), dimethylformamide (DMF), diethylformamide (DEF) and diethylacetamide (DE AC).

[0013] In certain embodiments of the first, second or third aspect, the hydrophobic solvent is selected from the group consisting of bis(2,2,2-trifluoroethyl) methylphosphonate (TFMP) and tris(2,2,2- trifluoroethyl) phosphate (TFEP).

[0014] In certain embodiments of the first, second or third aspect, the hybrid solvent consists of water and the at least one organic co-solvent. In some embodiments, the hybrid solvent consists of water and the at least one organic co-solvent in a volume ratio range of about 90% -10%: 10% -90%. In some embodiments, the at least one organic co-solvent is one organic co-solvent, two organic co-solvents or three organic co-solvents.

[0015] In certain embodiments of the first, second or third aspect, the hybrid solvent consists of water, the at least one organic co-solvent and the hydrophobic solvent. In some embodiments, the hybrid solvent consists of water, the at least one organic co-solvent and the hydrophobic solvent in a volume ratio range of about 85%-10%:10%-85%:<0%-5%, about 80%-10%:10%-80%:<0%-10%, about 75%-10%:10%- 75%:<0%-15%, about 70%-10%:10%-70%:<0%-20%, about 65%-10%:10%-65%:<0%-25%, about 60%- 10%:10%-60%:<0%-30%, about 55%-10%:10%-55%:<0%-35%, about 50%-10%:10%-50%:<0%-40%, about 45%-10%:10%-45%:<0%-45%, or about 40%-10%:10%-40%:<0%-50%. In some embodiments, the hybrid solvent consists of water, the at least one organic co-solvent and the hydrophobic solvent in a volume ratio range of about 85%- 10%: 10%-85%:5%, about 80%-10%:10%-80%:10%, about 75%- 10%:10%-75%:15%, about 70%-10%:10%-70%:20%, about 65%-10%:10%-65%:25%, about 60%- 10%:10%-60%:30%, about 55%-10%:10%-55%:35%, about 50%-10%:10%-50%:40%, about 45%- 10%:10%-45%:45%, or about 40%-10%:10%-40%:50%.

[0016] In certain embodiments of the first, second or third aspect, the hybrid solvent is a binary mixture of water and one organic co-solvent. In some embodiments, the hybrid solvent is a binary mixture of water and dimethyl methylphosphonate (DMMP). In some further embodiments, the hybrid solvent is a binary mixture of water and dimethyl methylphosphonate (DMMP) at a volume ratio of about 1:1.

[0017] In certain embodiments of the first, second or third aspect, the hybrid solvent is a ternary mixture of water and two organic co-solvents. In some embodiments, the hybrid solvent is a ternary mixture of water, dimethylacetamide (DMAC) and trimethyl phosphate (TMP). In some further embodiments, the hybrid solvent is a ternary mixture of water, dimethylacetamide (DM AC) and trimethyl phosphate (TMP) at a volume ratio of about 3:5:2.

[0018] In certain embodiments of the first, second or third aspect, the hybrid solvent is a ternary mixture of water, one organic co-solvent and one hydrophobic solvent. In some embodiments, the hybrid solvent is a ternary mixture of water, dimethyl methylphosphonate (DMMP) and bis(2,2,2-trifluoroethyl) methylphosphonate (TFMP). In some embodiments, the hybrid solvent is a ternary mixture of water, dimethyl methylphosphonate (DMMP) and bis(2,2,2-trifluoroethyl) methylphosphonate (TFMP) at a volume ratio of about 5:4:1.

[0019] In certain embodiments of the first, second or third aspect, the electrolyte of the electrochemical device comprises a zinc salt. In some embodiments, the electrolyte is a zinc salt. In some further embodiments, the zinc salt is selected from the group consisting of ZnCh, ZnSCH, Zn(ClC>4)2, Zn(BF4)2, Zn(CH3COO)2, Zn(CF3SC>3)2 (or Zn(OTf)2) and Zn(TFSI)2 (zinc bis(trifluoromethylsulfonyl)imide).

[0020] In certain embodiments of the first, second or third aspect, the electrochemical device is an ion battery. In some embodiments, the electrochemical device is a zinc ion battery. In some embodiments, the negative electrode material of the zinc ion battery is metallic zinc, for example zinc foil, and the positive electrode material of the zinc ion battery is selected from manganese oxide (MnCh), vanadium oxides such as V2O5 or M V2O5-nH2O (where M=Na, K, Zn or Ca and 0.05<x<l, 0<n<10), and Na3V2(PC>4)3.

[0021] In certain embodiments of the first, second or third aspect, the electrochemical device is operable at a temperature as low as about -20 °C, for example -20 °C to about 70 °C, -20 °C to about 50 °C, or -20 °C to about 30 °C. In some embodiments, the electrochemical device is operable at a temperature as low as about -30 °C, for example -30 °C to about 70 °C, -30 °C to about 50 °C, or -30 °C to about 30 °C. In some further embodiments, the electrochemical device is operable at a temperature range as low as about -40 °C, for example -40 °C to about 70 °C, -40 °C to about 50 °C, or about -40 °C to about 30 °C. In some further embodiments, the electrochemical device is operable at a temperature range as low as about -45 °C, for example -45 °C to about 70 °C, -45 °C to about 50 °C, or about -45 °C to about 30 °C. In even further embodiments, the electrochemical device is operable at a temperature as low as about -65 °C, for example -65 °C to about 70 °C, -65 °C to about 50 °C, or about -65 °C to about 30 °C. In other further embodiments, the electrochemical device is operable at a temperature as low as about -80 °C, for example -80 °C to about 50 °C, or about -80 °C to about 30 °C.

[0022] In certain embodiments of the first, second or third aspect, at 50 °C the electrochemical device delivers an initial specific capacity of about 265 mAh g ¹ and maintains a reversible capacity of about 194 mAh g ¹ (73%) after 300 cycles with an average Coulombic efficiency near 100%. In some embodiments, the electrochemical device delivers a capacity of about 140 mAh g ¹ without appreciable capacity fading for 2000 cycles at -20 °C. In some further embodiments, the electrochemical device runs about 300 cycles at 50 °C, and more than 2000 cycles at -20 °C. In some embodiments, at 70 °C, the electrochemical device delivers an initial specific capacity of about 207 mAh g ¹ and maintains a reversible capacity of 120 mAh g ¹ following 1400 cycles with a mean Coulombic efficiency (CE) near 100%. In some embodiments, at -40 °C, the electrochemical device exhibits a capacity of about 85 mAh g ¹ for 700 cycles.

[0023] In a fourth aspect, provided herein is a method of formulating a hybrid solvent for a hybrid electrolyte solution of an electrochemical device, wherein the method comprises combining water, at least one organic co-solvent and optionally a hydrophobic solvent, and the electrochemical device is operable in a temperature range of about -80 °C to about 70 °C.

[0024] In a fifth aspect, provided herein is a method of formulating a hybrid electrolyte solution for an electrochemical device, wherein the method comprises combining an electrolyte, water, at least one organic co-solvent and optionally a hydrophobic solvent, and the electrochemical device is operable in a temperature range of about -80 °C to about 70 °C.

[0025] In certain embodiments of the fourth or fifth aspect, the hybrid solvent or the hybrid electrolyte solution formulated is used for an electrochemical device. In some embodiments, the hybrid electrolyte solution formulated is used for an ion battery. In some further embodiments, the hybrid electrolyte solution formulated is used for a zinc ion battery.

[0026] In a sixth aspect, provided herein is use of a hybrid solvent in a hybrid electrolyte solution of an electrochemical device, wherein the hybrid solvent comprises water, at least one organic co-solvent and optionally a hydrophobic solvent, and the electrochemical device is operable in a temperature range of about -80 °C to about 70 °C.

[0027] In a seventh aspect, provided herein is use of a hybrid electrolyte solution in an electrochemical device, wherein the hybrid electrolyte solution comprises an electrolyte, water, at least one organic cosolvent and optionally a hydrophobic solvent, and the electrochemical device is operable in a temperature range of about -80 °C to about 70 °C.

[0028] In certain embodiments of the sixth or seventh aspect, the water, the at least one organic solvent and optionally the hydrophobic solvent and the electrolyte are combined together at the same time. In some embodiments, the water, the at least one organic solvent and optionally the hydrophobic solvent and the electrolyte are not combined at the same time. In some embodiments, the water, the at least one organic solvent and optionally the hydrophobic solvent and the electrolyte are combined in turn. [0029] Other features and embodiments of the fourth to seventh aspects may refer to those described above in relation to the first, second or third aspect.

BRIEF DESCRIPTION OF THE FIGURES

[0030] Non-limiting embodiments of the present disclosure will be discussed with reference to the accompanying figures wherein:

[0031] Figure 1 shows ignition tests on different electrolyte solutions: (a) IM Zn(OTf)2 in DMAC; (b) 1 M Zn(OTf)2 aqueous solution (denoted as AE); (c) IM Zn(OTf)2 in TMP; and (d) 1 M Zn(OTf)2 dissolved in DMAC/TMP/H2O (5:2:3 by volume) (denoted as HE).

[0032] Figure 2 shows the solvation structure of the hybrid electrolyte solution, 1 M Zn(OTf)2 dissolved in DMAC/TMP/H ₂ O.

[0033] Figure 3 shows (a) the electrochemical stability window of an aqueous electrolyte solution comprising IM Zn(OTf)2 (denoted as AE) and the hybrid electrolyte solution of 1 M Zn(OTf)2 dissolved in DMAC/TMP/H2O (denoted as HE); (b) the Coulombic efficiency of Zn||Cu cells using AE and HE as the electrolyte solution respectively.

[0034] Figure 4 shows the surface morphologies of deposited Zn in AE (a) and HE (b).

[0035] Figure 5 shows the cyclic stability and Coulombic efficiency of Zn||V20s batteries in AE and HE tested at room temperature.

[0036] Figure 6 shows the cyclic stability and Coulombic efficiency of Zn||V20s batteries tested at 70 °C in AE and HE respectively.

[0037] Figure 7 shows the cyclic stability and Coulombic efficiency of Zn||V2Os batteries tested at 50 °C in AE and HE respectively.

[0038] Figure 8 shows the cyclic stability and Coulombic efficiency of Zn||V2Os batteries tested at - 40 °C in HE.

[0039] Figure 9 shows the cyclic stability and Coulombic efficiency of Zn||V2Os batteries tested at - 20 °C in HE.

[0040] Figure 10 shows evaluation of the overall performance of (a) AE and (b) HE. [0041] Figure 11 shows ignition experiments of the conventional flammable (a) acetonitrile (AN)- based and (b) propylene carbonate (PC) based electrolyte solutions, as well as the fire-retardant (c) DMMP-H2O based and (d) TFMP-DMMP-H2O based electrolyte solutions.

[0042] Figure 12 shows the DSC curves of H2O electrolyte solution, hybrid DMMP-H2O electrolyte solution and hybrid TFMP-DMMP-H2O electrolyte solution when temperature decreases from 20 °C to - 65 °C.

[0043] Figure 13 shows the photos of electrolyte solutions (H: H2O electrolyte solution; D: DMMP- H2O electrolyte solution; T: TFMP-DMMP-H2O electrolyte solution) at various subzero temperatures.

[0044] Figure 14 shows (a) cycling of Zn|Zn symmetric battery with temperature decreasing from 0 °C to -80 °C; (b) cycling of V20s|Zn full battery under the temperature decreasing from 0 °C to -50 °C; (c) cycling of the V20s|Zn full battery with TFMP-DMMP-H2O at -50 °C at a current density of 500 mA g '.

[0045] Figure 15 shows the FT-IR spectra of (a) H2O electrolyte solution, (b) hybrid DMMP-H2O electrolyte solution, (c) hybrid TFMP-DMMP-H2O electrolyte solution within the range of 3000 cm ¹ to 3800 cm' ¹ ; the counter map plot of the real time FT-IR spectra of (d) H2O electrolyte solution, (e) hybrid DMMP-H2O electrolyte solution, (f) hybrid TFMP-DMMP-H2O electrolyte solution within the range of 2800 cm ¹ to 3800 cm ', with the temperature decreasing from 20 °C to -60 °C.

[0046] Figure 16 shows (a) the Columbic efficiencies of the Zn|Cu batteries with a H2O electrolyte solution, a hybrid DMMP-H2O electrolyte solution and a hybrid TFMP-DMMP-H2O electrolyte solution; (b) the LUMO and HOMO values of DMMP, TFMP and OTF anion.

[0047] Figure 17 illustrates H-bonds regulating mechanisms of employing an organic hydrophilic cosolvent such as DMMP and a hydrophobic solvent such as TFMP, as well as the interactions between different components. In particular, Zn ²⁺ can solvate with hydrophilic solvent DMMP, hydrophobic solvent TFMP and H2O. The interaction between H2O and TFMP is very weak, while that between H2O and DMMP is very strong, so that a solvent cage effect is developed, and three types of complexes are formed (complex 1: H2O-Zn ²⁺ ; complex 2: H2O-DMMP-Zn ²⁺ ; complex 3: H2O-DMMP-TFMP-Zn ²⁺ ).

DESCRIPTION OF EMBODIMENTS

[0048] The term “electrochemical device” used herein refers to a device that can convert chemical energy into electrical energy through an electrochemical reaction. Examples of the electrochemical device include a battery and a cell such as a coin cell.

[0049] The term “hybrid electrolyte solution” used herein generally refers to an electrolyte solution based on a hybrid solvent which may be a binary or higher order (e.g., ternary and quaternary) mixtures of solvents.

[0050] The term “co-solvent” used herein generally refers to a solvent that is added in conjunction with another solvent to dissolve a solute. For the purpose of the present disclosure, the at least one organic cosolvent would be miscible with water.

[0051] The term “temperature range” used herein generally refers to a temperature range that an electrochemical device may be subjected to during operation or storage.

[0052] The term “negative electrode material” used herein refers to an active material for the negative electrode of the electrochemical device. The term “positive electrode material” used herein refers to an active material for the positive electrode of the electrochemical device. The active materials may be combined with other materials such as a conductive agent and a binder to prepare a desirable electrode.

[0053] The term “hydrophobic solvent” used herein refers to a solvent that lacks affinity for water and can produce the hydrophobic effect.

[0054] The term “donor number” used herein is defined as the enthalpy change of the addition reaction of a solvent to the Lewis acid SbCL (antimony pentachloride) in 1 ,2-dichloroethane and is a measure of the ability of a solvent to solvate cations and Lewis acids.

[0055] The disclosure arises from the inventors’ research into extension of the operating temperature range of an electrochemical device. It has been surprisingly found that an organic co-solvent (for example, one or more organic co-solvents) can be selected and added to water to formulate a hybrid electrolyte solution, wherein the hydrogen bonds between water molecules are weakened and/or the O-H bonds of water molecules are strengthened, so that water molecules become less likely to decompose during operation of the electrochemical device and to transform into ordered ice at lower temperatures. Furthermore, a dipole-dipole interaction may be generated between the organic solvent(s) and water molecules and may in turn be helpful in lowering the freezing point of the hybrid electrolyte solution. Advantageously, the ionic conductivity of the hybrid electrolyte solution at sub-zero temperatures may be enhanced. It has also been surprisingly found that the addition of a hydrophobic solvent with strong hydrophobicity to the hybrid electrolyte solution, may further lower the freezing point thereof while allowing the electrochemical device to work.

[0056] Accordingly, disclosed herein are a hybrid solvent for a hybrid electrolyte solution of an electrochemical device, a hybrid electrolyte solution comprising the hybrid solvent and an electrolyte, and an electrochemical device comprising the hybrid electrolyte solution. The hybrid solvent comprises water and at least one organic co-solvent. The electrochemical device is operable in a temperature range of about -80 °C to about 70 °C. The hybrid solvent may further comprise a hydrophobic solvent to allow the electrochemical device to be operable in a temperature range of about -80 °C to about 70 °C.

[0057] The electrochemical device disclosed herein may be in the form of a battery or a cell. For example, the electrochemical device may be an ion battery, such as zinc ion batteries, lithium ion, sodium ion, potassium ion, calcium ion, magnesium ion and aluminium ion batteries. The electrochemical device may comprise a negative electrode and a positive electrode, which are connected to each other by the hybrid electrolyte solution disclosed herein. The following factors may be taken into account when formulating an electrolyte solution: (i) chemical inertness; (ii) wide liquid range and thermal stability; (iii) balanced viscosity; (iv) high ionic and no electronic conductivity; (v) interphase properties and control of by-products during the redox process; and (vi) availability. It may be desirable for the electrolyte solution to be modified by introducing corrosion inhibitors or complexing agents in order to make the electrolyte less corrosive.

[0058] An electrolyte solution provides an essential environment for multi-chemical reactions during operation of the electrochemical device, including Zn plating/stripping process and (de)intercalation process of Zn ²⁺ ion in the positive electrode material. Therefore, the electrolyte solution’s properties could greatly affect anode reversibility and cathode reaction mechanisms [16]. Moreover, an electrolyte solution also determines the ion migrations between the negative electrode and the positive electrode, the ESW, and temperature adaptability. It is noted that, if water is present in an electrolyte solution, the existence of the H-bonding could have a major influence on the structure of both liquid water and its solid phase, ice. At very low temperatures, the ions move slower through the electrolyte solution, resulting in a reduction of capacity. Additionally, low temperatures cause the charge transfer velocity to decrease and can make it difficult to charge a battery. If an electrochemical device is charged at a freezing temperature, a permanent solid electrolyte interphase (SEI) may build up on the negative electrode and cause irreversible damage to the device.

[0059] Through inclusion of the at least one organic co-solvent and optionally the hydrophobic solvent in an electrolyte solution comprising water, the operating temperature range of the electrochemical device disclosed herein may be from about -80 °C to about 70 °C, for example to about 50 °C, about 30 °C or to about 20 °C. For instance, a lower operating temperature such as about -30 °C, -40 °C, -45 °C, -60 °C, - 65 °C or -80 °C may be achieved. Any temperature mentioned herein is measured at ambient pressure. In some embodiments, the electrochemical device disclosed herein may be operated in a temperature range of about -40 °C to about 70 °C, for example, about -20 °C to about 50 °C. In other embodiments, the electrochemical device disclosed herein may be operated in a temperature range of about -80 °C to about 30 °C, for example about -80 °C to about 20 °C. [0060] For the purpose of the present disclosure, non-flammability may be considered in choosing the organic co-solvent. It may be beneficial for the organic co-solvent to have a donor number higher than about 18 kcal/mol, for example higher than about 23 kcal/mol. If desirable, the donor number may be lower than about 32.5 kcal/mol, for example lower than about 31 kcal/mol, or lower than about 28 kcal/mol. Some illustrative examples of the organic co-solvent that may be used herein include triethyl phosphate (TEP), trimethyl phosphate (TMP), tributyl phosphate (TBP), dimethyl methylphosphonate (DMMP), dimethylacetamide (DM AC), dimethylformamide (DMF), diethylformamide (DEF) and diethylacetamide (DE AC).

[0061] It is possible to employ one or more of the organic co-sol vents to form the hybrid solvent or formulate the hybrid electrolyte solution. It does not exclude the possibility that a solvent other than those recited herein is present as long as it will not substantially affect the technical effects to be achieved.

Specifically, the hybrid solvent may be a binary mixture of water and one organic co-solvent, or a ternary mixture of water and two organic co-solvents. In some embodiments, only dimethyl methylphosphonate (DMMP) is combined with water to form the hybrid solvent, for example at a volume ratio of about 1:1. In some other embodiments, both dimethylacetamide (DMAC) and trimethyl phosphate (TMP) are combined with water to form the hybrid solvent, for example at a volume ratio of water: DMAC: TMP being about 3:5:2. It has been demonstrated that the organic co-solvent(s) could alter the activity of water molecules, for example, the hydrogen bonds between water molecules being weakened and the O-H bonds of water molecules being strengthened. It is suggested that strong dipole-dipole interaction occurs between DMAC/TMP and water molecules, and this effectively increases the electron density of water proton. Generally, an electrochemical device which employs the hybrid solvent to formulate a hybrid electrolyte solution may have a wide operating temperature, like at a temperature as low as about -45 °C, -40 °C, -30 °C or -20 °C and at a temperature as high as about 70 °C or 50 °C. In addition, the negative electrode in the hybrid electrolyte solution may exhibit high plating/stripping efficiency, for example 99.5% over 2000 cycles at 1 mA cm ² , and superior anti-corrosion characteristics. The negative electrode, for example, using metallic zinc as the negative electrode material, may also display an appropriate crystallographic orientation, which assures a long lifespan of the negative electrode, for example, of more than 1600 hours even under high applied current density and plating capacity (5 mA cm ² , 5 mAh cm ² ). The positive electrode, for example using V2O5 as the positive electrode material, may undergo a much less lattice distortion during the (de)intercalation of Zn ²⁺ in the hybrid electrolyte solution, significantly promoting its long-term cycling performance.

[0062] If desirable, a hydrophobic solvent is used in combination with water and the at least one organic co-solvent to formulate the hybrid solvent. It is believed that the hydrophobic solvent may disrupt the H-bonding network of water and force it to reform around the hydrophobic molecules, making a cage of sorts around the hydrophobic molecules. It has been surprisingly found that inclusion of the hydrophobic solvent may further lower the freezing point of the hybrid electrolyte solution while allowing the electrochemical device to work. To this end, the hydrophobic solvent is expected to have strong hydrophobic groups so as to tune water coordination environment and prevent water from forming ordered network at a low temperature. Non-limiting examples of the hydrophobic solvent that may be used include bis(2,2,2-trifluoroethyl) methylphosphonate (TFMP) and tris(2,2,2-trifluoroethyl) phosphate (TFEP). The hybrid solvent may be prepared from water, dimethyl methylphosphonate (DMMP) and bis(2,2,2-trifluoroethyl) methylphosphonate (TFMP), for example, at a volume ratio of about 5:4:1. In some circumstances, the hybrid electrolyte solution comprising water, the at least one organic co-solvent and the hydrophobic solvent may allow an electrochemical device to operate at a temperature as low as about -30 °C, -40 °C, -45 °C, -65 °C, or even -80 °C.

[0063] In order to prepare a hybrid solvent or a hybrid electrolyte solution disclosed herein, it is possible to combine water, the at least one organic co-solvent and optionally the hydrophobic solvent and the electrolyte together at the same time or not at the same time. As for a hybrid solvent consisting of water and two organic co-solvents like DMAC and TMP, it may be possible to obtain a uniform mixture by stirring them together. Then to prepare a hybrid electrolyte solution, the hybrid solvent obtained may be combined with an electrolyte and, if any, an additional component such as a corrosion inhibitor. As for a hybrid solvent consisting of water, the at least one organic co-solvent and the hydrophobic solvent, it may be beneficial to mix water and the at least one organic co-solvent together first and add the hydrophobic solvent into the mixture prepared.

[0064] In the case that the hybrid solvent consists of water, the at least one organic co-solvent and the hydrophobic solvent, they may be in a volume ratio range of about 85%-10%:10%-85%:<0%-5%, about 80%-10%:10%-80%:<0%-10%, about 75%-10%:10%-75%:<0%-15%, about 70%-10%:10%-70%:<0%- 20%, about 65%-10%:10%-65%:<0%-25%, about 60%-10%:10%-60%:<0%-30%, about 55%-10%:10%- 55%:<0%-35%, about 50%-10%:10%-50%:<0%-40%, about 45%-10%:10%-45%:<0%-45%, or about 40%-10%:10%-40%:<0%-50%. Further, the hybrid solvent may consist of water, the at least one organic co-solvent and the hydrophobic solvent in a volume ratio range of about 85%-10%: 10%-85% :5%, about 80%-10%:10%-80%:10%, about 75%-10%:10%-75%:15%, about 70%-10%:10%-70%:20%, about 65%- 10%:10%-65%:25%, about 60%-10%:10%-60%:30%, about 55%-10%:10%-55%:35%, about 50%- 10%:10%-50%:40%, about 45%-10%:10%-45%:45%, or about 40%-10%:10%-40%:50%.

[0065] The hybrid solvent or the hybrid electrolyte solution may be used in an electrochemical device known in the art to replace its electrolyte solution or reformulate its electrolyte solution so as to expand its operating temperature range. Given that zinc ion batteries may be advantageous in their inherent merits such as safety, attractive gravimetric energy density, affordable cost, high abundance of Zn, and environmental friendliness, application of the hybrid solvent or the hybrid electrolyte solution in zinc ion batteries may be considered. In this situation, the electrolyte contained in the hybrid electrolyte solution disclosed herein may comprise or be composed of a zinc salt. Non-limiting examples of the zinc salt include ZnCl ₂ , ZnSO ₄ , Zn(C10 ₄ ) ₂ , Zn(BF ₄ ) ₂ , Zn(CH ₃ COO) ₂ , Zn(CF ₃ SO ₃ ) ₂ (or Zn(OTf) ₂ ) and Zn(TFSI) ₂ (zinc bis(trifluoromethylsulfonyl)imide). Only for the purpose of illustration, the concentration of the zinc salt in the hybrid electrolyte solution may be about 0.1M to 10M, for example IM to 3M.

[0066] For zinc ion batteries, a metallic Zn such as zinc foil may be employed as the negative electrode material. The zinc foil to be used may have a thickness of for example 100 pm. A Zn ²⁺ ion host material may be used as the positive electrode material. The Zn ²⁺ ion host material mentioned may include, but is not limited to, manganese oxide (MnO ₂ ), vanadium oxides, for example V ₂ Os and M ₁ V ₂ O ₃ -nH ₂ O (where M=Na, K, Zn or Ca and 0.05<x<l, 0<n<10), and Na ₃ V ₂ (PO ₄ ) ₃ . V ₂ Os powder can be synthesized through a dissolution-recrystallization method, which has nanobelt morphology. Furthermore, the loading of V ₂ Os for the positive electrode may be in the range of about 0.5 to about 6.0 mg- cm ² . The positive electrode can be simply prepared by forming a slurry comprising V ₂ Os, carbon black and polyvinylidene difluoride (PVDF), casting the slurry on a Ti foil and then allowing the coated foil to dry.

[0067] In fabricating the electrochemical device, other components such as a separator, a binder, a conductive agent, and a current collector may be employed. A separator serves to provide a barrier with no electrical conductivity between the negative electrode (anode) and the positive electrode (cathode) while allowing ion transport from one electrode to the other electrode. The separator is expected to retain chemical stability in the electrolyte solution while also having a high affinity for the electrolyte solution. It is also desirable for the separator to have good mechanical stability. Non-limiting examples of the separator include glass fibre separators, ceramic separators, polyolefin separators (e.g., polyolefin porous membrane), nonwoven separators, nylon66 (PA66) membrane, and porous polymer separators.

[0068] When powdered materials are used for the electrodes, a binder may be added to the electrodes to bring various components together and provide consistent mixing of electrode components so as to allow the electrodes to conduct the requisite amount of electrons and guarantee electronic contact during cycling of the electrochemical device. Non-limiting examples of the binder include polytetrafluoroethylene (PTFE), poly vinylidene fluoride (PVDF), and carboxymethyl cellulose (CMC).

[0069] The primary role of a conductive agent is to enhance conductivity of the electrodes. Nonlimiting examples of the conductive agent include carbon black, Ketjen black (KB), graphene, graphene oxide, conductive nano carbon fiber (VGCF), carbon nanotubes (CNTs), carbon nanofiber (CNF), and multi-walled carbon nanotubes (MWCNTs). Carbon black is commercially available from, for example, Sigma-Aldrich.

[0070] A current collector is a bridging component that collects electrical current generated at the electrodes and connects with external circuits. It can have a great influence on the capacity, rate capability and long-term stability of the electrochemical device. Non-limiting examples of the current collector include aluminium (Al) foil, copper (Cu) foil, carbon-coated aluminium, carbon-coated titanium (Ti) foil, and carbonaceous materials.

[0071] The hybrid electrolyte solution or the electrochemical device comprising the hybrid electrolyte solution disclosed herein may be advantageous in many aspects. It may be especially favourable in terms of a wide operating temperature range. In particular, the electrochemical device may be operable at a temperature as low as about -80 °C or as high as about 70 °C. It has been surprisingly found that the hybrid electrolyte solution disclosed herein may show highly reversible zinc plating/stripping behaviour for Zn|Zn cells within the temperature range of about -80 °C to 0 °C. The hybrid electrolyte solution disclosed herein may enable it to achieve an ideal full battery performance of 150 mAh g ¹ in VzOslZn at - 30 °C for 500 cycles. Furthermore, the hybrid electrolyte solution disclosed herein may allow the electrochemical device to work for 300 cycles at 50 °C, and more than 2000 cycles at -20 °C. It is worth mentioning that the hybrid electrolyte solution disclosed herein may also be non-flammable.

[0072] It has also been surprisingly found that the hybrid electrolyte solution disclosed herein may eliminate anode corrosion and dendrite growth by suppressing water activity or forming a protective inorganic interphase at anode. The hybrid electrolyte solution using water, the at least one organic cosolvent and the hydrophobic solvent allows Zn|Zn symmetric batteries to work stably for up to 1600 hours, which is much longer than the non-modified electrolyte solution and can be attributed to an appropriate crystallographic orientation at anode. The hybrid electrolyte solution disclosed herein may be helpful in maintaining the structural integrity of a positive electrode and achieving a long cycling performance for up to 1600 cycles.

[0073] On this basis, a method of fabricating an electrochemical device comprising a negative electrode, a solid positive electrode, and a hybrid electrolyte solution has been developed. The method comprises combining an electrolyte, water and at least one organic co-solvent. The electrochemical device is operable in a temperature range of about -80 °C to about 70 °C. Alternatively, an electrolyte, water, at least one organic co-solvent and a hydrophobic solvent may be combined to allow the hybrid electrolyte solution and the electrochemical device to be operable in a temperature range of about -80 °C to about 70 °C. It would be appreciated that an electrolyte, water, the at least one organic solvent and optionally the hydrophobic solvent may be combined together at the same time, not at the same time, or in turn.

[0074] The at least one organic co-solvent and the hydrophobic solvent can be selected and introduced into the electrochemical device with reference to the description herein including the Examples. Other components of the electrochemical device and assembly of the electrochemical device may refer to the detailed description herein and the guidance provided in the art. [0075] Also disclosed herein is use of a hybrid electrolyte solution in an electrochemical device, wherein the hybrid electrolyte solution comprises water and at least one organic co-solvent, and the electrochemical device is operable in a temperature range of about -80 °C to about 70 °C. The hybrid electrolyte solution may further comprise a hydrophobic solvent to allow the electrochemical device to be operable in a temperature range of about -80 °C to about 70 °C. It has been found by the inventors that inclusion of the hybrid electrolyte solution is helpful to expand the operating temperature range of the electrochemical device, so that the latter is promising to be used at ultra-low temperatures.

[0076] EXAMPLES

[0077] Example 1 A hybrid electrolyte solution prepared from water, DMAC and TMP

[0078] Chemical reagents

[0079] Dimethylacetamide (DMAC, 99.8%), trimethyl phosphate (TMP, 99%), zinc trifluoromethanesulfonate (Zn(OTf)2, 98%), vanadium pentoxide (V2O5, 98%) were purchased from Sigma-Aldrich.

[0080] Nano V2O5 synthesis

[0081] 100 ml NaCl aqueous solution was prepared with a concentration of 2 M L into which 3 g commercial V2O5 powder was added. It was followed by magnetic stirring for 72 hours. Orange powders as prepared were centrifuged and washed with deionised water and ethanol five times and then dried at 60 °C for 10 hours.

[0082] Preparation of the hybrid electrolyte solution

[0083] Water, DMAC and TMP were mixed with a volume ratio of 3:5:2 to form a hybrid solvent. Zn(OTf)2 was added to the hybrid solvent to obtain a 1 mol/L hybrid electrolyte solution.

[0084] Preparation of the V2O5 cathode and assembly of batteries

[0085] To prepare the V2O5 electrode, a slurry composed of V2O5, Super P carbon black, and polyvinylidene difluoride (PVDF) at a weight ratio of 7:1.5:1.5 as well as l-methyl-2-pyrrolidinone (NMP) was cast on a Ti foil having a thickness of 20 pm, which was followed by drying at 80 °C for 12 hours. CR2032-type coin cells were used for examination of all electrochemical performances. For batteries using an aqueous electrolyte, glass fiber (740 pm) was used as the separator. For batteries using the hybrid electrolyte solution or non-aqueous electrolyte solutions, nylon 66 membrane (130 pm) was employed as the separator. Before the long-term cycling test for Zn||V20s full batteries, they were activated at a current of 200 mA g ¹ for 5 cycles.

[0086] Characterisation of the hybrid electrolyte solution DMAC/TMP/H2O

[0087] Formulation of the electrolyte solution took into account the following aspects: 1) sufficient interactions with water; 2) non-flammability; 3) dendrite-free deposition of Zn; 4) good compatibility with V2O5 cathode. It was found that when the volume ratio of DMAC, TMP, and H2O is 5:2:3, the mixture cannot be ignited, the preferred orientation of the (002) plane appears, and the V2O5 cathode also delivers satisfactory capacity. As a result, it was confirmed that a preferable formula is 1 M Zn(OTf)2 dissolved in DMAC/TMP/H2O (5:2:3 by volume), which was denoted as HE. 1 M Zn(OTf)2 aqueous solution was denoted as AE. In Figure 1 , ignition tests intuitively confirmed the non-flammability of the HE. According to previous research, in dilute aqueous electrolytes, such as 1 M Zn(OTf)2 solution, Zn ²⁺ usually coordinates with 6 water molecules in the form of Zn[H2O]6 ²⁺ - To reveal the solvation structure of HE, molecular dynamics (MD) simulation was performed. It was found that organic solvents, DMAC and TMP, as well as the anion OTf -, take part in the solvation shells. Radial distribution functions (RDFs) further calculated the distribution of the nearest-neighbour molecules around a reference Zn ²⁺ (Figure 2). The coordination number of HE is 6, which includes 3.7 H2O molecules, 1 DMAC molecule, 0.5 TMP molecule, and 0.8 OTf anion, based on the statistical result. The electrochemical stability window (ESW) of HE was measured by linear sweep voltammetry (LSV). It was stable up to 2.25 V versus Zn ²⁺ /Zn at a scanning rate of 0.1 mV S which is obviously higher than that of the AE (1.93 V), confirming the higher stability of water molecules in HE than that in AE (Figure 3a). The extended ESW of HE will play an important role in Zn||V20s full battery testing. Figure 3b exhibits the Coulombic efficiency of Zn||Cu batteries using AE and HE respectively, at a current density of 1 mA cm ² and a plating/stripping capacity of 1 mAh cm ² . Clearly, HE shows an overwhelming advantage in improving the stability and reversibility of the Zn anode and reaches a Coulombic efficiency as high as 99.5%.

[0088] Zn deposition characters in HE

[0089] Morphological evolution over the formation of a solid metallic Zn from a liquid electrolyte is greatly affected by the solvents. When deposited in AE, flaky metallic Zn loosely piles up, resulting in a porous deposition layer on the copper current collector (Figure 4a). Once the flaky Zn loses its contact with the conductive substrate, it becomes inactive and irreversible in the subsequent plating/stripping processes. What is worse, the non-planar, porous morphology leads to inhomogeneous local charge density distribution and therefore induces dendrite growth, which is prone to pierce the separator and trigger a short circuit of batteries. In sharp contrast, the deposited Zn in HE shows a close-packed and stepped surface with a hexagonal-like crystalline structure, which is the typical character of (002) plane preferred crystal orientation. The exposed (002) basal plane has a relatively smooth surface and is conducive to dendrite-free deposition of Zn ²⁺ ions. [0090] Compatibility of electrolyte with V2O5 cathode and temperature adaptability

[0091] Z11IIV2O5 full batteries were further assembled to evaluate if the HE is compatible with cathode materials. V2O5 was synthesized via a dissolution-recrystallization method. Figure 5 compares the cycling performance of Zn||V20s batteries using AE and HE respectively at a current density of 500 mA g In AE, the V2O5 cathode experienced a rapid specific capacity increase in the first 40 cycles from 231 mAh g ¹ to 281 mAh g and then an obvious decline occurred in the subsequent cycling and failed completely after 300 cycles. In contrast, the specific capacity of the V2O5 cathode steadily improved in the first 200 cycles in HE and kept stable in the following cycles. It managed to maintain a specific capacity of 147 mAh g ¹ after 1600 cycles, which is 82% of its initial value.

[0092] To assess the performance of the electrolyte solutions in a high- or low-temperature environment, Zn||V20s batteries using HE were tested from 70 °C to -40 °C. The Zn||V20s battery in the presence of AE exhibited a rapid capacity degradation at 70 °C (Figure 6). In contrast, the Zn||V20s battery with HE exhibited an initial specific capacity of 207 mAh g ¹ and maintained a reversible capacity of 120 mAh g ¹ following 1400 cycles with a mean CE near 100%. As shown in Figure 7, the Zn||V20s battery in the presence of AE at 50 °C experienced a rapid capacity degradation in the initial 30 cycles and failed after 90 cycles. Since the self-ionization of water is an endothermic process, the hot environment causes aggravated side reactions, resulting in continuous water decomposition during the charging process. In sharp contrast, the Zn||V20s battery using HE delivered an initial specific capacity of 265 mAh g ¹ and maintained a reversible capacity of 194 mAh g ¹ (73%) after 300 cycles. The significantly boosted thermostability of HE is attributed to the presence of DMAC and TMP in the electrolyte solution. DMAC and TMP interact strongly with H2O, strengthening the O-H bonds of water molecules and therefore reducing the decomposition of H2O. Additionally, HE exhibited a freezing tolerance at sub-zero temperature. At -20 °C, the Zn||V20s battery exhibited a capacity of ca. 140 mAh g ¹ without apparent capacity fading for 2000 cycles (Figure 9), confirming that HE contributes to a highly reversible battery. At as low as -40 °C, the HE remained in liquid state and the Zn||V20s battery exhibted a capacity of ca. 85 mAh g ¹ (Figure 8). The mechanism for anti-freezing is attributed to the strong dipole-dipole interaction between DMAC/TMP and water molecules, which breaks the extension of the hydrogen-bonded network of water reducing the freezing point of the electrolyte solution.

[0093] Based on the consideration of multiple aspects, including dendrite suppressing, stability with Zn anode, compatibility with cathode materials, ESW, cost, and safety, the as proposed HE exhibits satisfactory comprehensive performance compared with AE (Figure 10). [0094] Example 2 A hybrid electrolyte solution prepared from water and DMMP or from water, DMMP and TFMP

[0095] Chemical reagents

[0096] Dimethyl methylphosphonate (DMMP), bis(2,2,2-trifluoroethyl) methylphosphonate (TFMP) and zinc trifluoromethanesulfonate (Zn(OTf)2, were purchased from Sigma Aldrich.

[0097] Preparation of the hybrid electrolyte solutions and the control electrolyte solution

[0098] An electrolyte solution with a concentration of 0.5M was prepared by using the components and volume ratios listed in Table 1. The electrolyte solutions were prepared by mixing the co-solvent DMMP, optionally the hydrophobic solvent TFMP, and water at various volume ratios (as seen in Table 1) in an atmospheric environment, and then the zinc salt (Zn(OTf)2) was added at a concentration of 0.5 mol/L (0.5M).

Table 1

[0099] Preparation of the V2O5 cathode and assembly of batteries

[0100] V2O5 electrodes were prepared by mixing commercial V2O5 powder (purity > 98%, Sigma Aldrich, without any purification), polyvinylidene difluoride (PVDF) and Super P, in a weight ratio of 8:1:1, as well as l-methyl-2-pyrrolidinone (NMP) together. The obtained slurry was coated on titanium foil (thickness 20 pm), then the coated titanium foil was dried in a vacuum oven for 12 hours. V2O5 full batteries were all assembled in R2036 type coin cells in the air, using glass fiber (740 pm) as separator, stainless steel shims and battery springs as supporters. Zinc foil (purity > 99.99%, thickness = 0.1mm) was employed as the negative electrode.

[0101] Ignition tests

[0102] As shown in Figure 11, unlike the previously reported electrolyte solution with flammable solvents, such as acetonitrile (AN) and propylene carbonate (PC), the electrolyte solutions with DMMP and/or TFMP were not ignited, showing good stability and safety at extremely high temperature. [0103] Performances of the hybrid electrolyte solutions

[0104] Compared with the aqueous electrolyte that starts to undergo phase transformation from -18 °C, the hybrid electrolyte solution prepared by the co-solvent strategy with DMMP and H2O at a volume ratio of 1:1 showed a significantly lower freezing point to -46 °C, as revealed by the results from the Differential Scanning Calorimetry (DSC) in Figure 12. Benefiting from the coordination between the organic components and water molecules through forming new hydrogen bonds, the original H-bonds between H2O molecules are weakened, preventing the order less water from transforming into ordered ice, as revealed by the photos of electrolyte solutions at subzero temperatures in Figure 13. The H2O electrolyte solution turned from transparent to white solid when the temperature decreased below -25 °C, while the DMMP-H2O electrolyte solution did not show much colour change until -45 °C.

[0105] When the TFMP hydrophobic solvent was added into the DMMP-H2O electrolyte, the freezing ability of the electrolyte solution was lowered, as seen in the DSC curve in Figure 12. No apparent heat peak was observed when temperature reducing from 20 °C to -65 °C, which suggests that the electrolyte solution using the hydrophobic solvent has a low phase transforming point (<-60 °C, from liquid to hydrogel). In addition, good electrochemical cycling performance in ZIBs at both room temperature and - 30 °C could be obtained with this hybrid electrolyte solution, as revealed by the cycling performance of the V20s|Zn full battery at -30 °C in Figure 14a and the highly reversible zinc plating/stripping behaviour of Zn|Zn cell within temperature range of -80 °C to 0 °C.

[0106] The coordination between the organic solvents and water molecules directly affects the H- bonding between H2O molecules, which could be characterised by the FT-IR spectra. Compared with H2O electrolyte solution comprising (Zn(OTf)2) (Figure 15a), in DMMP-H2O electrolyte solution comprising (Zn(OTf)2) (Figure 15b), the H-bonds between water molecules are largely weakened, benefiting from the strong coordination between DMMP and H2O. The addition of TFMP can also increase the coordination between organic solvents with H2O, as seen in Figure 15c. The anti-freezing property of the co-solvent based electrolyte solutions could be further evidenced by the real time FT-IR spectrum change of the electrolyte when the temperature decreases. As revealed in Figure 15d, the H2O electrolyte underwent notable H-bond peak variation when the temperature decreased to 0 °C, indicating the temperature can affect the coordination environment for water molecules. When temperature decreased to -20 °C, new peak at 3100 cm ¹ showed up, revealing the formation of ordered ice. The cosolvent DMMP can prevent the less ordered water molecules from transforming into ordered ice and lower the freezing point, as seen in Figure 15e. The combination of DMMP and TFMP can further enhance the solvation environment stability. As seen in Figure 15f, the coordination peak at around 3400 cm ¹ from DMMP and TFMP did not decrease or shift when the temperature dropped to -60 °C, indicating the significant effect of TFMP on further enhancement of the anti-freezing property of the water-based electrolyte. [0107] The electrolyte solution based on a binary mixture of DMMP and H2O can notably increase the zinc metal reversibility as seen in Figure 16 (a), as the Columbic efficiency could be increased compared to the pure aqueous electrolyte solution. The electrolyte solution based on a ternary mixture of TFMP- DMMP-H2O can further enhance the zinc anode stability and achieve a high Columbic efficiency of 99.3%. The enhanced reversibility of the hybrid electrolyte solutions towards the zinc anode could be explained by the passivation ability of the co-sol vents as seen in the computing data in Figure 16 (b), where the DMMP and TFMP showed much lower LUMO value than the OTF anion. The lower LUMO indicates a stronger reduction ability of the DMMP solvent than the OTF anion, which helps form a passivation layer to increase the zinc reversibility. The TFMP possesses lower LUMO than the DMMP, revealing the stronger reduction ability of forming a solid electrolyte interphase on the zinc anode, which may enable better protective ability than the layer derived from DMMP and therefore the better reversibility.

[0108] These results demonstrate the optimistic influence and feasibility of making hybrid organic- water electrolytes with representative DMMP and TFMP solvents. It is suggested that two different regulating H-bonds mechanisms work for other potential solvents: forming new H-bonds with H2O molecules and producing a caging effect with hydrophobic groups of the hydrophobic solvent to enhance the ultra-low temperature ability (Figure 17).

[0109] The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that such prior art forms part of the common general knowledge.

[0110] It will be understood that the terms “comprise” and “include” and any of their derivatives (e.g., comprises, comprising, includes, including) as used in this specification, and the claims that follow, is to be taken to be inclusive of features to which the term refers, and is not meant to exclude the presence of any additional features unless otherwise stated or implied.

[0111] In some cases, a single embodiment may, for succinctness and/or to assist in understanding the scope of the disclosure, combine multiple features. It is to be understood that in such a case, these multiple features may be provided separately (in separate embodiments), or in any other suitable combination. Alternatively, where separate features are described in separate embodiments, these separate features may be combined into a single embodiment unless otherwise stated or implied. This also applies to the claims which can be recombined in any combination. That is a claim may be amended to include a feature defined in any other claim. Further a phrase referring to “at least one of’ a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover: a, b, c, a-b, a-c, b-c, and a-b-c. [0112] It will be appreciated by those skilled in the art that the disclosure is not restricted in its use to the particular application or applications described. Neither is the present disclosure restricted in its preferred embodiment with regard to the particular elements and/or features described or depicted herein. It will be appreciated that the disclosure is not limited to the embodiment or embodiments disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the scope as set forth and defined by the following claims.

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