A water-based zinc ion battery electrolyte based on a bicontinuous phase microemulsion, a preparation method and applications thereof

Abstract

The application discloses a kind of water-based zinc ion battery electrolyte based on bicontinuous microemulsion and preparation method and application thereof.The application aims at the problems of narrow electrochemical window, irregular growth of zinc negative electrode dendrite and hydrogen evolution corrosion of traditional water-based zinc ion battery electrolyte, and provides a kind of thermodynamically stable bicontinuous microemulsion electrolyte, which is composed of water phase, oil phase and surfactant, and the volume percentage of the three is 45.5%-50.6%, 40.4%-45.5% and 5%-15% respectively.The electrolyte guarantees the efficient transmission of zinc ions through the continuous water phase channel, and at the same time, the continuous oil phase network is used as a physical barrier to block the direct contact of water molecules with the electrode, thereby effectively widening the electrochemical stability window to more than 2.8 V, significantly inhibiting the hydrogen evolution reaction and zinc dendrite growth, improving the cycle life, coulombic efficiency and corrosion resistance of the battery, and the preparation method is simple, with good application prospect.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage technology, specifically to an aqueous zinc-ion battery electrolyte, and more particularly to a microemulsion electrolyte, its preparation method, and its application in zinc-ion batteries. Background Technology

[0002] Aqueous zinc-ion batteries, with their advantages of high safety, low cost, environmental friendliness, and high theoretical capacity of zinc anodes, have shown broad application prospects in large-scale energy storage. However, the commercialization of this type of battery is still severely constrained by the inherent defects of traditional aqueous electrolytes, mainly manifested in the following three technical problems.

[0003] First, the electrochemical window is narrow: The theoretical decomposition voltage of water is only 1.23 V, which results in a narrow electrochemical stability window for traditional aqueous electrolytes, severely limiting the battery's operating voltage and energy density, making it difficult to meet the needs of high-energy-density energy storage devices.

[0004] Secondly, the zinc anode exhibits severe side reactions: In aqueous environments, the zinc anode surface is prone to hydrogen evolution and chemical corrosion, which not only consumes active materials and electrolyte but also leads to reduced battery coulombic efficiency and shortened cycle life. Simultaneously, zinc ions tend to nucleate unevenly and diffuse in two dimensions during deposition, triggering irregular dendrite growth. These dendrites may puncture the separator, causing internal short circuits and posing safety hazards.

[0005] Another issue is the degradation of the cathode material structure: commonly used cathode materials such as manganese-based and vanadium-based oxides are prone to dissolution and structural phase transitions in aqueous electrolyte environments, leading to loss of active materials and rapid capacity decay, which affects the long-cycle stability of the battery.

[0006] To address the above problems, existing improvement solutions mainly focus on the following technical routes: (1) Using electrolyte additives, the main body is still a water-based system, which has limited effect on broadening the electrochemical window; (2) Using high-concentration salt electrolytes, although they can broaden the window and suppress side reactions, they have shortcomings such as high cost, high viscosity, and poor low-temperature performance; (3) Using solid electrolytes, they face problems such as poor contact with the electrode interface and low ionic conductivity.

[0007] Microemulsions are thermodynamically stable dispersion systems composed of an aqueous phase, an oil phase, and an amphiphilic surfactant, capable of forming a homogeneous and stable liquid phase under oil-water coexistence conditions. Currently, some research has attempted to introduce microemulsion systems into the field of battery electrolytes, but these attempts are mainly limited to single-type oil-in-water or water-in-oil structures, making it difficult to achieve a balance between ensuring efficient ion transport and effectively suppressing water-related side reactions. How to simultaneously meet the dual requirements of ion conduction and interfacial stability in aqueous zinc-ion batteries through the microstructural design of microemulsions remains an unsolved technical challenge. Summary of the Invention

[0008] To address the aforementioned problems in existing technologies, this invention aims to solve key issues in traditional aqueous zinc-ion battery electrolytes, such as narrow electrochemical window, severe hydrogen evolution corrosion and irregular dendrite growth at the zinc anode, and structural degradation of the cathode material in aqueous environments. More specifically, this invention aims to provide a novel electrolyte system that can effectively suppress side reactions initiated by water molecules at the source while ensuring efficient zinc ion transport, thereby overcoming the technical bottlenecks of aqueous zinc-ion batteries in terms of cycle life, coulombic efficiency, and operating voltage.

[0009] The core of this invention lies in the development of a thermodynamically stable microemulsion system, resulting in an aqueous zinc-ion battery electrolyte with a dual-continuous-phase microstructure. This technical solution is based on the discovery that, under specific ratios of aqueous, oil, and surfactant components, the microemulsion can spontaneously form a three-dimensional network structure where the aqueous and oil phases are each continuous and intertwined—a dual-continuous-phase structure. This unique structure provides an ideal solution for simultaneously meeting the dual requirements of ion transport and interfacial stability in aqueous batteries.

[0010] Based on the above findings, this invention provides an aqueous zinc-ion battery electrolyte based on a bicontinuous microemulsion. The electrolyte is a thermodynamically stable bicontinuous phase system, and its composition includes: Aqueous phase: An aqueous solution formed by dissolving zinc salt in water, wherein the concentration of zinc salt is 0.5 mol / L to 5 mol / L; Oil phase: an organic solvent that is immiscible with water; Surfactants: used to stabilize the interface between the aqueous and oil phases, promoting the formation of a bicontinuous phase structure.

[0011] The volume percentages of the aqueous phase, oil phase, and surfactant are as follows: aqueous phase 45.5%~50.6%, oil phase 40.4%~45.5%, and surfactant 5%~15%, and the sum of the three is 100%, and the volume ratio of the aqueous phase to the oil phase, i.e., the water-oil ratio, is between 1 and 1.2.

[0012] Within this specific composition range, the electrolyte system is not a simple oil-water mixture or isolated droplet dispersion, but rather a thermodynamically balanced bicontinuous phase: the aqueous phase forms continuous polar channels, ensuring efficient solvation transport of zinc ions; the oil phase forms a continuous nonpolar three-dimensional network framework, serving as an intrinsic physical barrier preventing direct contact between water molecules and the electrodes. This water-oil bicontinuous microstructure is the essential characteristic that distinguishes this invention from existing microemulsion electrolytes or oil-water mixed electrolytes, endowing the electrolyte with the intrinsic function of "water-resistant ion conduction."

[0013] Furthermore, the zinc salt may be selected from at least one of zinc acetate, zinc methanesulfonate, and zinc trifluoromethanesulfonate.

[0014] Furthermore, the aqueous phase may also contain additives, which are at least one of a pH adjuster, a dendrite inhibitor, and a positive electrode stabilizer, such as MnSO4. Further, the pH adjuster is selected from sulfuric acid or boric acid, and the dendrite inhibitor is selected from polyvinylpyrrolidone or polyethylene glycol. The positive electrode stabilizer is, for example, MnSO4.

[0015] Furthermore, the oil phase may be selected from at least one of trimethyl phosphate, tetraethyl silicate, cyclohexane, decane, dodecane, toluene, n-butanol, and long-chain ethers.

[0016] Furthermore, the surfactant may be a nonionic surfactant, a cationic surfactant, anionic surfactant, or a mixture thereof. The nonionic surfactant is selected from PEG-7 glyceryl cocoate, Triton X-100, or PEG-20 glyceryl triisostearate; the cationic surfactant is such as hexadecyltrimethylammonium bromide; and the anionic surfactant may be such as sodium dodecyl sulfate.

[0017] The present invention also provides a method for preparing the above-mentioned aqueous zinc-ion battery electrolyte based on a dual continuous phase microemulsion, comprising the following steps: Step 1: Dissolve the zinc salt in deionized water and stir until homogeneous to obtain an aqueous solution. Further, the additive may optionally be added to this aqueous solution.

[0018] Step 2: Mix the surfactant with the oil phase to form a mixed solution and stir until homogeneous.

[0019] Step 3: While stirring continuously, the aqueous solution obtained in Step 1 is slowly added dropwise to the mixture in Step 2 to form a uniform and transparent microemulsion.

[0020] Step 4: After the addition is complete, continue stirring or sonication until the microemulsion becomes transparent and homogeneous, thus obtaining a stable electrolyte based on the bicontinuous microemulsion.

[0021] The present invention also provides an aqueous zinc-ion battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte as described above.

[0022] Compared with the prior art, the electrolyte based on bicontinuous microemulsion provided by the present invention achieves the following beneficial effects: First, it significantly broadens the electrochemical window: the continuous oil phase network serves as an insulating framework, which significantly increases the overpotential of water decomposition and broadens the intrinsic electrochemical stability window of the electrolyte to above 2.8 V, breaking the working voltage limitation of traditional conventional aqueous electrolytes.

[0023] Furthermore, a synergistically stable zinc anode was achieved: the oil-phase network physically isolates water molecules from direct contact with the zinc anode over a large area, significantly suppressing hydrogen evolution reaction and chemical corrosion at the source. Simultaneously, the unique ion transport pathway constructed by the bicontinuous phase structure guides zinc ions to undergo stable three-dimensional diffusion and uniform nucleation deposition, effectively suppressing irregular dendrite growth.

[0024] Meanwhile, it also takes into account both high ionic conductivity and high stability: thanks to the continuous aqueous phase channel that ensures the transport of zinc ions, the electrolyte maintains high ionic conductivity while also having excellent electrochemical stability, overcoming the contradiction that traditional single-phase or simple mixed systems cannot balance conductivity and interfacial stability.

[0025] Furthermore, the electrolyte preparation method of this invention is simple, the raw materials used are readily available, and it is easy to scale up production; and since it is mainly water, its safety is far higher than that of organic electrolyte systems, which meets the development requirements of green energy storage. Attached Figure Description

[0026] Figure 1 The graph shows a comparison of the long-cycle performance of zinc-zinc symmetric batteries assembled using the electrolytes based on bicontinuous microemulsions prepared in Examples 1 and 2 of this invention, the microemulsion electrolytes prepared in each comparative example, the conventional aqueous electrolyte of Comparative Example 1, and the oil-water mixed electrolyte without surfactant in Comparative Example 3.

[0027] Figure 2 This is a comparison diagram of the electrochemical windows of the microemulsion electrolytes prepared in Examples 1, 4, and 5 of the present invention, and the conventional aqueous electrolyte prepared in Example 1.

[0028] Figure 3 This is a comparison chart of the Tafel corrosion curves of the microemulsion electrolytes prepared in Examples 1, 4, and 5 of the present invention, and the conventional aqueous electrolyte prepared in Example 1.

[0029] Figure 4 The figure shows a comparison of the chronocurrent (CA) curves of the electrolyte based on the bicontinuous microemulsion prepared in Example 1 of the present invention and the conventional aqueous electrolyte prepared in Comparative Example 1 in a zinc-zinc symmetric cell.

[0030] Figure 5 The figure shows a comparison of the coulombic efficiency of the electrolyte based on the bicontinuous microemulsion prepared in Example 1 of the present invention and the conventional aqueous electrolyte prepared in Comparative Example 1 in a zinc-copper asymmetric battery.

[0031] Figure 6 The graph shows the conductivity trends of the microemulsion electrolytes with different water-to-oil ratios prepared in Example 1 and Comparative Examples 4 to 9 of this invention, as well as the pure oil phase in Comparative Example 2.

[0032] Figure 7 This is a comparison diagram of the apparent state of the microemulsion electrolytes prepared in Example 1 (water-oil ratio of 1) and Comparative Example 8 (water-oil ratio of 0.4).

[0033] Figure 8 This is a comparison chart of the long-cycle performance of zinc-manganese dioxide full cells assembled with the electrolyte based on the bicontinuous microemulsion prepared in Example 1 of the present invention and the conventional aqueous electrolyte prepared in Comparative Example 1. Detailed Implementation

[0034] To make the technical solution of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. However, the scope of protection of the present invention is not limited thereto.

[0035] The electrolyte based on a bicontinuous microemulsion described in this invention is based on the fact that the aqueous phase, oil phase, and surfactant reach thermodynamic equilibrium at a specific ratio, spontaneously forming a three-dimensional network structure in which the aqueous and oil phases are continuous and intertwined. Surfactant molecules adsorb at the oil-water interface, significantly reducing interfacial tension and allowing the interface to bend and expand into a continuous bicontinuous network framework.

[0036] The formation process of the specific structure of this bicontinuous phase can be determined by the change in the conductivity of the microemulsion: when the water content is extremely low, the aqueous phase is dispersed in the oil phase as isolated droplets, forming a water-in-oil microemulsion, at which point the conductivity is close to zero or extremely low; as the aqueous phase content gradually increases, the number of dispersed water droplets increases and they collide with each other, and the conductivity slowly increases; when the aqueous phase content continues to increase to the oil-water bicontinuous region, the aqueous phase channels interconnect to form a continuous conductive network, and the conductivity increases linearly and rapidly; if the aqueous phase continues to increase thereafter, the oil phase network breaks down, transforming into an oil-in-water emulsion, and the conductivity increases slowly with the increase of the aqueous phase. Therefore, by measuring the trend of the system's conductivity with the water-oil ratio, the formation of the bicontinuous phase can be determined. Whether a microemulsion with the above-mentioned bicontinuous phase microstructure can be formed is the key to achieving the purpose of this invention. If the components constituting the microemulsion deviate from the region where the bicontinuous phase is formed, water-in-oil, oil-in-water emulsions, or phase separation will occur, failing to achieve the synergistic effect of the biphase structure expected by this invention.

[0037] The following provides further explanation using specific embodiments and comparative examples. Example 1

[0038] This embodiment yields an electrolyte based on a bicontinuous microemulsion, which, by volume percentage, comprises an aqueous phase, an oil phase, and a surfactant, wherein the volume ratio of the aqueous phase to the oil phase, i.e., the water-to-oil ratio, is 1.0. The specific details of each phase in this embodiment are as follows.

[0039] The aqueous phase is a 3 mol / L zinc trifluoromethanesulfonate aqueous solution, which accounts for 45.5% of the volume of the electrolyte; the oil phase is the organic solvent trimethyl phosphate, which accounts for 45.5% of the volume of the electrolyte; the surfactant used is PEG-7 glycerol cocoate, which accounts for 9% of the volume of the electrolyte.

[0040] In this embodiment, the electrolyte based on the bicontinuous microemulsion was prepared using the following method.

[0041] Step 1: Weigh zinc trifluoromethanesulfonate and dissolve it in deionized water. Stir until completely dissolved to prepare an aqueous solution with a concentration of 3 mol / L, which is homogeneous and transparent.

[0042] Step 2: Using PEG-7 glyceryl cocoate as the surfactant and trimethyl phosphate as the oil phase, mix the two together and stir magnetically for 30 minutes to form a homogeneous solution. The amount of surfactant used is 9% of the total volume of the prepared electrolyte, and the amount of oil phase is equal to the volume of the aqueous solution prepared in Step 1.

[0043] Step 3: Under high-speed magnetic stirring at 1000 rpm, the aqueous solution obtained in Step 1 is slowly added dropwise to the mixed solution in Step 2. The entire addition process lasts for about 10 minutes.

[0044] Step 4: After the addition is complete, continue magnetic stirring at 1000 rpm for 2 hours to obtain a transparent, homogeneous microemulsion with certain viscoelasticity. Conductivity was measured at room temperature (25°C) to confirm the formation of a bicontinuous phase structure where the aqueous and oil phases are continuously interwoven, thus obtaining the electrolyte based on the bicontinuous phase microemulsion of this invention. Example 2

[0045] The electrolyte prepared in this embodiment based on a bicontinuous microemulsion has a water-to-oil ratio of 1.2 and, by volume percentage, its composition is: 50.6% aqueous phase, i.e., 3 mol / L zinc trifluoromethanesulfonate aqueous solution, 40.4% oil phase, trimethyl phosphate, and 9% surfactant, PEG-7 glyceryl cocoate.

[0046] The preparation method is the same as in Example 1, except that the volume ratio of the aqueous phase to the oil phase is adjusted. The resulting microemulsion is transparent and homogeneous, and its conductivity measurement confirms that it has a bicontinuous phase structure. Example 3

[0047] In this embodiment, zinc acetate was selected as the zinc salt, tetraethyl silicate as the oil phase, and Triton X-100 as the surfactant. Specifically, this embodiment prepared an electrolyte based on a bicontinuous microemulsion, which, by volume percentage, consisted of an aqueous phase, an oil phase, and a surfactant, wherein the volume ratio of the aqueous phase to the oil phase, i.e., the water-to-oil ratio, was 1.0. The specific phases in this embodiment are as follows.

[0048] The aqueous phase is a 3 mol / L zinc acetate aqueous solution, which accounts for 45.5% of the volume of the electrolyte; the oil phase is the organic solvent tetraethyl silicate, which accounts for 45.5% of the volume of the electrolyte; the surfactant used is the nonionic surfactant Triton X-100, which accounts for 9% of the volume of the electrolyte.

[0049] In this embodiment, the electrolyte based on the bicontinuous microemulsion was prepared using the following method.

[0050] Step 1: Weigh zinc acetate and dissolve it in deionized water, stirring until completely dissolved to prepare a 3 mol / L aqueous solution that is homogeneous and transparent.

[0051] Step 2: Using Triton X-100 as the surfactant and tetraethyl silicate as the oil phase, mix the two together and stir magnetically for 30 minutes to form a homogeneous solution. The amount of surfactant used is 9% of the total volume of the prepared electrolyte, and the amount of oil phase is equal to the volume of the aqueous solution prepared in Step 1.

[0052] Step 3: Under high-speed magnetic stirring at 1200 rpm, the aqueous solution obtained in Step 1 is slowly added dropwise to the mixed solution in Step 2. The entire addition process lasts for about 10 minutes.

[0053] Step 4: After the addition is complete, continue magnetic stirring at 1200 rpm for 2.5 hours to obtain a transparent and homogeneous microemulsion. Conductivity was measured at room temperature (25°C) to confirm the formation of a bicontinuous phase structure where the aqueous and oil phases are continuously interwoven, thus obtaining the electrolyte based on the bicontinuous phase microemulsion of this invention. Example 4

[0054] This embodiment describes the preparation of the electrolyte under conditions of low zinc salt concentration, low surfactant dosage, and the use of cationic surfactants and cyclohexane as the oil phase. Details are as follows.

[0055] This embodiment yields an electrolyte based on a bicontinuous microemulsion, which, by volume percentage, comprises an aqueous phase, an oil phase, and a surfactant, wherein the volume ratio of the aqueous phase to the oil phase, i.e., the water-to-oil ratio, is 1.0. The specific details of each phase in this embodiment are as follows.

[0056] The aqueous phase is a 0.5 mol / L aqueous solution of zinc trifluoromethanesulfonate, which accounts for 47.5% of the volume of the electrolyte; the oil phase is an organic solvent cyclohexane, which accounts for 47.5% of the volume of the electrolyte; the surfactant used is a cationic surfactant, cetyltrimethylammonium bromide, which accounts for 5% of the volume of the electrolyte.

[0057] In this embodiment, the electrolyte based on the bicontinuous microemulsion was prepared using the following method.

[0058] Step 1: Weigh zinc trifluoromethanesulfonate and dissolve it in deionized water. Stir until completely dissolved to prepare an aqueous solution with a concentration of 0.5 mol / L, which is homogeneous and transparent.

[0059] Step 2: Using hexadecyltrimethylammonium bromide as the surfactant and cyclohexane as the oil phase, mix the two together and stir magnetically for 30 minutes to form a homogeneous solution. The amount of surfactant used is 5% of the total volume of the prepared electrolyte, and the amount of oil phase is equal to the volume of the aqueous solution prepared in Step 1.

[0060] Step 3: Under high-speed magnetic stirring at 1000 rpm, the aqueous solution obtained in Step 1 is slowly added dropwise to the mixed solution in Step 2. The entire addition process lasts for about 12 minutes.

[0061] Step 4: After the addition is complete, continue magnetic stirring at 1000 rpm for 3 hours to obtain a transparent and homogeneous microemulsion. Conductivity was measured at room temperature (25°C) to confirm the formation of a bicontinuous phase structure where the aqueous and oil phases are continuously interwoven, thus obtaining the electrolyte based on the bicontinuous phase microemulsion of this invention. Example 5

[0062] This embodiment uses a high zinc salt concentration and anionic surfactant to prepare the electrolyte. Details are as follows.

[0063] This embodiment yields an electrolyte based on a bicontinuous microemulsion, which comprises an aqueous phase, an oil phase, and a surfactant by volume percentage, wherein the volume ratio of the aqueous phase to the oil phase, i.e., the water-to-oil ratio, is 1.2. The specific details of each phase in this embodiment are as follows.

[0064] The aqueous phase is a 5 mol / L zinc methanesulfonate aqueous solution, which accounts for 50.6% of the volume of the electrolyte; the oil phase is the organic solvent decane, which accounts for 40.4% of the volume of the electrolyte; the surfactant used is the anionic surfactant sodium dodecyl sulfate, which accounts for 9% of the volume of the electrolyte.

[0065] In this embodiment, the electrolyte based on the bicontinuous microemulsion was prepared using the following method.

[0066] Step 1: Weigh zinc methanesulfonate and dissolve it in deionized water. Stir until completely dissolved to prepare an aqueous solution with a concentration of 5 mol / L, which is homogeneous and transparent.

[0067] Step 2: Using sodium dodecyl sulfate as the surfactant and decane as the oil phase, mix the two together and stir magnetically for 40 minutes to form a homogeneous solution. The amount of surfactant used is 9% of the total volume of the prepared electrolyte, and the volume ratio of the oil phase to the aqueous phase solution prepared in Step 1 is 1.2:1.

[0068] Step 3: Under high-speed magnetic stirring at 1500 rpm, the aqueous solution obtained in Step 1 is slowly added dropwise to the mixed solution in Step 2. The entire addition process lasts for about 10 minutes.

[0069] Step 4: After the addition is complete, continue magnetic stirring at 1500 rpm for 2 hours to obtain a transparent and homogeneous microemulsion. Conductivity was measured at room temperature (25°C) to confirm the formation of a bicontinuous phase structure where the aqueous and oil phases are continuously interwoven, thus obtaining the electrolyte based on the bicontinuous phase microemulsion of this invention. Example 6

[0070] This embodiment increases the amount of surfactant used compared to Embodiment 1, and the microemulsion electrolyte is prepared under different nonionic surfactant conditions, as detailed below.

[0071] This embodiment yields an electrolyte based on a bicontinuous microemulsion, which, by volume percentage, comprises an aqueous phase, an oil phase, and a surfactant, wherein the volume ratio of the aqueous phase to the oil phase, i.e., the water-to-oil ratio, is 1.0. The specific details of each phase in this embodiment are as follows.

[0072] The aqueous phase is a 3 mol / L zinc trifluoromethanesulfonate aqueous solution, which accounts for 42.5% of the volume of the electrolyte; the oil phase is the organic solvent trimethyl phosphate, which accounts for 42.5% of the volume of the electrolyte; the surfactant used is the nonionic surfactant PEG-20 glycerol triisostearate, which accounts for 15% of the volume of the electrolyte.

[0073] In this embodiment, the electrolyte based on the bicontinuous microemulsion was prepared using the following method.

[0074] Step 1: Weigh zinc trifluoromethanesulfonate and dissolve it in deionized water. Stir until completely dissolved to prepare an aqueous solution with a concentration of 3 mol / L, which is homogeneous and transparent.

[0075] Step 2: Using PEG-20 glycerol triisostearate as the surfactant and trimethyl phosphate as the oil phase, mix the two together and stir magnetically for 30 minutes to form a homogeneous solution. The amount of surfactant used is 15% of the total volume of the prepared electrolyte, and the amount of oil phase is equal to the volume of the aqueous solution prepared in Step 1.

[0076] Step 3: Under high-speed magnetic stirring at 1000 rpm, the aqueous solution obtained in Step 1 is slowly added dropwise to the mixed solution in Step 2. The entire addition process lasts for about 10 minutes.

[0077] Step 4: After the addition is complete, continue magnetic stirring at 1000 rpm for 2 hours to obtain a transparent and homogeneous microemulsion. Conductivity was measured at room temperature (25°C) to confirm the formation of a bicontinuous phase structure where the aqueous and oil phases are continuously interwoven, thus obtaining the electrolyte based on the bicontinuous phase microemulsion of this invention. Example 7

[0078] This embodiment yields an electrolyte based on a bicontinuous microemulsion, which, by volume percentage, comprises an aqueous phase, an oil phase, and a surfactant, wherein the volume ratio of the aqueous phase to the oil phase, i.e., the water-to-oil ratio, is 1.1. The specific details of each phase in this embodiment are as follows.

[0079] The aqueous phase was a 2 mol / L zinc trifluoromethanesulfonate aqueous solution, which accounted for 47.8% of the volume of the electrolyte; the oil phase was the organic solvent dibutyl ether, which accounted for 43.0% of the volume of the electrolyte; the surfactant was a compound system of nonionic surfactant PEG-7 glycerol cocoate and anionic surfactant sodium dodecyl sulfate, with a mass ratio of 2:1, and the surfactant accounted for 9.2% of the total volume of the electrolyte.

[0080] In this embodiment, the electrolyte based on the bicontinuous microemulsion was prepared using the following method.

[0081] Step 1: Weigh zinc trifluoromethanesulfonate and dissolve it in deionized water. Stir until completely dissolved to prepare an aqueous solution with a concentration of 2 mol / L, which is homogeneous and transparent.

[0082] Step 2: Mix PEG-7 glyceryl cocoate and sodium dodecyl sulfate at a mass ratio of 2:1 as a compound surfactant. Use dibutyl ether as the oil phase. Mix the surfactant compound system with the oil phase while magnetically stirring for 30 minutes to form a homogeneous mixed solution. The total volume of the surfactant is 9.2% of the total volume of the prepared electrolyte, and the volume ratio of the oil phase to the aqueous phase solution prepared in Step 1 is 1:1.1.

[0083] Step 3: Under high-speed magnetic stirring at 1200 rpm, the aqueous solution obtained in Step 1 is slowly added dropwise to the mixed solution in Step 2. The entire addition process lasts for about 10 minutes.

[0084] Step 4: After the addition is complete, the resulting mixture is ultrasonically treated for 30 minutes, and then magnetically stirred at 1200 rpm for 1 hour to obtain a transparent and homogeneous microemulsion. Conductivity was measured at room temperature (25°C) to confirm the formation of a bicontinuous phase structure where the aqueous and oil phases are continuously interwoven, thus obtaining the electrolyte based on the bicontinuous phase microemulsion of this invention. Comparative Example 1

[0085] This comparative example uses a conventional aqueous electrolyte, specifically a 3 mol / L aqueous solution of zinc trifluoromethanesulfonate. The preparation method is as follows: Weigh 1.0906 g of zinc trifluoromethanesulfonate and dissolve it in 1 mL of deionized water, stirring until completely dissolved to obtain a homogeneous and transparent aqueous electrolyte. Comparative Example 2

[0086] This comparative example uses a pure oil phase, i.e., pure trimethyl phosphate. This comparative example is used to measure the conductivity of the pure oil phase, serving as a reference standard for the conductivity determination of microemulsion systems. Comparative Example 3

[0087] This comparative example is an oil-water mixture without added surfactant. The preparation steps are as follows: prepare a 3 mol / L aqueous solution of zinc trifluoromethanesulfonate, and directly mix the aqueous solution with trimethyl phosphate at a volume ratio of 1:1 without adding any surfactant. After stirring, a two-phase mixture of oil and water is obtained. Comparative Example 4

[0088] This comparative example provides a microemulsion electrolyte with a water-to-oil ratio of 1.4. By volume percentage, its composition is as follows: 53% aqueous phase, which is a 3 mol / L zinc trifluoromethanesulfonate aqueous solution; 38% oil phase trimethyl phosphate; and 9% surfactant PEG-7 glycerol cocoate.

[0089] The preparation method was the same as in Example 1, and a microemulsion electrolyte was obtained. Subsequent analysis showed that the microemulsion electrolyte prepared in this comparative example tended to be in an oil-in-water state. Comparative Example 5

[0090] This comparative example provides a microemulsion electrolyte with a water-to-oil ratio of 1.8. By volume percentage, its composition is as follows: the aqueous phase is a 3 mol / L zinc trifluoromethanesulfonate aqueous solution, accounting for 58.5%; the oil phase is trimethyl phosphate, accounting for 32.5%; and the surfactant is PEG-7 glycerol cocoate, accounting for 9%.

[0091] The preparation method is the same as in Example 1. This comparative example has a further higher water-to-oil ratio, further deviating from the bicontinuous phase structure region, and exhibits an oil-in-water state. Comparative Example 6

[0092] This comparative example provides a microemulsion electrolyte with a water-to-oil ratio of 0.8. By volume percentage, its composition is as follows: the aqueous phase is a 3 mol / L zinc trifluoromethanesulfonate aqueous solution, accounting for 40.4%; the oil phase is trimethyl phosphate, accounting for 50.6%; and the surfactant is PEG-7 glycerol cocoate, accounting for 9%. The preparation method is the same as in Example 1. Comparative Example 7

[0093] This comparative example provides a microemulsion electrolyte with a water-to-oil ratio of 0.6. By volume percentage, its composition is as follows: the aqueous phase is a 3 mol / L zinc trifluoromethanesulfonate aqueous solution, accounting for 34.1%; the oil phase is trimethyl phosphate, accounting for 56.9%; and the surfactant is PEG-7 glyceryl cocoate, accounting for 9%. The preparation method is the same as in Example 1. Comparative Example 8

[0094] This comparative example provides a microemulsion electrolyte with a water-to-oil ratio of 0.4. By volume percentage, its composition is as follows: the aqueous phase is a 3 mol / L zinc trifluoromethanesulfonate aqueous solution, accounting for 26%; the oil phase is trimethyl phosphate, accounting for 65%; and the surfactant is PEG-7 glyceryl cocoate, accounting for 9%. The preparation method is the same as in Example 1. Comparative Example 9

[0095] This comparative example provides a microemulsion electrolyte with a water-to-oil ratio of 0.2. By volume percentage, its composition is as follows: the aqueous phase is a 3 mol / L zinc trifluoromethanesulfonate aqueous solution, accounting for 15%; the oil phase is trimethyl phosphate, accounting for 76%; and the surfactant is PEG-7 glyceryl cocoate, accounting for 9%. The preparation method is the same as in Example 1.

[0096] Performance testing and results analysis: Battery assembly was conducted using the electrolytes from the various embodiments and comparative examples, and their long-cycle performance, electrochemical window, and other properties were tested. Specific test methods and results are as follows. The microemulsion electrolytes prepared in the embodiments listed above all achieved a dual-continuous-phase microstructure in terms of microemulsion state, various electrochemical properties, and battery application performance; the test results also showed that the data for each property were essentially equivalent. Below, we will only use Example 1 as an example to analyze the comparison between the data of the example and the comparative examples. Other embodiments are basically the same as Example 1 and will not be listed individually.

[0097] 1) Long-cycle performance test of zinc-zinc symmetric batteries Using commercial zinc foil as the negative and positive electrodes, symmetrical cells were assembled using microemulsion electrolytes prepared in Examples 1, 2, 4, 5, 7, and 9, the conventional aqueous electrolyte of Comparative Example 1, and the oil-water mixture electrolyte without surfactants in Comparative Example 3. The cells were tested at room temperature and a current density of 5 mA / cm². 2 5mAh / cm² 2 Constant current charge-discharge cycle tests were performed under the specified conditions. The test curves are shown below. Figure 1 As shown.

[0098] from Figure 1 It can be seen that the symmetric cells assembled using the electrolytes based on bicontinuous microemulsions in Examples 1 and 2 exhibit excellent long-cycle stability at 5 mA / cm². 2 5 mAh / cm 2 Under harsh conditions, it can be stably cycled for more than 650 hours and 500 hours respectively, and the overpotential remains stable. The mechanism is as follows: the continuous oil phase network in the dual-continuous phase structure effectively isolates most water molecules from direct contact with the zinc anode, significantly suppressing hydrogen evolution side reactions and chemical corrosion; at the same time, the unique three-dimensional interpenetrating ion transport channels of the dual-continuous phase guide zinc ions to undergo stable three-dimensional diffusion, promoting uniform nucleation and deposition of zinc on the electrode surface, thereby effectively suppressing irregular dendrite growth.

[0099] In contrast, the symmetric cell using the conventional aqueous electrolyte in Comparative Example 1 short-circuited after less than 20 hours of cycling under the same conditions, exhibiting a sharp drop in overpotential. This was due to severe hydrogen evolution reaction and uncontrolled zinc dendrite growth in the aqueous electrolyte. While the cycling performance of Comparative Example 4 (water-to-oil ratio 1.4) and Comparative Example 5 (water-to-oil ratio 1.8) was better than that of Comparative Example 1, it was far inferior to Example 1, indicating that when the aqueous content is too high, the formation of an oil-in-water state and the oil phase network are insufficient to effectively isolate water molecules, weakening the hydrogen evolution inhibition effect. The cycle life of Comparative Example 7 (water-to-oil ratio 0.6) and Comparative Example 9 (water-to-oil ratio 0.2) was significantly shortened, especially Comparative Example 9, whose overpotential was extremely unstable during cycling. This is because when the oil phase ratio is too high, the formation of an oil-in-water state and the continuity of the aqueous phase channels are disrupted, leading to a significant decrease in ionic conductivity, resulting in obstructed zinc ion transport and uneven deposition. The performance of the oil-water mixture electrolyte in Comparative Example 3 (without surfactant) was also extremely poor, verifying the crucial role of surfactants in forming a stable bicontinuous phase structure.

[0100] Overall, the cycling performance test results show that a stable bicontinuous phase structure can only be formed under the conditions of a certain proportion of surfactant stabilizing the interface, within the water-oil ratio range specified in the various embodiments of the present invention. Only then can the electrolyte synergistically achieve efficient ion transport and effective suppression of side reactions, thereby obtaining excellent long-cycle performance.

[0101] 2) Electrochemical window testing Using commercial zinc foil as the negative electrode and titanium foil as the positive electrode, coin cells were assembled using the microemulsion electrolytes of Example 1, Comparative Example 4, and Comparative Example 5, and the conventional aqueous electrolyte of Comparative Example 1, respectively. Linear scanning voltammetry was performed at a scan rate of 0.5 mV / s to measure the electrochemical stability window of the electrolytes. The test results are as follows: Figure 2 As shown.

[0102] Depend on Figure 2 It can be seen that the electrochemical stability window of the electrolyte based on the bicontinuous microemulsion in Example 1 is approximately 2.84V, significantly higher than that of the conventional aqueous electrolyte in Comparative Example 1. The mechanism for this widening is likely due to the continuous oil phase network in the bicontinuous phase structure, which acts as an insulating framework uniformly distributed throughout the electrolyte system. This effectively blocks the path for water molecules to form a continuous reaction interface on the electrode surface, thereby significantly increasing the overpotential for hydrogen evolution and oxygen evolution reactions, intrinsically widening the electrochemical stability window of the electrolyte. Comparing the test curves of Comparative Example 4 (water-to-oil ratio 1.4) and Comparative Example 5 (water-to-oil ratio 1.8), it can be seen that as the proportion of aqueous phase increases, the hydrogen evolution potential gradually decreases, indicating a gradual weakening of the ability to suppress hydrogen evolution. This further confirms that an appropriate amount of oil phase network is a key factor in achieving window widening.

[0103] 3) Tafel corrosion current test Using commercial zinc foil as both the working and counter electrodes, and Ag / AgCl as the reference electrode, Swagelok batteries were assembled using the microemulsion electrolytes of Example 1, Comparative Example 4, and Comparative Example 5, as well as the conventional aqueous electrolyte of Comparative Example 1. Tafel corrosion curve tests were then performed, and the results are as follows: Figure 3 As shown.

[0104] from Figure 3 It can be seen that the corrosion current density of the microemulsion system electrolyte is significantly lower than that of the conventional aqueous electrolyte. Specifically, Example 1 exhibits the lowest corrosion current density, while Comparative Examples 4 and 5 show progressively increasing densities. This indicates that the oil-phase network in the microemulsion effectively isolates water molecules from direct contact with the zinc electrode surface, significantly reducing the self-corrosion rate of the zinc anode. The decreasing trend of corrosion current density with increasing oil phase proportion provides direct evidence for the physical barrier effect of the oil-phase network.

[0105] 4) Timing current (CA) curve test Using commercial zinc foil as the positive and negative electrodes, coin cells were assembled using the electrolyte based on a bicontinuous microemulsion from Example 1 and the conventional aqueous electrolyte from Comparative Example 1, respectively. A constant voltage of -150 mV was applied, and the current response was recorded over 300 seconds, yielding the following results: Figure 4 The CA curve shown.

[0106] Depend on Figure 4As can be seen, the current density of the conventional aqueous electrolyte in Comparative Example 1 (labeled as "Zn(OTF)2" in the figure) increased rapidly and continuously during the test time, exhibiting typical two-dimensional diffusion characteristics. This indicates that zinc ions undergo disordered lateral diffusion and localized aggregation and deposition on the electrode surface, which easily induces dendrite growth. In stark contrast, the electrolyte in Example 1 (labeled as "bicontinuous phase microemulsion" in the figure), based on a bicontinuous phase microemulsion, showed a stable current density that remained at a low level after only a very short nucleation process, exhibiting typical three-dimensional diffusion characteristics. This result is mainly due to the three-dimensional interpenetrating ion transport network provided by the bicontinuous phase structure, which allows zinc ions to rapidly and uniformly reach various parts of the electrode surface from the electrolyte phase along multiple paths, achieving stable three-dimensional diffusion and uniform nucleation deposition, thereby effectively suppressing irregular dendrite growth.

[0107] 5.) Coulomb efficiency test Using commercial zinc foil as the negative electrode and commercial copper foil as the positive electrode, zinc-copper asymmetric half-cells were assembled using the electrolyte based on a bicontinuous microemulsion from Example 1 and the conventional aqueous electrolyte from Comparative Example 1, respectively, at a current density of 2 mA / cm². 2 Surface capacity 2 mAh / cm 2 Under these conditions, constant current charge-discharge cycles were performed. After discharging for 1 hour, the charge was increased to 0.5 V, and the change in coulombic efficiency was recorded. The results are as follows: Figure 5 As shown.

[0108] Figure 5 The results show that the zinc-copper half-cell using the electrolyte of Example 1 (labeled as "bicontinuous phase microemulsion" in the figure) exhibits extremely stable coulombic efficiency at a current density of 2 mA / cm². 2 Surface capacity 2mAh / cm 2 Under the specified conditions, the battery can be stably cycled approximately 750 times with a high coulombic efficiency. In contrast, the half-cell using a conventional aqueous electrolyte (as indicated by "Zn(OTF)2" in the figure) in Comparative Example 1 exhibited drastic fluctuations after less than 20 cycles under the same conditions, indicating a micro-short circuit occurring within the battery in a very short time. This was attributed to the rapid growth of zinc dendrites and the consumption of deposited zinc by the hydrogen evolution side reaction. The superior coulombic efficiency of Example 1 is attributed to the bicontinuous phase electrolyte suppressing side reactions at the source and guiding zinc through highly reversible and uniform deposition / stripping, with the zinc deposition and stripping processes being highly reversible in each cycle.

[0109] 6) Comparison of ionic conductivity and apparent state of microemulsions with different water-to-oil ratios The conductivity of the microemulsion electrolytes prepared in Example 1, Comparative Examples 4 to 9, and the pure oil phase in Comparative Example 2 was tested using a magnetic conductivity meter. The results are as follows: Figure 6 As shown. Simultaneously, the apparent states of microemulsions with different water-to-oil ratios were compared, such as... Figure 7As shown.

[0110] from Figure 7 The optical photographs show that when the oil phase content is high, such as in Comparative Example 8 where the water-to-oil ratio is 0.4, the microemulsion exhibits a slightly turbid and heterogeneous state. Figure 7 As shown in the cup on the left; when the water-to-oil ratio reaches 1.0, i.e., the microemulsion of Example 1, it exhibits a transparent, homogeneous, and viscoelastic stable state, as shown in the cup on the left. Figure 7 As shown in the cup on the right.

[0111] Combination Figure 6 Analysis of the conductivity trend shows that when the water-to-oil ratio increases from 0.2 to 1.0, the conductivity exhibits a significant upward trend, with a clear inflection point near the 1.0 ratio. When the water-to-oil ratio continues to increase beyond 1.0, the conductivity increase slows down. This trend is highly consistent with the theory of bicontinuous phase formation: in regions with a water-to-oil ratio less than 1.0, the aqueous phase is dispersed in the oil phase as isolated droplets, forming a water-in-oil structure. The conductive pathways are discontinuous, resulting in extremely low conductivity, which is unfavorable for ion migration dynamics. When the water-to-oil ratio reaches approximately 1.0, as defined in this invention, the aqueous and oil phases each form a continuous three-dimensional network, i.e., a bicontinuous phase structure. With the complete opening of the conductive pathways in the aqueous phase, the conductivity experiences a leap. Subsequently, as more aqueous phase enters the water-in-oil region, the aqueous phase becomes a continuous phase, and the conductivity increase slows down. Example 1 has a conductivity of approximately 17.8 μS / cm at 25°C, which is between that of a pure conventional aqueous electrolyte and a pure oil phase, and falls within the normal conductivity range of a bicontinuous microemulsion, confirming that it has indeed formed a bicontinuous phase structure.

[0112] 7) Full-cell long-cycle performance test Using commercial zinc foil as the negative electrode and γ-MnO2 as the positive electrode, full cells were assembled using the bicontinuous microemulsion-based electrolyte of Example 1 and the conventional aqueous electrolyte of Comparative Example 1, respectively. Charge-discharge cycle tests were conducted at a current density of 1 A / g, with a discharge cutoff voltage of 0.8 V and a charge cutoff voltage of 1.8 V. Cyclic performance is as follows: Figure 8 As shown.

[0113] Depend on Figure 8It can be seen that the full battery using the electrolyte of Example 1 still maintains a high discharge specific capacity and stable charge-discharge efficiency after 200 cycles, with slow capacity decay. In contrast, the full battery using the conventional aqueous electrolyte of Comparative Example 1 experiences a sharp decline in discharge specific capacity, maintaining only a low capacity of about 20 mAh / g after 200 cycles. The superior full battery performance of Example 1 is attributed to two synergistic effects: on the one hand, the oil phase network suppresses the side reactions between water molecules and the zinc anode, protecting the cycle stability of the anode; on the other hand, the efficient transport of zinc ions in the aqueous phase channel ensures the positive electrode reaction kinetics, while the oil phase network also reduces the direct contact between the positive electrode material (γ-MnO2) and water to a certain extent, slowing down the dissolution and structural degradation of the positive electrode active material.

[0114] The above test results demonstrate that the proper control of the water-to-oil ratio in the microemulsion electrolyte system is crucial for forming a bicontinuous phase structure and achieving synergistic performance optimization. When the proportion of the aqueous phase is too high (e.g., in Comparative Examples 4 and 5), the electrolyte's corrosion resistance and hydrogen evolution inhibition performance decrease; when the proportion of the oil phase is too high (e.g., in Comparative Examples 7-9), the electrolyte's ionic conductivity significantly decreases, leading to increased battery overpotential and shortened cycle life. Only within the water-to-oil ratio range (1-1.2) and corresponding component ratios specified in this invention can a stable bicontinuous phase microstructure be formed, enabling the electrolyte to simultaneously possess efficient ion transport channels and effective water molecule barrier properties. This synergistically solves key technical challenges faced by traditional aqueous zinc-ion batteries, such as narrow electrochemical window, zinc anode dendrite growth, and severe side reactions, significantly improving battery cycle life, coulombic efficiency, and electrochemical stability while maintaining reasonable ionic conductivity.

Claims

1. An aqueous zinc-ion battery electrolyte based on a bicontinuous microemulsion, characterized in that, The electrolyte comprises an aqueous phase, an oil phase, and a surfactant; wherein the aqueous phase is an aqueous solution of zinc salt dissolved in water; and the oil phase is an organic solvent that is immiscible with water. The electrolyte has a thermodynamically stable bicontinuous phase microstructure. The surfactant is adsorbed at the interface between the aqueous phase and the oil phase, so that the aqueous phase and the oil phase each form a continuous and intertwined three-dimensional network structure, i.e., the bicontinuous phase. The continuous aqueous phase forms a polar channel for the solvation transport of zinc ions, and the continuous oil phase forms a non-polar three-dimensional network framework, which serves as a physical barrier to prevent water molecules from directly contacting the electrodes, so that the electrolyte inherently has the function of water isolation and ion conduction.

2. The aqueous zinc-ion battery electrolyte based on a dual-continuous-phase microemulsion according to claim 1, characterized in that, The concentration of zinc salt dissolved in water in the aqueous phase is from 0.5 mol / L to 5 mol / L.

3. The aqueous zinc-ion battery electrolyte based on a dual-continuous-phase microemulsion according to claim 2, characterized in that, The volume percentages of the aqueous phase, oil phase, and surfactant are as follows: aqueous phase 45.5% to 50.6%, oil phase 40.4% to 45.5%, surfactant 5% to 15%, and the sum of the three is 100%, with the volume ratio of the aqueous phase to the oil phase being 1 to 1.

2.

4. The aqueous zinc-ion battery electrolyte based on a dual-continuous-phase microemulsion according to claim 2, characterized in that, The zinc salt is selected from at least one of zinc acetate, zinc methanesulfonate, and zinc trifluoromethanesulfonate.

5. The aqueous zinc-ion battery electrolyte based on a dual-continuous-phase microemulsion according to claim 2, characterized in that, The oil phase is selected from at least one of trimethyl phosphate, tetraethyl silicate, cyclohexane, decane, dodecane, toluene, n-butanol, and long-chain ethers.

6. The aqueous zinc-ion battery electrolyte based on a dual-continuous-phase microemulsion according to claim 2, characterized in that, The surfactant is a nonionic surfactant, a cationic surfactant, anionic surfactant, or a mixture thereof.

7. The aqueous zinc-ion battery electrolyte based on a dual-continuous-phase microemulsion according to claim 6, characterized in that, The nonionic surfactant is selected from PEG-7 glyceryl cocoate, Triton X-100 or PEG-20 glyceryl triisostearate; the cationic surfactant is hexadecyltrimethylammonium bromide; and the anionic surfactant is sodium dodecyl sulfate.

8. The aqueous zinc-ion battery electrolyte based on a dual-continuous-phase microemulsion according to claim 2, characterized in that, The aqueous phase also contains additives, which are at least one of pH adjusters, dendrite inhibitors, and positive electrode stabilizers.

9. A method for preparing an aqueous zinc-ion battery electrolyte based on a bicontinuous microemulsion as described in any one of claims 1 to 8, characterized in that, Includes the following steps: Step 1: Dissolve the zinc salt in deionized water and stir until homogeneous to obtain an aqueous solution; Step 2: Mix the surfactant with the oil phase to form a mixed solution and stir until homogeneous; Step 3: Under continuous stirring, the aqueous solution obtained in Step 1 is slowly added dropwise to the mixed solution in Step 2 to form a homogeneous and transparent microemulsion. Step 4: After the addition is complete, continue stirring or sonication until the microemulsion is transparent and homogeneous, thus obtaining the aqueous zinc-ion battery electrolyte based on the bicontinuous microemulsion.

10. The preparation method according to claim 9, characterized in that, In step 1, an additive is also added, which is at least one of a pH adjuster, a dendrite inhibitor, and a positive electrode stabilizer.

11. An aqueous zinc-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that, The electrolyte is the aqueous zinc-ion battery electrolyte based on a bicontinuous microemulsion as described in any one of claims 1 to 8.

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