A dual-phase electrolyte, a preparation method and application thereof in a water-based zinc-iodine battery

Abstract

The application discloses a kind of two-phase electrolyte, preparation method and its application in water-based zinc iodine battery, belong to two-phase electrolyte technical field, first choline chloride is mixed with trifluoroacetamide heating and forms eutectic solution, then after mixing ethylene glycol and water, zinc sulfate is added to obtain salt solution, the eutectic solution is mixed with salt solution according to proportion to form two-phase electrolyte with stable interface, the two-phase electrolyte can effectively inhibit the shuttle effect of polyiodide and the corrosion of zinc negative electrode, hydrogen evolution side reaction through the division of labor and cooperation of eutectic phase iodine fixation and aqueous phase ion conduction, so that the assembled water-based zinc iodine battery exhibits good charge-discharge reversibility, excellent rate performance and long cycle stability.

Description

Technical Field

[0001] This invention belongs to the field of biphase electrolyte technology, specifically a biphase electrolyte, its preparation method, and its application in aqueous zinc-iodine batteries. Background Technology

[0002] Zinc-metal aqueous batteries have attracted widespread attention due to their advantages such as abundant zinc reserves, low cost, high specific capacity, and moderate redox potential. Among them, aqueous zinc-iodine batteries not only inherit the safety and eco-friendly characteristics of aqueous electrolytes, but also have excellent rate performance due to the abundant iodine reserves on Earth, stable potential platform, and unique liquid phase conversion mechanism, making them a highly promising new generation of high-safety advanced battery technology.

[0003] However, aqueous zinc-iodine batteries still face serious interfacial instability and capacity decay problems during long-term cycling. In traditional aqueous electrolyte systems, solid iodine is prone to passivation of the electrode surface due to its poor conductivity. Furthermore, during charging and discharging, the iodine cathode generates a large number of water-soluble intermediate polyiodides. These free polyiodides easily migrate across the membrane to the zinc anode surface, causing not only continuous loss of the positive electrode active material but also corrosion reaction with highly active zinc metal. This promotes the formation of a large number of by-products at the zinc anode interface, ultimately creating a vicious cycle of loss of positive electrode active iodine and damage to the zinc anode structure, leading to rapid capacity decay and decreased long-term cycle stability.

[0004] Therefore, how to effectively block the vicious cycle caused by the cross-border migration of polyiodides, and thus construct an electrolyte system that can effectively retain the positive electrode active material and protect the zinc negative electrode interface, has become a core technical problem that urgently needs to be solved in the field of aqueous zinc-iodine batteries. Summary of the Invention

[0005] The purpose of this invention is to provide a two-phase electrolyte, its preparation method, and its application in aqueous zinc-iodine batteries. By constructing a two-phase electrolyte system consisting of a choline chloride-trifluoroacetamide eutectic phase and an ethylene glycol-composite zinc sulfate aqueous phase, the ion transport environment of the electrolyte is optimized and the reaction behavior of the positive and negative electrodes is regulated by utilizing the complementary functions of the two phases and the synergistic effect of the interface. This results in an electrolyte system that can simultaneously achieve efficient fixation of iodine active materials and stable operation of the zinc negative electrode, thus achieving a good balance between high specific capacity, excellent rate performance, and long cycle life in aqueous zinc-iodine batteries.

[0006] The objective of this invention can be achieved through the following technical solutions: This invention provides a two-phase electrolyte, wherein the upper solution after phase separation of a eutectic solution and a salt solution is the eutectic phase solution, and the lower solution is the aqueous phase solution. The electrolyte is obtained by mixing the eutectic solution and the salt solution evenly and allowing them to stand to achieve complete phase separation.

[0007] This invention also provides a method for preparing a two-phase electrolyte, comprising the following steps: The eutectic solution and salt solution were added to a glass sample vial, thoroughly shaken and mixed, and allowed to stand at 25°C for 12 hours to achieve phase separation, thus obtaining a two-phase electrolyte.

[0008] Furthermore, the volume ratio of the eutectic solution to the salt solution is 1:3.

[0009] Furthermore, the eutectic solution is obtained by heating a mixture of choline chloride and trifluoroacetamide.

[0010] The molar ratio of choline chloride to trifluoroacetamide is 1:2.

[0011] Furthermore, the salt solution is obtained by mixing ethylene glycol and water, and then adding zinc sulfate.

[0012] The volume ratio of ethylene glycol to water is 1:4, and the concentration of zinc sulfate is 2-3 mol / L.

[0013] The present invention also provides the application of biphase electrolyte in aqueous zinc-iodine batteries, with zinc sheet as negative electrode and iodine composite positive electrode sheet as positive electrode, and the assembly is carried out in the following order: negative electrode shell, negative electrode, glass fiber separator, positive electrode, gasket, spring sheet and positive electrode shell, to obtain aqueous zinc-iodine battery.

[0014] The glass fiber diaphragm is impregnated with an aqueous solution.

[0015] The positive electrode has a eutectic phase solution added to the side near the separator.

[0016] Furthermore, the iodine composite positive electrode sheet is obtained by weighing iodine, activated carbon, bacterial cellulose, carbon nanotubes and deionized water and placing them in a beaker, stirring until the activated carbon fully adsorbs the iodine active material, vacuum depressurizing and filtering, vacuum drying the product, and pressing it into a circular thin sheet.

[0017] The mass ratio of iodine, activated carbon, bacterial cellulose, carbon nanotubes and deionized water is 3:5:1:1:120.

[0018] The beneficial effects of this invention are: 1. The biphase electrolyte prepared by this invention exhibits the advantage of bidirectional synergistic interface regulation between the positive and negative electrodes by constructing a liquid-liquid interface between the eutectic phase and the aqueous phase. The eutectic phase has a strong coordination ability and can anchor the iodine active material on the positive electrode side through electrostatic interaction and hydrogen bonding, significantly suppressing the polyiodide shuttle effect. Meanwhile, the aqueous phase maintains a high ionic conductivity, providing a continuous channel for the rapid transport of zinc ions. This division of labor and synergistic mechanism of iodine fixation in the eutectic phase and conduction in the aqueous phase can better support the battery to maintain high electrochemical reversibility and long cycle life.

[0019] 2. The biphase electrolyte prepared by this invention can slow down the corrosion reaction between the zinc anode and the electrolyte by introducing the eutectic phase, and at the same time suppress the occurrence of hydrogen evolution side reaction. The stable two-phase interface can ensure the normal passage of zinc ions, and further block the diffusion of polyiodides to the anode side, thus providing a strong guarantee for the stable operation of the zinc anode and the long cycle performance of the battery.

[0020] 3. The biphase electrolyte prepared by this invention uses industrial-grade conventional chemical raw materials such as choline chloride, trifluoroacetamide, and zinc sulfate. The raw materials are widely available and inexpensive, and the preparation process is simple and easy to implement. When applied to aqueous zinc-iodine batteries, it not only retains the high safety of aqueous batteries, but also endows the batteries with good charge-discharge reversibility, excellent rate performance, and long-cycle stability. Attached Figure Description

[0021] Figure 1 The diagram shows the state of the biphase electrolytes prepared in Examples 1-3 of this invention.

[0022] Figure 2 The graph shows the long-cycle performance of zinc-iodine batteries assembled with the biphase electrolytes prepared in Examples 1-3 at a current density of 0.5 A / g.

[0023] Figure 3 The rate curves of zinc-iodine batteries assembled with the electrolytes prepared in Example 2 and Comparative Example 1 in the current density range of 0.5-5 A / g are shown.

[0024] Figure 4 The cyclic voltammetry curves of zinc-iodine batteries assembled with the electrolytes prepared in Example 2 and Comparative Example 1 are obtained at a scan rate of 0.2 mV / s.

[0025] Figure 5 The graph shows the long-cycle performance of zinc-iodine batteries assembled with the electrolytes prepared in Example 2 and Comparative Example 1 at a current density of 0.5 A / g.

[0026] Figure 6 The graph shows the long-cycle performance of zinc-iodine batteries assembled with the electrolytes prepared in Example 2 and Comparative Example 1 at a current density of 3 A / g.

[0027] Figure 7 The linear sweep voltammetry (LSV) curves were obtained by using the electrolytes prepared in Example 2 and Comparative Example 1, and constructing a three-electrode test system with zinc sheet as the working electrode, platinum sheet as the counter electrode, and Ag / AgCl as the reference electrode, at a scan rate of 0.5 mV / s.

[0028] Figure 8The Tafel curves were obtained by testing the electrolytes prepared in Example 2 and Comparative Example 1 with a three-electrode test system consisting of a zinc sheet as the working electrode, a platinum sheet as the counter electrode, and Ag / AgCl as the reference electrode at a scan rate of 1 mV / s. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Example 1: This example provides a two-phase electrolyte, prepared through the following steps: S1: Place choline chloride and trifluoroacetamide in a glass sample bottle with a molar ratio of 1:2. React at 60°C for 4 hours. After the reaction is complete, cool to room temperature to obtain a eutectic solution.

[0031] S2: Add ethylene glycol and water to a glass sample bottle at a volume ratio of 1:4, mix well, add zinc sulfate to the mixed solvent, and shake thoroughly to achieve a final zinc sulfate concentration of 2 mol / L, thus obtaining a salt solution.

[0032] S3: The upper layer of the mixture of eutectic solution and salt solution after phase separation is the eutectic phase solution, and the lower layer is the aqueous phase solution. The eutectic solution and salt solution are added to a glass sample bottle at a volume ratio of 1:3, thoroughly shaken and mixed, and allowed to stand at 25°C for 12 hours to achieve phase separation, thus obtaining a two-phase electrolyte.

[0033] Example 2: This example provides a two-phase electrolyte, prepared through the following steps: S1: Place choline chloride and trifluoroacetamide in a glass sample bottle with a molar ratio of 1:2. React at 60°C for 4 hours. After the reaction is complete, cool to room temperature to obtain a eutectic solution.

[0034] S2: Add ethylene glycol and water to a glass sample bottle at a volume ratio of 1:4, mix well, add zinc sulfate to the mixed solvent, and shake thoroughly to achieve a final zinc sulfate concentration of 2.5 mol / L, thus obtaining a salt solution.

[0035] S3: The upper layer of the mixture of eutectic solution and salt solution after phase separation is the eutectic phase solution, and the lower layer is the aqueous phase solution. The eutectic solution and salt solution are added to a glass sample bottle at a volume ratio of 1:3, thoroughly shaken and mixed, and allowed to stand at 25°C for 12 hours to achieve phase separation, thus obtaining a two-phase electrolyte.

[0036] Example 3: This example provides a two-phase electrolyte, prepared through the following steps: S1: Place choline chloride and trifluoroacetamide in a glass sample bottle with a molar ratio of 1:2. React at 60°C for 4 hours. After the reaction is complete, cool to room temperature to obtain a eutectic solution.

[0037] S2: Add ethylene glycol and water to a glass sample bottle at a volume ratio of 1:4, mix well, add zinc sulfate to the mixed solvent, and shake thoroughly until the final zinc sulfate concentration reaches 3 mol / L to obtain a salt solution.

[0038] S3: The upper layer of the mixture after phase separation of the eutectic solution and the salt solution is the eutectic phase solution, and the lower layer is the aqueous phase solution. The eutectic solution and the salt solution are added to the glass sample bottle at a volume ratio of 1:3. The system is thoroughly shaken to ensure uniform mixing, and then allowed to stand at 25°C for 12 hours to achieve phase separation, thus obtaining a two-phase electrolyte.

[0039] like Figure 1 As shown in the figure, from left to right, the biphase electrolytes prepared in Examples 1-3 above are shown. 2mol / L-3mol / L represents the concentration of zinc sulfate in Examples 1-3.

[0040] Example 4: This example provides an application of a two-phase electrolyte in an aqueous zinc-iodine battery, including the following steps: Step 1: Weigh iodine, activated carbon, bacterial cellulose, carbon nanotubes and deionized water in a mass ratio of 3:5:1:1:120 and place them in a beaker. Stir at 25°C for 24 hours until the activated carbon fully adsorbs the iodine active material. Vacuum filter to obtain a soft, paper-like composite. Dry under vacuum at 50°C and press into a circular sheet to obtain the iodine composite positive electrode sheet.

[0041] Step 2: Using a zinc sheet as the negative electrode and a composite iodine positive electrode as the positive electrode, assemble the battery in the following order: negative electrode shell - negative electrode - glass fiber membrane (Whatman, GF / D) containing aqueous phase solution - positive electrode containing eutectic phase solution near the membrane side - gasket - spring sheet - positive electrode shell to obtain an aqueous zinc-iodine battery.

[0042] The biphase electrolytes prepared in Examples 1-3 were used to prepare aqueous zinc-iodine batteries according to the scheme in Example 4, and their performance was tested.

[0043] Depend on Figure 2It can be seen that the Zn / I2 full cells assembled with the biphase electrolytes prepared in Examples 1-3 all exhibited good basic electrochemical performance. They could achieve stable reversible charge and discharge at a current density of 0.5 A / g, and the coulombic efficiency remained at a high level throughout the cycle. This indicates that the biphase electrolyte system of the present invention can effectively suppress the polyiodide migration effect and the side reaction of the zinc anode. Among them, Example 2 had the best overall cycle performance, with an initial discharge specific capacity of 507.95 mAh / g and no significant capacity decay after 1000 cycles. This shows that the biphase electrolyte ratio prepared in Example 2 can form a stable interfacial phase on the zinc anode surface, effectively balancing high specific capacity and long cycle life.

[0044] Comparative Example 1: The difference from Example 2 is that choline chloride and zinc sulfate were dissolved in water to obtain an electrolyte, and the concentration of choline chloride in the electrolyte was 2 mol / L and the concentration of zinc sulfate was 2.5 mol / L.

[0045] Referring to the scheme of Example 4, the composite iodine positive electrode sheet prepared in step one is used as the positive electrode and the zinc sheet is used as the negative electrode. The assembly is carried out in the following order: negative electrode shell - negative electrode - glass fiber separator (Whatman, GF / D) containing electrolyte prepared in Comparative Example 1 - positive electrode - gasket - spring sheet - positive electrode shell to obtain an aqueous zinc-iodine battery.

[0046] The iodine purchased in the above examples and comparative examples was produced by Shanghai Maclean Biochemical Technology Co., Ltd., and was elemental iodine with CAS number 7553-56-2; the activated carbon was produced by KELOD Company, model MA-EN-AN-0007; the carbon nanotubes were produced by KELOD Company, model MA-EN-CO-0014; the bacterial cellulose was produced by Guilin Qihong Technology Co., Ltd., and was a bacterial nanocellulose dispersion with a content of 0.8 wt%; the glass fiber diaphragm was produced by Whatman Company, model GF / D.

[0047] The performance of the aqueous zinc-iodine battery assembled with the biphase electrolyte prepared in Example 2 and the aqueous zinc-iodine battery assembled with the electrolyte prepared in Comparative Example 1 were tested.

[0048] Depend on Figure 3It can be seen that the biphase electrolyte prepared by the present invention has better rate performance than Comparative Example 1 in the current density range of 0.5-5 A / g. At a current density of 0.5 A / g, the average specific capacity of the battery prepared by the electrolyte of Example 2 is as high as 528 mAh / g, which is significantly improved compared with 450 mAh / g of the electrolyte of Comparative Example 1. Moreover, this capacity advantage is maintained throughout the entire test current density range, indicating that the electrolyte prepared by the present invention has better ion transport kinetics, which may effectively stimulate the capacity potential of the positive electrode active material, and significantly reduce polarization and loss of active material, thereby giving the system excellent rate response capability. This lays a solid foundation for the subsequent realization of high power and high energy density operation of zinc-iodine batteries under high current load.

[0049] Depend on Figure 4 It can be seen that the potential difference between the oxidation and reduction peaks in the electrolyte system of Example 2 is significantly smaller than that in the electrolyte system of Comparative Example 1, indicating that its polarization voltage is lower. This reduced polarization phenomenon suggests that the two-phase electrolyte prepared in this invention may be able to reduce interfacial charge transfer resistance and significantly optimize the kinetics of the redox reaction.

[0050] Depend on Figure 5 It can be seen that in the long-cycle performance test at a current density of 0.5 A / g, the battery using the electrolyte of Comparative Example 1 failed due to a short circuit after more than 200 cycles. The battery using the electrolyte of Example 2 not only had a good cycle life, but also maintained a higher coulombic efficiency throughout the entire test cycle. This indicates that the biphase electrolyte prepared in this invention may inhibit the rampant growth of zinc dendrites and the risk of membrane puncture. On the other hand, it may also alleviate the shuttle effect of polyiodides and interfacial side reactions, thereby giving the battery high electrochemical reversibility and operational safety.

[0051] Depend on Figure 6 It can be seen that in the long-cycle performance test at a current density of 3A / g, the battery using the electrolyte of Comparative Example 1 experienced a sharp capacity decay and battery failure after about 300 cycles. The full cell using the electrolyte of Example 2 showed excellent long-cycle stability. After 20,000 charge-discharge cycles, the capacity retention rate was 80.1%, and the overall average coulombic efficiency remained stable at 99.3%. This indicates that the electrolyte of Example 2 can maintain good cycle performance and stability even under high current load.

[0052] Depend on Figure 7It can be seen that, compared with the electrolyte of Comparative Example 1, the electrochemical stability window of the electrolyte of Example 2 is significantly widened, from 2.26V to 2.62V, which enables the electrolyte to maintain a stable charge and discharge process at a higher operating voltage. At the same time, the hydrogen evolution reaction overpotential of the electrolyte of Example 2 shifts to a more negative potential, indicating that the inhibitory effect of the electrolyte of Example 2 on the hydrogen evolution reaction is significantly enhanced, effectively reducing the occurrence of side reactions during charge and discharge.

[0053] Depend on Figure 8 As can be seen, compared with the electrolyte of Comparative Example 1, the zinc anode exhibited a higher corrosion potential and a lower corrosion current in the electrolyte of Example 2, indicating that the zinc anode showed a lower tendency to undergo corrosion. This suggests that the biphase electrolyte prepared in this invention may form a more stable protective interface on the zinc electrode surface, reducing the corrosion attack caused by polyiodide transmembrane migration on the zinc anode. This improves the corrosion resistance and chemical stability of the zinc anode during long-term cycling.

[0054] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A two-phase electrolyte, characterized in that, The biphase electrolyte is obtained by mixing the eutectic solution and the salt solution and then allowing them to stand to achieve complete phase separation. The eutectic solution was obtained by heating a mixture of choline chloride and trifluoroacetamide. The salt solution is obtained by mixing ethylene glycol and water, then adding zinc sulfate, and mixing thoroughly.

2. The biphase electrolyte according to claim 1, characterized in that, The volume ratio of the eutectic solution to the salt solution is 1:

3.

3. The biphase electrolyte according to claim 1, characterized in that, The molar ratio of choline chloride to trifluoroacetamide in the eutectic solution is 1:

2.

4. The biphase electrolyte according to claim 1, characterized in that, The volume ratio of ethylene glycol to water in the salt solution is 1:4, and the concentration of zinc sulfate is 2-3 mol / L.

5. The method for preparing a two-phase electrolyte according to claim 1, characterized in that, Prepared by the following steps: The eutectic solution and salt solution were added to a glass sample vial, thoroughly shaken and mixed, and allowed to stand at 25°C for 12 hours to achieve phase separation, thus obtaining a two-phase electrolyte.

6. The application of the biphase electrolyte as described in any one of claims 1-4 in an aqueous zinc-iodine battery, characterized in that, Using a zinc sheet as the negative electrode and an iodine composite positive electrode as the positive electrode, the components are assembled in the following order: negative electrode shell, negative electrode, glass fiber separator, positive electrode, gasket, spring sheet, and positive electrode shell, to obtain an aqueous zinc-iodine battery. The glass fiber diaphragm is impregnated with an aqueous solution; The positive electrode has a eutectic phase solution added to the side near the separator.

7. The application according to claim 6, characterized in that, The preparation process of the iodine composite positive electrode is as follows: Iodine, activated carbon, bacterial cellulose, carbon nanotubes and deionized water were weighed and placed in a beaker. The mixture was stirred until the activated carbon fully adsorbed the iodine active material. The mixture was then vacuum filtered under reduced pressure, and the product was vacuum dried and pressed into a circular sheet to obtain an iodine composite positive electrode sheet.

8. The application according to claim 7, characterized in that, The mass ratio of iodine, activated carbon, bacterial cellulose, carbon nanotubes and deionized water is 3:5:1:1:120.

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