Preparation method of ionic conductive elastomer electrolyte and solid-state zinc battery thereof

Abstract

The invention relates to the technical field of solid-state batteries, and discloses a preparation method of an ionic conductive elastomer electrolyte, which comprises the following steps: adding polyvinyl alcohol into deionized water, stirring and swelling at room temperature, and heating until the polyvinyl alcohol is completely dissolved; uniformly stirring the polyvinyl alcohol aqueous solution and the phytic acid aqueous solution; after bubbles are completely eliminated through a vacuum oven, the obtained mixture solution is poured into a polytetrafluoroethylene culture dish, then drying is conducted, and the viscoelastic ionic conductive elastomer film is obtained.The elastomer electrolyte shows excellent viscoelasticity and mechanical tensile property, tight contact on an electrode / electrolyte interface is facilitated, and the service life of the elastomer electrolyte is prolonged. The method adapts to volume change on an interface and inhibits growth of zinc dendrites; the preparation method of the ionic conductive elastomer electrolyte is simple and easy to implement, the raw materials are wide in source and easy to obtain, and the practical process of a solid-state zinc ion battery is promoted.

Description

Technical Field

[0001] The present invention relates to the technical field of solid-state batteries, and particularly to a preparation method of an ion-conductive elastomer electrolyte and a solid-state zinc-ion battery. Background Art

[0002] Aqueous zinc-ion batteries have received extensive attention due to their high energy density, high safety, low cost and other characteristics. These outstanding advantages make zinc ions a promising candidate for energy storage applications in the "post-lithium" era. However, the practical application of zinc-ion batteries is facing several key challenges, such as severe hydrogen evolution reaction, growth of zinc dendrites, corrosion problem of zinc anode, low Coulomb efficiency and limited service life.

[0003] Replacing liquid electrolyte with solid / gel electrolyte is a common strategy to solve the existing problems of zinc-ion batteries, which can effectively regulate ion flux, optimize ionic conductivity, improve electric field distribution and ionic solvation structure, etc. Among them, hydrogel electrolytes have received extensive attention due to their appropriate mechanical properties, good ionic conductivity and rich functional groups. At present, a series of polymers such as polyvinyl alcohol (PVA), polyacrylamide (PAM), polyvinylidene fluoride (PVDF), sodium polyacrylate (PANa), xanthan gum, gelatin, etc. have been successfully applied to hydrogel electrolytes. The rich hydrophilic functional groups in the polymer can effectively inhibit the hydrogen evolution reaction and side reactions on the zinc anode by adsorbing or restricting the electrochemical activity of free water molecules. At the same time, the interaction between Zn 2+ ions and the functional groups can optimize the diffusion kinetics of Zn 2+ ions, improve ionic conductivity, inhibit the formation of zinc dendrites, and thus greatly improve the cycle stability and reversibility of zinc-ion batteries.

[0004] However, hydrogel electrolytes generally face the problems of water evaporation at high temperatures and freezing crystallization of the hydrogel matrix at low temperatures. These temperature-induced changes can have a severe negative impact on the ionic conductivity of the gel electrolyte. At high temperatures, the loss of water not only reduces the number of mobile ions but also causes irreversible damage to the hydrogel structure; while at low temperatures, freezing crystallization significantly enhances the hydrogen bonding between water molecules, making the polymer segments tend to be rigid, further hindering the ion transport path and ultimately leading to a sharp drop in conductivity. In addition, the swelling behavior of some hydrogel electrolytes during charge and discharge will accelerate the attenuation of battery capacity and shorten the service life of energy storage devices. To solve the problem of poor stability of hydrogel electrolytes, some studies have proposed using ion gels composed of ionic liquids and polymer networks as alternatives to hydrogels. Such ion gel electrolytes have excellent ionic conductivity, non-volatility, and good thermal stability. However, for existing ion gel electrolytes, it is difficult to achieve a balance between ionic conductivity and mechanical properties. Generally speaking, adding a large amount of ionic liquid to the gel matrix can increase its conductivity, but it will inevitably lead to a decrease in mechanical properties (such as strength and modulus). At the same time, when the flexible battery undergoes repeated stretching or compression, the ionic liquid is very likely to leak, significantly shortening the service life of the flexible battery. Therefore, there is an urgent need to develop a new type of solid-state ion conductor to overcome the inherent disadvantages of hydrogel electrolytes and ion gel electrolytes. Summary of the Invention

[0005] The object of the present invention is to solve the deficiencies existing in the prior art and to propose a preparation method of an ion-conductive elastomer electrolyte and a solid-state zinc-ion battery.

[0006] To achieve the above object, the present invention adopts the following technical solutions: A preparation method of an ion-conductive elastomer electrolyte includes the following steps: Step 1: Add polyvinyl alcohol to deionized water, stir and swell at room temperature, and then heat to completely dissolve. Step 2: Stir the polyvinyl alcohol aqueous solution obtained in Step 1 and the phytic acid aqueous solution evenly. Step 3: After completely removing the bubbles with a vacuum oven, pour the mixture solution obtained in Step 2 into a polytetrafluoroethylene petri dish, and then dry to obtain a viscoelastic ion-conductive elastomer film. Step 4: Add ZnSO4·7H2O to deionized water, stir at room temperature until ZnSO4·7H2O is completely dissolved to obtain a ZnSO4 electrolyte solution. Step 5: Completely immerse the viscoelastic ion-conductive elastomer film obtained in Step 3 into the ZnSO4 electrolyte solution obtained in Step 4 and let it stand. Then, rinse it and wipe off the excess ZnSO4 electrolyte solution on the surface of the ion-conductive elastomer film with filter paper. After evaporating the solvent, an elastomeric solid electrolyte is obtained.

[0007] Preferably, the concentration of the polyvinyl alcohol aqueous solution in Step 1 is 5%.

[0008] Preferably, the heating temperature of the polyvinyl alcohol aqueous solution in Step 1 is 75 - 100 °C.

[0009] Preferably, the heating temperature of the polyvinyl alcohol aqueous solution in Step 1 is 90 °C.

[0010] Preferably, the concentration of the phytic acid aqueous solution in Step 2 is 70%.

[0011] Preferably, the molar ratio of the polyvinyl alcohol aqueous solution to the phytic acid aqueous solution in Step 2 is 20:1 to 1:1.

[0012] Preferably, the molar ratio of the polyvinyl alcohol aqueous solution to the phytic acid aqueous solution in Step 2 is 4:1.

[0013] Preferably, the temperature for evaporating the solvent in Step 5 is 60 °C.

[0014] Preferably, the drying heating temperature in Step 3 is 40 - 90 °C.

[0015] Preferably, the drying heating temperature in Step 3 is 70 °C.

[0016] A solid-state zinc-ion battery uses a Zn foil as the negative electrode, VO2 coated on carbon paper as the positive electrode, and the ion-conductive elastomer electrolyte described in any one of Claims 1 - 7 as the solid electrolyte to assemble a 2032-type button solid-state zinc-ion battery.

[0017] The beneficial effects of the present invention are: The present invention synthesizes an ion-conductive elastomeric electrolyte by a simple solvent evaporation method. During the water heating and evaporation process, the supramolecular encapsulation of phytic acid molecules by polyvinyl alcohol long chains is achieved through hydrogen bond cross-linking between polyvinyl alcohol and phytic acid molecules. The macromolecular structure of phytic acid helps to maintain the stretched conformation and uniform interpenetrating distribution of polyvinyl alcohol polymer chains and releases more free hydroxyl groups. Among them, the phytic acid molecules encapsulated within the polyvinyl alcohol chain segments serve as additional migration sites for zinc ion conduction, and the high-density hydrogen bond network constructed by polyvinyl alcohol and phytic acid helps to promote the efficient transport of zinc ions and uniform zinc deposition. The elastomeric electrolyte prepared by the present invention exhibits excellent viscoelasticity and mechanical tensile properties, which contribute to achieving close contact at the electrode / electrolyte interface, adapting to volume changes occurring at the interface, and inhibiting the growth of zinc dendrites. The ion-conductive elastomeric electrolyte prepared by the present invention solves the common problems of traditional hydrogel electrolytes with high water content, easy water loss and drying, and ion leakage in ion gel electrolytes, and significantly slows down the hydrogen evolution reaction and zinc negative electrode corrosion problems caused by free water.

[0018] The preparation method of the ion-conductive elastomeric electrolyte proposed by the present invention is simple and feasible, and the raw materials are widely available, which helps to promote the practical application process of solid-state zinc-ion batteries.

[0019] The solid-state zinc-ion battery of the present invention uses the ion-conductive elastomer of the present invention as a solid electrolyte. Therefore, the solid-state zinc-ion battery of the present invention exhibits significantly improved cycle life and capacity retention rate. Brief Description of the Drawings

[0020] Figure 1 It is a schematic diagram of the comparison of ion migration numbers for synthesizing the ion-conductive elastomeric electrolyte.

[0021] Figure 2 It is a schematic diagram of the potentiostatic polarization test results of the gel electrolyte in Example 3.

[0022] Figure 3 It is a schematic diagram of the cycling performance of the zinc symmetric battery assembled in Example 3.

[0023] Figure 4 It is a schematic diagram of the cycling performance of the zinc-ion battery assembled in Example 3. Detailed Description of the Invention

[0024] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0025] Example 1: Step 1: First, weigh 5.0 g of polyvinyl alcohol and add it to 95 mL of deionized water. Stir vigorously at room temperature for 6 h to obtain a swollen polyvinyl alcohol dispersion aqueous solution, and then heat and stir at 90 °C for 3 h to obtain a completely dissolved and transparent polyvinyl alcohol aqueous solution.

[0026] Step 2: Mix 100 g of a 5% polyvinyl alcohol aqueous solution cooled to room temperature with 107.2 g, 53.6 g, 26.8 g, 13.4 g, and 5.36 g of a 70% phytic acid aqueous solution respectively, and stir well for 0.5 h. Step 3: After completely removing the bubbles with a vacuum oven, pour the mixture solution obtained in Step 2 into a polytetrafluoroethylene petri dish respectively, and then dry at 60 °C for 15 h to obtain a viscoelastic ion-conductive elastomer membrane, which is named ICE-1, ICE-2, ICE-4, ICE-8, and ICE-20 according to the molar ratio. Step 4: Add ZnSO4·7H2O to deionized water and stir at room temperature until ZnSO4·7H2O is completely dissolved to obtain a ZnSO4 electrolyte solution. Step 5: Immerse the obtained viscoelastic ion-conductive elastomer membrane completely into a 2 M ZnSO4 electrolyte solution and let it stand for 2 days. Then, rinse with deionized water and wipe off the excess ZnSO4 electrolyte solution on the surface of the ion-conductive elastomer membrane with filter paper, and evaporate the solvent at 60 °C to obtain elastomeric solid electrolytes ZICE-1, ZICE-2, ZICE-4, ZICE-8, and ZICE-20.

[0027] In this example, the mechanical properties of the electrolyte membrane were tested. The tensile length of the ion-conductive elastomer electrolyte obtained in Example 1 increased with the increase of phytic acid content, and the Young's modulus decreased with the increase of phytic acid content; the electrochemical impedance test was carried out on the blocked battery assembled with the ion-conductive elastomer electrolyte membrane. The ionic conductivities calculated according to the thickness and impedance value of the electrolyte sheet ( , where σ is the ionic conductivity, L is the thickness of the electrolyte sheet, R is the impedance measured of the electrolyte sheet, and S is the area of the electrolyte sheet) were 35.60, 21.34, 6.05, 0.85, and 0.07 mS cm –1 ; As Figure 1 shown, the electrochemical impedance spectra of the ion-conductive elastomer electrolyte obtained in Example 1 before and after polarization were tested by the DC polarization method. The zinc ion transference numbers calculated by the formula ( , where I S is the steady-state current, I0 is the initial current, ∆V is the applied potential, and R0 and R S are the resistances before and after polarization respectively) were 0.12, 0.36, 0.68, 0.69, and 0.63.

[0028] Example 2: Step 1: First, weigh 5.0 g of polyvinyl alcohol and add it to 95 mL of deionized water. Stir vigorously at room temperature for 6 h to obtain a swollen polyvinyl alcohol dispersed aqueous solution, and then heat and stir at 90 °C for 3 h to obtain a completely dissolved and transparent polyvinyl alcohol aqueous solution; Step 2: Thoroughly mix and stir 100 g of a 5% polyvinyl alcohol aqueous solution cooled to room temperature and 26.8 g of a 70% phytic acid aqueous solution for 0.5 h; Step 3: After completely removing the bubbles with a vacuum oven, pour the obtained mixture solution into a polytetrafluoroethylene petri dish, and then dry it at 60 °C for 15 h to obtain a viscoelastic ion-conductive elastomer membrane ICE-4; Step 4: Add ZnSO4·7H2O to deionized water and stir at room temperature until ZnSO4·7H2O is completely dissolved to obtain a ZnSO4 electrolyte solution; Step 5: Completely immerse the obtained viscoelastic ion-conductive elastomer membrane ICE-4 in a 2M ZnSO4 electrolyte solution and let it stand for 2 days. Then, rinse it with deionized water and wipe off the excess ZnSO4 electrolyte solution on the surface of the ion-conductive elastomer membrane with filter paper, and evaporate the solvent at 60 °C to obtain an elastomeric solid electrolyte ZICE-4; Step 6: Zn is used as the negative electrode, and VO2 with a loading of 0.8 mg cm −2 coated on carbon cloth is used as the positive electrode, and the ion-conductive elastomer electrolyte membrane ZICE-4 is used as the solid electrolyte to assemble a solid-state zinc-ion battery.

[0029] In this example, a zinc-copper half-cell was assembled with the prepared ion-conductive elastomer electrolyte membrane to test its Coulomb efficiency for zinc deposition and stripping. At a current density of 0.5 mA cm –2 , after 700 cycles, its average Coulomb efficiency can be maintained at 98.5%. The assembled zinc symmetric battery shows that it can stably cycle for 2800 hours at a current density of 0.5 mA cm –2 , indicating that the ion-conductive elastomer solid electrolyte has good reversible zinc deposition and stripping ability. Finally, this solid electrolyte was applied to a zinc-ion battery, and at a current density of 1.0 A g –1 , after 400 cycles, the capacity retention rate is as high as 86.5%. The above battery test results show that the ion-conductive elastomer electrolyte can be used as an excellent solid-state zinc-ion conductor and is suitable for solid-state zinc-ion batteries.

[0030] Example 3: Step 1: First, weigh 5.0 g of polyvinyl alcohol and add it to 95 mL of deionized water. Stir vigorously at room temperature for 6 h to obtain a swollen polyvinyl alcohol dispersed aqueous solution, and then heat and stir at 90 °C for 3 h to obtain a completely dissolved and transparent polyvinyl alcohol aqueous solution; Step 2: Thoroughly mix and stir 100 g of a 5% polyvinyl alcohol aqueous solution cooled to room temperature and 26.8 g of a 70% phytic acid aqueous solution for 0.5 h; Step 3: After completely removing the bubbles with a vacuum oven, pour the obtained mixture solution into a 1 mm thick acrylic plate fixture, place it in a refrigerator at -20 °C and freeze for 10 h, then thaw at 20 °C for 2 h, and perform the freeze-thaw cycle 3 times to obtain a hydrogel with the same concentration as ICE-4; Step 4: Add ZnSO4·7H2O to deionized water and stir at room temperature until ZnSO4·7H2O is completely dissolved to obtain a ZnSO4 electrolyte solution; Step 5: Completely immerse the obtained hydrogel in a 2 M ZnSO4 electrolyte solution and let it stand for 2 days, then rinse the surface of the hydrogel with deionized water to remove the excess ZnSO4 electrolyte solution on the surface of the hydrogel to obtain a hydrogel electrolyte; Step 6: Use Zn as the negative electrode, and coat 0.8 mg cm −2 of VO2 on carbon cloth as the positive electrode, and use the hydrogel as the solid electrolyte to assemble a all-solid-state zinc-ion battery.

[0031] As shown in the example Figure 2 In this example, the ion transference number of the prepared gel electrolyte is 0.48, which is significantly lower than that of the ion-conductive elastomer electrolyte prepared in Example 2. This is because the freeze crystallization of polyvinyl alcohol in the hydrogel hinders the kinetics of polymer chain movement, which is not conducive to ion transport. As Figure 3 shown, the zinc symmetric battery assembled based on the hydrogel electrolyte can only stably cycle for 1300 h at a current density of 0.5 mA cm –2 , which is significantly lower than the cycling performance of the ion-conductive elastomer electrolyte. Figure 4 What is shown is the discharge curve of the solid-state zinc-ion battery prepared in Comparative Example 3 of the present invention at a current density of 1.0 A g –1 ; among them, at a current density of 1.0 A g –1 , the specific capacity of this battery is 183.4 mAh g −1 , and the capacity retention rate after 400 cycles is only 59.6%.

[0032] The solid electrolyte of the present invention is an ion-conductive elastomeric electrolyte. The supramolecular encapsulation of phytic acid molecules by polyvinyl alcohol long chains is achieved by a simple solvothermal evaporation method. The high-density hydrogen bond network between the two promotes the rapid and orderly transport of zinc ions and uniform zinc deposition. Benefiting from the inherent viscoelasticity and mechanical properties of the elastomeric electrolyte, the solid-state zinc-ion battery assembled therefrom exhibits excellent reversibility, rate performance, and cycle stability.

[0033] As mentioned above, the above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, making equivalent substitutions or changes, should be covered within the protection scope of the present invention.

Claims

1. A method for preparing an ion-conductive elastomer electrolyte, characterized in that: The following steps are involved: Step 1: Add polyvinyl alcohol to deionized water, stir to swell at room temperature, and then heat until completely dissolved; Step 2: Stir the polyvinyl alcohol aqueous solution obtained in step 1 and the phytic acid aqueous solution evenly; Step 3: After completely eliminating bubbles in a vacuum oven, the mixture solution obtained in step 2 is poured into a polytetrafluoroethylene culture dish, and then dried to obtain a viscoelastic ion conductive elastomer film; Step 4: Add ZnSO4·7H2O to deionized water and stir at room temperature until ZnSO4·7H2O is completely dissolved to obtain a ZnSO4 electrolyte; Step 5: The viscoelastic ion conductive elastomer membrane obtained in step 3 is completely immersed in the ZnSO4 electrolyte obtained in step 4 and allowed to stand, then rinsed and the excess ZnSO4 electrolyte on the surface of the ion conductive elastomer membrane is wiped off with filter paper, and the elastomer solid electrolyte is obtained after evaporating the solvent.

2. The method for preparing an ion-conductive elastomer electrolyte according to claim 1, characterized in that: The concentration of the polyvinyl alcohol aqueous solution in step 1 is 5%.

3. The method for preparing an ion-conductive elastomer electrolyte according to claim 1, characterized in that: The heating temperature of the polyvinyl alcohol aqueous solution in step 1 is 75-100°C.

4. The method for preparing an ion-conductive elastomer electrolyte according to claim 1, characterized in that: In step 2, the concentration of the phytic acid aqueous solution is 70%.

5. The method for preparing an ion-conductive elastomer electrolyte according to claim 1, characterized in that: In step 2, the molar ratio of the polyvinyl alcohol aqueous solution to the phytic acid aqueous solution is 20:1 to 1:

1.

6. The method for preparing an ion-conductive elastomer electrolyte according to claim 1, characterized in that: The temperature for evaporating the solvent in step 5 is 60°C.

7. The method for preparing an ion-conductive elastomer electrolyte according to claim 1, characterized in that: The drying heating temperature in step 3 is 40-90°C.

8. A solid-state zinc ion battery, characterized in that: A 2032-type button-type solid-state zinc ion battery is assembled using Zn foil as the negative electrode, VO2 coated on carbon paper as the positive electrode, and the ion-conductive elastomer electrolyte described in any one of claims 1 to 7 as the solid electrolyte.

Images