Hydrogel electrolyte, its preparation method and aqueous zinc-ion battery

Abstract

The present invention provides a hydrogel electrolyte, which comprises a composite hydrogel and a support framework material interspersed inside the composite hydrogel. The composite hydrogel comprises starch, a synthetic polymer, inorganic nanoparticles and a liquid electrolyte; there is a hydrogen bond interaction between the synthetic polymer and the starch; the weight ratio of the starch to the synthetic polymer is (0.4-2.4):1. The hydrogel electrolyte provided by the present invention, which has a composite hydrogel and a support framework structure interspersed inside the composite hydrogel, effectively improves the mechanical strength and stability of the electrolyte, thereby further improving the safety performance of the aqueous zinc-ion battery in which it is located.

Description

Technical Field

[0001] The present invention relates to the field of zinc-ion batteries, and in particular, to a hydrogel electrolyte, a preparation method thereof, and an aqueous zinc-ion battery. Background Art

[0002] Aqueous zinc-ion secondary batteries have received extensive attention from researchers due to their excellent safety, environmental friendliness, low and resource-unrestricted raw material costs. However, since water is used as a solvent in its electrolyte, there are many side reactions caused by water, such as corrosion on the surface of the metal zinc negative electrode, formation of electrochemically inert and irreversible by-products, decomposition of water, dissolution of the positive electrode active material, etc., which lead to problems such as an increase in battery polarization, attenuation of capacity, and swelling of the battery, further causing a decline in battery performance. In addition, the formation of dendrites due to the uneven deposition of the metal zinc negative electrode in the liquid electrolyte greatly affects the stability of battery operation. Therefore, there is an urgent need to develop measures suitable for industrial application to solve the water-induced side reactions in aqueous zinc-ion batteries and the dendrite growth problem of the metal zinc negative electrode. Among many measures, constructing and using a hydrogel material to construct an electrolyte can effectively reduce the water content in the electrolyte, homogenize the ion transport channels, inhibit the growth of zinc dendrites, and reduce the dissolution of the positive electrode active material. However, the existing hydrogel electrolytes are complex to construct, have high raw material costs, and the dry film materials of the hydrogel electrolytes have extremely poor mechanical strength after absorbing the electrolyte, rarely exceeding the MPa level, which greatly hinders the processing and practical application of the hydrogel electrolytes.

[0003] Patent CN114976300A discloses a polymer electrolyte based on a polysaccharide material, a preparation method of the electrolyte, and its application. The preparation method of the polymer electrolyte based on the polysaccharide material includes the following steps: dissolving the polysaccharide in a solvent to obtain a homogeneous and clear solution; controlling the thickness of the polysaccharide polymer film obtained by a casting method, a coating method, a hot pressing method, a freeze-drying method, an electrospinning method, a phase inversion method, an impregnation method, a foaming method, or a Bellcore method to be 5-500 μm; placing the polysaccharide polymer film obtained in step (2) in a vacuum drying oven and drying it at a temperature from room temperature to 300 °C to remove trace solvents; soaking the dried polysaccharide polymer film obtained in step (3) in a liquid electrolyte for 1 minute to 24 hours to obtain a polysaccharide polymer electrolyte. However, on the one hand, the polysaccharide polymer film is brittle after drying and has poor mechanical strength after absorbing liquid to form a gel. On the other hand, the polymer molecules in the polysaccharide polymer film are all formed into a film by a simple physical cross-linking method, and the stability is poor.

[0004] Patent CN115377487A discloses a ternary cross-linked gel electrolyte for zinc ion batteries, its preparation and application. By subjecting three polymer raw materials, namely polyacrylamide, polysaccharide derivatives rich in hydroxyl groups, and polyanionic natural polymers containing carboxylate groups, to a cross-linking polymerization reaction under thermal initiation conditions, a ternary cross-linked hydrogel is obtained. The polysaccharide derivatives rich in hydroxyl groups include one or more of soluble starch, locust bean gum, konjac gum, chitosan, xanthan gum, and carrageenan. However, the hydrogel disclosed in this patent has low mechanical strength and significant swelling after absorbing the electrolyte, which is not conducive to actual use and processing and cannot be practically applied.

[0005] Patent CN116344966A discloses a composite polyacrylamide gel electrolyte, its preparation method and application. The preparation method of this composite polyacrylamide gel electrolyte includes the following steps: (1) Using acrylamide as the raw material, N,N'-methylenebisacrylamide as the cross-linking agent, and deionized water as the solvent, adding an initiator and stirring evenly to form solution A; (2) Using Zn 2+ , Ba 2+ or Al 3+ as the coordination ion, dissolving it in deionized water and stirring evenly to form solution B; (3) Adding a natural polymer to solution B and stirring under inert gas protection to form solution C; (4) Adding solution C to solution A and forming solution D under inert gas protection; (5) Polymerizing solution D to obtain a gel; (6) Placing the gel in an electrolyte for ion exchange to obtain a composite polyacrylamide gel electrolyte. This invention aims to enhance the mechanical strength of the gel electrolyte by introducing a tough ion-coordination type natural polymer material into the PAM polymer backbone. However, the preparation method provided by this technical solution requires inert gas protection, has a complex process, and high costs; and directly forming a gel through polymerization reaction is not conducive to processing into a film for application in actual batteries.

[0006] Based on this, how to provide a hydrogel electrolyte that can simultaneously balance mechanical properties and stability, and is easy to produce and has high practical application value is one of the important technical problems to be solved in this field. Summary of the Invention

[0007] The main object of the present invention is to provide a hydrogel electrolyte, its preparation method and an aqueous zinc ion battery, so as to solve the problems in the prior art that the hydrogel electrolyte used for aqueous zinc ions cannot balance mechanical properties and stability, and is not easy to produce and scale up for application.

[0008] To achieve the above object, on the one hand, the present invention provides a hydrogel electrolyte, which includes a composite hydrogel and a support skeleton material interspersed inside the composite hydrogel. The composite hydrogel includes starch, a synthetic polymer, inorganic nanoparticles, and a liquid electrolyte; there is a hydrogen bond interaction between the synthetic polymer and the starch; the weight ratio of the starch to the synthetic polymer is (0.4 - 2.4):1.

[0009] Further, one or more of alcohol hydroxyl groups, amino groups, and amide groups are carried on the molecular chain of the synthetic polymer; preferably, the synthetic polymer is polyacrylamide.

[0010] Further, the starch is selected from one or more of corn starch, sweet potato starch, wheat starch, and potato starch, and preferably corn starch.

[0011] Further, the thickness of the hydrogel electrolyte is 10 - 400 μm, the support skeleton material is a two-dimensional material, and the thickness is 10 - 100 μm; preferably, the support skeleton material is a cellulose separator and / or a two-dimensional fiber material, and the two-dimensional fiber material is selected from membrane materials, felt materials, or cloth materials made of glass fiber, aramid fiber, cotton fiber, or basalt fiber; preferably, the support skeleton material is selected from one or more of hydrophilic non-woven fabric, glass fiber separator, and cellulose separator, and more preferably hydrophilic non-woven fabric.

[0012] Further, the D50 of the inorganic nanoparticles is 10 - 50 nm; based on the weight of the hydrogel electrolyte being 100%, the content of the inorganic nanoparticles is 0.8 - 1.0 wt%; preferably, the inorganic nanoparticles are selected from one or more of nano zinc oxide, fumed nano silicon dioxide, and nano aluminum oxide; more preferably, the inorganic nanoparticles are fumed nano silicon dioxide.

[0013] Further, based on the total weight of the hydrogel electrolyte being 100%, the content of the liquid electrolyte is 55 - 75%; the liquid electrolyte is an aqueous solution of a zinc salt, and the concentration of the aqueous solution of the zinc salt is 1.0 - 3.0 mol / L, preferably 1.8 - 2.0 mol / L; preferably, the zinc salt is selected from one or more of zinc sulfate, zinc acetate, and zinc trifluoromethanesulfonate, and more preferably zinc sulfate.

[0014] Another aspect of the present invention provides a method for preparing the above-mentioned hydrogel electrolyte, comprising: Step S1, adding a monomer of a synthetic polymer, a crosslinking agent, and inorganic nanoparticles into a first solvent to prepare a first solution; Step S2, adding starch into a second solvent, heating and stirring to obtain a second solution; Step S3, mixing the first solution and the second solution, stirring to form a slurry, and impregnating the slurry on a support framework material to obtain an intermediate product, the intermediate product comprising the slurry and the support framework material infiltrated in the slurry; Step S4, atomizing and spraying an aqueous solution of an initiator on the surface of the intermediate product, standing and then heating, and obtaining a hydrogel dry film through polymerization and crosslinking reactions; Step S5, soaking the hydrogel dry film in a liquid electrolyte to obtain a hydrogel electrolyte.

[0015] Further, in Step S1, the molar ratio of the monomer of the synthetic polymer to the crosslinking agent is (125 - 500):1, preferably (200 - 250):1; the first solvent is a mixed solvent of deionized water and ethylene glycol, and the volume ratio of deionized water to ethylene glycol is (3 - 10):1, preferably (5 - 6):1; in the first solvent, the concentration of the monomer of the synthetic polymer is 0.05 - 0.2 g / mL.

[0016] Further, in Step S2, the weight ratio of starch to the second solvent is 1:(3 - 15), preferably 1:(8 - 9); the heating and stirring time is 30 - 40 min, and the temperature is 65 - 90 °C, preferably 75 - 80 °C.

[0017] Further, in Step S3, the mixing is carried out at a temperature of 75 - 80 °C, and the stirring time is 10 - 15 min; in the aqueous solution of the initiator in Step S4, the mass concentration of the initiator is 0.5 - 5 mg / mL, and the initiator is ammonium persulfate and / or potassium persulfate; in Step S4, the standing time is 10 - 12 min, and the heating temperature is 70 - 75 °C, and the time is 1 - 1.5 h.

[0018] Further, the soaking time in Step S5 is ≥1 h; the liquid electrolyte is an aqueous solution of a zinc salt, and the concentration is 1.0 - 3.0 mol / L, preferably 1.8 - 2.0 mol / L; the zinc salt is selected from one or more of zinc sulfate, zinc acetate, and zinc trifluoromethanesulfonate, and more preferably zinc sulfate.

[0019] Another aspect of the present invention provides an aqueous zinc ion battery, comprising a positive electrode sheet, a negative electrode sheet, and an electrolyte, and the electrolyte is the above-mentioned hydrogel electrolyte.

[0020] Applying the technical solution of the present invention, a hydrogel electrolyte is provided, which has a composite hydrogel and a support skeleton structure interspersed inside the composite hydrogel. The composite hydrogel structure has two polymers and inorganic nanoparticles, which can improve the mechanical strength of the electrolyte, reduce the water content, improve the stability, and the enhanced skeleton improves the mechanical strength of the composite hydrogel body after being infiltrated with the electrolyte solution, thereby further improving the safety performance of the aqueous zinc-ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings forming a part of this application are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0022] Figure 1 It is the zinc deposition morphology diagram corresponding to Example 1;

[0023] Figure 2 It is the zinc deposition morphology diagram corresponding to Comparative Example 6;

[0024] Figure 3 It is the zinc deposition morphology diagram corresponding to Comparative Example 5;

[0025] Figure 4 It is the zinc deposition morphology diagram corresponding to the hydrophilic non-woven fabric without any treatment. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] It should be noted that, without conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the embodiments.

[0027] As described in the background art, in the prior art, there are problems that the hydrogel electrolyte used for aqueous zinc ions cannot balance mechanical properties and stability, and is not easy to produce and scale up. To solve the above technical problems, on the one hand, the present invention provides a hydrogel electrolyte, which includes a composite hydrogel and a support skeleton material interspersed inside the composite hydrogel. The composite hydrogel includes starch, synthetic polymer, inorganic nanoparticles and liquid electrolyte; there is a hydrogen bond interaction between the synthetic polymer and starch; the weight ratio of starch to synthetic polymer is (0.4 - 2.4):1.

[0028] In the present invention, by providing two polymer components, namely starch and synthetic polymer, in the composite hydrogel of the hydrogel electrolyte matrix, many problems of a single polymer matrix are avoided, and the stability of the obtained hydrogel electrolyte is effectively improved. In particular, by utilizing the hydrogen bond interaction between starch and synthetic polymer, i.e., providing physical crosslinking sites, a physical crosslinking network is formed inside the composite hydrogel, thereby further significantly enhancing the mechanical properties of the hydrogel electrolyte. At the same time, inorganic nanoparticles are introduced as fillers inside the composite hydrogel, i.e., high-mechanical-strength solid sites are further added to the above physical crosslinking network to provide higher mechanical strength and safety performance. The hydrogel electrolyte structure provided by the present invention further includes a support skeleton material interspersed inside the above composite hydrogel to further increase its mechanical strength, especially the anti-bending and tensile properties, and improve the stability of the hydrogel when used as an electrolyte.

[0029] Especially importantly, for the hydrogel electrolyte provided by the present invention, which includes a synthetic polymer and starch, it is also necessary to further control the weight ratio of starch to synthetic polymer to be (0.4 - 2.4):1. Under this weight ratio condition, more of the above hydrogen bond-based physical crosslinking networks can be successfully formed, thereby effectively reducing the voids between molecular chains and improving the mechanical properties. At the same time, under this weight ratio condition, the obtained hydrogel electrolyte has the most suitable liquid absorption rate, so as to ensure the safety performance to the greatest extent under higher electron conductivity conditions.

[0030] In several preferred embodiments, the molecular chains of the synthetic polymer carry alcohol hydroxyl groups and / or amino groups. The composite hydrogel system provided by the present invention first includes starch, which, as a natural polysaccharide polymer rich in hydroxyl groups, can form hydrogen bonds with various functional groups. Based on this feature, the present invention further preferably selects a synthetic polymer whose molecular chain carries one or more of alcohol hydroxyl groups, amino groups, and amide groups, and it is found that these three functional groups can better cooperate with the hydrophilic centers on the starch molecular chain, so as to play the self-healing role of the hydrogel while forming a hydrogen bond cross-linked network to enhance the mechanical properties and improve the stability. In particular, in a more preferred embodiment, the synthetic polymer is polyacrylamide. Through a large number of experiments and comparisons, the inventor further selects polyacrylamide from the above three specific types of synthetic polymers, and finds that this polymer can form a more stable hydrogel system with starch, and more significantly improve the mechanical properties and comprehensive electrochemical properties of the finally obtained hydrogel electrolyte. This may be because in addition to the amide groups in polyacrylamide that can form a physical cross-linked network based on hydrogen bonds with starch, the polyacrylamide formed by the reaction of acrylamide monomers with cross-linking agents has a more stable chemical cross-linked network structure and better stability. Therefore, the hydrogel system formed by it and starch achieves more excellent mechanical properties and electrochemical stability.

[0031] Furthermore, the starch is selected from one or more of corn starch, sweet potato starch, wheat starch, and potato starch, preferably corn starch. Through a large number of experiments, the inventor preferably selects corn starch as the type of starch. Since the amylose / amylopectin ratio of different starches is different, which has an obvious impact on their gelatinization temperature and gelation ability, in order to facilitate the preparation of the solution and at the same time effectively weaken the spontaneous formation of hydrogen bonds between the starch molecules themselves to form a gel, thereby affecting the formation of hydrogen bonds between the starch and the synthetic polymer and ultimately affecting the uniformity of the composite gel, the inventor further optimizes the type of starch and finds that when using corn starch, the obtained composite hydrogel has better uniformity and the final electrolyte structure is more stable.

[0032] In a more typical embodiment, the thickness of the hydrogel electrolyte is 10 - 400 μm, the supporting framework material is a two-dimensional material, and the thickness is 10 - 100 μm. Through a large number of experiments, the inventor optimized the thickness of the hydrogel electrolyte, the thickness of the supporting framework material traversing the composite hydrogel, and the shape of the supporting framework material, so as to improve the compatibility between the composite hydrogel and the supporting framework material, and finally obtain a hydrogel electrolyte with better mechanical properties. Preferably, the supporting framework material is a cellulose separator and / or a two-dimensional fiber material, and the two-dimensional fiber material is selected from membrane materials, felt materials or cloth materials made of glass fiber, aramid fiber, cotton fiber or basalt fiber. In theory, the supporting framework material can be selected from other two-dimensional materials commonly used in the art as long as it can be physically combined with the composite hydrogel. However, for the above system provided by the present invention, the inventor optimized it through a large number of experiments and found that when the supporting framework material meets the above conditions and types, the obtained hydrogel electrolyte has higher mechanical properties, and at the same time, it is not easy to exfoliate between the supporting framework material and the composite hydrogel, and the safety is higher.

[0033] In several preferred embodiments, the supporting framework material is selected from one or more of hydrophilic non-woven fabric, glass fiber separator and cellulose separator. Through a large number of experiments, the inventor optimized the specific types of the supporting framework material and obtained the above several types. It was found that when the three of them are combined with the composite hydrogel to form a hydrogel electrolyte, it has better mechanical properties, and at the same time, the liquid absorption rate is more appropriate, thus showing higher stability. In a more preferred embodiment, the supporting framework material is hydrophilic non-woven fabric, and the polypropylene fibers constituting it have excellent strength, good fiber length and flexibility, and low cost.

[0034] In order to more effectively exert the strengthening effect of the inorganic nanoparticles and improve the mechanical properties of the hydrogel electrolyte, the inventor further optimized: the D50 of the inorganic nanoparticles is 10 - 50 nm, and based on the weight of the hydrogel electrolyte being 100%, the content of the inorganic nanoparticles is 0.8 - 1.0 wt%. In several more typical embodiments, the inventor further optimized that the inorganic nanoparticles are selected from one or more of nano-zinc oxide, fumed nano-silica and nano-aluminum oxide, and found that these several can better cooperate with the hydrogen bond cross-linking network formed by starch and synthetic polymer, so as to more significantly improve the mechanical properties of the hydrogel electrolyte. In a more typical embodiment, the inorganic nanoparticles are fumed nano-silica.

[0035] Further, based on the total weight of the hydrogel electrolyte being 100%, the content of the liquid electrolyte is 55-75%; the liquid electrolyte is an aqueous solution of a zinc salt, and the concentration of the aqueous solution of the zinc salt is 1.0-3.0 mol / L. In the hydrogel electrolyte provided by the present invention, the liquid electrolyte is absorbed in the hydrogel polymer network structure. On this basis, the inventors preferably select the content, concentration and type of the liquid electrolyte as described above, so as to facilitate the mass transfer ability of the overall electrolyte and further improve the safety and stability. The inventors further preferably the concentration of the aqueous solution of the zinc salt to 1.8-2.0 mol / L through a large number of experiments, and find that the electrochemical performance of the obtained hydrogel electrolyte layer is higher in this concentration range. Preferably, the zinc salt is selected from one or more of zinc sulfate, zinc acetate and zinc trifluoromethanesulfonate, and more preferably zinc sulfate. The inventors find through a large number of experiments that compared with other types of zinc salts, zinc sulfate has a lower cost and is suitable for the large-scale production of electrolytes. Moreover, zinc sulfate can be fully ionized in an aqueous solution to ensure that the electrolyte has good ionic conductivity. In addition, zinc sulfate has better biosecurity.

[0036] Another aspect of the present invention provides a preparation method of the above-mentioned hydrogel electrolyte, including: Step S1, adding a monomer of a synthetic polymer, a crosslinking agent and inorganic nanoparticles into a first solvent to prepare a first solution; Step S2, adding starch into a second solvent, heating and stirring to obtain a second solution; Step S3, mixing and stirring the first solution and the second solution to form a slurry, and impregnating the slurry on a support skeleton material to obtain an intermediate product, the intermediate product including the slurry and the support skeleton material infiltrated in the slurry; Step S4, atomizing and spraying an aqueous solution of an initiator on the surface of the intermediate product, standing and then heating, and obtaining a hydrogel dry film through polymerization and crosslinking reactions; Step S5, soaking the hydrogel dry film in a liquid electrolyte to obtain a hydrogel electrolyte.

[0037] Regarding the above hydrogel electrolyte, the present invention correspondingly provides a preparation method thereof. First, a monomer to form a synthetic polymer, a crosslinking agent, and inorganic nanoparticles are formulated into a first solution. Then, a second solution, namely a starch solution, is provided. The two are mixed, impregnated in a support framework material, and then crosslinked to obtain a hydrogel dry film. Finally, a liquid electrolyte is introduced into the dry film by soaking to obtain the hydrogel electrolyte. The monomer of the synthetic polymer to be polymerized and starch are first dissolved separately and then mixed. Compared with directly dissolving and mixing the two in the same solvent system, it can improve the dispersion of nanoparticles in the solution and prevent nanoparticle aggregation. At the same time, it can avoid the influence on the sufficiency of starch gelatinization during co-dissolution and mixing. And crosslinking polymerization is achieved by heating in the presence of an initiator. Compared with common crosslinking methods in the art such as radiation crosslinking, it can greatly reduce the crosslinking cost, simplify the preparation process flow, and improve the feasibility and practicality of the method. At the same time, because the above process steps provided by the present invention are simple and easy to implement, do not involve complex processes and expensive equipment, the corresponding hydrogel electrolyte is easy to produce and suitable for large-scale applications.

[0038] Further, in step S1, the molar ratio of the monomer of the synthetic polymer to the crosslinking agent is (125 - 500):1. Regarding the composite hydrogel system of the present invention, in order to obtain a polymer network with a more suitable crosslinking degree, the inventor preferably sets the dosage of the crosslinking agent within the above range. On this basis, the inventor preferably sets the molar ratio of the monomer of the synthetic polymer to the crosslinking agent to (200 - 250):1 through a large number of experiments, and finds that crosslinking polymerization with this dosage ratio results in a more suitable rigidity of the obtained hydrogel electrolyte.

[0039] In a preferred embodiment, the first solvent is a mixed solvent of deionized water and ethylene glycol, and the volume ratio of deionized water to ethylene glycol is (3 - 10):1. In order to reduce the precipitation phenomenon of the starch component during the subsequent mixing process and balance the dispersion effect of the inorganic nanoparticles, the inventor preferably selects the above first solvent system through a large number of experiments, and better dispersion and mixing effects are achieved under this system. In order to obtain a hydrogel polymer network with a higher degree of uniformity, fewer defects, and better mechanical properties, the inventor further preferably sets the volume ratio of deionized water to ethylene glycol to (5 - 6):1 through a large number of experiments on this basis. And, in order to further improve the mixing effect and the uniformity of the final crosslinking polymerization, the inventor further preferably sets the concentration of the monomer of the synthetic polymer in the first solvent to 0.05 - 0.2 g / mL.

[0040] Accordingly, in order to improve the dispersion effect, in step S2, the inventors have preferably determined through a large number of experiments that the weight ratio of starch to the second solvent is 1: (3-15), and more preferably 1: (8-9), so as to obtain a more uniform intermediate system with better fluidity, thereby adapting the gelatinization effect of starch and obtaining a system to be mixed with a more suitable viscosity.

[0041] As mentioned above, the inventors have optimized the weight ratio of starch to the second solvent to improve the gelatinization effect of subsequent heating and stirring. The better the gelatinization effect, the more the original ordered structure of the starch molecules is destroyed, the more active groups that can form hydrogen bonds are exposed, and the hydrogen bond cross-linking effect is enhanced. After a large number of experiments, the inventors have optimized the heating and stirring time to be 30 to 40 minutes and the temperature to be 65 to 90°C, and further optimized the temperature to be 75 to 80°C, so as to obtain a more sufficient gelatinization effect at a lower energy consumption.

[0042] In a typical embodiment, in step S3, mixing is carried out at a temperature of 75 to 80°C, and the stirring time is 10 to 15 minutes. The temperature of the second solution obtained by heating and stirring in step S2 is preferably maintained at 75 to 80°C, and the first solution containing the monomer to be polymerized is mixed with it under this condition, so that the starch solution that has been gelatinized during the mixing process is less likely to be regenerated, thereby affecting the uniformity of the mixed solution. Further, in step S4, in the aqueous solution of the initiator, the mass concentration of the initiator is 0.5 to 5 mg / mL, and the initiator is ammonium persulfate and / or potassium persulfate. In order to enhance the effect of cross-linking polymerization and obtain a hydrogel electrolyte with a more uniform and stable structure, the inventors have optimized the above-mentioned initiator-related condition parameters through a large number of experiments. Furthermore, in step S4, the standing time is 10 to 12 minutes, the heating temperature is 70 to 75°C, and the time is 1 to 1.5 hours. Allowing the precursor solution to stand for 10 to 12 minutes between heating and inducing cross-linking is beneficial for fully wetting the support membrane material and preventing uneven wetting, so that the final prepared hydrogel dry film contains a large number of holes. The above temperature and time conditions can promote a more complete cross-linking reaction and a cleaner evaporation of the solvent.

[0043] After obtaining the hydrogel dry film, it is necessary to soak it so that the liquid electrolyte is absorbed, thereby finally forming a hydrogel material. In a typical embodiment, the soaking time in step S5 is ≥1h, so as to facilitate more sufficient absorption of the liquid electrolyte. In order to further improve the mass transfer capacity of the obtained electrolyte, the inventors have selected the liquid electrolyte as an aqueous solution of zinc salt after a large number of experiments, and the concentration is 1.0-3.0 mol / L, more preferably 1.8-2.0 mol / L. At the same time, the zinc salt is preferably selected from one or more of zinc sulfate, zinc acetate and zinc trifluoromethanesulfonate, more preferably zinc sulfate. In order to reduce the cost of hydrogel electrolytes and improve their biosafety and ionic conductivity.

[0044] Another aspect of the present invention provides an aqueous zinc ion battery, comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the electrolyte is the above-mentioned hydrogel electrolyte. Since the hydrogel electrolyte obtained by the present invention not only has excellent mass transfer effect, but also has very superior mechanical strength, when applied to an aqueous zinc ion battery, the corresponding battery can exhibit a longer cycle life, is not prone to failure due to dendrite formation and generate safety hazards, and has higher practical application value.

[0045] Specifically, the positive electrode plate in the aqueous zinc ion battery is selected from titanium foil, stainless steel foil, graphite foil, or is prepared from a three-dimensional carbon material current collector and a positive electrode active substance, a binder, and a conductive agent; the negative electrode plate adopts a zinc metal-containing plate, which can be a sheet-shaped conductive material made of zinc sheet and / or zinc powder.

[0046] The present application is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in the present application.

[0047] Unless otherwise defined, all professional terms used below have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0048] Example 1

[0049] A method for preparing a hydrogel electrolyte:

[0050] (1) using acrylamide (AM) as a monomer and N,N'-methylenebisacrylamide (MBA) as a crosslinking agent, and the molar ratio of acrylamide monomer to the crosslinking agent is 250:1, and using a mixture of deionized water and ethylene glycol in a volume ratio of 6:1 as a solvent, at a monomer concentration of 1 g / mL, the above substances are mixed and stirred uniformly, and fumed nano-silica particles with a D50 of 15 nm are added until a uniform solution 1 is formed;

[0051] (2) Using corn starch as the raw material, deionized water as the solvent, and with a mass ratio of starch to deionized water of 1:8, stir and mix at 80 °C for 30 min to obtain Solution 2;

[0052] (3) According to the mass ratio of acrylamide dissolved: starch of 1:1, add Solution 1 to Solution 2 at 80 °C, continue heating and stirring for 10 min to form a slurry. Coat the obtained slurry on a hydrophilic non-woven fabric with a thickness of 40 μm so that the hydrophilic non-woven fabric is impregnated in the slurry to obtain an intermediate product infiltrated with the hydrophilic non-woven fabric;

[0053] (4) Prepare an aqueous potassium persulfate solution with a mass concentration of 1 mg / mL, and spray it onto the surface of the above intermediate product by atomization. Then let it stand for 10 min. Initiate the cross-linking polymerization of acrylamide monomers in the slurry at a temperature of 70 °C and evaporate the solvent. After 1 h, obtain a hydrogel electrolyte dry film composed of starch and cross-linked polyacrylamide;

[0054] (5) Provide a 2 mol / L zinc sulfate solution as the liquid electrolyte, and immerse the hydrogel electrolyte dry film material obtained in step (4) in it for 2 h. Then take it out and wipe off the liquid electrolyte on the surface to obtain the hydrogel electrolyte. It is calculated that the liquid absorption rate of its dry film is 251.1%.

[0055] The total thickness of the obtained hydrogel electrolyte is 300 μm, where the weight ratio of starch to polyacrylamide is 1:1, the content of gas-phase nano-silica particles is 1.0 wt%, and based on the total weight of the obtained hydrogel electrolyte being 100%, the content of the liquid electrolyte is 251.1 / (251.1 + 100)×100% = 71.5%.

[0056] Example 2

[0057] A preparation method of a hydrogel electrolyte:

[0058] The difference between this example and Example 1 is only that: use nano-alumina with the same particle size and the same weight instead of gas-phase nano-silica.

[0059] Example 3

[0060] A preparation method of a hydrogel electrolyte:

[0061] The difference between this example and Example 1 is only that: use nano-zinc oxide with the same particle size and the same weight instead of gas-phase nano-silica.

[0062] Example 4

[0063] A preparation method of a hydrogel electrolyte:

[0064] The difference between this example and Example 1 is only that: the volume ratio of Solution 1 to Solution 2 in step (3) is changed, so that in the finally obtained hydrogel electrolyte, the weight ratio of starch to polyacrylamide is changed to 0.4:1.

[0065] Example 5

[0066] A preparation method of a hydrogel electrolyte:

[0067] The difference between this example and Example 1 is only that: the volume ratio of Solution 1 to Solution 2 in step (3) is changed, so that in the finally obtained hydrogel electrolyte, the weight ratio of starch to polyacrylamide is changed to 2.4:1.

[0068] Example 6

[0069] A preparation method of a hydrogel electrolyte:

[0070] The difference between this example and Example 1 is only that: the D50 of the gas-phase nano-silica particles is 5 nm, and the final content in the hydrogel electrolyte is 0.6 wt%; and a cellulose separator with a thickness of 5 μm is used to replace the hydrophilic non-woven fabric.

[0071] Example 7

[0072] A preparation method of a hydrogel electrolyte:

[0073] The difference between this example and Example 1 is only that: the D50 of the gas-phase nano-silica particles is 100 nm, and the final content in the hydrogel electrolyte is 1.2 wt%; and the thickness of the used hydrophilic non-woven fabric is 300 μm.

[0074] Example 8

[0075] A preparation method of a hydrogel electrolyte:

[0076] The difference between this example and Example 1 is only that: in the solvent used in step (1), the volume ratio of deionized water to ethylene glycol is 2:1.

[0077] Example 9

[0078] A preparation method of a hydrogel electrolyte:

[0079] The difference between this example and Example 1 is only that: in the solvent used in step (1), the volume ratio of deionized water to ethylene glycol is 12:1.

[0080] Example 10

[0081] A preparation method of a hydrogel electrolyte:

[0082] The difference between this embodiment and Embodiment 1 is only that: in step (3), when adding Solution 1 to Solution 2, the temperature of Solution 2 is 50°C instead of 80°C.

[0083] Comparative Example 1

[0084] A method for preparing a hydrogel electrolyte:

[0085] The difference between this comparative example and Embodiment 1 is only that: changing the volume ratio of Solution 1 to Solution 2 in step (3) such that in the finally obtained hydrogel electrolyte, the weight ratio of starch to polyacrylamide is changed to 0.1:1.

[0086] Comparative Example 2

[0087] A method for preparing a hydrogel electrolyte:

[0088] The difference between this comparative example and Embodiment 1 is only that: changing the volume ratio of Solution 1 to Solution 2 in step (3) such that in the finally obtained hydrogel electrolyte, the weight ratio of starch to polyacrylamide is changed to 9:1.

[0089] Comparative Example 3

[0090] A method for preparing an electrolyte:

[0091] The difference between this comparative example and Embodiment 1 is only that: only mixing the Solution 2 obtained in step (2) with the liquid electrolyte in step (5) in equal volume as the electrolyte, that is, the obtained electrolyte does not include synthetic polymer, inorganic nanoparticles, and supporting framework materials.

[0092] Comparative Example 4

[0093] A method for preparing an electrolyte:

[0094] The difference between this comparative example and Embodiment 1 is only that: using the Solution 1 obtained in step (1) after initiation as the hydrogel electrolyte dry film, and after soaking in step (5) as the electrolyte, that is, the obtained electrolyte does not include starch, inorganic nanoparticles, and supporting framework materials.

[0095] Comparative Example 5

[0096] A method for preparing an electrolyte:

[0097] The difference between this comparative example and Embodiment 1 is only that: in step (1), no inorganic nanoparticles are added, and at the same time, the coating in step (3) is not carried out. Instead, the polymer obtained by initiating the cross-linking polymerization of the slurry obtained by directly mixing Solution 1 and Solution 2 is used as the hydrogel electrolyte dry film, and after soaking in step (5) as the electrolyte, that is, the obtained electrolyte does not include inorganic nanoparticles and supporting framework materials.

[0098] Comparative Example 6

[0099] Preparation method of an electrolyte:

[0100] The difference between this comparative example and Example 1 is only that: in step (1), fumed silica particles are not added, that is, the obtained electrolyte does not include inorganic nanoparticles.

[0101] Comparative Example 7

[0102] Preparation method of an electrolyte:

[0103] The difference between this comparative example and Comparative Example 6 is only that: a glass fiber separator with equal thickness is used instead of the hydrophilic non-woven fabric.

[0104] Comparative Example 8

[0105] Preparation method of an electrolyte:

[0106] The difference between this comparative example and Comparative Example 6 is only that: a cellulose separator with equal thickness is used instead of the hydrophilic non-woven fabric.

[0107] Comparative Example 9

[0108] Preparation method of an electrolyte:

[0109] The difference between this comparative example and Example 1 is only that: in step (3), coating is not carried out, but the polymer obtained by initiating cross-linking polymerization of the slurry obtained by directly mixing Solution 1 and Solution 2 is used as the hydrogel electrolyte dry film, and after being soaked in step (5), it is used as the electrolyte, that is, the obtained electrolyte does not include the support framework material.

[0110] Comparative Example 10

[0111] Preparation method of an electrolyte:

[0112] The difference between this comparative example and Example 2 is only that: in step (3), coating is not carried out, but the polymer obtained by initiating cross-linking polymerization of the slurry obtained by directly mixing Solution 1 and Solution 2 is used as the hydrogel electrolyte dry film, and after being soaked in step (5), it is used as the electrolyte, that is, the obtained electrolyte does not include the support framework material.

[0113] Comparative Example 11

[0114] Preparation method of an electrolyte:

[0115] The difference between this comparative example and Example 3 is only that: in step (3), coating is not carried out, but the polymer obtained by initiating cross-linking polymerization of the slurry obtained by directly mixing Solution 1 and Solution 2 is used as the hydrogel electrolyte dry film, and after being soaked in step (5), it is used as the electrolyte, that is, the obtained electrolyte does not include the support framework material.

[0116] For easy comparison, the components in the electrolyte material structures obtained from the above embodiments and the comparative example are summarized and listed in Table 1.

[0117] Table 1

[0118]

[0119]

[0120] Electrolyte performance test:

[0121] Film-forming property: Observe whether a complete electrolyte dry film can be formed after the coating slurry is prepared by the above preparation method, and whether there are cracks, breakages, etc. in the electrolyte dry film; Excellent: It means that a uniform and flat complete electrolyte dry film can be formed, and the dry film has no cracks or breakages; Good: It means that a uniform and flat complete electrolyte dry film can be formed, and the dry film has slight cracks; Poor: It means that a uniform and flat complete electrolyte dry film cannot be formed, or the formed dry film has serious cracks or breakages.

[0122] Tensile strength: Use an electronic universal testing machine to perform mechanical tensile tests on the electrolyte dry film and the wet film after absorbing zinc sulfate solution respectively. The obtained results are described semi-quantitatively. Among them: When the tensile strength is greater than 10 MPa, it is defined as excellent; When the tensile strength is 10 MPa - 1 MPa, it is defined as good; When the tensile strength is 1 MPa - 50 kPa, it is defined as medium; When the tensile strength is less than 50 kPa or cannot be measured due to too poor film-forming property, it is defined as poor.

[0123] Liquid absorption rate: Weigh the electrolyte dry film to obtain mass 1, then soak this dry film in a 2 mol / L zinc sulfate solution for liquid absorption. After liquid absorption, take it out, dry the residual liquid on the surface, and then weigh it again to obtain mass 2; The difference between mass 2 and mass 1 is the mass of the absorbed zinc sulfate solution, denoted as mass 3, and the ratio of mass 3 to mass 1 is the liquid absorption rate. For the hydrogel electrolyte used in the battery, when its liquid absorption rate is 100 - 300%, it is most suitable for the performance of the battery. Too large or too small will cause performance deterioration.

[0124] Ionic conductivity: Clamp the wet film after absorbing zinc sulfate solution between two stainless steel sheets, assemble a stainless steel symmetric battery, and perform impedance testing in the range of 0.01 - 10 5 Hz to obtain the intrinsic resistance denoted as R, measure the thickness of the electrolyte wet film denoted as l, and the area of the electrolyte film denoted as S. The ionic conductivity σ = l / (R×S) is calculated through the formula.

[0125] Battery assembly and testing:

[0126] Battery cycle life: Clamp the wet film after absorbing zinc sulfate solution between two metal zinc electrodes, assemble a zinc symmetric battery, and at 2 mA / cm2 At a current density of 1 mAh / cm 2 The areal capacity of metallic zinc was used for cyclic charge and discharge tests until the battery short-circuited, and the cycling time was the battery cycle life.

[0127] Zinc deposition: Using the electrolytes obtained from each example and comparative example, 2 mAh / cm 2 Metallic zinc was deposited on a copper foil at a current density of 2 mA / cm 2 The surface morphology was observed and the corresponding SEM images were taken. Different symbols represent different situations. ◎: The surface is flat without dendrites; ○: The surface flatness is good and there are a small amount of dendrites; △: The surface flatness is average and there are a small number of dendrites; ×: The surface flatness is very poor and there are a large number of dendrites. And the number and severity of the formed dendrites are positively correlated with the performance of the cycle life.

[0128] And, Figure 1 Figure 15 shows the corresponding zinc deposition morphology diagram of Example 1, corresponding to ◎; Figure 2 Figure 17 shows the corresponding zinc deposition morphology diagram of Comparative Example 6, corresponding to ○; Figure 3 Figure 19 shows the corresponding zinc deposition morphology diagram of Comparative Example 5, corresponding to △; Figure 4 Figure 21 shows the corresponding zinc deposition morphology diagram of the hydrophilic non-woven fabric without any treatment, corresponding to ×.

[0129] The results of the above performance tests are shown in Table 2.

[0130] Table 2

[0131]

[0132]

[0133] From the above description, it can be seen that:

[0134] The nanoparticles in the electrolyte mainly play a role in promoting hydrogen bond cross-linking, enhancing the mechanical properties and ionic conductivity of the electrolyte. When the types of nanoparticles are fumed nano-silica, nano-zinc oxide, and nano-aluminum oxide, the influence on the electrolyte performance is small; when the particle size of the nanoparticles is less than the given range, it is easy to cause nanoparticle aggregation and poor uniformity, and when the particle size is greater than the given range, the dispersion uniformity is also poor.

[0135] When the ratio of starch to synthetic polymer in the electrolyte is within the given range, it affects the liquid absorption rate of the electrolyte, but has little impact on its overall performance. When it is outside the given range, on the one hand, the moldability becomes poor, and on the other hand, due to the influence of hydrogen bond cross-linking between the two, the wet film strength decreases. In addition, an excessive amount of starch will also lead to a decrease in the liquid absorption rate.

[0136] The supporting material has a great influence on the mechanical properties of the electrolyte, and the change in the type of the supporting material will also significantly affect the tensile strength of the electrolyte.

[0137] In the solvent used in step (1), the ratio of deionized water to ethylene glycol mainly affects the uniformity of the dispersion of the nanoparticles and the uniformity of the starch after the mixing of solution 1 and solution 2; if the proportion of ethylene glycol is too low, the nanoparticles will be unevenly dispersed, and if the proportion of ethylene glycol is too high, the uniformity of the starch after mixing will be reduced.

[0138] The temperature of solution 2 affects the degree of gelatinization of the starch, affects the uniformity of the starch after the mixing of the two solutions, and further affects the uniformity of the starch in the final electrolyte.

[0139] Moreover, the embodiments provided by the present invention achieve the improvement of the mechanical strength and stability of the hydrogel electrolyte, thereby further improving the safety performance of the aqueous zinc ion battery in which it is located.

[0140] It should be noted that the terms "first", "second", etc. in the specification and claims of this application are used to distinguish similar objects and do not necessarily need to describe a specific order or sequence. It should be understood that such terms can be interchanged under appropriate circumstances so that the embodiments of the present application described herein can be implemented in an order other than those described herein.

[0141] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A hydrogel electrolyte, characterized in that: The hydrogel electrolyte comprises a composite hydrogel and a supporting skeleton material interspersed inside the composite hydrogel, wherein the composite hydrogel comprises starch, a synthetic high molecular polymer, inorganic nanoparticles and a liquid electrolyte; There is a hydrogen bond between the synthetic high molecular polymer and the starch; The weight ratio of the starch to the synthetic high molecular polymer is (0.4-2.4): 1; The starch is corn starch; The D50 of the inorganic nanoparticles is 10-50 nm; Based on the weight of the hydrogel electrolyte being 100%, the content of the inorganic nanoparticles is 0.8-1.0 wt %.

2. The hydrogel electrolyte according to claim 1, characterized in that The synthetic high molecular polymer has one or more of alcoholic hydroxyl groups, amino groups and amide groups on its molecular chain.

3. The hydrogel electrolyte according to claim 1, characterized in that The synthetic high molecular polymer is polyacrylamide.

4. The hydrogel electrolyte according to any one of claims 1 to 3, characterized in that The hydrogel electrolyte has a thickness of 10-400 μm, and the supporting skeleton material is a two-dimensional material with a thickness of 10-100 μm.

5. The hydrogel electrolyte according to any one of claims 1 to 3, characterized in that The supporting skeleton material is a cellulose membrane and / or a two-dimensional fiber material, and the two-dimensional fiber material is selected from a membrane material, a felt material or a cloth material made of glass fiber, aramid fiber, cotton fiber or basalt fiber.

6. The hydrogel electrolyte according to claim 5, characterized in that The supporting skeleton material is selected from one or more of hydrophilic non-woven fabrics, glass fiber membranes and cellulose membranes.

7. The hydrogel electrolyte according to claim 5, characterized in that The supporting skeleton material is a hydrophilic non-woven fabric.

8. The hydrogel electrolyte according to any one of claims 1 to 3, characterized in that The inorganic nanoparticles are selected from one or more of nano zinc oxide, gas phase nano silicon dioxide and nano aluminum oxide.

9. The hydrogel electrolyte according to claim 8, characterized in that The inorganic nanoparticles are gas-phase nano-silicon dioxide.

10. The hydrogel electrolyte according to any one of claims 1 to 3, characterized in that Based on the total weight of the hydrogel electrolyte being 100%, the content of the liquid electrolyte is 55-75%; the liquid electrolyte is an aqueous solution of a zinc salt, and the concentration of the aqueous solution of the zinc salt is 1.0-3.0 mol / L.

11. The hydrogel electrolyte according to claim 10, characterized in that The concentration of the aqueous solution of the zinc salt is 1.8-2.0 mol / L.

12. The hydrogel electrolyte according to claim 10, characterized in that The zinc salt is selected from one or more of zinc sulfate, zinc acetate and zinc trifluoromethanesulfonate.

13. The hydrogel electrolyte according to claim 10, characterized in that The zinc salt is zinc sulfate.

14. A method for preparing the hydrogel electrolyte according to any one of claims 1 to 13, characterized in that: The preparation method comprises: Step S1, adding monomers for synthesizing high molecular polymers, a cross-linking agent and inorganic nanoparticles into a first solvent to prepare a first solution; Step S2, adding starch into the second solvent, heating and stirring to gelatinize the starch to obtain a second solution; Step S3, mixing and stirring the first solution and the second solution to form a slurry, and impregnating the slurry on the supporting skeleton material to obtain an intermediate product, wherein the intermediate product includes the slurry and the supporting skeleton material impregnated in the slurry; Step S4, spraying an aqueous solution of an initiator on the surface of the intermediate product in an atomized form, heating after standing, and obtaining a hydrogel dry film through polymerization and cross-linking reactions; Step S5, immersing the hydrogel dry film in a liquid electrolyte to obtain the hydrogel electrolyte.

15. The method for preparing a hydrogel electrolyte according to claim 14, characterized in that: In step S1, The molar ratio of the monomer of the synthetic high molecular polymer to the cross-linking agent is (125-500):1; The first solvent is a mixed solvent of deionized water and ethylene glycol, and the volume ratio of the deionized water to the ethylene glycol is (3-10):1; In the first solvent, the concentration of the monomer of the synthetic high molecular polymer is 0.05-0.2 g / mL.

16. The method for preparing a hydrogel electrolyte according to claim 15, characterized in that: In step S1, The molar ratio of the monomer of the synthetic high molecular polymer to the cross-linking agent is (200-250):1; The first solvent is a mixed solvent of deionized water and ethylene glycol, and the volume ratio of the deionized water to the ethylene glycol is (5-6):

1.

17. The method for preparing a hydrogel electrolyte according to claim 14, characterized in that: In step S2, The weight ratio of the starch to the second solvent is 1:(3-15); The heating and stirring time is 30-40 minutes, and the temperature is 65-90°C.

18. The method for preparing a hydrogel electrolyte according to claim 17, characterized in that: In step S2, The weight ratio of the starch to the second solvent is 1:(8-9); The temperature of the heating and stirring is 75-80°C.

19. The method for preparing a hydrogel electrolyte according to claim 14, characterized in that: In step S3, the mixing is performed at a temperature of 75-80° C., and the stirring time is 10-15 min; In step S4, in the aqueous solution of the initiator, the mass concentration of the initiator is 0.5-5 mg / mL, and the initiator is ammonium persulfate and / or potassium persulfate; In step S4, the standing time is 10-12 minutes, the heating temperature is 70-75° C., and the heating time is 1-1.5 hours.

20. The method for preparing a hydrogel electrolyte according to claim 14, characterized in that: The soaking time in step S5 is ≥ 1 h; The liquid electrolyte is an aqueous solution of zinc salt with a concentration of 1.0-3.0 mol / L; The zinc salt is selected from one or more of zinc sulfate, zinc acetate and zinc trifluoromethanesulfonate.

21. The method for preparing a hydrogel electrolyte according to claim 20, characterized in that: The liquid electrolyte is an aqueous solution of a zinc salt with a concentration of 1.8-2.0 mol / L; the zinc salt is zinc sulfate.

22. An aqueous zinc ion battery, comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, characterized in that: The electrolyte is the hydrogel electrolyte according to any one of claims 1 to 13.

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