Composite diaphragm for aqueous zinc ion battery and preparation method of composite diaphragm

Abstract

The invention discloses a composite diaphragm for a water-based zinc ion battery and a preparation method of the composite diaphragm, and belongs to the technical field of battery diaphragms.The composite diaphragm comprises a hydrophilic modified polymer diaphragm and a water-based diaphragm; the hydrophilic modified polymer diaphragm faces the negative electrode side of the water-based zinc ion battery, and the water-based diaphragm faces the positive electrode side of the water-based zinc ion battery; and the surface of the water-based diaphragm is coated with sodium alginate. The interfacial impedance of the hydrophilic modified polymer diaphragm is greatly reduced, the wettability and liquid retention capacity of the composite diaphragm are remarkably improved, and the interfacial polarization difference generated by compounding with a water-based diaphragm is shortened. The sodium alginate on the surface of the water-based diaphragm can improve the interface bonding force compounded with the polymer diaphragm and regulate and control the pores of the water-based diaphragm to obtain the composite diaphragm with a uniform pore structure, the energy efficiency of the battery can be improved by coating the sodium alginate, polar groups contained in the water-based diaphragm can be coordinated with zinc ions to form a protective layer, dendritic crystal puncture is avoided, and the service life of the battery is prolonged. The battery cycling stability is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of battery diaphragms, and specifically relates to a composite diaphragm for an aqueous zinc ion battery and a preparation method thereof. Background Art

[0002] With the development of human society and the urgent need for clean energy, people are forced to accelerate the construction of low-cost, environmentally friendly, and highly stable energy storage systems to meet the application in large-scale power grids. At present, high-energy-density lithium-ion batteries have achieved unprecedented development, but the limited reserves of lithium resources, high cost, uneven distribution, and unsafe organic electrolytes have restricted their further development.

[0003] As a new type of rechargeable battery technology, aqueous zinc-ion batteries have attracted widespread attention due to the intrinsic safety and economy of the materials they use. Compared with lithium-ion batteries using organic electrolytes, secondary aqueous zinc-ion batteries have the advantages of high cost-effectiveness, environmental friendliness, high reliability, low electrochemical potential, high theoretical mass specific capacity and volume specific capacity, and good stability of zinc in the environment.

[0004] Among them, the diaphragm is one of the key components in the battery system. It serves as a reservoir of electrolytes, mediates the transmission path of ions, and produces physical isolation, which can effectively prevent the battery from short circuiting during the charging and discharging process. The microstructure and physicochemical properties of the diaphragm have a significant impact on the electrochemical performance, service life and safety of aqueous zinc-ion batteries.

[0005] At present, common types of battery separators include glass fiber separators, polymer separators, etc. Glass fiber separators have strong hydrophilicity and liquid retention, and are suitable for aqueous zinc ion battery systems, but their mechanical properties are poor, and their porous structure is also prone to induce zinc dendrite growth; polymer separators have good mechanical properties and are not easily pierced by zinc dendrites to cause short circuits, but the poor hydrophilicity of polymer separators will directly affect the infiltration of electrolytes and the ion transport in the electrolyte. There are existing technologies that combine hydrophilic separators with hydrophobic separators by hot pressing or in-situ stacking, but the separators obtained by such a single composite often only enhance the mechanical strength, and the improvement of wettability and liquid retention is very limited.

[0006] Therefore, there is an urgent need to obtain a composite diaphragm that can greatly enhance the mechanical properties of the diaphragm while ensuring the liquid retention and wettability of the aqueous zinc ion battery diaphragm. Summary of the invention

[0007] The object of the present invention is to provide a composite diaphragm for aqueous zinc ion batteries and a preparation method thereof, so as to solve the problem that it is difficult to balance the liquid retention and mechanical properties of the diaphragm for batteries.

[0008] The purpose of the present invention can be achieved through the following technical solutions: In a first aspect, the present invention provides a composite diaphragm for an aqueous zinc ion battery, the composite diaphragm comprising a hydrophilically modified polymer diaphragm and an aqueous diaphragm; the hydrophilically modified polymer diaphragm faces the negative electrode side of the aqueous zinc ion battery, and the aqueous diaphragm faces the positive electrode side of the aqueous zinc ion battery; The surface of the water-based diaphragm is coated with sodium alginate.

[0009] Preferably, the amount of sodium alginate coated on the surface of the water-based diaphragm is 0.15 to 0.5 mg / cm 2 .

[0010] Preferably, the water-based membrane comprises any one of a glass fiber membrane, a cellulose membrane and a non-woven fabric membrane; the pore size of the water-based membrane is 1 to 5 μm, and the thickness is 100 to 600 μm.

[0011] By adopting the above technical scheme, since polymer membranes are generally weakly polar polymers with strong surface hydrophobicity, when applied to aqueous zinc batteries, the electrolyte of the aqueous zinc battery is difficult to fully infiltrate the microporous channels, which will increase the interfacial impedance and be unfavorable for dielectric ion transmission. A single composite hydrophilic aqueous membrane will cause severe polarization due to different polarities, making it difficult to solve this problem. Therefore, the composite of polymer membranes and aqueous membranes often only enhances the mechanical properties, and the effect of improving wettability and liquid retention is very limited.

[0012] Therefore, the present invention first performs hydrophilic modification on the polymer membrane. After the surface hydrophilic treatment, the affinity between the polymer membrane and the electrolyte is significantly improved, which can reduce the ion transmission resistance, improve the wettability of the membrane and enhance the liquid retention capacity of the membrane. At the same time, the hydrophilic groups introduced after the hydrophilic modification can fix zinc ions and homogenize the ion flow through electrostatic action, thereby inhibiting dendrite growth.

[0013] At the same time, in the composite membrane of the present invention, a polymer membrane is arranged to face the negative electrode side of the zinc ion battery, and an aqueous membrane is arranged to face the positive electrode side of the zinc ion battery, which can effectively prevent the zinc ions in the negative electrode of the zinc ion battery, i.e., zinc metal, from being induced by the aqueous membrane to form dendrites during the charge and discharge process, thereby preventing zinc dendrites from piercing the composite membrane and causing a short circuit.

[0014] However, during the composite process of hydrophilic modified polymer membranes and aqueous membranes, due to the large difference in polarity between the polymer membranes and the aqueous membranes, even after the hydrophilic modification of the polymer membranes, the retained hydrophobic groups will lead to weak interface bonding during the composite process of the two, and the membrane separation and other phenomena are prone to occur during the battery cycle, affecting the performance of the zinc battery. In addition, since polymer membranes have a smaller pore structure and aqueous membranes have a larger pore structure, the composite membrane obtained after the composite of the two may have a non-uniform pore distribution, resulting in differences in local electrolyte wettability and reduced long-term stability.

[0015] In order to solve this problem, the surface of the aqueous membrane of the present invention is also coated with sodium alginate. The polar groups contained in sodium alginate can give the aqueous membrane strong hydrophilicity and ion anchoring ability. As a binder, it can strengthen the binding force between the hydrophilic modified polymer membrane and the aqueous membrane through hydrogen bonds and van der Waals forces; it can also regulate the pore structure of the aqueous membrane so that the obtained composite membrane maintains a uniform flux of zinc ions during the battery cycle.

[0016] And after the surface of the aqueous diaphragm is coated with sodium alginate, on the one hand, the sodium ions in sodium alginate can enhance the ion concentration in the electrolyte of the aqueous zinc ion battery, improve the overall ionic conductivity of the electrolyte, and thus significantly improve the energy efficiency of the battery; on the other hand, the polar groups contained in sodium alginate, including carboxyl groups, can react with zinc ions to form a zinc salt protective film on the surface of the aqueous diaphragm, preventing water from directly contacting the negative electrode, inhibiting the corrosion and hydrogen evolution reaction of the zinc negative electrode, and enhancing the cycle stability of the aqueous zinc ion battery. Moreover, sodium alginate has a lower swelling rate than other modified additives, and can be used as an electrolyte additive even if it is dissolved in the electrolyte to improve the coulomb efficiency.

[0017] The composite diaphragm obtained by combining a hydrophilically modified polymer diaphragm with an aqueous diaphragm coated with sodium alginate on the surface solves the problem of poor wettability of a single composite of traditional diaphragms, and cooperates with sodium alginate to form a water-retaining network, thereby improving the water retention of the composite diaphragm. At the same time, it adjusts the pore structure of the composite diaphragm to block dendrite penetration, and the formed ion transmission channels are also evenly distributed. Under the bonding effect of sodium alginate, the interfacial bonding force of the composite diaphragm is also significantly enhanced, preventing the separation of the composite diaphragm during the circulation process, and can also effectively improve the mechanical properties of the composite diaphragm.

[0018] Preferably, the hydrophilically modified polymer membrane is prepared according to the following method: Acid washing: immersing the polymer membrane in a dilute acid solution with a mass fraction of 1 to 5%, ultrasonically treating for 30 to 60 minutes, washing and drying to obtain a pretreated polymer membrane; Hydrophilic modification: the pretreated polymer membrane is transferred to a hydrophilic modification solution, the pH value of the solution is adjusted to 5-6, and the hydrophilic modified polymer membrane is obtained after immersion treatment for 2-4 hours.

[0019] Preferably, the hydrophilic modification liquid comprises the following raw materials in parts by weight: 0.05-0.5 parts of foaming agent; 5-20 parts of hydrophilic modifier; 0.5-2 parts of pH regulator; 90 to 180 parts of solvent.

[0020] Preferably, the hydrophilic modifier includes a combination of one or more of polyurethane, polyacrylate and methyl allyl alcohol polyoxyethylene ether.

[0021] Preferably, the polymer membrane includes any one of a polyethylene membrane, a polypropylene membrane, a polyacrylonitrile membrane, a polyimide membrane, a polytetrafluoroethylene membrane, a polyvinylidene fluoride membrane and a polycarbonate membrane; the pore size of the polymer membrane is 30 to 200 nm, and the thickness is 5 to 25 μm.

[0022] Preferably, the dilute acid solution includes any one of a dilute sulfuric acid aqueous solution, a dilute hydrochloric acid aqueous solution and a dilute nitric acid aqueous solution.

[0023] Preferably, the foaming agent includes one or a combination of polyethylene glycol ether foaming agent and fatty alcohol polyoxyethylene ether foaming agent.

[0024] Preferably, the pH adjuster includes any one of acetic acid and citric acid.

[0025] Preferably, the solvent includes any one of acetone, ethyl acetate, benzene, toluene, ethylene dichloride and dimethylformamide.

[0026] By adopting the above technical scheme, during the hydrophilic treatment process, the polymer membrane is first pickled, and in a dilute acid solution, ultrasonic cleaning can induce a certain degree of oxidation reaction on the surface of the polymer membrane, generating a portion of polar groups such as carboxyl or carbonyl groups on the surface of the polymer membrane, thereby enhancing the bonding force between the polymer membrane and the hydrophilic modifier, and chemical grafting is performed by forming a strong hydrogen bond with the hydrophilic modifier; at the same time, the surface of the polymer membrane will be slightly etched during the pickling process, increasing the roughness of the membrane, providing conditions for the physical embedding of the hydrophilic modifier.

[0027] The pretreated polymer membrane obtained after pickling is immersed in a hydrophilic modification liquid. The foaming agent in the hydrophilic modification liquid can reduce the surface tension of the pretreated polymer membrane, improve the wettability of the hydrophilic modifier, and enable the hydrophilic modifier to be better spread on the surface of the pretreated polymer membrane. In addition, the present invention selects polymer modifiers such as polyurethane, polyacrylic acid and methyl allyl alcohol polyoxyethylene ether for hydrophilic modification. Compared with other hydrophilic modification methods, the polymer modifier can form a stable hydrophilic layer on the surface of the polymer membrane, avoiding the problem of easy detachment in the physical adsorption method. At the same time, it can also help improve the affinity between the membrane and zinc ions, regulate the solvation structure of zinc ions through coordination, form a uniform ion transmission channel, eliminate interface concentration polarization, and inhibit dendrite growth. Moreover, after being treated with the polymer modifier, the mechanical strength is also improved, the thermal stability is enhanced, and a hydrophilic modified polymer membrane with a stable structure is obtained.

[0028] After hydrophilic modification, the contact angle of the membrane surface can be reduced, the interfacial impedance can be reduced, the wettability of the composite membrane can be improved, the electrolyte can quickly penetrate the micropores, the interfacial polarization can be reduced, and it can help establish a uniform and continuous ion transmission channel, which is conducive to further composite with the aqueous membrane.

[0029] Preferably, the hydrophilic modification liquid further comprises 3 to 8 parts by weight of a cross-linking agent; the cross-linking agent comprises a combination of one or more of glutaraldehyde, succinaldehyde and glyoxal.

[0030] By adopting the above technical scheme, a cross-linking agent is also added to the hydrophilic modification liquid. The cross-linking agent of the present invention is mainly a dialdehyde structure compound, and both ends of the molecule contain active aldehyde groups, which can help form chemical grafting between the hydrophilic modifier and the polymer membrane after acid washing, and enhance the interfacial bonding force between the hydrophilic polymer and the hydrophobic polymer membrane. The hydroxyl groups contained on the surface of the polymer membrane after acid washing can condense with the cross-linking agent to form ether bonds, realize chemical anchoring, and form a three-dimensional cross-linked network to reinforce the formed hydrophilic modification layer.

[0031] At the same time, the addition of the cross-linking agent only participates in the cross-linking reaction at the interface, which will not affect the hydrophilic modification effect, can maintain good hydrophilicity, and can also help form a dense network between the hydrophilic modified polymer membrane and the sodium alginate on the surface of the water system membrane, thereby increasing the interfacial force between the composite membranes, and also increasing the puncture resistance, effectively preventing dendrite penetration.

[0032] Preferably, a strong oxidant with a mass fraction of 0.5-2% is also added to the dilute acid solution; the strong oxidant includes a combination of one or more of chlorine dioxide, hydrogen peroxide, sodium hypochlorite and sodium chlorite.

[0033] By adopting the above technical solution, a strong oxidant can also be added to the dilute acid solution for pickling. The oxidizing effect of dilute acid on polymer membranes is limited. Adding a strong oxidant during the pickling process can increase the active sites on the membrane surface. The strong oxidant can introduce oxygen-containing functional groups on the membrane surface through oxidation reactions, thereby increasing the surface polarity.

[0034] Strong oxidizing properties can also cooperate with dilute acid compounds to corrode the surface of polymer membranes, forming micropores or lattice defects, thereby enhancing the specific surface area and active site density of the polymer membrane surface, which is beneficial to the further grafting and compounding of hydrophilic modifiers and enhancing the hydrophilic modification process.

[0035] In a second aspect, the present invention provides a method for preparing a composite diaphragm for an aqueous zinc ion battery, comprising the following process steps: S1. dissolving sodium alginate in water to prepare a sodium alginate solution with a mass fraction of 1 to 5%, and then coating the sodium alginate solution on both sides of the water system diaphragm; S2. The hydrophilic modified polymer membrane is preheated and pressed at 60 to 80°C for 5 to 30 minutes; S3. The pre-heat-pressed hydrophilic modified polymer diaphragm and the aqueous diaphragm coated with sodium alginate are composited, and hot-pressed for 5 to 10 minutes at 100 to 150° C. and 2 to 10 MPa to obtain a composite diaphragm for an aqueous zinc ion battery.

[0036] By adopting the above technical scheme, sodium alginate is configured into an aqueous solution and then coated on both sides of the aqueous diaphragm to form a layer of sodium alginate on the surface of the aqueous diaphragm, which can not only improve the interfacial bonding force with the hydrophilic modified polymer diaphragm, but also improve the overall ionic conductivity of the electrolyte, and form a coordination with zinc ions. The formed zinc salt protective layer can effectively inhibit dendrite penetration and reduce the corrosion of the zinc negative electrode to the aqueous diaphragm.

[0037] The hydrophilic modified polymer diaphragm is first preheated and pressed to volatilize the solvent contained therein, thereby reducing the adverse effects of the solvent on the composite process. The resulting composite diaphragm not only has good mechanical properties, but also has excellent wettability and liquid retention, meeting the increasingly stringent requirements of aqueous zinc-ion batteries for diaphragms.

[0038] Beneficial effects of the present invention: 1. The composite membrane of the present invention is a composite of a hydrophilically modified polymer membrane and an aqueous membrane. The polymer membrane is first subjected to a hydrophilic modification treatment, which can greatly reduce the interface impedance and ion transmission resistance, improve the wettability and liquid retention capacity of the polymer membrane, and the introduced hydrophilic groups can homogenize the ion flow and inhibit dendrite growth; at the same time, the introduction of hydrophilic chain segments can also reduce the interface polarization difference between the aqueous membrane and the aqueous membrane, thereby enhancing the composite effect.

[0039] 2. The surface of the water-based diaphragm in the composite diaphragm of the present invention is also coated with sodium alginate. The introduction of sodium alginate can significantly improve the interfacial bonding force between the water-based diaphragm and the polymer-based diaphragm, reduce the separation risk of the composite diaphragm, and regulate the pore structure of the water-based diaphragm so that the obtained composite diaphragm has a uniform pore distribution, improves the electrolyte wettability, and increases long-term stability. The sodium ions in sodium alginate can also increase the ion concentration in the electrolyte and improve the energy efficiency of the battery; the polar groups can react with zinc ions to form a zinc salt protective film to avoid dendrite puncture, and also inhibit the corrosion of the zinc negative electrode to the diaphragm and the hydrogen evolution reaction, thereby enhancing the cycle stability of the water-based zinc ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The present invention will be further described below in conjunction with the accompanying drawings.

[0041] Figure 1 This is the dQ / dV curve of Example 1 in the performance test (1) of the present invention.

[0042] Figure 2 This is the dQ / dV curve of comparative example 5 in the performance test (1) of the present invention.

[0043] Figure 3.1 The composite diaphragm for aqueous zinc ion batteries obtained in Example 1 of the present invention, Figure 3.2 The aqueous zinc ion battery separator obtained in Comparative Example 4 is Figure 3.3 This is a schematic diagram of the composite diaphragm for aqueous zinc ion batteries of Comparative Example 2 that has not been hydrophilically treated. DETAILED DESCRIPTION

[0044] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0045] Preparation Example

[0046] Preparation Example 1: A hydrophilically modified polymer membrane is prepared according to the following method: Acid washing: a polypropylene membrane (average pore size of 100 nm, average thickness of 14 μm) was immersed in a 3% by mass dilute sulfuric acid solution, ultrasonically treated for 30 min, and washed and dried to obtain a pretreated polymer membrane; Hydrophilic modification: The pretreated polymer membrane is transferred into a hydrophilic modification solution, the pH value of the solution is adjusted to 6, and the hydrophilic modified polymer membrane is obtained after immersion treatment for 3 hours.

[0047] The hydrophilic modified liquid was prepared by the following method: 12 g of polyacrylate was added to 140 g of acetone, and after stirring and dissolving, 0.2 g of polyethylene glycol ether foaming agent was added, and acetic acid was added to adjust the pH value of the solution to 6 to obtain the hydrophilic modified liquid.

[0048] Preparation Example 2, a hydrophilic modified polymer membrane, is different from Preparation Example 1 only in that an equal amount of polyimide membrane (average pore size of 100 nm, average thickness of 20 μm) is used to replace the polypropylene membrane.

[0049] Preparation Example 3, a hydrophilically modified polymer membrane, is different from Preparation Example 1 only in that an equal amount of methyl allyl alcohol polyoxyethylene ether is used to replace polyacrylate.

[0050] Preparation Example 4, a hydrophilically modified polymer membrane, is different from Preparation Example 1 only in that an equal amount of polyurethane is used to replace polyacrylate.

[0051] Preparation Example 5 and Preparation Example 6 are hydrophilically modified polymer membranes. The only difference from Preparation Example 1 is that the raw material composition ratio of the hydrophilic modification liquid is adjusted, as shown in Table 1: Table 1 Hydrophilic modified liquid formula

[0052] The pH values ​​of the hydrophilic modified solutions obtained in Preparation Examples 5 and 6 were both adjusted to 6 using acetic acid.

[0053] Preparation Example 7, a hydrophilic modified polymer membrane, is different from Preparation Example 1 only in that, during the preparation of the hydrophilic modified liquid, 6 g of glutaraldehyde is added together with the polyethylene glycol ether foaming agent.

[0054] Preparation Example 8, a hydrophilically modified polymer membrane, is different from Preparation Example 7 only in that the amount of glutaraldehyde added is 1 g.

[0055] Preparation Example 9, a hydrophilically modified polymer membrane, is different from Preparation Example 7 only in that the amount of glutaraldehyde added is 10 g.

[0056] Preparation Example 10, a hydrophilic modified polymer membrane, is different from Preparation Example 1 only in that 1% by mass of sodium hypochlorite is added to the 3% by mass dilute sulfuric acid solution.

[0057] Preparation Example 11, a hydrophilic modified polymer membrane is prepared according to the following method: A polypropylene membrane (average pore size of 100 nm, average thickness of 14 μm) was placed in a hydrophilic modification solution, the pH value of the solution was adjusted to 6, and the hydrophilic modified polymer membrane was obtained after immersion treatment for 3 hours.

[0058] The hydrophilic modified liquid was prepared by the following method: 12 g of polyacrylate was added to 140 g of acetone, and after stirring and dissolving, 0.2 g of polyethylene glycol ether foaming agent was added, and acetic acid was added to adjust the pH value of the solution to 6 to obtain the hydrophilic modified liquid.

[0059] Preparation Example 12, a hydrophilic modified polymer membrane is prepared according to the following method: A polypropylene membrane (average pore size of 100 nm, average thickness of 14 μm) was immersed in a 3% by mass dilute sulfuric acid solution, ultrasonically treated for 30 minutes, and washed and dried to obtain a hydrophilic modified polymer membrane.

[0060] Preparation Example 13, a hydrophilic modified polymer membrane, is different from Preparation Example 1 only in that an equal amount of polypropylene membranes with an average pore size of 30 nm and an average thickness of 5 μm are used to replace the polypropylene membranes with an average pore size of 100 nm and an average thickness of 14 μm.

[0061] Preparation Example 14, a hydrophilic modified polymer membrane, is different from Preparation Example 1 only in that an equal amount of polypropylene membranes with an average pore size of 200 nm and an average thickness of 25 μm are used to replace the polypropylene membranes with an average pore size of 100 nm and an average thickness of 14 μm.

[0062] Example

[0063] Example 1, a composite diaphragm for an aqueous zinc ion battery, is prepared according to the following process steps: S1. Sodium alginate was dissolved in water to prepare a sodium alginate solution with a mass fraction of 3%. The sodium alginate solution was then coated on both sides of the glass fiber diaphragm (average pore size 2.76 μm, average thickness 350 μm). The sodium alginate coating amount on each side was 0.3 mg / cm 2 ; S2. The hydrophilic modified polymer membrane prepared in Preparation Example 1 was preheated and pressed at 60° C. for 10 min; S3. The hydrophilic modified polymer separator after the preheating and pressing treatment is composited with the glass fiber separator coated with sodium alginate, and hot-pressed at 120° C. and 6 MPa for 5 min to obtain a composite separator for aqueous zinc ion batteries.

[0064] Example 2, a composite separator for an aqueous zinc ion battery, differs from Example 1 only in that an equal amount of cellulose separator (average pore size of 3 μm, average thickness of 250 μm) is used to replace the glass fiber separator.

[0065] Example 3, a composite diaphragm for aqueous zinc ion batteries, differs from Example 1 only in that the coating amount of sodium alginate on each side is 0.15 mg / cm 2 .

[0066] Example 4, a composite diaphragm for aqueous zinc ion batteries, differs from Example 1 only in that the coating amount of sodium alginate on each side is 0.5 mg / cm 2 .

[0067] Example 5, a composite diaphragm for an aqueous zinc ion battery, differs from Example 1 only in that an equal amount of the hydrophilic modified polymer diaphragm prepared in Preparation Example 2 is used to replace the hydrophilic modified polymer diaphragm prepared in Preparation Example 1.

[0068] Example 6, a composite diaphragm for an aqueous zinc ion battery, differs from Example 1 only in that an equal amount of the hydrophilic modified polymer diaphragm prepared in Preparation Example 3 is used to replace the hydrophilic modified polymer diaphragm prepared in Preparation Example 1.

[0069] Example 7, a composite diaphragm for an aqueous zinc ion battery, differs from Example 1 only in that an equal amount of the hydrophilic modified polymer diaphragm prepared in Preparation Example 4 is used to replace the hydrophilic modified polymer diaphragm prepared in Preparation Example 1.

[0070] Example 8, a composite diaphragm for an aqueous zinc ion battery, differs from Example 1 only in that an equal amount of the hydrophilic modified polymer diaphragm prepared in Preparation Example 5 is used to replace the hydrophilic modified polymer diaphragm prepared in Preparation Example 1.

[0071] Example 9, a composite diaphragm for an aqueous zinc ion battery, differs from Example 1 only in that an equal amount of the hydrophilic modified polymer diaphragm prepared in Preparation Example 6 is used to replace the hydrophilic modified polymer diaphragm prepared in Preparation Example 1.

[0072] Example 10, a composite diaphragm for an aqueous zinc ion battery, differs from Example 1 only in that the coating amount of sodium alginate on each side is 0.05 mg / cm 2 .

[0073] Example 11, a composite diaphragm for aqueous zinc ion batteries, differs from Example 1 only in that the coating amount of sodium alginate on each side is 0.7 mg / cm 2 .

[0074] Example 12, a composite diaphragm for an aqueous zinc ion battery, differs from Example 1 only in that an equal amount of the hydrophilic modified polymer diaphragm prepared in Preparation Example 7 is used to replace the hydrophilic modified polymer diaphragm prepared in Preparation Example 1.

[0075] Example 13, a composite diaphragm for an aqueous zinc ion battery, differs from Example 1 only in that an equal amount of the hydrophilic modified polymer diaphragm prepared in Preparation Example 8 is used to replace the hydrophilic modified polymer diaphragm prepared in Preparation Example 1.

[0076] Example 14, a composite diaphragm for an aqueous zinc ion battery, differs from Example 1 only in that an equal amount of the hydrophilic modified polymer diaphragm prepared in Preparation Example 9 is used to replace the hydrophilic modified polymer diaphragm prepared in Preparation Example 1.

[0077] Example 15, a composite diaphragm for an aqueous zinc ion battery, differs from Example 1 only in that an equal amount of the hydrophilic modified polymer diaphragm prepared in Preparation Example 10 is used to replace the hydrophilic modified polymer diaphragm prepared in Preparation Example 1.

[0078] Example 16, a composite diaphragm for an aqueous zinc ion battery, differs from Example 1 only in that an equal amount of the hydrophilic modified polymer diaphragm prepared in Preparation Example 11 is used to replace the hydrophilic modified polymer diaphragm prepared in Preparation Example 1.

[0079] Example 17, a composite diaphragm for an aqueous zinc ion battery, differs from Example 1 only in that an equal amount of the hydrophilic modified polymer diaphragm prepared in Preparation Example 12 is used to replace the hydrophilic modified polymer diaphragm prepared in Preparation Example 1.

[0080] Example 18, a composite diaphragm for an aqueous zinc ion battery, differs from Example 1 only in that an equal amount of the hydrophilic modified polymer diaphragm prepared in Preparation Example 13 is used to replace the hydrophilic modified polymer diaphragm prepared in Preparation Example 1.

[0081] Example 19, a composite diaphragm for an aqueous zinc ion battery, differs from Example 1 only in that an equal amount of the hydrophilic modified polymer diaphragm prepared in Preparation Example 14 is used to replace the hydrophilic modified polymer diaphragm prepared in Preparation Example 1.

[0082] Example 20, a composite diaphragm for an aqueous zinc ion battery, differs from Example 1 only in that a glass fiber diaphragm with an average pore size of 2.76 μm and an average thickness of 350 μm is replaced by an equal amount of glass fiber diaphragms with an average pore size of 1 μm and an average thickness of 100 μm.

[0083] Example 21, a composite diaphragm for an aqueous zinc ion battery, differs from Example 1 only in that a glass fiber diaphragm having an average pore size of 2.76 μm and an average thickness of 350 μm is replaced by an equal amount of glass fiber diaphragms having an average pore size of 5 μm and an average thickness of 600 μm.

[0084] Comparative Example

[0085] Comparative Example 1, a composite diaphragm for an aqueous zinc ion battery, is prepared according to the following process steps: S1. The hydrophilic modified polymer membrane prepared in Preparation Example 1 was preheated and pressed at 60° C. for 10 min; S2. The hydrophilic modified polymer diaphragm and the glass fiber diaphragm (average pore size of 2.76 μm and average thickness of 350 μm) after the preheating and pressing treatment are composited and hot-pressed at 120°C and 6 MPa for 5 minutes to obtain a composite diaphragm for aqueous zinc ion batteries.

[0086] Comparative Example 2, a composite diaphragm for an aqueous zinc ion battery, differs from Example 1 only in that an equal amount of a polypropylene diaphragm (average pore size of 100 nm, average thickness of 20 μm) is used to replace the hydrophilic modified polymer diaphragm prepared in Preparation Example 1.

[0087] Comparative Example 3, a composite diaphragm for an aqueous zinc ion battery, is prepared according to the following process steps: A polypropylene separator (average pore size of 100 nm, average thickness of 14 μm) and a glass fiber separator (average pore size of 2.76 μm, average thickness of 350 μm) were compounded and hot pressed at 120°C and 6 MPa for 5 min to obtain a composite separator for aqueous zinc ion batteries.

[0088] Comparative Example 4, a separator for an aqueous zinc ion battery, adopts a glass fiber separator with an average pore size of 2.76 μm and an average thickness of 350 μm.

[0089] Comparative Example 5, a separator for an aqueous zinc ion battery, adopts a cellulose separator with an average pore size of 3 μm and an average thickness of 250 μm.

[0090] Comparative Example 6, a separator for an aqueous zinc ion battery, using the hydrophilic modified polymer separator prepared in Preparation Example 1.

[0091] Performance testing

[0092] Sample preparation: Vanadium dioxide is used as the positive electrode of the battery, metallic zinc is used as the negative electrode of the battery, and the diaphragm adopts the diaphragm for aqueous zinc ion batteries obtained in the embodiments and comparative examples, wherein the hydrophilic modified polymer diaphragm faces the negative electrode side of the aqueous zinc ion battery, and the aqueous diaphragm faces the positive electrode side of the aqueous zinc ion battery. The button-type aqueous zinc battery is assembled as a sample.

[0093] Performance Test: After the sample battery was assembled, it was left to stand for 12 hours and activated by cycling 10 times at a rate of 0.5C, with an activation voltage of 0.3-1.7V; then it was cycled for a long time at a rate of 3C, with a cycle voltage of 0.3-1.7V. The following tests were performed: (1) During the cycle, the ratio of the micro-capacity to the micro-voltage (dQ / dV) of the sample batteries of Example 1 and Comparative Example 5 is used to characterize the redox process during the charge and discharge process. The test results are as follows: Figure 1 and Figure 2 As shown; (2) The specific capacity decay rate of the battery after 500 cycles is used to characterize the battery's cycle performance: , The test results are shown in Table 2: Table 2 Cycle performance test results

[0094] According to Table 2, and Figure 1 and Figure 2 Combining Example 1 and Comparative Example 5, it can be seen that the specific capacity of Comparative Example 1 is significantly reduced compared with Example 1 after a long cycle, indicating that the composite membrane obtained by compounding the hydrophilic modified polymer membrane with the cellulose membrane has greatly improved cycle stability compared with the cellulose membrane, and the service life of the battery is significantly increased. Figure 1 and Figure 2 It can also be seen from the comparison that Figure 2 There are a lot of extra peaks and tails in the graph, indicating that a lot of side reactions occur during the cycle, which will directly affect the performance of the battery.

[0095] according to Figure 3.1 , Figure 3.2 and Figure 3.3 It can be seen that the composite membrane for aqueous zinc ion battery obtained in Example 1 has good liquid retention and mechanical properties. The glass fiber membrane in Comparative Example 4 has good liquid retention, but the membrane is easily wrinkled and damaged, and has poor mechanical strength. The composite membrane for aqueous zinc ion battery in Comparative Example 2, in which the polymer membrane has not been hydrophilically modified, Figure 3.3 It can be seen that the mechanical properties of the diaphragm are good, but on one side of the polymer diaphragm, the hydrophilicity is extremely poor, the wettability and liquid retention of the diaphragm are poor, and it is difficult to meet the needs of aqueous zinc-ion batteries.

[0096] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0097] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A composite diaphragm for an aqueous zinc ion battery, characterized in that: The composite membrane comprises a hydrophilic modified polymer membrane and an aqueous membrane; the hydrophilic modified polymer membrane faces the negative electrode side of the aqueous zinc ion battery, and the aqueous membrane faces the positive electrode side of the aqueous zinc ion battery; The surface of the water system diaphragm is coated with sodium alginate.

2. The composite diaphragm for aqueous zinc ion batteries according to claim 1, characterized in that The amount of sodium alginate coated on the surface of the water-based diaphragm is 0.15-0.5 mg / cm 2 .

3. The composite diaphragm for aqueous zinc ion batteries according to claim 1, characterized in that The water system membrane comprises any one of a glass fiber membrane, a cellulose membrane and a non-woven fabric membrane; the pore size of the water system membrane is 1 to 5 μm, and the thickness is 100 to 600 μm.

4. The composite diaphragm for aqueous zinc ion batteries according to claim 1, characterized in that: The hydrophilic modified polymer membrane is prepared according to the following method: Acid washing: immersing the polymer membrane in a dilute acid solution with a mass fraction of 1 to 5%, ultrasonically treating for 30 to 60 minutes, washing and drying to obtain a pretreated polymer membrane; the dilute acid solution includes any one of a dilute sulfuric acid aqueous solution, a dilute hydrochloric acid aqueous solution and a dilute nitric acid aqueous solution; Hydrophilic modification: the pretreated polymer membrane is transferred to a hydrophilic modification solution, the pH value of the solution is adjusted to 5-6, and the hydrophilic modified polymer membrane is obtained after immersion treatment for 2-4 hours.

5. The composite diaphragm for aqueous zinc ion batteries according to claim 4, characterized in that: The hydrophilic modification liquid comprises the following raw materials in parts by weight: 0.05-0.5 parts of foaming agent; 5-20 parts of hydrophilic modifier; 0.5-2 parts of pH regulator; 90-180 parts of solvent; The foaming agent comprises one or a combination of polyethylene glycol ether foaming agent and fatty alcohol polyoxyethylene ether foaming agent; The solvent includes any one of acetone, ethyl acetate, benzene, toluene, ethylene dichloride and dimethylformamide.

6. The composite diaphragm for aqueous zinc ion batteries according to claim 5, characterized in that: The hydrophilic modifier includes one or more combinations of polyurethane, polyacrylate and methyl allyl alcohol polyoxyethylene ether.

7. The composite diaphragm for aqueous zinc ion batteries according to claim 5, characterized in that: The hydrophilic modification liquid also includes 3 to 8 parts by weight of a cross-linking agent; the cross-linking agent includes a combination of one or more of glutaraldehyde, succinaldehyde and glyoxal.

8. The composite diaphragm for aqueous zinc ion batteries according to claim 4, characterized in that: A strong oxidant with a mass fraction of 0.5-2% is also added to the dilute acid solution; the strong oxidant includes a combination of one or more of chlorine dioxide, hydrogen peroxide, sodium hypochlorite and sodium chlorite.

9. The composite diaphragm for aqueous zinc ion batteries according to claim 4, characterized in that: The polymer membrane includes any one of a polyethylene membrane, a polypropylene membrane, a polyacrylonitrile membrane, a polyimide membrane, a polytetrafluoroethylene membrane, a polyvinylidene fluoride membrane and a polycarbonate membrane; the polymer membrane has a pore size of 30 to 200 nm and a thickness of 5 to 25 μm.

10. A method for preparing a composite diaphragm for an aqueous zinc ion battery according to any one of claims 1 to 9, characterized in that: The process includes the following steps: S1. dissolving sodium alginate in water to prepare a sodium alginate solution with a mass fraction of 1 to 5%, and then coating the sodium alginate solution on both sides of the water system diaphragm; S2. The hydrophilic modified polymer membrane is preheated and pressed at 60 to 80°C for 5 to 30 minutes; S3. The pre-heat-pressed hydrophilic modified polymer diaphragm and the aqueous diaphragm coated with sodium alginate are composited, and hot-pressed for 5 to 10 minutes at 100 to 150° C. and 2 to 10 MPa to obtain a composite diaphragm for an aqueous zinc ion battery.

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