A composite separator for aqueous zinc-ion batteries and its preparation method

Abstract

The present invention discloses a composite separator for aqueous zinc-ion batteries and a preparation method thereof, belonging to the technical field of battery separators. The composite separator includes a hydrophilic modified polymer separator and an aqueous separator; the hydrophilic modified polymer separator faces the negative electrode side of the aqueous zinc-ion battery, and the aqueous separator faces the positive electrode side of the aqueous zinc-ion battery; sodium alginate is coated on the surface of the aqueous separator. After hydrophilic modification, the interfacial impedance of the polymer separator is greatly reduced, significantly improving the wettability and liquid retention ability of the composite separator, and shortening the interfacial polarization difference generated by the composite with the aqueous separator. Sodium alginate on the surface of the aqueous separator can improve the interfacial bonding force with the polymer separator, regulate the pores of the aqueous separator, and obtain a composite separator with a uniform pore structure. Moreover, the coating of sodium alginate can also improve the energy efficiency of the battery. The polar groups contained can coordinate with zinc ions to form a protective layer, avoid dendrite piercing, and improve the cycle stability of the battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery separators, and particularly relates to a composite separator for aqueous zinc-ion batteries and a preparation method thereof. Background Art

[0002] With the development of human society and the urgent demand for clean energy, people are forced to continuously accelerate the construction of low-cost, environmentally friendly, and highly stable energy storage systems to meet their applications in large-scale grid power. Currently, high-energy-density lithium-ion batteries have seen unprecedented development. However, the limited reserves of lithium resources, high costs, uneven distribution, and the insecurity of organic electrolyte systems have restricted their further development.

[0003] As a new type of rechargeable battery technology, aqueous zinc-ion batteries have received extensive attention due to the intrinsic safety and economy of the materials used. 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 separator is one of the key components in the battery system. As a reservoir for electrolytes and a mediator for ion transport paths, and providing physical isolation, it can effectively prevent the battery from short-circuiting during charge and discharge. The microstructure and physicochemical properties of the separator have a significant impact on the electrochemical performance, service life, and safety of aqueous zinc-ion batteries.

[0005] Currently, common types of battery separators include glass fiber separators, polymer separators, etc. Glass fiber separators have strong hydrophilicity and liquid retention, which are suitable for aqueous zinc-ion battery systems. However, they have poor mechanical properties, and their porous structure is also prone to inducing the growth of zinc dendrites. Polymer separators have good mechanical properties and are not easily pierced by zinc dendrites to cause short circuits. However, polymer separators have poor hydrophilicity, which will directly affect the infiltration of electrolytes and the ion transport in electrolytes. Existing technologies have compounded hydrophilic separators and hydrophobic separators through hot pressing or in-situ stacking, but the separators obtained by such single compounding 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 separator that can greatly enhance the mechanical properties of the separator while ensuring the liquid retention and wettability of the separator for aqueous zinc-ion batteries. Summary of the Invention

[0007] The purpose of the present invention is to provide a composite separator for aqueous zinc-ion batteries and a preparation method thereof to solve the problem that it is difficult to balance the liquid retention and mechanical properties of the battery separator.

[0008] The object of the present invention can be achieved by the following technical solutions:

[0009] In a first aspect, the present invention provides a composite separator for an aqueous zinc-ion battery, which includes a hydrophilic modified polymer separator and an aqueous separator; the hydrophilic modified polymer separator faces the negative electrode side of the aqueous zinc-ion battery, and the aqueous separator faces the positive electrode side of the aqueous zinc-ion battery;

[0010] The surface of the aqueous separator is coated with sodium alginate.

[0011] Preferably, the coating amount of sodium alginate coated on the surface of the aqueous separator is 0.15 - 0.5 mg / cm 2 .

[0012] Preferably, the aqueous separator includes any one of a glass fiber separator, a cellulose separator, and a non-woven fabric separator; the pore size of the aqueous separator is 1 - 5 μm, and the thickness is 100 - 600 μm.

[0013] By adopting the above technical solutions, since polymer separators are generally weakly polar polymers with strong surface hydrophobicity, during the application 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 is not conducive to the transport of dielectric ions. And a single composite hydrophilic aqueous separator will cause serious polarization due to different polarities and it is difficult to solve this problem. Therefore, after the polymer separator and the aqueous separator are combined, only the mechanical properties are enhanced, and the improvement effect on wettability and liquid retention is very limited.

[0014] Therefore, the present invention first performs hydrophilic modification on the polymer separator. After the surface hydrophilic treatment, the affinity between the polymer separator and the electrolyte is significantly improved, which can reduce the ion transport resistance, improve the wettability of the separator and enhance the liquid retention ability of the separator at the same time. Meanwhile, the hydrophilic groups introduced after hydrophilic modification can fix zinc ions through electrostatic interaction and homogenize the ion flow, inhibiting dendrite growth.

[0015] At the same time, in the composite separator of the present invention, the polymer separator is arranged to face the negative electrode side of the zinc-ion battery, and the aqueous separator is arranged to face the positive electrode side of the zinc-ion battery, which can effectively prevent zinc ions from being induced by the aqueous separator to form dendrites during the charge and discharge process of the negative electrode of the zinc-ion battery, that is, zinc metal, and avoid the zinc dendrites piercing the composite separator to cause a short circuit.

[0016] However, during the composite process of hydrophilic modified polymer separators and aqueous separators, due to the large polarity difference between polymer separators and aqueous separators, even after the hydrophilic modification of polymer separators, the remaining hydrophobic groups will result in weak interfacial bonding force during the composite process of the two, and phenomena such as separator separation are likely to occur during the battery cycle, affecting the performance of zinc batteries. And because polymer separators have a smaller pore size structure and aqueous separators have a larger pore size structure, the composite separator obtained after the two are combined may have non-uniform pore distribution, resulting in differences in local electrolyte wettability and a decrease in long-term stability.

[0017] To solve this problem, sodium alginate is also coated on the surface of the aqueous separator of the present invention. The polar groups contained in sodium alginate can endow the aqueous separator with strong hydrophilicity and ion anchoring ability. As a binder, it can strengthen the bonding force between the hydrophilic modified polymer separator and the aqueous separator through hydrogen bonds and van der Waals forces; it can also regulate the pore structure of the aqueous separator so that the obtained composite separator can maintain a uniform zinc ion flux during the battery cycle.

[0018] And after the surface of the aqueous separator is coated with sodium alginate, on the one hand, the sodium ions in sodium alginate can increase the ion concentration in the electrolyte of the aqueous zinc ion battery and improve the overall ionic conductivity of the electrolyte, thereby significantly improving the energy efficiency of the battery; on the other hand, the polar groups contained in sodium alginate include carboxyl groups, which can undergo a coordination reaction with zinc ions, thereby forming a zinc salt protective film on the surface of the aqueous separator, 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 low swelling rate compared with other modified additives and can be used as an electrolyte additive even when dissolved in the electrolyte, improving the Coulomb efficiency.

[0019] The composite separator obtained by combining the hydrophilic modified polymer separator and the aqueous separator with sodium alginate coated on the surface solves the problem of poor single composite wettability of the traditional separator, forms a water retention network in cooperation with sodium alginate, improves the water retention property of the composite separator, adjusts the pore structure of the composite separator at the same time, blocks dendrite penetration, and the formed ion transport channels are also evenly distributed. Under the bonding action of sodium alginate, the interfacial bonding force of the composite separator is also significantly enhanced, preventing the composite separator from separating during the cycle, and can also effectively improve the mechanical properties of the composite separator.

[0020] Preferably, the hydrophilic modified polymer separator is prepared by the following method:

[0021] Pickling: Immerse the polymer separator in a dilute acid solution with a mass fraction of 1-5%, ultrasonically treat for 30-60 min, wash and dry to obtain a pretreated polymer separator;

[0022] Hydrophilic modification: Transfer the pretreated polymer separator to a hydrophilic modification solution, adjust the pH value of the solution to 5 - 6, and obtain a hydrophilic modified polymer separator after impregnation treatment for 2 - 4 h.

[0023] Preferably, the hydrophilic modification solution comprises raw materials in the following parts by mass:

[0024] Blowing agent: 0.05 - 0.5 part;

[0025] Hydrophilic modifier: 5 - 20 parts;

[0026] pH regulator: 0.5 - 2 parts;

[0027] Solvent: 90 - 180 parts.

[0028] Preferably, the hydrophilic modifier comprises one or a combination of more of polyurethane, polyacrylate, and methallyl alcohol polyoxyethylene ether.

[0029] Preferably, the polymer separator comprises any one of polyethylene separator, polypropylene separator, polyacrylonitrile separator, polyimide separator, polytetrafluoroethylene separator, polyvinylidene fluoride separator, and polycarbonate separator; the pore size of the polymer separator is 30 - 200 nm, and the thickness is 5 - 25 μm.

[0030] Preferably, the dilute acid solution comprises any one of dilute sulfuric acid aqueous solution, dilute hydrochloric acid aqueous solution, and dilute nitric acid aqueous solution.

[0031] Preferably, the blowing agent comprises one or a combination of two of polyethylene glycol ether blowing agents and fatty alcohol polyoxyethylene ether blowing agents.

[0032] Preferably, the pH regulator comprises any one of acetic acid and citric acid.

[0033] Preferably, the solvent comprises any one of acetone, ethyl acetate, benzene, toluene, dichloroethane, and dimethylformamide.

[0034] By adopting the above technical solution, during the hydrophilic treatment process, the polymer separator is first pickled. In the dilute acid solution, ultrasonic cleaning can initiate a certain degree of oxidation reaction on the surface of the polymer separator, generating some polar groups such as carboxyl groups or carbonyl groups on the surface of the polymer separator, thereby enhancing the binding force between the polymer separator and the hydrophilic modifier, and undergoing chemical grafting by forming strong hydrogen bond interactions with the hydrophilic modifier; meanwhile, the surface of the polymer separator will also be slightly etched during the pickling process, increasing the roughness of the separator and providing conditions for the physical embedding of the hydrophilic modifier.

[0035] The pretreated polymer separator obtained after pickling is immersed in a hydrophilic modification solution. The foaming agent in the hydrophilic modification solution can reduce the surface tension of the pretreated polymer separator, improve the wettability of the hydrophilic modifier, and enable the hydrophilic modifier to spread better on the surface of the pretreated polymer separator. Moreover, in the present invention, polymer modifiers such as polyurethane, polyacrylic acid, and methallyl alcohol polyoxyethylene ether are selected for hydrophilic modification treatment. Compared with other hydrophilic modification methods, the polymer modifier can form a stable hydrophilic layer on the surface of the polymer separator, avoiding the problem of easy detachment in the physical adsorption method. At the same time, it can also help improve the affinity between the separator and zinc ions, regulate the solvation structure of zinc ions through coordination, form a uniform ion transport channel, eliminate interfacial concentration polarization, inhibit dendrite growth, and after being treated with the polymer modifier, the mechanical strength is also improved and the thermal stability is enhanced, obtaining a hydrophilic modified polymer separator with a stable structure.

[0036] After hydrophilic modification, the contact angle of the separator surface can be reduced, the interfacial impedance can be decreased, the wettability of the composite separator 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 transport channel, which is beneficial for further composite with the aqueous separator.

[0037] Preferably, the hydrophilic modification solution further includes 3 - 8 parts by mass of a crosslinking agent; the crosslinking agent includes one or a combination of more of glutaraldehyde, succinaldehyde, and glyoxal.

[0038] By adopting the above technical solution, a crosslinking agent is also added to the hydrophilic modification solution. The crosslinking agent of the present invention is mainly a dialdehyde structure compound, and both ends of its molecule contain active aldehyde groups, which can help form a chemical graft between the hydrophilic modifier and the pickled polymer separator, enhance the interfacial binding force between the hydrophilic polymer and the hydrophobic polymer separator. The hydroxyl groups on the surface of the pickled polymer separator can condense with the crosslinking agent to form ether bonds, realizing chemical anchoring and forming a three-dimensional crosslinked network to reinforce the formed hydrophilic modification layer.

[0039] At the same time, the addition of the crosslinking agent only participates in the crosslinking reaction at the interface, does not affect the hydrophilic modification effect, can maintain good hydrophilicity, and can also help form a dense network between the hydrophilic modified polymer separator and sodium alginate on the surface of the aqueous separator, improve the interfacial force between the composite separators, and can also improve the puncture resistance strength and effectively block dendrite penetration.

[0040] Preferably, the dilute acid solution further includes 0.5 - 2% by mass of a strong oxidant; the strong oxidant includes one or a combination of more of chlorine dioxide, hydrogen peroxide, sodium hypochlorite, and sodium chlorite.

[0041] By adopting the above technical solution, a strong oxidant can also be added to the dilute acid solution for pickling. The oxidation effect of the dilute acid on the polymer diaphragm is limited. Adding a strong oxidant during the pickling process can increase the active sites on the diaphragm surface. The strong oxidant can introduce oxygen-containing functional groups on the diaphragm surface through an oxidation reaction, increasing the surface polarity.

[0042] The strong oxidizing property can also cooperate with the dilute acid compound to corrode the surface of the polymer diaphragm, forming micropores or lattice defects, thereby enhancing the specific surface area and the density of active sites on the polymer diaphragm surface, which is beneficial to the further grafting and compounding of the hydrophilic modifier and enhances the hydrophilic modification process.

[0043] In a second aspect, the present invention provides a method for preparing a composite diaphragm for an aqueous zinc-ion battery, including the following process steps:

[0044] S1. Dissolve sodium alginate in water to prepare a sodium alginate solution with a mass fraction of 1-5%, and then coat the sodium alginate solution on both sides of the aqueous diaphragm.

[0045] S2. Preheat and press the hydrophilic modified polymer diaphragm at 60-80 °C for 5-30 min.

[0046] S3. Composite the preheated and pressed hydrophilic modified polymer diaphragm and the aqueous diaphragm coated with sodium alginate, and hot press at 100-150 °C and 2-10 MPa for 5-10 min to obtain a composite diaphragm for an aqueous zinc-ion battery.

[0047] By adopting the above technical solution, after configuring sodium alginate into an aqueous solution and coating it on both sides of the aqueous diaphragm, a sodium alginate layer is formed 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, form a coordination with zinc ions, and the formed zinc salt protection layer can effectively inhibit dendrite penetration and reduce the corrosion of the zinc negative electrode to the aqueous diaphragm.

[0048] First, preheat and press the hydrophilic modified polymer diaphragm to volatilize the solvent contained therein, reducing the adverse effects of the solvent on the composite process. The obtained composite diaphragm not only has good mechanical properties, but also has excellent wettability and liquid retention, meeting the increasingly strict requirements of the aqueous zinc-ion battery for the diaphragm.

[0049] The beneficial effects of the present invention:

[0050] 1. The composite separator of the present invention is composed of a hydrophilic modified polymer separator and an aqueous separator. By first performing hydrophilic modification on the polymer separator, the interfacial impedance and ion transport resistance can be significantly reduced, the wettability and liquid retention capacity of the polymer separator can be improved, and the introduced hydrophilic groups can homogenize the ion flow and inhibit dendrite growth. At the same time, the introduction of hydrophilic segments can also reduce the interfacial polarization difference with the aqueous separator and enhance the composite effect.

[0051] 2. The surface of the aqueous separator in the composite separator of the present invention is also coated with sodium alginate. The introduction of sodium alginate can significantly enhance the interfacial bonding force between the aqueous separator and the polymer separator, reduce the separation risk of the composite separator, and can also regulate the pore structure of the aqueous separator, making the obtained composite separator have a uniform pore distribution, improving the electrolyte wettability, and increasing the 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, avoiding dendrite penetration, and also inhibiting the corrosion of the zinc negative electrode to the separator and the hydrogen evolution reaction, enhancing the cycle stability of the aqueous zinc ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The present invention will be further described below with reference to the accompanying drawings.

[0053] Figure 1 It is the dQ / dV curve graph of Example 1 in the performance test (1) of the present invention.

[0054] Figure 2 It is the dQ / dV curve graph of Comparative Example 5 in the performance test (1) of the present invention.

[0055] Figure 3.1 It is the composite separator for aqueous zinc ion battery obtained in Example 1 of the present invention. Figure 3.2 It is the separator for aqueous zinc ion battery obtained in Comparative Example 4. Figure 3.3 It is a schematic diagram of the composite separator for aqueous zinc ion battery without hydrophilic treatment in Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0056] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0057] PREPARATION EXAMPLE

[0058] Preparation Example 1, a hydrophilic modified polymer separator, is prepared according to the following method:

[0059] Pickling: Immerse a polypropylene separator (average pore size of 100 nm and average thickness of 14 μm) in a 3% by mass dilute sulfuric acid solution, perform ultrasonic treatment for 30 min, and obtain a pretreated polymer separator after washing and drying;

[0060] Hydrophilic modification: Transfer the pretreated polymer separator to a hydrophilic modification solution, adjust the pH value of the solution to 6, and obtain a hydrophilically modified polymer separator after impregnation treatment for 3 h.

[0061] Among them, the hydrophilic modification solution is prepared by the following method: Add 12 g of polyacrylate to 140 g of acetone, stir and dissolve, then add 0.2 g of a polyethylene glycol ether-based foaming agent, and adjust the pH value of the solution to 6 with acetic acid to obtain the hydrophilic modification solution.

[0062] Preparation Example 2, a hydrophilically modified polymer separator, the difference from Preparation Example 1 is only that an equal amount of polyimide separator (average pore size of 100 nm and average thickness of 20 μm) is used to replace the polypropylene separator.

[0063] Preparation Example 3, a hydrophilically modified polymer separator, the difference from Preparation Example 1 is only that an equal amount of methallyl alcohol polyoxyethylene ether is used to replace the polyacrylate.

[0064] Preparation Example 4, a hydrophilically modified polymer separator, the difference from Preparation Example 1 is only that an equal amount of polyurethane is used to replace the polyacrylate.

[0065] Preparation Examples 5 and 6, a hydrophilically modified polymer separator, the difference from Preparation Example 1 is only that the raw material composition ratio of the hydrophilic modification solution is adjusted, as shown in Table 1 specifically:

[0066] Table 1 Hydrophilic Modification Solution Formulation Table

[0067]

[0068] Among them, the pH values of the hydrophilic modification solutions obtained in Preparation Examples 5 and 6 are both adjusted to 6 with acetic acid.

[0069] Preparation Example 7, a hydrophilically modified polymer separator, the difference from Preparation Example 1 is only that during the preparation of the hydrophilic modification solution, 6 g of glutaraldehyde is added together with the polyethylene glycol ether-based foaming agent.

[0070] Preparation Example 8, a hydrophilically modified polymer separator, the difference from Preparation Example 7 is only that the addition amount of glutaraldehyde is 1 g.

[0071] Preparation Example 9, a hydrophilically modified polymer separator, the difference from Preparation Example 7 is only that the addition amount of glutaraldehyde is 10 g.

[0072] Preparation Example 10, a hydrophilic modified polymer separator, which is different from Preparation Example 1 only in that 1% by mass of sodium hypochlorite is further added to the 3% by mass dilute sulfuric acid solution.

[0073] Preparation Example 11, a hydrophilic modified polymer separator, which is prepared by the following method:

[0074] Put the polypropylene separator (average pore size is 100 nm, average thickness is 14 μm) into the hydrophilic modification liquid, adjust the pH value of the solution to 6, and obtain the hydrophilic modified polymer separator after impregnation treatment for 3 h.

[0075] Among them, the hydrophilic modification liquid is prepared by the following method: Add 12 g of polyacrylate to 140 g of acetone, stir and dissolve, then add 0.2 g of polyethylene glycol ether foaming agent, and add acetic acid to adjust the pH value of the solution to 6 to obtain the hydrophilic modification liquid.

[0076] Preparation Example 12, a hydrophilic modified polymer separator, which is prepared by the following method:

[0077] Immerse the polypropylene separator (average pore size is 100 nm, average thickness is 14 μm) in a 3% by mass dilute sulfuric acid solution, perform ultrasonic treatment for 30 min, wash and dry to obtain the hydrophilic modified polymer separator.

[0078] Preparation Example 13, a hydrophilic modified polymer separator, which is different from Preparation Example 1 only in that the polypropylene separator with an average pore size of 30 nm and an average thickness of 5 μm is used to replace the polypropylene separator with an average pore size of 100 nm and an average thickness of 14 μm in an equal amount.

[0079] Preparation Example 14, a hydrophilic modified polymer separator, which is different from Preparation Example 1 only in that the polypropylene separator with an average pore size of 200 nm and an average thickness of 25 μm is used to replace the polypropylene separator with an average pore size of 100 nm and an average thickness of 14 μm in an equal amount.

[0080] Examples

[0081] Example 1, a composite separator for aqueous zinc-ion batteries, which is prepared by the following process steps:

[0082] S1. Dissolve sodium alginate in water to prepare a 3% by mass sodium alginate solution, and then coat the sodium alginate solution on both sides of the glass fiber separator (average pore size is 2.76 μm, average thickness is 350 μm), and the coating amount of sodium alginate on each side is 0.3 mg / cm 2 ;

[0083] S2. Preheat and press the hydrophilic modified polymer separator prepared in Preparation Example 1 at 60 °C for 10 min;

[0084] S3. Compose the hydrophilic modified polymer-based separator after the above preheating and pressing treatment and the glass fiber separator coated with sodium alginate, and hot press for 5 min under the conditions of 120 °C and 6 MPa to obtain a composite separator for aqueous zinc-ion batteries.

[0085] Example 2. A composite separator for aqueous zinc-ion batteries, which is different from Example 1 only in that a cellulose separator (with an average pore size of 3 μm and an average thickness of 250 μm) of equal amount is used to replace the glass fiber separator.

[0086] Example 3. A composite separator for aqueous zinc-ion batteries, which is different from Example 1 only in that the coating amount of sodium alginate on each side is 0.15 mg / cm 2 。

[0087] Example 4. A composite separator for aqueous zinc-ion batteries, which is different from Example 1 only in that the coating amount of sodium alginate on each side is 0.5 mg / cm 2 。

[0088] Example 5. A composite separator for aqueous zinc-ion batteries, which is different from Example 1 only in that the hydrophilic modified polymer-based separator prepared in Preparation Example 2 of equal amount is used to replace the hydrophilic modified polymer-based separator prepared in Preparation Example 1.

[0089] Example 6. A composite separator for aqueous zinc-ion batteries, which is different from Example 1 only in that the hydrophilic modified polymer-based separator prepared in Preparation Example 3 of equal amount is used to replace the hydrophilic modified polymer-based separator prepared in Preparation Example 1.

[0090] Example 7. A composite separator for aqueous zinc-ion batteries, which is different from Example 1 only in that the hydrophilic modified polymer-based separator prepared in Preparation Example 4 of equal amount is used to replace the hydrophilic modified polymer-based separator prepared in Preparation Example 1.

[0091] Example 8. A composite separator for aqueous zinc-ion batteries, which is different from Example 1 only in that the hydrophilic modified polymer-based separator prepared in Preparation Example 5 of equal amount is used to replace the hydrophilic modified polymer-based separator prepared in Preparation Example 1.

[0092] Example 9. A composite separator for aqueous zinc-ion batteries, which is different from Example 1 only in that the hydrophilic modified polymer-based separator prepared in Preparation Example 6 of equal amount is used to replace the hydrophilic modified polymer-based separator prepared in Preparation Example 1.

[0093] Example 10. A composite separator for aqueous zinc-ion batteries, which is different from Example 1 only in that the coating amount of sodium alginate on each side is 0.05 mg / cm 2 。

[0094] Example 11. A composite separator for an aqueous zinc-ion battery, which is different from Example 1 only in that the coating amount of sodium alginate on each side is 0.7 mg / cm 2 .

[0095] Example 12. A composite separator for an aqueous zinc-ion battery, which is different from Example 1 only in that the hydrophilic modified polymer separator prepared in Preparation Example 7 is used to replace the hydrophilic modified polymer separator prepared in Preparation Example 1 in an equal amount.

[0096] Example 13. A composite separator for an aqueous zinc-ion battery, which is different from Example 1 only in that the hydrophilic modified polymer separator prepared in Preparation Example 8 is used to replace the hydrophilic modified polymer separator prepared in Preparation Example 1 in an equal amount.

[0097] Example 14. A composite separator for an aqueous zinc-ion battery, which is different from Example 1 only in that the hydrophilic modified polymer separator prepared in Preparation Example 9 is used to replace the hydrophilic modified polymer separator prepared in Preparation Example 1 in an equal amount.

[0098] Example 15. A composite separator for an aqueous zinc-ion battery, which is different from Example 1 only in that the hydrophilic modified polymer separator prepared in Preparation Example 10 is used to replace the hydrophilic modified polymer separator prepared in Preparation Example 1 in an equal amount.

[0099] Example 16. A composite separator for an aqueous zinc-ion battery, which is different from Example 1 only in that the hydrophilic modified polymer separator prepared in Preparation Example 11 is used to replace the hydrophilic modified polymer separator prepared in Preparation Example 1 in an equal amount.

[0100] Example 17. A composite separator for an aqueous zinc-ion battery, which is different from Example 1 only in that the hydrophilic modified polymer separator prepared in Preparation Example 12 is used to replace the hydrophilic modified polymer separator prepared in Preparation Example 1 in an equal amount.

[0101] Example 18. A composite separator for an aqueous zinc-ion battery, which is different from Example 1 only in that the hydrophilic modified polymer separator prepared in Preparation Example 13 is used to replace the hydrophilic modified polymer separator prepared in Preparation Example 1 in an equal amount.

[0102] Example 19. A composite separator for an aqueous zinc-ion battery, which is different from Example 1 only in that the hydrophilic modified polymer separator prepared in Preparation Example 14 is used to replace the hydrophilic modified polymer separator prepared in Preparation Example 1 in an equal amount.

[0103] Example 20. A composite separator for an aqueous zinc-ion battery, which is different from Example 1 only in that a glass fiber separator with an average pore size of 1 μm and an average thickness of 100 μm is used to replace the glass fiber separator with an average pore size of 2.76 μm and an average thickness of 350 μm.

[0104] Example 21. A composite separator for aqueous zinc-ion batteries, which is different from Example 1 only in that the glass fiber separator with an average pore size of 2.76 μm and an average thickness of 350 μm is replaced with a glass fiber separator with an equal amount, an average pore size of 5 μm, and an average thickness of 600 μm.

[0105] Comparative example

[0106] Comparative example 1. A composite separator for aqueous zinc-ion batteries is prepared according to the following process steps:

[0107] S1. Preheat and press the hydrophilic modified polymer separator prepared in Preparation Example 1 at 60 °C for 10 min;

[0108] S2. Composite the above-mentioned preheated and pressed hydrophilic modified polymer separator and a glass fiber separator (average pore size of 2.76 μm and average thickness of 350 μm), and hot press at 120 °C and 6 MPa for 5 min to obtain a composite separator for aqueous zinc-ion batteries.

[0109] Comparative example 2. A composite separator for aqueous zinc-ion batteries, which is different from Example 1 only in that the hydrophilic modified polymer separator prepared in Preparation Example 1 is replaced with an equal amount of polypropylene separator (average pore size of 100 nm and average thickness of 20 μm).

[0110] Comparative example 3. A composite separator for aqueous zinc-ion batteries is prepared according to the following process steps:

[0111] Composite a polypropylene separator (average pore size of 100 nm and average thickness of 14 μm) and a glass fiber separator (average pore size of 2.76 μm and average thickness of 350 μm), and hot press at 120 °C and 6 MPa for 5 min to obtain a composite separator for aqueous zinc-ion batteries.

[0112] Comparative example 4. A separator for aqueous zinc-ion batteries uses a glass fiber separator with an average pore size of 2.76 μm and an average thickness of 350 μm.

[0113] Comparative example 5. A separator for aqueous zinc-ion batteries uses a cellulose separator with an average pore size of 3 μm and an average thickness of 250 μm.

[0114] Comparative example 6. A separator for aqueous zinc-ion batteries uses the hydrophilic modified polymer separator prepared in Preparation Example 1.

[0115] Performance detection test

[0116] Sample preparation: Vanadium dioxide was used as the positive electrode of the battery, metallic zinc was used as the negative electrode of the battery, and the separator used was the separator for aqueous zinc-ion batteries obtained in the examples and comparative examples. Among them, the hydrophilic modified polymer-based separator faced the negative electrode side of the aqueous zinc-ion battery, and the aqueous separator faced the positive electrode side of the aqueous zinc-ion battery. A button-type aqueous zinc battery was assembled as the sample.

[0117] Performance test:

[0118] After the sample battery was assembled, it was left standing for 12 h, and then cycled 10 times at a rate of 0.5C to complete activation. The activation voltage was 0.3 - 1.7 V; then, long cycling was carried out at a rate of 3C, and the cycling voltage was 0.3 - 1.7 V. The following were tested respectively:

[0119] (1) During the cycling process, the ratio of the micro specific capacity to the micro voltage (dQ / dV) of the sample batteries of Example 1 and Comparative Example 5 was used to characterize the redox process during charge and discharge. The test results are as Figure 1 and Figure 2 shown;

[0120] (2) The specific capacity decay rate of the battery after 500 cycles was tested to characterize the cycling performance of the battery:

[0121] ,

[0122] The test results are shown in Table 2:

[0123] Table 2 Test results of cycling performance

[0124]

[0125] According to Table 2, and Figure 1 and Figure 2 , in combination with Example 1 and Comparative Example 5, it can be seen that the specific capacity of Comparative Example 1 decreased significantly compared with that of Example 1 after long cycling, indicating that the composite separator obtained after the hydrophilic modified polymer-based separator was compounded with the cellulose separator had greatly improved cycling stability compared with the cellulose separator, and the service life of the battery increased significantly. From the comparison between Figure 1 and Figure 2 , it can also be seen that Figure 2 had a large number of additional peaks and tails, indicating that a large number of side reactions occurred during the cycling process, which would directly affect the service performance of the battery.

[0126] According to Figure 3.1 , Figure 3.2 and Figure 3.3It can be seen that the liquid retention and mechanical properties of the composite diaphragm for aqueous zinc ions obtained in Example 1 are good. For the glass fiber diaphragm in Comparative Example 4, although the liquid retention is good, the diaphragm is prone to wrinkling and damage, and the mechanical strength is poor. For the composite diaphragm for aqueous zinc ion batteries in Comparative Example 2, the polymer diaphragm therein has not been hydrophilically modified. As can be seen from Figure 3.3 , the mechanical properties of the diaphragm are good, but on one side of the polymer diaphragm, the hydrophilicity is extremely poor, and the wettability and liquid retention of the diaphragm are poor, making it difficult to meet the requirements of aqueous zinc ion batteries.

[0127] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device.

[0128] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A composite separator for aqueous zinc-ion batteries, characterized in that, The composite separator includes a hydrophilic modified polymer separator and an aqueous separator; the hydrophilic modified polymer separator faces the negative electrode side of the aqueous zinc-ion battery, and the aqueous separator faces the positive electrode side of the aqueous zinc-ion battery; Sodium alginate is coated on both surfaces of the aqueous separator; The hydrophilic modification liquid of the hydrophilic modified polymer separator includes 5-20 parts of a hydrophilic modifier; the hydrophilic modifier includes one or a combination of more of polyurethane, polyacrylate, and methallyl alcohol polyoxyethylene ether; The hydrophilic modification liquid further includes 3-8 parts by mass of a crosslinking agent; the crosslinking agent includes one or a combination of more of glutaraldehyde, succinaldehyde, and glyoxal.

2. The composite separator for aqueous zinc ion battery according to claim 1, wherein The coating amount of sodium alginate coated on the surface of the aqueous system diaphragm is 0.15 to 0.5 mg / cm 2 .

3. The composite separator for aqueous zinc ion batteries according to claim 1, wherein The aqueous separator includes any one of a glass fiber separator, a cellulose separator, and a non-woven fabric separator; the pore size of the aqueous separator is 1-5 μm, and the thickness is 100-600 μm.

4. The composite separator for aqueous zinc-ion battery according to claim 1, wherein The hydrophilic modified polymer separator is prepared by the following method: Pickling: Immerse the polymer separator in a dilute acid solution with a mass fraction of 1-5%, perform ultrasonic treatment for 30-60 min, wash and dry to obtain a pretreated polymer separator; the dilute acid solution includes any one of dilute sulfuric acid aqueous solution, dilute hydrochloric acid aqueous solution, and dilute nitric acid aqueous solution; Hydrophilic modification: Transfer the pretreated polymer separator to the hydrophilic modification liquid, adjust the pH value of the solution to 5-6, and perform impregnation treatment for 2-4 h to obtain a hydrophilic modified polymer separator.

5. The composite separator for aqueous zinc-ion batteries according to claim 1, characterized in that, The hydrophilic modification liquid includes the following raw materials in parts by mass: Foaming agent 0.05-0.5 part; pH regulator 0.5-2 parts; Solvent 90-180 parts; The foaming agent includes one or a combination of two of polyethylene glycol ether foaming agents and fatty alcohol polyoxyethylene ether foaming agents; The solvent includes any one of acetone, ethyl acetate, benzene, toluene, dichloroethane, and dimethylformamide.

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

7. The composite separator for aqueous zinc ion battery according to claim 4, wherein The polymer separator includes any one of a polyethylene separator, a polypropylene separator, a polyacrylonitrile separator, a polyimide separator, a polytetrafluoroethylene separator, a polyvinylidene fluoride separator, and a polycarbonate separator; the pore size of the polymer separator is 30-200 nm, and the thickness is 5-25 μm.

8. A preparation method of the composite separator for the aqueous zinc ion battery according to any one of claims 1 to 7, characterized in that, It includes the following process steps: S1. Dissolve sodium alginate in water to prepare a sodium alginate solution with a mass fraction of 1-5%, and then coat the sodium alginate solution on both surfaces of the aqueous separator; S2. Preheat and press the hydrophilic modified polymer separator at 60-80 °C for 5-30 min; S3. Composite the preheated and pressed hydrophilic modified polymer separator and the aqueous separator coated with sodium alginate, and perform hot pressing at 100-150 °C and 2-10 MPa for 5-10 min to obtain a composite separator for an aqueous zinc-ion battery.

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