Fluorinated acrylate binder and preparation method thereof, solid electrolyte diaphragm and preparation method thereof, and solid-state battery

Abstract

The invention discloses a fluorinated acrylate binder and a preparation method thereof, a solid electrolyte diaphragm and a preparation method thereof, and a solid-state battery, and belongs to the technical field of batteries. The fluorinated acrylate binder is a graft polymer formed by grafting an acrylate monomer on a fluorine-containing polymer molecular chain in a controllable free radical polymerization mode under the action of a chain transfer agent. According to the invention, the fluorine-containing material is adopted to modify the acrylate binder, so that the chemical resistance, thermal stability and mechanical property of the fluorine-containing acrylate binder are improved, and the binder has good ionic conductivity; and by using the prepared binder as the binder for the solid electrolyte diaphragm, the ionic conduction speed of the solid electrolyte diaphragm is promoted, the interface impedance is reduced, and the stable long-term cycle performance and high-temperature performance of a solid-state battery are ensured.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a fluorinated acrylate binder and a preparation method thereof, a solid-state electrolyte separator and a preparation method thereof, and a solid-state battery. BACKGROUND

[0002] A solid-state battery is an energy storage device that uses a solid-state electrolyte to replace the traditional liquid-state electrolyte. The cell of a solid-state battery mainly consists of a positive electrode, a solid-state electrolyte, and a negative electrode, and the charging and discharging are achieved by the migration of lithium ions between the positive and negative electrodes. Unlike traditional lithium-ion batteries, the ion conduction mechanism can rely on lattice defects, ion channels, or chain segment movement to transfer ions, depending on the characteristics of the solid-state electrolyte used. Sulfide solid-state electrolytes have high ionic conductivity, good processability, and good interface compatibility, making them the most promising electrolyte route for full solid-state batteries. However, sulfide materials are usually highly sensitive to air and water vapor, so selecting a binder for a sulfide solid-state electrolyte system is a key and challenging task.

[0003] Acrylate is widely used in the field of battery binders due to its simple process and easy availability of raw materials. Patent CN117327460 uses ethylene acrylate copolymer to obtain a high-viscosity binder for sulfide solid-state batteries by adjusting the ester content in the copolymer to less than 30%; Patent CN109599561B uses a random or block copolymer of styrene structure and acrylate, ethylene ester, acrylamide, etc. as a binder, which can make the sulfide solid-state electrolyte stable and soluble in low-polarity organic solvents; Patent CN120025762A uses a binder obtained by modifying a copolymer of butyl acrylate and 2-acrylamido-2-methylpropane sulfonic acid lithium with polyisobutylene, which has excellent bonding properties and ion conduction capacity; Patent CN116190767A relates to a self-healing binder polymerized from methyl methacrylate and lipid monomers, which ensures stable and efficient long-term cycling of the battery.

[0004] However, sulfide solid-state electrolytes have strong nucleophilicity, and the ester group of acrylate binders is easily attacked by nucleophilic sulfide ions during long-term operation of the battery, leading to ester bond cleavage and causing the adhesion of the binder to decrease or forming a new high-resistance interface layer at the binder / electrolyte interface. The thermal stability and mechanical properties of acrylate binders need to be improved. Acrylate binders cannot conduct lithium ions, and in solid-state batteries, the binder occupies part of the space inside the electrode, which can hinder the ion transport path. SUMMARY

[0005] The main purpose of the present application is to provide a fluorinated acrylate binder, a preparation method thereof, a solid electrolyte separator and a solid-state battery, so as to solve the problems of low adhesion, poor thermal stability and inability to conduct lithium ions of the binder for sulfide solid electrolyte separator in the prior art, thereby causing poor ion conductivity, high interface impedance and poor mechanical properties of the solid electrolyte separator.

[0006] In order to achieve the above-mentioned purpose, according to one aspect of the present application, a fluorinated acrylate binder is provided, which is a graft polymer formed by grafting an acrylate monomer on a fluorine-containing polymer molecular chain under the action of a chain transfer agent through a controlled radical polymerization method.

[0007] Further, the grafting degree of the fluorinated acrylate binder is 50-120%, preferably 70-100%.

[0008] Further, the weight ratio of the acrylate monomer, the fluorine-containing polymer and the chain transfer agent is 40: (6-10): (0.04-0.2).

[0009] Further, the acrylate monomer is selected from at least one of methyl methacrylate, glycidyl methacrylate, butyl acrylate and 2- (dimethylamino) ethyl methacrylate.

[0010] Further, the molecular weight of the fluorine-containing polymer is 600-1300 million Da.

[0011] Further, the fluorine-containing polymer is selected from at least one of polyvinylidene fluoride, ethylene-tetrafluoroethylene copolymer, fluorinated ethylene-propylene copolymer and polytrifluorochloroethylene.

[0012] Further, the controlled radical polymerization is reversible addition-fragmentation chain transfer polymerization.

[0013] Further, the chain transfer agent is selected from at least one of 2-phenylpropane thio-benzoate, bis (thio-benzoyl) disulfide, benzyl dithio-benzoate and 2-phenethyl phenyl dithiolester.

[0014] Further, the weight of the chain transfer agent is 0.1-0.5 wt% of the acrylate monomer.

[0015] Further, the mass concentration of the organic solution of the fluorinated acrylate binder is 5-15 wt%.

[0016] According to a second aspect of the present application, a preparation method of the above-mentioned fluorinated acrylate binder is provided, comprising the following steps:

[0017] Step S1: activating the fluorine-containing polymer to obtain a fluorine-containing polymer with active radicals;

[0018] Step S2: performing a controlled radical polymerization reaction on the fluorine-containing polymer with active radicals, the acrylate monomer and the chain transfer agent in an inert atmosphere to obtain a fluorinated acrylate, and further obtaining the fluorinated acrylate adhesive.

[0019] Further, in step S2, the temperature of the controlled radical polymerization reaction is 55-70℃; and the time of the controlled radical polymerization reaction is 40-50 min.

[0020] Further, the weight ratio of the acrylate monomer, the fluorine-containing polymer and the chain transfer agent is 40: (6-10): (0.04-0.2).

[0021] Further, the weight of the chain transfer agent is 0.1-0.5wt% of the acrylate monomer.

[0022] Further, the inert atmosphere is argon.

[0023] Further, in step S1, the activation is radiation activation.

[0024] Further, the radiation activation is at least one activation mode selected from electron beam, ultraviolet light and plasma.

[0025] Further, the radiation energy of the electron beam is 50-150kGy.

[0026] Further, the acrylate monomer is at least one selected from methyl methacrylate, glycidyl methacrylate, butyl acrylate and 2- (dimethylamino) ethyl methacrylate.

[0027] Further, the molecular weight of the fluorine-containing polymer is 0.6-1.3 million Da.

[0028] Further, the fluorine-containing polymer is at least one selected from polyvinylidene fluoride, ethylene-tetrafluoroethylene copolymer, fluorinated ethylene propylene copolymer and polytrifluorochloroethylene.

[0029] Further, the controlled radical polymerization reaction is reversible addition-fragmentation chain transfer polymerization.

[0030] Further, the chain transfer agent is at least one selected from 2-phenylpropane thio-benzoate, bis (thio-benzoyl) disulfide, benzyl dithio-benzoate and 2-phenethyl phenyl dithiolester.

[0031] Further, in step S2, the fluorine-containing polymer with active radicals, the acrylate monomer and the chain transfer agent are subjected to the controlled radical polymerization reaction in a first solvent.

[0032] Further, the first solvent is at least one selected from N, N-dimethylformamide, dimethyl sulfoxide, N-methyl pyrrolidone and ethanol.

[0033] Further, the fluorinated acrylate is further sequentially subjected to a second solvent rinsing and drying to obtain the purified fluorinated acrylate.

[0034] Further, the second solvent is at least one selected from N,N-dimethylformamide, dimethyl sulfoxide, N-methyl pyrrolidone and ethanol.

[0035] Further, the step S2 is further followed by a step S3: mixing the fluorinated acrylate and the organic solution to obtain the fluorinated acrylate binder.

[0036] Further, the weight ratio of the fluorinated acrylate and the organic solution is (5-15):(85-95).

[0037] Further, the organic solution is at least one selected from isododecane, dipropylene glycol dimethyl ether, ethyl 3-ethoxypropionate and isobutyl isobutyrate.

[0038] According to a third aspect of the present application, a solid-state electrolyte separator is provided, comprising a sulfide solid-state electrolyte and a binder; wherein the binder is the fluorinated acrylate binder described above or the fluorinated acrylate binder prepared by the preparation method of the fluorinated acrylate binder described above.

[0039] Further, the fluorinated acrylate binder is 2-4 wt% of the solid-state electrolyte separator.

[0040] Further, the sulfide solid-state electrolyte is at least one selected from a glassy electrolyte, a glass-ceramic electrolyte and a crystalline electrolyte.

[0041] Further, the particle size D90 of the sulfide solid-state electrolyte is 1-5 μm.

[0042] Further, the thickness of the solid-state electrolyte separator is 80-120 μm.

[0043] According to a fourth aspect of the present application, a preparation method of the solid-state electrolyte separator described above is provided, comprising the following steps:

[0044] Step S1: mixing the sulfide solid-state electrolyte and the binder in a third solvent to obtain a film-forming slurry; wherein the binder is the fluorinated acrylate binder described above or the fluorinated acrylate binder prepared by the preparation method of the fluorinated acrylate binder described above;

[0045] Step S2: the film-forming slurry is subjected to blade coating and drying to obtain the solid-state electrolyte separator.

[0046] Further, the weight ratio of the fluorinated acrylate binder, the sulfide solid-state electrolyte and the third solvent is 1:(20-50):(15-40).

[0047] Further, the third solvent is selected from at least one of isododecane, dipropylene glycol dimethyl ether, ethyl 3-ethoxypropionate and isobutyl isobutyrate.

[0048] According to a fifth aspect of the present application, a solid-state battery is provided, comprising a positive electrode, a solid-state electrolyte separator and a negative electrode; the solid-state electrolyte separator is the solid-state electrolyte separator described above or obtained by the preparation method of the solid-state electrolyte separator described above.

[0049] Compared with the prior art, the present application has the following beneficial effects:

[0050] The present application improves the chemical resistance, thermal stability and mechanical properties of the fluorinated acrylic ester adhesive by modifying the acrylic ester adhesive with fluorine-containing materials, and makes the adhesive have good ionic conductivity; as an adhesive for solid-state electrolyte separator, it promotes the ion conduction speed of the solid-state electrolyte separator, reduces the interface impedance, and ensures that the solid-state battery has stable long-term cycle performance and high-temperature performance. DETAILED DESCRIPTION

[0051] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the embodiments.

[0052] As mentioned in the background, the sulfide solid-state electrolyte has strong nucleophilicity, and the ester group of the acrylic ester adhesive is easily attacked by the nucleophilic attack of sulfur ions during long-term operation of the battery, leading to the breaking of the ester bond and causing the adhesion of the adhesive to decrease or forming a new high impedance interface layer at the adhesive / electrolyte interface; the thermal stability and mechanical properties of the acrylic ester adhesive need to be improved; the acrylic ester adhesive cannot conduct lithium ions, and in the solid-state battery, the adhesive occupies part of the space inside the electrode, which will hinder the ion transmission path; in order to solve the above problems, the acrylic adhesive is modified as follows.

[0053] According to an aspect of the present application, a fluorinated acrylic ester adhesive is provided, which is a graft polymer formed by grafting an acrylic ester monomer on a fluorine-containing polymer molecular chain under the action of a chain transfer agent through controlled radical polymerization.

[0054] The present application modifies the acrylic ester adhesive with fluoride, which can significantly improve the following properties of the acrylic ester adhesive;

[0055] Chemical resistance: due to the small radius and high electronegativity of fluorine atom, the strong electron-withdrawing inductive effect of fluorine atom makes the carbon atom carry partial positive charge, and the whole C-F bond has very large polarity; the negatively charged fluorine atom tightly surrounds the carbon chain, when the negatively charged nucleophile tries to attack the partially positively charged carbon ion, it will first encounter the strong electrostatic repulsion of these "fluorine atoms", making it difficult to approach and react, making it more difficult to be attacked by nucleophilic anions in the sulfide electrolyte, reducing the risk of ester bond substitution or rupture by nucleophilic substitution, reducing the degradation of the adhesive itself and the production of harmful by-products.

[0056] Thermal stability: it requires higher energy to break the C-F bond (485 kJ / mol) than the conventional C-C (348 kJ / mol) or C-H (413 kJ / mol) bond, and the thermal decomposition temperature of fluorine-containing acrylate adhesive is higher than that of ordinary acrylate adhesive, and it has a wider application temperature range.

[0057] Mechanical properties: the strong polarity and high bond energy of C-F bond and the strong interaction between molecular chain bonds make fluorine-containing polymers have better hardness and better wear resistance, which helps to maintain the integrity of the electrode structure.

[0058] Ionic conductivity: the introduction of fluorine-containing polymers can increase the dielectric constant of acrylate, enhance its lithium salt dissociation ability, and thus improve its ionic conductivity to a certain extent.

[0059] Due to the high electronegativity, good thermal stability and chemical stability of the fluorine-containing material, it can endow the acrylic adhesive with more superior properties. In order to improve the fluorination modification effect of the acrylic adhesive, the fluorine content thereof is optimized. In some specific embodiments, the grafting degree of the fluorinated acrylic ester adhesive is 50% to 120%, preferably 70 to 100%; the fluorine content is 20 to 35 wt%; for example, polyvinylidene fluoride (PVDF) is grafted with methyl methacrylate (MMA), and when the grafting degrees are 50% and 120% respectively, the fluorine contents are 32.5% and 20.1% respectively. Further, the weight ratio of the acrylic ester monomer, the fluorine-containing polymer and the chain transfer agent is 40: (6 to 10): (0.04 to 0.2); for example, 40: (7 to 9): (0.04 to 0.1), and further for example, 40:8: (0.04 to 0.06), and specifically, 40:8:0.05. The chain transfer agent is 0.1 to 0.5 wt% of the acrylic ester monomer; preferably, 0.15 to 0.3 wt%; further preferably, 0.15 to 0.2 wt%. Controlling the fluorine content of the adhesive within the above range, the presence of appropriate amount of fluorine can protect the ester bond in the acrylic ester adhesive from the nucleophilic attack of the sulfur ions of the sulfide solid-state electrolyte, thereby delaying the aging process of the adhesive, improving the overall thermal decomposition temperature of the adhesive, and preventing the safety problem of the battery under high temperature conditions; the appropriate amount of fluorine has high hardness and wear resistance, which helps to maintain the stability of the electrode structure, can provide reasonable ionic conductivity, avoid the influence of excessive fluorine content on the electrolyte wettability, improve the interfacial compatibility of the adhesive and the sulfide solid-state electrolyte, reduce the interfacial impedance, and improve the overall efficiency of the battery.

[0060] In order to improve the modification effect of the fluorine-containing material on the acrylic ester adhesive, the fluorine-containing material and the acrylic ester monomer are selected to be compatible with each other; in some specific embodiments, the acrylic ester monomer is selected from at least one of methyl methacrylate (MMA), glycidyl methacrylate (GMA), butyl acrylate (BA) and 2- (dimethylamino) ethyl methacrylate (DMAEMA). The above-mentioned acrylic ester adhesive has excellent adhesive properties on the one hand, which can effectively bond the electrode materials together to form a stable electrode structure, and the adhesive has good chemical stability and thermal stability, which can resist the chemical corrosion of the battery environment and is suitable for the high temperature environment of the battery; on the other hand, the above-mentioned acrylic ester monomer is grafted onto the fluorine-containing polymer, which helps to form stable chemical bonds, maintain the flexibility and mechanical strength of the polymer; at the same time, the above-mentioned acrylic ester adhesive has good solubility and film-forming property, and is easy to prepare a solid-state electrolyte separator.

[0061] The fluorine-containing structure characteristics are particularly important for the modification effect of the fluorinated acrylate binder, and then the suitable molecular weight and type are selected; in some specific embodiments, the molecular weight of the fluorine-containing polymer is 600-1300 million Da, preferably 800-1200 million Da, and further preferably 90-100 million Da. Specifically, the fluorine-containing polymer is selected from at least one of polyvinylidene fluoride (PVDF), ethylene-tetrafluoroethylene copolymer (ETFE), fluorinated ethylene propylene copolymer (FEP), and polytrifluorochloroethylene (PCTFE). The high molecular weight fluorine-containing polymer is selected, which has better physical and mechanical properties itself, including higher strength and toughness. The long chain of the high molecular weight fluorine-containing polymer has strong intermolecular force, which helps to improve the cohesion of the binder and the structural stability of the electrode, and helps to reduce the crack and delamination phenomenon caused by the volume change of the electrode in the solid-state battery during the charge and discharge cycle, thereby prolonging the cycle life of the battery. The high molecular weight fluorine-containing polymer also has higher thermal stability, which can still maintain structural stability in the high temperature environment of battery operation and reduce thermal degradation. At the same time, the fluorine-containing polymer has excellent chemical stability, and the high molecular weight means that more fluorine atoms participate in the protection of the polymer main chain, further improving the chemical corrosion resistance of the binder. The above suitable molecular weight range can optimize the grafting reaction efficiency of the fluorine-containing polymer and the acrylate monomer, provide sufficient grafting sites, and at the same time maintain good processing fluidity and compatibility with the acrylate monomer.

[0062] In order to ensure that the binder has good bonding performance and ionic conductivity, and to facilitate use, the concentration thereof is regulated; in some specific embodiments, the fluorinated acrylate binder further comprises an organic solution, and the mass concentration of the binder is 5-15 wt%; for example, 8-12 wt%, and further for example, 10 wt%. Controlling the concentration of the binder in the range can ensure effective bonding between the electrode particles to form a stable electrode structure, prevent the electrode material from falling off and the electrode structure from being damaged during the charge and discharge cycle, and the binder with appropriate concentration also has better ionic conductivity and good processability.

[0063] According to a second aspect of the present application, a preparation method of the fluorinated acrylate binder is provided, comprising the following steps:

[0064] Step S1: activating the fluorine-containing polymer to obtain a fluorine-containing polymer with active radicals;

[0065] Step S2: performing a controllable free radical polymerization reaction on the fluorine-containing polymer with active radicals, the acrylate monomer, the chain transfer agent, and the first solvent in an inert atmosphere to obtain a fluorinated acrylate, and then obtaining the fluorinated acrylate binder.

[0066] The fluorine-containing acrylate binder is prepared by a radiation grafting method, and has simple process and strong applicability; a chain transfer agent is used, and a branched graft polymer is obtained by controlled radical polymerization.

[0067] In order to further improve the modification effect of the fluorine-containing polymer on the acrylate binder, the synthesis conditions and the synthesis ratio are further optimized; in some specific embodiments, in step S2, the inert atmosphere is argon; the temperature of the controlled radical polymerization reaction is 55-70°C; the time of the controlled radical polymerization reaction is 40-50 min; the weight ratio of the acrylate monomer, the fluorine-containing polymer and the chain transfer agent is 40:(6-10):(0.04-0.2); for example, 40:(7-9):(0.04-0.1), and for another example, 40:8:(0.04-0.06), and specifically, 40:8:0.05. The chain transfer agent is 0.1-0.5wt% of the acrylate monomer; preferably, 0.15-0.3wt%; and further preferably, 0.15-0.2wt%. In the above graft polymerization reaction, the fluorine-containing polymer serves as a substrate, the acrylate monomer is grafted thereon, the chain transfer agent ensures the controllability of the grafting process, and appropriate ratios of the acrylate monomer and the fluorine-containing polymer can maximize the grafting efficiency, ensure the effective combination of the binder and the electrode material, and reduce the probability of residual ungrafted monomers; the appropriate amount of the chain transfer agent can control the average molecular weight and the molecular weight distribution of the polymer, and under the above ratio, a polymer with moderate molecular weight and narrow distribution can be prepared; by precisely controlling the ratio of these components, the prepared fluorine-containing acrylate binder has excellent adhesion, chemical stability and ionic conductivity.

[0068] In some specific embodiments, the acrylate monomer is selected from at least one of methyl methacrylate (MMA), glycidyl methacrylate (GMA), butyl acrylate (BA) and 2-(dimethylamino)ethyl methacrylate (DMAEMA). The molecular weight of the fluorine-containing polymer is 0.6-1.3 million Da, preferably 0.8-1.2 million Da; and further preferably, 0.9-1 million Da. The fluorine-containing polymer is selected from at least one of polyvinylidene fluoride (PVDF), ethylene-tetrafluoroethylene copolymer (ETFE), fluorinated ethylene propylene copolymer (FEP) and polychlorotrifluoroethylene (PCTFE). The selected acrylate monomer has good adhesion, chemical stability, film-forming property and matching with the fluorine-containing polymer.

[0069] In the controllable radical polymerization, the fluoropolymer needs to be activated first to generate initial radicals, and then the radical polymerization reaction continues with the acrylate and chain transfer agent; for the fluoropolymer, a matching activation method is selected; in some embodiments, the activation method of the fluoropolymer includes radiation activation; the radiation activation is selected from at least one of electron beam, ultraviolet light and plasma; further preferably, the radiation energy of the electron beam is 50-150 kGy; preferably 80-135 kGy, and further preferably 100-125 kGy.

[0070] In some specific embodiments, the controllable radical polymerization is reversible addition-fragmentation chain transfer polymerization. The chain transfer agent is selected from at least one of 2-phenylpropane thio-benzoate (RAFT), bis(thiobenzoyl) disulfide, benzyl dithiobenzoate, and 2-phenylethyl phenyl disulfide. The above chain transfer agent is used to control the polymerization, so that the growth process of the polymer becomes highly predictable and controllable. The RAFT reagent exhibits active or pseudo-active characteristics through its unique chain transfer mechanism, so that the molecular weight and molecular weight distribution of the polymer can be accurately controlled, and the synthesis of graft structure can be realized; the above selected RAFT controllable radical polymerization obtains the expected branched uniform graft polymer.

[0071] In some specific embodiments, in step S2, the fluoropolymer with active radicals, acrylate monomers and chain transfer agent are subjected to controllable radical polymerization in a first solvent; preferably, the first solvent is selected from at least one of N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N-methyl pyrrolidone and ethanol, etc.

[0072] In some specific embodiments, the fluorinated acrylate is further sequentially washed with a second solvent (the same as the first solvent, such as ethanol) and dried to obtain the purified fluorinated acrylate. The selected solvent can dissolve the acrylate but is a non-solvent for fluorine-containing materials, so that a solid graft membrane is obtained after the polymerization reaction, and the residual monomers on the surface thereof can be removed by repeated washing with ethanol, and the graft polymer with high purity can be obtained.

[0073] In some embodiments, step S2 is followed by step S3: mixing the fluorinated acrylate and an organic solution to obtain a fluorinated acrylate binder; preferably, the weight ratio of the fluorinated acrylate and the organic solution is (5-15):(85-95); for example, (8-12):(88-92), and further for example, 10:90. The organic solution is selected from at least one of isododecane, dipropylene glycol dimethyl ether, 3-ethoxypropyl acetate, and isobutyl isobutyrate. The mixing process of the fluorinated acrylate and the organic solution specifically includes: stirring at a temperature of 90-110°C for 0.5-1.5h, and then stirring at a temperature of 180-220°C for 2-4h to obtain the fluorinated acrylate binder. By treating the fluorinated acrylate and the solvent obtained by the reaction as described above, a binder with a suitable concentration can be obtained, which is convenient to use.

[0074] According to a third aspect of the present application, a solid-state electrolyte separator is provided; it includes a sulfide solid-state electrolyte and a binder; wherein the binder is the fluorinated acrylate binder described above or the fluorinated acrylate binder prepared by the preparation method of the fluorinated acrylate binder described above. The solid-state electrolyte separator has better ion conductivity and mechanical strength, which helps to improve the cycle performance and high-temperature stability of the solid-state battery.

[0075] In some embodiments, the fluorinated acrylate binder is 2-4wt% of the solid-state electrolyte separator; further preferably, 2.5-3.5wt%. The sulfide solid-state electrolyte can be selected from at least one of glassy electrolytes such as 70Li2S 30P2S5, glass-ceramic electrolytes such as Li7P3S11, and crystalline electrolytes such as Li 10 GeP2S 12 , Li6PS5Cl, Li6PS5Br, Li6PS5I, etc.; the particle size D90 thereof is 1-5μm, preferably 3-4μm; and the thickness of the solid-state electrolyte separator is 80-120μm. By controlling the content of the binder within the above range, the structural stability of the solid-state electrolyte separator during the cycle of the battery can be ensured, the ion conductivity is improved, and the interface contact resistance is reduced. The above solid-state electrolyte has good electrochemical performance.

[0076] According to a fourth aspect of the present application, a preparation method of the above solid-state electrolyte separator is provided, which includes the following steps:

[0077] Step S1: mixing a sulfide solid-state electrolyte and a binder in a third solvent to obtain a film-forming slurry; wherein the binder is the fluorinated acrylate binder described above or the fluorinated acrylate binder prepared by the preparation method of the fluorinated acrylate binder described above;

[0078] Step S2: The film-forming slurry is scraped, dried, to obtain a solid electrolyte separator.

[0079] In some embodiments, the weight ratio of the fluorinated acrylate binder, the sulfide solid electrolyte and the third solvent is 1:(20~50):(15~40); for example, 1:(25~40):(20~35), further for example, 1:(30~39):(25~35), and more specifically, 1:39:31. The third solvent is at least one of isododecane, dipropylene glycol dimethyl ether, ethyl 3-ethoxypropionate and isobutyl isobutyrate. The scraping speed is 45~55 mm / min; the drying process includes: first drying at a temperature of 70~90℃ for 8~12h, and then drying at a temperature of 120~140℃ for 10~20min.

[0080] According to a fifth aspect of the present application, a solid-state battery is provided, which comprises a positive electrode, a solid electrolyte separator and a negative electrode; the solid electrolyte separator is the above-mentioned solid electrolyte separator.

[0081] The present application will be further described in detail below in conjunction with specific embodiments, which cannot be understood as limiting the scope of the present application.

[0082] The raw materials of the embodiments of the present application are all prior art and can be commercially available.

[0083] Example 1

[0084] The preparation method of the fluorinated methyl methacrylate binder (PVDF-g-MMA) comprises the following steps:

[0085] Step S1: The polyvinylidene fluoride film (PVDF, molecular weight 100 WD a) is subjected to 100 kGy electron beam activation to obtain activated PVDF, which is stored at -30℃ for standby;

[0086] Step S2: 100 g of methyl methacrylate (MMA) ethanol solution (40 wt.% content) is prepared, argon is introduced into the solution for 30 min to remove oxygen in the MMA ethanol solution, the temperature is raised to 60℃, 8 g of activated PVDF of step S1 and 60 mg of 2-phenylpropane thioester of thiobenzoic acid (RAFT reagent) are added, and the reaction is carried out for 45 min. The reaction product PVDF-g-gMMA is taken out after stopping heating, soaked in ethanol for 10 min, rinsed 3 times and dried for 24 h to obtain pure PVDF-g-MA, which is ready for use. 90 g of isododecane is added to a high-pressure reaction kettle, 10 g of PVDF-g-MMA is added, and the mixture is treated at 100℃ and 200 rpm for 1 h, and then treated at 200℃ and 300 rpm for 3 h to obtain a fluorinated acrylate binder solution (solution concentration 10 wt.%).

[0087] Preparation method of solid electrolyte separator: take 3.75 g of the fluorinated acrylate binder solution prepared in step S2, 14.625 g of sulfide solid electrolyte (Li6PS5Br, particle size 0.5-1 μm) and 11.625 g of isododecane, and mechanically stir at 300 rpm for 2 h to obtain a film-forming slurry. The film-forming slurry is coated by a 200 μm height doctor blade at 50 mm / min, treated at 80°C for 10 h, and treated at 130°C for 15 min to obtain a solid electrolyte separator with a thickness of 90 μm, and the binder content in the separator is 2.5 wt%.

[0088] Example 2

[0089] Example 2 differs from Example 1 in that the MMA in step S2 is replaced by glycidyl methacrylate (GMA); other operations are the same.

[0090] Example 3

[0091] Example 3 differs from Example 1 in that the MMA in step S2 is replaced by butyl acrylate (BA); other operations are the same.

[0092] Example 4

[0093] Example 4 differs from Example 1 in that the MMA in step S2 is replaced by 2- (dimethylamino) ethyl methacrylate (DMAEMA); other operations are the same.

[0094] Example 5

[0095] Example 5 differs from Example 1 in that the PVDF in step S1 is replaced by ethylene-tetrafluoroethylene copolymer (ETFE); other operations are the same.

[0096] Example 6

[0097] Example 6 differs from Example 1 in that the PVDF in step S1 is replaced by fluorinated ethylene propylene copolymer (FEP); other operations are the same.

[0098] Example 7

[0099] Example 7 differs from Example 1 in that the PVDF in step S1 is replaced by polytrifluorochloroethylene (PCTFE); other operations are the same.

[0100] Example 8

[0101] Example 8 differs from Example 1 in that the PVDF molecular weight in step S1 is replaced by 60 WD a; other operations are the same.

[0102] Example 9

[0103] Example 9 differs from Example 1 in that the PVDF molecular weight in Step S1 is replaced by 130 WDa; otherwise the same.

[0104] Example 10

[0105] Example 10 differs from Example 1 in that the RAFT is replaced by 40 mg of bis(thiobenzoyl) disulfide; otherwise the same.

[0106] Example 11

[0107] Example 11 differs from Example 1 in that the RAFT is replaced by 200 mg of benzyl dithiobenzoate; otherwise the same.

[0108] Example 12

[0109] Example 12 differs from Example 1 in that the binder in the solid-state electrolyte separator is replaced by 6 g of a fluorinated acrylate binder solution (concentration 10 wt%); otherwise the same.

[0110] Example 13

[0111] Example 13 differs from Example 1 in that the PVDF molecular weight in Step S1 is replaced by 50 WDa; otherwise the same.

[0112] Example 14

[0113] Example 14 differs from Example 1 in that the RAFT in Step S2 is replaced by 320 mg; otherwise the same.

[0114] Example 15

[0115] Example 15 differs from Example 1 in that the electron beam activation energy in Step S1 is replaced by 200 kGy; otherwise the same.

[0116] Comparative Example 1

[0117] Comparative Example 1 differs from Example 1 in that the binder in the solid-state electrolyte separator is replaced by polymethyl methacrylate (PMMA) which is not fluorinated; otherwise the same.

[0118] Performance Test:

[0119] The following tests are performed on the solid-state electrolyte separators prepared in each example and comparative example.

[0120] (1) Decomposition temperature: The decomposition temperature is tested by thermogravimetric analysis (TGA).

[0121] (2) Ionic conductivity: The resistance is obtained by the alternating current impedance method, and the ionic conductivity is calculated by the following formula:

[0122]

[0123] where σ is the ionic conductivity (S cm -1 ), R is the resistance (Ω), l is the thickness (cm), and A is the area (cm 2 ).

[0124] (3) Tensile strength: The tensile test was performed according to GB / T36363-2018, and the tensile rate was 50 mm / min; the test results are shown in Table 1.

[0125] Table 1

[0126]

[0127] The test results in Table 1 show that the decomposition temperature of the solid electrolyte separator prepared by each embodiment of the present application is 242-325℃; the ionic conductivity is 2.2-2.72 mS / cm, and the tensile strength is 1.61-2.63 MPa. The decomposition temperature of the solid electrolyte separator prepared by Comparative Example 1 using polymethyl methacrylate which is not modified by fluorination is 153℃; the ionic conductivity is 1.82 mS / cm, and the tensile strength is 0.67 MPa. In comparison, the decomposition temperature, ionic conductivity and tensile strength of the solid electrolyte separator prepared by the embodiments of the present application are all significantly improved; it is shown that the thermal stability, ionic conductivity and adhesion of the acrylate adhesive can be significantly improved by modifying the acrylate adhesive by fluorination, thereby improving the high temperature resistance, ionic conductivity and tensile strength of the solid electrolyte separator.

[0128] The fluorine-containing material modified acrylate adhesive proposed by the present application improves the chemical resistance, thermal stability and mechanical properties of the fluorine-containing acrylate adhesive, and makes the adhesive have good ionic conductivity; as an adhesive for solid electrolyte separator, it promotes the ion conduction speed of the solid electrolyte separator, reduces the interface impedance, and ensures that the solid-state battery has stable long-term cycle performance and high temperature performance.

[0129] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application are used to distinguish similar objects, and do not necessarily describe a specific order or sequence. It should be understood that the terms used in this way 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.

Claims

1. A fluorinated acrylate adhesive, characterized in that, The fluorinated acrylate binder is a graft polymer formed by grafting acrylate monomers onto the molecular chain of a fluorinated polymer through controlled free radical polymerization under the action of a chain transfer agent.

2. The fluorinated acrylate adhesive according to claim 1, characterized in that, The grafting degree of the fluorinated acrylate adhesive is 50-120%, preferably 70-100%; And / or, the weight ratio of the acrylate monomer, the fluoropolymer and the chain transfer agent is 40:(6~10):(0.04~0.2).

3. The fluorinated acrylate adhesive according to claim 1 or 2, characterized in that, The acrylate monomers are selected from at least one of methyl methacrylate, glycidyl methacrylate, butyl acrylate, and ethyl 2-(dimethylamino)methacrylate.

4. The fluorinated acrylate adhesive according to any one of claims 1 to 3, characterized in that, The molecular weight of the fluoropolymer is 600,000 to 1,300,000 Da; And / or, the fluoropolymer is selected from at least one of polyvinylidene fluoride, ethylene-tetrafluoroethylene copolymer, fluorinated ethylene propylene copolymer, and polychlorotrifluoroethylene.

5. The fluorinated acrylate adhesive according to any one of claims 1 to 4, characterized in that, The controlled free radical polymerization is a reversible addition-fragmentation chain transfer polymerization; And / or, the chain transfer agent is selected from at least one of 2-phenylpropane thiobenzoate, bis(thiobenzoyl) disulfide, benzyl dithiobenzoate and 2-phenylethylbenzene dithiol ester; And / or, the chain transfer agent is 0.1 to 0.5 wt% of the acrylate monomer.

6. A method for preparing a fluorinated acrylate adhesive according to any one of claims 1 to 5, characterized in that, The preparation method includes the following steps: Step S1: Activate the fluoropolymer to obtain a fluoropolymer with active free radicals; Step S2: The fluoropolymer with active free radicals, acrylate monomers and chain transfer agent are subjected to a controlled free radical polymerization reaction in an inert atmosphere to obtain fluorinated acrylate, and then to obtain the fluorinated acrylate adhesive.

7. The method for preparing the fluorinated acrylate adhesive according to claim 6, characterized in that, In step S2, the temperature of the controlled free radical polymerization reaction is 55~70℃; the time of the controlled free radical polymerization reaction is 40~50min. And / or, the weight ratio of the acrylate monomer, the fluoropolymer, and the chain transfer agent is 40:(6~10):(0.04~0.2). And / or, the chain transfer agent is 0.1 to 0.5 wt% of the acrylate monomer; And / or, the inert atmosphere is argon; And / or, in step S1, the activation is radiation activation; preferably, the radiation activation is selected from at least one activation method selected from electron beam, ultraviolet light and plasma; more preferably, the radiation energy of the electron beam is 50~150kGy; And / or, the acrylate monomers are selected from at least one of methyl methacrylate, glycidyl methacrylate, butyl acrylate, and ethyl 2-(dimethylamino)methacrylate; And / or, the molecular weight of the fluoropolymer is 600,000 to 1,300,000 Da; And / or, the fluoropolymer is selected from at least one of polyvinylidene fluoride, ethylene-tetrafluoroethylene copolymer, fluorinated ethylene propylene copolymer, and polychlorotrifluoroethylene; And / or, the controlled radical polymerization reaction is a reversible addition-fragmentation chain transfer polymerization reaction; And / or, the chain transfer agent is selected from at least one of 2-phenylpropane thiobenzoate, bis(thiobenzoyl) disulfide, benzyl dithiobenzoate and 2-phenylethylbenzene dithiol ester; And / or, in step S2, the fluoropolymer with active free radicals, the acrylate monomers, and the chain transfer agent undergo the controlled free radical polymerization reaction in a first solvent; preferably, the first solvent is selected from at least one of N,N-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, and ethanol; And / or, the fluorinated acrylate is further washed and dried in sequence with a second solvent to obtain the purified fluorinated acrylate; preferably, the second solvent is selected from at least one of N,N-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone and ethanol; And / or, step S2 is followed by step S3: mixing the fluorinated acrylate and the organic solution to obtain the fluorinated acrylate adhesive; preferably, the weight ratio of the fluorinated acrylate to the organic solution is (5~15):(85~95); preferably, the organic solution is selected from at least one of isododecane, dipropylene glycol dimethyl ether, ethyl 3-ethoxypropionate and isobutyl isobutyrate.

8. A solid electrolyte membrane; characterized in that, It includes a sulfide solid electrolyte and a binder; wherein the binder is the fluorinated acrylate binder according to any one of claims 1 to 5 or the fluorinated acrylate binder prepared by the preparation method of the fluorinated acrylate binder according to claim 6 or 7; Preferably, the fluorinated acrylate binder is 2-4 wt% of the solid electrolyte membrane; Preferably, the sulfide solid electrolyte is selected from at least one of glassy electrolytes, glass-ceramic electrolytes, and crystalline electrolytes; Preferably, the particle size D90 of the sulfide solid electrolyte is 1~5μm; Preferably, the thickness of the solid electrolyte membrane is 80~120μm.

9. A method for preparing the solid electrolyte membrane according to claim 8, characterized in that, The preparation method includes the following steps: Step S1: The sulfide solid electrolyte and the binder are mixed in a third solvent to obtain a film-forming slurry; wherein the binder is the fluorinated acrylate binder according to any one of claims 1 to 5, or the fluorinated acrylate binder obtained by the preparation method of the fluorinated acrylate binder according to claim 6 or 7; Step S2: The film-forming slurry is coated and dried to obtain the solid electrolyte membrane; Preferably, the weight ratio of the fluorinated acrylate binder, the sulfide solid electrolyte, and the third solvent is 1:(20~50):(15~40). Preferably, the third solvent is selected from at least one of isododecane, dipropylene glycol dimethyl ether, ethyl 3-ethoxypropionate, and isobutyl isobutyrate.

10. A solid-state battery, comprising a positive electrode, a solid electrolyte membrane, and a negative electrode; characterized in that, The solid electrolyte membrane is the solid electrolyte membrane of claim 8 or the solid electrolyte membrane of claim 9 prepared by the same method.

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