Solid-state electrolyte slurry, solid-state electrolyte membrane, solid-state battery and electrical apparatus

Abstract

A solid-state electrolyte slurry, a solid-state electrolyte membrane, a solid-state battery and an electrical apparatus. The solid-state electrolyte slurry comprises a first solvent, the polarity parameter of the first solvent being not greater than 4; and a first fluoropolymer, the first fluoropolymer being soluble in the first solvent. The low-polarity solvent has weak reactivity, so that the solid-state electrolyte still maintains high ionic conductivity after being treated by the low-polarity solvent. The fluoropolymer is soluble in the low-polarity solvent, which not only fully functions as a binder to bond the solid-state electrolyte into a membrane having a certain strength, but also does not have too much negative impact on the ionic conductivity of the electrolyte membrane, thus allowing the electrolyte to maintain interconnectivity during battery cycling, further resisting the stress and suppressing the increase in interfacial impedance, and improving the cycling performance of batteries.

Description

Solid electrolyte slurry, solid electrolyte membrane, solid-state battery and electrical device

[0001] Cross-references

[0002] This application refers to Chinese Patent Application No. 202311446247.1 filed on November 2, 2023, entitled “Solid Electrolyte Slurry, Solid Electrolyte Membrane, Solid-State Battery and Electrical Device,” which is incorporated herein by reference in its entirety. Technical Field

[0003] The present application relates to the field of solid-state battery technology, and in particular to a solid electrolyte slurry, a solid electrolyte membrane, a solid-state battery, and an electrical device. Background Art

[0004] With the energy crisis and environmental protection requirements, new energy batteries have received unprecedented attention. However, due to the use of liquid electrolytes, the safety of existing secondary batteries cannot fully meet the applicable requirements. In recent years, solid-state batteries using solid electrolytes have attracted widespread attention due to their higher safety.

[0005] Existing solid-state electrolytes include oxide, sulfide, and polymer electrolytes. Sulfide electrolytes are considered promising materials for industrialization due to their high ionic conductivity and excellent mechanical properties. However, existing electrolyte slurries struggle to effectively disperse and form sulfide electrolytes, severely impacting solid-state battery performance. Therefore, existing solid-state electrolyte slurries still require improvement.

[0006] Summary of the Invention

[0007] The present application is made in view of the above-mentioned problems, and its purpose is to provide a solid electrolyte slurry, which has excellent film-forming properties and is conducive to improving the electrochemical performance of solid-state batteries.

[0008] In a first aspect, the present application provides a solid electrolyte slurry, which includes a first solvent having a polarity parameter not exceeding 4; and a first fluoropolymer, which is soluble in the first solvent.

[0009] The first solvent, whose polarity parameter does not exceed 4, has low polarity. Low-polarity solvents have weak reactivity, and the solid electrolyte after treatment with the low-polarity solvent still maintains high ionic conductivity. The first fluoropolymer is soluble in the low-polarity solvent, fully utilizing its binder function to bond the solid electrolyte into a membrane with a certain strength while not excessively negatively affecting the ionic conductivity of the electrolyte membrane. This allows the electrolyte to remain interconnected during battery cycling, thereby resisting stress, suppressing the increase of interfacial impedance, and improving the battery's cycling performance.

[0010] In any embodiment, the first fluoropolymer comprises a structural unit represented by formula I and a structural unit represented by formula II, and the molar percentage of the structural unit represented by formula I is 15%-25%, optionally 17%-22%, based on the total molar number of the structural units in the first fluoropolymer.

[0011] Wherein, in Formula I, R1 and R2 each independently include one or more of hydrogen, fluorine, chlorine, and trifluoromethyl, and R1 and R2 are not hydrogen at the same time.

[0012] The first fluorine-containing polymer can be dissolved in a low-polarity solvent, and the low-polarity solution of the first fluorine-containing polymer can form a film, so that the electrolyte membrane has high ion conductivity and the battery has low impedance and high cycle stability.

[0013] In any embodiment, the first fluoropolymer is amorphous and the glass transition temperature of the fluoropolymer is from -100°C to -50°C.

[0014] The first fluoropolymer has low crystallinity and low glass transition temperature, can present a highly elastic state at room temperature, and has a large free volume for chain segment movement, which helps it dissolve in low-polarity solvents and the formation of electrolyte membranes and positive electrode membranes, thereby improving the cycle stability of the battery.

[0015] In any embodiment, the Mooney viscosity of the first fluoropolymer is

[0016] The first fluorine-containing polymer is in a rubbery state at room temperature and has a large free volume for chain segment movement, which is conducive to its dissolution in low-polarity solvents and the formation of electrolyte membranes and positive electrode membrane layers, thereby improving the cycle stability of the battery.

[0017] In any embodiment, the first fluoropolymer includes at least one of poly(vinylidene fluoride-hexafluoropropylene), poly(vinylidene fluoride-chlorotrifluoroethylene), poly(vinylidene fluoride-trifluoroethylene-hexafluoropropylene), and poly(vinylidene fluoride-chlorotrifluoroethylene-hexafluoropropylene).

[0018] The first fluorine-containing polymer has a high proportion of comonomers, poor molecular regularity, and is easily soluble in low-polarity solvents, so that the electrolyte membrane and the positive electrode membrane layer containing the solid electrolyte material can be formed with the help of the low-polarity solvent. At the same time, it is beneficial to maintain the high ionic conductivity of the solid electrolyte, reduce the battery impedance, and improve the cycle stability of the secondary battery.

[0019] In any embodiment, the first fluoropolymer is prepared by emulsion polymerization.

[0020] In emulsion polymerization, the system has low viscosity, which facilitates heat transfer, stirring, and pipeline transportation, making continuous operation easy. Using emulsion polymerization can not only increase the polymerization reaction rate, but also provide a high-purity reaction environment, which is conducive to increasing the degree of polymerization of the monomer represented by Formula I in the first fluorine-containing polymer.

[0021] In any embodiment, the first solvent includes at least one of n-heptane, toluene, n-hexane, xylene, n-butyl ether, anisole, or butyl butyrate.

[0022] Low-polarity solvents are beneficial to maintaining the ionic conductivity of the solid electrolyte. The first fluoropolymer can be dissolved in the low-polarity solvent and can fully play the role of the binder, so that the solid electrolyte can be bonded into a film, thereby being able to resist stress during the battery cycle, inhibiting the increase of interface impedance, and improving the battery's cycle performance.

[0023] In any embodiment, the solid electrolyte slurry further includes a first sulfide solid electrolyte. Optionally, the first sulfide solid electrolyte includes Li6PS5X, wherein X includes at least one of Cl, Br or I.

[0024] Because sulfide electrolytes are highly reactive, the use of low-polarity solvents can help improve the ionic conductivity of solid electrolyte membranes. Furthermore, the use of low-polarity solvents can reduce the surface roughness of solid electrolyte membranes caused by the rapid evaporation of polar solvents with high vapor pressures, thereby improving the uniformity and workability of the solid electrolyte membranes.

[0025] A second aspect of the present application provides a solid electrolyte membrane, which is prepared by using the solid electrolyte slurry in any embodiment.

[0026] In any embodiment, based on the total mass of the solid electrolyte membrane, the mass percentage of the first fluoropolymer is 1.0%-3.4%, optionally 1.2%-3.2%.

[0027] By controlling the mass content of the first fluoropolymer within an appropriate range, sufficient first fluoropolymer can be dispersed in the low-polarity solvent to bond the sulfide solid electrolyte to form a solid electrolyte membrane, keeping the solid electrolytes interconnected during the cycle to reduce interfacial impedance; it can also reduce the negative impact of the first fluoropolymer on the ionic conductivity of the electrolyte membrane, thereby comprehensively improving the cycle performance of the battery.

[0028] In any embodiment, the solid electrolyte membrane has an ionic conductivity of 0.12 mS / cm to 0.30 mS / cm.

[0029] A third aspect of the present application provides a solid-state battery, which includes the solid-state electrolyte membrane of the second aspect of the present application.

[0030] In any embodiment, the solid-state battery includes a positive electrode sheet, the positive electrode sheet includes a current collector and a positive electrode film layer provided on at least one surface of the current collector, the positive electrode film layer includes a second fluoropolymer, the second fluoropolymer includes a structural unit represented by formula I and a structural unit represented by formula II, based on the total molar number of the structural units in the second fluoropolymer, the molar percentage of the structural unit represented by formula I is 15%-25%, optionally 17%-22%,

[0031] Wherein, in the structural unit shown in Formula I, R1 and R2 each independently include one or more of hydrogen, fluorine, chlorine, and trifluoromethyl, and R1 and R2 are not hydrogen at the same time.

[0032] In any embodiment, based on the total mass of the positive electrode film layer, the mass content of the second fluorine-containing polymer is 1.0%-3.8%, and optionally 1.2%-2.6%.

[0033] Controlling the mass content of the second fluoropolymer within an appropriate range can not only allow sufficient second fluoropolymer to be dispersed in the low-polarity solvent to bond the solid electrolyte and the positive electrode active material in the positive electrode film layer to form a positive electrode film layer with a certain bonding strength; it can also reduce the negative impact of the use of the second fluoropolymer on the battery impedance and comprehensively improve the cycle stability of the battery.

[0034] In any embodiment, the positive electrode film layer includes a second sulfide solid electrolyte. Optionally, the second sulfide solid electrolyte includes Li6PS5X, wherein X includes at least one of Cl, Br or I.

[0035] In any embodiment, the bonding strength between the positive electrode film layer and the positive electrode current collector is 10 N / m-35 N / m.

[0036] In any embodiment, the positive electrode film layer is prepared by a positive electrode slurry including a second fluoropolymer and a second sulfide solid electrolyte, and the positive electrode slurry also includes a second solvent, and the polarity parameter of the second solvent does not exceed 4. Optionally, the second solvent includes at least one of n-heptane, toluene, n-hexane, xylene, n-butyl ether, anisole or butyl butyrate.

[0037] The fourth aspect of the present application provides an electrical device comprising the solid-state battery of the third aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] FIG1 is a schematic diagram of an electrical device using a solid-state battery as a power source according to an embodiment of the present application. DETAILED DESCRIPTION

[0039] Below, the embodiments of the solid electrolyte slurry, solid electrolyte membrane, solid-state battery and electrical device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0040] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0041] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0042] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0043] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0044] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0045] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0046] Forming a solid electrolyte membrane with high ionic conductivity and a certain mechanical strength is the basis for improving the performance of solid-state batteries. In the prior art, the method of forming a solid electrolyte membrane is generally to mix a solid electrolyte, a binder and a solvent to prepare a slurry and then apply it to form a film. The solid electrolyte dispersed in the solvent needs to be connected into a conductive network in the electrolyte membrane with the help of a binder. Solvents with high dispersibility for binders, such as N-methylpyrrolidone (NMP) and trimethyl phosphate, often have high polarity. The solid electrolyte will experience a sudden drop in ionic conductivity during contact with high-polarity solvents, which has a negative impact on the electrochemical performance of solid-state batteries. Low-polarity solvents are beneficial to maintaining the ionic conductivity of solid electrolytes, but it is difficult to disperse the binder in the prior art and affect subsequent film formation.

[0047] [Solid electrolyte slurry]

[0048] Based on this, the present application proposes a solid electrolyte slurry, which includes a first solvent, wherein the polarity parameter of the first solvent does not exceed 4; and a first fluoropolymer, wherein the first fluoropolymer can be dissolved in the first solvent.

[0049] Solid electrolyte slurry refers to a slurry containing a solid electrolyte and used to form an electrolyte component (such as a solid electrolyte membrane) in a secondary battery.

[0050] Solid electrolytes refer to electrolyte materials that have both solid-state characteristics and ionic conductivity comparable to that of molten strong electrolytes or strong electrolyte aqueous solutions.

[0051] The polarity parameter is a parameter used to characterize the polarity of a solvent. The larger the polarity parameter, the more polar the solvent. Polarity parameters can be obtained by consulting reference books. The lower the polarity parameter, the less polar the solvent. Solvents with a polarity parameter of 4 or less are generally considered low-polarity solvents.

[0052] In some embodiments, the first solvent includes at least one of n-heptane, toluene, n-hexane, xylene, n-butyl ether, anisole, or butyl butyrate.

[0053] In some embodiments, the first solvent comprises n-heptane. In some embodiments, the first solvent comprises n-butyl ether. In some embodiments, the first solvent comprises xylene. In some embodiments, the first solvent comprises butyl butyrate.

[0054] As used herein, the term "fluoropolymer" refers to a polymer containing the element fluorine. This includes, on the one hand, chemically homogeneous aggregates of macromolecules produced by polymerization, but varying in degree of polymerization, molar mass, and chain length. The term also includes derivatives of such aggregates of macromolecules formed by polymerization, i.e., compounds obtained by reactions of functional groups in the macromolecules, such as addition or substitution, and which may be chemically homogeneous or chemically heterogeneous.

[0055] As used herein, "the first fluoropolymer is soluble in the solvent" means that after the first fluoropolymer is dispersed in the solvent, the solution is transparent, not turbid. The solubility of the first fluoropolymer in the solvent can be tested by any known method. As an example, 25 g of the first fluoropolymer is dispersed in 475 mL of a solvent with a polarity parameter of no more than 4, stirred for 48 hours, and then allowed to stand for 3 hours. The solution is then observed. If the solution is transparent, the first fluoropolymer is considered soluble in the solvent.

[0056] In some embodiments, the solid content of the solid electrolyte slurry is 10%-50%, and can be 10%, 20%, 30%, 40%, 50% or any value therebetween.

[0057] In some embodiments, the solid electrolyte slurry is capable of forming a film.

[0058] The film-forming properties of a solid electrolyte slurry can be tested using any known method. For example, the solid electrolyte slurry is dried at 80°C for 72 hours to determine whether it forms a smooth, dense solid electrolyte membrane. If, after drying, the slurry still exhibits granular or regional surface agglomeration defects, it indicates poor film-forming properties. If, after drying, no granular or lumpy agglomerations are present, the surface demonstrates film-forming properties.

[0059] The film-forming properties of solid electrolyte slurries have a key impact on the performance of solid-state batteries. The solid electrolyte slurries provided in the embodiments of this application have good film-forming properties, allowing the solid electrolyte membrane to be tightly bonded to the electrode, thereby improving the electrochemical performance and cycle stability of solid-state batteries.

[0060] Polymer dissolution is a slow process involving two stages: swelling and dissolution. Swelling occurs due to the significant size disparity between polymer chains and solvent molecules. Solvent molecules penetrate the polymer material quickly, but polymer molecules diffuse slowly into the solvent. As a result, solvent molecules penetrate the spaces between polymer chains, causing them to expand in volume, but preventing the polymer chains from diffusing. Dissolution, on the other hand, occurs as solvent molecules continue to penetrate. The spaces between polymer chains increase. Furthermore, the infiltrating solvent molecules solvate the polymer chains, weakening the interactions between the polymer chains and allowing chain segments to move until they are free from the interaction of other segments, achieving dissolution. Fluoropolymers in existing technologies often swell in low-polarity solvents and are difficult to dissolve. Therefore, the binders used in existing solid electrolyte membranes are often non-fluoropolymers that are soluble in low-polarity solvents. However, non-fluoropolymers have low bonding strength, which is not conducive to improving battery cycling stability.

[0061] Low-polarity solvents have weak reactivity, and solid electrolytes treated with low-polarity solvents still maintain high ionic conductivity. The first fluoropolymer provided in the embodiments of the present application is soluble in low-polarity solvents, which can fully exert the role of a binder, allowing the solid electrolyte to bond into a membrane with a certain strength, while not having too much negative impact on the ionic conductivity of the electrolyte membrane. Furthermore, it can maintain the interconnection of the electrolytes during the battery cycle, thereby resisting stress, suppressing the increase of interfacial impedance, and improving the battery's cycle performance.

[0062] In some embodiments, the first fluoropolymer comprises a structural unit represented by Formula I and a structural unit represented by Formula II, and the molar percentage of the structural unit represented by Formula I is 15%-25%, optionally 17%-22%, based on the total molar number of the structural units in the first fluoropolymer.

[0063] Wherein, in the formula I, R1 and R2 each independently include one or more of hydrogen, fluorine, chlorine, and trifluoromethyl, and R1 and R2 are not hydrogen at the same time.

[0064] As used herein, the term "fluoro" refers to a -F group.

[0065] As used herein, the term "chloro" refers to a -Cl group.

[0066] As used herein, the term "trifluoromethyl" refers to a -CF3 group.

[0067] In some embodiments, R1 and R2 each independently include one or more of fluorine, chlorine, and trifluoromethyl.

[0068] In some embodiments, R1 includes fluorine and R2 includes trifluoromethyl. In some embodiments, R1 includes fluorine and R2 includes fluorine. In some embodiments, R1 includes fluorine and R2 includes chlorine. In some embodiments, R1 includes fluorine and R2 includes chlorine. In some embodiments, R1 includes trifluoromethyl and R2 includes trifluoromethyl.

[0069] In some embodiments, the mole percentage of the structural unit represented by Formula I, based on the total moles of the structural units in the first fluoropolymer, can be selected as 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25% or any value therebetween.

[0070] The first fluorine-containing polymer can be dissolved in a low-polarity solvent, and the low-polarity solution of the first fluorine-containing polymer can form a film, so that the electrolyte membrane has high ion conductivity and the battery has low impedance and high cycle stability.

[0071] In some embodiments, the first fluoropolymer is amorphous and the glass transition temperature of the first fluoropolymer is from -100°C to -50°C.

[0072] Herein, the term "amorphous state" refers to a state having no crystallinity or a crystallinity of less than 5%.

[0073] In the present application, the crystallinity test can be performed using methods known in the art, such as differential scanning calorimetry. In some embodiments, 0.5 g of the fluoropolymer is placed in an aluminum crucible, shaken flat, and covered with a lid. The crucible is then tested using a differential scanning calorimeter (DSC) (TA Instruments, USA, Model: Discovery 250) in a nitrogen atmosphere with a purge gas flow rate of 50 ml / min and a protective gas flow rate of 70 ml / min, at a heating rate of 10°C per minute, over a test temperature range of -100°C to 400°C, and the thermal history is erased.

[0074] This test will produce a DSC (Mw / mg) temperature-dependent curve of the fluoropolymer. If no obvious peaks or troughs appear in the DSC curve, or if the peaks or troughs that do appear are integrated, the peak area is the melting enthalpy ΔH (J / g) of the polymer. Polymer crystallinity = (ΔH / ΔHm) × 100%, where ΔHm is the standard melting enthalpy (crystal melting heat) of polyvinylidene fluoride, ΔHm = 104.7 J / g. A polymer with a crystallinity of less than 5% is considered amorphous.

[0075] In this article, the term "glass transition temperature" refers to the temperature at which a polymer changes from a glassy state to a highly elastic state, abbreviated as Tg.

[0076] In the present application, the glass transition temperature of the fluoropolymer can be tested by methods known in the art, such as differential scanning calorimetry (DSC). As an example, 1 to 3 mg of the fluoropolymer sample is weighed and the crucible lid is covered. The parameter settings include nitrogen atmosphere, purge gas at 50 mL / min, and protective gas at 100 mL / min. The temperature rise program includes a heating rate of 10°C / min, a temperature range of -100°C to 300°C, and insulation at 300°C for 3 minutes. The testing instrument is DSC 200CF3. All test processes require the elimination of thermal history. Wait for the test to end, analyze the curve, and take the intersection of the line with the same distance from the two extrapolated baselines and the curve as the Tg value of the fluoropolymer.

[0077] In some embodiments, the glass transition temperature of the first fluoropolymer may be -50°C, -55°C, -60°C, -65°C, -70°C, -75°C, -80°C, -85°C, -90°C, -95°C, -100°C, or a range consisting of any two of the above values.

[0078] The first fluoropolymer has low crystallinity and low glass transition temperature, can present a highly elastic state at room temperature, and has a large free volume for chain segment movement, which helps it dissolve in low-polarity solvents and the formation of electrolyte membranes and positive electrode membranes, thereby improving the cycle stability of the battery.

[0079] In some embodiments, the Mooney viscosity of the first fluoropolymer is

[0080] Wherein, 1M is the viscosity, the unit is Mooney value, L represents the large rotor, 1 represents the preheating time of 1 minute, 10 represents the rotation time of 10 minutes, and 121°C is the experimental temperature.

[0081] In this article, the term "Mooney viscosity" is a commonly used indicator to measure the degree of polymerization and molecular weight of rubber. It is expressed by the shear resistance encountered by the rotor when rotating in a closed chamber sample.

[0082] The first fluorine-containing polymer is in a rubbery state at room temperature and has a large free volume for chain segment movement, which is conducive to its dissolution in low-polarity solvents and the formation of electrolyte membranes and positive electrode membrane layers, thereby improving the cycle stability of the battery.

[0083] In this application, the Mooney viscosity of fluoropolymers can be measured using methods known in the art, such as using an MV2000 Mooney viscometer (manufactured by Alpha Technologies, Inc., USA) in accordance with the national standard GB / T 1232.1-2016. The Mooney viscosity of the polymer is measured at a temperature of 121°C, with a preheating time of 1 minute and a rotation time of 10 minutes.

[0084] In some embodiments, the first fluoropolymer includes at least one of poly(vinylidene fluoride-hexafluoropropylene), poly(vinylidene fluoride-chlorotrifluoroethylene), poly(vinylidene fluoride-trifluoroethylene-hexafluoropropylene), or poly(vinylidene fluoride-chlorotrifluoroethylene-hexafluoropropylene).

[0085] The first fluoropolymer has a high proportion of comonomers, poor molecular regularity, and is easily soluble in low-polarity solvents, so that the electrolyte membrane and the positive electrode membrane layer containing the solid electrolyte material can be formed with the help of low-polarity solvents. At the same time, it is beneficial to maintain the high ionic conductivity of the solid electrolyte, reduce the battery impedance, and improve the cycle stability of the secondary battery.

[0086] In some embodiments, the first fluoropolymer is prepared by emulsion polymerization.

[0087] Emulsion polymerization is a polymer processing method in which monomers are polymerized to form an emulsion in water under mechanical stirring or oscillation through the action of an emulsifier.

[0088] In emulsion polymerization, the system has low viscosity, which facilitates heat transfer, stirring, and pipeline transportation, making continuous operation easy. Using emulsion polymerization can not only increase the polymerization reaction rate, but also provide a high-purity reaction environment, which is conducive to increasing the degree of polymerization of the monomer represented by Formula I in the first fluorine-containing polymer.

[0089] In some embodiments, the solid electrolyte slurry further includes a first sulfide solid electrolyte. Optionally, the first sulfide solid electrolyte includes Li6PS5X, wherein X includes at least one of Cl, Br or I.

[0090] In some embodiments, the first sulfide solid electrolyte is Li6PS5Cl. In some embodiments, the first sulfide solid electrolyte is Li6PS5Br. In some embodiments, the first sulfide solid electrolyte is Li6PS5I.

[0091] Because sulfide electrolytes are highly reactive, the use of low-polarity solvents can help improve the ionic conductivity of solid electrolyte membranes. Furthermore, the use of low-polarity solvents can reduce the surface roughness of solid electrolyte membranes caused by the rapid evaporation of polar solvents with high vapor pressures, thereby improving the uniformity and workability of the solid electrolyte membranes.

[0092] In some embodiments, the method for preparing the first fluoropolymer includes: providing at least one monomer represented by formula III and a monomer represented by formula IV,

[0093] wherein R1 and R2 each independently include one or more of hydrogen, fluorine, chlorine, and trifluoromethyl, and R1 and R2 are not hydrogen at the same time;

[0094] Based on the total moles of the monomers represented by formula III and the monomers represented by formula IV, the mole percentage of the monomer represented by formula III is not less than 15%. Optionally, the mole percentage of the monomer represented by formula III is 15%-25%, optionally 17%-22%.

[0095] The fluorine-containing polymer has a high proportion of comonomers, poor molecular regularity, and is easily soluble in low-polarity solvents, so that the electrolyte membrane and the positive electrode film layer containing the solid electrolyte material can be formed with the help of the low-polarity solvent. At the same time, it is beneficial to maintain the high ionic conductivity of the solid electrolyte, reduce the battery impedance, and improve the cycle stability of the secondary battery.

[0096] In some embodiments, the molar percentage of the monomer represented by formula III can be 15%, 16%, 18%, 20%, 22%, 24%, 25% or any value therebetween based on the total moles of the monomer represented by formula III and the monomer represented by formula IV.

[0097] In some embodiments, the preparation of a fluorine-containing polymer by polymerizing monomers under polymerization conditions includes the following steps: conducting a first-stage polymerization reaction of at least one monomer represented by Formula III and a monomer represented by Formula IV and a reaction solvent in a non-reactive gas atmosphere; adding a chain transfer agent and conducting a second-stage polymerization reaction to obtain a fluorine-containing polymer.

[0098] In some embodiments, the first stage polymerization reaction further comprises the following steps: adding an aqueous solvent and an emulsifier to a container, evacuating the container, and then filling the container with a non-reactive gas; adding an initiator and a pH adjuster to the container, adjusting the pH to 6.5-7, and then adding at least one monomer represented by Formula III and a monomer represented by Formula IV to carry out the first stage polymerization reaction. In some embodiments, the monomer represented by Formula III comprises one or more of trifluoroethylene, chlorotrifluoroethylene, tetrafluoroethylene, and hexafluoropropylene.

[0099] In some embodiments, the reaction temperature of the first stage polymerization reaction is 80° C. to 125° C., the reaction time is 2 h to 10 h, and the initial polymerization pressure is 2.2 MPa to 10.4 MPa.

[0100] In some embodiments, the reaction temperature of the first stage polymerization reaction can be selected as 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, 120°C, 125°C, or a value in the range consisting of any two of the above points.

[0101] In some embodiments, the reaction time of the polymerization reaction may be 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, or a value in a range consisting of any two of the above points.

[0102] In some embodiments, the initial polymerization pressure is 2.2 MPa, 2.5 MPa, 3 MPa, 3.5 MPa, 4 MPa, 4.5 MPa, 5 MPa, 5.5 MPa, 6 MPa, 6.5 MPa, 7 MPa, 7.5 MPa, 8 MPa, 8.5 MPa, 9 MPa, 9.5 MPa, 10 MPa, 10.4 MPa, or a value in a range consisting of any two of the above points.

[0103] The above parameter range enables the fluorine-containing polymer to achieve a high copolymerization ratio of the monomer represented by formula III, and improves the solubility of the fluorine-containing polymer in low-polarity solvents.

[0104] In some embodiments, the non-reactive gas includes one or more of nitrogen, helium, argon, neon, hydrogen, and methane.

[0105] In some embodiments, the emulsifier includes one or more of ammonium perfluorooctanoate, perfluoropolyether carboxylic acid, and perfluoroalkyl sulfonate.

[0106] In some embodiments, the amount of the emulsifier is 0.1% to 0.3% of the total mass of the monomer represented by formula III and the monomer represented by formula IV.

[0107] In some embodiments, the amount of the emulsifier can be selected as 0.1%, 0.15%, 0.2%, 0.25%, 0.3% or a value within a range consisting of any two of the above values ​​based on the total mass of the monomer represented by Formula III and the monomer represented by Formula IV.

[0108] In some embodiments, the initiator is a peroxide; optionally, the peroxide includes one or more of persulfate, persulfate-bisulfite, and diisopropyl peroxydicarbonate (IPP).

[0109] In some embodiments, the amount of the initiator is 0.15% to 1% of the total mass of the monomer represented by formula III and the monomer represented by formula IV.

[0110] In some embodiments, the amount of the initiator can be selected as 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 0.95%, 1% of the total mass of the monomer represented by Formula III and the monomer represented by Formula IV, or a value in the range consisting of any two of the above points.

[0111] In some embodiments, the pH adjuster includes one or more of potassium carbonate, potassium bicarbonate, sodium carbonate, sodium bicarbonate, and ammonia solution.

[0112] In some embodiments, the amount of the pH adjuster is 0.1% to 0.3% of the total mass of the monomer represented by formula III and the monomer represented by formula IV.

[0113] In some embodiments, the amount of the pH adjuster can be selected as 0.1%, 0.15%, 0.2%, 0.25%, 0.3% or a value within a range consisting of any two of the above values ​​based on the total mass of the monomer represented by Formula III and the monomer represented by Formula IV.

[0114] In some embodiments, the second stage polymerization reaction specifically comprises the following steps: adding a chain transfer agent, performing the second stage polymerization reaction, and stopping the reaction when the pressure in the container drops to 1 MPa-3 MPa to obtain the fluorine-containing polymer.

[0115] In some embodiments, the chain transfer agent includes one or more of cyclohexane, carbon tetrachloride, methanol, acetone, diethyl malonate, dodecyl mercaptan, isopentane, isohexane, and ethyl acetate.

[0116] In some embodiments, the amount of the chain transfer agent is 2% to 5% of the total mass of the monomer represented by formula III and the monomer represented by formula IV.

[0117] In some embodiments, the amount of the chain transfer agent is 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or a value within a range consisting of any two of the above values ​​based on the total mass of the monomer represented by Formula III and the monomer represented by Formula IV.

[0118] [Solid electrolyte membrane]

[0119] In some embodiments, the present application provides a solid electrolyte membrane, which is prepared by the solid electrolyte slurry in some embodiments.

[0120] In some embodiments, based on the total mass of the solid electrolyte membrane, the mass content of the first fluoropolymer is 1.0%-3.4%, optionally 1.2%-3.2%.

[0121] In some embodiments, based on the total mass of the solid electrolyte membrane, the mass content of the first fluoropolymer may be 1.0%, 1.2%, 1.4%, 1.5%, 1.6%, 1.8%, 2.0%, 2.2%, 2.4%, 2.5%, 2.6%, 2.8%, 3.0%, 3.2%, 3.4% or a value in the range consisting of any two of the above points.

[0122] Controlling the mass content of the first fluoropolymer within an appropriate range can not only allow sufficient fluoropolymer to be dispersed in the low-polarity solvent to bond the sulfide solid electrolyte to form a solid electrolyte membrane, and keep the solid electrolytes interconnected during the cycle to reduce interfacial impedance; it can also reduce the negative impact of the fluoropolymer on the ionic conductivity of the electrolyte membrane, and comprehensively improve the cycle performance of the battery.

[0123] Based on the total mass of the solid electrolyte membrane, the mass percentage of the first fluorine-containing polymer is 1.2%-3.2%, and the cycle performance of the secondary battery is further improved.

[0124] In some embodiments, the solid electrolyte membrane has an ionic conductivity of 0.12 mS / cm to 0.30 mS / cm.

[0125] In some embodiments, the ionic conductivity of the solid electrolyte membrane may be selected as 0.12 mS / cm, 0.13 mS / cm, 0.14 mS / cm, 0.15 mS / cm, 0.16 mS / cm, 0.17 mS / cm, 0.20 mS / cm, 0.23 mS / cm, 0.25 mS / cm, 0.28 mS / cm, 0.30 mS / cm, or a value in a range consisting of any two of the above points.

[0126] The ionic conductivity of the solid electrolyte membrane is calculated by the following formula: σ = L / (R*S) (Formula I)

[0127] σ is the ionic conductivity of the solid electrolyte membrane, in S·cm -1 ; L is the thickness of the solid electrolyte membrane, in cm; S is the area of ​​the solid electrolyte membrane, in cm 2 and R is the AC impedance value of the solid electrolyte membrane, in Ω. The AC impedance value of the solid electrolyte membrane can be measured using an electrochemical workstation; the test frequency of the AC impedance is 105 Hz to 0.01 Hz.

[0128] [Solid-state battery]

[0129] In some embodiments, the present application provides a solid-state battery, which includes the solid-state electrolyte membrane in some embodiments.

[0130] A solid-state battery is a type of battery that uses solid electrodes and solid electrolytes. It can be understood that solid-state batteries include all-solid-state batteries and semi-solid-state batteries.

[0131] In some embodiments, the solid-state battery includes a positive electrode sheet, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, the positive electrode film layer includes a second fluoropolymer, the second fluoropolymer includes a structural unit represented by formula I and a structural unit represented by formula II, based on the total molar number of the structural units in the second fluoropolymer, the molar percentage of the structural unit represented by formula I is 15%-25%, optionally 17%-22%,

[0132] Wherein, in the structural unit represented by formula I, R1 and R2 each independently include one or more of hydrogen, fluorine, chlorine, and trifluoromethyl, and R1 and R2 are not hydrogen at the same time.

[0133] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0134] In some embodiments, based on the total mass of the positive electrode film layer, the mass content of the second fluorine-containing polymer is 1.0%-3.8%, optionally 1.0%-2.6%.

[0135] In some embodiments, based on the total mass of the positive electrode film layer, the mass content of the second fluoropolymer may be selected to be 1.0%, 1.2%, 1.4%, 1.5%, 1.6%, 1.8%, 2.0%, 2.2%, 2.4%, 2.5%, 2.6%, 2.8%, 3.0%, 3.2%, 3.4%, 3.5%, 3.6%, 3.8% or a value in the range consisting of any two of the above points.

[0136] Controlling the mass content of the second fluoropolymer in the positive electrode film layer within an appropriate range can not only allow sufficient fluoropolymer to be dispersed in the low-polarity solvent to bond the solid electrolyte and the positive electrode active material in the positive electrode film layer to form a positive electrode film layer with a certain bonding strength; it can also reduce the negative impact of the use of the fluoropolymer on the battery impedance and comprehensively improve the cycle stability of the battery.

[0137] In some embodiments, the positive electrode film layer includes a second sulfide solid electrolyte. Optionally, the second sulfide solid electrolyte includes Li6PS5X, wherein X includes at least one of Cl, Br or I.

[0138] In some embodiments, the second sulfide solid electrolyte is Li6PS5Cl. In some embodiments, the second sulfide solid electrolyte is Li6PS5Br. In some embodiments, the second sulfide solid electrolyte is Li6PS5I.

[0139] Including a second sulfide solid electrolyte in the positive electrode film layer helps to reduce the interface resistance between the positive electrode plate and the electrolyte membrane and improve the kinetic performance of the solid-state battery.

[0140] In some embodiments, the bonding strength between the positive electrode film layer and the positive electrode current collector is 10 N / m-35 N / m.

[0141] The bonding strength between the positive electrode film layer and the positive electrode current collector can be tested by any known method. As an example, double-sided tape is used to adhere one side of the positive electrode film layer and compacted with a roller to make it completely fit with the electrode; the other side of the double-sided tape of the sample is adhered to the stainless steel surface, and one end of the sample is bent in the opposite direction with a bending angle of 180°; a high-speed rail tensile tester is used for testing, one end of the stainless steel is fixed to the lower fixture of the tensile tester, and the bent end of the sample is fixed to the upper fixture. The angle of the sample is adjusted to ensure that the upper and lower ends are in a vertical position, and then the sample is stretched at a speed of 50 mm / min until the sample is completely peeled off from the substrate. The displacement and force during the process are recorded, and the force when the force is balanced is used as the adhesion force of the positive electrode film layer. The force divided by the adhesion length of the sample is used as the bonding strength between the positive electrode film layer and the positive electrode current collector.

[0142] In some embodiments, the bonding strength between the positive electrode film layer and the positive electrode current collector is 10 N / m, 15 N / m, 20 N / m, 25 N / m, 30 N / m, or any range therebetween.

[0143] In some embodiments, the positive electrode film layer is prepared by a positive electrode slurry including the second fluoropolymer and the second sulfide solid electrolyte, and the positive electrode slurry also includes a second solvent, and the polarity parameter of the second solvent does not exceed 4. Optionally, the second solvent includes at least one of n-heptane, toluene, n-hexane, xylene, n-butyl ether, anisole or butyl butyrate.

[0144] In some embodiments, the second fluoropolymer is soluble in the second solvent.

[0145] In some embodiments, a solid-state battery is made of a positive electrode sheet, a negative electrode sheet, and an electrolyte membrane through a lamination process.

[0146] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0147] In some embodiments, the positive electrode film layer includes a positive electrode active material. The positive electrode active material may be a positive electrode active material for a battery that is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: a lithium-containing phosphate with an olivine structure, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05O2) and its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0148] In some embodiments, the positive electrode film layer may further include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0149] [Electrical devices]

[0150] In addition, the present application also provides an electrical device, which includes at least one of the solid-state battery, battery module, or battery pack provided in the present application. The solid-state battery, battery module, or battery pack can be used as a power source for the electrical device, and can also be used as an energy storage unit for the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0151] As the electrical device, a solid-state battery, a battery module or a battery pack can be selected according to its usage requirements.

[0152] Figure 1 shows an example of an electric device. This device can be a pure electric vehicle, hybrid electric vehicle, or plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of solid-state batteries, a battery pack or battery module can be used.

[0153] Another example device may be a mobile phone, a tablet computer, a laptop computer, etc. Such a device is usually required to be lightweight and thin, and may use a solid-state battery as a power source.

[0154] Example

[0155] The following examples are provided. The examples described below are exemplary and are intended only to explain the present application and are not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the examples, the techniques or conditions described in the literature within the art or in the product specifications are used. Reagents or instruments not specified by manufacturer are commercially available conventional products.

[0156] 1. Preparation method

[0157] Preparation Example 1:

[0158] Synthesis of sulfide electrolytes

[0159] The sulfide electrolyte was synthesized using high-energy mechanical ball milling. In a glove box, LiCl, Li2S, and P2S5 were sealed in a zirconium milling jar at a molar ratio of 2:5:1. Different types of zirconium beads were added, with a ratio of 5mm diameter to 1mm diameter zirconium beads of 15:5. The mixture was milled clockwise at 500 rpm for 2 hours, followed by a 15-minute pause and then counterclockwise milling at the same speed for 2 hours. This process was repeated four times to prepare the Li6PS5Cl sulfide electrolyte.

[0160] Solvation treatment of solid electrolyte powder:

[0161] In a glove box with a water / oxygen content of less than or equal to 1 ppm, the Li6PS5Cl sulfide electrolyte powder prepared in Example 1 and n-butyl ether were stirred at a mass ratio of 1:3 for 8 h. The mixture was then placed in a watch glass and dried at 80°C for 72 h until the solvent was completely evaporated.

[0162] In Preparation Examples 2-8, different types of solvents were used to solvate the solid electrolyte powder. The specific types of solvents are shown in Table 1. The treatment method was the same as that in Preparation Example 1.

[0163] Example 1:

[0164] Synthesis of fluoropolymers

[0165] Synthesis of the First Fluoropolymer Poly(vinylidene fluoride-hexafluoropropylene)

[0166] 3.88 kg of deionized water and 1.8 g of ammonium perfluorooctanoate were added to a 10 L autoclave, and the mixture was evacuated and O2 was replaced with N2 three times. 5 g of persulfate and 2 g of sodium bicarbonate were added again, and 0.8 kg (12.5 mol) of vinylidene fluoride and 0.47 kg (3.13 mol) of hexafluoropropylene were charged. The monomers were added to make the pressure reach 7 MPa, mixed and stirred for 30 minutes, and the temperature was raised to 100° C. for polymerization reaction. After the reaction for 6 hours, 30 g of cyclohexane was added to continue the reaction. The reaction was stopped when the pressure in the reactor dropped to 2 MPa. The latex obtained by polymerization was frozen for coagulation, and the obtained crumb-like polymer was filtered, squeezed for dehydration, and dried for dehydration.

[0167] Synthesis of the Second Fluoropolymer Poly(vinylidene fluoride-hexafluoropropylene)

[0168] The second fluorine-containing polymer is prepared in the same manner as the first fluorine-containing polymer.

[0169] Synthesis of high molecular weight carboxyl-modified PVDF:

[0170] First stage polymerization reaction: 4 kg of deionized water and 2 g of methyl cellulose ether were added to 10 L autoclaves No. 1 and No. 2, respectively. The mixture was evacuated and O2 was replaced with N2 three times. 5 g of tert-butyl peroxypivalate and 2 g of sodium bicarbonate were added again. 1 kg of vinylidene fluoride monomer was added to the mixture until the pressure reached 5 MPa. The mixture was mixed and stirred for 30 min. The temperature was raised to 45°C. An aqueous solution containing 22.5 g of β-acryloyloxypropionic acid was added in multiple portions and the reaction was allowed to proceed for 3 h.

[0171] Second stage polymerization reaction: transfer the reaction liquid in reactors 1 and 2 to reactor 3, fill with nitrogen to a pressure of 7 MPa, raise the temperature to 70°C, and stir the reaction for 3 hours;

[0172] The third stage of polymerization reaction: After adding 40 g of cyclohexane, the reaction was continued for 1 hour, and then the reaction was stopped. The reaction system was centrifuged, and the solid phase was collected, washed, and dried to obtain a poly(vinylidene fluoride-β-acryloxypropionic acid) copolymer with a weight average molecular weight of 5 million.

[0173] Synthesis of sulfide electrolytes

[0174] Same as Preparation Example 1.

[0175] Preparation of positive electrode

[0176] The positive electrode active material lithium nickel cobalt manganese oxide NCM 811 , conductive agent carbon black, Li6PS5Cl sulfide electrolyte, and the second fluorine-containing polymer are dissolved in butyl butyrate solvent in a mass ratio of 94.5:1.5:2.0:2.0, stirred and mixed evenly to obtain a positive electrode slurry with a solid content of 65%; then the positive electrode slurry is evenly coated on both sides of the positive electrode collector, and then dried, cold pressed, and cut to obtain a positive electrode sheet with a compaction density of 3.5g / cm 3 .

[0177] Preparation of negative electrode sheet

[0178] The active material silicon-carbon composite material (wherein the mass ratio of silicon to graphite is 9:1), the conductive agent carbon nanotube slurry (wherein the solid content of carbon nanotubes is 2%), and the high molecular weight carboxyl-modified PVDF (poly (vinylidene fluoride-β-acryloxypropionic acid) copolymer) are dissolved in the solvent NMP according to the dry material mass ratio of 96:1:3, and mixed evenly to prepare the negative electrode slurry; the solid content of the slurry is 35%, and the negative electrode slurry is evenly coated on the negative electrode current collector copper foil once or multiple times. After drying, cold pressing, and slitting, the negative electrode sheet is obtained, and the compaction density is 1.7g / cm 3 .

[0179] Preparation of solid electrolyte membrane

[0180] In an argon atmosphere glove box (H2O <0.1ppm, O2 <0.1ppm), the solid sulfide electrolyte and the first fluoropolymer were dry-mixed at a mass ratio of 98:2. The mixture was then dispersed and dissolved in butyl butyrate solvent, with the dry material content reaching 30% of the total mass. The mixture was stirred at a rotation speed of 1000 rppm for 3 hours until fully dissolved. A solid electrolyte membrane with a thickness of 180μm was prepared using conventional solution casting techniques and dried.

[0181] Assembly of solid-state batteries:

[0182] The positive electrode sheet, solid electrolyte membrane, and negative electrode sheet of Example 1 were cut to the corresponding sizes, such that the negative electrode sheet capacity / positive electrode sheet capacity ratio was 1.1. The positive electrode sheet, solid electrolyte membrane, and negative electrode sheet were stacked in this order. The solid electrolyte membrane serves as both an ion conductor and a separator to produce a bare laminated battery. Tabs were then welded to the bare cells, which were then encased in an aluminum shell and baked at 80°C to remove moisture, yielding an uncharged battery. Hot pressing with a fixture and capacity testing were then performed to obtain the lithium-ion laminated battery product of Example 1.

[0183] In Example 2-5, the copolymerization ratio of hexafluoropropylene of the first fluorine-containing polymer in the solid electrolyte membrane was changed, and the other conditions were basically the same as those in Example 1, see Table 2.

[0184] In Example 6, the type of the comonomer of the first fluorine-containing polymer in the solid electrolyte membrane was changed. Other steps were basically the same as those in Example 1, see Table 2.

[0185] In Examples 7-10, the addition ratio of the first fluorine-containing polymer in the solid electrolyte membrane was changed, and the solid electrolyte content changed accordingly. Other aspects were basically the same as in Example 1, see Table 2.

[0186] The preparation methods of Examples 11-14 are basically the same as those of Example 1, except that the ratio of the comonomer of the second fluorine-containing polymer in the positive electrode film layer is adjusted. Specific parameters are shown in Table 3.

[0187] In Example 15, the type of comonomer of the fluorine-containing polymer in the positive electrode film layer was changed. The other parameters were basically the same as in Example 1. The specific parameters are shown in Table 3.

[0188] In Examples 16-19, the addition ratio of the second fluorine-containing polymer in the positive electrode film layer was changed, and accordingly, the content of the positive electrode active material was adjusted accordingly. Other parameters were basically the same as in Example 1. See Table 3 for specific parameters.

[0189] The preparation method of Comparative Example 1 is similar to that of Example 1, except that the synthesis method of the first fluoropolymer in the solid electrolyte membrane in Comparative Example 1 and the assembly method of the battery are different (since the electrolyte membrane is difficult to form using the first fluoropolymer in the comparative example, the battery assembly method is adjusted):

[0190] Synthesis of the first fluoropolymer

[0191] 3.88 kg of deionized water and 1.8 g of ammonium perfluorooctanoate were added to a 10 L autoclave, and the mixture was evacuated and O2 was replaced with N2 three times. 5 g of persulfate and 2 g of sodium bicarbonate were added again, and 0.8 kg of vinylidene fluoride (12.5 mol) and 0.28 kg of hexafluoropropylene (1.87 mol) were charged. The monomers were added to make the pressure reach 7 MPa, mixed and stirred for 30 minutes, and the temperature was raised to 44° C. to carry out polymerization reaction. After the reaction was carried out for 6 hours, 30 g of cyclohexane was added to continue the reaction. The reaction was stopped when the pressure in the reactor dropped to 2 MPa. The reaction system was centrifuged, the solid phase was collected, washed, and dried to obtain a poly(vinylidene fluoride-hexafluoropropylene) polymer.

[0192] Assembly of solid-state batteries:

[0193] Since the fluoropolymer in the comparative example has poor film-forming properties and is difficult to prepare an electrolyte membrane, a Swagelok cell mold was used to prepare a composite solid-state battery comprising a positive electrode, a negative electrode, and all-solid-state battery powder disposed between the positive and negative electrodes. The positive and negative electrodes comprise the positive and negative electrode sheets described in Example 1.

[0194] The binder of the solid electrolyte in Comparative Example 2 is PVDF homopolymer. Please see Table 2 for specific parameters.

[0195] The preparation method of Comparative Example 3 is basically the same as that of Comparative Example 1, except that no binder is added to the solid electrolyte membrane. Specific parameters are shown in Table 2.

[0196] The preparation method of Comparative Example 4 is basically the same as that of Example 1, except that the binder in the solid electrolyte membrane is butadiene rubber. Please see Table 2 for specific parameters.

[0197] The preparation method of Comparative Example 5 is basically the same as that of Example 1, except that the ratio of vinylidene fluoride and hexafluoropropylene in the second fluorine-containing polymer in the positive electrode film layer is adjusted so that the copolymerization ratio is adjusted. Please see Table 3 for specific parameters.

[0198] In Comparative Example 6, the second fluorine-containing polymer in the positive electrode film layer is a vinylidene fluoride homopolymer.

[0199] 2. Test Method

[0200] 1. Solid electrolyte powder ion conductivity test:

[0201] The prepared sulfide solid electrolyte powder material was placed in a test mold and pressed under high pressure using a tablet press to obtain a solid electrolyte sheet. The electrolyte's AC impedance value was obtained using an electrochemical workstation (CorrTest CS310H) at a test frequency of 105 Hz to 0.01 Hz.

[0202] The ionic conductivity of the solid electrolyte powder was calculated according to formula I.

[0203] Formula: σ = L / (R * S) (Formula I)

[0204] σ(S·cm -1 ) is the ionic conductivity of the electrolyte powder, L (cm) is the thickness of the electrolyte sheet, S (cm 2 ) is the electrolyte sheet area and R (Ω) is the AC impedance value of the electrolyte.

[0205] 2. Solid electrolyte membrane ion conductivity test

[0206] The prepared solid electrolyte membrane was subjected to an AC impedance test using an electrochemical workstation, and the ionic conductivity of the solid electrolyte membrane was calculated according to Formula I.

[0207] 3. Glass transition temperature test

[0208] Weigh 1-3 mg of fluoropolymer and cover the crucible. Set the parameters to a nitrogen atmosphere, a purge gas flow rate of 50 mL / min, and a shielding gas flow rate of 100 mL / min. The temperature ramp rate is 10°C / min from -100°C to 300°C, with a 3-min hold at 300°C. The test instrument is a DSC 200CF3. All tests require thermal history erasure. After the test is complete, analyze the curve and determine the polymer's Tg value at the intersection of the line with the two extrapolated baselines at equal distances.

[0209] 4. Crystallization test

[0210] 0.5 g of fluoropolymer was placed in an aluminum crucible, shaken flat, and covered with a crucible lid. Under a nitrogen atmosphere, with a purge gas of 50 ml / min and a protective gas of 70 ml / min, a heating rate of 10°C per minute, and a test temperature range of -100°C to 400°C, the test was performed using a differential scanning calorimeter (DSC) of TA Instruments, USA, model Discovery 250, and the thermal history was eliminated.

[0211] This test will produce a DSC (Mw / mg) temperature-dependent curve of the fluoropolymer. If no distinct peaks or troughs appear in the DSC curve, or if any peaks or troughs are integrated, the peak area is the polymer's melting enthalpy, ΔH (J / g). Polymer crystallinity = (ΔH / ΔHm) × 100%, where ΔHm is the standard melting enthalpy (crystal melting heat) of polyvinylidene fluoride, ΔHm = 104.7 J / g. A polymer with a crystallinity of less than 5% is considered amorphous.

[0212] 5. Mooney viscosity test

[0213] The first fluoropolymer of Examples 1-10 was tested using an MV2000 Mooney viscometer (Alpha Technologies, Inc., USA) in accordance with the method described in GB / T 1232.1-2016. The rotor diameter was 38.10 mm. The Mooney viscosity of the first fluoropolymer was measured using a temperature of 121°C, a preheating time of 1 minute, and a rotation time of 10 minutes.

[0214] 6. Solubility test of fluoropolymers in solvents

[0215] Take 25g of the first fluoropolymer and dissolve it in 475mL of solvent. After stirring for 48h, let it stand for 3h and observe the state of the solution. If the solution is transparent and can be dried in a container to form a complete film, it is considered that the solubility of the first fluoropolymer in the solvent is OK. If the solution is turbid, it is considered that the solubility of the first fluoropolymer in the solvent is NG.

[0216] 7. Slurry fluidity test

[0217] Use a spatula to take an appropriate amount of positive electrode slurry and observe whether it flows down smoothly. If it flows down smoothly, it is judged as OK. If the slurry appears jelly-like or lumpy, it indicates gelation and poor fluidity, which is judged as NG.

[0218] 8. Slurry film forming test

[0219] The prepared solid electrolyte slurry is poured into a polytetrafluoroethylene template and dried at 80°C for 72 hours to see if a smooth, dense solid electrolyte membrane can be formed. If granular or regional surface agglomeration defects remain after drying, it indicates poor film formation and is marked as NG. If no granular or blocky agglomeration occurs after drying, the surface shows film formation and is marked as OK.

[0220] 9. Bonding strength of pole piece

[0221] The positive electrode slurry is coated on the surface of the current collector (such as), dried and cold pressed to form a pole piece (compression 2.3g / cc), and the prepared pole piece is cut into a test sample of 20mm×100mm size for standby use; the pole piece is bonded to the positive electrode film layer with double-sided tape and compacted with a pressure roller to make it completely fit with the pole piece; the other side of the double-sided tape of the sample is attached to the stainless steel surface, and one end of the sample is bent in the opposite direction with a bending angle of 180°; a high-speed rail tensile tester is used for testing, one end of the stainless steel is fixed to the lower fixture of the tensile tester, and the bent end of the sample is fixed to the upper fixture, the angle of the sample is adjusted to ensure that the upper and lower ends are in a vertical position, and then the sample is stretched at a speed of 50mm / min until the sample is completely peeled off from the substrate, and the displacement and force during the process are recorded. The force at the time of force balance is taken as the adhesion force of the positive electrode film layer, and the force divided by the distance of 50mm in the smooth stage of the test curve is taken as the bonding strength between the positive electrode film layer and the positive current collector.

[0222] 10. Battery DC impedance test

[0223] At 25°C, the battery corresponding to Example 1 was charged at a constant current of 1 / 3C to 4.25V, then charged at a constant voltage of 4.25V to a current of 0.05C. After 5 minutes of rest, the voltage V1 was recorded. The battery was then discharged at 1 / 3C for 30 seconds, and the voltage V2 was recorded. The internal resistance DCR1 of the battery after the first cycle was calculated as (V2 - V1) / 1 / 3C. The internal resistance of the battery obtained from the second cycle was used as the full battery impedance.

[0224] 11. Battery cycle capacity retention rate

[0225] At 25°C, charge the battery at a constant current of 1 / 3C to 4.25V, then charge at a constant voltage of 4.25V to a current of 0.05C, let it rest for 5 minutes, and then discharge it at 1 / 3C to 2.8V. The resulting capacity is recorded as the initial capacity C0. Repeat the above steps for the same battery and record the discharge capacity Cn of the battery after the nth cycle. The battery capacity retention rate after each cycle is Pn = Cn / C0×100%. Record the battery cycle capacity retention rate after 400 cycles.

[0226] 3. Analysis of test results of various embodiments and comparative examples

[0227] Batteries of various embodiments and comparative examples were prepared according to the above methods, and various performance parameters were measured. The results are shown in Tables 1, 2, and 3 below.

[0228] Table 1

[0229] Table 2

[0230] Table 3

[0231] The ionic conductivity of Li6PS5Cl powder without solvent treatment is 5.2mS / cm. As can be seen from Table 1, when the sulfur-containing electrolyte is dissolved in a high-polarity solvent with a polarity parameter greater than 4, the ionic conductivity of the electrolyte will drop significantly. In order to reduce the degradation of battery performance caused by the attenuation of the ionic conductivity of the sulfur-containing electrolyte during the preparation process, the electrolyte slurry and the positive electrode slurry both include a low-polarity solvent, and the polarity parameter of the low-polarity solvent does not exceed 4. The fluorinated polymer provided in the embodiments of the present application can be dissolved in a low-polarity solvent with a polarity parameter not exceeding 4.

[0232] As can be seen from the examples in Tables 1 and 2, the first fluoropolymer includes (i) structural units derived from vinylidene fluoride and (ii) structural units derived from hexafluoropropylene and chlorotrifluoroethylene, and when the molar percentage of the structural units derived from hexafluoropropylene and chlorotrifluoroethylene is 15%-25% based on the total molar number of the structural units in the first fluoropolymer, the first fluoropolymer can be dissolved in a low-polarity solvent and the electrolyte slurry has film-forming properties.

[0233] The DSC curve of the fluoropolymer shows that the fluoropolymer includes (i) structural units derived from vinylidene fluoride and (ii) structural units derived from hexafluoropropylene and chlorotrifluoroethylene, and when the molar percentage of the structural units derived from hexafluoropropylene and chlorotrifluoroethylene is 15%-25% based on the total molar number of the structural units in the fluoropolymer, no obvious endothermic or exothermic peaks appear in the DSC curve of the fluoropolymer, but the baseline changes, indicating that the fluoropolymers in the examples are all amorphous polymers, and their glass transition temperatures are between -100°C and -50°C. The fluoropolymers are in a rubbery state at room temperature. The Mooney viscosity test results show that the Mooney viscosities of the fluoropolymers in Examples 1-10 are The fluoropolymers in Comparative Examples 1 and 2 are in granular or powder form at room temperature, and DSC testing indicates a crystallinity exceeding 20%. The fluoropolymers in these examples are easily soluble and dispersed in low-polarity solvents, enabling the electrolyte slurry to form a film. This allows the electrolyte membrane to maintain high ionic conductivity while exhibiting good processability, thereby improving battery cycling stability.

[0234] The solid electrolyte in Comparative Example 3 does not include a binder. Although it maintains high ionic conductivity of the solid electrolyte, the solid electrolyte is difficult to form a film and the particles cannot be tightly bonded together, resulting in large interface impedance. As the cycle progresses, dendrites grow inside the battery, making it difficult to cycle 400 times.

[0235] From the comparison between the embodiment and comparative example 3 in Table 2, it can be seen that although the addition of the fluoropolymer causes the ionic conductivity of the electrolyte membrane to decrease compared with the ionic conductivity of the pure solid electrolyte powder, it can effectively maintain the connection of the solid electrolyte during the cycle, maintain the stress of the electrolyte membrane on the electrode, thereby reducing the interfacial impedance, inhibiting dendrite growth, and improving the cycle stability of the battery.

[0236] As shown in Table 2, when the mass content of the first fluoropolymer in the solid electrolyte membrane is 1.0% to 3.4%, the electrolyte membrane maintains high ionic conductivity and the battery has a high cycle capacity retention rate. When the mass content of the first fluoropolymer in the electrolyte membrane is 1.2% to 3.2%, the ionic conductivity of the solid electrolyte membrane and the battery's cycle capacity retention rate are further improved.

[0237] From the comparison of Examples 1-10 and Comparative Example 4 in Table 2, it can be seen that at the same mass content of the first fluoropolymer as the binder, the solid electrolyte membrane using the first fluoropolymer as the binder has higher ionic conductivity than the solid electrolyte membrane using butadiene rubber as the binder in the prior art, and can increase the bonding strength, so that the battery has better cycle stability.

[0238] From the comparison of the examples and the comparative examples in Table 3, it can be seen that the second fluoropolymer in the positive electrode film layer includes (i) structural units derived from vinylidene fluoride and (ii) structural units derived from hexafluoropropylene and chlorotrifluoroethylene, and based on the total molar number of the structural units in the second fluoropolymer, when the molar percentage of the structural units derived from hexafluoropropylene and chlorotrifluoroethylene is 15%-25%, the second fluoropolymer has good dispersibility in low-polarity solvents, maintains high bonding strength of the electrode sheet, and makes the battery have low impedance, and the secondary battery has high cycle stability.

[0239] As shown in Table 3, when the mass content of the second fluoropolymer in the positive electrode film is 1.0%-3.8%, the battery exhibits low impedance and high cycle capacity retention. When the mass content of the second fluoropolymer in the positive electrode film is 1.2%-2.6%, the battery exhibits high bonding strength, low impedance, and high cycle stability. The addition of a solid electrolyte to the positive electrode film helps increase ion transport rate, reduce battery impedance, and improve battery cycle performance.

[0240] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A solid electrolyte slurry, characterized in that: The solid electrolyte slurry comprises: a first solvent having a polarity parameter of no more than 4; and A first fluorine-containing polymer, wherein the first fluorine-containing polymer is soluble in the first solvent.

2. The solid electrolyte slurry according to claim 1, characterized in that The first fluorine-containing polymer comprises a structural unit represented by formula I and a structural unit represented by formula II, and the molar percentage of the structural unit represented by formula I is 15%-25% based on the total molar number of the structural units in the first fluorine-containing polymer. Wherein, in the structural unit represented by formula I, R1 and R2 each independently include one or more of hydrogen, fluorine, chlorine, and trifluoromethyl, and R1 and R2 are not hydrogen at the same time.

3. The solid electrolyte slurry according to claim 2, characterized in that: Based on the total molar number of the structural units in the first fluorine-containing polymer, the molar percentage of the structural unit represented by formula I is 17%-22%.

4. The solid electrolyte slurry according to any one of claims 1 to 3, characterized in that The first fluorine-containing polymer is amorphous and has a glass transition temperature of -100°C to -50°C.

5. The solid electrolyte slurry according to any one of claims 1 to 4, characterized in that The Mooney viscosity of the first fluorine-containing polymer is 6. The solid electrolyte slurry according to any one of claims 1 to 5, characterized in that The first fluorine-containing polymer includes at least one of poly(vinylidene fluoride-hexafluoropropylene), poly(vinylidene fluoride-chlorotrifluoroethylene), poly(vinylidene fluoride-trifluoroethylene-hexafluoropropylene) or poly(vinylidene fluoride-chlorotrifluoroethylene-hexafluoropropylene).

7. The solid electrolyte slurry according to any one of claims 1 to 6, characterized in that: The first fluorine-containing polymer is prepared by emulsion polymerization.

8. The solid electrolyte slurry according to any one of claims 1 to 7, characterized in that: The first solvent includes at least one of n-heptane, toluene, n-hexane, xylene, n-butyl ether, anisole or butyl butyrate.

9. The solid electrolyte slurry according to any one of claims 1 to 8, characterized in that: The solid electrolyte slurry also includes a first sulfide solid electrolyte.

10. The solid electrolyte slurry according to claim 9, characterized in that: The first sulfide solid electrolyte includes Li6PS5X, wherein X includes at least one of Cl, Br or I.

11. A solid electrolyte membrane, characterized in that: The solid electrolyte membrane is prepared by the solid electrolyte slurry according to any one of claims 1 to 10.

12. The solid electrolyte membrane according to claim 11, characterized in that The mass content of the first fluorine-containing polymer is 1.0% to 3.4% based on the total mass of the solid electrolyte membrane.

13. The solid electrolyte membrane according to claim 11, characterized in that: The mass content of the first fluorine-containing polymer is 1.2%-3.2% based on the total mass of the solid electrolyte membrane.

14. The solid electrolyte membrane according to any one of claims 11 to 13, characterized in that The ionic conductivity of the solid electrolyte membrane is 0.12 mS / cm-0.30 mS / cm.

15. A solid-state battery, characterized in that: The solid-state battery comprises the solid-state electrolyte membrane according to any one of claims 11 to 14.

16. The solid-state battery according to claim 15, characterized in that: The solid-state battery comprises a positive electrode sheet, the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, the positive electrode film layer comprises a second fluorine-containing polymer, the second fluorine-containing polymer comprises a structural unit represented by formula I and a structural unit represented by formula II, and the molar percentage of the structural unit represented by formula I is 15%-25% based on the total molar number of the structural units in the second fluorine-containing polymer, Wherein, in the structural unit represented by formula I, R1 and R2 each independently include one or more of hydrogen, fluorine, chlorine, and trifluoromethyl, and R1 and R2 are not hydrogen at the same time.

17. The solid-state battery according to claim 16, characterized in that: Based on the total molar number of the structural units in the second fluorine-containing polymer, the molar percentage of the structural unit represented by formula I is 17%-22%.

18. The solid-state battery according to claim 16 or 17, characterized in that: Based on the total mass of the positive electrode film layer, the mass percentage of the second fluorine-containing polymer is 1.0%-3.8%.

19. The solid-state battery according to claim 16 or 17, characterized in that: Based on the total mass of the positive electrode film layer, the mass percentage of the second fluorine-containing polymer is 1.2%-2.6%.

20. The solid-state battery according to any one of claims 16 to 19, characterized in that: The positive electrode film layer includes a second sulfide solid electrolyte.

21. The solid-state battery according to claim 20, characterized in that: The second sulfide solid electrolyte includes Li6PS5X, wherein X includes at least one of Cl, Br or I.

22. The solid-state battery according to any one of claims 16 to 21, characterized in that: The bonding strength between the positive electrode film layer and the positive electrode current collector is 10N / m-35N / m.

23. The solid-state battery according to any one of claims 20 to 22, characterized in that: The positive electrode film layer is prepared by a positive electrode slurry including the second fluorine-containing polymer and the second sulfide solid electrolyte. The positive electrode slurry also includes a second solvent, and the polarity parameter of the second solvent is not more than 4.

24. The solid-state battery according to claim 23, characterized in that: The second solvent includes at least one of n-heptane, toluene, n-hexane, xylene, n-butyl ether, anisole or butyl butyrate.

25. An electrical device, characterized in that: A solid-state battery comprising the solid-state battery described in any one of claims 15 to 24.

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