Binder, preparation method, negative electrode slurry, negative electrode sheet, solid-state battery, and electric apparatus

Abstract

The present application provides a binder, a preparation method, negative electrode slurry, a negative electrode sheet, a solid-state battery and an electric apparatus. The binder comprises a fluorine-containing polymer, the fluorine-containing polymer comprises a structural unit derived from vinylidene fluoride and a structural unit derived from a monomer represented by formula I; on the basis of the total number of moles of the structural units in the fluorine-containing polymer, the molar content of the structural unit derived from the monomer represented by formula I is 0.3-2.5%, and the weight-average molecular weight of the fluorine-containing polymer is 1.5 million to 9 million. In formula I, R1, R2, and R3 each independently comprise at least one of hydrogen and a C1-3 alkyl group, and R4 comprises at least one of an ester group, a carbonyl group, a C1-3 alkyl group, and a single bond. The binder can enable the slurry to have high viscosity at low solid content, is suitable for a thin coating process, can improve the surface density uniformity of the electrode sheet, and can reduce the impedance of the solid-state battery, improving the cycle stability of the solid-state battery.

Description

Binder, preparation method, negative electrode slurry, negative electrode sheet, solid-state battery and electrical device

[0001] Cross-references

[0002] This application claims priority to Chinese Patent Application No. 202311449463.1 filed on November 2, 2023, entitled “Binder, Preparation Method, Negative Electrode Slurry, Negative Electrode Sheet, Solid-State Battery and Electrical Device,” which is incorporated herein by reference in its entirety. Technical Field

[0003] The present application relates to the technical field of secondary batteries, and in particular to a binder, a preparation method, a negative electrode slurry, a negative electrode plate, a solid-state battery, and an electrical device. Background Art

[0004] In recent years, secondary batteries have been widely used in energy storage systems such as hydropower, thermal, wind, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. With the widespread use of secondary batteries, higher requirements have been placed on their cycle performance and service life.

[0005] The electrode sheets formed by adhesives in the prior art often have a certain thickness, which is difficult to meet the manufacturing requirements of the thin electrode sheets of the new generation of batteries. Therefore, adhesives suitable for thin electrode sheets need to be further developed.

[0006] Summary of the Invention

[0007] This application is made in view of the above-mentioned issues, and its purpose is to provide an adhesive to meet the manufacturing needs of a new generation of thin battery electrodes.

[0008] A first aspect of the present application provides a binder, comprising a fluoropolymer, wherein the fluoropolymer comprises structural units derived from vinylidene fluoride and structural units derived from a monomer represented by Formula I, wherein the molar content of the structural units derived from the monomer represented by Formula I is 0.3% to 2.5% based on the total molar number of the structural units in the fluoropolymer; and the weight-average molecular weight of the fluoropolymer is 1.5 million to 9 million;

[0009] Wherein, R1, R2, and R3 each independently include hydrogen, C 1-3 At least one of the alkyl groups, R4 includes an ester group, a carbonyl group, a C 1-3 At least one of an alkyl group and a single bond.

[0010] The binder can effectively increase the viscosity of low-solid content slurry, improve the pole piece coating quality, improve the consistency of pole piece surface density, and especially improve the processing quality of thin coating process. Moreover, the binder has a higher weight-average molecular weight and is linearly distributed in the pole piece, which can reduce the coating of the active material in the pole piece, thereby increasing the transmission rate of active ions in the active material, reducing battery impedance, and improving battery cycle stability. Furthermore, relying on the carboxyl group introduced by the monomer shown in Formula I in the fluoropolymer, the binder has a tighter bonding effect with other materials in the pole piece, and can still effectively play a bonding role in the slurry with low solid content, play a role in suppressing rebound and further improving the cycle capacity retention rate in the pole piece. When the molar content of the structural unit of the monomer shown in Formula I is within a suitable range, the binder makes the slurry with low solid content have a suitable viscosity, effectively improves the uniformity of the pole piece surface density, reduces the full battery impedance of the solid-state battery, and improves the cycle performance of the solid-state battery.

[0011] In any embodiment, the weight average molecular weight of the fluoropolymer is 2 million to 6 million. Fluoropolymer binders with a weight average molecular weight of 2 million to 6 million can further improve the uniformity of the electrode surface density, reduce the full cell impedance of the solid-state battery, and enhance the cycle performance of the solid-state battery.

[0012] In any embodiment, the molar content of the structural unit derived from the monomer represented by formula I is 0.8% to 2% based on the total moles of the structural units in the fluorine-containing polymer.

[0013] In any embodiment, the polydispersity coefficient of the fluoropolymer is from 1.8 to 2.8, optionally from 1.8 to 2.5.

[0014] By controlling the polydispersity coefficient of the fluoropolymer within an appropriate range, the weight-average molecular weight of the fluoropolymer is evenly distributed and the performance is balanced, which effectively improves the consistency of the electrode surface density, reduces the full battery impedance of the solid-state battery, and improves the cycle performance of the solid-state battery.

[0015] In any embodiment, the crystallinity of the fluorine-containing polymer is 40% to 55%, and optionally 43% to 50%.

[0016] Fluoropolymers with a crystallinity within an appropriate range enable low-solid content slurries to have a suitable viscosity, effectively improving the uniformity of the electrode surface density, reducing the full-cell impedance of the solid-state battery, and improving the cycle performance of the solid-state battery.

[0017] In any embodiment, the Dv50 particle size of the fluorine-containing polymer is 1 um to 100 um, and can be optionally 30 um to 90 um.

[0018] Fluoropolymers with a Dv50 particle size within an appropriate range have good solubility, which enables the low-solid content slurry to have a suitable viscosity, effectively improving the uniformity of the electrode surface density, reducing the full-cell impedance of the solid-state battery, and improving the cycle performance of the solid-state battery.

[0019] In any embodiment, R4 of the fluoropolymer comprises an ester group.

[0020] The carboxyl group of the fluoropolymer is connected to the ester group rather than directly to the main chain, which can further reduce the ordered arrangement of the vinylidene fluoride structural units through the ester group, reduce the crystallinity of the fluoropolymer, further play a dispersing role in the slurry, improve the uniformity of the electrode, reduce the battery impedance, and improve the battery cycle performance.

[0021] In any embodiment, the monomer represented by formula I includes at least one of acrylic acid, methacrylic acid, β-acryloxypropionic acid, and maleic acid.

[0022] The above raw materials are simple and easy to obtain, which can greatly reduce production costs and increase output.

[0023] In any embodiment, the fluorine-containing polymer includes at least one of poly(vinylidene fluoride-acrylic acid), poly(vinylidene fluoride-methacrylic acid), poly(vinylidene fluoride-β-acryloyloxypropionic acid), and poly(vinylidene fluoride-maleic acid).

[0024] The second aspect of the present application further provides a method for preparing a binder, comprising the following steps:

[0025] Providing a vinylidene fluoride monomer, at least one monomer represented by formula I, and a solvent, and performing a first stage polymerization reaction to obtain a first product;

[0026] Wherein, R1, R2, and R3 each independently include hydrogen, C 1-3 At least one of the alkyl groups, R4 includes an ester group, a carbonyl group, a C 1-3 At least one of an alkyl group and a single bond;

[0027] subjecting the first product to a second-stage polymerization reaction under a water-insoluble gas atmosphere;

[0028] A chain transfer agent is added to carry out a third stage polymerization reaction to obtain a fluorine-containing polymer with a weight average molecular weight of 1.5 million to 9 million.

[0029] The use of a segmented polymerization method can effectively increase the molecular weight of the fluorinated polymer, so that the low-solid content slurry has a suitable viscosity, effectively improve the uniformity of the electrode surface density, reduce the full battery impedance of the solid-state battery, and improve the cycle performance of the solid-state battery.

[0030] In any embodiment, the reaction temperature of the first stage polymerization reaction is 30° C. to 60° C., the reaction time is 2 hours to 15 hours, and the initial polymerization pressure is 2.0 MPa to 7.0 MPa.

[0031] By controlling the reaction pressure, reaction time and reaction temperature of the polymerization reaction within an appropriate range, the uniformity of the weight-average molecular weight of the polymerization product can be controlled while increasing the weight-average molecular weight of the polymer, ensuring that the product has a lower polydispersity coefficient and improving the uniformity of product performance.

[0032] In any embodiment, the chain transfer agent includes one or more of cyclohexane, isopropanol, methanol, and acetone.

[0033] In any embodiment, the water-insoluble gas is selected from one or more of nitrogen, oxygen, hydrogen, and methane.

[0034] In any embodiment, the amount of the chain transfer agent is 0.5% to 5.5% of the total mass of the vinylidene fluoride monomer and the monomer represented by formula I.

[0035] The amount of the chain transfer agent is controlled within a suitable range, so that the polymer chain length can be controlled, thereby obtaining a polymer with a suitable molecular weight range.

[0036] In any embodiment, the first stage polymerization reaction comprises the following steps:

[0037] Adding a solvent and a dispersant into the container to remove oxygen from the reaction system;

[0038] Adding an initiator and a pH adjuster to the container, adjusting the pH value to 6.5-7, and then adding vinylidene fluoride monomer to make the pressure in the container reach 3.0 MPa-7.0 MPa;

[0039] After stirring for 30 to 60 minutes, the temperature is raised to 30° C. to 60° C., and the monomer represented by formula I is added simultaneously to carry out the first stage polymerization reaction.

[0040] In any embodiment, the amount of the solvent used is 2 to 8 times the total mass of the vinylidene fluoride monomer and the monomer represented by formula I.

[0041] In any embodiment, the dispersant comprises at least one of cellulose, cellulose ether and polyvinyl alcohol. Alternatively, the cellulose comprises one or more of hydroxypropyl methylcellulose, methyl cellulose ether and carboxyethyl cellulose ether.

[0042] In any embodiment, the amount of the dispersant used is 0.1% to 0.3% of the total mass of the vinylidene fluoride monomer and the monomer represented by formula I.

[0043] In any embodiment, the initiator includes at least one of tert-amyl peroxypivalate, tert-amyl peroxypivalate, 2-ethyl peroxydicarbonate, diisopropyl peroxydicarbonate, and tert-butyl peroxypivalate.

[0044] In any embodiment, the pH adjuster includes one or more of potassium carbonate, potassium bicarbonate, sodium carbonate, sodium bicarbonate, and aqueous ammonia.

[0045] In any embodiment, the amount of the pH adjuster is 0.05% to 0.2% of the total mass of the vinylidene fluoride monomer and the monomer represented by formula I.

[0046] In any embodiment, the monomer represented by formula I is added in multiple times during the first stage polymerization reaction.

[0047] The polymerization of the monomer represented by formula I and vinylidene fluoride is an exothermic reaction. Adding the monomer represented by formula I in multiple times can reduce solvent vaporization, stabilize the pressure in the reactor, improve the uniformity of the weight-average molecular weight of the fluoropolymer, reduce the polydispersity coefficient of the fluoropolymer, further improve the uniformity of the electrode surface density, reduce the full battery impedance of the solid-state battery, and improve the cycle performance of the solid-state battery.

[0048] A third aspect of the present application provides a negative electrode slurry, comprising the binder in any embodiment or the binder prepared by the preparation method in any embodiment.

[0049] In any embodiment, based on the total mass of the dry materials in the negative electrode slurry, the mass content of the binder is 1.0%-5.0%, and optionally 1.5%-4.5%.

[0050] By controlling the mass fraction of the binder within an appropriate range, the prepared negative electrode slurry has a higher solution viscosity at a low solid content, which can improve the uniformity of the electrode surface density, reduce the full battery impedance of the solid-state battery, and improve the cycle performance of the solid-state battery.

[0051] In any embodiment, the solid content of the negative electrode slurry is 25%-65%, and the viscosity of the negative electrode slurry is 4000mPa.s-8000mPa.s. Optionally, the solid content of the negative electrode slurry is 35%-55%, and the viscosity of the negative electrode slurry is 4500mPa.s-6000mPa.s.

[0052] Fluoropolymers enable the negative electrode slurry to have a higher solution viscosity at low solid content, which is particularly suitable for thin coating processes. It can improve the uniformity of the surface density in thin-coated electrodes, reduce the full battery impedance of solid-state batteries, and improve the cycle performance of solid-state batteries.

[0053] A fourth aspect of the present application provides a negative electrode plate, the negative electrode plate comprising a negative electrode film layer, wherein the negative electrode film layer is prepared from the negative electrode slurry of any embodiment.

[0054] In any embodiment, the surface density of the negative electrode film layer is 3 mg / cm 2 -6mg / cm 2 .

[0055] The negative electrode film layer has a low surface density, which can effectively reduce the growth of dendrites, especially inhibit the growth of dendrites in solid-state batteries and improve the cycle stability of the battery.

[0056] In any embodiment, the negative electrode film layer includes a silicon-based active material; optionally, the silicon-based active material includes at least one of a silicon-oxygen material, a silicon-carbon material, and elemental silicon.

[0057] Silicon-based active materials have high specific capacity, but they also suffer from high interlayer slippage, making effective compaction difficult and resulting in high rebound of the negative electrode film. Fluoropolymers can effectively bond silicon-based active materials, reducing the rebound of the negative electrode film after roller compaction, improving the uniformity of the electrode sheet and enhancing battery cycling stability.

[0058] The fifth aspect of the present application provides a solid-state battery, comprising the negative electrode sheet of the fourth aspect.

[0059] The sixth aspect of the present application provides an electrical device comprising the solid-state battery of the fifth aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] 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

[0061] Below, the binder, preparation method, negative electrode slurry, negative electrode sheet, solid-state battery and electric 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 structure 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.

[0062] " 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.

[0063] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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).

[0068] Solid-state batteries replace electrolytes with solid electrolytes, improving battery safety while increasing their energy density. However, solid-state batteries have high resistance, which is not conducive to the transmission of active ions between the positive and negative electrodes. Active ions are easily deposited and form dendrites during the transmission process, which in turn causes the battery to short-circuit and fail. Reducing the thickness of the electrode and reducing the transmission distance of active ions are effective means to inhibit the growth of dendrites in solid-state batteries. In order to achieve thinning of the electrode, the slurry needs to have a low solid content, that is, a certain viscosity to ensure the film-forming property of the slurry and the uniformity of the coating. However, the binders in the existing technology are difficult to use in thin coating processes, and the electrode consistency after coating is poor, and the electrochemical performance of the battery is reduced.

[0069] [Binder]

[0070] Based on this, the present application proposes a binder comprising a fluoropolymer, wherein the fluoropolymer comprises a structural unit derived from vinylidene fluoride and a structural unit derived from a monomer represented by formula I, wherein the molar content of the structural unit derived from the monomer represented by formula I is 0.3%-2.5% based on the total molar number of the structural units in the fluoropolymer; and the weight-average molecular weight of the fluoropolymer is 1.5 million to 9 million;

[0071] Wherein, R1, R2, and R3 each independently include hydrogen, C 1-3 At least one of the alkyl groups, R4 includes an ester group, a carbonyl group, a C 1-3 At least one of an alkyl group and a single bond.

[0072] As used herein, the term "binder" refers to a chemical compound, polymer, or mixture that forms a colloidal solution or colloidal dispersion in a dispersion medium.

[0073] As used herein, the term "polymer" includes, on the one hand, a collection of chemically homogeneous macromolecules prepared by polymerization, but differing in degree of polymerization, molar mass, and chain length. The term also includes derivatives of such collections of macromolecules formed by polymerization, i.e., compounds that can be obtained by reaction, for example, addition or substitution, of functional groups in the aforementioned macromolecules and that can be chemically homogeneous or chemically heterogeneous.

[0074] As used herein, the term "weight average molecular weight" refers to the sum of the weight fractions of molecules of different molecular weights in a polymer multiplied by their corresponding molecular weights.

[0075] As used herein, the term "ester group" refers to a group containing -C(O)O-.

[0076] As used herein, the term "carbonyl" refers to a group containing -C(O)-.

[0077] In this context, the term "alkyl" refers to a group having the general formula C n H 2n+1 A monovalent radical derived from a saturated, unbranched or branched aliphatic hydrocarbon by removing one hydrogen atom, wherein n is an integer. 1-3 Refers to an alkyl group wherein n is an integer between 1 and 3. In some embodiments, C 1-3 The alkyl group includes at least one of a methyl group, an ethyl group, a propyl group, and an isopropyl group.

[0078] In some embodiments, R4 includes a single bond, ie, the carboxyl functional group is directly attached to the carbon atom that is attached to the carbon-carbon double bond.

[0079] In some embodiments, the binder dispersion medium is an oily solvent. Examples of such oily solvents include, but are not limited to, dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, acetone, dimethyl carbonate, ethyl cellulose, and polycarbonate. That is, the binder is dissolved in the oily solvent.

[0080] In some embodiments, a binder is used to fix the electrode active material and / or the conductive agent in place and adhere them to the conductive metal component to form an electrode.

[0081] In some embodiments, the binder is used as a solid-state battery negative electrode binder to bind the negative electrode active material and / or the conductive agent to form a negative electrode film layer.

[0082] In the present application, the weight average molecular weight of the fluoropolymer can be tested by methods known in the art, such as gel chromatography, such as using a Waters 2695 Isocratic HPLC gel chromatograph (differential refractive index detector 2141). In some embodiments, the test method is to use a polystyrene solution sample with a mass fraction of 3.0% as a reference, and select a matching chromatographic column (oily: Styragel HT5DMF7.8×300mm+Styragel HT4). Use purified N-methylpyrrolidone (NMP) solvent to prepare a 3.0% fluoropolymer glue, and let the prepared solution stand for one day for use. During the test, first use a syringe to draw tetrahydrofuran, rinse, and repeat several times. Then draw 5 ml of the experimental solution, expel the air in the syringe, and wipe the needle tip dry. Finally, slowly inject the sample solution into the injection port. After the reading stabilizes, obtain the data and read the weight average molecular weight.

[0083] In some embodiments, the weight average molecular weight of the fluorinated polymer is any one of 1.5 million to 2.5 million, 2.5 million to 3.5 million, 3.5 million to 4.5 million, 4.5 million to 5.5 million, 5.5 million to 6.5 million, 6.5 million to 7.5 million, 7.5 million to 8.5 million, and 8.5 million to 9 million.

[0084] In some embodiments, based on the total molar number of structural units in the fluoropolymer, the molar content of the structural units derived from the monomer shown in formula I can be 0.3%, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5% or any value therebetween. The binder can effectively increase the viscosity of the low-solid content slurry, improve the coating quality of the pole piece, and enhance the consistency of the pole piece surface density, especially improve the processing quality of the thin coating process. Moreover, the binder has a high weight-average molecular weight and is linearly distributed in the pole piece, which can reduce the coating of the active material in the pole piece, thereby increasing the transmission rate of the active ions in the active material, reducing the battery impedance, and improving the battery cycle stability. Furthermore, relying on the carboxyl group introduced by the monomer shown in formula I in the fluoropolymer, the binder has a tighter bonding effect with other materials in the pole piece, and can still effectively play a bonding role in the slurry with a low solid content, playing a role in suppressing rebound in the pole piece and further improving the cycle capacity retention rate. When the molar content of the structural unit of the monomer represented by Formula I is within an appropriate range, the binder enables the low-solid content slurry to have a suitable viscosity, effectively improves the uniformity of the electrode surface density, reduces the full-cell impedance of the solid-state battery, and improves the cycle performance of the solid-state battery.

[0085] In any embodiment, the weight-average molecular weight of the fluoropolymer is 2 million to 6 million. Fluoropolymer binders with a weight-average molecular weight of 2 million to 6 million can further improve the uniformity of the electrode surface density, reduce the full-cell impedance of the solid-state battery, and enhance the cycle performance of the solid-state battery.

[0086] In some embodiments, the molar content of the structural unit derived from the monomer represented by Formula I is 0.8% to 2% based on the total moles of the structural units in the fluorine-containing polymer.

[0087] In some embodiments, the fluoropolymer has a polydispersity index of 1.8 to 2.8, optionally 1.8 to 2.5.

[0088] In some embodiments, the fluoropolymer has a polydispersity index of 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, or any value therebetween.

[0089] As used herein, the term "polydispersity index" refers to the ratio of the weight average molecular weight of a polymer to the number average molecular weight of the polymer.

[0090] As used herein, the term "number average molecular weight" refers to the sum of the products of the mole fractions of molecules of different molecular weights in a polymer and their corresponding molecular weights.

[0091] In the present application, the polydispersity coefficient can be tested by methods known in the art, such as gel chromatography, such as using a Waters 2695 Isocratic HPLC gel chromatograph (differential refractive index detector 2141). In some embodiments, a polystyrene solution sample with a mass fraction of 3.0% is used as a reference, and a matching chromatographic column is selected (oily: Styragel HT5DMF7.8×300mm+Styragel HT4). A 3.0% fluoropolymer glue is prepared with purified N-methylpyrrolidone (NMP) solvent, and the prepared solution is allowed to stand for one day for use. During the test, tetrahydrofuran is first drawn into a syringe and rinsed, and repeated several times. Then 5 ml of the experimental solution is drawn, the air in the syringe is expelled, and the needle tip is wiped dry. Finally, the sample solution is slowly injected into the injection port. After the reading stabilizes, the data is acquired. The weight average molecular weight a and the number average molecular weight b are read respectively. Polydispersity coefficient = a / b.

[0092] By controlling the polydispersity coefficient of the fluoropolymer within an appropriate range, the weight-average molecular weight of the fluoropolymer is evenly distributed and the performance is balanced, which effectively improves the consistency of the electrode surface density, reduces the full battery impedance of the solid-state battery, and improves the cycle performance of the solid-state battery.

[0093] The polydispersity coefficient of the fluoropolymer is in the range of 1.8-2.5. The weight-average molecular weight distribution of the fluoropolymer is more uniform and the performance is more balanced. It can further improve the consistency of the electrode surface density, reduce the full battery impedance of the solid-state battery, and improve the cycle performance of the solid-state battery.

[0094] In some embodiments, the fluoropolymer has a crystallinity of 40% to 55%, optionally 43% to 50%.

[0095] In some embodiments, the fluoropolymer has a crystallinity of 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 55%, or any value therebetween.

[0096] In this article, the term "crystallinity" refers to the proportion of crystalline regions in fluoropolymers. There are some regions with stable and regular arrangement of molecules in the microstructure, and the region where the molecules are regularly and closely arranged is called a crystalline region.

[0097] 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 fluoropolymer is placed in an aluminum crucible, shaken flat, and covered with a crucible lid. The test is performed in a nitrogen atmosphere with a purge gas flow of 50 ml / min and a protective gas flow of 70 ml / min at a heating rate of 8°C / min over a test temperature range of 30°C to 200°C using a differential scanning calorimeter (DSC) model DSC 200F30 from NETZSCH GmbH, Germany, and the thermal history is eliminated.

[0098] This test will obtain the DSC / (Mw / mg) temperature variation curve of the fluoropolymer and integrate it. The peak area is the melting enthalpy ΔH (J / g) of the fluoropolymer. The crystallinity of the fluoropolymer = ΔH / (ΔHm100%) × 100%, where ΔHm100% is the standard melting enthalpy (crystalline melting heat) of polyvinylidene fluoride, and ΔHm100% = 104.7 J / g.

[0099] Fluoropolymers with a crystallinity within an appropriate range enable low-solid content slurries to have a suitable viscosity, effectively improving the uniformity of the electrode surface density, reducing the full-cell impedance of the solid-state battery, and improving the cycle performance of the solid-state battery.

[0100] In some embodiments, the Dv50 particle size of the fluoropolymer is 1 μm to 100 μm, and may be 30 μm to 90 μm.

[0101] In some embodiments, the fluoropolymer has a Dv50 particle size of 1 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, or any value therebetween.

[0102] As used herein, the term "Dv50 particle size" refers to the particle size corresponding to when the cumulative volume distribution number of particles reaches 50% in a particle size distribution curve.

[0103] The Dv50 particle size can be measured by methods readily known in the art. As an example, the Dv50 of the fluoropolymer is tested with reference to GB / T 19077-2016 particle size distribution laser diffraction method. The specific method includes: weighing 0.1g to 0.13g of fluoropolymer powder in a 50ml beaker, then weighing 5g of anhydrous ethanol, adding it to the beaker containing the fluoropolymer powder, placing a stirring bar with a length of about 2.5mm, and sealing it with plastic wrap. The sample is placed in an ultrasonic machine for 5 minutes, transferred to a magnetic stirrer and stirred at a speed of 500r / min for more than 20 minutes, and 2 samples are taken from each batch of products for testing. The measurement is performed using a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer of Malvern Instruments Ltd. in the UK.

[0104] Fluoropolymers with a Dv50 particle size within an appropriate range have good solubility, which enables the low-solid content slurry to have a suitable viscosity, effectively improving the uniformity of the electrode surface density, reducing the full-cell impedance of the solid-state battery, and improving the cycle performance of the solid-state battery.

[0105] In some embodiments, R4 of the fluoropolymer comprises an ester group.

[0106] The carboxyl group of the fluoropolymer is connected to the ester group rather than directly to the main chain, which can further reduce the ordered arrangement of the vinylidene fluoride structural units through the ester group, reduce the crystallinity of the fluoropolymer, further play a dispersing role in the slurry, improve the uniformity of the electrode, reduce the battery impedance, and improve the battery cycle performance.

[0107] In some embodiments, the monomer represented by Formula I includes at least one of acrylic acid, methacrylic acid, β-acryloxypropionic acid, and maleic acid.

[0108] In some embodiments, the monomer of Formula I includes β-acryloxypropionic acid.

[0109] The above raw materials are simple and easy to obtain, which can greatly reduce production costs and increase output.

[0110] In some embodiments, the fluorine-containing polymer is at least one of poly(vinylidene fluoride-acrylic acid), poly(vinylidene fluoride-methacrylic acid), poly(vinylidene fluoride-β-acryloyloxypropionic acid), and poly(vinylidene fluoride-maleic acid).

[0111] In one embodiment of the present application, a method for preparing a binder is provided, comprising the following steps:

[0112] Providing a vinylidene fluoride monomer, at least one monomer represented by formula I, and a solvent, and performing a first stage polymerization reaction to obtain a first product;

[0113] Wherein, R1, R2, and R3 each independently include hydrogen, C 1-3 At least one of the alkyl groups, R4 includes an ester group, a carbonyl group, a C 1-3 At least one of an alkyl group and a single bond;

[0114] subjecting the first product to a second-stage polymerization reaction under a water-insoluble gas atmosphere;

[0115] A chain transfer agent is added to carry out a third stage polymerization reaction to obtain a fluorine-containing polymer with a weight average molecular weight of 1.5 million to 9 million.

[0116] It can be understood that the first product can be either the reaction liquid formed after the first stage polymerization reaction or the product after processing and purification of the above reaction liquid.

[0117] The use of a segmented polymerization method can effectively increase the molecular weight of the fluorinated polymer, so that the low-solid content slurry has a suitable viscosity, effectively improve the uniformity of the electrode surface density, reduce the full battery impedance of the solid-state battery, and improve the cycle performance of the solid-state battery.

[0118] In some embodiments, the reaction temperature of the first stage polymerization reaction is 30° C. to 60° C., the reaction time is 2 hours to 15 hours, and the initial polymerization pressure is 2.0 MPa to 7.0 MPa.

[0119] In some embodiments, the reaction temperature of the first stage polymerization reaction is 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, or any value therebetween.

[0120] In some embodiments, the reaction time of the first stage polymerization reaction is 2 hours, 4 hours, 6 hours, 8 hours, 10 hours, 12 hours, 15 hours, or any value therebetween.

[0121] In some embodiments, the initial polymerization pressure is 2 MPa, 3 MPa, 4 MPa, 5 MPa, 6 MPa, 7 MPa, or any value therebetween.

[0122] By controlling the reaction pressure, reaction time and reaction temperature of the polymerization reaction within an appropriate range, the uniformity of the weight-average molecular weight of the polymerization product can be controlled while increasing the weight-average molecular weight of the polymer, ensuring that the product has a lower polydispersity coefficient and improving the uniformity of product performance.

[0123] In some embodiments, the chain transfer agent includes one or more of cyclohexane, isopropanol, methanol, and acetone.

[0124] In some embodiments, the water-insoluble gas is selected from one or more of nitrogen, oxygen, hydrogen, and methane.

[0125] Water-insoluble gas refers to gas with solubility less than 0.1L. Gas solubility refers to the pressure of gas at 20℃ is 1.013×10 5 Pa, the volume of gas when it is dissolved in 1L of water to reach saturation.

[0126] In some embodiments, the amount of the chain transfer agent is 0.5% to 5.5% of the total mass of the vinylidene fluoride monomer and the monomer represented by formula I.

[0127] In some embodiments, the amount of chain transfer agent used is 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or any value therebetween based on the total mass of the vinylidene fluoride monomer and the monomer represented by Formula I.

[0128] The amount of the chain transfer agent is controlled within a suitable range, so that the polymer chain length can be controlled, thereby obtaining a polymer with a suitable molecular weight range.

[0129] In some embodiments, the first stage polymerization reaction comprises the following steps:

[0130] Adding a solvent and a dispersant into the container to remove oxygen from the reaction system;

[0131] Adding an initiator and a pH adjuster to the container, adjusting the pH value to 6.5-7, and then adding vinylidene fluoride monomer to make the pressure in the container reach 3.0 MPa-7.0 MPa;

[0132] After stirring for 30 to 60 minutes, the temperature is raised to 30° C. to 60° C., and the monomer represented by formula I is added simultaneously to carry out the first stage polymerization reaction.

[0133] In some embodiments, the amount of the solvent used is 2 to 8 times the total mass of the vinylidene fluoride monomer and the monomer represented by Formula I.

[0134] In some embodiments, the amount of the solvent is 2, 3, 4, 5, 6, 7, 8 times the total mass of the vinylidene fluoride monomer and the monomer represented by Formula I, or any value therebetween.

[0135] In some embodiments, the dispersant includes at least one of cellulose, cellulose ether and polyvinyl alcohol; alternatively, the cellulose includes hydroxypropyl methylcellulose, and the cellulose ether includes one or more of methyl cellulose ether and carboxyethyl cellulose ether.

[0136] In some embodiments, the amount of the dispersant used is 0.1% to 0.3% of the total mass of the vinylidene fluoride monomer and the monomer represented by formula I.

[0137] In some embodiments, the amount of the dispersant is 0.1%, 0.15%, 0.2%, 0.25%, 0.3% or any value therebetween, based on the total mass of the vinylidene fluoride monomer and the monomer represented by Formula I.

[0138] In some embodiments, the initiator includes one or more of t-amyl peroxypivalate, t-amyl peroxypivalate, 2-ethylperoxydicarbonate, diisopropyl peroxydicarbonate, and t-butyl peroxypivalate.

[0139] In some embodiments, the pH adjuster includes one or more of potassium carbonate, potassium bicarbonate, sodium carbonate, sodium bicarbonate, and aqueous ammonia.

[0140] In some embodiments, the amount of the pH adjuster is 0.05% to 0.2% of the total mass of the vinylidene fluoride monomer and the monomer represented by formula I.

[0141] In some embodiments, the amount of the pH adjuster is 0.05%, 0.1%, 0.15%, 0.2% or any value therebetween based on the total mass of the vinylidene fluoride monomer and the monomer represented by Formula I.

[0142] In some embodiments, the monomer represented by formula I is added in multiple times during the first stage polymerization reaction.

[0143] The polymerization of the monomer represented by formula I and vinylidene fluoride is an exothermic reaction. Adding the monomer represented by formula I in multiple times can reduce solvent vaporization, stabilize the pressure in the reactor, improve the uniformity of the weight-average molecular weight of the fluoropolymer, reduce the polydispersity coefficient of the fluoropolymer, further improve the uniformity of the electrode surface density, reduce the full battery impedance of the solid-state battery, and improve the cycle performance of the solid-state battery.

[0144] [Anode slurry]

[0145] In one embodiment of the present application, a negative electrode slurry is provided, wherein the negative electrode slurry includes a binder according to any embodiment or a binder prepared by a preparation method according to any embodiment.

[0146] In some embodiments, based on the total mass of the dry materials in the negative electrode slurry, the mass content of the binder is 1.0%-5.0%, optionally 1.5%-4.5%.

[0147] In some embodiments, the mass content of the binder is 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0% or any value therebetween based on the total mass of the dry material in the negative electrode slurry.

[0148] By controlling the mass fraction of the binder within an appropriate range, the prepared negative electrode slurry has a higher solution viscosity at a low solid content, which can improve the uniformity of the electrode surface density, reduce the full battery impedance of the solid-state battery, and improve the cycle performance of the solid-state battery.

[0149] In some embodiments, the negative electrode slurry has a solid content of 25%-65%, and a viscosity of the negative electrode slurry of 4000mPa.s-8000mPa.s. Alternatively, the negative electrode slurry has a solid content of 35%-55%, and a viscosity of the negative electrode slurry of 4500mPa.s-6000mPa.s.

[0150] In some embodiments, the solid content of the negative electrode slurry is 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65% or any value therebetween, and the viscosity of the negative electrode slurry is 3000mPa.s, 4000mPa.s, 5000mPa.s, 6000mPa.s, 7000mPa.s, 8000mPa.s, 9000mPa.s or any value therebetween.

[0151] Fluoropolymers enable the negative electrode slurry to have a higher solution viscosity at low solid content, which is particularly suitable for thin coating processes. It can improve the uniformity of the surface density in thin-coated electrodes, reduce the full battery impedance of solid-state batteries, and improve the cycle performance of solid-state batteries.

[0152] When the solid content of the negative electrode slurry is 35%-55% and the viscosity of the negative electrode slurry is 4500mPa.s-6000mPa.s, the uniformity of the pole piece is further improved, the full battery impedance of the solid-state battery is further reduced, and the cycle performance of the solid-state battery is further improved.

[0153] [Negative electrode]

[0154] In some embodiments, the present application provides a negative electrode plate, wherein the negative electrode plate includes a negative electrode film layer, and the negative electrode film layer is prepared from the negative electrode slurry of any embodiment.

[0155] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0156] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0157] In some embodiments, the surface density of the negative electrode film layer is 3 mg / cm 2 -6mg / cm 2 .

[0158] Areal density can be measured using methods readily known in the art. For example, a small disc is cut using a pole piece slicer. The areal density of the small disc is calculated using the formula σ = m / A, where m represents the coating mass of the small disc and A represents the coated area of ​​the small disc. The areal density of the small disc is the areal density of the pole piece coating.

[0159] In some embodiments, the surface density of the negative electrode film layer is 3 mg / cm 2 , 4mg / cm 2 , 5mg / cm 2 , 6mg / cm 2 or any value in between.

[0160] The negative electrode film layer has a low surface density, which can effectively reduce the growth of dendrites, especially inhibit the growth of dendrites in solid-state batteries and improve the cycle stability of the battery.

[0161] In some embodiments, the negative electrode film layer includes a silicon-based active material; optionally, the silicon-based active material includes at least one of a silicon-oxygen material, a silicon-carbon material, and elemental silicon.

[0162] Silicon-oxygen materials refer to compounds or composite materials containing silicon and oxygen.

[0163] Silicon-carbon materials refer to compounds or composite materials containing silicon and carbon elements.

[0164] Silicon-based active materials have high specific capacity, but they also suffer from high interlayer slippage, making effective compaction difficult and resulting in high rebound of the negative electrode film. Fluoropolymers can effectively bond silicon-based active materials, reducing the rebound of the negative electrode film after roller compaction, improving the uniformity of the electrode sheet and enhancing battery cycling stability.

[0165] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0166] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0167] [Solid-state battery]

[0168] In some embodiments, a solid-state battery includes the negative electrode sheet of some embodiments.

[0169] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the electrolyte membrane may be formed into an electrode assembly through a lamination process.

[0170] In some embodiments, the solid-state battery may include an outer packaging that can be used to encapsulate the electrode assembly.

[0171] In some embodiments, the outer packaging of the solid-state battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the solid-state battery can also be a soft shell, such as a pouch-type soft shell. The material of the soft shell can be plastic, and examples of plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0172] 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.

[0173] As the electrical device, a solid-state battery, a battery module or a battery pack can be selected according to its usage requirements.

[0174] 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.

[0175] 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.

[0176] Example

[0177] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0178] 1. Preparation method

[0179] Example 1:

[0180] Preparation of binder

[0181] 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. The atmosphere 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 achieve a pressure of 5 MPa. The mixture was 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. The reaction was allowed to proceed for 2.0 h.

[0182] 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;

[0183] The third stage of polymerization reaction: After adding 55 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 polyvinylidene fluoride copolymer with a weight average molecular weight of 1.5 million.

[0184] Synthesis of poly(vinylidene fluoride-hexafluoropropylene) polymer

[0185] 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 and 0.12 kg 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. After 6 hours of reaction, 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 stirred, washed, filtered, squeezed for dehydration, and dried for dehydration.

[0186] Synthesis of sulfide electrolytes

[0187] The sulfide electrolyte was synthesized using high-energy mechanical ball milling. In a glove box, various raw materials, including LiCl, Li2S, and P2S5, were sealed in a zirconium milling jar. 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.

[0188] Preparation of positive electrode

[0189] The positive electrode active material lithium nickel cobalt manganese oxide NCM 811 , conductive agent carbon black, sulfide electrolyte Li6PS5Cl, and poly (vinylidene fluoride-hexafluoropropylene) polymer are dissolved in butyl butyrate solution in a mass ratio of 94.5:1.5:3.0:1.0, stirred and mixed evenly to obtain a positive electrode slurry with a solid content of 60%; then the positive electrode slurry is evenly coated on the positive electrode collector, and then dried, cold pressed, and cut to obtain the positive electrode sheet.

[0190] Preparation of negative electrode sheet

[0191] The active material silicon-carbon negative electrode, CNT slurry with a solid content of 2.4%, and a binder are dissolved in the solvent NMP at a dry material mass ratio of 96:1:3, and mixed evenly to prepare a negative electrode slurry; the solvent content is adjusted so that the slurry's shipping viscosity is 4000mPa.s-8000mPa.s to meet the thin coating requirements, and the negative electrode slurry is evenly coated on the negative electrode collector copper foil once or multiple times, and the negative electrode sheet is obtained after drying, cold pressing, and slitting.

[0192] Preparation of composite solid electrolyte membrane

[0193] In an argon atmosphere glove box (H₂O <0.1 ppm, O₂ <0.1 ppm), a solid sulfide electrolyte and poly(vinylidene fluoride-hexafluoropropylene) polymer were dry-mixed at a mass ratio of 98:2. The mixture was then dispersed and dissolved in butyl butyrate solvent at a speed of 1000 rpm for 3 hours until fully dissolved. A composite electrolyte membrane with a thickness of 180 μm was prepared using conventional solution casting and drying.

[0194] Solid-state battery assembly

[0195] The positive electrode sheet, the negative electrode sheet of Example 1, and the solid electrolyte membrane were cut to the corresponding sizes and stacked in the order of the positive electrode sheet, solid electrolyte membrane, and negative electrode sheet. 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.

[0196] Examples 2 to 5

[0197] The results are basically the same as Example 1, except that the reaction time in the first polymerization reaction was adjusted to 3.0 h, 5.0 h, 5.0 h, and 8.0 h, respectively, and the temperature was adjusted to 42° C., 38° C., 45° C., and 45° C., respectively; the cyclohexane in the third polymerization reaction was adjusted to 48 g, 42 g, 35 g, and 20 g, respectively. The weight-average molecular weights of the prepared fluoropolymers were different, namely 2 million, 4 million, 6 million, and 9 million, respectively. The specific parameters are shown in Table 1.

[0198] Examples 6 to 9

[0199] The method is basically the same as Example 3, except that the molar content of β-acryloxypropionic acid is adjusted. The specific parameters are shown in Table 1 based on the total molar number of structural units in the fluorine-containing polymer.

[0200] Examples 10 to 13

[0201] It is basically the same as Example 3, except that the mass fraction of the vinylidene fluoride-β-acryloxypropionic acid copolymer is adjusted. Based on the total mass of the dry material in the negative electrode slurry, the total mass of the dry material of the negative electrode slurry remains unchanged. As the mass fraction of the binder changes, the mass content of the negative electrode active material is adjusted accordingly. The specific parameters are shown in Table 2.

[0202] Examples 14 to 16

[0203] The method is basically the same as Example 3, except that 1 mol% of β-acryloxypropionic acid is replaced by 1 mol% of acrylic acid, 1 mol% of methacrylic acid, and 1 mol% of maleic acid, respectively. The specific parameters are shown in Table 1.

[0204] Example 17

[0205] The process is basically the same as Example 3, except that, in the second stage polymerization reaction, the aqueous solution of β-acryloxypropionic acid is added at once. The specific parameters are shown in Table 1.

[0206] Example 18

[0207] The same as Example 3, except that the negative electrode slurry was coated with a normal coating density of 20 mg / cm 2 .

[0208] Comparative Example 1

[0209] Basically the same as Example 1, the binder used in the negative electrode slurry is polyvinylidene fluoride-acrylic acid copolymer with a weight average molecular weight of 1.1 million, purchased from Solvay, USA. The specific parameters are shown in Table 1.

[0210] Comparative Example 2

[0211] Basically the same as Example 3, the polymerization monomer is vinylidene fluoride, and the specific parameters are shown in Table 1.

[0212] 2. Test Method

[0213] 1. Fluoropolymer property test

[0214] 1) Weight average molecular weight test

[0215] A Waters 2695 Isocratic HPLC gel chromatograph (differential refractive index detector 2141) was used. A 3.0% polystyrene solution sample was used as a reference, and a matching chromatographic column was selected (oil-based: Styragel HT5DMF7.8×300mm+Styragel HT4). A 3.0% fluoropolymer glue was prepared using purified N-methylpyrrolidone (NMP) solvent. The prepared solution was allowed to stand for one day before use. During the test, tetrahydrofuran was first drawn into a syringe and rinsed several times. Then 5 ml of the experimental solution was drawn, the air in the syringe was expelled, and the needle tip was wiped dry. Finally, the sample solution was slowly injected into the injection port. After the reading stabilized, the data was acquired and the weight-average molecular weight was read.

[0216] 2) Polydispersity coefficient test

[0217] A Waters 2695 Isocratic HPLC gel chromatography instrument (differential refractive index detector 2141) was used. A 3.0% polystyrene solution sample was used as a reference, and a matching chromatographic column was selected (oil-based: Styragel HT5DMF7.8×300mm+Styragel HT4). A 3.0% fluoropolymer glue solution was prepared using purified N-methylpyrrolidone (NMP) solvent. The prepared solution was allowed to stand for one day before use. During the test, tetrahydrofuran was first drawn into a syringe and rinsed several times. Then, 5 ml of the experimental solution was drawn, the air in the syringe was expelled, and the needle tip was wiped dry. Finally, the sample solution was slowly injected into the injection port. The data was acquired after the reading stabilized. The weight average molecular weight a and number average molecular weight b were read separately. Polydispersity coefficient = a / b.

[0218] 3) Dv50 test

[0219] Refer to the particle size distribution laser diffraction method in GB / T 19077-2016. Weigh 0.1g–0.13g of fluoropolymer powder into a 50ml beaker. Then, weigh 5g of anhydrous ethanol and add it to the beaker containing the fluoropolymer powder. Place a stirring bar approximately 2.5mm long in the beaker and seal with plastic wrap. Ultrasonicate the sample for 5 minutes, then transfer it to a magnetic stirrer and stir at 500 rpm for at least 20 minutes. Two samples from each batch are tested. Determination is performed using a laser particle size analyzer, such as the Mastersizer 2000E from Malvern Instruments Ltd., UK.

[0220] 4) Crystallinity test

[0221] 0.5 g of fluoropolymer was placed in an aluminum crucible, shaken flat, and covered with a crucible lid. In a nitrogen atmosphere, with a purge gas of 50 ml / min and a protective gas of 70 ml / min, the heating rate was 8°C / min, and the test temperature range was 30°C to 200°C. A differential scanning calorimeter (DSC) model DSC 200F30 from NETZSCH, Germany, was used to test and eliminate the thermal history.

[0222] This test will obtain the DSC / (Mw / mg) temperature variation curve of the fluoropolymer and integrate it. The peak area is the melting enthalpy ΔH (J / g) of the fluoropolymer. The crystallinity of the fluoropolymer = ΔH / (ΔHm100%) × 100%, where ΔHm100% is the standard melting enthalpy (crystalline melting heat) of polyvinylidene fluoride, and ΔHm100% = 104.7 J / g.

[0223] 2. Anode slurry test

[0224] 1) Slurry viscosity

[0225] Select a suitable rotor, fix the viscometer, place the negative electrode slurry under the viscometer so that the slurry just submerges the scale line of the rotor. Instrument model: Shanghai Fangrui NDJ-5S, rotor: 63# (2000-10000mPa.s), 64# (10000-50000mPa.s), speed: 12r / min, test temperature: 25℃, test time is 5min, read the data after the display is stable.

[0226] 2) Slurry solid content test

[0227] Solid content of slurry = mass of dry material in slurry / total mass of slurry.

[0228] 3. Pole performance test

[0229] 1) Pole coating surface density and surface density coefficient of variation (cov) test

[0230] Cut small discs using a pole piece slicer. The formula for calculating the surface density of a small disc is σ = m / A, where m represents the coating mass of the small disc and A represents the coated area of ​​the small disc. The surface density of the small disc is the surface density of the pole piece coating.

[0231] The coefficient of variation of coating area density is calculated as follows:

[0232] cov=σ / u×100%,

[0233] Where σ represents the standard deviation of the surface density and u represents the average surface density. The larger the coefficient of variation cov of the coating surface density, the worse the coating uniformity.

[0234] Among them, X i is the surface density of the sample, and n is the number of samples.

[0235] 4. Battery performance test

[0236] 1) Battery DC impedance test

[0237] 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 standing, 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), which was used as the impedance of the entire battery.

[0238] 2) Battery cycle capacity retention rate

[0239] 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.

[0240] 3. Analysis of test results of various embodiments and comparative examples

[0241] Batteries of various examples and comparative examples were prepared according to the above methods, and various performance parameters were measured. The results are shown in Tables 1 and 2 below.

[0242] Table 1

[0243] Table 2

[0244] From the comparison of Examples 1 to 17 and Comparative Example 1, it can be seen that the carboxylic acid-modified fluorinated copolymer binder with a weight-average molecular weight of 1.5 million to 9 million can effectively improve the consistency of the electrode surface density, reduce the full-cell impedance of the solid-state battery, and improve the cycle performance of the solid-state battery compared to the low-molecular-weight carboxylic acid-modified fluorinated copolymer binder.

[0245] From the comparison of Examples 1 to 17 and Comparative Example 2, it can be seen that the carboxylic acid-modified fluorinated copolymer binder with a weight-average molecular weight of 1.5 million to 9 million can effectively improve the uniformity of the electrode surface density, reduce the full-cell impedance of the solid-state battery, and improve the cycle performance of the solid-state battery, compared with the high-molecular-weight vinylidene fluoride homopolymer.

[0246] From the comparison of Examples 6-9 and Comparative Example 2, it can be seen that the carboxylic acid-modified fluorinated copolymer binder with a weight-average molecular weight of 4 million can effectively reduce the viscosity of the slurry with the same solid content, improve the uniformity of the electrode surface density, reduce the full-cell impedance of the solid-state battery, and improve the cycle performance of the solid-state battery, compared with the vinylidene fluoride homopolymer with a weight-average molecular weight of 4 million.

[0247] As can be seen from Examples 1 to 5, a fluorinated polymer binder with a weight-average molecular weight of 2 million to 6 million can make the slurry have a viscosity of 4500 mPa˙s to 6500 mPa˙s at a solid content of 35% to 55%, which can further improve the uniformity of the electrode surface density, reduce the full-cell impedance of the solid-state battery, and enhance the cycle performance of the solid-state battery.

[0248] From the comparison between Examples 3, 6, 7 and Examples 8 and 9, it can be seen that when the molar content of the structural unit containing carboxyl groups is between 0.8% and 2%, the fluorine-containing polymer can further improve the uniformity of the electrode surface density, reduce the full battery impedance of the solid-state battery, and improve the cycle performance of the solid-state battery.

[0249] From the comparison between Examples 1 to 16 and Example 17, it can be seen that the fluorinated polymer with a polydispersity coefficient of 1.8 to 2.5 can further improve the uniformity of the electrode surface density, reduce the full battery impedance of the solid-state battery, and improve the cycle performance of the solid-state battery.

[0250] From the comparison between Example 3 and Examples 14 to 16, it can be seen that when the fluoropolymer includes structural units derived from β-acryloyloxypropionic acid, the viscosity of the slurry with the same solid content is further improved, the slurry has better film-forming properties, the coefficient of variation of the electrode surface density and the solid-state battery impedance are further reduced, and the cycle performance is further improved.

[0251] It can be seen from Examples 3 and 10 to 13 that when the mass fraction of the fluoropolymer binder in the negative electrode slurry is 1% to 5%, the negative electrode sheet using a thin coating process has a smaller surface density variation coefficient, and the solid-state battery has a lower full-cell impedance and excellent cycle performance.

[0252] From the comparison between Examples 3, 11, and 12 and Examples 10 and 13, it can be seen that when the mass fraction of the fluoropolymer binder in the negative electrode slurry is 1.5% to 4.5%, the negative electrode sheet has both excellent quality consistency and good cycle stability.

[0253] The test results show that in Example 18, the negative electrode coating density is 20 mg / cm 2 , the solid-state battery failed due to a short circuit caused by long dendrites after 300 cycles. This shows that thin-coated electrode sheets are beneficial to improving the cycle stability of solid-state batteries.

[0254] 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 binder, characterized in that: The binder comprises a fluorine-containing polymer, wherein the fluorine-containing polymer comprises a structural unit derived from vinylidene fluoride and a structural unit derived from a monomer represented by formula I, and the molar content of the structural unit derived from the monomer represented by formula I is 0.3%-2.5% based on the total molar number of the structural units in the fluorine-containing polymer; The weight average molecular weight of the fluorine-containing polymer is 1.5 million to 9 million; Wherein, R1, R2, and R3 each independently include hydrogen, C 1-3 At least one of the alkyl groups, R4 includes an ester group, a carbonyl group, a C 1-3 At least one of an alkyl group and a single bond.

2. The adhesive according to claim 1, characterized in that The weight average molecular weight of the fluorine-containing polymer is 2 million to 6 million.

3. The adhesive according to claim 1 or 2, characterized in that: Based on the total molar number of the structural units in the fluorine-containing polymer, the molar content of the structural units derived from the monomer represented by the formula I is 0.8%-2%.

4. The adhesive according to any one of claims 1 to 3, characterized in that The polydispersity coefficient of the fluorine-containing polymer is 1.8-2.

8.

5. The adhesive according to any one of claims 1 to 4, characterized in that The polydispersity coefficient of the fluorine-containing polymer is 1.8-2.

5.

6. The adhesive according to any one of claims 1 to 5, characterized in that The crystallinity of the fluorine-containing polymer is 40% to 55%.

7. The adhesive according to any one of claims 1 to 6, characterized in that The crystallinity of the fluorine-containing polymer is 43% to 50%.

8. The adhesive according to any one of claims 1 to 7, characterized in that The Dv50 particle size of the fluorine-containing polymer is 1 um to 100 um.

9. The adhesive according to any one of claims 1 to 8, characterized in that The Dv50 particle size of the fluorine-containing polymer is 30 um to 90 um.

10. The adhesive according to any one of claims 1 to 9, characterized in that: R4 of the fluorine-containing polymer includes an ester group.

11. The adhesive according to any one of claims 1 to 10, characterized in that The monomer represented by formula I includes at least one of acrylic acid, methacrylic acid, β-acryloxypropionic acid, and maleic acid.

12. The adhesive according to any one of claims 1 to 11, characterized in that The fluorine-containing polymer includes at least one of poly(vinylidene fluoride-acrylic acid), poly(vinylidene fluoride-methacrylic acid), poly(vinylidene fluoride-β-acryloxy propionic acid), and poly(vinylidene fluoride-maleic acid).

13. A method for preparing a binder, characterized in that: The following steps are involved: Providing a vinylidene fluoride monomer, at least one monomer represented by formula I and a solvent, and performing a first stage polymerization reaction to obtain a first product; Wherein, R1, R2, and R3 each independently include hydrogen, C 1-3 At least one of the alkyl groups, R4 includes an ester group, a carbonyl group, a C 1-3 At least one of an alkyl group and a single bond; subjecting the first product to a second stage polymerization reaction in a water-insoluble gas atmosphere; A chain transfer agent was added to carry out the third stage polymerization reaction to obtain a weight average molecular weight of 1.5 million ~9 million fluoropolymers.

14. The preparation method according to claim 13, characterized in that: The reaction temperature of the first stage polymerization reaction is 30° C. to 60° C., the reaction time is 2 hours to 15 hours, and the initial polymerization pressure is 2.0 MPa to 7.0 MPa.

15. The preparation method according to claim 13 or 14, characterized in that: The chain transfer agent includes at least one of cyclohexane, isopropanol, methanol and acetone.

16. The preparation method according to any one of claims 13 to 15, characterized in that: The water-insoluble gas includes at least one of nitrogen, oxygen, hydrogen and methane.

17. The preparation method according to any one of claims 13 to 16, characterized in that: The amount of the chain transfer agent used is 0.5% to 5.5% of the total mass of the vinylidene fluoride monomer and the monomer represented by formula I.

18. The preparation method according to any one of claims 13 to 17, characterized in that: The first stage polymerization reaction comprises the following steps: Adding a solvent and a dispersant into the container to remove oxygen from the reaction system; Adding an initiator and a pH adjuster into the container, adjusting the pH value to 6.5 to 7, and then adding the vinylidene fluoride monomer to make the pressure in the container reach 3.0 MPa to 7.0 MPa; After stirring for 30 to 60 minutes, the temperature is raised to 30° C. to 60° C., and the monomer represented by formula I is added simultaneously to carry out the first stage polymerization reaction.

19. The preparation method according to claim 18, characterized in that: The amount of the solvent used is 2 to 8 times the total mass of the vinylidene fluoride monomer and the monomer represented by formula I.

20. The preparation method according to claim 18 or 19, characterized in that: The dispersant includes at least one of cellulose, cellulose ether and polyvinyl alcohol.

21. The preparation method according to claim 20, characterized in that: The cellulose includes at least one of hydroxypropyl methylcellulose, methyl cellulose ether and carboxyethyl cellulose ether.

22. The preparation method according to any one of claims 18 to 21, characterized in that: The amount of the dispersant used is 0.1% to 0.3% of the total mass of the vinylidene fluoride monomer and the monomer represented by formula I.

23. The preparation method according to any one of claims 18 to 22, characterized in that: The initiator includes at least one of tert-amyl peroxypivalate, tert-amyl peroxypivalate, 2-ethyl peroxydicarbonate, diisopropyl peroxydicarbonate, and tert-butyl peroxypivalate.

24. The preparation method according to any one of claims 18 to 23, characterized in that: The pH adjuster includes at least one of potassium carbonate, potassium bicarbonate, sodium carbonate, sodium bicarbonate and ammonia water.

25. The preparation method according to any one of claims 18 to 24, characterized in that: The amount of the pH regulator used is 0.05% to 0.2% of the total mass of the vinylidene fluoride monomer and the monomer represented by formula I.

26. The preparation method according to any one of claims 18 to 25, characterized in that: The monomer represented by formula I is added in multiple times during the first stage polymerization reaction.

27. A negative electrode slurry, characterized in that: The negative electrode slurry includes the binder according to any one of claims 1 to 12 or the binder prepared by the preparation method according to any one of claims 13 to 26.

28. The negative electrode slurry according to claim 27, characterized in that: Based on the total mass of the dry materials in the negative electrode slurry, the mass content of the binder is 1.0%-5.0%.

29. The negative electrode slurry according to claim 27 or 28, characterized in that: Based on the total mass of dry materials in the negative electrode slurry, the mass content of the binder is 1.5%-4.5%.

30. The negative electrode slurry according to any one of claims 27 to 29, characterized in that: The solid content of the negative electrode slurry is 25%-65%, and the viscosity of the negative electrode slurry is 4000mPa.s-8000mPa.s.

31. The negative electrode slurry according to any one of claims 27 to 30, characterized in that: The solid content of the negative electrode slurry is 35%-55%, and the viscosity of the negative electrode slurry is 4500mPa.s-6000mPa.s.

32. A negative electrode plate, characterized in that: The negative electrode plate comprises a negative electrode film layer, and the negative electrode film layer is prepared from the negative electrode slurry according to any one of claims 27 to 31.

33. The negative electrode sheet according to claim 32, characterized in that: The surface density of the negative electrode film layer is 3 mg / cm 2 -6mg / cm 2 .

34. The negative electrode sheet according to claim 32 or 33, characterized in that: The negative electrode film layer includes silicon-based active materials.

35. The negative electrode sheet according to claim 34, characterized in that: The silicon-based active material includes at least one of silicon-oxygen material, silicon-carbon material, and elemental silicon.

36. A solid-state battery, characterized in that: The solid-state battery comprises the negative electrode sheet according to any one of claims 32 to 35.

37. An electrical device, characterized in that: Including the solid-state battery as described in claim 36.

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