Composite cathode binder and preparation method thereof, cathode sheet and preparation method thereof, and all-solid-state battery

Abstract

The application relates to the field of all-solid-state battery material preparation, in particular to a composite positive electrode binder and a preparation method thereof, a positive electrode sheet and a preparation method thereof, and an all-solid-state battery. 4 ~10 6 ; the first high molecular material comprises at least one of poly(ethylene-methacrylate-glycidyl methacrylate), poly(ethylene-glycidyl methacrylate) and polyglycidyl methacrylate; the second high molecular material comprises at least one of hydrogenated nitrile rubber (HNBR), nitrile rubber (NBR), ethyl cellulose (EC), styrene butadiene rubber (SBR) and polyvinylidene fluoride (PVDF); the binder is rich in polar groups and is easy to dissolve in a non-polar solvent, and cannot damage sulfide electrolyte. The prepared positive electrode sheet has higher ion / electron conductivity than that using a conventional binder, can widen a lithium ion transmission channel and improve battery cycle performance.

Description

Technical Field

[0001] This application relates to the field of all-solid-state battery material preparation, specifically to a composite positive electrode binder and its preparation method, a positive electrode sheet and its preparation method, and an all-solid-state battery. Background Technology

[0002] Currently, electric vehicles typically use lithium-ion batteries. However, the use of lithium-ion batteries poses significant safety risks because they usually contain highly flammable liquid electrolytes, which can lead to fires or explosions under abnormal operating conditions. Therefore, all-solid-state lithium batteries using solid-state electrolytes are considered a promising direction for the development of LIBs. Various solid-state electrolytes with high ionic conductivity and good interfacial contact with electrodes have been developed, typically polymer, inorganic, and composite electrolytes, to improve battery cycle performance. Among them, Li... 10 GeP2S 12 Sulfide-based solid electrolytes such as Li6PS5X (X = Cl, Br, I) and Li2S-P2S5 have the highest ionic conductivity (approximately 10). –2 S·cm –1 At room temperature, sulfide-based all-solid-state lithium batteries, comparable to liquid electrolytes, are a potential alternative to traditional lithium-ion batteries, offering significant improvements in energy density and safety. Furthermore, their ductility facilitates large-scale production, avoiding high-temperature sintering and enhancing the processability of the electrolyte and electrodes. However, achieving high energy density in sulfide-based batteries remains challenging due to the difficulty in producing sheet-like electrodes with high active mass loading. Selecting suitable binders and positive electrode active materials is crucial for achieving optimal cycle performance in sulfide-based all-solid-state lithium batteries, preventing delamination of the active materials, conductive carbon, and solid electrolyte in the positive electrode composition and mitigating mechanical stresses generated during cycling.

[0003] Therefore, there is an urgent need for a binder that can reduce the mechanical stress generated during the cycling process of solid-state battery cathodes, prevent cathode delamination, and maintain a high active mass load on the cathode. Summary of the Invention

[0004] To address the technical problem of poor stability in existing all-solid-state batteries, this invention provides a composite positive electrode binder, a positive electrode sheet, a method for preparing the same, and an all-solid-state battery. The positive electrode sheet prepared using the composite positive electrode binder can produce an all-solid-state battery with better performance and stability.

[0005] The first aspect of this invention provides a composite positive electrode binder for use in all-solid-state batteries, the composite positive electrode binder comprising a first polymer material and a second polymer material, wherein the polymer material has a molecular weight of 10. 4 ~10 6 .

[0006] In one embodiment, the first polymeric material includes at least one of poly(ethylene-methyl methacrylate-glycidyl methacrylate), poly(ethylene-methyl methacrylate), and poly(glycidyl methacrylate).

[0007] In one embodiment, the second polymeric material includes at least one of hydrogenated nitrile butadiene rubber (HNBR), nitrile butadiene rubber (NBR), ethyl cellulose (EC), styrene-butadiene rubber (SBR), and polyvinylidene fluoride (PVDF).

[0008] In one embodiment, the mass of the first polymer material is set to M, and the mass of the second polymer material is set to N, wherein M:N is (0.5~2):1;

[0009] A second aspect of the present invention provides a method for preparing a composite positive electrode binder, the method comprising the following steps:

[0010] S1. Dissolve the first polymer material and the second polymer material in a non-polar solvent;

[0011] S2. Heating and stirring during the dissolution process;

[0012] S3. Centrifugal drying yields the composite positive electrode binder.

[0013] In one embodiment, in the preparation method of the composite positive electrode binder, the mass ratio of the first polymer material and the second polymer material to the solvent in step S1 is 2% to 20%.

[0014] In one embodiment, the non-polar solvent in step S1 of the method for preparing the composite positive electrode binder includes at least one of anisole, butyl butyrate, isobutyl isobutyrate, p-xylene, and toluene.

[0015] A third aspect of the present invention provides a positive electrode sheet comprising the composite positive electrode binder, conductive agent, first solid electrolyte, and positive electrode active material described in the first and second embodiments.

[0016] A fourth aspect of the present invention provides a method for preparing a positive electrode sheet, the method comprising the following steps:

[0017] N1. The positive electrode active material, the first solid electrolyte, the conductive agent, and the composite positive electrode binder are added to the solvent;

[0018] N2, stir, and repeat the mixing twice to form a uniform slurry;

[0019] N3. Coat the mixed slurry from step N2 onto the positive current collector;

[0020] N4, drying;

[0021] N5, after drying, is rolled and slit to obtain the positive electrode sheet.

[0022] In one embodiment, in the method for preparing the positive electrode sheet, the positive electrode active material, the first solid electrolyte, the conductive agent and the composite positive electrode binder in step N1 are in the following mass ratio: (60-90):(8-38):(1-3):(1-3).

[0023] The fifth aspect of the present invention provides an all-solid-state battery, comprising the positive electrode, the negative electrode, and the second solid electrolyte as proposed in the third and fourth aspects.

[0024] The beneficial effects of this invention are:

[0025] The first polymer material exhibits excellent adhesion, significantly mitigating micro-cracking between the positive electrode and electrolyte during charging and discharging, thus improving battery stability. It also possesses higher ionic and electronic conductivity than traditional binders, broadening lithium-ion transport channels and improving battery cycle performance. Furthermore, the interaction between the second and first polymer materials allows for better dispersion and dissolution of the first polymer material in non-polar solvents. The resulting composite positive electrode binder is rich in polar groups, exhibiting excellent adhesion without damaging the sulfide electrolyte layer of the positive electrode material. Specifically, the resulting positive electrode sheet exhibits higher electronic and ionic conductivity than when using traditional binders, and the all-solid-state battery retains a higher capacity after 100 cycles. Attached Figure Description

[0026] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0027] Figure 1 This is the 0.1C charge / discharge curve of the battery in Embodiment 1 of the present invention. Specific Implementation

[0028] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0029] Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used in the detailed description is for the purpose of describing particular embodiments only and is not intended to limit the invention; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0030] In the description of specific embodiments of the present invention, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present invention, "multiple" means two or more, unless otherwise explicitly defined.

[0031] In this invention, the reference to "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this invention can be combined with other embodiments.

[0032] In the description of the embodiments of this invention, the term "and / or" is merely a description of the relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, in this invention, the character " / " generally indicates that the preceding and following associated objects have an "or" relationship.

[0033] Throughout this invention, numerical values ​​represent approximate measurements or limits of a range to cover minute deviations from a given value, as well as embodiments with approximately the mentioned value and embodiments with the exact mentioned value. Except for the working examples provided at the end of the detailed description, all numerical values ​​of parameters (e.g., quantities or conditions) in this specification (including the appended claims) should be understood to be modified in all cases by the term “about,” regardless of whether “about” actually appears before the numerical value. “About” indicates that the stated numerical value allows for some minor inaccuracy (approaching the exact value in some way; approximately or reasonably approaching the value; almost). If the inaccuracy provided by “about” is not otherwise understood in this general sense in the art, then “about” as used in this invention at least indicates a variation that can be produced by common methods of measuring and using such a parameter. For example, “about” may include a variation less than or equal to 5%, optionally less than or equal to 4%, optionally less than or equal to 3%, optionally less than or equal to 2%, optionally less than or equal to 1%, optionally less than or equal to 0.5%, and in some respects, optionally less than or equal to 0.1%.

[0034] Additionally, the disclosure of the range includes the disclosure of all values ​​across the entire range and the disclosure of further subdivided ranges, including the endpoints and subranges given for these ranges.

[0035] Currently, various solid electrolytes with high ionic conductivity and good interfacial contact with electrodes have been developed to improve battery cycle performance. These are typically polymer, inorganic, and composite electrolytes. Among them, Li... 10 GeP2S 12 Sulfide-based solid electrolytes such as Li6PS5X (X = Cl, Br, I) and Li2S-P2S5 have the highest ionic conductivity (approximately 10). -2 S·cm -1 At room temperature, sulfide-based all-solid-state lithium batteries, comparable to liquid electrolytes, are a potential alternative to traditional lithium-ion batteries, offering significant improvements in energy density and safety. Furthermore, their malleability facilitates large-scale production by avoiding high-temperature sintering and enhancing the processability of the electrolyte and electrodes. However, achieving high energy density in sulfide-based batteries remains challenging due to the difficulty in producing sheet-like electrodes with high active mass loading. Selecting suitable binders and positive electrode active materials is crucial for achieving optimal cycle performance in sulfide-based all-solid-state lithium batteries, preventing delamination of the active materials, conductive agents, and solid electrolyte in the positive electrode composition and mitigating mechanical stress during cycling. There is an urgent need for a binder that can alleviate mechanical stress generated during solid-state battery positive electrode cycling, prevent positive electrode delamination, and maintain a high active mass loading in the positive electrode.

[0036] To address the poor stability of existing all-solid-state batteries, this invention proposes a wet-process positive electrode binder for solid-state batteries, prepared from a first polymer material and a second polymer material in a specific ratio. This binder is rich in polar groups, exhibiting excellent adhesion. Furthermore, the interaction between the two polymer materials makes it easily soluble in non-polar solvents without damaging the sulfide electrolyte. When used in the positive electrode, it exhibits higher ionic / electronic conductivity than traditional binders, broadening the lithium-ion transport channels and improving battery cycle performance.

[0037] The technical solution of this invention is implemented as follows:

[0038] The first aspect of this invention provides a composite positive electrode binder for use in all-solid-state batteries, the composite positive electrode binder comprising a first polymer material and a second polymer material, wherein the polymer material has a molecular weight of 10. 4 ~10 6 .

[0039] In one embodiment, the first polymeric material includes at least one of poly(ethylene-methyl methacrylate-glycidyl methacrylate), poly(ethylene-methyl methacrylate), and poly(glycidyl methacrylate).

[0040] In one embodiment, the first polymer material has excellent adhesion, which can greatly alleviate micro-cracking between the positive electrode and the electrolyte during charging and discharging, and improve cycle stability; it also has higher ionic / electronic conductivity than traditional binders, which can broaden lithium-ion transport channels and improve battery rate performance and cycle characteristics.

[0041] In one embodiment, the second polymeric material includes at least one of hydrogenated nitrile butadiene rubber (HNBR), nitrile butadiene rubber (NBR), ethyl cellulose (EC), styrene-butadiene rubber (SBR), and polyvinylidene fluoride (PVDF).

[0042] In one embodiment, the second polymer material and the first polymer material interact with each other, enabling the first polymer material to be better dispersed and dissolved in the solvent.

[0043] In one embodiment, the mass of the first polymer material is set to M, and the mass of the second polymer material is set to N, wherein M:N is (0.5~2):1;

[0044] In one embodiment, the mass ratio M:N of the first polymer material to the second polymer material can be selected as 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2:1, etc. The numerical ratios listed above are merely examples, and the present invention does not impose any limitations on them.

[0045] A second aspect of the present invention provides a method for preparing a composite positive electrode binder, the method comprising the following steps:

[0046] S1. Dissolve the first polymer material and the second polymer material in a non-polar solvent;

[0047] S2. Heating and stirring during the dissolution process;

[0048] S3. Centrifugal drying yields the composite positive electrode binder.

[0049] In one embodiment, in the preparation method of the composite positive electrode binder, the mass ratio of the first polymer material and the second polymer material to the solvent in step S1 is 2% to 20%.

[0050] In one embodiment, in the preparation method of the composite positive electrode binder, the mass ratio of the first polymeric material and the second polymeric material to the nonpolar solvent in step S1 can be selected as 2%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, etc. The numerical ratios listed above are merely examples, and the present invention does not impose any limitations on them.

[0051] In one embodiment, the non-polar solvent in step S1 of the method for preparing the composite positive electrode binder includes at least one of anisole, butyl butyrate, isobutyl isobutyrate, p-xylene, and toluene.

[0052] In one embodiment, the preparation method of the composite positive electrode binder, the dissolution process in step S2 requires stirring and heating, with a stirring speed of 200 rpm to 600 rpm and a stirring temperature of 40°C to 80°C, until completely dissolved.

[0053] In one embodiment, in the preparation method of the composite positive electrode binder, the stirring speed in step S2 can be selected from 200 rpm, 300 rpm, 400 rpm, 500 rpm, 600 rpm, etc., and the stirring temperature can be selected from 40℃, 50℃, 60℃, 70℃, 80℃, etc. The numerical ratios listed above are merely examples, and the present invention does not impose any limitations on them.

[0054] In one embodiment, the preparation method of the composite positive electrode binder, in step S3, involves centrifugation at a speed of 2000 rpm to 8000 rpm for 5 min to 10 min, followed by drying of the solid sample at 60°C to 100°C for 6 h to 18 h.

[0055] In one embodiment, in the preparation method of the composite positive electrode binder, the centrifugation speed in step S3 can be selected as 2000 rpm, 3000 rpm, 4000 rpm, 5000 rpm, 6000 rpm, 7000 rpm, 8000 rpm, etc., the centrifugation time can be selected as 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, etc., the drying temperature can be selected as 60℃, 70℃, 80℃, 90℃, 100℃, etc., and the drying time can be selected as 6 h, 8 h, 10 h, 12 h, 14 h, 16 h, 18 h, etc. The numerical ratios listed above are merely examples, and the present invention does not impose any limitations thereon.

[0056] A third aspect of the present invention provides a positive electrode sheet comprising the composite positive electrode binder, conductive agent, first solid electrolyte, and positive electrode active material described in the first and second embodiments.

[0057] In one embodiment, the conductive agent material refers to one or more of conductive carbon black, conductive graphite, carbon nanotubes, carbon nanofibers, and graphene.

[0058] In one embodiment, the first solid electrolyte material refers to a sulfide solid electrolyte: Li6PS5X (LPSX, X = Cl, Br, I), Li 10 GeP2S 12 One or more of (LGPS); and / or.

[0059] In one embodiment, the positive electrode active material refers to one or more of lithium cobalt oxide (LCO), lithium manganese oxide (LMO), lithium nickel manganese oxide (LNMO), lithium nickel cobalt manganese oxide (NCM), lithium nickel cobalt aluminum oxide (NCA), and lithium-rich manganese-based oxide (LRMO).

[0060] A fourth aspect of the present invention provides a method for preparing a positive electrode sheet, the method comprising the following steps:

[0061] N1. The positive electrode active material, the first solid electrolyte, the conductive agent, and the composite positive electrode binder are added to the solvent;

[0062] N2, stir, and repeat the mixing twice to form a uniform slurry;

[0063] N3. Coat the mixed slurry from step N2 onto the positive current collector;

[0064] N4, drying;

[0065] N5, after drying, is rolled and slit to obtain the positive electrode sheet.

[0066] In one embodiment, in the method for preparing the positive electrode sheet, the positive electrode active material, the first solid electrolyte, the conductive agent and the composite positive electrode binder in step N1 are in the following mass ratio: (60-90):(8-38):(1-3):(1-3).

[0067] In one embodiment, in the method for preparing the positive electrode sheet, the positive electrode active material, the first solid electrolyte, the conductive agent, and the composite positive electrode binder in step N1 can be selected in a mass ratio of 60:35:2:3, 65:31:1:3, 70:27:1:2, 75:22:1:2, 80:18:1:1, 85:12:1:2, 90:7:1:2, etc. The numerical ratios listed above are merely examples, and the present invention does not impose any limitations on them.

[0068] In one embodiment, in the method for preparing the positive electrode sheet, the solid content of the positive electrode active material, the first solid electrolyte, the conductive agent, and the composite positive electrode binder mixed with the solvent in step N1 is 45% to 70%.

[0069] Solid content, or solid content, refers to the percentage of solid components in a composite cathode binder.

[0070] In one embodiment, in the method for preparing the positive electrode sheet, the solid content of the positive electrode active material, the first solid electrolyte, the conductive agent, and the composite positive electrode binder after mixing with the solvent in step N1 can be selected as 45%, 50%, 55%, 60%, 65%, 70%, etc. The values ​​listed above are merely examples, and the present invention does not impose any limitations on them.

[0071] In one embodiment, the preparation method of the positive electrode sheet includes step N2, in which the mixture is stirred for 10 min to 60 min at 1500 rpm to 300 rpm in a drying room at -60℃ to -30℃, followed by defoaming at 500 rpm to 1000 rpm for 5 min to 20 min, and the mixing is repeated twice to form a uniform slurry.

[0072] In one embodiment, in the method for preparing the positive electrode sheet, the temperature in step N2 within the drying chamber can be selected as -60℃, -55℃, -50℃, -45℃, -40℃, -35℃, -30℃, etc.; the rotation speed of the high-speed mixer can be selected as 1500rpm, 2000rpm, 2500rpm, 3000rpm, etc.; and the mixing time can be selected as 10min, 20min, 30min, 40min, 50min, 60min, etc. Subsequently, the defoaming rotation speed can be selected as 500rpm, 600rpm, 700rpm, 800rpm, 900rpm, 1000rpm, etc.; and the defoaming time can be selected as 5min, 10min, 15min, 20min, etc. The values ​​listed above are merely examples, and the present invention does not impose any limitations on them.

[0073] In one embodiment, in the method for preparing the composite positive electrode sheet, step N3 involves coating the mixed slurry onto the positive current collector, wherein the positive current collector is an aluminum foil.

[0074] In one embodiment, in the method for preparing the composite positive electrode sheet, step N4 involves drying at 80°C to 120°C for 8 to 16 hours, and step N5 involves rolling and slitting after drying to obtain the positive electrode sheet.

[0075] In one embodiment, in the method for preparing the composite positive electrode sheet, the drying temperature in step N4 can be selected as 80℃, 90℃, 100℃, 110℃, 120℃, etc., and the drying time can be selected as 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, etc. The values ​​listed above are merely examples, and the present invention does not impose any limitations on them.

[0076] The fifth aspect of the present invention provides an all-solid-state battery, comprising the positive electrode, the negative electrode, and the second solid electrolyte as proposed in the third and fourth aspects.

[0077] The present invention discloses a method for preparing a negative electrode sheet: 95% negative electrode active material, 2% solid electrolyte, 2% conductive agent, and 1% binder are mixed to form a negative electrode slurry. The negative electrode slurry is coated onto a negative electrode current collector (copper foil), dried, and then rolled and slit to obtain the negative electrode sheet. The negative electrode active material comprises graphite:silicon oxide in a ratio of 80%:20%.

[0078] The present invention discloses a method for preparing a solid electrolyte layer: the solid electrolyte layer is composed of a second solid electrolyte and a binder; the mass ratio of the two is 99:1.

[0079] In one embodiment, the second solid electrolyte material refers to a sulfide solid electrolyte: Li6PS5X (LPSX, X = Cl, Br, I), Li 10 GeP2S 12 One or more of (LGPS); and / or.

[0080] In one embodiment, the adhesive material refers to one or more of polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), nitrile rubber (NBR), carboxymethyl cellulose (CMC), polytetrafluoroethylene (PTFE), and polyacrylic acid (PAA).

[0081] The present invention discloses a method for preparing an all-solid-state battery: A positive electrode, a solid electrolyte layer, and a negative electrode are sequentially stacked and encapsulated in an aluminum-plastic film. After applying a vacuum to the aluminum-plastic film and sealing it, the battery is subjected to isostatic pressure at 460 MPa to obtain an all-solid-state lithium-ion battery.

[0082] The embodiments of the present invention will be described in more detail below through examples and comparative examples. All examples and comparative examples are all solid-state battery sample groups prepared using the same process.

[0083] To demonstrate the advantages of the present invention in a clear and comprehensive manner, all embodiments and comparative examples have been recorded or subjected to the following tests: electronic conductivity, ionic conductivity, initial discharge capacity at 0.1C, capacity retention rate after 100 cycles at 0.5C, and capacity retention rate after 100 cycles at 1C.

[0084] It should be noted that the embodiments of the present invention are not limited to these examples.

[0085] The following examples illustrate the application of M:N in all-solid-state batteries at different ratios, where M represents poly(ethylene-methacrylate-glycidyl methacrylate) and N represents hydrogenated nitrile rubber.

[0086] Example 1

[0087] I. Preparation of Composite Positive Electrode Binder

[0088] 1) Poly(ethylene-methacrylate-glycidyl methacrylate) and hydrogenated acrylonitrile butadiene rubber were dissolved in the solvent isobutyl isobutyrate at a mass ratio of M:N = 1:1.

[0089] 2) The dissolution process requires stirring and heating at a speed of 350 rpm and a temperature of 80°C to form a solution with a mass fraction of 8%.

[0090] 3) Centrifuge at 5000 rpm for 7 min, and dry the solid sample at 80℃ for 12 h to obtain the composite positive electrode binder.

[0091] II. Preparation of the positive electrode sheet

[0092] 1) The positive electrode active material, solid electrolyte, conductive agent and binder are added to the solvent isobutyl isobutyrate in a mass ratio of 70:27:1:2, with a solid content of 60%.

[0093] 2) Mix at 2000 rpm for 30 minutes in a drying room at -50℃ using a high-speed mixer, then defoam at 800 rpm for 10 minutes. Repeat the mixing process twice to form a uniform slurry.

[0094] 3) Next, in the drying room, use a scraper to coat the above slurry onto the positive current collector (aluminum foil).

[0095] 4) Transfer to a vacuum oven and dry at 100°C for 12 hours.

[0096] 5) After drying, the positive electrode sheet is obtained by rolling and slitting.

[0097] III. Preparation of Negative Electrode Sheets

[0098] A negative electrode slurry is prepared by mixing 95% negative electrode active material, 2% solid electrolyte Li6PS5Cl, 2% conductive agent conductive carbon black, and 1% binder PAA. This slurry is then coated onto a negative electrode current collector (copper foil), dried, and subsequently rolled and slit to obtain the negative electrode sheet. The negative electrode active material contains a graphite:silicon oxide ratio of 80%:20%.

[0099] IV. Preparation of Solid Electrolyte Layer

[0100] The solid electrolyte layer consists of a second solid electrolyte, Li6PS5Cl, and a binder, PTFE; the mass ratio of the two is 99:1.

[0101] V. Preparation of all-solid-state batteries

[0102] The positive electrode, solid electrolyte layer, and negative electrode are stacked sequentially and encapsulated in an aluminum-plastic film. After applying a vacuum to the aluminum-plastic film, it is sealed, and the battery is subjected to isostatic pressure at 460 MPa to obtain an all-solid-state lithium-ion battery.

[0103] Example 2

[0104] Example 1 provides a composite positive electrode binder, a positive electrode sheet and its preparation method, and an all-solid-state battery. The composite positive electrode binder, positive electrode sheet and preparation method used in Example 1 are the same as those in Example 1. The only difference from Example 1 is that in step 1) of the preparation method of the composite positive electrode binder, M:N is 0.5.

[0105] Example 3

[0106] Example 1 provides a composite positive electrode binder, a positive electrode sheet and its preparation method, and an all-solid-state battery. The composite positive electrode binder, positive electrode sheet and preparation method used in Example 1 are the same as those in Example 1. The only difference from Example 1 is that M:N is 0.8 in step 1) of the preparation method of the composite positive electrode binder.

[0107] Example 4

[0108] Example 1 provides a composite positive electrode binder, a positive electrode sheet and its preparation method, and an all-solid-state battery. The composite positive electrode binder, positive electrode sheet and preparation method used in Example 1 are the same as those in Example 1. The only difference from Example 1 is that M:N is 1.5 in step 1) of the preparation method of the composite positive electrode binder.

[0109] Example 5

[0110] Example 1 provides a composite positive electrode binder, a positive electrode sheet and its preparation method, and an all-solid-state battery. The composite positive electrode binder, positive electrode sheet and preparation method used in Example 1 are the same as those in Example 1. The only difference from Example 1 is that M:N is 2 in step 1) of the preparation method of the composite positive electrode binder.

[0111] Comparative Example 1

[0112] The difference between this comparative example and Example 1 is that the traditional binder NBR is used instead of the composite positive electrode binder prepared in step 1), and the positive electrode is prepared using the traditional binder NBR. The other steps are the same as in Example 1.

[0113] Comparative Example 2

[0114] The difference between this comparative example and Example 1 is that poly(ethylene-methacrylate-glycidyl methacrylate) is used instead of the composite positive electrode binder prepared in step 1), and only poly(ethylene-methacrylate-glycidyl methacrylate) is used as the binder to prepare the positive electrode. The other steps are the same as in Example 1.

[0115] Comparative Example 3

[0116] The difference between this comparative example and Example 1 is that hydrogenated nitrile butadiene rubber (HNBR) is used instead of the composite positive electrode binder prepared in step 1). Only hydrogenated nitrile butadiene rubber (HNBR) is used as the binder to prepare the positive electrode. The other steps are the same as in Example 1.

[0117] Comparative Example 4

[0118] The composite positive electrode binder, positive electrode sheet, and preparation method used in Example 1 are the same as those in Example 1. The difference from Example 1 is that in step 1) of the preparation method of the composite positive electrode binder, M:N is 0.05.

[0119] Comparative Example 5

[0120] The composite positive electrode binder, positive electrode sheet, and preparation method used in Example 1 are the same as those in Example 1. The difference from Example 1 is that M:N is 5 in step 1) of the preparation method of the composite positive electrode binder.

[0121] The composite cathode binders prepared in Examples 1-5 and Comparative Examples 1-5 were used in cathode sheets to prepare all-solid-state batteries. The performance of the all-solid-state batteries was tested, and the test results are shown in Table 1 below:

[0122] Electronic conductivity:

[0123] The electronic conductivity of a material is determined by measuring its resistivity. According to Ampere's formula R = U / I, the resistance of the conductor is calculated by measuring the current flowing through it and the voltage drop across it, and the geometric dimensions of the sample are measured. Then, the resistance is determined using the formula... Calculate the conductivity.

[0124] Ionic conductivity:

[0125] The AC impedance of the sample is measured, and then the ionic conductivity of the sample is calculated using the formula σ=L / (R×S), where L is the thickness, R is the impedance, and S is the cross-sectional area.

[0126] Cycle battery capacity retention:

[0127] At a temperature of 45℃, the battery is charged at currents of 0.5C and 1C to the charging cutoff voltage of 4.2V, then switched to constant voltage charging to the cutoff current of 0.05C, left to stand for 0.5h, and then discharged at currents of 0.5C and 1C to the cutoff voltage of 2.5V, left to stand for 0.5h, and then entered the next charge-discharge cycle. This process is repeated for a total of 100 charge-discharge cycles.

[0128] First discharge capacity test:

[0129] At room temperature (25℃), a fully charged battery is discharged at a constant current of 0.1C until the cutoff voltage of 2.5V to obtain the initial discharge capacity.

[0130] The performance test results are shown in Table 1.

[0131] Table 1. Performance test results of positive electrode and solid-state battery

[0132]

[0133]

[0134] As shown in the table above, comparing Examples 1-5 with Comparative Examples 1-5, this invention proposes a solid-state battery wet-process positive electrode binder prepared from a first polymer material and a second polymer material in a certain proportion. The first polymer material has excellent adhesion, which can greatly alleviate micro-cracking between the positive electrode and the electrolyte during charging and discharging, improving battery stability; it also has higher ionic and electronic conductivity than traditional binders, which can broaden the lithium-ion transport channels and improve battery cycle performance. In addition, the second polymer material and the first polymer material interact, enabling the first polymer material to be better dispersed and dissolved in non-polar solvents; the resulting composite positive electrode binder is rich in polar groups, has excellent adhesion, and will not damage the sulfide electrolyte of the positive electrode material layer. Specifically, the electronic conductivity and ionic conductivity of the obtained positive electrode sheet are higher than those using traditional binders, and the capacity retention rate of the all-solid-state battery is higher after 100 cycles.

[0135] In Examples 1-5, as the M:N ratio increases, the electronic conductivity, ionic conductivity, capacity retention after 100 cycles at 0.5C, and capacity retention after 100 cycles at 1C all show a trend of first increasing and then decreasing, with the battery performance reaching its peak at an M:N ratio of 1:1. Therefore, this composite cathode binder can improve the battery's electronic and ionic conductivity as well as its cycle performance.

[0136] Comparing Example 1 and Comparative Examples 1-5, the electronic and ion conductivity and battery cycle performance were the worst when using traditional binder NBR materials. Comparative Examples 2-3 show that the overall battery performance was slightly improved when only poly(ethylene-methacrylate-glycidyl methacrylate) and only hydrogenated nitrile butadiene rubber (HNBR) were used. Comparative Examples 4-5 show that the overall battery performance decreased when either of the two polymer materials was present in too little or too much content.

[0137] Figure 1 The 0.1C charge-discharge curve in Example 1 shows that the initial discharge specific capacity at 0.1C is 210 mAh g. -1 .

[0138] It should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A composite positive electrode binder for use in all-solid-state batteries, characterized in that, The composite positive electrode binder comprises a first polymer material and a second polymer material, wherein the molecular weight of the polymer material is 10. 4 ~10 6 ; The first polymer material is poly(ethylene-methacrylate-glycidyl methacrylate); The second polymer material is hydrogenated nitrile butadiene rubber; The mass of the first polymer material is set as M, and the mass of the second polymer material is set as N, wherein M:N is (0.5~2):

1.

2. A method for preparing the composite positive electrode binder as described in claim 1, characterized in that, The method includes the following steps: S1. Dissolve the first polymer material and the second polymer material in a non-polar solvent; S2. Heating and stirring during the dissolution process; S3. Centrifugal drying yields the composite positive electrode binder.

3. The method as described in claim 2, characterized in that, In step S1, the mass ratio of the first polymer material and the second polymer material to the solvent is 2% to 20%.

4. A positive electrode sheet, comprising the composite positive electrode binder, conductive agent, first solid electrolyte, and positive electrode active material as described in claim 1.

5. The method for preparing the positive electrode sheet as described in claim 4, characterized in that, Includes the following steps: N1. Add the positive electrode active material, the first solid electrolyte, the conductive agent, and the composite positive electrode binder to the solvent; N2, stir, and repeat the mixing twice to form a uniform slurry; N3. Coat the mixed slurry from step N2 onto the positive current collector; N4, drying; N5, after drying, is rolled and slit to obtain the positive electrode sheet.

6. The method as described in claim 5, characterized in that, In step N1, the positive electrode active material, the first solid electrolyte, the conductive agent and the composite positive electrode binder are in the following mass ratio: (60-90):(8-38):(1-3):(1-3).

7. An all-solid-state battery, comprising a positive electrode, a negative electrode, and a second solid electrolyte as described in claim 4.

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