All-solid-state negative electrode sheet, preparation method thereof, and all-solid-state battery

Abstract

The present invention provides an all-solid-state negative electrode sheet, a method for preparing the same, and an all-solid-state battery, specifically relating to the field of batteries. The all-solid-state negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer being disposed on at least one side of the negative electrode current collector. The negative electrode active material layer comprises a negative electrode active material, a solid electrolyte, a conductive agent, and a binder-lithium salt composition, wherein the binder-lithium salt composition has a uniformity of 20% to 40% within the negative electrode active material layer. The present invention can significantly improve comprehensive battery performance, including rate capability, cycle performance, and energy density.

Description

Technical Field

[0001] The present invention relates to the field of batteries, and in particular to an all-solid-state negative electrode plate and a preparation method thereof, and an all-solid-state battery. Background Art

[0002] All-solid-state batteries are considered the ultimate form of next-generation, high-performance, and high-safety power batteries. Their core feature is the use of a solid-state electrolyte (SSE) that completely replaces traditional flammable liquid electrolytes, theoretically significantly improving battery safety. Furthermore, all-solid-state batteries offer higher energy density and longer cycle life.

[0003] Wet slurry coating is one of the methods for preparing negative electrode sheets for all-solid-state batteries. During the wet slurry coating process, the binder fully wraps the surface of the negative electrode active material particles, solid electrolyte particles, and conductive agent particles in the form of an amorphous film, forming a bridging film layer between these particles. Although this continuous film structure is crucial for maintaining the mechanical integrity of the sheet and the bonding between the particles, since the binder itself is an insulating material, the binder covering other negative electrode components will seriously hinder ion and electron transport, thereby reducing negative electrode performance.

[0004] Furthermore, the negative electrode material experiences significant volume expansion during the battery's charge and discharge processes, which can damage the film layer formed by the binder and the bonding interface between the particles, causing the electrode structure to pulverize and fall off, affecting the battery's cycling performance. Therefore, effectively balancing the tension between the negative electrode's expansion stress and the binder's bonding and transport properties is one of the core challenges in developing all-solid-state batteries with long cycle life, high rate performance, and high energy density. Summary of the Invention

[0005] In view of the above problems existing in the prior art, the present invention provides an all-solid-state negative electrode plate and a preparation method thereof and an all-solid-state battery to improve the problems of poor rate performance and negative electrode expansion of the all-solid-state negative electrode plate.

[0006] To achieve the above-mentioned objectives and other related objectives, the first aspect of the present invention provides an all-solid-state negative electrode sheet, comprising a negative electrode current collector and a negative electrode active material layer, wherein the negative electrode active material layer is arranged on at least one side of the negative electrode current collector, wherein the negative electrode active material layer comprises a negative electrode active material, a solid electrolyte, a conductive agent and a binder-lithium salt composition, and the uniformity of the binder-lithium salt composition in the negative electrode active material layer is 20%~40%.

[0007] In one embodiment of the present invention, the uniformity of the binder-lithium salt composition in the negative electrode active material layer is X1%, the silicon content in the negative electrode active material is X2wt%, and the all-solid-state negative electrode sheet satisfies the following relationship: 23≤1.85X1-X2≤33.

[0008] In one embodiment of the present invention, the content of the binder-lithium salt composition in the negative electrode active material layer is 4 wt % to 10 wt %, the content of the negative electrode active material in the negative electrode active material layer is 60 wt % to 90 wt %, and / or the ionic conductivity of the binder-lithium salt composition is 10 -6 S / cm ~10 -4 S / cm.

[0009] In one embodiment of the present invention, the binder-lithium salt composition includes a binder and a lithium salt, the binder includes a modified polymer containing a polar side chain, and the binder includes one or more of polyvinylidene fluoride-grafted maleic anhydride, styrene-butadiene rubber-copolymerized hydroxyethyl acrylate, polymethyl methacrylate-copolymerized acrylic acid, and polybutyl acrylate-grafted maleic anhydride.

[0010] In one embodiment of the present invention, the lithium salt includes one or more of LiBF4, LiBF6, LiAsF6, LiPF6, LiClO4, LiFSI, LiTFSI, LiB(C6H5)4, LiAlCl4, LiBr, LiCF3SO3, and LiN(CF3SO2)2.

[0011] In one embodiment of the present invention, the negative electrode active material includes graphite material and / or silicon material.

[0012] In one embodiment of the present invention, the solid electrolyte includes at least one of an oxide solid electrolyte, a sulfide solid electrolyte, and a halide solid electrolyte.

[0013] In one embodiment of the present invention, the conductive agent is selected from at least one of graphite, graphene, carbon black, carbon fiber, and carbon nanotubes.

[0014] A second aspect of the present invention provides a method for preparing an all-solid-state negative electrode sheet, comprising the following steps:

[0015] dissolving a binder and a lithium salt in a first solvent to prepare an ion-conducting binder solution;

[0016] Adding a conductive agent to the ion-conducting adhesive solution and mixing them evenly to obtain an ion- and electron-conducting adhesive solution;

[0017] Adding negative electrode active material, solid electrolyte and second solvent to the ion and electron dual conductive gel solution, mixing them evenly to prepare an all-solid-state negative electrode slurry;

[0018] coating the all-solid-state negative electrode slurry on at least one side of a negative electrode current collector and drying the same to obtain an all-solid-state negative electrode sheet;

[0019] The polarity parameters of the first solvent and the second solvent both satisfy the range of 0 to 4, and the polarity parameter of the first solvent is greater than the polarity parameter of the second solvent, and the difference between the two is greater than 2.

[0020] In one embodiment of the present invention, the added amount of the binder accounts for X3wt% of the total mass of the negative electrode active material, the conductive agent, the solid electrolyte, the binder and the lithium salt, and the added amount of the lithium salt accounts for X4wt% of the total mass of the negative electrode active material, the conductive agent, the solid electrolyte, the binder and the lithium salt, then X3 and X4 satisfy the following relationship: 0≤0.5X3-X4≤1.

[0021] In one embodiment of the present invention, the polarity parameter of the first solvent is 2.4-4, and the polarity parameter of the second solvent is 0-0.2.

[0022] In one embodiment of the present invention, the first solvent includes at least one of butyl butyrate, benzene, and ethylene dichloride; and / or the second solvent includes at least one of trimethylpentane, dodecane, methylcyclohexane, and decalin.

[0023] In one embodiment of the present invention, the mass ratio of the first solvent to the second solvent in the all-solid-state negative electrode slurry is 1:(3-5).

[0024] In one embodiment of the present invention, the mass ratio of the first solvent to the second solvent in the all-solid-state negative electrode slurry is 1:X5, the uniformity of the binder-lithium salt composition in the negative electrode active material layer of the prepared all-solid-state negative electrode plate is X1%, and the all-solid-state negative electrode slurry satisfies the following relationship: 6.5≤X5+0.1X1≤7.5.

[0025] In one embodiment of the present invention, the solid content of the all-solid-state negative electrode slurry is 50 wt % to 80 wt %.

[0026] In one embodiment of the present invention, the drying step includes: a first drying stage, rapidly volatilizing the second solvent at 60°C~80°C for 1 minute to 5 minutes; and a second drying stage, slowly volatilizing the first solvent at 100°C~120°C for 1 hour to 2 hours.

[0027] A third aspect of the present invention provides an all-solid-state battery, comprising the above-mentioned all-solid-state negative electrode sheet or an all-solid-state negative electrode sheet prepared by any of the above-mentioned preparation methods.

[0028] In summary, the binder and lithium salt in the all-solid-state negative electrode sheet of the present invention are combined to form a binder-lithium salt composition, thereby transforming the insulating binder into an ion-conducting binder, significantly improving the ion transport capacity of the interface. Furthermore, by adjusting the uniformity of the binder-lithium salt composition in the negative electrode active material layer, the contact area between the binder and other negative electrode components can be reduced, further improving ion transport efficiency and enhancing the battery's rate performance.

[0029] Adjusting the uniformity of the binder-lithium salt composition in the negative electrode active material layer can also adjust the cohesion of the electrode, so that binders with different uniformities can match negative electrode active materials with different silicon contents, thereby matching the cohesion of the electrode with the intrinsic shrinkage and expansion of the silicon material, thereby improving the battery's cycle performance while increasing the battery's energy density.

[0030] Furthermore, the binder is a binder grafted with polar groups, which can significantly enhance the complexing ability of the binder and the lithium salt, so that the binder and the lithium salt are combined into an ion-conducting binder-lithium salt composition through physical blending, Lewis acid-base action, coordination action and strong complexing ability of the binder polar groups and the lithium salt.

[0031] When preparing an all-solid-state negative electrode plate, the present invention first adopts a low-polarity first solvent with good solubility and dispersion ability for the binder, conductive agent and lithium salt to dissolve the binder and lithium salt to form an ion-conducting glue, and then adds the conductive agent, which can solve the problem of conductive agent agglomeration and reduce side reactions on the solid electrolyte; subsequently, a second solvent with lower polarity that has poor dispersion of the binder, the negative electrode active material and the solid electrolyte are added, which can transform the binder from complete disentanglement to partial disentanglement, and by increasing the degree of entanglement of the binder, reduce the contact area between the binder and other negative electrode components, thereby improving the ion transmission capacity of the interface.

[0032] By adjusting the ratio of the first solvent to the second solvent, the uniformity of the binder-lithium salt in the electrode can be adjusted. Binder-lithium salt compositions with different uniformities can be matched to negative electrode active materials with different silicon contents, ensuring that the electrode cohesion matches the intrinsic shrinkage and expansion of the silicon material. This improves the battery's energy density while also reducing negative electrode expansion.

[0033] By minimizing the ratio of the first solvent to the second solvent, the influence of the solvent on the solid electrolyte can be minimized. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other embodiments can be obtained based on these drawings without paying any creative work.

[0035] Figure 1 Schematic diagram of the structure of an all-solid-state negative electrode plate in one embodiment of the present invention;

[0036] Figure 2 FIG1 is a flow chart of a method for preparing an all-solid-state negative electrode plate according to an embodiment of the present invention.

[0037] Component number description:

[0038] 100. All-solid-state negative electrode plate; 110. Negative electrode current collector; 120. Negative electrode active material layer. DETAILED DESCRIPTION

[0039] The following describes the embodiments of the present invention by means of specific examples. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. The various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the features in the following embodiments and examples can be combined with each other unless they conflict. The test methods for which specific conditions are not specified in the following examples are generally based on conventional conditions or the conditions recommended by the manufacturers.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention pertains. The terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the present invention.

[0041] Unless otherwise specified or incompatible herewith, the terms and phrases used herein shall have the following meanings:

[0042] As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0043] As used herein, "plurality," "multiple," "multiple times," etc., unless otherwise specified, refer to a quantity greater than or equal to 2. For example, "one or more" means one or more than or equal to two.

[0044] Herein, the terms "preferred," "better," and "more preferred" are merely used to describe preferred implementations or examples and should not be construed as limiting the scope of protection of the present invention. If multiple "preferred" terms appear in a technical solution, each "preferred" term is considered independent unless otherwise specified and there are no contradictions or mutual constraints.

[0045] Herein, “further”, “further”, “particularly”, etc. are used for descriptive purposes to indicate differences in content, but should not be understood as limiting the scope of protection of the present invention.

[0046] When referring to a numerical range herein, unless otherwise specified, the distribution of the values ​​within the numerical range is considered continuous and includes the two numerical endpoints (i.e., the minimum and maximum values) of the numerical range, as well as every value between the two numerical endpoints. When multiple numerical ranges are provided to describe a feature or characteristic, these numerical ranges may be combined.

[0047] The negative electrode is one of the core components of a battery, and its performance directly affects the battery's performance. The mainstream preparation method for all-solid-state negative electrode sheets is a wet process. Binders suitable for this process generally include styrene-butadiene rubber, sodium alginate, polyacrylonitrile, polyurethane, polyacrylic acid, ethylene-propylene-diene monomer, styrene-butadiene rubber, polyvinylidene fluoride, and fluororubber. However, these binders must be dissolved in a solvent and then evaporated. The final form of the binder in the negative electrode is an amorphous film-like substance, that is, a film layer that fully wraps around the negative electrode active material, solid electrolyte, and conductive agent, or can be understood as a bridging film layer between the negative electrode active material, solid electrolyte, and conductive agent. Because this type of binder covers a large area of ​​other negative electrode components and is inherently insulating, it affects the transmission of ions and electrons in the negative electrode sheet, reducing negative electrode performance. In addition, during the battery's charge and discharge process, the negative electrode material expands significantly in volume. In particular, in pursuit of higher energy density, high-capacity silicon-based materials have been introduced into the negative electrode. Silicon will undergo dramatic volume expansion during the charging and discharging process (up to 300% or more). The dramatic volume change will destroy the film layer formed by the binder and the bonding interface between the particles, resulting in particle contact failure and even powdering and falling of the electrode structure, thereby affecting the battery's cycle performance.

[0048] Based on this, the present invention provides an all-solid-state negative electrode plate, a preparation method thereof, and an all-solid-state battery, which integrates an insulating binder and a lithium salt to form a binder-lithium salt composition with certain ion conductivity, and adjusts the cohesion of the plate by adjusting the uniformity of the binder-lithium salt in the negative electrode, thereby adapting to negative electrode active materials with different volume expansions, thereby improving the battery's capacity, rate performance, and cycle stability.

[0049] See also Figure 1In a first aspect, the present invention provides an all-solid-state negative electrode sheet. The all-solid-state negative electrode sheet 100 includes a negative electrode current collector 110 and a negative electrode active material layer 120. The negative electrode current collector 110 can be made of any conductive material that can carry and support the negative electrode active material layer 120, such as copper foil, carbon-coated copper foil, etc. The negative electrode active material layer 120 is provided on at least one side of the negative electrode current collector 110 ( Figure 1 Only the case of single-side arrangement is shown). For example, the negative electrode current collector 110 has a first surface and a second surface arranged opposite to each other along its thickness direction. The negative electrode active material layer 120 can be arranged on one of the first surface and the second surface, or on both the first surface and the second surface.

[0050] The negative electrode active material layer 120 includes: a negative electrode active material, a solid electrolyte, a conductive agent, and a binder-lithium salt composition. The binder-lithium salt composition is composed of a binder and a lithium salt, and the uniformity of the binder-lithium salt composition in the negative electrode active material layer is 20% to 40%. At this point, the insulating binder combines with the lithium salt to form a composition with certain ion conductivity, which can significantly enhance the ion transport capacity within the negative electrode. It can also reduce the contact area between the binder and other negative electrode components, improving the transmission performance of electrons and ions. It also has sufficient cohesive force to resist the volume expansion of the negative electrode material and prevent the electrode structure from pulverizing and falling off, which affects the battery's cycling performance. It should be noted that the uniformity of the binder-lithium salt composition refers to the volume percentage of the binder-lithium salt composition in the entire area of ​​the negative electrode active material layer.

[0051] In some embodiments, the uniformity of the binder-lithium salt composition in the negative electrode active material layer 120 may be 20%, 25%, 30%, 35%, or 40%, etc. The higher the uniformity of the binder-lithium salt composition in the negative electrode active material layer 120, the stronger the cohesion of the negative electrode active material layer 120, and the more adaptable it is to negative electrode active materials with greater volume expansion. However, the higher the uniformity of the binder-lithium salt composition in the negative electrode active material layer 120, the higher the volume proportion of the binder-lithium salt composition in the negative electrode active material layer 120. Although the binder is transformed from an insulator to an ion-conducting binder after combining with the lithium salt, its ionic conductivity is lower than the ionic conductivity of the solid electrolyte. If the volume proportion of the binder-lithium salt composition in the negative electrode active material layer is too high, it will still affect the ion transport within the all-solid-state negative electrode plate. Therefore, controlling the uniformity of the binder-lithium salt composition to 20% to 40% can not only reduce the contact area between the binder and other negative electrode components and improve the transmission performance of electrons and ions, but also have sufficient cohesion to resist the volume expansion of the negative electrode material, preventing the plate structure from pulverizing and falling off, affecting the cycle performance of the battery.

[0052] The negative electrode active material, serving as the core material in the negative electrode active material layer 120, can be any material capable of lithium deintercalation and deintercalation. In some embodiments, the negative electrode active material includes a graphite material and / or a silicon material. The graphite material can be natural graphite, artificial graphite, or a composite material of natural and artificial graphite. Natural graphite includes, but is not limited to, bulk graphite, flake graphite, and earthy graphite. Artificial graphite includes, but is not limited to, single crystal graphite, polycrystalline graphite, pyrolytic graphite, and graphite fiber. Silicon materials include, but are not limited to, one or more of crystalline silicon, amorphous silicon, and organosilicon. That is, the negative electrode active material can be a single graphite material, such as flake graphite, pyrolytic graphite, or graphite fiber. It can also be a single silicon material, such as crystalline silicon or amorphous silicon. It can also be a combination of a graphite material and a silicon material, such as a combination of bulk graphite and single crystal graphite, a combination of single crystal graphite and crystalline silicon, or a combination of flake graphite, graphite fiber, and crystalline silicon. However, the types of negative electrode active materials are not limited to the materials listed above. Preferably, the negative electrode active material is a combination of graphite and silicon. Graphite has advantages such as high stability, long life, high initial efficiency, low cost, and proven reliability, but its specific capacity is relatively low. Silicon, on the other hand, has an extremely high theoretical specific capacity. Combining graphite and silicon can leverage the advantages of both and enhance the overall performance of the battery.

[0053] The silicon content (the percentage of silicon material to the total mass of the negative electrode active material) in the negative electrode active material is 0-100wt%. Furthermore, the silicon content is 0-50wt%, and furthermore, can be 13wt%, 26wt%, 50wt%, and so on. Because silicon material expands significantly during battery charge and discharge, the higher the silicon content in the negative electrode active material, the greater the volume expansion of the negative electrode active material. To balance the energy density and rate performance of the battery, extensive research has been conducted on the silicon content in the negative electrode active material and the uniformity of the binder-lithium salt composition. Assuming the uniformity of the binder-lithium salt composition in the negative electrode active material layer 120 is X1% and the silicon content in the negative electrode active material is X2wt%, the two satisfy the following relationship: 23≤1.85X1-X2≤33. This improves the ion transport capacity within the negative electrode while providing sufficient cohesion to resist negative electrode expansion, thereby increasing both the battery energy density and the rate performance.

[0054] In some embodiments, the content of the binder-lithium salt composition in the negative electrode active material layer 120 is 4 wt% to 10 wt%, and can be 4 wt%, 6 wt%, 8 wt% or 10 wt%, etc. Further, at 25°C, the ionic conductivity of the binder-lithium salt composition is 10 -6 S / cm ~10 -4S / cm, for example, can be 1×10 -6 S / cm, 5×10 -6 S / cm, 1×10 -5 S / cm, 5×10 -5 S / cm or 1×10 -4 S / cm, etc. Although the ionic conductivity of the binder-lithium salt combination is not high, it has greatly improved the ionic conductivity compared to the insulating binder. Therefore, the combination of the binder and the lithium salt can significantly improve the ion transport capacity in the negative electrode.

[0055] The binder-lithium salt composition is a composite of a binder and a lithium salt. In one embodiment, to enhance the ability of the binder to composite with the lithium salt, the binder is a binder grafted with polar groups. Furthermore, the binder is a modified polymer containing polar side chains. For example, the binder includes one or more of polyvinylidene fluoride grafted with maleic anhydride, styrene-butadiene rubber-co-hydroxyethyl acrylate, polymethyl methacrylate-co-acrylic acid, and polybutyl acrylate-grafted with maleic anhydride. In other words, the binder can be a single material, such as polyvinylidene fluoride grafted with maleic anhydride or styrene-butadiene rubber-co-hydroxyethyl acrylate. The binder can also be a combination of multiple materials, such as a combination of polyvinylidene fluoride grafted with maleic anhydride and styrene-butadiene rubber-co-hydroxyethyl acrylate in any proportion, or a combination of polyvinylidene fluoride grafted with maleic anhydride, polymethyl methacrylate-co-acrylic acid, and polybutyl acrylate grafted with maleic anhydride in any proportion, and so on. The binder can significantly enhance its complexing ability with lithium salts by grafting polar groups, and the two can be compounded by physical blending, Lewis acid-base interaction, coordination and the strong complexing ability of the binder polar groups with lithium salts. However, the types of binders are not limited to the materials listed above. Lithium salts include but are not limited to LiBF4, LiBF6, LiAsF6, LiPF6, LiClO4, LiFSI, LiTFSI, LiB(C6H5)4, LiAlCl4, LiBr, LiCF3SO3, LiN(CF3SO2)2. The lithium salt can be a single material or a composition of multiple materials mixed in any proportion. For example, the lithium salt can be LiBF4, or LiFSI, or a combination of LiPF6 and LiFSI, or a combination of LiClO4, LiFSI and LiB(C6H5)4, etc.

[0056] Solid-state electrolytes can provide a migration path for lithium ions, allowing lithium ions to shuttle smoothly back and forth between the positive and negative electrodes, thereby realizing the charge and discharge process of the battery. In addition, the solid-state electrolyte can be tightly combined with the negative electrode active material, reducing the occurrence of side reactions at the interface, reducing the interface resistance, and thus improving the overall performance and cycle life of the battery. In some embodiments, the solid-state electrolyte includes at least one of an oxide solid-state electrolyte, a sulfide solid-state electrolyte, and a halide solid-state electrolyte. For example, it can be an oxide solid-state electrolyte, a sulfide solid-state electrolyte, or a combination of an oxide solid-state electrolyte and a halide solid-state electrolyte, and so on.

[0057] Conductive agents inherently have excellent electrical conductivity. Adding them to the negative electrode can effectively improve the electrode's conductivity and reduce its resistance, thereby enhancing the battery's rate capability and charge / discharge rate. The mass ratio of the conductive agent to the negative electrode active material layer 120 is (1-5):100, for example, 1:100, 3:100, or 5:100, etc. Exemplarily, the conductive agent includes, but is not limited to, at least one of graphite, graphene, carbon black (Super P), carbon fiber (VGCF), and carbon nanotubes. For example, it can be graphite, carbon black, or a combination of carbon black and carbon fiber. Furthermore, the conductive agent is a combination of carbon black and carbon fiber, with a mass ratio of carbon black to carbon fiber of 1:(0.2-1.5), for example, 1:0.2, 1:0.8, 1:1.2, or 1:1.5, etc. Furthermore, the mass ratio of carbon black to carbon fiber is 1:1.

[0058] In some embodiments, the mass ratio of the negative electrode active material, solid electrolyte, conductive agent, and lithium salt-binder composition in the negative electrode active material layer 120 is (60-90):(5-25):(1-5):(4-10), wherein the mass ratio of the lithium salt to the binder in the lithium salt-binder composition is (1-3):(3-7). The ratios of the components can be selected within the above-mentioned ratio range according to actual production needs. For example, the mass ratio of the negative electrode active material, solid electrolyte, conductive agent, and lithium salt-binder composition can be 60:25:5:10, or 90:5:1:4, or 75:15:3:7, etc. The mass ratio of the lithium salt to the binder in the binder-lithium salt composition can be 3:7, or 1:3, or 2:5, etc.

[0059] See also Figure 2 The second aspect of the present invention provides a method for preparing an all-solid-state negative electrode sheet, comprising the following steps:

[0060] S1, dissolving a binder and a lithium salt in a first solvent to prepare an ion-conducting binder solution;

[0061] S2, adding a conductive agent to the ion-conducting adhesive solution and mixing them evenly to prepare an ion- and electron-conducting adhesive solution;

[0062] S3, adding the negative electrode active material, the solid electrolyte and the second solvent to the ion and electron dual conductive gel solution, mixing them evenly to prepare an all-solid-state negative electrode slurry;

[0063] S4, coating the all-solid-state negative electrode slurry on at least one side of the negative electrode current collector and drying it to obtain an all-solid-state negative electrode sheet;

[0064] The polarity parameters of the first solvent and the second solvent both satisfy 0-4, and the polarity parameter of the first solvent is greater than the polarity parameter of the second solvent, and the difference between the two is greater than 2.

[0065] Specifically, the first solvent in step S1 must have good solubility and dispersion capabilities for the binder, conductive agent, and lithium salt (referred to as a good solvent). Furthermore, the polarity parameter of the solvent must be less than 4 to minimize side reactions with the solid electrolyte. Furthermore, the polarity parameter of the first solvent is preferably between 2.4 and 4, and more preferably, 2.4, 3, 3.5, or 4, among others.

[0066] In some embodiments, the first solvent includes at least one of butyl butyrate, benzene, and ethylene dichloride. For example, the first solvent may be butyl butyrate, benzene, or ethylene dichloride, a mixture of butyl butyrate and benzene, or a mixture of butyl butyrate, benzene, and ethylene dichloride. The first solvent is not limited to the materials listed above; any solvent having a polarity parameter within the above-defined range may be used.

[0067] In step S1, a lithium salt and a binder are first dissolved in a first solvent. This allows the lithium salt and binder to form a binder-lithium salt composite through physical blending, Lewis acid-base interactions, coordination, and the strong complexing ability of the binder's polar groups with the lithium salt. This composite is dissolved in the first solvent to produce an ion-conducting binder solution. In this step, the mass ratio of lithium salt to binder is (1-3):(3-7), illustratively ranging from 1:3, 2:5, or 3:7. The amount of the first solvent added is not limited; it only needs to be sufficient to dissolve the lithium salt and binder.

[0068] Furthermore, the amount of binder added and the amount of lithium salt added satisfy the following relationship: 0≤0.5X3-X4≤1, where X3 represents the mass of the binder as a percentage of X3wt% of the total mass of the raw materials (negative electrode active material, solid electrolyte, binder, conductive agent, and lithium salt), and X4 represents the amount of lithium salt added as a percentage of X4wt% of the total mass of the raw materials. When the amounts of binder and lithium salt added satisfy the above relationship, the binder and lithium salt are completely compounded to form a binder-lithium salt composition.

[0069] Furthermore, the amount of the first solvent added must satisfy the concentration of the ion-conducting binder paste of 1wt%~30wt%, that is, the mass of the lithium salt and the binder accounts for 1wt%~30wt% of the total mass of the ion-conducting binder paste. For example, it can be 1wt%, 5wt%, 10wt%, 15wt%, 20wt%, 25wt% or 30wt%, etc.

[0070] In step S2, the conductive agent is added to the ion-conducting adhesive solution prepared in step S1, and the mixture is mixed and stirred until it is completely dissolved to prepare an ion- and electron-conducting adhesive solution, thereby improving the agglomeration problem of the conductive agent.

[0071] Step S3 adds a second solvent (which may be referred to as a poor solvent) that has a poor effect on dissolving and dispersing the binder, a negative electrode active material, and a solid electrolyte to the ion- and electron-conducting gel solution, and forms an all-solid-state negative electrode slurry through high-speed mixing. The polarity parameter of the second solvent in this step is less than 4, and the polarity parameter of the second solvent is at least 2 less than the polarity parameter of the first solvent. Furthermore, the polarity parameter of the second solvent is between 0 and 0.2, for example, it can be 0, 0.1, or 0.2, etc. The extremely low polarity second solvent can change the state of the binder in the all-solid-state negative electrode from complete disentanglement to partial disentanglement, and by increasing the degree of entanglement of the binder, reduce the contact area between the binder and other negative electrode components. When the polarity parameters of the first solvent and the second solvent meet the above-defined ranges, the effect of the solvent on the solid electrolyte can be greatly reduced.

[0072] In some embodiments, the second solvent comprises at least one of trimethylpentane, dodecane, methylcyclohexane, and decalin. That is, the second solvent may be any one of the materials listed above, or a combination of any two or more of the materials listed above. For example, the second solvent is trimethylpentane, or dodecane, or a combination of methylcyclohexane and decalin, or dodecane. Trimethylpentane is methylcyclohexane, and so on. The second solvent is not limited to the materials listed above; any solvent having a polarity parameter within the above-defined range may be used.

[0073] The mass ratio of the first solvent in step S1 to the second solvent in step S3 can affect the uniformity of the binder-lithium salt composition within the electrode. Binder-lithium salt compositions with varying uniformities can be used with negative electrode active materials having varying silicon contents to ensure that the electrode cohesion matches the intrinsic shrinkage and expansion of the silicon material.

[0074] In one embodiment, the mass ratio of the first solvent to the second solvent is 1:(3-5). For example, the mass ratio of the first solvent to the second solvent can be 1:3, 1:4, 1:5, and so on. When the mass ratio of the first solvent to the second solvent falls within the above range, the overall performance of the all-solid-state negative electrode plate can be improved. If the ratio of the second solvent is less than 3, the first solvent content is excessive. Excessive first solvent reacts with the solid electrolyte and increases the uniformity of the binder-lithium salt composition within the all-solid-state negative electrode plate, thereby increasing the area of ​​low ion conductivity and reducing the ion transport pathway within the all-solid-state negative electrode plate. If the ratio of the second solvent is greater than 5, the second solvent content is excessive, which has a poor solubility and dispersion effect on the binder and lithium salt. This can lead to precipitation of the binder and lithium salt, meaning that some of the binder and lithium salt cannot be dissolved. This can cause uneven negative electrode slurry and lead to problems such as powder shedding and cracking of the plate.

[0075] Furthermore, the mass ratio of the first solvent to the second solvent in the all-solid-state negative electrode slurry is 1:X5, and the uniformity of the binder-lithium salt composition in the negative electrode active material layer of the final all-solid-state negative electrode sheet is X1%. Therefore, the all-solid-state negative electrode slurry satisfies the following relationship: 6.5≤X5+0.1X1≤7.5. When this relationship is satisfied, a better all-solid-state negative electrode sheet can be obtained.

[0076] The speed and time of mixing and stirring in step S3 are not particularly limited, as long as the components can be mixed and stirred uniformly. For example, the speed of mixing and stirring is 2000-3000 rpm, for example, 2000 rpm, 2500 rpm, or 3000 rpm, and the time of mixing and stirring is 1-30 minutes, for example, 5 minutes, 10 minutes, 20 minutes, or 30 minutes, etc.

[0077] In one embodiment, the solid content of the all-solid-state negative electrode slurry prepared in step S3 is 50 wt % to 80 wt %, and illustratively, it can be 50 wt %, 60 wt %, 70 wt % or 80 wt %, etc.

[0078] Step S4, i.e., the coating step of the all-solid-state negative electrode slurry, is to uniformly coat the prepared all-solid-state negative electrode slurry on the negative electrode current collector in a conventional manner in the art, and dry it to form a negative electrode active material layer to prepare an all-solid-state negative electrode sheet.

[0079] Since solvents of different polarities have different boiling points and volatility, solvents with large polarity parameters have high boiling points and low volatility, and the drying process requires higher temperatures and longer times; solvents with small polarity parameters have low boiling points and high volatility, and are easier to dry. Therefore, this step uses a stepped temperature for drying, specifically including: a first drying stage and a second drying stage, wherein the first drying stage quickly evaporates the second solvent at 60°C~80°C for 1~5 minutes, and the second drying stage: slowly evaporates the good solvent at 100°C~120°C for 1~2 hours. The final wet-process all-solid-state negative electrode sheet capacity is 1~10 mAh cm -2 For example, the temperature of the first drying stage can be 60°C, 70°C or 80°C, and the drying time can be 1 minute, 3 minutes or 5 minutes; the temperature of the second drying stage can be 100°C, 110°C or 120°C, and the drying time can be 1 hour, 1.5 hours or 2 hours.

[0080] In step S4, the all-solid-state negative electrode slurry can be applied to one side of the negative electrode current collector or to both sides of the negative electrode current collector according to actual needs. When the all-solid-state negative electrode slurry is applied to both sides of the negative electrode current collector, it is necessary to apply one side of the negative electrode current collector first, wait for it to dry, and then apply the other side of the negative electrode current collector. Finally, it is dried to obtain a fully solid-state negative electrode sheet that meets the requirements. The surface capacity of the fully solid-state negative electrode sheet is 1~10mAh cm -2 , for example, 1 mAh cm -2 、3 mAh cm -2 , 5 mAh cm -2 、8 mAhcm -2 or 10 mAh cm -2 etc.

[0081] It should be noted that the mass ratio of the raw materials (negative electrode active material, solid electrolyte, conductive agent, lithium salt, and binder) in steps S1-S4 is: (60-90): (5-25): (1-5): (1-3): (3-7). The specific ratio can be selected within the above range based on actual production needs. The types of materials for the lithium salt, binder, conductive agent, negative electrode active material, and solid electrolyte are described above and are not further elaborated here.

[0082] When preparing the all-solid-state negative electrode sheet, the present invention first selects a first solvent that has good solubility and dispersion capabilities for the binder, conductive agent and lithium salt, and at the same time, the solvent has a low polarity to reduce side reactions on the solid electrolyte. The binder and lithium salt are dissolved in the first solvent, and then the conductive agent is added and mixed to obtain an ion and electron dual-conducting glue, which can improve the agglomeration problem of the conductive agent. Subsequently, a poor solvent for the binder, i.e., an extremely low polarity solvent, the negative electrode active material, the solid electrolyte and the conductive agent are added and mixed at high speed to form an all-solid-state negative electrode slurry, wherein the extremely low polarity solvent allows the binder to exist in the all-solid-state negative electrode from completely disentangled to partially disentangled, and by increasing the degree of entanglement of the binder, the contact area between the binder and other negative electrode components is reduced.

[0083] By adjusting the ratio of the first solvent to the second solvent, the uniformity of the binder-lithium salt combination in the electrode can be controlled. Binders with different uniformities can be matched to negative electrode active materials with different silicon contents, aligning the electrode cohesion with the intrinsic shrinkage and expansion of the silicon material. At the same time, by minimizing the mass ratio of the lower polarity solvent to the very low polarity solvent, the impact of the solvent on the solid electrolyte in the all-solid-state anode is minimized.

[0084] A third aspect of the present invention provides an all-solid-state battery, which includes the above-mentioned negative electrode plate.

[0085] Those skilled in the art should know that an all-solid-state battery also includes necessary components such as a positive electrode plate and a solid electrolyte layer. The solid electrolyte layer is arranged between the negative electrode plate and the positive electrode plate to provide a channel for ion transmission between the positive and negative electrodes, while preventing the transmission of electrons, thereby avoiding short circuits.

[0086] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one side of the positive electrode current collector. The positive electrode current collector may be, for example, aluminum foil or carbon-coated aluminum foil. The positive electrode active material layer may be disposed on one surface of the positive electrode current collector or on both surfaces. The positive electrode active material layer includes a positive electrode active material, a conductive agent, and a binder. The positive electrode active material includes, but is not limited to, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium-rich manganese-based oxides. It may be a single material, such as lithium cobalt oxide, lithium nickel cobalt manganese oxide, or lithium nickel manganese oxide, or a combination of multiple materials, such as a combination of lithium cobalt oxide and lithium nickel oxide, or a combination of lithium nickel cobalt aluminum oxide, a lithium-rich oxide, and lithium nickel cobalt manganese oxide. The conductive agent includes, but is not limited to, one or more of graphite, graphene, carbon black, carbon fiber, and carbon nanotubes. For example, it may be graphite or a combination of carbon black and carbon fiber. The binder includes one or more of polyvinylidene fluoride grafted with maleic anhydride, styrene-butadiene rubber copolymerized with hydroxyethyl acrylate, polymethyl methacrylate copolymerized with acrylic acid, and polybutyl acrylate grafted with maleic anhydride. The positive electrode sheet can be prepared using a wet process, similar to the preparation process for the negative electrode sheet. In other embodiments, the positive electrode sheet can also be prepared using a dry process, which is not described in detail here.

[0087] The solid electrolyte layer includes a solid electrolyte, including but not limited to oxide solid electrolytes, sulfide solid electrolytes, halide solid electrolytes, and polymer solid electrolytes. These can be a single material or a mixture of multiple materials. The solid electrolyte layer is prepared using either a wet or dry process. The specific process is not described in detail here.

[0088] All-solid-state battery assembly: The prepared all-solid-state negative electrode sheet and positive electrode sheet are placed on both sides of the solid electrolyte layer for assembly to obtain an all-solid-state battery.

[0089] It should be noted that the structures not described in detail in the above battery can be configured with reference to conventional techniques in the art and will not be described in detail here.

[0090] The all-solid-state battery of the present invention can be used in the form of a single cell, a battery module, or a battery pack to power electronic devices. Electronic devices include, but are not limited to, mobile phones, tablets, laptops, electric toys, electric vehicles, new energy vehicles, ships, spacecraft, and the like. Electric toys can include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, and spacecraft can include airplanes, rockets, space shuttles, and spacecraft. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or extended-range vehicles.

[0091] The technical solutions of the present invention are described in detail below through several specific examples and comparative examples. Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available or can be prepared by conventional methods in the art, and the instruments used in the examples are all commercially available.

[0092] Example 1

[0093] In a first aspect, the present embodiment provides an all-solid-state negative electrode plate, which includes a negative electrode current collector (carbon-coated copper foil) and a negative electrode active material layer arranged on both sides of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material (silicon-carbon material, Si-C) with a silicon content of 26%, a solid electrolyte (Li6PS5Cl), a conductive agent (super P and VGCF), and a binder-lithium salt composition (composed of polyvinylidene fluoride-grafted maleic anhydride and LiTFSI).

[0094] Li6PS5Cl comes from Shandong Xinjieneng Lithium Battery Co., Ltd., and its model is LPSCl.

[0095] LiTFSI comes from Guangzhou Tianci High-tech Materials Co., Ltd., and its model is LiTFSI.

[0096] The conductive agent was super p (Tianjin Youmeng Chemical Technology Co., Ltd., super p) and VGCF (Showa Denko Co., Ltd., VGCF-H) with a mass ratio of 1:1.

[0097] Polyvinylidene fluoride-grafted maleic anhydride, from Arkema, model number Kynar® Flex 2801.

[0098] The ratio of each raw material in the all-solid-state negative electrode plate is: the mass ratio of negative electrode active material, solid electrolyte, conductive agent, lithium salt and binder is 60:28:5:2:5.

[0099] A second aspect of this embodiment provides a method for preparing the above-mentioned all-solid-state negative electrode sheet, comprising the following steps:

[0100] (1) Preparation of ionic binder glue: 0.5 g of polyvinylidene fluoride-grafted maleic anhydride and 0.2 g of LiTFSI were dissolved in 1.3 g of butyl butyrate solvent to obtain ionic binder glue;

[0101] (2) Preparation of ionic and electronic dual-conducting glue: Mix the ionic binder glue with 0.25 g super p and 0.25 g VGCF composition to obtain ionic and electronic dual-conducting glue;

[0102] (3) Preparation of all-solid-state anode slurry: 6 g of silicon-carbon particles, 2.8 g of Li6PS5Cl, and 5.3 g of dodecane were added to the ion- and electron-conducting gel solution, and mixed at 2000 rpm for 10 min using a high-speed stirrer in a glove box, followed by defoaming at 500 rpm for 5 min to form an all-solid-state anode slurry with a solid content of 60 wt%;

[0103] (4) Coating: Use a scraper to coat the all-solid-state negative electrode slurry on the carbon-coated copper foil, quickly transfer it to a vacuum state, first dry it at 60-80℃ for 5 minutes, and then dry it at 100-120℃ for 2 hours. After that, a surface capacity of 5 mAh cm -2 All-solid-state negative electrode.

[0104] The mass ratio of the first solvent (butyl butyrate) to the second solvent (dodecane) in the all-solid-state anode slurry is 1:4, and the uniformity of the binder-lithium salt composition within the all-solid-state anode sheet is 31.5%. The polarity parameters of butyl butyrate are 2.8, and those of dodecane are 0.2.

[0105] A third aspect of this embodiment provides an all-solid-state lithium-ion battery comprising the above-mentioned all-solid-state negative electrode sheet, a counter electrode, and a solid electrolyte layer. The solid electrolyte layer comprises Li6PS5Cl, and the counter electrode comprises a lithium-indium alloy sheet (diameter φ = 10 mm).

[0106] The preparation steps of all-solid-state lithium-ion batteries are:

[0107] First, 1000 mg of Li6PS5Cl powder is placed in a mold with a diameter of 10 mm and pressurized to 100 MPa to obtain a solid electrolyte layer; then, the all-solid-state negative electrode sheet and lithium-indium alloy sheet are placed on both sides of the solid electrolyte layer for assembly; after assembly, the pressure is increased to 100 MPa and the nut at the top of the column is tightened to maintain constant pressure to obtain an all-solid-state lithium-ion battery.

[0108] Note: The assembly process was completed in an argon atmosphere glove box. The diameters of the all-solid-state anode electrode and the lithium-indium alloy sheet were both 10 mm.

[0109] Example 2

[0110] This example differs from Example 1 in that the mass ratio of the first solvent (butyl butyrate) to the second solvent (dodecane) in the all-solid-state anode slurry is 1:3, the uniformity of the binder-lithium salt composition in the all-solid-state anode electrode sheet is 39.6%, and the silicon content of the silicon-carbon material used as the anode active material is 50%.

[0111] Example 3

[0112] This example differs from Example 1 in that the mass ratio of the first solvent (butyl butyrate) to the second solvent (dodecane) in the all-solid-state anode slurry is 1:5, the uniformity of the binder-lithium salt composition in the all-solid-state anode electrode sheet is 20.3%, and the silicon content of the silicon-carbon material used as the anode active material is 13%.

[0113] Example 4

[0114] The difference between this embodiment and Example 1 is that the content of the binder and the lithium salt composition in the all-solid-state negative electrode plate is 4 wt %, wherein the content of polyvinylidene fluoride-grafted maleic anhydride is 3 wt %, the content of LiTFSI is 1 wt %, and the mass ratio of the negative electrode active material, the solid electrolyte and the conductive agent remains unchanged at 60:28:5.

[0115] Example 5

[0116] The difference between this embodiment and Example 1 is that the content of the binder and the lithium salt composition in the all-solid-state negative electrode plate is 10wt%, of which the content of polyvinylidene fluoride-grafted maleic anhydride is 7wt%, the content of LiTFSI is 3wt%, and the mass ratio of the negative electrode active material, the solid electrolyte and the conductive agent remains unchanged at 60:28:5.

[0117] Example 6

[0118] The difference between this embodiment and embodiment 1 is that the first solvent is ethylene dichloride, and the polarity parameter is 3.5; the second solvent is trimethylpentane, and the polarity parameter is 0.1.

[0119] Example 7

[0120] The difference between this embodiment and embodiment 1 is that the first solvent is ethylene dichloride, and the polarity parameter is 3.5; the second solvent is decalin, and the polarity parameter is 0.1.

[0121] Example 8

[0122] The difference between this embodiment and embodiment 1 is that the lithium salt is LiClO4.

[0123] Example 9

[0124] The difference between this embodiment and embodiment 1 is that the lithium salt is LiFSI.

[0125] Example 10

[0126] The difference between this embodiment and embodiment 1 is that: the counter electrode (lithium indium alloy) is replaced by an LNMO positive electrode sheet;

[0127] The LNMO positive electrode sheet composition: the mass ratio of LNMO, Li6PS5Cl, conductive carbon black and binder (PTFE) is 85:13:1:1;

[0128] The LNMO is specifically a single crystal LiNi coated with Li2ZrO3 0.5 Mn 1.5 O4; originated from Xiamen Tungsten Co., Ltd., model number is XW46.

[0129] Example 11

[0130] The difference between this comparative example and Example 1 is that the silicon content in the silicon-carbon material is 13%.

[0131] Example 12

[0132] The difference between this embodiment and embodiment 1 is that the silicon content in the silicon-carbon material is 50%.

[0133] Example 13

[0134] The difference between this embodiment and Example 1 is that the content of the binder-lithium salt composition in the all-solid-state negative electrode plate is 2 wt %, of which the content of polyvinylidene fluoride-grafted maleic anhydride is 1 wt %, and the content of LiTFSI is 1 wt %, and the mass ratio of the negative electrode active material, the solid electrolyte and the conductive agent remains unchanged at 60:28:5.

[0135] Example 14

[0136] The difference between this embodiment and Example 1 is that the content of the binder-lithium salt composition in the all-solid-state negative electrode plate is 12wt%, of which the content of polyvinylidene fluoride-grafted maleic anhydride is 10wt%, the content of LiTFSI is 2wt%, and the mass ratio of the negative electrode active material, solid electrolyte and conductive agent remains unchanged at 60:28:5.

[0137] Example 15

[0138] The difference between this embodiment and embodiment 3 is that the negative electrode active material uses pure graphite, which is sourced from BTR New Materials Group Co., Ltd. and has a model number of AGP-9.

[0139] Comparative Example 1

[0140] The difference between this comparative example and Example 1 is that the uniformity of the binder-lithium salt composition in the all-solid-state negative electrode sheet is 52.2%, and the mass ratio of the first solvent (butyl butyrate) to the second solvent (dodecane) in the all-solid-state negative electrode slurry is 1:2.

[0141] Comparative Example 2

[0142] The difference between this comparative example and Example 1 is that the mass ratio of the first solvent (butyl butyrate) to the second solvent (dodecane) in the all-solid-state negative electrode slurry is 1:6.

[0143] Comparative Example 3

[0144] The difference between this comparative example and Example 1 is that the order of using the first solvent (butyl butyrate) and the second solvent (dodecane) is exchanged. The preparation method specifically includes: attempting to dissolve 0.2 g of polyvinylidene fluoride-grafted maleic anhydride in 1.3 g of dodecane solvent.

[0145] Comparative Example 4

[0146] The difference between this comparative example and Example 1 is that the second solvent is acetonitrile and the polarity parameter is 6.2.

[0147] Comparative Example 5

[0148] The difference between this comparative example and Example 10 is that the uniformity of the binder-lithium salt composition in the all-solid-state negative electrode plate is 52.1%, and the mass ratio of the first solvent (butyl butyrate) to the second solvent (dodecane) in the all-solid-state negative electrode slurry is 1:2.

[0149] Comparative Example 6

[0150] The difference between this comparative example and Example 15 is that the uniformity of the binder-lithium salt composition in the all-solid-state negative electrode plate is 52.3%, and the mass ratio of the first solvent (butyl butyrate) to the second solvent (dodecane) in the all-solid-state negative electrode slurry is 1:2.

[0151] Table 1: Parameters of Examples 1-15 and Comparative Examples 1-6

[0152]

[0153] To verify the performance of the all-solid-state negative electrode sheets of the present invention, performance tests were conducted on the all-solid-state negative electrode sheets of Examples 1-15 and Comparative Examples 1-6 and all-solid-state lithium-ion batteries containing the same. The test methods are as follows. The test results are shown in Table 2.

[0154] (1) Test of uniformity of binder-lithium salt composition: To obtain the uniformity of the binder and lithium salt composition in the positive electrode, the specific type of lithium salt in the positive electrode can be confirmed by Fourier transform infrared spectroscopy (FTIR). For example, the type of lithium salt can be determined by directly detecting the surface of the positive electrode or scraping powder samples, and by the peak position of characteristic functional groups. For example, the PF bond peak position in LiPF6 is at ~840 cm-1 The S=O bond peak in LiTFSI is located at 1170 cm -1 and 1350 cm -1 After determining the specific type of lithium salt composition, since the binder and lithium salt are combined into one, the characteristic chemical bond in the lithium salt is selected as the characteristic signal. When the lithium salt is, for example, LiTFSI, the characteristic chemical bond can be SO2 - or NSO2 - The uniformity was then characterized using Time of Flight Secondary Ion Mass Spectrometry (TOF-SIMS). A time-of-flight secondary ion mass spectrometer (TOF-SIMS) was used to observe the cross-section of the all-solid-state negative electrode. Through continuous ion beam sputtering, TOF-SIMS was able to peel off the sample layer by layer to obtain cross-sections of different depths. The effective area sputtered and detected was 100×100μm. 2 , the total stripping depth is 80% of the total thickness of the negative electrode active material layer of the electrode, and the single stripping step is 2% of the total thickness. The uniformity of the binder-lithium salt composition can be observed from the TOF-SIMS 3D image. The specific uniformity is defined as the volume ratio of the fragment signal of the lithium salt to the whole area. Take 5 areas on the same horizontal line of the same electrode, with a spacing of 1mm between areas, and take the average value of the uniformity of the binder-lithium salt composition in the 5 areas as the final uniformity. This is because the binder and lithium salt are composited into one, and the fragment signal in the lithium salt also represents the binder-lithium salt composition. The same is true for other types of lithium salts. The characteristic fragments in the lithium salt are selected as the characterization object. For example, SO2 - or NSO2 - key.

[0155] (2) Binder-lithium salt composition content test: Use time-of-flight secondary ion mass spectrometry (TOF-SIMS) to test the content of the binder-lithium salt composition. Cut the all-solid-state negative electrode sheet into 5×5 mm 2 Pre-sputter the sample with an argon ion beam (low energy, such as 500 eV) for 10 seconds and place the sample on a liquid nitrogen-cooled sample stage (-100°C). 3+ (high sensitivity) or Cs + (High spatial resolution) as a sputtering source. - (m / z 31), SO2 - 2D distribution of (m / z 64), the effective area of ​​sputtering and detection is 100 × 100 μm 2 The total stripping depth is 80% of the total thickness of the negative electrode active material layer of the electrode, and the single stripping step is 2% of the total thickness. At the same time, the signals of binder and lithium salt fragments, such as CF⁻ (polyvinylidene fluoride-grafted maleic anhydride) and SO2 - For LiTFSI, the volume fraction of the binder-lithium salt combination is calculated through 3D reconstruction. Five regions on the same horizontal line of the same electrode, with 1 mm spacing between regions, are taken. The average volume fraction of the binder and lithium salt combination in these five regions is taken as the final volume fraction. Signal intensity is calibrated using standards with known mass ratios. A relative sensitivity factor (RSF) is introduced to eliminate differences in ion yields, and the volume fraction is converted to a mass fraction through density conversion. The final mass fraction is the content of the binder and lithium salt combination.

[0156] (3) Determination of the maximum proportion of poor solvents: Dissolve the binder in a good solvent, then add different amounts of poor solvents. The proportion of poor solvents when the binder precipitates is the highest value.

[0157] (4) Normal temperature cycle test: At 25°C, the all-solid-state lithium-ion batteries prepared in Examples 1 to 15 and Comparative Examples 1 to 6 were subjected to long-cycle charge and discharge after constant capacity, and the number of normal temperature cycle cycles was measured. The test conditions were as follows: the battery was constant capacity and then subjected to long-cycle charge and discharge test, during which the first-cycle reversible specific capacity and the number of normal temperature cycle cycles when the SOH was 80% were recorded. The operating voltage range was -0.615 to 1.4 V, the constant capacity current was 0.6 mA, and the normal temperature cycle test magnification was 0.3 C. For Example 10 and Comparative Example 5, the test method was the same as that of the other Examples and Comparative Examples, except that the operating voltage range was 2 to 4.85 V.

[0158] (5) Rate Performance Test: At 25°C, the all-solid-state lithium-ion batteries of Examples 1 to 15 and Comparative Examples 1 to 6, after the normal temperature cycle test, were subjected to rate testing. The discharge specific capacity was measured as the rate performance under the conditions of an operating voltage range of -0.615 to 1.4 V and a rate of 2C. For Example 10 and Comparative Example 5, the testing method was the same as that for the other Examples and Comparative Examples, except that the operating voltage range was 2 to 4.85 V.

[0159] Table 2: Performance test results of all-solid-state lithium-ion batteries of Examples 1-15 and Comparative Examples 1-6

[0160]

[0161] As shown in Tables 1 and 2, in Examples 1-3, while maintaining the same raw material components, the uniformity of the binder-lithium salt composition within the all-solid-state anode sheet can be adjusted by adjusting the ratio of the first solvent to the second solvent to accommodate anode active materials with varying silicon contents. A higher uniformity of the binder-lithium salt composition enhances the cohesive strength of the all-solid-state anode sheet, preventing powder shedding and cracking. This allows for adaptation to high-silicon-content anode active materials (which experience large volume expansion) and improves battery cycle performance. Furthermore, silicon has a high theoretical specific capacity, which contributes to higher battery energy density. However, due to the inherent insulating properties of the binder, even when combined with a lithium salt, its ion conductivity is far lower than that of a solid electrolyte. Therefore, a higher uniformity of the binder-lithium salt composition indicates a larger area occupied by the binder and lithium salt composition, resulting in fewer ion and electron transport pathways within the all-solid-state anode, impacting the battery's rate performance. Therefore, controlling the uniformity of the binder-lithium salt composition within 20% to 40% can improve the battery's cycle performance, rate performance, and capacity. In Example 1, Comparative Examples 1, and Comparative Examples 2, the silicon content in the negative electrode active material remained consistent. The test results for the three demonstrate that Example 1 offers the best overall performance. However, the high uniformity of the binder-lithium salt composition in Comparative Example 1 impairs ion transport, thereby impacting the battery's capacity, cycle, and rate performance. In Comparative Example 2, the high proportion of the extremely low-polarity second solvent caused the lithium salt and binder to precipitate from the solvent, preventing electrode coating and making uniformity untestable.

[0162] In Examples 1, 4, 5, and Examples 13 and 14, other conditions were kept the same, and the content of the binder-lithium salt composition in the all-solid-state negative electrode plate was adjusted. Comparative test results show that within a certain range, as the content of the binder-lithium salt composition increases, the first-cycle reversible specific capacity and rate performance of the all-solid-state lithium-ion battery gradually decrease, while the cycle performance gradually increases. This is because the binder itself is insulating. Even if it combines with the lithium salt to form a composition with a certain ion conductivity, its ion conductivity is relatively low. The higher the content of the binder-lithium salt composition, the greater the impact on the transmission of lithium ions in the negative electrode, thereby affecting the capacity, cycle performance, and rate performance of the battery. However, if the content of the binder-lithium salt composition is too low, the cohesion of the negative electrode plate will be low, resulting in powder loss or detachment of the negative electrode, thereby affecting the performance of the battery. If the content of the binder-lithium salt composition is too high, it will hinder the transmission of lithium ions, thereby affecting various performance of the battery.

[0163] In Example 1, Example 6 and Example 7 and Comparative Examples 3-4, other conditions are kept the same, and the materials or order of the first solvent and the second solvent are adjusted. From the comparison test results, it can be seen that compared with Example 1, Examples 6 and 7 only replace the solvent material, but their polarity parameters still fall within the range defined in this application, and the performance of the battery fluctuates only slightly, indicating that all solvents within the range of polarity parameters defined in this application can achieve the same effect. Comparative Example 3 adjusts the order of the first solvent and the second solvent. Dodecane has too low polarity, and polyvinylidene fluoride-grafted maleic anhydride cannot be dissolved in dodecane, and thus cannot be combined with lithium salts to form a composition, and the obtained material cannot be used. The second solvent of Comparative Example 4 is replaced with acetonitrile with a polarity parameter of 6.2. Since the polarity parameter of the solvent is too large, it will react with the solid electrolyte in the negative electrode, resulting in poor capacity, cycle and rate performance of the battery.

[0164] In Examples 1, 8, and 9, the types of lithium salts in the negative electrode were adjusted while keeping other conditions unchanged. The test results showed that the battery performance did not change much, with only slight fluctuations, indicating that the type of lithium salt did not affect the compounding with the binder, and thus did not affect the battery performance.

[0165] In Examples 1 and 11-12, while maintaining the uniformity of the binder-lithium salt composition within the negative electrode and other conditions unchanged, the silicon content in the negative electrode active material was varied. Test results showed that higher silicon content in the negative electrode active material increased the battery's first-cycle reversible specific capacity, but cycling performance initially improved and then gradually deteriorated. This is because silicon has a high theoretical specific capacity. A higher silicon content in the negative electrode active material increases the battery's energy density and capacity. However, silicon also expands significantly. As silicon content increases, the negative electrode expands during charge and discharge. When the negative electrode's volumetric expansion exceeds its internal cohesive force, it can cause powder shedding and cracking, impacting the battery's cycling performance.

[0166] In Example 10 and Comparative Example 5, the counter electrode was replaced with an LNMO positive electrode sheet. The uniformity of the binder-lithium salt composition in Example 10 was 31.4% (falling within the range of 20% to 40%), and the uniformity of the binder-lithium salt composition in Comparative Example 5 was 52.1% (greater than 40%). The test results of the two showed that the first-cycle reversible specific capacity, cycle performance, and rate performance of the battery in Example 10 were all better than those in Comparative Example 5, indicating that the mechanism of adjusting the uniformity of the binder-lithium salt composition to adjust the comprehensive performance of the battery is applicable to different active materials (both full and half cells).

[0167] The negative electrode active materials of Example 15 and Comparative Example 6 both use pure graphite (silicon content is 0). The test results show that the capacity, rate performance and cycle performance of Example 15 are significantly improved compared with those of Comparative Example 6. This is because when graphite is used as the negative electrode active material, the negative electrode expands less and there is no need to use a highly uniform binder-lithium salt composition. On the contrary, a highly uniform binder-lithium salt composition will affect lithium ion transmission, thereby affecting the capacity, cycle and rate performance of the battery.

[0168] In the all-solid-state negative electrode plate provided by the present invention, the binder and the lithium salt are combined into one to form a binder-lithium salt composition, thereby converting the insulating binder into an ion-conducting binder, which can significantly improve the ion transmission capacity of the interface. In addition, by adjusting the uniformity of the binder-lithium salt composition in the negative electrode active material layer, the contact area between the binder and other negative electrode components can be reduced, further improving the ion transmission efficiency and improving the rate performance of the battery. Adjusting the uniformity of the binder-lithium salt composition in the negative electrode active material layer can also adjust the cohesion of the electrode plate, so that binders with different uniformities can match negative electrode active materials with different silicon contents, thereby matching the cohesion of the electrode plate with the intrinsic shrinkage and expansion of the silicon material, and improving the cycle performance of the battery while increasing the battery energy density. Therefore, the present invention effectively overcomes some practical problems in the prior art and has high utilization value and use significance.

[0169] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. An all-solid-state negative electrode plate, characterized in that: include: negative electrode current collector; A negative electrode active material layer is provided on at least one side of the negative electrode current collector; Wherein, the negative electrode active material layer includes a negative electrode active material, a solid electrolyte, a conductive agent and a binder-lithium salt composition, and the uniformity of the binder-lithium salt composition in the negative electrode active material layer is 20% to 40%, and the uniformity of the binder-lithium salt composition refers to the volume percentage of the binder-lithium salt composition in the entire area of ​​the negative electrode active material layer; The uniformity of the binder-lithium salt composition in the negative electrode active material layer is X1%, the silicon content in the negative electrode active material is X2 wt%, and the all-solid-state negative electrode sheet satisfies the following relationship: 23≤1.85X1-X2≤33; The method for preparing the all-solid-state negative electrode plate comprises: dissolving a binder and a lithium salt in a first solvent to prepare an ion-conducting binder paste; adding a conductive agent to the ion-conducting binder paste, mixing uniformly, to prepare an ion- and electron-conducting paste; adding a negative electrode active material, a solid electrolyte, and a second solvent to the ion- and electron-conducting paste, mixing uniformly, to prepare an all-solid-state negative electrode slurry; coating the all-solid-state negative electrode slurry on at least one side of a negative electrode current collector, and drying to prepare an all-solid-state negative electrode plate; The polarity parameter of the first solvent is 2.4~4, the polarity parameter of the second solvent is 0~0.2, the mass ratio of the first solvent to the second solvent is 1:(3~5), the added amount of the binder accounts for X3 wt% of the total mass of the negative electrode active material, the conductive agent, the solid electrolyte, the binder and the lithium salt, and the added amount of the lithium salt accounts for X4 wt% of the total mass of the negative electrode active material, the conductive agent, the solid electrolyte, the binder and the lithium salt, then X3 and X4 satisfy the following relationship: 0≤0.5X3-X4≤1.

2. The all-solid-state negative electrode according to claim 1, wherein: The content of the binder-lithium salt composition in the negative electrode active material layer is 4 wt % to 10 wt %, the content of the negative electrode active material in the negative electrode active material layer is 60 wt % to 90 wt %, and / or the ionic conductivity of the binder-lithium salt composition is 10 -6 S / cm ~10 -4 S / cm.

3. The all-solid-state negative electrode according to claim 1, characterized in that: The binder-lithium salt composition includes a binder and a lithium salt. The binder includes a modified polymer containing polar side chains. The binder includes one or more of polyvinylidene fluoride-grafted maleic anhydride, styrene-butadiene rubber-copolymerized hydroxyethyl acrylate, polymethyl methacrylate-copolymerized acrylic acid, and polybutyl acrylate-grafted maleic anhydride.

4. The all-solid-state negative electrode according to claim 3, characterized in that: Include at least one of the following characteristics: The lithium salt includes one or more of LiBF4, LiBF6, LiAsF6, LiPF6, LiClO4, LiFSI, LiTFSI, LiB(C6H5)4, LiAlCl4, LiBr, LiCF3SO3, and LiN(CF3SO2)2; The negative electrode active material includes graphite material and / or silicon material; The solid electrolyte includes at least one of an oxide solid electrolyte, a sulfide solid electrolyte, and a halide solid electrolyte; The conductive agent is selected from at least one of graphite, graphene, carbon black, carbon fiber and carbon nanotubes.

5. A method for preparing the all-solid-state negative electrode sheet according to any one of claims 1 to 4, characterized in that: The following steps are involved: dissolving a binder and a lithium salt in a first solvent to prepare an ion-conducting binder solution; Adding a conductive agent to the ion-conducting adhesive solution and mixing them evenly to obtain an ion- and electron-conducting adhesive solution; Adding negative electrode active material, solid electrolyte and second solvent to the ion and electron dual conductive gel solution, mixing them evenly to prepare an all-solid-state negative electrode slurry; The all-solid-state negative electrode slurry is coated on at least one side of a negative electrode current collector and dried to obtain an all-solid-state negative electrode sheet.

6. The method for preparing an all-solid-state negative electrode sheet according to claim 5, characterized in that: The first solvent includes at least one of butyl butyrate, benzene, and ethylene dichloride; and / or the second solvent includes at least one of trimethylpentane, dodecane, methylcyclohexane, and decalin.

7. The method for preparing an all-solid-state negative electrode sheet according to claim 5, characterized in that: Include at least one of the following characteristics: The mass ratio of the first solvent to the second solvent in the all-solid-state negative electrode slurry is 1:X5, the uniformity of the binder-lithium salt composition in the negative electrode active material layer of the prepared all-solid-state negative electrode plate is X1%, and the all-solid-state negative electrode slurry satisfies the following relationship: 6.5≤X5+0.1X1≤7.5; The solid content of the all-solid-state negative electrode slurry is 50 wt % to 80 wt %.

8. The method for preparing an all-solid-state negative electrode sheet according to claim 5, wherein: The drying step includes: a first drying stage, rapidly volatilizing the second solvent at 60°C to 80°C for 1 minute to 5 minutes; and a second drying stage, slowly volatilizing the first solvent at 100°C to 120°C for 1 hour to 2 hours.

9. An all-solid-state battery, characterized in that: It comprises the all-solid-state negative electrode sheet according to any one of claims 1 to 4, or the all-solid-state negative electrode sheet prepared by the preparation method according to any one of claims 5 to 8.

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