Negative electrode sheet, battery, and electric device

Abstract

This invention discloses a negative electrode sheet, a battery, and an electrical device. The negative electrode sheet includes a negative electrode current collector, a first negative electrode active material layer, and a second negative electrode material layer. The first negative electrode active material layer is disposed on at least one surface of the negative electrode current collector and includes a first negative electrode active material. The second negative electrode material layer is disposed on the surface of the first negative electrode active material layer away from the negative electrode current collector and includes a second negative electrode material and a first electrolyte. The second negative electrode material includes a carbon-based material. According to the negative electrode sheet of this invention, while improving the lithium storage capacity and energy density of the negative electrode sheet, the second negative electrode material layer can protect the first negative electrode active material layer, suppressing the problem of electrolyte layer cracking induced by volume change of the negative electrode sheet, thereby improving the cycle life of the battery using the above-mentioned negative electrode sheet.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a negative electrode, a battery, and an electrical device. Background Technology

[0002] The active materials commonly used in negative electrode plates are prone to volume changes during cycling, leading to destructive effects in the solid electrolyte system. When the local expansion stress exceeds the yield strength of the electrolyte layer in a solid-state battery, microcracks propagate within the electrolyte layer. More seriously, the crack network generated during cycling can gradually expand to form macroscopic cracks in the electrolyte layer, easily creating micro-short-circuit hotspots, resulting in abnormal coulombic efficiency and battery failure.

[0003] The failure mechanism of solid-state battery cycle performance degradation can be attributed to: the volume change caused by the phase change of the active material of the negative electrode, which induces a three-stage failure evolution of microcrack nucleation → propagation → penetration in the electrolyte layer through the stress coupling effect of the negative electrode-electrolyte interface, ultimately leading to micro-short circuit inside the solid-state battery, manifested as a sharp inflection point of capacity degradation in the middle of the cycle (usually 100-200 cycles). Summary of the Invention

[0004] The present invention aims to at least solve one of the technical problems existing in the prior art. Therefore, one object of the present invention is to provide a negative electrode sheet that improves the energy density of the negative electrode sheet and the battery using the aforementioned negative electrode sheet, while suppressing the problem of electrolyte layer cracking induced by volume change of the negative electrode sheet, thereby improving the cycle life of the battery using the aforementioned negative electrode sheet.

[0005] According to a first aspect of the present invention, a negative electrode sheet includes: a negative electrode current collector; a first negative electrode active material layer disposed on at least one side surface of the negative electrode current collector, the first negative electrode active material layer including a first negative electrode active material; and a second negative electrode material layer disposed on the side surface of the first negative electrode active material layer away from the negative electrode current collector, the second negative electrode material layer including a second negative electrode material and a first electrolyte, wherein the second negative electrode material includes a carbon-based material.

[0006] According to embodiments of the present invention, the negative electrode sheet improves the lithium storage capacity of the negative electrode sheet and the energy density of the negative electrode sheet and the battery using the aforementioned negative electrode sheet through the first negative electrode active layer. Simultaneously, the second negative electrode material layer is disposed on the side of the first negative electrode active material layer away from the current collector, which helps protect the first negative electrode active material layer and improves the cycle stability of the negative electrode sheet. The second negative electrode material includes a carbon-based material that can absorb the expansion stress of the first negative electrode active material layer, thereby helping to suppress the problem of electrolyte layer cracking induced by volume change of the negative electrode sheet and improving the cycle life of the battery using the aforementioned negative electrode sheet.

[0007] According to some embodiments of the present invention, the first negative electrode active material comprises a silicon-based material.

[0008] According to some embodiments of the present invention, the first negative electrode active material includes at least one of silicon, silicon-carbon, and silicon-oxygen; preferably, the first negative electrode active material includes only silicon; and / or, the second negative electrode material includes at least one of natural graphite, artificial graphite, hard carbon, and soft carbon.

[0009] According to some embodiments of the present invention, the mass percentage of the second negative electrode material in the second negative electrode material layer is 20% to 70%; and / or, the thickness of the second negative electrode material layer is 10 μm to 50 μm; and / or, the D50 particle size of the second negative electrode material is 5 μm to 15 μm.

[0010] According to some embodiments of the present invention, the mass percentage of the first electrolyte in the second negative electrode material layer is 28% to 80%; and / or, the first electrolyte is a solid electrolyte; preferably, the first electrolyte includes at least one of a sulfide solid electrolyte and a halide solid electrolyte.

[0011] According to some embodiments of the present invention, the sulfide solid electrolyte includes Li3PS4 and Li7P3S. 11 Li 11 GeP2S 12 Li6PS5Cl, Li7P2S8I, Li 10 SnP2S 12 Li 3.25 Ge 0.25 P 0.75 At least one of S4; and / or, the halide solid electrolyte includes at least one of LiAlCl4, Li3YCl6, Li3InCl6, Li3InBr6, and Li3ScCl6.

[0012] According to some embodiments of the present invention, the second negative electrode material layer comprises, by weight percentage, 0.5% to 3% of the first binder and 0% to 3% of the first conductive agent.

[0013] According to some embodiments of the present invention, the first adhesive comprises at least one selected from polyacrylate, polyimide, polyurethane, polyvinylidene fluoride, styrene-butadiene rubber, polytetrafluoroethylene, hydrogenated nitrile rubber, and fluorinated rubber; and / or, the first conductive agent comprises at least one selected from acetylene black, carbon black, carbon nanotubes, carbon fibers, and graphene.

[0014] According to some embodiments of the present invention, the first negative electrode active material layer further includes a second binder, wherein the second binder accounts for 1% to 5% of the first negative electrode active material by mass percentage.

[0015] According to some embodiments of the present invention, the second adhesive comprises at least one selected from polyacrylic acid, polyvinylidene fluoride, styrene-butadiene rubber, hydrogenated nitrile rubber, sodium carboxymethyl cellulose, and polytetrafluoroethylene.

[0016] A battery according to a second aspect of the present invention includes: a negative electrode sheet according to the first aspect of the present invention described above, wherein the battery is any one of a single cell, a battery module, and a battery pack.

[0017] An electrical device according to a third embodiment of the present invention includes: a negative electrode sheet according to the first embodiment of the present invention, or a battery according to the second embodiment of the present invention.

[0018] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0019] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a scanning electron microscope image according to Embodiment 1 of the present invention, showing a cross-sectional view of the pouch cell.

[0020] Figure label: 1: First negative electrode active material layer; 2: Second negative electrode material layer; 3: Electrolyte layer; 4: Positive electrode sheet. Detailed Implementation

[0021] A negative electrode sheet according to an embodiment of the first aspect of the present invention is described.

[0022] According to a first aspect of the present invention, the negative electrode sheet includes a negative electrode current collector, a first negative electrode active material layer 1, and a second negative electrode material layer 2.

[0023] Specifically, a first negative electrode active material layer 1 is disposed on at least one side surface of the negative electrode current collector, and the first negative electrode active material layer 1 includes a first negative electrode active material. A second negative electrode material layer 2 is disposed on the side surface of the first negative electrode active material layer 1 away from the negative electrode current collector, and the second negative electrode material layer 2 includes a second negative electrode material and a first electrolyte, wherein the second negative electrode material includes a carbon-based material.

[0024] Reference Figure 1A first negative electrode active material layer 1 and a second negative electrode material layer 2 are sequentially disposed along the direction away from the negative electrode current collector. The side of the second negative electrode material layer 2 away from the negative electrode current collector can be adjacent to the electrolyte layer 3 of the battery. The second negative electrode material layer 2 is disposed outside the first negative electrode active material layer 1, which can form a protective layer for the electrolyte layer 3. By using the buffering effect of the second negative electrode material layer 2, the damage caused by the expansion and deformation of the first negative electrode active material layer 1 is reduced, thereby suppressing the problem of electrolyte layer 3 cracking induced by the volume change of the negative electrode sheet, and thus improving the cycle life of the battery using the above-mentioned negative electrode sheet.

[0025] The second negative electrode material layer 2 is located on the side of the first negative electrode active material layer 1 away from the current collector, which helps protect the first negative electrode active material layer 1 and improves the cycle stability of the negative electrode sheet. The plastic deformation characteristics of carbon-based materials can effectively absorb the expansion stress of the first negative electrode active material. At the same time, the high strength of carbon-based materials helps to improve the structural strength of the negative electrode sheet. Carbon-based materials can inhibit the crack propagation of the first negative electrode active material layer 1 through the pinning effect. When cracks encounter carbon-based materials, they may change their path or terminate, thereby weakening the cracking process of the electrolyte layer 3, improving the structural strength of the negative electrode sheet, and extending the cycle life of the negative electrode sheet and the battery using the above-mentioned negative electrode sheet.

[0026] Therefore, the second negative electrode material can suppress crack propagation in the first negative electrode active material layer 1 through the "pinning effect," thereby reducing the risk of cracking in the electrolyte layer 3 adjacent to the second negative electrode material layer 2, avoiding the occurrence of micro-short circuit hotspots, and improving the cycle life of the battery using the above-mentioned negative electrode sheet. Simultaneously, the continuous distribution of the first electrolyte in the second negative electrode material layer 2 forms a stable ion transport network, enabling the negative electrode sheet to be charged and discharged normally. Thus, the negative electrode sheet of this application not only fully utilizes the first negative electrode active material but also reduces multi-field coupling failure problems through mechano-electrochemical coupling design, which is beneficial for extending the cycle life of the battery using the above-mentioned negative electrode sheet.

[0027] According to embodiments of the present invention, the negative electrode sheet improves the lithium storage capacity of the negative electrode sheet and the energy density of the negative electrode sheet and the battery using the aforementioned negative electrode sheet through the first negative electrode active layer. Simultaneously, the second negative electrode material layer 2 is disposed on the side of the first negative electrode active material layer 1 away from the current collector, which helps protect the first negative electrode active material layer 1 and improves the cycle stability of the negative electrode sheet. At the same time, the second negative electrode material can absorb the expansion stress of the first negative electrode active material layer 1, thereby helping to suppress the problem of electrolyte layer 3 cracking induced by volume change of the negative electrode sheet and improving the cycle life of the battery using the aforementioned negative electrode sheet.

[0028] According to some embodiments of the present invention, the first negative electrode active material includes a silicon-based material. Silicon-based materials have a higher theoretical specific capacity, which is beneficial for increasing the energy density of the negative electrode. Crack propagation in the silicon-based material as the first negative electrode active material layer 1 can be suppressed by the pinning effect of the carbon-based material of the second negative electrode, thereby weakening the cracking process of the electrolyte layer 3. This achieves both improved structural strength of the negative electrode and extended cycle life of the negative electrode and the battery using the aforementioned negative electrode.

[0029] According to other embodiments of the present invention, the first negative electrode active material includes at least one of silicon, silicon-carbon, and silicon-oxygen. Silicon has a relatively large theoretical specific capacity, which is beneficial for increasing the energy density of the negative electrode. Silicon-carbon helps to alleviate volume expansion, improve cycle stability, and enhance the conductivity of the negative electrode. Silicon-oxygen can also alleviate volume expansion and improve cycle stability; moreover, silicon-oxygen is simple to synthesize, which helps to reduce the cost of the negative electrode.

[0030] According to other embodiments of the present invention, the first negative electrode active material comprises only silicon. Silicon not only has a theoretical specific capacity, which can improve the energy density of the battery; moreover, the silicon-lithium compound after lithium intercalation has a high ionic conductivity, which can further improve the lithium intercalation activity and reduce the use of solid electrolyte.

[0031] The second anode material includes at least one of natural graphite, artificial graphite, hard carbon, and soft carbon. Natural graphite has high crystallinity and high capacity. Artificial graphite's structure can be controlled through precursor selection and graphitization processes (e.g., reducing defects and optimizing particle size distribution), resulting in good cycle performance and rate performance. Soft carbon has a short ion diffusion path and excellent rate performance. Hard carbon has high capacity, numerous surface active sites, and readily forms an SEI film (solid electrolyte interface).

[0032] According to other embodiments of the present invention, preferably, the second negative electrode material includes natural graphite and artificial graphite. Graphite has a regular layered structure and better ductility and deformability, which can better solve the problem of negative electrode cracking caused by the expansion of silicon-based materials.

[0033] According to some embodiments of the present invention, the mass percentage of the second negative electrode material in the second negative electrode material layer 2 is 20% to 70%. Therefore, the content of the second negative electrode material in the second negative electrode material layer 2 is relatively reasonable, which is conducive to fully utilizing the function of the second negative electrode material to pin down cracks generated in the first negative electrode active material layer 1, thereby extending the service life of the battery cell. At the same time, it ensures that the second negative electrode material does not occupy a large mass percentage in the second negative electrode material layer 2, allowing the remaining components in the second negative electrode material layer 2 to function effectively.

[0034] The thickness of the second negative electrode material layer 2 is 10μm to 50μm. Therefore, the thickness of the second negative electrode material layer 2 is reasonable. In the thickness direction, the second negative electrode material of the second negative electrode material layer 2 can fully exert the effect of suppressing the cracks generated by the first negative electrode active material layer 1. At the same time, reasonable control of the thickness of the second negative electrode material layer 2 is beneficial to control the cost of the negative electrode sheet and the energy density requirements of the negative electrode sheet.

[0035] The D50 particle size of the second anode material is 5 μm to 15 μm. The D50 particle size indicates that in the volumetric particle size distribution of the material, 50% of the particles are smaller than this value, and the other 50% are larger than this value. This limitation on the D50 particle size of the second anode material is reasonable, as it facilitates the "pinning effect," inhibits crack propagation, and ensures good ion conductivity of the layer.

[0036] According to some specific embodiments of the present invention, the mass percentage of the first electrolyte in the second negative electrode material layer 2 is 28% to 80%. The content of the first electrolyte in the second negative electrode material layer 2 is reasonable, which is conducive to meeting the ion transport efficiency of the negative electrode sheet and giving full play to the buffering effect of the second negative electrode material layer 2.

[0037] The first electrolyte is a solid electrolyte, preferably comprising at least one of a sulfide solid electrolyte and a halide solid electrolyte. Solid electrolytes are materials that possess ion conductivity in a solid state. Sulfide solid electrolytes exhibit ultra-high ionic conductivity and good mechanical ductility, which helps reduce interfacial impedance and meet the high-power output requirements of batteries. Halide solid electrolytes offer higher ionic conductivity, chemical stability, and cost advantages.

[0038] Furthermore, sulfide solid electrolytes include Li3PS4 and Li7P3S. 11 Li 11 GeP2S 12 Li6PS5Cl, Li7P2S8I, Li 10 SnP2S 12 Li 3.25 Ge 0.25 P 0.75 At least one of S4. Among them, Li6PS5Cl belongs to the argyrodite type sulfide, exhibiting high ionic conductivity and good electrochemical stability. Li7P3S 11 It is a metastable superionic conductor with high ion mobility, which can provide better charge and discharge performance for batteries.

[0039] Halogen solid electrolytes include LiAlCl4, Li3YCl6, and Li3InC. l6At least one of Li3InBr6 and Li3ScCl6. LiAlCl4 is a typical aluminochlorochlorophosphate electrolyte, while Li3YCl6 offers advantages such as a wide electrochemical window and high-voltage compatibility. Li3InC l6 Li3InBr6 can be synthesized in batches via aqueous phase, and the increase in interfacial impedance is small after multiple cycles. It exhibits superionic phase transition, high conductivity, and high-pressure compatibility. Li3ScCl6 shows high capacity retention, minimal decrease in interfacial impedance, and high-pressure performance.

[0040] The electrolyte described above can meet the conductivity requirements of the first electrolyte, which is beneficial to improving the conductivity of the negative electrode. At the same time, the first electrolyte and the second negative electrode material have good compatibility.

[0041] According to some embodiments of the present invention, the second negative electrode material layer 2 comprises, by mass percentage, 0.5% to 3% of a first binder and 0% to 3% of a first conductive agent. The core function of the first binder is to bond with the surface of the adherend (e.g., the second negative electrode material) through intermolecular forces (van der Waals forces, hydrogen bonds) or chemical adsorption (functional group reactions), while simultaneously forming a continuous "bridging layer" through its own film-forming properties. The first conductive agent can be used to construct electron transport channels, facilitating the formation of a continuous conductive network between the particles of the second negative electrode material and reducing electron transport resistance.

[0042] Conductive agents are prone to agglomeration, requiring a binder to disperse them through molecular chain entanglement or electrostatic interaction to form a uniform mixture. The content of the first binder and the first conductive agent is reasonable, avoiding excessive aggregation of the first binder that hinders electron transport while ensuring adhesion, thus guaranteeing the stable existence of the conductive network. The reasonable content of the first conductive agent ensures electron transport and rate performance while controlling the cost of the first conductive agent. The second negative electrode material layer 2 may not include the first conductive agent to achieve conductivity.

[0043] Furthermore, the first adhesive includes at least one of polyacrylate, polyimide, polyurethane, polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), polytetrafluoroethylene (PTFE), hydrogenated nitrile butadiene rubber (HNBR), and fluorinated rubber (FKM). Among these, polyurethane (where polar urethane bonds can form hydrogen bonds with polar surfaces), PVDF (where the crystalline region is in close contact with the surface of the adherend), and polyacrylate (where ester groups interact with dipole-dipole interactions of polar materials) exhibit strong adhesive properties. SBR (where elastomer molecular chains entangle) and HNBR (where nitrile groups adsorb onto polar surfaces) provide both adhesive strength and stress buffering. Polyimide (where the rigid structure results in a small interfacial contact area) and PTFE / fluorinated rubber (which are non-polar, relying solely on van der Waals forces) meet adhesive strength requirements while also exhibiting high-temperature resistance. Additionally, PTFE in these adhesives is resistant to almost all chemical reagents, fluorinated rubber is resistant to oils and solvents, and polyimide is resistant to acids and alkalis. Therefore, using the first adhesive described above is beneficial to meet the compatibility and bonding requirements of various components in the second negative electrode material layer 2, which helps to improve the structural stability of the negative electrode sheet and extend its service life.

[0044] The first conductive agent includes at least one of acetylene black, carbon black, carbon nanotubes, carbon fibers, and graphene. Acetylene black / carbon black can form a point-to-point conductive network through physical contact between particles, suitable for filling the tiny gaps in the second negative electrode material layer 2. Carbon nanotubes / carbon fibers utilize their aspect ratio advantage to form a line-to-surface conductive network, connecting the dispersed second negative electrode material across large distances, thus effectively conducting electricity. Graphene forms a two-dimensional conductive network through surface-to-surface contact, with a large contact area with the second negative electrode material and a short electron transport path, suitable for improving the capacity and rate capability of the negative electrode sheet. The aforementioned first conductive agent has good compatibility with the first binder and the second negative electrode material, and is suitable for uniform dispersion through the first binder, which helps ensure the conductivity and structural stability of the negative electrode sheet.

[0045] According to some embodiments of the present invention, the first negative electrode active material layer 1 further includes a second binder, which accounts for 1% to 5% of the first negative electrode active material by mass percentage. The content of the second binder in the first negative electrode active material is reasonable, which is conducive to giving full play to the bonding effect, so as to fully improve the structural stability of the first negative electrode active material, reduce the risk of material shedding, and extend the service life of the negative electrode sheet.

[0046] Furthermore, the second binder includes at least one of polyacrylic acid (PAA), polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), hydrogenated nitrile butadiene rubber (HNBR), sodium carboxymethyl cellulose (CMC), and polytetrafluoroethylene (PTFE). Among these, polyacrylic acid (PAA) is highly polar, water-soluble, and has high molecular chain flexibility, readily forming hydrogen bonds or coordination bonds with hydroxyl groups and metal ions on the surface of the active material. Simultaneously, PAA's high flexibility allows it to stretch with particle expansion / contraction, alleviating stress concentration and reducing negative electrode cracking. Polyvinylidene fluoride is resistant to organic electrolytes (carbonates, ethers), does not swell or react, and has a wide electrochemical stability window, which helps ensure the mechanical strength of the negative electrode. Styrene-butadiene rubber forms physical adsorption through molecular chain entanglement, mitigating minor volume expansion and reducing the risk of negative electrode embrittlement. Furthermore, styrene-butadiene rubber is an aqueous dispersion, requiring no organic solvents, making it suitable for large-scale production. Hydrogenated nitrile butadiene rubber (HNBR) is oil- and electrolyte-resistant, possessing both elasticity and toughness. The high elasticity of HNBR allows it to deform as the particles expand, which helps maintain the structural integrity of the negative electrode sheet. Sodium carboxymethyl cellulose (CMC) has good water solubility and adhesion, which helps improve the adhesion of the first negative electrode active material layer 1 to the negative electrode current collector. Polytetrafluoroethylene (PTFE) is resistant to almost all chemical reagents (strong acids, strong alkalis, and organic solvents) and high temperatures. Therefore, the aforementioned second binder effectively meets the needs of the first negative electrode active material layer, exhibits good compatibility with the other components in the first negative electrode active material layer, and helps improve the structural uniformity and stability of the first negative electrode active material layer.

[0047] In addition, the first negative electrode active material layer may also include a second conductive agent and / or a second electrolyte.

[0048] The second electrolyte includes at least one of a sulfide solid electrolyte and a halide solid electrolyte; the sulfide solid electrolyte includes Li3PS4 and Li7P3S. 11 Li 11 GeP2S 12 Li6PS5Cl, Li7P2S8I, Li 10 SnP2S 12 Li 3.25 Ge 0.25 P 0.75 At least one of S4; and / or, the halide solid electrolyte includes at least one of LiAlCl4, Li3YCl6, Li3InCl6, Li3InBr6, and Li3ScCl6.

[0049] The second conductive agent includes at least one of acetylene black, carbon black, carbon nanotubes, carbon fibers, and graphene.

[0050] The second electrolyte may be the same as or different from the first electrolyte. Similarly, the second conductive agent may be the same as or different from the first conductive agent. No specific limitations are imposed here. According to some embodiments of the present invention, a method for preparing a negative electrode sheet includes the following steps: Preparation of the first negative electrode active coating; A first negative electrode active coating is applied to at least one side surface of the negative electrode current collector to form a first negative electrode active material layer 1; A second negative electrode active coating is prepared by mixing the second negative electrode material and the first electrolyte. The second negative electrode active coating is applied onto the first negative electrode active material layer 1 to form the second negative electrode material layer 2, thus obtaining the negative electrode sheet.

[0051] According to the method for preparing the negative electrode sheet according to the embodiments of the present invention, the above preparation method is relatively simple, which is beneficial to improving the preparation efficiency of the negative electrode sheet and reducing the cost of the negative electrode sheet.

[0052] Further, the first negative electrode active coating is applied to at least one side surface of the negative electrode current collector and dried to obtain the first negative electrode active material layer 1, wherein the drying temperature is 50℃~100℃. Applying the first negative electrode active coating to at least one side surface of the negative electrode current collector and then drying it at the aforementioned temperature facilitates the drying of the first negative electrode active material layer 1 and ensures it is firmly attached to the negative electrode current collector. This avoids changes in the composition of the second negative electrode active coating due to higher temperatures. Simultaneously, the dried surface of the first negative electrode active material layer 1 forms a stable physical or chemical structure, providing a good adhesion base for the second negative electrode material layer 2 and preventing interference between the first negative electrode active material layer 1 and the second negative electrode material layer 2.

[0053] The second negative electrode active coating is applied onto the first negative electrode active material layer 1 and dried to obtain the second negative electrode material layer 2. The drying temperature is 70℃~120℃. At the above drying temperature, the second negative electrode material layer 2 is dried and firmly set on the negative electrode current collector, avoiding changes in the composition of the second negative electrode active coating due to high temperature. At the same time, it helps to improve the structural integrity of the second negative electrode material layer 2.

[0054] According to a second aspect of the present invention, a battery includes: a negative electrode sheet as described in the first aspect of the present invention, wherein the battery is any one of a single cell, a battery module, and a battery pack.

[0055] The battery according to embodiments of the present invention helps to reduce the battery's expansion rate, while also improving the battery's stability and extending its lifespan, thereby enhancing the battery's market competitiveness.

[0056] An electrical device (not shown) according to a third aspect embodiment of the present invention includes: a negative electrode sheet according to the first aspect embodiment of the present invention, or a battery according to the second aspect embodiment of the present invention.

[0057] According to the embodiments of the present invention, the power supply stability of the electrical equipment is relatively high, which is conducive to improving the user experience and thus enhancing the market competitiveness of the electrical equipment.

[0058] The electrical equipment can be vehicles, aircraft, ferries, computers, or energy storage cabinets. No specific limitations are specified here.

[0059] The embodiments of the present invention are described in detail below. It should be noted that the embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. In addition, unless otherwise specified, all reagents used in the following embodiments are commercially available or can be synthesized according to the methods described herein or known to others. For reaction conditions not listed, they are also readily available to those skilled in the art.

[0060] The method for preparing the negative electrode includes the following steps: (1) Wet preparation of the first negative electrode active coating. The second binder is added to the solvent and stirred to dissolve. The first negative electrode active material is added and stirred to disperse to obtain the first negative electrode active coating. The content of the first binder is more than 1 part by mass and less than 5 parts by mass relative to 100 parts by mass of the first negative electrode active material. The first negative electrode active coating is coated on the surface of the negative electrode current collector and dried at 50℃~100℃ to obtain a negative electrode sheet containing the first negative electrode active material layer 1.

[0061] (2) Wet preparation of the second negative electrode active coating. The first binder is dissolved in a solvent, and the second negative electrode material, the first electrolyte, and the first conductive agent are added sequentially to obtain the second negative electrode active coating. Among all solid components, the second negative electrode material accounts for 20% to 70% by mass, the first electrolyte accounts for 28% to 80% by mass, the first binder accounts for 0.5% to 3% by mass, and the first conductive agent accounts for 0% to 3% by mass.

[0062] (3) The second negative electrode active coating is applied to the surface of the negative electrode sheet obtained in step (1) and dried at 70℃~120℃ to obtain the negative electrode sheet.

[0063] The components in the first negative electrode active material layer 1 and the second negative electrode material layer 2 are defined as shown in Examples 1-11 and Comparative Example 1.

[0064] Example 1 The first negative electrode active material in the first negative electrode active material layer 1 is pure silicon, and the second binder is PAA. The mass of the second binder accounts for 3% of the mass of the first negative electrode active material.

[0065] The second negative electrode material in the second negative electrode material layer 2 is artificial graphite, accounting for 59% by mass, and the D50 particle size of the second negative electrode material is 10 μm; the first electrolyte is Li6PS5Cl solid electrolyte, accounting for 38% by mass; the first binder is hydrogenated nitrile rubber, accounting for 2% by mass; and the first conductive agent is carbon black, accounting for 1% by mass. The thickness of the second negative electrode material layer 2 is 30 μm.

[0066] Example 2 This embodiment is largely the same as Embodiment 1, except that the mass percentage of the second negative electrode material in the second negative electrode material layer 2 is 70%, the mass percentage of the first electrolyte is 28%, the mass percentage of the first binder is 1%, and the mass percentage of the first conductive agent is 1%.

[0067] Example 3 This embodiment is largely the same as Embodiment 1, except that the mass percentage of the second negative electrode material is 20%, the mass percentage of the first electrolyte is 78%, the mass percentage of the first binder is 1%, and the mass percentage of the first conductive agent is 1%.

[0068] Example 4 This embodiment is largely the same as Embodiment 1, except that the thickness of the second negative electrode material layer is 50 μm.

[0069] Example 5 This embodiment is largely the same as Embodiment 1, except that the thickness of the second negative electrode material layer is 10 μm.

[0070] Example 6 This embodiment is largely the same as Embodiment 1, except that the D50 particle size of the second negative electrode material is 15 μm.

[0071] Example 7 This embodiment is largely the same as Embodiment 1, except that the D50 particle size of the second negative electrode material is 5 μm.

[0072] Example 8 This embodiment is largely the same as Embodiment 1, except that the thickness of the second negative electrode material layer is 60 μm.

[0073] Example 9 This embodiment is largely the same as Embodiment 1, except that the thickness of the second negative electrode material layer is 5 μm and the D50 particle size of the second negative electrode material is 3 μm.

[0074] Example 10 This embodiment is largely the same as Embodiment 1, except that the particle size of the second negative electrode material D50 is 20 μm.

[0075] Example 11 This embodiment is largely the same as Embodiment 1, except that the D50 particle size of the second negative electrode material is 3 μm.

[0076] Example 12 This embodiment is basically the same as Embodiment 1, except that the mass ratio of the second negative electrode material is 90%, the mass ratio of the first electrolyte is 8%, the mass ratio of the first binder is 1%, and the mass ratio of the first conductive agent is 1%.

[0077] Example 13 This embodiment is basically the same as Embodiment 1, except that the mass ratio of the second negative electrode material is 10%, the mass ratio of the first electrolyte is 88%, the mass ratio of the first binder is 1%, and the mass ratio of the first conductive agent is 1%.

[0078] Comparative Example 1 Comparative Example 1 is basically the same as Example 1, except that it only has a first negative electrode active material layer 1 and no second negative electrode material layer 2.

[0079] Performance testing (1) Thickness test of the second negative electrode material layer 2: After the 0% SOC cell is disassembled, its cross-sectional morphology is observed by scanning electron microscope (SEM) in backscatter mode. The thickness of the second negative electrode material layer 2 in at least 3 regions is measured and the average value is calculated.

[0080] (2) Particle size test: Under SEM (accelerating voltage 5 kV to 15 kV, magnification 5000 to 20000 times), clear images of multiple regions are acquired. Using software such as ImageJ, the particles are binarized, separated by adhesion, and the circumscribed circle diameter is measured based on the particle projection area. After collecting data from at least 300 particles, they are arranged in ascending order. The particle size when the cumulative distribution reaches 50% is D50 (it is necessary to combine EDS to distinguish active substances and calibrate the scale to avoid agglomeration error).

[0081] (3) Assembly and performance testing of batteries using the above-mentioned negative electrode: Preparation of positive electrode 4 LiNi, a positive electrode active material, is a lithium nickel cobalt manganese oxide (LiNi). 0.8 Co 0.1 Mn 0.1 O2, conductive carbon black, silicogermanium sulfide solid electrolyte (Li6PS5Cl), and styrene-butadiene rubber binder are dispersed together in a xylene solution at a mass ratio of 70:28:1:1 and stirred until homogeneous. The positive electrode slurry is then uniformly coated onto the positive electrode current collector, followed by drying, cold pressing, and slitting to obtain positive electrode sheet 4. The electrode surface capacity is controlled at 3 mAh / cm². 2 ~4mAh / cm 2 .

[0082] Preparation of electrolyte layer 3 A sulfide solid electrolyte (Li6PS5Cl) of silver-germanium sulfide and a binder styrene-butadiene rubber were mixed at a mass ratio of 97:3. Xylene was added as a solvent and the mixture was stirred under vacuum until the system was homogeneous to obtain an electrolyte slurry. The electrolyte slurry was uniformly coated on the surface of the aluminum foil substrate, dried at room temperature, and then transferred to an oven for further drying to form an electrolyte layer 3.

[0083] Assembly of a battery using the above-mentioned negative electrode The electrolyte layer 3 is rolled onto the negative electrode sheet, and the substrate aluminum foil is peeled off. The negative electrode, electrolyte, and positive electrode sheet 4 are sequentially stacked to form a battery cell, such that the capacity ratio of the negative electrode sheet to the positive electrode sheet 4 is 1.1. The prepared battery cell is then pressurized at 500 MPa to prepare an all-solid-state lithium-ion battery. The above battery preparation process is carried out in a dry environment with a dew point below -50°C.

[0084] Electrochemical tests were conducted on the assembled batteries using the aforementioned negative electrode using a battery testing system to evaluate their electrochemical performance. The discharge specific capacity was tested under the following conditions: voltage range of 2.5V to 4.2V, test pressure of 30MPa, and test temperature of 45 degrees Celsius. A first cycle of constant current charge-discharge was performed at 0.1C, and the discharge specific capacity was recorded.

[0085] The test conditions for cycle capacity retention were as follows: apply a pressure of 30 MPa to the battery, charge it to 4.2V at 0.5C at 45℃, let it rest for 10 minutes, and then discharge it to 2.5V at 0.5C. This was repeated for 200 cycles. The discharge capacity of the first cycle was recorded as C1, and the capacity after 200 cycles was recorded as C... 200 The battery's capacity retention rate after 200 cycles is C. 200 / C1.

[0086] Table 1. Parameters of the negative electrode sheets of Examples 1-13 and Comparative Example 1, and test results of the all-solid-state pouch cells.

[0087] Test Result Analysis (1) Comparative Example 1 is a conventional untreated silicon anode without the second anode material layer 2. Through the test results of the all-solid-state soft-pack battery, it can be found that the cycle stability of Examples 1-13 containing the second anode material layer 2 is significantly better than that of Comparative Example 1. The latter has a capacity retention rate of only 53.2% after 200 cycles, indicating that the anode sheet of this application has a significant improvement on the battery cycle life.

[0088] (2) The cycle life of the all-solid-state soft-pack batteries in Examples 12-13 is lower than that in Examples 1-7. In Example 12, the content of the second negative electrode material in the second negative electrode material layer 2 is too high, which leads to a significant increase in the polarization of the negative electrode sheet and a significant decrease in the specific capacity. In Example 13, the content of the first electrolyte in the second negative electrode material layer 2 is too high, the effect of suppressing the cracking of the electrolyte layer 3 is generally poor, and the improvement in cycle life is not obvious.

[0089] (3) The performance of Examples 8 and 9 is worse than that of Example 1. In Example 8, the second negative electrode material layer 2 is thicker, which is not conducive to ion transport on the surface of the negative electrode sheet, increases the polarization of the negative electrode sheet, and leads to a decrease in specific capacity. In Example 9, the second negative electrode material layer 2 is thinner, which is also difficult to suppress the cracking effect of the electrolyte layer 3.

[0090] (4) The performance of Examples 10 and 11 is worse than that of Example 1. In Example 10, the D50 particle size of the second negative electrode material in the second negative electrode material layer 2 is larger, which leads to obstruction of ion transport pathways, increased polarization, and reduced specific capacity. In Example 11, the D50 particle size of the second negative electrode material in the second negative electrode material layer 2 is smaller, which cannot play a good "pinning effect". The strength of the second negative electrode material layer 2 is poor, the effect of inhibiting electrolyte layer cracking is poor, and the cycle life is average.

[0091] Therefore, through the comparison of Examples 1-13, it was found that there are differences in the content of the second negative electrode material, the content of the first electrolyte, the thickness of the second negative electrode material layer 2, and the particle size of the second negative electrode material, which have different effects on the performance of the battery. Under certain combinations, the performance can be better, and there is an optimal value.

[0092] Other configurations and operations of the batteries, battery packs, and electrical devices according to embodiments of the present invention are known to those skilled in the art and will not be described in detail here.

[0093] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example.

[0094] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A negative electrode sheet, characterized in that, include: Negative electrode current collector; A first negative electrode active material layer is disposed on at least one side surface of the negative electrode current collector, and the first negative electrode active material layer includes a first negative electrode active material. A second negative electrode material layer is disposed on the surface of the first negative electrode active material layer away from the negative electrode current collector. The second negative electrode material layer includes a second negative electrode material and a first electrolyte. The second negative electrode material includes a carbon-based material.

2. The negative electrode sheet according to claim 1, characterized in that, The first negative electrode active material includes silicon-based materials.

3. The negative electrode sheet according to claim 1, characterized in that, The first negative electrode active material includes at least one of silicon, silicon-carbon, and silicon-oxygen; preferably, the first negative electrode active material includes only silicon; and / or, The second negative electrode material includes at least one of natural graphite, artificial graphite, hard carbon, and soft carbon.

4. The negative electrode sheet according to claim 1, characterized in that, The mass percentage of the second negative electrode material in the second negative electrode material layer is 20% to 70%; and / or, The thickness of the second negative electrode material layer is 10 μm to 50 μm; and / or, The D50 particle size of the second negative electrode material is 5μm to 15μm.

5. The negative electrode sheet according to any one of claims 1-4, characterized in that, The mass percentage of the first electrolyte in the second negative electrode material layer is 28% to 80%; and / or, The first electrolyte is a solid electrolyte; preferably, the first electrolyte includes at least one of a sulfide solid electrolyte and a halide solid electrolyte.

6. The negative electrode sheet according to claim 5, characterized in that, The sulfide solid electrolyte includes Li3PS4 and Li7P3S. 11 Li 11 GeP2S 12 Li6PS5Cl, Li7P2S8I, Li 10 SnP2S 12 Li 3.25 Ge 0.25 P 0.75 At least one of S4; and / or, The halide solid electrolyte includes at least one of LiAlCl4, Li3YCl6, Li3InCl6, Li3InBr6, and Li3ScCl6.

7. The negative electrode sheet according to any one of claims 1-5, characterized in that, The second negative electrode material layer comprises, by weight percentage, 0.5% to 3% of the first binder and 0% to 3% of the first conductive agent.

8. The negative electrode sheet according to claim 7, characterized in that, The first adhesive comprises at least one selected from polyacrylate, polyimide, polyurethane, polyvinylidene fluoride, styrene-butadiene rubber, polytetrafluoroethylene, hydrogenated nitrile butadiene rubber, and fluorinated rubber; and / or, The first conductive agent includes at least one of acetylene black, carbon black, carbon nanotubes, carbon fibers, and graphene.

9. The negative electrode sheet according to claim 1, characterized in that, The first negative electrode active material layer also includes a second binder, which accounts for 1% to 5% of the first negative electrode active material by mass percentage.

10. The negative electrode sheet according to claim 9, characterized in that, The second adhesive includes at least one of polyacrylic acid, polyvinylidene fluoride, styrene-butadiene rubber, hydrogenated nitrile rubber, sodium carboxymethyl cellulose, and polytetrafluoroethylene.

11. A battery, characterized in that, include: The negative electrode sheet according to any one of claims 1-10, wherein the battery is any one of a single cell, a battery module, and a battery pack.

12. An electrical appliance, characterized in that, include: The negative electrode sheet according to any one of claims 1-10, or the battery according to claim 11.

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