Negative electrode sheet, lithium ion battery

Abstract

This invention relates to the field of battery technology, specifically to a negative electrode sheet and a lithium-ion battery; the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector, the negative electrode active material layer comprising a negative electrode active material, the negative electrode active material comprising a silicon-carbon composite material; a solid electrolyte layer is disposed on at least a portion of the surface of the silicon-carbon composite material; the silicon-carbon composite material has a D... 50 The pore size is 5µm to 10µm; the pore size distribution of the negative electrode exhibits a bimodal characteristic, with the peak pore size of the first peak ranging from 0.01µm to 2.5µm and the peak pore size of the second peak ranging from 2.5µm to 4.0µm. Compared with the prior art, this invention sets a solid electrolyte layer on the surface of the silicon-carbon composite material to physically isolate silicon from the electrolyte, fundamentally suppressing interfacial side reactions and the repeated formation of unstable solid electrolyte interfaces, thereby improving interfacial stability and cycle performance.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to negative electrode sheets and lithium-ion batteries. Background Technology

[0002] Lithium-ion batteries (LIBs) have been widely used in consumer electronics, electric vehicles, and large-scale energy storage. With the continued growth in demand for high-energy-density batteries, traditional graphite anodes (theoretical capacity 372 mAh g⁻¹) are becoming increasingly important. -1 Silicon (Si) is no longer sufficient to meet the needs of next-generation batteries due to its ultra-high theoretical specific capacity (3579 mAh g⁻¹). -1 And a relatively high lithium intercalation potential (~0.4V vs. Li / Li) + Silicon-carbon composites (hereinafter referred to as "deposited silicon-carbon") are considered core candidates for next-generation anode materials. In industrial practice, deposited silicon-carbon composites formed by uniformly depositing nano-silicon within a porous carbon framework using chemical vapor deposition (CVD) technology, followed by an outer carbon coating, have demonstrated good structural stability and engineering feasibility. However, deposited silicon-carbon still faces three major bottlenecks in practical applications: interfacial side reactions and SEI instability, limited ion transport kinetics and poor temperature adaptability, and difficulty in controlling volume expansion and electrode expansion rate. Summary of the Invention

[0003] In view of this, the present invention aims to at least partially solve one of the technical problems in the related art. To this end, the present invention provides a negative electrode and a lithium-ion battery, which physically isolate the silicon-carbon composite material from the electrolyte by setting a solid electrolyte layer on the surface of the silicon-carbon composite material, thereby suppressing the repeated formation of interfacial side reactions and unstable solid electrolyte interfaces from the source, protecting the active lithium, significantly improving the cycle capacity retention rate and reducing the electrode volume expansion.

[0004] To solve the above-mentioned technical problems, the present invention is implemented as follows: According to one aspect of the present invention, a negative electrode sheet is provided, comprising a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector, wherein the negative electrode active material layer comprises a negative electrode active material, and the negative electrode active material comprises a silicon-carbon composite material. At least a portion of the surface of the silicon-carbon composite material is provided with a solid electrolyte layer; The silicon-carbon composite material D 50 The thickness is 5µm to 10µm; The pore size distribution of the negative electrode exhibits a bimodal characteristic, with the peak pore size of the first peak ranging from 0.01µm to 2.5µm and the peak pore size of the second peak ranging from 2.5µm to 4.0µm.

[0005] In some embodiments, the solid electrolyte layer includes LiAlO2, Li x SiO y At least one of Li3PO4 and LiF, wherein, in Li x SiO y In the middle, 0 <x≤4,0<y≤4。

[0006] In some of these embodiments, the thickness of the solid electrolyte layer is 5µm to 18µm.

[0007] In some embodiments, the silicon-carbon composite material includes a porous carbon skeleton, nano-silicon particles dispersed within the porous carbon skeleton, a carbon layer disposed on the outer surface of the porous carbon skeleton, and a solid electrolyte layer disposed on the outer surface of the carbon layer.

[0008] In some embodiments, the negative electrode active material further includes graphite.

[0009] In some embodiments, the negative electrode active material layer further includes a negative electrode conductive agent and a negative electrode binder.

[0010] In some of these embodiments, the porosity of the negative electrode is 25% to 40%.

[0011] In some embodiments, the compaction density of the negative electrode is 1.5 g / cm³. 3 ~1.75g / cm 3 .

[0012] In some embodiments, the thickness of the negative electrode sheet is 50µm to 90µm.

[0013] In some embodiments, the interface resistance of the negative electrode is 2.0 mΩ·cm. 2 ~8.0mΩ·cm 2 .

[0014] In some embodiments, the electrode peel strength of the negative electrode is 15 N / m to 30 N / m.

[0015] In some of these embodiments, the negative electrode retains ≥82.9% of its capacity after 600 cycles of 1C / 1C charge / discharge.

[0016] In some of these embodiments, the negative electrode has an expansion rate of ≤30% after 600 cycles of 1C / 1C charge / discharge.

[0017] According to one aspect of the present invention, a lithium-ion battery is provided, further comprising a positive electrode, a separator, and a negative electrode; wherein the negative electrode is the negative electrode described in the above technical solution.

[0018] In some of these embodiments, the lithium-ion battery includes a liquid lithium-ion battery, a semi-solid lithium-ion battery, or an all-solid lithium-ion battery.

[0019] Implementing the technical solution of the present invention has at least the following beneficial effects: (1) This invention provides a solid electrolyte layer on at least a portion of the surface of the silicon-carbon composite material, physically isolating silicon from the electrolyte, thereby suppressing interfacial side reactions at the source and preventing the repeated formation of organic-enriched unstable SEI, thus improving interfacial stability. Simultaneously, the D... 50 By controlling the particle size within a specific range of 5µm to 10µm, the problems of excessively small particles leading to excessively large specific surface area and exacerbating side reactions, and excessively large particles leading to internal stress concentration and cracking, are avoided, thus balancing chemical activity and structural integrity. Furthermore, the negative electrode is constructed with a structure featuring a specific bimodal pore size distribution. The smaller pore size peak provides a large number of lithium-ion transport channels and capillary wetting, while the larger pore size peak provides buffer space for the volume expansion of silicon particles and maintains high-speed electrolyte penetration. These three factors synergistically achieve high and excellent cycle capacity retention, significantly reduced electrode expansion rate, and low interfacial resistance.

[0020] (2) This invention controls the porosity to 25%~40%, providing sufficient channels for electrolyte penetration and ion migration, while reserving space to absorb the expansion of silicon-carbon particles; combined with 1.5g / cm 3 ~1.75g / cm 3 The compaction density and electrode thickness of 50µm~90µm ensure high energy density while maintaining good electrical contact and ion diffusion paths between particles; the resulting electrode structure maintains an interfacial resistance of 2.0mΩ·cm. 2 ~8.0mΩ·cm 2 The low level of heat ensures rapid charge and discharge capability, while the peel strength of 15N / m to 30N / m ensures that the negative electrode active material layer does not fall off during repeated expansion and contraction, thus comprehensively achieving high rate performance, long cycle life and low electrode expansion rate.

[0021] 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

[0022] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0023] Figure 1 This is a pore size distribution diagram of the negative electrode sheets obtained in Embodiment 1 and Comparative Example 3 of the present invention. Detailed Implementation

[0024] The present application will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0025] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and such ranges or values ​​should be understood to include values ​​close to such ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges or individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0026] In the description of this application, "same chemical composition" should be interpreted broadly, that is, the main components of the two have the same chemical composition, or the two have substantially the same chemical composition, but may have errors or impurities within the acceptable range that can be understood by those skilled in the art.

[0027] In the description of this application, "A and / or B" can include any of the cases of A alone, B alone, or A and B, where A and B are merely examples and can be any technical feature connected by "and / or" in this application.

[0028] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0029] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0030] Unless otherwise specified, all technical features and optional technical features of this invention can be combined to form new technical solutions.

[0031] Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order; for example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0032] Lithium-ion batteries (LIBs) have been widely used in consumer electronics, electric vehicles, and large-scale energy storage. With the continued growth in demand for high-energy-density batteries, traditional graphite anodes (theoretical capacity 372 mAh g⁻¹) are becoming increasingly important. -1 Silicon (Si) is no longer sufficient to meet the needs of next-generation batteries due to its ultra-high theoretical specific capacity (3579 mAh g⁻¹). -1 And a relatively high lithium intercalation potential (~0.4V vs. Li / Li) + Silicon-carbon composites (hereinafter referred to as "deposited silicon-carbon") are considered core candidates for next-generation anode materials. In industrial practice, deposited silicon-carbon composites formed by uniformly depositing nano-silicon inside a porous carbon framework using chemical vapor deposition (CVD) technology and then coating it with an outer carbon layer have shown good structural stability and engineering feasibility.

[0033] However, the inventors found that the deposition of silicon-carbon still faces three major bottlenecks in practical applications: (1) Interfacial side reactions and SEI instability: When the silicon-based anode comes into direct contact with the electrolyte, continuous side reactions occur at the interface, which continuously consume active lithium ions and form a solid electrolyte interface (SEI) film enriched with organic components. This organically enriched SEI has low mechanical modulus and poor thermal stability, and it is difficult to withstand the repeated volume changes (up to 300% or more) of silicon particles during the lithium insertion / extraction process, which leads to repeated SEI breakage and regeneration, continuously consuming electrolyte and active lithium, manifested as low initial coulombic efficiency (usually <80%), insufficient cycle stability and corrosion of silicon particles by electrolyte decomposition products (such as HF). (2) Limited ion transport kinetics and poor temperature adaptability: The organically enriched SEI formed on the electrolyte side has a large resistance to lithium ion transport, which leads to deterioration of rate performance and narrow temperature adaptability window, which seriously restricts the practical application of the deposited silicon-carbon anode. (3) Difficulty in controlling volume expansion and electrode expansion rate: Although the deposited silicon-carbon material reduces particle-level volume expansion to a certain extent through nano-silicon embedding + porous carbon skeleton buffer, repeated expansion at the electrode level still exists (usually >40%), which restricts the battery life and safety.

[0034] To address the above issues, the existing technologies have the following shortcomings: ① Although electrolyte additives (such as FEC and VC) can partially improve SEI, the effect weakens after the additives are consumed; ② Electrode material surface modification methods are cumbersome and costly; ③ Commercially available engineering solutions combining deposited silicon-carbon with artificial SEI are not yet systematic.

[0035] Based on this, the present invention solves the core problems of poor interface stability, limited ion transport, and insufficient wide temperature adaptability of silicon-based anodes by depositing a solid electrolyte layer on the surface of silicon-carbon composite material to physically isolate the silicon-carbon composite material from the electrolyte. Furthermore, the anode sheet structure design is optimized to achieve a comprehensive performance improvement in high first-cycle efficiency, high cycle stability, low expansion rate, and wide temperature adaptability.

[0036] Specifically, the present invention adopts the following technical solution: According to one aspect of the present invention, a negative electrode sheet is provided, comprising a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector, wherein the negative electrode active material layer comprises a negative electrode active material, and the negative electrode active material comprises a silicon-carbon composite material. At least a portion of the surface of the silicon-carbon composite material is provided with a solid electrolyte layer; The silicon-carbon composite material D 50 The thickness is 5µm to 10µm; The pore size distribution of the negative electrode exhibits a bimodal characteristic, with the peak pore size of the first peak ranging from 0.01µm to 2.5µm and the peak pore size of the second peak ranging from 2.5µm to 4.0µm.

[0037] In this application, "silicon-carbon composite material" refers to any substance that can mitigate silicon volume expansion by combining silicon and carbon materials at the microscale and can be used as an active material for the negative electrode of lithium-ion batteries.

[0038] In this application, "porous carbon framework" refers to a carbon matrix material with abundant nanoscale to microscale pore structures, which serves to provide confined deposition space for nano-silicon particles and buffer their volume expansion.

[0039] In this application, "D" 50 "The particle size refers to the particle size at which the cumulative particle size distribution percentage of a powder sample reaches 50%, and is used to characterize the statistical average size of a particle group."

[0040] In a specific embodiment of the present invention, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes a silicon-carbon composite material. The silicon-carbon composite material has a D... 50The particle size is 5µm to 10µm, specifically 5µm, 6µm, 7µm, 8µm, 9µm, 10µm, and any value between these two ranges. The particle size range selected in this invention represents a balance between chemically active surface area and particle structural stability: the particle size is not set too small to avoid exacerbating interfacial side reactions due to excessive surface area; nor is the particle size set too large to reduce the tendency for particle cracking caused by internal concentration gradient stress during lithium insertion / extraction.

[0041] In a specific embodiment of the present invention, at least a portion of the surface of the silicon-carbon composite material is provided with a solid electrolyte layer, which can form a physical isolation between the electrode material and the electrolyte, so that the interface film changes from being dominated by organic components to being dominated by inorganic components, thereby suppressing the interface side reactions caused by direct contact and the process of repeated rupture and reconstruction of the interface film from the source, thus protecting the active lithium and helping to maintain a low interface resistance.

[0042] In a specific embodiment of the present invention, the silicon-carbon composite material comprises a porous carbon framework, nano-silicon particles dispersed within the porous carbon framework, a carbon layer disposed on the outer surface of the porous carbon framework, and a solid electrolyte layer disposed on the outer surface of the carbon layer. The inner porous carbon framework absorbs the volumetric strain of the nano-silicon particles through pore confinement, the middle carbon layer stabilizes the overall particle structure and provides a continuous electron transport path, and the outermost solid electrolyte layer isolates the electrolyte. This multilayer structure buffers and constrains the volume changes of silicon during charging and discharging, preventing the pulverization of electrode particles and the destruction of the conductive network, while improving electron and ion transport efficiency, achieving high capacity, long cycling, and low expansion.

[0043] In a specific embodiment of the present invention, the nano-silicon particles dispersed within the porous carbon framework have a grain size of 1µm to 6µm, specifically 1µm, 2µm, 3µm, 4µm, 5µm, 6µm, or any value between these two. The present invention selects the aforementioned nano-silicon particle size so that the nano-silicon particles can be effectively confined within the nanopores of the porous carbon framework. Utilizing the steric hindrance effect of the pore walls, the volume expansion of silicon during charging and discharging is absorbed within the space reserved in the pores, avoiding damage to the entire particle or even the electrode structure.

[0044] In a specific embodiment of the present invention, the solid electrolyte layer includes LiAlO2 and Li x SiO y At least one of Li3PO4 and LiF, wherein, in Li x SiO yIn the formula, 0 < x ≤ 4 and 0 < y ≤ 4. The present invention selects the above-mentioned solid electrolyte layer, which can provide transmission channels for lithium ions while isolating electrons, reduce interface impedance, and form mechanical constraints on the volume change of nano-silicon particles, preventing the carbon layer and the solid electrolyte layer from cracking during cycling, thereby improving both rate performance and cycling stability.

[0045] In a specific embodiment of the present invention, the thickness of the solid electrolyte layer is 5µm to 18µm, specifically 5µm, 7µm, 9µm, 11µm, 13µm, 15µm, 18µm, and any value between any two of the above values. The thickness of the solid electrolyte layer selected in the present invention enables the layer to simultaneously have effective electronic insulation and shielding capability and a low lithium-ion penetration barrier: the thickness is not set too small to ensure mechanical integrity and the blocking effect on electron tunneling; the thickness is not set too large to avoid the increase of interface resistance caused by the lengthening of diffusion path, thereby maintaining a low impedance level and interface structural integrity during long-term cycling.

[0046] In a specific embodiment of the present invention, the negative electrode active material further comprises graphite. The low volume expansion and good electrical conductivity of graphite can dilute and buffer the volume change of the silicon-carbon composite material and participate in constructing a conductive network.

[0047] In a specific embodiment of the present invention, the negative electrode active material layer further comprises a negative electrode conductive agent and a negative electrode binder. The negative electrode conductive agent comprises one or more of single-walled carbon nanotubes (SWCNT), multi-walled carbon nanotubes (MWCNT) and conductive carbon black (Super P); the negative electrode binder comprises one or more of sodium carboxymethyl cellulose (CMC-Na), polyacrylic acid (PAA), polyacrylonitrile (PAN), polystyrene-acrylic acid and styrene butadiene rubber (SBR).

[0048] In a specific embodiment of the present invention, the porosity of the negative electrode sheet is 25% to 40%, specifically 25%, 30%, 35%, 40%, and any value between any two of the above values. The porosity selected in the present invention provides channels for electrolyte penetration and lithium ion migration, and simultaneously reserves space for absorbing the expansion of the silicon-carbon composite material.

[0049] In a specific embodiment of the present invention, as Figure 1As shown, the pore size distribution of the negative electrode exhibits a bimodal characteristic. The peak pore size of the first peak is located in the range of 0.01µm to 2.5µm, and the peak pore size of the second peak is located in the range of 2.5µm to 4.0µm. This bimodal pore size distribution configuration aims to balance the rapid penetration of the electrolyte with the buffering requirements of volume expansion. The peaks with smaller pore sizes provide a strong capillary driving force, promoting the wetting of the active material deep within the negative electrode by the electrolyte, ensuring that lithium ions can quickly reach the reaction interface. Meanwhile, the peaks with larger pore sizes provide the necessary buffer volume for the volume expansion of the silicon-carbon composite material, preventing expansion stress from directly acting on the pore walls, which could lead to pore collapse and permanent damage to the electrode structure. This invention utilizes the aforementioned pore structure in the negative electrode, enabling it to achieve both high rate performance and low cycle expansion rate without sacrificing too much compaction density.

[0050] In a specific embodiment of the present invention, the compaction density of the negative electrode sheet is 1.5 g / cm³. 3 ~1.75g / cm 3 Specifically, it can be 1.5g / cm 3 1.55g / cm 3 1.6g / cm 3 1.65g / cm 3 1.7g / cm 3 1.75g / cm 3 The thickness of the negative electrode sheet is 50µm to 90µm, specifically 50µm, 60µm, 70µm, 80µm, 90µm, or any value between any two of the above. The present invention selects the above-mentioned compaction density and thickness of the negative electrode sheet to maintain sufficient internal porosity to support ion migration and volume buffering while ensuring high volumetric energy density. If the compaction density is too low or the negative electrode sheet is too thick, although it is beneficial for ion transport and expansion buffering, it will reduce the energy density of the battery. Conversely, if the compaction density is too high or the negative electrode sheet is too thin, although more active material can be loaded in a limited space, porosity will be sacrificed, leading to obstructed ion transport and a surge in expansion rate.

[0051] In a specific embodiment of the present invention, the interface resistance of the negative electrode is 2.0 mΩ·cm. 2 ~8.0mΩ·cm 2 Specifically, it can be 2.0 mΩ·cm 2 3.0mΩ·cm 2 4.0 mΩ·cm 2 5.0 mΩ·cm 2 6.0 mΩ·cm 2 7.0 mΩ·cm 2 8.0 mΩ·cm 2The value is , and any value between the two mentioned above. This low interfacial resistance is a comprehensive reflection of the efficient lithium conduction of the solid electrolyte interface layer, the full wetting of the electrolyte, and the integrity of the conductive network, ensuring the battery's dynamic capabilities during rapid charge and discharge.

[0052] In a specific embodiment of the present invention, the peel strength of the negative electrode sheet is 15 N / m to 30 N / m, specifically 15 N / m, 20 N / m, 25 N / m, 30 N / m, or any value between these two. This peel strength reflects the bonding force between the negative electrode active material layer and the negative electrode current collector. If the peel strength is too low, under long-term cyclic volumetric stress, the negative electrode active material layer is prone to cracking, blistering, or even large-scale detachment, leading to battery failure. If the peel strength is too high, additional negative electrode adhesive or complex processing may be required, which may adversely affect energy density or ion transport.

[0053] In a specific embodiment of the present invention, the negative electrode retains a capacity of ≥82.9% after 600 cycles of 1C / 1C charge / discharge.

[0054] In a specific embodiment of the present invention, the electrode expansion rate of the negative electrode after 600 cycles of 1C / 1C charge-discharge is ≤30%.

[0055] According to one aspect of the present invention, a method for preparing a negative electrode sheet is provided, specifically comprising the following steps: S1. Introduce silicon source gas and perform chemical vapor deposition with the porous carbon framework to obtain a silicon-carbon framework. S2. Carbon coating is applied to the silicon-carbon framework to form a carbon layer, thus obtaining a silicon-carbon substrate; S3. Mix silicon-carbon substrate with aluminum salt and lithium salt, and heat-treat to form a solid electrolyte layer to obtain silicon-carbon composite material; S4. A negative electrode slurry containing silicon-carbon composite material is coated on at least one side of the negative electrode current collector, and then dried and rolled to obtain a negative electrode sheet.

[0056] A silicon source gas is introduced and chemically vapor-deposited with a porous carbon framework to obtain a silicon-carbon framework. This process causes the silicon source gas to thermally decompose and deposit into nano-silicon particles within the nanopores of the porous carbon framework, resulting in uniformly dispersed nano-silicon particles within the pores.

[0057] In a specific embodiment of the present invention, the silicon source gas includes silane and nitrogen, and the volume ratio of silane to nitrogen is 1:2 to 8, specifically 1:2, 1:3, 1:4, 1:5, 1:6, and any value between the two mentioned above.

[0058] In a specific embodiment of the present invention, the temperature of the chemical vapor deposition is 470℃~500℃, specifically 470℃, 480℃, 490℃, 500℃, and any value between the two mentioned above; the time of the chemical vapor deposition is 5h~10h, specifically 5h, 6h, 7h, 8h, 9h, 10h, and any value between the two mentioned above.

[0059] After obtaining the silicon-carbon framework, the silicon-carbon framework is coated with carbon to form a carbon layer, thus obtaining a silicon-carbon substrate.

[0060] In a specific embodiment of the present invention, the carbon coating is carried out in an acetylene atmosphere, and the carbon coating temperature is 510℃~560℃, specifically 510℃, 520℃, 530℃, 540℃, 550℃, 560℃, and any value between the two mentioned above; the carbon coating time is 2h~6h, specifically 2h, 3h, 4h, 5h, 6h, and any value between the two mentioned above.

[0061] After obtaining the silicon-carbon substrate, the silicon-carbon substrate is mixed with aluminum salt and lithium salt, and then heat-treated to form a solid electrolyte layer, thus obtaining a silicon-carbon composite material.

[0062] In a specific embodiment of the present invention, the heat treatment sequentially includes water bath heating and calcination. The water bath heating temperature is 70℃~90℃, specifically 70℃, 75℃, 80℃, 85℃, 90℃, or any value between two of the above; the water bath heating time is 30min~60min, specifically 30min, 40min, 50min, 60min, or any value between two of the above. The calcination is carried out in an inert atmosphere, and the calcination temperature is 500℃~700℃, specifically 500℃, 550℃, 600℃, 650℃, 700℃, or any value between two of the above; the calcination time is 3h~6h, specifically 3h, 4h, 5h, 6h, or any value between two of the above.

[0063] After obtaining the silicon-carbon composite material, the negative electrode slurry containing the silicon-carbon composite material is coated on at least one side of the negative electrode current collector, and then dried and rolled to obtain the negative electrode sheet.

[0064] In a specific embodiment of the present invention, the negative electrode slurry further includes graphite, a negative electrode conductive agent, and a negative electrode binder. The negative electrode conductive agent includes one or more of single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), and conductive carbon black (Super P); the negative electrode binder includes one or more of sodium carboxymethyl cellulose (CMC-Na), polyacrylic acid (PAA), polyacrylonitrile (PAN), polystyrene-acrylic acid, and styrene-butadiene rubber (SBR).

[0065] In a specific embodiment of the present invention, the negative electrode current collector is preferably a copper foil, and the thickness of the copper foil is preferably 8µm to 12µm, specifically 8µm, 9µm, 10µm, 11µm, 12µm, and any value between the two mentioned above.

[0066] In a specific embodiment of the present invention, the drying includes vacuum drying, the temperature of which is 60℃~90℃, specifically 60℃, 70℃, 80℃, 90℃, and any value between the two mentioned above; the time of which is 6h~12h, specifically 6h, 7h, 8h, 9h, 10h, 11h, 12h, and any value between the two mentioned above.

[0067] According to one aspect of the present invention, a lithium-ion battery is provided, further comprising a positive electrode, a separator, and a negative electrode; wherein the negative electrode is the negative electrode described in the above technical solution.

[0068] In a specific embodiment of the present invention, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one side surface of the positive current collector. The positive active material layer includes a positive active material, a positive binder, and a positive conductive agent. The positive active material includes, but is not limited to, one or more of lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium cobalt oxide, and lithium manganese oxide; the positive binder includes, but is not limited to, one or more of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS); the positive conductive agent includes, but is not limited to, one or more of conductive carbon, acetylene black, conductive carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0069] In a specific embodiment of the present invention, the positive electrode sheet can be prepared by the following method: mixing positive electrode active material, positive electrode binder and positive electrode conductive agent in a certain proportion, adding them to N-methylpyrrolidone (NMP) organic solvent and stirring to prepare positive electrode slurry, uniformly coating the positive electrode slurry on aluminum foil current collector, and obtaining the positive electrode sheet after drying and rolling.

[0070] In a specific embodiment of the present invention, the separator includes a base membrane and a coating disposed on at least one surface of the base membrane. The base membrane preferably includes a polyolefin microporous separator, specifically a polypropylene (PP) membrane, a polyethylene (PE) membrane, a PP / PE / PP composite membrane, etc.; the coating is preferably a ceramic coating and / or a PVDF coating. The separator selected in this invention provides sufficient mechanical strength to prevent internal short circuits without excessively increasing ion transport resistance, and exhibits good wettability and compatibility with the electrolyte system.

[0071] In a specific embodiment of the present invention, the lithium-ion battery includes a liquid lithium-ion battery, a semi-solid lithium-ion battery, or an all-solid lithium-ion battery.

[0072] The following describes the implementation methods of this application. The implementation methods described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the implementation methods, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents, materials, or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0073] Example 1 (1) Preparation of negative electrode: D 50 A porous carbon framework with a particle size of 7µm was placed in a fluidized bed reactor. A mixture of silane (SiH4) and nitrogen (SiH4 to nitrogen volume ratio of 1:6) was introduced at 480℃ and a flow rate of 20 L / min for chemical vapor deposition (CVD) for 8 h, resulting in the uniform deposition of nano-silicon (particle size of 1~6 nm) within the pores of the porous carbon framework. Subsequently, carbon coating was performed at 530℃ in an acetylene atmosphere for 4 h to obtain a Si-C substrate (D). 50 =7µm).

[0074] Si-C substrate was ultrasonically dispersed in anhydrous ethanol. A 0.20 mol / L Al(NO3)3 solution and a 0.30 mol / L lithium acetate (LiAc) solution were added to achieve a Li:Al molar ratio of 3:2 and a mass ratio of Al(NO3)3 to Si-C substrate of 1:99. After stirring for 45 min, the mixture was transferred to an 80°C water bath for heating. Urea solution was added dropwise, and stirring continued until the liquid was completely evaporated. The evaporated powder was collected and calcined at 600°C for 4 h under an Ar atmosphere at a heating rate of 5°C / min. After calcination, the mixture was naturally cooled to room temperature to obtain Si-C@LiAlO2 powder with a LiAlO2 coating thickness of 12 nm, denoted as Si-C@A,D. 50 =7µm.

[0075] Si-C@A, artificial graphite, conductive carbon black, and sodium carboxymethyl cellulose were added to deionized water at a mass ratio of 15:80:3:2 and thoroughly mixed to prepare a negative electrode slurry with a solid content of 50wt%. The negative electrode slurry was coated on both sides of a 10µm thick copper foil and dried in a vacuum oven at 75℃ for 8 hours. The negative electrode sheet was then obtained by rolling with a double-roll cold press.

[0076] The compaction density of the negative electrode is 1.65 g / cm³. 3 The thickness is 70µm, the porosity is 32%, and the pore size distribution has a bimodal characteristic, with the first peak pore size located between 0.01 and 2.5µm and the second peak pore size located between 2.5 and 4µm.

[0077] (2) Preparation of the positive electrode: NCM811 (D) 50 =10µm, BET=0.35m 2 / g), conductive carbon black (Super P, BET=62m) 2 Multi-walled carbon nanotubes (MWCNTs, diameter 10-20 nm, length 5-7 µm) and polyvinylidene fluoride (PVDF, Mw≈300000) were added to N-methylpyrrolidone (NMP) solvent at a mass ratio of 96:1:1:2. The mixture was stirred in a dual planetary stirrer at 30 rpm revolution and 1800 rpm rotation for 4 hours until homogeneous to prepare the positive electrode slurry. The positive electrode slurry was then double-sided coated onto aluminum foil using a slot coating process, with a target double-sided areal density of 35.0 mg / cm³. 2 After drying in four drying tunnels (100 / 110 / 120 / 130℃, each section for 80 seconds), it is rolled to a compacted density of 3.50 g / cm³. 3 Cut it to the required size to obtain the positive electrode sheet.

[0078] (3) Preparation of electrolyte: An electrolyte was prepared by mixing lithium hexafluorophosphate (LiPF6), ethylene carbonate (EC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), ethylene sulfate (DTD), and vinylene carbonate (VC) in a mass percentage ratio of 11.5:21.6:52.6:2.95:6.88:4.92, with a LiPF6 concentration of 1 mol / L.

[0079] (4) Preparation of the diaphragm: A 9µm thick PE membrane was selected as the base membrane, and a 1.0µm thick ceramic coating was applied to both sides of the base membrane. After drying, a separator was obtained with a porosity of 40.5%.

[0080] (5) Preparation of lithium-ion batteries: After the positive and negative electrode sheets are rolled and slit, they are wound together with the separator according to a set process to form a 21700 cylindrical battery core. Subsequently, the battery core is fixed to pre-made connecting pieces by welding and then installed into a metal battery casing. After completing key processes such as electrolyte injection, sealing, and formation, a lithium-ion battery is obtained. This lithium-ion battery uses a cylindrical casing with external dimensions of 21.0 mm in diameter and 70.0 mm in length, conforming to the 21700 standard specifications.

[0081] Example 2 The difference between Example 2 and Example 1 is that in step (1), the concentration of Al(NO3)3 solution is 0.08 mol / L; the stirring time is 30 min; and it is calcined at 500℃ for 3 h under Ar atmosphere to obtain Si-C@LiAlO2 powder with a LiAlO2 coating thickness of 5 nm.

[0082] Example 3 The difference between Example 3 and Example 1 is that in step (1), the concentration of Al(NO3)3 solution is 0.12 mol / L; the stirring time is 40 min; and it is calcined at 550℃ for 4 h under Ar atmosphere to obtain Si-C@LiAlO2 powder with a LiAlO2 coating thickness of 8 nm.

[0083] The initial coulombic efficiency of the lithium-ion battery is 82.8%.

[0084] Example 4 The difference between Example 4 and Example 1 is that in step (1), the concentration of Al(NO3)3 solution is 0.30 mol / L; the stirring time is 60 min; and it is calcined at 650℃ for 5 h under Ar atmosphere to obtain Si-C@LiAlO2 powder with a LiAlO2 coating thickness of 18 nm.

[0085] Example 5 The difference between Example 5 and Example 1 is that in step (1), the rolling pressure is increased to control the compaction density of the negative electrode sheet to 1.75 g / cm³. 3 It has a thickness of 63µm and a porosity of 25%.

[0086] The initial coulombic efficiency of the lithium-ion battery is 83.8%.

[0087] Example 6 The difference between Example 6 and Example 1 is that in step (1), the rolling pressure is increased to control the compaction density of the negative electrode sheet to 1.70 g / cm³. 3 It has a thickness of 68µm and a porosity of 30%.

[0088] Example 7 The difference between Example 7 and Example 1 is that in step (1), the rolling pressure is reduced to control the compaction density of the negative electrode sheet to 1.60 g / cm³. 3 It has a thickness of 74µm and a porosity of 35%.

[0089] Example 8 The difference between Example 8 and Example 1 is that in step (1), the rolling pressure is reduced to control the compaction density of the negative electrode sheet to 1.50 g / cm³. 3 It has a thickness of 78µm and a porosity of 40%.

[0090] Example 9 The difference between Example 9 and Example 1 is that in step (1), D is selected. 50 A porous carbon framework of 5µm was obtained; D 50 =5µm Si-C@A.

[0091] Example 10 The difference between Example 10 and Example 1 is that in step (1), D is selected. 50 A porous carbon framework with a diameter of 10µm was obtained; D 50 =10µm Si-C@A.

[0092] Example 11 Example 11 differs from Example 1 in that, in step (1), the Si-C substrate was ultrasonically dispersed in anhydrous ethanol, and 0.15 mol / L tetraethyl orthosilicate (TEOS) and 0.20 mol / L lithium acetate (LiAc) were added. After stirring for 45 min, the mixture was transferred to an 80°C water bath for heating, and ammonia was added dropwise to adjust the pH to 8.5. Stirring continued until the liquid was completely evaporated. The evaporated powder was collected and calcined at 600°C for 4 h under an Ar atmosphere at a heating rate of 5°C / min. After calcination, the mixture was naturally cooled to room temperature to obtain Li. 1.3 SiO 2.7 Si-C@Li with a coating thickness of 12nm x SiO y Powder, D 50 =7µm.

[0093] The initial coulombic efficiency of the lithium-ion battery is 82.8%.

[0094] Example 12 Example 12 differs from Example 1 in that, in step (1), the Si-C substrate was ultrasonically dispersed in anhydrous ethanol, and 0.10 mol / L phosphoric acid (H3PO4) and 0.30 mol / L lithium acetate (LiAc) were added. After stirring for 45 min, the mixture was transferred to an 80°C water bath for heating, and stirring was continued until the liquid was completely evaporated. The dried powder was collected and calcined at 550°C for 4 h under an Ar atmosphere at a heating rate of 5°C / min. After calcination, the powder was naturally cooled to room temperature to obtain Si-C@Li3PO4 powder with a Li3PO4 coating thickness of 12 nm. 50 =7µm.

[0095] Example 13 Example 13 differs from Example 1 in that, in step (1), the Si-C substrate was ultrasonically dispersed in anhydrous ethanol, and 0.15 mol / L ammonium hydrogen fluoride (NH4HF2) and 0.15 mol / L lithium acetate (LiAc) were added. After stirring for 45 min, the mixture was transferred to an 80°C water bath for heating, and stirring was continued until the liquid was completely evaporated. The dried powder was collected and calcined at 500°C for 3 h under an Ar atmosphere at a heating rate of 5°C / min. After calcination, the powder was naturally cooled to room temperature to obtain Si-C@LiF powder with a LiF coating thickness of 12 nm. 50 =7µm.

[0096] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that in step (1), the concentration of Al(NO3)3 solution is 0.05 mol / L; the stirring time is 30 min; and it is calcined at 500℃ for 3 h under Ar atmosphere to obtain Si-C@LiAlO2 powder with a LiAlO2 coating thickness of 3 nm.

[0097] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that in step (1), the concentration of Al(NO3)3 solution is 0.45 mol / L; the stirring time is 60 min; and it is calcined at 650 °C for 6 h under Ar atmosphere to obtain Si-C@LiAlO2 powder with a LiAlO2 coating thickness of 25 nm.

[0098] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that in step (1), the rolling pressure is increased to control the compaction density of the negative electrode sheet to 1.80 g / cm³. 3 It has a thickness of 57µm and a porosity of 20%.

[0099] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that in step (1), the rolling pressure is reduced to control the compaction density of the negative electrode sheet to 1.40 g / cm³. 3 It has a thickness of 86µm and a porosity of 48%.

[0100] Comparative Example 5 The difference between Comparative Example 5 and Example 1 is that in step (1), D is selected. 50 A porous carbon framework with a diameter of 3µm was obtained by chemical vapor deposition for 6 hours; D 50 =3µm Si-C@A.

[0101] Comparative Example 6 The difference between Comparative Example 6 and Example 1 is that in step (1), D is selected. 50 A porous carbon framework with a diameter of 15µm was obtained; D 50 =15µm Si-C@A.

[0102] Comparative Example 7 The difference between Comparative Example 7 and Example 1 is that in step (1), LiAlO2 coating was not performed, and Si-C substrate, artificial graphite, conductive carbon black and sodium carboxymethyl cellulose were added to deionized water to prepare negative electrode slurry.

[0103] Performance testing: The performance of the silicon-carbon composite material, negative electrode, and lithium-ion battery prepared by the above embodiments and comparative examples was tested, as follows: (1) Method for determining the size of silicon nanoparticles in silicon-carbon composite materials: Silicon-carbon composite material samples were cut by focused ion beam (FIB) to preserve the porous structure of the carbon matrix (thickness ≤100nm). The grain size of silicon was directly determined by high-resolution transmission electron microscopy (HRTEM) with the help of high resolution imaging and EDS mapping.

[0104] (2) Method for determining the size of silicon-carbon composite material: Take a small amount of silicon-carbon composite material powder and spread it evenly on conductive tape. Then, take clear particle images of at least 5 different regions under a scanning electron microscope (SEM). Import the images using ImageJ software, calibrate the scale, and manually or automatically measure the projected diameter of more than 200 particles. Arrange the data in ascending order and plot the cumulative distribution curve. Take the particle size value corresponding to 50% of the cumulative percentage as D. 50 At the same time, it is necessary to exclude data containing obvious aggregates to ensure accuracy.

[0105] (3) Method for determining the porosity of the negative electrode: Cut the negative electrode sample into pieces of approximately 2cm. 2 A small piece of mercury was weighed, its mass and geometric volume were measured, and then placed into the sample chamber of a high-precision mercury porosimeter. Pressure was gradually applied to allow mercury to penetrate the pores of the electrode, from low pressure to high pressure (0.1 MPa to 60 MPa), and the mercury penetration volume at each pressure was recorded. Based on the ratio of mercury volume to the total geometric volume of the sample, the porosity ε was calculated, and pore size distribution information was also obtained (see [link to sample chamber]). Figure 1 Calculate porosity using the following formula: ; in, This represents the volume of mercury that seeps in under pressure. This represents the total geometric volume of the electrode.

[0106] (4) Negative electrode interface resistance test method: The film resistance of the negative electrode was determined using the 46-probe method (45 probes arranged in a square matrix, with one probe serving as a ground probe) of the RM2610 resistance testing system. The sample was placed on the testing device, and the pressure applied by the probes was adjusted using a pressure gauge to ensure good contact between the probes and the sample, with a contact area of ​​0.01 cm². 2 During the test, a constant current was applied to the 20 peripheral probes, allowing the current to flow through the surface, interface, and copper foil of the negative electrode, while the 25 central probes measured the voltage change in real time. Finally, the membrane resistance was calculated using Ohm's law and fitting analysis. Nine square grids were randomly selected from the front, middle, and rear sections of the electrode for membrane resistance measurement, and the obtained values ​​were recorded as R1, R2, R3, R4, R5, R6, R7, R8, and R9, respectively. Finally, the arithmetic mean of these values ​​was calculated to obtain the average membrane resistance of the actual tested negative electrode: R = (R1 + R2 + R3 + R4 + R5 + R6 + R7 + R8 + R9) / 9.

[0107] (5) Peel strength test method for negative electrode sheet: First, use double-sided tape to fix the negative electrode sheet sample on a flat thin steel plate, ensuring that the tape is pasted in the center of the steel plate. Then, peel off the protective layer of the double-sided tape, paste the strip sample of the electrode sheet to be tested onto the double-sided tape, and use a pressure roller to evenly press the strip sample to ensure good adhesion. Subsequently, tear off the unpainted end, bend the natural end of the torn electrode sheet upward, and clamp it in the upper fixture of the tensile testing machine for a 180° peel test. Record the tensile force curve. The stage where the tensile force changes by no more than 10% is selected as the stable peel segment. Finally, divide the average tensile force of this segment by the width of the strip sample electrode sheet to calculate the peel strength of the negative electrode sheet. Peel force test experiments are conducted on the front, middle, and back segments of the electrode sheet, and the obtained values ​​are recorded as N1, N2, and N3, respectively. Finally, by calculating the arithmetic mean of these values, the average peel force of the actual tested negative electrode sheet is obtained as N = (N1 + N2 + N3) / 3.

[0108] (6) 6C charging capacity retention rate test method: Discharge the lithium battery to 2.5V and place it in a 25℃ constant temperature chamber for 6 hours. Perform the test according to the following steps: ① Charge the battery at 1C with constant current and constant voltage to 4.2V, with a cutoff current of 0.1C, and let it stand for 30 minutes. The capacity at 4.2V is recorded as Q1 (constant current capacity); ② Discharge the battery at 1C with constant current to 2.5V, with a cutoff current of 0.1C, and let it stand for 30 minutes; ③ Charge the battery at 6C with constant current and constant voltage to 4.2V, with a cutoff current of 0.1C, and let it stand for 30 minutes. The capacity at 4.2V is recorded as Q6; ④ Discharge the battery at 1C with constant current to 2.5V, with a cutoff current of 0.1C, and let it stand for 30 minutes. Then, the 6C charging capacity retention rate (%) of the lithium battery at 25℃ = Q1 / Q6 × 100%.

[0109] (7) 1C Cycle Performance Test Method: Place the battery in a 25℃ constant temperature chamber for 6 hours and test according to the following steps: ① First cycle of constant current and constant voltage charging: Charge at a constant current of 1C to 4.2V, then switch to constant voltage charging until the current drops to 0.1C. After charging is completed, let it stand for 30 minutes. ② Perform constant current discharge, discharging at a rate of 1C to 2.5V. ③ Repeat the above charge and discharge process for a total of 600 cycles. Calculate the discharge capacity Q1 and Q after 1 cycle and 600 cycles. 600 Then the battery capacity decay rate (%) = (Q1 - Q 600 ) / Q1×100%.

[0110] (8) Method for determining the electrode expansion rate after 600 cycles: Take the lithium battery after 600 cycles, rinse it with dimethyl carbonate and vacuum dry it to obtain a dry and clean negative electrode. Use a micrometer to measure the thickness at 9 points on the electrode and take the average value, i.e., T. 600 Calculate the electrode expansion rate E using the following formula: E= ×100%; Where T0 is the initial thickness of the dried electrode before cycling, T 600 The thickness of the electrode after 600 cycles of washing and drying with dimethyl carbonate.

[0111] (9) Initial Coulombic Efficiency Test Method: CR2032 coin cell half-cells were used for testing. Under constant temperature and humidity conditions of 25℃±1℃, a coin cell was assembled with lithium metal sheet as counter electrode and reference electrode, Celgard2400 polypropylene membrane as separator, the above negative electrode sheet and electrolyte. After standing for 12 hours to allow the electrolyte to fully wet, the cell was first charged at 0.1C current to 0.01V at 25℃, and then charged at constant voltage until the current dropped to 0.05C to ensure complete lithium intercalation. The initial charge (lithium intercalation) capacity was recorded. Then, the cell was discharged at 0.1C current to 1.5V, and the initial discharge (lithium deintercalation) capacity was recorded. The initial coulombic efficiency was calculated as follows: Initial coulombic efficiency (%) = (initial discharge capacity / initial charge capacity) × 100%. At least 3 parallel cells were tested for each sample. After removing outliers, the average value was taken as the final test result.

[0112] The test results are shown in Table 1 below.

[0113] Table 1 Performance test data for the examples and comparative examples Referring to Table 1, Examples 1-4 and Comparative Examples 1-2 investigated the effect of changing only the LiAlO2 deposition thickness on electrochemical performance. The selected thickness of 12 nm in Example 1 represents a golden balance between "interface shielding" and "ion penetration": when the thickness is only 3 nm, the coating layer, due to insufficient mechanical strength and quantum tunneling effect, cannot completely block the reduction reaction between electrons and the electrolyte on the surface, leading to continuous rupture and regeneration of the SEI film during cycling, resulting in low capacity retention; while when the thickness is increased to 25 nm, although the protective effect is improved, the significantly extended inorganic layer path increases the diffusion resistance of lithium ions (Li... + The penetration barrier causes a surge in interface resistance, limiting the kinetic performance at high rates such as 6C. The 12nm LiAlO2 layer provides sufficient Young's modulus to constrain the primary expansion of silicon while maintaining efficient ionic conductivity, thus achieving the lowest impedance and optimal cycling stability.

[0114] The control of electrode porosity is essentially a dynamic balance between the "expansion buffer space" and the "ion / electron transport pathway" inside the electrode. As shown in Table 1, as the porosity increased from 20% (Comparative Example 3) to 32% (Example 1), the electrode expansion rate decreased from 42.6% to 16.9%, and the interfacial resistance decreased from 11.2 mΩ·cm. 2 Optimized to 3.8 mΩ·cm 2This indicates that a porosity of 32% can effectively absorb the large volumetric strain during lithium intercalation of silicon-carbon particles and ensure sufficient electrolyte wetting to maintain rapid ion transport. However, when the porosity increases excessively to 48% (Comparative Example 4), the effective contact between the negative electrode active materials decreases, leading to a sharp drop in peel strength to 8.6 N / m. The electrode is prone to particle pulverization and shedding during cycling, resulting in a significant deterioration in capacity retention. Therefore, a porosity of 32% is the optimal process window for achieving a synergistic optimization of high kinetic performance, long cycle life, and extremely low expansion rate.

[0115] Particle size D of composite silicon-carbon materials 50 This directly addresses the key trade-off between "chemically active specific surface area" and "physical structural stability." As shown in Table 1, the 7µm particles selected in Example 1 achieve the optimal electrochemical performance. This is because: when the particle size is too small (e.g., 3µm), the significantly increased specific surface area leads to more side reaction sites at the electrolyte interface and loss of active lithium, resulting in increased interfacial resistance and decreased cycle stability. Conversely, when the particle size is too large (e.g., 15µm), the long-distance diffusion of lithium ions within the particles causes a huge concentration gradient stress, which easily triggers mechanical cracking or even pulverization of the particles during charge and discharge. This not only damages the conductive network but also continuously exposes the fresh silicon surface, generating new side reactions. Consequently, the electrode expansion rate rises to 28.8% after 600 cycles, and the capacity retention rate deteriorates significantly.

[0116] The choice of solid electrolyte layer material determines the upper limit of the physical strength and ion transport efficiency of the negative electrode interface during cycling. As shown in Table 1, due to the continuous decomposition of the electrolyte to form an unstable organic SEI, the interfacial resistance of the uncoated comparative example 7 reaches as high as 15.8 mΩ·cm. 2 Furthermore, the expansion rate ran out of control to 45.2%, while the LiAlO2 used in Example 1 exhibited comprehensive performance advantages, with a capacity retention of 85.8% after 600 cycles and electrode expansion controlled to a minimum level of 16.9%. This is mainly attributed to the fact that LiAlO2 not only has extremely high lithium-ion mobility, ensuring excellent fast-charging kinetics (6C retention of 83.5%), but also possesses excellent chemical stability and high Young's modulus, strongly confining the volume expansion of silicon particles and shielding against corrosive substances such as HF; in contrast, Li x SiO y The mechanical confinement of Li3PO4 is slightly weaker, while LiF, although highly stable, suffers from a lower interfacial resistance (8.2 mΩ·cm) due to its lower ionic conductivity. 2 The values ​​of ) are too large, and none of them can achieve a perfect synergy between structural stability and charge transfer like LiAlO2.

[0117] The parts of this invention not described in detail are techniques known to those skilled in the art.

[0118] The basic principles of the present invention have been described above with reference to specific embodiments. However, it should be noted that the advantages, benefits, and effects mentioned in the present invention are merely examples and not limitations, and should not be considered as essential features of each embodiment of the present invention. Furthermore, the specific details disclosed above are for illustrative and facilitative purposes only, and are not limitations. These details do not limit the present invention to the necessity of employing the aforementioned specific details.

[0119] In the foregoing description of this specification, references to terms such as "one embodiment," "another embodiment," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment is included in at least one embodiment of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples. Additionally, it should be noted that in this specification, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features.

[0120] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A negative electrode sheet, characterized in that, It includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes a silicon-carbon composite material; At least a portion of the surface of the silicon-carbon composite material is provided with a solid electrolyte layer; The silicon-carbon composite material D 50 The thickness is 5µm to 10µm; The pore size distribution of the negative electrode exhibits a bimodal characteristic, with the peak pore size of the first peak ranging from 0.01µm to 2.5µm and the peak pore size of the second peak ranging from 2.5µm to 4.0µm.

2. The negative electrode sheet according to claim 1, characterized in that, The solid electrolyte layer includes LiAlO2 and Li x SiO y At least one of Li3PO4 and LiF, wherein, in Li x SiO y In the middle, 0 <x≤4,0<y≤4。 3. The negative electrode sheet according to claim 1, characterized in that, The thickness of the solid electrolyte layer is 5µm to 18µm.

4. The negative electrode sheet according to claim 1, characterized in that, The silicon-carbon composite material includes a porous carbon skeleton, nano-silicon particles dispersed inside the porous carbon skeleton, a carbon layer disposed on the outer surface of the porous carbon skeleton, and a solid electrolyte layer disposed on the outer surface of the carbon layer.

5. The negative electrode sheet according to claim 1, characterized in that, The negative electrode active material also includes graphite; And / or, the negative electrode active material layer further includes a negative electrode conductive agent and a negative electrode binder.

6. The negative electrode sheet according to claim 1, characterized in that, The porosity of the negative electrode sheet is 25%~40%; And / or, the compaction density of the negative electrode sheet is 1.5 g / cm³. 3 ~1.75g / cm 3 ; And / or, the thickness of the negative electrode sheet is 50µm~90µm; And / or, the interface resistance of the negative electrode is 2.0 mΩ·cm. 2 ~8.0mΩ·cm 2 ; And / or, the electrode peel strength of the negative electrode is 15N / m to 30N / m.

7. The negative electrode sheet according to claim 1, characterized in that, The negative electrode retains ≥82.9% of its capacity after 600 cycles of 1C / 1C charge / discharge.

8. The negative electrode sheet according to claim 1, characterized in that, The negative electrode has an expansion rate of ≤30% after 600 cycles of 1C / 1C charge / discharge.

9. A lithium-ion battery, characterized in that, It also includes a positive electrode, a separator, and a negative electrode; the negative electrode is the negative electrode as described in any one of claims 1 to 8.

10. The lithium-ion battery according to claim 9, characterized in that, The lithium-ion battery includes liquid lithium-ion battery, semi-solid lithium-ion battery or all-solid lithium-ion battery.

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