Negative electrode sheet and its manufacturing method, battery

Abstract

This invention relates to the field of battery technology, specifically to a negative electrode sheet, its manufacturing method, and a 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 active material layer comprises an active material, which includes particulate matter and lamellar matter. The ratio of the long axis to the short axis of the particulate matter ranges from 1.0 to 1.3. The particulate matter includes a core and a coating layer disposed on at least a portion of the surface of the core. The core includes a porous carbon framework and nano-silicon embedded within the porous carbon framework, and the coating layer is a carbon coating layer. Compared with existing technologies, this invention achieves better overall interaction through a multi-scale stress-controlled structure of porous carbon framework / embedded nano-silicon / outer carbon coating, resulting in a negative electrode sheet with higher cycle performance and lower expansion performance, thereby improving battery capacity utilization, cycle stability, and safety performance.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to a negative electrode sheet, a method for manufacturing the same, and a battery. Background Technology

[0002] In the development of high-energy-density lithium-ion batteries, silicon-based anodes are considered a core approach to improving overall battery energy density due to their high specific capacity. However, the volume expansion of silicon during lithium intercalation can reach 250%–300%, leading to structural disasters such as particle pulverization, electrode cracking, interface instability, and irreversible lithium consumption. This is especially true in batteries with high compaction densities (1.5–1.8 g / cm³). 3 In dynamic anode designs with low porosity (20–40%), silicon expansion is limited by the compaction frame, which exacerbates stress accumulation and results in a cycle expansion rate that is typically as high as 30–60%, making it difficult to meet the requirements of electric vehicles for long life and low expansion. Summary of the Invention

[0003] In view of this, the present invention aims to at least partially solve the technical problems in the related art. To this end, the present invention provides a negative electrode sheet and its manufacturing method, as well as a battery, by constructing a multi-scale stress-regulating structure based on a spherical (or near-spherical) porous carbon framework / embedded nano-silicon / outer carbon coating (i.e., particulate matter). The spherical (or near-spherical) particles have a geometric morphology that closely approximates a sphere with a major-to-minor axis ratio of 1.0 to 1.3, giving them a stronger isotropic pressure-resistant structure during compression molding, and a more compact and uniform arrangement between particles, significantly reducing local stress concentration during compression molding. Simultaneously, the porous carbon framework and the outer carbon coating provide an internal cavity that can buffer volume changes. Through the above design, the energy density, cycle life, and low expansion effect of the negative electrode sheet can be improved, thereby effectively improving battery performance.

[0004] To solve the above-mentioned technical problems, the present invention is implemented as follows:

[0005] According to one aspect of the present invention, a negative electrode sheet is provided, comprising:

[0006] Negative electrode current collector;

[0007] A negative electrode active material layer is disposed on at least one side surface of the negative electrode current collector, the negative electrode active material layer includes active materials, the active materials include particulate matter and sheet-like matter;

[0008] The ratio of the major axis to the minor axis of the particulate matter ranges from 1.0 to 1.3;

[0009] The particulate matter includes a core and a coating layer disposed on at least a portion of the surface of the core. The core includes a porous carbon skeleton and nano-silicon embedded within the porous carbon skeleton, and the coating layer is a carbon coating layer.

[0010] In some of these embodiments, the size of the nano-silicon is 1 nm to 6 nm.

[0011] In some embodiments, the porous carbon framework has a particle size distribution of 1.5 μm to 10 μm.

[0012] In some of these embodiments, the porosity of the negative electrode is 20% to 40%.

[0013] In some of these embodiments, the interface resistance of the negative electrode is 2.0 mΩ·cm. 2 ~8mΩ·cm 2 .

[0014] In some embodiments, the peel strength of the negative electrode is 10.0 N / m to 22.0 N / m.

[0015] In some embodiments, the thickness of the negative electrode is 50 μm to 120 μm.

[0016] In some embodiments, the active material layer of the negative electrode is 40-90 μm thick.

[0017] In some embodiments, the compaction density of the negative electrode is 1.5 g / cm³. 3 ~1.8g / cm 3 .

[0018] In some of these embodiments, the expansion rate of the negative electrode sheet satisfies The The mass fraction of silicon in the active material particles, the The porosity of the negative electrode sheet, the The ratio of the long axis to the short axis of the active material particles is denoted by PD, which is the compaction density of the negative electrode sheet.

[0019] In some embodiments, the layered material in the negative electrode active material includes natural graphite and / or artificial graphite.

[0020] In some embodiments, the negative electrode further includes a conductive agent, which includes at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, and conductive carbon black.

[0021] In some embodiments, the negative electrode further includes a binder, the binder comprising at least one of sodium carboxymethyl cellulose, polyacrylic acid, polyacrylonitrile, styrene-butadiene rubber, and polystyrene-acrylic acid.

[0022] According to another aspect of the present invention, the present invention provides a method for manufacturing the negative electrode sheet described above, comprising the following steps:

[0023] a) The carbon source solution is pretreated to obtain precursor particles, the precursor particles are subjected to first carbonization, and a porous carbon framework is etched.

[0024] b) Silane deposition is performed on a porous carbon framework to obtain a porous carbon material with embedded silicon, and a second carbon source is introduced to perform a second carbonization to obtain particulate matter.

[0025] c) A negative electrode active material slurry is prepared by combining particulate matter, sheet-like matter, conductive agent, and binder. This slurry is coated on at least one side of the negative electrode current collector, cured, and then cold-pressed a second time to obtain a negative electrode sheet.

[0026] In some of these embodiments, in step a), the carbon source solution includes a first carbon source, which includes at least one of phenolic resin, coconut shell, starch, and cellulose.

[0027] In some embodiments, in step a), the preparation of the carbon source solution includes dissolving a first carbon source in an alcohol solvent, said alcohol solvent including at least one selected from methanol, ethanol, propanol, isopropanol, butanol, ethylene glycol, propylene glycol, and glycerol.

[0028] In some of these embodiments, the pretreatment in step a) includes spray drying.

[0029] In some of these embodiments, in step a), the carbonization temperature of the first carbonization is 600°C to 1000°C, the carbonization time is 2h to 5h, and the heating rate of the first carbonization is 3°C / min to 8°C / min.

[0030] In some embodiments, in step a), the first carbonization process further includes the introduction of an inert gas for protection.

[0031] In some of these embodiments, in step a), the etching process includes etching with an etching gas and an auxiliary gas.

[0032] In some of these embodiments, in step a), the first carbon source accounts for 25 wt% to 45 wt% of the mass of the carbon source solution.

[0033] In some of these embodiments, in step a), the inlet temperature of the spray dryer is 160°C to 210°C, the outlet temperature is 100°C to 130°C, the spray flow rate is 3 ml / min to 7 ml / min, and the droplet diameter is 7 μm to 10 μm.

[0034] In some of these embodiments, in step a), the inert gas includes at least one of helium, neon, nitrogen, and argon.

[0035] In some of these embodiments, in step a), the etching gas includes at least one of CO2 and CO.

[0036] In some of these embodiments, in step a), the auxiliary gas includes at least one of water vapor and hydrogen.

[0037] In some of these embodiments, in step a), the auxiliary gas accounts for 15% to 30% of the total gas.

[0038] In some of these embodiments, in step a), the etching flow rate is 100 ml / min to 300 ml / min, and the etching time is 1 h to 4 h.

[0039] In some embodiments, in step a), the etching process further includes cooling with an inert gas, the inert gas including at least one of helium, neon, nitrogen, and argon.

[0040] In some embodiments, in step b), the silane deposition process includes introducing a carrier gas and a silicon source gas into a porous carbon framework, the reaction temperature of the silane deposition is 400°C to 500°C; the carrier gas includes at least one of helium, neon, and nitrogen, and the silicon source gas includes at least one of silane, disilane, propane, and methylsilane; the volume ratio of the carrier gas to the silicon source gas is 1:(5 to 8), the gas flow rate of the silane deposition process is 10 L / min to 30 L / min, and the deposition time is 8 h to 12 h.

[0041] In some of these embodiments, in step b), the second carbon source includes at least one of acetylene, ethylene, propylene, methane, and ethane.

[0042] In some of these embodiments, in step b), the second carbonization temperature is 550°C to 700°C, the carbonization time is 3h to 6h, and the gas flow rate is 3L / min to 8L / min.

[0043] In some of these embodiments, in step c), the mass ratio of the particulate matter, the sheet-like matter, the conductive agent, and the binder is 5~32:70~90:0.5~2:0.5~2.5.

[0044] In some of these embodiments, in step c), the pressure of the first cold pressing is 10 MPa to 15 MPa, and the pressure of the second cold pressing is 6 MPa to 10 MPa.

[0045] According to another aspect of the present invention, the present invention provides a battery comprising the negative electrode sheet described in the above technical solution or the negative electrode sheet obtained by the manufacturing method described in the above technical solution.

[0046] Implementing the technical solution of the present invention has at least the following beneficial effects:

[0047] In this embodiment of the invention, the provided negative electrode sheet, through the design of a multi-scale stress-controlled structure of negative electrode active material particles with a porous carbon skeleton / embedded nano-silicon / outer carbon coating, solves to some extent the volume expansion problem during the cycling process of deposited silicon-carbon materials. Therefore, the negative electrode sheet can improve the energy density, cycle life and low expansion effect of the negative electrode sheet, thereby effectively improving battery performance.

[0048] 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

[0049] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0050] Figure 1 This is a SEM image of the negative electrode material particles provided in Embodiment 1 of the present invention.

[0051] Explanation of reference numerals in the attached figures:

[0052] 1—Particulate matter; 2—Negative electrode active material layer.

[0053] The accompanying drawings have illustrated specific embodiments of the invention, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the invention in any way, but rather to illustrate the concept of the invention to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0054] The present application will be further described below with reference to 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.

[0055] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0060] Unless otherwise specified, all technical features and optional technical features of this invention can be combined to form new technical solutions.

[0061] 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.

[0062] As the demand for specific capacity in lithium-ion batteries increases, silicon-based anodes are considered a core approach to improving overall battery energy density due to their high specific capacity. However, the volume expansion of silicon during lithium intercalation can reach 250%–300%, easily leading to adverse consequences such as pulverization of active particles, cracking of the anode sheet, interface instability, and irreversible lithium consumption. Especially in power-type anode designs with high compaction density and low porosity, the expansion of silicon is limited by the compaction framework, further exacerbating stress accumulation and resulting in a cycle expansion rate as high as 30–60%, which is difficult to meet the requirements of electric vehicles for long life and low expansion. At the same time, traditional silicon-carbon materials are mostly deposited in bulk, with irregular particle morphology and large differences in long and short axes, resulting in uneven contact between particles during compaction, local stress concentration, and high compaction difficulty. In addition, the expansion direction of silicon-carbon particles after lithium intercalation is uncontrollable, which can easily lead to large variations in the thickness of the electrode area. Furthermore, traditional active particles are prone to forming "sharp stress zones" after electrode pressing, causing repeated rupture of the SEI film, which in turn affects the rate performance and cycle stability of the battery.

[0063] Based on this, the present invention constructs a multi-scale stress-regulating structure based on a spherical (or near-spherical) porous carbon framework / embedded nano-silicon / outer carbon coating. The particles have a near-spherical geometry with a major-to-minor axis ratio of 1.0~1.3, giving them a stronger isotropic pressure-resistant structure during compression molding. The particles are arranged more tightly and uniformly, significantly reducing local stress concentration during compression. Simultaneously, the porous carbon framework and outer carbon coating provide an internal cavity to buffer volume changes. Secondary cold pressing further homogenizes the pore structure in the negative electrode sheet and can further disperse the expansion stress of deposited silicon and carbon, achieving a low expansion effect of "spherical particles + buffer structure = 1+1>2," thereby solving the technical problems existing in the prior art.

[0064] Specifically, the present invention adopts the following technical solution:

[0065] According to one aspect of the present invention, a negative electrode sheet is provided, comprising:

[0066] Negative electrode current collector;

[0067] A negative electrode active material layer is disposed on at least one side surface of the negative electrode current collector, the negative electrode active material layer includes active materials, the active materials include particulate matter and sheet-like matter;

[0068] The ratio of the major axis to the minor axis of the particulate matter ranges from 1.0 to 1.3;

[0069] The particulate matter includes a core and a coating layer disposed on at least a portion of the surface of the core. The core includes a porous carbon skeleton and nano-silicon embedded within the porous carbon skeleton, and the coating layer is a carbon coating layer.

[0070] In some embodiments of the present invention, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on one or both of the two opposite surfaces of the positive electrode current collector. The negative electrode current collector may be a copper foil or a composite current collector. For example, the composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be formed by forming (copper, copper alloy) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.). The ratio of the long axis to the short axis of the active material particles ranges from 1.0 to 1.3, which is to enable the active material particles to have a stronger isotropic pressure-resistant structure during the compression molding process, and the particles are arranged more closely and uniformly, significantly reducing local stress concentration during tableting.

[0071] In some embodiments of the present invention, the size of the nano-silicon is 1nm to 6nm, for example, 1nm, 3nm, 5nm, 6nm or any ratio between two of them. By controlling the size of the nano-silicon within the above range, volume expansion can be significantly alleviated and cycle stability can be improved.

[0072] In some embodiments of the present invention, the mass of the nano-silicon in the active material particles accounts for 2.5wt% to 25wt% of the mass of the active material particles, for example, 2.5wt%, 5wt%, 7.5wt%, 10wt%, 15wt%, 20wt%, 25wt%, or any range between two of these. By controlling the mass fraction of nano-silicon in the active material particles, the energy density and volume expansion risk of the active material particles can be balanced. At the same time, the agglomeration phenomenon caused by excessive silicon content can be avoided, which may destroy the continuity of the conductive network of the carbon skeleton, resulting in obstructed electron conduction and decreased rate performance.

[0073] In some embodiments of the present invention, the particle size distribution of the porous carbon framework is between 1.5 μm and 10 μm, for example, 1.5 μm, 5 μm, 10 μm or any two of them. By controlling the particle size of the porous carbon within the above range, the volume expansion buffering requirements of nano-silicon can be better matched. At the same time, when the particle size is greater than 1.5 μm, electrode pore blockage or mass transfer obstruction caused by excessively fine particles can be avoided. When the particle size is greater than 10 μm, the ion transport path inside the framework becomes longer, which will reduce the rate performance.

[0074] In some embodiments of the present invention, the porosity of the negative electrode is 20% to 40%, for example, 20%, 30%, 40% or any two of these ranges. By controlling the porosity of the negative electrode within the above range, it can be ensured that the electrolyte fully wets the electrode to form a continuous ion transport network, while also promoting the formation of a uniform SEI film and reducing the generation of side reactions.

[0075] In some embodiments of the present invention, the interface resistance of the negative electrode is 2.0 mΩ·cm. 2 ~8mΩ·cm 2 For example, 2.0 mΩ·cm 2 4.0 mΩ·cm 2 8.0 mΩ·cm 2， By controlling the interface resistance of the negative electrode within the range of any two of these parameters, efficient electron and ion transport can be ensured, and a better balance between interface stability and electrochemical efficiency can be achieved.

[0076] In some embodiments of the present invention, the peel strength of the negative electrode sheet is 10 N / m to 22 N / m, for example, 10 N / m, 15 N / m, 20 N / m, 22 N / m or any two of them. By controlling the peel strength of the negative electrode sheet within the above range, it can be ensured that a strong interfacial bond is formed between the negative electrode active material layer and the current collector, while avoiding the problem of stress concentration caused by excessive peel strength.

[0077] In some embodiments of the present invention, the thickness of the negative electrode sheet is 50 μm to 120 μm, for example, 50 μm, 70 μm, 100 μm, 120 μm or any two of them. By controlling the thickness of the negative electrode sheet within the above range, the volumetric energy density of the negative electrode can be better balanced, while also avoiding ion transport obstruction caused by excessive electrode sheet thickness, thereby ensuring the high-rate charge and discharge performance of the battery.

[0078] In some embodiments of the present invention, the compaction density of the negative electrode sheet is 1.5 g / cm³. 3 ~1.8g / cm 3 For example, 1.5g / cm³ 3 1.6g / cm 3 1.8g / cm 3 By controlling the compaction density within the range of either of these ranges, the loading of active material per unit volume can be increased by moderately compressing the electrode, effectively improving the volumetric energy density of the negative electrode. At the same time, it can also avoid the collapse of the porous carbon skeleton channels due to excessive compaction density.

[0079] In some embodiments of the present invention, the inventors have discovered that the expansion rate of the negative electrode sheet satisfies... The The mass fraction of silicon in the active material particles, the The porosity of the negative electrode sheet, the The ratio of the long axis to the short axis of the active material particles is given by , and PD is the compaction density of the negative electrode. This model establishes a direct mapping relationship between microstructural parameters and macroscopic expansion behavior for the first time, providing an engineerable and reversibly controllable structural prediction tool for negative electrode design.

[0080] In some embodiments of the present invention, the layered material in the negative electrode active material includes natural graphite and / or artificial graphite. In some embodiments of the present invention, the negative electrode further includes a conductive agent, which includes at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, and conductive carbon black. In this application, there are no particular limitations on the source and type of the conductive agent, as long as it can achieve the conductive function.

[0081] In some embodiments of the present invention, the negative electrode sheet further includes an adhesive, which includes at least one of sodium carboxymethyl cellulose, polyacrylic acid, polyacrylonitrile, styrene-butadiene rubber, and polystyrene-acrylic acid. In this application, there is no particular limitation on the source and type of adhesive, as long as it can firmly bond the conductive agent and active material particles.

[0082] In some embodiments of the present invention, the active material particles are designed with a multi-scale stress-controlled structure of porous carbon framework / embedded nano-silicon / outer carbon coating, and the ratio of the long axis to the short axis of the active material particles is limited. By limiting the above-mentioned specific structure, the active material particles can form uniform particles during the compression molding process, which significantly reduces the phenomenon of local stress concentration, reduces the interface resistance of the negative electrode, and effectively reduces the electrode expansion rate.

[0083] According to another aspect of the present invention, the present invention provides a method for manufacturing the negative electrode sheet described above, comprising the following steps:

[0084] a) The carbon source solution is pretreated to obtain precursor particles, the precursor particles are subjected to first carbonization, and a porous carbon framework is etched.

[0085] b) Silane deposition is performed on a porous carbon framework to obtain a porous carbon material with embedded silicon, and a second carbon source is introduced to perform a second carbonization to obtain particulate matter.

[0086] c) A negative electrode active material slurry is prepared by combining particulate matter, sheet-like matter, conductive agent, and binder. This slurry is coated on at least one side of the negative electrode current collector, cured, and then cold-pressed a second time to obtain a negative electrode sheet.

[0087] This invention first prepares a porous carbon framework through a first carbonization process, then embeds nano-silicon inside the porous carbon framework through silane deposition, and obtains active material particles by carbon coating through a second carbonization process. Finally, the active material particles, conductive agent, and binder are combined to prepare a negative electrode active material slurry, which is coated on the surface of the negative electrode current collector and then cold-pressed twice to obtain a negative electrode sheet.

[0088] In some embodiments of the present invention, the negative electrode current collector is the same as that described in the above technical solutions, and will not be repeated here. Preferably, the negative electrode active material slurry is coated on one surface of the negative electrode current collector. Specifically, the negative electrode current collector has two surfaces along its thickness direction, and the negative electrode active material slurry can be coated on either one surface; the present invention does not have any particular limitation in this regard.

[0089] In some embodiments of the present invention, the coating method is preferably a transfer coating machine well known to those skilled in the art, which can ensure that the slurry is uniformly coated on the surface of the positive electrode current collector. The present invention does not have any special limitations in this regard.

[0090] In some embodiments of the present invention, in step a), the carbon source solution includes a first carbon source, which includes at least one of phenolic resin, coconut shell, starch, and cellulose. In this application, there are no particular limitations on the type and source of the first carbon source, as long as the compound can form a continuous amorphous carbon network during carbonization and generate gas to form pores during pyrolysis.

[0091] In some embodiments of the present invention, in step a), the preparation of the carbon source solution includes dissolving the first carbon source in an alcohol solvent, wherein the alcohol solvent includes at least one of methanol, ethanol, propanol, isopropanol, butanol, ethylene glycol, propylene glycol, and glycerol. In a preferred embodiment of the present application, methanol is selected as the alcohol solvent. In the present application, there are no particular restrictions on the type and source of the alcohol solvent, as long as it can dissolve the first carbon source.

[0092] In some embodiments of the present invention, the pretreatment includes spray drying. By using spray drying, the morphology of the active material particles can be precisely controlled, ensuring the uniformity of sphericity and structure. The particle size can be adjusted by designing the parameters of spray drying.

[0093] In some embodiments of the present invention, the carbonization temperature of the first carbonization is 600℃~1000℃, the carbonization time is 2h~5h, and the heating rate of the first carbonization is 3℃ / min~8℃ / min. By controlling the carbonization temperature of the first carbonization within the above range, it can be ensured that the first carbon source can be fully pyrolyzed and cross-linked to form a continuous conductive network, while avoiding excessive graphitization and pore structure collapse caused by excessive temperature. Controlling the carbonization time within the above range can ensure that pyrolysis fully reduces the impurity content of the carbon skeleton and improves the mechanical strength and structural stability of the carbon skeleton.

[0094] In some embodiments of the present invention, the first carbonization process further includes the introduction of an inert gas for protection. The inert gas includes at least one of helium, neon, nitrogen, and argon. In a preferred embodiment of this application, nitrogen is selected as the inert gas. In this application, there is no particular limitation on the type and source of the inert gas, as long as it can prevent the carbon source or carbon skeleton from being oxidized and prevent the material from being oxidized by air during the cooling process.

[0095] In some embodiments of the present invention, the etching gas includes at least one of CO2 and CO. In a preferred embodiment of this application, CO2 is selected as the etching gas. It should be further noted that, compared with wet etching, CO2 / CO vapor phase etching does not damage the continuous conductive network of the carbon skeleton, nor does it cause the carbon skeleton to collapse.

[0096] In some embodiments of the present invention, the auxiliary gas includes at least one of water vapor and hydrogen. In a preferred embodiment of this application, water vapor is selected as the auxiliary gas. The auxiliary gas can accelerate the etching speed and improve the etching efficiency, while leaving no impurities and ensuring the purity of the carbon skeleton.

[0097] In some embodiments of the present invention, the auxiliary gas accounts for 15% to 30% of the total gas, for example, 15%, 20%, 25%, 30%, or any range between two of these. By controlling the amount of auxiliary gas added, the etching speed can be accelerated, while avoiding excessive etching of the carbon skeleton due to excessive auxiliary gas.

[0098] In some embodiments of the present invention, the etching flow rate is 100 ml / min to 300 ml / min, and the etching time is 1 h to 4 h. By controlling the etching flow rate within the above range, it can be ensured that the active material particles are fully etched, while avoiding excessively high gas flux that accelerates the etching reaction rate, easily forming excessively large channels or through cracks, thus damaging the mechanical stability of the carbon skeleton and the continuity of the conductive network. By controlling the etching time within the above range, it can be avoided that over-etching leads to a sharp decrease in the mechanical strength of the carbon skeleton.

[0099] In some embodiments of the present invention, the etching process further includes cooling with an inert gas, which includes at least one of helium, neon, nitrogen, and argon. In a preferred embodiment of this application, nitrogen is selected as the inert gas. In this application, there is no particular limitation on the type and source of the inert gas, as long as it can prevent the material from being oxidized by air during the cooling process.

[0100] In some embodiments of the present invention, the silane deposition process includes introducing a carrier gas and a silicon source gas into a porous carbon framework. The reaction temperature for silane deposition is 400°C to 500°C. The carrier gas includes at least one of helium, neon, and nitrogen. The silicon source gas includes at least one of silane, disilane, propane, and methylsilane. The volume ratio of the carrier gas to the silicon source gas is 1:(5-8). The gas flow rate for the silane deposition process is 10 L / min to 30 L / min, and the deposition time is 8 h to 12 h. By controlling the reaction temperature within the above range, the silicon source gas can be fully pyrolyzed, avoiding rapid pyrolysis of the silicon source gas that could lead to agglomeration of nano-silicon or excessively large particle size. By controlling the carrier gas and silicon source gas within the above range, a sufficient supply of silicon source can be ensured, while uniform deposition can be achieved by diluting the carrier gas. By controlling the gas flow rate within the above range, sufficient residence and uniform diffusion of the silicon source gas within the pores can be ensured. By controlling the deposition time within the above range, the mass percentage of nano-silicon can be precisely controlled to be stable at 2.5 wt% to 25 wt%.

[0101] In some embodiments of the present invention, the second carbon source includes at least one of acetylene, ethylene, propylene, methane, and ethane. In a preferred embodiment of the application, the second carbon source is selected as acetylene. In this application, there is no particular limitation on the type and selection of the second carbon source, as long as it can efficiently form a thin and uniform carbon coating layer on the surface and in the pores of the silicon-embedded porous carbon material.

[0102] In some embodiments of the present invention, the temperature of the second carbonization is 550°C to 700°C, the carbonization time is 3h to 6h, and the gas flow rate is 3L / min to 8L / min. By controlling the temperature of the second carbonization within the above range, it can be ensured that the second carbon source is fully decomposed, while avoiding sintering of the carbon skeleton pore walls caused by excessively high temperature. Controlling the second carbonization within the above time range can ensure the integrity of the carbon coating, while also avoiding excessively thick carbon coating layers that block the channels of the porous carbon skeleton, prolong the lithium-ion diffusion path, and reduce the battery rate performance. Controlling the gas flow rate within the above range can ensure that the second carbon source gas is uniformly distributed and efficiently deposited in the reactor, while also avoiding excessively fast flow rates that could impact the active material particles, causing the active material particles to agglomerate and affecting the uniformity of subsequent electrode preparation.

[0103] In some embodiments of the present invention, the mass ratio of the spherical (or near-spherical) particulate matter, the sheet-like conductive agent, and the binder is 5~32:70~90:0.5~2:0.5~2.5.

[0104] In some embodiments of the present invention, in the secondary cold pressing, the pressure of the primary cold pressing is 10 MPa to 15 MPa, and the pressure of the secondary cold pressing is 6 MPa to 10 MPa. The advantage of controlling the negative electrode sheet to perform secondary cold pressing is that it releases the internal stress of the primary cold pressing, avoids the electrode sheet from becoming brittle, and optimizes the microstructure of the electrode sheet, balancing the conductive network and ion transport channels.

[0105] According to another aspect of the present invention, a battery is provided, comprising the negative electrode sheet described in the above-described technical solution or the negative electrode sheet obtained by the manufacturing method described in the above-described technical solution. Thus, the battery possesses all the features and advantages of the negative electrode sheet described in the above-described technical solution, which will not be repeated here.

[0106] Specifically, the battery manufacturing process includes rolling and slitting the positive and negative electrode sheets, then winding them together with the separator according to a set process to form a 21700 cylindrical battery core. Subsequently, the battery core is fixed to a pre-made connecting piece 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. The specific conditions and parameters for each step in the above manufacturing process can be achieved using techniques well-known to those skilled in the art; this invention does not impose any special limitations on these aspects.

[0107] In some embodiments of the present invention, the positive electrode is specifically a positive electrode sheet, including a positive electrode current collector and a positive electrode active material layer disposed on at least one side surface of the positive electrode current collector along the thickness direction; the positive electrode active material layer includes a positive electrode active material. The present invention does not impose any special restrictions on the specific type of the positive electrode active material, and active materials known in the art that can be used for battery positive electrodes can be used. Those skilled in the art can select according to actual needs. Specifically: the positive electrode active material may include, but is not limited to, at least one of lithium transition metal oxides, lithium phosphates with olivine structures, and their respective modified compounds; examples of lithium transition metal oxides may include, but are not limited to, at least one of lithium cobalt oxides, lithium nickel oxides, lithium manganese oxides, lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides, lithium nickel cobalt aluminum oxides, and their modified compounds; examples of lithium phosphates with olivine structures may include, but are not limited to, at least one of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composites, and their modified compounds. These materials are all commercially available.

[0108] In some embodiments of the present invention, the positive electrode active material layer may also include a positive electrode binder, a positive electrode conductive agent, and other optional additives. As examples, the positive electrode binder may include at least one selected from styrene-butadiene rubber (SBR), waterborne acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB); the positive electrode conductive agent may include at least one selected from conductive carbon black, acetylene black, Ketjen black, carbon dots, carbon nanotubes, Super P (SP), graphene, and carbon nanofibers. These materials are all commercially available.

[0109] In some embodiments of the present invention, the preparation method of the positive electrode sheet adopts a method well known to those skilled in the art: first, the raw materials are mixed in a solvent in a certain proportion to form a slurry, and then the positive electrode slurry is coated on the positive electrode current collector. After drying, pressing and other processes, the positive electrode sheet can be obtained.

[0110] In some embodiments of the present invention, the separator can be a commercially available separator known to those skilled in the art for battery manufacturing, including but not limited to at least one of polyethylene (PE) film, polypropylene (PP) film, polyimide (PI) film, and polypropylene-polyethylene composite film. In a preferred embodiment of the present invention, the separator is a PE porous polymer film.

[0111] In this invention, the separator is disposed between the positive and negative electrodes, mainly to prevent short circuits between the positive and negative electrodes, while allowing ions to pass through; the electrolyte plays the role of conducting ions between the positive and negative electrodes.

[0112] In a specific embodiment of the present invention, the electrolyte preferably includes a lithium salt and a solvent; the present invention does not impose any special restrictions on the source of the lithium salt and solvent, and commercially available products well known to those skilled in the art can be used.

[0113] In specific embodiments of the present invention, the lithium salt preferably includes lithium bis(oxalatoborate)borate (LiBOB), lithium difluorooxalatoborate (LiDFOB), and / or lithium hexafluorophosphate (LiPF6), more preferably lithium hexafluorophosphate (LiPF6). The lithium salts selected in this invention possess good ionic conductivity (ensuring Li…). + It can both transmit and form a dense and flexible SEI film; in a preferred embodiment of the present invention, lithium hexafluorophosphate is used as the lithium salt in the electrolyte.

[0114] In a specific embodiment of the present invention, the solvent preferably includes one or more of fluoroethylene carbonate (FEC), ethylene carbonate (EC), ethylene sulfate (DTD), and vinylene carbonate (VC). By adding the above-mentioned solvents, the present invention helps to improve the compactness and resistance to damage of the SEI film, adjust the electrolyte viscosity, and optimize the Li+ transport efficiency.

[0115] In a specific embodiment of the present invention, the electrolyte is 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: 52.1: 2.95: 6.88: 4.92, wherein the concentration of LiPF6 is 1 mol / L.

[0116] This invention does not impose any particular limitation on the preparation method of the electrolyte; conventional methods well-known to those skilled in the art can be used. In a preferred embodiment of this invention, the electrolyte is obtained by uniformly mixing the various components.

[0117] The present invention does not impose any special restrictions on the preparation method of the battery. Any technical means known to those skilled in the art for assembling the above-mentioned positive electrode, negative electrode, separator and electrolyte can be used. In a preferred embodiment of the present invention, the battery is a lithium-ion battery.

[0118] In a specific embodiment of the present invention, the battery preferably further includes an outer packaging. The outer packaging can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc., or it can be a soft pack, such as a pouch-type soft pack. The material of the soft pack can be plastic, and examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0119] The present invention does not impose any particular restrictions on the shape of the battery; it can be cylindrical, square, or any other arbitrary shape, and those skilled in the art can choose according to specific practical needs.

[0120] The present application will be described in detail below with reference to the accompanying drawings and embodiments. However, the implementation and protection of the present invention are not limited thereto. The following embodiments are only some embodiments of the present application and are not intended to limit the present application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0121] Example 1

[0122] A 30% (w / w) phenolic resin solution was dissolved in an alcohol solvent to form a homogeneous carbon source solution. The solution was stirred and ultrasonically dispersed for 30 minutes to ensure uniformity and prevent agglomeration. This solution was then atomized into droplets through a nozzle or rotary spray dryer, and rapidly dehydrated and solidified in an airflow with an inlet temperature of 180 °C and an outlet temperature of 120 °C, forming spherical (or near-spherical) phenolic resin particles. By adjusting the droplet diameter (8.5 μm) and the spray velocity (5 mL / min), precursor particles with a high degree of spherical shape were obtained.

[0123] Spherical precursor particles obtained by spray drying were placed in an inert atmosphere (such as nitrogen) and heated to 800°C for 3 hours. The heating rate was controlled (5°C / min) to obtain carbides. The obtained carbides were loaded into a fluidized bed and placed under a N2 atmosphere, heated to 800°C at a rate of 10°C / min. Then, a CO2 / H2O mixed gas (20% water vapor by volume) was introduced at a flow rate of 200 mL / min for 2 hours of etching. After completion, the steam was cut off, and the bed was purged with N2 gas until cooled to <30°C. The particles were then removed and vacuum / dried to obtain porous carbon.

[0124] (2) Preparation of active material particles:

[0125] The porous carbon was placed in a fluidized bed reactor for silane deposition. Silane was introduced at 490°C using nitrogen as a diluent gas, with a silane to nitrogen volumetric flow rate ratio of 6:1 and a flow rate of 20 L / min. The reaction lasted for 10 h, resulting in uniform deposition of silicon within the material's pores.

[0126] Subsequently, the silicon-supported composite framework was heated to 580 °C in a fluidized bed, switched to an acetylene atmosphere, and maintained at a flow rate of 5 L / min for 4 h to allow the acetylene to decompose on the surface and form a carbon coating layer. The mixture was then purged with inert N2 gas until cooled to <30 °C.

[0127] Finally, the above products are sieved to obtain the final spherical particulate material (deposited silicon carbon), in which =1, deposited silicon-carbon (Si mass percentage = 78.125%).

[0128] (3) Preparation of negative electrode sheet

[0129] The negative electrode sheet comprises a copper foil current collector and a negative electrode coating material coated on both sides of the copper foil. The above-mentioned deposited silicon carbide, artificial graphite, single-walled carbon nanotubes (SWCNTs), conductive carbon black (SuperP), sodium carboxymethyl cellulose (CMC), and polyacrylic acid (PAA) were added to a deionized water medium in a slurry mixer and thoroughly mixed and dispersed, with a solid content of 50%, according to a mass percentage ratio of 16:80:1:1:1:1. The uniform and stable slurry was then uniformly coated onto a 15 μm thick copper foil current collector and dried in a vacuum oven at 70°C for 10 hours to remove residual solvents and moisture, resulting in a structurally stable dried electrode sheet. Finally, the dried electrode sheet underwent a secondary cold pressing treatment using a two-roll cold press (front roller pressure 13 MPa, rear roller pressure 8 MPa, roller speed 2 mm / s), achieving a compaction of 1.7 mg / cm³. 3 The negative electrode active material layer has a thickness of 55 μm and serves as the negative electrode in lithium-ion battery assembly. The silicon content in the negative electrode is 12%. (See also...) Figure 1 As shown, Figure 1 The image shown is a scanning electron microscope image of the negative electrode sheet in Example 1, where 1 represents particulate matter and 2 represents the negative electrode active material layer.

[0130] (4) Method for manufacturing positive electrode plates:

[0131] Take positive electrode active material (LiNi) 0.8 Co 0.1 Mn 0.1 O2, conductive carbon black (Super P), multi-walled carbon nanotubes (HCNT), and polyvinylidene fluoride (PVDF) were thoroughly mixed in an N-methylpyrrolidone (NMP) solvent system at a mass ratio of 96:1:1:2 to obtain a positive electrode coating material. This positive electrode coating material was then coated onto a 12.0 μm thick aluminum foil. After drying and cold pressing, a positive electrode sheet was obtained, with a compaction density of 3.5 mg / cm². 3 .

[0132] (5) Preparation of electrolyte:

[0133] 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: 52.1: 2.95: 6.88: 4.92, with a LiPF6 concentration of 1 mol / L.

[0134] (6) Selection of diaphragm:

[0135] A high-porosity membrane was selected, in which the thickness of the PE base membrane is 9μm, the thickness of the ceramic coating on both sides of the base membrane is 1.0μm, and the porosity is 40.5%.

[0136] (7) Assembly of lithium-ion batteries:

[0137] 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 a pre-made connecting piece by welding and then installed into a metal battery casing. After completing key processes such as electrolyte injection, sealing, and formation, the lithium-ion battery described in Example 1 is obtained. This lithium-ion battery uses a cylindrical casing with an external dimension of 21.0 mm in diameter and 70.0 mm in length, conforming to the 21700 standard specification.

[0138] Example 2

[0139] The method is the same as in Example 1, except that the phenolic resin precursor particles are sprayed out through a spray flow rate of 1 mL / min, and the aspect ratio of the final product of the active material particles is [missing information]. =1.05, and everything else is the same as in Example 1.

[0140] Example 3

[0141] The method is the same as in Example 1, except that the phenolic resin precursor particles are sprayed out at a spray flow rate of 3 mL / min, and the aspect ratio of the active material particles to the final product is different. =1.1, and everything else is the same as in Example 1.

[0142] Example 4

[0143] The method is the same as in Example 1, except that the phenolic resin precursor particles are sprayed out at a spray velocity of 7.5 mL / min, and the aspect ratio of the active material particles to the final product is different. =1.2, and everything else is the same as in Example 1.

[0144] Example 5

[0145] The method is the same as in Example 1, except that the phenolic resin precursor particles are sprayed out through a spray flow rate of 10 mL / min, and the aspect ratio of the active material particles to the final product is different. The value is 1.3, and everything else is the same as in Example 1.

[0146] Example 6

[0147] The method is the same as in Example 1, except that the dried electrode sheet undergoes a secondary cold pressing process using a two-roll cold press (front roller pressure 10 MPa, rear roller pressure 6 MPa, roller speed 2 mm / s), resulting in a compaction of 1.5 mg / cm³. 3 Everything else is the same as in Example 1.

[0148] Example 7

[0149] The method is the same as in Example 1, except that the dried electrode sheet undergoes a secondary cold pressing process using a two-roll cold press (front roller pressure 12 MPa, rear roller pressure 7 MPa, roller speed 2 mm / s), resulting in a compaction of 1.55 mg / cm³. 3 Everything else is the same as in Example 1.

[0150] Example 8

[0151] The method is the same as in Example 1, except that the dried electrode sheet undergoes a secondary cold pressing process using a two-roll cold press (front roller pressure 14 MPa, rear roller pressure 9 MPa, roller speed 2 mm / s), resulting in a compaction of 1.7 mg / cm³. 3 Everything else is the same as in Example 1.

[0152] Example 9

[0153] The method is the same as in Example 1, except that the dried electrode sheets undergo a secondary cold pressing process using a two-roll cold press (front roller pressure 15 MPa, rear roller pressure 10 MPa, roller speed 2 mm / s), resulting in a compaction of 1.8 mg / cm³. 3 Everything else is the same as in Example 1.

[0154] Example 10

[0155] The method of Example 1 is the same as that of Example 1, except that the dried electrode is subjected to a second cold pressing process by a double roller cold press (the front roller pressure is 13 MPa, the rear roller pressure is 8 MPa, and the roller pressing speed is 0.5 mm / s). The porosity of the electrode is 20%, and everything else is the same as that of Example 1.

[0156] Example 11

[0157] The method of Example 1 is the same as that of Example 1, except that the dried electrode is subjected to a second cold pressing process by a double roller cold press (the front roller pressure is 13 MPa, the rear roller pressure is 8 MPa, and the roller pressing speed is 1.0 mm / s). The porosity of the electrode is 25%, and everything else is the same as that of Example 1.

[0158] Example 12

[0159] The method of Example 1 is the same as that of Example 1, except that the dried electrode is subjected to a second cold pressing process by a two-roll cold press (the front roller pressure is 13 MPa, the rear roller pressure is 8 MPa, and the roller pressing speed is 4 mm / s). The porosity of the electrode is 35%, and everything else is the same as that of Example 1.

[0160] Example 13

[0161] The method of Example 1 is the same as that of Example 1, except that the dried electrode is subjected to a second cold pressing process by a double roller cold press (the front roller pressure is 13 MPa, the rear roller pressure is 8 MPa, and the roller pressing speed is 6 mm / s). The porosity of the electrode is 40%, and everything else is the same as that of Example 1.

[0162] Example 14

[0163] The method is the same as in Example 1, except that the ratio of deposited silicon carbon to artificial graphite in the active material layer of the negative electrode is adjusted so that the silicon content in the negative electrode is 5%. Everything else is the same as in Example 1.

[0164] Example 15

[0165] The method is the same as in Example 1, except that the ratio of deposited silicon carbon to artificial graphite in the active material layer of the negative electrode is adjusted so that the silicon content in the negative electrode is 7.5%. All other aspects are the same as in Example 1.

[0166] Example 16

[0167] The method is the same as in Example 1, except that the ratio of deposited silicon carbon to artificial graphite in the active material layer of the negative electrode is adjusted so that the silicon content in the negative electrode is 17.5%. All other aspects are the same as in Example 1.

[0168] Example 17

[0169] The method is the same as in Example 1, except that the ratio of deposited silicon carbon to artificial graphite in the active material layer of the negative electrode is adjusted so that the silicon content in the negative electrode is 25%.

[0170] Comparative Example 1

[0171] The difference between this comparative example and Example 1 is that random deposition of silicon carbon was used; otherwise, they are the same as in Example 1.

[0172] Comparative Example 2

[0173] The difference between this comparative example and Example 1 is that secondary rolling is not used (single roller pressure is 14 MPa, rolling speed is 2 mm / s), the electrode compaction is 1.6, and the porosity is 26%. Everything else is the same as in Example 1.

[0174] Comparative Example 3

[0175] The difference between this comparative example and Example 1 is that the mass percentages of deposited silicon-carbon, artificial graphite, single-walled carbon nanotubes (SWCNT), conductive carbon black (Super P), sodium carboxymethyl cellulose (CMC), and polyacrylic acid (PAA) in the negative electrode are 54:42:1:1:1:1, while all other aspects are the same as in Example 1 (silicon content 40%).

[0176] Comparative Example 4

[0177] The difference between this comparative example and Example 1 is that the dried electrode sheet is subjected to a second cold pressing process using a two-roll cold press (the front roller pressure is 13 MPa, the rear roller pressure is 8 MPa, and the roller pressing speed is 10 mm / s). The porosity of the electrode sheet is 50%, and everything else is the same as in Example 1.

[0178] Comparative Example 5

[0179] The difference between this comparative example and Example 1 is that the dried electrode sheet is subjected to a second cold pressing process using a double-roll cold press (the front roller pressure is 13 MPa, the rear roller pressure is 8 MPa, and the roller pressing speed is 0.2 mm / s). The porosity of the electrode sheet is 10%, and everything else is the same as in Example 1.

[0180] Performance testing:

[0181] The performance of the lithium batteries prepared according to the above embodiments and comparative examples was tested, as follows:

[0182] (1) Characterization method for silicon particle size in deposited silicon-carbon porous carbon framework:

[0183] The samples were cut using focused ion beam (FIB) to preserve the porous structure of the carbon matrix (thickness ≤100 nm). The grain size of silicon was determined by high-resolution transmission electron microscopy (HRTEM) with the help of high-resolution imaging and EDS mapping.

[0184] (2) Method for determining the size of deposited silicon-carbon particles:

[0185] Take a small amount of 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 or Nanomeasure 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 10% of the cumulative percentage as D10, the particle size value corresponding to 50% of the cumulative percentage as D50, and the particle size value corresponding to 90% of the cumulative percentage as D90. At the same time, it is necessary to exclude the interference data of obvious agglomerates to ensure accuracy.

[0186] (3) Method for determining silicon content in negative electrode:

[0187] A sample of the negative electrode (m1 ≈ 100 mg) was scraped and digested in a mixture of hydrofluoric acid (HF) and nitric acid (HNO3) until completely dissolved. Subsequently, the silicon content m in the solution was determined using inductively coupled plasma optical emission spectroscopy (ICP-OES) or intracellular mass spectrometry (ICP-MS). si The mass fraction α of silicon in the negative electrode was calculated based on the initial mass of the sample. Si .

[0188] α Si (%) = ×100

[0189] (4) Method for testing the interface resistance of the negative electrode:

[0190] 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 apparatus, 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. During the test, a constant current was applied to the outer 20 probes, allowing the current to flow through the surface, interface, and current collector of the negative electrode, while the voltage change was measured in real time by the middle 25 probes. Finally, the film 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 film 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 film resistance of the negative electrode: R = (R1 + R2 + R3 + R4 + R5 + R6 + R7 + R8 + R9) / 9.

[0191] (5) Test method for peel strength of negative electrode:

[0192] First, use double-sided tape to fix the strip sample onto a flat, thin steel plate, ensuring the tape is centered on the plate. Then, peel off the protective layer of the double-sided tape and attach the strip sample to be tested onto the tape. Use a pressure roller to evenly press the strip sample to ensure good adhesion. Next, tear off the unattached end, bend the torn end of the electrode upwards, and clamp it in the upper fixture of a tensile testing machine for a 180° peel test. Record the tensile force curve. The segment 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 to calculate the peel strength of the negative electrode. Peel force tests are conducted on the front, middle, and rear segments of the electrode, and the obtained values ​​are recorded as N1, N2, and N3, respectively. Finally, the arithmetic mean of these values ​​is calculated to obtain the average peel force N of the actual tested negative electrode (N = (N1 + N2 + N3) / 3).

[0193] (6) Method for determining the porosity of the negative electrode:

[0194] The negative electrode sample was cut into pieces approximately 2cm in size. 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 (e.g., 0.1~60 MPa), and the mercury penetration volume at each pressure was recorded. The porosity ε was calculated based on the ratio of mercury volume to the total geometric volume of the sample, and pore size distribution information was also obtained. The porosity was calculated using the following formula:

[0195]

[0196] in This represents the volume of mercury that seeps in under pressure. This represents the total geometric volume of the electrode.

[0197] (7) Test method for discharge performance at 25℃ rate:

[0198] The lithium battery was discharged to 2.5V and placed in a 25℃ constant temperature chamber for 6 hours, and then tested according to the following steps:

[0199] (1) Under 1C conditions, constant current and constant voltage charging to 4.2V, cutoff current is 0.1C, and stand for 30 minutes. The capacity of constant current charging to 4.2V is Q1 (constant current segment capacity).

[0200] (2) Discharge under constant current at 1C until 2.5V cutoff, with a cutoff current of 0.1C, and let stand for 30 minutes;

[0201] (3) Under 6C conditions, constant current and constant voltage charging to 4.2V, the cutoff current is 0.1C, and it is left to stand for 30 minutes. The capacity meter that is constant current charged to 4.2V is Q6.

[0202] (4) Discharge under constant current at 1C until 2.5V cutoff, with a cutoff current of 0.1C, and let stand for 30 minutes;

[0203] The calculation method for the 6C charging capacity retention rate of a lithium battery at 25℃ is: Q6 / Q1 100%.

[0204] (8) 1C cycle performance test method:

[0205] Place the battery in a 25°C constant temperature chamber for 6 hours and test it according to the following steps:

[0206] (1) First round 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.

[0207] (2) Let it stand for 30 minutes after charging is complete.

[0208] (3) Perform constant current discharge, and discharge to 2.5V at a rate of 1C.

[0209] (4) Cyclic charge and discharge process: Charge at a constant current rate of 1C to 4.2V. Let stand for 30 minutes again. Discharge at a constant current rate of 1C to 2.5V.

[0210] (5) Repeat the above charging and discharging process for a total of 600 cycles.

[0211] The discharge capacities Q1 and Q600 of the battery after 1 cycle and 600 cycles were calculated, and the capacity retention rate of the battery after 600 cycles was calculated as: Q600 / Q1×100%.

[0212] (9) Method for determining the electrode expansion rate after 600 cycles:

[0213] Take the lithium battery that has undergone 600 cycles as described above, and obtain dry and clean electrode sheets according to the pretreatment steps outlined above. Measure the thickness of the electrode sheet at nine points using a micrometer, and take the average value, i.e., T. 600 Electrode expansion rate (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.

[0214] The test results are shown in Tables 1 to 5 below.

[0215] Table 1 Experimental parameters of Examples 1 to 5

[0216]

[0217] Comparing Examples 1 to 5, it is evident that the spraying speed significantly affects the sphericity of the silicon-carbon anode particles, their electrochemical performance, and electrode expansion. As the spraying speed increases from 1 mL / min to 10 mL / min, the particle length-to-short axis ratio (x / y) increases from 1.0 to 1.3, meaning the particles gradually transform from highly spherical to slightly elongated quasi-spherical. This change in microstructure directly regulates the compaction uniformity, interfacial stability, and cycling expansion behavior of the electrode. Specifically, highly spherical particles (x / y = 1.0) form a uniform interparticle contact network during the compaction and shaping process, significantly reducing local stress concentration. This results in the lowest interfacial resistance (approximately 3.5 mΩ·cm²), the highest coulombic efficiency in the first cycle (approximately 88.0%), the best capacity retention at 6C rate and after 600 cycles (91%), and the lowest electrode expansion rate (predicted 7.0%, measured 6.8%). This clearly demonstrates that spherical particles can effectively buffer the volume expansion caused by silicon lithium intercalation and reduce repeated SEI film rupture. As particles deviate from a spherical shape (x / y = 1.1~1.3), the interfacial resistance gradually increases, and the initial efficiency, rate capability, and cycle performance decrease. Simultaneously, the electrode expansion rate increases, reflecting that non-spherical particles easily form localized stress concentrations and microcracks in high-pressure negative electrodes, reducing structural stability. The aforementioned expansion trend highly matches the prediction formula established based on silicon content, electrode porosity, and particle sphericity, verifying the direct mapping relationship between microstructural parameters and macroscopic expansion behavior. This demonstrates that the multi-scale stress-controlled structure constructed in this invention—a spherical (or near-spherical) porous carbon framework / embedded nano-silicon / outer carbon coating—can significantly reduce cycle expansion while maintaining high specific capacity.

[0218] Table 2 Experimental data for Examples 1, 6-9

[0219]

[0220] Data from Examples 1, 6 to 9 show that the roller pressure before and after the secondary cold pressing has a significant impact on the compaction degree, electrochemical performance, and cycle expansion of the anode sheet. As the secondary cold pressing pressure gradually increases from 10 / 6 to 15 / 10 (MPa), the electrode compaction degree shows an upward trend. Correspondingly, the first-cycle coulombic efficiency and interfacial resistance show an initial improvement followed by a slight decrease, indicating that moderate pressing helps form a uniform and dense interparticle contact network and optimizes the conductive structure. However, excessive pressure can cause localized stress concentration or microcracks, affecting cycle stability and rate performance. The electrode expansion rate increases slightly with increasing compaction degree, reflecting that while high compaction improves energy density, it also increases the volumetric stress caused by silicon lithium intercalation. Overall, moderate secondary cold pressing pressure can effectively control cycle expansion while ensuring compaction and conductivity optimization, achieving high stability and low expansion effect for silicon-carbon anodes.

[0221] Table 3 Examples 1, 10 to 13

[0222]

[0223] Data from Examples 1, 10, and 13 show that the secondary cold-pressing speed has a significant impact on the porosity, electrochemical performance, and cycle expansion of the anode sheet. With increasing pressing speed (0.5 mm / s → 6 mm / s), the electrode porosity gradually increases (20% → 40%), while the first-cycle coulombic efficiency, interfacial resistance, rate capability, and cycle performance show corresponding changes: a moderate pressing speed maintains a good pore structure, forming a uniform interparticle contact network, thereby reducing interfacial resistance and improving cycle stability; too slow a pressing speed leads to excessive electrode density, insufficient porosity, increased interfacial resistance, and slightly increased cycle expansion; while too fast a pressing speed, although increasing porosity, still maintains a low expansion rate and good rate performance. The overall trend indicates that by adjusting the secondary cold-pressing speed, electrode expansion can be effectively controlled while ensuring conductivity and uniform pore structure, achieving high stability and low expansion of the silicon-carbon anode.

[0224] Table 4 Examples 1, 14 to 17

[0225]

[0226] Comparing Examples 1 to 17, it is evident that the silicon content in the negative electrode significantly affects electrochemical performance and cycle expansion. As the silicon content gradually increases, the first-cycle coulombic efficiency and rate performance show a slight decreasing trend, while the interface resistance of the negative electrode gradually increases. This indicates that while high silicon content can improve specific capacity, it also increases local stress and interface instability, affecting cycle performance. Simultaneously, the electrode expansion rate increases significantly with increasing silicon content, and both the predicted and measured expansion rates show a consistent trend, indicating that the volume expansion caused by silicon lithium intercalation is more pronounced in high-silicon negative electrodes. The overall trend suggests that by rationally controlling the silicon content, it is possible to improve energy density while maintaining cycle stability and low expansion characteristics, achieving high structural stability and engineered controllable expansion of silicon-carbon negative electrodes.

[0227] Table 5. Experimental results of Example 1, Comparative Examples 1 to 2

[0228]

[0229] Comparing Example 1 and Comparative Example 1, it is evident that the use of non-spherical deposited silicon-carbon particles with a significantly larger aspect ratio (1.7) resulted in uneven particle contact during electrode pressing, leading to noticeable localized stress concentration. This resulted in a decrease in coulombic efficiency during the first cycle, an increase in interfacial resistance, and a significant reduction in 6C rate performance and long-cycle capacity retention. Simultaneously, the electrode expansion rate was significantly higher than in Example 1. These results validate the importance of spherical or near-spherical particles for compaction uniformity, conductive network integrity, and expansion buffering effect.

[0230] Comparing Example 1 and Comparative Example 2, it can be seen that by eliminating the secondary cold pressing while retaining the spherical shape of the particles, the electrode porosity is slightly higher and the compaction degree is slightly lower. Although the particles still have a good geometric morphology, the pore distribution is not uniform enough, the conductive network density after compaction is reduced, the interface resistance is slightly increased, and the initial efficiency and rate performance are slightly lower than in Example 1. At the same time, the electrode expansion rate is increased. The results show that secondary cold pressing plays an important role in forming a uniform pore structure, enhancing the integrity of the pressed sheet structure, and alleviating silicon expansion stress.

[0231] Comparing Example 1 and Comparative Example 3, it can be seen that the actual electrode expansion rate is as high as 26% when using a negative electrode design with high silicon content, while the empirical model electrode expansion rate is only 14.5%. This result shows that the prediction model is effective only within a certain range of silicon addition.

[0232] Comparing Example 1 with Comparative Examples 4 and 5, it can be seen that a suitable secondary cold pressing speed is needed to balance the first-cycle coulombic efficiency, increased interface resistance, 6C rate performance, long-cycle capacity retention, and electrode expansion. Too fast or too slow speeds will seriously affect the performance.

[0233] In summary, this invention employs a multi-scale stress-controlled structure of a spherical (or near-spherical) porous carbon framework / embedded nano-silicon / outer carbon coating, combined with an optimized secondary cold pressing process, to achieve uniform pore distribution and a dense particle contact network in the negative electrode sheet under high actual density. This effectively reduces local stress concentration and interface resistance, significantly improves first-cycle coulombic efficiency, rate performance, and long-cycle stability, while controlling the volume expansion caused by silicon lithium intercalation. This results in a silicon-carbon negative electrode with low expansion and high structural stability, providing an engineerable and reversibly controllable structural optimization scheme for the design of high-energy-density power lithium-ion battery negative electrodes.

[0234] The parts of this invention not described in detail are techniques known to those skilled in the art.

[0235] 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.

[0236] 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, 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, without contradiction. 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.

[0237] 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, include: Negative electrode current collector; A negative electrode active material layer is disposed on at least one side surface of the negative electrode current collector, the negative electrode active material layer includes active materials, the active materials include particulate matter and sheet-like matter; The ratio of the major axis to the minor axis of the particulate matter ranges from 1.0 to 1.3; The particulate matter includes a core and a coating layer disposed on at least a portion of the surface of the core. The core includes a porous carbon framework and nano-silicon embedded in the porous carbon framework. The coating layer is a carbon coating layer. The interface resistance of the negative electrode is 2.0 mΩ·cm. 2 ~8mΩ·cm 2 ; The peel strength of the negative electrode sheet is 10.0 N / m to 22.0 N / m; The predicted expansion rate of the negative electrode sheet satisfies The The mass fraction of silicon in the active material particles, the The porosity of the negative electrode sheet, the The ratio of the long axis to the short axis of the active material particles is denoted by PD, which is the compaction density of the negative electrode sheet.

2. The negative electrode sheet according to claim 1, characterized in that, The thickness of the negative electrode is 50μm to 120μm; And / or, the thickness of the active material layer of the negative electrode is 40~90μm; And / or, the compaction density of the negative electrode sheet is 1.5 g / cm³. 3 ~1.8g / cm 3 ; And / or, the porosity of the negative electrode is 20% to 40%.

3. The negative electrode sheet according to claim 1, characterized in that, The size of the nano-silicon is 1nm to 6nm; And / or, the particle size distribution of the porous carbon framework is 1.5 μm to 10 μm; And / or, the mass of the nano-silicon accounts for 2.5wt% to 25wt% of the mass of the active material.

4. The negative electrode sheet according to claim 1, characterized in that, The layered material in the negative electrode active material includes natural graphite and / or artificial graphite; And / or, the negative electrode further includes a conductive agent, the conductive agent including at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes and conductive carbon black; And / or, the negative electrode sheet further includes a binder, the binder including at least one of sodium carboxymethyl cellulose, polyacrylic acid, polyacrylonitrile, styrene-butadiene rubber, and polystyrene-acrylic acid.

5. A method for manufacturing a negative electrode sheet according to any one of claims 1 to 4, characterized in that, Includes the following steps: a) The carbon source solution is pretreated to obtain precursor particles, the precursor particles are subjected to first carbonization, and a porous carbon framework is etched. b) Silane deposition is performed on a porous carbon framework to obtain a porous carbon material with embedded silicon, and a second carbon source is introduced to perform a second carbonization to obtain particulate matter. c) A negative electrode active material slurry is prepared by combining particulate matter, sheet-like matter, conductive agent, and binder. This slurry is coated on at least one side of the negative electrode current collector, cured, and then cold-pressed a second time to obtain a negative electrode sheet.

6. The manufacturing method according to claim 5, characterized in that, In step a): The carbon source solution includes a first carbon source, which includes at least one of phenolic resin, coconut shell, starch, and cellulose. And / or, the preparation of the carbon source solution includes dissolving a first carbon source in an alcohol solvent, wherein the alcohol solvent includes at least one selected from methanol, ethanol, propanol, isopropanol, butanol, ethylene glycol, propylene glycol, and glycerol; And / or, the pretreatment includes spray drying; And / or, the carbonization temperature of the first carbonization is 600℃~1000℃, the carbonization time is 2h~5h, and the heating rate of the first carbonization is 3℃ / min~8℃ / min; And / or, the first carbonization process further includes the introduction of an inert gas for protection; And / or, the etching process includes etching by introducing an etching gas and an auxiliary gas.

7. The manufacturing method according to claim 6, characterized in that, In step a): The first carbon source accounts for 25 wt% to 45 wt% of the carbon source solution mass; And / or, the spray dryer has an inlet temperature of 160℃~210℃, an outlet temperature of 100℃~130℃, a spray flow rate of 3ml / min~7ml / min, and a droplet diameter of 7μm~10μm; And / or, the inert gas includes at least one of helium, neon, nitrogen, and argon; And / or, the etching gas includes at least one of CO2 and CO; And / or, the auxiliary gas includes at least one of water vapor and hydrogen; And / or, the auxiliary gas accounts for 15% to 30% of the total gas; And / or, the etching flow rate is 100 ml / min to 300 ml / min, and the etching time is 1 h to 4 h; And / or, the etching process further includes cooling with an inert gas, the inert gas including at least one of helium, neon, nitrogen, and argon.

8. The manufacturing method according to claim 5, characterized in that, In step b): The silane deposition process includes introducing a carrier gas and a silicon source gas into a porous carbon framework. The reaction temperature for silane deposition is 400℃ to 500℃. The carrier gas includes at least one of helium, neon, and nitrogen. The silicon source gas includes at least one of silane, disilane, propane, and methylsilane. The volume ratio of the carrier gas to the silicon source gas is 1:(5 to 8). The gas flow rate for the silane deposition process is 10 L / min to 30 L / min, and the deposition time is 8 h to 12 h. And / or, the second carbon source includes at least one of acetylene, ethylene, propylene, methane, and ethane; The second carbonization temperature is 550℃~700℃, the carbonization time is 3h~6h, and the gas flow rate is 3L / min~8L / min.

9. The manufacturing method according to claim 5, characterized in that, In step c), the mass ratio of the particulate material, the sheet-like conductive agent, and the binder is 5~32:70~90:0.5~2:0.5~2.5; And / or, in the secondary cold pressing, the pressure of the primary cold pressing is 10 MPa to 15 MPa, and the pressure of the secondary cold pressing is 6 MPa to 10 MPa.

10. A battery, characterized in that, Includes the negative electrode sheet as described in any one of claims 1 to 4 or the negative electrode sheet obtained by the manufacturing method described in any one of claims 5 to 9.

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