Negative electrode material, negative electrode sheet and secondary battery

Abstract

The present application relates to the field of electrochemical energy storage. Disclosed are a negative electrode material, a negative electrode sheet and a secondary battery. The negative electrode material comprises an inner core and a coating layer, wherein the inner core comprises a carbon matrix and an active substance, and at least part of the coating layer is located on part of the surface of the inner core. The protective strength of the coating layer is γ, γ=0.0129T0-0.323, wherein 4≤γ≤9, and T0 is the initial temperature of the negative electrode material when undergoing mass increase in a thermogravimetric analysis test, with the atmosphere of the thermogravimetric analysis being an oxygen atmosphere. The negative electrode material of the present application has a relatively high protective strength γ value, where 4≤γ≤9, such that the inner core of the negative electrode material is oxidized only at a relatively high temperature, which indicates that the compactness and uniformity of the coating layer of the negative electrode material are relatively high, and thus the gas production inhibition effect of the negative electrode material is better during the homogenate and electrolyte contact process.

Description

Negative electrode materials, negative electrode sheets, and secondary batteries

[0001] This application claims priority to two Chinese patent applications filed with the State Intellectual Property Office on August 19, 2024, application number 202411131892.9, entitled "Anode Material, Electrode and Electrochemical Device", and filed with the State Intellectual Property Office on September 3, 2024, application number 202411230209.7, entitled "Anode Material, Anode Sheet and Secondary Battery", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of electrochemical energy storage, specifically to a negative electrode material, a negative electrode sheet, and a secondary battery. Background Technology

[0003] Anode materials may include a matrix and active materials distributed in the pores of the matrix or on the surface of the matrix. Taking silicon particles, i.e. elemental silicon, as an example, during the homogenization or battery cycling process, some elemental silicon dissolves out and comes into contact with and reacts with water or electrolyte in the homogenate, resulting in gas production. In addition, elemental silicon will also expand abnormally during battery cycling, producing an undesirable volume effect. These problems limit the long-cycle use of anode materials and secondary batteries. Summary of the Invention

[0004] This application provides a negative electrode material, a negative electrode sheet, and a secondary battery to solve the problem of poor cycle performance of the negative electrode material and the secondary battery.

[0005] To achieve the above objectives, this application provides a negative electrode material, comprising a core and a coating layer. The core includes a matrix and an active material, wherein the matrix is ​​a carbon matrix, and the coating layer is located on at least a portion of the surface of the core. The protective strength of the coating layer is γ, where γ = 0.0129T0 - 0.323, 4 ≤ γ ≤ 9, T0 is the initial temperature at which the mass of the negative electrode material increases during thermogravimetric analysis, and the atmosphere for the thermogravimetric analysis is an oxygen atmosphere.

[0006] This application also provides a negative electrode sheet, including a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, wherein the negative electrode active material layer includes the aforementioned negative electrode material.

[0007] This application also provides a secondary battery, including the aforementioned negative electrode.

[0008] This application uses the protective strength γ of the coating layer to characterize the density, thickness and uniformity of the coating layer. When 4≤γ≤9, it indicates that the coating layer has good density, thickness and uniformity. The active material in the coated core is not easily exposed, nor is it easy to seep out through the coating layer and react with external substances (such as slurry or electrolyte). This is beneficial to reduce the gas generation phenomenon of the negative electrode material and improve the cycle performance of the negative electrode material and the secondary battery. Attached Figure Description

[0009] Figure 1 is a schematic diagram of the structure of a secondary battery provided in one embodiment of this application during charging.

[0010] Figure 2 is a schematic diagram of the structure of a secondary battery provided in one embodiment of this application during discharge.

[0011] Figure 3 is a scanning electron microscope (SEM) image of the negative electrode material prepared in Example 9 of this application.

[0012] Figure 4 is an X-ray diffraction pattern of the negative electrode material prepared in Example 9 of this application.

[0013] Figure 5 shows the thermogravimetric analysis (TG) curve of the negative electrode material prepared in Example 12 of this application.

[0014] Figure 6 shows the thermogravimetric analysis curve of the negative electrode material prepared in Example 14 of this application.

[0015] Figure 7 shows the thermogravimetric analysis curve of the negative electrode material prepared in Comparative Example 4 of this application.

[0016] Explanation of main component symbols: Electrode assembly 100, Positive electrode 101, Negative electrode 102, Separator 103. Detailed Implementation

[0017] The embodiments of this application are described in detail below. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application; it should be noted that, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; where there is no conflict, the implementation methods and features of the implementation methods of this application can be combined with each other; many specific details are set forth in the following description to provide a full understanding of this application, and the described implementation methods are only a part of the implementation methods of this application, and not all of the implementation methods.

[0018] One embodiment of this application provides a secondary battery, including a casing, an electrode assembly, and an electrolyte. Both the electrode assembly and the electrolyte are located within the casing.

[0019] The outer casing can be a packaging bag encapsulated with a sealing film (such as aluminum-plastic film), for example, a pouch battery. In other embodiments, it can also be a steel-cased battery, an aluminum-cased battery, etc.

[0020] Referring to Figure 1, the electrode assembly 100 includes a positive electrode 101, a negative electrode 102, and a separator 103, with the separator 103 disposed between the positive electrode 101 and the negative electrode 102. When an electrolyte (not shown) is present, during charging (referring to Figure 1), active ions (such as lithium ions) are extracted from the positive electrode material (such as a lithium-ionized intercalated compound) of the positive electrode 101, pass through the separator 103 via the electrolyte, reach the negative electrode 102, and are embedded in the negative electrode material. Electrons correspondingly travel from the positive electrode 101 to the negative electrode 102 via an external circuit. During discharging (referring to Figure 2), active ions (such as lithium ions) are extracted from the negative electrode material of the negative electrode 102, pass through the separator 103 via the electrolyte, reach the positive electrode 101, and are embedded in the positive electrode material (such as a lithium-ionized intercalated compound). Electrons correspondingly travel from the negative electrode 102 to the positive electrode 101 via an external circuit.

[0021] In some embodiments, the electrode assembly 100 may be a stacked structure, which is formed by alternatingly stacking a positive electrode 101, a separator 103, and a negative electrode 102. In other embodiments, the electrode assembly 100 may also be a wound structure, which is formed by sequentially stacking and then winding the positive electrode 101, the separator 103, and the negative electrode 102.

[0022] Positive electrode film

[0023] The positive electrode 101 includes a positive current collector and a positive electrode material active layer disposed on at least one surface of the positive current collector. The positive current collector can be aluminum foil or nickel foil, or any composite current collector disclosed in the prior art, such as, but not limited to, current collectors formed by combining the aforementioned conductive foil and polymer substrate. The positive electrode material active layer includes a positive electrode active material, which includes a compound that reversibly inserts and extracts lithium ions (i.e., a lithiation intercalation compound). In some embodiments, the positive electrode active material may include a lithium transition metal composite oxide. This lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese, and nickel. In some embodiments, the positive electrode active material may include, but is not limited to, lithium cobalt oxide (LiCoO2), lithium nickel manganese cobalt ternary materials (NCM), lithium manganese oxide (LiMn2O4), and lithium nickel manganese oxide (LiNi). 0.5 Mn 1.5 At least one of O4 and lithium iron phosphate (LiFePO4).

[0024] The positive electrode material active layer also includes an adhesive for bonding the positive electrode active material particles to facilitate the formation of the film layer, and also to improve the bonding force between the positive electrode material active layer and the positive electrode current collector. In some embodiments, the adhesive may include, but is not limited to, at least one of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc.

[0025] The positive electrode material active layer may further include a conductive material, which includes, but is not limited to, carbon-based materials, metal-based materials, conductive polymers, or any combination thereof. In some embodiments, carbon-based materials may include, but are not limited to, natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, metal-based materials may include, but are not limited to, metal powders or metal fibers, such as copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer may be a polyphenylene derivative.

[0026] negative electrode sheet

[0027] The negative electrode sheet 102 includes a negative electrode current collector and a negative electrode material active layer disposed on at least one surface of the negative electrode current collector. The negative electrode material active layer is sometimes also called a film. The negative electrode material active layer can be formed by mixing the negative electrode material with a conductive agent, binder, solvent, etc. to form a slurry and then drying it. The negative electrode current collector can be at least one of copper foil, nickel foil, stainless steel foil, titanium foil, carbon-based current collector, etc., or any composite current collector disclosed in the prior art, such as, but not limited to, current collectors formed by combining the aforementioned conductive foil and polymer substrate. The negative electrode material active layer includes a negative electrode material, which includes a core and a coating layer. The core includes a matrix and an active material. The matrix includes a carbon matrix. The coating layer is located on at least a portion of the surface of the core. The protective strength of the coating layer is γ, where γ = 0.0129T0 - 0.323, 4 ≤ γ ≤ 9, T0 is the initial temperature at which the negative electrode material increases in mass during thermogravimetric analysis, and the atmosphere for thermogravimetric analysis is an oxygen atmosphere. For example, the protective strength γ of the coating layer can be 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, or any value within the range of any two of the above values.

[0028] This application obtains the protective strength γ of the coating layer by performing thermogravimetric analysis (TG) on the negative electrode material under oxygen atmosphere, measuring the temperature T0 at which the mass of the negative electrode material increases. The principle is as follows: Under normal circumstances, due to the microscopic pores in the material forming the coating layer, oxygen molecules can pass through these pores, allowing oxygen to contact the core covered by the coating layer. Then, because the active material in the core (such as elemental silicon) has high reactivity, oxygen tends to preferentially react with the active material (such as elemental silicon) to form oxides (such as silicon oxide), thus increasing the mass of the negative electrode material. When the porosity of the coating layer changes, making it more difficult for oxygen molecules to pass through, increasing the temperature helps to intensify the thermal motion of gas molecules, increasing the collision frequency between molecules and the average kinetic energy of the molecules. This accelerates the diffusion rate of gas molecules in space, allowing oxygen molecules to pass through these pores again, penetrate the coating layer, and cause the negative electrode material to oxidize again, leading to a further increase in mass. Therefore, in the above TG test, the temperature T0 at which the mass of the negative electrode material increases can effectively reflect the protective strength of the coating layer on the core. A higher temperature T0 indicates better protection of the core by the coating layer, making it less likely for oxygen to react with the active material in the core. Consequently, the initial mass increase temperature T0 due to the oxidation of the active material will be higher. Conversely, a lower protective strength of the coating layer results in a lower initial mass increase temperature T0. Therefore, this application defines the protective strength of the coating layer as γ. When T0 = 25℃, γ = 0; when T0 = 800℃, γ = 10. Thus, T0 and γ can be correlated using the formula γ = 0.0129T0 - 0.323.

[0029] The aforementioned protective strength γ can be used to characterize the density, thickness, and uniformity of the coating layer. When γ satisfies 4 ≤ γ ≤ 9, the core of the negative electrode material will only oxidize at a relatively high temperature, indicating that the coating layer has good density, thickness, and uniformity. The active material in the coated core is not easily exposed, nor is it easy for it to seep through the coating layer and react with external substances (such as slurry or electrolyte), thus helping to reduce gas generation in the negative electrode material and improve the electrochemical performance of the secondary battery. However, when γ < 4, the density, thickness, or uniformity of the coating layer is poor. When coating the core, some active material in the core is easily exposed, leading to direct contact with external substances, or when active material detaches, it can easily penetrate the coating layer and contact with external substances, resulting in instability of the negative electrode material, severe gas generation, and thus seriously reducing the electrochemical performance of the secondary battery.

[0030] The negative electrode material also includes oxygen. The percentage of oxygen atoms at any point X, defined as X, at the surface of the negative electrode material is denoted as P. x 60nm≤X≤160nm, 2%≤P x≤8%. For example, the percentage of oxygen atoms (P) x It can be 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, or any value within the range of any two of the above values.

[0031] This application further proposes that the oxygen element at depth X (60nm≤X≤160nm) mainly originates from the oxidation of the active material (such as elemental silicon). Generally, the outermost layer of the anode material is a coating layer, followed by the active material (such as elemental silicon) and the substrate, with the active material distributed within the substrate. During the distribution of the active material, some of it is oxidized, forming an oxide layer. A certain amount of oxide layer can act as a buffer medium, reducing the expansion pressure during cycling and also reducing the direct contact between elemental silicon and water or electrolyte. However, excessive oxide layer can cause a decrease in capacity and initial coulombic efficiency, therefore, the oxygen content needs to be controlled. When the percentage of oxygen P at depth X is... x Satisfying 2% ≤ P x ≤8%, the corresponding oxide layer can provide protection for active materials (such as silicon), which is beneficial to reducing the gas production value and expansion rate of the negative electrode material.

[0032] Furthermore, this application also discovered that controlling the percentage content P of the aforementioned oxygen element... x Satisfying 2% ≤ P x ≤8%, the aforementioned oxide layer also helps to maintain or increase the protective strength γ of the coating layer to a certain extent, thereby helping to ensure that the protective strength γ of the coating layer meets a specific range. This may be because an appropriate oxygen content can promote better nucleation and growth of the coating layer material by influencing the pyrolysis and surface reaction kinetics of the coating layer precursor material, thereby helping to improve the density, thickness, or uniformity of the coating layer. Furthermore, P x The concentration should be 2%–3.5% or 6.9%–8%, and P should be controlled. x Within the aforementioned range, it helps to further improve the structural stability of the anode material and reduce the expansion effect during the cycling process of the anode material.

[0033] In some embodiments, P is located along the direction from the surface of the negative electrode material to the interior of the negative electrode material. xThe trend is initially decreasing and then increasing. The percentage of oxygen atoms on the surface of the negative electrode material is relatively high because the negative electrode material is exposed to air and adsorbs oxygen-containing groups on its surface. As the depth increases, the coating layer is detected first. The coating layer originates from the cracking of the coating layer precursor material. The probability of introducing oxygen during this process is small, resulting in a decrease in the percentage of oxygen atoms. As the detection depth further increases, the active material region is detected. During the formation and distribution of the active material on the substrate, it is partially oxidized, forming an oxide layer, which increases the detected percentage of oxygen atoms. The oxide layer inside the negative electrode material at a certain depth is beneficial as a buffer layer for the substrate or active material, improving the stability of the substrate or active material, thereby further improving the cycle stability of the negative electrode material. In this application, the direction from the surface of the negative electrode material to the interior of the negative electrode material refers to the direction of X-ray photoelectron spectroscopy testing of the negative electrode material using the Thermo Scientific K-Alpha equipment, which is the direction in which the depth of each argon ion sputtering is set.

[0034] In some embodiments, the specific surface area of ​​the carbon matrix is ​​800 m². 2 / g to 3000m 2 / g. For example, the specific surface area of ​​a carbon matrix can be 800m². 2 / g, 1000m 2 / g、1200m 2 / g, 1400m 2 / g, 1600m 2 / g、1800m 2 / g、2000m 2 / g、2300m 2 / g、2500m 2 / g、2800m 2 / g、3000m 2 / g or any value within the range of any two of the above values. Controlling the specific surface area of ​​the carbon matrix within the above range is beneficial for the uniform dispersion and stable adhesion of the active material on the carbon matrix, thereby reducing the risk of the active material detaching from the carbon matrix and improving the stability and durability of the active material. Furthermore, the specific surface area of ​​the carbon matrix is ​​1000 m². 2 / g to 3000m 2 / g.

[0035] In some embodiments, the carbon matrix has pores, which provides more deposition sites for active materials, allowing them to be deposited within the pores. Simultaneously, the porous framework of the carbon matrix can form a conductive network, facilitating electron transport during charge and discharge, thereby reducing polarization of the battery material and improving conductivity and cycle stability.

[0036] In some embodiments, the total pore volume of the carbon matrix is ​​0.5 cm³, based on the mass of the carbon matrix. 3 / g to 2.0cm 3 / g. For example, the total pore volume of the carbon matrix can be 0.5 cm³. 3 / g, 0.8cm 3 / g, 1cm 3 / g, 1.2cm 3 / g, 1.5cm 3 / g, 1.8cm 3 / g、2cm 3 / g or any value within the range of any two of the above values. When the carbon matrix has abundant pores, these pores can accommodate the active material and reserve space for the volume expansion of the accommodated active material. To further balance the specific capacity and cycle stability of the anode material, the total pore volume of the carbon matrix is ​​0.5 cm³. 3 / g to 1.4cm 3 / g. For example, the total pore volume could be 0.5 cm³. 3 / g, 0.8cm 3 / g, 1cm 3 / g, 1.2cm 3 / g, 1.4cm 3 / g or any value within the range of any two of the above values.

[0037] In some embodiments, the carbon matrix has pores, and the porosity of the carbon matrix is ​​40% to 80%. For example, the porosity of the carbon matrix can be 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or any value within the range of any two of the above values. Porosity refers to the percentage of pore volume in a material to the total volume of the material in its natural state. Controlling the porosity of the carbon matrix within the above range is beneficial for the good deposition of active particles, thereby reducing the volume expansion effect of the obtained negative electrode material, helping to maintain the stability of the negative electrode material structure, and further improving the cycle performance of the negative electrode material.

[0038] In some embodiments, the average particle size of the active material is from 0.1 nm to 100 nm. For example, the average particle size of the active material can be 0.1 nm, 0.5 nm, 1 nm, 3 nm, 5 nm, 8 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 65 nm, 80 nm, 95 nm, 100 nm, or any value within the range of any two of the above values. For example, the active material can be a silicon-based material. By setting the average particle size of the silicon-based material within the above range, the mechanical stress during volume expansion of the silicon-based material can be reduced, allowing the secondary battery to maintain a better battery capacity and reducing irreversible capacity loss. It can also shorten the electron and ion transport paths. At the same time, controlling the average particle size of the silicon-based material within the above range can also increase the distance between adjacent silicon-based material particles, thereby reserving space for volume expansion of the silicon-based material.

[0039] In some embodiments, the average thickness of the coating layer is from 1 nm to 60 nm. For example, the average thickness of the coating layer can be 1 nm, 3 nm, 5 nm, 8 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, or any value within the range of any two of the above values. Controlling the average thickness of the coating layer within the above range is beneficial for maintaining the stability of the particle structure of the anode material during cycling, reducing the probability of surface active material exposure, thereby reducing the amount of SEI generated during charge and discharge, and improving the specific capacity and electrochemical performance of the anode material.

[0040] In some embodiments, the coating layer comprises one or more of carbon materials, metal oxides, amorphous silicon, conductive polymers, fluorides, phosphates, and nitrides. When the coating layer comprises carbon materials, the resulting carbon coating layer is beneficial for improving the stability and conductivity of the substrate. The carbon coating layer can also coat the active material exposed on the surface of the carbon substrate, reducing the continuous oxidation of the exposed active material during storage and reducing the risk of a decrease in the specific capacity and first coulombic efficiency (ICE) of the anode material. The carbon coating layer can also reduce the direct contact between the active material and the electrolyte, improving the stability of the SEI film, thereby improving the first coulombic efficiency of the anode material.

[0041] In some embodiments, the carbon coating layer can be a single-layer carbon coating layer formed from a single material, a carbon coating layer formed from a combination of multiple materials, a multi-layer carbon coating layer formed from a single material, or a multi-layer carbon coating layer formed from multiple materials, etc., and the layer structure of the carbon coating layer can be selected according to actual needs. It is understood that when the carbon coating layer has a multi-layer coating structure, its density is higher.

[0042] In some embodiments, the mass percentage of the coating layer in the negative electrode material is less than or equal to 10%. For example, the mass percentage of the coating layer can be 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, or any value within the range of any two of the above values. A mass percentage of the coating layer in the negative electrode material within the above range allows for sufficient intercalation of active ions into the electrode, thereby enabling the battery to have a higher charge / discharge capacity.

[0043] In some embodiments, the volumetric median particle size D50 of the negative electrode material is between 3 μm and 15 μm. For example, the median particle size D50 of the negative electrode material can be 3 μm, 4 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 15 μm, or any value within the range of any two of the above values. Controlling the volumetric median particle size D50 of the negative electrode material within the above range is beneficial to improving the cycle performance of the negative electrode material.

[0044] In some embodiments, the specific surface area of ​​the negative electrode material is 1m². 2 / g to 10m 2 / g. For example, the specific surface area of ​​the negative electrode material can be 1m². 2 / g、2m 2 / g、3m 2 / g、4m 2 / g、5m 2 / g、6m 2 / g、7m 2 / g、8m 2 / g、9m 2 / g, 10m 2 / g or any value within the range of any two of the above values. Controlling the specific surface area of ​​the negative electrode material within the above range is beneficial for improving the battery's first discharge specific capacity and first coulombic efficiency.

[0045] In some embodiments, the carbon matrix includes one or more of hard carbon, soft carbon, graphite, carbon nanotubes, carbon fibers, and graphene. The selection of any of these materials as the carbon matrix can provide distribution sites for active substances and form a conductive network.

[0046] In some embodiments, the carbon matrix includes one or more of the following: artificial graphite, natural graphite, amorphous carbon, activated carbon, mesophase carbon microspheres, carbon nanotubes, carbon nanofibers, and graphene. The selection of any of these materials as the carbon matrix can provide distribution sites for active substances and form a conductive network.

[0047] In some embodiments, the active material includes one or more of silicon-based materials, Li, Na, K, Sn, Ge, Fe, Mg, Ti, Zn, Al, P, and Cu.

[0048] In some embodiments, the silicon-based material includes one or more of amorphous silicon, crystalline silicon, silicon oxide, silicon alloy, and composites of crystalline and amorphous silicon. When the active material includes a silicon-based material, the silicon-based material is used as a component of the negative electrode active material, which can improve the specific capacity of the negative electrode material, thereby increasing the energy density of the secondary battery. Preferably, the silicon-based material includes amorphous silicon. When the active material further includes amorphous silicon, the amorphous silicon expands isotropically during lithium intercalation, which can reduce pore collapse, suppress the rapid decay of the specific capacity of the negative electrode material, and is more conducive to improving the cycle performance of the negative electrode material.

[0049] In some embodiments, the active material includes a silicon-based material, and the coating layer includes a carbon coating layer. Based on the mass of the negative electrode material, the mass percentage of silicon in the negative electrode material is 20% to 65%. For example, the mass percentage of silicon in the negative electrode material can be 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, or any value within the range of any two of the above values. A negative electrode material obtained by combining a carbon matrix (such as porous carbon) with a silicon-based material can effectively alleviate the expansion problem of silicon-based materials during cycling, maintain the stability of the battery material, and improve the volumetric capacity of the material. Controlling the mass percentage of silicon within the above range results in a secondary battery that can store a higher amount of electricity, i.e., a higher initial discharge specific capacity. Further, based on the mass of the negative electrode material, the mass percentage of silicon in the negative electrode material is 45% to 55%. For example, it can be 45%, 48%, 50%, 52%, 54%, 55%, or any value within the range of any two of the above values. In this way, the volumetric capacity of the anode material can be increased, and the expansion problem of silicon during cycling can be improved.

[0050] In some embodiments, the active material includes a silicon-based material, and the coating layer includes a carbon coating layer. Based on the mass of the anode material, the mass percentage of carbon in the anode material is 30% to 60%. For example, the mass percentage of carbon in the anode material can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, or any value within the range of any two of the above values. The carbon matrix combined with the silicon-based material can provide a conductive platform and buffer space for the silicon-based material, improving the structural instability and poor conductivity of the silicon-based material during cycling. The carbon in the anode material mainly originates from the carbon matrix and the carbon coating layer. Controlling the mass percentage of carbon within the above range allows for the establishment of a sufficient carbon-based substrate, providing ample distribution sites for the active material, which is beneficial for forming an effective conductive network and improving conductivity and cycle stability. Further, based on the mass of the anode material, the mass percentage of carbon in the anode material is 45% to 55%. For example, it can be 45%, 48%, 50%, 52%, 54%, 55%, or any value within the range of any two of the above values.

[0051] In some embodiments, the coating layer includes a carbon coating layer.

[0052] In some embodiments, the carbon coating layer comprises a carbon material, including one or more of graphene, soft carbon, and hard carbon. Located on the outer layer of the anode material, the carbon coating layer exhibits good electrical conductivity, thereby improving the conductivity of the anode material. Furthermore, it coats the active material exposed on the surface of the carbon matrix, reducing the continuous oxidation of the exposed active material during storage and minimizing the decrease in specific capacity and initial coulombic efficiency (ICE) of the anode material. The coating layer also reduces direct contact between the active material and the electrolyte, improving the stability of the SEI film and thus enhancing the initial coulombic efficiency of the anode material.

[0053] In some embodiments, the coating layer includes a carbon coating layer, and also includes one or more of an oxide coating layer, a metal salt coating layer, and a polymer coating layer.

[0054] When the coating layer includes an oxide coating layer, the reaction between the negative electrode material and the electrolyte can be reduced, extending the battery cycle life. Additionally, some oxides, such as metal oxides, possess good mechanical stability and anti-expansion properties, which can reduce the solid-phase expansion of the negative electrode material during charge and discharge, further improving battery cycle life. Common oxide coating materials include aluminum oxide, zinc oxide, tin oxide, and titanium oxide, which exhibit good stability, conductivity, and anti-expansion properties.

[0055] When the coating layer includes a polymer coating layer, it can improve the conductivity of the negative electrode material, reduce resistance, and improve the charging and discharging efficiency of the battery. On the other hand, it can prevent the active material from directly contacting the electrolyte and improve the chemical stability of the negative electrode material.

[0056] In some embodiments, the average thickness of the coating layer is 5 nm to 500 nm. For example, the average thickness of the coating layer can be 5 nm, 30 nm, 50 nm, 150 nm, 200 nm, 250 nm, 300 nm, 500 nm, or any value within the range of any two of the above values. Controlling the average thickness of the coating layer within the above range is beneficial for maintaining the stability of the particle structure of the anode material during cycling, reducing the amount of exposed active material on the surface of the anode material, reducing the generation of a large amount of SEI during charge and discharge due to exposed active material, and improving the specific capacity and electrochemical performance of the anode material. Further, the average thickness of the coating layer can be 10 nm to 100 nm. In this way, the strength of the coating layer can be guaranteed without affecting the energy density.

[0057] In some embodiments, the mass percentage of carbon in the anode material is 40% to 60%, based on the mass of the anode material. The method for testing the mass percentage of carbon in the anode material includes: using a Bruker G4 ICARUS HF infrared carbon-sulfur analyzer (Germany), the sample is burned under high temperature and oxygen-rich conditions, and the carbon contained therein is oxidized to carbon dioxide. The generated gas enters the infrared detector along with the carrier gas, and the carbon content can be calculated by quantitatively analyzing the changes in the carbon dioxide signal.

[0058] In some embodiments, the active material includes a silicon-based material, and the mass percentage of silicon in the anode material is 20% to 55% based on the mass of the anode material. Further, the mass fraction of silicon can be 45% to 55%. This improves both the volumetric capacity of the anode material and mitigates the expansion problem of silicon during cycling. The mass of silicon can be obtained through the following steps: calcination in an oxygen atmosphere using a box-type atmosphere furnace (brand: Nanyang Xinyu, model: SA2-9-17TP) causes silicon and silicon suboxide in the sample to react to form silicon dioxide, and carbon is burned and discharged as carbon dioxide. The silicon content is then calculated by weighing.

[0059] In some embodiments, the active material may be, but is not limited to, silicon-based materials, metallic materials, doped atoms, etc. Silicon-based materials may be, but are not limited to, amorphous silicon (also known as amorphous silicon), crystalline silicon, silicon oxide, silicon alloys, composites of crystalline and amorphous silicon, etc. Metallic materials may be, but are not limited to, tin (Sn), germanium (Ge), titanium (Ti), zinc (Zn), aluminum (Al), and copper (Cu). Doped atoms may be, but are not limited to, nitrogen and phosphorus (P, red phosphorus).

[0060] In some embodiments, combining porous carbon with silicon-based materials, where the theoretical capacity of silicon-based materials is much higher than that of porous carbon, can improve the volumetric capacity of the anode material and mitigate the expansion problem of silicon-based materials during cycling, thus maintaining the stability of the anode material. Combining porous carbon with metallic materials can induce lithium (or sodium, potassium) to precipitate within the pores in alloy form, thereby increasing the lithium (or sodium, potassium) storage space of the porous carbon. Combining porous carbon with phosphorus can both improve conductivity and reduce the volume change of the anode material during discharge / charge.

[0061] In some embodiments, the average particle size of the active material is 0.1 nm to 50 nm. For example, the average particle size of the active material can be 0.1 nm, 0.5 nm, 1 nm, 3 nm, 5 nm, 8 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, or any value within the range of any two of the above values. By setting the average particle size of the active material, the mechanical stress during volume expansion of the active material can be reduced, allowing the secondary battery to maintain a better battery capacity and reducing irreversible capacity loss. It can also shorten the electron and ion transport paths. At the same time, the smaller size of the active material increases the gap between adjacent active materials, reserving space for volume expansion of the active material.

[0062] In some embodiments, the average particle size of the active material is further preferably 0.1 nm to 5 nm. For example, the average particle size of the active material can be 0.1 nm, 0.3 nm, 0.5 nm, 0.8 nm, 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, or any value within the range of any two of the above values.

[0063] In some embodiments, the morphology of the active substance includes one or more of the following: dot-like, spherical, ellipsoidal, and sheet-like.

[0064] In some embodiments, the purity of the active material is greater than 99%. Taking silicon-based materials as an example, high-purity silicon-based materials are more conducive to Li-Si alloying with lithium, thereby improving the cycle performance of lithium-ion batteries.

[0065] In some embodiments, the pore volume of the carbon matrix is ​​0.5 cm³, based on the mass of the carbon matrix. 3 / g~2.0cm 3 / g. For example, the pore volume of the carbon matrix can be 0.5 cm³. 3 / g, 0.8cm 3 / g, 1cm 3 / g, 1.5cm 3 / g, 1.8cm 3 / g、2cm 3 / g or any value within the range of any two of the above values. When the carbon matrix has abundant pores, these pores can accommodate active materials and allow space for the volume expansion of the active materials.

[0066] In some embodiments, the pore volume of the carbon matrix is ​​0.5 cm³. 3 / g to 1.4cm 3 / g. For example, the pore volume can be 0.5cm³. 3 / g, 0.8cm 3 / g, 1cm 3 / g, 1.2cm 3 / g, 1.4cm 3 / g or any value within the range of any two of the above values.

[0067] The negative electrode material after removing the active material (such as silicon-based material) is a carbon matrix. All test data for the carbon matrix in this application were obtained by testing the negative electrode material after removing the active material. Etching method: The negative electrode material was soaked in a 1M nitric acid solution for 4 hours. Then, a 20% HF acid solution was added dropwise to the negative electrode material, producing yellow fumes. This process was repeated until no more yellow fumes were produced in the solution. Finally, the residue was digested with a 1M nitric acid solution, and then washed and dried with distilled water to obtain the negative electrode material after removing the active material.

[0068] In some embodiments, the carbon matrix has pores, including micropores, wherein the volume percentage of micropores in the matrix is ​​greater than or equal to 70%, and the pore size of the micropores is less than 2 nm. For example, the volume percentage of micropores in the matrix can be 70%, 75%, 80%, 85%, 90%, 95%, 99%, or any value within a range of any two of the above values. Controlling the micropore percentage of the matrix within the above range can improve the loading of active material in the matrix and the uniformity of active material distribution, thereby improving the specific capacity and mechanical properties of the obtained anode material.

[0069] The active layer of the negative electrode material also includes a binder to bond the negative electrode active material particles, thereby facilitating the formation of the film layer and improving the bonding force between the active layer of the negative electrode material and the negative electrode current collector. In some embodiments, the binder may include, but is not limited to, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon, etc.

[0070] The active layer of the negative electrode material may further include a conductive material, which includes, but is not limited to, carbon-based materials, metal-based materials, conductive polymers, or any combination thereof. In some embodiments, carbon-based materials may include, but are not limited to, natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, metal-based materials may include, but are not limited to, metal powders or metal fibers, such as copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer may be a polyphenylene derivative.

[0071] Separating membrane

[0072] The separator 103 includes a membrane layer with a porous structure, and its material includes, but is not limited to, at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, the separator 103 may be a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane, etc.

[0073] electrolytes

[0074] The electrolyte serves to conduct ions between the positive and negative electrodes. The electrolyte can be in one or more states, such as gel, solid, and liquid. In some embodiments, the electrolyte is a liquid electrolyte solution. The liquid electrolyte solution conducts active ions between the positive and negative electrodes. In some embodiments, the liquid electrolyte solution includes lithium salt and organic solvent. The lithium salt may be selected from, but is not limited to, one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium perchlorate (LiClO4), lithium tetraphenylborate (LiB(C6H5)4), lithium methanesulfonate (LiCH3SO3), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethanesulfonyl)imide (LiN(SO2CF3)2), lithium tris(trifluoromethanesulfonyl)methyllithium (LiC(SO2CF3)3), lithium dioxolaneborate (LiBOB), and lithium difluorophosphate (LiPO2F2). For example, LiPF6 is selected as the lithium salt because it provides high ionic conductivity and improves cycling characteristics. The organic solvent may be a carbonate compound, a carboxylic acid ester compound, or an ether. Compounds, nitrile compounds, other organic solvents, or combinations thereof. Examples of carbonate compounds include, but are not limited to, diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, or combinations thereof.

[0075] Another embodiment of this application also provides a method for preparing a negative electrode material, including:

[0076] Step 1: Provide a matrix precursor and perform heat treatment on the matrix precursor in a mixed gas atmosphere. The mixed gas includes an inert gas and hydrogen. The inert gas includes one or more of nitrogen, helium, neon, argon, and krypton. The volume percentage of hydrogen in the mixed gas is less than 35%, thus obtaining the first intermediate.

[0077] Taking the preparation of a carbon matrix as an example, the matrix precursor can be a carbon material. The matrix precursor is heat-treated using a mixture of the aforementioned inert gas and hydrogen. Hydrogen has reducing properties and can combine with oxygen atoms in oxygen-containing groups to generate water (H₂O) or other compounds with low oxygen content. This reduction reaction helps to adjust the oxide layer on the material surface, improving the surface properties of the material. This reduces the oxygen content in the carbon matrix, thereby regulating the oxide layer content around the active material. Controlling the hydrogen content in the mixed gas within the aforementioned range is beneficial for obtaining P. x Anode materials that meet the preset range.

[0078] In some embodiments, the heat treatment temperature is from 400°C to 1000°C, and the time is from 0.5 h to 10 h. For example, the heat treatment temperature can be 400°C, 500°C, 600°C, 700°C, 800°C, 900°C, 1000°C, or any value within the range of any two of the above values. The heat treatment time can be 0.5 h, 1 h, 2 h, 3 h, 4 h, 6 h, 8 h, 10 h, or any value within the range of any two of the above values.

[0079] Step 2: Mix the first intermediate with the gaseous carrier of the active substance and heat it to deposit at least part of the active substance onto the first intermediate to obtain the second intermediate.

[0080] When the matrix precursor has pores, the corresponding first intermediate also has pores. Under heating conditions, the active material vapor carrier can partially deposit the active material within the pores of the first intermediate and partially adhere to its surface, thus obtaining the second intermediate. Simultaneously, to control the deposition reaction rate and reduce the risk of over-deposition, the content of the active material vapor carrier can be kept constant throughout the reaction process.

[0081] In some embodiments, "mixing the first intermediate with the active material gaseous carrier" further includes adding nitrogen and hydrogen for mixing. Adding nitrogen as an inert gas helps reduce the risk of oxidation of the active material gaseous carrier under heating conditions, while adding hydrogen helps to ensure uniform distribution of the active material gaseous carrier and reduce agglomeration of the active material, thereby contributing to improved density and uniformity of the active material deposition. To control the deposition reaction rate and reduce the risk of over-deposition, the hydrogen content can also be appropriately increased during the reaction process.

[0082] In some embodiments, the heating temperature is between 300°C and 800°C, and the heating time is between 2 hours and 15 hours. For example, the heating temperature can be 300°C, 400°C, 500°C, 600°C, 700°C, 800°C, or any value within the range of any two of the above values. The heating time can be 2 hours, 3 hours, 5 hours, 7 hours, 9 hours, 10 hours, 12 hours, 14 hours, 15 hours, or any value within the range of any two of the above values.

[0083] Step 3: Coating the second intermediate, including one or more of carbon coating, oxide coating, metal salt coating and polymer coating; carbon coating includes introducing carbon material and carrier gas, the carrier gas includes nitrogen, argon and hydrogen, and the volume percentage of hydrogen in the carrier gas is greater than or equal to 2%.

[0084] When carbon-coating the second intermediate, the aforementioned carrier gas is introduced along with the carbon material. This controls the reaction rate of the carbon material and slows down its decomposition, thereby improving the density and uniformity of the coating layer. Nitrogen in the carrier gas helps to isolate oxygen; hydrogen is also produced during the decomposition of the carbon material. Controlling the hydrogen concentration within the aforementioned range in the carrier gas slows down the gaseous decomposition rate of the carbon material, further improving the density and uniformity of the carbon coating layer. Argon in the carrier gas enhances the surface reaction of the material, promoting efficient deposition of the carbon coating layer. Higher density and better uniformity of the coating layer result in stronger protection of the second intermediate (i.e., the core). This effectively suppresses the reaction between silicon and water during the slurry preparation process and the reaction between silicon and the electrolyte during battery cycling, thus alleviating gas generation problems.

[0085] In some embodiments, the introduced carbon material includes one or more of gaseous carbon, liquid carbon, and solid carbon. Gaseous carbon may include one or more of methane, acetylene, ethylene, ethane, propane, propylene, benzene, toluene, xylene, ethanol, cyclohexane, methanol, and acetone; liquid carbon may include one or more of n-hexane, toluene, benzene, xylene, methanol, ethanol, propanol, butanol, pentanol, acetone, butanone, 2-pentanone, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, amyl acetate, and glycerol; solid carbon may include one or more of polyvinyl chloride, polyvinyl butyral, polyacrylonitrile, polyacrylic acid, polyethylene glycol, polypyrrole, polyaniline, sucrose, glucose, maltose, citric acid, asphalt, furfural resin, epoxy resin, and phenolic resin.

[0086] In another embodiment of this application, a method for preparing a negative electrode material is provided, including steps S10 to S30.

[0087] Step S10: Add active material to carbon matrix to obtain core.

[0088] In some embodiments, the carbon matrix is ​​porous carbon, with the active material filling the pores within the carbon matrix. This allows the carbon matrix to act as a supporting framework, while the porous carbon also possesses good electrical conductivity, ensuring excellent conductivity of the anode material. Specifically, porous carbon includes at least one of amorphous carbon, carbon nanotubes, carbon nanofibers, graphene, hard carbon, soft carbon, graphite, mesophase carbon microspheres, activated carbon, and carbon gel. The specific surface area of ​​the porous carbon is 1000 m². 2 / g~3000m 2 / g. In porous carbon, the total pore volume of all pores can be 0.5cm³. 3 / g~2.0cm 3 / g, with an average pore size of 0.1nm to 6.0nm. Among them, the pores of porous carbon include micropores, which account for more than 70% of the volume of the pores in the carbon matrix, and the pore size of the micropores is less than 2nm.

[0089] In some embodiments, the active material may be, but is not limited to, silicon-based materials, metallic materials, doped atoms, etc. Silicon-based materials may be, but are not limited to, amorphous silicon (also known as amorphous silicon), crystalline silicon, silicon oxide, silicon alloys, composites of crystalline and amorphous silicon, etc., and silicon oxide may be silicon monoxide (SiO), etc. Metallic materials may be, but are not limited to, Sn, Ge, Ti, Zn, Al, Cu. Doped atoms may be, but are not limited to, nitrogen and phosphorus (P, red phosphorus).

[0090] In some embodiments, combining porous carbon with silicon-based materials, where the theoretical capacity of silicon-based materials is much higher than that of porous carbon, can improve the volumetric capacity of the resulting anode material and mitigate the expansion problem of silicon-based materials during cycling, thus maintaining the stability of the anode material. Combining porous carbon with metallic materials can induce lithium (or sodium, potassium) to precipitate within the pores in alloy form, thereby increasing the lithium (or sodium, potassium) storage space of the porous carbon. Combining porous carbon with phosphorus can improve conductivity and reduce the volume change of the anode material during discharge and charge. Combining porous carbon with nitrogen can improve the conductivity of the anode material and also help improve its chemical stability.

[0091] In some embodiments, the average particle size of the silicon-based material is 0.1 nm to 50 nm. This allows the silicon nanostructure to remain stable during lithiation, mitigating the volume effect caused by expansion.

[0092] In some embodiments, when the active material is amorphous silicon, the core can be obtained by vapor deposition on porous carbon, and the vapor deposition step may include S11 to S13.

[0093] Step S11: Mix the silicon source gas with the first carrier gas. The carrier gas is used to dilute the concentration of the silicon source gas to ensure a suitable deposition reaction rate and to transport the silicon source gas into the reaction chamber. The volume percentage of the silicon source gas can be 15%, and the silicon source gas can be a silane with a high conversion rate, such as silane (SiH4) or silane (Si2H6). The first carrier gas can be nitrogen (N2) and hydrogen (H2); or, the first carrier gas can be argon (Ar) and hydrogen (H2); or, the first carrier gas can be nitrogen and argon; or, the first carrier gas can be nitrogen, argon, and hydrogen; or, the first carrier gas can be nitrogen; or, the first carrier gas can be argon. When the first carrier gas contains hydrogen, the volume percentage of hydrogen is 5% to 10% based on the total volume of the silicon source gas and the first carrier gas. Hydrogen, as a component of the first carrier gas, can slow down the cracking rate of the silicon source gas, which helps the silicon source gas to be evenly distributed in the reaction chamber, thereby enabling the silicon-based material to be uniformly deposited in the porous carbon, reducing the agglomeration of the silicon-based material, and improving the density of the silicon-based material deposition.

[0094] Step S12: The mixed gas is delivered into the heated reaction chamber at a flow rate of 1 L / min to 10 L / min. The gas flow rate must be stable and uniform during the delivery process. The temperature of the reaction chamber is controlled at 300℃ to 800℃. After reacting for 2 to 18 hours, proceed to the next step.

[0095] In some embodiments, before introducing the mixture of silicon source gas and carrier gas, the reaction chamber is repeatedly purged with nitrogen (3 to 5 times) to remove oxygen from the reaction chamber.

[0096] Step S13: Keep the volume percentage of silicon source gas constant at 15%, and increase the volume percentage of hydrogen gas to 15% to 25% to slow down the silicon source deposition reaction rate and ensure that the deposition is not excessive. After 1 to 3 hours of reaction, the deposition ends and porous carbon (core) filled with silicon-based material is obtained.

[0097] In other embodiments, when the active material is a metal such as Sn, Ge, Ti, Zn, Al, or Cu, the metal material can be filled into the pores of the porous carbon by electroplating. In other embodiments, when the active material is phosphorus, the porous carbon can be mixed evenly with elemental red phosphorus, dried, and then calcined in a sealed container, followed by further calcination in an inert atmosphere tube furnace to obtain phosphorus-doped porous carbon (i.e., the core).

[0098] Step S20: Place the core into the reaction chamber, introduce a mixed gas into the reaction chamber, and heat treat it at 700℃~750℃ for 1h~4h to form a carbon coating layer on the surface of the core.

[0099] The mixed gas comprises a second carrier gas and a carbon source gas, with the carbon source gas accounting for 10%–15% of the mixed gas by volume. The carbon source gas includes one or more of propylene, acetylene, methane, ethane, and propane. Under high-temperature conditions, the carbon source gas decomposes into carbon, thus forming a carbon coating layer on the surface of the core. The second carrier gas includes nitrogen, argon, and hydrogen. Nitrogen in the second carrier gas helps to isolate oxygen. Hydrogen is also produced during the decomposition of the aforementioned carbon source gas; therefore, hydrogen in the second carrier gas can slow down the decomposition rate of the carbon source gas, which is beneficial to improving the density and uniformity of the carbon coating layer. Argon in the second carrier gas can enhance the surface reaction of the material, thereby promoting the efficient deposition of the carbon coating layer. The higher the density and the better the uniformity of the coating layer, the stronger the protection of the core by the coating layer. This effectively suppresses the reaction between silicon and water during the slurry preparation process and also suppresses the reaction between silicon and the electrolyte during battery cycling, thus alleviating gas generation problems.

[0100] In some embodiments, based on the total volume of the second carrier gas, the volume ratio of hydrogen is 5% to 10%. Hydrogen as a second carrier gas component can slow down the cracking rate of the carbon source gas, which helps the carbon source gas to be evenly distributed in the reaction chamber, thereby improving the density and uniformity of the carbon coating layer in the negative electrode material.

[0101] In some embodiments, the volume ratio of nitrogen, argon and hydrogen in the second carrier gas may be 14:5:1.

[0102] In some embodiments, the heat treatment temperature may be 700°C, 710°C, 720°C, 730°C, 740°C, 750°C, or any value between any two adjacent values ​​mentioned above, and the heat treatment time may be 1 hour, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, or any value between any two adjacent values ​​mentioned above. For example, the heat treatment temperature may be 700°C and the time may be 4 hours; or, the heat treatment temperature may be 750°C and the time may be 1 hour.

[0103] In some embodiments, after the heat treatment is completed, the second carrier gas and carbon source gas are turned off, and nitrogen gas can be introduced into the reaction chamber to remove the remaining unreacted carbon source gas in the reaction chamber.

[0104] In some embodiments, the anode material preparation process is complete after a carbon coating layer is formed on the surface of the core. In other embodiments, after forming the carbon coating layer on the surface of the core, step S30 can be performed: forming an oxide coating layer on the surface of the carbon coating layer. Forming an oxide coating layer on the surface of the carbon coating layer can further improve the overall protective strength of the coating layer to a certain extent.

[0105] In some embodiments, the step of "forming an oxide coating layer on the surface of the carbon coating layer" further includes S31 to S33.

[0106] S31, Dissolve an inorganic metal salt in anhydrous ethanol to obtain a metal salt solution. The inorganic metal salt may be, but is not limited to, niobium pentachloride (NbCl5).

[0107] S32, disperse the core with carbon coating (i.e. the product obtained in step S20) in anhydrous ethanol to obtain a suspension.

[0108] S33, the metal salt solution and suspension are mixed and stirred, and hydrothermally reacted at 170℃~200℃ for 18h~20h. After filtration, washing and drying, a negative electrode material with niobium pentoxide (Nb2O5) oxide coating and carbon coating is obtained.

[0109] In some embodiments, the step of "forming an oxide coating layer on the surface of the carbon coating layer" further includes S301 to S304.

[0110] S301, an organometallic salt is dissolved in deionized water, and then a quaternary ammonium salt is added to obtain a first mixture. The organometallic salt may be, but is not limited to, isopropyl titanate and lithium acetate, and the quaternary ammonium salt may be, but is not limited to, hexadecyltrimethylammonium bromide (CTAB).

[0111] S302, a chelating agent and a core with a carbon coating (i.e., the product obtained in step S20) are added to the first mixture, and the mixture is stirred to obtain a second mixture. The chelating agent may be, but is not limited to, citric acid.

[0112] S303, the second mixture is stirred in a water bath at 60℃~80℃ for 10h~12h to obtain a slurry.

[0113] S304, the slurry is spray-dried to obtain lithium titanate (Li4Ti5O) 12 Anode materials with oxide coating and carbon coating.

[0114] The present application's solution will be explained below with reference to embodiments. Those skilled in the art will understand that the following examples are for illustrative purposes only and should not be construed as limiting the present application. Unless otherwise stated, reagents, software, and instruments involved in the following embodiments that are not specifically mentioned are all conventional commercially available products or open-source materials.

[0115] Example 1

[0116] A negative electrode material based on carbon matrix and silicon matrix, the preparation method of which includes:

[0117] S1, the porous carbon matrix (i.e., the matrix precursor) is placed in the reaction chamber and heated to 800°C under a nitrogen atmosphere. Then, the porous carbon is heat-treated for 2 hours with a first carrier gas, i.e., a mixture of nitrogen and hydrogen, to obtain the first intermediate. In the mixture, nitrogen:hydrogen (v:v) = 90:10.

[0118] S2, a mixture of silane, nitrogen and hydrogen (first carrier gas) is introduced into the heated chamber at a gas rate of 10 L / min. Nitrogen provides an inert atmosphere, and hydrogen is used to help the silane to be evenly distributed in the reaction chamber. The silane concentration is controlled at 15%, the temperature is raised to 520℃, and the reaction is carried out for 12 hours to obtain the second intermediate.

[0119] S3. After the obtained second intermediate is cooled to room temperature, a carrier gas containing nitrogen, argon and hydrogen is continuously introduced. The ratio of nitrogen:argon:hydrogen (v:v:v) in the carrier gas is 14:5:1. At the same time, methane gas with a concentration of 15% is introduced. The mixture is heat-treated at 700℃ for 4 hours. Then, the methane gas is turned off and nitrogen gas is introduced to cool the mixture to room temperature.

[0120] S4. The obtained sample is screened and graded to obtain the negative electrode material.

[0121] Example 2

[0122] The difference from Example 1 is that in S1, the nitrogen:hydrogen (v:v) ratio in the mixed gas is 85:15, and the heat treatment time is adjusted to 1 hour.

[0123] In S3, "simultaneously introduce methane gas at a concentration of 15%" is adjusted to "simultaneously use a bubbling device to vaporize xylene, adjust the concentration to 15%, and enter the reaction chamber together with the carrier gas". Correspondingly, after the heat treatment and heat preservation are completed, "turn off methane gas" is adjusted to "turn off the bubbling device".

[0124] Example 3

[0125] The difference from Example 1 is that in S1, the nitrogen:hydrogen (v:v) ratio in the mixed gas is 88:12, and the heat treatment time is adjusted to 3 hours.

[0126] S3 involves cooling the obtained second intermediate to room temperature, mixing the second intermediate and asphalt at a mass ratio of 50:15, and then placing the mixed material into a high-temperature box furnace, introducing the same carrier gas (nitrogen:argon:hydrogen (v:v:v) = 14:5:1), and heat-treating at 800℃ for 2 hours.

[0127] Example 4

[0128] The difference from Example 1 is that in S3, the carrier gas is adjusted to nitrogen:argon:hydrogen (v:v:v) = 10:5:5.

[0129] Example 5

[0130] The difference from Example 1 is that in S1, the nitrogen:hydrogen (v:v) ratio in the mixed gas is 95:5, and the heat treatment time is adjusted to 1 hour;

[0131] In S3, "simultaneously introduce methane gas at a concentration of 15%, heat treat at 700℃ for 4 hours, and then turn off the methane gas" is adjusted to "simultaneously introduce propylene gas at a concentration of 10%, heat treat at 750℃ for 1 hour, and then turn off the propylene gas".

[0132] A new step S3-1 is added after S3 to further coat the material obtained in S3 with a metal salt, including: adding 14.2g of isopropyl titanate and 1.98g of lithium acetate to deionized water, then adding 0.345g of cetyltrimethylammonium bromide (CTAB) and stirring to obtain mixture A; adding 2.89g of chelating agent citric acid to mixture A, adding 345g of the sample obtained in S3, and stirring for 1h to obtain suspension B; then transferring the mixed solution to a beaker and stirring in a water bath at 60℃ for 12h to obtain slurry C; spray drying slurry C to obtain the metal salt Li4Ti5O. 12 Covering material;

[0133] Finally, the negative electrode material is obtained through step S4.

[0134] Example 6

[0135] The difference from Example 1 is that in S3, the carrier gas is adjusted to nitrogen:argon:hydrogen (v:v) = 25:3:1, and the methane gas is simultaneously introduced at a concentration of 15%, and heat-treated at 700°C for 4 hours, and then the methane gas is turned off. This is changed to "the propylene gas is simultaneously introduced at a concentration of 10%, and heat-treated at 750°C for 1 hour, and then the propylene gas is turned off".

[0136] Example 7

[0137] The difference from Example 1 is that in S1, a porous carbon matrix (i.e., a matrix precursor) is placed in a reaction chamber to obtain a first intermediate. That is, the porous carbon is not heat-treated in S1.

[0138] Example 8

[0139] The difference from Example 1 is that in S1, the nitrogen:hydrogen (v:v) ratio in the mixed gas is 60:40.

[0140] Example 9

[0141] In step S10, the porous carbon matrix is ​​placed in the reaction chamber, which is then repeatedly purged with nitrogen (3-5 times). Next, silane (SiH4) and a first carrier gas are introduced into the reaction chamber at a flow rate of 10 L / min. The concentration of silane (by volume of all gases) is 15%, and the first carrier gas consists of nitrogen and hydrogen, with the hydrogen concentration (by volume of all gases) being 10%. The temperature is then raised to 520°C, and the reaction is carried out for 12 hours. Then, while maintaining the silane volume percentage at 15%, the hydrogen volume percentage is increased to 25%, and the reaction is continued for 3 hours until deposition is complete, yielding the core.

[0142] S20: After the core has cooled to room temperature, a second carrier gas (nitrogen:argon:hydrogen = 14:5:1, i.e., hydrogen accounts for 5% of the volume in the second carrier gas) and propylene gas are introduced into the reaction chamber. The concentration of propylene (by volume percentage of all gases) is 15%. The chamber is then heat-treated at 700℃ for 4 hours. Subsequently, the propylene gas is shut off, and nitrogen is introduced to remove any remaining propylene from the reaction chamber. The chamber is then cooled to room temperature. The obtained sample is sieved and graded to obtain the negative electrode material.

[0143] The scanning electron microscope image of the negative electrode material in Example 9 is shown in Figure 3. As can be seen from Figure 3, the negative electrode material is a micron-sized powder.

[0144] X-ray diffraction (XRD) was used to test the anode material to identify the type of silicon through diffraction peaks. As shown in Figure 4, the amorphous silicon material exhibited a characteristic peak at 2θ = 28.4 ± 0.3°, indicating that the active material filling the core included amorphous silicon.

[0145] Example 10

[0146] The difference from Example 9 is that in S10, the concentration of hydrogen (by volume percentage of all gases) is maintained at 10%, and the deposition ends after 15 hours of reaction, yielding the core.

[0147] Example 11

[0148] The difference from Example 9 is that after S20, there is an additional S30 step. 30g of NbCl5 is dissolved in 1000mL of anhydrous ethanol and magnetically stirred for 30min to obtain a metal salt solution. 70g of the carbon-coated core (i.e., the product obtained in step S20) is dispersed in 1000mL of anhydrous ethanol and magnetically stirred for 30min to obtain a suspension. The metal salt solution and suspension are mixed and stirred at room temperature for 1h, followed by a hydrothermal reaction at 170℃ for 20h to coat with Nb2O5 oxide. The reaction system is filtered and washed with anhydrous ethanol, then dried in a vacuum oven at 80℃. The obtained sample is sieved and graded to obtain the negative electrode material.

[0149] Example 12

[0150] The difference from Example 9 is that after S20, there is an additional S30 step, in which 14.2g of isopropyl titanate (organometallic salt) and 1.98g of lithium acetate (organometallic salt) are added to deionized water, followed by 0.345g of CTAB (quaternary ammonium salt), and the mixture is stirred to obtain a first mixture. 2.89g of citric acid (chelating agent) and 345g of a carbon-coated core (i.e., the product obtained in step S20) are added to the first mixture, and the mixture is stirred for 1 hour to obtain a second mixture. The second mixture is then stirred in a water bath at 60°C for 12 hours to obtain a slurry. The slurry is spray-dried to obtain Li4Ti5O. 12 Coating layer. The obtained sample is sieved and graded to obtain the aforementioned negative electrode material.

[0151] Example 13

[0152] The difference from Example 9 is that in S20, a second carrier gas (nitrogen:argon:hydrogen = 13:5:2, that is, the volume percentage of hydrogen in the second carrier gas is 10%) and propylene gas are introduced into the reaction chamber, and the concentration of propylene (the volume percentage of all gases) is 15%.

[0153] Example 14

[0154] The difference from Example 9 is that in S20, a second carrier gas (nitrogen:argon:hydrogen = 13.5:5:1.5, that is, the volume percentage of hydrogen in the second carrier gas is 7.5%) and propylene gas are introduced into the reaction chamber, and the concentration of propylene (the volume percentage of all gases) is 15%.

[0155] Comparative Example 1

[0156] The difference from Example 2 is that in S3, the carrier gas is adjusted to contain only nitrogen.

[0157] Comparative Example 2

[0158] The difference from Example 3 is that in S1, a porous carbon matrix (i.e., matrix precursor) is placed in a reaction chamber to obtain a first intermediate; that is, the porous carbon is not heat-treated in S1.

[0159] In S3, the carrier gas is adjusted to nitrogen:argon:hydrogen (v:v:v) = 50:2:1.

[0160] Comparative Example 3

[0161] The difference from Example 3 is that in S1, the mixed gas is adjusted to 60% nitrogen and 40% hydrogen;

[0162] In S3, the carrier gas is adjusted to nitrogen:argon:hydrogen = 50:2:1.

[0163] Comparative Example 4

[0164] The difference from Example 9 is that in S20, the heat preservation time is 1 hour.

[0165] Comparative Example 5

[0166] The difference from Example 9 is that in S20, a second carrier gas (nitrogen:argon:hydrogen = 12:5:3, that is, hydrogen accounts for 15% of the volume in the second carrier gas) and propylene gas are introduced into the reaction chamber, and the concentration of propylene (accounting for 15% of the total volume of all gases) is 15%.

[0167] Comparative Example 6

[0168] The difference from Example 9 is that in S20, a second carrier gas (nitrogen:argon:hydrogen = 13.5:5:0.5, that is, hydrogen accounts for 2.6% of the volume in the second carrier gas) and propylene gas are introduced into the reaction chamber, and the concentration of propylene (as a percentage of the total volume of all gases) is 15%.

[0169] Comparative Example 7

[0170] The difference from Example 9 is that in S20, no second carrier gas is introduced.

[0171] Comparative Example 8

[0172] The difference from Example 9 is that in S20, the second carrier gas introduced is nitrogen.

[0173] Comparative Example 9

[0174] The difference from Example 9 is that in S20, the second carrier gas introduced is a mixture of nitrogen and argon (nitrogen:argon = 15:5).

[0175] The physical, chemical, and electrochemical properties of the anode materials obtained in the above embodiments and comparative examples were tested using the following methods:

[0176] 1. Test methods for specific surface area, pore volume, and proportion of materials:

[0177] The measurement was performed according to GB / T 19587-2004 "Determination of Specific Surface Area of ​​Solid Materials by Gas Adsorption BET Method" or the equipment manual. The TriStar 3000 & 3020 equipment from Micron Technology (USA) and the BET pore size distribution test method were used. The pore size distribution data of the material was obtained through DFT simulation analysis using the isothermal adsorption characteristic curve of nitrogen gas, and then the specific surface area, average pore size, and the proportion of each pore volume of micropores, mesopores, and macropores in the total pore volume were obtained. The method for removing silicon-based materials from the negative electrode material was as follows: the negative electrode material was soaked in 1M concentrated nitric acid for 4 hours, and then 20% HF acid solution was added dropwise to the negative electrode material, producing yellow fumes. This was repeated several times until no more yellow fumes were produced in the solution. Finally, the residue was digested with 1M concentrated nitric acid, and then washed and dried to obtain the negative electrode material after removing the silicon-based material. In this application, the material from which the silicon-based material was removed in the negative electrode material can be considered to be a carbon matrix.

[0178] 2. Test method for median particle size of negative electrode materials:

[0179] The particle size distribution range of the negative electrode material was tested using a Malvern laser particle size analyzer (Mastersizer 3000). The cumulative particle size distribution based on volume was determined by laser diffraction. D10 represents the particle size corresponding to a cumulative particle size distribution percentage of 10%, D50 represents the particle size corresponding to a cumulative particle size distribution percentage of 50%, and D90 represents the particle size corresponding to a cumulative particle size distribution percentage of 90%. Thus, the particle size distribution of the negative electrode material (D90-D10) / D50 can be obtained.

[0180] 3. Average thickness of the coating layer:

[0181] The material was cross-sectioned using a FIB-SEM device. Ten particles were randomly selected from the SEM, and the coating thickness of each particle was measured three times to calculate the average coating thickness.

[0182] 4. Powder resistivity test:

[0183] A four-probe method was used to determine the volume resistivity of the sample. The MCP-PD51 powder conductivity meter from Mitsubishi Chemicals (Japan) was used to measure the conductivity of the powder at five pressure points: 4 kN, 8 kN, 12 kN, 16 kN, and 20 kN. The resistivity of the powder was then automatically calculated by a computer.

[0184] 5. Method for testing the mass content of carbon: The sample is burned under high temperature and oxygen-rich conditions. The carbon is oxidized into carbon dioxide. The generated gas enters the infrared detector with the carrier gas. The carbon content can be calculated by quantitatively analyzing the changes in the carbon dioxide signal.

[0185] 6. Method for testing the mass content of silicon: The sample was burned in an oxygen atmosphere using a Nanyang Xinyu SA2-9-17TP box-type atmosphere furnace. The silicon in the sample reacted to form silicon dioxide, and the carbon was burned and discharged as carbon dioxide. The silicon content was then calculated by weighing.

[0186] 7. Average particle size of active material:

[0187] The active materials in the negative electrode material are observed by field emission scanning electron microscopy or transmission electron microscopy. The particle size of 10 active materials is directly measured by scale bar, and the average particle size is taken as the final average particle size of the active materials.

[0188] 8. Gas production test method:

[0189] a) Put 5g of negative electrode material into a sealed container and add deionized water until the remaining volume at the top of the container is 60mL.

[0190] b) Seal the container, mix well, and store at room temperature for one day;

[0191] c) After 24 hours, shake the container thoroughly again to disperse the precipitate into the liquid.

[0192] d) Open the container lid, use a hydrogen detector to measure the hydrogen concentration, and convert it to cc / (kg·day).

[0193] 9. Coating Strength γ Test: The protective strength of the coating layer was characterized using thermogravimetric analysis (TG) under an oxygen atmosphere, with a test temperature range of 25℃ to 1200℃. The initial temperature T0 of the first mass increase was obtained from the TG curve, and the γ value of each negative electrode material was obtained using the formula "γ = 0.0129T0 - 0.323". Figures 5-7 show the thermogravimetric analysis curves of Examples 12, 14, and Comparative Example 4. T0 was determined through the following steps: smoothing and baseline correction of the TG curve to eliminate noise and systematic errors; identifying the plateau segment with a mass change rate ≤ 0.01% / ℃, and fitting a straight line (tangent to the plateau segment, slope ≈ 0) at the last 5-10℃ data points; identifying the first weight gain interval after the plateau segment, and fitting a straight line (tangent to the weight gain segment, slope ≈ 0) at the initial weight gain (mass increase ≤ 5%) at 5-10℃ data points; the temperature corresponding to the intersection of the two tangents is T0. The test needs to be repeated 3 times, and the average value (deviation ≤ 3℃) is taken to ensure reliability.

[0194] 10. Percentage of oxygen content (P) at different depths xTesting: X-ray photoelectron spectroscopy (XPS) of the anode material was performed using a Thermo Scientific K-Alpha instrument. The entire testing process was conducted in an argon-filled glove box. Each spectral acquisition required fine-spectrum analysis of C, O, and Si elements. The argon ion sputtering depth was set to 20 nm per cycle, with 3–8 sputtering passes. In this application, the depth of the first sputtering pass is defined as 20 nm, the second as 40 nm, and so on. The above tests were repeated on any 20 different regions at the same depth of the anode material, and the average value was taken as the percentage of oxygen atoms (P) at that depth. x .

[0195] 11. Electrochemical performance testing:

[0196] a) The negative electrode material was mixed with sodium carboxymethyl cellulose, styrene-butadiene rubber, conductive graphite (KS-6) and carbon black (SP) in a ratio of 92:2:2:2:2 to form a slurry. The slurry was uniformly coated on copper foil and dried to form a negative electrode sheet. The negative electrode sheet was assembled into a button cell in an argon atmosphere glove box. The separator used was a polypropylene microporous membrane. The electrolyte used was 1 mol / L lithium hexafluorophosphate (the solvent was a mixed slurry of ethylene carbonate, methyl ethyl carbonate and dimethyl carbonate, wherein the volume ratio of ethylene carbonate, methyl ethyl carbonate and dimethyl carbonate was 1:1:1). The counter electrode used was a lithium metal sheet.

[0197] b) Perform charge-discharge cycles on a battery programmable tester. The test conditions for the first discharge specific capacity and first coulombic efficiency are as follows: charge-discharge rate of 0.1C, voltage range of 0.01V to 1.5V; calculate the average value C of the first charge capacity of the four coin cells. (cha) The unit is the average value of milliampere-hours (mAh) and the initial discharge capacity, C. (dis) The unit is milliampere-hours (mAh); calculate the initial charge specific capacity Q of the sample. (cha) Initial discharge specific capacity Q (dis) The initial coulomb efficiency E, where Q (cha) =C (cha) / m、Q (dis) =C (dis) / m、E=Q (dis) / Q (cha) ×100%, where m is the mass of the active substance in grams (g).

[0198] c) Each battery was subjected to cycle performance testing on the Blue Electric CT2001A battery testing system. The test steps for 100-cycle capacity retention are as follows: (1) Rest for 6 hours; (2) 0.1C constant current discharge to 0.01V, constant voltage discharge to 0.05C; (3) Rest for 30 minutes; (4) 0.1C constant current charge to 1.5V; (5) Rest for 30 minutes; (6) 0.1C constant current discharge to 0.01V, constant voltage discharge to 0.05C; (7) Rest at 25℃ for 180 minutes; (8) 1C constant current charge to 1.5V; (9) Rest for 60 minutes; (10) 1C constant current discharge to 0.01V, constant voltage discharge to 0.05C; (11) Rest for 30 minutes; (12) Repeat steps (8) to (11) 100 times, then stop the test. Wherein, the 100-cycle capacity retention rate = discharge capacity after 100 cycles / discharge capacity in the first cycle.

[0199] 12. Expansion Rate Test: The coin cell battery was subjected to 50 repeated charge-discharge cycles at a current density of 1C within a charge-discharge range of 0.01V to 1.5V. The electrode was then observed using a scanning electron microscope (SEM), and the average particle size of the silicon-based material before lithium intercalation was obtained as D1 according to the corresponding scale. After charge-discharge cycles, the coin cell battery was disassembled, the electrode was cleaned with a DEC, and the electrode was observed using a scanning electron microscope (SEM). The average particle size of the silicon-based material after lithium intercalation was obtained as D2 according to the corresponding scale. If the silicon-based material is considered as a quasi-spherical structure, then the expansion rate is (D2-D1) / D1.

[0200] The test results are shown in Tables 1 and 2.

[0201] Table 1. Test results of physical and chemical properties of the negative electrode materials of the embodiments and comparative examples of this application.

[0202] Table 2. Electrochemical performance test results of the negative electrode materials of the embodiments and comparative examples of this application.

[0203] As shown in Tables 1 and 2, the coating strength γ of the negative electrode material in this application embodiment satisfies: 4≤γ≤9, its 50-week expansion rate is less than 70.5%, and its 24-hour gas production is less than 15cc / (kg·day), which significantly improves the stability of the battery. In addition, the initial discharge specific capacity of the negative electrode material is higher than 1750mAh / g, and the initial coulombic efficiency is higher than 85%, which is beneficial to improving the capacity of the secondary battery using this negative electrode material.

[0204] In addition, the coating protection strength γ and oxygen percentage content P of the negative electrode materials in Examples 1-6 of this application are... x Both satisfy 4≤γ≤9 and 2%≤P x≤8%, these negative electrode materials, as measured, also exhibit significantly lower gas production values. When applied to coin cells, these negative electrode materials also show significantly lower expansion rates, and the coin cells all demonstrate significantly higher initial specific capacity and initial coulombic efficiency. This indicates that when the protective strength γ of the coating layer meets the preset range, the coating layer has good density, thickness, and uniformity. The silicon-based material in the coated core is not easily exposed, nor is it easy for it to seep out through the coating layer and react with external substances (such as slurry or electrolyte), thus helping to reduce gas production in the negative electrode material and improve the electrochemical performance of the secondary battery. Furthermore, when the oxygen percentage P... x When the preset range is met, the corresponding oxide layer can provide protection for silicon-based materials, which is beneficial to reducing the gas production value and expansion rate of the negative electrode material.

[0205] Compared to Example 1, Example 7, due to the absence of heat treatment on the porous carbon matrix, has a higher percentage of oxygen in its matrix, resulting in a higher P content in the obtained negative electrode material. x If the concentration is too high, there will be a large amount of oxide layer around the silicon-based material. During charge-discharge cycles, the silicon oxide in the oxide layer will form lithium silicate compounds. This part of lithium cannot participate in the reversible reaction, resulting in relatively low initial coulombic efficiency and reversible capacity of the resulting coin cell.

[0206] Compared to Example 1, in Example 8, the hydrogen content in the mixed gas was too high during the heat treatment of the porous carbon matrix, resulting in a lower percentage of oxygen in the matrix and consequently lower P content in the resulting negative electrode material. x If the temperature is too low, there will be less oxide layer around the silicon-based material, which will significantly reduce the protective effect on the silicon-based material, resulting in severe gas generation and a severe expansion rate, thus affecting the electrochemical performance of the resulting coin cell.

[0207] The test results from Examples 1 and 7-8 also show that the negative electrode materials obtained in Examples 7-8 contain not only P x The protective strength γ of its coating layer is also lower than that of Example 1, indicating that P x Exceeding the preset range (too high or too low) will also have a certain adverse effect on the protective strength γ of the negative electrode material coating layer. Controlling P x Within a preset range, negative electrode materials with γ that meet the preset range can be obtained more efficiently, while simultaneously improving the undesirable phenomena of gas generation and expansion of negative electrode materials, thereby improving the electrochemical performance of coin cells.

[0208] As can be seen from the preparation methods and test results of Examples 9 to 14, the coating layer of Examples 9 to 12 has an enhanced protective strength γ (4 or more, which is greater than the protective strength γ of the comparative example), which makes the gas production of the negative electrode material less than 10cc / (kg·day), which is much lower than the gas production of the negative electrode material in the comparative example, and significantly improves the stability of the battery.

[0209] As can be seen from Examples 9 and 10, since silicon is deposited in a single step in step S10 of Example 10, the deposition effect is slightly worse than the stepwise deposition in Example 9. Therefore, the protective strength γ of the coating layer in Example 10 is slightly lower than that in Example 9. As can be seen from Examples 9 and 11-12, since the coating layers in Examples 11-12 include not only a carbon coating layer but also an oxide coating layer (Nb2O5 coating layer or Li4Ti5O)... 12 The coating layer is denser, therefore the protective strength γ of Examples 11 and 12 is higher than that of Example 9. As can be seen from Examples 9 and Examples 13-14, when the proportion of hydrogen in the second carrier gas is higher, the protective strength γ of the coating layer is not significantly different.

[0210] Compared to Example 2, in Comparative Example 1, the carrier gas only contained nitrogen and lacked hydrogen and argon during carbon coating. The carbon material used for carbon coating will generate hydrogen during high-temperature pyrolysis. Due to the lack of hydrogen in the reaction environment, it is difficult to control the pyrolysis rate of the carbon material, resulting in a decrease in the density and uniformity of the carbon coating layer. Furthermore, due to the lack of argon, the surface reactivity of the material is also reduced, resulting in a poor carbon coating effect. Consequently, the protective strength γ of the coating layer of the obtained negative electrode material is low, making the silicon-based material more easily exposed to direct contact with external substances, or more likely to penetrate the coating layer and contact with external substances when it falls off. This leads to instability of the negative electrode material, severe gas generation during the reaction, and thus seriously reduces the electrochemical performance of the secondary battery.

[0211] Compared to Example 3, Comparative Example 2 did not involve heat treatment of the porous carbon matrix, while Comparative Example 3 involved heat treatment of the porous carbon matrix with excessively high hydrogen content in the mixed gas, resulting in a decrease in P in Comparative Example 2. x Excessively high and comparative example 3 P x Too low. Furthermore, both Comparative Examples 2 and 3 reduced the proportion of hydrogen in the carrier gas during the carbon coating process. Insufficient hydrogen content made it difficult to control the cracking rate of the carbon material, resulting in a decrease in the density and uniformity of the carbon coating layer. The protective strength γ of the coating layer of the formed negative electrode material was also too low, ultimately leading to severe gas generation behavior and expansion of the material, which seriously reduced the initial specific capacity and initial coulombic efficiency of the obtained coin cell.

[0212] Compared to Example 9, the coating time in Comparative Example 4 was insufficient, the protective strength γ value of the coating layer was significantly lower than that of the negative electrode material in Example 9, the gas production was significantly increased, and the electrical performance of the battery was significantly worse than that of Example 9.

[0213] As can be seen from Example 9 and Comparative Example 5, when the proportion of hydrogen in the second carrier gas is too high, the coating layer is less effective, and the protection strength γ of Comparative Example 5 is much lower than that of Example 9.

[0214] As can be seen from Example 9 and Comparative Example 6, when the proportion of hydrogen in the second carrier gas is too low, the effect of the coating layer is also poor. The protection strength γ of Comparative Example 6 is much lower than the protection strength γ of Example 9.

[0215] Compared to Example 9, no second carrier gas was introduced in Comparative Example 7, which affected the density and uniformity of the coating layer. Therefore, the γ value was significantly lower than that of Example 1 and also lower than that of other comparative examples.

[0216] As can be seen from Example 9 and Comparative Example 8, since the second carrier gas in Comparative Example 8 is only nitrogen, the γ value of Comparative Example 8 is significantly lower than that of Example 9, but slightly higher than that of Comparative Example 4.

[0217] As can be seen from Example 9 and Comparative Example 9, the second carrier gas in Comparative Example 9 contains nitrogen and argon, and its γ value is significantly lower than that of Example 9, but slightly higher than that of Comparative Example 8.

[0218] The above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to the above preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of this application should not depart from the spirit and scope of the technical solutions of this application.

Claims

1. A negative electrode material, characterized in that, The anode material comprises a core and a coating layer. The core includes a matrix and an active material. The matrix includes a carbon matrix. The coating layer is located on at least a portion of the surface of the core. The protective strength of the coating layer is γ, where γ = 0.0129T0 - 0.323, 4 ≤ γ ≤ 9, T0 is the initial temperature at which the mass of the anode material increases during thermogravimetric analysis, and the thermogravimetric analysis is conducted in an oxygen atmosphere.

2. The negative electrode material as described in claim 1, characterized in that, The negative electrode material also includes oxygen, and the atomic percentage content of oxygen at any point X, on the surface of the negative electrode material, is defined as P. x The negative electrode material satisfies at least one of the following conditions: 60nm ≤ X ≤ 160nm (1)2％≤P x ≤8％； (2)P x The value is any value within the range of 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, or any two of the above values. (3) Along the surface of the negative electrode material pointing towards the interior of the negative electrode material, the P x It shows a trend of first decreasing and then increasing.

3. The negative electrode material as described in claim 1, characterized in that, The protection strength γ is any value within the range of 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, or any two of the above values.

4. The negative electrode material as described in claim 2, characterized in that, The carbon matrix satisfies at least one of the following conditions: (1) The specific surface area of ​​the carbon matrix is ​​800 m². 2 / g to 3000m 2 / g; (2) The carbon matrix has pores, and the total pore volume of the carbon matrix is ​​0.5 cm³. 3 / g to 2.0cm 3 / g; (3) The carbon matrix has pores, and the porosity of the carbon matrix is ​​40% to 80%.

5. The negative electrode material as described in claim 2, characterized in that, The negative electrode material satisfies at least one of the following conditions: (1) The average particle size of the active substance is 0.1 nm to 100 nm; (2) The average thickness of the coating layer is 1 nm to 60 nm; (3) The coating layer includes one or more of the following: carbon materials, metal oxides, amorphous silicon, conductive polymers, fluorides, phosphates, and nitrides; (4) Based on the mass of the negative electrode material, the mass percentage of the coating layer is less than or equal to 10%; (5) The median particle size D50 of the negative electrode material is 3 μm to 15 μm; (6) The specific surface area of ​​the negative electrode material is 1m². 2 / g to 10m 2 / g.

6. The negative electrode material as described in claim 1 or 2, characterized in that, The negative electrode material satisfies at least one of the following conditions: (1) The carbon matrix includes one or more of hard carbon, soft carbon, graphite, carbon nanotubes, carbon fibers, and graphene; (2) The carbon matrix includes one or more of the following: artificial graphite, natural graphite, amorphous carbon, activated carbon, mesophase carbon microspheres, carbon nanotubes, carbon nanofibers, and graphene.

7. The negative electrode material as described in claim 2, characterized in that, The active material includes one or more of silicon-based materials, Li, Na, K, Sn, Ge, Fe, Mg, Ti, Zn, Al, P, and Cu; The silicon-based material includes one or more of amorphous silicon, crystalline silicon, silicon oxide, silicon alloy, and composites of crystalline and amorphous silicon.

8. The negative electrode material as described in claim 2, characterized in that, The active material includes a silicon-based material, the coating layer includes a carbon coating layer, and the anode material further satisfies at least one of the following conditions: (1) Based on the mass of the negative electrode material, the mass percentage of silicon in the negative electrode material is 20% to 65%; (2) Based on the mass of the negative electrode material, the mass percentage of silicon in the negative electrode material is 45% to 55%; (3) Based on the mass of the negative electrode material, the mass percentage of carbon in the negative electrode material is 30% to 60%; (4) Based on the mass of the negative electrode material, the mass percentage of carbon in the negative electrode material is 45% to 55%.

9. The negative electrode material as described in claim 1, characterized in that, The negative electrode material satisfies at least one of the following conditions: (1) The coating layer includes a carbon coating layer; (2) The coating layer includes a carbon coating layer, and also includes one or more of oxide coating layers, metal salt coating layers, and polymer coating layers; (3) The average thickness of the coating layer is 5nm to 500nm.

10. The negative electrode material as described in claim 1, characterized in that, The negative electrode material satisfies at least one of the following conditions: (1) Based on the mass of the negative electrode material, the mass percentage of carbon in the negative electrode material is 40% to 60%; (2) The active material includes silicon-based materials, and the mass percentage of silicon in the negative electrode material is 20% to 55% based on the mass of the negative electrode material.

11. The negative electrode material as described in claim 1, characterized in that, The negative electrode material satisfies at least one of the following conditions: (1) The active material includes one or more of silicon-based materials, metallic materials, and doped atoms; (2) The active material includes silicon-based materials, which include one or more of amorphous silicon, crystalline silicon, silicon oxide, silicon alloy, and composites of crystalline silicon and amorphous silicon, and the average particle size of the silicon-based material is 0.1 nm to 50 nm. (3) The active substance includes a metallic material, which includes one or more of tin, germanium, titanium, zinc, aluminum, and copper; (4) The active material includes doped atoms, and the doped atoms include one or more of nitrogen and phosphorus.

12. The negative electrode material as described in claim 1, characterized in that, The negative electrode material satisfies at least one of the following conditions: (1) Based on the mass of the carbon matrix, the pore volume of the carbon matrix is ​​0.5 cm³. 3 / g~2.0cm 3 / g; (2) The carbon matrix has pores, including micropores, wherein the volume percentage of the micropores in the pores of the carbon matrix is ​​greater than or equal to 70%, and the pore diameter of the micropores is less than 2 nm.

13. The negative electrode material as described in claim 1, characterized in that, The resistivity of the negative electrode material is 0.9 Ω·m to 1.3 Ω·m.

14. A negative electrode sheet, comprising a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, characterized in that, The negative electrode active material layer comprises the negative electrode material as described in any one of claims 1 to 13.

15. A secondary battery, characterized in that, Includes the negative electrode as described in claim 14.

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