Negative electrode material and battery

Abstract

The application provides a negative electrode material and a battery, the negative electrode material comprising a silicon-based active substance and a carbon material on at least part of the surface of the silicon-based active substance, the silicon-based active substance comprising silicon, oxygen and a metal M element; the thermal conductivity of the negative electrode material at 373.15K is g1 W / (m·K), the thermal conductivity of the negative electrode material at 873.15K is g2 W / (m·K), the variation coefficient of the thermal conductivity of the negative electrode material is σ=(1-g1 / g2) 2 / 0.57, 0.80<σ<1.50; the surface doping degree of the negative electrode material is β, 2<β<10. The negative electrode material has excellent initial coulombic efficiency and specific capacity, and can improve the cycle capacity retention rate under low-temperature and high-temperature conditions.

Description

Technical Field

[0001] This application relates to the technical field of anode materials, and more specifically, to anode materials and batteries. Background Art

[0002] Electrified new energy vehicles are the future development direction of the automotive market, and their core component is the lithium-ion battery. With the development of the market, the demand for high-capacity-density batteries is increasing. Adopting new high-specific-capacity anode and cathode materials is one of the important methods to improve the energy density of the battery.

[0003] Silicon-based anode materials are considered as the next-generation anode materials. Their ultra-high theoretical specific capacity (4200 mAh / g), relatively low de-lithiation potential (<0.5 V), and the voltage plateau of silicon being slightly higher than that of graphite, which is difficult to cause surface lithium deposition during charging and has better safety performance, have made them highly praised. However, silicon anodes have a severe volume expansion effect during cycling, resulting in material pulverization, fragmentation, and rapid cycle attenuation of the battery.

[0004] Silicon oxide (general formula SiO x , 0 < x ≤ 2) has a specific capacity several times that of graphite (about 1500 mAh / g). The reversible lithiation products formed by the reaction of SiO x with lithium during charging, such as lithium-silicon alloys, are dispersed in an inert matrix such as SiO2, irreversible lithiation products (lithium oxide, lithium silicate, etc.), thus significantly improving the volume expansion and cycle life characteristics of silicon materials. However, the initial Coulombic efficiency (ICE) of SiO x is relatively low. When assembled into a lithium-ion battery, it will consume more active lithium ions, resulting in an increase in manufacturing costs.

[0005] In addition, during the application of anode materials, silicon oxide is usually mixed with graphite anode materials in a certain proportion and used together as the anode active material of the anode electrode. Due to the huge difference in the thermal conductivity between silicon oxide materials and graphite, the heat generated by silicon oxide materials during charge and discharge is difficult to disperse quickly. The formation of temperature differences between silicon oxide material particles and between silicon oxide and graphite hinders the transport of lithium ions, leading to an exacerbation of the capacity attenuation of the anode material. Summary of the Invention

[0006] This application proposes an anode material and a battery. The anode material has an appropriate degree of surface doping, a reduced disordered structure on the surface of the anode material, an improved degree of crystallization within the anode material particles, and excellent thermal conductivity. It can quickly conduct the heat generated during charge and discharge at different temperatures, improve the capacity attenuation of the anode material, enabling the anode material to have excellent initial Coulombic efficiency and specific capacity while also improving the cycle capacity retention rate under low-temperature and high-temperature conditions.

[0007] In a first aspect, this application provides a negative electrode material, the negative electrode material comprising a silicon-based active material and a carbon material located on at least a portion of the surface of the silicon-based active material, the silicon-based active material comprising silicon, oxygen, and metal M;

[0008] The thermal conductivity of the negative electrode material is g1 W / (m·K) at 373.15K and g2 W / (m·K) at 873.15K. The coefficient of change of thermal conductivity of the negative electrode material is σ=(1-g1 / g2). 2 / 0.57, 0.80 < σ < 1.50;

[0009] The surface doping degree of the negative electrode material is β, where 2 < β < 10; wherein, the surface doping degree of the negative electrode material is measured by the following method:

[0010] The mass ratio of oxygen to metal M in the negative electrode material was determined by X-ray photoelectron spectroscopy as A, and by ONH elemental analyzer and ICP spectrometer as B, with β = A / B.

[0011] In some implementations, 0.15 ≤ g1 ≤ 0.4.

[0012] In some implementations, 0.5 ≤ g2 ≤ 2.5.

[0013] In some implementations, 5 ≤ A ≤ 40.

[0014] In some implementations, 2 ≤ B ≤ 5.

[0015] In some embodiments, the metal element M is selected from at least one of Li, Mg, Al, Ca, and Zn.

[0016] In some embodiments, the mass percentage of metallic element M in the negative electrode material is 6% to 15%.

[0017] In some embodiments, the metal element M exists in the negative electrode material in at least one of the silicates of M and oxides of M.

[0018] In some embodiments, the average particle strength of the negative electrode material is >200 MPa.

[0019] In some embodiments, the negative electrode material contains Si grains, and in the X-ray diffraction pattern of the negative electrode material, the size of the Si grains on the (220) crystal plane is 5 nm to 12 nm.

[0020] In some embodiments, when the cumulative particle size distribution of the negative electrode material reaches 50%, the corresponding particle size Dn(50) is 0.3μm to 3μm.

[0021] In some embodiments, the silicon-based active material includes at least one of elemental silicon, silicon oxide, and silicon alloy.

[0022] In some embodiments, the silicon-based active material comprises silicon oxide, the general chemical formula of which is SiO. x , 0 < x ≤ 2.

[0023] In some embodiments, the carbon content in the negative electrode material is 2% to 8% by mass.

[0024] In some embodiments, the carbon material includes at least one of graphite, graphene, amorphous carbon, carbon nanotubes, and carbon fibers.

[0025] In some embodiments, the carbon material forms a carbon layer on at least a portion of the surface of the silicon-based active material, the thickness of the carbon layer being 10 nm to 300 nm.

[0026] In some embodiments, the specific surface area of ​​the negative electrode material is ≤10m². 2 / g.

[0027] In some embodiments, the tap density of the negative electrode material is 0.9 g / cm³. 3 ~1.3g / cm 3 .

[0028] In some embodiments, the pore volume of the negative electrode material is ≤0.03 cm³. 3 / g.

[0029] Secondly, this application provides a battery comprising the negative electrode material described in the first aspect.

[0030] The technical solution of this application has at least the following beneficial effects:

[0031] The negative electrode material provided in this application includes a silicon-based active material and a carbon material. The silicon-based active material includes silicon, oxygen, and a metallic element (M). The thermal conductivity of the silicon-based active material is related to the degree of order in its internal atomic arrangement. The silicon-based active material in this application is doped with a metallic element (M), which enables the atoms within the silicon-based active material to recombine and form a highly stable and ordered crystal structure. The content of disordered structures within the silicon-based active material is at a low level, which can improve its thermal conductivity. As the content of disordered structures decreases, the crystallinity of the silicon-based active material increases, resulting in better thermal conductivity. However, this leads to an increase in grain boundary defects, increased side reactions with the electrolyte, and a decrease in the structural stability of the negative electrode material particles. With the synergistic effect of the carbon material on the surface of the silicon-based active material, the side reactions between the negative electrode material and the electrolyte are reduced, the structural strength of the negative electrode material is improved, and the degree of volume expansion of the negative electrode material can be effectively controlled. This application controls the surface doping degree of the negative electrode material to be 2 < β < 10. A higher surface doping degree reduces surface defects, decreases side reactions between the negative electrode material and the electrolyte, and improves the structural strength of the negative electrode material surface. At the same time, the thermal conductivity variation coefficient σ of the negative electrode material is controlled within the range of 0.80 < σ < 1.50. The negative electrode material has excellent thermal conductivity at different temperatures and can quickly conduct the heat generated during charging and discharging at different temperatures. This reduces the temperature difference between negative electrode material particles during electrochemical charging and discharging after the negative electrode material is made into a battery, and lowers the lithium-ion transport energy barrier. Under the synergistic effect of the thermal conductivity variation coefficient σ and the surface doping degree β, the negative electrode material not only has excellent initial coulombic efficiency and specific capacity, but also improves the cycle capacity retention rate under low temperature and high temperature conditions, and improves the capacity decay of the negative electrode material. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the discharge state of a battery provided in an embodiment of this application. Detailed Implementation

[0033] The following are preferred embodiments of the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principle of the present invention, and these improvements and modifications are also considered to be within the protection scope of the present invention.

[0034] In a first aspect, this application provides a negative electrode material, the negative electrode material comprising a silicon-based active material and a carbon material located on at least a portion of the surface of the silicon-based active material, the silicon-based active material comprising silicon, oxygen, and metal M;

[0035] The thermal conductivity of the negative electrode material is g1 W / (m·K) at 373.15K and g2 W / (m·K) at 873.15K. The coefficient of change of thermal conductivity of the negative electrode material is σ=(1-g1 / g2). 2 / 0.57, 0.80<σ<1.50; and the surface doping degree of the negative electrode material is β, 2<β<10;

[0036] The surface doping degree of the negative electrode material was measured in the following manner:

[0037] The mass ratio of oxygen to metal M in the negative electrode material was determined by X-ray photoelectron spectroscopy as A, and by ONH elemental analyzer and ICP spectrometer as B, with β = A / B.

[0038] The negative electrode material provided in this application includes a silicon-based active material and a carbon material. The silicon-based active material includes silicon, oxygen, and a metallic element (M). The thermal conductivity of the silicon-based active material is related to the degree of order in its internal atomic arrangement. The silicon-based active material in this application is doped with a metallic element (M), which enables the atoms within the silicon-based active material to recombine and form a highly stable and ordered crystal structure. The content of disordered structures within the silicon-based active material is at a low level, which can improve its thermal conductivity. As the content of disordered structures decreases, the crystallinity of the silicon-based active material increases, resulting in better thermal conductivity. However, this leads to an increase in grain boundary defects, increased side reactions with the electrolyte, and a decrease in the structural stability of the negative electrode material particles. With the synergistic effect of the carbon material on the surface of the silicon-based active material, the side reactions between the negative electrode material and the electrolyte are reduced, and the structural strength of the negative electrode material surface is improved, effectively controlling the degree of volume expansion of the negative electrode material. This application controls the surface doping degree of the negative electrode material to be 2 < β < 10. A higher surface doping degree reduces surface defects, decreases side reactions between the negative electrode material and the electrolyte, and improves the structural strength of the negative electrode material. At the same time, the thermal conductivity variation coefficient σ of the negative electrode material is controlled within the range of 0.80 < σ < 1.50. The negative electrode material has excellent thermal conductivity at different temperatures and can quickly conduct the heat generated during charging and discharging at different temperatures. This reduces the temperature difference between the negative electrode material particles during electrochemical charging and discharging after the negative electrode material is made into a battery, and lowers the lithium-ion transport energy barrier. Under the synergistic effect of the thermal conductivity variation coefficient σ and the surface doping degree β, the negative electrode material not only has excellent initial coulombic efficiency and specific capacity, but also improves the cycle capacity retention rate under low temperature and high temperature conditions, and improves the capacity decay of the negative electrode material.

[0039] In some embodiments, 0.15 W / (m·K) ≤ g1 ≤ 0.4 W / (m·K), and the thermal conductivity of the negative electrode material at a temperature of 373.15 K (i.e., 100 °C) can specifically be 0.15 W / (m·K), 0.2 W / (m·K), 0.25 W / (m·K), 0.28 W / (m·K), 0.3 W / (m·K), 0.32 W / (m·K), 0.35 W / (m·K), or 0.4 W / (m·K), etc. Of course, it can also be other values ​​within the above range, which are not limited here.

[0040] In some embodiments, 0.5 W / (m·K) ≤ g2 ≤ 2.5 W / (m·K), and the thermal conductivity of the negative electrode material at a temperature of 873.15 K (i.e. 600 °C) can specifically be 0.5 W / (m·K), 0.8 W / (m·K), 1.0 W / (m·K), 1.2 W / (m·K), 1.5 W / (m·K), 1.8 W / (m·K), 2.0 W / (m·K), or 2.5 W / (m·K), etc. Of course, it can also be other values ​​within the above range, which are not limited here.

[0041] In some embodiments, the coefficient of thermal conductivity variation σ of the negative electrode material can specifically be 0.81, 0.85, 0.9, 1.0, 1.1, 1.2, 1.3, 1.35, 1.4, or 1.49, etc., and of course, other values ​​within the above range are also possible, without limitation. When σ≤0.8, the thermal conductivity of the negative electrode material is poor at different temperatures, and the heat generated by the negative electrode material during charging and discharging is difficult to dissipate quickly. The existence of temperature difference hinders the transport of lithium ions. In particular, when the negative electrode material is mixed with graphite as the negative electrode active material, the negative electrode material exhibits lower initial efficiency and capacity under low temperature conditions. When σ≥1.5, the degree of crystallization of the negative electrode material is high, and more disordered Si-O bonds are destroyed, making it difficult to maintain good mechanical toughness of the negative electrode material to resist volume changes during charging and discharging. This leads to particle breakage and structural collapse of the negative electrode material, causing rapid deterioration of cycle performance. When the coefficient of thermal conductivity variation σ of the negative electrode material is controlled within 0.8 < σ < 1.5, the negative electrode material can conduct the heat generated during charging and discharging relatively quickly at different temperatures, reduce the uneven temperature difference within or between the negative electrode material particles, lower the lithium-ion transport energy barrier, and the negative electrode material can also have a high specific capacity and first coulombic efficiency under lower temperature conditions.

[0042] X-ray photoelectron spectroscopy (XPS) can be used to probe and analyze the surface layer of anode materials. Currently, the detection depth of X-ray photoelectron spectroscopy is generally limited to a depth of 10 nm inwards from the particle surface. The surface layer of the anode material is a portion of this 10 nm depth. With the advancement of X-ray photoelectron spectroscopy, its detection depth may reach even deeper regions; however, this is not limited here.

[0043] In some embodiments, the surface doping degree of the negative electrode material is β, β = A / B, 2 < β < 10, specifically 2.1, 2.5, 3, 4, 5, 6, 7, 8, 9, 9.5, 9.6, 9.8 or 9.9, etc., and of course, other values ​​within the above range are also possible, which are not limited here.

[0044] When β ≥ 10, the ratio of Si-O bonds to OM bonds on the surface of the negative electrode material is high, and the large number of disordered Si-O bonds reduces the thermal conductivity of the negative electrode material. When β ≤ 2, it indicates that the ratio of Si-O bonds to OM bonds on the surface of the negative electrode material is low, and more disordered Si-O bonds are destroyed, making it difficult to maintain the good mechanical toughness of the negative electrode material to resist volume changes during charging and discharging. This leads to increased surface defects, resulting in increased consumption of active lithium ions and a decrease in the initial coulombic efficiency of the negative electrode material. This application controls 2 < β < 10, achieving a suitable ratio of Si-O bonds to OM bonds on the surface of the negative electrode material. This results in a higher degree of surface doping, reduced surface defects, fewer side reactions with the electrolyte, and improved structural strength of the negative electrode material surface, effectively controlling the degree of volume expansion of the negative electrode material.

[0045] In some implementations, A ranges from 5 to 40, specifically 5, 10, 15, 20, 30, 35, or 40, etc. Of course, it can also be other values ​​within the above range, which are not limited here.

[0046] In some implementations, B ranges from 2 to 5, specifically 2, 2.5, 3, 3.5, 4, 4.5 or 5, etc. Of course, it can also be other values ​​within the above range, which are not limited here.

[0047] In some embodiments, the metal element M is selected from at least one of Li, Mg, Al, Ca, and Zn.

[0048] In some embodiments, the metal element M exists in the negative electrode material in at least one of the silicates of M and oxides of M.

[0049] In some embodiments, the mass content of metallic element M in the negative electrode material is 6% to 15%, specifically 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15%, etc., and other values ​​within the above range are also possible, without limitation. When the mass content of metallic element M in the negative electrode material is <6%, the doping amount of metallic element M in the negative electrode material is low, the improvement of grain refinement of silicon oxide by metallic element M is limited, the degree of crystallization in the silicon-based active material is low, the number of disordered Si-O bonds increases, the thermal conductivity of the negative electrode material decreases, and the initial coulombic efficiency also decreases. When the mass content of metallic element M in the negative electrode material is >15%, the doping of metallic element M leads to excessively high crystallization in the silicon-based active material, a significant increase in defects and porosity in the silicon-based active material, a decrease in the structural stability of the negative electrode material, and a decrease in the cycle performance of the negative electrode material. This application controls the mass content of metallic M element in the negative electrode material to be within the range of 6% to 15%, and the crystal phase structure in the silicon-based active material to be within a suitable range, which is conducive to achieving a balance between structural stability and thermal conductivity in the negative electrode material.

[0050] In some embodiments, the average particle strength of the negative electrode material is >200 MPa, specifically 201 MPa, 210 MPa, 220 MPa, 230 MPa, 240 MPa, 250 MPa, 280 MPa, 300 MPa, 320 MPa, 350 MPa, or 385 MPa, etc., and of course, other values ​​within the above range are also possible, without limitation. The average particle strength of the negative electrode material is controlled within the above range because the appropriate doping of the metal element M improves the crystal phase structure of the silicon-based active material, thereby increasing the structural stability of the negative electrode material. During charge-discharge cycles, it can withstand its own large volume changes, reducing particle breakage and improving the cycle capacity retention rate of the negative electrode material.

[0051] In some embodiments, when the cumulative particle size distribution of the negative electrode material reaches 50%, the corresponding particle size Dn(50) is 0.3μm to 3μm, specifically 0.3μm, 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, or 3μm, etc., and of course, other values ​​within the above range are also possible, which are not limited here. When Dn(50) < 0.3μm, the specific surface area of ​​the negative electrode material is too large, and the side reactions between the negative electrode material and the electrolyte during charging and discharging are aggravated, resulting in accelerated capacity decay of the battery. When Dn(50) > 3μm, the heat conduction path within the silicon-based active material is too long, and the heat generated during charging and discharging is difficult to conduct out effectively and quickly. The temperature barrier generated between the negative electrode material particles hinders the transport of lithium ions, and the negative electrode material particles are difficult to quickly accept heat to activate the internal lithium storage capacity, thus exhibiting lower initial efficiency and capacity under low temperature conditions. When Dn(50) is controlled within the above range, the particle size of the negative electrode material is moderate and has a suitable heat conduction path, which can quickly conduct the heat generated during charging and discharging, reduce the uneven temperature difference between particles, reduce the lithium ion transport energy barrier, and the faster temperature conduction increases the temperature of the negative electrode material itself, thereby activating the internal lithium storage capacity. The negative electrode material can also exhibit superior electrochemical performance under low temperature conditions, especially capacity and first coulombic efficiency.

[0052] In some embodiments, the silicon-based active material includes at least one of elemental silicon, silicon oxide, and silicon alloy. Elemental silicon can be amorphous silicon and / or crystalline silicon, and silicon alloy can be lithium silicon alloy, magnesium silicon alloy, nickel silicon alloy, etc. In some cases, the silicon-based active particles include elemental silicon particles and silicon alloys.

[0053] In some embodiments, the general chemical formula of silicon oxide is SiO. x Where 0 < x ≤ 2. Specifically, it can be SiO2. 0.5 SiO 0.8 SiO 0.9 SiO, SiO 1.1 SiO 1.2 SiO 1.5 Or SiO2, etc. It can be a material formed by silicon particles dispersed in SiO2, or it can be a material with tetrahedral structural units, with silicon atoms located at the center of the tetrahedral structural units and silicon atoms and / or oxygen atoms located at the four vertices of the tetrahedral structural units.

[0054] In some embodiments, the negative electrode material contains Si grains. In the X-ray diffraction pattern of the negative electrode material, the size of the Si grains on the (220) crystal plane is 5 nm to 12 nm, specifically 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, or 12 nm, etc., and of course, other values ​​within the above range are also possible, which are not limited here. This application controls the silicon grain size of the negative electrode material within the above range, so that the negative electrode material has a suitable degree of crystallization, which can not only improve the conductivity of the negative electrode material, but also improve the structural stability and cycle stability of the negative electrode material.

[0055] In some embodiments, in the negative electrode material, carbon material exists on the surface of the silicon-based active material and / or is dispersed between the silicon-based active material particles. Specifically, the silicon-based active material particles can be embedded within the carbon material, using the carbon material as a matrix.

[0056] In some embodiments, carbon material forms a carbon layer on at least a portion of the surface of the silicon-based active material.

[0057] In some embodiments, the thickness of the carbon layer is 10 nm to 300 nm, specifically 10 nm, 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, or 300 nm, etc., and of course, other values ​​within the above range are also possible, without limitation. It is understood that by limiting the thickness of the carbon layer within the above range, the carbon layer can more completely coat the active material, reducing direct contact between the active material and the electrolyte, thereby reducing the formation of the SEI film, reducing the consumption of active lithium ions, and improving the first coulombic efficiency of the anode material.

[0058] In some embodiments, the carbon material includes at least one selected from graphite, graphene, amorphous carbon, carbon nanotubes, and carbon fibers. The amorphous carbon can be soft carbon and / or hard carbon, and the graphite can be artificial graphite and / or natural graphite. Understandably, the carbon material can improve the conductivity of silicon-based active materials. Graphite is a material with high conductivity, low volume expansion, high initial efficiency, and stable cycle performance; preferably, the carbon material is graphite.

[0059] In some embodiments, the carbon content in the anode material is 2% to 8% by mass, specifically 2%, 3%, 4%, 5%, 6%, 7%, or 8%, etc., and of course, other values ​​within the above range are also possible, without limitation. It is understood that a carbon content within the above range in the anode material can reduce structural damage caused by the volume expansion of silicon, improve the cycle performance of the anode material, facilitate the formation of a stable and thin solid electrolyte interphase (SEI) film, reduce the consumption of active lithium ions, improve the first coulombic efficiency of the anode material, and further enhance the cycle performance of the anode material.

[0060] In some embodiments, the silicon content in the anode material is 48% to 63% by mass, specifically 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 60%, 61%, or 63%, etc., and other values ​​within the above range are also possible, without limitation. When the silicon content is too low, the specific capacity of the anode material is low, making it difficult to meet the requirements of high-energy-density lithium-ion batteries; when the silicon content is too high, the volume expansion of the anode material is too large, leading to severe degradation of the material's cycle performance.

[0061] In some embodiments, the specific surface area of ​​the negative electrode material is ≤10m². 2 / g, specifically 10m 2 / g、9m 2 / g、8m 2 / g、7m 2 / g、6m 2 / g、5m 2 / g、4m 2 / g、3m 2 / g、2m 2 / g or 1m 2 / g, etc., can also be other values ​​within the above range, and are not limited here. Understandably, when the specific surface area of ​​the negative electrode material is within the above range, the contact area between the negative electrode material and the electrolyte is small, and there are fewer reaction sites. This helps reduce the occurrence of side reactions between the negative electrode material and the electrolyte, thereby improving the high-temperature storage performance of the negative electrode material. At the same time, a lower specific surface area results in less exposure of reduced Si in the negative electrode material, which is beneficial for improving the specific capacity and first coulombic efficiency (ICE) of the negative electrode material.

[0062] In some embodiments, the tap density of the negative electrode material is 0.9 g / cm³. 3 ~1.3g / cm 3 Specifically, it could be 0.9 g / cm³. 3 0.95g / cm 3 1.0g / cm 3 1.1g / cm 3 1.15g / cm 3 1.2g / cm 3 Or 1.3g / cm 3 Of course, other values ​​within the above range are also possible and are not limited here. Understandably, if the tap density of the negative electrode material is within the above range, it indicates that the negative electrode material has good processing performance, which can reduce the difficulty in electrode coating and battery manufacturing processes. At the same time, it is also beneficial to maintain the structural stability of the electrode during cycling, thereby improving the cycle performance of the material and the energy density of the battery.

[0063] In some embodiments, the pore volume of the negative electrode material is ≤0.03 cm³.3 / g, specifically 0.03cm 3 / g, 0.028cm 3 / g, 0.025cm 3 / g, 0.02cm 3 / g, 0.018cm 3 / g, 0.015cm 3 / g, 0.01cm 3 / g, 0.008cm 3 / g or 0.005cm 3 / g, etc., can also be other values ​​within the above range, and are not limited here. It is understandable that when the pore volume of the negative electrode material is within the above range, the contact area between the negative electrode material and the electrolyte is small and the number of reaction sites is small, which helps to reduce the occurrence of side reactions between the negative electrode material and the electrolyte, thereby improving the high-temperature storage performance of the negative electrode material.

[0064] Secondly, this application provides a method for preparing a negative electrode material, the method comprising the following steps:

[0065] Step S10: Under vacuum conditions, the mixture of silicon-oxygen material raw material and metal M dopant is heated and vaporized and kept at a constant temperature. The resulting silicon source vapor and metal M vapor are mixed and co-deposited, and then cooled to obtain the precursor.

[0066] In step S20, the precursor, silicon dioxide and metal M are mixed in a mass ratio of 100:1:(1~3), and the mixture is pre-sintered under a protective atmosphere to obtain a pre-sintered product.

[0067] Step S30: The pre-sintered product and flux are mixed at a mass ratio of 1:(2~3) and then subjected to secondary sintering treatment. The flux in the sintered product is removed to obtain silicon-based active material.

[0068] Step S40: The silicon-based active material is carbon-coated to obtain a negative electrode material, wherein the negative electrode material includes the silicon-based active material and the carbon material.

[0069] The method for preparing the anode material provided in this application first involves heating and vaporizing the silicon-oxygen material raw material and the metal M dopant separately. The resulting silicon source vapor and metal M vapor are then mixed and co-deposited to obtain a precursor. Next, silicon dioxide, metal M, and the precursor are mixed, and secondary doping of the precursor surface structure by metal M is achieved during pre-sintering. The doping of metal M causes the Si-O bonds to break, and the atoms rearrange and recombine to form Si-OM bonds. The formation of Si-OM bonds alters the crystal structure of silicon dioxide. M doping increases the surface doping degree of the anode material and reduces the content of disordered structures within the particles, thus improving the thermal conductivity of the anode material. Furthermore, the silicate formed by the reaction of doped M with silicon dioxide exhibits extremely weak side reactions with the electrolyte during the charging and discharging process of the lithium-ion battery, effectively improving the initial coulombic efficiency of the anode material. Finally, the defects and pores within the silicon-based active material are repaired using a molten salt method, improving the density and thermal conductivity of the anode material. The thermal conductivity variation coefficient and surface doping degree of the anode material in this application are controlled within a suitable range. Under the synergistic effect, the anode material not only has excellent initial coulombic efficiency and specific capacity, but also improves the cycle capacity retention rate under low temperature and high temperature conditions.

[0070] The preparation method provided in this scheme is described in detail below:

[0071] Step S10: Under vacuum conditions, the silicon-oxygen material raw material and the metal M dopant are heated and vaporized and kept at a constant temperature. The resulting silicon source vapor and metal M vapor are mixed and co-deposited to obtain the precursor.

[0072] In some embodiments, the raw materials for silicon-oxygen materials include Si and SiO. y Mixtures of SiO2 and SiO y At least one of the following: a mixture of Si and SiO2, wherein 0 < y < 2.

[0073] In some embodiments, the raw materials for the silicon-oxygen material include a mixture of Si and SiO2, wherein the molar ratio of Si to SiO2 is 1:1.

[0074] In some embodiments, the mass ratio of the silicon-oxygen material raw material to the metal M dopant is 1:(0.05~0.2), specifically 1:0.05, 1:0.08, 1:0.1, 1:0.12, 1:0.13, 1:0.15, 1:0.16, 1:0.18, 1:0.19 or 1:0.2, etc. Of course, other values ​​within the above range are also possible, and are not limited here.

[0075] In some embodiments, the vacuum pressure during the heating and vaporization process is 0.1 Pa to 1000 Pa, specifically 0.1 Pa, 1 Pa, 10 Pa, 50 Pa, 100 Pa, 500 Pa, 800 Pa or 1000 Pa, etc. Of course, it can also be other values ​​within the above range, which are not limited here.

[0076] In some embodiments, the heating and vaporization temperature is 800℃ to 1300℃, specifically 800℃, 850℃, 900℃, 1000℃, 1100℃, 1200℃ or 1300℃, etc., and of course, other values ​​within the above range are also possible, which are not limited here.

[0077] In some embodiments, the heating time for the raw materials of silicon-oxygen materials and the metal M dopant is 10h to 15h, specifically 10h, 11h, 12h, 13h, 14h, 15h, etc., which is not limited here.

[0078] In this application, both the raw materials and dopants of the silicon-oxygen material are heated and vaporized. The silicon vapor and metal vapor formed by evaporation are in a stable output state, which can improve the uniformity of the distribution of metal M element in the negative electrode material.

[0079] In some embodiments, the co-deposition temperature is 600℃ to 900℃, specifically 600℃, 650℃, 700℃, 750℃, 800℃, 850℃ or 900℃, etc., and of course other values ​​within the above range are also possible, which are not limited here.

[0080] Step S20: The precursor is mixed with silicon dioxide and metal M at a mass ratio of 100:1:(1-3), and the mixture is pre-sintered under a protective atmosphere to obtain a pre-sintered product.

[0081] In some embodiments, the mass ratio of the precursor to silicon dioxide and metal M is 100:1:1, 100:1:1.5, 100:1:2, 100:1:2.5 or 100:1:3, etc. Of course, other values ​​within the above range are also possible and are not limited here.

[0082] In some embodiments, the temperature of the pre-sintering treatment is 300℃ to 500℃, specifically 300℃, 350℃, 400℃, 450℃, 480℃ or 500℃, etc., and of course other values ​​within the above range are also possible, which are not limited here.

[0083] In some implementations, the pre-sintering treatment time is 2h to 3h, specifically 2h, 2.5h or 3h, or other values ​​within the above range, which are not limited here.

[0084] In some embodiments, the pre-sintering process is carried out under a protective atmosphere, which includes at least one of nitrogen, argon, neon, and helium.

[0085] Step S30: The pre-sintered product and flux are mixed at a mass ratio of 1:(2~3) and then subjected to secondary sintering treatment. The flux in the sintered product is removed to obtain silicon-based active material.

[0086] In some embodiments, the mass ratio of the pre-sintered product to the flux is 1:2, 1:2.2, 1:2.5, 1:2.8 or 1:3, etc. Of course, other values ​​within the above range are also possible and are not limited here.

[0087] In some embodiments, the flux includes at least one of sodium chloride and potassium chloride.

[0088] In some embodiments, the temperature of the secondary sintering treatment is 600℃~800℃, specifically 600℃, 650℃, 700℃, 750℃, 780℃ or 800℃, etc., and of course other values ​​within the above range are also possible, which are not limited here.

[0089] In some implementations, the secondary sintering process takes 3 to 5 hours, specifically 3 hours, 4 hours, or 5 hours, or other values ​​within the above range, which are not limited here.

[0090] In some embodiments, the flux removal from the sintered product includes repeatedly washing, filtering and drying the sintered product.

[0091] Step S40: The silicon-based active material is carbon-coated to obtain a negative electrode material, wherein the negative electrode material includes the silicon-based active material and the carbon material.

[0092] In some embodiments, a carbon material forms a carbon layer on at least a portion of the surface of the silicon-based active material, and the carbon layer can improve the conductivity of the negative electrode material.

[0093] In some embodiments, the carbon coating treatment includes at least one of gas phase carbon coating treatment, solid phase carbon coating treatment and liquid phase carbon coating treatment.

[0094] In some embodiments, the gaseous carbon source used in the gaseous carbon coating process includes at least one of methane, propane, butane, acetylene, benzene, and toluene.

[0095] In some embodiments, the flow rate of the gaseous carbon source is 1.0 L / min to 2.5 L / min, specifically 1.0 L / min, 1.2 L / min, 1.5 L / min, 1.8 L / min, 2.0 L / min, 2.1 L / min, 2.3 L / min or 2.5 L / min, etc. Of course, other values ​​within the above range are also possible, and no limitation is made here.

[0096] In some embodiments, the temperature of the vapor phase coating treatment is 600℃ to 1200℃, specifically 600℃, 700℃, 800℃, 900℃, 1000℃, 1100℃ or 1200℃, etc., and of course other values ​​within the above range are also possible, which are not limited here.

[0097] In some embodiments, the coating time of the gas phase coating process is 2h to 10h, specifically 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h or 10h, etc., and of course other values ​​within the above range are also possible, which are not limited here.

[0098] In some embodiments, the coating material used in the liquid-phase carbon coating treatment includes at least one of graphite, graphene, amorphous carbon, carbon nanotubes, and carbon fibers. These coating materials can effectively improve the conductivity of the anode material and enhance its electrochemical performance.

[0099] Thirdly, this application provides a battery comprising the negative electrode material described in the first aspect or the negative electrode material prepared by the method described in the second aspect.

[0100] The battery provided in this application can be a secondary battery (such as a lithium-ion battery, sodium-ion battery, etc.), including a casing, electrode assembly, and electrolyte. Both the electrode assembly and electrolyte are located inside the casing. The casing can be a packaging bag sealed with an encapsulating film (such as an aluminum-plastic film), for example, a pouch battery for the secondary battery. In other embodiments, the secondary battery can also be a steel-cased battery, an aluminum-cased battery, etc. Figure 1 This is a schematic diagram of the discharge state of the battery provided in the embodiments of this application, such as... Figure 1 As shown, the battery includes a casing and an electrode assembly. The electrode assembly includes a positive electrode 1, a negative electrode 2, and a separator 3, with the separator 3 disposed between the positive electrode 1 and the negative electrode 2. The electrode assembly can be a stacked structure, formed by alternately stacking the positive electrode 1, the separator 3, and the negative electrode 2. In other embodiments, the electrode assembly can also be a wound structure, formed by sequentially stacking and winding the positive electrode, the separator, and the negative electrode.

[0101] In some embodiments, the positive electrode 1 includes a positive current collector 101 and a positive active layer 102 disposed on at least one surface of the positive current collector 101.

[0102] In some embodiments, the positive current collector 101 may be made of 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 (aluminum foil or nickel foil, etc.) with a polymer substrate. The positive active layer 102 comprises a positive active material, which includes compounds that reversibly insert and deintercalate metal ions.

[0103] In some embodiments, the positive electrode active material may include lithium transition metal composite oxides, sodium transition metal composite oxides, etc. The lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese, and nickel.

[0104] 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 lithium iron phosphate (LiFePO4) or lithium iron phosphate (LiFePO4).

[0105] In some embodiments, the negative electrode 2 includes a negative electrode current collector 201 and a negative electrode active material layer 202 disposed on at least one surface of the negative electrode current collector.

[0106] In some embodiments, the negative electrode current collector 201 can be at least one of copper foil, nickel foil, stainless steel foil, titanium foil, or carbon-based current collector, 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 active material layer 202 includes a negative electrode material, which is the negative electrode material described in the first aspect or the negative electrode material prepared by the aforementioned preparation method. The battery provided in this application embodiment has the advantages of high capacity, high initial efficiency, long cycle life, excellent rate performance, and low expansion. The battery can be a lithium-ion battery, a sodium-ion battery, a solid electrolyte battery, etc., and is not limited thereto.

[0107] The embodiments of the present invention will be further described below with reference to several examples. However, the embodiments of the present invention are not limited to the specific embodiments described below. Appropriate modifications can be made within the scope of unchanged main claims. Test method:

[0108] (1) XPS testing method: The mass content of metallic M and O elements in the surface layer (approximately 1 nm to 10 nm depth range) of the negative electrode material was measured using X-ray photoelectron spectroscopy (Thermo Scientific K-Alpha). The excitation source used was Al Kα rays with a beam spot of 400 μm. The pass energy of the full spectrum scan was 100 eV and the step size was 1 eV. Finally, the atomic mass ratio A of O and metallic M elements was analyzed using Avantage software.

[0109] (2) Complete dissolution ICP test method: 0.500g of negative electrode material was placed in a clean platinum crucible and then calcined in a muffle furnace in air atmosphere at 750℃ for 2 hours to completely remove carbon elements; the cooled calcined residue was fully reacted with 4mL HNO3 and 6mL HF mixed acid, and then the platinum crucible containing the solution was placed on a 350℃ hot plate until the solvent was completely evaporated; after the crucible cooled, 6mL concentrated HCl was added, and the mixture was heated until the residue was completely dissolved and then diluted to 100mL plastic volumetric flask; finally, the mass content of all metal M elements in the negative electrode material was determined by ICP spectrometer (Agilent 5800VDVICP-OES).

[0110] (3) Thermal conductivity test of negative electrode material: A thermal conductivity meter (Hot Disk TPS2500S) was used for testing. The test atmosphere was nitrogen, and the test temperatures were 100℃ and 600℃. Before the test, an appropriate amount of powder sample was poured into a 30mm infrared mold and pressed into two samples with a pressure of 20MPa. A suitable probe was selected, and the sample and probe were sandwiched together with the probe coil directly below the pressure screw. The flat surfaces of the two samples were clamped between the probe, ensuring as few gaps as possible. Then, the test parameters were adjusted, and the measurement time and test power were adjusted to make the thermal conductivity of the sample reach a stable value. The thermal conductivity g1 and g2 at 100℃ (373.15K) and 600℃ (873.15K) were measured, with units of W / (m·K).

[0111] (4) Test method for oxygen content in negative electrode material: Weigh 10mg to 13mg of negative electrode material, wrap it in nickel foil, and then put it into the graphite crucible in the ONH elemental analyzer (ONH-2000) for testing to obtain the total oxygen content of the negative electrode material.

[0112] (5) Test method for tap density: Refer to GB / T 5162-2006 / ISO 3953:1993 "Determination of tap density of metal powders" or the equipment instruction manual for measurement. Use a tap density meter (Kunta DAT-4-220) for measurement. The number of vibrations is 3000.

[0113] (6) Average particle strength of the negative electrode material: Tested using a dynamic ultra-microhardness tester (DUH-211S). The sample was transferred to a standard block, and single particles with a diameter of 5-10 μm were found under a 50x eyepiece. The crushing point mode was set, with a load force of 100 mN and a descent speed of 2.8 mN / s, to crush the single particles. Ten single particles of the same size range were randomly tested to obtain ten particle strength values, and the average value was taken as the average particle strength of the sample.

[0114] (7) Test method for specific surface area and pore volume: A specific surface area and pore volume analyzer (McASAP2460-2) was used for measurement, with N2 as the adsorbed gas. A certain amount of sample was weighed and placed into a special bubble tube for specific surface area. The sample was purged with nitrogen at 300℃ for a certain period of time in the degassing station. After degassing, the sample was cooled to room temperature. The actual mass of the sample was weighed, and the special bubble tube containing the sample was installed into the specific surface area and pore volume analyzer. After inputting the sample mass, the specific surface area of ​​the sample was measured. For details, please refer to GB / T 19587-2004 "Determination of Specific Surface Area of ​​Solid Substances by Gas Adsorption BET Method" or the equipment instruction manual.

[0115] (8) Particle size testing method: The particle size testing method refers to GB / T 19077-2016. The particle size distribution of the negative electrode material is determined by the Malvern laser particle size analyzer (Mastersizer 3000) and laser diffraction method. The cumulative particle size distribution is determined by the number of particles, and Dn(50) represents the particle size corresponding to the cumulative particle size distribution reaching 50%.

[0116] (9) Test method for carbon content: Refer to Appendix A of GB / T 38823-2020 "Test method for carbon content". Measured using an infrared carbon-sulfur analyzer.

[0117] (10) Test method for carbon layer thickness: The negative electrode material is cut by an ion mill and the average thickness of the carbon coating layer on the material surface is measured by SEM.

[0118] (11) Electrochemical performance testing (negative electrode material): A mixture of negative electrode material, conductive agent (SuTer P), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) at a mass ratio of 92:2:2:2 was uniformly coated onto a copper foil current collector and dried to obtain a negative electrode sheet for later use. The dried electrode sheet was then rolled under a pressure of 3 MPa to obtain the negative electrode sheet. The rolled negative electrode sheet was tested as a coin cell. Battery assembly was performed in an argon glove box, using a lithium metal sheet as the negative electrode, a 1 mol / L lithium hexafluorophosphate + ethylene carbonate (EC) + methyl ethyl carbonate (EMC) electrolyte, and a polyethylene / propylene composite microporous membrane as the separator. The assembled coin cells were placed in a constant temperature test chamber (0℃ / 50℃) and connected to a battery testing instrument for testing. The charge / discharge voltage was 0.01–1.5V. Initial coulombic efficiency = initial lithium insertion capacity / initial lithium extraction capacity. Battery cycle life is the lithium extraction capacity retention rate after 50 charge / discharge cycles.

[0119] (12) Electrochemical performance testing (negative electrode material + graphite): The negative electrode material, graphite, conductive agent (Super P), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) were mixed evenly in an aqueous solvent at a mass ratio of 9.2:82.8:2:2:2. The mixture was then coated onto a copper foil current collector and dried to obtain a negative electrode sheet for later use. The dried electrode sheet was rolled under a pressure of 3 MPa to obtain a negative electrode sheet with a certain compaction density. The rolled negative electrode sheet was tested as a coin cell. The battery assembly was carried out in an argon glove box, with a lithium metal sheet as the negative electrode, an electrolyte of 1 mol / L lithium hexafluorophosphate + ethylene carbonate (EC) + methyl ethyl carbonate (EMC), and a polyethylene / propylene composite microporous membrane as the separator. The assembled coin cells were placed in a constant temperature test chamber (0℃ / 50℃) and connected to a battery testing instrument for testing. The charge and discharge voltage was 0.01~1.5V. Initial coulombic efficiency = initial lithium insertion capacity / initial lithium extraction capacity. Battery cycle life is the rate of lithium removal capacity retention after 50 charge-discharge cycles.

[0120] The embodiments of the present invention will be further described below with reference to several examples. However, the embodiments of the present invention are not limited to the specific embodiments described below. Appropriate modifications can be made within the scope of the original claims.

[0121] Example 1

[0122] A method for preparing a negative electrode material includes the following steps:

[0123] (1) Put 8 kg of Mg particles, 28 kg of Si particles and 60 kg of SiO2 particles into the vacuum furnace reaction chamber, and adjust the vacuum furnace pressure to 10 Pa. Control the vacuum furnace reactor to heat to 1300 °C to generate SiO gas and Mg gas. Transport the SiO and Mg mixed gas to the vacuum furnace collection device to cool and condense it. Control the temperature of the cooling plate to 750 °C throughout the reaction process.

[0124] (2) After the reaction is completed, the product collected by the cooling plate is crushed and classified, and the powder particle size Dn(50) is controlled to be 0.4μm.

[0125] (3) The pulverized product is mixed with SiO2 and Mg at a secondary doping mass ratio of 100:1:2. The mixture is then pre-sintered in a box furnace under Ar atmosphere protection at a pre-sintering temperature of 400℃ and a pre-sintering time of 3h to obtain the pre-sintered product.

[0126] (4) The pre-sintered product is broken up and mixed with NaCl at a mass ratio of 1:3. Then, it is sintered again in a box furnace under Ar atmosphere protection at a temperature of 700℃ for 4 hours. The sintered product is repeatedly washed and filtered to remove the NaCl flux. After drying, silicon-based active materials are obtained, including Mg-doped SiO2. x .

[0127] (5) Place the silicon-based active material in a chemical vapor deposition (CVD) device, introduce nitrogen gas at 5 L / min as a protective gas, then heat it to 800℃ and keep it at that temperature, introduce acetylene gas at 1.5 L / min into the CVD device, and carry out a gas phase carbon coating reaction for 3 hours to obtain the negative electrode material.

[0128] The negative electrode material prepared in the embodiments of this application includes silicon-based active material and carbon material, wherein the silicon-based active material includes Mg-doped SiO₂. x .

[0129] Following the preparation steps of Example 1, Examples 2-14 and Comparative Examples 1-4 were prepared. The specific process parameters for each example are shown in Table 1.

[0130] Table 1. Preparation process parameters of negative electrode materials

[0131]

[0132]

[0133] The performance of the anode materials prepared in the examples and comparative examples was tested, and the results of the performance tests are shown in Table 2:

[0134] Table 2. Performance test results of the negative electrode materials in each embodiment and comparative example

[0135] sample A B β [cl] <![CDATA[g2]]> σ Example 1 20.4 4.01 5.1 0.23 2.40 1.43 Example 2 8.1 3.82 2.1 0.21 1.48 1.29 Example 3 39.3 4.14 9.5 0.19 0.68 0.91 Example 4 19.7 2.05 9.6 0.38 2.91 1.32 Example 5 10.2 4.6 2.2 0.17 0.53 0.81 Example 6 16.4 3.95 4.2 0.19 0.78 1.00 Example 7 18.3 3.89 4.7 0.24 2.96 1.47 Example 8 20.7 4.08 5.1 0.19 0.66 0.89 Example 9 10.5 4.14 2.5 0.16 0.56 0.89 Example 10 7.2 3.38 2.1 0.23 2.59 1.45 Example 11 19.6 4.05 4.8 0.22 2.38 1.44 Example 12 20.4 3.94 5.2 0.21 2.42 1.46 Example 13 13.6 3.89 3.5 0.24 2.37 1.41 Example 14 11.4 4.02 2.8 0.23 2.38 1.43 Comparative Example 1 6.5 4.05 1.6 0.12 0.36 0.78 Comparative Example 2 56.3 4.15 13.6 0.16 0.53 0.85 Comparative Example 3 19.6 3.98 4.9 0.17 0.48 0.73 Comparative Example 4 17.4 4.07 4.3 0.26 3.63 1.51

[0136] Table 3. Performance test results of the negative electrode materials in each embodiment and comparative example (II)

[0137]

[0138]

[0139] Table 4. Summary of Electrochemical Performance Test Results of Anode Materials

[0140]

[0141] Table 5. Summary of Electrochemical Performance Test Results of Anode Material and Graphite Used Together as Anode Active Materials

[0142]

[0143]

[0144] According to the test data in Tables 2 to 5, the surface doping degree of the anode material in this application is controlled to satisfy 2 < β < 10. This reduces surface defects and defects within the silicon-based active material, improving the thermal conductivity of the anode material. Simultaneously, controlling the thermal conductivity variation coefficient σ within the range of 0.80 < σ < 1.50 reduces the temperature difference between anode material particles, lowers the lithium-ion transport barrier, and improves the cycle capacity retention rate. The anode material exhibits excellent initial coulombic efficiency and initial delithiation capacity, while also improving cycle capacity retention under low and high temperature conditions and mitigating capacity decay. According to the test data from Example 1 and Comparative Example 1, Comparative Example 1 did not undergo pre-sintering or secondary sintering treatment, resulting in an excessively low surface doping degree β, increased surface defects, a higher proportion of disordered structures within the silicon-based active material, and an excessively low thermal conductivity variation coefficient σ. The anode material exhibits poor thermal conductivity at different temperatures, showing low initial coulombic efficiency and initial delithiation capacity at all temperatures.

[0145] According to the test data of Example 1 and Comparative Example 2, the amount of secondary doped metal M added during the pre-sintering process in Comparative Example 2 was too small, the ratio of Si-O bonds to OM bonds on the surface of the negative electrode material was high, the surface doping degree β of the negative electrode material was too high, and there were a large number of disordered Si-O bonds on the surface of the negative electrode material. Although the degree of crystallization in the silicon-based active material was appropriate and the coefficient of change of thermal conductivity σ of the negative electrode material was within a suitable range, the excessive disordered structure on the surface of the negative electrode material led to an increase in side reactions, and the first coulombic efficiency and the first delithiation capacity of the negative electrode material at different temperatures decreased compared with Example 1.

[0146] According to the test data of Example 1 and Comparative Example 3, the secondary sintering temperature of Comparative Example 3 is too low, which makes it difficult for some metal M to be effectively doped into the negative electrode material. The internal disorder structure of the negative electrode material is more, the thermal conductivity g2 of the negative electrode material at 873.15K decreases, the coefficient of thermal conductivity change σ also decreases, the thermal conductivity of the negative electrode material decreases, and the initial coulombic efficiency and initial delithiation capacity of the negative electrode material at different temperatures are lower than those of Example 1.

[0147] According to the test data of Example 1 and Comparative Example 4, the secondary sintering temperature of Comparative Example 4 was too low, which caused excessive metal M doping into the negative electrode material. The disordered Si-O bonds were destroyed in large quantities, making it difficult to maintain the good mechanical toughness of the negative electrode material to resist the volume change during the charging and discharging process. This resulted in the particle breakage and structural collapse of the negative electrode material, which led to a rapid deterioration of the cycle performance and a significant decrease in the capacity retention rate of the negative electrode material.

[0148] Although this application discloses preferred embodiments as described above, it is not intended to limit the claims. Any person skilled in the art can make several possible changes and modifications without departing from the concept of this application. Therefore, the scope of protection of this application should be determined by the scope defined in the claims of this application.

Claims

1. A negative electrode material, characterized in that, The negative electrode material includes a silicon-based active material and a carbon material located on at least a portion of the surface of the silicon-based active material. The silicon-based active material includes silicon, oxygen, and metal M. The thermal conductivity of the negative electrode material is g1 W / (m·K) at 373.15K and g2 W / (m·K) at 873.15K. The coefficient of change of thermal conductivity of the negative electrode material is σ=(1-g1 / g2). 2 / 0.57, 0.80 < σ < 1.50; The surface doping degree of the negative electrode material is β, where 2 < β < 10; wherein, the surface doping degree of the negative electrode material is measured by the following method: The mass ratio of oxygen to metal M in the negative electrode material was determined by X-ray photoelectron spectroscopy as A, and by ONH elemental analyzer and ICP spectrometer as B, with β = A / B.

2. The negative electrode material according to claim 1, characterized in that, It satisfies at least one of the following characteristics: (1)0.15≤g1≤0.4； (2)0.5≤g2≤2.5； (3)5≤A≤40； (4)2≤B≤5。 3. The negative electrode material according to claim 1, characterized in that, It satisfies at least one of the following characteristics: (1) The metal element M is selected from at least one of Li, Mg, Al, Ca and Zn; (2) The mass percentage of the metal M element in the negative electrode material is 6% to 15%; (3) In the negative electrode material, the metal element M exists in at least one of the silicates of M and the oxides of M.

4. The negative electrode material according to claim 1, characterized in that, The average particle strength of the negative electrode material is >200 MPa.

5. The negative electrode material according to claim 1, characterized in that, The negative electrode material contains Si grains, and in the X-ray diffraction pattern of the negative electrode material, the size of the Si grains on the (220) crystal plane is 5 nm to 12 nm.

6. The negative electrode material according to claim 1, characterized in that, When the cumulative particle size distribution of the negative electrode material reaches 50%, the corresponding particle size Dn(50) is 0.3μm to 3μm.

7. The negative electrode material according to claim 1, characterized in that, It satisfies at least one of the following characteristics: (1) The silicon-based active material includes at least one of elemental silicon, silicon oxide and silicon alloy; (2) The silicon-based active material includes silicon oxide, and the general chemical formula of the silicon oxide is SiO₂. x , 0 < x ≤ 2.

8. The negative electrode material according to claim 1, characterized in that, The negative electrode material satisfies at least one of the following characteristics: (1) The mass content of carbon in the negative electrode material is 2% to 8%; (2) The carbon material includes at least one of graphite, graphene, amorphous carbon, carbon nanotubes and carbon fibers; (3) The carbon material forms a carbon layer on at least part of the surface of the silicon-based active material, and the thickness of the carbon layer is 10 nm to 300 nm.

9. The negative electrode material according to any one of claims 1 to 8, characterized in that, The negative electrode material satisfies at least one of the following characteristics: (1) The specific surface area of ​​the negative electrode material is ≤10m² 2 / g; (2) The tap density of the negative electrode material is 0.9 g / cm³. 3 ~1.3g / cm 3 ; (3) The pore volume of the negative electrode material is ≤0.03 cm³. 3 / g.

10. A battery, characterized in that, Includes the negative electrode material as described in any one of claims 1 to 9.

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