Negative electrode material and battery

Abstract

The present application relates to a negative electrode material. The negative electrode material comprises an active substance which comprises silicon, oxygen and a metal M element. The mass ratio of oxygen to the metal M element of the negative electrode material obtained by means of an X-ray photoelectron spectrometer test is A; the mass ratio of oxygen in the negative electrode material obtained by means of an ONH element analyzer test to the metal M element in the negative electrode material obtained by means of an ICP spectrometer test is B; and the surface oxidation degree of the negative electrode material is γ, where γ = A / B, and 2＜γ＜10. The technical solution of the present application improves the oxidation resistance of the negative electrode material, and can effectively reduce irreversible reactions generated from the negative electrode material during the first charge and discharge process, thereby improving the initial coulomb efficiency, specific capacity, and high-temperature storage performance of the negative electrode material.

Description

Negative electrode material and battery

[0001] The present application claims priority to the Chinese patent application No. 202411102630.X, filed on August 12, 2024, entitled "Negative electrode material and preparation method thereof, and battery", the Chinese patent application No. 202411549706.3, filed on October 31, 2024, entitled "Negative electrode material and battery", and the Chinese patent application No. 202510099932.4, filed on January 21, 2025, entitled "Negative electrode material and battery", the contents of which are incorporated herein by reference. TECHNICAL FIELD

[0002] The present application relates to the technical field of negative electrode materials, in particular to a negative electrode material and a battery. BACKGROUND

[0003] Lithium ion batteries have the advantages of high energy density, long cycle life, low environmental pollution and no memory effect, and are widely used in electric vehicles and consumer electronics. The negative electrode material is an important component of lithium ion batteries, which directly affects the key indicators such as energy density, cycle life and safety performance of the battery. At present, commercial lithium ion batteries mainly use graphite-based negative electrode materials, but its theoretical specific capacity is only 372 mAh / g, which is difficult to meet the demand of high energy density lithium ion batteries. Silicon-based negative electrode material as a negative electrode material of lithium ion battery has very high specific capacity, and is one of the candidate materials for the next generation of high energy density lithium ion batteries. However, silicon-based negative electrode material will produce huge volume change during charge and discharge cycles, resulting in material / pole piece structure degradation, unstable solid electrolyte interface film (SEI), and thus sharp decline in its electrochemical performance.

[0004] Silicon oxide (general formula: SiO x , 0 < x ≤ 2) has several times the specific capacity of graphite (about 1500 mAh / g), and also has a complex structure: it can be a material formed by dispersing nano-silicon particles in SiO2; it can also be a material with tetrahedral structure units, with silicon atoms at the center of the tetrahedral structure units and silicon atoms and / or oxygen atoms at the four vertices of the tetrahedral structure units. Such a structure makes SiO x The reversible lithiation products formed by reacting with lithium during charging, such as lithium-silicon alloy, are dispersed in inert matrix such as SiO2, and irreversible lithiation products (lithium oxide, lithium silicate, etc.), thereby greatly improving the volume expansion and cycle life characteristics of silicon material. However, SiO xThe initial coulombic efficiency (ICE) of SiO is low (about 75%), which will consume more positive electrode material to match when assembled into lithium ion batteries to offset the irreversible lithium loss, resulting in increased manufacturing cost.

[0005] To improve this problem, one method proposed is to dope SiO x with metal doping to convert the irreversible lithium intercalation component in SiO x into an inert component such as SiO2, thereby reducing the irreversible lithium intercalation component in SiO x and improving the initial coulombic efficiency (ICE) of lithium capture during charging. At present, SiO x can be partially converted into magnesium silicate and silicon by Mg doping in the prior art to improve the initial coulombic efficiency (ICE) of the material, but the improvement of the initial coulombic efficiency (ICE) is limited due to the easy oxidation of the reduced silicon in the material, especially on the surface of the material, in the air, that is, the utilization rate of the doped Mg is low. And Mg doping also causes the generation of defects and pores in the material, increases the contact sites with the electrolyte after being made into lithium ion batteries, and reduces the high-temperature storage performance.

[0006] SUMMARY

[0007] The present application provides a negative electrode material and a preparation method thereof, and a battery. The negative electrode material has a suitable surface oxidation degree, can reduce defects and pores in the negative electrode material, reduce the side reaction contact sites of the negative electrode material with the electrolyte, and thus can improve the high-temperature storage performance, the initial coulombic efficiency and the specific capacity of the negative electrode material.

[0008] In a first aspect, the present application provides a negative electrode material, which comprises an active substance, and the active substance comprises silicon elements, oxygen elements and metal M elements; the mass ratio of the oxygen elements and the metal M elements of the negative electrode material is A obtained by X-ray photoelectron spectroscopy; the mass ratio of the oxygen elements in the negative electrode material obtained by ONH element analyzer and the metal M elements in the negative electrode material obtained by ICP spectrometer is B; the surface oxidation degree of the negative electrode material is γ, and γ = A / B, 2 < γ < 10.

[0009] In the present application, the value of the surface oxidation degree γ of the negative electrode material is controlled between 2 and 10 (not including 2 and 10), the oxidation degree of the surface of the negative electrode material is low, the silicon oxide of the surface layer of the negative electrode material can effectively fill and close the defects and pores on the surface of the negative electrode material, the contact sites of the side reaction between the negative electrode material and the electrolyte can be reduced, the SEI film between the negative electrode material and the electrolyte can be reduced, and the defects and pores in the negative electrode material can be closed after being closed. The contact between the negative electrode material and the air is reduced, the oxidation resistance of the negative electrode material is improved, the irreversible reaction of the negative electrode material formed in the first charge and discharge process can be effectively reduced, and thus the first coulombic efficiency, the specific capacity and the high-temperature storage performance of the negative electrode material are improved. BRIEF DESCRIPTION OF DRAWINGS

[0010] FIG. 1 is a schematic diagram of a discharge state of a battery provided by an embodiment of the present application. DETAILED DESCRIPTION

[0011] In order to better understand the technical solutions of the present application, the embodiments of the present application will be described in detail below with reference to the drawings.

[0012] It should be clear that the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0013] The terms used in the embodiments of the present application are only for the purpose of describing the specific embodiments, and are not intended to limit the present application. The singular forms "a", "said" and "the" used in the embodiments of the present application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0014] It should be understood that the term "and / or" used herein is only to describe the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which means that there are three cases of A alone, A and B together, and B alone. In addition, the character " / " in this paper generally represents that the front and rear associated objects are a "or" relationship.

[0015] In a first aspect, the present application provides a negative electrode material, the negative electrode material comprising an active substance, the active substance comprising a silicon element, an oxygen element and a metal M element;

[0016] The mass ratio of the oxygen element and the metal M element of the negative electrode material is A obtained by X-ray photoelectron spectroscopy;

[0017] The mass ratio of the oxygen element in the negative electrode material and the metal M element in the negative electrode material is B obtained by ONH element analyzer and ICP spectrometer;

[0018] The surface oxidation degree of the negative electrode material is γ, γ=A / B, 2<γ<10.

[0019] In the above scheme, the negative electrode material comprises an active substance, and the active substance comprises a silicon element, an oxygen element and a metal M element. In the present application, the value of the surface oxidation degree γ of the negative electrode material is controlled to be between 2 and 10 (not including 2 and 10), the oxidation degree of the surface of the negative electrode material is low, the silicon oxide of the surface layer of the negative electrode material can effectively fill and seal the defects and pores on the surface of the negative electrode material, the contact sites of the side reaction of the negative electrode material and the electrolyte can be reduced, the generation of the SEI film between the negative electrode material and the electrolyte can be reduced, the contact of the negative electrode material and air can be reduced after the defects and pores of the negative electrode material are sealed, the oxidation resistance of the negative electrode material is improved, the irreversible reaction of the negative electrode material in the first charge and discharge process can be effectively reduced, and thus the first coulombic efficiency, the specific capacity and the high-temperature storage performance of the negative electrode material are improved.

[0020] In a second aspect, the present application provides a negative electrode material, which comprises an active substance, and the active substance comprises a silicon, a silicon oxide, a magnesium silicate and a carbon element, the metal M element is a magnesium element, and at least part of the carbon element is located inside the particles of the active substance.

[0021] The mass ratio of the oxygen element and the metal M element of the negative electrode material is A, which is obtained by an X-ray photoelectron spectrometer;

[0022] The mass ratio of the oxygen element in the negative electrode material and the metal M element in the negative electrode material is B, which is obtained by an ONH element analyzer and an ICP spectrometer respectively;

[0023] The surface oxidation degree of the negative electrode material is γ, γ=A / B, 2<γ<10.

[0024] In the above scheme, the negative electrode material comprises an active substance, the active substance comprises silicon, silicon oxide, magnesium silicate and carbon elements, at least part of the carbon elements are located inside the particles of the active substance, which can reduce defects and pores in the negative electrode material, thereby effectively reducing the contact sites of side reactions between the negative electrode material and the electrolyte, and improving the high-temperature storage performance of the negative electrode material. Among them, the value of A can represent the mass ratio of oxygen elements and magnesium elements in the surface layer of the negative electrode material, and the value of B can represent the mass ratio of oxygen elements and magnesium elements in the whole particles of the negative electrode material; define the surface oxidation degree of the negative electrode material as γ, γ=A / B, 2<γ<10, that is, the value of A is much larger than the value of B. Since the distribution contents of magnesium elements in the internal and surface layer of the negative electrode material generally have little difference, but the mass ratio of oxygen elements and magnesium elements can reflect the difference, and further, the difference between the values of A and B can indicate that the silicon oxide in the surface layer of the negative electrode material is more. In this application, the value of the surface oxidation degree γ of the negative electrode material is controlled between 2 and 10 (not including 2 and 10), the oxidation degree of the surface of the negative electrode material is low, the silicon oxide in the surface layer of the negative electrode material can effectively fill and close the defects and pores on the surface of the negative electrode material, and the carbon elements inside the active substance can also reduce the material defects to a certain extent, reduce the contact sites of side reactions between the negative electrode material and the electrolyte, and reduce the generation of SEI film between the negative electrode material and the electrolyte; at the same time, after the defects and pores in the negative electrode material are closed, the contact between the negative electrode material and air is also reduced, the oxidation resistance of the negative electrode material is improved, the irreversible reactions formed in the first charge-discharge process of the negative electrode material can be effectively reduced, and thus the first coulombic efficiency, specific capacity and high-temperature storage performance of the negative electrode material are improved.

[0025] X-ray photoelectron spectroscopy (abbreviated as XPS) can be used for detecting and analyzing the surface layer of the negative electrode material. Since the current detection depth of X-ray photoelectron spectroscopy can generally reach a depth range of 10 nm inside the particle surface, the surface layer of the negative electrode material is the part of the region with a depth of 10 nm inside the particle surface of the negative electrode material. With the upgrading of X-ray photoelectron spectroscopy, its detection depth can reach a deeper region, which is not limited here.

[0026] In some embodiments, the surface oxidation degree of the negative electrode material is γ, γ = A / B, 2 < γ < 10, which can be 2.1, 2.5, 3, 4, 5, 6, 7, 8, 9, 9.5, 9.6, 9.8, or 9.9, and can also be other values within the above range, which is not limited herein. When γ≥10, the surface oxidation degree of the negative electrode material is high, because a large amount of defects and pores are not filled with silicon oxide, the surface of the negative electrode material is easy to adsorb oxygen and other gases to cause surface oxidation, and the defects and pores make the XPS detection depth deeper, so that the A value is larger; the content of defects and pores on the surface of the negative electrode material is high, the reaction sites on the surface of the negative electrode material are too many, the side reaction of the negative electrode material with the electrolyte is intensified, and the high defects and pores also lead to easy oxidation of the negative electrode material, which reduces the utilization of Mg doping, and the specific capacity and initial efficiency of the negative electrode material are also reduced. When γ≤2, the surface of the negative electrode material is too much silicon oxide, mainly caused by the thick carbon particle coverage; although the defects and pores on the surface of the negative electrode material are greatly reduced, the thick silicon oxide SiO x Itself will cause irreversible lithiumation reaction, leading to excessive consumption of active lithium ions, and the first coulombic efficiency of the negative electrode material is reduced. x

[0027] The present application controls 2 < γ < 10, the defects and pores in the negative electrode material are well closed, effectively reducing the side reaction contact sites of the negative electrode material with the electrolyte, so that the negative electrode material obtains good high-temperature storage performance. At the same time, after the defects and pores in the negative electrode material are closed, the contact between the negative electrode material and air is also effectively reduced, the oxidation resistance of the negative electrode material is improved, the irreversible reaction formed in the first charge and discharge process of the negative electrode material can be effectively reduced, thereby improving the first coulombic efficiency and specific capacity of the negative electrode material.

[0028] In some embodiments, A ranges from 5 to 45, which can be 5, 10, 15, 20, 30, 35, 40, or 45, and can also be other values within the above range, which is not limited herein.

[0029] In some embodiments, B ranges from 2 to 5, which can be 2, 2.5, 3, 3.5, 4, 4.5, or 5, and can also be other values within the above range, which is not limited herein.

[0030] ​In some embodiments, the negative electrode material with a mass of 0.3-0.5 g is soaked in a mixture of 6 mL of concentrated hydrochloric acid and 2 mL of concentrated nitric acid, heated in a graphite digestion instrument at 50°C for 30 minutes, and then filtered and diluted to volume. The mass content of the metal M element (i.e., magnesium element) in the negative electrode material is less than 0.8%, specifically 0.75%, 0.7%, 0.65%, 0.5%, 0.4%, 0.3%, 0.2%, 0.15%, or 0.1%, etc., and of course can also be other values within the above range, which are not limited herein. It can be understood that a lower content of the magnesium element that can be dissolved on the surface of the negative electrode material indicates that the Mg element is difficult to dissolve, i.e., there are fewer defects and pores exposed on the surface of the negative electrode material, the contact sites between the negative electrode material and the electrolyte are reduced, and the magnesium that can be dissolved is less. Therefore, the negative electrode material is not prone to react with the electrolyte, which is beneficial to improve the high-temperature storage performance of the negative electrode material. At the same time, fewer defects and pores are beneficial to control the degree of oxidation of the negative electrode material, thereby improving the specific capacity and the first coulombic efficiency of the negative electrode material.

[0031] In some embodiments, the mass content of the metal M element (i.e., magnesium element) in the negative electrode material is 5%-15%, specifically 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15%, etc., and of course can also be other values within the above range, which are not limited herein. When the mass content of the magnesium element in the negative electrode material is <5%, the doping amount of the magnesium element in the negative electrode material is less, the utilization rate of the active substance is lower, and the first coulombic efficiency of the negative electrode material is less improved, which is difficult to meet the market demand. When the mass content of the magnesium element in the negative electrode material is >15%, the doped Mg reduces SiO x x, and the defects and pores caused by the reduction are obviously increased, which significantly increases the contact reaction sites between the negative electrode material and the electrolyte, intensifies the side reaction, and at the same time, the high-temperature storage performance of the negative electrode material is reduced.

[0032] In some embodiments, the mass content of the oxygen element in the negative electrode material is 20%-34%, specifically 20%, 22%, 24%, 25%, 26%, 28%, 30%, 31%, 32%, 33%, or 34%, etc., and of course can also be other values within the above range, which are not limited herein.

[0033] In some embodiments, the chemical formula of the silicon oxide is SiO x , 0 x Specifically, it can be SiO 0.5 , SiO 0.8 , SiO 0.9 , SiO, SiO 1.1 , SiO 1.2 , SiO 1.5SiO2, etc. It can be a material formed by dispersing silicon particles in SiO2, or a material having tetrahedral structural units with silicon atoms at the center and silicon and / or oxygen atoms at the four vertices.

[0034] In some embodiments, the negative electrode material contains Si grains, and the size of the Si grains in the negative electrode material 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 it can also be other values within the above range, which is not limited here.

[0035] In some embodiments, the negative electrode material further includes a carbon layer on at least part of the surface of the active material.

[0036] In some embodiments, the carbon layer includes amorphous carbon.

[0037] In some embodiments, the thickness of the carbon layer is 1 nm to 500 nm, specifically 1 nm, 5 nm, 10 nm, 50 nm, 100 nm, 200 nm, 300 nm, 400 nm, or 500 nm, etc., and of course it can also be other values within the above range, which is not limited here. It can be understood that by limiting the thickness of the carbon layer within the above range, the carbon layer can more completely coat the active material, reduce the direct contact between the active material and the electrolyte, thereby reducing the generation of the SEI film, reducing the consumption of active lithium ions, and improving the first coulomb efficiency of the negative electrode material.

[0038] In some embodiments, the mass content of carbon elements in the negative electrode material is 2% to 8%, specifically 2%, 3%, 4%, 5%, 6%, 7%, or 8%, etc., and of course it can also be other values within the above range, which is not limited here. It can be understood that the mass content of carbon elements in the negative electrode material within the above range can reduce the structural damage of the negative electrode material due to the volume expansion of silicon, improve the cycle performance of the negative electrode material, be conducive to the formation of a stable and thin solid electrolyte interface (SEI) film, reduce the consumption of active lithium ions, improve the first coulomb efficiency of the negative electrode material, and also be conducive to the improvement of the cycle performance of the negative electrode material.

[0039] In some embodiments, the mass content of silicon element in the negative electrode material is 48% to 63%, and can be 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 60%, 61% or 63%, and can also be other values in the above range, which is not limited herein. When the mass content of silicon element is too low, the specific capacity of the negative electrode material is low, which is difficult to meet the demand of high energy density lithium ion battery; when the mass content of silicon element is too high, the volume expansion of the negative electrode material is too large, which can cause serious degradation of the cycle performance of the material.

[0040] In some embodiments, the specific surface area of the negative electrode material is ≤8m 2 / g, and can be 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, and can also be other values in the above range, which is not limited herein. It can be understood that when the specific surface area of the negative electrode material is in the above range, the contact area between the negative electrode material and the electrolyte is small, and the reaction sites are few, which is beneficial 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. At the same time, the low specific surface area exposes less reduced Si in the negative electrode material, which is beneficial to improve the specific capacity and the initial coulombic efficiency (ICE) of the negative electrode material.

[0041] In some embodiments, the oil absorption value of the negative electrode material is 30mL / 100g to 40mL / 100g, and can be 30mL / 100g, 31mL / 100g, 32mL / 100g, 33mL / 100g, 34mL / 100g, 35mL / 100g, 36mL / 100g, 38mL / 100g or 40mL / 100g, and can also be other values in the above range, which is not limited herein. It can be understood that when the oil absorption value of the negative electrode material is controlled in the above range, it indicates that the defects and pores on the surface of the negative electrode material are less, which can guarantee the wettability of the negative electrode material and the electrolyte, improve the conduction efficiency of lithium ions, and improve the electrochemical performance of the negative electrode material.

[0042] In some embodiments, the tap density of the negative electrode material is 0.9g / cm 3 ~1.3g / cm 3 , and can be 0.9g / cm 3 , 0.95g / cm 3 , 1.0g / cm 3 , 1.1g / cm 3 , 1.15g / cm3 1.2 g / cm3 3 or 1.3 g / cm3 3 or other values within the above range, which are not limited herein. It can be understood that the tap density of the negative electrode material within the above range indicates that the negative electrode material has good processability, which can reduce the difficulty in the process of electrode coating and battery manufacturing, and is also conducive to maintaining the structural stability of the electrode during the cycle process, improving the cycle performance of the material and the energy density of the battery.

[0043] In some embodiments, the true density of the negative electrode material is 2.3 g / cm3 3 ~ 2.66 g / cm3 3 , specifically 2.3 g / cm3 3 , 2.4 g / cm3 3 , 2.45 g / cm3 3 , 2.5 g / cm3 3 , 2.6 g / cm3 3 , 2.62 g / cm3 3 or 2.66 g / cm3 3 or other values within the above range, which are not limited herein. It can be understood that the true density of the negative electrode material within the above range is conducive to improving the energy density of the battery made of the negative electrode material.

[0044] In some embodiments, the pH of the negative electrode material is 6.5 ~ 9.5, specifically 6.5, 7, 7.5, 8, 8.5, 9, 9.1, 9.3 or 9.5, or other values within the above range, which are not limited herein.

[0045] In some embodiments, the median particle size Dn(50) of the negative electrode material is 2 μm ~ 12 μm, specifically 2 μm, 5 μm, 6 μm, 8 μm, 10 μm or 12 μm, or other values within the above range, which are not limited herein. It can be understood that controlling the median particle size Dn(50) of the negative electrode material within the above range is conducive to improving the cycle performance of the negative electrode material.

[0046] In some embodiments, the pore volume of the negative electrode material is < 0.03 cm3 3 / g, specifically 0.028 cm3 3 / g, 0.025 cm3 3 / g, 0.02 cm3 3 / g, 0.018 cm3 3 / g, 0.015 cm3 3 / g, 0.01 cm3 3 / g, 0.008 cm3 3 / g or 0.005 cm3 3 / g, of course, can also be other values within the above range, which are not limited herein. It can be understood that 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 reaction sites are few, which is beneficial 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.

[0047] The application also provides a preparation method of the negative electrode material according to the second aspect, and the preparation method comprises the following steps:

[0048] In step S100, the raw material of the silicon-oxygen material and magnesium are heated and gasified and heat preserved respectively under vacuum conditions, the obtained silicon source vapor and magnesium vapor are mixed and co-deposited to obtain a precursor; wherein the heating and gasification temperature of the raw material of the silicon-oxygen material is T1 ℃, the heat preservation time of the raw material of the silicon-oxygen material is t1 h, the heating and gasification temperature of the magnesium is T2 ℃, the heat preservation time of the magnesium is t2 h, T1 > T2, and t1 > t2, and the difference t1-t2 between t1 and t2 is 1-7;

[0049] In step S200, carbon dioxide gas and / or carbon monoxide gas are introduced, and gas phase deposition is performed on the precursor to obtain an active substance, and the negative electrode material comprises the active substance.

[0050] The preparation method of the negative electrode material provided by the application first co-deposits the raw material of the silicon-oxygen material and magnesium by heating and gasifying the raw material of the silicon-oxygen material and the magnesium respectively, and then controls the heating and gasification temperature and time of the raw material of the silicon-oxygen material and the magnesium to regulate the generation rate and time of the silicon source vapor and the magnesium vapor, so that the silicon-oxygen material and the magnesium can be uniformly co-deposited, at this time, the magnesium is uniformly dispersed in the silicon-oxygen material, and defects and pores are generated in the co-deposition process due to the magnesium hot reduction reaction of the silicon-oxygen material and the magnesium. In the application, the heating and gasification time of the raw material of the silicon-oxygen material is prolonged, the deposition of the silicon-oxygen material is continued on the co-deposition product of the silicon-oxygen material and the magnesium, so that more silicon oxide is deposited on the surface of the precursor, and the silicon oxide can fill and seal the defects and pores, so that the surface oxidation degree of the negative electrode material is lower than that of the internal particles of the negative electrode material. Then, carbon dioxide gas and / or carbon monoxide gas are introduced to react with the silicon exposed on the surface of the precursor to generate silicon oxide SiO xand carbon, wherein the silicon oxide and carbon can further fill defects and pores inside the active material, thereby further reducing defects and pores in the negative electrode material, reducing the contact site of the side reaction between the negative electrode material and the electrolyte; at the same time, the generated silicon oxide and amorphous carbon cover the exposed silicon (Si) surface of the negative electrode material, which can synergistically control the surface oxidation degree of the negative electrode material, inhibit the further reaction of carbon dioxide gas and / or carbon monoxide gas with silicon (Si), and at the same time reduce the reaction of silicon with oxygen in the air, and also reduce the oxidation of the negative electrode material in the air, thereby effectively improving the specific capacity and the first coulombic efficiency of the negative electrode material.

[0051] The preparation method provided by the present scheme is described in detail below.

[0052] In step S100, the raw material of the silicon-oxygen material and magnesium are heated and vaporized and heat preserved respectively under vacuum conditions, the obtained silicon source vapor and magnesium vapor are mixed and co-deposited to obtain a precursor; wherein the heating and vaporization temperature of the raw material of the silicon-oxygen material is T1℃, the heat preservation time of the raw material of the silicon-oxygen material is t1h, the heating and vaporization temperature of the magnesium is T2℃, the heat preservation time of the magnesium is t2h, T1>T2, and t1>t2, the difference t1-t2 between t1 and t2 is 1-7.

[0053] In some embodiments, the raw material of the silicon-oxygen material includes at least one of a mixture of Si, SiO y and Si, a mixture of Si and SiO2, wherein 0 y and Si, a mixture of Si and SiO2, wherein 0

[0054] In some embodiments, the raw material of the silicon-oxygen material includes a mixture of Si and SiO2, and the molar ratio of Si to SiO2 is 1:1.

[0055] In some embodiments, the mass ratio of the raw material of the silicon-oxygen material to magnesium is 1:(0.05-0.2), which can be 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., and of course can also be other values within the above range, which are not limited herein.

[0056] In some embodiments, the vacuum pressure in the heating and vaporization process is 0.1 Pa-1000 Pa, which can be 0.1 Pa, 1 Pa, 10 Pa, 50 Pa, 100 Pa, 500 Pa, 800 Pa or 1000 Pa, etc., and of course can also be other values within the above range, which are not limited herein.

[0057] In some embodiments, the heating and vaporization temperature of the raw material of the silicon-oxygen material is T1 ℃, 800≤T1≤1600, which can be 800, 850, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600 or other values within the above range.

[0058] In some embodiments, the holding time of the raw material of the silicon-oxygen material is t1 h, 10≤t1≤30, which can be 10, 12, 15, 18, 20, 22, 24, 26, 28, 30 or other values within the above range.

[0059] In some embodiments, the heating and vaporization temperature of the magnesium is T2 ℃, 400≤T2≤600, which can be 400, 420, 450, 480, 500, 530, 550, 560, 580, 600 or other values within the above range.

[0060] In some embodiments, the holding time of the magnesium is t2 h, 1≤t2≤7, which can be 1, 2, 3, 4, 5, 6, 7 or other values within the above range.

[0061] In some embodiments, the ratio T1 / T2 of T1 and T2 is (2-3):1, which can be 2:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, 2.6:1, 2.7:1, 2.8:1, 2.9:1, 3:1 or other values within the above range. It can be understood that controlling the ratio T1 / T2 of the heating and vaporization temperature T1 of the raw material of the silicon-oxygen material and the heating and vaporization temperature T2 of the magnesium within the above range can regulate the generation rate of silicon source vapor and magnesium vapor in the co-deposition process, which is conducive to regulating the mass content of doped magnesium in the negative electrode material, reducing the defects and pores generated by the magnesium thermal reduction reaction of the silicon-oxygen material and the magnesium in the co-deposition process, reducing the surface oxidation degree of the negative electrode material, reducing the occurrence of side reactions between the negative electrode material and the electrolyte, and improving the first coulomb efficiency, specific capacity and high-temperature storage performance of the negative electrode material. When T1 / T2>3:1, the generation rate of magnesium vapor is too slow, and the mass content of doped magnesium in the negative electrode material is too low, which can cause the first coulomb efficiency of the negative electrode material to decrease. When T1 / T2<2:1, the generation rate of magnesium vapor is too fast, and the mass content of doped magnesium in the negative electrode material is too high, which can significantly increase the defects and pores generated by the magnesium thermal reduction reaction of the silicon-oxygen material and the magnesium in the co-deposition process, cause the surface of the negative electrode material to be easily oxidized, and significantly increase the contact sites of side reactions between the negative electrode material and the electrolyte, thereby causing the high-temperature storage performance of the negative electrode material to decrease.

[0062] In some embodiments, the difference t1-t2 between t1 and t2 is 1-7, specifically can be 1, 2, 3, 4, 5, 6 or 7, and of course can also be other values within the above range, which are not limited herein. It can be understood that during the co-deposition process, defects and pores will be generated due to the magnesium hot reduction reaction of the silicon-oxygen material and magnesium. In the present application, the difference t1-t2 between the holding time t1 of the raw material of the silicon-oxygen material and the holding time t2 of the magnesium is within the above range, and the defects and pores generated during the co-deposition process can be closed by further deposition of the silicon-oxygen material, so as to reduce the defects and pores in the negative electrode material, reduce the secondary reaction contact sites between the negative electrode material and the electrolyte, and improve the electrochemical performance of the negative electrode material. When t1-t2<1, the deposition time of the silicon-oxygen material is too short, and it is difficult to close the defects and pores generated during the co-deposition process due to the magnesium hot reduction reaction of the silicon-oxygen material and magnesium, resulting in a large number of defects and pores in the negative electrode material, high degree of surface oxidation of the negative electrode material, and many secondary reaction contact sites between the negative electrode material and the electrolyte, which is not conducive to the improvement of the electrochemical performance of the negative electrode material. When t1-t2<7, the deposition time of the silicon-oxygen material is too long, although the defects and pores on the surface of the negative electrode material are well closed, but the thick silicon oxide SiO x It will itself undergo irreversible lithiation reaction, resulting in excessive consumption of active lithium ions and decrease of the first coulombic efficiency of the negative electrode material.

[0063] In some embodiments, the co-deposition temperature is 600-1000℃, specifically can be 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, 950℃ or 1000℃, and of course can also be other values within the above range, which are not limited herein.

[0064] In step S200, carbon dioxide gas and / or carbon monoxide gas are introduced, and vapor deposition is performed on the precursor to obtain an active material. The negative electrode material comprises the active material.

[0065] In some embodiments, the vacuum pressure for vapor deposition is 1-10 kPa, specifically 1 kPa, 2 kPa, 3 kPa, 4 kPa, 5 kPa, 6 kPa, 7 kPa, 8 kPa, 9 kPa or 10 kPa, and of course other values within the above range are also possible and are not limited herein. It can be understood that controlling the vacuum pressure for vapor deposition within the above range is conducive to controlling the amount of carbon dioxide gas and / or carbon monoxide gas introduced, which can ensure that the amount of carbon dioxide gas and / or carbon monoxide gas introduced during vapor deposition can fully react with the silicon exposed on the surface of the precursor to generate silicon oxide and carbon and effectively fill the defects and pores inside the precursor, thereby reducing the defects and pores in the negative electrode material, reducing the contact sites of side reactions between the negative electrode material and the electrolyte, and improving the high-temperature storage performance of the negative electrode material. At the same time, it can also ensure that the amount of carbon dioxide gas and / or carbon monoxide gas introduced will not excessively react with the silicon exposed on the surface of the precursor, so that the defects and pores in the negative electrode material are too high in sealing degree, thereby limiting the transport of lithium ions and being detrimental to the improvement of the initial efficiency of the negative electrode material.

[0066] In some embodiments, the temperature for vapor deposition is 600-1000℃, specifically 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, 950℃ or 1000℃, and of course other values within the above range are also possible and are not limited herein.

[0067] In some embodiments, the time for vapor deposition is >1 h.

[0068] In some embodiments, the preparation method further comprises: performing carbon coating treatment on the active material to obtain the negative electrode material, wherein the negative electrode material comprises the active material and a carbon layer on at least part of the surface of the active material. The carbon layer on the surface of the active material can improve the electrical conductivity of the negative electrode material.

[0069] In some embodiments, the carbon coating treatment comprises at least one of gas-phase carbon coating treatment, solid-phase carbon coating treatment and liquid-phase carbon coating treatment.

[0070] In some embodiments, the gas-phase carbon source for gas-phase carbon coating treatment comprises at least one of methane, propane, butane, acetylene, benzene and toluene.

[0071] In some embodiments, the flow rate of the gas-phase carbon source is 1.0-2.5 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, and of course other values within the above range are also possible and are not limited herein.

[0072] In some embodiments, the temperature of the gas phase coating treatment is 600-1200℃, and can be 600℃, 700℃, 800℃, 900℃, 1000℃, 1100℃ or 1200℃, or other values within the above range.

[0073] In some embodiments, the coating time of the gas phase coating treatment is 2-10h, and can be 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h or 10h, or other values within the above range.

[0074] In some embodiments, the solid phase carbon source used in the solid phase carbon coating treatment includes at least one of sucrose, fructose, glucose, pitch, phenol formaldehyde resin, polyimide, citric acid, epoxy resin, amino resin, polystyrene, polyacrylic acid, carboxymethyl cellulose and cellulose acetate butyrate.

[0075] In a third aspect, the present application provides a negative electrode material, which includes a silicon-based active material and a carbon material, wherein the silicon-based active material includes silicon element, oxygen element and metal M element.

[0076] Energy spectrum analysis is performed on the particle section of the negative electrode material, n1 test points are randomly selected in the section of a single negative electrode material particle for point scanning analysis to obtain the mass percentage content of n1 metal M elements, the standard deviation k1 of the mass percentage content of the n1 metal M elements is calculated, and k1≤4.

[0077] The section of n2 negative electrode material particles is randomly selected for surface scanning analysis to obtain the mass percentage content of n2 metal M elements, the standard deviation k2 of the mass percentage content of the n2 metal M elements is calculated, and k2≤6; wherein n1 and n2 are natural numbers greater than or equal to 5.

[0078] The surface oxidation degree of the negative electrode material is γ, and 2<γ<10.

[0079] The surface oxidation degree of the negative electrode material is measured by the following method:

[0080] The mass ratio of the oxygen element and the metal M element of the negative electrode material is A, which is obtained by X-ray photoelectron spectroscopy, the mass ratio of the oxygen element in the negative electrode material and the metal M element in the negative electrode material is B, which is obtained by ONH element analysis, and γ=A / B.

[0081] In the above scheme, the negative electrode material includes a silicon-based active material and a carbon material, the silicon-based active material includes silicon elements, oxygen elements and metal M elements; k1 and k2 are controlled within the scope of the present application, indicating that the metal M elements can be uniformly distributed in a single particle and between multiple particles of the negative electrode material, and in the subsequent charging and discharging process, the local expansion stress of the negative electrode material particles is reduced. At the same time, the surface oxidation degree of the negative electrode material satisfies 2<γ<10, the oxidation degree of the surface of the negative electrode material is low, which can close and / or reduce the defects and pores on the surface of the negative electrode material through appropriate oxidation degree, reduce the contact sites of the side reaction of the negative electrode material and the electrolyte, and can effectively reduce the irreversible reaction formed in the first charging and discharging process of the negative electrode material. Under the synergistic action of the two, the negative electrode material not only has excellent first coulombic efficiency and specific capacity, but also can improve the cycle capacity retention rate. In some embodiments, n1 test points are randomly selected in the section of a single negative electrode material particle to measure the standard deviation k1 of the mass percentage of the metal M elements, the calculation formula of k1 is shown in the following formula I, k1≤4, k1 can be specifically 4, 3.5, 3.2, 3.0, 2.8, 2.6, 2.0, 1.8, 1.6, 1.5, 1.2, 1.0, 0.8, 0.5, 0.2 or 0.1, etc., of course, it can also be other values within the above range, which is not limited herein. In the present application, k1≤4, indicating that the distribution uniformity of the metal M elements in the single particle of the negative electrode material is good.

[0082] Wherein, n1 is all test points in the section of a single negative electrode material particle, m i is the mass percentage of the metal M elements measured at any test point, m0 is the average value of the mass percentage of the metal M elements measured at all test points.

[0083] In some embodiments, the standard deviation k2 of the mass percentage of the metal M elements in n2 negative electrode material particles is randomly selected, the calculation formula of k2 is shown in the following formula II, k2≤6, k2 can be specifically 6, 5.8, 5.5, 5, 4.5, 4, 3.5, 3.2, 3.0, 2.8, 2.6, 2.0, 1.8, 1.6, 1.5, 1.2, 1.0, 0.8, 0.5, 0.2 or 0.1, etc., of course, it can also be other values within the above range, which is not limited herein. In the present application, k2≤6, indicating that the distribution uniformity of the metal M elements in each particle of the negative electrode material is good.

[0084] Wherein, n1 is all test points in the section of a single negative electrode material particle, m j is the mass percentage of the metal M elements measured at any test point, m0 is the average value of the mass percentage of the metal M elements measured at all test points.

[0085] In some embodiments, the negative electrode material further satisfies: 0.2≤k1 / k2≤1. When k1 / k2 is too small, the uniformity of the metal M element is poor, which further exacerbates the formation of defects and pores in the negative electrode material particles. By controlling k1 / k2 within the above range, it can be seen that the standard deviation of the mass percentage of the metal M element in the negative electrode material particles is close to the standard deviation of the mass percentage of the metal M element between the particles. The metal M element in each particle of the negative electrode material can be uniformly distributed, which can alleviate the silicon expansion stress and improve the first coulombic efficiency and cycle performance of the negative electrode material.

[0086] In some embodiments, 0.2≤k1 / k2≤1; specifically, it can be 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1, and of course it can also be other values within the above range, which are not limited herein. It can be seen that the metal M element can be uniformly distributed in a single particle and between multiple particles of the negative electrode material. When k1 / k2 is too small, the distribution of the metal M element between the particles of the negative electrode material is uneven, which causes excessive doping of the metal M element in some particles, resulting in larger silicon grain size in some negative electrode materials, which is not conducive to improving the cycle performance of the negative electrode material. At the same time, it also causes a large number of defects and pores to be generated in some negative electrode material particles, which exacerbates the side reaction between the negative electrode material and the electrolyte, and reduces the cycle stability. When k1 / k2 is too large, the metal M element is unevenly distributed in a single particle of the negative electrode material, which causes the local silicon grain size in a single particle of the negative electrode material to be large, which is not conducive to improving the cycle performance of the negative electrode material. Similarly, it also causes defects and pores to be generated in a single particle of the negative electrode material, which exacerbates the side reaction between the negative electrode material and the electrolyte, and reduces the cycle stability.

[0087] In some embodiments, the surface oxidation degree of the negative electrode material is γ, γ=A / B, 2<γ<10, specifically, it can be 2.1, 2.5, 3, 4, 5, 6, 7, 8, 9, 9.5, 9.6, 9.8 or 9.9, and of course it can also be other values within the above range, which are not limited herein. When γ≥10, the surface oxidation degree of the negative electrode material is high. This is because a large number of defects and pores are not filled with silicon oxide, the surface of the negative electrode material is easy to adsorb oxygen and other gases to cause surface oxidation, and the presence of defects and pores makes the XPS detection depth deeper, so the A value is larger. The content of defects and pores on the surface of the negative electrode material is high, the reaction sites on the surface of the negative electrode material are too many, the side reaction between the negative electrode material and the electrolyte is exacerbated, and the high defects and pores also cause the negative electrode material to be easy to oxidize, which reduces the utilization rate of the doped metal M, and the specific capacity and first efficiency of the negative electrode material are also reduced. When γ≤2, it means that there is too much silicon oxide on the surface of the negative electrode material, mainly SiO xcaused by thicker carbon particle coverage; although the defects and pores on the surface of the negative electrode material are greatly reduced, the thicker silicon oxide SiO x It will itself undergo an irreversible lithiation reaction, resulting in excessive consumption of active lithium ions, and a decrease in the first coulombic efficiency of the negative electrode material.

[0088] The present application controls 2 < γ < 10, the defects and pores in the negative electrode material are well closed, effectively reducing the contact sites of the negative electrode material with the electrolyte, and the negative electrode material obtains good high-temperature storage performance. At the same time, after the defects and pores in the negative electrode material are closed, the contact of the negative electrode material with air is also effectively reduced, the oxidation resistance of the negative electrode material is improved, the irreversible reaction formed in the first charge and discharge process of the negative electrode material can be effectively reduced, and thus the first coulombic efficiency and specific capacity of the negative electrode material are improved.

[0089] In some embodiments, A ranges from 5 to 45, and can be specifically 5, 10, 15, 20, 30, 35, 40 or 45, and can also be other values within the above range, which are not limited herein.

[0090] In some embodiments, B ranges from 2 to 5, and can be specifically 2, 2.5, 3, 3.5, 4, 4.5 or 5, and can also be other values within the above range, which are not limited herein.

[0091] In some embodiments, the negative electrode material with a mass of 0.3 g to 0.5 g is soaked in a mixture of 6 mL of concentrated hydrochloric acid and 2 mL of concentrated nitric acid, heated at 50°C for 30 minutes in a graphite digestion instrument, and then filtered and diluted. The mass content of the metal M element in the negative electrode material in the digestion solution is less than 0.8% as tested by an ICP spectrometer, and can be specifically 0.75%, 0.7%, 0.65%, 0.5%, 0.4%, 0.3%, 0.2%, 0.15% or 0.1%, and can also be other values within the above range, which are not limited herein. It can be understood that a lower content of the metal M element that can be dissolved on the surface of the negative electrode material indicates that the metal M element is difficult to dissolve, i.e., there are fewer defects and pores exposed on the surface of the negative electrode material, and the contact sites of the negative electrode material with the electrolyte are reduced, and the metal M element that can be dissolved is less. Therefore, the negative electrode material is not prone to reaction with the electrolyte, which is conducive to improving the high-temperature storage performance of the negative electrode material. At the same time, fewer defects and pores are conducive to controlling the oxidation degree of the negative electrode material, thereby improving the specific capacity and first coulombic efficiency of the negative electrode material.

[0092] In some embodiments, the metal M element is selected from at least one of Mg, Al and Ca.

[0093] In some embodiments, the mass content of the metal M element in the negative electrode material is 5% to 15%, and can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15%, or other values within the above range, which are not limited herein. When the mass content of the metal M element in the negative electrode material is < 5%, the doping amount of the metal M element in the negative electrode material is small, the utilization rate of the silicon-based active substance is low, the first coulombic efficiency of the negative electrode material is low, and it is difficult to meet the market demand. When the mass content of the metal M element in the negative electrode material is > 15%, the defects and pores in the silicon-based active substance increase significantly, the contact reaction sites between the negative electrode material and the electrolyte increase significantly, the side reaction is intensified, and the high-temperature storage performance of the negative electrode material is reduced.

[0094] In some embodiments, the silicon-based active substance includes at least one of elemental silicon, silicon oxide, and silicon alloy. The elemental silicon can be amorphous silicon and / or crystalline silicon, and the silicon alloy can be silicon-lithium alloy, silicon-magnesium alloy, silicon-nickel alloy, etc. In some cases, the silicon-based active substance includes silicon elemental particles and silicon alloy.

[0095] In some embodiments, the silicon oxide has a general formula of SiO x , and 0 < x ≤ 2. Specifically, it can be SiO 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 dispersing silicon particles in SiO2, or a material having a tetrahedral structural unit, in which a silicon atom is located at the center of the tetrahedral structural unit, and a silicon atom and / or an oxygen atom is located at four vertices of the tetrahedral structural unit.

[0096] In some embodiments, the negative electrode material contains Si grains, and in the X-ray diffraction spectrum of the negative electrode material, the size of the Si grains in the negative electrode material on the (220) crystal face is 5 nm to 12 nm, and can be 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, or 12 nm, or other values within the above range, which are not limited herein.

[0097] In some embodiments, in the negative electrode material, the silicon-based active substance and the carbon material are dispersed in the form of particles.

[0098] In some embodiments, in the negative electrode material, the silicon-based active substance is dispersed in the carbon material. The application does not limit the compounding mode of the carbon material and the silicon-based active substance, and they can be compounded with each other.

[0099] In some embodiments, the carbon material is present on the surface of the silicon-based active material and / or dispersed between the silicon-based active materials. Specifically, the silicon-based active material can be matrixed with the carbon material and embedded within the carbon material.

[0100] In some embodiments, the carbon material is located on at least part of the surface of the silicon-based active material to form a carbon layer.

[0101] In some embodiments, the thickness of the carbon layer is 1 nm to 500 nm, specifically, 1 nm, 5 nm, 10 nm, 50 nm, 100 nm, 200 nm, 300 nm, 400 nm or 500 nm, and of course, other values within the above range are also possible and are not limited herein. It can be understood that by limiting the thickness of the carbon layer within the above range, the silicon-based active material can be more completely coated by the carbon layer, reducing direct contact between the silicon-based active material and the electrolyte, thereby reducing the generation of the SEI film, reducing the consumption of active lithium ions, and improving the first coulombic efficiency of the negative electrode material.

[0102] In some embodiments, the carbon material includes at least one of graphite, graphene, amorphous carbon, carbon nanotubes and carbon fibers. The graphite can be artificial graphite and / or natural graphite.

[0103] In some embodiments, the carbon material includes amorphous carbon, which can be soft carbon and / or hard carbon. It can be understood that the carbon material can improve the electrical conductivity of the silicon-based active material.

[0104] In some embodiments, the mass content of carbon elements in the negative electrode material is 2% to 8%, specifically, 2%, 3%, 4%, 5%, 6%, 7% or 8%, and of course, other values within the above range are also possible and are not limited herein. It can be understood that the mass content of carbon elements in the negative electrode material within the above range can reduce the structural damage of the negative electrode material due to the volume expansion of the silicon material, improve the cycle performance of the negative electrode material, be conducive to the formation of a stable and thin solid electrolyte interface (SEI) film, reduce the consumption of active lithium ions, improve the first coulombic efficiency of the negative electrode material, and also be conducive to the improvement of the cycle performance of the negative electrode material.

[0105] In some embodiments, the mass content of silicon elements in the negative electrode material is 48% to 63%, specifically, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 60%, 61% or 63%, and of course, other values within the above range are also possible and are not limited herein. When the mass content of silicon elements is too low, the specific capacity of the negative electrode material is low, which is difficult to meet the demand of high energy density lithium ion batteries; when the mass content of silicon elements is too high, the volume expansion of the negative electrode material is too large, which can cause serious degradation of the cycle performance of the material.

[0106] In some embodiments, the specific surface area of the negative electrode material is ≤8 m 2 / g, specifically 8 m 2 / g, 7 m 2 / g, 6 m 2 / g, 5 m 2 / g, 4 m 2 / g, 3 m 2 / g, 2 m 2 / g, or 1 m 2 / g, etc., and of course can also be other values within the above range, which are not limited herein. It can be understood that the specific surface area of the negative electrode material is within the above range, the contact area of the negative electrode material with the electrolyte is small, and the reaction sites are few, which is conducive to reducing 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, the low specific surface area exposes less reduced Si in the negative electrode material, which is conducive to improving the specific capacity and initial coulombic efficiency (ICE) of the negative electrode material.

[0107] In some embodiments, the oil absorption value of the negative electrode material is 30 mL / 100 g to 40 mL / 100 g, specifically 30 mL / 100 g, 31 mL / 100 g, 32 mL / 100 g, 33 mL / 100 g, 34 mL / 100 g, 35 mL / 100 g, 36 mL / 100 g, 38 mL / 100 g, or 40 mL / 100 g, etc., and of course can also be other values within the above range, which are not limited herein. It can be understood that the oil absorption value of the negative electrode material is controlled within the above range, which indicates that the defects and pores on the surface of the negative electrode material are less, which can ensure the wettability of the negative electrode material with the electrolyte, improve the conduction efficiency of lithium ions, and improve the electrochemical performance of the negative electrode material.

[0108] In some embodiments, the tap density of the negative electrode material is 0.9 g / cm 3 to 1.3 g / cm 3 , specifically 0.9 g / cm 3 , 0.95 g / cm 3 , 1.0 g / cm 3 , 1.1 g / cm 3 , 1.15 g / cm 3 , 1.2 g / cm 3 , or 1.3 g / cm 3 , etc., and of course can also be other values within the above range, which are not limited herein. It can be understood that the tap density of the negative electrode material is within the above range, which indicates that the processing performance of the negative electrode material is good, which can reduce the difficulty in the processes of electrode coating and battery manufacturing, and at the same time is also conducive to maintaining the structural stability of the electrode sheet during the cycle process, improving the cycle performance of the material and the energy density of the battery.

[0109] In some embodiments, the true density of the negative electrode material is 2.3 g / cm 3 ~ 2.66 g / cm 3 , specifically can be 2.3 g / cm 3 , 2.4 g / cm 3 , 2.45 g / cm 3 , 2.5 g / cm 3 , 2.6 g / cm 3 , 2.62 g / cm 3 or 2.66 g / cm 3 , and of course can also be other values within the above range, which are not limited herein. It can be understood that the true density of the negative electrode material within the above range is beneficial to improve the energy density of the battery made of the negative electrode material.

[0110] In some embodiments, the pH of the negative electrode material is 6.5 ~ 9.5, specifically can be 6.5, 7, 7.5, 8, 8.5, 9, 9.1, 9.3 or 9.5, and of course can also be other values within the above range, which are not limited herein.

[0111] In some embodiments, the median particle size Dn(50) of the negative electrode material is 2 μm ~ 12 μm, specifically can be 2 μm, 5 μm, 6 μm, 8 μm, 10 μm or 12 μm, and of course can also be other values within the above range, which are not limited herein. It can be understood that controlling the median particle size Dn(50) of the negative electrode material within the above range is beneficial to improve the cycle performance of the negative electrode material.

[0112] In some embodiments, the pore volume of the negative electrode material is < 0.03 cm 3 / g, specifically can be 0.028 cm 3 / g, 0.025 cm 3 / g, 0.02 cm 3 / g, 0.018 cm 3 / g, 0.015 cm 3 / g, 0.01 cm 3 / g, 0.008 cm 3 / g or 0.005 cm 3 / g, and of course can also be other values within the above range, which are not limited herein. It can be understood that the pore volume of the negative electrode material within the above range is beneficial to reduce the contact area and reaction sites of the negative electrode material with the electrolyte, thereby reducing the occurrence of side reactions between the negative electrode material and the electrolyte, and improving the high-temperature storage performance of the negative electrode material.

[0113] The application also provides a preparation method of the negative electrode material according to the third aspect, which comprises the following steps:

[0114] In step S10, the raw material of the silicon-oxygen material and the dopant containing the metal M element are heated and gasified respectively under vacuum, and the silicon source vapor and the metal M vapor obtained after mixing are co-deposited to obtain a precursor; wherein the heating and gasification temperature of the raw material of the silicon-oxygen material is T1 ℃, and the first temperature rising rate is continued to rise for t1 h, the heating and gasification temperature of the dopant containing the metal M element is T2 ℃, and the second temperature rising rate is continued to rise for t2 h, T1 > T2, the first temperature rising rate is 20-30 ℃ / h, and the second temperature rising rate is 10-15 ℃ / h;

[0115] In step S20, carbon dioxide gas and / or carbon monoxide gas are introduced, and gas phase deposition is performed on the precursor to obtain a silicon-based active material.

[0116] In step S30, the silicon-based active material is subjected to carbon coating treatment to obtain a negative electrode material, and the negative electrode material comprises the silicon-based active material and a carbon material.

[0117] The preparation method of the negative electrode material provided in the present application first co-deposits the raw material of the silicon-oxygen material and the dopant containing the metal M element by heating and gasifying them respectively, and then controls the heating and gasification temperature and the temperature rising rate of the raw material of the silicon-oxygen material and the dopant containing the metal M element to adjust the generation rate and the generation time of the silicon source vapor and the metal M vapor, so that the silicon-oxygen material and the metal M can be uniformly co-deposited, the metal M element is uniformly dispersed in the silicon-oxygen material, the uniform distribution degree of the metal M element in the particles and between the multiple particles of the negative electrode material tends to be consistent, the distribution uniformity of the metal M element in the negative electrode material is improved, and the first coulomb efficiency and the cycle stability of the negative electrode material can be improved. In the co-deposition process, defects and pores are generated due to the thermal reduction reaction between the silicon-oxygen material and the metal M. In the present application, the heating and gasification time of the raw material of the silicon-oxygen material is controlled, and the deposition of the silicon-oxygen material is continued on the co-deposition product of the silicon-oxygen material and the metal M, so that more silicon oxide is deposited on the surface of the precursor, the silicon oxide can fill and seal the defects and pores, and the surface oxidation degree of the negative electrode material is higher than that in the particles of the negative electrode material. Then, carbon dioxide gas and / or carbon monoxide gas are introduced to react with the silicon exposed on the surface of the precursor to generate silicon oxide SiO xand carbon, wherein the silicon oxide and carbon can further fill defects and pores in the active material, thereby further reducing defects and pores in the negative electrode material, reducing the contact sites of side reactions between the negative electrode material and the electrolyte; at the same time, the generated silicon oxide and amorphous carbon cover the exposed silicon (Si) surface of the negative electrode material, which can synergistically control the surface oxidation degree of the negative electrode material, inhibit the further reaction of carbon dioxide gas and / or carbon monoxide gas with silicon (Si), and reduce the reaction of silicon with oxygen in the air, thereby effectively improving the specific capacity and the first coulombic efficiency of the negative electrode material.

[0118] The preparation method provided by the present scheme is described in detail below.

[0119] In step S10, the raw material of the silicon-oxygen material and the dopant containing the metal M element are heated and gasified and heat preserved respectively under vacuum conditions, the obtained silicon source vapor and metal M vapor are mixed and co-deposited to obtain a precursor; wherein the heating and gasification temperature of the raw material of the silicon-oxygen material is T1 ℃, and the first temperature rising rate is continued to rise for t1 h, the heating and gasification temperature of the dopant is T2 ℃, and the second temperature rising rate is continued to rise for t2 h, T1 > T2, the first temperature rising rate is 20 ℃ / h-30 ℃ / h, and the second temperature rising rate is 10 ℃ / h-15 ℃ / h.

[0120] In some embodiments, the raw material of the silicon-oxygen material includes at least one of a mixture of Si, SiO y and Si, a mixture of Si and SiO2, wherein 0 < y < 2. y and Si, a mixture of Si and SiO2, wherein 0 < y < 2.

[0121] In some embodiments, the raw material of the silicon-oxygen material includes a mixture of Si and SiO2, and the molar ratio of Si to SiO2 is 1:1.

[0122] In some embodiments, the mass ratio of the raw material of the silicon-oxygen material to the dopant containing the metal M element is 1:(0.05-0.2), which can be 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, and of course can also be other values within the above range, which are not limited herein.

[0123] In some embodiments, the vacuum pressure in the heating and gasification process is 0.1 Pa-1000 Pa, which can be 0.1 Pa, 1 Pa, 10 Pa, 50 Pa, 100 Pa, 500 Pa, 800 Pa or 1000 Pa, and of course can also be other values within the above range, which are not limited herein.

[0124] In some embodiments, the raw material of the silicon-oxygen material is heated and vaporized at a temperature T1, 800≤T1≤1200, which can be 800, 850, 900, 1000, 1100, 1200, or other values within the above range.

[0125] In some embodiments, the raw material of the silicon-oxygen material is heated at a first temperature increasing rate of 20-30℃ / h, which can be 20℃ / h, 22℃ / h, 24℃ / h, 25℃ / h, 26℃ / h, 28℃ / h, 30℃ / h, or other values within the above range.

[0126] In some embodiments, the dopant containing the metal M element is heated and vaporized at a temperature T2, 400≤T2≤600, which can be 400, 420, 450, 480, 500, 530, 550, 560, 580, 600, or other values within the above range.

[0127] In some embodiments, the dopant containing the metal M element is heated at a second temperature increasing rate of 10-15℃ / h, which can be 10℃ / h, 11℃ / h, 12℃ / h, 13℃ / h, 14℃ / h, 15℃ / h, or other values within the above range.

[0128] In some embodiments, the raw material of the silicon-oxygen material and the dopant containing the metal M element are heated for 10-15h, which can be 10h, 11h, 12h, 13h, 14h, 15h, or other values within the above range.

[0129] In the present application, the raw material of the silicon-oxygen material and the dopant containing the metal M element are both in a process of constant temperature increase, and the evaporation rates of the two raw materials are affected differently by the temperature increasing rate. Controlling the temperature increasing rate of the raw material of the silicon-oxygen material to be higher than that of the dopant containing the metal M element can make the silicon vapor and the metal vapor formed by evaporation both in a stable output state, and the content of the vapor remains relatively uniform with the temperature increasing time, thereby improving the uniformity of the distribution of the metal M element in the negative electrode material.

[0130] In some embodiments, the co-deposition temperature is 600-1000℃, which can be 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, 1000℃, or other values within the above range.

[0131] In step S20, carbon dioxide gas and / or carbon monoxide gas are introduced, and vapor deposition is performed on the precursor to obtain a silicon-based active material.

[0132] In some embodiments, the vacuum pressure for the vapor deposition is 1-10 kPa, specifically 1 kPa, 2 kPa, 3 kPa, 4 kPa, 5 kPa, 6 kPa, 7 kPa, 8 kPa, 9 kPa or 10 kPa, and of course other values within the above range are also possible and are not limited herein. It can be understood that controlling the vacuum pressure for the vapor deposition within the above range is conducive to controlling the amount of carbon dioxide gas and / or carbon monoxide gas introduced, which can ensure that the amount of carbon dioxide gas and / or carbon monoxide gas introduced during the vapor deposition can fully react with the silicon exposed on the surface of the precursor to generate silicon oxide and carbon and effectively fill the defects and pores inside the precursor, thereby reducing the defects and pores in the negative electrode material, reducing the contact sites of the side reactions between the negative electrode material and the electrolyte, and improving the high-temperature storage performance of the negative electrode material. At the same time, it can also ensure that the amount of carbon dioxide gas and / or carbon monoxide gas introduced will not excessively react with the silicon exposed on the surface of the precursor, so that the defects and pores in the negative electrode material are too high in sealing degree, thereby limiting the transport of lithium ions and being not conducive to improving the initial efficiency of the negative electrode material.

[0133] In some embodiments, the temperature for the vapor deposition is 600-1000℃, specifically 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, 950℃ or 1000℃, and of course other values within the above range are also possible and are not limited herein.

[0134] In some embodiments, the time for the vapor deposition is >2 h.

[0135] In step S30, the silicon-based active material is subjected to carbon coating treatment to obtain a negative electrode material, which comprises the silicon-based active material and a carbon material.

[0136] In some embodiments, the carbon material forms a carbon layer on at least part of the surface of the silicon-based active material, which can improve the electrical conductivity of the negative electrode material.

[0137] In some embodiments, the carbon coating treatment comprises at least one of vapor-phase carbon coating treatment, solid-phase carbon coating treatment and liquid-phase carbon coating treatment.

[0138] In some embodiments, the vapor-phase carbon source for the vapor-phase carbon coating treatment comprises at least one of methane, propane, butane, acetylene, benzene and toluene.

[0139] In some embodiments, the flow rate of the gaseous carbon source is 1.0 L / min to 2.5 L / min, and can be 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, and the like, and can also be other values within the above range, which are not limited herein.

[0140] In some embodiments, the temperature of the gaseous coating treatment is 600℃ to 1200℃, and can be 600℃, 700℃, 800℃, 900℃, 1000℃, 1100℃, or 1200℃, and the like, and can also be other values within the above range, which are not limited herein.

[0141] In some embodiments, the coating time of the gaseous coating treatment is 2 h to 10 h, and can be 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, or 10 h, and the like, and can also be other values within the above range, which are not limited herein.

[0142] In some embodiments, the solid-phase carbon source used in the solid-phase carbon coating treatment includes at least one of sucrose, fructose, glucose, pitch, phenolic resin, polyimide, citric acid, epoxy resin, amino resin, polystyrene, polyacrylic acid, carboxymethyl cellulose, and cellulose acetate butyrate.

[0143] In a fourth aspect, the present application provides a negative electrode material, which includes a silicon-based active material and a carbon material on at least part of the surface of the silicon-based active material, and the silicon-based active material includes silicon, oxygen, and a metal M.

[0144] The surface oxidation degree of the negative electrode material is γ, and 2 < γ < 10.

[0145] The surface oxidation degree of the negative electrode material is measured by the following method:

[0146] The mass ratio of the oxygen element and the metal M element of the negative electrode material is A, which is obtained by X-ray photoelectron spectroscopy, and the mass ratio of the oxygen element in the negative electrode material and the metal M element in the negative electrode material is B, which is obtained by ONH elemental analysis and ICP spectrometer, and γ = A / B. In the present application, the surface oxidation degree of the negative electrode material is the surface doping degree of the negative electrode material.

[0147] The negative electrode material provided in the application comprises a silicon-based active substance and a carbon material, the silicon-based active substance comprises silicon elements, oxygen elements and metal M elements; the thermal conductivity of the silicon-based active substance is related to the order degree of the atomic arrangement in the silicon-based active substance. The silicon-based active substance in the application is doped with metal M elements, which can make the atoms in the silicon-based active substance recombine to form a crystal structure with high stability and order, and the content of disordered structure in the silicon-based active substance is at a low level, so that the thermal conductivity of the silicon-based active substance can be improved. With the decrease of the content of disordered structure, the crystallization degree of the silicon-based active substance is improved, and the thermal conductivity of the silicon-based active substance is better, but it will cause the increase of crystal boundary defects and the increase of side reactions with electrolyte, and the structural stability of the negative electrode material particles is reduced. Under the synergistic effect of the carbon material on the surface of the silicon-based active substance, the side reactions of the negative electrode material with electrolyte are reduced, the structural strength of the negative electrode material is improved, and the degree of volume expansion change of the negative electrode material can be effectively controlled. The surface oxidation degree of the negative electrode material is controlled to 2<γ<10, the surface oxidation degree of the negative electrode material is low, the silicon oxide on the surface layer of the negative electrode material can effectively fill and seal the defects and pores on the surface of the negative electrode material, the surface defects are reduced, the side reactions of the negative electrode material with electrolyte are reduced, and the structural strength of the surface of the negative electrode material is improved.

[0148] 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), and the thermal conductivity variation coefficient σ of the negative electrode material is σ=(1-g1 / g2) 2 / 0.57, 0.80<σ<1.50; by controlling the thermal conductivity variation coefficient σ of the negative electrode material in the range of 0.80<σ<1.50, the negative electrode material has excellent thermal conductivity at different temperatures, can quickly conduct the heat generated in the charging and discharging process at different temperatures, reduces the temperature difference between the negative electrode material particles when the battery made of the negative electrode material is electrochemically charged and discharged, reduces the transport energy barrier of lithium ions, under the synergistic effect of the thermal conductivity variation coefficient σ and the surface oxidation degree γ, 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, and improve the capacity attenuation of the negative electrode material.

[0149] In some embodiments, 0.15 W / (m·K)≤g1≤0.4 W / (m·K), the thermal conductivity of the negative electrode material at a temperature of 373.15 K (i.e., 100°C) can be specifically 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), and of course can also be other values within the above range, which are not limited herein. The negative electrode material has a higher thermal conductivity at a lower temperature, and the heat generated by the negative electrode material during charging and discharging can be quickly dispersed, and the negative electrode material exhibits higher initial efficiency and capacity under low temperature conditions.

[0150] In some embodiments, 0.5 W / (m·K)≤g2≤2.5 W / (m·K), the thermal conductivity of the negative electrode material at a temperature of 873.15 K (i.e., 600°C) can be specifically 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), and of course can also be other values within the above range, which are not limited herein. The negative electrode material has a higher thermal conductivity at a higher temperature, and the heat generated by the negative electrode material during charging and discharging can be quickly dispersed, and the negative electrode material exhibits higher initial efficiency and capacity under high temperature conditions.

[0151] In some embodiments, the negative electrode material has a thermal conductivity variation coefficient σ, which can be 0.81, 0.85, 0.9, 1.0, 1.1, 1.2, 1.3, 1.35, 1.4, or 1.49, and can also be other values within the above range, without limitation. When σ≤0.8, the negative electrode material has poor thermal conductivity at high temperatures, and the heat generated by the negative electrode material during charging and discharging is difficult to quickly dissipate. The temperature difference hinders the transmission of lithium ions, especially when the negative electrode material is mixed with graphite to serve as the negative electrode active material of the negative electrode sheet. The negative electrode material exhibits low initial efficiency and capacity at high temperatures. When σ≥1.5, the negative electrode material has too good thermal conductivity at high temperatures, that is, the content of the metal M element in the negative electrode material is too high. The high content of the metal element in the negative electrode material leads to a high degree of crystallization of the negative electrode material, and the disordered Si-O bonds in the negative electrode material are destroyed more, which makes it difficult to maintain the good mechanical toughness of the negative electrode material to resist the volume change during charging and discharging, thereby causing the negative electrode material particles to break and the structure to collapse, and the cycle performance to rapidly deteriorate. When the thermal conductivity variation coefficient σ of the negative electrode material is controlled to 0.8<σ<1.5, the negative electrode material can quickly conduct the heat generated during charging and discharging at different temperatures, reduce the non-uniform temperature difference between the particles or the particles of the negative electrode material, and reduce the transmission energy barrier of lithium ions. The negative electrode material can also have high specific capacity and high initial coulombic efficiency at low temperatures.

[0152] In some embodiments, the negative electrode material has a surface oxidation degree γ, γ=A / B, 2<γ<10, which can be 2.1, 2.5, 3, 4, 5, 6, 7, 8, 9, 9.5, 9.6, 9.8, or 9.9, and can also be other values within the above range, without limitation.

[0153] When γ≥10, the ratio of Si-O bonds to O-M bonds on the surface of the negative electrode material is high, and a large number of disordered Si-O bonds reduce the thermal conductivity of the negative electrode material. When γ≤2, the ratio of Si-O bonds to O-M bonds on the surface of the negative electrode material is low, and the disordered Si-O bonds are destroyed more, which makes it difficult to maintain the good mechanical toughness of the negative electrode material to resist the volume change during charging and discharging. The surface defects increase, leading to an increase in consumption of active lithium ions and a decrease in the initial coulombic efficiency of the negative electrode material. The present application controls 2<γ<10, the ratio of Si-O bonds to O-M bonds on the surface of the negative electrode material is appropriate, the surface oxidation degree of the negative electrode material is high, the surface defects are reduced, the side reaction with the electrolyte is reduced, and the structural strength of the surface of the negative electrode material is improved, which can effectively control the degree of volume expansion of the negative electrode material.

[0154] In some embodiments, A is in the range of 5-40, which can be 5, 10, 15, 20, 30, 35, or 40, and can also be other values within the above range, without limitation.

[0155] In some embodiments, B ranges from 2 to 5, specifically can be 2, 2.5, 3, 3.5, 4, 4.5 or 5, and of course can also be other values within the above range, which are not limited herein.

[0156] In some embodiments, the metal M element is selected from at least one of Li, Mg, Al, Ca and Zn.

[0157] In some embodiments, in the negative electrode material, the metal M element exists in the form of at least one of a silicate of M, an oxide of M.

[0158] In some embodiments, the mass content of the metal M element in the negative electrode material is 6% to 15%, specifically can be 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14% or 15%, and of course can also be other values within the above range, which are not limited herein. When the mass content of the metal M element in the negative electrode material is < 6%, the doping amount of the metal M element in the negative electrode material is small, the grain refinement improvement of the silicon oxide by the metal M element is limited, the crystallization degree in the silicon-based active substance is low, the disordered structure Si-O bond increases, the thermal conductivity of the negative electrode material decreases, and the first coulombic efficiency also decreases. When the mass content of the metal M element in the negative electrode material is > 15%, the doping of the metal M element leads to a too high crystallization degree in the silicon-based active substance, the defects and pores in the silicon-based active substance increase significantly, the structural stability of the negative electrode material decreases, and the cycle performance of the negative electrode material decreases. The mass content of the metal M element in the negative electrode material is controlled in the range of 6% to 15% in the present application, the crystal structure in the silicon-based active substance is in a suitable range, which is beneficial to achieving a balance between the structural stability and the thermal conductivity of the negative electrode material.

[0159] In some embodiments, the average particle strength of the negative electrode material is > 200 MPa, specifically can be 201 MPa, 210 MPa, 220 MPa, 230 MPa, 240 MPa, 250 MPa, 280 MPa, 300 MPa, 320 MPa, 350 MPa or 385 MPa, and of course can also be other values within the above range, which are not limited herein. The average particle strength of the negative electrode material is controlled in the above range, because of the appropriate doping of the metal M element, the crystal structure of the silicon-based active substance is improved, the structural stability of the negative electrode material is improved, the negative electrode material can withstand its own huge volume change during the charge and discharge cycle process, the particle breakage can be reduced, and the cycle capacity retention rate of the negative electrode material is improved.

[0160] In some embodiments, the cumulative particle size distribution of the negative electrode material reaches 50% at a particle size Dn(50) of 0.3 μm to 3 μm, specifically 0.3 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm or 3 μm, and of course other values within the above range are also possible, which are not limited herein. When Dn(50) < 0.3 μm, the specific surface area of the negative electrode material is too large, and the side reaction between the negative electrode material and the electrolyte during the charging and discharging process is intensified, and the capacity attenuation of the battery is intensified. When Dn(50) > 3 μm, the heat conduction path in the negative electrode material is too long, and the heat generated during the charging and discharging process is difficult to effectively and quickly conduct out, and the temperature difference between the negative electrode material particles generates a barrier to the transmission of lithium ions, and the negative electrode material particles are difficult to quickly accept heat to activate the internal lithium storage capacity, thereby exhibiting lower initial efficiency and capacity under low temperature conditions. When Dn(50) is controlled within the above range, the negative electrode material particle size is moderate, and has a suitable heat conduction path, which can quickly conduct the heat generated during the charging and discharging process, reduce the uneven temperature difference between the particles, reduce the transmission energy barrier of lithium ions, and the faster temperature conduction causes the temperature of the negative electrode material itself to increase to activate the internal lithium storage capacity, and the negative electrode material can also exhibit excellent electrochemical performance under low temperature conditions, especially capacity and initial coulombic efficiency.

[0161] In some embodiments, the silicon-based active material includes at least one of elemental silicon, silicon oxide, and silicon alloy. The elemental silicon can be amorphous silicon and / or crystalline silicon, and the silicon alloy can be a silicon-lithium alloy, a silicon-magnesium alloy, a silicon-nickel alloy, etc. In some cases, the silicon-based active particle includes silicon elemental particles and silicon alloy.

[0162] In some embodiments, the silicon oxide has a general chemical formula of SiOx x , where 0 < x ≤ 2. Specifically, it can be SiO 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 in which silicon particles are dispersed in SiO2, or a material having a tetrahedral structural unit, with a silicon atom at the center of the tetrahedral structural unit and silicon atoms and / or oxygen atoms at the four vertices of the tetrahedral structural unit.

[0163] In some embodiments, the negative electrode material contains Si grains, and the size of the Si grains in the negative electrode material 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, and of course, it can also be other values within the above range, which is not limited herein. The present application controls the size of the silicon grains in the negative electrode material within the above range, and the negative electrode material has a suitable crystallization degree, which can improve the conductivity of the negative electrode material and also improve the structural stability and cycle stability of the negative electrode material.

[0164] In some embodiments, in the negative electrode material, the carbon material exists on the surface of the silicon-based active material and / or is dispersed between the silicon-based active materials. Specifically, the silicon-based active material can be embedded in the carbon material with the carbon material as the matrix.

[0165] In some embodiments, the carbon material is located on at least part of the surface of the silicon-based active material to form a carbon layer.

[0166] 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, and of course, it can also be other values within the above range, which is not limited herein. It can be understood that by limiting the thickness of the carbon layer within the above range, the carbon layer can more completely coat the active material, reduce the direct contact between the active material and the electrolyte, thereby reducing the generation of the SEI film, reducing the consumption of active lithium ions, and improving the first coulomb efficiency of the negative electrode material.

[0167] In some embodiments, the carbon material includes at least one of graphite, graphene, amorphous carbon, carbon nanotubes and carbon fibers. The graphite can be artificial graphite and / or natural graphite.

[0168] In some embodiments, the carbon material includes amorphous carbon, which can be soft carbon and / or hard carbon. It can be understood that the carbon material can improve the conductivity of the silicon-based active material.

[0169] In some embodiments, the mass content of carbon elements in the negative electrode material is 2% to 8%, specifically, 2%, 3%, 4%, 5%, 6%, 7% or 8%, and of course, it can also be other values within the above range, which is not limited herein. It can be understood that the mass content of carbon elements in the negative electrode material within the above range can reduce the structural damage of the negative electrode material due to the volume expansion of silicon, improve the cycle performance of the negative electrode material, be conducive to the formation of a stable and thin solid electrolyte interface (SEI) film, reduce the consumption of active lithium ions, improve the first coulomb efficiency of the negative electrode material, and also be conducive to the improvement of the cycle performance of the negative electrode material.

[0170] In some embodiments, the mass content of silicon element in the negative electrode material is 48% to 63%, and can be 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 60%, 61% or 63%, and can also be other values in the above range, which is not limited herein. When the mass content of silicon element is too low, the specific capacity of the negative electrode material is low, which is difficult to meet the demand of high energy density lithium ion battery; when the mass content of silicon element is too high, the volume expansion of the negative electrode material is too large, which can cause serious degradation of the cycle performance of the material.

[0171] In some embodiments, the specific surface area of the negative electrode material is ≤10m 2 / g, and can be 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, and can also be other values in the above range, which is not limited herein. It can be understood that when the specific surface area of the negative electrode material is in the above range, the contact area of the negative electrode material with the electrolyte is small and the reaction sites are few, which is beneficial 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. At the same time, the low specific surface area exposes less reduced Si in the negative electrode material, which is beneficial to improve the specific capacity and the initial coulombic efficiency (ICE) of the negative electrode material.

[0172] In some embodiments, the tap density of the negative electrode material is 0.9g / cm 3 ~1.3g / cm 3 , and can be 0.9g / cm 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 , and can also be other values in the above range, which is not limited herein. It can be understood that when the tap density of the negative electrode material is in the above range, the processing performance of the negative electrode material is good, which can reduce the difficulty in the process of coating the electrode sheet and manufacturing the battery, and at the same time is beneficial to maintaining the structural stability of the electrode sheet in the cycle process, improving the cycle performance of the material and the energy density of the battery.

[0173] In some embodiments, the pore volume of the negative electrode material is ≤0.03cm3 / g, specifically 0.03 cm 3 / g, 0.028 cm 3 / g, 0.025 cm 3 / g, 0.02 cm 3 / g, 0.018 cm 3 / g, 0.015 cm 3 / g, 0.01 cm 3 / g, 0.008 cm 3 / g or 0.005 cm 3 / g, etc., and of course can also be other values within the above range, which are not limited herein. It can be understood that 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 reaction sites are few, which is beneficial 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.

[0174] The application also provides a preparation method of the negative electrode material according to the fourth aspect, and the preparation method comprises the following steps:

[0175] Step S1, under vacuum conditions, a mixture of raw materials of silicon-oxygen materials and metal M dopants is heated and gasified and heat preserved, and the obtained silicon source vapor and metal M vapor are mixed and co-deposited, and the precursor is obtained after cooling.

[0176] Step S2, the precursor, silicon dioxide and metal M dopants are mixed according to a mass ratio of 100:1:(1-3), and the mixed product is pre-sintered under a protective atmosphere to obtain a pre-sintered product.

[0177] Step S3, the pre-sintered product is mixed with a flux according to a mass ratio of 1:(2-3) and then subjected to secondary sintering treatment, and the flux in the sintered product is removed to obtain a silicon-based active substance.

[0178] Step S4, the silicon-based active substance is subjected to carbon coating treatment to obtain a negative electrode material, and the negative electrode material comprises the silicon-based active substance and a carbon material.

[0179] The preparation method of the negative electrode material provided in the application first obtains a precursor by separately heating and vaporizing raw materials of a silicon-oxygen material and a metal M dopant, mixing silicon source vapor and metal M vapor obtained after co-deposition, and then mixing silicon dioxide, the metal M dopant and the precursor to realize secondary doping of the metal M dopant to the surface layer structure of the precursor in a pre-sintering process. The doping of the metal M element causes the Si-O bond to break, and each atom is rearranged and combined to form a Si-O-M bond. The formation of the Si-O-M bond changes the crystal structure of the silicon dioxide, the metal M doping improves the surface oxidation degree of the negative electrode material, and the content of the disordered structure in the particle is reduced, which can improve the thermal conductivity of the negative electrode material. In addition, the silicate generated by the reaction of the doped M element and the silicon dioxide has very weak side reactions with the electrolyte during the charging and discharging process of the lithium ion battery, effectively improving the first coulomb efficiency of the negative electrode material. Then, the defects and pores in the silicon-based active material are repaired by a molten salt method, and the compactness and thermal conductivity of the negative electrode material are improved. The thermal conductivity variation coefficient and the surface oxidation degree of the negative electrode material of the application are controlled within a suitable range. Under the synergistic effect, the negative electrode material not only has excellent first coulomb efficiency and specific capacity, but also can improve the cycle capacity retention rate under low temperature and high temperature conditions.

[0180] The preparation method provided in the present application is described in detail below.

[0181] In step S1, the raw materials of the silicon-oxygen material and the metal M dopant are separately heated and vaporized and preserved under vacuum conditions, and the silicon source vapor and the metal M vapor obtained after mixing and co-deposition are used to obtain a precursor.

[0182] In some embodiments, the raw materials of the silicon-oxygen material include at least one of a mixture of Si, SiO y and Si, a mixture of Si and SiO2, a mixture of Si, SiO y and Si, a mixture of Si and SiO2, a mixture of Si, SiO

[0183] In some embodiments, the raw materials of the silicon-oxygen material include a mixture of Si and SiO2, and the molar ratio of Si and SiO2 is 1:1.

[0184] In some embodiments, the mass ratio of the raw materials of the silicon-oxygen material to the metal M dopant is 1:(0.05-0.2), which can be 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, and of course can also be other values within the above range, which are not limited herein.

[0185] In some embodiments, the vacuum pressure in the heating and vaporization process is 0.1 Pa to 1000 Pa, and can be 0.1 Pa, 1 Pa, 10 Pa, 50 Pa, 100 Pa, 500 Pa, 800 Pa, or 1000 Pa, and can also be other values in the above range, which are not limited herein.

[0186] In some embodiments, the temperature of the heating and vaporization is 800℃ to 1300℃, and can be 800℃, 850℃, 900℃, 1000℃, 1100℃, 1200℃, or 1300℃, and can also be other values in the above range, which are not limited herein.

[0187] In some embodiments, the heating time of the raw material of the silicon-oxygen material and the metal M dopant is 10 h to 15 h, and can be 10 h, 11 h, 12 h, 13 h, 14 h, or 15 h, which are not limited herein.

[0188] In the present application, the raw material of the silicon-oxygen material and the metal M dopant are both heated and vaporized, and the silicon vapor and the metal vapor formed by evaporation can be in a stable output state, which can improve the uniformity of the metal M element in the negative electrode material.

[0189] In some embodiments, the co-deposition temperature is 600℃ to 900℃, and can be 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, or 900℃, and can also be other values in the above range, which are not limited herein.

[0190] In step S2, the precursor, the silicon dioxide, and the metal M dopant are mixed in a mass ratio of 100:1:(1-3), and the mixed product is subjected to a pre-sintering treatment in a protective atmosphere to obtain a pre-sintered product.

[0191] In some embodiments, the mass ratio of the precursor, the silicon dioxide, and the metal M dopant is 100:1:1, 100:1:1.5, 100:1:2, 100:1:2.5, or 100:1:3, and can also be other values in the above range, which are not limited herein.

[0192] In some embodiments, the pre-sintering treatment temperature is 300℃ to 500℃, and can be 300℃, 350℃, 400℃, 450℃, 480℃, or 500℃, and can also be other values in the above range, which are not limited herein.

[0193] In some embodiments, the pre-sintering treatment time is 2 h to 3 h, and can be 2 h, 2.5 h, or 3 h, and can also be other values in the above range, which are not limited herein.

[0194] In some embodiments, the pre-sintering process is performed under a protective atmosphere, which includes at least one of nitrogen, argon, neon, and helium.

[0195] In step S3, the pre-sintering product is mixed with a fluxing agent at a mass ratio of 1:(2-3) and then subjected to a secondary sintering process, and the fluxing agent in the sintering product is removed to obtain a silicon-based active material.

[0196] In some embodiments, the mass ratio of the pre-sintering product to the fluxing agent is 1:2, 1:2.2, 1:2.5, 1:2.8, or 1:3, and can also be other values within the above range, which are not limited herein.

[0197] In some embodiments, the fluxing agent includes at least one of sodium chloride and potassium chloride.

[0198] In some embodiments, the temperature of the secondary sintering process is 600-800°C, and can be 600°C, 650°C, 700°C, 750°C, 780°C, or 800°C, and can also be other values within the above range, which are not limited herein.

[0199] In some embodiments, the time of the secondary sintering process is 3-5h, and can be 3h, 4h, or 5h, and can also be other values within the above range, which are not limited herein.

[0200] In some embodiments, the way of removing the fluxing agent in the sintering product includes repeatedly washing, filtering, and drying the sintering product.

[0201] In step S4, the silicon-based active material is subjected to a carbon coating process to obtain a negative electrode material, which includes the silicon-based active material and a carbon material.

[0202] In some embodiments, the carbon material forms a carbon layer on at least part of the surface of the silicon-based active material, and the carbon layer can improve the electrical conductivity of the negative electrode material.

[0203] In some embodiments, the carbon coating process includes at least one of a gas-phase carbon coating process, a solid-phase carbon coating process, and a liquid-phase carbon coating process.

[0204] In some embodiments, the gas-phase carbon source used in the gas-phase carbon coating process includes at least one of methane, propane, butane, acetylene, benzene, and toluene.

[0205] In some embodiments, the flow rate of the gaseous carbon source is 1.0 L / min to 2.5 L / min, and can be 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, and the like, and can also be other values within the above range, which are not limited herein.

[0206] In some embodiments, the temperature of the gaseous carbon coating treatment is 600°C to 1200°C, and can be 600°C, 700°C, 800°C, 900°C, 1000°C, 1100°C, or 1200°C, and the like, and can also be other values within the above range, which are not limited herein.

[0207] In some embodiments, the coating time of the gaseous carbon coating treatment is 2 h to 10 h, and can be 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, or 10 h, and the like, and can also be other values within the above range, which are not limited herein.

[0208] 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 electrical conductivity of the negative electrode material and improve the electrochemical performance of the negative electrode material.

[0209] In a fifth aspect, the embodiments of the present application also provide a battery. FIG. 1 is a schematic diagram of a discharging state of a battery provided by the embodiments of the present application. As shown in FIG. 1, the battery includes a shell and an electrode assembly. The electrode assembly includes a positive electrode sheet 1, a negative electrode sheet 2, and a separator 3. The separator 3 is arranged between the positive electrode sheet 1 and the negative electrode sheet 2. The electrode assembly can be a stacked structure, which is formed by alternately stacking the positive electrode sheet 1, the separator 3, and the negative electrode sheet 2 in sequence. In other embodiments, the electrode assembly can also be a wound structure, which is formed by winding the positive electrode sheet, the separator, and the negative electrode sheet in sequence after being stacked in sequence.

[0210] In some embodiments, the positive electrode sheet 1 includes a positive electrode current collector 101 and a positive electrode active layer 102 arranged on at least one surface of the positive electrode current collector 101.

[0211] In some embodiments, the positive electrode current collector 101 can use an aluminum foil or a nickel foil, or any composite current collector disclosed in the prior art, such as but not limited to a current collector formed by combining the aforementioned conductive foil (aluminum foil or nickel foil, etc.) and a polymer substrate. The positive electrode active layer 102 contains a positive electrode active material, and the positive electrode active material includes a compound that can reversibly intercalate and deintercalate metal ions.

[0212] 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.

[0213] 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), and lithium manganese oxide (LiMn2O3). 4) Lithium nickel manganese oxide (LiNi) 0.5 Mn 1.5 At least one of lithium iron phosphate (LiFePO4) or lithium iron phosphate (LiFePO4).

[0214] 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.

[0215] In some embodiments, the negative electrode current collector 201 may 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.

[0216] The battery provided in this application 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-state electrolyte battery, etc., and is not limited thereto.

[0217] [Testing Method]

[0218] (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.

[0219] (2) Total dissolution ICP test method: 0.500 g of the negative electrode material was placed in a clean platinum crucible, then calcined at 750°C for 2 hours in a muffle furnace in an air atmosphere to completely remove carbon elements; the cooled calcined residue was mixed with 4 mL of HNO3, 6 mL of HF acid, and then the platinum crucible containing the solution was placed on a 350°C hot plate until the solvent was completely evaporated; after the crucible cooled, 6 mL of concentrated HCl was added, heated to completely dissolve the residue, and diluted to 100 mL in a plastic volumetric flask; finally, the mass content of all metal M elements in the negative electrode material was tested by ICP spectrometer (Agilent 5800 VD VICP-OES).

[0220] (3) Test method for the content of soluble metal M elements on the surface of the negative electrode material: according to GB / T 24533-2019 Appendix H "Test method for trace metal elements", 0.3g-0.5g of the negative electrode material was immersed in 6 mL of concentrated hydrochloric acid and 2 mL of concentrated nitric acid mixture, heated at 50°C for 30 minutes in a graphite digestion instrument, then filtered and diluted, and the mass content of the soluble metal M elements on the surface of the negative electrode material was tested by ICP spectrometer (Agilent 5800 VD VICP-OES).

[0221] (4) Test method for the mass content of oxygen elements in the negative electrode material: 10mg-13mg of the negative electrode material was wrapped in a nickel foil, then sent to a graphite crucible in an ONH element analyzer (ONH-2000) for testing, and the total oxygen element mass content of the negative electrode material was obtained.

[0222] (5) Test method for tap density: measured according to GB / T 5162-2006 / ISO 3953:1993 "Determination of tap density of metal powders" or the equipment manual. The tap density was measured using a tap density instrument (KANTO DAT-4-220). The number of vibrations was 3000 times.

[0223] (6) Test method for oil absorption value: measured according to GB / T 3780.2-2017 "Carbon black Part 2: Determination of oil absorption" or the equipment manual. The oil absorption value Q was tested using an ASAHI S-500 oil absorption value tester from Japan ASAHISOUKEN, and the oil absorption value Q was the amount of dibutyl phthalate added when the torque generated by the change in viscosity characteristics reached 70% of the maximum torque, with units of mL / 100g.

[0224] (7) The test method of specific surface area and pore volume: refer to GB / T 19587-2004 “Determination of the specific surface area of solid materials by gas adsorption BET method” or the equipment instruction. The specific surface and pore size analyzer (Micromeritics ASAP 2460-2) is used for measurement. The adsorption gas used is N2. A certain amount of sample is weighed and loaded into the specific surface area special bubble tube, and the nitrogen gas is blown at 300℃ for a certain time in the degassing station. After degassing is completed, the sample is cooled to room temperature, and the actual mass of the sample is weighed. After the sample quality is input, the specific surface area of the sample is determined.

[0225] (8) The test method of particle size: refer to GB / T 19077.1-2008 “Particle size analysis - Laser diffraction methods - Part 1: General principles” or the equipment instruction. The quantity cumulative particle size distribution of the negative electrode material particle size distribution is measured by the Malvern laser particle size analyzer (Mastersizer 3000) by laser diffraction method. The median particle size Dn(50) represents the particle size corresponding to the quantity cumulative particle size distribution reaching 50%.

[0226] (9) The test method of true density: refer to GB / T 24533-2019 Appendix D “Test method of true density”. The true density tester is used for measurement.

[0227] (10) The test method of mass content of carbon element: refer to GB / T 38823-2020 Appendix A “Test method of carbon content”. The infrared carbon and sulfur analyzer is used for measurement.

[0228] (11) The test method of mass content of silicon element: the infrared carbon and sulfur analyzer is used to test the carbon content C% of the material, the oxygen and nitrogen and hydrogen element analyzer is used to test the oxygen content O% of the material, the total metal content M% of the material is measured by the total dissolution ICP method, and the Si element content of the material = 1-C%-O%-M%.

[0229] (12) The test method of carbon layer thickness: the cross-section of the negative electrode material is treated by the Hitachi E-3500 ion mill, and the average thickness of the carbon layer on the surface of the material is measured in the SEM.

[0230] (13) Thermal conductivity of the negative electrode material: The thermal conductivity was tested using a thermal conductivity instrument (Hot Disk TPS2500S). The test atmosphere was nitrogen, and the test temperature points were 100°C and 600°C. Before testing, an appropriate amount of powder sample was poured into a 30 mm size infrared mold, and the sample was pressed at a pressure of 20 MPa to obtain two samples. A suitable probe was selected, and the sample and the probe were arranged in a sandwich manner, with the circular coil part of the probe directly below the pressure screw. The two flat surfaces of the samples were clamped to hold the probe without gaps, and then the test parameters were adjusted. The measurement time and test power were adjusted to stabilize the sample thermal conductivity value. The thermal conductivities g1 and g2 at 100°C (373.15 K) and 600°C (873.15 K) were measured, with the unit being W / (m·K).

[0231] (14) Average particle strength of the negative electrode material: The dynamic ultramicro hardness tester (DUH-211S) was used for testing. The sample was transferred to the marker block, and a single particle with a particle size of 5-10 μm was found under a 50-fold magnifying lens. The breaking point mode was set, the load force was set to 100 mN, and the drop speed was set to 2.8 mN / s. The single particle was crushed. Ten single particles with the same particle size range were randomly tested, and the average value of the ten particle strength values was taken as the average particle strength of the sample.

[0232] (15) Electrochemical performance test (negative electrode material): The negative electrode material, conductive agent (SuTer T), carboxymethyl cellulose sodium (CMC), and butadiene rubber (SBR) were mixed in a mass ratio of 92:2:2:2, and then coated on a copper foil current collector. After drying, a negative electrode sheet was obtained for standby use. The dried electrode sheet was rolled under a pressure of 3 MTa to obtain a negative electrode sheet. The rolled negative electrode sheet was subjected to a coin cell test. The battery was assembled in an argon glove box, and lithium metal was used as the negative electrode. The electrolyte was 1 mol / L lithium hexafluorophosphate + ethylene carbonate (EC) + methyl ethyl carbonate (EMC), and the separator was a polyethylene / polypropylene composite microporous membrane. The electrochemical performance was tested on a battery tester, and the charge and discharge voltage was 0.01-1.5 V.

[0233] First coulombic efficiency = first cycle lithium extraction capacity / first cycle lithium intercalation capacity.

[0234] The discharge capacity was recorded as the remaining capacity of the lithium ion battery after 50 cycles. The capacity retention rate = remaining capacity / initial capacity * 100%.

[0235] (16) Electrochemical performance test (negative electrode material + graphite): the negative electrode material, graphite, conductive agent (Super P), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) are mixed in a mass ratio of 9.2:82.8:2:2:2 in an aqueous solvent, and then coated on a copper foil current collector to obtain a negative electrode sheet for standby after drying. The dried electrode sheet is rolled under a pressure of 3 MPa to obtain a negative electrode sheet with a certain compactness. The rolled negative electrode sheet is subjected to a coin cell test, and the battery is assembled 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 cell is placed in a constant temperature test box (0°C / 50°C) and connected to a battery testing instrument for testing, with a charge / discharge voltage of 0.01-1.5 V. The first coulombic efficiency = the first lithium intercalation capacity / the first lithium extraction capacity. The battery cycle life is the lithium extraction capacity retention rate after 50 charge / discharge cycles.

[0236] (17) Test method for high-temperature storage performance: the test method for high-temperature storage performance uses a cylindrical cell test, i.e., an electric cell containing the negative electrode material is stored at 60°C for 15 days at 100% SOC after formation and capacity retention rate is detected at room temperature. The preparation of the electric cell is a common method in the art, which is not limited here, for example, the negative electrode sheet formula is a mixture of the negative electrode material, graphite, conductive agent (Super P), and polyacrylic acid binder in a ratio of 4:90:3:3, and the positive electrode sheet formula is a mixture of lithium nickel cobalt manganese oxide NCM811, conductive agent (Super P), and polyvinylidene fluoride binder in a ratio of 94:3:3.

[0237]

The negative electrode material prepared by the preparation method according to the second aspect has the following embodiments

[0238] Example 1

[0239] (1) A mixture of 30 kg of silicon particles and 30 kg of silicon dioxide particles in a molar ratio of 1:1 is placed in a vacuum furnace reaction chamber 1, and 2.4 kg of Mg particles are placed in a vacuum furnace reaction chamber 2, and the pressure of the vacuum furnace is adjusted to 10 Pa.

[0240] (2) The vacuum furnace reaction chamber 1 is controlled to heat to 1300°C to generate SiO gas in the reaction chamber 1, and the holding time of the reaction chamber 1 is controlled to 24 hours; the vacuum furnace reaction chamber 2 is controlled to heat to 550°C to generate Mg gas in the reaction chamber 2, and the holding time of the reaction chamber 2 is controlled to 20 hours; at the same time, the SiO gas generated in the vacuum furnace reaction chamber 1 and the Mg gas generated in the vacuum furnace reaction chamber 2 are mixed and deposited on a cooling plate, and the temperature of the cooling plate is controlled to 800°C.

[0241] (3) After the end of the heat preservation, CO2 gas is introduced until the vacuum pressure reaches 5 kPa, the cooling plate temperature is maintained at 800°C, and the temperature is kept constant for 2 hours, the temperature is lowered and the normal pressure is restored, and the reaction product is obtained.

[0242] (4) The reaction product is crushed and classified to an average particle size of 5 μm, and an active material is obtained.

[0243] (5) The active material is placed in a chemical vapor deposition (CVD) device, 5 L / min of nitrogen gas is introduced as a protective gas, then the temperature is raised to 800°C and kept constant, 1.5 L / min of acetylene is introduced into the CVD device, and a vapor deposition reaction is performed for 3 h, and a negative electrode material is obtained.

[0244] The negative electrode material prepared in this example includes an active material, and the active material includes silicon, silicon oxide (SiO), magnesium silicate, and carbon particles, and at least part of the carbon particles are located inside the particles of the active material.

[0245] Example 2

[0246] The difference from Example 1 is that:

[0247] In step (2), the heat preservation time of the vacuum furnace reaction bin 1 is controlled to be 26 hours.

[0248] The negative electrode material prepared in this example includes an active material, and the active material includes silicon, silicon oxide (SiO), magnesium silicate, and carbon particles, and at least part of the carbon particles are located inside the particles of the active material.

[0249] Example 3

[0250] The difference from Example 1 is that:

[0251] In step (2), the heat preservation time of the vacuum furnace reaction bin 1 is controlled to be 22 hours.

[0252] The negative electrode material prepared in this example includes an active material, and the active material includes silicon, silicon oxide (SiO), magnesium silicate, and carbon particles, and at least part of the carbon particles are located inside the particles of the active material.

[0253] Example 4

[0254] The difference from Example 1 is that:

[0255] (3) After the end of the heat preservation, CO2 gas is introduced until the vacuum pressure reaches 5 kPa, the cooling plate temperature is maintained at 800°C, and the temperature is kept constant for 4 hours, the temperature is lowered and the normal pressure is restored, and the reaction product is obtained.

[0256] The negative electrode material prepared in the embodiment comprises active substance, and the active substance comprises silicon, silicon oxide (SiO), magnesium silicate and carbon particles. At least part of the carbon particles are located inside the particles of the active substance.

[0257] Example 5

[0258] Different from the example 1, the steps are as follows:

[0259] (1) Put 30 kg of mixture of silicon particles and silicon dioxide particles with a molar ratio of 1:1 into the reaction chamber 1 of the vacuum furnace, and put 4.5 kg of Mg particles into the reaction chamber 2 of the vacuum furnace, and adjust the pressure of the vacuum furnace to 10 Pa.

[0260] (2) Control the heating temperature of the reaction chamber 1 of the vacuum furnace to 1300 ℃ to generate SiO gas in the reaction chamber 1, and control the holding time of the reaction chamber 1 to 24 hours; control the heating temperature of the reaction chamber 2 of the vacuum furnace to 650 ℃ to generate Mg gas in the reaction chamber 2, and control the holding time of the reaction chamber 2 to 20 hours; at the same time, mix and deposit the SiO gas generated in the reaction chamber 1 of the vacuum furnace and the Mg gas generated in the reaction chamber 2 of the vacuum furnace on the cooling plate, and control the temperature of the cooling plate to 800 ℃.

[0261] The negative electrode material prepared in the embodiment comprises active substance, and the active substance comprises silicon, silicon oxide (SiO), magnesium silicate and carbon particles. At least part of the carbon particles are located inside the particles of the active substance.

[0262] Example 6

[0263] Different from the example 1, the steps are as follows:

[0264] Step (2) controls the heating temperature of the reaction chamber 1 of the vacuum furnace to 1600 ℃.

[0265] The negative electrode material prepared in the embodiment comprises active substance, and the active substance comprises silicon, silicon oxide (SiO), magnesium silicate and carbon particles. At least part of the carbon particles are located inside the particles of the active substance.

[0266] Example 7

[0267] Different from the example 1, the steps are as follows:

[0268] Step (2) controls the holding time of the reaction chamber 2 of the vacuum furnace to 17 hours.

[0269] The negative electrode material prepared in the embodiment comprises active substance, and the active substance comprises silicon, silicon oxide (SiO), magnesium silicate and carbon particles. At least part of the carbon particles are located inside the particles of the active substance.

[0270] Example 8

[0271] Different from Example 1 is that:

[0272] (3) After the end of the heat preservation, CO2 gas is introduced until the vacuum pressure reaches 5 kPa, the cooling plate temperature is maintained at 800°C, and the temperature is kept constant for 1.5 hours, and the temperature is lowered and the normal pressure is restored to obtain the reaction product.

[0273] The negative electrode material prepared in this example includes an active substance, and the active substance includes silicon, silicon oxide (SiO), magnesium silicate, and carbon particles. At least part of the carbon particles is located inside the particles of the active substance.

[0274] Example 9

[0275] Different from Example 1 is that:

[0276] (3) After the end of the heat preservation, CO2 gas is introduced until the vacuum pressure reaches 1 kPa, the cooling plate temperature is maintained at 800°C, and the temperature is kept constant for 2 hours, and the temperature is lowered and the normal pressure is restored to obtain the reaction product.

[0277] The negative electrode material prepared in this example includes an active substance, and the active substance includes silicon, silicon oxide (SiO), magnesium silicate, and carbon particles. At least part of the carbon particles is located inside the particles of the active substance.

[0278] Example 10

[0279] Different from Example 1 is that:

[0280] Step (3) uses CO gas instead of CO2 gas.

[0281] The negative electrode material prepared in this example includes an active substance, and the active substance includes silicon, silicon oxide (SiO), magnesium silicate, and carbon particles. At least part of the carbon particles is located inside the particles of the active substance.

[0282] Example 11

[0283] Different from Example 1 is that:

[0284] Step (3) uses a mixed gas of CO and CO2 instead of CO2 gas.

[0285] The negative electrode material prepared in this example includes an active substance, and the active substance includes silicon, silicon oxide (SiO), magnesium silicate, and carbon particles. At least part of the carbon particles is located inside the particles of the active substance.

[0286] Example 12

[0287] Different from Example 1 is that:

[0288] Step (2) controls the heat preservation time of the vacuum furnace reaction bin 1 to be 27 hours.

[0289] The negative electrode material prepared in this example includes an active material, and the active material includes silicon, silicon oxide (SiO), magnesium silicate, and carbon particles. At least part of the carbon particles is located inside the particles of the active material.

[0290] Comparative Example 1

[0291] Different from Example 1 is that:

[0292] Step (2) controls the holding time of the vacuum furnace reaction chamber 1 to be 20 hours, and step (3) is not performed.

[0293] Comparative Example 2

[0294] Different from Example 1 is that:

[0295] Step (3) is not performed.

[0296] Comparative Example 3

[0297] Different from Example 1 is that:

[0298] Step (2) controls the holding time of the vacuum furnace reaction chamber 1 to be 20 hours.

[0299] Comparative Example 4

[0300] Different from Example 1 is that:

[0301] Step (2) controls the holding time of the vacuum furnace reaction chamber 1 to be 30 hours.

[0302] The test results are shown in Tables 1 and 2.

[0303] Table 1: Performance test results of each example and comparative example

[0304] Table 2: Performance test results of each example and comparative example

[0305] According to the test data in Tables 1 and 2, the value of the surface oxidation degree γ of the negative electrode material is controlled to be between 2 and 10, the defects and pores in the negative electrode material are well closed, the contact sites of the side reactions between the negative electrode material and the electrolyte are effectively reduced, the negative electrode material has good high-temperature storage performance. At the same time, the defects and pores in the negative electrode material are closed, which effectively reduces the contact between the negative electrode material and air, improves the oxidation resistance of the negative electrode material, effectively reduces the irreversible reactions formed in the first charge and discharge process of the negative electrode material, and improves the first coulombic efficiency and specific capacity of the negative electrode material.

[0306] According to the test data of Example 1 and Example 12, since the difference between the heating and gasification time of the raw material of the silicon-oxygen material and the holding time after the magnesium is heated and gasified is too large, that is, the silicon-oxygen material deposited in the precursor is too much after the co-deposition of the silicon-oxygen material and the magnesium is completed, the surface oxidation degree γ of the negative electrode material is too small, the closure degree of the defects and pores in the negative electrode material is very good, the contact sites between the negative electrode material and the electrolyte for the side reaction are effectively reduced, and the negative electrode material has good high-temperature storage performance; however, the closure degree of the defects and pores in the negative electrode material is too high, which limits the lithium ion transmission, and the initial efficiency of the negative electrode material of Example 12 is lower than that of Example 1.

[0307] According to the test data of Example 1 and Comparative Example 1, neither the holding time after the heating and gasification of the raw material of the silicon-oxygen material is prolonged (that is, the deposition time of the silicon-oxygen material on the precursor is not prolonged), nor the carbon dioxide gas is introduced to perform the vapor deposition on the precursor, the surface oxidation degree γ of the negative electrode material is too large, the closure degree of the defects and pores in the negative electrode material is poor, and there are many reaction sites on the surface of the negative electrode material, which causes a large amount of side reaction between the negative electrode material and the electrolyte, and thus the high-temperature storage performance of the negative electrode material is reduced. At the same time, the defects and pores in the negative electrode material are prone to oxidation, which reduces the utilization rate of the doped Mg, and thus the specific capacity and the initial efficiency of the negative electrode material are reduced.

[0308] According to the test data of Example 1 and Comparative Example 3, the holding time after the heating and gasification of the raw material of the silicon-oxygen material is not prolonged (that is, the deposition time of the silicon-oxygen material on the precursor is not prolonged), the surface oxidation degree γ of the negative electrode material is too large, which causes the closure degree of the defects and pores in the negative electrode material to be poor, and the contact sites between the negative electrode material and the electrolyte are increased, which increases the generation of unstable SEI film between the negative electrode material and the electrolyte in the cycle process, and thus the high-temperature storage performance of the negative electrode material is reduced. At the same time, the defects and pores in the negative electrode material are prone to oxidation in the process of contacting with air, which increases the generation of irreversible side reactions (such as electrolyte decomposition, generation of a large amount of unstable SEI film to consume electrolyte, etc.) of the negative electrode material in the charge and discharge process, and thus the specific capacity and the initial efficiency of the negative electrode material are reduced.

[0309] According to the test data of Example 1 and Comparative Example 2, the carbon dioxide gas is not introduced to perform the vapor deposition on the precursor, the surface oxidation degree γ of the negative electrode material is too large, which causes a large amount of defects and pores in the negative electrode material, and the defects and pores increase the contact sites between the negative electrode material and the electrolyte for the side reaction, which causes the negative electrode material and the electrolyte to continuously react to generate unstable SEI film, and thus the high-temperature storage performance of the negative electrode material is reduced. At the same time, the defects and pores in the negative electrode material are prone to oxidation, which causes the generation of irreversible side reactions of the negative electrode material in the cycle process to increase, and thus the specific capacity and the initial efficiency of the negative electrode material are reduced.

[0310] According to the test data of Example 1 and Comparative Example 4, it can be known that, in the preparation process of Comparative Example 4, the holding time of the vacuum furnace reaction chamber 1 is 30 hours, that is, the deposition time of the silicon-oxygen material is too long, and the surface oxidation degree γ of the negative electrode material is too small. Although the defects and pores on the surface of the negative electrode material are greatly reduced, the relatively thick SiO x It will occur irreversible lithiation reaction, resulting in excessive consumption of active lithium ions, and the first coulombic efficiency (initial efficiency) of the negative electrode material decreases, which cannot simultaneously have high capacity retention rate and high initial efficiency.

[0311] The negative electrode material prepared by the preparation method of the negative electrode material according to the third aspect is as follows:

[0312] Example 201

[0313] A preparation method of a negative electrode material, comprising the following steps:

[0314] (1) Put 30 kg of SiO particles into the vacuum furnace reaction chamber 1, and put 2.4 kg of Mg particles into the vacuum furnace reaction chamber 2, and adjust the pressure of the vacuum furnace to 10 Pa.

[0315] (2) Control the vacuum furnace reactor 1 to be rapidly heated to 1200℃, and then continue to heat at a first heating rate of 23℃ / h, so that the reaction chamber 1 generates SiO gas; control the vacuum furnace reactor 2 to be rapidly heated to 400℃, and then continue to heat at a second heating rate of 11℃ / h, so that the reaction chamber 2 generates Mg gas; control the heating time of the reaction chamber 1 and the reaction chamber 2 to be 12 hours, and there is no holding process; control the cooling plate temperature to be 800℃ during the reaction process.

[0316] (3) After the deposition is completed, CO2 gas is introduced until the vacuum pressure reaches 5kPa, the cooling plate temperature is kept at 800℃, and the temperature is kept constant for 3 hours, and then the temperature is lowered and the normal pressure is restored, to obtain a deposition product.

[0317] (4) The deposition product is crushed and classified to an average particle size of 5μm to obtain an active substance.

[0318] (5) The active substance is placed in a chemical vapor deposition (CVD) device, 5L / min of nitrogen gas is introduced as a protective gas, then the temperature is raised to 800℃ and kept constant, 1.5L / min of acetylene is introduced into the CVD device, and a gas phase carbon coating reaction is carried out for 3h to obtain a negative electrode material.

[0319] The negative electrode material prepared by the example of the present application comprises a silicon-based active substance and a carbon material, the silicon-based active substance is carbon-coated SiO, and the carbon material is artificial graphite.

[0320] According to the preparation steps of Example 201, Examples 201-213 and Comparative Examples 201-203 were prepared, and the process parameters of each example are shown in Table 3:

[0321] Table 3. Preparation process parameters of negative electrode materials

[0322] The performance of the negative electrode materials prepared in the examples and comparative examples was tested, and the results of the above performance tests are shown in Table 4:

[0323] Table 4. Performance test results of each example and comparative example

[0324] Table 5. Summary table of electrochemical performance results of negative electrode materials

[0325] According to the test data in Table 4 and Table 5, when the negative electrode material controls k1≤4 and k2≤6 at the same time, the surface oxidation degree satisfies 2<γ<10, the metal M element in each particle of the negative electrode material is uniformly distributed, the silicon crystal grains grow uniformly and the size is controllable, which can relieve the silicon expansion stress; at the same time, the oxidation degree of the surface of the negative electrode material is small, which can reduce the defects and pores on the surface of the negative electrode material, reduce the secondary reaction contact sites between the negative electrode material and the electrolyte, and can effectively reduce the irreversible reaction formed in the first charge and discharge process of the negative electrode material. Under the synergistic action of the two, the negative electrode material not only has excellent cycle capacity retention rate, but also can improve the initial coulombic efficiency and specific capacity of the negative electrode material.

[0326] According to the test data of Example 201 and Comparative Example 201, without passing carbon dioxide gas to carry out vapor deposition on the precursor, the negative electrode material satisfies k1≤4 and k2≤6, but the surface oxidation degree γ of the negative electrode material is too high, resulting in a large number of defects and pores in the negative electrode material. The existence of these defects and pores increases the secondary reaction contact sites between the negative electrode material and the electrolyte, which causes the negative electrode material and the electrolyte to continuously react to form unstable SEI film, resulting in a decrease in the specific capacity of the negative electrode material and a decrease in the initial coulombic efficiency; in the charge and discharge process, the negative electrode material continuously forms SEI film on the surface, consumes a large amount of active lithium ions, and the cycle capacity retention rate of the negative electrode material also decreases.

[0327] According to the test data of Example 201 and Comparative Example 202, the holding time of the vacuum furnace reaction chamber 1 is 30 hours, that is, the deposition time of the silicon-oxygen material is too long, and the surface oxidation degree γ of the negative electrode material is too small. Although the defects and pores on the surface of the negative electrode material are greatly reduced, the thick SiO x It will cause irreversible lithiumation reaction, resulting in excessive consumption of active lithium ions, decrease of the initial coulombic efficiency of the negative electrode material, and inability to have high capacity and high initial efficiency.

[0328] According to the test data of the embodiment 201 and the comparative example 203, the heating rate in the vacuum reaction chamber 1 is too fast, the metal M element distribution uniformity between the particles of the negative electrode material is poor, k2 is too large, and the vacuum chamber does not introduce carbon dioxide gas for gas deposition on the precursor, the surface oxidation degree γ of the negative electrode material is too high, which leads to the decrease of the specific capacity, the first coulombic efficiency and the cycle capacity retention rate of the negative electrode material.

[0329]

The following embodiments are prepared according to the preparation method of the negative electrode material according to the fourth aspect

[0330] Embodiment 301

[0331] A preparation method of a negative electrode material, comprising the following steps:

[0332] (1) Put 8 kg of Mg particles, 28 kg of Si particles and 60 kg of SiO2 particles into the vacuum furnace reaction chamber, adjust the pressure of the vacuum furnace to 10 Pa, control the vacuum furnace reactor to heat to 1300 ℃ to generate SiO gas and Mg gas, transport the mixed SiO and Mg gas into the vacuum furnace collection device, and cool and condense it, and control the cooling plate temperature to be 750 ℃ throughout the reaction process.

[0333] (2) After the reaction is completed, the product collected by the cooling plate is crushed and classified, and the deposition product powder particle Dn(50) is controlled to be 0.4 μm.

[0334] (3) Mix the crushed product with SiO2 particles and Mg particles according to a secondary doping mass ratio of 100:1:2.0, and then perform pre-sintering on the mixture in an Ar atmosphere protection box furnace, the pre-sintering temperature is 400 ℃, and the pre-sintering time is 3 h, to obtain a pre-sintered product.

[0335] (4) Disperse the pre-sintered product, mix it with NaCl according to a mass ratio of 1:3, and then perform secondary sintering in an Ar atmosphere protection box furnace, the secondary sintering temperature is 700 ℃, and the secondary sintering time is 4 h, to obtain a sintered product, which is repeatedly washed with water, filtered to remove the NaCl fluxing agent, dried to obtain a silicon-based active substance, and the silicon-based active substance includes Mg-doped SiO x .

[0336] (5) Place the silicon-based active substance in a chemical vapor deposition (CVD) equipment, introduce 5 L / min of nitrogen gas as a protective gas, then heat to 800 ℃ and keep the temperature, introduce 1.5 L / min of acetylene carbon source into the CVD equipment, and perform gas phase carbon coating reaction for 3 h to obtain a negative electrode material.

[0337] The negative electrode material prepared by the embodiment of the present application includes a silicon-based active substance and a carbon material, and the silicon-based active substance includes Mg-doped SiOx .

[0338] According to the preparation steps of Example 301, Examples 302-314 and Comparative Examples 301-304 were prepared, and the process parameters of each example are shown in Table 6:

[0339] Table 6. Process parameters for preparing negative electrode materials

[0340] The performance of the negative electrode materials prepared in the examples and comparative examples was tested, and the results of the above performance tests are shown in Table 7:

[0341] Table 7. Performance test results of negative electrode materials of each example and comparative example

[0342] Table 8. Performance test results of negative electrode materials of each example and comparative example

[0343] Table 9. Summary table of electrochemical performance test results of negative electrode materials

[0344] Table 10. Summary table of electrochemical performance test results of negative electrode materials and graphite as negative electrode active materials

[0345] According to the test data in Tables 6-10, the surface oxidation degree of the negative electrode material controlled by the present application satisfies 2<γ<10, the surface defects of the negative electrode material and the defects in the silicon-based active material are reduced, the thermal conductivity of the negative electrode material can be improved, the coefficient of change σ of the thermal conductivity of the negative electrode material is controlled in the range of 0.80<σ<1.50, the temperature difference between the negative electrode material particles can be reduced, the transport energy barrier of lithium ions is reduced, the cycle capacity retention rate of the negative electrode material is improved, the negative electrode material has excellent first coulombic efficiency and first delithiation capacity, and the cycle capacity retention rate under low temperature and high temperature conditions is also improved, and the capacity decay of the negative electrode material is improved.

[0346] According to the test data of Example 301 and Comparative Example 301, Comparative Example 301 did not undergo pre-sintering and secondary sintering treatment, resulting in too low surface oxidation degree γ of the negative electrode material, too many surface defects, and more disordered structure in the silicon-based active material of the negative electrode material. The coefficient of change σ of the thermal conductivity of the negative electrode material is too low, the thermal conductivity of the negative electrode material at high temperature is poor, and the battery prepared from the negative electrode material exhibits low first coulombic efficiency and first delithiation capacity at different temperatures.

[0347] According to the test data of example 301 and comparative example 302, it can be seen that the amount of the second doped metal M in the pre-sintering process of comparative example 302 is too small, the ratio of Si-O bond to O-M bond on the surface of the negative electrode material is high, the surface oxidation degree γ of the negative electrode material is too high, and there are a large number of disordered Si-O bonds on the surface of the negative electrode material. Although the crystallization degree in the silicon-based active material is appropriate, and the thermal conductivity variation coefficient σ of the negative electrode material is within the appropriate range, the first coulombic efficiency and the first delithiation capacity of the battery prepared by the negative electrode material at different temperatures are lower than those of example 301 due to too many disordered structures on the surface of the negative electrode material and the increase of side reactions.

[0348] According to the test data of example 301 and comparative example 303, it can be seen that the secondary sintering temperature of comparative example 303 is too low, which makes it difficult for part of the metal M to be effectively doped into the negative electrode material, and the disordered structure in the negative electrode material is more. The thermal conductivity of the negative electrode material at 873.15K is g2, and the thermal conductivity variation coefficient σ also decreases, the heat conduction capacity of the negative electrode material decreases, and the first coulombic efficiency and the first delithiation capacity of the negative electrode material at different temperatures are lower than those of example 301.

[0349] According to the test data of example 301 and comparative example 304, it can be seen that the secondary sintering temperature of comparative example 304 is too high, which makes part of the metal M doped into the negative electrode material in excess. Although the thermal conductivity of the negative electrode material at 873.15K is g2, the disordered Si-O bonds in the negative electrode material are destroyed more, and it is difficult to maintain the good mechanical toughness of the negative electrode material to resist the volume change in the charging and discharging process, thereby causing the negative electrode material particles to break and the structure to collapse, which makes the cycle performance quickly deteriorate, and the capacity retention rate of the negative electrode material decreases significantly.

[0350] The above are only preferred embodiments of the present application and are not used to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the scope of protection of the present application.

Claims

1. A negative electrode material, characterized by, The negative electrode material comprises an active substance, and the active substance comprises silicon elements, oxygen elements and metal M elements; The mass ratio of the oxygen elements and the metal M elements of the negative electrode material is A, which is obtained by X-ray photoelectron spectroscopy; The mass ratio of the oxygen elements in the negative electrode material and the metal M elements in the negative electrode material is B, which is obtained by ONH elemental analysis and ICP spectroscopy; The surface oxidation degree of the negative electrode material is γ, and γ=A / B, 2<γ<10.

2. The negative electrode material according to claim 1, characterized in that, The active substance comprises silicon, silicon oxide, magnesium silicate and carbon elements, and the metal M elements are magnesium elements, and at least part of the carbon elements are located inside the particles of the active substance.

3. The negative electrode material of claim 1, wherein, The negative electrode material further comprises a carbon material; Energy spectrum analysis is performed on the section of the particles of the negative electrode material, n1 test points are randomly selected in the section of a single negative electrode material particle for point scanning analysis to obtain n1 mass percentage contents of the metal M elements, and the standard deviation k1 of the n1 mass percentage contents of the metal M elements is calculated, k1≤4; n2 sections of the particles of the negative electrode material are randomly selected for surface scanning analysis to obtain n2 mass percentage contents of the metal M elements, and the standard deviation k2 of the n2 mass percentage contents of the metal M elements is calculated, k2≤6; wherein n1 and n2 are natural numbers greater than or equal to 5.

4. The negative electrode material according to claim 2 or 3, characterized in that, The negative electrode material satisfies at least one of the following characteristics: (1) A is in the range of 5-45; and / or, A is 5, 10, 15, 20, 30, 35, 40, 45 or in the range between any two of the above values; (2) B is in the range of 2-5; and / or, B is 2, 2.5, 3, 3.5, 4, 4.5, 5 or in the range between any two of the above values; (3) γ is 2.1, 2.5, 3, 4, 5, 6, 7, 8, 9, 9.5, 9.6, 9.8, 9.9 or in the range between any two of the above values.

5. The negative electrode material according to claim 2 or 3, characterized in that, The negative electrode material satisfies at least one of the following characteristics: (1) 0.3g-0.5g of the negative electrode material is immersed in a mixture of 6mL concentrated hydrochloric acid and 2mL concentrated nitric acid, heated at 50°C in a graphite digestion instrument for 30 minutes, then filtered and diluted, and the mass content of the M elements in the negative electrode material is less than 0.8% by ICP spectroscopy; (2) The mass content of the metal M elements in the negative electrode material is 5%-15%.

6. The negative electrode material of claim 2, wherein, The negative electrode material satisfies at least one of the following characteristics: (1) the chemical formula of the silicon oxide is SiO x , 0 < x ≤ 2; (2) The negative electrode material further comprises a carbon layer located on at least part of the surface of the active substance; (3) The negative electrode material further comprises a carbon layer located on at least part of the surface of the active substance, and the carbon layer comprises amorphous carbon; (4) The negative electrode material further comprises a carbon layer located on at least part of the surface of the active substance, and the thickness of the carbon layer is 1nm-500nm.

7. The negative electrode material of claim 3, wherein, The negative electrode material satisfies at least one of the following characteristics: (1) The active substance comprises at least one of elemental silicon, silicon oxide and silicon alloy; (2) the active material comprises a silicon oxide having a general chemical formula of SiO x , 0 < x < 2; (3) The metal M elements are selected from at least one of Mg, Al and Ca; (4) the carbon material comprises at least one of graphite, graphene, amorphous carbon, carbon nanotube and carbon fiber.

8. The negative electrode material according to claim 2 or 3, characterized in that, The negative electrode material satisfies at least one of the following characteristics: (1) the mass content of carbon element in the negative electrode material is 2% to 8%; (2) the mass content of oxygen element in the negative electrode material is 20% to 34%; (3) the mass content of silicon element in the negative electrode material is 48% to 63%; (4) the oil absorption value of the negative electrode material is 30 mL / 100 g to 40 mL / 100 g.

9. The negative electrode material according to claim 2 or 3, 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 ≤ 8 m 2 / g; (2) the tap density of the negative electrode material is 0.9 g / cm 3 ~ 1.3 g / cm 3 ; (3) the true density of the negative electrode material is 2.3 g / cm 3 ~ 2.66 g / cm 3 ; (4) the pH of the negative electrode material is 6.5 to 9.5; (5) the median particle size Dn(50) of the negative electrode material is 2 μm to 12 μm; (6) the pore volume of the negative electrode material is < 0.03 cm 3 / g.

10. The negative electrode material of claim 1, wherein, The active material comprises a silicon-based active material, and the silicon-based active material comprises silicon element, oxygen element and metal M element. The negative electrode material further comprises a carbon material located on at least part of the surface of the active material.

11. The negative electrode material according to claim 10, characterized in that, The negative electrode material satisfies at least one of the following characteristics: (1) the thermal conductivity of the negative electrode material at 373.15 K temperature is g1 W / (m·K), 0.15≤g1≤0.4; (2) the thermal conductivity of the negative electrode material at 873.15 K temperature is g2 W / (m·K), 0.5≤g2≤2.5; (3) the thermal conductivity of the negative electrode material at a temperature of 373.15K is g1 W / (m·K), the thermal conductivity of the negative electrode material at a temperature of 873.15K is g2 W / (m·K), and the variation coefficient σ of the thermal conductivity of the negative electrode material is σ=(1-g1 / g2) 2 / 0.57, 0.80<σ<1.50; (4) σ is 0.81, 0.85, 0.9, 1.0, 1.1, 1.2, 1.3, 1.35, 1.4, 1.49 or within a range between any two of the above values.

12. The negative electrode material of claim 10, wherein, The negative electrode material satisfies at least one of the following characteristics: (1)5≤A≤40； (2)2≤B≤5； (3) γ is 2.1, 2.5, 3, 4, 5, 6, 7, 8, 9, 9.5, 9.6, 9.8, 9.9 or within a range between any two of the above values.

13. The negative electrode material of claim 10, wherein, The negative electrode material satisfies at least one of the following characteristics: (1) the metal M element is selected from at least one of Li, Mg, Al, Ca and Zn; (2) the mass percentage content of the metal M element in the negative electrode material is 6% to 15%; (3) in the negative electrode material, the existing form of the metal M element comprises at least one of a silicate of M and an oxide of M; (4) the average particle strength of the negative electrode material is >200 MPa.

14. The negative electrode material of claim 10, wherein, The negative electrode material satisfies at least one of the following characteristics: (1) the silicon-based active material comprises at least one of elemental silicon, silicon oxide and silicon alloy; (2) the silicon-based active material comprises a silicon oxide having a general chemical formula of SiO x , 0 < x < 2.

15. The negative electrode material of claim 10, wherein, The negative electrode material satisfies at least one of the following characteristics: (1) the mass content of carbon element in the negative electrode material is 2% to 8%; (2) the carbon material comprises at least one of graphite, graphene, amorphous carbon, carbon nanotube and carbon fiber; (3) the carbon material is located on at least part of the surface of the silicon-based active material to form a carbon layer, and the thickness of the carbon layer is 10 nm to 300 nm.

16. The negative electrode material according to any one of claims 10 to 15, characterized by, The negative electrode material satisfies at least one of the following characteristics: (1) the specific surface area of the negative electrode material is ≤ 10 m 2 / g; (2) the tap density of the negative electrode material is 0.9 g / cm 3 ~ 1.3 g / cm 3 ; (3) the pore volume of the negative electrode material is ≤ 0.03 cm3 / g 3 / g; (4) the particle size Dn(50) corresponding to the cumulative number particle size distribution of 50% of the negative electrode material is 0.3 μm to 3 μm.

17. The negative electrode material of claim 2 or 3 or 10, wherein, The negative electrode material contains Si crystal grains, and in an X-ray diffraction spectrum of the negative electrode material, the size of the Si crystal grains in the negative electrode material on a (220) crystal face is 5 nm to 12 nm.

18. The negative electrode material of claim 3, wherein, The negative electrode material also satisfies 0.2 ≤ k1 / k2 ≤ 1.

19. A battery, characterized by A battery including the negative electrode material as claimed in any one of claims 1 to 18.

Images