Negative electrode material, preparation method thereof and battery

Abstract

The invention relates to a negative electrode material and a preparation method thereof, and a battery, the negative electrode material comprises an active substance, the active substance comprises silicon, a silicon oxide, magnesium silicate and a carbon element, and at least part of the carbon element is located in particles of the active substance; testing through an X-ray photoelectron spectrometer to obtain the mass ratio A of the oxygen element to the magnesium element in the depth range of 10nm below the surface of the negative electrode material; the mass ratio B of the oxygen element to the magnesium element in the negative electrode material is obtained through testing of an ONH element analyzer and an ICP spectrograph; the surface oxidation degree of the negative electrode material is gamma, gamma = A / B, and gamma is greater than 2 and less than 10. The negative electrode material disclosed by the invention has a proper surface oxidation degree, defects and pores in the negative electrode material can be reduced, and side reaction contact sites of the negative electrode material and an electrolyte are effectively reduced, so that the high-temperature storage performance, the first coulombic efficiency and the specific capacity of the negative electrode material can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of negative electrode materials, and particularly to negative electrode materials, their preparation methods, and batteries. Background Art

[0002] Lithium-ion batteries have the advantages of high energy density, long cycle life, low environmental pollution, and no memory effect, and are thus widely used in electric vehicles and consumer electronic products. The negative electrode material is an important component of lithium-ion batteries, which directly affects key indicators such as the energy density, cycle life, and safety performance of the batteries. At present, commercial lithium-ion batteries mainly use graphite-based negative electrode materials, but their theoretical specific capacity is only 372 mAh / g, making it difficult to meet the requirements of high-energy-density lithium-ion batteries. As a negative electrode material for lithium-ion batteries, silicon-based negative electrode materials have a high specific capacity and are one of the candidate materials for the next generation of high-energy-density lithium-ion batteries. However, silicon-based negative electrode materials will undergo a huge volume change during the charge-discharge cycle, leading to the deterioration of the material / electrode structure and the instability of the solid electrolyte interface film (SEI), thereby causing a sharp decline in their electrochemical performance.

[0003] Silicon oxide (general formula SiO x , 0 < x ≤ 2) has a specific capacity several times that of graphite (about 1500 mAh / g), and at the same time has a complex structure: it can be a material formed by dispersing nano-silicon particles in SiO2; it can also be a material with a tetrahedral structural unit, where a silicon atom is located at the center of the tetrahedral structural unit, and silicon atoms and / or oxygen atoms are located at the four vertices of the tetrahedral structural unit. Such a structure enables the reversible lithiated products formed by the reaction of SiO x with lithium during charging, such as lithium-silicon alloy, etc., to be dispersed in an inert matrix such as SiO2 and irreversible lithiated products (lithium oxide, lithium silicate, etc.), thereby greatly improving the volume expansion and cycle life characteristics of silicon materials. However, the initial Coulombic efficiency (ICE) of SiO x is relatively low (about 75%), and when it is assembled into a lithium-ion battery, more positive electrode materials need to be consumed to match it to offset the irreversible lithium loss, resulting in an increase in manufacturing costs.

[0004] To improve this problem, one method that has been proposed is to dope SiO x , and by doping with metals, the irreversible lithium intercalation components in SiO x are converted into inert components such as SiO2, thereby reducing the irreversible lithium capture of SiO x during charging and increasing the initial Coulombic efficiency (ICE). Currently, in the prior art, Mg doping is used to dope SiO xPartially converting into magnesium silicate and silicon can improve the initial coulombic efficiency (ICE) of the material, but the improvement of the initial coulombic efficiency (ICE) is limited due to the silicon, especially the reduced silicon on the surface of the material, being easily oxidized in air, i.e. the utilization of the doped Mg is low. Moreover, the Mg doping can also cause the generation of defects and pores in the material, and the contact sites with the electrolyte increase after the material is made into a lithium ion battery, thereby reducing the high-temperature storage performance. SUMMARY

[0005] 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, and reduce the contact sites of side reactions between the negative electrode material and the electrolyte, thereby improving the high-temperature storage performance, the initial coulombic efficiency and the specific capacity of the negative electrode material.

[0006] In a first aspect, the present application provides a negative electrode material, which comprises an active substance, and the active substance comprises silicon, silicon oxide, magnesium silicate and carbon elements, and at least part of the carbon elements are located inside the particles of the active substance.

[0007] The mass ratio of oxygen elements and magnesium elements in the negative electrode material within a depth range of 10 nm below the surface is A by X-ray photoelectron spectroscopy.

[0008] The mass ratio of oxygen elements and magnesium elements in the negative electrode material is B by ONH element analyzer and ICP spectrometer.

[0009] The surface oxidation degree of the negative electrode material is γ, and γ = A / B, 2 < γ < 10.

[0010] In some embodiments, A ranges from 5 to 45.

[0011] In some embodiments, B ranges from 2 to 5.

[0012] In some embodiments, 0.3 g to 0.5 g of the negative electrode material 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, then filtered and diluted, and the mass content of magnesium elements in the digestion solution in the negative electrode material is less than 0.8% by ICP spectrometer.

[0013] In some embodiments, the mass content of magnesium elements in the negative electrode material ranges from 5% to 15%.

[0014] In some embodiments, the chemical formula of the silicon oxide is SiO x , and 0 < x ≤ 2.

[0015] 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 face is 5 nm to 12 nm in the X-ray diffraction spectrum of the negative electrode material.

[0016] In some embodiments, the negative electrode material further comprises a carbon layer on at least part of the surface of the active material.

[0017] In some embodiments, the carbon layer comprises amorphous carbon.

[0018] In some embodiments, the thickness of the carbon layer is 1 nm to 500 nm.

[0019] In some embodiments, the mass content of carbon element in the negative electrode material is 2% to 8%.

[0020] In some embodiments, the mass content of oxygen element in the negative electrode material is 20% to 34%.

[0021] In some embodiments, the mass content of silicon element in the negative electrode material is 48% to 63%.

[0022] In some embodiments, the specific surface area of the negative electrode material is ≤8 m 2 / g.

[0023] In some embodiments, the oil absorption value of the negative electrode material is 30 mL / 100 g to 40 mL / 100 g.

[0024] In some embodiments, the tap density of the negative electrode material is 0.9 g / cm 3 ~ 1.3 g / cm 3 .

[0025] In some embodiments, the true density of the negative electrode material is 2.3 g / cm 3 ~ 2.66 g / cm 3 .

[0026] In some embodiments, the pH of the negative electrode material is 6.5 to 9.5.

[0027] In some embodiments, the median particle size of the negative electrode material is 2 μm to 12 μm.

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

[0029] In a second aspect, the present application provides a preparation method of a negative electrode material, which comprises the following steps:

[0030] The raw material of the silicon-oxygen material and magnesium are heated and vaporized and kept warm respectively under vacuum condition, and 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 keeping warm time of the raw material of the silicon-oxygen material is t1 h, the heating and vaporization temperature of the magnesium is T2 ℃, the keeping warm time of the magnesium is t2 h, T1 > T2, and t1 > t2, and the difference t1-t2 between t1 and t2 is 1-7;

[0031] Carbon dioxide gas and / or carbon monoxide gas are introduced, and vapor deposition is performed on the precursor to obtain an active substance, and the negative electrode material comprises the active substance.

[0032] In some embodiments, the raw material of the silicon-oxygen material comprises at least one of a mixture of Si, SiO y and Si, a mixture of Si and SiO2, and a mixture of Si, SiO y and Si, a mixture of Si and SiO2, and a mixture of Si, SiO

[0033] In some embodiments, the raw material of the silicon-oxygen material comprises a mixture of Si and SiO2, and the molar ratio of Si to SiO2 is 1:1.

[0034] In some embodiments, the mass ratio of the raw material of the silicon-oxygen material to the magnesium is 1:(0.05-0.2).

[0035] In some embodiments, the vacuum pressure in the heating and vaporization process is 0.1 Pa-1000 Pa.

[0036] In some embodiments, the heating and vaporization temperature of the raw material of the silicon-oxygen material is T1 ℃, and 800≤T1≤1600.

[0037] In some embodiments, the keeping warm time of the raw material of the silicon-oxygen material is t1 h, and 10≤t1≤28.

[0038] In some embodiments, the heating and vaporization temperature of the magnesium is T2 ℃, and 400≤T2≤600.

[0039] In some embodiments, the keeping warm time of the magnesium is t2 h, and 8≤t2≤25.

[0040] In some embodiments, the ratio T1 / T2 of T1 to T2 is (2-3):1.

[0041] In some embodiments, the co-deposition temperature is 600 ℃-1000 ℃.

[0042] In some embodiments, the vacuum pressure in the vapor deposition is 1 kPa-10 kPa.

[0043] In some embodiments, the temperature for the vapor deposition is 600-1000℃.

[0044] In some embodiments, the time for the vapor deposition is >1h.

[0045] 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.

[0046] In a third aspect, the present application provides a battery, wherein the battery comprises the negative electrode material of the first aspect or the negative electrode material prepared by the preparation method of the second aspect.

[0047] Compared with the prior art, the technical scheme of the present application has at least the following beneficial effects:

[0048] The negative electrode material provided by the present application comprises an active material, the active material comprises silicon, silicon oxide, magnesium silicate and carbon elements, and at least part of the carbon elements are located inside the particles of the active material, 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. 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; the surface oxidation degree of the negative electrode material is defined as γ, γ=A / B, 2<γ<10, that is, the value of A is greater than the value of B. Since the distribution contents of magnesium elements in the inside and surface layer of the negative electrode material generally have little difference, the difference can be reflected by the mass ratio of oxygen elements and magnesium elements, and further, the difference between the values of A and B can indicate that the surface oxidation degree of the negative electrode material is higher, that is, the silicon oxide in the surface layer of the negative electrode material is more. 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), and the oxidation degree of the surface of the negative electrode material is higher. This is because the silicon oxide effectively fills and seals the defects and pores on the surface of the negative electrode material, reduces the contact sites of side reactions between the negative electrode material and the electrolyte, and reduces the generation of SEI films between the negative electrode material and the electrolyte. At the same time, after the defects and pores in the negative electrode material are sealed, 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 are effectively reduced, and thus the first coulombic efficiency, specific capacity and high-temperature storage performance of the negative electrode material are improved.

[0049] The preparation method of the negative electrode material provided in the application first obtains a precursor by mixing silicon source vapor and magnesium vapor obtained by separately heating and vaporizing raw materials of a silicon-oxygen material and magnesium, and controls the generation rate and generation time of the silicon source vapor and the magnesium vapor by controlling the temperature and holding time for heating and vaporizing the raw materials of the silicon-oxygen material and the magnesium particles, 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 vaporization time of the raw materials of the silicon-oxygen material is prolonged, and the deposition of the silicon-oxygen material on the co-deposition product of the silicon-oxygen material and the magnesium is continued, so that more silicon oxide is deposited on the surface of the precursor, and the silicon oxide can fill and close the defects and pores, so that the surface oxidation degree of the negative electrode material is higher than that of the internal particles of the negative electrode material. Then, carbon dioxide gas and / or carbon monoxide gas is introduced to react with the silicon exposed on the surface of the precursor to generate silicon oxide SiOx and carbon, wherein the silicon oxide and the carbon can further fill the defects and pores in the active material, so as to further reduce the defects and pores in the negative electrode material and reduce the contact sites of the side reaction of the negative electrode material and the electrolyte; at the same time, the generated silicon oxide and amorphous carbon cover the silicon (Si) surface of the negative electrode material, which can cooperatively control the surface oxidation degree of the negative electrode material, inhibit the further reaction of the carbon dioxide gas and / or the carbon monoxide gas with the silicon (Si), and reduce the reaction of the silicon with oxygen in the air and 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. BRIEF DESCRIPTION OF DRAWINGS

[0050] The application will be further described below in combination with the drawings and examples.

[0051] Figure 1 The discharge state schematic diagram of the battery provided in the application is shown.

[0052] Figure 1 In the application,

[0053] 1-positive electrode sheet; 11-positive electrode current collector; 12-positive electrode active layer; 2-negative electrode sheet; 21-negative electrode current collector; 22-negative electrode active material layer; 3-separation film. DETAILED DESCRIPTION

[0054] In order to better understand the technical solutions of the application, the embodiments of the application will be described in detail below in combination with the drawings.

[0055] It should be clear that the described embodiments are only some of the embodiments of the application, not all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor belong to the scope of protection of the application.

[0056] The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in the description of the application and the appended claims, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0057] It should be understood that the term "and / or" as used herein merely describes associated objects, which can exist in three relationships, for example, A and / or B can represent three cases: A exists alone, A and B exist together, and B exists alone. In addition, the character " / " herein generally represents an "or" relationship between the front and rear associated objects.

[0058] In a first aspect, the application provides a negative electrode material, the negative electrode material comprising an active substance, the active substance comprising silicon, silicon oxide, magnesium silicate and carbon elements, at least part of the carbon elements being located inside the particles of the active substance;

[0059] The mass ratio of oxygen elements and magnesium elements in the negative electrode material within a depth range of 10 nm below the surface is A, which is obtained by X-ray photoelectron spectroscopy;

[0060] The mass ratio of oxygen elements and magnesium elements in the negative electrode material is B, which is obtained by ONH element analyzer and ICP spectrometer;

[0061] The surface oxidation degree of the negative electrode material is γ, and γ=A / B, 2<γ<10.

[0062] 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), and the oxidation degree of the surface of the negative electrode material is higher. This is because the silicon oxide effectively fills and seals 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 sealed, the contact between the negative electrode material and the air is also reduced, the oxidation resistance of the negative electrode material is improved, the irreversible reaction formed in the first charge-discharge process of the negative electrode material is effectively reduced, and thus the first coulombic efficiency, specific capacity and high-temperature storage performance of the negative electrode material are improved.

[0063] X-ray photoelectron spectroscopy (abbreviated as XPS) can be used for detecting and analyzing the negative electrode material, and the detection depth can reach a depth range of 10 nm inside the particle surface. When there are defects and pores on the surface of the negative electrode material, X-ray signals can pass through the defects and pores, and then the deeper part inside the negative electrode material can be detected, and the values of A and B measured are closer. When the defects and pores on the surface of the negative electrode material are less, the values of A and B measured by X-ray will show obvious difference, and therefore γ can be used to measure the sealing degree of defects and pores on the surface of the negative electrode material.

[0064] 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 in the above range, which is not limited herein. When γ ≥ 10, it can be seen that the surface oxidation degree of the negative electrode material is high, 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 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 and the electrolyte is intensified, and the high defects and pores also lead to easy oxidation of the negative electrode material, which reduces the utilization rate of the doped Mg, and the specific capacity and the initial efficiency of the negative electrode material are also reduced. When γ ≤ 2, it means that the surface of the negative electrode material is too much silicon oxide, mainly caused by the thick coverage of carbon particles; 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, which leads to excessive consumption of active lithium ions and reduces the initial coulombic efficiency of the negative electrode material. x

[0065] The present application controls 2 < γ < 10, the defects and pores in the negative electrode material are well closed, which effectively reduces the side reaction contact sites of the negative electrode material and the electrolyte, so that the negative electrode material obtains good high-temperature storage performance. At the same time, the defects and pores in the negative electrode material are closed, which also effectively reduces the contact of the negative electrode material with air, improves the oxidation resistance of the negative electrode material, can effectively reduce the irreversible reaction formed in the first charge and discharge process of the negative electrode material, and thus improves the initial coulombic efficiency and the specific capacity of the negative electrode material.

[0066] 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 in the above range, which is not limited herein.

[0067] 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 in the above range, which is not limited herein.

[0068] ​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 magnesium 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, it can also be other values within the above range, which are not limited herein) as determined by ICP spectrometer. It can be understood that a lower content of magnesium 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 oxidation degree of the negative electrode material, thereby improving the specific capacity and the first coulombic efficiency of the negative electrode material.

[0069] In some embodiments, the mass content of magnesium 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, it can also be other values within the above range, which are not limited herein). When the mass content of magnesium in the negative electrode material is <5%, the doping amount of magnesium in the negative electrode material is small, and the utilization rate of the active material is low, which leads to a low increase in the first coulombic efficiency of the negative electrode material, and is difficult to meet market demand. When the mass content of magnesium in the negative electrode material is >15%, the doping of Mg reduces the oxidation of SiO x , the defects and pores 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 decreases.

[0070] In some embodiments, the mass content of oxygen 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, it can also be other values within the above range, which are not limited herein).

[0071] 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.

[0072] 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.

[0073] In some embodiments, the negative electrode material further includes a carbon layer on at least part of the surface of the active material.

[0074] In some embodiments, the carbon layer includes amorphous carbon.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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, 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.

[0080] 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 and so on, and of course other values within the above range are also possible and are not limited herein. It will be appreciated 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 of electrode coating and battery production, and is also conducive to maintaining the structural stability of the electrode during cycling, improving the cycling performance of the material and the energy density of the battery.

[0081] 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 and so on, and of course other values within the above range are also possible and are not limited herein. It will be appreciated that the true density of the negative electrode material within the above range is conducive to improving the energy density of the battery made from the negative electrode material.

[0082] 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 and so on, and of course other values within the above range are also possible and are not limited herein.

[0083] In some embodiments, the median particle size of the negative electrode material is 2 μm ~ 12 μm, specifically 2 μm, 5 μm, 6 μm, 8 μm, 10 μm or 12 μm and so on, and of course other values within the above range are also possible and are not limited herein. It will be appreciated that controlling the median particle size of the negative electrode material within the above range is conducive to improving the cycling performance of the negative electrode material.

[0084] 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.

[0085] In a second aspect, the application provides a preparation method of a negative electrode material, which comprises the following steps:

[0086] 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;

[0087] 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.

[0088] The preparation method of the negative electrode material provided in the application first co-deposits the raw material of the silicon-oxygen material and magnesium by heating and gasifying them 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 above-mentioned defects and pores, so that the surface oxidation degree of the negative electrode material is higher than that of the internal particles of the negative electrode material. Then, carbon dioxide gas and / or carbon monoxide gas are introduced again 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.

[0089] The preparation method provided by the present scheme is described in detail below.

[0090] 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 t1 h, the heating and vaporization 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.

[0091] 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.

[0092] 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.

[0093] 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, and of course can also be other values within the above range, which are not limited herein.

[0094] 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, and of course can also be other values within the above range, which are not limited herein.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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, although the defects and pores on the surface of the negative electrode material are well closed, the relatively 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.

[0101] 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.

[0102] 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.

[0103] 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.

[0104] In some embodiments, the temperature for vapor deposition is 600-1000°C, specifically 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C or 1000°C, and of course other values within the above range are also possible and are not limited herein.

[0105] In some embodiments, the time for vapor deposition is >1 h.

[0106] 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.

[0107] 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.

[0108] In some embodiments, the gas-phase carbon source used in the gas-phase carbon coating treatment comprises at least one of methane, propane, butane, acetylene, benzene and toluene.

[0109] 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.

[0110] In some embodiments, the temperature of the vapor phase coating treatment is 600℃ to 1200℃, specifically 600℃, 700℃, 800℃, 900℃, 1000℃, 1100℃ or 1200℃, etc., and of course other values ​​within the above range are also possible, which are not limited here.

[0111] In some embodiments, the coating time of the gas phase coating process is 2h to 10h, specifically 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h or 10h, etc., and of course other values ​​within the above range are also possible, which are not limited here.

[0112] In some embodiments, the solid carbon source used in the solid 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.

[0113] Thirdly, this application provides a battery comprising the negative electrode material described in the first aspect or the negative electrode material prepared by the method described in the second aspect.

[0114] The battery provided in this application can be a secondary battery (such as a lithium-ion battery, sodium-ion battery, etc.), including a casing, electrode assembly, and electrolyte. Both the electrode assembly and electrolyte are located inside the casing. The casing can be a packaging bag sealed with an encapsulating film (such as an aluminum-plastic film), such as a pouch battery for secondary batteries.

[0115] In other embodiments, the secondary battery may also be a steel-cased battery, an aluminum-cased battery, etc.

[0116] Figure 1 This is a schematic diagram of the discharge state of the battery provided in the embodiments of this application, such as... Figure 1 As shown, the battery includes a casing and an electrode assembly. The electrode assembly includes a positive electrode 1, a negative electrode 2, and a separator 3, with the separator 3 disposed between the positive electrode 1 and the negative electrode 2. The electrode assembly can be a stacked structure, formed by alternately stacking the positive electrode 1, the separator 3, and the negative electrode 2. In other embodiments, the electrode assembly can also be a wound structure, formed by sequentially stacking and winding the positive electrode, the separator, and the negative electrode.

[0117] In some embodiments, the positive electrode 1 includes a positive current collector 11 and a positive active layer 12 disposed on at least one surface of the positive current collector 11.

[0118] In some embodiments, the positive electrode current collector 11 can use an aluminum foil or a nickel foil, or the like, and can also be 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, or the like) and a polymer substrate. The positive electrode active layer 12 includes a positive electrode active material, which includes a compound that reversibly intercalates and deintercalates metal ions.

[0119] In some embodiments, the positive electrode active material can include a lithium transition metal composite oxide, a sodium transition metal composite oxide, or the like. The lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese, and nickel.

[0120] In some embodiments, the positive electrode active material can include, but is not limited to, at least one of lithium cobaltate (LiCoO2), lithium nickel manganese cobalt ternary material (NCM), lithium manganate (LiMn2O4), lithium nickel manganese cobalt phosphate (LiNi0.5Mn1.5O4), or lithium iron phosphate (LiFePO4). 4) 0.5 1.5

[0121] In some embodiments, the negative electrode sheet 2 includes a negative electrode current collector 21 and a negative electrode active material layer 22 disposed on at least one surface of the negative electrode current collector.

[0122] In some embodiments, the negative electrode current collector 21 can use at least one of a copper foil, a nickel foil, a stainless steel foil, a titanium foil, or a carbon-based current collector, or the like, and can also be 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 and a polymer substrate. The negative electrode active material layer 22 includes a negative electrode material, which is the negative electrode material of the aforementioned first aspect or the resulting negative electrode material prepared by the aforementioned preparation method.

[0123] Embodiment

[0124] Embodiment 1

[0125] (1) A mixture of 30 kg of silicon particles and 30 kg of silicon dioxide particles in a 1:1 molar ratio was placed in the vacuum furnace reaction chamber 1, and 2.4 kg of Mg particles were placed in the vacuum furnace reaction chamber 2, and the pressure of the vacuum furnace was adjusted to 10 Pa.

[0126] (2) The vacuum furnace reaction chamber 1 was controlled to heat to 1300°C to generate SiO gas in the reaction chamber 1, and the holding time of the reaction chamber 1 was controlled to 24 hours; the vacuum furnace reaction chamber 2 was controlled to heat to 550°C to generate Mg gas in the reaction chamber 2, and the holding time of the reaction chamber 2 was 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 were mixed and deposited on the cooling plate, and the temperature of the cooling plate was controlled to 800°C. ​​​

[0127] (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.

[0128] (4) The reaction product is crushed and classified to an average particle size of 5 μm, and an active material is obtained.

[0129] (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.

[0130] 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.

[0131] Example 2

[0132] The difference from Example 1 is that:

[0133] In step (2), the heat preservation time of the vacuum furnace reaction bin 1 is controlled to be 26 hours.

[0134] 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.

[0135] Example 3

[0136] The difference from Example 1 is that:

[0137] In step (2), the heat preservation time of the vacuum furnace reaction bin 1 is controlled to be 22 hours.

[0138] 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.

[0139] Example 4

[0140] The difference from Example 1 is that:

[0141] (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.

[0142] The negative electrode material prepared in this embodiment comprises active substance, and the active substance comprises silicon, silicon oxide (SiO), magnesium silicate and carbon particles, and at least part of the carbon particles are located inside the active substance particles.

[0143] Example 5

[0144] Different from Example 1, the following steps are taken:

[0145] (1) Put 30 kg of a mixture of silicon particles and silicon dioxide particles with a molar ratio of 1:1 into the vacuum furnace reaction chamber 1, and put 4.5 kg of Mg particles into the vacuum furnace reaction chamber 2, and adjust the pressure of the vacuum furnace to 10 Pa.

[0146] (2) Control the heating temperature of the vacuum furnace reaction chamber 1 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 vacuum furnace reaction chamber 2 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 vacuum furnace reaction chamber 1 and the Mg gas generated in the vacuum furnace reaction chamber 2 on the cooling plate, and control the temperature of the cooling plate to 800 ℃.

[0147] The negative electrode material prepared in this embodiment comprises active substance, and the active substance comprises silicon, silicon oxide (SiO), magnesium silicate and carbon particles, and at least part of the carbon particles are located inside the active substance particles.

[0148] Example 6

[0149] Different from Example 1, the following steps are taken:

[0150] Step (2) controls the heating temperature of the vacuum furnace reaction chamber 1 to 1600 ℃.

[0151] The negative electrode material prepared in this embodiment comprises active substance, and the active substance comprises silicon, silicon oxide (SiO), magnesium silicate and carbon particles, and at least part of the carbon particles are located inside the active substance particles.

[0152] Example 7

[0153] Different from Example 1, the following steps are taken:

[0154] Step (2) controls the holding time of the vacuum furnace reaction chamber 2 to 17 h.

[0155] The negative electrode material prepared in this embodiment comprises active substance, and the active substance comprises silicon, silicon oxide (SiO), magnesium silicate and carbon particles, and at least part of the carbon particles are located inside the active substance particles.

[0156] Example 8

[0157] Different from Example 1 is that:

[0158] (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.

[0159] 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.

[0160] Example 9

[0161] Different from Example 1 is that:

[0162] (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.

[0163] 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.

[0164] Example 10

[0165] Different from Example 1 is that:

[0166] Step (3) uses CO gas instead of CO2 gas.

[0167] 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.

[0168] Example 11

[0169] Different from Example 1 is that:

[0170] Step (3) uses a mixed gas of CO and CO2 instead of CO2 gas.

[0171] 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.

[0172] Example 12

[0173] Different from Example 1 is that:

[0174] Step (2) controls the heat preservation time of the vacuum furnace reaction bin 1 to be 27 hours.

[0175] 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.

[0176] Comparative Example 1

[0177] Different from Example 1 is that:

[0178] Step (2) controls the holding time of the vacuum furnace reaction chamber 1 to be 20 hours, and step (3) is not performed.

[0179] Comparative Example 2

[0180] Different from Example 1 is that:

[0181] Step (3) is not performed.

[0182] Comparative Example 3

[0183] Different from Example 1 is that:

[0184] Step (2) controls the holding time of the vacuum furnace reaction chamber 1 to be 20 hours.

[0185] Comparative Example 4

[0186] Different from Example 1 is that:

[0187] Step (2) controls the holding time of the vacuum furnace reaction chamber 1 to be 30 hours.

[0188] Test Method

[0189] (1) XPS Test Method: The mass content of Mg element and O element in the surface layer (about 1 nm to 10 nm in depth) of the negative electrode material is tested by using an X-ray photoelectron spectrometer (Thermo Scientific K-Alpha). The excitation source used is Al Kα ray, the beam spot is 400 μm, the pass energy of full spectrum scanning is 100 eV, and the step length is 1 eV; finally, the full spectrum scanning data is analyzed by using Avantage software to obtain the atomic mass ratio A of O element and Mg element.

[0190] (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 Mg elements in the negative electrode material was obtained by ICP spectrometer (Agilent 5800 VDV ICP-OES) test.

[0191] (3) Test method for soluble magnesium element content on the surface of the negative electrode material: according to GB / T 24533-2019 Appendix H "Test method for trace metal elements", 0.3 g to 0.5 g 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 magnesium element on the surface of the negative electrode material was obtained by ICP spectrometer (Agilent 5800 VDV ICP-OES) test.

[0192] (4) Test method for mass content of oxygen element in the negative electrode material: 10 mg to 13 mg 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.

[0193] (5) Test method for tap density: measured according to GB / T 5162-2006 / ISO 3953:1993 "Determination of tap density of metal powders" or equipment manual. Measured by tap density instrument (KANTO DAT-4-220). The number of vibrations is 3000 times.

[0194] (6) Test method for oil absorption value: measured according to GB / T 3780.2-2017 "Carbon black - Part 2: Determination of oil absorption" or equipment manual. Measured by oil absorption value tester (ASAHI S-500). The absorption liquid used is dibutyl phthalate.

[0195] (7) Test method for specific surface area and pore volume: measured according to GB / T 19587-2004 "Determination of specific surface area of solid substances by gas adsorption BET method" or equipment manual. Measured by specific surface and pore size analyzer (Micromeritics ASAP 2460-2). The adsorption gas used is N2.

[0196] (8) Particle size test method: measured according to GB / T 19077.1-2008 "Particle size analysis - Laser diffraction methods - Part 1: General principles" or equipment instruction. Measured by laser particle size analyzer (Malvern Panalytical MS3000).

[0197] (9) True density test method: measured according to GB / T 24533-2019 Appendix D "Test method for true density". Measured by true density tester.

[0198] (10) Test method for mass content of carbon element: measured according to GB / T 38823-2020 Appendix A "Test method for carbon content". Measured by infrared carbon and sulfur analyzer.

[0199] (11) Test method for mass content of silicon: the carbon content C% of the material is tested by infrared carbon and sulfur analyzer, the oxygen content O% of the material is tested by oxygen, nitrogen and hydrogen element analyzer, the total metal content M% of the material is measured by total dissolution ICP method, and the Si element content of the material = 1-C%-O%-M%.

[0200] (12) Test method for carbon layer thickness: the average thickness of the carbon coating layer on the surface of the material is measured in SEM by ion milling machine for section treatment.

[0201] (13) Test method for high temperature storage performance: the test method for high temperature storage performance adopts cylindrical cell test, that is, the 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 cell is a common method in the art, which is not limited here, for example, the negative electrode sheet formula is mixed and slurried in a ratio of 4:90:3:3 to prepare the negative electrode sheet, and the positive electrode sheet formula is mixed and slurried in a ratio of 94:3:3 to prepare the positive electrode sheet.

[0202] The above test results are shown in Table 1 and Table 2.

[0203] Table 1 Performance test results of each example and comparative example

[0204]

[0205]

[0206] Table 2 Performance test results of each example and comparative example

[0207]

[0208] According to the test data in Table 1 and Table 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 reaction 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 reaction of the negative electrode material in the first charge-discharge process, and thus improves the initial coulombic efficiency and specific capacity of the negative electrode material.

[0209] According to the test data of Example 1 and Example 12, the difference between the heating and gasification time of the raw material of the silicon-oxygen material and the holding time after the heating and gasification of magnesium is too large, that is, after the co-deposition of the silicon-oxygen material and magnesium is completed, the amount of the silicon-oxygen material deposited in the precursor is too much, the surface oxidation degree γ of the negative electrode material is too small, the defects and pores in the negative electrode material are well closed, the contact sites of the side reaction between the negative electrode material and the electrolyte are effectively reduced, and the negative electrode material has good high-temperature storage performance. However, the defects and pores in the negative electrode material are closed too much, which limits the transmission of lithium ions, and thus the initial efficiency of the negative electrode material of Example 12 is lower than that of Example 1.

[0210] 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 for vapor deposition of the precursor, the surface oxidation degree γ of the negative electrode material is too large, the defects and pores in the negative electrode material are poorly closed, 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 high, which causes the negative electrode material to be easily oxidized, reduces the utilization rate of the doped Mg, and reduces the specific capacity and initial efficiency of the negative electrode material.

[0211] According to the test data of Example 1 and Comparative Example 2, 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 prolonged), the surface oxidation degree γ of the negative electrode material is too large, which causes the defects and pores in the negative electrode material to be poorly closed, the contact sites between the negative electrode material and the electrolyte are increased, the generation of unstable SEI film between the negative electrode material and the electrolyte in the cycle process is increased, 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 high, which causes the negative electrode material to be easily oxidized in the process of contacting with air, increases the generation of irreversible side reactions (such as decomposition of electrolyte, generation of a large amount of unstable SEI film to consume electrolyte, etc.) of the negative electrode material in the charge-discharge process, and thus reduces the specific capacity and initial efficiency of the negative electrode material.

[0212] According to the test data of the embodiment 1 and the comparative example 3, without the carbon dioxide gas being introduced into the precursor for the vapor deposition, the surface oxidation degree γ of the negative electrode material is too large, and the negative electrode material has a large number of defects and pores, the defects and pores increase the contact sites of the side reaction between the negative electrode material and the electrolyte, and the negative electrode material and the electrolyte continuously react to generate the unstable SEI film, thereby reducing the high-temperature storage performance of the negative electrode material; meanwhile, the large number of defects and pores in the negative electrode material make the negative electrode material be easily oxidized, and the generation of the irreversible side reaction in the cycle process of the negative electrode material is increased, thereby reducing the specific capacity and the initial efficiency of the negative electrode material.

[0213] According to the test data of the embodiment 1 and the comparative example 4, in the preparation process of the comparative example 4, the holding time of the vacuum furnace reaction bin 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, but the thick SiO x The irreversible lithiumization reaction of the negative electrode material itself occurs, the active lithium ions are consumed too much, the initial coulombic efficiency (initial efficiency) of the negative electrode material is reduced, and the negative electrode material cannot have both the high capacity retention rate and the high initial efficiency.

[0214] The above is only the preferred embodiment of the present application, and is not used to limit the present application, any modification, equivalent replacement, improvement, etc. within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A negative electrode material, characterized in that, The negative electrode material includes an active material, which includes silicon, silicon oxide, magnesium silicate, and carbon, with at least a portion of the carbon located inside the particles of the active material. The mass ratio of oxygen to magnesium in the negative electrode material within a depth of 10 nm below the surface was determined by X-ray photoelectron spectroscopy as A. The mass ratio of oxygen to magnesium in the negative electrode material was determined to be B by an ONH elemental analyzer and an ICP spectrometer. The surface oxidation degree of the negative electrode material is γ, where γ = A / B and 2 < γ < 10.

2. The negative electrode material according to claim 1, characterized in that, The negative electrode material has at least one of the following characteristics (1) to (5): (1) The range of A is 5 to 45; (2) The range of B is 2 to 5; (3) Immerse 0.3g to 0.5g of negative electrode material in a mixture of 6mL concentrated hydrochloric acid and 2mL concentrated nitric acid, heat at 50°C for 30 minutes in a graphite digester, then filter and dilute to volume. The mass content of magnesium in the digestion solution in the negative electrode material is less than 0.8% as determined by an ICP spectrometer. (4) The mass content of magnesium in the negative electrode material is 5% to 15%; (5) The general chemical formula of the silicon oxide is SiO2. x , 0 < x ≤ 2.

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

4. The negative electrode material according to claim 1, characterized in that, The negative electrode material also includes a carbon layer located on at least a portion of the surface of the active material.

5. The negative electrode material according to claim 4, characterized in that, The negative electrode material has at least one of the following characteristics (1) to (5): (1) The carbon layer comprises amorphous carbon; (2) The thickness of the carbon layer is 1 nm to 500 nm; (3) The carbon content in the negative electrode material is 2% to 8% by mass; (4) The mass content of oxygen in the negative electrode material is 20% to 34%; (5) The mass content of silicon in the negative electrode material is 48% to 63%.

6. The negative electrode material according to claim 1, characterized in that, The negative electrode material has at least one of the following characteristics (1) to (7): (1) The specific surface area of ​​the negative electrode material is ≤8m² 2 / g; (2) The oil absorption value of the negative electrode material is 30mL / 100g to 40mL / 100g; (3) The tap density of the negative electrode material is 0.9 g / cm³. 3 ~1.3g / cm 3 ; (4) The true density of the negative electrode material is 2.3 g / cm³. 3 ~2.66g / cm 3 ; (5) The pH of the negative electrode material is 6.5–9.5; (6) The median particle size of the negative electrode material is 2 μm to 12 μm; (7) The pore volume of the negative electrode material is <0.03 cm³. 3 / g.

7. A method for preparing a negative electrode material, characterized in that, The preparation method includes the following steps: Under vacuum conditions, the raw materials of silicon-oxygen material and magnesium are heated and vaporized and held at a certain temperature, respectively. The resulting silicon source vapor and magnesium vapor are mixed and co-deposited to obtain a precursor. The temperature at which the raw materials of silicon-oxygen material are heated and vaporized is T1℃, and the holding time of the raw materials of silicon-oxygen material is t1 h. The temperature at which the raw materials of magnesium are heated and vaporized is T2℃, and the holding time of the magnesium is t2 h. T1 > T2, and t1 > t2. The difference between t1 and t2, t1-t2, is 1 to 7. Carbon dioxide gas and / or carbon monoxide gas are introduced and vapor-phase deposition is performed on the precursor to obtain an active material, and the negative electrode material includes the active material.

8. The preparation method according to claim 7, characterized in that, The preparation method satisfies at least one of the following features (1) to (13): (1) The raw materials of the silicon-oxygen material include Si and SiO2. y Mixtures of SiO2 and SiO y At least one of the following: a mixture of Si and SiO2, wherein 0 < y < 2; (2) The raw materials of the silicon-oxygen material include a mixture of Si and SiO2, with a molar ratio of Si to SiO2 of 1:1; (3) The mass ratio of the raw material of the silicon-oxygen material to the magnesium is 1:(0.05~0.2); (4) The vacuum pressure during the heating and vaporization process is 0.1 Pa to 1000 Pa; (5) The heating and vaporization temperature of the raw material of the silicon-oxygen material is T1℃, 800≤T1≤1600; (6) The heat preservation time of the raw material of the silicon-oxygen material is t1 h, 10≤t1≤28; (7) The temperature at which the magnesium is heated and vaporized is T2℃, 400≤T2≤600; (8) The heat preservation time of the magnesium is t2 h, where 8 ≤ t2 ≤ 25; (9) The ratio of T1 to T2, T1 / T2, is (2~3):1; (10) The temperature of the co-deposition is 600℃~1000℃; (11) The vacuum pressure of the vapor deposition is 1 kPa to 10 kPa; (12) The temperature of the vapor deposition is 600℃~1000℃; (13) The time for vapor deposition is >1h.

9. The preparation method according to claim 7, characterized in that, The preparation method further includes: carbon coating the active material to obtain a negative electrode material, wherein the negative electrode material includes the active material and a carbon layer located on at least a portion of the surface of the active material.

10. A battery, characterized in that, The battery comprises the negative electrode material according to any one of claims 1 to 6 or the negative electrode material prepared by the preparation method of the negative electrode material according to any one of claims 7 to 9.

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