Negative electrode material, negative electrode sheet, and battery

Abstract

The present application provides a negative electrode material, a negative electrode sheet, and a battery. The negative electrode material comprises an active substance, and the active substance comprises silicon, a silicon oxide, and a compound of a metal element M, wherein the compound of a metal element M comprises a silicate of the metal element M and / or an oxide of the metal element M. The negative electrode material is determined by means of electron paramagnetic resonance; and the measured g-factor value of the electron spin resonance signal of an oxygen atom is X, where 2.00601≤X≤2.00699, and the oxygen vacancy intensity is Y, where 10G≤Y≤400G. The negative electrode material provided in the present application has a suitable oxygen vacancy; there is a stable lithium-ion channel during the cycle process of a battery; and the negative electrode material can relieve the expansion effect of the negative electrode material, thereby improving the cycle stability.

Description

Negative electrode materials, negative electrode sheets, and batteries

[0001] This application claims priority to Chinese patent application 202411216049.0, filed on August 30, 2024. The entire contents of the aforementioned Chinese patent application are incorporated herein by reference. Technical Field

[0002] This invention relates to the field of negative electrode materials technology, and more particularly to negative electrode materials, negative electrode sheets, and batteries. Background Technology

[0003] Lithium-ion batteries possess advantages such as high energy density, long cycle life, low environmental pollution, and no memory effect, making them widely used in electric vehicles and consumer electronics. The anode material is a crucial component of lithium-ion batteries, directly impacting key performance indicators such as energy density, cycle life, and safety. Currently, silicon-based materials exhibit high specific capacity, making them suitable for anodes in future lithium-ion batteries with even higher energy densities. To improve the electrochemical performance of silicon-based anode materials, doping with the metal element M is generally used to enhance the properties of Si and SiO. x The internal structure between the components, however, during the charge-discharge cycle of a lithium-ion battery, the Si and SiO in the silicon-based anode material... x A certain volume change will occur, resulting in significant structural loosening in some areas of the negative electrode material and a decrease in the lithium-ion transport performance of the solid electrolyte interphase (SEI) membrane, leading to volume expansion and capacity decay, and a sharp decline in battery performance.

[0004] Therefore, how to improve the specific capacity of anode materials while mitigating the volume expansion of silicon-based anode materials in lithium-ion batteries is a technical problem that still needs to be solved. Summary of the Invention

[0005] This application provides an anode material, an anode sheet, and a battery. The anode material provided by this application has a high specific capacity and can slow down the volume expansion of the anode material in the lithium-ion battery, thereby improving the rate performance.

[0006] In a first aspect, this application provides a negative electrode material, the negative electrode material comprising an active substance, the active substance comprising silicon, silicon oxide and a compound of metal element M, wherein the compound of metal element M comprises silicate of metal element M and / or oxide of metal element M;

[0007] Electron paramagnetic resonance was used to measure the negative electrode material. The g-factor value of the electron spin resonance signal of oxygen atoms was X, 2.00601≤X≤2.00699; the oxygen vacancy intensity was Y, 10G≤Y≤400G.

[0008] Secondly, this application provides a negative electrode sheet, the negative electrode sheet comprising the negative electrode material described in the first aspect.

[0009] Thirdly, this application provides a battery comprising the negative electrode material described in the first aspect.

[0010] Compared with the prior art, the technical solution of this application has at least the following beneficial effects:

[0011] The negative electrode material provided in this application includes an active material comprising silicon, silicon oxide, and compounds of metal element M, wherein the compounds of metal element M include silicates and / or oxides of metal element M. By controlling the g-factor value X of the electron spin resonance signal caused by oxygen atom vacancy defects within the negative electrode material and the oxygen vacancy intensity Y, the lattice defects formed by oxygen vacancies in the negative electrode material can be controlled. Oxygen vacancies not only affect the structural defects of the lattice but also the electronic arrangement defects. Larger values ​​of X and Y indicate a higher oxygen vacancy content in the negative electrode material, providing space for silicon expansion. Therefore, during the lithium insertion / extraction process, the negative electrode material has sufficient space to buffer the volume expansion of silicon and silicon oxide. The lattice defects formed by oxygen vacancies in the negative electrode material can also form stable lithium-ion transport channels, improving the lithium-ion transport efficiency of the negative electrode material; furthermore, it can enrich the active sites of the negative electrode material, which is beneficial for lithium-ion insertion and extraction. However, excessively high oxygen vacancy content can lead to a decrease in the structural strength of the negative electrode material, making it prone to particle breakage and pulverization during cycling, resulting in a decline in the cycle performance of the manufactured battery. Therefore, this application controls the X and Y values ​​of the negative electrode material within the aforementioned range, enabling the negative electrode material to possess good electrochemical performance and appropriate space buffering for internal expansion. This achieves both high specific capacity and improved cycle performance while reducing expansion. Attached Figure Description

[0012] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0013] Figure 1 is a schematic flowchart of the preparation method of the negative electrode material provided in the embodiment of this application.

[0014] Figure 2 is the Raman spectrum of the negative electrode material provided in Example 2 of this application.

[0015] Figure 3 is a graph plotted by an electron paramagnetic resonance spectrometer, showing the negative electrode material provided in Embodiment 2 of this application. The graph is plotted with magnetic field strength as the abscissa and signal strength value as the ordinate.

[0016] Figure 4 is a graph plotted by an electron paramagnetic resonance spectrometer, showing the negative electrode material provided in Embodiment 2 of this application, with the g-factor value on the x-axis and the signal intensity value on the y-axis.

[0017] Figure 5 is a schematic diagram of the discharge state of the secondary battery provided in the embodiment of this application. Detailed Implementation

[0018] To better understand the technical solution of the present invention, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0019] It should be understood that the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0020] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” as used in the embodiments of this invention and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0021] It should be understood that the term "and / or" used in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0022] In a first aspect, this application provides a negative electrode material, comprising an active material, wherein the active material comprises silicon, silicon oxide and a compound of metal element M, wherein the compound of metal element M comprises silicate of metal element M and / or oxide of metal element M.

[0023] Electron paramagnetic resonance was used to measure the negative electrode material. The g-factor value of the electron spin resonance signal of oxygen atoms was X, 2.00601≤X≤2.00699; the oxygen vacancy intensity was Y, 10G≤Y≤400G.

[0024] The negative electrode material provided in this application includes an active material comprising silicon, silicon oxide, and compounds of metal element M, wherein the compounds of metal element M include silicates and / or oxides of metal element M. By controlling the g-factor value X of the electron spin resonance signal caused by oxygen atom vacancy defects within the negative electrode material and the oxygen vacancy intensity Y, the lattice defects formed by oxygen vacancies in the negative electrode material can be controlled. Oxygen vacancies not only affect the structural defects of the lattice but also the electronic arrangement defects. The larger the values ​​of X and Y, the higher the oxygen vacancy content in the negative electrode material. During the lithium insertion / extraction process, the negative electrode material made from this material provides sufficient space to buffer the volume expansion of the silicon oxide. The lattice defects formed by oxygen vacancies in the negative electrode material can also form stable lithium-ion transport channels, improving the lithium-ion transport efficiency of the negative electrode material; it can also enrich the active sites of the negative electrode material, which is beneficial for lithium-ion insertion and extraction. However, excessively high oxygen vacancy content can lead to a decrease in the structural strength of the negative electrode material, making it prone to particle breakage and pulverization during cycling, resulting in a decrease in the cycle performance of the manufactured battery. Therefore, this application controls the X and Y values ​​of the negative electrode material within the above-mentioned range, enabling the negative electrode material to possess good electrochemical performance and suitable space buffer for internal expansion. While maintaining a high specific capacity, it also improves the cycle performance of the negative electrode material and reduces expansion.

[0025] In some implementations, 2.00601≤X≤2.00699, where X can specifically be 2.00601, 2.00605, 2.00610, 2.00625, 2.00650, 2.00680, 2.00685, 2.00699, or any value within the range of any two of the above values. Of course, it can also be other values ​​within the above range, which are not limited here. For example, the value of X can be 2.00601≤X≤2.00625, or 2.00605≤X≤2.00650, or 2.00625≤X≤2.00680, or 2.00605≤X≤2.00680, or 2.00650≤X≤2.00699.

[0026] In some implementations, 10G≤Y≤400G, where Y can be 10G, 20G, 40G, 100G, 200G, 300G, 380G, 400G, or any value within the range of any two of the above values. Of course, it can also be other values ​​within the above range, which are not limited here. For example, the value of Y can be 10G≤Y≤20G, or 10G≤Y≤100G, or 100G≤Y≤200G, or 200G≤Y≤400G, or 300G≤Y≤400G.

[0027] Both X and Y values ​​can be used to measure the strength of the oxygen vacancy electron spin resonance signal. Higher X and Y values ​​indicate a higher oxygen vacancy content in the anode material. During cycling, the anode material has sufficient redundant space to buffer the volume expansion of the active material and can also form stable lithium-ion transport channels to improve the lithium-ion transport rate. When X < 2.00601 and Y < 10 G, the oxygen vacancy content in the anode material is too low, resulting in more bond breakage due to volume expansion during cycling and deteriorating the cycling performance. When X > 2.00699 and Y > 400 G, the oxygen vacancy content in the anode material is too high, leading to excessive porosity and a significant decrease in structural strength. During cycling expansion, the anode material particles are prone to breakage or pulverization, resulting in deteriorated rate performance.

[0028] In some implementations, 2.00601≤X≤2.00624 and 10G≤Y≤45.51G, when X and Y are within the above ranges, the oxygen vacancy content in the negative electrode material is more suitable, the negative electrode material has good lithium-ion channel transport efficiency, the negative electrode material has high specific capacity, and can also suppress volume expansion.

[0029] In some implementations, 2.00624 < X ≤ 2.00699 and 45.51 G ≤ Y ≤ 400 G. When X and Y are within the above ranges, the oxygen vacancy content in the negative electrode material is relatively large, which can significantly improve the cycle performance and rate performance.

[0030] In some embodiments, the metal element M includes at least one of Mg, Li, Fe, Al, Mn, and Cu. Understandably, metal element M typically reacts with silicon-oxygen materials, with M atoms combining with O atoms to form oxides or silicates of metal M. This process disrupts the original crystal structure of the silicon-oxygen material, resulting in an interleaved arrangement of different atoms and the formation of a certain number of oxygen vacancies between atoms. This means that a certain number of oxygen atoms are missing from the normal ordered atomic arrangement, creating "holes" in the atomic structure. A small number of oxygen vacancies facilitate the transport and transfer of lithium ions, and the internal "holes" can effectively reduce the volume expansion effect. Preferably, M is Mg and / or Li. Understandably, Mg and / or Li have stronger reducing properties compared to other metals, making it easier to lose electrons and react with silicon-oxygen materials to obtain oxides of Mg and / or Li, or silicates of Mg and / or Li. Furthermore, due to the relatively small atomic size of Mg and Li, during the doping process, in addition to reacting with SiO₂… x In addition to the normal oxygen absorption reaction, it tends to cause the original SiO₂ to... x Oxygen atoms in the crystal lattice detach, and Mg and Li atoms combine with the detached oxygen to form oxygen vacancies. Therefore, the concentration of oxygen vacancies formed by magnesium and lithium doping is more suitable.

[0031] In some embodiments, the negative electrode material is analyzed using Raman spectroscopy at 500 cm⁻¹. -1 ~540cm -1 Characteristic peaks with Si-Si bonds within the range, with the highest peak intensity being I1, at 900 cm⁻¹. -1 ~1000cm -1 The characteristic peak of Si-O bonds within the specified range has a maximum intensity of I2, satisfying 4 ≤ I1 / I2 ≤ 12. Specifically, the ratio of I1 / I2 can be 4, 5, 6, 7, 8, 9, 10, 11, 12, or any value within the range of any two of the above values. Other values ​​within the specified range are also possible and are not limited here. For example, the value of I1 / I2 can be 4 ≤ I1 / I2 ≤ 8, or 4 ≤ I1 / I2 ≤ 10, or 6 ≤ I1 / I2 ≤ 10, or 6 ≤ I1 / I2 ≤ 12, or 8 ≤ I1 / I2 ≤ 12. It should be noted that I1 represents the silicon-silicon bond strength, and I2 represents the silicon-oxygen bond strength. The higher the oxygen vacancy content, the weaker the silicon-oxygen bond strength due to the lack of oxygen atoms, resulting in a larger I1 / I2 ratio and generally a larger X value. When I1 / I2 < 4, the strength of Si-Si bonds is low and the strength of Si-O bonds is high, indicating that the proportion of doping elements is low. At this time, the oxygen vacancy X value in the negative electrode material is small, and there are more bond breaks caused by volume expansion during cycling, resulting in a deterioration of the cycling performance of the negative electrode material. When I1 / I2 > 12, the strength of Si-Si bonds is high and the strength of Si-O bonds is low, indicating that the proportion of doping elements is high. At this time, the oxygen vacancy X value in the negative electrode material is large, the porosity inside the material is too large, the structural strength of the negative electrode material decreases significantly, and it is easy to crack or pulverize, leading to a deterioration in rate performance.

[0032] In some embodiments, the silicon oxide comprises silicon and oxygen, wherein the atomic molar ratio of silicon to oxygen is 0 to 2, excluding 0.

[0033] In some embodiments, the general chemical formula of silicon oxide is SiO. x Where 0 < x ≤ 2. Specifically, SiO x Specifically, it could be SiO 0.5 SiO 0.7 SiO 0.9 SiO, SiO 1.2 SiO 1.5 SiO 1.8 SiO 1.9 etc., without limitation. Silicon oxide can be represented by the general formula SiO. x (0 < x ≤ 2), which can be a material formed by silicon particles dispersed in SiO2, or silicon particles dispersed in SiO, with the interface between the two being SiO. xHowever, it is not limited to this. It should be noted that the x value in silicon oxide affects the range of the g-factor value X. In addition, the g-factor value X is also affected by other factors, such as the degree of lattice defects in the anode material mentioned above.

[0034] Understandably, silicon oxide has a high specific capacity, which can improve the energy density of the anode material. Doping the active material with metal element M, which forms a compound with O and Si elements, can improve the interface and internal structure of the active material and enhance the electrochemical performance of the anode material.

[0035] In some embodiments, the compound of the metal element M includes an oxide of the metal element M and / or a silicate of the metal element M, wherein the oxide of the metal element M and / or the silicate of the metal element M are uniformly distributed within the particles of the active material.

[0036] In some embodiments, the Si crystallite size in the silicon oxide is ≤20nm; specifically, the Si crystallite size in the silicon oxide can be 20nm, 18nm, 15nm, 12nm, 10nm, 9.2nm, 8nm, 6.7nm, 6nm, 5nm, or 3nm, etc., but is not limited to the listed values; other unlisted values ​​within this range are also applicable. Preferably, the Si crystallite size in the silicon oxide is ≤10nm, indicating that the volume of the negative electrode Si grains is small and the Si crystallites in the silicon oxide are dispersed. Controlling the Si crystallite size within the above range can effectively reduce silicon volume expansion and improve cycle performance.

[0037] In some embodiments, the negative electrode material further includes a carbon material, which is present on the surface of the active material and / or between the active material particles.

[0038] In some embodiments, the carbon material includes at least one of amorphous carbon and graphitized carbon. The carbon material forms a carbon layer on at least a portion of the surface of the active material. Understandably, the carbon layer on the surface of the active material can prevent the repeated formation of the SEI film from causing particle breakage of the negative electrode material, which is beneficial for improving the cycle performance of the negative electrode material and reducing the volume expansion caused by SEI film formation. It should be noted that the graphitized carbon can be a partially graphitized carbon material formed during the high-temperature carbonization process of the carbon material.

[0039] In some embodiments, the carbon content in the negative electrode material is 0.5% to 10% by mass; specifically, it can be 0.5%, 1%, 2%, 3%, 5%, 8% or 10%, etc., and is not limited here.

[0040] In some embodiments, the silicon content in the anode material is 40% to 65% by mass; specifically, it can be 40%, 45%, 50%, 55%, 60%, or 65%, etc., and is not limited thereto. When the silicon content is below 40% by mass, the specific capacity of the anode material is low, which cannot meet the requirements of high-energy-density lithium-ion batteries. When the silicon content is above 65% by mass, the volume expansion of the anode material is too large, and the cycle performance deteriorates severely. This application controls the silicon content within the above-mentioned range, which can improve the expansion effect of the anode material while ensuring its high specific capacity.

[0041] In some embodiments, the mass content of oxygen in the negative electrode material is 26% to 33%; specifically, it can be 26%, 27%, 28%, 29%, 30%, 31%, 32% or 33%, etc., and is not limited here.

[0042] In some embodiments, the mass content of metal element M in the negative electrode material is 5% to 20%; specifically, it can be 5%, 7%, 8%, 10%, 12%, 15%, 16%, 17%, 19%, or 20%, etc., and is not limited here. The doping amount of metal element M in the negative electrode material is an important indicator affecting the amount of oxygen vacancy defects in the negative electrode material. After doping, metal element M reacts with silicon oxide to form a certain oxygen vacancy structure. When the mass content of metal element M in the negative electrode material is <5%, the oxygen vacancy content in the negative electrode material is too low, and the silicon crystallite size of the negative electrode material itself is too small, which is not conducive to the transport, insertion, and extraction of lithium ions. When the mass content of metal element M in the negative electrode material is >20%, the oxygen vacancy content in the negative electrode material is too high, and the bond structure of the negative electrode material itself has breakpoints due to the large presence of oxygen vacancies, which easily leads to the expansion and cracking of the negative electrode material during battery cycling, resulting in a decrease in cycle performance.

[0043] In some embodiments, the specific surface area of ​​the negative electrode material is ≤10m². 2 / g, specifically 1.0m 2 / g, 1.5m 2 / g, 1.8m 2 / g, 2.0m 2 / g, 2.5m 2 / g, 3.0m 2 / g, 3.6m 2 / g, 4.0m 2 / g、5m 2 / g, 5.5m 2 / g, 6.0m 2 / g, 7.0m 2 / g, 8.0m 2 / g, 8.5m 2 / g、9m 2 / g or 10m 2 / g, but not limited to the listed values, and is not restricted here. When the specific surface area of ​​the negative electrode material is too large, the surface structure of the negative electrode material particles is not compact enough, and the outer layer structure is loose and porous, which is not conducive to the overall structural uniformity of the material. Dislocation is prone to occur during expansion, affecting the electrochemical performance of the material surface. This application controls the specific surface area of ​​the negative electrode material within the above range, and the negative electrode material particles have a suitable surface structure, which is beneficial to maintaining the consistency of the material expansion direction during battery cycling and improving the cycle stability of the negative electrode material.

[0044] In some implementations, the particle size of the negative electrode material satisfies: 1.0 μm ≤ D 10 ≤3.0μm; 4.5μm≤D 50 ≤7.0μm; 8.0μm≤D 90 ≤12.0μm.

[0045] In some embodiments, the true density of the negative electrode material is ≥2.4 g / cm³. 3 The true density of the negative electrode material can specifically be 2.4 g / cm³. 3 2.5g / cm 3 2.6g / cm 3 2.7g / cm 3 2.8g / cm 3 2.9g / cm 3 3.0g / cm 3 3.2g / cm 3 3.4g / cm 3 or 3.5g / cm 3 The following are not specified here. True density is the actual density of the negative electrode material after removing internal pores or voids between particles, and it is one of the standards for measuring the compactness of the negative electrode material's structure. When the true density of the negative electrode material is too low, there are large internal cavities and pores in the negative electrode material, and the structural strength of the negative electrode material particles is poor, which is not conducive to maintaining stable cycle performance. This application controls the true density of the negative electrode material within the above-mentioned range, indicating that the silicon and silicon oxide in the negative electrode material are in close contact with the metal element M, the pore volume in the negative electrode material is small, and the overall structure is compact, which is conducive to the uniformity of overall directional expansion during battery cycling and improves the cycle stability of the negative electrode material.

[0046] In some embodiments, the pH of the negative electrode material is 6 to 10, specifically 6, 7, 8, 9, 10, etc., which are not limited here. Preferably, the pH of the negative electrode material is 9 to 10.

[0047] In some embodiments, the water content in the negative electrode material is ≤0.5 wt%; specifically, it can be 0.5 wt%, 0.4 wt%, 0.35 wt%, 0.3 wt%, 0.25 wt%, 0.2 wt%, 0.15 wt%, 0.1 wt%, or 0.05 wt%, or other values ​​within the above range. Controlling the water content in the negative electrode material within the above range is beneficial for improving the storage stability of the negative electrode material.

[0048] In some embodiments, the average desorption pore size of the negative electrode material is 6nm to 9nm, specifically 6nm, 7nm, 8nm, 8.5nm or 9nm, etc., and of course, other values ​​within the above range are also possible, which are not limited here.

[0049] In some embodiments, the cumulative desorption pore volume of the negative electrode material is 0.02 cm³. 3 / g~0.04cm 3 / g, specifically 0.02cm 3 / g, 0.025cm 3 / g, 0.03cm 3 / g, 0.035cm 3 / g or 0.04cm 3 / g, etc., can also be other values ​​within the above range, and are not limited here. Controlling the cumulative desorption pore volume of the negative electrode material within the above range allows for the buffering of expansion stress caused by the expansion of the active material, and also improves lithium-ion transport efficiency. However, if the pore volume of the negative electrode material is too large, the structural stability of the negative electrode material decreases, and particle cracking and pulverization are prone to occur during cycling. Therefore, this application controls the pore volume of the negative electrode material within the above range, which is beneficial to improving the structural strength of the negative electrode material and reducing volume expansion.

[0050] Secondly, this application provides a method for preparing a negative electrode material, as shown in Figure 1, including the following steps:

[0051] Step S100: Press the mixture of silicon oxide material raw material and metal dopant into a mixed block, wherein the mass ratio of silicon oxide material raw material to metal dopant is (8-9.5):(0.5-2);

[0052] Step S200: Under a mixture of inert gas and reducing gas, the mixed block is heated and vaporized, and then co-deposited to obtain a precursor, wherein the volume percentage of reducing gas in the mixed gas is 5% to 20%.

[0053] In step S300, the precursor is immersed in an acidic solution for treatment, and the product is then washed with water and dried to obtain a negative electrode material containing active substances.

[0054] The method for preparing the anode material provided in this application involves first pressing a mixture of silicon-oxygen material raw materials and metal dopants into a block. This compressed mixture reduces volume, minimizing temperature differences and improving reaction uniformity. It also increases the contact area between components, allowing the metal dopants to react more effectively with the silicon-oxygen material raw materials. The tighter the block, the larger the contact area between the metal dopants and the silicon-oxygen material, resulting in a faster reaction and improved uniformity of element distribution within the particles. Next, the mixture is heated and vaporized, then co-deposited to achieve mutual doping of gaseous molecules. During co-deposition, the participation of reducing gases causes the silicon oxide to lose some oxygen atoms, creating oxygen vacancies. Furthermore, the doping of the metal element M disrupts the original structure of the silicon oxide, altering its crystal structure and also creating oxygen vacancies. Finally, soaking the precursor in an acidic solution further increases the number of oxygen vacancies on the surface of the anode material. The preparation method provided in this application controls the mass ratio of silicon-oxygen material raw materials to metal dopants, as well as the volume ratio of reducing gas, so that the oxygen vacancy content in the final anode material is controlled within a suitable range, namely 2.00601≤X≤2.00699, 10G≤Y≤400G. The holes of oxygen vacancies can serve as electron transfer channels, thereby improving the conductivity of the anode material. The lattice defects caused by oxygen vacancies can also form stable lithium-ion transport channels, improving the lithium-ion transport efficiency of the anode material. This allows the anode material to have suitable space buffer for internal expansion, improving the cycle performance of the anode material while maintaining a high specific capacity and reducing expansion.

[0055] The following is a detailed introduction to this plan:

[0056] Step S100: The mixture of silicon oxide material raw material and metal dopant is pressed into a mixed block.

[0057] In some embodiments, the raw materials for the silicon-oxygen material include Si and SiO. y Mixtures of SiO2 and SiO y At least one of the following: a mixture of Si and SiO2, wherein 0 < y < 2.

[0058] In some embodiments, the raw materials of the silicon-oxygen material include a mixture of Si and SiO2, wherein the molar ratio of Si to SiO2 is 1:1.

[0059] In some embodiments, the mass ratio of the silicon-oxygen material to the metal dopant is (8-9.5):(0.5-2), specifically 8:2, 8.5:1.5, 9:1, 9.2:0.8, or 9.5:05, etc., or other values ​​within the above range, which are not limited here. Controlling the mass ratio of silicon-oxygen material to metal dopant can control the oxygen vacancy content in the obtained negative electrode material within a suitable range. Too much metal dopant results in an excessively high oxygen vacancy content in the negative electrode material, leading to a decrease in the structural strength of the negative electrode material. During cycling, the negative electrode material is prone to particle breakage and pulverization, resulting in a decrease in the cycle performance of the battery. Too little metal dopant results in an excessively low oxygen vacancy content in the negative electrode material, lacking sufficient redundancy space to buffer the volume expansion of the active material. During cycling, the volume expansion leads to more bond breakage, deteriorating the cycle performance of the negative electrode material.

[0060] In some embodiments, the metal dopant includes at least one selected from elemental metal M, oxide of metal element M, and silicate of metal element M. Exemplarily, it can be Mg powder, Li powder, Al powder, etc., and is not limited thereto.

[0061] In some embodiments, the pressure used when pressing the mixed block is 5 MPa to 20 MPa, and the pressure is maintained for 10 min to 30 min. Specifically, the pressure can be 5 MPa, 10 MPa, 12 MPa, 15 MPa, 18 MPa, 19 MPa, or 20 MPa, and the pressure maintenance time can be 10 min, 12 min, 15 min, 18 min, 20 min, 22 min, 25 min, 28 min, or 30 min, etc. Of course, other values ​​within the above range are also possible and are not limited here.

[0062] In step S200, the mixed bulk material is heated and vaporized under the action of inert gas and reducing gas, and then co-deposited to obtain a precursor; wherein the volume percentage of the reducing gas is 5% to 20%.

[0063] In some embodiments, the volume percentage of the reducing gas in the mixed gas is 5% to 20%, specifically 5%, 6%, 8%, 10%, 15%, 18%, 19%, or 20%, etc., and other values ​​within the above range are also possible and are not limited here. Understandably, the volume percentage of the inert gas in the mixed gas is 80% to 95%. If the volume percentage of the reducing gas in the mixed gas is too high, the faster the reaction rate involving the reducing gas, the more pronounced the porosity of the synthesized negative electrode material tends to be. While this is beneficial for buffering the cyclic expansion process, it makes it difficult to effectively cover the surface of the negative electrode material particles during subsequent carbon coating, resulting in decreased coating uniformity and a decline in overall performance. Conversely, if the volume percentage of the reducing gas in the mixed gas is too low, the oxygen vacancy content in the prepared negative electrode material is low, resulting in a lower lithium-ion transport rate and reduced rate performance. Preferably, the volume percentage of the reducing gas in the mixed gas is 8% to 12%.

[0064] In some embodiments, the reducing gas includes at least one of hydrogen, carbon monoxide, and sulfur monoxide.

[0065] In some embodiments, the inert gas includes at least one of argon, helium, nitrogen, krypton, and neon.

[0066] In some embodiments, the vacuum pressure during the heating and vaporization process is 10 Pa to 100 Pa. Specifically, it can be 10 Pa, 20 Pa, 30 Pa, 40 Pa, 50 Pa, 60 Pa, 70 Pa, 80 Pa, or 100 Pa, etc. Of course, it can also be other values ​​within the above range, which are not limited here.

[0067] In some embodiments, the temperature during the heating and vaporization process is 1100℃ to 1400℃, specifically 1100℃, 1150℃, 1200℃, 1250℃, 1300℃, 1350℃ or 1400℃, etc. Of course, other values ​​within the above range are also possible, and no limitation is made here.

[0068] In some embodiments, the heating and vaporization process takes 4 to 20 hours, specifically 4 hours, 5 hours, 6 hours, 8 hours, 10 hours, 12 hours, 15 hours, 18 hours, or 20 hours, or other values ​​within the above range, which are not limited here.

[0069] By controlling reaction parameters such as the volume ratio of reducing gas, vacuum pressure, heating vaporization temperature and time during the reaction process, silicon oxide can react with reducing gas during deposition, resulting in the formation of an appropriate amount of oxygen vacancies inside the deposition product. By controlling various reaction parameters, it is beneficial to control the content and distribution uniformity of oxygen vacancies in the deposition product.

[0070] In step S300, the precursor is immersed in an acidic solution for treatment, and the product is then washed with water and dried to obtain the active material, wherein the negative electrode material includes the active material.

[0071] Understandably, soaking the precursor in an acidic solution can further increase the number of oxygen vacancies on the surface of the negative electrode material. These oxygen vacancies can serve as electron transfer channels to improve the conductivity of the negative electrode material.

[0072] In some embodiments, the preparation method further includes: shaping and sieving the precursor, and then soaking the sieved precursor in an acidic solution.

[0073] Understandably, by shaping the precursor, the particle size can be controlled, which helps to increase the energy density of the negative electrode material and can also effectively improve the charging and discharging efficiency of lithium ions during battery cycling.

[0074] In some embodiments, the acidic solution includes at least one of oxalic acid, hydrochloric acid, nitric acid, and sulfuric acid.

[0075] In some embodiments, the mass fraction of the acidic substance in the acidic solution is 10% to 30%.

[0076] In some embodiments, the soaking time is 1 hour to 3 hours, specifically 1 hour, 1.5 hours, 2 hours, 2.5 hours or 3 hours, or other values ​​within the above range, which are not limited here.

[0077] In some embodiments, the soaked product is thoroughly washed with water until it is neutral, and then dried so that the water in the product can be evaporated, and the water content of the product is controlled within a low range.

[0078] In some embodiments, 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 the carbon material.

[0079] Understandably, the presence of carbon material on the surface of the active material can work in synergy with oxygen vacancies on the surface of the active material to further improve the conductivity of the negative electrode material.

[0080] In some embodiments, the carbon coating process includes one or more combinations of liquid phase coating, solid phase coating, and gas phase coating.

[0081] In some embodiments, the carbon coating process specifically includes uniformly mixing the carbon source and the mixture particles, followed by heat treatment.

[0082] In some implementations, the mixing method includes at least one of VC mixing, fusion, triple eccentric mixing, hand mixing, kneading, spiral mixing, and ball milling.

[0083] In some embodiments, the heat treatment method includes at least one of roller kiln, pusher kiln, box furnace, tube furnace, CVD furnace, and fluidized bed.

[0084] In some embodiments, the carbon source includes at least one of pitch-based, coal-based, petroleum-based, biomass, alkanes, alkenes, alkynes, polyesters, ethers, phenols, sucrose, and citric acid.

[0085] In some embodiments, the temperature of the carbon coating treatment is 700℃ to 1000℃, specifically 700℃, 800℃, 900℃, 950℃ or 1000℃, etc., and of course other values ​​within the above range are also possible, which are not limited here.

[0086] In some embodiments, the carbon coating treatment time is 2h to 8h, specifically 2h, 4h, 5h, 6h, 7h or 8h, etc., and of course other values ​​within the above range are also possible, which are not limited here.

[0087] In some embodiments, the carbon coating process is carried out in an oxygen-free atmosphere.

[0088] In some embodiments, the non-oxygen atmosphere includes at least one of vacuum, hydrogen, argon, helium, nitrogen, krypton, and neon.

[0089] In some embodiments, the carbon material formed after heat treatment forms a carbon layer on the surface of the active material.

[0090] In some embodiments, the carbon coating process includes sieving, specifically using a 200-400 mesh sieve.

[0091] Thirdly, this application provides a negative electrode sheet comprising the aforementioned negative electrode material. Because the aforementioned negative electrode material possesses suitable space to buffer internal expansion, it exhibits both high specific capacity and cycle performance. Therefore, the application of a negative electrode sheet containing the aforementioned negative electrode material in batteries is beneficial for improving battery capacity, cycle performance, and lifespan.

[0092] Fourthly, this application provides a battery including the aforementioned negative electrode material. The battery may specifically be a lithium-ion battery, a sodium-ion battery, etc., and is not limited thereto.

[0093] One embodiment of this application provides a secondary battery (such as a lithium-ion battery, sodium-ion battery, etc.), including a casing, an electrode assembly, and an electrolyte / electrolyte. Both the electrode assembly and the electrolyte / electrolyte are located within the casing.

[0094] The outer casing can be a packaging bag sealed with an encapsulating film (such as aluminum-plastic film), for example, a pouch battery for a secondary battery. In other embodiments, the secondary battery can also be a steel-cased battery, an aluminum-cased battery, etc.

[0095] Figure 5 shows a schematic diagram of the battery in a discharged state, i.e., during operation. As shown in Figure 5, the electrode assembly includes a positive electrode 110, a negative electrode 120, and a separator 130, with the separator disposed between the positive and negative electrode sheets. The electrode assembly can be a stacked structure, formed by alternating layers of the positive electrode, separator, and negative electrode. In other embodiments, the electrode assembly can also be a wound structure, formed by winding the positive electrode, separator, and negative electrode after they have been stacked in sequence.

[0096] Positive electrode film

[0097] The positive electrode 110 includes a positive current collector 111 and a positive active layer 112 disposed on at least one surface of the positive current collector. The positive current collector can be aluminum foil or nickel foil, or any composite current collector disclosed in the prior art, such as, but not limited to, current collectors formed by combining the aforementioned conductive foil and polymer substrate. The positive active layer contains a positive active material, which includes compounds capable of reversibly intercalating and deintercalating metal ions. In some embodiments, the positive 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.

[0098] In some embodiments, the positive electrode active material may include, but is not limited to, lithium cobalt oxide (LiCoO2), lithium nickel manganese cobalt ternary materials (NCM), lithium manganese oxide (LiMn2O4), and lithium nickel manganese oxide (LiNi). 0.5 Mn 1.5 At least one of lithium iron phosphate (LiFePO4) or lithium iron phosphate (LiFePO4).

[0099] negative electrode sheet

[0100] The negative electrode 120 includes a negative electrode current collector 121 and a negative electrode active material layer 122 disposed on at least one surface of the negative electrode current collector. The negative electrode current collector can be at least one of copper foil, nickel foil, stainless steel foil, titanium foil, or carbon-based current collectors, 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 122 includes the aforementioned negative electrode material.

[0101] During battery operation, i.e. when the battery is in a discharge state, metal ions 140 (e.g., lithium ions) in the negative electrode are released from the lattice of the negative electrode material, pass through the electrolyte / electrolyte through the separator 130, and are embedded in the lattice of the positive electrode material.

[0102] Conversely, when the battery is charged by applying an external circuit, the oxidation of the positive electrode material causes metal ions (such as lithium ions) in the positive electrode to be released from the lattice of the positive electrode material, pass through the electrolyte / electrolyte through the separator, and move to the negative electrode; at the same time, the negative electrode material undergoes a reduction reaction, causing metal ions to be embedded in the lattice of the negative electrode material.

[0103] As metal ions move back and forth between the positive and negative electrodes, the battery can achieve the discharge and charge process in thousands of cycles.

[0104] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0105] Example

[0106] Example 1

[0107] (1) Mix 900g of Si and SiO2 mixture powder (where the molar ratio of Si to SiO2 is 1:1) and 100g of Mg metal powder evenly, and press the mixture powder with a pressure of 15MPa for 20min to form a mixed block.

[0108] (2) The mixed block was put into a vacuum device and heated and vaporized at 1300℃. At the same time, a mixture of argon and carbon monoxide was introduced, with carbon monoxide accounting for 10% of the volume. The vacuum degree was controlled at 100Pa and the holding time was 10h. The deposited product was prepared by evaporation-deposition method.

[0109] (3) The deposited product was crushed to obtain powder with a maximum particle size Dmax of 20 μm. It was soaked in 20% oxalic acid solution for 2 hours, then washed with water and dried to obtain active material.

[0110] (4) The active material is subjected to gas phase carbon coating treatment in methane gas and kept at 800℃ for 5h to obtain the negative electrode material.

[0111] The negative electrode material prepared in this embodiment includes an active material, which includes silicon, silicon oxide (SiO), and magnesium silicate.

[0112] Other parameters of the negative electrode material are detailed in Table 1.

[0113] Example 2

[0114] The difference from Example 1 is:

[0115] (1) Mix 850g of Si and SiO2 powder (where the molar ratio of Si to SiO2 is 1:1) and 150g of Mg powder uniformly, and press it under a pressure of 15MPa for 20min to form a mixed block.

[0116] The negative electrode material prepared in this embodiment includes an active material having pores, and the active material includes silicon, silicon oxide (SiO), and magnesium silicate.

[0117] Figure 2 shows the Raman spectrum of the negative electrode material provided in Embodiment 2 of this application. As shown in Figure 2, the I1 / I2 ratio of the negative electrode material is 8.51. Other parameters of the negative electrode material are detailed in Table 1.

[0118] Example 3

[0119] The difference from Example 1 is:

[0120] (1) Mix 825g of Si and SiO2 powder (where the molar ratio of Si to SiO2 is 1:1) and 175g of Mg powder uniformly, and press it under a pressure of 15MPa for 20min to form a mixed block.

[0121] The negative electrode material prepared in this embodiment includes an active material having pores, and the active material includes silicon, silicon oxide (SiO), and magnesium silicate.

[0122] Other parameters of the negative electrode material are detailed in Table 1.

[0123] Example 4

[0124] The difference from Example 1 is:

[0125] (1) Mix 800g of Si and SiO2 powder (where the molar ratio of Si to SiO2 is 1:1) and 200g of Mg powder uniformly, and press it under a pressure of 15MPa for 20min to form a mixed block.

[0126] The negative electrode material prepared in this embodiment includes an active material having pores, and the active material includes silicon, silicon oxide (SiO), and magnesium silicate.

[0127] Other parameters of the negative electrode material are detailed in Table 1.

[0128] Example 5

[0129] The difference from Example 2 is:

[0130] (2) The mixed block was placed in a vacuum device and heated at 1400℃. At the same time, a mixture of argon and carbon monoxide was introduced, with carbon monoxide accounting for 10% of the volume. The vacuum degree was controlled at 100Pa and the holding time was 10h. The composite was prepared by evaporation-deposition method.

[0131] The negative electrode material prepared in this embodiment includes an active material having pores, and the active material includes silicon, silicon oxide (SiO), and magnesium silicate.

[0132] Other parameters of the negative electrode material are detailed in Table 1.

[0133] Example 6

[0134] The difference from Example 2 is:

[0135] (2) The mixed block was put into a vacuum device and heated at 1100℃. At the same time, a mixture of argon and carbon monoxide was introduced, with carbon monoxide accounting for 10% of the volume. The vacuum degree was controlled at 100Pa and the holding time was 10h. The composite was prepared by evaporation-deposition method.

[0136] The negative electrode material prepared in this embodiment includes an active material having pores, and the active material includes silicon, silicon oxide (SiO), and magnesium silicate.

[0137] Other parameters of the negative electrode material are detailed in Table 1.

[0138] Example 7

[0139] The difference from Example 2 is:

[0140] (1) Mix 850g of Si and SiO2 powder (where the molar ratio of Si to SiO2 is 1:1) and 150g of Li powder uniformly, and press it under a pressure of 15MPa for 20min to form a mixed block.

[0141] Example 8

[0142] The difference from Example 2 is:

[0143] (1) Mix 850g of Si and SiO2 powder (where the molar ratio of Si to SiO2 is 1:1) and 150g of Al powder uniformly, and press it under a pressure of 15MPa for 20min to form a mixed block.

[0144] Example 9

[0145] The difference from Example 2 is:

[0146] (1) Mix 850g of Si and SiO2 powder (where the molar ratio of Si to SiO2 is 1:1) and 150g of Mg powder uniformly, and press it under a pressure of 5MPa for 20min to form a mixed block.

[0147] Example 10

[0148] The difference from Example 2 is:

[0149] (4) The active material is subjected to gas phase carbon coating treatment in acetylene gas and kept at 800℃ for 5h to obtain the negative electrode material.

[0150] Example 11

[0151] The difference from Example 1 is:

[0152] (1) Mix 925g of Si and SiO2 powder (where the molar ratio of Si to SiO2 is 1:1) and 75g of Mg powder uniformly, and press it under a pressure of 15MPa for 20min to form a mixed block.

[0153] The negative electrode material prepared in this embodiment includes an active material having pores, and the active material includes silicon, silicon oxide (SiO), and magnesium silicate.

[0154] Other parameters of the negative electrode material are detailed in Table 1.

[0155] Example 12

[0156] The difference from Example 2 is:

[0157] (2) The mixed block was put into a vacuum device and heated and vaporized at 1300℃. At the same time, a mixture of argon and carbon monoxide was introduced, with carbon monoxide accounting for 5% of the volume. The vacuum degree was controlled at 100Pa and the holding time was 10h. The deposited product was prepared by evaporation-deposition method.

[0158] Example 13

[0159] The difference from Example 2 is:

[0160] (2) The mixed block was put into a vacuum device and heated and vaporized at 1300℃. At the same time, a mixture of argon and carbon monoxide was introduced, with carbon monoxide accounting for 20% of the volume. The vacuum degree was controlled at 100Pa and the holding time was 10h. The deposited product was prepared by evaporation-deposition method.

[0161] Example 14

[0162] The difference from Example 2 is:

[0163] Step (4) is not performed.

[0164] Comparative Example 1

[0165] The difference from Example 1 is:

[0166] (1) Press 1000g of Si and SiO2 mixture powder (where the Si:SiO2 molar ratio is 1:1) under a pressure of 15MPa for 20min to form a mixed block.

[0167] Comparative Example 2

[0168] The difference from Example 1 is:

[0169] (1) Mix 750g of Si and SiO2 powder (where the molar ratio of Si to SiO2 is 1:1) and 250g of Mg powder uniformly, and press it under a pressure of 15MPa for 20min to form a mixed block.

[0170] Comparative Example 3

[0171] The difference from Example 2 is:

[0172] (2) The mixed block was placed in a vacuum device and heated at 1300℃. Argon gas was introduced and the temperature was maintained for 10 hours. The composite was prepared by evaporation-deposition method.

[0173] Comparative Example 4

[0174] The difference from Example 2 is:

[0175] (1) Mix 850g of Si and SiO2 mixture powder (where the molar ratio of Si to SiO2 is 1:1) and 150g of Mg metal powder evenly to obtain mixed powder.

[0176] (2) The mixed powder was put into a vacuum device and heated at 1300°C. At the same time, a mixture of argon and carbon monoxide was introduced, with carbon monoxide accounting for 10% of the volume. The vacuum degree was controlled at 100 Pa and the holding time was 10 h. The composite was prepared by evaporation-deposition method.

[0177] Comparative Example 5

[0178] The difference from Example 2 is:

[0179] Step (3) is not performed.

[0180] Comparative Example 6

[0181] The difference from Example 2 is:

[0182] (2) The mixed block is put into a vacuum device and heated and vaporized at 1300℃. At the same time, a mixture of argon and carbon monoxide is introduced, wherein the volume ratio of carbon monoxide is 50%. The vacuum degree is controlled at 100Pa and the holding time is 10h. The deposition product is prepared by evaporation-deposition method.

[0183] Comparative Example 7

[0184] The difference from Example 2 is:

[0185] (1) Mix 850g of Si and SiO2 powder (where the molar ratio of Si to SiO2 is 1:1) and 150g of Mg powder uniformly, and press it under a pressure of 30MPa for 20min to form a mixed block.

[0186] Comparative Example 8

[0187] The difference from Example 2 is:

[0188] (3) The deposited product was crushed to obtain powder with a maximum particle size Dmax of 20 μm. It was soaked in 50% oxalic acid solution for 2 hours, then washed with water and dried to obtain active material.

[0189] Step (4) is not performed.

[0190] Test methods

[0191] (1) Particle size of the negative electrode material:

[0192] The particle size was tested according to GB / T 19077.1-2008 "Particle size analysis by laser diffraction - Part 1: General rules", using a laser particle size analyzer (Malvin Panaco MS3000).

[0193] The particle size distribution range of the negative electrode material was tested using a Malvern laser particle size analyzer (Mastersizer 3000). The cumulative particle size distribution based on volume was determined by laser diffraction. D05 represents the particle size corresponding to a cumulative particle size distribution percentage of 0.5%, D50 represents the particle size corresponding to a cumulative particle size distribution percentage of 50%, and D80 represents the particle size corresponding to a cumulative particle size distribution percentage of 80%.

[0194] (2) Oxygen vacancy test method:

[0195] Electron paramagnetic resonance spectrometry (Bruker EMX PLUS, Germany) was used for measurement. 100 mg of the sample to be tested was weighed and placed into a quartz tube. The quartz tube was then placed in the sample chamber, ensuring that the sample was located in the center of the sample chamber. The test was conducted at room temperature in a dark environment.

[0196] A curve is plotted with magnetic field strength as the abscissa and signal strength value as the ordinate, as shown in Figure 3. The coordinates of the highest peak in the curve are (m1, n1) and the coordinates of the lowest peak are (m2, n2). The oxygen vacancy intensity is calculated as Y = |n1-n2|×|m1-m2|, with the unit being G.

[0197] Substitute the magnetic field strength into the following formula, and plot the curve with the obtained g-factor value on the x-axis and the signal strength value on the y-axis, as shown in Figure 4. The g-factor number corresponding to the signal strength being 0 is the g-factor value X of the electron spin resonance signal of the oxygen atom in the measured material.

[0198] g = hv / βH; where h = 4.135 × 10 -15 eV·s is Planck's constant; v is the resonant frequency, determined by the equipment parameters during testing; β = 5.788 × 10⁻⁶. -5 eV·T -1 , is the Bohr magneton; H is the magnetic field strength, measured in G.

[0199] (3) True density test of negative electrode material:

[0200] The measurement was performed according to GB / T 24533-2019, Appendix D, "Determination of True Density" or the equipment instruction manual. A true density meter (Bestde 3H-2000TD) was used. Helium was used as the gas.

[0201] (4) Specific surface area test of negative electrode material:

[0202] The measurement was performed according to GB / T 19587-2004 "Determination of Specific Surface Area of ​​Solid Substances by Gas Adsorption BET Method" or the equipment manual. A specific surface area and pore size analyzer (McASAP2460-2) was used for measurement. The adsorbed gas used was N2.

[0203] (5) Raman testing of negative electrode materials:

[0204] The Raman spectra of the powder were tested using a Renishaw In Via microconfocal Raman spectrometer (Japan). The test parameters were: laser wavelength 532 nm, test range 120 μm × 120 μm, and step size 4 μm. The test results were processed using the instrument's built-in software. During data processing, baseline removal was performed on the Raman spectra of all sampling points. Peak finding parameters were adjusted to find the peaks at 500 cm⁻¹. -1 ~540cm -1 The peaks within the range exhibit characteristic peaks of Si-Si bonds, with the highest peak intensity of the Si-Si bond characteristic peak being I1, at 900 cm⁻¹. -1 ~1000cm -1The range contains characteristic peaks of Si-O bonds, and the highest peak intensity of the characteristic peaks of the Si-O bonds is I2. I1 / I2 is calculated.

[0205] (6) Test method for the mass content of carbon in negative electrode materials:

[0206] The mass content m of amorphous carbon was determined by thermogravimetric analysis. C .

[0207] (7) Test method for the mass content of oxygen in negative electrode materials:

[0208] The oxygen mass content (m) of the negative electrode material was measured using an oxygen, nitrogen, and hydrogen analyzer. O .

[0209] (8) Test method for the mass content of element M in negative electrode material:

[0210] The negative electrode material was calcined at 750°C to constant weight under an oxygen-containing atmosphere, and then dissolved using a mixed acid consisting of concentrated HF, concentrated HCl, and concentrated HNO3 until no more bubbles were produced in the solution. The mixture of the mixed acid was then added in equal amounts until no more bubbles were produced. Solid-state separation yielded the digestion solution of the negative electrode material. Electro-coupled plasma atomic emission spectrometry was used to determine the mass content (m) of element M in the digestion solution. M .

[0211] (9) Test method for the mass content of silicon in negative electrode materials:

[0212] Based on the measured mass content m of carbon in the negative electrode material C Mass content of oxygen element m O and the mass content m of element M M The mass content of silicon element, m, was calculated. Si =1-m C -m O -m M .

[0213] (10) pH value test of negative electrode material:

[0214] Take 10g of negative electrode material, add 10g of water, stir for 30min, and measure the pH value of the solid-liquid separated liquid.

[0215] (11) Test method for water content in negative electrode materials:

[0216] The water content was tested according to GB / T 6283-2008 "Determination of Moisture Content in Chemical Products - Karl Fischer Method (General Method)".

[0217] (12) Test methods for the average desorption pore size and cumulative desorption pore volume of negative electrode materials:

[0218] The pore volume of anode materials can be measured through gas adsorption. Nitrogen adsorption is a technique that characterizes the porosity and pore size distribution of a material by condensing a gas within the pores of a solid. As pressure increases, the gas first condenses in the pores with the smallest diameter, and the pressure continues to rise until a saturation point is reached, at which point all pores are filled with liquid. The nitrogen pressure is then gradually decreased to allow the liquid to evaporate from the system. Analysis of the adsorption and desorption isotherms allows for the determination of the pore volume and the average pore size.

[0219] (13) Test methods for rate performance:

[0220] The prepared negative electrode material was mixed with sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR) binder, Super-P conductive agent, and KS-6 conductive agent in a mass ratio of 92:2:2:2:2 to form a slurry. The slurry was coated onto copper foil and vacuum dried. The dried electrode was then rolled under a pressure of 3 MPa to prepare the negative electrode sheet. The counter electrode was a lithium sheet. A 1 mol / L LiPF6 / ethylene carbonate + methyl ethyl carbonate (v / v = 1:1) electrolyte and a polyethylene / propylene composite microporous membrane were used to assemble a coin cell.

[0221] The LAND battery testing system was used for testing. At room temperature, the charge / discharge voltage ranged from 0.01V to 1.5V. The battery cycle life was defined as the number of charge / discharge cycles (N) performed before the capacity retention rate decreased to 80%. Test results are detailed in Table 2.

[0222] Table 1. Test results of negative electrode material performance

[0223] Table 2. Test results of negative electrode materials used to fabricate electrode sheets and batteries.

[0224] According to the data in Table 1, the oxygen vacancy content in the negative electrode materials prepared in Examples 1-4 increases further with the increase of Mg doping, and the X value gradually increases. According to the data in Tables 1 and 2, the negative electrode materials with X values ​​in the range of 2.00601 to 2.00699 exhibit good rate performance; the cumulative release capacity of Examples 3-4 is somewhat reduced. Preferably, the overall electrochemical performance of the negative electrode material is optimal when the X value is between 2.0062 and 2.0067. With Y values ​​in the range of 10G to 400G, the negative electrode material has sufficient space to buffer the volume expansion of silicon oxide, and the lattice defects formed by oxygen vacancies in the negative electrode material can also form stable lithium-ion transport channels, improving the lithium-ion transport efficiency of the negative electrode material. This application controls the X and Y values ​​of the negative electrode material within the above ranges, enabling the negative electrode material to possess good electrochemical performance and suitable space to buffer internal expansion, thus improving the cycle performance and reducing expansion while maintaining a high specific capacity.

[0225] The negative electrode materials prepared in Examples 2 and 5-6 exhibit increased rate performance as the heating and vaporization temperature increases. This leads to more intense alteration and distortion of the original crystal lattice by the dopant elements during the reaction, resulting in an increased oxygen vacancy content in the product. Conversely, decreasing the heating and vaporization temperature weakens the alteration of the original crystal lattice by the dopant elements during the reaction, slightly reducing the oxygen vacancy content in the product and decreasing the rate performance.

[0226] The negative electrode materials prepared in Examples 2 and 7-8 show that different doping elements affect the electrochemical performance of the negative electrode materials. In Example 7, the doping metal element is Li, which has a smaller atomic number. Since the atomic radius of Li is smaller than that of Mg, the doping resistance is smaller, and the reaction between the doping element and the silicon-based material is more intense during the reaction process. As a result, the doping element content in the obtained negative electrode material increases, and the oxygen vacancy content increases. However, the reaction is too fast, which can easily cause heat accumulation in some areas, resulting in uneven distribution of oxygen vacancy and affecting the cycle performance of the negative electrode material. In Example 8, when the doping element is Al, which has a larger atomic number, the reaction rate slows down and the oxygen vacancy content decreases. However, the larger atomic radius will cause greater damage to the structure of the silicon-based material itself, resulting in a significant decrease in cycle performance.

[0227] The negative electrode materials prepared in Examples 2 and Examples 9-11 show that, in Example 9, the reduced pressure of the compaction block leads to a decrease in the contact area of ​​each component of the raw materials, a decrease in the overall reaction rate, a decrease in the concentration of oxygen vacancies generated by doping, and a tendency for selective deposition of the negative electrode material during the synthesis process, which easily forms large holes, resulting in a decrease in true density, a loose internal structure of the negative electrode material, a decrease in cycle life, and a decrease in rate performance.

[0228] In Example 10, when acetylene gas is selected for gas-phase coating, macromolecular groups are easily formed on the material surface, resulting in uneven overall coating layer. Some areas are prone to direct contact with the electrolyte, affecting cycle life and rate performance.

[0229] In Example 11, the content of metal element M in the raw materials was reduced so that the doped element in the obtained negative electrode material was about 5%. At this time, the specific capacity of the negative electrode material was relatively high, the cycle life was greatly affected by expansion and showed a low level, and the oxygen vacancy content was low, the lithium ion transport efficiency was low, and the rate performance of the negative electrode material was close to the lower limit.

[0230] The negative electrode materials prepared in Examples 2 and 12-13 show that as the volume ratio of reducing gas in the mixed gas increases, the oxygen vacancy content in the prepared negative electrode materials also increases. Since the reaction rate of reducing gas is faster, the synthesized negative electrode materials tend to be porous. Although this is beneficial for buffering the cyclic expansion process, it is difficult to effectively cover the surface of the negative electrode material particles during subsequent carbon coating, resulting in decreased coating uniformity and a decline in overall performance. Conversely, when the volume ratio of reducing gas in the mixed gas is low, the oxygen vacancy content in the prepared negative electrode materials is low, the lithium-ion transport rate is low, and the rate performance decreases.

[0231] Example 14: Without carbon coating, only the prepared active material was tested. The true density of the active material was slightly lower, the specific surface area was larger, the oxygen vacancy content was increased, and there were more active sites on the surface. These factors made it easy for the surface to react with the electrolyte during battery cycling to form a thicker SEI film. Although the specific capacity was improved due to the increase in silicon ratio, the cycle performance decreased and the rate performance was also reduced.

[0232] Compared with the negative electrode material of Comparative Example 1, no metal element M was doped during the preparation process. The oxygen vacancy content of the negative electrode material decreased significantly, the true density of the product increased, and the specific surface area decreased. However, the lack of lithium-ion transport channels led to a significant decrease in charge and discharge efficiency. Moreover, the internal space was insufficient during the cycle expansion process, and the crystals were prone to mutual compression and breakage. The original lithium-ion transport was also hindered due to structural changes, resulting in a significant reduction in cycle life and rate performance.

[0233] In contrast to the negative electrode material of Comparative Example 2, the excessive doping of metal element M during the preparation process severely damaged the structure of the silicon-based material itself, resulting in a low true density, a significantly increased specific surface area, and a loose and porous internal structure. This material is prone to breakage during expansion, causing powder shedding and seriously affecting the electrochemical performance of the battery.

[0234] In Comparative Example 3, no reducing gas was introduced during the preparation of the anode material. During the evaporation and deposition synthesis of the silicon-oxygen material raw materials, there were not enough oxygen vacancies to form inside. Although the true density of the anode material was slightly improved and the capacity was correspondingly increased, the lithium-ion channels inside the anode material were reduced, the lithium-ion transport efficiency decreased, which was not conducive to subsequent charge-discharge cycles and affected the cycle life of the anode material.

[0235] In the negative electrode material of Comparative Example 4, the raw materials of silicon-oxygen material and metal dopants were not pressed into blocks, and the mixed powder was directly heated and vaporized. The contact between the components of the raw materials was poor, and the reaction rate was limited by its significantly reduced fluidity. Due to the slow evaporation rate, selective growth between atoms was likely to occur during deposition. The introduction of dopants could easily lead to a more porous internal structure of the deposited product, resulting in a deterioration of the material structure, a weakening of its anti-expansion performance, a reduction in cycle life, and a decrease in rate performance.

[0236] In Comparative Example 5, the negative electrode material was not acid-washed during the preparation process. The resulting negative electrode material had smaller surface pores and a lower oxygen vacancy concentration, which reduced the number of active sites on the surface of the negative electrode material. This was not conducive to the insertion and desorption of lithium ions, resulting in a decrease in lithium ion transport efficiency and a reduction in the cycle performance of the negative electrode material.

[0237] Compared to the negative electrode material in Example 6, the proportion of reducing gas during the preparation process was too high. During the evaporation and deposition synthesis of silicon-oxygen materials, the internal oxygen vacancy content was too high. That is, although the g-factor value X of the electron spin resonance signal of oxygen atoms satisfies 2.00601≤X≤2.00699, when the oxygen vacancy intensity Y is too high, although the silicon content in the negative electrode material is slightly increased and the capacity is correspondingly improved, there are too many vacancy structures inside the negative electrode material, the true density is too small, the surface porosity is too large, the internal structural strength of the material deteriorates, the anti-expansion performance weakens, and the cycle performance of the negative electrode material is affected.

[0238] Compared to the anode material in Example 7, the excessive pressure during the pressing process of the silicon-oxygen material raw materials and metal dopants led to an excessively fast reaction rate between the raw materials, resulting in a high evaporation rate. During deposition, the molecular clusters exhibited disordered assembly, settling primarily in cluster form, resulting in poor overall structural strength. While the oxygen vacancy intensity Y of the anode material satisfied 10G≤Y≤400G, the g-factor value X of the electron spin resonance signal of oxygen atoms was too high, failing to meet the condition 2.00601≤X≤2.00699. Consequently, although the resulting anode material had high true density, small pores, and a certain oxygen vacancy concentration, its internal structure was chaotic and disordered, hindering the internal transport of lithium ions. Furthermore, the inconsistent internal expansion direction during cycling easily led to breakage and powder shedding, resulting in decreased cycle life and reduced rate performance.

[0239] Compared with the active material of Comparative Example 8, the acid concentration in the pickling step during the preparation process is too high, which will cause more oxides to be washed off from the material surface and form more pores. Although this is beneficial for the buffer space of cycle expansion, it will also make the material surface more porous, the structural strength will be worse, and the oxygen vacancy content will be too high. During battery cycling, the material surface reacts with the electrolyte to form a thicker SEI film, and the surface layer is prone to cracking during cycling, resulting in a significant decrease in cycle life and a reduction in rate performance.

[0240] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

A negative electrode material, characterized in that, The negative electrode material includes an active material, which includes silicon, silicon oxide and a compound of metal element M, wherein the compound of metal element M includes silicate of metal element M and / or oxide of metal element M. The negative electrode material was measured using the electron paramagnetic resonance method. The g-factor value of the electron spin resonance signal of oxygen atoms was X, 2.00601≤X≤2.00699; the oxygen vacancy intensity was Y, 10G≤Y≤400G. The negative electrode material according to claim 1 is characterized in that, The negative electrode material was analyzed by Raman spectroscopy, and the negative electrode material was found to be spectral at 500 cm⁻¹. -1 ~540cm -1 The range contains characteristic peaks of Si-Si bonds, with the highest peak intensity of the Si-Si bond characteristic peak being I1, at 900 cm⁻¹. -1 ~1000cm -1 The range contains characteristic peaks of Si-O bonds, and the highest peak intensity of the characteristic peaks of the Si-O bonds is I2, which satisfies that 4≤I1 / I2≤12. The negative electrode material according to claim 1 is characterized in that, X satisfies one of the following conditions: X is 2.00601, 2.00605, 2.00610, 2.00625, 2.00650, 2.00680, 2.00685, 2.00699, or within any two of the above values; or 2.00601≤X≤2.00625, or 2.00605≤X≤2.00650, or 2.00625≤X≤2.00680, or 2.00605≤X≤2.00680, or 2.00650≤X≤2.00699. The negative electrode material according to claim 1 is characterized in that, Y satisfies one of the following conditions: Y is 10G, 20G, 40G, 100G, 200G, 300G, 380G, 400G, or within any two of the above values; or 10G≤Y≤20G, or 10G≤Y≤100G, or 100G≤Y≤200G, or 200G≤Y≤400G, or 300G≤Y≤400G. The negative electrode material according to claim 2 is characterized in that, The I1 / I2 satisfy one of the following conditions: I1 / I2 is 4, 5, 6, 7, 8, 9, 10, 11, 12 or within any two of the above values; or 4≤I1 / I2≤8, or 4≤I1 / I2≤10, or 6≤I1 / I2≤10, or 6≤I1 / I2≤12, or 8≤I1 / I2≤12. The negative electrode material according to claim 1 is characterized in that, The negative electrode material has at least one of the following characteristics (1) to (3): (1) The metal element M includes at least one of Mg, Li, Fe, Al, Mn and Cu; (2) The general chemical formula of the silicon oxide is SiO x , 0 < x ≤ 2; (3) The silicon oxide includes silicon and oxygen, and the atomic molar ratio of silicon to oxygen is 0 to 2, excluding 0. The negative electrode material according to claim 1 is characterized in that, The negative electrode material further includes carbon material, and the carbon material is present on the surface of the active material and / or between the active material particles. The negative electrode material according to claim 1 is characterized in that, 2.00601≤X≤2.00624 and 10G≤Y≤45.51G. The negative electrode material according to claim 1 is characterized in that, 2.00624<X≤2.00699 and 45.51G≤Y≤400G. The negative electrode material according to claim 7 is characterized in that, The negative electrode material has at least one of the following characteristics (1) to (2): (1) The carbon material includes at least one of amorphous carbon and graphitized carbon; (2) The carbon material forms a carbon layer on at least a portion of the surface of the active substance. The negative electrode material according to claim 7 is characterized in that, The negative electrode material has at least one of the following characteristics (1) to (4): (1) The carbon content in the negative electrode material is 0.5% to 10% by mass; (2) The mass content of oxygen in the negative electrode material is 26% to 33%; (3) The mass content of silicon in the negative electrode material is 40% to 65%; (4) The mass content of M in the negative electrode material is 5% to 20%. The negative electrode material according to claim 1 is characterized in that, The negative electrode material has at least one of the following characteristics (1) to (4): (1) The specific surface area of ​​the negative electrode material is ≤10m² 2 / g; (2) The true density of the negative electrode material is ≥2.4 g / cm³. 3 ; (3) The pH of the negative electrode material is 6 to 10; (4) The water content in the negative electrode material is ≤0.5wt%. The negative electrode material according to claim 1 is characterized in that, The negative electrode material has at least one of the following characteristics (1) to (5): (1) The particle size of the negative electrode material satisfies: 1.0μm≤D10≤3.0μm; 4.5μm≤D50≤7.0μm; 8.0μm≤D90≤12.0μm; (2) The average desorption pore size of the negative electrode material is 6 nm to 9 nm; (3) The cumulative desorption pore volume of the negative electrode material is 0.02 cm³. 3 / g~0.04cm 3 / g; (4) The size of Si crystallites in the silicon oxide is ≤20nm; (5) The pH of the negative electrode material is 9 to 10. A negative electrode sheet, characterized in that, The negative electrode sheet comprises the negative electrode material according to any one of claims 1 to 13. A battery characterized in that, The battery comprises the negative electrode material as described in any one of claims 1 to 13.

Images