Negative electrode material and manufacturing method thereof, lithium ion battery

Abstract

The present invention discloses a negative electrode material, its manufacturing method and application. [Solution] The negative electrode material includes a core and a coating layer located on at least a part of the surface of the core, the core includes a silicon-oxygen material, the negative electrode material includes lithium element, the mass ratio of lithium element to oxygen element in the negative electrode material is a, and when the negative electrode material is measured by an X-ray photoelectron spectrometer (Thermo Scientific K-Alpha), the mass ratio of lithium element to oxygen element in a region corresponding to information detectable in the process of detection by the photoelectron spectrometer from the surface of the negative electrode material toward the inner central region of the negative electrode material is b, the relationship between a and b satisfies 0.4>a>b. In this application, the ratio of lithium element to oxygen element in the surface layer of the negative electrode material is controlled to be smaller than the ratio of lithium element to oxygen element in the entire material, and more lithium element is present in the inner central region of the material, thereby reducing the content of lithium element on the surface, thereby reducing the erosion effect of the aqueous solvent on the Si crystal grains in the inner central region of the silicon-oxygen material and improving the processing stability of the slurry.

Description

[Technical Field]

[0001] This application claims priority to a Chinese patent application bearing application number 202211698602.X and entitled "Silicon-based negative electrode material, its manufacturing method and use" filed with the China Patent Office on December 28, 2022, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to the technical field of anode materials, and more particularly to anode materials, their manufacturing methods and applications. [Background technology]

[0003] Silicon-oxygen materials are used as negative electrode materials in lithium-ion batteries because they have high specific capacity and good structural stability. Prelithiation technology allows the SiO x Lithiated framework SiO x , for example, Li2SiO3, Li2Si2O5, etc., which can effectively solve the problem of low initial coulomb efficiency of silicon-oxygen materials.

[0004] However, if the silicon-oxygen material is directly prelithiated, the pores in the silicon-oxygen material will open, exposing the internal silicon crystal grains. The surface of the material will contain abundant lithium-containing compounds, such as Li2SiO3, LiOH, and Li2CO3, which exhibit extremely strong hydrophilicity. During the production of aqueous slurry, the water solvent will easily infiltrate the prelithiated silicon-oxygen material and penetrate into the material, where it will come into contact with the silicon crystal grains. Under alkaline conditions, the reaction with the silicon crystal grains will accelerate, generating large amounts of hydrogen, which will destroy the stability of the slurry and significantly deteriorate its processing performance.

[0005] Furthermore, the lithium-containing compounds present in abundance on the surface of the material are highly alkaline, which accelerates the corrosion of the silicon crystal grains inside the silicon-oxygen material by the water solvent, while also corroding the slurry production equipment.

[0006] Therefore, there is an urgent need to use lithium silicon-oxygen raw materials, which have excellent electrochemical properties and good processing performance, as negative electrode materials. Summary of the Invention [Problem to be solved by the invention]

[0007] The objective of the present invention is to provide an anode material and a manufacturing method thereof, and a lithium ion battery, which significantly improve the stability of aqueous slurry processing while ensuring the electrochemical properties of the anode material. [Means for solving the problem]

[0008] In a first aspect, the present invention provides an anode material, the anode material comprising a core and a coating layer located on at least a portion of a surface of the core, the core comprising a silicon-oxygen material, and the anode material comprising elemental lithium; When the mass ratio of lithium element to oxygen element in the negative electrode material is a, and when the negative electrode material is measured using an X-ray photoelectron spectrometer (Thermo Scientific K-Alpha), the mass ratio of lithium element to oxygen element in a region corresponding to information that can be detected in the process of detection by the photoelectron spectrometer from the surface of the negative electrode material toward the central region inside the negative electrode material is b, the relationship between a and b satisfies 0.4>a>b.

[0009] In some embodiments, the negative electrode material has at least one of the following characteristics (1) to (7): (1) the mass ratio a of lithium element to oxygen element in the negative electrode material satisfies 0.35>a>0.15; (2) The b satisfies the relationship 0.30>b>0.01; (3) When the negative electrode material is measured using an X-ray photoelectron spectrometer (Thermo Scientific K-Alpha), the thickness of the region corresponding to the information detectable by the photoelectron spectrometer in the process of detecting from the surface of the negative electrode material toward the central region inside the negative electrode material is 1 nm to 10 nm; (4) The silicon-oxygen material is SiO x , including 0 <x≦2である; (5) the silicon-oxygen material comprises a lithium-containing compound including at least one of Li2SiO3, Li2Si2O5, and Li4SiO4; (6) When the mass of the negative electrode material is 100%, the mass ratio of the lithium element in the negative electrode material is 1 wt% to 15 wt%; (7) The molar ratio of Si element to O element in the negative electrode material is (0.8-1.2):1.

[0010] In some embodiments, the coating layer comprises a first coating layer and a second coating layer, and the second coating layer is located between the core and the first coating layer and / or in an area on the surface of the core that is not covered by the first coating layer.

[0011] In some embodiments, the negative electrode material has at least one of the following characteristics (1) to (6): (1) The second coating layer includes at least one of a silicon phosphate compound, an aluminum phosphate compound, an ammonium phosphate compound, and an aluminum-phosphorus composite oxide; (2) the material of the first coating layer includes a carbon material; (3) the mass ratio of the first coating layer to the negative electrode material is 0.1% to 5%; (4) The mass ratio of the second coating layer to the negative electrode material is 0.1% to 8%; (5) The thickness of the first coating layer is 1 nm to 1000 nm; (6) The thickness of the second coating layer is 1 nm to 1000 nm.

[0012] In some embodiments, the negative electrode material has at least one of the following characteristics (1) to (2): (1) The coating layer is a carbon layer; (2) The thickness of the coating layer is 1 nm to 1000 nm.

[0013] In some embodiments, the negative electrode material has at least one of the following characteristics (1) to (5): (1) The pore volume of the negative electrode material is less than 0.01 cm 3 / g; (2) The specific surface area of the negative electrode material is less than 4 m 2 / g; (3) When the contact angle θ of the negative electrode material with respect to acetone is measured by the Washburn method, θ > 20°; (4) The pH of the negative electrode material satisfies 7 < pH < 11.5; (5) The median diameter of the negative electrode material is 3.0 μm to 10.0 μm.

[0014] In a second aspect, an embodiment of the present application is a method for manufacturing a negative electrode material, comprising: a step of pre-lithiating a silicon oxygen raw material to obtain a pre-lithiated material containing lithium element and silicon oxygen raw material in a mass ratio of (0.02 to 0.16):1; a step of performing a first heat treatment on a mixture containing the pre-lithiated material and a polyvalent carboxylic acid to cure the mixture and obtain a precursor; and a step of performing a second heat treatment on the precursor to carbonize the precursor and obtain a negative electrode material.

[0015] In some embodiments, the manufacturing method has at least one of the following characteristics (1) to (13): (1) The temperature of the first heat treatment is 150°C to 250°C; (2) The time of the first heat treatment is 5 h to 12 h; (3) The first heat treatment is performed in an air atmosphere; (4) Before performing the first heat treatment on the mixture containing the pre-lithiated material and the polyvalent carboxylic acid, the method further includes a step of drying the mixture containing the pre-lithiated material and the polyvalent carboxylic acid; (5) The method further includes a step of drying the mixture containing the prelithiated material and the polycarboxylic acid before subjecting the mixture containing the prelithiated material and the polycarboxylic acid to a first heat treatment, wherein the drying temperature is 45°C to 90°C; (6) performing a first heat treatment on the mixture containing the prelithiated material and the polycarboxylic acid, and then washing, separating the material obtained by the first heat treatment into solid and liquid, and drying the material, thereby obtaining a precursor; (7) a step of subjecting the mixture containing the prelithiated material and the polycarboxylic acid to a first heat treatment, and then washing, separating the material obtained by the first heat treatment into solid and liquid, and drying the material, wherein the solvent used for the washing includes at least one of water and ethanol; (8) a step of subjecting the mixture containing the prelithiated material and the polycarboxylic acid to a first heat treatment, and then washing the material obtained by the first heat treatment, subjecting it to solid-liquid separation, and drying, wherein the solid-liquid mass ratio during the washing is (1 to 4):1; (9) a step of subjecting the mixture containing the prelithiated material and the polycarboxylic acid to a first heat treatment, and then washing, separating the material obtained by the first heat treatment into solid and liquid, and drying the material, wherein the washing time is 1 hour to 5 hours; (10) A method of carrying out a first heat treatment on the mixture containing the prelithiated material and the polycarboxylic acid, followed by washing, solid-liquid separation, and drying the material obtained by the first heat treatment, wherein the drying temperature is 80°C to 120°C; (11) The temperature of the second heat treatment is 500°C to 800°C; (12) The duration of the second heat treatment is 5 hours to 12 hours; (13) The second heat treatment is carried out in a protective gas atmosphere.

[0016] In some embodiments, the method of preparing the mixture containing the prelithiated material and the polycarboxylic acid includes dissolving the polycarboxylic acid in a solvent to obtain a carbon source solution containing the polycarboxylic acid, and mixing the prelithiated material with the carbon source solution containing the polycarboxylic acid to obtain a mixture containing the prelithiated material and the polycarboxylic acid.

[0017] In some embodiments, the manufacturing method has at least one of the following characteristics (1) to (4): (1) The concentration of the carbon source solution is 3 mg / mL to 7 mg / mL; (2) The polycarboxylic acid includes at least one of citric acid, tartaric acid, maleic acid, trimesic acid, terephthalic acid, malic acid, and ethylenediaminetetraacetic acid; (3) the solvent comprises at least one of acetone, water, ethanol, methanol, isopropanol, dimethylformamide, toluene, and tetrahydrofuran; (4) The mass ratio of the prelithiated material to the polycarboxylic acid is (20 to 200):1.

[0018] In some embodiments, the silicon / oxygen source material is a silicon / oxygen material having a coating layer, and the method for producing the silicon / oxygen material having a coating layer includes providing a silicon / oxygen material; mixing the silicon / oxygen material with a coating material, and then performing a third heat treatment to obtain the silicon / oxygen material having a coating layer.

[0019] In some embodiments, the manufacturing method has at least one of the following characteristics (1) to (4): (1) the mass ratio of the silicon-oxygen material to the coating material is 1:(0.005-0.05); (2) the coating material includes at least one of a carbon material, a silicon phosphate compound, an aluminum phosphate compound, an ammonium phosphate compound, and an aluminum-phosphorus composite oxide; (3) The temperature of the third heat treatment is 500°C to 1000°C; (4) The duration of the third heat treatment is 1 hour to 6 hours.

[0020] In some embodiments, prelithiating the silicon oxygen material includes combining the silicon oxygen feedstock with a lithium source followed by a fourth heat treatment to obtain a prelithiated material.

[0021] In some embodiments, the manufacturing method has at least one of the following features (1) to (7): (1) The silicon oxygen raw material contains SiO y (0 < y ≤ 2); (2) The lithium source contains at least one of metallic lithium, lithium hydride, lithium carbonate, lithium hydroxide, lithium borohydride, and lithium aluminum hydride; (3) The mass ratio of the silicon oxygen raw material to the lithium source is 100:(2 - 16); (4) The temperature of the fourth heat treatment is 100°C to 900°C; (5) The time of the fourth heat treatment is 1 h to 24 h; (6) The silicon oxygen raw material is a silicon oxygen material having a coating layer; (7) The silicon oxygen raw material is a silicon oxygen material having a coating layer, and the material of the coating layer contains at least one of a carbon material, a phosphate compound of silicon, a phosphate compound of aluminum, a phosphate compound of ammonium, and an aluminum phosphorus composite oxide.

[0022] In a third aspect, the present invention provides a lithium ion battery including a negative electrode material manufactured by the manufacturing method of the negative electrode material described in the first aspect or the negative electrode material described in the second aspect.

Advantages of the Invention

[0023] The present invention provides the following beneficial effects. The present application limits the mass ratio of lithium to oxygen in a negative electrode material to a. When the negative electrode material is measured using an X-ray photoelectron spectrometer (Thermo Scientific K-Alpha), the mass ratio of lithium to oxygen in a region corresponding to information detectable by the photoelectron spectrometer from the surface of the negative electrode material toward the central region of the negative electrode material is b. The negative electrode material includes a core and a coating layer located on at least a portion of the core, the core being primarily located in a region inside the negative electrode material particles that cannot be detected by the X-ray photoelectron spectrometer, and the mass of oxygen in the negative electrode material is much greater than the mass of oxygen in a region corresponding to information detectable by the X-ray photoelectron spectrometer from the surface of the negative electrode material toward the central region of the negative electrode material. Therefore, if a > b, the relative content of lithium in the surface layer of the negative electrode material of the present application is low, i.e., lithium is primarily present in a region close to the internal center of the negative electrode material. Thus, during the processing and slurry preparation of the anode material, lithium elements are primarily located in the central region of the anode material, effectively reducing the infiltration of aqueous solvent molecules into the anode material, reducing the erosion of the silicon crystal grains of the anode material, and improving the stability of the anode material during the slurry processing process. The value of a is primarily related to the lithium content in the core. A higher a value corresponds to a higher initial efficiency of the material, so a higher a is preferred. A lower b value of the material is beneficial for improving the hydrophobicity of the material, thereby making it more difficult for the aqueous solvent to infiltrate and penetrate the material, effectively blocking contact between the Si crystal grains inside the material and the aqueous solvent, and improving the processing stability of the slurry. In this application, both a and b have upper limits. When the relationship 0.4>a>b is satisfied, anode materials with high initial efficiency and good slurry processability can be guaranteed. The content of lithium-containing compounds exposed on the surface of the product is reduced. [Brief explanation of the drawings]

[0024] In order to more clearly explain the technical solutions of the embodiments of the present invention, the following briefly introduces drawings necessary for the embodiments. Obviously, the following drawings only illustrate some embodiments of the present invention, and therefore should not be considered as limiting the scope. Those skilled in the art can obtain other related drawings based on these drawings without any creative efforts. [Figure 1] 1 is a schematic diagram showing the structure of a negative electrode material provided by the present invention. [Figure 2] 2 is a schematic diagram 2 showing the structure of the negative electrode material provided by the present invention. [Figure 3] 1 is a flowchart of a method for producing a negative electrode material provided by the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0025] In order to clarify the objectives, technical solutions and advantages of the embodiments of the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention. In the examples, unless specific conditions are specified, the procedures are carried out according to the general conditions or conditions provided by the manufacturer. For reagents or equipment used, unless the manufacturer is specified, they are all conventional products obtained by commercial purchase.

[0026] In conventional technology, after carbon-coated silicon-oxygen materials are prelithiated, voids form in the carbon layer, exposing the Li2Si2O5, Li2SiO3, etc. inside the material, which then absorbs H2O, CO2, etc. from the air to form lithium-containing compounds such as Li2CO3, LiOH, etc. The presence of these lithium-containing compounds makes the material sufficiently hydrophilic, allowing water solvent molecules to easily infiltrate and erode the Si crystal grains inside the material during slurry preparation. Therefore, reducing the exposure of the lithium-containing compounds in the material is the key to improving slurry processability.

[0027] In view of this, an embodiment of the present invention provides a negative electrode material, which, as shown in FIG. 1 , includes a core 100 and a coating layer 300 formed on at least a portion of the surface of the core 100, wherein the core 100 includes a silicon-oxygen material and the negative electrode material includes a lithium element 200. When the mass ratio of lithium element 200 to oxygen element in the negative electrode material is a, and when the negative electrode material is measured using an X-ray photoelectron spectrometer (Thermo Scientific K-Alpha), the mass ratio of lithium element 200 to oxygen element in a region corresponding to information that can be detected in the process of detection by the photoelectron spectrometer from the surface of the negative electrode material toward the central region inside the negative electrode material is b, the relationship between a and b satisfies 0.4>a>b.

[0028] In the above technical solution, the present application specifies that the mass ratio of lithium to oxygen in the negative electrode material is a, and that when the negative electrode material is measured using an X-ray photoelectron spectrometer (Thermo Scientific K-Alpha), the mass ratio of lithium to oxygen in the region corresponding to the information detectable by the photoelectron spectrometer from the surface of the negative electrode material toward the central region of the negative electrode material is b. The negative electrode material includes a core and a coating layer located on at least a portion of the core, and the core is primarily located in a region inside the negative electrode material particles that cannot be detected by the X-ray photoelectron spectrometer. The mass of oxygen in the negative electrode material is much greater than the mass of oxygen in the region corresponding to the information detectable by the X-ray photoelectron spectrometer from the surface of the negative electrode material toward the central region of the negative electrode material. Therefore, if a > b, the relative content of lithium in the surface layer of the negative electrode material of the present application is low, i.e., lithium is primarily present in a region close to the inner center of the negative electrode material. Thus, during the processing and slurry preparation of the anode material, lithium elements are primarily located in the central region of the anode material, effectively reducing the infiltration of aqueous solvent molecules into the anode material, reducing the erosion of the silicon crystal grains of the anode material, and improving the stability of the anode material during the slurry processing process. The value of a is primarily related to the lithium content in the core. A higher a value corresponds to a higher initial efficiency of the material, so a higher a is preferred. A lower b value of the material is beneficial for improving the hydrophobicity of the material, thereby making it more difficult for the aqueous solvent to infiltrate and penetrate the material, effectively blocking contact between the Si crystal grains inside the material and the aqueous solvent, and improving the processing stability of the slurry. In this application, both a and b have upper limits. When the relationship 0.4>a>b is satisfied, anode materials with high initial efficiency and good slurry processability can be guaranteed. The content of lithium-containing compounds exposed on the surface of the product is reduced.

[0029] In this application, when the relationship between a and b satisfies a>b, it means that the lithium content in the negative electrode material is much greater than that in the second region. When a is greater than 0.4, that is, the lithium doping degree in the core is too high, the silicon crystal grains inside the material grow abnormally, which is unfavorable to improving the cycle performance of the negative electrode material.

[0030] As shown in FIG. 2 , the negative electrode material particles of the present application may be divided into two regions, i.e., the negative electrode material particles of the present application have a first region 1 and a second region 2. The second region 2 corresponds to information that can be detected by an X-ray photoelectron spectrometer (Thermo Scientific K-Alpha) when measuring the negative electrode material from the surface of the negative electrode material toward the central region inside the negative electrode material. The first region 1 is a region inside the negative electrode material particle that cannot be detected by the X-ray photoelectron spectrometer. In some embodiments, the first region 1 includes the core 100 and the partial coating layer 300 (shown in FIG. 2 ), and the second region 2 is a region other than the first region 1 in the negative electrode material. In other embodiments, the first region 1 includes the complete core 100 or the partial core 100, and the second region 2 is a region other than the first region 1 in the negative electrode material. The present application does not specifically limit the specific boundary between the first region and the second region, and as can be understood, the region where the first region and the second region contact each other may be a region where there is a clear interface, such as the edge of a coating layer, or a region where there is a smooth transition without a clear interface.

[0031] In this application, the test methods a and b are shown below. (1) The mass content of Li in the entire anode material was measured using total melting ICP. Specifically, 0.500 g of the anode material was placed in a clean platinum crucible and then calcined in an air muffle furnace at 750 °C for 2 hours to completely remove carbon. After cooling, the calcined residue was thoroughly reacted with a mixed acid of 34 mL of HNO and 6 mL of HF. The platinum crucible containing the solution was then placed on an electric hotplate at 350 °C until the solvent was completely evaporated. After the crucible cooled, an additional 6 mL of HCl was added and heated until the residue was completely dissolved, and the resulting mixture was then transferred to a 100 mL plastic measuring flask. Finally, the Li content of the entire material was measured using an ICP spectrometer (Agilent 5800VDV ICP-OES).

[0032] (2) The mass content of the O element in the entire negative electrode material was measured using an ONH elemental analyzer (ONH-2000). Specifically, 10 mg to 13 mg of the negative electrode material was weighed and wrapped in nickel foil, and then transferred to the graphite crucible of the ONH elemental analyzer for measurement. a was calculated from the above data.

[0033] (3) The mass contents of Li and O in the second region were measured using an X-ray photoelectron spectrometer (Thermo Scientific K-Alpha) using the following steps: the anode material of the present application was attached to a sample holder using double-sided carbon conductive adhesive or ordinary double-sided tape, and the sample holder with the anode material was placed in an X-ray photoelectron spectrometer. The excitation source used in the X-ray photoelectron spectrometer was AlKα radiation, the beam spot was 400 μm, the pass energy of the full spectrum scan was 100 eV, and the step was 1 eV. After the full spectrum scan data was obtained, the Avantage software was used to read the full spectrum scan data to obtain the contents of Li and O, and then the mass ratio b of Li and O was calculated.

[0034] In some embodiments, a satisfies 0.35 > a > 0.15. Specifically, on the premise that a > b is satisfied, the value of a may be, for example, 0.16, 0.18, 0.2, 0.22, 0.24, 0.26, 0.28, 0.30, 0.32, or 0.34. Naturally, other values within the above range may also be possible, and the present application is not limited here.

[0035] In some embodiments, b satisfies 0.30 > b > 0.01. Specifically, the value of b may be, for example, 0.02, 0.04, 0.06, 0.08, 0.1, 0.12, 0.14, 0.16, 0.18, 0.20, 0.22, 0.24, 0.26, or 0.28. Naturally, other values within the above range may also be possible, and the present application is not limited here.

[0036] By controlling the value ranges of a and b within the above ranges, the stability of the slurry processing of the negative electrode material can be further improved. That is, no bubbles are generated in the produced slurry, and the slurry can be uniformly and flatly coated on the current collector during the coating process, and the negative electrode can exhibit better electrochemical properties.

[0037] In some embodiments, the silicon oxygen material contains silicon oxide SiO x and 0 < x ≤ 2. The silicon oxide contains oxygen atoms and silicon atoms, and the molar ratio of oxygen atoms to silicon atoms is 0 to 2, which is a silicon oxygen composite that does not contain 0. This may be a composite of two or more of Si, SiO 0.2 , SiO 0.5 , SiO 0.8 , SiO, SiO 1.2 , SiO 1.5 , SiO 1.8 or SiO2, etc., or it may be a compound with the chemical formula SiO x . Naturally, other values within the above range may also be possible, and the present application is not limited here.

[0038] In some embodiments, the lithium element in the negative electrode material is present in the form of a lithium-containing compound, including, but not limited to, at least one of Li2SiO3, Li2Si2O5, and Li4SiO4.

[0039] In some embodiments, when the mass of the negative electrode material is calculated as 100%, the mass ratio of lithium element in the negative electrode material is 1 wt% to 15 wt%, for example, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, or 15 wt%, etc., and of course, other values ​​within the above range may also be used, and the present application is not limited thereto.

[0040] In some embodiments, the molar ratio of Si to O is (0.8-1.2):1. For example, it may be 0.8:1, 0.9:1, 1.0:1, 1.1:1, or 1.2:1, and of course, it may be other values ​​within the above range, and the present application is not limited thereto. The molar ratio of Si to O is measured as follows.

[0041] The ONH elemental analyzer measures the total O content of the material, the carbon-sulfur analyzer measures the total C content of the material, the total Li content of the material is measured using a total melt ICP, and the total impurity element content of the material, such as Fe, Mn, Ni, Cu, Mg, etc., is measured using a total melt ICP. The remainder of the material is the default Si content. The Si / O molar ratio can be obtained by simply converting the O content to the Si content.

[0042] In some embodiments, the coating layer comprises a first coating layer and a second coating layer, the second coating layer being located between the core and the first coating layer and / or in an area on the surface of the core that is not covered by the first coating layer.

[0043] In some embodiments, as shown in FIG. 1, the coating layer 300 includes a second coating layer 302 distributed on at least a portion of the surface of the core 100 and a first coating layer 301 distributed on at least a portion of the surface of the second coating layer 302.

[0044] In some embodiments, the material of the first coating layer 301 includes a carbon material.

[0045] In some embodiments, the second coating layer 302 includes at least one of a carbon material, a silicon phosphate compound, an aluminum phosphate compound, an ammonium phosphate compound, and an aluminum phosphorus composite oxide.

[0046] In some embodiments, the mass proportion of the first coating layer 301 in the negative electrode material is 0.1% to 5%. Specifically, it may be 0.1%, 0.5%, 1%, 2%, 3%, 4%, or 5%, etc., and of course, it may be other values ​​within the above range, and the present application is not limited thereto.

[0047] In some embodiments, the mass proportion of the second coating layer 302 in the negative electrode material is 0.1% to 8%. Specifically, it may be 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, or 8%, etc., and of course, it may be other values ​​within the above range, and the present application is not limited thereto.

[0048] In some embodiments, the thickness of the first coating layer 301 is 1 nm to 1000 nm. Specifically, it may be 1 nm, 10 nm, 100 nm, 300 nm, 500 nm, 800 nm, 1000 nm, etc., and of course, it may be other values ​​within the above range, and the present application is not limited thereto.

[0049] In some embodiments, the thickness of the second coating layer 302 is 1 nm to 1000 nm. Specifically, it may be 1 nm, 10 nm, 100 nm, 300 nm, 500 nm, 800 nm, 1000 nm, etc., and of course, it may be other values ​​within the above range, and the present application is not limited thereto.

[0050] As can be understood, if the first coating layer 301 and the second coating layer 302 are made of the same material, the coating layer can be considered as a single layer structure, ie, the coating layer 300 is a carbon layer.

[0051] In some embodiments, the thickness of the coating layer 300 is 1 nm to 1000 nm, such as 1 nm, 50 nm, 100 nm, 300 nm, 500 nm, 700 nm, or 1000 nm, and of course, may be other values ​​within the above range, and the present application is not limited thereto.

[0052] In some embodiments, the pore volume of the negative electrode material is less than 0.01 cm 3 / g. Specifically, it is less than 0.001 cm 3 / g, 0.003cm 3 / g, 0.005cm 3 / g, or 0.008 cm 3 / g, etc., and of course, other values ​​within the above range are also possible, and the present application is not limited thereto. The pore volume of the negative electrode material of the present application is small, making it difficult for the aqueous solvent to infiltrate or penetrate into the material, effectively blocking contact between the Si crystal grains inside the material and the aqueous solvent.

[0053] In some embodiments, the specific surface area of ​​the negative electrode material is 4 m 2 / g. Specifically, it is less than 0.5m 2 / g, 1m 2 / g, 2m 2 / g or 3m 2 / g, etc., and of course, other values ​​within the above ranges are also possible, and the present application is not limited thereto.

[0054] The pore volume and specific surface area of ​​the negative electrode material are both parameters that reflect the outer surface of the negative electrode material, and the present application limits the pore volume and specific surface area to within the above ranges. It can be seen that the outermost surface of the negative electrode material of the present application is mainly a dense coating layer, which contributes to preventing penetration and erosion by the aqueous solvent during the slurry production process.

[0055] The pore volume is V, and the specific surface area S can be measured by a conventional method, for example, by the gas adsorption BET method, where the adsorption gas used in the gas adsorption BET method may be, for example, N2.

[0056] In some embodiments, the contact angle θ of the negative electrode material with acetone measured by the Washburn method was found to be >20°. Specifically, θ may be 25°, 30°, 35°, 40°, 45°, or 50°, and of course, other values ​​within the above range are also possible, and the present application is not limited thereto. Within the above-mentioned range, the negative electrode material of the present application exhibits good hydrophobicity. It can be seen that a lower b value of the negative electrode material is beneficial for improving the hydrophobicity of the material, thereby making it more difficult for the aqueous solvent to infiltrate and penetrate the material, effectively blocking contact between the Si crystal grains inside the material and the aqueous solvent, and improving the processing stability of the slurry. Because the outermost surface of the negative electrode material is covered with a dense coating layer, the negative electrode material exhibits good hydrophobicity.

[0057] The contact angle θ was measured as follows: The negative electrode material was filled into a glass tube with a filter at the bottom and brought into contact with the test solution. After the test solution had stopped rising, the mass increase in the tube and the time were recorded, and the contact angle was calculated using the Washburn equation. During the measurement process, n-hexane was used as the test solution, and the capillary constant after powder filling was measured, assuming the contact angle of n-hexane to be 0 degrees. The powder was then filled again using the same filling method, and the contact angle was measured with acetone.

[0058] In some embodiments, the pH value of the negative electrode material satisfies 7 < pH < 11.5. Specifically, the pH may be 8, 8.5, 9, 9.5, 10, 10.5, 11, or 11.3, etc. Of course, it may also be other values within the above range, and the present application is not limited here. Within the above limited range, the low content of the lithium-containing compound on the surface of the negative electrode material of the present application indicates that it is advantageous for alleviating the reaction between the aqueous solvent and the internal Si crystal grains and promoting the stability of the slurry. Also, corrosion of the slurry preparation device can be avoided even at a low pH.

[0059] Note that the method for measuring the pH value of the negative electrode material is as follows. 5 g of the negative electrode material was ultrasonically dispersed in 45 g of water and then measured with a pH meter.

[0060] In some embodiments, the median diameter of the negative electrode material is 3.0 μm to 10.0 μm. Specifically, it may be 3.0 μm, 4.0 μm, 5.0 μm, 6.0 μm, 7.0 μm, 8.0 μm, 9.0 μm, or 10.0 μm, etc. Of course, it may also be other values within the above range, and the present application is not limited here.

[0061] In some embodiments, as shown in FIG. 3, the present application provides a method for manufacturing a negative electrode material including the following steps. Pre-lithiate the silicon oxygen raw material to obtain a pre-lithiated material, and the mass ratio of lithium element to silicon oxygen raw material in the pre-lithiated material is (0.02 - 0.16):1; Perform a first heat treatment on the mixture containing the pre-lithiated material and the polyvalent carboxylic acid to cure the mixture and obtain a precursor; Perform a second heat treatment on the precursor to carbonize the precursor and obtain a negative electrode material.

[0062] In the above technical proposal, the present application uses a polycarboxylic acid to perform a first heat treatment and coating process on a lithium-containing silicon-oxygen raw material. Due to the strong bonding strength between the polycarboxylic acid and the lithium-containing compound, the polycarboxylic acid bonds with the lithium-containing compound to form derived carbon, which tends to shield the lithium-containing compound at certain points rather than being randomly distributed on the surface of the silicon-oxygen raw material. The derived carbon primarily fills the voids in the material, repairing the voids that appear in the material after prelithiation. By limiting the mass ratio of lithium to silicon-oxygen raw material in the prelithiated material to (0.02-0.16:1) and further coating the surface of the prelithiated material with polycarboxylic acid, the lithium content in the surface layer of the manufactured negative electrode material is reduced, resulting in a negative electrode material exhibiting a 0.4>a>b relationship. Subsequently, the lithium-containing compound remaining on the surface of the material is removed by a cleaning operation, leaving a small amount of voids. Finally, a second heat treatment, high-temperature carbonization, gradually reduces and closes the voids on the surface of the material, forming a dense carbon coating layer. This effectively reduces the penetration of water solvent molecules into the anode material during processing and slurry preparation, reducing the erosion of silicon crystal grains in the anode material and improving the stability of the anode material during slurry processing. The manufacturing method of the present application improves the specific capacity, structural stability, and initial efficiency of the material by pre-lithiation, and efficiently shields the lithium-containing compound by using a polycarboxylic acid as a carbon source. Due to the strong bonding ability between the polycarboxylic acid and the lithium-containing compound, the polycarboxylic acid tends to coat the lithium-containing compound in an oriented manner rather than randomly coating the material surface. This solves the problem of slurry processing stability and avoids the reduction in specific capacity of the material due to an excessively thick carbon coating layer. The carbonized anode material exhibits a 0.4>a>b ratio, ensuring not only high initial efficiency but also good slurry processability.

[0063] The following are detailed steps of the manufacturing method of the examples of the present application. S100, prelithiate the silicon-oxygen raw material to obtain a prelithiated material, and the mass ratio of lithium element to silicon-oxygen raw material is (0.02-0.16):1.

[0064] In some embodiments, the silicon oxygen source is silicate, SiO y , including 0 <y≦2である。SiO y is SiO 0.2 , SiO 0.5 , SiO 0.8 , SiO, SiO 1.2 , SiO 1.5 , SiO 1.8 or SiO2, etc., and of course, other values ​​within the above range may be used, and the present application is not limited thereto. In this process, the SiO2 in the silicon-oxygen material is formed by prelithiation. y The framework can be converted to lithium-containing compounds such as Li2SiO3 and Li2Si2O5, improving the first coulombic efficiency of the material.

[0065] In some embodiments, the silicon-oxygen raw material is a silicon-oxygen material having a coating layer, and performing prelithiation using the silicon-oxygen material having a coating layer makes the prelithiation reaction process milder, which is advantageous for uniform distribution of lithium element in the core.

[0066] In some embodiments, when the silicon-oxygen source material is a silicon-oxygen material having a coating layer, in S100: providing a silicon-oxygen material, mixing the silicon-oxygen material with the coating material, and performing a third heat treatment to form a SiO y / Obtain a coating layer, that is, a silicon-oxygen material having a coating layer, SiO y / The coating layer is subjected to a prelithiation treatment to obtain a prelithiated material.

[0067] In some embodiments, the mass ratio of the silicon-oxygen material to the coating material is 1:(0.005-0.05). For example, it may be 1:0.005, 1:0.008, 1:0.01, 1:0.02, 1:0.03, 1:0.04, or 1:0.05. Of course, other values ​​within the above range are also possible, and the present application is not limited thereto. Within the above limited range, not only can the silicon-oxygen material be effectively coated, but also a decrease in the specific capacity of the negative electrode material due to the presence of the coating material can be avoided.

[0068] In some embodiments, the coating material includes at least one of a carbon material, a silicon phosphate compound, an aluminum phosphate compound, an ammonium phosphate compound, and an aluminum-phosphorus composite oxide. The coating material can react with lithium-containing compounds inside the material, such as Li2SiO3 and Li2SiO5, to anchor them to the material surface, and can also shield or reduce the exposure of the lithium-containing compounds on the material surface. In addition, the coating material has good thermal and ionic conductivity, which can improve heat distribution during the prelithiation reaction, promote uniform insertion of lithium ions into the surface of the silicon-oxygen material, and allow the prelithiation reaction to proceed uniformly and gently.

[0069] In some embodiments, the temperature of the third heat treatment is 500°C to 1000°C. For example, it may be 500°C, 600°C, 700°C, 800°C, 900°C, or 1000°C, and of course, it may be other values ​​within the above range, and the present application is not limited thereto.

[0070] In some embodiments, the time for the third heat treatment is 1 hour to 6 hours, and may be, for example, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, or 6 hours, etc., and of course, may be other values ​​within the above range, and the present application is not limited thereto.

[0071] As can be seen, the manufacturing method of coating the silicon-oxygen raw material can be omitted, and the silicon-oxygen material with the coating layer can be directly purchased from the market.

[0072] In some embodiments, prelithiating the silicon oxygen material includes combining the silicon oxygen feedstock with a lithium source followed by a fourth heat treatment to obtain the prelithiated material.

[0073] In some embodiments, the lithium source comprises at least one of metallic lithium, lithium hydride, lithium carbonate, lithium hydroxide, lithium borohydride, and lithium aluminum hydride.

[0074] In some embodiments, the mass ratio of the silicon-oxygen raw material to the lithium source is 100:(2 to 16). Specifically, it may be 100:2, 100:3, 100:5, 100:8, 100:10, 100:12, 100:14, or 100:16, etc., and of course, it may be other values ​​within the above range, and the present application is not limited thereto.

[0075] In some embodiments, the temperature of the fourth heat treatment is 100° C. to 900° C. For example, the reaction temperature may be 100° C., 200° C., 300° C., 400° C., 500° C., 600° C., 700° C., 800° C., or 900° C., etc., and of course, may be other values ​​within the above range, and the present application is not limited thereto.

[0076] In some embodiments, the time for the fourth heat treatment is 1 hour to 24 hours, and may be specifically 1 hour, 3 hours, 5 hours, 8 hours, 10 hours, 13 hours, 15 hours, 18 hours, 20 hours, or 24 hours, etc., and of course, may be other values ​​within the above range, and the present application is not limited thereto.

[0077] S200: A first heat treatment is performed on the mixture containing the prelithiated material and the polycarboxylic acid to harden the mixture and obtain a precursor.

[0078] In some embodiments, the prelithiated material and the polycarboxylic acid are mixed to obtain a mixture comprising the prelithiated material and the polycarboxylic acid.

[0079] In some embodiments, the polycarboxylic acid includes at least one of citric acid, tartaric acid, maleic acid, trimesic acid, terephthalic acid, malic acid, and ethylenediaminetetraacetic acid. The polycarboxylic acid has strong complex-forming ability, allowing it to tightly bond with the lithium-containing compound exposed on the surface of the silicon-oxygen feedstock. The polycarboxylic acid-derived carbon coating layer, forming "fixed points," fills the voids in the surface coating layer of the silicon-oxygen feedstock. A dense carbon layer is then formed during the carbonization process, effectively shielding the lithium-containing compound on the surface of the silicon-oxygen feedstock. Due to the shielding effect of the polycarboxylic acid-derived carbon, the Li / O ratio in the second region of the negative electrode material is lower than that in the interior of the negative electrode material, exhibiting a relationship of 0.4>a>b. The surface layer of the negative electrode material of the present application has a low relative content of lithium, i.e., lithium is mainly present in the first region of the negative electrode material, effectively preventing the intrusion and penetration of water molecules from the solvent during the process of preparing a slurry for the negative electrode material. This is advantageous in that it avoids the erosion of silicon crystal grains inside the negative electrode material and the generation of gas, and allows the slurry to be applied uniformly and evenly to the current collector, allowing the negative electrode to exhibit better electrochemical properties.

[0080] The polycarboxylic acid is a polycarboxylic acid containing two or more carboxylic acid functional groups, and includes at least one of citric acid, tartaric acid, maleic acid, trimesic acid, terephthalic acid, malic acid, and ethylenediaminetetraacetic acid. The polycarboxylic acid has a strong complexing ability and can be used to form complexes with Li. + The polycarboxylic acid-derived carbon can strongly interact with the surface of the prelithiated material, thereby tightly bonding with the lithium-containing compounds on the surface of the prelithiated material. After carbonization, the polycarboxylic acid-derived carbon can fill the voids and completely coat the lithium-containing compounds on the surface of the material, thereby improving the hydrophobicity of the material and effectively blocking contact between the Si crystal grains inside the material and the water solvent, thereby solving the problem of slurry processing stability.

[0081] In some embodiments, the polycarboxylic acid is dissolved in a solvent, i.e., the polycarboxylic acid is placed in a solvent to obtain a carbon source solution containing the polycarboxylic acid, and the prelithiated material is mixed with the carbon source solution to obtain a mixture containing the prelithiated material and the polycarboxylic acid, which is then subjected to a first heat treatment to harden the mixture, and then washed to obtain a precursor.

[0082] In some embodiments, the concentration of the carbon source solution is 3 mg / mL to 7 mg / mL. Specifically, it may be 3 mg / mL, 4 mg / mL, 5 mg / mL, 6 mg / mL, or 7 mg / mL, etc., and of course, it may be other values ​​within the above range, and the present application is not limited thereto.

[0083] In some embodiments, the mass ratio of the prelithiated material to the polycarboxylic acid is (20 to 200): 1. Specifically, the mass ratio of the prelithiated material to the polycarboxylic acid may be 20: 1, 50: 1, 80: 1, 100: 1, 120: 1, 150: 1, 180: 1, or 200: 1, etc., and of course, other values ​​within the above range may also be used, and the present application is not limited thereto.

[0084] The present application can ensure the effect of carbon coating by controlling the concentration of the carbon source solution and the mass ratio of the prelithiated material to the polycarboxylic acid.

[0085] In some embodiments, the solvent comprises at least one of acetone, water, ethanol, methanol, isopropanol, dimethylformamide, toluene, and tetrahydrofuran.

[0086] In some embodiments, the method further comprises drying the mixture before subjecting the mixed material to the first heat treatment.

[0087] In some embodiments, the drying temperature is 45°C to 90°C. Specifically, the temperature may be 45°C, 55°C, 65°C, 70°C, 80°C, 85°C, or 90°C, and of course, other values ​​within the above range are also possible, and the present application is not limited thereto. In actual operation, the prelithiated material and the carbon source solution are mixed, stirred under heated conditions, and evaporated to dryness, removing components such as the solvent, and only the polycarboxylic acid and the prelithiated material are retained.

[0088] In some embodiments, the temperature of the first heat treatment is 150°C to 250°C. Specifically, the temperature of the heat curing treatment may be 150°C, 180°C, 200°C, 230°C, or 250°C, etc., and of course, other values ​​within the above range are also possible, and the present application is not limited thereto. Within the above temperature range, the mixture of the prelithiated material and the polycarboxylic acid can be partially carbonized to form a polycarboxylic acid cured layer, which serves the purpose of preforming, so that subsequent washing can remove soluble lithium-containing compounds remaining on the material surface. As can be seen, washing removes the soluble lithium-containing compounds remaining on the material surface, thereby forming certain voids on the material surface.

[0089] In some embodiments, the time for the first heat treatment is 5 hours to 12 hours, and the specific treatment time may be 5 hours, 8 hours, 10 hours, or 12 hours, etc., and of course, other values ​​within the above range may also be used, and the present application is not limited thereto.

[0090] In some embodiments, the first heat treatment may be performed in, but is not limited to, an air atmosphere.

[0091] The present application forms a pre-hardened layer by controlling the temperature and time of the first heat treatment, and prevents subsequent washing from affecting the coating of the carbon source.

[0092] In some embodiments, the first heat treatment is followed by a step of washing, solid-liquid separation, and drying the material obtained by the first heat treatment, and the washing step may also remove moisture from the material.

[0093] In some embodiments, the washed solvent comprises at least one of water and ethanol.

[0094] In some embodiments, the washed liquid-solid mass ratio is (1-4): 1. The specific liquid-solid mass ratio may be 1:1, 2:1, 3:1, or 4:1, etc., and of course, may be other values ​​within the above range, and the present application is not limited thereto.

[0095] In some embodiments, the washing time is 1 hour to 5 hours, and the water washing time may be 1 hour, 2 hours, 3 hours, 4 hours, or 5 hours, etc., and of course, other values ​​within the above range may also be used, and the present application is not limited thereto.

[0096] In the present invention, the lithium-containing compound remaining on the surface of the material is sufficiently removed by controlling the liquid-solid mass ratio and the cleaning time.

[0097] In some embodiments, the temperature of the drying treatment is 80° C. to 120° C. Specifically, the temperature may be 80° C., 90° C., 100° C., 110° C., or 120° C., and of course, other values ​​within the above range may also be used, and the present application is not limited thereto.

[0098] In step S300, the precursor is subjected to a second heat treatment to carbonize the precursor and obtain a negative electrode material.

[0099] In some embodiments, the second heat treatment temperature is 500° C. to 800° C. Specifically, the second heat treatment temperature may be 500° C., 600° C., 700° C., or 800° C., etc., and of course, may be other values ​​within the above range, and the present application is not limited thereto.

[0100] In some embodiments, the second heat treatment time is 5 hours to 12 hours. Specifically, the second heat treatment time may be 5 hours, 7 hours, 9 hours, 11 hours, or 12 hours, etc., and of course, may be other values ​​within the above range, and the present application is not limited thereto.

[0101] In this process, during the high-temperature carbonization process of the second heat treatment, the voids on the surface of the polycarboxylic acid cured layer gradually shrink and close, ultimately forming a void-free carbon coating layer and reducing the content of the lithium-containing compound exposed on the surface of the product. The present invention reduces the porosity on the material surface by controlling the temperature and time of the heat treatment, forming a dense coating layer that is substantially void-free.

[0102] In some embodiments, the second heat treatment is performed in a protective gas atmosphere, which may be an inert gas such as argon.

[0103] In some embodiments, when the material of the coating layer of the silicon-oxygen material having a coating layer is a carbon material, the coating layer in the produced negative electrode material is a carbon layer. When the material of the coating layer of the silicon-oxygen material having a coating layer includes at least one of a silicon phosphate compound, an aluminum phosphate compound, an ammonium phosphate compound, and an aluminum-phosphorus composite oxide, the produced negative electrode material includes two composite coating layers.

[0104] As described above, in the manufacturing method of the present application, the polycarboxylic acid has strong complex-forming ability and can strongly interact with lithium ions. When the polycarboxylic acid is mixed with a lithium-containing silicon-oxygen raw material in a solution, the polycarboxylic acid tends to bond closely with the lithium-containing compound exposed on the material surface. A polycarboxylic acid-derived carbon coating layer, forming "fixed points," fills the voids in the carbon layer on the material surface. The first heat treatment partially carbonizes the polycarboxylic acid coating layer to form a pre-hardened layer. A small amount of lithium-containing compound is embedded on the surface of the cured polycarboxylic acid layer. The subsequent water washing process removes the lithium-containing compound remaining on the surface of the cured polycarboxylic acid layer, leaving only a few voids. During the high-temperature carbonization process, the voids on the surface of the cured polycarboxylic acid layer gradually shrink and close, ultimately forming a void-free carbon coating layer, reducing the content of lithium-containing compound exposed on the surface of the product.

[0105] Embodiments of the present invention further provide a lithium ion battery including the above-described negative electrode material or a negative electrode material produced by the above-described method of production.

[0106] The features and performance of the present invention will be explained in more detail below with reference to examples.

[0107] Example 1 This example provides a method for producing a negative electrode material, which is produced by the following method. (1) 1 kg of carbon-coated silicon-oxygen material SiO / C was reacted with 100 g of metallic lithium at 500°C for 3 hours to obtain prelithiated carbon-coated silicon-oxygen material Li-SiO / C with a lithium content of 10 wt%. (2) 100 g of Li-SiO / C and 1 g of citric acid were dispersed in 200 mL of acetone, stirred at 45°C, and evaporated to dryness. (3) The evaporated and dried product was subjected to a heat curing treatment in an air atmosphere at a temperature of 200°C for 12 hours. (4) 100 g of the thermoset product was dispersed in 200 mL of water, stirred at room temperature for 3 hours, filtered by suction, and dried at 100°C. (5) The dried product was carbonized with Ar gas, the heating rate was controlled at 1°C / min, the carbonization temperature was controlled at 500°C, and the carbonization time was controlled at 12 hours. After natural cooling, the product was dispersed and sieved to obtain the final product.

[0108] As shown in Figure 1, the negative electrode material produced in this example has a bottom layer of prelithium SiO, an original carbon layer of the raw carbon-coated silicon-oxygen material inside the dashed line, and a dense outer layer of carbon coating layer outside the dashed line formed from a polycarboxylic acid carbon source. The lithium-containing compound is mainly present within the original carbon layer of the raw carbon-coated silicon-oxygen material, and its content in the dense outer layer is low.

[0109] Example 2 The only differences from the first embodiment are as follows. In step (2), 200 g of Li-SiO / C and 1 g of citric acid were dispersed in 200 mL of acetone, stirred at 45°C, and evaporated to dryness. (3) The evaporated and dried product was subjected to a heat curing treatment in an air atmosphere at a temperature of 250°C for 5 hours.

[0110] Example 3 The only differences from the first embodiment are as follows. (2) 50 g of Li-SiO / C and 1 g of citric acid were dispersed in 200 mL of acetone, stirred at 45°C, and evaporated to dryness. (3) The evaporated and dried product was subjected to a heat curing treatment in an air atmosphere at a temperature of 150°C for 12 hours.

[0111] Example 4 The only difference from Example 1 is the carbonization conditions: in step (5), the carbonization temperature was 800° C. and the carbonization time was 5 hours.

[0112] Example 5 The main difference from Example 1 is that citric acid in step (2) is replaced with an equal amount of ethylenediaminetetraacetic acid.

[0113] Example 6 The main difference from Example 1 is that citric acid in step (2) is replaced with an equal amount of tartaric acid.

[0114] Example 7 The main difference from Example 1 is the lithium content of the product of step (1). (1) 1 kg of carbon-coated silicon-oxygen material SiO / C was reacted with 50 g of metallic lithium at 500°C for 3 hours to obtain prelithiated carbon-coated silicon-oxygen material Li-SiO / C with a lithium content of 5 wt%.

[0115] Example 8 The main difference from Example 1 is the lithium content of the product of step (1). 1 kg of carbon-coated silicon-oxygen material SiO / C was reacted with 120 g of metallic lithium at 500°C for 3 hours to obtain prelithiated carbon-coated silicon-oxygen material Li-SiO / C with a lithium content of 12 wt%.

[0116] Example 9 The main difference from Example 1 is the silicon-oxygen material precursor in step (1). (1) 1 kg of aluminum phosphate-coated silicon-oxygen material SiO / C-AlPO4 was reacted with 100 g of metallic lithium at a reaction temperature of 500°C for 3 hours to obtain a prelithiated carbon-coated silicon-oxygen material Li-SiO / C-AlPO4 with a lithium content of 10 wt%.

[0117] Example 10 The main difference from Example 1 is the silicon-oxygen material precursor in step (1). 1 kg of phosphorus oxide / carbon-coated silicon-oxygen material SiO / C-P2O5 was reacted with 100 g of metallic lithium at a reaction temperature of 500°C for 3 hours to obtain a prelithiated carbon-coated silicon-oxygen material Li-SiO / C-P2O5 with a lithium content of 10 wt%.

[0118] Example 11 The main difference from Example 3 is the lithium content of the product of step (1). 1 kg of carbon-coated silicon-oxygen material SiO / C was reacted with 50 g of metallic lithium at 500°C for 3 hours to obtain prelithiated carbon-coated silicon-oxygen material Li-SiO / C with a lithium content of 5 wt%.

[0119] Comparative Example 1 (1) 1 kg of carbon-coated silicon-oxygen material SiO / C was reacted with 100 g of metallic lithium at 500°C for 3 hours to obtain prelithiated carbon-coated silicon-oxygen material Li-SiO / C with a lithium content of 10 wt%. In Comparative Example 1, only step (1) of Example 1 was carried out.

[0120] Comparative Example 2 Comparative Example 2 is a prelithiated carbon-coated silicon-oxygen material Li-SiO / C prepared by a conventional method, which has a lithium content of 5 wt% by reacting the carbon-coated silicon-oxygen material SiO / C with metallic lithium. In Comparative Example 2, only step (1) of Example 7 was carried out.

[0121] Comparative Example 3 The main difference from Example 1 is that citric acid was replaced with an equal amount of pitch. The specific steps were as follows: 100 g of Li-SiO / C and 1 g of pitch were dispersed in 200 mL of toluene, stirred at 100°C, and evaporated to dryness.

[0122] Comparative Example 4 The only difference from Example 1 is that steps (3) and (4) are not performed.

[0123] Test Example 1 As shown in Tables 1 and 2, the characteristic parameters and electrochemical properties of the negative electrode active materials obtained in Examples 1-11 and Comparative Examples 1-4 were measured.

[0124] Test method: The silicon-oxygen composite negative electrode materials obtained in Examples 1-11 and Comparative Examples 1-4 were used as the negative electrode active material. The active material was mixed uniformly with sodium carboxymethylcellulose (CMC) and styrene butadiene rubber (SBR) in a mass ratio of 96.5:1.5:2, and then coated onto a copper foil current collector. After drying, the resulting negative electrode pieces were used as described below. First, button cell measurements were performed on the resulting electrode pieces. The batteries were assembled in an argon glove box. A metallic lithium sheet was used as the negative electrode, the electrolyte was LiPF 61 mol / L + ethylene carbonate (EC) + methyl ethyl carbonate (EMC), and the separator was a polyethylene / propylene composite microporous membrane. Electrochemical performance was measured using a battery measuring device. The battery capacity was set to the standard 480 mAh / g, the charge / discharge voltage was 0.01 to 1.5 V, and the charge / discharge rate was 0.1 C.

[0125] Measurement of gas generation rate of slurry: After the preparation of the slurry was completed, 20 g of the slurry was weighed and sealed in aluminum plastic film, and then stored at room temperature for 72 hours. The volume change of the aluminum plastic film before and after storage was measured using the drainage method to obtain the gas generation rate of the slurry.

[0126] Slurry stability measurement: After the slurry preparation was completed, 500 g of the slurry was weighed and placed in a beaker. After storing it at room temperature for 72 hours, it was observed whether or not a floating blue color appeared on the surface of the slurry. If a floating blue color was observed, it indicated that the styrene butadiene rubber (SBR) was not uniformly dispersed in the slurry, causing delamination and poor slurry stability.

[0127] [Table 1]

[0128] [Table 2]

[0129] The data in Tables 1 and 2 indicate that the presently disclosed negative electrode material comprises a core and a coating layer, the core comprising a silicon-oxygen material, and the negative electrode material comprising lithium. When the mass ratio of lithium to oxygen in the negative electrode material is a, and when the negative electrode material is measured using an X-ray photoelectron spectrometer (Thermo Scientific K-Alpha), the mass ratio of lithium to oxygen in the region corresponding to the information detected by the photoelectron spectrometer in the process of detecting from the surface of the negative electrode material toward the central region of the negative electrode material, the relationship 0.4>a>b is satisfied. This indicates that the relative content of lithium in the surface layer of the negative electrode material is low, i.e., lithium is mainly present in the region (i.e., the first region) that cannot be detected by the X-ray photoelectron spectrometer relative to the interior of the negative electrode material particles. This effectively reduces the intrusion of water solvent molecules into the negative electrode material during the processing and slurry preparation process, reduces the erosion of silicon crystal grains in the negative electrode material, improves the stability of the negative electrode material during the slurry processing process, and improves the overall electrochemical properties of the material. Furthermore, as can be seen from Table 1, the outermost surface of the negative electrode material prepared in the examples was substantially void-free, with almost no gas generation. The dense carbon layer in the outermost layer effectively blocked contact between the silicon crystal grains inside the material and the aqueous solvent, thereby resolving the problem of slurry processing stability.

[0130] In Comparative Examples 1 and 2, the anode material was prepared by prelithiation using only silicon-oxygen raw material with a coating layer. The surface contained a large amount of lithium element, and a>b was not satisfied. Therefore, during the processing and slurry preparation process of the anode material, water solvent molecules easily entered the anode material, eroding the silicon crystal grains and affecting the stability of the anode material. As a result, the specific capacity, initial coulombic efficiency, and cycle stability of the anode material were all poor.

[0131] In Comparative Example 3, when pitch was used to coat the prelithiated material, the pitch was unable to bond tightly with the lithium-containing compound exposed on the material surface, resulting in numerous voids in the material, a large amount of gas generation, and a large amount of lithium element contained on the material surface, which did not satisfy a > b. As a result, during the processing and slurry preparation of the anode material, water solvent molecules were easily absorbed into the anode material, eroding the silicon crystal grains and affecting the stability of the anode material, resulting in poor specific capacity, initial coulombic efficiency, and cycle stability of the anode material.

[0132] In Comparative Example 4, polycarboxylic acid is used for coating and then directly carbonized, and the voids generated in the initial decomposition process of polycarboxylic acid cause some lithium-containing compound to be exposed again, that is, some lithium-containing compound is still not completely coated, forming a mosaic structure, which is retained in the later carbonization process, that is, some lithium-containing compound is still exposed, and the material does not satisfy a>b, which affects the stability of the negative electrode material, and the specific capacity, initial coulombic efficiency and cycle stability of the negative electrode material are all poor.

[0133] The above is merely a preferred embodiment of the present invention, and is not intended to limit the present invention. Those skilled in the art can make various modifications and changes to the present invention. Any modifications, equivalent replacements, improvements, etc. made within the scope of the spirit and principle of the present invention should be included in the protection scope of this application. [Explanation of symbols]

[0134] In Figure 1 100-core 200-Lithium element 300-Covering layer 301-1st coating layer 302-Second coating layer 1-First area 2-Second area

Claims

1. A negative electrode material comprising a core and a coating layer located on at least a portion of a surface of the core, the core comprises a silicon-oxygen material, and the negative electrode material comprises elemental lithium; a mass ratio of lithium element to oxygen element in the negative electrode material is a, and b is a mass ratio of lithium element to oxygen element in a region corresponding to information that can be detected in a process in which the negative electrode material is measured using an X-ray photoelectron spectrometer (Thermo Scientific K-Alpha) from the surface of the negative electrode material toward a central region inside the negative electrode material, the relationship between a and b satisfying 0.4>a>b, A negative electrode material characterized in that, when a contact angle θ of the negative electrode material with acetone is measured by a Washburn method, θ is greater than 20°.

2. 2. The negative electrode material according to claim 1, characterized in that it has at least one of the following characteristics (1) to (7): (1) the mass ratio (a) of lithium element to oxygen element in the negative electrode material satisfies 0.35>a>0.15; (2) b satisfies 0.30 > b > 0.01; (3) When the negative electrode material is measured using an X-ray photoelectron spectrometer (Thermo Scientific K-Alpha), the thickness of the region corresponding to information detectable by the photoelectron spectrometer in the process of detecting from the surface of the negative electrode material toward the central region inside the negative electrode material is 1 nm to 10 nm; (4) The silicon-oxygen material is silicon oxide SiO ｘ (0<x≦2) (5) The silicon-oxygen material is Li ２ SiO ３ , Li ２ Si ２ O ５ and Li ４ SiO ４ The lithium-containing compound includes at least one of: (6) When the mass of the negative electrode material is 100%, the mass ratio of the lithium element in the negative electrode material is 1 wt % to 15 wt %; (7) The molar ratio of Si element to O element in the negative electrode material is (0.8-1.2):

1.

3. 2. The negative electrode material according to claim 1, wherein the coating layer includes a first coating layer and a second coating layer, and the second coating layer is located between the core and the first coating layer and / or in an area of ​​the surface of the core that is not covered by the first coating layer.

4. The negative electrode material according to claim 3, characterized in that it has at least one of the following characteristics (1) to (6): (1) The second coating layer contains at least one of a silicon phosphate compound, an aluminum phosphate compound, an ammonium phosphate compound, and an aluminum-phosphorus composite oxide; (2) The material of the first coating layer includes a carbon material; (3) The mass ratio of the first coating layer to the negative electrode material is 0.1% to 5%; (4) The mass ratio of the second coating layer to the negative electrode material is 0.1% to 8%; (5) The thickness of the first coating layer is 1 nm to 1000 nm; (6) The thickness of the second coating layer is 1 nm to 1000 nm.

5. 2. The negative electrode material according to claim 1, characterized in that it has at least one of the following characteristics (1) to (2): (1) The coating layer is a carbon layer; (2) The thickness of the coating layer is 1 nm to 1000 nm.

6. 2. The negative electrode material according to claim 1, characterized in that it has at least one of the following characteristics (1) to (4): (1) The pore volume of the negative electrode material is 0.01 cm ３ / g or less; (2) The specific surface area of ​​the negative electrode material is 4 m ２ / g or less; (3) The pH of the negative electrode material satisfies the condition 7<pH<11.5; (4) The median diameter of the negative electrode material is 3.0 μm to 10.0 μm.

7. prelithiated a silicon-oxygen source to obtain a prelithiated material containing lithium element and silicon-oxygen source in a mass ratio of (0.02-0.16):1; a step of performing a first heat treatment on a mixture containing the prelithiated material and a polycarboxylic acid to harden the mixture, and then washing, separating the obtained material into solid and liquid, and drying the obtained material to obtain a precursor; and performing a second heat treatment on the precursor to carbonize the precursor and obtain an anode material.

8. The manufacturing method according to claim 7, characterized in that it has at least one of the following characteristics (1) to (12): (1) The temperature of the first heat treatment is 150°C to 250°C; (2) The duration of the first heat treatment is 5 hours to 12 hours; (3) The first heat treatment is performed in an air atmosphere; (4) further comprising a step of drying the mixture containing the prelithiated material and the polycarboxylic acid before subjecting the mixture containing the prelithiated material and the polycarboxylic acid to a first heat treatment; (5) The method further includes a step of drying the mixture containing the prelithiated material and the polycarboxylic acid before subjecting the mixture containing the prelithiated material and the polycarboxylic acid to a first heat treatment, wherein the drying temperature is 45°C to 90°C; (6) The solvent used for the cleaning includes at least one of water and ethanol; (7) The solid-liquid mass ratio during the washing is (1 to 4):1; (8) The washing time is 1 hour to 5 hours; (9) The drying temperature is 80°C to 120°C; (10) The temperature of the second heat treatment is 500°C to 800°C; (11) The time of the second heat treatment is 5 hours to 12 hours; (12) The second heat treatment is performed in a protective gas atmosphere.

9. 8. The method for producing the mixture containing the prelithiated material and the polycarboxylic acid according to claim 7, comprising: adding the polycarboxylic acid to a solvent to obtain a carbon source solution containing the polycarboxylic acid; and mixing the prelithiated material with the carbon source solution containing the polycarboxylic acid to obtain a mixture containing the prelithiated material and the polycarboxylic acid.

10. 10. The method according to claim 9, wherein the method has at least one of the following characteristics (1) to (4): (1) The concentration of the carbon source solution is 3 mg / mL to 7 mg / mL; (2) The polycarboxylic acid includes at least one of citric acid, tartaric acid, maleic acid, trimesic acid, terephthalic acid, malic acid, and ethylenediaminetetraacetic acid; (3) the solvent includes at least one of acetone, water, ethanol, methanol, isopropanol, dimethylformamide, toluene, and tetrahydrofuran; (4) The mass ratio of the prelithiated material to the polycarboxylic acid is (20 to 200):

1.

11. 8. The method of claim 7, wherein the silicon / oxygen raw material is a silicon / oxygen material having a coating layer, and the method for producing the silicon / oxygen material having a coating layer includes providing a silicon / oxygen material, mixing the silicon / oxygen material with a coating material, and then performing a third heat treatment to obtain the silicon / oxygen material having a coating layer.

12. The manufacturing method according to claim 11, characterized in that it has at least one of the following characteristics (1) to (4): (1) the mass ratio of the silicon-oxygen material to the coating material is 1:(0.005-0.05); (2) The coating material includes at least one of a carbon material, a silicon phosphate compound, an aluminum phosphate compound, an ammonium phosphate compound, and an aluminum-phosphorus composite oxide; (3) The temperature of the third heat treatment is 500°C to 1000°C; (4) The time for the third heat treatment is 1 hour to 6 hours.

13. 8. The method of claim 7, wherein the step of prelithiating the silicon-oxygen source comprises mixing the silicon-oxygen source with a lithium source and then performing a fourth heat treatment to obtain a prelithiated material.

14. The manufacturing method according to claim 13, characterized in that it has at least one of the following characteristics (1) to (7): (1) The silicon-oxygen raw material is SiO ｙ (0<y≦2) (2) the lithium source comprises at least one of metallic lithium, lithium hydride, lithium carbonate, lithium hydroxide, lithium borohydride, and lithium aluminum hydride; (3) the mass ratio of the silicon-oxygen source to the lithium source is 100:(2-16); (4) The temperature of the fourth heat treatment is 100°C to 900°C; (5) The time of the fourth heat treatment is 1 hour to 24 hours; (6) The silicon-oxygen raw material is a silicon-oxygen material having a coating layer; (7) The silicon-oxygen raw material is a silicon-oxygen material having a coating layer, and the material of the coating layer includes at least one of a carbon material, a silicon phosphate compound, an aluminum phosphate compound, an ammonium phosphate compound, and an aluminum-phosphorus composite oxide.

15. A lithium ion battery comprising the negative electrode material according to any one of claims 1 to 6.

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