Negative electrode material, its preparation method, and lithium ion battery

Abstract

The present invention relates to a negative electrode material and a preparation method thereof, and to a lithium ion battery. [Solution] The anode material comprises a core and a first coating layer covering at least a portion of the surface of the core, the core comprising a silicon-based material, the first coating layer comprising a carbon material, a fibrous material distributed on at least a portion of the surface of the first coating layer, and the fibrous material and the anode material satisfy the mathematical formula (I). The presence of the fibrous material on the surface of the first coating layer of the present invention allows the anode material to accept electrons and lithium ions at a high speed, improving the conductivity of the anode material and thereby improving the rate performance of the anode material. TIFF2025538257000009.tif17170 (In formula (I), D wire is the minimum fiber diameter (nm) of the fiber material, and D 10 is the particle size (nm) corresponding to when the cumulative particle size distribution number of the negative electrode material reaches 10%, and ρ is the powder conductivity (S / cm) of the negative electrode material.

Description

[Technical Field]

[0001] This application claims priority based on a Chinese patent application filed with the China Patent Office on December 29, 2022, bearing application number 202211711132.6 and entitled "Negative electrode material and preparation method thereof, and lithium ion battery," the disclosure of which is incorporated herein in its entirety.

[0002] The present application relates to the technical field of negative electrode materials, and more particularly to negative electrode materials and methods for preparing the same, and lithium ion batteries. [Background technology]

[0003] Silicon-based anode materials are one of the most important materials for high-energy-density lithium-ion batteries. However, conventional silicon-based materials have problems such as large expansion and poor rate performance, which affect the wide application of silicon-based anode materials in lithium batteries. Therefore, how to suppress expansion and improve the cycle rate performance of silicon-based materials is a prerequisite for the wide application of silicon-based materials.

[0004] In the process of designing and improving silicon-based anode materials, the design of the material structure is key to improving their performance. Conventional thin-film batteries typically use nanosilicon wire-based anode materials. However, for lithium-ion battery anodes, these materials typically need to be processed into powder or granular structures, which makes nanosilicon wire structures incompatible. This limits the improvement of the material's conductivity and further limits the improvement of the anode's rate performance. Furthermore, while conventional anode materials improve their cycling performance by forming an SEI, the SEI is typically formed using insulating materials, and the use of insulating materials also reduces the rate performance of the material.

[0005] Therefore, there is currently an urgent need to improve conventional silicon-based anode materials to improve the rate performance of the materials. Summary of the Invention [Problem to be solved by the invention]

[0006] The present application provides a negative electrode material that can improve the rate performance of the negative electrode material, a preparation method thereof, and a lithium ion battery. [Means for solving the problem]

[0007] In a first aspect, an embodiment of the present application is an anode material including a core and a first coating layer that coats at least a portion of a surface of the core, wherein the core includes a silicon-based material, the first coating layer includes a carbon material, and a fibrous material is distributed on at least a portion of a surface of the first coating layer; The fiber material and the negative electrode material provide a negative electrode material that satisfies the relational expression of the following formula (I).

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[0008] In some embodiments of the first aspect, the negative electrode material has at least one selected from the following characteristics (1) to (7). (1) The fiber diameter of the fiber material is 2 nm to 200 nm. (2) The first coating layer also contains a fiber material. (3) The fiber material includes at least one selected from carbon-based fibers and silicon-based fibers. (4) The fiber material includes at least one selected from carbon-based fibers and silicon-based fibers, and the carbon-based fibers include at least one selected from carbon fibers, carbon nanotubes, and polymer fibers. (5) The fiber material includes at least one selected from carbon-based fibers and silicon-based fibers, and the silicon-based fibers include at least one selected from silicon fibers and silicate fibers. (6) The fiber material includes at least one selected from carbon-based fibers and silicon-based fibers, the carbon-based fibers include at least one selected from carbon fibers, carbon nanotubes, and polymer fibers, and the polymer fibers include at least one selected from polypropylene fibers, polyester-based fibers, polyamide-based fibers, polyacrylic-based fibers, polyenzyme-based fibers, and polyamine-based fibers. (7) The carbon material includes at least one material selected from amorphous carbon, graphite, graphene, and diamond-like carbon.

[0009] In some embodiments of the first aspect, the negative electrode material has at least one selected from the following characteristics (1) to (4). (1) The first coating layer further contains a salt substance including an inorganic salt and an organic salt. (2) The first coating layer further contains a salt substance including an inorganic salt and an organic salt, and the inorganic salt includes at least one selected from fluorides, lithium salts, carbonates, silicates, phosphates, nitrates, titanates, thioates, and vanadates. (3) The first coating layer further contains a salt substance including an inorganic salt and an organic salt, and the organic salt contains at least one selected from a carboxylate, an alkoxide, and an aromatic salt compound. (4) The first coating layer further contains a salt substance, and the thickness of the first coating layer is 0.1 μm to 1.2 μm.

[0010] In some embodiments of the first aspect, the negative electrode material has at least one selected from the following characteristics (1) to (6). (1) The thickness of the first coating layer is 0.01 μm to 1 μm. (2) The first coating layer contains a first doping element including at least one element selected from N, P, B, S, O, F, Cl, Br, and I. (3) The first coating layer contains a first doping element, and the content of the first doping element in the first coating layer is 0.01% to 5%. (4) The core contains at least one selected from crystalline silicon and silicide. (5) The core includes at least one selected from crystalline silicon and a silicide, and the silicide includes at least one selected from silicate, silicon oxide, silicon phosphide, silicon carbide, silicon nitride, and a silicon alloy. (6) The content of metal elements in the core is 0 to 15 wt %, and the metal elements include at least one selected from lithium, sodium, magnesium, aluminum, copper, titanium, boron, beryllium, calcium, vanadium, chromium, lanthanum, and selenium.

[0011] In some embodiments of the first aspect, the negative electrode material further includes a second coating layer disposed between the core and the first coating layer, and / or a second coating layer disposed on an area of ​​the surface of the core that is not covered by the first coating layer.

[0012] In some embodiments of the first aspect, the second coating layer has at least one selected from the following characteristics (1) to (5). (1) The second coating layer contains a salt substance including an inorganic salt and an organic salt. (2) The second coating layer contains a salt substance including an inorganic salt and an organic salt, and the inorganic salt includes at least one selected from fluorides, lithium salts, carbonates, silicates, phosphates, nitrates, titanates, thioates, and vanadates. (3) The second coating layer contains a salt substance including an inorganic salt and an organic salt, and the organic salt contains at least one selected from a carboxylate, an alkoxide, and an aromatic salt compound. (4) The second coating layer contains a salt, and the content of the salt in the negative electrode material is 0.01 wt % to 3.0 wt %. (5) The thickness of the second coating layer is 0 μm to 1 μm.

[0013] In some embodiments of the first aspect, the negative electrode material includes at least one selected from the following characteristics (1) to (7): (1) The negative electrode material contains a salt substance, and the mass ratio of the salt substance is 0 wt % to 3.0 wt %. (2) The carbon element content in the negative electrode material is 0.5 wt % to 10 wt %. (3) Median diameter D of the negative electrode material 50 is 2.0 μm to 10.0 μm. (4) The particle size D of the negative electrode material having a particle cumulative distribution of 10% 10 is 0.5 μm to 4 μm. (5) The powder conductivity of the negative electrode material is 0.01 S / cm to 500 S / cm. (6) The silicon-oxygen ratio of the negative electrode material is Si / O=0.5 to 3.0. (7) The porosity of the negative electrode material is 0.5% to 15%.

[0014] In a second aspect, the present embodiment comprises: A step of performing a first heat treatment on a mixture containing a silicon / oxygen raw material and at least two kinds of salt substances to form the salt substances into a molten salt and obtain a first precursor; The method for preparing the negative electrode material includes a step of mixing the first precursor with a carbon source, followed by a second heat treatment to obtain the negative electrode material.

[0015] In the second aspect, in some embodiments, the mixture comprising the silicon and oxygen source and at least two salt substances further comprises a metal source.

[0016] In some embodiments of the second aspect, the preparation method has at least one selected from the following characteristics (1) to (3). (1) The metal source includes at least one selected from metallic lithium, metallic magnesium, metallic sodium, metallic calcium, metallic copper, and metallic titanium. (2) The metal source includes an active hydride formed from at least one source selected from a lithium source, a magnesium source, a sodium source, a calcium source, a copper source, and a titanium source. (3) The content of the metal source in the first precursor is 0 wt % to 15 wt %.

[0017] In some embodiments of the second aspect, the preparation method includes at least one selected from the following features (1) to (10): (1) The silicon-oxygen raw material is silicon oxide SiO x (where 0.05≦x≦2). (2) The salt substances include inorganic salts and organic salts. (3) The salt substance includes an inorganic salt and an organic salt, and the inorganic salt includes at least one selected from fluorides, lithium salts, carbonates, silicates, phosphates, nitrates, titanates, thioates, and vanadates. (4) The salt substance includes an inorganic salt and an organic salt, and the organic salt includes at least one selected from a carboxylate, an alkoxide, and an aromatic salt compound. (5) The content of the salt substance in the first precursor is 1.0 wt% to 20 wt%. (6) The temperature of the first heat treatment is 400°C to 1200°C. (7) The temperature retention time for the first heat treatment is 3 to 24 hours. (8) The temperature rise rate in the first heat treatment is 1° C. / min to 10° C. / min. (9) The pressure in the first heat treatment is 0.1 MPa to 20 MPa. (10) The first heat treatment is performed in a first protective atmosphere, and the first protective atmosphere contains at least one gas selected from nitrogen gas, helium gas, and argon gas.

[0018] In some embodiments of the second aspect, the preparation method has at least one selected from the following characteristics (1) to (6). (1) The carbon source includes at least one selected from a solid carbon source and a gaseous carbon source. (2) The carbon source includes at least one selected from a solid carbon source and a gaseous carbon source, and the solid carbon source includes at least one selected from pitch, an epoxy resin, and a phenol resin. (3) The carbon source includes at least one selected from a solid carbon source and a gaseous carbon source, and the gaseous carbon source includes at least one selected from methane, acetylene, ethylene, and propane. (4) The carbon source includes a gaseous carbon source, and the flow rate of the gaseous carbon source is 0.5 L / min to 3 L / min. (5) The carbon source includes a solid carbon source, and the mass ratio of the first precursor to the carbon source is 1:(0.01-0.1). (6) The carbon source includes a solid carbon source, the second heat treatment is performed in a second protective atmosphere, and the second protective atmosphere includes at least one gas selected from nitrogen gas, helium gas, and argon gas.

[0019] In some embodiments of the second aspect, the preparation method has at least one selected from the following characteristics (1) to (3). (1) The temperature of the second heat treatment is 400°C to 1000°C. (2) The temperature retention time for the second heat treatment is 0.5 to 10 hours. (3) The temperature rise rate in the second heat treatment is 1° C. / min to 10° C. / min.

[0020] In the second aspect, in some embodiments, after the second heat treatment, the method further comprises the step of washing the material obtained by the second heat treatment with water and drying it.

[0021] In some embodiments of the second aspect, the preparation method has at least one selected from the following characteristics (1) to (5). (1) The time for the water washing is 30 to 90 minutes. (2) The flow rate of the water wash is 5 L / min to 20 L / min. (3) The drying method includes at least one method selected from air drying and vacuum drying. (4) The drying temperature is 25°C to 120°C. (5) The drying time is 3 to 48 hours.

[0022] In the second aspect, in some embodiments, the method further comprises the step of soaking the material obtained by the second heat treatment in water and filtering the material before washing the material obtained by the second heat treatment with water.

[0023] In some embodiments of the second aspect, the preparation method has at least one selected from the following characteristics (1) to (3). (1) The immersion time is 10 to 60 minutes. (2) The immersion is carried out under stirring conditions, and the stirring speed is 100 r / min to 500 r / min. (3) The immersion is carried out under stirring conditions, and the solution temperature during the immersion is 25°C to 80°C.

[0024] In a third aspect, embodiments of the present application provide a lithium-ion battery, the lithium-ion battery comprising the negative electrode material according to the first aspect or the negative electrode material prepared by the preparation method according to the second aspect. [Effects of the Invention]

[0025] The technical solution of the present application has at least the following beneficial effects:

[0026] In the anode material of the present application, a fiber material is present on the surface of the first coating layer, and the fiber material and the anode material satisfy formula (I), which allows the fiber material of the anode material to grow well radially. The fiber material with good radial growth effectively reduces charge transfer resistance due to lithium absorption, improves mass transfer efficiency, and forms high-speed lithium absorption channels, which is beneficial for in-situ conduction between the anode material and the lithium source. By reducing interfacial barriers, the lithium conductivity of the anode material is improved, allowing the anode material to accept electrons and lithium ions at high speeds, improving the conductivity of the anode material and further improving the cycle performance and rate performance of the anode material. At the same time, the anode material of the present application has a core-shell structure, and the shell includes a coating layer containing a carbon material, which increases the conductive contact area of ​​the anode material and further improves the rate performance of the anode material.

[0027] The present invention relates to a method for preparing a negative electrode material by first heat-treating a mixture containing a silicon / oxygen source and at least two salts, thereby forming a liquid molten salt mixture. The first precursor is then mixed with a carbon source, followed by a second heat-treating process. The carbon source forms a carbon layer, coating the surface of the silicon / oxygen source, thereby increasing the conductive contact area and improving the electrical conductivity of the negative electrode material. At the same time, some carbon and / or silicon elements are catalyzed by the molten salt mixture, growing into fibrous material and extending to the surface of the carbon layer. The fibers then exist on the surface of the carbon layer, thereby improving the mass transport and charge transport capabilities of the negative electrode material and improving the rate performance and initial efficiency of the negative electrode material. The preparation process described herein is simple and suitable for large-scale industrialization. [Brief explanation of the drawings]

[0028] The present application will now be further described with reference to the figures and examples.

[0029] [Figure 1] FIG. 2 is a structural schematic diagram of a coating layer in the negative electrode material of the present application having a single-layer structure. [Figure 2]FIG. 1 is a structural schematic diagram of a first coating layer in a negative electrode material of the present application, which is a composite layer made of a carbon material and a salt substance. [Figure 3] 1 is a structural schematic diagram of a negative electrode material of the present application having a double coating layer. [Figure 4] 1 is a flowchart for preparing a negative electrode material according to the present invention. [Figure 5] FIG. 2 is a comparative diagram of surface SEM images of Examples 1, 2, 3, Comparative Examples 1, 2, and 3 of the present application. [Figure 6] FIG. 1 is a comparative performance diagram of low-temperature capacity tests of complete batteries prepared with the negative electrode materials of Examples 1 to 8 and Comparative Examples 1 to 4 of the present application. [Figure 7] FIG. 1 is an EDS test diagram of Example 2 of the present application. [Figure 8] FIG. 1 is an EDS test diagram of Comparative Example 4 of the present application. DETAILED DESCRIPTION OF THE INVENTION

[0030] In order to better understand the technical solution of the present application, the following describes in detail the embodiments of the present application with reference to the accompanying drawings.

[0031] It should be clear that the described embodiments are only some of the embodiments of the present application, and do not represent all of the embodiments. Based on the embodiments of the present application, any other embodiments that a person skilled in the art can make without requiring any effort equivalent to an inventive step fall within the scope of protection of the present application.

[0032] The terms used in the examples of this application are used only to describe particular examples and are not intended to limit the application. As used in the examples and claims of this application, the singular forms "a," "the," and "the" are intended to include the plural forms unless the context clearly dictates otherwise.

[0033] It is understood that the term "and / or" used in this specification is only a relational relationship describing related objects, and indicates that three types of relationships may exist. For example, ΔJ and / or B can indicate three situations: ΔJ exists alone, ΔJ and B exist simultaneously, and B exists alone. In addition, the symbol " / " in this specification generally indicates that the related objects before and after are in an "or" relationship.

[0034] The present application provides a negative electrode material, and as shown in FIG. 1 , the negative electrode material includes a core 1 and a first coating layer 2 that coats at least a portion of the surface of the core 1, the core 1 including a silicon-based material, the first coating layer 2 including a carbon material, and a fiber material 4 distributed on at least a portion of the surface of the first coating layer 2. The fiber material 4 and the negative electrode material satisfy the relational expression of the following formula (I).

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[0035] In the above technical proposal, the present anode material has a fiber material 4 on the surface of the first coating layer 2, and the fiber material and the anode material satisfy formula (I), resulting in good radial growth of the fiber material 4 in the anode material. The well-growing fiber material 4 effectively reduces charge transfer resistance due to lithium absorption, improves mass transfer efficiency, and forms high-speed lithium absorption channels, favoring in-situ conduction between the anode material and the lithium source. By reducing interfacial barriers, the lithium conductivity of the anode material is improved, allowing the anode material to accept electrons and lithium ions at high speeds, improving the conductivity of the anode material and further improving the cycle performance and rate performance of the anode material. At the same time, the present anode material has a core-shell structure, and the shell includes a coating layer containing a carbon material, increasing the conductive contact area of ​​the anode material and further improving the rate performance of the anode material.

[0036] In the present application, the value of ΔJ may be, but is not limited to, 0.005, 0.008, 0.04, 0.05, 0.08, 0.1, 0.12, 0.15, etc., and may of course be other values ​​within the above range. wire , particle size of negative electrode material D 10 Based on the conductivity ρ of the negative electrode material, the ability of the fiber material 4 to form electron-ion mass transfer channels was evaluated. Specifically, when ΔJ is within the above range, the fiber material 4 of the negative electrode material grows well in the radial direction, effectively reducing the charge transfer resistance due to lithium absorption, improving mass transfer efficiency, forming high-speed lithium absorption channels, improving the charge transfer resistance between material interfaces, and improving the rate performance and low-temperature performance of the negative electrode material. Furthermore, compared to powder-type materials, the fiber material 4 of the present application has a wider mass transfer and charge transfer region and a higher degree of elongation, allowing it to effectively bond with the cell conductive network, improving the cycle performance of the negative electrode material. A ΔJ value exceeding 0.15 leads to material degradation. This application also shows that D 10 This controls the distribution of small particles in the negative electrode material. The small particle powder has a high specific surface area and generates strong interactions with the fiber material, which affects the radial growth and distribution of the fiber material and thus the electrochemical performance of the negative electrode material.

[0037] The diameter of the fiber material 4 in a single negative electrode material may vary greatly, and the D wire The minimum diameter of the fiber in the sample that can be measured is used for calculation, and the minimum diameter of the fiber in the sample is understood to be measured in accordance with the national standard "GB / T 268260-2011 Method for Determining the Diameter of Carbon Nanotubes." (Depending on the diameter size) The fiber diameter is quantitatively measured using an electron microscope (SEM / TEM), with a dot resolution better than 0.3 nm. First, the sample is prepared and photographed using an electron microscope to obtain a certain number of TEM / SEM images of the effective field of view. Then, all the images of the effective field of view are analyzed, and the fiber diameter is measured and statistically analyzed. Finally, a diameter distribution diagram of the fiber sample is plotted, and the average diameter and standard deviation are calculated, and the lower limit is taken as the D of this application. wire The sample is then analyzed using TEM / SEM with a representative effective field of view of at least 10, and the total number of fibers whose diameters can be measured in one TEM / SEM image exceeds 200. This application involves performing TEM / SEM measurement and analysis on the sample, measuring and recording the diameter data of all fibers whose diameters can be identified in the image. The specific measurement method involves creating a line perpendicular to the fiber axis, measuring the outer diameter of each line, and converting the measurement results to an actual scale of fiber diameter based on the TEM / SEM image markings.

[0038] In calculating the results, the fiber diameter distribution of one negative electrode material powder sample is statistically analyzed, and the fiber fraction is expressed as a columnar histogram. Each column in the histogram represents the fiber fraction distributed within that section, i.e., the percentage of the statistical number of fibers within a certain diameter range relative to the total number of fibers. The width of the histogram section is the distance between the centers of adjacent columns, and this value can be determined according to actual needs. The present invention limits the particle size range to 10 equal sections for statistical analysis of the diameter distribution. Finally, based on the diameter measurement data, the average diameter and standard deviation are calculated according to the following formulas (1) and (2), and the lower limit is taken, i.e., the D in this application. wire is the value.

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[0039] In some embodiments, when the amount of fibrous material 4 on the surface of the first coating layer 2 is small, the fibrous material 4 is scattered and distributed on the surface of the first coating layer 2, and when the amount of fibrous material 4 on the surface of the first coating layer 2 is large, the fibrous material 4 may be coated on the surface of the first coating layer 2 as a coating layer (shown as a coating layer by dashed lines in Figure 1).

[0040] 1, in some embodiments, the fiber material 4 is also distributed within the first coating layer 2. In one example, the fiber material 4 is distributed both within and on the surface of the first coating layer 2, i.e., the fiber material 4 penetrates the first coating layer 2 and is distributed on the surface of the first coating layer 2. It is understood that the fiber material 4 can form high-speed lithium absorption channels between the surface of the core 1 and the surface of the negative electrode material, thereby significantly improving the ion and electron transport performance of the negative electrode material.

[0041] In some embodiments, the fiber material 4 includes at least one selected from carbon-based fibers and silicon-based fibers.

[0042] In some embodiments, the carbon-based fibers include at least one selected from carbon fibers, carbon nanotubes, and polymer fibers. Here, the polymer fibers include at least one selected from polypropylene fibers, polyester fibers, polyamide fibers, polyacrylic fibers, polyenzyme fibers, and polyamine fibers. Exemplary polymer fibers include polyethylene oxide fibers, polyacrylonitrile fibers, polyvinylidene fluoride fibers, polymethyl methacrylate fibers, polypropylene oxide fibers, and polyvinylidene chloride fibers.

[0043] In some embodiments, the silicon-based fibers comprise at least one selected from silicon fibers and silicate fibers.

[0044] In this application, when comparing carbon-based fibers and silicon-based fibers, carbon-based fibers have the smallest fiber diameter and are elongated and curved. Silicon-based fibers have relatively large diameters; specifically, silicon fibers have intermediate fiber diameters, while silicate fibers have the largest fiber diameters. Silicon fibers and silicate fibers are essentially upright and not curved. Therefore, negative electrode materials can be distinguished by fiber diameter and morphology through SEM / EDS analysis. They can also be distinguished by elemental composition. Note that the thickness of the fiber material 4 in Figure 1 is merely an example and does not represent the actual diameter distribution of the fiber material 4.

[0045] In some embodiments, the fiber diameter of the fiber material 4 is 2 nm to 200 nm. Specifically, the fiber diameter of the fiber material 4 may be 2 nm, 5 nm, 10 nm, 30 nm, 50 nm, 80 nm, 100 nm, 150 nm, 180 nm, 200 nm, etc., and of course, other values ​​within the above range are also possible, but are not limited to these. If the fiber diameter of the fiber material 4 exceeds 200 nm, a bulk structure appears on the material surface, increasing the mass transfer resistance of the material. If the fiber diameter of the fiber material 4 is below 2 nm, the influence area of ​​the fiber material 4 is too small. Therefore, although it is necessary to increase the fiber ratio to achieve high mass transfer and charge transfer performance, this will result in a decrease in the material capacity.

[0046] In some embodiments, the carbon material comprises at least one selected from amorphous carbon, graphite, graphene, and diamond-like carbon (DLC), where diamond-like carbon is also called diamond-like carbon and is primarily composed of a large amount of sp 3 It contains a mixture of amorphous carbon and also contains small amounts of diamond crystallites and graphite crystallites.

[0047] In some embodiments, the material of the first coating layer 2 further includes a salt. See FIG. 2. FIG. 2 is a structural diagram of a negative electrode material in which the first coating layer 2 includes a carbon material and a salt. The carbon material further improves the conductive properties of the material. The salt has excellent chemical stability, compactness, and adhesive properties. The presence of the first coating layer 2 forms a rigid skeleton, improving the structural stability of the negative electrode material. The rigid skeleton facilitates the deposition of the SEI, forming a rigid layer. This stabilizes the SEI interface, suppresses irreversible expansion of the material, and improves the cycle capacity retention and cycle performance of the negative electrode material. In this example, the combination of the coating layer containing the carbon material and the salt with the fiber material 4 improves the rate performance and capacity of the negative electrode material and suppresses irreversible expansion of the negative electrode material.

[0048] In some embodiments, the salt substance includes an inorganic salt and an organic salt. Specifically, the inorganic salt includes at least one selected from fluorides, lithium salts, carbonates, silicates, phosphates, nitrates, titanates, thioates, and vanadates. Exemplary inorganic salts include lithium fluoride, lithium thiophosphate, lithium vanadate, lithium titanate, lithium carbonate, lithium phosphate, lithium silicate, lithium nitrate, aluminum fluoride, aluminum carbonate, sodium carbonate, potassium carbonate, magnesium carbonate, calcium carbonate, lithium sodium carbonate, lithium potassium carbonate, potassium fluoride, sodium fluoride, lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium hexafluoroarsenate. The organic salt includes at least one selected from carboxylates, alkoxides, and aromatic salt compounds. Exemplary organic salts include lithium acetate, aluminum formate, magnesium acetate, aluminum isopropoxide, magnesium ethoxide, and lithium benzenesulfonate.

[0049] In some embodiments, the first coating layer 2 comprises a first doping element comprising at least one selected from N, P, B, S, O, F, Cl, Br, and I. The presence of the first doping element is understood to stabilize the SEI interface and inhibit irreversible expansion of the material.

[0050] In some embodiments, the content of the first doping element in the first coating layer 2 is 0.01% to 5%. Exemplarily, the content of the first doping element in the first coating layer 2 may be 0.01%, 0.05%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, etc., and of course, may be other values ​​within the above range, but is not limited thereto.

[0051] In some embodiments, the material of the core 1 includes crystalline silicon and a silicide. Specifically, the silicide includes at least one selected from silicate, silicon oxide, silicon phosphate, silicon carbide, silicon nitride, and silicon alloy.

[0052] In the present application, silicon oxide is a silicon-oxygen complex containing oxygen atoms and silicon atoms, with the molar ratio of oxygen atoms to silicon atoms being 0.5 to 2. It is usually represented by the general formula SiO x (0.5≦x≦2) and may be a material in which silicon particles are dispersed in SiO2, or a material having a tetrahedral structural unit in which the silicon atom is located at the center of the tetrahedral structural unit and the silicon atom and oxygen atom are located at the four vertices of the tetrahedral structural unit.

[0053] In some embodiments, the content of the metal element in Core 1 is 0% to 15%, and the metal element includes at least one selected from lithium, sodium, magnesium, aluminum, copper, titanium, boron, beryllium, calcium, vanadium, chromium, lanthanum, and selenium. Exemplarily, the content of the metal element in Core 1 may be, but is not limited to, 0%, 3%, 5%, 8%, 10%, 12%, 15%, etc., and may of course be other values ​​within the above range.

[0054] In some embodiments, as shown in FIG. 3 , the negative electrode material further includes a second coating layer 3 disposed between the core 1 and the first coating layer 2. The second coating layer 3 comprises a salt. That is, the coating layer of the present application may have a two-layer structure, formed by sequentially coating the surface of the core 1 with the second coating layer 3 and the first coating layer 2. The salt in the second coating layer 3 primarily functions as a fiber additive, controlling the growth of the fiber material. Specifically, it acts as a crystal nucleus to control the density, length, and diameter of the fiber material. By controlling the fiber material (length and diameter), a three-dimensional network mass transport system is established, creating dense, network-like fast ion transport channels. This significantly improves the low-temperature ion transport efficiency of the negative electrode material, reduces ion diffusion paths, realizes low-temperature, fast ion conduction, and improves the rate and low-temperature performance of the negative electrode material. In particular, selecting an inorganic salt as the salt is advantageous for controlling inorganic products in the SEI layer formed on the surface of the negative electrode material during cycling of the prepared battery, stabilizing the SEI layer interface, and improving the material's cycling performance.

[0055] In some embodiments, the second coating layer 3 is provided on the area of ​​the core surface of the negative electrode material that is not covered with the first coating layer 2 .

[0056] In some embodiments, the fibrous material 4 is also distributed in the second coating layer 3 .

[0057] In some embodiments, when the first coating layer 2 is a carbon layer, the thickness of the first coating layer 2 is 0.01 μm to 1 μm. Specifically, the thickness of the first coating layer 2 may be, for example, 0.01 μm, 0.05 μm, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, etc., and of course, may be other values ​​within the above range, but is not limited to these. Preferably, the thickness of the first coating layer 2 is 0.1 μm to 0.5 μm.

[0058] In some embodiments, when the first coating layer 2 is a composite coating layer containing a carbon material and a salt substance, the thickness of the first coating layer 2 is 0.1 μm to 1.2 μm. Specifically, the thickness of the first coating layer 2 may be, for example, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.2 μm, etc., and of course, may be other values ​​within the above range, but is not limited to these.

[0059] In some embodiments, the thickness of the second coating layer 3 is 0 μm to 1 μm. Specifically, the thickness of the second coating layer 3 may be, for example, 0 μm, 0.05 μm, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, etc., and of course, may be other values ​​within the above range, but is not limited to these. Preferably, the thickness of the second coating layer 3 is 0.05 μm to 0.2 μm.

[0060] In some embodiments, the salt content in the negative electrode material is 0 wt% to 3.0 wt%. For example, the salt content in the negative electrode material may be 0 wt%, 0.5 wt%, 1.0 wt%, 1.5 wt%, 2.0 wt%, 2.5 wt%, 3.0 wt%, etc., and may of course be other values ​​within the above range, but is not limited thereto.

[0061] In some embodiments, the carbon content of the negative electrode material is 0.5 wt% to 10 wt%. Exemplary values ​​include 0.5 wt%, 1 wt%, 3 wt%, 5 wt%, 7 wt%, 9 wt%, and 10 wt%, and may be other values ​​within the above ranges. Preferably, the mass ratio of carbon to the negative electrode material is 2.5 wt% to 6 wt%.

[0062] In some embodiments, the median diameter D of the negative electrode material 50is 2.0 μm to 10.0 μm. Specifically, the median diameter of the negative electrode material may be 2.0 μm, 3.0 μm, 4.0 μm, 5.0 μm, 6.0 μm, 7.0 μm, 8.0 μm, 9.0 μm, 10.0 μm, etc., and of course may be other values ​​within the above range, but is not limited to these. Preferably, the median diameter of the negative electrode material is 4.0 μm to 8.0 μm.

[0063] In some embodiments, the negative electrode material has a particle size D 10 Specifically, the D of the negative electrode material is 10 may be 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, etc., and of course may be other values ​​within the above range, but are not limited to these.

[0064] In some embodiments, the powder conductivity of the negative electrode material is 0.01 S / cm to 500 S / cm. Exemplarily, the powder conductivity of the negative electrode material may be, but is not limited to, 0.01 S / cm, 0.1 S / cm, 1 S / cm, 5 S / cm, 10 S / cm, 30 S / cm, 50 S / cm, 100 S / cm, 150 S / cm, 200 S / cm, 300 S / cm, 400 S / cm, and 500 S / cm, etc., and of course, other values ​​within the above ranges may also be used.

[0065] In some embodiments, the silicon / oxygen ratio (Si / O) of the negative electrode material is 0.5 to 3.0. Exemplarily, the silicon / oxygen ratio (Si / O) of the negative electrode material may be, but is not limited to, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, etc., and may of course be other values ​​within the above range.

[0066] In some embodiments, the porosity of the negative electrode material is 0.5% to 15%. For example, the porosity of the negative electrode material may be 0.5%, 1%, 3%, 5%, 8%, 10%, 12%, 15%, etc., and of course, other values ​​within the above range may also be used, but are not limited to these. It is understood that the presence of the fiber material 4 provides a certain amount of voids between the core 1 and the coating layer and within the coating layer, which can improve the blister resistance of the negative electrode material to some extent.

[0067] As shown in FIG. 4, the present application further provides a method for preparing a negative electrode material, comprising: performing a first heat treatment on a mixture containing a silicon-oxygen raw material and at least two salt substances under a sealed condition to obtain a first precursor; and mixing the first precursor with a carbon source and then performing a second heat treatment to obtain a negative electrode material.

[0068] In the above technical solution, the present application performs a first heat treatment on a mixture containing a silicon / oxygen source and at least two salts in a sealed environment. During the first heat treatment, the pressure in the sealed environment increases, causing the salts to form a liquid molten salt mixture. After mixing the first precursor with a carbon source, a second heat treatment is performed, causing the carbon source to form a carbon layer that coats the surface of the silicon / oxygen source, thereby increasing the conductive contact area of ​​the anode material and improving its conductivity. At the same time, some of the carbon grows into carbonaceous fibers in the presence of the molten salt mixture, extending to the surface of the carbon layer. The presence of the fibers on the surface of the carbon layer improves the mass transport and charge transport capabilities of the anode material, thereby improving the rate performance and initial efficiency of the anode material. The preparation process of the present application is simple and suitable for large-scale industrialization.

[0069] The preparation method of the present invention will be specifically described below with reference to examples.

[0070] Step S100: A mixture containing a silicon and oxygen raw material and at least two kinds of salt substances is subjected to a first heat treatment to form the salt substances into a molten salt, thereby obtaining a first precursor. Specifically, a silicon / oxygen raw material and at least two salt substances are mixed to obtain a mixture, and the mixture is subjected to a first heat treatment to obtain a first precursor.

[0071] During this process, at least two salts can form a liquid mixed salt molten system during the first heat treatment. The liquid mixed salt molten system further forms a molten salt under the conditions of the first heat treatment, which coats the surface of the silicon / oxygen material to form a uniformly coated skeletal layer. This skeletal coating layer can facilitate SEI deposition and form a rigid layer, thereby stabilizing the SEI interface and suppressing irreversible expansion of the material, thereby improving the cycle capacity retention and cycle performance of the anode material. It is understood that the molten salt can be distributed between the silicon / oxygen raw material and the carbon layer to form a second coating layer 3 and / or distributed in the carbon layer to form a composite coating layer. Finally, during the first heat treatment, some of the salts can enter the core 1 to form doping elements, improving the conductivity of the material.

[0072] In some embodiments, the first heat treatment is performed under sealed conditions, and the pressure in the sealed environment increases with the heat treatment of the first heat treatment, which is favorable for the formation of molten salts and broadens the selectivity of salt substances, and salt substances that are easy to sublimate can also be applied to the present application.

[0073] In some embodiments, the silicon oxygen source is silicon oxide, SiO x (0.05≦x≦2) The raw material may further include silicon element and silicates, and silicates include lithium silicate, magnesium silicate, aluminum silicate, binary silicates (e.g., lithium aluminum silicate, lithium magnesium silicate), and the like.

[0074] In some embodiments, the salt substance includes an inorganic salt and an organic salt, which has excellent chemical stability, compactness, and adhesion, and can form a rigid skeleton, making it easy for the SEI layer to adhere to the material surface.

[0075] In some embodiments, the inorganic salt comprises at least one selected from fluorides, lithium salts, carbonates, silicates, phosphates, nitrates, titanates, thioates, and vanadates. Exemplary inorganic salts include lithium fluoride, lithium thiophosphate, lithium vanadate, lithium titanate, lithium carbonate, lithium phosphate, lithium silicate, lithium nitrate, aluminum fluoride, aluminum carbonate, sodium carbonate, potassium carbonate, magnesium carbonate, calcium carbonate, lithium sodium carbonate, lithium potassium carbonate, potassium fluoride, sodium fluoride, lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium hexafluoroarsenate.

[0076] In some embodiments, the organic salt comprises at least one selected from the group consisting of carboxylates, alkoxides, and aromatic salts. Exemplary organic salts include lithium acetate, aluminum formate, magnesium acetate, aluminum isopropoxide, magnesium ethoxide, and lithium benzenesulfonate.

[0077] In some embodiments, the salt content in the first precursor is 1.0 wt% to 20 wt%. Specifically, the salt content in the first precursor may be, for example, 1 wt%, 5 wt%, 10 wt%, 15 wt%, or 20 wt%, and may be other values ​​within the above range, but is not limited thereto. If the salt content in the first precursor exceeds 20 wt%, the capacity of the material decreases. If the salt content in the first precursor is less than 1 wt%, the amount of molten salt system formed is too small, resulting in a small amount of fiber material 4, or even failure to produce the fiber material 4.

[0078] In some embodiments, the mixing is performed in a protective atmosphere comprising at least one selected from helium gas and argon gas.

[0079] In some embodiments, the mixing time is 30 minutes to 360 minutes. Exemplary mixing times include 30 minutes, 60 minutes, 90 minutes, 180 minutes, 210 minutes, 240 minutes, 280 minutes, 300 minutes, 350 minutes, and 360 minutes, and may of course be other values ​​within the above ranges, but are not limited thereto.

[0080] In some embodiments, the mixing is carried out under stirring conditions, and the mixing device may be, for example, a stirrer or a ball mill.

[0081] In some embodiments, the mixture containing the silicon and oxygen source and the salt material further contains a metal source, i.e., in step S100, the silicon and oxygen source, the metal source, and the salt material are mixed to obtain a mixture, and the mixture is subjected to a first heat treatment to obtain a first precursor.

[0082] In the first heat treatment process, the presence of the molten salt system consisting of the above mixed salts can improve the activity of the doping metal source and increase the doping depth of the metal source, causing the silicon-oxygen raw material, molten salt system, and metal source to form a eutectic activation, and the silicon-oxygen raw material forms silicon-based fibers (silicon fibers and silicate fibers) through the catalytic action of the doping metal source, thereby improving the conductivity of the negative electrode material and improving the lithium conduction ability of the negative electrode material, allowing the negative electrode material to accept electrons and lithium ions at a high speed, and improving the rate performance and initial efficiency of the negative electrode material.

[0083] In some embodiments, the metal source includes at least one selected from metallic lithium, metallic magnesium, metallic sodium, metallic calcium, metallic copper, and metallic titanium. The metal source may further include an active hydride of at least one selected from a lithium source, a magnesium source, a sodium source, a calcium source, a copper source, and a titanium source. Specifically, the metal source may be, for example, lithium, magnesium, aluminum, lithium hydride, aluminum hydride, magnesium hydride, or the like.

[0084] In some embodiments, the content of the metal source in the first precursor is 0 wt% to 15 wt%. Specifically, the content of the metal source in the first precursor may be, for example, 0 wt%, 3 wt%, 5 wt%, 7 wt%, 10 wt%, 12 wt%, 15 wt%, etc., and of course, other values ​​within the above range may also be used, but are not limited to these. If the content of the metal source in the first precursor exceeds 15 wt%, the conductivity of the material will be poor and the capacity will be reduced.

[0085] In some embodiments, the first heat treatment apparatus is a high-pressure reactor.

[0086] In some embodiments, the temperature of the first heat treatment is 400°C to 1200°C. Specifically, the temperature of the first heat treatment may be, for example, but not limited to, 400°C, 500°C, 600°C, 700°C, 800°C, 900°C, 1000°C, 1100°C, and 1200°C, and may also be other values ​​within the above range. The above heat treatment temperature range is advantageous for improving the capacity and cycle performance of the material.

[0087] In some embodiments, the incubation time for the first heat treatment is 3 hours to 24 hours. Specifically, the incubation time for the first heat treatment may be, for example, 3 hours, 5 hours, 8 hours, 10 hours, 15 hours, 18 hours, 20 hours, 24 hours, etc., and may of course be other values ​​within the above range, but is not limited to these.

[0088] In some embodiments, the temperature rise rate in the first heat treatment is 1° C. / min to 10° C. / min. Specifically, the temperature rise rate in the first heat treatment may be, for example, 1° C. / min, 2° C. / min, 3° C. / min, 4° C. / min, 5° C. / min, 6° C. / min, 7° C. / min, 8° C. / min, 9° C. / min, 10° C. / min, etc., and may of course be other values ​​within the above range, but is not limited to these.

[0089] In some embodiments, the pressure of the first heat treatment is 0.1 MPa to 0.3 MPa, specifically, the pressure of the first heat treatment is 0.1 MPa, 0.15 MPa, 0.2 MPa, 0.25 MPa, 0.3 MPa, etc., and of course, other values ​​within the above range may also be used, and are not limited to these.

[0090] In some embodiments, the first heat treatment is performed in a first protective atmosphere, and the first protective atmosphere includes at least one selected from nitrogen gas, helium gas, and argon gas.

[0091] In step S200, the first precursor and the carbon source are mixed together, and then a second heat treatment is performed to obtain the negative electrode material.

[0092] In this process, after mixing the first precursor and the carbon source, a second heat treatment is carried out. Due to the catalytic action of the molten salt material skeleton on the surface of the first precursor, a portion of the carbon source generates carbon-based fibers, which grow to the surface of the material, and silicon-based fibers also grow to the surface of the material. In other words, both silicon-based fibers and carbon-based fibers are distributed on the surface of the material. The presence of the above-mentioned fiber material 4 can improve the conductivity of the negative electrode material and the rate performance of the material.

[0093] It is understood that after the first and second heat treatments, a composite coating layer containing a mixture of salts and coating materials, or a two-layer coating layer, can be obtained. In the two-layer coating layer, the second coating layer 3 located in the inner layer contains salts, and the first coating layer 2 located in the outer layer contains a carbon material. Furthermore, when forming a two-layer coating layer, during the second heat treatment, some of the salt-containing material penetrates into the outer coating layer (i.e., the carbon layer) to form a doping element, which stabilizes the SEI interface and suppresses irreversible expansion of the material. Here, the doping element includes at least one element selected from N, P, B, S, O, F, Cl, Br, and I.

[0094] In some embodiments, the carbon source comprises at least one selected from a solid carbon source and a gaseous carbon source. The solid carbon source comprises at least one selected from pitch, epoxy resin, and phenolic resin. The gaseous carbon source comprises at least one selected from methane, acetylene, ethylene, and propane.

[0095] In some embodiments, when the carbon source is a gaseous carbon source, the feed flow rate of the gaseous carbon source is 0.5 L / min to 3 L / min. Specifically, the feed flow rate of the gaseous carbon source may be, for example, 0.5 L / min, 1 L / min, 1.5 L / min, 2 L / min, 2.5 L / min, 3 L / min, etc., and may of course be other values ​​within the above range, but is not limited thereto.

[0096] In some embodiments, when the carbon source is a gaseous carbon source, the temperature of the second heat treatment is 500° C. to 1000° C. Specifically, the temperature of the second heat treatment may be, for example, but not limited to, 500° C., 600° C., 700° C., 800° C., 900° C., and 1000° C., and may of course be other values ​​within the above range.

[0097] In some embodiments, when the carbon source is a gaseous carbon source, the incubation time for the second heat treatment is 0.5 to 5 hours. Specifically, the incubation time for the first heat treatment may be, for example, 0.5 hours, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, etc., and may of course be other values ​​within the above range, but is not limited to these.

[0098] In some embodiments, when the carbon source is a solid carbon source, the mass ratio of the first precursor to the carbon source is 1:(0.01-0.1). Exemplary mass ratios of the first precursor to the carbon source may be, but are not limited to, 1:0.01, 1:0.05, 1:0.1, 1:0.5, 1:0.8, and 1:0.1, and may be other values ​​within the above range.

[0099] In some embodiments, when the carbon source is a solid carbon source, the temperature of the second heat treatment is 400° C. to 800° C. Specifically, the temperature of the second heat treatment may be, for example, 400° C., 500° C., 600° C., 700° C., 800° C., etc., and of course, may be other values ​​within the above range, but is not limited thereto.

[0100] In some embodiments, when the carbon source is a solid carbon source, the incubation time for the second heat treatment is 0.5 to 10 hours. Specifically, the incubation time for the first heat treatment may be, for example, 0.5 hours, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, etc., and may of course be other values ​​within the above range, but is not limited to these.

[0101] In some embodiments, when the carbon source is a solid carbon source, the second heat treatment is performed in a second protective atmosphere, and the second protective atmosphere comprises at least one selected from nitrogen gas, helium gas, and argon gas.

[0102] In some embodiments, the temperature rise rate of the second heat treatment is 1° C. / min to 10° C. / min. Exemplary rates of the second heat treatment may be, but are not limited to, 1° C. / min, 2° C. / min, 3° C. / min, 5° C. / min, 8° C. / min, 10° C. / min, etc., and may of course be other values ​​within the above range.

[0103] In some embodiments, the preparation method further comprises, after the second heat treatment, washing the material obtained by the second heat treatment with water and drying the material, which removes excess water-soluble salts in the material, increases the silicon-oxygen ratio of the material, and improves the capacity of the negative electrode material.

[0104] In some embodiments, the method further comprises the step of immersing the product obtained by the second heat treatment in water and filtering the product to thoroughly dissolve the salts before washing with water, and the step of further washing the solid obtained by filtration with water.

[0105] In some embodiments, the immersion time is 10 minutes to 60 minutes. Specifically, the immersion time may be, for example, 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, 60 minutes, etc., and may of course be other values ​​within the above range, but is not limited to these.

[0106] In some embodiments, the immersion is performed under stirring conditions, and the stirring speed is 100 r / min to 500 r / min. Specifically, the stirring speed may be, for example, but not limited to, 100 r / min, 150 r / min, 200 r / min, 250 r / min, 300 r / min, 350 r / min, 400 r / min, and 500 r / min, and may of course be other values ​​within the above range.

[0107] In some embodiments, the soaking temperature is 25° C. to 80° C. Specifically, the soaking temperature may be, but is not limited to, 25° C., 30° C., 40° C., 50° C., 60° C., 70° C., and 80° C., and may of course be other values ​​within the above range.

[0108] In some embodiments, the water washing time is 30 to 90 minutes. Specifically, the water washing time may be, for example, 30 minutes, 40 minutes, 50 minutes, 60 minutes, 70 minutes, 80 minutes, 90 minutes, etc., and may of course be other values ​​within the above range, but is not limited to these.

[0109] In some embodiments, the flow rate of the water wash is 5 L / min to 20 L / min, specifically, but not limited to, 5 L / min, 10 L / min, 15 L / min, 20 L / min, etc., and may of course be other values ​​within the above range.

[0110] In the process of preparing an anode material, the present application provides a method for adding a salt and a metal source to catalyze the growth of a fibrous material on the core and / or carbon material, wherein the metal source is used as a catalyst to catalyze the core in a molten salt system containing the salt to produce silicon-based fibers, which are radially distributed within the core and coating layer and primarily distributed on the surface of the anode material. The carbon material can also be catalyzed in a molten salt system containing the salt to produce carbon-based fibers, which are distributed within and on the surface of the coating layer.

[0111] The present application further provides a lithium ion battery, which includes the above-described negative electrode material.

[0112] The present invention will be further described below with reference to specific examples. [Example]

[0113] Example 1 (1) 900 g of silicon monoxide, 80 g of lithium hydride, 7.5 g of lithium fluoride, 7.5 g of lithium carbonate, and 5 g of lithium phosphate were weighed, and the above materials were dry-blended in a reaction vessel in an argon atmosphere for 30 minutes at a stirring speed of 500 r / min. (2) The materials mixed in step (1) are transferred to a high-pressure reactor, and the temperature is raised to 650°C at 10°C / min in an argon atmosphere, after which the reaction is carried out for 10 hours, while the pressure inside the reactor is maintained at normal pressure (approximately 0.1 MPa). (3) The material obtained in step (2) is subjected to chemical vapor deposition to form a carbon coating layer. In the preparation process, the carbon source is methane, the methane feed rate is 2 L / min, the temperature is 800 °C, and the deposition time is 0.5 hours. (4) The material obtained in step (3) is immersed in 5 kg of deionized water and stirred in a water bath at 80°C for 1 hour at a speed of 200 r / min, and then transferred to a centrifuge. The washing time by centrifugation is 30 minutes, and the flow rate of deionized water during washing is 20 L / min. After washing is completed, the centrifugation is continued for 120 minutes. After completion of centrifugation, the material is dried to obtain a negative electrode material. The SEM image of the negative electrode material prepared in this example is shown in Figure 5(a). The negative electrode material prepared in this example includes silicon monoxide, a salt coating layer and a carbon layer, which coat the surface of the silicon monoxide in that order. The salt coating layer is a deposit of a solid solution of lithium fluoride, lithium carbonate, and lithium phosphate. Carbon fibers, silicon fibers, and silicate fibers are distributed on the surface of the carbon layer, with the carbon fiber being the main component.

[0114] Example 2 (1) Weigh out 900 g of silicon monoxide, 80 g of metallic aluminum powder, 5 g of lithium fluoride, 5 g of lithium carbonate, 5 g of aluminum fluoride, and 5 g of aluminum carbonate, and dry blend the above materials in a reaction vessel for 30 minutes under an argon atmosphere at a stirring speed of 500 r / min. (2) The materials mixed in step (1) are transferred to a high-pressure reactor, heated to 900°C at a rate of 10°C / min under an argon atmosphere, and then reacted for 10 hours, while the pressure inside the reactor is maintained at normal pressure (approximately 0.2 MPa). (3) The calcined product obtained in step (2) is subjected to chemical vapor deposition to form a carbon coating layer. In the preparation process, the carbon source is methane, the methane feed rate is 2 L / min, the temperature is 800°C, and the deposition time is 0.5 hours. (4) The coated product obtained in step (3) is immersed in 5 kg of deionized water and stirred in a water bath at 80°C at a speed of 200 r / min for 1 hour, and then transferred to a centrifuge. The washing time by centrifugation is 30 minutes, and the flow rate of deionized water during washing is 20 L / min. After washing is completed, the centrifugation is continued for 120 minutes. After completion of centrifugation, the product is dried to obtain a negative electrode material. The SEM image of the negative electrode material prepared in this example is shown in Figure 5(b). The negative electrode material prepared in this example includes a silicon monoxide core and a composite coating layer of salts and amorphous carbon that coats the surface of the silicon monoxide core. The salts are a fused deposit of lithium fluoride, aluminum fluoride, lithium carbonate, and aluminum carbonate. As shown in Figure 5(b), carbon fibers, silicon fibers, and silicate fibers are distributed on the surface of the composite coating layer, with silicon fibers being the main component.

[0115] Example 3 (1) 900 g of silicon monoxide, 80 g of metallic magnesium powder, 5 g of lithium fluoride, 5 g of lithium carbonate, 5 g of magnesium fluoride, and 5 g of magnesium carbonate were weighed, and the above materials were dry-blended in a reaction vessel for 30 minutes in an argon atmosphere at a stirring speed of 500 r / min. (2) The materials mixed in step (1) were transferred to a high-pressure reactor, and the temperature was raised to 800°C at 10°C / min in an argon atmosphere, after which the reaction was carried out for 10 hours, while the pressure inside the reactor was maintained at normal pressure (approximately 0.15 MPa). (3) The calcined product obtained in step (2) is subjected to chemical vapor deposition to form a carbon coating layer. In the preparation process, the carbon source is methane, the methane feed rate is 2 L / min, the temperature is 800°C, and the deposition time is 0.5 hours. (4) The calcined product obtained in step (3) is immersed in 5 kg of deionized water and stirred in a water bath at 80°C at a speed of 200 r / min for 1 hour, and then transferred to a centrifuge. The washing time by centrifugation is 30 minutes, and the flow rate of deionized water during washing is 20 L / min. After washing is completed, the centrifugation is continued for 120 minutes. After completion of the centrifugation, the product is dried to obtain a negative electrode material. The SEM image of the negative electrode material prepared in this example is shown in Figure 5(c). The negative electrode material prepared in this example includes a silicon monoxide core and a composite coating layer of salts and amorphous carbon that coats the surface of the silicon monoxide core. The salts are deposits of a solid solution of lithium fluoride, magnesium fluoride, lithium carbonate, and magnesium carbonate. As shown in Figure 5(c), carbon fibers, silicon fibers, and silicate fibers are distributed on the surface of the composite coating layer, and the composite coating layer mainly consists of silicate fibers (magnesium silicate and lithium silicate fibers).

[0116] Example 4 (1) Weigh out 900 g of silicon monoxide, 40 g of metallic lithium, 40 g of metallic aluminum, 5 g of lithium fluoride, 5 g of lithium titanate, 5 g of aluminum fluoride, and 5 g of aluminum carbonate, and dry blend the above materials in an argon atmosphere in a reaction vessel for 30 minutes at a stirring speed of 500 r / min. (2) The materials mixed in step (1) are transferred to a high-pressure reactor, and the temperature is raised to 1000°C at 10°C / min in an argon atmosphere. After that, the reaction is carried out for 10 hours, and the pressure inside the reactor is maintained at normal pressure (approximately 0.1 MPa). (3) The calcined product obtained in step (2) is subjected to chemical vapor deposition to form a carbon coating layer. In the preparation process, the carbon source is methane, the methane feed rate is 2 L / min, the temperature is 800°C, and the deposition time is 0.5 hours. (4) The calcined product obtained in step (3) is immersed in 5 kg of deionized water and stirred in a water bath at 80°C at a speed of 200 r / min for 1 hour, and then transferred to a centrifuge. The washing time by centrifugation is 30 minutes, and the flow rate of deionized water during washing is 20 L / min. After washing is completed, the centrifugation is continued for 120 minutes. After completion of the centrifugation, the product is dried to obtain a negative electrode material. The negative electrode material prepared in this example includes a silicon monoxide core, a salt coating layer and a carbon layer, which coat the silicon monoxide core in order. The salt coating layer is made of a solid solution deposit of lithium fluoride, aluminum fluoride, lithium titanate, and aluminum carbonate. The surface of the carbon layer is distributed with carbon fibers, silicon fibers, and silicate fibers, with silicon fibers being the main component.

[0117] Example 5 The same procedure as in Example 1 was carried out, except that in step (1) the salt substances "7.5 g of lithium fluoride, 7.5 g of lithium carbonate, and 5 g of lithium phosphate" were replaced with "5 g of lithium titanate, 5 g of lithium carbonate, 5 g of lithium phosphate, and 5 g of lithium nitrate." The negative electrode material prepared in this example includes a silicon monoxide core and a carbon layer covering the surface of the silicon monoxide core. The molten salt is removed by washing with water in step (4). Carbon fibers, silicon fibers, and silicate fibers are distributed on the surface of the carbon layer, and the carbon fibers are mainly carbon fibers.

[0118] Example 6 (1) 900 g of silicon monoxide, 80 g of lithium hydride, 10 g of lithium fluoride, and 10 g of lithium carbonate were weighed, and the above materials were dry-blended in a reaction vessel in an argon atmosphere for 30 minutes at a stirring speed of 500 r / min. (2) The materials mixed in step (1) are transferred to a high-pressure reactor, and the temperature is raised to 650°C at 10°C / min in an argon atmosphere, after which the reaction is carried out for 10 hours, while the pressure inside the reactor is maintained at normal pressure (approximately 0.1 MPa). (3) The material obtained in step (2) is subjected to chemical vapor deposition to form a carbon coating layer. In the preparation process, the carbon source is methane, the methane feed rate is 2 L / min, the temperature is 800 °C, and the deposition time is 0.5 hours. (4) The material obtained in step (3) is immersed in 5 kg of deionized water and stirred in a water bath at 80°C for 1 hour at a speed of 200 r / min, and then transferred to a centrifuge. The washing time by centrifugation is 30 minutes, and the flow rate of deionized water during washing is 20 L / min. After washing is completed, the centrifugation is continued for 120 minutes. After completion of centrifugation, the material is dried to obtain a negative electrode material. The negative electrode material prepared in this example includes silicon monoxide, a salt coating layer and a carbon layer, which coat the surface of the silicon monoxide in that order. The salt coating layer is made of a solid solution deposit of lithium fluoride and lithium carbonate. Carbon fibers, silicon fibers, and silicate fibers are distributed on the surface of the carbon layer, with the carbon fiber being the main component.

[0119] Example 7 (1) 900 g of silicon monoxide, 80 g of aluminum powder, 7.5 g of lithium fluoride, 7.5 g of lithium carbonate, and 5 g of lithium phosphate were weighed, and the above materials were dry-blended in an argon atmosphere in a reaction vessel for 30 minutes at a stirring speed of 500 r / min. (2) The materials mixed in step (1) are transferred to a high-pressure reactor, and the temperature is raised to 650°C at 10°C / min in an argon atmosphere, after which the reaction is carried out for 10 hours, while the pressure inside the reactor is maintained at normal pressure (approximately 0.1 MPa). (3) The calcined product obtained in step (2) is subjected to chemical vapor deposition to obtain a carbon coating layer. In the preparation process, the carbon source is methane, the methane feed rate is 2 L / min, the temperature is 800°C, and the deposition time is 0.5 hours, resulting in a negative electrode material. (4) The calcined product obtained in step (3) was immersed in 5 kg of deionized water and stirred in a water bath at 80°C at a speed of 200 r / min for 1 hour, then transferred to a centrifuge. The centrifugation time was 30 min, and the flow rate of deionized water during the water washing was 20 L / min. After the water washing was completed, the centrifugation continued for 120 min. After the centrifugation was completed, the product was dried. The negative electrode material prepared in this example includes a silicon monoxide core and a composite coating layer of salts and amorphous carbon covering the surface of the silicon monoxide core. The salts are deposits of a solid solution of lithium fluoride, lithium carbonate, and lithium phosphate. Carbon fibers, silicon fibers, and silicate fibers are distributed on the surface of the composite coating layer, and the composite coating layer is mainly composed of silicon fibers and silicate fibers.

[0120] Example 8 (1) 980 g of silicon monoxide, 7.5 g of lithium fluoride, 7.5 g of lithium carbonate, and 5 g of lithium phosphate were weighed, and the above materials were dry-blended in a reaction vessel in an argon atmosphere for 30 minutes at a stirring speed of 500 r / min. (2) The materials mixed in step (1) are transferred to a high-pressure reactor, and the temperature is raised to 650°C at 10°C / min in an argon atmosphere. After that, the reaction is carried out for 10 hours, and the reactor is sealed and the pressure is maintained at 10 MPa. (3) The calcined product obtained in step (2) is subjected to chemical vapor deposition to obtain a carbon coating layer. In the preparation process, the carbon source is methane, the methane feed rate is 2 L / min, the temperature is 800 °C, and the deposition time is 0.5 h. (4) The calcined product obtained in step (3) is immersed in 5 kg of deionized water and stirred in a water bath at 80°C at a speed of 200 r / min for 1 hour, and then transferred to a centrifuge. The washing time by centrifugation is 30 minutes, and the flow rate of deionized water during washing is 20 L / min. After washing is completed, the centrifugation is continued for 120 minutes. After completion of the centrifugation, the product is dried to obtain a negative electrode material. The negative electrode material prepared in this example includes silicon monoxide, and a salt coating layer and a carbon layer that coat the surface of the silicon monoxide in that order. The salt coating layer is made of a deposit of a solid solution of lithium fluoride, lithium carbonate, and lithium phosphate, and carbon fibers are distributed on the surface of the carbon layer.

[0121] Comparative Example 1 (1) Weigh out 900 g of silicon monoxide and prepare a carbon coating layer by chemical vapor deposition. In the preparation process, the carbon source is methane, the methane feed rate is 2 L / min, the temperature is 800 °C, and the deposition time is 0.5 hours to obtain a negative electrode material. The negative electrode material prepared in this comparative example includes a silicon monoxide core and a carbon layer covering the surface of the silicon monoxide core. The surface of the carbon layer is smooth. The SEM image of the negative electrode material is shown in FIG. 5(d), which shows that the negative electrode material prepared in this comparative example does not include fibrous material.

[0122] Comparative Example 2 (1) 900 g of silicon monoxide and 80 g of lithium hydride were weighed out, and the above materials were dry-blended in a reaction vessel in an argon atmosphere for 30 minutes at a stirring speed of 500 r / min. (2) The materials mixed in step (1) are transferred to a high-pressure reactor, and the temperature is raised to 650°C at 10°C / min in an argon atmosphere. After that, the reactor is reacted for 10 hours, and the internal pressure is kept at normal pressure (approximately 0.1 MPa). (3) The calcined product obtained in step (3) is subjected to chemical vapor deposition to obtain a carbon coating layer. In the preparation process, the carbon source is methane, the methane feed rate is 2 L / min, the temperature is 800 °C, and the deposition time is 0.5 h. (4) The calcined product obtained in step (3) is immersed in 5 kg of deionized water and stirred in a water bath at 80°C at a speed of 200 r / min for 1 hour, and then transferred to a centrifuge. The washing time by centrifugation is 30 minutes, and the flow rate of deionized water during washing is 20 L / min. After washing is completed, the centrifugation is continued for 120 minutes. After completion of the centrifugation, the product is dried to obtain a negative electrode material. The negative electrode material prepared in this comparative example includes a silicon monoxide core and a carbon layer covering the surface of the silicon monoxide core. The surface of the carbon layer is smooth. The SEM image of the negative electrode material is shown in FIG. 5(e), which shows that the negative electrode material prepared in this comparative example does not include fibrous material.

[0123] Comparative Example 3 The procedure was the same as in Example 1, except that step (3) was not performed. The anode material prepared in this comparative example includes a silicon monoxide core and a coating layer covering the surface of the silicon monoxide core. The coating layer is made of a solid solution deposit of lithium fluoride, lithium carbonate, and lithium phosphate. The SEM image of this anode material is shown in Figure 5(f). A small amount of fibrous material, primarily silicon fiber, is distributed on the surface of the coating layer.

[0124] Comparative Example 4 The same procedure as in Example 1 was carried out except that "7.5 g of lithium fluoride, 7.5 g of lithium carbonate, and 5 g of lithium phosphate" as the salt substance in step (1) was replaced with "20 g of lithium carbonate." In step (2), the materials mixed in step (1) were transferred to a high-pressure reactor, heated to 1000°C at a rate of 10°C / min in an argon atmosphere, and then reacted for 10 hours, while allowing the pressure inside the sealed reactor to rise freely.

[0125] Performance Measurement (1) The specific capacity and initial charge / discharge coulombic efficiency of the negative electrode material were measured by assembling a button cell battery according to the equipment and method of BTRTC / ZY / 01-020 "Operational Protocol for Button Cell Battery Methods." The counter electrode was a lithium metal sheet, the separator was a 19.2mm diameter PP-PE-PP composite membrane, the electrolyte composition was EC / EMC / DMC=1 / 1 / 1, and the concentration of lithium salt (LiPF6) was 1.05mol / L. The measurement method was to use a button cell charge / discharge device to charge the battery at a constant current of 0.1C to 10mV, then charge it at a constant current of 0.02C to 5mV, and discharge it at a constant current of 0.1C to 1.5V. (2) In preparing a complete battery, lithium cobalt oxide was used as the positive electrode, and the negative electrode materials of Examples 1 to 8 and Comparative Examples 1 to 4 were used as the negative electrode of a lithium-ion battery. The electrolyte was 1 mol / L LiPF6 / EC+PC+DEC+EMC (volume ratio 1:0.3:1:1). The separator was a three-layer separator of PP / PE / PP with a thickness of 16 μm. A soft-pack battery of about 3 Ah was fabricated and used to measure the complete battery performance of the material. (3) In a half-cell 50-cycle test using a button battery charge / discharge device, in cycle 1, the battery was discharged at 0.1C to 0.01V, discharged at 0.01C in a stepwise decreasing manner to 0.01V, discharged at 0.01C to 0.005V, and charged at 0.1C to 1.5V. In cycle 2, the battery was discharged at 0.2C to 0.01V, discharged at 0.02C in a stepwise decreasing manner to 0.01V, discharged at 0.02C to 0.005V, and charged at 0.2C to 1.5V. In cycle 3, the battery was discharged at 0.5C to 0.01V, discharged at 0.05C in a stepwise decreasing manner to 0.01V, discharged at 0.05C to 0.005V, and charged at 0.5C to 1.5V. From cycle 4 to cycle 50, discharge at 1 C to 0.01 V, discharge at 0.1 C to 0.01 V with a stepwise decrease, discharge at 0.1 C to 0.005 V, and charge at 1 C to 1.5 V. In cycle 51, discharge at 0.1 C to 0.01 V, discharge at 0.01 C to 0.01 V with a stepwise decrease, discharge at 0.01 C to 0.01 V, and discharge at 0.01 C to 0.005 V. (4) In a complete battery rate performance test, the charge / discharge capacity at 0.5C is measured at an operating voltage of 2.75 to 4.2V, and then the charge / discharge capacity at 3C / 0.5C is measured. The capacities are compared to determine the capacity retention rate, which is the rate performance at 3C / 0.5C. (5) In the low-temperature performance test of the complete battery, charge and discharge are performed at low temperatures (-10°C and -20°C) at 2.75-4.2V and 0.2C, and the capacity retention rate is measured. (6) The thickness of the coating layer of the negative electrode material is measured by the SEM electron microscope test method. (7) Using a combination of a transmission electron microscope and a scanning electron microscope, measure the fiber diameter according to "GB / T 268260-2011 Method for Determining the Diameter of Carbon Nanotubes," and select the lower limit of the fiber diameter from the measurement results as the minimum fiber diameter. (8) The doping elements and their contents in the core and coating layers are measured using the ICP method. Approximately 0.5g of a battery silicon-based material sample is weighed out, placed in a platinum crucible, and baked at 750°C for 2 hours until the carbon element is completely sintered. 34mL of HNO and 6mL of HF are added. After the reaction between the mixed acid and the sample stabilizes, the platinum crucible is placed on a 350°C hot plate and heated until the hydrofluoric acid evaporates without producing white smoke. After the crucible cools, an additional 6mL of HCl is added and heated until the residue is completely dissolved. Finally, the mixture is transferred to a 100mL plastic measuring flask and the total content is measured using an ICP spectrometer. (9) In the powder conductivity test, the conductivity of the sample was measured using a fully automatic powder resistivity measurement system, and the measured value was the conductivity value when the sample pressure was 20KN. (10) In the particle size test, the material median diameter and D10 are measured using a Zetasizer.

[0126] The test results are shown in Tables 1 and 2.

[0127] Table 1. Parameter test results for negative electrode materials of each example and comparative example 1 [Table 1]

[0128] Table 1. Performance test results of negative electrode materials for each example and comparative example 2 [Table 2]

[0129] As shown in Tables 1 and 2, the anode materials prepared in Examples 1 to 8 of this application comprise a core and a coating layer covering at least the surface of the core. Fiber material is distributed on at least a portion of the surface of the coating layer. The presence of fiber material on the material surface, along with the fiber and anode material satisfying formula (I), results in favorable radial growth of the fiber material 4 in the anode material. The favorable radial growth of fiber material 4 effectively reduces charge transfer resistance due to lithium absorption, improves mass transfer efficiency, and allows for the formation of high-speed lithium absorption channels, favoring in-situ conduction between the material and the lithium source. This reduces interfacial inhibition, improves the lithium conductivity of the anode material, and allows the anode material to rapidly accept electrons and lithium ions, improving its conductivity and thereby improving its rate performance. At the same time, the core-shell structure of this anode material, combined with the carbon material as the coating layer, increases the conductive contact area of ​​the material, further improving the rate performance of the anode material.

[0130] In Figure 5, Figures 5(a), 5(b), 5(c), 5(d), 5(e), and 5(f) are surface SEM images of Examples 1, 2, 3, Comparative Examples 1, 2, and 3, respectively. Comparing the SEM images of Examples 1, 2, and 3 in Figure 5, the minimum diameter of the fiber material increases, primarily due to differences in the selection of the metal source and the silicate. The fiber material in Example 1 is primarily carbon fiber, while the fiber materials in Examples 2 and 3 include carbon fiber, silicon fiber, and silicate fiber. Comparing Examples 1, 2, and 3, it can be seen that the different metal sources and salt environments cause differences in the morphology of the resulting fibers. The surface SEM images of Comparative Examples 1 and 2 in Figure 5 show that the surfaces of the negative electrode materials are smooth and free of fiber growth. The surface SEM image of Comparative Example 3 shows that the surface is rough and small fibers are growing on the surface.

[0131] The negative electrode material prepared in Example 5 can still exhibit high mass and charge transfer performance due to the carbon fiber-carbon coating-core structure in a molten salt system without salt deposition.

[0132] Figure 6 compares the low-temperature capacity test performance of complete batteries prepared with the anode materials of Examples 1-8 and Comparative Examples 1-4. The low-temperature capacity retention rates of the anode materials of Examples 1, 2, 3, 4, and 5, which have a fibrous structure, are all higher than those of the other Examples and Comparative Examples. This indicates that the combination of a fibrous material and a core can improve the low-temperature and rate performance of the anode material. This is because the nanofibers of the material can establish high-speed mass and charge transfer channels, effectively alleviating the charge transfer resistance caused by low powder conductivity, improving mass transfer efficiency, and reducing interfacial charge transfer resistance, thereby improving the low-temperature performance of the anode material. Furthermore, the anode material containing a fibrous material has a larger mass and charge transfer region, a higher degree of elongation, and can effectively connect with the cell conductive network, improving the cycle performance of the anode material.

[0133] The negative electrode material prepared in Comparative Example 3 has fibrous material distributed on the surface of the material, but no coating layer on the surface of the material, so the performance of the negative electrode material is deteriorated.

[0134] As shown in Figures 7 and 8, Figure 7 is a fiber EDS diagram of the negative electrode material prepared in Example 2 of the present application, and Figure 8 is a fiber EDS diagram of the negative electrode material prepared in Comparative Example 4 of the present application. Analysis of the elemental proportions reveals that in Example 2, the fibers are primarily fibrous material, while in Comparative Example 4, they are primarily silicon fibers and silicate fibers. Because the doping source in Comparative Example 4 is different, the processing temperature increases, the fibers become thicker, and the ΔJ value, which is the relationship between fiber diameter, particle size of the negative electrode material, and electrical conductivity, does not satisfy the mathematical formula (I) disclosed herein, resulting in poor material performance. Comparing Example 2 and Comparative Example 4, it can be seen that an appropriate molten salt system on the surface can effectively reduce the processing temperature, which is beneficial to the generation of nanowire pipe diameters and reduces the generation of bulk.

[0135] As can be seen from Table 2, the negative electrode material prepared in the present application has a charging capacity of about 0.5C at room temperature for a typical negative electrode material, whereas the negative electrode active material of the lithium ion battery according to the embodiment of the present application can meet the usual needs for fast charging at room temperature at 3C and can maintain good performance even at low temperatures.

[0136] The above-described contents are merely preferred embodiments of the present application and are not intended to limit the present application, and those skilled in the art may have various modifications and variations to the present application. Any modifications, equivalent replacements, improvements, etc. made based on the ideas and principles of the present application shall be included within the scope of protection of the present application. [Explanation of symbols]

[0137] 1-core 2-First coating layer 3-Second coating layer 4-Fiber materials

Claims

1. A negative electrode material including a core and a first coating layer that coats at least a portion of a surface of the core, the core comprises a silicon-based material; the first coating layer contains a carbon material, a fibrous material is distributed on at least a portion of the surface of the first coating layer; The fiber material and the negative electrode material satisfy the mathematical formula of the following formula (I): [Equation 1] (In formula (I), D ｗｉｒｅ is the minimum fiber diameter (nm) of the fiber material, and D １０ is the particle size (nm) corresponding to when the cumulative particle size distribution number of the negative electrode material reaches 10%, and ρ is the powder conductivity (S / cm) of the negative electrode material.

2. The negative electrode material according to claim 1, having at least one selected from the following characteristics (1) to (7): (1) The fiber diameter of the fiber material is 2 nm to 200 nm. (2) The first coating layer also contains a fiber material. (3) The fiber material includes at least one selected from carbon-based fibers and silicon-based fibers. (4) The fiber material includes at least one selected from carbon-based fibers and silicon-based fibers, and the carbon-based fibers include at least one selected from carbon fibers, carbon nanotubes, and polymer fibers. (5) The fiber material includes at least one selected from carbon-based fibers and silicon-based fibers, and the silicon-based fibers include at least one selected from silicon fibers and silicate fibers. (6) The fiber material includes at least one selected from carbon-based fibers and silicon-based fibers, the carbon-based fibers include at least one selected from carbon fibers, carbon nanotubes, and polymer fibers, and the polymer fibers include at least one selected from polypropylene fibers, polyester-based fibers, polyamide-based fibers, polyacrylic-based fibers, polyenzyme-based fibers, and polyamine-based fibers. (7) The carbon material includes at least one selected from amorphous carbon, graphite, graphene, and diamond-like carbon.

3. The negative electrode material according to claim 1, having at least one selected from the following characteristics (1) to (4): (1) The first coating layer further contains a salt substance including an inorganic salt and an organic salt. (2) The first coating layer further contains a salt substance including an inorganic salt and an organic salt, and the inorganic salt includes at least one selected from fluorides, lithium salts, carbonates, silicates, phosphates, nitrates, titanates, thioates, and vanadates. (3) The first coating layer further contains a salt substance including an inorganic salt and an organic salt, and the organic salt contains at least one selected from a carboxylate, an alkoxide, and an aromatic salt compound. (4) The first coating layer further contains a salt substance, and the thickness of the first coating layer is 0.1 μm to 1.2 μm.

4. The negative electrode material according to claim 1, having at least one selected from the following characteristics (1) to (6): (1) The thickness of the first coating layer is 0.01 μm to 1 μm. (2) The first coating layer contains a first doping element including at least one element selected from N, P, B, S, O, F, Cl, Br, and I. (3) The first coating layer contains a first doping element, and the content of the first doping element in the first coating layer is 0.01% to 5%. (4) The core contains at least one selected from crystalline silicon and silicide. (5) The core includes at least one selected from crystalline silicon and a silicide, and the silicide includes at least one selected from silicate, silicon oxide, silicon phosphide, silicon carbide, silicon nitride, and a silicon alloy. (6) The content of metal elements in the core is 0 to 15 wt %, and the metal elements include at least one selected from lithium, sodium, magnesium, aluminum, copper, titanium, boron, beryllium, calcium, vanadium, chromium, lanthanum, and selenium.

5. 2. The negative electrode material according to claim 1, further comprising a second coating layer provided between the core and the first coating layer, and / or a second coating layer provided on an area of ​​the surface of the core that is not covered by the first coating layer.

6. The negative electrode material according to claim 5, wherein the second coating layer has at least one selected from the following characteristics (1) to (5): (1) The second coating layer contains a salt substance including an inorganic salt and an organic salt. (2) The second coating layer contains a salt substance including an inorganic salt and an organic salt, and the inorganic salt contains at least one selected from fluorides, lithium salts, carbonates, silicates, phosphates, nitrates, titanates, thioates, and vanadates. (3) The second coating layer contains a salt substance including an inorganic salt and an organic salt, and the organic salt contains at least one selected from a carboxylate, an alkoxide, and an aromatic salt compound. (4) The second coating layer contains a salt, and the content of the salt in the negative electrode material is 0.01 wt % to 3.0 wt %. (5) The thickness of the second coating layer is 0 μm to 1 μm.

7. The negative electrode material according to claim 1, having at least one selected from the following characteristics (1) to (7): (1) The negative electrode material contains a salt substance, and the mass ratio of the salt substance to the negative electrode material is 0 wt % to 3.0 wt %. (2) The carbon element content in the negative electrode material is 0.5 wt % to 10 wt %. (3) Median diameter D of the negative electrode material ５０ is 2.0 μm to 10.0 μm. (4) The particle diameter D at which the cumulative particle distribution of the negative electrode material becomes 10% １０ is 0.5 μm to 4 μm. (5) The powder conductivity of the negative electrode material is 0.01 S / cm to 500 S / cm. (6) The silicon-oxygen ratio of the negative electrode material is Si / O=0.5 to 3.

0. (7) The porosity of the negative electrode material is 0.5% to 15%.

8. A step of subjecting a mixture containing a silicon / oxygen raw material and at least two salt substances to a first heat treatment to form the salt substances into a molten salt, thereby obtaining a first precursor; a step of mixing the first precursor with a carbon source and then performing a second heat treatment to obtain a negative electrode material.

9. The method according to claim 8, wherein the mixture containing the silicon and oxygen source and at least two salt substances further contains a metal source.

10. The preparation method according to claim 9, which has at least one selected from the following characteristics (1) to (3): (1) The metal source includes at least one selected from metallic lithium, metallic magnesium, metallic sodium, metallic calcium, metallic copper, and metallic titanium. (2) The metal source includes an active hydride formed from at least one source selected from the group consisting of a lithium source, a magnesium source, a sodium source, a calcium source, a copper source, and a titanium source. (3) The content of the metal source in the first precursor is 0 wt % to 15 wt %.

11. The preparation method according to claim 8, which has at least one selected from the following characteristics (1) to (10): (1) The silicon-oxygen raw material is silicon oxide SiO ｘ (0.05≦x≦2). (2) The salt substances include inorganic salts and organic salts. (3) The salt substance includes an inorganic salt and an organic salt, and the inorganic salt includes at least one selected from fluorides, lithium salts, carbonates, silicates, phosphates, nitrates, titanates, thioates, and vanadates. (4) The salt substance includes an inorganic salt and an organic salt, and the organic salt includes at least one selected from a carboxylate, an alkoxide, and an aromatic salt compound. (5) The content of the salt substance in the first precursor is 1.0 wt % to 20 wt %. (6) The temperature of the first heat treatment is 400°C to 1200°C. (7) The temperature retention time for the first heat treatment is 3 to 24 hours. (8) The temperature rising rate in the first heat treatment is 1° C. / min to 10° C. / min. (9) The pressure of the first heat treatment is 0.1 MPa to 20 MPa. (10) The first heat treatment is performed in a first protective atmosphere, and the first protective atmosphere contains at least one gas selected from nitrogen gas, helium gas, and argon gas.

12. The preparation method according to claim 8, which has at least one selected from the following characteristics (1) to (6): (1) The carbon source includes at least one selected from a solid carbon source and a gaseous carbon source. (2) The carbon source includes at least one selected from a solid carbon source and a gaseous carbon source, and the solid carbon source includes at least one selected from pitch, an epoxy resin, and a phenol resin. (3) The carbon source includes at least one selected from a solid carbon source and a gaseous carbon source, and the gaseous carbon source includes at least one selected from methane, acetylene, ethylene, and propane. (4) The carbon source includes a gaseous carbon source, and the flow rate of the gaseous carbon source is 0.5 L / min to 3 L / min. (5) The carbon source includes a solid carbon source, and the mass ratio of the first precursor to the carbon source is 1:(0.01 to 0.1). (6) The carbon source includes a solid carbon source, the second heat treatment is performed in a second protective atmosphere, and the second protective atmosphere includes at least one gas selected from nitrogen gas, helium gas, and argon gas.

13. The preparation method according to claim 8, which has at least one selected from the following characteristics (1) to (3): (1) The temperature of the second heat treatment is 400°C to 1000°C. (2) The temperature retention time for the second heat treatment is 0.5 to 10 hours. (3) The temperature rising rate in the second heat treatment is 1° C. / min to 10° C. / min.

14. 9. The method of claim 8, further comprising the step of washing the material obtained by the second heat treatment with water and drying the material after the second heat treatment.

15. The preparation method according to claim 14, which has at least one selected from the following characteristics (1) to (5): (1) The time for the water washing is 30 to 90 minutes. (2) The flow rate of the water wash is 5 L / min to 20 L / min. (3) The drying method includes at least one method selected from air drying and vacuum drying. (4) The drying temperature is 25°C to 120°C. (5) The drying time is 3 to 48 hours.

16. 15. The method of claim 14, further comprising the step of soaking the material resulting from the second heat treatment in water and filtering it before washing the material resulting from the second heat treatment with water.

17. The preparation method according to claim 16, which has at least one selected from the following characteristics (1) to (3): (1) The immersion time is 10 to 60 minutes. (2) The immersion is carried out under stirring conditions, and the stirring speed is 100 r / min to 500 r / min. (3) The immersion is carried out under stirring conditions, and the temperature of the immersion solution is 25°C to 80°C.

18. A lithium ion battery comprising the negative electrode material according to any one of claims 1 to 7 or the negative electrode material prepared by the preparation method according to any one of claims 8 to 17.

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