Silicon-carbon negative electrode material, preparation method thereof, lithium ion battery and electric device

Abstract

The application provides a silicon-carbon negative electrode material, a preparation method thereof, a lithium ion battery and an electric device. The silicon-carbon negative electrode material comprises a core and a functional layer arranged on the surface of the core; the core comprises graphite with silicon carbide and silicon arranged on the surface; and the functional layer comprises amorphous carbon; the silicon-carbon negative electrode material satisfies: I a / I b = 0.02-0.10, I c / I a = 0.10-0.30; wherein, I a is the (111) crystal face peak intensity of silicon, I b is the (002) crystal face peak intensity of graphite, and I c is the (111) crystal face peak intensity of silicon carbide. The application improves the cycle stability of the lithium ion battery by coating the surface with amorphous carbon, and simultaneously regulates the material matching ratio of the 'graphite-silicon carbide-silicon' core material of the silicon-carbon negative electrode material, so that the cycle stability and rate performance of the prepared lithium ion battery can be significantly improved.

Description

Technical Field

[0001] This invention relates to the field of anode material technology, and in particular to a silicon-carbon anode material and its preparation method, lithium-ion batteries, and electrical devices. Background Technology

[0002] In recent years, with the rapid development of the new energy vehicle industry, people have placed higher demands on the energy density of rechargeable lithium-ion batteries. Traditional graphite anode materials have advantages such as strong electronic conductivity, excellent cycle performance, and economic and environmental friendliness, but their low theoretical specific capacity (372mAh / g) limits the further improvement of the energy density of lithium-ion batteries.

[0003] Among the few existing lithium-ion battery anode materials, silicon is the preferred choice for high-energy lithium-ion batteries due to its theoretical specific capacity of up to 4200 mAh / g. Adding a small amount of silicon to graphite can effectively improve the battery's energy density. However, silicon anode materials suffer from poor electronic conductivity and large volume expansion (approximately 300%), leading to silicon particle pulverization and failure, loss of electrical contact with the current collector, and continuous formation of a solid electrolyte film on the particle surface. These issues result in a decrease in battery capacity and severely impact the battery's rate performance and cycle performance.

[0004] Therefore, it is necessary to further optimize the anode materials for lithium-ion batteries and provide a silicon-carbon anode material for lithium-ion batteries with excellent cycle performance and high discharge rate performance. Summary of the Invention

[0005] The purpose of this invention is to address the issue that the cycle stability and rate performance of existing lithium-ion batteries need further improvement, and to provide a silicon-carbon anode material for lithium-ion batteries with excellent cycle performance and high discharge rate performance. This invention improves the cycle stability of lithium-ion batteries by coating the surface with amorphous carbon, and simultaneously enhances the structural stability of the anode material by controlling the material ratio of the "graphite-silicon carbide-silicon" core material. This also improves the capacity utilization of the anode material, significantly improving the cycle stability and rate performance of the prepared lithium-ion batteries.

[0006] In a first aspect, the present invention provides a silicon-carbon anode material, the silicon-carbon anode material comprising a core and a functional layer coated on the surface of the core: the core comprises graphite having silicon carbide and silicon disposed on its surface, and the functional layer comprises amorphous carbon;

[0007] The silicon-carbon anode material satisfies: I a / I b =0.02~0.10, I c / I a =0.10~0.30;

[0008] Among them, I a I represents the peak intensity of the (111) crystal plane of silicon. b I represents the peak intensity of the (002) crystal plane of graphite. c The peak intensity of the (111) crystal plane of silicon carbide.

[0009] As an embodiment of the present invention, in the silicon-carbon anode material, I a / I b =0.04~0.08.

[0010] As an embodiment of the present invention, in the silicon-carbon anode material, I c / I a =0.15~0.25.

[0011] As an embodiment of the present invention, in the silicon-carbon anode material, the weight ratio of graphite, silicon carbide and silicon is 1:(0.9-1.8):(0.1-0.2).

[0012] As an embodiment of the present invention, the specific surface area of ​​the silicon-carbon anode material is 1-3 m². 2 / g.

[0013] As an embodiment of the present invention, the powder compaction density of the silicon-carbon anode material under 3T pressure is 1.5–2.0 g / cm³. 3 .

[0014] As an embodiment of the present invention, the powder resistivity of the silicon-carbon anode material under 2T pressure is 0.003~0.005Ω*cm.

[0015] As an embodiment of the present invention, the D of the silicon-carbon anode material V50 The diameter is 5–25 μm, D v50 This refers to the particle size corresponding to a cumulative volume percentage of 50% for the silicon-carbon anode material.

[0016] As an embodiment of the present invention, the thickness of the functional layer is 10-80 nm.

[0017] As an embodiment of the present invention, the thickness of the functional layer is 30-70 nm.

[0018] A second aspect of the present invention provides a method for preparing the silicon-carbon anode material, comprising the following steps:

[0019] S1. After mixing graphite and silicon, silicon carbide and silicon are embedded into the graphite surface through a melting reaction in an inert atmosphere;

[0020] S2. The product obtained in step S1 and the precursor of amorphous carbon are mixed and then carbonized in an inert atmosphere to obtain the silicon-carbon anode material.

[0021] As an embodiment of the present invention, the specific melting process in step S1 is as follows: the temperature is increased to 1500-1600°C at a heating rate of 1-10°C / min, held at the temperature for 1-3 hours, and then cooled to 20-30°C at a rate of 10-20°C / min.

[0022] As an embodiment of the present invention, the specific process of carbonization treatment in step S2 is as follows: heating to 800-1000°C at a heating rate of 1-10°C, holding at that temperature for 1-3 hours, and then cooling naturally.

[0023] As an embodiment of the present invention, the precursor of amorphous carbon includes at least one of glucose, sucrose, soluble starch, cyclodextrin, pitch, phenolic resin, epoxy resin, carboxymethyl cellulose, and citric acid.

[0024] A third aspect of the present invention provides a lithium-ion battery, comprising a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode film disposed on at least one side of the negative electrode current collector, the negative electrode film comprising the above-described silicon-carbon negative electrode material or a silicon-carbon negative electrode material prepared by the above-described preparation method.

[0025] A fourth aspect of the present invention provides an electrical device including the lithium-ion battery.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] This invention improves the cycle stability of lithium-ion batteries by coating the surface with amorphous carbon. At the same time, it controls the material ratio of the "graphite-silicon carbide-silicon" core material of the silicon-carbon anode material to further improve the structural stability of the anode material and enhance its capacity utilization. This can significantly improve the cycle stability and rate performance of the prepared lithium-ion battery. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the silicon-carbon anode material of the present invention. In the figure, 1 represents graphite, 2 represents silicon carbide, 3 represents silicon, and 4 represents amorphous carbon. Detailed Implementation

[0029] To better illustrate the purpose, technical solution, and advantages of this invention, the invention will be further described below with reference to specific embodiments and accompanying drawings. However, the embodiments do not limit the invention in any way. Unless otherwise specified, the reagents, methods, and equipment used in this invention are conventional reagents, methods, and equipment in this technical field. Unless otherwise specified, all reagents and materials used in this invention are commercially available.

[0030] An embodiment of the present invention provides a silicon-carbon anode material, comprising a core and a functional layer coated on the surface of the core: the core comprises graphite with silicon carbide and silicon embedded on its surface, and the functional layer comprises amorphous carbon;

[0031] The silicon-carbon anode material satisfies: I a / I b =0.02~0.10, I c / I a =0.10~0.30;

[0032] Among them, I a I represents the peak intensity of the (111) crystal plane of silicon. b I represents the peak intensity of the (002) crystal plane of graphite. c The peak intensity of the (111) crystal plane of silicon carbide.

[0033] It should be noted that the amorphous carbon in the coating layer of the silicon-carbon anode material of this invention can be identified by Raman spectroscopy. Crystal plane peak intensity I a I b I c It can be calculated from the XRD pattern obtained by CuKα-ray scanning. In the XRD pattern, 2θ is the peak intensity of the (111) crystal plane of silicon at 28.2° to 28.6°, denoted as I. a The peak intensity of the (002) crystal plane of graphite is located at 26.2°–26.8°, denoted as I. b The peak intensity of the (111) crystal plane of silicon carbide is located at 35.3°–35.9°, denoted as I. c .

[0034] This invention improves the cycle stability of lithium-ion batteries by coating the surface with amorphous carbon. Specifically: 1) Silicon carbide and silicon are embedded in the graphite surface in a condensed state, maintaining a relatively stable structure during lithium insertion / extraction, unlike traditional silicon particles which are prone to pulverization and failure, thus exhibiting superior electrochemical cycle performance; 2) Some silicon reacts with graphite to form silicon carbide, which can reduce the overall volume expansion of the silicon-carbon anode material, enhance its structural stability, and further improve its electrochemical cycle performance. However, the formation of silicon carbide causes a small amount of silicon to lose its electrochemical activity, resulting in a loss of battery capacity; 3) Adding an amorphous carbon shell can further enhance the structure of the silicon-carbon anode material, providing expansion space to alleviate the volume changes of the core graphite and silicon during lithium insertion / extraction, improving the electrochemical cycle performance of the silicon-carbon anode material. At the same time, the amorphous carbon shell can construct a three-dimensional electronic conductive network on the material surface, and its isotropic structure is conducive to lithium-ion insertion, which can improve the rate performance of the silicon-carbon anode material.

[0035] Through further research, the inventors of this invention have also discovered that by simultaneously controlling the material ratio of the "graphite-silicon carbide-silicon" core material in the silicon-carbon anode material, the capacity utilization of the anode material can be improved, compensating for the capacity loss caused by the deactivation of a small amount of silicon; at the same time, the structural stability of the anode material can be further improved, significantly enhancing the cycle stability and rate performance of the prepared lithium-ion battery.

[0036] In the silicon-carbon anode material of the present invention, the amounts of silicon carbide, silicon, and amorphous carbon will affect the performance of the prepared battery:

[0037] While silicon carbide can improve the structural stability of silicon-carbon anode materials, if its content is too high, a large amount of silicon will lose its electrochemical activity, resulting in a decrease in the material's capacity and an increase in its impedance, which is not conducive to improving its electrochemical performance. If the silicon carbide content is too low, the active silicon content in the material will be too high, resulting in excessive volume changes during the lithium insertion and extraction process and a deterioration in structural stability.

[0038] If the silicon content is too high, the silicon layer on the graphite surface will be too thick, resulting in excessive volume changes during lithium insertion / extraction, which can easily damage the material structure; if the silicon content is too low, it will be detrimental to improving the battery capacity.

[0039] Therefore, in the silicon-carbon anode material of the present invention, the weight ratio of graphite, silicon carbide and silicon is 1:(0.9-1.8):(0.1-0.2).

[0040] By rationally controlling the ratio of specific crystal planes in silicon carbide to specific crystal planes in silicon crystal (I... c / I a This method can significantly reduce the impact of silicon carbide on the capacity of silicon-carbon anode materials, significantly improve the capacity utilization of anode materials, and compensate for the capacity loss caused by the deactivation of a small amount of silicon. At the same time, it can further improve the structural stability of anode materials and significantly improve the cycle stability and rate performance of the prepared lithium-ion batteries.

[0041] In some embodiments of the present invention, the I c / I a It ranges from 0.15 to 0.25. For example, I c / I a It can be 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, or a range consisting of any two of the above values.

[0042] In some embodiments of the present invention, the I a / I b It ranges from 0.04 to 0.08. For example, I a / I bIt can be 0.04, 0.05, 0.06, 0.07, 0.08, or a range consisting of any two of the above values.

[0043] Amorphous carbon coating of graphite cores already embedded with condensed silicon carbide and silicon forms an amorphous carbon layer on the core surface, preventing direct contact between silicon and electrolyte and generating a relatively stable solid electrolyte film on the material surface. This reduces reversible lithium consumption and improves the electrochemical cycling performance of the anode material. Furthermore, the amorphous carbon layer can construct a three-dimensional electronic conductive network on the material surface, allowing lithium ions to simultaneously embed into the silicon-carbon anode material particles from various directions, effectively improving the rate performance of the silicon-carbon anode material.

[0044] Both excessively thin and excessively thick amorphous carbon layers are detrimental to improving the rate performance of silicon-carbon anode materials. When the amorphous carbon layer is too thin, it cannot fully cover the core surface, failing to form a large-area three-dimensional electronic conductive network. When the amorphous carbon layer is too thick, the diffusion path of lithium ions in the particle shell is prolonged, reducing the lithium-ion diffusion coefficient of the silicon-carbon anode material, resulting in a significant decrease in the capacity retention of the lithium-ion battery at high rates. Therefore, in some embodiments of the present invention, the thickness of the amorphous carbon layer is 10–80 nm. For example, the thickness of the amorphous carbon layer can be 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, or any combination of two of the above values.

[0045] In some embodiments of the present invention, the thickness of the amorphous carbon layer is 30–70 nm.

[0046] In some embodiments of the present invention, the D of the silicon-carbon anode material V50 The value is 5–25 μm, specifically 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 23 μm, 25 μm, or any combination of two of the above values. D v50 This refers to the particle size corresponding to a cumulative volume percentage of 50% for the silicon-carbon anode material.

[0047] In some embodiments of the present invention, the powder compaction density of the silicon-carbon anode material under 3T pressure is 1.5–2.0 g / cm³. 3 For example, the powder compaction density of silicon-carbon anode materials under 3T pressure can be 1.5 g / cm³. 3 1.6g / cm 3 1.7g / cm 3 1.8g / cm 3 1.9g / cm 3 2.0g / cm 3 Or a range consisting of any two of the above values.

[0048] In some embodiments of the present invention, the silicon-carbon anode material has a specific surface area of ​​1–3 m². 2 / g. For example, the specific surface area of ​​silicon-carbon anode materials can be 1m². 2 / g, 1.5m 2 / g, 2.0m 2 / g, 2.5m 2 / g, 3.0m 2 / g or a range consisting of any two of the above values.

[0049] In some embodiments of the present invention, the powder resistivity of the silicon-carbon anode material at a pressure of 2T is 0.003 to 0.005 Ω*cm. For example, the powder resistivity of the silicon-carbon anode material at a pressure of 2T can be 0.003 Ω*cm, 0.0035 Ω*cm, 0.004 Ω*cm, 0.0045 Ω*cm, 0.005 Ω*cm, or any combination of two of the above values.

[0050] Embodiments of the present invention also provide a method for preparing the above-mentioned silicon-carbon anode material, comprising the following steps:

[0051] S1. After mixing graphite and silicon, silicon carbide and silicon are embedded into the graphite surface through a melting reaction in an inert atmosphere;

[0052] S2. The product obtained in step S1 and the precursor of amorphous carbon are mixed and then carbonized in an inert atmosphere to obtain the silicon-carbon anode material.

[0053] In an embodiment of the present invention, the silicon in step S1 is nano-silicon, and the particle size of the nano-silicon is 30-500 nm, preferably 50-100 nm.

[0054] In an embodiment of the present invention, the specific melting process in step S1 is as follows: the temperature is increased to 1500-1600°C at a heating rate of 1-10°C / min, held at the temperature for 1-3 hours, and then cooled to 20-30°C at a rate of 10-20°C / min.

[0055] In an embodiment of the present invention, the specific process of carbonization treatment in step S2 is as follows: heating to 800-1000°C at a heating rate of 1-10°C, holding at that temperature for 1-3 hours, and then cooling naturally.

[0056] In an embodiment of the present invention, the inert atmosphere in step S2 is an atmosphere formed by at least one gas selected from helium, neon, argon, and nitrogen.

[0057] In embodiments of the present invention, the precursor of amorphous carbon includes at least one selected from glucose, sucrose, soluble starch, cyclodextrin, pitch, phenolic resin, epoxy resin, carboxymethyl cellulose, and citric acid.

[0058] An embodiment of the present invention also provides a lithium-ion battery, including a negative electrode sheet, the negative electrode sheet including a negative electrode current collector and a negative electrode film disposed on at least one side of the negative electrode current collector, the negative electrode film including the above-described silicon-carbon negative electrode material or the silicon-carbon negative electrode material prepared by the above-described preparation method.

[0059] The present invention also protects electrical devices that include the lithium-ion battery.

[0060] The present invention provides the following embodiments to facilitate understanding of the invention. These embodiments are provided not to limit the scope of the claims.

[0061] Example 1

[0062] This embodiment provides a silicon-carbon anode material, which is prepared by a method including the following steps:

[0063] S1. Add 10g of graphite (D v50 (13μm) and 1g nano-silicon (D v50 The mixture (10 nm) was placed in a ball mill jar and ball-milled at 300 r / min for 2 h to obtain a mixture. In a nitrogen atmosphere, the mixture was heated to 1500 °C at a heating rate of 10 °C / min and held for 2 h. Then it was slowly cooled to room temperature (25 °C) at a cooling rate of 15 °C / min to obtain graphite embedded with silicon carbide and silicon.

[0064] S2. The product obtained in step S1 is mixed with 2g of asphalt and placed in a ball mill jar. The mixture is ball milled at a speed of 300r / min for 2h. Then, under a nitrogen atmosphere, the temperature is raised to 800℃ at a heating rate of 10℃ / min and held for 2h. After the material is naturally cooled to room temperature (below 30℃, for example 25℃), the silicon-carbon anode material is obtained.

[0065] Examples 2-4

[0066] A series of silicon-carbon anode materials are provided, which are prepared according to the preparation method of Example 1. The difference from Example 1 is that the amount of nano-silicon added in step S1 is 0.5g, 1.5g and 2.0g respectively.

[0067] Examples 5-10

[0068] A series of silicon-carbon anode materials are provided, which are prepared according to the preparation method of Example 1. The difference from Example 1 is that the amount of amorphous carbon precursor added in step S2 is changed to change the thickness of the amorphous carbon layer in the silicon-carbon anode material (the specific thickness parameters are detailed in Table 1).

[0069] Examples 11-15

[0070] A series of silicon-carbon anode materials are provided, prepared according to the preparation method of Example 1. The difference from Example 1 is that the mass of nano-silicon in step S1 is replaced by particle size (D). v50 The nanometers of silicon are 25nm, 30nm, 50nm, 150nm, and 500nm, respectively. Other fabrication process conditions (such as heating rate) were also modified to ensure... c / I a The value remains unchanged.

[0071] Examples 16-17

[0072] A series of silicon-carbon anode materials are provided, which are prepared according to the preparation method of Example 1. The difference from Example 1 is that in step S2, the types of amorphous carbon precursors are replaced with phenolic resin and sucrose, and their addition amounts are changed to ensure that the thickness of the amorphous carbon layer is the same as that of Example 1.

[0073] Examples 18-24, Comparative Examples 1-5

[0074] A series of silicon-carbon anode materials are provided, prepared according to the preparation method of Example 1. By adjusting the preparation process parameters (such as heating rate, reaction temperature, and time) in Example 1, different Ia values ​​are obtained. a / I b I c / I a Silicon-carbon anode materials.

[0075] Examples 25-26

[0076] A series of silicon-carbon anode materials are provided, prepared according to the preparation method of Example 1, the difference being that the D of graphite is... v50 The sizes are 5μm and 25μm, respectively.

[0077] The parameters of the silicon-carbon anode material prepared by the above embodiments of the present invention are detailed in Table 1.

[0078] In Table 1, the particle size D of the silicon-carbon anode material is shown. v50 The specific testing method is as follows: The silicon-carbon anode material sample is dispersed in ethanol as a dispersant, and after sonication for 30 minutes, the sample is added to a Malvern particle size analyzer to test the Dsize of the silicon-carbon anode material. v50 .

[0079] Crystal plane peak intensity I a I b I c The values ​​were calculated from the XRD pattern obtained by CuKα-ray scanning. In the XRD pattern, the peak intensity of the (111) crystal plane of silicon is located at 2θ = 28.4°, denoted as I. a The peak intensity of the (002) crystal plane of graphite is located at 2θ = 26.5°, denoted as I. b The peak intensity of the (111) crystal plane of silicon carbide is located at 2θ = 35.6°, denoted as I. c .

[0080] Powder compaction density of silicon-carbon anode material (unit: g / cm³) 3 The test result was obtained by referring to the test method in the standard GB / T 24533-2009, where the test pressure was 3T and the test time was 30s.

[0081] The resistivity of silicon-carbon anode material powder (unit: Ω*cm): obtained using a resistivity tester, with a test pressure of 2T.

[0082] The specific surface area (BET) of silicon-carbon anode materials is measured in m². 2 / g): Measured using a specific surface area analyzer.

[0083] Table 1. Parameters of silicon-carbon anode materials prepared in the examples and comparative examples.

[0084]

[0085]

[0086] Performance testing

[0087] The silicon-carbon anode materials prepared in the above examples and comparative examples were assembled into lithium-ion batteries, and the electrochemical performance of the lithium-ion batteries was tested. The specific test items and test methods are as follows:

[0088] The specific assembly process of lithium-ion batteries is as follows: the prepared negative electrode material is mixed with SP, SBR and CMC in a mass ratio of 80:10:5:5, and ultrapure water is used as a solvent to mix the mixture into a slurry. The slurry is then uniformly coated on copper foil and vacuum dried at 120°C for 12 hours to obtain the battery electrode. Lithium foil is then used as the counter electrode, and a four-component mixed solvent of LiPF6 with a molar concentration of 1 mol / L (in a mass ratio of EC:DMC:EMC:FEC=3:4:2:1) is used as the electrolyte. Polypropylene membrane is used as the separator, and CR2032 type button half cell is assembled in a vacuum glove box.

[0089] 1. Cyclic performance test: The coin cell half-cell was discharged to 5mV under constant current 0.1C and charged to 1.5V under constant current 0.1C. Similarly, it was discharged to 5mV under constant current 0.1C and charged to 1.5V under constant current 0.1C. The discharge capacity C1 (mAh / g) of the first cycle was recorded and the initial coulombic efficiency (%) was calculated. After repeating 99 cycles, the discharge capacity of the battery was tested and recorded as C100 (mAh / g). The capacity retention rate after 100 cycles (100%) was calculated as (C1-C100) / C1*100%. See Table 2 for details.

[0090] 2. Rate Performance Test: ① Discharge the coin cell half-cell to 5mV at a constant current of 0.1C, then charge it to 1.5V at a constant current of 0.1C. Record the discharge capacity C1 (mAh / g) at this point. ② Perform charge-discharge cycles as described in step ①. After 10 cycles, test the discharge capacity C2 (mAh / g). Then increase the current to 0.2C. After 20 cycles (calculated from the first cycle as the starting cycle number), test the discharge capacity C3 (mAh / g). Then increase the current to 0.3C. After 30 cycles, test the discharge capacity C4 (mAh / g). Then increase the current to 0.5C. After 40 cycles, test the discharge capacity C5 (mAh / g). Then, the current was increased to 1C, and after 10 cycles, the discharge capacity C6 (mAh / g) of the battery was tested; ③ The capacity retention rate (%) of the battery after 10 cycles at 0.1C was calculated as follows: (C1-C2) / C1*100%; the capacity retention rate (%) of the battery after 10 cycles at 0.2C was calculated as follows: (C2-C3) / C2*100%; the capacity retention rate (%) of the battery after 10 cycles at 0.3C was calculated as follows: (C3-C4) / C3*100%; the capacity retention rate (%) of the battery after 10 cycles at 0.5C was calculated as follows: (C4-C5) / C4*100%; the capacity retention rate (%) of the battery after 10 cycles at 1C was calculated as follows: (C5-C6) / C5*100%. The test results are shown in Table 2.

[0091] Table 2 shows the performance of lithium-ion batteries prepared using silicon-carbon anode materials from the examples and comparative examples.

[0092]

[0093] As can be seen from the results of the above embodiments and comparative examples:

[0094] This invention improves the cycle stability of lithium-ion batteries by coating the surface with amorphous carbon. The lithium-ion batteries prepared using the silicon-carbon anode material of this invention exhibit an initial discharge capacity of over 500 mAh / g; after 100 cycles, the battery capacity retention rate remains above 80%, reaching as high as 93%; and at a 5C current density, the capacity retention rate is above 30%, reaching as high as 42%.

[0095] The results of Comparative Examples 1 to 5 show that the proportional relationship between the specific crystal plane intensities of graphite, silicon carbide, and carbon materials is not within the scope of protection of this invention, and the capacity, cycle stability, or rate performance of lithium-ion batteries prepared from silicon-carbon anode materials are significantly worse than those of the embodiments of this invention.

[0096] The comparative results of the above comparative examples and embodiments further demonstrate that: regulating the crystal structure composition of the "graphite-silicon carbide-silicon" core material of the silicon-carbon anode material can further improve the structural stability of the anode material, while improving the capacity utilization of the anode material, and significantly improving the cycle stability and rate performance of the prepared lithium-ion battery.

[0097] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A silicon-carbon anode material, characterized in that, The silicon-carbon anode material includes a core and a functional layer disposed on the surface of the core. The core includes graphite with silicon carbide and silicon disposed on its surface, and the functional layer includes amorphous carbon. The core has a "graphite-silicon carbide-silicon" interface structure, in which silicon carbide and silicon are embedded in the graphite surface in a condensed state, and the silicon carbide is generated by the reaction of silicon and graphite. The silicon-carbon anode material satisfies: I a / I b =0.02~0.10, I c / I a =0.10~0.30; Among them, I a I is the peak intensity of the (111) crystal plane of silicon. b I represents the peak intensity of the (002) crystal plane of graphite. c The peak intensity of the (111) crystal plane of silicon carbide.

2. The silicon-carbon anode material according to claim 1, characterized in that, The silicon-carbon anode material satisfies at least one of the following conditions: (1)I a / I b =0.04~0.08; (2)I c / I a =0.15~0.25; (3) Specific surface area is 1~3 m² 2 / g; (4) The compacted density of the powder under 3T pressure is 1.5~2.0 g / cm³. 3 ; (5) The resistivity of the powder under 2T pressure is 0.003~0.005 Ω*cm; (6) D V50 The value is 5~25μm, D v50 This refers to the particle size corresponding to a cumulative volume percentage of 50% for the silicon-carbon anode material.

3. The silicon-carbon anode material according to claim 1, characterized in that, The thickness of the functional layer is 10~80 nm.

4. The silicon-carbon anode material according to claim 3, characterized in that, The thickness of the functional layer is 30~70 nm.

5. The method for preparing the silicon-carbon anode material according to any one of claims 1 to 4, characterized in that, Includes the following steps: S1. After mixing graphite and silicon, silicon carbide and silicon are embedded into the graphite surface through a melting reaction in an inert atmosphere; S2. The product obtained in step S1 is mixed with the precursor of amorphous carbon and then carbonized in an inert atmosphere to obtain the silicon-carbon anode material.

6. The method for preparing the silicon-carbon anode material according to claim 5, characterized in that, The specific melting process in step S1 is as follows: heat to 1500-1600℃ at a heating rate of 1-10℃ / min, hold at the temperature for 1-3 hours, and then cool down to 20-30℃ at a rate of 10-20℃ / min.

7. The method for preparing the silicon-carbon anode material according to claim 5, characterized in that, The specific process of carbonization in step S2 is as follows: heat to 800-1000℃ at a heating rate of 1-10℃ / min, hold for 1-3 hours, and then cool naturally.

8. The method for preparing the silicon-carbon anode material according to claim 5, characterized in that, The precursor of the amorphous carbon includes at least one of glucose, sucrose, soluble starch, cyclodextrin, pitch, phenolic resin, epoxy resin, carboxymethyl cellulose, and citric acid.

9. A lithium-ion battery, comprising a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode film disposed on at least one side of the negative electrode current collector, characterized in that, The negative electrode film comprises the silicon-carbon negative electrode material according to any one of claims 1 to 4 or the silicon-carbon negative electrode material prepared by the preparation method according to any one of claims 5 to 8.

10. An electrical appliance, characterized in that, Including the lithium-ion battery as described in claim 9.

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