A silicon-carbon composite material, a battery negative electrode, and a preparation method thereof

Abstract

The present invention provides a silicon-carbon composite material, a battery negative electrode and a preparation method thereof. The preparation method of the composite material includes: mixing silicon, a metal-carbon source and water to carry out a hydrothermal reaction to obtain a first composite material; mixing the first composite material with a carbon source to obtain a second composite material; granulating and sintering the second composite material to obtain the silicon-carbon composite material. The carbon-metal source of the present invention provides both a carbon source and a metal source at the same time, the process is simple to implement and has high repeatability; the functions of carbon coating and pre-metallization of magnesium / copper / potassium / sodium / calcium / manganese, etc. are realized, greatly solving the problems of low initial efficiency and poor cycling performance.

Description

Technical Field

[0001] The present invention relates to the field of batteries, and in particular, to a silicon-carbon composite material, a battery negative electrode, and a preparation method thereof. Background Art

[0002] Since the 21st century, the demand for new energy vehicles and 3C electronic products has increased sharply, so the market has a great demand for batteries. Lithium-ion batteries have been widely used in consumer electronics, new energy vehicles, electric two-wheelers and other fields due to their excellent performance such as high working voltage, no memory effect, small self-discharge, and green environmental protection and non-toxicity. However, the too low energy density of the battery core restricts the development of the industry. Therefore, it is urgent to improve the energy density of lithium-ion batteries.

[0003] Developing new negative electrode materials is an important way to improve the energy density of batteries. Currently, the commercial lithium-ion battery negative electrode materials use graphite materials. Graphite materials have the advantages of stable working voltage, small cyclic volume expansion, and high number of recyclable cycles. However, its theoretical capacity is only 372 mAh / g, which has become one of the key factors restricting the further improvement of the energy density of lithium-ion batteries. And silicon-based negative electrode materials, because their theoretical capacity is 5-10 times that of graphite negative electrodes, are widely regarded as the next-generation negative electrode materials.

[0004] However, the three problems restricting the commercialization of silicon-based negative electrode materials are: First, the cyclic volume expansion is serious, about 300%, which is 20 times that of graphite negative electrodes. During the volume expansion process, silicon itself will be broken or pulverized. Secondly, the surrounding materials will be squeezed and shrunk during the expansion process, and it is easy to lose electrical contact with the current collector, resulting in a capacity drop. Second, the silicon-based material has poor electrical conductivity, and the intrinsic conductivity of silicon is small (2.52×10-4 / (mΩ)), resulting in a high internal resistance of the battery, further affecting the cycle life. At the same time, it will also restrict the migration of lithium ions, resulting in a decline in the rate performance of the material. Third, the first Coulomb efficiency of the silicon-based negative electrode material is too low, making the cycle / rate performance further deteriorate. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides a silicon-carbon composite material, which can achieve uniform carbon coating and pre-metallization.

[0006] The present invention provides a preparation method of a silicon-carbon composite material, including:

[0007] Mixing silicon, a metal-carbon source and water for hydrothermal reaction to obtain a first composite material;

[0008] Mixing the first composite material with a carbon source to obtain a second composite material;

[0009] Granulating and sintering the second composite material to obtain the silicon-carbon composite material.

[0010] Further, the mass ratio of the silicon, the metal-carbon source and the carbon source is 1-5:5-20:1-10. 2. Further, the metal-carbon source is at least one of magnesium gluconate, copper gluconate, zinc gluconate, ferrous gluconate, sodium gluconate, potassium gluconate, calcium gluconate, nickel gluconate, manganese gluconate, cobalt gluconate, chromium gluconate, aluminum stearate, magnesium stearate, calcium stearate, zinc stearate, magnesium citrate or lithium citrate;

[0011] and / or the carbon source is at least one of glucose solution, PVP, starch or sucrose solution.

[0012] Further, the conditions of the hydrothermal reaction are: temperature 170-260 °C, time 6-12 h;

[0013] Preferably, the temperature is 170-220 °C.

[0014] Further, the conditions of the sintering are: temperature 700-1000 °C, heating rate 1-10 °C / min, sintering time 2-8 h.

[0015] Further, the particle size of the silicon is 50 nm-2 μm.

[0016] There is also provided a silicon-carbon composite material, comprising: silicon, a metal element layer and a carbon layer coated on the outside of the silicon.

[0017] Further, the metal element is at least one of magnesium, copper, zinc, ferrous, sodium, potassium, calcium, nickel, manganese, cobalt, chromium, aluminum and lithium.

[0018] Further, the coating thickness of the carbon layer is 100-500 nm.

[0019] There is also provided a battery anode material, comprising the above-mentioned silicon-carbon composite material.

[0020] The beneficial effects of this patent are as follows:

[0021] First, the carbon-metal source provides both the carbon source and the metal source at the same time, the process is simple to implement and has high repeatability; second, the functions of carbon coating and pre-metallization of magnesium / copper / potassium / sodium / calcium / manganese, etc. are realized, greatly solving the problems of low initial efficiency and poor conductivity; third, the carbon coating obtained by the hydrothermal method is a porous structure, reserving space for the volume expansion of silicon; fourth, by introducing metal sources such as metal magnesium, metal manganese, metal copper, metal zinc, metal nickel, metal iron, metal chromium, metal cobalt, etc. through the carbon-metal source, different-shaped and -structured nano metal particles, metal fragments and metal wires can be prepared by regulating the hydrothermal reaction time, concentration and silicon particle size, which perfectly solves the poor conductivity of silicon-based materials and improves the cycle stability.

[0022] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings are used to provide a further understanding of the technical solution of the present invention and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the technical solution of the present invention and do not constitute a limitation on the technical solution of the present invention.

[0024] Figure 1 It is a schematic diagram of the preparation of a product according to an embodiment of the present invention;

[0025] Figures 2-4 is a SEM image of the product of Example 1 of the present invention;

[0026] Figure 5 It is the energy spectrum diagram of the product of Example 1 of the present invention. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solution and advantages of the embodiment of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings of the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all of the embodiments. Based on the described embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] An embodiment of the present invention provides a method for preparing a silicon-carbon composite material, comprising: mixing silicon, a metal-carbon source and water for a hydrothermal reaction to obtain a first composite material; mixing the first composite material with a carbon source to obtain a second composite material; and granulating and sintering the second composite material to obtain the silicon-carbon composite material.

[0029] The present application uses only one substance, a metal-carbon source, to provide a carbon source and a metal source. During the hydrothermal reaction, the metal-carbon source will produce a large number of carboxyl groups, which will dehydrate and condense with the hydroxyl groups on the silicon surface to form a stable complex. At the same time, the hydrothermal process will form a carbon element containing a small amount of functional groups. After the metal ions in the metal-carbon source are reduced, they will be in situ grown and deposited on the silicon surface to obtain very uniform nano-metal-doped silicon microspheres.

[0030] The doped metal elements can greatly improve the electrical conductivity. For example, the doped magnesium can play a good role in magnesium supplementation and improve the initial efficiency; the doped copper, iron, cobalt, nickel, zinc, etc. have good electrical conductivity, and the internal resistance decreases, and there is still a high capacity retention rate after multiple cycles; the doped potassium will also participate in the battery reaction, resulting in volume expansion but enhancing conductivity, and the cycle performance is partially improved; the ferrous doping can improve the conductivity although iron consumes lithium during the self-discharge and charge-discharge processes of the negative electrode, and the cycle performance is slightly improved; the doping of nickel, manganese or chromium can improve the cycle performance due to the good electrical conductivity of the metal; the cobalt doping is reduced to the elemental form after high temperature and is coated in the carbon shell. The Co element has good electrical conductivity and electrocatalytic performance, which helps to accelerate the transmission of lithium ions; in addition, the copper or zinc in the double doping of magnesium and copper or zinc can act as a conductive agent to improve its electrical conductivity, and the magnesium ions improve the initial efficiency, thereby improving the cycle performance.

[0031] The carbon-coated microspheres prepared by the hydrothermal method have a porous structure, which reserves a certain space for the volume expansion of silicon during charge and discharge, and well solves the problems of volume expansion and poor electrical conductivity of silicon.

[0032] By granulation, the particle size can be made uniform, the specific surface area can be increased, and the lithium ion insertion amount can be improved. In addition, the advantage of the hydrothermal method is that the carbon source coating thickness and particle size are controllable. By adjusting the concentration of the carbon-metal source, controlling the hydrothermal reaction time and temperature, etc., particles with different particle sizes can be obtained. As the hydrothermal time becomes longer, the particle size becomes larger, and as the metal-carbon source concentration becomes larger, the particle size also becomes larger.

[0033] The silicon source deposits on its surface as crystal nuclei, and the metal nucleation quantity and morphology can be adjusted by the concentration of the carbon-metal source / preparation process together, such as metal nanoparticles, metal fiber wires, metal sheets. In addition, it can also be used as the negative electrode to improve part of the capacity.

[0034] In this application, through the secondary coating of carbon, and dehydrogenation and deoxidation are realized at high temperature during the carbonization process, and the carbon source forms a stable and dense carbon layer. The dense core-shell can well prevent the volume expansion from damaging the structure and prevent a large amount of electrolyte from entering and reacting with silicon to deactivate.

[0035] In another embodiment of the present invention, the mass ratio of the silicon, the metal-carbon source and the carbon source is 1-5:5-20:1-10.

[0036] When the above raw materials are not within this range, it will lead to uneven silicon coating, poor cycle stability and more attenuation.

[0037] In another embodiment of the present invention, the metal-carbon source is at least one of magnesium gluconate, copper gluconate, zinc gluconate, ferrous gluconate, sodium gluconate, potassium gluconate, calcium gluconate, nickel gluconate, manganese gluconate, cobalt gluconate, chromium gluconate, aluminum stearate, magnesium stearate, calcium stearate, zinc stearate, magnesium citrate or lithium citrate.

[0038] In another embodiment of the present invention, the carbon source is at least one of glucose solution, PVP, starch or sucrose solution.

[0039] The above metal-carbon source provides both metal elements and carbon elements, and has a wide source and low price, which is more conducive to industrial production.

[0040] In another embodiment of the present invention, the conditions of the hydrothermal reaction are: temperature 170 - 260 °C, time 6 - 12 h;

[0041] When the temperature is higher than 260 °C, the particle size of the first composite material is too large, resulting in too small overall specific surface area.

[0042] In another embodiment of the present invention, the temperature is 170 - 220 °C.

[0043] In another embodiment of the present invention, the conditions of carbonization are: temperature 700 - 1000 °C, heating rate 1 - 10 °C / min, carbonization time 2 - 8 h.

[0044] In another embodiment of the present invention, the particle size of the silicon is 40 nm - 2 μm.

[0045] When the particle size of silicon is large (greater than 150 nm, especially 2 μm), silicon will expand in volume, damaging the SEI film, resulting in continuous consumption of lithium ions to form the SEI film during charge and discharge. Macroscopically, it is manifested as rapid attenuation of battery capacity. When the particle size is small (less than 40 nm), the cost will increase and the specific surface area will be large, consuming more lithium ions, which will affect the initial efficiency.

[0046] An embodiment of the present invention also provides a silicon-carbon composite material, including: silicon, a metal element layer and a carbon layer coated on the outside of the silicon.

[0047] The silicon-carbon composite material prepared by the method of the present invention has a moderate porosity. The BET coefficient of the final product is about 0.5 (the BET coefficient is the ratio of the specific surface area of the final product to the specific surface area of the silicon-containing substance). Higher than 0.8 indicates fewer silicon-containing voids or larger particles, and lower than 0.2 indicates too many silicon-containing voids (too many voids will lead to incomplete hydrothermal reaction and more exposed silicon. Silicon and lithium ions will form a silicon-lithium alloy during charge and discharge, and the irreversible reaction will reduce the initial efficiency). It shows that the product of this application has a moderate porosity, providing sufficient space for the volume expansion of silicon substances. In electrochemical tests, it shows advantages such as high initial efficiency and good cycling performance.

[0048] In another embodiment of the present invention, the metal element is at least one of magnesium, copper, zinc, ferrous, sodium, potassium, calcium, nickel, manganese, cobalt, chromium, aluminum and lithium.

[0049] In another embodiment of the present invention, the coating thickness of the carbon layer is 100 - 500 nm.

[0050] An embodiment of the present invention also provides a battery anode material, comprising the above-mentioned silicon-carbon composite material.

[0051] In order to more clearly express the solution of the present application, the following specific embodiments are described.

[0052] Example 1

[0053] Mix 3 g of 100-nm nano-silicon with 50 mL of water and ultrasonicate for 2 h. Then dissolve 16.21 g of copper gluconate in 20 mL of deionized water and mix it with the ultrasonically treated silicon slurry to obtain a reaction solution. Among them, the concentration of copper gluconate is 0.5 mol / L. After mixing the reaction solution, pour it into a 100-ml hydrothermal reaction kettle, heat it to 190 °C and keep it warm for 6 h for hydrothermal reaction. Separate the solid and liquid of the obtained product, and dry it to obtain a silicon-carbon precursor.

[0054] Use 10% wt of PVP of the silicon-carbon precursor to coat it in an ethanol solution for 2 h, and then perform spray drying.

[0055] Finally, perform carbonization treatment on the obtained solid product in a nitrogen atmosphere, heat it to 900 °C at a heating rate of 5 °C / min, keep it warm for 3 h and then cool it naturally to obtain a silicon-carbon anode material.

[0056] Mix the prepared anode material with commercial graphite in a certain proportion to obtain a lithium-ion battery anode material with a specific capacity of 650 mAh / g. Mix the obtained lithium-ion battery anode material with 3% carbon black, 4% sodium carboxymethyl cellulose, and 3% SBR evenly in an aqueous solvent to form a battery slurry. Coat it on a copper foil, dry it and cut it into a circular piece with a diameter of 12 mm. After vacuum drying at 110 °C for 12 hours, assemble a half-cell in a glove box and evaluate its electrochemical performance. In addition, the phase morphology and the like of the anode material are also tested.

[0057] The thickness of the carbon coating layer is 300 nm.

[0058] From Figures 2-4 It can be clearly seen that the silicon powder is evenly dispersed in the copper gluconate, and the morphological structure is porous, with traces of coating on the surface showing a shell structure.

[0059] Figure 5 From the energy spectrum diagram, it is found that only a small amount of silicon is exposed on the surface, indicating that the silicon microspheres prepared by the hydrothermal method can well coat the silicon

[0060] Example 2

[0061] Replace the copper gluconate in Example 1 with magnesium gluconate, and the other processes are the same as those in Example 1. The thickness of the carbon coating layer is 200 nm.

[0062] The battery is assembled and tested in the same manner as in Example 1 above. The test results of the first-week cycle efficiency and the 100-week capacity retention rate are recorded in Table 1.

[0063] Example 3

[0064] Replace the copper gluconate in Example 1 with zinc gluconate, and the other processes are the same as those in Example 1. The thickness of the carbon coating layer is 250 nm.

[0065] The battery is assembled and tested in the same manner as in Example 1 above. The test results of the first-week cycle efficiency and the 100-week capacity retention rate are recorded in Table 1.

[0066] Example 4

[0067] Replace the copper gluconate in Example 1 with ferrous gluconate, and the other processes are the same as those in Example 1. The thickness of the carbon coating layer is 310 nm.

[0068] The battery is assembled and tested in the same manner as in Example 1 above. The test results of the first-week cycle efficiency and the 100-week capacity retention rate are recorded in Table 1.

[0069] Example 5

[0070] Replace the copper gluconate in Example 1 with sodium gluconate, and the other processes are the same as those in Example 1. The thickness of the carbon coating layer is 200 nm.

[0071] The battery is assembled and tested in the same manner as in Example 1 above. The test results of the first-week cycle efficiency and the 100-week capacity retention rate are recorded in Table 1.

[0072] Example 6

[0073] Replace the copper gluconate in Example 1 with potassium gluconate, and the other processes are the same as those in Example 1. The thickness of the carbon coating layer is 400 nm.

[0074] The battery is assembled and tested in the same manner as in Example 1 above. The test results of the first-week cycle efficiency and the 100-week capacity retention rate are recorded in Table 1.

[0075] Example 7

[0076] Replace the copper gluconate in Example 1 with calcium gluconate, and the other processes are the same as those in Example 1. The thickness of the carbon coating layer is 300 nm.

[0077] The battery assembly and testing were carried out in the same manner as in Example 1 above. The test results of the first-week cycle efficiency and the 100-week capacity retention rate are recorded in Table 1.

[0078] Example 8

[0079] Replace copper gluconate in Example 1 with cobalt gluconate, and the other processes are the same as in Example 1. The thickness of the carbon coating layer is 305 nm.

[0080] The battery assembly and testing were carried out in the same manner as in Example 1 above. The test results of the first-week cycle efficiency and the 100-week capacity retention rate are recorded in Table 1.

[0081] Example 9

[0082] Replace copper gluconate in Example 1 with nickel gluconate, and replace PVP with a sucrose solution. The other processes are the same as in Example 1. The thickness of the carbon coating layer is 290 nm.

[0083] The battery assembly and testing were carried out in the same manner as in Example 1 above. The test results of the first-week cycle efficiency and the 100-week capacity retention rate are recorded in Table 1.

[0084] Example 10

[0085] Replace copper gluconate in Example 1 with manganese gluconate, and replace PVP with a starch solution. The other processes are the same as in Example 1. The thickness of the carbon coating layer is 310 nm.

[0086] The battery assembly and testing were carried out in the same manner as in Example 1 above. The test results of the first-week cycle efficiency and the 100-week capacity retention rate are recorded in Table 1.

[0087] Example 11

[0088] Replace copper gluconate in Example 1 with cobalt gluconate, the hydrothermal time is 12 h, and the others are the same as in Example 1. The thickness of the carbon coating layer is 380 nm.

[0089] The battery assembly and testing were carried out in the same manner as in Example 1 above. The test results of the first-week cycle efficiency and the 100-week capacity retention rate are recorded in Table 1.

[0090] Example 12

[0091] Replace copper gluconate in Example 1 with chromium gluconate, and replace PVP with a glucose solution. The other processes are the same as in Example 1. The thickness of the carbon coating layer is 305 nm.

[0092] The battery assembly and testing were carried out in the same manner as in Example 1 above, and the test results of the first-week cycle efficiency and the 100-week capacity retention rate are recorded in Table 1.

[0093] Example 13

[0094] Magnesium gluconate (7.4 g) and copper gluconate (8.1 g) were selected for co-doping with a molar ratio of 1:1 and a total concentration of 0.5 mol / L. The other conditions were the same as in Example 1. The thickness of the carbon coating layer was 310 nm.

[0095] The battery assembly and testing were carried out in the same manner as in Example 1 above, and the test results of the first-week cycle efficiency and the 100-week capacity retention rate are recorded in Table 1.

[0096] Example 14

[0097] Magnesium gluconate and copper gluconate were selected for co-doping with a molar ratio of 1:1 and a total concentration of 1 mol / L. The other processes were the same as in Example 1. The thickness of the carbon coating layer was 330 nm.

[0098] The battery assembly and testing were carried out in the same manner as in Example 1 above, and the test results of the first-week cycle efficiency and the 100-week capacity retention rate are recorded in Table 1.

[0099] Example 15

[0100] 3 g of nanosilicon (150 nm) was mixed with 50 mL of water and ultrasonicated for 2 h; then 3 g of copper gluconate was dissolved in 20 mL of deionized water and mixed with the ultrasonicated silicon slurry to obtain a reaction solution. Among them, the concentration of copper gluconate was 0.5 mol / L. After mixing the reaction solution, it was poured into a 100 ml hydrothermal reaction kettle, heated to 220 °C and kept warm for 10 h for hydrothermal reaction. The obtained product was subjected to solid-liquid separation and dried to obtain a silicon-carbon precursor; the addition amount of PVP was 20 wt% of the silicon-carbon precursor, and the carbonization (sintering) conditions were 700 °C, the heating rate was 1 °C / min, and the carbonization (sintering) time was 8 h.

[0101] The remaining steps were the same as in Example 1, and the thickness of the carbon coating layer was 400 nm. The battery assembly and testing were carried out in the same manner as in Example 1 above, and the test results of the first-week cycle efficiency and the 100-week capacity retention rate are recorded in Table 1.

[0102] Example 16

[0103] Mix 3 g of silicon spheres (2 μm) with 50 mL of water and sonicate for 2 h. Then dissolve 50.69 g of magnesium citrate in 20 mL of deionized water and mix it with the sonicated silicon slurry to obtain a reaction solution. Among them, the concentration of copper gluconate is 0.5 mol / L. After mixing the reaction solution, pour it into a 100 ml hydrothermal reactor, heat it to 260 °C and keep it at this temperature for 12 h for hydrothermal reaction. Separate the solid and liquid of the obtained product, and dry it to obtain a silicon-carbon precursor; the addition amount of PVP is 50 wt% of the silicon-carbon precursor. The carbonization temperature is 1000 °C, the heating rate is 10 °C / min, and the carbonization time is 2 h.

[0104] The remaining steps are the same as those in Example 1, and the thickness of the carbon coating layer is 300 nm. Assemble and test the battery in the same manner as in Example 1 above. The test results of the first-week cycle efficiency and the 100-week capacity retention rate are recorded in Table 1.

[0105] Example 17

[0106] Replace the copper gluconate in Example 1 with magnesium citrate, and the other processes are the same as those in Example 1. The thickness of the carbon coating layer is 310 nm.

[0107] Assemble and test the battery in the same manner as in Example 1 above. The test results of the first-week cycle efficiency and the 100-week capacity retention rate are recorded in Table 1.

[0108] Example 18

[0109] Replace nano-silicon, copper gluconate, and PVP with 5 g (5 μm) of silicon powder, 3 g of copper gluconate, and 3 g of PVP. The temperature of the hydrothermal reaction is 300 °C and the time is 20 h; the carbonization temperature is 500 °C, the heating rate is 15 °C / min, and the carbonization time is 1 h. The others are the same as those in Example 1. The thickness of the carbon coating layer is 200 nm.

[0110] Assemble and test the battery in the same manner as in Example 1 above. The test results of the first-week cycle efficiency and the 100-week capacity retention rate are recorded in Table 1.

[0111] Comparative Example 1

[0112] Select glucose to participate in the hydrothermal reaction, which only provides a carbon source and does not introduce a metal source. The concentration of glucose is 0.5 mol / L, and the others are the same as those in Example 1.

[0113] The thickness of the carbon coating layer is 295 nm.

[0114] Assemble and test the battery in the same manner as in Example 1 above. The test results of the first-week cycle efficiency and the 100-week capacity retention rate are recorded in Table 1.

[0115] Comparative Example 2

[0116] Mix 3 g of nano-silicon (100 nm) with 50 mL of water and sonicate for 2 h. After mixing the reaction solutions, dissolve 16.21 g of copper gluconate in 20 mL of deionized water and mix it with the sonicated silicon slurry to obtain a reaction solution. Among them, the concentration of copper gluconate is 0.5 mol / L. Pour it into a 100 ml glass flask for reaction and stir for 4 h. Spray-dry the obtained product and dry it to obtain a silicon-carbon precursor. The subsequent steps are the same as those in Example 1. The thickness of the carbon coating layer is 100 nm.

[0117] Perform battery assembly and testing in the same manner as in Example 1 above. The test results of the first-week cycle efficiency and the 100-week capacity retention rate are recorded in Table 1.

[0118] Comparative Example 3

[0119] After preparing the precursor according to the method of Example 1, directly calcine it without secondary carbon coating to obtain a negative electrode product. The thickness of the carbon coating layer is 120 nm.

[0120] Perform battery assembly and testing in the same manner as in Example 1 above. The test results of the first-week cycle efficiency and the 100-week capacity retention rate are recorded in Table 1.

[0121] Comparative Example 4

[0122] Directly coat 3 g of nano-silicon with 10% wt of PVP by stirring in an ethanol solution for 2 h, and then perform spray drying. The subsequent steps are the same as those in Example 1. The thickness of the carbon coating layer is 200 nm.

[0123] Perform battery assembly and testing in the same manner as in Example 1 above. The test results of the first-week cycle efficiency and the 100-week capacity retention rate are recorded in Table 1.

[0124] Comparative Example 5

[0125] Do not granulate, and the others are the same as in Example 1. The thickness of the carbon coating layer is 100 nm.

[0126] Test the products of the examples and comparative examples, and the results are shown in Table 1.

[0127] Table 1 Performance of Examples and Comparative Examples

[0128]

[0129]

[0130] It can be concluded from the above table that the performance of the battery negative electrode sheet prepared by the examples of the present application is far superior to that of the comparative examples.

[0131] Although the embodiments disclosed in the present invention are as described above, the content described is only an embodiment adopted for the convenience of understanding the present invention and is not intended to limit the present invention. Any person skilled in the art within the field to which the present invention pertains may make any modifications and changes in the form of implementation and details without departing from the spirit and scope disclosed in the present invention. However, the scope of patent protection of the present invention shall still be subject to the scope defined by the appended claims.

Claims

1. A preparation method of a silicon-carbon composite material, characterized in that, it includes: mixing silicon, a metal-carbon source and water for hydrothermal reaction to obtain a first composite material; mixing the first composite material with a carbon source to obtain a second composite material; granulating and sintering the second composite material to obtain the silicon-carbon composite material; wherein, the metal-carbon source is at least one of magnesium gluconate, copper gluconate, zinc gluconate, ferrous gluconate, sodium gluconate, potassium gluconate, calcium gluconate, nickel gluconate, manganese gluconate, cobalt gluconate, chromium gluconate, aluminum stearate, magnesium stearate, calcium stearate, zinc stearate, magnesium citrate or lithium citrate.

2. The preparation method according to claim 1, characterized in that, the mass ratio of the silicon, the metal-carbon source and the carbon source is 1-5:5-20:1-10.

3. The preparation method according to claim 1, characterized in that, the carbon source is at least one of a glucose solution, PVP, starch or a sucrose solution.

4. The preparation method according to claim 1, characterized in that, the conditions of the hydrothermal reaction are: temperature 170-260 °C, time 6-12 h.

5. The preparation method according to claim 4, characterized in that, the temperature is 170-220 °C.

6. The preparation method according to claim 1, characterized in that, the conditions of the sintering are: temperature 700-1000 °C, heating rate 1-10 °C / min, sintering time 2-8 h.

7. The preparation method according to claim 1, characterized in that, the particle size of the silicon is 50 nm-2 μm.

8. A silicon-carbon composite material, characterized in that, it is prepared by the preparation method according to any one of claims 1-7, and includes: silicon, a metal element layer and a carbon layer coated outside the silicon.

9. The silicon-carbon composite material according to claim 8, characterized in that, the metal element is at least one of magnesium, copper, zinc, ferrous, sodium, potassium, calcium, nickel, manganese, cobalt, chromium, aluminum and lithium.

10. The silicon-carbon composite material according to claim 9, characterized in that, the coating thickness of the carbon layer is 100-500 nm.

11. A battery anode material, characterized in that, it includes the silicon-carbon composite material according to any one of claims 8-10.

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