A silicon-carbon negative electrode material, a preparation method thereof, an application thereof, and a lithium-ion battery

Abstract

The present invention belongs to the field of silicon-carbon anode materials, and discloses a silicon-carbon anode material, a preparation method, an application thereof, and a lithium-ion battery. The method includes: (1) soaking a silicon source in a catalyst solution, filtering and drying it, then mixing it with lithium hydroxide and performing high-temperature pyrolysis in a mixed gas atmosphere to obtain a precursor; the mixed gas includes an inert gas, a carbon source gas, a reducing gas, and "a gas containing an oxygen-containing group and / or a gas containing a nitrogen-containing group", the molar ratio of the silicon source to lithium hydroxide is 100:(0.1-5), the flow ratio of the carbon source gas is 0.5%-5%, and the flow ratio of the reducing gas is 0.5%-5%; the temperature of the high-temperature pyrolysis is 600-1050°C; (2) mixing the precursor with a solid carbon source, granulating and carbonizing. The silicon-carbon anode material prepared by the present invention can reduce the silicon expansion rate before and after charge and discharge and improve the cycle life of the material.

Description

Technical Field

[0001] The present invention belongs to the field of silicon-carbon anode materials, and particularly relates to a silicon-carbon anode material, a preparation method thereof, an application thereof, and a lithium-ion battery. Background Art

[0002] As the anode material of a lithium-ion battery, the silicon-based anode is considered to be the key material for the anode of the next-generation high-energy density battery because it has a theoretical specific capacity as high as 4200 mAh / g, which is much higher than that of the graphite anode. However, currently, silicon materials are only used for less than 10% graphite doping, and it is difficult to fully utilize its high specific capacity characteristics. The main reason is that silicon will undergo a huge volume expansion during charge and discharge, which leads to the pulverization of the electrode material, the destruction of the electrode structure, and the repeated formation of the solid electrolyte interface (SEI) film, seriously affecting the battery cycle.

[0003] Due to its unique size effect, nano-sized silicon can relieve the stress caused by volume expansion to a certain extent, and can also be further compounded with carbon to improve its electrochemical performance. However, silicon itself has low conductivity and low lithium-ion diffusion rate, and the overall expansion of the battery will still occur after the close packing expansion of nano-silicon, thus it is difficult to meet the actual battery application requirements. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the problem of poor cycle rate performance caused by the high expansion rate and poor conductivity of the silicon-based anode material in the prior art, and to provide a silicon-carbon anode material, a preparation method thereof, an application thereof, and a lithium-ion battery. The silicon-carbon anode material prepared by the present invention can reserve expansion space for silicon materials, reduce the silicon expansion rate before and after charge and discharge, and improve the cycle life of the material.

[0005] The present invention adopts a chemical vapor deposition method, and simultaneously introduces an inert gas, a carbon source gas, a reducing gas, and "a gas containing an oxygen-containing group and / or a gas containing a nitrogen-containing group" into the reaction system. The "gas containing an oxygen-containing group and / or a gas containing a nitrogen-containing group" pyrolyzes at high temperature to generate highly reactive oxygen-containing and nitrogen-containing free radicals, which can react with the silicon source and lithium hydroxide, thereby generating a layer of Li x SiO y and / or Li x SiN y on the surface of the silicon source, while the carbon source gas is catalytically grown into carbon nanotubes to form a precursor with a loose elastic coating structure; wherein, Li x SiO y and / or Li x SiN yIt can be formed on the surface of the silicon source, avoiding the exposure of the silicon source on the surface, blocking the direct contact between the silicon source and the electrolyte, preventing the pulverization of the silicon source, and improving the interface stability and ion mobility; the carbon nanotubes can play a role in fixing the silicon source, dispersing the silicon source to avoid agglomeration, and suppressing the expansion of the silicon source through the elastic network of the carbon nanotubes, reserving expansion space for the silicon material, and reducing the silicon expansion rate before and after charge and discharge; then a solid carbon source is used to perform carbon coating on the surface of the precursor to prepare a multi-layer carbon structure with an elastic and porous conductive network inside and a rigid carbon coating outside; the further coating of the solid carbon source can prevent the pulverization of silicon particles from damaging the electron channel, and also avoid side reactions caused by excessive wetting of the electrolyte on the silicon surface, improving the cycle life and first Coulomb efficiency of the material; the external coating of the rigid carbon layer shell helps to maintain the internal elastic microstructure and block the excessive contact between silicon and the electrolyte, resulting in side reactions.

[0006] The present invention solves the above technical problems through the following technical solutions:

[0007] The present invention provides a preparation method of a silicon-carbon negative electrode material, which comprises the following steps:

[0008] (1) Immerse the silicon source in a catalyst solution, then filter and dry it, and then mix it with lithium hydroxide and perform high-temperature pyrolysis in a mixed gas atmosphere to obtain a precursor; wherein, the molar ratio of the silicon source to the lithium hydroxide is 100:(0.1-5), the mixed gas includes an inert gas, a carbon source gas, a reducing gas and "a gas containing oxygen-containing groups and / or a gas containing nitrogen-containing groups", the flow ratio of the inert gas in the introduced mixed gas is 85%-99%, the flow ratio of the carbon source gas in the introduced mixed gas is 0.5%-5%, and the flow ratio of the reducing gas in the introduced mixed gas is 0.5%-5%; the temperature of the high-temperature pyrolysis is 600-1050 °C, and the time of the high-temperature pyrolysis is 0.1 h-3 h;

[0009] (2) Mix the precursor and the solid carbon source according to a mass ratio of (3-20):1, then granulate and carbonize to obtain the silicon-carbon negative electrode material.

[0010] In step (1), the "gas containing oxygen-containing groups and / or a gas containing nitrogen-containing groups" generates highly reactive oxygen-containing and nitrogen-containing free radicals upon high-temperature pyrolysis, which can react with the silicon source and lithium hydroxide, thereby forming a layer of Li x SiO y and / or Li x SiN y on the surface of the silicon source, which can avoid the exposure of the silicon source on the surface, block the direct contact between the silicon source and the electrolyte, prevent the pulverization of the silicon source, and improve the interface stability and ion mobility. When the gas containing oxygen-containing groups is introduced, Li x SiO y; When the gas containing nitrogen groups is introduced, Li is generated x SiN y .

[0011] In step (1), the silicon source is preferably silicon and / or silicon monoxide, more preferably silicon monoxide. The particle size of the silicon source can be 30 nm - 10 μm, preferably 30 - 300 nm, such as 200 nm.

[0012] In step (1), the catalyst is preferably an inorganic salt of a transition metal. The transition metal is preferably one or more of Fe, Ni, Cu, and Co. The inorganic salt is preferably a halide, sulfate, or nitrate. The halide is preferably a hydrochloride of a transition metal.

[0013] In step (1), the concentration of the catalyst solution can be 0.2 - 2 mol / L, preferably 0.2 - 1 mol / L, such as 0.5 mol / L.

[0014] In step (1), the solvent in the catalyst solution can be one or more of deionized water, ethanol, acetone, isopropanol, and chloroform, such as deionized water.

[0015] In a specific embodiment, the catalyst is 0.5 mol / L NiCl 2 aqueous solution or 0.5 mol / L nickel nitrate aqueous solution.

[0016] In step (1), the molar ratio of the silicon source to the metal ions in the catalyst solution is preferably (40 - 120):1, such as 50:1, 60:1, 80:1, or 100:1.

[0017] In step (1), the molar ratio of the silicon source to the lithium hydroxide is preferably 100:(1 - 3), such as 100:2.

[0018] In step (1), the soaking time is preferably 5 - 30 min, such as 10 min, 15 min or 20 min. The soaking is generally carried out at room temperature. In step (1), the inert gas can be conventional in the art, such as argon, helium or nitrogen. The flow ratio of the inert gas in the introduced mixed gas is preferably 90% - 99%, such as 95.5%, 96.1% or 98%. The carbon source gas is preferably one or more of natural gas, methane, acetylene and ethylene, and preferably acetylene. The flow ratio of the carbon source gas in the introduced mixed gas is preferably 0.8% - 3%, such as 0.98%, 1%, 1.5%, 1.91%, 1.92% or 2%. The reducing gas can be conventional in the art, generally one or more of hydrogen, carbon monoxide and hydrogen sulfide, such as hydrogen. The flow ratio of the reducing gas in the introduced mixed gas is preferably 0.8% - 3%, such as 0.98%, 1%, 1.5%, 1.91%, 1.92% or 2%. The gas containing oxygen-containing groups is preferably ethanol gas and / or methanol gas. The flow ratio of the gas containing oxygen-containing groups in the introduced mixed gas can be 0.1% - 3%, preferably 0.1% - 2%, such as 0.2%, 0.4%, 0.6% or 1%. The gas containing nitrogen-containing groups is preferably one or more of ammonia, methylamine, ethylamine and propylamine, such as ammonia. The flow ratio of the gas containing nitrogen-containing groups in the introduced mixed gas is preferably 0.1% - 2%, such as 0.5%, 0.64%, 1% or 2%. The flow ratio of the "gas containing oxygen-containing groups and / or gas containing nitrogen-containing groups" in the introduced mixed gas can be 0.1% - 3%. The flow rate of the introduced mixed gas can be 800 - 2000 sccm, preferably 1000 - 1700 sccm, such as 1530 sccm, 1560 sccm or 1570 sccm.

[0019] When the raw material of the "gas containing oxygen-containing groups and / or gas containing nitrogen-containing groups" is a gas, it can be directly introduced into the reaction system; when the raw material of the "gas containing oxygen-containing groups and / or gas containing nitrogen-containing groups" is a liquid, it can be converted into a gas by bubbling or heating. The bubbling can be obtained, for example, by introducing part of the inert gas into the corresponding liquid raw material of the "gas containing oxygen-containing groups and / or gas containing nitrogen-containing groups" and then discharging it.

[0020] In step (1), when the raw material corresponding to the "gas containing oxygen-containing group and / or gas containing nitrogen-containing group" is a liquid, the mixed gas is preferably obtained through the following steps: introducing a part of the inert gas through the first gas passage; introducing the carbon source gas and the reducing gas through the second gas passage; introducing another part of the inert gas into the raw material liquid corresponding to the "gas containing oxygen-containing group and / or gas containing nitrogen-containing group" through the third gas passage, and discharging it from the liquid by the bubbling method; and combining the three-way gases to obtain the mixed gas. The sum of the introduced gas flow rates of the inert gas, the carbon source gas, and the reducing gas can be 1000 - 2000 sccm, preferably 1400 - 1800 sccm. The sum of the introduced gas flow rates of the carbon source gas and the reducing gas can be 20 - 100 sccm, such as 30 sccm or 60 sccm. The ratio of the introduced gas flow rate of the carbon source gas to that of the reducing gas can be 1:(0.5 - 2), such as 1:1. The carbon source gas accounts for 0.8% - 3% of the sum of the introduced gas flow rates of the inert gas, the carbon source gas, and the reducing gas, such as 0.98%, 1%, 1.5%, 1.92%, or 2%. The reducing gas accounts for 0.8% - 3% of the sum of the introduced gas flow rates of the inert gas, the carbon source gas, and the reducing gas, such as 0.98%, 1%, 1.5%, 1.92%, or 2%. The amount of the inert gas introduced through the third gas passage accounts for 20% - 40% of the total introduced gas flow rate of the inert gas, such as 33.3%. The volume of the raw material liquid corresponding to the "gas containing oxygen-containing group and / or gas containing nitrogen-containing group" can be 200 - 1000 mL, such as 500 mL.

[0021] In step (1), when the raw material corresponding to the "gas containing oxygen-containing group and / or gas containing nitrogen-containing group" is a gas, the mixed gas is preferably obtained through the following steps: introducing the inert gas through the first gas passage; introducing the carbon source gas and the reducing gas through the second gas passage; introducing the "gas containing oxygen-containing group and / or gas containing nitrogen-containing group" through the third gas passage; and combining the three-way gases to obtain the mixed gas.

[0022] In step (1), according to the routine in the art, the high-temperature pyrolysis is generally carried out in a tubular furnace.

[0023] In step (1), the temperature of the high-temperature pyrolysis is preferably 700 - 900 °C, such as 800 °C. The time of the high-temperature pyrolysis can be 0.1 h - 2 h, such as 0.2 h or 0.5 h, and is preferably 0.3 - 1 h. The rate of heating up to the temperature of the high-temperature pyrolysis can be 2 - 10 °C / min; preferably 3 - 5 °C / min. The process of heating up to the temperature of the high-temperature pyrolysis is generally carried out in an inert gas atmosphere. The gas flow rate of the inert gas introduced can be 1000 - 2000 sccm. According to the routine in the art, after the high-temperature pyrolysis is generally completed, it is also necessary to naturally cool to room temperature.

[0024] According to the routine in the art, generally, it is first heated up to the temperature of the high-temperature pyrolysis in an inert gas atmosphere, and then the inert gas is switched to the above-mentioned mixed gas, and the high-temperature pyrolysis is carried out in the atmosphere of the mixed gas.

[0025] In step (2), the solid carbon source can be one or more of pitch, petroleum coke, and phenolic resin, and pitch is preferred. The mass ratio of the precursor to the solid carbon source is preferably (5 - 20):1, such as 10:1 or 15:1.

[0026] In step (2), the granulation is preferably spray granulation. The operation and conditions of the spray granulation can be conventional in the art. Before the spray granulation, generally, the mixture of the precursor and the solid carbon source needs to be made into a slurry first, and then the slurry is pumped into a spray granulator for spray granulation. The components of the slurry can include the mixture of the precursor and the solid carbon source, deionized water, and PVP. By weight fraction, the mixture of the precursor and the solid carbon source: deionized water: PVP can be (60 - 80):(90 - 110):(3 - 10), such as 70:100:5. Before the spray granulation, generally, the slurry needs to be mixed evenly. The process parameters of the spray granulation can be an inlet air temperature of 170 - 220 °C (such as 190 °C) and an outlet air temperature of 80 - 110 °C (such as 95 °C).

[0027] In step (2), the carbonization is generally carried out in a tube furnace. According to the routine in the art, the carbonization is generally carried out under the protection of an inert gas. The inert gas is, for example, nitrogen or argon.

[0028] In step (2), the temperature of the carbonization can be 300 - 800 °C, such as 400 °C, 500 °C, or 600 °C. The time of the carbonization can be 0.5 h - 3 h, such as 1 h or 2 h.

[0029] The present invention also provides a silicon-carbon anode material prepared by the preparation method as described above.

[0030] In the present invention, the morphology of the silicon-carbon negative electrode material is preferably spherical. The size of the silicon-carbon negative electrode material can be 2 - 50 μm.

[0031] In the present invention, the silicon-carbon negative electrode material generally has a core-shell structure. The core includes a silicon source, "Li x SiO y and / or Li x SiN y ", and carbon nanotubes. The shell is amorphous carbon. In the core, "Li x SiO y and / or Li x SiN y " is coated on the surface of the silicon source, and the carbon nanotubes are coated on the surface of "Li x SiO y and / or Li x SiN y ".

[0032] Among them, the silicon source can be silicon and / or silicon monoxide. The particle size of the silicon source can be 30 nm - 10 μm, preferably 30 - 300 nm. The coating thickness of "Li x SiO y and / or Li x SiN y " can be 1 - 10 nm. The coating thickness of the carbon nanotubes can be 30 - 500 nm. The coating thickness of the amorphous carbon can be 100 - 800 nm.

[0033] Among them, in the Li x SiO y , preferably, 1 < x < 4, 0.5 < y < 2.

[0034] Among them, in the Li x SiN y , preferably, 1 < x < 8, 0.5 < y < 4.

[0035] The present invention also provides an application of the silicon-carbon negative electrode material as described above in a lithium-ion battery.

[0036] The present invention also provides a lithium-ion battery, which includes a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode includes the silicon-carbon negative electrode material as described above.

[0037] On the basis of conforming to the common knowledge in the art, the above preferred conditions can be combined arbitrarily to obtain various preferred examples of the present invention.

[0038] The reagents and raw materials used in the present invention are all commercially available.

[0039] The positive progressive effect of the present invention lies in:

[0040] The silicon-carbon anode material prepared by the present invention can prevent the silicon source from being exposed on the surface, block the direct contact between the silicon source and the electrolyte, avoid pulverization of the silicon source, reserve expansion space for the silicon material, and reduce the silicon expansion rate before and after charge and discharge; when applied to lithium-ion batteries, it has good electronic conductivity and cycle stability. Description of the Drawings

[0041] Figure 1 Schematic structural diagram of the silicon-carbon anode materials prepared in Examples 1-9;

[0042] Figure 2 SEM image of the silicon-carbon anode material prepared in Example 5;

[0043] Figure 3 Part (a) is the SEM image of the pulverized sample of the silicon-carbon anode material prepared in Example 5 after grinding; Figure 3 Part (b) is the SEM image of the local internal structure of the pulverized sample of the silicon-carbon anode material prepared in Example 5 after grinding;

[0044] Figure 4 XRD pattern of the silicon-carbon anode material prepared in Example 5.

[0045] Reference Signs

[0046] Silicon source 1

[0047] Li x SiO y And / or Li x SiN y 2

[0048] Carbon nanotube 3

[0049] Amorphous carbon 4 Detailed Embodiments

[0050] The present invention will be further illustrated by the following examples, but the present invention is not limited to the scope of the described examples. The experimental methods without specific conditions in the following examples are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0051] The silicon powder used in the following examples and comparative examples was purchased from Aladdin, with a purity of 99.9% and a particle size of about 1 μm.

[0052] Example 1

[0053] (1) At room temperature, immerse the silicon powder in 0.5 M NiCl 2 aqueous solution for 10 minutes (the Ni in the silicon powder and NiCl 2 aqueous solution 2+with a molar ratio of 50:1), filtered, dried, and then mixed with lithium hydroxide. The molar ratio of silicon powder to lithium hydroxide is 100:2. After mixing them evenly, put them into a crucible and place it in a tube furnace. Pass the first gas Ar into the tube furnace at a flow rate of 1000 sccm, and heat it to 800 °C at a heating rate of 5 °C / min in an Ar atmosphere. Then, on the premise of continuously passing the first gas Ar into the tube furnace at a flow rate of 1000 sccm, additionally pass the second gas and the third gas. The second gas is a mixture of 30 sccm of acetylene and 30 sccm of hydrogen; the third gas is 500 sccm of Ar. Pass the third Ar into the inlet of a gas collecting bottle containing 500 mL of ethanol (analytical grade, ambient temperature 25 °C) and discharge it from the outlet of the gas collecting bottle, so as to carry the ethanol out of the gas collecting bottle. Combine these three gases to obtain a mixed gas and pass it into the tube furnace. Continuously pass the mixed gas of the above three gases into the tube furnace at 800 °C for 0.5 h, and after cooling to room temperature, obtain the precursor A;

[0054] The connection method of the three-gas passage is shown in Figure 1 : Preparation of Graphene Films by Low-Hydrogen Atmospheric Pressure CVD Method with Ethanol as Carbon Source and Its Growth Mechanism, Li Liang et al., Atomic Energy Science and Technology, Vol. 49, No. 3.

[0055] (2) Mix the precursor A and asphalt (Shandong Shouhua Chemical Co., Ltd., softening point 60 °C - 90 °C, 98%) according to a mass ratio of 10:1 to obtain a mixture; by weight, add 70 parts of the mixture, 100 parts of deionized water, and 5 parts of PVP-K30 to a mixer and stir to mix evenly to obtain a precursor slurry. Pump the precursor slurry into a spray granulator and perform spray granulation under the conditions that the inlet air temperature is 190 °C and the outlet air temperature is 95 °C to obtain the precursor B; heat the precursor B in a tube furnace in a nitrogen atmosphere at a heating rate of 3 °C / min to 500 °C, keep it at this temperature for 1 h, and then cool it down to room temperature to obtain the silicon-carbon anode material.

[0056] Example 2

[0057] Compared with Example 1, except that acetylene in step (1) is replaced by natural gas (Sichuan Zhongce, standard gas, industrial grade), and the heating temperature is replaced by 1000 °C, the other parameters and conditions are the same as those in Example 1.

[0058] Example 3

[0059] Compared with Example 1, except that the heating time in step (1) is replaced from 0.5 h to 0.2 h, the other parameters and conditions are the same as those in Example 1.

[0060] Example 4

[0061] Compared with Example 1, except that the second gas in step (1) is adjusted to 15 sccm of acetylene and 15 sccm of hydrogen, the other parameters and conditions are the same as those in Example 1.

[0062] Example 5

[0063] Compared with Example 1, except that the silicon powder is replaced by sand-ground silicon powder (the silicon powder is sand-ground in an ethanol medium to a diameter of about 200 nm), the other parameters and conditions are the same as those in Example 1.

[0064] Example 6

[0065] Compared with Example 1, except that silicon powder is replaced by silicon oxide powder (Shanghai Maoguo, particle size 1 μm, purity 99.9%), other parameters and conditions are the same as those in Example 1.

[0066] Example 7

[0067] Compared with Example 1, except that the asphalt in step (2) is replaced by petroleum coke (Hebei Houkang, low-sulfur coke), the other parameters and conditions are the same as those in Example 1.

[0068] Example 8

[0069] Compared with Example 1, except that the asphalt in step (2) is replaced by phenolic resin (Shandong Guohua Chemical, melting point 94° C., water-soluble), the other parameters and conditions are the same as those in Example 1.

[0070] Example 9

[0071] Step (1): Immerse silicon powder in 0.5M NiCl at room temperature. 2 After immersion in aqueous solution for 10 minutes (silicon powder and NiCl 2 Ni in aqueous solution 2+ The molar ratio is 50:1), filtered, dried, put into a crucible, added into a tube furnace, introduced into a first gas Ar at a flow rate of 1500sccm, heated to 800°C at a heating rate of 5°C / min in an argon atmosphere; then, while maintaining the first gas Ar at a flow rate of 1500sccm, introduced into a second gas and a third gas, the second gas is 30sccm of acetylene and 30sccm of hydrogen, the third gas is 10sccm of ammonia, the three gases are combined to obtain a mixed gas, the mixed gas of the three gases is continuously introduced at 800°C for 0.5h, and the precursor A is obtained after cooling to room temperature;

[0072] Step (2): Same as Example 1.

[0073] Comparative Example 1

[0074] Silica powder.

[0075] Comparative Example 2

[0076] Precursor A in Example 1.

[0077] Comparative Example 3

[0078] Silicon powder and asphalt (Shandong Shouhua Chemical Co., Ltd., softening point 60℃~90℃, 98%) were mixed in a mass ratio of 10:1, heated to 500℃ at a heating rate of 3℃ / min in a tubular furnace in a nitrogen atmosphere, kept warm for 1h, and then cooled to room temperature to obtain a silicon-carbon negative electrode material.

[0079] Comparative Example 4

[0080] Step (1): Immerse silicon powder in 0.5M NiCl at room temperature. 2 After immersion in aqueous solution for 10 minutes (silicon powder and NiCl 2 Ni in aqueous solution 2+ The molar ratio is 50:1), filtered, dried, put into a crucible, added into a tube furnace, introduced into a first gas Ar at a flow rate of 1500sccm, and heated to 800°C at a heating rate of 5°C / min in an argon atmosphere; then, while maintaining the first gas Ar at a flow rate of 1500sccm, introduced into a second gas, the second gas being 30sccm of acetylene and 30sccm of hydrogen, the two gases are combined to obtain a mixed gas and introduced into the tube furnace; the mixed gas of the above two gases is continuously introduced at 800°C for 0.5h, and after cooling to room temperature, a precursor A is obtained;

[0081] Step (2): Same as Example 1.

[0082] Effect Example

[0083] (1) Morphology characterization and XRD testing

[0084] The structural schematic diagram of the silicon-carbon negative electrode material prepared in Examples 1-9 of the present invention is as follows Figure 1 As shown, the silicon-carbon negative electrode material has a core-shell structure, the core includes a silicon source 1, "Li x SiO y and / or Li x S N y ” 2 and carbon nanotubes 3, the outer shell is amorphous carbon 4; in the core, “Li x SiO y and / or Li x S N y "2 is coated on the surface of silicon source 1, and carbon nanotubes 3 are coated on "Li x SiO y and / or Li x S Ny ”2. The silicon source may be silicon and / or silicon monoxide. The particle size of the silicon source may be 30nm-10μm. Li x SiO y Layer and / or Li x S N y The thickness of the layer can be 1-10 nm. x SiO y In, 1<x<4, 0.5<y<2. Li x S N y 1<x<8, 0.5<y<4. The coating thickness of the carbon nanotubes may be 30-500 nm. The coating thickness of the amorphous carbon may be 100-800 nm.

[0085] Figure 2 This is the SEM image of the silicon-carbon negative electrode material prepared in Example 5. Figure 2 It can be seen that the prepared silicon-carbon negative electrode material is microspherical with a size of 2-50μm. Figure 3 Part (a) is a SEM image of a ground and pulverized sample of the silicon-carbon negative electrode material prepared in Example 5; Figure 3 Part (b) is a SEM image of the local internal structure of the ground and pulverized sample of the silicon-carbon negative electrode material prepared in Example 5. From the image, it can be seen that the three-dimensional carbon tube network structure is wrapped around the surface of the nano-silicon particles. Figure 4 This is the XRD diagram of the silicon-carbon negative electrode material prepared in Example 1.

[0086] (2) Electrochemical performance test

[0087] The silicon-carbon negative electrode materials prepared in Examples 1 to 9 and the materials prepared in Comparative Examples 1 to 4 were subjected to half-cell tests. The test method is: the above-mentioned materials to be tested are uniformly mixed with the binder CMC (sodium carboxymethyl cellulose) and the conductive carbon black in a mass ratio of 85:5:10, adjusted into a slurry, coated on a copper foil with a coating thickness of 100 microns, and dried at 90°C in vacuum for 12 hours to prepare a lithium battery negative electrode sheet. The simulated battery assembly was carried out in an argon-filled glove box, using 1 mol / L LiPF 6 The electrolyte (solvent is EC, EMC and DMC, EC: EMC: DMC = 1:1:1 (volume ratio), polypropylene microporous membrane is used as the separator, and metal lithium sheet is used as the counter electrode. The electrochemical performance test was carried out on a Land CT2001A battery tester at a temperature of 20 °C and a charge and discharge voltage range of 0.01 to 1.5 V (1 C = 250 mAh g −1 ). The test results are shown in Table 1.

[0088] Table 1

[0089]

[0090] According to the above experimental results, it can be seen that the silicon-carbon anode material prepared by the present invention has excellent electrochemical performance, especially has better specific capacity and cycle life.

[0091] According to Example 1 and Comparative Example 4, when ethanol is not introduced into the mixed gas, the initial charge specific capacity and the capacity retention rate after 100 cycles of the prepared silicon-carbon anode material are significantly reduced.

[0092] Although the specific embodiments of the present invention have been described above, those skilled in the art should understand that this is only an example, and the protection scope of the present invention is defined by the appended claims. Without departing from the principle and essence of the present invention, those skilled in the art can make various changes or modifications to these embodiments, but these changes and modifications all fall within the protection scope of the present invention.

Claims

1. A method for preparing a silicon-carbon negative electrode material, characterized in that: The following steps are involved: (1) soaking a silicon source in a catalyst solution, filtering and drying it, mixing it with lithium hydroxide and then pyrolyzing it at high temperature in a mixed gas atmosphere to obtain a precursor; wherein the molar ratio of the silicon source to the lithium hydroxide is 100:(0.1-5), the mixed gas comprises an inert gas, a carbon source gas, a reducing gas and "a gas containing oxygen groups and / or a gas containing nitrogen groups", the inert gas accounts for 85%-99% of the flow rate of the mixed gas introduced, the carbon source gas accounts for 0.5%-5% of the flow rate of the mixed gas introduced, the reducing gas accounts for 0.5%-5% of the flow rate of the mixed gas introduced, the oxygen-containing gas is ethanol gas and / or methanol gas, and the nitrogen-containing gas is one or more of ammonia, methylamine, ethylamine and propylamine; the temperature of the high temperature pyrolysis is 600-1050°C, and the time of the high temperature pyrolysis is 0.1h-3h; (2) The precursor and the solid carbon source are mixed in a mass ratio of (3-20):1, and then granulated and carbonized to obtain the silicon-carbon negative electrode material.

2. The method for preparing the silicon-carbon negative electrode material according to claim 1, characterized in that: The mixed gas meets one or more of the following conditions: (1) The inert gas is argon, helium or nitrogen; (2) The carbon source gas is one or more of natural gas, methane, acetylene and ethylene; (3) The flow rate ratio of the carbon source gas to the introduced mixed gas is 0.8%-3%; (4) The reducing gas is one or more of hydrogen, carbon monoxide and hydrogen sulfide; (5) The flow rate ratio of the reducing gas to the introduced mixed gas is 0.8%-3%; (6) The flow rate ratio of the "oxygen-containing gas and / or nitrogen-containing gas" to the introduced mixed gas is 0.1%-3%; (7) The flow rate of the mixed gas is 800-2000 sccm; (8) The flow rate ratio of the inert gas to the introduced mixed gas is 90%-99%.

3. The method for preparing the silicon-carbon negative electrode material according to claim 1, characterized in that: Step (1) satisfies one or more of the following conditions: (1) The silicon source is silicon and / or silicon monoxide; (2) The particle size of the silicon source is 30nm-10μm; (3) The catalyst is an inorganic salt of a transition metal; (4) The concentration of the catalyst solution is 0.2-2 mol / L; (5) The solvent in the catalyst solution is one or more of deionized water, ethanol, acetone, isopropanol and chloroform; (6) The molar ratio of the silicon source to the lithium hydroxide is 100:(1-3).

4. The method for preparing the silicon-carbon negative electrode material according to claim 1, characterized in that: Step (1) satisfies one or more of the following conditions: (1) The molar ratio of the silicon source to the metal ions in the catalyst solution is (40-120):1; (2) The soaking time is 5-30 min; (3) The temperature of the high temperature pyrolysis is 700-900°C; (4) The high temperature pyrolysis time is 0.1h-2h.

5. The method for preparing the silicon-carbon negative electrode material according to claim 1, characterized in that: When the raw material corresponding to the "gas containing oxygen groups and / or the gas containing nitrogen groups" is liquid, the mixed gas is obtained by the following steps: introducing a part of the inert gas from the first gas passage; introducing the carbon source gas and the reducing gas from the second gas passage; introducing another part of the inert gas from the third gas passage into the raw material liquid corresponding to the "gas containing oxygen groups and / or the gas containing nitrogen groups", and discharging from the liquid by bubbling; combining the three gases to obtain the mixed gas; When the raw material corresponding to the "gas containing oxygen groups and / or gas containing nitrogen groups" is gas, the mixed gas is preferably obtained through the following steps: introducing the inert gas from the first gas passage; introducing the carbon source gas and the reducing gas from the second gas passage; introducing the "gas containing oxygen groups and / or gas containing nitrogen groups" from the third gas passage; and combining the three gases to obtain the mixed gas.

6. The method for preparing the silicon-carbon negative electrode material according to claim 1, characterized in that: Step (2) satisfies one or more of the following conditions: (1) The solid carbon source is one or more of asphalt, petroleum coke and phenolic resin; (2) The mass ratio of the precursor to the solid carbon source is (5-20):1; (3) The carbonization temperature is 300-800°C; (4) The carbonization time is 0.5h to 3h; (5) The granulation is spray granulation.

7. The method for preparing the silicon-carbon negative electrode material according to claim 6, characterized in that: Before the spray granulation, the mixture of the precursor and the solid carbon source is first made into a slurry, and then the slurry is pumped into a spray granulator for spray granulation; And / or, the process parameters of the spray granulation are an air inlet temperature of 170-220°C and an air outlet temperature of 80-110°C.

8. A silicon-carbon negative electrode material, characterized in that: It is prepared according to the method for preparing the silicon-carbon negative electrode material as described in any one of claims 1 to 7.

9. Use of the silicon-carbon negative electrode material as claimed in claim 8 in a lithium-ion battery.

10. A lithium ion battery, characterized in that: It comprises a positive electrode, a negative electrode, an electrolyte and a separator, wherein the negative electrode comprises the silicon-carbon negative electrode material as claimed in claim 8.

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