Preparation method and application of silicon-carbon composite material

Abstract

The present invention discloses a preparation method and application of a silicon-carbon composite material, and relates to the technical field of lithium-ion battery materials. The preparation method of the silicon-carbon composite material comprises the following steps: mixing pitch coke, an organic metal compound and an organic base, heating and treating, introducing carbon dioxide for activation, and obtaining a metal oxide-doped porous carbon material; introducing silane gas and a reducing gas into the metal oxide-doped porous carbon material for vapor deposition, and obtaining a metal-doped silicon-carbon precursor material; depositing an organic lithium salt on the surface of the metal-doped silicon-carbon precursor material under vacuum conditions, introducing a carbon source for vapor coating, and obtaining a silicon-carbon composite material. The present invention improves the electronic and ionic conductivity of the silicon-carbon composite material by doping metal in the core and coating the lithium compound in the shell, and improves the rate performance and first efficiency of a lithium-ion battery using the silicon-carbon composite material of the present invention to prepare the negative electrode material.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion battery materials, and in particular to a preparation method and application of a silicon-carbon composite material. Background Art

[0002] The new silicon-carbon materials currently on the market are composed of porous carbon and nano-silicon deposited in the pores. They have defects such as poor electronic conductivity and deviation in compressive resistance, which result in deviation in the fast charging performance of the material and low compaction density. At the same time, due to the large number of defects in the inner core porous carbon, there is a problem of low first-effect efficiency. Summary of the invention

[0003] The main purpose of the present invention is to provide a method for preparing a silicon-carbon composite material, aiming to solve the problem of poor electronic and ionic conductivity of existing silicon-carbon materials.

[0004] To achieve the above object, the present invention provides a method for preparing a silicon-carbon composite material, which comprises the following steps:

[0005] S10, mixing the pitch coke, the organometallic compound and the organic base, heating them, and introducing carbon dioxide to activate them, so as to obtain a metal oxide-doped porous carbon material;

[0006] S20, introducing silane gas and reducing gas into the metal oxide-doped porous carbon material to perform vapor deposition to obtain a metal-doped silicon-carbon precursor material;

[0007] S30. Under vacuum conditions, depositing an organic lithium salt on the surface of the metal-doped silicon-carbon precursor material, introducing a carbon source for vapor-phase coating, and obtaining a silicon-carbon composite material.

[0008] In one embodiment, in step S10:

[0009] The mass ratio of the pitch coke, the organometallic compound and the organic base is 100:(1-5):(10-30); and / or,

[0010] The organometallic compound includes at least one of magnesium citrate, magnesium stearate, magnesium acetate, magnesium salicylate, lithium octanoate, lithium pyruvate, lithium trifluoromethanesulfonate and lithium diisopropylamine; and / or,

[0011] The organic base comprises at least one of pyridine, imidazole, indole and pyrrole; and / or,

[0012] The temperature of the heating treatment is 800°C to 1200°C; and / or,

[0013] The heating time is 1h to 6h; and / or,

[0014] The temperature for introducing carbon dioxide for activation is 800°C to 1200°C; and / or,

[0015] The activation time of introducing carbon dioxide is 1 hour to 3 hours; and / or,

[0016] The pressure of introducing carbon dioxide for activation is 1.1Mpa to 5.1Mpa.

[0017] In one embodiment, in step S20:

[0018] The silane gas includes at least one of propyltrimethoxysilane, butyltrimethoxysilane, dimethylsilane, dimethoxydimethylsilane, trimethoxymethylsilane, methyltrimethoxysilane and dichlorovinylmethylsilane; and / or,

[0019] The reducing gas includes hydrogen.

[0020] In one embodiment, in step S30:

[0021] The carbon source comprises at least one of methane, ethane, propane, ethylene, acetylene and butene; and / or,

[0022] The temperature for introducing the carbon source for gas phase coating is 600°C to 900°C; and / or,

[0023] The flow rate of the carbon source is 100 SCCM to 500 SCCM; and / or,

[0024] The time for introducing the carbon source for gas phase coating is 30 min to 300 min.

[0025] In one embodiment, in step S20, silane gas and reducing gas are introduced in the form of a mixed gas of silane gas and reducing gas, wherein:

[0026] The flow rate of the mixed gas is 100 SCCM to 500 SCCM; and / or,

[0027] In the mixed gas, the volume ratio of the silane gas to the reducing gas is 10:(1-3).

[0028] In one embodiment, in step S20:

[0029] The temperature of the vapor deposition is 400°C to 600°C; and / or,

[0030] The vapor deposition time is 1 h to 10 h; and / or,

[0031] The pressure of vapor deposition is 0.1Mpa~0.5Mpa.

[0032] In one embodiment, in step S30, the step of depositing an organic lithium salt on the surface of the metal-doped silicon-carbon precursor material includes:

[0033] The organic lithium salt solution is atomized and then introduced into the metal-doped silicon-carbon precursor material for deposition.

[0034] In one embodiment, in the step of atomizing the organic lithium salt solution and then introducing the organic lithium salt solution into the metal-doped silicon-carbon precursor material for deposition:

[0035] The solute of the organic lithium salt solution includes at least one of lithium 4-methylbenzenesulfonate, lithium trifluoromethanesulfonate, lithium perfluorohexanesulfonate and lithium perfluorobutylsulfonate; and / or,

[0036] The solvent of the organic lithium salt solution includes dimethyl carbonate; and / or,

[0037] The concentration of the solute in the organic lithium salt solution is 5 wt % to 10 wt %.

[0038] In one embodiment, in the step of atomizing the organic lithium salt solution and then introducing the organic lithium salt solution into the metal-doped silicon-carbon precursor material for deposition:

[0039] The deposition temperature is 100°C to 200°C; and / or,

[0040] The deposition pressure is 1Mpa to 3Mpa; and / or,

[0041] The deposition time is 10 min to 60 min.

[0042] The present invention also provides an application of the silicon-carbon composite material prepared by the method for preparing the silicon-carbon composite material in a lithium-ion battery.

[0043] In the technical solution provided by the present invention, asphalt coke, organic metal compound and organic base are mixed and sintered, and pores are formed by carbon dioxide to obtain metal oxide doped porous carbon, and the metal oxide is used to improve the electronic and ionic conductivity of the material, and the organic base is sintered to generate porous carbon with large pores, thereby reducing the expansion of nano silicon during charging and discharging; the specific capacity is improved by depositing nano silicon decomposed by liquid silane gasification in the metal oxide, and the metal oxide is reduced by hydrogen to generate metal to improve the electronic and ionic conductivity of the material; the organic lithium salt is deposited on the surface of the metal-doped silicon-carbon precursor material to reduce its irreversible capacity and further improve the ionic conductivity of the material; then amorphous carbon is coated on the outermost layer to improve the electronic and ionic conductivity of the material and reduce side reactions. Therefore, the preparation method of the silicon-carbon composite material provided by the present invention can improve the electronic and ionic conductivity of the silicon-carbon composite material, and can improve the first efficiency and rate performance of the battery when applied to the preparation of negative electrode materials for lithium ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0045] Figure 1 This is a SEM image of the silicon-carbon composite material prepared in Example 1 of the present invention.

[0046] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0047] To make the purpose, technical scheme and advantages of the embodiment of the present invention clearer, the technical scheme in the embodiment of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiment, it is carried out according to the normal conditions or the conditions recommended by the manufacturer. If the reagents or instruments used do not specify the manufacturer, they are all conventional products that can be purchased commercially. In addition, the meaning of "and / or" appearing in the full text includes three parallel schemes, taking "A and / or B" as an example, including scheme A, or scheme B, or schemes that A and B meet at the same time. In addition, the technical schemes between the various embodiments can be combined with each other, but must be based on the ability of ordinary technicians in the field to achieve. When the combination of technical solutions is contradictory or cannot be achieved, it should be considered that the combination of such technical solutions does not exist, and is not within the scope of protection required by the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work belong to the scope of protection of the present invention.

[0048] The new silicon-carbon materials currently on the market are composed of porous carbon and nano-silicon deposited in the pores. They have defects such as poor electronic and ionic conductivity and deviation in their compressive resistance, which result in deviations in the fast charging performance of the material and low compaction density. At the same time, due to the large number of defects in the porous carbon in the inner core, there is a problem of low first-effect efficiency.

[0049] In view of this, the present invention proposes a method for preparing a silicon-carbon composite material, aiming to improve the electronic and ionic conductivity of the silicon-carbon composite material, and to improve the initial efficiency and rate performance of the lithium-ion battery after being applied to the lithium-ion battery.

[0050] The method for preparing the silicon-carbon composite material provided by the present invention comprises the following steps:

[0051] S10, mixing the pitch coke, the organometallic compound and the organic base, heating them, and introducing carbon dioxide to activate them, so as to obtain a metal oxide-doped porous carbon material;

[0052] S20, introducing silane gas and reducing gas into the metal oxide-doped porous carbon material to perform vapor deposition to obtain a metal-doped silicon-carbon precursor material;

[0053] S30. Under vacuum conditions, depositing an organic lithium salt on the surface of the metal-doped silicon-carbon precursor material, introducing a carbon source for vapor-phase coating, and obtaining a silicon-carbon composite material.

[0054] In the technical solution provided by the present invention, asphalt coke, organic metal compound and organic base are mixed and sintered, and pores are formed by carbon dioxide to obtain metal oxide doped porous carbon, and the metal oxide is used to improve the electronic and ionic conductivity of the material, and the organic base is sintered to generate porous carbon with large pores, thereby reducing the expansion of nano silicon during charging and discharging; the specific capacity is improved by depositing nano silicon decomposed by liquid silane gasification in the metal oxide, and the metal oxide is reduced by hydrogen to generate metal to improve the electronic and ionic conductivity of the material; the organic lithium salt is deposited on the surface of the metal-doped silicon-carbon precursor material to reduce its irreversible capacity and further improve the ionic conductivity of the material; then amorphous carbon is coated on the outermost layer to improve the electronic and ionic conductivity of the material and reduce side reactions. Therefore, the preparation method of the silicon-carbon composite material provided by the present invention can improve the electronic and ionic conductivity of the silicon-carbon composite material, and can improve the first efficiency and rate performance of the battery when applied to the preparation of negative electrode materials for lithium ion batteries.

[0055] It should be noted that the obtained carbon-silicon composite material includes an inner core and a lithium compound coating layer and an amorphous carbon coating layer prepared in sequence outside the inner core, wherein the inner core includes a porous carbon matrix and nano-silicon deposited in the pores of the porous carbon matrix, and the porous carbon matrix is ​​doped with metal.

[0056] In step S10, during the specific operation, the asphalt coke, the organometallic compound and the organic base can be mixed first, transferred to a tubular furnace for heating treatment, and then carbon dioxide gas is introduced, and then the temperature is naturally reduced to obtain a metal oxide-doped porous carbon material. Among them, the asphalt coke provides a carbon source for the silicon-carbon composite material, the organometallic compound provides a metal source for the silicon-carbon composite material, and the organic base is sintered to obtain a porous carbon material with a large pore size. In addition, carbon dioxide enters the interior of the material by dissolution, diffusion or penetration, and precipitates during the cooling process to form pores, thereby reducing the expansion of nano-silicon in the silicon-carbon composite material during charging and discharging. The organic base can also provide an alkaline environment and provide heteroatoms to reduce the impedance of the material. At the same time, the decomposition temperature of the organic base is low, which can reduce energy consumption.

[0057] Further, in step S10:

[0058] The mass ratio of the asphalt coke, the organometallic compound and the organic base is 100:(1-5):(10-30); specifically, the mass ratio of the asphalt coke, the organometallic compound and the organic base can be 100:1:10, 100:3:20, 100:5:30, etc. The use of the asphalt coke, the organometallic compound and the organic base in the above mass ratio can produce a silicon-carbon composite material with better electronic conductivity.

[0059] The organometallic compound includes at least one of magnesium citrate, magnesium stearate, magnesium acetate, magnesium salicylate, lithium octanoate, lithium pyruvate, lithium trifluoromethanesulfonate and lithium diisopropylamine; it should be noted that the present invention is not limited to using only the above raw materials, and the lithium ions and / or magnesium ions provided by the above compounds are reduced in subsequent steps to obtain metallic lithium and / or metallic magnesium, thereby obtaining a metal-doped silicon-carbon composite material. Preferably, only one of the above materials can be used.

[0060] The organic base includes at least one of pyridine, imidazole, indole and pyrrole; the above substances have unshared electron pairs and can form complexes with metal ions. This reactivity helps to interact with metal ions during the material preparation process, thereby facilitating the formation of pore structures; in addition, it has good solubility and can be evenly dispersed in the material, thereby ensuring the uniformity of the pore structure in the material. Preferably, only one of the above materials can be used.

[0061] The temperature of the heating treatment is 800°C to 1200°C, and the time of the heating treatment is 1h to 6h. Specifically, the temperature of the heating treatment is 800°C, 950°C, 1200°C, etc., and the time of the heating treatment is 1h, 3h, 6h, etc. Heating the mixture within this temperature range can form uniform pores.

[0062] The temperature for activation by introducing carbon dioxide is 800°C to 1200°C, the time for activation by introducing carbon dioxide is 1h to 3h, and the pressure for activation by introducing carbon dioxide is 1.1Mpa to 5.1Mpa. Specifically, the temperature for activation by introducing carbon dioxide can be 800°C, 950°C, 1200°C, etc., the time for activation by introducing carbon dioxide is 1h, 2h, 3h, etc., the pressure for activation by introducing carbon dioxide is 1.1Mpa, 3Mpa, 5.1Mpa, etc., and the above activation conditions are used for pore formation to obtain a large number of uniform pores to increase the specific surface area and porosity of the metal oxide-doped porous carbon material.

[0063] In some embodiments, asphalt coke, organometallic compounds and organic bases can be mixed evenly in a mass ratio of 100:(1-5):(10-30), transferred to a tubular furnace, heated to 800°C-1200°C and kept warm for 1h-6h, and then carbon dioxide gas is introduced at this temperature, and the pressure of the cavity is maintained at 1.1Mpa-5.1Mpa for 1h-3h, and then naturally cooled to room temperature to obtain a metal oxide-doped porous carbon material.

[0064] It should be noted that in step S20, the silane gas refers to gaseous silane, not specifically silane that is gaseous at room temperature, but also silane gas obtained by heating and vaporizing silane that is liquid at room temperature. In some embodiments, the silane gas includes at least one of propyltrimethoxysilane, butyltrimethoxysilane, dimethylsilane, dimethoxydimethylsilane, trimethoxymethylsilane, methyltrimethoxysilane and dichlorovinylmethylsilane. The nano-silicon obtained by vapor deposition and gasification decomposition of the above silane can be more evenly incorporated into the metal oxide-doped porous carbon material.

[0065] Furthermore, in step S20, silane gas and reducing gas are introduced in the form of a mixed gas of silane gas and reducing gas. When silane gas is introduced, the silane gas decomposes at high temperature to obtain nano-silicon to silicon-dope the metal oxide-doped porous carbon material; the reducing gas is introduced to reduce the metal oxide to metal to improve the electronic and ionic conductivity of the material and improve the rate performance. The reducing gas includes hydrogen, which has a strong reducing ability and is not easy to react with the silane gas. Therefore, the use of hydrogen can better reduce the metal oxide to metal to obtain a metal-doped carbon silicon material.

[0066] The flow rate of the mixed gas is 100 SCCM to 500 SCCM, and the flow rate of the mixed gas is 100 SCCM, 300 SCCM, 500 SCCM, etc. The use of the above intake flow rate can make the mixed gas and the metal oxide-doped porous carbon material react more fully.

[0067] Furthermore, in the mixed gas, the volume ratio of the silane gas to the reducing gas is 10:(1-3), specifically, the volume ratio of the silane gas to the reducing gas is 10:1, 10:2, 10:3, etc. The above volume ratio can make the reduction reaction and silicon doping fully react.

[0068] In addition, in step S20, the temperature of vapor deposition is 400°C to 600°C, the time of vapor deposition is 1h to 10h, and the pressure of vapor deposition is 0.1Mpa to 0.5Mpa. Specifically, the temperature of vapor deposition can be 400°C, 500°C, 600°C, etc., the time of vapor deposition is 1h, 5h, 10h, etc., and the pressure of vapor deposition is 0.1Mpa, 0.3Mpa, 0.5Mpa, etc. Using the above conditions for vapor deposition can not only obtain a suitable silicon doping rate and silicon doping effect, but also obtain a better metal doping effect.

[0069] It should be noted that in step S20, the metal oxide-doped porous carbon material can be transferred to a fluidized bed, an inert gas is introduced to exhaust the air in the pipe, the temperature is raised to 400°C to 600°C, and the pressure in the cavity is maintained at less than 0.01Mpa, and a mixed gas of silane gas and hydrogen reducing gas is introduced at the same time, with a gas flow rate of 100SCCM to 500SCCM, and the pressure in the cavity is maintained at 0.1 to 0.5Mpa, and vapor deposition is carried out for 1h to 10h to obtain a metal-doped silicon-carbon precursor material.

[0070] In step S30, an organic lithium salt is first deposited on the surface of the metal-doped silicon-carbon precursor material under vacuum conditions. In some embodiments, the step of depositing the organic lithium salt on the surface of the metal-doped silicon-carbon precursor material includes: atomizing the organic lithium salt solution, and then passing it into the metal-doped silicon-carbon precursor material for deposition. Specifically, the metal-doped silicon-carbon precursor material can be transferred to a vacuum deposition chamber, and a vaporized organic salt solution is passed into the chamber for deposition, so that the organic lithium salt is deposited on the surface of the metal-doped silicon-carbon precursor material to form a first coating layer.

[0071] Furthermore, in the step of atomizing the organic lithium salt solution and then introducing it into the metal-doped silicon-carbon precursor material for deposition:

[0072] The solute of the organic lithium salt solution includes at least one of lithium 4-methylbenzenesulfonate, lithium trifluoromethanesulfonate, lithium perfluorohexanesulfonate and lithium perfluorobutylsulfonate. The use of the above-mentioned organic lithium salt can better reduce the defects of the obtained carbon-silicon composite material and better improve the ionic conductivity of the carbon-silicon composite material, so that the lithium-ion battery has better first efficiency and better fast charging performance.

[0073] The solvent of the organic lithium salt solution includes dimethyl carbonate, which is a polar solvent that can effectively dissolve organic lithium salts and organic lithium salts that are poorly soluble in water, so that the organic lithium salts can be evenly dispersed to better coat the metal-doped silicon-carbon precursor material.

[0074] The concentration of the solute in the organic lithium salt solution is 5wt% to 10wt%, specifically, the concentration of the solute in the organic lithium salt solution can be 5wt%, 8wt%, 10wt%. Wherein, wt% is weight percentage, that is, in the organic lithium salt solution, the ratio of the mass of the solute to the mass of the organic lithium salt solution is (5-10):100. Within the above range, the solute can be better dissolved and dispersed, so as to obtain a better coating effect.

[0075] Furthermore, in the step of atomizing the organic lithium salt solution and then passing it into the metal-doped silicon-carbon precursor material for deposition: the deposition temperature is 100°C to 200°C, the deposition pressure is 1Mpa to 3Mpa, and the deposition time is 10min to 60min. Specifically, the deposition temperature can be 100°C, 150°C, 200°C, etc., the deposition pressure can be 1Mpa, 2Mpa, 3Mpa, etc., and the deposition time can be 10min, 30min, 60min, etc. Deposition of the organic lithium salt under the above conditions makes the deposition effect better, thereby improving the performance of the silicon-carbon composite material.

[0076] After the organic lithium salt is introduced for primary coating, the carbon source is introduced for secondary coating of the metal-doped silicon-carbon precursor material, thereby improving the electronic and ionic conductivity of the material and reducing side reactions, improving rate performance and initial efficiency. The carbon source includes at least one of methane, ethane, propane, ethylene, acetylene and butene. Preferably, one of methane, ethylene and acetylene can obtain a better coating effect, thereby reducing the full-charge expansion rate of the negative electrode sheet made of the silicon-carbon negative electrode material.

[0077] Among them, the temperature of the carbon source for gas phase coating is 600°C to 900°C, the flow rate of the carbon source is 100SCCM to 500SCCM, and the time of the carbon source for gas phase coating is 30min to 300min. Specifically, the temperature of the carbon source for gas phase coating can be 600°C, 800°C, 900°C, etc., the flow rate of the carbon source is 100SCCM, 300SCCM, 500SCCM, etc., and the time of the carbon source for gas phase coating is 30min, 120min, 300min, etc. Carbon coating under the above conditions can make the coating more uniform and the coating effect is good, thereby improving the performance of the silicon-carbon composite material.

[0078] It should be noted that in step S30, the metal-doped silicon-carbon precursor material can be transferred to a vacuum deposition chamber, and an organic lithium salt solution is introduced for vaporization and deposition at a temperature of 100°C to 200°C and a pressure of 1Mpa to 3Mpa. The deposition time is 10min to 60min, so as to deposit organic lithium salt on the surface of the metal-doped silicon-carbon precursor material. Thereafter, the temperature is raised to 600°C to 900°C, and a carbon source gas is introduced. The secondary coating is performed at a flow rate of 100SCCM to 500SCCM for 30min to 300min to obtain a silicon-carbon composite material.

[0079] The present invention also proposes an application of the silicon-carbon composite material prepared by the preparation method of the silicon-carbon composite material in a lithium-ion battery. The use of the silicon-carbon composite material to prepare a negative electrode sheet of a lithium-ion battery can increase the initial discharge specific capacity and initial efficiency of the lithium-ion battery and improve the rate performance of the lithium-ion battery.

[0080] The technical solution of the present invention is further described in detail below in conjunction with specific embodiments and drawings. It should be understood that the following embodiments are only used to explain the present invention and are not used to limit the present invention.

[0081] Example 1

[0082] A method for preparing a silicon-carbon composite material is provided, comprising the following steps:

[0083] S10, 100g of pitch coke, 3g of magnesium citrate and 20g of pyridine were mixed evenly, transferred to a tube furnace, heated to 950°C and kept warm for 3h, then carbon dioxide gas was introduced at this temperature, the pressure of the cavity was maintained at 3Mpa and kept warm for 2h, and then naturally cooled to room temperature to obtain a metal oxide-doped porous carbon material;

[0084] S20, transferring the metal oxide-doped porous carbon material to a fluidized bed, introducing argon gas to exhaust the air in the pipe, raising the temperature to 500°C, and maintaining the pressure of the cavity at 0.005 MPa, and simultaneously introducing a mixed gas of propyltrimethoxysilane gas and hydrogen (the volume ratio of propyltrimethoxysilane gas to hydrogen is 10:2), with a gas flow rate of 300 SCCM, and maintaining the pressure of the cavity at 0.3 MPa, and performing vapor deposition for 6 hours to obtain a metal-doped silicon-carbon precursor material;

[0085] S30. Transfer the metal-doped silicon-carbon precursor material to a vacuum deposition chamber, and introduce a vaporized 10% 4-methylbenzenesulfonate solution at a temperature of 150°C and a pressure of 2 MPa for deposition for 30 minutes to deposit 4-methylbenzenesulfonate on the surface of the metal-doped silicon-carbon precursor material. Then, raise the temperature to 800°C and introduce methane gas at a gas flow rate of 300 SCCM. Deposit for 120 minutes for secondary coating to obtain a silicon-carbon composite material.

[0086] The SEM image of the obtained silicon-carbon composite material is as follows: Figure 1 shown.

[0087] Example 2

[0088] A method for preparing a silicon-carbon composite material is provided, comprising the following steps:

[0089] S10, 100g of asphalt coke, 1g of magnesium stearate, and 10g of imidazole were mixed evenly, transferred to a tube furnace, heated to 800°C and kept warm for 6h, then carbon dioxide gas was introduced at this temperature, the pressure of the cavity was maintained at 5.1Mpa and kept warm for 1h, and then naturally cooled to room temperature to obtain a metal oxide-doped porous carbon material;

[0090] S20, transferring the metal oxide-doped porous carbon material to a fluidized bed, introducing argon gas to exhaust the air in the pipe, raising the temperature to 400°C, and maintaining the pressure of the cavity at 0.005 MPa, and simultaneously introducing a mixed gas of butyltrimethoxysilane gas and hydrogen (the volume ratio of butyltrimethoxysilane gas to hydrogen is 10:1), with a gas flow rate of 100 SCCM, and maintaining the pressure of the cavity at 0.1 MPa, and performing vapor deposition for 1 hour to obtain a metal-doped silicon-carbon precursor material;

[0091] S30. The metal-doped silicon-carbon precursor material is transferred to a vacuum deposition chamber. At a temperature of 100°C and a pressure of 3 MPa, a vaporized 4-trifluoromethanesulfonate solution with a mass concentration of 10% is introduced for deposition. The deposition time is 60 minutes to deposit lithium trifluoromethanesulfonate on the surface of the metal-doped silicon-carbon precursor material. Then, the temperature is raised to 600°C and acetylene gas is introduced with a gas flow rate of 100 SCCM. The secondary coating is performed for 300 minutes to obtain a silicon-carbon composite material.

[0092] Example 3

[0093] A method for preparing a silicon-carbon composite material is provided, comprising the following steps:

[0094] S10, 100g of pitch coke, 5g of magnesium acetate, and 30g of indole were mixed evenly, transferred to a tube furnace, heated to 1200°C and kept warm for 1h, then carbon dioxide gas was introduced at this temperature, the pressure of the cavity was maintained at 1.1Mpa and kept warm for 3h, and then naturally cooled to room temperature to obtain a metal oxide-doped porous carbon material;

[0095] S20, transferring the metal oxide-doped porous carbon material to a fluidized bed, introducing argon gas to exhaust the air in the pipe, raising the temperature to 600° C., and maintaining the pressure of the cavity at 0.005 MPa, and simultaneously introducing a mixed gas of dimethylsilane gas and hydrogen (the volume ratio of dimethylsilane gas to hydrogen is 10:3), with a gas flow rate of 500 SCCM, and maintaining the pressure of the cavity at 0.5 MPa, and performing vapor deposition for 1 hour to obtain a metal-doped silicon-carbon precursor material;

[0096] S30. Transfer the metal-doped silicon-carbon precursor material to a vacuum deposition chamber, and introduce a vaporized lithium perfluorohexane sulfonate solution with a mass concentration of 10% for deposition at a temperature of 200°C and a pressure of 1 MPa for 60 minutes to deposit lithium perfluorohexane sulfonate on the surface of the metal-doped silicon-carbon precursor material. Then, raise the temperature to 900°C and introduce ethylene gas with a gas flow rate of 500 SCCM. Deposit for 30 minutes for secondary coating to obtain a silicon-carbon composite material.

[0097] Comparative Example 1

[0098] Except that magnesium stearate and imidazole are not added in step S10, other steps are the same as those in Example 1.

[0099] Comparative Example 2

[0100] Step S30 is changed to: transferring the metal-doped silicon-carbon precursor material into a vacuum deposition chamber, heating it to 800° C., introducing methane gas with a gas flow rate of 300 SCCM, and depositing it for 120 minutes for secondary coating to obtain a silicon-carbon composite material.

[0101] The other steps are the same as those in Example 1.

[0102] Silicon-carbon composite material performance test

[0103] Referring to the national standard GB / T 38823-2020 "Silicon Carbon", the specific surface area and tap density of the silicon-carbon composite materials obtained in Examples 1 to 3 and Comparative Examples 1 to 2 were tested, and the powder conductivity of each silicon-carbon composite material was tested using a four-probe tester. The pore size and pore volume of the metal oxide-doped porous carbon in Examples 1 to 3 and Comparative Examples 1 to 2 were also tested, and the test results are shown in Table 1 below.

[0104] Table 1 Physical and chemical properties test table of silicon-carbon composite materials obtained in Examples 1 to 3 and Comparative Examples 1 to 2

[0105]

[0106] As can be seen from Table 1, compared with Comparative Examples 1 to 2, the silicon-carbon composite materials provided in Examples 1 to 3 have higher powder density, larger powder conductivity, larger pore size, and smaller pore volume. Therefore, the silicon-carbon composite materials provided in the present application can reduce the defects of the material by doping metal in porous carbon and improve the electronic and ionic conductivity of the material. As a result, the silicon-carbon composite materials provided in the present application can improve the rate performance and cycle performance of the battery as the negative electrode of the lithium-ion battery.

[0107] Button battery performance test

[0108] The silicon-carbon composite materials corresponding to Examples 1 to 3 and Comparative Examples 1 to 2 were used as negative electrode materials for lithium-ion batteries to prepare button batteries according to the following method:

[0109] Add binder, conductive agent and solvent to each corresponding silicon-carbon composite material, stir to make slurry, apply on copper foil, dry and roll to obtain negative electrode sheet; the binder used is LA132, the conductive agent is SP (conductive carbon black), the solvent is NMP, the usage ratio of composite material, SP, LA132 and NMP is 95g:1g:4g:220mL; the electrolyte is LiPF 6The electrolyte solution has a concentration of 1 mol / L, wherein the solvent is a mixture of EC and DEC in a volume ratio of 1:1; the metal lithium sheet is the counter electrode, and the diaphragm is a polypropylene (PP) film.

[0110] Each button cell was assembled in an argon-filled glove box and then subjected to the following performance tests:

[0111] 1. Electrochemical performance test: The electrochemical performance was specifically tested on a Wuhan Blue Electric CT2001A battery tester, with a charge and discharge voltage range of 0.005V to 2.0V and a charge and discharge rate of 0.1C. The discharge specific capacity and initial efficiency of the corresponding button cell were tested. At the same time, the rate performance (1C / 0.1C) of the corresponding button cell was tested. The test results are shown in Table 2.

[0112] 2. Full-charge expansion. The specific test process is: test the thickness D1 of the negative electrode of the button battery after rolling, then dissect the full-charge thickness D2 of the negative electrode when the button battery is fully charged to 100% SOC, and then calculate the expansion rate of the negative electrode (expansion rate = (D1-D2) / D1*100%); the test results are shown in Table 2.

[0113] Table 2 Performance test table of button batteries obtained from Examples 1 to 3 and Comparative Examples 1 to 2

[0114]

[0115] It can be seen from Table 2 above that, compared with Comparative Examples 1 to 2, the button batteries obtained by using the silicon-carbon composite materials provided in Examples 1 to 3 as the negative electrode sheets of button batteries have higher first discharge specific capacity, higher first efficiency, higher rate performance and smaller full charge expansion.

[0116] It is explained that the silicon-carbon composite material provided in the present application can improve the electronic and ionic conductivity of the material and reduce the defects of the material by doping metals into the porous carbon, so that the obtained silicon-carbon composite material can improve the initial efficiency of the battery when used as the negative electrode of a lithium-ion battery. At the same time, by depositing organic lithium salts and amorphous carbon on the surface of the carbon-silicon material, the expansion of the material is restrained and the electronic and ionic conductivity of the material is improved, thereby improving the rate performance of the battery.

[0117] Soft pack battery performance test

[0118] The silicon-carbon composite materials corresponding to Examples 1 to 3 and Comparative Examples 1 to 2 were doped with 90% artificial graphite as negative electrode materials (i.e., negative electrode plates) and positive electrode ternary materials (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2), electrolyte and separator are assembled into a 5Ah soft-pack battery; wherein the separator is celegard 2400, the electrolyte is LiPF6 solution (the solvent is a mixed solution of EC and DEC with a volume ratio of 1:1, and the concentration of LiPF6 is 1.1 mol / L), and a soft-pack battery is prepared.

[0119] The following performance tests were performed on the soft-pack batteries obtained in Examples 1 to 3 and Comparative Examples 1 to 2:

[0120] A. HPPC test, 3C pulse for 10S and then test the charging DCR under different SOC. The test data is shown in Table 3.

[0121] Table 3 HPPC test table of soft-pack batteries obtained in Examples 1 to 3 and Comparative Examples 1 to 2

[0122]

[0123] It can be seen from Table 3 that the HPPC of the silicon-carbon composite material provided in Examples 1 to 3 is better than that in Comparative Examples 1 to 2, indicating that the silicon-carbon composite material provided in the present application can reduce the DCR of the battery and improve the rate performance of the battery as a negative electrode sheet for a lithium-ion battery.

[0124] B. Cycle performance test:

[0125] The test conditions of the cycle performance test are: charge and discharge voltage range of 2.5 ~ 4.2V, temperature of 25 ± 3.0 ° C, charge and discharge rate of 1.0C / 1.0C, cycle number of 500 times, and test its initial charge DCR (50% SOC), the test results are shown in Table 4;

[0126] Table 4 Cycle performance test table of soft pack batteries obtained from Examples 1 to 3 and Comparative Examples 1 to 2

[0127]

[0128] It can be seen from Table 4 that the cycle performance of the soft-pack lithium-ion battery prepared using the silicon-carbon composite material provided in Examples 1 to 3 is significantly better than that of Comparative Examples 1 to 2. The silicon-carbon composite material provided in the present application can improve the liquid retention performance of the material and the lower full-charge expansion, thereby improving the cycle performance.

[0129] The above description is only a preferred embodiment of the present invention, and does not limit the patent scope of the present invention. All equivalent structural changes made by using the contents of the present invention specification and drawings under the inventive concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A method for preparing a silicon-carbon composite material, characterized in that: The following steps are involved: S10, mixing the pitch coke, the organometallic compound and the organic base, heating them, and introducing carbon dioxide to activate them, so as to obtain a metal oxide-doped porous carbon material; S20, introducing silane gas and reducing gas into the metal oxide-doped porous carbon material to perform vapor deposition to obtain a metal-doped silicon-carbon precursor material; S30, under vacuum conditions, depositing an organic lithium salt on the surface of the metal-doped silicon-carbon precursor material, introducing a carbon source for vapor phase coating, and obtaining a silicon-carbon composite material; In step S10: The organometallic compound includes at least one of magnesium citrate, magnesium stearate, magnesium acetate, magnesium salicylate, lithium octanoate, lithium pyruvate, lithium trifluoromethanesulfonate and lithium diisopropylamine; The organic base comprises at least one of pyridine, imidazole, indole and pyrrole; The temperature of the heating treatment is 800℃~1200℃; The heating treatment time is 1h~6h; The temperature for introducing carbon dioxide for activation is 800℃~1200℃; The activation time of carbon dioxide is 1h~3h; The pressure of introducing carbon dioxide for activation is 1.1Mpa~5.1Mpa.

2. The method for preparing the silicon-carbon composite material according to claim 1, characterized in that: In step S10: The mass ratio of the asphalt coke, the organic metal compound and the organic base is 100:(1-5):(10-30).

3. The method for preparing the silicon-carbon composite material according to claim 1, characterized in that: In step S20; The silane gas includes at least one of propyltrimethoxysilane, butyltrimethoxysilane, dimethylsilane, dimethoxydimethylsilane, trimethoxymethylsilane, methyltrimethoxysilane and dichlorovinylmethylsilane; and / or, The reducing gas includes hydrogen.

4. The method for preparing the silicon-carbon composite material according to claim 1, characterized in that: In step S30: The carbon source comprises at least one of methane, ethane, propane, ethylene, acetylene and butene; and / or, The temperature for introducing the carbon source for gas phase coating is 600°C to 900°C; and / or, The flow rate of the carbon source is 100 SCCM to 500 SCCM; and / or, The time for introducing the carbon source for gas phase coating is 30min~300min.

5. The method for preparing the silicon-carbon composite material according to claim 1, characterized in that: In step S20, silane gas and reducing gas are introduced in the form of a mixed gas of silane gas and reducing gas, wherein: The flow rate of the mixed gas is 100 SCCM to 500 SCCM; and / or, In the mixed gas, the volume ratio of the silane gas to the reducing gas is 10:(1-3).

6. The method for preparing the silicon-carbon composite material according to claim 1, characterized in that: In step S20: The temperature of the vapor deposition is 400°C to 600°C; and / or, The vapor deposition time is 1h~10h; and / or, The pressure of vapor deposition is 0.1Mpa~0.5Mpa.

7. The method for preparing the silicon-carbon composite material according to claim 1, characterized in that: In step S30, the step of depositing an organic lithium salt on the surface of the metal-doped silicon-carbon precursor material includes: The organic lithium salt solution is atomized and then introduced into the metal-doped silicon-carbon precursor material for deposition.

8. The method for preparing the silicon-carbon composite material according to claim 7, characterized in that: In the step of atomizing the organic lithium salt solution and then introducing the solution into the metal-doped silicon-carbon precursor material for deposition: The solute of the organic lithium salt solution includes at least one of lithium 4-methylbenzenesulfonate, lithium trifluoromethanesulfonate, lithium perfluorohexanesulfonate and lithium perfluorobutylsulfonate; and / or, The solvent of the organic lithium salt solution includes dimethyl carbonate; and / or, The concentration of the solute in the organic lithium salt solution is 5wt%-10wt%.

9. The method for preparing the silicon-carbon composite material according to claim 7, characterized in that: In the step of atomizing the organic lithium salt solution and then introducing the solution into the metal-doped silicon-carbon precursor material for deposition: The deposition temperature is 100°C to 200°C; and / or, The deposition pressure is 1Mpa~3Mpa; and / or, The deposition time is 10min~60min.

10. Use of the silicon-carbon composite material prepared by the method for preparing the silicon-carbon composite material according to any one of claims 1 to 9 in a lithium-ion battery.

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