Silicon-based composite negative electrode material and preparation method and application thereof

Abstract

The invention relates to the technical field of lithium ion battery negative electrode materials, in particular to a silicon-based composite negative electrode material and a preparation method and application thereof. According to the preparation method, firstly, nano silicon, a carbon source and an ionic conductor are granulated into secondary particles with pore structures in a spray granulation mode, and the nano silicon, the carbon source and the ionic conductor can form more pore structures in the secondary particles through a stacking effect in the spray granulation process; a pore structure is formed between the nanometer silicon and / or the ion conductor, and a carbon source is filled between the nanometer silicon and / or the ion conductor; then carrying out calcination treatment to convert the carbon source into amorphous carbon, and tightly bonding the nano silicon and / or the ionic conductor by using the amorphous carbon; and secondly, distributing nano silicon in pore structures in the secondary particles by adopting a chemical vapor deposition technology, and performing chemical vapor deposition of titanium nitride to obtain a titanium nitride coating layer, thereby forming the silicon-based composite negative electrode material with the core-shell structure.

Description

Technical Field

[0001] The present invention relates to the technical field of negative electrode materials for lithium-ion batteries, and particularly to a silicon-based composite negative electrode material, a preparation method thereof, and an application thereof. Background Art

[0002] At present, the commercially used lithium-ion batteries mainly use pure graphite or a graphite / silicon-carbon mixture doped with a small amount of silicon as the negative electrode material. However, due to the theoretical specific capacity of graphite being only 372 mAh / g, the specific capacity of the graphite / silicon-carbon mixture is generally also below 500 mAh / g, which limits the further improvement of the specific energy of lithium-ion batteries and results in their inability to meet the development needs of new energy industries such as current electric vehicles. The silicon negative electrode based on the alloying reaction has a theoretical lithium storage capacity as high as 4200 mAh / g and is an ideal choice for the next-generation negative electrode material of lithium-ion batteries. However, the huge volume expansion (>300%) of silicon during the alloying reaction with lithium leads to particle pulverization and inactivation, resulting in poor cycle stability, especially for the high specific capacity silicon-carbon negative electrode.

[0003] The prior art uses various methods to prepare porous silicon-based negative electrode materials, which can effectively alleviate the drastic volume change of porous silicon-based substances during charge and discharge cycles and improve their structural stability. However, due to the absence of conductive particles between the pores, the conductivity of the particles is poor, resulting in a decline in the rate performance of the silicon-based negative electrode material. In addition, during the process of compaction and forming into a pole piece, the porous structure is also prone to collapse and cracking, leading to direct contact between silicon and the electrolyte, resulting in a decline in the cycle performance of the battery. Therefore, how to simultaneously improve the cycle performance and rate performance of porous silicon-based negative electrode materials is still a problem to be solved at present. Summary of the Invention

[0004] The purpose of the present invention is to overcome the defects of poor cycle stability and obvious decline in rate performance of the silicon-based negative electrode material existing in the prior art, and to provide a silicon-based composite negative electrode material, a preparation method thereof, and an application thereof. The silicon-based composite negative electrode material has the characteristics of high rate performance and good cycle stability. The preparation method provided by the present invention has a simple process and low production cost, and has great commercial application prospects in the field of power batteries with strong market demand.

[0005] The purpose of the present invention is achieved by the following technical solutions:

[0006] A preparation method of a silicon-carbon composite negative electrode material, wherein the preparation method comprises the following steps:

[0007] (1) Mix nano-silicon particles, a carbon source, an ion conductor, a dispersant, and water to obtain a slurry, and perform spray granulation and calcination treatment on the slurry to prepare an intermediate product;

[0008] (2) Chemically vapor deposit silicon on the intermediate product of step (1) to prepare a silicon-carbon ion conductor composite core;

[0009] (3) Chemically vapor deposit titanium nitride on the silicon-carbon ion conductor composite core of step (2) to prepare the silicon-based composite anode material.

[0010] According to an embodiment of the present invention, in step (1), the median particle size D of the nano-silicon particles 50 is 30 - 500 nm, preferably 30 - 100 nm, such as 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 200 nm, 300 nm, 400 nm or 500 nm.

[0011] According to an embodiment of the present invention, in step (1), the carbon source is selected from one or more of pitch, phenolic resin, epoxy resin, glucose and sucrose.

[0012] According to an embodiment of the present invention, in step (1), the dispersant is selected from one or more of PVP (polyvinylpyrrolidone), CTAB (cetyltrimethylammonium bromide), polyethylene glycol and SDS (sodium dodecyl sulfate).

[0013] According to an embodiment of the present invention, in step (1), the ion conductor is selected from at least one of nano-Al2O3, nano-TiN, nano-VN and nano-NiN.

[0014] According to an embodiment of the present invention, in step (1), the solid content of the slurry is 10 - 40 wt%, preferably 20 - 30 wt%.

[0015] According to an embodiment of the present invention, in step (1), the mass ratio of the nano-silicon to the carbon source is (40 - 70):(5 - 30), preferably (50 - 65):(8 - 20).

[0016] According to an embodiment of the present invention, in step (1), the mass ratio of the nano-silicon to the ion conductor is (40 - 70):(5 - 35), preferably (50 - 65):(10 - 30).

[0017] According to an embodiment of the present invention, in step (1), the mass ratio of the nano-silicon to the dispersant is (40 - 70):(5 - 25), preferably (50 - 65):(5 - 20).

[0018] According to an embodiment of the present invention, in step (1), there is no special definition for the mixing time, and it is only necessary to mix the nano-silicon particles, carbon source, ion conductor, dispersant and water evenly.

[0019] According to an embodiment of the present invention, in step (1), the inlet temperature of the spray granulation is 150 - 210 °C; the outlet temperature of the spray granulation is 90 - 110 °C; the spray granulation is carried out under a nitrogen atmosphere.

[0020] According to an embodiment of the present invention, in step (1), the calcination treatment is carried out under an inert atmosphere; preferably, the inert atmosphere includes nitrogen or argon.

[0021] According to an embodiment of the present invention, in step (1), the temperature of the calcination treatment is 800 - 1200 °C, such as 850 °C, 900 °C, 950 °C, 1000 °C, 1050 °C, 1100 °C, 1150 °C or 1200 °C; the time of the calcination treatment is 1 - 3 hours.

[0022] According to an embodiment of the present invention, in step (1), the intermediate product is a secondary particle having a plurality of pore structures; preferably, the intermediate product is a secondary particle formed by granulating nanosilicon, an ion conductor and amorphous carbon having a plurality of pore structures with pore sizes of 10 - 40 nm. The intermediate product includes nanosilicon, an ion conductor and amorphous carbon; preferably, the intermediate product includes nanosilicon, an ion conductor and amorphous carbon, and amorphous carbon is in-situ formed between some nanosilicon and / or ion conductors, and a pore structure is formed between some nanosilicon and / or ion conductors, and the pore size of the pore structure is 10 - 40 nm.

[0023] According to an embodiment of the present invention, in step (1), during the spray granulation process, the nanosilicon and the ion conductor will undergo a stacking effect, so that a pore structure is formed between the nanosilicon and / or the ion conductor, and a secondary particle having a plurality of pore structures with pore sizes of 10 - 40 nm is obtained; during the spray granulation process, the stacking effect between the nanosilicon and the ion conductor will also fill the carbon source between the nanosilicon and / or the ion conductor, and after the calcination treatment, a secondary particle in which amorphous carbon is in-situ formed between some nanosilicon and / or ion conductors and a pore structure is formed between some nanosilicon and / or ion conductors is obtained. Among them, between the nanosilicon and / or the ion conductor means at least one of between nanosilicon, between ion conductors, and between nanosilicon and ion conductors.

[0024] According to an embodiment of the present invention, in step (2), the chemical vapor deposition of silicon includes the following steps: First, put the intermediate product of step (1) into a chemical vapor deposition furnace, introduce nitrogen to displace the air, then raise the temperature of the chemical vapor deposition furnace and introduce silane gas at this temperature and keep it warm for a certain time. The silane gas decomposes into nanosilicon, and the nanosilicon fills the pores of the intermediate product. After the insulation time, stop introducing the silane gas and cool it to room temperature with the furnace, and stop introducing nitrogen to achieve the preparation of the silicon-carbon ion conductor composite core.

[0025] According to an embodiment of the present invention, in step (2), the chemical vapor deposition of silicon comprises the following steps: First, place the intermediate product of step (1) into a chemical vapor deposition furnace at room temperature, introduce nitrogen gas for 20 - 40 minutes to displace the air in the chemical vapor deposition furnace, then raise the temperature of the chemical vapor deposition furnace to 450 - 650 °C and introduce silane gas at this temperature and keep it warm for 1 - 5 hours. The silane gas decomposes into nano - silicon, and the nano - silicon fills the pores of the intermediate product. After the heat preservation, stop introducing the silane gas and cool it to room temperature with the furnace, and stop introducing nitrogen gas to achieve the preparation of the silicon - carbon ion conductor composite core.

[0026] According to an embodiment of the present invention, in step (2), the volume - mass ratio of the silane gas to the intermediate product of step (1) is 1 - 6 L / g, that is, 1 - 6 L of silane gas is introduced into 1 g of the intermediate product of step (1) to ensure that nano - silicon fills the pores of the intermediate product; exemplarily, the volume - mass ratio of the silane gas to the intermediate product of step (1) is 1 L / g, 2 L / g, 3 L / g, 4 L / g, 5 L / g or 6 L / g.

[0027] According to an embodiment of the present invention, in step (2), the silane gas is monosilane or disilane.

[0028] According to an embodiment of the present invention, in step (2), through the chemical vapor deposition method, the silane gas can enter the pore structure of the intermediate product of step (1) more fully, and the nano - silicon can be evenly dispersed in the pore structure of the intermediate product of step (1).

[0029] According to an embodiment of the present invention, in step (2), the silicon - carbon ion conductor composite core comprises nano - silicon, an ion conductor and amorphous carbon; preferably, the silicon - carbon ion conductor composite core is a secondary particle formed by granulating nano - silicon, an ion conductor and amorphous carbon, and amorphous carbon is in - situ formed between some nano - silicon and / or ion conductors, and nano - silicon is in - situ deposited in the pore structure between some nano - silicon and / or ion conductors.

[0030] According to an embodiment of the present invention, in step (3), the chemical vapor deposition of titanium nitride comprises the following steps: Place the silicon - carbon ion conductor composite core of step (2) into a chemical vapor deposition furnace, and at the same time introduce a nitrogen - source gas and a titanium - source gas into the chemical vapor deposition furnace, and perform chemical vapor deposition on the surface of the silicon - carbon ion conductor composite core to obtain a titanium nitride coating layer.

[0031] According to an embodiment of the present invention, the heating rate of the chemical vapor deposition is 5-8 °C / min; the temperature of the chemical vapor deposition is 1010-1025 °C, such as 1015 °C or 1020 °C; the time of the chemical vapor deposition is 0.5-3 hours, such as 0.5 hour, 1 hour, 1.5 hours, 2 hours, 2.5 hours or 3 hours.

[0032] According to an embodiment of the present invention, the flow rate of the nitrogen source gas is 80-200 sccm, such as 80 sccm, 90 sccm, 100 sccm, 120 sccm, 150 sccm, 160 sccm, 180 sccm or 200 sccm.

[0033] According to an embodiment of the present invention, the titanium source gas is a gas containing titanium tetrachloride, for example, a protective gas containing titanium tetrachloride obtained by the bubbling method, such as argon containing titanium tetrachloride; the protective gas is one or more of argon, helium and hydrogen; the nitrogen source gas is nitrogen.

[0034] According to an embodiment of the present invention, in step (3), the chemical vapor deposition of titanium nitride includes the following steps: placing the silicon-carbon ion conductor composite core of step (2) in a chemical vapor deposition furnace, raising the temperature of the chemical vapor deposition furnace to 1010-1025 °C at a heating rate of 5-8 °C / min, and introducing a nitrogen source gas, a titanium source gas and a protective gas at this temperature and keeping it warm for 0.5-3 hours to obtain a titanium nitride coating layer on the surface of the silicon-carbon ion conductor composite core.

[0035] According to an embodiment of the present invention, in step (3), after the chemical vapor deposition of titanium nitride, there is also a cooling step, and the cooling step includes: first, the chemical vapor deposition furnace stops heating, and stops introducing the titanium source gas into the chemical vapor deposition furnace. When the temperature of the chemical vapor deposition furnace drops to 800-900 °C, stop introducing the nitrogen source gas into the chemical vapor deposition furnace, continue to cool down. When the temperature of the chemical vapor deposition furnace drops to 200-400 °C, stop introducing the protective gas, and cool it to room temperature with the furnace.

[0036] According to an embodiment of the present invention, in step (3), the volume-mass ratio of the titanium source gas to the silicon-carbon ion conductor composite core of step (2) is 1-4 mL / g, that is, 1-4 mL of the titanium source gas is introduced into 1 g of the silicon-carbon ion conductor composite core of step (2).

[0037] The present invention also provides a silicon-based composite anode material prepared by the above method.

[0038] According to an embodiment of the present invention, the silicon-based composite anode material includes nano-silicon, amorphous carbon, an ion conductor, and titanium nitride; preferably, the silicon-based composite anode material is a composite composed of nano-silicon, amorphous carbon, an ion conductor, and titanium nitride.

[0039] According to an embodiment of the present invention, the amorphous carbon is distributed between the nano-silicon and / or the ion conductor; the amorphous carbon can bond the nano-silicon and / or the ion conductor into a spherical shape.

[0040] According to an embodiment of the present invention, the ion conductor and the nano-silicon have a uniform distribution, and the ion conductor can relieve the expansion of the nano-silicon during cycling.

[0041] According to an embodiment of the present invention, the titanium nitride is distributed on the surface of the composite composed of nano-silicon, amorphous carbon, and an ion conductor.

[0042] According to an embodiment of the present invention, the silicon-based composite anode material has a core-shell structure, including a core and a shell layer; the core includes nano-silicon, amorphous carbon, and an ion conductor; the amorphous carbon is distributed between the nano-silicon and / or the ion conductor; the shell layer includes titanium nitride.

[0043] According to an embodiment of the present invention, the mass of the nano-silicon accounts for 60-80% of the total mass of the core, such as 60%, 62%, 65%, 66%, 68%, 70%, 72%, 74%, 75%, 76%, 78%, or 80%.

[0044] According to an embodiment of the present invention, the mass of the amorphous carbon accounts for 1-10% of the total mass of the core, such as 1%, 2%, 3%, 5%, 6%, 8%, or 10%.

[0045] According to an embodiment of the present invention, the mass of the ion conductor accounts for 10-30% of the total mass of the core, such as 10%, 12%, 15%, 16%, 18%, 20%, 24%, 25%, 26%, 28%, or 30%.

[0046] According to an embodiment of the present invention, the thickness of the shell layer is 10-50 nm, for example, 10 nm, 12 nm, 15 nm, 18 nm, 20 nm, 22 nm, 24 nm, 25 nm, 26 nm, 28 nm, or 30 nm.

[0047] According to an embodiment of the present invention, the median particle size D of the silicon-graphite-based composite anode material 50 is 5 μm - 16 μm, for example, 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 15 μm, or 16 μm.

[0048] The present invention also provides a use of the silicon-graphite-based composite negative electrode material, which is used for preparing a negative electrode of a lithium-ion battery.

[0049] The present invention also provides a negative electrode of a lithium ion battery, which comprises the above silicon-based composite negative electrode material.

[0050] The present invention also provides a lithium ion battery, which comprises the above silicon-based composite negative electrode material or the above negative electrode of the lithium ion battery.

[0051] Beneficial effects of the present invention:

[0052] The present invention firstly granulates nano silicon, carbon source and ion conductor into secondary particles with pore structure in the form of spray granulation. The nano silicon, carbon source and ion conductor form more pore structures inside the secondary particles through stacking in the spray granulation process, specifically, pore structures are formed between the nano silicon and / or ion conductor, and the carbon source is also filled between the nano silicon and / or ion conductor; then calcination treatment is performed to convert the carbon source into amorphous carbon, and the nano silicon and / or ion conductor are tightly bonded by the amorphous carbon; secondly, chemical vapor deposition technology is used to distribute the nano silicon in the pore structure inside the secondary particles, and then chemical vapor deposition of titanium nitride is performed to obtain a titanium nitride coating layer to form a silicon-based composite negative electrode material with a core-shell structure.

[0053] On the one hand, by utilizing the characteristics of high hardness of nano-ion conductors and titanium nitride, the internal nano-ion conductors and the titanium nitride on the outer surface jointly stabilize the structure of the material, which can buffer the volume expansion of nano-silicon during the process of lithium ion extraction and insertion during the cycle, thereby improving the cycle performance of silicon-based composite negative electrode materials; the nano-silicon deposited in the pore structure makes the prepared silicon-based composite negative electrode material have good mechanical properties, and the particles will not break during the compaction process and the process of making the pole piece, further improving the cycle performance of the silicon-based composite negative electrode material. On the other hand, by utilizing the high conductivity of the ion conductor, not only can the conduction rate of lithium ions inside the silicon-based composite negative electrode material be accelerated, but also the overall conductivity of the silicon-based composite negative electrode material can be enhanced; the silicon-based composite negative electrode material is applied to lithium-ion batteries, and through the combined action of nano-silicon, the ion conductor inside the matrix and the titanium nitride coated on the outside, the lithium-ion battery has the characteristics of high rate performance and long cycle life. DETAILED DESCRIPTION

[0054] The preparation method of the present invention will be described in further detail below in conjunction with specific examples. It should be understood that the following examples are only exemplary illustrations and explanations of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are included in the scope that the present invention is intended to protect.

[0055] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods; unless otherwise specified, the reagents, materials, etc. used in the following examples can all be obtained from commercial sources.

[0056] Example 1

[0057] (1) 60 g of nano-silicon (D 50 with a size of 80 nm), 20 g of asphalt, 30 g of Al2O3 (D 50 with a size of 50 nm), and 18 g of PVP were successively dispersed in deionized water to prepare a slurry, and the solid content of the slurry was adjusted to 20 wt%; the dispersed slurry was spray granulated in a nitrogen atmosphere (the inlet temperature was 185 °C and the outlet temperature was 110 °C) to obtain the core after spray granulation; the core after spray granulation was sintered at 1000 °C for 3 hours in a nitrogen atmosphere and cooled to room temperature to obtain an intermediate product;

[0058] (2) First, 100 g of the intermediate product from step (1) was placed in a chemical vapor deposition furnace at room temperature, and nitrogen was introduced for 30 minutes to replace the air in the chemical vapor deposition furnace. Then, the temperature of the chemical vapor deposition furnace was raised to 480 °C, and 200 L of silane gas was introduced at this temperature and held for 1.5 hours. The silane gas decomposed into nano-silicon, and the nano-silicon filled the pores of the intermediate product. After holding for the specified time, the introduction of silane gas was stopped and the furnace was cooled to room temperature, and the introduction of nitrogen was stopped to prepare a silicon-carbon ion conductor composite core;

[0059] (3) 100 g of the silicon-carbon ion conductor composite core from step (2) was placed in a chemical vapor deposition furnace, and the temperature of the chemical vapor deposition furnace was raised to 1015 °C at a heating rate of 5 °C / min, and nitrogen (flow rate: 120 sccm) and argon containing titanium tetrachloride (100 mL of titanium tetrachloride, argon flow rate: 60 sccm) were introduced at this temperature and held for 2 hours to obtain a titanium nitride coating layer on the surface of the silicon-carbon ion conductor composite core; after holding for the specified time, the heating of the chemical vapor deposition furnace was first stopped, and the introduction of titanium tetrachloride into the chemical vapor deposition furnace was stopped. When the temperature of the chemical vapor deposition furnace dropped to 800 °C, the introduction of nitrogen into the chemical vapor deposition furnace was stopped, and the temperature continued to drop. When the temperature of the chemical vapor deposition furnace dropped to 200 °C, the introduction of argon was stopped, and the furnace was cooled to room temperature to prepare the silicon-based composite anode material.

[0060] The silicon-based composite anode material of the present invention has a core-shell structure, including a core and a shell layer; the core includes nano-silicon, amorphous carbon, and an ion conductor; the amorphous carbon is distributed between the nano-silicon and / or the ion conductor; the shell layer includes titanium nitride, and the thickness of the titanium nitride shell layer is 25 nm.

[0061] Example 2

[0062] (1)Disperse 60 g of nano-silicon (D 50 with a size of 60 nm), 15 g of asphalt, 25 g of TiN (D 50 with a size of 60 nm), and 20 g of PVP in deionized water in sequence to prepare a slurry, and adjust the solid content of the slurry to 20 wt%; Spray granulate the dispersed slurry in a nitrogen atmosphere (the inlet temperature is 185 °C and the outlet temperature is 110 °C) to obtain the core after spray granulation; Sinter the core after spray granulation at 1000 °C in a nitrogen atmosphere for 3 hours, and cool it to room temperature to obtain an intermediate product;

[0063] (2) First, put 100 g of the intermediate product in step (1) into a chemical vapor deposition furnace at room temperature, introduce nitrogen for 30 minutes to replace the air in the chemical vapor deposition furnace, then raise the temperature of the chemical vapor deposition furnace to 530 °C and introduce 300 L of silane gas at this temperature, keep it warm for 1.5 hours, the silane gas decomposes into nano-silicon, and the nano-silicon fills the pores of the intermediate product. After keeping it warm, stop introducing silane gas and cool it to room temperature with the furnace, and stop introducing nitrogen to prepare a silicon-carbon ion conductor composite core;

[0064] (3) Place 100 g of the silicon-carbon ion conductor composite core in step (2) in a chemical vapor deposition furnace, raise the temperature of the chemical vapor deposition furnace to 1010 °C at a heating rate of 6 °C / min and introduce nitrogen (flow rate is 150 sccm) and argon containing titanium tetrachloride (130 mL of titanium tetrachloride, argon flow rate is 80 sccm) at this temperature, keep it warm for 2 hours to obtain a titanium nitride coating layer on the surface of the silicon-carbon ion conductor composite core; After keeping it warm, first stop heating the chemical vapor deposition furnace, stop introducing argon containing titanium tetrachloride into the chemical vapor deposition furnace, when the temperature of the chemical vapor deposition furnace drops to 800 °C, stop introducing nitrogen into the chemical vapor deposition furnace, continue to cool down, when the temperature of the chemical vapor deposition furnace drops to 200 °C, stop introducing argon, and cool it to room temperature with the furnace to prepare the silicon-based composite anode material.

[0065] The silicon-based composite anode material of the present invention has a core-shell structure, including a core and a shell layer; the core includes nano-silicon, amorphous carbon and an ion conductor; the amorphous carbon is distributed between the nano-silicon and / or the ion conductor; the shell layer includes titanium nitride, and the thickness of the titanium nitride shell layer is 30 nm.

[0066] Example 3

[0067] (1)Disperse 60 g of nano-silicon (D 50 with a size of 80 nm), 15 g of asphalt, 20 g of VN (D 5060 g of nano-silicon (80 nm), 10 g of asphalt, 15 g of TiN (50 nm), and 20 g of PVP were successively dispersed in deionized water to prepare a slurry, and the solid content of the slurry was adjusted to 20 wt%; the dispersed slurry was spray granulated in a nitrogen atmosphere (the inlet temperature was 185 °C and the outlet temperature was 110 °C) to obtain the core after spray granulation; the core after spray granulation was sintered at 1000 °C for 3 hours in a nitrogen atmosphere and cooled to room temperature to obtain an intermediate product;

[0068] (2) First, 100 g of the intermediate product obtained in step (1) was placed in a chemical vapor deposition furnace at room temperature, and nitrogen was introduced for 30 minutes to replace the air in the chemical vapor deposition furnace. Then, the temperature of the chemical vapor deposition furnace was raised to 580 °C, and 360 L of silane gas was introduced at this temperature and held for 1.5 hours. The silane gas decomposed into nano-silicon, and the nano-silicon filled the pores of the intermediate product. After holding, the silane gas was stopped being introduced and the furnace was cooled to room temperature with the nitrogen flow stopped, and a silicon-carbon ion conductor composite core was prepared;

[0069] (3) 100 g of the silicon-carbon ion conductor composite core obtained in step (2) was placed in a chemical vapor deposition furnace, and the temperature of the chemical vapor deposition furnace was raised to 1015 °C at a heating rate of 5 °C / min, and nitrogen (flow rate: 130 sccm) and argon containing titanium tetrachloride (150 mL of titanium tetrachloride, argon flow rate: 50 sccm) were introduced at this temperature and held for 2 hours to obtain a titanium nitride coating layer on the surface of the silicon-carbon ion conductor composite core; after holding, the chemical vapor deposition furnace was first stopped from heating, and the argon containing titanium tetrachloride was stopped from being introduced into the chemical vapor deposition furnace. When the temperature of the chemical vapor deposition furnace dropped to 800 °C, the nitrogen was stopped from being introduced into the chemical vapor deposition furnace, and the furnace continued to cool. When the temperature of the chemical vapor deposition furnace dropped to 200 °C, the argon was stopped from being introduced, and the furnace was cooled to room temperature with the furnace to prepare the silicon-based composite anode material.

[0070] The silicon-based composite anode material of the present invention has a core-shell structure, including a core and a shell layer; the core includes nano-silicon, amorphous carbon, and an ion conductor; the amorphous carbon is distributed between the nano-silicon and / or the ion conductor; the shell layer includes titanium nitride, and the thickness of the titanium nitride shell layer is 36 nm.

[0071] Example 4

[0072] (1) 60 g of nano-silicon (80 nm), 10 g of asphalt, 15 g of TiN (50 nm), and 20 g of PVP were successively dispersed in deionized water to prepare a slurry, and the solid content of the slurry was adjusted to 20 wt%; the dispersed slurry was spray granulated in a nitrogen atmosphere (the inlet temperature was 185 °C and the outlet temperature was 110 °C) to obtain the core after spray granulation; the core after spray granulation was sintered at 1000 °C for 3 hours in a nitrogen atmosphere and cooled to room temperature to obtain an intermediate product;

[0073] (2) First, put 100 g of the intermediate product from step (1) into a chemical vapor deposition furnace at room temperature, introduce nitrogen gas for 30 minutes to displace the air in the chemical vapor deposition furnace, then raise the temperature of the chemical vapor deposition furnace to 620 °C and introduce 400 L of silane gas at this temperature. Keep it warm for 1.5 hours. The silane gas decomposes into nano-silicon, and the nano-silicon fills the pores of the intermediate product. After the heat preservation time, stop introducing the silane gas and cool it down to room temperature with the furnace, and then stop introducing nitrogen gas to obtain the silicon-carbon ion conductor composite core.

[0074] (3) Place 100 g of the silicon-carbon ion conductor composite core from step (2) into the chemical vapor deposition furnace, raise the temperature of the chemical vapor deposition furnace to 1015 °C at a heating rate of 5 °C / min and introduce nitrogen gas (flow rate: 120 sccm) and argon gas containing titanium tetrachloride (200 mL of titanium tetrachloride, argon gas flow rate: 100 sccm) at this temperature. Keep it warm for 2 hours to obtain a titanium nitride coating layer on the surface of the silicon-carbon ion conductor composite core. After the heat preservation time, first stop heating the chemical vapor deposition furnace and stop introducing the argon gas containing titanium tetrachloride into the chemical vapor deposition furnace. When the temperature of the chemical vapor deposition furnace drops to 800 °C, stop introducing nitrogen gas into the chemical vapor deposition furnace, continue to cool down. When the temperature of the chemical vapor deposition furnace drops to 200 °C, stop introducing argon gas and cool it down to room temperature with the furnace to obtain the silicon-based composite anode material.

[0075] The silicon-based composite anode material of the present invention has a core-shell structure, including a core and a shell layer; the core includes nano-silicon, amorphous carbon, and an ion conductor; the amorphous carbon is distributed between the nano-silicon and / or the ion conductor; the shell layer includes titanium nitride, and the thickness of the titanium nitride shell layer is 42 nm.

[0076] Comparative Example 1

[0077] (1) Disperse 60 g of nano-silicon (80 nm), 20 g of asphalt, and 18 g of PVP in deionized water in sequence to prepare a slurry, and adjust the solid content of the slurry to 20 wt%; spray granulate the dispersed slurry in a nitrogen atmosphere (inlet temperature: 185 °C, outlet temperature: 110 °C) to obtain the granulated core after spray granulation; sinter the granulated core at 1000 °C in a nitrogen atmosphere for 3 hours and cool it to room temperature to obtain an intermediate product.

[0078] (2) Place 100 g of the intermediate product from step (1) into a chemical vapor deposition furnace. Increase the temperature of the chemical vapor deposition furnace to 1015 °C at a heating rate of 5 °C / min, and at this temperature, introduce nitrogen (flow rate: 120 sccm) and argon containing titanium tetrachloride (100 mL of titanium tetrachloride, argon flow rate: 60 sccm). Keep the temperature for 2 hours to obtain a titanium nitride coating layer on the surface of the intermediate product. After the temperature holding time, first stop heating the chemical vapor deposition furnace and stop introducing argon containing titanium tetrachloride into the chemical vapor deposition furnace. When the temperature of the chemical vapor deposition furnace drops to 800 °C, stop introducing nitrogen into the chemical vapor deposition furnace. Continue to cool down. When the temperature of the chemical vapor deposition furnace drops to 200 °C, stop introducing argon, and cool down to room temperature with the furnace to prepare the silicon-based composite anode material.

[0079] The silicon-based composite anode material has a core-shell structure, including a core and a shell layer; the core includes nano-silicon and amorphous carbon; the amorphous carbon is distributed between the nano-silicon; the shell layer includes titanium nitride.

[0080] Comparative Example 2

[0081] (1) Disperse 60 g of nano-silicon (80 nm), 20 g of pitch, 30 g of Al2O3 (50 nm), and 18 g of PVP in deionized water in sequence to prepare a slurry, and adjust the solid content of the slurry to 20 wt%. Spray granulate the dispersed slurry in a nitrogen atmosphere (inlet temperature: 185 °C, outlet temperature: 110 °C) to obtain the sprayed granulated inner core; sinter the sprayed granulated inner core at 1000 °C in a nitrogen atmosphere for 3 hours, and cool to room temperature to obtain an intermediate product;

[0082] (2) Place 100 g of the intermediate product from step (1) into a chemical vapor deposition furnace. Increase the temperature of the chemical vapor deposition furnace to 1015 °C at a heating rate of 5 °C / min, and at this temperature, introduce nitrogen (flow rate: 120 sccm) and argon containing titanium tetrachloride (100 mL of titanium tetrachloride, argon flow rate: 200 sccm). Keep the temperature for 2 hours to obtain a titanium nitride coating layer on the surface of the intermediate product. After the temperature holding time, first stop heating the chemical vapor deposition furnace and stop introducing argon containing titanium tetrachloride into the chemical vapor deposition furnace. When the temperature of the chemical vapor deposition furnace drops to 800 °C, stop introducing nitrogen into the chemical vapor deposition furnace. Continue to cool down. When the temperature of the chemical vapor deposition furnace drops to 200 °C, stop introducing argon, and cool down to room temperature with the furnace to prepare the silicon-based composite anode material.

[0083] The silicon-based composite anode material has a core-shell structure, including a core and a shell layer; the core includes nano-silicon, amorphous carbon, and an ion conductor; the amorphous carbon is distributed between the nano-silicon and / or the ion conductor; the shell layer includes titanium nitride.

[0084] Electrochemical performance test

[0085] Half-cell test method: The silicon-based composite materials prepared in the examples and comparative examples, conductive carbon black (SP), carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) were mixed evenly at a mass ratio of 95:1:1.5:2.5, coated on copper foil, and the coated electrode was placed in a vacuum drying oven at 120 °C for 12 hours. The simulated battery assembly was carried out in a Braun glove box under argon protection. The electrolyte was 1M-LiPF6 + EC:DEC:DMC (volume ratio 1:1:1), and the lithium metal sheet was used as the counter electrode. The simulated battery test was carried out in a Neware battery test cabinet at 5V and 10mA. The charge and discharge voltage was 0.01-1.5V, and the charge and discharge rate was 0.1C. The first discharge capacity and efficiency obtained from the test are listed in Table 1.

[0086] Full-cell test method: Using the silicon-based composite materials prepared in Examples 1-4 and Comparative Examples 1-2 as the negative electrode, lithium cobaltate as the positive electrode, and 1M-LiPF6 + EC:DEC:DMC (volume ratio 1:1:1) solution as the electrolyte to assemble a full cell. The voltage range was 0.01-1.5V. The initial specific capacity, charge and discharge efficiency, cycle performance, and rate performance obtained from the test are listed in Table 1.

[0087] Table 1. Electrochemical performance test results

[0088]

[0089] Compared with Example 1, the silicon-based composite negative electrode material of Comparative Example 1 first granulated the nanosilicon into nanosilicon particles with a pore structure by spray granulation, and no ion conductor was introduced. Moreover, since titanium nitride nanoparticles could not be deposited into the internal pore structure formed by spray granulation during subsequent chemical vapor deposition, only the outer shell of titanium nitride nanoparticles and the pores in the core could be relied on to relieve the expansion of the nanosilicon in the core during cycling, resulting in a significant reduction in cycle performance. On the other hand, due to the non-deposited nanosilicon in the core, the particles of the silicon-based composite negative electrode material would break during the compaction process and the process of making the electrode, further reducing the cycle performance of the silicon-based composite negative electrode material. In addition, due to the absence of an ion conductor, the rate performance of the silicon-based composite negative electrode material was also reduced.

[0090] Compared with Example 1, the silicon-based composite negative electrode material of Comparative Example 2 first granulates nano-silicon and ion conductors into composite particles of nano-silicon and ion conductors having a porous structure by spray granulation; since nano-titanium nitride cannot be deposited into these porous structures in the subsequent chemical vapor deposition, there are still many porous structures in the core of the obtained silicon-based composite negative electrode material, and this structure is unstable and easily broken during the cycle process, resulting in the silicon-based composite negative electrode material having a lower cycle performance. In addition, since no chemical vapor deposition of nano-silicon is performed in the core, the capacity is reduced.

[0091] The above is an explanation of the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation method of a silicon-carbon composite anode material, wherein, The preparation method includes the following steps: (1) Mix nano-silicon particles, a carbon source, an ion conductor, a dispersant, and water to obtain a slurry. Perform spray granulation and calcination on the slurry to prepare an intermediate product; (2) Perform chemical vapor deposition of silicon on the intermediate product of step (1) to prepare a silicon-carbon ion conductor composite core; (3) Perform chemical vapor deposition of titanium nitride on the silicon-carbon ion conductor composite core of step (2) to prepare the silicon-based composite anode material.

2. The preparation method according to claim 1, wherein In step (1), the carbon source is selected from one or more of pitch, phenolic resin, epoxy resin, glucose, and sucrose; and / or, in step (1), the dispersant is selected from one or more of PVP (polyvinylpyrrolidone), CTAB (cetyltrimethylammonium bromide), polyethylene glycol, and SDS (sodium dodecyl sulfate); and / or, in step (1), the ion conductor is selected from at least one of nano-Al2O3, nano-TiN, nano-VN, and nano-NiN. Preferably, in step (1), the mass ratio of the nano-silicon to the carbon source is (40 - 70):(5 - 30), preferably (50 - 65):(8 - 20); and / or, in step (1), the mass ratio of the nano-silicon to the ion conductor is (40 - 70):(5 - 35), preferably (50 - 65):(10 - 30); and / or, in step (1), the mass ratio of the nano-silicon to the dispersant is (40 - 70):(5 - 25), preferably (50 - 65):(5 - 20). Preferably, in step (1), the inlet temperature of the spray granulation is 150 - 210°C; the outlet temperature of the spray granulation is 90 - 110°C; the spray granulation is carried out in a nitrogen atmosphere. Preferably, in step (1), the temperature of the calcination treatment is 800 - 1200°C; the time of the calcination treatment is 1 - 3 hours.

3. The preparation method according to claim 1 or 2, wherein In step (1), the intermediate product is a secondary particle formed by granulation of nano-silicon, an ion conductor, and amorphous carbon with a pore structure having a plurality of pore sizes of 10 - 40 nm. The intermediate product includes nano-silicon, an ion conductor, and amorphous carbon; preferably, the intermediate product includes nano-silicon, an ion conductor, and amorphous carbon, and amorphous carbon is in-situ formed between some nano-silicon and / or ion conductors, and a pore structure is formed between some nano-silicon and / or ion conductors, and the pore size of the pore structure is 10 - 40 nm.

4. The preparation method according to any one of claims 1-3, wherein, In step (2), the chemical vapor deposition of silicon includes the following steps: First, put the intermediate product of step (1) into a chemical vapor deposition furnace, introduce nitrogen to displace air, then raise the temperature of the chemical vapor deposition furnace and introduce silane gas at this temperature and keep it warm for a certain time. The silane gas decomposes into nano-silicon, and the nano-silicon fills the pores of the intermediate product. After the insulation time, stop introducing the silane gas and cool it to room temperature with the furnace, and stop introducing nitrogen to achieve the preparation of the silicon-carbon ion conductor composite core. Preferably, in step (2), the chemical vapor deposition of silicon comprises the following steps: First, the intermediate product of step (1) is placed in a chemical vapor deposition furnace at room temperature, and nitrogen is introduced for 20 - 40 minutes to displace the air in the chemical vapor deposition furnace. Then, the temperature of the chemical vapor deposition furnace is raised to 450 - 650 °C, and silane gas is introduced at this temperature and held for 1 - 5 hours. The silane gas decomposes into nano - silicon, and the nano - silicon fills the pores of the intermediate product. After the holding time, the silane gas is stopped from being introduced and the furnace is cooled to room temperature with the furnace, and the nitrogen introduction is stopped to obtain the core of the silicon - carbon ion conductor composite. Preferably, in step (2), the volume - mass ratio of the silane gas to the intermediate product of step (1) is 1 - 6 L / g. Preferably, in step (2), the silane gas is monosilane or disilane.

5. The preparation method according to any one of claims 1-4, wherein, In step (2), the core of the silicon - carbon ion conductor composite is a secondary particle formed by granulation of nano - silicon, an ion conductor, and amorphous carbon, and amorphous carbon is in - situ formed between some nano - silicon and / or ion conductors, and nano - silicon is in - situ deposited in the pore structure between some nano - silicon and / or ion conductors.

6. The preparation method according to any one of claims 1-5, wherein, In step (3), the chemical vapor deposition of titanium nitride comprises the following steps: The core of the silicon - carbon ion conductor composite obtained in step (2) is placed in a chemical vapor deposition furnace, and at the same time, a nitrogen - source gas and a titanium - source gas are introduced into the chemical vapor deposition furnace, and chemical vapor deposition is carried out on the surface of the core of the silicon - carbon ion conductor composite to obtain a titanium nitride coating layer. Preferably, the heating rate of the chemical vapor deposition is 5 - 8 °C / min; the temperature of the chemical vapor deposition is 1010 - 1025 °C; the time of the chemical vapor deposition is 0.5 - 3 hours. Preferably, the titanium - source gas is a gas containing titanium tetrachloride; the protective gas is one or more of argon, helium, and hydrogen; the nitrogen - source gas is nitrogen. Preferably, in step (3), the volume - mass ratio of the titanium - source gas to the core of the silicon - carbon ion conductor composite obtained in step (2) is 1 - 4 mL / g.

7. A silicon - based composite anode material prepared by the method according to any one of claims 1 - 6.

8. The silicon-based composite anode material according to claim 7, wherein The silicon - based composite anode material comprises nano - silicon, amorphous carbon, an ion conductor, and titanium nitride; the amorphous carbon is distributed between nano - silicon and / or the ion conductor; the titanium nitride is distributed on the surface of the composite composed of nano - silicon, amorphous carbon, and the ion conductor. Preferably, the silicon - based composite anode material has a core - shell structure, including a core and a shell layer; the core includes nano - silicon, amorphous carbon, and an ion conductor; the amorphous carbon is distributed between nano - silicon and / or the ion conductor; the shell layer includes titanium nitride. Preferably, the mass of the nano - silicon accounts for 60 - 80% of the total mass of the core; the mass of the amorphous carbon accounts for 1 - 10% of the total mass of the core; the mass of the ion conductor accounts for 10 - 30% of the total mass of the core.

9. A negative electrode of a lithium - ion battery, which comprises the silicon - based composite anode material according to claim 7 or 8.

10. A lithium-ion battery, which comprises the silicon-based composite negative electrode material described in claim 7 or 8 or the negative electrode of the lithium-ion battery described in claim 9.

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