A negative electrode material, a preparation method therefor, and an application thereof

Abstract

The application discloses a kind of negative electrode material and its preparation method and application, belong to lithium ion battery technical field.The single particle of silicon carbon negative electrode material of the present application includes one or more 1~4 μm inner core, the inner core is porous structure, the inner core exists the conductive single-arm carbon tube traversing pore, the outer existence of inner core is conductive carbon layer, carbon layer dispersively distributes carbon tube and graphene and forms conductive 3D network.The present application adopts small size inner core deposition nanometer silicon, shortens lithium ion transmission particle size, then carries out granulation and surface modification to inner core by mixing carbon source slurry, one or more core is compounded, and the finished product with slightly larger size is formed, and by inner core composite single-arm carbon tube, it is connected through each pore of inner core, improves the ion and electron transport fast channel, improves the rate capability of material;The "reinforced concrete" type structure is formed, increases the structural strength of inner core, increases the anti-expansion type of material, improves its electrochemical performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a negative electrode material, its preparation method, and its application. Background Technology

[0002] Currently, the application scenarios of lithium-ion batteries are gradually increasing, and high energy density and long cycle life are required for lithium-ion batteries. There are usually several ways to improve energy density: (1) increase the specific capacity of the positive electrode material, but the specific capacity of the positive electrode material has been developed to its limit; (2) reduce the electrolyte retention coefficient, but this will affect the cycle life; (3) reduce the weight of the casing; (4) increase the specific capacity of the negative electrode. The high specific capacity of silicon negative electrode has attracted much attention, but during the charging and discharging process, the lithium insertion and extraction reaction of silicon will be accompanied by a large volume change (>300%), which will cause the destruction of the material structure and mechanical pulverization, resulting in the separation between electrode materials and between electrode materials and current collectors, separation between particles, and loss of electrical contact, which will cause the capacity to decay rapidly and the cycle performance to deteriorate. Due to the severe volume effect, the SEI film on the silicon surface is in a dynamic process of destruction-reconstruction, and there are many side reactions with the cell, which will cause continuous lithium-ion consumption and further affect the cycle performance. Currently, the silicon anode industry is pursuing two parallel research routes: pre-lithiated silicon-oxygen and novel silicon-carbon. While pre-lithiated silicon-oxygen is relatively mature and exhibits good batch stability, novel silicon-carbon has become a research hotspot due to its lower expansion and better cycle performance. Currently, novel silicon-carbon mainly involves depositing nano-silicon within the pores of a porous carbon matrix. The microporous structure of the porous carbon matrix inhibits silicon growth, resulting in amorphous / microcrystalline nano-silicon with excellent cycle performance. However, this type of novel silicon-carbon material has a porous structure, leading to a longer lithium-ion transport path within the material and numerous silicon-carbon interfaces, affecting lithium-ion insertion / extraction. Consequently, the rate performance of this material is poor. Furthermore, the material is mostly based on a microporous carbon matrix with a large specific surface area, making it difficult to achieve complete and uniform coating, resulting in a large specific surface area and more side reactions with the electrolyte. Summary of the Invention

[0003] The purpose of this invention is to provide an anode material, its preparation method, and its application. The silicon-carbon anode material of this invention has the characteristics of both high rate performance and long cycle performance.

[0004] This invention first provides a method for preparing a silicon-carbon anode material, comprising the following steps:

[0005] (1) Disperse the single-arm carbon nanotubes in a solvent to obtain solution A; then mix solution A with formaldehyde solution to obtain solution B;

[0006] (2) Dissolve bisphenol A in the solution B, heat it, and then add a catalyst to adjust the pH of the solution to 7-10, so that the solution is completely solidified to obtain solid C; crush the solid C to obtain carbon precursor D;

[0007] (3) The carbon precursor D and the alkali activator are mixed and calcined to obtain mixture E; the mixture E is washed to obtain porous carbon matrix F;

[0008] (4) The porous carbon matrix F is placed in a fluidized bed, a mixture of silane and nitrogen is introduced, and the mixture is heated and kept warm; then a mixture of acetylene and argon is introduced, and the mixture is heated and kept warm to obtain product G;

[0009] (5) Carbon is deposited on the surface of product G using chemical vapor deposition to obtain product H;

[0010] (6) The product H and the mixed carbon source slurry are mixed and calcined to obtain the silicon-carbon anode material.

[0011] The method of this invention employs small-sized core deposition of nano-silicon, shortening the lithium-ion transport particle size. Then, the core is granulated and surface modified by mixing carbon source slurry, and one or more cores are composited to form a slightly larger finished product. Furthermore, single-arm carbon nanotubes are composited with the core, connecting all channels of the core, improving the fast channels for ion and electron transport and enhancing the rate performance of the material. The graphene and carbon nanotubes in the mixed carbon source slurry form a "reinforced concrete" structure in the outer coating layer, increasing the structural strength of the core, enhancing the material's resistance to expansion, and improving its electrochemical performance.

[0012] In the above-mentioned method for preparing silicon-carbon anode materials, in step (1), the diameter of the single-arm carbon tube is 0.5~1nm and the length is 2~20nm;

[0013] The solvent is anhydrous ethanol;

[0014] In solution A, the solid content of single-arm carbon nanotubes is 0.5%~5%;

[0015] The formaldehyde solution has a mass percentage concentration of 35-37%.

[0016] The mass ratio of the single-arm carbon nanotube to formaldehyde is 1:35~80;

[0017] In step (2), the mass ratio of bisphenol A to solution B is 1:5~8;

[0018] The catalyst is at least one of sodium carbonate solution, sodium hydroxide solution, and ammonium hydroxide solution; specifically, the concentration of the sodium carbonate solution, sodium hydroxide solution, or ammonium hydroxide solution is 0.5~1 mol / L; more specifically, it can be 0.5 mol / L.

[0019] The solid C is crushed into blocky particles with a particle size of 1~4μm, which is the carbon precursor D.

[0020] In the above-mentioned method for preparing silicon-carbon anode materials, in step (2), the heating temperature is 180~200℃.

[0021] The specific operation of step (2) in the above-mentioned method for preparing silicon-carbon anode material is as follows: dissolve bisphenol A in the solution B, heat the resulting solution to 180~200℃, then add a catalyst to adjust the pH of the solution to 7~10, stop when the solution begins to show solids, continue stirring until it is completely solidified to obtain solid C; crush the solid C to obtain carbon precursor D.

[0022] In the above-mentioned method for preparing silicon-carbon anode materials, in step (3), the alkaline activator is at least one of potassium hydroxide, sodium hydroxide, and lithium hydroxide;

[0023] The mass ratio of the carbon precursor D to the alkaline activator is 1:1~4;

[0024] The calcination is carried out in an inert atmosphere; specifically, the inert atmosphere is a nitrogen or argon atmosphere.

[0025] The calcination temperature is 700~900℃; the calcination time is 1~5h;

[0026] The washing process involves sequentially applying hydrochloric acid solution and water; specifically, the concentration of the hydrochloric acid is 0.1~2 mol / L; more specifically, it can be 0.2 mol / L.

[0027] In the above-mentioned method for preparing silicon-carbon anode materials, the washing operation in step (3) is as follows: the mixture E is placed in hydrochloric acid solution and stirred and washed for 10~60 min, and then washed with water multiple times until the solution pH≤8;

[0028] Specifically, the mass ratio of the mixture E to the hydrochloric acid solution can be 1:2~5.

[0029] The porous carbon matrix F has a pore size of 0.3~3 nm and a specific surface area of ​​1600~2200 μm. 2 / g, with a pore volume of 0.8~1.0 cc / g.

[0030] The specific operation of step (4) in the above-mentioned method for preparing silicon-carbon anode material is as follows: the porous carbon matrix F is placed in a fluidized bed, and a mixture of silane and nitrogen with a volume ratio of 5:1 to 1:5 is introduced and kept at 400 to 700°C for 2 to 6 hours; then a mixture of acetylene and argon with a gas flow ratio of 2:1 to 1:3 is introduced and kept at 650 to 750°C for 1 to 3 hours to obtain product G;

[0031] The silane is either methylsilane or disilane.

[0032] The specific operation of step (5) in the above-mentioned method for preparing silicon-carbon anode material is as follows: Place the product G in a chemical vapor deposition reactor, introduce a mixture of acetylene and argon gas at a gas flow ratio of 2:1 to 1:2, keep it at 650 to 750°C for 1 to 4 hours, and obtain product H.

[0033] In the above-mentioned method for preparing silicon-carbon anode materials, in step (6), the mass ratio of product H to mixed carbon source slurry is 10:1 to 15:1;

[0034] The mixed carbon source slurry is obtained by dispersing graphene, carbon nanotubes and low-temperature pitch in anhydrous ethanol; specifically, the mass ratio of graphene, carbon nanotubes and low-temperature pitch can be 1:1:2; the solid content of the mixed carbon source slurry can be 30%~40%; the diameter of the carbon nanotubes can be 3~20nm single-arm carbon nanotubes.

[0035] The calcination is carried out in an inert atmosphere; specifically, the inert atmosphere is a nitrogen or argon atmosphere.

[0036] The calcination temperature is 600~900℃; the calcination time is 4~6h.

[0037] The low-temperature asphalt is asphalt with a softening point below 200℃; specifically, it can be at least one of Xinjiang medium carbon 150# coated asphalt and 180# coated asphalt;

[0038] The present invention further provides a silicon-carbon anode material prepared by the above preparation method.

[0039] Specifically, the particle size of the silicon-carbon anode material is 3~10μm.

[0040] The application of the aforementioned silicon-carbon anode material in the preparation of lithium-ion battery anodes also falls within the scope of protection of this invention.

[0041] The silicon-carbon anode material of the present invention includes a single particle containing one or more 1-4 μm cores. The core is one or more porous carbon matrixes with a porous structure, in which nano-silicon particles are grown in confined space. At the same time, conductive single-arm carbon nanotubes are present inside the cores, and a conductive carbon layer is present outside the cores. Carbon nanotubes and graphene are dispersedly distributed in the carbon layer to form a conductive 3D network.

[0042] The present invention has the following beneficial effects:

[0043] (1) The silicon-carbon anode material of the present invention uses a small core (1~3μm porous carbon matrix) to deposit nano-silicon, which shortens the lithium-ion transport particle size; then the core is granulated and surface modified by using a mixed carbon source slurry; the core is coated with pitch or granulated in the mixed carbon source slurry to wrap multiple cores, and after carbonization, a high ion conductor carbon layer is formed on the surface of the core, which can also reduce the specific surface area of ​​the material (the particle size becomes larger), reduce the negative reaction with the electrolyte, and improve the first efficiency (the SEI film is reduced).

[0044] (2) In the mixed carbon source slurry, graphene and carbon nanotubes form a conductive network between the cores in a single fast-charging long-cycle silicon-carbon material particle, increasing the connection strength of each core and forming a "steel-cement" type structure. The entire outer coating layer and the porous carbon matrix of the core inhibit the expansion of silicon and improve the electrochemical performance of the material.

[0045] (3) By incorporating single-arm carbon nanotubes into the carbon precursor, the porous carbon matrix, i.e. the core, contains single-arm carbon nanotubes that connect all the channels of the core, which improves the fast channels for ion and electron transport and improves the rate performance of the material. In addition, the core itself also forms a "steel-cement" structure, which increases the structural strength of the core (porous carbon matrix), increases the material's resistance to expansion, and improves its electrochemical performance. Attached Figure Description

[0046] Figure 1 The image shows the XRD pattern of the fast-charging, long-cycle silicon-carbon anode material prepared in Example 2 of this invention.

[0047] Figure 2 This is a schematic diagram of the porous carbon matrix F of the present invention.

[0048] Figure 3 This is a schematic diagram of the structure of the fast-charging, long-cycle silicon-carbon anode material of the present invention.

[0049] Figure 4 The image shows the cycling results of a 7Ah soft-pack battery using the fast-charging, long-cycle silicon-carbon anode material prepared in Example 2 of this invention. Detailed Implementation

[0050] The present invention will be further described in detail below with reference to specific embodiments. The embodiments given are only for illustrating the present invention and are not intended to limit the scope of the present invention.

[0051] Unless otherwise specified, the experimental methods described in the following examples are conventional methods.

[0052] In the quantitative experiments in the following examples, three replicate experiments were set up, and the average value of the results was taken.

[0053] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0054] Low-temperature asphalt is one of Xinjiang medium carbon 150# coated asphalt or 180# coated asphalt;

[0055] Example 1

[0056] (1) Disperse a single-arm carbon nanotube with a diameter of 0.5 nm and a length of 2 nm into anhydrous ethanol to form a solution with a solid content of 0.5% (mass fraction). Then add a 36% formaldehyde solution with a mass fraction of 1:35 to obtain solution B.

[0057] (2) Heat bisphenol A to 170°C, then add it to solution B and stir. The mass ratio of bisphenol A to solution B is 1:5. Heat the resulting solution to 180°C, add 0.5 mol / L sodium carbonate solution to adjust the pH of the solution to 7, and stop when solid begins to appear. Continue stirring until it is completely solidified to obtain solid C. Then crush solid C into block particles with a particle size of 1 μm to obtain carbon precursor D.

[0058] (3) Carbon precursor D and potassium hydroxide were mixed evenly at a mass ratio of 1:1 and calcined at 700℃ for 1 h under a nitrogen atmosphere to obtain mixture E; then it was placed in 0.2 mol / L hydrochloric acid solution and stirred and washed for 20 min, wherein the mass ratio of mixture E to hydrochloric acid solution was 1:2; after drying, it was washed multiple times with distilled water until the solution pH ≤ 8, and after drying, a pore size of 0.3 nm and a specific surface area of ​​1600 nm were obtained. 2 / g, porous carbon matrix F with a pore volume of 0.8cc / g;

[0059] (4) Place the porous carbon matrix F into a fluidized bed, introduce a mixture of silane and nitrogen at a volume ratio of 5:1, heat to 400℃ and hold for 2 hours, introduce a mixture of acetylene and argon at a gas flow ratio of 2:1, hold at 650℃ for 1 hour, and obtain product G.

[0060] (5) Place product G in a chemical vapor deposition furnace and introduce a mixture of acetylene and argon at a gas flow ratio of 2:1. Keep it at 650℃ for 1 hour to obtain product H. Then put it into a mixed carbon source slurry. The mass ratio of product H to mixed carbon source slurry is 10:1. The mixed carbon source slurry is obtained by dispersing graphene, carbon nanotubes and Xinjiang Zhongtan 150# coated pitch in anhydrous ethanol at a mass ratio of 1:1:2. The solid content of the mixed carbon source slurry is 35% (mass fraction). The carbon nanotubes are single-arm carbon nanotubes with a diameter of 3~20nm. After filtration and drying, calcine at 600℃ in an argon atmosphere for 4 hours to obtain product I with a particle size of 3μm, which is the fast-charging long-cycle silicon-carbon anode material.

[0061] The obtained fast-charging, long-cycle silicon-carbon anode material and lithium metal sheet were used to assemble a CR2032 half-cell for electrochemical performance testing. The assembly sequence was: anode shell, lithium metal sheet, separator, fast-charging, long-cycle silicon-carbon anode material electrode, gasket, and positive electrode shell. The electrolyte used was Xinzhoubang LBC3021H43. Testing was conducted at 0.1C (initial cycle) + 0.5C (cycle), with charge / discharge voltages ranging from 0.005 to 0.8V. The results showed that the discharge specific capacity of the anode electrode could reach 1605 mAh / g, with an initial efficiency of 81.6%, and after 50 cycles, it still retained 81.1% of its capacity.

[0062] The obtained long-cycle silicon-carbon anode material was mixed with graphite at a mass ratio of 18:82 to form a composite anode material. Using NCM622 as the positive electrode, a 7Ah soft-pack battery was assembled by performing processes such as slurry preparation, coating, rolling, slitting, die cutting, stacking, electrode tab welding, top and side sealing, baking, and electrolyte injection (Xinzhoubang LBC3021H43). After capacity testing, the battery was tested at room temperature under a 1C / 1C current density. The initial efficiency of the cell was 86.5%, and the capacity retention rate was 85.5% after 650 cycles of the full battery.

[0063] Example 2

[0064] (1) Disperse a single-arm carbon nanotube with a diameter of 0.8 nm and a length of 5 nm into anhydrous ethanol to form a solution with a solid content of 2% (mass fraction). Then add a 36% formaldehyde solution with a mass fraction of 1:42 to obtain solution B.

[0065] (2) Heat bisphenol A to 170°C, then add it to solution B and stir. The mass ratio of bisphenol A to solution B is 1:6. Heat the resulting solution to 190°C, add 0.5 mol / L sodium carbonate solution to adjust the pH of the solution to 8, and stop when solid begins to appear. Continue stirring until it is completely solidified to obtain solid C. Then crush solid C into block particles with a particle size of 1.5 μm to obtain carbon precursor D.

[0066] (3) Carbon precursor D and sodium hydroxide were mixed evenly at a mass ratio of 1:2 and calcined at 750℃ for 2 hours under a nitrogen atmosphere to obtain mixture E; then it was placed in a 0.2 mol / L hydrochloric acid solution and stirred and washed for 20 minutes, wherein the mass ratio of mixture E to hydrochloric acid solution was 1:3; after drying, it was washed multiple times with distilled water until the solution pH ≤ 8, and after drying, a pore size of 1.2 nm and a specific surface area of ​​1800 nm were obtained. 2 / g, porous carbon matrix F with a pore volume of 0.9 cc / g;

[0067] (4) Place the porous carbon matrix F into a fluidized bed, introduce a mixture of silane and nitrogen at a volume ratio of 1:1, heat to 500℃ and hold for 2 hours, introduce a mixture of acetylene and argon at a gas flow ratio of 1:1.5, hold at 690℃ for 2 hours, and obtain product G;

[0068] (5) Product G was placed in a chemical vapor deposition furnace, and a mixture of acetylene and argon was introduced at a gas flow ratio of 1:1. The mixture was kept at 680℃ for 1.5 h to obtain product H. Then, it was placed in a mixed carbon source slurry with a mass ratio of 10:1 between product H and the mixed carbon source slurry. The mixed carbon source slurry was obtained by dispersing graphene, carbon nanotubes, and Xinjiang Zhongtan 180# coated pitch in anhydrous ethanol at a mass ratio of 1:1:2. The solid content of the mixed carbon source slurry was 35% (mass fraction), and the carbon nanotubes were single-arm carbon nanotubes with a diameter of 3~20 nm. After filtration and drying, the mixture was calcined at 650℃ in an argon atmosphere for 4.5 h to obtain product I with a particle size of 5 μm, which is the fast-charging long-cycle silicon-carbon anode material. Figure 1 As shown, the XRD pattern of the fast-charging, long-cycle silicon-carbon anode material shows no obvious silicon characteristic peaks, indicating a uniform internal structure and good cycle performance.

[0069] The obtained fast-charging long-cycle silicon-carbon anode material and lithium metal sheet were used to assemble a CR2032 half-cell for electrochemical performance testing. The assembly sequence was: anode shell, lithium metal sheet, separator, fast-charging long-cycle silicon-carbon anode material electrode, gasket, and positive electrode shell. The electrolyte was Xinzhoubang LBC3021H43. The test rate was 0.1C (initial) + 0.5C (cycle). The results showed that the discharge specific capacity of the anode electrode could reach 1680 mAh / g, the initial efficiency was 82.9%, and after 50 cycles, it could still maintain 83.8% of the capacity.

[0070] The 7Ah pouch cell was assembled according to the method in Example 1. After capacity testing, it was subjected to room temperature cycling test at 1C / 1C current density. The initial efficiency of the cell was 87.5%, and the capacity retention rate was 89.5% after 790 cycles of the full cell.

[0071] Figure 4 This is a full-cell cycling result diagram of the fast-charging, long-cycle silicon-carbon anode material prepared in Example 2. Figure 4 It can be seen that the full battery has excellent cycle performance. After 790 cycles at room temperature, the capacity retention rate is 89.5%, the trend capacity retention rate is 80%, and the cycle life can exceed 1200 cycles.

[0072] Figure 2This is a schematic diagram of the porous carbon matrix F of the present invention. The porous carbon matrix F of the present invention has channels with a pore size of 1.2 nm. The porous carbon matrix F has single-arm carbon nanotubes that connect the various channels of the core, which improves the fast channels for ion and electron transport, improves the rate performance of the material, and forms a "reinforced concrete" structure, which increases the structural strength of the core (porous carbon matrix), increases the material's resistance to expansion, and improves its electrochemical performance.

[0073] Figure 3 This is a schematic diagram of the structure of the fast-charging, long-cycle silicon-carbon anode material of the present invention. The fast-charging, long-cycle silicon-carbon anode material of the present invention contains multiple small-sized cores (1~3μm porous carbon matrix) with deposited nano-silicon, shortening the lithium-ion transport particle size. By mixing carbon source slurry to granulate and surface-modify the cores, a highly ion-conducting carbon layer is formed on the surface, which also reduces the specific surface area of ​​the material (increasing particle size), reduces negative reactions with the electrolyte, and improves the first-stage efficiency (reducing SEI film). The graphene and carbon nanotubes in the surface coating layer form a conductive network between the cores within a single fast-charging, long-cycle silicon-carbon material particle, increasing the connection strength between the cores and forming a "reinforced concrete" structure. The entire outer coating layer and the porous carbon matrix of the cores inhibit silicon expansion, improving the electrochemical performance of the material.

[0074] Example 3

[0075] (1) Disperse a single-arm carbon nanotube with a diameter of 0.8 nm and a length of 10 nm into anhydrous ethanol to form a solution with a solid content of 2% (mass fraction). Then add a 36% formaldehyde solution with a mass fraction of 1. The mass ratio of the single-arm carbon nanotube to formaldehyde is 1:42 to obtain solution B.

[0076] (2) Heat bisphenol A to 170°C, then add it to solution B and stir. The mass ratio of bisphenol A to solution B is 1:6. Heat the resulting solution to 190°C, add 0.5 mol / L sodium carbonate solution to adjust the pH of the solution to 9, and stop when solid begins to appear. Continue stirring until it is completely solidified to obtain solid C. Then crush solid C into block particles with a particle size of 2 μm to obtain carbon precursor D.

[0077] (3) Carbon precursor D and sodium hydroxide were mixed evenly at a mass ratio of 1:2 and calcined at 750℃ for 2 hours under an argon atmosphere to obtain mixture E; then it was placed in a 0.2 mol / L hydrochloric acid solution and stirred and washed for 20 minutes, wherein the mass ratio of mixture E to hydrochloric acid solution was 1:3; after drying, it was washed multiple times with distilled water until the solution pH ≤ 8, and after drying, a pore size of 1.5 nm and a specific surface area of ​​2050 nm were obtained. 2 / g, porous carbon matrix F with a pore volume of 0.91 cc / g;

[0078] (4) Place the porous carbon matrix F into a fluidized bed, introduce a mixture of silane and hydrogen at a volume ratio of 1:3, heat to 500℃ and hold for 2 hours, introduce a mixture of acetylene and argon at a gas flow ratio of 1:1.5, hold at 690℃ for 2 hours, and obtain product G;

[0079] (5) Place product G in a chemical vapor deposition furnace and introduce a mixture of acetylene and argon at a gas flow ratio of 1:1.5. Keep it at 700℃ for 3 hours to obtain product H. Then put it into a mixed carbon source slurry. The mass ratio of product H to mixed carbon source slurry is 10:1. The mixed carbon source slurry is obtained by dispersing graphene, carbon nanotubes and Xinjiang Zhongtan 180# coated pitch in anhydrous ethanol at a mass ratio of 1:1:2. The solid content of the mixed carbon source slurry is 35% (mass fraction). The carbon nanotubes are single-arm carbon nanotubes with a diameter of 3~20nm. After filtration and drying, calcine at 650℃ in an argon atmosphere for 4.5 hours to obtain finished product I with a particle size of 5μm, namely fast-charging long-cycle silicon-carbon anode material.

[0080] The obtained fast-charging long-cycle silicon-carbon anode material and lithium metal sheet were used to assemble a CR2032 half-cell for electrochemical performance testing. The assembly sequence was: anode shell, lithium metal sheet, separator, fast-charging long-cycle silicon-carbon anode material electrode, gasket, and positive electrode shell. The electrolyte was Xinzhoubang LBC3021H43. The test rate was 0.1C (initial) + 0.5C (cycle). The results showed that the discharge specific capacity of the anode electrode could reach 1696mAh / g, the initial efficiency was 82.1%, and after 50 cycles, it could still maintain 83.2% of the capacity.

[0081] The obtained long-cycle silicon-carbon anode material was mixed with graphite at a mass ratio of 5:95 to form a composite anode material. Using NCM622 as the positive electrode, a 7Ah soft-pack battery was assembled by performing processes such as slurry preparation, coating, rolling, slitting, die cutting, stacking, electrode tab welding, top and side sealing, baking, and electrolyte injection (Xinzhoubang LBC3021H43). After capacity testing, the battery was tested at room temperature under a 1C / 1C current density. The initial efficiency of the cell was 86.5%, and the capacity retention rate was 84.7% after 647 cycles of the full battery.

[0082] Example 4

[0083] (1) Disperse a single-arm carbon nanotube with a diameter of 0.9 nm and a length of 15 nm into anhydrous ethanol to form a solution with a solid content of 4% (mass fraction). Then add a 36% formaldehyde solution with a mass fraction of 1:60 to obtain solution B.

[0084] (2) Heat bisphenol A to 170°C, then add it to solution B and stir. The mass ratio of bisphenol A to solution B is 1:7. Heat the resulting solution to 190°C, add 0.5 mol / L sodium carbonate solution to adjust the pH of the solution to 9.5. Stop stirring when solid begins to appear in the solution, and continue stirring until it is completely solidified to obtain solid C. Then crush solid C into block particles with a particle size of 3 μm to obtain carbon precursor D.

[0085] (3) Carbon precursor D and lithium hydroxide were mixed evenly at a mass ratio of 1:3 and calcined at 800℃ for 3 hours under a nitrogen atmosphere to obtain mixture E; then it was placed in a 0.2 mol / L hydrochloric acid solution and stirred and washed for 20 minutes, wherein the mass ratio of mixture E to hydrochloric acid solution was 1:4; after drying, it was washed multiple times with distilled water until the solution pH ≤ 8, and after drying, a pore size of 2 nm and a specific surface area of ​​2100 nm were obtained. 2 / g, porous carbon matrix F with a pore volume of 0.93 cc / g;

[0086] (4) Place the porous carbon matrix F into a fluidized bed, introduce a mixture of silane and nitrogen at a volume ratio of 1:4, heat to 600℃ and hold for 4 hours, introduce a mixture of acetylene and argon at a gas flow ratio of 1:2, hold at 700℃ for 3 hours, and obtain product G.

[0087] (5) Place product G in a chemical vapor deposition furnace and introduce a mixture of acetylene and argon at a gas flow ratio of 1:2. Keep it at 700℃ for 3.5h to obtain product H. Then put it into a mixed carbon source slurry. The mass ratio of product H to mixed carbon source slurry is 10:1. The mixed carbon source slurry is obtained by dispersing graphene, carbon nanotubes and Xinjiang Zhongtan 150# coated pitch in anhydrous ethanol at a mass ratio of 1:1:2. The solid content of the mixed carbon source slurry is 35% (mass fraction). The carbon nanotubes are single-arm carbon nanotubes with a diameter of 3~20nm. After filtration and drying, calcine at 800℃ in an argon atmosphere for 5.5h to obtain finished product I with a particle size of 8μm, namely fast-charging long-cycle silicon-carbon anode material.

[0088] The obtained fast-charging long-cycle silicon-carbon anode material and lithium metal sheet were used to assemble a CR2032 half-cell for electrochemical performance testing. The assembly sequence was: anode shell, lithium metal sheet, separator, fast-charging long-cycle silicon-carbon anode material electrode, gasket, and positive electrode shell. The electrolyte was Xinzhoubang LBC3021H43. The test rate was 0.1C (initial) + 0.5C (cycle). The results showed that the discharge specific capacity of the anode electrode could reach 1600 mAh / g, the initial efficiency was 82.8%, and after 50 cycles, it could still maintain 84.9% of the capacity.

[0089] The obtained long-cycle silicon-carbon anode material was mixed with graphite at a mass ratio of 5:95 to form a composite anode material. Using NCM622 as the positive electrode, a 7Ah soft-pack battery was assembled by performing processes such as slurry preparation, coating, rolling, slitting, die cutting, stacking, electrode tab welding, top and side sealing, baking, and electrolyte injection (Xinzhoubang LBC3021H43). After capacity testing, the battery was tested at room temperature under a 1C / 1C current density. The initial efficiency of the cell was 87.4%, and the capacity retention rate was 94.1% after 450 cycles of the entire battery.

[0090] Example 5

[0091] (1) Disperse a single-arm carbon nanotube with a diameter of 1 nm and a length of 20 nm into anhydrous ethanol to form a solution with a solid content of 5% (mass fraction). Then add a 36% formaldehyde solution with a mass fraction of 1. The mass ratio of the single-arm carbon nanotube to formaldehyde is 1:80 to obtain solution B.

[0092] (2) Heat bisphenol A to 170°C, add it to solution B and stir. The mass ratio of bisphenol A to solution B is 1:8. Heat the resulting solution to 200°C and add 0.5 mol / L sodium carbonate solution to adjust the pH of the solution to 10. Stop stirring when solids begin to appear in the solution and continue stirring until it is completely solidified to obtain solid C. Then crush solid C into block particles with a particle size of 4 μm to obtain carbon precursor D.

[0093] (3) Carbon precursor D and lithium hydroxide were mixed evenly at a mass ratio of 1:4 and calcined at 900℃ for 5 h under a nitrogen atmosphere to obtain mixture E; then it was placed in 0.2 mol / L hydrochloric acid solution and stirred and washed for 20 min, wherein the mass ratio of mixture E to hydrochloric acid solution was 1:5; after drying, it was washed multiple times with distilled water until the solution pH ≤ 8, and after drying, a pore size of 3 nm and a specific surface area of ​​2200 nm were obtained. 2 / g, porous carbon matrix F with a pore volume of 1.0 cc / g;

[0094] (4) Place the porous carbon matrix F into a fluidized bed, introduce a mixture of silane and nitrogen at a volume ratio of 1:5, heat to 700℃ and hold for 6 hours, introduce a mixture of acetylene and argon at a gas flow ratio of 1:3, hold at 750℃ for 3 hours, and obtain product G.

[0095] (5) Place product G in a chemical vapor deposition furnace and introduce a mixture of acetylene and argon at a gas flow ratio of 1:2. Keep it at 750℃ for 4 hours to obtain product H. Then put it into a mixed carbon source slurry. The mass ratio of product H to mixed carbon source slurry is 10:1. The mixed carbon source slurry is obtained by dispersing graphene, carbon nanotubes and Xinjiang Zhongtan 180# coated pitch in anhydrous ethanol at a mass ratio of 1:1:2. The solid content of the mixed carbon source slurry is 35% (mass fraction). The carbon nanotubes are single-arm carbon nanotubes with a diameter of 3~20nm. After filtration and drying, calcine at 900℃ in an argon atmosphere for 6 hours to obtain product I with a particle size of 10μm, which is the fast-charging long-cycle silicon-carbon anode material.

[0096] The obtained fast-charging long-cycle silicon-carbon anode material and lithium metal sheet were used to assemble a CR2032 half-cell for electrochemical performance testing. The assembly sequence was: anode shell, lithium metal sheet, separator, fast-charging long-cycle silicon-carbon anode material electrode, gasket, and positive electrode shell. The electrolyte was Xinzhoubang LBC3021H43. The test rate was 0.1C (initial) + 0.5C (cycle). The results showed that the discharge specific capacity of the anode electrode could reach 1580 mAh / g, the initial efficiency was 82.0%, and after 50 cycles, it could still maintain 83.1% of the capacity.

[0097] The obtained long-cycle silicon-carbon anode material was mixed with graphite at a mass ratio of 5:95 to form a composite anode material. Using NCM622 as the positive electrode, a 7Ah soft-pack battery was assembled by performing processes such as slurry preparation, coating, rolling, slitting, die cutting, stacking, electrode tab welding, top and side sealing, baking, and electrolyte injection (Xinzhoubang LBC3021H43). After capacity testing, the battery was tested at room temperature under a 1C / 1C current density. The initial efficiency of the cell was 87.2%, and the capacity retention rate was 92.5% after 450 cycles of the full battery.

[0098] Comparative Example 1

[0099] The porous carbon matrix of Shaanxi Coal Technology Research Institute with a D50 of 8 μm (pore size of 2.2 nm, specific surface area of ​​1800 μm) was used. 2 The silicon-carbon anode material (with a pore volume of 0.8 cc / g) was placed in a fluidized bed, and a mixture of silane and hydrogen was introduced at a gas volume ratio of 2:1. The mixture was heated to 700℃ and held for 6 hours. Then, a mixture of acetylene and argon was introduced at a gas volume ratio of 1:3, and the mixture was held at 750℃ for 3 hours to obtain the silicon-carbon anode material.

[0100] The silicon-carbon anode material obtained in this comparative example was used to assemble a half-cell with lithium metal, and the electrochemical performance was tested (same as in Example 1). The test rate was 0.1C (initial) + 0.5C (cycle), and the charge / discharge voltage was 0.005~0.8V. The results showed that the discharge specific capacity of the anode sheet could reach 1580 mAh / g, the initial efficiency was 82.0%, and after 50 cycles, it could still retain 51.1% of the capacity.

[0101] As demonstrated by the performance results of the embodiments, this invention employs a small-sized core (1~3μm porous carbon matrix F) to deposit nano-silicon, shortening the lithium-ion transport particle size. Then, the core is granulated and surface-modified using a mixed carbon source slurry. One or more cores are then composited to form a slightly larger finished product. Furthermore, single-arm carbon nanotubes are composited with the core, connecting all the pores of the core, thus improving the rapid ion and electron transport channels, enhancing the material's rate performance, and forming a "reinforced concrete" structure. This increases the structural strength of the core, improves the material's resistance to expansion, and enhances its electrochemical performance. The graphene and carbon nanotubes in the mixed carbon source slurry create a "reinforced concrete" structure in the outer coating layer, resulting in a high-strength material with excellent electrical conductivity and high rate capability.

Claims

1. A method for preparing a silicon-carbon anode material, comprising the following steps: (1) Disperse single-walled carbon nanotubes in a solvent to obtain solution A; then mix solution A with formaldehyde solution to obtain solution B; (2) Dissolve bisphenol A in the solution B, heat it, and then add a catalyst to adjust the pH of the solution to 7-10 so that the solution is completely solidified to obtain solid C; crush the solid C into block particles with a particle size of 1-4 μm to obtain carbon precursor D; (3) The carbon precursor D and the alkali activator are mixed and calcined to obtain mixture E; the mixture E is washed to obtain porous carbon matrix F; (4) The porous carbon matrix F is placed in a fluidized bed, a mixture of silane and nitrogen is introduced, and the mixture is heated and kept warm; then a mixture of acetylene and argon is introduced, and the mixture is heated and kept warm to obtain product G; (5) Carbon is deposited on the surface of product G using chemical vapor deposition to obtain product H; (6) The product H and the mixed carbon source slurry are mixed and calcined to obtain the silicon-carbon anode material; The mixed carbon source slurry is obtained by dispersing graphene, carbon nanotubes and low-temperature pitch in anhydrous ethanol.

2. The method for preparing silicon-carbon anode material according to claim 1, characterized in that: In step (1), the diameter of the single-walled carbon nanotube is 0.5~1nm and the length is 2~20nm; The solvent is anhydrous ethanol; In solution A, the solid content of single-walled carbon nanotubes is 0.5%~5%; The formaldehyde solution has a mass percentage concentration of 35% to 37%. The mass ratio of the single-walled carbon nanotubes to formaldehyde is 1:35~80; In step (2), the mass ratio of bisphenol A to solution B is 1:5~8; The catalyst is at least one of sodium carbonate solution, sodium hydroxide solution, and ammonium hydroxide solution.

3. The method for preparing silicon-carbon anode material according to claim 1, characterized in that: The specific operation of step (2) is as follows: dissolve bisphenol A in the solution B, heat the resulting solution to 180~200℃, then add a catalyst to adjust the pH of the solution to 7~10, stop when the solution begins to show solids, and continue stirring until it is completely solidified to obtain solid C.

4. The method for preparing silicon-carbon anode material according to claim 1, characterized in that: In step (3), the alkaline activator is at least one of potassium hydroxide, sodium hydroxide, and lithium hydroxide; The mass ratio of the carbon precursor D to the alkaline activator is 1:1~4; The calcination is carried out in an inert atmosphere; The calcination temperature is 700~900℃; the calcination time is 1~5h; The washing process involves sequentially applying hydrochloric acid solution and water.

5. The method for preparing the silicon-carbon anode material according to claim 4, characterized in that: The concentration of the hydrochloric acid is 0.1~2 mol / L.

6. The method for preparing the silicon-carbon anode material according to claim 4, characterized in that: In step (3), the washing operation is as follows: put the mixture E into hydrochloric acid solution and stir and wash for 10~60 min, and then wash with water multiple times until the solution pH≤8.

7. The method for preparing silicon-carbon anode material according to claim 6, characterized in that: The mass ratio of the mixture E to the hydrochloric acid solution is 1:2~5.

8. The method for preparing silicon-carbon anode material according to claim 1, characterized in that: The specific operation of step (4) is as follows: the porous carbon matrix F is placed in a fluidized bed, and a mixture of silane and nitrogen with a volume ratio of 5:1 to 1:5 is introduced and kept at 400 to 700°C for 2 to 6 hours; then a mixture of acetylene and argon with a gas flow ratio of 2:1 to 1:3 is introduced and kept at 650 to 750°C for 1 to 3 hours to obtain product G; The silane is either methylsilane or disilane.

9. The method for preparing silicon-carbon anode material according to claim 1, characterized in that: The specific operation of step (5) is as follows: Place the product G in a chemical vapor deposition reactor, introduce a mixture of acetylene and argon gas at a gas flow ratio of 2:1 to 1:2, keep it at 650 to 750°C for 1 to 4 hours, and obtain product H.

10. The method for preparing the silicon-carbon anode material according to claim 1, characterized in that: In step (6), the mass ratio of product H to mixed carbon source slurry is 10:1 to 15:1; The mass ratio of graphene, carbon nanotubes, and low-temperature asphalt is 1:1:2; the solid content of the mixed carbon source slurry is 30%~40%; the carbon nanotubes are single-walled carbon nanotubes with a diameter of 3~20nm. The calcination is carried out in an inert atmosphere; The calcination temperature is 600~900℃; the calcination time is 4~6h.

11. The silicon-carbon anode material prepared by the preparation method according to any one of claims 1-10.

12. The application of the silicon-carbon anode material according to claim 11 in the preparation of lithium-ion battery anodes.

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