Silicon-carbon negative electrode material, preparation method and application thereof

Abstract

The present application relates to a kind of silicon-carbon negative electrode materials, including porous carbon and carbon-silicon inner core consisting of silicon crystal particles, and oxidation layer, inorganic layer and carbon deposition layer are successively coated on the surface of carbon-silicon inner core from inside to outside;Silicon crystal particles are distributed in porous carbon;The porous carbon contains carbonized cellulose acetate, and carbonized cellulose acetate is embedded in porous carbon;The oxidation layer contains silicon element and oxygen element;The inorganic layer contains one or more of phosphate, metacinnabar, silicate.The silicon-carbon negative electrode material in the present application is a kind of multilayer coated negative electrode material, the material has the advantages of high internal lithium ion transmission capacity, low polarization, strong material compression resistance, good rate performance, high battery life of the applied battery.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a silicon-carbon anode material, its preparation method, and its application. Background Technology

[0002] With the rise of green energy, the energy density of current state-of-the-art lithium-ion batteries (LIBs) is limited. Developing electrode materials with high specific capacity is an effective way to improve the energy density of lithium-ion batteries. In this regard, silicon materials, due to their outstanding capacity advantage (4200 mAhg), environmental friendliness, and cost-effectiveness, have become one of the best candidate materials to replace commercial graphite anodes.

[0003] However, silicon anode materials have poor stability. To improve the cycle stability of silicon anode particles, coating the silicon material with carbon is a common method. By coating silicon anode particles with amorphous carbon, electrodes constructed from this carbon-coated silicon-carbon anode material exhibit high initial specific capacity and certain cycle stability. However, the internal lithium-ion transport capacity of amorphous carbon-coated silicon is low, making it prone to polarization and resulting in low compressive strength, which is detrimental to the rate performance of the material and leads to a shorter battery life. This problem limits the application of silicon-carbon anode materials. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a silicon-carbon anode material, its preparation method, and its applications.

[0005] This invention is achieved through the following scheme: The first objective of this invention is to provide a silicon-carbon anode material, comprising porous carbon and a silicon-carbon core composed of silicon crystal particles, and an oxide layer, an inorganic layer, and a carbon deposition layer sequentially coated on the surface of the silicon-carbon core from the inside out; the silicon crystal particles are distributed in the porous carbon; the porous carbon contains carbonized cellulose acetate, which is embedded in the porous carbon; the oxide layer contains silicon and oxygen elements; and the inorganic layer contains one or more of phosphates, aluminates, and silicates.

[0006] Furthermore, the diameter of the carbon-silicon core is 0.3-80 μm; the thickness of the oxide layer is 2 nm-200 nm; the thickness of the inorganic layer is 2 nm-50 nm; and the thickness of the carbon deposition layer is 2 nm-65 nm.

[0007] In one embodiment of the present invention: a) The silicon crystal particles are distributed in porous carbon by deposition, and the silicon crystal particles include crystalline silicon and amorphous silicon, and the particle size of crystalline silicon is ≤4nm; b) The specific surface area of ​​the negative electrode material is 0.7-6.0 m². 2 / g; c) The median particle size Dv50 of the negative electrode material is 3-18 μm; d) The mass ratio of silicon and carbon elements in the negative electrode material is 90%-99.9%.

[0008] Furthermore, the cellulose acetate is diacetate fiber and / or triacetate fiber.

[0009] The second objective of this invention is to provide a method for preparing a silicon-carbon anode material, comprising the following steps: (1) Mix the carbon source and cellulose acetate mixture, heat to form carbon, wash and crush to obtain porous carbon; (2) Porous carbon is placed in a deposition device, and silane is deposited in the pores of the porous carbon to obtain a carbon silicon core; the carbon silicon core is mixed with inorganic salt, and ball milled and sieved to obtain a carbon silicon core with an oxide layer and an inorganic layer on the surface. (3) The carbon silicon core with the surface covered with oxide layer and inorganic layer is sent to the deposition device, and a gaseous carbon source is introduced to perform carbon deposition to obtain a silicon-carbon anode material with oxide layer, inorganic layer and carbon deposition layer on the surface of the carbon silicon core from the inside to the outside.

[0010] In one embodiment of the present invention, in step (1): The carbon source is one or more of polyvinyl alcohol, phenolic resin, epoxy resin, polyethylene oxide, furfural resin, and urea-formaldehyde resin. The cellulose acetate mixture is prepared by dispersing 5-30 parts by weight of diacetate cellulose and / or triacetate cellulose in 100 parts by weight of an ionic liquid, wherein the ionic liquid is an aqueous solution containing 1-15 wt% of one or more of sodium hydroxide, potassium hydroxide, sodium hypochlorite, potassium hypochlorite, sodium oxalate, sodium phosphate, or lithium phosphate. The mass ratio of the cellulose acetate mixture to the carbon source is (0.001-0.12):1.

[0011] In one embodiment of the present invention, in step (1): The conditions for heating to carbon are: heating temperature 1000-1600℃, heating time 4-12h; The washing conditions are as follows: washing temperature 60-95℃, washing time 1-3h.

[0012] In one embodiment of the present invention, in step (2): The method for preparing silane deposition in the pores of porous carbon is as follows: the reaction temperature of the deposition apparatus is 300-750℃, an inert gas is introduced to remove internal air, and a mixed silane with a flow rate of 0.05-2L / s is introduced for silicon cracking for 2-8 hours. The mixed silane is a mixture of silane and inert gas, and the gas flow ratio of silane to inert gas is 1:(0.05-8). Before ball milling, the mass ratio of the silicon carbide core to the inorganic salt is 1:(0.001-0.012).

[0013] In one embodiment of the present invention, in step (2): The inorganic salts include one or more of the following: sodium tripolyphosphate, ammonium phosphate, lithium phosphate, sodium phosphate, lithium fluorophosphate, sodium fluorophosphate, ammonium fluorophosphate, magnesium phosphate, aluminum phosphate, potassium phosphate, lithium aluminate, magnesium aluminate, lithium silicate, aluminum silicate, and magnesium silicate. The silane is one or more of methylsilane, ethylsilane, and propane; The inert gas is one or more of nitrogen, argon, helium, and xenon. In one embodiment of the present invention, in step (3): The gaseous carbon source includes one or more of methane, ethane, propane, acetylene, propyne, butyne, and ethylene; The carbon deposition preparation method is as follows: a gaseous carbon source is decomposed on the surface of a carbon silicon core coated with an oxide layer and an inorganic layer at a temperature of 400-750℃ until a carbon deposition layer with a thickness of 2nm-65nm is deposited.

[0014] A third objective of this invention is to provide a negative electrode sheet, comprising a binder material, a graphite material, a conductive material, and the aforementioned silicon-carbon negative electrode material or the silicon-carbon negative electrode material prepared by the above-described preparation method.

[0015] In one embodiment of the present invention, the mass ratio of the silicon-carbon anode material, graphite material, binder material and conductive material is (2-45):(30-98):(0.4-6):(0.4-6).

[0016] The fourth objective of this invention is to provide a method for preparing a negative electrode sheet, comprising the following steps: first, placing conductive material, silicon-carbon negative electrode material, and graphite material in the mixing bowl of a mixer and mixing for 30 min to 3 h; then adding deionized water solvent and binder material to a container; drawing the mixing bowl to a vacuum state; continuing to stir for 3-8 h; and then adding deionized water solvent until the viscosity is between 1-6.0 Pa·s to obtain an electrode slurry; then pressing the electrode slurry onto a thin film material, drying, and rolling to obtain the negative electrode sheet.

[0017] A fifth objective of the present invention is to provide a secondary battery comprising the aforementioned negative electrode.

[0018] The sixth objective of this invention is to provide a method for preparing a secondary battery, comprising the following steps: stacking and winding a negative electrode sheet, a separator, and a positive electrode sheet in sequence to obtain a bare cell; welding the tabs; placing the bare cell into a battery aluminum shell / soft-pack aluminum-plastic film; sealing the top and sides; drying to remove moisture; injecting electrolyte into the battery shell; forming; determining the capacity; venting and sealing; and finally obtaining a secondary battery.

[0019] The reason for the formation of the oxide layer described in this invention is that, under the condition of coating the inorganic layer, the silicon in the outer layer of the silicon-carbon core will be oxidized to obtain silicon suboxide. That is, the oxide layer is formed after the core is coated with inorganic salt, and the main component of the oxide layer is silicon suboxide.

[0020] The cellulose acetate mixture is a complex formed by hydrogen bonds between free cations in an aqueous solution and the hydroxyl protons of cellulose. The surface of cellulose acetate has numerous active functional groups (-COC-, -OH, -COOH), which can form strong intermolecular forces (hydrogen bonds) with cations. This makes cellulose acetate electronegative within a specific area of ​​its surface and attracts it to be uniformly distributed within the carbon source through electrostatic adsorption, reducing agglomeration. This facilitates the uniform embedding of carbonized cellulose within porous carbon, thereby increasing the strength of the porous carbon skeleton. This improves the dispersion of the porous carbon skeleton, resisting expansion and contraction stresses, and enhancing its compressive strength. Consequently, it improves the material's compressive strength, processing performance, and compaction limit.

[0021] The technical solution of the present invention has the following advantages compared with the prior art: The silicon-carbon anode material designed in this invention consists of a silicon-carbon core composed of porous carbon and silicon crystal particles. Carbonized cellulose acetate is embedded within the porous carbon of the silicon-carbon core, and an oxide layer, an inorganic layer, and a carbon deposition layer are sequentially coated on the surface of the silicon-carbon core from the inside out. This improves the material's compressive strength and processing performance, and also enhances its overall lithium transport capacity, conductivity, and structural toughness against expansion and contraction. Firstly, thanks to the carbon source and cellulose acetate mixture being heated to form carbon, the embedding of cellulose acetate shortens the electron conduction distance in the core bulk phase, reduces the electrode contact resistance, accelerates electron mobility, and effectively increases the migration rate of lithium ions in the electrode material. Secondly, the porous carbon substrate acts as a buffer medium, and the embedding of cellulose acetate within the porous carbon regulates the volume change of the silicon-carbon anode during lithium insertion / extraction, improves the dispersion of the porous carbon framework to resist expansion and contraction stress, reduces cracking and the appearance of fresh interfaces and electrolyte consumption, and improves the cycle performance of the silicon-carbon composite material. Encapsulating the silicon-carbon core with oxide and carbon deposition layers can, to some extent, alleviate the expansion and pulverization of silicon-carbon anode materials. Inorganic coating can shorten the lithium-ion diffusion path and increase the lithium-ion migration rate, thereby improving the rate performance of the material.

[0022] In summary, the silicon-carbon anode material in this invention is a multilayer coated anode material with advantages such as high internal lithium-ion transport capacity, low polarization, strong compressive strength, good rate performance, and long battery life. Attached Figure Description

[0023] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein... Figure 1 This is a schematic diagram of the silicon-carbon anode material structure obtained in Example 1 of the present invention; wherein, 1, silicon; 2, carbon; 3, carbonized cellulose; 4, oxide layer; 5, inorganic layer; 6, carbon deposition layer; 7, silicon-carbon core; Figure 2 These are the electrochemical impedance diagrams of Examples 1 and 2 of the present invention. Detailed Implementation

[0024] To address the technical problems of existing carbon-coated silicon anodes, such as low internal lithium-ion transport capacity, susceptibility to polarization, low compressive strength, hindering rate performance, and short battery life, this invention provides a silicon-carbon anode material, its preparation method, and its application, achieved through the following means: The first objective of this invention is to provide a silicon-carbon anode material, comprising porous carbon and a silicon-carbon core composed of silicon crystal particles, and an oxide layer, an inorganic layer, and a carbon deposition layer sequentially coated on the surface of the silicon-carbon core from the inside out; the silicon crystal particles are distributed in the porous carbon; the porous carbon contains carbonized cellulose acetate, which is embedded in the porous carbon; the oxide layer contains silicon and oxygen elements; and the inorganic layer contains one or more of phosphates, aluminates, and silicates.

[0025] Furthermore, the diameter of the silicon carbide core is 0.3-80 μm, specifically 0.3-10 μm, 10-20 μm, 20-30 μm, 30-40 μm, 40-50 μm, 50-60 μm, 60-70 μm, 70-80 μm, and other values, including but not limited to those listed above.

[0026] Furthermore, the thickness of the oxide layer is 2nm-200nm, specifically it can be 2nm, 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 120nm, 150nm, 180nm, 200nm, etc., including but not limited to the values ​​listed above.

[0027] Furthermore, the thickness of the inorganic layer is 2nm-50nm; specifically, it can be 2nm, 8nm, 13nm, 14nm, 18nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, or 50nm, including but not limited to the values ​​listed above.

[0028] Furthermore, the thickness of the carbon deposition layer is 2nm-65nm, specifically it can be 2nm, 7nm, 8nm, 12nm, 16nm, 20nm, 25nm, 30nm, 40nm, 50nm, 55nm, 60nm, 65nm, etc., including but not limited to the values ​​listed above.

[0029] a) The silicon crystal particles are distributed in porous carbon by deposition, and the silicon crystal particles include crystalline silicon and amorphous silicon, and the particle size of crystalline silicon is ≤4nm; b) The specific surface area of ​​the negative electrode material is 0.7-6.0 m². 2 / g; c) The median particle size Dv50 of the negative electrode material is 3-18 μm; d) The mass ratio of silicon and carbon elements in the negative electrode material is 90%-99.9%.

[0030] In one embodiment of the present invention: Furthermore, the particle size of crystalline silicon can vary from 1-2nm, 2-3nm, to 3-4nm, including but not limited to the values ​​listed above.

[0031] Furthermore, the specific surface area of ​​the negative electrode material is 0.7 m². 2 / g, 2.0m 2 / g, 3.0m 2 / g, 5.0m 2 / g, 6.0m 2 / g varies and includes, but is not limited to, the values ​​listed above.

[0032] Furthermore, the median particle size Dv50 of the negative electrode material is 3μm, 5μm, 6μm, 8μm, 9μm, 10μm, 12μm, 14μm, 16μm, 18μm, etc., including but not limited to the values ​​listed above.

[0033] Furthermore, the mass percentages of silicon and carbon in the negative electrode material vary, including but not limited to the values ​​listed above, ranging from 90%, 91%, 93%, 95%, 96%, 97%, 98%, 99%, to 99.9%. The carbon element includes the total amount of carbon in the porous carbon and the carbon deposition layer; the silicon element includes the total amount of silicon in the silicon grains and the oxide layer.

[0034] Furthermore, the cellulose acetate is diacetate fiber and / or triacetate fiber.

[0035] The second objective of this invention is to provide a method for preparing a silicon-carbon anode material, comprising the following steps: (1) Mix the carbon source and cellulose acetate mixture, heat to form carbon, wash and crush to obtain porous carbon; (2) Porous carbon is placed in a deposition device, and silane is deposited in the pores of the porous carbon to obtain a carbon silicon core; the carbon silicon core is mixed with inorganic salt, and ball milled and sieved to obtain a carbon silicon core with an oxide layer and an inorganic layer on the surface. (3) The carbon silicon core with the surface covered with oxide layer and inorganic layer is sent to the deposition device, and a gaseous carbon source is introduced to perform carbon deposition to obtain a silicon-carbon anode material with oxide layer, inorganic layer and carbon deposition layer on the surface of the carbon silicon core from the inside to the outside.

[0036] In one embodiment of the present invention, step (1) satisfies the following condition: The carbon source is one or more of polyvinyl alcohol, phenolic resin, epoxy resin, polyethylene oxide, furfural resin, and urea-formaldehyde resin. The cellulose acetate mixture is prepared by dispersing 5-30 parts by weight of diacetate cellulose and / or triacetate cellulose in 100 parts by weight of an ionic liquid, wherein the ionic liquid is an aqueous solution containing 1-15 wt% of one or more of sodium hydroxide, potassium hydroxide, sodium hypochlorite, potassium hypochlorite, sodium oxalate, sodium phosphate, or lithium phosphate. The mass ratio of the cellulose acetate mixture to the carbon source is (0.001-0.12):1. An excessively high mass ratio of the cellulose acetate mixture to the carbon source is detrimental to the pyrolysis of the carbon source to obtain porous hard carbon, while an excessively low mass ratio prevents the cellulose acetate from achieving its optimal effect.

[0037] Furthermore, the cellulose acetate mixture is an aqueous solution in which free cations form hydrogen bonds with the hydroxyl protons of cellulose acetate to form a complex, which allows cellulose acetate to be stably dispersed in the ionic liquid, which is beneficial for mixing with the carbon source, and the carbonized cellulose is embedded in the carbon source that is heated to carbon.

[0038] In one embodiment of the present invention, in step (1), the following condition is satisfied: The conditions for heating to carbonize are as follows: the heating equipment is a tubular furnace, the heating temperature is 1000-1600℃, and the heating time is 4-12 hours. The washing conditions are as follows: washing temperature 60-95℃, washing time 1-3h.

[0039] In one embodiment of the present invention, step (2) satisfies the following condition: The method for preparing silane deposition in the pores of porous carbon is as follows: the reaction temperature of the deposition apparatus is 300-750℃, an inert gas is introduced to remove internal air, and a mixed silane with a flow rate of 0.05-2L / s is introduced for silicon cracking for 2-8 hours. The mixed silane is a mixture of silane and inert gas, and the gas flow ratio of silane to inert gas is 1:(0.05-8). Before ball milling, the mass ratio of the silicon carbide core to the inorganic salt is 1:(0.001-0.012). When the ratio is too high, the material coating effect deteriorates, lithium-ion diffusion becomes poor, resistance is high, and the cycle life of the material is low. When the ratio is too low, the inorganic layer cannot achieve the coating effect of the core and cannot improve the lithium-ion migration rate of the core.

[0040] In one embodiment of the present invention, in step (2), the following condition is satisfied: 1) The ball milling conditions are: rotation speed 300-800 r / min, ball milling time 30 min-8 h.

[0041] 2) The deposition device is a fluidized bed or a rotary kiln.

[0042] 3) The inorganic salts include one or more of the following: sodium tripolyphosphate, ammonium phosphate, lithium phosphate, sodium phosphate, lithium fluorophosphate, sodium fluorophosphate, ammonium fluorophosphate, magnesium phosphate, aluminum phosphate, potassium phosphate, lithium aluminate, magnesium aluminate, lithium silicate, aluminum silicate, and magnesium silicate. 4) The silane is one or more of methylsilane, ethylsilane, and propane; 5) The inert gas is one or more of nitrogen, argon, helium, and xenon.

[0043] Furthermore, in step (2), the carbon silicon core is ball-milled with inorganic salt. On the one hand, the heat generated is conducive to the formation of inorganic layer coating. On the other hand, the ball milling condition will oxidize the core surface to form a silicon oxide layer. The porous carbon contains carbonized cellulose acetate, which is embedded in the porous carbon. The carbon silicon core is then coated with an inorganic layer, which increases the distance of electron conduction in the core bulk phase and accelerates the electron movement rate. At the same time, it can also effectively increase the migration rate of lithium ions through the inorganic layer to the core.

[0044] In one embodiment of the present invention, step (3) satisfies the following condition: The gaseous carbon source includes one or more of methane, ethane, propane, acetylene, propyne, butyne, and ethylene; The carbon deposition preparation method involves: a gaseous carbon source being decomposed on the surface of a carbon-silicon core coated with an oxide layer and an inorganic layer at a temperature of 400-750℃ until a carbon deposition layer with a thickness of 2nm-65nm is deposited. If the carbon deposition layer is too small, the coating effect will not be achieved; if it is too large, the layer will be too thick, which is not conducive to the diffusion of lithium ions.

[0045] Furthermore, in step (3), the gaseous carbon source is cracked and accumulated on the core surface to form amorphous carbon, avoiding direct contact with the electrolyte, forming a carbon deposition layer that protects the oxide layer and inorganic layer. The carbon spacing of the carbon deposition layer is relatively large, which is conducive to the rapid diffusion of lithium ions into the interior.

[0046] A third objective of this invention is to provide a negative electrode sheet, comprising a binder material, a graphite material, a conductive material, and the aforementioned silicon-carbon negative electrode material or the silicon-carbon negative electrode material prepared by the above-described preparation method.

[0047] In one embodiment of the present invention, the mass ratio of the silicon-carbon anode material, graphite material, binder material and conductive material is (2-45):(30-98):(0.4-6):(0.4-6).

[0048] The fourth objective of this invention is to provide a method for preparing a negative electrode sheet, comprising the following steps: first, placing conductive material, silicon-carbon negative electrode material, and graphite material in the mixing bowl of a mixer and mixing for 30 min to 3 h; then adding deionized water solvent and binder material to a container; drawing the mixing bowl to a vacuum state; continuing to stir for 3-8 h; and then adding deionized water solvent until the viscosity is between 1-6.0 Pa·s to obtain an electrode slurry; then pressing the electrode slurry onto a thin film material, drying, and rolling to obtain the negative electrode sheet.

[0049] In one embodiment of the present invention, the adhesive material is one or more of the following: polythiophene, polypyrrole, polyimide, polyaniline, carboxymethyl cellulose, sodium carboxymethyl cellulose, polyacrylic acid, sodium polyacrylate, lithium polyacrylate, polyacrylamide, styrene-butadiene rubber, sodium alginate, and lithium alginate.

[0050] In one embodiment of the present invention, the conductive material is selected from one or more of the following: vapor-grown carbon fiber, vapor-grown carbon nanofiber, conductive graphite powder, conductive silver powder, conductive carbon black, conductive acetylene black, and carbon nanotubes.

[0051] In one embodiment of the present invention, the graphite material is selected from one or more of needle coke, pitch tar, and petroleum coke.

[0052] In one embodiment of the present invention, the median particle size Dv50 of the graphite material is 0.8-45 μm.

[0053] In one embodiment of the present invention, the film material is selected from one or more of copper foil, foamed copper foil, nickel foil, and nickel-plated copper foil.

[0054] In one embodiment of the present invention, the thickness of the negative electrode sheet after rolling is 55-380 μm.

[0055] Furthermore, the thickness of the negative electrode sheet varies from 55-70μm, 70-80μm, 80-100μm, 100-120μm, 120-150μm, 150-180μm, 180-200μm, 200-230μm, 230-250μm, 25-300μm, 300-350μm, to 350-380μm, including but not limited to the values ​​listed above.

[0056] A fifth objective of the present invention is to provide a secondary battery comprising the aforementioned negative electrode.

[0057] The sixth objective of this invention is to provide a method for preparing a secondary battery, comprising the following steps: stacking and winding a negative electrode sheet, a separator, and a positive electrode sheet in sequence to obtain a bare cell; welding the tabs; placing the bare cell into a battery aluminum shell / soft-pack aluminum-plastic film; sealing the top and sides; drying to remove moisture; injecting electrolyte into the battery shell; forming; determining the capacity; venting and sealing; and finally obtaining a secondary battery.

[0058] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0059] Example 1: This invention provides silicon-carbon anode materials, their preparation methods, and applications: (I) Silicon-carbon anode materials and their preparation methods: 1. Silicon-carbon anode material: The silicon-carbon anode material consists of a 3.8-26 μm core, a 30 nm thick oxide layer, a 14 nm thick inorganic layer, and an 8 nm thick carbon deposition layer; the specific surface area of ​​the silicon-carbon anode material is 2 m². 2 / g; the median particle size Dv50 of the anode material is 8μm; the mass percentage of carbon in the silicon-carbon anode material is 49%, the mass percentage of silicon in the silicon-carbon anode material is 50%, and the mass percentage of silicon and carbon in the silicon-carbon anode material is 99%.

[0060] 2. Preparation method of silicon-carbon anode material: 2.1 Preparation of porous carbon: A mixture of phenolic resin carbon source and cellulose acetate (diacetate fiber) was mixed evenly (the amount of cellulose acetate mixture added was 0.04 of phenolic resin). The preparation process of the cellulose acetate mixture was as follows: 5 parts of cellulose acetate were dispersed in 100 parts of an aqueous solution containing 15 wt% sodium phosphate (cellulose acetate has a large number of active functional groups on its surface, which can form strong intermolecular forces (hydrogen bonds) with cations, which makes cellulose acetate electronegative in a specific range on its surface, and it is uniformly distributed inside the phenolic resin by electrostatic adsorption). Then it was sent to a tube furnace for carbonization at 1000℃ for 12 h, washed at 75℃ for 2 h, and crushed to obtain porous carbon. 2.2 Inorganic layer coated carbon-silicon core: Porous carbon is placed in the fluidized bed chamber of a fluidized bed. The reaction temperature of the fluidized bed chamber is 650℃. Inert gas is introduced to remove internal air. Mixed silane at a flow rate of 0.27L / s is introduced to perform silicon cracking for 5h (silane and argon flow ratio is 1:0.4) to obtain the core. The core and lithium aluminate are mixed in a mass ratio of 1:0.02 in a ball mill jar and ball-milled at 300r / min for 6h. After sieving, the core (containing oxide layer and inorganic layer) is obtained (the heat generated by ball milling the core and lithium aluminate is beneficial to the formation of inorganic layer on the one hand, and on the other hand, the ball milling environment will oxidize the surface of the core to form a silicon-oxygen oxide layer). 2.3 Carbon deposition: The above-mentioned core is fed into the fluidization chamber of the fluidized bed, and a butyne carbon source with a flow rate of 0.16 L / s is introduced to perform carbon deposition (butyne is cracked on the surface of the core at 650℃ to form a carbon accumulation deposition layer with a thickness of 8 nm), thus obtaining a carbon deposition layer, that is, a multilayer silicon-carbon anode material.

[0061] (II) Applications of silicon-carbon anode materials: 3. Negative electrode sheet and its preparation method: First, 2 parts by weight of conductive carbon black, 9 parts by weight of the above-mentioned silicon-carbon anode material, and 86 parts by weight of graphitized petroleum coke graphite anode material are placed in the mixing bowl of a mixer and premixed for 2 hours. Then, deionized water and 3 parts by weight of binder material (40 wt% lithium polyacrylate + 60 wt% styrene-butadiene rubber) are added to the container. The mixing bowl is then evacuated to a vacuum state and stirred for another 4 hours. Deionized water is then added until the viscosity reaches 6 Pa·s to obtain the electrode slurry. The electrode slurry is then extruded onto copper foil thin film material, dried, and rolled to a thickness of 130 μm to obtain the anode sheet. 4. Secondary battery: This includes secondary batteries prepared using the above-mentioned negative electrode sheet, specifically including the following preparation steps: Sequentially, the separator, negative electrode sheet, alumina-coated polypropylene separator, and LiNi containing 96% were added. 0.63 Co 0.07 Mn 0.30The positive electrode active material is bonded, wound, and welded to obtain the battery cell. The battery cell is placed in the battery casing, vacuum dried and dehydrated, and an electrolyte solution (a solution of 1.2 mol / L lithium hexafluorophosphate (LiPF6), 8 wt% fluorinated ethylene carbonate (FEC), ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) (the volume ratio of EC, DMC, and DEC is 1:1.5:1.5) is injected into the battery casing, encapsulated, and aged to obtain a 3.3 Ah lithium-ion battery.

[0062] Example 2: This invention provides silicon-carbon anode materials, their preparation methods, and applications: (I) Silicon-carbon anode materials and their preparation methods: 1. Silicon-carbon anode material: The silicon-carbon anode material consists of a 3.8-26 μm core, a 30 nm thick oxide layer, an 18 nm thick inorganic layer, and a 7 nm thick carbon deposition layer; the specific surface area of ​​the silicon-carbon anode material is 3 m². 2 / g; the median particle size Dv50 of the anode material is 10μm; the mass percentage of carbon in the silicon-carbon anode material is 47%, the mass percentage of silicon in the silicon-carbon anode material is 49%, and the mass percentage of silicon and carbon in the silicon-carbon anode material is 96%.

[0063] 2. Preparation method of silicon-carbon anode material: 2.1 Preparation of porous carbon: A mixture of phenolic resin carbon source and cellulose acetate (diacetate fiber) was mixed evenly (the amount of cellulose acetate mixture added was 0.06 of the phenolic resin; the preparation process of the cellulose acetate mixture was as follows: 10 parts of cellulose acetate were dispersed in 100 parts of an aqueous solution containing 15 wt% sodium phosphate), and then sent to a tube furnace for carbonization at 1000℃ for 12 h, washing treatment at 75℃ for 2 h, and crushing to obtain porous carbon; 2.2 Inorganic layer coated carbon-silicon core: Porous carbon is placed in the fluidized bed chamber of a fluidized bed. The reaction temperature of the fluidized bed chamber is 650℃. Inert gas is introduced to remove internal air. Mixed silane at a flow rate of 0.27L / s is introduced to perform silicon cracking for 5h (silane and argon flow ratio is 1:0.4) to obtain the core. The core and lithium aluminate are mixed in a mass ratio of 1:0.02 in a ball mill jar and ball milled at 300r / min for 6h. After sieving, the core (containing oxide layer and inorganic layer) is obtained. 2.3 Carbon deposition: The above-mentioned core is fed into the fluidization chamber of the fluidized bed, and a butyne carbon source with a flow rate of 0.8 L / s is introduced to perform carbon deposition (the gaseous carbon source is decomposed on the surface of the core at 650℃ to form a carbon deposition layer with a thickness of 7 nm), thus obtaining a carbon deposition layer, which is a multilayer silicon-carbon anode material.

[0064] (II) Applications of silicon-carbon anode materials: 3. Negative electrode sheet and its preparation method: First, 2 parts by weight of conductive carbon black, 9 parts by weight of the above-mentioned silicon-carbon anode material, and 86 parts by weight of graphitized petroleum coke graphite anode material are placed in the mixing bowl of a mixer and premixed for 30 minutes. Then, deionized water and 3 parts by weight of binder material (40 wt% lithium polyacrylate + 60 wt% styrene-butadiene rubber) are added to the container. The mixing bowl is then evacuated to a vacuum state, and stirring is continued for 4 hours. Deionized water is then added until the viscosity reaches 2 Pa·s to obtain the electrode slurry. The electrode slurry is then extruded onto copper foil thin film material, dried, and rolled to a thickness of 130 μm to obtain the anode sheet. 4. Secondary battery: This includes secondary batteries prepared using the above-mentioned negative electrode sheet, specifically including the following preparation steps: Sequentially, the separator, negative electrode sheet, polypropylene separator coated with alumina 3μm thickness, and LiNi containing 96% were added. 0.63 Co 0.07 Mn 0.30 The positive electrode active material is bonded, wound, and welded to obtain the battery cell. The battery cell is placed in the battery casing, vacuum dried and dehydrated, and an electrolyte solution (a solution of 1.2 mol / L lithium hexafluorophosphate (LiPF6), 8 wt% fluorinated ethylene carbonate (FEC), ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) (the volume ratio of EC, DMC, and DEC is 1:1.5:1.5) is injected into the battery casing, encapsulated, and aged to obtain a 3.3 Ah lithium-ion battery.

[0065] Example 3: This invention provides silicon-carbon anode materials, their preparation methods, and applications: (I) Silicon-carbon anode materials and their preparation methods: 1. Silicon-carbon anode material: The silicon-carbon anode material consists of a 3.1-24 μm core, a 40 nm thick oxide layer, a 13 nm thick inorganic layer, and a 12 nm thick carbon deposition layer; the specific surface area of ​​the silicon-carbon anode material is 5 m² / m³. 2 / g; the median particle size Dv50 of the anode material is 9μm; the mass percentage of carbon in the silicon-carbon anode material is 54%, the mass percentage of silicon in the silicon-carbon anode material is 44%, and the mass percentage of silicon and carbon in the silicon-carbon anode material is 98%.

[0066] 2. Preparation method of silicon-carbon anode material: 2.1 Preparation of porous carbon: The carbon source of urea-formaldehyde resin and the mixture of cellulose acetate (diacetate fiber) were mixed evenly (the amount of cellulose acetate mixture added was 0.05 of that of urea-formaldehyde resin; the preparation process of the cellulose acetate mixture was as follows: 5 parts of cellulose acetate were dispersed in 100 parts of an aqueous solution containing 5 wt% potassium hydroxide), and then sent to a tube furnace for carbonization at 1600℃ for 6 hours, washing treatment at 75℃ for 2 hours, and crushing to obtain porous carbon; 2.2 Inorganic layer coated carbon-silicon core: Porous carbon is placed in the fluidized bed cavity of a fluidized bed. The reaction temperature of the fluidized bed cavity is 650℃. Inert gas is introduced to remove internal air. Mixed silane at a flow rate of 0.33L / s is introduced to perform silicon cracking for 6h (silane and argon gas flow ratio is 1:0.5) to obtain the core. The core and ammonium phosphate are mixed in a ball mill jar at a mass ratio of 1:0.04 and ball milled at 450r / min for 4h. After sieving, the core (containing oxide layer and inorganic layer) is obtained. 2.3 Carbon deposition: The above-mentioned core is fed into the fluidization chamber of the fluidized bed, and a butyne carbon source with a flow rate of 0.3 L / s is introduced to perform carbon deposition (the gaseous carbon source is decomposed on the surface of the core at 650℃ to form a carbon deposition layer with a thickness of 12 nm), thus obtaining a carbon deposition layer, which is a multilayer silicon-carbon anode material.

[0067] (II) Applications of silicon-carbon anode materials: 3. Negative electrode sheet and its preparation method: First, place 2 parts by weight of conductive carbon black, 24 parts by weight of the above-mentioned silicon-carbon anode material, and 69 parts by weight of graphitized petroleum coke graphite anode material into the mixing bowl of a mixer and mix for 30 min to 3 h. Add deionized water and 5 parts by weight of binder material (50 wt% lithium polyacrylate + 40 wt% styrene-butadiene rubber + 10 wt% sodium carboxymethyl cellulose) into a container, and evacuate the mixing bowl to a vacuum state. Continue stirring for 3.5 h, and continue to add deionized water until the viscosity reaches 6 Pa·s to obtain an electrode slurry. Extrude the electrode slurry onto copper foil thin film material, dry it, and roll it to a thickness of 104 μm to obtain the anode sheet. 4. Secondary battery: This includes secondary batteries prepared using the above-mentioned negative electrode sheet, specifically including the following preparation steps: Sequentially, the separator, negative electrode sheet, polypropylene separator coated with alumina 3μm thickness, and LiNi containing 96% were added. 0.63 Co 0.07 Mn 0.30The positive electrode active material is bonded, wound, and welded to obtain the battery cell. The battery cell is placed in the battery casing, vacuum dried and dehydrated, and an electrolyte solution (a solution of 1.2 mol / L lithium hexafluorophosphate (LiPF6), 8 wt% fluorinated ethylene carbonate (FEC), ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) (the volume ratio of EC, DMC, and DEC is 1:1.5:1.5) is injected into the battery casing, encapsulated, and aged to obtain a 3.3 Ah lithium-ion battery.

[0068] Example 4: This invention provides silicon-carbon anode materials, their preparation methods, and applications: (I) Silicon-carbon anode materials and their preparation methods: 1. Silicon-carbon anode material: The silicon-carbon anode material consists of a 3.1-24 μm core, a 40 nm thick oxide layer, a 13 nm thick inorganic layer, and a 16 nm thick carbon deposition layer; the specific surface area of ​​the silicon-carbon anode material is 3 m². 2 / g; the median particle size Dv50 of the anode material is 6μm; the mass percentage of carbon in the silicon-carbon anode material is 51%, the mass percentage of silicon in the silicon-carbon anode material is 46%, and the mass percentage of silicon and carbon in the silicon-carbon anode material is 97%.

[0069] 2. Preparation method of silicon-carbon anode material: 2.1 Preparation of porous carbon: A mixture of urea-formaldehyde resin carbon source and cellulose acetate (triacetate fiber) was mixed evenly (the amount of cellulose acetate mixture added was 0.08 of that of urea-formaldehyde resin; the preparation process of the cellulose acetate mixture was as follows: 5 parts of cellulose acetate were dispersed in 100 parts of an aqueous solution containing 10 wt% potassium hydroxide), and then sent to a tube furnace for carbonization at 1600℃ for 6 hours, washing at 75℃ for 2 hours, and crushing to obtain porous carbon; 2.2 Inorganic layer coated carbon-silicon core: Porous carbon is placed in the fluidized bed chamber of a fluidized bed. The reaction temperature of the fluidized bed chamber is 650℃. Inert gas is introduced to remove internal air. Mixed silane at a flow rate of 0.33L / s is introduced to perform silicon cracking for 6h (silane and argon gas flow ratio is 1:0.5) to obtain the core. The core and ammonium phosphate are mixed in a ball mill jar at a mass ratio of 1:0.08 and ball milled at 450r / min for 4h. After sieving, the core (containing oxide layer and inorganic layer) is obtained. 2.3 Carbon deposition: The above-mentioned core is fed into the fluidization chamber of the fluidized bed, and a butyne carbon source with a flow rate of 1.2 L / s is introduced to perform carbon deposition (the gaseous carbon source is decomposed on the surface of the core at 650℃ to form a carbon deposition layer with a thickness of 16 nm), thus obtaining a carbon deposition layer, which is a multilayer silicon-carbon anode material.

[0070] (II) Applications of silicon-carbon anode materials: 3. Negative electrode sheet and its preparation method: First, 2 parts by weight of conductive carbon black, 24 parts by weight of the above-mentioned silicon-carbon anode material, and 69 parts by weight of graphitized petroleum coke graphite anode material are placed in the mixing bowl of a mixer and premixed for 2 hours. Then, deionized water and 5 parts by weight of binder material (50 wt% lithium polyacrylate + 40 wt% styrene-butadiene rubber + 10 wt% sodium carboxymethyl cellulose) are added to a container. The mixing bowl is then evacuated to a vacuum state and stirred for 3.5 hours. Deionized water is then added until the viscosity reaches 4 Pa·s to obtain an electrode slurry. The electrode slurry is then extruded onto copper foil thin film material, dried, and rolled to a thickness of 104 μm to obtain the anode sheet. 4. Secondary battery: This includes secondary batteries prepared using the above-mentioned negative electrode sheet, specifically including the following preparation steps: Sequentially, the separator, negative electrode sheet, polypropylene separator coated with alumina 3μm thickness, and LiNi containing 96% were added. 0.63 Co 0.07 Mn 0.30 The positive electrode active material is bonded, wound, and welded to obtain the battery cell. The battery cell is placed in the battery casing, vacuum dried and dehydrated, and an electrolyte solution (a solution of 1.2 mol / L lithium hexafluorophosphate (LiPF6), 8 wt% fluorinated ethylene carbonate (FEC), ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) (the volume ratio of EC, DMC, and DEC is 1:1.5:1.5) is injected into the battery casing, encapsulated, and aged to obtain a 3.3 Ah lithium-ion battery.

[0071] Comparative Example 1: The difference from Example 1 is that in step 2.1, the phenolic resin carbon source was not mixed with the cellulose acetate mixture during porous carbon preparation.

[0072] Comparative Example 2: The difference from Example 1 is that lithium aluminate was not added to the core for ball milling in step 2.2.

[0073] Test example: 1. Material compressive strength test: The negative electrode materials prepared in Examples 1-4 and Comparative Examples 1-3 were compacted to 1.2 g / cm³ using a powder compaction density meter. 3 The material after pressing is denoted as the negative electrode material. The Dv50 of both the unpressed and pressed negative electrode materials was measured using a laser particle size analyzer. The change in Dv50 was calculated as: (Dv50 of unpressed negative electrode material - Dv50 of pressed negative electrode material) / Dv50 of unpressed negative electrode material. The compressive strength and processing performance of the material were evaluated based on the magnitude of the Dv50 change (the smaller the Dv50 change, the stronger the compressive strength and processing capability). The experimental results are shown in Table 1.

[0074] 2. Electrochemical rate discharge performance test: Batteries from Examples 1-4 and Comparative Examples 1-3 were connected to a charge / discharge cabinet. They were discharged at a constant current of 1.65A to 2.7V, allowed to rest for 5 minutes, and then fully charged at 1.65A AC to 4.2V, allowed to rest for 5 minutes. After being fully charged to 4.2V, they were discharged at constant currents of 3.3A, 6.6A, and 9.9A to 2.7V respectively. The discharge capacities at 1.65A, 3.3A, 6.6A, and 9.9A were recorded. The 1C rate discharge ratio = 3.3A constant current discharge capacity / 1.65A constant current discharge capacity; the 2C rate discharge ratio = 6.6A constant current discharge capacity / 1.65A constant current discharge capacity; and the 3C rate discharge ratio = 9.9A constant current discharge capacity / 1.65A constant current discharge capacity. The experimental results are shown in Table 2.

[0075] 3. Electrochemical charge-discharge cycle performance test: The batteries from Examples 1-4 and Comparative Examples 1-3 were connected to a charge / discharge cabinet and discharged at a constant current of 1.65A to 2.7V. After resting for 5 minutes, they were fully charged at 1.65A AC to 4.2V. This charge / discharge cycle was repeated. The capacity of the batteries from Examples 1-4 and Comparative Examples 1-3 initially fully charged to 4.2V and then initially discharged to 2.7V was recorded as C0. The number of cycles corresponding to the discharge capacity decreasing to 0.8C0 was recorded. The experimental results are shown in Table 3.

[0076] 4. Electrochemical impedance spectroscopy: The batteries from Examples 1 and 2, and Comparative Examples 1 and 2 were discharged to 2.7V. The positive and negative electrodes were connected to an electrochemical workstation, and electrochemical impedance spectroscopy was performed at 25°C with a frequency range of 0.05-100000Hz and a perturbation voltage of 0.005V. The experimental results are shown below. Figure 2 .

[0077] Table 1. Dv50 of the negative electrode materials in the examples and comparative examples.

[0078] Table 2 Battery discharge rate in the examples and comparative examples

[0079] Table 3. Number of weeks in which battery capacity decayed to 0.8 C0 in the examples and comparative examples.

[0080] In Examples 1-4: The negative electrode material carbonized cellulose in Examples 1-4 is uniformly embedded in porous carbon and coated with an inorganic layer. The internal porous carbon structure is stable, and the Dv50 change is small. It improves the dispersion of the porous carbon skeleton to resist expansion and contraction stress, reduces cracking and the appearance of fresh interfaces and electrolyte consumption. When the capacity of the assembled lithium-ion battery is reduced to 0.8 C0, the number of cycles is higher than 1200 cycles, and the 3C rate discharge ratio is high. In Comparative Examples 1-2: The porous carbon anode material of Comparative Example 1 did not contain embedded carbonized cellulose, resulting in the largest change in Dv50. The material exhibited poor compressive strength and processing performance. The anode material of Comparative Example 2 lacked an inorganic coating. The anode material of Comparative Example 3 used alcohol instead of lithium aluminate. The anode material (containing an oxide layer) was obtained by ball milling for 6 hours and sieving. When the cycle discharge capacity of Comparative Examples 2 and 3 decreased to 0.8 C0, the cycle times were 992 and 974 cycles respectively, indicating low 3C rate discharge ratios. In the impedance diagrams, the slopes of the impedance curves of Comparative Examples 1 and 2 were lower than the slope of the internal lithium-ion impedance curve (a steeper slope indicates faster diffusion), indicating lower lithium-ion diffusion rates in Comparative Examples 1 and 2.

[0081] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A silicon-carbon anode material, characterized in that, It includes porous carbon and a silicon-carbon core composed of silicon crystal particles, and an oxide layer, an inorganic layer and a carbon deposition layer that are sequentially coated on the surface of the silicon-carbon core from the inside out. Silicon crystal particles are distributed within porous carbon; The porous carbon contains carbonized cellulose acetate, which is embedded in the porous carbon, and the cellulose acetate is diacetate fiber and / or triacetate fiber. The oxide layer contains silicon and oxygen. The inorganic layer contains one or more of phosphates, aluminates, and silicates; The diameter of the silicon carbide core is 0.3-80 μm; The thickness of the oxide layer is 2nm-200nm; The thickness of the inorganic layer is 2nm-50nm; The thickness of the carbon deposition layer is 2nm-65nm.

2. The silicon-carbon anode material according to claim 1, characterized in that, The silicon crystal particles are distributed in porous carbon by deposition. The silicon crystal particles include crystalline silicon and amorphous silicon, and the particle size of crystalline silicon is ≤4nm. The specific surface area of ​​the negative electrode material is 0.7-6.0 m². 2 / g; The median particle size Dv50 of the negative electrode material is 3-18 μm; Silicon and carbon elements account for 90%-99.9% of the mass of the anode material.

3. The method for preparing the silicon-carbon anode material according to any one of claims 1-2, characterized in that, Includes the following steps: (1) Mix the carbon source and cellulose acetate mixture, heat to form carbon, wash and crush to obtain porous carbon; (2) Porous carbon is placed in a deposition apparatus, and silane is deposited in the pores of the porous carbon to obtain a carbon-silicon core; A carbon silicon core and an inorganic salt are mixed, ball-milled, and sieved to obtain a carbon silicon core with an oxide layer and an inorganic layer on the surface. (3) The carbon silicon core with the surface covered with oxide layer and inorganic layer is sent to the deposition device, and a gaseous carbon source is introduced to perform carbon deposition to obtain a silicon-carbon anode material with oxide layer, inorganic layer and carbon deposition layer on the surface of the carbon silicon core from the inside to the outside.

4. The preparation method according to claim 3, characterized in that, In step (1): The carbon source is one or more of polyvinyl alcohol, phenolic resin, epoxy resin, polyethylene oxide, furfural resin, and urea-formaldehyde resin. The cellulose acetate mixture is prepared by dispersing 5-30 parts by weight of diacetate cellulose and / or triacetate cellulose in 100 parts by weight of an ionic liquid, wherein the ionic liquid is an aqueous solution containing 1-15 wt% of one or more of sodium hydroxide, potassium hydroxide, sodium hypochlorite, potassium hypochlorite, sodium oxalate, sodium phosphate, or lithium phosphate. The mass ratio of the cellulose acetate mixture to the carbon source is (0.001-0.12):

1.

5. The preparation method according to claim 4, characterized in that, In step (1), The conditions for heating to carbon are: heating temperature 1000-1600℃, heating time 4-12h; The washing conditions are as follows: washing temperature 60-95℃, washing time 1-3h.

6. The preparation method according to claim 3, characterized in that, In step (2), The method for preparing silane deposition in the pores of porous carbon is as follows: the reaction temperature of the deposition apparatus is 300-750℃, an inert gas is introduced to remove internal air, and a mixed silane with a flow rate of 0.05-2L / s is introduced for silicon cracking for 2-8h. The mixed silane is a mixture of silane and inert gas, and the gas flow ratio of silane to inert gas is 1:(0.05-8). Before ball milling, the mass ratio of the silicon carbide core to the inorganic salt is 1:(0.001-0.012).

7. The preparation method according to claim 6, characterized in that, In step (2), The inorganic salts include one or more of the following: sodium tripolyphosphate, ammonium phosphate, lithium phosphate, sodium phosphate, lithium fluorophosphate, sodium fluorophosphate, ammonium fluorophosphate, magnesium phosphate, aluminum phosphate, potassium phosphate, lithium aluminate, magnesium aluminate, lithium silicate, aluminum silicate, and magnesium silicate. The silane is one or more of methylsilane, ethylsilane, and propane; The inert gas is one or more of nitrogen, argon, helium, and xenon.

8. The preparation method according to claim 3, characterized in that, In step (3), The gaseous carbon source includes one or more of methane, ethane, propane, acetylene, propyne, butyne, and ethylene; The carbon deposition preparation method is as follows: a gaseous carbon source is decomposed on the surface of a carbon silicon core coated with an oxide layer and an inorganic layer at a temperature of 400-750℃ until a carbon deposition layer with a thickness of 2nm-65nm is deposited.

9. A negative electrode sheet, comprising a binder material, a graphite material, and a conductive material, characterized in that, It also includes the silicon-carbon anode material according to any one of claims 1-2 or the silicon-carbon anode material prepared by any one of claims 3-8.

10. The negative electrode sheet according to claim 9, characterized in that, The mass ratio of the silicon-carbon anode material, graphite material, binder material, and conductive material is (2-45):(30-98):(0.4-6):(0.4-6).

11. A secondary battery, characterized in that, Includes the negative electrode sheet as described in claim 9 or 10.

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