Composite negative electrode material and preparation method and application thereof

Abstract

The invention relates to the technical field of batteries, in particular to a composite negative electrode material as well as a preparation method and application thereof. The composite negative electrode material comprises a base material and a carbon coating layer coating at least part of the surface of the base material, the base material comprises porous carbon and barium titanate, and a silicon material is loaded in pores of the porous carbon. In the negative electrode material, the piezoelectric effect of barium titanate can be induced by virtue of the huge volume expansion effect of the silicon material, and the diffusion speed of lithium ions is increased through the synergistic effect of volume expansion and voltage, so that the first efficiency, the specific capacity and the rate capability of the composite negative electrode material are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and more particularly, to a composite anode material, a preparation method thereof, and an application thereof. Background Art

[0002] Silicon-carbon materials are applied to high specific energy density lithium-ion batteries due to their advantages such as high specific capacity and wide material sources. However, their high swelling at full charge and poor cycling performance limit their application to only power tools, digital devices, etc., and they cannot be applied to fields such as EVs.

[0003] The reason for the large swelling of the silicon-carbon material is that the silicon grains of the silicon-carbon material prepared by the sanding method are relatively large (about 20 nm), resulting in poor cycling performance. To improve the cycling performance and reduce swelling, it is necessary to start from reducing the size of the silicon grains. The nano-silicon prepared by the silane pyrolysis method for silicon-carbon materials has small silicon grains (2-3 nm), low swelling, and good cycling performance. However, the power performance of the porous carbon structure is poor, reducing its rate performance. Moreover, after infiltrating nano-silicon, there is still a contact force between the silicon nanoparticles, and the nano-silicon still has a certain degree of swelling.

[0004] In view of this, the present invention is specifically proposed. Summary of the Invention

[0005] An object of the present invention is to provide a composite anode material to solve the technical problems of high swelling and poor rate performance of the silicon-carbon composite material in the prior art. The composite anode material of the present invention can improve the diffusion rate of lithium ions through the synergistic effect of volume expansion and voltage, thereby improving the rate performance of the anode material.

[0006] Another object of the present invention is to provide a preparation method of the composite anode material. The method is simple and easy to implement, and a composite anode material with excellent electrochemical performance can be obtained through the cooperation of each step.

[0007] Another object of the present invention is to provide an anode sheet.

[0008] Another object of the present invention is to provide a battery.

[0009] To achieve the above objects of the present invention, the following technical solutions are specifically adopted:

[0010] A composite anode material includes a matrix material and a carbon coating layer covering at least a part of the surface of the matrix material; the matrix material includes porous carbon and barium titanate, and silicon material is loaded in the pores of the porous carbon.

[0011] In one embodiment, the silicon material includes nano-silicon.

[0012] In one embodiment, part of the barium titanate is loaded in the pores of the porous carbon.

[0013] In one embodiment, the mass of the barium titanate accounts for 0.1% - 10% of the sum of the masses of the porous carbon and the carbon coating layer.

[0014] In one embodiment, the mass of the silicon material accounts for 5% - 85% of the mass of the composite anode material.

[0015] The preparation method of the composite anode material as described above includes the following steps:

[0016] Mix the porous carbon raw material and the barium titanate raw material to obtain a first material; perform a first chemical vapor deposition on the first material under the atmosphere of a silicon source gas and a protective gas to obtain a matrix material; perform a second chemical vapor deposition on the matrix material under the atmosphere of an organic carbon source and a protective gas.

[0017] In one embodiment, the mass of the barium titanate raw material is 0.1% - 10% of the mass of the porous carbon raw material.

[0018] In one embodiment, the average pore diameter of the porous carbon raw material is 0.5 - 10 nm, the specific surface area of the porous carbon raw material is 1000 - 2500 m 2 / g, and the D50 particle size of the porous carbon raw material is 4 - 10 μm.

[0019] In one embodiment, the mixing treatment includes solid-phase mixing and / or wet mixing.

[0020] In one embodiment, the solid-phase mixing includes ball milling.

[0021] In one embodiment, the time of the solid-phase mixing is 2 - 10 h, the rotation speed of the solid-phase mixing is 300 - 500 rpm, and the ball-to-material ratio of the solid-phase mixing is (8 - 10):1.

[0022] In one embodiment, the wet mixing specifically includes: subjecting the mixed system of the porous carbon raw material, the barium titanate raw material, and an organic solvent to ultrasonic treatment, and then performing solid-liquid separation to collect the solid matter.

[0023] In one embodiment, during the wet mixing process, the power of the ultrasonic treatment is 300 - 500 W, the time of the ultrasonic treatment is 1 - 2 h; the dosage ratio of the barium titanate raw material to the organic solvent is 1 g:(10 - 30) mL.

[0024] In one embodiment, the silicon source gas includes silane, and / or disilane, and / or trichlorosilane, and / or dichlorosilane, and / or propylsilane, and / or trichlorosilane, and / or silicon chloride.

[0025] In one embodiment, the mass ratio of the silicon source gas to the porous carbon raw material is (90 to 120):(30 to 50).

[0026] In one embodiment, the flow rate of the silicon source gas is 5 to 15 mL / min.

[0027] In one embodiment, the first chemical vapor deposition specifically includes: introducing the silicon source gas into a chamber containing a first material, and then performing a first heat treatment.

[0028] In one embodiment, during the first chemical vapor deposition, the temperature of the first heat treatment is 500 to 700 °C, and the heat preservation time is 2 to 6 h.

[0029] In one embodiment, during the first chemical vapor deposition, the heating rate of the first heat treatment is 3 to 6 °C / min.

[0030] In one embodiment, during the first chemical vapor deposition, a protective gas is continuously introduced.

[0031] In one embodiment, the carbon source gas includes polyethylene, and / or acetylene, and / or methane, and / or ethylene, and / or propylene.

[0032] In one embodiment, the flow rate of the carbon source gas is 5 to 15 mL / min.

[0033] In one embodiment, the second chemical vapor deposition specifically includes: introducing the carbon source gas into the matrix material, and performing a second heat treatment.

[0034] In one embodiment, during the second chemical vapor deposition, the temperature of the second heat treatment is 500 to 800 °C, and the heat preservation time is 2 to 6 h.

[0035] In one embodiment, during the second chemical vapor deposition, a protective gas is continuously introduced.

[0036] In one embodiment, after the second chemical vapor deposition, it further includes: cooling to room temperature.

[0037] A negative electrode sheet includes the composite negative electrode material described above.

[0038] A battery includes the negative electrode sheet described above.

[0039] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0040] (1) In the negative electrode material of the present invention, barium titanate has a piezoelectric effect (a two-way physical phenomenon in which the material generates a charged state due to deformation of the body when an external force is applied or generates deformation when an electric field is applied); in the obtained silicon-carbon material (composite negative electrode material), by virtue of the huge volume expansion effect of the silicon material, the piezoelectric effect of barium titanate can be induced, and through the synergistic action of volume expansion and voltage, the diffusion rate of lithium ions is increased, thereby improving the rate performance of the composite negative electrode material.

[0041] (2) The preparation method of the composite negative electrode material of the present invention is simple and feasible, and through the cooperation of each step, a negative electrode material with excellent electrochemical performance can be obtained.

[0042] (3) The battery of the present invention has excellent rate performance, cycle performance and safety. Description of the Drawings

[0043] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0044] Figure 1 It is a diffusion coefficient curve graph of the batteries prepared from the negative electrode materials in Example 1 and Comparative Example 1 of the present invention. Detailed Embodiments

[0045] The following will describe the implementation plans of the present invention in detail in conjunction with the embodiments. However, those skilled in the art will understand that the following embodiments are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. For those conditions not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments not specified in the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0046] According to one aspect of the present invention, the present invention relates to a composite negative electrode material, which includes a matrix material and a carbon coating layer covering at least a part of the surface of the matrix material; the matrix material includes porous carbon and barium titanate (BTO), and silicon material is loaded in the pores of the porous carbon.

[0047] Barium titanate has a cubic structure above 120 °C, which is an ideal perovskite structure. Below 120 °C, the crystal is distorted and becomes a tetragonal structure, and Ba 2+ and Ti 4+ ions relative to O 2-A displacement occurs, resulting in a dipole moment. Usually, the transition temperature of 120 °C is called the Curie temperature or Curie point. Above the Curie point, there is no ferroelectricity, and below the Curie point, there is ferroelectricity. At room temperature, the BTO material has a tetragonal crystal structure, so it has good ferroelectric and piezoelectric properties. Since BTO is a piezoelectric metal oxide, its piezoelectric constant is d33 = 350 pC·N -1 ; The coordination of barium titanate and porous carbon is more conducive to alleviating volume expansion. The loaded silicon material will produce volume expansion during the cycling process, and the resulting mechanical pressure induces the piezoelectric effect of barium titanate, making it a pole, thus forming a local piezoelectric electric field to promote the diffusion of lithium ions, affecting the mobility of lithium ions, and thereby improving the rate performance. Through the coordinated cooperation of each component, the negative electrode material of the present invention simultaneously has high capacity, high initial efficiency, excellent rate performance and long cycle performance, and can be applied to lithium ion secondary batteries.

[0048] In one embodiment, the silicon material includes nanosilicon. In one embodiment, part of the barium titanate is loaded in the pores of the porous carbon; the remaining part of the barium titanate is located outside the porous carbon and exists in a mixed form. Increasing barium titanate is equivalent to pre-modifying the porous carbon, which can interact with the nanosilicon inside the pores during the subsequent silicon loading process. The nanosilicon can induce the piezoelectric effect of BTO during the charging and discharging expansion process, making it a pole, thus forming a local piezoelectric electric field to promote the diffusion of lithium ions, affecting the mobility of lithium ions, and thereby improving the rate performance.

[0049] In one embodiment, the mass of the barium titanate accounts for 0.1% - 10% of the sum of the masses of the porous carbon and the carbon coating layer, including but not limited to 0.1%, 0.5%, 1%, 2%, 3%, 5%, 8% or 10%, etc. By using an appropriate amount of barium titanate, it can better play a coordinating role with the porous carbon to improve the electrochemical performance of the finally obtained negative electrode material. Doping too much barium titanate will block the channels for silicon infiltration and is not conducive to silicon loading, while too little barium titanate is not conducive to the exertion of the piezoelectric effect and weakens the modification effect. In one embodiment, the content and distribution of Ba and Ti elements can be tested by EDS.

[0050] In one embodiment, the mass of the silicon material accounts for 5% - 85% of the mass of the composite negative electrode material, including but not limited to 5%, 10%, 20%, 30%, 50%, 60%, 70% or 80%, etc.

[0051] In the composite negative electrode material of the present invention, each component has an appropriate mass ratio, which can better improve the conductivity of the negative electrode material, so as to improve the rate performance, cycle stability performance and safety performance of the battery prepared therefrom.

[0052] According to another aspect of the present invention, the present invention also relates to a method for preparing the composite negative electrode material as described above, comprising the following steps:

[0053] Mix the porous carbon raw material and the barium titanate raw material to obtain a first material; perform a first chemical vapor deposition on the first material in a silicon source gas atmosphere to obtain a matrix material; perform a second chemical vapor deposition on the matrix material in a carbon source gas atmosphere.

[0054] The method for preparing the composite negative electrode material of the present invention is simple and easy to implement. Through the cooperation of each step, a negative electrode material with excellent electrochemical performance can be obtained.

[0055] In one embodiment, the mass of the barium titanate raw material is 0.1% to 10% of the mass of the porous carbon raw material, such as 0.1%, 0.5%, 1%, 2%, 3%, 5%, 6%, 8% or 10%, etc.

[0056] In one embodiment, the average pore diameter of the porous carbon raw material is 0.5 to 10 nm, such as 0.5 nm, 1 nm, 2 nm, 3 nm, 5 nm or 8 nm, etc.; the specific surface area of the porous carbon raw material is 1000 to 2500 m 2 / g, such as 1000 m 2 / g, 1200 m 2 / g, 1500 m 2 / g, 1800 m 2 / g, 1820 m 2 / g, 1850 m 2 / g, 1880 m 2 / g, 1900 m 2 / , 2000 m 2 / g, 2500 m 2 / g, etc.; the D50 particle size of the porous carbon raw material is 4 to 10 μm, such as 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 10 μm, etc. The present invention uses a suitable porous carbon raw material, which is more conducive to the loading of silicon materials and better plays a synergistic effect with barium titanate.

[0057] In one embodiment, the mixing treatment includes solid-phase mixing and / or wet mixing.

[0058] In one embodiment, the solid-phase mixing includes ball milling. The time for the solid-phase mixing is 2 to 10 h, such as 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 10 h, etc. The rotation speed for the solid-phase mixing is 300 to 500 rpm, such as 300 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm, etc.; the ball-to-material ratio for the solid-phase mixing is (8 to 10):1, such as 8:1, 8.5:1, 9:1, 10:1, etc. By adopting the above suitable solid-phase mixing conditions in combination, the present invention ensures that the materials are fully mixed, and part of the barium titanate raw material will enter the pores of the porous carbon raw material.

[0059] In one embodiment, the wet mixing specifically includes: subjecting the mixed system of the porous carbon raw material, the barium titanate raw material, and the organic solvent to ultrasonic treatment, and then performing solid-liquid separation to collect the solid matter. In one embodiment, during the wet mixing process, the power of the ultrasonic treatment is 300 to 500 W, such as 300 W, 350 W, 400 W, 450 W, 500 W, etc.; the time for the ultrasonic treatment is 1 to 2 h, such as 1 h, 1.5 h, or 2 h, etc.; the dosage ratio of the barium titanate raw material to the organic solvent is 1 g:(10 to 30) mL, such as 1 g:10 mL, 1 g:15 mL, 1 g:20 mL, 1 g:30 mL, etc. In one embodiment, heat treatment is performed during the ultrasonic treatment. Through the above wet mixing conditions, the materials are uniformly dispersed, and part of the barium titanate raw material is loaded in the pores of the porous carbon raw material, which is beneficial to improving the electrochemical performance of the negative electrode material.

[0060] In one embodiment, the silicon source gas includes silane, and / or acetylene, and / or methane, and / or ethylene, and / or propylene. The silicon source of the present invention may include any one of the above, or a combination of at least two of them. In some embodiments, the silicon source that is liquid at room temperature can participate in the reaction in the form of vapor.

[0061] In one embodiment, the mass ratio of the silicon source gas to the porous carbon raw material is (90 to 120):(30 to 50), such as 90:30, 100:35, 110:40, 120:50, etc.

[0062] In one embodiment, the flow rate of the silicon source gas is 5 to 15 mL / min, such as 5 mL / min, 6 mL / min, 8 mL / min, 10 mL / min, or 15 mL / min.

[0063] In one embodiment, the first vapor deposition specifically includes: passing the silicon source gas into a chamber containing the first material, and then performing a first heat treatment. In one embodiment, the chamber includes a CVD rotary furnace. In one embodiment, during the first vapor deposition, the temperature of the first heat treatment is 500-700°C, such as 500°C, 550°C, 600°C, 650°C, 700°C, etc.; the holding time is 2-6h, such as 2h, 3h or 4h, etc. In one embodiment, during the first vapor deposition, the heating rate of the first heat treatment is 3-6°C / min, such as 3°C / min, 5°C / min, etc. In one embodiment, during the first vapor deposition, a protective gas is continuously introduced, and the protective gas includes at least one of nitrogen and an inert gas. The present invention adopts a suitable first vapor deposition condition, so that the silicon element is better deposited in the pores of the porous carbon material, so as to better exert the synergistic effect of each component and improve the electrochemical performance of the negative electrode material.

[0064] In one embodiment, a protective gas is first introduced into the CVD rotary furnace, and then a mixed gas of a silicon source gas and a protective gas is introduced, wherein the concentration of the silicon source gas in the mixed gas is 10% to 50%, for example, 10%, 20%, 30%, 40% or 50%, etc. In one embodiment, the rotation speed of the rotary furnace is 20 to 100 seconds per revolution.

[0065] In one embodiment, the carbon source gas includes at least one of polyethylene, acetylene, methane, ethylene and propylene. In one embodiment, the flow rate of the carbon source gas is 5 to 15 mL / min, such as 5 mL / min, 6 mL / min, 8 mL / min, 10 mL / min or 15 mL / min.

[0066] In one embodiment, the second vapor deposition specifically includes: introducing a carbon source gas into the matrix material and performing a second heat treatment. During the second vapor deposition process, the temperature of the second heat treatment is 500-800°C, such as 500°C, 550°C, 600°C, 650°C, 700°C, 800°C, etc.; the insulation time is 2-6h, such as 2h, 3h, 5h, etc. In one embodiment, during the second vapor deposition process, a protective gas, such as at least one of nitrogen and an inert gas, is continuously introduced. After the second vapor deposition, it also includes: cooling to room temperature.

[0067] In one embodiment, after the first vapor deposition is completed, the supply of the silicon source gas is turned off, and the protective gas is continuously introduced into the rotary furnace at a flow rate of 0.5 to 1.5 L / min. After maintaining for 25 to 35 min, the furnace temperature is raised to 500 to 800 °C, and a mixed gas of the carbon source gas and the protective gas is introduced. The concentration of the carbon source in the mixed gas is 30% to 50%, such as 30%, 35%, 40% or 50%, etc. The rotation speed of the rotary furnace is controlled to be 20 to 100 s / revolution.

[0068] In a preferred embodiment, the method for preparing the composite negative electrode material includes the following steps:

[0069] (a) Solid-phase mixing and / or wet mixing of the porous carbon raw material and the barium titanate raw material to obtain a first material; wherein, the solid-phase mixing is ball milling; the time of the solid-phase mixing is 2 to 10 h, the rotation speed of the solid-phase mixing is 300 to 500 rpm, and the ball-to-material ratio of the solid-phase mixing is (8 to 10):1; the wet mixing specifically includes: subjecting the mixed system of the porous carbon raw material, the barium titanate raw material and the organic solvent to ultrasonic treatment, and then performing solid-liquid separation to collect the solid; during the wet mixing process, the power of the ultrasonic treatment is 300 to 500 W, the time of the ultrasonic treatment is 1 to 2 h; the dosage ratio of the barium titanate raw material to the organic solvent is 1 g:(10 to 30) mL;

[0070] (b) Subjecting the first material to a first vapor deposition in a silicon source gas atmosphere to obtain a matrix material; the first vapor deposition specifically includes: introducing a protective gas into the rotary furnace chamber containing the first material, then introducing a mixed gas of the silicon source gas and the protective gas, and then performing a first heat treatment. The temperature of the first heat treatment is 500 to 700 °C, the heat preservation time is 2 to 6 h, and the heating rate of the first heat treatment is 3 to 6 °C / min; the mass ratio of the silicon source gas to the porous carbon raw material is (90 to 120):(30 to 50); the flow rate of the silicon source gas is 5 to 15 mL / min; the concentration of the silicon source gas in the mixed gas is 10% to 50%;

[0071] (c) After the first vapor deposition is completed, subjecting the matrix material to a second vapor deposition in a carbon source gas atmosphere; the second vapor deposition specifically includes: turning off the silicon source gas, introducing the protective gas for 25 to 35 min, then introducing a mixed gas of the carbon source gas and the protective gas into the above-mentioned rotary furnace, and performing a second heat treatment; the temperature of the second heat treatment is 500 to 800 °C, the heat preservation time is 2 to 6 h, the carbon source gas includes at least one of polyethylene, acetylene, methane, ethylene and propylene, the flow rate of the carbon source gas is 5 to 15 mL / min; the concentration of the carbon source in the mixed gas is 30% to 50%; after the second vapor deposition, it also includes: cooling to room temperature.

[0072] According to another aspect of the present invention, the present invention also relates to a negative electrode sheet, comprising the composite negative electrode material described above.

[0073] In one embodiment, the negative electrode sheet comprises a current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector; the negative electrode material layer comprises the above composite negative electrode material. It may also include a binder and a conductive agent.

[0074] According to another aspect of the present invention, the present invention also relates to a battery, comprising the negative electrode sheet described above.

[0075] In one embodiment, the battery comprises the above negative electrode sheet, a positive electrode sheet, a separator and an electrolyte. The battery of the present invention has excellent rate performance, cycle performance and safety performance.

[0076] The following is further explained and illustrated in conjunction with specific examples and comparative examples.

[0077] Example 1

[0078] A preparation method of a composite negative electrode material, comprising the following steps:

[0079] (1) Weigh 40 g of porous carbon (pore diameter 2 nm, specific surface area 1800 m 2 / g, particle size: 5 μm), 2 g (addition amount 5 wt%) of BTO barium titanate and put them into a ball mill to be ball milled until uniform. Among them, the ball milling time is 5 h, the ball milling speed is 400 rpm, and the ball-to-material ratio of ball milling is 10:1 to obtain a first material;

[0080] (2) Transfer the first material to a CVD rotary furnace. The rotation speed of the rotary furnace is 50 s / turn. First, introduce nitrogen for treatment, and then introduce a mixed gas of silane gas and argon gas. The silane gas is 100 g, the flow rate is 10 mL / min, and the concentration of the silane gas in the mixed gas is 50%. Then, heat it up to 600 °C at a heating rate of 5 °C / min for co-deposition and keep it warm for 3 h to obtain a matrix material;

[0081] (3) After completing the deposition in step (2), close the silane gas. After argon is introduced at a flow rate of 1 L / min for 30 min, the temperature of the rotary furnace is raised to 600 °C at a heating rate of 5 °C / min, and then a mixed gas of polyethylene gas and argon gas is introduced. The polyethylene gas is 30 g, the flow rate is 10 mL / min, and the concentration of the polyethylene gas accounts for 50% of the polyethylene gas; deposit and keep it warm at 600 °C for 3 h, and then cool it down to room temperature to obtain the composite negative electrode material.

[0082] Example 2

[0083] The preparation method of the composite negative electrode material is the same as that of Example 1 except that the ball milling time is 2 h.

[0084] Example 3

[0085] The preparation method of the composite negative electrode material is the same as that of Example 1 except that the ball milling time is 10 h.

[0086] Example 4

[0087] The preparation method of the composite negative electrode material is the same as that of Example 1 except that the added mass of barium titanate is 4 g.

[0088] Example 5

[0089] The preparation method of the composite negative electrode material: except that in step (2), the silane gas is 80 g, and it is heated to 700 °C at a heating rate of 5 °C / min for co-deposition and kept warm for 3 h; other conditions are the same as those of Example 1.

[0090] Example 6

[0091] The preparation method of the composite negative electrode material: except that in step (2), the silane gas is 120 g, and it is heated to 800 °C at a heating rate of 5 °C / min for co-deposition and kept warm for 2 h; other conditions are the same as those of Example 1.

[0092] Example 7

[0093] The preparation method of the composite negative electrode material: except that in step (3), the polyethylene gas is 20 g, and it is deposited at 700 °C and kept warm for 2 h, other conditions are the same as those of Example 1.

[0094] Example 8

[0095] The preparation method of the composite negative electrode material: except that in step (3), the polyethylene gas is 40 g, and it is deposited at 500 °C and kept warm for 3 h, other conditions are the same as those of Example 1.

[0096] Example 9

[0097] The preparation method of the composite negative electrode material includes the following steps:

[0098] (1) Prepare the first material by wet mixing, specifically including: weighing 40 g of porous carbon (pore diameter 2 nm, specific surface area 1800 m 2 / g, particle size: 5 μm), 2 g of barium titanate and 50 mL of absolute ethanol, ultrasonically treating the mixed system, then performing solid-liquid separation, and collecting the solid; the power of the ultrasonic treatment is 450 W, and the time of the ultrasonic treatment is 1.5 h;

[0099] (2) Transfer the first material to the CVD rotary furnace. The rotation speed of the rotary furnace is 50 s / turn. First, introduce nitrogen for treatment, and then introduce a mixed gas of silane gas and argon. The silane gas is 100 g, the flow rate is 10 mL / min, and the concentration of the silane gas in the mixed gas is 50%. Then, heat it up to 600 °C at a heating rate of 5 °C / min for co-deposition and keep it warm for 3 h to obtain the substrate material;

[0100] (3) After completing the deposition in step (2), turn off the silane gas. After introducing argon at a flow rate of 1 L / min for 30 min, raise the temperature of the rotary furnace to 600 °C at a heating rate of 5 °C / min, and then introduce a mixed gas of polyethylene gas and argon. The polyethylene gas is 30 g, the flow rate is 10 mL / min, and the concentration of the polyethylene gas accounts for 50% of the polyethylene gas; Deposit at 600 °C and keep it warm for 3 h, and then cool it down to room temperature to obtain the composite negative electrode material.

[0101] Comparative Example 1

[0102] A method for preparing a composite negative electrode material, except that barium titanate is not added in step (1), and other conditions are the same as in Example 1.

[0103] Experimental Example

[0104] I. Conductivity Test

[0105] Perform conductivity tests on the composite negative electrode materials of each example and comparative example, as shown in Table 1.

[0106] Conductivity test: According to the national standard GB / T 24533-2019, it can be tested by powder resistivity; use a powder resistivity meter, diameter, 10; automatic pressure, 1000 Kg; constant pressure time, 30 s.

[0107] Table 1 Conductivity test results of composite negative electrode materials

[0108]

[0109]

[0110] II. Performance Test of the Battery

[0111] Prepare the negative electrode materials of each example and comparative example into button cells respectively. The specific preparation method includes:

[0112] The composite anode materials prepared in the examples and comparative examples were mixed according to the mass ratio of composite anode material: polyacrylic acid resin (PAA): single-walled carbon nanotubes (CNT): conductive carbon black (SP) = 82:7:1:10, made into a slurry with deionized water, uniformly coated on a copper foil, and vacuum dried at 80 °C for 24 h to obtain the battery electrode sheets for experiments. Then, using a lithium sheet as the counter electrode, an electrolyte of 1.1 mol / L LiPF6 with a solvent of a four-component mixed solvent, ethylene carbonate (EC): vinylene carbonate (VC): dimethyl carbonate (DMC): fluoroethylene carbonate (FEC) = 1:1:1:1 (volume ratio), and a polypropylene microporous film as the separator, a CR2025-type button half-cell was assembled in a vacuum glove box.

[0113] A battery test system (a half-cell test using an American Arbin multi-channel battery test system and a German Braun Labstar (1200 / 780) type glove box) was used to test the capacity, initial charge-discharge efficiency (first efficiency), and cycle retention rate.

[0114] The performance test results of the battery are shown in Table 2.

[0115] Table 2 Performance Test Results of the Battery

[0116]

[0117]

[0118] III. Test of Lithium-Ion Diffusion Coefficient

[0119] The constant current intermittent titration method (GITT) was used to test the batteries of Example 1 and Comparative Example 1 respectively. The test parameters included: standing for 24 h, constant current discharge of 0.005 V, constant current discharge of 0.005 V, standing for 10 min, constant current charge of 2 V, standing for 10 min, cycling 3 times, constant current discharge of 12 min, and standing for 30 min. The diffusion coefficient curve of the battery is as Figure 1 shown. It can be seen that the anode material obtained by the method of the present invention can improve the lithium-ion diffusion coefficient of the battery and enhance the rate performance of the battery.

[0120] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A composite negative electrode material, characterized in that, It includes a matrix material and a carbon coating layer covering at least a part of the surface of the matrix material; the matrix material includes porous carbon and barium titanate, and a silicon material is loaded in the pores of the porous carbon.

2. The composite anode material according to claim 1, wherein It includes at least one of the following features (1) to (4): (1) The silicon material includes nanosilicon; (2) Part of the barium titanate is loaded in the pores of the porous carbon; (3) The mass of the barium titanate accounts for 0.1% - 10% of the sum of the masses of the porous carbon and the carbon coating layer; (4) The mass of the silicon material accounts for 5% - 85% of the mass of the composite anode material.

3. The preparation method of the composite anode material according to any one of claims 1 to 2, characterized in that, It includes the following steps: Mix the porous carbon raw material and the barium titanate raw material to obtain a first material; Perform a first chemical vapor deposition on the first material under a silicon source gas to obtain a matrix material; Perform a second chemical vapor deposition on the matrix material under a carbon source gas to obtain the composite anode material.

4. The preparation method of the composite anode material according to claim 3, characterized in that, It includes at least one of the following features (1) to (2): (1) The mass of the barium titanate raw material is 0.1% - 10% of the mass of the porous carbon raw material; (2) The average pore diameter of the porous carbon raw material is 0.5 to 10 nm, the specific surface area of the porous carbon raw material is 1000 to 2500 m 2 / g, and the D50 particle size of the porous carbon raw material is 4 to 10 μm.

5. The preparation method of the composite negative electrode material according to claim 3, wherein, It includes at least one of the following features (1) to (4): (1) The mixing process includes solid-phase mixing and / or wet mixing; (2) In the mixing process, the time of solid-phase mixing is 2 - 10 h, the rotation speed of solid-phase mixing is 300 - 500 rpm, and the ball-to-material ratio of solid-phase mixing is (8 - 10):1; (3) In the mixing process, the wet mixing specifically includes: subjecting the mixed system of the porous carbon raw material, the barium titanate raw material and an organic solvent to ultrasonic treatment, then performing solid-liquid separation, and collecting the solid; (4) In the wet mixing of the mixing process, the power of ultrasonic treatment is 300 - 500 W, and the time of ultrasonic treatment is 1 - 2 h; the dosage ratio of the barium titanate raw material to the organic solvent is 1 g:(10 - 30) mL.

6. The preparation method of the composite negative electrode material according to claim 3, characterized in that, It includes at least one of the following features (1) to (3): (1) The silicon source gas includes silane, and / or disilane, and / or trichlorosilane, and / or dichlorosilane, and / or propylsilane, and / or trichlorosilane, and / or silicon chloride; (2) The mass ratio of the silicon source gas to the porous carbon raw material is (90 - 120):(30 - 50); (3) The flow rate of the silicon source gas is 5 - 15 mL / min.

7. The preparation method of the composite anode material according to claim 3, characterized in that, It includes at least one of the following features (1) to (4): (1) The first chemical vapor deposition specifically includes: introducing the silicon source gas into a chamber containing the first material, and then performing a first heat treatment; (2) During the first chemical vapor deposition, the temperature of the first heat treatment is 500 - 700 °C, and the heat preservation time is 2 - 6 h; (3) During the first chemical vapor deposition, the heating rate of the first heat treatment is 3 - 6 °C / min; (4) During the first chemical vapor deposition, a protective gas is continuously introduced.

8. The preparation method of the composite negative electrode material according to claim 3, characterized in that, It includes at least one of the following features (1) to (6): (1) The carbon source gas includes polyethylene, and / or acetylene, and / or methane, and / or ethylene, and / or propylene; (2) The flow rate of the carbon source gas is 5 - 15 mL / min; (3) The second vapor deposition specifically includes: introducing a carbon source gas into the substrate material and performing a second heat treatment; (4) During the second vapor deposition, the temperature of the second heat treatment is 500-800 °C, and the heat preservation time is 2-6 h; (5) During the second vapor deposition, a protective gas is continuously introduced; (6) After the second vapor deposition, it further includes: cooling to room temperature.

9. A negative electrode sheet, characterized in that, It includes the composite negative electrode material according to any one of claims 1-2.

10. A battery, characterized in that, It includes the negative electrode sheet according to claim 9.

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