Coated negative electrode material and preparation method and application thereof

Abstract

The invention belongs to the technical field of battery material preparation, and particularly relates to a coated negative electrode material as well as a preparation method and application thereof. The coated negative electrode material comprises a porous carbon skeleton and a carbon coating layer coating the porous carbon skeleton, the porous carbon skeleton is provided with a plurality of holes; a silicon layer and a functional layer are attached to the surfaces of part of the holes; the silicon layer comprises silicon, the functional layer comprises a functional material, and the functional material comprises lithium aluminum fluoride. The coated negative electrode material provided by the invention has the properties of low expansion, high lithium ion conduction, few byproducts and the like, and is suitable for a solid battery; the battery energy density is ensured, and the problems that an effective lithium ion path cannot be formed due to contact failure of an active substance caused by high volume expansion of a silicon-based material in the circulation process and contact failure of the active material and a solid electrolyte in a solid-state battery, and performance degradation is caused by negative electrode side polarization increase in the circulation process are solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery material preparation, and in particular relates to a coated negative electrode material and a preparation method and application thereof. Background Art

[0002] Solid-state batteries boast an energy density of up to 400Wh / kg, and can offer twice the range of liquid-based batteries of the same mass. Because solid-state batteries avoid electrolytes and separators, which pose safety risks, they have become a key focus for the development of the new energy industry.

[0003] The vast majority of negative electrode materials are graphite, which has a theoretical capacity of 372mAh / g and cannot meet the energy density requirements of solid-state batteries. Although lithium metal has a higher energy density, the dendrites produced during the cycle can easily cause the battery to puncture and short-circuit, posing a major safety hazard. Silicon negative electrodes have a higher energy density (4200mAh / g) and are abundant in reserves, making them the most promising negative electrode material for next-generation batteries. However, silicon-based materials experience volume expansion and deterioration in ionic conductivity during cycling, leading to performance drops and failure during cycling.

[0004] At present, the effective method to solve the expansion of silicon-based materials is to combine silicon materials and carbon materials, and use carbon materials to limit the volume expansion of silicon during the cycle, thereby improving the cycle performance of the battery. Recently, many studies have shown that using porous carbon materials as a substrate and depositing silicon in the carbon pores to obtain silicon-carbon materials can reduce the volume expansion during the cycle. Among them, the porous carbon skeleton is mainly a hard carbon material that has been activated to form pores. When it is used in liquid batteries, due to the sufficient infiltration of the electrolyte, a connected lithium ion path can be formed in the electrode structure. However, solid-state batteries cannot form an effective lithium ion path due to certain contact failures between the active material and the solid electrolyte. When silicon-carbon materials are applied to solid-state batteries, the polarization on the negative electrode side will be greatly increased during the cycle. In addition, the lithium ion conductivity of hard carbon materials is poor, and the lithium ion transmission resistance during the cycle is large. Therefore, in addition to solving the intrinsic volume expansion of silicon-based materials, the application of silicon-carbon materials in solid-state batteries also requires enhancing lithium ion transmission at the electrode level. Summary of the Invention

[0005] The purpose of the present invention is to provide a coated negative electrode material and its preparation method and application, so as to solve the technical problems of existing silicon-carbon materials such as expansion, poor lithium ion transmission, and generation of by-products by the reaction between electrolyte and silicon.

[0006] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is as follows.

[0007] A coated negative electrode material comprises a porous carbon skeleton and a carbon coating layer coating the porous carbon skeleton; the porous carbon skeleton has a plurality of pores; a silicon layer and a functional layer are attached to the surface of some of the pores; the silicon layer comprises silicon, the functional layer comprises a functional material, and the functional material comprises lithium aluminum fluoride.

[0008] Based on the above technical means, the coated negative electrode material provided by the present invention has the properties of low expansion, high lithium ion conductivity, and low by-products. It is suitable for solid-state batteries. While ensuring the battery energy density, it also solves the problems of active material contact failure caused by the high volume expansion of silicon-based materials during the cycle process, and the contact failure between the active material and the solid electrolyte in solid-state batteries, which cannot form an effective lithium ion path. During the cycle, the increased polarization on the negative electrode side leads to performance degradation. The negative electrode material of the present invention is suitable for liquid batteries and solid-state batteries. In particular, when it is used in liquid batteries, it can reduce the problem of by-products generated by the reaction between the electrolyte and silicon.

[0009] The porous carbon skeleton of the present invention has a number of pores, some of which have silicon and functional materials attached to their surfaces. The pores with silicon and functional materials attached also have excess space, which can buffer the volume expansion of silicon during cycling, reduce the stress generated by the negative electrode during cycling, and mitigate electrode failure. The porous carbon skeleton has the characteristics of high strength and low volume expansion during charging and discharging, which can maintain the strength of the negative electrode material, improve the strength of the negative electrode material, and promote better stability and integrity during the cycling process, and buffer the volume expansion of the silicon material during cycling. Filling the pores of the porous carbon skeleton with silicon can increase the energy density of the negative electrode material. Functional materials include lithium aluminum fluoride. First, lithium aluminum fluoride can construct a lithium ion transmission path in a porous carbon skeleton, shorten the lithium ion transmission path, improve the contact failure between the active material and the solid electrolyte in the solid-state battery, and cannot form a lithium ion path defect, thereby reducing the polarization and capacity decay that occur on the negative electrode side during the cycle; second, lithium aluminum fluoride is an electronic insulator, which can reduce electron transmission, reduce the side reaction of electrons obtained by the solid electrolyte, and improve the first charge and discharge coulomb efficiency; third, lithium aluminum fluoride is attached to the porous carbon skeleton to reduce the specific surface area of ​​the negative electrode material, reduce contact with the electrolyte, thereby reducing side reactions, and reducing processing difficulty. The present invention is coated with a carbon coating layer on the outside of the porous carbon skeleton, which plays a role in reducing the specific surface area, reducing the direct contact between the negative electrode material and the electrolyte, reducing the side reactions between the electrolyte and the negative electrode silicon caused by the large specific surface area during the cycle, and improving the battery electrical performance.

[0010] Furthermore, the thickness of the functional layer is 2nm-10nm;

[0011] Preferably, the thickness of the functional layer is 2-4 nm. Exemplarily, the thickness of the functional layer is 2 nm, 3 nm, 5 nm, 8 nm, 9 nm, etc.

[0012] Based on the aforementioned technical means, the present invention adjusts the thickness of the functional layer to form a functional layer of a certain thickness on the surface of the porous carbon skeleton. This functional layer has the effect of high ionic conductivity, reduced electron transport, and reduced side reactions in the battery system. Adjusting the thickness of the functional layer is beneficial to improving ionic conductivity.

[0013] Furthermore, the particle size D90 of the porous carbon skeleton is ≤40 μm; illustratively, D90 is 10 μm, 20 μm, 30 μm, 40 μm, etc.;

[0014] And / or, the average pore size of the pores is 0.2nm-2nm; illustratively, the average pore size of the pores is 0.2nm, 0.4nm, 0.6nm, 0.8nm, 1nm, 1.2nm, 1.4nm, 1.6nm, 1.8nm, etc.

[0015] And / or, the specific surface area of ​​the pores is 0.8-700m 2 / g; For example, the specific surface area of ​​the pores is 0.8m 2 / g、5m 2 / g、10m 2 / g, 40m 2 / g、80m 2 / g、100m 2 / g, 200m 2 / g, 400m 2 / g、500m 2 / g、600m 2 / g、700m 2 / g, etc.

[0016] And / or, the porous carbon skeleton is a hard carbon material.

[0017] According to the aforementioned technical approach, the pore diameters of the porous carbon framework in the coated negative electrode material of the present invention fall within the aforementioned range. This indicates that during the formation of the silicon layer, the capillary adsorption of the micropores and / or mesopores can draw the vapor-phase silicon source into the pores, where it is deposited and formed within the pores. This helps the carbon framework buffer the volume expansion of silicon during cycling, effectively suppressing expansion. The hard carbon material exhibits a volume strain of ≤5% during charge and discharge, effectively buffering silicon volume expansion and slowing the failure of the negative electrode.

[0018] Furthermore, the silicon is amorphous silicon;

[0019] And / or, the carbon coating layer has a thickness of 5 nm to 10 nm.

[0020] Based on the aforementioned technical approach, the present invention incorporates amorphous silicon onto the pore surfaces of a porous carbon framework. During lithium insertion, amorphous silicon expands much less than crystalline silicon, reducing the absolute expansion rate of the silicon-carbon material during charge and discharge, thereby mitigating electrode failure during the material's charge and discharge cycles. The present invention regulates the thickness of the carbon coating to meet the aforementioned range, thereby improving energy density and reducing side reactions.

[0021] Furthermore, a method for preparing a coated negative electrode material comprises the following steps:

[0022] (1) depositing a silicon source in the pores of the porous carbon skeleton to form a silicon layer; the silicon source is a gas;

[0023] (2) A functional layer is formed by atomic layer deposition; the precursor of the functional layer includes a lithium source, a fluorine source and an aluminum source; the lithium source includes at least one of lithium dimethyl ketone, n-butyl lithium, lithium hydroxide, lithium carbonate and lithium tert-butoxide; the fluorine source includes at least one of 2-fluoroethylamine, aluminum trifluoromethanesulfonate, aluminum trifluoroacetate and hexafluoro-2,4-pentanedione aluminum; the aluminum source includes at least one of trimethylaluminum, aluminum trifluoromethanesulfonate, aluminum trifluoroacetate and hexafluoro-2,4-pentanedione aluminum; it should be noted that the precursor generates lithium aluminum fluoride after reaction, and the structural formula is LiAlF4.

[0024] (3) using a vapor deposition method to deposit a carbon source on the surface of the porous carbon skeleton obtained in step (2) to form a carbon coating layer.

[0025] According to the above technical means, the present invention utilizes capillary adsorption to deposit a gas-phase silicon source in the pores of a porous carbon skeleton, and then deposits it again in the pores to form a lithium aluminum fluoride functional layer, and finally coats the surface of the porous carbon skeleton with a macromolecular carbon source. The negative electrode material prepared by the preparation method of the present invention has properties such as low expansion and high lithium ion conduction, and is suitable for solid batteries. While ensuring the energy density of the battery, it solves the problems of contact failure of active substances caused by high volume expansion of silicon-based materials during the cycle, and contact failure of active materials and solid electrolytes in solid-state batteries, which make it impossible to form an effective lithium ion path. During the cycle, the polarization of the negative electrode side increases, resulting in performance degradation. The negative electrode material of the present invention is suitable for liquid batteries and solid-state batteries.

[0026] The negative electrode material with a porous structure has a certain void space and a large specific surface area. When lithium is first inserted, too many byproducts are formed, resulting in a decrease in the first coulombic efficiency of the battery. The large voids will also cause the lithium ion transmission path to become longer, affecting the performance of the material. The present invention fills the pores of the porous carbon skeleton with a lithium aluminum fluoride functional layer. On the one hand, lithium aluminum fluoride can construct a lithium ion transmission path in the porous carbon skeleton, shorten the lithium ion transmission path, improve the defect of contact failure between the active material and the solid electrolyte in the solid-state battery, and cannot form a lithium ion path, and reduce the polarization and capacity attenuation on the negative electrode side during the cycle; on the other hand, filling the porous carbon skeleton with lithium aluminum fluoride can reduce the specific surface area of ​​the negative electrode material, reduce contact with the electrolyte, thereby reducing side reactions and reducing processing difficulty. The carbon coating layer plays the role of plugging the pores, reducing the specific surface area, retaining the material's gram capacity, reducing the direct contact between the negative electrode material and the electrolyte, which is beneficial to improving the lithium ion conductivity in solid-state batteries and reducing the contact between the negative electrode material and the electrolyte in liquid batteries. The negative electrode material prepared by the present invention can improve the initial charge and discharge coulombic efficiency and improve the cycle performance when used in liquid batteries; and can enhance the overall ionic conductivity and improve the cycle performance when used in solid-state batteries.

[0027] It should be noted that the lithium aluminum fluoride of the present invention is a chemical substance generated by the reaction of a lithium source, an aluminum source, and a fluorine source. Aluminum trifluoromethanesulfonate, aluminum trifluoroacetate, and aluminum hexafluoro-2,4-pentanedione can serve as both a fluorine source and an aluminum source.

[0028] Furthermore, in step (1), the deposition temperature is 400°C-1500°C, and the time is 400min-800min; illustratively, the temperature is 450°C, 500°C, 700°C, 900°C, 1300°C, 1400°C, etc.; the time is 400min, 450min, 500min, 550min, 600min, 700min, 800min, etc.

[0029] And / or, the silicon source includes silane and / or trichlorosilane.

[0030] According to the above technical effects, before the deposition of the silicon layer, the pores of the porous carbon skeleton include micropores and / or mesopores, and the gaseous silicon source can be sucked into the pores by the capillary adsorption effect to deposit and form the silicon layer. The carbon skeleton can be used to buffer the volume expansion of silicon during the cycle. The silane can be monosilane, disilane, trisilane, butadienesilane, etc. The average pore size of the negative electrode material obtained by the method of the present invention is 0.2nm-2nm, and the specific surface area of ​​the material is 0.8-700m 2 / g.

[0031] Furthermore, in step (2), the temperature of the atomic layer deposition method is 150-250°C, and the pressure is 10-30MPa; illustratively, the temperature is 150°C, 170°C, 190°C, 220°C, 250°C, etc.; the pressure is 10MPa, 12MPa, 14MPa, 18MPa, 20MPa, 22MPa, 24MPa, 28MPa, 30MPa, etc.

[0032] And / or, in the atomic layer deposition method, the carrier gas volume ratio is ≥50%; illustratively, the carrier gas volume ratio is 50%, 52%, 55%, 60%, etc.

[0033] And / or, in step (2), the number of depositions is 10-30 times; the thickness of the functional layer formed by a single deposition is 0.1 nm-1 nm. Exemplarily, the number of depositions is 10, 13, 15, 18, 20, 24, 27, 30, etc. The thickness of the functional layer formed by a single deposition is 0.1 nm, 0.2 nm, 0.3 nm, 0.5 nm, 0.7 nm, 0.9 nm, 1 nm, etc.

[0034] It should be noted that during atomic layer deposition, the precursor is converted into precursor gas, which is attached to the inner surface of the pores of the porous carbon skeleton after reaction; the carrier gas volume ratio refers to the precursor gas volume / (precursor gas volume + nitrogen gas volume) × 100%.

[0035] Furthermore, in step (3), the deposition temperature is 500-700°C; the pressure is 90-150kPa; illustratively, the temperature is 500°C, 550°C, 600°C, 650°C, 700°C, etc.; the pressure is 90kPa, 100kPa, 110kPa, 120kPa, 130kPa, 140kPa, 150kPa, etc.;

[0036] And / or, the carbon source includes propyne, propane, n-butene or butane.

[0037] According to the above technical means, the present invention uses a macromolecular carbon source to reduce the penetration of the carbon source into the porous carbon skeleton matrix, forming a carbon coating layer on the surface, which is beneficial to improving the overall theoretical capacity.

[0038] Beneficial effects of the present invention:

[0039] (1) The coated negative electrode material provided by the present invention comprises a porous carbon skeleton and a carbon coating layer coating the porous carbon skeleton; the porous carbon skeleton has a plurality of pores; a silicon layer and a functional layer are attached to the surface of some of the pores; the silicon layer comprises silicon, the functional layer comprises a functional material, and the functional material comprises lithium aluminum fluoride. The coated negative electrode material provided by the present invention has the properties of low expansion, high lithium ion conductivity, and few by-products, and is suitable for solid batteries. While ensuring the energy density of the battery, it solves the problems of contact failure of active materials due to high volume expansion of silicon-based materials during the cycle process, and contact failure of active materials and solid electrolytes in solid-state batteries, which cannot form an effective lithium ion path, and performance degradation caused by increased polarization on the negative electrode side during the cycle. The negative electrode material of the present invention is suitable for liquid batteries and solid-state batteries. In particular, when it is applied to liquid batteries, it can reduce the problem of by-products generated by the reaction of electrolyte and silicon.

[0040] The porous carbon skeleton of the present invention has a number of pores, some of which have silicon and functional materials attached to their surfaces. The pores with silicon and functional materials attached also have excess space, which can buffer the volume expansion of silicon during cycling, reduce the stress generated by the negative electrode during cycling, and mitigate electrode failure. The porous carbon skeleton has the characteristics of high strength and low volume expansion during charging and discharging, which can maintain the strength of the negative electrode material, improve the strength of the negative electrode material, and promote better stability and integrity during the cycling process, and buffer the volume expansion of the silicon material during cycling. Filling the pores of the porous carbon skeleton with silicon can increase the energy density of the negative electrode material. Functional materials include lithium aluminum fluoride. First, lithium aluminum fluoride can construct a lithium ion transmission path in a porous carbon skeleton, shorten the lithium ion transmission path, improve the contact failure between the active material and the solid electrolyte in the solid-state battery, and cannot form a lithium ion path defect, thereby reducing the polarization and capacity decay that occur on the negative electrode side during the cycle; second, lithium aluminum fluoride is an electronic insulator, which can reduce electron transmission, reduce the side reaction of electrons obtained by the solid electrolyte, and improve the first charge and discharge coulomb efficiency; third, lithium aluminum fluoride is attached to the porous carbon skeleton to reduce the specific surface area of ​​the negative electrode material, reduce contact with the electrolyte, thereby reducing side reactions, and reducing processing difficulty. The present invention is coated with a carbon coating layer on the outside of the porous carbon skeleton, which plays a role in reducing the specific surface area, reducing the direct contact between the negative electrode material and the electrolyte, reducing the side reactions between the electrolyte and the negative electrode silicon caused by the large specific surface area during the cycle, and improving the battery electrical performance.

[0041] (2) The present invention adjusts the thickness of the functional layer to form a functional layer of a certain thickness on the surface of the porous carbon skeleton. This functional layer has the effect of high ionic conductivity and reduced electron transport, thereby reducing the side reactions of the battery system. Adjusting the thickness of the functional layer is beneficial to improving ionic conductivity.

[0042] (3) The present invention provides a method for preparing a coated negative electrode material. The present invention utilizes capillary adsorption to deposit a gas-phase silicon source in the pores of a porous carbon skeleton, and then deposits it again in the pores to form a lithium aluminum fluoride functional layer, and finally coats a macromolecular carbon source on the surface of the porous carbon skeleton. The negative electrode material prepared by the preparation method of the present invention has properties such as low expansion and high lithium ion conduction, and is suitable for solid batteries. While ensuring the energy density of the battery, it solves the problems of contact failure of active substances caused by high volume expansion of silicon-based materials during the cycle, and contact failure between active materials and solid electrolytes in solid-state batteries, which makes it impossible to form an effective lithium ion path. During the cycle, the polarization of the negative electrode side increases, resulting in performance degradation. The negative electrode material of the present invention is suitable for liquid batteries and solid-state batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is a schematic diagram of the preparation process of the coated negative electrode material according to Example 1 of the present invention. DETAILED DESCRIPTION

[0044] The following describes the embodiments of the present invention with reference to the accompanying drawings and preferred embodiments. Those skilled in the art will readily appreciate the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the various details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are intended only to illustrate the present invention and are not intended to limit the scope of protection of the present invention.

[0045] It should be noted that the illustrations provided in the following embodiments are merely schematic illustrations of the basic concept of the present invention. Therefore, the illustrations only show components related to the present invention and are not drawn according to the number, shape, and size of components in actual implementation. In actual implementation, the type, quantity, and proportion of each component may be changed arbitrarily, and the component layout may also be more complex.

[0046] Example 1

[0047] This embodiment provides a method for preparing a negative electrode material. The reaction process is as follows: Figure 1 As shown, the following steps are included:

[0048] (1) 400 g of a porous hard carbon matrix with a particle size of approximately 25 μm (D90) was placed in a reactor and vacuumed to ≤-95 kPa to expel the air inside the porous carbon matrix. The reactor was then heated to 300°C for preheating. Monosilane gas was introduced into the reactor until the pressure in the reactor reached normal pressure and the reactor was allowed to stand for 12 hours. During the standing period, monosilane gas was continuously introduced to maintain the pressure in the reactor at one atmosphere. The porous hard carbon matrix had micropores and mesopores. At this time, the monosilane gas was adsorbed in the pores of the porous carbon matrix by capillary adsorption. After the standing period, the reactor was heated at a rate of 10°C / min. After the temperature reached 500°C and the temperature was maintained for 10 hours, the silane gas was decomposed to form elemental silicon that was adsorbed in the pores inside the porous carbon material, forming a silicon layer to obtain a vapor-deposited silicon-carbon material.

[0049] (2) The vapor-deposited silicon-carbon material prepared in the above steps is placed in a deposition reactor, and nitrogen and a precursor mixture gas are introduced, wherein the volume ratio of the precursor mixture gas to nitrogen is 52:48, and the precursor includes n-butyl lithium and aluminum trifluoroacetate in a molar ratio of 1:2, and the aluminum trifluoroacetate is in excess; an atomic layer deposition method is used to form a functional layer, the temperature inside the deposition reactor is 170°C, the pressure is 20 MPa, the number of depositions is 15 times, the thickness of the functional layer formed by a single deposition is 0.2 nm, and the total thickness of the obtained functional layer is 3 nm.

[0050] (3) The silicon-carbon material obtained in step (2) is dried, added to a reactor, evacuated to ≤-95 kPa, the internal air is discharged, and heated to 300 ° C for preheating; propyne gas is introduced into the reactor until the pressure in the reactor is normal pressure, and the reactor is allowed to stand for 12 hours. During the standing period, propyne gas is continuously introduced to maintain the pressure in the reactor at one atmospheric pressure of 101.325 kPa. After the standing period is completed, the reactor is heated at a heating rate of 10 ° C / min. After the temperature is raised to 550 ° C and kept warm for 10 hours, the propyne will be cracked into carbon element to form a carbon coating layer.

[0051] This embodiment provides a coated negative electrode material, including a porous hard carbon skeleton and a carbon coating layer coating the porous hard carbon skeleton, wherein the porous hard carbon skeleton has a plurality of pores, and silicon and lithium aluminum fluoride are attached to the surface of some of the pores; the particle size D90 of the porous hard carbon skeleton particles is 25 μm, the average pore size of the pores is 0.6 nm, and the specific surface area is 1.7 m 2 / g carbon coating layer is 5.5nm.

[0052] Example 2

[0053] This embodiment provides a method for preparing a negative electrode material, which is basically the same as that of Example 1, except that the precursor is different. The precursor of this embodiment is lithium tert-butoxide, 2-fluoroethylamine, and trimethylaluminum in a molar ratio of 1:4:1.

[0054] This embodiment provides a coated negative electrode material, including a porous hard carbon skeleton and a carbon coating layer coating the porous hard carbon skeleton, wherein the porous hard carbon skeleton has a plurality of pores, and silicon and lithium aluminum fluoride are attached to the surface of some of the pores; the particle size D90 of the porous hard carbon skeleton particles is 25 μm, the average pore size of the pores is 0.48 nm, and the specific surface area is 1.5 m 2 / g; the carbon coating layer is 5.2nm.

[0055] Example 3

[0056] (1) 400 g of a porous hard carbon matrix with a particle size of approximately 25 μm (D90) was placed in a reactor and vacuumed to ≤-95 kPa to expel the air inside the porous carbon matrix. The reactor was then heated to 300°C for preheating. Monosilane gas was introduced into the reactor until the pressure in the reactor reached normal pressure and the reactor was allowed to stand for 12 hours. Disilane gas was continuously introduced during the standing period to maintain the pressure in the reactor at one atmosphere. The porous hard carbon matrix has micropores and mesopores. At this time, disilane gas is adsorbed in the pores of the porous carbon matrix by capillary adsorption. After the standing period, the reactor was heated at a rate of 10°C / min to 800°C and then maintained at this temperature for 12 hours. At this time, the silane gas was decomposed to form elemental silicon that was adsorbed in the pores inside the porous carbon material, forming a silicon layer to obtain a vapor-deposited silicon-carbon material.

[0057] (2) The vapor-deposited silicon-carbon material prepared in the above steps is placed in a deposition reactor, and nitrogen and a precursor mixture gas are introduced, wherein the volume ratio of the precursor mixture gas to nitrogen is 55:45, and the precursor includes n-butyl lithium and aluminum trifluoroacetate in a molar ratio of 1:2; an atomic layer deposition method is used to form a functional layer, the temperature inside the deposition reactor is 230°C, the pressure is 22 MPa, the number of depositions is 18 times, the thickness of the functional layer formed by a single deposition is 0.4 nm, and the total thickness of the obtained functional layer is 7.2 nm.

[0058] (3) The silicon-carbon material obtained in step (2) is dried, added to a reactor, evacuated to ≤-95 kPa, the internal air is discharged, and heated to 300 ° C for preheating; butane gas is introduced into the reactor until the pressure in the reactor is normal pressure, and the reactor is allowed to stand for 12 hours. During the standing period, butane gas is continuously introduced to maintain the pressure in the reactor at one atmospheric pressure of 120 kPa. After the standing period is completed, the reactor is heated at a heating rate of 10 ° C / min. After the temperature is raised to 550 ° C, it is kept warm for 12 hours. At this time, the butane will be cracked into carbon element to form a carbon coating layer.

[0059] This embodiment provides a coated negative electrode material, including a porous hard carbon skeleton and a carbon coating layer coating the porous hard carbon skeleton, wherein the porous hard carbon skeleton has a plurality of pores, and silicon and lithium aluminum fluoride are attached to the surface of some of the pores; the particle size D90 of the porous hard carbon skeleton particles is 25 μm, the average pore size of the pores is 0.3 nm, and the specific surface area is 1.2 m2 / g; the carbon coating layer is 8nm.

[0060] Comparative Example 1

[0061] This comparative example provides a method for preparing a negative electrode material, which is basically the same as Example 1, except that the functional material synthesis method and the material itself are different. In step (2) of the functional material synthesis of this comparative example, LiF is deposited by vapor deposition to synthesize a silicon-carbon material; the deposition temperature of the vapor deposition method is 630°C, the time is 270 min, and the thickness of the obtained LiF layer is 3.2 nm.

[0062] This comparative example provides a coated negative electrode material, comprising a porous hard carbon skeleton and a carbon coating layer coating the porous hard carbon skeleton, wherein the porous hard carbon skeleton has a plurality of pores, and silicon and LiF are attached to the surface of some of the pores; the particle size D90 of the porous hard carbon skeleton particles is 25 μm, the average pore size of the pores is 0.58 nm, and the specific surface area is 1.5 m 2 / g; the carbon coating layer is 5.5nm.

[0063] Comparative Example 2

[0064] This comparative example provides a method for preparing a negative electrode material, which is basically the same as Example 1. The main difference lies in the functional material synthesis method and the material itself. Step (2) in the synthesis of the functional material in this comparative example is to use a liquid phase deposition method to form a polyvinylidene fluoride layer, and the polyvinylidene fluoride is present in the pores of the porous carbon skeleton and on the surface of the porous carbon skeleton.

[0065] Test Case

[0066] This test example provides the performance test of the negative electrode materials of each embodiment and comparative example, as follows:

[0067] Battery: The negative electrode materials prepared in each embodiment and comparative example were homogenized and coated to prepare negative electrode sheets; lithium nickel cobalt manganese oxide was used as the ternary positive electrode material to prepare positive electrode sheets, and an electrolyte was injected to obtain a liquid soft-pack battery cell.

[0068] Test method for silicon loading: Use oxidation treatment method to test the silicon content in the negative electrode material. After oxidation treatment, the negative electrode material reacts with molten alkali to generate soluble silicate, and then the silicon content is determined by spectrometry.

[0069] Specific surface area test method: The BJH (Barrett-Joyner-Halenda) test method is used to test the specific surface area of ​​the sample. First, the sample is degassed under high temperature conditions, and then placed in an adsorption instrument at liquid nitrogen temperature. The amount of nitrogen adsorption and desorption at different relative pressures is measured, and the pore size distribution and specific surface area of ​​the material are calculated.

[0070] Gram Capacity Testing Method: The negative electrode materials from each example and comparative example were fabricated into negative electrode sheets, which were then composited with a separator and a lithium sheet to form a coin-type half-cell. The charge capacity of the materials was measured during a 0.1C discharge / 0.1C charge / discharge cycle. Initial Coulombic Efficiency Testing Method: The initial charge capacity of the material in the coin-type half-cell was divided by the initial discharge capacity to obtain the initial Coulombic Efficiency.

[0071] Test method for full charge expansion rate: Use an in-situ expansion tester to test the volume change of the liquid soft-pack battery prepared above during the charge and discharge process. The thickness of the battery before the cycle is recorded as d1, the thickness of the battery after the first full charge is recorded as d2, and the full charge expansion rate is d2 / d1.

[0072] Test method for 3C capacity retention rate: When testing the capacity retention rate of the liquid soft-pack battery cell prepared above, set a 0.1C discharge / 3C charge test program, and divide the gram capacity value obtained during the 3C charging process by the gram capacity value obtained during the first cycle of 0.1C charging to obtain the 3C capacity retention rate.

[0073] Cycle life test method: Test the cycle performance of the liquid soft-pack battery prepared above. After performing a 0.1C charge / 0.1C discharge program in the first and second cycles, perform a 0.33C charge / 0.33C discharge program subsequently. The capacity retention rate can be obtained by dividing the discharge capacity of each cycle by the 0.33C discharge capacity of the third cycle. The test is terminated when the capacity retention rate drops to 80%. At this time, the number of cycles is the cycle life of the battery.

[0074] Table 1 Test results of various embodiments and comparative examples

[0075]

[0076] The above results demonstrate that batteries made with the coated anode material of the present invention exhibit high initial coulombic efficiency, good capacity retention, and excellent cycling performance. The functional material, lithium aluminum fluoride, is embedded within the pores of the porous carbon skeleton of the coated anode material, enhancing lithium ion transport, improving capacity decay during battery cycling, and reducing side reactions, thereby improving initial coulombic efficiency and cycling performance.

[0077] The above embodiments are only preferred embodiments for fully illustrating the present invention, and the protection scope of the present invention is not limited thereto. Any equivalent substitution or modification made by those skilled in the art based on the present invention is within the protection scope of the present invention.

Claims

1. A coated negative electrode material, characterized in that: It comprises a porous carbon skeleton and a carbon coating layer coating the porous carbon skeleton; the porous carbon skeleton has a plurality of holes; a silicon layer and a functional layer are attached to the surface of some of the holes; the silicon layer contains silicon, the functional layer contains a functional material, and the functional material includes lithium aluminum fluoride.

2. The coated negative electrode material according to claim 1, characterized in that The thickness of the functional layer is 2nm-10nm; Preferably, the thickness of the functional layer is 2-4 nm.

3. The coated negative electrode material according to claim 1, characterized in that The particle size D90 of the porous carbon skeleton is ≤40 μm; and / or, the average pore size of the pores is 0.2 nm to 2 nm; And / or, the specific surface area of ​​the pores is 0.8-700m 2 / g; And / or, the porous carbon skeleton is a hard carbon material.

4. The coated negative electrode material according to claim 1, characterized in that The silicon is amorphous silicon; And / or, the carbon coating layer has a thickness of 5 nm to 10 nm.

5. A method for preparing the coated negative electrode material according to any one of claims 1 to 4, characterized in that: The following steps are involved: (1) depositing a silicon source in the pores of the porous carbon skeleton to form a silicon layer; the silicon source is a gas; (2) A functional layer is formed by atomic layer deposition; the precursor of the functional layer includes a lithium source, a fluorine source and an aluminum source; the lithium source includes at least one of lithium dimethyl ketone, n-butyl lithium, lithium hydroxide, lithium carbonate and lithium tert-butoxide; the fluorine source includes at least one of 2-fluoroethylamine, aluminum trifluoromethanesulfonate, aluminum trifluoroacetate and aluminum hexafluoro-2,4-pentanedione; the aluminum source includes at least one of trimethylaluminum, aluminum trifluoromethanesulfonate, aluminum trifluoroacetate and aluminum hexafluoro-2,4-pentanedione; (3) using a vapor deposition method to deposit a carbon source on the surface of the porous carbon skeleton obtained in step (2) to form a carbon coating layer.

6. The preparation method according to claim 5, characterized in that In the step (1), the deposition temperature is 400° C. to 1500° C. and the deposition time is 400 min to 800 min. And / or, the silicon source includes silane and / or trichlorosilane.

7. The preparation method according to claim 5 or 6, characterized in that: In step (2), the temperature of the atomic layer deposition method is 150-250° C. and the pressure is 10-30 MPa; And / or, the carrier gas volume ratio in the atomic layer deposition method is ≥50%; And / or, in the step (2), the deposition is performed 10 to 30 times; and the thickness of the functional layer formed by a single deposition is 0.1 nm to 1 nm.

8. The preparation method according to any one of claims 5 to 7, characterized in that In step (3), the deposition temperature is 500-700° C. and the pressure is 90-150 kPa; And / or, the carbon source includes propyne, propane, n-butene or butane.

9. A negative electrode plate, characterized in that: The invention comprises the coated negative electrode material according to any one of claims 1 to 4 or the coated negative electrode material prepared by the preparation method according to any one of claims 5 to 8.

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

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