Negative electrode composite, preparation method thereof, negative electrode sheet and lithium ion battery

Abstract

The present application relates to the technical field of lithium ion batteries, and particularly relates to a negative electrode composite material, a preparation method thereof, a negative electrode sheet and a lithium ion battery, the negative electrode composite material comprising: a gradient porous carbon matrix; the gradient porous carbon matrix has a hierarchical pore structure, the hierarchical pore structure comprises macropores and mesopores in sequence from the inside to the surface pores; metal oxide@metal core-shell particles or metal nitride particles; the metal oxide@metal core-shell particles or the metal nitride particles are embedded on the gradient porous carbon matrix, wherein the metal comprises at least one of Sn, V, Ti and Co; and a conductive material interface layer; the conductive material interface layer is coated on at least part of the outer surface of the gradient porous carbon matrix embedding the metal oxide@metal core-shell particles or the metal nitride particles. The negative electrode composite material provided by the present application has high discharge efficiency in a low-temperature environment and can effectively delay capacity decay at low temperature.

Description

Technical Field

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

[0002] Lithium-ion batteries, as the core of modern energy storage and transmission technology, are widely used in electric vehicles, portable electronic products, and energy storage systems. However, low-temperature performance has always been a significant factor restricting the widespread application of lithium-ion batteries. Especially in cold climates, the performance of lithium-ion batteries deteriorates significantly, including reduced discharge efficiency, capacity degradation, and shortened cycle life, greatly affecting their application. In current technologies, graphite is commonly used as the negative electrode material for lithium-ion batteries. Traditional graphite negative electrode materials perform well at room temperature, but their performance is poor at low temperatures, primarily manifested in capacity degradation: due to the reduced diffusion rate of lithium ions at low temperatures, the discharge efficiency of the negative electrode material is greatly reduced, leading to severe capacity degradation.

[0003] Therefore, how to provide a negative electrode material with high discharge efficiency in low-temperature environments is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0004] To address the aforementioned shortcomings in the existing technology, the present invention aims to provide a negative electrode composite material and its preparation method, a negative electrode sheet, and a lithium-ion battery. The negative electrode composite material provided by the present invention comprises a porous carbon matrix with macropores and mesopores sequentially arranged from the inside to the surface, metal oxide@metal core-shell particles or metal nitride particles embedded in the carbon matrix, and a conductive material interface layer covering at least part of the outer surface of the matrix. This results in high discharge efficiency at low temperatures and effectively delays capacity decay at low temperatures.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a negative electrode composite material, the negative electrode composite material comprising:

[0007] Gradient porous carbon matrix: The gradient porous carbon matrix has a multi-level pore structure, wherein the multi-level pore structure includes macropores and mesopores from the inside to the surface.

[0008] Metal oxide@metal core-shell particles or metal nitride particles: The metal oxide@metal core-shell particles or metal nitride particles are embedded in the gradient porous carbon matrix, wherein the metal includes at least one of Sn, V, Ti, and Co;

[0009] Conductive material interface layer: The conductive material interface layer is coated on at least a portion of the outer surface of the gradient porous carbon matrix inlaid with the metal oxide@metal core-shell particles or metal nitride particles.

[0010] The negative electrode composite material provided by the present invention comprises a porous carbon matrix with macropores and mesopores sequentially from the inside to the surface, metal oxide@metal core-shell particles or metal nitride particles embedded in the carbon matrix, and a conductive material interface layer covering at least part of the outer surface of the matrix, which enables it to have high discharge efficiency at low temperature and effectively delay capacity decay at low temperature.

[0011] Furthermore, the pore size of the macropore is 50-150 nm, and the pore size of the mesopore is 5-15 nm;

[0012] And / or, the BET specific surface area of ​​the gradient porous carbon matrix is ​​700-900 m². 2 / g;

[0013] And / or, the gradient porous carbon matrix comprises a core layer with macropores and a shell layer with mesopores, wherein the porosity of the core layer is 60-70%;

[0014] And / or, the metal oxide@metal core-shell particles or metal nitride particles are embedded in the pores and / or surface of the gradient porous carbon matrix;

[0015] And / or, the metal oxide@metal core-shell particles include SnO2@Sn core-shell particles, and the metal nitride includes at least one of VN, TiN, and CoH3N, wherein the SnO2@Sn core-shell particles have Sn as the core layer and SnO2 as the shell layer;

[0016] And / or, the D50 particle size of the metal oxide@metal core-shell particles or metal nitride particles is 15-25 nm;

[0017] And / or, the areal density of the metal oxide@metal core-shell particles or metal nitride particles is 8-12 mg / cm³. 2 ;

[0018] And / or, the metal oxide@metal core-shell particles are obtained by depositing a metal source, glucose and a complexing agent on the gradient porous carbon matrix; or, the metal nitride particles are obtained by depositing a metal source and a nitrogen source on the gradient porous carbon matrix.

[0019] And / or, the conductive material interface layer includes at least one of carbon nanotubes and graphene;

[0020] And / or, the conductive material interface layer further includes a doping element, wherein the doping element includes at least one of boron, nitrogen, and sulfur;

[0021] And / or, in the conductive material interface layer, the content of doped elements is 1.2-1.8 at%.

[0022] And / or, the conductive material interface layer has 2-3 layers;

[0023] And / or, the interlayer spacing of the conductive material interface layer is 0.42-0.48 nm;

[0024] And / or, the coverage of the conductive material interface layer is >95%;

[0025] And / or, in the negative electrode composite material, the mass of the gradient porous carbon matrix accounts for 50-70% of the mass of the negative electrode composite material, the mass of the metal oxide@metal core-shell particles or metal nitride particles accounts for 20-40% of the mass of the negative electrode composite material, and the mass of the conductive material interface layer accounts for 3%-10% of the mass of the negative electrode composite material.

[0026] In a second aspect, the present invention provides a method for preparing the negative electrode composite material as described in the first aspect, the method comprising the following steps:

[0027] S1. Preparation of gradient porous carbon matrix:

[0028] A carbon source, a block copolymer, and a pore-expanding agent are dissolved in a mixed solvent and stirred at high speed to form a composite micelle solution. Then, an alkaline catalyst is added to the composite micelle solution and stirring is continued to form an intermediate core with macropores. The carbon source includes a phenolic compound, the block copolymer includes a hydrophobic segment and a hydrophilic segment, and the pore-expanding agent is insoluble in water.

[0029] After low-speed stirring to form a core-shell mesoscopic structure, the material is then centrifuged and washed before being calcined at low temperature in air and then at high temperature in a protective gas atmosphere to obtain the gradient porous carbon matrix.

[0030] S2. Preparation of metal oxide@metal core-shell particles or metal nitride particle mosaic layers:

[0031] A metal source, glucose, and a complexing agent are deposited on the gradient porous carbon matrix to obtain a gradient porous carbon matrix inlaid with the metal oxide@metal core-shell particles; or, a metal source and a nitrogen source are deposited on the gradient porous carbon matrix to obtain a gradient porous carbon matrix inlaid with the metal nitride particles.

[0032] S3. Preparation of the conductive material interface layer:

[0033] A conductive material interface layer is directly grown on a gradient porous carbon matrix inlaid with metal oxide@metal core-shell particles or metal nitride particles by chemical vapor deposition.

[0034] Furthermore, in step S1, the carbon source includes tannic acid;

[0035] And / or, in step S1, the block copolymer includes at least one of Pluronic F127, Pluronic P123, Pluronic F108, Pluronic P103, and Pluronic F68;

[0036] And / or, in step S1, the pore-expanding agent includes mesitylene;

[0037] And / or, in step S1, the mixed solvent includes ethanol and water, wherein the volume ratio of ethanol to water is 1:1 to 3:1;

[0038] And / or, in step S1, the content of the block copolymer in the composite micelle solution is 0.001-0.03 g / mL;

[0039] And / or, in step S1, the content of the carbon source in the composite micelle solution is 0.003 to 0.009 g / mL; the volume ratio of the pore-expanding agent to the mixed solvent is 1 to 3:100;

[0040] And / or, in step S1, the high-speed stirring speed is 450-550 rpm; the time is 20-40 min;

[0041] And / or, in step S1, the alkaline catalyst comprises ammonia;

[0042] And / or, in step S1, the stirring time continues for 0.5-2 hours;

[0043] And / or, in step S1, the low-speed stirring speed is 250-350 rpm, and the time is 2-4 h;

[0044] And / or, in step S1, the low-temperature calcination temperature is 280-320℃ and the time is 2-4h;

[0045] And / or, in step S1, the protective gas includes N2;

[0046] And / or, in step S1, the high-temperature calcination temperature is 850-950℃ and the time is 1-3h.

[0047] Furthermore, the metal oxide@metal core-shell particle mosaic layer includes a SnO2@Sn core-shell particle mosaic layer, and the deposition reaction of the metal source, glucose, and complexing agent on the gradient porous carbon matrix includes the following steps:

[0048] The tin source and glucose were mixed in a solvent in the presence of a complexing agent to obtain a precursor solution.

[0049] The gradient porous carbon matrix is ​​added to the precursor solution and reacted under heating conditions to obtain a gradient porous carbon matrix embedded with SnO2@Sn core-shell particles.

[0050] Furthermore, in the step of mixing the tin source and glucose in a solvent in which the complexing agent is present, the tin source includes at least one of tetraethyltin, stannous sulfate, tin acetate and nano-tin powder, and the complexing agent includes at least one of sodium citrate, sodium tartrate and sodium gluconate.

[0051] And / or, in the step of mixing the tin source and glucose in a solvent in the presence of the complexing agent, the molar ratio of tin element in the tin source, glucose and the complexing agent is 1:(2-3):(0.1-0.2);

[0052] And / or, in the step of mixing the tin source and glucose in a solvent in the presence of the complexing agent, the tin source is added as an ethanol solution of the tin source, the glucose is added as an ethanol solution of glucose, and the complexing agent is added as an aqueous solution of the complexing agent;

[0053] And / or, the ratio of the amount of tin in the tin source to the mass of the gradient porous carbon matrix is ​​1:(300-500)mol / g;

[0054] And / or, the reaction under heating conditions to obtain a gradient porous carbon matrix embedded with SnO2@Sn core-shell particles includes: performing the reaction using microwave deposition under argon protection throughout; firstly, within 1-4 minutes, linearly increasing the microwave power from 0W to 500-1000W while simultaneously monitoring the temperature rise from 25℃ to 55-65℃, to promote the penetration of the precursor solution into the macropores and mesopores of the gradient porous carbon matrix; then, performing reduction deposition at 500-1000W and 70-95℃ for 10-30 minutes to form Sn cores on the gradient porous carbon matrix; finally, within 2-6 minutes, linearly decreasing the microwave power from 500-1000W to 100-300W to achieve directional coating of the SnO2 shell on the surface of the Sn cores.

[0055] Furthermore, the conductive material interface layer includes a boron-doped graphene interface layer. The direct growth of the conductive material interface layer onto a gradient porous carbon matrix inlaid with metal oxide@metal core-shell particles or metal nitride particles via chemical vapor deposition includes the following steps: The gradient porous carbon matrix inlaid with metal oxide@metal core-shell particles or metal nitride particles is first heated in a mixed atmosphere of reducing gas and inert gas; then CH4 and TEB gases are introduced for a second heating; finally, the mixture is switched to the mixed atmosphere of reducing gas and inert gas and cooled to room temperature to obtain the negative electrode composite material.

[0056] Furthermore, in the process of directly growing boron-doped graphene interface layer on a gradient porous carbon matrix inlaid with the metal oxide@metal core-shell particles or metal nitride particles by chemical vapor deposition, the reducing gas includes H2 and the inert gas includes argon.

[0057] And / or, in the process of directly growing boron-doped graphene interface layer on a gradient porous carbon matrix inlaid with the metal oxide@metal core-shell particles or metal nitride particles by chemical vapor deposition, the temperature of the first heating is 700-800℃ and the time of the first heating is 20-40min.

[0058] And / or, in the process of directly growing boron-doped graphene interface layer on a gradient porous carbon matrix embedded with metal oxide@metal core-shell particles or metal nitride particles by chemical vapor deposition, the temperature of the second heating is 700-800℃ and the time of the second heating is 30-60min.

[0059] And / or, in the process of directly growing a boron-doped graphene interface layer on a gradient porous carbon matrix inlaid with the metal oxide@metal core-shell particles or metal nitride particles by chemical vapor deposition, the flow rate of CH4 is 20-40 mL / min and the flow rate of TEB is 1-1.5 mL / min.

[0060] And / or, in the process of directly growing a boron-doped graphene interface layer on a gradient porous carbon matrix inlaid with the metal oxide@metal core-shell particles or metal nitride particles by chemical vapor deposition, the ratio of the flow rate of CH4 to the flow rate of TEB is (15-35):1.

[0061] Thirdly, the present invention provides a negative electrode sheet, the negative electrode sheet comprising the negative electrode composite material described in the first aspect or the negative electrode composite material prepared by the preparation method described in the second aspect.

[0062] Fourthly, the present invention provides a lithium-ion battery, the lithium-ion battery comprising the negative electrode composite material described in the first aspect, or the negative electrode composite material prepared by the preparation method described in the second aspect, or the negative electrode sheet described in the third aspect.

[0063] Compared with the prior art, the beneficial effects of the present invention include at least one of the following:

[0064] (1) The negative electrode composite material provided by the present invention has high discharge efficiency at low temperature by including a porous carbon matrix comprising macropores and mesopores from the inside to the surface, metal oxide@metal core-shell particles or metal nitride particles embedded in the carbon matrix, and a conductive material interface layer covering at least part of the outer surface of the matrix.

[0065] (2) The present invention can significantly improve the discharge capacity of lithium-ion batteries in low-temperature environments. Especially under low-temperature conditions such as -20℃ and -40℃, the battery can still maintain a high capacity and good discharge efficiency, effectively delaying capacity decay at low temperatures and extending the battery's service life. At the same time, the negative electrode material provided by the present invention has good cycle stability and low resistance.

[0066] (3) Through composite material design and surface modification, the internal resistance of the battery is effectively reduced, thereby improving the energy utilization rate of the battery at low temperatures.

[0067] (4) In this invention, the gradient porous carbon can buffer the volume expansion stress in layers, avoid the cracking of the SEI film caused by mechanical stress, reduce the risk of SEI film rupture, avoid safety hazards under low temperature conditions, and improve the overall safety of the battery; the metal oxide@metal core-shell particle or metal nitride particle embedded layer: inhibits the pulverization and agglomeration of metal oxide@metal core-shell particle or metal nitride particle, and reduces the SEI film reconstruction caused by exposure of active materials; the conductive material interface layer: regulates the uniformity of ion flow + mechanical constraint, and forms a thin and stable SEI film.

[0068] (5) In this invention, carbon nanotubes, graphene and other materials with stronger conductivity are introduced through composite design of negative electrode materials, which significantly improves the conductivity and lithium ion diffusion ability of the materials; surface modification technology, such as coating metal oxide@metal composite and nitride, is used to improve the stability of the materials and the electrochemical performance at low temperature; the microstructure of the negative electrode material is optimized to increase the specific surface area and adjust the particle morphology to promote fast charging and discharging at low temperature; the crystal structure of the negative electrode material is optimized through doping technology to improve its low temperature performance. Detailed Implementation

[0069] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Those skilled in the art should understand that the embodiments described are merely illustrative of the invention and should not be considered as specific limitations thereof. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. Process parameters in the following embodiments that do not specify specific conditions are generally based on conventional conditions, unless otherwise specified, indicating that all raw materials are commercially available or commonly used in this industry.

[0070] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0071] In a first aspect, the present invention provides a negative electrode composite material, the negative electrode composite material comprising:

[0072] Gradient porous carbon matrix: The gradient porous carbon matrix has a hierarchical pore structure, wherein the pores from the interior to the surface successively include macropores and mesopores; (the interior of the gradient porous carbon matrix has macropores, and the surface of the gradient porous carbon matrix has mesopores).

[0073] Metal oxide@metal core-shell particles or metal nitride particles: The metal oxide@metal core-shell particles or metal nitride particles are embedded in the gradient porous carbon matrix, wherein the metal includes at least one of Sn, V, Ti, and Co;

[0074] Conductive material interface layer: The conductive material interface layer is coated on at least a portion of the outer surface of the gradient porous carbon matrix inlaid with the metal oxide@metal core-shell particles or metal nitride particles.

[0075] The negative electrode composite material provided by this invention has a macroscopic structure of granules (functionalized microspheres).

[0076] The surface mesopores on a gradient porous carbon matrix can solve the problems of electrolyte wetting and lithium-ion distribution; the internal macropores can ensure high-speed lithium-ion transport in the bulk phase; and the gradient transition can achieve a path with minimized impedance. If the gradient porous carbon matrix only includes macropores, it will lead to poor electrolyte wetting, resulting in a "dry zone" and uncontrolled interfacial reactions that cause lithium dendrites; if it only includes mesopores, the nanopores will be prone to freezing and blockage, and the expansion stress will have nowhere to be released.

[0077] The negative electrode composite material provided by the present invention comprises a porous carbon matrix with macropores and mesopores sequentially from the inside to the surface, metal oxide@metal core-shell particles or metal nitride particles embedded in the carbon matrix, and a conductive material interface layer covering at least part of the outer surface of the matrix, which enables it to have high discharge efficiency at low temperature and effectively delay capacity decay at low temperature.

[0078] In the above-mentioned negative electrode composite material, as an optional embodiment, the pore size of the macropore is 50-150nm (for example, it can be 50nm, 60nm, 70nm, 80nm, 90nm, 100nm or 150nm), and the pore size of the mesopore is 5-15nm (for example, it can be 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 13nm or 15nm).

[0079] In the aforementioned negative electrode composite material, as an optional embodiment, the BET specific surface area of ​​the gradient porous carbon matrix is ​​700-900 m². 2 / g, for example, can be 700m 2 / g、720m 2 / g、740m 2 / g、780m 2 / g、800m 2 / g、820m 2 / g、840m 2 / g、860m 2 / g、880m 2 / g or 900m 2 / g.

[0080] In the above-mentioned negative electrode composite material, as an optional embodiment, the gradient porous carbon matrix includes a core layer with macropores and a shell layer with mesopores. The porosity of the core layer is 60-70%, for example, it can be 60%, 62%, 64%, 66%, 68% or 70%.

[0081] In the above-mentioned negative electrode composite material, as an optional embodiment, the metal oxide@metal core-shell particles or metal nitride particles are embedded in the pores and / or surface of the gradient porous carbon matrix.

[0082] In the aforementioned negative electrode composite material, as an optional embodiment, the metal oxide@metal core-shell particles include SnO2@Sn core-shell particles, and the metal nitride includes at least one of VN, TiN, and CoH3N, wherein the SnO2@Sn core-shell particles have Sn as the core layer and SnO2 as the shell layer. In this invention, replacing the SnO2@Sn core-shell particles with SnO2 particles will degrade the electrochemical performance, specifically in terms of initial efficiency, low-temperature performance, accelerated electrolyte decomposition, and reduced cycle life.

[0083] In the above-mentioned negative electrode composite material, as an optional embodiment, the D50 particle size of the metal oxide@metal core-shell particles or metal nitride particles is 15-25nm, for example, it can be 15nm, 17nm, 19nm, 21nm, 23nm or 25nm.

[0084] In the aforementioned negative electrode composite material, as an optional embodiment, the areal density of the metal oxide@metal core-shell particles or metal nitride particles is 8-12 mg / cm³. 2 For example, it can be 8 mg / cm², 9 mg / cm², 10 mg / cm², or 11 mg / cm². The areal density is the mass of the metal oxide@metal core-shell or metal nitride particles per unit actual surface area of ​​the carbon matrix. Excessive areal density can lead to uncontrolled volume expansion stress, ion transport blockage, and breakage of the conductive network; insufficient areal density can result in insufficient energy density, excessive exposure of the carbon matrix, and low utilization of gradient porosity.

[0085] In the above-mentioned negative electrode composite material, as an optional embodiment, the metal oxide@metal core-shell particles are obtained by depositing a metal source, glucose and a complexing agent on the gradient porous carbon matrix; or, the metal nitride particles are obtained by depositing a metal source and a nitrogen source on the gradient porous carbon matrix.

[0086] In the above-mentioned negative electrode composite material, as an optional embodiment, the conductive material interface layer includes at least one of carbon nanotubes and graphene, preferably graphene.

[0087] In the aforementioned negative electrode composite material, as an optional embodiment, the conductive material interface layer further includes a dopant element, which includes at least one of boron, nitrogen, and sulfur. The conductive material interface layer, by including the dopant element, has the following beneficial effects: 1. Electronic structure reconstruction: the dopant element becomes the acceptor level → raising the Fermi level → enhancing electron transition capability; 2. Optimization of ion transport kinetics: the interlayer spacing expansion effect prevents ion channels from freezing at low temperatures; 3. Inducing the electrolyte decomposition path to inorganic form.

[0088] In the aforementioned negative electrode composite material, as an optional embodiment, the content of doped elements in the conductive material interface layer is 1.2-1.8 at%, for example, it can be 1.2 at%, 1.4 at%, 1.6 at%, or 1.8 at%.

[0089] In the above-mentioned negative electrode composite material, as an optional embodiment, the number of conductive material interface layers is 2-3 layers.

[0090] In the above-mentioned negative electrode composite material, as an optional embodiment, the interlayer spacing of the conductive material interface layer is 0.42-0.48 nm, for example, it can be 0.42 nm, 0.44 nm, 0.46 nm or 0.48 nm.

[0091] In the aforementioned negative electrode composite material, as an optional embodiment, the coverage of the conductive material interface layer is >95%. Coverage = (Surface area of ​​the carbon matrix completely covered by the conductive material interface layer / Total surface area of ​​the carbon matrix) * 100%.

[0092] In the above-mentioned negative electrode composite material, as an optional embodiment, the mass of the gradient porous carbon matrix accounts for 50-70% of the mass of the negative electrode composite material (e.g., 50%, 55%, 60%, 65%, or 70%), the mass of the metal oxide@metal core-shell particles or metal nitride particles accounts for 20-40% of the mass of the negative electrode composite material (e.g., 20%, 25%, 30%, 35%, or 40%), and the mass of the conductive material interface layer accounts for 3%-10% of the mass of the negative electrode composite material (e.g., 3%, 5%, 7%, or 10%). Excessive porous carbon matrix leads to insufficient active material loading, decreased energy density, and low areal capacity. Insufficient matrix results in insufficient core strength, breakage during volume expansion, faster cycle decay, and increased internal resistance. Excessive metal oxide@metal core-shell particles or metal nitride particles cause expansion stress to exceed the yield strength of the carbon skeleton. After multiple cycles, cracks extend to the conductive material layer, increasing polarization voltage. Insufficient matrix prevents full utilization of internal macropores, resulting in decreased areal capacity. Excessive conductive material interface layer increases interlayer spacing, raises the ion diffusion barrier, and reduces rate charge retention. Insufficient matrix results in coverage <90%, a thicker SEI film, and lower initial efficiency.

[0093] In a second aspect, the present invention provides a method for preparing the negative electrode composite material as described in the first aspect, the method comprising the following steps:

[0094] S1. Preparation of gradient porous carbon matrix:

[0095] A carbon source, block copolymer, and pore expander are dissolved in a mixed solvent and stirred at high speed to form a composite micelle solution. Then, an alkaline catalyst is added to the composite micelle solution and stirring is continued to form a macroporous intermediate core (the intermediate core is a PDA (polydopamine) intermediate core). The carbon source includes a phenolic compound, the block copolymer includes hydrophobic and hydrophilic segments, and the pore expander is insoluble in water.

[0096] After low-speed stirring to form a core-shell mesoscopic structure, the material is then centrifuged and washed before being calcined at low temperature in air and then at high temperature in a protective gas atmosphere to obtain the gradient porous carbon matrix.

[0097] S2. Preparation of metal oxide@metal core-shell particles or metal nitride particle mosaic layers:

[0098] A metal source, glucose, and a complexing agent are deposited on the gradient porous carbon matrix to obtain a gradient porous carbon matrix inlaid with the metal oxide@metal core-shell particles; or, a metal source and a nitrogen source are deposited on the gradient porous carbon matrix to obtain a gradient porous carbon matrix inlaid with the metal nitride particles.

[0099] S3. Preparation of the conductive material interface layer:

[0100] A conductive material interface layer is directly grown on a gradient porous carbon matrix inlaid with metal oxide@metal core-shell particles or metal nitride particles by chemical vapor deposition.

[0101] In step S1, the low-temperature heat treatment in an air (oxygen) atmosphere causes a partial oxidative crosslinking reaction in the organic PDA polymer. This process improves the thermal stability of the material, helping to maintain its porous structure and morphology during subsequent calcination in an inert atmosphere at higher temperatures and preventing structural collapse. Simultaneously, it also partially burns away residual organic matter (such as incompletely decomposed F127), increasing the carbonization yield.

[0102] In the above-mentioned method for preparing the negative electrode composite material, as an optional embodiment, in step S1, the carbon source includes tannic acid.

[0103] In the above-mentioned method for preparing the negative electrode composite material, as an optional embodiment, in step S1, the block copolymer includes at least one of Pluronic F127 (polyoxyethylene-polyoxypropylene-polyoxyethylene (PEO-PPO-PEO)), Pluronic P123, Pluronic F108, Pluronic P103, and Pluronic F68.

[0104] In the above-mentioned method for preparing the negative electrode composite material, as an optional embodiment, in step S1, the pore-expanding agent includes mesitylene.

[0105] In the above-mentioned method for preparing negative electrode composite material, as an optional embodiment, in step S1, the mixed solvent includes ethanol and water, and the volume ratio of ethanol to water is 1:1-3:1, for example, it can be 1:1, 2:1 or 3:1.

[0106] In the above-mentioned method for preparing the negative electrode composite material, as an optional embodiment, in step S1, the content of the block copolymer in the composite micelle solution is 0.001-0.03 g / mL, for example, it can be 0.001 g / mL, 0.005 g / mL, 0.01 g / mL, 0.02 g / mL or 0.03 g / mL.

[0107] In the above-mentioned method for preparing the negative electrode composite material, as an optional embodiment, in step S1, the content of the carbon source in the composite micelle solution is 0.003 to 0.009 g / mL (for example, it can be 0.003 g / mL, 0.004 g / mL, 0.005 g / mL, 0.007 g / mL or 0.009 g / mL); the volume ratio of the pore-expanding agent to the mixed solvent is 1 to 3:100, for example, it can be 1:100, 2:100 or 3:100.

[0108] In the above-mentioned method for preparing negative electrode composite material, as an optional embodiment, in step S1, the high-speed stirring speed is 450-550 rpm (for example, it can be 450 rpm, 500 rpm or 550 rpm); the time is 20-40 min.

[0109] In the above-mentioned method for preparing the negative electrode composite material, as an optional embodiment, in step S1, the alkaline catalyst includes ammonia. The amount of the alkaline catalyst is determined based on stabilizing the pH of the reaction system between 8.0 and 9.5.

[0110] In the above-mentioned method for preparing the negative electrode composite material, as an optional embodiment, in step S1, the stirring time is 0.5-2h, for example, 0.5h, 1h, 1.5h or 2h.

[0111] In the above-mentioned method for preparing negative electrode composite material, as an optional embodiment, in step S1, the speed of the low-speed stirring is 250-350 rpm (for example, it can be 250 rpm, 270 rpm, 290 rpm, 310 rpm, 330 rpm or 350 rpm), and the time is 2-4 hours.

[0112] In the above-mentioned method for preparing the negative electrode composite material, as an optional embodiment, in step S1, the low-temperature calcination temperature is 280-320℃ (for example, it can be 280℃, 290℃, 300℃, 310℃, or 320℃), and the time is 2-4 hours. If the temperature is too low, the oxidative crosslinking reaction will be incomplete, and the violent shrinkage during high-temperature calcination will cause the pore structure to collapse, resulting in insufficient crosslinking of the polymer skeleton. If the temperature is too high, the mesopore walls will fuse, the macropore-mesopore gradient will disappear excessively, and the water-insoluble pore-expanding agent will decompose and deposit carbon at high temperatures, blocking the pores.

[0113] In the above-mentioned method for preparing the negative electrode composite material, as an optional embodiment, in step S1, the protective gas includes N2.

[0114] In the above-mentioned method for preparing the negative electrode composite material, as an optional embodiment, in step S1, the high-temperature calcination temperature is 850-950℃ (for example, 850℃, 870℃, 890℃, 910℃, 930℃, or 950℃), and the time is 1-3 hours. If the temperature is too low, the degree of graphitization will be insufficient, the pore structure will not be stable, and the electrochemical performance will be affected; if the temperature is too high, the pore structure will collapse, the mesopore walls will shrink due to graphitization, the gradient pores will be destroyed, the active sites will be lost, and the energy consumption and cost will increase.

[0115] In the above-mentioned method for preparing the negative electrode composite material, as an optional embodiment, the metal oxide@metal core-shell particle mosaic layer includes a SnO2@Sn core-shell particle mosaic layer, and the deposition reaction of the metal source, glucose, and complexing agent on the gradient porous carbon matrix includes the following steps:

[0116] The tin source and glucose were mixed in a solvent in the presence of a complexing agent to obtain a precursor solution.

[0117] The gradient porous carbon matrix is ​​added to the precursor solution and reacted under heating conditions to obtain a gradient porous carbon matrix embedded with SnO2@Sn core-shell particles.

[0118] In the negative electrode material provided by this invention, a cascaded conductive network is formed by carbon matrix → SnO2 shell → Sn core, thereby optimizing electron transport.

[0119] In this invention, when preparing a gradient porous carbon matrix inlaid with SnO2@Sn core-shell particles, the following effects will occur if a complexing agent is not added: uncontrolled SnO2@Sn particle morphology: Sn core size increases significantly (possibly reaching 50-100 nm or even larger); particles severely agglomerate, losing nanoscale dispersion; unable to form a uniform SnO2 shell coating (insufficient oxidation or uneven thickness); gradient porous carbon matrix loading failure: the precursor only adheres to the carbon matrix surface and cannot effectively fill macropores and mesopores; the inlay areal density decreases sharply (possibly <1 mg / cm2); the contact area between the active material (SnO2@Sn) and the carbon matrix decreases, and the electrochemical performance deteriorates.

[0120] Compared to direct deposition on a porous carbon matrix, synthesizing SnO2@Sn core-shell particles first and then mixing them with a porous carbon matrix has the following effects: uncontrollable particle distribution and size: the distribution and size of particles cannot be restricted by the pore size of the porous matrix, resulting in a significant increase in particle size and severe particle agglomeration; pore blockage blocking ion transport and hindering charge transport; uncontrolled volume expansion; weakened interface protection; and overall degradation of electrical properties.

[0121] In the above-mentioned method for preparing the negative electrode composite material, as an optional embodiment, in the step of mixing the tin source and glucose in a solvent in the presence of a complexing agent, the tin source includes at least one of tetraethyltin, stannous sulfate, tin acetate and nano-tin powder, and the complexing agent includes at least one of sodium citrate, sodium tartrate and sodium gluconate.

[0122] In the above-mentioned method for preparing the negative electrode composite material, as an optional embodiment, in the step of mixing the tin source and glucose in a solvent in which the complexing agent is present, the molar ratio of tin element in the tin source, glucose and the complexing agent is 1:(2-3):(0.1-0.2).

[0123] In the above-mentioned method for preparing the negative electrode composite material, as an optional embodiment, in the step of mixing the tin source and glucose in a solvent in which the complexing agent is present, the tin source is added as an ethanol solution of the tin source, the glucose is added as an ethanol solution of glucose, and the complexing agent is added as an aqueous solution of the complexing agent.

[0124] In the above-mentioned method for preparing the negative electrode composite material, as an optional embodiment, the ratio of the amount of tin element in the tin source to the mass of the gradient porous carbon matrix is ​​1:(300-500)mol / g, for example, it can be 1:300mol / g, 1:320mol / g, 1:340mol / g, 1:360mol / g, 1:380mol / g, 1:400mol / g, 1:450mol / g or 1:500mol / g.

[0125] In the above-mentioned method for preparing the negative electrode composite material, as an optional embodiment, the reaction under heating conditions to obtain a gradient porous carbon matrix embedded with SnO2@Sn core-shell particles includes: performing the reaction using a microwave deposition method under argon protection throughout the process; firstly, within 1-4 minutes (e.g., 1 minute, 2 minutes, 3 minutes, or 4 minutes), linearly increasing the microwave power from 0W to 500-1000W (e.g., 500W, 550W, 600W, 650W, 700W, 750W, 800W, 900W, or 1000W), while simultaneously monitoring the temperature rise from 25℃ to 55-65℃ (e.g., 55℃, 60℃, or 65℃), to promote the rapid penetration of the precursor solution into the macropores and mesopores of the gradient porous carbon matrix; then, at 500-1000W (e.g., 500W, 2 minutes, 3 minutes, or 4 minutes), linearly increasing the microwave power from 0W to 500-1000W (e.g., 500W, 550W, 60℃, or 1000W), while simultaneously monitoring the temperature rise from 25℃ to 55-65℃ (e.g., 55℃, 60℃, or 65℃), promoting the rapid penetration of the precursor solution into the macropores and mesopores of the gradient porous carbon matrix; subsequently, at 500-1000W (e.g., 500W, 2 minutes, 3 minutes, or 4 minutes), linearly increasing the microwave power from 0W to ... A reduction deposition process is performed at 500W, 550W, 600W, 650W, 700W, 750W, 800W, 900W, or 1000W) and 70-95℃ (e.g., 70℃, 75℃, 80℃, 85℃, 90℃, or 95℃) for 10-30 minutes (e.g., 10 minutes, 12 minutes, 14 minutes, 16 minutes, 18 minutes, 20 minutes, 25 minutes, or 30 minutes) to form Sn cores on the gradient porous carbon matrix. Finally, the microwave power is linearly reduced from 500-1000W to 100-300W (e.g., 100W, 150W, 200W, 250W, or 300W) over 2-6 minutes (e.g., 2 minutes, 3 minutes, 4 minutes, 5 minutes, or 6 minutes) to achieve directional coating of the SnO2 shell on the Sn core surface. This invention avoids steam blockage at the orifice caused by a sudden increase in power by gradually increasing the power, and inhibits particle agglomeration by gradually decreasing the power.

[0126] In this invention, the SnO2 shell is formed during the final cooling stage by a controlled oxidation reaction between newly generated, highly reactive Sn nuclei and dissolved oxygen (or adsorbed oxygen) in the system. The main source of dissolved oxygen is the trace amount of oxygen initially dissolved in the precursor solution. The role of argon protection is to prevent oxygen from the external atmosphere from entering the reaction system to replenish oxygen, thereby controlling the degree of oxidation and achieving directional coating to form the SnO2 shell, rather than completely oxidizing the Sn nuclei into SnO2.

[0127] In the above-mentioned method for preparing the negative electrode composite material, as an optional embodiment, the conductive material interface layer includes a boron-doped graphene interface layer. The step of directly growing the conductive material interface layer on a gradient porous carbon matrix inlaid with metal oxide@metal core-shell particles or metal nitride particles via chemical vapor deposition includes directly growing the boron-doped graphene interface layer on the gradient porous carbon matrix inlaid with metal oxide@metal core-shell particles or metal nitride particles via chemical vapor deposition. This step includes the following steps: The gradient porous carbon matrix inlaid with metal oxide@metal core-shell particles or metal nitride particles is first heated in a mixed atmosphere of reducing gas and inert gas; then CH4 and TEB (triethylboron) gas are introduced for a second heating; finally, the mixture is switched to a mixed atmosphere of reducing gas and inert gas and cooled to room temperature in the mixed atmosphere of reducing gas and inert gas to obtain the negative electrode composite material.

[0128] In the above-mentioned method for preparing the negative electrode composite material, as an optional embodiment, in the process of directly growing a boron-doped graphene interface layer on a gradient porous carbon matrix inlaid with the metal oxide@metal core-shell particles or metal nitride particles by chemical vapor deposition, the reducing gas includes H2 and the inert gas includes argon.

[0129] In the above-mentioned method for preparing the negative electrode composite material, as an optional embodiment, during the direct growth of a boron-doped graphene interface layer onto a gradient porous carbon matrix embedded with metal oxide@metal core-shell particles or metal nitride particles via chemical vapor deposition, the temperature of the first heating is 700-800℃ (e.g., 700℃, 720℃, 740℃, 760℃, 780℃, or 800℃), and the duration of the first heating is 20-40 min (e.g., 20 min, 25 min, 30 min, 35 min, or 40 min). During the first heating process, H2 reduces oxygen-containing functional groups (such as -COOH, -OH) on the surface of the carbon matrix, which can clean the surface and enhance the adhesion of subsequent carbon deposition.

[0130] In the above-mentioned method for preparing the negative electrode composite material, as an optional embodiment, during the process of directly growing a boron-doped graphene interface layer on a gradient porous carbon matrix inlaid with metal oxide@metal core-shell particles or metal nitride particles by chemical vapor deposition, the temperature of the second heating is 700-800℃ (for example, it can be 700℃, 720℃, 740℃, 760℃, 780℃ or 800℃), and the time of the second heating is 30-60min, for example, it can be 30min, 40min, 50min or 60min.

[0131] In the above-mentioned method for preparing the negative electrode composite material, as an optional embodiment, during the process of directly growing a boron-doped graphene interface layer on a gradient porous carbon matrix inlaid with the metal oxide@metal core-shell particles or metal nitride particles by chemical vapor deposition, the flow rate of CH4 is 20-40 mL / min (for example, it can be 20 mL / min, 25 mL / min, 30 mL / min, 35 mL / min or 40 mL / min), and the flow rate of TEB is 1-1.5 mL / min.

[0132] In the above-mentioned method for preparing the negative electrode composite material, as an optional embodiment, during the process of directly growing a boron-doped graphene interface layer on a gradient porous carbon matrix inlaid with metal oxide@metal core-shell particles or metal nitride particles by chemical vapor deposition, the ratio of the flow rate of CH4 to the flow rate of TEB is (15-35):1, for example, it can be 15:1, 20:1, 25:1, 30:1 or 35:1.

[0133] Thirdly, the present invention provides a negative electrode sheet, the negative electrode sheet comprising the negative electrode composite material described in the first aspect or the negative electrode composite material prepared by the preparation method described in the second aspect.

[0134] Fourthly, the present invention provides a lithium-ion battery, the lithium-ion battery comprising the negative electrode composite material described in the first aspect, or the negative electrode composite material prepared by the preparation method described in the second aspect, or the negative electrode sheet described in the third aspect.

[0135] The present invention will now be described in further detail with reference to specific embodiments and comparative examples.

[0136] Example 1

[0137] The method for preparing the negative electrode composite material provided in this embodiment includes the following steps:

[0138] 1. Preparation of gradient porous carbon matrix:

[0139] 0.10 g of tannic acid (TA), 0.20 g of polyether block copolymer (Pluronic F127), 0.18 mL of mesitylene (TMB), 8 mL of water, and 10 mL of ethanol were mixed and stirred at 500 rpm for 30 min to form F127 / TMB / TA composite micelles. Then, 1 mL of 1 mol / L NH4OH solution was added, and stirring continued for 1 h to form a macroporous PDA core. Subsequently, the stirring speed was reduced to 300 rpm, and stirring continued for 3 h to form smaller composite micelles, forming a core-shell mesoscopic structure. The product was then collected by centrifugation, washed three times each with ethanol and water, and calcined at 300 °C in air for 3 h, followed by calcination at 900 °C in N2 atmosphere for 2 h to obtain a gradient porous carbon matrix with a core-shell structure. The matrix has a hierarchical pore structure, which includes macropores and mesopores sequentially from the interior to the surface. The macropores have a diameter of 50-100 nm, and the mesopores have a diameter of 5-10 nm. The BET specific surface area of ​​the gradient porous carbon matrix is ​​850 m². 2 / g. The gradient porous carbon matrix comprises a core layer with macropores and a shell layer with mesopores, the porosity of which is 65%.

[0140] 2. SnO2@Sn core-shell particle mosaic layer:

[0141] First, the precursor solution was synthesized: 50 mL of 0.3 mol / L tetraethyltin ethanol solution was mixed with 75 mL of 0.5 mol / L glucose ethanol solution, and then 10 mL of 0.2 mol / L sodium citrate aqueous solution was added. The mixture was stirred by ultrasonication until the solution became transparent, thus obtaining the precursor solution.

[0142] Microwave deposition reaction: 5g of gradient porous carbon matrix was added to the precursor solution, and the reaction was carried out using microwave deposition under argon protection. First, the microwave power was linearly increased from 0W to 750W within 2 minutes, while the temperature was simultaneously monitored and increased from 25℃ to 60℃, promoting rapid penetration of the precursor solution into the macropores and mesopores of the gradient porous carbon matrix. Then, reduction deposition was performed at 750W and 85℃ for 15 minutes to form Sn cores on the gradient porous carbon matrix. Finally, the microwave power was linearly reduced from 750W to 200W within 3 minutes to achieve directional coating of the SnO2 shell on the Sn core surface. The matrix was then removed, centrifuged, and washed (three times each with ethanol and water) to obtain a gradient porous carbon matrix with embedded SnO2@Sn core-shell particles. The D50 particle size of the SnO2@Sn core-shell particles was 18nm, and the areal density of the SnO2@Sn core-shell particles was 10mg / cm³. 2 .

[0143] 3. Boron-doped graphene interface layer:

[0144] Gradient porous carbon embedded with SnO2@Sn core-shell particles was heated in a tube furnace to 750°C at a rate of 15°C / min, and then heated for 30 min in an H2 / Ar (volume ratio 1:1) mixed gas atmosphere for surface activation. Subsequently, CH4 (flow rate 30 mL / min) and TEB gas (flow rate 1.25 mL / min) were introduced, and the temperature was maintained at 750°C for 45 min. Finally, the gas was switched to an H2 / Ar mixed gas atmosphere and cooled to room temperature to obtain tin / boron-doped graphene@gradient porous carbon. In the boron-doped graphene interface layer, the boron content was 1.6 at%. In this embodiment, the boron-doped graphene interface layer consisted of two layers with an interlayer spacing of 0.46 nm and a coverage of 96.5%.

[0145] In the negative electrode composite material prepared in this embodiment, the mass of the gradient porous carbon matrix accounts for 65% of the mass of the negative electrode composite material, the mass of the SnO2@Sn core-shell particles accounts for 30% of the mass of the negative electrode composite material, and the mass of the boron-doped graphene interface layer accounts for 5% of the mass of the negative electrode composite material.

[0146] Example 2

[0147] The preparation method of the negative electrode composite material provided in this embodiment is basically the same as that in Example 1, except that the boron-doped graphene interface layer in step 3 is modified as follows: (a) impregnate the gradient porous carbon embedded with SnO2@Sn core-shell particles in an ethanol solution of ferric nitrate, dry it, and then load the catalyst; (b) introduce acetylene (flow rate of 30 mL / min), nitrogen (10 mL / min), and hydrogen (20 mL / min) into a plasma-enhanced CVD reactor and grow it at 650 °C for 15 minutes; (c) remove the catalyst residue by acid washing to obtain the nitrogen-doped carbon nanotube interface layer; the coverage of the nitrogen-doped carbon nanotube interface layer is 94.3%.

[0148] Example 3

[0149] The preparation method of the negative electrode composite material provided in this embodiment is basically the same as that in Example 1, except that the second step of SnO2@Sn core-shell particle mosaic layer is modified as follows: (a) impregnate the carbon matrix with a precursor solution containing 0.1 mol / L ammonia metavanadate and 0.80 mol / L urea; (b) generate an intermediate through hydrothermal reaction at a reaction temperature of 180°C for 8 hours; (c) nitrid at 400°C for 2.5 hours in an ammonia atmosphere to generate VN particles with a D50 particle size of 25 nm and a mosaic surface density of 8 mg / cm³. 2 .

[0150] Example 4

[0151] The preparation method of the negative electrode composite material provided in this embodiment is basically the same as that in Example 1, except that in step 1, the amount of mesitylene is 0.54 mL, the high-speed stirring speed is 550 rpm, 3 mL of 1 mol / L NH4OH solution (ammonia water) is added, the stirring time after adding ammonia water is 2 h, the high-temperature calcination temperature is 850℃, the pore size of the macropores in the porous carbon matrix is ​​80-150 nm, and the pore size of the mesopores is 6-12 nm. The BET specific surface area of ​​the gradient porous carbon matrix is ​​782 m². 2 / g. The gradient porous carbon matrix comprises a core layer with macropores and a shell layer with mesopores, the porosity of the core layer being 70%.

[0152] In step 2: the mass of the gradient porous carbon matrix is ​​7g. The microwave deposition method includes: first, within 3 minutes, the microwave power is linearly increased from 0W to 900W, while simultaneously monitoring the temperature increase from 25℃ to 65℃, to promote the rapid penetration of the precursor solution into the macropores and mesopores of the gradient porous carbon matrix; then, reduction deposition is performed at 900W and 90℃ for 10 minutes to form Sn cores on the gradient porous carbon matrix; finally, within 4 minutes, the microwave power is linearly reduced from 900W to 300W to achieve directional coating of the SnO2 shell on the Sn core surface. The D50 particle size of the SnO2@Sn core-shell particles is 22nm, and the mosaic areal density of the SnO2@Sn core-shell particles is 9mg / cm³. 2 .

[0153] In step 3: the flow rate of CH4 is 20 mL / min. The boron-doped graphene interface layer prepared in this embodiment consists of two layers. The interlayer spacing of the boron-doped graphene interface layer is 0.46 nm. The coverage of the boron-doped graphene interface layer is 95.2%.

[0154] In the negative electrode composite material prepared in this embodiment, the mass of the gradient porous carbon matrix accounts for 69.5% of the mass of the negative electrode composite material, the mass of the SnO2@Sn core-shell particles accounts for 27.5% of the mass of the negative electrode composite material, and the mass of the boron-doped graphene interface layer accounts for 3% of the mass of the negative electrode composite material.

[0155] Comparative Example 1

[0156] The preparation method of the negative electrode composite material (gradient porous carbon matrix with embedded SnO2@Sn core-shell particles) provided in this comparative example is basically the same as that in Example 1, except that step 3 is not included.

[0157] Comparative Example 2

[0158] The preparation method of the negative electrode composite material (boron-doped graphene@gradient porous carbon) provided in this comparative example is basically the same as that in Example 1, except that step 2 is not included.

[0159] Comparative Example 3

[0160] The negative electrode material provided in this comparative example is a commercially available conventional graphite negative electrode.

[0161] Comparative Example 4

[0162] The preparation method of the negative electrode composite material provided in this comparative example is basically the same as that in Example 1, except that step 1 is different. The purpose is to obtain a porous carbon matrix with macropores on the surface and mesopores inside. Specifically, it includes: mixing 0.10 g of tannic acid (TA), 0.20 g of polyether block copolymer (Pluronic F127), 8 mL of water and 10 mL of ethanol, and stirring at 300 rpm for 30 min to form F127 / TA composite micelles. Then, 1 mL of 1 mol / L NH4OH solution is added, and stirring is continued for 1 h. Then, 0.18 mL of mesitylene (TMB) is added, and the stirring speed is increased to 500 rpm, and stirring is continued for 3 h to form large composite micelles, forming a core-shell mesoscopic structure. The product is then collected by centrifugation, washed three times each with ethanol and water, calcined at 300 °C in air for 3 h, and then calcined at 900 °C in N2 atmosphere for 2 h to obtain a gradient porous carbon matrix with a core-shell structure. The gradient porous carbon matrix comprises a core layer with mesopores and a shell layer with macropores.

[0163] Comparative Example 5

[0164] The preparation method of the negative electrode composite material provided in this comparative example is basically the same as that in Example 1, except that in step 2, SnO2@Sn core-shell particles are synthesized first and then mixed with a porous carbon matrix. Specifically, this includes: firstly, synthesizing a precursor solution: mixing 50 mL of 0.3 mol / L tetraethyltin ethanol solution with 75 mL of 0.5 mol / L glucose ethanol solution, and then adding 10 mL of... A 0.2 mol / L sodium citrate aqueous solution was continuously ultrasonically stirred until the solution became transparent to obtain a precursor solution. The reaction was carried out using microwave heating under argon protection throughout. First, the microwave power was linearly increased from 0 W to 750 W within 2 minutes, while the temperature was monitored as it rose from 25℃ to 60℃. Then, a reduction reaction was carried out at 750 W and 85℃ for 15 minutes. Finally, the microwave power was linearly reduced from 750 W to 200 W within 3 minutes to achieve directional coating of the SnO2 shell onto the Sn core surface. The SnO2@Sn core-shell particles were then removed, centrifuged, and washed (three times each with ethanol and water) to obtain SnO2@Sn core-shell particles. 5 g of gradient porous carbon matrix was added to water and, after thorough dispersion, the SnO2@Sn core-shell particles were dispersed in the gradient porous carbon matrix aqueous solution and stirred at 800 rpm for 30 minutes. After centrifugation and drying, a gradient porous carbon matrix embedded with SnO2@Sn core-shell particles was obtained.

[0165] Performance testing

[0166] Assembly and testing of lithium-ion batteries:

[0167] Lithium iron phosphate, SP conductive agent and PVDF were mixed in a mass ratio of 97:1:2 to prepare a positive electrode slurry. The positive electrode slurry was then uniformly coated onto carbon-coated aluminum foil using a transfer coating machine to obtain a positive electrode sheet.

[0168] The negative electrode material, SP conductive agent, CMC and SBR prepared in the examples or comparative examples are mixed in a mass ratio of 95.5:1:1.5:2.0 to prepare a negative electrode slurry. The negative electrode slurry is then uniformly coated on copper foil using a transfer coating machine to obtain a negative electrode sheet.

[0169] A lithium-ion battery is assembled from components such as the negative electrode, positive electrode, electrolyte, and separator using conventional methods.

[0170] The assembled lithium-ion batteries were subjected to charge-discharge cycle tests to evaluate their low-temperature discharge performance, cycle stability, and DCR.

[0171] The DCR test method is as follows: 1) Let stand at 25℃ for 30 min; 2) Discharge at 0.5C constant current to 2.5V (time limit 2.5h); 3) Let stand for 30 min; 4) Charge at 0.5C constant current and constant voltage to 3.65V, cutoff current 0.05C (time limit 2.5h); 5) Let stand for 30 min; 6) Discharge at 0.5C constant current to 2.5V, record the discharge capacity as C0 (time limit 2.5h); 7) Let stand for 30 min; 8) Charge at 0.5C constant current and constant voltage to 3.65V, cutoff current 0.05C (time limit 2.5h); 9) Set aside for 2 hours; 10) Discharge at 2C constant current for 30 seconds, and record the discharge capacity as C1 (sampling interval 0.1s); 11) Set aside for 30 minutes; 12) Adjust the SOC state by 0.5C constant current discharge (adjust the capacity to 50% SOC (discharge capacity 0.2*C0-C1)); 13) Set aside for 2 hours, and record the end voltage U1; 14) Discharge at 2C for 30 seconds, and record the discharge capacity as C1 (sampling interval 0.1s), and record the end voltage U2. DCR=(U1-U2) / 2C.

[0172] The -20℃ low-temperature discharge test method and calculation method are as follows: 1) Place at 25℃ for 2 hours; 2) Discharge at a constant current of 1C to 2.5V (time limit 1.5 hours); 3) Place for 30 minutes; 4) Charge at a constant current and voltage of 0.5C to 3.65V, with a cutoff current of 0.05C (time limit 2.5 hours); 5) Place for 30 minutes; 6) Discharge at a constant current of 1C to 2.5V (time limit 1.5 hours); 7) Place for 30 minutes; 8) Repeat steps 4) to 7) 3 times, and use the average discharge capacity of the 3 times as the initial capacity C0; 9) Charge at a constant current and voltage of 0.5C to 3.65V, with a cutoff current of 0.05C (time limit 2.5 hours); 10) Adjust the temperature to -20℃; 11) Place for 24 hours; 12) Discharge at a constant current of 0.33C to 2.5V (time limit 1.5 hours), and record the discharge capacity C1; 23) End. Discharge efficiency at -20℃ = -20℃ discharge capacity C1 / 25℃ discharge capacity C0 * 100%.

[0173] The 500-cycle capacity retention test method is as follows: (1) rest at 25℃±2℃ for 120 min; (2) charge to 3.65V with 1 / 3C CCCV (constant current constant voltage) and cut-off current of 0.05C; (3) charge at 1 / 3C (4) Discharge CC (constant current) to 2.5V, (5) Let stand for 30 minutes, (6) Repeat steps 2-4 for two weeks, (7) Charge 1 / 3C constant current and constant voltage to 3.65V, cut-off current 0.05C, (8) Let stand for 30 minutes; (9) Discharge 1 / 3C constant current to 2.5V, (10) Let stand for 30 minutes; (11) Record the capacity as C0, and the capacity is corrected every 100 cycles); (12) Charge 3C0 constant current and constant voltage to 3.65V, cut-off current 0.05C0; let stand for 30 minutes; (13) Discharge 1C0 constant current to 2.5V; let stand for 30 minutes; (14) Repeat steps 10-11 for 100 cycles, (15) Let stand for 24 hours, (16) Repeat steps 6-13 until 500 cycles are completed and the discharge capacity of the 500th cycle / the discharge capacity of the 1st cycle is the capacity retention rate of the 500th cycle.

[0174] The test results are shown in Table 1.

[0175] Table 1

[0176]

[0177]

[0178] At least the following points can be observed from Table 1:

[0179] (1) Comparing Examples 1-4 with Comparative Examples 1-3, it can be seen that the negative electrode composite material provided by the present invention, through a porous carbon matrix comprising macropores and mesopores sequentially from the inside to the surface, metal oxide@metal core-shell particles or metal nitride particles embedded in the carbon matrix, and a conductive material interface layer covering at least part of the outer surface of the matrix, results in high discharge efficiency at low temperatures and significantly better low-temperature performance than conventional graphite materials. In addition, the negative electrode material provided by the present invention has low resistance and high cycle stability.

[0180] (2) Comparing Example 1 with Comparative Example 4, it can be seen that when the surface of the porous carbon matrix is ​​distributed with macropores and the interior with mesopores, the discharge efficiency at low temperature is significantly reduced, while the resistance increases and the cycle stability decreases. The applicant speculates that the reason may be that if the surface is macropores and the interior is mesopores, the following effects will occur: the electrolyte wetting effect will be worse; the ion transport path will be blocked; the volume will expand, thus causing structural damage; and the SEI film formation will be out of control.

[0181] (3) Comparing Example 1 with Comparative Example 5, it can be seen that when SnO2@Sn core-shell particles are synthesized first and then mixed with a porous carbon matrix, the discharge efficiency at low temperature is significantly reduced, while the resistance increases and the cycle stability decreases. The applicant speculates that the reason may be that in Comparative Example 5, the distribution and size of SnO2@Sn core-shell particles cannot be restricted by the pore size of the porous matrix, resulting in a significant increase in particle size and severe particle aggregation; the pores are blocked, blocking ion transport and hindering charge transport; volume expansion is out of control; and interface protection is weakened.

[0182] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A negative electrode composite material, characterized in that, The negative electrode composite material includes: Gradient porous carbon matrix: The gradient porous carbon matrix has a multi-level pore structure, wherein the multi-level... The pore structure, from the inside to the surface, includes macropores and mesopores in sequence; Metal oxide@metal core-shell particles or metal nitride particles: The metal oxide@metal core-shell particles or metal nitride particles are embedded in the gradient porous carbon matrix, wherein the metal includes at least one of Sn, V, Ti, and Co; Conductive material interface layer: The conductive material interface layer is coated on at least a portion of the outer surface of the gradient porous carbon matrix inlaid with the metal oxide@metal core-shell particles or metal nitride particles; The macropores have a diameter of 50-150 nm, and the mesopores have a diameter of 5-15 nm. The gradient porous carbon matrix comprises a core layer with macropores and a shell layer with mesopores, wherein the porosity of the core layer is 60-70%. The metal nitride is at least one of VN, TiN, and CoH3N; The metal oxide@metal core-shell particles are obtained by depositing a metal source, glucose, and a complexing agent onto a gradient porous carbon matrix; or, the metal nitride particles are obtained by depositing a metal source and a nitrogen source onto a gradient porous carbon matrix. The conductive material interface layer includes at least one of carbon nanotubes and graphene.

2. The negative electrode composite material according to claim 1, characterized in that, The gradient porous carbon matrix has a BET specific surface area of ​​700-900 m². 2 / g; And / or, the metal oxide@metal core-shell particles or metal nitride particles are embedded in the pores and / or surface of the gradient porous carbon matrix; And / or, the metal oxide@metal core-shell particles include SnO2@Sn core-shell particles, wherein the SnO2@Sn core-shell particles have Sn as the core layer and SnO2 as the shell layer; And / or, the D50 particle size of the metal oxide@metal core-shell particles or metal nitride particles is 15-25 nm; And / or, the areal density of the metal oxide@metal core-shell particles or metal nitride particles is 8-12 mg / cm³. 2 ; And / or, the conductive material interface layer further includes a doping element, wherein the doping element includes at least one of boron, nitrogen, and sulfur; And / or, in the conductive material interface layer, the content of doped elements is 1.2-1.8 at%; And / or, the conductive material interface layer has 2-3 layers; And / or, the interlayer spacing of the conductive material interface layer is 0.42-0.48 nm; And / or, the coverage of the conductive material interface layer is >95%; And / or, in the negative electrode composite material, the mass of the gradient porous carbon matrix accounts for 50-70% of the mass of the negative electrode composite material, the mass of the metal oxide@metal core-shell particles or metal nitride particles accounts for 20-40% of the mass of the negative electrode composite material, and the mass of the conductive material interface layer accounts for 3%-10% of the mass of the negative electrode composite material.

3. A method for preparing the negative electrode composite material as described in claim 1 or 2, characterized in that, The preparation method includes the following steps: S1. Preparation of gradient porous carbon matrix: A carbon source, a block copolymer, and a pore-expanding agent are dissolved in a mixed solvent and stirred at high speed to form a composite micelle solution. Then, an alkaline catalyst is added to the composite micelle solution and stirring is continued to form an intermediate core with macropores. The carbon source includes a phenolic compound, the block copolymer includes a hydrophobic segment and a hydrophilic segment, and the pore-expanding agent is insoluble in water. After low-speed stirring to form a core-shell mesoscopic structure, the material is then centrifuged and washed before being calcined at low temperature in air and then at high temperature in a protective gas atmosphere to obtain the gradient porous carbon matrix. S2. Preparation of metal oxide@metal core-shell particles or metal nitride particle mosaic layers: A metal source, glucose, and a complexing agent are deposited on the gradient porous carbon matrix to obtain a gradient porous carbon matrix inlaid with the metal oxide@metal core-shell particles; or, a metal source and a nitrogen source are deposited on the gradient porous carbon matrix to obtain a gradient porous carbon matrix inlaid with the metal nitride particles. S3. Preparation of the conductive material interface layer: A conductive material interface layer is directly grown on a gradient porous carbon matrix inlaid with metal oxide@metal core-shell particles or metal nitride particles by chemical vapor deposition.

4. The method for preparing the negative electrode composite material according to claim 3, characterized in that, In step S1, the carbon source includes tannic acid; And / or, in step S1, the block copolymer includes at least one of Pluronic F127, Pluronic P123, Pluronic F108, Pluronic P103, and Pluronic F68; And / or, in step S1, the pore-expanding agent includes mesitylene; And / or, in step S1, the mixed solvent includes ethanol and water, wherein the volume ratio of ethanol to water is 1:1 to 3:1; And / or, in step S1, the content of the block copolymer in the composite micelle solution is 0.001-0.03 g / mL; And / or, in step S1, the content of the carbon source in the composite micelle solution is 0.003~0.009 g / mL; the volume ratio of the pore-expanding agent to the mixed solvent is 1~3:100; And / or, in step S1, the high-speed stirring speed is 450-550 rpm; the time is 20-40 min; And / or, in step S1, the alkaline catalyst comprises ammonia; And / or, in step S1, the stirring time continues for 0.5-2 hours; And / or, in step S1, the low-speed stirring speed is 250-350 rpm, and the time is 2-4 h; And / or, in step S1, the low-temperature calcination temperature is 280-320℃ and the time is 2-4h; And / or, in step S1, the protective gas includes N2; And / or, in step S1, the high-temperature calcination temperature is 850-950℃ and the time is 1-3h.

5. The method for preparing the negative electrode composite material according to claim 3, characterized in that, The The metal oxide@metal core-shell particle mosaic layer includes a SnO2@Sn core-shell particle mosaic layer. The deposition reaction of the metal source, glucose, and complexing agent on the gradient porous carbon matrix includes the following steps: The tin source and glucose were mixed in a solvent in the presence of a complexing agent to obtain a precursor solution. The gradient porous carbon matrix is ​​added to the precursor solution and reacted under heating conditions to obtain a gradient porous carbon matrix embedded with SnO2@Sn core-shell particles.

6. The method for preparing the negative electrode composite material according to claim 5, characterized in that, In the step of mixing a tin source and glucose in a solvent in the presence of a complexing agent, the tin source includes at least one of tetraethyltin, stannous sulfate, tin acetate, and nano-tin powder, and the complexing agent includes at least one of sodium citrate, sodium tartrate, and sodium gluconate. And / or, in the step of mixing the tin source and glucose in a solvent in the presence of the complexing agent, the molar ratio of tin element in the tin source, glucose and the complexing agent is 1:(2-3):(0.1-0.2). And / or, in the step of mixing the tin source and glucose in a solvent in the presence of the complexing agent, the tin source is added as an ethanol solution of the tin source, the glucose is added as an ethanol solution of glucose, and the complexing agent is added as an aqueous solution of the complexing agent; And / or, the ratio of the amount of tin in the tin source to the mass of the gradient porous carbon matrix is ​​1:(300-500)mol / g; And / or, the reaction under heating conditions to obtain a gradient porous carbon matrix embedded with SnO2@Sn core-shell particles includes: performing the reaction using microwave deposition under argon protection throughout; firstly, within 1-4 minutes, linearly increasing the microwave power from 0 W to 500-1000 W while simultaneously monitoring the temperature rise from 25°C to 55-65°C, to promote the penetration of the precursor solution into the macropores and mesopores of the gradient porous carbon matrix; then, performing reduction deposition at 500-1000 W and 70-95°C for 10-30 minutes to form Sn cores on the gradient porous carbon matrix; finally, within 2-6 minutes, linearly decreasing the microwave power from 500-1000 W to 100-300 W to achieve directional coating of the SnO2 shell on the surface of the Sn cores.

7. The method for preparing the negative electrode composite material according to claim 3, characterized in that, The conductive material interface layer includes a boron-doped graphene interface layer. The direct growth of the conductive material interface layer onto a gradient porous carbon matrix inlaid with metal oxide@metal core-shell particles or metal nitride particles via chemical vapor deposition includes the following steps: The gradient porous carbon matrix inlaid with metal oxide@metal core-shell particles or metal nitride particles is first heated in a mixed atmosphere of reducing gas and inert gas; then CH4 and TEB gases are introduced for a second heating; finally, the mixture is switched to the mixed atmosphere of reducing gas and inert gas and cooled to room temperature to obtain the negative electrode composite material.

8. The method for preparing the negative electrode composite material according to claim 7, characterized in that, In the process of directly growing boron-doped graphene interface layer on a gradient porous carbon matrix inlaid with metal oxide@metal core-shell particles or metal nitride particles by chemical vapor deposition, the reducing gas includes H2 and the inert gas includes argon. And / or, in the process of directly growing boron-doped graphene interface layer on a gradient porous carbon matrix inlaid with the metal oxide@metal core-shell particles or metal nitride particles by chemical vapor deposition, the temperature of the first heating is 700-800℃ and the time of the first heating is 20-40min. And / or, in the process of directly growing boron-doped graphene interface layer on a gradient porous carbon matrix embedded with metal oxide@metal core-shell particles or metal nitride particles by chemical vapor deposition, the temperature of the second heating is 700-800℃ and the time of the second heating is 30-60min. And / or, during the process of directly growing a boron-doped graphene interface layer on a gradient porous carbon matrix inlaid with the metal oxide@metal core-shell particles or metal nitride particles by chemical vapor deposition, the flow rate of CH4 is 20-40 mL / min and the flow rate of TEB is 1-1.5 mL / min. And / or, during the process of directly growing a boron-doped graphene interface layer on a gradient porous carbon matrix inlaid with the metal oxide@metal core-shell particles or metal nitride particles by chemical vapor deposition, the ratio of the flow rate of CH4 to the flow rate of TEB is (15-35):

1.

9. A negative electrode sheet, characterized in that, The negative electrode sheet includes the negative electrode composite material as described in claim 1 or 2, or the negative electrode composite material prepared by any one of claims 3-8.

10. A lithium-ion battery, the lithium-ion battery comprising the negative electrode composite material of claim 1 or 2, or the negative electrode composite material prepared by any one of claims 3-8, or the negative electrode sheet of claim 9.

Images