Metal-doped biomass carbon negative electrode material and preparation method thereof

Abstract

The application provides a metal-doped biomass carbon negative electrode material and a preparation method thereof, wherein the preparation method comprises the following steps: soaking biomass powder in an acidic activator, adding a pore inducer, and performing high-temperature activation treatment to obtain activated porous carbon; a mixed metal salt solution is prepared, the activated porous carbon is added into the mixed metal salt solution, and stirring and standing are sequentially performed; after being dried through suction filtration, an intermediate is obtained; the intermediate is placed into a gas-phase deposition reaction cavity, heating is performed under the protection of nitrogen, a silicon source gas and a germanium source gas are introduced to perform a deposition reaction, and the metal-doped biomass carbon negative electrode material is obtained after cooling. Through structural design and element function synergistic integration, the comprehensive electrochemical performance of the metal-doped biomass carbon negative electrode material is significantly improved, and the problems of insufficient stability and capacity utilization rate of traditional doped materials are overcome.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion batteries, and particularly relates to a metal-doped biomass carbon negative electrode material and a preparation method thereof. BACKGROUND

[0002] The negative electrode material of a lithium ion battery is a key component for embedding and releasing lithium ions in the battery, and directly determines the core performances of the battery such as energy density, rate performance and cycle life. The common negative electrode materials at present include graphite, amorphous carbon, silicon-based materials and metal-based materials. Graphite (natural graphite and artificial graphite) is the most widely used commercial negative electrode material, and has advantages such as stable structure, low cost and good cycle performance, but its theoretical specific capacity is low (372 mAh / g), which limits the further improvement of energy density. New carbon materials such as amorphous carbon, biomass carbon, hard carbon and soft carbon have higher rate performance and good low-temperature characteristics, and are suitable for fast charging and low-temperature scenarios, but the problems of low first coulomb efficiency and large irreversible capacity still need to be solved. Silicon-based materials and metal-based materials have extremely high theoretical specific capacity, which can reach 4200 mAh / g and 1000-1600 mAh / g respectively, and also have relatively good electrical conductivity, but they generally have significant volume expansion problems, resulting in short cycle life and structural failure. In addition, high cost is also an important factor restricting its large-scale application.

[0003] In the operation process of a lithium ion battery, the core function of the negative electrode material is to absorb lithium ions to realize lithium intercalation in the charging process, and to release lithium ions to realize lithium extraction in the discharging process, while the material is required to have good structural stability, electronic conductivity and interface stability to ensure efficient electrochemical performance and long cycle life. In order to improve the performance of carbon-based negative electrode materials, in recent years, researchers have introduced metal doping technology, that is, introducing metal elements into carbon materials, through atomic-level regulation and interface engineering, to realize the multiple improvement of electrical conductivity, capacity and cycle stability. Metal-doped carbon negative electrode materials have many advantages: first, metal atoms or metal oxides have excellent electronic conductivity, which helps to build an efficient carbon skeleton conductive network, and some active metals themselves have lithium storage capacity, which can provide additional specific capacity.

[0004] However, metal doping has a significant volume expansion problem, which is easy to cause material pulverization or peeling, interrupt the transmission path of electrons and lithium ions, thereby significantly reducing the specific capacity and rate performance of the electrode, and may also trigger side reactions, block pores, and further increase the risk of internal resistance and heating. At the same time, due to the high reactivity of metal ions, irreversible side reactions may occur in the material during the first charge and discharge process, resulting in a decrease in the first coulombic efficiency, which means that the proportion of actual reversible stored lithium ions is low during the first charge and discharge process, resulting in permanent loss of a portion of lithium ions, irreversible loss of battery capacity, low initial capacity, and significant decrease in user available battery capacity, especially affecting high energy density scenarios such as consumer batteries and power batteries. Long-term operation is more likely to cause capacity attenuation and performance degradation, resulting in shortened cycle life and poor battery life. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a metal-doped biomass carbon negative electrode material and a preparation method thereof, aiming to solve the problem of coexistence of structural instability and electrochemical irreversible reaction caused by metal doping of the negative electrode material, and further causing capacity attenuation and cycle life reduction.

[0006] To solve the above technical problems, the present application is implemented as follows, the present application provides a preparation method of a metal-doped biomass carbon negative electrode material, for making a lithium ion battery, comprising the following steps:

[0007] S1, soaking the biomass powder with an acidic activator, and then adding a pore inducer for high-temperature activation treatment to obtain activated porous carbon;

[0008] S2, preparing a mixed metal salt solution, adding the activated porous carbon into the mixed metal salt solution, and sequentially stirring and standing, and then drying by suction filtration to obtain an intermediate;

[0009] S3, placing the intermediate into a gas phase deposition reaction cavity, heating under nitrogen protection, and introducing silicon source gas and germanium source gas for deposition reaction, and then cooling to obtain the metal-doped biomass carbon negative electrode material.

[0010] In some embodiments, step S1 comprises:

[0011] S1.1, crushing and sieving the biomass material to 100-300 mesh particles to obtain biomass powder, vacuum drying at 60℃ first, and then dispersing the biomass powder in an acidic activator solution with a mass ratio of 1:10 of 0.1-0.5 mol / L, magnetically stirring at room temperature for 3 hours, and continuing to stand for 24 hours;

[0012] S1.2, mechanically mix the powder treated in step S1.1 with the pore inducing agent at a mass ratio of 5:1 for 20 minutes, heat up to 400-500°C at a rate of 5°C / min and keep for 2 hours, then heat up to 800-1000°C at a rate of 10°C / min and keep for 1 hour, to obtain activated porous carbon.

[0013] In some embodiments, in step S1, the biomass material comprises at least one of coconut shell, seaweed dry, tea residue, the acidic active agent comprises at least one of phosphoric acid, nitric acid, oxalic acid, and the pore inducing agent comprises at least one of sodium bicarbonate, ammonium carbonate, sodium citrate, magnesium carbonate, and potassium hydroxide.

[0014] In some embodiments, step S2 comprises:

[0015] S2.1, prepare a mixed metal salt solution of 0.1 mol / L by mixing the nickel salt and the vanadium salt at a molar ratio of 1:1 and stirring magnetically at 60°C for 30 minutes;

[0016] S2.2, add the activated porous carbon to the mixed metal salt solution, control the solid-liquid mass ratio to be 1:20, and perform magnetic stirring treatment at 60°C for 4 hours under constant temperature conditions, then perform solid-liquid separation using a suction filtration device, wash the obtained filter cake with deionized water for 3 times, and obtain a wet filter cake;

[0017] S2.3, place the wet filter cake in a vacuum drying oven at 80°C for 12 hours, then perform precalcination at 300°C for 1 hour under an inert atmosphere, and control the heating rate to be 2-3°C / min, to obtain an intermediate.

[0018] In some embodiments, in step S2, the nickel salt comprises at least one of nickel nitrate, nickel acetate, and nickel chloride, and the vanadium salt comprises at least one of ammonium metavanadate, divanadium pentoxide, and vanadium sulfate.

[0019] In some embodiments, step S3 comprises:

[0020] S3.1, place the intermediate in a CVD reaction cavity, open a nitrogen protective atmosphere, set the flow rate to be 200 mL / min, and heat up to 500°C at a rate of 5°C / min, and keep the temperature constant for 10 minutes;

[0021] S3.2, introduce germanium source gas, silicon source gas, and auxiliary gas, set the volume ratio of the gases to be silicon source gas: germanium source gas: auxiliary gas = 40:5:1, control the total flow rate of the gases to be 300-400 mL / min, and keep the reaction time to be 100-200 minutes;

[0022] S3.3, after the end of the deposition reaction, continue to pass nitrogen to keep warm for 10 minutes to flush the reaction cavity residual gas, reduce the temperature to 400 DEG C, under the protection of nitrogen, pass in carbon source gas, continue to pass in at a flow rate of 2L / min for 100 minutes, reduce the temperature to room temperature, to obtain the metal doped biomass carbon negative electrode material.

[0023] In some embodiments, in step S3, the germanium source gas includes at least one of germane, germanium tetrachloride, ethyl germanium, the silicon source gas includes at least one of silane, dichlorosilane, trimethylsilane, the carbon source gas includes at least one of acetylene, propyne, methane, and the auxiliary gas is ammonia.

[0024] The present application provides a kind of metal doped biomass carbon negative electrode material, which is prepared by the preparation method of metal doped biomass carbon negative electrode material as described above.

[0025] Compared with the prior art, the metal doped biomass carbon negative electrode material and the preparation method thereof have the following beneficial effects:

[0026] S1. Under the condition of high-temperature pyrolysis, a biomass carbon skeleton with high specific surface area and multi-level pore structure is constructed through the synergistic effect of an acidic activator and a pore inducer, which improves the ion diffusion performance and metal loading capacity of the material, and provides structural support for subsequent doping. S2. The activated porous carbon is fully contacted with a mixed metal salt solution, metal ions are preliminarily anchored in the carbon skeleton to form uniformly distributed precursor metal sites, and a part of the metal oxide or coordination structure is induced to form by precalcination, which improves the interface bonding strength and alleviates the agglomeration and shedding of the doped metal. S3. Germanium source gas and silicon source gas are introduced by chemical vapor deposition process, which not only realizes in-situ deposition of conductive germanium nanoparticles on the carbon surface, but also generates a thin layer of silicon source at high temperature to effectively inhibit the volume expansion of germanium and metal ions, thereby improving the structural stability and cycle life. In summary, the process integrates structural design and element function through synergistic integration, which significantly improves the comprehensive electrochemical performance of the metal-doped biomass carbon negative electrode material and overcomes the problems of insufficient stability and capacity utilization of traditional doped materials. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a flowchart of the metal-doped biomass carbon negative electrode material in an embodiment of the present application. DETAILED DESCRIPTION

[0028] To make the purpose, technical scheme and advantages of the present application clearer, the present application is further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.

[0029] The application provides a preparation method of a metal-doped biomass carbon negative electrode material for manufacturing a lithium ion battery.

[0030] S1, soaking in an acidic activator, and then adding a pore inducer for high-temperature activation treatment to obtain activated porous carbon.

[0031] Step S1 includes:

[0032] S1.1, crushing and sieving the biomass material into 100-300 mesh particles to obtain biomass powder, vacuum drying at 60°C, and then dispersing the biomass powder in an acidic activator solution with a mass ratio of 1:10, magnetic stirring at room temperature for 3 hours, and continuing to soak for 24 hours; the biomass material includes at least one of coconut shell, seaweed dry, and tea dregs, and the acidic activator includes at least one of phosphoric acid, nitric acid, and oxalic acid.

[0033] Step S1.1 significantly improves the structural uniformity and surface reactivity of the carbon source by sieving, drying and acidic activation of the biomass powder, and builds a basic skeleton suitable for subsequent pore regulation and metal doping. Sieving the raw material to 100-300 mesh can improve the exposure degree of the specific surface area, ensure the consistency of the reaction and the uniformity of pyrolysis, and is also conducive to the uniform penetration of the adsorbent and the gas. Vacuum drying at 60°C helps to remove the adsorbed water in the raw material, avoiding the collapse of the structure caused by the violent evaporation of water during heat treatment.

[0034] The introduction of the acidic activator is a key link in structure regulation. Phosphoric acid can undergo esterification with the hydroxyl and phenolic hydroxyl groups in the biomass, promoting the crosslinking of the carbon skeleton, and the gas released during thermal decomposition induces the formation of microporous structures; nitric acid has strong oxidizing properties and can introduce oxygen-containing functional groups such as carboxyl and hydroxyl groups, providing chemical active sites for subsequent coordination and adsorption of metal ions, and inducing the generation of surface defects; oxalic acid can complex natural impurities such as calcium and magnesium, helping to purify the skeleton, and the gas generated during thermal decomposition forms micro-pores. After this treatment, the biomass carbon source has a rich surface functional group, reduced impurities, higher gold affinity and higher active site density, laying a foundation for efficient loading of metal ions and forming a uniform pore structure.

[0035] S1.2, mechanically mixing the powder treated in step S1.1 with a pore inducer at a mass ratio of 5:1 for 20 minutes, heating to 400-500°C at a rate of 5°C / min and holding for 2 hours, and then heating to 800-1000°C at a rate of 10°C / min and holding for 1 hour to obtain activated porous carbon. The pore inducer includes at least one of sodium bicarbonate, ammonium carbonate, sodium citrate, magnesium carbonate, and potassium hydroxide.

[0036] Step S1.2 realizes the continuous construction of microporous-mesoporous structure through the synergistic effect of pore inducers and high-temperature programmed heat treatment, so as to obtain three-dimensional activated porous carbon materials with high specific surface area, high pore volume and synergistically existing multi-scale channels. Sodium bicarbonate decomposes to produce carbon dioxide gas at 400-500°C, which can induce the formation of micropores by initiating implosion-type gas etching; ammonium carbonate decomposes to produce carbon dioxide and ammonia, which not only can expand the pore channel, but also can introduce nitrogen doping in situ to improve the polarity and lithium affinity of the material; the complex inducer formed by sodium citrate and magnesium carbonate decomposes at 500-800°C, releasing small molecule gases while leaving inorganic salt residues, which helps to construct the support structure and form the mesoporous network. Potassium hydroxide reacts with carbon at high temperature to generate potassium carbonate, carbon monoxide gas and other gases, which will etch the carbon skeleton and induce the formation of microporous and mesoporous structures, thereby significantly increasing the specific surface area.

[0037] The programmed temperature path is designed as a key thermal control strategy. The first stage is to heat to 400-500°C at 5°C / min and keep for 2h, which helps to pyrolyze the cellulose component smoothly, so that the carbon skeleton is initially formed and the primary pore structure is formed; the second stage is to heat to 800-1000°C at 10°C / min and keep for 1h, so that the carbon skeleton is rearranged and graphitized to form a stable conductive network and expand the three-dimensional connected channels. The specific surface area of the finally obtained porous carbon material is more than 1600m 2 / g, the pore size distribution is concentrated in 0.1-10nm, has high electrolyte wettability and fast ion diffusion capacity, and can provide a structural platform and interface matching guarantee for subsequent metal doping, vapor deposition and other steps.

[0038] S2, a mixed metal salt solution is prepared, the activated porous carbon is added to the mixed metal salt solution, and stirring and standing are sequentially performed, and an intermediate is obtained after suction filtration and drying;

[0039] Step S2 includes:

[0040] S2.1, a mixed metal salt solution of 0.1 mol / L is prepared by stirring nickel salt and vanadium salt at a molar ratio of 1:1 at 60°C for 30 minutes; the nickel salt includes at least one of nickel nitrate, nickel acetate and nickel chloride, and the vanadium salt includes at least one of ammonium metavanadate, vanadium pentoxide and vanadium sulfate.

[0041] In step S2.1, the nickel salt and the vanadium salt are prepared into a mixed metal salt solution with a concentration of 0.1 mol / L at a molar ratio of 1:1, which can ensure the charge balance and reaction activity balance between the doping components and provide a chemical basis for the subsequent synergistic effect. The nickel nitrate and ammonium metavanadate can be completely dissociated into divalent nickel ions and metavanadate ions in water, which provides excellent solubility and reaction activity; while the nickel acetate and vanadium pentoxide can slowly release metal ions under weakly acidic or heated conditions to form stable complex states, which is helpful for the uniform adsorption of metal ions on the surface of porous carbon. The co-configuration system of such metal salts has good complexing ability and can form mixed metal oxide or metal alloy particles in the subsequent heating, thereby improving the sodium storage capacity and rate performance of the negative electrode material.

[0042] In step S2.2, the activated porous carbon is added to the mixed metal salt solution, and the solid-liquid mass ratio is controlled to be 1:20. The mixture is subjected to magnetic stirring treatment at 60°C for 4 hours, and then subjected to solid-liquid separation by using a suction filtration device. The obtained filter cake is washed with deionized water for 3 times to obtain a wet filter cake.

[0043] In step S2.2, the solid-liquid mass ratio of the activated porous carbon and the mixed metal salt solution is controlled to be 1:20, which ensures the sufficient contact and diffusion adsorption process between the metal ions and the carbon material. Under this ratio, the metal ions in the solution can enter the pores through capillary action, van der Waals force and coordination, and combine with the polar functional groups such as carboxyl and hydroxyl groups on the surface of the porous carbon to form a stable adsorption state. The magnetic stirring at 60°C for 4 hours can enhance the uniformity of the ion distribution in the pores, while avoiding the phenomenon of particle sedimentation or agglomeration. The synergistic effect of the porous structure and the functional groups makes the metal ions uniformly anchored on the surface and inside the pores of the carbon-based material, which lays a foundation for the in-situ reduction and crystal nucleation in the subsequent heat treatment. In addition, the suction filtration and the three times of deionized water washing can effectively remove the unadsorbed free metal ions and residual salts, improve the purity of the intermediate and inhibit the side reactions in the subsequent heat treatment process.

[0044] In step S2.3, the wet filter cake is dried in a vacuum drying oven at 80°C for 12 hours, and then subjected to precalcination at 300°C for 1 hour under an inert atmosphere, with a heating rate of 2-3°C / min, to obtain an intermediate.

[0045] The vacuum drying process in step S2.3 can slowly remove free moisture and part of weakly bound water in the wet filter cake at 80°C, preventing structural damage and pore collapse caused by rapid evaporation of moisture in subsequent heat treatment. The dried intermediate is precalcined at 23°C / min to 300°C under an inert atmosphere, and held for 1 h, which has the following important technical effects: first, pyrolysis reaction gradually decomposes metal salts adsorbed on carbon-based materials into corresponding metal oxides or intermediate complex states, such as nickel oxide and vanadium pentoxide, improving thermal stability and interface adhesion; second, the calcination process can promote the formation of nanoscale distribution of metal precursors on the pore surface, which helps the uniformity and structure control of the subsequent deposition stage. This step provides the necessary precursor morphology and structural support for the formation of stable and uniformly distributed metal-doped sites.

[0046] In some embodiments, the preparation step of the mixed metal salt solution can be:

[0047] (1) Dissolve two or more metal salts (such as nickel nitrate and iron chloride) in deionized water, then add a certain amount of chelating agent, such as ethylenediaminetetraacetic acid (EDTA), sodium citrate or ammonia, adjust the solution pH to 6-8, and complex the metal ions with the chelating agent under stirring conditions to form a stable complex system, obtaining a transparent or slightly turbid mixed metal salt solution.

[0048] (2) Dissolve metal salts (such as cobalt nitrate and manganese chloride) in water, slowly add a weak alkaline adjusting agent (such as sodium carbonate, urea, ammonia) under constant temperature conditions of 60-80°C, adjust the reaction liquid pH to slightly alkaline (about 7.59), induce the formation of colloidal metal hydroxide coprecipitation, and obtain a mixed metal salt solution with structural precursor.

[0049] (3) Dissolve metal organic complexes (such as isopropyl titanate and zirconium acetate) and soluble metal salts (such as vanadous sulfate and copper nitrate) in a mixed solvent system composed of ethanol, water and ethanolamine in proportion, forming a transparent and uniform mixed metal salt solution. Introduce the sol into the activated porous carbon, complete the penetration and filling by capillary adsorption, and then form a precursor adsorbate.

[0050] S3, place the intermediate into a gas phase deposition reaction chamber, heat under nitrogen protection, introduce silicon source gas and germanium source gas for deposition reaction, cool after deposition reaction to obtain a metal-doped biomass carbon negative electrode material.

[0051] Step S3 includes:

[0052] S3.1, place the intermediate in the CVD reaction chamber, open the nitrogen protection atmosphere, set the flow rate to 200 mL / min, and increase the temperature to 500°C at a rate of 5°C / min, and hold at this temperature for 10 minutes.

[0053] The intermediate is placed in a chemical vapor deposition (CVD) reaction chamber, and 200 mL / min of nitrogen is introduced to form a protective inert atmosphere, which can effectively prevent the intermediate from being oxidized or incompletely thermally decomposed during the heating process. The heating rate is controlled at 5°C / min, which is conducive to the uniform distribution of the internal thermal field of the material, reduces the risk of explosion of the residual metal salt pre-calcination, and reduces the collapse of the surface structure. Holding at 500°C for 10 minutes can promote the decarboxylation and dehydration of the surface of the intermediate and generate active sites, providing a stable interface for the subsequent deposition of germanium source and carbon source.

[0054] S3.2, germanium source gas, silicon source gas and auxiliary gas are introduced, and the volume ratio of the gases is set to silicon source gas: germanium source gas: auxiliary gas = 40:5:1, the total flow rate of the gases is controlled at 300-400 mL / min, and the reaction time is maintained at 100-200 minutes; the germanium source gas includes at least one of germane, germanium tetrachloride and ethyl germanium, the silicon source gas includes at least one of silane, dichlorosilane and trimethylsilane, and the auxiliary gas is ammonia.

[0055] This step realizes in-situ construction of a germanium-silicon co-doped layer on the surface of the activated porous carbon skeleton by introducing germanium source gas and silicon source gas on the surface of the intermediate under nitrogen protection and constant temperature reaction conditions. The germanium source and the silicon source are introduced in a volume ratio of 1:5-10, which can effectively control the Ge / Si ratio and improve the structural stability and cycle life of the deposit. The germanium source (such as germane, germanium tetrachloride) has high electrical conductivity and can form a conductive network after deposition, improving the specific capacity and rate performance of the material; the silicon source (such as silane, dichlorosilane) can form a stable Si oxide film or buffer layer after deposition, which helps to alleviate the volume change of germanium during charging and discharging, thereby reducing the risk of active particle shedding and enhancing the structural integrity. In addition, a higher proportion of silicon source gas helps to induce the formation of germanium-silicon co-deposition phases (such as Ge-Si alloy), improving the dispersibility of germanium and the reversibility of lithium intercalation behavior. The total flow rate of the gases is controlled at 300-400 mL / min, which can achieve a stable deposition rate and ensure uniform and dense deposition layer. By precisely controlling the gas composition, flow rate and reaction time, a Ge-Si hybrid layer with moderate thickness, excellent flexibility and dual electronic / ionic conduction is formed on the surface of the porous carbon, laying a foundation for subsequent construction of high-capacity and high-stability metal-doped carbon negative electrode materials.

[0056] S3.3, after the deposition reaction is completed, nitrogen is continuously introduced to hold for 10 minutes to flush the reaction chamber of residual gas, the temperature is reduced to 400°C, and carbon source gas is introduced under nitrogen protection, with a flow rate of 2 L / min for 100 minutes, and then the temperature is reduced to room temperature to obtain a metal-doped biomass carbon negative electrode material. The carbon source gas includes at least one of acetylene, propyne and methane.

[0057] After the deposition reaction, nitrogen gas is continuously introduced and the temperature is maintained for 10 minutes. This helps to remove residual active gases from the reaction chamber and prevents secondary reactions or heterogeneous modifications to the material structure during cooling. The temperature is then lowered to 400℃, and a carbon source gas (such as acetylene or propyne) is introduced at a rate of 2 L / min into a nitrogen atmosphere. This induces the decomposition of acetylene / propyne under intermediate temperature conditions to form a dense carbon film, achieving secondary self-limiting deposition. This dense carbon layer can coat germanium particles and Ni / V doping sites, constructing a flexible conductive protective layer. This layer effectively buffers volume changes, prevents the migration of active components, and improves electronic connectivity and overall electrode structural stability, ultimately yielding a high-performance metal-doped biomass carbon anode material.

[0058] Example 1:

[0059] S1.1. Crush the coconut shells and sieve them to 100~300 mesh particles. First, vacuum dry them at 60℃, then disperse them in 0.2mol / L phosphoric acid at a mass ratio of 1:10. Stir magnetically for 3 hours at room temperature, and then let them stand and soak for 24 hours.

[0060] S1.2. Coconut shell powder and potassium hydroxide are mechanically mixed at a mass ratio of 5:1 for 20 minutes. The temperature is increased to 500℃ at 5℃ / min and kept at that temperature for 2 hours. Then the temperature is increased to 800℃ and carbonized rapidly at 10℃ / min for 1 hour to obtain activated porous carbon.

[0061] S2.1. Prepare a 0.1 mol / L mixed metal salt solution by magnetically stirring nickel nitrate and ammonium metavanadate at a molar ratio of 1:1 for 30 minutes at 60°C.

[0062] S2.2 Add activated porous carbon to the mixed metal salt solution, control the solid-liquid mass ratio at 1:20, and perform magnetic stirring at a constant temperature of 60℃ for 4 hours. Use a vacuum filter to separate the solid and liquid. Wash the obtained filter cake three times with deionized water to obtain a wet filter cake.

[0063] S2.3. The wet filter cake is dried in a vacuum drying oven at 80℃ for 12 hours, and then pre-calcined at 300℃ for 1 hour under an inert atmosphere, with the heating rate controlled at 2℃ / min, to obtain the intermediate.

[0064] S3.1 Place the intermediate in the CVD reaction chamber, turn on the nitrogen protective atmosphere, set the flow rate to 200 mL / min, raise the temperature to 500℃ at a rate of 5℃ / min, and hold the temperature at that temperature for 10 minutes.

[0065] S3.2. Introduce germane, silane, and ammonia. The volume ratio of the gases is set to silane:germane:ammonia = 40:5:1. The total gas flow rate is controlled at 300 mL / min, and the reaction time is maintained at 200 minutes.

[0066] S3.3, after the deposition reaction is completed, continue to pass nitrogen to keep warm for 10 minutes to flush the reaction cavity residual gas, reduce the temperature to 400℃, pass in acetylene gas under the protection of nitrogen, continue to pass at a flow rate of 2L / min for 100 minutes, reduce the temperature to room temperature, to obtain a metal-doped biomass carbon negative electrode material.

[0067] Example 2:

[0068] S1.1, the coconut shell is crushed and sieved into 100-300 mesh particles, first vacuum dried at 60℃, then dispersed in 0.2mol / L phosphoric acid at a mass ratio of 1:10, magnetically stirred at room temperature for 3 hours, and continue to soak for 24 hours;

[0069] S1.2, mechanically mix the coconut shell powder with potassium hydroxide at a mass ratio of 5:1, mix for 20 minutes, heat to 500℃ at a heating rate of 5℃ / min and keep for 2 hours, then continue to heat to 800℃ at a heating rate of 10℃ / min for rapid carbonization for 1 hour, to obtain activated porous carbon;

[0070] S2.1, dissolve nickel nitrate and ammonium metavanadate in deionized water at a molar ratio of 1:1, magnetically stir at 60℃ for 30 minutes, to prepare a mixed metal salt solution of 0.1mol / L;

[0071] S2.2, add the activated porous carbon to the mixed metal salt solution, control the solid-liquid mass ratio to be 1:20, magnetically stir at 60℃ for 4 hours under constant temperature conditions, then use suction filtration to separate the solid and liquid, wash the obtained filter cake with deionized water 3 times to obtain a wet filter cake;

[0072] S2.3, dry the wet filter cake in a vacuum drying oven at 80℃ for 12 hours, then heat to 300℃ at a heating rate of 2℃ / min and keep for 1 hour under inert atmosphere for precalcination treatment, to obtain an intermediate;

[0073] S3.1, place the intermediate in a chemical vapor deposition reaction chamber, open a nitrogen protective atmosphere, set the nitrogen flow rate to 200mL / min, heat to 500℃ at a heating rate of 5℃ / min, and keep at this temperature for 10 minutes to stabilize the material structure and remove surface adsorbates;

[0074] S3.2, pass in germane, silane and ammonia as reaction gases while maintaining the reaction chamber temperature at 500℃, the volume ratio of silane, germane and ammonia is set to 40:5:1, the total gas flow rate is controlled at 300mL / min, the deposition reaction lasts for 200 minutes, to form a silicon Ge co-deposition structure; after step S3.2, the temperature of the reaction chamber was kept at 500℃, the introduction of germane and silane was stopped, and a mixed gas composed of 5% ammonia and 95% argon was introduced, the total flow rate of the mixed gas was controlled at 400 mL / min, and the introduction was continued for 20 minutes, so as to make the deposited silicon The Ge structure undergoes a surface reconstruction reaction in a doped atmosphere, inducing the formation of a secondary nitrogen-doped and activated layer;

[0075] S3.3, stop the introduction of the mixed gas, continue to introduce nitrogen and keep warm for 10 minutes to flush the residual active gas in the reaction chamber, then reduce the reaction temperature to 400℃, introduce acetylene gas under the protection of nitrogen, the flow rate of acetylene gas is controlled at 2L / min, and the introduction is continued for 100 minutes to form an outer carbon-coated structure, and finally naturally cool to room temperature to obtain a metal-doped biomass carbon negative electrode material.

[0076] Comparative Example 1:

[0077] Compared with Example 1, the difference is that in step S3.2, only silane gas is introduced, and germane gas and ammonia gas are not introduced.

[0078] Comparative Example 2:

[0079] Compared with Example 1, the difference is that in step S3.2, a volume ratio of 2:1 of silane gas to germane gas is introduced.

[0080] Comparative Example 3:

[0081] Compared with Example 1, the difference is that in step S3.2, a volume ratio of 60:1 of silane gas to germane gas is introduced.

[0082] Comparative Example 4:

[0083] Compared with Example 1, the difference is that borane gas is used instead of germane gas.

[0084] Comparative Example 5:

[0085] Compared with Example 1, the difference is that germane is replaced by arsine.

[0086] Comparative Example 6:

[0087] Compared with Example 1, the difference is that in step S3.3, a molar ratio of 30:1 of acetylene to germane is introduced in the acetylene gas phase.

[0088] Comparative Example 7:

[0089] Compared with Example 1, the difference is that in step S3.3, a molar ratio of 60:1 of acetylene to germane is introduced in the acetylene gas phase.

[0090] Table 1: Electrical experimental data.

[0091]

[0092] The metal-doped biomass carbon negative electrode materials of Examples 1-2 and Comparative Examples 1-7, conductive carbon black, and binder CMC were weighed, added into deionized water to prepare a uniform slurry, and the ratio of the metal-doped silicon carbon negative electrode material: conductive carbon black: binder CMC solid content was 95:1.5:3.5. The slurry was sieved and uniformly coated on a copper foil, and then dried in a 90°C vacuum drying oven. The dried electrode was rolled and cut into a circular electrode of a certain size, and the electrode mass was recorded. In an argon glove box, a lithium sheet was used as a counter electrode, and a coin cell was assembled with the above- obtained electrode, a separator, a gasket, and the like, and a silicon-carbon special electrolyte was used as the electrolyte.

[0093] After the charge-discharge cycles of Examples 1-2 and Comparative Examples 1-7, the experimental data obtained are shown in Table 1,

[0094] Comparing Examples 1 and Comparative Examples 1, it can be seen that the metal-doped biomass carbon negative electrode material after doping with metal has excellent cycle performance, and the doping of germanium has a significant improvement effect on the electrochemical performance such as the initial efficiency, cycle performance, and rate performance. The addition of germanium in the deposition layer can strengthen the linkage between the silicon layer and the inner and outer carbon structure layers, optimize the overall structure of the material, and be beneficial to the expression of the electrochemical performance, thereby effectively improving the charging efficiency and service life of the lithium ion battery.

[0095] Comparing Examples 1 and Comparative Examples 2 and 3, it can be seen that too high or too low germanium concentration is not conducive to the improvement of electrochemical performance, and too low germanium concentration is more reflected in no electrochemical performance improvement effect, and too high germanium concentration is more reflected in negative benefits of electrochemical performance, indicating that the improvement of electrochemical performance needs a suitable doping gas concentration range.

[0096] Comparing Examples 1 and Comparative Example 4, it can be seen that the electrochemical performance of non-metallic element doping such as boron is not as good as that of metal elements, and metal elements have the best electrochemical performance improvement effect under the preparation conditions of the experiment.

[0097] Comparing Examples 1 and Comparative Example 5, it can be seen that other metals such as arsenic in addition to germanium also have an electrochemical performance improvement effect.

[0098] Comparing Examples 1 and Comparative Examples 6 and 7, it can be seen that the introduction of high or low concentration of metal deposition elements in the acetylene stage has an adverse effect on the final material performance, and the cycle performance is particularly affected, which may be due to the fact that the metal elements affect the formation of the acetylene-coated carbon layer.

[0099] It can be seen from the comparison between Example 1 and Example 2 that the introduction of the secondary atmosphere regulation step after deposition on the basis of the original preparation process has a positive effect on the overall electrochemical performance of the metal-doped biomass carbon negative electrode material. In Example 2, after the deposition of silicon and germanium, the surface of the material is subjected to secondary regulation by introducing a nitrogen-containing atmosphere at a higher temperature, which makes the doping structure more uniform and stable, thereby further improving the lithium storage behavior of the material.

[0100] Specifically, the secondary atmosphere treatment helps to form stable nitrogen-doped structures and active defect sites on the carbon skeleton and its surface, enhances the continuity of the electron transmission channel, and at the same time improves the diffusion efficiency of lithium ions inside the material. This structure regulation not only improves the reaction activity of the material, but also to some extent alleviates the influence of the volume change of the silicon and germanium deposition phase on the structural integrity during the cycling process.

[0101] The present application provides a kind of metal-doped biomass carbon negative electrode material, which is prepared by a kind of metal-doped biomass carbon negative electrode material preparation method.

[0102] The above is only the preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a metal-doped biomass carbon anode material for manufacturing lithium-ion batteries, characterized in that the steps include... include: S1. Add an acidic activator to biomass powder and soak it, then add a pore inducer and perform high-temperature activation treatment to obtain activated porous carbon. Step S1 includes: S1.

1. Crush and sieve the biomass material to 100~300 mesh particles to obtain biomass powder. First, vacuum dry it at 60℃. Then, disperse the biomass powder in an acidic activator solution at a mass ratio of 1:

10. Stir it magnetically at room temperature for 3 hours and continue to let it stand and soak for 24 hours. S1.

2. The biomass powder and the pore inducer are mechanically mixed at a mass ratio of 5:1 for 20 minutes. The temperature is increased to 400~500℃ at 5℃ / min and kept at that temperature for 2 hours. Then the temperature is increased to 800~1000℃ at 10℃ / min and kept at that temperature for 1 hour to obtain activated porous carbon. S2. Prepare a mixed metal salt solution, add activated porous carbon to the mixed metal salt solution, stir and let stand in sequence, filter and dry to obtain an intermediate; Step S2 includes: S2.

1. Mix nickel salt and vanadium salt in a molar ratio of 1:1 and stir magnetically for 30 minutes at 60°C to prepare a 0.1 mol / L mixed metal salt solution. The nickel salt includes at least one of nickel nitrate, nickel acetate, and nickel chloride, and the vanadium salt includes at least one of ammonium metavanadate, vanadium pentoxide, and vanadium sulfate. S2.2 Add activated porous carbon to the mixed metal salt solution, control the solid-liquid mass ratio at 1:20, and perform magnetic stirring at a constant temperature of 60℃ for 4 hours. Use a vacuum filter to separate the solid and liquid. Wash the obtained filter cake three times with deionized water to obtain a wet filter cake. S2.

3. The wet filter cake is dried in a vacuum drying oven at 80℃ for 12 hours, and then pre-calcined at 300℃ for 1 hour under an inert atmosphere, with the heating rate controlled at 2~3℃ / min, to obtain the intermediate. S3. The intermediate is placed in the vapor deposition reaction chamber and heated under nitrogen protection. Silicon source gas and germanium source gas are introduced to carry out the deposition reaction. After the deposition reaction is completed, the material is cooled to obtain metal-doped biomass carbon anode material. Step S3 includes: S3.1 Place the intermediate in the CVD reaction chamber, turn on the nitrogen protective atmosphere, set the flow rate to 200 mL / min, raise the temperature to 500℃ at a rate of 5℃ / min, and hold at 500℃ for 10 minutes. S3.

2. Introduce germanium source gas, silicon source gas, and auxiliary gas. The volume ratio of the gases is set to silicon source gas: germanium source gas: auxiliary gas = 40:5:

1. The total gas flow rate is controlled at 300~400mL / min, and the reaction time is maintained at 100~200 minutes. S3.3 After the deposition reaction is completed, nitrogen gas is continuously introduced for 10 minutes to flush the residual gas in the reaction chamber. The temperature is then lowered to 400°C. Carbon source gas is introduced under nitrogen protection at a flow rate of 2L / min for 100 minutes. The temperature is then lowered to room temperature to obtain metal-doped biomass carbon anode material.

2. The method for preparing a metal-doped biomass carbon anode material according to claim 1, characterized in that, In step S1, the biomass material includes at least one of coconut shell, dried seaweed, and tea residue; the acidic surfactant includes at least one of phosphoric acid, nitric acid, and oxalic acid; and the pore inducing agent includes at least one of sodium bicarbonate, ammonium carbonate, sodium citrate, magnesium carbonate, and potassium hydroxide.

3. The method for preparing a metal-doped biomass carbon anode material according to claim 1, characterized in that, In step S3, the germanium source gas includes at least one of germane, germanium tetrachloride, and ethyl germanium; the silicon source gas includes at least one of silane, dichlorosilane, and trimethylsilane; the carbon source gas includes at least one of acetylene, propyne, and methane; and the auxiliary gas is ammonia.

4. A metal-doped biomass carbon anode material, characterized in that, It is prepared by the method for preparing a metal-doped biomass carbon anode material as described in any one of claims 1-3.

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