Modified hard carbon negative electrode material, preparation method and application thereof

Abstract

The present application relates to the technical field of sodium ion battery negative electrode material, and specifically to modified hard carbon negative electrode material and its preparation method and application, the present application takes biomass waste oil tea shell as raw material, adopts sulfuric acid and phosphoric acid as dopant, carries out porosification and activation, obtains P, S double atom doping pre-carbonization porous carbon material after carbonization, takes tetraethyl orthosilicate as raw material to prepare nano SiO2 microspheres under catalysis, carries out carbonization after blending nano SiO2 microspheres and P, S double atom doping pre-carbonization porous carbon material, obtains modified hard carbon negative electrode material through pyrolysis reaction with magnesium powder at the same time of carbonization, the element doping in modified hard carbon negative electrode material provides more active sites for sodium ion storage, improves the theoretical capacity and conductivity of the material, and the nanoscale silicon powder reduces the pulverization phenomenon caused by volume expansion when silicon is used as the negative electrode material of sodium ion battery due to the special size effect, reduces the attenuation of battery capacity.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery anode material technology, specifically to modified hard carbon anode materials, their preparation methods, and applications. Background Technology

[0002] In recent years, with the advancement of science and technology, energy storage materials have been widely applied in many areas of life, such as electric vehicles, mobile phones, computers, and other portable electronic devices. Lithium-ion batteries are currently widely used in these fields. However, traditional lead-acid and nickel-cadmium batteries have low energy efficiency and cause serious pollution, while lithium-ion batteries are expensive and their safety needs improvement. With the surge in demand from the new energy vehicle market, these batteries are unable to meet market needs. Scientists have discovered that sodium, which belongs to the same group as lithium, has similar chemical properties. Sodium resources are abundant, accounting for approximately 2.64% of the earth's crustal element reserves. Obtaining sodium is also simple, widely distributed, low-cost, and has no development bottlenecks. Furthermore, sodium-ion batteries offer advantages such as high safety, low cost, and environmental friendliness, making them highly favored by researchers and promoting their application in power batteries. Therefore, sodium-ion batteries can be considered one of the best candidates for lithium-ion batteries. Developing high-performance sodium storage materials is an urgent need in the energy storage industry and a key research direction for scientists.

[0003] However, Na The ionic radius is greater than that of Li This leads to significant volume changes during the cycle, a higher diffusion barrier, and sluggish reaction kinetics. Furthermore, due to Na… + The large radius makes traditional graphite materials unable to meet the requirements. Therefore, sodium-ion batteries mainly use hard carbon as the negative electrode material. However, if hard carbon is used directly, it usually has a low initial coulombic efficiency, porosity utilization, and the resulting energy density and plateau capacity, making it difficult to further promote the application of hard carbon.

[0004] Silicon-based anode materials have obvious advantages in energy density, with a theoretical specific capacity of up to 4200 mAh / g. They are also low in cost and have good environmental compatibility, making them the most promising next-generation sodium-ion battery anode materials. However, silicon-based materials face two main obstacles in actual use: (1) During the charging and discharging process, silicon volume expands by 300%, and the huge volume effect causes the silicon structure to collapse, ultimately leading to rapid capacity decay during cycling; (2) Silicon is a semiconductor with poor conductivity, resulting in a high degree of irreversibility during sodium ion insertion and extraction, which undoubtedly further reduces its specific capacity and charging and discharging efficiency.

[0005] Camellia oil is a unique natural high-grade edible oil in my country. The shell of the camellia fruit accounts for 60% of the total weight of the fruit and contains no oil at all. Therefore, a large amount of camellia shells are discarded or burned directly every year, causing serious environmental pollution. Research has found that biomass waste camellia shells are a promising carbon precursor that can be used for large-scale production of low-cost porous carbon materials.

[0006] Based on the above description, there is a need for a hard carbon material prepared from camellia shells that can solve the technical defects of both conventional hard carbon materials and silicon-based materials. Summary of the Invention

[0007] To address the aforementioned technical shortcomings, the present invention aims to provide a modified hard carbon anode material, its preparation method, and its application. This invention uses camellia oil shells (a biomass waste) as raw material, employing sulfuric acid and phosphoric acid as dopants for pore formation and activation. After carbonization, a P / S diatom-doped pre-carbonized porous carbon material is obtained. Nano-SiO2 microspheres are prepared using tetraethyl orthosilicate as a raw material under catalysis. The nano-SiO2 microspheres and the P / S diatom-doped pre-carbonized porous carbon material are then blended and carbonized. Simultaneously, a pyrolysis reaction is carried out with magnesium powder to obtain the modified hard carbon anode material. The elemental doping in the modified hard carbon anode material provides more active sites for sodium ion storage, improving the material's theoretical capacity and conductivity. Furthermore, the nano-sized silicon powder, due to its unique size effect, reduces the pulverization phenomenon caused by volume expansion when silicon is used as a sodium-ion battery anode material, thus reducing battery capacity decay.

[0008] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0009] The preparation method of modified hard carbon anode material includes the following steps:

[0010] S1. Prepare nano-SiO2 microspheres by catalysis using tetraethyl orthosilicate;

[0011] S2. After crushing and grinding the camellia oleifera shells, place them in deionized water, add the dopant, and stir for 12-24 hours to obtain a mixture.

[0012] The dopant is composed of a 98% H2SO4 solution and an 85% H3PO4 solution.

[0013] After freeze-drying the mixture, it was carbonized at 500-700℃ for 2-4 hours in an inert atmosphere to obtain P,S diatomic doped pre-carbonized porous carbon material.

[0014] S3. Mix the P, S diatomic doped pre-carbonized porous carbon material from step S2, the nano-SiO2 microspheres from step S1, the dispersant, and the organic solvent to obtain a suspension.

[0015] S4. Evaporate the solvent from the suspension in step S3 to obtain the precursor. Place the precursor and magnesium powder in two crucibles respectively, and calcine them at 800-1000℃ for 3-5 hours in an inert atmosphere. Then cool to obtain the modified hard carbon anode material.

[0016] Preferably, the nano-SiO2 microspheres in step S1 are prepared according to the following steps:

[0017] Tetraethyl orthosilicate and a catalyst were mixed in deionized water and then reacted at 30-45℃ for 4-5 hours to obtain a solution containing nano-SiO2 microspheres. After separation, washing and drying, nano-SiO2 microspheres were obtained.

[0018] The catalyst is selected from ammonia, oxalic acid or citric acid, and the molar ratio of tetraethyl orthosilicate to deionized water is 1:2-4.

[0019] Preferably, in step S2, the camellia seed shells are ground to the micron level; the mass ratio of camellia seed shells, deionized water, H2SO4 solution, and H3PO4 solution is 10:10-20:2-2.5:4-5.

[0020] Preferably, in step S3, the dispersant is selected from sodium stearate, sodium dodecylbenzene sulfonate, polysorbate, polyoxyethylene fatty acid ester, polyoxyethylene fatty alcohol ether, glycerol, and pentaerythritol, and the organic solvent is selected from ketones, lipids, ethers, and tetrahydrofuran.

[0021] Preferably, in step S3, the mass ratio of P and S diatomic doped pre-carbonized porous carbon material, nano-SiO2 microspheres, and dispersant is 3-6:10:15-20.

[0022] This invention also protects the modified hard carbon anode material prepared by the above-described preparation method.

[0023] This invention also protects a sodium-ion battery negative electrode sheet prepared from modified hard carbon negative electrode material, wherein the negative electrode sheet is prepared according to the following steps:

[0024] Modified hard carbon anode material, conductive agent and water-based binder are mixed and then dissolved in deionized water to obtain slurry. Aluminum foil is used as current collector, and the slurry is uniformly coated on the surface of the current collector. After drying, sodium-ion battery anode sheet is obtained.

[0025] The water-based binder is selected from a mixture of styrene-butadiene rubber and sodium carboxymethyl cellulose, with a mass ratio of 4:1; the conductive agent is selected from SuperP conductive carbon black.

[0026] The mass ratio of modified hard carbon anode material, conductive agent and water-based binder is 8-9.5:0.25-1:0.25-1.

[0027] This invention also protects the application of sodium-ion battery negative electrode sheets in the preparation of sodium-ion batteries, wherein the sodium-ion batteries are prepared according to the following steps:

[0028] Positive electrode preparation: sodium metal is compressed and cut into sheets;

[0029] Preparation of electrolyte: Sodium hexafluorophosphate was dissolved in an organic solvent to prepare a sodium hexafluorophosphate electrolyte with a concentration of 1 mol / L;

[0030] The organic solvent is composed of ethylene carbonate, propylene carbonate and fluoroethylene carbonate in a volume ratio of 47.5:47.5:5.

[0031] Sodium-ion battery preparation: The positive electrode, glass fiber separator, electrolyte and negative electrode are assembled in sequence, and sodium-ion battery is obtained through formation and standing process.

[0032] Compared with the prior art, the beneficial effects of the present invention are:

[0033] 1. This invention uses tetraethyl orthosilicate as raw material to prepare nano-silica microspheres under the catalysis of acid or alkali. Then, magnesium powder and nano-silica are pyrolyzed under an inert atmosphere to obtain nano-silica powder. Due to the special size effect of nano-silica, it can reduce the pulverization phenomenon caused by volume expansion when silicon is used as the negative electrode of sodium-ion battery, and reduce the capacity decay of battery.

[0034] 2. This invention uses natural biomass camellia shells as raw materials and H2SO4 and H3PO4 as activators, which can not only create pores but also serve as both S and P sources. Through carbonization, S and P dual-atom doped porous carbon materials are prepared. When the porous carbon material is blended with nano-silica microspheres, the nano-silica adheres to the surface of the porous carbon material or accumulates in the pores of the porous carbon material. After pyrolysis with magnesium powder, the nano-silica is dispersed on the surface and in the pores of the porous carbon material, which can effectively alleviate particle aggregation and electrode pulverization, adapt to long-term volume fluctuations, and maintain the stability of the nanostructure.

[0035] 3. Due to its unique porous structure, porous carbon materials, when doped with elements, can provide more active sites for sodium ion storage, thereby improving the material's theoretical capacity and conductivity. Porous carbon buffers the volume effect of silicon and maintains stable electrical contact, improving charge-discharge efficiency. In this invention, phosphorus and sulfur doping increases the interlayer spacing of the carbon material, facilitating the passage of charged ions through the carbon layer and their reaction with the internal silicon particles. Furthermore, there is a synergistic effect between the doped atoms; phosphorus doping promotes the formation of -CSC- bonds and inhibits the formation of unfavorable -C-SO4 bonds. xThe formation of -C- bonds and the combined effect of S and P diatomic doping promote the formation of a dense and stable solid electrolyte interphase (SEI) film on the surface of carbon materials, thereby improving the cycling performance of hard carbon materials. Attached Figure Description

[0036] Figure 1 The XPS spectrum of the modified hard carbon anode material prepared in Example 1 of this invention is shown below.

[0037] Figure 2 The rate performance diagram is shown for the modified hard carbon anode material prepared using Example 2 of the present invention.

[0038] Figure 3 This is a cycle performance diagram of the modified hard carbon anode material prepared in Example 2 of the present invention. Detailed Implementation

[0039] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. Unless otherwise specified, the experimental methods described in the embodiments of the present invention are conventional methods.

[0040] Example 1

[0041] The preparation method of modified hard carbon anode material includes the following steps:

[0042] S1. Prepare nano-SiO2 microspheres by catalysis using tetraethyl orthosilicate;

[0043] Tetraethyl orthosilicate and a catalyst were mixed in deionized water and then reacted at 30°C for 5 hours to obtain a solution containing nano-SiO2 microspheres. After separation, washing and drying, nano-SiO2 microspheres were obtained.

[0044] The catalyst is ammonia water, and the molar ratio of tetraethyl orthosilicate to deionized water is 1:2.

[0045] S2. After crushing and grinding the camellia oleifera shells to the micron level, place them in deionized water, add a dopant, and stir for 12 hours to obtain a mixture.

[0046] The dopant is composed of 98% H2SO4 solution and 85% H3PO4 solution, and the mass ratio of camellia seed shell, deionized water, H2SO4 solution and H3PO4 solution is 10:20:2:5.

[0047] After freeze-drying the mixture, it was carbonized at 500℃ for 4 hours in an argon atmosphere to obtain P,S diatomic doped pre-carbonized porous carbon material.

[0048] S3. Mix the P, S diatomic doped pre-carbonized porous carbon material from step S2, the nano-SiO2 microspheres from step S1, the dispersant, and the organic solvent to obtain a suspension.

[0049] The dispersant is selected from sodium stearate, the organic solvent is selected from tetrahydrofuran, and the mass ratio of P,S diatomic doped pre-carbonized porous carbon material, nano-SiO2 microspheres and sodium stearate is 6:1:20.

[0050] S4. Evaporate the solvent from the suspension in step S3 to obtain the precursor. Place the precursor and magnesium powder in two crucibles respectively, and calcine them at 1000℃ for 3 hours in an argon atmosphere. Then cool to obtain the modified hard carbon anode material.

[0051] Example 2

[0052] The preparation method of modified hard carbon anode material includes the following steps:

[0053] S1. Prepare nano-SiO2 microspheres by catalysis using tetraethyl orthosilicate;

[0054] Tetraethyl orthosilicate and a catalyst were mixed in deionized water and then reacted at 40°C for 4.5 h to obtain a solution containing nano-SiO2 microspheres. After separation, washing and drying, nano-SiO2 microspheres were obtained.

[0055] The catalyst is oxalic acid, and the molar ratio of tetraethyl orthosilicate to deionized water is 1:3.

[0056] S2. After crushing and grinding the camellia oleifera shells to the micron level, place them in deionized water, add a dopant, and stir for 18 hours to obtain a mixture.

[0057] The dopant is composed of 98% H2SO4 solution and 85% H3PO4 solution, and the mass ratio of camellia seed shell, deionized water, H2SO4 solution and H3PO4 solution is 10:15:2:4.5.

[0058] After freeze-drying the mixture, it was carbonized at 600℃ for 3 hours in an argon atmosphere to obtain P and S diatomic doped pre-carbonized porous carbon material.

[0059] S3. Mix the P, S diatomic doped pre-carbonized porous carbon material from step S2, the nano-SiO2 microspheres from step S1, the dispersant, and the organic solvent to obtain a suspension.

[0060] The dispersant was selected from polysorbate, the organic solvent was selected from ethyl acetate, and the mass ratio of P, S diatomic doped pre-carbonized porous carbon material, nano-SiO2 microspheres and polysorbate was 5:1:18.

[0061] S4. Evaporate the solvent from the suspension in step S3 to obtain the precursor. Place the precursor and magnesium powder in two crucibles respectively, and calcine them at 800-1000℃ for 3-5 hours in an argon atmosphere. Then cool to obtain the modified hard carbon anode material.

[0062] Example 3

[0063] The preparation method of modified hard carbon anode material includes the following steps:

[0064] S1. Prepare nano-SiO2 microspheres by catalysis using tetraethyl orthosilicate;

[0065] Tetraethyl orthosilicate and a catalyst were mixed in deionized water and then reacted at 45°C for 4 hours to obtain a solution containing nano-SiO2 microspheres. After separation, washing and drying, nano-SiO2 microspheres were obtained.

[0066] The catalyst is citric acid, and the molar ratio of tetraethyl orthosilicate to deionized water is 1:4.

[0067] S2. After crushing and grinding the camellia oleifera shells to the micron level, place them in deionized water, add a dopant, and stir for 24 hours to obtain a mixture.

[0068] The dopant is composed of 98% H2SO4 solution and 85% H3PO4 solution, and the mass ratio of camellia seed shell, deionized water, H2SO4 solution and H3PO4 solution is 10:10:2.5:4.

[0069] After freeze-drying the mixture, it was carbonized at 700℃ for 2 hours in an argon atmosphere to obtain P,S diatomic doped pre-carbonized porous carbon material.

[0070] S3. Mix the P, S diatomic doped pre-carbonized porous carbon material from step S2, the nano-SiO2 microspheres from step S1, the dispersant, and the organic solvent to obtain a suspension.

[0071] The dispersant is selected from polyoxyethylene fatty acid ester, the organic solvent is selected from dimethyl ether, and the mass ratio of P, S diatomic doped pre-carbonized porous carbon material, nano-SiO2 microspheres and polyoxyethylene fatty acid ester is 3:1:15.

[0072] S4. Evaporate the solvent from the suspension in step S3 to obtain the precursor. Place the precursor and magnesium powder in two crucibles respectively, and calcine them at 800°C for 5 hours in an argon atmosphere. Then cool to obtain the modified hard carbon anode material.

[0073] In Examples 1-3 of this invention, modified hard carbon anode materials with excellent electrochemical performance were all obtained, and the effects were parallel. The modified hard carbon anode material obtained in Example 2 is used as an example for further research. The specific research methods and results are as follows:

[0074] Figure 1 The results show that the modified hard carbon anode material prepared by this invention contains O, C, S, Si and P elements, indicating that the preparation method of this application realizes diatomic doping and carbon-silicon composite to modify hard carbon and improve its electrochemical performance.

[0075] The electrochemical performance of the modified hard carbon anode material prepared in Example 2 was tested using the following methods:

[0076] Preparation of negative electrode materials:

[0077] SuperP conductive carbon black was used as the conductive agent, and a mixture of styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC) was used as the water-based binder. The ratio of SBR to CMC was 4:1. During the mixing process, in order to prevent the SBR from breaking during stirring, CMC was added first and stirred until it became a black paste before adding the SBR. The solid content of the SBR used was 40%, and the solid content of the CMC used was 2.5%. The solid content refers to the mass fraction of SBR and CMC in the emulsion / solution prepared with deionized water.

[0078] The modified hard carbon anode material, conductive agent, and water-based binder prepared in Example 2 were mixed in a mass ratio of 8:1:1. The modified hard carbon anode material and conductive agent were ground for 5 minutes. The modified hard carbon anode material, conductive agent, and binder were then placed in a homogenizing bottle and stirred. Deionized water was added dropwise while stirring until the material was uniformly mixed into a black paste. Stirring was continued for 15 minutes to obtain the anode slurry. The anode slurry was coated on a smooth and flat aluminum foil and placed in a vacuum drying oven. It was dried at 80°C for 12 hours to obtain the anode sheet.

[0079] Preparation of sodium-ion batteries:

[0080] Positive electrode preparation: Sodium metal is compressed and cut into sheets;

[0081] Preparation of electrolyte: Sodium hexafluorophosphate was dissolved in an organic solvent to prepare a sodium hexafluorophosphate electrolyte with a concentration of 1 mol / L;

[0082] The organic solvent is composed of ethylene carbonate, propylene carbonate and fluoroethylene carbonate in a volume ratio of 47.5:47.5:5.

[0083] Sodium-ion battery preparation: The positive electrode, glass fiber separator, electrolyte and negative electrode are assembled in sequence, and sodium-ion battery is obtained through formation and standing process.

[0084] Charge / discharge test: Charge / discharge tests were conducted on the Newway Battery Test System (BTS82), set to constant current charge / discharge mode, with the current density set to the pre-defined value. The charging cutoff voltage was 2.5V, and the discharging cutoff voltage was 0.01V. The test results are shown below:

[0085] Figure 2 The rate performance diagram of the modified hard carbon anode material in Example 2 of this invention shows that the surface-modified hard carbon material exhibits significant performance improvement at high current density (1A / g). The results indicate that the discharge curve is in a "slope-plateau" state. The increase in specific capacity of the modified hard carbon material mainly comes from the plateau region, i.e., the process of sodium ions embedding into the hard carbon micropores. This indicates that after modification, sodium ions have a faster migration speed in the modified hard carbon anode material, and the modified hard carbon anode material exhibits a smaller overpotential under high current operation.

[0086] Figure 3 The diagram shows the reversible capacity of the modified hard carbon anode material in Example 2 after 300 cycles at 1C (current density of 0.1C for cycles 1-3, 1C = 300mAh / g). The results show that the capacity retention is still 88% after 300 cycles.

[0087] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for preparing modified hard carbon anode material, characterized in that, Includes the following steps: S1. Prepare nano-SiO2 microspheres by catalysis using tetraethyl orthosilicate; S2. After crushing and grinding the camellia oleifera shells, place them in deionized water, add the dopant, and stir for 12-24 hours to obtain a mixture. The dopant is composed of a 98% H2SO4 solution and an 85% H3PO4 solution. After freeze-drying the mixture, it was carbonized at 500~700℃ for 2~4h in an inert atmosphere to obtain P,S diatomic doped pre-carbonized porous carbon material. S3. Mix the P, S diatomic doped pre-carbonized porous carbon material from step S2, the nano-SiO2 microspheres from step S1, the dispersant, and the organic solvent to obtain a suspension. S4. Evaporate the solvent from the suspension in step S3 to obtain the precursor. Place the precursor and magnesium powder in two crucibles respectively, and calcine them at 800-1000℃ for 3-5 hours in an inert atmosphere. Then cool to obtain the modified hard carbon anode material. In step S2, the camellia seed shells are ground to the micron level; the mass ratio of camellia seed shells, deionized water, H2SO4 solution, and H3PO4 solution is 10:10-20:2-2.5:4-5.

2. The method for preparing the modified hard carbon anode material according to claim 1, characterized in that, The nano-SiO2 microspheres in step S1 are prepared according to the following steps: Tetraethyl orthosilicate and a catalyst were mixed in deionized water and then reacted at 30-45℃ for 4-5 hours to obtain a solution containing nano-SiO2 microspheres. After separation, washing and drying, nano-SiO2 microspheres were obtained. The catalyst is selected from ammonia, oxalic acid or citric acid, and the molar ratio of tetraethyl orthosilicate to deionized water is 1:2-4.

3. The method for preparing the modified hard carbon anode material according to claim 1, characterized in that, In step S3, the dispersant is selected from sodium stearate, sodium dodecylbenzene sulfonate, polysorbate, polyoxyethylene fatty acid ester, polyoxyethylene fatty alcohol ether, glycerol, and pentaerythritol, and the organic solvent is selected from ketones, esters, ethers, and tetrahydrofuran.

4. The method for preparing the modified hard carbon anode material according to claim 1, characterized in that, In step S3, the mass ratio of P and S diatomic doped pre-carbonized porous carbon material, nano-SiO2 microspheres, and dispersant is 3-6:1:15-20.

5. A modified hard carbon anode material prepared by the preparation method according to any one of claims 1-4.

6. A sodium-ion battery negative electrode sheet prepared using the modified hard carbon negative electrode material according to claim 5, characterized in that, The negative electrode sheet is prepared according to the following steps: Modified hard carbon anode material, conductive agent and water-based binder are mixed and then dissolved in deionized water to obtain slurry. Aluminum foil is used as current collector, and the slurry is uniformly coated on the surface of the current collector. After drying, sodium-ion battery anode sheet is obtained. The water-based binder is selected from a mixture of styrene-butadiene rubber and sodium carboxymethyl cellulose, with a mass ratio of 4:1; the conductive agent is selected from super P conductive carbon black. The mass ratio of modified hard carbon anode material, conductive agent and water-based binder is 8-9.5:0.25-1:0.25-1.

7. An application of the sodium-ion battery negative electrode sheet according to claim 6 in the preparation of sodium-ion batteries, characterized in that, The sodium-ion battery is prepared according to the following steps: Positive electrode preparation: Sodium metal is compressed and cut into sheets; Preparation of electrolyte: Sodium hexafluorophosphate was dissolved in an organic solvent to prepare a sodium hexafluorophosphate electrolyte with a concentration of 1 mol / L; The organic solvent is composed of ethylene carbonate, propylene carbonate and fluoroethylene carbonate in a volume ratio of 47.5:47.5:

5. Sodium-ion battery preparation: The positive electrode, glass fiber separator, electrolyte and negative electrode are assembled in sequence, and sodium-ion battery is obtained through formation and standing process.

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