Silicon-carbon negative electrode material and preparation method and application thereof

Abstract

The invention provides a silicon-carbon negative electrode material and a preparation method and application thereof, and relates to the technical field of negative electrode materials. The preparation method of the silicon-carbon negative electrode material comprises the following steps: S1, uniformly mixing lignosulfonate and an alkaline solvent, drying, carbonizing, washing and drying to obtain a sulfur-doped porous carbon material; s2, performing silicon deposition reaction on the sulfur-doped porous carbon material to obtain a sulfur-doped porous silicon carbon precursor material; s3, a urea solution, formaldehyde and formic acid are added into the sulfur-doped porous silicon carbon precursor material, stirring, standing, acid soaking, washing, drying and carbonization are performed, and the sulfur-doped porous silicon carbon composite material is obtained. The silicon-carbon negative electrode material provided by the invention has excellent electrochemical performance.

Description

Technical Field

[0001] The present invention relates to the technical field of negative electrode materials, and in particular to a silicon-carbon negative electrode material and a preparation method and application thereof. Background Art

[0002] In the field of new energy, lithium-ion batteries have attracted widespread attention from researchers around the world due to their many advantages, such as high specific energy, good cycle stability and portability. This battery technology has been widely used in various electronic devices, electric vehicles and portable storage devices. Silicon, as an emerging negative electrode material for lithium-ion batteries, has a theoretical specific capacity of up to 4000mAh / g, showing great potential. However, silicon materials will experience significant volume expansion during the charging and discharging process, which can easily lead to material pulverization and shedding. In addition, the conductivity of micron-sized silicon materials is not ideal. These factors have seriously affected the service life of silicon negative electrode materials. Especially during the first charge, lithium ions react with silicon oxide to generate new compounds. This process not only consumes a large amount of active lithium, but also leads to low first-time charging efficiency.

[0003] Heteroatom doping can improve the electrochemical activity of electrode materials. For example, sulfur doping can improve the storage capacity of electrode materials for lithium ions and improve the specific capacity and cycle performance of the battery. In addition, nitrogen doping can increase the specific surface area of ​​the electrode material, thereby improving the overall electrochemical activity of the electrode. Heteroatom doping can effectively alleviate the structural damage of silicon materials caused by volume expansion and contraction during charging and discharging. The doped heteroatoms help stabilize the structure of the electrode material, reduce the pulverization and shedding of the material, and thus improve the cycle life of the battery. Therefore, the development of a silicon-carbon negative electrode material that can effectively reduce volume expansion, ensure battery cycle stability, and have high initial charge efficiency and excellent cycle performance is still an urgent technical challenge facing the field of lithium-ion batteries. Summary of the invention

[0004] Based on the technical problems existing in the background technology, the present invention proposes a silicon-carbon negative electrode material and a preparation method and application thereof.

[0005] The present invention provides a method for preparing a silicon-carbon negative electrode material, comprising the following steps:

[0006] S1, mixing lignin sulfonate and an alkaline solvent uniformly, drying, carbonizing, washing, and drying to obtain a sulfur-doped porous carbon material;

[0007] S2, subjecting the sulfur-doped porous carbon material to a silicon deposition reaction to obtain a sulfur-doped porous silicon-carbon precursor material;

[0008] S3. Add urea solution, formaldehyde and formic acid to the sulfur-doped porous silicon-carbon precursor material, stir, let stand, soak in acid, wash, dry and carbonize to obtain.

[0009] The silicon-carbon negative electrode material prepared by the preparation method of the present invention can effectively improve the first-round coulombic efficiency of the battery, alleviate the volume expansion of micron-sized silicon materials, and enhance the overall electrochemical activity of the electrode. The lithium-ion battery assembled therefrom has better cycle performance.

[0010] Preferably, in S1, the lignin sulfonate is selected from one or more of sodium lignin sulfonate and calcium lignin sulfonate.

[0011] Lignin sulfonate is used as a precursor, pores are formed using an alkaline solvent, and then washed, dried, and carbonized to obtain sulfur-doped porous carbon.

[0012] Preferably, in S1, the alkaline solvent is selected from one or more of potassium hydroxide solution, sodium hydroxide solution, sodium carbonate solution and potassium carbonate solution.

[0013] Preferably, in said S1, the mass fraction of the alkaline solvent is 25%-35%.

[0014] Preferably, in said S1, the mass ratio of lignin sulfonate to alkaline solvent is 1:(1-3).

[0015] The mass ratio of lignin sulfonate to alkaline solvent is conducive to the dissolution of lignin and better pore formation within a certain range.

[0016] Preferably, in S1, the drying is vacuum drying at 60-90°C.

[0017] Preferably, in S1, carbonization comprises: carbonization for 1-3 hours at 400-600° C. in a protective gas atmosphere.

[0018] The purpose of carbonization is to carbonize the organic components in the material to generate a carbonaceous structure. The carbonized material has higher conductivity, which helps to reduce the internal resistance of the battery and improve the charging and discharging efficiency. Secondly, the carbonized material has stronger stability, which can reduce the structural changes during the charging and discharging process, thereby extending the service life of the lithium battery. Moreover, the carbonized negative electrode material has a higher specific capacity, which means that the battery can store more energy.

[0019] More preferably, the protective gas is selected from one or more of nitrogen and argon.

[0020] More preferably, the flow rate of the protective gas is 5-35 L / min.

[0021] Preferably, in said S1, washing comprises: washing with water until neutral.

[0022] Preferably, in S2, the silicon deposition reaction comprises: introducing a protective gas into the sulfur-doped porous carbon material to raise the temperature to 500-600° C., then introducing a silicon source gas for primary deposition, and finally introducing an acetylene / nitrogen mixed gas for secondary deposition.

[0023] The role of silicon deposition reaction is to synthesize silicon-carbon materials as a silicon source. The addition of silicon can significantly increase the capacity of the material. In order to prevent silane from exploding when it contacts the air, a protective gas is introduced for protection. The role of introducing silicon source gas and acetylene / nitrogen mixed gas for deposition is to first deposit silane, and then continuously use acetylene as a carbon source to perform carbon coating on the surface of the composite material to prevent oxidation of silicon.

[0024] More preferably, the protective gas is selected from one or more of nitrogen and argon.

[0025] More preferably, the silicon source gas is selected from one or more of monosilane, methylchlorosilane, cyclosiloxane, alkoxysilane, and dimethyldichlorosilane.

[0026] By selecting different silicon source gases, silicon is deposited on porous carbon to obtain a silicon-carbon composite material, which can significantly improve the capacity of the material.

[0027] More preferably, the one-time deposition time is 2-30 hours.

[0028] More preferably, the secondary sedimentation time is 2-8h.

[0029] More preferably, the flow rate of the protective gas is 5-35 L / min; the flow rate of the silicon source gas is 2-30 L / min; the volume ratio of acetylene / nitrogen in the acetylene / nitrogen mixture is 1:(2-6); and the flow rate of acetylene is 2-5 L / min.

[0030] Controlling the gas flow rate within a certain range helps to control the amount of silicon deposited.

[0031] More preferably, the amount of silicon-containing gas deposited in the sulfur-doped porous silicon-carbon precursor material after the silicon deposition reaction is 30%-50%.

[0032] Preferably, in S3, the mass ratio of the sulfur-doped porous silicon-carbon precursor material to the urea solution is (5-10):100.

[0033] Preferably, in S3, the concentration of the urea solution is 0.4-0.6 mol / L.

[0034] Preferably, in said S3, the mass fraction of formaldehyde is 1-4%.

[0035] Preferably, in said S3, the mass fraction of formic acid is 0.5-1%.

[0036] Controlling the concentration and mass fraction of raw materials within a certain range helps control the formation of resin.

[0037] Preferably, in S3, the stirring time is 0.5-2h.

[0038] Preferably, in S3, the standing time is 18-30 hours.

[0039] Preferably, in said S3, the acid soaking comprises soaking in a hydrochloric acid solution for 36-72 hours, and the concentration of the hydrochloric acid solution is 0.5-2 mol / L.

[0040] Preferably, in said S3, washing is washing with water until neutral.

[0041] Preferably, in S3, the drying is performed at 50-80° C. in vacuum for 6-24 h.

[0042] Preferably, in S3, carbonization includes introducing protective gas, first keeping warm at 200-300°C for 4-6 hours, and then keeping warm at 700-900°C for 2-3 hours.

[0043] Two-stage carbonization can improve the pore structure and distribution of porous carbon and optimize its specific surface area and pore volume. Through staged temperature control treatment, the formation of pores can be more accurately regulated, which helps to obtain a more uniform pore size distribution. This process can also effectively improve the electrochemical performance and adsorption capacity of porous carbon.

[0044] More preferably, the flow rate of the protective gas is 5-35 L / min.

[0045] More preferably, the protective gas is selected from one or more of nitrogen and argon.

[0046] The present invention also proposes a silicon-carbon negative electrode material prepared by the above preparation method, wherein the silicon-carbon negative electrode material has a multi-layer coating structure, wherein the inner layer is a sulfur-doped porous silicon-carbon material, and the outer layer is a uniformly coated nitrogen-doped carbonaceous structure.

[0047] Preferably, in the silicon-carbon negative electrode material, the S content is 0.5-2wt%, the N content is 1-3wt%, the Si content is 45-55wt%, and the C content is 40-55wt%.

[0048] The internal porous silicon is well dispersed in the porous carbon structure, which plays a positive role in the expansion and aggregation of silicon during the battery charging and discharging process.

[0049] An application of the above silicon-carbon negative electrode material or the silicon-carbon negative electrode material prepared by the above preparation method in a lithium-ion battery.

[0050] The beneficial effects of the present invention are:

[0051] The present invention forms a lignin solution by mixing lignin sulfonate powder with a strong alkaline solution, and then carbonizes it into a sulfur-containing porous carbon material by evaporation, stirring and drying. The porous carbon is placed in a fluidized bed, heated under an inert gas, evacuated, and silane gas is introduced for vapor deposition to obtain a sulfur-containing silicon-carbon precursor material. The sulfur-containing silicon-carbon precursor, urea and formaldehyde are then mixed, solidified under alkaline conditions, and then carbonized at high temperature to obtain a heteroatom (nitrogen and sulfur) silicon-carbon negative electrode material. This method uses biomass-based self-doped sulfur as an activated carbon carrier, achieves silicon introduction by filling pores, and the secondary surface doping of nitrogen elements is activated by coating with urea-formaldehyde resin, and a unique structure and heteroatom-doped silicon-carbon negative electrode material is cleverly obtained, which significantly improves the cycle performance of the negative electrode material. The silicon particles are effectively filled in the carbon ball coating structure, which effectively avoids the aggregation and expansion of silicon during the battery charging and discharging process. Heteroatom doping can effectively alleviate the structural damage caused by volume expansion and contraction of silicon materials during charging and discharging. The doped heteroatoms help stabilize the structure of the electrode material, reduce the pulverization and shedding of the material, and thus improve the cycle life of the battery. This ingenious structural design significantly improves the cycle performance of heteroatom-doped silicon-carbon negative electrode materials. The benefit of the present invention lies in the use of sulfur-doped porous carbon as a substrate for silane deposition, which not only alleviates the expansion effect of silicon during the charge and discharge process, but also the sulfur doping increases the storage capacity of the electrode material for lithium ions, which can improve the rate performance of the material; the outer layer is coated with phenolic resin carbon to reduce the oxidation of silicon. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 Schematic diagram of the structure of the silicon-carbon negative electrode material of the present invention; 1-sulfur-doped porous carbon material, 2-sulfur-doped porous silicon-carbon precursor material, 3-nitrogen-containing carbon-coated sulfur-doped silicon-carbon material.

[0053] Figure 2 This is the XRD diagram of the silicon-carbon negative electrode material prepared in Example 2 of the present invention.

[0054] Figure 3 It is a cycle curve diagram of a lithium ion battery using the negative electrode sheet prepared with the silicon-carbon negative electrode material prepared in Example 2 of the present invention and the comparative example as the working electrode.

[0055] Figure 4 It is a first-week charge and discharge curve diagram of a lithium-ion battery using the negative electrode sheet prepared with the silicon-carbon negative electrode material prepared in Example 2 of the present invention and the comparative example as the working electrode. DETAILED DESCRIPTION

[0056] The technical solution of the present invention is described in detail through specific embodiments.

[0057] Unless otherwise specified, the materials, reagents, etc. used in the following examples and comparative examples can be obtained from commercial sources.

[0058] Example 1

[0059] A method for preparing a silicon-carbon negative electrode material comprises the following steps:

[0060] S1. Sodium lignin sulfonate and 30% by mass KOH solution were mixed in a mass ratio of 1:2, vacuum dried at 80°C, heated to 500°C in a tube furnace under an argon atmosphere for 2 hours, washed with distilled water and vacuum dried at 80°C to obtain a sulfur-doped porous carbon material;

[0061] S2, the sulfur-doped porous carbon material is transferred to a fluidized bed, argon gas is introduced at a gas flow rate of 8 L / min, after the temperature is raised to 500°C, monosilane gas is introduced at a gas flow rate of 6 L / min, and the deposition is carried out for 5 hours, and finally nitrogen / acetylene mixed gas is introduced, and the deposition is continued for 6 hours to obtain a sulfur-doped porous silicon-carbon precursor material; the volume ratio of nitrogen / acetylene in the nitrogen / acetylene mixed gas is 5:1, and the gas flow rate of acetylene is 3 L / min;

[0062] S3. Add 100mL of 0.5mol / L urea solution, 2% formaldehyde by mass and 1% formic acid by mass to 9g of sulfur-doped porous silicon-carbon precursor material, stir at 500r / min for 30min, let stand for 18h, soak and solidify in 1mol / L hydrochloric acid for 36h, wash repeatedly with deionized water until the solution is neutral, dry in a vacuum drying oven at 80℃ for 24h, put into a porcelain boat, pyrolyze and carbonize in a tubular furnace protected by nitrogen atmosphere, keep warm at 300℃ for 4h, then keep warm at 800℃ for 2h, cool to room temperature to obtain nitrogen-carbon-coated sulfur-doped silicon-carbon material, i.e., silicon-carbon negative electrode material.

[0063] Example 2

[0064] A method for preparing a silicon-carbon negative electrode material comprises the following steps:

[0065] S1. Sodium lignin sulfonate and 30% by mass KOH solution were mixed in a mass ratio of 1:2, vacuum dried at 80°C, heated to 500°C in a tube furnace under an argon atmosphere for 2 hours, washed with distilled water and vacuum dried at 80°C to obtain a sulfur-doped porous carbon material;

[0066] S2, the sulfur-doped porous carbon material is transferred to a fluidized bed, argon gas is introduced at a gas flow rate of 8 L / min, after the temperature is raised to 500°C, monosilane gas is introduced at a gas flow rate of 6 L / min, and the deposition is carried out for 6 hours, and finally nitrogen / acetylene mixed gas is introduced, and the deposition is continued for 6 hours to obtain a sulfur-doped porous silicon-carbon precursor material; the volume ratio of nitrogen / acetylene in the nitrogen / acetylene mixed gas is 5:1, and the gas flow rate of acetylene is 3 L / min;

[0067] S3. Add 100mL of 0.5mol / L urea solution, 2% formaldehyde and 1% formic acid to 9g of sulfur-doped porous silicon-carbon precursor material, stir at 500r / min for 30min, let stand for 18h, soak and cure in 1mol / L hydrochloric acid for 36h, wash repeatedly with deionized water until the solution is neutral, dry in a vacuum drying oven at 80℃ for 24h, put in a porcelain boat, pyrolyze and carbonize in a tubular furnace protected by nitrogen atmosphere, keep warm at 300℃ for 4h, then keep warm at 800℃ for 2h, cool to room temperature, and obtain.

[0068] Example 3

[0069] A method for preparing a silicon-carbon negative electrode material comprises the following steps:

[0070] S1. Sodium lignin sulfonate and 30% by mass KOH solution were mixed in a mass ratio of 1:2, vacuum dried at 80°C, heated to 500°C in a tube furnace under an argon atmosphere for 2 hours, washed with distilled water and vacuum dried at 80°C to obtain a sulfur-doped porous carbon material;

[0071] S2, the sulfur-doped porous carbon material was transferred to a fluidized bed, argon gas was introduced at a gas flow rate of 8 L / min, and after heating to 500°C, monosilane gas was introduced at a gas flow rate of 6 L / min, and the deposition was continued for 6.8 hours. Finally, nitrogen / acetylene mixed gas was introduced and the deposition was continued for 6 hours to obtain a sulfur-doped porous silicon-carbon precursor material; the volume ratio of nitrogen / acetylene in the nitrogen / acetylene mixed gas was 5:1, and the gas flow rate of acetylene was 3 L / min;

[0072] S3. Add 100mL of 0.5mol / L urea solution, 2% formaldehyde and 1% formic acid to 9g of sulfur-doped porous silicon-carbon precursor material, stir at 500r / min for 30min, let stand for 18h, soak and cure in 1mol / L hydrochloric acid for 36h, wash repeatedly with deionized water until the solution is neutral, dry in a vacuum drying oven at 80℃ for 24h, put in a porcelain boat, pyrolyze and carbonize in a tubular furnace protected by nitrogen atmosphere, keep warm at 300℃ for 4h, then keep warm at 800℃ for 2h, cool to room temperature, and obtain.

[0073] Comparative Example 1

[0074] A method for preparing a silicon-carbon negative electrode material comprises the following steps:

[0075] S1. Sodium lignin sulfonate and 30% by mass fraction of sulfur-doped carbon are mixed uniformly in a mass ratio of 1:2, vacuum dried at 80°C, heated to 500°C in a tube furnace under an argon atmosphere for 2 hours, washed with distilled water and vacuum dried at 80°C to obtain a sulfur-doped porous carbon material;

[0076] S2, the sulfur-doped porous carbon material is transferred to a fluidized bed, argon gas is introduced at a gas flow rate of 8 L / min, after the temperature is raised to 500°C, monosilane gas is introduced at a gas flow rate of 6 L / min, and the deposition is carried out for 6 hours, and finally nitrogen / acetylene mixed gas is introduced, and the deposition is continued for 6 hours to obtain a sulfur-doped porous silicon-carbon precursor material; the volume ratio of nitrogen / acetylene in the nitrogen / acetylene mixed gas is 5:1, and the gas flow rate of acetylene is 3 L / min;

[0077] S3. Add 100 mL of phenol / formaldehyde mixture to 9 g of sulfur-doped porous silicon-carbon precursor material, wherein the molar ratio of phenol to formaldehyde is 6:5; stir at 500 r / min for 30 min, let stand for 18 h, soak and cure in 1 mol / L hydrochloric acid for 36 h, repeatedly wash with deionized water until the solution is neutral, dry in a vacuum drying oven at 80 °C for 24 h, put in a porcelain boat, pyrolyze and carbonize in a tubular furnace protected by nitrogen atmosphere, keep warm at 300 °C for 4 h, then keep warm at 800 °C for 2 h, cool to room temperature, and obtain.

[0078] The above silicon-carbon negative electrode material was made into a negative electrode sheet, which was assembled with a positive electrode sheet, a separator, and an electrolyte to obtain a lithium-ion battery. The electrochemical performance of the battery was tested, and the test results are shown in Table 1.

[0079] Table 1

[0080]

[0081] It can be seen from Table 1 that the first reversible specific capacity of the material obtained in Example 1 is 1927.5 mAh / g, the first coulombic efficiency is 90.3%, and the capacity retention rate after 100 cycles is 84.5%. The first reversible specific capacity of the material obtained in Example 2 is 1973.6 mAh / g, the first coulombic efficiency is 91.7%, and the capacity retention rate after 100 cycles is 87.3%. The first reversible specific capacity of the material obtained in this Example 3 is 2020.3 mAh / g, the first coulombic efficiency is 92.2%, and the capacity retention rate after 100 cycles is 83.9%. The first reversible specific capacity of the material obtained in the comparative example is 1872.4 mAh / g, the first coulombic efficiency is 85.4%, and the capacity retention rate after 100 cycles is 78.6%. It shows that the silicon-carbon negative electrode material prepared by the present invention has excellent electrochemical properties.

[0082] In summary, the silicon-carbon negative electrode material provided by the present invention has excellent electrochemical properties and helps to improve the cycle performance of the battery.

[0083] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for preparing a silicon-carbon negative electrode material, characterized in that: The following steps are involved: S1, mixing lignin sulfonate and an alkaline solvent uniformly, drying, carbonizing, washing, and drying to obtain a sulfur-doped porous carbon material; S2, subjecting the sulfur-doped porous carbon material to a silicon deposition reaction to obtain a sulfur-doped porous silicon-carbon precursor material; S3. Add urea solution, formaldehyde and formic acid to the sulfur-doped porous silicon-carbon precursor material, stir, let stand, soak in acid, wash, dry and carbonize to obtain.

2. The preparation method according to claim 1, characterized in that: In the above-mentioned S2, the silicon deposition reaction comprises: introducing a protective gas into the sulfur-doped porous carbon material to raise the temperature to 500-600° C., then introducing a silicon source gas for primary deposition, and finally introducing an acetylene / nitrogen mixed gas for secondary deposition.

3. The preparation method according to claim 2, characterized in that: The protective gas is selected from one or more of nitrogen and argon; the silicon source gas is selected from one or more of monosilane, methylchlorosilane, cyclosiloxane, alkoxysilane, and dimethyldichlorosilane.

4. The preparation method according to claim 2, characterized in that: The flow rate of the protective gas is 5-35 L / min; the flow rate of the silicon source gas is 2-30 L / min; the volume ratio of acetylene / nitrogen in the acetylene / nitrogen mixed gas is 1:(2-6); the flow rate of acetylene is 2-5 L / min.

5. The preparation method according to claim 1, characterized in that: In the above S1, carbonization includes: carbonization for 1-3h at 400-600°C in a protective gas atmosphere; the protective gas is selected from one or more of nitrogen and argon.

6. The preparation method according to claim 1, characterized in that: In the S1, the lignin sulfonate is selected from one or more of sodium lignin sulfonate and calcium lignin sulfonate; the alkaline solvent is selected from one or more of potassium hydroxide solution, sodium hydroxide solution, sodium carbonate solution and potassium carbonate solution; the mass fraction of the alkaline solvent is 25%-35%; the mass ratio of the lignin sulfonate to the alkaline solvent is 1:(1-3); and the drying is vacuum drying at 60-90°C.

7. The preparation method according to claim 1, characterized in that: In the S3, the concentration of the urea solution is 0.4-0.6 mol / L; the mass fraction of formaldehyde is 1-4%; the mass fraction of formic acid is 0.5-1%; the acid soaking includes soaking in a hydrochloric acid solution for 36-72 hours, and the concentration of the hydrochloric acid solution is 0.5-2 mol / L.

8. The preparation method according to claim 1, characterized in that: In the S3, the carbonization includes introducing a protective gas, first keeping the temperature at 200-300°C for 4-6 hours, and then keeping the temperature at 700-900°C for 2-3 hours, and the protective gas is selected from one or more of nitrogen and argon.

9. A silicon-carbon negative electrode material obtained by the preparation method according to any one of claims 1 to 8, characterized in that: In the silicon-carbon negative electrode material, the content of S is 0.5-2wt%, the content of N is 1-3wt%, the content of Si is 45-55wt%, and the content of C is 40-55wt%.

10. Use of the silicon-carbon negative electrode material obtained by the preparation method according to any one of claims 1 to 8 or the silicon-carbon negative electrode material according to claim 9 in a lithium-ion battery.

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