Preparation Method and Application of a Low-Expansion Silicon-Carbon Anode Material

Abstract

The present invention relates to the technical field of anode materials, and particularly to a preparation method and application of a low-expansion silicon-carbon anode material, which includes the following steps: pretreating silicon particles in a piranha solution, uniformly sprinkling magnesium powder on the surface after washing and drying, heating and cooling to obtain porous silicon; mixing a nano-metal mixed suspension and the porous silicon, ultrasonicating, centrifuging to collect the solid, washing, and drying to obtain nano-metal doped porous silicon; adding a carbon source, mixing and grinding, drying, and then putting it into a tube furnace to obtain a pyrolysis product; mixing with polyvinylpyrrolidone, grinding, and then heating in a tube furnace, and cooling to obtain the silicon-carbon anode material. The preparation method and application of a low-expansion silicon-carbon anode material adopting the above steps of the present invention, the doping of nano-metal particles effectively alleviates the local expansion of porous silicon, and the carbon source wraps the nano-metal doped porous silicon therein, effectively alleviating the expansion of porous silicon.

Description

Technical Field

[0001] The present invention relates to the technical field of anode materials, and particularly to a preparation method and application of a low-expansion silicon-carbon anode material. Background Art

[0002] One of the development directions of lithium-ion batteries is higher energy density, and developing new electrode materials is an effective means to improve energy density. In terms of anode materials, the actual capacity of the widely commercialized graphite currently used has approached its theoretical capacity. Therefore, it is necessary to develop new high-capacity anode materials to further improve the energy density of the battery.

[0003] Among all the new anode materials, pure silicon anode materials are considered to be the most promising next-generation anode materials due to their high theoretical specific capacity, low redox potential, rich reserves, and environmental friendliness. However, the huge volume change (exceeding 300%) during charge and discharge and low electron and ion conductivities brought about by high capacity have led to many problems such as low cycle life due to repeated rupture of the SEI, consumption of irreversible Li, and low capacity utilization in actual applications, seriously hindering the application of pure silicon anode materials in full batteries. And a large number of micropores below 1 nm will result in too high specific surface area of porous carbon, which will reduce the first efficiency when preparing silicon-carbon anode materials. Summary of the Invention

[0004] The purpose of the present invention is to provide a preparation method and application of a low-expansion silicon-carbon anode material. The doping of nano-metal particles effectively alleviates the local expansion of porous silicon, and the carbon source wraps the nano-metal-doped porous silicon, effectively alleviating the expansion of porous silicon and improving the first-cycle Coulomb efficiency.

[0005] To achieve the above purpose, the present invention provides a preparation method of a low-expansion silicon-carbon anode material, including the following steps,

[0006] S1. Pretreat silicon particles in piranha solution, then wash them with deionized water until neutral, dry them, evenly sprinkle magnesium powder on the surface, heat at 800 - 1200 °C for 1 - 5 h, wash after cooling to room temperature, and dry with nitrogen to obtain porous silicon;

[0007] S2. Mix the nano-metal mixed suspension and the porous silicon in S1, then ultrasonicate, collect the solid by centrifugation, wash it, and dry it to obtain nano-metal-doped porous silicon;

[0008] S3. Mix the nano-metal-doped porous silicon obtained in S2 and the carbon source, grind them, dry them, and then put them into a tube furnace for pyrolysis under an inert atmosphere to obtain a pyrolysis product;

[0009] S4. Mix the pyrolysis product in S3 with polyvinylpyrrolidone, grind the mixture, then place it in a tube furnace and heat it under an inert atmosphere. After cooling, a silicon-carbon anode material is obtained.

[0010] Preferably, in S1, during washing, concentrated hydrochloric acid and deionized water are used for washing in sequence, and the washing is carried out 2 - 5 times.

[0011] Preferably, in S2, the drying is carried out at 70 - 90 °C for 8 - 12 h.

[0012] Preferably, in S2, the nano-metals in the nano-metal mixed suspension include one or more of nano-antimony, nano-tin, nano-titanium, nano-aluminum, and nano-iron.

[0013] Preferably, in S2, the grinding is carried out under the protection of an inert atmosphere, the grinding speed is 500 - 1200 rpm / min, and the grinding time is 1 - 8 h.

[0014] Preferably, in S3, the carbon source includes one or more of cyclodextrin, graphene, asphalt, carbon nanotubes, biomass carbon, and polystyrene.

[0015] Preferably, in S3, the pyrolysis temperature is 800 - 1200 °C, and the time is 1 - 5 h.

[0016] Preferably, in S4, the mass ratio of the pyrolysis product to polyvinylpyrrolidone is 5 - 12:1.

[0017] Preferably, in S4, the heating is carried out at 1200 - 1800 °C for heat preservation for 2 - 5 h.

[0018] An application of a low-expansion silicon-carbon anode material, the silicon-carbon anode material prepared by the above preparation method is applied to the anode of a lithium battery.

[0019] Therefore, the present invention adopts the above preparation method and application of a low-expansion silicon-carbon anode material, and its beneficial effects are as follows:

[0020] 1. In the silicon-carbon anode material provided by the present invention, nano-metal particles are doped in porous silicon to optimize the electron and ion transport paths. The nano-metal particles provide mechanical support for the porous silicon to enhance the mechanical strength and structural stability of the porous silicon, reduce the capacity attenuation during cycling, and at the same time, the porous silicon structure is beneficial to the penetration of the electrolyte;

[0021] 2. In the silicon-carbon anode material provided by the present invention, the carbon source material forms a shell to wrap the nano-metal doped porous silicon inside. The cyclodextrin on the carbon shell reacts with polyvinylpyrrolidone. The cyclodextrin makes the polyvinylpyrrolidone evenly distributed on the surface of the silicon-carbon anode and partially wraps the pore diameter of the silicon-carbon anode, thereby adjusting the pores of the silicon-carbon anode material and improving the initial Coulomb efficiency;

[0022] 3. The nano-metal particles used in the present invention can be used as a buffer layer to absorb and disperse the stress generated by the expansion of porous silicon, and form a conductive network to improve the ion transport path and reduce the phenomenon of local expansion;

[0023] 4. The present invention reduces the production cost by using carbon sources such as biomass charcoal.

[0024] The technical solutions of the present invention will be further described in detail below with reference to the drawings and embodiments. Description of the Drawings

[0025] Figure 1 It is the XRD pattern of the silicon-carbon negative electrode, Si and β-cyclodextrin in Example 4 of the present invention;

[0026] Figure 2 It is the first charge-discharge curve of Application Example 1 and Comparative Example 1 of the present invention. Detailed Embodiments

[0027] The present invention will be further described below with reference to the drawings and embodiments. Unless otherwise defined, the technical terms or scientific terms used in the present invention should have the ordinary meaning understood by those of ordinary skill in the field to which the present invention belongs. The above-mentioned features mentioned in the present invention or the features mentioned in the specific examples can be combined arbitrarily. These specific embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. The described embodiments are only a part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0028] Example 1

[0029] S1. The silicon particles are pretreated in a piranha solution (3:1, V / V, concentrated sulfuric acid: hydrogen peroxide) for 1 h, then washed with deionized water until neutral, dried, and magnesium powder is evenly sprinkled on the surface. After heating at 1000 °C for 1.5 h and cooling to room temperature, it is washed, successively washed with concentrated hydrochloric acid and deionized water for 5 times, and blown dry with nitrogen to obtain porous silicon.

[0030] S2. The nano-metal mixed suspension (nano-antimony and nano-tin are mixed in a mass ratio of 1:1) and the porous silicon in S1 are mixed and then ultrasonicated. After centrifugation, the solid is collected, washed alternately with ethanol and deionized water, and dried at 80 °C for 9 h to obtain nano-metal doped porous silicon, and the nano-metal doping amount is 10%.

[0031] S3. Mix the nano-metal doped porous silicon obtained in S2 and the carbon source (a mixture of β-cyclodextrin and biomass carbon with a mass ratio of 1:2) at a mass ratio of 1:3, grind them, dry them, put them into a tubular furnace, and pyrolyze them under an inert atmosphere at a pyrolysis temperature of 1200 °C for 2 h to obtain a pyrolysis product.

[0032] S4. Mix the pyrolysis product in S3 and polyvinylpyrrolidone at a mass ratio of 10:1, grind them at 500 rpm for 10 h, then put them into a tubular furnace, keep them at 1500 °C for 3 h under an inert atmosphere, and cool them to obtain a silicon-carbon anode material.

[0033] Example 2

[0034] S1. Pretreat silicon particles in piranha solution (3:1, V / V, concentrated sulfuric acid: hydrogen peroxide) for 1 h, then wash them with deionized water until neutral, dry them, evenly sprinkle magnesium powder on the surface, heat them at 1000 °C for 1.5 h, cool them to room temperature, wash them, wash them successively with concentrated hydrochloric acid and deionized water for 5 times, and dry them with nitrogen to obtain porous silicon.

[0035] S2. Mix the nano-metal mixed suspension (a mixture of nano-tin and nano-titanium with a mass ratio of 1:1) and the porous silicon in S1, ultrasonicate them, collect the solid after centrifugation, wash it alternately with ethanol and deionized water, and dry it at 70 °C for 12 h to obtain nano-metal doped porous silicon, and the doping amount of nano-metal is 12%.

[0036] S3. Mix the nano-metal doped porous silicon obtained in S2 and the carbon source (a mixture of β-cyclodextrin and pitch with a mass ratio of 1:2) at a mass ratio of 1:2, grind them, dry them, put them into a tubular furnace, and pyrolyze them under an inert atmosphere at a pyrolysis temperature of 1200 °C for 2 h to obtain a pyrolysis product.

[0037] S4. Mix the pyrolysis product in S3 and polyvinylpyrrolidone at a mass ratio of 10:1, grind them at 500 rpm for 10 h, then put them into a tubular furnace, keep them at 1500 °C for 3 h under an inert atmosphere, and cool them to obtain a silicon-carbon anode material.

[0038] Example 3

[0039] S1. Pretreat silicon particles in piranha solution (3:1, V / V, concentrated sulfuric acid: hydrogen peroxide) for 1 h, then wash them with deionized water until neutral, dry them, evenly sprinkle magnesium powder on the surface, heat them at 1000 °C for 1.5 h, cool them to room temperature, wash them, wash them successively with concentrated hydrochloric acid and deionized water for 5 times, and dry them with nitrogen to obtain porous silicon.

[0040] S2. Mix the nano-metal mixed suspension (nano-titanium and nano-aluminum are mixed at a mass ratio of 3:1) with the porous silicon in S1, ultrasonicate, collect the solid after centrifugation, wash it alternately with ethanol and deionized water, and dry it at 90 °C for 8 h to obtain nano-metal-doped porous silicon with a nano-metal doping amount of 15%.

[0041] S3. Mix the nano-metal-doped porous silicon obtained in S2 with a carbon source (β-cyclodextrin and graphene are mixed at a mass ratio of 1:2) at a mass ratio of 1:3, grind, dry, and then put it into a tube furnace for pyrolysis under an inert atmosphere. The pyrolysis temperature is 1200 °C and the time is 2 h to obtain a pyrolysis product.

[0042] S4. Mix the pyrolysis product in S3 with polyvinylpyrrolidone at a mass ratio of 10:1, grind at 500 rpm / min for 10 h, then put it into a tube furnace, keep it at 1500 °C for 3 h under an inert atmosphere, and cool to obtain a silicon-carbon anode material.

[0043] Example 4

[0044] S1. Pretreat silicon particles in a piranha solution (3:1, V / V, concentrated sulfuric acid: hydrogen peroxide) for 1 h, then wash with deionized water until neutral, dry, evenly sprinkle magnesium powder on the surface, heat at 1000 °C for 1.5 h, wash after cooling to room temperature, wash successively with concentrated hydrochloric acid and deionized water for 5 times, and blow dry with nitrogen to obtain porous silicon.

[0045] S2. Mix the nano-metal mixed suspension (nano-antimony and nano-titanium are mixed at a mass ratio of 1:2) with the porous silicon in S1, ultrasonicate, collect the solid after centrifugation, wash it alternately with ethanol and deionized water, and dry it at 80 °C for 10 h to obtain nano-metal-doped porous silicon with a nano-metal doping amount of 18%.

[0046] S3. Mix the nano-metal-doped porous silicon obtained in S2 with a carbon source (β-cyclodextrin and carbon nanotubes are mixed at a mass ratio of 1:2) at a mass ratio of 1:2, grind, dry, and then put it into a tube furnace for pyrolysis under an inert atmosphere. The pyrolysis temperature is 1200 °C and the time is 2 h to obtain a pyrolysis product.

[0047] S4. Mix the pyrolysis product in S3 with polyvinylpyrrolidone at a mass ratio of 10:1, grind at 500 rpm / min for 10 h, then put it into a tube furnace, keep it at 1500 °C for 3 h under an inert atmosphere, and cool to obtain a silicon-carbon anode material.

[0048] Example 5

[0049] S1. Pretreat the silicon particles in piranha solution (3:1, V / V, concentrated sulfuric acid: hydrogen peroxide) for 1 h, then wash them with deionized water until neutral, dry them, evenly sprinkle magnesium powder on the surface, heat at 1000 °C for 1.5 h, wash after cooling to room temperature, wash successively with concentrated hydrochloric acid and deionized water for 5 times, and blow dry with nitrogen to obtain porous silicon.

[0050] S2. Mix the nano-metal mixed suspension (nano-tin and nano-iron mixed at a mass ratio of 1:1.5) and the porous silicon in S1, ultrasonicate, collect the solid after centrifugation, wash alternately with ethanol and deionized water, and dry at 70 °C for 12 h to obtain nano-metal doped porous silicon, with the nano-metal doping amount being 20%.

[0051] S3. Mix the nano-metal doped porous silicon obtained in S2 and the carbon source (β-cyclodextrin and polystyrene mixed at a mass ratio of 1:2) at a mass ratio of 1:3, grind, dry, put it into a tube furnace, pyrolyze under an inert atmosphere, with the pyrolysis temperature being 1200 °C and the time being 2 h, to obtain the pyrolysis product.

[0052] S4. Mix the pyrolysis product in S3 and polyvinylpyrrolidone at a mass ratio of 10:1, grind, then put it into a tube furnace, keep it at 1500 °C for 3 h under an inert atmosphere, and cool to obtain the silicon-carbon negative electrode material.

[0053] Application Example 1

[0054] Mix the silicon-carbon negative electrode material in Example 2 with a binder, carbon black and a solvent to obtain a negative electrode slurry, coat the negative electrode slurry on a copper foil current collector to obtain a negative electrode sheet, and then prepare a lithium-ion battery together with the positive electrode sheet, separator and electrolyte.

[0055] Comparative Example 1

[0056] S1. Pretreat the silicon particles in piranha solution (3:1, V / V, concentrated sulfuric acid: hydrogen peroxide) for 1 h, then wash them with deionized water until neutral, dry them, evenly sprinkle magnesium powder on the surface, heat at 1000 °C for 1.5 h, wash after cooling to room temperature, wash successively with concentrated hydrochloric acid and deionized water for 5 times, and blow dry with nitrogen to obtain porous silicon.

[0057] S2. Mix the porous silicon obtained in S1 and the carbon source (β-cyclodextrin and pitch mixed at a mass ratio of 1:2), grind, dry, put it into a tube furnace, pyrolyze under an inert atmosphere, with the pyrolysis temperature being 1200 °C and the time being 2 h, and cool to obtain the silicon-carbon negative electrode material.

[0058] According to the method in Application Example 1, use the silicon-carbon negative electrode material in Comparative Example 1 to prepare a lithium-ion battery.

[0059] Comparative Example 2

[0060] S1. Pretreat the silicon particles in piranha solution (3:1, V / V, concentrated sulfuric acid: hydrogen peroxide) for 1 h, then wash with deionized water until neutral, dry, evenly sprinkle magnesium powder on the surface, heat at 1000 °C for 1.5 h, wash after cooling to room temperature, wash successively with concentrated hydrochloric acid and deionized water for 5 times, and dry with nitrogen to obtain porous silicon.

[0061] S2. Mix the porous silicon obtained in S1 with carbon source pitch, grind, dry, and then put it into a tubular furnace for pyrolysis under an inert atmosphere. The pyrolysis temperature is 1200 °C and the time is 2 h to obtain a pyrolysis product.

[0062] S3. Mix the pyrolysis product in S2 with polyvinylpyrrolidone at a mass ratio of 10:1, grind, and then put it into a tubular furnace to keep it at 1500 °C for 3 h under an inert atmosphere. After cooling, a silicon-carbon negative electrode material is obtained.

[0063] Test Example

[0064] a. Perform charge-discharge tests on the batteries assembled in Application Example 1 and Comparative Example 1 on a LAND charge-discharge tester.

[0065] Perform cyclic tests at a charge-discharge rate of 0.2C (1C = 1600 mA / g) in the voltage range of 0.005 - 1.5 V. The discharge capacity in the first cycle is 2857.0 mAh / g, the first Coulombic efficiency is 90.3%, and the discharge capacity retention rate after 500 cycles is 91.0%.

[0066] Perform charge-discharge tests on the battery assembled in Comparative Example 1 on a LAND charge-discharge tester. Perform cyclic tests at a charge-discharge rate of 0.2C (1C = 1600 mA / g) in the voltage range of 0.005 - 1.5 V. The discharge capacity in the first cycle is 2552.0 mAh / g, the first Coulombic efficiency is 78.3%, and the discharge capacity retention rate after 500 cycles is 72.4%.

[0067] From the data comparison between Comparative Example 1 and Application Example 1, it can be seen that the first Coulombic efficiency of Application Example 1 is significantly improved, indicating that adjusting the pores on the carbon coating layer by polyvinylpyrrolidone can effectively improve the first Coulombic efficiency.

[0068] b. Perform XRD tests on the silicon-carbon negative electrode material obtained in Example 4. The results are as Figure 1 shown. It can be seen that the silicon-carbon negative electrode material in Example 4 shows characteristic peaks of silicon near 29°, 48°, and 57°, and a characteristic peak of the carbon coating layer appears near 20°, indicating the successful synthesis of the silicon-carbon negative electrode material.

[0069] c. For Application Example 1 and Comparative Example 1 at 0.1Ag -1The first charge-discharge test was carried out at a current density of Figure 2 as shown below.

[0070] Therefore, the present invention adopts the preparation method and application of a low-expansion silicon-carbon anode material with the above steps. The doping of nano-metal particles effectively alleviates the local expansion of porous silicon, and the carbon source wraps the nano-metal-doped porous silicon, effectively alleviating the expansion of porous silicon.

[0071] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify or equivalently replace the technical solutions of the present invention, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A preparation method of a low-expansion silicon-carbon anode material, characterized in that: It includes the following steps: S1. Pretreat the silicon particles in piranha solution, then wash them with deionized water until neutral. After drying, evenly sprinkle magnesium powder on the surface, heat at 800 - 1200 °C for 1 - 5 h, wash after cooling to room temperature, and dry with nitrogen to obtain porous silicon; S2. Mix the nano - metal mixed suspension and the porous silicon in S1, then ultrasonicate, collect the solid by centrifugation, wash, and dry to obtain nano - metal - doped porous silicon; In S2, the nano - metals in the nano - metal suspension include one or more of nano - antimony, nano - tin, nano - titanium, nano - aluminum, and nano - iron; S3. Mix the nano - metal - doped porous silicon obtained in S2 and the carbon source, then grind, dry, and put it into a tubular furnace for pyrolysis in an inert atmosphere to obtain a pyrolysis product; In S3, the carbon source includes one of cyclodextrin and biomass carbon, cyclodextrin and asphalt, cyclodextrin and graphene, cyclodextrin and carbon nanotubes, cyclodextrin and polystyrene; In S3, the pyrolysis temperature is 800 - 1200 °C and the time is 1 - 5 h; S4. Mix the pyrolysis product in S3 and polyvinylpyrrolidone, then grind, and put it into a tubular furnace for heating in an inert atmosphere. After cooling, obtain the silicon - carbon anode material; In S4, the mass ratio of the pyrolysis product to polyvinylpyrrolidone is 5 - 12:1; In S4, the heating is carried out at 1200 - 1800 °C for heat preservation for 2 - 5 h; The carbon - source material forms a shell to wrap the nano - metal - doped porous silicon inside. The cyclodextrin on the carbon shell reacts with polyvinylpyrrolidone. The cyclodextrin makes polyvinylpyrrolidone evenly distributed on the surface of the silicon - carbon anode and partially wraps the pore diameter of the silicon - carbon anode, thereby adjusting the pores of the silicon - carbon anode material.

2. The preparation method of a low-expansion silicon-carbon anode material according to claim 1, characterized in that: In S1, during washing, use concentrated hydrochloric acid and deionized water in sequence for washing, and wash 2 - 5 times.

3. The preparation method of a low-expansion silicon-carbon anode material according to claim 1, wherein: In S2, the drying is carried out at 70 - 90 °C for 8 - 12 h.

4. The preparation method of a low-expansion silicon-carbon anode material according to claim 1, characterized in that: In S2, the grinding is carried out under the protection of an inert atmosphere, the grinding speed is 500 - 1200 rpm / min, and the grinding time is 1 - 8 h.

5. Application of a low-expansion silicon-carbon anode material, characterized in that: The silicon - carbon anode material prepared by the preparation method according to any one of claims 1 - 4 is applied to the anode of a lithium battery.

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