A carbon-coated silicon-based negative electrode material and a preparation method thereof, and a lithium ion battery

Abstract

The application relates to the technical field of lithium ion batteries, in particular to a repaired carbon-coated silicon-based negative electrode material, a preparation method thereof and a lithium ion battery. The preparation method of the repaired carbon-coated silicon-based negative electrode material comprises the following steps: uniformly mixing a carbon source precursor and silicon-based negative electrode material raw powder, heat-treating at 500-1100 DEG C for 1.5-10 h to obtain a composite material; the silicon-based negative electrode material raw powder is composed of at least one of silicon and an oxide of silicon; the molar ratio of oxygen to silicon in the silicon-based negative electrode material raw powder is 0.1-1.9:1; mixing the composite material with a repairing agent in a solvent, removing the solvent, and then heat-treating at 700-1200 DEG C for 1-6 h under the protection of an inert gas. The repaired carbon-coated silicon-based negative electrode material can perform secondary repair on silicon-based material particles, form a complete coating layer on the surface of the silicon-based material particles, reduce the resistivity of the material, reduce the contact between the material and electrolyte, optimize the carbon structure, and improve the cycle performance of the negative electrode material.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a silicon-based negative electrode material coated with carbon, a preparation method thereof and a lithium ion battery. BACKGROUND

[0002] With the application range of lithium ion batteries becoming wider, higher requirements for the energy density of lithium ion batteries are put forward in many application fields. When improving the energy density of lithium ion batteries, increasing the specific capacity of electrode materials is an effective means. At present, the negative active material used in the mass production of lithium ion batteries is mainly graphite material. The theoretical specific capacity of graphite is only 372 mAh / g, which cannot meet the current demand for high energy density energy storage. The theoretical capacity of silicon-based material as negative active material is as high as 4200 mAh / g, which can greatly improve the energy density of the battery.

[0003] However, the silicon-based material has a volume expansion of more than 300% when deintercalating lithium, and the volume expansion effect will cause the capacity retention rate of the silicon-based material to continue to decrease rapidly during the charge and discharge cycle. In order to reduce the influence of the volume expansion effect of the silicon-based material, carbon coating is a commonly used method to modify the silicon-based negative electrode material.

[0004] When carbon coating is modified, there are many types of carbon sources that can be selected, among which carbon chain polymers have the advantages of low cost and easy dispersion, and have become a commonly used organic pyrolytic carbon source. However, when using carbon chain polymers as carbon sources, the inevitable volatilization and carbon source thermal decomposition reaction during the heat treatment process will introduce a large number of pores into the silicon-carbon material obtained by the final coating, which greatly weakens the mechanical support of the carbon shell, and at the same time increases the contact area between the electrolyte and the silicon-based material, causing the decrease of the first charge and discharge efficiency, the instability of the SEI layer, and the decrease of the capacity retention rate during the cycle.

[0005] A Chinese invention patent with publication number CN112768644A discloses a method for modifying the interface of a silicon-carbon composite negative electrode material coated with modified asphalt. In this method, phenolic resin is added to the asphalt, and then nano-silicon and graphite are mixed and ball milled before high-temperature sintering, so as to form a relatively dense nano-carbon coating layer on the surface of nano-silicon and graphite with low porosity defects, thereby repairing the cracks, pores and other defects existing on the surface of nano-silicon and graphite.

[0006] However, in this method, the phenolic resin is ball milled with the asphalt to form a modified asphalt, and then the nano-silicon and graphite are coated. During high-temperature sintering, both the asphalt and the phenolic resin carbonize, and pores are formed during the carbonization process. The phenolic resin itself also undergoes thermal cracking, producing pore structures, and the repairing effect on the pores formed after sintering of the asphalt is very limited.

[0007] A Chinese invention patent with publication number CN106532017A discloses a preparation method of SiO x / C surface-coated graphite negative electrode material. SiO x / C material is prepared by adding SiO x / C material, pitch, organic acid and dispersant into a ball mill tank to prepare a uniformly mixed slurry, and then using a spray granulation and high-temperature pyrolysis method to prepare SiO x / C material, graphite, additive, resin and curing agent are uniformly mixed, and then SiO x / C surface-coated graphite negative electrode material is prepared by spray granulation, high-temperature pyrolysis and classification screening process.

[0008] The method uses twice high-temperature pyrolysis to composite carbon material and SiO x / C material, but after SiO x / C material, graphite and resin and curing agent are mixed and sintered, the used resin and process cannot form effective repair to the pores in SiO x / C material, and the surface of the prepared negative electrode material particle is rough, still has many pores, and it is difficult to form a high-quality complete carbon coating layer structure, and the contact between silicon material and electrolyte cannot be sufficiently reduced. SUMMARY

[0009] In order to improve the integrity of the carbon coating layer on the surface of silicon material and reduce the contact between silicon material and electrolyte, the present application provides a repaired carbon-coated silicon-based negative electrode material, a preparation method thereof and a lithium ion battery.

[0010] In a first aspect, the present application provides a preparation method of a repaired carbon-coated silicon-based negative electrode material, which adopts the following technical scheme:

[0011] A preparation method of a repaired carbon-coated silicon-based negative electrode material, comprising the following steps:

[0012] 1) uniformly mixing a carbon source precursor and a silicon-based negative electrode material raw powder, heat treating at 500-1100℃ for 1.5-10h to obtain a composite material;

[0013] The carbon source precursor is an organic pyrolysis carbon source;

[0014] The silicon-based negative electrode material raw powder is an oxide of silicon or is composed of an oxide of silicon and silicon; the molar ratio of oxygen to silicon in the silicon-based negative electrode material raw powder is 0.1-1.9:1;

[0015] 2) uniformly mixing the composite material obtained in step 1) and a repairing agent in a solvent, removing the solvent, and then heat treating at 700-1200℃ for 1-6h under inert gas protection to obtain the repaired carbon-coated silicon-based negative electrode material;

[0016] The repair agents are fulvic acid, brown humic acid, tannic acid, black humic acid, humic acid, alginic acid, malic acid, tannic acid, mandelic acid, caffeic acid, methyl cinnamate, modified epoxy resin, modified acrylic resin, modified alkyd resin, melatonin, β-phenylpropionic acid, anthraquinone-2,6-disulfonate, and Supelite. TM DAX-8, EPA 8020B At least one of XAD7HP.

[0017] By adopting the above scheme, the carbon source precursor is mixed evenly with the silicon-based anode material powder and then heat-treated at 500-1100℃. During the heat treatment at this temperature, the carbon source precursor can be pre-carbonized, and the pre-carbonized product coats the surface of the silicon-based particles to form a carbon-coated silicon-based composite material.

[0018] The carbon source precursor is an organic pyrolytic carbon source, which can undergo carbonization or pre-carbonization by heat treatment at 500-1100℃. Further, the carbon source precursor is at least one of the following: asphalt, glucose, sucrose, starch, polyvinyl alcohol, polyvinylpyrrolidone, poly(4-ethylphenol), 2-(pyrrolidone-1-yl)phenyl-1-pentanone, polyvinylpyrrolidone copolymer, vitamin C, citric acid, polyethylene, polypropylene, polystyrene, polyacrylonitrile, phenolic resin, epoxy resin, and urea-formaldehyde resin.

[0019] In subsequent steps, the composite material and the repair agent are mixed in a solvent. Because the repair agent used in this application has good solubility and dispersibility in the solvent, it adheres to the surface of the composite material particles after dispersion and easily penetrates into the pores of the particles, enabling secondary repair of the particle surface. After sintering, a complete carbon coating structure is obtained. This not only reduces the resistivity of the negative electrode material and improves the integrity of the carbon coating, but also effectively reduces the contact between silicon-based particles and the electrolyte, thereby reducing the probability of side reactions in the negative electrode material during battery cycling and improving the cycle performance of the negative electrode material.

[0020] The repaired and intact carbon layer coating structure can also provide better mechanical stress to offset the volume expansion of silicon-based materials during battery cycling, further improving the cycle performance of the anode material.

[0021] The repair agent used in this application has strong binding ability, and the repaired carbon layer is more complete and stable. It is not easy for the structure to collapse during charge-discharge cycles, and it has good conductivity, which can effectively improve the cycle stability and carrier transport capability of silicon-based anode materials.

[0022] Further preferably, the repairing agent is at least one of fulvic acid, humic acid, xanthic acid, tannic acid, quercetin, caffeic acid, methyl cinnamate, melanin, β-phenylpropionic acid, and anthraquinone-2,6-disulfonate. Further preferably, the repairing agent is at least one of fulvic acid, humic acid, xanthic acid, tannic acid, quercetin, caffeic acid, and β-phenylpropionic acid. Further, the repairing agent is preferably a repairing agent having an aromatic ring in the molecule or a substance containing a molecule having an aromatic ring in the repairing agent. Further, the mass fraction of the substance having an aromatic ring in the repairing agent is greater than 20%. The substance having an aromatic ring has a molecular weight greater than 1000 and a C / H atomic ratio greater than 1.26. Further preferably, the aromatic ring is a benzene ring.

[0023] The particle size of the silicon-based negative electrode material raw powder used in the present application is as small as possible. Generally, the particle size of the silicon-based negative electrode material raw powder is 0.1-50 μm, so that the small particle size of the silicon-based negative electrode material raw powder is completely covered by the carbon source precursor, and a relatively complete coating layer is formed on the particle surface after pre-carbonization.

[0024] Further, the oxide of silicon in step 1) is at least one of SiO and SiO2. The silicon-based negative electrode material raw powder can be obtained by mixing the oxide of silicon and elemental silicon, and only the molar ratio of oxygen to silicon in the silicon-based negative electrode material raw powder needs to be 0.1-1.9:1. Preferably, the molar ratio of oxygen to silicon in the silicon-based negative electrode material raw powder is 1.0-1.9:1.

[0025] Further, the mass ratio of the carbon source precursor to the silicon-based negative electrode material raw powder in step 1) is 0.1-50:100. Preferably, the mass ratio of the carbon source precursor to the silicon-based negative electrode material raw powder is 1-10:100.

[0026] By using the above scheme, the amount of the carbon source precursor is relatively small compared with the amount of the silicon-based negative electrode material raw powder, so that the thickness of the coating layer of the carbon source precursor coated on the surface of the silicon-based negative electrode material raw powder particle is relatively small, generally only 1 nm-1 μm, which not only ensures the formation of a relatively complete coating layer on the particle surface, but also reduces the influence of the carbon layer on the overall capacity of the negative electrode material, and ensures that the silicon-based negative electrode material raw powder particles inside the coating layer fully exhibit their high capacity characteristics.

[0027] The heat treatment in step 1) is carried out under the protection of inert gas. The inert gas is at least one of nitrogen and argon. When the heat treatment is carried out in a mixer under the protection of inert gas, the outlet pressure of the inert gas is 0.01 MPa. The flow rate of the inert gas is 30-100 mL / min. The heat treatment at 500-1100°C is carried out at a temperature rising rate of 1-20°C / min to 500-1100°C. After the temperature is raised to 500-1100°C, the stirring is carried out first, and then the temperature is kept for 1.5-5 h. The stirring speed is 100-500 r / min, and the stirring time is 15-60 min. Preferably, the stirring speed is 200-400 r / min, and the stirring time is 15-30 min.

[0028] Further, the mass ratio of the repairing agent to the composite material in step 2) is 0.1-1:10-20. Preferably, the mass ratio of the repairing agent to the composite material in step 2) is 0.1-1:10-15. Further preferably, the mass ratio of the repairing agent to the composite material in step 2) is 0.1-0.5:12.5.

[0029] By using the above scheme, the amount of the repairing agent is very small relative to the composite material, so that the repairing agent can enter the pores of the composite material particles with the solvent and sufficiently repair the pores, and too much repairing agent is not left on the surface of the pre-carbonized coating layer formed in step 1).

[0030] Further, the mixing of the composite material and the repairing agent in the solvent in step 2) is to mix the repairing agent and the solvent first, and then add the composite material and mix uniformly. Further, when the repairing agent and the solvent are mixed uniformly, the vacuum stirring is carried out at a speed of 900-1200 rpm for 5-10 min. When the composite material is added and mixed uniformly, the vacuum stirring is carried out at a speed of 900-1200 rpm for 10-15 min.

[0031] By using the above scheme, the repairing agent is mixed with the solvent first, so that the repairing agent can be fully dissolved in the solvent and easily enter the small pores of the composite material particles.

[0032] The solvent in step 2) is water or an organic solvent, and the organic solvent is any one of ethanol, acetone and N,N-dimethylformamide.

[0033] The water or the organic solvent can make the repairing agent dissolve as much as possible to form a solution or be uniformly dispersed, so as to facilitate the repairing agent to enter the small pores of the composite material particles with the solvent.

[0034] Further, the removing of the solvent in step 2) is that the mixture of the composite material and the repairing agent in the solvent is firstly vacuum-rotary evaporated, and then heated and dried. The temperature of the vacuum-rotary evaporation is 50-60℃, and the rotation speed is 60-120rpm. The temperature of the heating and drying is 75-95℃, and the drying time is 1-3h. The heating and drying is preferably water-bath heating and drying.

[0035] By using the above scheme, the vacuum-rotary evaporation increases the evaporation area of the material particles, so that the solvent immersed in the pores of the silicon-based negative electrode material raw powder is more easily volatilized and escaped, and the probability of the capillary phenomenon caused by the small pores of the material carrying out the repairing agent is reduced. After the vacuum-rotary evaporation, most of the solvent has been volatilized and escaped, and then the residual solvent is completely dried at a lower temperature.

[0036] In step 2), the grinding is performed after the removing of the solvent.

[0037] Further, in step 2), the temperature is first increased to 700-1200℃ at a heating rate of 1-20℃ / min, and then the temperature is kept for 1-6h.

[0038] By using the above scheme, the heating rate is controlled to be small, the duration of the heating process is prolonged, the decomposition of the repairing agent during the heating is gradually slow, and each stage of the carbonization process can be fully performed.

[0039] Further, when the composite material and the repairing agent are mixed in step 2), carbon nanotubes are also added, and the mass ratio of the carbon nanotubes to the repairing agent is 0.1-1:0.01-0.1.

[0040] Although the carbon nanotubes have a small diameter, due to the very small pore size of the pores on the surface of the silicon-carbon material, in the prior art, it is difficult for the carbon nanotubes to enter and be fixed in the small pores of the silicon-carbon material, and it is also difficult for the carbon nanotubes to be firmly attached to the surface of the silicon-carbon material. In the present application, the repairing agent is added, and the carbon nanotubes enter the small pores on the surface of the silicon-carbon material with the repairing agent, and after high-temperature treatment, the generated carbon material can firmly fix the carbon nanotubes on the surface of the silicon-carbon particles. Preferably, the length of the carbon nanotubes is 5-15μm, and the tube diameter is 40-60nm. Further preferably, when the carbon nanotubes are added, the repairing agent contains a benzene ring in the molecule or contains a substance with a molecule containing a benzene ring, so that the large π bond in the benzene ring can produce a certain attraction between the carbon nanotubes, and the carbon nanotubes are better fixed.

[0041] In step 2), the inert gas is at least one of nitrogen and argon. The flow rate of the inert gas is 5-200mL / min. Preferably, the flow rate of the inert gas is 45-80mL / min.

[0042] Step 2) is kept at 700-1200℃ for 1-6h, then cooled down, grinded and sieved. The sieving is through a 200 mesh sieve.

[0043] In a second aspect, the application provides a repaired carbon-coated silicon-based negative electrode material, which adopts the following technical solution:

[0044] A repaired carbon-coated silicon-based negative electrode material prepared by the above preparation method.

[0045] Further, the carbon content in the repaired carbon-coated silicon-based negative electrode material is 1.83-10.86%. The powder resistivity of the repaired carbon-coated silicon-based negative electrode material is 0.12-5.23Ω·m.

[0046] In a third aspect, the application provides a lithium ion battery, which adopts the following technical solution:

[0047] A lithium ion battery includes a positive electrode, a negative electrode, a separator, and an electrolyte. The negative electrode includes a negative electrode current collector and a negative electrode material layer coated on the surface of the negative electrode current collector. The negative electrode material layer includes a negative electrode active material, and the negative electrode active material is the repaired carbon-coated silicon-based negative electrode material described above.

[0048] The positive electrode includes a positive electrode current collector and a positive electrode material layer coated on the surface of the positive electrode current collector. The positive electrode material layer includes a positive electrode active material, and the positive electrode active material can be any one of lithium iron phosphate and ternary materials. The ternary material is NCM or NCA.

[0049] Beneficial effects:

[0050] The preparation method of the repaired carbon-coated silicon-based negative electrode material of the application first coats the surface of the silicon-based particles with a carbon source precursor, and then forms a carbon coating layer after sintering. Then, the liquid phase material formed in the solvent by the repairing agent is used to repair the surface of the material particles, so that the pores formed in the material particles due to high-temperature sintering are plugged, and a complete carbon coating layer structure is obtained. Not only can the resistivity of the negative electrode material be reduced, but also the contact between the silicon-based particles and the electrolyte can be effectively reduced, and the cycle performance of the negative electrode material is improved.

[0051] Further, the preparation method of the repaired carbon-coated silicon-based negative electrode material of the application does not introduce toxic, environmentally unfriendly catalysts, flammable gases, or other harsh conditions. The process is green and environmentally friendly, and the cost is low, which is suitable for large-scale promotion. BRIEF DESCRIPTION OF DRAWINGS

[0052] Figure 1 is a schematic diagram of the preparation process of the repaired carbon-coated silicon-based negative electrode material of the application; wherein 1 is the particle structure before repair, and 2 is the particle structure after repair.

[0053] Figure 2is a scanning electron microscope image of the repaired carbon-coated silicon-based negative electrode material of Example 1.

[0054] Figure 3 is a scanning electron microscope image of the carbon-coated silicon-based negative electrode material of Comparative Example 1.

[0055] Figure 4 is a scanning electron microscope image of the repaired carbon-coated silicon-based negative electrode material of Example 4.

[0056] Figure 5 is a scanning electron microscope image of the carbon-coated silicon-based negative electrode material of Comparative Example 5.

[0057] Figure 6 is a charge-discharge cycle curve of a lithium ion battery made of the negative electrode material of Examples 1-4 and Comparative Example 1. DETAILED DESCRIPTION

[0058] The technical solutions of the present application will be described in detail below in conjunction with specific examples. In the following examples, the raw materials used are all commercially available unless otherwise specified.

[0059] In the following examples, polyvinylpyrrolidone is generally one of K30 and K60. The polyvinylpyrrolidone copolymer is a vinylpyrrolidone-vinyl acetate copolymer. The polyvinyl alcohol used is high-polymerization-degree polyvinyl alcohol.

[0060] The polyethylene used is commercially available HDPE; the polypropylene used is high-density polypropylene, generally having an average molecular weight of more than one million; the average molecular weight of the polystyrene is 1.5-3 million; and the average molecular weight of the polyacrylonitrile is 0.8-1.5 million. The phenolic resin is linear phenolic resin; and the epoxy resin is bisphenol A epoxy resin.

[0061] In the following examples, the humic acid can be a corresponding humic acid potassium salt or sodium salt.

[0062] In the following examples, Supelite TM DAX-8, EPA 8020B, XAD7HP are all commercially available macroporous resins.

[0063] When the silicon-based negative electrode material raw powder is mixed from Si, SiO, and SiO2, the mass of SiO is higher than the sum of the masses of Si and SiO2. In the following examples, the ratio of the sum of the masses of Si and SiO2 to the mass of SiO is 1:3.

[0064] The principle diagram of the preparation method of the repaired carbon-coated silicon-based negative electrode material of the present application is shown in Figure 1 .

[0065] Example 1

[0066] The preparation method of the repaired carbon-coated silicon-based negative electrode material of the embodiment comprises the following steps:

[0067] 1) 50 g of silicon-based negative electrode material raw powder is weighed, the silicon-based negative electrode material raw powder is mixed by Si, SiO, and SiO2, the molar ratio of oxygen element to silicon element is 1:1, and the particle size of the silicon-based negative electrode material raw powder is 5 μm;

[0068] 2 g of pitch is weighed and added into the VCR mixer (VC reaction mixer) with the above-mentioned 50 g of silicon-based negative electrode material raw powder, heated to 650°C at a heating rate of 10°C / min under the protection of nitrogen atmosphere, then stirred at a speed of 300 r / min for 20 min, and then kept at 650°C for 2 h to obtain a composite material A;

[0069] 2) 0.2 g of humic acid is added into 25 mL of deionized water, vacuum mixed in a homogenizer for 6 min, the speed of the homogenizer is 1000 rpm during vacuum mixing; then 12.5 g of the composite material A obtained in step 1) is added into the homogenizer, and vacuum mixed in the homogenizer for 13 min, the speed of the homogenizer is 1000 rpm during vacuum mixing; to obtain a mixed solution;

[0070] 3) The mixed solution obtained in step 2) is subjected to vacuum rotary evaporation, the temperature of vacuum rotary evaporation is 55°C, the speed is 100 rpm, and after 15 min of vacuum rotary evaporation, an intermediate material is obtained;

[0071] 4) The material after vacuum rotary evaporation in step 3) is heated and dried in a water bath at 80°C for 2 h, then ground to obtain a composite material B;

[0072] 5) The composite material B prepared in step 4) is placed in a tube furnace, nitrogen gas with a flow rate of 60 mL / min is introduced as a protective gas, the temperature is raised to 900°C at a heating rate of 5°C / min, kept for 2 h, then naturally cooled to room temperature, ground and sieved with a 200 mesh screen, and then obtained.

[0073] The repaired carbon-coated silicon-based negative electrode material of the embodiment is prepared by the above preparation method.

[0074] The lithium ion battery of the embodiment comprises a positive electrode, a negative electrode, a separator, and an electrolyte, the negative electrode comprises a negative electrode current collector copper foil and a negative electrode material layer coated on the surface of the negative electrode current collector, the negative electrode material layer comprises a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder, and the negative electrode active material is the repaired carbon-coated silicon-based negative electrode material described above.

[0075] The positive electrode comprises a positive electrode current collector aluminum foil and a positive electrode material layer coated on the surface of the positive electrode current collector, the positive electrode material layer comprises a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder, and the positive electrode active material is lithium iron phosphate.

[0076] Example 2

[0077] The preparation method of the repaired carbon-coated silicon-based negative electrode material of the present embodiment comprises the following steps:

[0078] 1) Take 50 g of silicon-based negative electrode material raw powder, which is mixed from Si, SiO, and SiO2, and the molar ratio of oxygen element to silicon element is 1:1, and the particle size of the silicon-based negative electrode material raw powder is 5 μm;

[0079] Take 2 g of pitch and add it to the above-mentioned 50 g of silicon-based negative electrode material raw powder in a VCR mixer, heat it to 650℃ at a heating rate of 10℃ / min under nitrogen atmosphere protection, then stir it at a speed of 300 r / min for 20 min, and then keep it at 650℃ for 2 h to obtain a composite material A;

[0080] 2) Add 0.2 g of humic acid to 25 mL of deionized water, and mix it in a homogenizer under vacuum for 6 min, and the speed of the homogenizer during vacuum mixing is 1000 rpm; then add 12.5 g of the composite material A obtained in step 1) to the homogenizer, and mix it in the homogenizer under vacuum for 13 min, and the speed of the homogenizer during vacuum mixing is 1000 rpm; to obtain a mixed solution;

[0081] 3) Perform vacuum rotary evaporation on the mixed solution obtained in step 2), the temperature for vacuum rotary evaporation is 55℃, the speed is 100 rpm, and after 15 min of vacuum rotary evaporation, an intermediate material is obtained;

[0082] 4) Heat and dry the material after vacuum rotary evaporation in step 3) in a water bath at 80℃ for 2 h, then grind it to obtain a composite material B;

[0083] 5) Place the composite material B prepared in step 4) in a tube furnace, pass nitrogen gas with a flow rate of 60 mL / min as protective gas, heat it to 1000℃ at a heating rate of 5℃ / min, keep it at 1000℃ for 2 h, then naturally cool it to room temperature, grind it, and sieve it through a 200 mesh sieve to obtain the repaired carbon-coated silicon-based negative electrode material.

[0084] The repaired carbon-coated silicon-based negative electrode material of the present embodiment is prepared by the above preparation method.

[0085] The lithium ion battery of the present embodiment comprises a positive electrode, a negative electrode, a separator, and an electrolyte, the negative electrode comprises a negative electrode current collector copper foil and a negative electrode material layer coated on the surface of the negative electrode current collector, the negative electrode material layer comprises a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder, and the negative electrode active material is the repaired carbon-coated silicon-based negative electrode material mentioned above.

[0086] The positive electrode comprises a positive electrode current collector aluminum foil and a positive electrode material layer coated on the surface of the positive electrode current collector, the positive electrode material layer comprises a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder, and the positive electrode active material is NCM811.

[0087] Example 3

[0088] The preparation method of the repaired carbon-coated silicon-based negative electrode material of the present example comprises the following steps:

[0089] 1) 50 g of silicon-based negative electrode material raw powder was weighed, which was mixed by Si, SiO, and SiO2, wherein the molar ratio of oxygen element to silicon element was 1:1, and the particle size of the silicon-based negative electrode material raw powder was 5 μm;

[0090] 2 g of pitch was weighed and added to the VCR mixer with the above 50 g of silicon-based negative electrode material raw powder, and under the protection of nitrogen atmosphere, the temperature was raised to 650℃ at a heating rate of 10℃ / min, then stirred at a speed of 300 r / min for 20 min, and then kept at 650℃ for 2 h to obtain a composite material A;

[0091] 2) 0.1 g of humic acid and 0.11 g of tannic acid were added to 25 mL of deionized water, and vacuum mixed in a homogenizer for 6 min, and the rotation speed of the homogenizer was 1000 rpm during vacuum mixing; then 12.5 g of the composite material A obtained in step 1) was added to the homogenizer, and vacuum mixed in the homogenizer for 13 min, and the rotation speed of the homogenizer was 1000 rpm during vacuum mixing; to obtain a mixed solution;

[0092] 3) The mixed solution obtained in step 2) was vacuum rotary evaporated, the temperature of vacuum rotary evaporation was 55℃, the rotation speed was 100 rpm, and after vacuum rotary evaporation for 15 min, an intermediate material was obtained;

[0093] 4) The material after vacuum rotary evaporation in step 3) was dried in a water bath at 80℃ for 2 h, and then ground to obtain a composite material B;

[0094] 5) The composite material B prepared in step 4) was placed in a tube furnace, nitrogen gas with a flow rate of 60 mL / min was introduced as a protective gas, the temperature was raised to 900℃ at a heating rate of 5℃ / min, and after keeping for 2 h, it was naturally cooled to room temperature, and then ground and sieved with a 200 mesh screen to obtain the product.

[0095] The repaired carbon-coated silicon-based negative electrode material of the present example was prepared by the above preparation method.

[0096] The lithium ion battery of the present example was the same as that of Example 2.

[0097] Example 4

[0098] The preparation method of the repaired carbon-coated silicon-based negative electrode material of the present example comprises the following steps:

[0099] 1) Take 50 g of silicon-based negative electrode material raw powder, which is mixed by Si, SiO, SiO2, and the molar ratio of oxygen element to silicon element is 1:1, and the particle size of the silicon-based negative electrode material raw powder is 5 μm;

[0100] Take 2 g of pitch and the above-mentioned 50 g of silicon-based negative electrode material raw powder together into a VCR mixer, and heat to 650℃ at a heating rate of 10℃ / min under the protection of nitrogen atmosphere, then stir at a speed of 300 r / min for 20 min, and then keep the temperature at 650℃ for 2 h to obtain a composite material A;

[0101] 2) Add 0.1 g of humic acid, 0.11 g of tannic acid, and 0.05 g of carbon nanotubes into 25 mL of deionized water, and mix in a homogenizer for 6 min under vacuum, and the speed of the homogenizer is 1000 rpm during vacuum mixing; the length of the carbon nanotubes is 10 μm, and the tube diameter is 40 nm;

[0102] Then add 12.5 g of the composite material A obtained in step 1) into the homogenizer, and mix in the homogenizer for 13 min under vacuum, and the speed of the homogenizer is 1000 rpm during vacuum mixing; to obtain a mixed solution;

[0103] 3) Perform vacuum rotary evaporation on the mixed solution obtained in step 2), and the temperature of the vacuum rotary evaporation is 55℃, and the speed is 100 rpm, and after 15 min of vacuum rotary evaporation, an intermediate material is obtained;

[0104] 4) Heat and dry the material after vacuum rotary evaporation in step 3) in a water bath at 80℃ for 2 h, and then grind to obtain a composite material B;

[0105] 5) Put the composite material B prepared in step 4) into a tube furnace, and pass nitrogen gas with a flow rate of 60 mL / min as a protective gas, and heat to 1000℃ at a heating rate of 5℃ / min, keep the temperature for 2 h, and then naturally cool to room temperature, and after grinding, sieve with a 200 mesh sieve, and then obtain the product.

[0106] The repaired carbon-coated silicon-based negative electrode material of the present embodiment is prepared by the above preparation method.

[0107] The lithium ion battery of the present embodiment is the same as that of embodiment 2.

[0108] Embodiments 5-12

[0109] In the preparation method of the repaired carbon-coated silicon-based negative electrode material in embodiments 5-12, the types and masses of the carbon source precursors in step 1) are shown in the following table, and the others are the same as those in embodiment 4.

[0110] Table 1 Types and masses of raw materials in embodiments 5-12

[0111]

[0112] In other embodiments, the carbon source precursor can also be any one or a combination of glucose, starch, polyvinyl alcohol, polyvinylpyrrolidone copolymer, vitamin C, citric acid, polyethylene, polypropylene, polyacrylonitrile, epoxy resin, urea-formaldehyde resin.

[0113] Examples 13-17

[0114] In the preparation method of the repaired carbon-coated silicon-based negative electrode material in Examples 13-17, the types of the repairing agent in step 2) and the mass of the repairing agent and the composite material A are shown in the following table, and the others are the same as in Example 4.

[0115] Table 2 Types and masses of raw materials in Examples 13-17

[0116]

[0117]

[0118] In other embodiments, the repairing agent in Example 4 can be replaced by any one or a combination of fulvic acid, humic acid, brown humic acid (trifolinic acid), black humic acid (humic substance), alginic acid, malic acid, bitter almond acid, coffee acid, modified epoxy resin, modified acrylic resin, modified alkyd resin, melanin, β-phenylpropionic acid, anthraquinone-2,6-disulfonate, Supelite TM DAX-8, EPA8020B, XAD7HP, any one or a combination of nano-oxidized graphene. Among them, the modified epoxy resin can use commercially available silicone-modified epoxy resin, the modified acrylic resin can use commercially available silicone-modified acrylic resin, and the modified alkyd resin can use commercially available acrylic-modified alkyd resin. When graphene oxide is used as the repairing agent, water is selected as the solvent, but only a uniform dispersion of graphene oxide is prepared.

[0119] Examples 18-21

[0120] In the preparation method of the repaired carbon-coated silicon-based negative electrode material in Examples 18-21, the heat treatment temperature in step 1) and the holding time after stirring are shown in the following table, and the others are the same as in Example 4.

[0121] Table 3 Heat treatment parameters in Examples 18-21

[0122] Heat treatment temperature Soaking time after stirring Example 18 600℃ 2h Example 19 700℃ 2h Example 20 650℃ 1.5h Example 21 650℃ 3.5h

[0123] Examples 22-25

[0124] The temperature and time of the heat preservation in step 5) in the preparation method of the repaired carbon-coated silicon-based negative electrode material in examples 22-25 are shown in the following table, and the others are the same as in example 4.

[0125] Table 4 Heat preservation parameters in examples 22-25

[0126] Temperature of soaking Soaking time Example 22 700℃ 2h Example 23 1100℃ 2h Example 24 1000℃ 5h Example 25 1000℃ 1h

[0127] Example 26

[0128] The difference between this example and example 4 is that the temperature rising rate in step 5) is 30℃ / min, and the others are the same as in example 4.

[0129] Example 27

[0130] The difference between this example and example 4 is that 0.1g humic acid, 0.11g tannic acid and 12.5g of the composite material A obtained in step 1) are added into 25mL deionized water, and mixed in a homogenizer under vacuum for 19min, and the rotation speed of the homogenizer is 1000rpm during the vacuum mixing, to obtain a mixed solution. The others are the same as in example 4.

[0131] Example 28

[0132] The difference between this example and example 4 is that steps 3) and 4) are replaced by:

[0133] The mixed solution obtained in step 2) is heated and dried in a water bath at 80℃ for 2h, and then ground to obtain a composite material B.

[0134] The others are the same as in example 4.

[0135] Comparative example 1

[0136] The preparation method of the carbon-coated silicon-based negative electrode material in this comparative example comprises the following steps:

[0137] 1) 50g of a silicon-based negative electrode material raw powder is weighed, the silicon-based negative electrode material raw powder is mixed by Si, SiO and SiO2, the molar ratio of oxygen element to silicon element is 1:1, and the particle size of the silicon-based negative electrode material raw powder is 5μm;

[0138] 2g of pitch is weighed and added into the VCR mixer with the above 50g of the silicon-based negative electrode material raw powder, heated to 650℃ at a temperature rising rate of 10℃ / min under the protection of nitrogen atmosphere, then stirred at a rotation speed of 300r / min for 20min, and then heat preserved at 650℃ for 2h to obtain a composite material A;

[0139] 2) Put the composite material A prepared in step 1) into a tube furnace, and pass nitrogen gas as a protective gas at a flow rate of 60 mL / min, and heat to 900℃ at a heating rate of 5℃ / min, and after heat preservation for 2h, naturally cool to room temperature, and after grinding, sieve with a 200 mesh sieve, to obtain.

[0140] Comparative Example 2

[0141] The preparation method of the carbon-coated silicon-based negative electrode material in the present comparative example is different from that in Example 1 in that the humic acid in step 2) is replaced by pitch, and the others are the same as in Example 1.

[0142] Comparative Example 3

[0143] The preparation method of the carbon-coated silicon-based negative electrode material in the present comparative example is different from that in Example 1 in that the humic acid in step 2) is replaced by glucose, and the others are the same as in Example 1.

[0144] Comparative Example 4

[0145] The silicon-based negative electrode material raw powder in the present comparative example is mixed from Si and SiO2, wherein the molar ratio of oxygen element to silicon element is 1:1, and the others are the same as in Example 1.

[0146] Comparative Example 5

[0147] The preparation method of the carbon-coated silicon-based negative electrode material in the present comparative example is different from that in Example 4 in that 0.1g of humic acid, 0.11g of tannic acid, and 0.05g of carbon nanotubes in step 2) are replaced by 0.26g of carbon nanotubes, and the others are the same as in Example 4.

[0148] Experimental Example

[0149] (1) Morphology test

[0150] Take the repaired carbon-coated silicon-based negative electrode material prepared in Example 1 and the carbon-coated silicon-based negative electrode material prepared in Comparative Example 1, and perform scanning electron microscope test, and the results are shown in Figure 2 and Figure 3 respectively.

[0151] From Figure 2 and Figure 3 it can be seen that the particle surface of the repaired carbon-coated silicon-based negative electrode material prepared in the present application is smooth, has high flatness, and has good continuity, and there is no obvious pore, while the particle surface of the carbon-coated silicon-based negative electrode material prepared in Comparative Example 1 has many pores, and the particle surface flatness is poor.

[0152] Take the repaired carbon-coated silicon-based negative electrode material prepared in Example 4 and the carbon-coated silicon-based negative electrode material prepared in Comparative Example 5, and perform scanning electron microscope test, and the results are shown in Figure 4 andFigure 5 As shown.

[0153] From Figure 4 And Figure 5 It can be seen that the surface flatness of the repaired carbon-coated silicon-based negative electrode material particles prepared in the present application is high, and it can be clearly seen that the carbon nanotubes are firmly attached to the particle surface and extend along the particle surface, and can play a certain connecting role between the particles.

[0154] (2) Carbon content test

[0155] The carbon-coated silicon-based negative electrode material prepared in Examples 1-4 and the carbon-coated silicon-based negative electrode material in Comparative Example 1 were taken, and the carbon content in the negative electrode material was tested by the method of burning in an R-944B high-frequency infrared carbon-sulfur analyzer combined with infrared absorption, and the test results are shown in Table 5.

[0156] As can be seen from Table 5, the carbon content of the repaired carbon-coated silicon-based negative electrode material prepared in Examples 1-4 is only slightly higher than that of the carbon-coated silicon-based negative electrode material prepared in Comparative Example 1, such as the carbon content of the repaired carbon-coated silicon-based negative electrode material prepared in Example 1 is only 0.59% higher than that of the carbon-coated silicon-based negative electrode material prepared in Comparative Example 1, which shows that compared with the carbon-coated silicon-based negative electrode material without repair, the increase in carbon content caused by the repair agent will hardly form a carbon coating layer on the surface of the carbon-coated silicon-based particles, and hardly increase the thickness of the carbon coating layer outside the silicon material. The carbon formed by the repair agent is filled in the small pores on the surface of the carbon-coated silicon particles.

[0157] By comparing the test results of Example 1 and Comparative Example 2, it is found that when bitumen is used for secondary coating, the carbon content is greatly improved, and the repair effect of bitumen secondary coating on the pores on the surface of the carbon-coated silicon particles is poor.

[0158] By comparing the test results of Example 1 and Comparative Example 3, it is found that when glucose is used as a repair agent, its effect is still close to secondary coating of carbon, and glucose cannot effectively enter and fix in the micropores on the surface of the silicon-carbon particles.

[0159] (3) Coating integrity test

[0160] The repaired carbon-coated silicon-based negative electrode material prepared in Examples 1-4 and the carbon-coated silicon-based negative electrode material in Comparative Example 1 were taken, and the coating integrity was tested according to the following method:

[0161] The 25 mL of 6% KOH solution was added into the aluminum plastic film bag, and then 50 mg of the negative electrode material was added into the aluminum plastic film bag, and the aluminum plastic film bag was sealed by a sealing machine. Then, the aluminum plastic film bag was placed in a 60°C water bath to observe the volume change of the aluminum plastic film bag, and the volume at 0 h, 4 h, 10 h, 14 h, and 17 h was recorded, so as to obtain the quantitative final coating integrity value, as shown in Table 5.

[0162] As can be seen from Table 5, the coating integrity of the repaired carbon-coated silicon-based negative electrode material prepared in Examples 1-4 is much higher than that of the material in Comparative Example 1, which is consistent with the results shown in the SEM pictures.

[0163] Further, the repaired carbon-coated silicon-based negative electrode material prepared in Examples 13-17 was found to have a slightly higher coating integrity than that of Example 1 when the humic acid and tannic acid were combined to form the repairing agent.

[0164] The carbon-coated silicon-based negative electrode material in Comparative Example 2 was found to have a lower coating integrity than that of Example 1 after the coating integrity test.

[0165] (4) Resistivity test

[0166] The repaired carbon-coated silicon-based negative electrode material prepared in Examples 1-4 and the carbon-coated silicon-based negative electrode material in Comparative Example 1 were taken, and the resistivity was tested by using a ST-2722 type semiconductor powder resistance tester, and the test results are shown in Table 5.

[0167] Table 5 Comparison of test results of materials in Examples 1-4 and Comparative Example 1

[0168] Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Carbon content (%) 4.76 4.82 4.75 4.87 4.17 Coating integrity (mL) 4.14 2.14 2.52 1.56 7.74 Resistivity (Ω-cm) 1.8 1.59 1.45 1.24 2.46

[0169] As can be seen from Table 5, the resistivity of the repaired carbon-coated silicon-based negative electrode material prepared in Examples 1-4 is lower, which is good for the conductivity during the charging and discharging process, and is beneficial to improve the initial charging and discharging efficiency and specific capacity of the negative electrode material.

[0170] (5) Electrochemical performance test

[0171] The repaired carbon-coated silicon-based negative electrode material prepared in Examples 1-4 and the carbon-coated silicon-based negative electrode material in Comparative Example 1 were taken as the negative electrode active material, and were mixed according to the mass ratio of the negative electrode active material, the binder LA136, and the conductive carbon black SP of 80:10:10, and deionized water was added to prepare a negative electrode slurry, which was uniformly coated on the surface of a copper foil, and was dried at 80°C for 24 h in a vacuum, and was cut to prepare a negative electrode sheet.

[0172] A lithium sheet is used as the counter electrode, and the electrolyte is a 1.1 mol / L LiPF6 solution. The solvent of the electrolyte is a mixture of ethylene carbonate (EC), vinylene carbonate (VC), dimethyl carbonate (DMC), and fluoroethylene carbonate (FEC) in a volume ratio of 1:1:1:1. The separator is a polypropylene microporous membrane.

[0173] The CR2025 button cell was assembled in a vacuum glove box.

[0174] Then, the circuit was charged at a rate of 0.1C and discharged at a rate of 0.1C, and subjected to charge-discharge cycles at a temperature of 25℃ and a humidity of 50%. The test results are as follows. Figure 6 As shown.

[0175] from Figure 6 It can be seen that the batteries made from the repaired carbon-coated silicon-based anode materials prepared in Examples 1-4 of this application exhibit slower capacity decay during charge-discharge cycles, with a capacity retention rate of 67.99-83.14% after 30 cycles.

[0176] By comparing the test results of the negative electrode materials prepared in Example 1 and Comparative Example 4, it was found that the specific capacity of the negative electrode material prepared in Example 1 was relatively high, and the decay rate during the charge-discharge cycle was relatively slow.

[0177] By comparing the test results of the negative electrode materials prepared in Examples 1, 4, and 5, it was found that the specific capacity of the negative electrode material prepared in Example 4 was close to that of the negative electrode material in Example 1, but the capacity decay rate during charge-discharge cycles was significantly lower than that in Example 1. The specific capacity and cycle performance of the negative electrode materials prepared in Examples 1 and 4 were superior to those of the negative electrode material in Comparative Example 5.

Claims

1. A method for preparing a carbon-coated silicon-based anode material for repairing, characterized in that, The method comprises the following steps: 1) uniformly mixing a carbon source precursor with a silicon-based negative electrode material raw powder, heat treating at 500-1100 DEG C for 1.5-10h to obtain a composite material; The carbon source precursor is an organic pyrolysis carbon source; The silicon-based negative electrode material raw powder is an oxide of silicon or is composed of silicon and an oxide of silicon; the molar ratio of oxygen to silicon in the silicon-based negative electrode material raw powder is 0.1-1.9:1; 2) uniformly mixing the composite material obtained in step 1) with a repairing agent in a solvent, removing the solvent, and then heat treating at 700-1200 DEG C for 1-6h under inert gas protection, i.e. first heating at a heating rate of 1-20 DEG C / min to 700-1200 DEG C and then heat treating, to obtain the repairing carbon-coated silicon-based negative electrode material; The repairing agent is at least one of fulvic acid, humic acid, brown acid, black acid, alginic acid, malic acid, tannic acid, bitter almond acid, coffee acid, cinnamic acid methyl ester, melanin, beta-phenylpropionic acid, and anthraquinone-2,6-disulfonate; The oxide of silicon in step 1) is at least one of SiO and SiO2; the mass ratio of the carbon source precursor to the silicon-based negative electrode material raw powder in step 1) is 0.1-50:100; The mass ratio of the repairing agent to the composite material in step 2) is 0.1-1:10-20; in step 2), the composite material and the repairing agent are uniformly mixed in the solvent by first uniformly mixing the repairing agent with the solvent and then adding the composite material; In step 2), carbon nanotubes are also added when the composite material and the repairing agent are mixed in the solvent; the mass ratio of the carbon nanotubes to the repairing agent is 0.1-1:0.01-0.

1.

2. The carbon-coated silicon-based anode material for repairing prepared by the method according to claim 1, characterized in that, The powder resistivity of the repairing carbon-coated silicon-based negative electrode material is 0.12-5.23 ohm-m.

3. A lithium ion battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, the negative electrode comprising a negative electrode current collector and a negative electrode material layer coated on the surface of the negative electrode current collector, the negative electrode material layer comprising a negative electrode active material, characterized in that, The negative electrode active material is the repairing carbon-coated silicon-based negative electrode material according to claim 2.

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