Lithium-doped silicon-carbon composite material, preparation method thereof, negative plate and lithium ion battery

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a lithium-doped silicon-carbon composite material, a preparation method thereof, a negative plate and a lithium ion battery. The preparation method of the lithium-doped silicon-carbon composite material comprises the following steps: carrying out reduction reaction and activated pore-forming on a mixed material containing a carbon source, an organic pore-forming agent, a lithium supplement agent and a reducing agent to obtain lithium-doped porous carbon; performing first deposition on the lithium-doped porous carbon and mixed gas containing an inorganic lithium compound and an organic lithium compound; carrying out second deposition on the material obtained after the first deposition and silane gas to obtain a lithium compound doped silicon carbon precursor material; and mixing the lithium compound doped silicon carbon precursor material, an organic metal compound, asphalt and an organic solvent, performing spray drying, and then performing carbonization. According to the preparation method, the initial efficiency and the power performance of the silicon-carbon composite material can be improved.

Description

TECHNICAL FIELD

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

[0002] Silicon-carbon materials are applied in high-energy-density lithium ion batteries due to their high specific capacity and low expansion, etc. However, since the silicon-carbon material is composed of porous carbon and nano-silicon deposited in the pores thereof, the first efficiency and power performance of the silicon-carbon material are poor due to the low first efficiency of the porous carbon itself, and it is necessary to dope or coat the silicon-carbon material to improve the first efficiency and fast-charging performance of the material.

[0003] The current doping methods mainly include doping of heteroatoms and conductive agents in the porous carbon, or coating of amorphous carbon, fast ion conductors and oxides thereof on the surface of the porous carbon, etc. However, this can only improve the electronic conductivity of the material, and the ionic conductivity of the material is not improved, so that the first efficiency and power performance of the material are not obviously improved.

[0004] In view of this, the present application is proposed. SUMMARY

[0005] The first object of the present application is to provide a preparation method of a lithium-doped silicon-carbon composite material. Lithium-doped porous carbon with large pore size is obtained by doping a lithium supplementing agent in a porous carbon precursor and through reduction reaction and activation pore-making, and organic lithium compounds and inorganic lithium compounds are deposited in the pore structure of the lithium-doped porous carbon with large pore size to reduce defects and improve the ion diffusion coefficient, and then nano-silicon is deposited and coated on the surface, so that the first efficiency and power performance of the silicon-carbon composite material can be improved.

[0006] The second object of the present application is to provide a lithium-doped silicon-carbon composite material, which has the advantages of high specific surface area, high ionic conductivity, low powder resistivity, low expansion, high lithium ion diffusion coefficient, etc.

[0007] The third object of the present application is to provide a negative electrode sheet, and the battery prepared by using the negative electrode sheet has high discharge specific capacity, high first efficiency, good rate performance and excellent cycle performance.

[0008] The fourth object of the present application is to provide a lithium ion battery, which has the advantages of high discharge specific capacity, high first efficiency, good rate performance and excellent cycle performance, etc.

[0009] In order to achieve the above objects of the present application, the following technical solutions are adopted:

[0010] The present application provides a preparation method of a lithium-doped silicon-carbon composite material, comprising the following steps: (a) reducing and activating a mixed material containing a carbon source, an organic pore-forming agent, a lithium supplementing agent and a reducing agent to obtain a lithium-doped porous carbon; (b) performing a first deposition on the lithium-doped porous carbon with a mixed gas containing an inorganic lithium compound and an organic lithium compound, and then performing a second deposition on the material obtained after the first deposition with a silane gas to obtain a lithium compound-doped silicon-carbon precursor material; (c) mixing the lithium compound-doped silicon-carbon precursor material, an organic metal compound, pitch and an organic solvent, then spray drying, and then carbonizing to obtain the lithium-doped silicon-carbon composite material.

[0011] Further, in step (a), the carbon source includes at least one of petroleum pitch, coal pitch, phenolic resin and sucrose.

[0012] Further, in step (a), the organic pore-forming agent includes at least one of methyl methacrylate, polyvinyl butyral, methyl cellulose, polystyrene, polyethylene glycol and polyglycolic acid.

[0013] Further, in step (a), the lithium supplementing agent includes at least one of Li5FeO4, Li6CoO4, Li2O2, LiNiO2 and Li2MnO3.

[0014] Further, in step (a), the reducing agent includes at least one of ethanol, ethylene glycol, acetone and glucose.

[0015] Further, in step (a), the mass ratio of the carbon source, the organic pore-forming agent, the lithium supplementing agent and the reducing agent in the mixed material is 100:1-5:1-5:1-5.

[0016] Further, in step (a), the reducing reaction and the activation pore-forming are performed by microwave heating, the temperature of the reducing reaction and the activation pore-forming is 900-1100℃, and the time of the reducing reaction and the activation pore-forming is 30-300min.

[0017] Further, in step (a), during the reducing reaction and the activation pore-forming, carbon dioxide is introduced at a flow rate of 10-100ml / min.

[0018] Further, in step (b), the inorganic lithium compound includes at least one of lithium fluoride, lithium carbonate, lithium hydroxide and lithium oxide.

[0019] Further, in step (b), the organic lithium compound includes at least one of lithium acetate, lithium acrylate and lithium triflate.

[0020] Further, in step (b), the volume ratio of the inorganic lithium compound to the organic lithium compound in the mixed gas is 1:0.5-2.

[0021] Further, in step (b), the silane gas comprises at least one of trichlorosilane, disilane, monosilane and dimethylsilane.

[0022] Further, in step (b), the temperature of the first deposition is 900-1100℃, and the time of the first deposition is 60-600 min.

[0023] Further, in step (b), the flow rate of the mixed gas containing the inorganic lithium compound and the organic lithium compound is 1-10 ml / min.

[0024] Further, in step (b), the temperature of the second deposition is 400-600℃, and the time of the second deposition is 30-300 min.

[0025] Further, in step (b), the flow rate of the silane gas is 10-100 ml / min.

[0026] Further, in step (c), the organic metal compound comprises at least one of ferrocene, bismuth iso-octoate, bismuth laurate and bismuth neodecanoate.

[0027] Further, in step (c), the mass ratio of the lithium compound-doped silicon-carbon precursor material, the organic metal compound and the pitch is 100:1-5:1-5.

[0028] Further, in step (c), the carbonization temperature is 1000-1300℃, and the carbonization time is 1-6 h.

[0029] The present application further provides a lithium-doped silicon-carbon composite material prepared by the above method.

[0030] The present application further provides a negative electrode sheet comprising the above lithium-doped silicon-carbon composite material.

[0031] The present application further provides a lithium ion battery comprising the above negative electrode sheet.

[0032] Compared with the prior art, the present application has the following advantages:

[0033] (1) The preparation method of the lithium-doped silicon-carbon composite material provided by the application can reduce the expansion by doping a lithium supplement in a porous carbon precursor and obtaining a large-pore lithium-doped porous carbon through a reduction reaction and activation pore-making, and the lithium doping can reduce defects and improve the ionic conductivity of the material; then a small amount of organic lithium compounds and inorganic lithium compounds can be deposited in the pore structure of the large-pore lithium-doped porous carbon to reduce the impedance, improve the ion diffusion coefficient, and further improve the ionic conductivity of the material; and then the deposition and surface coating of nano-silicon are performed, and the metal-doped amorphous carbon coating layer formed after carbonization can reduce the defects of the core, improve the electronic conductivity of the coating layer, and improve the rate performance of the material.

[0034] (2) The lithium-doped silicon-carbon composite material provided by the application has the advantages of high specific surface area, high ionic conductivity, low powder resistivity, low expansion, high lithium ion diffusion coefficient, etc., and the battery prepared by using the lithium-doped silicon-carbon composite material has high discharge specific capacity, high first efficiency, good rate performance, and excellent cycle performance. BRIEF DESCRIPTION OF DRAWINGS

[0035] In order to more clearly illustrate the specific embodiments of the application or the technical solutions in the prior art, the drawings needed in the specific embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0036] Figure 1 The SEM image of the lithium-doped silicon-carbon composite material prepared by Example 1 provided by the application. DETAILED DESCRIPTION

[0037] The technical solutions of the application will be described clearly and completely in combination with the drawings and specific embodiments below, but those skilled in the art will understand that the following described embodiments are part of the embodiments of the application, not all the embodiments, and are only used to illustrate the application, and should not be regarded as limiting the scope of the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the application. The specific conditions not mentioned in the embodiments are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments not mentioned by the manufacturer are all conventional products that can be purchased on the market.

[0038] In a first aspect, the application provides a preparation method of a lithium-doped silicon-carbon composite material, comprising the following steps:

[0039] (a) reducing and activating a mixed material containing a carbon source, an organic pore-forming agent, a lithium supplement agent, and a reducing agent to obtain a lithium-doped porous carbon with a large pore diameter.

[0040] The organic pore-forming agent mainly functions as a pore-forming agent, and the carbon source forms a porous carbon with a pore structure after being subjected to pore-forming. The porous carbon can reduce swelling. The reducing and activating pore-forming are simultaneously performed. The lithium supplement agent decomposes to form a pore structure after a reducing reaction with the reducing agent. That is, the organic pore-forming agent and the lithium supplement agent both function as pore-forming agents, and the two agents cooperatively form a large pore diameter. Moreover, the material formed after the reaction of the lithium supplement agent is dispersedly doped in the porous carbon, which can reduce defects and improve the ionic conductivity of the material.

[0041] (b) transferring the lithium-doped porous carbon to a fluidized bed, performing a first deposition by gas-phase deposition to 5-10 Pa, and mixing a mixed gas containing an inorganic lithium compound and an organic lithium compound to deposit the inorganic lithium compound and the organic lithium compound in the pore structure of the lithium-doped porous carbon. Then, under a pressure of 0.01-0.1 MPa, the material obtained after the first deposition is mixed with silane gas and subjected to a second deposition to obtain a lithium compound-doped silicon-carbon precursor material.

[0042] The inorganic lithium compound and the organic lithium compound are deposited in the pores of the lithium-doped porous carbon in a small amount by the gas-phase method to form a porous carbon composite with a structure similar to a SEI film to reduce impedance and improve the diffusion coefficient of lithium ions in the charging and discharging process. At the same time, the inner wall of the porous carbon is modified by deposition of the lithium salt (the inorganic lithium compound and the organic lithium compound), which is also conducive to the deposition of nano-silicon generated by the cracking of silane gas.

[0043] It can be understood that the three agents, the lithium supplement agent, the inorganic lithium compound, and the organic lithium compound, cooperatively improve the ionic conductivity of the material. The lithium supplement agent is doped in the porous carbon, and the inorganic lithium compound and the organic lithium compound are deposited on the inner surface of the pore structure of the lithium-doped porous carbon.

[0044] (c) mixing the lithium compound-doped silicon-carbon precursor material, an organic metal compound, pitch, and an organic solvent, then spray drying, and then carbonizing to obtain the lithium-doped silicon-carbon composite material.

[0045] Specifically, the mixing step includes: first dissolving the organic metal compound and the pitch in the organic solvent (such as N-methyl pyrrolidone) to disperse uniformly, and then adding the lithium compound-doped silicon-carbon precursor material to disperse uniformly. In the mixing process, the organic metal compound and the pitch coat the lithium compound-doped silicon-carbon precursor material.

[0046] The organic metal compound decomposes after carbonization to form amorphous carbon with a porous structure, which reduces swelling and improves liquid retention performance.

[0047] The application provides a preparation method of lithium-doped silicon-carbon composite material. The method is characterized by doping a lithium supplement and an organic pore-forming agent in a carbon source, and performing reduction reaction and activation pore-forming. The macroporous carbon formed can reduce expansion, and lithium doping can reduce defects and improve the ionic conductivity of the material. The lithium supplement can reduce defects and improve the ionic conductivity of the material.

[0048] In addition, the application can reduce impedance by co-depositing inorganic lithium compounds and organic lithium compounds in the pore structure of the lithium-doped porous carbon. Lithium compounds can form a lithium compound similar to a man-made SEI film in the core of the porous carbon during the charging and discharging process, which can further improve the ionic conductivity of the material and improve the ionic diffusion coefficient, the first efficiency and the rate performance of the porous carbon.

[0049] In addition, the application can reduce defects in the core, improve the electronic conductivity of the coating layer and improve the rate performance of the material by coating the surface of the lithium compound-doped silicon-carbon precursor material with an organic metal compound and pitch, and forming a metal-doped amorphous carbon coating layer after carbonization.

[0050] In some specific embodiments, in step (a), the carbon source includes at least one of petroleum pitch, coal tar pitch, phenolic resin and sucrose.

[0051] In some specific embodiments, in step (a), the organic pore-forming agent includes at least one of methyl methacrylate, polyvinyl butyral, methyl cellulose, polystyrene, polyethylene glycol and polyglycolic acid.

[0052] In some specific embodiments, in step (a), the lithium supplement includes at least one of Li5FeO4, Li6CoO4, Li2O2, LiNiO2 and Li2MnO3.

[0053] It can be understood that the pore size of the lithium-doped porous carbon is mainly affected by the category of the organic pore-forming agent and the category of the lithium supplement. The use of the above-mentioned categories of organic pore-forming agents and lithium supplements can obtain a suitable pore size.

[0054] In some specific embodiments, in step (a), the reducing agent includes at least one of ethanol, ethylene glycol, acetone and glucose.

[0055] In some specific embodiments, in step (a), the mass ratio of the carbon source, the organic pore-forming agent, the lithium supplement and the reducing agent in the mixed material is 100:1-5 (for example, 1, 2, 3, 4 or 5):1-5 (for example, 1, 2, 3, 4 or 5):1-5 (for example, 1, 2, 3, 4 or 5).

[0056] In some embodiments, the method for preparing the mixed material in step (a) comprises: mixing the carbon source, the organic pore-forming agent, the lithium supplementing agent, the reducing agent and the organic solvent uniformly, and then spray drying. The organic solvent can be any organic solvent commonly used in the art, such as cyclohexane, but is not limited thereto.

[0057] In some embodiments, the reducing reaction and the activation pore-forming in step (a) are performed by microwave heating, which can improve the preparation efficiency, and microwave heating is internal evaporation of the material, which is more likely to generate a large pore structure.

[0058] In some embodiments, the temperature of the reducing reaction and the activation pore-forming in step (a) is 900-1100°C, such as 900°C, 950°C, 1000°C, 1050°C or 1100°C.

[0059] In some embodiments, the total time of the reducing reaction and the activation pore-forming in step (a) is 30-300 min, such as 30 min, 60 min, 90 min, 150 min, 180 min, 240 min, 270 min or 300 min.

[0060] In some embodiments, the reducing reaction and the activation pore-forming in step (a) are performed by flowing carbon dioxide into the reaction system at a flow rate of 10-100 ml / min (such as 10 ml / min, 20 ml / min, 30 ml / min, 50 ml / min, 80 ml / min or 100 ml / min). The carbon dioxide is mainly used for activation pore-forming.

[0061] In some embodiments, the inorganic lithium compound in step (b) comprises at least one of lithium fluoride, lithium carbonate, lithium hydroxide and lithium oxide.

[0062] In some embodiments, the organic lithium compound in step (b) comprises at least one of lithium acetate, lithium acrylate and lithium triflate.

[0063] In some embodiments, the volume ratio of the inorganic lithium compound to the organic lithium compound in the mixed gas in step (b) is 1:0.5-2, such as 1:0.5, 1:0.7, 1:1, 1:1.3, 1:1.5, 1:1.8 or 1:2. A suitable deposition amount can improve the electronic and ionic conductivity of the porous carbon with a large pore size, reduce the defects of the porous carbon, improve the first efficiency of the porous carbon, the structural stability and the cycle performance.

[0064] In some embodiments, in step (b), the silane gas includes at least one of trichlorosilane, disilane, monosilane, and dimethylsilane.

[0065] In some embodiments, in step (b), during the second deposition of the material obtained after the first deposition with the silane gas, a mixed gas of the silane gas and an inert gas such as nitrogen is used, and the volume ratio of the silane gas to the inert gas is 1 to 5: 10.

[0066] In some embodiments, in step (b), the temperature of the first deposition is 900 to 1100°C, for example, 900°C, 950°C, 1000°C, 1050°C, or 1100°C.

[0067] In some embodiments, in step (b), the time of the first deposition is 60 to 600 minutes, for example, 60 minutes, 90 minutes, 150 minutes, 180 minutes, 240 minutes, 270 minutes, 300 minutes, 360 minutes, 420 minutes, 540 minutes, or 600 minutes.

[0068] In some embodiments, in step (b), the flow rate of the mixed gas containing the inorganic lithium compound and the organic lithium compound is 1 to 10 ml / min, for example, 1 ml / min, 2 ml / min, 3 ml / min, 5 ml / min, 6 ml / min, 8 ml / min, or 10 ml / min.

[0069] By controlling the flow rate of the mixed gas containing the inorganic lithium compound and the organic lithium compound, the temperature, and the time of the first deposition, a lithium salt deposition layer having a suitable thickness can be obtained.

[0070] In some embodiments, in step (b), the temperature of the second deposition is 400 to 600°C, for example, 400°C, 450°C, 500°C, 550°C, or 600°C.

[0071] In some embodiments, in step (b), the time of the second deposition is 30 to 300 minutes, for example, 30 minutes, 60 minutes, 90 minutes, 150 minutes, 180 minutes, 240 minutes, 270 minutes, or 300 minutes.

[0072] In some embodiments, in step (b), the flow rate of the silane gas is 10 to 100 ml / min, for example, 10 ml / min, 30 ml / min, 50 ml / min, 60 ml / min, 80 ml / min, or 100 ml / min.

[0073] By controlling the flow rate of the silane gas, the temperature and the time of the second deposition, the content of the obtained nanosilicon can be adjusted.

[0074] In some embodiments, the organic metal compound in step (c) comprises at least one of ferrocene, bismuth iso-octoate, bismuth laurate and bismuth neodecanoate.

[0075] In some embodiments, the mass ratio of the lithium compound doped silicon-carbon precursor material, the organic metal compound and the pitch in step (c) is 100:1-5 (e.g. 1, 2, 3, 4 or 5):1-5 (e.g. 1, 2, 3, 4 or 5).

[0076] In some embodiments, the temperature of the carbonization in step (c) is 1000-1300℃, e.g. 1000℃, 1050℃, 1100℃, 1150℃, 1200℃, 1250℃ or 1300℃.

[0077] In some embodiments, the time of the carbonization in step (c) is 1-6h, e.g. 1h, 2h, 3h, 4h, 5h or 6h.

[0078] In a second aspect, the present application provides a lithium doped silicon-carbon composite material prepared by the method described above.

[0079] The lithium doped silicon-carbon composite material prepared by the present application has high specific surface area, high ionic conductivity, low powder resistivity, low expansion, high lithium ion diffusion coefficient and other advantages. The battery prepared by using the lithium doped silicon-carbon composite material has high discharge specific capacity, high first efficiency, good rate performance and excellent cycle performance.

[0080] The lithium doped silicon-carbon composite material comprises a core and a coating layer. The core is a lithium (mainly lithium oxide (product after decomposition of lithium supplementing agent)) doped porous carbon with a pore structure, i.e. lithium elements are uniformly doped in the porous carbon. At the same time, the pore structure contains at least inorganic lithium product (mainly lithium fluoride and / or lithium oxide), organic lithium product (mainly lithium oxide) and nanosilicon (product after reaction of silane gas).

[0081] The main component of the coating layer is metal doped amorphous carbon, wherein the metal elements include iron and / or bismuth.

[0082] In a third aspect, the present application provides a negative electrode sheet comprising the lithium doped silicon-carbon composite material described above, i.e. the lithium doped silicon-carbon composite material is used as a negative electrode active material.

[0083] The battery prepared by using the negative electrode sheet has high discharge specific capacity, high first efficiency, good rate performance and excellent cycle performance.

[0084] Optionally, the negative electrode sheet further comprises a conductive agent and / or a binder, which are not limited by the present application.

[0085] In a fourth aspect, the present application provides a lithium ion battery comprising the above negative electrode sheet.

[0086] The lithium ion battery has the advantages of high specific discharge capacity, high first efficiency, good rate performance, excellent cycle performance, and the like.

[0087] Optionally, the lithium ion battery further comprises a positive electrode sheet, a separator, and an electrolyte, which are not limited by the present application.

[0088] Embodiments of the present application will be described in detail below with reference to examples, but those skilled in the art will understand that the following examples are only used to illustrate the present application and should not be regarded as limiting the scope of the present application. If no specific conditions are specified in the examples, the conventional conditions or the conditions recommended by the manufacturer are used. If no manufacturer of the reagent or instrument is specified, it is a conventional product that can be obtained by purchase.

[0089] Example 1

[0090] The preparation method of the lithium-doped silicon-carbon composite material provided in this example comprises the following steps:

[0091] (1) 3 g of Li5FeO4, 3 g of methyl methacrylate, and 100 g of petroleum pitch were dissolved in 1000 g of cyclohexane organic solvent and uniformly dispersed, then 3 g of ethylene glycol was added and mixed for 3 h (i.e. the mass ratio of carbon source, organic pore-forming agent, lithium supplement, and reducing agent was 100:3:3:3), then spray drying was performed to obtain a mixed material. The mixed material was subjected to microwave heating at 1000°C, during which carbon dioxide was introduced at a flow rate of 50 ml / min to perform reduction reaction and activation and pore formation, and after 150 min, a macroporous lithium-doped porous carbon was obtained.

[0092] (2) 100 g of the macroporous lithium-doped porous carbon was transferred to a fluidized bed, and by gas phase deposition method, heated to 1000°C, vacuumed to 8 Pa, then lithium fluoride and lithium acetate mixed gas (volume ratio 1:1) was introduced at a flow rate of 5 ml / min to perform first deposition for 300 min. Then, the temperature was lowered to 500°C, the pressure was controlled to be 0.05 MPa, and disilane mixed gas (volume ratio, disilane:nitrogen = 3:10) was introduced at a flow rate of 50 ml / min to perform second deposition for 150 min, to obtain a lithium compound-doped silicon-carbon precursor material.

[0093] (3) 3 g of ferrocene and 3 g of liquid pitch were dissolved in 500 g of N-methyl pyrrolidone organic solvent and uniformly dispersed, 100 g of lithium compound doped silicon-carbon precursor material was then added and uniformly dispersed (i.e., the mass ratio of lithium compound doped silicon-carbon precursor material, organic metal compound and pitch was 100:3:3), followed by spray drying, and then the obtained material was carbonized at 1200°C for 3 h to obtain a lithium doped silicon-carbon composite material.

[0094] The lithium doped silicon-carbon composite material prepared in this embodiment 1 was subjected to scanning electron microscope (SEM) test, and the results are shown in FIG. 1. Figure 1 As can be seen from FIG. 1, the lithium doped silicon-carbon composite material has a spherical structure, and the particle size is between 1 μm and 5 μm. Figure 1

[0095] Embodiment 2

[0096] The preparation method of the lithium doped silicon-carbon composite material provided in this embodiment includes the following steps:

[0097] (1) 1 g of Li6CoO4, 1 g of polyvinyl butyral and 100 g of phenol formaldehyde resin were dissolved in 500 g of cyclohexane organic solvent and uniformly dispersed, 1 g of glucose was then added and mixed for 3 h (i.e., the mass ratio of carbon source, organic pore forming agent, lithium supplement agent and reducing agent was 100:1:1:1), followed by spray drying to obtain a mixed material. The mixed material was subjected to microwave heating at 900°C, during which carbon dioxide was introduced at a flow rate of 10 ml / min to perform reduction reaction and activation and pore forming, and after 300 min, a lithium doped porous carbon with large pore size was obtained.

[0098] (2) 100 g of the lithium doped porous carbon with large pore size was transferred into a fluidized bed, and by gas phase deposition method, heated to 900°C, and vacuumed to 5 Pa, and then lithium carbonate and lithium acrylate mixed gas (volume ratio of lithium carbonate to lithium acrylate = 1:0.5) was introduced at a flow rate of 1 ml / min to perform first deposition for 600 min. Then, the temperature was lowered to 400°C, the pressure was controlled to be 0.01 MPa, and ethylsilane mixed gas (volume ratio, ethylsilane:nitrogen = 1:10) was introduced at a flow rate of 10 ml / min to perform second deposition for 300 min, to obtain a lithium compound doped silicon-carbon precursor material.

[0099] (3) 1 g of bismuth isooctanoate and 3 g of liquid pitch were dissolved in 500 g of N-methyl pyrrolidone organic solvent and uniformly dispersed, 100 g of lithium compound doped silicon-carbon precursor material was then added and uniformly dispersed (i.e., the mass ratio of lithium compound doped silicon-carbon precursor material, organic metal compound and pitch was 100:1:1), followed by spray drying, and then the obtained material was carbonized at 1000°C for 6 h to obtain a lithium doped silicon-carbon composite material. ​

[0100] Example 3

[0101] The preparation method of the lithium-doped silicon-carbon composite material provided in this embodiment comprises the following steps:

[0102] (1) 5 g of LiNiO2, 5 g of polystyrene, and 100 g of phenolic resin were dissolved in 500 g of cyclohexane organic solvent and uniformly dispersed, 5 g of acetone was then added thereto and mixed for 3 h (i.e., the mass ratio of the carbon source, the organic pore-forming agent, the lithium supplement, and the reducing agent was 100:5:5:5), and then spray drying was performed to obtain a mixed material. The mixed material was subjected to microwave heating at 1100℃, during which carbon dioxide was introduced at a flow rate of 100 ml / min to perform reduction reaction and activation and pore formation, and after 30 min, a lithium-doped macroporous carbon was obtained.

[0103] (2) 100 g of the lithium-doped macroporous carbon was transferred to a fluidized bed, and by using a gas deposition method, heating was performed to 1100℃, vacuum was extracted to 10 Pa, and then a mixed gas of lithium hydroxide and lithium triflate (volume ratio of lithium hydroxide to lithium triflate = 1:2) was introduced at a flow rate of 10 ml / min to perform first deposition for 60 min. Then, the temperature was lowered to 600℃, the pressure was controlled to be 0.1 MPa, and a dimethylsilane mixed gas (volume ratio of dimethylsilane to nitrogen = 5:10) was introduced at a flow rate of 100 ml / min to perform second deposition for 30 min, thereby obtaining a lithium compound-doped silicon-carbon precursor material.

[0104] (3) 5 g of bismuth laurate and 5 g of liquid pitch were dissolved in 500 g of N-methylpyrrolidone organic solvent and uniformly dispersed, 100 g of the lithium compound-doped silicon-carbon precursor material was then added thereto and uniformly dispersed (i.e., the mass ratio of the lithium compound-doped silicon-carbon precursor material, the organic metal compound, and the pitch was 100:5:5), and then spray drying was performed, and the obtained material was carbonized at 1300℃ for 1 h, thereby obtaining a lithium-doped silicon-carbon composite material.

[0105] Example 4

[0106] The preparation method of the lithium-doped silicon-carbon composite material provided in this embodiment is basically the same as that in Example 1, except that in step (1), methyl methacrylate (the organic pore-forming agent) was replaced by an equal amount of methyl cellulose.

[0107] Example 5

[0108] The preparation method of the lithium-doped silicon-carbon composite material provided in this embodiment is basically the same as that in Example 1, except that in step (1), methyl methacrylate (the organic pore-forming agent) was replaced by an equal amount of polyglycolic acid.

[0109] Example 6

[0110] The preparation method of the lithium-doped silicon-carbon composite material provided in the embodiment is basically the same as that in Embodiment 1, except that in step (1), Li5FeO4 (lithium supplement) is replaced with Li2O2 of the same mass.

[0111] Embodiment 7

[0112] The preparation method of the lithium-doped silicon-carbon composite material provided in the embodiment is basically the same as that in Embodiment 1, except that in step (1), Li5FeO4 (lithium supplement) is replaced with Li2MnO3 of the same mass.

[0113] Comparative Example 1

[0114] The preparation method of the lithium-doped silicon-carbon composite material provided in the embodiment is basically the same as that in Embodiment 1, except that in step (1), Li5FeO4 is not added.

[0115] Comparative Example 2

[0116] The preparation method of the lithium-doped silicon-carbon composite material provided in the embodiment is basically the same as that in Embodiment 1, except that in step (2), the mixed gas of lithium fluoride and lithium acetate is not passed through.

[0117] Comparative Example 3

[0118] The preparation method of the lithium-doped silicon-carbon composite material provided in the embodiment is basically the same as that in Embodiment 1, except that in step (3), ferrocene is not added.

[0119] Comparative Example 4

[0120] The preparation method of the lithium-doped silicon-carbon composite material provided in the embodiment is basically the same as that in Embodiment 1, except that in step (1), ethylene glycol is not added.

[0121] Comparative Example 5

[0122] The preparation method of the lithium-doped silicon-carbon composite material provided in the embodiment is basically the same as that in Embodiment 1, except that in step (1), the mass of Li5FeO4 is replaced with 10 g.

[0123] Comparative Example 6

[0124] The preparation method of the lithium-doped silicon-carbon composite material provided in the embodiment is basically the same as that in Embodiment 1, except that in step (2), the mixed gas of lithium fluoride and lithium acetate is replaced with lithium fluoride gas of the same flow rate (i.e., no organic lithium compound is added).

[0125] Comparative Example 7

[0126] The preparation method of the lithium-doped silicon-carbon composite material provided in this embodiment is basically the same as that in Embodiment 1, except that in step (2), the mixed gas of lithium fluoride and lithium acetate is replaced by lithium acetate gas with the same flow rate (i.e., no inorganic lithium compound is added).

[0127] Comparative Example 8

[0128] The preparation method of the lithium-doped silicon-carbon composite material provided in this embodiment is basically the same as that in Embodiment 1, except that in step (2), the first deposition time is replaced by 1200 min.

[0129] Comparative Example 9

[0130] The preparation method of the lithium-doped silicon-carbon composite material provided in this embodiment is basically the same as that in Embodiment 1, except that in step (3), the mass of ferrocene is replaced by 10 g.

[0131] Experimental Example

[0132] The lithium-doped silicon-carbon composite materials prepared in each embodiment and each comparative example were respectively subjected to physical and chemical performance tests: the pore volume and pore size of each lithium-doped silicon-carbon composite material were tested according to the national standards GB / T-38949-2020 “Determination of Pore Size of Porous Membrane-Standard Particle Method” and GB / T7702.20-2008 “Coal Quality Activated Carbon Pore Volume Detection”; the specific surface area and tap density of each lithium-doped silicon-carbon composite material were tested according to the national standard GB / T38823-2020 “Silicon Carbon”; and the powder conductivity of each lithium-doped silicon-carbon composite material was tested using a four-probe tester. The test results are shown in Table 1.

[0133] Table 1: Results of physical and chemical performance tests of each lithium-doped silicon-carbon composite material

[0134]

[0135] Further, the lithium-doped silicon-carbon composite materials prepared by each of the embodiments and each of the comparative examples were used as negative active materials of lithium ion batteries, and button cells were prepared according to the following method: the negative active material, a binder, a conductive agent and a solvent were mixed (in a ratio of 70 g: 15 g: 15 g: 300 mL) to prepare a slurry, which was then coated on a copper foil, and a negative electrode sheet was prepared by drying and rolling. The binder used was LA132, the conductive agent was SP (conductive carbon black), and the solvent was NMP. The electrolyte was a solution of LiPF6 as an electrolyte, with a concentration of 1 mol / L, and the solvent was a mixture of EC and DEC in a volume ratio of 1:1. A lithium sheet was used as the counter electrode, and a polypropylene (PP) film was used as the separator. Each button cell was assembled in an argon-filled glove box. Then, each button cell was tested for the following performances: (1) electrochemical performance was tested on a Wuhan Lan electric CT2001A battery tester, with a charge-discharge voltage range of 0.005 V to 2.0 V, a charge-discharge rate of 0.1 C, and the discharge specific capacity and the first efficiency of the corresponding button cell were tested, and the cycle performance (0.1 C / 0.1 C, 100 cycles) of the corresponding button cell was also tested. (2) Full charge expansion test: the thickness of the rolled electrode sheet D1 was tested, and the thickness of the electrode sheet after full charging to 100% SOC was D2, and the full charge expansion was (D2-D1) / D1. (3) The lithium ion diffusion coefficient of the material was tested by GITT. The test results are shown in Table 2.

[0136] Table 2: Electrochemical performance test results of each button cell

[0137]

[0138]

[0139] As can be seen from Tables 1 and 2, compared with each of the comparative examples, the lithium-doped silicon-carbon composite material prepared by each of the embodiments has a larger specific surface area, a higher tap density and a lower powder resistivity. The reason is that the lithium supplement agent is doped in the preparation process of each of the embodiments, which improves the electronic and ionic conductivity of the material, reduces the polarization, and improves the discharge specific capacity and the first efficiency of the material. At the same time, since the inorganic lithium compound and the organic lithium compound are deposited in the pore structure of the porous carbon in the preparation process of each of the embodiments, the lithium ion diffusion coefficient is significantly improved. In addition, the lithium-doped silicon-carbon composite material prepared by each of the embodiments has a reasonable pore distribution and low expansion, thereby improving the cycle performance of the material.

[0140] Specifically, since no lithium supplement agent was added in Comparative Example 1, the number of lithium ions was small, and the first efficiency and the diffusion coefficient were low.

[0141] Comparative Example 2: Since no inorganic lithium compound and organic lithium compound is added, the diffusion coefficient of lithium ions is reduced and the defects are more, resulting in the reduction of the initial efficiency and diffusion coefficient, and the reduction of the cycle performance.

[0142] Comparative Example 3: Since the organic metal compound is not coated, the impedance is large, and the expansion of the material is small.

[0143] Comparative Example 4: Since no reducing agent is added, the impedance of the metal oxide is large compared with the metal.

[0144] Comparative Example 5: Since the amount of lithium supplementing agent is too much, although it is beneficial to the initial efficiency and diffusion coefficient, it causes the expansion to be large, which is not conducive to the cycle performance.

[0145] Comparative Example 6: Since no organic lithium compound is added, the ion diffusion coefficient is poor, and the initial efficiency and cycle performance are reduced.

[0146] Comparative Example 7: Since no inorganic lithium compound is added, the ion diffusion coefficient is poor, and the initial efficiency and cycle performance are reduced.

[0147] Comparative Example 8: Since the amount of deposited inorganic lithium compound and organic lithium compound is too much, the proportion of active material is reduced, and the specific capacity is reduced.

[0148] Comparative Example 9: Since the amount of coated organic metal compound is too much, the expansion is large, and the cycle performance is reduced.

[0149] Further, the lithium-doped silicon-carbon composite materials prepared in each of the examples and each of the comparative examples are respectively used to prepare negative electrode sheets, and then the negative electrode sheets are respectively assembled into 5 Ah soft package batteries with ternary material LiNi 0.6 Co 0.2 Mn 0.2 O2 as the positive electrode material; LiPF6 as the electrolyte in the electrolyte, and a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1:1 as the solvent; and Celgard 2400 film as the separator.

[0150] Table 3: Performance test results of each soft package battery

[0151]

[0152]

[0153] As shown in Table 3, the soft-pack lithium-ion batteries prepared using the lithium-doped silicon-carbon composite materials obtained in each embodiment have better rate performance and cycle performance than those in the comparative examples. This is because the lithium-doped silicon-carbon composite materials obtained in each embodiment have low full-charge expansion and high specific surface area, which improves the cycle performance of the material. At the same time, the lithium-doped silicon-carbon composite materials obtained in each embodiment have low powder resistivity, which improves the fast-charging performance of the material.

[0154] In contrast, Comparative Example 1, due to the absence of a lithium replenishing agent, resulted in a deterioration in the lithium-ion transport rate and diffusion coefficient of the material, leading to a reduction in the lithium-ion transport rate during charging and discharging, as well as reduced rate performance and cycle performance.

[0155] Comparative Example 2, due to the absence of inorganic and organic lithium compounds, resulted in a higher core impedance, reducing rate performance. However, the higher porosity had a limited impact on material expansion, slightly reducing cycle performance.

[0156] Comparative Example 3, due to the lack of coating with organometallic compounds, resulted in a higher interfacial impedance, which reduced its rate performance.

[0157] In Comparative Example 4, the absence of a reducing agent led to the formation of metal oxides by the doping elements, resulting in higher impedance. However, this had a limited impact on the material's expansion performance and slightly reduced its cycle performance.

[0158] In Comparative Example 5, the excessive addition of lithium supplementer resulted in an excessively high content of metal compounds after carbonization, causing it to expand and reduce its cycle performance, while having little impact on the diffusion rate of lithium ions.

[0159] Comparative Example 6, due to the lack of added organic lithium compounds, had limited effect on improving the diffusion rate of lithium ions, thus reducing its rate performance.

[0160] Comparative Example 7, due to the lack of added inorganic lithium compounds, had limited effect on improving the diffusion rate of lithium ions, thus reducing its rate performance.

[0161] In Comparative Example 8, the excessive amount of deposited inorganic and organic lithium compounds led to a decrease in the porosity of porous carbon, resulting in a lower deposition amount of nano-silicon. This limited buffer space during the expansion of nano-silicon resulted in greater expansion and severely deteriorated cycle performance.

[0162] Comparative Example 9 showed that excessive amounts of coated organometallic compounds led to increased expansion and decreased cycle performance.

[0163] In summary, the preparation method of the lithium-doped silicon-carbon composite material provided by the application, by doping a lithium supplement in a porous carbon precursor and through a reduction reaction and activation pore-forming, a macroporous lithium-doped porous carbon is obtained, the porous carbon can reduce expansion, the lithium doping can reduce defects and improve the ionic conductivity of the material; then organic lithium compounds and inorganic lithium compounds are deposited in the pore structure of the macroporous lithium-doped porous carbon, which can reduce impedance, improve the ion diffusion coefficient, and further improve the ionic conductivity of the material; then deposition of nano-silicon and surface coating are performed, and the metal-doped amorphous carbon coating layer formed after carbonization can reduce the defects of the core, improve the electronic conductivity of the coating layer, and improve the rate performance of the material.

[0164] Furthermore, by optimizing the parameters, the comprehensive electrochemical performance of the battery can be further improved.

[0165] Although the application has been illustrated and described with reference to specific embodiments, it is noted that these are only used to illustrate the technical solutions of the application, and are not intended to limit the application; it should be understood by those skilled in the art that the technical solutions recorded in the foregoing embodiments can be modified, or some or all of the technical features can be replaced equivalently, without departing from the spirit and scope of the application; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the application; therefore, this means that all these replacements and modifications within the scope of the application are included in the appended claims.

Claims

1. A method for preparing a lithium-doped silicon-carbon composite material, characterized by, Comprising the following steps: (a) reducing and activating pore-forming of a mixed material containing a carbon source, an organic pore-forming agent, a lithium supplement agent and a reducing agent to obtain a lithium-doped porous carbon; (b) performing a first deposition of the lithium-doped porous carbon with a mixed gas containing an inorganic lithium compound and an organic lithium compound; and then performing a second deposition of the material obtained after the first deposition with a silane gas to obtain a lithium compound-doped silicon-carbon precursor material; (c) mixing the lithium compound-doped silicon-carbon precursor material, an organic metal compound, pitch and an organic solvent, then spray drying, and then carbonizing to obtain the lithium-doped silicon-carbon composite material.

2. The method for preparing the lithium-doped silicon-carbon composite material according to claim 1, characterized in that, Step (a) satisfies at least one of the following conditions: (1) the carbon source comprises at least one of petroleum pitch, coal tar pitch, phenolic resin and sucrose; (2) the organic pore-forming agent comprises at least one of methyl methacrylate, polyvinyl butyral, methyl cellulose, polystyrene, polyethylene glycol and polyglycolic acid; (3) the lithium supplement agent comprises at least one of Li5FeO4, Li6CoO4, Li2O2, LiNiO2 and Li2MnO3; (4) the reducing agent comprises at least one of ethanol, ethylene glycol, acetone and glucose; (5) the mass ratio of the carbon source, the organic pore-forming agent, the lithium supplement agent and the reducing agent in the mixed material is 100:1-5:1-5:1-5.

3. The method of claim 1, wherein the lithium-doped silicon-carbon composite material is prepared by the steps of: mixing a silicon source and a carbon source to form a mixture; and heating the mixture to form the lithium-doped silicon-carbon composite material. Step (a) satisfies at least one of the following conditions: (1) the reducing reaction and the activation pore-forming use microwave heating, the temperature of the reducing reaction and the activation pore-forming is 900-1100℃, and the time of the reducing reaction and the activation pore-forming is 30-300min; (2) during the reducing reaction and the activation pore-forming, carbon dioxide is introduced at a flow rate of 10-100ml / min.

4. The method of claim 1, wherein the lithium-doped silicon-carbon composite material is prepared by the steps of: mixing a silicon source and a carbon source to form a mixture; and heating the mixture to form the lithium-doped silicon-carbon composite material. Step (b) satisfies at least one of the following conditions: (1) the inorganic lithium compound comprises at least one of lithium fluoride, lithium carbonate, lithium hydroxide and lithium oxide; (2) the organic lithium compound comprises at least one of lithium acetate, lithium acrylate and lithium triflate; (3) the volume ratio of the inorganic lithium compound to the organic lithium compound in the mixed gas is 1:0.5-2; (4) the silane gas comprises at least one of trichlorosilane, disilane, silane and dimethylsilane.

5. The method of claim 1, wherein the lithium-doped silicon-carbon composite material is prepared by the steps of: mixing a silicon source and a carbon source to form a mixture; and heating the mixture to form the lithium-doped silicon-carbon composite material. Step (b) satisfies at least one of the following conditions: (1) the temperature of the first deposition is 900-1100℃, and the time of the first deposition is 60-600min; (2) the flow rate of the mixed gas containing the inorganic lithium compound and the organic lithium compound is 1-10ml / min; (3) the temperature of the second deposition is 400-600℃, and the time of the second deposition is 30-300min; (4) the flow rate of the silane gas is 10-100ml / min.

6. The method of claim 1 to 5, wherein the lithium-doped silicon-carbon composite material is prepared by the steps of: Step (c) satisfies at least one of the following conditions: (1) the organic metal compound comprises at least one of ferrocene, bismuth iso-octoate, bismuth laurate and bismuth neodecanoate; (2) the mass ratio of the lithium compound-doped silicon-carbon precursor material, the organic metal compound and the pitch is 100:1-5:1-5.

7. The method for preparing the lithium-doped silicon-carbon composite material according to any one of claims 1 to 5, characterized in that, In step (c), the temperature of the carbonization is 1000-1300°C, and the time of the carbonization is 1-6h.

8. A lithium-doped silicon-carbon composite material, characterized by, The lithium-doped silicon-carbon composite material is prepared by the method of any one of claims 1-7.

9. A negative electrode sheet characterized by comprising: The lithium-doped silicon-carbon composite material of claim 8 is included.

10. A lithium-ion battery, characterized by, The negative electrode sheet of claim 9 is included.

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