WO2024187562A1 - Near-spherical silicon-carbon negative electrode material, and preparation method therefor and use thereof - Google Patents

Abstract

The present application relates to the technical field of electrode materials, and provides a near-spherical silicon-carbon negative electrode material, and a preparation method therefor and the use thereof. The preparation method comprises the following steps: sequentially subjecting a mixed solution of a soluble ammonium salt and a carbon source to a sintering treatment, a pore-forming treatment, a pyrolysis treatment with a silane compound and a carbon coating treatment after spray granulation to obtain a near-spherical silicon-carbon negative electrode material. The near-spherical silicon-carbon negative electrode material provided in the present application has a relatively high initial efficiency and specific capacity, and also has a relatively low charging volume expansion effect.

Description

Quasi-spherical silicon-carbon negative electrode material and preparation method and application thereof

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Chinese patent application number 202310250745.2, filed with the State Intellectual Property Office of China on March 15, 2023, and entitled “Spherical silicon-carbon negative electrode material, preparation method and application thereof”, the entire contents of which are incorporated by reference into this application.

Technical Field

The present application relates to the technical field of electrode materials, and in particular to a quasi-spherical silicon-carbon negative electrode material and a preparation method and application thereof.

Background Art

The theoretical capacity of graphite negative electrode material is 372mAh/g. In the application fields where the performance of traditional graphite negative electrode material is difficult to meet, mixing 10-50% silicon-carbon negative electrode material can greatly improve the specific capacity of battery negative electrode material, thereby improving the energy density of the battery. However, it will increase the expansion thickness of the negative electrode material when fully charged, and excessive expansion thickness will easily cause the negative electrode material particles to break and pulverize, causing the solid electrolyte membrane to grow repeatedly, and ultimately leading to the attenuation of negative electrode capacity and the reduction of charge and discharge efficiency, which will cause the cycle performance to continue to decline, that is, the energy density of the battery will be reduced.

There are a large number of micropores inside the hard carbon material, which has a high specific capacity and a small volume expansion effect during the charge and discharge process. The porous hard carbon prepared by further pore formation treatment in the gas phase/liquid phase can effectively alleviate the charging volume expansion of silicon materials and is an ideal silicon-deposited carbon skeleton. At present, the preparation of silicon-carbon negative electrode materials in the industry mostly uses silicon materials and irregular carbon materials or graphite for compounding. Since the irregular carbon material has a small packing density, poor fluidity, poor coating uniformity, and the silicon material has a large charging volume expansion, it is not conducive to improving the energy density of the battery.

In view of this, this application is hereby filed.

Summary of the invention

One object of the present application is to provide a method for preparing a spherical silicon-carbon negative electrode material, which can at least improve the initial efficiency and specific capacity of the silicon-carbon negative electrode material, while allowing the negative electrode material to have a lower charging volume expansion effect.

Another object of the present application is to provide a spherical silicon-carbon negative electrode material having a higher initial efficiency, a higher specific capacity and a lower charging volume expansion effect. When used as a negative electrode material for a lithium-ion secondary battery, it is beneficial to increase the energy density of the lithium-ion battery and improve the initial charge and discharge efficiency.

Another object of the present application is to provide an application of a spherical silicon-carbon negative electrode material, which can increase the energy density of lithium-ion batteries and improve the initial charge and discharge efficiency.

This application achieves the above objectives from the following aspects:

On the one hand, the present application provides a method for preparing a spherical silicon-carbon negative electrode material, which may include the following steps:

After spray granulation, the mixed solution of soluble ammonium salt and carbon source is sequentially subjected to sintering treatment, pore-forming treatment, thermal decomposition treatment with silane compound and carbon coating treatment to obtain the quasi-spherical silicon-carbon negative electrode material.

In some embodiments, the soluble ammonium salt may include at least one of ammonium chloride, ammonium nitrate, ammonium acetate, ammonium carbonate, ammonium bicarbonate, ammonium phosphate, diammonium hydrogen phosphate, diammonium phosphate, and ammonium polyphosphate;

Optionally, the carbon source includes starch;

Optionally, the starch includes at least one of millet starch, rice starch, mung bean starch, sorghum starch, potato starch, wheat starch, water chestnut starch, sweet potato starch, cassava starch, lotus root starch, corn starch and pea starch;

Optionally, the solvent of the mixed solution includes at least one of water, anhydrous ethanol and isopropanol;

Optionally, the solid content of the mixed solution is 10 to 30 wt %;

Optionally, the mass ratio of the soluble ammonium salt to the carbon source is 1:100 to 40:100.

Optionally, the viscosity of the mixed solution is below 100 mPa·s.

In some embodiments, the median particle size D50 of the spray granulation may be between 15 and 25 microns;

Optionally, the average sphericity of the spray granulation is above 0.7.

In some embodiments, the sintering process may include a first sintering process and a second sintering process performed sequentially;

Optionally, the temperature of the first sintering process is lower than the temperature of the second sintering process.

Optionally, the temperature of the first sintering treatment is 100 to 500° C., and the time is 2 to 24 hours;

Optionally, the temperature of the second sintering treatment is 800-1500° C., and the time is 2-24 hours.

In some embodiments, the pore-forming process may include at least one of a gas-phase pore-forming process and a liquid-phase pore-forming process;

Optionally, the gas used in the gas-phase pore-forming treatment includes at least one of water vapor, air, carbon dioxide, chlorine, sulfur dioxide and nitrogen dioxide;

Optionally, the liquid for the liquid-phase pore-forming treatment includes a strong oxidizing acid;

Optionally, the strong oxidizing acid includes at least one of concentrated sulfuric acid, perchloric acid and concentrated nitric acid;

Optionally, the pore-forming treatment is performed at a temperature of 100 to 1000° C. for a time of 2 to 48 hours;

Optionally, the pore structure after the pore-forming treatment includes at least one of micropores, mesopores and macropores;

Optionally, the pore volume after the pore-forming treatment is 0.1-2 cm ³ /g.

In some embodiments, the silane compound may include at least one of monosilane, dimethylsilane, difluorosilane, trifluoromethylsilane, tetrafluorosilane, trimethylfluorosilane, chlorosilane, chloromethylsilane, and dichlorosilane;

Optionally, the gas flow rate of the silane compound during the pyrolysis treatment is 0.1 to 3 L/min;

Optionally, the pyrolysis treatment is performed at a temperature of 400 to 800° C. and a time of 0.5 to 24 h;

Optionally, the pyrolysis treatment is carried out in an inert gas;

Optionally, the silicon element after pyrolysis treatment is distributed in the pores and/or surface of the hard carbon material;

Optionally, the silicon element after the pyrolysis treatment is nano silicon particles;

Optionally, the median particle size D50 of the nano-silicon particles is less than 50 nm.

In some embodiments, the carbon-coated organic carbon source may include at least one of methane, acetylene, toluene, glucose, petroleum asphalt, coal asphalt, mesophase asphalt, polymethyl methacrylate, phenolic resin, polystyrene and polyacrylonitrile;

Optionally, the carbon coating treatment is performed at a temperature of 400 to 800° C. and a time of 0.5 to 12 h;

Optionally, the carbon coating process is performed in an inert gas;

Optionally, the coating layer after the carbon coating treatment accounts for 0.1 to 10% of the mass of the silicon-carbon negative electrode material.

On the other hand, the present application provides a spherical silicon-carbon negative electrode material prepared according to the above preparation method.

In some embodiments, the hard carbon-carbon interlayer spacing d ₀₀₂ of the quasi-spherical silicon-carbon negative electrode material may be 0.35 to 0.41 nm;

Optionally, the water content of the quasi-spherical silicon-carbon negative electrode material is below 1 wt %;

Optionally, the specific surface area of the quasi-spherical silicon-carbon negative electrode material is 1 to 10 m ² /g, preferably 2 to 8 m ² /g;

Optionally, the median particle size D50 of the quasi-spherical silicon-carbon negative electrode material is 3 to 15 μm, preferably 7 to 15 μm;

Optionally, the tap density of the quasi-spherical silicon-carbon negative electrode material is 0.8 to 1.2 g/cm ³ ;

Optionally, the proportion of silicon in the spherical silicon-carbon negative electrode material is 20-75wt%.

On the other hand, the present application provides an application of the above-mentioned spherical silicon-carbon negative electrode material in a lithium-ion battery.

Compared with the related art, this application has at least the following beneficial effects:

The preparation method of spherical silicon-carbon negative electrode material provided in the present application, spray granulation and subsequent specific treatment can make the silicon-carbon negative electrode material have better sphericity and lower specific surface area. Specifically, during the spray granulation process, the solution containing the carbon source will be quickly thrown out, and the solution will be atomized, so that the solvent will evaporate rapidly, so that the carbon source (such as starch) particles can maintain a good spherical shape, and during the sintering process, the carbon source (such as starch) will lose a lot of weight, and release carbon dioxide and water. Therefore, through process control, the integrity of the silicon-carbon negative electrode material particles can be ensured; the present application can deposit nano-silicon through pyrolysis treatment, and nano-silicon has a lower volume expansion effect. The spherical hard carbon material has a higher stacking density. Depositing nano-silicon in the pores of porous spherical hard carbon has a positive effect on improving battery energy density and reducing expansion effect.

The spherical silicon-carbon negative electrode material provided in the present application has high first charge and discharge efficiency and specific capacity. In the lithium-ion battery test system, the first reversible capacity is above 1800 mA·h/g, the first coulombic efficiency is above 92%, and the material mixed with graphite has a lower charging volume expansion effect.

The application of the spherical silicon-carbon negative electrode material provided in the present application can increase the energy density of lithium-ion batteries and improve the initial charge and discharge efficiency, and has outstanding application effects.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the specific implementation methods of this application or the technical solutions in the related technologies, the specific implementation methods will be described below. The accompanying drawings required for use in the method or related technical description are briefly introduced. Obviously, the accompanying drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying any creative work.

FIG1 is a 1000-fold scanning electron microscope image of the hard carbon material provided in Example 1 of the present application;

FIG2 is a 30,000-fold scanning electron microscope image of the hard carbon material provided in Example 1 of the present application;

FIG3 is an XRD diffraction pattern of the hard carbon material provided in Example 1 of the present application;

FIG4 is a 1000-fold scanning electron microscope image of the silicon-carbon negative electrode material provided in Example 1 of the present application;

FIG5 is a 30,000-fold scanning electron microscope image of the silicon-carbon negative electrode material provided in Example 1 of the present application;

FIG6 is a scanning electron microscope image and an energy spectrum diagram of an ion milled cross-section of a pole piece prepared from a silicon-carbon negative electrode material provided in Example 1 of the present application;

FIG7 is an XRD diffraction pattern of the silicon-carbon negative electrode material provided in Example 1 of the present application;

FIG8 is a graph showing the first charge and discharge curves of a lithium button cell made of silicon-carbon negative electrode material obtained in Experimental Example 2 of the present application.

DETAILED DESCRIPTION

The technical solution of the present application will be described clearly and completely below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present application.

According to a first aspect of the present application, a method for preparing a spherical silicon-carbon negative electrode material is provided, comprising the following steps:

After spray granulation, the mixed solution of soluble ammonium salt and carbon source is sequentially subjected to sintering treatment, pore-forming treatment, thermal decomposition treatment with silane compound and carbon coating treatment to obtain spherical silicon-carbon negative electrode material.

The preparation method of spherical silicon-carbon negative electrode material provided in the present application, spray granulation and subsequent specific treatment can make the silicon-carbon negative electrode material have better sphericity and lower specific surface area. Specifically, during the spray granulation process, the solution containing the carbon source will be quickly thrown out, and the solution will be atomized, so that the solvent will evaporate rapidly, so that the carbon source (such as starch) particles can maintain a good spherical shape, and during the sintering process, the carbon source (such as starch) will lose a lot of weight, and release carbon dioxide and water. Therefore, through process control, the integrity of the silicon-carbon negative electrode material particles can be ensured; the present application can deposit nano-silicon through pyrolysis treatment, and nano-silicon has a lower volume expansion effect. The spherical hard carbon material has a higher stacking density. Depositing nano-silicon in the pores of porous spherical hard carbon has a positive effect on improving battery energy density and reducing expansion effect.

The soluble ammonium salt and carbon source in the present application can be commercially available products known to those skilled in the art. For example, the soluble ammonium salt can be at least one of ammonium chloride, ammonium nitrate, ammonium acetate, ammonium carbonate, ammonium bicarbonate, ammonium phosphate, diammonium hydrogen phosphate, diammonium phosphate and ammonium polyphosphate, but is not limited thereto. When the soluble ammonium salt is two or more of the above substances, the present application does not have any special restrictions on the ratio of the combination, and can be mixed in any ratio; in the present application, carbon The source can preferably be starch, for example, it can be at least one of millet starch, rice starch, mung bean starch, sorghum starch, potato starch, wheat starch, water chestnut starch, sweet potato starch, cassava starch, lotus root starch, corn starch and pea starch, but is not limited thereto. When the carbon source is two or more of the above substances, the present application does not have any special limitation on the ratio of their combination, and they can be mixed in any ratio.

In a preferred embodiment, a soluble ammonium salt, a carbon source and a solvent are mixed (the mixing process is not particularly limited, and a process or technology well known to those skilled in the art can be used) to obtain a mixed solution, which is then spray granulated to obtain spherical particles, wherein the mass ratio of the soluble ammonium salt to the carbon source can be 1:100 to 40:100, and its typical but non-limiting mass ratio is, for example, 5:100, 10:100, 15:100, 20:100, 25:100, 30:100, 35:1 00, 40:100, but not limited to this, it can be further preferably 10:100-30:100, and further preferably 15:100-25:100, which is more conducive to the formation of spherical particles by spray granulation; if the proportion of soluble ammonium salt is too low, the volatile matter is insufficient during the spray granulation process, resulting in low sphericity of the formed particles; if the proportion of soluble ammonium salt is too high, it will not volatilize completely in a short time during the spray granulation process, and most of the ammonium salt will remain on the surface of the particles. The decomposition and volatilization of the ammonium salt during the sintering process will affect the sphericity of the particles.

The present application does not impose any special limitation on the solvent, for example, it can be at least one of water, anhydrous ethanol and isopropanol, and can be further preferably pure water, but is not limited to this. When the solvent is two or more of the above substances, the present application does not impose any special limitation on the ratio of their combination, and they can be mixed in any ratio.

In a preferred embodiment, the solid content of the mixed solution can be 10-30wt%, and its typical but non-limiting solid content is, for example, 10wt%, 13wt%, 16wt%, 18wt%, 21wt%, 24wt%, 27wt%, 30wt%, and can be further preferably 16-24wt%, and further preferably 18-21wt%, which is more conducive to the mixed solution being in a suitable viscosity range, and the mixed solution forms spherical droplets of suitable particle size under the centrifugal action of the atomizer; if the solid content is too high, it will lead to increased solution viscosity, and the droplets formed by atomization and centrifugation will be too large, or even unable to form droplets by centrifugation, and dry on the atomizer to cause blockage; if the solid content is low, the viscosity of the mixed solution is reduced, the fluidity of the solution is large, and it will be atomized to form small droplets containing a large amount of solvent. The particle size of the particles obtained after the solvent evaporates is small, and the particles of small size and small mass are easily carried away by the airflow, resulting in a reduced yield.

In a preferred embodiment, the viscosity of the mixed solution may be below 100 mPa·s, which is more conducive to improving the effect of the granular product after spray granulation.

In a preferred embodiment, the spray granulation equipment may be a spray dryer, but is not limited thereto.

In a preferred embodiment, the inlet temperature of the spray dryer may be below 220°C, and typical but non-limiting temperatures include, for example, 190°C, 195°C, 200°C, 205°C, 210°C, 215°C, and 220°C, and may be further preferably 200-210°C, which is more conducive to making the atomized droplets in a dry or semi-dry state; if the temperature is too high, a large amount of heat of the volatile components after volatilization will remain on the dry particles, and the dry particles will absorb heat and decompose, resulting in the material Deterioration; if the temperature is too low, the volatile components will not evaporate completely, and the remaining part of the solution will concentrate and thicken, agglomerate or stick to the wall, resulting in agglomeration of the material and a reduction in yield.

In a preferred embodiment, the rotation speed of the atomizing disk of the spray dryer can be above 10000rpm, and its typical but non-limiting temperatures are, for example, 10000rpm, 11000rpm, 12000rpm, 13000rpm, 14000rpm, 15000rpm, 16000rpm, and 17000rpm, and can be further preferably 12000-14000rpm, which is more conducive to forming droplets of appropriate particle size from the mixed solution and ensuring the particle size and sphericity of the particles; when the rotation speed is too high, the atomized droplets will quickly form particles and be thrown onto the cavity wall by excessive centrifugal force, causing a large amount of material accumulation in the columnar part of the drying cavity; when the rotation speed is too low, the centrifugal force provided is insufficient for the mixed solution to overcome the surface tension to form separate droplets, and an umbrella-shaped film is easily formed.

In a preferred embodiment, the median particle size D50 of the spray granulation is between 15 and 25 microns, for example, it can be 15 microns, 16 microns, 17 microns, 18 microns, 19 microns, 20 microns, 21 microns, 22 microns, 23 microns, 24 microns, 25 microns, but not limited to this; the average value of the sphericity of the spray granulation is above 0.7, and can be further preferably 0.75 to 0.8, for example, it can be 0.75, 0.76, 0.77, 0.78, 0.79, 0.8, but not limited to this.

The median particle size D50 and sphericity after spray granulation in the present application are more conducive to making the silicon-carbon negative electrode material prepared in the subsequent process have high initial efficiency and specific capacity, as well as low charging volume expansion effect.

In a preferred embodiment, the sintering process includes a first sintering process and a second sintering process performed sequentially, wherein the temperature of the first sintering process is lower than the temperature of the second sintering process, and the first and second sintering processes can be performed under a protective atmosphere.

In a preferred embodiment, the temperature of the first sintering treatment can be 100-500°C, and typical but non-limiting temperatures are, for example, 100°C, 200°C, 300°C, 400°C, and 500°C, and can be further preferably 200-500°C, and further preferably 300-400°C; the holding time of the first sintering treatment can be 2-24h, and typical but non-limiting times are, for example, 2h, 8h, 14h, 20h, and 24h, and can be further preferably 8-20h, and further preferably 12-16h.

In a preferred embodiment, the temperature of the second sintering treatment can be 800-1500°C, and typical but non-limiting temperatures are, for example, 800°C, 900°C, 1000°C, 1100°C, 1200°C, 1300°C, 1400°C, and 1500°C, and may be further preferably 900-1400°C, and further preferably 1000-1300°C; the holding time of the second sintering treatment can be 2-24h, and typical but non-limiting times are, for example, 2h, 8h, 14h, 20h, and 24h, and may be further preferably 8-20h, and further preferably 12-16h.

The temperature and time of the first and second sintering treatments in the present application are more conducive to maintaining the sphericity of the obtained hard carbon material above 0.7.

In a preferred embodiment, the pore-forming treatment includes but is not limited to at least one of a gas phase pore-forming treatment and a liquid phase pore-forming treatment.

In the present application, the gas used in the gas phase pore forming treatment includes but is not limited to at least one of water vapor, air, carbon dioxide, chlorine, sulfur dioxide and nitrogen dioxide; the liquid used in the liquid phase pore forming treatment includes but is not limited to strong oxidizing acids, wherein the strong oxidizing acids include but are not limited to at least one of concentrated sulfuric acid, perchloric acid and concentrated nitric acid.

In the present application, the temperature of the pore-forming treatment can be 100-1000°C, and typical but non-limiting temperatures are, for example, 100°C, 200°C, 300°C, 400°C, 500°C, 600°C, 700°C, 800°C, 900°C, and 1000°C. The time can be 2-48h, and typical but non-limiting times are, for example, 2h, 4h, 6h, 8h, 10h, 15h, 20h, 25h, 30h, 35h, 40h, 45h, and 48h.

The temperature and time of the pore-forming treatment in the present application are more conducive to improving the pore-forming effect. The pore structure after pore-forming includes but is not limited to at least one of micropores, mesopores and macropores. The pore volume after pore-forming can be 0.1-2 cm ³ /g, which is more conducive to the subsequent pyrolysis treatment, and deposits nano-silicon in the pores of porous spherical hard carbon to increase energy density and reduce expansion effect.

In a preferred embodiment, the silane compound used in the thermal decomposition treatment includes but is not limited to at least one of monosilane, dimethylsilane, difluorosilane, trifluoromethylsilane, tetrafluorosilane, trimethylfluorosilane, chlorosilane, chloromethylsilane and dichlorosilane.

In a preferred embodiment, the gas flow rate of the silane compound in the pyrolysis treatment can be 0.1-3 L/min, and its typical but non-limiting flow rates are, for example, 0.1 L/min, 0.5 L/min, 1 L/min, 1.5 L/min, 2 L/min, 2.5 L/min, and 3 L/min; the temperature of the pyrolysis treatment can be 400-800°C, and its typical but non-limiting temperatures are, for example, 400°C, 500°C, 600°C, 700°C, and 800°C, and can be further preferably 400-600°C. The time can be 0.5-24h, and its typical but non-limiting time is, for example, 0.5h, 1h, 1.5h, 2h, 4h, 6h, 8h, 10h, 15h, 20h, and 24h.

The gas flow rate, temperature and time of the pyrolysis treatment in the present application are more conducive to cracking the silane compound into nano-silicon and depositing and distributing it in the internal pores and/or surface of the porous spherical hard carbon, which can improve the energy density and reduce the expansion effect.

In the present application, the pyrolysis treatment can be carried out in an inert gas, and the silicon element after the pyrolysis treatment is nano-silicon particles, wherein the average particle size D50 is below 50 nm, which is more conducive to reducing the volume expansion of the silicon material during the charging process and reducing the possibility of silicon cracking and pulverization; if the particle size is too large, it will lead to an increase in the charging volume expansion effect of the silicon material, which will easily cause the silicon material particles to crack and pulverize, causing the solid electrolyte membrane to grow repeatedly, resulting in reversible capacity attenuation.

In a preferred embodiment, the organic carbon source for carbon coating treatment includes but is not limited to at least one of methane, acetylene, toluene, glucose, petroleum asphalt, coal asphalt, mesophase asphalt polymethyl methacrylate, phenolic resin, polystyrene and polyacrylonitrile.

In a preferred embodiment, the temperature of the carbon coating treatment can be 400-800°C, and typical but non-limiting temperatures are, for example, 400°C, 500°C, 600°C, 700°C, and 800°C, and can be further preferably 400-600°C. The time can be 0.5-12h, and typical but non-limiting times are, for example, 0.5h, 1h, 1.5h, 2h, 4h, 6h, 8h, 10h, and 12h.

The carbon coating treatment temperature and time in the present application are more conducive to improving the effect of cracking the organic carbon source, and are more conducive to forming a coating layer on the organic carbon source to wrap the silicon-carbon negative electrode material.

In the present application, the carbon coating treatment can be carried out under an inert gas, and the coating layer formed after the carbon coating treatment can account for 0.1 to 10% of the mass of the silicon-carbon negative electrode material, and its typical but non-limiting mass proportion is, for example, 0.1%, 0.2%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, and 10%.

A typical preparation method of a spherical silicon-carbon negative electrode material comprises the following steps:

The soluble ammonium salt, the carbon source and the solvent are mixed and then spray granulated to obtain spherical particles;

Sintering the obtained quasi-spherical particles to obtain a quasi-spherical hard carbon material, wherein the sintering includes a first sintering and a second sintering performed in sequence, and the temperature of the first sintering is lower than the temperature of the second sintering;

The obtained spherical hard carbon material is subjected to pore-forming treatment to obtain a porous spherical hard carbon material, wherein the pore-forming treatment includes gas phase and/or liquid phase pore-forming treatment;

Then, the obtained porous quasi-spherical hard carbon material is pyrolyzed and contacted with a silane compound by chemical vapor deposition to complete silicon deposition, thereby obtaining a quasi-spherical silicon-carbon material precursor;

Finally, the obtained spherical silicon-carbon material precursor is carbon-coated by cracking an organic carbon source to obtain a spherical silicon-carbon negative electrode material.

According to a second aspect of the present application, a spherical silicon-carbon negative electrode material prepared by any of the preparation methods described above is provided.

The spherical silicon-carbon negative electrode material provided in the present application has high initial charge and discharge efficiency and specific capacity. In the lithium-ion battery test system, the initial reversible capacity is above 1800 mA·h/g, the initial coulombic efficiency is above 92%, and the material after being mixed with graphite has a lower charging volume expansion effect.

The hard carbon carbon interlayer spacing _d002 of the quasi-spherical silicon-carbon negative electrode material provided in the present application is between 0.35 and 0.41 nm. Compared with the interlayer spacing of graphite of 0.33, the carbon interlayer spacing in the present application is significantly increased, so it has better rate performance and more stable cycle performance. The irregularly arranged carbon layer structure of the material can provide more abundant lithium storage sites, so it has a higher specific capacity than graphite; at the same time, the material provided in the present application has a quasi-spherical particle morphology, which can not only improve the material's tap density (0.8-1.2 g/ ^cm3 ), but also reduce its specific surface area (1-10 ^m2 /g), so when used as a secondary battery negative electrode material, it can effectively improve the battery's energy density and significantly improve the initial charge and discharge efficiency.

In a preferred embodiment, the water content of the spherical silicon-carbon negative electrode material provided in the present application is below 1 wt %, the specific surface area thereof is between 2 and 8 m ² /g, and the bulk density of the spherical hard carbon material used is between 0.4 and 0.6 g/cm ³ .

In a preferred embodiment, the particle size D10 of the spherical silicon-carbon negative electrode material provided in the present application is above 2 μm; the median particle size D50 is between 3 and 15 μm, and may be further preferably 7 to 15 μm; and the particle size D100 is below 60 μm.

In a preferred embodiment, the mass proportion of silicon in the spherical silicon-carbon negative electrode material of the present application can be 20-75wt%, and its typical but non-limiting mass proportion is, for example, 20wt%, 22wt%, 24wt%, 26wt%, 28wt%, 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, 65wt%, 70wt%, 75wt%, are more conducive to improving the specific capacity of silicon-carbon negative electrode materials, and can buffer the charging volume expansion of silicon to ensure a higher reversible capacity; if the mass proportion of silicon element is too low, although the charging volume expansion is small, the specific capacity of the material is low, which is not conducive to improving the overall energy density of the battery; if the mass proportion of silicon element is too high, although the specific capacity is high, too little carbon element is not enough to buffer the charging volume expansion of silicon, which can easily cause the silicon material particles to break during the charge and discharge cycle, and the solid electrolyte membrane to grow repeatedly, eventually leading to reversible capacity decay.

According to a third aspect of the present application, there is provided a use of the spherical silicon-carbon negative electrode material described in any one of the above items in a lithium-ion battery.

The application of the spherical silicon-carbon negative electrode material provided in the present application can increase the energy density of lithium-ion batteries and improve the initial charge and discharge efficiency, and has outstanding application effects.

In the present application, the lithium-ion battery is a secondary battery. The conductive agent used in the secondary battery includes but is not limited to at least one of SUPER-P, Ketjen black, acetylene black, carbon nanotubes and KS-6. When the conductive agent is two or more of the above substances, the present application does not have any special restrictions on the ratio of their combination, and they can be mixed in any ratio; the binder used in the electrode plate of the secondary battery includes but is not limited to at least one of CMC, SBR, PVDF, LA133 and BP-7. When the binder is two or more of the above substances, the present application does not have any special restrictions on the ratio of their combination, and they can be mixed in any ratio; the solvent used in the preparation of the electrode plate of the secondary battery includes but is not limited to ultrapure water and/or methyl pyrrolidone.

The separator used in the lithium-ion secondary battery in the present application can be three-layer PP/PE/PP, double-layer PP/PE or PP+ceramic coating; wherein the total thickness of PE+ceramic coating can be 10 to 50 μm.

The current collector used in the lithium ion secondary battery in the present application may be a commercial aluminum foil with a thickness of 13 to 30 μm or a copper foil with a thickness of 4 to 20 μm, but is not limited thereto.

The electrolyte used in the lithium-ion secondary battery in the present application is mainly composed of three parts: lithium salt, solvent and additive. Among them, the lithium salt includes but is not limited to at least one of lithium hexafluorophosphate, lithium perchlorate and lithium tetrafluoroborate. When the lithium salt is two or more of the above substances, the present application does not have any special restrictions on the ratio of their combination, and they can be mixed in any ratio; wherein the electrolyte includes but is not limited to at least one of ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC).

The present application is further described below by way of examples. Unless otherwise specified, the materials in the examples are prepared according to relevant methods or purchased directly from the market.

Example 1

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

S1: 200 g of soluble ammonium salt (ammonium carbonate), 1000 g of carbon source (corn starch) and 5000 g of solvent (pure water) were mixed to obtain a mixed solution, which was then granulated by a spray dryer to obtain spherical particles;

The solid content of the mixed solution is 19.4 wt %, and the viscosity of the mixed solution is 13.4 mPa·s;

The inlet temperature of the spray dryer was 205°C, and the rotation speed of the atomizing disk was 13000 rpm;

S2: performing a first sintering treatment and a second sintering treatment on the spherical particles in sequence to obtain a spherical hard carbon material;

The first sintering process was carried out at a temperature of 400°C, for 12 hours, in a nitrogen atmosphere; the second sintering process was carried out at a temperature of 1300°C, for 12 hours, in a nitrogen atmosphere;

The morphology of the hard carbon material was tested by field emission scanning electron microscopy (SEM) (JSM-7800F). The obtained SEM images are shown in Figure 1 (magnified 1000 times) and Figure 2 (magnified 30000 times). It can be seen that the morphology of the hard carbon material is spherical.

The hard carbon material was subjected to XRD testing, and the obtained XRD diffraction pattern is shown in FIG3 , which shows that the carbon interlayer spacing of the hard carbon material is 0.38 nm;

S3: subjecting the spherical hard carbon material to a water vapor pore-forming treatment to obtain a porous spherical hard carbon material;

The pore-forming treatment temperature is 900°C and the pore-forming treatment time is 6 hours;

S4: subjecting the porous spherical hard carbon material to pyrolysis contact with monosilane to obtain a spherical silicon-carbon negative electrode material precursor;

The flow rate of monosilane was 0.6 L/min, the pyrolysis temperature was 600 °C, the pyrolysis time was 6 h, and the atmosphere was nitrogen.

S5: performing acetylene pyrolysis and carbon coating on a quasi-spherical silicon-carbon negative electrode material precursor to obtain a quasi-spherical silicon-carbon negative electrode material;

The acetylene flow rate was 2 L/min, the pyrolysis temperature was 550° C., the pyrolysis time was 1.5 h, and the atmosphere was nitrogen.

The morphology of the silicon-carbon negative electrode material obtained in this embodiment was tested by SEM using a field emission scanning electron microscope (SEM) (JSM-7800F). The obtained scanning electron microscope images are shown in FIG4 (magnified 1000 times) and FIG5 (magnified 30000 times). It can be seen that the morphology of the silicon-carbon negative electrode material obtained in this embodiment is spherical;

The ion milling cross-section scanning electron microscope image and energy spectrum of the electrode prepared by the silicon-carbon negative electrode material obtained in this embodiment are shown in FIG6 . It can be seen that the internal pores of the porous spherical hard carbon contain 41.68 wt% of silicon. The porous structure of the hard carbon is conducive to buffering the charging volume expansion of the silicon element in the pores. At the same time, the silicon element in the pores can also obtain good conductive properties.

The silicon-carbon negative electrode material obtained in this embodiment was subjected to an XRD test, and the obtained XRD diffraction pattern is shown in FIG7 . It can be seen that the crystal form of the silicon-carbon negative electrode material obtained in this embodiment is amorphous silicon carbon.

Example 2

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

S1: 150 g of soluble ammonium salt (ammonium chloride), 1500 g of carbon source (rice starch) and 4600 g of solvent (pure water) were mixed to obtain a mixed solution, and then granulated by a spray dryer to obtain spherical particles;

The solid content of the mixed solution is 26.4 wt %, and the viscosity of the mixed solution is 86 mPa·s;

The inlet temperature of the spray dryer was 200 °C, and the rotation speed of the atomizing disk was 12000 rpm;

S2: performing a first sintering treatment and a second sintering treatment on the spherical particles in sequence to obtain a spherical hard carbon material;

The first sintering process was carried out at a temperature of 500°C, for 15 hours, in a nitrogen atmosphere; the second sintering process was carried out at a temperature of 1400°C, for 15 hours, in a nitrogen atmosphere;

S3: subjecting the spherical hard carbon material to a water vapor pore-forming treatment to obtain a porous spherical hard carbon material;

The pore-forming treatment temperature is 900°C and the pore-forming treatment time is 10 h.

S4: subjecting the porous spherical hard carbon material to pyrolysis contact with monosilane to obtain a spherical silicon-carbon negative electrode material precursor;

The flow rate of monosilane was 1.1 L/min, the pyrolysis temperature was 650°C, the pyrolysis time was 5 h, and the atmosphere was nitrogen;

S5: performing acetylene pyrolysis and carbon coating on a quasi-spherical silicon-carbon negative electrode material precursor to obtain a quasi-spherical silicon-carbon negative electrode material;

The acetylene flow rate was 1.5 L/min, the pyrolysis temperature was 650° C., the pyrolysis time was 3 h, and the atmosphere was nitrogen.

Example 3

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

S1: 200 g of soluble ammonium salt (ammonium nitrate), 4500 g of carbon source (potato starch) and 24000 g of solvent (anhydrous ethanol) were mixed to obtain a mixed solution, which was then granulated by a spray dryer to obtain spherical particles;

The solid content of the mixed solution is 16.4 wt %, and the viscosity of the mixed solution is 13.1 mPa·s;

The inlet temperature of the spray dryer was 210 °C, and the rotation speed of the atomizing disk was 13000 rpm;

S2: performing a first sintering treatment and a second sintering treatment on the spherical particles in sequence to obtain a spherical hard carbon material;

The first sintering process was carried out at a temperature of 200°C, for 8 hours, in an oxygen atmosphere; the second sintering process was carried out at a temperature of 1150°C, for 8 hours, in a nitrogen atmosphere;

S3: subjecting the spherical hard carbon material to a carbon dioxide pore-forming treatment to obtain a porous spherical hard carbon material;

The pore-forming treatment temperature is 900°C and the pore-forming treatment time is 24h.

S4: subjecting the porous spherical hard carbon material to pyrolysis contact with monosilane to obtain a spherical silicon-carbon negative electrode material precursor;

The flow rate of monosilane was 1.5 L/min, the pyrolysis temperature was 550°C, the pyrolysis time was 12 h, and the atmosphere was nitrogen;

S5: performing acetylene pyrolysis and carbon coating on a quasi-spherical silicon-carbon negative electrode material precursor to obtain a quasi-spherical silicon-carbon negative electrode material;

The acetylene flow rate was 1.0 L/min, the pyrolysis temperature was 480° C., the pyrolysis time was 12 h, and the atmosphere was nitrogen.

Example 4

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

S1: 100 g of soluble ammonium salt (ammonium acetate), 700 g of carbon source (wheat starch) and 6500 g of solvent (isopropanol) were mixed to obtain a mixed solution, which was then granulated using a spray dryer to obtain spherical particles;

The solid content of the mixed solution is 11wt%, and the viscosity of the mixed solution is 10.5mPa·s;

The inlet temperature of the spray dryer was 200 °C, and the rotation speed of the atomizing disk was 12000 rpm;

S2: performing a first sintering treatment and a second sintering treatment on the spherical particles in sequence to obtain a spherical hard carbon material;

The first sintering process was carried out at a temperature of 250°C for 14 hours in an air atmosphere; the second sintering process was carried out at a temperature of 1400°C for 10 hours in a nitrogen atmosphere;

S3: treating the spherical hard carbon material with concentrated sulfuric acid to form pores, thereby obtaining a porous spherical hard carbon material;

The pore-forming treatment temperature is 150°C and the pore-forming treatment time is 2 h.

S4: subjecting the porous spherical hard carbon material to pyrolysis contact with monosilane to obtain a spherical silicon-carbon negative electrode material precursor;

The flow rate of monosilane was 0.3 L/min, the pyrolysis temperature was 500 °C, the pyrolysis time was 8 h, and the atmosphere was nitrogen.

S5: performing acetylene pyrolysis and carbon coating on a quasi-spherical silicon-carbon negative electrode material precursor to obtain a quasi-spherical silicon-carbon negative electrode material;

The acetylene flow rate was 0.5 L/min, the pyrolysis temperature was 750° C., the pyrolysis time was 4 h, and the atmosphere was nitrogen.

Example 5

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

S1: 100 g of soluble ammonium salt (ammonium bicarbonate), 2000 g of carbon source (sweet potato starch) and 6000 g of solvent (pure water) were mixed to obtain a mixed solution, which was then granulated by a spray dryer to obtain spherical particles;

The solid content of the mixed solution is 25.9wt%, and the viscosity of the mixed solution is 76.5mPa·s;

The inlet temperature of the spray dryer was 210 °C, and the rotation speed of the atomizing disk was 13000 rpm;

S2: performing a first sintering treatment and a second sintering treatment on the spherical particles in sequence to obtain a spherical hard carbon material;

The first sintering process was carried out at a temperature of 450°C for 9 hours in a nitrogen atmosphere; the second sintering process was carried out at a temperature of 900°C for 14 hours in a nitrogen atmosphere;

S3: subjecting the spherical hard carbon material to a water vapor pore-forming treatment to obtain a porous spherical hard carbon material;

The pore-forming treatment temperature is 800°C and the pore-forming treatment time is 18h.

S4: subjecting the porous spherical hard carbon material to pyrolysis contact with monosilane to obtain a spherical silicon-carbon negative electrode material precursor;

The flow rate of monosilane was 2.4 L/min, the pyrolysis temperature was 700 °C, the pyrolysis time was 3 h, and the atmosphere was nitrogen;

S5: performing acetylene pyrolysis and carbon coating on a quasi-spherical silicon-carbon negative electrode material precursor to obtain a quasi-spherical silicon-carbon negative electrode material;

The acetylene flow rate was 0.7 L/min, the pyrolysis temperature was 600° C., the pyrolysis time was 9 h, and the atmosphere was nitrogen.

Example 6

The difference between this embodiment and embodiment 1 is that the carbon source of this embodiment is mung bean starch, and the remaining steps and parameters are According to Example 1, a spherical silicon-carbon negative electrode material is obtained.

Example 7

The difference between this embodiment and embodiment 1 is that the temperature of the second sintering treatment in step S2 of this embodiment is 1050° C. and the time is 8 hours. The remaining steps and their parameters refer to embodiment 1 to obtain a spherical silicon-carbon negative electrode material.

Example 8

The difference between this embodiment and embodiment 1 is that the temperature of silane thermal decomposition deposition in step S4 of this embodiment is 450° C. and the time is 7 hours. The remaining steps and their parameters refer to embodiment 1 to obtain a spherical silicon-carbon negative electrode material.

Example 9

The difference between this embodiment and embodiment 1 is that the sintering process in this embodiment is a single sintering process, the sintering temperature is 1300° C., the time is 8 hours, the atmosphere is a nitrogen atmosphere, and the remaining steps and parameters are referred to embodiment 1 to obtain a spherical silicon-carbon negative electrode material.

Comparative Example 1

The difference between this embodiment and embodiment 1 is that in this embodiment, no soluble ammonium salt is added in step S1, and the remaining steps and parameters are referred to embodiment 1 to obtain a spherical silicon-carbon negative electrode material.

Comparative Example 2

The difference between this embodiment and embodiment 1 is that in step S1, the spray granulation is replaced by stirring, heating and drying. The stirring, heating and drying conditions are stirring at a temperature of 200° C. (rotation speed of 200 rpm) until the solvent evaporates to obtain a dry powder.

The remaining steps and parameters are the same as those in Example 1 to obtain a spherical silicon-carbon negative electrode material.

Comparative Example 3

The difference between this embodiment and embodiment 1 is that the pore-forming treatment in step S3 is not performed in this embodiment, and the remaining steps and their parameters are referred to embodiment 1 to obtain a spherical silicon-carbon negative electrode material.

Comparative Example 4

The difference between this embodiment and embodiment 1 is that the carbon coating in step S5 is not performed in this embodiment, and the remaining steps and parameters thereof are referred to embodiment 1 to obtain a spherical silicon-carbon negative electrode material.

Test Example 1

The physical and chemical parameters of the hard carbon materials provided by Examples 1-9 and Comparative Examples 1-4 are shown in Table 1.

The particle size (μm) range of the material was tested using Dandong Better Laser Particle Sizer BT-9300ST;

The material phase analysis was performed using XRD diffractometer (Panalytical X’PERT PRO MPD, Netherlands);

The specific surface area (m ² /g) of the material was tested using a JW-DX dynamic adsorption specific surface area instrument produced by Jingwei Gaobo;

The compaction density (g/cm ³ ) of the powder was measured using a CARVER compaction density tester;

The bulk density (g/cm ³ ) of powder was tested using the AS-200 Scott volumetric bulk density meter of Huimei Technology;

The tap density (g/cm ³ ) of the negative electrode material was measured using a tap density analyzer (Dandong Better BT-311).

Table 1

It can be seen from Table 1 that in Examples 1-8, the type of carbon source, the type of soluble ammonium salt, the raw material ratio, the drying method and the calcination process all affect the particle morphology, sphericity and physicochemical indicators of the hard carbon material to a certain extent; the hard carbon materials obtained in Examples 1-8 and Comparative Examples 3-4 have a higher sphericity, and the corresponding compacted density is also higher (above 1.0 g/cm ³ ), and the corresponding loose density is also higher (above 0.45 g/cm ³ ); In Comparative Examples 1-2 and Example 9, no soluble ammonium salt is added, or only one sintering is performed, or no spray drying is performed, and the sphericity of the obtained hard carbon material is significantly reduced, and the physical and chemical indicators also deteriorate.

The physical and chemical index parameters of the silicon-carbon negative electrode materials provided in Examples 1-9 and Comparative Examples 1-4 are shown in Table 2.

Table 2

It can be seen from Table 2 that in Examples 1-8, the particle size and specific surface area of silicon-carbon negative electrode materials prepared by different carbon sources and processes have great differences, and the preparation and treatment of hard carbon materials have a great influence on the particle size of silicon-carbon negative electrode materials; it can be seen from Comparative Examples 1-4 and Example 9 that spray drying and pore-forming processes have a good control effect on the particle size of silicon-carbon negative electrode materials, and carbon coating is a key factor in reducing the specific surface area of silicon-carbon negative electrode materials.

Test Example 2

Lithium button cell battery test:

The first reversible capacity and first efficiency of the silicon-carbon negative electrode materials obtained in Examples 1-9 and Comparative Examples 1-4 were tested as follows:

Silicon-carbon negative electrode material, conductive carbon black and binder are mixed in pure water at a mass ratio of 94.5:1.5:4, homogenized, and the solid content is controlled to be 48wt%, coated on a copper foil current collector, vacuum-baked at 100°C for 8h, pressed and formed, and then punched to prepare a negative electrode sheet;

Assemble button half-cells in an argon-filled glove box. The counter electrode is a metal lithium sheet, the separator is PE, and the electrolyte is 1 mol/L LiPF ₆ EC/DMC (Vol 1:1). Perform charge and discharge tests on the button cell. The test process is 0.2C DC to 0V, 0.05C DC to 0V, 0V CV 50μA, 0.01C DC to 0V, 0V CV 20μA, Rest 10min, 0.2C CC to 2V.

The first reversible capacity and efficiency of silicon-carbon anode materials were measured. The button battery test equipment was Wuhan Landian LAND battery testing system from Electronics Co., Ltd.

Expansion rate test of silicon carbon material S600:

The silicon-carbon negative electrode materials obtained in Examples 1-9 and Comparative Examples 1-4 were tested for their first reversible capacity by the above-mentioned charge-withdrawal test method, and then a certain amount of the same graphite negative electrode was mixed according to the calculation, and the silicon-carbon negative electrode materials were mixed to 600±5 mAh/g, abbreviated as S600;

Mix silicon-carbon material, conductive carbon black and binder (mass ratio 92:2:6) in pure water according to S600, homogenize, control the solid content to 48%, apply it on the current collector with copper foil as the substrate, then vacuum bake at 90°C for 8h, press and form with a roller press, and then slice with a slicing device to prepare a negative electrode sheet; use a micrometer to detect the thickness of the negative electrode sheet, record it as T1, detect the thickness of the substrate, record it as T2, and record the data;

Assemble button half-cells in an argon-filled glove box, with a metal lithium sheet as the counter electrode, a PE diaphragm, and an electrolyte of 1 mol/L LiPF ₆ EC/DMC (Vol 1:1); perform charge and discharge tests on the button cell, with the test process of 0.1C DC to 0.005V, 0.05C DC to 0.005V, 0.02C DC to 0.005V, Rest 10min, 0.1C CC to 1.5V, 0.1C DC to 0.005V, 0.05C DC to 0.005V, 0.02C DC to 0.005V; measure the first reversible capacity and efficiency of the silicon-carbon material;

The battery is disassembled and the thickness of the silicon-carbon material obtained by disassembly is detected and recorded as T3. The first full-charge expansion data of the silicon-carbon material is calculated according to the formula F=(T3-T1)/(T1-T2), and F is the first full-charge expansion rate.

The button cell testing equipment is the LAND battery testing system of Wuhan Landian Electronics Co., Ltd.; the slicing equipment is the MSK-T10 button half-cell slicing equipment of Kejing; the micrometer detection equipment is Japan Mitutoyo 293-100-10; the rolling equipment is the MSK-HRP-05 button half-cell slicing equipment of Kejing.

The above test results are shown in Table 3, and the first charge and discharge curve of the lithium button cell of the silicon-carbon negative electrode material of Example 1 is shown in Figure 8.

Table 3

It can be seen from Table 3 that the silicon-carbon negative electrode materials prepared in Examples 1-8 have higher specific capacity and first efficiency. In the lithium-ion battery test system, the first reversible capacity is greater than 1900 mA·h/g, and the first coulombic efficiency is above 92%; the changes in the type of carbon source and the preparation process in Examples 1-8 can greatly affect the S600 first expansion rate of the silicon-carbon negative electrode material. The hard carbon material after pore formation treatment makes the deposited nano-silicon distributed in the pores and surface of the porous hard carbon material. After carbon coating treatment, the surface nano-silicon is isolated from direct contact with the electrolyte, and the volume expansion change of the silicon material during the lithium insertion process is buffered during the charging process, so that the overall volume expansion of the material is reduced; in Comparative Examples 1-2 and Example 9, no soluble ammonium salt is added or the slurry drying process does not use spray drying (but stirring and heating drying), or the sintering process is directly increased to high Temperature (without staged sintering), the sphericity of the obtained hard carbon material will be significantly deteriorated, and the compacted density and loose density of the obtained particles will also be significantly reduced, thereby reducing the sphericity of the silicon-carbon material prepared from the particles and worsening the electrochemical performance; the first reversible capacity and first efficiency of Example 9 and Comparative Examples 1-2 are relatively high, indicating that the silicon deposition and carbon coating treatment effects are better, and the S600 first expansion is large because the prepared hard carbon precursor has a low sphericity, which leads to uneven silicon deposition and carbon coating of the prepared silicon-carbon negative electrode material; the S600 first expansion rate of the silicon-carbon material obtained without pore-forming treatment in Comparative Example 3 is the highest, because the hard carbon material is not pore-formed, and nano-silicon is deposited on the surface of the hard carbon material, which aggravates the expansion of the silicon material during charging and discharging, thereby reducing the first reversible capacity of the silicon-carbon negative electrode material; Comparative Example 4 is not carbon-coated, resulting in nano-silicon deposited on the surface of the hard carbon material. Silicon is in direct contact with the electrolyte during the charging and discharging process, continuously forming irreversible compounds, which increases the irreversible capacity, resulting in reduced first efficiency and reduced reversible capacity.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Industrial Applicability

The present application provides a quasi-spherical silicon-carbon negative electrode material and a preparation method and application thereof. The preparation method comprises the following steps: a mixed solution of a soluble ammonium salt and a carbon source is subjected to sintering treatment, pore-forming treatment, thermal decomposition treatment with a silane compound, and carbon coating treatment in sequence after spray granulation to obtain a quasi-spherical silicon-carbon negative electrode material. The quasi-spherical silicon-carbon negative electrode material provided by the present application has a high first efficiency and specific capacity, and has a low charging volume expansion effect.

In addition, it is understood that the quasi-spherical silicon-carbon negative electrode material and its preparation method and application of the present application are reproducible and can be used in a variety of industrial applications. For example, the quasi-spherical silicon-carbon negative electrode material and its preparation method and application of the present application can be used in the technical field of the technical field of electrode materials.

Claims (11)

1. A method for preparing a spherical silicon-carbon negative electrode material, characterized in that it comprises the following steps:

   After spray granulation, the mixed solution of soluble ammonium salt and carbon source is sequentially subjected to sintering treatment, pore-forming treatment, thermal decomposition treatment with silane compound and carbon coating treatment to obtain the quasi-spherical silicon-carbon negative electrode material.
2. The preparation method according to claim 1, characterized in that the soluble ammonium salt comprises at least one of ammonium chloride, ammonium nitrate, ammonium acetate, ammonium carbonate, ammonium bicarbonate, ammonium phosphate, diammonium hydrogen phosphate, diammonium phosphate and ammonium polyphosphate;

   Preferably, the carbon source comprises starch;

   Preferably, the starch comprises at least one of millet starch, rice starch, mung bean starch, sorghum starch, potato starch, wheat starch, water chestnut starch, sweet potato starch, cassava starch, lotus root starch, corn starch and pea starch;

   Preferably, the solvent of the mixed solution includes at least one of water, anhydrous ethanol and isopropanol;

   Preferably, the solid content of the mixed solution is 10 to 30 wt%;

   Preferably, the mass ratio of the soluble ammonium salt to the carbon source is 1:100 to 40:100.
3. The preparation method according to claim 1 or 2, characterized in that the viscosity of the mixed solution is below 100 mPa·s.
4. The preparation method according to claim 1 or 2, characterized in that the median particle size D50 of the spray granulation is between 15 and 25 microns;

   Preferably, the average sphericity of the spray granulation is above 0.7.
5. The preparation method according to any one of claims 1 to 3, characterized in that the sintering process comprises a first sintering process and a second sintering process performed sequentially;

   Preferably, the temperature of the first sintering process is lower than the temperature of the second sintering process.

   Preferably, the temperature of the first sintering treatment is 100-500° C. and the time is 2-12 hours;

   Preferably, the temperature of the second sintering treatment is 800-1500° C., and the time is 2-12 hours.
6. The preparation method according to any one of claims 1 to 5, characterized in that the pore-forming treatment comprises at least one of a gas phase pore-forming treatment and a liquid phase pore-forming treatment;

   Preferably, the gas used in the gas phase pore forming treatment includes at least one of water vapor, air, carbon dioxide, chlorine, sulfur dioxide and nitrogen dioxide;

   Preferably, the liquid for the liquid-phase pore-forming treatment comprises a strong oxidizing acid;

   Preferably, the strong oxidizing acid comprises at least one of concentrated sulfuric acid, perchloric acid and concentrated nitric acid;

   Preferably, the pore-forming treatment is performed at a temperature of 100 to 1000° C. for a time of 2 to 48 hours;

   Preferably, the pore structure after the pore-forming treatment includes at least one of micropores, mesopores and macropores;

   Preferably, the pore volume after the pore-forming treatment is 0.1-2 cm ³ /g.
7. The preparation method according to any one of claims 1 to 6, characterized in that the silane compound comprises at least one of monosilane, dimethylsilane, difluorosilane, trifluoromethylsilane, tetrafluorosilane, trimethylfluorosilane, chlorosilane, chloromethylsilane and dichlorosilane;

   Preferably, the gas flow rate of the silane compound during the pyrolysis treatment is 0.1 to 3 L/min;

   Preferably, the temperature of the pyrolysis treatment is 400-800°C and the time is 0.5-24h;

   Preferably, the pyrolysis treatment is carried out in an inert gas;

   Preferably, the silicon element after pyrolysis treatment is distributed in the pores and/or surface of the hard carbon material;

   Preferably, the silicon element after the pyrolysis treatment is nano silicon particles;

   Preferably, the median particle size D50 of the nano-silicon particles is less than 50 nm.
8. The preparation method according to any one of claims 1 to 7, characterized in that the organic carbon source treated with carbon coating comprises at least one of methane, acetylene, toluene, glucose, petroleum asphalt, coal asphalt, mesophase asphalt, polymethyl methacrylate, phenolic resin, polystyrene and polyacrylonitrile;

   Preferably, the temperature of the carbon coating treatment is 400-800°C and the time is 0.5-12h;

   Preferably, the carbon coating treatment is carried out in an inert gas;

   Preferably, the coating layer after the carbon coating treatment accounts for 0.1 to 10% of the mass of the silicon-carbon negative electrode material.
9. A spherical silicon-carbon negative electrode material prepared according to the preparation method according to any one of claims 1 to 8.
10. The quasi-spherical silicon-carbon negative electrode material according to claim 9, characterized in that the hard carbon-carbon interlayer spacing d ₀₀₂ of the quasi-spherical silicon-carbon negative electrode material is 0.35 to 0.41 nm;

    Preferably, the water content of the spherical silicon-carbon negative electrode material is below 1 wt%;

    Preferably, the specific surface area of the quasi-spherical silicon-carbon negative electrode material is 1 to 10 m ² /g, preferably 1 to 5 m ² /g;

    Preferably, the median particle size D50 of the quasi-spherical silicon-carbon negative electrode material is 3 to 15 μm, preferably 7 to 15 μm;

    Preferably, the tap density of the quasi-spherical silicon-carbon negative electrode material is 0.8 to 1.2 g/cm ³ ;

    Preferably, the proportion of silicon in the spherical silicon-carbon negative electrode material is 20-75 wt%.
11. A use of the spherical silicon-carbon negative electrode material according to claim 9 or 10 in a lithium-ion battery.