CN111082006B - Silicon oxide composite negative electrode material and preparation method thereof, and lithium ion battery - Google Patents

Abstract

The invention discloses a silicon oxide composite negative electrode material, a preparation method thereof, and a lithium ion battery, comprising the following steps: S1. Providing silicon oxide powder, and the silicon oxide powder is a silicon oxide powder without disproportionation treatment ; S2. carbon coating is carried out to the silicon oxide powder to obtain a first precursor; S3. carbon nanofibers are grown in situ on the surface of the first precursor to obtain a second precursor; S4. the first precursor is The two precursors are subjected to secondary granulation to obtain the silicon oxide composite negative electrode material. In the present invention, carbon coating is performed on the silicon oxide powder to obtain a first precursor, and carbon nanofibers are grown in-situ on the surface of the first precursor, so that the silicon oxide powder can be well connected. Up to now, a good conductive network is formed, which alleviates the deficiency of poor conductivity of silicon oxide, further improves the first efficiency, and improves the volume effect of the silicon oxide composite negative electrode material.

Description

Silicon oxide composite negative electrode material and preparation method thereof, and lithium ion battery

technical field

The invention relates to the technical field of lithium ion batteries, in particular to a silicon oxide composite negative electrode material, a preparation method thereof, and a lithium ion battery.

Background technique

At present, graphite materials are still widely used anode materials in lithium-ion batteries, mainly because of their abundant raw material sources, high first Coulomb efficiency, excellent cycle performance, and relatively low cost. However, with the advancement of technology, in the fields of 3C digital and electric vehicles, where lithium-ion batteries are used the most, higher requirements are placed on the energy density of lithium-ion batteries. However, the theoretical limit of 372mAh/g of traditional graphite anode materials The capacity has gradually been unable to meet the requirements of high energy density.

Due to its theoretical gram capacity of 4200mAh/g, silicon anode is considered to be a very promising and most likely new anode material for industrialization. Significant pulverization and shedding occurred during the discharge process, which seriously affected the cycle performance. In order to solve this problem, researchers have made many attempts, such as nano-sized silicon particles and combined with carbon materials to form silicon/carbon composite materials, wherein the carbon materials can use amorphous carbon, hard and soft carbon, carbon fiber or carbon nanotubes. For example, Chinese Patent Publication No. CN107623110A discloses a preparation method of silicon-carbon composite material. Nano-silicon is embedded in the hollow through holes of carbon fibers, so that the negative electrode has good structural stability and high conductivity. However, the negative electrode material obtained by this method has a high specific surface area, which will lead to negative effects such as difficulty in slurry processing and low first Coulomb efficiency. Another example is the Chinese patents with the authorization announcement numbers of CN103305965B and CN103311523B, which disclose a preparation method of silicon-carbon composite material. The silicon-carbon composite material is obtained by carbonization, and the invention reserves a buffer space for the expansion of the nano-silicon particles and at the same time ensures the overall electron transport capability of the material. However, this method also has the disadvantages of low production efficiency and high cost. At the same time, due to the simple physical mixing of nano-silicon and carbon fiber, the bonding force is poor, and the nano-silicon cannot be well dispersed, and the improvement of cycle performance is also limited.

In recent years, a silicon oxide material has been gradually applied to lithium-ion batteries. Since its structure is that nano-silicon particles are dispersed in the surrounding silica matrix, silica plays a good role in restraining the expansion of silicon. At the same time, due to the small size of nano-silicon particles, the overall expansion rate (200%) of this material is significantly smaller than that of pure silicon material (300%). However, silicon oxide also has some disadvantages such as low initial efficiency and many side reactions. At present, it is mainly applied with heterogeneous silicon oxide after disproportionation reaction. The distribution uniformity of SiO2 and Si particles formed after disproportionation reaction cannot be achieved. Strictly control, a significant stress difference will be formed during the lithium insertion process between crystalline Si and amorphous SiO2. The low electrical conductivity and ionic conductivity of SiO2 also increase the polarization during the lithium insertion process, which will affect the silicon oxide-based silicon carbon. Cycling performance of anode materials.

In view of this, it is necessary to develop a silicon oxide anode material that can effectively improve the kinetic performance, first-time efficiency and cycle performance of the silicon oxide lithium intercalation process.

SUMMARY OF THE INVENTION

In order to make up for the defects of the prior art, the present invention provides a silicon oxide composite negative electrode material, a preparation method thereof, and a lithium ion battery.

The technical problem to be solved by this invention is realized through the following technical solutions:

A preparation method of a silicon oxide composite negative electrode material, comprising the following steps:

S1. provide silicon oxide powder, and the silicon oxide powder is a silicon oxide powder without disproportionation;

S2. carbon coating is performed on the silicon oxide powder to obtain a first precursor;

S3. growing carbon nanofibers in situ on the surface of the first precursor to obtain a second precursor;

S4. Perform secondary granulation on the second precursor to obtain the silicon oxide composite negative electrode material.

Further, the preparation method of the silicon oxide powder is as follows: after the silicon powder and the silicon dioxide powder are mixed uniformly, in an inert atmosphere or a vacuum environment, heating to generate silicon monoxide gas, and cooling and precipitation to obtain silicon oxide block; crushing and pulverizing the silicon oxide block to obtain silicon oxide powder.

Further, the molar ratio of the silicon powder and the silicon dioxide powder is (0.3-0.7): (0.7-0.3); the particle size D50 of the silicon powder is 1-100 μm, and the particle size of the silicon dioxide powder is D50 is 0.01-1 μm; the heating temperature is 900-1600° C.; the chemical formula of the silicon oxide powder is SiOx, wherein the x value is 0.8-1.3; the particle size D50 of the silicon oxide powder is 0.1-1 μm.

Further, the method used for carbon coating includes solid phase coating, liquid phase coating or gas phase coating.

Further, the specific steps of the liquid phase coating are as follows: dispersing the siliceous oxide powder in the first organic solvent, gradually adding the soft carbon precursor, fully mixing to obtain a first mixed solution, and then spray-drying and granulating The composite is obtained, and the composite is subjected to heat treatment to obtain a first precursor; the specific steps of the gas phase coating are: passing the silicon oxide powder into a fluidized bed atmosphere furnace, heating under the protection of an inert gas When the temperature reaches 600-800°C, the carbon source gas is introduced, and the temperature is kept for 0.5-10 hours. Then, the carbon source gas is turned off, and the temperature is lowered to room temperature to obtain the first precursor.

Further, in the liquid phase coating, the first organic solvent is one or more of ethanol, propanol, isopropanol, and tetrahydrofuran; the quality of the soft carbon precursor and the silicon oxide powder is The ratio is (0.5-5): 1; the soft carbon precursor is one or more of pitch, citric acid, and polyvinylpyrrolidone; the solid content of the first mixed solution is 10-50%; the The heat treatment method is as follows: the composite is placed in an inert gas, and heated at a constant temperature of 500-800°C for 1-10 hours at a heating rate of 0.5-15°C/min; in the gas phase coating, the The volume ratio of carbon source gas and inert gas is (0.1-5): (10-30); the carbon source gas is one or more of acetylene, ethylene, methane and ethane, and the inert gas is nitrogen , one or more of argon and helium.

Further, the specific steps of growing carbon nanofibers in situ on the surface of the first precursor are: dispersing the first precursor in a second organic solvent, and then gradually adding a catalyst to mix well to obtain a second mixed solution, Then, drying is performed to obtain catalyst-supported carbon-coated silicon oxide powder; the obtained catalyst-supported carbon-coated silicon oxide powder is placed in a reactor, heated to 600-850 ° C under the protection of inert gas, and then The mixed gas of hydrogen and carbon source gas is introduced, and the temperature is kept for 0.5-10 hours, then the carbon source gas is turned off, and the temperature is lowered to room temperature to obtain the second precursor.

Further, the second organic solvent is one or more of ethanol, methanol, propanol, isopropanol, ethylene glycol, and glycerol, and the catalyst is Fe(NO ₃ ) ₃ ·9H ₂ O one or more of , FeSO ₄ •7H ₂ O, FeCl ₃ • 6H ₂ O, Co(NO ₃ ) ₂ • 6H ₂ O, Ni(NO ₃ ) ₂ • 6H ₂ O; the catalyst and the first The precursor mass ratio is 1: (1-1000); the solid content of the second mixed solution is 10-50%; the volume ratio of the carbon source gas, hydrogen and inert gas is (0.1-5): 1: (10-30), the carbon source gas is one or more of acetylene, ethylene, methane and ethane, and the inert gas is one or more of nitrogen, argon and helium; the The length of carbon nanofibers is 0.01-100 μm, and the diameter is 0.1-20 nm.

Further, the specific steps of secondary granulation of the second precursor are as follows: dispersing the second precursor in the third organic solvent, and then gradually adding the soft carbon precursor for thorough mixing to obtain a third mixed solution , and then spray-drying and granulating to obtain a secondary granulated silicon oxide composite negative electrode material.

Further, the third organic solvent is one or more of ethanol, propanol, isopropanol, and tetrahydrofuran; the soft carbon precursor is one or more of pitch, citric acid, and polyvinylpyrrolidone ; the mass ratio of the soft carbon precursor and the second precursor is (0.5-5): 1; the solid content of the third mixed solution is 10-50%; the particle size of the silicon oxide composite negative electrode material D50 is 5-10 μm; the carbon content in the silicon oxide composite negative electrode material is 5%-20%.

The present invention also provides a silicon oxide composite negative electrode material, which is prepared by the above preparation method.

The present invention also provides a lithium ion battery, which includes the above-mentioned silicon oxide composite negative electrode material.

The present invention has the following beneficial effects:

In the present invention, carbon coating is performed on the silicon oxide powder to obtain a first precursor, and carbon nanofibers are grown in situ on the surface of the first precursor, so that the silicon oxide powder can be well connected. Up to now, a good conductive network is formed, which alleviates the deficiency of poor conductivity of silicon oxide, further improves the first efficiency, and improves the volume effect of the silicon oxide composite negative electrode material.

In the present invention, the silicon oxide powder without disproportionation treatment is used as the raw material, and by adjusting the reaction temperature in the subsequent carbon coating and surface in-situ growth of carbon nanofibers, carbon nanofibers are formed on the surface, and the concentration of silicon oxide is controlled at the same time. The degree of disproportionation ensures that the silicon particles inside the silicon oxide material do not grow significantly, and the generation of SO ₂ is reduced, which can reduce the impedance of the silicon oxide material and improve its dynamic performance.

In the present invention, by adopting secondary granulation, the silicon oxide composite negative electrode material is designed into the structural form of secondary particles, which can better alleviate the problem of particle pulverization caused by the volume change of silicon oxide in the later cycle process. The electronic contact deactivation of SiO2, coupled with the interconnection of carbon fibers on the surface, can greatly improve the cycling performance of SiO2.

The preparation method of the invention has the advantages of simple and convenient process, low cost and easy industrial production.

Description of drawings

Fig. 1 is the structural representation of the silicon oxide composite negative electrode material of the present invention;

2 is the XRD patterns of Example 1 and Comparative Example 4 of the present invention.

In the figure: 1. Amorphous carbon formed by secondary granulation, 2. Carbon nanofibers grown in situ, 3. Silica powder, 4. Amorphous carbon formed by carbon coating.

Detailed ways

In the description of the present invention, it should be understood that the terms "first" and "second" are only used for description purposes, and cannot be interpreted as indicating or implying relative importance or the number of indicated technical features. Thus, a feature defined as "first" or "second" may expressly or implicitly include one or more of that feature. In the description of the present invention, "plurality" means two or more, unless otherwise expressly and specifically defined.

In a first aspect, the present invention provides a method for preparing a silicon oxide composite negative electrode material, comprising the following steps:

S1. provide silicon oxide powder, and the silicon oxide powder is a silicon oxide powder without disproportionation;

S2. carbon coating is performed on the silicon oxide powder to obtain a first precursor;

S3. growing carbon nanofibers in situ on the surface of the first precursor to obtain a second precursor;

S4. Perform secondary granulation on the second precursor to obtain the silicon oxide composite negative electrode material.

Wherein, in step S1, the preparation method of the silicon oxide powder is as follows: after the silicon powder and the silicon dioxide powder are mixed uniformly, in an inert atmosphere or a vacuum environment, heating to generate silicon monoxide gas, and cooling and precipitation to obtain Silicon oxide block; crushing and pulverizing the silicon oxide block to obtain silicon oxide powder.

Specifically, the molar ratio of the silicon powder and the silicon dioxide powder is (0.3-0.7): (0.7-0.3), for example, 0.3:0.7, 0.4:0.6, 0.5:0.5, 0.6:0.4, 0.7:0.3 . The particle size D50 of the silicon powder is 1-100 μm, and the particle size D50 of the silicon dioxide powder is 0.01-1 μm. The heating temperature is 900-1600°C, such as 900°C, 1000°C, 1100°C, 1200°C, 1300°C, 1400°C, 1500°C, 1600°C; the chemical formula of the silicon oxide powder is SiOx, wherein The value of x is 0.8-1.3, for example, it can be 0.8, 0.9, 1, 1.1, 1.2, 1.3; the particle size D50 of the silicon oxide powder is 0.1-1 μm.

In the present invention, by heating, silicon powder and silicon dioxide powder generate silicon vapor and silicon dioxide vapor, and the two react chemically to generate silicon monoxide gas.

In the present invention, the crushing preferably adopts a jaw crusher to crush the silicon oxide blocks to particles with an average particle size of 0.5-8 mm. It can be understood that the crushing equipment in the present invention includes but is not limited to those listed above, Other crushing devices not listed in this embodiment but known to those skilled in the art can also be used.

In the present invention, the pulverizing equipment is preferably a jet pulverizer. It can be understood that the pulverizing equipment in the present invention includes, but is not limited to, those listed above, and may also be other equipment not listed in this embodiment but used by those skilled in the art. Other equipments well known to persons may be, for example, planetary ball mills, rolling mills, Raymond mills, mechanical pulverizers, ultra-low temperature pulverizers, and superheated steam pulverizers.

In the prior art, the preparation method of silicon oxide powder is as follows: heating a mixture of silicon dioxide and silicon to generate silicon monoxide gas, cooling and precipitation to obtain silicon oxide blocks; in an inert environment, at 900-1150 ℃ to carry out heat treatment to carry out disproportionation reaction; then to crush and pulverize to obtain silicon oxide powder. The silicon oxide powder obtained by this method is a heterogeneous silicon oxide after a disproportionation reaction, and a composite negative electrode material using it as a raw material has a problem of high impedance. In the present invention, the silicon oxide powder without disproportionation treatment is used as the raw material, and by adjusting the reaction temperature in the subsequent process of carbon coating and surface in-situ growth of carbon nanofibers, carbon nanofibers are formed on the surface, and the concentration of silicon oxide is controlled at the same time. The degree of disproportionation ensures that the silicon particles inside the silicon oxide material do not grow significantly, and the generation of SO ₂ is reduced, which can reduce the impedance of the silicon oxide material and improve its dynamic performance.

Wherein, in step S2, the carbon coating method includes solid phase coating, liquid phase coating or gas phase coating.

Preferably, the method used for carbon coating is liquid-phase coating, and the specific steps are as follows: dispersing siliceous oxide powder in a first organic solvent, gradually adding soft carbon precursor, and fully mixing to obtain a first mixed solution , and then spray-drying and granulating to obtain a composite, and subjecting the composite to heat treatment to obtain a first precursor. Specifically, in the liquid phase coating, the first organic solvent is one or more of ethanol, propanol, isopropanol, and tetrahydrofuran. The mass ratio of the soft carbon precursor and the silicon oxide powder is (0.5-5):1, for example, it can be 0.5:1, 1:1, 1.5:1, 2:1, 2.5:1, 3:1 , 3.5:1, 4:1, 4.5:1, 5:1. The soft carbon precursor is one or more of pitch, citric acid, and polyvinylpyrrolidone. It can be understood that the soft carbon precursor in the present invention includes but is not limited to the several materials listed above, and can also be other materials not listed. Materials in this example but well known to those skilled in the art. The solid content of the first mixed solution is 10-50%, such as 10%, 20%, 30%, 40%, 50%; the choice of the solid content of the first mixed solution can not be too high, spray drying The purpose is to evenly coat a layer of amorphous carbon on the surface of silicon oxide, not for secondary granulation, the particle size D50 obtained after spray drying in this step is basically unchanged compared to before coating. The heat treatment method is as follows: placing the composite in an inert gas, and heating at a constant temperature of 500-800° C. for 1-10 hours at a heating rate of 0.5-15° C./min. The type of the inert gas is not particularly limited in the present invention, and the inert gas can be one or more of nitrogen, argon and helium.

It should be noted that, in order to make the components in the compound obtained by spray drying evenly distributed, before spray drying, the first mixed solution needs to be fully mixed evenly, and mechanical stirring can be used, the stirring speed is 300-2000 r/min, and the time is 2-8 hours.

More preferably, the carbon coating method is gas-phase coating, and the specific steps are as follows: passing the silicon oxide powder into a fluidized bed atmosphere furnace, heating it to 600-800 ° C under the protection of an inert gas, Then, the carbon source gas is introduced, and the temperature is kept for 0.5-10 h, then the carbon source gas is turned off, and the temperature is lowered to room temperature to obtain the first precursor. Specifically, in the gas phase coating, the volume ratio of the carbon source gas and the inert gas is (0.1-5): (10-30), for example, 0.1:10, 2:10, 3:10, 4 :10, 5:10, 0.1:20, 2:20, 3:20, 4:20, 5:20, 0.1:30, 2:30, 3:30, 4:30, 5:30; the carbon The source gas is one or more of acetylene, ethylene, methane and ethane, and the inert gas is one or more of nitrogen, argon and helium.

It should be noted that, in the gas phase coating, an inert gas needs to be introduced in the whole process to ensure that the silicon oxide powder is not oxidized. Just after the temperature reaches the required temperature, the carbon source gas is introduced in time, and the carbon source gas is turned off immediately after reaching the required time.

When silicon oxide is used as a composite anode material, its first coulombic efficiency is low. In the present invention, the silicon oxide powder is coated with carbon, and the surface of the silicon oxide powder is uniformly coated with amorphous carbon, which improves the problem of low coulombic efficiency for the first time. , adding conductive carbon black to form a point-line-bonded conductive network, which significantly improves the cycle performance.

Wherein, in step S3, the specific step of growing carbon nanofibers in situ on the surface of the first precursor is as follows: dispersing the first precursor in the second organic solvent, and then gradually adding a catalyst and fully mixing to obtain a second Mix the solution, and then dry it to obtain catalyst-supported carbon-coated silicon oxide powder; place the obtained catalyst-supported carbon-coated silicon oxide powder in a reactor, and under the protection of inert gas, heat to 600-850 °C ℃, then a mixture of hydrogen and carbon source gas is introduced, and the temperature is kept for 0.5-10 hours, then the carbon source gas is turned off, and the temperature is lowered to room temperature to obtain the second precursor.

Specifically, the second organic solvent is one or more of ethanol, methanol, propanol, isopropanol, ethylene glycol, and glycerol, and the catalyst is Fe(NO ₃ ) ₃ •9H ₂ O one or more of , FeSO ₄ •7H ₂ O, FeCl ₃ • 6H ₂ O, Co(NO ₃ ) ₂ • 6H ₂ O, Ni(NO ₃ ) ₂ • 6H ₂ O; the catalyst and the first The precursor mass ratio is 1:(1-1000), for example, it can be 1:1, 1:10, 1:50, 1:100, 1:200, 1:300, 1:400, 1:500, 1: 600, 1:700, 1:800, 1:900, 1:1000.

The solid content of the second mixed solution is 10-50%, such as 10%, 20%, 30%, 40%, 50%. In the present invention, the purpose of spray drying is to enable the catalyst to be evenly distributed on the carbon. Coating the surface of silicon oxide is not for secondary granulation.

The volume ratio of the carbon source gas, hydrogen and inert gas is (0.1-5):1:(10-30), for example, it can be 0.1:1:10, 0.1:1:20, 0.1:1:30, 1 :1:10, 1:1:20, 1:1:30, 3:1:10, 3:1:20, 3:1:30, 5:1:10, 5:1:20, 5:1 :30.

The carbon source gas is one or more of acetylene, ethylene, methane and ethane, and the inert gas is one or more of nitrogen, argon and helium; the length of the carbon nanofibers is 0.01 -100μm, diameter in the range of 0.1-20nm.

The drying is preferably, but not limited to, spray drying.

It should be noted that, in order to make the catalyst evenly supported on the surface of the silica powder, before drying, the second mixed solution needs to be fully mixed evenly, and mechanical stirring can be used, the stirring speed is 300-2000 r/min, and the time is 2- 8 hours.

It should be noted that, when carbon nanofibers are grown in-situ on the surface of the first precursor, an inert gas needs to be introduced throughout the entire process to ensure that the silicon oxide powder is not oxidized. Just after the temperature reaches the required temperature, the carbon source gas is introduced in time, and the carbon source gas is turned off immediately after reaching the required time.

In the present invention, by in-situ growth of carbon nanofibers on the surface of the first precursor, the bonding force between the carbon nanofibers and the silicon oxide powder is stronger, the separation of the silicon oxide powder from the carbon fibers during expansion and contraction is prevented, and the improvement of The disadvantage of poor electronic conductivity of silicon oxide.

Wherein, in step S4, the specific steps of secondary granulation of the second precursor are as follows: dispersing the second precursor in the third organic solvent, and then gradually adding the soft carbon precursor for thorough mixing to obtain the first The three mixed solutions are then spray-dried and granulated to obtain a secondary granulated silicon oxide composite negative electrode material.

Specifically, the third organic solvent is one or more of ethanol, propanol, isopropanol, and tetrahydrofuran; the soft carbon precursor is one or more of pitch, citric acid, and polyvinylpyrrolidone It can be understood that the soft carbon precursor in the present invention includes but is not limited to the several materials listed above, and can also be other materials not listed in this embodiment but well known to those skilled in the art. The mass ratio of the soft carbon precursor and the second precursor is (0.5-5): 1, for example, it can be 0.5:1, 1:1, 2:1, 3:1, 4:1, 5:1; The solid content of the third mixed solution is 10-50%, such as 10%, 20%, 30%, 40%, 50%; since the purpose of spray drying in this step is secondary granulation, the third mixed solution The solid content of the powder should not be too low, otherwise the secondary particles will not be formed. The particle size D50 of the silicon oxide composite negative electrode material is 5-10 μm; the carbon content in the silicon oxide composite negative electrode material is 5%-20%.

In the present invention, by using secondary granulation, the volume change of silicon oxide during the circulation process can be better relieved, and the electronic contact deactivation caused by particle breakage can be prevented. In addition, the surface carbon fibers are connected to each other, which can greatly improve the silicon oxide. cycle performance.

In a second aspect, the present invention also provides a silicon oxide composite negative electrode material, which is prepared by the above preparation method.

In a third aspect, the present invention also provides a lithium ion battery, which includes the above-mentioned silicon oxide composite negative electrode material. Since the silicon oxide containing the above-mentioned lithium ion battery conforms to the negative electrode material, it has better kinetic performance, first efficiency and cycle performance.

The present invention will be described in detail below with reference to the examples. The examples are only preferred embodiments of the present invention and are not intended to limit the present invention.

Example 1

The silicon oxide composite negative electrode material, the preparation method steps are as follows:

S1. provide silicon oxide powder, and the silicon oxide powder is a silicon oxide powder without disproportionation treatment; the preparation method of the silicon oxide powder is: mixing silicon powder and silicon dioxide powder uniformly Then, in an inert atmosphere or a vacuum environment, it is heated to 1400° C. to generate silicon monoxide gas, which is cooled and precipitated on a deposition plate to obtain a silicon oxide block; the silicon oxide block is crushed by a jaw crusher. Particles with an average particle size of 0.5-8mm are then pulverized and pulverized by air flow to obtain silicon oxide powder with a particle size D50 of 0.1-1 μm; wherein, the molar ratio of the silicon powder and the silicon dioxide powder is 0.5:0.5; The particle size D50 of the silicon powder is 1-100 μm, and the particle size D50 of the silicon dioxide powder is 0.01-1 μm; the chemical formula of the silicon oxide powder is SiOx, wherein the value of x is 0.8-1.3;

S2. carbon coating is carried out on the silicon oxide powder to obtain a first precursor; the method used for the carbon coating is gas-phase coating; the specific steps of the gas-phase coating are: Passed into a fluidized bed atmosphere furnace, heated to 750 ℃ under the protection of inert gas, and then passed into carbon source gas, kept for 6 hours, then turned off the carbon source gas, and cooled to room temperature to obtain the first precursor; The volume ratio of the carbon source gas and the inert gas is 3:20; the carbon source gas is acetylene; the inert gas is nitrogen;

S3. In-situ carbon nanofibers are grown on the surface of the first precursor to obtain a second precursor; specifically: the first precursor is dispersed in methanol, and then a catalyst is gradually added to mix well to obtain a second mixed solution , and then dried to obtain catalyst-supported carbon-coated silicon oxide powder; the obtained catalyst-supported carbon-coated silicon oxide powder was placed in a fluidized bed atmosphere furnace, and heated to 800 ° C under nitrogen protection. , and then feed into the mixture of hydrogen and carbon source gas, keep the temperature for 6h, then turn off the carbon source gas, cool down to room temperature, and obtain the second precursor; wherein, the catalyst is Fe(NO ₃ ) ₃ •9H ₂ O; The mass ratio of the catalyst to the first precursor is 1:400; the solid content of the second mixed solution is 30%; the volume ratio of the carbon source gas, hydrogen and nitrogen is 3:1:2, and the carbon source The gas is acetylene, the length of the carbon nanofibers is 0.01-100 μm, and the diameter is 0.1-20 nm;

S4. Carry out secondary granulation to the second precursor to obtain the silicon oxide composite negative electrode material. The specific steps are: dispersing the second precursor in ethanol, and then gradually adding citric acid to fully mix to obtain The third mixed solution is then spray-dried and granulated to obtain a secondary granulated silicon oxide composite negative electrode material; wherein, the mass ratio of the citric acid and the second precursor is 3:1; The solid content is 30%; the particle size D50 of the silicon oxide composite negative electrode material is 5-10 μm.

Example 2

The silicon oxide composite negative electrode material, the preparation method steps are as follows:

S1. provide silicon oxide powder, and the silicon oxide powder is a silicon oxide powder without disproportionation treatment; the preparation method of the silicon oxide powder is: mixing silicon powder and silicon dioxide powder uniformly Then, in an inert atmosphere or a vacuum environment, it is heated to 900 ° C to generate silicon monoxide gas, which is cooled and precipitated on a deposition plate to obtain a silicon oxide block; the silicon oxide block is crushed by a jaw crusher. Particles with an average particle size of 0.5-8mm are then pulverized and pulverized by air flow to obtain silicon oxide powder with a particle size D50 of 0.1-1 μm; wherein, the molar ratio of the silicon powder and the silicon dioxide powder is 0.6:0.4; The particle size D50 of the silicon powder is 1-100 μm, and the particle size D50 of the silicon dioxide powder is 0.01-1 μm; the chemical formula of the silicon oxide powder is SiOx, wherein the value of x is 0.8-1.3;

S2. carbon coating is performed on the silicon oxide powder to obtain a first precursor; the method used for the carbon coating is liquid phase coating; the specific steps of the liquid phase coating are: The powder is dispersed in ethanol, and asphalt is gradually added to fully mix to obtain a first mixed solution, and then spray-drying and granulation are performed to obtain a composite, and the composite is subjected to heat treatment to obtain a first precursor; the asphalt and silicon oxide are mixed. The mass ratio of the powder is 2:1; the solid content of the first mixed solution is 30%; the heat treatment method is: placing the composite in an inert gas, and at a heating rate of 5°C/min, Heating at a constant temperature of 800°C for 6 hours;

S3. In-situ carbon nanofibers are grown on the surface of the first precursor to obtain a second precursor; specifically: the first precursor is dispersed in ethylene glycol, and then a catalyst is gradually added to mix well to obtain a second precursor. Mix the solution, and then dry it to obtain catalyst-supported carbon-coated silicon oxide powder; place the obtained catalyst-supported carbon-coated silicon oxide powder in a reactor, and heat it to 850° C. under the protection of helium gas, Then, a mixture of hydrogen and carbon source gas was introduced, kept for 10 hours, and then the carbon source gas was turned off, and the temperature was lowered to room temperature to obtain a second precursor; wherein, the catalyst was FeCl ₃ •6H ₂ O; the catalyst and the first precursor were The precursor mass ratio is 1:1000; the solid content of the second mixed solution is 50%; the volume ratio of the carbon source gas, hydrogen and helium is 5:1:30, and the carbon source gas is methane, The length of the carbon nanofibers is 0.01-100 μm, and the diameter is 0.1-20 nm;

S4. Carry out secondary granulation to the second precursor to obtain the silicon oxide composite negative electrode material, the specific steps are: dispersing the second precursor in propanol, and then gradually adding polyvinylpyrrolidone to fully mix evenly , to obtain a third mixed solution, and then spray-dried and granulated to obtain a secondary granulated silicon oxide composite negative electrode material; wherein, the mass ratio of the polyvinylpyrrolidone and the second precursor is 0.5:1; the third The solid content of the mixed solution is 10%; the particle size D50 of the silicon oxide composite negative electrode material is 5-10 μm.

Example 3

The silicon oxide composite negative electrode material, the preparation method steps are as follows:

S1. provide silicon oxide powder, and the silicon oxide powder is a silicon oxide powder without disproportionation treatment; the preparation method of the silicon oxide powder is: mixing silicon powder and silicon dioxide powder uniformly Then, in an inert atmosphere or a vacuum environment, it is heated to 1600 ° C to generate silicon monoxide gas, which is cooled and precipitated on a deposition plate to obtain a silicon oxide block; the silicon oxide block is crushed by a jaw crusher. Particles with an average particle size of 0.5-8 mm are then pulverized and pulverized by air flow to obtain silicon oxide powder with a particle size D50 of 0.1-1 μm; wherein, the molar ratio of the silicon powder to the silicon dioxide powder is 0.7:0.3; The particle size D50 of the silicon powder is 1-100 μm, and the particle size D50 of the silicon dioxide powder is 0.01-1 μm; the chemical formula of the silicon oxide powder is SiOx, wherein the value of x is 0.8-1.3;

S2. carbon coating is performed on the silicon oxide powder to obtain a first precursor; the method used for the carbon coating is liquid phase coating; the specific steps of the liquid phase coating are: The powder is dispersed in propanol, gradually added with citric acid, and fully mixed to obtain a first mixed solution, then spray-dried and granulated to obtain a compound, and the compound is subjected to heat treatment to obtain a first precursor; wherein, the lemon The mass ratio of acid and silicon oxide powder is 0.5:1; the solid content of the first mixed solution is 10-50%; the heat treatment method is: placing the compound in an inert gas, and adding 0.5 ℃/min heating rate, constant temperature heating at 500 ℃ for 10 hours;

S3. In-situ growth of carbon nanofibers on the surface of the first precursor to obtain a second precursor; specifically: dispersing the first precursor in propanol, and then gradually adding a catalyst to fully mix evenly to obtain a second mixture solution, and then dried to obtain catalyst-supported carbon-coated siliceous oxide powder; the obtained catalyst-supported carbon-coated siliceous oxide powder was placed in a reactor, heated to 600 ° C under argon protection, and then The mixed gas of hydrogen and carbon source gas was introduced, kept for 0.5h, then the carbon source gas was turned off, and the temperature was lowered to room temperature to obtain the second precursor; wherein, the catalyst was FeSO ₄ •7H ₂ O; The mass ratio of the precursor is 1:1; the solid content of the second mixed solution is 10%; the volume ratio of the carbon source gas, hydrogen and argon is 0.1:1:10, and the carbon source gas is ethylene, The length of the carbon nanofibers is 0.01-100 μm, and the diameter is 0.1-20 nm;

S4. the second precursor is subjected to secondary granulation to obtain the silicon oxide composite negative electrode material, and the specific steps are: dispersing the second precursor in isopropanol, and then gradually adding asphalt for adequate mixing, A third mixed solution is obtained, and then spray-drying and granulation are performed to obtain a secondary granulated silicon oxide composite negative electrode material; wherein, the mass ratio of the pitch and the second precursor is 5:1; the mass ratio of the third mixed solution is The solid content is 10-0%; the particle size D50 of the silicon oxide composite negative electrode material is 5-10 μm.

Example 4

The silicon oxide composite negative electrode material, the preparation method steps are as follows:

S1. provide silicon oxide powder, and the silicon oxide powder is a silicon oxide powder without disproportionation treatment; the preparation method of the silicon oxide powder is: mixing silicon powder and silicon dioxide powder uniformly Then, in an inert atmosphere or a vacuum environment, heating to 1500 ° C to generate silicon monoxide gas, which is cooled and precipitated on a deposition plate to obtain a silicon oxide block; the silicon oxide block is crushed by a jaw crusher into Particles with an average particle size of 0.5-8mm are then pulverized and pulverized by air flow to obtain silicon oxide powder with a particle size D50 of 0.1-1 μm; wherein, the molar ratio of the silicon powder and the silicon dioxide powder is 0.4:0.6; The particle size D50 of the silicon powder is 1-100 μm, and the particle size D50 of the silicon dioxide powder is 0.01-1 μm; the chemical formula of the silicon oxide powder is SiOx, wherein the value of x is 0.8-1.3;

S2. carbon coating is carried out on the silicon oxide powder to obtain a first precursor; the method used for the carbon coating is gas-phase coating; the specific steps of the gas-phase coating are: Passed into a fluidized bed atmosphere furnace, heated to 850 ℃ under the protection of inert gas, and then passed into carbon source gas, kept for 10h, then turned off the carbon source gas, and cooled to room temperature to obtain the first precursor; The volume ratio of the carbon source gas and the inert gas is 0.1:10; the carbon source gas is ethylene, and the inert gas is argon;

S3. In-situ carbon nanofibers are grown on the surface of the first precursor to obtain a second precursor; specifically, the first precursor is dispersed in glycerol and methanol, and then a catalyst is gradually added to mix well to obtain the first precursor. The two mixed solutions were then dried to obtain catalyst-supported carbon-coated siliceous oxide powder; the obtained catalyst-supported carbon-coated siliceous oxide powder was placed in a reactor, heated to 700° C. under nitrogen protection, Then a mixture of hydrogen and carbon source gas was introduced, kept for 5 hours, then the carbon source gas was turned off, and the temperature was lowered to room temperature to obtain a second precursor; wherein, the catalyst was Fe(NO ₃ ) ₃ 9H ₂ O and Ni ( NO ₃ ) ₂ •6H ₂ O; the mass ratio of the catalyst to the first precursor is 1:300; the solid content of the second mixed solution is 25%; the volume ratio of the carbon source gas, hydrogen and nitrogen is 3:1:10, the carbon source gas is acetylene and ethane, the length of the carbon nanofibers is 0.01-100 μm, and the diameter is 0.1-20 nm;

S4. Carry out secondary granulation to the second precursor to obtain the silicon oxide composite negative electrode material, and the specific steps are: dispersing the second precursor in tetrahydrofuran, and then gradually adding the soft carbon precursor to fully mix evenly , obtain a third mixed solution, and then spray-dry granulation to obtain a secondary granulated silicon oxide composite negative material; wherein, the third organic solvent is one of ethanol, propanol, isopropanol, and tetrahydrofuran or several; the soft carbon precursor is pitch and polyvinylpyrrolidone; the mass ratio of the soft carbon precursor and the second precursor is 2:1; the solid content of the third mixed solution is 40%; the The particle size D50 of the silicon oxide composite negative electrode material is 5-10 μm.

Comparative Example 1

Based on Example 1, the only difference is that Step S2 is omitted in this Comparative Example 1.

Comparative Example 2

Based on Example 1, the only difference is that Step S3 is omitted in this Comparative Example 2.

Comparative Example 3

Based on Example 1, the only difference is that Step S4 is omitted in this Comparative Example 3.

Comparative Example 4

Based on Example 1, the only difference is that: the preparation method of siliceous oxide powder in Comparative Example 4 is as follows: after uniformly mixing silicon powder and silica powder, heating to 1400°C in an inert atmosphere or a vacuum environment , to generate silicon monoxide gas, which is cooled and precipitated on the deposition plate to obtain siliceous oxide blocks; in an inert environment, heat treatment at 900-1150 ° C to implement disproportionation reaction, and then crushed into an average particle size of 0.5 by a jaw crusher -8mm particles, and then through jet pulverization and pulverization to obtain silicon oxide powder with a particle size D50 of 0.1-1 μm; wherein, the molar ratio of the silicon powder and the silicon dioxide powder is 0.5:0.5; the silicon powder The particle size D50 of the silica powder is 1-100 μm, and the particle size D50 of the silica powder is 0.01-1 μm.

Test example

The materials prepared in Examples 1-4 and Comparative Examples 1-4 are mixed with graphite in proportion (the gram capacity after mixing is 500mAh/g) as a composite negative electrode material, and are mixed with binder sodium carboxymethyl cellulose (CMC), conductive agent (conductive carbon black) and binder styrene-butadiene rubber (SBR) were mixed according to the mass ratio of 94:1.5:2:2.5, and an appropriate amount of deionized water was added as a dispersant to make a slurry, which was coated on copper foil, and After vacuum drying and rolling, a negative electrode sheet was prepared. A CR2025 type battery was assembled in a glove box (M Braun), with pure Li sheet as the negative electrode, Celgard 2300 as the separator, and EC:DMC (1:1 volume ratio, 1 mol/L LiPF6, Samsung) as the electrolyte.

Normal temperature cycle test: charge at a constant current of 0.1C at a constant temperature of 25°C until the voltage is 5mV, then discharge at a current of 0.1C to 1.5V, and repeat the charge-discharge cycle for 50 times; record the discharge capacity of the battery during the cycle. The percentage of the 50th discharge capacity and the first discharge capacity was taken as the capacity retention rate.

In the XRD pattern: the peak at 2θ=28.4° represents the <111> plane diffraction peak of Si. It can be seen from Figure 2 that in Example 1, the peak intensity is weak here, indicating that the disproportionation degree is low, and the disproportionation degree is low, indicating that the size of the nano-silicon particles is small, which is beneficial to improve the cycle performance. However, in Comparative Example 4, the peak-to-peak intensity is relatively high, indicating that the disproportionation degree is relatively large, and the corresponding nano-silicon particle size is relatively large, which will deteriorate the cycle performance.

In the present invention, in the preparation of the silicon oxide composite negative electrode material, (1) carbon coating is performed on the silicon oxide powder; (2) carbon nanofibers are grown in situ; (3) secondary granulation; (4) control of the silicon oxide powder The degree of disproportionation of silicon; these four processes are interrelated and inseparable, and the four together affect the kinetic performance of lithium-ion batteries. And the cycle performance has been greatly improved, the technical effect of "1+1+1+1>4" has been achieved, and unexpected technical effects have been achieved. Without any one of these four processes, the battery cannot have good kinetic performance, first-time efficiency and cycle performance.

The above-mentioned embodiment only expresses the embodiment of the present invention, and its description is more specific and detailed, but it should not be construed as a limitation on the scope of the present invention, but all technical solutions obtained in the form of equivalent replacement or equivalent transformation , should fall within the protection scope of the present invention.

Claims (6)

1. The preparation method of the silicon monoxide composite negative electrode material is characterized by comprising the following steps:

s1, providing silicon monoxide powder which is not subjected to disproportionation treatment;

s2, performing carbon coating on the silica powder to obtain a first precursor;

s3, growing carbon nanofibers on the surface of the first precursor in situ to obtain a second precursor;

s4, performing secondary granulation on the second precursor to obtain the silicon monoxide composite negative electrode material;

the preparation method of the silicon monoxide powder comprises the following steps: uniformly mixing silicon powder and silicon dioxide powder, heating to generate silicon monoxide gas in an inert atmosphere or a vacuum environment, and cooling to separate out silicon monoxide gas to obtain a silicon monoxide block; crushing and crushing the silicon monoxide block to obtain silicon monoxide powder;

the carbon coating adopts a method comprising solid phase coating, liquid phase coating or gas phase coating; the liquid phase coating comprises the following specific steps: dispersing the silica powder in a first organic solvent, gradually adding a soft carbon precursor, fully and uniformly mixing to obtain a first mixed solution, then carrying out spray drying granulation to obtain a compound, and carrying out heat treatment on the compound to obtain a first precursor; the gas phase coating comprises the following specific steps: introducing the silica powder into a fluidized bed type atmosphere furnace, heating to 600-800 ℃ under the protection of inert gas, introducing a carbon source gas, preserving heat for 0.5-10h, closing the carbon source gas, and cooling to room temperature to obtain a first precursor;

the method for in-situ growth of the carbon nanofibers on the surface of the first precursor comprises the following specific steps: dispersing the first precursor in a second organic solvent, gradually adding a catalyst, fully and uniformly mixing to obtain a second mixed solution, and then drying to obtain catalyst-loaded carbon-coated silicon monoxide powder; placing the obtained catalyst-loaded carbon-coated silica powder in a reactor, heating to 600-850 ℃ under the protection of inert gas, introducing mixed gas of hydrogen and carbon source gas, preserving heat for 0.5-10h, closing the carbon source gas, and cooling to room temperature to obtain a second precursor;

the second precursor is granulated for the second time, which comprises the following specific steps: dispersing the second precursor in a third organic solvent, gradually adding the soft carbon precursor, fully and uniformly mixing to obtain a third mixed solution, and then carrying out spray drying granulation to obtain a secondary granulated silicon oxide composite negative electrode material; wherein the third organic solvent is one or more of ethanol, propanol, isopropanol and tetrahydrofuran; the soft carbon precursor is one or more of asphalt, citric acid and polyvinylpyrrolidone; the mass ratio of the soft carbon precursor to the second precursor is (0.5-5) to 1; the solid content of the third mixed solution is 10-50%; the particle size D50 of the silicon oxide composite negative electrode material is 5-10 μm; the carbon content of the silicon monoxide composite negative electrode material is 5-20%.

2. The method for preparing the silicon monoxide composite negative electrode material as claimed in claim 1, wherein the molar ratio of the silicon powder to the silicon dioxide powder is (0.3-0.7) to (0.7-0.3); the particle size D50 of the silicon powder is 1-100 μm, and the particle size D50 of the silicon dioxide powder is 0.01-1 μm; the heating temperature is 900-1600 ℃; the chemical formula of the silicon monoxide powder is SiOx, wherein the value of x is 0.8-1.3; the particle size D50 of the monox powder is 0.1-1 μm.

3. The method for preparing the silicon monoxide composite negative electrode material as claimed in claim 1, wherein in the liquid phase coating, the first organic solvent is one or more of ethanol, propanol, isopropanol and tetrahydrofuran; the mass ratio of the soft carbon precursor to the silicon monoxide powder is (0.5-5) to 1; the soft carbon precursor is one or more of asphalt, citric acid and polyvinylpyrrolidone; the solid content of the first mixed solution is 10-50%; the heat treatment method comprises the following steps: placing the compound in inert gas, and heating at a constant temperature of 500-800 ℃ for 1-10 hours at a heating rate of 0.5-15 ℃/min; in the gas phase coating, the volume ratio of the carbon source gas to the inert gas is (0.1-5) to (10-30); the carbon source gas is one or more of acetylene, ethylene, methane and ethane, and the inert gas is one or more of nitrogen, argon and helium.

4. The method for preparing the silica composite anode material according to claim 1, wherein the second organic solvent is one or more of ethanol, methanol, propanol, isopropanol, ethylene glycol and glycerol, and the catalyst is one or more of Fe (NO3) 3.9H 2O, FeSO 4.7H 2O, FeCl 3.6H 2O, Co (NO3) 2.6H 2O and Ni (NO3) 2.6H 2O; the mass ratio of the catalyst to the first precursor is 1: 1-1000; the solid content of the second mixed solution is 10-50%; the volume ratio of the carbon source gas, the hydrogen and the inert gas is (0.1-5) to 1 to (10-30), the carbon source gas is one or more of acetylene, ethylene, methane and ethane, and the inert gas is one or more of nitrogen, argon and helium; the length of the nano carbon fiber is 0.01-100 μm, and the diameter is 0.1-20 nm.

5. A silica composite negative electrode material, characterized in that it is produced by the production method according to any one of claims 1 to 4.

6. A lithium ion battery comprising the negative electrode material of claim 5.

Images