CN111653759A - A kind of silicon-based composite material and preparation method thereof - Google Patents

Abstract

The invention provides a silicon-based composite material and a preparation method thereof. The silicon-based composite material provided by the present invention comprises: a silicon-based substrate, a fast ion conductor layer coated on the surface of the silicon-based substrate, and a carbon layer coated on the surface of the fast ion conductor layer; the fast ion conductor The fast ionic conductor of the layer is _LiAlSixOy , where x≥1 and _y≥1 . The invention sequentially coats a specific fast ion conductor layer LiAlSi _x O _y and a carbon coating on the surface of the silicon-based substrate, which effectively improves the problems of high charge transfer resistance and low power output of the silicon-based negative electrode material, and is beneficial to the rate performance. At the same time, the combination of the above-mentioned specific double cladding layers can effectively alleviate the expansion of the silicon-based material and improve the cycle performance.

Description

A kind of silicon-based composite material and preparation method thereof

technical field

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

Background technique

Over the past 20 years, lithium-ion batteries have dominated the portable electronics market and have made great strides in the electric vehicle industry. Graphite is the most widely used anode material for lithium-ion batteries, with a theoretical capacity of 372mAh/g and an energy density below 150Wh/kg, which is far from meeting the requirements of an energy density of 350Wh/kg. Therefore, research on new anode materials for lithium-ion batteries is imminent.

Due to its theoretical capacity of up to 3590mAh/g, high working platform voltage, environmental friendliness and abundant reserves, silicon anode materials are considered to be the most promising to replace graphite and will occupy a major position in the future anode material market. However, there are also many challenges in the actual use of the silicon anode. During the charging and discharging process of the silicon anode, the volume expansion is as high as 300%, which causes the pulverization of the silicon material and the rupture and regeneration of the SEI film, which makes the silicon anode material The capacity drops rapidly, and the first coulomb efficiency is low. At the same time, in terms of market applications, there are also higher requirements for fast charging and fast discharging performance.

In order to solve the above problems, a large number of researchers have used various methods to improve the expansion and improve the cycle stability and rate performance of the material. The main technical means include two types: one is to directly design the structure of silicon materials, including: the design of solid structures such as thin films, nanowires, nanorods, and the design of hollow structures such as nanotubes, hollow spheres, and porous silicon; the second is to introduce other functional materials. It is compounded with silicon-based materials, and comprehensive structural design optimization, such as metal material modification, conductive carbon material modification, complex structure design optimization, etc. For example, in CN108682796A, an alloy is used as the coating layer, in CN108493428A, fast ion lithium salt is used as the coating layer, and in CN109950481A, a polymer electrolyte is used as the coating layer. However, the above-mentioned coating materials still cannot effectively improve the cycle stability and rate performance, and the preparation method has disadvantages such as complicated process, low strength of the coating layer, and uneven coating thickness.

SUMMARY OF THE INVENTION

In view of this, the purpose of the present invention is to provide a silicon-based composite material and a preparation method thereof. The silicon-based composite material provided by the invention can effectively improve cycle stability and rate performance. The preparation method provided by the invention is simple and easy to implement and has good coating effect.

The present invention provides a silicon-based composite material, comprising:

silicon base,

The fast ion conductor layer coated on the surface of the silicon-based substrate,

and a carbon layer covering the surface of the fast ion conductor layer;

The fast ion conductor of the fast ion conductor layer is _LiAlSix O _y , where x≥1 and y≥1.

Preferably, the silicon-based matrix is SiO _z , wherein 0.6≦z≦1.6.

Preferably, the fast ion conductor is selected from one or more of LiAlSiO ₄ , LiAlSi ₂ O ₆ and LiAlSi ₃ O ₈ .

Preferably, the mass ratio of the silicon-based substrate to the fast ion conductor layer is 1:(0.01-10);

The mass ratio of the silicon-based substrate to the carbon layer is 1:(0.001-0.5).

The present invention also provides a preparation method of the silicon-based composite material described in the above technical scheme, comprising the following steps:

a) dissolving the aluminum salt compound, the lithium salt compound and the silicon dioxide in a solvent and then sintering to obtain a fast ion coating agent;

b) mixing the silicon-based matrix with the fast ion coating agent to obtain a precursor powder;

c) mixing the precursor powder, the carbon source and the liquid-phase coating agent, and sintering to obtain a silicon-based composite material.

Preferably, the aluminum salt compound is selected from one or more of aluminum isopropoxide, aluminum sec-butoxide, aluminum sulfate and aluminum nitrate;

The lithium salt compound is selected from one or more of lithium carbonate, lithium hydroxide, lithium acetate and lithium citrate.

Preferably, the D50 particle size of the silicon-based substrate is 2-10 μm.

Preferably, in the step a), the mass ratio of the aluminum salt compound, the lithium salt compound and the silicon dioxide is 1:(0.5-1):(1.5-3);

In the step c), the mass ratio of the precursor powder, the carbon source and the liquid-phase coating agent is (80-100):(0-10):(0-10).

Preferably, in the step a), the sintering temperature is 850-1200° C., and the holding time is 3-5 h.

In the step c), the sintering temperature is 500-850° C., and the holding time is 3-5 h.

Preferably, in the step c):

The carbon source is selected from one or more of pitch, glucose, sucrose and chitosan;

The liquid phase coating agent is selected from one or more of heavy oil, liquid phenolic resin and liquid epoxy resin;

In the step a), the solvent is an alcohol solvent.

The present invention provides a silicon-based composite material, comprising: a silicon-based substrate, a fast ion conductor layer coated on the surface of the silicon-based substrate, and a carbon layer coated on the surface of the fast ion conductor layer; The fast ion conductor of the ion conductor layer is _LiAlSix O _y , where x≥1 and y≥1. The invention sequentially coats a specific fast ion conductor layer LiAlSi _x O _y and a carbon coating on the surface of the silicon-based substrate, which effectively improves the problems of high charge transfer resistance and low power output of the silicon-based negative electrode material, and is beneficial to the rate performance. At the same time, the combination of the above-mentioned specific double cladding layers can effectively alleviate the expansion of the silicon-based material and improve the cycle performance.

The test results show that the silicon-based composite material provided by the present invention is used as a negative electrode material for a lithium ion battery, and its 0.2C first discharge specific capacity reaches more than 1609mAh·g ^-1 , its first efficiency reaches more than 80%, and its discharge capacity at 1C, 2C and 3C rates. The retention rates are over 93%, over 92% and over 84%, respectively. After 200 cycles at 0.2C, the discharge specific capacity can still be maintained over 1284mAh·g ^-1 , and the capacity retention rate is over 79%.

Description of drawings

In order to explain the embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the accompanying drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only It is an embodiment of the present invention. For those of ordinary skill in the art, other drawings can also be obtained according to the provided drawings without creative work.

Fig. 1 is the XRD pattern of fast ion coating agent in embodiment 1;

Fig. 2 is the SEM image of the composite material obtained in Example 1;

3 is a graph showing the cycle performance of the composite material obtained in Example 1 as a negative electrode material.

Detailed ways

The present invention provides a silicon-based composite material, comprising:

silicon base,

The fast ion conductor layer coated on the surface of the silicon-based substrate,

and a carbon layer covering the surface of the fast ion conductor layer;

The fast ion conductor of the fast ion conductor layer is _LiAlSix O _y , where x≥1 and y≥1.

The invention sequentially coats a specific fast ion conductor layer LiAlSi _x O _y and a carbon coating on the surface of the silicon-based substrate, which effectively improves the problems of high charge transfer resistance and low power output of the silicon-based negative electrode material, and is beneficial to the rate performance. At the same time, the combination of the above-mentioned specific double cladding layers can effectively alleviate the expansion of the silicon-based material and improve the cycle performance.

In the present invention, the silicon-based substrate is preferably a silicon oxide material SiO _z , wherein 0.6≦z≦1.6. Compared with other silicon-based materials (such as nano-silicon, etc.), the present invention adopts the siliceous oxide material SiO _z , which can better improve the rate performance and cycle performance through the above-mentioned coating. In some embodiments of the present invention, the silicon-based substrate is SiO _z , and z is 0.9.

In the present invention, the particle size D50 of the silicon-based substrate is preferably 2-10 μm, more preferably 3-5 μm. If the particle size is too high, the electrochemical performance of the composite material will decline rapidly during the charging and discharging process, which cannot meet the requirements of use. If the particle size is too small, it is not conducive to dispersion, and it is difficult to prepare and obtain a composite material with good performance.

In the present invention, the fast ion conductor of the fast ion conductor layer is LiAlSi _x O _y , wherein x≥1, preferably 1-3; y≥1, preferably 4-8. Compared with other fast ion conductors, the use of the above fast ion conductors in the present invention can better match the carbon layer, significantly improve the silicon base layer, and improve the rate performance and cycle performance of the material. The fast ion conductor is more preferably one or more of LiAlSiO ₄ , LiAlSi ₂ O ₆ and LiAlSi ₃ O ₈ .

In the present invention, the carbon layer is preferably an amorphous carbon layer.

In the present invention, the composite material includes three layers: silicon-based matrix core layer-fast ion conductor middle layer-carbon outer layer. Wherein, the mass ratio of the silicon-based substrate to the fast ion conductor layer is preferably 1:(0.01-0.5); in some embodiments of the present invention, the above-mentioned mass ratio is 1:0.03, 1:0.05 or 1:0.1. The mass ratio of the silicon-based substrate to the carbon layer is preferably 1:(0.001-0.5). In the present invention, the particle size of the composite material is preferably 3-5 μm.

The present invention also provides a preparation method of the silicon-based composite material described in the above technical scheme, comprising the following steps:

a) dissolving the aluminum salt compound, the lithium salt compound and the silicon dioxide in a solvent and then sintering to obtain a fast ion coating agent;

b) mixing the silicon-based matrix with the fast ion coating agent to obtain a precursor powder;

c) mixing the precursor powder, the carbon source and the liquid-phase coating agent, and sintering to obtain a silicon-based composite material.

Regarding step a):

In the present invention, the aluminum salt compound is preferably one or more of aluminum isopropoxide, aluminum sec-butoxide, aluminum sulfate and aluminum nitrate. The lithium salt compound is preferably one or more of lithium carbonate, lithium hydroxide, lithium acetate and lithium citrate. The particle size of the silica is preferably 0.5-2 μm, more preferably 1-1.2 μm. In the present invention, the mass ratio of the aluminum salt compound, the lithium salt compound and the silicon dioxide is preferably 1:(0.5-1):(1.5-3); in some embodiments of the present invention, the mass ratio is 1:0.5:1.5 or 1:1:3.

In the present invention, the solvent is preferably an alcohol solvent, more preferably one or more of ethanol, n-propanol, isopropanol, ethylene glycol and glycerol.

In the present invention, the mass fraction of the total solid raw materials (aluminum salt compound, lithium salt compound and silica) in the solvent is preferably 10% to 90%. After the solid raw materials are dissolved and dispersed uniformly in the solvent, a mixed solution is obtained.

In the present invention, the mixing process of the solid raw material and the solvent is preferably accompanied by stirring; the stirring speed is preferably 100-400 r/min, and the stirring time is preferably 1-6 h; for better dispersion, the stirring time is more preferably 6h. After the above treatment, the solid raw material is uniformly dispersed in the solvent.

In the present invention, after the above-mentioned mixing, drying is preferably performed. The drying temperature is preferably 60-120° C., and the drying time is preferably 3-8 h.

In the present invention, after the above drying, it is preferable to further grind. After the above drying, the particles adhere together into flakes or agglomerates, and the particles are dispersed by grinding to obtain uniformly dispersed particles without changing the particle size of the particles themselves.

In the present invention, after grinding, sintering is performed. In the present invention, the sintering is preferably carried out in an inert gas atmosphere; the present invention does not have a special limitation on the type of the inert gas, and can be a conventional inert gas well known to those skilled in the art, such as argon and the like. In the present invention, the sintering temperature is preferably 850-1200°C; in some embodiments of the present invention, the sintering temperature is 1000°C. The incubation time is preferably 3 to 5 hours; in some embodiments of the present invention, the incubation time is 5 hours. The heating rate in the sintering is preferably 4-8°C/min; in some embodiments of the present invention, the heating rate is 5°C/min. After sintering, the above-mentioned raw materials react to form a fast ion conductor coating agent _LiAlSixOy , where x≥1 and _y≥1 .

Regarding step b):

In the present invention, the silicon-based base material is the same as that described in the above technical solutions, and details are not repeated here. In the present invention, the mass ratio of the silicon-based substrate to the fast ion coating agent is preferably 1:(0.001-0.5); in some embodiments of the present invention, the above-mentioned mass ratio is 1:0.03, 1:0.05 or 1:0.1.

In the present invention, the mixing is preferably ball milling. The rotational speed of the ball milling is preferably 200-500 r/min, more preferably 400 r/min; the ball-milling time is preferably 0.5-4 h, more preferably 2 h. After mixing by ball milling, the precursor powder is obtained.

Regarding step c):

In the present invention, the carbon source is preferably one or more of pitch, glucose, sucrose and chitosan. The liquid phase coating agent is preferably one or more of heavy oil, liquid phenolic resin and liquid epoxy resin.

In the present invention, the mass ratio of the precursor powder, the carbon source and the liquid-phase coating agent is preferably (80-100):(0-10):(0-10), wherein the carbon source and the liquid-phase coating are agent is not 0. In some embodiments of the present invention, the above mass ratio is 90:5:5.

In the present invention, the mixing temperature of the precursor powder, the carbon source and the liquid-phase coating agent is not particularly limited, and may be room temperature. In the present invention, the equipment used for the mixing can be a fusion machine, a VC mixer or a ball mill. The rotation speed of the mixing process is preferably 100-400 r/min, and the mixing time is preferably 30-300 min.

In the present invention, sintering is performed after mixing uniformly. In the present invention, the sintering is preferably carried out in an inert gas atmosphere; the present invention does not have a special limitation on the type of the inert gas, and can be a conventional inert gas well known to those skilled in the art, such as argon and the like. In the present invention, the sintering temperature is preferably 500-850°C; in some embodiments of the present invention, the sintering temperature is 650°C. The incubation time is preferably 3 to 5 hours; in some embodiments of the present invention, the incubation time is 5 hours. The heating rate in the sintering is preferably 4-8°C/min; in some embodiments of the present invention, the heating rate is 5°C/min. After sintering, the surface of the silicon-based substrate is tightly coated with an aluminum silicate fast ion conductor layer, and a carbon coating layer is formed on the surface of the aluminum silicate coating layer, thereby obtaining a silicon-based composite material with a three-layer structure.

The preparation method provided by the present invention is simple and easy to implement, and the coating is uniform, thereby improving the coating effect.

The present invention has the following beneficial effects:

(1) Design a double cladding layer on the surface of the silicon-based substrate, followed by a fast ion _conductor layer _LiAlSixOy and a carbon layer. The coated composite material is used as a negative electrode material for lithium-ion batteries, and its first discharge specific capacity at 0.2C reaches 1609 mAh·g ^-1 or more, the first efficiency reaches more than 80%, and the discharge capacity retention rates at 1C, 2C, and 3C are respectively 93%. %, 92% and 84%, the discharge specific capacity can still be maintained above 1284mAh·g ^-1 after 200 cycles at 0.2C, and it has great potential as a negative electrode material for lithium-ion batteries.

(2) The present invention utilizes aluminum-containing compound, lithium-containing compound, and silicon dioxide powder to synthesize lithium aluminum silicate, a fast ion conductor, as a coating material. The chemical synthesis method is used to uniformly coat the surface of the silicon-based substrate, and a coating layer is formed after firing. The new silicon-based negative electrode material that is in close contact with the material has the effect of reducing the obstruction of lithium ion transmission, providing a fast transmission channel for lithium ion transmission, so that the ion transmission is not hindered, reducing the polarization of the battery electrode, and achieving the purpose of reducing the internal resistance of the battery , and does not reduce the battery discharge specific capacity after coating.

(3) Lithium aluminum silicate is used as an excellent coating material for conducting lithium ions, and its precursor forms a coating layer with better crystallinity after firing, which is conducive to the de-intercalation of lithium ions in the material and improves the material's performance. At the same time, as the coating layer, it relieves the volume expansion to a certain extent, and cooperates with the carbon layer to better improve the expansion problem and improve the cycle performance of the material.

In order to further understand the present invention, the preferred embodiments of the present invention are described below in conjunction with the examples, but it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention. The experimental methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials used are obtained from commercial sources unless otherwise specified. Among them, the particle size of the SiO ₂ powder is 0.5-2 μm.

Example 1

S1. Weigh 20 g of aluminum sec-butoxide, 10 g of lithium carbonate, and 30 g of SiO ₂ powder, dissolve them in 50 mL of ethanol solution, stir with a magnetic stirrer for 4 h, stir evenly, and dry them at 80 °C for 5 h. Grind to give mixture A. Then sintering is carried out in an argon atmosphere, the heating rate is 5°C/min, and the temperature is raised to 1000°C for 5 hours to obtain a fast ion coating agent.

S2. Weigh 200 g of silicon oxide SiO _z (z is 0.9, particle size is 3 μm) and 10 g of fast ion coating agent, put them into a ball mill, and mill them at a rotational speed of 400 r/min for 2 hours to obtain a precursor powder.

S3, adding the precursor powder, pitch and liquid phenolic resin into the fusion machine in a mass ratio of 90:5:5, stirring at room temperature, rotating speed 300r/min, and mixing for 30min to obtain a mixture.

S4, put the mixture into a crucible, sinter in an argon atmosphere, the heating rate is 5°C/min, and the temperature is raised to 650°C for 5 hours to obtain a composite material.

The X-ray diffraction test is performed on the fast ion coating agent obtained in step S1, and the result is shown in Fig. 1, which is the XRD pattern of the fast ion coating agent in Example 1 of the present invention. It is proved that the obtained fast ion coating agent is LiAlSi ₃ O ₈ .

The composite material obtained in step S4 is characterized by scanning electron microscope, and the result is shown in FIG. 2 , which is the SEM image of the composite material obtained in Example 1. It can be seen that the particle size of the obtained composite material is 3-5 μm; the coating layer on the particle surface is uniform.

Example 2

S1. Weigh 20 g of aluminum sec-butoxide, 10 g of lithium carbonate, and 30 g of SiO ₂ powder, dissolve them in 50 mL of ethanol solution, stir with a magnetic stirrer for 4 h, stir evenly, and dry them at 80 °C for 5 h. Grind to give mixture A. Then sintering is carried out in an argon atmosphere, the heating rate is 5°C/min, and the temperature is raised to 1000°C for 5 hours to obtain a fast ion coating agent.

S2. Weigh 100 g of silicon oxide SiO _z (z is 0.9, particle size is 3 μm) and 10 g of fast ion coating agent, put it into a ball milling jar for ball milling, rotate at 400 r/min, and ball mill for 2 h to obtain a precursor powder.

S3, adding the precursor powder, pitch and liquid phenolic resin into the fusion machine in a mass ratio of 90:5:5, stirring at room temperature, rotating speed 300r/min, and mixing for 30min to obtain a mixture.

S4, put the mixture into a crucible, sinter in an argon atmosphere, the heating rate is 5°C/min, and the temperature is raised to 650°C for 5 hours to obtain a composite material.

The X-ray diffraction test was performed on the fast ion coating agent obtained in step S1 according to the analysis and testing method of Example 1, and the results showed that the obtained fast ion coating agent was LiAlSi ₃ O ₈ .

Example 3

S1. Weigh 20 g of aluminum sec-butoxide, 10 g of lithium carbonate, and 30 g of SiO ₂ powder, dissolve them in 50 mL of ethanol solution, stir with a magnetic stirrer for 4 h, stir evenly, and dry them at 80 °C for 5 h. Grind to give mixture A. Then sintering is carried out in an argon atmosphere, the heating rate is 5°C/min, and the temperature is raised to 1000°C for 5 hours to obtain a fast ion coating agent.

S2. Weigh 300 g of silicon oxide SiO _z (z is 0.9, particle size is 3 μm) and 10 g of fast ion coating agent, put it into a ball mill, and mill it at a rotational speed of 400 r/min for 2 hours to obtain a precursor powder.

S3, adding the precursor powder, pitch and liquid phenolic resin into the fusion machine in a mass ratio of 90:5:5, stirring at room temperature, rotating speed 300r/min, and mixing for 30min to obtain a mixture.

S4, put the mixture into a crucible, sinter in an argon atmosphere, the heating rate is 5°C/min, and the temperature is raised to 650°C for 5 hours to obtain a composite material.

The X-ray diffraction test was performed on the fast ion coating agent obtained in step S1 according to the analysis and testing method of Example 1, and the results showed that the obtained fast ion coating agent was LiAlSi ₃ O ₈ .

Example 4

S1. Weigh 10 g of aluminum sec-butoxide, 10 g of lithium carbonate, and 30 g of SiO ₂ powder, dissolve them in 50 mL of ethanol solution, stir with a magnetic stirrer for 4 h, and after stirring evenly, dry them at 80 °C for 5 h, and then carry out the drying process. Grind to give mixture A. Then sintering is carried out in an argon atmosphere, the heating rate is 5°C/min, and the temperature is raised to 1000°C for 5 hours to obtain a fast ion coating agent.

S2. Weigh 200 g of silicon oxide SiO _z (z is 0.9, particle size is 3 μm) and 10 g of fast ion coating agent, put them into a ball mill, and mill them at a rotational speed of 400 r/min for 2 hours to obtain a precursor powder.

S3, adding the precursor powder, pitch and liquid phenolic resin into the fusion machine in a mass ratio of 90:5:5, stirring at room temperature, rotating speed 300r/min, and mixing for 30min to obtain a mixture.

S4, put the mixture into a crucible, sinter in an argon atmosphere, the heating rate is 5°C/min, and the temperature is raised to 650°C for 5 hours to obtain a composite material.

The X-ray diffraction test was carried out on the fast ion coating agent obtained in step S1 according to the analysis and testing method of Example 1. The results showed that the obtained fast ion coating agent was LiAlSi ₃ O ₈ and contained a small amount of impurity LiSi ₃ O ₆ .

Example 5

S1. Weigh 20 g of aluminum sec-butoxide, 10 g of lithium citrate, and 30 g of SiO ₂ powder, dissolve them in 50 mL of ethanol solution, stir with a magnetic stirrer for 4 h, stir evenly, and dry at 80 °C for 5 h, after which the dried Milling was carried out to obtain mixture A. Then sintering is carried out in an argon atmosphere, the heating rate is 5°C/min, and the temperature is raised to 1000°C for 5 hours to obtain a fast ion coating agent.

S2. Weigh 300 g of silicon oxide SiO _z (z is 0.9, particle size is 3 μm) and 10 g of fast ion coating agent, put it into a ball mill, and mill it at a rotational speed of 400 r/min for 2 hours to obtain a precursor powder.

S3, adding the precursor powder, pitch and liquid phenolic resin into the fusion machine in a mass ratio of 90:5:5, stirring at room temperature, rotating speed 300r/min, and mixing for 30min to obtain a mixture.

S4, put the mixture into a crucible, sinter in an argon atmosphere, the heating rate is 5°C/min, and the temperature is raised to 650°C for 5 hours to obtain a composite material.

The X-ray diffraction test was performed on the fast ion coating agent obtained in step S1 according to the analysis and testing method of Example 1, and the results showed that the obtained fast ion coating agent was LiAlSi ₃ O ₈ .

Example 6

S1. Weigh 20 g of aluminum sulfate, 10 g of lithium citrate, and 30 g of SiO ₂ powder, dissolve them in 50 mL of ethanol solution, stir with a magnetic stirrer for 4 h, stir evenly, and dry at 80 °C for 5 h, and then grind the dried material , to obtain mixture A. Then sintering is carried out in an argon atmosphere, the heating rate is 5°C/min, and the temperature is raised to 1000°C for 5 hours to obtain a fast ion coating agent.

S2. Weigh 300 g of silicon oxide SiO _z (z is 0.9, particle size is 3 μm) and 10 g of fast ion coating agent, put it into a ball mill, and mill it at a rotational speed of 400 r/min for 2 hours to obtain a precursor powder.

S3, adding the precursor powder, pitch and liquid phenolic resin into the fusion machine in a mass ratio of 90:5:5, stirring at room temperature, rotating speed 300r/min, and mixing for 30min to obtain a mixture.

S4, put the mixture into a crucible, sinter in an argon atmosphere, the heating rate is 5°C/min, and the temperature is raised to 650°C for 5 hours to obtain a composite material.

The X-ray diffraction test was performed on the fast ion coating agent obtained in step S1 according to the analysis and testing method of Example 1, and the results showed that the obtained fast ion coating agent was LiAlSi ₃ O ₈ .

Example 7

S1. Weigh 20 g of aluminum sec-butoxide, 10 g of lithium carbonate, and 30 g of SiO ₂ powder, dissolve them in 50 mL of ethanol solution, stir with a magnetic stirrer for 4 h, stir evenly, and dry them at 80 °C for 5 h. Grind to give mixture A. Then sintering is carried out in an argon atmosphere, the heating rate is 5°C/min, and the temperature is raised to 1000°C for 5 hours to obtain a fast ion coating agent.

S2. Weigh 200 g of silicon oxide SiO _z (z is 0.9, particle size is 4 μm) and 10 g of fast ion coating agent, put it into a ball mill, and mill it at a rotational speed of 400 r/min for 2 hours to obtain a precursor powder.

S3, adding the precursor powder, pitch and liquid phenolic resin into the fusion machine in a mass ratio of 90:5:5, stirring at room temperature, rotating speed 300r/min, and mixing for 30min to obtain a mixture.

S4, put the mixture into a crucible, sinter in an argon atmosphere, the heating rate is 5°C/min, and the temperature is raised to 650°C for 5 hours to obtain a composite material.

The X-ray diffraction test was performed on the fast ion coating agent obtained in step S1 according to the analysis and testing method of Example 1, and the results showed that the obtained fast ion coating agent was LiAlSi ₃ O ₈ .

Example 8

S1. Weigh 20 g of aluminum sec-butoxide, 10 g of lithium carbonate, and 30 g of SiO ₂ powder, dissolve them in 50 mL of ethanol solution, stir with a magnetic stirrer for 4 h, stir evenly, and dry them at 80 °C for 5 h. Grind to give mixture A. Then sintering is carried out in an argon atmosphere, the heating rate is 5°C/min, and the temperature is raised to 1000°C for 5 hours to obtain a fast ion coating agent.

S2. Weigh 200 g of silicon oxide SiO _z (z is 0.9, particle size is 5 μm) and 10 g of fast ion coating agent, put it into a ball milling jar for ball milling, rotate at 400 r/min, and ball mill for 2 h to obtain a precursor powder.

S3, adding the precursor powder, pitch and liquid phenolic resin into the fusion machine in a mass ratio of 90:5:5, stirring at room temperature, rotating speed 300r/min, and mixing for 30min to obtain a mixture.

S4, put the mixture into a crucible, sinter in an argon atmosphere, the heating rate is 5°C/min, and the temperature is raised to 650°C for 5 hours to obtain a composite material.

The X-ray diffraction test was performed on the fast ion coating agent obtained in step S1 according to the analysis and testing method of Example 1, and the results showed that the obtained fast ion coating agent was LiAlSi ₃ O ₈ .

Comparative Example 1

S1. Weigh 10 g of lithium carbonate and 30 g of SiO ₂ powder, dissolve them in 50 mL of ethanol solution, stir with a magnetic stirrer for 4 h, and after stirring evenly, dry at 80° C. for 5 h, and then grind the dried material to obtain mixture A. Then sintering is carried out in an argon atmosphere, the heating rate is 5°C/min, and the temperature is raised to 1000°C for 5 hours to obtain a fast ion coating agent.

S2. Weigh 200 g of silicon oxide SiO _z (z is 0.9, particle size is 3 μm) and 10 g of fast ion coating agent, put them into a ball mill, and mill them at a rotational speed of 400 r/min for 2 hours to obtain a precursor powder.

S3, adding the precursor powder, pitch and liquid phenolic resin into the fusion machine in a mass ratio of 90:5:5, stirring at room temperature, rotating speed 300r/min, and mixing for 30min to obtain a mixture.

S4, put the mixture into a crucible, sinter in an argon atmosphere, the heating rate is 5°C/min, and the temperature is raised to 650°C for 5 hours to obtain a composite material.

The X-ray diffraction test was carried out on the fast ion coating agent obtained in step S1 according to the analysis and testing method of Example 1. The results showed that the obtained fast ion coating agent was LiSi ₃ O ₆ , and since no aluminum salt was added to the raw material, it failed to form Lithium aluminum silicate fast ion conductor.

Comparative Example 2

S1. Weigh 20 g of aluminum sec-butoxide and 30 g of SiO ₂ powder, dissolve them in 50 mL of ethanol solution, stir with a magnetic stirrer for 4 h, after stirring evenly, dry at 80 °C for 5 h, and then grind the dried material to obtain a mixture A. Then sintering is carried out in an argon atmosphere, the heating rate is 5°C/min, and the temperature is raised to 1000°C for 5 hours to obtain a coating agent.

S2. Weigh 200 g of silicon oxide SiO _z (z is 0.9, particle size is 3 μm) and 10 g of coating agent, put it into a ball-milling jar and ball-milled at a rotational speed of 400r/min and ball-milled for 2h to obtain a precursor powder.

S3, adding the precursor powder, pitch and liquid phenolic resin into the fusion machine in a mass ratio of 90:5:5, stirring at room temperature, rotating speed 300r/min, and mixing for 30min to obtain a mixture.

S4, put the mixture into a crucible, sinter in an argon atmosphere, the heating rate is 5°C/min, and the temperature is raised to 650°C for 5 hours to obtain a composite material.

X-ray diffraction test was carried out on the coating agent obtained in step S1 according to the analysis and testing method of Example 1. The results showed that the obtained coating agent was Al ₂ O ₃ and SiO ₂ ; since there is no lithium salt in the raw material, it is impossible to generate a fast ion conductor , aluminum salts and SiO ₂ do not work.

Example 9

Electrochemical performance test is carried out to the silicon-based composite material obtained from the above embodiment and comparative example, and the process is as follows:

The obtained silicon-based composite negative electrode material, conductive carbon black, CMC, SBR and deionized water solvent were mixed and beaten according to a mass ratio of 53:24:7:16:90, and the beating time was 12 hours. The beaten slurry was evenly coated on the copper foil (the coating thickness was 20 mm), and air-dried at 80° C. for 12 h; and then the negative electrode sheet was obtained by cutting and rolling. The lithium sheet is used as the counter electrode, the electrolyte is LiPF ₆ solution (the mass fraction of the solution is 35%, the solvent is DMC, EMC and EC, and the volume ratio of the three is 1:1:1), and the diaphragm is polyethylene microporous membrane 2400, Assembled into a button-type simulated battery, the electrochemical performance was tested after standing for 5 hours.

The blue battery system was used to test the charge and discharge performance. The test current density was 0.1C/g, 0.2C/g, and the charge and discharge test was carried out in the voltage range of 0.005 to 2V.

The test results are shown in Table 1.

Table 1 Electrochemical properties of examples and comparative examples

Among them, the cycle performance curve of the silicon-based composite negative electrode material of Example 1 at 0.2C is shown in FIG. 3 , and FIG. 3 is a cycle performance curve diagram of the composite material obtained in Example 1 as a negative electrode material.

It can be seen from the test results in Table 1 that, compared with the comparative example, the specific capacity of the first discharge, the capacity retention rate at different rates and the first coulomb efficiency of the materials obtained in the embodiment of the present invention are significantly improved. At the same time, the capacity after 200 cycles of And the capacity retention rate is also significantly improved, which proves that the material provided by the present invention can effectively improve the rate performance and cycle stability.

The descriptions of the above embodiments are only used to help understand the method and the core idea of the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (10)

1. A silicon-based composite, comprising:

a silicon-based matrix, a silicon-based substrate,

a fast ion conductor layer coated on the surface of the silicon-based substrate,

and a carbon layer coated on the surface of the fast ion conductor layer;

the fast ion conductor of the fast ion conductor layer is LiAlSi_xO_yWherein x is more than or equal to 1, and y is more than or equal to 1.

2. The composite material according to claim 1,the silicon-based matrix is SiO_zWherein z is more than or equal to 0.6 and less than or equal to 1.6.

3. The composite material of claim 1, wherein the fast ion conductor is selected from the group consisting of LiAlSiO₄、LiAlSi₂O₆And LiAlSi₃O₈One or more of them.

4. The composite material of claim 1, wherein the mass ratio of the silicon-based matrix to the fast ion conductor layer is 1: 0.01-10;

the mass ratio of the silicon-based matrix to the carbon layer is 1: 0.001-0.5.

5. A preparation method of the silicon-based composite material as defined in any one of claims 1-4, comprising the following steps:

a) dissolving an aluminum salt compound, a lithium salt compound and silicon dioxide in a solvent and then sintering to obtain a fast ion coating agent;

b) mixing a silicon-based matrix with the fast ion coating agent to obtain precursor powder;

c) and mixing the precursor powder, a carbon source and a liquid phase coating agent, and sintering to obtain the silicon-based composite material.

6. The preparation method according to claim 5, wherein the aluminum salt compound is selected from one or more of aluminum isopropoxide, aluminum sec-butoxide, aluminum sulfate and aluminum nitrate;

the lithium salt compound is selected from one or more of lithium carbonate, lithium hydroxide, lithium acetate and lithium citrate.

7. The preparation method according to claim 5, wherein the silicon-based matrix has a D50 particle size of 2-10 μm.

8. The preparation method according to claim 5, wherein in the step a), the mass ratio of the aluminum salt compound to the lithium salt compound to the silicon dioxide is 1: 0.5-1: 1.5-3;

in the step c), the mass ratio of the precursor powder, the carbon source and the liquid phase coating agent is (80-100) to (0-10).

9. The preparation method of claim 5, wherein in the step a), the sintering temperature is 850-1200 ℃ and the holding time is 3-5 h.

In the step c), the sintering temperature is 500-850 ℃, and the heat preservation time is 3-5 h.

10. The method of claim 5, wherein in step c):

the carbon source is selected from one or more of asphalt, glucose, sucrose and chitosan;

the liquid phase coating agent is selected from one or more of heavy oil, liquid phenolic resin and liquid epoxy resin;

in the step a), the solvent is an alcohol solvent.

Images