CN110828811A - Silicon oxide-graphite composite negative electrode material for lithium ion battery and preparation method thereof - Google Patents

Abstract

The invention discloses a spherical silicon oxide-graphite composite negative electrode material for a lithium ion battery and a preparation method thereof. The synthesis process is simple, the process conditions are easy to control, and industrialization is easy to realize; the prepared spherical silicon oxide-graphite composite negative electrode material has good circulation and small expansion coefficient, and can be used as a negative electrode material of a new generation lithium ion power battery.

Description

A kind of silicon oxide-graphite composite negative electrode material for lithium ion battery and its preparation method

technical field

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

Background technique

The theoretical capacity of graphite anode material is 372mAh/g, which can no longer meet the high energy density requirements of new lithium-ion batteries. Therefore, it is crucial to develop new anode materials for high-capacity lithium-ion batteries.

At present, the main technical way to improve the energy density of batteries at home and abroad is to use silicon carbon anode materials to replace traditional graphite anode materials. Silicon-based materials have the highest theoretical specific capacity (4200mAh/g) in lithium-ion battery anode materials, and are currently the best choice for high-energy density lithium-ion battery anode materials.

However, there is a problem of excessive volume expansion (≥300%) in the process of lithium intercalation of pure silicon materials. The oxide of silicon also has a higher theoretical specific capacity, and compared with pure silicon, the oxide of silicon has a smaller volume effect in the process of lithium intercalation. There is a Si-O bond with a higher bond energy in the material, which can effectively The volume expansion of silicon is suppressed, so the cycle performance is more advantageous.

However, Li ₂ O and Li ₄ SiO ₄ will be formed in Si oxide during the lithium intercalation process. These inactive phases can well buffer the volume expansion of the material, but the generated inactive phases also consume part of the lithium. Silicon materials also have the problem of low first efficiency. At present, the main methods to improve the electrochemical performance of SiO2 include nano-sized particles, composite with various carbon materials, composite with metals and metal oxides, pre-lithiation and coating modification.

Coating modification is the most common modification method at present. Prior art CN103647056B discloses a _SiOx -based composite negative electrode material, a preparation method and a battery, the negative electrode material comprises a silicon oxide material, a carbon material and an amorphous carbon coating layer, and the silicon oxide material is wrapped on the surface of the carbon material particles, and the The crystalline carbon coating layer is the outermost coating layer, and in this invention, the silicon oxide material is wrapped on the surface of the carbon material particles.

However, in the existing coating modified materials, the outermost coating layer has a very limited effect on inhibiting the expansion of the silicon oxide particles, and the coating layer is easily peeled off from the particle surface after several charge-discharge cycles, resulting in the material The cycle performance is very poor, and does not essentially solve the problem of siliceous oxide materials. Therefore, it is a technical problem in the art to develop a silicon oxide-based negative electrode material with good cycle performance and small volume expansion effect and a preparation method thereof.

SUMMARY OF THE INVENTION

In order to solve the above technical problems, the present invention provides a silicon oxide-graphite composite negative electrode material for lithium ion batteries and a preparation method thereof.

The technical scheme adopted in the present invention is:

A silicon oxide-graphite composite negative electrode material, the silicon oxide-graphite composite negative electrode material is an integrated fusion material, which is formed by the joint fusion of a silicon oxide matrix, a graphite matrix and amorphous carbon, and the silicon oxide- The D50 of the graphite composite negative electrode material is 10-30 μm.

Preferably, the silicon oxide matrix is nanometer or submicron silicon oxide particles, the chemical formula is SiO _x , where 0.8≤x≤1.2, and the particle size is 0.05-1 μm; the particle size of the graphite matrix is 0.1-3 μm .

The size of the matrix has an important influence on the structure and electrochemical performance of the composite material: if the size of the SiO2 matrix particles is too large, the particles will be seriously pulverized during the charge and discharge process; if the SiO2 matrix particles are too small, the specific surface will be larger and the electrolyte will be adversely affected. More reactions affect the cycle performance. The particle size of graphite matrix is too large, and it is difficult to form an integrated fusion material with silicon oxide during the spraying process, but a core-shell structure with large particles of graphite as the core and small particles of silicon oxide as the shell is formed, which cannot effectively inhibit the The expansion and shrinkage of silicon during the charging and discharging process is pulverized; if the graphite matrix is too small, the occurrence of side reactions will also increase. Therefore, choosing the appropriate particle size is the basis for the material to have good properties. The particle size of the material selected in the present invention can be effectively fused to form an integrated silicon oxide-graphite composite negative electrode material.

Preferably, the mass fraction of silicon oxide matrix in the silicon oxide-graphite composite negative electrode material is 5% to 90%, the mass fraction of graphite matrix is 10% to 95%, and the mass fraction of amorphous carbon is 1% to 90%. 10%.

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

1) Mixing the siliceous oxide matrix with absolute ethanol uniformly and carrying out ball milling treatment until the median particle size is 0.05-1 μm, to obtain a siliceous oxide slurry 1, and the siliceous oxide matrix is nanometer or submicron _SiOx particles, where 0.8≤x≤1.2,

2) uniformly mixing the graphite matrix raw material with absolute ethanol, and performing ball milling until the median particle size is 0.1-3 μm to obtain graphite slurry 2;

3) Silica slurry 1, graphite slurry 2, pitch, aluminum isopropoxide and other organic carbon sources are ball-milled and mixed in a ball-milling tank for 0.5-10 hours to obtain slurry 3;

4) spray-drying slurry 3, and the spray-drying inlet temperature is 100°C to 300°C to obtain powder 1;

5) Under an inert atmosphere, the powder 1 is raised to 700°C to 1100°C at a heating rate of 1°C to 10°C/min, and heat treated at a constant temperature for 1 to 24 hours to obtain a silicon oxide-graphite composite negative electrode material product.

Silica and by-product silicon oxide will generate Li ₂ O and Li ₄ SiO ₄ during the lithium intercalation process. These inactive phases can well buffer the volume expansion of materials, but these inactive phases also consume part of the lithium. , resulting in the problem of low initial efficiency of silicon oxide materials.

The aluminum isopropoxide added in the present invention can consume the by-product SiO ₂ generated by the oxidation of SiO _x , convert SiO ₂ into silicate that does not consume lithium, reduce the irreversible capacity loss caused by silicon oxide, and improve the performance of the material. first efficiency.

Preferably, in the step 3), the mass of the aluminum isopropoxide is 0.1-2% of the mass of the silicon oxide matrix.

The content of aluminum isopropoxide is too small to completely react with SiO to achieve the purpose of removing by-products _{; the content of aluminum isopropoxide is too high, and inert Al 2 O impurities} are introduced into the product. Therefore, isopropanol The aluminum content is one of the key factors for the present invention. Through experiments, it is found that when the mass of aluminum isopropoxide is 0.1-2% of the mass of the siliceous oxide matrix, aluminum isopropoxide can just completely react the SiO ₂ produced by the oxidation of SiO _x , and the effect of removing by-products is better. Thereby, the first efficiency of the silicon oxide material is effectively improved.

Preferably, the pitch in the step 3) is one or both of coal pitch or petroleum pitch.

Preferably, the mass of the pitch in the step 3) is 5% to 15% of the total mass of the silicon oxide matrix and the graphite matrix.

The pitch plays a role in fusion bonding in the present invention, so a certain content is required to bond the siliceous oxide matrix and the graphite matrix together; but if the pitch is too high, the carbon generated by the high-temperature carbonization of the pitch is amorphous carbon, Excess amorphous carbon also consumes lithium in the electrolyte, which in turn affects the performance of the material. 5% to 15% is a more suitable content.

Preferably, other organic carbon sources in the step 3) are one or more of glucose, sucrose, polyethylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, and phenolic resin.

Preferably, the mass of other organic carbon sources in the step 3) is 1% to 10% of the total mass of the silicon oxide matrix and the graphite matrix.

The above silicon oxide-graphite composite negative electrode material and the silicon oxide-graphite composite negative electrode material prepared by the above preparation method can be well used in lithium ion batteries.

The beneficial effects of the present invention are:

1) The present invention fundamentally overcomes the defect of low initial effect of silicon oxide, and the aluminum isopropoxide added in the melting process can consume the by-product SiO ₂ generated by SiO _x oxidation, so that SiO ₂ is converted into silicon that does not consume lithium. acid salt, which reduces the irreversible capacity loss caused by silicon oxide, and essentially improves the first efficiency of the material;

2) Compared with the prior art, the present invention obtains a spherical silicon oxide-graphite composite material through the ball milling process, spray drying process and high temperature carbonization process which are easy to realize industrialization: the material first ball-mills the silicon oxide raw material It is formed into sub-micron particles, which greatly shortens the transmission distance of lithium ions inside SiO _x particles, and has great advantages in cycling compared with micron-sized silicon oxide;

3) Different from the traditional carbon layer covering the outer layer, the present invention first grinds the graphite balls into micron-sized particles, and utilizes the fusion bonding effect of pitch and other organic carbon sources under low-temperature heating conditions, and utilizes the instant drying of spray drying. (limiting the segregation phenomenon to the micrometer scale) and spheroidization, the siliceous oxide particles and flake graphite are fused together, and finally a spherical-like siliceous oxide-graphite composite material is obtained through high temperature disproportionation reaction and carbonization treatment.

The advantage of this quasi-spherical SiO2-graphite composite material is that SiO2 and flake graphite are fused together instead of coating the surface of SiO2 on the surface of graphite particles, which can effectively suppress the volume of SiO2 during charging and discharging. Swelling, preventing particle pulverization and maintaining the integrity of the original structure, thereby increasing the cycle life of the material.

Description of drawings

Fig. 1 is a scanning electron microscope photograph of the silicon oxide-graphite composite negative electrode material prepared in Comparative Example 1;

2 is a scanning electron microscope photograph of the silicon oxide-graphite composite negative electrode material prepared in Example 1;

3 is a first charge-discharge curve diagram of the silicon oxide-graphite composite negative electrode material prepared in Example 1;

FIG. 4 is a cycle performance diagram of the silicon oxide-graphite composite negative electrode material prepared in Example 1. FIG.

Detailed ways

The technical solutions of the present invention will be described in detail below with reference to the accompanying drawings and embodiments.

Example 1

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

1) Mix 120g of silicon oxide raw materials with 1kg of absolute ethanol and perform ball milling, and ball mill to a median particle size of 0.5um to obtain silicon oxide slurry 1;

2) 1kg of natural graphite raw material and 2kg of dehydrated alcohol are uniformly mixed and ball-milled, and ball-milled to a median particle size of 1.5um to obtain graphite slurry 2;

3) Silica slurry 1, graphite slurry 2, 100g medium-temperature coal tar pitch, 20g polyvinylpyrrolidone, 1g aluminum isopropoxide were ball-milled and mixed in a ball-milling tank for 4h;

4) spray drying the slurry with an inlet temperature of 150°C to obtain powder 1;

5) Raising the powder 1 to 980°C at a heating rate of 2°C/min under a nitrogen atmosphere, and heat treatment at a constant temperature for 2 hours, to obtain the spherical silica-graphite composite negative electrode material.

Comparative Example 1

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

1) Mix 120g of silicon oxide raw materials with 1kg of absolute ethanol and perform ball milling, and ball mill to a median particle size of 0.5um to obtain silicon oxide slurry 1;

2) Silica slurry 1, 1kg of natural graphite raw material with a median particle size of 12um, 100g of medium-temperature coal tar pitch, 20g of polyvinylpyrrolidone, 1g of aluminum isopropoxide and 2kg of absolute ethanol were ball-milled and mixed in a ball-milling tank for 4h;

3) spray-drying the slurry with an inlet temperature of 150° C. to obtain powder 1;

4) The powder 1 is raised to 980°C at a heating rate of 2°C/min under a nitrogen atmosphere, and heat treated at a constant temperature for 2 hours to obtain a silicon oxide-graphite composite negative electrode material.

Comparative Example 2

Compared with embodiment 1, step 3) is changed into:

3) Ball milling and mixing 100 g of medium-temperature coal tar pitch and 20 g of polyvinylpyrrolidone in a ball-milling tank for 4h;

Other step parameters remain unchanged.

Comparative Example 3

Compared with embodiment 1, step 3) is changed into:

3) Silica slurry 1, graphite slurry 2, 100g medium-temperature coal tar pitch, 20g polyvinylpyrrolidone, 0.08g aluminum isopropoxide were ball-milled and mixed in a ball-milling tank for 4h;

Other step parameters remain unchanged.

Comparative Example 4

Compared with embodiment 1, step 3) is changed into:

3) Ball milling and mixing 100 g of medium-temperature coal tar pitch, 20 g of polyvinylpyrrolidone, and 3 g of aluminum isopropoxide in a ball milling tank for 4 hours;

Other step parameters remain unchanged.

Example 2

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

1) Mix 90g of silicon oxide raw material with 1kg of absolute ethanol and carry out ball milling, and ball mill to a median particle size of 0.5um to obtain silicon oxide slurry 1;

2) 1kg of natural graphite raw material and 2kg of dehydrated alcohol are uniformly mixed and ball-milled, and ball-milled to a median particle size of 1.5um to obtain graphite slurry 2;

3) Ball milling and mixing SiO2 slurry 1, graphite slurry 2, 95g medium-temperature coal tar pitch, 20g polyvinylpyrrolidone, and 0.9g aluminum isopropoxide in a ball mill for 4h;

4) spray drying the slurry with an inlet temperature of 150°C to obtain powder 1;

5) Put the powder material 1 into an appropriate amount of anhydrous ethanol solution for washing, then pour out the ethanol solution, replace it with a new absolute ethanol solution and wash it again, repeat three times, and then obtain the powder material after filtering and drying. 2;

6) Raising the powder 3 to 980°C at a heating rate of 2°C/min under a nitrogen atmosphere, and heat treatment at a constant temperature for 2 hours, to obtain the spherical silica-graphite composite negative electrode material.

Example 3

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

1) Mix 120g of silicon oxide raw materials with 1kg of absolute ethanol and perform ball milling, and ball mill to a median particle size of 0.5um to obtain silicon oxide slurry 1;

2) 1kg of natural graphite raw material and 2kg of dehydrated alcohol are uniformly mixed and ball-milled, and ball-milled to a median particle size of 1.5um to obtain graphite slurry 2;

3) Silica slurry 1, graphite slurry 2, 100g medium-temperature coal tar pitch, 20g polyethylene glycol 2000, 1g aluminum isopropoxide were ball-milled and mixed in a ball-milling tank for 4h;

4) spray drying the slurry with an inlet temperature of 150°C to obtain powder 1;

5) Put the powder material 1 into an appropriate amount of anhydrous ethanol solution for washing, then pour out the ethanol solution, replace it with a new absolute ethanol solution and wash it again, repeat three times, and then obtain the powder material after filtering and drying. 2;

6) Raising the powder 2 to 980°C at a heating rate of 2°C/min under a nitrogen atmosphere, and thermally treating it at a constant temperature for 2 hours to obtain the spherical silicon oxide-graphite composite negative electrode material.

Example 4

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

1) Mix 170g of silicon oxide raw materials with 1kg of absolute ethanol and perform ball milling to obtain a silicon oxide slurry 1;

2) 1kg of natural graphite raw material and 2kg of dehydrated alcohol are uniformly mixed and ball-milled, and ball-milled to a median particle size of 1.5um to obtain graphite slurry 2;

3) Ball milling and mixing 105g medium-temperature coal tar pitch, 20g polyvinylpyrrolidone, and 1.2g aluminum isopropoxide in a ball mill tank for 4h;

4) spray drying the slurry with an inlet temperature of 180°C to obtain powder 1;

5) Put the powder material 1 into an appropriate amount of anhydrous ethanol solution for washing, then pour out the ethanol solution, replace it with a new absolute ethanol solution and wash it again, repeat three times, and then obtain the powder material after filtering and drying. 2;

6) Raising the powder 2 to 1000°C at a heating rate of 2°C/min in a nitrogen atmosphere, and heat treatment at a constant temperature for 2 hours to obtain the spherical silicon oxide-graphite composite negative electrode material.

Example 5

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

1) Mix 120g of silicon oxide raw materials with 1kg of absolute ethanol and perform ball milling, and ball mill to a median particle size of 0.5um to obtain silicon oxide slurry 1;

2) 1kg of natural graphite raw material and 2kg of dehydrated alcohol are uniformly mixed and ball-milled, and ball-milled to a median particle size of 1.5um to obtain graphite slurry 2;

3) Silica slurry 1, graphite slurry 2, 100g medium-temperature coal tar pitch, 20g polyvinyl alcohol, and 1g aluminum isopropoxide were ball-milled and mixed in a ball-milling tank for 4h;

4) spray drying the slurry with an inlet temperature of 150°C to obtain powder 1;

5) Put the powder material 1 into an appropriate amount of anhydrous ethanol solution for washing, then pour out the ethanol solution, replace it with a new absolute ethanol solution and wash it again, repeat three times, and then obtain the powder material after filtering and drying. 2;

6) Raising the powder 2 to 980°C at a heating rate of 2°C/min under a nitrogen atmosphere, and thermally treating it at a constant temperature for 2 hours to obtain the spherical silicon oxide-graphite composite negative electrode material.

Experimental situation:

The electrochemical performance test results of the composite negative electrode materials prepared in Examples 1-5 and Comparative Examples 1-4 are shown in Table 1. The test conditions of the button battery are: 23℃±2℃, LR2032, first charge and discharge I=0.1C, cycle I=0.2C, 0.005～2.0V vs. Li/Li ⁺ .

Table 1 Product electrochemical performance test results

It can be seen from the above comparative data that the electrochemical properties such as the first coulombic efficiency and cycle stability of the spherical silicon oxide-graphite composite negative electrode materials prepared in Examples 1 to 5 of the present invention are better than those of the negative electrode materials in the comparative examples. , especially the cycle performance, thanks to the excellent structure of the graphite-silicon oxide composite: the effective fusion of amorphous carbon and small particles of micron-scale graphite and silicon oxide particles plays a role of confinement, thereby effectively The expansion and pulverization of silicon oxide during charging and discharging are suppressed, and there is no problem of falling off of the coating carbon layer in the traditional technology.

Figures 3 and 4 show the first charge-discharge curve and cycle performance of the silicon oxide-graphite composite negative electrode material prepared in Example 1. It can be seen that the material prepared in Example 1 has a first reversible specific capacity of 469.7mAh/ g, the 100-cycle capacity retention rate can reach 98.2%, showing excellent electrochemical performance.

In Comparative Example 1, the graphite was not pre-milled into small particles. Therefore, the spray-dried spheres were silicon oxide particles attached to the surface of large graphite particles. Figure 1 is the SEM image of the material prepared in Comparative Example 1. This structure cannot effectively inhibit the expansion, shrinkage and pulverization of silicon oxide during the charging and discharging process, so the performance is obviously lower than that of the ball-milled Example 1.

Comparative example 2 does not add aluminum isopropoxide, so it cannot consume the by-product SiO ₂ produced during the material synthesis process. The SiO ₂ by-product will also insert lithium and consume the lithium source during the first charge and discharge process, resulting in a decrease in the first efficiency, thus affecting The first effect of Comparative Example 2 was obtained.

The addition amount of aluminum isopropoxide has a great influence on the properties of the product. The amount of aluminum isopropoxide added in comparative example 3 is less, resulting in incomplete reaction to consume by-product SiO ₂ , while the amount of aluminum isopropoxide added in comparative example 4 is more, and more Al ₂ O ₃ inert secondary Therefore, the addition amount of aluminum isopropoxide has a great influence on the properties of the material.

Fig. 1 is the SEM photo of the silicon oxide-graphite composite negative electrode material prepared in Comparative Example 1; Fig. 2 is the SEM photo of the silicon oxide-graphite composite negative electrode material prepared in Example 1; The graphite in the ratio 1 has not been ball-milled into small particles in the early stage. Therefore, an obvious core-shell structure will be formed after the spray drying process. This structure cannot embed the silicon oxide particles in the graphite spheres and cannot effectively inhibit the oxidation. The expansion and shrinkage of silicon dioxide is pulverized, while in Example 1, the primary particle size is reduced by ball milling of graphite, and the gap with the silicon oxide particle size is narrowed, so that the core-shell structure will not be formed during the spray drying process, but the second particle size is reduced. The structure of embedding silicon oxide in graphite can effectively inhibit the expansion and contraction of silicon oxide during the charging and discharging process, thereby effectively improving the cycle performance.

To sum up, the content of the present invention is not limited to the above-mentioned embodiments. Persons of insight in the same field can easily propose other embodiments within the technical guidance of the present invention. All are included in the scope of the present invention.

Claims (10)

1. A silicon oxide-graphite composite negative electrode material is characterized in that: the silicon oxide-graphite composite negative electrode material is an integrated fusion material and is formed by fusing a silicon oxide matrix, a graphite matrix and amorphous carbon together, and the D50 of the silicon oxide-graphite composite negative electrode material is 10-30 mu m.

2. The silica-graphite composite anode material according to claim 1, characterized in that: the silicon monoxide matrix is nano or submicron silicon monoxide particles with a chemical formula of SiO_xWherein x is more than or equal to 0.8 and less than or equal to 1.2, and the particle size is 0.05-1 mu m; of the graphite matrixThe particle size of the particles is 0.1-3 μm.

3. The silica-graphite composite anode material according to claim 1, characterized in that: in the silicon oxide-graphite composite negative electrode material, the mass fraction of a silicon oxide matrix is 5-90%, the mass fraction of a graphite matrix is 10-95%, and the mass fraction of amorphous carbon is 1-10%.

4. A preparation method of a silicon oxide-graphite composite negative electrode material is characterized by comprising the following steps:

1) uniformly mixing a silica matrix and absolute ethyl alcohol, and performing ball milling treatment until the median particle size is 0.05-1 mu m to obtain silica slurry 1, wherein the silica matrix is nano or submicron SiO_xParticles, wherein x is more than or equal to 0.8 and less than or equal to 1.2;

2) uniformly mixing a graphite matrix and absolute ethyl alcohol, and performing ball milling treatment until the median particle size is 0.1-3 mu m to obtain graphite slurry 2;

3) carrying out ball milling and mixing on the silicon monoxide slurry 1, the graphite slurry 2, the asphalt, the aluminum isopropoxide and other organic carbon sources in a ball milling tank for 0.5-10 h to obtain a slurry 3;

4) spray drying the slurry 3 at an inlet temperature of 100-300 ℃ to obtain powder 1;

5) and (3) raising the temperature of the powder 1 to 700-1100 ℃ at a heating rate of 1-10 ℃/min in an inert atmosphere, and carrying out constant-temperature heat treatment for 1-24 h to obtain a product of the silicon oxide-graphite composite negative electrode material.

5. The method of claim 4, wherein: in the step 3), the mass fraction of the silica matrix is 5-90% and the mass fraction of the graphite matrix is 10-95% based on the total mass of the silica matrix and the graphite matrix.

6. The method of claim 4, wherein: in the step 3), the mass of the aluminum isopropoxide is 0.1-2% of that of the silica matrix.

7. The method of claim 4, wherein: the asphalt in the step 3) is one or two of coal asphalt or petroleum asphalt.

8. The method of claim 4, wherein: the mass of the asphalt in the step 3) is 5-15% of the total mass of the silica matrix and the graphite matrix.

9. The method of claim 4, wherein: and in the step 3), other organic carbon sources are one or more of glucose, sucrose, polyethylene glycol, polyvinyl alcohol, polyvinylpyrrolidone and phenolic resin.

10. The method of claim 4, wherein: the mass of other organic carbon sources in the step 3) is 1-10% of the total mass of the silica matrix and the graphite matrix.

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