CN114188533B - Negative electrode material and preparation method and application thereof - Google Patents

Abstract

The invention provides a negative electrode material, a preparation method and application thereof, wherein the preparation method comprises the following steps: (1) Carrying out gas corrosion and pore-forming treatment on a graphite raw material to obtain a porous graphite precursor; (2) Performing vapor deposition coating carbonization treatment on the porous graphite precursor obtained in the step (1) and a nitrogen-containing polymer to obtain nitrogen-doped porous graphite; (3) Mixing the nitrogen doped porous graphite obtained in the step (2), a silicon source and a liquid phase coating agent, and performing heating treatment to obtain the negative electrode material. The material has the characteristics of low expansion, high capacity, high compaction and high rate capability.

Description

A kind of negative electrode material and its preparation method and application

technical field

The invention belongs to the technical field of lithium ion batteries, and relates to a negative electrode material and a preparation method and application thereof.

Background technique

Fuel vehicle exhaust emissions cause air pollution, which is becoming more and more serious with the increase of the total number of motor vehicles. Countries that are highly concerned about environmental pollution have begun to vigorously improve the structure of energy use, reduce emissions and increase the development of green energy. With the rapid development of new energy vehicles, as the power source of electric vehicles, lithium-ion battery technology and market have developed greatly.

Lithium-ion batteries are widely used in the automotive industry due to their high energy density, self-discharge capability, and high charging efficiency. However, the long charging time and low mileage make electric vehicles unable to fully meet people's travel needs. Therefore, There is an urgent need for a battery that charges quickly and has a long range. Graphite is one of the main anode materials for lithium-ion batteries. In recent years, how to quickly realize the fast charging performance of graphite has become one of the research hotspots.

CN109935793A discloses a preparation method of a high-capacity high-rate composite graphene negative electrode material for a lithium-ion battery, which coats part of the graphene material on the graphite surface, thereby improving the material rate performance, but graphene is difficult to prepare, and the so-called "Graphene" is multi-layer graphite, which has poor consistency and cannot meet the conditions for mass production.

CN111392723A discloses a preparation method of porous graphite and its products and applications. It places graphite raw materials in corrosive gas for heat treatment to obtain porous graphite; the corrosive gas is selected from carbon dioxide, air or oxygen-containing atmosphere, but the graphite after corrosion The particle crystal structure is destroyed, and its material energy density has an irreversible effect.

CN109437153A discloses a high-current pulsed electron beam preparation method and application of mesoporous carbon. The high-current pulsed electron beam used in it makes holes in graphite, and also forms some voids in the graphite crystal to improve the material rate performance, but its The specific surface area of the material is increased, and its storage life is short.

The anode material prepared by the above scheme has the problems of poor consistency, poor energy density or short storage life. Therefore, it is very necessary to develop an anode material with good consistency, good energy density and long storage life.

Contents of the invention

The purpose of the present invention is to provide a negative electrode material and its preparation method and application. In the present invention, after corroding the graphite raw material to form pores, the vapor phase deposition method is used to repair the pores, and then chemical doping and silicon-based materials are used for coating. particles to obtain the negative electrode material. The material of the invention has low expansion, high capacity, high compaction and high rate performance.

To achieve this purpose of the invention, the present invention adopts the following technical solutions:

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

(1) The graphite raw material is subjected to gas corrosion and pore-forming treatment to obtain a porous graphite precursor;

(2) Carrying out vapor deposition coating carbonization treatment on the porous graphite precursor obtained in step (1) and the nitrogen-containing polymer, to obtain nitrogen-doped porous graphite;

(3) Mix the nitrogen-doped porous graphite obtained in step (2), the silicon source and the liquid-phase coating agent, and heat-treat to obtain the negative electrode material.

The present invention granulates the pores of the graphite raw material, provides lithium ion intercalation channels, and greatly improves the rate performance. At the same time, it adopts nitrogen doping and vapor deposition coating carbonization, which reduces the negative reaction caused by pores, and then uses silicon oxide composite Coating improves the energy density of the material. This patent can meet the energy density requirements of the battery for the material, and can also meet the rate performance of the battery, and ensure that the compacted density of the material is not affected.

Preferably, the graphite raw material in step (1) includes any one or a combination of at least two of petroleum coke, needle coke, pitch coke and flake graphite.

Preferably, the graphite raw material is subjected to shaping treatment before the pore-forming treatment.

Preferably, the particle size of the graphite raw material is 5-20 μm, for example: 5 μm, 8 μm, 10 μm, 15 μm or 20 μm.

Preferably, the method of pore-making treatment described in step (1) is:

Dissolve the pore-forming agent in deionized water, add the corroded graphite raw material, mix through a fusion machine, and perform high-temperature graphitization on the mixed graphite precursor.

The present invention carries out gas corrosion pore formation on graphite raw materials, adopts gas corrosion, the pore formation is uniform, and the material is easy to obtain. The gaps on the surface of the particles thus formed provide a channel for lithium ions to be embedded and extracted, and the pore-forming agent is used to carry out the internal pore formation of the particles. Longitudinal pore formation, penetrating from the surface layer to the deep layer, further increases the speed of lithium ion insertion and extraction.

Preferably, the mass ratio of the pore forming agent to the graphite raw material is 0.05˜0.2:1, for example: 0.05:1, 0.08:1, 0.1:1, 0.15:1 or 0.2:1, etc.

Preferably, the temperature of the high-temperature graphitization is 2600-3200°C, for example: 2600°C, 2700°C, 2800°C, 2900°C, 3000°C, 3100°C or 3200°C.

Preferably, the specific surface area of the porous graphite precursor is 5-20m ² /g, for example: 5m ² /g, 8m ² /g, 10m ² /g, 15m ² /g or 20m ² /g.

Preferably, the porosity of the porous graphite precursor is 10-20%, for example: 10%, 12%, 15%, 18% or 20%.

Preferably, the vapor-phase deposition-coated carbonization treatment method in step (2) is to mix the porous graphite precursor and the nitrogen-containing polymer, pass through the cladding gas, and obtain nitrogen-doped porous graphite through vapor-phase deposition.

In the invention, the pore is repaired by a gas phase deposition method, and the gas coating agent impregnates the inside of the particles to modify the pore structure, and the pore is an amorphous carbon structure.

Preferably, the nitrogen-containing polymer includes any one or a combination of at least two of melamine, polyacrylonitrile, polyurethane or polyaniline.

Preferably, the mass ratio of the nitrogen-containing polymer to the porous graphite precursor is 0.05˜0.3:1, for example: 0.05:1, 0.1:1, 0.15:1, 0.2:1 or 0.3:1, etc.

Preferably, the blanket gas includes any one or a combination of at least two of ethylene, acetylene or methane.

Preferably, the speed of introducing the covering gas is 100-1000mL/min, for example: 100mL/min, 200mL/min, 500mL/min, 800mL/min or 1000mL/min.

Preferably, the pore carbon residue value of the nitrogen-doped porous graphite is 0.5-5%, for example: 0.5%, 1%, 2%, 3%, 4% or 5%.

Preferably, the silicon source in step (3) includes spherical silicon oxide.

Preferably, the particle size of the spherical silicon oxide is 50-100 nm, for example: 50 nm, 60 nm, 70 nm, 80 nm, 90 nm or 100 nm.

Preferably, the liquid-phase coating agent includes any one or a combination of at least two of liquid asphalt, phenolic resin or heavy oil.

Preferably, the mass ratio of the nitrogen-doped porous graphite, the silicon source and the liquid-phase coating agent is 1:(0.005-0.1):(0.01-0.05), for example: 1:0.005:0.01, 1:0.01:0.002 , 1:0.05:0.003, 1:0.08:0.004 or 1:0.1:0.05 etc.

Preferably, the temperature of the heat treatment is 1000-1300°C, for example: 1000°C, 1100°C, 1200°C, 1250°C or 1300°C.

The present invention uses chemical doping and silicon-based materials for coating and granulation, modifies the surface of graphite materials, and adopts liquid phase coating and granulation to perfectly compound silicon and graphite, improve the energy density of materials, and utilize The characteristics of graphite porous structure can absorb the expansion of silicon negative electrode, thereby reducing the overall expansion of the material.

In a second aspect, the present invention provides a negative electrode material, which is prepared by the method described in the first aspect, the negative electrode material includes an inner core and a cladding layer, and the thickness of the cladding layer is 5-20 nm , for example: 5nm, 10nm, 15nm or 20nm, etc.

In the inner core of the negative electrode material of the present invention, porous graphite particles and nano-scale silicon oxide materials are bonded together, and the coating layer is a layer of dense and uniform amorphous carbon.

In a third aspect, the present invention provides a negative electrode sheet, the negative electrode sheet comprising the negative electrode material as described in the second aspect.

In a fourth aspect, the present invention provides a lithium-ion battery, which includes the negative electrode sheet as described in the third aspect.

Compared with the prior art, the present invention has the following beneficial effects:

(1) The present invention provides lithium ion intercalation channels through pore granulation of graphite raw materials, which greatly improves the rate performance. At the same time, nitrogen doping and vapor deposition coating carbonization are used to reduce the negative reactions caused by pores. Sub-silicon composite coating improves the energy density of the material.

(2) The specific surface area of the negative electrode material of the present invention can reach below 8.24m ² /g, the gram capacity can reach above 407.5mAh/g, and the initial efficiency can reach above 89.9%. It can reach more than 91.8%, and the capacity retention rate can reach more than 87.7% after 500 cycles of 3C/1C cycle at 25°C. Meet the high energy density requirements of materials. Electrochemical tests show that the 3C charging constant current ratio is as high as 96.4%, and it exhibits excellent cycle stability at high current density, and still maintains 92.3% capacity after 500 cycles.

Description of drawings

FIG. 1 is a schematic structural view of the negative electrode material described in Example 1 of the present invention.

Fig. 2 is a schematic structural view of nitrogen-doped and vapor-phase deposited-coated porous graphite according to Example 1 of the present invention.

Detailed ways

The technical solutions of the present invention will be further described below through specific embodiments. It should be clear to those skilled in the art that the examples are only for helping to understand the present invention, and should not be regarded as specific limitations on the present invention.

Example 1

This embodiment provides a negative electrode material, and the preparation method of the negative electrode material is as follows:

(1) After crushing the petroleum coke to 5 μm, carry out gas corrosion treatment, dissolve the pore-forming agent in deionized water, the mass ratio of the pore-forming agent and petroleum coke is 0.1:1, and add it to the corroded precursor, Fully mixed by a fusion machine, graphitized at 3000°C to obtain a porous graphite precursor with a specific surface area of 10m ² /g and a porosity of 15%;

(2) Mix the porous graphite precursor obtained in step (1) with melamine according to a mass ratio of 1:0.05, put it into a vapor deposition carbonization furnace, feed methane at a rate of 500mL/min, heat up and stir, and complete vapor deposition carbonization The process obtains nitrogen-doped porous graphite, and the structural schematic diagram of the nitrogen-doped porous graphite is shown in Figure 2;

(3) The nitrogen-doped porous graphite particle size obtained in step (2) is 100nm silicon oxide and liquid pitch are placed in a heating VC machine according to a mass ratio of 1:0.05:0.003, and sintered at 1200 ° C, A negative electrode material with a coating layer thickness of 15 nm was obtained, and a schematic structural diagram of the negative electrode material is shown in FIG. 1 .

Example 2

This embodiment provides a negative electrode material, and the preparation method of the negative electrode material is as follows:

(1) After the pitch coke is crushed to 20 μm, the gas corrosion treatment is carried out, and the pore-forming agent is dissolved in deionized water. The mass ratio of the pore-forming agent and the pitch coke is 0.2:1, and then added to the corroded precursor, Fully mixed by a fusion machine, graphitized at 2900°C to obtain a porous graphite precursor with a specific surface area of 12m ² /g and a porosity of 12%;

(2) Mix the porous graphite precursor obtained in step (1) with melamine according to a mass ratio of 1:0.3, put it into a vapor deposition carbonization furnace, feed methane at a rate of 100mL/min, heat up and stir, and complete vapor deposition carbonization process to obtain nitrogen-doped porous graphite;

(3) The nitrogen-doped porous graphite particle size obtained in step (2) is 100nm silicon oxide and liquid pitch are placed in a heating VC machine according to a mass ratio of 1:0.05:0.1, and sintered at 1200 ° C, A negative electrode material with a coating layer thickness of 12 nm was obtained.

Example 3

The only difference between this example and Example 1 is that the mass ratio of the pore-forming agent and the graphite raw material in step (1) is 0.03:1, and other conditions and parameters are exactly the same as those in Example 1.

Example 4

The only difference between this example and Example 1 is that the mass ratio of the pore-forming agent to the graphite raw material in step (1) is 0.25:1, and other conditions and parameters are exactly the same as those in Example 1.

Example 5

The only difference between this example and Example 1 is that the mass ratio of the nitrogen-containing polymer to the porous graphite precursor in step (2) is 0.03:1, and other conditions and parameters are exactly the same as those in Example 1.

Example 6

The only difference between this example and Example 1 is that the mass ratio of the nitrogen-containing polymer to the porous graphite precursor in step (2) is 0.35:1, and other conditions and parameters are exactly the same as those in Example 1.

Comparative example 1

The only difference between this comparative example and Example 1 is that no nitrogen-containing polymer is added, and other conditions and parameters are exactly the same as those of Example 1.

Comparative example 2

The only difference between this comparative example and Example 1 is that vapor deposition coating is not carried out, and other conditions and parameters are exactly the same as those of Example 1.

Comparative example 3

The only difference between this comparative example and Example 1 is that silicon oxide is not added, and other conditions and parameters are exactly the same as those of Example 1.

Performance Testing:

Get the negative electrode material that embodiment 1-6 and comparative example 1-3 obtain and conduction carbon black (SP), sodium carboxymethyl cellulose and styrene-butadiene rubber mix with the mass ratio of 96.2:1.0:1.3:1.5, obtain negative electrode The slurry is coated on the copper foil to obtain the negative electrode sheet, and lithium iron phosphate, conductive carbon black (SP), polyvinylidene fluoride and carbon nanotubes are mixed in a mass ratio of 96.:0.5:2:0.7 to obtain The positive electrode slurry is coated on the aluminum foil to obtain the positive electrode sheet;

Make the prepared positive and negative electrodes into a 505070 lithium iron phosphate soft pack battery, charge it to 3.65V with 3C current at 25°C, and record the charging capacity in the constant current section as C ₁ , and record the total charging capacity as C _2. The constant current ratio can be expressed as C ₁ /C ₂ *100%. 25°C 3C/1C cycle capacity retention rate specifically refers to, under the environment of 25°C, using 3C current, constant current and constant voltage charge to 3.65V, record the charging capacity in the first week as C3, and then use 1C current constant current to discharge to 2.5V V, cycle for 500 cycles, record the constant current discharge capacity at the 500th cycle as C4, and the capacity retention rate after 500 cycles of 3C/1C cycle at 25°C is expressed as C4/C3*100%. The test results are shown in Table 1:

Table 1

As can be seen from Table 1, it can be obtained from Examples 1-6 that the specific surface area of the negative electrode material of the present invention can reach below 8.24m ² /g, the gram capacity can reach above 407.5mAh/g, and the initial efficiency can reach 89.9%. Above, the constant current ratio of the battery at 25°C 3C charging can reach more than 91.8%, and the capacity retention rate of 25°C 3C/1C cycle for 500 cycles can reach more than 87.7%.

From the comparison of Example 1 and Examples 3-4, it can be obtained that the mass ratio of the pore-forming agent and the graphite raw material will affect the performance of the negative electrode material, and the mass ratio of the pore-forming agent and the graphite raw material is controlled at 0.05～ 0.2:1, the performance of the negative electrode material is better. If the amount of pore-forming agent added is too large, the specific surface area of the negative electrode material will be larger, and there will be more exposed defects. Larger contact area and more side reactions cause faster cycle attenuation. If the amount of pore-forming agent added is too small, the negative electrode material will have fewer pores. When charging at a high rate, lithium ions cannot be quickly inserted into the center of graphite particles. Can't be satisfied.

By comparing Example 1 and Examples 5-6, the mass ratio of the nitrogen-containing polymer and the porous graphite precursor can affect the performance of the negative electrode material, and the nitrogen-containing polymer and the porous graphite precursor The mass ratio is controlled at 0.05-0.3:1, and the performance of the obtained negative electrode material is better. If the addition amount of nitrogen-containing polymer is too large, more defects will be formed in the graphite crystal structure. On the one hand, these defects will become lithium storage units. , to increase the gram capacity of the material. On the other hand, more defect structures will intensify the side reaction with the electrolyte, causing faster cycle attenuation. If the amount of nitrogen-containing polymer added is too small, less defect structures will be formed, and the material gram The capacity and conductivity are slightly insufficient, and its energy density and rate performance are relatively poor.

From the comparison of Example 1 and Comparative Example 1, it can be seen that the present invention can significantly improve the rate performance of the material by nitrogen doping the negative electrode material.

From the comparison of Example 1 and Comparative Example 2, it can be obtained that the present invention coats the graphite pores by vapor deposition, which can reduce the specific surface area of the material, and after the pores are filled, the lithium storage positions increase, the gram capacity of the material increases, and the first-time efficiency increases. The material rate performance will also be greatly improved.

From the comparison of Example 1 and Comparative Example 3, it can be seen that the graphite material and silicon oxide material are combined in the present invention, and the gram capacity of the material is significantly increased, which can meet the energy density requirement.

The applicant declares that the above description is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto, and those skilled in the art should understand that any person skilled in the art should be aware of any disclosure in the present invention Within the technical scope, easily conceivable changes or substitutions all fall within the scope of protection and disclosure of the present invention.

Claims (17)

1. A method for preparing a negative electrode material, comprising the steps of:

(1) Carrying out gas corrosion and pore-forming treatment on a graphite raw material to obtain a porous graphite precursor;

(2) Performing vapor deposition coating carbonization treatment on the porous graphite precursor obtained in the step (1) and a nitrogen-containing polymer to obtain nitrogen-doped porous graphite;

(3) Mixing the nitrogen-doped porous graphite obtained in the step (2), a silicon source and a liquid-phase coating agent, and performing heating treatment to obtain the anode material;

the method of the vapor deposition coating carbonization treatment in the step (2) comprises the steps of mixing a porous graphite precursor and a nitrogen-containing polymer, introducing coating gas, and obtaining nitrogen-doped porous graphite through vapor deposition, wherein the nitrogen-containing polymer comprises any one or a combination of at least two of melamine, polyacrylonitrile, polyurethane and polyaniline, and the coating gas comprises any one or a combination of at least two of ethylene, acetylene and methane;

the liquid phase coating agent in the step (3) comprises any one or a combination of at least two of liquid asphalt, phenolic resin and heavy oil, the temperature of the heating treatment is 1000-1300 ℃, and the silicon source is spherical silicon oxide.

2. The method of claim 1, wherein the graphite material of step (1) comprises any one or a combination of at least two of petroleum coke, needle coke, pitch coke, and flake graphite.

3. The method of claim 1, wherein the graphite material is shaped prior to the pore-forming treatment.

4. The method according to claim 1, wherein the graphite raw material has a particle diameter of 5 to 20. Mu.m.

5. The method of claim 1, wherein the pore-forming treatment in step (1) comprises:

and dissolving the pore-forming agent in deionized water, adding the corroded graphite raw material, mixing by a fusion machine, and graphitizing the mixed graphite precursor at a high temperature.

6. The method according to claim 5, wherein the mass ratio of the pore-forming agent to the graphite raw material is 0.05-0.2:1.

7. The method of claim 5, wherein the high temperature graphitization is at a temperature of 2600 ℃ to 3200 ℃.

8. The method according to claim 1, wherein the porous graphite precursor has a specific surface area of 5 to 20m ² /g。

9. The method of claim 1, wherein the porous graphite precursor has a porosity of 10 to 20%.

10. The method of claim 1, wherein the mass ratio of the nitrogen-containing polymer to the porous graphite precursor is 0.05-0.3:1.

11. The method according to claim 1, wherein the velocity of the introducing the coating gas is 100 to 1000mL/min.

12. The method of claim 1, wherein the nitrogen-doped porous graphite has a pore carbon residue value of 0.5 to 5%.

13. The method according to claim 1, wherein the spherical silica has a particle diameter of 50 to 100nm.

14. The preparation method according to claim 1, wherein the mass ratio of the nitrogen-doped porous graphite, the silicon source and the liquid-phase cladding agent is 1 (0.005-0.1): 0.01-0.05.

15. A negative electrode material, characterized in that it is produced by the method according to any one of claims 1 to 14, comprising a core and a coating layer, the thickness of the coating layer being 5 to 20nm.

16. A negative electrode tab comprising the negative electrode material of claim 15.

17. A lithium ion battery comprising the negative electrode tab of claim 16.

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