CN116314638A

CN116314638A - Composite negative electrode material, preparation method thereof and lithium ion battery

Info

Publication number: CN116314638A
Application number: CN202211091136.9A
Authority: CN
Inventors: 杨程; 刘若琦; 黄健; 杨书展; 任建国; 贺雪琴
Original assignee: BTR New Material Group Co Ltd
Current assignee: BTR New Material Group Co Ltd
Priority date: 2022-09-07
Filing date: 2022-09-07
Publication date: 2023-06-23

Abstract

The application provides a composite anode material, a preparation method thereof and a lithium ion battery, wherein the composite anode material comprises a graphite core, a connecting layer positioned on the surface of the graphite core and a carbon layer positioned on the surface of the connecting layer, the connecting layer comprises amorphous carbon containing doping elements, and the carbon layer comprises amorphous carbon containing doping elements; the connecting layer of the composite anode material has at least one chemical bond of C-N, C-P, C-B, C-F, C-O and C-S as measured by X-ray photoelectron spectroscopy XPS; the mass content of the doping element in the connecting layer is P1, and the mass content of the doping element in the carbon layer is P2, wherein P1 is more than P2. The composite anode material and the preparation method thereof can give consideration to high capacity, high initial efficiency, excellent multiplying power performance and low temperature performance.

Description

Composite negative electrode material, preparation method thereof and lithium ion battery

Technical Field

The application relates to the technical field of negative electrode materials, in particular to a composite negative electrode material, a preparation method thereof and a lithium ion battery.

Background

Graphite is one of the main raw materials of lithium ion batteries, has the advantages of high capacity, high compaction, environmental friendliness, low price and the like, and is widely applied to the fields of 3C, electric tools and the like. Carbon-coated graphite has become the main negative electrode material of fast-charging lithium ion batteries, mainly because the amorphous carbon coating layer has a larger interlayer spacing than graphite and more surface defects, and promotes lithium ion diffusion. However, in recent years, there is a higher demand for lithium ion batteries in the market, and not only is a high capacity and high initial efficiency of the carbon-coated graphite negative electrode material required, but also excellent rate performance and low temperature performance are required.

The traditional carbon-coated graphite generally adopts solid asphalt as a coating material, and the rate performance and the low-temperature performance are improved by optimizing a coating method and a coating amount. Increasing the amount of asphalt coating generally improves the rate capability and low temperature capability, but excessively increasing the amount of asphalt coating significantly reduces the capacity and initial efficiency of the graphite anode material. Therefore, the carbon-coated graphite is prepared by a method of increasing the asphalt coating amount, and the carbon-coated graphite anode material is difficult to realize that the high capacity, the high initial efficiency, the excellent rate capability and the low-temperature capability are simultaneously achieved, so that the higher requirements of the market on lithium ion batteries are difficult to meet.

Therefore, how to make the composite negative electrode material have high capacity, high initial efficiency, excellent rate performance and low temperature performance, which is a problem to be solved at present.

Disclosure of Invention

In view of the above, the application provides a composite anode material, a preparation method thereof and a lithium ion battery, which can achieve high capacity, high initial efficiency, excellent rate performance and low temperature performance.

In a first aspect, the present application provides a composite anode material, the composite anode material including a graphite core, a connection layer located on a surface of the graphite core, and a carbon layer located on a surface of the connection layer, the connection layer including amorphous carbon containing a doping element, the carbon layer including amorphous carbon containing a doping element; the connecting layer of the composite anode material has at least one chemical bond of C-N, C-P, C-B, C-F, C-O and C-S as measured by X-ray photoelectron spectroscopy XPS; and the mass content of the doping element in the connection layer is greater than the mass content of the doping element in the carbon layer.

In some embodiments, the graphite comprises at least one of artificial graphite and natural graphite.

In some embodiments, the graphite has a median particle size of from 5 μm to 20 μm.

In some embodiments, the tie layer has a thickness of 0.01 μm to 1 μm.

In some embodiments, the carbon layer has a thickness of 0.01 μm to 1 μm.

In some embodiments, the doping elements in the connection layer and the carbon layer include at least one of N, P, B, F, O and S.

In some embodiments, the mass content of the doping element in the connection layer is P1,1% < P1 ∈10%.

In some embodiments, the mass content of the doping element in the carbon layer is P2,0% < P2 ∈1%.

In some embodiments, the composite anode material is measured at 1200cm by raman spectroscopy testing ^-1 ～1500cm ^-1 Peak area at I _D And at 1500cm ^-1 ～1800cm ^-1 Peak area at I _G Ratio I of (2) _D /I _G 0.5 to 3.0.

In some embodiments, the composite anode material is coated uniformly with C, 0.50.ltoreq.C.ltoreq.1.50.

In some embodiments, the composite anode material has a median particle size of from 5 μm to 22 μm.

In some embodiments, the composite anode material has a specific surface area of 0.2m ² /g～10m ² /g。

In some embodiments, the composite anode material has a tap density of 0.6g/cm ³ ～1.4g/cm ³ 。

In some embodiments, the composite anode material has a compacted density of 1.6g/cm at 5T pressure ³ ～2.2g/cm ³ 。

In some embodiments, the amorphous carbon content of the composite anode material is 0.1% -10% by mass.

In a second aspect, the present application provides a method for preparing a composite anode material, the method comprising the steps of:

placing a mixture containing graphite, a liquid coating agent and a doping agent in a heat treatment at 150-300 ℃ to obtain a precursor;

and carbonizing the mixture containing the precursor and asphalt to obtain the composite anode material.

In some embodiments, the carbon element content of the graphite is greater than or equal to 95% by mass.

In some embodiments, the liquid coating agent comprises at least one of a liquid asphalt and a liquid rubber plasticizer;

in some embodiments, the liquid coating agent comprises a liquid asphalt comprising at least one of petroleum-based liquid asphalt and coal-based liquid asphalt.

In some embodiments, the liquid coating agent includes a liquid rubber plasticizer including at least one of a petroleum-based plasticizer, a coal tar-based plasticizer, a pine-based plasticizer, a fat-based plasticizer, and a synthetic plasticizer.

In some embodiments, the dopant comprises at least one of urea, melamine phosphate, ammonium dihydrogen phosphate, boron oxide, ammonium borate, polyvinylidene fluoride, ammonium bifluoride, ammonium sulfate, ammonium bisulfate, and thiourea.

In some embodiments, the mass ratio of the graphite, the liquid capping agent, and the dopant is 100: (10-100): (5-50).

In some embodiments, the bitumen comprises at least one of petroleum-based bitumen and coal-based bitumen.

In some embodiments, the mass ratio of graphite to pitch is 100: (1-10).

In some embodiments, the heat treatment is performed under at least one atmosphere of air and a protective gas.

In some embodiments, the protective atmosphere comprises at least one of nitrogen, helium, neon, argon, krypton, and xenon.

In some embodiments, the heat treatment has a ramp rate of 0.5 ℃/min to 5.0 ℃/min.

In some embodiments, the heat treatment is performed for a holding time of 0.5h to 10h.

In some embodiments, the carbonization treatment is performed under a protective atmosphere.

In some embodiments, the carbonization treatment is performed under a protective atmosphere comprising at least one of nitrogen, helium, neon, argon, krypton, and xenon.

In some embodiments, the carbonization treatment is at a temperature of 600 ℃ to 1500 ℃.

In some embodiments, the carbonization treatment has a heating rate of 0.5 ℃/min to 5.0 ℃/min.

In some embodiments, the carbonization treatment is maintained for a period of time ranging from 0.5h to 10h.

In some embodiments, the method of making further comprises: and shaping the natural crystalline flake graphite to obtain spherical graphite.

In some embodiments, the shaping comprises at least one of crushing, spheroidizing, and classifying.

In a third aspect, the present application provides a lithium ion battery comprising the composite anode material according to the first aspect or the composite anode material produced according to the production method of the second aspect.

The technical scheme of the application has the following beneficial effects:

In the composite anode material provided by the application, the composite anode material comprises a graphite core, a connecting layer positioned on the surface of the graphite core and a carbon layer positioned on at least part of the surface of the connecting layer, wherein the connecting layer and the carbon layer both comprise amorphous carbon containing doping elements; the connecting layer of the composite anode material is provided with at least one chemical bond of C-N, C-P, C-B, C-F, C-O and C-S, and doping elements in the connecting layer can increase lithium storage active sites and improve the migration speed of lithium ions; at least one chemical bond of C-N, C-P, C-B, C-F, C-O and C-S formed on the interface of the connecting layer and the carbon layer has strong polarity, and can promote the surface of the connecting layer to form a carbon layer with good uniformity, and effectively improve the uniformity of the carbon layer, thereby improving the rate performance and low-temperature performance of the composite anode material. The carbon layer uniformly coats the connecting layer, so that the consumption of electrolyte caused by defects formed by doping elements in the connecting layer can be effectively inhibited, and the high capacity and first effect of the composite anode material are ensured. In combination, the composite anode material can achieve high capacity, high initial efficiency, excellent multiplying power performance and low temperature performance.

In the preparation method of the composite anode material, the mixture containing graphite, the liquid coating agent and the doping agent is subjected to heat treatment and then mixed with asphalt to be subjected to carbonization treatment. During carbonization, the dopant decomposes to produce H ₂ O、CO ₂ The isogas is discharged, and element doping is carried out in the connecting layer, so that lithium storage active sites can be increased, and the migration speed of lithium ions can be improved; at least one chemical bond of C-N, C-P, C-B, C-F, C-O and C-S formed on the connecting layer, wherein the chemical bond has strong polarity, can react with asphalt to prevent asphalt from self-polymerization, thereby forming a carbon layer with good uniformity on the surface of the connecting layer, and improving the connecting layer and carbonThe connection strength of the layers can improve the rate performance and the low-temperature performance of the composite anode material. The carbon layer uniformly coats the connecting layer, and in the carbonization process, a small amount of doping elements in the doping agent in the connecting layer can be doped into the carbon layer at the outer side, so that the content of the doping elements in the carbon layer is obviously less than that in the connecting layer, the consumption of electrolyte caused by defects formed by the doping elements in the connecting layer can be effectively inhibited, and the high capacity and first effect of the composite anode material are ensured. In a comprehensive view, the preparation method can improve the rate capability and the low-temperature capability of the composite negative electrode material while ensuring the high capacity and the first effect of the composite negative electrode material.

Drawings

Fig. 1 is a schematic flow chart of a preparation method of a composite anode material provided in an embodiment of the present application;

FIG. 2 is a sectional view of a scanning electron microscope of the composite anode material provided in example 1 of the present application;

fig. 3 is a scanning electron microscope image of the composite anode material provided in embodiment 1 of the present application;

fig. 4 is a scanning electron microscope image of the composite anode material provided in comparative example 1 of the present application.

Detailed Description

For better illustrating the present application, the technical solutions of the present application are easy to understand, and the present application is further described in detail below. The following examples are merely illustrative examples of the present application and are not intended to represent or limit the scope of the claims of the present application.

In a first aspect, the present application provides a composite anode material, the composite anode material including a graphite core, a connection layer located on a surface of the graphite core, and a carbon layer located on a surface of the connection layer, the connection layer including amorphous carbon containing a doping element, the carbon layer including amorphous carbon containing a doping element;

the connecting layer of the composite anode material has at least one chemical bond of C-N, C-P, C-B, C-F, C-O and C-S as measured by X-ray photoelectron spectroscopy XPS; the mass content of the doping element in the connecting layer is P1, and the mass content of the doping element in the carbon layer is P2, wherein P1 is more than P2.

The composite anode material comprises a graphite core, a connecting layer positioned on the surface of the graphite core and a carbon layer positioned on at least part of the surface of the connecting layer, wherein the connecting layer and the carbon layer both comprise amorphous carbon containing doping elements; the connecting layer of the composite anode material is provided with at least one chemical bond of C-N, C-P, C-B, C-F, C-O and C-S, and doping elements in the connecting layer can increase lithium storage active sites and improve the migration speed of lithium ions; at least one chemical bond of C-N, C-P, C-B, C-F, C-O and C-S formed on the connecting layer has strong polarity, can react with asphalt, and prevents asphalt from self-aggregation, so that a carbon layer with good uniformity is formed on the surface of the connecting layer, the connection strength of the connecting layer and the carbon layer is improved, and the rate performance and low-temperature performance of the composite anode material are improved. The carbon layer uniformly coats the connecting layer, a small amount of doping elements in the doping agent can also be doped into the carbon layer in the carbonization process, the content of the doping elements in the carbon layer is obviously less than that in the connecting layer, and the consumption of electrolyte caused by defects formed by the doping elements in the connecting layer can be effectively inhibited, so that the high capacity and first effect of the composite anode material are ensured. In combination, the composite anode material can achieve high capacity, high initial efficiency, excellent multiplying power performance and low temperature performance.

The natural graphite is crystalline flake graphite, is shaped like fish phosphorus, belongs to a hexagonal system, is in a layered structure, and has good performances of high temperature resistance, electric conduction, heat conduction, lubrication, plasticity, acid and alkali resistance and the like.

The artificial graphite is a graphite material obtained by carbonizing organic matters and then graphitizing the organic matters at high temperature.

In some embodiments, the graded material in the spheroidization process of natural crystalline flake graphite is shaped to yield spheroidal graphite.

In some embodiments, the graphite has a median particle diameter of 5 μm to 20 μm, more specifically, 5 μm, 6 μm, 8 μm, 9 μm, 10 μm, 11.5 μm, 12 μm, 12.5 μm, 14 μm, 15 μm, 16 μm, 18 μm, 20 μm, etc., but is not limited to the recited values, and other non-recited values within the range of values are equally applicable. Through multiple experiments, the median particle diameter of the graphite is controlled within the range, which is beneficial to the processability, capacity and multiplying power of the graphite. Preferably, the graphite has a median particle diameter of 6 μm to 15. Mu.m.

In some embodiments, the carbon content of the graphite is greater than or equal to 95%, and may specifically be 95%, 96%, 97%, 97.5%, 98.3%, 98.8%, 99%, etc., but is not limited to the recited values, and other non-recited values within the range of values are equally applicable. Preferably, the mass content of carbon in the graphite is more than or equal to 99.95%.

In some embodiments, the connection layer includes amorphous carbon including a doping element.

In some embodiments, the thickness of the connection layer is 0.01 μm to 1 μm, specifically, may be 0.01 μm, 0.05 μm, 0.1 μm, 0.2 μm, 0.5 μm, 0.6 μm, 07 μm, 0.8 μm, 0.9 μm, 1 μm, or the like, and is not limited herein.

In some embodiments, the doping elements in the connection layer and the carbon layer include at least one of N, P, B, F, O and S. Preferably, the doping elements in the connection layer and the carbon layer include N and/or B.

In some embodiments, the carbon layer comprises amorphous carbon comprising a doping element.

In some embodiments, the thickness of the carbon layer may be 0.01 μm to 1 μm, specifically, 0.01 μm, 0.05 μm, 0.1 μm, 0.2 μm, 0.5 μm, 0.6 μm, 07 μm, 0.8 μm, 0.9 μm, 1 μm, or the like, and is not limited herein.

In some embodiments, the amorphous carbon in the carbon layer may be derived from at least one of petroleum-based pitch and coal-based pitch. The asphalt may be solid asphalt or liquid asphalt.

In some embodiments, the median particle diameter of the composite anode material is 5 μm to 22 μm, specifically, may be 5 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 14 μm, 15 μm, 16 μm, 19 μm, 20 μm, 22 μm, or the like, and is not limited herein. Preferably, the composite anode material has a median particle diameter of 6 μm to 17 μm.

In some embodiments, the amorphous carbon content in the composite anode material is 0.1% -10%, specifically may be 0.1%, 0.2%, 0.3%, 0.5%, 0.8%, 1.0%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%, etc., and is not limited herein. The proper amount of amorphous carbon can ensure that the composite anode material has high capacity and multiplying power performance.

In some embodiments, the composite anode material is measured at 1200cm by raman spectroscopy testing ^-1 ～1500cm ^-1 Peak area at I _D And at 1500cm ^-1 ～1800cm ^-1 Peak area at I _G Ratio I of (2) _D /I _G The ratio is 0.5 to 3.0, specifically, 0.5, 0.8, 1.0, 1.2, 1.5, 1.8, 2.2, 2.5, 2.8, 3.0, etc., and is not limited thereto. Suitable I _D /I _G The value can ensure that the composite anode material has high initial efficiency and multiplying power performance.

In some embodiments, the composite anode material has a coating uniformity of C of 0.50 c.ltoreq.1.50, wherein the coating uniformity C is obtained by the following test method:

10 parts of composite anode material particles are randomly obtained, and the composite anode material is measured to be 1200cm by Raman spectrum test ^-1 ～1500cm ^-1 Peak area at I _D And at 1500cm ^-1 ～1800cm ^-1 Peak area at I _G Ratio I of (2) _D /I _G Has a value of R _n N=1, 2,3 … 10;10 parts of composite anode material particles I _D /I _G The average value of (2) is R; i _D /I _G The standard deviation of (2) is B; cladding uniformity c=n ^0.25 ·B ^0.5 。

In some embodiments, the coating uniformity C of the composite anode material may be specifically 0.5, 0.6, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, or 1.5, etc., without limitation herein.

In some embodiments, the composite anode material has a specific surface area of 0.2m ² /g～10m ² /g; in particular it may be 0.2m ² /g、0.3m ² /g、0.5m ² /g、1.0m ² /g、1.8m ² /g、2.6m ² /g、3.5m ² /g、5.3m ² /g、6.0m ² /g、7.8m ² /g or 10m ² Other numbers within the above range are needless to say, and the number of the above is not limited. The inventor finds that the specific surface area of the composite anode material is controlled within the range, which is beneficial to improving the initial effect and the cycle performance of a lithium battery made of the composite anode material. Preferably, the specific surface area of the composite anode material is 0.2m ² /g～3.0m ² /g。

In some embodiments, the composite anode material has a tap density of 0.6g/cm ³ ～1.4g/cm ³ The method comprises the steps of carrying out a first treatment on the surface of the Specifically, it may be 0.6g/cm ³ 、0.7g/cm ³ 、0.75g/cm ³ 、0.8g/cm ³ 、0.85g/cm ³ 、0.9g/cm ³ 、0.95g/cm ³ 、1.0g/cm ³ 、1.2g/cm ³ Or 1.4g/cm ³ And the like, but are not limited to the recited values, and other non-recited values within the range of values are equally applicable. By filling and coating the amorphous carbon, the pores of the graphite are filled or blocked, the porosity of the composite anode material is reduced, and the low porosity can effectively reduce side reactions in the charge and discharge process, so that the expansion of the pole piece and the reduction of the cycle performance caused by the side reactions are reduced. Preferably, the tap density of the composite anode material is 0.8g/cm ³ ～1.2g/cm ³ 。

In some embodiments, the composite anode material has a compacted density of 1.6g/cm ³ ～2.2g/cm ³ The method comprises the steps of carrying out a first treatment on the surface of the Specifically, it may be 1.6g/cm ³ 、1.75g/cm ³ 、1.8g/cm ³ 、1.85g/cm ³ 、1.9g/cm ³ 、1.95g/cm ³ 、2.0g/cm ³ 、2.05g/cm ³ Or 2.2g/cm ³ And the like, but are not limited to the recited values, and other non-recited values within the range of values are equally applicable. Preferably, the composite anode material has a compacted density of 1.8g/cm under 5T pressure ³ ～2.1g/cm ³ 。

In a second aspect, as shown in fig. 1, the present application provides a method for preparing a composite anode material, including the following steps:

s10, performing heat treatment on a mixture containing graphite, a liquid coating agent and a doping agent to obtain a precursor;

and S20, carbonizing the compound containing the precursor and asphalt to obtain the composite anode material.

According to the preparation method of the composite anode material, the mixture containing graphite, the liquid coating agent and the doping agent is subjected to heat treatment and then mixed with asphalt to be subjected to carbonization treatment. During carbonization, the dopant decomposes to produce H ₂ O、CO ₂ The isogas is discharged, and element doping is carried out in the connecting layer, so that lithium storage active sites can be increased, and the migration speed of lithium ions can be improved; at least one chemical bond of C-N, C-P, C-B, C-F, C-O and C-S formed on the interface of the connecting layer and the carbon layer has strong polarity, can react with asphalt, prevents asphalt from self-aggregation, and forms a carbon layer with good uniformity on the surface of the connecting layer, thereby improving the rate performance and low-temperature performance of the composite anode material. The carbon layer uniformly coats the connecting layer, so that the consumption of electrolyte caused by defects formed by doping elements in the connecting layer can be effectively inhibited, and the high capacity and first effect of the composite anode material are ensured. In a comprehensive view, the preparation method can improve the rate capability and the low-temperature capability of the composite negative electrode material while ensuring the high capacity and the first effect of the composite negative electrode material.

The preparation method provided by the scheme is described in detail below:

before step S10, the preparation method further includes:

and shaping the natural crystalline flake graphite to obtain spherical graphite.

The natural crystalline flake graphite is natural crystalline graphite, has a shape similar to fish phosphorus, belongs to a hexagonal system, is in a layered structure, and has good performances of high temperature resistance, electric conduction, heat conduction, lubrication, plasticity, acid and alkali resistance and the like.

In some embodiments, the shaping comprises at least one of crushing, spheroidizing, or classifying.

The natural graphite can be shaped in a spheroidizing mode, the spheroidizing speed is controlled to be 500 r/min-5000 r/min, and the spheroidizing time is controlled to be 0.2-10 h.

The graphite obtained by shaping may have a median particle diameter of 5 μm to 20. Mu.m, more specifically, 5 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 14 μm, 15 μm, 16 μm, 19 μm or 20 μm, etc., but is not limited to the recited values, and other values not recited in the numerical range are applicable. Through multiple experiments, the median particle diameter of the graphite is controlled within the range, which is beneficial to considering the processability, capacity and multiplying power. Preferably, the graphite has a median particle diameter of 6 μm to 15. Mu.m.

In some embodiments, artificial graphite may also be selected.

In some embodiments, the carbon content in the graphite is greater than or equal to 95% by mass, and may specifically be 95%, 96%, 97%, 97.5%, 98.3%, 98.8% or 99%, etc., but is not limited to the recited values, and other non-recited values within the range of values are equally applicable.

In some embodiments, the liquid coating agent includes at least one of a liquid asphalt and a liquid rubber plasticizer.

In some embodiments, the liquid asphalt comprises at least one of petroleum-based liquid asphalt and coal-based liquid asphalt. Specifically, the petroleum-based liquid asphalt may be petroleum asphalt, modified asphalt, mesophase asphalt, or the like.

In some embodiments, the liquid rubber plasticizer includes at least one of petroleum-based plasticizers, coal tar-based plasticizers, pine-based plasticizers, fat-based plasticizers, and synthetic plasticizers.

In some embodiments, the dopant comprises at least one of urea, melamine phosphate, ammonium dihydrogen phosphate, boron oxide, ammonium borate, polyvinylidene fluoride, ammonium bifluoride, ammonium sulfate, ammonium bisulfate, and thiourea. Preferably, the dopant is selected from at least one of ammonium borate, ammonium fluoride, urea, ammonium dihydrogen phosphate and ammonium sulfate. This is because doping of the amorphous carbon with the N element and the B element can effectively reduce the uniformity of the coating of the carbon layer, which is beneficial to improving the rate capability of the composite anode material and reducing the low temperature resistance.

S10, performing heat treatment on a mixture containing graphite, a liquid coating agent and a doping agent to obtain a precursor.

In some embodiments, the mass ratio of graphite, liquid coating agent to dopant is 100: (10-100): (5-50), specifically, may be 100:10:5, 100:10:10, 100:10:25, 100:10:50, 100:20:10, 100:20:40, 100:20:50, 100:50:50, or 100:100:50, etc., but not limited to the recited values, other non-recited values within the range of values are equally applicable. Excessive doping agent can reduce the first effect of the composite anode material; too little dopant can reduce the rate capability and low temperature capability of the composite anode material.

In some embodiments, the graphite, liquid coating agent, and dopant are thoroughly mixed to form a mixture, the mixing means including at least one of mechanical agitation and ultrasonic dispersion. When mechanical stirring is used for mixing, a propeller stirrer, a turbine stirrer, a flat propeller stirrer, etc. may be used, and the order of addition of the components is not limited, as long as the components are sufficiently and uniformly mixed.

Stirring may be carried out at normal temperature or in a preheated state, and preferably, the stirring temperature may be controlled to 25 to 80 ℃. It will be appreciated that appropriate preheating facilitates thorough mixing of the graphite, liquid coating agent and dopant to form a uniform liquid slurry of each component.

In some embodiments, the stirring speed is 10r/min to 1000r/min, specifically, may be 10r/min, 50r/min, 70r/min, 100r/min, 120r/min, 150r/min, 200r/min, 300r/min, 350r/min, 400r/min, 500r/min, 1000r/min, or the like, and is not limited herein. Stirring will cause the graphite, liquid coating agent and dopant to mix more uniformly. Too slow stirring speed can result in poor homogeneity of the mixture; too fast stirring speed will require higher equipment and increase the cost.

In some embodiments, the temperature of the heat treatment is 150 ℃ to 300 ℃ and the time of the drying treatment is 0.5h to 10h.

In some embodiments, the temperature of the heat treatment is 150 ℃ to 300 ℃, specifically 150 ℃, 180 ℃, 200 ℃, 220 ℃, 250 ℃, 260 ℃, 280 ℃, 300 ℃ or the like, the time of the heat treatment is 0.5h to 10h, specifically 0.5h, 1h, 3h, 5h, 7h, 8h, 9h or 10h or the like, and the heat treatment mode can be, for example, oven drying, stirring and steaming drying, spray drying or the like, and the heat treatment mode in this example is oven drying.

In some embodiments, the heating rate of the heat treatment is 0.5 to 5.0 ℃ per minute, specifically, 0.5, 1.0, 2.0, 3.0, 4.0, or 5.0 ℃ per minute, but the present invention is not limited to the recited values, and other non-recited values within the range are equally applicable.

In some embodiments, the mass ratio of graphite to pitch is 100: (1-10), specifically, may be 100:1, 100:2, 100:3, 100:4, 100:5, 100:6, 100:7, 100:8, 100:9, or 100:10, etc., but not limited to the recited values, and other non-recited values within the range of values are equally applicable.

In some embodiments, the reaction temperature of the carbonization treatment is 600 ℃ to 1500 ℃, specifically, 600 ℃, 650 ℃, 670 ℃, 700 ℃, 800 ℃, 950 ℃, 1080 ℃, 1300 ℃, 1400 ℃, 1500 ℃, or the like can be used, but the present invention is not limited to the recited values, and other non-recited values within the range of the recited values are equally applicable. It will be appreciated that suitableThe carbonization temperature of the carbon layer is suitable for the amorphous carbon of the surface connecting layer of the graphite core and the carbon layer _D /I _G The value ensures that the composite anode material has high initial efficiency and multiplying power performance. Preferably, the temperature of the carbonization treatment is 800 to 1300 ℃.

In some embodiments, the heat-preserving time of the carbonization treatment is 0.5h to 10h, specifically, 0.5h, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h or 10h, etc., but not limited to the recited values, and other non-recited values within the range of values are equally applicable. Preferably, the heat preservation time of the carbonization treatment is 1 h-3 h,

Alternatively, the heating rate of the carbonization treatment is 0.5 to 5 ℃ per minute, specifically, 0.5, 1, 2, 3, 4, or 5 ℃ per minute, etc., but the present invention is not limited to the recited values, and other values not recited in the range of values are equally applicable.

In some embodiments, the gas flow rate of the protective atmosphere is 2ml/s to 100ml/s, specifically may be 2ml/s, 5ml/s, 10ml/s, 15ml/s, 20ml/s, 30ml/s, 50ml/s, 60ml/s, 70ml/s, 89ml/s, 100ml/s, or the like, and is not limited herein.

In some embodiments, the carbonization treatment is further followed by at least one of comminution, sieving, and demagnetizing; preferably, the carbonization treatment is followed by pulverization, demagnetization and sieving in this order.

In some embodiments, the comminution means is any one of a mechanical mill, a jet mill, and a cryogenic mill.

In some embodiments, the screening mode is any one of a fixed screen, a roller screen, a resonance screen, a roller screen, a vibrating screen and a chain screen, the screening mesh is 200-500 meshes, specifically can be 200-300 meshes, 400 meshes or 500 meshes, and the particle size of the anode material is controlled within the range, so that the improvement of the processing performance of the anode material is facilitated.

In some embodiments, the demagnetizing device is any one of a permanent magnet cylinder type magnetic separator, an electromagnetic iron removing machine and a pulsating high gradient magnetic separator, and the demagnetizing is used for controlling the magnetic substance content of the negative electrode material, avoiding the influence of the magnetic substance on the charge and discharge of the lithium ion battery, and ensuring the safety of the battery in the use process.

In a third aspect, the present application provides a lithium ion battery, which includes the composite anode material described in the first aspect or the composite anode material prepared by the preparation method described in the second aspect.

Those skilled in the art will appreciate that the above-described methods of preparing lithium ion batteries are merely examples. Other methods commonly used in the art may be employed without departing from the disclosure of the present application.

The embodiments of the present application are further described below in terms of a number of examples. The embodiments of the present application are not limited to the following specific embodiments. The modification can be appropriately performed within the scope of protection.

Example 1

The preparation method of the composite anode material of the embodiment comprises the following steps:

(1) Artificial graphite powder with a median particle diameter of 12 mu m is selected, and the mass ratio of the artificial graphite powder, the petroleum liquid rubber plasticizer and the urea doping agent is 100:100:50, fully mixing to obtain a mixture, carbonizing in a tubular carbonizing furnace under nitrogen atmosphere, heating to 300 ℃ at a heating rate of 5 ℃/min, preserving heat for 0.5h, and cooling to obtain a precursor;

(2) Adding petroleum solid asphalt powder into the precursor, wherein the mass ratio of the artificial graphite powder to the asphalt is 100:10, fully mixing to obtain a compound;

(3) And (3) carbonizing the composite in a tubular carbonizing furnace under nitrogen atmosphere, heating to 1500 ℃ at a heating rate of 5 ℃/min, keeping the temperature for 0.5h, and cooling to obtain the composite anode material.

Fig. 2 is an SEM sectional view of the composite anode material prepared in example 1, as shown in fig. 2, the composite anode material includes a graphite core, a connection layer located on the surface of the graphite core, and a carbon layer located on at least part of the surface of the connection layer. As shown in fig. 2, the surface of the composite anode material was very flat, indicating a uniform carbon layer.

The median particle diameter of the composite anode material is 14 mu m, and the specific surface area is 1.8m ² Per gram, tap density of 0.86g/cm ³ A compaction density of 1.82g/cm at 5T pressure ³ The thickness of the connection layer was 1 μm, the thickness of the carbon coating layer was 1 μm, the N content of the connection layer was 9.1%, the N content of the carbon coating layer was 0.8%, and the mass content of amorphous carbon in the composite anode material was 6%.

The graphite cathode material is prepared by Raman spectroscopy at 1200cm ^-1 ～1500cm ^-1 Peak area at I _D And at 1500cm ^-1 ～1800cm ^-1 Peak area at I _G Ratio I of (2) _D /I _G The average value of (2.72) and the coating uniformity C was 1.12.

Example 2

Unlike example 1, in step (1), an artificial graphite powder having a median particle diameter of 5 μm was selected.

The composite anode material prepared by the embodiment comprises a graphite core, a connecting layer positioned on the surface of the graphite core and a carbon layer positioned on at least part of the surface of the connecting layer.

The median particle diameter of the composite anode material is 7 mu m, and the specific surface area is 2.7m ² Per gram, tap density of 0.60g/cm ³ A compaction density of 1.60g/cm at 5T pressure ³ The thickness of the connection layer was 1 μm, the thickness of the carbon coating layer was 1 μm, the N content of the connection layer was 9.3%, the N content of the carbon coating layer was 0.7%, and the mass content of amorphous carbon in the composite anode material was 6%.

The graphite cathode material is prepared by Raman spectroscopy at 1200cm ^-1 ～1500cm ^-1 Peak area at I _D And at 1500cm ^-1 ～1800cm ^-1 Peak area at I _G Ratio I of (2) _D /I _G Is 2.81; the coating uniformity C is 1.01.

Example 3

Unlike example 1, in step (1), an artificial graphite powder having a median particle diameter of 20 μm was selected.

The median particle diameter of the composite anode material is 22 mu m, and the specific surface area is 1.4m ² Per gram, tap density of 1.12g/cm ³ A compaction density of 1.94g/cm at 5T pressure ³ The thickness of the connection layer was 1 μm, the thickness of the carbon coating layer was 1 μm, the N content of the connection layer was 8.9%, the N content of the carbon coating layer was 0.9%, and the mass content of amorphous carbon in the composite anode material was 6%.

The graphite cathode material is prepared by Raman spectroscopy at 1200cm ^-1 ～1500cm ^-1 Peak area at I _D And at 1500cm ^-1 ～1800cm ^-1 Peak area at I _G Ratio I of (2) _D /I _G Is 2.51; the coating uniformity C is 1.21.

Example 4

(1) Selecting artificial graphite powder with a median particle size of 5 mu m, and mixing the artificial graphite powder, a petroleum liquid rubber plasticizer and a urea doping agent according to a mass ratio of 100:10:5, fully mixing to obtain a mixture, carbonizing in a tubular carbonizing furnace under nitrogen atmosphere, heating to 300 ℃ at a heating rate of 5 ℃/min, preserving heat for 0.5h, and cooling to obtain a precursor;

(2) Adding petroleum solid asphalt powder into the precursor, wherein the mass ratio of the artificial graphite powder to the asphalt is 100:1, fully mixing to obtain a compound;

(3) And (3) carbonizing the composite in a tubular carbonizing furnace under nitrogen atmosphere, heating to 1500 ℃ at a heating rate of 5 ℃/min, keeping the temperature for 10 hours, and cooling to obtain the composite anode material.

The median particle diameter of the composite anode material is 5 mu m, and the specific surface area is 3.4m ² Per gram, tap density of 0.74g/cm ³ A compaction density of 1.72g/cm at 5T pressure ³ The thickness of the connection layer was 0.01 μm, the thickness of the carbon coating layer was 0.01 μm, the N content of the connection layer was 1.2%, the N content of the carbon coating layer was 0.3%, and the mass content of amorphous carbon in the composite anode material was 0.1%.

The graphite cathode material is prepared by Raman spectroscopy at 1200cm ^-1 ～1500cm ^-1 Peak area at I _D And at 1500cm ^-1 ～1800cm ^-1 Peak area at I _G Ratio I of (2) _D /I _G Is 0.71; the cladding uniformity C is 1.22.

Example 5

(1) Artificial graphite powder with a median particle diameter of 20 mu m is selected, and the mass ratio of the artificial graphite powder to the petroleum liquid rubber plasticizer to the urea doping agent is 100:10:5, fully mixing to obtain a mixture, carbonizing in a tubular carbonizing furnace under nitrogen atmosphere, heating to 300 ℃ at a heating rate of 5 ℃/min, preserving heat for 0.5h, and cooling to obtain a precursor;

The median particle diameter of the composite anode material is 20 mu m, and the specific surface area is 1.5m ² Per gram, tap density of 1.40g/cm ³ A compaction density of 2.20g/cm at 5T pressure ³ The thickness of the connecting layer isThe thickness of the carbon coating layer was 0.01 μm, the N content of the connection layer was 1.1%, the N content of the carbon coating layer was 0.4%, and the mass content of amorphous carbon in the composite anode material was 0.1%.

The graphite cathode material is prepared by Raman spectroscopy at 1200cm ^-1 ～1500cm ^-1 Peak area at I _D And at 1500cm ^-1 ～1800cm ^-1 Peak area at I _G Ratio I of (2) _D /I _G Is 0.50; the coating uniformity C is 1.28.

Example 6

(1) Natural graphite powder with a median particle diameter of 5 mu m is selected, and artificial graphite powder, petroleum liquid rubber plasticizer and urea doping agent are mixed according to a mass ratio of 100:10:5, fully mixing to obtain a mixture, carbonizing in a tubular carbonizing furnace under nitrogen atmosphere, heating to 300 ℃ at a heating rate of 5 ℃/min, preserving heat for 0.5h, and cooling to obtain a precursor;

The median particle diameter of the composite anode material is 5 mu m, and the specific surface area is 1.00m ² Per gram, tap density of 0.82g/cm ³ A compaction density of 1.62g/cm at 5T pressure ³ The thickness of the connection layer was 0.01 μm, the thickness of the carbon coating layer was 0.01 μm, the N content of the connection layer was 1.1%, the N content of the carbon coating layer was 0.2%, and the mass content of amorphous carbon in the composite anode material was 0.1%.

The graphite is negative by Raman spectroscopyThe polar material is 1200cm ^-1 ～1500cm ^-1 Peak area at I _D And at 1500cm ^-1 ～1800cm ^-1 Peak area at I _G Ratio I of (2) _D /I _G Is 0.76; the coating uniformity C is 1.18.

Example 7

Unlike example 1, in step (1), a coal tar-based liquid rubber plasticizer was selected.

The median particle diameter of the composite anode material is 14 mu m, and the specific surface area is 2.2m ² Per gram, tap density of 0.89g/cm ³ A compaction density of 1.85g/cm at 5T pressure ³ The thickness of the connection layer was 1 μm, the thickness of the carbon coating layer was 1 μm, the N content of the connection layer was 9.0%, the N content of the carbon coating layer was 0.9%, and the mass content of amorphous carbon in the composite anode material was 6%.

The graphite cathode material is prepared by Raman spectroscopy at 1200cm ^-1 ～1500cm ^-1 Peak area at I _D And at 1500cm ^-1 ～1800cm ^-1 Peak area at I _G Ratio I of (2) _D /I _G Is 2.91; the cladding uniformity C is 1.42.

Example 8

Unlike example 1, in step (1), a petroleum-based liquid asphalt was used.

The median particle diameter of the composite anode material is 14 mu m, and the specific surface area is 1.5m ² Per gram, tap density of 0.85g/cm ³ A compaction density of 1.81g/cm at 5T pressure ³ The thickness of the connection layer was 1 μm, the thickness of the carbon coating layer was 1 μm, the N content of the connection layer was 9.3%, the N content of the carbon coating layer was 0.6%, and the mass content of amorphous carbon in the composite anode material was 6%.

The graphite cathode material is prepared by Raman spectroscopy at 1200cm ^-1 ～1500cm ^-1 Peak area at I _D And at 1500cm ^-1 ～1800cm ^-1 Peak area at I _G Ratio I of (2) _D /I _G Is 2.52; the cladding uniformity C is 0.90.

Example 9

Unlike example 1, in step (1), coal-based liquid asphalt was used.

The median particle diameter of the composite anode material is 14 mu m, and the specific surface area is 1.9m ² Per gram, tap density of 0.88g/cm ³ A compaction density of 1.84g/cm at 5T pressure ³ The thickness of the connection layer was 1 μm, the thickness of the carbon coating layer was 1 μm, the N content of the connection layer was 8.9%, the N content of the carbon coating layer was 0.8%, and the mass content of amorphous carbon in the composite anode material was 6%.

The graphite cathode material is prepared by Raman spectroscopy at 1200cm ^-1 ～1500cm ^-1 Peak area at I _D And at 1500cm ^-1 ～1800cm ^-1 Peak area at I _G Ratio I of (2) _D /I _G Is 2.66; the coating uniformity C is 1.27.

Example 10

Unlike example 1, in step (1), a monoammonium phosphate dopant was selected.

The median particle diameter of the composite anode material is 14 mu m, and the specific surface area is 2.0m ² Per gram, tap density of 0.90g/cm ³ A compaction density of 1.85g/cm at 5T pressure ³ The thickness of the connecting layer is 1 mu m, the thickness of the carbon coating layer is 1 mu m, the N content and the P content of the connecting layer are 3.9 percent and 2.8 percent respectively, and the carbon coating layerThe N content and the P content of the coating layer were 0.3% and 0.2%, respectively, and the mass content of amorphous carbon in the composite anode material was 6%.

The graphite cathode material is prepared by Raman spectroscopy at 1200cm ^-1 ～1500cm ^-1 Peak area at I _D And at 1500cm ^-1 ～1800cm ^-1 Peak area at I _G Ratio I of (2) _D /I _G Is 2.84; the coating uniformity C is 1.33.

Example 11

Unlike example 1, in step (1), an ammonium borate dopant was selected.

The median particle diameter of the composite anode material is 14 mu m, and the specific surface area is 1.4m ² Per gram, tap density of 0.83g/cm ³ A compaction density of 1.78g/cm at 5T pressure ³ The thickness of the connection layer was 1 μm, the thickness of the carbon coating layer was 1 μm, the N content and B content of the connection layer were 2.1% and 5.2%, respectively, the N content and B content of the carbon coating layer were 0.2% and 0.5%, respectively, and the mass content of amorphous carbon in the composite anode material was 6%.

The graphite cathode material is prepared by Raman spectroscopy at 1200cm ^-1 ～1500cm ^-1 Peak area at I _D And at 1500cm ^-1 ～1800cm ^-1 Peak area at I _G Ratio I of (2) _D /I _G Is 2.66; the coating uniformity C is 1.01.

Example 12

Unlike example 1, in step (1), an ammonium fluoride dopant was selected.

The median particle diameter of the composite anode material is 14 mu m, and the specific surface area is 1.9m ² Per gram, tap density of 0.88g/cm ³ At 5T pressureA compaction density of 1.83g/cm ³ The thickness of the connection layer was 1 μm, the thickness of the carbon coating layer was 1 μm, the N content and F content of the connection layer were 7.1% and 3.2%, respectively, the N content and F content of the carbon coating layer were 0.5% and 0.3%, respectively, and the mass content of amorphous carbon in the composite anode material was 6%.

The graphite cathode material is prepared by Raman spectroscopy at 1200cm ^-1 ～1500cm ^-1 Peak area at I _D And at 1500cm ^-1 ～1800cm ^-1 Peak area at I _G Ratio I of (2) _D /I _G Is an average value of 2.76; the coating uniformity C is 1.18.

Example 13

Unlike example 1, in step (1), an ammonium sulfate dopant was selected.

The median particle diameter of the composite anode material is 14 mu m, and the specific surface area is 2.1m ² Per gram, tap density of 0.91g/cm ³ A compaction density of 1.86g/cm at 5T pressure ³ The thickness of the connection layer was 1 μm, the thickness of the carbon coating layer was 1 μm, the N content and S content of the connection layer were 4.1% and 2.2%, respectively, the N content and S content of the carbon coating layer were 0.3% and 0.1%, respectively, and the mass content of amorphous carbon in the composite anode material was 6%.

Example 14

Unlike example 1, in step (1), a boron oxide dopant was selected.

The composite anode material had a median particle diameter of 14 μm, a specific surface area of 1.8m2/g, a tap density of 0.92g/cm3, a compacted density under 5T pressure of 1.88g/cm3, a thickness of the connecting layer of 1 μm, a thickness of the carbon coating layer of 1 μm, an O content and a B content of the connecting layer of 5.2% and 3.2%, respectively, an O content and a B content of the carbon coating layer of 0.5% and 0.3%, respectively, and a mass content of amorphous carbon in the composite anode material of 6%.

The graphite cathode material is prepared by Raman spectroscopy at 1200cm ^-1 ～1500cm ^-1 Peak area at I _D And at 1500cm ^-1 ～1800cm ^-1 Peak area at I _G Ratio I of (2) _D /I _G Is 2.81; the cladding uniformity C is 1.36.

Example 15

Unlike example 1, in step (2), coal-based solid pitch powder was selected.

The median particle diameter of the composite anode material is 14 mu m, and the specific surface area is 2.0m ² Per gram, tap density of 0.90g/cm ³ A compaction density of 1.85g/cm at 5T pressure ³ The thickness of the connection layer was 1 μm, the thickness of the carbon coating layer was 1 μm, the N content of the connection layer was 8.8%, the N content of the carbon coating layer was 0.7%, and the mass content of amorphous carbon in the composite anode material was 6%.

The graphite cathode material is prepared by Raman spectroscopy at 1200cm ^-1 ～1500cm ^-1 Peak area at I _D And at 1500cm ^-1 ～1800cm ^-1 Peak area at I _G Ratio I of (2) _D /I _G Is 2.84; the coating uniformity C is 1.24.

Example 16

Unlike example 1, in step (3), carbonization treatment was performed in a tubular carbonization furnace under an argon atmosphere, and the temperature was raised to 600℃at a temperature-raising rate of 0.5℃per minute, and the temperature was maintained for 0.5 hours.

The median particle diameter of the composite anode material is 14 mu m, and the specific surface area is 2.4m ² Per gram, tap density of 0.81g/cm ³ A compaction density of 1.78g/cm at 5T pressure ³ The thickness of the connection layer was 1 μm, the thickness of the carbon coating layer was 1 μm, the N content of the connection layer was 9.4%, the N content of the carbon coating layer was 0.6%, and the mass content of amorphous carbon in the composite anode material was 10%.

The graphite cathode material is prepared by Raman spectroscopy at 1200cm ^-1 ～1500cm ^-1 Peak area at I _D And at 1500cm ^-1 ～1800cm ^-1 Peak area at I _G Ratio I of (2) _D /I _G Is 3.00; the cladding uniformity C is 1.36.

Comparative example 1

The difference from example 1 is that in step (1) no urea dopant is added.

The composite anode material prepared in the comparative example comprises a graphite core, a connecting layer positioned on the surface of the graphite core and a carbon layer positioned on at least part of the surface of the connecting layer.

Fig. 3 is an SEM image of the composite anode material prepared in comparative example 1, and as shown in fig. 3, the coating layer on the surface of the composite anode material is very uneven and cracks occur, indicating that no dopant is added to the coating uniformity.

The median particle diameter of the composite anode material is 14 mu m, and the specific surface area is 2.4m ² Per gram, tap density of 0.89g/cm ³ A compaction density of 1.85g/cm at 5T pressure ³ The thickness of the connection layer was 1 μm, the thickness of the carbon coating layer was 1 μm, and the mass content of amorphous carbon in the composite anode material was 6%.

The graphite cathode material is prepared by Raman spectroscopy at 1200cm ^-1 ～1500cm ^-1 Peak area at I _D And at 1500cm ^-1 ～1800cm ^-1 Peak area at I _G Ratio I of (2) _D /I _G Is a flat part of (2)The average value is 2.48; the coating uniformity C is 1.73.

Comparative example 2

The difference from example 1 is that: in the step (1), the petroleum-based liquid rubber plasticizer is not added.

The composite anode material prepared in the comparative example comprises a graphite core and a carbon layer positioned on the surface of the graphite core.

The median particle diameter of the composite anode material is 13 mu m, and the specific surface area is 2.8m ² Per gram, tap density of 0.92g/cm ³ A compaction density of 1.88g/cm at 5T pressure ³ The thickness of the carbon coating layer was 1 μm, the N content of the carbon coating layer was 0.4%, and the mass content of amorphous carbon in the composite anode material was 3%.

The graphite cathode material is prepared by Raman spectroscopy at 1200cm ^-1 ～1500cm ^-1 Peak area at I _D And at 1500cm ^-1 ～1800cm ^-1 Peak area at I _G Ratio I of (2) _D /I _G Is 2.02; the cladding uniformity C is 1.76.

Comparative example 3

The difference from example 1 is that: in step (1), the petroleum-based liquid rubber plasticizer and the urea dopant are not added.

The median particle diameter of the composite anode material is 13 mu m, and the specific surface area is 2.6m ² Per gram, tap density of 0.94g/cm ³ A compaction density of 1.90g/cm at 5T pressure ³ The thickness of the carbon coating layer was 1 μm, and the mass content of amorphous carbon in the composite anode material was 3%.

The graphite cathode material is prepared by Raman spectroscopy at 1200cm ^-1 ～1500cm ^-1 Peak area at I _D And at 1500cm ^-1 ～1800cm ^-1 Peak area at I _G Ratio I of (2) _D /I _G Is 1.77; the coating uniformity C is 1.83.

Test method

(1) The method for testing the median particle diameter of the composite anode material comprises the following steps:

the particle size distribution range of the composite anode material is tested by a Markov laser particle sizer.

(2) The method for testing the tap density of the composite anode material comprises the following steps:

and (3) placing the composite anode material in a sample bin of a tap density meter, vibrating for 1000 times, and recording the sample volume at the moment, so that the tap density can be obtained according to the calculation of the mass-volume ratio.

(3) The specific surface area test method of the composite anode material comprises the following steps:

after the adsorption amount of the gas on the solid surface at different relative pressures is measured at a constant temperature and a low temperature, the adsorption amount of the sample monolayer is obtained based on the Yu Bulang Noll-Eltt-Taylor adsorption theory and a formula (BET formula) thereof, so that the specific surface area of the material is calculated.

(4) The method for testing the compaction density of the composite anode material comprises the following steps:

The compaction density is tested by adopting a national standard lithium ion battery graphite anode material GB/T24533-2009 test method, and the test pressure is 5 tons.

(5) The method for testing the thicknesses of the connecting layer and the carbon layer of the composite anode material comprises the following steps:

the composite negative electrode material powder was made into SEM cut samples, and the average thicknesses of the connection layer and the carbon layer were measured in SEM images.

(6) The method for testing the doping element content of the connecting layer and the carbon layer of the composite anode material comprises the following steps:

and directly measuring the doping element content P2 of the outermost carbon layer of the composite anode material by X-ray photoelectron spectroscopy XPS. And removing the outermost carbon layer of the composite anode material by adopting a fusion machine through fusion physical action, and measuring the doping element content P1 of the composite material connecting layer by XPS.

(7) The test method for the coating uniformity of the composite anode material comprises the following steps:

the Raman spectrum measurement adopts a Jobin Yvon LabRAM HR spectrometer, the light source is 532nm, and the test range is 0cm ^-1 ～4000cm ^-1 . The test range was 100 μm by 100 μm.

10 parts of composite anode material particles are randomly obtained,the composite anode material is measured to be 1200cm by Raman spectrum test ^-1 ～1500cm ^-1 Peak area at I _D And at 1500cm ^-1 ～1800cm ^-1 Peak area at I _G Ratio I of (2) _D /I _G Has a value of R _n N=1, 2,3 … 10;10 parts of composite anode material particles I _D /I _G The average value of (2) is R; i _D /I _G The standard deviation of (2) is B; cladding uniformity c=n ^0.25 ·B ^0.5 。

(8) And (3) testing the multiplying power performance of the lithium ion button type half battery:

the graphite composite materials prepared in each example and comparative example are respectively used as active substances according to the following active substances: conductive carbon black: CMC: sbr=95.3:1.5:1.4:1.8, and the coated surface density was 6.5±0.1mg/cm ² After vacuum drying at 90 ℃, a pole piece is obtained, and the pole piece is rolled to a compaction density of 1.50+/-0.02 g/cc. Pole piece, lithium piece, electrolyte (1 mol/L LiPF) ₆ Ec:emc dmc=1:1:1) and Celgard 2400 separator were assembled into 2016 type button half-cells. And (3) performing rate performance test on the button half battery at the temperature of 25+/-2 ℃ to obtain the charge-discharge specific capacities and coulombic efficiencies of 0.1C, 0.2C, 1C and 2℃. Multiplying power test condition: (1) placing 0.1C to 0.01V, keeping constant pressure to 0.01C, and charging 0.1C to 1.5V; (2) placing 0.2C to 0.01V, keeping constant pressure to 0.01C, and charging 0.2C to 1.5V; (3) 1C is put to 0.01V, constant pressure is kept to 0.01C, and 0.2C is filled to 1.5V; (4) the 2C was placed at 0.01V, constant pressure to 0.01C, and 0.2C was charged to 1.5V. The 1C/0.2C discharge capacity retention rate was calculated by dividing the 1C discharge specific capacity by the 0.2C discharge specific capacity.

(9) Lithium ion button half cell ac impedance (EIS) test:

the button half cell is activated for 2 weeks at the temperature of 25+/-2 ℃ under the activation condition: placing 0.1C to 0.01V, keeping constant pressure to 0.01C, and charging 0.1C to 1.5V; then discharging to 50% SOC for EIS test to obtain the impedance R of the semicircular arc area _z ，R _z Comprises SEI film impedance, li ⁺ Diffusion resistance and charge transfer resistance within the electrode pores. EIS test conditions: (1) The amplitude of the alternating current signal is 5mV, and the scanning frequency range is 0.03 Hz-10 ⁵ Hz, temperature 25±2 ℃; (2) The amplitude of the alternating current signal is 5mV, and the scanning frequency range is 0.03-10 ⁵ Hz, temperature is-5+ -2 ℃.

The results of the above performance tests are as follows:

TABLE 1 Performance comparison results Table

The lithium ion button half cell rate performance and EIS test results of the graphite composite materials in examples and comparative examples are shown in table 1.

As is clear from examples 1, 2 and 3, the median particle diameter of the artificial graphite affects the coating uniformity, and when the median particle diameter of the artificial graphite is reduced, the coating uniformity is also reduced, so that the coating uniformity can be improved, thereby improving the rate performance of the graphite anode material and reducing the normal temperature and low temperature resistance.

As can be seen from examples 2, 3, 4 and 5, decreasing the ratio of dopant to liquid coating agent increases the uniformity of coating, which is detrimental to improving coating uniformity, while decreasing I _D /I _G The disorder degree of the carbon is reduced, so that the rate capability of the graphite anode material is reduced, and the normal temperature and low temperature resistance is increased.

From examples 4 and 6, it is understood that the natural graphite coated product has a higher capacity but has inferior initial efficiency, rate capability and resistance compared to the artificial graphite coated product.

As is clear from examples 1, 7, 8 and 9, the coal-based liquid coating agent increases coating uniformity due to the inclusion of more impurities than the petroleum-based liquid coating agent, which is disadvantageous in improving coating uniformity, thereby reducing capacity, initial efficiency and rate performance of the graphite anode material and increasing normal temperature and low temperature resistance. Preferably, the graphite surface is modified by the combination of the petroleum-based liquid asphalt coating agent and the doping agent.

From examples 1, 10, 11, 12, 13 and 14, it is clear that the effect of the dopant on the improvement of the coating uniformity: the doping of N and B can effectively reduce the coating uniformity, and is more beneficial to improving the coating uniformity, thereby improving the multiplying power performance of the graphite anode material and reducing the impedance at normal temperature and low temperature.

As is clear from examples 1 and 15, the coal-based solid asphalt increases the coating uniformity due to the inclusion of more impurities, which is disadvantageous for improving the coating uniformity, thereby reducing the capacity, initial efficiency and rate capability of the graphite anode material and increasing the resistance at normal and low temperatures, as compared with the petroleum-based solid asphalt.

As can be seen from examples 1 and 16, decreasing the carbonization temperature increases the uniformity of coating, which is detrimental to improving the coating uniformity, while increasing I _D /I _G The carbon disorder degree is improved, so that the first effect and the multiplying power performance of the graphite anode material are reduced, and the normal temperature and low temperature impedance is increased.

As is clear from examples 1, 2 and 3, the synergistic effect of the petroleum-based liquid rubber plasticizer and the urea dopant greatly reduces the coating uniformity, and is more beneficial to improving the coating uniformity, thereby more effectively improving the capacity, first effect and rate capability of the graphite anode material and more effectively reducing the normal temperature and low temperature resistance.

While the preferred embodiment has been described, it is not intended to limit the scope of the claims, and any person skilled in the art can make several possible variations and modifications without departing from the spirit of the invention, so the scope of the invention shall be defined by the claims.

Claims

1. The composite anode material is characterized by comprising a graphite core, a connecting layer positioned on the surface of the graphite core and a carbon layer positioned on the surface of the connecting layer, wherein the connecting layer comprises amorphous carbon containing doping elements, and the carbon layer comprises amorphous carbon containing doping elements;

2. The composite anode material of claim 1, wherein the composite anode material meets at least one of the following characteristics:

(1) The graphite comprises at least one of artificial graphite and natural graphite;

(2) The median particle diameter of the graphite is 5-20 mu m;

(3) The thickness of the connecting layer is 0.01-1 mu m;

(4) The thickness of the carbon layer is 0.01-1 mu m;

(5) The doping elements in the connection layer and the carbon layer include at least one of N, P, B, F, O and S;

(6) The mass content of the doping element in the connecting layer is P1, and P1 is 1 percent and less than or equal to 10 percent;

(7) The mass content of the doping element in the carbon layer is P2, and P2 is more than 0% and less than or equal to 1%;

(8) The composite anode material is measured to be 1200cm by Raman spectrum test ^-1 ～1500cm ^-1 Peak area at I _D And at 1500cm ^-1 ～1800cm ^-1 Peak area at I _G Ratio I of (2) _D /I _G 0.5 to 3.0;

(9) The coating uniformity of the composite anode material is C, and C is more than or equal to 0.50 and less than or equal to 1.50.

3. The composite anode material according to claim 1 or 2, characterized in that the composite anode material satisfies at least one of the following characteristics:

(1) The median particle diameter of the composite anode material is 5-22 mu m;

(2) The specific surface area of the composite anode material is 0.2m ² /g～10m ² /g；

(3) The tap density of the composite anode material is 0.6g/cm ³ ～1.4g/cm ³ ；

(4) Pressing the composite anode material under 5T pressureThe solid density is 1.6g/cm ³ ～2.2g/cm ³ ；

(5) The mass content of amorphous carbon in the composite anode material is 0.1-10%.

4. A method for preparing a composite anode material, the method comprising the steps of:

and carbonizing the compound containing the precursor and asphalt to obtain the composite anode material.

5. The method of preparation of claim 4, wherein the method meets at least one of the following characteristics:

(2) The median particle diameter of the graphite is 5-20 mu m;

(3) The mass content of carbon element in the graphite is more than or equal to 95%;

(4) The liquid coating agent comprises at least one of liquid asphalt and liquid rubber plasticizer;

(5) The liquid coating agent comprises liquid asphalt, and the liquid asphalt comprises at least one of petroleum-based liquid asphalt and coal-based liquid asphalt;

(6) The liquid coating agent comprises a liquid rubber plasticizer, wherein the liquid rubber plasticizer comprises at least one of petroleum plasticizer, coal tar plasticizer, pine oil plasticizer, fat plasticizer and synthetic plasticizer;

(7) The doping agent comprises at least one of urea, melamine phosphate, ammonium dihydrogen phosphate, boron oxide, ammonium borate, polyvinylidene fluoride, ammonium bifluoride, ammonium sulfate, ammonium bisulfate and thiourea;

(8) The mass ratio of the graphite to the liquid coating agent to the doping agent is 100: (10-100): (5-50).

6. The method of preparation according to claim 4 or 5, wherein the method meets at least one of the following characteristics:

(1) The asphalt comprises at least one of petroleum asphalt and coal asphalt;

(2) The mass ratio of the graphite to the asphalt is 100: (1-10).

7. The method of any one of claims 4 to 6, wherein the method satisfies at least one of the following characteristics:

(1) The heat treatment is performed under at least one atmosphere of air and a protective gas;

(2) The protective atmosphere comprises at least one of nitrogen, helium, neon, argon, krypton and xenon;

(3) The heating rate of the heat treatment is 0.5-5.0 ℃/min;

(4) The heat preservation time of the heat treatment is 0.5 h-10 h.

8. The method of any one of claims 4 to 6, wherein the method satisfies at least one of the following characteristics:

(1) The carbonization treatment is carried out under a protective atmosphere;

(3) The carbonization temperature is 600-1500 ℃;

(4) The heating rate of the carbonization treatment is 0.5-5.0 ℃/min;

(5) The heat preservation time of the carbonization treatment is 0.5-10 h.

9. The method of any one of claims 4 to 6, wherein the method satisfies at least one of the following characteristics:

(1) The preparation method further comprises the following steps: shaping natural crystalline flake graphite to obtain spherical graphite;

(2) The shaping includes at least one of crushing, spheroidizing, and classifying.

10. A lithium ion battery characterized in that it comprises the negative electrode material according to any one of claims 1 to 3 or the negative electrode material produced according to the production method of any one of claims 4 to 9.