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

Abstract

The application provides a composite negative electrode material and a preparation method thereof and a lithium ion battery. The composite negative electrode material comprises a graphite core, a connecting layer on the surface of the graphite core, and a carbon layer on the surface of the connecting layer. The connecting layer comprises amorphous carbon containing a doping element, and the carbon layer comprises amorphous carbon containing a doping element. The connecting layer of the composite negative electrode material has at least one chemical bond selected from C-N, C-P, C-B, C-F, C-O and C-S, which is 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, and P1>P2. The composite negative electrode material and the preparation method thereof can balance high capacity, high initial efficiency, excellent rate performance and low-temperature performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of negative electrode materials, in particular to a composite negative electrode material and a preparation method thereof, and a lithium ion battery. BACKGROUND

[0002] Graphite is one of the main raw materials of lithium ion batteries, has the advantages of high capacity, high compaction, environmental friendliness and low price, and is widely used in 3C, power tools and other fields. 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, which promotes the diffusion of lithium ions. However, in recent years, the market has put forward higher demands for lithium ion batteries, not only requiring carbon-coated graphite negative electrode materials to have high capacity and high initial efficiency, but also requiring them to have excellent rate performance and low-temperature performance.

[0003] Traditional carbon-coated graphite generally uses solid pitch as a coating material, and the rate performance and low-temperature performance are improved by optimizing the coating method and coating amount. Increasing the pitch coating amount generally improves the rate performance and low-temperature performance, but excessive increase in the pitch coating amount will significantly reduce the capacity and initial efficiency of the graphite negative electrode material. Therefore, it is difficult to achieve carbon-coated graphite negative electrode materials with high capacity, high initial efficiency, excellent rate performance and low-temperature performance by increasing the pitch coating amount, thereby failing to meet the higher demands of the market for lithium ion batteries.

[0004] Therefore, how to make the composite negative electrode material have high capacity, high initial efficiency, excellent rate performance and low-temperature performance is a problem to be solved at present. SUMMARY

[0005] In view of this, the present application provides a composite negative electrode material and a preparation method thereof, and a lithium ion battery, which can have high capacity, high initial efficiency, excellent rate performance and low-temperature performance.

[0006] In a first aspect, the present application provides a composite negative electrode material, which comprises a graphite core, a connecting layer located on the surface of the graphite core, and a carbon layer located on the surface of the connecting layer, the connecting layer comprises amorphous carbon containing a doping element, and the carbon layer comprises amorphous carbon containing a doping element; the connecting layer of the composite negative electrode material has at least one of C-N, C-P, C-B, C-F, C-O and C-S chemical bonds measured by X-ray photoelectron spectroscopy XPS; and the mass content of the doping element in the connecting layer is greater than the mass content of the doping element in the carbon layer.

[0007] In some embodiments, the graphite comprises at least one of artificial graphite and natural graphite.

[0008] In some embodiments, the median particle size of the graphite is 5 μm to 20 μm.

[0009] In some embodiments, the thickness of the connecting layer is 0.01 μm to 1 μm.

[0010] In some embodiments, the thickness of the carbon layer is 0.01 μm to 1 μm.

[0011] In some embodiments, the doping elements in the connecting layer and the carbon layer include at least one of N, P, B, F, O, and S.

[0012] In some embodiments, the mass content of the doped element in the interconnect layer is P1, 1%. <P1≤10%。

[0013] In some embodiments, the mass content of the dopant element in the carbon layer is P2, 0%. <P2≤1%。

[0014] In some embodiments, the composite anode material is measured to have a Raman spectroscopy intensity of 1200 cm⁻¹. -1 ~1500cm -1 Peak area I at D With at 1500cm -1 ~1800cm -1 Peak area I at G The ratio I D / I G The value ranges from 0.5 to 3.0.

[0015] In some embodiments, the coating density of the composite negative electrode material is C, where 0.50 ≤ C ≤ 1.50.

[0016] In some embodiments, the median particle size of the composite anode material is 5 μm to 22 μm.

[0017] In some embodiments, the specific surface area of ​​the composite negative electrode material is 0.2 m². 2 / g~10m 2 / g.

[0018] In some embodiments, the tap density of the composite negative electrode material is 0.6 g / cm³. 3 ~1.4g / cm 3 .

[0019] In some embodiments, the compaction density of the composite negative electrode material under 5T pressure is 1.6 g / cm³. 3 ~2.2g / cm 3 .

[0020] In some embodiments, the mass content of amorphous carbon in the composite negative electrode material is 0.1% to 10%.

[0021] In a second aspect, the present application provides a method for preparing a composite negative electrode material, the method comprising the following steps:

[0022] subjecting a mixture comprising graphite, a liquid coating agent and a dopant to heat treatment at 150°C to 300°C to obtain a precursor;

[0023] subjecting a mixture comprising the precursor and pitch to carbonization treatment to obtain the composite negative electrode material.

[0024] In some embodiments, the graphite comprises at least one of artificial graphite and natural graphite.

[0025] In some embodiments, the graphite has a median particle size of 5 μm to 20 μm.

[0026] In some embodiments, the graphite has a mass content of carbon element of ≥ 95%.

[0027] In some embodiments, the liquid coating agent comprises at least one of liquid pitch and liquid rubber plasticizer.

[0028] In some embodiments, the liquid coating agent comprises liquid pitch, and the liquid pitch comprises at least one of petroleum-based liquid pitch and coal-based liquid pitch.

[0029] In some embodiments, the liquid coating agent comprises liquid rubber plasticizer, and the liquid rubber plasticizer comprises at least one of petroleum-based plasticizer, coal tar-based plasticizer, pine oil-based plasticizer, fatty-based plasticizer and synthetic plasticizer.

[0030] In some embodiments, the dopant comprises at least one of urea, melamine, melamine phosphate, ammonium dihydrogen phosphate, boron oxide, ammonium borate, polyvinylidene fluoride, ammonium fluoride, ammonium bifluoride, ammonium sulfate, ammonium bisulfate and thiourea.

[0031] In some embodiments, the mass ratio of the graphite, the liquid coating agent and the dopant is 100:(10 to 100):(5 to 50).

[0032] In some embodiments, the pitch comprises at least one of petroleum-based pitch and coal-based pitch.

[0033] In some embodiments, the mass ratio of the graphite and the pitch is 100:(1 to 10).

[0034] In some embodiments, the heat treatment is performed in an atmosphere of at least one of air and protective gas.

[0035] In some embodiments, the protective atmosphere comprises at least one of nitrogen, helium, neon, argon, krypton and xenon.

[0036] In some embodiments, the heating rate of the heat treatment is 0.5-5.0℃ / min.

[0037] In some embodiments, the holding time of the heat treatment is 0.5-10h.

[0038] In some embodiments, the carbonization treatment is performed under a protective atmosphere.

[0039] In some embodiments, the carbonization treatment is performed under a protective atmosphere, and the protective atmosphere comprises at least one of nitrogen, helium, neon, argon, krypton and xenon.

[0040] In some embodiments, the temperature of the carbonization treatment is 600-1500℃.

[0041] In some embodiments, the heating rate of the carbonization treatment is 0.5-5.0℃ / min.

[0042] In some embodiments, the holding time of the carbonization treatment is 0.5-10h.

[0043] In some embodiments, the preparation method further comprises: performing a shaping treatment on the natural flake graphite to obtain spherical graphite.

[0044] In some embodiments, the shaping comprises at least one of crushing, spheroidizing and grading.

[0045] In a third aspect, the present application provides a lithium ion battery, which comprises the composite negative electrode material according to the first aspect or the composite negative electrode material prepared by the preparation method according to the second aspect.

[0046] The technical solution of the present application has at least the following beneficial effects:

[0047] The composite negative electrode material provided in the application comprises a graphite inner core, a connecting layer on the surface of the graphite inner core, and a carbon layer on at least part of the surface of the connecting layer, wherein the connecting layer and the carbon layer both comprise amorphous carbon containing a doping element; the connecting layer of the composite negative electrode material has at least one of chemical bonds of C-N, C-P, C-B, C-F, C-O and C-S, the doping element in the connecting layer can increase lithium storage active sites and improve the migration speed of lithium ions; at least one of the chemical bonds of C-N, C-P, C-B, C-F, C-O and C-S formed on the interface between the connecting layer and the carbon layer has strong polarity, can promote the formation of a carbon layer with good uniformity on the surface of the connecting layer, effectively improve the uniformity of the carbon layer, and thus improve the rate performance and low-temperature performance of the composite negative electrode material. The carbon layer uniformly covers the connecting layer, can effectively inhibit the consumption of electrolyte by defects formed by the doping element in the connecting layer, and thus ensures the high capacity and initial efficiency of the composite negative electrode material. In summary, the composite negative electrode material can have high capacity, high initial efficiency, excellent rate performance and low-temperature performance.

[0048] In the preparation method of the composite negative electrode material provided in the application, a mixture containing graphite, a liquid coating agent and a dopant is subjected to heat treatment, and then mixed with pitch and subjected to carbonization treatment. During the carbonization process, the dopant decomposes to generate gases such as H2O and CO2, and at the same time, element doping is performed in the connecting layer, which can increase lithium storage active sites and improve the migration speed of lithium ions; at least one of the chemical bonds of C-N, C-P, C-B, C-F, C-O and C-S formed on the connecting layer has strong polarity and can react with pitch to prevent the self-aggregation of pitch, thereby forming a carbon layer with good uniformity on the surface of the connecting layer, improving the connection strength between the connecting layer and the carbon layer, and thus improving the rate performance and low-temperature performance of the composite negative electrode material. The carbon layer uniformly covers the connecting layer, and during the carbonization process, a small amount of doping elements in the dopant in the connecting layer can also be doped into the outer carbon layer, the content of the doping elements in the carbon layer is significantly less than that in the connecting layer, which can effectively inhibit the consumption of electrolyte by defects formed by the doping elements in the connecting layer, and thus ensure the high capacity and initial efficiency of the composite negative electrode material. In summary, the preparation method can improve the rate performance and low-temperature performance of the composite negative electrode material while ensuring its high capacity and initial efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0049] Figure 1 A flowchart of the preparation method of the composite negative electrode material provided in the application is shown in the figure;

[0050] Figure 2 A scanning electron microscope cross-sectional view of the composite negative electrode material provided in Example 1 of the application is shown in the figure;

[0051] Figure 3A scanning electron microscope image of the composite negative electrode material provided for Example 1 of the present application;

[0052] Figure 4 A scanning electron microscope image of the composite negative electrode material provided for Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0053] In order to better illustrate the present application and facilitate the understanding of the technical solutions of the present application, the present application is further described in detail below. However, the following examples are only simple examples of the present application and do not represent or limit the protection scope of the present application. The protection scope of the present application is subject to the claims.

[0054] In a first aspect, the present application provides a composite negative electrode material, which comprises a graphite inner core, a connecting layer located on the surface of the graphite inner core, and a carbon layer located on the surface of the connecting layer. The connecting layer comprises amorphous carbon containing a doping element, and the carbon layer comprises amorphous carbon containing a doping element.

[0055] The connecting layer of the composite negative electrode material has at least one chemical bond selected from 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, P1>P2.

[0056] The composite negative electrode material provided by the present application comprises a graphite inner core, a connecting layer located on the surface of the graphite inner core, and a carbon layer located on at least part of the surface of the connecting layer. The connecting layer and the carbon layer both comprise amorphous carbon containing a doping element. The connecting layer of the composite negative electrode material has at least one chemical bond selected from C-N, C-P, C-B, C-F, C-O and C-S. The doping element in the connecting layer can increase the lithium storage active sites and improve the migration speed of lithium ions. At least one chemical bond selected from C-N, C-P, C-B, C-F, C-O and C-S is formed on the connecting layer. The above chemical bonds have strong polarity and can react with pitch to prevent self-aggregation of pitch, thereby forming a carbon layer with good uniformity on the surface of the connecting layer, improving the connection strength between the connecting layer and the carbon layer, and thus improving the rate performance and low temperature performance of the composite negative electrode material. The carbon layer uniformly coats the connecting layer. During the carbonization process, a small amount of doping elements in the dopant can also be doped into the carbon layer. The content of the doping elements in the carbon layer is significantly less than that in the connecting layer, which can effectively inhibit the consumption of electrolyte by the defects formed by the doping elements in the connecting layer, thereby ensuring the high capacity and initial efficiency of the composite negative electrode material. In summary, the composite negative electrode material can balance high capacity, high initial efficiency, excellent rate performance and low temperature performance.

[0057] In some embodiments, the graphite comprises at least one of artificial graphite and natural graphite.

[0058] Natural graphite is flake graphite, which is a natural crystalline graphite. It has a fish scale-like shape, belongs to hexagonal system, and has a layered structure. It has good high-temperature resistance, electrical conductivity, thermal conductivity, lubricity, plasticity, and acid and alkali resistance.

[0059] Artificial graphite is a graphite material obtained by carbonizing an organic substance and then performing a graphitization high-temperature treatment.

[0060] In some embodiments, the classified material in the sphericalization treatment of natural flake graphite is shaped to obtain spherical graphite.

[0061] In some embodiments, the median particle size of the graphite is 5 μm to 20 μm, and more particularly, can be 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, or 20 μm, etc., but is not limited to the listed values, and other values not listed in the range are also applicable. It has been found through repeated experiments that controlling the median particle size of the graphite in the above range is beneficial to the graphite in terms of processing performance, capacity, and rate performance. Preferably, the median particle size of the graphite is 6 μm to 15 μm.

[0062] In some embodiments, the mass content of carbon in the graphite is ≥ 95%, and more particularly, can be 95%, 96%, 97%, 97.5%, 98.3%, 98.8%, or 99%, etc., but is not limited to the listed values, and other values not listed in the range are also applicable. Preferably, the mass content of carbon in the graphite is ≥ 99.95%.

[0063] In some embodiments, the connecting layer comprises amorphous carbon containing a doping element.

[0064] In some embodiments, the thickness of the connecting layer is 0.01 μm to 1 μm, and more particularly, can 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, or 1 μm, etc., without being limited herein.

[0065] In some embodiments, the doping element in the connecting layer and the carbon layer comprises at least one of N, P, B, F, O, and S. Preferably, the doping element in the connecting layer and the carbon layer comprises N and / or B.

[0066] In some embodiments, the mass content of the doping element in the connecting layer is P1, and 1% < P1≤ 10%.

[0067] In some embodiments, the carbon layer comprises amorphous carbon containing a doping element.

[0068] In some embodiments, the thickness of the carbon layer is 0.01 μm to 1 μm, specifically it can be 0.01 μm, 0.05 μm, 0.1 μm, 0.2 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm or 1 μm, etc., and is not limited here.

[0069] In some embodiments, the mass content of the dopant element in the carbon layer is P2, 0%. <P2≤1%。

[0070] In some embodiments, the amorphous carbon in the carbon layer may be derived from at least one of petroleum-based bitumen and coal-based bitumen. The bitumen may be solid bitumen or liquid bitumen.

[0071] In some embodiments, the median particle size of the composite anode material is 5 μm to 22 μm, specifically, it can be 5 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 14 μm, 15 μm, 16 μm, 19 μm, 20 μm, or 22 μm, etc., and is not limited thereto. Preferably, the median particle size of the composite anode material is 6 μm to 17 μm.

[0072] In some embodiments, the mass content of amorphous carbon in the composite anode material is 0.1% to 10%, specifically 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 thereto. An appropriate amount of amorphous carbon can ensure that the composite anode material maintains both high capacity and rate performance.

[0073] In some embodiments, the composite anode material is measured to have a Raman spectroscopy intensity of 1200 cm⁻¹. -1 ~1500cm -1 Peak area I at D With at 1500cm -1 ~1800cm -1 Peak area I at G The ratio I D / I G The value ranges from 0.5 to 3.0, specifically 0.5, 0.8, 1.0, 1.2, 1.5, 1.8, 2.2, 2.5, 2.8, or 3.0, etc., and is not limited here. A suitable I D / I G This value ensures that the composite anode material can achieve both high initial efficiency and rate performance.

[0074] In some embodiments, the coating uniformity of the composite negative electrode material is C, where 0.50 ≤ C ≤ 1.50, and the coating uniformity C is obtained by the following test method:

[0075] Ten composite anode material particles were randomly selected and subjected to Raman spectroscopy. The results showed that the composite anode material exhibited a high Raman spectroscopy intensity at 1200 cm⁻¹. -1 ~1500cm -1 Peak area I at D With at 1500cm -1 ~1800cm -1 Peak area I at G The ratio I D / I G The value is R n n = 1, 2, 3…10; I of 10 parts of composite negative electrode material particles D / I G The average value is R; I D / I G The standard deviation is B; the uniformity of the coating is C = n. 0.25 ·B 0.5 .

[0076] In some embodiments, the coating uniformity C of the composite negative electrode material can be 0.5, 0.6, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4 or 1.5, etc., and is not limited here.

[0077] In some embodiments, the specific surface area of ​​the composite negative electrode material is 0.2 m². 2 / g~10m 2 / g; specifically, it can 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 / g, etc., can also be other numbers within the above range, and are not limited here. Through numerous experiments, the inventors discovered that controlling the specific surface area of ​​the composite anode material within the above range is beneficial for improving the first-efficiency and cycle performance of lithium batteries made from this composite anode material. Preferably, the specific surface area of ​​the composite anode material is 0.2m². 2 / g~3.0m 2 / g.

[0078] In some embodiments, the tap density of the composite negative electrode material is 0.6 g / cm³. 3 ~1.4g / cm 3 Specifically, it could be 0.6 g / cm³.3 0.7 g / cm 3 0.75 g / cm 3 0.8 g / cm 3 0.85 g / cm 3 0.9 g / cm 3 0.95 g / cm 3 1.0 g / cm 3 1.2 g / cm 3 or 1.4 g / cm 3 and so on, but not limited to the listed values, and other unlisted values within the range are also applicable. By filling and coating with amorphous carbon, the pores of the graphite are filled or blocked, reducing the porosity of the composite negative electrode material. Low porosity can effectively reduce the side reactions that occur during charging and discharging, thereby reducing the expansion of the electrode and the decline in cycle performance caused by side reactions. Preferably, the tap density of the composite negative electrode material is 0.8 g / cm 3 1.2 g / cm 3 .

[0079] In some embodiments, the compacted density of the composite negative electrode material is 1.6 g / cm 3 2.2 g / cm 3 ; specifically, 1.6 g / cm 3 , 1.75 g / cm 3 , 1.8 g / cm 3 , 1.85 g / cm 3 , 1.9 g / cm 3 , 1.95 g / cm 3 , 2.0 g / cm 3 , 2.05 g / cm 3 , or 2.2 g / cm 3 , etc., but not limited to the listed values, and other unlisted values within the range are also applicable. Preferably, the compacted density of the composite negative electrode material under a 5T pressure is 1.8 g / cm 3 2.1 g / cm 3 .

[0080] In a second aspect, as shown in Figure 1 , the application provides a preparation method of a composite negative electrode material, comprising the following steps:

[0081] S10, a mixture comprising graphite, a liquid coating agent, and a dopant is heat-treated to obtain a precursor;

[0082] S20, a composite comprising the precursor and pitch is subjected to carbonization treatment to obtain a composite negative electrode material.

[0083] The preparation method of the composite negative electrode material provided by the application comprises the following steps: mixing graphite, a liquid coating agent and a dopant to obtain a mixture; performing heat treatment on the mixture; and mixing the mixture after the heat treatment with pitch and performing carbonization treatment. During the carbonization process, the dopant is decomposed to generate H2O, CO2 and other gases, and element doping is performed in the connecting layer, which can increase the lithium storage active sites and improve the migration speed of lithium ions; at least one of C-N, C-P, C-B, C-F, C-O and C-S chemical bonds is formed on the interface between the connecting layer and the carbon layer, the above chemical bonds have strong polarity and can react with the pitch to prevent the pitch from self-aggregation, and a carbon layer with good uniformity is formed on the surface of the connecting layer, so that the rate performance and low-temperature performance of the composite negative electrode material are improved. The carbon layer uniformly covers the connecting layer, which can effectively inhibit the consumption of the electrolyte by the defects formed by the doped elements in the connecting layer, so as to ensure the high capacity and initial efficiency of the composite negative electrode material. In summary, the preparation method can improve the rate performance and low-temperature performance of the composite negative electrode material while ensuring the high capacity and initial efficiency of the composite negative electrode material.

[0084] The preparation method provided by the present application is described in detail below.

[0085] Before step S10, the preparation method further comprises:

[0086] The natural flake graphite is subjected to shaping treatment to obtain spherical graphite.

[0087] The natural flake graphite is a natural crystalline graphite, which has a fish scale-like shape, belongs to the hexagonal system, has a layered structure, and has good high-temperature resistance, electrical conductivity, thermal conductivity, lubricity, plasticity, acid and alkali resistance and other properties.

[0088] In some embodiments, the shaping comprises at least one of crushing, spheroidizing or grading.

[0089] The natural graphite can be shaped by spheroidization, and the spheroidization rate is controlled to be 500 r / min to 5000 r / min, and the spheroidization time is controlled to be 0.2 to 10 hours.

[0090] The median particle size of the shaped graphite is 5 μm to 20 μm, and more specifically, can be 5 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 14 μm, 15 μm, 16 μm, 19 μm or 20 μm, but is not limited to the listed values, and other values not listed in the range are also applicable. It is found through multiple tests that the median particle size of the graphite controlled in the above range is beneficial to balancing the processing performance, capacity and rate performance. Preferably, the median particle size of the graphite is 6 μm to 15 μm.

[0091] In some embodiments, artificial graphite can also be selected.

[0092] In some embodiments, the mass content of carbon in the graphite is ≥ 95%, specifically can be 95%, 96%, 97%, 97.5%, 98.3%, 98.8% or 99%, etc., but not only limited to the listed values, other values not listed in the range are also applicable.

[0093] In some embodiments, the liquid coating agent comprises at least one of liquid asphalt and liquid rubber plasticizer.

[0094] 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 can be petroleum asphalt, modified asphalt and mesophase pitch, etc.

[0095] In some embodiments, the liquid rubber plasticizer comprises at least one of petroleum-based plasticizer, coal tar-based plasticizer, pine oil-based plasticizer, fatty-based plasticizer and synthetic plasticizer.

[0096] In some embodiments, the dopant comprises at least one of urea, melamine, melamine phosphate, ammonium dihydrogen phosphate, boron oxide, ammonium borate, polyvinylidene fluoride, ammonium 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 the doping of N element and B element to amorphous carbon can more effectively reduce the coating uniformity of carbon layer, which is beneficial to improve the rate performance of the composite negative electrode material and reduce the impedance at room temperature and low temperature.

[0097] S10, heat-treating the mixture comprising graphite, liquid coating agent and dopant to obtain a precursor.

[0098] In some embodiments, the mass ratio of graphite, liquid coating agent and dopant is 100:(10-100):(5-50), specifically can 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 only limited to the listed values, other values not listed in the range are also applicable. Too much dopant will reduce the initial efficiency of the composite negative electrode material; too little dopant will reduce the rate performance and low temperature performance of the composite negative electrode material.

[0099] In some embodiments, the graphite, the liquid coating agent and the dopant are mixed to form a mixture, and the mixing is performed by at least one of mechanical stirring and ultrasonic dispersion. When the mixing is performed by mechanical stirring, a propeller stirrer, a turbine stirrer, a flat blade stirrer, etc. can be used, and the order of adding the components is not limited as long as the components are mixed uniformly.

[0100] The stirring can be performed at room temperature or in a preheated state, and preferably, the stirring temperature is controlled to be in a range of 25°C to 80°C. It is understood that appropriate preheating is beneficial to the mixing of the graphite, the liquid coating agent and the dopant to form a liquid slurry with uniform components.

[0101] In some embodiments, the stirring rate is in a range of 10 r / min to 1000 r / min, and specifically can be 10 r / min, 50 r / min, 70 r / min, 100 r / min, 120 r / min, 150 r / min, 200 r / min, 300 r / min, 350 r / min, 400 r / min, 500 r / min or 1000 r / min, etc. The stirring makes the graphite, the liquid coating agent and the dopant more uniformly mixed. Too slow stirring rate results in low uniformity of the mixture, and too fast stirring rate requires a high-performance equipment and increases the cost.

[0102] In some embodiments, the temperature of the heat treatment is in a range of 150°C to 300°C, and the drying treatment time is in a range of 0.5 h to 10 h.

[0103] In some embodiments, the temperature of the heat treatment is in a range of 150°C to 300°C, and specifically can be 150°C, 180°C, 200°C, 220°C, 250°C, 260°C, 280°C or 300°C, etc., and the heat treatment time is in a range of 0.5 h to 10 h, and specifically can be 0.5 h, 1 h, 3 h, 5 h, 7 h, 8 h, 9 h or 10 h, etc. The heat treatment can be performed by, for example, oven drying, stirring evaporation, spray drying, etc. The heat treatment in the present embodiment is performed by oven drying.

[0104] In some embodiments, the temperature increasing rate of the heat treatment is in a range of 0.5°C / min to 5.0°C / min, and specifically can be 0.5°C / min, 1.0°C / min, 2.0°C / min, 3.0°C / min, 4.0°C / min or 5.0°C / min, etc. but is not limited to the listed values, and other values not listed in the range are also applicable.

[0105] S20, performing carbonization treatment on the composite containing the precursor and the pitch to obtain a composite negative electrode material.

[0106] In some embodiments, the pitch includes at least one of a petroleum-based pitch and a coal-based pitch.

[0107] In some embodiments, the mass ratio of the graphite to the pitch is 100:(1-10), which can be 100:1, 100:2, 100:3, 100:4, 100:5, 100:6, 100:7, 100:8, 100:9, 100:10, or the like, but is not limited to the listed values, and other values not listed in the range are also applicable.

[0108] In some embodiments, the reaction temperature of the carbonization treatment is 600-1500°C, which can be 600°C, 650°C, 670°C, 700°C, 800°C, 950°C, 1080°C, 1300°C, 1400°C, 1500°C, or the like, but is not limited to the listed values, and other values not listed in the range are also applicable. Understandably, a suitable carbonization temperature allows the amorphous carbon of the surface connection layer and the carbon layer of the graphite core to have a suitable I D / I G value, ensuring that the composite negative electrode material has both high initial efficiency and rate performance. Preferably, the temperature of the carbonization treatment is 800-1300°C.

[0109] In some embodiments, the holding time of the carbonization treatment is 0.5-10h, which can be 0.5h, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 10h, or the like, but is not limited to the listed values, and other values not listed in the range are also applicable. Preferably, the holding time of the carbonization treatment is 1-3h,

[0110] Optionally, the heating rate of the carbonization treatment is 0.5-5°C / min, which can be 0.5°C / min, 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, or the like, but is not limited to the listed values, and other values not listed in the range are also applicable.

[0111] In some embodiments, the carbonization treatment is carried out under a protective atmosphere, and the protective atmosphere includes at least one of nitrogen, helium, neon, argon, krypton, and xenon.

[0112] In some embodiments, the gas flow rate of the protective atmosphere is 2-100ml / s, which can 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, without limitation.

[0113] In some embodiments, after the carbonization treatment, at least one of the following is further performed: crushing, screening, and magnetic removal; preferably, after the carbonization treatment, crushing, magnetic removal, and screening are sequentially performed.

[0114] In some embodiments, the crushing method is any one of a mechanical crusher, an air flow crusher, and a low-temperature crusher.

[0115] In some embodiments, the screening method is any one of a fixed screen, a drum screen, a resonance screen, a roller screen, a vibrating screen, and a chain screen, and the mesh size is 200-500 mesh, specifically 200 mesh, 300 mesh, 400 mesh, or 500 mesh, etc. The particle size of the negative electrode material is controlled within the above range, which is beneficial to the improvement of the processability of the negative electrode material.

[0116] In some embodiments, the magnetic removal device is any one of a permanent magnetic cylinder magnetic separator, an electromagnetic iron remover, and a pulsating high gradient magnetic separator. The magnetic removal is to control the content of magnetic substances in the negative electrode material, to avoid the influence of the magnetic substances on the charging and discharging of the lithium ion battery, and to ensure the safety of the battery during use.

[0117] In a third aspect, the present application provides a lithium ion battery comprising the composite negative electrode material of the first aspect or the composite negative electrode material prepared by the preparation method of the second aspect.

[0118] Those skilled in the art will understand that the above-described preparation method of the lithium ion battery is only an example. Other methods commonly used in the art can be used without departing from the content disclosed in the present application.

[0119] The embodiments of the present application are further described below in multiple examples. The embodiments of the present application are not limited to the following specific examples. Within the scope of protection, appropriate changes can be made.

[0120] Example 1

[0121] The preparation method of the composite negative electrode material of the present embodiment comprises the following steps:

[0122] (1) Selecting artificial graphite powder with a median particle size of 12 μm, the artificial graphite powder, a petroleum-based liquid rubber plasticizer, and a urea dopant are mixed at a mass ratio of 100:100:50 to obtain a mixture, and the mixture is subjected to carbonization treatment in a tubular carbonization furnace under a nitrogen atmosphere, and is heated to 300℃ at a heating rate of 5℃ / min, and is kept at 300℃ for 0.5 h, and is cooled to obtain a precursor;

[0123] (2) Adding petroleum-based solid pitch powder to the precursor, and mixing the artificial graphite powder and the pitch at a mass ratio of 100:10 to obtain a composite;

[0124] (3) The composite is carbonized in a tube furnace under a nitrogen atmosphere, heated to 1500°C at a heating rate of 5°C / min, held for 0.5h, and then cooled to obtain the composite anode material.

[0125] Figure 2 Here is a SEM cross-sectional image of the composite anode material prepared in Example 1, as shown. Figure 2 As shown, the composite anode material includes a graphite core, a connecting layer located on the surface of the graphite core, and a carbon layer located on at least a portion of the surface of the connecting layer. Figure 2 As shown, the surface of the composite negative electrode material is very smooth, indicating that it has a uniform carbon layer.

[0126] The median particle size of the composite anode material is 14 μm, and the specific surface area is 1.8 m². 2 / g, tap density is 0.86g / cm³ 3 The compaction density under 5T pressure is 1.82 g / cm³. 3 The thickness of the connecting layer is 1 μm, the thickness of the carbon coating layer is 1 μm, the N content of the connecting layer is 9.1%, the N content of the carbon coating layer is 0.8%, and the mass content of amorphous carbon in the composite anode material is 6%.

[0127] The graphite anode material was analyzed by Raman spectroscopy at 1200 cm⁻¹. -1 ~1500cm -1 Peak area I at D With at 1500cm -1 ~1800cm -1 Peak area I at G The ratio I D / I G The average value is 2.72, and the coating uniformity C is 1.12.

[0128] Example 2

[0129] Unlike Example 1, in step (1), artificial graphite powder with a median particle size of 5 μm is selected.

[0130] The composite anode material prepared in this embodiment includes a graphite core, a connecting layer located on the surface of the graphite core, and a carbon layer located on at least a portion of the surface of the connecting layer.

[0131] The median particle size of the composite anode material is 7 μm, and the specific surface area is 2.7 m². 2 / g, tap density is 0.60g / cm³ 3 The compaction density under 5T pressure is 1.60 g / cm³. 3The thickness of the connecting layer is 1 μm, the thickness of the carbon coating layer is 1 μm, the N content of the connecting layer is 9.3%, the N content of the carbon coating layer is 0.7%, and the mass content of amorphous carbon in the composite anode material is 6%.

[0132] The graphite anode material was analyzed by Raman spectroscopy at 1200 cm⁻¹. -1 ~1500cm -1 Peak area I at D With at 1500cm -1 ~1800cm -1 Peak area I at G The ratio I D / I G The average value was 2.81; the coating uniformity C was 1.01.

[0133] Example 3

[0134] Unlike Example 1, in step (1), artificial graphite powder with a median particle size of 20 μm is selected.

[0135] The composite anode material prepared in this embodiment includes a graphite core, a connecting layer located on the surface of the graphite core, and a carbon layer located on at least a portion of the surface of the connecting layer.

[0136] The median particle size of the composite anode material is 22 μm, and the specific surface area is 1.4 m². 2 / g, tap density is 1.12g / cm³ 3 The compaction density under 5T pressure is 1.94 g / cm³. 3 The thickness of the connecting layer is 1 μm, the thickness of the carbon coating layer is 1 μm, the N content of the connecting layer is 8.9%, the N content of the carbon coating layer is 0.9%, and the mass content of amorphous carbon in the composite anode material is 6%.

[0137] The graphite anode material was analyzed by Raman spectroscopy at 1200 cm⁻¹. -1 ~1500cm -1 Peak area I at D With at 1500cm -1 ~1800cm -1 Peak area I at G The ratio I D / I G The average value was 2.51; the coating uniformity C was 1.21.

[0138] Example 4

[0139] The preparation method of the composite negative electrode material in this embodiment includes the following steps:

[0140] (1) selecting artificial graphite powder with a median particle size of 5 μm, mixing the artificial graphite powder, a petroleum-based liquid rubber plasticizer and a urea dopant at a mass ratio of 100:10:5 to obtain a mixture, and performing carbonization treatment on the mixture in a tubular carbonization furnace under a nitrogen atmosphere, heating to 300°C at a heating rate of 5°C / min, maintaining the temperature for 0.5 h, and cooling to obtain a precursor;

[0141] (2) adding petroleum-based solid pitch powder to the precursor, the mass ratio of artificial graphite powder to pitch being 100:1, and mixing thoroughly to obtain a composite;

[0142] (3) performing carbonization treatment on the composite in a tubular carbonization furnace under a nitrogen atmosphere, heating to 1500°C at a heating rate of 5°C / min, maintaining the temperature for 10 h, and cooling to obtain the composite negative electrode material.

[0143] The composite negative electrode material prepared in this example comprises a graphite core, a connecting layer on the surface of the graphite core, and a carbon layer on at least part of the surface of the connecting layer.

[0144] The composite negative electrode material has a median particle size of 5 μm, a specific surface area of 3.4 m 2 / g, a tap density of 0.74 g / cm 3 , a compacted density under a pressure of 5T of 1.72 g / cm 3 , a thickness of the connecting layer of 0.01 μm, a thickness of the carbon coating layer of 0.01 μm, a N content of the connecting layer of 1.2%, a N content of the carbon coating layer of 0.3%, and a mass content of amorphous carbon in the composite negative electrode material of 0.1%.

[0145] The graphite negative electrode material has an average value of the ratio I -1 / I -1 of the peak area I D at 1200 cm -1 -1500 cm -1 to the peak area I G at 1500 cm D -1800 cm G of 0.71 by Raman spectroscopy, and a uniformity of the C coating of 1.22.

[0146] Example 5

[0147] The preparation method of the composite negative electrode material of this example comprises the following steps:

[0148] (1) selecting artificial graphite powder with a median particle size of 20 μm, mixing the artificial graphite powder, a petroleum-based liquid rubber plasticizer and a urea dopant at a mass ratio of 100:10:5 to obtain a mixture, and performing carbonization treatment on the mixture in a tubular carbonization furnace under a nitrogen atmosphere, heating to 300°C at a heating rate of 5°C / min, maintaining the temperature for 0.5 h, and cooling to obtain a precursor;

[0149] (2) adding petroleum-based solid pitch powder to the precursor, the mass ratio of artificial graphite powder to pitch being 100:1, and mixing thoroughly to obtain a composite;

[0150] (3) performing carbonization treatment on the composite in a tubular carbonization furnace under a nitrogen atmosphere, heating to 1500°C at a heating rate of 5°C / min, maintaining the temperature for 10 h, and cooling to obtain the composite negative electrode material.

[0151] The composite negative electrode material prepared in this example comprises a graphite core, a connecting layer on the surface of the graphite core, and a carbon layer on at least part of the surface of the connecting layer.

[0152] The composite negative electrode material has a median particle size of 20 μm, a specific surface area of 1.5 m 2 / g, a tap density of 1.40 g / cm 3 , a compacted density of 2.20 g / cm 3 under a pressure of 5T, a thickness of the connecting layer of 0.01 μm, a thickness of the carbon coating layer of 0.01 μm, a N content of the connecting layer of 1.1%, a N content of the carbon coating layer of 0.4%, and a mass content of amorphous carbon in the composite negative electrode material of 0.1%.

[0153] The graphite negative electrode material has an average value of the ratio I -1 / I -1 of the peak area I D at 1200 cm -1 -1500 cm -1 to the peak area I G at 1500 cm D -1800 cm G of 0.50 by Raman spectroscopy, and a uniformity of the C coating of 1.28.

[0154] Example 6

[0155] The preparation method of the composite negative electrode material of this example comprises the following steps:

[0156] (1) natural graphite powder with a median particle size of 5 μm is selected, artificial graphite powder, a petroleum-based liquid rubber plasticizer and a urea dopant are mixed at a mass ratio of 100:10:5 to obtain a mixture, and the mixture is subjected to carbonization treatment in a tube furnace under a nitrogen atmosphere, heated to 300°C at a heating rate of 5°C / min, and kept at 300°C for 0.5 h, and then cooled to obtain a precursor;

[0157] (2) petroleum-based solid pitch powder is added to the precursor, and the mass ratio of artificial graphite powder to pitch is 100:1, and the mixture is mixed to obtain a composite;

[0158] (3) the composite is subjected to carbonization treatment in a tube furnace under a nitrogen atmosphere, heated to 1500°C at a heating rate of 5°C / min, and kept at 1500°C for 10 h, and then cooled to obtain the composite negative electrode material.

[0159] The composite negative electrode material prepared in this example comprises a graphite core, a connecting layer located on the surface of the graphite core, and a carbon layer located on at least part of the surface of the connecting layer.

[0160] The composite negative electrode material has a median particle size of 5 μm, a specific surface area of 1.00 m 2 / g, a tap density of 0.82 g / cm 3 , a compacted density of 1.62 g / cm 3 under a pressure of 5T, a thickness of the connecting layer of 0.01 μm, a thickness of the carbon coating layer of 0.01 μm, a N content of the connecting layer of 1.1%, a N content of the carbon coating layer of 0.2%, and a mass content of amorphous carbon in the composite negative electrode material of 0.1%.

[0161] The graphite negative electrode material has an average value of the ratio I -1 / I -1 of the peak area I D at 1200 cm -1 -1500 cm -1 to the peak area I G at 1500 cm D -1800 cm G of 0.76 by Raman spectroscopy, and a uniformity of the C coating of 1.18.

[0162] Example 7

[0163] Different from Example 1, in step (1), a coal tar-based liquid rubber plasticizer is selected.

[0164] The composite negative electrode material prepared in this example comprises a graphite core, a connecting layer located on the surface of the graphite core, and a carbon layer located on at least part of the surface of the connecting layer.

[0165] The median particle size of the composite negative electrode material is 14 μm, the specific surface area is 2.2 m 2 / g, the tap density is 0.89 g / cm 3 , the compacted density under 5T pressure is 1.85 g / cm 3 , the thickness of the connecting layer is 1 μm, the thickness of the carbon coating layer is 1 μm, the N content of the connecting layer is 9.0%, the N content of the carbon coating layer is 0.9%, and the mass content of amorphous carbon in the composite negative electrode material is 6%.

[0166] The average value of the ratio I -1 / I -1 of the peak area I D at 1200 cm -1 - 1500 cm -1 to the peak area I G at 1500 cm D - 1800 cm G of the graphite negative electrode material by Raman spectroscopy is 2.91; and the average coating degree of uniform carbon is 1.42.

[0167] Example 8

[0168] Different from Example 1, in step (1), petroleum-based liquid pitch is selected.

[0169] The composite negative electrode material prepared in this example comprises a graphite core, a connecting layer on the surface of the graphite core, and a carbon layer on at least part of the surface of the connecting layer.

[0170] The median particle size of the composite negative electrode material is 14 μm, the specific surface area is 1.5 m 2 / g, the tap density is 0.85 g / cm 3 , the compacted density under 5T pressure is 1.81 g / cm 3 , the thickness of the connecting layer is 1 μm, the thickness of the carbon coating layer is 1 μm, the N content of the connecting layer is 9.3%, the N content of the carbon coating layer is 0.6%, and the mass content of amorphous carbon in the composite negative electrode material is 6%.

[0171] The average value of the ratio I -1 / I -1 of the peak area I D at 1200 cm -1 - 1500 cm -1 to the peak area I G at 1500 cm D - 1800 cm G of the graphite negative electrode material by Raman spectroscopy is 2.52; and the average coating degree of uniform carbon is 0.90.

[0172] Example 9

[0173] Unlike Example 1, in step (1), coal-based liquid pitch is used.

[0174] The composite anode material prepared in this embodiment includes a graphite core, a connecting layer located on the surface of the graphite core, and a carbon layer located on at least a portion of the surface of the connecting layer.

[0175] The median particle size of the composite anode material is 14 μm, and the specific surface area is 1.9 m². 2 / g, tap density is 0.88g / cm³ 3 The compaction density under 5T pressure is 1.84 g / cm³. 3 The thickness of the connecting layer is 1 μm, the thickness of the carbon coating layer is 1 μm, the N content of the connecting layer is 8.9%, the N content of the carbon coating layer is 0.8%, and the mass content of amorphous carbon in the composite anode material is 6%.

[0176] The graphite anode material was analyzed by Raman spectroscopy at 1200 cm⁻¹. -1 ~1500cm -1 Peak area I at D With at 1500cm -1 ~1800cm -1 Peak area I at G The ratio I D / I G The average value was 2.66; the coating uniformity C was 1.27.

[0177] Example 10

[0178] Unlike Example 1, in step (1), ammonium dihydrogen phosphate dopant is selected.

[0179] The composite anode material prepared in this embodiment includes a graphite core, a connecting layer located on the surface of the graphite core, and a carbon layer located on at least a portion of the surface of the connecting layer.

[0180] The median particle size of the composite anode material is 14 μm, and the specific surface area is 2.0 m². 2 / g, tap density is 0.90g / cm³ 3 The compaction density under 5T pressure is 1.85 g / cm³. 3 The thickness of the connecting layer is 1 μm, the thickness of the carbon coating layer is 1 μm, the N content and P content of the connecting layer are 3.9% and 2.8% respectively, the N content and P content of the carbon coating layer are 0.3% and 0.2% respectively, and the mass content of amorphous carbon in the composite anode material is 6%.

[0181] The graphite anode material was analyzed by Raman spectroscopy at 1200 cm⁻¹. -1 ~1500cm-1 the peak area I at 1200cm-1 D the peak area I at 1500cm-1 -1 the peak area I at 1800cm-1 -1 the peak area I at 1200cm-1 G the ratio I D / I G The average value of I

[0182] Example 11

[0183] The difference between this example and Example 1 is that in step (1), an ammonium borate dopant is selected.

[0184] The composite negative electrode material prepared in this example comprises a graphite core, a connecting layer on the surface of the graphite core, and a carbon layer on at least part of the surface of the connecting layer.

[0185] The composite negative electrode material has a median particle size of 14 μm, a specific surface area of 1.4 m 2 / g, a tap density of 0.83 g / cm 3 , a compacted density under a 5T pressure of 1.78 g / cm 3 , a thickness of the connecting layer of 1 μm, a thickness of the carbon coating layer of 1 μm, N and B contents of the connecting layer of 2.1% and 5.2% respectively, N and B contents of the carbon coating layer of 0.2% and 0.5% respectively, and a mass content of amorphous carbon in the composite negative electrode material of 6%.

[0186] By Raman spectroscopy, the graphite negative electrode material has a peak area I at 1200cm-1 -1 1500cm-1 -1 the peak area I at 1500cm-1 D the peak area I at 1800cm-1 -1 the peak area I at 1200cm-1 -1 the ratio I G / I D The average value of I G / I

[0187] Example 12

[0188] The difference between this example and Example 1 is that in step (1), an ammonium fluoride dopant is selected.

[0189] The composite negative electrode material prepared in this example comprises a graphite core, a connecting layer on the surface of the graphite core, and a carbon layer on at least part of the surface of the connecting layer.

[0190] The composite negative electrode material has a median particle size of 14 μm, a specific surface area of 1.9 m 2 / g, a tap density of 0.88 g / cm 3, the compaction density under 5T pressure is 1.83 g / cm 3 , the thickness of the connecting layer is 1 μm, the thickness of the carbon coating layer is 1 μm, the N content and the F content of the connecting layer are 7.1% and 3.2% respectively, the N content and the F content of the carbon coating layer are 0.5% and 0.3% respectively, and the mass content of amorphous carbon in the composite negative electrode material is 6%.

[0191] The average value of the ratio I -1 / I -1 of the peak area I D at 1200 cm -1 -1500 cm -1 to the peak area I G at 1500 cm D -1800 cm G of the graphite negative electrode material is 2.76 by Raman spectroscopy, and the average degree of carbon coating is 1.18.

[0192] Example 13

[0193] Different from Example 1, an ammonium sulfate dopant is selected in step (1).

[0194] The composite negative electrode material prepared in this example comprises a graphite core, a connecting layer on the surface of the graphite core, and a carbon layer on at least part of the surface of the connecting layer.

[0195] The median particle size of the composite negative electrode material is 14 μm, the specific surface area is 2.1 m 2 / g, the tap density is 0.91 g / cm 3 , the compaction density under 5T pressure is 1.86 g / cm 3 , the thickness of the connecting layer is 1 μm, the thickness of the carbon coating layer is 1 μm, the N content and the S content of the connecting layer are 4.1% and 2.2% respectively, the N content and the S content of the carbon coating layer are 0.3% and 0.1% respectively, and the mass content of amorphous carbon in the composite negative electrode material is 6%.

[0196] The average value of the ratio I -1 / I -1 of the peak area I D at 1200 cm -1 -1500 cm -1 to the peak area I G at 1500 cm D -1800 cm G of the graphite negative electrode material is 2.91 by Raman spectroscopy, and the average degree of carbon coating is 1.42.

[0197] Example 14

[0198] Unlike Example 1, boron oxide dopant is used in step (1).

[0199] The composite anode material prepared in this embodiment includes a graphite core, a connecting layer located on the surface of the graphite core, and a carbon layer located on at least a portion of the surface of the connecting layer.

[0200] The composite anode material has a median particle size of 14 μm, a specific surface area of ​​1.8 m² / g, a tap density of 0.92 g / cm³, a compaction density of 1.88 g / cm³ under 5T pressure, a bonding layer thickness of 1 μm, a carbon coating layer thickness of 1 μm, O and B contents of 5.2% and 3.2% respectively in the bonding layer, O and B contents of 0.5% and 0.3% respectively in the carbon coating layer, and an amorphous carbon mass content of 6% in the composite anode material.

[0201] The graphite anode material was analyzed by Raman spectroscopy at 1200 cm⁻¹. -1 ~1500cm -1 Peak area I at D With at 1500cm -1 ~1800cm -1 Peak area I at G The ratio I D / I G The average value was 2.81; the coating uniformity C was 1.36.

[0202] Example 15

[0203] Unlike Example 1, in step (2), coal-based solid pitch powder is used.

[0204] The composite anode material prepared in this embodiment includes a graphite core, a connecting layer located on the surface of the graphite core, and a carbon layer located on at least a portion of the surface of the connecting layer.

[0205] The median particle size of the composite anode material is 14 μm, and the specific surface area is 2.0 m². 2 / g, tap density is 0.90g / cm³ 3 The compaction density under 5T pressure is 1.85 g / cm³. 3 The thickness of the connecting layer is 1 μm, the thickness of the carbon coating layer is 1 μm, the N content of the connecting layer is 8.8%, the N content of the carbon coating layer is 0.7%, and the mass content of amorphous carbon in the composite anode material is 6%.

[0206] The graphite anode material was analyzed by Raman spectroscopy at 1200 cm⁻¹. -1 ~1500cm -1 Peak area I at D With at 1500cm -1 ~1800cm-1 Peak area I at G The ratio I D / I G The average value was 2.84; the coating uniformity C was 1.24.

[0207] Example 16

[0208] Unlike Example 1, in step (3), carbonization is carried out in a tubular carbonization furnace under an argon atmosphere, with the temperature increased to 600°C at a rate of 0.5°C / min and held for 0.5 hours.

[0209] The composite anode material prepared in this embodiment includes a graphite core, a connecting layer located on the surface of the graphite core, and a carbon layer located on at least a portion of the surface of the connecting layer.

[0210] The median particle size of the composite anode material is 14 μm, and the specific surface area is 2.4 m². 2 / g, tap density is 0.81g / cm³ 3 The compaction density under 5T pressure is 1.78 g / cm³. 3 The thickness of the connecting layer is 1 μm, the thickness of the carbon coating layer is 1 μm, the N content of the connecting layer is 9.4%, the N content of the carbon coating layer is 0.6%, and the mass content of amorphous carbon in the composite negative electrode material is 10%.

[0211] The graphite anode material was analyzed by Raman spectroscopy at 1200 cm⁻¹. -1 ~1500cm -1 Peak area I at D With at 1500cm -1 ~1800cm -1 Peak area I at G The ratio I D / I G The average value was 3.00; the coating uniformity C was 1.36.

[0212] Comparative Example 1

[0213] The difference from Example 1 is that no urea dopant is added in step (1).

[0214] The composite anode material prepared in this comparative example includes a graphite core, a connecting layer located on the surface of the graphite core, and a carbon layer located on at least a portion of the surface of the connecting layer.

[0215] Figure 3 Here is a SEM image of the composite anode material prepared in Comparative Example 1, as shown. Figure 3 As shown, the coating layer on the surface of the composite negative electrode material is very uneven and cracked, indicating that not adding dopants is not conducive to coating uniformity.

[0216] The median particle diameter of the composite negative electrode material is 14 μm, the specific surface area is 2.4 m 2 / g, the tap density is 0.89 g / cm 3 , and the compacted density under a pressure of 5 T is 1.85 g / cm 3 The thickness of the connecting layer is 1 μm, the thickness of the carbon coating layer is 1 μm, and the mass content of amorphous carbon in the composite negative electrode material is 6%.

[0217] The average value of the ratio I -1 / I -1 of the peak area I D at 1200 cm -1 - 1500 cm -1 to the peak area I G at 1500 cm D - 1800 cm G of the graphite negative electrode material is 2.48; and the average coating degree of carbon is 1.73.

[0218] Comparative Example 2

[0219] The difference from Example 1 is that no petroleum-based liquid rubber plasticizer is added in step (1).

[0220] The composite negative electrode material produced in this comparative example includes a graphite core and a carbon layer on the surface of the graphite core.

[0221] The median particle diameter of the composite negative electrode material is 13 μm, the specific surface area is 2.8 m 2 / g, the tap density is 0.92 g / cm 3 , the compacted density under a pressure of 5 T is 1.88 g / cm 3 , the thickness of the carbon coating layer is 1 μm, the N content of the carbon coating layer is 0.4%, and the mass content of amorphous carbon in the composite negative electrode material is 3%.

[0222] The average value of the ratio I -1 / I -1 of the peak area I D at 1200 cm -1 - 1500 cm -1 to the peak area I G at 1500 cm D - 1800 cm G of the graphite negative electrode material is 2.02; and the average coating degree of carbon is 1.76.

[0223] Comparative Example 3

[0224] The difference from Example 1 is that in step (1), no petroleum-based liquid rubber plasticizer and urea dopant are added.

[0225] The composite negative electrode material prepared in this comparative example comprises a graphite inner core and a carbon layer on the surface of the graphite inner core.

[0226] The composite negative electrode material has a median particle size of 13 μm, a specific surface area of 2.6 m 2 / g, a tap density of 0.94 g / cm 3 , a compacted density of 1.90 g / cm 3 under a 5T pressure, a carbon coating layer thickness of 1 μm, and an amorphous carbon mass content of 3% in the composite negative electrode material.

[0227] The graphite negative electrode material has an average value of 1.77 for the ratio I -1 / I -1 of the peak area I D at 1200 cm -1 - 1500 cm -1 to the peak area I G at 1500 cm D - 1800 cm G , and a coating uniformity of 1.83.

[0228] Test Methods

[0229] (1) Test method for the median particle size of the composite negative electrode material:

[0230] The particle size distribution range of the composite negative electrode material is tested by a Malvern laser particle size analyzer.

[0231] (2) Test method for the tap density of the composite negative electrode material:

[0232] The composite negative electrode material is placed in the sample bin of the tap density tester, and the sample volume at this time is recorded after 1000 vibrations, so that the tap density can be calculated according to the mass / volume ratio.

[0233] (3) Test method for the specific surface area of the composite negative electrode material:

[0234] Under constant temperature and low temperature, the adsorption amount of gas on the surface of the solid at different relative pressures is determined, and then the monolayer adsorption amount of the sample is obtained based on the Brunauer-Emmett-Teller adsorption theory and its formula (BET formula), so that the specific surface area of the material is calculated.

[0235] (4) Test method for the compacted density of the composite negative electrode material:

[0236] The test of the compacted density is carried out by the test method of lithium ion battery graphite negative material GB / T 24533-2009, and the test pressure is 5 tons.

[0237] (5) Test method of the thickness of the connecting layer and the carbon layer of the composite negative material:

[0238] The composite negative material powder is made into an SEM section sample, and the average thickness of the connecting layer and the carbon layer is measured in the SEM image.

[0239] (6) Test method of the content of the doping elements of the connecting layer and the carbon layer of the composite negative material:

[0240] The content P2 of the doping elements of the outermost carbon layer of the composite negative material is directly measured by X-ray photoelectron spectroscopy XPS. The outermost carbon layer of the composite negative material is removed by fusion physical action by using a fusion machine, and the content P1 of the doping elements of the connecting layer of the composite material is measured by XPS.

[0241] (7) Test method of the coating uniformity of the composite negative material:

[0242] The Raman spectrum measurement adopts a Jobin Yvon LabRAM HR spectrometer, the light source is 532 nm, and the test range is 0 cm -1 ~ 4000 cm -1 . The test range is 100 μm*100 μm.

[0243] Ten composite negative material particles are randomly obtained, and the peak area I -1 at 1200 cm -1 ~ 1500 cm D and the peak area I -1 at 1500 cm -1 ~ 1800 cm G of the composite negative material are measured by Raman spectrum test, and the ratio I D / I G is R n , n = 1, 2, 3…10; the average value of I D / I G of the ten composite negative material particles is R; the standard deviation of I D / I G is B; the coating uniformity C = n 0.25 ·B 0.5 .

[0244] (8) Rate performance test of lithium ion button half-cell:

[0245] The graphite composite prepared in each example and comparative example was mixed as an active material at a mass ratio of active material: conductive carbon black: CMC: SBR = 95.3: 1.5: 1.4: 1.8, and then coated on a copper foil after being mixed with deionized water as a solvent to form a slurry, with a coating density of 6.5 ± 0.1 mg / cm 2 After vacuum drying at 90°C, a pole piece was obtained, and the pole piece was rolled to a compaction density of 1.50 ± 0.02 g / cc. A 2016 type button half-cell was assembled from the pole piece, a lithium piece, an electrolyte (1 mol / L LiPF6, EC: EMC: DMC = 1: 1: 1), and a Celgard 2400 separator. The button half-cell was subjected to rate performance testing in an environment at 25 ± 2°C, and the charge and discharge specific capacities and coulombic efficiency at 0.1C, 0.2C, 1C, and 2C were obtained. The rate test conditions were as follows: ① 0.1C discharge to 0.01V, constant voltage to 0.01C, 0.1C charge to 1.5V; ② 0.2C discharge to 0.01V, constant voltage to 0.01C, 0.2C charge to 1.5V; ③ 1C discharge to 0.01V, constant voltage to 0.01C, 0.2C charge to 1.5V; and ④ 2C discharge to 0.01V, constant voltage to 0.01C, 0.2C charge 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.

[0246] (9) Lithium ion button half-cell electrochemical impedance spectroscopy (EIS) test:

[0247] The button half-cell was activated in an environment at 25 ± 2°C for 2 weeks under the following conditions: 0.1C discharge to 0.01V, constant voltage to 0.01C, 0.1C charge to 1.5V; and then discharged to 50% SOC for EIS testing to obtain the impedance R z in the semicircle region z , which includes the SEI film impedance, Li + diffusion impedance in the electrode pores, and charge transfer impedance. The EIS test conditions were as follows: (1) an alternating signal amplitude of 5 mV, a scanning frequency range of 0.03 Hz to 10 5 Hz, and a temperature of 25 ± 2°C; and (2) an alternating signal amplitude of 5 mV, a scanning frequency range of 0.03 to 10 5 Hz, and a temperature of -5 ± 2°C.

[0248] The results of the above performance tests are as follows:

[0249] Table 1. Performance comparison results table

[0250]

[0251] The rate performance and EIS test results of the graphite composite lithium ion button half-cell in the examples and comparative examples are shown in Table 1.

[0252] From Examples 1, 2 and 3, it can be seen that the median particle size of artificial graphite affects the coating uniformity, and when the median particle size of artificial graphite decreases, the coating uniformity also decreases, thereby improving the coating uniformity, thereby improving the rate performance of the graphite negative electrode material and reducing the impedance at normal temperature and low temperature.

[0253] From Examples 2, 3, 4 and 5, it can be seen that reducing the ratio of the dopant and the liquid coating agent increases the coating uniformity, which is not conducive to improving the coating uniformity, and at the same time reduces the capacity, the initial efficiency and the rate performance of the graphite negative electrode material, and increases the impedance at normal temperature and low temperature. D / I G , and reduces the carbon disorder degree, thereby reducing the rate performance of the graphite negative electrode material and increasing the impedance at normal temperature and low temperature.

[0254] From Examples 4 and 6, it can be seen that compared with the artificial graphite coating product, the capacity of the natural graphite coating product is higher, but the initial efficiency, the rate performance and the impedance are poorer.

[0255] From Examples 1, 7, 8 and 9, it can be seen that compared with the petroleum-based liquid coating agent, the coal-based liquid coating agent contains more impurities, which increases the coating uniformity, which is not conducive to improving the coating uniformity, thereby reducing the capacity, the initial efficiency and the rate performance of the graphite negative electrode material, and increasing the impedance at normal temperature and low temperature. Preferably, the petroleum-based liquid pitch coating agent is used in combination with the dopant to modify the surface of the graphite.

[0256] From Examples 1, 10, 11, 12, 13 and 14, it can be seen that the improvement effect of the dopant on the coating uniformity is: ammonium borate > ammonium fluoride ≈ urea > ammonium dihydrogen phosphate > boron oxide > ammonium sulfate, indicating that N and B doping can more effectively reduce the coating uniformity, which is more conducive to improving the coating uniformity, thereby improving the rate performance of the graphite negative electrode material and reducing the impedance at normal temperature and low temperature.

[0257] From Examples 1 and 15, it can be seen that compared with the petroleum-based solid pitch, the coal-based solid pitch contains more impurities, which increases the coating uniformity, which is not conducive to improving the coating uniformity, thereby reducing the capacity, the initial efficiency and the rate performance of the graphite negative electrode material, and increasing the impedance at normal temperature and low temperature.

[0258] From Examples 1 and 16, it can be seen that reducing the carbonization temperature increases the coating uniformity, which is not conducive to improving the coating uniformity, and at the same time increases the capacity, the initial efficiency and the rate performance of the graphite negative electrode material, and increases the impedance at normal temperature and low temperature. D / I G , and improves the carbon disorder degree, thereby reducing the initial efficiency and the rate performance of the graphite negative electrode material, and increasing the impedance at normal temperature and low temperature.

[0259] As can be seen from Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3, the synergistic effect of the petroleum-based liquid rubber plasticizer and the urea dopant can greatly reduce the coating uniformity, more favorably improve the coating uniformity, thereby more effectively improve the capacity, initial efficiency and rate performance of the graphite negative electrode material, and more effectively reduce the impedance at room temperature and low temperature.

[0260] Although the present application is disclosed with the preferred embodiments as above, it is not intended to limit the claims, and any person skilled in the art can make several possible changes and modifications without departing from the concept of the present application, therefore the protection scope of the present application should be defined by the scope of the claims of the present application.

Claims

1. A composite negative electrode material, characterized by, The composite negative electrode material comprises a graphite inner core, a connecting layer on the surface of the graphite inner core, and a carbon layer on the surface of the connecting layer, the connecting layer comprises amorphous carbon containing a doping element, and a raw material for forming the connecting layer comprises a liquid coating agent and a doping agent containing a doping element, the liquid coating agent comprises at least one of liquid pitch and liquid rubber plasticizer; The carbon layer comprises amorphous carbon containing a doping element; and the graphite has a median particle size of 5 μm to 20 μm. The connecting layer of the composite negative electrode material has at least one of chemical bonds 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, P1>P2; The coating uniformity of the composite negative electrode material is C, and 0.50≤C≤1.

50.

2. The composite negative material of claim 1, wherein, The composite negative electrode material satisfies at least one of the following characteristics: (1) The graphite comprises at least one of artificial graphite and natural graphite; (2) The thickness of the connecting layer is 0.01 μm to 1 μm; (3) The thickness of the carbon layer is 0.01 μm to 1 μm; (4) The doping element in the connecting layer and the carbon layer comprises at least one of N, P, B, F, O and S; (5) The mass content of the doping element in the connecting layer is P1, and 1% <P1≤10%; (6) The mass content of the doping element in the carbon layer is P2, and 0% <P2≤1%; (7) The ratio of the peak area I at 1200cm-1~1500cm-1 to the peak area I at 1500cm-1~1800cm-1 of the composite negative electrode material is 0.5~3.0, which is measured by Raman spectrum test. -1 -1 D -1 -1 G D G ;​​​​​​​ (8) The liquid rubber plasticizer comprises at least one of petroleum-based plasticizers, coal tar-based plasticizers, pine oil-based plasticizers, fatty-based plasticizers and synthetic plasticizers; (9) The doping agent comprises at least one of urea, melamine, phosphonium melamine, ammonium dihydrogen phosphate, boron oxide, ammonium borate, polyvinylidene fluoride, ammonium fluoride, ammonium bifluoride, ammonium sulfate, ammonium bisulfate and thiourea.

3. The composite negative material according to claim 1 or 2, characterized in that, The composite negative electrode material satisfies at least one of the following characteristics: (1) The composite negative electrode material has a median particle size of 5 μm to 22 μm; (2) the specific surface area of the composite negative electrode material is 0.2 m 2 / g~10 m 2 / g; (3) the tap density of the composite negative electrode material is 0.6 g / cm 3 ~ 1.4 g / cm 3 ; (4) the compounding negative material has a compaction density of 1.6 g / cm 3 ~ 2.2 g / cm 3 ; (5) The mass content of amorphous carbon in the composite negative electrode material is 0.1% to 10%.

4. A method for preparing a composite negative electrode material, characterized by, The method comprises the following steps: The mixture comprising graphite, a liquid coating agent and a doping agent is subjected to heat treatment at 150 ℃ to 300 ℃ to obtain a precursor; wherein the mass ratio of the graphite, the liquid coating agent and the doping agent is 100:(10-100):(5-50), the graphite has a median particle size of 5 μm to 20 μm; the liquid coating agent comprises at least one of liquid pitch and liquid rubber plasticizer; and the doping agent comprises at least one of urea, melamine, phosphonium melamine, ammonium dihydrogen phosphate, boron oxide, ammonium borate, polyvinylidene fluoride, ammonium fluoride, ammonium bifluoride, ammonium sulfate, ammonium bisulfate and thiourea; The composite comprising the precursor and pitch is subjected to carbonization treatment at a temperature of 600 ℃ to 1500 ℃ to obtain a composite negative electrode material.

5. The production method according to claim 4, characterized by, The method satisfies at least one of the following characteristics: (1) The graphite comprises at least one of artificial graphite and natural graphite; (2) The carbon content in the graphite is ≥95% by mass; (3) The liquid asphalt includes at least one of petroleum-based liquid asphalt and coal-based liquid asphalt; (4) The liquid rubber plasticizer includes at least one of petroleum-based plasticizers, coal tar-based plasticizers, pine oil-based plasticizers, aliphatic plasticizers and synthetic plasticizers.

6. The production method according to claim 4 or 5, characterized by, The method satisfies at least one of the following characteristics: (1) The asphalt includes 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 production method according to claim 4 or 5, characterized by, The method satisfies at least one of the following characteristics: (1) The heat treatment is carried out in at least one atmosphere of air and protective gas; (2) The heat treatment is carried out in an atmosphere of at least one of air and a protective gas, wherein the protective gas includes at least one of nitrogen, helium, neon, argon, krypton and xenon; (3) The heating rate of the heat treatment is 0.5℃ / min to 5.0℃ / min; (4) The heat treatment holding time is 0.5h to 10h.

8. The production method according to claim 4 or 5, characterized by, The method satisfies at least one of the following characteristics: (1) The carbonization process is carried out under a protective atmosphere; (2) The carbonization process is carried out under a protective atmosphere, which includes at least one of nitrogen, helium, neon, argon, krypton and xenon. (3) The heating rate of the carbonization treatment is 0.5℃ / min to 5.0℃ / min; (4) The heat preservation time for the carbonization treatment is 0.5h to 10h.

9. The production method according to claim 4 or 5, characterized by, The method satisfies at least one of the following characteristics: (1) The preparation method further includes: shaping natural flake graphite to obtain spherical graphite; (2) The preparation method further includes: shaping natural flake graphite to obtain spherical graphite. The shaping process includes at least one of crushing, spheroidizing, and grading.

10. A lithium-ion battery, characterized by, The lithium-ion battery includes the negative electrode material according to any one of claims 1 to 3 or the negative electrode material prepared by the preparation method according to any one of claims 4 to 9.

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