WO2017050260A1

WO2017050260A1 - Method for preparing composite graphite, composite graphite and lithium ion battery

Info

Publication number: WO2017050260A1
Application number: PCT/CN2016/099767
Authority: WO
Inventors: 周海辉; 苗恒; 潘修军; 谯渭川
Original assignee: 深圳市贝特瑞新能源材料股份有限公司
Priority date: 2015-09-25
Filing date: 2016-09-22
Publication date: 2017-03-30
Also published as: CN105098184A

Abstract

Provided are a method for preparing a composite graphite, a composite graphite prepared by the method and a lithium ion battery. The method comprises the following steps: S1, providing an ultrafine carbon powder, wherein the ultrafine carbon powder comprises a green coke and/or raw mesocarbon microspheres; S2, mixing the ultrafine carbon powder with a binder to obtain a mixture A, mixing the mixture A with a catalyst to obtain a mixture B, and then subjecting the mixture B to a combined treatment so as to obtain a precursor; S3, subjecting the precursor to a graphitization treatment so as to obtain a half-finished product; and S4, crushing, spheroidizing, cladding and sieving the half-finished product so as to obtain the composite graphite. The method overcomes the problems that a composite graphite prepared by a method in the prior art has low energy density, poor high-rate charge and discharge properties and a high expansion rate in the charging and discharging processes. The composite graphite prepared by the present method has high energy density, good liquid absorption and retention properties, good isotropic properties, good high-rate charge and discharge properties and a low expansion rate in the charging and discharging processes.

Description

Preparation method of composite graphite, composite graphite and lithium ion battery

Technical field

The present invention relates to a method for preparing composite graphite and composite graphite prepared by the method, and a lithium ion battery including the composite graphite.

Background technique

In recent years, with the development of mobile communication and portable electronic devices, higher requirements have been placed on the performance of lithium ion batteries that provide energy. The anode material has a significant impact on the performance of lithium-ion batteries. In the existing anode materials, new high-capacity anodes such as Si-based, Sn-based and Al-based have not been popularized due to their cost and technical factors, while traditional graphite-based anode materials Due to its stable performance, mature technology and low cost, it will continue to dominate the negative electrode market for a period of time.

At present, the actual capacity of the graphite-based anode is close to the theoretical capacity, and further increasing the volume-to-weight energy density under the condition that the mass ratio is the same as the energy density is one of the possible improvement directions. It is well known that graphite particles undergo a layer spacing change and SEI film thickening during deintercalation of lithium, which in turn leads to expansion of the negative electrode tab, SEI film cracking or even active material peeling and membrane breakage, affecting cycle performance and safety performance. In order to prevent deterioration of battery performance caused by expansion of the negative pole piece, the practice of preserving the expansion space of the pole piece in the battery design is mainly adopted, and the method cannot solve the problem of pole piece expansion fundamentally, and also limits the increase of energy density.

The development of a new generation of digital communication equipment represented by the Apple mobile phone has made the problem of slow charging of the graphite negative electrode become a serious problem affecting the user experience.

In order to solve the above problem, the patent CN1645653A proposes a method of combining sheet-like or flat-shaped coke-like particles into a spherical or spheroidal precursor by a binder, and then graphitizing to obtain composite secondary graphite particles, the secondary particles having macroscopic Isotropic.

In actual production, the combination of coke particles and binder is poor, the sphericity of the finished product is low, and it is prone to cracking and pulverization in the crushing and spheroidizing process after graphitization, and becomes anisotropic sheet or flat graphite. Particles.

Patent CN103811758A, the anisotropic graphite raw material is obtained by pulverization, classification and sieving to obtain ultrafine graphite powder with an average particle diameter of 2-10 μm, and then treated by secondary granulation technology to improve the isotropicity of graphite particles and graphite. The end/base ratio of the particles to improve the material during the intercalation process Volume expansion and contraction effects and high current charge and discharge properties of materials.

The raw materials used in this scheme are artificial graphite or natural graphite. The raw material cost is high, the bonding strength between graphite and binder is poor, and the ratio of binder required for compounding is high, which limits the further improvement of tap density and specific capacity, only from isotropy. The angle improves the lithium insertion rate and the rate performance is limited.

Patent CN103855369A heats and stirs a mixture of carbon powder, binder and catalyst, press molding, carbonization and graphitization.

The solution has the problems of low specific capacity, low initial effect and low compaction density.

Patent CN103682347A mixes the optimized proportion of needle coke, isotropic coke and natural graphite uniformly, and puts the mixture material into the graphitization furnace for graphitization and purification treatment, and finally obtains the negative electrode material of lithium ion secondary battery, further after graphitization The powder is shaped, classified, and sieved to obtain a composite lithium ion battery anode material.

The graphite particles prepared by the method have limited performance improvement and cannot improve the orientation.

Summary of the invention

In view of the deficiencies of the prior art, the object of the present invention is to provide a method for preparing composite graphite. The composite graphite prepared by the method has high energy density, good liquid absorption and liquid retention performance, good isotropic performance, and large magnification charging and discharging. Good performance, low expansion rate during charging and discharging.

The technical solution adopted by the present invention to solve the above technical problems is as follows:

A method for preparing composite graphite is provided, which comprises the following steps:

S1, providing ultrafine carbon powder; the ultrafine carbon powder comprises green coke and/or mesocarbon microspheres;

S2, mixing the ultrafine carbon powder with the binder to obtain a mixture A, the mixture A and the catalyst are mixed to obtain a mixture B, and then the mixture B is subjected to a composite treatment to obtain a precursor;

S3, performing graphitization on the precursor to obtain a semi-finished product;

S4, pulverizing, spheroidizing, coating, and sieving the semi-finished product to obtain the composite graphite.

Meanwhile, the present invention also provides a composite graphite prepared by the above method.

In addition, the present invention also provides a lithium ion battery comprising a positive electrode, a separator and a negative electrode which are sequentially stacked; the negative electrode includes a negative electrode current collector and a negative electrode material on the negative electrode current collector, the negative electrode material including as before The composite graphite.

In the preparation method of the composite graphite provided by the invention, the raw material used contains raw coke and/or mesocarbon microspheres, and the raw coke or mesocarbon microspheres are fully utilized to reduce the binder usage. It is beneficial to reduce costs, increase tapping, compaction density and specific capacity. And adding a catalyst to the coke and When the composite treatment is carried out, the catalyst can partially enter the inside of the coke particles, the catalysis is more uniform, and the catalyst utilization rate is higher.

At the same time, the invention realizes the secondary granulation of the ultrafine carbon powder by mixing the ultrafine carbon powder and the binder, thereby facilitating the improvement of the isotropic performance, the improvement of the rate performance and the reduction of the pole piece expansion ratio.

The secondary granulation of superfine carbon powder and the addition of catalyst increase the porosity, improve the liquid absorption and liquid retention performance, and improve the charge and discharge performance of large magnification; the post-treatment adopts the spheroidization and coating process to make up for the secondary particle tapping, The shortcoming of the first effect is low.

In addition, the present invention combines isotropic particles with anisotropic particles to provide more lithium ion insertion channels and to ensure the specific capacity and compaction of the finished product.

The composite graphite prepared by the method disclosed by the invention has a first specific capacity of more than 360 mAg/g, a first efficiency of more than 95%, and a pole piece compaction density of more than 1.75 g/cc. Its outstanding features are high porosity, good liquid retention and liquid retention, good isotropic performance, good charge and discharge performance at large rate, and low expansion rate during charge and discharge. It is of positive significance for lithium batteries to further increase energy density and shorten charging time.

DRAWINGS

1 is a graph showing the rate performance test of a lithium ion battery prepared by using the composite graphite prepared in Examples 1-6 and Comparative Examples 1-2 of the present invention;

2 is an SEM image of the composite graphite prepared in Example 6 provided by the present invention.

detailed description

The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It is understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

The preparation method of the composite graphite provided by the invention comprises the following steps:

According to the invention, the above ultrafine carbon powder contains at least coke and/or mesocarbon microspheres. Wherein, the raw coke may be one or more of needle coke focus, pitch coke coke, and homogenous coke coke.

In the present invention, by preparing composite graphite on the basis of ultrafine carbon powder containing green coke and/or mesophase carbon microspheres, the coke viscosity can be fully utilized, the amount of binder can be reduced, and the cost can be reduced. Improve tapping, compaction density and specific capacity.

Specifically, the ultrafine carbon powder may include various carbon materials, for example, one or more of needle coke, pitch coke, isotropic coke, natural graphite, artificial graphite, and mesocarbon microbeads. .

The needle coke is needle coke and/or needle coke; the pitch coke is pitch coke and/or pitch coke; the homologous coke is isotropic coke and/or isotropic coke Cooked coke.

In the present invention, preferably, the volatile matter of the above various green cokes is 5 to 40%. If the above various cooked cokes are used, the volatile content is less than 5%. Further preferably, the needle coke, the pitch coke, and the homologous coke used in the ultrafine carbon powder are both coke and have a volatile content of 5-20%.

For the above needle coke, it is preferred that the ash content is less than 0.5%. For the above homogenous coke, it is preferred that the crystallinity is less than 30%.

It can be understood that when the needle coke is needle coke, the ultrafine carbon powder necessarily contains other kinds of green coke or mesocarbon microspheres. The same applies to the case where the pitch coke is pitch coke or the same coke is coke. On the contrary, if there is no mesocarbon microbeads in the ultrafine carbon powder, at least one of the above cokes is inevitably contained.

In the present invention, preferably, the ultrafine carbon powder includes one or more of natural graphite, needle coke, isotropic coke, and mesocarbon microbeads. Further preferably, the natural graphite content is 70% by weight or less, the needle coke content is 70% by weight or less, the isotropic coke content is 30% by weight or less, and the mesophase carbon microspheres have a green ball content of 70% by weight or less. More preferably, the above natural graphite contains 0 to 10% by weight of microcrystalline graphite based on the total weight of the ultrafine carbon powder.

The same-focus coke provides more lithium-ion insertion channels, but its capacity is lower. Mesophase carbon microspheres provide more lithium ion intercalation channels with high capacity but higher cost. The needle coke has a high capacity and good circulation, but its rate performance is poor. Natural graphite increases capacity and compaction density, but its rate performance and cycle performance are poor.

In the present invention, by using the above various raw materials in combination, isotropic particles (for example, homo- or co-phase carbon microspheres) are compounded with anisotropic particles (for example, natural graphite or needle coke) to provide more lithium. The ion-embedded channel ensures the specific capacity and compaction of the finished product, and has excellent cycle performance and rate performance.

According to the present invention, preferably, in the above ultrafine carbon powder, the sum of the weight of the natural graphite and the needle coke focus is 70 to 90% by weight, and the isotropic coke content is 10 to 30% by weight.

Alternatively, the sum of the mesophase carbon microspheres and the natural graphite weight is greater than 50% by weight, the isotropic coke content is less than 20% by weight, and the isotropic coke and/or needle coke content is less than 30% by weight.

More preferably, the ratio of the total weight of the green coke to the mesophase carbon microspheres is 50-70 wt%, the ratio of natural graphite is 30-50 wt%, and the ratio of cooked coke is less than 20%. Wherein, the ratio of the mesophase carbon microspheres to the total weight of the ultrafine carbon powder is more than 30% by weight.

According to the invention, it is preferred that the ultrafine carbon powder has a D _{50 of} from 2 to 10 μm, more preferably from 7 to 8 μm.

In the present invention, the above ultrafine carbon powder can be directly obtained by purchasing various raw material powders satisfying the above conditions and obtained by mixing. It can also be prepared by using a conventional raw material, for example, obtaining various raw materials of a desired ratio, and then mixing, pulverizing, classifying, sieving, and spheroidizing to obtain an ultrafine carbon powder. According to the actual situation, it is preferable that the ultrafine carbon powder obtained after spheroidization has a D ₅₀ of 2 to 10 μm.

The specific process steps and methods for pulverization, classification, sieving, and spheronization are well known in the art and will not be described in detail in the present invention.

After obtaining the above ultrafine carbon powder as described in step S2, it further comprises mixing the ultrafine carbon powder with a binder to obtain a mixture A, and the mixture A and the catalyst are mixed to obtain a mixture B.

The above binder may be any of various binders conventionally known in the art, and for example, one or more of medium-low temperature asphalt, phenol resin, epoxy resin, polyester resin or polyamide resin may be specifically used. As is known to those skilled in the art, when the above binder is used, it may be dissolved by an organic solvent and then mixed according to a specific case.

In the present invention, preferably, the above binder is a medium-low temperature asphalt. The medium-low temperature asphalt may be coal-based or oil-based pitch. More preferably, the medium-low temperature asphalt has a softening point of 50 to 100 °C.

According to the present invention, as described above, since the ultrafine carbon powder contains coke and/or mesocarbon microspheres, it is only necessary to use a relatively small amount of binder to prepare a product composite graphite having excellent properties. Preferably, in the mixture B, the ratio of the binder content to the ultrafine carbon powder is less than 20% by weight.

In the above mixture B, the catalyst may be a conventional catalyst, for example, one or more selected from the group consisting of silicon, a silicon compound, iron, an iron compound, boron, and a boron compound. In the mixture B, the ratio of the catalyst content to the ultrafine carbon powder is less than 30% by weight.

In the present invention, preferably, the catalyst is a silicon compound. In the mixture B, the ratio of the catalyst content to the ultrafine carbon powder is 5 to 20% by weight.

As described above, the above ultrafine carbon powder contains coke and/or mesocarbon microspheres, and after the catalyst is added and combined, the catalyst can partially enter the inside of the coke particles, and the catalytic effect is more uniform. The catalyst utilization rate is higher. On the other hand, the amount of catalyst used can be reduced and the cost can be reduced.

According to the present invention, after the above mixture B is obtained, the mixture B is subjected to a composite treatment to obtain a precursor.

Specifically, the composite treatment may adopt various existing composite treatment methods, for example, one selected from the group consisting of solid phase kneading, liquid phase kneading, sheet rolling, fusion, spray drying, molding, isostatic pressing, and carbonization. A variety.

In the present invention, preferably, the composite treatment may include first performing liquid phase kneading and then molding. More preferably, the mixture B is first subjected to liquid phase kneading, followed by rolling, molding, isostatic pressing, and carbonization to obtain the precursor.

For the above liquid phase kneading, it is preferably at a temperature of from 100 to 300 ° C for a period of from 1 to 2 h. When the binder is a medium-low temperature asphalt, it is more preferred that the liquid phase kneading temperature is 50-90 ° C higher than the softening point of the medium-low temperature asphalt.

Since the invention combines the ultrafine carbon powder with the binder and then combines the treatment, the secondary granulation of the ultrafine carbon powder is realized, which is advantageous for improving the isotropic performance, and is advantageous for improving the rate performance and reducing the expansion rate of the pole piece.

According to the present invention, as in step S3, the precursor is subjected to graphitization to obtain a semi-finished product. The above described methods of graphitization are well known in the art. In the present invention, preferably, the temperature of the graphitization treatment is 2700 to 3200 °C.

The finished product can be obtained by the above graphitization treatment. Finally, in step S4, the semi-finished product is pulverized, spheroidized, coated, and sieved to obtain the composite graphite.

Specifically, the semi-finished product can be mechanically pulverized, ball milled, and then spheroidized.

The above coating treatment may specifically be one of conventional liquid phase, solid phase coating or mechanical fusion. The coating material used in the coating treatment is selected from one or more of asphalt, resin, and conductive graphite. Preferably, the coating material is medium-low temperature asphalt and conductive graphite, or resin and medium-low temperature asphalt.

According to the present invention, preferably, the coating treatment is a liquid phase coating, and a carbonization treatment is further included before the sieving treatment after the liquid phase coating.

The above carbonization treatment temperature is preferably from 600 to 1500 °C. The sieve particle size D ₅₀ is preferably from 4 to 30 μm.

The post-treatment of the invention adopts the spheroidization and coating process to make up for the shortcomings of secondary particle tapping and low first effect.

The materials, structures and preparation methods of the lithium ion battery can adopt various methods in the prior art, and the present invention will not be described again.

The invention is further illustrated by the following examples.

Example 1

This embodiment is for explaining the preparation method of the composite graphite disclosed in the present invention.

Step 1. Mixing the same-focus coke and coke-like coke raw materials, respectively, using mechanical pulverization and jet pulverization to a D ₅₀ of 4-5 μm to obtain ultrafine carbon powder.

Step 2, the ultrafine carbon powder obtained in the step 1 is added to the kneader according to the ratio of the same coke coke: needle coke: coke trioxide = 30:70:15, and heated to 200 ° C, according to the mixture A dry powder: low temperature Asphalt = 100:20 was added to the molten low-temperature asphalt, and after kneading for 1 hour, it was taken out and subjected to press molding to obtain a precursor.

Step 3. The block precursor obtained in the step 2 is graphitized to obtain a semi-finished product.

Step 4: The semi-finished product obtained in the step 3 is sequentially mechanically crushed and sieved to obtain a composite graphite product having a D ₅₀ of 12-13 μm.

The obtained physical and chemical indicators are shown in Table 1, and the rate performance is shown in Figure 1.

Example 2

Step 1. Mixing the same-focus coke, needle coke and needle coke raw materials, respectively, using mechanical pulverization and jet pulverization to a D ₅₀ of 4-5 μm to obtain ultrafine carbon powder.

Step 2, the ultrafine carbon powder obtained in the step 1 is added to the kneader according to the same-spot coke focus: needle coke focus: needle coke cooked coke: boron trioxide = 30:40:30:15, heated to 200 °C, the molten low-temperature pitch was added according to the mixture A dry powder: low-temperature pitch = 100:10, and kneaded for 1 hour, and then taken out and subjected to press molding to obtain a precursor.

Example 3

Step 1. Mixing the same-focus coke and coke-like coke raw materials, respectively, using mechanical pulverization and airflow pulverization to a D ₅₀ of 4-5 μm to obtain ultrafine carbon powder.

Step 2, the ultrafine carbon powder obtained in the step 1, according to the same coke coke: needle coke coke: boron trioxide = 30:70:15 ratio into a kneader, heated to 200 ° C, without binder, After kneading for 1 hour, it was taken out and subjected to press molding to obtain a precursor.

Example 4

Step 1. Mixing the homogenous coke coke and the needle coke cooked coke raw material, and using mechanical pulverization and jet pulverization to a D ₅₀ of 4-5 μm to obtain an ultrafine carbon powder.

Step 2, the ultrafine carbon powder obtained in the step 1 is added to the kneader according to the ratio of the same coke coke: needle coke: coke trioxide = 30:70:15, and heated to 200 ° C, according to the mixture A dry powder: low temperature Asphalt = 100:20 was added to the molten low-temperature pitch, kneaded for 2 hours, and then taken out for rolling, pulverization, and compression molding to obtain a precursor.

Step 3. The block precursor obtained in the step 2 is graphitized, and the graphitization temperature is 3000 ° C for 14 d to obtain a semi-finished product.

Step 4: The semi-finished product obtained in the step 3 is mechanically crushed, spheroidized, and sieved to obtain a composite graphite product having a D ₅₀ of 12-13 μm.

Example 5

Step 1. Mixing needle coke, coke coke and natural graphite raw materials, and mechanically pulverizing and jet milling to a D ₅₀ of 7-8 μm to obtain ultrafine carbon powder.

Step 2, the ultrafine carbon powder obtained in the step 1 is added to the kneader according to the homogenous coke focus: needle coke coke: natural graphite: silicon carbide = 20:30:50:15, heated to 200 ° C, according to the mixture A Dry powder: low temperature asphalt = 100: 15 was added to melt low temperature asphalt, kneaded for 2 hours, and then taken out for rolling, pulverization, and compression molding to obtain a precursor.

Step 4: The semi-finished product obtained in the step 3 is sequentially mechanically crushed, spheroidized, sieved, and the composite graphite having a D ₅₀ of 12-13 μm is finished.

Example 6

Step 1. The needle coke coke, the mesophase carbon microsphere green ball and the natural graphite raw material are mixed, and mechanically pulverized and air jet pulverized to a D ₅₀ of 7-8 μm to obtain an ultrafine carbon powder.

Step 2, the ultrafine carbon powder obtained in the step 1, according to mesophase carbon microspheres: needle coke: natural graphite: silicon carbide = 40:20:30:10 ratio into a kneader, heated to 200 ° C, The molten low-temperature pitch was added according to the mixture A dry powder: low-temperature pitch = 100:5, kneaded for 2 hours, and then taken out, subjected to rolling, pulverization, and compression molding to obtain a precursor.

Step 4: The semi-finished product obtained in the step 3 is mechanically crushed, spheroidized, coated with solid phase asphalt, coated with 1.5%, carbonized at 1100 ° C, and sieved to obtain a composite graphite product having a D ₅₀ of 12-13 μm.

The obtained physical and chemical indicators are shown in Table 1. The rate performance is shown in Figure 1. The SEM morphology is shown in Figure 2.

Comparative example 1

This comparative example is used to compare and explain the preparation method of the composite graphite disclosed in the present invention.

Step 2, the ultrafine carbon powder obtained in the step 1, according to the same-spot coke: needle coke: coke: SiC = 30:70:15 ratio into a kneader, heated to 200 ° C, according to the mixture A dry powder: low temperature asphalt = 100: 40 was added to melt low-temperature asphalt, kneaded for 1 hour, and then taken out for press molding to obtain a precursor.

Comparative example 2

Step 1. The natural graphite is mixed with the same-focus coke and the coke-like coke, and is mechanically pulverized and air-pulverized to D50=3-5 μm to obtain ultrafine carbon powder.

Step 2, the ultrafine carbon powder obtained in the step 1, according to the same-spot coke: needle coke: natural graphite: silicon carbide = 50:20:30:15 ratio into a kneader, heated to 200 ° C, according to the mixture A Dry powder: low temperature asphalt = 100:40 was added to melt low temperature asphalt, kneaded for 1 hour, and then taken out for compression molding to obtain a precursor.

Performance Testing

The composite graphite prepared in the above Examples 1-6 and Comparative Example 1-2 was observed by Hitachi S4800 scanning electron microscope to observe the surface morphology and particle size of the sample; X-ray diffractometer X'Pert Pro, PANalytical test material was used. Graphitization and degree of anisotropy; the specific surface area of the material was tested using the Tristar 3000 fully automatic surface area and porosity analyzer from Mike Instruments. The particle size range of the material and the average particle size of the raw material particles were measured using a Malvern laser particle size tester MS 2000. The tap density of the material was tested using a Quantachrome AutoTap tap density meter.

Electrochemical performance testing of materials

The composite graphite prepared in the above Examples 1-6 and Comparative Example 1-2, CMC (solid content: 1.2%), and binder SBR (solid content: 50%) were respectively mixed at a mass ratio of 96.5:1.5:2. The slurry was then uniformly coated on a 11 μm thick copper foil and dried to obtain an areal density of 70 g/m ² , and a pole piece of 1.75 g/cm ³ was compacted and then punched into a circular pole piece having a diameter of 16 mm and dried in a vacuum. Dry in a box at 120 ° C for 10 hours.

The pole piece prepared above was used as the working electrode, the lithium piece was used as the counter electrode, and the electrolyte was made of EC/DMC/EMC (volume ratio of 1:1:1) of 1 mol/L LiPF ₆ in the German Braun glove box. The two-electrode electrolytic cell was assembled and subjected to constant current charge and discharge at a current density of 0.1 C. The voltage range was from 0.001 V to 2.5 V, and the first delithiation capacity of the material and the first coulombic efficiency were measured.

The pole piece prepared above was used as the working electrode, the lithium cobaltate positive electrode was used as the counter electrode, and the electrolyte was made of 1 mol/L LiPF ₆ EC/DMC/EMC (volume ratio: 1:1), in Braun, Germany. The electrode displacement measuring cell is assembled in the glove box. The above battery is subjected to constant current charge and discharge at a current density of 0.1 C, and the voltage range is from 0.001 V to 2.5 V. The second cycle starts with a constant current charge and discharge cycle at a current density of 0.5 C. After 20 cycles, the battery is directly measured by electrode displacement. Readings, calculate the expansion rate before and after the pole piece cycle.

The physicochemical test results prepared in Examples 1-6 and Comparative Examples 1-2 are shown in Table 1.

Table 1

It can be seen from the test results of Table 1 that the composite graphite prepared in Examples 1-6 has a comprehensive performance superior to Comparative Examples 1-2 in terms of compaction, delithiation specific capacity, magnification, and pole piece expansion ratio.

The above is only the preferred embodiment of the present invention, and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection of the present invention. Within the scope.

Claims

A method for preparing composite graphite, comprising the steps of:

S1, providing ultrafine carbon powder; the ultrafine carbon powder comprises green coke and/or mesocarbon microspheres;

S2, mixing the ultrafine carbon powder with the binder to obtain a mixture A, the mixture A and the catalyst are mixed to obtain a mixture B, and then the mixture B is subjected to a composite treatment to obtain a precursor;

S3, performing graphitization on the precursor to obtain a semi-finished product;

S4, pulverizing, spheroidizing, coating, and sieving the semi-finished product to obtain the composite graphite.
The preparation method according to claim 1, wherein in the step S1, the ultrafine carbon powder has a D 50 of 2 to 10 μm; and the green coke has a volatile content of 5 to 40%.
The preparation method according to claim 1 or 2, wherein the ultrafine carbon powder comprises one of needle coke, pitch coke, isotropic coke, natural graphite, artificial graphite, mesophase carbon microspheres Or a variety;

The needle coke is needle coke and/or needle coke; the pitch coke is pitch coke and/or pitch coke; the homologous coke is isotropic coke and/or homosexual Focused coke

The needle coke ash content is less than 0.5%; the isotropic coke crystallinity is less than 30%.
The preparation method according to claim 3, wherein the natural graphite content is 70% by weight or less, the needle coke content is 70% by weight or less, and the isotropic coke content is 30% by weight or less, and the mesophase carbon microspheres are produced by mass ratio. The content is 70% by weight or less.
The preparation method according to claim 4, wherein in the ultrafine carbon powder, the sum of the weight of the natural graphite and the needle coke focus is 70 to 90% by weight, and the homogenous coke content is 10 to 30% by weight.
The preparation method according to claim 4, wherein in the ultrafine carbon powder, the sum of the weight of the mesophase carbon microspheres and the natural graphite is more than 50% by weight, the homogenous coke content is less than 20% by weight, and the isotropic coke The cooked coke and/or needle coke content is less than 30% by weight.
The preparation method according to any one of claims 1 to 6, wherein in the step S2, the binder is selected from the group consisting of medium and low temperature asphalt, phenolic resin, epoxy resin, polyester resin or polyamide. One or more of the resins;

Preferably, the medium and low temperature asphalt has a softening point of 50 to 100 °C.
The preparation method according to any one of claims 1 to 7, wherein in the step S2, the catalyst is selected from one of silicon, a silicon compound, iron, an iron compound, boron, a boron compound or Multiple

In the mixture B, the ratio of the binder content to the ultrafine carbon powder is less than 20% by weight; and the ratio of the catalyst content to the ultrafine carbon powder is less than 30% by weight.
The preparation method according to any one of claims 1 to 8, wherein in the step S2, the composite treatment is selected from the group consisting of solid phase kneading, liquid phase kneading, rolling, fusion, spray drying, molding, One or more of isostatic pressing and carbonization; the liquid phase kneading temperature is 100-300 ° C, and the liquid phase kneading time is 1-2 h;

In the step S3, the temperature of the graphitization treatment is 2700-3200 ° C;

In the step S4, the coating treatment is selected from one of liquid phase coating, solid phase coating or mechanical fusion; the coating material used in the coating treatment is selected from the group consisting of asphalt, resin and conductive graphite. One or more

The sieve particle size D 50 is 4-30 μm.
The preparation method according to claim 9, wherein the coating treatment is liquid phase coating, and further includes carbonization treatment before the liquid phase coating, and the carbonization treatment temperature is 600 -1500 ° C.
A composite graphite characterized in that the composite graphite is produced by the method according to any one of claims 1-10.
A lithium ion battery comprising: a positive electrode, a separator and a negative electrode which are sequentially stacked; the negative electrode includes a negative electrode current collector and a negative electrode material on the negative electrode current collector, the negative electrode material comprising the method of claim 11 Composite graphite.