Lithium ion battery negative electrode material, preparation method therefor, and lithium ion battery

Abstract

A lithium ion battery negative electrode material, a preparation method therefor, and a lithium ion battery. The negative electrode material comprises a graphite core and a carbon coating layer coated on the surface of the single-particle graphite core. The coating dominant eigenvalue of the carbon coating layer is Y=T / (J-Z). The theoretical carbon value of a coating agent forming the carbon coating layer is T%. The coating response value of the carbon coating layer is J=Dv50 / Dv50aggregate, wherein Dv50 represents the corresponding particle size when the volume distribution percentage of the negative electrode material reaches 50%, and Dv50aggregate represents the corresponding particle size when the volume distribution percentage of the graphite core reaches 50%. The coating anchoring parameter of the carbon coating layer is Z=Dv95 / Dv95aggregate, wherein Dv95 represents the corresponding particle size when the volume distribution percentage of the negative electrode material reaches 95%, and Dv95aggregate represents the corresponding particle size when the volume distribution percentage of the graphite core reaches 95%. The negative electrode material has better coating uniformity and charging and discharging capacity.

Description

Lithium ion battery negative electrode material and preparation method thereof, lithium ion battery Technical Field

[0001] The present application relates to the field of lithium-ion batteries, and in particular to a lithium-ion battery negative electrode material and a preparation method thereof, and a lithium-ion battery. Background Art

[0002] The negative electrode material of commercial lithium-ion batteries is mainly graphite, which mainly includes artificial graphite, natural graphite and mesophase graphite made from mesophase carbon microbeads (MCMB). Due to the limitation of the theoretical capacity of positive and negative electrode materials, the overall energy density of lithium-ion batteries cannot be increased indefinitely, so energy anxiety can only be solved by increasing the charging speed. With the rapid growth of lithium battery vehicles and energy storage base stations in recent years, and the upgrading of 5G mobile phones, the demand for corresponding graphite negative electrode materials has also doubled year by year. The demand for fast-charging graphite negative electrode materials has also exploded.

[0003] Traditional fast-charging negative electrode materials are primarily coated graphite or uncoated graphite with a particle size less than 6μm. Conventional coated graphite materials primarily coat the graphite structure of secondary particles, which hinders further improvement in fast-charging performance. Furthermore, the secondary particle aggregates have numerous surface structural defects, preventing effective full coating. Uncoated graphite also suffers from poor processing properties and insufficient fast-charging performance.

[0004] Therefore, it is necessary to provide a graphite negative electrode material with a higher rate of fast charging.

[0005] Summary of the Invention

[0006] The present application provides a lithium-ion battery negative electrode material and a preparation process thereof. The lithium-ion battery negative electrode material includes a graphite core and a carbon coating layer covering the surface of the graphite core, so that the carbon coating layer achieves a more uniform and complete effect, and the carbon coating layer enables the surface of the negative electrode material to have more lithium ion diffusion channels. At the same time, the disordered carbon layer of the carbon coating layer enables the negative electrode material to have lower surface resistance and higher rate fast charging performance.

[0007] On the one hand, an embodiment of the present application provides a lithium-ion battery negative electrode material, comprising a graphite core and a carbon coating layer coated on the surface of the graphite core of a single particle, wherein the coating advantage characteristic value Y of the carbon coating layer is Y=T / (JZ), wherein the theoretical carbon value of the coating agent forming the carbon coating layer is T%; the coating response value J of the carbon coating layer is J=Dv50 / Dv50 骨料 The Dv50 represents the particle size corresponding to when the volume distribution percentage of the negative electrode material reaches 50%. 骨料represents the particle size corresponding to when the volume distribution percentage of the graphite core reaches 50%; the coating anchoring parameter Z of the carbon coating layer = Dv95 / Dv95 骨料 , Dv95 represents the particle size corresponding to when the volume distribution percentage of the negative electrode material reaches 95%, Dv95 骨料 It represents the particle size corresponding to when the volume distribution percentage of the graphite core reaches 95%.

[0008] In some embodiments of the present application, T ranges from 1 to 5, J ranges from 1.00 to 1.30, and Z ranges from 1.00 to 1.30, and J is greater than Z, and Y>8.5.

[0009] In some embodiments of the present application, the characteristic response number of the carbon residue in the carbon coating layer is A=R 容量 / R 骨料容量 ×T / L+5×D 振实 / S 比表 , where R 容量 is the charge-off test capacity of the negative electrode material, R 骨料容量 is the charge-discharge test capacity of the graphite core, D 振实 is the tap density of the negative electrode material (g / cm 3 ), S 比表 is the specific surface area of ​​the negative electrode material, the theoretical carbon value of the coating agent of the negative electrode material is T%, and the Raman characteristic value of the negative electrode material is L=Id / Ig.

[0010] In some embodiments of the present application, the characteristic response number A of the residual carbon in the carbon coating layer is greater than or equal to 6.5 and less than or equal to 35.

[0011] In some embodiments of the present application, the Raman characteristic value distribution range of the negative electrode material is 0.20 to 0.60. In some embodiments of the present application, the oil absorption value OA of the negative electrode material is 40 to 70.

[0012] In some embodiments of the present application, the carbon coating layer is amorphous carbon, and the thickness of the carbon coating layer is 5 to 100 nm.

[0013] The present application also provides a method for preparing a negative electrode material for a lithium-ion battery, comprising: performing a crushing step to crush a raw material to form a first powder; performing a graphitization step to convert the first powder into a graphite core; performing a coating step to coat a carbon coating agent on the surface of the graphite core of a single particle; performing a carbonization step to convert the carbon coating agent into a carbon coating layer, wherein the coating advantage characteristic value Y of the carbon coating layer is Y=T / (JZ), wherein the theoretical carbon value of the carbon coating agent is T%; and the coating response value J of the carbon coating layer is J=Dv50 / Dv50. 骨料The Dv50 represents the particle size corresponding to when the volume distribution percentage of the negative electrode material reaches 50%. 骨料 represents the particle size corresponding to when the volume distribution percentage of the graphite core reaches 50%; the coating anchoring parameter Z of the carbon coating layer = Dv95 / Dv95 骨料 , Dv95 represents the particle size corresponding to when the volume distribution percentage of the negative electrode material reaches 95%, Dv95 骨料 It represents the particle size corresponding to when the volume distribution percentage of the graphite core reaches 95%.

[0014] In some embodiments of the present application, T ranges from 1 to 5, J ranges from 1.00 to 1.30, and Z ranges from 1.00 to 1.30, and J is greater than Z, and Y>8.5.

[0015] In some embodiments of the present application, the characteristic response number of the carbon residue in the carbon coating layer is A=R 容量 / R 骨料容量 ×T / L+5×D 振实 / S 比表 , where R 容量 is the charge-off test capacity of the negative electrode material, R 骨料容量 is the charge-discharge test capacity of the graphite core, D 振实 is the tap density of the negative electrode material (g / cm 3 ), S 比表 is the specific surface area of ​​the negative electrode material, the theoretical carbon value of the coating agent of the negative electrode material is T%, and the Raman characteristic value of the negative electrode material is L=Id / Ig.

[0016] In some embodiments of the present application, the characteristic response number A of the residual carbon in the carbon coating layer is greater than or equal to 6.5 and less than or equal to 35.

[0017] In some embodiments of the present application, the raw material is selected from needle coke with a volatile content of 5-7%, or petroleum coke with a volatile content of 8-11% and an S content of 1.0-3.0%.

[0018] In some embodiments of the present application, the volume distribution particle size Dv50 of the first powder is 第一粉料 The particle size distribution D of the first powder is 4 to 18 μm, and the range of the particle size distribution D of the first powder is 0.8 to 1.5, D=(Dv90 第一粉料 -Dv10 第一粉料 ) / Dv50 第一粉料 , wherein the Dv50 第一粉料 Dv90 represents the particle size corresponding to when the volume distribution percentage of the first powder reaches 50%. 第一粉料 represents the particle size corresponding to when the volume distribution percentage of the first powder reaches 90%, Dv10 第一粉料It represents the particle size corresponding to when the volume distribution percentage of the first powder reaches 10%.

[0019] In some embodiments of the present application, the carbon coating agent is selected from petroleum asphalt with a softening point of 140-250°C, resin with a molecular weight lower than 1000, or tar asphalt with a softening point lower than 20°C, and the total theoretical residual carbon value of the carbon coating agent is preferably 1-5%.

[0020] In some embodiments of the present application, the carbonization step is carried out under constant temperature conditions, the carbonization temperature is 800-1300° C., and the constant temperature time is greater than 2 hours and less than 12 hours.

[0021] In some embodiments of the present application, the oil absorption value OA of the negative electrode material ranges from 40 to 70.

[0022] In some embodiments of the present application, the carbon coating layer is amorphous carbon, and the thickness of the carbon coating layer is 5 to 100 nm.

[0023] The embodiment of the present application also provides a lithium-ion battery, wherein the negative electrode is made of any one of the negative electrode materials described in the embodiment of the present application.

[0024] Compared with the prior art, the preparation method of the negative electrode material described in the embodiment of the present application, through the crushing step, makes the first powder formed have a higher sphericity, thereby making the single-particle graphite core achieve a more uniform and complete effect in the coating step; the negative electrode material after forming the carbon coating layer has more lithium ion diffusion channels, and at the same time, the disordered carbon layer of the carbon coating layer makes the negative electrode material have a lower surface resistance, and the structure ensures the fast charging capability of the negative electrode material. The single-particle negative electrode material is bonded together in the process of forming the battery negative electrode, which can further increase the orientation of the material, ensure the pores of the single particle of the negative electrode material in the porous structure of the electrode piece, increase the wettability of the negative electrode material in the electrolyte therein, further improve the fast charging performance of the negative electrode material, and have better processing performance and liquid absorption performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The following figures describe in detail exemplary embodiments disclosed in this application. Identical reference numerals denote similar structures in several views of the drawings. Those skilled in the art will appreciate that these embodiments are non-limiting, exemplary embodiments, and that the drawings are for illustration and description purposes only and are not intended to limit the scope of this application. Other embodiments may also achieve the same inventive intent as described in this application. It should be understood that the drawings are not drawn to scale. Among them:

[0026] FIG1 is a schematic diagram of a process flow of a method for preparing a negative electrode material for a lithium-ion battery according to an embodiment of the present application. DETAILED DESCRIPTION

[0027] The following description provides specific application scenarios and requirements of the present application, with the purpose of enabling those skilled in the art to make and use the content of this application. Various local modifications to the disclosed embodiments will be apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of this application. Therefore, this application is not limited to the embodiments shown, but is intended to be of the widest scope consistent with the claims.

[0028] On the one hand, an embodiment of the present application provides a lithium-ion battery negative electrode material, comprising a graphite core and a carbon coating layer coated on the surface of the graphite core of a single particle, wherein the coating advantage characteristic value Y of the carbon coating layer is Y=T / (JZ), wherein the theoretical carbon value of the coating agent forming the carbon coating layer is T%; the coating response value J of the carbon coating layer is J=Dv50 / Dv50 骨料 The Dv50 represents the particle size corresponding to when the volume distribution percentage of the negative electrode material reaches 50%. 骨料 represents the particle size corresponding to when the volume distribution percentage of the graphite core reaches 50%; the coating anchoring parameter Z of the carbon coating layer = Dv95 / Dv95 骨料 , Dv95 represents the particle size corresponding to when the volume distribution percentage of the negative electrode material reaches 95%, Dv95 骨料 It represents the particle size corresponding to when the volume distribution percentage of the graphite core reaches 95%.

[0029] In some embodiments of the present application, the carbon coating layer is any one or more of hard carbon amorphous carbon or soft carbon amorphous carbon, such as amorphous carbon, and the thickness of the carbon coating layer is 5 to 100 nm, such as 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, etc. The coating advantage characteristic value Y of the carbon coating layer represents the single-particle coating effect of the carbon coating layer on the graphite core during coating. The larger the value, the better the coating effect, and the better the rate performance of the finished negative electrode material. Optionally, Y>8.5, in some other embodiments, Y is greater than or equal to 9.0.

[0030] In some embodiments of the present application, to ensure that the carbon coating layer has a sufficiently high single-particle coating effect on the graphite core, i.e., a coating advantage characteristic value, the coating agent forming the carbon coating layer may include asphalt and resin coating agents, preferably soft petroleum asphalt with a softening point of 140-250°C, or a resin with a molecular weight of less than 1000, or a tar pitch with a softening point of less than 20°C. If the theoretical carbon value of the coating agent forming the carbon coating layer ranges from 1-5%, then T ranges from 1-5; alternatively, if the theoretical carbon value of the coating agent forming the carbon coating layer ranges from 2-4%, then T ranges from 2-4.

[0031] In some embodiments of the present application, the coating response value of the carbon coating layer is J=Dv50 / Dv50 骨料 , characterizes the coating effect of a single particle coating during the process of coating a single particle of graphite core with a carbon coating agent, the Dv50 represents the particle size corresponding to when the volume distribution percentage of the negative electrode material reaches 50%, and the Dv50 aggregate represents the particle size corresponding to when the volume distribution percentage of the graphite core reaches 50%. The aggregate mentioned in the embodiment of the present application refers to the graphite core before being coated with a coating agent. Among them, Dv50 骨料 The numerical range of Dv50 is 7 microns to 11 microns, and the numerical range of Dv50 is 7 microns to 13.5 microns. Optionally, the coating response value J of the carbon coating layer ranges from 1.00 to 1.30.

[0032] In some embodiments of the present application, the coating anchoring parameter Z of the carbon coating layer is Z=Dv95 / Dv95 骨料 , characterizes the coating effect of the carbon coating layer on the single-particle graphite core, Dv95 represents the particle size corresponding to when the volume distribution percentage of the negative electrode material reaches 95%, Dv95 骨料 represents the particle size corresponding to when the volume distribution percentage of the graphite core reaches 95%. Optionally, the coating anchor parameter Z of the carbon coating layer ranges from 1.00 to 1.30, and J is greater than Z.

[0033] In some embodiments of the present application, the characteristic response number of the carbon residue in the carbon coating layer is A=R 容量 / R 骨料容量 ×T / L+5×D 振实 / S 比表 , where R 容量 is the charge-off test capacity of the negative electrode material, R 骨料容量 is the charge-discharge test capacity of the graphite core, D 振实 is the tap density of the negative electrode material (g / cm 3 ), characterizes the roughness of the negative electrode material and the size of the pores between the particles, S 比表 is the specific surface area of ​​the negative electrode material, the theoretical carbon value of the coating agent forming the carbon coating layer is T%, and the Raman characteristic value of the negative electrode material is L=Id / Ig.

[0034] The characteristic response number of the residual carbon in the carbon coating layer indicates the uniformity of the carbon coating layer and the processability of the negative electrode material for use in the electrode sheet. The processability refers to the performance of the negative electrode material during slurrying and screening during the process of forming the negative electrode sheet. In some embodiments of the present application, the characteristic response number A of the residual carbon in the carbon coating layer is greater than or equal to 6.5 and less than or equal to 35, indicating excellent coating uniformity and electrode sheet processability.

[0035] In some embodiments of the present application, the Raman characteristic value distribution range of the negative electrode material is 0.20 to 0.60. Optionally, the Raman characteristic value distribution range of the negative electrode material is 0.20 to 0.50. The Raman characteristic value of the negative electrode material is the median of 2500 scan points of Id / Ig in the Raman spectrum. The Raman characteristic value indicates the coating uniformity of the carbon coating layer of the negative electrode material. A larger value of the Raman characteristic value indicates poorer coating uniformity.

[0036] In some embodiments of the present application, the oil absorption value OA of the negative electrode material ranges from 40 to 70. The oil absorption value indicates the processability of the negative electrode material in the pulping process during battery production. The lower the value, the higher the processability and the higher the yield rate of the processing.

[0037] The present application also provides a method for preparing a negative electrode material for a lithium-ion battery, comprising: performing a crushing step to crush a raw material to form a first powder; performing a graphitization step to convert the first powder into a graphite core; performing a coating step to coat a carbon coating agent on the surface of the graphite core of a single particle; performing a carbonization step to convert the carbon coating agent into a carbon coating layer, wherein the coating advantage characteristic value Y of the carbon coating layer is Y=T / (JZ), wherein the theoretical carbon value of the carbon coating agent is T%; and the coating response value J of the carbon coating layer is J=Dv50 / Dv50. 骨料 The Dv50 represents the particle size corresponding to when the volume distribution percentage of the negative electrode material reaches 50%. 骨料 represents the particle size corresponding to when the volume distribution percentage of the graphite core reaches 50%; the coating anchoring parameter Z of the carbon coating layer = Dv95 / Dv95 骨料 , Dv95 represents the particle size corresponding to when the volume distribution percentage of the negative electrode material reaches 95%, Dv95 骨料 It represents the particle size corresponding to when the volume distribution percentage of the graphite core reaches 95%.

[0038] The pulverization step described in the embodiment of the present application is a raw material processing step, which may include heat treatment and pulverization of the raw materials. The main purpose of the pulverization step is to pulverize the raw materials to achieve the desired designed particle size.

[0039] The raw materials described in the embodiments of the present application are selected from coke materials. Different coke materials have different properties, which directly affect the morphology after crushing and the capacity, specific surface area, etc. of the final negative electrode material. In some embodiments of the present application, in order to ensure the coating effect of the carbon coating layer in the formed negative electrode material, the raw materials are selected from needle coke with a volatile content of 5-7%, or petroleum coke with a volatile content of 8-11% and a S content of 1.0-3.0%, or asphalt, etc. Volatile matter refers to the amount of organic matter and minerals in the raw materials that decompose into gas and liquid and escape when the raw materials are heated at a certain temperature in an airtight state. The mass percentage content of the escaped substances is the amount of the substance after deducting the water content in the raw materials.

[0040] The heat treatment may involve, for example, subjecting the raw materials, such as needle coke, petroleum coke, or asphalt, to a temperature of 0 to 1400°C to effect changes in the structure and physical and chemical properties of the raw materials. The raw materials after the heat treatment may be pulverized and shaped using methods including, but not limited to, mechanical grinding or roller milling to form a first powder. Optionally, the heat treatment temperature is 500°C to 1400°C.

[0041] In some embodiments of the present application, the particle size distribution D of the first powder is in the range of 0.8 to 1.5, D=(Dv90 第一粉料 -Dv10 第一粉料 ) / Dv50 第一粉料 , wherein the Dv50 第一粉料 Dv90 represents the particle size corresponding to when the volume distribution percentage of the first powder reaches 50%. 第一粉料 represents the particle size corresponding to when the volume distribution percentage of the first powder reaches 90%, Dv10 第一粉料 It represents the particle size corresponding to when the volume distribution percentage of the first powder reaches 10%.

[0042] In some embodiments of the present application, the volume distribution particle size Dv50 of the first powder is 第一粉料 4 to 18 μm, optionally, the Dv50 第一粉料 In some embodiments, the Dv50 第一粉料 For example, 5μm, 8μm, 10μm, 12μm, etc.

[0043] Perform a graphitization step to convert the first powder into a graphite core. The graphitization step described in the embodiment of the present application refers to pyrolyzing the first powder at a high temperature to form a graphite structure with a high degree of crystallinity. This graphite structure is the graphite core of the negative electrode material described in the embodiment of the present application. During the graphitization process, the molecular spacing of the graphite material is reduced and the lattice structure is more ordered. This structural change enables the graphite material to have better electrical conductivity and cycle stability. The graphite core formed after the graphitization step mainly includes carbon elements and may also include trace amounts of O elements. In the embodiment of the present application, the equipment for performing the graphitization step is not limited to a crucible furnace, a box furnace, an inner series furnace, etc. The graphitization temperature is higher than 2700°C. For example, the graphitization temperature is 2800-3200°C. Optionally, the graphitization temperature is 2900-3100°C.

[0044] Perform a coating step to coat the surface of the graphite core of the single particle with a carbon coating agent. The coating step described in the embodiment of the present application includes a solid-phase coating process and a liquid-phase coating process, that is, the carbon coating agent used includes a solid-phase coating agent and a liquid-phase coating agent. The solid-phase coating process includes directly coating the mixed asphalt or resin material as a coating agent on the surface of the graphite core; the liquid-phase coating process can coat the asphalt or resin coating agent on the surface of the graphite core after heating and melting it in a horizontal reactor or a vertical reactor; or a low-coking value solvent can be used to prepare a coating agent that is liquid at room temperature and coated on the surface of the graphite core using a fusion machine.

[0045] The coating step is the core process of the negative electrode material preparation method of this embodiment to achieve the fast charging capability of the negative electrode material. In order to ensure that the coating effect, that is, the coating advantage characteristic value, is sufficiently high, the carbon coating agent is preferably an asphalt or resin coating agent. In some embodiments of the present application, the carbon coating agent is selected from petroleum asphalt with a softening point of 140 to 250°C, a resin with a molecular weight of less than 1000, or a tar asphalt with a softening point of less than 20°C, and the theoretical carbon value of the coating agent of the carbon coating layer is preferably 1 to 5%, for example, 2 to 4%. The coating equipment used in the embodiments of the present application can be selected from a kneader, a vertical mixer, a screw ribbon mixer, a horizontal reactor, a vertical reactor, a normal temperature fusion machine, etc., more preferably a vertical mixer, a horizontal reactor or a fusion machine, etc.

[0046] A carbonization step is performed to convert the carbon coating agent into a carbon coating layer. After the carbonization step, the carbon coating agent is fixed on the surface of the graphite core of the single particle, while avoiding secondary adhesion caused by carbonization of the particles of the graphite core. In the embodiment of the present application, since the order of the graphite core is higher than that of the carbon coating layer, the carbon coating layer can improve the fast charging performance of the negative electrode material. For example, when the carbon coating layer is amorphous carbon, the amorphous carbon can increase the embedding speed of lithium ions in the negative electrode surface layer, which can improve the pulse charging performance of the negative electrode material. Therefore, the pulse charging requirements of the battery cell made of the negative electrode material can be met by directional design of the coating amount of the carbon coating layer. In some embodiments of the present application, the carbon coating layer is amorphous carbon of hard carbon or soft carbon type and a mixture of the two, such as amorphous carbon, and the thickness of the carbon coating layer is 5 to 100 nm, for example, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, etc.

[0047] The carbonization treatment step described in the embodiments of the present application can be performed using carbonization equipment such as a rotary kiln, roller kiln, or tunnel kiln under constant temperature conditions, for example, at a temperature of 800-1300°C for a constant temperature time of greater than 2 hours and less than 12 hours, thereby improving the electrochemical performance of the carbon coating. The preferred carbonization equipment in the embodiments of the present application is a roller kiln. The reaction temperature of the carbonization step is preferably 1000-1200°C, and the reaction time is preferably greater than 3 hours and less than 8 hours.

[0048] After performing the carbonization treatment step, in order to better realize industrialization and mass production, the method described in the embodiment of the present application may also include a finished product processing step, that is, completing the processing of the finished product stage through screening and demagnetization treatment to meet the requirements for shipment.

[0049] The coating advantage characteristic value of the carbon coating layer in the embodiment of the present application is Y=T / (JZ), wherein the theoretical carbon value of the coating agent forming the carbon coating layer is T%; J=Dv50 / Dv50 骨料 , the Dv50 represents the particle size corresponding to when the volume distribution percentage of the negative electrode material reaches 50%, and the Dv50 aggregate represents the particle size corresponding to when the volume distribution percentage of the graphite core reaches 50%; Z = Dv95 / Dv95 骨料 , DV95 represents the particle size corresponding to when the volume distribution percentage of the negative electrode material reaches 95%, and Dv95 aggregate represents the particle size corresponding to when the volume distribution percentage of the graphite core reaches 95%.

[0050] The coating advantage characteristic value Y of the carbon coating layer represents the coating effect of the carbon coating layer on the single particle of the graphite core during coating. A larger value indicates a better coating effect, and thus better rate performance of the finished negative electrode material. Optionally, Y>8.5. In some other embodiments, Y is greater than or equal to 9.0.

[0051] In some embodiments of the present application, the theoretical carbon value of the coating agent forming the carbon coating layer is in the range of 1-5%, and the range of T is 1-5; optionally, the theoretical carbon value of the coating agent forming the carbon coating layer is 2-4%, and the range of T is 2-4.

[0052] In some embodiments of the present application, the coating response value of the carbon coating layer is J=Dv50 / Dv50 骨料 , characterizes the coating effect of the coating agent forming the carbon coating layer on the single particle coating of the graphite core during the coating process, the Dv50 represents the particle size corresponding to when the volume distribution percentage of the negative electrode material reaches 50%, and the Dv50 aggregate represents the particle size corresponding to when the volume distribution percentage of the graphite core reaches 50%. The aggregate mentioned in the embodiment of the present application refers to the graphite core before being coated with the coating agent. Among them, Dv50 骨料 The numerical range of Dv50 is 7 microns to 11 microns, and the numerical range of Dv50 is 7 microns to 13.5 microns. Optionally, the coating response value J of the carbon coating layer ranges from 1.00 to 1.30.

[0053] In some embodiments of the present application, the coating anchoring parameter Z of the carbon coating layer is Z=Dv95 / Dv95 骨料 , characterizing the coating effect of the carbon coating layer on the single-particle graphite core. DV95 represents the particle size corresponding to the volume distribution percentage of the negative electrode material reaching 95%, and Dv95 aggregate represents the particle size corresponding to the volume distribution percentage of the graphite core reaching 95%. Z ranges from 1.00 to 1.30, and J is greater than Z.

[0054] In some embodiments of the present application, the characteristic response number of the carbon residue in the carbon coating layer is A=R 容量 / R 骨料容量 ×T / L+5×D 振实 / S 比表 , where R 容量 is the charge-off test capacity of the negative electrode material, R 骨料容量 is the charge-discharge test capacity of the graphite core, D 振实 is the tap density of the negative electrode material (g / cm 3 ), characterizes the roughness of the negative electrode material and the size of the pores between the particles, S 比表is the specific surface area of ​​the negative electrode material, the theoretical carbon value of the coating agent forming the carbon coating layer is T%, and the Raman characteristic value of the negative electrode material is L=Id / Ig.

[0055] The lithium battery buckle test is a method to evaluate the capacity and performance of lithium batteries. By measuring the voltage change of the battery under specific conditions, the battery capacity can be determined and the battery performance and life can be evaluated.

[0056] The characteristic response number of the residual carbon in the carbon coating layer indicates the uniformity of the carbon coating layer and the processability of the negative electrode material for use in the electrode sheet. The processability refers to the performance of the negative electrode material during slurrying and screening during the process of forming the negative electrode sheet. In some embodiments of the present application, the characteristic response number A of the residual carbon in the carbon coating layer is greater than or equal to 6.5 and less than or equal to 35, preferably greater than or equal to 6.5 and less than or equal to 25, indicating excellent coating uniformity and electrode sheet processability.

[0057] In some embodiments of the present application, the Raman characteristic value distribution range of the negative electrode material is 0.20 to 0.60. Optionally, the Raman characteristic value distribution range of the negative electrode material is 0.20 to 0.50. The Raman characteristic value of the negative electrode material is the median of 2500 scan points of Id / Ig in the Raman spectrum. The Raman characteristic value indicates the coating uniformity of the carbon coating layer of the negative electrode material. A larger value of the Raman characteristic value indicates poorer coating uniformity.

[0058] In some embodiments of the present application, the oil absorption value OA of the negative electrode material ranges from 40 to 70, preferably from 45 to 60. The oil absorption value indicates the processability of the negative electrode material in the pulping process during battery production. The lower the value, the higher the processability and the higher the yield rate of the processing process.

[0059] The method for preparing the negative electrode material described in the embodiment of the present application provides a first powder having a higher sphericity through the pulverization step, so that the single-particle graphite core can achieve a more uniform and complete effect in the coating step; the negative electrode material after forming the carbon coating layer has more lithium ion diffusion channels, and the disordered carbon layer of the carbon coating layer gives the negative electrode material a lower surface resistance. The structure ensures the fast charging capability of the negative electrode material. The disordered stacking of the negative electrode material in the process of forming the battery negative electrode plate can further increase the orientation of the material, ensure the pores of the single particle of the negative electrode material in the porous structure of the plate, increase the wettability of the negative electrode material with the electrolyte therein, and further improve the fast charging performance of the negative electrode material.

[0060] The present application also provides a lithium-ion battery negative electrode material, which is prepared using any of the above-mentioned methods for preparing lithium-ion battery negative electrode materials.

[0061] The following further describes the embodiments of the present application based on Reference Examples 1 to 8 and Comparative Examples 1 to 3.

[0062] Examples 1 to 8:

[0063] Example 1

[0064] Step (1): Grind the needle coke with volatile content of 6.5% into Dv50 第一粉料 Equal to 10.9μm, particle size distribution D=(Dv90 第一粉料 -Dv10 第一粉料 ) / Dv50 第一粉料 =1.20 first powder;

[0065] Step (2): subjecting the first powder formed in step (1) to a graphitization treatment at a maximum temperature of 3050° C. to convert the first powder into a graphite core;

[0066] Step (3): a graphite core having a mass of M1 and an asphalt having a mass of M2 and a softening point of 205°C are placed in a horizontal reactor for coating treatment, wherein the graphite core and the asphalt are converted to a theoretical residual carbon value of 2.0% (theoretical residual carbon value = M2 × asphalt coking value / M1) according to the asphalt coking value, to obtain a pre-coated material having a single particle of the graphite core coated with a carbon coating agent;

[0067] Step (4): The pre-coated material from step (3) was carbonized in a roller kiln at a constant temperature of 1150° C. for 5 hours. After cooling, the material was removed from the kiln and mixed and sieved to obtain a negative electrode material having a carbon coating layer on the surface of a graphite core as sample 1.

[0068] Example 2

[0069] Step (1) Dv50 in Example 1 第一粉料 Change to 8.0, particle size distribution D = (Dv90 第 一粉料 -Dv10 第一粉料 ) / Dv50 第一粉 The sample of Example 2 was obtained by changing the material content to 1.25, changing the softening point of step (3) to 155°C, changing the horizontal reactor to a vertical reactor, and keeping other conditions and ratio parameters unchanged.

[0070] Example 3

[0071] The needle coke in step (1) of Example 1 was changed to petroleum coke with a volatile matter content of 10.1% and an S content of 2.2%, the softening point in step (3) was changed to 240°C, the carbonization time in step (4) was changed to 1250°C, the constant temperature time was changed to 3h, and other conditions and ratio parameters remained unchanged to obtain the sample of Example 3.

[0072] Example 4

[0073] The Dv50 of step (1) in Example 1 was 第一粉料 The sample of Example 4 was obtained by changing the reaction temperature of step (2) to 13.0μ, changing the graphitization temperature of step (2) to 2950°C, changing the horizontal reactor of step (3) to a vertical reactor, and keeping other conditions and ratio parameters unchanged.

[0074] Example 5

[0075] The asphalt mass M2 with a softening point of 205° C. in step (3) of Example 1 was replaced with a resin with a molecular weight of 600, while other conditions and ratio parameters remained unchanged to obtain the sample of Example 5.

[0076] Example 6

[0077] The theoretical carbon residue value in step (3) of Example 1 was changed to 4.0%, the horizontal reactor was changed to a fusion machine, and other conditions and ratio parameters remained unchanged to obtain the sample of Example 6.

[0078] Comparative Example 1

[0079] The particle size distribution D in step (1) of Example 1 is Dv90 第一粉料 -Dv10 第一粉料 ) / Dv50 第一粉料 =1.90, and other conditions and ratio parameters remain unchanged to obtain comparative sample 1.

[0080] Comparative Example 2

[0081] The particle size distribution D in step (1) of Example 1 was changed to 1.5, the theoretical carbon residue value in step (3) was changed to 6.0%, the horizontal kettle was changed to a mixer, and other conditions and ratio parameters remained unchanged to obtain the sample of Comparative Example 2.

[0082] Comparative Example 3

[0083] The asphalt mass M2 with a softening point of 205°C in step (3) of Example 1 was changed to a resin with a molecular weight of 2000, the theoretical carbon residue value was changed to 1%, and other conditions and ratio parameters remained unchanged to obtain Comparative Example 3.

[0084] The graphite core materials in Examples 1 to 6 and Comparative Examples 1 to 3 and the negative electrode materials after the graphite core surface is coated with a carbon coating layer were subjected to particle size measurement, tap density test, specific surface area test, and oil absorption value test, and the test results were calculated as shown in Table 1, wherein the particle size measurement method is: using a laser diffraction particle size distribution measuring instrument to measure the particle size distribution according to the particle size distribution laser diffraction method.

[0085] The tap density test method involves placing the test sample in a graduated cylinder of a specified volume and vibrating it 3000 times at a frequency of 250 times / min. The tap density is calculated based on the volume after vibration. The specific surface area test is performed using a specific surface area meter using nitrogen physical adsorption to determine the specific surface area value. The oil absorption value is tested using an oil absorption meter.

[0086] The materials in Examples 1 to 6 and Comparative Examples 1 to 3 were respectively subjected to confocal Raman spectroscopy (Renishaw) testing. The G peak ("Graphite" band) was located at about 1580 cm -1 The D peak (“Defect” band) is located at about 1360 cm-1, corresponding to the E2g vibration mode. -1 The Raman eigenvalue L = Id / Ig was calculated by scanning 2500 points and performing distribution statistics.

[0087] Coin-type batteries were prepared using the negative electrode materials prepared in Examples 1-6 and Comparative Examples 1-3 for performance testing. The button-type battery testing method was as follows: conductive carbon black was added to a carboxymethyl cellulose (CMC) aqueous solution, followed by the negative electrode materials prepared in the Examples or Comparative Examples, and finally, styrene-butadiene rubber (SBR). The mixture was stirred evenly, and the slurry was evenly coated on a copper foil on a coater to form a pole piece. The coated pole piece was placed in a vacuum drying oven at 110°C and dried for 4 hours. The pole piece was then removed and rolled on a roller press for later use. A simulated battery was assembled in an argon-filled German Braun glove box. The electrolyte consisted of 1M LiPF6 + EC:DEC:DMC = 1:1:1 (volume ratio), and a metal lithium sheet was used as the counter electrode. Capacity testing was performed on an Arbin BT2000 battery tester from the United States, with a charge and discharge voltage range of 0.005 to 2.0V and a charge and discharge rate of 0.1C. The electrochemical properties of the materials obtained in the embodiment and the comparative example were compared to calculate the coating advantage characteristic value Y and the coating characteristic response number.

[0088] The coating advantage characteristic value of the carbon coating layer is Y=T / (JZ), wherein the theoretical carbon value of the coating agent forming the carbon coating layer is T%; J=Dv50 / Dv50 骨料 , the Dv50 represents the particle size corresponding to when the volume distribution percentage of the negative electrode material reaches 50%, and the Dv50 aggregate represents the particle size corresponding to when the volume distribution percentage of the graphite core reaches 50%; Z = Dv95 / Dv95 骨料 , DV95 represents the particle size corresponding to when the volume distribution percentage of the negative electrode material reaches 95%, and Dv95 aggregate represents the particle size corresponding to when the volume distribution percentage of the graphite core reaches 95%.

[0089] In some embodiments of the present application, T ranges from 1 to 5, J ranges from 1.00 to 1.30, Z ranges from 1.00 to 1.30, and Y>8.5.

[0090] In some embodiments of the present application, the characteristic response number of the carbon residue in the carbon coating layer is A=R 容量 / R 骨料容量 ×T / L+5×D 振实 / S 比表 , where R 容量 is the charge-off test capacity of the negative electrode material, R 骨料容量 is the charge-discharge test capacity of the graphite core, D 振实 is the tap density of the negative electrode material (g / cm 3 ), S 比表 is the specific surface area of ​​the negative electrode material, the theoretical carbon value of the coating agent of the negative electrode material is T%, and the Raman characteristic value of the negative electrode material is L=Id / Ig.

[0091] Table 1 Comparison of performance indicators of examples and comparative examples

[0092] It can be seen from Table 1 that the coating advantage characteristic values ​​of the samples prepared in Examples 1 to 6 of the present application are all above 8.5, indicating that the coating effect is good, and the oil absorption value and the coating characteristic response number are both within the corresponding range. The negative electrode materials described in the embodiments of the present application have high processability in the back-end battery processing link; while the coating advantage characteristic values ​​of the samples prepared in Comparative Examples 1 to 3 are less than 8.5, and the oil absorption values ​​of the samples prepared in Comparative Examples 1 to 3 are all on the high side, indicating that the samples prepared in the Comparative Examples have poor processability as negative electrode materials.

[0093] Finally, it should be understood that the embodiments of the application disclosed herein are illustrations of the principles of the embodiments of the present application. Other modified embodiments are also within the scope of the present application. Therefore, the embodiments disclosed in the present application are merely examples and not limitations. Those skilled in the art can adopt alternative configurations based on the embodiments in the present application to implement the applications in the present application. Therefore, the embodiments of the present application are not limited to those embodiments that have been precisely described in the application.

Claims

1. A negative electrode material for a lithium-ion battery, comprising a graphite core and a carbon coating layer coated on the surface of each single particle of the graphite core, characterized in that The coating advantage characteristic value Y of the carbon coating layer is Y = T / (J - Z), where the theoretical carbon value of the coating agent forming the carbon coating layer is T%; the coating response value J of the carbon coating layer is J = Dv50 / Dv50 骨料 , where Dv50 represents the particle size corresponding to when the volume distribution percentage of the negative electrode material reaches 50%, and Dv50 骨料 represents the particle size corresponding to when the volume distribution percentage of the graphite core reaches 50%; the coating anchoring parameter Z of the carbon coating layer is Z = Dv95 / Dv95 骨料 , where Dv95 represents the particle size corresponding to when the volume distribution percentage of the negative electrode material reaches 95%, and Dv95 骨料 represents the particle size corresponding to when the volume distribution percentage of the graphite core reaches 95%.

2. The negative electrode material of the lithium ion battery according to claim 1, wherein The range of T is 1 to 5, the range of J is 1.00 to 1.30, the range of Z is 1.00 to 1.30, and J is greater than Z, Y > 8.

5.

3. The negative electrode material for a lithium ion battery according to claim 1, wherein The characteristic response number A of the residual carbon in the carbon coating layer = R 容量 / R 骨料容量 ×T / L + 5×D 振实 / S 比表 , Among them, R 容量 is the galvanostatic charge-discharge test capacity of the negative electrode material, R 骨料容量 is the galvanostatic charge-discharge test capacity of the graphite core, D 振实 is the tapped density of the negative electrode material, S 比表 is the specific surface area of the negative electrode material, the theoretical carbon value of the coating agent forming the carbon coating layer is T%, and the Raman characteristic value L of the negative electrode material is L = Id / Ig.

4. The negative electrode material of the lithium ion battery according to claim 3, characterized in that, The characteristic response number A of the residual carbon in the carbon coating layer is greater than or equal to 6.5 and less than or equal to 35.

5. The negative electrode material for a lithium ion battery according to claim 3, characterized in that, The Raman characteristic value distribution range of the negative electrode material is 0.20 to 0.

60.

6. The negative electrode material for a lithium ion battery according to claim 1, characterized in that, The oil absorption value OA of the negative electrode material ranges from 40 to 70.

7. The negative electrode material for a lithium-ion battery according to claim 1, characterized in that, The carbon coating layer is amorphous carbon, and the thickness of the carbon coating layer is 5 to 100 nm.

8. A method for preparing a negative electrode material for a lithium-ion battery, characterized in that, Including: A pulverizing step of pulverizing raw materials to form a first powder; A graphitization step of converting the first powder into a graphite core; A coating step of coating a carbon coating agent on the surface of each single particle of the graphite core; Carbonization step to convert the carbon coating agent into a carbon coating layer, and the coating advantage characteristic value Y of the carbon coating layer is Y = T / (J - Z), where the theoretical carbon value of the carbon coating agent is T%; the coating response value J of the carbon coating layer is J = Dv50 / Dv50 骨料 , where Dv50 represents the particle size corresponding to when the volume distribution percentage of the negative electrode material reaches 50%, and Dv50 骨料 represents the particle size corresponding to when the volume distribution percentage of the graphite core reaches 50%; the coating anchoring parameter Z of the carbon coating layer is Z = Dv95 / Dv95 骨料 , where Dv95 represents the particle size corresponding to when the volume distribution percentage of the negative electrode material reaches 95%, and Dv95 骨料 represents the particle size corresponding to when the volume distribution percentage of the graphite core reaches 95%.

9. The preparation method of the negative electrode material of the lithium ion battery according to claim 8, characterized in that, The range of T is 1 to 5, the range of J is 1.00 to 1.30, the range of Z is 1.00 to 1.30, and J is greater than Z, Y > 8.

5.

10. The preparation method of the anode material for a lithium-ion battery according to claim 8, wherein, The characteristic response number A of the residual carbon in the carbon coating layer = R 容量 / R 骨料容量 ×T / L + 5×D 振实 / S 比表 , Among them, R 容量 is the galvanostatic charge-discharge test capacity of the negative electrode material, R 骨料容量 is the galvanostatic charge-discharge test capacity of the graphite core, D 振实 is the tap density of the negative electrode material, S 比表 is the specific surface area of the negative electrode material, the theoretical carbon value of the coating agent for forming the carbon coating layer is T%, and the Raman characteristic value L of the negative electrode material is L = Id / Ig.

11. The preparation method of the negative electrode material of the lithium ion battery according to claim 10, characterized in that, The characteristic response number A of the residual carbon in the carbon coating layer is greater than or equal to 6.5 and less than or equal to 35.

12. The preparation method of the negative electrode material of the lithium ion battery according to claim 10, wherein, The Raman characteristic value distribution range of the negative electrode material is 0.20 to 0.

60.

13. The preparation method of the anode material for a lithium-ion battery according to claim 8, wherein The raw material is needle coke with a volatile content of 5 to 7%, or petroleum coke with a volatile content of 8 to 11% and an S content of 1.0 to 3.0%.

14. The preparation method of the anode material for a lithium-ion battery according to claim 8, characterized in that, The volume distribution particle size Dv50 of the first powder material 第一粉料 is 4 to 18 μm, and the particle size distribution D of the first powder material ranges from 0.8 to 1.5, D = (Dv90 第一粉料 - Dv10 第一粉料 ) / Dv50 第一粉料 , where the Dv50 第一粉料 represents the particle size corresponding to when the volume distribution percentage of the first powder material reaches 50%, Dv90 第一粉料 represents the particle size corresponding to when the volume distribution percentage of the first powder material reaches 90%, and Dv10 第一粉料 represents the particle size corresponding to when the volume distribution percentage of the first powder material reaches 10%.

15. The preparation method of the anode material for a lithium-ion battery according to claim 8, characterized in that, The carbon coating agent is petroleum pitch with a softening point of 140 to 250°C, a resin with a molecular weight lower than 1000, or tar pitch with a softening point lower than 20°C, and the total theoretical residual carbon value of the carbon coating agent is 1 to 5%.

16. The preparation method of the anode material for a lithium-ion battery according to claim 8, characterized in that, The carbonization step is carried out under constant temperature conditions, the carbonization temperature is 800 to 1300°C, and the constant temperature time is greater than 2 h and lower than 12 h.

17. The preparation method of the negative electrode material of the lithium ion battery according to claim 8, characterized in that, The oil absorption value OA of the negative electrode material ranges from 40 to 70.

18. The preparation method of the anode material for a lithium-ion battery according to claim 1, characterized in that, The carbon coating layer is amorphous carbon, and the thickness of the carbon coating layer is 5 to 100 nm.

19. A lithium-ion battery, characterized in that, A negative electrode is made of any one of the negative electrode materials according to claims 1 to 9.

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