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

Abstract

This application provides a graphite anode material, its preparation method, and a lithium-ion battery. The graphite anode material includes a first graphite material and a second graphite core. The first graphite material includes a first graphite core and a carbon coating layer covering the surface of the first graphite core particles. The second graphite core is formed by secondary particle graphitization. The first graphite core is obtained by graphitizing a first powder. The first powder is formed from raw materials through heat treatment and pulverization and shaping. Wherein, 1≤D150×(0.71+0.39×D150×(1+0.01T))+M 可逆克容量 / 372≤100, T is the temperature of the heat treatment, D150 is the first median particle size of the first powder, M 可逆克容量 The reversible specific capacity of the formed graphite anode material. The graphite anode material has better coating uniformity and charge / discharge capability.

Description

Graphite negative electrode material and preparation method thereof, and 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 graphite negative electrode material and a preparation method thereof, and a lithium-ion battery. Background Art

[0002] Today, the new energy industry is booming, driven by the development of lithium-ion batteries. Simultaneously, the demand for battery applications is evolving rapidly, with a growing demand for power batteries. High volumetric energy density, excellent fast-charging performance, low temperature rise and electrode expansion, and excellent high-temperature performance are all key indicators of battery performance.

[0003] Artificial graphite negative electrode material is a material with a certain particle size distribution obtained by crushing and granulating raw materials such as needle coke, petroleum coke, and asphalt coke, and then undergoing high-temperature graphitization treatment to form a graphite flake structure.

[0004] Although artificial graphite negative electrode materials have undergone decades of development, the industry still has a high demand for improvement in the charging and discharging performance of negative electrode materials, such as the demand for fast charging of battery cells, the demand for expansion of battery cells, and the demand for improvement in the target capacity of negative electrode materials.

[0005] Therefore, it is necessary to provide a graphite negative electrode material with better charge and discharge performance and a method for preparing the same.

[0006] Summary of the Invention

[0007] The present application provides a graphite negative electrode material and a preparation process thereof, as well as a lithium-ion battery, which have better charge and discharge performance.

[0008] On the one hand, an embodiment of the present application provides a method for preparing a graphite negative electrode material, comprising: selecting raw materials, performing heat treatment and crushing and shaping treatment on the raw materials to form a first powder of single particles having a first median particle size, wherein 1≤D150×(0.71+0.39×D150×(1+0.01T))+M 可逆克容量 / 372≤100, T is the temperature of the heat treatment, D150 is the first median particle size, M 可逆克容量The invention relates to a method for forming a reversible gram capacity of the graphite negative electrode material; performing a secondary treatment on the first powder so that the single particles of the first powder are bonded to each other to form secondary particles; performing a graphitization treatment on the first powder to form a first graphite core of a single particle, and performing a graphitization treatment on the secondary particles to form a second graphite core; coating the surface of the first graphite core of the single particle with a carbon coating layer to form a first graphite material; and uniformly mixing the first graphite material and the second graphite core in proportion to form the graphite negative electrode material.

[0009] In some embodiments, the heat treatment temperature is 0-1400° C., the reversible gram capacity of the graphite negative electrode material is 320-365 mAh / g, and the first median particle size is 5-20 μm.

[0010] In some embodiments, 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 a sulfur content of 1.0-3.0%.

[0011] In some embodiments, the particle size distribution K value of the first powder is in the range of 0.8 to 1.5, K=(Dv90 第一粉料 -Dv10 第一粉料 ) / Dv50 第一粉料 , wherein the Dv50 第一粉料 Dv90 is the particle size corresponding to when the volume distribution percentage of the first powder reaches 50%. 第一粉料 Dv10 is the particle size corresponding to when the volume distribution percentage of the first powder reaches 90%. 第一粉料 It is the particle size corresponding to when the volume distribution percentage of the first powder reaches 10%.

[0012] In some embodiments, the powder OI value G of the graphite negative electrode material is OI The granulation degree γ of the secondary particles formed by the bonding between the single particles of the first powder satisfies the relationship: 1≤100 / (γ+3.3×G OI )≤25, wherein, γ=(D250-D150) / D150×100%, and D250 is the second median particle size of the secondary particles.

[0013] In some embodiments, the powder OI value of the graphite negative electrode material is 1 to 20, and the granulation degree is 10% to 200%.

[0014] In some embodiments, coating the surface of the first graphite core of a single particle with a carbon coating layer to form a first graphite material includes: performing a coating step to coat the surface of the first graphite core of the single particle with a carbon coating agent; and performing a carbonization step to convert the carbon coating agent into a carbon coating layer.

[0015] In some embodiments, the carbon coating agent is petroleum asphalt with a softening point of 140-250°C, a resin with a molecular weight less than 1000, or tar asphalt with a softening point less than 20°C; the coating layer is any one or more of hard carbon amorphous carbon or soft carbon amorphous carbon, and its thickness is 5-100 nm.

[0016] In some embodiments, the carbonization step is performed under constant temperature conditions, the carbonization temperature is 800-1500° C., and the constant temperature time is greater than 2 hours and less than 12 hours.

[0017] In some embodiments, the Raman spectrum median of the graphite negative electrode material is D / I G The coating amount of the carbon coating layer in the first graphite material, the mixing ratio of the first graphite material and the second graphite core satisfy the relationship: 0.01≤α(D150×γ+1+T%)+0.1×β×T 包覆量 ≤5.0, where β is the mixing ratio of the first graphite material and the second graphite core, T 包覆量 is the coating amount of the carbon coating layer in the first graphite material, T is the temperature of the heat treatment, γ is the granulation degree of the first powder material to form secondary particles by bonding between single particles, and α is the I of the graphite negative electrode material. D / I G Median Raman spectrum.

[0018] In some embodiments, the mixing ratio of the first graphite material to the second graphite core is 1:9 to 9:1 by mass.

[0019] On the other hand, the present application also provides a graphite battery negative electrode material, comprising a first graphite material and a second graphite core, wherein the first graphite material comprises a first graphite core and a carbon coating layer coated on the surface of the first graphite core of a single particle, the second graphite core is formed by graphitizing a secondary particle, the first graphite core is obtained by graphitizing a first powder, and the first powder is formed by heat treatment and crushing and shaping a raw material, wherein 1≤D150×(0.71+0.39×D150×(1+0.01T))+M 可逆克容量 / 372≤100, T is the temperature of the heat treatment, D150 is the first median particle size of the first powder, M 可逆克容量 The reversible gram capacity of the graphite negative electrode material formed.

[0020] In some embodiments, the heat treatment temperature is 0-1400° C., the reversible gram capacity of the graphite negative electrode material is 320-365 mAh / g, and the first median particle size is 5-20 μm.

[0021] In some embodiments, the raw material is needle coke with a volatile content of 5-7%, or petroleum coke with a volatile content of 8-11% and a sulfur content of 1.0-3.0%.

[0022] In some embodiments, the particle size distribution K value of the first powder is in the range of 0.8 to 1.5, K=(Dv90 第一粉料 -Dv10 第一粉料 ) / Dv50 第一粉料 , wherein the Dv50 第一粉料 Dv90 is the particle size corresponding to when the volume distribution percentage of the first powder reaches 50%. 第一粉料 Dv10 is the particle size corresponding to when the volume distribution percentage of the first powder reaches 90%. 第一粉料 It is the particle size corresponding to when the volume distribution percentage of the first powder reaches 10%.

[0023] In some embodiments, the powder OI value G of the graphite negative electrode material is OI The granulation degree γ of the secondary particles formed by the bonding between the single particles of the first powder satisfies the relationship: 1≤100 / (γ+3.3×G OI )≤25, wherein, γ=(D250-D150) / D150×100%, and D250 is the second median particle size of the secondary particles.

[0024] In some embodiments, the powder OI value of the graphite negative electrode material is 1 to 20, and the granulation degree is 10% to 200%.

[0025] In some embodiments, the Raman spectrum median of the graphite negative electrode material is D / I G The coating amount of the carbon coating layer in the first graphite material, the mixing ratio of the first graphite material and the second graphite core satisfy the relationship: 0.01≤α(D150×γ+1+T%)+0.1×β×T 包覆量 ≤5.0, where β is the mixing ratio of the first graphite material and the second graphite core, T 包覆量 is the coating amount of the carbon coating layer in the first graphite material, T is the temperature of the heat treatment, γ is the granulation degree of the first powder material to form secondary particles by bonding between single particles, and α is the I of the graphite negative electrode material. D / I G Median Raman spectrum.

[0026] In some embodiments, the mixing ratio of the first graphite material and the second graphite core is 3:7 to 7:3.

[0027] An embodiment of the present application further provides a lithium-ion battery, comprising a negative electrode, wherein the negative electrode is made of any one of the negative electrode materials described in the embodiment of the present application.

[0028] Compared with the prior art, the preparation method of the graphite negative electrode material described in the embodiment of the present application, through the crushing step, makes the formed first powder have higher sphericity, so that the single-particle first graphite core can achieve a more uniform and complete coating effect in the coating step; the first graphite 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 graphite negative electrode material have a lower surface resistance, and the structure ensures the fast charging capability of the graphite negative electrode material; the mixed second graphite core is a secondary particle, which can further increase the orientation degree of the material, ensure the pores of the graphite negative electrode material in the porous structure of the electrode piece, increase the wettability of the graphite negative electrode material in the electrolyte therein, and further improve the fast charging performance of the graphite negative electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] 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:

[0030] FIG1 is a schematic diagram of a process flow of a method for preparing a graphite negative electrode material according to an embodiment of the present application. DETAILED DESCRIPTION

[0031] 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.

[0032] In one embodiment of the present application, a method for preparing a graphite negative electrode material is provided, as shown in FIG1 , comprising:

[0033] Step S1: Select raw materials, perform heat treatment and crushing and shaping treatment on the raw materials to form a first powder of single particles with a first median particle size, wherein 1≤D150×(0.71+0.39×D150×(1+0.01T))+M 可逆克容量 / 372≤100, T is the temperature of the heat treatment, D150 is the first median particle size, M 可逆克容量 The reversible gram capacity of the formed graphite negative electrode material;

[0034] Step S2: performing a secondary treatment on the first powder material, so that the single particles of the first powder material are bonded together to form secondary particles;

[0035] Step S3: graphitizing the first powder to form a first graphite core of a single particle, and graphitizing the secondary particles to form a second graphite core;

[0036] Step S4: coating a carbon coating layer on the surface of the first graphite core of the single particle to form a first graphite material;

[0037] Step S5: uniformly mixing the first graphite material and the second graphite core in proportion to form the graphite negative electrode material.

[0038] First, step S1 is performed: selecting raw materials, performing heat treatment and crushing and shaping treatment on the raw materials to form a first powder of single particles with a first median 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 key indicators of the final negative electrode material, such as capacity, specific surface area and tap density. The raw materials include needle coke, petroleum coke, or asphalt, etc. The volatile matter of the raw materials is 0.01% to 20%, preferably 0.01% to 15%. 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 matter of 5 to 7%, or petroleum coke with a volatile matter of 8 to 11% and an S content of 1.0 to 3.0%. Volatile matter refers to the raw material that is heated in an airtight state at a certain temperature. A part of the organic matter and minerals in the raw material will decompose into gas and liquid and escape. The mass percentage content of the escaped substance after deducting the water content in the raw material.

[0040] The processing of raw materials in the present application may include heat treatment and crushing and shaping of the raw materials. The heat treatment step is a heating and modification step of the raw materials. In some embodiments, the raw materials such as needle coke, petroleum coke, or asphalt are heat treated at a temperature of 0 to 1400°C to cause certain changes in the structure and physicochemical properties of the raw materials. The different heat treatment temperatures affect the morphology after crushing and the key indicators such as the reversible gram capacity, specific surface area and tap density of the negative electrode material finally formed. In some embodiments of the present application, the temperature of the heat treatment is preferably 500 to 1400°C.

[0041] The primary purpose of the pulverization and shaping step is to pulverize the heat-treated raw material and, through shaping, form a first powder of single particles having a first median particle size. In this embodiment of the present application, the pulverization and shaping step can be performed using equipment such as a mechanical mill, roller mill, or ball mill to form the first powder. The first median particle size D150 is used to indicate the uniformity and particle size of the first powder formed after the pulverization step.

[0042] In some embodiments of the present application, the pulverizing and shaping step adopts physical pulverization, and the method for measuring the first median particle size of the first powder 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.

[0043] Gram capacity refers to the ratio of the amount of charge released by the active material within a battery to the mass of the active material. Reversible gram capacity refers to the ratio of the amount of charge released by the active material during the charge and discharge process in a battery or supercapacitor to the mass of the electrode, in other words, the reversibility of the charge during the charge and discharge process. It is usually expressed in units of mAh / g or Ah / kg. Reversible gram capacity reflects the charge loss of a battery or supercapacitor during the charge and discharge process and is one of the important indicators for evaluating the performance of batteries or supercapacitors.

[0044] In the embodiment of the present application, the first median particle size of the first powder formed by the pulverization step in the marking step S1 is D150, the temperature of the heat treatment is T, and the reversible gram capacity of the graphite negative electrode material finally formed is M 可逆克容量 , then 1≤D150×(0.71+0.39×D150×(1+0.01T))+M 可逆克容量 / 372≤100. The first median particle size of the first powder is D150, the temperature of the heat treatment is T, and the reversible gram capacity of the graphite negative electrode material finally formed is M 可逆克容量 The relationship between the heat treatment temperature in the pulverization step and the value or value range of the first median particle size can be accurately adjusted.

[0045] Optional, 1≤D150×(0.71+0.39×D150×(1+0.01T))+M 可逆克容量 / 372≤50.

[0046] In some embodiments of the present application, the heat treatment temperature T is 0 to 1400°C, and the reversible capacity of the graphite negative electrode material finally formed is 320 to 365 mAh / g. Then, 1≤D150×(0.71+0.39×D150×(1+0.01T))+M 可逆克容量 / 372≤100, it can be obtained that the first median particle size of the first powder is 5 to 20 μm.

[0047] In some embodiments of the present application, the heat treatment temperature T is 500-1400°C, and the reversible capacity of the graphite negative electrode material finally formed is 335-360 mAh / g. Then, by 1≤D150×(0.71+0.39×D150×(1+0.01T))+M 可逆克容量 / 372≤50, it can be obtained that the first median particle size of the first powder is 7 to 15 μm.

[0048] In some embodiments of the present application, the particle size distribution K value of the first powder is in the range of 0.8 to 1.5. Optionally, the particle size distribution K value of the first powder is in the range of 1.0 to 1.3, wherein K=(Dv90 第一粉料 -Dv10 第一粉料 ) / Dv50 第一粉料 , wherein the Dv50 第一粉料 Dv90 is the particle size corresponding to when the volume distribution percentage of the first powder reaches 50%. 第一粉料 Dv10 is the particle size corresponding to when the volume distribution percentage of the first powder reaches 90%. 第一粉料 It is the particle size corresponding to when the volume distribution percentage of the first powder reaches 10%.

[0049] In some embodiments of the present application, the range of Dv50 is 4 to 18 μm, optionally, the range of Dv50 is 6 to 13 μm; the range of Dv10 is greater than or equal to 1.5 μm, optionally, the range of Dv10 is 2 to 6 μm; the range of Dv90 is less than or equal to 40 μm, optionally, the range of Dv90 is 10 to 30 μm. In some embodiments, Dv50 is 5 μm, Dv10 is 2.5 μm, and Dv90 is 11.0 μm; or Dv50 is 8 μm, Dv10 is 3.6 μm, and Dv90 is 16.0 μm; or Dv50 is 10 μm, Dv10 is 4.1 μm, and Dv90 is 19.0 μm; or Dv50 is 12 μm, Dv10 is 5.6 μm, and Dv90 is 22.0 μm, etc.

[0050] Executing step S2: performing a secondary treatment on the first powder material, so that the single particles of the first powder material are bonded to each other to form secondary particles.

[0051] In an embodiment of the present application, the secondary treatment is to add a binder to the first powder, and under the temperature condition of 500-700°C, the single particles of the first powder are bonded to each other to form secondary particles. The binder includes materials such as asphalt or resin, and the amount of the binder added is less than or equal to 30% (mass percentage). Optionally, the amount of the binder added is less than or equal to 20% (mass percentage), such as 15%, 10%, 8%, 6%, 3%, etc. The amount of the asphalt or resin material added can also be 0. The equipment for the secondary treatment includes a horizontal reactor, a vertical reactor, a drum furnace or a rotary kiln, etc.

[0052] In the embodiment of the present application, the second median particle size D250 of the secondary particles is greater than the first median particle size D150. The granulation degree γ of the first powder material, in which single particles are bonded to form secondary particles, is defined as the difference between the second median particle size D250 and the first median particle size D150 divided by the percentage of the first median particle size D150, that is:

[0053] γ=(D250-D150) / D150×100%.

[0054] In some embodiments of the present application, the granulation degree γ is 10% to 200%. Optionally, the granulation degree γ is 40% to 150%.

[0055] In which, the first powder in the secondary treatment process can be a part of the first powder prepared in step S1, for example, 10% to 90% of the first powder prepared in step S1. Optionally, the first powder in the secondary treatment process is 30% to 70% of the first powder prepared in step S1. Further, the first powder in the secondary treatment process is 40% to 50% of the first powder prepared in step S1.

[0056] The powder orientation index (Orientation Index) of the graphite negative electrode material is abbreviated as powder OI value. The powder OI value indicates the expansion level of the negative electrode of the battery cell, and reflects the isotropy of each crystal phase of the grains of the negative electrode of the battery cell at the electrode level. The smaller the powder OI value, the better the isotropy of the negative electrode of the battery cell at the electrode level, that is, the lower the expansion level of the negative electrode of the battery cell.

[0057] In the embodiment of the present application, the powder OI value of the graphite negative electrode material can be marked as G OI , then G OI =S004 / S110, wherein S004 is the peak area of ​​the 004 characteristic diffraction peak in the X-ray diffraction spectrum of the graphite negative electrode material, and S110 is the peak area of ​​the 110 characteristic diffraction peak in the X-ray diffraction spectrum of the graphite negative electrode material.

[0058] In some embodiments of the present application, the powder OI value G of the graphite negative electrode material is OI The granulation degree γ of the secondary particles formed by the bonding between the single particles of the first powder satisfies the relationship: 1≤100 / (γ+3.3×G OI )≤25, optionally, 2≤100 / (γ+3.3×GOI)≤15.

[0059] In some embodiments of the present application, the powder OI value of the graphite negative electrode material is 1 to 15, then according to 1≤100 / (γ+3.3×G OI )≤25, the granulation degree can be 10% to 200%. In some embodiments of the present application, the powder OI value of the graphite negative electrode material is 1 to 10, according to 2≤100 / (γ+3.3×G OI )≤15, the granulation degree can be obtained to be 40% to 150%.

[0060] Executing step S3: graphitizing the first powder to form a first graphite core of a single particle, and graphitizing the secondary particles to form a second graphite core;

[0061] The graphitization treatment of the first powder as described in the embodiment of the present application refers to pyrolyzing the first powder at a high temperature so that the first powder forms a graphite structure with a high degree of crystallinity, and the graphite structure is the first graphite core of a single particle. During the graphitization treatment, the lattice structure of the graphite material changes: the molecular spacing is reduced, and the lattice structure is more ordered. The structural change makes the first graphite core have better electrical conductivity and cyclic stability. The first graphite core formed after the graphitization treatment 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 treatment includes an Acheson furnace, a box furnace, an inner series furnace or a continuous graphitization furnace, etc. The graphitization temperature is higher than 2700°C, for example, the graphitization temperature is 2800~3200°C, and optionally, the graphitization temperature is 2900~3100°C.

[0062] The embodiment of the present application also includes graphitizing the secondary particles to form a second graphite core, wherein the process and equipment for graphitizing the secondary particles are the same as the process and equipment for graphitizing the first powder, and the process for graphitizing the secondary particles and the process for graphitizing the first powder can be performed simultaneously in different reaction chambers of the same equipment, or can be performed successively in the same or different reaction chambers of the same equipment.

[0063] Step S4: coating the surface of the first graphite core of the single particle with a carbon coating layer to form a first graphite material.

[0064] In an embodiment of the present application, coating the surface of the first graphite core of a single particle with a carbon coating layer includes: performing a coating step to coat the surface of the first graphite core of the single particle with a carbon coating agent; and performing a carbonization step to convert the carbon coating agent into a carbon coating layer.

[0065] The coating step described in the embodiment of the present application includes a solid-phase coating process and a liquid-phase coating process. The solid-phase coating process includes coating the surface of the first graphite core with a solid-phase coating agent, and the solid-phase coating agent is, for example, asphalt, a resin-like material, or a mixture of asphalt and resin-like materials. The liquid-phase coating process includes: first heating and melting the solid-phase coating agent in a horizontal reactor or a vertical reactor to form a liquid-phase coating agent, and then coating the surface of the first graphite core with the liquid-phase coating agent, and the solid-phase coating agent is, for example, asphalt, a resin-like material, or a mixture of asphalt and resin-like materials. The liquid-phase coating process can also use a solvent with a low coking value to prepare a coating agent that is liquid at room temperature, and use a fusion machine to coat the surface of the first graphite core.

[0066] The coating step is the core process for realizing the fast charging capability of the graphite negative electrode material in this embodiment. In order to ensure that the coating effect, that is, the coating advantage characteristic value, is sufficiently high, 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 amount of the carbon coating agent added is 1 to 10% (mass percentage content), for example, 3 to 7% or 4 to 6%. The coating equipment used in the embodiment of the present application can be selected from a fusion machine, a kneading machine, a vertical mixer, a screw ribbon mixer, a horizontal reactor, a vertical reactor, etc., more preferably a vertical mixer, a horizontal reactor or a fusion machine, etc.

[0067] 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 first graphite core of the single particle, while avoiding secondary adhesion caused by the carbonization of the particles of the first graphite core. In an embodiment of the present application, the order of the first graphite core is higher than that of the carbon coating layer, so 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, by limiting the coating amount of the carbon coating layer, the pulse charging requirements of the battery cell made of the graphite negative electrode material can be met. In some embodiments of the present application, the coating layer is any one or more of hard carbon amorphous carbon or soft carbon amorphous carbon, and its thickness is 5 to 100 nm. The coating amount of the carbon coating layer is less than or equal to 5.0%, such as 2%, 3% or 4%.

[0068] The carbonization treatment step described in the embodiment of the present application can use carbonization equipment such as a rotary kiln, a roller kiln or a tunnel kiln, and the carbonization step is carried out under constant temperature conditions, for example, at a temperature of 800 to 1500°C, and the constant temperature time is greater than 2 hours (hours) and less than 12 hours (hours), thereby improving the electrochemical properties of the carbon coating. The preferred carbonization equipment in the embodiment of the present application is a roller kiln. The reaction temperature of the carbonization step is preferably 1000 to 1200°C, and the reaction time is preferably greater than 3 hours (hours) and less than 8 hours (hours).

[0069] Step S5: Evenly mixing the first graphite material and the second graphite core in a certain proportion to form the graphite negative electrode material. The mixing ratio of the first graphite material to the second graphite core, by mass, is, for example, 3:7 to 7:3. Alternatively, the mixing ratio is 4:6, 5:5, or 6:4.

[0070] The Raman spectrum median of the graphite negative electrode material is D / I G The coating amount of the carbon coating layer in the first graphite material and the mixing ratio β of the first graphite material and the second graphite core satisfy the relationship: 0.01≤α×(D50×γ+1+T%)+0.1×β×T 包覆量 ≤5.0),

[0071] Among them, T 包覆量 is the coating amount of the carbon coating layer in the first graphite material, T is the temperature of the heat treatment in step S1, γ is the degree of granulation of the first powder bonded into secondary particles in step S2, that is, the difference between the second median particle size D250 and the first median particle size D150 divided by the percentage of the first median particle size D150, α is the I of the graphite negative electrode material D / I G Median Raman spectrum.

[0072] The Raman spectrum test results reflect the disorder degree of the surface of the negative electrode material. In the graphite negative electrode material, the higher the proportion of the carbon coating layer in the first graphite material, the higher the disorder degree of the surface of the negative electrode material. D / I G The higher the median of the Raman spectrum, the higher the mixing ratio of the first graphite material in the graphite negative electrode material, and the higher the degree of disorder of the graphite negative electrode material. The higher degree of disorder on the surface of the graphite negative electrode material can increase the rate of lithium ion insertion into the negative electrode surface, thereby improving the charging performance of the negative electrode material.

[0073] 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.

[0074] The method for preparing the graphite negative electrode material described in the embodiment of the present application is to make the first powder formed have a higher sphericity through the crushing step, so that the single-particle first graphite core can achieve a more uniform and complete coating effect in the coating step; the first graphite 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 graphite negative electrode material have a lower surface resistance. The structure ensures the fast charging capability of the graphite negative electrode material. The mixed second graphite core is a secondary particle, which can further increase the orientation degree of the material, ensure the pores of the graphite negative electrode material in the porous structure of the electrode piece, increase the wettability of the graphite negative electrode material in the electrolyte therein, and further improve the fast charging performance of the graphite negative electrode material.

[0075] On the other hand, the present application also provides a graphite battery negative electrode material, comprising a first graphite material and a second graphite core, wherein the first graphite material comprises a first graphite core and a carbon coating layer coated on the surface of the first graphite core of a single particle, the second graphite core is formed by graphitizing a secondary particle, the first graphite core is obtained by graphitizing a first powder, and the first powder is formed by heat treatment and crushing and shaping a raw material, wherein, 1≤D150×(0.71+0.39×D150×(1+0.01T))+M 可逆克容量 / 372≤100, T is the temperature of the heat treatment, D150 is the first median particle size of the first powder, M 可逆克容量 The reversible gram capacity of the graphite negative electrode material formed.

[0076] In some embodiments, the heat treatment temperature is 0-1400° C., the reversible gram capacity of the graphite negative electrode material is 320-365 mAh / g, and the first median particle size is 5-20 μm.

[0077] In some embodiments, 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 a sulfur content of 1.0-3.0%.

[0078] In some embodiments, the particle size distribution K value of the first powder is in the range of 0.8 to 1.5, K=((Dv90 第一粉料 -Dv10 第一粉料 ) / Dv50 第一粉料 , wherein the Dv50 第一粉料 Dv90 is the particle size corresponding to when the volume distribution percentage of the first powder reaches 50%. 第一粉料 Dv10 is the particle size corresponding to when the volume distribution percentage of the first powder reaches 90%. 第一粉料 It is the particle size corresponding to when the volume distribution percentage of the first powder reaches 10%.

[0079] In some embodiments, the powder OI value G of the graphite negative electrode material is OI The granulation degree γ of the secondary particles formed by the bonding between the single particles of the first powder satisfies the relationship: 1≤100 / (γ+3.3×G OI )≤25, wherein, γ=(D250-D150) / D150×100%, and D250 is the second median particle size of the secondary particles.

[0080] In some embodiments, the powder OI value of the graphite negative electrode material is 1 to 20, and the granulation degree is 10% to 200%.

[0081] In some embodiments, the Raman spectrum median of the graphite negative electrode material is D / I G The coating amount of the carbon coating layer in the first graphite material, the mixing ratio of the first graphite material and the second graphite core satisfy the relationship: 0.01≤α(D150×γ+1+T%)+0.1×β×T 包覆量 ≤5.0), wherein β is the mixing ratio of the first graphite material and the second graphite core, and the mixing ratio is the ratio of the mixed mass, T 包覆量 is the coating amount of the carbon coating layer in the first graphite material, T is the temperature of the heat treatment, γ is the granulation degree of the first powder material to form secondary particles by bonding between single particles, and α is the I of the graphite negative electrode material. D / I G Median Raman spectrum.

[0082] In some embodiments, the mixing ratio of the first graphite material and the second graphite core is 3:7 to 7:3.

[0083] The present application also provides a lithium-ion battery negative electrode material, which is prepared using any of the above-mentioned methods for preparing the graphite negative electrode material.

[0084] The following further describes the embodiments of the present application based on Reference Examples 1 to 9 and Comparative Examples 1 to 4.

[0085] Examples 1 to 9:

[0086] Example 1

[0087] Step (1): Select needle coke with a volatile matter of 6.0% as the raw material, perform heat treatment and crushing and shaping on the raw material to form a first powder of single particles with a first median particle size of 9 μm, the heat treatment temperature is 1200 degrees Celsius, and the K value of the first powder is 1.3.

[0088] Step (2): 50% of the first powder prepared in step (1) is taken out, and the taken out first powder is subjected to a secondary treatment, wherein the secondary additive is 6% petroleum asphalt, the secondary equipment is a rotary kiln, and the secondary temperature is 600 degrees Celsius, so that the single particles of the first powder are bonded to each other to form secondary particles with a second median particle size of 13.5 μm.

[0089] Step (3): taking out the remaining 50% of the first powder prepared in step (1), graphitizing it at a graphitization temperature of 3000 degrees to form a first graphite core of a single particle, and graphitizing the secondary particles obtained in step (2) at a graphitization temperature of 3000 degrees to form a second graphite core;

[0090] Step (4): coating the surface of the first graphite core of the single particle formed in step (3) with liquid asphalt containing 2% residual carbon, using a horizontal reactor as the coating equipment, and then carbonizing the first graphite core carbon coated with asphalt at a carbonization temperature of 1150° for 5 hours to convert the coated asphalt into an amorphous carbon coating to form a first graphite material;

[0091] Step (5): The first graphite material obtained in step (4) and the second graphite core obtained in step (3) are mixed in a mass percentage ratio of 6:4, and after mixing homogeneously, a graphite negative electrode material is formed.

[0092] Example 2

[0093] The heat treatment temperature in step (1) of Example 1 was changed to 900° to form a first powder of single particles with a first median particle size of 10.5 μm. At the same time, the mass ratio of the first graphite material and the second graphite mixed in step (5) was changed to 7:3, and other conditions remained unchanged to obtain the sample of Example 2.

[0094] Example 3

[0095] The needle coke raw material with 6% volatile matter in step (1) of Example 1 is replaced with a petroleum coke raw material with 10% volatile matter, and without heat treatment, it is crushed to form a first powder of single particles with a first median particle size of 8.5 μm. At the same time, the mixing ratio of the first graphite material and the second graphite core in step (5) is changed to 5:5, and other conditions remain unchanged to obtain the sample of Example 3.

[0096] Example 4

[0097] Step (1): Select a petroleum coke raw material with a volatile matter of 10% and a needle coke raw material with a volatile matter of 6%, respectively, and grind and shape the two raw materials without heat treatment to form a first powder of single particles with a first median particle size of 8.0 μm, and the K value of the first powder is 1.3.

[0098] Step (2): The first powder prepared from the petroleum coke raw material with a volatile content of 10% in step (1) is subjected to secondary treatment, wherein the additive for the secondary treatment is 6% petroleum asphalt, the secondary treatment equipment is a rotary kiln, and the secondary treatment temperature is 600 degrees Celsius, so that the single particles of the first powder are bonded to each other to form secondary particles with a second median particle size of 13.5 μm. Step (3): The first powder prepared from the needle coke raw material with a content of 6% in step (1) is graphitized at a temperature of 3000 degrees to form a first graphite core of a single particle, and the secondary particles obtained in step (2) are graphitized at a temperature of 3000 degrees to form a second graphite core. In step (5), the first graphite core prepared in step (3) and the second graphite core are mixed in a mass ratio of 7:3 to obtain the sample of Example 4.

[0099] Example 5

[0100] The step (1) of heat treating the needle coke raw material with a volatile content of 6% in Example 1 was removed, the step (4) of coating the surface of the first graphite core of a single particle with an amorphous carbon coating layer in Example 4 was omitted, and the first graphite core and the second graphite core obtained in step (3) were mixed in step (5). Other conditions were the same as in Example 4 to obtain the sample of Example 5.

[0101] Example 6

[0102] The step (1) of heat treating the needle coke raw material with a volatile matter content of 6% in Example 1 is removed, and the step (4) of coating the surface of the first graphite core of a single particle with an amorphous carbon coating layer in Example 1 is omitted. In step (5), the first graphite core and the second graphite core obtained in step (3) are mixed in a mass ratio of 4:6. Other conditions are the same as in Example 1 to obtain the sample of Example 6.

[0103] Example 7

[0104] The step (1) of heat-treating the needle coke raw material with a volatile matter content of 6% in Example 1 is removed to form a first powder of a single particle with a first median particle size of 10.0 μm. At the same time, the step (4) of coating the surface of the first graphite core of the single particle with an amorphous carbon coating is changed to: forming a carbon coating on the surface of the second graphite core formed in step (3). The process for forming the carbon coating is the same as that in Example 1, and other conditions are also the same as those in Example 1, to obtain the sample of Example 7.

[0105] Example 8

[0106] The petroleum coke raw material in step (1) of Example 2 is heat treated at a temperature of 600 degrees Celsius, and in step (4): a carbon coating layer is formed on the surface of the second graphite core formed in step (3), and the coating agent is a phenolic resin with a mass percentage of 2%. The other process conditions are the same as those in Example 1, and the sample of Example 8 is obtained.

[0107] Example 9

[0108] The carbonization temperature in step (4) of Example 1 was changed to 1500° C., while other conditions remained unchanged, to obtain the sample of Example 9.

[0109] Comparative Example 1

[0110] The raw materials in step (1) of Example 1 were crushed with a K value of 1.8, while other parameters remained unchanged, to obtain the sample of Comparative Example 1.

[0111] Comparative Example 2

[0112] The needle coke with a volatile matter of 6.0% in step (1) of Example 1 is used as a raw material, and the raw material is directly crushed and shaped to form a first powder of single particles with a first median particle size of 8.0 μm. (4) After the single particles are coated, they are carbonized at a temperature of 700 degrees Celsius. At the same time, the first graphite material and the second graphite core in step (5) are mixed in a mass ratio of 5:5 to obtain a sample of Comparative Example 2.

[0113] Comparative Example 3

[0114] The step (1) of heat treating the needle coke raw material with a volatile matter content of 6% in Example 1 was removed, and all the materials in step (2) were subjected to secondary treatment while other conditions remained unchanged to obtain the sample of Comparative Example 3.

[0115] Comparative Example 4

[0116] The step (1) of heat treating the needle coke raw material with a volatile matter content of 6% in Example 1 was removed, and all the materials in step (2) of Example 1 were not subjected to secondary treatment, while other conditions remained unchanged, thereby obtaining the sample of Comparative Example 4.

[0117] The first graphite core material and the formed graphite negative electrode material in Examples 1 to 9 and Comparative Examples 1 to 4 were subjected to median particle size measurement, tap density test, specific surface area test, powder compaction density test, and powder OI 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. Examples 1 to 9

[0118] The tap density test method is as follows: the test sample is placed in a measuring cylinder of a certain volume and vibrated 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 by nitrogen physical adsorption using a specific surface area tester to measure the sample and obtain the specific surface area value.

[0119] Table 1 Test data of the first graphite core material and the formed graphite negative electrode material in Examples 1 to 9 and Comparative Examples 1 to 4

[0120] From Table 1, it can be seen that the median particle size of the first powder is different, the mixing ratio β of the first graphite material and the second graphite core is different, and in Examples 1 to 9, the tap density of the graphite negative electrode material formed is higher than that of the comparative example (greater than or equal to 1.0), proving that the silicon-carbon negative electrode material formed by the method of the embodiment of the present application has better processing performance. At the same time, the powder OI value of the silicon-carbon negative electrode material formed by the method of the embodiment of the present application is low. The low powder OI value makes the battery cell prepared using the silicon-carbon negative electrode material expand less, thereby improving the cycle performance of the battery cell during the charge and discharge cycle. The silicon-carbon negative electrode material in Examples 1 to 9 mixes the first graphite material and the second graphite core in different proportions, and its processability is also enhanced compared with the case of using only the first graphite material or the second graphite core in Comparative Examples 3 and 4.

[0121] Table 2 shows the median α of the Raman spectra of the graphite negative electrode materials in Example 1, Example 2 and Example 8 and the coating amount T of the carbon coating layer in the first graphite material. 包覆量 , the mixing ratio β of the first graphite material and the second graphite core, the granulation degree γ of the first powder material at which single particles are bonded to form secondary particles, the temperature T of the heat treatment, the median particle size D150 of the first powder material, and the test data of the mixing ratio β of the first graphite material and the second graphite core, A = α(D150×γ+1+T%)+0.1×β×T 包覆量 ,It can be seen from Table 2 that the value of A satisfies 0.01≤A≤5.0. Furthermore, A is greater than or equal to 2 and less than or equal to 5.

[0122] Table 2

[0123] 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 method for preparing a graphite negative electrode material, characterized in that, Comprising: Select raw materials, perform heat treatment and crushing and shaping treatment on the raw materials to form a first powder of single particles with a first median particle size, where 1 ≤ D150×(0.71 + 0.39×D150×(1 + 0.01T)) + M 可逆克容量 / 372 ≤ 100, T is the temperature of the heat treatment, D150 is the first median particle size, M 可逆克容量 is the reversible specific capacity of the formed graphite negative electrode material; Performing a secondary treatment on the first powder material so that the single particles of the first powder material bond to each other to form secondary particles; Performing graphitization treatment on the first powder material to form a single-particle first graphite core, and performing graphitization treatment on the secondary particles to form a second graphite core; Coating a carbon coating layer on the surface of the single-particle first graphite core to form a first graphite material; Uniformly mixing the first graphite material and the second graphite core in proportion to form the graphite negative electrode material.

2. The preparation method of the graphite anode material according to claim 1, wherein, The temperature of the heat treatment is 0 to 1400 °C, the reversible specific capacity of the graphite negative electrode material is 320 to 365 mAh / g, and the first median particle size is 5 to 20 μm.

3. The preparation method of the graphite anode material according to claim 1, 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%.

4. The preparation method of the graphite anode material according to claim 1, characterized in that, The range of the K value of the particle size distribution of the first powder material is 0.8 to 1.5, where K = (Dv90 第一粉料 - Dv10 第一粉 料 ) / Dv50 第一粉料 , and among them, the Dv50 第一粉料 is the particle size corresponding to when the volume distribution percentage of the first powder material reaches 50%, the Dv90 第一粉料 is the particle size corresponding to when the volume distribution percentage of the first powder material reaches 90%, and the Dv10 第一粉料 is the particle size corresponding to when the volume distribution percentage of the first powder material reaches 10%.

5. The preparation method of the graphite anode material according to claim 1, wherein, The OI value G of the powder of the graphite negative electrode material OI and the granulation degree γ of the single-particle bonding between the first powder material to form secondary particles satisfy the relationship: 1 ≤ 100 / (γ + 3.3×G OI ) ≤ 25, where γ = (D250 - D150) / D150×100%, and D250 is the second median diameter of the secondary particles.

6. The preparation method of the graphite anode material according to claim 5, characterized in that, The powder OI value of the graphite negative electrode material is 1 to 20, and the granulation degree is 10% to 200%.

7. The preparation method of the graphite anode material according to claim 1, wherein, Coating a carbon coating layer on the surface of the single-particle first graphite core to form a first graphite material includes: performing a coating step of coating a carbon coating agent on the surface of the single-particle first graphite core; and performing a carbonization step of converting the carbon coating agent into a carbon coating layer.

8. The preparation method of the graphite negative electrode material according to claim 7, wherein 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; the coating layer is hard carbon amorphous carbon or soft carbon amorphous carbon, and its thickness is 5 to 100 nm.

9. The preparation method of the graphite anode material according to claim 7, wherein, The carbonization step is carried out under a constant temperature condition, the carbonization temperature is 800 to 1500 °C, and the constant temperature time is greater than 2 h and less than 12 h.

10. The method for preparing a graphite negative electrode material according to claim 1, wherein The median I of the Raman spectrum of the graphite anode material D / I G and the coating amount of the carbon coating layer in the first graphite material, the mixing ratio of the first graphite material and the second graphite core satisfy the relationship: 0.01 ≤ α(D150×γ + 1 + T%) + 0.1×β×T 包覆量 ≤ 5.0 Among them, β is the mixing ratio of the first graphite material and the second graphite core, T 包覆量 is the coating amount of the carbon coating layer in the first graphite material, γ is the granulation degree of the first powder material that is bonded between single particles to form secondary particles, and α is the I D / I G Raman spectrum median value.

11. The preparation method of the graphite anode material according to claim 10, characterized in that, In terms of mass ratio, the mixing ratio of the first graphite material and the second graphite core is 3:7 to 7:

3.

12. A graphite battery anode material, characterized in that, Including a first graphite material and a second graphite core, wherein the first graphite material includes a first graphite core and a carbon coating layer coated on the surface of the single-particle first graphite core, the second graphite core is formed by graphitization treatment of secondary particles, the first graphite core is obtained by graphitization treatment of the first powder material, and the first powder material is formed by heat treatment and pulverization and shaping treatment of the raw material, Wherein, 1 ≤ D150 × (0.71 + 0.39 × D150 × (1 + 0.01T)) + M 可逆克容量 / 372 ≤ 100, T is the temperature of the heat treatment, D150 is the first median particle size of the first powder material, M 可逆克容量 is the reversible specific capacity of the formed graphite negative electrode material.

13. The graphite negative electrode material according to claim 12, characterized in that, The temperature of the heat treatment is 0 to 1400 °C, the reversible specific capacity of the graphite negative electrode material is 320 to 365 mAh / g, and the first median particle size is 5 to 20 μm.

14. The graphite negative electrode material according to claim 12, 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%.

15. The graphite negative electrode material according to claim 12, characterized in that, The range of the K value of the particle size distribution of the first powder material is 0.8 to 1.5, where K = (Dv90 第一粉料 - Dv10 第一粉料 ) / Dv50 第一粉料 , wherein, the Dv50 第一粉料 is the particle size corresponding to when the volume distribution percentage of the first powder material reaches 50%, and Dv90 第一粉料 is the particle size corresponding to when the volume distribution percentage of the first powder material reaches 90%, and Dv10 第一粉料 is the particle size corresponding to when the volume distribution percentage of the first powder material reaches 10%.

16. The graphite negative electrode material according to claim 12, wherein The OI value G of the powder of the graphite negative electrode material OI and the granulation degree γ of the bonding between single particles of the first powder material to form secondary particles satisfy the relationship: 1 ≤ 100 / (γ + 3.3×G OI ) ≤ 25, where γ = (D250 - D150) / D150×100%, and D250 is the second median particle size of the secondary particles.

17. The graphite anode material according to claim 16, wherein The powder OI value of the graphite negative electrode material is 1 to 20, and the granulation degree γ is 10% to 200%.

18. The graphite negative electrode material according to claim 16, wherein The median I of the Raman spectrum of the graphite anode material D / I G and the coating amount of the carbon coating layer in the first graphite material, the mixing ratio of the first graphite material and the second graphite core satisfy the relationship: 0.01 ≤ α(D150 × γ + 1 + T%) + 0.1 × β × T 包覆量 ≤ 5.0 Among them, β is the mixing ratio of the first graphite material and the second graphite core, T 包覆量 is the coating amount of the carbon coating layer in the first graphite material, and α is the I D / I G Raman spectrum median value.

19. The graphite negative electrode material according to claim 18, characterized in that, The mixing ratio of the first graphite material and the second graphite core is 3:7 to 7:

3.

20. A lithium-ion battery, characterized in that, Including a negative electrode, and the negative electrode is made of any one of the negative electrode materials in claims 12 to 19.

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