Negative electrode material, and preparation method therefor and use thereof

Abstract

A negative electrode material, comprising composite particles. Each of the composite particles comprises a core and an amorphous carbon coating layer located on the surface of the core, wherein the core comprises a graphite framework and amorphous carbon in the graphite framework; and the amorphous carbon coating layer has a thickness of 10-50 nm. Raman spectral area scanning is performed on the negative electrode material, and there are 400 Raman spectral area scanning points; and the average ID / IG value of the Raman spectrum of the negative electrode material is 0.10-0.20, wherein the proportion of the number of scanning points having a single-point ID / IG value of less than 0.2 is greater than 60%. The negative electrode material has a high compaction density, a high capacity, a low expansion rate, good rate performance, and good high-temperature cycling performance.

Description

Anode materials, their preparation methods and applications

[0001] Cross-reference to related applications

[0002] This disclosure claims priority to Chinese Patent Application No. 202410790233X, filed on June 19, 2024, entitled “Anode Material and Preparation Method Thereof and Application”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to the field of battery technology, and more specifically, to a negative electrode material, its preparation method, and its application. Background Technology

[0004] Lithium-ion batteries, as a new type of rechargeable battery, possess advantages such as high operating voltage, large specific capacity, flat discharge potential curve, low self-discharge, long cycle life, good low-temperature performance, environmental friendliness, no pollution, and no memory effect. They are widely used in 3C products, power devices, and energy storage equipment. In recent years, with the increasing demands for miniaturization, lightweighting, multi-functionality, and long-duration operation in electronic products, vehicles, and energy storage devices, the requirements for high energy density, high rate performance, and long cycle life of lithium-ion batteries have been continuously increasing.

[0005] Existing technical documents:

[0006] Reference 1: Chinese Patent CN114843508A discloses a modified natural graphite material and its preparation method, negative electrode sheet and lithium-ion battery. Due to the large amount of modifier used, the carbonized material has high mechanical strength, low compaction density and poor high-temperature cycle performance.

[0007] Reference 2: Chinese Patent CN114873591A. Reference 2 discloses a low-temperature long-life natural graphite anode material, its preparation method and uses. The method involves large equipment investment, complex and dangerous processes, large amount of low-temperature asphalt, and a large thickness of amorphous carbon coating on the surface of natural graphite after carbonization, resulting in high mechanical strength of the carbonized product, low material compaction density and poor high-temperature performance; the large amount of solvent used is harmful to the environment and operators.

[0008] Reference 3: Chinese Patent CN116730333A discloses a method for preparing modified natural graphite anode material. This method uses a large amount of toxic and harmful organic cleaning agents, which will cause harm to the environment and operators.

[0009] In view of this, this disclosure is hereby made. Summary of the Invention

[0010] One objective of this disclosure is to provide a negative electrode material whose surface has a more regular stacking of graphite-like microcrystalline wafer layers, an appropriate thickness of amorphous carbon coating layer, and features high compaction density, high capacity, low expansion rate, good rate performance, and good high-temperature cycling performance.

[0011] Another objective of this disclosure is to provide a method for preparing a negative electrode material. This method is simple and easy to implement. Through the coordination of each step, the thickness of the amorphous carbon coating layer can be controlled within a suitable range, the content of surface defect sites can be reduced, the capacity and compaction of the negative electrode material can be improved, the expansion rate can be reduced, and the high-temperature cycling performance can be good.

[0012] Another objective of this disclosure is to provide a negative electrode.

[0013] Another object of this disclosure is to provide a battery.

[0014] In order to achieve the above-mentioned objectives of this disclosure, the following technical solution is adopted:

[0015] A negative electrode material includes composite particles, each comprising a core and an amorphous carbon coating layer on the surface of the core. The core comprises a graphite framework and amorphous carbon filled within the graphite framework. The thickness of the amorphous carbon coating layer is 10–50 nm. Raman spectroscopy of the negative electrode material is performed using 400 scanning points. The average ID / IG ratio of the Raman spectrum of the negative electrode material is 0.10–0.20, with more than 60% of the scanning points having an ID / IG ratio less than 0.2.

[0016] In some embodiments, the thickness of the amorphous carbon coating layer is 10–30 nm.

[0017] In some embodiments, the average ID / IG value of the Raman spectrum of the negative electrode material is 0.10 to 0.14, and the number of scan points with an ID / IG value less than 0.2 accounts for 65% to 91%.

[0018] In some implementations, the particle size Dv50 of the graphite skeleton is 5–25 μm.

[0019] In some implementations, the graphite framework comprises natural graphite.

[0020] In some embodiments, the pore volume of the graphite framework is 0.02–0.05 cm³. 3 / g.

[0021] In some implementations, the compaction density of the negative electrode material under 2 tons of pressure is greater than 1.65 g / cm³. 3 .

[0022] In some embodiments, the interlayer spacing d002 of the X-ray diffraction pattern of the negative electrode material is 0.335775–0.335934 nm.

[0023] In some embodiments, the true density of the negative electrode material is greater than 2.190 g / cm³. 3 .

[0024] In some embodiments, the pore volume of the negative electrode material is less than 0.005 cm³. 3 / g;

[0025] In some implementations, the specific capacity of the negative electrode material is greater than 360 mAh / g.

[0026] In some implementations, the initial coulombic efficiency of the negative electrode material is greater than 94%.

[0027] A method for preparing any of the aforementioned negative electrode materials includes the following steps:

[0028] The mixture of graphite skeleton and organic carbon source is heat-treated under negative pressure to obtain the first material; the first material is then subjected to low-temperature carbonization treatment, oxidation ablation treatment and high-temperature carbonization treatment in sequence.

[0029] In some implementations, the graphite framework comprises natural graphite.

[0030] In some embodiments, the particle size D50 of the graphite skeleton is 5 to 25 μm, and the carbon content of the graphite skeleton is greater than 99.9%.

[0031] In some embodiments, the pore volume of the graphite framework is 0.02–0.05 cm³. 3 / g;

[0032] In some embodiments, the organic carbon source includes at least one of petroleum pitch, coal tar pitch, and thermoplastic resin.

[0033] In some implementations, the coking value of the organic carbon source heated at 550°C under a protective atmosphere for 2 hours is greater than 70%.

[0034] In some implementations, the mass ratio of graphite framework to organic carbon source is 75:25 to 90:10.

[0035] In some implementations, the vacuum level during the heat treatment process is less than 0.05 MPa absolute pressure.

[0036] In some implementations, the vacuum level of the environment in which the mixture is located before heat treatment is less than 0.03 MPa.

[0037] In some embodiments, the heat treatment temperature is 300–500°C, and the heat treatment time is 1–5 hours.

[0038] In some embodiments, the mixture is stirred during the heat treatment process at a speed of 100–300 r / min.

[0039] In some implementations, the heat-treated material is further cooled to room temperature.

[0040] In some embodiments, the second material obtained by low-temperature carbonization has a volatile content of less than 2% and a graphitization degree of 89% to 92%.

[0041] In some embodiments, the temperature of the low-temperature carbonization treatment is 500–800°C, and the time of the low-temperature carbonization treatment is 2–8 hours.

[0042] In some implementations, the low-temperature carbonization process is carried out under protective gas conditions.

[0043] In some embodiments, the third material obtained by oxidative ablation treatment comprises a graphite core and an amorphous carbon layer; the average thickness of the amorphous carbon layer is 100–300 nm; the average ID / IG value of the Raman spectrum of the third material is 0.19–0.50; and the powder compaction density of the third material under 2 tons of pressure is greater than 1.55 g / cm³. 3 The interlayer spacing d002 of the X-ray diffraction pattern of the third material is 0.335932–0.336270 nm.

[0044] In some embodiments, the temperature of the oxidation ablation treatment is 600–900°C, and the time of the oxidation ablation treatment is 3–10 hours.

[0045] In some embodiments, the atmosphere for the oxidation ablation treatment is an oxygen-containing atmosphere with a flow rate of 1–5 m³ / h. 3 / h.

[0046] In some embodiments, the high-temperature carbonization treatment is carried out at a temperature of 1500–1800°C for 6–12 hours.

[0047] In some implementations, the high-temperature carbonization process is carried out under protective gas conditions.

[0048] A negative electrode sheet comprising any of the aforementioned negative electrode materials, or a negative electrode material prepared by any of the aforementioned negative electrode material preparation methods.

[0049] A battery including a negative electrode.

[0050] Compared with the prior art, the beneficial effects of this disclosure are as follows:

[0051] (1) The anode material disclosed herein has an appropriate thickness of amorphous carbon coating layer, a small ID / IG ratio in the Raman spectrum of the anode material, and a high content of points with a single point value of ID / IG less than 0.2, indicating that the defect site content of graphite-like microcrystals on the surface of the anode material is low, the graphite-like microcrystal wafer stack is more regular, and the anode material has high compaction density, high capacity, low expansion rate, good rate performance, and good high temperature cycling performance.

[0052] (2) This disclosure uses a high-temperature negative pressure method to fill a large amount of organic carbon source into the interior of graphite particles and coat the surface of graphite particles. The organic carbon source is solidified and shaped by low-temperature carbonization to convert it into amorphous carbon, and volatile matter is removed, so that the amorphous carbon has good reactivity and the graphite-like microcrystal size is relatively uniform. Further, an oxidation ablation treatment is used to control the thickness of the amorphous carbon coating layer on the particle surface within an appropriate range, thereby improving the compaction density, cell volumetric energy density and mass energy density of the material, reducing the proportion of active sites in the residual amorphous carbon layer on the surface, and reducing the side reactions between amorphous carbon and electrolyte. Further, a high-temperature carbonization treatment is used to recrystallize the amorphous carbon after oxidation ablation treatment and remove the remaining volatile matter, thereby reducing the defect sites of amorphous carbon and reducing the specific surface area. The combination of these steps can obtain a negative electrode material with high capacity, high compaction, low expansion rate and good rate performance, which can significantly improve the high-temperature performance of the material.

[0053] (3) The battery obtained by the negative electrode material disclosed herein has high capacity, high first efficiency, high rate performance and excellent high temperature cycling performance. Attached Figure Description

[0054] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this disclosure and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0055] Figure 1 is a scanning electron microscope image of the negative electrode material polished by argon ion polishing in Embodiment 2 of this disclosure;

[0056] Figure 2 is a scanning electron microscope image of the negative electrode material polished by argon ion polishing in Embodiment 2 of this disclosure;

[0057] Figure 3 is an ID / IG distribution diagram of the negative electrode material in Embodiment 2 of this disclosure;

[0058] Figure 4 is an argon-ion polishing scanning electron microscope image of the negative electrode material in Comparative Example 1 of this disclosure;

[0059] Figure 5 is an ID / IG distribution diagram of the negative electrode material in Comparative Example 1 of this disclosure. Detailed Implementation

[0060] The embodiments of this disclosure will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of this disclosure. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0061] The endpoints and any values ​​of the ranges disclosed in this disclosure are not limited to the precise ranges or values, and such ranges or values ​​should be understood to include values ​​close to such ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed herein.

[0062] This disclosure provides an anode material, comprising composite particles. The composite particles include a core and an amorphous carbon coating layer located on the surface of the core. The core includes a graphite framework and amorphous carbon filled in the graphite framework. The thickness of the amorphous carbon coating layer is 10–50 nm. Raman spectroscopy is performed on the anode material, with 400 Raman spectral scanning points. The average ID / IG (peak intensity ratio) of the Raman spectrum of the anode material is 0.10–0.20, wherein the number of scanning points with an ID / IG value less than 0.2 accounts for more than 60%.

[0063] The anode material disclosed herein has an appropriate thickness of amorphous carbon coating layer, a small ID / IG ratio in the Raman spectrum, and a high content of points with an ID / IG ratio less than 0.2. This indicates that the defect site content of the graphite-like microcrystals on the surface of the anode material is low, the graphite-like microcrystal wafer layer is more regularly stacked, and the anode material has high compaction density, high capacity, low expansion rate, good rate performance, and good high-temperature cycling performance.

[0064] In some embodiments, the thickness of the amorphous carbon coating layer is 10–50 nm, for example, but not limited to, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, or 50 nm, or any combination thereof. The amorphous carbon coating layer of this disclosure has the aforementioned suitable thickness, which is beneficial for increasing the specific capacity and compaction density of the material. Preferably, the thickness of the amorphous carbon coating layer is 10–30 nm.

[0065] In some embodiments, the average ID / IG value of the Raman spectrum of the negative electrode material is 0.10 to 0.20, for example, but not limited to 0.10, 0.12, 0.15, 0.18, or 0.20, or any combination of both. A Raman spectrometer scans 400 points, and the percentage of scan points with an ID / IG value less than 0.2 is greater than 60%, for example, but not limited to 61%, 65%, 68%, 70%, 72%, 75%, 80%, 85%, 90%, 91%, 95%, 96%, or 98%, or any combination of both. The negative electrode material of this disclosure has a low average ID / IG value in its Raman spectrum, indicating a lower defect site content on the surface of the negative electrode material. This results in a more regular accumulation of the residual graphite-like microcrystal layer on the surface of the negative electrode material, leading to better compatibility between the graphite-like microcrystals on the coating layer surface and the electrolyte, and excellent high-temperature cycling performance of the negative electrode material.

[0066] In some embodiments, the average ID / IG value of the Raman spectrum of the negative electrode material is 0.10 to 0.14, and the number of scan points with an ID / IG value less than 0.2 accounts for 65% to 91%.

[0067] The average ID / IG ratio of pure graphitized graphite materials (such as artificial and natural graphite) in Raman spectra is typically between 0.03 and 0.05. The number of scan points with an ID / IG ratio less than 0.1 accounts for more than 99%. The high purity of graphite crystals leads to relatively poor rate performance of pure graphitized materials. Carbon coating can improve rate performance. When the ID / IG ratio of amorphous carbon in the surface coating layer gradually increases, the crystallinity of graphite-like crystals in the amorphous carbon begins to deteriorate and the number of crystal defect sites increases. The rate performance of the material improves, but the high-temperature cycling performance deteriorates.

[0068] Unbound by theory, the applicant has discovered that ID / IG = 0.2 is the critical value for the deterioration of high-temperature cycling performance of amorphous carbon coatings. ID / IG exceeding 0.2 results in excellent rate performance but poor high-temperature cycling performance; ID / IG between 0.1 and 0.2 balances both rate performance and high-temperature cycling performance; and ID / IG less than 0.1 results in excellent high-temperature cycling performance but poor rate performance. When the percentage of scan points with ID / IG less than 0.2 is 65%–91%, even better rate performance and high-temperature cycling performance can be achieved.

[0069] In some embodiments, the particle size Dv50 of the graphite skeleton is 5 to 25 μm, for example, but not limited to 5 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm or 25 μm, or any combination of both.

[0070] In some implementations, the particle size Dv50 of the graphite skeleton is 10–20 μm.

[0071] In some embodiments, the graphite skeleton comprises natural graphite. In other embodiments, the graphite skeleton may also be artificial graphite. This disclosure preferably uses natural graphite as the graphite skeleton. Natural graphite, due to its numerous surface defects and highly porous structure, has a negative impact on its large-scale application. This disclosure modifies natural graphite to enable its application as a high-performance anode material.

[0072] In some embodiments, the pore volume of the graphite framework is 0.02–0.05 cm³. 3 / g, for example, can be, but is not limited to, 0.02cm 3 / g, 0.025cm 3 / g, 0.03cm 3 / g, 0.035cm 3 / g, 0.04cm 3 / g, 0.045cm 3 / g, 0.048cm 3 / g or 0.05cm 3 / g, or any combination thereof. The graphite framework of this disclosure has a suitable pore volume, which enables the final anode material to achieve excellent overall performance. If the pore volume is too high, more amorphous carbon needs to be filled, resulting in low compaction density and low specific capacity of the final product; if the pore volume is too small or there are virtually no pores (i.e., it is basically a solid sphere or sheet), the amorphous carbon cannot fill the interior of the particles, resulting in slow diffusion rate of lithium ions inside the particles during lithium insertion / extraction, which is detrimental to improving rate performance.

[0073] In some implementations, the compaction density of the negative electrode material under 2 tons of pressure is greater than 1.65 g / cm³. 3 For example, it could be, but is not limited to, 1.66 g / cm³. 3 1.67 g / cm 3 1.68g / cm 3 1.69 g / cm 3 1.70g / cm 3 Or 1.71 g / cm 3 The value can be a range of values, or any combination of both. Preferably, the compaction density of the negative electrode material under 2 tons of pressure is greater than 1.65 g / cm³. 3 And less than or equal to 1.75 g / cm³ 3 The negative electrode material disclosed herein has a suitable compaction density, which can ensure sufficient contact between particles, prevent blockage of ion movement channels, ensure good conductivity of electrons and rapid ion movement during high current discharge, reduce discharge polarization, increase discharge plateau voltage, and improve the rate performance and cycle performance of the battery.

[0074] In some embodiments, the interlayer spacing d002 of the X-ray diffraction pattern of the negative electrode material is 0.335775–0.335934 nm, for example, but not limited to, 0.335775 nm, 0.335815 nm, 0.335875 nm, or 0.335915 nm, or any combination thereof. The negative electrode material of this disclosure has a suitable interlayer spacing d002 and a high degree of graphitization.

[0075] In some embodiments, the true density of the negative electrode material is greater than 2.190 g / cm³. 3 For example, it could be, but is not limited to, 2.203 g / cm³. 3 2.215g / cm 3 2.228 g / cm 3 Or 2.237 g / cm 3 The value can be a range of values, or any combination of both. Preferably, the true density of the negative electrode material is 2.210–2.240 g / cm³. 3 The negative electrode material disclosed herein has a suitable true density, thereby ensuring that the battery has excellent energy density and specific capacity.

[0076] In some embodiments, the pore volume of the negative electrode material is less than 0.005 cm³. 3 / g, for example, can be, but is not limited to, 0.001cm 3 / g, 0.002cm 3 / g, 0.003cm 3 / g, 0.004cm 3 / g or 0.0045cm 3 / g, or any combination thereof. The negative electrode material disclosed herein has a small pore volume, which can reduce side reactions between the negative electrode material surface and the electrolyte, and is beneficial to improving high-temperature cycling performance.

[0077] In some embodiments, the specific capacity of the negative electrode material is greater than 360 mAh / g, for example, but not limited to, 365 mAh / g, 368 mAh / g, or 370 mAh / g, or any range of both. Preferably, the specific capacity of the negative electrode material is greater than 360 mAh / g and less than or equal to 364 mAh / g. The negative electrode material of this disclosure has high specific capacity and excellent cycle performance.

[0078] In some embodiments, the initial coulombic efficiency of the negative electrode material is greater than 94%, for example, but not limited to, 94.5%, 95%, 95.5%, 96%, 96.5%, or 97%, or any combination thereof. Preferably, the initial coulombic efficiency of the negative electrode material is greater than 94% and less than or equal to 95.2%. The negative electrode material of this disclosure has excellent initial coulombic efficiency.

[0079] According to another aspect of this disclosure, this disclosure also relates to a method for preparing any of the aforementioned negative electrode materials, comprising the following steps:

[0080] The mixture of graphite framework and organic carbon source was heat-treated under negative pressure to obtain the first material. The first material was then subjected to low-temperature carbonization, oxidation ablation, and high-temperature carbonization treatments in sequence.

[0081] This disclosure describes a method of filling a large amount of organic carbon source into the interior and coating the surface of graphite particles using high temperature and negative pressure. The organic carbon source is then solidified and shaped through low-temperature carbonization, transforming it into amorphous carbon. However, the applicant has discovered that the resulting material suffers from an excessively thick surface coating. This is because conventional organic carbon sources lack directional selectivity during filling; they cannot spontaneously aggregate into the pores within the particles. To ensure effective filling within the particles, a large amount of organic carbon source must be added, even with the application of external forces (negative pressure, high pressure, or mechanical stirring). Ultimately, a thick layer of organic carbon source is coated onto the surface of the particles. After carbonization, this amorphous carbon not only fills the interior of the particles in large quantities but also forms a thick coating layer on the particle surface. The surface-coated amorphous carbon has many active sites, which has a significant advantage in improving the low-temperature performance and rate performance of the anode material. However, excessive surface coating of amorphous carbon will increase the rigidity of the material, resulting in low compaction density, which is not conducive to improving the bulk energy density of the cell. Moreover, the theoretical specific capacity of amorphous carbon is low, which will also reduce the overall specific capacity of the material, resulting in low cell mass energy density. On the other hand, excessive amorphous carbon will exacerbate the side reactions with the electrolyte at high temperatures, causing the high-temperature cycling performance of the material to plummet, and in severe cases, it may induce thermal runaway. In response to this situation, this disclosure employs an oxidation ablation treatment method. First, the thickness of the amorphous carbon coating layer on the particle surface is controlled within a certain range. This not only improves the compaction density and volumetric energy density of the material and the mass energy density of the cell, but also reduces the proportion of active sites in the residual amorphous carbon layer on the surface (during the oxidation ablation process, oxygen molecules first react with carbon microcrystals with good activity and many defects, and then react with carbon microcrystals with slightly weaker activity and regular structure. The whole process macroscopically presents a layer-by-layer ablation of carbon microcrystals). This reduces the side reactions between amorphous carbon and the electrolyte, and significantly improves the high-temperature performance of the material.

[0082] In some embodiments, the graphite skeleton comprises natural graphite. In other embodiments, the graphite skeleton may also be artificial graphite. This disclosure preferably uses natural graphite as the graphite skeleton. Natural graphite, due to its numerous surface defects and highly porous structure, has a negative impact on its large-scale application. This disclosure modifies natural graphite to enable its application as a high-performance anode material.

[0083] In some embodiments, the particle size D50 of the graphite skeleton is 5–25 μm, for example, but not limited to 5 μm, 10 μm, 15 μm, 20 μm, or 25 μm, or any combination thereof. The carbon content of the graphite skeleton is greater than 99.9%. The graphite skeleton of this disclosure uses a suitable particle size to ensure subsequent coating and to guarantee the electrochemical performance of the anode material.

[0084] In some embodiments, the pore volume of the graphite framework is 0.02–0.05 cm³. 3 / g. The graphite framework disclosed herein has a suitable pore volume, which enables the final anode material to achieve excellent overall performance. If the pore volume is too high, more amorphous carbon needs to be filled, resulting in low compaction density or low specific capacity of the final product; if the pore volume is too small or there are virtually no pores (i.e., it is basically a solid sphere or sheet), the amorphous carbon cannot fill the interior of the particles, resulting in slow diffusion rate of lithium ions inside the particles during lithium insertion / extraction, which is detrimental to improving rate performance.

[0085] In some embodiments, the organic carbon source includes at least one of petroleum asphalt, coal tar pitch, and thermoplastic resin, such as a combination of petroleum asphalt and coal tar pitch, or a combination of coal tar pitch and thermoplastic resin. In some embodiments, the coking value of the organic carbon source heated at 550°C under a protective atmosphere for 2 hours is greater than 70%, for example, it can be, but is not limited to, 72%, 75%, 78%, 80%, 82%, 85%, or 90%, or any combination thereof.

[0086] In some embodiments, the mass ratio of graphite skeleton to organic carbon source is 75:25 to 90:10, for example, but not limited to 75:25, 78:22, 80:20, 85:15, or 90:10, or any range of both. The appropriate mass ratio of graphite skeleton to organic carbon source in this disclosure ensures that the pores of the graphite skeleton can accommodate the organic carbon source, and the surface is coated with a suitable thickness of carbon source. This means that the core pores of the final negative electrode material can be filled with a suitable amount of amorphous carbon, and the core surface is coated with a suitable amount and thickness of amorphous carbon coating layer, thereby ensuring that the negative electrode material has a low expansion rate, good rate performance, and excellent high-temperature cycling performance.

[0087] In some embodiments, the vacuum degree during the heat treatment process is an absolute pressure of less than 0.05 MPa, such as, but not limited to, 0.02 MPa, 0.03 MPa, or 0.05 MPa, or any combination thereof. In some embodiments, the vacuum degree of the environment in which the mixed system is located before heat treatment is an absolute pressure of less than 0.03 MPa, such as, but not limited to, 0.005 MPa, 0.01 MPa, or 0.02 MPa, or any combination thereof. The vacuum degree of the environment in which the mixed system is located before heat treatment refers to: placing the mixed system into a reaction vessel, sealing the reaction vessel, and evacuating it until the vacuum degree is an absolute pressure of less than 0.03 MPa.

[0088] In some embodiments, the heat treatment temperature is 300–500°C, for example, but not limited to 300°C, 350°C, 400°C, 450°C, or 500°C, or any combination thereof. The heat treatment time is 1–5 hours, for example, but not limited to 1 hour, 2 hours, 3 hours, 4 hours, or 5 hours, or any combination thereof. In some embodiments, during the heat treatment, the mixture is stirred at a speed of 100–300 r / min, for example, but not limited to 100 r / min, 150 r / min, 200 r / min, 250 r / min, or 300 r / min, or any combination thereof. In some embodiments, the heat-treated material is further cooled to room temperature. This disclosure employs suitable heat treatment temperature, time, and stirring speed to ensure that the organic carbon source can better enter the porous structure of the graphite framework and coat its surface.

[0089] In some embodiments, the temperature of the low-temperature carbonization treatment is 500–800°C, for example, but not limited to 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, or 800°C, or any combination thereof. The duration of the low-temperature carbonization treatment is 2–8 hours, for example, but not limited to 2 hours, 2.5 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, or 8 hours, or any combination thereof. The low-temperature carbonization treatment is carried out under a protective gas atmosphere. In some embodiments, the second material obtained from the low-temperature carbonization treatment has a volatile matter content of less than 2%, for example, but not limited to 0.5%, 1%, 1.5%, or 1.8%, or any combination thereof. The degree of graphitization is 89%–92%, for example, but not limited to 89%, 90%, 91%, or 92%, or any combination thereof. The effects of the low-temperature carbonization treatment disclosed herein include: 1) removing volatiles and preventing deflagration during the oxidation and ablation process, which is beneficial to production safety; 2) the low-temperature carbonization treatment at a suitable temperature produces amorphous carbon with good reactivity and relatively uniform graphite-like microcrystal size, which is beneficial to controlling the thickness of the amorphous carbon layer in subsequent oxidation and ablation.

[0090] In some embodiments, the third material obtained by oxidative ablation treatment comprises a graphite core and an amorphous carbon layer; the average thickness of the amorphous carbon layer is 100–300 nm, for example, but not limited to 100 nm, 150 nm, 180 nm, 200 nm, 250 nm, or 300 nm, or any combination thereof. The average ID / IG value of the Raman spectrum of the third material is 0.19–0.50, for example, but not limited to 0.19, 0.2, 0.22, 0.25, 0.3, 0.4, or 0.5, or any combination thereof. The powder compaction density of the third material under 2 tons of pressure is greater than 1.55 g / cm³. 3 For example, it can be, but is not limited to, 1.55 g / cm³. 3 1.28g / cm 3 1.6g / cm 3 Or 1.65g / cm 3 The interlayer spacing d002 of the X-ray diffraction pattern of the third material is 0.335932 to 0.336270 nm, for example, but not limited to 0.335932 nm, 0.336032 nm, 0.336055 nm or 0.336270 nm, or any combination of the two.

[0091] In some embodiments, the temperature of the oxidation ablation treatment is 600–900°C, for example, but not limited to 600°C, 650°C, 700°C, 750°C, 800°C, or 900°C, or any combination thereof. The duration of the oxidation ablation treatment is 3–10 hours, for example, but not limited to 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, or 10 hours, or any combination thereof. The atmosphere for the oxidation ablation treatment is an oxygen-containing atmosphere, such as air, with a flow rate of 1–5 m³ / h. 3 / h, for example, can be, but is not limited to, 1m 3 / h、2m 3 / h or 5m 3 / h, or any combination of both. This disclosure employs suitable oxidation ablation treatment conditions to control the thickness of the amorphous carbon coating layer on the particle surface within a suitable range, thereby improving the material's compaction density, cell volumetric energy density, and gravimetric energy density. It also more effectively reduces the proportion of active sites in the residual amorphous carbon layer on the surface, reduces side reactions between amorphous carbon and the electrolyte, and significantly improves the high-temperature performance of the anode material.

[0092] In some embodiments, the high-temperature carbonization treatment temperature is 1500–1800°C, for example, but not limited to 1500°C, 1550°C, 1600°C, 1650°C, 1700°C, or 1800°C, or any combination thereof; the high-temperature carbonization treatment time is 6–12 hours, for example, but not limited to 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, or 12 hours, or any combination thereof. The high-temperature carbonization treatment is carried out under a protective gas environment, such as an inert gas like nitrogen. This disclosure employs suitable high-temperature carbonization treatment conditions to recrystallize and remove residual volatiles from amorphous carbon after oxidation and ablation treatment, reducing defect sites in amorphous carbon, decreasing specific surface area, and improving high-temperature cycling performance.

[0093] According to another aspect of this disclosure, this disclosure also relates to a negative electrode sheet, including any of the aforementioned negative electrode materials, or a negative electrode material prepared by any of the aforementioned negative electrode materials.

[0094] The negative electrode sheet disclosed herein includes a negative electrode current collector and a negative electrode material layer disposed on at least one side surface of the negative electrode current collector; the negative electrode material layer includes the aforementioned negative electrode material.

[0095] According to another aspect of this disclosure, this disclosure also relates to a battery including a negative electrode.

[0096] The battery disclosed herein includes the aforementioned negative electrode, positive electrode, separator, and electrolyte.

[0097] The battery disclosed herein exhibits excellent rate performance, low expansion rate, and excellent high-temperature cycle performance.

[0098] The following explanation, in conjunction with specific embodiments and comparative examples, further clarifies the situation.

[0099] Example 1

[0100] A method for preparing a negative electrode material includes the following steps:

[0101] (1) Mix 2.5 kg of coal tar pitch (coking value 75%) and 7.5 kg of natural graphite (D50 = 5 μm, carbon content 99.91%, and pore volume 0.05 cm³). 3 / g) is added to the mixing equipment, and the material is mixed evenly by high-speed stirring to obtain a mixture.

[0102] (2) Place the mixture into the reactor and vacuum the sealed reactor until the vacuum degree is 0.02 MPa.

[0103] (3) The reactor with qualified vacuum degree is heated and stirred at a temperature of 300℃ and a speed of 300r / min for 5h. During the heat preservation period, the vacuum degree is maintained at an absolute pressure of 0.02Mpa. After the heating is finished and cooled, the material is released to obtain the first material.

[0104] (4) The first material is subjected to low-temperature carbonization treatment at a temperature of 500°C for 8 hours under a nitrogen atmosphere. After heating is completed and the material is cooled to room temperature, the second material is obtained. The volatile content of the second material is 1.8%, and the degree of graphitization is 89.0%.

[0105] (5) The second material is subjected to oxidation and ablation treatment at a temperature of 600℃ for 10 hours, with an air flow rate of 5 m³ / h. 3 After heating for 1 hour and cooling to room temperature, the third material was obtained. The average thickness of the amorphous carbon in the third material was 200 nm. The average ID / IG (peak intensity ratio) of 400 points scanned by a Raman spectrometer was 0.50. The compacted density of the powder under 2 tons was 1.56 g / cm³. 3 The D002 measured by XRD is 0.336270 nm.

[0106] (6) The third material is subjected to high-temperature carbonization treatment at a temperature of 1500℃ for 6 hours under a nitrogen atmosphere. After cooling to room temperature, natural graphite anode material is obtained.

[0107] Example 2

[0108] A method for preparing a negative electrode material includes the following steps:

[0109] (1) Mix 1.5 kg of petroleum asphalt (coking value 75%) and 8.5 kg of natural graphite (D50 = 15 μm, carbon content 99.95%, and pore volume 0.034 cm³). 3 / g) is added to the mixing equipment, and the material is mixed evenly by high-speed stirring to obtain a mixture.

[0110] (2) Put the mixture into the reactor and vacuum the sealed reactor until the vacuum degree is 0.015 MPa.

[0111] (3) The reactor with qualified vacuum degree is heated and stirred at a temperature of 400℃, a rotation speed of 200r / min, and a holding time of 3h. During the holding time, the vacuum degree is maintained at an absolute pressure of 0.03Mpa. After the heating is finished and cooled, the material is released to obtain the first material.

[0112] (4) The first material is subjected to low-temperature carbonization treatment at a temperature of 700°C for 4 hours under a nitrogen atmosphere. After heating is completed and the material is cooled to room temperature, the second material is obtained. The volatile content of the second material is 1.3% and the degree of graphitization is 90.5%.

[0113] (5) The second material undergoes an oxidation ablation treatment at a temperature of 800℃ for 7 hours, with an air flow rate of 3 m³ / h. 3 After heating for 1 hour and cooling to room temperature, the third material was obtained. The average thickness of the amorphous carbon in the third material was 160 nm. The average ID / IG (peak intensity ratio) of 400 points scanned by a Raman spectrometer was 0.34. The compacted density of the powder was 1.63 g / cm³ after 2 tons of heating. 3 The D002 measured by XRD is 0.33604 nm.

[0114] (6) The third material is subjected to high-temperature carbonization treatment at a temperature of 1650°C for 9 hours under a nitrogen atmosphere. After cooling to room temperature, natural graphite anode material is obtained.

[0115] The scanning electron microscope image of the negative electrode material in this embodiment is shown in Figure 1.

[0116] Figure 2 shows the argon-ion polished scanning electron microscope image of the negative electrode material in this embodiment.

[0117] Figure 3 shows the ID / IG distribution of the negative electrode material in this embodiment 2.

[0118] Example 3

[0119] A method for preparing a negative electrode material includes the following steps:

[0120] (1) Mix 1 kg of coal tar pitch and petroleum pitch (coking value 75%) with 9 kg of natural graphite (D50 = 25 μm, carbon content 99.96%, and pore volume 0.02 cm³). 3 / g) is added to the mixing equipment, and the material is mixed evenly by high-speed stirring to obtain a mixture.

[0121] (2) Put the mixture into the reactor and vacuum the sealed reactor until the vacuum degree is 0.01 MPa.

[0122] (3) The reactor with qualified vacuum degree is heated and stirred at a temperature of 500℃ and a speed of 100 rpm for 1 hour. During the heat preservation period, the vacuum degree is maintained at an absolute pressure of 0.04 MPa. After the heating is finished and cooled, the material is released to obtain the first material.

[0123] (4) The first material is subjected to low-temperature carbonization treatment at a temperature of 800°C and a high-temperature carbonization treatment time of 1 hour under a nitrogen atmosphere. After the heating is completed and cooled to room temperature, the second material is obtained. The volatile content of the second material is 1% and the degree of graphitization is 92%.

[0124] (5) The first and second materials are subjected to oxidation and ablation treatment at a temperature of 900℃ for 3 hours, with an air flow rate of 1 m³ / h. 3 After heating for 1 hour and cooling to room temperature, the third material was obtained. The amorphous carbon thickness of the third material was 100 nm. The average ID / IG (peak intensity ratio) of 400 points scanned by a Raman spectrometer was 0.19. The compacted density of the powder under 2 tons was 1.68 g / cm³. 3 The D002 measured by XRD was 0.335932nm.

[0125] (6) The third material is subjected to high-temperature carbonization treatment at a temperature of 1800℃ for 12 hours under a nitrogen atmosphere. After cooling to room temperature, natural graphite anode material is obtained.

[0126] Example 4

[0127] A method for preparing a negative electrode material, which differs from Example 2, is as follows:

[0128] Step (5): Perform an oxidation ablation treatment on the first and second materials. The oxidation ablation treatment temperature is 750℃, the oxidation ablation treatment time is 7.5h, and the air flow rate is 1m³ / h. 3 After heating for 1 hour and cooling to room temperature, the third material was obtained. The amorphous carbon thickness of the third material was 180 nm. The average ID / IG (peak intensity ratio) of 400 points scanned by a Raman spectrometer was 0.38. The compacted density of the powder under 2 tons was 1.61 g / cm³. 3The D002 measured by XRD is 0.336190nm.

[0129] Example 5

[0130] A method for preparing a negative electrode material, which differs from Example 2, is as follows:

[0131] Step (5): The first and second materials are subjected to oxidation and ablation treatment at a temperature of 650℃ for 8.5 hours and an air flow rate of 1 m³ / h. 3 After heating for 1 hour and cooling to room temperature, the third material was obtained. The amorphous carbon thickness of the third material was 190 nm. The average ID / IG (peak intensity ratio) of 400 points scanned by a Raman spectrometer was 0.43. The compacted density of the powder under 2 tons was 1.58 g / cm³. 3 The D002 measured by XRD is 0.336263nm.

[0132] Example 6

[0133] A method for preparing a negative electrode material is basically the same as in Example 2, except that the pore volume of natural graphite in this comparative example is 0.013 cm³. 3 / g.

[0134] Example 7

[0135] A method for preparing a negative electrode material is basically the same as in Example 2, except that the pore volume of natural graphite in this comparative example is 0.068 cm³. 3 / g.

[0136] Comparative Example 1

[0137] A method for preparing a negative electrode material includes the following steps:

[0138] (1) Mix 1.5 kg of coal tar pitch (coking value 75%) and 8.5 kg of natural graphite (D50 = 15 μm, carbon content 99.95%, and pore volume 0.034 cm³). 3 / g) is added to the mixing equipment, and the material is mixed evenly by high-speed stirring to obtain a mixture.

[0139] (2) The mixture is placed into the reactor, and the reactor is heated and stirred at a temperature of 400℃, a speed of 200r / min, and a holding time of 3h. After the heating is finished and the mixture is cooled, the material is released to obtain the first material.

[0140] (3) The first material is subjected to high-temperature carbonization treatment at a temperature of 1650℃ for 9 hours under a nitrogen atmosphere. After cooling to room temperature, natural graphite anode material is obtained.

[0141] The scanning electron microscope image of the negative electrode material in this comparative example is shown in Figure 4.

[0142] Figure 5 shows the ID / IG distribution of the negative electrode material in this comparative example.

[0143] Comparative Example 2

[0144] A method for preparing a negative electrode material includes the following steps:

[0145] (1) Mix 1.5 kg of coal tar pitch (coking value 75%) and 8.5 kg of natural graphite (D50 = 15 μm, carbon content 99.95%, and pore volume 0.034 cm³). 3 / g) is added to the mixing equipment, and the material is mixed evenly by high-speed stirring to obtain a mixture.

[0146] (2) Put the mixture into the reactor and vacuum the sealed reactor until the vacuum degree is 0.015 MPa.

[0147] (3) The reactor with qualified vacuum degree is heated and stirred at a temperature of 400℃, a rotation speed of 200r / min, and a holding time of 3h. During the holding time, the vacuum degree is maintained at an absolute pressure of 0.03Mpa. After the heating is finished and cooled, the material is released to obtain the first material.

[0148] (4) The first material is subjected to low-temperature carbonization treatment at a temperature of 700°C for 4 hours under a nitrogen atmosphere. After cooling to room temperature, the second material is obtained. The volatile content of the second material is 1.3%, and the degree of graphitization is 90.5%.

[0149] (5) The second material is subjected to high-temperature carbonization treatment at a temperature of 1650°C for 6 hours under a nitrogen atmosphere. After cooling to room temperature, natural graphite anode material is obtained.

[0150] Comparative Example 3

[0151] A method for preparing a negative electrode material, which differs from Example 2, is as follows:

[0152] Step (5): Perform oxidation ablation treatment on the first and second materials. The oxidation ablation treatment temperature is 950℃, the oxidation ablation treatment time is 3h, and the air flow rate is 1m. 3 After heating for 1 hour and cooling to room temperature, the third material was obtained. The amorphous carbon thickness of the third material was 80 nm. The average ID / IG (peak intensity ratio) of 400 points scanned by a Raman spectrometer was 0.15. The compacted density of the powder under 2 tons was 1.66 g / cm³. 3 The D002 measured by XRD was 0.335914.

[0153] Experimental Example

[0154] I. Performance Testing of Anode Materials

[0155] The negative electrode materials obtained in each embodiment and comparative example were subjected to performance tests, and the test methods are as follows:

[0156] 1. Particle size testing

[0157] Particle size is measured using a laser particle size analyzer, such as the Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0158] 2. Test of compacted density

[0159] The pressure method is adopted, which basically refers to the test method of powder compaction density recorded in "GBT 24533-2009 Graphite Anode Materials for Lithium-ion Batteries". The only difference is that the test pressure in this disclosure is 2 tons.

[0160] 3. Scanning electron microscopy testing

[0161] Scanning electron microscopy (SEM) characterization was performed on a transmission electron microscope at an operating voltage of 200 kV to observe the structure of the negative electrode material.

[0162] 4. Testing of carbon coating thickness

[0163] The material was cross-sectioned using a FIB-SEM device. A random area of ​​the sample cross-section was photographed using a 20,000x scanning electron microscope. For each particle in the 20,000x image, a center point was selected, and a vertical crosshair was randomly drawn at that center. The thickness of the amorphous carbon layer at the intersection of the crosshair and the edge of the particle cross-section was recorded. The average thickness of the amorphous carbon layer of a single particle was calculated. Then, the average thickness of the amorphous carbon layer of all particles in the 20,000x image was averaged to obtain the average thickness of the carbon coating layer of the sample.

[0164] 5. Raman ID / IG testing

[0165] The peak intensity of peak D of the material (1350 cm⁻¹) was measured using a Renishaw microconfocal Raman spectrometer. -1 Boundary vibration modes near the disorder-induced hexagonal Brillouin zone are used for defect characterization. (and the peak intensity of the G peak (1580 cm⁻¹)) -1 The stretching vibration modes near the carbon atom, belonging to the in-plane bonds, are related to the degree of graphitization. The peak intensity ratio of the D and G peaks is ID / IG. A 532nm semiconductor laser with a power ≥50mW is used. Testing conditions: a neon lamp is used as the signal source, a high-resolution grating with ≥1800 lines is employed, and 17086 ABScm is tested. -1 The luminous line has a full width at half maximum (FWHM) less than or equal to 1 wavenumber (FWHM ≤ 1 cm).-1 Spatial resolution: ≤0.3μm(XY); ≤1μm(Z); Scan step size: 5μm; Area scan range: -47μm≤X≤48μm; -47μm≤Y≤48μm; 400 points per area scan.

[0166] 6. Pore volume testing

[0167] The pore volume of the material was determined by static BET adsorption using a specific surface area and pore size analyzer.

[0168] 7. True density test

[0169] After the sample was immersed in liquid and then degassed in a vacuum, its density at 30°C was tested using the specific gravity bottle method.

[0170] 8. Test of graphitization degree

[0171] When X-rays are projected into a crystal, they are scattered by atoms and electrons within the crystal. Due to the periodic arrangement of atoms in the crystal, these scattered waves have a fixed phase difference, causing interference in space. This results in the scattered waves reinforcing each other in some scattering directions and canceling each other out in others, thus producing diffraction. The diffractometer automatically records the diffraction pattern of the sample and analyzes the diffraction pattern to obtain sample information. Using silicon as an internal standard, it is added to graphite and mixed thoroughly before XRD testing. The d002 is calculated, and the degree of graphitization is calculated as 100 × (3.44 - d002) / (3.44 - 3.354) (unit: %).

[0172] The performance test results of the negative electrode material are shown in Table 1.

[0173] Table 1 Performance test results of the anode material

[0174] II. Battery Performance Testing

[0175] The negative electrode materials obtained in each embodiment and comparative example were respectively mixed with CMC, SP, and SBR in a mass ratio of 95:2:1:2 in pure aqueous solution to prepare slurries. The slurries were then coated onto the surface of copper foil to obtain negative electrode sheets. Lithium foil was used as the positive electrode sheet, and a microporous polypropylene membrane was used as the separator. The electrolyte composition was: 1M LiPF6 dissolved in a mixed solution of EC, DMC, and EMC, with a volume ratio of EC, DMC, and EMC of 1:1:1. The mixed solution also contained 1% VC by mass. The negative electrode sheet, positive electrode sheet, separator, and electrolyte were assembled into a lithium-ion battery with a charge / discharge cutoff voltage of 0.005–2V.

[0176] Battery performance testing includes: 1) initial reversible capacity; 2) initial coulombic efficiency; 3) 50 cycles at 25℃ and 1C, with disassembly testing of graphite electrode expansion rate; 4) using half-cell and lithium sheet as negative electrode, graphite as positive electrode, 3C discharge, and plotting the second derivative curve of DV / DQ, with the inflection point of the curve slope indicating the lithium plating SOC position; the 3C lithium plating performance of the negative electrode material is approximately positively correlated with the rate performance, and the better the 3C lithium plating performance, the better the rate performance usually is; 5) capacity retention rate at 45℃ and 1C for 300 cycles.

[0177] Cyclic capacity retention, etc., the specific test results are shown in Table 2.

[0178] Table 2 Battery performance test results

[0179] As shown in Figures 1 and 4, the method for preparing the negative electrode material disclosed herein can effectively fill the particle interior with organic carbon source by heating and stirring under negative pressure.

[0180] As can be seen from the performance data of the negative electrode material in Table 1 and the battery performance data in Table 2, compared with Comparative Example 1, after the organic carbon source filled the inside of the particles in Examples 1-7 and Comparative Examples 2-3, the diffusion of lithium ions inside the material became easier, resulting in a significant reduction in the electrode expansion rate and a significant improvement in the 3C lithium plating performance (rate performance).

[0181] As shown in Table 1 (performance of the negative electrode material), Table 2 (performance data of the battery), and Figures 2, 3, and 5, compared to Comparative Examples 1-2, after oxidation ablation treatment, Examples 1-7 and Comparative Example 3 showed a thinner amorphous carbon layer on the particle surface, resulting in a significant improvement in the material's compaction density and initial reversible capacity. The average ID / IG ratio of the amorphous carbon layer on the particle surface was significantly reduced, while the proportion of points with an ID / IG value < 0.2 significantly increased. This indicates that oxidation ablation can reduce the number of defect sites in the amorphous carbon layer on the surface, improve the compatibility between the material surface and the electrolyte, and enhance high-temperature cycling performance, ultimately leading to a significant improvement in the material's initial coulombic efficiency and capacity retention during 45°C cycling.

[0182] Compared to Example 2, the graphite framework pore volume of Example 6 is smaller (less than 0.02 cm). 3 The amorphous carbon content in the filler is low ( / g), which is not conducive to the rapid diffusion of lithium ions inside the graphite particles, resulting in a deterioration in the 3C lithium plating performance of the material; the graphite framework in Example 7 has a large pore volume (greater than 0.05 cm). 3 The high content of amorphous carbon in the filler ( / g) results in a low powder compaction density, which is detrimental to the material's energy density.

[0183] Compared to Example 2, Comparative Example 3 also uses a negative pressure heating and stirring method to fill the organic matter into the particles and uses an oxidation ablation method to improve the number of defect sites in the amorphous carbon layer on the particle surface. However, the oxidation ablation temperature is too high, resulting in an excessively thin amorphous carbon layer on the surface. The active sites of the amorphous carbon layer are basically completely ablated, exposing even worse defect sites in the graphite body. Consequently, the 3C lithium plating performance and 45°C high-temperature cycling performance of the material deteriorate.

[0184] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this disclosure, and are not intended to limit them. Although this disclosure has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this disclosure. Industrial applicability

[0185] The negative electrode material disclosed herein produces batteries with high capacity, high initial efficiency, high rate performance, and excellent high-temperature cycle performance, making it highly practical for industrial applications.

Claims

1. A negative electrode material, characterized in that, The composite particles include a core and an amorphous carbon coating layer on the surface of the core, wherein the core includes a graphite skeleton and amorphous carbon filled in the graphite skeleton. The thickness of the amorphous carbon coating layer is 10–50 nm. The negative electrode material was subjected to Raman spectral surface scanning with 400 scanning points. The average ID / IG value of the Raman spectrum of the negative electrode material was 0.10 to 0.20, and the number of scanning points with an ID / IG value less than 0.2 accounted for more than 60%.

2. The negative electrode material according to claim 1, characterized in that, It includes at least one of the following features (1) to (2): (1) The thickness of the amorphous carbon coating layer is 10-30 nm; (2) The average value of ID / IG in the Raman spectrum of the negative electrode material is 0.10 to 0.14, and the number of scan points with a single point value of ID / IG less than 0.2 accounts for 65% to 91%.

3. The negative electrode material according to claim 1 or 2, characterized in that, It includes at least one of the following features (1) to (9): (1) The particle size Dv50 of the graphite skeleton is 5-25 μm; (2) The graphite skeleton includes natural graphite; (3) The pore volume of the graphite framework is 0.02–0.05 cm³. 3 / g; (4) The compaction density of the negative electrode material under 2 tons of pressure is greater than 1.65 g / cm³. 3 ; (5) The interlayer spacing d002 of the X-ray diffraction pattern of the negative electrode material is 0.335775~0.335934nm; (6) The true density of the negative electrode material is greater than 2.190 g / cm³. 3 ; (7) The pore volume of the negative electrode material is less than 0.005 cm³. 3 / g; (8) The specific capacity of the negative electrode material is greater than 360 mAh / g; (9) The initial coulombic efficiency of the negative electrode material is greater than 94%.

4. The negative electrode material according to claim 2 or 3, characterized in that, The particle size Dv50 of the graphite skeleton is 10–20 μm.

5. The negative electrode material according to any one of claims 2 to 4, characterized in that, The compaction density of the negative electrode material under 2 tons of pressure is greater than 1.65 g / cm³. 3 And less than or equal to 1.75 g / cm³ 3 .

6. The negative electrode material according to any one of claims 2 to 5, characterized in that, The true density of the negative electrode material is 2.210–2.240 g / cm³. 3 .

7. The negative electrode material according to any one of claims 2 to 6, characterized in that, The specific capacity of the negative electrode material is greater than 360 mAh / g and less than or equal to 364 mAh / g.

8. The negative electrode material according to any one of claims 2 to 7, characterized in that, The initial coulombic efficiency of the negative electrode material is greater than 94% and less than or equal to 95.2%.

9. A method for preparing a negative electrode material as described in any one of claims 1 to 8, characterized in that, Includes the following steps: The mixture of graphite framework and organic carbon source was heat-treated under negative pressure to obtain the first material; The first material was subjected to low-temperature carbonization, oxidation ablation, and high-temperature carbonization in sequence.

10. The method for preparing the negative electrode material according to claim 9, characterized in that, It includes at least one of the following features (1) to (11): (1) The graphite skeleton includes natural graphite; (2) The particle size Dv50 of the graphite skeleton is 5 to 25 μm, and the carbon content of the graphite skeleton is greater than 99.9%. (3) The pore volume of the graphite framework is 0.02–0.05 cm³. 3 / g; (4) The organic carbon source includes at least one of petroleum asphalt, coal tar pitch and thermoplastic resin; (5) The coking value of the organic carbon source after heating at 550°C under a protective atmosphere for 2 hours is greater than 70%; (6) The mass ratio of the graphite skeleton to the organic carbon source is 75:25 to 90:10; (7) The vacuum degree during the heat treatment process is an absolute pressure of less than 0.05 MPa; (8) The vacuum degree of the environment in which the mixed system is located before heat treatment is less than 0.03 MPa; (9) The temperature of the heat treatment is 300-500℃, and the time of the heat treatment is 1-5h; (10) During the heat treatment process, the mixture is stirred at a speed of 100 to 300 r / min. (11) also includes: cooling the heat-treated material to room temperature.

11. The method for preparing the negative electrode material according to claim 9 or 10, characterized in that, It includes at least one of the following features (1) to (3): (1) The second material obtained by the low-temperature carbonization treatment has a volatile content of less than 2% and a graphitization degree of 89% to 92%. (2) The temperature of the low-temperature carbonization treatment is 500-800℃, and the time of the low-temperature carbonization treatment is 2-8h; (3) The low-temperature carbonization process is carried out under protective gas conditions.

12. The method for preparing the negative electrode material according to any one of claims 9 to 11, characterized in that, It includes at least one of the following features (1) to (3): (1) The third material obtained by the oxidation ablation treatment comprises a graphite core and an amorphous carbon layer; the average thickness of the amorphous carbon layer is 100–300 nm; the average ID / IG value of the Raman spectrum of the third material is 0.19–0.50; and the powder compaction density of the third material under 2 tons of pressure is greater than 1.55 g / cm³. 3 The interlayer spacing d002 of the X-ray diffraction pattern of the third material is 0.335932–0.336270 nm. (2) The temperature of the oxidation ablation treatment is 600-900℃, and the time of the oxidation ablation treatment is 3-10h; (3) The atmosphere for the oxidation and ablation treatment is an oxygen-containing atmosphere with a flow rate of 1-5 m³ / h. 3 / h.

13. The method for preparing the negative electrode material according to any one of claims 9 to 12, characterized in that, It includes at least one of the following features (1) to (2): (1) The temperature of the high-temperature carbonization treatment is 1500-1800℃, and the time of the high-temperature carbonization treatment is 6-12h; (2) The high-temperature carbonization treatment is carried out under protective gas conditions.

14. A negative electrode sheet, characterized in that, The negative electrode material includes any one of claims 1 to 8, or the negative electrode material prepared by any one of claims 9 to 13.

15. The negative electrode sheet according to claim 14, characterized in that, It also includes a negative electrode current collector and a negative electrode material layer disposed on at least one side surface of the negative electrode current collector; the negative electrode material layer includes the negative electrode material.

16. A battery, characterized in that, Includes the negative electrode sheet as described in claim 14.

17. The battery according to claim 16, characterized in that, It also includes the positive electrode, the separator, and the electrolyte.

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