A negative electrode material, a preparation method thereof, a negative electrode sheet, a battery, and a power-using device

Abstract

This invention relates to the field of secondary battery anode material technology, specifically to an anode material and its preparation method, an anode electrode sheet, a battery, and an electrical device. The anode material comprises composite particles, each including a core and an amorphous carbon coating layer covering the outer surface of the core. The core includes a graphite framework and amorphous carbon filled within the graphite framework. The average thickness of the amorphous carbon coating layer is 15–45 nm. Raman spectroscopy of the anode material is performed using 400 scanning points. The average ID / IG value of the Raman spectrum of the anode material is 0.40–0.50, with more than 70% of the scanning points having an ID / IG value > 0.4. This anode material exhibits low expansion rate and good rate performance.

Description

Technical Field

[0001] This invention relates to the field of secondary battery negative electrode materials technology, and more specifically, to a negative electrode material and its preparation method, a negative electrode sheet, a battery, and an electrical device. Background Technology

[0002] 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. Especially with the rapid development of new energy vehicles, consumers have increasingly higher demands for charging time and driving range of electric vehicles. Fast-charging lithium-ion batteries have become a core competitive advantage for power battery companies in the future market. The anode material, as a major component of power batteries, has a significant impact on the development of fast-charging technology. Developing low-expansion, high-rate-capacity anode materials is becoming a trend in the anode material market. When natural graphite is used as an anode material, its small interlayer spacing and poor rate performance result in high expansion rate during high-rate charging and discharging. Furthermore, the numerous internal pores lead to uneven stress release during material expansion and a large increase in SEI film thickness during cycling, further increasing the material's expansion rate.

[0003] Patent document CN111320171B discloses a low-expansion graphite anode material, its preparation method, and a lithium-ion battery. The method involves first mixing graphite, a modifier, and a water-soluble salt pore-forming agent. The mixed sample is then subjected to low-temperature heating to fill the particles with the modifier and pore-forming agent and coat their surface. The sample is then subjected to high-temperature heating, followed by washing, drying, dispersing, and sieving. Patent document CN114873591A discloses a low-temperature, long-life natural graphite anode material, its preparation method, and its applications. The method involves first evacuating the air, then filling the pores of natural graphite with solvent-diluted low-temperature asphalt under high temperature and pressure, and coating the particles on the surface. A pressurized thermal polymerization reaction is then performed to convert the low-temperature asphalt into mesophase asphalt. An isostatic pressing process is then performed to compact the mesophase asphalt with the curled flake graphite layers within the natural graphite, eliminating gaps within the natural graphite. Finally, the material is dispersed and carbonized.

[0004] Patent document CN116730333A discloses a method for preparing modified natural graphite anode material. The method involves filling the internal pores of natural graphite and coating the particle surface with a modifier through a single pressurized impregnation process. Then, an organic cleaning agent is used to clean the excessive modifier coating on the surface of the natural graphite. The cleaned precursor is then separated from the cleaning agent, and finally, the precursor is carbonized.

[0005] After in-depth research, the applicant of this invention discovered that:

[0006] The natural graphite anode material prepared by the method disclosed in CN111320171B exhibits poor internal filling effect and minimal reduction in expansion rate after high-temperature treatment. The surface-coated carbon, consisting of highly crystalline amorphous carbon or artificial graphite, also does not significantly improve the material's rate performance.

[0007] The method disclosed in CN114873591A requires the use of a high-temperature, high-pressure reactor and an isostatic press, which involves large equipment investment and complex and dangerous processes. The mesophase asphalt formed by low-temperature asphalt conversion, after carbonization, is amorphous carbon with good crystallinity, which is not conducive to improving the rate performance of the material and leads to a high expansion rate at high magnification.

[0008] The method disclosed in CN116730333A uses a large amount of toxic and harmful organic cleaning agents, which will harm the environment and operators, and does not conform to the green development concept of new energy.

[0009] Therefore, it is of great significance to provide a negative electrode material with low expansion and high rate capability.

[0010] In view of this, the present invention is hereby proposed. Summary of the Invention

[0011] The primary objective of this invention is to provide a negative electrode material with low expansion rate and good rate performance.

[0012] The second objective of this invention is to provide a method for preparing a negative electrode material. First, the air inside the graphite skeleton is removed under vacuum. Then, an organic carbon source is filled into the graphite skeleton particles and coated on the surface through high-temperature vacuum. Next, the amorphous carbon-based graphite crystal structure inside and outside the graphite skeleton is modified by microwave pyrolysis and plasma etching, which can improve the path of lithium ion insertion into the graphite particles, reduce the expansion rate of the obtained negative electrode material, and improve its rate performance. Finally, high-temperature carbonization further removes hydrogen, which can improve the high-temperature cycle performance of the negative electrode material.

[0013] The third objective of this invention is to provide a negative electrode sheet that has advantages such as low expansion rate, high compaction density, high rate performance, and good high-temperature cycling performance.

[0014] The fourth objective of this invention is to provide a battery that not only has a low expansion rate and high rate performance, but also excellent cycle performance.

[0015] The fifth objective of this invention is to provide an electrical appliance.

[0016] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0017] The present invention first provides a negative electrode material, including composite particles, wherein the composite particles include a core and an amorphous carbon coating layer covering the outer surface of the core, and the core includes a graphite skeleton and amorphous carbon filled in the graphite skeleton.

[0018] The average thickness of the amorphous carbon coating layer is 15–45 nm.

[0019] 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 0.40 to 0.50, and the number of scanning points with a single point ID / IG value > 0.4 accounted for more than 70%.

[0020] Preferably, the average thickness of the amorphous carbon coating layer is 15–35 nm.

[0021] Preferably, the number of scan points with an ID / IG value greater than 0.4 in the Raman spectrum of the negative electrode material accounts for 71% to 90%.

[0022] Preferably, the anode material is subjected to thermogravimetric analysis in an air atmosphere, and the thermogravimetric differential curve of the anode material has peaks and valleys in the temperature range of 530℃ to 550℃.

[0023] Preferably, the compaction density of the negative electrode material under 2 tons of pressure is >1.63 g / cm³. 3 .

[0024] Preferably, the interlayer spacing d002 of the X-ray diffraction pattern of the negative electrode material is 0.3360–0.3365 nm.

[0025] Preferably, the true density of the negative electrode material is 2.140–2.180 g / cm³. 3 .

[0026] Preferably, the pore volume of the negative electrode material is <0.005 cm³. 3 / g.

[0027] Preferably, the compaction density of the negative electrode material is 1.65 g / cm³. 3 The OI value of the negative electrode is 3.0 to 10.0.

[0028] Preferably, the negative electrode sheet containing the negative electrode material has an expansion rate of <25% after 50 cycles at 25°C and 1C.

[0029] Preferably, the 3C lithium plating performance of the battery containing the negative electrode material is >45%.

[0030] Preferably, the battery containing the negative electrode material has a first coulombic efficiency of >93.7% at 0.05C.

[0031] Preferably, the battery containing the negative electrode material has a 0.05C initial reversible capacity > 360 mAh / g.

[0032] Preferably, the graphite skeleton comprises natural graphite.

[0033] Preferably, the carbon content of the graphite skeleton is >99.9 wt.%.

[0034] Preferably, the pore volume of the graphite framework is 0.02–0.05 cm³. 3 / g.

[0035] This invention further provides a method for preparing a negative electrode material, comprising the following steps:

[0036] The mixture of graphite skeleton and organic carbon source is heat-treated under negative pressure to obtain the first material;

[0037] The first material is subjected to microwave pyrolysis and plasma etching to obtain the second material;

[0038] The second material is carbonized to obtain the negative electrode material.

[0039] Preferably, the graphite skeleton comprises natural graphite.

[0040] Preferably, the carbon content of the graphite skeleton is >99.9 wt.%.

[0041] Preferably, the particle size Dv50 of the graphite skeleton is 5–25 μm.

[0042] Preferably, the pore volume of the graphite framework is 0.02–0.05 cm³. 3 / g.

[0043] Preferably, the organic carbon source includes at least one of petroleum asphalt, coal tar pitch, and resin.

[0044] Preferably, the coking value of the organic carbon source is >70%.

[0045] Preferably, the mass ratio of the graphite skeleton to the organic carbon source is 75:25 to 90:10.

[0046] Preferably, the vacuum degree during the heat treatment process is an absolute pressure of less than 0.05 MPa.

[0047] Preferably, the vacuum degree of the environment in which the mixture is located before the heat treatment is less than 0.03 MPa.

[0048] Preferably, the heat treatment temperature is 300–500°C, and the heat treatment time is 1–5 hours.

[0049] Preferably, during the heat treatment process, the mixture is stirred at a speed of 100-300 r / min.

[0050] Preferably, the heating rate of the microwave pyrolysis is 40–80 °C / min.

[0051] Preferably, the microwave pyrolysis temperature is 700–900°C, and the microwave pyrolysis time is 1–3 hours.

[0052] Preferably, a plasma cleaning machine is used for the plasma etching; the output power of the plasma etching is 700-1000W, the processing speed is 1-5m / min, and the temperature is 20-30℃.

[0053] Preferably, the second material comprises a graphite core and an amorphous carbon layer; wherein the average thickness of the amorphous carbon layer is 200–400 nm; the average ID / IG value of 400 surface scan points in the Raman spectrum of the second material is 0.60–1.00; and the powder compaction density of the second material under 2 tons of pressure is >1.5 g / cm³. 3 The interlayer spacing d002 of the X-ray diffraction pattern of the second material is 0.336894–0.337679 nm.

[0054] Preferably, the carbonization temperature is 1500–1800°C, and the carbonization time is 6–12 hours.

[0055] Preferably, the carbonization is carried out under an inert atmosphere.

[0056] The present invention further provides a negative electrode sheet, comprising the negative electrode material or the negative electrode material prepared by the method of preparing the negative electrode material.

[0057] The present invention also provides a battery, including the aforementioned negative electrode sheet.

[0058] The present invention also provides an electrical device including the battery.

[0059] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0060] (1) The negative electrode material provided by the present invention has a low expansion rate and good rate performance.

[0061] (2) The negative electrode material provided by the present invention has both excellent cycle performance, high capacity and high first efficiency.

[0062] (3) The negative electrode material provided by the present invention has a high compaction density.

[0063] (4) The method for preparing the negative electrode material provided by this invention first involves removing the air from the graphite skeleton under vacuum, then filling the graphite skeleton particles with organic carbon sources and coating their surfaces using high-temperature vacuum. Next, microwave pyrolysis combined with plasma etching is used to modify the amorphous carbon-based graphite crystal structure inside and outside the graphite skeleton, which improves the path for lithium ions to embed into the graphite particles, reduces the expansion rate of the resulting negative electrode material, and enhances its rate performance. Finally, high-temperature carbonization further dehydrogenates the material, improving its high-temperature cycling performance. Attached Figure Description

[0064] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0065] Figure 1 A CP-SEM image of the negative electrode material prepared in Example 2 of this invention, magnified at 1000x.

[0066] Figure 2 A CP-SEM image of the negative electrode material prepared in Example 2 of this invention, magnified at 50,000 times.

[0067] Figure 3 The ID / IG distribution diagram of the negative electrode material prepared in Example 2 of this invention;

[0068] Figure 4 Thermogravimetric (DTG) curve of the negative electrode material prepared in Example 2 of this invention;

[0069] Figure 5 CP-SEM image of the negative electrode material prepared in Comparative Example 1 provided by the present invention;

[0070] Figure 6 ID / IG distribution diagram of the negative electrode material prepared in Comparative Example 1 provided by the present invention;

[0071] Figure 7 Thermogravimetric (DTG) curve of the negative electrode material prepared in Comparative Example 1 provided by the present invention. Detailed Implementation

[0072] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0073] Unless otherwise specified, in this invention, terms such as "first aspect," "second aspect," "third aspect," and "fourth aspect" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, terms such as "first," "second," "third," and "fourth" serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0074] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0075] Unless otherwise specified, in this invention, "one or more" or "at least one" refers to any one, any two, or any two or more of the listed items. "Several" refers to any two or more.

[0076] In a first aspect, the present invention provides a low-expansion natural graphite anode material, comprising composite particles, wherein the composite particles comprise a core and an amorphous carbon coating layer covering the outer surface of the core.

[0077] The core comprises a graphite framework and amorphous carbon filling the graphite framework.

[0078] The average thickness of the amorphous carbon coating layer is 15-45 nm, including but not limited to a point value of any one of 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, and 45 nm, or a range between any two.

[0079] The amorphous carbon coating layer provided by the present invention has the above-mentioned suitable thickness, which is beneficial to improving the specific capacity of the negative electrode material and increasing the compaction density of the negative electrode material.

[0080] The negative electrode material is subjected to Raman spectral surface scanning with 400 scanning points. The average value of the ID / IG (peak intensity ratio) of the Raman spectrum of the negative electrode material is 0.40 to 0.50, including but not limited to any one of 0.40, 0.41, 0.42, 0.43, 0.44, 0.45, 0.46, 0.47, 0.48, 0.49, and 0.50, or any range between two values.

[0081] Among them, the number of scan points with a single point value of ID / IG > 0.4 accounts for more than 70%, including but not limited to any one of the following: 70%, 71%, 75%, 77%, 80%, 82%, 85%, 88%, 90%, 93%, 95%, etc., or any range between two of them.

[0082] The negative electrode material provided by this invention features micronized graphite crystals on the inside and outside of the graphite skeleton (smaller grain size and larger interlayer spacing), and the amorphous carbon on the surface has point defects (missing single atoms in the carbon layer), line defects (micro-deformation and dislocation of surface crystals), and surface defects (cracks at grain boundaries, expanding surface defects of the crystals), which improves the rate performance of the negative electrode material and reduces the expansion rate.

[0083] Among them, ID / IG reflects the disorder of amorphous carbon-based graphite microcrystals on the material surface. The greater the disorder, the more active sites on the material surface, which is more conducive to lithium ion intercalation and beneficial to improving rate performance and reducing expansion rate. Due to the increased number of defect sites in the material of this invention, the average value of ID / IG of the material is increased.

[0084] An average ID / IG ratio exceeding 0.4 is beneficial for improving the rate performance of anode materials and reducing their expansion rate.

[0085] Furthermore, by controlling the average value of ID / IG in the Raman spectrum of the negative electrode material to be 0.40 to 0.50, and the number of scan points with a single point value of ID / IG > 0.4 accounting for more than 70%, the present invention can also take into account the cycling performance.

[0086] In some specific embodiments, the average thickness of the amorphous carbon coating layer is 15-35 nm; including but not limited to point values ​​or ranges between any one of 15 nm, 17 nm, 18 nm, 20 nm, 23 nm, 25 nm, 28 nm, 30 nm, 32 nm, and 35 nm.

[0087] In some specific embodiments, the number of scan points with a single-point value greater than 0.4 in the Raman spectrum of the negative electrode material accounts for 71% to 90%, including but not limited to point values ​​or ranges between any one of 71%, 72%, 73%, 74%, 75%, 78%, 80%, 82%, 83%, 85%, 88%, and 90%.

[0088] Specifically, the average ID / IG ratio should not exceed 0.5, and the content of points with an ID / IG ratio greater than 0.4 should not exceed 90%. Excessive point content or an excessively high average value will lead to poor cycling performance of the material. Because excessive disorder in the material results in too many active sites, it will exacerbate the side reactions between the amorphous carbon on the surface and the electrolyte, leading to very low initial coulombic efficiency and poor cycling performance, which is detrimental to practical applications.

[0089] In some specific embodiments, the anode material is subjected to thermogravimetric analysis (TGA) in an air atmosphere. The differential thermogravimetric curve (DTG curve) of the anode material exhibits peaks and valleys within a temperature range of 530℃ to 550℃ (including but not limited to points at any one of 530℃, 535℃, 540℃, 545℃, and 550℃, or ranges between any two). That is, the first peak of the DTG curve of the anode material in an air atmosphere is within the temperature range of 530℃ to 550℃. Here, a peak and valley refer to the lowest point of the peak, and the derivative weight of the peak and valley is greater than -0.05% / ℃.

[0090] The increased number of defect sites in the material leads to a forward shift of the first DTG peak in the thermogravimetric atmosphere of the negative electrode material (making the reaction between amorphous carbon and oxygen molecules easier).

[0091] In some specific embodiments, the compaction density of the negative electrode material under 2 tons of pressure is >1.63 g / cm³. 3 ; including but not limited to 1.64g / cm 3 1.65g / cm 3 1.66 g / cm 3 1.67 g / cm 3 1.68g / cm 3 1.69 g / cm 3 1.70g / cm 3 1.71g / cm 3 1.72g / cm 3 1.73g / cm 3 1.74 g / cm 3 1.75g / cm 3 1.76 g / cm 3 1.78g / cm 31.80g / cm 3 The point value of any one of them or the range value between any two.

[0092] It can be seen that the negative electrode material provided by the present invention has a high compaction density.

[0093] In some specific embodiments, the interlayer spacing d002 of the X-ray diffraction (XRD) pattern of the negative electrode material is 0.3360–0.3365 nm; including but not limited to point values ​​or ranges between any one of 0.336050 nm, 0.336100 nm, 0.336107 nm, 0.336117 nm, 0.336126 nm, 0.336150 nm, 0.336200 nm, 0.336250 nm, and 0.336500 nm.

[0094] The increased number of defect sites in the material leads to an increase in the interlayer spacing d002 of the negative electrode material.

[0095] In some specific embodiments, the true density of the negative electrode material is 2.140–2.180 g / cm³. 3 ; including but not limited to 2.140g / cm 3 2.150g / cm 3 2.160g / cm 3 2.170g / cm 3 2.180g / cm 3 The point value of any one of them or the range value between any two.

[0096] The negative electrode material provided by this invention has a suitable true density, which can improve the energy density and specific capacity of the battery made therefrom.

[0097] In some specific embodiments, the pore volume of the negative electrode material is <0.005 cm³. 3 / g; including but not limited to 0.0040cm 3 / g, 0.0030cm 3 / g, 0.0025cm 3 / g, 0.0023cm 3 / g, 0.0021cm 3 / g, 0.0020cm 3 / g, 0.0018cm 3 / g, 0.0015cm 3 / g, 0.0010cm 3 The point value of any one of / g or the range value between any two.

[0098] The negative electrode material provided by this invention has a small pore volume, which can reduce the side reactions between the negative electrode material surface and the electrolyte, thereby improving the cycle performance of the battery.

[0099] In some specific embodiments, the compaction density of the negative electrode material is 1.65 g / cm³. 3 The OI value of the negative electrode is 3.0 to 10.0; including but not limited to the point value of any one of 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, and 10.0 or the range between any two.

[0100] This invention reduces the OI value of the electrode, thereby increasing the lithium-ion insertion path and lowering the lithium-ion insertion energy barrier, thus giving the negative electrode material the advantage of low expansion rate at high rates.

[0101] In some specific embodiments, the negative electrode sheet containing the negative electrode material has an expansion rate of <25% after 50 cycles at 25°C and 1C; including but not limited to point values ​​of any one of 24%, 23%, 22%, 21%, 20%, 19%, 18%, 17%, 16%, and 15%, or a range between any two.

[0102] It can be seen that the expansion rate of the negative electrode material provided by the present invention is low.

[0103] In some specific embodiments, the 3C lithium plating performance of the battery containing the negative electrode material is >45%; including but not limited to any one of 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 58%, 60% or any range between two.

[0104] The 3C lithium plating performance and rate performance of the anode material are approximately positively correlated; the better the 3C lithium plating performance, the better the rate performance. Therefore, the battery assembled with the anode material provided by this invention exhibits excellent rate performance.

[0105] The battery assembled using the negative electrode material provided by this invention also has the advantages of high initial coulombic efficiency and high initial reversible capacity.

[0106] In some specific embodiments, the 0.05C initial coulombic efficiency (hereinafter referred to as initial efficiency) of the battery containing the negative electrode material is >93.7%; including but not limited to any one of 93.8%, 93.9%, 94.0%, 94.1%, 94.2%, 94.4%, 94.5%, 94.6%, 94.8%, 95% or any range between two of them.

[0107] In some specific embodiments, the 0.05C initial reversible capacity of the battery containing the negative electrode material is >360mAh / g; including but not limited to any one of 361mAh / g, 362mAh / g, 363mAh / g, 364mAh / g, 365mAh / g, 366mAh / g, 368mAh / g, and 370mAh / g, or a range between any two.

[0108] In some specific embodiments, the graphite skeleton comprises natural graphite. In other embodiments, the graphite skeleton may also be artificial graphite. Preferably, the graphite skeleton of this invention comprises natural graphite because natural graphite has defects such as small interlayer spacing, poor rate performance, high expansion rate during high-rate charge and discharge, and numerous internal pores, which adversely affect its large-scale application. This invention, by modifying natural graphite, enables its application as a high-performance anode material.

[0109] In some specific embodiments, the carbon content of the graphite skeleton is >99.9 wt.%. This ensures the specific capacity of the obtained negative electrode material and avoids the occurrence of side reactions.

[0110] In some specific embodiments, the pore volume of the graphite framework is 0.02–0.05 cm³. 3 / g, including but 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, 0.05cm 3 The point value of any one of / g or the range value between any two.

[0111] The graphite skeleton of the present invention has a suitable pore volume, which enables the final anode material to have excellent overall performance. If the pore volume is too high, more amorphous carbon needs to be filled, which will lead to low compaction density and low specific capacity of the anode material; if the pore volume is too small or there are basically no pores (i.e., it is basically a solid sphere or sheet), the amorphous carbon cannot fill into the graphite skeleton, resulting in a slow diffusion rate of lithium ions inside the particles during lithium insertion and extraction, which is not conducive to improving rate performance.

[0112] Secondly, the present invention provides a method for preparing a negative electrode material, comprising the following steps:

[0113] The mixture of graphite skeleton and organic carbon source is heat-treated under negative pressure and then cooled to obtain the first material.

[0114] The first material is subjected to microwave pyrolysis and plasma etching in sequence to obtain the second material.

[0115] The second material is carbonized and cooled to obtain the negative electrode material.

[0116] This invention fills a large amount of organic carbon source into the interior of a graphite skeleton and coats the surface of the graphite skeleton through high-temperature vacuum, followed by rapid microwave pyrolysis. Utilizing the rapid heating characteristic of microwave pyrolysis, the amorphous carbon-based graphite crystals inside and outside the graphite skeleton are micronized (grain size decreases, interlayer spacing increases). This improves the diffusion and embedding channels of lithium ions inside and on the surface of the particles, increasing the rate performance of the anode material and reducing its expansion rate. Subsequently, plasma etching technology is used to modify the defect sites of the amorphous carbon coating on the graphite skeleton surface. This generates more point defects (missing single atoms in the carbon layer), line defects (micro-deformation and dislocation of surface crystals), and planar defects (cracks at grain boundaries, expanding planar defects). This gives the amorphous carbon surface more active sites, lowers the lithium ion embedding barrier on the material surface, increases the interfacial electrochemical reaction rate, and further improves the rate performance and reduces the expansion rate of the anode material. Furthermore, high-temperature carbonization further dehydrogenates the material, which can improve the high-temperature cycle performance of the anode material and prevent the high-temperature performance of the material from decreasing too significantly.

[0117] This invention employs a microwave pyrolysis + plasma etching method to modify the graphite-like crystal structure of amorphous carbon in the material, thereby improving the ID / IG ratio of the negative electrode material, reducing the OI value of the negative electrode material, increasing the lithium ion insertion path, and lowering the lithium ion insertion energy barrier, ultimately giving the material a low expansion rate at high magnification.

[0118] Specifically, microwave pyrolysis combined with plasma etching can peel away the amorphous carbon-like microcrystalline layer on the surface of graphite framework powder particles along a certain direction, creating line defects in the crystal. Furthermore, the plasma impacts the surface carbon atoms, causing localized carbon atom loss and generating point defects. Simultaneously, cracks are generated at grain boundaries, expanding the planar defects and improving the crystal's orientation. These point defects (the loss of a single carbon atom), line defects (micro-deformation and dislocation of surface crystals), and planar defects (cracks at grain boundaries, expanding planar defects) can lower the lithium-ion intercalation barrier on the material surface, increase the interfacial electrochemical reaction rate, thereby improving the rate performance of the anode material and reducing its expansion rate.

[0119] The aforementioned defects in the anode material are evident from the characteristics of ID / IG, D002, and DTG peaks. The increased number of defect sites leads to an increase in D002 and ID / IG, and a forward shift of the first DTG peak under thermogravimetric air conditions (making the reaction between amorphous carbon and oxygen molecules easier).

[0120] In some specific embodiments, the graphite framework comprises natural graphite.

[0121] In other embodiments, the graphite skeleton can also be artificial graphite. Preferably, the graphite skeleton of this invention comprises natural graphite, because natural graphite has defects such as small interlayer spacing, poor rate performance, high expansion rate during high-rate charging and discharging, and numerous internal pores, which adversely affect its large-scale application. However, this invention modifies natural graphite, enabling it to be used as a high-performance anode material.

[0122] In some specific embodiments, the carbon content of the graphite framework is >99.9 wt.%.

[0123] In some specific embodiments, the particle size Dv50 of the graphite skeleton is 5 to 25 μm; including but not limited to point values ​​of any one of 5 μm, 10 μm, 15 μm, 20 μm, and 25 μm, or a range of values ​​between any two.

[0124] The graphite skeleton provided by this invention uses a suitable particle size, which can ensure subsequent coating and thus ensure the electrochemical performance of the anode material.

[0125] In some specific embodiments, the pore volume of the graphite framework is 0.02–0.05 cm³. 3 / g; including but 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, 0.05cm 3 The point value of any one of / g or the range value between any two.

[0126] The graphite skeleton of the present invention has a suitable pore volume, which enables the final anode material to have excellent overall performance. If the pore volume is too high, more amorphous carbon needs to be filled, which will lead to low compaction density and low specific capacity of the anode material; if the pore volume is too small or there are basically no pores (i.e., it is basically a solid sphere or sheet), the amorphous carbon cannot fill into the graphite skeleton, resulting in a slow diffusion rate of lithium ions inside the particles during lithium insertion and extraction, which is not conducive to improving rate performance.

[0127] In some specific embodiments, the organic carbon source includes at least one of petroleum asphalt, coal tar pitch, and resin, or any two or three of them.

[0128] In some specific embodiments, the coal tar pitch comprises coal liquefaction pitch and / or coal tar pitch.

[0129] In some specific embodiments, the resin includes natural resins and / or synthetic resins, such as thermoplastic resins, but is not limited thereto.

[0130] In some specific embodiments, the coking value of the organic carbon source is >70%; including but not limited to point values ​​of any one of 71%, 73%, 75%, 78%, and 80%, or range values ​​between any two.

[0131] In some specific embodiments, the mass ratio of the graphite skeleton to the organic carbon source is 75:25 to 90:10; including but not limited to any one of 75:25, 78:22, 80:20, 85:15, 90:10 or any range between the two.

[0132] The above-mentioned graphite skeleton and organic carbon source are used in a suitable mass ratio to ensure that the organic carbon source can enter the pores of the graphite skeleton and be coated with a carbon source of a suitable thickness on the surface. That is, 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 an amorphous carbon coating layer of a suitable amount and thickness, thereby ensuring the low expansion rate, high rate performance and excellent high temperature cycling performance of the negative electrode material.

[0133] In some specific embodiments, the vacuum degree during the heat treatment process is an absolute pressure of less than 0.05 MPa; including but not limited to a point value of any one of 0.02 MPa, 0.03 MPa, 0.04 MPa, and 0.05 MPa, or a range between any two.

[0134] In some specific embodiments, the vacuum degree of the environment in which the mixture is located before the heat treatment is less than 0.03 MPa; including but not limited to the point value of any one of 0.01 MPa and 0.02 MPa or the range between any two.

[0135] In some specific embodiments, the heat treatment temperature is 300 to 500°C, including but not limited to any one of 300°C, 350°C, 400°C, 450°C, and 500°C, or any range between two of them; the heat treatment time is 1 to 5 hours, including but not limited to any one of 1 hour, 2 hours, 3 hours, 4 hours, and 5 hours, or any range between two of them.

[0136] In some specific embodiments, during the heat treatment process, the mixture is stirred at a speed of 100 to 300 r / min, wherein the speed includes, but is not limited to, any one of 100 r / min, 150 r / min, 200 r / min, 250 r / min, and 300 r / min or any range between two of them.

[0137] The present invention employs appropriate heat treatment temperature and time, as well as appropriate stirring speed, to ensure that the organic carbon source can better enter the porous structure of the graphite skeleton and uniformly coat its surface.

[0138] In some specific embodiments, the heat treatment of the mixture of graphite skeleton and organic carbon source under negative pressure conditions specifically includes: adding the mixture of graphite skeleton and organic carbon source into a reaction vessel, first evacuating the reaction vessel to remove air, then heating and stirring the reaction vessel after air removal, maintaining a certain degree of vacuum during heating, and cooling to room temperature after heating to obtain the first material.

[0139] In some specific embodiments, the heating rate of the microwave pyrolysis is 40 to 80°C / min; including but not limited to any one of 40°C / min, 50°C / min, 60°C / min, 70°C / min, and 80°C / min, or any range between two of them.

[0140] The present invention employs the above-mentioned heating rate for rapid microwave pyrolysis, which can micronize the amorphous carbon-based graphite crystals inside and outside the graphite skeleton (smaller grain size and larger interlayer spacing), improve the diffusion and embedding channels of lithium ions inside and on the graphite skeleton, thereby improving the rate performance of the anode material and reducing the expansion rate of the anode material.

[0141] In some specific embodiments, the microwave pyrolysis temperature is 700-900℃, including but not limited to any one of 700℃, 750℃, 800℃, 850℃, and 900℃ or any range between two of them; the microwave pyrolysis time is 1-3h, including but not limited to any one of 1h, 2h, and 3h or any range between two of them.

[0142] In some specific embodiments, a plasma cleaning machine is used to perform the plasma etching.

[0143] In some specific embodiments, the output power of the plasma etching is 700-1000W, including but not limited to any one of 700W, 800W, 900W, and 1000W or any range between two; the processing speed of the plasma etching is 1-5m / min, including but not limited to any one of 1m / min, 2m / min, 3m / min, 4m / min, and 5m / min or any range between two; the temperature of the plasma etching is 20-30℃, including but not limited to any one of 20℃, 22℃, 25℃, 28℃, and 30℃ or any range between two.

[0144] In some specific embodiments, the second material comprises a graphite core and an amorphous carbon layer.

[0145] In some specific embodiments, the average thickness of the amorphous carbon layer is 200 to 400 nm; including but not limited to a point value of any one of 200 nm, 250 nm, 300 nm, 350 nm, and 400 nm, or a range of any two.

[0146] In some specific embodiments, the surface scan points of the Raman spectrum of the second material are 400 points with an average ID / IG value of 0.60 to 1.00; including but not limited to point values ​​of any one of 0.60, 0.70, 0.80, 0.90, and 1.00 or a range of values ​​between any two.

[0147] In some specific embodiments, the compacted density of the second material under a pressure of 2 tons is >1.5 g / cm³. 3 ; including but not limited to 1.51g / cm 3 1.52g / cm 3 1.53g / cm 3 1.54g / cm 3 1.55g / cm 3 1.56g / cm 3 1.57g / cm 3 1.58g / cm 3 1.59g / cm 3 1.60g / cm 3 The point value of any one of them or the range value between any two.

[0148] In some specific embodiments, the interlayer spacing d002 of the X-ray diffraction pattern of the second material is 0.336894 to 0.337679 nm; including but not limited to point values ​​of any one of 0.336894 nm, 0.337000 nm, 0.337328 nm, 0.337500 nm, and 0.337679 nm, or a range between any two.

[0149] In some specific embodiments, the carbonization temperature is 1500–1800°C, including but not limited to any one of 1500°C, 1550°C, 1600°C, 1650°C, 1700°C, and 1800°C, or a range between any two; the carbonization time is 6–12 hours, including but not limited to any one of 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, and 12 hours, or a range between any two.

[0150] In some specific embodiments, the carbonization is carried out under an inert atmosphere.

[0151] In some specific embodiments, the inert atmosphere includes a nitrogen atmosphere and / or an argon atmosphere.

[0152] The present invention employs suitable carbonization conditions, which is beneficial to further improve the high-temperature cycle performance of the anode material.

[0153] Thirdly, the present invention provides a negative electrode sheet comprising the above-mentioned negative electrode material, or a negative electrode material prepared by the above-mentioned method for preparing the negative electrode material.

[0154] This negative electrode sheet has advantages such as low expansion rate, high compaction density, high rate performance, and good high-temperature cycling performance.

[0155] Optionally, the negative electrode sheet may further include a conductive agent and / or a binder, which is not limited in this invention.

[0156] Fourthly, the present invention provides a battery comprising the aforementioned negative electrode sheet.

[0157] The battery provided by this invention not only has a low expansion rate and high rate performance, but also excellent cycle performance.

[0158] Optionally, the battery may further include a positive electrode, a separator, and an electrolyte, which are not limited in this invention.

[0159] The battery includes, but is not limited to, a secondary battery, such as a lithium-ion battery.

[0160] Fifthly, the present invention provides an electrical device including the aforementioned battery.

[0161] The electrical equipment includes any device or apparatus that includes the aforementioned battery, such as electric vehicles, electric motorcycles, electric bicycles, power tools, starting power supplies, energy storage devices, electronic products, and office equipment, but is not limited thereto.

[0162] The embodiments of the present invention 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 the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0163] Example 1

[0164] The method for preparing the negative electrode material provided in this embodiment includes the following steps:

[0165] (1) Mix 2.5 kg of coal tar pitch (coal tar pitch, coking value 75%) and 7.5 kg of natural graphite (Dv50 = 5 μm, carbon content 99.91 wt.%, 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 the precursor. The precursor is placed into a reaction vessel, and the sealed reaction vessel is evacuated until the vacuum degree reaches an absolute gauge pressure of 0.02 MPa. The reaction vessel with qualified vacuum degree is then heated (i.e., heat treatment) and stirred. The heating temperature is 300℃, the stirring speed is 300 r / min, and the holding time is 5h. During the holding time, the vacuum degree is maintained at an absolute gauge pressure of 0.02 MPa. After the heating is completed and cooled, the material is released to obtain the first material.

[0166] (2) The first material was subjected to microwave pyrolysis at a temperature of 700℃, a pyrolysis time of 1 hour, and a heating rate of 40℃ / min. Then, plasma etching was performed using a plasma cleaner at an output power of 800W, a processing speed of 3m / min, and a temperature of 25℃ to obtain the second material. This second material consists of a graphite core and an amorphous carbon layer; the average thickness of the amorphous carbon is 400nm, the average ID / IG (peak intensity ratio) of 400 points scanned by a Raman spectrometer is 0.60, and the compacted density of the powder at 2 tons is 1.52g / cm³. 3 The interlayer spacing d002 measured by XRD is 0.336894 nm.

[0167] (3) The second material was subjected to high-temperature carbonization under a nitrogen atmosphere. The carbonization temperature was 1500℃ and the carbonization time was 6h. After cooling to room temperature, natural graphite anode material was obtained.

[0168] The negative electrode material prepared in this embodiment includes composite particles, which include a core and an amorphous carbon coating layer covering the outer surface of the core. The core includes a graphite skeleton and amorphous carbon filled in the graphite skeleton. The following parameters are specified: average thickness of the amorphous carbon coating layer (referred to as carbon layer thickness); average value of ID / IG (peak intensity ratio) of 400 points obtained from Raman spectroscopy of the negative electrode material; percentage of scan points with ID / IG (peak intensity ratio) values ​​> 0.4 (i.e., point content); and compaction density of the negative electrode material containing this material is 1.65 g / cm³. 3 The performance test results of the negative electrode OI value, the compaction density of the negative electrode material under 2 tons of pressure, the interlayer spacing d002 of the X-ray diffraction pattern of the negative electrode material, the true density and pore volume of the negative electrode material, and the temperature values ​​of the peak and valley of the thermogravimetric DTG curve of the negative electrode material in the temperature range of 530℃~550℃ (i.e. the temperature corresponding to the first peak of the DTG weight loss rate) are all shown in Table 1.

[0169] Example 2

[0170] The method for preparing the negative electrode material provided in this embodiment includes the following steps:

[0171] (1) Mix 1.5 kg of petroleum asphalt (coking value 75%) and 8.5 kg of natural graphite (Dv50 = 15 μm, carbon content 99.95 wt.%, pore volume 0.034 cm³). 3 (g) is added to a mixing device, and the material is mixed evenly by high-speed stirring to obtain a precursor. The precursor is placed into a reaction vessel, and the sealed reaction vessel is evacuated until the vacuum degree reaches an absolute gauge pressure of 0.015 MPa. The reaction vessel with qualified vacuum degree is then heated (i.e., heat treatment) and stirred at a temperature of 400℃, a rotation speed of 200 r / min, and a holding time of 3 h, maintaining a vacuum degree of 0.03 MPa absolute gauge pressure during the holding time. After heating is completed and the mixture is cooled, the material is released to obtain the first material.

[0172] (2) The first material was subjected to microwave pyrolysis at a temperature of 800℃ for 2 hours and a heating rate of 60℃ / min. Then, plasma etching was performed using a plasma cleaner at an output power of 800W, a processing speed of 3m / min, and a temperature of 25℃ to obtain the second material. This second material consists of a graphite core and an amorphous carbon layer; the amorphous carbon layer has an average thickness of 300nm, an average ID / IG (peak intensity ratio) of 0.82 across 400 points scanned by a Raman spectroscopy panel, and a compacted density of 1.57g / cm³ at 2 tons. 3 The interlayer spacing d002 measured by XRD is 0.337328 nm.

[0173] (3) The second material was subjected to high-temperature carbonization treatment under nitrogen atmosphere. The carbonization temperature was 1650℃ and the carbonization time was 9h. After cooling to room temperature, natural graphite anode material was obtained.

[0174] The negative electrode material prepared in this embodiment includes composite particles, which include a core and an amorphous carbon coating layer covering the outer surface of the core. The core includes a graphite skeleton and amorphous carbon filled in the graphite skeleton. The following parameters are specified: average thickness of the amorphous carbon coating layer (referred to as carbon layer thickness); average value of ID / IG (peak intensity ratio) of 400 points obtained from Raman spectroscopy of the negative electrode material; percentage of scan points with ID / IG (peak intensity ratio) values ​​> 0.4 (i.e., point content); and compaction density of the negative electrode material containing this material is 1.65 g / cm³. 3 The performance test results of the negative electrode OI value, the compaction density of the negative electrode material under 2 tons of pressure, the interlayer spacing d002 of the X-ray diffraction pattern of the negative electrode material, the true density and pore volume of the negative electrode material, and the temperature values ​​of the peak and valley of the thermogravimetric DTG curve of the negative electrode material in the temperature range of 530℃~550℃ (i.e. the temperature corresponding to the first peak of the DTG weight loss rate) are all shown in Table 1.

[0175] The CP-SEM image of the negative electrode material prepared in this embodiment, magnified at 1000x, is shown below. Figure 1 As shown. The CP-SEM image of the negative electrode material prepared in this embodiment, magnified at 50,000x, is shown below. Figure 2 As shown ( Figure 2 The thickness indicated is the specific thickness of the amorphous carbon coating layer, while the thickness in Table 1 is the average thickness of the amorphous carbon coating layer.

[0176] The ID / IG distribution diagram of the negative electrode material prepared in this embodiment can be found in [reference needed]. Figure 3 As shown.

[0177] The thermogravimetric (DTG) curve of the negative electrode material prepared in this embodiment is shown in the figure. Figure 4 As shown.

[0178] Example 3

[0179] The method for preparing the negative electrode material provided in this embodiment includes the following steps:

[0180] (1) Mix 1 kg of coal tar pitch (coal tar pitch) and petroleum pitch (coking value 75%, mass ratio of coal tar pitch to petroleum pitch 1:1) and 9 kg of natural graphite (Dv50 = 25 μm, carbon content 99.96 wt.%, pore volume 0.02 cm³). 3(g) is added to a mixing device, and the material is mixed evenly by high-speed stirring to obtain a precursor. The precursor is placed into a reaction vessel, and the sealed reaction vessel is evacuated until the vacuum degree reaches an absolute gauge pressure of 0.01 MPa. The reaction vessel with qualified vacuum degree is heated and stirred at a temperature of 500℃, a rotation speed of 100 r / min, and a holding time of 1 h, while maintaining the vacuum degree at an absolute gauge pressure of 0.04 MPa during the holding time. After heating is completed and cooling is achieved, the material is released to obtain the first material.

[0181] (2) The first material was subjected to microwave pyrolysis at a temperature of 900℃ for 3 hours and a heating rate of 80℃ / min. Then, plasma etching was performed using a plasma cleaner at an output power of 800W, a processing speed of 3m / min, and a temperature of 25℃ to obtain the second material. This second material consists of a graphite core and an amorphous carbon layer; the amorphous carbon layer has an average thickness of 200nm, an average ID / IG (peak intensity ratio) of 1.00 across 400 points scanned by a Raman spectrometer, and a compacted density of 1.59g / cm³ at 2 tons. 3 The interlayer spacing d002 measured by XRD is 0.337679 nm.

[0182] (3) The second material was subjected to high-temperature carbonization under a nitrogen atmosphere. The carbonization temperature was 1800℃ and the carbonization time was 12h. After cooling to room temperature, natural graphite anode material was obtained.

[0183] The negative electrode material prepared in this embodiment includes composite particles, which include a core and an amorphous carbon coating layer covering the outer surface of the core. The core includes a graphite skeleton and amorphous carbon filled in the graphite skeleton. The following parameters are specified: average thickness of the amorphous carbon coating layer (referred to as carbon layer thickness); average value of ID / IG (peak intensity ratio) of 400 points obtained from Raman spectroscopy of the negative electrode material; percentage of scan points with ID / IG (peak intensity ratio) values ​​> 0.4 (i.e., point content); and compaction density of the negative electrode material containing this material is 1.65 g / cm³. 3 The OI value of the negative electrode sheet, the compaction density of the negative electrode material under 2 tons of pressure, the interlayer spacing d002 of the X-ray diffraction pattern of the negative electrode material, the true density and pore volume of the negative electrode material, and the temperature values ​​of the peak and valley of the thermogravimetric DTG curve of the negative electrode material in the temperature range of 530℃~550℃ (i.e. the temperature corresponding to the first peak of the DTG weight loss rate) are all shown in Table 1.

[0184] Example 4

[0185] The preparation method of the negative electrode material provided in this embodiment is basically the same as that in embodiment 2. The difference is that in step (1), petroleum asphalt is replaced with an equal mass of thermoplastic phenolic resin with a coking value of 82%.

[0186] Comparative Example 1

[0187] The method for preparing the negative electrode material provided in this comparative example does not involve vacuuming during heat treatment (i.e., it is carried out at atmospheric pressure) and does not involve microwave pyrolysis or plasma etching. Specifically, it includes the following steps:

[0188] (1) Mix 1.5 kg of petroleum asphalt (coking value 75%) and 8.5 kg of natural graphite (Dv50 = 15 μm, carbon content 99.95 wt.%, 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 the precursor. The precursor is placed into the reaction vessel, and the reaction vessel is heated and stirred at a temperature of 400℃, a speed of 200r / min, and a holding time of 3h. After the heating is completed and cooled, the material is released to obtain the first material.

[0189] (2) The first material was subjected to high-temperature carbonization under a nitrogen atmosphere. The carbonization temperature was 1650℃ and the carbonization time was 9h. After cooling to room temperature, natural graphite anode material was obtained.

[0190] The CP-SEM image of the anode material prepared in this comparative example is shown below. Figure 5 As shown. The ID / IG distribution of the anode material prepared in this comparative example is shown in the figure. Figure 6 As shown. By Figure 5 It can be seen that the anode material prepared in this comparative example includes a core and an amorphous carbon coating layer covering the outer surface of the core (the graphite framework contains almost no amorphous carbon). The average thickness of the amorphous carbon coating layer (referred to as carbon layer thickness), the average value of the ID / IG (peak intensity ratio) of 400 points scanned by a Raman spectrometer on the anode material, the percentage of scan points with an ID / IG (peak intensity ratio) value > 0.4 (i.e., point content), and the compaction density of the anode material are all measured. The compaction density is 1.65 g / cm³. 3 The performance test results of the negative electrode OI value, the compaction density of the negative electrode material under 2 tons of pressure, the interlayer spacing d002 of the X-ray diffraction pattern of the negative electrode material, the true density and pore volume of the negative electrode material are shown in Table 1.

[0191] The thermogravimetric (DTG) curve of the anode material prepared in this comparative example is shown in the figure below. Figure 7 As shown. (Through) Figure 7 It can be seen that the first peak of the DTG weight loss rate is at 590℃, meaning there are no peaks or valleys in the temperature range of 530℃ to 550℃.

[0192] Comparative Example 2

[0193] The preparation method of the negative electrode material provided in this comparative example is basically the same as that in Example 2. The difference is that step (2) is not included, that is, microwave pyrolysis and plasma etching are not performed, but the first material is directly subjected to high-temperature carbonization treatment.

[0194] The anode material prepared in this comparative example includes composite particles, which consist of a core and an amorphous carbon coating layer covering the outer surface of the core. The core includes a graphite framework and amorphous carbon filling the graphite framework. The following parameters are specified: average thickness of the amorphous carbon coating layer (referred to as carbon layer thickness); average ID / IG (peak intensity ratio) of 400 points obtained from Raman spectroscopy of the anode material; percentage of scan points with an ID / IG (peak intensity ratio) value > 0.4 (i.e., point content); and compaction density of the anode material containing this material is 1.65 g / cm³. 3 The OI value of the negative electrode, the compaction density of the negative electrode material under 2 tons of pressure, the interlayer spacing d002 of the X-ray diffraction pattern of the negative electrode material, the true density and pore volume of the negative electrode material are all shown in Table 1.

[0195] The thermogravimetric (DTG) curves of the anode material prepared in this comparative example under air atmosphere show that the first peak of the DTG weight loss rate is at 580℃, meaning there are no peaks or valleys in the temperature range of 530℃ to 550℃.

[0196] Comparative Example 3

[0197] The preparation method of the negative electrode material provided in this comparative example is basically the same as that in Example 2, except that plasma etching is not performed in step (2).

[0198] The anode material prepared in this comparative example includes composite particles, which consist of a core and an amorphous carbon coating layer covering the outer surface of the core. The core includes a graphite framework and amorphous carbon filling the graphite framework. The following parameters are specified: average thickness of the amorphous carbon coating layer (referred to as carbon layer thickness); average ID / IG (peak intensity ratio) of 400 points obtained from Raman spectroscopy of the anode material; percentage of scan points with an ID / IG (peak intensity ratio) value > 0.4 (i.e., point content); and compaction density of the anode material containing this material is 1.65 g / cm³. 3 The OI value of the negative electrode, the compaction density of the negative electrode material under 2 tons of pressure, the interlayer spacing d002 of the X-ray diffraction pattern of the negative electrode material, the true density and pore volume of the negative electrode material are all shown in Table 1.

[0199] The thermogravimetric (DTG) curves of the anode material prepared in this comparative example under air atmosphere are shown, with the first peak of the DTG weight loss rate at 560℃.

[0200] Comparative Example 4

[0201] The preparation method of the negative electrode material provided in this comparative example is basically the same as that in Example 2. The difference is that the microwave pyrolysis temperature is 1000℃, the pyrolysis time is 5h, and the heating rate is 120℃ / min in step (2).

[0202] The anode material prepared in this comparative example includes composite particles, which consist of a core and an amorphous carbon coating layer covering the outer surface of the core. The core includes a graphite skeleton and amorphous carbon filling the graphite skeleton. The average thickness of the amorphous carbon coating layer (referred to as carbon layer thickness), the average ID / IG (peak intensity ratio) of 400 points scanned by a Raman spectrometer on the anode material, the percentage of scan points with an ID / IG (peak intensity ratio) value > 0.4 (i.e., point content), the OI value of the anode electrode containing this anode material with a compaction density of 1.65 g / cm³, the compaction density of the anode material under 2 tons of pressure, the interlayer spacing d002 of the X-ray diffraction pattern of the anode material, and the performance test results of the true density and pore volume of the anode material are all shown in Table 1.

[0203] The thermogravimetric (DTG) curves of the anode material prepared in this comparative example under air atmosphere show that the first peak of the DTG weight loss rate is at 525℃, meaning there are no peaks or troughs within the temperature range of 530℃ to 550℃. In this invention, the performance of the anode material was tested according to the following method:

[0204] Particle size testing: Particle size is tested using a laser particle size analyzer, such as the Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0205] Compacted density test: The pressure method is adopted, which is basically the same as the powder compacted density test method recorded in "GBT 24533-2009 Graphite Anode Materials for Lithium-ion Batteries". The only difference is that the test pressure in this invention is 2 tons.

[0206] Scanning electron microscopy (SEM) testing: 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.

[0207] Carbon coating thickness testing: The material was cross-sectioned using FIB-SEM equipment. A 20,000x scanning electron microscope image was taken of any area of ​​the sample cross-section. For each particle in the 20,000x image, a center was selected, and a vertical crosshair was randomly drawn at the 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.

[0208] Raman ID / IG testing: Peak intensity of the material's D peak (1350 cm⁻¹) was measured using a Renishaw microconfocal Raman spectrometer. -1 The boundary vibration modes near the disorder-induced hexagonal Brillouin zone (used for defect characterization) and the peak intensity of the G peak (1580 cm⁻¹) are shown. -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.

[0209] Pore ​​volume testing: The pore volume of the material was determined using the static BET adsorption method with a specific surface area and pore size analyzer.

[0210] True density test: After the sample is immersed in liquid and the air is degassed, its density at 30°C is tested using the specific gravity bottle method.

[0211] Interlayer spacing d002 test: 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. Silicon is used as an internal standard, added to graphite, mixed thoroughly, and then XRD is performed to calculate d002.

[0212] OI value testing of the negative electrode: In the OI value testing of the negative electrode, X-ray diffraction analysis can be performed according to standard JISK 0131-1996 using an X-ray diffractometer (e.g., a Bruker D8 Discover X-ray diffractometer). In the X-ray diffraction analysis, a copper target can be used as the anode target, and a 0.02 mm thick Ni filter can be used to filter CuKβ rays. CuKα rays are used as the radiation source, with the ray wavelength (the weighted average of Kα1 and Kα2) and a scanning 2θ angle range of 20°–80°, at a scanning rate of 4° / min. Specifically, in this application, the OI value testing method for the negative electrode is as follows: The prepared electrode with a compacted density of 1.65 g / cm³... 3The negative electrode sheet was placed directly in an X-ray diffractometer. The peak area of ​​the 004 crystal plane diffraction peak and the peak area of ​​the 110 crystal plane diffraction peak of the negative electrode active material were obtained by X-ray diffraction analysis. The OI value of the negative electrode sheet was C004 / C110.

[0213] TG test: Weigh 5 mg and place it in the sample chamber, introduce air at a flow rate of 50 ml / min, program the temperature rise rate to 5℃ / min, and heat to 800℃. Perform first derivative processing on the thermogravimetric curve (TG) (first derivative of mass content percentage with respect to temperature) to obtain the differential thermogravimetric curve (DTG).

[0214] Table 1 Performance test results of the anode material

[0215]

[0216] Furthermore, the negative electrode materials obtained in each embodiment and comparative example were respectively mixed with CMC, SP, and SBR in a pure aqueous solution at a mass ratio of 95:2:1:2 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, wherein the volume ratio of EC, DMC, and EMC was 1:1:1, and 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.

[0217] The battery performance tests included: 1) initial reversible capacity at 25℃ and 0.05C; 2) initial coulombic efficiency at 25℃ and 0.05C; 3) expansion rate of the graphite electrode after disassembly and testing at 25℃ and 1C for 50 cycles; 4) using a half-cell with lithium sheet as the negative electrode and graphite as the positive electrode, discharging at 25℃ and 3C, and plotting the second derivative curve of DV / DQ, with the inflection point of the curve slope indicating the state of charge (SOC) for lithium plating; the 3C lithium plating performance of the negative electrode material is approximately positively correlated with the rate performance, and better 3C lithium plating performance usually results in better rate performance; 5) capacity retention after 300 cycles at 45℃ and 1C. The battery performance test results are shown in Table 2.

[0218] Table 2 Battery performance test results

[0219]

[0220] Depend on Figure 5 , Figure 6 As can be seen from Tables 1 and 2, in Comparative Example 1, due to the simple heating and mixing coating, most of the asphalt is coated on the surface of the particles, which is not good for filling the particles and is not conducive to reducing the expansion rate of the material and improving the ratio performance of the material.

[0221] Comparative Example 2 was filled and coated by heating and stirring under vacuum, which improved the filling effect inside the particles, improved the rate performance of the material and reduced the expansion rate. The rate performance and expansion rate of the material in Comparative Example 2 were improved, but the improvement was not significant. In particular, the crystallinity of the graphite-like crystals with amorphous carbon layer on the surface after carbonization was still very good, with small D002, small ID / IG, and large OI value of the electrode, which was not conducive to improving the rate performance of the material. The expansion rate was still high at high magnification.

[0222] Comparative Example 3 did not undergo plasma etching, and the improvement in the rate performance of the material was not significant. Although microwave pyrolysis can refine the microcrystals of amorphous carbon-based graphite, the microcrystal defects are still insufficient, resulting in a lack of significant improvement in the rate performance and a decrease in the expansion rate of the material.

[0223] Compared to Comparative Example 2, Embodiment 2 of the present invention also uses a vacuum heating and stirring method to fill a large amount of organic carbon source into the interior of the particles and coat the surface of the particles, thereby filling the internal pores of the particles as much as possible (e.g., Figure 1 As shown, the pores inside the carbonized particles are basically gone, which to some extent improves the poor rate performance and reduces the expansion rate of the material. However, the amorphous carbon on the surface of the carbonized particles has good crystallinity, which is not conducive to the insertion and diffusion of lithium ions, and has an adverse effect on the rate performance and expansion rate of the material. Therefore, Example 2 of this invention further incorporates microwave pyrolysis + plasma etching treatment based on Comparative Example 2. This method first reduces the crystal size of amorphous carbon-based graphite microcrystals inside and outside the graphite particles, making the microcrystals finer. Secondly, it further modifies the defect sites of the amorphous carbon-based graphite microcrystals in the surface coating layer, giving the material surface more active sites. While reducing the thickness of the amorphous carbon coating layer, it increases the D002 and ID / IG of the amorphous carbon, lowers the oxidation and ablation temperature of the amorphous carbon on the graphite surface (the first peak of DTG shifts forward), reduces the OI value of the electrode, and improves the electrode orientation. This has a significant effect on improving the rate performance and reducing the expansion rate of the material, as shown in Tables 1 and 2 of Example 2. As a natural graphite carbide lithium battery anode material, the material not only has a low expansion rate and good rate performance, but also a high compaction density. In addition, it also has high capacity and first-time efficiency.

[0224] Furthermore, in Comparative Example 4, the average ID / IG ratio exceeded 0.5, and the content of sites with an ID / IG ratio greater than 0.4 exceeded 90%. This high content of sites and excessively high average value led to poorer cycle performance. The excessive disorder in the material resulted in too many active sites, exacerbating the side reactions between the amorphous carbon on the surface and the electrolyte. This resulted in very low initial coulombic efficiency and poor cycle performance, negatively impacting practical applications.

[0225] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can 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, without departing from the spirit and scope of the present invention; and these 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 the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A negative electrode material, characterized in that, The composite particles include a core and an amorphous carbon coating layer covering the outer surface of the core. The core includes a graphite skeleton and amorphous carbon filling the graphite skeleton. The average thickness of the amorphous carbon coating layer is 15~45 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 0.40~0.50, and the number of scanning points with an ID / IG value > 0.4 accounted for more than 70%. Thermogravimetric analysis (TGA) of the negative electrode material was performed in an air atmosphere, and the TGA differential curve of the negative electrode material showed peaks and valleys in the temperature range of 530℃ to 550℃.

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 average thickness of the amorphous carbon coating layer is 15~35 nm; (2) The number of scan points with a single-point value of ID / IG greater than 0.4 in the Raman spectrum of the negative electrode material accounts for 71% to 90%.

3. The negative electrode material according to claim 1, characterized in that, It includes at least one of the following features (1) to (12): (1) the negative electrode material has a compaction density under 2 tons of pressure > 1.63 g / cm 3 ; (2) The interlayer spacing d002 of the X-ray diffraction pattern of the negative electrode material is 0.3360~0.3365 nm; (3) The true density of the negative electrode material is 2.140~2.180 g / cm³. 3 ; (4) The pore volume of the negative electrode material is <0.005 cm³. 3 / g; (5) The compaction density of the negative electrode material is 1.65 g / cm³. 3 The OI value of the negative electrode is 3.0~10.0; (6) The negative electrode sheet containing the negative electrode material has an expansion rate of <25% after 50 cycles at 25°C and 1C. (7) The 3C lithium plating performance of the battery containing the negative electrode material is >45%; (8) The 0.05C initial coulombic efficiency of the battery containing the negative electrode material is >93.7%; (9) The 0.05C first reversible capacity of the battery containing the negative electrode material is >360mAh / g; (10) The graphite skeleton includes natural graphite; (11) The carbon content of the graphite skeleton is >99.9 wt.%; (12) The pore volume of the graphite skeleton is 0.02~0.05 cm³. 3 / g.

4. The method for preparing the negative electrode material according to any one of claims 1 to 3, characterized in that, Includes the following steps: The mixture of graphite skeleton and organic carbon source is heat-treated under negative pressure to obtain the first material; The first material is subjected to microwave pyrolysis and plasma etching to obtain the second material; The second material is carbonized to obtain the negative electrode material.

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

6. The method for preparing the negative electrode material according to claim 4, characterized in that, It includes at least one of the following features (1) to (6): (1) The heating rate of the microwave pyrolysis is 40~80℃ / min; (2) The temperature of the microwave pyrolysis is 700~900℃, and the time of the microwave pyrolysis is 1~3h; (3) The plasma etching is performed using a plasma cleaner; the output power of the plasma etching is 700~1000W, the processing speed is 1~5m / min, and the temperature is 20~30℃. (4) The second material comprises a graphite core and an amorphous carbon layer; wherein the average thickness of the amorphous carbon layer is 200~400 nm; the average ID / IG value of 400 surface scan points of the Raman spectrum of the second material is 0.60~1.00; the powder compaction density of the second material under 2 tons of pressure is >1.5 g / cm³. 3 The interlayer spacing d002 of the X-ray diffraction pattern of the second material is 0.336894~0.337679 nm. (5) The carbonization temperature is 1500~1800℃, and the carbonization time is 6~12h; (6) The carbonization is carried out in an inert atmosphere.

7. A negative electrode sheet, characterized in that, Includes the negative electrode material as described in any one of claims 1 to 3, or the negative electrode material prepared by the method described in any one of claims 4 to 6.

8. A battery, characterized in that, Includes the negative electrode sheet as described in claim 7.

9. An electrical appliance, characterized in that, Includes the battery as described in claim 8.

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