Negative electrode material and preparation method therefor, negative electrode sheet, battery and electric device

Abstract

The present disclosure relates to the technical field of negative electrode materials of a secondary battery, and particularly relates to a negative electrode material and a preparation method therefor, a negative electrode sheet, a battery and an electric device. The negative electrode material comprises composite particles, and the composite particles comprise an inner core and an amorphous carbon coating layer coating the outer surface of the inner core, wherein the inner core comprises a graphite skeleton and amorphous carbon filled in the graphite skeleton; and the average thickness of the amorphous carbon coating layer is 15-45 nm. The negative electrode material is subjected to Raman spectrum surface scanning, wherein the number of Raman spectrum surface scanning points is 400. The average value of ID / IG of the Raman spectrum of the negative electrode material is 0.40-0.50, wherein the number of the scanning points having an ID / IG single point value greater than 0.4 is greater than 70%. The negative electrode material has a low expansion rate and good rate capability.

Description

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

[0001] Cross-reference to Related Applications

[0002] The present application claims priority to the Chinese patent application No. 2024108928182, filed on July 4, 2024, and entitled "A negative electrode material, a preparation method thereof, a negative electrode sheet, a battery, and a power utilization device", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0003] The present disclosure relates to the technical field of secondary battery negative electrode materials, in particular, to a negative electrode material, a preparation method thereof, a negative electrode sheet, a battery, and a power utilization device. BACKGROUND

[0004] Lithium ion batteries, as a new type of rechargeable battery, have the advantages of high working voltage, large specific capacity, flat discharge potential curve, small self-discharge, long cycle life, good low-temperature performance, environmental protection, no pollution, and no memory effect, and are widely used in 3C products, power devices, and energy storage equipment fields. Especially with the rapid development of new energy vehicles, consumers have increasingly high requirements for the charging time and range of electric vehicles. Fast-charging lithium ion batteries have become the core competitiveness of power battery enterprises in future market competition. As a major component of power batteries, the negative electrode material has a great influence on the development of fast-charging technology, and the development of low-swelling and high-rate negative electrode materials is becoming a trend in the negative electrode material market. When natural graphite is used as a negative electrode material, the interlayer spacing is small, the rate performance is poor, the swelling rate is high during high-rate charging and discharging, and the stress is not uniformly released during the swelling process due to the many internal pores, resulting in a large increase in the thickness of the SEI film during the cycle process, which further increases the material swelling rate.

[0005] CN111320171B patent document discloses a low-swelling graphite negative electrode material, a preparation method thereof, and a lithium ion battery. First, graphite, a modifier, and a water-soluble salt pore-forming agent are mixed, and the mixed sample is subjected to low-temperature heating treatment. The modifier and the pore-forming agent are filled in the internal pores of the particles and coated on the surface of the particles. Then, the sample after low-temperature heating is subjected to high-temperature heating treatment. Finally, the sample after high-temperature heating treatment is subjected to water washing, drying, scattering, and screening treatment. CN114873591A patent document discloses a low-temperature long-life natural graphite negative electrode material, a preparation method thereof, and an application. First, the air is evacuated by vacuumizing, and then the solvent-diluted low-temperature pitch is filled in the internal pores of the natural graphite and coated on the surface of the particles by high temperature and high pressure. Then, the low-temperature pitch is converted into mesophase pitch by pressure polymerization reaction. Then, the mesophase pitch is compacted with the internal crimped graphite layers of the natural graphite by isostatic pressing, so that there is no gap in the natural graphite. Finally, the block is scattered and carbonized.

[0006] CN116730333A patent document discloses a preparation method of a modified natural graphite negative electrode material. The modifier is filled into the internal pores of the natural graphite and coated on the surface of the particles by one-time pressurized impregnation, then the excessive modifier coated on the surface of the natural graphite is cleaned with an organic cleaning agent, the precursor after cleaning is separated from the cleaning agent, and finally the precursor is carbonized.

[0007] The present disclosure applicant found after in-depth research that:

[0008] The natural graphite negative electrode material prepared by the method disclosed in CN111320171B has poor internal filling effect after high temperature treatment, and the expansion rate is not obviously reduced. The surface-coated carbon is amorphous carbon or artificial graphite with good crystallinity, and the material's rate performance is not obviously improved.

[0009] The method disclosed in CN114873591A needs to use a high-temperature and high-pressure reaction kettle and an isostatic pressing machine, which has large equipment investment, complex process and danger. The mesophase pitch formed by low-temperature pitch conversion is amorphous carbon with good crystallinity after carbonization, which is not conducive to the improvement of the material's rate performance, resulting in high expansion rate at high rate.

[0010] The method disclosed in CN116730333A uses a large amount of toxic and harmful organic cleaning agent, which can cause harm to the environment and operating personnel, and does not conform to the green development concept of new energy.

[0011] Therefore, it is of great significance to provide a negative electrode material with low expansion and high rate.

[0012] Therefore, the present disclosure is proposed.

[0013] Application content

[0014] The first object of the present disclosure is to provide a negative electrode material with low expansion rate and good rate performance.

[0015] The second object of the present disclosure is to provide a preparation method of a negative electrode material. The air in the internal pores of the graphite framework is first discharged under vacuum, the organic carbon source is then filled into the internal pores of the graphite framework particles and coated on the surface by high-temperature vacuum, and then the amorphous carbon graphite crystal structure inside and outside the graphite framework is modified by microwave pyrolysis + plasma etching method, which can improve the path of lithium ion embedding into the graphite particles, reduce the expansion rate of the obtained negative electrode material, and improve its rate performance. Finally, high-temperature carbonization further dehydrogenates, which can improve the high-temperature cycle performance of the negative electrode material.

[0016] The third object of the present disclosure is to provide a negative electrode sheet with low expansion rate, high compaction density, high rate performance, good high-temperature cycle performance and other advantages.

[0017] A fourth object of the present disclosure is to provide a battery which not only has a low expansion rate and high rate capability, but also has excellent cycle performance.

[0018] A fifth object of the present disclosure is to provide an electric device.

[0019] In order to achieve the above objects of the present disclosure, the following technical solutions are adopted:

[0020] The present disclosure first provides a negative electrode material, comprising a composite particle, the composite particle comprising an inner core and an amorphous carbon coating layer coated on the outer surface of the inner core, the inner core comprising a graphite framework and amorphous carbon filled in the graphite framework.

[0021] The average thickness of the amorphous carbon coating layer is 15-45 nm.

[0022] The negative electrode material is subjected to Raman spectrum area scanning, the Raman spectrum area scanning points are 400, the average value of ID / IG of the Raman spectrum of the negative electrode material is 0.40-0.50, and the number of scanning points with a single-point value of ID / IG greater than 0.4 accounts for more than 70%.

[0023] Further, the average thickness of the amorphous carbon coating layer is 15-35 nm.

[0024] Further, the number of scanning points with a single-point value of ID / IG of the Raman spectrum of the negative electrode material greater than 0.4 accounts for 71%-90%.

[0025] Further, the negative electrode material is subjected to thermogravimetric testing in an air atmosphere, and the thermogravimetric differential curve of the negative electrode material has a peak valley in the temperature range of 530-550℃.

[0026] Further, the tap density of the negative electrode material under a pressure of 2 tons is greater than 1.63 g / cm 3 .

[0027] Further, the interlayer spacing d002 of the X-ray diffraction pattern of the negative electrode material is 0.3360-0.3365 nm.

[0028] Further, the true density of the negative electrode material is 2.140-2.180 g / cm 3 .

[0029] Further, the pore volume of the negative electrode material is less than 0.005 cm 3 / g.

[0030] Further, the tap density of the negative electrode material containing the negative electrode material is 1.65 g / cm 3The OI value of the negative electrode sheet is 3.0-10.0.

[0031] Further, the negative electrode sheet containing the negative electrode material has a sheet expansion rate < 25% after 50 cycles at 25°C and 1C.

[0032] Further, the 3C lithium precipitation performance of the battery containing the negative electrode material is > 45%.

[0033] Further, the 0.05C initial coulombic efficiency of the battery containing the negative electrode material is > 93.7%.

[0034] Further, the 0.05C initial reversible capacity of the battery containing the negative electrode material is > 360 mAh / g.

[0035] Further, the graphite framework comprises natural graphite.

[0036] Further, the carbon content of the graphite framework is > 99.9 wt.%.

[0037] Further, the pore volume of the graphite framework is 0.02-0.05 cm 3 / g.

[0038] The present disclosure further provides a preparation method of a negative electrode material, comprising the following steps:

[0039] heat-treating the mixture of the graphite framework and the organic carbon source under negative pressure to obtain a first material;

[0040] microwave pyrolyzing and plasma etching the first material to obtain a second material;

[0041] carbonizing the second material to obtain the negative electrode material.

[0042] Further, the graphite framework comprises natural graphite.

[0043] Further, the carbon content of the graphite framework is > 99.9 wt.%.

[0044] Further, the particle size Dv50 of the graphite framework is 5-25 μm.

[0045] Further, the pore volume of the graphite framework is 0.02-0.05 cm 3 / g.

[0046] Further, the organic carbon source comprises at least one of petroleum pitch, coal pitch and resin.

[0047] Further, the coking value of the organic carbon source is > 70%.

[0048] Further, the mass ratio of the graphite framework and the organic carbon source is 75:25-90:10.

[0049] Further, the vacuum degree in the heat treatment process is less than 0.05 MPa in absolute pressure.

[0050] Further, the vacuum degree of the environment where the mixture is located before the heat treatment is less than 0.03 MPa in absolute pressure.

[0051] Further, the temperature of the heat treatment is 300-500℃, and the time of the heat treatment is 1-5 h.

[0052] Further, the mixture is stirred at a rotating speed of 100-300 r / min during the heat treatment.

[0053] Further, the temperature rising rate of the microwave pyrolysis is 40-80℃ / min.

[0054] Further, the temperature of the microwave pyrolysis is 700-900℃, and the time of the microwave pyrolysis is 1-3 h.

[0055] Further, the plasma etching is performed by using a plasma cleaning machine; the output power of the plasma etching is 700-1000 W, the processing speed is 1-5 m / min, and the temperature is 20-30℃.

[0056] Further, the second material comprises a graphite core and an amorphous carbon layer; the average thickness of the amorphous carbon layer is 200-400 nm; the average value of ID / IG of the Raman spectrum of the second material is 0.60-1.00 at a point of 400 in area scanning; the powder compaction density of the second material under a pressure of 2 tons is >1.5 g / cm 3 ; the interlayer spacing d002 of the X-ray diffraction pattern of the second material is 0.336894-0.337679 nm.

[0057] Further, the temperature of the carbonization is 1500-1800℃, and the time of the carbonization is 6-12 h.

[0058] Further, the carbonization is performed in an inert atmosphere.

[0059] The present disclosure further provides a negative electrode tab comprising the negative electrode material or the negative electrode material prepared by the preparation method.

[0060] The present disclosure further provides a battery comprising the negative electrode tab.

[0061] The present disclosure further provides an electric device comprising the battery. BRIEF DESCRIPTION OF DRAWINGS

[0062] In order to more clearly illustrate the technical solutions in the specific embodiments of the present disclosure or the prior art, the drawings required to be used in the specific embodiments or prior art description will be briefly introduced as follows. Obviously, the drawings in the following description are some embodiments of the present disclosure, and other drawings can be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0063] FIG. 1 is a CP-SEM image of the negative electrode material prepared in Example 2 provided by the present disclosure at a magnification of 1000 times;

[0064] FIG. 2 is a CP-SEM image of the negative electrode material prepared in Example 2 provided by the present disclosure at a magnification of 50000 times;

[0065] FIG. 3 is an ID / IG distribution diagram of the negative electrode material prepared in Example 2 provided by the present disclosure;

[0066] FIG. 4 is a thermogravimetric DTG curve diagram of the negative electrode material prepared in Example 2 provided by the present disclosure;

[0067] FIG. 5 is a CP-SEM image of the negative electrode material prepared in Comparative Example 1 provided by the present disclosure;

[0068] FIG. 6 is an ID / IG distribution diagram of the negative electrode material prepared in Comparative Example 1 provided by the present disclosure;

[0069] FIG. 7 is a thermogravimetric DTG curve diagram of the negative electrode material prepared in Comparative Example 1 provided by the present disclosure. DETAILED DESCRIPTION

[0070] The technical solutions of the present disclosure will be described clearly and completely in combination with the drawings and specific embodiments, but those skilled in the art will understand that the following described embodiments are part of the embodiments of the present disclosure, not all the embodiments, and are only used to illustrate the present disclosure, and should not be regarded as limiting the scope of the present disclosure. Based on the embodiments in the present disclosure, all other embodiments obtained by those skilled in the art without any creative effort are within the scope of protection of the present disclosure. The specific conditions are not specified in the embodiments, and the conventional conditions or the conditions recommended by the manufacturer are used. The reagents or instruments used are not specified by the manufacturer, and are conventional products that can be purchased on the market.

[0071] If there is no special indication, in the present disclosure, "first aspect", "second aspect", "third aspect", "fourth aspect" and the like are only for the purpose of description, and cannot be understood as indicating or implying relative importance or quantity, nor can it be understood as implying the importance or quantity of the indicated technical features. Moreover, "first", "second", "third", "fourth" and the like only serve the purpose of non-exhaustive enumeration description, and should be understood as not constituting a closed limitation on the quantity.

[0072] If there is no special indication, the "includes" and "contains" mentioned in the present disclosure represent an open type, and can also be a closed type. For example, the "includes" and "contains" can mean that other components not listed can also be included or contained, or only the listed components can be included or contained.

[0073] If there is no special indication, in the present disclosure, "one or more" or "at least one" means any one, any two or any two or more of the listed items. Among them, "several" means any two or more.

[0074] In a first aspect, the present disclosure provides a low-expansion natural graphite negative electrode material, comprising a composite particle, the composite particle comprising a core and an amorphous carbon coating layer coated on the outer surface of the core.

[0075] Among them, the core comprises a graphite framework and amorphous carbon filled in the graphite framework.

[0076] The average thickness of the amorphous carbon coating layer is 15-45 nm, including but not limited to any one of 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm or a range value between any two of them.

[0077] The amorphous carbon coating layer provided by the present disclosure has the above suitable thickness, which is beneficial to improve the specific capacity of the negative electrode material and improve the compaction density of the negative electrode material.

[0078] The negative electrode material is subjected to Raman spectrum area scanning, the Raman spectrum area scanning points are 400, and the average value of the ID / IG (peak intensity ratio) of the Raman spectrum of the negative electrode material is 0.40-0.50, 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, 0.50 or a range value between any two of them.

[0079] Among them, the number of scanning points with a single-point value of ID / IG > 0.4 accounts for more than 70%, including but not limited to any one of 70%, 71%, 75%, 77%, 80%, 82%, 85%, 88%, 90%, 93%, 95% and the like or a range value between any two of them.

[0080] The negative electrode material provided by the present disclosure has graphite crystal micro-particles in the graphite framework and on the outer surface of the graphite framework, and the amorphous carbon on the surface has point defects (loss of single atoms of carbon layers), line defects (micro-deformation and misplacement of surface crystals), and surface defects (cracks at the grain boundaries of the crystals, expanding the surface defects of the crystals), which improves the rate performance of the negative electrode material and reduces the expansion rate.

[0081] The ID / IG reflects the disorder degree of the amorphous carbon graphite microcrystals on the surface of the material. The greater the disorder degree, the more active sites on the surface of the material, which is more conducive to the embedding of lithium ions, and is beneficial to improving the rate performance and reducing the expansion rate. The average value of ID / IG of the material of the present disclosure increases due to the increase of the defect sites.

[0082] An average value of ID / IG greater than 0.4 is beneficial to improving the rate performance of the negative electrode material and reducing the expansion rate.

[0083] In addition, the present disclosure can also take into account the cycle performance by controlling the average value of ID / IG of the Raman spectrum of the negative electrode material to be 0.40-0.50, and the number of scanning points with a single-point value of ID / IG greater than 0.4 accounting for greater than 70%.

[0084] In some specific embodiments, the average thickness of the amorphous carbon coating layer is 15-35 nm, including but not limited to any one of 15 nm, 17 nm, 18 nm, 20 nm, 23 nm, 25 nm, 28 nm, 30 nm, 32 nm, 35 nm, or a range value between any two of them.

[0085] In some specific embodiments, the number of scanning points with a single-point value of ID / IG greater than 0.4 accounts for 71%-90% of the Raman spectrum of the negative electrode material, including but not limited to any one of 71%, 72%, 73%, 74%, 75%, 78%, 80%, 82%, 83%, 85%, 88%, 90%, or a range value between any two of them.

[0086] The average value of ID / IG should not exceed 0.5, and the point content of ID / IG greater than 0.4 should not exceed 90%. Too much point content or too high average value will cause the cycle performance of the material to deteriorate. Because the disorder degree of the material is too large, the active sites are too many, which will intensify the side reaction of the surface amorphous carbon and the electrolyte, resulting in very low first coulomb efficiency and poor cycle performance of the material, which is not conducive to practical application.

[0087] In some specific embodiments, the thermogravimetric test of the negative electrode material is carried out in an air atmosphere, and the thermogravimetric differential curve (DTG curve) of the negative electrode material has a peak valley in a temperature range of 530-550°C (including but not limited to any one of 530°C, 535°C, 540°C, 545°C, 550°C or a range value between any two of them).

[0088] Due to the increase of defect sites of the material, the first peak of the thermogravimetric DTG curve of the negative electrode material under air atmosphere is shifted forward (the reaction of amorphous carbon and oxygen molecules becomes easier).

[0089] In some specific embodiments, the compaction density of the negative electrode material under a pressure of 2 tons is >1.63 g / cm 3 ; including but not limited to any one of 1.64 g / cm 3 , 1.65 g / cm 3 , 1.66 g / cm 3 , 1.67 g / cm 3 , 1.68 g / cm 3 , 1.69 g / cm 3 , 1.70 g / cm 3 , 1.71 g / cm 3 , 1.72 g / cm 3 , 1.73 g / cm 3 , 1.74 g / cm 3 , 1.75 g / cm 3 , 1.76 g / cm 3 , 1.78 g / cm 3 , 1.80 g / cm 3 or a range value between any two of them.

[0090] It can be seen that the compaction density of the negative electrode material provided by the present disclosure is high.

[0091] In some specific embodiments, the interlayer spacing d002 of the X-ray diffraction (XRD) spectrum of the negative electrode material is 0.3360-0.3365 nm; including but not limited to 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, 0.336500 nm or a range value between any two of them.

[0092] As the defect sites of the material increase, the interlayer spacing d002 of the negative electrode material increases.

[0093] In some specific embodiments, the true density of the negative electrode material is 2.140-2.180 g / cm 3 ; including but not limited to any one of the point values of 2.140 g / cm 3 , 2.150 g / cm 3 , 2.160 g / cm 3 , 2.170 g / cm 3 , 2.180 g / cm 3 or a range value between any two of them.

[0094] The negative electrode material provided by the present disclosure has a suitable true density, which can improve the energy density and specific capacity of the battery made therefrom.

[0095] In some specific embodiments, the pore volume of the negative electrode material is <0.005 cm 3 / g; including but not limited to any one of the point values of 0.0040 cm 3 / g, 0.0030 cm 3 / g, 0.0025 cm 3 / g, 0.0023 cm 3 / g, 0.0021 cm 3 / g, 0.0020 cm 3 / g, 0.0018 cm 3 / g, 0.0015 cm 3 / g, 0.0010 cm 3 / g or a range value between any two of them.

[0096] The negative electrode material provided by the present disclosure has a small pore volume, which can reduce the side reaction between the surface of the negative electrode material and the electrolyte, thereby improving the cycle performance of the battery.

[0097] In some specific embodiments, the OI value of the negative electrode sheet containing the negative electrode material with a compacted density of 1.65 g / cm 3 is 3.0-10.0; including but not limited to any one of the point values of 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0 or a range value between any two of them.

[0098] The present disclosure can increase the lithium ion insertion path and reduce the lithium ion insertion energy barrier by reducing the sheet OI value of the material, thereby making the negative electrode material have the advantage of low expansion rate at high rate.

[0099] In some specific embodiments, the negative electrode sheet containing the negative electrode material has a sheet expansion rate < 25% after 50 cycles at 25°C, 1C; including but not limited to any one of 24%, 23%, 22%, 21%, 20%, 19%, 18%, 17%, 16%, 15% or a range value between any two of them.

[0100] It can be seen that the negative electrode material provided by the present disclosure has a low expansion rate.

[0101] In some specific embodiments, the battery containing the negative electrode material has a 3C lithium precipitation performance > 45%; including but not limited to any one of 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 58%, 60% or a range value between any two of them.

[0102] The 3C lithium precipitation performance of the negative electrode material is approximately positively correlated with the rate performance, and the better the 3C lithium precipitation performance, the better the rate performance will generally be. Therefore, the battery assembled by the negative electrode material provided by the present disclosure has excellent rate performance.

[0103] The battery assembled by the negative electrode material provided by the present disclosure also has the advantages of high first coulomb efficiency and high first reversible capacity.

[0104] In some specific embodiments, the battery containing the negative electrode material has a 0.05C first coulomb efficiency (first efficiency for short) > 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 a range value between any two of them.

[0105] In some specific embodiments, the battery containing the negative electrode material has a 0.05C first reversible capacity > 360 mAh / g; including but not limited to any one of 361 mAh / g, 362 mAh / g, 363 mAh / g, 364 mAh / g, 365 mAh / g, 366 mAh / g, 368 mAh / g, 370 mAh / g or a range value between any two of them.

[0106] In some specific embodiments, the graphite framework includes natural graphite. In other embodiments, the graphite framework can also be artificial graphite. Further, the graphite framework includes natural graphite, because natural graphite has defects such as small interlayer spacing, poor rate performance, high expansion rate at large rate charge and discharge, and many internal pores, which adversely affect its large-scale application, but after modification by the present disclosure, it can be used as a high-performance negative electrode material.

[0107] In some embodiments, the graphite framework has a carbon content of >99.9 wt.%. This can ensure the gravimetric capacity of the obtained negative electrode material and avoid the occurrence of side reactions.

[0108] In some embodiments, the graphite framework has a pore volume of 0.02-0.05 cm 3 / g, including but not limited to 0.02 cm 3 / g, 0.025 cm 3 / g, 0.03 cm 3 / g, 0.035 cm 3 / g, 0.04 cm 3 / g, 0.045 cm 3 / g, 0.05 cm 3 / g, or a range value between any two of the above.

[0109] The graphite framework of the present disclosure has a suitable pore volume, which can endow the final negative electrode material with excellent comprehensive performance. If the pore volume is too high, too much amorphous carbon needs to be filled, which can result in low tap density and low gravimetric capacity of the negative electrode material. If the pore volume is too small or there is basically no pore (i.e., the graphite framework is basically a solid sphere or a sheet), the amorphous carbon cannot be filled into the graphite framework, which can result in slow diffusion of lithium ions in the particle interior during lithium extraction, which is not conducive to the improvement of the rate performance.

[0110] In a second aspect, the present disclosure provides a method for preparing a negative electrode material, comprising the following steps:

[0111] The mixture of the graphite framework and the organic carbon source is subjected to heat treatment under negative pressure, and the first material is obtained after cooling.

[0112] The first material is subjected to microwave pyrolysis and plasma etching in sequence to obtain a second material.

[0113] The second material is subjected to carbonization, and the negative electrode material is obtained after cooling.

[0114] The present disclosure fills a large amount of organic carbon source into the interior of the graphite framework and coats the surface of the graphite framework by high-temperature vacuum, and then rapidly microwave pyrolyzes, utilizes the characteristics of rapid temperature rise, and makes the graphite framework inside and the amorphous carbon coating layer outside the graphite framework microparticulate (grain size becomes smaller, interlayer spacing becomes larger), which can improve the diffusion and embedding channel of lithium ions inside and on the surface of the particles, improve the rate performance of the negative electrode material, and reduce the expansion rate of the negative electrode material. Then, the defect sites of the amorphous carbon coating layer on the surface of the graphite framework are modified by plasma etching technology, so that more point defects (loss of single atoms in the carbon layer), line defects (micro-deformation and misplacement of surface crystals), and surface defects (cracks at the grain boundaries of the crystal, which enlarge the surface defects of the crystal) of the amorphous carbon microcrystal on the surface are generated, so that the surface of the amorphous carbon has more active sites, reduces the embedding energy barrier of lithium ions on the surface of the material, improves the electrochemical reaction rate of the interface, further improves the rate performance of the negative electrode material, and reduces the expansion rate of the negative electrode material. Further, high-temperature carbonization further dehydrogenates, which can improve the high-temperature cycle performance of the negative electrode material and prevent the high-temperature performance of the material from decreasing too obviously.

[0115] The present disclosure adopts the microwave pyrolysis + plasma etching method to modify the graphite-like crystal structure of the amorphous carbon of the material, improve the ID / IG of the negative electrode material, reduce the OI value of the negative electrode material, increase the embedding path of lithium ions, reduce the embedding energy barrier of lithium ions, and finally make the material have the characteristics of low expansion rate at a large rate.

[0116] Specifically, the microwave pyrolysis + plasma etching method can make the graphite-like microcrystal layers of the amorphous carbon on the surface of the graphite framework powder particles peel off in a certain direction, make the crystal produce line defects, and the plasma will also impact the surface carbon atoms to cause the loss of local carbon atoms and produce point defects; at the same time, cracks will also be generated at the grain boundaries of the crystal, which enlarge the surface defects of the crystal and improve the orientation of the crystal. The point defects (loss of single atoms in the carbon layer), line defects (micro-deformation and misplacement of surface crystals), and surface defects (cracks at the grain boundaries of the crystal, which enlarge the surface defects of the crystal) of the crystal can reduce the embedding energy barrier of lithium ions on the surface of the material, improve the electrochemical reaction rate of the interface, thereby improving the rate performance of the negative electrode material and reducing the expansion rate.

[0117] According to the characteristics of ID / IG, D002, and DTG peak, the negative electrode material has the above defects. Because the defect sites of the material increase, the D002 and ID / IG of the material increase, and the first peak of DTG under thermogravimetric air atmosphere shifts forward (the reaction between amorphous carbon and oxygen molecules becomes easier).

[0118] In some specific embodiments, the graphite framework includes natural graphite.

[0119] In some embodiments, the graphite framework can also be artificial graphite. Further, the graphite framework comprises natural graphite, because natural graphite has defects such as small interlayer spacing, poor rate performance, high expansion rate at large rate charge and discharge, and many internal pores, which adversely affect its large-scale application. However, after modification of the natural graphite according to the present disclosure, the modified natural graphite can be used as a high-performance negative electrode material.

[0120] In some specific embodiments, the graphite framework has a carbon content of > 99.9 wt.%.

[0121] In some specific embodiments, the graphite framework has a particle size Dv50 of 5-25 μm; including but not limited to any one of the point values of 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, or a range value between any two of them.

[0122] The graphite framework provided by the present disclosure has a suitable particle size, which can ensure subsequent coating, and thus ensure the electrochemical performance of the negative electrode material.

[0123] In some specific embodiments, the graphite framework has a pore volume of 0.02-0.05 cm 3 / g; including but not limited to any one of the point values of 0.02 cm 3 / g, 0.025 cm 3 / g, 0.03 cm 3 / g, 0.035 cm 3 / g, 0.04 cm 3 / g, 0.045 cm 3 / g, 0.05 cm 3 / g, or a range value between any two of them.

[0124] The graphite framework of the present disclosure has a suitable pore volume, which can enable the final negative electrode material to have excellent comprehensive performance. If the pore volume is too high, too much amorphous carbon needs to be filled, which can result in low tap density and low specific capacity of the negative electrode material. If the pore volume is too small or there is essentially no pore (i.e., essentially a solid sphere or a sheet), the amorphous carbon cannot be filled into the graphite framework, which results in slow diffusion of lithium ions in the particle interior when lithium ions are extracted, which is not conducive to improving the rate performance.

[0125] In some specific embodiments, the organic carbon source comprises at least one of petroleum pitch, coal pitch, and resin, and any two or all of them can also be used.

[0126] In some specific embodiments, the coal pitch comprises coal liquefaction pitch and / or coal tar pitch.

[0127] In some embodiments, the resin comprises a natural resin and / or a synthetic resin, such as a thermoplastic resin, but is not limited thereto.

[0128] In some embodiments, the coking value of the organic carbon source is >70%, including but not limited to any of the point values of 71%, 73%, 75%, 78%, 80% or a range between any two of these values.

[0129] In some embodiments, the mass ratio of the graphite framework to the organic carbon source is 75:25-90:10, including but not limited to any of the point values of 75:25, 78:22, 80:20, 85:15, 90:10 or a range between any two of these values.

[0130] The graphite framework and the organic carbon source described above are used in a suitable mass ratio to ensure that the organic carbon source can enter the pores of the graphite framework and coat the surface with a suitable thickness of the carbon source, i.e., the inner core pores of the final negative electrode material can be filled with a suitable amount of amorphous carbon, and the inner core surface is coated with a suitable amount and thickness of the amorphous carbon coating layer, thereby ensuring low expansion rate, high rate performance, and excellent high-temperature cycle performance of the negative electrode material.

[0131] In some embodiments, the vacuum degree during the heat treatment process is less than 0.05 MPa in absolute pressure, including but not limited to any of the point values of 0.02 MPa, 0.03 MPa, 0.04 MPa, 0.05 MPa or a range between any two of these values.

[0132] In some embodiments, the vacuum degree of the environment in which the mixture is placed before the heat treatment is less than 0.03 MPa in absolute pressure, including but not limited to any of the point values of 0.01 MPa, 0.02 MPa or a range between any two of these values.

[0133] In some embodiments, the temperature of the heat treatment is 300-500°C, including but not limited to any of the point values of 300°C, 350°C, 400°C, 450°C, 500°C or a range between any two of these values; and the time of the heat treatment is 1-5 h, including but not limited to any of the point values of 1 h, 2 h, 3 h, 4 h, 5 h or a range between any two of these values.

[0134] In some embodiments, the mixture is stirred at a rotation speed of 100-300 r / min during the heat treatment, wherein the rotation speed includes but is not limited to any of the point values of 100 r / min, 150 r / min, 200 r / min, 250 r / min, 300 r / min or a range between any two of these values.

[0135] The present disclosure can ensure that the organic carbon source enters the pore structure of the graphite framework better and is uniformly coated on the surface of the graphite framework by using appropriate heat treatment temperature and time and appropriate stirring speed.

[0136] In some specific embodiments, the heat treatment of the mixture of the graphite framework and the organic carbon source under negative pressure specifically comprises: adding the mixture of the graphite framework and the organic carbon source into a reaction kettle, first evacuating the reaction kettle to remove air, then heating and stirring the reaction kettle after the air is removed, maintaining a certain vacuum degree during heating, and cooling to room temperature after heating is completed to obtain a first material.

[0137] In some specific embodiments, the temperature of the microwave pyrolysis is 700-900°C, including but not limited to any one of 700°C, 750°C, 800°C, 850°C, 900°C or a range value between any two of them; the time of the microwave pyrolysis is 1-3h, including but not limited to any one of 1h, 2h, 3h or a range value between any two of them.

[0138] The present disclosure can make the graphite framework inside and the coating layer outside be amorphous carbon graphite crystal microparticles (grain size becomes smaller and interlayer spacing becomes larger) by using the above-mentioned heating rate for rapid microwave pyrolysis, which can improve the diffusion and embedding channels of lithium ions in the graphite framework inside and surface, and further improve the rate performance of the negative electrode material and reduce the expansion rate of the negative electrode material.

[0139] In some specific embodiments, the temperature of the microwave pyrolysis is 700-900°C, including but not limited to any one of 700°C, 750°C, 800°C, 850°C, 900°C or a range value between any two of them; the time of the microwave pyrolysis is 1-3h, including but not limited to any one of 1h, 2h, 3h or a range value between any two of them.

[0140] In some specific embodiments, the plasma etching is performed by using a plasma cleaning machine.

[0141] 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, 1000W or a range value between any two of them; 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, 5m / min or a range value between any two of them; the temperature of the plasma etching is 20-30°C, including but not limited to any one of 20°C, 22°C, 25°C, 28°C, 30°C or a range value between any two of them.

[0142] In some embodiments, the second material includes a graphite core and an amorphous carbon layer.

[0143] In some embodiments, the average thickness of the amorphous carbon layer is 200-400 nm, including but not limited to any one of 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, or a range between any two of them.

[0144] In some embodiments, the average value of ID / IG of the Raman spectrum of the second material is 0.60-1.00 at a point scan of 400 points, including but not limited to any one of 0.60, 0.70, 0.80, 0.90, 1.00, or a range between any two of them.

[0145] In some embodiments, the powder compaction density of the second material under a pressure of 2 tons is >1.5 g / cm 3 , including but not limited to any one of 1.51 g / cm 3 , 1.52 g / cm 3 , 1.53 g / cm 3 , 1.54 g / cm 3 , 1.55 g / cm 3 , 1.56 g / cm 3 , 1.57 g / cm 3 , 1.58 g / cm 3 , 1.59 g / cm 3 , 1.60 g / cm 3 , or a range between any two of them.

[0146] In some embodiments, the interlayer spacing d002 of the X-ray diffraction pattern of the second material is 0.336894-0.337679 nm, including but not limited to any one of 0.336894 nm, 0.337000 nm, 0.337328 nm, 0.337500 nm, 0.337679 nm, or a range between any two of them.

[0147] In some embodiments, the carbonization temperature is 1500-1800℃, including but not limited to any one of 1500℃, 1550℃, 1600℃, 1650℃, 1700℃, 1800℃, or a range between any two of them; and the carbonization time is 6-12 h, including but not limited to any one of 6 h, 7 h, 8 h, 9 h, 10 h, 12 h, or a range between any two of them.

[0148] In some embodiments, the carbonization is performed under an inert atmosphere.

[0149] In some specific embodiments, the inert atmosphere includes a nitrogen atmosphere and / or an argon atmosphere.

[0150] The present disclosure employs appropriate carbonization conditions, which is conducive to further improving the high-temperature cycle performance of the negative electrode material.

[0151] In a third aspect, the present disclosure provides a negative electrode sheet, which comprises the negative electrode material described above or the negative electrode material prepared by the preparation method of the negative electrode material.

[0152] The negative electrode sheet has the advantages of low expansion rate, high compaction density, high rate performance, and good high-temperature cycle performance.

[0153] Further, the negative electrode sheet further comprises a conductive agent and / or a binder, which is not limited by the present disclosure.

[0154] In a fourth aspect, the present disclosure provides a battery comprising the negative electrode sheet described above.

[0155] The battery provided by the present disclosure not only has low expansion rate and high rate performance, but also has excellent cycle performance.

[0156] Further, the battery further comprises a positive electrode sheet, a separator, and an electrolyte, which is not limited by the present disclosure.

[0157] The battery includes a secondary battery, such as a lithium ion battery, but is not limited thereto.

[0158] In a fifth aspect, the present disclosure provides a power consumption device comprising the battery described above.

[0159] The power consumption device includes any device or apparatus comprising the battery described above, such as an electric vehicle, an electric motorcycle, an electric bicycle, an electric tool, a starting power source, an energy storage device, an electronic product, and an office equipment, but is not limited thereto.

[0160] Embodiments of the present disclosure will be described in detail below with reference to examples, but those skilled in the art will understand that the following examples are only used to illustrate the present disclosure and should not be regarded as limiting the scope of the present disclosure. The specific conditions are not specified in the examples, and the conventional conditions or the conditions recommended by the manufacturer are used. The reagents or instruments used are not specified by the manufacturer, and are conventional products that can be obtained by purchase.

[0161] Example 1

[0162] The preparation method of the negative electrode material provided in this example comprises the following steps:

[0163] (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.

[0164] (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.

[0165] (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.

[0166] 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.

[0167] Example 2

[0168] The preparation method of the negative electrode material provided in the embodiment comprises the following steps:

[0169] (1) 1.5 kg of petroleum pitch (coking value 75%) and 8.5 kg of natural graphite (Dv50 = 15 μm, carbon content 99.95 wt.%, pore volume 0.034 cm 3 / g) are added into a mixing device, and the materials are uniformly mixed by high-speed stirring to obtain a precursor. The precursor is placed in a reaction kettle, and the vacuumized reaction kettle is subjected to vacuumizing treatment until the vacuum degree is 0.015 MPa (absolute pressure) and the vacuumizing is stopped. The reaction kettle with qualified vacuum degree is subjected to heating (i.e. heat treatment) and stirring treatment, the temperature is 400 ℃, the rotating speed is 200 r / min, the holding time is 3 h, the vacuum degree is maintained at 0.03 MPa (absolute pressure) during the holding period, and the first material is obtained after the heating is completed and the material is discharged after cooling.

[0170] (2) The first material is subjected to microwave pyrolysis, the microwave pyrolysis temperature is 800 ℃, the pyrolysis time is 2 h, and the temperature rising rate is 60 ℃ / min, and then the plasma etching is performed by using a plasma cleaning machine, the output power is 800 W, the processing speed is 3 m / min, and the temperature is 25 ℃, to obtain a second material. The second material comprises a graphite inner core and an amorphous carbon layer; wherein the average thickness of the amorphous carbon is 300 nm, the average value of 400-point ID / IG (peak intensity ratio) of the Raman spectrometer is 0.82, and the powder compaction density under 2 tons is 1.57 g / cm 3 . The interlayer spacing d002 measured by XRD is 0.337328 nm.

[0171] (3) The second material is subjected to high-temperature carbonization treatment under a nitrogen atmosphere, the carbonization temperature is 1650 ℃, the carbonization time is 9 h, and the natural graphite negative electrode material is obtained after cooling to room temperature.

[0172] The negative electrode material prepared in the embodiment comprises composite particles, the composite particles comprise an inner core and an amorphous carbon coating layer coated on the outer surface of the inner core, and the inner core comprises a graphite framework and amorphous carbon filled in the graphite framework. The average thickness of the amorphous carbon coating layer (referred to as carbon layer thickness), the average value of 400-point ID / IG (peak intensity ratio) of the Raman spectrometer for the negative electrode material, and the number ratio of the scanning points (i.e. point content) with ID / IG (peak intensity ratio) single-point value > 0.4, the compaction density of the negative electrode material is 1.65 g / cm 3The performance test results of the negative electrode sheet OI value of the negative electrode material, 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 value at which the peak valley of the thermogravimetric DTG curve of the negative electrode material in the temperature range of 530°C to 550°C under an air atmosphere is located (i.e., the temperature corresponding to the first peak of the DTG weight loss rate) are shown in Table 1.

[0173] The CP-SEM image of the negative electrode material prepared in this example at a magnification of 1000 times is shown in FIG. 1. The CP-SEM image of the negative electrode material prepared in this example at a magnification of 50000 times is shown in FIG. 2 (the thickness indicated in FIG. 2 is the specific thickness of the amorphous carbon coating layer, and the thickness in Table 1 is the average thickness of the amorphous carbon coating layer).

[0174] The ID / IG distribution diagram of the negative electrode material prepared in this example is shown in FIG. 3.

[0175] The thermogravimetric DTG curve of the negative electrode material prepared in this example is shown in FIG. 4.

[0176] Example 3

[0177] The preparation method of the negative electrode material provided in this example includes the following steps:

[0178] (1) 1 kg of a mixture of coal pitch (coal tar pitch) and petroleum pitch (coking value 75%, mass ratio of coal pitch to petroleum pitch 1:1) and 9 kg of natural graphite (Dv50 = 25 μm, carbon content 99.96 wt.%, pore volume 0.02 cm 3 / g) were added to a mixing device, and the materials were uniformly mixed by high-speed stirring to obtain a precursor. The precursor was placed in a reaction kettle, and the sealed reaction kettle was subjected to vacuum treatment until the vacuum degree was 0.01 MPa (absolute pressure) and the vacuum treatment was stopped. The reaction kettle with qualified vacuum degree was subjected to heating and stirring treatment, the temperature was 500°C, the rotation speed was 100 r / min, the holding time was 1 h, the vacuum degree was maintained at 0.04 MPa (absolute pressure) during the holding period, and the material was discharged after cooling to obtain a first material.

[0179] (2) The first material was subjected to microwave pyrolysis, the microwave pyrolysis temperature was 900°C, the pyrolysis time was 3 h, and the heating rate was 80°C / min, and then plasma etching was performed using a plasma cleaning machine, the output power was 800 W, the processing speed was 3 m / min, and the temperature was 25°C to obtain a second material. The second material included a graphite core and an amorphous carbon layer; the average thickness of the amorphous carbon was 200 nm, the average value of ID / IG (peak intensity ratio) of 400 points of face scanning by a Raman spectrometer was 1.00, the powder compaction density under 2 tons was 1.59 g / cm 3The interlayer spacing d002 measured by XRD is 0.337679 nm.

[0180] (3) The second material is subjected to high-temperature carbonization treatment under a nitrogen atmosphere, the carbonization temperature is 1800℃, and the carbonization time is 12h. After cooling to room temperature, a natural graphite negative electrode material is obtained.

[0181] The negative electrode material prepared in this example includes composite particles, and the composite particles include a core and an amorphous carbon coating layer coated on the outer surface of the core. The core includes a graphite framework and amorphous carbon filled in the graphite framework. The average thickness of the amorphous carbon coating layer (referred to as the carbon layer thickness), the average value of the ID / IG (peak intensity ratio) of the negative electrode material subjected to Raman spectrometer face scanning of 400 points, the proportion of the number of scanning points (i.e., the point content) with ID / IG (peak intensity ratio) single point value >0.4, the OI value of the negative electrode tab containing the negative electrode material with a compaction density of 1.65g / cm 3 The performance test results of the compaction density of the negative electrode material under a pressure of 2 tons, 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 value (i.e., the temperature corresponding to the first peak of the DTG weight loss rate) of the peak valley of the thermogravimetric DTG curve of the negative electrode material in the temperature range of 530℃-550℃ under an air atmosphere are shown in Table 1.

[0182] Example 4

[0183] The preparation method of the negative electrode material provided in this example is basically the same as that of Example 2, except that in step (1), the petroleum pitch is replaced by an equal amount of thermoplastic phenolic resin with a coking value of 82%.

[0184] Comparative Example 1

[0185] The preparation method of the negative electrode material provided in this comparative example does not perform vacuum extraction during heat treatment (i.e., under normal pressure) and does not perform microwave pyrolysis and plasma etching, and specifically includes the following steps:

[0186] (1) 1.5kg of petroleum pitch (coking value 75%) and 8.5kg of natural graphite (Dv50=15μm, carbon content 99.95wt.%, pore volume 0.034cm 3 / g) are added to a mixing device, and high-speed stirring is performed to uniformly mix the materials to obtain a precursor. The precursor is placed in a reaction kettle, and heating and stirring treatment are performed on the reaction kettle, the temperature is 400℃, the rotation speed is 200r / min, and the holding time is 3h. After cooling, the material is discharged to obtain a first material.

[0187] (2) high-temperature carbonization treatment of the first material under a nitrogen atmosphere, carbonization temperature 1650℃, carbonization time 9h, after cooling to room temperature, to obtain the natural graphite negative electrode material.

[0188] The CP-SEM image of the negative electrode material prepared in the present comparative example is shown in FIG. 5. The ID / IG distribution graph of the negative electrode material prepared in the present comparative example is shown in FIG. 6. As can be seen from FIG. 5, the negative electrode material prepared in the present comparative example includes an inner core and an amorphous carbon coating layer coated on the outer surface of the inner core (almost no amorphous carbon is contained in the graphite framework). The average thickness of the amorphous carbon coating layer (referred to as carbon layer thickness), the average value of ID / IG (peak intensity ratio) of the negative electrode material by Raman spectrometer face scanning 400 points, and the proportion of the number of scanning points (i.e. point content) with ID / IG (peak intensity ratio) single point value > 0.4, the OI value of the negative electrode tab containing the negative electrode material with a compaction density of 1.65 g / cm 3 The performance test results of the negative electrode material prepared in the present comparative example, including the average thickness of the amorphous carbon coating layer (referred to as carbon layer thickness), the average value of ID / IG (peak intensity ratio) of the negative electrode material by Raman spectrometer face scanning 400 points, and the proportion of the number of scanning points (i.e. point content) with ID / IG (peak intensity ratio) single point value > 0.4, the OI value of the negative electrode tab containing the negative electrode material with a compaction density of 1.65 g / cm

[0189] The thermogravimetric DTG curve of the negative electrode material prepared in the present comparative example is shown in FIG. 7. As can be seen from FIG. 7, the first peak of DTG weight loss rate is at 590℃, i.e. there is no peak valley in the temperature range of 530℃-550℃.

[0190] Comparative Example 2

[0191] The preparation method of the negative electrode material provided in the present comparative example is basically the same as that of Example 2, except that step (2) is not included, i.e. no microwave pyrolysis and plasma etching are performed, but the first material is directly subjected to high-temperature carbonization treatment.

[0192] The negative electrode material prepared in the present comparative example includes composite particles, and the composite particles include an inner core and an amorphous carbon coating layer coated on the outer surface of the inner core, and the inner core includes a graphite framework and amorphous carbon filled in the graphite framework. The average thickness of the amorphous carbon coating layer (referred to as carbon layer thickness), the average value of ID / IG (peak intensity ratio) of the negative electrode material by Raman spectrometer face scanning 400 points, and the proportion of the number of scanning points (i.e. point content) with ID / IG (peak intensity ratio) single point value > 0.4, the OI value of the negative electrode tab containing the negative electrode material with a compaction density of 1.65 g / cm 3 The performance test results of the negative electrode material prepared in the present comparative example, including the average thickness of the amorphous carbon coating layer (referred to as carbon layer thickness), the average value of ID / IG (peak intensity ratio) of the negative electrode material by Raman spectrometer face scanning 400 points, and the proportion of the number of scanning points (i.e. point content) with ID / IG (peak intensity ratio) single point value > 0.4, the OI value of the negative electrode tab containing the negative electrode material with a compaction density of 1.65 g / cm

[0193] The negative electrode material prepared in the present comparative example shows a thermogravimetric DTG curve under air atmosphere, and the first peak of DTG weight loss rate is at 580 ℃, i.e. there is no peak valley in the temperature range of 530-550 ℃.

[0194] Comparative Example 3

[0195] The preparation method of the negative electrode material provided in the present comparative example is basically the same as that in Example 2, except that the plasma etching is not performed in step (2).

[0196] The negative electrode material prepared in the present comparative example comprises composite particles, and the composite particles comprise a core and an amorphous carbon coating layer coated on the outer surface of the core. The core comprises a graphite framework and amorphous carbon filled in the graphite framework. The average thickness of the amorphous carbon coating layer (referred to as carbon layer thickness), the average value of ID / IG (peak intensity ratio) of the negative electrode material scanned by a Raman spectrometer for 400 points, and the proportion of the number of scanning points (i.e. point content) with ID / IG (peak intensity ratio) single point value > 0.4, and the performance test results of the negative electrode sheet containing the negative electrode material with a compaction density of 1.65 g / cm 3 The performance test results of the negative electrode material prepared in the present comparative example, including the average thickness of the amorphous carbon coating layer (referred to as carbon layer thickness), the average value of ID / IG (peak intensity ratio) of the negative electrode material scanned by a Raman spectrometer for 400 points, and the proportion of the number of scanning points (i.e. point content) with ID / IG (peak intensity ratio) single point value > 0.4, and the negative electrode sheet containing the negative electrode material with a compaction density of 1.65 g / cm

[0197] The negative electrode material prepared in the present comparative example shows a thermogravimetric DTG curve under air atmosphere, and the first peak of DTG weight loss rate is at 560 ℃.

[0198] Comparative Example 4

[0199] The preparation method of the negative electrode material provided in the present comparative example is basically the same as that in Example 2, except that the microwave pyrolysis temperature is 1000 ℃, the pyrolysis time is 5 h, and the heating rate is 120 ℃ / min in step (2).

[0200] The negative electrode material prepared in the present comparative example comprises composite particles, and the composite particles comprise a core and an amorphous carbon coating layer coated on the outer surface of the core. The core comprises a graphite framework and amorphous carbon filled in the graphite framework. The average thickness of the amorphous carbon coating layer (referred to as carbon layer thickness), the average value of ID / IG (peak intensity ratio) of the negative electrode material scanned by a Raman spectrometer for 400 points, and the proportion of the number of scanning points (i.e. point content) with ID / IG (peak intensity ratio) single point value > 0.4, and the performance test results of the negative electrode sheet containing the negative electrode material with a compaction density of 1.65 g / cm

[0201] The negative electrode material prepared in the present comparative example shows a thermogravimetric DTG curve in air atmosphere, and the first peak of DTG weight loss rate is at 525℃, i.e. there is no peak valley in the temperature range of 530℃-550℃. In the present disclosure, the performance of the negative electrode material is tested according to the following method:

[0202] Test of particle size: The particle size of the particles is tested by a laser particle size analyzer, such as a Mastersizer 3000 laser particle size analyzer of Malvern Instruments Ltd., UK.

[0203] Test of compacted density: The compacted density is tested by a pressurization method, basically in accordance with the test method for powder compacted density described in GBT 24533-2009 Lithium Ion Battery Graphite Anode Material, except that the test pressure in the present disclosure is 2 tons.

[0204] Test of scanning electron microscope: The scanning electron microscope (SEM) characterization is performed on a projection electron microscope, and the operating voltage is 200kv. The structure of the negative electrode material is observed.

[0205] Test of thickness of carbon coating layer: The cross-section of the material is processed by a FIB-SEM device, and a 20,000 times scanning electron microscope is used to take a picture of an arbitrary area of the sample cross-section. The center of each particle in the 20,000 times picture is selected, and a vertical cross line is randomly drawn at the center. The thickness of the amorphous carbon layer at the intersection point of the cross line and the edge of the particle cross-section is recorded, and the average thickness of the amorphous carbon layer of a single particle is calculated. Then, the average thickness of the amorphous carbon layer of all particles in the 20,000 times picture is averaged to obtain the average thickness of the carbon coating layer of the sample.

[0206] Test of Raman ID / IG: The D peak intensity (1350cm -1 nearby, belonging to the boundary vibration mode of the hexagonal Brillouin zone induced by disorder, for defect characterization) and the G peak intensity (1580cm -1 nearby, belonging to the stretching vibration mode of the in-plane bond of carbon atoms, related to the degree of graphitization) are tested by a Renishaw microconfocal Raman spectrometer. The ratio of the peak intensity of the D peak and the G peak, i.e. ID / IG, is obtained. A 532nm semiconductor laser with a power of ≥50mW is used. The test conditions are as follows: a neon lamp is used as a signal source, a high-resolution grating with ≥1800 lines, and a test 17086ABScm -1 emitting line with a full width at half maximum of less than or equal to 1 wavenumber (FWHM≤1cm -1 ); spatial resolution: ≤0.3μm (XY); ≤1μm (Z); scanning step: 5μm; face scanning range: -47μm≤X≤48μm; -47μm≤Y≤48μm; face scanning: 400 points.

[0207] Test of pore volume: The pore volume of the material is detected by a specific surface area and pore size analyzer using a static BET adsorption method.

[0208] Test of true density: The density of the sample at 30℃ is tested by the pycnometer method after the sample is immersed in liquid and degassed in vacuum.

[0209] Test of interlayer spacing d002: When X-rays are projected into a crystal, they are scattered by atoms and electrons in the crystal. Due to the periodic arrangement of atoms in the crystal, there is a fixed phase difference between the scattered waves, which interfere with each other in space, resulting in the reinforcement of scattered waves in some directions and the cancellation of each other in some directions, thereby causing diffraction. The diffractometer automatically records the diffraction pattern of the sample and analyzes the diffraction pattern, thereby obtaining sample information; silicon is used as an internal standard, added to graphite and mixed, then XRD is tested, and d002 is calculated.

[0210] Test of OI value of negative electrode tab: In the test of OI value of the negative electrode tab, the X-ray diffraction analysis can refer to the standard JIS K0131-1996, and an X-ray diffractometer (such as a Bruker D8 Discover X-ray diffractometer) is used for testing. In the X-ray diffraction analysis test, a copper target can be used as an anode target, a Ni filter with a thickness of 0.02 mm is used to filter CuKβ, CuKα rays are used as the radiation source, the ray wavelength (the weighted average of Kα1 and Kα2 is taken), the scanning 2θ angle range is 20°-80°, and the scanning rate is 4° / min. In the present application, specifically, the OI value test method of the negative electrode tab is as follows: the prepared negative electrode tab with a compacted density of 1.65 g / cm 3 is directly placed in the X-ray diffractometer, the peak area C004 of the 004 crystal face diffraction peak and the peak area C110 of the 110 crystal face diffraction peak of the negative electrode active material in the negative electrode tab are obtained by X-ray diffraction analysis, and the OI value of the negative electrode tab = C004 / C110.

[0211] TG test: 5 mg is weighed and placed in the sample chamber, air is introduced at a flow rate of 50 ml / min, the temperature is raised at a rate of 5℃ / min to 800℃, and the thermal weight loss curve (TG) is first-order derivative processed (the first-order derivative of the mass content percentage with respect to temperature), to obtain the differential thermal gravimetric curve (DTG).

[0212] Table 1 Performance test results of negative electrode materials

[0213] Further, the negative electrode material obtained in each of the examples and each of the comparative examples is respectively mixed with CMC, SP and SBR in a mass ratio of 95:2:1:2 in a pure water solution to prepare a slurry, and the slurry is coated on the surface of a copper foil to obtain a negative electrode sheet; a lithium foil is used as a positive electrode sheet, a microporous polypropylene film is used as a separator, and an electrolyte is composed of 1M LiPF6 dissolved in a mixed solution of EC, DMC and EMC, wherein the volume ratio of EC, DMC and EMC is 1:1:1, and the mixed solution further contains 1% VC in terms of mass content. The negative electrode sheet, the positive electrode sheet, the separator and the electrolyte are assembled into a lithium ion battery, and the charge and discharge cutoff voltage is 0.005-2V.

[0214] The performance tests of the battery include: 1) 25℃, 0.05C first reversible capacity; 2) 25℃, 0.05C first coulombic efficiency; 3) 25℃, 1C cycle for 50 weeks, the expansion rate of the graphite electrode sheet is tested after disassembly; 4) half-cell, lithium sheet as negative electrode, graphite as positive electrode, 25℃, 3C discharge, DV / DQ second-order derivative curve is drawn, and the curve slope inflection point is the lithium precipitation SOC position; the 3C lithium precipitation performance of the negative electrode material is approximately positively correlated with the rate performance, and the better the 3C lithium precipitation performance, the better the rate performance is generally; 5) capacity retention rate at 45℃, 1C cycle for 300 weeks. The performance test results of the battery are shown in Table 2.

[0215] Table 2 Performance test results of the battery

[0216] As can be seen from FIGS. 5, 6, Table 1 and Table 2, in the comparative example 1, since the coating is simply performed by heating and stirring, most of the pitch is coated on the surface of the particles, and the filling effect in the particles is poor, which is not conducive to reducing the expansion rate of the material and improving the rate performance of the material.

[0217] In the comparative example 2, the filling and coating are performed by heating and stirring under vacuum, and the filling effect in the particles is improved, the rate performance of the material is improved, and the expansion rate is reduced. The rate performance and the expansion rate of the material in the comparative example 2 are improved, but the improvement is not obvious. In particular, the crystallinity of the graphite-like crystal with the amorphous carbon layer on the surface after carbonization is still very good, the D002 is small, the ID / IG is small, and the OI value of the electrode sheet is large, which is not conducive to improving the rate performance of the material, and the expansion rate is still high at a large rate.

[0218] In the comparative example 3, the plasma etching is not performed, and the rate performance of the material is not obviously improved. Although the microwave pyrolysis can make the amorphous carbon graphite-like crystallite fine-grained, the crystalline defects are still not enough, so that the rate performance of the material is not obviously improved, and the expansion rate is not obviously reduced.

[0219] Compared with Comparative Example 2, Example 2 of the present disclosure also fills a large amount of organic carbon source into the particle interior and coats the particle surface by heating and stirring under vacuum, and fills the particle interior pores as much as possible (as shown in FIG. 1, the pores in the particle interior after carbonization are basically not filled), thereby improving the rate performance difference of the material to some extent and reducing the expansion rate of the material, but the crystallinity of the graphite-like crystal of the amorphous carbon on the surface after carbonization is good, which is not conducive to the embedding and spreading of lithium ions, and has an adverse effect on the rate performance and expansion rate of the material. Therefore, Example 2 of the present disclosure further processes the microwave pyrolysis + plasma etching method on the basis of Comparative Example 2. This method first reduces the crystal size of the graphite-like microcrystal of the amorphous carbon inside and outside the graphite particle, and then further modifies the defect sites of the graphite-like microcrystal of the amorphous carbon coating layer on the surface, so that the material surface has more active sites. While reducing the thickness of the amorphous carbon coating layer, the D002 of the amorphous carbon becomes larger, the ID / IG becomes larger, the oxidation ablation temperature of the amorphous carbon on the surface of the graphite decreases (the first peak of the DTG moves forward), the OI value of the material electrode sheet becomes smaller, the orientation of the material electrode sheet is improved, and the rate performance of the material is improved and the expansion rate is reduced. As shown in Table 1 and Table 2, Example 2, as a carbonized product of natural graphite lithium battery negative electrode material, the material not only has low expansion rate, good rate performance, but also has high compaction density. In addition, it also has high capacity and high initial efficiency.

[0220] In addition, in Comparative Example 4, the average value of ID / IG is more than 0.5, and the point content of ID / IG greater than 0.4 is more than 90%. The large point content and the high average value lead to poor cycle performance of the material. Because the disorder degree of the material is too large, the active sites are too many, which exacerbates the side reaction of the surface amorphous carbon and the electrolyte, resulting in low first coulombic efficiency and poor cycle performance of the material, which is not conducive to practical application.

[0221] Compared with the prior art, the present disclosure has the following beneficial effects:

[0222] (1) The negative electrode material provided by the present disclosure has low expansion rate and good rate performance.

[0223] (2) The negative electrode material provided by the present disclosure has excellent cycle performance, high capacity and high initial efficiency.

[0224] (3) The negative electrode material provided by the present disclosure has high compaction density.

[0225] (4) The preparation method of the negative electrode material provided by the present disclosure first discharges air from the inside of the graphite framework under vacuum, fills organic carbon sources into the inside of the graphite framework particles and coats the surface by high-temperature vacuum, and then modifies the amorphous carbon graphite crystal structure inside and outside the graphite framework by using the microwave pyrolysis + plasma etching method, which can improve the path of lithium ion embedding into the graphite particles, reduce the expansion rate of the obtained negative electrode material, and improve its rate performance. Finally, high-temperature carbonization further dehydrogenates, which can improve the high-temperature cycle performance of the negative electrode material.

[0226] Although the present disclosure has been illustrated and described with specific embodiments, it should be realized that the above embodiments are only used to illustrate the technical solutions of the present disclosure, and are not limiting thereof; those skilled in the art should understand that the technical solutions recorded in the foregoing embodiments can be modified, or some or all of the technical features thereof can be replaced equivalently without departing from the spirit and scope of the present disclosure; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present disclosure; therefore, this means that all these replacements and modifications within the scope of the present disclosure are included in the appended claims. Industrial applicability

[0227] The negative electrode material of the present disclosure comprises a composite particle, which comprises an inner core and an amorphous carbon coating layer coated on the outer surface of the inner core, the inner core comprises a graphite framework and amorphous carbon filled in the graphite framework; the average thickness of the amorphous carbon coating layer is 15-45 nm; the Raman spectrum area scanning of the negative electrode material is performed, the Raman spectrum area scanning points are 400, and the average value of the ID / IG of the Raman spectrum of the negative electrode material is 0.40-0.50, wherein the number of scanning points with a single-point value of ID / IG>0.4 accounts for more than 70%. The negative electrode material has low expansion rate and good rate performance.

Claims

1. A negative electrode material, characterized by, The composite particle comprises an inner core and an amorphous carbon coating layer coated on the outer surface of the inner core, the inner core comprising a graphite framework and amorphous carbon filled in the graphite framework; The average thickness of the amorphous carbon coating layer is 15-45 nm; The average value of ID / IG of the Raman spectrum of the negative electrode material is 0.40-0.50, and the number of scanning points with a single-point value of ID / IG greater than 0.4 accounts for more than 70%.

2. The negative electrode material of claim 1, wherein, At least one of the following features (1) to (2) is included: (1) The average thickness of the amorphous carbon coating layer is 15-35 nm; (2) The number of scanning points with a single-point value of ID / IG of the Raman spectrum of the negative electrode material greater than 0.4 accounts for 71%-90%.

3. The negative electrode material according to at least one of claims 1 to 2, characterized in that The negative electrode material is subjected to a thermogravimetric test in an air atmosphere, and the thermogravimetric differential curve of the negative electrode material has a peak valley in the temperature range of 530-550 DEG C.

4. The negative electrode material according to at least one of claims 1 to 3, characterized in that At least one of the following features (1) to (12) is included: (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 / cm 3 ; (4) the pore volume of the negative electrode material is < 0.005 cm3 / g 3 / g; (5) the OI value of the negative electrode sheet containing the negative electrode material is 3.0 to 10.0 3 of 1.65 g / cm3 (6) The electrode sheet containing the negative electrode material has an electrode sheet expansion rate of less than 25% after 50 cycles at 25 DEG C and 1C; (7) The 3C lithium extraction performance of the battery containing the negative electrode material is greater than 45%; (8) The 0.05C initial coulombic efficiency of the battery containing the negative electrode material is greater than 93.7%; (9) The 0.05C initial reversible capacity of the battery containing the negative electrode material is greater than 360 mAh / g; (10) The graphite framework comprises natural graphite; (11) The carbon content of the graphite framework is greater than 99.9 wt.%; (12) the graphite skeleton has a pore volume of 0.02 to 0.05 cm3 / g 3 / g.

5. A method for producing a negative electrode material, characterized by, The method comprises the following steps: The mixture of the graphite framework and the organic carbon source is subjected to heat treatment under negative pressure to obtain a first material; The first material is subjected to microwave pyrolysis and plasma etching to obtain a second material; The second material is subjected to carbonization to obtain the negative electrode material.

6. The method of claim 5, wherein the negative electrode material is prepared by mixing the carbon material, the silicon material, and the binder. At least one of the following features (1) to (11) is included: (1) The graphite framework comprises natural graphite; (2) The carbon content of the graphite framework is greater than 99.9 wt.%; (3) The particle size Dv50 of the graphite framework is 5-25 μm; (4) the graphite skeleton has a pore volume of 0.02 to 0.05 cm3 / g 3 / g; (5) The organic carbon source comprises at least one of petroleum pitch, coal tar pitch and resin; (6) The coking value of the organic carbon source is greater than 70%; (7) The mass ratio of the graphite framework to the organic carbon source is 75:25-90:10; (8) The vacuum degree in the heat treatment process is less than 0.05 MPa in absolute pressure; (9) The vacuum degree of the environment before the heat treatment of the mixture is less than 0.03 MPa in absolute pressure; (10) The temperature of the heat treatment is 300-500 DEG C, and the time of the heat treatment is 1-5 h; (11) The mixture is stirred at a speed of 100-300 r / min during the heat treatment.

7. The method of producing a negative electrode material according to at least one of claims 5 to 6, characterized by, At least one of the following features (1) to (6) is included: (1) the temperature rising 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 by using a plasma cleaning machine; 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 inner core and an amorphous carbon layer; wherein the average thickness of the amorphous carbon layer is 200-400 nm; the average value of ID / IG of the second material is 0.60-1.00 at a Raman spectrum point of 400; the powder compaction density of the second material under a pressure of 2 tons is >1.5 g / cm 3 ; the interlayer spacing d002 of the second material in an X-ray diffraction pattern is 0.336894-0.337679 nm; (5) the temperature of the carbonization is 1500-1800℃, and the time of the carbonization is 6-12h; (6) the carbonization is performed in an inert atmosphere.

8. A negative electrode sheet characterized by comprising: The negative electrode material comprises the negative electrode material according to any one of claims 1-4, or the negative electrode material prepared by the preparation method according to any one of claims 5-7.

9. A battery, characterized by The negative electrode sheet comprises the negative electrode material according to claim 8.

10. An electric device, characterized by The battery comprises the battery according to claim 9.

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