Composite negative electrode material, preparation method thereof and battery

Abstract

The application discloses a kind of composite negative material and its preparation method, battery.The preparation method of the composite negative material includes the following steps: oxide, carbon nanotube, pitch and graphite base material are fused, carbonization treatment, and composite negative material is prepared;Wherein, the rotating speed when fusing is 300-1000 revolutions / min;Fusion time is 1-15min;The temperature of carbonization treatment is 900-1500 DEG C.The preparation method of the composite negative material of the application is simple, environment-friendly, and the composite negative material prepared is applied in battery, and under the premise of meeting the better safety performance and keeping the better energy density, it also has better kinetic performance.

Description

Technical Field

[0001] This invention relates to a composite negative electrode material, its preparation method, and a battery. Background Technology

[0002] Lithium-ion batteries, as high-performance energy storage devices, dominate the market due to their advantages such as high specific capacity, high cycle performance, environmental friendliness, and no memory effect. They are widely used in portable electronic devices and power equipment, thus placing increasingly higher demands on the dynamic and safety performance of lithium batteries. Traditionally, lithium battery safety was considered to be mainly related to factors such as battery design, electrolyte, and positive electrode materials. However, with the in-depth development of lithium batteries and their negative electrode materials, the safety requirements for negative electrode materials used in lithium batteries are also becoming increasingly stringent. Therefore, negative electrode materials must balance fast-charging performance with high-temperature safety performance within lithium batteries.

[0003] Chinese patent document CN113363445A discloses a graphite anode material modified with a mesh-like γ-alumina coating, which effectively improves the compatibility of graphite materials with electrolytes and enhances their kinetic performance while maintaining safety. The method involves adjusting the pH value of aluminum salts with an alkaline solution and then further aging and calcining to obtain the γ-alumina-coated graphite anode material (see Invention Content [0005-0013]). The composite material prepared by this method shows a capacity reduction of more than 3 mAh / g compared to the unmodified version, and the highest 3C lithium plating SOC is only 36% (see Table 1 in Invention Content). Furthermore, the preparation process is complex, requiring the use of alkaline solutions to adjust the pH value, which is environmentally unfriendly. Summary of the Invention

[0004] This invention aims to overcome the shortcomings of existing composite anode materials, such as the need for pH adjustment using alkaline solutions and poor kinetic performance in batteries. It provides a composite anode material, its preparation method, and a battery. The preparation method of this composite anode material is simple and environmentally friendly. Furthermore, the resulting composite anode material, when used in batteries, exhibits excellent kinetic performance while maintaining good safety and energy density.

[0005] The present invention solves the above problems through the following technical solutions:

[0006] This invention provides a method for preparing a composite anode material, comprising the following steps: fusing oxides, carbon nanotubes, pitch and graphite matrix, and performing carbonization treatment to obtain the composite anode material;

[0007] The fusion rotation speed is 300-1000 rpm; the fusion time is 1-15 min; and the carbonization temperature is 900-1500℃.

[0008] In this invention, the oxide can be a conventional oxide with high heat resistance. High heat resistance indicates the property of maintaining its excellent physical and mechanical properties even at 1500°C. The oxide can be Al₂O₃ and / or MgO.

[0009] In this invention, the particle size D50 of the oxide can be 10nm-500nm, preferably 30nm-100nm, for example 50nm.

[0010] In this invention, the mass of the oxide can be 0-3% of the mass of the graphite matrix, but not 0%, preferably 0.5%-1.5%, for example 1%. When the content of the oxide is greater than 3%, the energy density of the composite anode material obtained and used in a battery is lower than that of the composite anode material obtained when the content of the oxide is 0-3% but not 0.

[0011] In this invention, the carbon nanotubes (CNTs) can be conventional in the art. The aspect ratio of the carbon nanotubes can be 1000 or higher, for example, 1200.

[0012] In this invention, the mass of the carbon nanotubes can be 0-0.5% of the mass of the graphite base material, but not 0, preferably 0.01%-0.1%, for example 0.05%.

[0013] In this invention, the asphalt can be coal tar pitch or petroleum asphalt. The coal tar pitch can be medium-temperature coal tar pitch or high-temperature coal tar pitch. The petroleum asphalt can be medium-temperature petroleum asphalt or high-temperature petroleum asphalt. "Medium-temperature" indicates that the softening point of the asphalt is 120℃-200℃. "High-temperature" indicates that the softening point of the asphalt is 200℃-300℃.

[0014] In this invention, the mass of the asphalt can be 0-5% of the mass of the graphite base material, but not 0%; for example, 0.5%, 1%, 2% or 3%, preferably 0.8%-3.5%.

[0015] In this invention, the process of fusing the oxide, the carbon nanotube, the asphalt, and the graphite base material preferably includes the following steps: first, mixing the oxide, the carbon nanotube, and the asphalt with a solvent, and then fusing them with the graphite base material.

[0016] The solvent may be a conventional solvent in the art capable of dispersing the oxide, the carbon nanotubes, and the pitch, such as cyclohexane.

[0017] In this invention, the graphite base material can be a conventional graphite base material used in the battery field, such as artificial graphite.

[0018] In this invention, the particle size D50 of the graphite matrix can be 8-20 μm, for example 8 μm, 10 μm, 13 μm, 15 μm or 20 μm, preferably 10-15 μm.

[0019] In this invention, the rotation speed during fusion is preferably 500-800 rpm.

[0020] In this invention, the fusion time can be 3-10 min, preferably 4-8 min, for example 5 min or 7 min.

[0021] In this invention, the equipment used for carbonization treatment can be conventional in the art, such as an atmosphere furnace.

[0022] In this invention, the carbonization temperature is preferably 1000-1300℃, for example 1100℃ or 1200℃.

[0023] In this invention, the carbonization treatment time can be 2-10 hours, preferably 3-8 hours, for example 5 hours.

[0024] In this invention, the carbonization process generally includes steps of cooling, mixing, and sieving.

[0025] In this invention, the preparation process of the composite negative electrode material does not require the addition of alkali solution.

[0026] This invention provides a composite anode material, which is prepared by the method described above.

[0027] This invention provides a composite anode material comprising a core and a shell;

[0028] The core is a graphite-based material; the outer shell comprises oxides, carbon nanotubes, and amorphous soft carbon; the thickness of the outer shell is 22-50 nm; and the specific surface area of ​​the composite anode material is 0.9-1.3 cm². 2 / g.

[0029] In this invention, the mass of the oxide can be 0-3% of the mass of the graphite base, but not 0%, preferably 0.5%-1.5%, for example 1%.

[0030] In this invention, the mass of the carbon nanotubes can be 0-0.5% of the mass of the graphite base material, but not 0, preferably 0.01%-0.1%, for example 0.05%.

[0031] In this invention, the amorphous soft carbon can be obtained by carbonizing asphalt. The mass of the asphalt can be 0-5% of the mass of the graphite base material, but not 0%; for example, 0.5%, 1%, 2% or 3%, preferably 0.8%-3.5%.

[0032] In this invention, the thickness of the outer shell is preferably 28-32 nm.

[0033] In this invention, the specific surface area of ​​the composite negative electrode material is preferably 1.2-1.28 cm². 2 / g.

[0034] The present invention also provides a battery comprising the composite negative electrode material as described above.

[0035] In this invention, the battery is preferably a lithium-ion secondary battery.

[0036] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0037] The reagents and raw materials used in this invention are all commercially available.

[0038] The positive and progressive effects of this invention are as follows:

[0039] This invention fuses and carbonizes oxides, carbon nanotubes, pitch, and graphite-based materials. By controlling the process parameters during fusion (such as the rotation speed and fusion time) and the carbonization temperature, a composite anode material can be obtained. The preparation method of this composite anode material is simple. The resulting anode material has a uniform coating layer and a robust core-shell structure. When applied to batteries, this anode material exhibits superior safety performance, excellent kinetic performance, and high energy density. Attached Figure Description

[0040] Figure 1 The image shows the composite anode material prepared in Example 4 as observed at 500x magnification using SEM.

[0041] Figure 2 The image shows the composite anode material prepared in Example 4 under SEM magnification of 10,000. Detailed Implementation

[0042] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0043] All raw materials used in the examples and comparative examples were commercially available. MgO was purchased from Yimei Energy Chemical; Al2O3 from Sumitomo Chemical; CNTs were purchased from Tiannai Technology, with an aspect ratio of 1200; medium-temperature asphalt was purchased from Xinde New Materials, with a softening point of 120℃; high-temperature asphalt was purchased from Xinde New Materials, with a softening point of 200℃; and the graphite base material was artificial graphite purchased from Shanghai Shanshan Technology, model SK3-H, with a D50 of 13μm.

[0044] Example 1

[0045] MgO (10 nm in size, 50 g in weight), CNT (50 g in weight), and 100 g of medium-temperature asphalt were dispersed in an appropriate amount of cyclohexane solvent (the amount of solvent was sufficient to wet the material) to obtain a dispersion. The dispersion was then fused with artificial graphite matrix (8 μm in size, 10 kg in weight) in a high-speed fusion machine for 3 min at a speed of 300 rpm to obtain a composite raw material. The composite raw material was placed in a sealed atmosphere furnace and carbonized at 900℃ for 2 hours. Finally, it was cooled to room temperature, discharged, mixed, and sieved to obtain the composite anode material.

[0046] Example 2

[0047] MgO (500 nm in size, 300 g in weight), CNT (1 g in weight), and 100 g of medium-temperature asphalt were dispersed in an appropriate amount of cyclohexane solvent (the amount of solvent was sufficient to wet the material) to obtain a dispersion. The dispersion was then fused with 10 kg of artificial graphite matrix (20 μm in particle size) in a high-speed fusion machine for 1 min at a speed of 300 rpm to obtain a composite raw material. The composite raw material was placed in a sealed atmosphere furnace and carbonized at 1500 °C for 2 hours. Finally, it was cooled to room temperature, discharged, mixed, and sieved to obtain the composite anode material.

[0048] Example 3

[0049] Al2O3 with a particle size of 100 nm and a weight of 150 g, CNT 10 g, and 300 g of high-temperature asphalt were dispersed in an appropriate amount of cyclohexane solvent (the amount of solvent was sufficient to wet the material) to obtain a dispersion. The dispersion was then fused with artificial graphite matrix with a particle size of 10 μm and a weight of 10 kg in a high-speed fusion machine for 3 min at a speed of 1000 rpm to obtain a composite raw material. The composite raw material was placed in a sealed atmosphere furnace and carbonized at 1300 °C for 8 hours. Finally, it was cooled to room temperature, discharged, mixed, and sieved to obtain the composite anode material.

[0050] Example 4

[0051] Al₂O₃ (50 nm in size, 100 g in weight), CNTs (5 g in weight), and 200 g of medium-temperature asphalt were dispersed in an appropriate amount of cyclohexane solvent (the amount of solvent was sufficient to wet the material) to obtain a dispersion. The dispersion was then fused with 10 kg of artificial graphite matrix (15 μm in size) in a high-speed fusion machine for 10 min at a speed of 800 rpm to obtain a composite raw material. The composite raw material was placed in a sealed atmosphere furnace and carbonized at 1000 °C for 3 hours. Finally, it was cooled to room temperature, discharged, mixed, and sieved to obtain the composite anode material.

[0052] Example 5

[0053] MgO (50 nm in size, 50 g in weight), CNT (1 g in weight), and 50 g of medium-temperature asphalt were dispersed in an appropriate amount of cyclohexane solvent (the amount of solvent was sufficient to wet the material) to obtain a dispersion. The dispersion was then fused with 10 kg of artificial graphite matrix (13 μm in size) in a high-speed fusion machine for 5 min at a speed of 500 rpm to obtain a composite raw material. The composite raw material was placed in a sealed atmosphere furnace and carbonized at 1100 °C for 5 hours. Finally, it was cooled to room temperature, discharged, mixed, and sieved to obtain the composite anode material.

[0054] Example 6

[0055] MgO and Al2O3 (10 nm in size, 50 g each), CNT (50 g), and 100 g of medium-temperature asphalt were dispersed in an appropriate amount of cyclohexane solvent (the amount of solvent was sufficient to wet the material) to obtain a dispersion. The dispersion was then fused with 10 kg of artificial graphite matrix (8 μm in size) in a high-speed fusion machine for 3 min at a speed of 300 rpm to obtain a composite raw material. The composite raw material was placed in a sealed atmosphere furnace and carbonized at 900 °C for 2 hours. Finally, it was cooled to room temperature, discharged, mixed, and sieved to obtain the composite anode material.

[0056] Example 7

[0057] MgO (10 nm in size, 50 g in weight), CNT (50 g in weight), and 100 g of medium-temperature asphalt were dispersed in an appropriate amount of cyclohexane solvent (the amount of solvent was sufficient to wet the material) to obtain a dispersion. The dispersion was then fused with 10 kg of artificial graphite matrix with a particle size of 8 μm in a high-speed fusion machine for 7 min at a rotation speed of 300 rpm to obtain a composite raw material. The composite raw material was placed in a sealed atmosphere furnace and carbonized at 900 °C for 2 hours. Finally, it was cooled to room temperature, discharged, mixed, and sieved to obtain the composite anode material.

[0058] Example 8

[0059] MgO (10 nm in size, 50 g in weight), CNT (50 g in weight), and 100 g of medium-temperature asphalt were dispersed in an appropriate amount of cyclohexane solvent (the amount of solvent was sufficient to wet the material) to obtain a dispersion. The dispersion was then fused with artificial graphite matrix (8 μm in size, 10 kg in weight) in a high-speed fusion machine for 10 min at a speed of 300 rpm to obtain a composite raw material. The composite raw material was placed in a sealed atmosphere furnace and carbonized at 900℃ for 2 hours. Finally, it was cooled to room temperature, discharged, mixed, and sieved to obtain the composite anode material.

[0060] Example 9

[0061] MgO (10 nm in size, 50 g in weight), CNT (50 g in weight), and 100 g of medium-temperature asphalt were dispersed in an appropriate amount of cyclohexane solvent (the amount of solvent was sufficient to wet the material) to obtain a dispersion. The dispersion was then fused with 10 kg of artificial graphite matrix with a particle size of 8 μm in a high-speed fusion machine for 15 min at a rotation speed of 300 rpm to obtain a composite raw material. The composite raw material was placed in a sealed atmosphere furnace and carbonized at 900 °C for 2 hours. Finally, it was cooled to room temperature, discharged, mixed, and sieved to obtain the composite anode material.

[0062] Example 10

[0063] MgO (10 nm in size, 50 g in weight), CNT (50 g in weight), and 100 g of medium-temperature asphalt were dispersed in an appropriate amount of cyclohexane solvent (the amount of solvent was sufficient to wet the material) to obtain a dispersion. The dispersion was then fused with 10 kg of artificial graphite matrix with a particle size of 8 μm in a high-speed fusion machine for 3 min at a rotation speed of 500 rpm to obtain a composite raw material. The composite raw material was placed in a sealed atmosphere furnace and carbonized at 900 °C for 2 hours. Finally, it was cooled to room temperature, discharged, mixed, and sieved to obtain the composite anode material.

[0064] Example 11

[0065] MgO (10 nm in size, 50 g in weight), CNT (50 g in weight), and 100 g of medium-temperature asphalt were dispersed in an appropriate amount of cyclohexane solvent (the amount of solvent was sufficient to wet the material) to obtain a dispersion. The dispersion was then fused with 10 kg of artificial graphite matrix with a particle size of 8 μm in a high-speed fusion machine for 3 min at a rotation speed of 800 rpm to obtain a composite raw material. The composite raw material was placed in a sealed atmosphere furnace and carbonized at 900 °C for 2 hours. Finally, it was cooled to room temperature, discharged, mixed, and sieved to obtain the composite anode material.

[0066] Example 12

[0067] MgO (10 nm in size, 50 g in weight), CNT (50 g in weight), and 100 g of medium-temperature asphalt were dispersed in an appropriate amount of cyclohexane solvent (the amount of solvent was sufficient to wet the material) to obtain a dispersion. The dispersion was then fused with 10 kg of artificial graphite matrix with a particle size of 8 μm in a high-speed fusion machine for 3 min at a speed of 1000 rpm to obtain a composite raw material. The composite raw material was placed in a sealed atmosphere furnace and carbonized at 900 °C for 2 hours. Finally, it was cooled to room temperature, discharged, mixed, and sieved to obtain the composite anode material.

[0068] Example 13

[0069] MgO (10 nm in size, 50 g in weight), CNT (50 g in weight), and 100 g of medium-temperature asphalt were dispersed in an appropriate amount of cyclohexane solvent (the amount of solvent was sufficient to wet the material) to obtain a dispersion. The dispersion was then fused with 10 kg of artificial graphite matrix with a particle size of 8 μm in a high-speed fusion machine for 3 min at a rotation speed of 300 rpm to obtain a composite raw material. The composite raw material was placed in a sealed atmosphere furnace and carbonized at 1200℃ for 2 hours. Finally, it was cooled to room temperature, discharged, mixed, and sieved to obtain the composite anode material.

[0070] Example 14

[0071] MgO (10 nm in size, 50 g in weight), CNT (50 g in weight), and 100 g of medium-temperature asphalt were dispersed in an appropriate amount of cyclohexane solvent (the amount of solvent was sufficient to wet the material) to obtain a dispersion. The dispersion was then fused with 10 kg of artificial graphite matrix with a particle size of 8 μm in a high-speed fusion machine for 3 min at a rotation speed of 300 rpm to obtain a composite raw material. The composite raw material was placed in a sealed atmosphere furnace and carbonized at 1500℃ for 2 hours. Finally, it was cooled to room temperature, discharged, mixed, and sieved to obtain the composite anode material.

[0072] Comparative Example 1

[0073] Graphite matrix with a particle size of 13μm was used directly as a reference.

[0074] Comparative Example 2

[0075] MgO and CNT (50g each, 100nm in size) were dispersed in an appropriate amount of cyclohexane solvent (the amount of solvent was sufficient for wetting) to obtain a dispersion. The dispersion was then fused with graphite matrix (10kg each, 12μm in size) in a high-speed fusion machine for 8 minutes at a speed of 800 rpm to obtain a composite raw material. The composite raw material was placed in a sealed atmosphere furnace and carbonized at 1200℃ for 5 hours. Finally, it was cooled to room temperature, discharged, mixed, and sieved to obtain the composite anode material.

[0076] Comparative Example 3

[0077] Al2O3 with a particle size of 50 nm and a weight of 50 g and 100 g of medium-temperature asphalt were dispersed in an appropriate amount of cyclohexane solvent (the amount of solvent was sufficient to wet the material) to obtain a dispersion. The dispersion was then mixed directly with graphite base material with a particle size of 15 μm and a weight of 10 kg using a common stirring device to obtain a composite raw material. The composite raw material was placed in a sealed atmosphere furnace and carbonized at 1200 °C for 5 hours. Finally, it was cooled to room temperature, discharged, mixed, and sieved to obtain the composite anode material.

[0078] Comparative Example 4

[0079] 5g of CNT and 100g of high-temperature asphalt were dispersed in an appropriate amount of cyclohexane solvent (the amount of solvent was sufficient to wet the material) to obtain a dispersion. The dispersion was then fused with 10kg of graphite matrix with a particle size of 10μm in a high-speed fusion machine for 5 minutes at a speed of 500 rpm to obtain a composite raw material. The composite raw material was placed in a sealed atmosphere furnace and carbonized at 1000℃ for 5 hours. Finally, it was cooled to room temperature, discharged, mixed, and sieved to obtain the composite anode material.

[0080] Comparative Example 5

[0081] MgO (10 nm in size, 50 g in weight), CNT (50 g in weight), and 100 g of medium-temperature asphalt were dispersed in an appropriate amount of cyclohexane solvent (the amount of solvent was sufficient to wet the material) to obtain a dispersion. The dispersion was then fused with 10 kg of artificial graphite matrix with a particle size of 8 μm in a high-speed fusion machine for 20 min at a speed of 300 rpm to obtain a composite raw material. The composite raw material was placed in a sealed atmosphere furnace and carbonized at 900 °C for 2 hours. Finally, it was cooled to room temperature, discharged, mixed, and sieved to obtain the composite anode material.

[0082] Comparative Example 6

[0083] MgO (10 nm in size, 50 g in weight), CNT (50 g in weight), and 100 g of medium-temperature asphalt were dispersed in an appropriate amount of cyclohexane solvent (the amount of solvent was sufficient to wet the material) to obtain a dispersion. The dispersion was then fused with 10 kg of artificial graphite matrix with a particle size of 8 μm in a high-speed fusion machine for 3 min at a rotation speed of 100 rpm to obtain a composite raw material. The composite raw material was placed in a sealed atmosphere furnace and carbonized at 900 °C for 2 hours. Finally, it was cooled to room temperature, discharged, mixed, and sieved to obtain the composite anode material.

[0084] Comparative Example 7

[0085] MgO (10 nm in size, 50 g in weight), CNT (50 g in weight), and 100 g of medium-temperature asphalt were dispersed in an appropriate amount of cyclohexane solvent (the amount of solvent was sufficient to wet the material) to obtain a dispersion. The dispersion was then fused with 10 kg of artificial graphite matrix with a particle size of 8 μm in a high-speed fusion machine for 3 min at a speed of 1500 rpm to obtain a composite raw material. The composite raw material was placed in a sealed atmosphere furnace and carbonized at 900 °C for 2 hours. Finally, it was cooled to room temperature, discharged, mixed, and sieved to obtain the composite anode material.

[0086] Comparative Example 8

[0087] MgO (10 nm in size, 50 g in weight), CNT (50 g in weight), and 100 g of medium-temperature asphalt were dispersed in an appropriate amount of cyclohexane solvent (the amount of solvent was sufficient to wet the material) to obtain a dispersion. The dispersion was then fused with 10 kg of artificial graphite matrix with a particle size of 8 μm in a high-speed fusion machine for 3 min at a rotation speed of 300 rpm to obtain a composite raw material. The composite raw material was placed in a sealed atmosphere furnace and carbonized at 600 °C for 2 hours. Finally, it was cooled to room temperature, discharged, mixed, and sieved to obtain the composite anode material.

[0088] Comparative Example 9

[0089] MgO (10 nm in size, 50 g in weight), CNT (50 g in weight), and 100 g of medium-temperature asphalt were dispersed in an appropriate amount of cyclohexane solvent (the amount of solvent was sufficient to wet the material) to obtain a dispersion. The dispersion was then fused with 10 kg of artificial graphite matrix with a particle size of 8 μm in a high-speed fusion machine for 3 min at a rotation speed of 300 rpm to obtain a composite raw material. The composite raw material was placed in a sealed atmosphere furnace and carbonized at 1800℃ for 2 hours. Finally, it was cooled to room temperature, discharged, mixed, and sieved to obtain the composite anode material.

[0090] Example 1

[0091] The composite anode material prepared in Example 4 was observed by SEM at 500x and 10000x magnification, respectively. The results are as follows: Figure 1 and Figure 2 As shown.

[0092] The composite anode materials prepared in Examples 1-14 and Comparative Examples 1-9 were subjected to shell thickness testing. The testing method was as follows: first, the coating layer was observed at a low magnification (e.g., 500 nm) using TEM to check its integrity; then, 5-10 points of the composite anode material were observed at a high magnification (e.g., 20 nm) to determine the shell thickness, and the average value was taken to obtain the average shell thickness. The data for the average shell thickness are shown in Table 1.

[0093] The specific surface area of ​​the composite negative electrode materials prepared in Examples 1-14 and Comparative Examples 1-9 was tested using a NOVATouch2000 specific surface area meter.

[0094] Example 2

[0095] The composite anode material was prepared 15 times each according to the methods of Examples 1-14 and Comparative Examples 1-9, and 15 lithium-ion secondary batteries were prepared according to the following preparation methods:

[0096] A slurry was prepared by mixing 95.5 parts of composite negative electrode material with 200 parts of an aqueous solution containing conductive agent (SP), binder (CMC and SBR); wherein the aqueous solution containing conductive agent (SP) and binder (CMC and SBR) was prepared by mixing 5 parts of CMC, SP and SBR in a mass ratio of 1.5:1.5:1.5 with 195 parts of water.

[0097] The above slurry was coated onto a 15 μm thick copper foil, dried, and rolled into an electrode sheet. A lithium foil was used as the counter electrode, forming a lithium-ion secondary battery with the copper foil electrode. The electrolyte consisted of 1 mol / L lithium hexafluorophosphate (LiPF6) and solvents (the solvents included ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 1:1:1). A 20 μm thick three-layer microporous membrane of polypropylene / polyethylene / polypropylene (PP / PE / PP) was used.

[0098] The lithium-ion secondary battery prepared above was subjected to capacity and initial coulombic efficiency tests under the following conditions: charge / discharge current density of 0.6 mA / cm². 2 The cutoff charge / discharge voltage is 0.005-2.000V, and the test data are shown in Table 1.

[0099] The lithium-ion secondary battery prepared above was subjected to an 800-cycle capacity retention test. The test conditions were: temperature 24℃ and charge / discharge rate 0.1C. The test data are shown in Table 1.

[0100] The lithium-ion secondary battery prepared above was subjected to a 3C lithium plating point SOC test. The test conditions were: one cycle of charge and discharge at a rate of 0.1C, followed by discharge at a rate of 3C. The resulting rate discharge curve was differentiated to obtain a differential curve with SOC value on the horizontal axis and dV / dQ on the vertical axis. The inflection point of the differential curve (i.e., the intersection of the tangent of the plateau and the tangent of the "sloping line extending backward along the plateau") is the lithium plating point. The test results are shown in Table 1.

[0101] The fully charged lithium-ion secondary batteries prepared above were subjected to a hot chamber test. The test method was as follows: the batteries were placed in a hot chamber and heated from room temperature to 132℃±1℃ at a heating rate of 5±1℃ / min, and then the temperature was kept constant while recording the temperature change over time. The batteries were kept in the hot chamber for 60 minutes, and their combustion and explosion were observed. If no combustion or explosion occurred within the above time, it was considered a pass; if combustion or explosion occurred within the above time, it was considered a fail. The test results are shown in Table 1.

[0102] Table 1

[0103]

[0104]

[0105] Compared to Example 1, Comparative Example 2 did not use asphalt, and the lithium battery prepared therein had a 3C lithium plating SOC of only 38%; Comparative Example 3 did not use carbon nanotubes, and the lithium battery prepared therein had an initial coulombic efficiency of only 91.9%; Comparative Example 4 did not use aluminum oxide or magnesium oxide, and the lithium battery prepared therein performed poorly in the hot box test, with only 3 out of a total of 15 batteries passing. Compared to Example 1, Comparative Example 5 used a fusion time of 20 min, resulting in a 3C lithium plating SOC of 50% and a capacity retention rate of 88% after 800 cycles; compared to Example 1, Comparative Example 6 used a fusion speed of 100 rpm, resulting in a 3C lithium plating SOC of 42% and a hot box pass rate of 80%; compared to Example 1, Comparative Example 7 used a fusion speed of 1500 rpm, resulting in a capacity retention rate of 85% after 800 cycles; compared to Example 1, Comparative Example 8 used a sintering temperature of 600°C, resulting in an initial efficiency of 90.2% and a hot box pass rate of 87%; compared to Example 1, Comparative Example 9 used a sintering temperature of 1800°C, resulting in a 3C lithium plating SOC of 40%.

[0106] Examples 1-14 are composite anode materials obtained according to the technical solution of the present invention. They exhibit good performance in terms of capacity, kinetics, and hot box testing. The battery pass rate in the hot box test is 100%, the 3C lithium plating point SOC is above 47%, the initial coulombic efficiency is above 92.7%, and the capacity retention rate after 800 cycles is above 90%.

[0107] For those skilled in the art, the present invention includes, but is not limited to, the details of the exemplary embodiments described above, and can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the above embodiments are exemplary and non-limiting, meaning the scope of the invention is defined by the appended claims rather than the foregoing description, and thus all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention.

[0108] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style of the specification is merely for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing a composite negative electrode material, characterized in that, It includes the following steps: fusing oxides, carbon nanotubes, pitch and graphite matrix, and carbonizing them to obtain the composite anode material; The process of fusing the oxide, the carbon nanotubes, the pitch and the graphite base material includes the following steps: first, mixing the oxide, the carbon nanotubes and the pitch with a solvent, and then fusing them with the graphite base material; The oxide is Al2O3 or MgO; the mass of the oxide is 0.5%-1% of the mass of the graphite base material. The rotation speed during fusion is 300-800 rpm; the fusion time is 3-7 minutes. The carbonization treatment temperature is 900-1200℃; The mass of the carbon nanotubes is 0.1%-0.5% of the mass of the graphite matrix; the particle size D50 of the oxide is 10nm-500nm; and the aspect ratio of the carbon nanotubes is greater than 1000. The mass of the asphalt is 0.5-2% of the mass of the graphite base material.

2. The method for preparing the composite negative electrode material as described in claim 1, characterized in that, The rotation speed during fusion is 500-800 rpm; The fusion time is 4-7 minutes; The carbonization treatment temperature is 1000-1200℃; The carbonization process takes 2-10 hours.

3. The method for preparing the composite negative electrode material as described in claim 1, characterized in that, The fusion time is 5 minutes or 7 minutes; The carbonization treatment temperature is 1100℃ or 1200℃; The carbonization process takes 3-8 hours.

4. The method for preparing the composite negative electrode material as described in claim 1, characterized in that, The carbonization process takes 5 hours.

5. The method for preparing the composite negative electrode material as described in claim 1, characterized in that, The aspect ratio of the carbon nanotubes is 1200; The asphalt is coal tar pitch or petroleum asphalt.

6. The method for preparing the composite negative electrode material as described in claim 1, characterized in that, The mass of the oxide is 1% of the mass of the graphite base material; The mass of the asphalt is 0.5%, 1%, or 2% of the mass of the graphite base material.

7. The method for preparing the composite negative electrode material as described in claim 1, characterized in that, The mass of the asphalt is 0.8%-2% of the mass of the graphite base material.

8. The method for preparing the composite negative electrode material as described in claim 1, characterized in that, The solvent is cyclohexane.

9. A composite negative electrode material, characterized in that, It is prepared by any one of the preparation methods described in claims 1-8.

10. The composite negative electrode material as described in claim 9, characterized in that, It includes a kernel and a shell; The core is a graphite-based material; the outer shell comprises oxides, carbon nanotubes, and amorphous soft carbon; the thickness of the outer shell is 22-50 nm; and the specific surface area of ​​the composite anode material is 0.9-1.3 cm². 2 / g.

11. The composite negative electrode material as described in claim 10, characterized in that, The amorphous soft carbon is obtained by carbonizing asphalt.

12. The composite negative electrode material as described in claim 10 or 11, characterized in that, The thickness of the outer shell is 28-32 nm; The specific surface area of ​​the composite negative electrode material is 1.2-1.28 cm². 2 / g.

13. A battery, characterized in that, It includes the composite anode material as described in any one of claims 10-12.

14. The battery as claimed in claim 13, characterized in that, The battery is a lithium-ion rechargeable battery.

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