Negative electrode material and preparation method thereof, and lithium ion battery

Abstract

The application provides a negative electrode material, a preparation method thereof and a lithium ion battery. The negative electrode material comprises a core layer and an amorphous carbon shell layer; the core layer is a modified cobalt-based alloy secondary particle, the modified cobalt-based alloy secondary particle comprises a plurality of cobalt-based alloy primary particles and graphene nanosheets dispersed between the cobalt-based alloy primary particles, and the graphene nanosheets are loaded with metal ions; and the amorphous carbon shell layer is coated on the outer surface of the core layer. The graphene nanosheets loaded with metal ions can serve as high-mobility channels of the overall material conductive path, thereby shortening the product relaxation time and increasing the effective fluidity. The amorphous carbon coated on the outer surface of the core layer can effectively prevent the cracking and expansion of the core layer particles, thereby improving the cycle performance of the product.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries, and more specifically, to a negative electrode material and its preparation method, and a lithium-ion battery. Background Technology

[0002] For lithium-ion batteries, the mainstream anode material, graphite, is no longer sufficient to meet the ever-increasing energy density requirements due to its relatively low theoretical specific capacity (372 mAh / g). Therefore, the prerequisite for further applications of lithium-ion batteries is to develop anode materials with suitable operating voltage, excellent cycle performance, and high energy density.

[0003] Cobalt-based composite materials (oxides, sulfides, phosphides, and alloys) boast specific capacities as high as 700–1000 mAh / g, 2–3 times that of graphite anodes, and are widely applicable, stable, and environmentally friendly. Therefore, an increasing number of researchers are now favoring cobalt-based composite materials to replace conventional graphite as anode materials. However, cobalt-based alloys have low electron mobility, resulting in batteries with poor charge-discharge performance (e.g., poor initial efficiency, initial discharge capacity, and impedance). Therefore, it is necessary to provide a new cobalt-based composite anode material to enable batteries with superior charge-discharge performance. Summary of the Invention

[0004] The main objective of this invention is to provide an anode material and its preparation method, as well as a lithium-ion battery, to solve the problem of poor battery charge and discharge performance caused by cobalt-based anode materials in the prior art.

[0005] To achieve the above objectives, according to one aspect of the present invention, a negative electrode material is provided, the negative electrode material comprising: a core layer, the core layer being modified cobalt-based alloy secondary particles, the modified cobalt-based alloy secondary particles comprising a plurality of cobalt-based alloy primary particles and graphene nanosheets dispersed among the cobalt-based alloy primary particles, wherein metal ions are loaded on the graphene nanosheets; and an amorphous carbon shell layer covering the outer surface of the core layer.

[0006] Furthermore, the metal element of the metal ion is selected from one of the elements in Group VIII, Group IIA, Group IIIA, Group IB, or Group IIB.

[0007] Furthermore, the metal ions are selected from one or more of trivalent iron ions, divalent copper ions, trivalent aluminum ions, divalent magnesium ions, divalent calcium ions, or divalent zinc ions; the cobalt-based alloy primary particles are selected from CoSb3.

[0008] Furthermore, in the anode material, the weight ratio of the core layer to the amorphous carbon shell layer is 1:(9-99); in the core layer, the weight ratio of cobalt-based alloy primary particles to graphene nanosheets is (20-40):1; and the metal ion loading is 0.01-0.08 g per gram of graphene nanosheets. Preferably, in the anode material, the weight ratio of the core layer to the amorphous carbon shell layer is 1:(25-35).

[0009] Furthermore, the particle size of the negative electrode material is 400–600 nm; the particle size of the modified cobalt-based alloy secondary particles is 300–500 nm; and the thickness of the graphene nanosheets is 6–8 nm, with 1–2 layers.

[0010] To achieve the above objectives, according to one aspect of the present invention, a method for preparing the aforementioned negative electrode material is provided, the method comprising the following steps: step S1, providing a core layer; step S2, coating an amorphous carbon shell layer on the outer surface of the core layer.

[0011] Furthermore, the core layer is prepared by the following method: metal chloride and graphite are mixed in a mixed atmosphere of hydrogen and argon to obtain a mixture; the mixture is heat-treated in a vacuum environment of 0.1-100 MPa (preferably 40-70 MPa) and at a temperature of 300-500°C for 18-24 hours, and then washed and dried to obtain graphene nanosheets loaded with metal ions; the dispersion containing graphene nanosheets and cobalt-based alloy primary particles is dried and then subjected to spark plasma sintering to obtain the core layer.

[0012] Furthermore, in the mixed atmosphere, the volume of argon gas accounts for 5-10% of the total volume; the discharge plasma sintering is carried out in a vacuum environment with a vacuum degree of 0.1-100 MPa (preferably 40-70 MPa); and the sintering temperature is 600-800℃, and the sintering time is 5-10 min.

[0013] Further, the dispersion containing the core layer and carbon source is dried and then carbonized to coat the outer surface of the core layer with an amorphous carbon shell layer to obtain the negative electrode material; the carbon source is selected from asphalt and / or petroleum coke; the carbonization treatment temperature is 700-1000℃ and the treatment time is 1-6h.

[0014] According to another aspect of the present invention, a lithium-ion battery is provided, comprising the aforementioned negative electrode material, or a negative electrode material prepared by the aforementioned method for preparing the negative electrode material.

[0015] Dispersing metal ion-loaded graphene nanosheets among multiple cobalt-based alloy primary particles offers several advantages: First, these graphene nanosheets act as high-mobility channels in the overall conductive path of the product, particularly by weakening the Schottky barrier to compensate for the low mobility in grain boundary regions, thereby significantly improving battery mobility. This, in turn, facilitates lithium-ion insertion and extraction during subsequent charge and discharge processes, effectively improving the structural stability of the anode material, increasing the battery's insertion / extraction capacity, reducing battery impedance, and ultimately enhancing the battery's discharge specific capacity, initial efficiency, and cycle performance. Second, this arrangement shortens the relaxation time of the anode material, increasing its effective fluidity and improving battery safety and lifespan. Third, using cobalt-based alloys as the matrix material for the anode results in a specific capacity 2-3 times higher than conventional graphite anodes, with wider applicability, better stability, and greater environmental friendliness. Fourth, this arrangement also imparts high conductivity to the anode material and improves the battery's constant current ratio, enabling excellent fast-charging performance. Furthermore, the present invention also coats the core layer with an amorphous carbon shell layer, which can not only reduce defects on the material surface and reduce the irreversible capacity of the battery, but also effectively prevent alloy particles from expanding and cracking, thereby improving the cycle stability of the battery. Attached Figure Description

[0016] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0017] Figure 1 The SEM test image of the negative electrode material in an embodiment of the present invention is shown. Detailed Implementation

[0018] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0019] As described in the background section of this invention, existing cobalt-based anode materials result in poor charge and discharge performance in batteries. To address this issue, this invention provides an anode material comprising a core layer and an amorphous carbon shell layer; the core layer is composed of modified cobalt-based alloy secondary particles, which include multiple cobalt-based alloy primary particles and graphene nanosheets dispersed among the primary particles, with metal ions loaded on the graphene nanosheets; the amorphous carbon shell layer coats the outer surface of the core layer.

[0020] Dispersing metal ion-loaded graphene nanosheets among multiple cobalt-based alloy primary particles offers several advantages: First, these graphene nanosheets act as high-mobility channels in the overall conductive path of the product, particularly by weakening the Schottky barrier to compensate for the low mobility in grain boundary regions, thereby significantly improving battery mobility. This, in turn, facilitates lithium-ion insertion and extraction during subsequent charge and discharge processes, effectively improving the structural stability of the anode material, increasing the battery's insertion / extraction capacity, reducing battery impedance, and ultimately enhancing the battery's discharge specific capacity, initial efficiency, and cycle performance. Second, this arrangement shortens the relaxation time of the anode material, increasing its effective fluidity and improving battery safety and lifespan. Third, using cobalt-based alloys as the matrix material for the anode results in a specific capacity 2-3 times higher than conventional graphite anodes, with wider applicability, better stability, and greater environmental friendliness. Fourth, this arrangement also imparts high conductivity to the anode material and improves the battery's constant current ratio, enabling excellent fast-charging performance. Furthermore, the present invention also coats the core layer with an amorphous carbon shell layer, which can not only reduce defects on the material surface and reduce the irreversible capacity of the battery, but also effectively prevent alloy particles from expanding and cracking, thereby improving the cycle stability of the battery.

[0021] To further improve the aforementioned superior performance of the material, in a preferred embodiment, the metal element of the metal ion is selected from elements of Group VIII, Group IIA, Group IIIA, Group IB, and Group IIB. Based on this, the battery exhibits superior discharge specific capacity, initial efficiency, and cycle performance. More preferably, the metal ion is selected from one or more of trivalent iron ions, divalent copper ions, trivalent aluminum ions, divalent magnesium ions, divalent calcium ions, or divalent zinc ions; the cobalt-based alloy primary particles are selected from CoSb3.

[0022] To further balance the aforementioned superior performance of the material, the preferred weight ratio of cobalt-based alloy primary particles to graphene nanosheets in the core layer is (20-40):1, for example, 20:1, 25:1, 30:1, 35:1, or 40:1. Excessive graphene nanosheets can lead to excessive conductivity and safety hazards; while excessive cobalt-based alloy primary particles can slightly decrease the material's conductivity. The metal ion loading is 0.01-0.08 g per gram of graphene nanosheets, for example, 0.01 g, 0.02 g, 0.03 g, 0.04 g, 0.05 g, 0.06 g, 0.07 g, or 0.08 g. Limiting the metal ion loading to this range further balances the battery's superior performance. However, excessive metal ion loading can cause graphene nanosheets to aggregate; while insufficient loading can result in an insufficient number of ion channels generated in the product.

[0023] To further balance the aforementioned superior properties of the material, the weight ratio of the core layer to the amorphous carbon shell in the anode material is 1:(9-99), more preferably 1:(25-35). An excessively heavy core layer can lead to particle cracking in the cobalt-based alloy; while an excessively heavy shell layer can affect the lithium-ion transport rate.

[0024] In a preferred embodiment, the average particle size of the negative electrode material is 400–600 nm. This results in better performance uniformity when the negative electrode material is subsequently applied to a battery. Preferably, the particle size of the modified cobalt-based alloy secondary particles is 300–500 nm; the thickness of the graphene nanosheets is 6–8 nm, and the number of layers is 1–2.

[0025] The present invention also provides a method for preparing the aforementioned negative electrode material, the method comprising the following steps: step S1, providing a core layer, the core layer comprising cobalt-based alloy primary particles and graphene nanosheets dispersed between the cobalt-based alloy primary particles, wherein metal ions are loaded on the graphene nanosheets; step S2, coating an amorphous carbon shell layer on the outer surface of the core layer.

[0026] Based on the reasons mentioned above, firstly, such graphene nanosheets can serve as high-mobility channels for the overall conductive path, particularly by weakening the Schottky barrier to compensate for the low mobility of grain boundary regions, thereby significantly improving the battery's mobility. Furthermore, this facilitates lithium-ion insertion and extraction during subsequent battery charging and discharging, effectively improving the structural stability of the anode material, increasing the battery's insertion / extraction capacity, reducing battery impedance, and ultimately enhancing the battery's discharge specific capacity, initial efficiency, and cycle performance. Secondly, this design can also shorten the relaxation time of the anode material, thereby increasing its effective fluidity and improving battery safety and lifespan. Thirdly, using cobalt-based alloys as the matrix material for the anode material results in a specific capacity 2-3 times that of conventional graphite anodes, with wider applicability, better stability, and greater environmental friendliness. Fourthly, this design also gives the anode material high conductivity and improves the battery's constant current ratio, enabling excellent fast-charging performance. Fifth, the present invention coats the above-mentioned core layer with an amorphous carbon shell layer, which can not only reduce defects on the material surface and reduce the irreversible capacity of the battery, but also effectively prevent alloy particles from expanding and cracking, thereby improving the cycle stability of the battery.

[0027] In a preferred embodiment, the core layer is prepared by the following method: metal chloride and graphite are mixed in a mixed atmosphere of hydrogen and argon to obtain a mixture; the mixture is heat-treated in a vacuum environment of 0.1-100 MPa (preferably 40-70 MPa) and at a temperature of 300-500°C for 18-24 hours, and then washed and dried to obtain graphene nanosheets loaded with metal ions; the dispersion containing graphene nanosheets and cobalt-based alloy primary particles is dried and then subjected to spark plasma sintering to obtain the core layer.

[0028] Specifically, the aforementioned metal chloride and graphite are mixed in a horizontal tube furnace. During this mixing process, the volumetric amount of argon in the mixing atmosphere is 5-10%; the gas flow rate of the mixing atmosphere is 8-10 mL / min; the metal element of the metal chloride is selected from one of Group VIII, Group IIIA, Group IB, or Group IIB elements, more preferably selected from one or more of ferric chloride, copper chloride, aluminum chloride, magnesium chloride, calcium chloride, or zinc chloride. The weight ratio of metal chloride to graphite is 6:(1-3). The above heat treatment is carried out in a stainless steel autoclave. In the above washing process, the heat-treated material is first washed with a dilute hydrochloric acid aqueous solution (hydrogen chloride volume accounts for 5-10% of the solution volume), and then washed a second time with deionized water. The washed solid product is dispersed in an organic solvent (e.g., one or more of methanol, nitromethane, ethylene glycol, DMF, or NMP) and ultrasonicated (ultrasonicated at 50-100 Hz for 20-30 min). The ultrasonically treated mixture is then centrifuged, and the precipitate after centrifugation is washed a third time with ethanol. After drying the material after the third wash, graphene nanosheets loaded with metal ions are obtained.

[0029] Specifically, those skilled in the art can first disperse the graphene nanosheets loaded with metal ions in an organic solvent (e.g., one or more of methanol, ethanol, nitromethane, ethylene glycol, DMF, or NMP) under stirring and ultrasonication, and then add the cobalt-based alloy primary particles to the dispersion. Preferably, allylamine may also be dissolved in the organic solvent to further improve the dispersion uniformity of the graphene nanosheets loaded with metal ions. Next, after washing the dispersion with ethanol, it is filtered through a vacuum filtration system for 30-50 minutes. The filtered liquid is dried in a vacuum drying oven at 50-70°C for 1-4 hours and then transferred to a carbon mold for the above-mentioned spark plasma sintering (SPS). The spark plasma sintering process is carried out in a vacuum environment with a vacuum degree of 0.1-100 MPa (preferably 40-70 MPa); and the sintering temperature is 600-800°C, and the sintering time is 5-10 minutes. Finally, the sintered material is placed in a ball mill for ball milling to obtain granular core material.

[0030] Specifically, the dispersion containing the core layer and carbon source is dried and then carbonized to obtain the negative electrode material; the carbon source is selected from asphalt and / or petroleum coke; the carbonization treatment temperature is 700-1000℃ and the treatment time is 1-6h.

[0031] The present invention also provides a lithium-ion battery, which includes the aforementioned negative electrode material, or a negative electrode material prepared by the aforementioned method for preparing negative electrode material.

[0032] Based on the reasons stated above, firstly, the battery of this invention exhibits excellent discharge specific capacity, initial efficiency, and cycle performance. Secondly, the battery of this invention also possesses excellent safety performance and lifespan. Thirdly, the raw materials used in the battery of this invention are more widely available, have better stability, and are more environmentally friendly. Fourthly, the battery of this invention has a high constant current ratio and excellent fast-charging performance.

[0033] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0034] Example 1

[0035] S1: Anhydrous ferric chloride and graphite are mixed in a horizontal tube furnace at a weight ratio of 3:1 under a mixed atmosphere of hydrogen and argon at a flow rate of 10 mL / min (the volume of argon is 5% of the volume of hydrogen) to obtain a mixture; the mixture is then heat-treated at a vacuum of 50 MPa and a temperature of 400 °C for 18 h to obtain the heat-treated material.

[0036] S2: The heat-treated material was washed sequentially with dilute hydrochloric acid aqueous solution (hydrogen chloride volume accounting for 5% of the solution volume) and deionized water. The washed solid product was then dispersed in DMF and sonicated (at 50 Hz for 30 min). The sonicated mixture was then centrifuged, and the precipitate was washed with ethanol. Finally, the washed material was dried to obtain graphene nanosheets loaded with metal ions.

[0037] S3: 5g of graphene nanosheets loaded with metal ions were dispersed in an ethanol solution containing allylamine under stirring and ultrasonication to form a dispersion. Then, 95g of CoSb3 powder was weighed and added to the dispersion. The dispersion was then washed with ethanol and filtered for 30 minutes using a vacuum filtration system.

[0038] S4: After filtration, the liquid is dried in a vacuum drying oven at 50°C for 2 hours and then transferred to a carbon mold. It is then sintered by discharge plasma at 600°C under a vacuum of 60 MPa for 5 minutes. Finally, the sintered material is placed in a ball mill for ball milling (500 r / min for 1 hour) to obtain granular core material.

[0039] S5: Dissolve 4g of asphalt (softening point 150℃) in 500mL of carbon tetrachloride organic solvent and disperse evenly. Then add 100g of the above granular core material, disperse evenly, spray dry, transfer to a tube furnace, and carbonize at 700℃ for 6h to obtain the negative electrode material.

[0040] In the aforementioned anode materials: the thickness of the graphene nanosheets is 6–8 nm, and the number of layers is 1–2; the metal ion loading per gram of graphene nanosheets is between 0.01 and 0.08 g. The weight ratio of the core layer to the amorphous carbon shell layer is 1:25; the weight ratio of cobalt-based alloy primary particles to graphene nanosheets is 19:1.

[0041] Example 2

[0042] S1: Anhydrous copper chloride and graphite are mixed in a horizontal tube furnace at a weight ratio of 3:1 under a mixed atmosphere of hydrogen and argon at a flow rate of 10 mL / min (the volume of argon is 5% of the volume of hydrogen) to obtain a mixture; the mixture is then heat-treated at a vacuum of 50 MPa and a temperature of 400 °C for 18 h to obtain the heat-treated material.

[0043] S2: The heat-treated material was washed sequentially with dilute hydrochloric acid aqueous solution (hydrogen chloride volume accounting for 5% of the solution volume) and deionized water. The washed solid product was then dispersed in DMF and sonicated (at 50 Hz for 35 min). The sonicated mixture was then centrifuged, and the precipitate was washed with ethanol. Finally, the washed material was dried to obtain graphene nanosheets loaded with metal ions.

[0044] S3: 3g of graphene nanosheets loaded with metal ions were dispersed in an ethanol solution containing allylamine under stirring and ultrasonication to form a dispersion. Then, 95g of CoSb3 powder was weighed and added to the dispersion. The dispersion was then washed with ethanol and filtered for 30 minutes using a vacuum filtration system.

[0045] S4: After filtration, the liquid was dried in a vacuum drying oven at 50°C for 2 hours and then transferred to a carbon mold. It was then sintered by discharge plasma at 600°C under a vacuum of 60 MPa for 10 minutes. Finally, the sintered material was placed in a ball mill for ball milling (500 r / min for 1.5 hours) to obtain granular core material.

[0046] S5: Dissolve 3g of asphalt (softening point 150℃) in 500mL of carbon tetrachloride organic solvent and disperse evenly. Then add 100g of the above granular core material, disperse evenly, spray dry, transfer to a tube furnace, and carbonize at 700℃ for 6h to obtain the negative electrode material.

[0047] The weight ratio of the core layer to the amorphous carbon shell is approximately 1:33; the weight ratio of cobalt-based alloy primary particles to graphene nanosheets is approximately 32:1.

[0048] Example 3

[0049] S1: Anhydrous aluminum chloride and graphite are mixed in a horizontal tube furnace at a weight ratio of 3:1 under a mixed atmosphere of hydrogen and argon at a flow rate of 10 mL / min (the volume of argon is 5% of the volume of hydrogen) to obtain a mixture; the mixture is then heat-treated at a vacuum of 50 MPa and a temperature of 400 °C for 18 h to obtain the heat-treated material.

[0050] S2: The heat-treated material was washed sequentially with dilute hydrochloric acid aqueous solution (hydrogen chloride volume accounting for 5% of the solution volume) and deionized water. The washed solid product was then dispersed in DMF and sonicated (at 50 Hz for 25 min). The sonicated mixture was then centrifuged, and the precipitate was washed with ethanol. Finally, the washed material was dried to obtain graphene nanosheets loaded with metal ions.

[0051] S3: 3g of graphene nanosheets loaded with metal ions were dispersed in an ethanol solution containing allylamine under stirring and ultrasonication to form a dispersion. Then, 97g of CoSb3 powder was weighed and added to the dispersion. The dispersion was then washed with ethanol and filtered for 30 minutes using a vacuum filtration system.

[0052] S4: After filtration, the liquid was dried in a vacuum drying oven at 50°C for 2 hours and then transferred to a carbon mold. It was then sintered by discharge plasma at 600°C under a vacuum of 60 MPa for 7 minutes. Finally, the sintered material was placed in a ball mill for ball milling (500 r / min for 1 hour) to obtain granular core material.

[0053] S5: Dissolve 2g of asphalt (softening point 150℃) in 500mL of carbon tetrachloride organic solvent and disperse evenly. Then add 100g of the above granular core material, disperse evenly, spray dry, transfer to a tube furnace, and carbonize at 700℃ for 6h to obtain the negative electrode material.

[0054] The weight ratio of the core layer to the amorphous carbon shell is 1:50; the weight ratio of cobalt-based alloy primary particles to graphene nanosheets is approximately 32:1.

[0055] Example 4

[0056] S1: Anhydrous ferric chloride and graphite are mixed in a horizontal tube furnace at a weight ratio of 3:1 under a mixed atmosphere of hydrogen and argon at a flow rate of 10 mL / min (the volume of argon is 5% of the volume of hydrogen) to obtain a mixture; the mixture is then heat-treated at a vacuum of 50 MPa and a temperature of 400 °C for 18 h to obtain the heat-treated material.

[0057] S2: The heat-treated material was washed sequentially with dilute hydrochloric acid aqueous solution (hydrogen chloride volume accounting for 5% of the solution volume) and deionized water. The washed solid product was then dispersed in DMF and sonicated (at 50 Hz for 30 min). The sonicated mixture was then centrifuged, and the precipitate was washed with ethanol. Finally, the washed material was dried to obtain graphene nanosheets loaded with metal ions.

[0058] S3: 0.5 g of graphene nanosheets loaded with metal ions were dispersed in an ethanol solution containing allylamine under stirring and ultrasonication to form a dispersion. Then, 99.5 g of CoSb3 powder was weighed and added to the dispersion. The dispersion was then washed with ethanol and filtered for 30 min using a vacuum filtration system.

[0059] S4: After filtration, the liquid is dried in a vacuum drying oven at 50°C for 2 hours and then transferred to a carbon mold. It is then sintered by discharge plasma at 600°C under a vacuum of 60 MPa for 5 minutes. Finally, the sintered material is placed in a ball mill for ball milling (500 r / min for 1 hour) to obtain granular core material.

[0060] S5: Dissolve 4g of asphalt (softening point 150℃) in 500mL of carbon tetrachloride organic solvent and disperse evenly. Then add 100g of the above granular core material, disperse evenly, spray dry, transfer to a tube furnace, and carbonize at 700℃ for 6h to obtain the negative electrode material.

[0061] The weight ratio of cobalt-based alloy primary particles to graphene nanosheets is 199:1.

[0062] Example 5

[0063] S1: Anhydrous ferric chloride and graphite are mixed in a horizontal tube furnace at a weight ratio of 3:1 under a mixed atmosphere of hydrogen and argon at a flow rate of 10 mL / min (the volume of argon is 5% of the volume of hydrogen) to obtain a mixture; the mixture is then heat-treated at a vacuum of 50 MPa and a temperature of 400 °C for 18 h to obtain the heat-treated material.

[0064] S2: The heat-treated material was washed sequentially with dilute hydrochloric acid aqueous solution (hydrogen chloride volume accounting for 5% of the solution volume) and deionized water. The washed solid product was then dispersed in DMF and sonicated (at 50 Hz for 30 min). The sonicated mixture was then centrifuged, and the precipitate was washed with ethanol. Finally, the washed material was dried to obtain graphene nanosheets loaded with metal ions.

[0065] S3: 11g of graphene nanosheets loaded with metal ions were dispersed in an ethanol solution containing allylamine under stirring and ultrasonication to form a dispersion. Then, 89g of CoSb3 powder was weighed and added to the dispersion. The dispersion was then washed with ethanol and filtered for 30 minutes using a vacuum filtration system.

[0066] S4: After filtration, the liquid is dried in a vacuum drying oven at 50°C for 2 hours and then transferred to a carbon mold. It is then sintered by discharge plasma at 600°C under a vacuum of 60 MPa for 5 minutes. Finally, the sintered material is placed in a ball mill for ball milling (500 r / min for 1 hour) to obtain granular core material.

[0067] S5: Dissolve 4g of asphalt (softening point 150℃) in 500mL of carbon tetrachloride organic solvent and disperse evenly. Then add 100g of the above granular core material, disperse evenly, spray dry, transfer to a tube furnace, and carbonize at 700℃ for 6h to obtain the negative electrode material.

[0068] The weight ratio of cobalt-based alloy primary particles to graphene nanosheets is approximately 8:1.

[0069] Comparative Example 1

[0070] 4g of asphalt (softening point 150℃) was dissolved in 500mL of carbon tetrachloride organic solvent and dispersed evenly. 100g of CoSb3 was ball-milled at 400r / min for 1h and then added to the mixture. The mixture was dispersed evenly, spray-dried, and then transferred to a tube furnace and carbonized at 700℃ for 6h to obtain amorphous carbon-coated CoSb3 material.

[0071] Performance characterization:

[0072] 1. Physical and chemical property testing of alloy composite materials

[0073] 1.1 SEM Testing

[0074] The alloy composite material prepared in Example 1 was subjected to SEM testing, and the test results are as follows: Figure 1 As shown in the figure, the alloy composite material exhibits a granular structure with a uniform size distribution, and its particle size is between (400~600) nm.

[0075] 1.2 Testing of the physicochemical properties of powder

[0076] The tap density, specific surface area, and specific capacity of the alloy composite anode materials prepared in the examples and comparative examples were tested according to GB / T 24533-2019 "Graphite Anode Materials for Lithium-ion Batteries". The test results are shown in Table 1.

[0077] Table 1

[0078]

[0079] As shown in Table 1, the electrical conductivity of the alloy composite materials prepared in Examples 1-5 of this invention is significantly higher than that of Comparative Example 1, but the tap density is not significantly different. This is because in Examples 1-5, the conductivity of the materials is improved by primary particle modification of graphene nanosheets loaded with metal ions and cobalt-based alloys through plasma discharge sintering. Thus, different amounts of graphene nanosheets loaded with metal ions have different effects on the conductivity of the materials, hence the significantly higher electrical conductivity of the alloy composite materials prepared in Examples 1-5 compared to Comparative Example 1. However, the alloy has a high density, so doping with graphene nanosheets loaded with metal ions has little effect on its density.

[0080] The negative electrode materials from Examples 1-5 and Comparative Example 1 were assembled into coin cells, respectively. The assembly method was as follows: binder, conductive agent, and solvent were added to the negative electrode material, stirred to form a slurry, coated onto copper foil, and then dried and rolled to obtain the negative electrode sheet. The coin cell assembly was carried out in a hydrogen-filled glove box, and the electrochemical performance was tested using a Wuhan Landian CT2001A battery tester. The charge / discharge voltage range was 0.005V to 2.0V, and the charge / discharge rate was 0.1C. The test results are shown in Table 2.

[0081] Table 2

[0082]

[0083] As can be seen from Table 2, the first discharge capacity and first charge-discharge efficiency of the lithium-ion battery using the composite negative electrode materials obtained in Examples 1-5 are significantly higher than those of Comparative Example 1. Graphene loaded with metal ions can reduce impedance and improve the material's intercalation and deintercalation capacity, thereby improving the material's discharge specific capacity and first efficiency. At the same time, the coating of amorphous carbon materials also reduces defects on the surface of the composite material and reduces irreversible capacity.

[0084] 2. Soft-pack battery test

[0085] Using the alloy composite material from the examples and comparative examples as the negative electrode material, negative electrode sheets were prepared. Ternary materials (LiNi) were used... 1 / 3 Co 1 / 3 Mn1 / 3 A 5Ah pouch cell was fabricated using O2 as the positive electrode, LiPF6 solution (solvent: EC+DEC, volume ratio 1:1, LiPF6 concentration 1.3mol / L) as the electrolyte, and Celegard 2400 as the separator. The cycle performance and rate performance of the pouch cell were then tested.

[0086] Cyclic performance test conditions: charge / discharge current 1C / 1C, voltage range 2.8-4.2V, number of cycles 500.

[0087] Rate performance test conditions: charging rate: 1C / 3C / 5C / 8C, discharging rate: 1C; voltage range: 2.8-4.2V.

[0088] The test results are shown in Tables 3 and 4.

[0089] Table 3

[0090]

[0091] As can be seen from Table 3, the pouch battery prepared with the negative electrode material of the present invention has better cycle performance than the comparative example. The reason is that, in terms of 1C / 1C rate cycle performance, the amorphous carbon wrapped in the outer layer can reduce defects on the material surface and prevent alloy particles from expanding and cracking. At the same time, the addition of graphene with metal ions promotes the insertion and extraction of lithium ions during charging and discharging, reduces impedance and improves the structural stability of the material, thereby improving cycle performance.

[0092] Table 4

[0093]

[0094] As can be seen from Table 4, the soft-pack batteries prepared with the negative electrode materials of Examples 1-5 of the present invention have a better constant current ratio. The high conductivity of graphene with metal ions improves the constant current ratio of the material and enhances the fast charging performance.

[0095] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A negative electrode material, characterized in that, The negative electrode material includes: The core layer is a modified cobalt-based alloy secondary particle, which comprises multiple cobalt-based alloy primary particles and graphene nanosheets dispersed among the primary particles, wherein the graphene nanosheets are loaded with metal ions; and An amorphous carbon shell covers the outer surface of the core layer; The metal ion is selected from one or more of the following: ferric ion, copper ion, aluminum ion, magnesium ion, calcium ion, or zinc ion. The primary particles of the cobalt-based alloy are selected from CoSb3; The core layer is prepared by the following method: metal chloride and graphite are mixed in a mixed atmosphere of hydrogen and argon to obtain a mixture; the mixture is heat-treated in a vacuum environment of 0.1~100MPa and a temperature of 300~500℃ for 18~24h, and then washed and dried to obtain graphene nanosheets loaded with metal ions; the dispersion containing the graphene nanosheets and cobalt-based alloy primary particles is dried and then subjected to spark plasma sintering to obtain the core layer; The negative electrode material is prepared by the following method: the dispersion containing the core layer and the carbon source is dried and then carbonized to coat the outer surface of the core layer with the amorphous carbon shell layer, thereby obtaining the negative electrode material. The carbon source is selected from pitch and / or petroleum coke; The carbonization process is carried out at a temperature of 700-1000℃ for 1-6 hours.

2. The negative electrode material according to claim 1, characterized in that, In the negative electrode material, the weight ratio of the core layer to the amorphous carbon shell layer is 1:(9~99). In the core layer, the weight ratio of the cobalt-based alloy primary particles to the graphene nanosheets is (20~40):1; the loading of metal ions is 0.01~0.08g per gram of graphene nanosheets.

3. The negative electrode material according to claim 1, characterized in that, The particle size of the negative electrode material is 400~600 nm; The particle size of the modified cobalt-based alloy secondary particles is 300~500nm; The graphene nanosheets have a thickness of 6-8 nm and have 1-2 layers.

4. A method for preparing a negative electrode material according to any one of claims 1 to 3, characterized in that, The preparation method includes the following steps: Step S1, providing a core layer, wherein the core layer is modified cobalt-based alloy secondary particles, the modified cobalt-based alloy secondary particles include multiple cobalt-based alloy primary particles and graphene nanosheets dispersed between the cobalt-based alloy primary particles, and the graphene nanosheets are loaded with metal ions. Step S2: Coat the outer surface of the core layer with an amorphous carbon shell to obtain the negative electrode material.

5. The method for preparing the negative electrode material according to claim 4, characterized in that, The core layer was prepared using the following method: Metal chloride and graphite are mixed in a mixed atmosphere of hydrogen and argon to obtain a mixture. The mixture is heat-treated in a vacuum environment of 0.1~100MPa and a temperature of 300~500℃ for 18~24h, and then washed and dried to obtain graphene nanosheets loaded with metal ions. The dispersion containing the graphene nanosheets and cobalt-based alloy primary particles is dried and then subjected to spark plasma sintering to obtain the core layer.

6. The method for preparing the negative electrode material according to claim 5, characterized in that, In the mixed atmosphere, argon gas accounts for 5-10% of the total volume; The discharge plasma sintering is carried out in a vacuum environment with a vacuum degree of 0.1~100MPa; and the sintering temperature is 600~800℃, and the sintering time is 5~10min.

7. The method for preparing the negative electrode material according to claim 5, characterized in that, The dispersion containing the core layer and the carbon source is dried and then carbonized to coat the outer surface of the core layer with the amorphous carbon shell layer, thereby obtaining the negative electrode material. The carbon source is selected from pitch and / or petroleum coke; The carbonization process is carried out at a temperature of 700-1000℃ for 1-6 hours.

8. A lithium-ion battery, characterized in that, The lithium-ion battery includes the negative electrode material according to any one of claims 1 to 3, or the negative electrode material prepared by the method of preparing the negative electrode material according to any one of claims 4 to 7.

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