Battery negative electrode, preparation method thereof and lithium ion battery

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a battery negative electrode and a preparation method thereof and a lithium ion battery, and the preparation method of the battery negative electrode comprises the following steps: mixing a carbon source and a nitrogen source, and heating at 250-350 DEG C in an inert gas atmosphere to obtain a nitrogen-doped raw material; mixing and ball-milling the nitrogen-doped raw material and lithium hydroxide to obtain a lithium-doped raw material; the lithium-doped raw material is heated in a graphitization furnace at the temperature of 1300-1500 DEG C, and a graphitized carbon material is obtained; and in a vacuum environment, taking the graphitized carbon material as a target material, taking a copper foil as a substrate, taking inert gas and hydrogen sulfide gas as working gases, and carrying out a magnetron sputtering technology to obtain the battery negative electrode. The pole piece formed by depositing the active substance on the copper foil through the magnetron sputtering technology is compact and firm, can be directly used for assembling the battery, does not need slurry preparation, does not contain an adhesive, does not contain conductive carbon black, and is beneficial to improving the specific capacity.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and particularly to a battery negative electrode, a preparation method thereof, and a lithium-ion battery. Background Art

[0002] With the wide application of lithium-ion batteries in fields such as electric vehicles and portable electronic devices, the requirements for negative electrode materials are getting higher and higher.

[0003] Currently, the commercially applied negative electrode materials are mainly carbon materials. Among various carbon materials, graphite is the most widely used negative electrode material.

[0004] Although traditional graphite negative electrode materials have a high theoretical lithium storage capacity, they have the problem of low specific capacity in practical applications and are increasingly unable to meet people's needs for lithium-ion batteries. Summary of the Invention

[0005] In order to solve the problem of low specific capacity of graphite negative electrode materials in the prior art, the present invention provides a preparation method of a battery negative electrode. This preparation method combines graphitization and magnetron sputtering technologies to deposit graphitized carbon materials on a copper foil to form a pole piece, making the carbon materials on the copper foil dense and firm, which can be directly used for battery assembly without the need for slurry preparation, without binders, without conductive carbon black, with high utilization rate of active substances, helping to improve the specific capacity, and solving the problem of low specific capacity of graphite negative electrode materials in the prior art.

[0006] The technical solution adopted by the present invention to solve its technical problems is as follows: A preparation method of a battery negative electrode, comprising the following steps: S1: Mix a carbon source and a nitrogen source, and heat in an inert gas atmosphere at 250 - 350 °C to obtain a nitrogen-doped raw material; S2: Mix and ball-mill the nitrogen-doped raw material with lithium hydroxide to obtain a lithium-doped raw material; S3: Heat the lithium-doped raw material in a graphitization furnace at 1300 - 1500 °C to obtain graphitized carbon materials; S4: In a vacuum environment, use the graphitized carbon materials as a target and a copper foil as a substrate, and use an inert gas and hydrogen sulfide gas as working gases, and obtain a battery negative electrode through magnetron sputtering technology.

[0007] Optionally, the carbon source is starch.

[0008] Optionally, the nitrogen source is urea.

[0009] Optionally, the mass ratio range of the carbon source to the nitrogen source is (8 - 10):1.

[0010] Optionally, the mass ratio of the carbon source to the nitrogen source is 9:1.

[0011] Optionally, the mass ratio range of the nitrogen-doped raw material to the lithium hydroxide is (8 - 10):1.

[0012] Optionally, in step S4, the volume ratio of the inert gas to the hydrogen sulfide gas is 1:1.

[0013] Optionally, the process parameters of magnetron sputtering in step S4 are: sputtering power is 160W - 180W, sputtering time is 4 - 6 hours, substrate temperature is 500°C, and sputtering pressure is 0.5Pa.

[0014] Another object of the present invention is to provide a battery negative electrode prepared by the preparation method of the battery negative electrode as described above.

[0015] Another object of the present invention is to provide a lithium-ion battery including the battery negative electrode as described above.

[0016] The beneficial effects of the present invention are: The preparation method of the battery negative electrode provided by the present invention deposits the active material on the copper foil through magnetron sputtering technology to form a pole piece, which is dense and firm, can be directly used for battery assembly, does not require slurry preparation, does not contain binders, does not contain conductive carbon black, realizes 100% utilization of the active material, and helps to improve the specific capacity; moreover, N doping is achieved through the nitrogen source, and S doping is achieved through lithium sulfide, which will increase the specific surface area and porosity of the material, provide more active sites, and thus improve the Coulomb efficiency; while performing S doping, lithium sulfide salt is also introduced, and through its prelithiation effect, it helps to further improve the cycle performance. Detailed Embodiments

[0017] The present invention will now be further described in detail. The embodiments described below are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0018] To solve the problem of low specific capacity of graphite negative electrode materials in the prior art, the present invention provides a preparation method of a battery negative electrode, which includes the following steps: S1: Mix the carbon source and the nitrogen source, and heat at 250 - 350°C in an inert gas atmosphere to obtain a nitrogen-doped raw material; Preferably, in this step, the carbon source and the nitrogen source are added to deionized water, stirred evenly, the moisture is dried, and the obtained solid is placed in a tube furnace, heated to 250 - 350°C, and kept warm for 3 - 5 hours. In this process, the elimination of impurities and the doping of nitrogen elements are completed; N doping can improve the wettability of carbon materials, enhance their contact area with the electrolyte, provide a better interface for electrochemistry, and thus improve the electrochemical performance. S2: Mix the nitrogen-doped raw material with lithium hydroxide and ball-mill them, preferably for 2 - 5 hours, to obtain the lithium-doped raw material. S3: Heat the lithium-doped raw material in a graphitization furnace at 1300 - 1500 °C to obtain the graphitized carbon material. S4: In a vacuum environment, use the graphitized carbon material as the target and copper foil as the substrate, and use inert gas and hydrogen sulfide gas as the working gases. Through magnetron sputtering technology, obtain the battery negative electrode.

[0019] In step S4, hydrogen sulfide reacts with lithium hydroxide in the material to generate lithium sulfide salt, realizing sulfur doping while completing prelithiation.

[0020] The preparation method of the battery negative electrode provided by the present invention deposits the active material on the copper foil through magnetron sputtering technology to form a pole piece, which is dense and firm, can be directly used for battery assembly, does not require slurry preparation, does not contain binders, does not contain conductive carbon black, realizes 100% utilization of the active material, and helps to improve the specific capacity. Moreover, through the nitrogen source, N doping is achieved, and through lithium sulfide, S doping is achieved, which will increase the specific surface area and porosity of the material, provide more active sites, and thus improve the Coulomb efficiency. When performing S doping, lithium sulfide salt is also introduced, and through its prelithiation effect, it helps to further improve the cycle performance.

[0021] The present invention first performs nitrogen doping on the carbon source, then lithium doping, then graphitizes the carbon material, and deposits the graphitized carbon material on the copper foil through magnetron sputtering technology. And during the magnetron sputtering process, hydrogen sulfide is introduced to react with the lithium hydroxide introduced by lithium doping, realizing sulfur doping while achieving prelithiation. Through the synergistic effect between various steps, while improving the electrochemical performance, the preparation steps are reduced and the process is simplified.

[0022] The present invention prepares the battery negative electrode through magnetron sputtering. Since magnetron sputtering technology has high target utilization rate and production efficiency, it is suitable for industrial production.

[0023] To ensure the electrochemical performance, the present invention preferably uses starch as the carbon source, urea as the nitrogen source, and preferably the mass ratio range of the carbon source to the nitrogen source is (8 - 10):1, and further preferably the mass ratio of the carbon source to the nitrogen source is 9:1.

[0024] The present invention preferably has the mass ratio range of the nitrogen-doped raw material to lithium hydroxide as (8 - 10):1, and further preferably the mass ratio range of the nitrogen-doped raw material to lithium hydroxide is 9:1.

[0025] To balance the pre-lithiation effect, sulfur doping effect, and the smooth progress of magnetron sputtering, the present invention preferably sets the volume ratio of inert gas to hydrogen sulfide gas in step S4 to 1:1, and preferably sets the process parameters of magnetron sputtering in step S4 as follows: the sputtering power is 160W - 180W, the sputtering time is 4 - 6 hours, the substrate temperature is 500°C, and the sputtering pressure is 0.5Pa.

[0026] Another object of the present invention is to provide a battery negative electrode, which is prepared by the preparation method of the battery negative electrode as described above.

[0027] In the preparation process of the battery negative electrode provided by the present invention, the active material is deposited on the copper foil by magnetron sputtering technology to form a pole piece, which is dense and firm, can be directly used for battery assembly, does not require slurry preparation, does not contain adhesives, does not contain conductive carbon black, realizes 100% utilization of the active material, and helps to improve the specific capacity; moreover, N doping is achieved through a nitrogen source, and S doping is achieved through lithium sulfide, which will increase the specific surface area and porosity of the material, provide more active sites, and thus improve the Coulomb efficiency; while performing S doping, lithium sulfide salt is also introduced, and through its pre-lithiation effect, it helps to further improve the cycle performance.

[0028] Another object of the present invention is to provide a lithium-ion battery, which includes the battery negative electrode as described above.

[0029] In the lithium-ion battery provided by the present invention, in the preparation process of the battery negative electrode used, the active material is deposited on the copper foil by magnetron sputtering technology to form a pole piece, which is dense and firm, can be directly used for battery assembly, does not require slurry preparation, does not contain adhesives, does not contain conductive carbon black, realizes 100% utilization of the active material, and helps to improve the specific capacity; moreover, N doping is achieved through a nitrogen source, and S doping is achieved through lithium sulfide, which will increase the specific surface area and porosity of the material, provide more active sites, and thus improve the Coulomb efficiency; while performing S doping, lithium sulfide salt is also introduced, and through its pre-lithiation effect, it helps to further improve the cycle performance.

[0030] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following detailed description of the specific embodiments of the present invention is provided.

[0031] Example 1 This example provides a preparation method of a battery negative electrode, including the following steps: Raw material preparation: Using wheat starch as a precursor, at room temperature, wheat starch and urea are stirred evenly in deionized water according to a mass ratio of 9:1, the moisture is dried, and the solid is heated to 300°C in an argon atmosphere in a tubular furnace and kept warm for 4 hours to discharge tar and ammonia. This process completes the removal of impurities and the doping of N elements to obtain a nitrogen-doped raw material. Lithium doping: Mix the nitrogen-doped raw material with lithium hydroxide in a mass ratio of 9:1 and ball-mill for 3 hours. This process completes lithium doping to obtain the lithium-doped raw material; Graphitization: Heat the above-mentioned lithium-doped raw material in a graphitization furnace to 1400 °C, keep it warm for 5 hours and then cool it to room temperature to complete the graphitization of the carbon material and obtain the graphitized carbon material; Magnetron sputtering: In a vacuum environment, use the graphitized carbon material as the target and the cleaned copper foil as the substrate. Use Ar gas and hydrogen sulfide gas as the working gases, with a volume ratio of 1:1. Set the sputtering power to 170 W, the sputtering time to 4 hours, the substrate temperature to 500 °C, and the sputtering pressure to 0.5 Pa. During the magnetron sputtering process, make hydrogen sulfide react with lithium hydroxide to generate lithium sulfide salt, which has a prelithiation effect and also realizes sulfur doping to obtain the battery negative electrode.

[0032] Example 2 This example provides a method for preparing a battery negative electrode, which includes the following steps: Raw material preparation: Use corn starch as the precursor. At room temperature, stir the corn starch and urea evenly in deionized water in a mass ratio of 9:1, dry the moisture, and heat the solid in a tubular furnace under argon atmosphere to 300 °C and keep it warm for 4 hours to discharge tar and ammonia. This process completes the removal of impurities and the doping of N element to obtain the nitrogen-doped raw material; Lithium doping: Mix the nitrogen-doped raw material with lithium hydroxide in a mass ratio of 9:1 and ball-mill for 3 hours. This process completes lithium doping to obtain the lithium-doped raw material; Graphitization: Heat the above-mentioned lithium-doped raw material in a graphitization furnace to 1400 °C, keep it warm for 5 hours and then cool it to room temperature to complete the graphitization of the carbon material and obtain the graphitized carbon material; Magnetron sputtering: In a vacuum environment, use the graphitized carbon material as the target and the cleaned copper foil as the substrate. Use Ar gas and hydrogen sulfide gas as the working gases, with a volume ratio of 1:1. Set the sputtering power to 160 W, the sputtering time to 4 hours, the substrate temperature to 500 °C, and the sputtering pressure to 0.5 Pa. During the magnetron sputtering process, make hydrogen sulfide react with lithium hydroxide to generate lithium sulfide salt, which has a prelithiation effect and also realizes sulfur doping to obtain the battery negative electrode.

[0033] Example 3 This example provides a method for preparing a battery negative electrode, which includes the following steps: Raw material preparation: Using potato starch as a precursor, at room temperature, potato starch and urea are stirred evenly in deionized water at a mass ratio of 9:1, the water is dried, and the solid is heated to 300 °C in an argon atmosphere in a tubular furnace and kept warm for 4 hours to discharge tar and ammonia. This process completes the removal of impurities and the doping of N element to obtain a nitrogen-doped raw material; Lithium doping: The nitrogen-doped raw material and lithium hydroxide are mixed and ball-milled for 3 hours at a mass ratio of 9:1. This process completes lithium doping to obtain a lithium-doped raw material; Graphitization: The above-mentioned lithium-doped raw material is heated to 1400 °C in a graphitization furnace, kept warm for 5 hours and then cooled to room temperature to complete the graphitization of the carbon material and obtain a graphitized carbon material; Magnetron sputtering: In a vacuum environment, the graphitized carbon material is used as a target, and the cleaned copper foil is used as a substrate. Ar gas and hydrogen sulfide gas are used as working gases, and their volume ratio is 1:1. The sputtering power is set to 180 W, the sputtering time is 4 hours, the substrate temperature is 500 °C, and the sputtering pressure is 0.5 Pa. During the magnetron sputtering process, hydrogen sulfide reacts with lithium hydroxide to generate lithium sulfide salt, which has a prelithiation effect and also realizes sulfur doping.

[0034] Example 4 This example provides a method for preparing a battery negative electrode, including the following steps: Raw material preparation: Using sweet potato starch as a precursor, at room temperature, sweet potato starch and urea are stirred evenly in deionized water at a mass ratio of 9:1, the water is dried, and the solid is heated to 300 °C in an argon atmosphere in a tubular furnace and kept warm for 4 hours to discharge tar and ammonia. This process completes the removal of impurities and the doping of N element to obtain a nitrogen-doped raw material; Lithium doping: The nitrogen-doped raw material and lithium hydroxide are mixed and ball-milled for 3 hours at a mass ratio of 9:1. This process completes lithium doping to obtain a lithium-doped raw material; Graphitization: The above-mentioned lithium-doped raw material is heated to 1400 °C in a graphitization furnace, kept warm for 5 hours and then cooled to room temperature to complete the graphitization of the carbon material and obtain a graphitized carbon material; Magnetron sputtering: In a vacuum environment, the graphitized carbon material is used as a target, and the cleaned copper foil is used as a substrate. Ar gas and hydrogen sulfide gas are used as working gases, and their volume ratio is 1:1. The sputtering power is set to 170 W, the sputtering time is 4 hours, the substrate temperature is 500 °C, and the sputtering pressure is 0.5 Pa. During the magnetron sputtering process, hydrogen sulfide reacts with lithium hydroxide to generate lithium sulfide salt, which has a prelithiation effect and also realizes sulfur doping to obtain a battery negative electrode.

[0035] Example 5 This example provides a method for preparing a battery negative electrode, including the following steps: Raw material preparation: Using wheat starch as a precursor, at room temperature, wheat starch and urea are stirred evenly in deionized water according to a mass ratio of 8:1, the moisture is dried, and the solid is heated to 300 °C in an argon atmosphere in a tube furnace, held for 4 hours, and tar and ammonia are discharged. This process completes the removal of impurities and the doping of N elements, obtaining a nitrogen-doped raw material; Lithium doping: The nitrogen-doped raw material and lithium hydroxide are mixed and ball-milled for 3 hours according to a mass ratio of 8:1. This process completes lithium doping, obtaining a lithium-doped raw material; Graphitization: The above-mentioned lithium-doped raw material is heated to 1400 °C in a graphitization furnace, held for 5 hours and then cooled to room temperature to complete the graphitization of the carbon material, obtaining a graphitized carbon material; Magnetron sputtering: In a vacuum environment, the graphitized carbon material is used as a target, and the cleaned copper foil is used as a substrate. Ar gas and hydrogen sulfide gas are used as working gases, and their volume ratio is 1:1. The sputtering power is set to 170 W, the sputtering time is 4 hours, the substrate temperature is 500 °C, and the sputtering pressure is 0.5 Pa. During the magnetron sputtering process, hydrogen sulfide reacts with lithium hydroxide to generate lithium sulfide salt, which has a prelithiation effect and also realizes sulfur doping, obtaining a battery negative electrode.

[0036] Example 6 This example provides a method for preparing a battery negative electrode, including the following steps: Raw material preparation: Using wheat starch as a precursor, at room temperature, wheat starch and urea are stirred evenly in deionized water according to a mass ratio of 10:1, the moisture is dried, and the solid is heated to 300 °C in an argon atmosphere in a tube furnace, held for 4 hours, and tar and ammonia are discharged. This process completes the removal of impurities and the doping of N elements, obtaining a nitrogen-doped raw material; Lithium doping: The nitrogen-doped raw material and lithium hydroxide are mixed and ball-milled for 3 hours according to a mass ratio of 10:1. This process completes lithium doping, obtaining a lithium-doped raw material; Graphitization: The above-mentioned lithium-doped raw material is heated to 1400 °C in a graphitization furnace, held for 5 hours and then cooled to room temperature to complete the graphitization of the carbon material, obtaining a graphitized carbon material; Magnetron sputtering: In a vacuum environment, a graphitized carbon material is used as the target, and a washed copper foil is used as the substrate. Ar gas and hydrogen sulfide gas are used as the working gases, with a volume ratio of 1:1. The sputtering power is set to 170 W, the sputtering time is 4 hours, the substrate temperature is 500 °C, and the sputtering pressure is 0.5 Pa. During the magnetron sputtering process, hydrogen sulfide reacts with lithium hydroxide to form lithium sulfide salt, which not only has a prelithiation effect but also realizes sulfur doping to obtain a battery negative electrode.

[0037] Comparative Example 1 This comparative example provides a method for preparing a battery negative electrode, including the following steps: Raw material preparation: Using wheat starch as the precursor, the moisture of wheat starch is dried at room temperature. The solid is heated to 300 °C in an argon atmosphere in a tubular furnace and held for 4 hours to remove tar, and this process completes the removal of impurities. Lithium doping: The solid with impurities removed is mixed with lithium hydroxide in a mass ratio of 9:1 and ball-milled for 3 hours, and this process completes lithium doping to obtain a lithium-doped raw material. Graphitization: The above lithium-doped raw material is heated to 1400 °C in a graphitization furnace, held for 5 hours, and then cooled to room temperature to complete the graphitization of the carbon material, obtaining a graphitized carbon material. Magnetron sputtering: In a vacuum environment, a graphitized carbon material is used as the target, and a washed copper foil is used as the substrate. Ar gas and hydrogen sulfide gas are used as the working gases, with a volume ratio of 1:1. The sputtering power is set to 170 W, the sputtering time is 4 hours, the substrate temperature is 500 °C, and the sputtering pressure is 0.5 Pa. During the magnetron sputtering process, hydrogen sulfide reacts with lithium hydroxide to form lithium sulfide salt, which not only has a prelithiation effect but also realizes sulfur doping to obtain a battery negative electrode.

[0038] Comparative Example 2 This comparative example provides a method for preparing a battery negative electrode, including the following steps: Raw material preparation: Using wheat starch as the precursor, wheat starch and urea are stirred evenly in deionized water in a mass ratio of 9:1 at room temperature, dried to remove moisture, and the solid is heated to 300 °C in an argon atmosphere in a tubular furnace and held for 4 hours to remove tar and ammonia. This process completes the removal of impurities and the doping of N element to obtain a nitrogen-doped raw material. Graphitization: The above nitrogen-doped raw material is heated to 1400 °C in a graphitization furnace, held for 5 hours, and then cooled to room temperature to complete the graphitization of the carbon material, obtaining a graphitized carbon material. Magnetron sputtering: In a vacuum environment, a graphitized carbon material is used as a target, a cleaned copper foil is used as a substrate, Ar gas and hydrogen sulfide gas are used as working gases, with a volume ratio of 1:1. The sputtering power is set to 170 W, the sputtering time is 4 hours, the substrate temperature is 500 °C, and the sputtering pressure is 0.5 Pa. Sulfur doping is achieved during the magnetron sputtering process to obtain a battery negative electrode.

[0039] Comparative Example 3 This comparative example provides a method for preparing a battery negative electrode, which includes the following steps: Raw material preparation: Using wheat starch as a precursor, at room temperature, wheat starch and urea are stirred evenly in deionized water according to a mass ratio of 9:1, the moisture is dried, and the solid is heated to 300 °C in an argon atmosphere in a tubular furnace and kept warm for 4 hours to discharge tar and ammonia. This process completes the removal of impurities and the doping of N elements to obtain a nitrogen-doped raw material; Lithium doping: The nitrogen-doped raw material and lithium hydroxide are mixed and ball-milled for 3 hours according to a mass ratio of 9:1. This process completes lithium doping to obtain a lithium-doped raw material; Graphitization: The above lithium-doped raw material is heated to 1400 °C in a graphitization furnace, kept warm for 5 hours, and then cooled to room temperature to complete the graphitization of the carbon material and obtain a graphitized carbon material; Magnetron sputtering: In a vacuum environment, the graphitized carbon material is used as a target, a cleaned copper foil is used as a substrate, Ar gas is used as a working gas, the sputtering power is set to 170 W, the sputtering time is 4 hours, the substrate temperature is 500 °C, and the sputtering pressure is 0.5 Pa to obtain a battery negative electrode.

[0040] Comparative Example 4 This comparative example provides a method for preparing a battery negative electrode, which includes the following steps: Raw material preparation: Using wheat starch as a precursor, at room temperature, wheat starch and urea are stirred evenly in deionized water according to a mass ratio of 9:1, the moisture is dried, and the solid is heated to 300 °C in an argon atmosphere in a tubular furnace and kept warm for 4 hours to discharge tar and ammonia. This process completes the removal of impurities and the doping of N elements to obtain a nitrogen-doped raw material; Magnetron sputtering: In a vacuum environment, the above nitrogen-doped raw material is used as a target, a cleaned copper foil is used as a substrate, Ar gas is used as a working gas, the sputtering power is set to 160 W, the sputtering time is 4 hours, the substrate temperature is 500 °C, and the sputtering pressure is 0.5 Pa to obtain a battery negative electrode.

[0041] Comparative Example 5 This comparative example provides a method for preparing a negative electrode material, which includes the following steps: Raw material preparation: Using wheat starch as a precursor, at room temperature, wheat starch and urea are stirred evenly in deionized water at a mass ratio of 9:1, the moisture is dried, and the solid is heated to 300 °C in an argon atmosphere in a tubular furnace and held for 4 hours to remove tar and ammonia. This process completes the removal of impurities and the doping of N element, obtaining a nitrogen-doped raw material; Lithium doping: The nitrogen-doped raw material and lithium hydroxide are mixed and ball-milled for 3 hours at a mass ratio of 9:1. This process completes lithium doping, obtaining a lithium-doped raw material; Graphitization: The above-mentioned lithium-doped raw material is heated to 1400 °C in a graphitization furnace, held for 5 hours and then cooled to room temperature to complete the graphitization of the carbon material, obtaining a graphitized carbon material, which is the negative electrode material.

[0042] The negative electrode slices prepared in the above-mentioned examples and comparative examples 1-4 are directly used for button cell preparation, and the preparation method is as follows: The negative electrode sheets obtained in the examples and comparative examples 1-4 are directly cut into the sizes required for button cell testing. Using a PP film as the button cell separator and a lithium metal sheet as the counter electrode, the above-mentioned obtained negative electrode sheets are assembled into 2430 button cells in a glove box to test their electrochemical performance and conduct tests; the test voltage is (0-3) V and the current is 0.05C; The negative electrode material prepared in comparative example 5 is prepared for button cell as follows: The material prepared in comparative example 5 is used as the negative electrode active material, and is mixed evenly with polyvinylidene fluoride (PVDF) (dissolved in N-methylpyrrolidone) and conductive carbon black at a mass ratio of 90:5:5, coated into an electrode film, placed in a vacuum drying oven and dried at 120 °C for 12 h, rolled and punched to obtain a negative electrode sheet; using a PP film as the button cell separator and a lithium metal sheet as the counter electrode, the above-mentioned obtained negative electrode sheets are assembled into 2430 button cells in a glove box to test their electrochemical performance and conduct tests; the test voltage is (0-3) V and the current is 0.05C; Then, the electrochemical performance is tested, and the test results are shown in Table 1: Table 1 Serial number Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Coulombic efficiency 93.5% 92% 94% 92.8% 91.6% 92% 87.6% 92.1% 86.9% 81.6% 83.5% Specific capacity mAh / g 402 391 387 397 381 382 394 362 353 267 281 Cycling performance (capacity retention after 100 cycles at 1C) 95.5% 93.8% 96.3% 94.2% 93.9% 94.3% 75.2% 82.0% 89.5% 65.1% 70.3% From the above data, it can be seen that the batteries prepared with the negative electrodes prepared in the examples of the present invention all have high specific capacity, excellent cycle stability and Coulomb efficiency.

[0043] Comparative Example 1 did not perform N doping compared with Example 1, and had poor Coulombic efficiency and cycling performance; Comparative Example 2 did not perform Li doping compared with Example 1, lacking the effect of prelithiation, and the Coulombic efficiency and cycling performance decreased; Comparative Example 3 did not introduce hydrogen sulfide during the magnetron sputtering process compared with Example 1, lacking sulfur element doping, and the Coulombic efficiency and cycling performance decreased, but the decrease was not very obvious; Comparative Example 4 did not perform graphitization before magnetron sputtering, nor did it perform Li doping and S doping. The conductivity of the sputtering raw material was poor, so all the indexes of the prepared negative electrode were not ideal; Comparative Example 5 directly used graphitized materials for coin cell preparation. The coin cell material formula contained a conductive agent and a binder. The proportion of the active material decreased compared with Example 1, the specific capacity decreased, and this comparative example did not perform S doping, and the Coulombic efficiency and cycling performance also decreased.

[0044] Inspired by the ideal embodiments of the present invention described above, through the above description, relevant staff can completely make various changes and modifications without departing from the technical idea of the present invention. The technical scope of the present invention is not limited to the content in the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A method for preparing a negative electrode of a battery, characterized in that, It includes the following steps: S1: Mix a carbon source and a nitrogen source, and heat them at 250 - 350 °C in an inert gas atmosphere to obtain a nitrogen-doped raw material; S2: Mix and ball-mill the nitrogen-doped raw material with lithium hydroxide to obtain a lithium-doped raw material; S3: Heat the lithium-doped raw material in a graphitization furnace at 1300 - 1500 °C to obtain a graphitized carbon material; S4: In a vacuum environment, use the graphitized carbon material as a target and a copper foil as a substrate, and use an inert gas and hydrogen sulfide gas as working gases. Through magnetron sputtering technology, a battery negative electrode is obtained.

2. The method for preparing the negative electrode of the battery according to claim 1, characterized in that, The carbon source is starch.

3. The method for preparing the negative electrode of the battery according to claim 1, characterized in that, The nitrogen source is urea.

4. The preparation method of the battery negative electrode according to claim 1, characterized in that, The mass ratio range of the carbon source to the nitrogen source is (8 - 10):

1.

5. The preparation method of the battery negative electrode according to claim 1, characterized in that, The mass ratio of the carbon source to the nitrogen source is 9:

1.

6. The method for preparing the negative electrode of the battery according to claim 1, characterized in that, The mass ratio range of the nitrogen-doped raw material to the lithium hydroxide is (8 - 10):

1.

7. The method for preparing the negative electrode of the battery according to claim 1, wherein, In step S4, the volume ratio of the inert gas to the hydrogen sulfide gas is 1:

1.

8. The method for preparing the negative electrode of the battery according to claim 1, characterized in that, The process parameters of magnetron sputtering in step S4 are: sputtering power is 160W - 180W, sputtering time is 4 - 6 hours, substrate temperature is 500 °C, and sputtering pressure is 0.5 Pa.

9. A battery negative electrode, characterized in that, It is prepared by the preparation method of the battery negative electrode according to any one of claims 1 - 8.

10. A lithium-ion battery, characterized in that, It includes the battery negative electrode according to claim 9.