High-entropy graphite composite anode material and its preparation method, and its application in lithium-ion batteries.

Abstract

This invention relates to the field of batteries, and discloses a high-entropy graphite composite anode material, its preparation method, and an anode and lithium-ion battery. The preparation method includes mixing graphite and a surfactant in a first solvent to obtain solution A, mixing multiple transition metal element sources in a second solvent to obtain solution B, mixing solutions A and B, removing the first and second solvents, and then heat-treating in an oxygen-free environment to obtain the anode material. The multiple transition metal element sources are selected from five or more of scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, zirconium, niobium, molybdenum, tantalum, and tungsten sources. The anode material prepared by this invention, by coating the graphite surface with a coating layer formed by multiple transition metal elements, can significantly improve conductivity, provide more lithium storage active sites, reduce the impedance during the lithium intercalation process, help increase the reversible capacity of the material, and is also beneficial to improving its initial efficiency.

Description

Technical Field

[0001] This invention relates to the field of batteries, specifically to a high-entropy graphite composite anode material and its preparation method, as well as the anode and lithium-ion battery. Background Technology

[0002] Although graphite is currently the primary anode material used in commercial lithium-ion batteries, its layered structure and low lithiation potential prevent it from meeting the requirements for low-temperature fast charging applications. At low temperatures, the lithium-ion transport rate in graphite anodes decreases with decreasing temperature. Furthermore, under fast charging conditions, the inconsistent lithium-ion transport rates between the graphite anode surface and interlayer layers easily lead to the formation of lithium dendrites on the graphite surface, causing battery performance degradation and even damaging the battery structure. Summary of the Invention

[0003] The purpose of this invention is to overcome the problem of severe performance degradation of anode materials during low-temperature fast charging, and to provide a high-entropy graphite composite anode material, its preparation method, and an anode and lithium-ion battery. The high-entropy graphite composite anode material provided by this invention forms a coating layer on the surface of graphite using various transition metal elements, reducing the anisotropy of lithium-ion transport in graphite, increasing the material's reversible capacity and initial efficiency, and showing good application prospects in low-temperature fast charging.

[0004] To achieve the above objectives, the first aspect of the present invention provides a method for preparing a high-entropy graphite composite anode material, wherein the preparation method includes: mixing graphite and a surfactant in a first solvent to obtain solution A; mixing multiple transition metal element sources in a second solvent to obtain solution B; mixing solution A and solution B in a third mixture; removing the first solvent and the second solvent to obtain a graphite composite; and heat-treating the graphite composite in an oxygen-free environment to obtain the anode material.

[0005] The various transition metal element sources are selected from five or more of the following: scandium source, titanium source, vanadium source, chromium source, manganese source, iron source, cobalt source, nickel source, copper source, zinc source, zirconium source, niobium source, molybdenum source, tantalum source, and tungsten source.

[0006] A second aspect of the present invention provides a high-entropy graphite composite anode material, wherein, based on the total amount of the anode material, the amount of graphite is 96-99.5 wt%, and the amount of transition metal elements is 0.5-4 wt%.

[0007] A third aspect of the present invention provides a negative electrode, comprising a negative electrode material prepared by the preparation method according to the first aspect of the present invention or a negative electrode material according to the second aspect of the present invention.

[0008] A fourth aspect of the present invention provides a lithium-ion battery, including the negative electrode described in the third aspect of the present invention.

[0009] In preparing a negative electrode material coated with multiple transition metal elements, this invention first modifies the graphite surface using a surfactant, dispersing it uniformly in a first solvent to form solution A. Simultaneously, multiple transition metal element sources are dissolved in a second solvent to form solution B. Then, solutions A and B are mixed, and the first and second solvents are removed. The resulting graphite composite is then heat-treated under oxygen-free conditions to obtain the negative electrode material coated with multiple transition metal elements. In other words, this invention utilizes a liquid-phase method to disperse multiple transition metal element sources on the graphite surface. After heat treatment, the multiple transition metal elements combine and are uniformly distributed on the graphite surface to form a coating layer, reducing the anisotropy of the graphite material and thus improving its lithium storage performance.

[0010] The preparation method provided by this invention is simple, safe, low-cost, and has good continuity, making it suitable for mass production.

[0011] The graphite anode material coated with various transition metal elements provided in this invention includes five or more of the following elements: scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, zirconium, niobium, molybdenum, tantalum, and tungsten. The coating layer formed by these transition metal elements can significantly improve conductivity, provide more lithium storage active sites, reduce impedance during lithium intercalation, and help increase the reversible capacity of the graphite anode material. Furthermore, the transition metal elements can effectively expand the interlayer spacing, which is beneficial for lithium ion insertion and extraction, and enhances lithium ion diffusion and insertion kinetics, thus improving the first-stage efficiency of the graphite anode. Using the graphite anode material coated with transition metal elements provided in this invention as a negative electrode material for lithium-ion batteries shows good application prospects in low-temperature fast charging. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the structure of the negative electrode material prepared in Example 1;

[0013] Figure 2 This is the EDS image of the negative electrode material prepared in Example 1;

[0014] Figure 3 This is the 0.1C cycle rate test chart of Example 1.

[0015] Figure 4 This is a cycle rate test chart of 1C in Example 1. Detailed Implementation

[0016] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0017] The terms “first,” “second,” and “third” are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as “first,” “second,” or “third” may explicitly or implicitly include one or more of that feature.

[0018] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0019] The first aspect of the present invention provides a method for preparing a high-entropy graphite composite anode material, wherein the preparation method includes: mixing graphite and a surfactant in a first solvent to obtain solution A; mixing multiple transition metal element sources in a second solvent to obtain solution B; mixing solution A and solution B in a third mixture; removing the first solvent and the second solvent to obtain a graphite composite; and heat-treating the graphite composite in an oxygen-free environment to obtain the anode material.

[0020] The various transition metal element sources are selected from five or more of the following: scandium source, titanium source, vanadium source, chromium source, manganese source, iron source, cobalt source, nickel source, copper source, zinc source, zirconium source, niobium source, molybdenum source, tantalum source, and tungsten source.

[0021] This invention utilizes a surfactant to surface-activate graphite to obtain a modified graphite solution A. The modified graphite solution A is then mixed with a solution B containing multiple transition metal element sources, and heat-treated in an oxygen-free environment to obtain a high-entropy graphite composite anode material coated with multiple transition metal elements. In other words, this invention uses a liquid-phase method to uniformly distribute transition metal elements on the graphite surface, forming a uniform coating layer, thereby improving the stability of the material, enhancing the lithium storage performance of graphite, and improving the low-temperature fast-charging performance of the material.

[0022] The graphite can be artificial graphite, natural graphite, etc., and there are no special requirements for the type of graphite.

[0023] In some embodiments, preferably, the mass ratio of graphite to surfactant is 5-25:1.

[0024] In some embodiments, preferably, the mass ratio of graphite to surfactant is 10-20:1.

[0025] The mass ratio of graphite to surfactant affects the uniformity of graphite dispersion, which in turn affects the uniformity of the coating layer. The uniformity of the coating layer affects the specific capacity of the material. This invention can further improve the specific capacity of the anode material by optimizing the mass ratio of graphite to surfactant. The mass ratio of graphite to surfactant can be any value between any two numbers from 5:1, 7:1, 10:1, 13:1, 15:1, 17:1, 20:1, 22:1, and 25:1.

[0026] In some embodiments, preferably, the total mass ratio of the graphite and surfactant to the total mass ratio of the multiple transition metal element sources is 20-80:1.

[0027] In some embodiments, preferably, the total mass ratio of the graphite and surfactant to the total mass ratio of the multiple transition metal element sources is 30-40:1.

[0028] The total mass ratio of graphite and surfactant to the total mass ratio of various transition metal source elements affects the thickness of the coating layer, and thus the specific capacity of the material. The preferred mass ratio of the two elements in this invention can further improve the above-mentioned properties. The mass ratio of graphite to various transition metal source elements can be any value between any two numbers from 20:1, 30:1, 31:1, 32:1, 33:1, 34:1, 35:1, 36:1, 37:1, 38:1, 39:1, 40:1, 50:1, 60:1, 70:1, and 80:1.

[0029] In some embodiments, preferably, the heat treatment temperature is 700-800°C and the time is 1-4 hours.

[0030] In some embodiments, preferably, the heating rate of the heat treatment is 4-6°C / min.

[0031] During heat treatment, parameters such as temperature, time, and heating rate affect the performance of the anode material, including reversible specific capacity, coulombic efficiency, and capacity retention. The preferred heat treatment temperature, time, and heating rate of this invention can further improve these properties. The heat treatment temperature can be any value between any two of the following: 700℃, 710℃, 720℃, 730℃, 740℃, 750℃, 760℃, 770℃, 780℃, 790℃, and 800℃. The heat treatment time can be any value between any two of the following: 1h, 2h, 3h, and 4h. The heating rate can be any value between any two of the following: 4℃ / min, 5℃ / min, and 6℃ / min.

[0032] In some embodiments, preferably, the first solvent and the second solvent are water and / or ethanol, respectively, independently. Using water and / or ethanol as solvents facilitates subsequent removal and improves operational safety. When the solvents are water and ethanol, there are no particular requirements regarding their ratio.

[0033] In some embodiments, preferably, the concentration of solution A is 0.1-0.5 g / mL.

[0034] In some embodiments, preferably, the concentration of solution B is 0.01-0.05 g / mL.

[0035] Solution A comprises graphite, a surfactant, and a first solvent, while solution B comprises multiple transition metal element sources and a second solvent. The concentrations of solutions A and B affect the thickness and uniformity of the coating layer, and consequently, the specific capacity of the negative electrode material. The preferred concentrations of the two solutions in this invention are beneficial for further improving the aforementioned performance. The concentration of solution A can be any value between any two numbers from 0.1 g / mL, 0.2 g / mL, 0.3 g / mL, 0.4 g / mL, and 0.5 g / mL, and the concentration of solution B can be any value between any two numbers from 0.01 g / mL, 0.02 g / mL, 0.03 g / mL, 0.04 g / mL, and 0.05 g / mL.

[0036] In some embodiments, preferably, the surfactant comprises polyvinylpyrrolidone and / or hexadecyltrimethylammonium bromide. These surfactants are widely available and inexpensive, and facilitate low-temperature decomposition reactions.

[0037] In some embodiments, preferably, the scandium source includes one or more of scandium chloride, scandium carbonate, scandium sulfate, and scandium nitrate.

[0038] In some embodiments, preferably, the titanium source includes one or more of titanium chloride, titanium carbonate, titanium sulfate, and titanium nitrate.

[0039] In some embodiments, preferably, the vanadium source includes one or more of vanadium chloride, vanadium carbonate, vanadium sulfate, and vanadium nitrate.

[0040] In some embodiments, preferably, the chromium source includes one or more of chromium chloride, chromium carbonate, chromium sulfate, and chromium nitrate.

[0041] In some embodiments, preferably, the manganese source includes one or more of manganese chloride, manganese carbonate, manganese sulfate, and manganese nitrate.

[0042] In some embodiments, preferably, the iron source includes one or more of ferric chloride, ferric carbonate, ferric sulfate, and ferric nitrate.

[0043] In some embodiments, preferably, the cobalt source includes one or more of cobalt chloride, cobalt carbonate, cobalt sulfate, and cobalt nitrate.

[0044] In some embodiments, preferably, the nickel source includes one or more of nickel chloride, nickel carbonate, nickel sulfate, and nickel nitrate.

[0045] In some embodiments, preferably, the copper source includes one or more of copper chloride, copper carbonate, copper sulfate, and copper nitrate.

[0046] In some embodiments, preferably, the zinc source includes one or more of zinc chloride, zinc carbonate, zinc sulfate, and zinc nitrate.

[0047] In some embodiments, preferably, the zirconium source includes one or more of zirconium chloride, zirconium carbonate, zirconium sulfate, and zirconium nitrate.

[0048] In some embodiments, preferably, the niobium source includes one or more of niobium chloride, niobium carbonate, niobium sulfate, and niobium nitrate.

[0049] In some embodiments, preferably, the molybdenum source includes one or more of molybdenum chloride, molybdenum carbonate, molybdenum sulfate, and molybdenum nitrate.

[0050] In some embodiments, preferably, the tantalum source includes one or more of tantalum chloride, tantalum carbonate, tantalum sulfate, and tantalum nitrate.

[0051] In some embodiments, preferably, the tungsten source includes one or more of tungsten chloride, tungsten carbonate, tungsten sulfate, and tungsten nitrate.

[0052] The scandium source, titanium source, vanadium source, chromium source, manganese source, iron source, cobalt source, nickel source, copper source, zinc source, zirconium source, niobium source, molybdenum source, tantalum source, and tungsten source mentioned above can all undergo low-temperature decomposition reactions, which is beneficial for forming a surface coating layer.

[0053] In some embodiments, preferably, the particle size D of the graphite is... 50 The particle size is 100-200 μm. Smaller graphite particles have a larger specific surface area and better ionic conductivity, which is beneficial for improving the low-temperature fast-charging performance of the anode material. The particle size of graphite can be any value between any two of 100 μm, 150 μm, and 200 μm.

[0054] In some embodiments, preferably, the method for removing the first solvent and the second solvent includes: spray drying, solvent evaporation, freeze drying, filtration, and centrifugation of the third mixed solution.

[0055] When using solvent evaporation, simply mix the mixture and then evaporate the solvent. The temperature for evaporating the solvent is generally 60-140℃. Evaporate until the solution becomes gelatinous, and then weigh it every 10-20 minutes. The solvent is considered to have been evaporated when the weight difference between two consecutive weighings does not exceed 0.005g.

[0056] In some embodiments, preferably, the method for removing the first solvent and the second solvent includes: spray drying the third mixed solution, wherein the outlet temperature of the spray dryer is 60-120°C. The outlet temperature during spray drying can be any value between any two of 60°C, 80°C, 100°C, and 120°C.

[0057] In some embodiments, preferably, the freeze-drying temperature is -20°C to -10°C, and the time is 24-32 hours. When freeze-drying is used, the temperature can be any value between any two of -20°C, -15°C, and -10°C, and the time can be any value between any two of 24 hours, 26 hours, 28 hours, 30 hours, and 32 hours.

[0058] In some embodiments, preferably, the first mixing, the second mixing, and the third mixing each independently include stirring. This invention uses a liquid-phase method to disperse multiple transition metal element sources on the graphite surface. The graphite and transition metal elements exhibit good dispersion uniformity, thus requiring only simple stirring and mixing, making the operation simple.

[0059] In some embodiments, preferably, the oxygen-free environment is a vacuum environment or an inert gas environment.

[0060] In some embodiments, preferably, the vacuum degree of the vacuum environment is 500-10 Pa. The vacuum degree only needs to meet the requirement of oxygen exclusion, and the vacuum degree can be any value between any two numbers from 10 Pa, 50 Pa, 100 Pa, 150 Pa, 200 Pa, 300 Pa, 400 Pa, and 500 Pa.

[0061] In some embodiments, preferably, the inert gas in the inert gas environment includes one or more of helium, neon, argon, and krypton.

[0062] A second aspect of the present invention provides a high-entropy graphite composite anode material, wherein the high-entropy graphite composite anode material comprises graphite and a layer of multiple transition metal elements coated on the surface of the graphite, wherein the multiple transition metal elements are selected from five or more of scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, zirconium, niobium, molybdenum, tantalum and tungsten.

[0063] In some embodiments, preferably, based on the total amount of the entropy graphite composite anode material, the amount of graphite is 96-99.5 wt%, and the total amount of the various transition metal elements is 0.5-4 wt%.

[0064] In some embodiments, preferably, based on the total amount of the negative electrode material, the amount of each transition metal element in the multiple transition metal element sources is independently 0-0.8 wt%.

[0065] In some embodiments, preferably, based on the total amount of the negative electrode material, the amount of each transition metal element in the multiple transition metal element sources is independently 0-0.4 wt%.

[0066] Based on the total amount of the entropy-graphite composite anode material, the amount of graphite can be any value between any two of the following: 96wt%, 96.5wt%, 97wt%, 97.5wt%, 98wt%, 98.1wt%, 98.2wt%, 98.3wt%, 98.4wt%, 98.5wt%, 98.6wt%, 98.7wt%, 98.8wt%, 98.9wt%, 99wt%, 99.2wt%, 99.4wt%, and 99.5wt%. The total amount of various transition metal elements can be 0.5wt%, 1wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.7wt%, 1.8wt%, 1.9wt%, 2wt%, 2.5wt%, and 3wt%. The amounts of various transition metal elements in the source are any values ​​between any two numbers from 0, 0.02wt%, 0.05wt%, 0.08wt%, 0.1wt%, 0.13wt%, 0.15wt%, 0.17wt%, 0.2wt%, 0.22wt%, 0.25wt%, 0.3wt%, 0.33wt%, 0.35wt%, 0.38wt%, 0.4wt%, 0.42wt%, 0.45wt%, 0.47wt%, 0.48wt%, 0.5wt%, 0.52wt%, 0.55wt%, 0.58wt%, 0.6wt%, 0.7wt%, and 0.8wt%.

[0067] A third aspect of the present invention provides a negative electrode, comprising a negative electrode material prepared by the preparation method according to the first aspect of the present invention or a negative electrode material according to the second aspect of the present invention.

[0068] A fourth aspect of the present invention provides a lithium-ion battery, including the negative electrode described in the third aspect of the present invention.

[0069] In preparing a high-entropy anode material coated with multiple transition metal elements, this invention first modifies the graphite surface using a surfactant, uniformly dispersing it in a first solvent to form solution A. Simultaneously, multiple transition metal element sources are dissolved in a second solvent to form solution B. Solutions A and B are then mixed, and the solvent is removed. The mixture is then heat-treated under oxygen-free conditions to obtain a high-entropy anode material coated with at least five transition metal elements. In other words, this invention utilizes a liquid-phase method to disperse multiple transition metal element sources on the graphite surface. Through heat treatment, the multiple transition metal elements combine and uniformly coat the graphite surface, reducing the anisotropy of the graphite material and thus improving its lithium storage performance. In this invention, by controlling the ratio of graphite to surfactant, the ratio of graphite to multiple transition metal elements, and parameters such as temperature and time during heat treatment, the structure and properties of the transition metal element-coated graphite can be effectively improved.

[0070] The preparation method provided by this invention is simple, safe, low-cost, and has good continuity, making it suitable for mass production.

[0071] The high-entropy anode material of graphite coated with transition metal elements provided by this invention includes five or more of the following elements: scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, zirconium, niobium, molybdenum, tantalum, and tungsten. The high-entropy transition metal element coating layer can significantly improve the conductivity of the material, provide more lithium storage active sites, reduce the impedance during lithium intercalation, and help increase the reversible capacity of the graphite anode material. Furthermore, the high-entropy metal can effectively expand the interlayer spacing of the material, which is beneficial for lithium-ion insertion and extraction, and enhances lithium-ion diffusion and insertion kinetics, thus improving the first-stage efficiency of the prepared anode material. Using the high-entropy graphite composite anode material provided by this invention as a lithium-ion battery anode material has good application prospects in low-temperature fast charging.

[0072] According to a particularly preferred embodiment of the present invention, the preparation method includes: mixing graphite and a surfactant in a first solvent to obtain solution A; mixing multiple transition metal element sources in a second solvent to obtain solution B; mixing solution A and solution B in a third mixture; removing the first solvent and the second solvent to obtain a graphite composite; and heat-treating the graphite composite in an oxygen-free environment to obtain a negative electrode material.

[0073] The various transition metal element sources include manganese, cobalt, nickel, copper, and zinc.

[0074] The mass ratio of graphite to surfactant is 12-18:1;

[0075] The total mass ratio of the graphite and surfactant to the total mass ratio of the various transition metal element sources is 33-28:1;

[0076] The heat treatment temperature is 720-750℃, the time is 2-3 hours, and the heating rate is 5℃ / min.

[0077] The present invention will be described in detail below through examples. Unless otherwise specified in the examples and comparative examples, conditions were performed under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used, unless otherwise specified, are all commercially available products.

[0078] In the following examples and comparative examples, the distribution of transition metal elements was detected using a field emission scanning electron microscope (Hitachi, Japan).

[0079] The graphite content in the high-entropy graphite composite anode material was analyzed using a thermogravimetric analyzer TGA2 (Mettler, Switzerland). The carbon content in the sample could be determined by the change in mass. The content of transition metal elements was tested using an inductively coupled plasma atomic emission spectrometer (Agilent 725ES & Agilent 5110).

[0080] Example 1

[0081] Step (1): Weigh 100g of artificial graphite with a particle size of 150μm and 6.67g of polyvinylpyrrolidone, then add them to 533mL of water and stir at 500rpm for 12h on a magnetic stirrer to obtain modified graphite solution A.

[0082] Step (2): Weigh 0.60g nickel nitrate, 0.60g cobalt nitrate, 0.59g manganese nitrate, 0.62g copper nitrate and 0.63g zinc nitrate respectively, add them to 60.95ml water, and stir on a magnetic stirrer at 500rpm for 12h to obtain solution B;

[0083] Step (3): Mix solution A and solution B and stir at 500 rpm for 12 hours on a magnetic stirrer to obtain a mixed solution. The mixed solution is then spray-dried to obtain a graphite composite, wherein the outlet temperature of the spray dryer is 120°C.

[0084] Step (4): The graphite composite is heated to 740°C at a vacuum of 10 Pa at a rate of 5°C / min and held for 3 hours to obtain a high-entropy graphite composite anode material, denoted as A1.

[0085] Example 2

[0086] Step (1): Weigh 100g of artificial graphite with a particle size of 150μm and 10.00g of polyvinylpyrrolidone, then add them to 550mL of water and stir at 500rpm for 12h on a magnetic stirrer to obtain modified graphite solution A.

[0087] Step (2): Weigh 0.73g nickel nitrate, 0.73g cobalt nitrate, 0.71g manganese nitrate, 0.75g copper nitrate and 0.75g zinc nitrate respectively, add them to 73.33ml water, and stir on a magnetic stirrer at 500rpm for 12h to obtain solution B;

[0088] Step (3): Mix solution A and solution B and stir at 500 rpm for 12 hours on a magnetic stirrer to obtain a mixed solution. The mixed solution is then spray-dried to obtain a graphite composite, wherein the outlet temperature of the spray dryer is 120°C.

[0089] Step (4): The graphite composite was heated to 740℃ at a vacuum of 10 Pa at a rate of 5℃ / min and held for 3 hours to obtain a high-entropy graphite composite anode material, denoted as A2.

[0090] Example 3

[0091] Step (1): Weigh 100g of artificial graphite with a particle size of 150μm and 5.00g of polyvinylpyrrolidone, then add them to 525mL of water and stir at 500rpm for 12h on a magnetic stirrer to obtain modified graphite solution A.

[0092] Step (2): Weigh 0.52g nickel nitrate, 0.52g cobalt nitrate, 0.51g manganese nitrate, 0.53g copper nitrate and 0.54g zinc nitrate respectively, add them to 52.55ml water, and stir on a magnetic stirrer at 500rpm for 12h to obtain solution B;

[0093] Step (3): Mix solution A and solution B and stir at 500 rpm for 12 hours on a magnetic stirrer to obtain a mixed solution. The mixed solution is then spray-dried to obtain a graphite composite, wherein the outlet temperature of the spray dryer is 120°C.

[0094] Step (4): The graphite composite was heated to 740℃ at a vacuum of 10 Pa at a rate of 5℃ / min and held for 3 hours to obtain a high-entropy graphite composite anode material, denoted as A3.

[0095] Example 4

[0096] Step (1): Weigh 100g of artificial graphite with a particle size of 150μm and 20.00g of polyvinylpyrrolidone, then add them to 600mL of water and stir at 500rpm for 12h on a magnetic stirrer to obtain modified graphite solution A.

[0097] Step (2): Weigh 1.19g nickel nitrate, 1.19g cobalt nitrate, 1.17g manganese nitrate, 1.22g copper nitrate and 1.23g zinc nitrate respectively, add them to 120ml water, and stir on a magnetic stirrer at 500rpm for 12h to obtain solution B;

[0098] Step (3): Mix solution A and solution B and stir at 500 rpm for 12 hours on a magnetic stirrer to obtain a mixed solution. The mixed solution is then spray-dried to obtain a graphite composite, wherein the outlet temperature of the spray dryer is 60°C.

[0099] Step (4): The graphite composite is heated to 700℃ at a vacuum of 10 Pa and held for 4 h to obtain a high-entropy graphite composite anode material, denoted as A4.

[0100] Example 5

[0101] Step (1): Weigh 100g of artificial graphite with a particle size of 100μm and 4.00g of polyvinylpyrrolidone, then add them to 520mL of water and stir at 500rpm for 12h on a magnetic stirrer to obtain modified graphite solution A.

[0102] Step (2): Weigh 0.26g nickel nitrate, 0.26g cobalt nitrate, 0.25g manganese nitrate, 0.26g copper nitrate and 0.27g zinc nitrate respectively, add them to 26ml water, and stir on a magnetic stirrer at 500rpm for 12h to obtain solution B;

[0103] Step (3): Mix solution A and solution B and stir at 500 rpm for 12 hours on a magnetic stirrer to obtain a mixed solution. The mixed solution is then spray-dried to obtain a graphite composite, wherein the outlet temperature of the spray dryer is 90°C.

[0104] Step (4): The graphite composite is heated to 800℃ at a vacuum of 10 Pa and held for 1.5 h to obtain a high-entropy graphite composite anode material, denoted as A5.

[0105] Example 6

[0106] The procedure was carried out in accordance with Example 1, except that nickel nitrate, cobalt nitrate, manganese nitrate, copper nitrate, and zinc nitrate were replaced with equal masses of nickel chloride, cobalt chloride, manganese chloride, copper chloride, and zinc chloride, respectively.

[0107] Example 7

[0108] The procedure was carried out in accordance with Example 1, except that nickel nitrate, cobalt nitrate, manganese nitrate, copper nitrate, and zinc nitrate were replaced with equal masses of nickel carbonate, cobalt carbonate, manganese carbonate, copper carbonate, and zinc carbonate, respectively.

[0109] Example 8

[0110] The process is carried out in accordance with Example 1, except that in step (3), the solvent is removed by solvent evaporation, that is, at 100°C, the mixture is stirred at 500 rpm until the solution is completely evaporated, and the resulting negative electrode material is denoted as A8.

[0111] Example 9

[0112] The process was carried out in accordance with Example 1, with the only difference being that: in step (3), the solvent was removed by freeze-drying, i.e., the mixed solution was cooled with liquid nitrogen, and then freeze-dried for 24 hours in a freeze dryer with the cold well temperature set to -59°C. The resulting negative electrode material was denoted as A9.

[0113] Example 10

[0114] The process was carried out in accordance with Example 1, except that the heat treatment temperature was 600°C and the resulting negative electrode material was denoted as A10.

[0115] Example 11

[0116] The process was carried out in accordance with Example 1, except that the heat treatment temperature was 900°C and the resulting negative electrode material was denoted as A11.

[0117] Example 12

[0118] The procedure was carried out in accordance with Example 1, except that the mass of polyvinylpyrrolidone was 50g.

[0119] Example 13

[0120] The procedure was carried out in accordance with Example 1, except that the mass of polyvinylpyrrolidone was 3.33 g.

[0121] Example 14

[0122] The procedure was carried out in accordance with Example 1, with the only difference being that the masses of nickel nitrate, cobalt nitrate, manganese nitrate, copper nitrate, and zinc nitrate were 2.12 g, 2.24 g, 2.12 g, 2.1 g, and 2.09 g, respectively.

[0123] Example 15

[0124] The procedure was carried out in accordance with Example 1, with the only difference being that the masses of nickel nitrate, cobalt nitrate, manganese nitrate, copper nitrate, and zinc nitrate were 0.21g, 0.2g, 0.19g, 0.22g, and 0.25g, respectively.

[0125] Comparative Example 1

[0126] The procedure was carried out in accordance with Example 1, except that no surfactant was added, and the resulting material was denoted as D1.

[0127] Comparative Example 2

[0128] The process was carried out in accordance with Example 1, except that no mixture of multiple transition metal sources was added, and the resulting material was denoted as D2.

[0129] Comparative Example 3

[0130] The process was carried out in accordance with Example 1, except that: the mixture of artificial graphite, surfactant and multiple transition metal sources was added together to 593.95 mL of water, stirred, and then spray dried and heat-treated (i.e., mixed once, without being mixed separately). The resulting material was denoted as D3.

[0131] Comparative Example 4

[0132] 100g of artificial graphite with a particle size of 150μm was weighed, and 0.60g of nickel nitrate, 0.60g of cobalt nitrate, 0.59g of manganese nitrate, 0.62g of copper nitrate and 0.63g of zinc nitrate were weighed separately. They were ball-milled with a ball-to-material ratio of 20:1, a rotation speed of 400rpm and a time of 6h. The ball-milled material was then heat-treated according to the method in Example 1. The obtained material was denoted as D4.

[0133] The materials obtained in Examples 1-15 above have little difference in appearance. Taking Example 1 as an example, its structural schematic diagram is as follows: Figure 1 As shown in the image (the side view is cut off to observe its internal structure), it can be seen that the surface of graphite is coated with a layer of transition metal elements, as indicated by its EDS scan. Figure 2 As shown in the figure, it can be clearly observed that the graphite surface layer contains five transition metal elements: Ni, Co, Cu, Mn, and Zn. It is evident that multiple transition metal elements have been successfully coated on the graphite surface layer.

[0134] The composition content of the materials obtained in Examples 1-15 and Comparative Examples 1-4 was tested, and the results are shown in Table 1.

[0135] Table 1 Results of component content test

[0136]

[0137]

[0138] The negative electrode materials obtained in Examples 1-15 and Comparative Examples 1-4 were assembled into lithium-ion batteries, and their electrochemical performance was tested. The specific methods are as follows:

[0139] (1) Weigh the negative electrode material (A1-A15 and D1-D4), conductive agent conductive carbon black Super P, and binder (a 1:1 mixture of binder sodium carboxymethyl cellulose CMC and binder styrene-butadiene rubber SBR) to be tested in a mass ratio of 8:1:0.5:0.5 respectively, mix them to form a slurry, and then coat the slurry onto copper foil with a 100μm coater. After vacuum drying at 80℃ and rolling, the negative electrode sheet of lithium-ion battery is formed.

[0140] (2) Using the prepared negative electrode sheet, with a lithium metal sheet as the counter electrode and Celgard 2325 as the separator, the electrolyte is 0.9 mol / L lithium bis(fluorosulfonyl)imide (LiFSI) and 0.1 mol / L lithium difluorooxalate borate (LiDFOB) dissolved in a mixed solution of isoxazole (IZ) and fluoroethylene carbonate (FEC) (volume ratio of 1:1). The CR2025 button cell is completed in a glove box under argon atmosphere (H2O < 0.1 ppm, O2 < 0.1 ppm).

[0141] The constant current charge-discharge test of the negative electrode material was performed using the Land CT2001A from Wuhan Landian Electronics Co., Ltd., and the battery was tested at -20℃ and within a voltage range of 0.01-1.5V (1C=372mA / g).

[0142] Taking Example 1 as an example, its first reversible specific capacity and first coulombic efficiency at 0.1C are as follows: Figure 3 As shown in the figure (the first three cycles were performed at room temperature (25°C), activated at 0.1C, and then tested at -20°C at 0.1C), its first reversible specific capacity and first coulombic efficiency at 1C are as follows: Figure 4 As shown (the first three circles in the figure were activated at 0.1C at room temperature (25℃) and then tested at 1C at -20℃). From Figure 3 and 4 It can be seen that the lithium-ion battery with negative electrode sheet made of the negative electrode material of Example 1 has good cycle stability and capacity retention at high rate, indicating that the coating layer formed by multiple transition metal elements can effectively improve the cycle stability of graphite negative electrode at low temperature and high rate.

[0143] Specifically, the test results of Examples A1-A15 and Comparative Examples D1-D4 at 0.1C and 1C are shown in Tables 2 and 3, respectively. In Table 2, the first reversible specific capacity and first coulombic efficiency are the test results for the first cycle at room temperature, while in Table 3, the first reversible specific capacity at 1C refers to the test results for the first cycle at -20℃ and 1C after activation.

[0144] Table 2 Electrochemical performance test results at 0.1C

[0145]

[0146] Table 3. Electrochemical performance test results at 1C

[0147]

[0148]

[0149] As can be seen from Tables 2 and 3, compared with Comparative Examples 1-4, lithium-ion batteries with negative electrode sheets made from the negative electrode materials of Examples 1-15 have both higher first-cycle coulombic efficiency and capacity retention, indicating that the coating of transition metal elements can effectively improve the cycle performance and reversible specific capacity of lithium-ion batteries.

[0150] As can be seen from Examples 1, 6, and 7, when the transition metal element source is nitrate, the anisotropic properties of the prepared negative electrode material are superior to those of other types of transition metal element salts.

[0151] As can be seen from Examples 1, 8, and 9, spray drying to remove solvent can further improve the initial reversible specific capacity and capacity retention of the anode material compared to freeze drying and solvent evaporation. Spray drying is superior to freeze drying. Freeze drying is due to solvent evaporation, mainly because spray drying can coat and granulate the original graphite particles, which is conducive to further performance improvement. Freeze drying makes the material fluffy, while solvent evaporation simply coats the transition metal elements on the graphite surface.

[0152] As can be seen from Examples 1, 10, and 11, the electrochemical performance of the electrode material decreases when the heat treatment temperature is too low or too high, indicating that a heat treatment temperature of 700-800℃ can further improve the above-mentioned performance.

[0153] As can be seen from Examples 1 and 12-15, when the mass ratio of graphite to surfactant or the total amount of graphite and surfactant to the total amount of various transition metal elements is too low or too high, the electrochemical performance of the electrode material is poor. This indicates that the preferred mass ratio of graphite to surfactant and / or the ratio of the total amount of graphite and surfactant to the total amount of various transition metal elements in this invention can further improve the above-mentioned performance.

[0154] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing a high-entropy graphite composite anode material, characterized in that, The preparation method includes: mixing graphite and surfactant in a first solvent to obtain solution A; mixing multiple transition metal element sources in a second solvent to obtain solution B; mixing solution A and solution B in a third solvent; removing the first solvent and the second solvent to obtain a graphite composite; and heat-treating the graphite composite in an oxygen-free environment to obtain a negative electrode material. The various transition metal source sources are manganese, cobalt, nickel, copper and zinc, and the surfactants include polyvinylpyrrolidone and / or hexadecyltrimethylammonium bromide. The mass ratio of graphite to surfactant is 5-25:1, and the total mass ratio of graphite and surfactant to the total mass ratio of the various transition metal element sources is 20-80:

1. The heat treatment is performed at a temperature of 700-800℃ for 1-4 hours. The manganese source includes manganese carbonate and / or manganese nitrate; The cobalt source includes cobalt carbonate and / or cobalt nitrate; The nickel source includes nickel carbonate and / or nickel nitrate; The copper source includes copper carbonate and / or copper nitrate; The zinc source includes zinc carbonate and / or zinc nitrate.

2. The preparation method according to claim 1, wherein, The mass ratio of graphite to surfactant is 10-20:1; And / or, the total mass ratio of the graphite and surfactant to the total mass ratio of the various transition metal element sources is 30-40:

1.

3. The preparation method according to claim 1 or 2, wherein, The heating rate of the heat treatment is 4-6℃ / min.

4. The preparation method according to claim 3, wherein, The first solvent and the second solvent are water and / or ethanol, respectively, independently; And / or, the concentration of solution A is 0.1-0.5 g / mL; And / or, the concentration of solution B is 0.01-0.05 g / mL.

5. The preparation method according to claim 1 or 2, wherein, The particle size D of the graphite 50 It is 100-200μm.

6. The preparation method according to claim 5, wherein, The method for removing the first solvent and the second solvent includes: spray drying, solvent evaporation, freeze drying, filtration, and centrifugation of the third mixed solution.

7. The preparation method according to claim 6, wherein, The method for removing the first solvent and the second solvent includes: spray drying the third mixed solution, wherein the outlet temperature of the spray dryer is 60-120°C.

8. The preparation method according to claim 1, 2, 4, 6 or 7, wherein, The first mixture, the second mixture, and the third mixture each independently include stirring; And / or, the oxygen-free environment is a vacuum environment or an inert gas environment.

9. A high-entropy graphite composite anode material prepared by the preparation method according to any one of claims 1-8, characterized in that, The high-entropy graphite composite anode material includes graphite and a layer of multiple transition metal elements coated on the surface of the graphite, wherein the multiple transition metal elements are manganese, cobalt, nickel, copper and zinc. Based on the total amount of the high-entropy graphite composite anode material, the amount of graphite is 96-99.5 wt%, and the total amount of the various transition metal elements is 0.5-4 wt%.

10. The negative electrode material according to claim 9, wherein, Based on the total amount of the negative electrode material, the amount of each transition metal element in the multiple transition metal element sources is independently 0.1-0.8 wt%.

11. The negative electrode material according to claim 10, wherein, Based on the total amount of the negative electrode material, the amount of each transition metal element in the multiple transition metal element sources is independently 0.1-0.4 wt%.

12. A negative electrode, characterized in that, This includes the negative electrode material prepared by any one of the preparation methods according to claims 1-8 or the negative electrode material according to any one of claims 9-11.

13. A lithium-ion battery, characterized in that, Includes the negative electrode as described in claim 12.

Images