Graphite composite material and preparation method and application thereof

Abstract

The invention discloses a graphite composite material as well as a preparation method and application thereof, and belongs to the technical field of preparation of negative electrode materials. The graphite composite material has a core-shell structure, and the core of the core-shell structure comprises magnetic metal oxide doped porous graphite; and the shell of the core-shell structure comprises a carbon nanotube, a lithium supplement agent and amorphous carbon. The specific capacity is improved by doping the magnetic oxide in the porous graphite, and the carbon nanotube lithium supplement agent amorphous carbon is coated on the porous graphite, so that the energy density and the fast charging performance of the battery are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of negative electrode material preparation, and in particular to a graphite composite material and a preparation method and application thereof. Background Art

[0002] As market demands for lithium-ion battery energy density and fast-charging performance continue to increase, the anode materials used in lithium-ion batteries are required to have both high energy density and fast-charging performance. Commonly used anode materials include graphite, silicon-based materials, and metal oxides. While graphite has excellent fast-charging and cycling performance, it has a low energy density. Silicon-based materials have high energy density but suffer from large expansion upon full charge and poor cycling performance. Metal oxides offer high specific capacity and good power performance, but suffer from low initial efficiency and large expansion.

[0003] In order to further improve the performance of negative electrode materials, doping and coating are currently used to improve the initial efficiency and reduce expansion. Some researchers have combined graphite with metal oxides to improve the energy density of the material, but there are still problems such as large expansion and deviation in fast charging performance. For example, patent CN116454229A discloses a method for preparing a negative electrode material of lithium cerate coated graphite iron oxide. Although the specific capacity and initial efficiency of the obtained material are improved, the fast charging performance of the negative electrode material is not significantly improved, and the lithium cerate in the coating layer has limited improvement in the lithium ion transmission rate and low temperature.

[0004] Therefore, there is an urgent need to provide new negative electrode materials to solve the above technical problems. Summary of the Invention

[0005] Based on this, the present invention provides a graphite composite material and a preparation method and application thereof to solve the above technical problems.

[0006] In a first aspect of the present invention, a graphite composite material is provided, wherein the graphite composite material has a core-shell structure.

[0007] The core of the core-shell structure includes magnetic metal oxide-doped porous graphite;

[0008] The shell of the core-shell structure comprises carbon nanotubes, a lithium supplement and amorphous carbon.

[0009] Preferably, based on the total mass of the graphite composite material being 100%, the mass of the shell accounts for 5 to 10%;

[0010] Preferably, based on the total mass of the shell being 100%, the mass of the carbon nanotubes accounts for 1-5%, the mass of the lithium supplement accounts for 1-5%, and the balance is amorphous carbon;

[0011] Preferably, in the inner core, the mass ratio of the magnetic metal oxide to the porous graphite is 5-15:85-95.

[0012] Preferably, the magnetic metal oxide includes at least one of Fe3O4, Co3O4, and NiO.

[0013] A second aspect of the present invention provides a method for preparing the graphite composite material according to the first aspect, comprising the following steps:

[0014] S1: mixing coke raw material, metal oxide, functional additive and catalyst to obtain a mixture, and calcining the mixture in three stages to obtain porous graphite;

[0015] S2: adding an alkaline compound, a catalyst solution, and the porous graphite prepared in step S1 to the magnetic metal oxide solution, uniformly dispersing the mixture, performing a hydrothermal reaction, and filtering to obtain a core;

[0016] S3: introducing a carbon source gas into the core prepared in step S2 to perform carbonization sintering to obtain a core with surface-grown carbon nanotubes;

[0017] S4: After dispersing the lithium supplement agent in an organic solvent, cellulose salt and the core of the surface-grown carbon nanotubes in step S3 are added, dispersed evenly, and spray-dried to obtain a graphite composite material.

[0018] Preferably, in step S1, the mass ratio of the coke raw material, the metal oxide, the functional additive and the catalyst is 100:5-10:1-5:1-5;

[0019] Preferably, the coke raw material includes at least one of coal-based needle coke, petroleum coke, and pitch coke;

[0020] Preferably, the metal oxide includes at least one of iron oxide, tin oxide, silicon oxide, and molybdenum oxide;

[0021] Preferably, the functional additive comprises at least one of ethylene vinyl acetate, polyethylene, polyethylene oxide, ethylene propylene copolymer, ethylene / propylene / diene terpolymer, and polyisoprene;

[0022] Preferably, the catalyst comprises at least one of iron, cobalt, nickel, and copper;

[0023] More preferably, the particle size of the catalyst is 100 to 500 nm.

[0024] Preferably, in step S1, the three-stage temperature-raising calcination comprises: heating the mixture to t1 for a first calcination, then continuing to heat the mixture to t2 for a second calcination, and finally heating the mixture to t3 for a third calcination;

[0025] Preferably, the temperature t1 is 450-650°C;

[0026] Preferably, the first calcination time is 1 to 6 hours;

[0027] Preferably, the temperature t2 is 1200-1500°C;

[0028] Preferably, the second calcination time is 1 to 6 hours;

[0029] Preferably, the temperature t3 is 2800-3200°C;

[0030] Preferably, the second calcination time is 6 to 24 hours.

[0031] Preferably, in step S2, the mass ratio of the magnetic metal oxide in the magnetic metal oxide solution, the alkaline compound, the catalyst in the catalyst solution, and the porous graphite is 5-15:10-30:1-5:100;

[0032] Preferably, the magnetic metal oxide solution is prepared by adding water to the magnetic metal oxide;

[0033] Preferably, the mass concentration of the magnetic metal oxide solution is 0.5-1.5%;

[0034] Preferably, the alkaline compound is an organic amine compound;

[0035] More preferably, the organic amine compound includes at least one of ethanolamine, ethylenediamine, diethylamine, triethylamine, dimethylamine, hydroxyethylethylenediamine or aminoethanolamine;

[0036] Preferably, the catalyst solution is obtained by dispersing the catalyst in water;

[0037] Preferably, the mass concentration of the catalyst solution is 8 to 15%;

[0038] Preferably, the catalyst is a metal chloride;

[0039] More preferably, the metal chloride includes at least one of ferric chloride, cobalt chloride, nickel chloride, and copper chloride;

[0040] Preferably, the temperature of the hydrothermal reaction is 100-200°C;

[0041] Preferably, the hydrothermal reaction time is 1 to 6 hours;

[0042] Preferably, after the filtration, the method further comprises the step of drying the filtered residue;

[0043] Preferably, the drying is vacuum drying.

[0044] Preferably, in step S3, the carbon source gas includes at least one of methane, acetylene, and ethylene;

[0045] Preferably, the temperature of the carbonization sintering is 800-1200°C;

[0046] Preferably, the carbonization sintering time is 1 to 6 hours;

[0047] In step S4, the mass ratio of the lithium supplement agent, the organic solvent, the cellulose salt, and the core of the surface-grown carbon nanotubes is 1-5:500-1500:1-5:100;

[0048] Preferably, the lithium supplement comprises at least one of Li5FeO4, Li2NiO2, Li6CoO4, and Li4V3O8;

[0049] Preferably, the organic solvent comprises at least one of N-methylpyrrolidone, cyclohexane, and carbon tetrachloride;

[0050] Preferably, the cellulose salt comprises at least one of carboxymethyl cellulose salt and hydroxymethyl cellulose salt;

[0051] Preferably, the hydroxymethyl cellulose salt comprises at least one of lithium hydroxymethyl cellulose, magnesium hydroxymethyl cellulose, and sodium hydroxymethyl cellulose;

[0052] Preferably, the carboxymethyl cellulose salt comprises at least one of lithium carboxymethyl cellulose, magnesium carboxymethyl cellulose, and sodium carboxymethyl cellulose;

[0053] More preferably, the carboxymethylcellulose salt is lithium carboxymethylcellulose.

[0054] A third aspect of the present invention provides a negative electrode, comprising a negative electrode active material, wherein the negative electrode active material comprises the graphite composite material described in the first aspect; or the graphite composite material prepared by the preparation method described in the second aspect.

[0055] According to a fourth aspect of the present invention, a secondary battery is provided. The secondary battery comprises a positive electrode, a negative electrode and an electrolyte, wherein the negative electrode comprises the negative electrode described in the third aspect.

[0056] The beneficial technical effects of the present invention are:

[0057] The present invention obtains a core-shell graphite composite material by doping a magnetic metal oxide into porous graphite, directly growing carbon nanotubes on its surface, and simultaneously coating a lithium supplement agent and amorphous carbon. Doping the porous graphite with a magnetic metal oxide improves the specific capacity of the composite material, thereby improving the energy density of the prepared battery. At the same time, the magnetic metal oxide has high isotropy, which can improve the fast charging performance of the prepared battery. The magnetic metal oxide has high magnetism, which can improve the isotropy of carbon-based materials and improve the rate performance of the prepared battery. Directly growing carbon nanotubes on the surface of the core doped with the magnetic metal oxide can improve electronic conductivity, while reducing resistance and improving the fast charging performance of the battery. Coating the lithium supplement agent on the shell can release lithium ions during the charge and discharge process, thereby improving the initial efficiency of the material. Furthermore, the shell's carbon nanotube / lithium supplement agent / amorphous carbon composite, relying on the high electronic conductivity and high specific surface area of ​​the carbon nanotubes, can restrain the expansion of the magnetic metal oxide. The lithium supplement agent releases lithium ions during charge and discharge, increasing the number of lithium ions during charge and discharge and improving the rate performance. Amorphous carbon is coated on the surface to reduce side reactions with the electrolyte and improve initial efficiency.

[0058] The porous graphite used in the graphite composite material provided by the present invention is obtained by doping metal oxides and functional additives into coke raw materials and calcining them to obtain porous graphite with different pore structures. The three calcinations avoid insufficient reaction of the metal oxides, which leads to a large number of pores in the material, thereby improving the tap density. At the same time, the prepared porous structure improves the liquid retention of the composite material, thereby improving the cycle performance of the prepared battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 This is a SEM image of the graphite composite material of Example 1 of the present invention. DETAILED DESCRIPTION

[0060] Reference will now be made in detail to embodiments of the present invention, one or more examples of which are described below. Each example is provided to illustrate, not to limit, the present invention. Indeed, it will be apparent to those skilled in the art that various modifications and variations may be made to the present invention without departing from the scope or spirit of the invention. For example, features illustrated or described as part of one embodiment may be used in another embodiment to produce further embodiments.

[0061] Therefore, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. Other objects, features, and aspects of the present invention are disclosed in or are obvious from the following detailed description. Those skilled in the art will appreciate that this discussion is merely a description of exemplary embodiments and is not intended to limit the broader aspects of the present invention.

[0062] In the present invention, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0063] In the present invention, when referring to numerical ranges, unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Furthermore, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed in the present invention should be understood to include any and all subranges subsumed therein.

[0064] In the present invention, when referring to a data range, if the unit is only after the right endpoint, it means that the units of the left and right endpoints are the same. For example, 100-150nm means that the units of the left endpoint "100" and the right endpoint "150" are both nm (nanometers).

[0065] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0066] Unless otherwise specified, all technical features and optional technical features of the present invention can be combined with each other to form a new technical solution.

[0067] Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, preferably sequentially. For example, "the method includes steps (a) and (b)" indicates that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, "the method may further include step (c)" indicates that step (c) may be added to the method in any order, for example, the method may include steps (a), (b), and (c), or may include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0068] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0069] In response to the problem that traditional technologies cannot balance energy density and fast charging performance, the present invention proposes a high-energy-density graphite composite material and its preparation method and application to solve the above-mentioned technical problems existing in traditional polymer electrolytes.

[0070] In a first aspect, the present invention provides a graphite composite material having a core-shell structure, wherein the core of the core-shell structure comprises magnetic metal oxide-doped porous graphite; and the shell of the core-shell structure comprises carbon nanotubes, a lithium supplement and amorphous carbon.

[0071] It is understood that the present invention obtains a core-shell graphite composite material by doping porous graphite with magnetic metal oxides, directly growing carbon nanotubes on its surface, and simultaneously coating a lithium supplement and amorphous carbon. Doping the porous graphite with magnetic metal oxides increases the specific capacity of the composite material and the energy density of the prepared battery. At the same time, the magnetic metal oxide has high fast-charging performance, thereby improving the fast-charging performance of the prepared battery. Furthermore, the magnetic metal oxide has high magnetism, which can improve the isotropy of the carbon-based material and improve the rate performance of the prepared battery. Directly growing carbon nanotubes on the surface of the core doped with magnetic metal oxides can improve electronic conductivity, while reducing resistance and improving the fast-charging performance of the battery. Coating the lithium supplement in the shell releases lithium ions during the charge and discharge process, improving the initial efficiency of the material. Furthermore, the shell's carbon nanotube / lithium supplement / amorphous carbon composite, relying on the high electronic conductivity and high specific surface area of ​​the carbon nanotubes, can restrain the expansion of the magnetic metal oxide. The lithium supplement releases lithium ions during charge and discharge, increasing the number of lithium ions during charge and discharge and improving the rate performance. Amorphous carbon is coated on the surface to reduce side reactions with the electrolyte and improve initial efficiency.

[0072] In some embodiments, based on the total mass of the graphite composite material being 100%, the mass of the shell accounts for 5-10%, including but not limited to 5%, 6%, 7%, 8%, 9%, and 10%.

[0073] It is understandable that too much shell material will reduce the energy density, while too little shell material will result in a lower improvement in the fast charging and initial efficiency of the material.

[0074] In some embodiments, based on the total mass of the shell being 100%, the mass of the carbon nanotubes accounts for 1-5%, the mass of the lithium supplement accounts for 1-5%, and the balance is amorphous carbon. The mass of the carbon nanotubes includes, but is not limited to, 1%, 2%, 3%, 4%, or 5%; the mass of the lithium supplement includes, but is not limited to, 1%, 2%, 3%, 4%, or 5%.

[0075] In some embodiments, in the inner core, the mass ratio of the magnetic metal oxide to the porous graphite is 5-15:85-95, including but not limited to 5:85, 5:90, 5:95, 10:85, 10:90, 10:95, 15:85, 15:90, and 15:95.

[0076] In some embodiments, the magnetic metal oxide includes at least one of Fe3O4, Co3O4, and NiO.

[0077] It is understandable that the magnetic metal oxide used in the present invention has a high specific capacity, which can increase the specific capacity of graphite. At the same time, the high isotropy of the magnetic metal oxide improves the fast charging performance of the composite material. The high magnetic properties of the magnetic metal oxide can improve the isotropy of the carbon-based material, thereby improving the rate performance of the prepared battery. However, too much magnetic metal oxide will reduce the energy density, and too little will limit the rate improvement.

[0078] A second aspect of the present invention provides a method for preparing the graphite composite material according to the first aspect, comprising the following steps:

[0079] S1: mixing coke raw material, metal oxide, functional additive and catalyst to obtain a mixture, and calcining the mixture in three stages to obtain porous graphite;

[0080] S2: adding an alkaline compound, a catalyst solution, and the porous graphite prepared in step S1 to the magnetic metal oxide solution, uniformly dispersing the mixture, performing a hydrothermal reaction, and filtering to obtain a core;

[0081] S3: introducing a carbon source gas into the core prepared in step S2 to perform carbonization sintering to obtain a core with surface-grown carbon nanotubes;

[0082] S4: After dispersing the lithium supplement agent in an organic solvent, cellulose salt and the core of the surface-grown carbon nanotubes in step S3 are added, dispersed evenly, and spray-dried to obtain a graphite composite material.

[0083] In some embodiments, in step S1, the mass ratio of the coke raw material, the metal oxide, the functional additive and the catalyst is 100:5-10:1-5:1-5, including but not limited to 100:5:1:1, 100:10:5:5, 100:8:3:3, 100:5:5:5, and 100:10:5:5.

[0084] In some embodiments, the coke raw material includes at least one of coal-based needle coke, petroleum coke, and pitch coke;

[0085] In some embodiments, the metal oxide includes at least one of iron oxide, tin oxide, silicon oxide, and molybdenum oxide.

[0086] In some embodiments, the functional additive includes at least one of ethylene vinyl acetate, polyethylene, oxidized polyethylene, ethylene propylene copolymer, ethylene / propylene / diene terpolymer, and polyisoprene.

[0087] In some embodiments, the catalyst includes at least one of iron, cobalt, nickel, and copper.

[0088] In some embodiments, the particle size of the catalyst is 100 to 500 nm, including but not limited to 100 nm, 200 nm, 300 nm, 400 nm, and 500 nm.

[0089] In some embodiments, in step S1, the three-stage temperature-raising calcination includes: heating the mixture to t1 for a first calcination, then continuing to heat the mixture to t2 for a second calcination, and finally heating the mixture to t3 for a third calcination.

[0090] In some embodiments, the t1 is 450-650°C, including but not limited to 450°C, 500°C, 550°C, 600°C, and 650°C.

[0091] In some embodiments, the first calcination time is 1 to 6 hours, including but not limited to 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, and 6 hours.

[0092] In some embodiments, the temperature t2 is 1200-1500°C, including but not limited to 1200°C, 1300°C, 1400°C, and 1500°C.

[0093] In some embodiments, the second calcination time is 1 to 6 hours, including but not limited to 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, and 6 hours.

[0094] In some embodiments, the t3 is 2800-3200°C, including but not limited to 2800°C, 2900°C, 3000°C, 3100°C, and 3200°C.

[0095] In some embodiments, the second calcination time is 6 to 24 hours, including but not limited to 6 hours, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, and 24 hours.

[0096] It can be understood that the present invention dopes the coke raw material with metal oxides, functional additives and catalysts. During the heating process, the functional additives will first decompose to form nano-micron pores, while the catalyst accelerates the rearrangement of carbon to form porous graphite. The metal oxide generates gas during the graphitization process at 2800-3200°C, which will also leave pores. Since the decomposition temperatures of the metal oxide and its functional additive are different, pore structures of different sizes and shapes will be generated. The functional additive is a polymer material and can generate circular structural pores, while the metal oxide will grow irregular structural pores. Pores of different morphologies can increase the tap density of the material. In addition, through three calcinations, the insufficient reaction of the metal oxide, which leads to low specific capacity and initial efficiency, is avoided, thereby improving the energy density of the material. At the same time, the prepared porous structure improves the liquid retention of the composite material, thereby improving the cycle performance of the prepared battery.

[0097] In some embodiments, in step S2, the mass ratio of the magnetic metal oxide in the magnetic metal oxide solution, the alkaline compound, the catalyst in the catalyst solution, and the porous graphite is 5-15:10-30:1-5:100; including but not limited to 5:10:1:100, 15:30:5:100, 10:20:3:100, 5:30:5:100, and 15:10:1:100.

[0098] In some embodiments, the magnetic metal oxide solution is prepared by adding water to the magnetic metal oxide.

[0099] In some embodiments, the mass concentration of the magnetic metal oxide solution is 0.5-1.5%, including but not limited to 0.5%, 1%, and 1.5%.

[0100] In some embodiments, the basic compound is an organic amine compound.

[0101] In some further embodiments, the organic amine compound includes at least one of ethanolamine, ethylenediamine, diethylamine, triethylamine, dimethylamine, hydroxyethylethylenediamine, or aminoethanolamine.

[0102] It is understood that the alkaline compound of the present invention can provide an alkaline environment for the reaction. At the same time, the alkaline oxide used in the present invention has an etching effect on the carbon material, which can accelerate the acquisition of porous graphite.

[0103] In some embodiments, the catalyst solution is obtained by dispersing the catalyst in water.

[0104] In some embodiments, the mass concentration of the catalyst solution is 8-15%, including but not limited to 8%, 10%, 12%, 14%, and 15%.

[0105] In some embodiments, the catalyst is a metal chloride.

[0106] In some further embodiments, the metal chloride comprises at least one of ferric chloride, cobalt chloride, nickel chloride, and copper chloride.

[0107] In some embodiments, the temperature of the hydrothermal reaction is 100-200°C, including but not limited to 100°C, 150°C, and 200°C.

[0108] In some embodiments, the hydrothermal reaction time is 1 to 6 hours, including but not limited to 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, and 6 hours.

[0109] In some embodiments, after the filtration, the method further includes drying the filtered residue.

[0110] In some embodiments, the drying is vacuum drying.

[0111] In some embodiments, in step S3, the carbon source gas includes at least one of methane, acetylene, and ethylene.

[0112] In some embodiments, the carbonization sintering temperature is 800-1200°C, including but not limited to 800°C, 1000°C, and 1200°C;

[0113] In some embodiments, the carbonization sintering time is 1 to 6 hours, including but not limited to 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, and 6 hours.

[0114] In some embodiments, the mass proportion of carbon nanotubes in the inner core of the surface-grown carbon nanotubes is 1-6%, including but not limited to 1%, 2%, 3%, 4%, 5%, and 6%.

[0115] In step S4, the mass ratio of the lithium supplement agent, the organic solvent, the cellulose salt, and the core of the surface-grown carbon nanotubes is 1-5:500-1500:1-5:100, including but not limited to 1:500:1:100, 5:1500:5:100, 3:1000:3:100, 1:1500:5:100, 5:500:1:100, and 3:1500:1:100.

[0116] In some embodiments, the lithium supplement includes at least one of Li5FeO4, Li2NiO2, Li6CoO4, and Li4V3O8.

[0117] In some embodiments, the organic solvent includes at least one of N-methylpyrrolidone, cyclohexane, and carbon tetrachloride.

[0118] In some embodiments, the cellulose salt includes at least one of carboxymethyl cellulose salt and hydroxymethyl cellulose salt.

[0119] In some embodiments, the hydroxymethylcellulose salt includes at least one of lithium hydroxymethylcellulose, magnesium hydroxymethylcellulose, and sodium hydroxymethylcellulose.

[0120] In some embodiments, the carboxymethyl cellulose salt includes at least one of lithium carboxymethyl cellulose, magnesium carboxymethyl cellulose, and sodium carboxymethyl cellulose.

[0121] In some embodiments, the carboxymethylcellulose salt is lithium carboxymethylcellulose.

[0122] It is understood that the cellulose salt in the present invention contains hydrophilic groups, which can enhance the dispersion uniformity of the material and improve processing performance. Furthermore, when lithium carboxymethyl cellulose is used, the initial efficiency of the battery can be further improved. Furthermore, the cellulose salt can be carbonized with a lithium salt to form lithium-doped amorphous carbon, which also enhances initial efficiency.

[0123] A third aspect of the present invention provides a negative electrode, comprising a negative electrode active material, wherein the negative electrode active material comprises the graphite composite material described in the first aspect; or the graphite composite material prepared by the preparation method described in the second aspect.

[0124] According to a fourth aspect of the present invention, a secondary battery is provided. The secondary battery comprises a positive electrode, a negative electrode and an electrolyte, wherein the negative electrode comprises the negative electrode described in the third aspect.

[0125] The following are specific examples.

[0126] Example 1

[0127] A method for preparing a high energy density graphite composite material for lithium ion batteries comprises the following steps:

[0128] S1: 100g coal-based needle coke, 8g iron oxide, 3g ethylene vinyl acetate, and 3g nano-iron were mixed evenly, then heated to 550℃ for shallow calcination for 3h, then heated to 1350℃ for medium calcination for 3h, and finally heated to 3000℃ for graphitization for 12h, and cooled to room temperature in a nitrogen atmosphere to obtain porous graphite.

[0129] S2: Add 10g of Fe3O4 to 1000g of deionized water to prepare a 1wt% solution, then add 20g of ethanolamine, 30g of a 10wt% ferric chloride aqueous solution, and add 100g of porous graphite to disperse evenly. Hydrothermally react at a temperature of 150°C for 3h, and vacuum dry at 80°C for 24h to obtain the core material, i.e., magnetic metal oxide-doped porous graphite.

[0130] S3: The core material prepared in step S2 is transferred to a tube furnace, and ethylene gas is introduced (flow rate 20 ml / min, 150 min), and carbonization sintering is carried out at a temperature of 1000°C for 3 hours to obtain a carbon nanotube-iron tetroxide-doped graphite material. The mass fraction of carbon nanotubes in the carbon nanotube-iron tetroxide-doped graphite material is 3%.

[0131] S4: 3g of Li5FeO4 was added to 1000g of N-methylpyrrolidone organic solvent and dispersed evenly, and 3g of lithium carboxymethyl cellulose and 100g of carbon nanotube ferroferric oxide-doped graphite material were added and dispersed evenly, and spray-dried to obtain a lithium supplement complex-coated graphite iron oxide composite material.

[0132] Example 2

[0133] A method for preparing a high energy density graphite composite material for lithium ion batteries comprises the following steps:

[0134] S1: 100g coal-based needle coke, 5g tin oxide, 1g polyethylene, and 1g nano-nickel were mixed uniformly, then heated to 450°C for shallow calcination for 6h, then heated to 1200°C for medium calcination for 6h, and finally heated to 2800°C for graphitization for 24h, and then cooled to room temperature in a nitrogen atmosphere to obtain porous graphite;

[0135] S2: Add 5g of Co3O4 to 500g of deionized water to prepare a 1wt% solution, then add 10g of ethylenediamine, 10g of 10wt% nickel chloride solution, and add 100g of porous graphite to disperse evenly. Hydrothermal reaction is carried out at a temperature of 100°C for 6h, and vacuum drying is carried out at 80°C for 24h to obtain an intermediate material.

[0136] S3: The intermediate material is transferred to a tube furnace and acetylene gas is introduced (flow rate 10 ml / min, 100 min), and carbonization sintered at a temperature of 800°C for 6 hours to obtain a carbon nanotube cobalt oxide doped graphite material. The mass fraction of carbon nanotubes in the carbon nanotube ferroferric oxide doped graphite material is 1%.

[0137] S4: Add 1g of Li2NiO2 to 500g of N-methylpyrrolidone and disperse evenly, and add 1g of lithium carboxymethyl cellulose and 100g of carbon nanotube cobalt oxide-doped graphite material and disperse evenly, spray dry, and obtain a lithium supplement complex-coated graphite cobalt oxide composite material.

[0138] Example 3

[0139] A method for preparing a high energy density graphite composite material for lithium ion batteries comprises the following steps:

[0140] S1: 100g petroleum coke, 10g silicon oxide, 5g polyethylene oxide, and 5g metal cobalt powder were mixed uniformly, then heated to 650℃ for shallow calcination for 1h, then heated to 1500℃ for medium calcination for 1h, and finally heated to 3200℃ for graphitization for 6h, and then cooled to room temperature under nitrogen atmosphere to obtain porous graphite;

[0141] S2: Add 15g NiO to 1500g deionized water to prepare a 1wt% solution, then add 30g triethylamine, 50g 10wt% cobalt chloride solution, and add 100g porous graphite to disperse evenly. Hydrothermal reaction is carried out at a temperature of 200°C for 1h, and vacuum drying is carried out at 80°C for 24h to obtain an intermediate material.

[0142] S3: The intermediate material is transferred to a tube furnace and methane gas is introduced (flow rate 30 ml / min, 200 min), and carbonization sintering is carried out at a temperature of 1200°C for 1 hour to obtain a carbon nanotube nickel oxide doped graphite material. The mass fraction of carbon nanotubes in the carbon nanotube ferroferric oxide doped graphite material is 6%.

[0143] S4: Add 5g of Li6CoO4 to 1500g of N-methylpyrrolidone organic solvent and disperse evenly, then add 5g of lithium carboxymethyl cellulose and 100g of carbon nanotube nickel oxide doped graphite material and disperse evenly, spray dry, and obtain a lithium supplement complex coated with graphite nickel oxide composite material.

[0144] Example 4

[0145] The method is basically the same as Example 1, except that in step S1, the mass ratio of coal-based needle coke: iron oxide: ethylene vinyl acetate: nano-iron is 100:4:5:2. That is, the amount of iron oxide is adjusted from 8g to 4g, and the rest remain unchanged.

[0146] Example 5

[0147] The method is basically the same as Example 1, except that in step S1, the mass ratio of coal-based needle coke: iron oxide: ethylene vinyl acetate: nano-iron is 100:15:5:2. That is, the amount of iron oxide is adjusted from 8g to 15g, and the rest remain unchanged.

[0148] Example 6

[0149] The process is basically the same as Example 1, except that step S1 does not contain the functional additive ethylene vinyl acetate, and the amount of iron oxide is adjusted to 11 g.

[0150] Example 7

[0151] The process is basically the same as Example 1, except that step S1 does not contain iron oxide, and the amount of ethylene vinyl acetate is adjusted to 11 g.

[0152] Example 8

[0153] The method is basically the same as Example 1, except that a two-stage calcination is used in step S1. Specifically, step S1 comprises: uniformly mixing 100 g of coal-based needle coke, 8 g of iron oxide, 3 g of ethylene vinyl acetate, and 3 g of nano-iron; then heating the mixture to 550°C for shallow calcination for 3 h; then heating the mixture to 3000°C for graphitization for 12 h; and finally cooling the mixture to room temperature under a nitrogen atmosphere to obtain porous graphite.

[0154] Example 9

[0155] The process is basically the same as Example 1, except that 20 g of sodium hydroxide is used instead of 20 g of ethanolamine in step S2.

[0156] Example 10

[0157] The process is basically the same as Example 1, except that lithium carboxymethyl cellulose is not added in step S4.

[0158] Example 11

[0159] The method is basically the same as Example 1, except that the type of magnetic metal oxide in step S2 is changed. In this embodiment, Fe3O4 is replaced by chromium dioxide.

[0160] Comparative Example 1

[0161] The process is basically the same as Example 1, except that ferric chloride solution and ethanolamine are not added in step S2.

[0162] Comparative Example 2

[0163] The process is basically the same as Example 1, except that Li5FeO4 is not added in step S4.

[0164] Comparative Example 3

[0165] The method is basically the same as Example 1, except that step S3 is not included. Step S4 is to directly mix commercially available carbon nanotubes with the core material, lithium supplement, organic solvent, and lithium carboxymethyl cellulose. Step S4 is specifically as follows:

[0166] 3g of Li5FeO4 was added to 1000g of N-methylpyrrolidone organic solvent and dispersed evenly, and 3g of lithium carboxymethyl cellulose, 3g of carbon nanotubes (purchased from Zhenjiang Tiannai Technology Co., Ltd.) and 97g of core material were added and dispersed evenly, and spray dried to obtain a lithium supplement complex-coated graphite iron oxide composite material.

[0167] Comparative Example 4

[0168] The method is basically the same as Example 1, except that the Fe3O4 in step S2 is replaced by non-magnetic oxide magnesium oxide.

[0169] Test example:

[0170] (1) SEM test

[0171] The lithium supplement composite prepared in Example 1 and coated with graphite iron oxide composite material were subjected to SEM test. The results are as follows: Figure 1 As shown. Figure 1 It can be seen that the obtained composite material presents a granular structure with slight bonding, the particle size is between 10-15 μm, and the size distribution is uniform.

[0172] (2) Performance test of composite materials and button batteries prepared therefrom

[0173] The specific surface area, powder conductivity, and powder OI value of the composite materials prepared in the examples and comparative examples were tested in accordance with the national standard GB / T-24533-2019 "Graphite Anode Materials for Lithium-ion Batteries".

[0174] The above powder material is placed in a powder compaction density test, and the compaction density of the above negative electrode material is tested under a pressure of 2T.

[0175] The lithium supplement composite coated graphite iron oxide composite material prepared in each example and the graphite composite negative electrode material of each comparative example were assembled into button batteries according to the following method:

[0176] A binder, conductive agent, and solvent were added to the negative electrode material and stirred to form a negative electrode slurry. The slurry was then coated onto copper foil, dried, rolled, and cut to produce negative electrode sheets. The binder was polyvinylidene fluoride, the conductive agent was SP conductive agent, and the solvent was NMP. The weight ratio of the negative electrode material, SP conductive agent, polyvinylidene fluoride, and NMP was 95:1:4:220. The battery was assembled in an argon-filled glove box using a metallic lithium sheet as the positive electrode, polyethylene (PE) film, polypropylene (PP) film, and polyethylene propylene (PEP) composite film as the separator, and LiPF6 / EC+DEC (LiPF6 concentration of 1.3 mol / L, EC:DEC volume ratio of 1:1) as the electrolyte.

[0177] The prepared button cells were installed in a Newwell CT-4008-5V10mA battery tester and charged and discharged at a 0.1C rate over a voltage range of 0.005V to 2.0V. The initial discharge capacity and initial discharge efficiency were measured. The 2C rate discharge capacity was tested, and the rate performance (2C / 0.1C), cycle performance (0.1C / 0.1C, 100 cycles), and initial charge DCR (50% SOC) were calculated.

[0178] The above test results are shown in Table 1-2.

[0179] Table 1 Performance test of the composite materials of the embodiments and comparative examples

[0180]

[0181] Table 2 Test results of button batteries corresponding to the composite materials of the embodiments and comparative examples

[0182]

[0183]

[0184] As can be seen from Table 1-2, the discharge specific capacity, initial efficiency, and rate performance of the lithium-supplementing agent-coated graphite oxide composite materials prepared in Examples 1-3 are significantly higher than those in the comparative examples. This may be because the graphite materials in the examples are doped with a high-capacity, high-power magnetic metal oxide material to enhance the material's fast-charging performance and specific capacity, and the lithium-supplementing agent is coated on its surface, reducing its irreversible capacity and improving its initial efficiency by relying on the lithium ions released during the charge and discharge process.

[0185] Comparing Example 1 with Examples 4-7, it can be seen that the pore structure of porous graphite affects the specific surface area of ​​the material and its compaction density, OI value, fast charging performance and cycle performance. Comparing Example 1 with Example 8, segmented carbonization is used to improve the compaction density of the material. Comparing Example 1 with Example 9, it can be seen that compared with inorganic alkaline solutions, the specific surface area of ​​the material is increased and its pores are fewer, so that the compaction density of the material is higher and the rate performance is preferred. Comparing Example 1 with Example 10, it can be seen that when lithium carboxymethyl cellulose is not present, the lithium ion diffusion rate of the material is slow, the first efficiency of the prepared battery is low, and the rate performance will deteriorate. Comparing Example 1 with Example 11, it can be seen that changes in the type of magnetic metal oxide will also affect the orientation of the material. The battery prepared in Example 1 has a low OI value, and the rate performance will be improved.

[0186] (3) Soft pack battery test

[0187] The negative electrode was prepared using the graphite composite negative electrode materials prepared in Examples 1-11 and Comparative Examples 1-4, respectively; the positive electrode was prepared using lithium iron phosphate as the positive electrode material; a 2Ah soft-pack battery was prepared using LiPF6 (solvent is EC+DEC, volume ratio 1:1, concentration 1.1 mol / L) as the electrolyte and celegard2400 as the diaphragm.

[0188] To prepare the negative electrode, a binder, conductive agent, and solvent are added to the negative electrode material and stirred to form a negative electrode slurry. The slurry is then coated onto copper foil, dried, rolled, and cut to produce negative electrode sheets. The binder is LA132, the conductive agent is SP, and the solvent is double-distilled water. The weight ratio of the negative electrode material, SP conductive agent, LA132 binder, and double-distilled water is 95:1:4:220.

[0189] During cathode preparation, a binder, conductive agent, and solvent are added to the cathode material and stirred to form a cathode slurry. The slurry is then coated onto aluminum foil, dried, rolled, and cut to form cathode sheets. The binder is PVDF, the conductive agent is SP, and the solvent is N-methylpyrrolidone. The weight ratio of the cathode material, conductive agent, binder, and solvent is 93:3:4:140.

[0190] The prepared soft-pack battery was tested for its initial efficiency and initial discharge specific capacity at a charge and discharge rate of 0.3C.

[0191] 3.1 Rate performance test

[0192] The charge and discharge voltage range is 2.8~4.2V, the test temperature is 25±3.0℃, and the charging is performed at 1.0C, 2.0C, 5.0C, and 10.0C, and the discharge is performed at 1.0C. The constant current ratio of the battery is tested under different charging modes. The results are shown in Table 3.

[0193] Table 3 Performance test of soft pack batteries prepared from composite materials of Examples and Comparative Examples

[0194]

[0195]

[0196] As shown in Table 3, the rate charging performance and initial charge-discharge efficiency of the soft-pack batteries of the examples of the present invention are significantly better than those of the comparative examples, and the charging time is shorter, indicating that the composite negative electrode material of the present invention has good fast-charging performance. This may be due to the high powder conductivity of the example material and the lithium supplementation agent coated on the outer layer, which increases the diffusion coefficient of the material and improves the rate performance. Furthermore, the examples have a better initial discharge capacity than the comparative examples.

[0197] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0198] The above description is merely a preferred embodiment of the present invention, and the present invention is not limited to the above embodiment. It is understood that other improvements and variations directly derived or imagined by those skilled in the art without departing from the spirit and concept of the present invention should be considered to be included in the scope of protection of the present invention.

Claims

1. A graphite composite material, characterized in that: The graphite composite material has a core-shell structure, The core of the core-shell structure includes magnetic metal oxide-doped porous graphite; The shell of the core-shell structure comprises carbon nanotubes, a lithium supplement and amorphous carbon.

2. The graphite composite material according to claim 1, characterized in that Based on the total mass of the graphite composite material being 100%, the mass of the shell accounts for 5 to 10%; Preferably, based on the total mass of the shell being 100%, the mass of the carbon nanotubes accounts for 1-5%, the mass of the lithium supplement accounts for 1-5%, and the balance is amorphous carbon; Preferably, in the inner core, the mass ratio of the magnetic metal oxide to the porous graphite is 5-15:85-95.

3. The graphite composite material according to claim 1, characterized in that The magnetic metal oxide includes at least one of Fe3O4, Co3O4, and NiO.

4. A method for preparing the graphite composite material according to any one of claims 1 to 3, characterized in that: The steps include: S1: mixing coke raw material, metal oxide, functional additive and catalyst to obtain a mixture, and calcining the mixture in three stages to obtain porous graphite; S2: adding an alkaline compound, a catalyst solution, and the porous graphite prepared in step S1 to the magnetic metal oxide solution, uniformly dispersing the mixture, performing a hydrothermal reaction, and filtering to obtain a core; S3: introducing a carbon source gas into the core prepared in step S2 to perform carbonization sintering to obtain a core with surface-grown carbon nanotubes; S4: After dispersing the lithium supplement agent in an organic solvent, cellulose salt and the core of the surface-grown carbon nanotubes in step S3 are added, dispersed evenly, and spray-dried to obtain a graphite composite material.

5. The preparation method according to claim 4, characterized in that In step S1, the mass ratio of the coke raw material, the metal oxide, the functional additive and the catalyst is 100:5-10:1-5:1-5; Preferably, the coke raw material includes at least one of coal-based needle coke, petroleum coke, and pitch coke; Preferably, the metal oxide includes at least one of iron oxide, tin oxide, silicon oxide, and molybdenum oxide; Preferably, the functional additive comprises at least one of ethylene vinyl acetate, polyethylene, polyethylene oxide, ethylene propylene copolymer, ethylene / propylene / diene terpolymer, and polyisoprene; Preferably, the catalyst comprises at least one of iron, cobalt, nickel, and copper; More preferably, the particle size of the catalyst is 100 to 500 nm.

6. The preparation method according to claim 4, characterized in that In step S1, the three-stage temperature-raising calcination includes: heating the mixture to t1 for a first calcination, then continuing to heat the mixture to t2 for a second calcination, and finally heating the mixture to t3 for a third calcination; Preferably, the temperature t1 is 450-650°C; Preferably, the first calcination time is 1 to 6 hours; Preferably, the temperature t2 is 1200-1500°C; Preferably, the second calcination time is 1 to 6 hours; Preferably, the temperature t3 is 2800-3200°C; Preferably, the third calcination time is 6 to 24 hours.

7. The preparation method according to claim 4, characterized in that In step S2, the mass ratio of the magnetic metal oxide in the magnetic metal oxide solution, the alkaline compound, the catalyst in the catalyst solution, and the porous graphite is 5-15:10-30:1-5:100; Preferably, the magnetic metal oxide solution is prepared by adding water to the magnetic metal oxide; Preferably, the mass concentration of the magnetic metal oxide solution is 0.5-1.5%; Preferably, the alkaline compound is an organic amine compound; More preferably, the organic amine compound includes at least one of ethanolamine, ethylenediamine, diethylamine, triethylamine, dimethylamine, hydroxyethylethylenediamine, and aminoethanolamine; Preferably, the catalyst solution is obtained by dispersing the catalyst in water; Preferably, the mass concentration of the catalyst solution is 8 to 15%; Preferably, the catalyst is a metal chloride; More preferably, the metal chloride includes at least one of ferric chloride, cobalt chloride, nickel chloride, and copper chloride; Preferably, the temperature of the hydrothermal reaction is 100-200°C; Preferably, the hydrothermal reaction time is 1 to 6 hours; Preferably, after the filtration, the method further comprises the step of drying the filtered residue; Preferably, the drying is vacuum drying.

8. The preparation method according to claim 4, characterized in that In step S3, the carbon source gas includes at least one of methane, acetylene, and ethylene; Preferably, the temperature of the carbonization sintering is 800-1200°C; Preferably, the carbonization sintering time is 1 to 6 hours; In step S4, the mass ratio of the lithium supplement agent, the organic solvent, the cellulose salt, and the core of the surface-grown carbon nanotubes is 1-5:500-1500:1-5:100; Preferably, the cellulose salt comprises at least one of carboxymethyl cellulose salt and hydroxymethyl cellulose salt; Preferably, the hydroxymethyl cellulose salt comprises at least one of lithium hydroxymethyl cellulose, magnesium hydroxymethyl cellulose, and sodium hydroxymethyl cellulose; Preferably, the carboxymethyl cellulose salt comprises at least one of lithium carboxymethyl cellulose, magnesium carboxymethyl cellulose, and sodium carboxymethyl cellulose; More preferably, the carboxymethyl cellulose salt is lithium carboxymethyl cellulose; Preferably, the lithium supplement comprises at least one of Li5FeO4, Li2NiO2, Li6CoO4, and Li4V3O8; Preferably, the organic solvent includes at least one of N-methylpyrrolidone, cyclohexane, and carbon tetrachloride.

9. A negative electrode, characterized in that The negative electrode includes a negative electrode active material, and the negative electrode active material includes the graphite composite material according to any one of claims 1 to 3; or the graphite composite material prepared by the preparation method according to any one of claims 4 to 8.

10. A secondary battery, characterized in that: The secondary battery includes a positive electrode, a negative electrode, and an electrolyte, and the negative electrode includes the negative electrode according to claim 9.

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