Graphite composite negative electrode material and preparation method thereof, negative electrode sheet and lithium battery

Abstract

The application relates to the field of lithium ion batteries, and discloses a graphite composite negative electrode material and a preparation method thereof, a negative electrode sheet and a lithium battery. The graphite composite negative electrode material disclosed by the application is doped with metals generated by thermal decomposition of copper fluoride and metal nitride and undecomposed metal nitride on the surface and / or inside of graphite. The application realizes multiple metal doping of graphite at a molecular level through a thermal decomposition reaction, makes the distribution of metal atoms on the graphite more uniform, fully plays the synergistic effect between the metals, retains the advantages of good cycle performance and high specific surface area of the graphite, reduces the impedance of the graphite through the metal doping, and improves the conductivity of the graphite negative electrode material. In addition, trace undecomposed nitride doping can improve and enhance the electrochemical performance of the graphite, and ensures sufficient utilization of the nitride. The whole preparation method avoids complicated operation steps, does not need to use expensive machines and equipment, and fully saves manpower and material resources.

Description

Technical Field

[0001] This application relates to the field of lithium-ion batteries, and in particular to a graphite composite anode material and its preparation method, as well as an anode sheet and a lithium battery. Background Technology

[0002] With continuous societal progress, the demands on batteries from energy storage, electric vehicles, portable electronic devices, and power tools are increasing. As a crucial component of batteries, the negative electrode material has a particularly significant impact on overall battery performance. Graphite-based electrode materials possess advantages such as low charge / discharge voltage plateau, low cost, and good safety, making them the primary negative electrode material for current lithium-ion batteries. However, the anisotropic structure of graphite restricts the diffusion of metal ions within its structure. Selectively incorporating other non-carbon elements into graphite negative electrode materials can effectively alter the ion intercalation behavior within the graphite electrode. Doping graphite materials with metal elements can effectively improve their load-bearing capacity, increase current density, and accelerate charge transport.

[0003] Currently, most metal element doping processes involve complex steps. For example, in "Modification of Natural Graphite Anode Materials by Metal Element Ion Doping" (Li Jianjun et al., Proceedings of the 10th National Electrochemical Conference, 1999), graphite needs to be first subjected to liquid-phase oxidation or chlorination, then immersed in a metal ion solution, and then heat-treated at temperatures above 800°C. This process not only results in uneven distribution of the doped metal, thus affecting the performance of the anode material, but also consumes a lot of energy, requires a lot of equipment, and does not significantly improve its electrochemical performance. In addition, the obtained anode material also needs to be washed and dried. Summary of the Invention

[0004] In view of this, the purpose of this application is to provide a graphite composite anode material that can improve the first-stage efficiency of the battery.

[0005] Another objective of this application is to provide a graphite composite anode material that can improve the cycle performance of the battery.

[0006] Another objective of this application is to provide a graphite composite anode material that can improve the rate performance of a battery.

[0007] Another objective of this application is to provide a method for preparing the graphite composite anode material, which enables the graphite to be doped with metal at the molecular level, resulting in a more uniform distribution of metal atoms on the graphite, while the process steps are simpler and the energy consumption is lower.

[0008] Another objective of this application is to provide a negative electrode sheet and a lithium battery based on the aforementioned negative electrode material.

[0009] In order to solve the above-mentioned technical problems / achieve the above-mentioned objectives, or at least partially solve the above-mentioned technical problems / achieve the above-mentioned objectives, as a first aspect of this application, a graphite composite negative electrode material is provided, which is doped with metals produced by the thermal decomposition of copper fluoride and metal nitrides and undecomposed metal nitrides on the surface and / or inside of graphite; the metal nitrides are selected from one or more of Ni3N2, Zn3N2, and Fe6N2.

[0010] Optionally, the molar ratio of copper fluoride to metal nitride is 10:(1-10).

[0011] Optionally, the ratio of graphite to copper fluoride is 100g:(0.05-0.15mol).

[0012] Optionally, the thermal decomposition environment is between 100-650°C.

[0013] As a second aspect of this application, a method for preparing the aforementioned graphite composite anode material is provided, comprising:

[0014] In an ammonia atmosphere, a mixture of graphite, copper fluoride, and metal nitride is heated to convert copper fluoride into copper nitride.

[0015] The ammonia atmosphere is replaced with a protective gas or a reducing gas atmosphere, and the mixture is heated further. Copper nitride and metal nitride decompose and the metals adhere to the graphite surface and / or interior, resulting in the graphite composite anode material that can be used directly without cleaning.

[0016] Optionally, the heating treatment temperature in the ammonia atmosphere is 280-350℃.

[0017] Optionally, the heating treatment temperature in the protective gas or reducing gas atmosphere is 400-650°C.

[0018] Optionally, the reducing gas includes one or more of hydrogen, carbon monoxide, hydrogen sulfide, methane, and sulfur monoxide.

[0019] As a third aspect of this application, a negative electrode sheet is provided, using the graphite composite negative electrode material described in this application or the graphite composite negative electrode material prepared by the preparation method described in this application as the active material.

[0020] As a fourth aspect of this application, a lithium battery includes a positive electrode, a separator, an electrolyte, and a negative electrode as described in this application.

[0021] Compared with conventional metal-doped graphite processes, this application has at least the following outstanding advantages:

[0022] 1. Graphite is doped at the molecular level through thermal decomposition, resulting in a uniform distribution of metal atoms on the graphite. This retains the advantages of graphite, such as good cycle performance and high specific surface area, while reducing the impedance of graphite and improving the conductivity of the graphite anode material through metal doping.

[0023] 2. The specific capacity of incompletely decomposed nitrides is higher than that of graphite. Trace amounts of nitride doping can improve the electrochemical performance of graphite and ensure 100% utilization of nitrides.

[0024] 3. The only variables in the preparation process are time and temperature, avoiding complicated operating steps. The entire experimental process only requires a tube furnace, eliminating the need for expensive machinery and equipment, thus significantly saving labor and material costs;

[0025] 4. By doping graphite with multiple metals, the synergistic effect between the metals is fully utilized, thereby improving the conductivity of graphite.

[0026] 5. The entire preparation process does not require high temperatures. During the heating process, different nitrides will decompose into metals, making full use of the heat energy during the heating process and reducing energy waste. The gases used are all environmentally friendly gases, which can reduce environmental pollution. Attached Figure Description

[0027] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments of this application and their descriptions are used to explain this application and do not constitute an undue limitation of this application.

[0028] Figure 1 The image shown is a SEM image of the graphite composite anode material described in this application. Detailed Implementation

[0029] This application discloses a graphite composite anode material and its preparation method, as well as an anode sheet and a lithium battery. Those skilled in the art can refer to the content of this application and appropriately modify the process parameters to achieve the desired result. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in this application. The products, processes, and applications described in this application have been described through preferred embodiments. Those skilled in the art can obviously modify or appropriately change and combine the methods described herein without departing from the content, spirit, and scope of this application to realize and apply the technology of this application. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0030] It should be noted that, in this document, relational terms such as "first" and "second," "step 1" and "step 2," and "(1)" and "(2)" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. Moreover, the embodiments and features described in this application can be combined with each other without conflict.

[0031] The graphite composite anode material of this application is uniformly doped with metals through a thermal decomposition method. By reducing and decomposing CuF2, Ni3N2, Zn3N2, and Fe6N2 under heating conditions, they are uniformly distributed on the surface and inside of the graphite, thereby improving its various electrochemical properties.

[0032] The graphite composite anode material of this application has good conductivity, which is greater than that of single graphite electrode material. It also has excellent cycle stability, with a maximum capacity loss of only 4.7% after 500 cycles. The initial efficiency is greater than 98.9%, and the specific capacity is above 365 mAh / g.

[0033] In the first aspect of this application, a graphite composite anode material is provided, wherein the graphite surface and / or interior are doped with metals produced by the thermal decomposition of copper fluoride and metal nitrides, as well as undecomposed metal nitrides; the metal nitrides are selected from one or more of Ni3N2, Zn3N2, and Fe6N2, and their SEM images are shown below. Figure 1 .

[0034] In some embodiments of this application, the molar ratio of copper fluoride to metal nitride is 10:(1-10); in other embodiments of this application, the molar ratio of copper fluoride to metal nitride is 10:1, 10:2, 10:3, 10:4, 10:5, 10:6, 10:7, 10:8, 10:9 or 10:10.

[0035] In some embodiments of this application, the ratio of graphite to copper fluoride is 100g:(0.05-0.15mol); in some embodiments of this application, the ratio of graphite to copper fluoride is 100g:0.05mol, 100g:0.06mol, 100g:0.07mol, 100g:0.08mol, 100g:0.09mol, 100g:0.10mol, 100g:0.11mol, 100g:0.12mol, 100g:0.13mol, 100g:0.14mol, or 100g:0.15mol.

[0036] In some embodiments of this application, the thermal decomposition environment is 120-650℃; in some embodiments of this application, the thermal decomposition is a heating treatment at 120-650℃ for 2-12 hours; in other embodiments of this application, the thermal decomposition temperature can be 200-600℃, 250-400℃, 120-350℃, 280-350℃, or 400-650℃, and can be specifically selected as 120℃. ℃, 150℃, 200℃, 250℃, 280℃, 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, 600℃ or 650℃; in other embodiments of this application, the thermal decomposition time can be 2-10h, 2-8h, 2-6h, or 2-4h, and can be specifically selected as 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h or 12h.

[0037] In a second aspect of this application, a method for preparing the aforementioned graphite composite anode material is provided, comprising:

[0038] In an ammonia atmosphere, a mixture of graphite, copper fluoride, and metal nitride is heated to convert copper fluoride into copper nitride.

[0039] The ammonia atmosphere is replaced with a protective gas or a reducing gas atmosphere, and the mixture is heated further. Copper nitride and metal nitride decompose and the metals adhere to the graphite surface and / or interior, resulting in the graphite composite anode material that can be used directly without cleaning.

[0040] In an ammonia atmosphere, copper nitride reacts with ammonia under heat treatment conditions as follows:

[0041] CuF₂ + NH₃ → Cu₃N + N₂ + NH₄F

[0042] In this stage, Ni3N2 in the metal nitride can directly release decomposed metallic nickel, which adheres to the graphite surface and / or interior, as shown in the following reaction formula:

[0043] Ni3N2 → Ni + N2 (Decomposition temperature above 120℃)

[0044] In a protective gas atmosphere, the Cu3N and Fe6N2 obtained from the initial heat treatment will further decompose upon heating to produce metallic copper and metallic iron, as shown in the following reaction formula:

[0045] Cu3N → Cu + N2 (Decomposition temperature above 300℃)

[0046] Fe6N2→Fe+N2 (Decomposition temperature above 400℃)

[0047] In a reducing gas atmosphere, the Cu3N and Zn3N2 obtained from the initial heat treatment will further decompose upon heating to produce metallic copper and metallic zinc, as shown in the following reaction formula:

[0048] Cu3N → Cu + N2 (Decomposition temperature above 300℃)

[0049] Zn3N2 + H2 → Zn + NH3 (Decomposition temperature above 400℃)

[0050] In some embodiments of this application, the heating treatment temperature in the ammonia atmosphere is 280-350℃, and the time can be selected as 2-8h, or 2-4h, for example 2h, 3h, 4h, 5h, 6h, 7h or 8h; the temperature can also be selected from 280℃, 290℃, 300℃, 310℃, 320℃, 330℃, 340℃ or 350℃.

[0051] In some embodiments of this application, the heating treatment temperature in the protective gas or reducing gas atmosphere is 400-650°C, and the time can be selected as 2-12h, or 2-10h or 2-8h, for example 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h or 12h; the temperature can also be selected from 400°C, 450°C, 500°C, 550°C, 600°C or 650°C.

[0052] In some embodiments of this application, the reducing gas includes one or more of hydrogen, carbon monoxide, hydrogen sulfide, methane, and sulfur monoxide; for safety and environmental protection purposes, hydrogen may be selected.

[0053] In some embodiments of this application, the protective gas includes one or more of nitrogen and rare gases, such as nitrogen, argon, xenon, helium, neon, krypton, and radon.

[0054] In some embodiments of this application, the preparation method of the graphite composite anode material includes:

[0055] Weigh the raw materials according to the ratio CuF2:Ni3N2 / Zn3N2 / Fe6N2=10:(1-10), grind them together with graphite to make them evenly mixed, and obtain a mixture.

[0056] The ground mixture was placed in an ammonia gas stream and heated at 120-350℃ for 2-8 hours.

[0057] Replace ammonia with nitrogen, hydrogen, or a rare gas, raise the temperature to 400-650℃, and heat for 2-12 hours.

[0058] The graphite composite anode material obtained can be used directly without cleaning.

[0059] In a third aspect of this application, a negative electrode sheet is provided, using the graphite composite negative electrode material described in this application as the active material or the graphite composite negative electrode material prepared by the preparation method described in this application as the active material.

[0060] In some embodiments of this application, the negative electrode sheet includes a current collector and an active material coated on the current collector; wherein, the current collector may be selected from a metal foil with good conductivity, such as copper foil; the active material includes the graphite composite negative electrode material described in this application, as well as a binder, a conductive agent, and a solvent. The binder, conductive agent, and solvent, and their amounts, are selected in accordance with conventional methods, and this application does not impose specific limitations. For example, the binder may be polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC), etc.; the conductive agent may be conductive carbon black (SP), acetylene black, etc.; and the solvent may be N-methylpyrrolidone (NMP), deionized water, etc. The ratio of graphite composite negative electrode material: conductive agent: binder is 8:1:1.

[0061] In a fourth aspect of this application, a lithium battery is provided, including a positive electrode, a separator, an electrolyte, and the negative electrode described in this application; in some embodiments of this application, the lithium-ion battery is a full cell, a pouch cell, or a button cell.

[0062] In some embodiments of this application, the positive electrode is a lithium metal sheet or lithium iron phosphate, high-nickel ternary, lithium-rich manganese-based material, etc.; the separator is a PP separator or a Celegard series separator; the electrolyte is a 1.0-1.5 mol / L LiPF6 solution, for example, a LiPF6 electrolyte with a volume ratio of ethylene carbonate (EC) and diethyl carbonate (DEC) as solvents of 1:1.

[0063] In the comparative experiments provided in this application, unless otherwise specified, all experimental conditions and materials remain consistent to ensure comparability. Furthermore, all materials used in this application are commercially available.

[0064] The following provides a further description of a graphite composite anode material, its preparation method, anode sheet, and lithium battery provided in this application.

[0065] Example 1:

[0066] Take 100g of graphite, 10.16g of CuF2 (0.1mol), and 2.04g of Ni3N2 (0.01mol) and place them in a mortar. Grind for 3 hours to make the mixture uniform.

[0067] The ground mixture was placed in an alumina container and then placed in a quartz tube. It was heated at 280°C for 4 hours in an ammonia gas stream to convert CuF2 into Cu3N and Ni3N2 into nickel metal upon heating.

[0068] CuF₂ + NH₃ → Cu₃N + N₂ + NH₄F

[0069] Ni3N2→Ni+N2

[0070] Replace the ammonia gas in the quartz tube with nitrogen gas, raise the temperature to 450℃ and heat for 4 hours to decompose copper nitride into copper metal and attach it to the graphite.

[0071] Cu3N→Cu+N2

[0072] The sample can be directly used as the negative electrode material after being removed from the quartz tube, without the need for cleaning.

[0073] Example 2:

[0074] Take 100g of graphite, 10.16g of CuF2 (0.1mol), and 10.20g of Ni3N2 (0.05mol) and place them in a mortar. Grind for 3 hours to make the mixture uniform.

[0075] The ground mixture was placed in an alumina container and then placed in a quartz tube. It was heated at 300°C for 8 hours in an ammonia gas stream to convert CuF2 into Cu3N and Ni3N2 into nickel metal upon heating.

[0076] CuF₂ + NH₃ → Cu₃N + N₂ + NH₄F

[0077] Ni3N2→Ni+N2

[0078] Replace the ammonia gas in the quartz tube with nitrogen gas, raise the temperature to 550℃ and heat for 8 hours to decompose copper nitride into copper metal and attach it to the graphite.

[0079] Cu3N→Cu+N2

[0080] The sample can be directly used as the negative electrode material after being removed from the quartz tube, without the need for cleaning.

[0081] Example 3:

[0082] Take 100g of graphite, 10.16g of CuF2 (0.1mol), and 20.40g of Ni3N2 (0.1mol) and place them in a mortar. Grind for 3 hours to make the mixture uniform.

[0083] The ground mixture was placed in an alumina container and then placed in a quartz tube. It was heated at 350°C for 2 hours in an ammonia gas stream to convert CuF2 into Cu3N and Ni3N2 into nickel metal upon heating.

[0084] CuF₂ + NH₃ → Cu₃N + N₂ + NH₄F

[0085] Ni3N2→Ni+N2

[0086] Replace the ammonia gas in the quartz tube with nitrogen gas, raise the temperature to 650℃ and heat for 2 hours to decompose copper nitride into copper metal and attach it to the graphite.

[0087] Cu3N→Cu+N2

[0088] The sample can be directly used as the negative electrode material after being removed from the quartz tube, without the need for cleaning.

[0089] Example 4:

[0090] Take 100g of graphite, 15.24g of CuF2 (0.15mol), and 11.23g of Zn3N2 (0.05mol) and place them in a mortar. Grind for 3 hours to make the mixture uniform.

[0091] The ground mixture was placed in an alumina container and then placed in a quartz tube. It was then heated at 280°C for 4 hours in an ammonia gas stream to convert CuF2 into Cu3N.

[0092] CuF₂ + NH₃ → Cu₃N + N₂ + NH₄F

[0093] Replace the ammonia gas in the quartz tube with hydrogen gas, raise the temperature to 450℃ and heat for 4 hours to decompose copper nitride and zinc nitride into the corresponding metals and attach them to the graphite.

[0094] Cu3N→Cu+N2

[0095] Zn3N2 + H2 → Zn + NH3

[0096] The sample can be directly used as the negative electrode material after being removed from the quartz tube, without the need for cleaning.

[0097] Example 5:

[0098] Take 100g of graphite, 5.08g of CuF2 (0.05mol), and 10.89g of Fe6N2 (0.03mol) and place them in a mortar, grind for 3 hours to make them evenly mixed;

[0099] The ground mixture was placed in an alumina container and then placed in a quartz tube. It was then heated at 280°C for 4 hours in an ammonia gas stream to convert CuF2 into Cu3N.

[0100] CuF₂ + NH₃ → Cu₃N + N₂ + NH₄F

[0101] The ammonia gas in the quartz tube was replaced with nitrogen gas, and the temperature was raised to 450℃ and heated for 4 hours to decompose copper nitride and iron nitride into the corresponding metals and attach them to the graphite.

[0102] Cu3N→Cu+N2

[0103] Fe6N2→Fe+N2

[0104] The sample can be directly used as the negative electrode material after being removed from the quartz tube, without the need for cleaning.

[0105] Comparative Example 1:

[0106] Place 100g of graphite in a mortar and grind for 3 hours.

[0107] The ground graphite was placed in an alumina container and then placed in a quartz tube. The container was then heated at 450°C for 4 hours in a nitrogen atmosphere.

[0108] The sample can be directly used as the negative electrode material after being removed from the quartz tube, without the need for cleaning.

[0109] Comparative Example 2:

[0110] The only difference from Example 1 is that only copper is doped into the graphite, specifically:

[0111] Place 100g of graphite and 10.16g of CuF2 (0.1mol) into a mortar and grind for 3 hours to mix them evenly.

[0112] The ground mixture was placed in an alumina container and then placed in a quartz tube. It was then heated at 280°C for 4 hours in an ammonia gas stream to convert CuF2 into Cu3N.

[0113] Replace the ammonia gas in the quartz tube with nitrogen gas, raise the temperature to 450℃ and heat for 4 hours to decompose copper nitride into copper metal and attach it to the graphite.

[0114] The sample can be directly used as the negative electrode material after being removed from the quartz tube, without the need for cleaning.

[0115] Comparative Example 3:

[0116] Take 100g of graphite, 10.16g of CuF2 (0.1mol), and 1.02g of Ni3N2 (0.005mol) and place them in a mortar. Grind for 3 hours to make the mixture uniform.

[0117] The ground mixture was placed in an alumina container and then placed in a quartz tube. It was heated at 280°C for 4 hours in an ammonia gas stream to convert CuF2 into Cu3N and Ni3N2 into nickel metal upon heating.

[0118] Replace the ammonia gas in the quartz tube with nitrogen gas, raise the temperature to 450℃ and heat for 4 hours to decompose copper nitride into copper metal and attach it to the graphite.

[0119] The sample can be directly used as the negative electrode material after being removed from the quartz tube, without the need for cleaning.

[0120] Comparative Example 4:

[0121] Take 100g of graphite, 10.16g of CuF2 (0.1mol), and 22.40g of Ni3N2 (0.11mol) and place them in a mortar. Grind for 3 hours to make the mixture uniform.

[0122] The ground mixture was placed in an alumina container and then placed in a quartz tube. It was heated at 280°C for 4 hours in an ammonia gas stream to convert CuF2 into Cu3N and Ni3N2 into nickel metal upon heating.

[0123] Replace the ammonia gas in the quartz tube with nitrogen gas, raise the temperature to 450℃ and heat for 4 hours to decompose copper nitride into copper metal and attach it to the graphite.

[0124] The sample can be directly used as the negative electrode material after being removed from the quartz tube, without the need for cleaning.

[0125] Comparative Example 5:

[0126] Take 100g of graphite, 10.16g of CuF2 (0.1mol), and 8.73g of GaN (0.1mol) and place them in a mortar, grind for 3 hours to make the mixture uniform;

[0127] The ground mixture was placed in an alumina container and then placed in a quartz tube. It was heated at 1050°C for 4 hours in an ammonia gas stream to convert CuF2 into Cu3N, which then decomposed into copper metal upon heating. GaN was decomposed into gallium metal upon heating.

[0128] GaN → Ga + N2 (Decomposition temperature above 1050℃)

[0129] The sample can be directly used as the negative electrode material after being removed from the quartz tube, without the need for cleaning.

[0130] Experimental Example 1:

[0131] 1. SEM testing

[0132] By performing SEM tests on the graphite anode material doped in Example 3, it can be observed that metal atoms exist on the surface of graphite and between layers, indicating that the nitride decomposes into metal atoms and is uniformly distributed in graphite. The SEM images of the materials in other examples are basically consistent with those in Example 3.

[0133] 2. Physicochemical property testing

[0134] The conductivity, tap density, specific surface area, and particle size of the graphite composite anode materials in Examples 1-5 and the graphite anode materials in the comparative examples were tested according to the test methods in standard GB / T-24533-2019 "Graphite Anode Materials for Lithium-ion Batteries". The test results are shown in Table 1.

[0135] Table 1

[0136]

[0137]

[0138] As shown in Table 1, the conductivity of the metal-doped graphite composite anode materials prepared in Examples 1-5 is significantly higher than that of the comparative examples. The conductivity of the materials in Examples 1-3 is 1-2 orders of magnitude higher than that of the comparative examples. This may be due to the higher conductivity of the doped metals and the synergistic effect between the metals; both factors reduce the impedance of graphite and increase its conductivity. Furthermore, the high density of metal elements deposited on graphite can improve the tap density. In addition, since the metal nitride particles are smaller than graphite particles, the undecomposed trace amounts of nitride can fill the gaps between graphite particles, thereby improving the tap density.

[0139] 3. Initial charge and discharge performance test of button cells

[0140] The graphite anode materials in Examples 1-5 and Comparative Examples 1-5 were assembled into coin cells and named A1, A2, A3, A4, A5 and B1, B2, B3, B4, B5, respectively.

[0141] The assembly method is as follows: A binder, conductive agent, and solvent are added to the graphite anode material, stirred to form a slurry, coated onto copper foil, and then dried and rolled to obtain the anode sheet. The binder used is polyvinylidene fluoride (PVDF), the conductive agent is acetylene black, and the solvent is N-methylpyrrolidone (NMP). The anode materials used are the graphite anode materials in the examples and comparative examples. The ratio of each component is: anode material: conductive agent: binder = 8:1:1. The electrolyte is 1 mol / L LiPF6, the lithium metal sheet is the positive electrode of the button cell, and the separator is Celegard 2400. The button cells are assembled in a glove box with argon and water content both below 0.1 ppm. Electrochemical performance testing is conducted on a Wuhan Landian CT2001A battery tester, with a charge / discharge voltage range of 0.05V to 2V and a charge / discharge rate of 1C.

[0142] Table 2

[0143] Initial discharge specific capacity (mAh / g) 383.7 397.9 416.1 375.4 367.4 First-time efficiency (%) 99.1 99.3 99.4 99.5 98.9 B1 B2 B3 B4 B5 Initial discharge specific capacity (mAh / g) 354.2 362.9 356.2 417.5 357.5 First-time efficiency (%) 98.4 98.5 98.3 97.2 98.5

[0144] As shown in Table 2, compared with Comparative Example 1, the lithium-ion batteries prepared by the double-doped graphite composite materials in Examples 1-5, used as graphite anode materials, exhibit significantly higher initial discharge specific capacity and initial charge-discharge efficiency than the graphite composite materials prepared in Comparative Example 1. This is because the metals doped between the graphite layers can improve the conductivity of the lithium-ion battery, thereby improving its initial efficiency; the undecomposed nitrides, due to their higher specific capacity than graphite and their ability to improve tap density, further enhance the specific capacity of the graphite anode material.

[0145] Compared with Comparative Example 2, the lithium-ion batteries prepared by the double-doped graphite composite material in Examples 1-5, which are used as graphite anode materials, have significantly higher initial discharge specific capacity and initial charge-discharge efficiency than the graphite composite material prepared in Comparative Example 2. This indicates that double doping has a better performance improvement effect on graphite anode materials than single doping.

[0146] As can be seen from Examples 1-3 compared with Comparative Example 3, although trace amounts of non-copper metals can increase the capacity of graphite materials, the increase is small.

[0147] As can be seen from Examples 1-3 and Comparative Example 4, when the amount of non-copper metals is too large, although the first discharge specific capacity can be improved, the first efficiency will decrease, and it is impossible to obtain a negative electrode material with good first discharge specific capacity and first efficiency.

[0148] As can be seen from Examples 1-5 compared with Comparative Example 5, the metal nitrides used in this application can reduce nitrides to metals at lower decomposition temperatures, greatly saving energy, and can improve the electrochemical performance of graphite better than other non-limited nitrides.

[0149] 4. Cycle performance and rate performance testing of pouch batteries

[0150] Anode sheets were prepared using graphite materials from Examples 1-5 and the comparative example as the anode material. Ternary materials (LiNi) were also used. 1 / 3 Co 1 / 3 Mn 1 / 3 Using O2 as the positive electrode, LiPF6 solution (solvent: EC+DEC, volume ratio 1:1, LiPF6 concentration 1.3mol / L) as the electrolyte, and Celegard 2400 as the separator, soft-pack batteries A1, A2, A3, A4, A5 and B1, B2, B3, B4, B5 are assembled.

[0151] Cyclic performance test conditions: discharge current 2C / 2C, voltage range 2.6-4.2V, number of cycles 500.

[0152] Rate performance test conditions: charging rate: 1C / 2C / 3C / 5C / 8C, discharging rate: 1C; voltage range: 2.6-4.2V.

[0153] Table 3

[0154]

[0155]

[0156] As can be seen from Table 3, the cycle performance of the soft-pack battery prepared by the graphite composite anode material of this application is significantly better than that of the comparative example. In terms of cycle performance, the deposition of two metals on the graphite surface and between layers can improve electronic conductivity and reduce its side reactions; at the same time, metal nitrides promote the insertion and extraction of lithium ions during charging and discharging, reduce impedance and improve the structural stability of the material, thereby improving cycle performance.

[0157] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A graphite composite anode material, characterized in that, The graphite surface and / or interior are doped with metals produced by the thermal decomposition of copper fluoride and metal nitrides, as well as undecomposed metal nitrides; the metal nitrides are selected from one or more of Ni3N2, Zn3N2, and Fe6N2. The preparation method of graphite composite anode material includes: heating a mixture of graphite, copper fluoride and metal nitride in an ammonia atmosphere to convert copper fluoride into copper nitride; wherein the molar ratio of copper fluoride to metal nitride is 10:(1-10). The ammonia atmosphere is replaced with a protective or reducing gas atmosphere, and the mixture is further heated. Copper nitride and metal nitride decompose and the metals adhere to the graphite surface and / or interior, resulting in the graphite composite anode material that can be used directly without cleaning.

2. The graphite composite anode material according to claim 1, characterized in that, The ratio of graphite to copper fluoride is 100g: (0.05-0.15mol).

3. The graphite composite anode material according to claim 1, characterized in that, The thermal decomposition occurs at 400-650℃.

4. The method for preparing the graphite composite anode material according to claim 1, characterized in that, include: In an ammonia atmosphere, a mixture of graphite, copper fluoride, and metal nitride is heated to convert copper fluoride into copper nitride. The ammonia atmosphere is replaced with a protective gas or a reducing gas atmosphere, and the mixture is heated further. Copper nitride and metal nitride decompose and the metal adheres to the graphite surface and / or interior, resulting in the graphite composite anode material that can be used directly without cleaning.

5. The preparation method according to claim 4, characterized in that, The heating treatment temperature in the ammonia atmosphere is 280-350℃.

6. The preparation method according to claim 4, characterized in that, The heating treatment temperature in the protective gas or reducing gas atmosphere is 100-650℃.

7. The preparation method according to claim 4, characterized in that, The reducing gas includes one or more of hydrogen, carbon monoxide, hydrogen sulfide, methane, and sulfur monoxide.

8. A negative electrode sheet, characterized in that, The graphite composite anode material according to any one of claims 1-3 or the graphite composite anode material prepared by the preparation method according to any one of claims 4-7 is used as the active material.

9. A lithium battery, characterized in that, It includes a positive electrode, a separator, an electrolyte, and a negative electrode as described in claim 8.

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