Long-circulation lithium battery negative electrode material, preparation method thereof, negative electrode sheet and lithium battery

Abstract

The application relates to the field of lithium ion batteries, and discloses a long-cycle lithium battery negative electrode material, a preparation method thereof, a negative electrode sheet and a lithium battery. The negative electrode material comprises a core, an intermediate layer for coating the core and an outer layer for coating the intermediate layer; the core comprises a carbon-based negative electrode active material, the intermediate layer comprises fluorine-doped amorphous carbon, and the outer layer comprises a film-forming auxiliary agent. The fluorine-doped amorphous carbon layer coated on the surface of the carbon-based negative electrode active material can effectively inhibit the co-intercalation of solvated lithium ions, prevent the structural damage of the active material in the cycle process, and the fluorine-doped amorphous carbon layer formed by using a gas phase deposition coating process has the best effect; and the film-forming auxiliary agent layer uniformly loaded on the surface of the outer layer is beneficial to the formation of a uniform and stable SEI film on the negative electrode surface, and guarantees the cycle performance, stability and service life of the assembled battery.

Description

Technical Field

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

[0002] With the continuous development of energy and environmental issues, the development and utilization of new energy sources has become an urgent need. As an advanced and efficient energy storage device, lithium-ion batteries have received widespread attention and have been greatly developed. Lithium-ion batteries have advantages such as high energy density, high power density, low self-discharge rate, and high safety, and are widely used in new energy vehicles, energy storage, consumer electronics and other fields. With the continuous development of the market and the energy storage field, the requirements for the cycle life of lithium-ion batteries are becoming increasingly higher.

[0003] Currently, graphite is the primary anode material for lithium-ion batteries. During the initial charge and discharge cycle, graphite anode materials form a solid electrolyte interphase (SEI) film at the interface between the anode and the electrolyte. This SEI film acts as an insulator for electrons and an excellent conductor for lithium ions. It also isolates the anode material from the electrolyte, preventing structural damage caused by the insertion of solvated lithium ions. To improve the stability of the SEI film, the industry typically adds film-forming additives to the electrolyte. These additives include unsaturated esters, sulfur-containing additives, lithium salt additives, inorganic compound additives, and other additives. Their function is generally to preferentially undergo reduction reactions before electrolyte molecules, inhibiting the decomposition of the electrolyte solvent, forming a stable SEI film, and preventing damage to the electrode. However, film-forming additives in the electrolyte not only affect the negative electrode but also the positive electrode. For example, vinylene carbonate (VC), a representative negative electrode film-forming additive, can form a stable SEI film on the negative electrode surface. However, VC has poor compatibility with high-capacity, high-voltage positive electrode materials (such as high-nickel ternary materials NCM and lithium-rich manganese-based materials OLO), resulting in an unstable positive electrolyte membrane (CEI) that leads to battery capacity decay. Therefore, modifying battery performance through the electrolyte also has certain limitations.

[0004] To address the aforementioned issues, existing technologies disclose the addition of lithium salt film-forming additives during the negative electrode slurry preparation process. These additives, along with active materials, conductive agents, thickeners, and binders, are used to form a slurry, which is then coated onto a current collector copper foil and dried to obtain a negative electrode sheet. However, the film-forming additives added during the slurry preparation process do not bond tightly enough with the active material after forming the electrode sheet, and they are difficult to migrate within the electrode sheet after drying. Therefore, it is difficult to generate a tightly bonded and complete SEI film with the active material of the electrode sheet.

[0005] In addition, other existing technologies use unsaturated lithium carboxylate and graphite-based carbon materials as a combination of dual active materials as the negative electrode material for lithium-ion batteries, but they cannot guarantee that the unsaturated lithium carboxylate is uniformly distributed on the surface of the graphite-based carbon materials, so it is difficult to form a stable and uniform SEI film. Summary of the Invention

[0006] In view of this, the purpose of this application is to provide a long-cycle lithium battery anode material and its preparation method, so that the anode material can improve the long-cycle performance of the lithium battery;

[0007] Another objective of this application is to provide a negative electrode sheet and a lithium battery based on the aforementioned negative electrode material.

[0008] 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 long-cycle lithium battery anode material is provided, comprising a core, an intermediate layer covering the core, and an outer layer covering the intermediate layer; the core comprises a carbon-based anode active material, the intermediate layer comprises fluorine-doped amorphous carbon, and the outer layer comprises a film-forming aid.

[0009] Optionally, the mass ratio of the total mass of the carbon-based negative electrode active material and the fluorine-doped amorphous carbon to the mass of the film-forming aid is 100:0.1-1.

[0010] Optionally, the carbon-based negative electrode active material includes one or more of natural graphite, artificial graphite, hard carbon, soft carbon, and mesophase carbon microspheres.

[0011] Optionally, the fluorine-doped amorphous carbon is formed by gas-phase coating and / or high-temperature carbonization of a carbon source and a fluorine source; further optionally, the carbon source is a gaseous carbon source, which includes one or more of C1-C4 alkanes, C2-C4 alkenes, and C2-C4 alkynes.

[0012] Optionally, the fluorine source is a gaseous fluorine source; more preferably, the gaseous fluorine source includes one or more of carbon tetrafluoride, trifluoromethane, difluoromethane, octafluorocyclobutane, perfluorobutadiene, and octafluorocyclopentene.

[0013] Optionally, the film-forming aid includes one or more of vinylene carbonate (VC), fluoroethylene carbonate (FEC), vinyl ethylene carbonate (VEC), allyl ethyl carbonate (AEC), vinyl acetate (VA), and catechol carbonate (CC).

[0014] As a second aspect of this application, a method for preparing the negative electrode material is provided, comprising:

[0015] The carbon-based anode active material is vapor-phase coated and / or high-temperature carbonized in a carbon source and fluorine source environment to form a fluorine-doped amorphous carbon coating layer, thereby obtaining a fluorine-doped amorphous carbon-coated carbon-based anode intermediate.

[0016] Fluorine-doped amorphous carbon-coated carbon-based anode intermediate is added to a film-forming aid solution, dispersed evenly, and spray-dried to obtain the anode material.

[0017] As a third aspect of this application, a negative electrode sheet is provided, using the negative electrode material described in this application as the active material.

[0018] As a fourth aspect of this application, a lithium-ion battery is provided, including a positive electrode, a separator, an electrolyte, and the negative electrode described in this application.

[0019] Compared with conventional anode materials, this application coats the surface of carbon-based anode active material with a fluorine-doped amorphous carbon layer, which can effectively suppress the co-intercalation of solvated lithium ions and prevent structural damage to the active material during cycling. In particular, the fluorine-doped amorphous carbon layer formed by vapor deposition coating process has the best effect. Furthermore, the uniform loading of film-forming aids on the outer surface is conducive to the formation of a uniform and stable SEI film on the anode surface, ensuring the cycle performance, stability and service life of the assembled battery. Attached Figure Description

[0020] 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.

[0021] Figure 1 The diagram shown is a structural schematic of the negative electrode material described in this application;

[0022] Figure 2 The image shown is a SEM image of the negative electrode material described in this application. Detailed Implementation

[0023] This application discloses a long-cycle lithium battery anode material and its preparation method, as well as the anode sheet and 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.

[0024] 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.

[0025] The CF bonds in the fluorine-doped amorphous carbon coating layer of the negative electrode material described in this application can enhance the structural stability of the active material, prevent graphite structure damage during cycling, and reduce Li... + Resistance during the diffusion process increases specific capacity and improves the charge-discharge performance of the material;

[0026] Spray drying facilitates the uniform loading of SEI film-forming aids. The film-forming aid loading layer on the material surface helps to form a stable, thin, and uniform SEI film that is tightly bonded to the active material on the surface of the negative electrode during the early stages of battery charging and discharging. This greatly improves the formation efficiency and quality of the SEI film, effectively protects the structure of the negative electrode active material from damage, and enhances the cycle life and safety performance of the negative electrode material. At the same time, it can reduce the adverse side effects on the positive electrode and electrolyte caused by the SEI film-forming additives added to the electrolyte.

[0027] In the first aspect of this application, a long-cycle lithium-ion battery anode material is provided, comprising a core, an intermediate layer covering the core, and an outer layer covering the intermediate layer; the core comprises a carbon-based anode active material, the intermediate layer comprises fluorine-doped amorphous carbon, and the outer layer comprises a film-forming aid, the schematic diagram of which is shown in [Figure number missing]. Figure 1 SEM image (see) Figure 2 .

[0028] In some embodiments of this application, the mass ratio of the total mass of the carbon-based anode active material and the fluorine-doped amorphous carbon to the film-forming aid is 100:0.1-1, for example, 100:0.1, 100:0.2, 100:0.3, 100:0.4, 100:0.5, 100:0.6, 100:0.7, 100:0.8, 100:0.9, or 100:1; in other embodiments of this application, the mass ratio of the carbon-based anode active material and the fluorine-doped amorphous carbon is 100:0.1-0.5, for example, 100:0.1, 100:0. 2, 100:0.3, 100:0.4, or 100:0.5; In some other embodiments of this application, the fluorine-doped amorphous carbon is uniformly coated on the surface of the carbon-based negative electrode active material (core) to form a fluorine-doped amorphous carbon coating layer (intermediate layer) with a thickness of 10-100 nm, such as 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, or 100 nm; the film-forming aid is uniformly coated on the surface of the fluorine-doped amorphous carbon coating layer to form an SEI film-forming aid loading layer (outer layer).

[0029] In some embodiments of this application, the carbon-based negative electrode active material includes one or more of natural graphite, artificial graphite, hard carbon, soft carbon, and mesophase carbon microspheres.

[0030] In some embodiments of this application, the fluorine-doped amorphous carbon is formed by chemical vapor deposition and / or high-temperature carbonization of a carbon source and a fluorine source; in other embodiments of this application, the carbon source is a gaseous carbon source, and a fluorine-doped amorphous carbon layer is coated on the surface of the carbon-based negative electrode active material by gas phase coating and high-temperature carbonization, which has good coating effect, high uniformity, and precise adjustable coating amount. The high-temperature carbonization is carried out at 700-1150℃ for 3-6 hours, and the heating rate can be selected as 1-10℃ / min; in other embodiments of this application, the gaseous carbon source includes one or more of C1-C4 alkanes, C2-C4 alkenes, and C2-C4 alkynes, such as methane, ethane, ethylene, acetylene, etc.

[0031] In some embodiments of this application, the fluorine source is a gaseous fluorine source; in other embodiments of this application, the gaseous fluorine source includes one or more of carbon tetrafluoride, trifluoromethane, difluoromethane, octafluorocyclobutane, perfluorobutadiene, and octafluorocyclopentene.

[0032] In some embodiments of this application, when the carbon source and fluorine source are gases, the volume ratio of the carbon source gas to the fluorine source gas is 100:1-30, for example, 100:1, 100:5, 100:10, 100:15, 100:20, 100:25 or 100:30; the flow rate is 100-400 ml / min, for example, 100 ml / min, 150 ml / min, 200 ml / min, 250 ml / min, 300 ml / min, 350 ml / min or 400 ml / min; in other embodiments of this application, the carbon source is methane and the fluorine source is carbon tetrafluoride.

[0033] In some embodiments of this application, the film-forming aid includes one or more of vinylene carbonate (VC), fluoroethylene carbonate (FEC), vinyl ethylene carbonate (VEC), allyl ethyl carbonate (AEC), vinyl acetate (VA), and catechol carbonate (CC).

[0034] In a second aspect of this application, a method for preparing the negative electrode material is provided, comprising:

[0035] The carbon-based anode active material is vapor-phase coated and / or high-temperature carbonized in a carbon source and fluorine source environment to form a fluorine-doped amorphous carbon coating layer, thereby obtaining a fluorine-doped amorphous carbon-coated carbon-based anode intermediate.

[0036] Fluorine-doped amorphous carbon-coated carbon-based anode intermediate is added to a film-forming aid solution, dispersed evenly, and spray-dried to obtain the anode material.

[0037] In some embodiments of this application, both the carbon source and the fluorine source are in a gaseous state. The carbon source is selected from one or more of C1-C4 alkanes, C2-C4 alkenes, and C2-C4 alkynes, such as methane, ethane, ethylene, and acetylene. The fluorine source is selected from one or more of carbon tetrafluoride, trifluoromethane, difluoromethane, octafluorocyclobutane, perfluorobutadiene, and octafluorocyclopentene. The volume ratio of the two is 100:1-30.

[0038] In some embodiments of this application, the film-forming aid is dispersed in an organic solvent to form a film-forming aid solution, wherein the organic solvent includes one or more of toluene, pentane, hexane, ethanol, diethyl ether, and acetone; in other embodiments of this application, the mass percentage concentration of the film-forming aid solution is 0.1-0.5%, specifically selected from 0.1%, 0.2%, 0.3%, 0.4%, or 0.5%.

[0039] In some embodiments of this application, the method for preparing the negative electrode material includes:

[0040] The carbon-based anode active material is placed in a tube furnace, and an inert gas is introduced to remove the air. Then, a mixture of carbon source gas and fluorine source gas is introduced and heated to 700-1150℃ at a certain heating rate. The temperature is held for 3-6 hours and then cooled to obtain a fluorine-doped amorphous carbon-coated carbon-based anode intermediate.

[0041] The SEI film-forming aid was uniformly dispersed in an organic solvent to prepare a solution. Then, fluorine-doped amorphous carbon-coated carbon-based anode intermediate was added and uniformly dispersed, and then dispersed in a ball mill to obtain a precursor.

[0042] The precursor is spray-dried to obtain the negative electrode material of this application.

[0043] In a third aspect of this application, a negative electrode sheet is provided, using the negative electrode material described in this application as the active material.

[0044] 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 or aluminum foil; the active material includes the 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 styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC), the conductive agent may be conductive carbon black (SP), and the solvent may be deionized water. The ratio of negative electrode material:SP:CMC:SBR may be selected as 94.5:2.5:1.5:1.5.

[0045] 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.

[0046] 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; the electrolyte is a LiPF6 solution, for example, an electrolyte with a volume ratio of 1:1 of ethylene carbonate (EC) and diethyl carbonate (DEC) as solvents and a LiPF6 concentration of 1.0-1.5 mol / L; or an electrolyte with a volume ratio of 1:1:1 of ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) as solvents and a LiPF6 concentration of 1.0-1.5 mol / L.

[0047] 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.

[0048] The following provides a further description of a long-cycle lithium battery anode material, its preparation method, the anode sheet, and the lithium battery provided in this application.

[0049] Example 1:

[0050] (1) Place 100g of artificial graphite in a tube furnace, introduce inert argon gas to remove air from the tube, then switch to a mixture of carbon source gas and fluorine source gas (methane: carbon tetrafluoride = 100:10, flow rate 400ml / min), heat to 950℃ at a heating rate of 5℃ / min, hold for 4 hours, and after natural cooling, obtain an artificial graphite intermediate coated with fluorine-doped amorphous carbon with a mass ratio of 100:0.5.

[0051] (2) Dissolve 0.1g of SEI film-forming aid VC (ethylene carbonate) in organic solvent ethanol and disperse it evenly to prepare a solution with a VC concentration of 0.1wt%. Then add 100g of fluorine-doped amorphous carbon-coated artificial graphite intermediate (the mass ratio of fluorine-doped amorphous carbon-coated artificial graphite intermediate to VC aid is 100:0.1) and disperse it evenly. Then ball mill it at 200r / min for 12h to obtain the precursor dispersion.

[0052] (3) The precursor dispersion is spray-dried to obtain the long-cycle lithium-ion battery anode material.

[0053] Example 2:

[0054] (1) Place 100g of artificial graphite in a tube furnace, introduce inert argon gas to remove air from the tube, then switch to a mixture of carbon source gas and fluorine source gas (methane: carbon tetrafluoride = 100:10, flow rate 100ml / min), heat to 950℃ at a heating rate of 5℃ / min, hold for 4 hours, and after natural cooling, obtain an artificial graphite intermediate coated with fluorine-doped amorphous carbon with a mass ratio of 100:0.1.

[0055] (2) Dissolve 0.5g of SEI film-forming aid VC (ethylene carbonate) in organic solvent ethanol and disperse it evenly to prepare a solution with a VC concentration of 0.5wt%. Then add 100g of fluorine-doped amorphous carbon-coated artificial graphite intermediate (the mass ratio of fluorine-doped amorphous carbon-coated artificial graphite intermediate to VC aid is 100:0.5) and disperse it evenly. Then ball mill it at 200r / min for 12h to obtain the precursor dispersion.

[0056] (3) The precursor dispersion is spray-dried to obtain the long-cycle lithium-ion battery anode material.

[0057] Example 3:

[0058] (1) Place 100g of natural graphite in a tube furnace, introduce inert argon gas to remove air from the tube, then switch to a mixture of carbon source gas and fluorine source gas (ethylene: trifluoromethane = 100:5, flow rate 150ml / min), heat to 750℃ at a heating rate of 2℃ / min, hold for 6 hours, and after natural cooling, obtain a natural graphite: fluorine-doped amorphous carbon coated natural graphite intermediate with a mass ratio of 100:0.2.

[0059] (2) Dissolve 1.0g of SEI film-forming aid FEC (fluoroethylene carbonate) in the organic solvent toluene and disperse it evenly to prepare a solution with an FEC concentration of 1.0wt%. Then add 100g of fluorine-doped amorphous carbon-coated natural graphite intermediate (the mass ratio of fluorine-doped amorphous carbon-coated natural graphite intermediate to FEC aid is 100:1.0) and disperse it evenly. Then ball mill it in a ball mill at 200r / min for 12h to obtain a precursor dispersion.

[0060] (3) The precursor dispersion is spray-dried to obtain the long-cycle lithium-ion battery anode material.

[0061] Example 4:

[0062] (1) Place 100g of hard carbon in a tube furnace, introduce inert argon gas to remove air from the tube, then switch to a mixture of carbon source gas and fluorine source gas (ethane: octafluorocyclobutane = 100: 20, flow rate 200ml / min), heat to 1150℃ at a heating rate of 8℃ / min, hold for 3 hours, and after natural cooling, obtain a hard carbon intermediate coated with fluorine-doped amorphous carbon with a mass ratio of hard carbon: fluorine-doped amorphous carbon of 100: 0.3;

[0063] (2) Dissolve 0.3g of SEI film-forming aid VEC (vinyl ethylene carbonate) in organic solvent diethyl ether and disperse it evenly to prepare a solution with a VEC concentration of 0.3wt%. Then add 100g of fluorine-doped amorphous carbon-coated hard carbon intermediate (the mass ratio of fluorine-doped amorphous carbon-coated hard carbon intermediate to VEC aid is 100:0.3) and disperse it evenly. Then ball mill it at 200r / min for 12h to obtain the precursor dispersion.

[0064] (3) The precursor dispersion is spray-dried to obtain the long-cycle lithium-ion battery anode material.

[0065] Example 5:

[0066] (1) Place 100g of mesophase carbon microspheres in a tube furnace, introduce inert argon gas to remove air from the tube, and then switch to a mixture of carbon source gas and fluorine source gas (acetylene: octafluorocyclopentene = 100:30, flow rate 300ml / min), heat to 800℃ at a heating rate of 10℃ / min, hold for 5 hours, and after natural cooling, obtain mesophase carbon microspheres: fluorine-doped amorphous carbon with a mass ratio of 100:0.4, mesophase carbon microspheres coated with fluorine-doped amorphous carbon intermediate;

[0067] (2) Dissolve 0.8g of SEI film-forming aid VA (vinyl acetate) in the organic solvent acetone and disperse it evenly to prepare a solution with a VA concentration of 0.8wt%. Then add 100g of fluorine-doped amorphous carbon-coated mesophase carbon microsphere intermediate (the mass ratio of fluorine-doped amorphous carbon-coated mesophase carbon microsphere intermediate to VA aid is 100:0.8) and disperse it evenly. Then ball mill it in a ball mill at 200r / min for 12h to obtain the precursor dispersion.

[0068] (3) The precursor dispersion is spray-dried to obtain the long-cycle lithium-ion battery anode material.

[0069] Comparative Example 1:

[0070] (1) Place 100g of artificial graphite in a tube furnace, introduce inert argon gas to remove air from the tube, then switch to a mixture of carbon source gas and fluorine source gas (methane: carbon tetrafluoride = 100:10, flow rate 150ml / min), heat to 950℃ at a heating rate of 5℃ / min, hold for 4 hours, and after natural cooling, obtain an artificial graphite intermediate coated with fluorine-doped amorphous carbon with a mass ratio of 100:0.1.

[0071] (2) Dissolve 1.5g of SEI film-forming aid VC (ethylene carbonate) in organic solvent ethanol and disperse it evenly to prepare a solution with a VC concentration of 1.5wt%. Then add 100g of fluorine-doped amorphous carbon-coated artificial graphite intermediate (the mass ratio of fluorine-doped amorphous carbon-coated artificial graphite intermediate to VC aid is 100:1.5) and disperse it evenly. Then ball mill it at 200r / min for 12h to obtain the precursor dispersion.

[0072] (3) The precursor dispersion is spray-dried to obtain the long-cycle lithium-ion battery anode material.

[0073] Comparative Example 2:

[0074] (1) Place 100g of artificial graphite in a tube furnace, introduce inert argon gas to remove air from the tube, then switch to a mixture of carbon source gas and fluorine source gas (methane: carbon tetrafluoride = 100:10, flow rate 150ml / min), heat to 950℃ at a heating rate of 5℃ / min, hold for 4 hours, and after natural cooling, obtain an artificial graphite intermediate coated with fluorine-doped amorphous carbon with a mass ratio of 100:0.1.

[0075] (2) 100g of fluorine-doped amorphous carbon-coated artificial graphite intermediate was dispersed in organic solvent ethanol and ball-milled at 200r / min for 12h to obtain precursor dispersion.

[0076] (3) The precursor dispersion is spray-dried to obtain the lithium-ion battery anode material.

[0077] Comparative Example 3:

[0078] (1) Place 100g of artificial graphite in a tube furnace, introduce inert gas argon to remove air from the tube, then switch to carbon source gas (methane, flow rate 150ml / min), heat to 950℃ at a heating rate of 5℃ / min, hold for 4 hours, and after natural cooling, obtain an amorphous carbon-coated artificial graphite intermediate with a mass ratio of artificial graphite to amorphous carbon of 100:0.1.

[0079] (2) Dissolve 0.5g of SEI film-forming aid VC (ethylene carbonate) in organic solvent ethanol and disperse it evenly to prepare a solution with a VC concentration of 0.5wt%. Then add 100g of amorphous carbon-coated artificial graphite intermediate (the mass ratio of amorphous carbon-coated artificial graphite intermediate to VC aid is 100:0.5) and disperse it evenly. Then ball mill it at 200r / min for 12h to obtain the precursor dispersion.

[0080] (3) The precursor dispersion is spray-dried to obtain the long-cycle lithium-ion battery anode material.

[0081] Comparative Example 4:

[0082] (1) 100g of artificial graphite and 0.5g of medium-temperature asphalt and polytetrafluoroethylene mixture (solid carbon source and fluorine source, wherein the mass ratio of medium-temperature asphalt to polytetrafluoroethylene is 100:10) were stirred evenly and placed in a tube furnace. Inert gas argon was introduced to remove the air in the tube, and the temperature was raised to 950℃ at a heating rate of 5℃ / min under argon protection. The temperature was held for 4 hours and then naturally cooled to obtain an artificial graphite intermediate with a mass ratio of artificial graphite to fluorine-doped amorphous carbon of 100:0.5.

[0083] (2) Dissolve 0.1g of SEI film-forming aid VC (ethylene carbonate) in organic solvent ethanol and disperse it evenly to prepare a solution with a VC concentration of 0.1wt%. Then add 100g of fluorine-doped amorphous carbon-coated artificial graphite intermediate (the mass ratio of fluorine-doped amorphous carbon-coated artificial graphite intermediate to VC aid is 100:0.1) and disperse it evenly. Then ball mill it at 200r / min for 12h to obtain the precursor dispersion.

[0084] (3) The precursor dispersion is spray-dried to obtain the long-cycle lithium-ion battery anode material.

[0085] Experimental Example 1:

[0086] 1. Initial discharge capacity and initial coulombic efficiency test

[0087] The negative electrode materials prepared in the examples and comparative examples were assembled into coin cells.

[0088] A binder, conductive agent, and solvent are added to the negative electrode material and stirred evenly to obtain a slurry. The slurry is coated onto copper foil, dried, and rolled to obtain a negative electrode sheet. The negative electrode sheet, along with a lithium metal sheet, a separator, and an electrolyte, are assembled into a coin cell in an argon-glove box. The fabricated coin cell is then tested at 0.1C charge and discharge on a Blue Electric CT3002A battery testing device, with a test voltage range of 0.005V-2.0V, to measure capacity and initial efficiency. The binder is SBR (45% solids content) and CMC, the conductive agent is SP, and the solvent is deionized water. The ratio of active material:SP:CMC:SBR is 94.5:2.5:1.5:1.5. The separator is a PP separator, and the electrolyte is 1M LiPF6 / (EC+DEC+DMC)=1:1:1.

[0089] 2. Cyclic performance test

[0090] The materials prepared in the examples and comparative examples were used as negative electrodes, lithium iron phosphate as positive electrodes, and 1M LiPF6 / (EC+DMC=1:1) as electrolyte to assemble full cells, and the cycle capacity retention rate under 1C charge and discharge conditions was tested.

[0091] 3. Test Results

[0092] Table 1

[0093]

[0094] As shown in Table 1, the coin cell composed of the embodiments has a better discharge capacity and initial coulombic efficiency than the coin cells composed of the comparative embodiments. In terms of the long-cycle performance of the full cell, the full cell composed of the negative electrode material of this application has a significantly higher capacity retention rate than the cells of the comparative embodiments, whether at 1000 cycles or 2000 cycles.

[0095] 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 long-cycle lithium battery anode material, characterized in that, The device comprises a core, an intermediate layer covering the core, and an outer layer covering the intermediate layer; the core comprises a carbon-based anode active material, the intermediate layer comprises fluorine-doped amorphous carbon, and the outer layer comprises a film-forming aid; the mass ratio of the total mass of the carbon-based anode active material and the fluorine-doped amorphous carbon to the mass of the film-forming aid is 100:0.1-1; the film-forming aid comprises one or more of vinylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, allyl ethyl carbonate, vinyl acetate, and catechol carbonate.

2. The negative electrode material according to claim 1, characterized in that, The carbon-based negative electrode active material includes one or more of the following: natural graphite, artificial graphite, hard carbon, soft carbon, and mesophase carbon microspheres.

3. The negative electrode material according to claim 1, characterized in that, The fluorine-doped amorphous carbon is formed by gas-phase coating and / or high-temperature carbonization of a carbon source and a fluorine source.

4. The negative electrode material according to claim 3, characterized in that, The carbon source is a gaseous carbon source, which includes one or more of C1-C4 alkanes, C2-C4 alkenes, and C2-C4 alkynes.

5. The negative electrode material according to claim 3, characterized in that, The fluorine source is a gaseous fluorine source, which includes one or more of the following: carbon tetrafluoride, trifluoromethane, difluoromethane, octafluorocyclobutane, perfluorobutadiene, and octafluorocyclopentene.

6. The method for preparing the negative electrode material according to claim 1, characterized in that, include: The carbon-based anode active material is subjected to gas-phase coating and / or high-temperature treatment in a carbon source and fluorine source environment to form a fluorine-doped amorphous carbon coating layer, thereby obtaining a fluorine-doped amorphous carbon-coated carbon-based anode intermediate. Fluorine-doped amorphous carbon-coated carbon-based anode intermediate is added to a film-forming aid solution, dispersed evenly, and spray-dried to obtain the anode material.

7. A negative electrode sheet, characterized in that, The negative electrode material according to any one of claims 1-5 is used as the active material.

8. A lithium battery, characterized in that, It includes a positive electrode, a separator, an electrolyte, and the negative electrode as described in claim 7.

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