Negative electrode material, preparation method thereof, negative electrode sheet, and battery

Abstract

The application discloses a negative electrode material and a preparation method thereof, a negative electrode sheet and a battery. The negative electrode material comprises a graphite base and a cucurbituril coating layer. The cucurbituril coating layer coats the graphite base. The cucurbituril coating layer has ion channels for active ion migration. In the negative electrode material, the cucurbituril coating layer forms a nanometer-scale protective layer on the surface of the graphite base, which can reduce the direct contact between the graphite base and electrolyte, thereby inhibiting the occurrence of side reactions. The cucurbituril coating layer has a molecular cage form and multiple ion channel structures, which can serve as channels for lithium ion migration and prevent other ions or solvent molecules from entering, thereby improving the diffusion efficiency of active ions such as lithium ions on the negative electrode surface and reducing the internal resistance of the battery. After the cucurbituril coating layer is combined with the graphite base, the generation of by-products such as lithium fluoride in the electrolyte can be reduced, which helps to slow down the excessive growth of the SEI film, thereby improving the cycle stability and energy efficiency of the battery.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a negative electrode material and its preparation method, a negative electrode sheet, and a battery. Background Technology

[0002] Currently, graphite is the widely used negative electrode material in lithium-ion batteries. The theoretical specific capacity of graphite is 372 mAh / g. However, after long-term use, due to structural damage and the presence of side reactions, the layered structure of graphite may undergo irreversible expansion or contraction, further reducing the reversible capacity. At the same time, the electrolyte continuously decomposes on the surface of the negative electrode, forming a solid electrolyte interphase (SEI) film, which increases the internal resistance of the battery and affects the cycle life. Summary of the Invention

[0003] The purpose of this application is to provide a negative electrode material and its preparation method, a negative electrode sheet and a battery, to solve the problem of capacity and cycle life decline after long-term use of graphite negative electrode materials.

[0004] To achieve the objectives of this application, the following technical solution is provided: In a first aspect, the present invention provides a negative electrode material comprising a graphite matrix and a cucurbita coating layer, wherein the cucurbita coating layer coats the graphite matrix and has ion channels for the migration of active ions in the battery.

[0005] In one embodiment, the aperture of the ion channel is 0.5 nm-1 nm; and / or, the porosity of the cucurbituril coating layer is 25%-30%.

[0006] In one embodiment, the mass ratio of the cucurbita coating layer to the graphite matrix is ​​(0.5-1.5):100.

[0007] In one embodiment, the thickness of the cucurbita coating layer is 5nm-10nm; and / or, the particle size of the graphite matrix is ​​10μm-18μm.

[0008] Secondly, the present invention provides a method for preparing a negative electrode material, used to prepare the negative electrode material as described in any of the various embodiments of the first aspect, comprising the following steps: Provides graphite matrix and cucurbituril monomer; The graphite matrix is ​​dispersed in a first solvent to form a first suspension; The cucurbituril monomer was added to the first suspension, reacted, and filtered to obtain the negative electrode material.

[0009] In one embodiment, the reaction temperature for adding the cucurbituril monomer to the first suspension is 60°C-70°C; and / or The reaction time for adding the cucurbituril monomer to the first suspension is 6-8 hours; and / or The pH after adding the cucurbituril monomer to the first suspension is 7-8.

[0010] In one embodiment, a graphite matrix is ​​provided, comprising: The pretreated graphite was placed in a second solvent and heated under reflux. The second solvent is a mixed solution of concentrated sulfuric acid and potassium permanganate, wherein the mass ratio of the concentrated sulfuric acid to the potassium permanganate is (0.2-0.8):1.

[0011] In one embodiment, a cucurbituril monomer is provided, comprising: The urea solution was dissolved and dispersed in concentrated sulfuric acid to obtain the first pre-solution; Paraformaldehyde was added to the first presol to obtain the first gel; The first gel was heated and refluxed using a condenser to obtain a fluidized second presol; The second presol was evaporated under reduced pressure and mixed with acetone to obtain the third presol; The third presol was filtered under reduced pressure and then washed and dried to obtain the cucurbituril monomer.

[0012] In one embodiment, the reaction temperature using a condenser reflux is 95°C-105°C; and / or The reaction time using reflux with a condenser is 9-11 hours; and / or The mass ratio of the glycosuria to the paraformaldehyde is (1.8-2.5):1.

[0013] Thirdly, the present invention provides a negative electrode sheet, the negative electrode sheet comprising the negative electrode material described in any one of the various embodiments of the first aspect or the negative electrode material prepared by the method for preparing the negative electrode material according to any one of the various embodiments of the second aspect.

[0014] Fourthly, the present invention provides a battery comprising a positive electrode and a negative electrode as described in any of the various embodiments of the third aspect.

[0015] The negative electrode material of this invention has a cucurbituril coating layer outside the graphite matrix. Cucurbituril is an oligomeric amide compound with a macrocyclic cage structure, possessing unique molecular recognition capabilities and chemical stability. It can encapsulate the graphite matrix, forming a nanoscale protective layer that reduces direct contact between the graphite matrix and the electrolyte, thereby suppressing side reactions. Furthermore, the cucurbituril coating layer, being a molecular cage morphology, has multiple ion channel structures, serving as channels for the migration of active ions such as lithium ions, while preventing the entry of other ions or solvent molecules. This improves the diffusion efficiency of active ions such as lithium ions on the negative electrode surface and reduces the battery's internal resistance. After the cucurbituril coating layer is combined with the graphite matrix, it can reduce the formation of byproducts such as lithium fluoride (LiF) in the electrolyte, helping to slow down the excessive growth of the solid electrolyte interphase (SEI) film, thereby improving the battery's cycle stability and energy efficiency. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0017] Figure 1 This is a cross-sectional view of a negative electrode material according to one embodiment; Figure 2 This is a partially enlarged view of the negative electrode material in one embodiment; Figure 3 This is a flowchart of a method for preparing a negative electrode material according to one embodiment; Figure 4 This is a flowchart of one step in a method for preparing a negative electrode material according to one embodiment.

[0018] Explanation of reference numerals in the attached figures: 100 - Negative electrode material, 10 - Graphite matrix, 20 - Cucurbitaurea coating layer, 21 - Ion channel. Detailed Implementation

[0019] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0020] It should be noted that when a component is said to be "fixed" to another component, it can be directly on the other component or it can be in a middle component. When a component is said to be "connected" to another component, it can be directly connected to the other component or it may be in a middle component.

[0021] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. The terminology used in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used in this application includes any and all combinations of one or more of the associated listed items.

[0022] The following detailed description of some embodiments of this application is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0023] Please refer to Figure 1 and Figure 2 The present invention provides a negative electrode material 100, comprising a graphite substrate 10 and a cucurbituril coating layer 20, wherein the cucurbituril coating layer 20 coats the graphite substrate 10 and has ion channels 21 for the migration of active ions.

[0024] Optionally, the cucurbituril molecules (CB[n]) in the cucurbituril coating layer 20 are composed of multiple glycoure units forming a closed ring structure through methylene bridges. The number of glycoure units can be 6-13, specifically CB[6], CB[8], CB

[10] , CB

[13] , etc. The cucurbituril molecules have a highly symmetrical barrel configuration.

[0025] Furthermore, the cucurbita coating layer 20 has a rigid cage-like structure, which can withstand the approximately 10% volume expansion of the graphite matrix 10 during negative electrode charging and discharging, thus preventing the cucurbita coating layer 20 from cracking and falling off. If it is a flexible oligomeric macrocyclic ring (such as some flexible crown ether derivatives), the coating layer will undergo structural deformation as the graphite matrix 10 expands, and the ion channel 21 will collapse and fail.

[0026] The negative electrode material 100 of the present invention has a cucurbituril coating layer 20 disposed outside a graphite substrate 10. Cucurbituril is an oligomeric amide compound with a macrocyclic cage structure, which has unique molecular recognition ability and chemical stability. It can encapsulate the graphite substrate 10 to form a nanoscale protective layer, which can reduce the direct contact between the graphite substrate 10 and the electrolyte, thereby suppressing the occurrence of side reactions. Moreover, the cucurbituril coating layer 20 is in the form of a molecular cage and has multiple ion channel structures 21, which can serve as channels for the migration of active ions such as lithium ions, while preventing other ions or solvent molecules from entering, thereby improving the diffusion efficiency of active ions such as lithium ions on the negative electrode surface and reducing the internal resistance of the battery. After the cucurbituril coating layer 20 is combined with the graphite substrate 10, it can reduce the generation of by-products such as lithium fluoride (LiF) in the electrolyte, which helps to slow down the excessive growth of the solid electrolyte interphase (SEI) film, thereby improving the cycle stability and energy efficiency of the battery.

[0027] In one embodiment, the aperture of ion channel 21 is 0.5 nm-1 nm. The aperture of ion channel 21 is the diameter at its port. The cucurbitacin coating layer 20 has strongly polar groups such as hydroxyl and amino groups distributed at the port of ion channel 21, which preferentially adsorb lithium ions through ion-dipole interactions, reducing transport resistance, while simultaneously repelling anions. The carbonyl group at the port of cucurbitacin is the core functional group, while the oligomeric macrocycle without polar ports would result in a significant decrease in ion selectivity. Optionally, the diameter of ion channel 21 can be 0.4 nm-0.6 nm, specifically 0.4 nm, 0.45 nm, 0.48 nm, 0.5 nm, 0.55 nm, 0.58 nm, 0.6 nm, etc., without limitation.

[0028] Optionally, the aperture of ion channel 21 can be 0.5 nm, 0.6 nm, 0.7 nm, 0.8 nm, 0.9 nm, 1 nm, etc., without limitation. In the electrolyte, lithium ions combine with solvent molecules (such as EC, DMC, EMC, etc.) through electrostatic interactions to form a solvated sheath layer. The size of this sheath layer is the diameter of the solvated lithium ions, which is approximately 0.2 nm to 0.4 nm. If the aperture of ion channel 21 is too small, active ions such as solvated lithium ions may not be able to migrate through ion channel 21; if the aperture of ion channel 21 is too large, it may block other solvent molecules and transition metal ions, affecting the migration of active ions. Controlling the aperture of ion channel 21 ensures that ion channel 21 allows only active ions to pass through smoothly.

[0029] And / or, the porosity of the cucurbitacin coating layer 20 is 25%-30%. Optionally, the cucurbitacin coating layer 20 is only a protective film on the surface of the graphite substrate 10, without dense stacking. The porosity of the cucurbitacin coating layer 20 can be 25%, 26%, 27%, 28%, 29%, 30%, etc., without limitation. Excessive porosity will reduce the density and strength of the cucurbitacin coating layer 20, making it prone to stress concentration and deformation during charging and discharging on the graphite substrate 10, thus shortening the battery's cycle life. Insufficient porosity will limit the wetting range of the electrolyte in the cucurbitacin coating layer 20 and the graphite substrate 10, causing some active materials to fail to fully contact the electrolyte, thereby reducing the battery's charge and discharge performance. A moderate porosity balances ion transport efficiency and structural stability.

[0030] In one embodiment, the mass ratio of the cucurbitacin coating layer 20 to the graphite substrate 10 is (0.5-1.5):100. Optionally, the mass ratio of the cucurbitacin coating layer 20 to the graphite substrate 10 can be 0.5:100, 0.6:100, 0.7:100, 0.8:100, 0.9:100, 1:100, 1.1:100, 1.2:100, 1.3:100, 1.4:100, 1.5:100, etc., and is not limited. When the mass proportion of the cucurbitacin coating layer 20 is too high, the cucurbitacin coating layer 20 will have multiple layers, which may lead to local aggregation and hinder the effective transport of lithium ions. If the mass ratio of the cucurbitacin coating layer 20 is too low, it may not be able to fully coat the graphite substrate 10. The cucurbitacin coating layer 20 will be distributed in an island-like pattern, resulting in discontinuous protection, exacerbating side reactions in the graphite substrate 10, and thickening the SEI film. By limiting the mass ratio of the cucurbitacin coating layer 20 to the graphite substrate 10, the cucurbitacin coating layer 20 can adequately protect the graphite substrate 10 without affecting lithium-ion transport.

[0031] In one embodiment, the thickness of the cucurbita coating layer 20 is 5nm-10nm. Optionally, the thickness of the cucurbita coating layer 20 can be 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, etc., without limitation. If the cucurbita coating layer 20 is too thick, it will make it relatively difficult for lithium ions to be inserted and extracted from the graphite substrate 10, reducing the charge and discharge efficiency of the battery. If the cucurbita coating layer 20 is too thin, it cannot effectively prevent side reactions between the graphite substrate 10 and the electrolyte, conductive agent, etc. Limiting the thickness of the cucurbita coating layer 20 neither affects the lithium ion insertion and extraction from the graphite substrate 10 nor reduces side reactions in the graphite substrate 10.

[0032] And / or, the particle size of the graphite matrix 10 is 10μm-18μm. Optionally, the particle size of the graphite matrix 10 can be 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, etc., without limitation. If the particle size of the graphite matrix 10 is too large, it will prolong the lithium-ion insertion / extraction path, leading to increased diffusion resistance and accelerating battery capacity decay. If the particle size of the graphite matrix 10 is too small, it is prone to agglomeration, forming large particles or pores, resulting in uneven electrode conductivity, excessively high local current density, and accelerated capacity decay. Limiting the particle size of the graphite matrix 10 reduces the impact of the negative electrode material 100 on battery capacity decay during battery use.

[0033] Please refer to Figure 3 This invention provides a method for preparing a negative electrode material, used to prepare the negative electrode material as described in any of the foregoing embodiments, comprising the following steps: Step S10: Provide a graphite matrix and a cucurbituril monomer.

[0034] Step S20: The graphite matrix is ​​dispersed in a first solvent to form a first suspension.

[0035] Step S30: Add cucurbituril monomer to the first suspension, react and filter to obtain the negative electrode material.

[0036] Optionally, in step S20, the first solvent is ethanol, and the dispersion operation is carried out by stirring at room temperature, with the temperature being 25℃-30℃. The mass ratio of the graphite matrix to the first solvent is (0.4-0.6):1, specifically 0.4:1, 0.45:1, 0.5:1, 0.55:1, 0.6:1, etc., without limitation.

[0037] In step S30, the cucurbituril monomer undergoes self-assembly or chemical bonding with the graphite matrix. Step S30 also includes filtration followed by drying, with the drying temperature being 50℃-60℃.

[0038] In one embodiment, the reaction temperature for adding cucurbituril monomer to the first suspension is 60℃-70℃. Specifically, it can be 60℃, 61℃, 62℃, 63℃, 64℃, 65℃, 66℃, 67℃, 68℃, 69℃, 70℃, etc., without limitation. Controlling the reaction temperature provides the reaction kinetics, promotes the uniform spreading and crystallization of cucurbituril monomer on the graphite matrix surface, results in a moderate assembly rate, and leads to a well-oriented and strongly adhered cucurbituril coating layer. If the reaction temperature is too low, aggregation is likely to occur, resulting in uneven thickness of the cucurbituril coating layer and morphological defects. If the reaction temperature is too high, the molecular thermal motion intensifies, making the cucurbituril coating layer prone to detachment and disrupting the host-guest interaction.

[0039] And / or, the reaction time for adding cucurbituril monomer to the first suspension is 6-8 hours. Specifically, it can be 6 hours, 6.5 hours, 7 hours, 7.5 hours, 8 hours, etc., without limitation. An excessively long reaction time will prevent the formation of a uniform and complete cucurbituril coating layer and prolong the experimental cycle. Controlling the reaction time improves the production efficiency of the negative electrode material.

[0040] And / or, the pH after adding cucurbituril monomer to the first suspension is 7-8. The specific pH can be 7, 7.1, 7.2, 7.3, 7.4, 7.5, 7.6, 7.7, 7.8, 7.9, 8, etc., without limitation. Controlling the pH of the reaction can change the carbonyl protonation state at the CB[n] port and the surface charge of the graphite matrix, thereby affecting the assembly strength, film uniformity, and ion transport. Too low a pH will result in an overly dense cucurbituril coating layer, affecting the port diameter of the cucurbituril coating layer. Too high a pH will cause the formed cucurbituril coating layer to easily detach. Controlling the pH to neutral conditions results in protonation at the CB[n] port, strong π–π interactions with the graphite matrix, and a uniform thickness and high porosity of the formed cucurbituril coating layer.

[0041] In one embodiment, step S10 provides a graphite matrix by placing pretreated graphite in a second solvent and performing a heating and reflux operation.

[0042] The second solvent is a mixed solution of concentrated sulfuric acid and potassium permanganate, with a mass ratio of (0.2-0.8):1. Specific mass ratios of concentrated sulfuric acid and potassium permanganate can be 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, etc., without limitation. Potassium permanganate is used to oxidize carbon atoms at the edges and defects of the pretreated graphite, forming oxygen-containing functional groups such as hydroxyl (-OH), carboxyl (-COOH), and epoxy groups. Concentrated sulfuric acid molecules insert into the interlayer of the pretreated graphite through the defect sites created by oxidation, forming graphite interlayer compounds. This intercalation process further weakens the van der Waals forces between graphite layers, providing conditions for subsequent exfoliation or expansion. Controlling the ratio of the two solvents ensures good oxidation and intercalation effects in the modified graphite matrix, prevents excessive damage to the graphite matrix structure, and guarantees the economic efficiency of the preparation process.

[0043] Optionally, washing with deionized water until neutral may also be included. This step is used to remove impurities from the pretreated graphite and introduce oxygen-containing groups, thereby improving the surface activity of the graphite matrix.

[0044] Please refer to Figure 4 In one embodiment, step S10 provides a cucurbituril monomer, comprising: Step S11: Dissolve and disperse urea in concentrated sulfuric acid to obtain the first pre-solution.

[0045] Step S12: Paraformaldehyde is added to the first presol to obtain the first gel.

[0046] Step S13: Heat the first gel and reflux using a condenser to obtain a fluidized second presol.

[0047] Step S14: The second presol is evaporated under reduced pressure and mixed with acetone to obtain the third presol.

[0048] Step S15: Filter the third presol under reduced pressure and perform washing and drying operations to obtain cucurbituril monomer.

[0049] Optionally, in step S11, the dispersion operation includes stirring at room temperature and placing the mixture in an ultrasonic disperser to ensure complete dissolution of the urea. In step S12, paraformaldehyde is added and stirred at room temperature until the first gel is a yellow gel.

[0050] Specifically, in step S13, the viscous oligomers transform into dissolved, regular cage-like monomers, forming a fluidized second pre-solution. The failure to form a fluidized system indicates insufficient reaction in step S12; the system remains a viscous suspension / gel, primarily composed of uncyclized oligomers, amorphous polymers, and a small amount of irregular CB[n] microcrystals. It cannot form a definite structure or regular channels, the size sieving effect fails, and both anions and solvent molecules can penetrate the protective layer, initiating side reactions on the graphite matrix surface. Simultaneously, agglomerated particles block ion transport pathways, exacerbating concentration polarization. The fluidized second pre-solution is generally a brownish-yellow oily solution.

[0051] Optionally, in step S14, the second pre-solution is evaporated under reduced pressure to 35 mL-45 mL, and the volume of the acetone solution is 200 mL-250 mL. During the mixing process, the acetone needs to be stirred at high speed to avoid precipitation in the second pre-solution, which would affect the dispersion of the final product.

[0052] Optionally, the washing and drying operation in step S15 is as follows: wash 3-4 times with acetone solution and vacuum dry to obtain cucurbita urea monomer in the form of a light yellow powder.

[0053] In one embodiment, the reaction temperature using a reflux condenser is 95℃-105℃. Specifically, it can be 95℃, 96℃, 97℃, 98℃, 99℃, 100℃, 101℃, 102℃, 103℃, 104℃, 105℃, etc., without limitation. If the reaction temperature is too low, the final product cucurbita monomer will be mainly oligomers with low crystallinity and disordered ion channels 21. If the reaction temperature is too high, it will destroy the cage structure of the cucurbita monomer, resulting in the failure of the sieving effect. Controlling the reaction temperature ensures that the main product of the synthesized cucurbita monomer is CB[6], in which the port of CB[6] has a large number of carbonyl groups, which is beneficial for its bonding with the graphite matrix.

[0054] And / or, the reaction time using a reflux condenser is 9-11 hours. Specifically, it can be 9 hours, 9.5 hours, 10 hours, 10.5 hours, 11 hours, etc., without limitation. An excessively long reaction time will prevent the formation of a uniform and complete cucurbita coating layer and prolong the experimental cycle. Controlling the reaction time improves the production efficiency of the negative electrode material.

[0055] And / or, the mass ratio of glycosuria to paraformaldehyde is (1.8-2.5):1. Specifically, the mass of glycosuria is 45g-50g, the mass of paraformaldehyde is 20g-25g, and the volume of concentrated sulfuric acid is 150ml-160ml. The mass ratio of glycosuria to paraformaldehyde can be 1.8:1, 1.9:1, 2:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, etc., without limitation. Too little paraformaldehyde may lead to incomplete reaction, and the glycosuria molecules may not be able to fully condense to form the cage-like structure of cucurbitaurea. Too much paraformaldehyde may cause side reactions such as formaldehyde self-polymerization or excessive oxidation in the actual process. Controlling the ratio of the two can generate stable cucurbitaurea molecular cages, and the product has good purity.

[0056] The present invention provides a negative electrode sheet, wherein the negative electrode sheet comprises the negative electrode material described in any of the foregoing embodiments or the negative electrode material prepared by the preparation method of the negative electrode material described in any of the foregoing embodiments.

[0057] Optionally, the negative electrode sheet may also include a conductive agent, a binder, and a negative electrode current collector. This invention does not specifically limit the materials such as the conductive agent and binder; suitable materials can be selected according to actual application requirements. The negative electrode material, conductive agent, and binder are uniformly mixed and dispersed in NMP (N-methylpyrrolidone), coated onto the negative electrode current collector, and baked to obtain the negative electrode sheet.

[0058] The conductive agent includes one or more of graphite, carbon black, acetylene black, graphene, carbon fiber, C60 (carbon 60), and carbon nanotubes; the binder includes one or more of polyvinylidene chloride, soluble polytetrafluoroethylene, styrene-butadiene rubber, hydroxypropyl methylcellulose, methylcellulose, carboxymethyl cellulose, polyvinyl alcohol, acrylonitrile copolymer, sodium alginate, chitosan, and chitosan derivatives, without limitation. This application does not specifically limit these materials, and appropriate materials can be selected according to actual application requirements. The negative electrode current collector includes, but is not limited to, any one of copper foil, composite copper foil, or carbon-coated copper foil.

[0059] The present invention provides a battery comprising a positive electrode and a negative electrode as described in any of the foregoing embodiments.

[0060] The battery can be a prismatic battery, a cylindrical battery, or other types such as a prismatic battery, without any restrictions.

[0061] Optionally, the battery also includes a separator, with several layers of separators separating the positive and negative electrode sheets. The separator can be any of the following: woven membrane, non-woven membrane (non-woven fabric), microporous membrane, composite membrane, rolled membrane, etc., without limitation. The positive electrode sheet includes a positive current collector and a positive active material layer. The positive current collector includes, but is not limited to, any of the following: aluminum foil, composite aluminum foil, or carbon-coated aluminum foil. The positive active material layer includes components such as positive electrode material, conductive agent, and binder. This invention does not specifically limit these materials; suitable materials can be selected according to actual application requirements. The negative electrode material can be a carbon-based compound, silicon-based compound, titanium-based compound, etc., without limitation.

[0062] The technical solution of this application will be described in detail below through specific embodiments.

[0063] Example 1 This embodiment provides a negative electrode material, comprising a graphite matrix and a cucurbita coating layer. The cucurbita coating layer coats the graphite matrix and has ion channels 21. The aperture of the ion channels 21 is 0.6 nm; the porosity of the cucurbita coating layer is 28%; the mass ratio of the cucurbita coating layer to the graphite matrix is ​​0.9:100; the thickness of the cucurbita coating layer is 6 nm; and the particle size of the graphite matrix is ​​15 μm. The chemical formula of the cucurbita molecule in the cucurbita coating layer is C36H36N24O12, and the structural formula of the cucurbita molecule is shown in Formula 1. Formula 1 The preparation method in this embodiment is as follows: A graphite matrix is ​​placed in a mixed solution of concentrated sulfuric acid and potassium permanganate, with a mass ratio of concentrated sulfuric acid to potassium permanganate of 0.6:1, and heated under reflux. The matrix is ​​then washed with deionized water until neutral to obtain the graphite matrix.

[0064] 48.0 g of cucurbituril was dissolved in 155 ml of concentrated sulfuric acid, stirred at room temperature, and placed in an ultrasonic disperser to ensure complete dissolution, yielding a first presol. 21.0 g of paraformaldehyde was added to the first presol, and stirred at room temperature until a yellow gel-like first gel was obtained. The first gel was heated to 100°C and refluxed using a condenser for 10 h to obtain a fluidized second presol. The second presol was rotary evaporated under reduced pressure to 41 mL, and while still hot, it was slowly introduced into 230 mL of acetone and stirred at high speed to obtain a third presol. The third presol was filtered under reduced pressure, washed four times with acetone solution, and dried under vacuum to obtain a pale yellow powder of cucurbituril monomer.

[0065] A graphite matrix was dispersed in an ethanol solvent at a mass ratio of 0.5:1, and the mixture was stirred at 25°C to form a first suspension. Cucurbita urea monomer was added to the first suspension, and the pH of the solution was controlled at 7.5. The reaction temperature was 65°C, and the reaction time was 7 hours. The mixture was then filtered and dried at 60°C to obtain the negative electrode material.

[0066] Example 2 This embodiment provides a negative electrode material. The difference from Embodiment 1 is that the graphite matrix is ​​not pretreated with concentrated sulfuric acid and potassium permanganate. The remaining steps are the same as in Embodiment 1.

[0067] Example 3 This embodiment provides a negative electrode material. The difference from Embodiment 1 is that the urea solution is dissolved in concentrated sulfuric acid without ultrasonic treatment. The remaining steps are the same as in Embodiment 1.

[0068] Example 4 This embodiment provides a negative electrode material, which differs from Embodiment 1 in that the first gel is heated at a temperature less than 95°C, while the remaining steps are the same as in Embodiment 1.

[0069] Example 5 This embodiment provides a negative electrode material, which differs from Embodiment 1 in that the first gel is heated to a temperature greater than 105°C, while the remaining steps are the same as in Embodiment 1.

[0070] Example 6 This embodiment provides a negative electrode material, which differs from Embodiment 1 in that a condenser tube reflux is not used, while the remaining steps are consistent with Embodiment 1.

[0071] Example 7 This embodiment provides a negative electrode material. The difference from Embodiment 1 is that the acetone was not stirred at high speed during the process of adding acetone after the second presolution was evaporated under reduced pressure. The remaining steps are the same as in Embodiment 1.

[0072] Example 8 This embodiment provides a negative electrode material. The difference from Embodiment 1 is that cucurbituril monomer is added to the first suspension and the pH value of the solution is controlled to be <7.0. The remaining steps are the same as in Embodiment 1.

[0073] Example 9 This embodiment provides a negative electrode material. The difference from Embodiment 1 is that cucurbituril monomer is added to the first suspension and the pH value of the solution is controlled to be >8.0. The remaining steps are the same as in Embodiment 1.

[0074] Example 10 This embodiment provides a negative electrode material. The difference from Embodiment 1 is that cucurbituril monomer is added to the first suspension and the reaction temperature is controlled to be less than 60°C. The remaining steps are the same as in Embodiment 1.

[0075] Example 11 This embodiment provides a negative electrode material. The difference from Embodiment 1 is that cucurbituril monomer is added to the first suspension and the reaction temperature is controlled to be greater than 70°C. The remaining steps are the same as in Embodiment 1.

[0076] Example 12 This embodiment provides a negative electrode material, which differs from Embodiment 1 in that the aperture of the ion channel 21 is 0.2 nm.

[0077] Example 13 This embodiment provides a negative electrode material, which differs from Embodiment 1 in that the aperture of the ion channel 21 is 1.5 nm.

[0078] Example 14 This embodiment provides a negative electrode material, which differs from Embodiment 1 in that the porosity of the cucurbituril coating layer is 20%.

[0079] Example 15 This embodiment provides a negative electrode material, which differs from Embodiment 1 in that the porosity of the cucurbituril coating layer is 40%.

[0080] Example 16 This embodiment provides a negative electrode material, which differs from Embodiment 1 in that the mass ratio of the cucurbituril coating layer to the graphite matrix is ​​0.2:100, and the thickness of the cucurbituril coating layer is 1 nm.

[0081] Example 17 This embodiment provides a negative electrode material, which differs from Embodiment 1 in that the mass ratio of the cucurbituril coating layer to the graphite matrix is ​​2:100, and the thickness of the cucurbituril coating layer is 20 nm.

[0082] Example 18 This embodiment provides a negative electrode material, which differs from Embodiment 1 in that the particle size of the graphite matrix is ​​8 μm.

[0083] Example 19 This embodiment provides a negative electrode material, which differs from Embodiment 1 in that the particle size of the graphite matrix is ​​20 μm.

[0084] Comparative Example 1 This comparative example provides a negative electrode material that differs from Example 1 in that it lacks a cucurbituril coating layer.

[0085] The negative electrode materials provided in Examples 1-19 and Comparative Example 1 were assembled to form a negative electrode sheet and a battery. The remaining components of the battery are the same, as shown below: Negative electrode sheet: Negative electrode material, conductive carbon black (Super P), carboxymethyl cellulose (CMC), and binder PVDF are mixed with deionized water at a mass ratio of 96:0.5:0.5:0.8:2.2 and stirred evenly to obtain a negative electrode slurry. The obtained negative electrode slurry is uniformly coated onto a 5μm thick copper foil and dried to obtain the negative electrode sheet.

[0086] Positive electrode sheet: The positive electrode material (lithium iron phosphate, LFP), conductive carbon black (Super P), binder PVDF, and dispersant (polypyrrolidone) are mixed in a mass ratio of 97.4:0.5:1.5:0.06 with N-methylpyrrolidone (NMP) solvent and stirred until homogeneous to obtain a positive electrode slurry. The obtained positive electrode slurry is uniformly coated onto a 12μm aluminum foil and dried to obtain the positive electrode sheet.

[0087] Diaphragm: Adhesive-coated diaphragm.

[0088] Electrolyte: Ethylene carbonate and ethyl methyl carbonate are mixed in a volume ratio of 3:7, and LiPF6 (lithium hexafluorophosphate) is added to form an electrolyte with a concentration of 1 mol / L.

[0089] The battery manufacturing process includes: electrode cutting, stacking, casing, vacuum baking, electrolyte injection, settling, and capacity testing.

[0090] The electrochemical performance of each battery assembled in the above examples and comparative examples was tested for cycle stability and EIS (electrochemical impedance spectroscopy) under the following conditions: Cyclic stability test: The battery is placed in the Blue Battery test cabinet for charging and discharging. The charging and discharging current is 1C=150mA / g, and the voltage range is 2.00V-4.25V.

[0091] EIS testing: The battery was discharged to 50% SOC (state of charge) on a Gammary electrochemical workstation at a frequency of 100 kHz - 0.05 Hz.

[0092] The test results are shown in Table 1 below.

[0093] Table 1

[0094] Comparing Examples 1-19 and Comparative Example 1 in Table 1, it can be seen that the internal resistance of the batteries corresponding to Comparative Example 1 without the cucurbita coating is greater than that of the batteries corresponding to Examples 1-19 with the cucurbita coating negative electrode material. The capacity retention rate of the batteries corresponding to Comparative Example 1 is lower than that of the batteries corresponding to Examples 1-19, and the energy conversion efficiency of the batteries corresponding to Comparative Example 1 is lower than that of the batteries corresponding to Examples 1-19. This is because the ion channels 21 of the cucurbita coating can improve the diffusion efficiency of active ions such as lithium ions on the negative electrode surface, reducing the battery's internal resistance. After the cucurbita coating combines with the graphite matrix, it can reduce the formation of byproducts such as lithium fluoride in the electrolyte, helping to slow down the excessive growth of the solid electrolyte interphase (SEI) film, thereby improving the battery's cycle stability and energy efficiency.

[0095] Comparing Examples 1 and 2 in Table 1, it can be seen that the battery prepared using the untreated graphite substrate has worse internal resistance, capacity retention, and energy conversion efficiency than that of Example 1. This is because the untreated graphite substrate has poor surface activity, which affects its normal use. However, it is still better than Comparative Example 1.

[0096] Comparing Examples 1 and 3 in Table 1, it can be seen that the battery prepared by dissolving cucurbitacin in concentrated sulfuric acid without ultrasonic dispersion has worse internal resistance, capacity retention, and energy conversion efficiency than that of Example 1. This is because the cucurbitacin was not sufficiently dispersed, resulting in poor uniformity of the final product, which in turn affects the integrity and uniformity of the cucurbitacin coating layer. However, it is still better than Comparative Example 1.

[0097] Comparing Examples 1 and 4-5 in Table 1, it can be seen that as the heating temperature of the first gel increases, the internal resistance of the corresponding battery first decreases and then increases, while the capacity retention rate and energy conversion efficiency of the corresponding battery first increase and then decrease. Too low a reaction temperature leads to low crystallinity of the product and disordered ion channels 21, while too high a reaction temperature destroys the cage-like structure; therefore, it is necessary to limit the heating temperature of the first gel. However, both are superior to Comparative Example 1.

[0098] Comparing Examples 1 and 6 in Table 1, it can be seen that without the reflux operation using the condenser, the internal resistance, capacity retention, and energy conversion efficiency of the corresponding batteries are all worse than those of Example 1. Using the reflux operation with the condenser helps to achieve a homogeneous phase reaction of the product, making the second presol solution a stable fluid state, which helps to homogenize the generated cucurbituril monomer. However, all are superior to Comparative Example 1.

[0099] Comparing Examples 1 and 7 in Table 1, it can be seen that in the process of adding acetone after vacuum rotary evaporation of the second presolution, the acetone was not subjected to high-speed stirring. The internal resistance, capacity retention, and energy conversion efficiency of the corresponding batteries were all worse than those in Example 1. The lack of high-speed stirring resulted in precipitation, leading to poor dispersion of the final product and affecting the distribution of the cucurbituril coating layer. Therefore, attention should be paid to the dispersion operation during the preparation process. However, all were superior to Comparative Example 1.

[0100] Comparing Examples 1 and 8-9 in Table 1, it can be seen that as the pH increases after adding cucurbituril monomer to the first suspension, the internal resistance of the corresponding battery first decreases and then increases, while the capacity retention rate and energy conversion efficiency of the corresponding battery first increase and then decrease. This is because too low a pH will affect the port diameter of the cucurbituril coating layer, while too high a pH will make the formed cucurbituril coating layer easy to detach. Therefore, the pH should be controlled to be neutral. However, both are better than Comparative Example 1.

[0101] Comparing Examples 1 and 10-11 in Table 1, it can be seen that as the reaction temperature of adding cucurbita monomer to the first suspension increases, the internal resistance of the corresponding battery shows a trend of first decreasing and then increasing, while the capacity retention rate and energy conversion efficiency of the corresponding battery show a trend of first increasing and then decreasing. This is because excessively low temperatures will cause uneven thickness of the formed cucurbita coating layer, while excessively high temperatures will cause the formed cucurbita coating layer to easily detach. Therefore, it is necessary to control the temperature appropriately. However, both are superior to Comparative Example 1.

[0102] Comparing Examples 1 and 12-13 in Table 1, it can be seen that, with other parameters remaining the same, as the aperture of the ion channel increases, the internal resistance of the corresponding battery gradually decreases, while the capacity retention rate and energy conversion efficiency gradually increase. This is because a small aperture will affect the transport of active ions, while a large aperture will allow other solvent molecules and transition metal ions to pass through. Therefore, it is necessary to limit the aperture of the ion channel within a certain range. However, both are superior to Comparative Example 1.

[0103] Comparing Examples 1 and 14-15 in Table 1, it can be seen that, with other parameters remaining the same, as the porosity of the cucurbita coating increases, the internal resistance of the battery first decreases and then increases, while the capacity retention rate and energy conversion efficiency first increase and then decrease. This is because excessively low porosity will prevent some active materials from fully contacting the electrolyte, while excessively high porosity will easily lead to stress concentration and deformation in the cucurbita coating, shortening the cycle life of the battery. Therefore, it is necessary to limit the porosity of the cucurbita coating to a certain range. However, both are superior to Comparative Example 1.

[0104] Comparing Examples 1 and 16-17 in Table 1, it can be seen that, with other parameters remaining the same, as the mass ratio of the cucurbita coating layer to the graphite matrix and the thickness of the cucurbita coating layer increase, the internal resistance of the corresponding battery gradually increases, while the capacity retention rate and energy conversion efficiency gradually decrease. This is because an excessively thick and proportionate cucurbita coating layer results in multiple layers, hindering the effective transport of lithium ions. However, an excessively thin and proportionate cucurbita coating layer reduces the protective effect on the graphite matrix. Therefore, it is necessary to limit the mass ratio of the cucurbita coating layer to the graphite matrix and the thickness of the cucurbita coating layer to a certain range. However, both are superior to Comparative Example 1.

[0105] Comparing Examples 1 and 18-19 in Table 1, it can be seen that when other parameters are the same, if the particle size of the graphite matrix is ​​too large, the internal resistance of the corresponding battery increases significantly, and the capacity retention rate and energy conversion efficiency of the corresponding battery decrease significantly. This is because an excessively large particle size of the graphite matrix prolongs the lithium-ion insertion / extraction path, leading to increased diffusion resistance and accelerating battery capacity decay. If the particle size of the graphite matrix is ​​too small, agglomeration may occur during the production process; therefore, the particle size of the graphite matrix needs to be limited to a certain range. However, all are superior to Comparative Example 1.

[0106] In the description of the embodiments of this application, it should be noted that the orientation or positional relationship of the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and other indicators are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0107] The above-disclosed embodiments are merely preferred embodiments of this application and should not be construed as limiting the scope of this application. Those skilled in the art will understand that all or part of the processes for implementing the above embodiments and equivalent variations made in accordance with the claims of this application are still within the scope of this application.

Claims

1. A negative electrode material, characterized in that, It includes a graphite matrix and a cucurbituril coating layer, wherein the cucurbituril coating layer coats the graphite matrix and has ion channels for the migration of active ions.

2. The negative electrode material according to claim 1, characterized in that, The aperture of the ion channel is 0.5 nm-1 nm; and / or the porosity of the cucurbituril coating layer is 25%-30%.

3. The negative electrode material according to claim 1, characterized in that, The mass ratio of the cucurbita coating layer to the graphite matrix is ​​(0.5-1.5):

100.

4. The negative electrode material according to any one of claims 1-3, characterized in that, The thickness of the cucurbita coating layer is 5nm-10nm; and / or the particle size of the graphite matrix is ​​10μm-18μm.

5. A method for preparing a negative electrode material, characterized in that, The method for preparing the negative electrode material as described in any one of claims 1 to 4 comprises the following steps: Provides graphite matrix and cucurbituril monomer; The graphite matrix is ​​dispersed in a first solvent to form a first suspension; The cucurbituril monomer was added to the first suspension, reacted, and filtered to obtain the negative electrode material.

6. The method for preparing the negative electrode material according to claim 5, characterized in that, The reaction temperature for adding the cucurbituril monomer to the first suspension is 60℃-70℃; and / or The reaction time for adding the cucurbituril monomer to the first suspension is 6-8 hours; and / or The pH after adding the cucurbituril monomer to the first suspension is 7-8.

7. The method for preparing the negative electrode material according to claim 5, characterized in that, Provide a graphite matrix, including: The pretreated graphite was placed in a second solvent and heated under reflux. The second solvent is a mixed solution of concentrated sulfuric acid and potassium permanganate, wherein the mass ratio of the concentrated sulfuric acid to the potassium permanganate is (0.2-0.8):

1.

8. The method for preparing the negative electrode material according to claim 5, characterized in that, Provide cucurbituril monomers, including: The urea solution was dissolved and dispersed in concentrated sulfuric acid to obtain the first pre-solution; Paraformaldehyde was added to the first presol to obtain the first gel; The first gel was heated and refluxed using a condenser to obtain a fluidized second presol; The second presol was evaporated under reduced pressure and mixed with acetone to obtain the third presol; The third presol was filtered under reduced pressure and then washed and dried to obtain the cucurbituril monomer.

9. The method for preparing the negative electrode material according to claim 8, characterized in that, The reaction temperature using reflux with a condenser is 95°C-105°C; and / or The reaction time using reflux with a condenser is 9-11 hours; and / or The mass ratio of the glycosuria to the paraformaldehyde is (1.8-2.5):

1.

10. A negative electrode sheet, characterized in that, The negative electrode sheet comprises the negative electrode material as described in any one of claims 1-4 or the negative electrode material prepared by the method for preparing the negative electrode material as described in any one of claims 5-9.

11. A battery, characterized in that, It includes a positive electrode and a negative electrode as described in claim 10.

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