A negative electrode material for improving cycle performance of a lithium ion battery and a preparation method thereof

Abstract

The application relates to a negative electrode material for improving the cycle performance of a lithium ion battery and a preparation method thereof, and belongs to the technical field of graphene negative electrode materials; a modifier is self-prepared, the modifier is grafted onto graphene oxide to obtain modified graphene material, the modifier constructs a rigid three-dimensional structure with a central nitrogen atom and three non-coplanar benzene rings, can inhibit the stacking of graphene sheet layers, and can maintain an open ion transmission channel; the electrophilic electrolyte property and the lithium-philic site function of sulfonate lithium in the modifier can not only enhance the dispersion stability of the material, help the uniform electrode forming, but also can promote the formation of a stable solid electrolyte interface film and the transmission of lithium ions; the ester bond in the modifier can strengthen the interfacial bonding force with a binder, improve the mechanical strength of the electrode, the aromatic ring structure can enhance the electronic coupling and conductivity through pi-pi stacking, and the multi-effect synergy can improve the cycle stability of the negative electrode of the lithium ion battery.

Description

Technical Field

[0001] This invention belongs to the field of carbon-based anode technology, specifically, it relates to an anode material for improving the cycle performance of lithium-ion batteries and its preparation method. Background Technology

[0002] Lithium-ion batteries, as the core of today's high-performance energy storage devices, directly determine technological advancements in key areas such as electric vehicles and portable electronic devices due to their energy density, power density, and cycle life. Anode materials, as a crucial component of lithium-ion batteries, are of paramount importance in terms of performance. Currently, while commercially available graphite anode materials offer advantages such as low cost and stable potential plateau, their theoretical specific capacity is limited, and their rate performance is constrained by the slow lithium-ion solid-state diffusion kinetics, making it difficult to meet future demands for high energy density and fast charging.

[0003] Strong π-π interactions and van der Waals forces exist between graphene sheets, making them highly susceptible to irreversible recombination during the drying and compaction processes of electrode fabrication. This results in the burial of most active surfaces, blockage of ion transport channels, and difficulty in effectively wetting the internal regions with electrolyte, leading to a significantly lower actual specific capacity than the theoretical value and poor rate performance. Furthermore, pristine graphene exhibits poor wettability and dispersibility in conventional organic electrolytes. This results in poor solid-liquid interface contact between the electrode and electrolyte, high ion migration resistance, and potential inhomogeneity in the electrode reaction. Existing technologies introduce molecules or polymers through π-π stacking or ion adsorption. While this method can improve dispersibility to some extent, the binding force is weak, and it is prone to desorption in long-term cycling or polar solvents, resulting in insufficient stability. In addition, existing modification strategies often focus on solving single problems, lacking a systematic design for key issues such as ion transport kinetics, interface stability, mechanical integrity, and the durability of the conductive network.

[0004] Based on this, the present invention will provide a negative electrode material for improving the cycle performance of lithium-ion batteries and a method for preparing the same. Summary of the Invention

[0005] The purpose of this invention is to provide a negative electrode material and its preparation method for improving the cycle performance of lithium-ion batteries, thereby solving the problems mentioned in the background art.

[0006] The objective of this invention can be achieved through the following technical solutions: A negative electrode material for improving the cycle performance of lithium-ion batteries and its preparation method, comprising the following steps: Step 1: Mix graphite powder and concentrated sulfuric acid in a reaction vessel and react at 0-5℃ for 1-3 hours. Then add potassium permanganate and react at room temperature for 2-3 hours. After the reaction is complete, add distilled water and raise the system temperature to 95-98℃ for 15-20 minutes. Then add distilled water and continue the reaction for 10-20 minutes. Then add hydrogen peroxide and continue the reaction for 10-20 minutes. After the reaction is complete, filter the mixture and retain the solid. Wash the obtained solid with hydrochloric acid aqueous solution, anhydrous ethanol and distilled water respectively. Centrifuge at high speed to discard the upper acid layer. Dilute the lower layer of graphene oxide with distilled water and then sonicate for 1-2 hours to peel it off to a monolayer. After drying and grinding, graphene oxide is obtained. The second step involves mixing graphene oxide and N,N-dimethylformamide in a reaction vessel and ultrasonically vibrating at room temperature for 1–2 hours to obtain a graphene oxide dispersion. The graphene oxide dispersion and modifier are then added to a reaction vessel and reacted at 80–100°C for 12–16 hours. After the reaction is completed, the mixture is cooled to room temperature, and the reaction solution is poured into isopropanol. The precipitated solid is filtered and the solid is retained. The solid is then dried to obtain modified graphene.

[0007] Furthermore, the concentrated sulfuric acid in the first step has a mass fraction of 92-98%.

[0008] Furthermore, the hydrogen peroxide in the first step has a mass fraction of 30-50%.

[0009] Furthermore, the hydrochloric acid aqueous solution in the first step has a mass fraction of 5-20%.

[0010] Furthermore, in the first step, the mass ratio of graphite powder, concentrated sulfuric acid, potassium permanganate, distilled water, and hydrogen peroxide is 18–20: 720–800: 54–60: 2700–3000: 180–200.

[0011] Furthermore, in the second step, the mass ratio of graphene oxide, N,N-dimethylformamide and modifier is 12-14:60-80:1.5-1.9.

[0012] Furthermore, the modifier is prepared by the following steps: S1. Add 4,4',4'',4'''-methanetetrabenzoic acid, unsaturated fatty alcohol, 4-dimethylaminopyridine and N,N-dimethylformamide to a reaction vessel, raise the system temperature to 50-60℃, and then add 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide. React for 4-6 hours. After the reaction is completed and cooled to room temperature, pour the reaction solution into water and wait for the solid to precipitate. Filter the solution and retain the solid. Then dry the solid to obtain rigid spacer units. S2. Add rigid spacer units, amino sulfonic acid compounds, potassium hydroxide and ethanol to a three-necked flask, attach a condenser and a thermometer, turn on magnetic stirring, and react at room temperature for 3-5 hours. After the reaction is complete, remove the solvent by rotary evaporation of the reaction solution, and then wash the product with saturated brine and dry it to obtain the modifier precursor. S3. Add the modifier precursor and lithium hydroxide aqueous solution to the reaction vessel and react at 40-60℃ for 16-24h. After the reaction is completed and cooled to room temperature, pour the reaction solution into isopropanol to precipitate the solid, filter and retain the solid, and then dry the obtained solid to obtain the modifier.

[0013] Further, in step S1, the mass ratio of 4,4',4'',4'''-methanetetrabenzoic acid, unsaturated fatty alcohol, 4-dimethylaminopyridine, N,N-dimethylformamide and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide is 2.8–4:1.5–1.9:0.8–1.2:80–100:4–5.8.

[0014] Furthermore, the aminoaryl sulfonic acid compound in step S2 is one of 4-aminobenzenesulfonic acid, 4-naphthylamine-1-sulfonic acid, and 5-amino-1-naphthylsulfonic acid.

[0015] Furthermore, in step S2, the mass ratio of the rigid spacer unit, aminosulfonic acid compound, potassium hydroxide, and ethanol is 2.6–3: 2.9–3.3: 0.8–1: 50–60.

[0016] Furthermore, the mass fraction of the lithium hydroxide aqueous solution in step S3 is 10–20%.

[0017] Furthermore, in step S3, the mass ratio of the modifier precursor to the lithium hydroxide aqueous solution is 3.8–4:1.39:–2.78.

[0018] A negative electrode material for improving the cycle performance of lithium-ion batteries is prepared by any of the above preparation steps to obtain a modified graphene material.

[0019] The beneficial effects of this invention are: 1) The modifier grafted onto the modified graphene of this invention connects multiple sterically hindered aromatic ring groups to a central carbon atom, forming a three-dimensional molecular structure. This structure can suppress interlayer stacking of graphene sheets after compaction as electrode materials, increase the contact area with active particles, enhance the conductivity of the composite conductive agent, and enable sufficient and rapid charge-discharge reactions under high current, thereby improving rate performance. It also effectively exposes the internal surface, maintaining open ion transport channels to ensure electrolyte wetting and ion arrival at most interfaces. Furthermore, the lithium sulfonate group in the modifier has strong polarity, which can significantly improve the dispersion stability of modified graphene in slurries composed of polar organic solvents and promote the contact between graphene and electrolyte, facilitating lithium ion diffusion, constructing a more three-dimensional electronic and ion conductive pathway, reducing the movement distance of electrons and ions, and thus maintaining the structural integrity and conductive network stability of the electrode material during long-term cycling.

[0020] 2) The ester bonds in the modifier molecules of this invention provide a certain degree of polarity, which helps to enhance compatibility with polar solvents and binders, thereby improving dispersibility and interfacial bonding. This helps to form a composite electrode film with better mechanical strength and flexibility, reducing cracks or peeling caused by volume changes of active materials during charging and discharging, and improving the cycle stability of modified graphene as a lithium-ion battery. In addition, the aromatic ring structure in the modifier molecules is firmly bonded to graphene through π-π conjugation effect, ensuring stable grafting of the modifier on the graphene surface. This strong interaction helps to form a uniform modified layer on the graphene surface, and due to its conjugation characteristics, the modification has a relatively small hindering effect on the intrinsic electron conduction channels of graphene. Detailed Implementation

[0021] The technical solutions of the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments in this application specification, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection claimed in this application.

[0022] The raw materials used in this invention are not particularly restricted in terms of their source; they can be purchased from the market or prepared using conventional methods known to those skilled in the art.

[0023] The parts mentioned in the following examples and comparative examples are by weight.

[0024] Example 1 A method for preparing a negative electrode material to improve the cycle performance of lithium-ion batteries includes the following steps: Step 1: Mix 18 parts of graphite powder and 720 parts of 92% concentrated sulfuric acid in a reaction vessel and react at 0°C for 3 hours. Then add 54 parts of potassium permanganate and react at room temperature for 2 hours. After the reaction is complete, add 900 parts of distilled water and raise the system temperature to 95°C for 20 minutes. Then add 1800 parts of distilled water and continue the reaction for 20 minutes. Then add 180 parts of 30% hydrogen peroxide and continue the reaction for 20 minutes. After the reaction is complete, filter the mixture and retain the solid. Wash the obtained solid with 5% hydrochloric acid solution, anhydrous ethanol and distilled water respectively. Centrifuge at high speed to discard the upper acid layer. Dilute the lower layer of graphene oxide with distilled water and then sonicate for 1 hour to peel it off to a monolayer. After drying and grinding, obtain graphene oxide. The second step involves mixing 12 parts of graphene oxide and 60 parts of N,N-dimethylformamide in a reaction vessel and ultrasonically vibrating at room temperature for 1 hour to obtain a graphene oxide dispersion. Then, the graphene oxide dispersion and 1.5 parts of modifier are added to the reaction vessel and reacted at 80°C for 16 hours. After the reaction is completed, the mixture is cooled to room temperature, and the reaction solution is poured into isopropanol. After the solid precipitates, it is filtered and the solid is retained. The solid is then dried to obtain the modified graphene anode material. The modifier is prepared by the following steps: S1. Add 2.8 parts of 4,4',4'',4'''-methanetetrabenzoic acid, 1.5 parts of vinyl alcohol, 0.8 parts of 4-dimethylaminopyridine and 80 parts of N,N-dimethylformamide to a reaction vessel. After raising the system temperature to 50°C, add 4 parts of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide. React for 6 hours. After the reaction is completed and cooled to room temperature, pour the reaction solution into water and filter it after the solid precipitates. Then retain the solid and dry it to obtain rigid spacer units. S2. Add 2.6 parts of rigid spacer unit, 2.9 parts of 4-aminobenzenesulfonic acid, 0.8 parts of potassium hydroxide and 50 parts of ethanol to a three-necked flask, attach a condenser and a thermometer, turn on magnetic stirring, and react at room temperature for 3 hours. After the reaction is completed, remove the solvent by rotary evaporation of the reaction solution, and then wash the product with saturated brine and dry it to obtain the modifier precursor. S3. Add 3.8 parts of the modifier precursor and 1.39 parts of a 20% lithium hydroxide aqueous solution to the reaction vessel and react at 60°C for 24 hours. After the reaction is completed and cooled to room temperature, pour the reaction solution into isopropanol to precipitate the solid, filter and retain the solid, and then dry the obtained solid to obtain the modifier.

[0025] A modified graphene anode material for improving the cycle performance of lithium-ion batteries is prepared by the above preparation steps.

[0026] Example 2 A method for preparing a negative electrode material to improve the cycle performance of lithium-ion batteries includes the following steps: Step 1: Mix 18.5 parts of graphite powder and 740 parts of 94% concentrated sulfuric acid in a reaction vessel and react at 1°C for 2.5 h. Then add 55.5 parts of potassium permanganate and react at room temperature for 2.2 h. After the reaction is complete, add 950 parts of distilled water and raise the system temperature to 96°C for 18 min. Then add 1850 parts of distilled water and continue the reaction for 17 min. Then add 185 parts of 35% hydrogen peroxide and continue the reaction for 17 min. After the reaction is complete, filter the mixture and retain the solid. Wash the obtained solid with 9% hydrochloric acid solution, anhydrous ethanol and distilled water respectively. Centrifuge at high speed to discard the upper acid layer. Dilute the lower layer of graphene oxide with distilled water and then sonicate for 1.25 h to peel it off to a monolayer. After drying and grinding, graphene oxide is obtained. The second step involves mixing 12.5 parts of graphene oxide and 65 parts of N,N-dimethylformamide in a reaction vessel and ultrasonically vibrating at room temperature for 1.2 hours to obtain a graphene oxide dispersion. Then, the graphene oxide dispersion and 1.6 parts of modifier are added to the reaction vessel and reacted at 85°C for 15 hours. After the reaction is completed, the mixture is cooled to room temperature, and the reaction solution is poured into isopropanol. After the solid precipitates, it is filtered and the solid is retained. The solid is then dried to obtain the modified graphene anode material. The modifier is prepared by the following steps: S1. Add 3.0 parts of 4,4',4'',4'''-methanetetramethyltetrabenzoic acid, 1.6 parts of allyl alcohol, 0.9 parts of 4-dimethylaminopyridine and 85 parts of N,N-dimethylformamide to a reaction vessel. After raising the system temperature to 52°C, add 4.5 parts of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide. React for 5.5 hours. After the reaction is completed and cooled to room temperature, pour the reaction solution into water. After the solid precipitates, filter and retain the solid. Then dry the solid to obtain rigid spacer units. S2. Add 2.7 parts of rigid spacer unit, 3.0 parts of 4-naphthylamine-1-sulfonic acid, 0.85 parts of potassium hydroxide and 52 parts of ethanol to a three-necked flask, attach a condenser and a thermometer, turn on magnetic stirring, and react at room temperature for 3.5 h. After the reaction is completed, remove the solvent by rotary evaporation of the reaction solution, and then wash the product with saturated brine and dry it to obtain the modifier precursor. S3. Add 3.85 parts of the modifier precursor and 1.76 parts of a 12% (w / w) lithium hydroxide aqueous solution to a reaction vessel and react at 45°C for 20 h. After the reaction is completed and cooled to room temperature, pour the reaction solution into isopropanol to precipitate the solid, filter and retain the solid, and then dry the obtained solid to obtain the modifier.

[0027] A modified graphene anode material for improving the cycle performance of lithium-ion batteries is prepared by the above preparation steps.

[0028] Example 3 A method for preparing a negative electrode material to improve the cycle performance of lithium-ion batteries includes the following steps: Step 1: Mix 19 parts of graphite powder and 760 parts of 95% concentrated sulfuric acid in a reaction vessel and react at 3°C ​​for 2 hours. Then add 57 parts of potassium permanganate and react at room temperature for 2.4 hours. After the reaction is complete, add 980 parts of distilled water and raise the system temperature to 97°C for 17 minutes. Then add 1900 parts of distilled water and continue the reaction for 15 minutes. Then add 190 parts of 40% hydrogen peroxide and continue the reaction for 15 minutes. After the reaction is complete, filter the mixture and retain the solid. Wash the obtained solid with 12% hydrochloric acid solution, anhydrous ethanol and distilled water respectively. Centrifuge at high speed to discard the upper acid layer. Dilute the lower layer of graphene oxide with distilled water and then sonicate for 1.5 hours to peel it off to a monolayer. After drying and grinding, obtain graphene oxide. The second step involves mixing 13 parts of graphene oxide and 70 parts of N,N-dimethylformamide in a reaction vessel and ultrasonically vibrating at room temperature for 1.4 hours to obtain a graphene oxide dispersion. Then, the graphene oxide dispersion and 1.7 parts of modifier are added to the reaction vessel and reacted at 90°C for 14 hours. After the reaction is completed, the mixture is cooled to room temperature, and the reaction solution is poured into isopropanol. After the solid precipitates, it is filtered and the solid is retained. The solid is then dried to obtain the modified graphene anode material. The modifier is prepared by the following steps: S1. Add 3.3 parts of 4,4',4'',4'''-methanetetramethyltetrabenzoic acid, 1.7 parts of 2-propenol, 1.0 parts of 4-dimethylaminopyridine and 90 parts of N,N-dimethylformamide to a reaction vessel, raise the system temperature to 55°C, and then add 5.0 parts of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide. React for 5 hours. After the reaction is completed and cooled to room temperature, pour the reaction solution into water. After the solid precipitates, filter and retain the solid. Then dry the solid to obtain rigid spacer units. S2. Add 2.8 parts of rigid spacer unit, 3.1 parts of 5-amino-1-naphthalenesulfonic acid, 0.9 parts of potassium hydroxide and 55 parts of ethanol to a three-necked flask, attach a condenser and a thermometer, turn on magnetic stirring, and react at room temperature for 4 hours. After the reaction is completed, remove the solvent by rotary evaporation of the reaction solution, and then wash the product with saturated brine and dry it to obtain the modifier precursor. S3. Add 3.9 parts of the modifier precursor and 2.13 parts of a 15% lithium hydroxide aqueous solution to the reaction vessel and react at 50°C for 18 hours. After the reaction is completed and cooled to room temperature, pour the reaction solution into isopropanol to precipitate the solid, filter and retain the solid, and then dry the obtained solid to obtain the modifier.

[0029] A modified graphene anode material for improving the cycle performance of lithium-ion batteries is prepared by the above preparation steps.

[0030] Example 4 A method for preparing a negative electrode material to improve the cycle performance of lithium-ion batteries includes the following steps: Step 1: Mix 19.5 parts of graphite powder and 780 parts of 97% concentrated sulfuric acid in a reaction vessel and react at 4°C for 1.5 h. Then add 58.5 parts of potassium permanganate and react at room temperature for 2.6 h. After the reaction is complete, add 990 parts of distilled water and raise the system temperature to 97.5°C for 16 min. Then add 1950 parts of distilled water and continue the reaction for 12 min. Then add 195 parts of 45% hydrogen peroxide and continue the reaction for 12 min. After the reaction is complete, filter the mixture and retain the solid. Wash the obtained solid with 16% hydrochloric acid solution, anhydrous ethanol and distilled water respectively. Centrifuge at high speed to discard the upper acid layer. Dilute the lower layer of graphene oxide with distilled water and then sonicate for 1.75 h to peel it off to a monolayer. After drying and grinding, graphene oxide is obtained. The second step involves mixing 13.5 parts of graphene oxide and 75 parts of N,N-dimethylformamide in a reaction vessel and ultrasonically vibrating at room temperature for 1.6 hours to obtain a graphene oxide dispersion. Then, the graphene oxide dispersion and 1.8 parts of modifier are added to the reaction vessel and reacted at 95°C for 13 hours. After the reaction is completed, the mixture is cooled to room temperature, and the reaction solution is poured into isopropanol. After the solid precipitates, it is filtered and the solid is retained. The solid is then dried to obtain the modified graphene anode material. The modifier is prepared by the following steps: S1. Add 3.6 parts of 4,4',4'',4'''-methanetetramethyltetrabenzoic acid, 1.8 parts of vinyl alcohol, 1.1 parts of 4-dimethylaminopyridine and 95 parts of N,N-dimethylformamide to a reaction vessel. After raising the system temperature to 58°C, add 5.4 parts of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide. React for 4.5 h. After the reaction is completed and cooled to room temperature, pour the reaction solution into water. After the solid precipitates, filter and retain the solid. Then dry the solid to obtain rigid spacer units. S2. Add 2.9 parts of rigid spacer unit, 3.2 parts of 4-aminobenzenesulfonic acid, 0.95 parts of potassium hydroxide and 58 parts of ethanol to a three-necked flask, attach a condenser and a thermometer, turn on magnetic stirring, and react at room temperature for 4.5 h. After the reaction is completed, remove the solvent by rotary evaporation of the reaction solution, and then wash the product with saturated brine and dry to obtain the modifier precursor. S3. Add 3.95 parts of the modifier precursor and 2.45 parts of 18% lithium hydroxide aqueous solution to the reaction vessel and react at 55°C for 17 hours. After the reaction is completed and cooled to room temperature, pour the reaction solution into isopropanol to precipitate the solid, filter and retain the solid, and then dry the obtained solid to obtain the modifier.

[0031] A modified graphene anode material for improving the cycle performance of lithium-ion batteries is prepared by the above preparation steps.

[0032] Example 5 A method for preparing a negative electrode material to improve the cycle performance of lithium-ion batteries includes the following steps: Step 1: Mix 20 parts of graphite powder and 800 parts of 98% concentrated sulfuric acid in a reaction vessel and react at 5°C for 1 hour. Then add 60 parts of potassium permanganate and react at room temperature for 2.8 hours. After the reaction is complete, add 1000 parts of distilled water and raise the system temperature to 98°C for 15 minutes. Then add 2000 parts of distilled water and continue the reaction for 10 minutes. Then add 200 parts of 50% hydrogen peroxide and continue the reaction for 10 minutes. After the reaction is complete, filter the mixture and retain the solid. Wash the obtained solid with 20% hydrochloric acid solution, anhydrous ethanol and distilled water respectively. Centrifuge at high speed to discard the upper acid layer. Dilute the lower layer of graphene oxide with distilled water and then sonicate for 2 hours to peel it off to a monolayer. After drying and grinding, graphene oxide is obtained. The second step involves mixing 14 parts of graphene oxide and 80 parts of N,N-dimethylformamide in a reaction vessel and ultrasonically vibrating at room temperature for 1.8 hours to obtain a graphene oxide dispersion. Then, the graphene oxide dispersion and 1.9 parts of modifier are added to the reaction vessel and reacted at 100°C for 12 hours. After the reaction is completed, the mixture is cooled to room temperature, and the reaction solution is poured into isopropanol. After the solid precipitates, it is filtered and the solid is retained. The solid is then dried to obtain the modified graphene anode material. The modifier is prepared by the following steps: S1. Add 4.0 parts of 4,4',4'',4'''-methanetetramethyltetrabenzoic acid, 1.9 parts of allyl alcohol, 1.2 parts of 4-dimethylaminopyridine and 100 parts of N,N-dimethylformamide to a reaction vessel. After raising the system temperature to 60°C, add 5.8 parts of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide. React for 4 hours. After the reaction is completed and cooled to room temperature, pour the reaction solution into water. After the solid precipitates, filter and retain the solid. Then dry the solid to obtain rigid spacer units. S2. Add 3.0 parts of rigid spacer unit, 3.3 parts of 4-naphthylamine-1-sulfonic acid, 1.0 parts of potassium hydroxide and 60 parts of ethanol to a three-necked flask, attach a condenser and a thermometer, turn on magnetic stirring, and react at room temperature for 5 hours. After the reaction is completed, remove the solvent by rotary evaporation of the reaction solution, and then wash the product with saturated brine and dry it to obtain the modifier precursor. S3. Add 4.0 parts of the modifier precursor and 2.78 parts of a 20% (w / w) lithium hydroxide aqueous solution to the reaction vessel and react at 60°C for 16 h. After the reaction is completed and cooled to room temperature, pour the reaction solution into isopropanol to precipitate the solid, filter and retain the solid, and then dry the obtained solid to obtain the modifier.

[0033] A modified graphene anode material for improving the cycle performance of lithium-ion batteries is prepared by the above preparation steps.

[0034] Comparative Example 1 19 parts of graphite powder and 760 parts of 95% concentrated sulfuric acid were mixed in a reaction vessel and reacted at 3°C ​​for 2 hours. Then, 57 parts of potassium permanganate were added and reacted at room temperature for 2.4 hours. After the reaction was completed, 980 parts of distilled water were added, and the system temperature was raised to 97°C and reacted for 17 minutes. Then, 1900 parts of distilled water were added and the reaction was continued for 15 minutes. Then, 190 parts of 40% hydrogen peroxide were added and the reaction was continued for 15 minutes. After the reaction was completed, the mixture was filtered and the solid was retained. The obtained solid was then washed with 12% hydrochloric acid solution, anhydrous ethanol and distilled water respectively. After centrifugation at high speed, the upper acid layer was discarded, and the lower layer of graphene oxide was diluted with distilled water. Then, it was ultrasonically treated for 1-2 hours to peel it off to a monolayer. After drying and grinding, graphene oxide was obtained.

[0035] Experimental Example 1 The graphene anode materials from Examples 1-5 and Comparative Example 1 Coin cell fabrication: Coin cells were fabricated using a mass ratio of polyvinylpyrrolidone, graphene material, and N-methylpyrrolidone (1:2:94), and lithium iron phosphate cathode material, graphene conductive paste, and polyvinylidene fluoride (93:2.5:1.5). Polyvinylpyrrolidone, graphene, and N-methylpyrrolidone were added to a reaction vessel and stirred at high speed. Then, a graphene conductive slurry was obtained by grinding for 60 minutes. Polyvinylidene fluoride and lithium iron phosphate were added sequentially to the slurry, and after degassing and stirring for 40 minutes, a positive electrode slurry was obtained. The slurry was then coated onto a 15 mm aluminum foil with a scraper gap of 200 μm. The positive electrode sheet was vacuum dried at 60 °C for 2 hours, then pressed at 15 MPa, and subsequently vacuum dried at 80 °C for 12 hours to obtain the positive electrode sheet. A CR2032 coin cell was fabricated in an argon-atmosphere glove box using a lithium sheet as the negative electrode, a Celgard 2500 polyethylene porous membrane as the separator, and a 1 mol / L LiPF6 / EC-EMC-DMC solution as the electrolyte. Performance testing was then conducted. Rate performance: The capacity retention rate of each group of graphene materials was tested at a current density of 2C, in accordance with GB / T33827-2017 "Test method for magnetic material content in nano-anode materials for lithium batteries". Dispersion stability: Place each group of graphene materials at a low temperature of 0-5℃ and visually inspect whether there is any sedimentation in each group of graphene materials; Cyclic stability: The capacity retention rate of each group of graphene materials after 500 cycles was tested in accordance with GB / T37202-2018 "Technical Specification for Discharge Tester for Supercapacitors". The test results are shown in Table 1.

[0036] Table 1 As shown in Table 1, compared with Comparative Example 1, Examples 1-5 have higher initial coulombic efficiency, capacity retention at a current density of 2C, capacity retention after 500 cycles, and better dispersion stability. This indicates that the initial coulombic efficiency, rate performance, dispersion stability, and cycle stability of Examples 1-5 are all superior to those of Comparative Example 1. Combined with Comparative Example 1, it can be seen that the modification of graphene oxide by the modifier can significantly improve the SEI film quality, rate performance, dispersion stability, and cycle stability of graphene by introducing aromatic rings and lithium sulfonate structures into graphene.

[0037] The descriptions of the above embodiments are merely illustrative of the methods and core ideas of the present invention. 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 the invention. Therefore, the present invention 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 disclosed herein.

Claims

1. A method for preparing a negative electrode material to improve the cycle performance of lithium-ion batteries, characterized in that, Includes the following steps: The first step is to oxidize graphite powder with concentrated sulfuric acid and potassium permanganate as oxidants to obtain graphene oxide. The modifier connects multiple sterically hindered aromatic ring groups with a central carbon atom to form a three-dimensional molecular structure. The second step is to graft the modifier onto graphene oxide to obtain the modified graphene anode material.

2. The method for preparing a negative electrode material to improve the cycle performance of a lithium-ion battery according to claim 1, characterized in that, The mass fraction of concentrated sulfuric acid is 92-98%.

3. The method for preparing a negative electrode material to improve the cycle performance of a lithium-ion battery according to claim 1, characterized in that, The mass ratio of graphite powder, concentrated sulfuric acid, and potassium permanganate is 18–20:720–800:54–60.

4. The method for preparing a negative electrode material to improve the cycle performance of a lithium-ion battery according to claim 1, characterized in that, The modifier is prepared by the following steps: A modifier precursor is obtained by Michael addition of a rigid spacer unit and an amino-aryl sulfonic acid compound. The modifier precursor is then subjected to an acid-base neutralization reaction with an aqueous lithium hydroxide solution to obtain the modifier.

5. The method for preparing a negative electrode material to improve the cycle performance of a lithium-ion battery according to claim 4, characterized in that, Amino aryl sulfonic acid compounds are one of 4-aminobenzenesulfonic acid, 4-naphthylamine-1-sulfonic acid, and 5-amino-1-naphthylsulfonic acid.

6. The method for preparing a negative electrode material to improve the cycle performance of a lithium-ion battery according to claim 4, characterized in that, The mass ratio of rigid spacer units to aminosulfonic acid compounds is 2.6–3:2.9–3.3, and the mass ratio of modifier precursor to lithium hydroxide aqueous solution is 3.8–4:1.39:–2.

78.

7. The method for preparing a negative electrode material to improve the cycle performance of a lithium-ion battery according to claim 4, characterized in that, Rigid spacer units are manufactured by the following steps: Rigid spacer units were obtained by esterification of 4,4',4'',4'''-methanetetrabenzoic acid and unsaturated fatty alcohols.

8. The method for preparing a negative electrode material to improve the cycle performance of a lithium-ion battery according to claim 7, characterized in that, Unsaturated fatty alcohols are one of vinyl alcohol, allyl alcohol, and 2-propenol.

9. A method for preparing a negative electrode material to improve the cycle performance of a lithium-ion battery according to claim 7, characterized in that, The mass ratio of 4,4',4'',4'''-methanetetrabenzoic acid to unsaturated fatty alcohol is 2.8–4:1.5–1.

9.

10. A negative electrode material for improving the cycle performance of lithium-ion batteries, characterized in that, The modified graphene anode material is prepared by the preparation method described in any one of claims 1 to 9.

Images