Graphene-coated lithium-ion battery negative electrode material and preparation method thereof

Abstract

This invention discloses a graphene-coated lithium-ion battery anode material and its preparation method, relating to the field of lithium-ion battery technology. The graphene-coated lithium-ion battery anode material comprises, by weight, the following components: modified silicon-based active material: 30-60 parts; artificial graphite: 20-40 parts; graphene: 1-8 parts; amorphous carbon precursor: 5-20 parts; conductive carbon black: 1-5 parts; metal oxide additive: 0.5-5 parts; binder precursor: 1-10 parts. This invention reduces fresh silicon exposure and side reactions by constructing a "conductive bridge / interface coupling layer" on the silicon surface and forming a more stable carbonized interface shielding layer through subsequent heat treatment, thereby inhibiting repeated SEI rupture and regeneration, thus improving the first-cycle efficiency of the battery.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a graphene-coated lithium-ion battery anode material and its preparation method. Background Technology

[0002] With the rapid development of new energy technologies, lithium-ion batteries have been widely used in portable electronic devices, electric vehicles, and energy storage systems due to their advantages such as high energy density, long cycle life, and environmental friendliness. As a crucial component of lithium-ion batteries, the performance of the anode material directly affects the battery's specific capacity, initial coulombic efficiency, and cycle stability. Currently, commercially available lithium-ion battery anode materials are mainly graphite; however, graphite has a relatively low theoretical specific capacity, which is insufficient to meet the development demands of high-energy-density batteries.

[0003] Silicon-based materials, with a theoretical specific capacity of approximately 4200 mAh / g, are considered highly promising next-generation lithium-ion battery anode active materials. However, in practical applications, silicon-based materials undergo drastic volume expansion and contraction during charge and discharge, with volume changes exceeding 300%. This easily leads to electrode structure pulverization, active material detachment, and instability at the electrode / electrolyte interface, resulting in rapid capacity decay and poor cycle performance. Furthermore, silicon-based materials are prone to side reactions with the electrolyte during the first charge and discharge cycle, forming an unstable solid electrolyte interphase (SEI) film that consumes a large amount of active lithium, resulting in low initial coulombic efficiency and severely limiting their practical application.

[0004] To improve the electrochemical performance of silicon-based anode materials, existing technologies typically employ methods such as carbon coating, structural design, or composite modification to modify the silicon-based materials. While these methods alleviate the volume effect and improve cycle performance to some extent, they still generally suffer from limited initial efficiency improvement and insufficient capacity retention over long cycles. In particular, after multiple charge-discharge cycles, the stability of the electrode structure remains difficult to maintain, making it challenging to meet the comprehensive performance requirements of high-performance lithium-ion batteries for anode materials.

[0005] Therefore, there is an urgent need for a modified silicon-based anode material that can effectively improve the initial coulombic efficiency of silicon-based active materials and maintain a high capacity retention rate after multiple cycles, so as to enhance its overall electrochemical performance and application value. Summary of the Invention

[0006] The purpose of this invention is to address the problems existing in the prior art by providing a graphene-coated lithium-ion battery anode material and its preparation method. This invention effectively improves the initial charge-discharge efficiency of the material through structural and interface optimization, and maintains a high capacity retention rate after multiple cycles, thereby significantly improving its electrochemical performance.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is: a graphene-coated lithium-ion battery anode material, wherein the anode material comprises the following components by mass parts:

[0008] Modified silicon-based active material: 30-60 parts;

[0009] Artificial graphite: 20-40 parts;

[0010] Graphene: 1-8 parts;

[0011] Amorphous carbon precursor: 5-20 parts;

[0012] Conductive carbon black: 1-5 parts;

[0013] Metal oxide additives: 0.5-5 parts;

[0014] Adhesive precursor: 1-10 parts;

[0015] The preparation method of the modified silicon-based active material includes the following steps:

[0016] (1) Pretreatment: Take nano-silicon powder with a particle size of 50-150nm, disperse it in a mixed solvent of ethanol and deionized water with a volume ratio of 4:1, add 20% polyvinylpyrrolidone relative to the mass of nano-silicon powder as a dispersant, disperse it by ultrasonication and then centrifuge and wash it; then soak it in HCl aqueous solution to obtain surface silanol groups, wash it with water until neutral and dry it.

[0017] (2) Aminoation: The dried nano-silicon was dispersed in anhydrous toluene, and 2%-3% of 3-aminopropyltriethoxysilane was added. The mixture was refluxed under nitrogen protection, centrifuged, washed and dried to obtain aminated nano-silicon.

[0018] (3) Activation: Dissolve the conductive additive in anhydrous N,N-dimethylformamide, add 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide to react and generate an active ester;

[0019] (4) Grafting: The aminated nano-silicon obtained in step (2) is added to the reaction system of step (3) and stirred to react, so that the small molecule conductive agent is anchored on the surface of the nano-silicon. After the reaction is completed, the unreacted material is washed away and dried to obtain the modified silicon-based active material.

[0020] The mass ratio of the nano-silicon powder, conductive additive, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride to N-hydroxysuccinimide is 100:(15-30):25:15.

[0021] The conductive additive is 4-(4,6-bis(4-(tert-butyl)phenyl)-1,3,5-triazine-2-yl)benzoic acid.

[0022] Furthermore, the chemical structural formula of the 4-(4,6-bis(4-(tert-butyl)phenyl)-1,3,5-triazin-2-yl)benzoic acid is as follows: .

[0023] Furthermore, the mechanism of action of the modified silicon-based active material is as follows: First, nano-silicon is fully dispersed in an ethanol / water system using PVP and then acid-treated to enrich -Si-OH sites on its surface, reducing agglomeration and providing reaction anchors for subsequent silanization; then, 3-aminopropyltriethoxysilane is used to form a siloxane bonding layer on the surface of the nano-silicon and introduce -NH2 functional groups, enabling the silicon particles to obtain a chemically coupled "functional interface"; then, EDC / NHS is used to activate the -COOH of the conductive additive to generate an active ester, which undergoes an amidation reaction with -NH2 on the silicon surface to achieve covalent grafting, thereby constructing a "conductive bridge / interface coupling" on the surface of the nano-silicon. The "layer" significantly reduces the contact resistance between silicon and the external carbon / graphite phase, improving the continuity of electron transport. On the other hand, it enhances the interfacial bonding strength between silicon and the subsequent coating phase and reduces interfacial peeling caused by charge-discharge volume effects. During the subsequent inert atmosphere heat treatment, the organic graft layer and the amorphous carbon precursor are co-carbonized and retained on the silicon surface as a tightly attached carbonized residue layer / doped carbon layer. This transforms the "chemical anchoring" into a more heat-resistant and stable interfacial conductive and shielding structure, reducing the exposure of the "fresh silicon" surface, suppressing repeated SEI cracking and regeneration and lithium consumption by side reactions, and ultimately achieving the first coulombic efficiency improvement and enhanced long-cycle structural stability.

[0024] Furthermore, the metal oxide additive is selected from one or more of magnesium oxide, aluminum oxide, titanium dioxide, and zinc oxide.

[0025] Furthermore, the binder precursor is selected from one or more of polyvinyl alcohol, sucrose, and carboxymethyl cellulose.

[0026] Furthermore, the graphene is a single-layer or few-layer graphene, with 1-10 layers and a specific surface area of ​​200-1000 m². 2 / g.

[0027] Furthermore, the amorphous carbon precursor is selected from one or more of glucose, sucrose, pitch, and polyacrylonitrile.

[0028] A method for preparing a graphene-coated lithium-ion battery anode material includes the following steps:

[0029] 1) The modified silicon-based active material, artificial graphite, conductive carbon black and metal oxide additives are mixed in proportion and ball-milled to obtain a first mixture;

[0030] 2) The graphene is dispersed in a solvent and a stable graphene dispersion is formed by ultrasonic or high-speed shearing.

[0031] 3) Add the first mixture to the graphene dispersion, stir and mix, and dry to obtain the graphene composite precursor;

[0032] 4) Add the amorphous carbon precursor and binder precursor to the graphene composite precursor, mix them evenly, and then perform heat treatment to obtain graphene-coated lithium-ion battery anode material.

[0033] Furthermore, in step 1), the ball milling time is 2-10 hours, and the ball-to-material ratio is 5:1-15:1.

[0034] Furthermore, the solvent in step 2) is one or more of deionized water, ethanol, or N-methylpyrrolidone.

[0035] Furthermore, the heat treatment in step 4) is carried out under an inert atmosphere at a temperature of 600-1000℃ for 1-5 hours.

[0036] Furthermore, the concentration of the graphene dispersion is 0.1-5 mg / mL.

[0037] Furthermore, the heating rate in step 4) is 1-10℃ / min, and it is carried out under a nitrogen atmosphere.

[0038] The formulation of this invention addresses the technical problems of silicon-based anode volume expansion leading to structural pulverization / detachment, interface (SEI) instability causing rapid capacity decay, and low initial coulombic efficiency through the synergistic combination of a chemically anchored silicon-based high-capacity core, a multi-scale carbon / graphite conductive framework, and a stable interface and buffer structure. First, the anode is primarily composed of modified silicon-based active materials, compounded with artificial graphite, graphene, amorphous carbon precursors, conductive carbon black, metal oxide additives, and binder precursors, balancing high capacity with overall electrode structure and conductivity. The modified silicon-based active material, by introducing reactive functional groups onto the silicon surface and covalently grafting conductive additives, constructs a "conductive bridge / interface coupling layer," which reduces the contact resistance between silicon and the external carbon / graphite phase, improves electron transport continuity, and enhances the interfacial bonding strength between silicon and the subsequent coating phase, thereby mitigating interface peeling caused by charge / discharge volume effects. Subsequently, an inert... During the heat treatment process, the grafted layer and the amorphous carbon precursor are co-carbonized to form a tightly adhered carbonized residual layer / doped carbon layer on the silicon surface. This reduces the exposure of "fresh silicon" and inhibits repeated SEI breakage and regeneration, as well as lithium consumption from side reactions. This fundamentally improves the initial coulombic efficiency and enhances the structural stability during long cycles. At the same time, artificial graphite, as a relatively stable lithium intercalation framework, can dilute the drastic volume changes of silicon and improve the uniformity of electrode forming. Graphene (single / few layers, high specific surface area) and conductive carbon black work together to build a flexible and continuous conductive network, which bridges the silicon particles and disperses stress. Metal oxide additives and binder precursors further improve the interparticle adhesion and electrode framework stability, and reduce the risk of structural damage during cycling. Thus, while addressing the problem of "volume change >300% leading to interface instability, capacity decay and low initial efficiency" in silicon-based materials, it achieves a simultaneous improvement in initial efficiency and cycle capacity retention.

[0039] Compared with the prior art, the beneficial effects of the present invention are:

[0040] 1. By constructing a “conductive bridge / interface coupling layer” on the silicon surface and forming a more stable carbonized interface shielding layer in subsequent heat treatment, the exposure of “fresh silicon” and side reactions are reduced, and the repeated cracking and regeneration of SEI are suppressed, thereby improving the efficiency of the first cycle.

[0041] 2. The stable framework of artificial graphite "dilutes / buffers" the volume effect of silicon. Graphene and carbon black build a flexible and continuous conductive network and disperse stress. Combined with metal oxides and a binding system, it enhances the adhesion between particles and the strength of the electrode framework, reducing pulverization / detachment during cycling and maintaining better overall long-term performance.

[0042] 3. Covalent grafting results in lower contact resistance and a more continuous electron transport path. At the same time, a more stable interface / SEI makes the charge transfer impedance deteriorate more slowly with cycling, resulting in a smaller impedance increase. Attached Figure Description

[0043] Figure 1 This is a SEM scan image of a graphene-coated lithium-ion battery anode material prepared in Example 1 of the present invention.

[0044] Figure 2 This is an X-ray photoelectron spectroscopy (XPS) image of a graphene-coated lithium-ion battery anode material prepared in Example 1 of the present invention. Detailed Implementation

[0045] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0046] Preparation Example 1

[0047] Preparation of conductive additives:

[0048] A three-necked flask equipped with a mechanical stirrer, thermometer, and constant-pressure dropping funnel was purged with nitrogen three times. Under a nitrogen flow, 5g of 2,4,6-trichloro-1,3,5-triazine (TCT) and 50ml of anhydrous DCM were added sequentially. The temperature was lowered to -5℃, and 8.68g of anhydrous aluminum trichloride was slowly added, keeping the temperature below 5℃, and the mixture was stirred for 30min. 7.64g of tert-butylbenzene was dissolved in 20ml of anhydrous DCM and slowly added dropwise to the above system, keeping the temperature below 0℃. After the addition was complete, the mixture was allowed to rise naturally to room temperature and stirred for 4h. After the reaction was completed, the reaction solution was slowly poured into a mixture of 150 mL ice water and 15 mL concentrated hydrochloric acid under vigorous stirring, and the temperature was controlled not to exceed 20 °C. The mixture was stirred for 10 min. The organic phase was separated, and the aqueous phase was extracted with DCM (20 mL × 2). The organic phases were combined. The mixture was washed successively with 1 M HCl aqueous solution, 100 mL saturated NaHCO3 aqueous solution, and 100 mL saturated saline solution, ensuring that the pH of the last water wash was neutral. The organic phase was dried with anhydrous sodium sulfate and evaporated to dryness to obtain the crude product. The crude product was purified by silica gel column chromatography, eluted with ethyl acetate / n-heptane (1:3), and evaporated to dryness to obtain 7.79 g of 2,4-bis(4-(tert-butyl)phenyl)-6-chloro-1,3,5-triazine.

[0049] A three-necked flask equipped with a mechanical stirrer, thermometer, and constant-pressure dropping funnel was purged with nitrogen three times. Under a nitrogen flow, 7.79 g of 2,4-bis(4-(tert-butyl)phenyl)-6-chloro-1,3,5-triazine, 4.08 g of 4-carboxyphenylboronic acid, and 60 ml of 1,4-dioxane were added sequentially. The mixture was bubbled with nitrogen for 10 min to remove oxygen. Then, 30 ml of water, 6.52 g of sodium carbonate, and 0.71 g of tetraphenylphosphine palladium were added. The mixture was bubbled with nitrogen for 10 min to remove oxygen. After stirring until homogeneous, the mixture was reacted at 105 °C for 16 h under a continuous nitrogen flow. The reaction solution was cooled to room temperature and filtered through a diatomaceous earth pad. The filter cake was washed with 20 ml of hot EtOAc at 60°C. The filtrate was concentrated under reduced pressure, leaving mainly an aqueous phase. Water (50 mL) was added to dilute the residue. Under stirring, 2 M HCl aqueous solution was slowly added dropwise to adjust the pH to 3-4. The mixture was then directly filtered. The filter cake was washed with water until neutral and then washed with 10 ml of cold ethanol to remove impurities. The filter cake was dried to obtain the crude product. The crude product was dissolved in 30 ml of toluene at 80°C and stirred for 1 h. The mixture was filtered while hot, and the filtrate was allowed to stand at 4°C for 4 h. After filtration and drying, 7.22 g of 4-(4,6-bis(4-(tert-butyl)phenyl)-1,3,5-triazine-2-yl)benzoic acid was obtained.

[0050] Mass spectrum of 4-(4,6-bis(4-(tert-butyl)phenyl)-1,3,5-triazin-2-yl)benzoic acid: m / z 466 M+1;

[0051] NMR (CDCl3) of 4-(4,6-bis(4-(tert-butyl)phenyl)-1,3,5-triazin-2-yl)benzoic acid:

[0052] δ7.86-7.60(m,5H),7.60-7.48(m,4H),7.44-7.28(m,3H),1.31(s,18H).

[0053] Preparation Example 2

[0054] Preparation of modified silicon-based active materials:

[0055] (1) Pretreatment: Weigh 10.0g of nano-silicon powder with a particle size of 80-120nm, add it to 200mL of a mixed solvent of ethanol and deionized water with a volume ratio of 4:1, and then add 2.0g of polyvinylpyrrolidone as a dispersant. Disperse under ultrasonic conditions of 300W for 30min to obtain a uniform dispersion. Place the dispersion in a high-speed centrifuge and centrifuge at 8000r / min for 15min. Collect the precipitate and wash it 3 times with ethanol. Add the washed precipitate to 100mL of 1mol / L HCl aqueous solution and soak it at room temperature for 2h to enrich silanol groups (-Si-OH) on the surface of nano-silicon. Then wash it repeatedly with deionized water until the pH of the washing solution is neutral. Place the product in a vacuum drying oven at 80℃ and dry it for 12h to obtain pretreated nano-silicon.

[0056] (2) Aminoation: Take 10.0 g of the pretreated nano-silicon after drying and disperse it in 200 mL of anhydrous toluene. Sonicate the dispersion for 10 min to form a stable suspension. Add 5.0 mL of 2.5% 3-aminopropyltriethoxysilane to the suspension. Heat the mixture to 110 °C under nitrogen protection and reflux for 6 h. After the reaction is completed, cool to room temperature and centrifuge at 10000 r / min for 20 min. Collect the solid product, wash it 3 times with anhydrous toluene and 2 times with ethanol, and then dry it in a vacuum drying oven at 80 °C for 4 h to obtain aminated nano-silicon.

[0057] (3) Activation: Weigh 2.0g of conductive additive 4-(4,6-bis(4-(tert-butyl)phenyl)-1,3,5-triazine-2-yl)benzoic acid, add it to 100mL of anhydrous N,N-dimethylformamide (DMF), stir to dissolve, then add 2.5g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) and 1.5g of N-hydroxysuccinimide (NHS) in sequence. Stir and react for 2h under nitrogen protection and room temperature to activate the carboxyl group (-COOH) in the conductive additive molecule to generate an active ester, and obtain the activated reaction solution;

[0058] (4) Grafting: 10.0g of aminated nano-silicon prepared in step (2) is slowly added to the activation reaction solution in step (3). The reaction is continuously stirred for 12h under nitrogen protection and room temperature conditions. The conductive additive is covalently grafted onto the surface of the aminated nano-silicon through amidation reaction. After the reaction is completed, the solid product is centrifuged at 12000r / min for 25min. The solid product is collected and washed twice with anhydrous DMF, twice with ethanol, and twice with deionized water to remove unreacted conductive additive, EDC and NHS. The washed product is placed in a vacuum drying oven at 80℃ and dried for 12h to obtain the modified silicon-based active material.

[0059] Comparative Preparation Example 1

[0060] The modified silicon-based active material was prepared by referring to the preparation method of Preparation Example 2, except that the conductive additive was replaced with benzoic acid, and the rest remained the same as in Preparation Example 2.

[0061] Comparative Preparation Example 2

[0062] The modified silicon-based active material was prepared by referring to the preparation method of Preparation Example 2, except that the conductive additive was replaced with quinoline-6-carboxylic acid, and the rest remained the same as in Preparation Example 2. Example 1

[0063] Preparation of a graphene-coated lithium-ion battery anode material:

[0064] 1. Raw material components by weight:

[0065] Modified silicon-based active material: 45 parts (using the modified silicon-based active material prepared in Preparation Example 2);

[0066] Artificial graphite: 30 parts (particle size 10-20μm);

[0067] Graphene: 3 parts (2-3 layers, specific surface area 400-600 m²) 2 / g);

[0068] Amorphous carbon precursor: 12 parts (glucose is selected);

[0069] Conductive carbon black: 2 parts;

[0070] Metal oxide additive: 1.5 parts (alumina is selected);

[0071] Adhesive precursor: 6.5 parts (polyvinyl alcohol is selected).

[0072] 2. Preparation method:

[0073] 1) Preparation of the first mixture: Weigh the modified silicon-based active material, artificial graphite, conductive carbon black and alumina according to the above mass proportions, put them into the ball mill jar of the planetary ball mill, select agate balls as the ball milling medium, control the ball-to-material ratio to be 10:1, and continue ball milling for 4 hours at a speed of 300 r / min. Nitrogen gas is introduced during the ball milling process to protect the material from oxidation. After the ball milling is completed, the product is collected to obtain a uniformly mixed first mixture.

[0074] 2) Preparation of graphene dispersion: Weigh 3 parts of graphene and add them to 3000 mL of deionized water. Use an ultrasonic device with a power of 300W to ultrasonically disperse the graphene for 60 min. Stir once every 15 min during the process to ensure that the graphene is fully dispersed and form a stable graphene dispersion with a concentration of 1 mg / mL.

[0075] 3) Preparation of graphene composite precursor: The first mixture obtained in step 1) is slowly added to the graphene dispersion in step 2), and mechanically stirred for 2 hours at room temperature and 500 r / min to ensure that the first mixture and the graphene dispersion are fully mixed; then the mixture is placed in a vacuum drying oven at 80℃ and dried for 12 hours to remove the solvent and obtain the dried graphene composite precursor.

[0076] 4) Heat treatment to prepare the target product: Add 12 parts by mass of glucose and 6.5 parts by mass of polyvinyl alcohol to the graphene composite precursor obtained in step 3), place it in a high-speed mixer, and mix for 30 minutes at a speed of 800 r / min to ensure uniform dispersion of each component; load the mixed material into a quartz boat, place it in a tube furnace, use nitrogen as a protective atmosphere, control the heating rate at 5℃ / min, raise the furnace temperature to 800℃, and hold at this temperature for 3 hours for heat treatment; after heat treatment, allow the furnace to cool naturally to room temperature, remove the product, crush it, and pass it through a 200-mesh sieve to obtain graphene-coated lithium-ion battery anode material. Example 2

[0077] Preparation of a graphene-coated lithium-ion battery anode material:

[0078] 1. Raw material components by weight:

[0079] Modified silicon-based active material: 30 parts (same as Example 1);

[0080] Artificial graphite: 20 parts (same as Example 1);

[0081] Graphene: 1 part (same as in Example 1);

[0082] Amorphous carbon precursor: 5 parts (same as Example 1);

[0083] Conductive carbon black: 1 part;

[0084] Metal oxide additive: 0.5 parts (same as in Example 1);

[0085] Adhesive precursor: 1 part (same as in Example 1).

[0086] 2. The preparation method is the same as that in Example 1. Example 3

[0087] Preparation of a graphene-coated lithium-ion battery anode material:

[0088] 1. Raw material components by weight:

[0089] Modified silicon-based active material: 60 parts (same as Example 1);

[0090] Artificial graphite: 40 parts (same as Example 1);

[0091] Graphene: 8 parts (same as Example 1);

[0092] Amorphous carbon precursor: 20 parts (same as Example 1);

[0093] Conductive carbon black: 5 parts;

[0094] Metal oxide additive: 5 parts (same as in Example 1);

[0095] Adhesive precursor: 10 parts (same as Example 1).

[0096] 2. The preparation method is the same as that in Example 1.

[0097] Comparative Example 1

[0098] The preparation of a graphene-coated lithium-ion battery anode material is carried out by referring to the preparation method of Example 1, except that the modified silicon-based active material is replaced with the modified silicon-based active material prepared in Comparative Preparation Example 1, and the rest is the same as in Example 1.

[0099] Comparative Example 2

[0100] The preparation of a graphene-coated lithium-ion battery anode material is carried out by referring to the preparation method of Example 1, except that the modified silicon-based active material is replaced with the modified silicon-based active material prepared in Comparative Preparation Example 2, and the rest is the same as in Example 1.

[0101] Comparative Example 3

[0102] The preparation of a graphene-coated lithium-ion battery anode material is carried out by referring to the preparation method of Example 1, except that the modified silicon-based active material is replaced with nano-silicon powder with a particle size of 80-120nm, and the rest is the same as in Example 1.

[0103] Comparative Example 4

[0104] The preparation of a graphene-coated lithium-ion battery anode material is carried out according to the preparation method of Example 1, except that the amorphous carbon precursor is not added, and the rest is the same as in Example 1.

[0105] Performance testing:

[0106] 1. Sample Preparation: The active material (the negative electrode material of this invention), conductive carbon black (SuperP), and binder (polyvinylidene fluoride, PVDF) were mixed at a mass ratio of 8:1:1. N-methylpyrrolidone (NMP) solvent was added, and the mixture was stirred for 6 hours to form a uniform slurry. The slurry was coated onto the surface of a copper foil (10 μm thick) using a doctor blade, with the wet film thickness controlled at 100 μm. After standing at room temperature for 12 hours, the film was dried in a vacuum drying oven at 80℃ for 12 hours to remove the solvent. The film was then rolled at a pressure of 5 MPa using a roller press and cut into circular electrode sheets with a diameter of 14 mm. The mass load of the electrode sheets was controlled at 1.0 ± 0.1 mg / cm². 2 Before use, dry in an 80℃ vacuum drying oven for 4 hours (to remove residual moisture).

[0107] Half-cell assembly: In an argon glove box (O2 content < 0.1 ppm, H2O content < 0.1 ppm), the prepared electrode sheet was used as the working electrode, the lithium metal sheet (thickness 500 μm, diameter 16 mm) was used as the counter electrode, Celgard 2400 was used as the separator, and 1 mol / L LiPF6 / EC+DMC+EMC (volume ratio 1:1:1) was used as the electrolyte; CR2032 coin cell half-cells were assembled, and electrochemical tests were performed after standing for 24 h (ensuring that the electrolyte fully wetted the electrodes).

[0108] 2. Initial charge / discharge capacity and initial coulombic efficiency test:

[0109] The Blue Electric CT2001A battery testing system was used at room temperature, with a voltage range of 0.01-1.5V (vs. Li). + / Li), current density 0.1C (calculated based on the theoretical specific capacity of silicon 4200mAh / g, i.e., current density = 420mA / g); first constant current discharge (lithium insertion) to 0.01V, then constant current charging (lithium extraction) to 1.5V, and record the capacity data during the charging and discharging process;

[0110] Calculation method:

[0111] Initial discharge specific capacity (mAh / g) = total initial discharge capacity / mass of active material in the electrode;

[0112] First charge specific capacity (mAh / g) = First charge total capacity / Mass of active material in electrode;

[0113] Initial coulombic efficiency (%) = (initial charge specific capacity / initial discharge specific capacity) × 100%, as shown in Table 1.

[0114] 3. Cyclic stability test

[0115] The Blue Electric CT2001A battery testing system was used at room temperature, with a voltage range of 0.01-1.5V (vs. Li). + / Li), cyclic current density 0.2C; 200 consecutive cycles, record the discharge specific capacity of each charge and discharge cycle;

[0116] Calculation method: Capacity retention rate of the 200th cycle (%) = (Specific capacity of the 200th discharge / Specific capacity of the 2nd discharge) × 100% (based on the 2nd cycle), and the data is shown in Table 1.

[0117] 4. Electrochemical Impedance Spectroscopy (EIS) Test

[0118] The CHI660E electrochemical workstation was used at room temperature, with a test frequency range of 100kHz-0.01Hz and an AC signal amplitude of 5mV. The test conditions were after the battery had been allowed to stabilize (tested before and after 50 cycles). The impedance spectrum was fitted using ZView software to extract the charge transfer impedance (Rct) and SEI film impedance (Rsei). The changes in Rct before and after cycling were compared. The smaller the increase in Rct, the better the conductivity and stability of the material interface. The data are shown in Table 1.

[0119] Table 1

[0120]

[0121] As shown in Table 1, when the anode system simultaneously possesses a "chemically anchored" silicon interface and a "multi-scale carbon network / coating," electron transport is smoother, the contact resistance between silicon and carbon phases is lower, and the carbonized residual layer / doped carbon layer reduces the exposure of the "fresh silicon" surface, suppresses repeated SEI rupture and regeneration, and inhibits lithium consumption by side reactions. Therefore, the irreversible reaction in the first cycle is suppressed, resulting in a higher first efficiency. At the same time, the flexible conductive framework of graphene and the stable lithium intercalation framework of artificial graphite together "dilute and buffer" the stress concentration caused by the >300% volume change of silicon. Combined with the metal oxide and binder precursor to enhance the adhesion between particles and the overall strength of the electrode framework, the structure is less prone to pulverization / detachment during cycling, and the interface is more stable, resulting in better long-cycle retention. The same mechanism is also reflected in the impedance evolution—a more stable interface and a denser SEI that does not repeatedly thicken result in a smaller increase in charge transfer impedance. Conversely, removing any one of these key components makes the silicon surface more susceptible to continuous exposure and side reactions, the SEI more prone to cracking and regeneration, and the electrical contact between particles more prone to deterioration. Consequently, the initial efficiency deteriorates, cycle decay accelerates, and impedance increases more significantly. Among these, the "unmodified silicon" exhibits the worst overall performance due to its weak interfacial bonding and the most severe volume effect.

[0122] 5. Scanning electron microscope (SEM):

[0123] SEM scanning imaging was performed on a graphene-coated lithium-ion battery anode material prepared in Example 1, as shown below. Figure 1As shown, the electrode material exhibits a composite structure dominated by micron-sized secondary particles, with relatively regular particle morphology and rough surfaces. Nanoscale silicon-based active materials are uniformly distributed and fixed on the surface of a graphite / carbon-based framework. The outer layer of the particles is coated with a continuous carbon layer structure, and locally a conductive network composed of graphene and amorphous carbon can be formed, effectively enhancing the connectivity between particles. This multi-scale composite structure helps alleviate the volume expansion of silicon-based materials during charging and discharging, improving the structural stability and electronic conductivity of the material. This indicates that the preparation method described in this invention can achieve effective coating and uniform composite of silicon-based active materials, resulting in a material with stable morphology and a reasonable structure.

[0124] 6. X-ray photoelectron spectroscopy (XPS) test:

[0125] X-ray photoelectron spectroscopy (XPS) was performed on the graphene-coated lithium-ion battery anode material prepared in Example 1. The spectrum is shown below. Figure 2 As shown in the figure. The results indicate that the sample surface is mainly composed of elements such as C, Si, O, and Al. A distinct C 1s characteristic peak appears at approximately 284.8 eV in the full spectrum, indicating that the material surface is rich in carbon components, originating from graphene, amorphous carbon coatings, and conductive carbon black. The Si 2p peak is located in the range of approximately 99-104 eV, indicating that silicon exists in Si and its oxidation state. The appearance of the O 1s peak corresponds to Si-O, CO, and Al-O bonds in metal oxides. The Al 2p signal confirms the presence of metal oxide additives. High-resolution spectral fitting of each element shows that the C 1s spectrum contains components such as CC / C=C, CO, and C=O; the Si 2p spectrum simultaneously contains Si-Si and Si-O bonds; and the O 1s spectrum can be decomposed to reveal characteristic peaks of Si-O, CO, and Al-O, indicating that a stable carbon coating and interfacial bonding structure has formed on the surface of the silicon-based active material. The above results demonstrate that the components in the negative electrode material prepared by this invention are successfully composited, and the surface of the silicon-based active material is modified to form a stable interface with the carbon phase and additives, which is beneficial to improving the structural stability and electrochemical performance of the material.

[0126] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A graphene-coated lithium-ion battery anode material, characterized in that, Its preparation method includes the following steps: 1) Mix 30-60 parts of modified silicon-based active material, 20-40 parts of artificial graphite, 1-5 parts of conductive carbon black and 0.5-5 parts of metal oxide additive in a certain proportion, and then ball mill them to obtain the first mixture; 2) Disperse 1-8 parts of graphene in a solvent and form a stable graphene dispersion by ultrasonic or high-speed shearing. 3) Add the first mixture to the graphene dispersion, stir and mix, and dry to obtain the graphene composite precursor; 4) Add 5-20 parts of amorphous carbon precursor and 1-10 parts of binder precursor to the graphene composite precursor, mix evenly and then perform heat treatment to obtain graphene-coated lithium-ion battery anode material. The heat treatment in step 4) is carried out in an inert atmosphere at a temperature of 600-1000℃ for 1-5 hours. The preparation method of the modified silicon-based active material includes the following steps: (1) Pretreatment: Take nano-silicon powder with a particle size of 50-150nm, disperse it in a mixed solvent of ethanol and deionized water with a volume ratio of 4:1, add 20% polyvinylpyrrolidone relative to the mass of nano-silicon powder as a dispersant, disperse it by ultrasonication and then centrifuge and wash it; then soak it in HCl aqueous solution to obtain surface silanol groups, wash it with water until neutral and dry it. (2) Aminoation: The dried nano-silicon was dispersed in anhydrous toluene, and 2%-3% of 3-aminopropyltriethoxysilane was added. The mixture was refluxed under nitrogen protection, centrifuged, washed and dried to obtain aminated nano-silicon. (3) Activation: Dissolve the conductive additive in anhydrous N,N-dimethylformamide, add 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide to react and generate an active ester; (4) Grafting: The aminated nano-silicon obtained in step (2) is added to the reaction system of step (3) and stirred to react, so that the small molecule conductive agent is anchored on the surface of the nano-silicon. After the reaction is completed, the unreacted material is washed away and dried to obtain the modified silicon-based active material. The mass ratio of the nano-silicon powder, conductive additive, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride to N-hydroxysuccinimide is 100:(15-30):25:

15. The conductive additive is 4-(4,6-bis(4-(tert-butyl)phenyl)-1,3,5-triazine-2-yl)benzoic acid.

2. The graphene-coated lithium-ion battery anode material according to claim 1, characterized in that, The metal oxide additive is selected from one or more of magnesium oxide, aluminum oxide, titanium dioxide, and zinc oxide.

3. The graphene-coated lithium-ion battery anode material according to claim 1, characterized in that, The binder precursor is selected from one or more of polyvinyl alcohol, sucrose, and carboxymethyl cellulose.

4. The graphene-coated lithium-ion battery anode material according to claim 1, characterized in that, The graphene is a single-layer or few-layer graphene, with 1-10 layers and a specific surface area of ​​200-1000 m². 2 / g.

5. The graphene-coated lithium-ion battery anode material according to claim 1, characterized in that, The amorphous carbon precursor is selected from one or more of glucose, sucrose, pitch, and polyacrylonitrile.

6. The graphene-coated lithium-ion battery anode material according to claim 1, characterized in that, In step 1), the ball milling time is 2-10 hours, and the ball-to-material ratio is 5:1-15:

1. The solvent in step 2) is one or more of deionized water, ethanol, or N-methylpyrrolidone.

7. The graphene-coated lithium-ion battery anode material according to claim 1, characterized in that, The concentration of the graphene dispersion is 0.1-5 mg / mL; The heating rate in step 4) is 1-10℃ / min, and it is carried out under a nitrogen atmosphere.

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