High-rate graphite negative electrode material and preparation method thereof

Abstract

The application relates to the technical field of sodium ion batteries, in particular to a high-rate graphite negative electrode material and a preparation method thereof, which comprises the following steps: mixing a graphite dispersion liquid and a graphene oxide dispersion liquid, carrying out ultrasonic treatment and drying to obtain a graphite compound; dispersing the graphite compound in an aqueous solution containing sodium styrenesulfonate, acrylamide and ethylene glycol diacrylate, adding an initiator, stirring and reacting by controlling the temperature, and carrying out post-treatment to obtain the high-rate graphite negative electrode material. The high-rate graphite negative electrode material prepared by adding graphene oxide and polymer coating has obvious advantages in electrochemical performance, has high high-rate charge-discharge performance, good cycle stability, high initial coulomb efficiency, a large sodium ion diffusion coefficient and small electrochemical impedance.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, and in particular to a high-rate graphite anode material and its preparation method. Background Technology

[0002] Lithium-ion batteries, as a mature electrochemical energy storage system, have dominated fields such as portable electronic devices. However, the limited reserves and high cost of lithium resources restrict their application in large-scale energy storage systems. In contrast, sodium-ion batteries, due to the abundance, wide distribution, and low cost of sodium resources, are considered a potential alternative to lithium-ion batteries in large-scale energy storage. However, the radius of sodium ions is much larger than that of lithium ions, resulting in slow insertion / extraction kinetics in electrode materials, directly limiting the rate performance of the battery. Therefore, developing efficient and fast sodium storage anode materials is crucial. Graphite possesses a highly ordered layered structure, excellent electronic conductivity, and good structural stability. Its regular carbon layers can provide diffusion channels for sodium ions. By controlling the interlayer spacing, introducing defects, or surface modification, the sodium storage capacity and reaction kinetics can be further improved, making it an important foundation for constructing high-rate, long-cycle sodium-ion battery anode systems. Furthermore, although graphite has been commercially applied in lithium-ion batteries, due to the large radius of sodium ions and unfavorable thermodynamic factors, it is difficult to form stable intercalation compounds in traditional electrolytes, resulting in poor sodium storage performance.

[0003] Patent publication number CN114229914A discloses a method for preparing a graphene-based sodium-ion battery anode material. The method includes: first, dispersing graphene oxide in anhydrous ethanol and ultrasonically treating it at a certain temperature to form a graphene oxide alcohol dispersion; then preparing a sodium hexanitrocobaltate solution and adding the aforementioned graphene oxide alcohol dispersion to it, allowing solid precipitation through alcohol precipitation, followed by solid-liquid separation to obtain a solid; subsequently, calcining the solid under oxygen-free conditions, and finally washing and drying to obtain the graphene-based sodium-ion battery anode material. This method utilizes the abundant nitro groups in sodium hexanitrocobaltate to achieve nitrogen doping of graphene oxide, while simultaneously introducing cobalt monoxide, thereby effectively improving the specific capacity and cycle performance of the material.

[0004] However, sodium ions face a high diffusion barrier and slow migration rate within the narrow interlayers of graphite. This prevents them from rapidly penetrating the graphite structure during high-current-density charge-discharge cycles, leading to severe polarization and a sharp decrease in capacity. In most conventional carbonate-based electrolytes, sodium ions tend to co-intercalate with solvent molecules within the graphite layers. This process triggers dramatic expansion, peeling, and even pulverization of the electrode structure, resulting in extremely low initial cycle coulombic efficiency and rapid capacity decay. Summary of the Invention

[0005] To address the problems mentioned in the background section, this invention provides a high-rate graphite anode material and its preparation method.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a high-rate graphite anode material includes the following steps: S1. The graphite dispersion and the graphene oxide dispersion are mixed, and then subjected to ultrasonic treatment and drying to obtain the graphite composite. S2. The graphite composite is dispersed in an aqueous solution containing sodium styrene sulfonate, acrylamide and ethylene glycol diacrylate, an initiator is added, the temperature is controlled and the reaction is stirred, and after post-treatment, a high-rate graphite anode material is obtained.

[0007] Further, in step S1, the mass ratio of graphite to graphene oxide is 1:(0.05-0.15), the concentration of the graphene oxide aqueous dispersion is 1.5-2.5 mg / mL, and the concentration of the graphite dispersion is 4-6 mg / mL. The graphene oxide dispersion is prepared by mixing graphene oxide powder with deionized water and dispersing it by ultrasonication at 200-300W power for 0.3-0.5 h. The graphite dispersion is prepared by mixing natural or artificial graphite raw materials with deionized water and stirring at a stirring rate of 150-200 rpm for 0.5-1 h, and its particle size D50 is 10-100 μm.

[0008] Furthermore, in step S1, the ultrasonic treatment is carried out under ice-water bath conditions at 0-5℃, the ultrasonic power is 250-350W, and the ultrasonic time is 0.5-1.5h.

[0009] Further, in step S2, the mass ratio of sodium styrene sulfonate, acrylamide, and ethylene glycol diacrylate is (3-5):(4-6):(0.5-1.5), and the total mass of sodium styrene sulfonate, acrylamide, and ethylene glycol diacrylate accounts for 30-50% of the mass of the graphite composite. In this case, deionized water is used as the solvent in the aqueous solution, and sodium styrene sulfonate, acrylamide, and ethylene glycol diacrylate are added to the deionized water in proportion.

[0010] Furthermore, in step S2, the initiator is selected from ammonium persulfate, and its amount is 3-7% of the total mass of sodium styrene sulfonate, acrylamide, and ethylene glycol diacrylate. The initiator is added in the form of an aqueous solution with a concentration of 3-5 mg / mL. The initiator aqueous solution is prepared by mixing solid ammonium persulfate with deionized water and stirring at a stirring speed of 180-220 rpm for 20-30 min until completely dissolved, and is used immediately after preparation.

[0011] Furthermore, the conditions for controlling the temperature and stirring reaction in step S2 are as follows: under the protection of an inert gas, the reaction temperature is controlled at 65-75℃, the stirring rate is 200-300rpm, and the reaction time is 4-10h. The inert gas is selected from one or more of nitrogen and argon, preferably nitrogen. The inert gas introduction rate is 50-100mL / min, the reaction temperature is preferably 68-72℃, the stirring rate is preferably 220-280rpm, and the reaction time is preferably 6-8h.

[0012] Further, the post-processing in step S2 includes washing and drying, specifically: after the reaction is completed, the product is cooled to room temperature, and washed 2-4 times by alternating centrifugation with deionized water and anhydrous ethanol. The centrifugation speed is 8000-10000 rpm, the centrifugation temperature is controlled at 0-5℃, and the centrifugation time is 10-15 min each time. The order of washing with deionized water and anhydrous ethanol is: first wash with deionized water, then wash with anhydrous ethanol, and so on. During each wash, the solid-liquid ratio is 1:10-1:15 (g / mL). After centrifugation, the supernatant is poured off, and the precipitate is retained. After washing, the product is placed in a vacuum oven at 75-85℃ and dried for 20-28 h. After drying, it is pulverized and passed through a 200-mesh sieve.

[0013] According to another aspect of the present invention, a high-rate graphite anode material prepared by the above preparation method is provided, wherein the high-rate graphite anode material has a particle size of 5-20 μm, a specific surface area of ​​10-30 m² / g, and a bulk density of 0.8-1.2 g / cm³.

[0014] According to another aspect of the present invention, a sodium-ion battery is provided, comprising a positive electrode, a separator, an electrolyte, and a negative electrode, wherein the negative electrode is the high-rate graphite negative electrode material prepared above; the electrolyte is a carbonate-based electrolyte containing sodium salt, wherein the sodium salt is selected from one or more of sodium hexafluorophosphate, sodium perchlorate, and sodium tetrafluoroborate, the electrolyte concentration is 0.8-1.2 mol / L, and the carbonate solvent in the electrolyte is selected from one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate, preferably ethylene carbonate and... Dimethyl carbonate is mixed in a volume ratio of 1:1 to 1:2; the separator is a polyolefin separator, which is selected from polypropylene separators and polyethylene separators, with a separator thickness of 10-20 μm and a porosity of 40-60%; the positive electrode is selected from one or more of layered oxides and polyanionic compounds, with the layered oxide positive electrode selected from one or more of NaNiO2 and NaFeO2, and the polyanionic compound positive electrode selected from one or more of Na3V2(PO4)3 and Na2FePO4F.

[0015] The beneficial effects of this invention are: 1. This invention involves mixing a graphite dispersion with a graphene oxide dispersion, followed by ultrasonic treatment to uniformly disperse and insert graphene oxide sheets into the graphite interlayers, simultaneously achieving surface coating. After drying, a graphite composite is formed, constructing a composite structure of graphite core and graphene oxide intercalation phase. The two-dimensional sheet structure of graphene oxide effectively widens the originally narrow interlayer space of graphite, reduces the diffusion barrier of sodium ions in the bulk phase, and accelerates the migration rate of sodium ions. The oxygen-containing functional groups on its surface can serve as surface active sites, forming a synergistic effect with the intrinsic intercalation sodium storage mechanism of the graphite matrix. This helps optimize the sodium storage reaction kinetics, alleviates the polarization phenomenon caused by slow sodium ion diffusion during high current density charging and discharging, reduces capacity decay, and improves the poor sodium storage performance of traditional graphite.

[0016] 2. In this invention, a graphite composite is dispersed in an aqueous solution containing sodium styrene sulfonate, acrylamide, and ethylene glycol diacrylate. An initiator is added, and the reaction is carried out under controlled temperature and stirring. A three-dimensional covalently cross-linked hydrophilic polymer shell phase is formed on the surface and interlayer edges of the graphite composite through free radical polymerization. The hydrophilic functional groups such as sulfonic acid groups and amide groups contained in this polymer shell phase can optimize the wettability between the electrode and the carbonate electrolyte, reduce interfacial contact resistance, and accelerate interfacial charge transfer. The negatively charged sulfonic acid groups can enrich sodium ions in the electrolyte through electrostatic interaction, further improving interfacial ion transport efficiency. Simultaneously, the three-dimensionally covalently cross-linked polymer network has good structural stability and viscoelasticity, which can buffer the volume stress generated during sodium ion intercalation / deintercalation, reduce the co-intercalation phenomenon of sodium ions and solvent molecules, and inhibit the expansion, peeling, or pulverization of the electrode structure. Furthermore, the polymer shell phase can isolate the active sites of the electrolyte and the graphite composite, regulate the growth of the solid electrolyte interfacial film, and form a thin and stable interfacial film, which helps improve the initial cycle coulombic efficiency of the material and slow down the rate of capacity decay.

[0017] 3. In this invention, the graphene oxide sheets form a continuous conductive network between graphite particles, which can reduce the contact resistance between particles and improve the overall electronic conduction efficiency of the electrode. Meanwhile, the cross-linked polymer shell phase optimizes the ion transport environment. The synergistic effect of the two achieves a good match between electronic conduction and ion transport rates, further improving the polarization problem at high rates. At the same time, the graphene oxide intercalation phase anchors the graphite sheets through weak interactions, inhibiting interlayer delamination, while the cross-linked polymer shell phase provides surface protection and buffers volume stress, effectively improving the long-term integrity of the electrode structure. This allows the material to maintain high sodium storage capacity while possessing superior high-rate charge-discharge performance and long-cycle stability. Attached Figure Description

[0018] Figure 1 This is a process flow diagram of the present invention; Figure 2This is a schematic diagram of a sodium-ion battery structure provided by the present invention. Detailed Implementation

[0019] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only 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.

[0020] In the following preparation examples and embodiments, graphite (particle size D50 of 10-20 μm, purity ≥99.9%, battery grade) and aqueous dispersion of graphene oxide (solid content 2.0 wt%, monolayer ratio ≥95%) were purchased from Qingdao Baichen Graphite Co., Ltd.; sodium styrene sulfonate (CAS No.: 2695-37-6, purity ≥99%) and acrylamide (CAS No.: 79-06-1 (purity ≥99%) was purchased from Jinan Henghua Technology Co., Ltd.; ethylene glycol diacrylate (CAS No.: 2274-11-5, purity ≥95%) was purchased from Shanghai Maclean Biochemical Technology Co., Ltd.; ammonium persulfate (CAS No.: 7727-54-0, purity ≥98%, analytical grade) was purchased from Sinopharm Chemical Reagent Co., Ltd.; sodium hexafluorophosphate (CAS No.: 21324-39-0, purity ≥99.9%, battery grade) was purchased from Duoduo Chemical Reagent (Suzhou) Co., Ltd.; carbonate electrolyte solvent (ethylene carbonate / diethyl carbonate, volume ratio 1:1, battery grade) and polyolefin separator were purchased from Jiangsu Huayi Lithium Battery Materials Co., Ltd.; sodium-ion battery cathode material was purchased from Hefei Kejing Materials Technology Co., Ltd.

[0021] Example 1 A method for preparing a high-rate graphite anode material includes the following steps: S1. Weigh 1.19g of graphene oxide powder and mix it with 793.3mL of deionized water. Disperse the powder evenly by ultrasonication at 200W for 0.3h to obtain a graphene oxide aqueous dispersion with a concentration of 1.5mg / mL. Select 23.81g of natural graphite raw material with a D50 of 10μm and mix it with 5952.5mL of deionized water. Stir at 150rpm for 0.5h to obtain a graphite dispersion with a concentration of 4mg / mL. Mix the above graphite dispersion and graphene oxide dispersion (total mass 25g) at a graphite to graphene oxide mass ratio of 1:0.05. Ultrasonicate the mixture at 250W for 0.5h under 0℃ ice-water bath conditions, and then dry to obtain the graphite composite.

[0022] S2. Using deionized water as solvent, add 1.2g sodium styrene sulfonate, 1.6g acrylamide, and 0.2g ethylene glycol diacrylate (total mass 3g), and stir to dissolve. Weigh 0.09g ammonium persulfate solid and mix with 30mL deionized water, stirring at 180rpm for 20min until completely dissolved, to prepare an initiator aqueous solution with a concentration of 3mg / mL, the amount of which is 3% of the total mass of the three monomers. Disperse the graphite composite in the above monomer-containing aqueous solution, purge with nitrogen gas, add the initiator aqueous solution, control the reaction temperature at 65℃, and react at a stirring rate of 220rpm for 6h. After the reaction is completed, cool to room temperature, and wash twice by alternating centrifugation with 280mL deionized water and 280mL anhydrous ethanol at a solid-liquid ratio of 1:10 (g / mL), centrifuging at 8000rpm and 0℃ for 10min each time. After centrifugation, discard the supernatant and retain the precipitate. After washing, the product was placed in a vacuum oven at 75°C and dried for 20 hours. After drying, it was pulverized and passed through a 200-mesh sieve to obtain a high-ratio graphite anode material.

[0023] Example 2 A method for preparing a high-rate graphite anode material includes the following steps: S1. Weigh 2.27g of graphene oxide powder and mix with 1135mL of deionized water. Disperse the powder evenly by ultrasonication at 250W for 0.4h to obtain a graphene oxide aqueous dispersion with a concentration of 2.0mg / mL. Select 22.73g of artificial graphite raw material with a D50 of 50μm and mix with 4546mL of deionized water. Stir at 180rpm for 0.8h to obtain a graphite dispersion with a concentration of 5mg / mL. Mix the above graphite dispersion and graphene oxide dispersion (total mass 25g) at a graphite to graphene oxide mass ratio of 1:0.1. Ultrasonicate at 300W for 1.0h under 3℃ ice-water bath conditions, and then dry to obtain the graphite composite.

[0024] S2. Using deionized water as a solvent, add 4g of sodium styrene sulfonate, 5g of acrylamide, and 1g of ethylene glycol diacrylate (total mass 10g), and stir to dissolve. Weigh 0.5g of ammonium persulfate solid and mix with 125mL of deionized water, stirring at 200rpm for 25min until completely dissolved, to prepare an initiator aqueous solution with a concentration of 4mg / mL, the amount of which is 5% of the total mass of the three monomers. Disperse the graphite composite in the above monomer-containing aqueous solution, purge with nitrogen as a protective gas, add the initiator aqueous solution, control the reaction temperature at 70℃, and react at a stirring rate of 250rpm for 7h. After the reaction is completed, cool to room temperature, and wash three times by alternating centrifugation with 360mL of deionized water and 360mL of anhydrous ethanol at a solid-liquid ratio of 1:12 (g / mL), centrifuging at 9000rpm and 3℃ for 12min each time. After centrifugation, discard the supernatant and retain the precipitate. After washing, the product was placed in an 80℃ vacuum oven and dried for 24 hours. After drying, it was pulverized and passed through a 200-mesh sieve to obtain high-ratio graphite anode material.

[0025] Example 3 A method for preparing a high-rate graphite anode material includes the following steps: S1. Weigh 3.26g of graphene oxide powder and mix it with 1304mL of deionized water. Disperse the powder evenly by ultrasonication at 300W for 0.5h to obtain a graphene oxide aqueous dispersion with a concentration of 2.5mg / mL. Select 21.74g of natural graphite raw material with a D50 of 100μm and mix it with 3623.3mL of deionized water. Stir at 200rpm for 1.0h to obtain a graphite dispersion with a concentration of 6mg / mL. Mix the above graphite dispersion and graphene oxide dispersion (total mass 25g) at a graphite to graphene oxide mass ratio of 1:0.15. Ultrasonicate the mixture at 350W for 1.5h under 5℃ ice-water bath conditions, and then dry to obtain the graphite composite.

[0026] S2. Using deionized water as solvent, add 5g sodium styrene sulfonate, 6g acrylamide, and 1.5g ethylene glycol diacrylate (total mass 12.5g), and stir to dissolve. Weigh 0.875g ammonium persulfate solid and mix with 175mL deionized water, stirring at 220rpm for 30min until completely dissolved, to prepare an initiator aqueous solution with a concentration of 5mg / mL, the amount of which is 7% of the total mass of the three monomers. Disperse the graphite composite in the above monomer-containing aqueous solution, purge with nitrogen as a protective gas, add the initiator aqueous solution, control the reaction temperature at 75℃, and react at a stirring rate of 280rpm for 8h. After the reaction is completed, cool to room temperature, and wash 4 times by alternating centrifugation with 562.5mL deionized water and 562.5mL anhydrous ethanol at a solid-liquid ratio of 1:15 (g / mL), centrifuging at 10000rpm and 5℃ for 15min each time. After centrifugation, discard the supernatant and retain the precipitate. After washing, the product was placed in a vacuum oven at 85°C and dried for 28 hours. After drying, it was pulverized and passed through a 200-mesh sieve to obtain a high-ratio graphite anode material.

[0027] Example 4 This embodiment is basically the same as Embodiment 1, with the main difference being: In S1, the mass ratio of graphite to graphene oxide is 1:0.08, the concentration of graphene oxide dispersion is 1.8 mg / mL (prepared by mixing 1.83 g of graphene oxide powder with 1016.7 mL of deionized water), the concentration of graphite dispersion is 4.5 mg / mL (prepared by mixing 22.92 g of natural graphite with 5093.3 mL of deionized water), and the ultrasonic treatment power is 300 W for 1.0 h.

[0028] S2 contains 1.75g ​​sodium styrene sulfonate, 2.33g acrylamide, and 0.42g ethylene glycol diacrylate (total mass 4.5g, accounting for 35% of the graphite composite mass). The initiator aqueous solution concentration is 3.5mg / mL (prepared by mixing 0.18g ammonium persulfate with 51.4mL deionized water), and the amount used is 4% of the total monomer mass. The reaction temperature is 68℃, the stirring speed is 240rpm, and the reaction time is 6.5h.

[0029] Example 5 This embodiment is basically the same as Embodiment 1, with the main difference being: The concentration of graphene oxide dispersion in S1 was 2.2 mg / mL (prepared by mixing 2.61 g of graphene oxide powder with 1186.4 mL of deionized water), and the concentration of graphite dispersion was 5.5 mg / mL (prepared by mixing 24.57 g of natural graphite with 4467.3 mL of deionized water). The mass ratio of graphite to graphene oxide was 1:0.12, and the ultrasonic treatment time was 1.2 h.

[0030] S2 contains 2.4g sodium styrene sulfonate, 2.4g acrylamide, and 0.6g ethylene glycol diacrylate (total mass 5.4g). The initiator aqueous solution concentration is 4.5mg / mL (prepared by mixing 0.32g ammonium persulfate with 71.1mL deionized water), which is 6% of the total monomer mass. The reaction temperature is 72℃, the stirring speed is 260rpm, the reaction time is 7.5h, the centrifugation speed is 9500rpm, and the drying temperature is 82℃ for 25h.

[0031] Example 6 This embodiment is basically the same as Embodiment 1, with the main difference being: In S1, the graphite raw material has a D50 of 80 μm, the graphite dispersion concentration is 5.0 mg / mL (prepared by mixing 23.40 g of artificial graphite with 4680 mL of deionized water), the graphene oxide dispersion concentration is 1.6 mg / mL (prepared by mixing 1.40 g of graphene oxide powder with 875 mL of deionized water), and the mass ratio of graphite to graphene oxide is 1:0.06.

[0032] S2 contains 1.9g sodium styrene sulfonate, 2.85g acrylamide, and 0.57g ethylene glycol diacrylate (total mass 5.32g). The amount of initiator is 5.5% of the total monomer mass (0.29g ammonium persulfate was weighed and mixed with 72.5mL deionized water to prepare an initiator aqueous solution), and the reaction time is 7h.

[0033] Comparative Example 1 The difference between this comparative example and Example 1 is that no graphene oxide dispersion was added in S1, while the remaining steps are the same as in Example 1.

[0034] Comparative Example 2 The difference between this comparative example and Example 2 is that sodium styrene sulfonate and acrylamide were not used in S2, while the remaining steps were the same as in Example 2.

[0035] Comparative Example 3 The difference between this comparative example and Example 3 is that ethylene glycol diacrylate was not added in S2, while the remaining steps are the same as in Example 3.

[0036] Comparative Example 4 The difference between this comparative example and Example 4 is that the polymer coating step was not performed in S2, and the S1 step was retained, that is, the graphite composite was directly used as the negative electrode material after drying. The remaining steps are the same as in Example 4.

[0037] The high-rate graphite anode materials prepared in Examples 1-6 and the comparative materials prepared in Comparative Examples 1-4 were dried, pulverized through a 200-mesh sieve, and sealed in an argon-filled glove box for later use. All samples underwent a uniform process to prepare the working electrode. Each test sample, conductive carbon black, and binder (sodium carboxymethyl cellulose) were weighed at a mass ratio of 8:1:1, and added to deionized water and stirred until a homogeneous slurry with a solid content of 40% was formed. The slurry was coated onto the surface of a copper foil (10 μm thick), covering an area of ​​1 cm², with a coating thickness controlled to 100 μm. After coating, the foil was dried in an 80℃ vacuum oven for 12 hours, and then compacted using a tablet press at a pressure of 10 MPa, achieving a uniform compaction density of 1.0 g / cm³. The final active material loading of the working electrode was controlled to be 1.0 ± 0.05 mg / cm², and the electrode was cut and sealed for later use.

[0038] CR2032 coin cells were assembled, with the positive electrode being a polyanionic compound, Na3V2(PO4)3; the separator was a polyolefin polypropylene membrane, 15 μm thick with a porosity of 50%, cut into 16 mm diameter discs; the electrolyte was a carbonate electrolyte containing sodium hexafluorophosphate at a concentration of 1.0 mol / L, with ethylene carbonate and dimethyl carbonate mixed at a volume ratio of 1:1.5 as the solvent, and 50 μL of electrolyte was injected into each cell. Three parallel cells were assembled for each sample and allowed to stand for 12 hours before use.

[0039] (I) High-rate charge-discharge performance, cycle stability and initial coulombic efficiency test: Referring to GB / T 44027.1-2024 "Determination of Carbon Materials - Part 1: Determination of Initial Discharge Specific Capacity, Initial Coulombic Efficiency and Capacity Retention Rate at Different Rates" and GB / T 31486-2024 "Electrical Performance Requirements and Test Methods for Power Batteries for Electric Vehicles", the Blue Electric CT2001A battery test system was used in constant current charge-discharge mode, and the charge-discharge voltage range was uniformly set to 0.01-2.0V (vs Na⁺ / Na).

[0040] The high-rate charge-discharge performance test procedure is as follows: first, activate the battery by charging and discharging at 0.1C for 2 cycles, then charge and discharge at 0.5C, 1C, 2C, 5C, and 10C for 5 cycles each, and finally return to 0.1C for 5 cycles. During the test, the discharge specific capacity, charge specific capacity, and coulombic efficiency at each rate are recorded. Using the discharge capacity of the second cycle at 0.1C as a benchmark, the capacity retention rate at each rate is calculated as follows: Capacity retention rate (%) = (Average of discharge specific capacity over 5 cycles at a certain test rate / Discharge specific capacity of the second cycle at 0.1C) × 100%.

[0041] The specific parameters for the cycle stability test are as follows: 500 continuous constant current charge-discharge cycles are performed using a 1C rate. During the test, the discharge specific capacity and coulombic efficiency are recorded for each cycle. Subsequently, based on the discharge capacity of the 5th cycle, the capacity retention rate and average capacity decay rate per cycle are calculated after 500 cycles. The capacity retention rate (%) after 500 cycles = (discharge specific capacity of the 500th cycle / discharge specific capacity of the 5th cycle) × 100%, and the average capacity decay rate per cycle (%) = [(discharge specific capacity of the 5th cycle - discharge specific capacity of the 500th cycle) / discharge specific capacity of the 5th cycle / 500 cycles] × 100%.

[0042] The specific parameters for the first coulomb efficiency test are as follows: perform one cycle of constant current charge and discharge at a rate of 0.1C, record the first charge capacity and the first discharge capacity during the test, and calculate the first coulomb efficiency. First coulomb efficiency (%) = (first discharge capacity / first charge capacity) × 100%.

[0043] The results are shown in Table 1-3: Table 1. Test results of high-rate charge and discharge performance Table 2. Cyclic stability test results Table 3. Results of the first coulomb efficiency test (II) Sodium ion diffusion coefficient and electrochemical impedance spectroscopy (EIS) test: The CHI660E electrochemical workstation was used, and the relevant voltage parameters were consistent with those in (I) test.

[0044] The sodium ion diffusion coefficient was tested using a potentiostatic step test (GITT) mode. The specific test conditions were: a step current density of 10 mA / g, a step time of 300 s, and a resting period of 1800 s after each step, until the test voltage reached the cutoff range of 0.01-2.0 V. Voltage-time response curves were recorded during the test, and the bulk diffusion coefficient (Di) of sodium ions in the anode material was calculated based on the obtained GITT curves. Na⁺ The migration efficiency of sodium ions within the material is characterized by this factor. The calculation formula is as follows: Where L is the thickness of the active material layer in the working electrode (approximately 0.008 cm), and t 1 / 2 This represents the half-peak time of the voltage step segment in the GITT curve.

[0045] The specific conditions for EIS testing were as follows: the test was conducted at the battery open-circuit voltage, with a test frequency range of 100kHz-0.01Hz and an AC signal amplitude of 5mV. The test consisted of three stages: 12 hours of rest after battery assembly (initial state), activation after two cycles of 0.1C charge-discharge, and 100 cycles of 1C. After the test, the impedance spectrum data were fitted and analyzed to obtain the solution resistance, interfacial charge transfer resistance, and SEI film resistance. EIS testing was performed only on Examples 1-3 and Comparative Example 1.

[0046] The results are shown in Table 4-5: Table 4. Results of sodium ion diffusion coefficient test Table 5. Electrochemical Impedance Spectroscopy Results As shown in Table 1, the second discharge specific capacity at 0.1C in Examples 1-6 is relatively high, and the capacity retention rate at different rates is also relatively good. This indicates that the high-rate graphite anode materials prepared in these examples can maintain good capacity and have good reversibility during high-rate charge-discharge processes. During the preparation process, graphene oxide was added and formed a composite with graphite. Graphene oxide has a large specific surface area and good conductivity, providing more channels and active sites for sodium ion insertion and extraction. Simultaneously, the polymer coating layer improves the surface structure and electrochemical properties of the material, enhancing its conductivity and structural stability, thereby enabling the material to better retain its capacity during high-rate charge-discharge.

[0047] The specific capacity of Comparative Examples 1-4 at 0.1C second discharge and the capacity retention at various rates were significantly lower than those of the Example. Comparative Example 1 lacked graphene oxide, thus failing to provide additional conductive channels and active sites; Comparative Examples 2 and 3 lacked some polymer monomers, resulting in incomplete or poor-performing coatings, which could not effectively improve the surface structure and electrochemical performance of the materials; Comparative Example 4 lacked polymer coating, resulting in poor surface structure and stability, making it prone to structural damage during charge and discharge, leading to rapid capacity decay.

[0048] As shown in Table 1, Examples 1-6 exhibited high capacity retention after 500 cycles and low average capacity decay per cycle, indicating that the materials prepared in these examples possess good cycle stability. The composite structure formed by graphene oxide and graphite, along with the polymer coating, can buffer the volume changes of the material during charge and discharge, reduce electrode material pulverization and shedding, and suppress side reactions between the electrolyte and electrode material, thereby improving the cycle stability of the material.

[0049] The capacity retention rate of Comparative Examples 1-4 after 500 cycles was significantly lower than that of the Example, with a higher average capacity decay rate per cycle. Similar to the high-rate charge-discharge performance, the comparative examples, due to the lack of graphene oxide or polymer coating, exhibited poorer structural stability and electrochemical performance, making them more prone to structural damage and side reactions during cycling, resulting in faster capacity decay.

[0050] As shown in Table 3, the initial coulombic efficiencies of Examples 1-6 were all between 89.6% and 91.2%, indicating that the materials exhibit high reversibility during the first charge-discharge process. The synergistic effect of graphene oxide and the polymer coating layer resulted in the formation of a stable SEI film on the material surface, reducing electrolyte decomposition and side reactions. Simultaneously, it improved the material's conductivity and ion transport performance, increasing the efficiency of sodium ion insertion and extraction during the first charge-discharge process, thereby enhancing the initial coulombic efficiency.

[0051] The initial coulombic efficiency of Comparative Examples 1-4 was significantly lower than that of the Examples. Due to the lack of graphene oxide or polymer coating layers, the surface structure of the materials in the Comparative Examples was unstable, making it prone to forming an unstable SEI film during the first charge-discharge cycle. This led to electrolyte decomposition and increased side reactions. Simultaneously, the materials exhibited poor conductivity and ion transport properties, resulting in reduced sodium ion insertion and extraction efficiency during the first charge-discharge cycle, thus lowering the initial coulombic efficiency.

[0052] As shown in Table 4, the sodium ion diffusion coefficients of Examples 1-6 are significantly higher than those of Comparative Examples 1-4. Graphene oxide possesses a unique two-dimensional structure, providing a rapid channel for sodium ion diffusion. Simultaneously, the polymer coating improves the surface structure of the material, increasing its porosity and specific surface area, further enhancing the sodium ion diffusion rate. In contrast, the comparative examples, lacking either graphene oxide or a polymer coating, have structures unfavorable for sodium ion diffusion, resulting in lower sodium ion diffusion coefficients.

[0053] As shown in Table 5, the solution resistance, interfacial charge transfer resistance, and SEI film resistance of Examples 1-6 at different test nodes are significantly lower than those of Comparative Examples 1-4. The graphene oxide and polymer coating layers can improve the conductivity of the material and reduce the interfacial charge transfer resistance; at the same time, they form a stable SEI film, reducing the SEI film resistance, thereby reducing the electrochemical impedance of the entire battery system and improving the electrochemical performance of the battery. In contrast, the comparative examples, lacking graphene oxide or polymer coating layers, have poorer conductivity and surface structure, resulting in higher interfacial charge transfer resistance and SEI film resistance, increasing the electrochemical impedance of the entire battery system and affecting battery performance.

[0054] In summary, the high-rate graphite anode material prepared by adding graphene oxide and polymer coating in the examples exhibits significant advantages in electrochemical performance, including high high-rate charge-discharge performance, good cycle stability, high initial coulombic efficiency, large sodium ion diffusion coefficient, and low electrochemical impedance.

[0055] In the description of this specification, the reference to terms such as "embodiment," "various embodiments," etc., indicates that a specific feature, structure, material, or characteristic described in connection with that embodiment or preparation example is included in at least one embodiment of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments.

[0056] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a high-rate graphite anode material, characterized in that, Includes the following steps: S1. The graphite dispersion and the graphene oxide dispersion are mixed, and then subjected to ultrasonic treatment and drying to obtain the graphite composite. S2. The graphite composite is dispersed in an aqueous solution containing sodium styrene sulfonate, acrylamide and ethylene glycol diacrylate, an initiator is added, the temperature is controlled and the reaction is stirred, and after post-treatment, a high-rate graphite anode material is obtained.

2. The preparation method according to claim 1, characterized in that, In step S1, the mass ratio of graphite to graphene oxide is 1:(0.05-0.15), the concentration of the graphene oxide aqueous dispersion is 1.5-2.5 mg / mL, and the concentration of the graphite dispersion is 4-6 mg / mL.

3. The preparation method according to claim 1, characterized in that, In step S1, the ultrasonic treatment is carried out under ice-water bath conditions at 0-5℃, the ultrasonic power is 250-350W, and the ultrasonic time is 0.5-1.5h.

4. The preparation method according to claim 1, characterized in that, In step S2, the mass ratio of sodium styrene sulfonate, acrylamide, and ethylene glycol diacrylate is (3-5):(4-6):(0.5-1.5), and the total mass of sodium styrene sulfonate, acrylamide, and ethylene glycol diacrylate accounts for 30-50% of the mass of the graphite composite.

5. The preparation method according to claim 1, characterized in that, In step S2, the initiator is selected from ammonium persulfate, and its amount is 3-7% of the total mass of sodium styrene sulfonate, acrylamide, and ethylene glycol diacrylate. The initiator is added in the form of an aqueous solution, and the concentration of the initiator aqueous solution is 3-5 mg / mL.

6. The preparation method according to claim 1, characterized in that, The conditions for controlling the temperature and stirring reaction in step S2 are as follows: under the protection of inert gas, the reaction temperature is controlled at 65-75℃, the stirring rate is 200-300rpm, and the reaction time is 4-10h.

7. The preparation method according to claim 1, characterized in that, The post-processing in step S2 includes washing and drying. Specifically, after the reaction is completed, the product is cooled to room temperature and washed 2-4 times by alternating centrifugation with deionized water and anhydrous ethanol at a speed of 8000-10000 rpm for 10-15 min each time. After washing, the product is placed in a vacuum oven at 75-85℃ and dried for 20-28 h.

8. A high-rate graphite anode material, prepared by the preparation method described in any one of claims 1-7.

9. A sodium-ion battery, characterized in that, The device includes a positive electrode, a separator, an electrolyte, and a negative electrode. The negative electrode is the high-rate graphite negative electrode material as described in claim 8. The electrolyte is a sodium-containing carbonate electrolyte, wherein the sodium salt is selected from one or more of sodium hexafluorophosphate, sodium perchlorate, and sodium tetrafluoroborate, and the electrolyte concentration is 0.8-1.2 mol / L. The separator is a polyolefin separator. The positive electrode is selected from one or more of layered oxides and polyanionic compounds.

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