Modified graphite negative electrode material for potassium ion battery and preparation method and application thereof

Abstract

This invention discloses a modified graphite anode material for potassium-ion batteries, its preparation method, and its applications. The method includes acidification and intercalation treatment of nano-graphite powder, followed by thermal reduction with hydrazine hydrate to obtain a few-layer graphite material (GNS) with expanded interlayer spacing and abundant defects. The hydrazine hydrate reduction restores the conductivity of graphite while inducing a large number of intrinsic defects, providing additional capacitive potassium storage sites. The resulting material possesses both expanded interlayer channels and abundant defect structures, effectively alleviating the volumetric strain of potassium ion insertion / extraction and significantly improving ion diffusion kinetics. Potassium-ion batteries assembled based on GNS exhibit a reversible capacity exceeding the theoretical value of graphite in conventional low-concentration electrolytes, reaching 500 mA g. ‑1 After 1000 cycles, the capacity retention rate is no less than 87%, demonstrating excellent rate performance and cycle stability. This invention features a simple process and controllable cost, providing a highly promising anode material solution for potassium-ion batteries.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage and battery materials technology, and particularly relates to a modified graphite anode material suitable for potassium-ion batteries, its preparation method, and its application in potassium-ion batteries. Specifically, this invention relates to a few-layer graphite material obtained by chemically modifying commercial nano-graphite powder, which has expanded interlayer spacing, retains a long-range ordered layered structure, and introduces abundant and stable defects. This aims to solve the problems faced by graphite as a potassium-ion battery anode, such as slow ion diffusion kinetics, severe volume expansion, and short cycle life. Background Technology

[0002] With the explosive growth in global demand for renewable energy storage and electric vehicles, the development of high-energy-density, low-cost, and long-life rechargeable battery systems is crucial. While lithium-ion batteries have achieved widespread commercialization, the limited distribution of lithium resources and their ever-increasing cost restrict their further application in large-scale energy storage. Sodium-ion and potassium-ion batteries, due to the high abundance of sodium and potassium in the Earth's crust and their low cost, have become highly promising supplementary or alternative systems. Among them, potassium-ion batteries, due to their more negative standard electrode potential (K0), are particularly promising. + / K is -2.93 V vs. SHE, close to Li + / Li (-3.04 V) is expected to achieve higher operating voltage and energy density, and K + Having a lower Stokes radius in electrolytes may result in faster ion migration.

[0003] Graphite, as a mature anode material for commercial lithium-ion batteries, has a theoretical capacity of 372 mAh g⁻¹. -1 It also exhibits potassium storage potential in potassium-ion batteries, with a theoretical capacity of approximately 279 mAh g⁻¹. -1 While possessing a low and stable charge / discharge voltage plateau, potassium ions (1.38 Å) have a much larger radius than lithium ions (0.76 Å), posing a significant challenge to their insertion / extraction between graphite layers. The large ionic radius leads to slow diffusion kinetics and severe volume expansion (approximately 61%), easily causing pulverization and damage to the graphite structure, and continuously undermining the solid electrolyte interphase (SEI) film on the electrode surface. These issues collectively contribute to the bottleneck of poor rate performance, rapid capacity decay, and short cycle life of traditional graphite anodes in potassium-ion batteries.

[0004] To improve the potassium storage performance of graphite, current research mainly focuses on two aspects: first, structural modification of the graphite material itself, such as preparing expanded graphite, graphene, or introducing heteroatom doping to increase interlayer spacing, improve conductivity, and provide more active sites; second, development of novel electrolyte systems, such as using high-concentration electrolytes or adding functional additives to construct a more stable electrode / electrolyte interface. However, the former often struggles to maintain the long-range ordered conductive framework of graphite while increasing interlayer spacing, and the process is complex and costly; while the latter can improve interfacial stability, high-concentration electrolytes suffer from high viscosity, poor wettability, high cost, and decreased ionic conductivity, which are detrimental to practical applications.

[0005] Therefore, developing a graphite anode material that is simple to process, cost-controllable, and capable of simultaneously expanding the graphite interlayer spacing, effectively exfoliating the layered structure, and controlling the introduction of defects under mild conditions, and achieving stable long-cycle operation in traditional low-concentration, low-cost electrolytes, is of great practical significance for promoting the commercialization of potassium-ion batteries. Summary of the Invention

[0006] The purpose of this invention is to overcome the defects of graphite as a negative electrode in potassium-ion batteries, such as slow ion diffusion, large volume change, and poor cycle stability. In particular, it addresses the problems of limited defect control ability and difficulty in effectively exfoliating graphite layers in existing oxidation-calcination modification methods, and provides a modified graphite negative electrode material, its simple preparation method, and its application.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing a modified graphite anode material for potassium-ion batteries includes the following steps: (1) Oxidation intercalation treatment: Nano-graphite powder, sodium nitrate and concentrated sulfuric acid are mixed under ice bath conditions, and potassium permanganate is slowly added under continuous stirring to carry out low-temperature oxidation reaction; then the temperature is raised to 30-40℃ and kept at the temperature for a period of time to allow the oxidant to fully insert into the graphite interlayer and carry out deep oxidation. (2) Termination and cleaning: Add a large amount of deionized water to the reaction system of step (1) to dilute it, and add hydrogen peroxide to terminate the reaction and reduce the residual high-valence manganese compounds until the solution turns bright yellow; then filter it and wash the filter cake repeatedly with dilute hydrochloric acid solution and deionized water until it is neutral, and dry it to obtain the oxidized intercalated graphite intermediate. (3) Thermal reduction treatment: The intermediate obtained in step (2) is uniformly dispersed in deionized water to form a dispersion; hydrazine hydrate is added to the dispersion as a reducing agent, and the mixture is stirred and refluxed in an oil bath at 90-100℃ for several hours. This step is crucial. Using hydrazine hydrate for mild chemical reduction can not only effectively restore the conductivity of the graphite skeleton, but more importantly, it can reduce oxygen-containing functional groups more uniformly and gently, generating a large number of stable intrinsic defects (such as vacancies, edge defects, etc.) in the process. These defects can serve as additional potassium ion storage active sites, contributing pseudocapacitance, thereby enabling the material to obtain a high reversible capacity that exceeds the theoretical capacity of graphite. At the same time, the mild liquid-phase reduction process helps to maintain the interlayer spacing opened by the previous oxidation intercalation step and promotes the exfoliation of graphite sheets to form a stacked structure of few-layer graphene nanosheets, providing more channels for the rapid diffusion of potassium ions, thereby significantly improving the rate performance.

[0008] (4) Post-processing: The product after reduction in step (3) is filtered and repeatedly washed with deionized water until the filtrate is neutral. Finally, it is dried under vacuum or inert atmosphere to obtain the final modified graphite material, denoted as GNS.

[0009] Further, in step (1), the mass ratio of the nano-graphite powder, sodium nitrate and potassium permanganate is 4: 2.5-3.5: 4-6; the amount of concentrated sulfuric acid used is 60-80 mL per gram of nano-graphite powder; the ice bath stirring time is 1-3 hours, and the temperature holding reaction time after heating is 10-14 hours.

[0010] Furthermore, in step (3), the amount of hydrazine hydrate added is 15-25 mL per gram of intermediate; the thermal reduction reaction time is 6-10 hours. By controlling the conditions of hydrazine hydrate reduction, the degree of defect and interlayer spacing of the final product can be effectively regulated, thereby optimizing the electrochemical performance.

[0011] Another objective of this invention is to provide a modified graphite anode material (GNS) prepared by the above-described method. This material has a loose, porous structure composed of stacked few-layer graphene nanosheets, with its (002) interplanar spacing (d-spacing) increased to over 0.360 nm, preferably 0.360-0.370 nm, significantly larger than the interlayer spacing of the original nano-graphite powder (approximately 0.334 nm). Simultaneously, the material maintains the long-range ordered layered crystal structure of graphite. After reduction with hydrazine hydrate, the intensity ratio of the D peak to the G peak in its Raman spectrum (ID / IG) is significantly increased (up to 1.0 or higher), indicating the introduction of abundant structural defects. These defects provide numerous additional adsorption sites for potassium ions, which is crucial for achieving high capacity (especially exceeding the theoretical capacity of graphite). Furthermore, its (BET) specific surface area is significantly increased to 35-50 m2. 2 g-1 It is much higher than the specific surface area of ​​the raw materials (approximately 4 m²). 2 g -1 ).

[0012] Another objective of this invention is to provide a potassium-ion battery anode comprising the aforementioned modified graphite anode material as the active material. The preparation method of this anode includes: mixing GNS active material, a conductive agent (such as acetylene black, Super P), and a binder (such as polyvinylidene fluoride PVDF) at a mass ratio of (7-8.5):(0.5-1.5):(0.5-1.5); adding an appropriate amount of N-methyl-2-pyrrolidone (NMP) solvent; grinding or stirring to form a uniform slurry; uniformly coating the slurry onto a copper foil current collector; and obtaining an electrode sheet after drying, rolling, and stamping.

[0013] The present invention also provides a potassium-ion battery, comprising a positive electrode, a separator, an electrolyte, and the aforementioned potassium-ion battery negative electrode. The electrolyte is preferably a conventional low-concentration potassium salt organic electrolyte, for example, with a concentration of 0.5-1.2 mol / L. -1 Potassium hexafluorophosphate (KPF6) was dissolved in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (volume ratio 1:1).

[0014] This invention further provides the application of the above-mentioned modified graphite anode material in potassium-ion batteries. Benefiting from the abundant defects introduced by hydrazine hydrate reduction and the expanded interlayer spacing due to oxide intercalation, this material can achieve stable long-term cycling in batteries using conventional low-concentration potassium salt electrolytes, exhibiting high reversible capacity exceeding the theoretical capacity of graphite and excellent rate performance at 500 mA g. -1 The capacity retention rate after 1000 cycles at the specified current density is no less than 85%.

[0015] A method for improving the cycle stability and potassium storage capacity of graphite anodes in potassium-ion batteries involves preparing modified graphite materials with expanded interlayer spacing and rich in defects as the anode active material. This material is then used in conjunction with a conventional organic electrolyte containing potassium salts. The expanded interlayer spacing alleviates the volumetric strain caused by potassium ion insertion / extraction, while the abundant defects provide additional capacitive potassium storage sites to enhance capacity and improve ion diffusion kinetics. This significantly improves the reversible capacity, cycle life, and rate performance of the battery.

[0016] The beneficial effects are as follows: the unique structural advantages of this GNS material enable it to exhibit excellent electrochemical performance even when using inexpensive, traditional low-concentration electrolytes. Firstly, the abundant structural defects introduced by the reduction of hydrazine hydrate provide numerous capacitive potassium storage sites, resulting in a reversible capacity significantly higher than the theoretical potassium intercalation capacity of graphite, achieving a breakthrough in capacity. Secondly, the expanded interlayer spacing and the highly conductive few-layer structure obtained after reduction provide low-resistance diffusion channels for potassium ions, while the abundant defects contribute to rapid capacitive kinetics. These two factors work synergistically to significantly improve ion migration rate and rate performance. Simultaneously, the expanded space effectively buffers the volumetric strain caused by potassium ion insertion / extraction, enhancing the structural stability of the material and reducing the pulverization of the active material and repeated rupture of the SEI film during cycling. The abundant defects and increased specific surface area provide additional potassium ion adsorption sites, contributing to improved reversible capacity. Therefore, potassium-ion batteries based on GNS anodes exhibit high reversible capacity, excellent rate performance, and ultra-long cycle life. Attached Figure Description

[0017] Figure 1 The diagram shows the process flow and structural evolution of the modified graphite material (GNS) in Example 1 of this invention, illustrating the transformation from commercial nano graphite powder to the final few-layer, wide-spacing GNS. Figure 2 The images show a comparison of the microstructure of the original nano-graphite powder used in Comparative Example 1 and the GNS obtained in Example 1, including (a) SEM image of nano-graphite powder, (b, c) SEM image of GNS, (d) TEM image of nano-graphite powder, and (e, f) TEM and high-resolution TEM images of GNS. Figure 3 The figures show the electrochemical performance of the potassium-ion batteries assembled based on the GNS anode in Examples 2 and 3 of this invention, including (a) 0.1 mV s -1 Cyclic voltammetry curves at scan rate, (b) 100 mA g -1 (c) Charge-discharge curves at different current densities; (d) Rate performance comparison chart; (e) 100 mA g -1 The following is a long-cycle performance graph, (f) 500 mA g -1 Long-cycle performance graph below; Figure 4 The structural characterization comparison diagrams of GNS obtained in Example 1 and nano-graphite powder used in Comparative Example 1 include (a) XRD pattern, (b) Raman spectrum, and (c) nitrogen adsorption-desorption isotherm and specific surface area analysis. Figure 5The in-situ XRD pattern of the GNS negative electrode in Example 4 of this invention during the charging and discharging process shows the periodic change in intensity and structural stability of the (002) crystal plane diffraction peaks of the material during potassium ion insertion / extraction. Detailed Implementation

[0018] 1. Experimental Materials and Pretreatment Nano-graphite powder, sodium nitrate (NaNO3), potassium permanganate (KMnO4), concentrated sulfuric acid (H2SO4, 98%), hydrogen peroxide (H2O2, 30%), and hydrazine hydrate (N2H4·H2O, 85%) were all purchased from Sinopharm Chemical Reagent Co., Ltd. Potassium hexafluorophosphate (KPF6, battery grade), ethylene carbonate (EC), and ethyl methyl carbonate (EMC) were purchased from Suzhou Duoduo Chemical Co., Ltd. Acetylene black conductive agent, polyvinylidene fluoride (PVDF) binder, and N-methyl-2-pyrrolidone (NMP) were purchased from Aladdin Reagent Co., Ltd. All solvents were dried using molecular sieves before use, with the moisture content controlled below 20 ppm. Electrode preparation and battery assembly were carried out in a glove box filled with high-purity argon gas (purity >99.999%) (H2O and O2 contents both below 0.1 ppm).

[0019] 2. Preparation of modified graphite anode material (GNS) Example 1: Standard preparation process of GNS (1) Oxidative intercalation: In a 2000 mL beaker, 4.0 g of nano-graphite powder and 3.0 g of NaNO3 were mixed. The beaker was placed in an ice-water bath, and 300 mL of concentrated H2SO4 was slowly added under mechanical stirring. The temperature was kept below 5°C, and stirring was continued for 2 hours. Subsequently, 5.0 g of KMnO4 was slowly added in batches under stirring, and the temperature was controlled not to exceed 10°C. After the addition was completed, the ice bath was removed, the reaction system was heated to 35°C, and the reaction was continued to be stirred at this temperature for 12 hours. The solution gradually turned into a dark brown viscous state.

[0020] (2) Termination, washing, and drying: Transfer the beaker to an ice-water bath for cooling. While stirring vigorously, slowly add 500 mL of deionized water for dilution; the system releases heat at this point. Subsequently, slowly add 15 mL of H2O2 (30%); the solution gradually turns bright yellow, indicating that the high-valence manganese compound has been reduced. Filter the reaction mixture, and wash the resulting filter cake three times with 5% dilute hydrochloric acid solution, then repeatedly wash with a large amount of deionized water until the pH of the filtrate is close to 7. Place the washed solid in a vacuum oven at 70°C and dry for 24 hours to obtain the intermediate product of oxidized intercalated graphite.

[0021] (3) Thermal reduction: Weigh 1.0 g of the dried intermediate product and disperse it in 500 mL of deionized water. Sonicate the mixture for 1 hour to ensure uniform dispersion. Add 20 mL of hydrazine hydrate (85%) to the dispersion and then transfer the mixture to a round-bottom flask equipped with a reflux condenser. Heat the mixture in a 95°C oil bath and reflux with stirring for 8 hours.

[0022] (4) Post-processing: After the reaction is complete, the product is allowed to cool naturally to room temperature. The product is filtered and the filter cake is washed repeatedly with a large amount of deionized water until the filtrate is neutral. The final product is dried in a vacuum oven at 45°C for 72 hours. After grinding, a black, fluffy powder is obtained, which is denoted as GNS.

[0023] 3. Electrode fabrication and battery assembly examples Example 2: Preparation of GNS negative electrode and assembly of half cell (1) Preparation of negative electrode: The GNS active material prepared in Example 1, acetylene black conductive agent, and PVDF binder were mixed in a mortar at a mass ratio of 8:1:1. A suitable amount of NMP solvent was gradually added, and the mixture was thoroughly ground until a uniform, viscous slurry was formed. The slurry was uniformly coated onto a 10 μm thick copper foil current collector using a scraper. The coated electrode was first placed in an 80°C forced-air oven for initial drying for 2 hours, and then transferred to a 100°C vacuum oven for drying for 12 hours to completely remove the solvent. After being lightly pressed by a roller mill, it was punched into a circular sheet with a diameter of 12 mm. By controlling the coating thickness, the surface loading of the active material was controlled to be approximately 1.0 mg / cm². -2 .

[0024] (2) Electrolyte preparation: In an argon atmosphere glove box, KPF6 salt was dissolved in a 1:1 volume ratio of EC and EMC mixed solvent, and magnetically stirred until completely dissolved to prepare a solution with a concentration of 0.8 mol / L. -1 Traditional electrolytes.

[0025] (3) Button cell assembly: A CR2032 battery case was used. The negative electrode case and GNS negative electrode sheet (active side up) were placed in sequence, and 50 μL of the above electrolyte was dropped onto the negative electrode sheet. Then a glass fiber separator (Whatman GF / D, diameter 16 mm) was covered, and another 50 μL of electrolyte was dropped onto the separator. Subsequently, a potassium metal sheet (diameter 14 mm) was placed as the counter electrode / reference electrode, and a gasket and spring were added. Finally, the positive electrode case was covered, and the cells were sealed under 10 MPa pressure using a sealing machine to obtain a K|GNS half cell.

[0026] Example 3: Preparation of the control electrode (original nano-graphite powder negative electrode) and battery assembly Except for replacing the active material with untreated commercial nano-graphite powder, the electrode preparation process, electrolyte formulation and battery assembly steps were exactly the same as in Example 2. The resulting battery was denoted as KǁGraphite and served as Comparative Example 1.

[0027] 4. Examples of Material Structure Characterization and Electrochemical Performance Testing Example 4: Characterization of the physicochemical properties of materials The GNS prepared in Example 1 and the original nanographite powder used in Comparative Example 1 were systematically characterized, and the results are shown in the appendix. Figure 2 and 4 As shown.

[0028] (1) Morphology and structure (corresponding) Figure 2 The microstructure of the material was observed using field emission scanning electron microscopy (SEM, Hitachi S-4800) and transmission electron microscopy (TEM, FEI Tecnai G2 F20). For example... Figure 2 As shown in a and d, the original nano-graphite powder has a bulk stacked structure with thick and densely packed sheets. However, after acidification and reduction treatment, GNS exhibits a distinct thin-layered, wrinkled sheet-like structure. Figure 2 (b, c, e) , with a significantly increased specific surface area. High-resolution TEM (HR-TEM, Figure 2 f) The lattice fringes of GNS are clear, and the interplanar spacing of (002) is measured to be 0.366 nm, which is significantly larger than the original nano-graphite powder of 0.334 nm, which directly confirms the successful expansion of the interlayer spacing.

[0029] (2) Crystal structure and defect analysis (corresponding) Figure 4 a, b): Analysis was performed using X-ray diffraction (XRD, RigakuSmartLab) and Raman spectroscopy (Raman, Renishaw inVia). XRD patterns of GNS ( Figure 4 a) A broadened (002) diffraction peak appears at approximately 24.3°, with a calculated interlayer spacing of d = 0.366 nm. This peak is significantly shifted to the left and broadened compared to the sharp peak (d = 0.334 nm) at 26.5° observed in the original nano-graphite powder. Raman spectroscopy ( Figure 4 b) shows the D peak of GNS (1336 cm⁻¹). -1 ) and G peak (1580 cm) -1 The strength ratio (ID / IG) of the original nano-graphite powder is approximately 1.69, significantly higher than the 0.30 of the original nano-graphite powder, confirming that the reduction treatment with hydrazine hydrate introduced a large number of structural defects into the material. These defects are key structural features for improving potassium storage capacity (especially the pseudocapacitive contribution) and rate performance.

[0030] (3) Specific surface area and pore size analysis (corresponding to) Figure 4 c): Nitrogen adsorption-desorption tests were performed using a specific surface area and porosity analyzer (Micromeritics ASAP 2460). GNS has a BET specific surface area as high as 40 m². 2 g -1 The original nano-graphite powder is only 4 μm. 2 g -1 The significant increase in specific surface area helps to provide more active sites and improve electrolyte wettability.

[0031] (4) In-situ XRD: During the charge and discharge process, the intensity of the (002) peak of GNS changes periodically (weakens when potassium is inserted and strengthens when potassium is removed), but the peak position remains basically unchanged, which proves that the insertion / extraction of potassium ions is highly reversible and the interlayer spacing of the material remains stable during cycling, which is the key reason for its long-term cycling stability.

[0032] Example 5: Electrochemical Energy Storage Performance Test Electrochemical tests were performed on the batteries assembled in Examples 2 and 3. The main results are shown in the appendix. Figure 3 .

[0033] (1) Cyclic voltammetry (CV) test: using an electrochemical workstation (CHI 660E) at 0.01–3.0 V (vs. K) + Within the voltage range of / K, at 0.1 mV s -1 The scan rate was tested. The CV curve of the GNS electrode is shown below. Figure 3 As shown in Figure a, during the first discharge cycle, a broad irreversible reduction peak appears at approximately 0.5 V, corresponding to the formation of a solid electrolyte interphase (SEI) film due to electrolyte decomposition. A sharp reduction peak appearing near 0.1 V corresponds to K... + Potassium-graphite intercalation compounds are formed by embedding within the graphite interlayer. In subsequent anodic scans, two oxidation peaks appear near 0.25 V and 0.5 V, corresponding to K... + The desorption process. Starting from the second cycle, the CV curves highly overlap, indicating that the electrode reaction has high reversibility and excellent cycling stability.

[0034] (2) Constant current charge and discharge test: The test was conducted using the LAND CT2001A battery test system. Figure 3 b demonstrates GNS at 100 mA g -1 Charge-discharge curves at current density. The specific capacity during the first discharge and charge cycles is 840 mAh g. -1 and 290 mAh g -1The irreversible capacity primarily originates from SEI formation. From the second cycle onwards, the charge-discharge curves almost completely overlap, and the coulombic efficiency rapidly increases and stabilizes above 99%. It is worth emphasizing that its approximately 290 mAh g⁻¹... -1 The reversible capacity has exceeded the theoretical specific capacity (279 mAh g) of graphite as a potassium-ion battery anode. -1 This phenomenon, exceeding the theoretical capacity, strongly demonstrates that the abundant defects introduced by the hydrazine hydrate reduction treatment in the material of this invention provide additional capacitive storage sites for potassium ions, thereby contributing additional capacity. Figure 3 c shows the charge-discharge curves at different current densities, even at 2000 mA g. -1 Even at high magnification, it can still maintain low polarization and a stable voltage plateau.

[0035] (3) Ratio performance ( Figure 3 d): Battery capacity at 100, 200, 300, 500, 1000, 2000 mA g -1 After 10 cycles at current densities of [specific values], the GNS electrode provided approximately 300, 255, 240, 218, 195, and 158 mAh g⁻¹, respectively. -1 The average reversible capacity. When the current density returns to 100 mA g. -1 At that time, the capacity can be restored to 290 mAh g. -1 The GNS electrode exhibits excellent rate performance and structural reversibility. Its superior rate performance can be attributed to its unique structure: the expanded interlayer spacing ensures rapid ion insertion / extraction between layers, while the abundant defects generated by hydrazine hydrate reduction not only provide additional active sites, but their dominant capacitive behavior also facilitates rapid charge / discharge processes. This synergistic effect allows the material to maintain high rate even at 2000 mAg. -1 It can still maintain 158 mAh g at high current density -1 The reversible capacity of the original nano-graphite powder anode is significantly worse in terms of rate performance and capacity decay is rapid.

[0036] (4) Long-cycle performance Figure 3 e, f): at 100 mA g -1 After 150 cycles at the current density, the capacity retention of the GNS electrode is close to 100%, with no significant capacity decay. Figure 3 e). At the more demanding 500 mA g -1 Long-cycle testing under high current ( Figure 3 f), after 1000 cycles, the GNS electrode still retains approximately 210 mAh g⁻¹. -1The reversible capacity of the electrode exceeds 87%, with an average coulombic efficiency of 99.5%. In contrast, the capacity of the original nano-graphite powder electrode rapidly decays in the early stages of cycling under the same conditions.

[0037] Example 6: Study on potassium storage mechanism and structural stability (in-situ XRD analysis) To further investigate the potassium storage mechanism and structural stability of GNS during cycling, in-situ XRD tests were performed on the GNS electrode (corresponding to...). Figure 5 Using an X-ray diffractometer (Bruker D8 ADVANCE) equipped with an electrochemical cell accessory, at 100 mA g... -1 The system was charged and discharged at a current density, while XRD patterns were continuously acquired. For example... Figure 5 As shown, in the initial state (before discharge), a (002) diffraction peak located at approximately 24.2° can be observed. As the discharge progresses (K... + (Embedded), the diffraction peak intensity is significantly reduced, becoming broad and diffuse, due to K + The embedding of [something] causes a temporary decrease in the interlayer order of graphite. During the subsequent charging process (K... + During the deintercalation process, the intensity of the (002) diffraction peak gradually recovered. Importantly, the position of the (002) diffraction peak did not shift significantly throughout the entire charge-discharge cycle, indicating that the interlayer spacing of GNS remained basically stable during the repeated insertion and extraction of potassium ions, without irreversible structural collapse or excessive expansion. This excellent structural stability is one of the fundamental reasons why the GNS anode can achieve an ultra-long cycle life in conventional electrolytes.

[0038] Comparative Example 1: Anode Performance of Original Nano-Graphite Powder In direct comparison, the original nano-graphite powder anode (prepared according to Example 3) exhibited poorer electrochemical performance under the same test conditions (data integrated from...). Figure 3 d, e). Its rate capability is low, at 500 mA g. -1 The capacity was already very low. At 100 mA g... -1 After 150 cycles, the capacity decayed to only about 60 mAh g. -1 Its poor performance is attributed to the narrow interlayer spacing, which leads to K... + Diffusion difficulties and structural damage caused by volumetric strain during cycling.

[0039] In summary, this invention successfully prepared modified graphite materials with increased interlayer spacing, abundant defects, and high specific surface area through a simple chemical oxidation-reduction method. This material effectively alleviates the K... +By addressing diffusion kinetics constraints and volumetric strain issues during the embedding process, a balance of high reversible capacity, excellent rate performance, and ultra-long cycle life has been achieved in potassium-ion batteries using low-cost conventional electrolytes, demonstrating enormous potential for commercial applications.

Claims

1. A method for preparing a modified graphite anode material for potassium-ion batteries, characterized in that, Includes the following steps: S1. Oxidation intercalation treatment: Nano-graphite powder, sodium nitrate and concentrated sulfuric acid are mixed under ice bath conditions, potassium permanganate is added under continuous stirring, and then the reaction system is heated to 30-40℃ and maintained for 10-14 hours for deep oxidation to carry out the oxidation intercalation reaction. S2. Termination and Cleaning: Add deionized water and hydrogen peroxide to the reaction system of step S1 until the reaction solution turns bright yellow to terminate the reaction. After washing, filtering and drying, the oxidized intercalated graphite intermediate is obtained. S3. Thermal reduction treatment: Disperse the oxidized intercalated graphite intermediate in deionized water, add hydrazine hydrate and perform thermal reduction treatment at 90-100℃ for 6-10 hours; S4. Post-processing: The reduced product is washed, filtered, and dried to obtain modified graphite material with expanded interlayer spacing.

2. The method for preparing the modified graphite anode material for potassium-ion batteries as described in claim 1, characterized in that: In step S1, the mass ratio of nano-graphite powder, sodium nitrate and potassium permanganate is 4: (2.5~3.5): (4~6); the amount of concentrated sulfuric acid used is 60-80 mL per gram of nano-graphite powder, and the stirring time in an ice bath is 1-3 hours.

3. The method for preparing the modified graphite anode material for potassium-ion batteries as described in claim 1, characterized in that: In step S3, the amount of hydrazine hydrate added is 15-25 mL per gram of oxidized intercalated graphite intermediate.

4. The modified graphite anode material prepared by the preparation method according to any one of claims 1-3, characterized in that: This material is a loose, porous structure composed of stacked few-layer graphene nanosheets, with its (002) interplanar spacing increased to over 0.360 nm. It possesses a long-range ordered layered crystal structure and is rich in structural defects induced by the reduction process of hydrazine hydrate. Its BET specific surface area is 35-50 m². 2 g -1 .

5. A potassium-ion battery negative electrode, characterized in that, It includes the modified graphite anode material as described in claim 4 as the active material.

6. The potassium-ion battery negative electrode as described in claim 5, characterized in that, The method for preparing the negative electrode includes: mixing the modified graphite negative electrode material as described in claim 4, the conductive agent and the binder in a mass ratio of (7~8.5): (0.5~1.5): (0.5~1.5), adding a solvent to make a slurry, coating it on the current collector, and then drying and rolling it to obtain the final product.

7. The potassium-ion battery negative electrode as described in claim 6, characterized in that: The conductive agent is one or more of acetylene black, Ketjen black, Super P, carbon nanotubes, or graphene; the binder is one or more of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, or polyacrylic acid; and the current collector is copper foil.

8. A potassium-ion battery, characterized in that, It comprises a positive electrode, a separator, an electrolyte, and a potassium-ion battery negative electrode as described in any one of claims 5-7.

9. The potassium-ion battery as described in claim 8, characterized in that: The electrolyte is an organic solvent electrolyte containing potassium salt, wherein the potassium salt in the electrolyte is one or more of potassium hexafluorophosphate, potassium bis(trifluoromethanesulfonyl)imide, or potassium bis(fluorosulfonyl)imide, and its concentration in the organic solvent is 0.5-1.2 mol / L; the organic solvent is one or a mixture of several of ethylene carbonate, diethyl carbonate, methyl ethyl carbonate, propylene carbonate, fluoroethylene carbonate, or ethylene glycol dimethyl ether.

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