A method for preparing a fluorine-doped Co2NiO4@RGO three-dimensional heterostructure electrode material, its application, and a sodium-ion battery.

Abstract

The application belongs to the technical field of electrode material applied in sodium ion batteries, and discloses a preparation method and application of fluorine-doped Co2NiO4@RGO three-dimensional heterostructure electrode material and a sodium ion battery, the preparation method comprises the steps of NF pretreatment, RGO / NF precursor preparation, hydrothermal synthesis of fluorine-doped Co2NiO4@RGO and post-treatment, fluorine atoms are doped on the RGO-wrapped nickel foam by one-step hydrothermal method, Co2NiO4 nanosheets are in-situ grown, and a regular and ordered interwoven nanosheet structure is formed. The material utilizes the synergistic effect of the high conductivity of RGO and the electronic structure regulation of fluorine doping, and optimizes the application effect of the electrode material in the sodium ion battery. The application realizes the multi-dimensional synergistic effect of the substrate and the active material, heteroatoms and the host material, and provides a universal method for the controllable preparation of high-performance energy storage electrodes. The electrode material can be applied to the negative material of the sodium ion battery, so that the sodium ion battery can realize efficient and stable operation.

Description

Technical Field

[0001] This invention relates to the technical field of electrode materials used in sodium-ion batteries, and in particular to a method for preparing a fluorine-doped Co2NiO4@RGO three-dimensional heterostructure electrode material, its application, and a sodium-ion battery thereof. Background Technology

[0002] With the depletion of fossil fuels, humanity urgently needs to find a renewable green energy source, making green electricity the preferred choice. However, these green energy sources face significant geographical and temporal limitations. Therefore, electrochemical energy storage has emerged as a green energy storage technology with significant advantages and has been widely applied and researched. Sodium-ion batteries (SIBs) use sodium as the charge carrier, and their working principle is highly similar to that of lithium-ion batteries. Their core advantages are the abundance of sodium resources, low cost, and good low-temperature and safety performance. Currently, their energy density is gradually increasing, accelerating their large-scale application. Breakthroughs are focused on upgrading material systems, optimizing interface and solid-state technologies, controlling processes and costs, and expanding application scenarios.

[0003] Cobalt nickel oxide (Co₂NiO₄) is considered a promising electrode material candidate for sodium-ion batteries due to its variable oxidation state, environmentally friendly properties, higher theoretical specific capacitance compared to single cobalt oxide and nickel oxide, and its simple preparation method and wide applicability. However, single-structure Co₂NiO₄ exhibits poor conductivity, small specific surface area, and is prone to agglomeration and volume deformation during cycling. Heteroatom doping (such as F, N, P) and carbon material composites (such as RGO) are effective strategies to optimize its performance. - Incorporating metal oxides can effectively increase the polarity of chemical bonds (e.g., doping F into Co₂NiO₄ to form Ni-OF and Co-OF bonds), thus increasing the number of active sites. Simultaneously, the strong electron absorption capacity allows for a higher metal valence state in the main catalyst, thereby enhancing the intrinsic activity of the active sites and further improving sodium storage capacity. Reduced graphene oxide (RGO) possesses a large active surface area, good carrier mobility, high flexibility, and good chemical stability, and can be used to improve the conductivity and specific capacitance of electrode materials. In summary, the strong electronegativity of fluorine atoms can induce lattice distortion and regulate electronic structure, while RGO can improve conductivity and dispersibility.

[0004] However, in existing technologies, the synergistic effect of heteroatom doping and carbon material composites has not been fully realized, and there is still a lack of electrode material design schemes that combine high energy density, long cycle stability, and potential for large-scale preparation.

[0005] In view of this, the inventor of this case conducted in-depth research, which led to the creation of this case. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing and applying a fluorine-doped Co2NiO4@RGO three-dimensional heterostructure electrode material that overcomes the performance bottleneck of traditional Co2NiO4-based electrode materials.

[0007] Another objective of this invention is to provide an application of a fluorine-doped Co2NiO4@RGO three-dimensional heterostructure electrode material in sodium-ion batteries, which overcomes the performance bottleneck of traditional Co2NiO4-based electrode materials.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows:

[0009] A method for preparing a fluorine-doped Co2NiO4@RGO three-dimensional heterostructure electrode material includes the following steps:

[0010] Step 1, NF pretreatment: After cutting the NF sheet, clean it with deionized water and ethanol alternately by ultrasonic cleaning and then dry it for later use.

[0011] Step 2, Preparation of RGO / NF precursor: Disperse RGO in deionized water, add NF pretreated in Step 1, stir for 6-12 hours and then dry to obtain RGO / NF precursor;

[0012] Step 3, hydrothermal synthesis of fluorine-doped Co2NiO4@RGO: Dissolve 1 mmol cobalt nitrate, 1 mmol nickel nitrate, 3 mmol ammonium fluoride and 4-8 mmol urea completely in 30-40 mL of deionized water, add the RGO / NF precursor from step 2, transfer to a high-pressure reactor, and hydrothermally react at 120-150℃ for 6-8 hours;

[0013] Step 4, Post-processing: The reaction product is washed with deionized water and ethanol to remove surface deposits, and dried to obtain a fluorine-doped Co2NiO4@RGO three-dimensional heterostructure electrode material, denoted as CN@RGO / NF-F. The total active material loading of fluorine-doped Co2NiO4 and RGO on the nickel foam surface is 3~5 mg / cm³. 2 .

[0014] Furthermore, in step 3, the cobalt nitrate is cobalt nitrate hexahydrate, and the nickel nitrate is nickel nitrate hexahydrate.

[0015] Furthermore, the specific surface area of ​​the CN@RGO / NF-F is 10-30 m². 2 / g, with a mesopore size distribution of 2~50nm.

[0016] An application of a fluorine-doped Co2NiO4@RGO three-dimensional heterostructure electrode material is shown, which is used in sodium-ion batteries as a negative electrode material.

[0017] A sodium-ion battery, using CN@RGO / NF-F as the working electrode, a sodium sheet as the counter electrode, a glass fiber membrane as the separator, and sodium hexafluorophosphate electrolyte, is assembled into a 2016 coin-type sodium-ion half-cell.

[0018] After adopting the above technical solution, the preparation method of the fluorine-doped Co2NiO4@RGO three-dimensional heterostructure electrode material of the present invention has the following beneficial effects:

[0019] 1. Material Design Innovation: By integrating multiple preparation processes through a one-step hydrothermal method, the process is simplified and the uniformity is improved. This breaks through the limitations of the traditional electrode material process of "substrate modification - active material growth - heteroatom doping" which involves multiple separate steps. Through a single-step hydrothermal reaction, the uniform coating of RGO on the surface of nickel foam (NF), the in-situ growth of Co2NiO4 nanosheets, and the precise doping of fluorine atoms are achieved simultaneously. This avoids the problems of weak interface bonding and uneven composition caused by multi-step operations, making it suitable for large-scale production.

[0020] 2. Innovation of Multiple Synergistic Regulation Mechanisms of Fluorine Doping: Optimizing Electronic Structure and Reaction Kinetics to Achieve the Dual Role of "Lattice Distortion - Electronic Structure Regulation" by Utilizing the High Electronegativity of Fluorine Atoms: F - Replacement part O 2- (Atomic radius 0.71 Å > 0.66 Å) induces lattice expansion in Co₂NiO₄ [(004) interplanar spacing increases from 0.246 nm to 0.248 nm], regulating Co 2 + / Co 3+ Ni 2+ / Ni 3+ Valence ratio, accelerating OH - Adsorption and redox reactions.

[0021] 3. Dual support of RGO and nickel foam - synergistic innovation in conductivity: The high conductivity of RGO (excellent carrier mobility) and the rigid three-dimensional framework of nickel foam work synergistically. RGO constructs an electron transport network and improves the overall conductivity of the electrode. Nickel foam buffers the volume shrinkage / expansion of Co2NiO4 during charge and discharge. Combined with the elastic deformation capability of the interwoven nanosheet structure, the coulombic efficiency is close to 99% after 1000 cycles under high current.

[0022] 4. Rate Performance Analysis: Rate performance is a core performance indicator of sodium-ion batteries, and its key role is mainly reflected in two aspects: First, it determines the adaptability of the battery to different application scenarios. This performance directly supports the stable operation of the battery at different charge and discharge rates. The test results of sodium-ion half-cells assembled with A-CN@RGO / NF-F as the negative electrode show that the electrode exhibits excellent rate performance in a wide current density range of 0.1–5 A / g, and it can still maintain good electrochemical response when the current density recovers to 0.1 A / g. This phenomenon not only intuitively reflects the high efficiency of the electrode's reaction kinetics, but also experimentally confirms the scientific and rational design of the material structure. Second, it improves the convenience and economy of battery use. Excellent rate performance can effectively shorten the charging time, enabling the battery to better adapt to complex and variable actual working conditions, thereby helping sodium-ion energy storage systems achieve efficient and stable operation.

[0023] 5. Clear electrochemical activation mechanism: Co is activated through multi-cycle CV pretreatment with a potential window of 0.01-3 V. 2+ →Co 3+ Ni 2+ →Ni 3+ The partial irreversibility of the process, the high-valence Co and Ni ions help to provide more active sites, which helps to improve the electrochemical capacity and provides a clear activation pathway for the performance optimization of battery-type electrode materials.

[0024] 6. Universal Design Strategy: Providing a reference for transition metal oxide energy storage electrodes, a two-dimensional synergistic strategy of "substrate structure modification (three-dimensional conductive framework) + precise heteroatom doping (electronic structure regulation)" is proposed. It is not limited to the Co2NiO4 system - it can be extended to the composite of other transition metal oxides such as Mn and Fe with carbon materials, providing a general technical framework for the controllable preparation of high-performance energy storage electrodes.

[0025] In summary, this invention achieves synergistic integration of fluorine doping and RGO / nickel foam substrate through a one-step hydrothermal method, constructing a three-dimensional heterostructure and overcoming the performance bottleneck of traditional Co2NiO4-based electrode materials. A conductive agent-free and binder-free electrode material is designed for use in sodium-ion batteries. The electrode material achieves high specific capacitance and high stability through the synergistic effect of fluorine doping regulating the electronic structure and the structural support of the RGO / nickel foam substrate. The application of this electrode material in sodium-ion batteries achieves simultaneous improvement in energy density and cycle stability. Attached Figure Description

[0026] Figure 1 A schematic diagram of the synthesis of CN@RGO / NF-F;

[0027] Figure 2Electron micrographs of RGO / NF, CN / NF-F, CN@RGO / NF, and CN@RGO / NF-F;

[0028] (a) is an electron microscope image of RGO / NF, (b) is an electron microscope image of CN / NF-F, (c) is an electron microscope image of CN@RGO / NF; (d) is an electron microscope image of CN@RGO / NF-F, and (ef) is a projection image and lattice analysis of CN@RGO / NF-F.

[0029] in,

[0030] RGO / NF is a precursor of CN@RGO / NF-F (as described in Example 1);

[0031] CN / NF-F refers to generated materials that have not undergone RGO packaging operations (as described in Comparative Example 2).

[0032] CN@RGO / NF is undoped Co2NiO4@RGO (as described in Comparative Example 1);

[0033] CN@RGO / NF-F is fluorine-doped Co2NiO4@RGO (as described in Example 1);

[0034] Figure 3 EDS (energy dispersive spectroscopy) plot of CN@RGO / NF-F composite material;

[0035] Figure 4 Characterization diagrams of CN / NF-F, CN@RGO / NF, and CN@RGO / NF-F materials;

[0036] (a) is the XRD pattern, (b) is the Co 2p fine spectrum, (c) is the Ni 2p fine spectrum, (d) is the C 1s fine spectrum, (e) is the F 1s fine spectrum, and (f) is the O 1s fine spectrum.

[0037] Figure 5 Specific surface area plots for CN / NF-F, CN@RGO / NF, and CN@RGO / NF-F;

[0038] Where (a) is the N2 adsorption-desorption isotherm and specific surface area, and (b) is the pore size distribution;

[0039] Figure 6 The cyclic voltammetry (CV) curves of the CN@RGO / NF-F electrode material at a current density of 0.1 mV and a scan rate of 0 mV are shown for the first three cycles.

[0040] Figure 7 The impedance test curves of CN@RGO / NF-F electrode material, CN@RGO / NF electrode material and CN / NF-F electrode material at room temperature are shown.

[0041] Figure 8 Rate curves of CN@RGO / NF-F electrode material at different current densities at room temperature;

[0042] Figure 9 Long-cycle curves of CN@RGO / NF-F electrode materials, CN@RGO / NF electrode materials, and CN / NF-F electrode materials after 100 cycles at a current density of 1 A / g;

[0043] Figure 10 The long-cycle charge-discharge curves of CN@RGO / NF-F electrode material after 1000 cycles at high current density (10 A / g) are shown. Detailed Implementation

[0044] I. Preparation of Electrode Materials

[0045] Example 1

[0046] A method for preparing a fluorine-doped Co2NiO4@RGO three-dimensional heterostructure electrode material, such as... Figure 1 As shown, the preparation of CN@RGO / NF-F includes the following steps:

[0047] Step 1, Nickel Foam (NF) Pretreatment:

[0048] Cut 1×2 cm NF sheets, ultrasonically clean them with deionized water for 20 minutes, then ultrasonically clean them with ethanol for 20 minutes, repeat twice, and dry them at 60℃ for 2 hours for later use.

[0049] Step 2, Preparation of RGO / NF precursor:

[0050] Weigh 0.05 g of RGO and disperse it in 30 mL of deionized water. Sonicate the mixture for 30 minutes until homogeneous. Add the pretreated NF and stir at 200 r / min for 6 hours on a magnetic stirrer. Dry at 60℃ for 4 hours to obtain the RGO / NF precursor.

[0051] Step 3, hydrothermal synthesis:

[0052] Weigh 1 mmol of cobalt nitrate hexahydrate [Co(NO3)2] 6H2O], 1 mmol nickel nitrate hexahydrate [Ni(NO3)2] 6H2O], 3 mmol ammonium fluoride (NH4F) and 6 mmol urea (CH4N2O) were added sequentially to 30 mL of deionized water and stirred for 30 minutes until completely dissolved; the RGO / NF precursor was immersed in the solution and transferred to a 50 mL polytetrafluoroethylene-lined high-pressure reactor and reacted at 120℃ for 8 hours.

[0053] In hydrothermal synthesis, the relative amounts of each reactant are added according to the same proportions as described above, and the amount of any particular reactant is not limited here.

[0054] Step 4, Post-processing:

[0055] After the reaction was completed, the mixture was allowed to cool naturally to room temperature. The product was then washed three times with deionized water and twice with ethanol. It was then vacuum dried at 60°C for 6 hours to obtain CN@RGO / NF-F, in which the total active material loading of fluorine-doped Co2NiO4 and RGO on the nickel foam surface was 4.2 mg / cm³. 2 .

[0056] Comparative Example 1: Preparation of CN@RGO / NF

[0057] The main difference between Comparative Example 1 and Example 1 is that ammonium fluoride was not added during the hydrothermal synthesis.

[0058] The preparation of CN@RGO / NF includes the following steps:

[0059] Step 1, Nickel foam pretreatment:

[0060] Cut 1×2 cm NF sheets, ultrasonically clean them with deionized water for 20 minutes, then ultrasonically clean them with ethanol for 20 minutes, repeat twice, and dry them at 60℃ for 2 hours for later use.

[0061] Step 2, Preparation of RGO / NF precursor:

[0062] Weigh 0.05 g of RGO and disperse it in 30 mL of deionized water. Sonicate the mixture for 30 minutes until homogeneous. Add the pretreated NF and stir at 200 r / min for 6 hours on a magnetic stirrer. Dry at 60℃ for 4 hours to obtain the RGO / NF precursor.

[0063] Step 3, hydrothermal synthesis:

[0064] Weigh out 1 mmol Co(NO3)2 6H2O, 1 mmol Ni(NO3)2 6H2O and 6 mmol of urea were added sequentially to 30 mL of deionized water and stirred for 30 minutes until completely dissolved. The RGO / NF precursor was immersed in the solution and transferred to a 50 mL polytetrafluoroethylene-lined high-pressure reactor. The reactor was kept at 120 °C for 8 hours.

[0065] Step 4, Post-processing:

[0066] After the reaction was completed, the mixture was allowed to cool naturally to room temperature. The product was then washed three times with deionized water and twice with ethanol. It was then vacuum-dried at 60°C for 6 hours to obtain CN@RGO / NF, in which the total active material loading of Co2NiO4 and RGO on the nickel foam surface was 2.8 mg / cm³. 2 .

[0067] Comparative Example 2: Preparation of CN / NF-F

[0068] The difference between this comparative example and Example 1 is that no RGO wrapping operation was performed.

[0069] Step 1, Nickel foam pretreatment:

[0070] Cut 1×2 cm NF sheets, ultrasonically clean them with deionized water for 20 minutes, then ultrasonically clean them with ethanol for 20 minutes, repeat twice, and dry them at 60℃ for 2 hours for later use.

[0071] Step 2, hydrothermal synthesis:

[0072] Weigh out 1 mmol Co(NO3)2 6H2O, 1 mmol Ni(NO3)2 6H2O, 3 mmol NH4F and 6 mmol urea were added sequentially to 30 mL of deionized water and stirred for 30 minutes until completely dissolved; the NF pretreated in step 1 was immersed in the solution and transferred to a 50 mL polytetrafluoroethylene-lined high-pressure reactor and reacted at 120℃ for 8 hours.

[0073] Step 3, Post-processing:

[0074] After the reaction was completed, the product was allowed to cool naturally to room temperature. It was then washed three times with deionized water and twice with ethanol. The product was then vacuum-dried at 60°C for 6 hours to obtain CN / NF-F, in which the loading of Co2NiO4 active material on the fluorine-doped nickel foam surface was 2.7 mg / cm³. 2 .

[0075] II. Characterization of CN@RGO / NF-F Electrode Materials

[0076] 1. SEM and TEM characterization:

[0077] Morphology was observed using FE-SEM (NOVANanoSEM450) and TEM (Tecnai G2 F20 S-TWIN). Figure 2 Electron micrographs of RGO / NF, CN / NF-F, CN@RGO / NF, and CN@RGO / NF-F are shown below. Figure 2 As shown, Figure 2 a) RGO encapsulates nickel foam (NF). The two-dimensional lamellar structure of RGO provides more growth sites. The RGO / NF substrate can provide support and dispersion for the subsequent growth of active materials, prevent the aggregation of active materials, and facilitate the exposure of more active sites. Figure 2 The CN / NF-F structure of b is dense, exhibiting a rhombic nanobulb stack, which is not conducive to sufficient contact with the electrolyte. Figure 2 The CN@RGO / NF of c mainly exhibits a nanoneedle structure, which tends to collapse and aggregate under long-term cycling, negatively impacting long-term cycling stability. In contrast, Figure 2 The CN@RGO / NF-F exhibits a regular and ordered interwoven nanosheet structure. This is due to the synergistic effect of RGO and F atoms. RGO provides more growth sites, the strong electronegativity of F atoms affects the interatomic forces and chemical bond formation, and the presence of CF bonds affects the distribution of active substances on the material surface, which helps to regulate the material morphology. Figure 2 e is a TEM image of CN@RGO / NF-F, which shows the presence of RGO (the area circled in yellow), confirming the successful synthesis of CN@RGO / NF-F. Figure 2 Lattice spacing analysis in f confirmed that CN@RGO / NF-F is mainly composed of Co2NiO4, with the blue circle indicating the presence of RGO, consistent with the TEM results.

[0078] 2. XRD and XPS characterization:

[0079] Figure 3 The EDS diagram of the CN@RGO / NF-F composite material prepared in Example 1 is shown below. Figure 3 As shown, the material contains nickel (Ni), cobalt (Co), carbon (C), fluorine (F), and oxygen (O), and the distribution of each element is relatively uniform. This indicates the successful synthesis of nickel cobalt oxide and the successful doping of fluorine. The uniform distribution of elements helps the material achieve a more stable and efficient electrochemical reaction during sodium ion storage, reducing problems such as excessive or insufficient local reactions caused by uneven element distribution. Combined with the uniform spherical morphology, this provides a good structural basis for the composite material to serve as a negative electrode for sodium-ion batteries in terms of electrochemical performance.

[0080] like Figure 4As shown in Figure a, the crystal structure and phase purity of the three samples CN@RGO / NF-F, CN / NF-F, and CN@RGO / NF were analyzed using X-ray diffraction (XRD) technology. All peaks of CN@RGO / NF-F, CN / NF-F, and CN@RGO / NF could be normalized to the Co2NiO4 standard spectrum (PDF#02-1074). Figure 4 XPS analysis detected the presence of Co, Ni, C, F, and O elements in CN@RGO / NF-F. 2+ / Co 3+ and Ni 2+ / Ni 3+ coexist, Figure 4 The F 1s spectrum of e shows FM (684.2 eV) and F x The presence of -C (685.8 eV) bonds confirms successful fluorine doping.

[0081] 3. Specific surface area and pore size:

[0082] like Figure 5 As shown in Figure a, the N2 adsorption-desorption test (Cryososorb-IQ) shows that CN@RGO / NF-F is H Ⅳ Type I isotherm, specific surface area 15.6 m² 2 / g, far exceeding CN@RGO / NF (6.2 m 2 / g) and CN / NF-F (8.5 m 2 ( / g), a large specific surface area can effectively increase active sites, thereby improving the performance of CN@RGO / NF-F. Figure 5 b represents the pore size distribution of four materials: CN@RGO / NF-F, CN@RGO / NF, CN / NF-F, and RGO / NF. It can be clearly seen that CN@RGO / NF-F has a wider pore size distribution range and a significant contribution to pore volume in the mesopore range (defined as 2-50 nm), indicating that it has a rich mesopore structure.

[0083] III. Applications of CN@RGO / NF-F Electrode Materials

[0084] Application Example 1

[0085] Using the negative electrode of a sodium-ion battery, specifically the CN@RGO / NF-F electrode material of Example 1, the CN / NF-F electrode material of Comparative Example 2, and the CN@RGO / NF electrode material of Comparative Example 1 as the working electrode, a sodium sheet as the counter electrode, and glass fiber as the separator, a sodium hexafluorophosphate electrolyte was used to assemble a 2016 coin-type sodium-ion half-cell.

[0086] Application Example 2

[0087] Electrochemical performance experiments were conducted using CR2025 half-cells on the CN@RGO / NF-F electrode material of Example 1 to confirm its performance as an anode (i.e., negative electrode) of sodium-ion batteries (SIBs). Figure 6 Cyclic voltammetry (CV) curves of the CN@RGO / NF-F electrode are presented. The initial cathode scan shows an irreversible reduction peak at 1.23 V, which may be related to the formation of the solid electrolyte interphase (SEI) film. The good overlap of the CV curves during the second and third cycles indicates that the material tends to stabilize in sodium-ion batteries.

[0088] Application Example 3

[0089] Figure 7 The impedance test curves of CN@RGO / NF-F, CN / NF-F, and CN@RGO / NF electrode materials at room temperature show that the charge transfer impedance of CN@RGO / NF-F electrode material (26Ω) is much smaller than that of CN@RGO / NF electrode material (35Ω) and CN / NF-F electrode material (48Ω). This indicates that fluorine doping successfully induced interface modulation of Co2NiO4@RGO, further activated the ion channels, significantly reduced the interface impedance, and accelerated the Na+ ion transfer. + The diffusion rate.

[0090] Application Example 4

[0091] Using CN@RGO / NF-F electrode material as the working electrode, a 2016 coin-type sodium-ion half-cell was assembled and subjected to charge-discharge tests. The test voltage window was 0.01~3V, and the test currents were 0.1A / g, 0.2A / g, 0.5A / g, 1A / g, 2A / g, and 5A / g, respectively. Finally, the current was restored to 0.1A / g, and the rate performance of the battery was tested. Figure 8 It can be seen that the CN@RGO / NF-F electrode material exhibits excellent rate performance at all current densities, with discharge capacities of 594.5, 512.3, 439.6, 370.8, 305.3 and 240.5 mAh / g at 0.1 A / g, 0.2 A / g, 0.5 A / g, 1 A / g, 2 A / g and 5 A / g, respectively.

[0092] Application Example 5

[0093] Using CN@RGO / NF-F electrode material, CN / NF-F electrode material, and CN@RGO / NF electrode material as working electrodes, respectively, 2016 coin-type sodium-ion half-cells were assembled and electrochemical tests were conducted. The test voltage window was 0.01-3 V, the test current was 1 A / g, and the cycle was 100 times. Then, using CN@RGO / NF-F electrode material as the working electrode, the cells were cycled for 1000 times at a high current density of 10 A / g.

[0094] Figure 9 The cycling curves for CN@RGO / NF-F, CN / NF-F, and CN@RGO / NF electrode materials after 100 cycles at a current density of 1 A / g are shown. It is clearly observed that the CN@RGO / NF-F electrode material outperforms the CN / NF-F and CN@RGO / NF electrode materials. First, the CN@RGO / NF-F electrode material exhibits a first-cycle discharge capacity of 365.8 mAh / g at 1 A / g current density, which is superior to the CN / NF-F electrode material (290.2 mAh / g) and CN@RGO / NF electrode material (226.3 mAh / g). Furthermore, after 100 cycles, the CN@RGO / NF-F electrode material retains 87.0% of its capacitance, which is superior to the CN / NF-F electrode material (51.4%) and CN@RGO / NF electrode material (62.8%).

[0095] Figure 10 The CN@RGO / NF-F electrode material was cycled 1000 times at a high sweep rate and a current density of 10 A / g. The charge-discharge curves showed near-overlapping, with a coulombic efficiency approaching 99%. The CN@RGO / NF-F electrode material exhibited an initial discharge capacity of 213.9 mAh / g at 10 A / g, and after 1000 cycles, the retention rate reached 84.9%, demonstrating excellent cycling stability. This is attributed to the two-dimensional layered structure of RGO providing more growth sites, inhibiting Co2NiO4 agglomeration, and the nickel foam reinforcement structure providing structural support and buffering volumetric strain during cycling.

[0096] This invention reveals the intrinsic mechanism behind the superior performance of CN@RGO / NF-F through materials characterization and electrochemical testing:

[0097] 1. Fluorine doping effect: The highly electronegative fluorine (F) atoms induce lattice distortion in Co₂NiO₄, modulating the electronic structure and prompting Co and Ni atoms to transfer electrons to F, forming electronic defect states, thus affecting the Co crystal structure. 2+ / Co 3+ Ni 2+ / Ni 3+ Valence equilibrium reconstruction significantly accelerates redox reaction kinetics and the reaction with OH. - Adsorption capacity;

[0098] 2. RGO / Nickel Foam Synergy: RGO has excellent electronic conductivity, providing high-efficiency electronic transport for electrode materials. At the same time, the two-dimensional sheet structure of RGO provides more growth sites and inhibits Co2NiO4 agglomeration. Nickel foam reinforces the structural support and buffers the volumetric strain during cycling.

[0099] 3. Three-dimensional structural advantages: The 2-50 nm mesoporous structure formed by interwoven nanosheets shortens the diffusion path of electrolyte ions. Simultaneously, the 15.6 nm... 2 The high specific surface area of ​​ / g increases the electrode / electrolyte contact interface, reduces charge transfer resistance, and improves rate performance and cycle stability;

[0100] 4. Activation mechanism of active sites in electrochemical activation

[0101] During activation, multiple cycles of CV treatment within a potential window of 0–0.6 V induce Co 2+ →Co 3+ Ni 2+ →Ni 3+ The partial irreversibility of the process increases the number of oxygen vacancies (the proportion of oxygen vacancies increases by 12% after activation), increases the number of active sites, and fully releases the energy storage potential of the material.

[0102] 5. Multi-dimensional synergistic mechanism of heteroatom doping-carbon material composite

[0103] This heteroatom-doped carbon composite structure, used as the anode in sodium-ion batteries, offers multi-dimensional synergistic enhancements to sodium storage performance: fluorine doping optimizes the intrinsic conductivity of the carbon-based material and the active sites for sodium ion adsorption through electronic structure modulation, significantly reducing the sodium ion insertion / extraction barrier; the two-dimensional sheet structure of reduced graphene oxide (RGO) effectively inhibits the aggregation of active components while constructing abundant porous structures to expand the specific surface area, providing ample transport channels and storage sites for sodium ions; the three-dimensional conductive network of nickel foam not only improves the overall conductivity of the electrode to accelerate charge transfer but also enhances the stability of the electrode structure, mitigating the structural collapse problem caused by volume expansion during charging and discharging. The synergistic effect of these three elements overcomes the trade-offs between specific capacity, rate performance, and cycle stability inherent in single modification strategies, achieving simultaneous improvements in high specific capacitance, excellent rate performance, and long cycle life. Furthermore, the fabrication process of this composite structure is compatible with existing battery production systems, demonstrating its potential for large-scale application.

[0104] The above embodiments and accompanying drawings are not intended to limit the preparation method and application of the present invention. Any appropriate changes or modifications made by those skilled in the art should be considered as not departing from the patent scope of the present invention.

Claims

1. A method for preparing a fluorine-doped Co2NiO4@RGO three-dimensional heterostructure electrode material, characterized in that: Includes the following steps: Step 1, NF pretreatment: After cutting the NF sheet, it is ultrasonically cleaned alternately with deionized water and ethanol, and then dried for later use. The NF is nickel foam. Step 2, Preparation of RGO / NF precursor: Disperse RGO in deionized water, add NF pretreated in Step 1, stir for 6-12 hours and then dry to obtain RGO / NF precursor; Step 3: Hydrothermal synthesis of fluorine-doped Co2NiO4@RGO: 1 mmol cobalt nitrate, 1 mmol nickel nitrate, 3 mmol ammonium fluoride, and 4-8 mmol urea are completely dissolved in 30-40 mL of deionized water. The RGO / NF precursor from Step 2 is added, and the mixture is transferred to a high-pressure reactor. The reaction is carried out hydrothermally at 120-150℃ for 6-8 hours. The cobalt nitrate is cobalt nitrate hexahydrate, and the nickel nitrate is nickel nitrate hexahydrate. Step 4, Post-processing: The reaction product is washed with deionized water and ethanol to remove surface deposits. After drying, a fluorine-doped Co2NiO4@RGO three-dimensional heterostructure electrode material is obtained, denoted as CN@RGO / NF-F. The total active material loading of fluorine-doped Co2NiO4 and RGO on the nickel foam surface is 3~5 mg / cm³. 2 ; The CN@RGO / NF-F exhibits a regular and ordered interwoven nanosheet structure, which forms a mesoporous structure. The specific surface area of ​​the CN@RGO / NF-F is 10-30 m². 2 / g, with a mesopore size distribution of 2~50 nm.

2. The application of the fluorine-doped Co2NiO4@RGO three-dimensional heterostructure electrode material as described in claim 1, characterized in that: It is used in sodium-ion batteries as a negative electrode material.

3. A sodium-ion battery, characterized in that: Using the CN@RGO / NF-F described in claim 1 as the working electrode, a sodium sheet as the counter electrode, a glass fiber membrane as the separator, and sodium hexafluorophosphate electrolyte, a 2016 coin cell sodium-ion half-cell is assembled.

Images