A v3o4 / vo2 homo-hetero composite carbon superstructure shell porous carbon nanofiber self-supporting electrode and a preparation method and application thereof

Abstract

The application discloses a V3O4 / VO2 homologous heterogeneous composite carbon superstructure shell layer porous carbon nanofiber self-supporting electrode and a preparation method and application thereof. Polyacrylonitrile, polytetrafluoroethylene nanoparticles and a first vanadium source are dissolved in N,N-dimethylformamide to prepare a precursor fiber membrane through an electrostatic spinning technology; the precursor fiber membrane is pre-oxidized in an air atmosphere, and then annealed to obtain vanadium-containing porous carbon nanofibers; the vanadium-containing porous carbon nanofibers are immersed in an acidic solution containing aniline monomers and ammonium persulfate to perform an oxidation polymerization reaction, dried, and then annealed to obtain polyphenylamine derivative carbon superstructure shell layer coated porous vanadium-containing carbon nanofibers; and the vanadium-containing carbon nanofibers are placed in a mixed solution containing a second vanadium source, oxalic acid and potassium ferricyanide to perform a hydrothermal reaction, dried, and then annealed to obtain the V3O4 / VO2 homologous heterogeneous composite carbon superstructure shell layer porous carbon nanofiber self-supporting electrode.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage, and relates to a V3O4 / VO2 homogeneous heterogeneous composite carbon superstructure shell porous carbon nanofiber self-supporting electrode, its preparation method and application. Background Technology

[0002] Zinc-ion energy storage devices, with their advantages of abundant zinc resources, low cost, high safety, and environmental friendliness, have shown broad application prospects in emerging fields such as flexible electronics and wearable devices. However, the relatively lagging development of cathode materials is a key bottleneck restricting the performance improvement of zinc-ion energy storage devices.

[0003] The energy storage mechanism of capacitive carbon electrodes mainly relies on double-layer adsorption and weak pseudocapacitance, which limits the theoretical improvement of specific capacity and makes it difficult to meet the urgent need for high energy density in flexible electronic devices. In contrast, battery-type vanadium-based oxide electrodes, with their multi-electron redox reactions and reversible zinc ion insertion / extraction mechanisms, have a much higher theoretical specific capacity than carbon-based materials, making them the core choice for overcoming the energy density bottleneck of zinc ion energy storage devices.

[0004] However, vanadium-based oxide electrodes still suffer from inherent defects such as low intrinsic electronic conductivity, sluggish zinc ion diffusion kinetics, and susceptibility to volume expansion and lattice collapse during charge and discharge. Furthermore, vanadium active materials are easily dissolved and lost in aqueous electrolytes, leading to poor cycle stability. Simultaneously, traditional vanadium-based oxide powder electrodes require the introduction of binders and current collectors, which not only increases interfacial impedance but also severely impairs the electrode's mechanical flexibility, making it difficult to adapt to the application requirements of flexible energy storage devices. In addition, when vanadium-based oxides are combined with carbon-based materials, problems such as active material agglomeration and weak interfacial bonding easily occur, failing to fully realize the synergistic energy storage effect of the two.

[0005] In recent years, researchers have made some progress in the field of vanadium-based composite electrodes. For example, Rao et al. synthesized an amorphous VOx-doped nitrogen-doped carbon fiber framework (VOx@GC) using gelatin and ammonium metavanadate via electrospinning, and used it for zinc anode modification. However, the VOx was amorphous and only served as a negative electrode modification layer, without involving the crystal phase control of the positive electrode active material. Another study reported a nitrogen-doped beaded hollow carbon nanofiber encapsulated ultra-small V2O3 composite material (V2O3@NHCNFs) prepared by combining electrospinning and template methods. Although this material exhibited high energy storage capacity, its vanadium oxide existed only as a single V2O3 crystal phase and was converted to hydrated vanadium oxide (VOH) through electrochemical oxidation, limiting its crystal phase diversity and interfacial synergistic effects. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a V3O4 / VO2 homogeneous and heterogeneous composite carbon superstructure shell porous carbon nanofiber self-supporting electrode, its preparation method and application, which has high energy density, excellent rate performance and long-term cycling stability.

[0007] To achieve the above objectives, the present invention employs the following technical solution: A method for preparing a V3O4 / VO2 homogeneous heterogeneous composite carbon superstructured porous carbon nanofiber self-supporting electrode includes the following steps: After dissolving polyacrylonitrile, polytetrafluoroethylene nanoparticles and a first vanadium source in N,N-dimethylformamide and mixing them, a precursor fiber membrane was prepared by electrospinning. The precursor fiber membrane was pre-oxidized in an air atmosphere and then annealed in an inert atmosphere to obtain vanadium-containing porous carbon nanofibers. Vanadium-containing porous carbon nanofibers were immersed in an acidic solution containing aniline monomer and ammonium persulfate to carry out an oxidative polymerization reaction. After washing and drying, they were annealed in an inert atmosphere to obtain porous vanadium-containing carbon nanofibers coated with a polyaniline-derived carbon superstructure shell. Porous vanadium-containing carbon nanofibers coated with a polyaniline-derived carbon superstructure shell were placed in a mixed solution containing a second vanadium source, oxalic acid, and potassium ferricyanide for hydrothermal reaction. After washing and drying, the nanofibers were annealed in an inert atmosphere to obtain a V3O4 / VO2 homogeneous heterogeneous composite carbon superstructure shell porous carbon nanofiber self-supporting electrode.

[0008] Optionally, the mass ratio of polyacrylonitrile, polytetrafluoroethylene nanoparticles to the first vanadium source is 0.5:0.5:0.5~1.5; the average particle size of the polytetrafluoroethylene nanoparticles is 30~100nm; and the spinning voltage in the electrospinning technology is 10~20kV, and the receiving distance is 15~25cm.

[0009] Optionally, the pre-oxidation temperature of the precursor fiber membrane in air is 230~270℃, and the pre-oxidation time is 1.5~2.5 hours; the annealing temperature of the precursor fiber membrane, vanadium-containing porous carbon nanofibers, and the washed and dried products after hydrothermal reaction in an inert atmosphere is 700~900℃, and the annealing time is 1.5~3 hours.

[0010] Optionally, the concentration of aniline monomer in the acidic solution is 0.3~0.8M; the amount of ammonium persulfate added per 25 mL of acidic solution is 0.05~0.2 g; the acidic solution is a sulfuric acid solution with a concentration of 0.5~2M; the temperature of the oxidative polymerization reaction is -10~0℃, and the time of the oxidative polymerization reaction is 18~30 hours.

[0011] Optionally, the molar ratio of the second vanadium source, oxalic acid and potassium ferricyanide in the mixed solution is 1:0.5~1.5:1; the volume ratio of N,N-dimethylformamide to deionized water in the mixed solution is 0.5~2:1; the hydrothermal reaction temperature is 140~180℃, and the hydrothermal reaction time is 6~12 hours.

[0012] Optionally, the first vanadium source is selected from at least one of vanadium acetylacetonate, ammonium metavanadate, or vanadium oxalate; the second vanadium source is selected from at least one of vanadium acetylacetonate, ammonium metavanadate, or vanadium oxalate; and the mass ratio of the first vanadium source to the second vanadium source is 1:0.5~2.

[0013] Optionally, the inert atmosphere is selected from at least one of nitrogen, argon, or helium.

[0014] A V3O4 / VO2 homogeneous heterogeneous composite carbon superstructure shell porous carbon nanofiber self-supporting electrode, comprising vanadium-containing porous carbon nanofibers. The outer surface of the vanadium-containing porous carbon nanofibers is covered with a polyaniline-derived carbon shell, and the surface of the polyaniline-derived carbon shell is attached with V3O4 / VO2 homogeneous heterogeneous junctions; the interior of the vanadium-containing porous carbon nanofibers contains vanadium-based anchor points formed by pre-embedded carbonization; the outer side of the polyaniline-derived carbon shell has a nano-spiky array structure; V3O4 phase and VO2 phase are co-distributed within the V3O4 / VO2 homogeneous heterogeneous junctions.

[0015] Optionally, the mass ratio of V3O4 phase to VO2 phase in the V3O4 / VO2 homogeneous junction is 1:0.3 to 1:3; the polyaniline-derived carbon shell is doped with nitrogen atoms derived from polyaniline, and the nitrogen atoms are connected to the V3O4 / VO2 homogeneous junction by VNC chemical bonds.

[0016] Application of a V3O4 / VO2 homogeneous heterogeneous composite carbon superstructure shell porous carbon nanofiber self-supporting electrode as a positive electrode in zinc-ion batteries or flexible zinc-ion capacitors.

[0017] Compared with the prior art, the present invention has the following beneficial effects: This invention employs a two-stage vanadium source supply strategy involving pre-embedded and exogenous sources. First, a first vanadium source is pre-embedded in a polyacrylonitrile and polytetrafluoroethylene system via electrospinning. Pre-oxidation and annealing create pores within carbon nanofibers, forming pre-embedded vanadium-based anchor points to provide sufficient independent nucleation sites for the active material and prevent severe aggregation. Subsequently, an in-situ polyaniline-derived carbon superstructure shell is coated through oxidative polymerization under acidic conditions and re-annealing. The unique nanospike array morphology of this shell not only constructs a continuous three-dimensional conductive network, significantly reducing interfacial charge transfer resistance, but also, through the dual effects of VNC chemical bonding and confinement formed by nitrogen atoms doped in the shell and vanadium oxides, fundamentally inhibits the dissolution and loss of vanadium active material during charging and discharging. Finally, hydrothermal treatment is performed in a system containing potassium ferricyanide. Through growth and annealing, the structure-directing effect of the Prussian blue analog intermediate and the independent control of vanadium concentration in two stages induce the directional recombination of the exogenous second vanadium source and the pre-embedded anchor point, achieving controllable and uniform co-existence of V3O4 and VO2 at the nanoscale. The constructed V3O4 / VO2 homogeneous phase junction synergistically leverages the high electronic conductivity and rigid framework provided by the metallic V3O4 phase and the advantages of the rapid zinc ion insertion / extraction channel provided by the tunnel structure VO2 phase at the microscopic level. At the same time, the shell and framework double-locked structure formed by the PANI-derived carbon shell and the Prussian blue analog derived carbon framework effectively buffers lattice collapse and volume expansion, ultimately endowing the binder-free self-supporting electrode with excellent high-rate electrochemical kinetics and long-cycle structural stability. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the preparation process of V3O4 / VO2-PC-VPCNF according to the present invention; Figure 2 The images are scanning electron microscope (SEM) images of VPCNF, PC-VPCNF, V3O4 / VO2-VPCNF and V3O4 / VO2-PC-VPCNF of the present invention; wherein (a) and (b) are VPCNF, (c) and (d) are PC-VPCNF, (e) and (f) are V3O4 / VO2-VPCNF, (g) and (h) are V3O4 / VO2-PC-VPCNF, and (i) is the elemental mapping diagram of V3O4 / VO2-PC-VPCNF; Figure 3 The Raman spectra of VPCNF, PC-VPCNF, V3O4 / VO2-VPCNF and V3O4 / VO2-PC-VPCNF of the present invention are shown below. Figure 4 XRD patterns of VPCNF, PC-VPCNF, V3O4 / VO2-VPCNF, V3O4 / VO2-PC-VPCNF, and powder precursors C-V3O4 and V-PBA of the present invention; Figure 5The XPS spectra of V3O4 / VO2-PC-VPCNF of the present invention are shown below; (a) is the full spectrum, (b) is the C1s high-resolution spectrum, (c) is the O1s high-resolution spectrum, (d) is the N1s high-resolution spectrum, and (e) is the V2p high-resolution spectrum. Figure 6 The following are electrochemical performance graphs of the ZIC devices assembled by the present invention from VPCNF, PC-VPCNF, V3O4 / VO2-VPCNF, and V3O4 / VO2-PC-VPCNF; where (a) is the CV curve, (b) is the GCD curve, (c) is the GCD curve of V3O4 / VO2-PC-VPCNF at different current densities, and (d) is the rate performance graph. Figure 7 This is a Ragone diagram of V3O4 / VO2-PC-VPCNF of the present invention; Figure 8 The present invention provides V3O4 / VO2-PC-VPCNF and V3O4 / VO2-VPCNF at 5 A·g - ¹Long-cycle stability plot at current density; Figure 9 The figures show the electrochemical kinetic analysis of V3O4 / VO2-PC-VPCNF and V3O4 / VO2-VPCNF of this invention; where (a) is the EIS diagram and (b) is the low-frequency region Z′ and ω. -0 · 5 The relationship diagram, (c) shows the GITT charge-discharge curve and Zn². + Diffusion coefficient; Figure 10 The diagram shows the CV curves and kinetic analysis of the V3O4 / VO2-PC-VPCNF at different scan rates in this invention; where (a) is the CV curve at different scan rates, (b) is the kinetic analysis of peak current versus scan rate, and (c) is the peak current at 0.2 mV·s. - ¹ represents the capacitance contribution, and (d) represents the capacitance contribution rate at different scan rates; Figure 11 The graphs show the electrochemical performance of the flexible zinc-ion capacitor based on V3O4 / VO2-PC-VPCNF of this invention; where (a) is the GCD curve at different folding angles, (b) is the rate performance evaluation, and (c) is the cycle stability test under bending conditions. Detailed Implementation

[0019] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0020] The following disclosure provides many different embodiments or examples for implementing various structures of the invention. To simplify the disclosure, specific examples of components and arrangements are described below. These are merely examples and are not intended to limit the invention. Furthermore, reference numerals and / or letters may be repeated in different examples; such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. In addition, examples of various specific processes and materials are provided in this invention, but those skilled in the art will recognize the application of other processes and / or the use of other materials.

[0021] The present invention describes a method for preparing a V3O4 / VO2 homogeneous heterogeneous composite carbon superstructured porous carbon nanofiber self-supporting electrode, such as... Figure 1 As shown, it includes the following steps: 1) Preparation of precursor fibers: Polyacrylonitrile, polytetrafluoroethylene nanoparticles and a first vanadium source were dissolved in N,N-dimethylformamide, stirred and mixed evenly, and precursor fiber membranes were prepared by electrospinning technology.

[0022] The mass ratio of polyacrylonitrile, polytetrafluoroethylene nanoparticles to the first vanadium source is 0.5:0.5:0.5~1.5.

[0023] The average particle size of polytetrafluoroethylene nanoparticles is 30~100nm.

[0024] The voltage for electrospinning is 10~20kV, and the receiving distance is 15~25cm.

[0025] 2) Pre-oxidation and carbonization: The precursor fiber membrane obtained in step 1) is pre-oxidized in air at 230~270℃ for 1.5~2.5 hours, and then annealed in an inert atmosphere at 700~900℃ for 1.5~3 hours to obtain vanadium-containing porous carbon nanofibers.

[0026] 3) Polyaniline coating and carbonization: The vanadium-containing porous carbon nanofibers obtained in step 2) are immersed in an acidic solution containing aniline monomer and ammonium persulfate and subjected to an oxidative polymerization reaction at -10~0℃ for 18~30 hours to grow a polyaniline nano-spiky array on the fiber surface in situ. After washing and drying, the fibers are annealed at 700~900℃ for 1.5~3 hours in an inert atmosphere to obtain porous vanadium-containing carbon nanofibers coated with a polyaniline-derived carbon superstructure shell.

[0027] The concentration of aniline monomer is 0.3~0.8M, the amount of ammonium persulfate added is 0.05~0.2g, and the acidic solution is 0.5~2M H2SO4.

[0028] 4) In-situ composite of V3O4 / VO2 homogeneous and heterogeneous structures: The material obtained in step 3) is placed in a mixed solution containing a second vanadium source, oxalic acid and potassium ferricyanide, and hydrothermally reacted at 140~180℃ for 6~12 hours. After washing and drying, it is annealed at 700~900℃ for 1.5~3 hours in an inert atmosphere to obtain a V3O4 / VO2 homogeneous and heterogeneous composite carbon superstructure shell porous carbon nanofiber self-supporting electrode.

[0029] The molar ratio of the second vanadium source, oxalic acid and potassium ferricyanide is 1:0.5~1.5:1, and the volume ratio of DMF to deionized water in the mixed solution is 0.5~2:1.

[0030] The first vanadium source is at least one of vanadium acetylacetonate, ammonium metavanadate, or vanadium oxalate, and the second vanadium source is at least one of vanadium acetylacetonate, ammonium metavanadate, or vanadium oxalate, with a mass ratio of the first vanadium source to the second vanadium source of 1:0.5~2.

[0031] In the V3O4 / VO2 homogeneous structure, the mass ratio of the V3O4 phase to the VO2 phase is controlled within the range of 1:0.3 to 1:3 by adjusting the relative contents of the first vanadium source in step 1) and the second vanadium source in step 4).

[0032] The inert atmosphere is at least one of N2, Ar or He.

[0033] The V3O4 / VO2 homogeneous and heterogeneous composite carbon superstructured porous carbon nanofiber self-supporting electrode prepared by the above method V3O4 / VO2 homogeneous heterogeneous composite carbon superstructure shell porous carbon nanofiber self-supporting electrode is used as a positive electrode in zinc-ion batteries or flexible zinc-ion capacitors.

[0034] The self-supporting electrode serves directly as the positive electrode, eliminating the need for binders and current collectors. The electrolyte in zinc-ion batteries or flexible zinc-ion capacitors is an aqueous solution of zinc trifluoromethanesulfonate or a PVA / ZnOTF gel electrolyte.

[0035] This invention employs a two-stage vanadium source supply strategy involving pre-embedded and external sources. By pre-setting vanadium source anchor points inside the carbon fiber and directionally depositing vanadium source on the carbon shell surface, it provides abundant active nucleation sites and independent regulatory dimensions for the in-situ uniform symbiosis of V3O4 / VO2. This avoids severe agglomeration of active materials or weak interfacial adhesion. At the same time, it achieves for the first time precise control of the ratio of V3O4 to VO2 within the range of 1:0.3 to 1:3.

[0036] This invention constructs a continuous three-dimensional conductive network with a nanospike-like morphology by coating a PANI-derived carbon superstructure shell, which significantly reduces the charge transfer resistance. At the same time, the dissolution and loss of vanadium active material are effectively suppressed by the dual effects of chemical bonding and physical confinement at the VNC interface. The dual-locked structure of shell and framework (PANI-derived carbon shell + V-PBA-derived carbon framework) further enhances the structural stability.

[0037] In the V3O4 / VO2 homogeneous-heterogeneous composite electrode prepared by this invention, the V3O4 phase with metallic properties (resistivity ~10) - The VO2 phase (3Ω·cm) provides excellent electronic conductivity and a rigid three-dimensional framework. The tunnel structure provides a fast insertion / extraction channel for zinc ions. The homogeneous-heterogeneous junction formed at the interface of the two phases significantly reduces the interfacial charge transfer resistance and synergistically improves the electrochemical performance—this is the first report of its kind in the cathode material of zinc ion energy storage devices.

[0038] The self-supporting electrode prepared by this invention does not require the addition of binders and current collectors, thus avoiding increased interfacial impedance and damage to mechanical flexibility, and can be directly used to assemble flexible zinc-ion capacitors.

[0039] The electrode of this invention is at 0.2 A·g - ¹Specific capacity up to 270.13mAh·g - ¹, at 10A·g - ¹Still maintains 153.54 mAh·g at high rates - ¹The reversible capacity, at 5 A·g - ¹After 5000 cycles, the capacity retention rate reached 79.7%, and after being assembled into a flexible device, it exhibited excellent bending stability. Its overall performance was superior to existing V2O3@NHCNFs and VOx@GC.

[0040] Example 1 Step 1) Preparation of precursor fibers.

[0041] 0.5 g of polyacrylonitrile (PAN), 0.5 g of polytetrafluoroethylene nanoparticles (PTFENPs) with an average particle size of 30 nm, and 0.5 mmol (approximately 0.13 g) of vanadium acetylacetonate (VO(acac)2) were added to 5 mL of N,N-dimethylformamide (DMF). The mixture was stirred vigorously at 80 °C for 1 hour to obtain a dark green suspension. Subsequently, stirring was continued at 60 °C for 2 hours to obtain a dark green-white sol, which served as the precursor solution for electrospinning. During electrospinning, the high voltage between the spinning needle and the receiver was set to 10 kV, and the distance was fixed at 15 cm. The electrospun PTFENPs-V@PAN fiber membrane was dried in ambient air overnight.

[0042] Step 2) Pre-oxidation and carbonization.

[0043] The dried PTFENPs-V@PAN fiber membrane was pre-oxidized in air at 230°C for 1.5 hours. After cooling, it was annealed in N2 atmosphere at 700°C for 1.5 hours, with a heating rate of 5°C / min. During the carbonization process, the high-temperature decomposition and removal of PTFENPs and the formation of vanadium oxides occurred simultaneously, ultimately yielding a vanadium-containing porous carbon nanofiber (VPCNF) membrane.

[0044] Step 3) Polyaniline coating and carbonization.

[0045] A 25 mL solution containing 0.3 M aniline monomer and 0.5 M H₂SO₄ was prepared, and 0.05 g of ammonium persulfate (APS) was added. After thorough stirring, the VPCNF membrane was immersed in the solution, and an oxidative polymerization reaction was carried out at -10 °C for 18 hours. The sample was removed, cleaned, dried, and then annealed again at 700 °C for 1.5 hours under a N₂ atmosphere with a heating rate of 5 °C / min to obtain a polyaniline-derived carbon shell porous vanadium-containing carbon nanofiber (PC-VPCNF) membrane.

[0046] Step 4) In-situ composite of V3O4 / VO2 homogeneous heterogeneous structures.

[0047] The PC-VPCNF membrane was placed in a 20 mL mixed solution containing 0.5 mmol of vanadium acetylacetonate (VO(acac)2), 0.25 mmol of oxalic acid, and 0.5 mmol of potassium ferricyanide (K3[Fe(CN)6]) (DMF:water = 0.5:1) and subjected to hydrothermal reaction at 140 °C for 6 hours. After the reaction was completed, the sample was removed, repeatedly washed with deionized water and ethanol, dried, and annealed at 700 °C for 1.5 hours under a N2 atmosphere at a heating rate of 5 °C / min to obtain a V3O4 / VO2 homogeneous composite carbon superstructured porous carbon nanofiber (V3O4 / VO2-PC-VPCNF) self-supporting electrode. XRD and Rietveld refinement analysis showed that the mass ratio of the V3O4 phase to the VO2 phase in the product obtained in this example was approximately 1:0.3.

[0048] Example 2 Step 1) Preparation of precursor fibers.

[0049] 0.5 g of polyacrylonitrile (PAN), 0.5 g of polytetrafluoroethylene nanoparticles (PTFENPs) with an average particle size of 50 nm, and 1.0 mmol (approximately 0.27 g) of vanadium acetylacetonate (VO(acac)2) were added to 5 mL of N,N-dimethylformamide (DMF). The mixture was stirred vigorously at 80 °C for 1 hour to obtain a dark green suspension. Subsequently, stirring was continued at 60 °C for 2 hours to obtain a dark green-white sol, which served as the precursor solution for electrospinning. During electrospinning, the high voltage between the spinning needle and the receiver was set to 15 kV, and the distance was fixed at 18 cm. The electrospun PTFENPs-V@PAN fiber membrane was dried in ambient air overnight.

[0050] Step 2) Pre-oxidation and carbonization.

[0051] The dried PTFENPs-V@PAN fiber membrane was pre-oxidized at 250°C for 2 hours in air. After cooling, it was annealed at 800°C for 2 hours in N2 atmosphere, with a heating rate of 5°C / min. During the carbonization process, the high-temperature decomposition and removal of PTFENPs and the formation of vanadium oxides occurred simultaneously, ultimately yielding a vanadium-containing porous carbon nanofiber (VPCNF) membrane.

[0052] Step 3) Polyaniline coating and carbonization.

[0053] A 25 mL solution containing 0.5 M aniline monomer and 1 M H₂SO₄ was prepared, and 0.1 g ammonium persulfate (APS) was added. After thorough stirring, the VPCNF membrane was immersed in the solution, and an oxidative polymerization reaction was carried out at -4 °C for 24 hours. The sample was removed, washed, dried, and then annealed again at 800 °C for 2 hours under a N₂ atmosphere with a heating rate of 5 °C / min to obtain a polyaniline-derived carbon shell porous vanadium-containing carbon nanofiber (PC-VPCNF) membrane.

[0054] Step 4) In-situ composite of V3O4 / VO2 homogeneous heterogeneous structures.

[0055] The PC-VPCNF membrane was placed in a 20 mL mixed solution containing 1.0 mmol of vanadium acetylacetonate (VO(acac)2), 1.0 mmol of oxalic acid, and 1.0 mmol of potassium ferricyanide (K3[Fe(CN)6]) (DMF:water = 1:1) and subjected to hydrothermal reaction at 160 °C for 8 hours. After the reaction was completed, the sample was removed, repeatedly washed with deionized water and ethanol, dried, and annealed at 800 °C for 2 hours under a N2 atmosphere at a heating rate of 5 °C / min to obtain a V3O4 / VO2 homogeneous composite carbon superstructured porous carbon nanofiber (V3O4 / VO2-PC-VPCNF) self-supporting electrode. XRD and Rietveld refinement analysis showed that the mass ratio of the V3O4 phase to the VO2 phase in the product obtained in this example was approximately 1:1.

[0056] Example 3 Step 1) Preparation of precursor fibers.

[0057] 0.5 g of polyacrylonitrile (PAN), 0.5 g of polytetrafluoroethylene nanoparticles (PTFENPs) with an average particle size of 100 nm, and 1.5 mmol (approximately 0.40 g) of vanadium acetylacetonate (VO(acac)2) were added to 5 mL of N,N-dimethylformamide (DMF). The mixture was stirred vigorously at 80 °C for 1 hour to obtain a dark green suspension. Subsequently, stirring was continued at 60 °C for 2 hours to obtain a dark green-white sol, which served as the precursor solution for electrospinning. During electrospinning, the high voltage between the spinning needle and the receiver was set to 20 kV, and the distance was fixed at 25 cm. The electrospun PTFENPs-V@PAN fiber membrane was dried in ambient air overnight.

[0058] Step 2) Pre-oxidation and carbonization.

[0059] The dried PTFENPs-V@PAN fiber membrane was pre-oxidized in air at 270°C for 2.5 hours. After cooling, it was annealed in N2 atmosphere at 900°C for 3 hours at a heating rate of 5°C / min. During the carbonization process, the high-temperature decomposition and removal of PTFENPs and the formation of vanadium oxides occurred simultaneously, ultimately yielding a vanadium-containing porous carbon nanofiber (VPCNF) membrane.

[0060] Step 3) Polyaniline coating and carbonization.

[0061] A 25 mL solution containing 0.8 M aniline monomer and 2 M H₂SO₄ was prepared, and 0.2 g of ammonium persulfate (APS) was added. After thorough stirring, the VPCNF membrane was immersed in the solution and subjected to oxidative polymerization at 0 °C for 30 hours. The sample was then removed, washed, dried, and annealed again at 900 °C for 3 hours under a N₂ atmosphere at a heating rate of 5 °C / min to obtain a polyaniline-derived carbon shell porous vanadium-containing carbon nanofiber (PC-VPCNF) membrane.

[0062] Step 4) In-situ composite of V3O4 / VO2 homogeneous heterogeneous structures.

[0063] The PC-VPCNF membrane was placed in a 20 mL mixed solution containing 1.5 mmol of vanadium acetylacetonate (VO(acac)2), 2.25 mmol of oxalic acid, and 1.5 mmol of potassium ferricyanide (K3[Fe(CN)6]) (DMF:water = 2:1) and subjected to hydrothermal reaction at 180 °C for 12 hours. After the reaction was completed, the sample was removed, repeatedly washed with deionized water and ethanol, dried, and annealed at 900 °C for 3 hours under N2 atmosphere at a heating rate of 5 °C / min to obtain a V3O4 / VO2 homogeneous composite carbon superstructured porous carbon nanofiber (V3O4 / VO2-PC-VPCNF) self-supporting electrode. XRD and Rietveld refinement analysis showed that the mass ratio of the V3O4 phase to the VO2 phase in the product obtained in this example was approximately 1:3.

[0064] Comparative Example 1 The preparation steps are basically the same as in Example 2, except that step 3, polyaniline coating and carbonization, is not performed. Instead, step 4, hydrothermal growth and annealing, is performed directly on the VPCNF film to obtain the control sample V3O4 / VO2-VPCNF.

[0065] Comparative Example 2 The preparation steps are basically the same as in Example 2, except that potassium ferricyanide is not added in step 4, that is, no vanadium-based Prussian blue analog intermediate is formed, and vanadium oxide is directly grown hydrothermally on the PC-VPCNF surface.

[0066] Example 4 Assembly of Zinc-ion coin cells: The V3O4 / VO2-PC-VPCNF film prepared in Example 2 was cut into 12mm diameter circular cathodes using a slicer and used directly as self-supporting positive electrodes without the need for binders or current collectors. The active material mass of the electrode was 0.5-1.0 mg. A 14mm zinc foil was used as the anode. CR2032 coin cells were assembled using a 3M ZnOTF aqueous solution as the electrolyte.

[0067] Example 5 Assembly of the flexible zinc-ion capacitor: The V3O4 / VO2-PC-VPCNF membrane prepared in Example 2 was cut into 1cm × 1cm rectangles as the cathode, and soft zinc foil was used as the anode. The PVA / ZnOTF gel electrolyte was prepared as follows: 2g of PVA was dissolved in 20mL of 1M ZnOTF electrolyte at 90℃, stirred for 1 hour, and then placed in a -20℃ freezer for 5 freeze-thaw cycles. The gel electrolyte was sandwiched between the anode and cathode, and stainless steel foil was used as the electrode current collector, extending into tabs. Finally, the stacked battery structure was encapsulated in an aluminum-plastic film to obtain the flexible zinc-ion capacitor.

[0068] Example 6 Electrochemical performance testing: The coin cells assembled in Example 4 were subjected to electrochemical performance testing. Figure 6 As shown, at 0.2 A·g - ¹At current density, the specific capacity of the V3O4 / VO2-PC-VPCNF electrode reaches as high as 270.13 mAh·g. - ¹, significantly better than VPCNF (112.51 mAh·g). - ¹), PC-VPCNF (184.13mAh·g - ¹) and V3O4 / VO2-VPCNF (241.85mAh·g - ¹). When the current density is increased to 10 A·g - At ¹, V3O4 / VO2-PC-VPCNF can still maintain 153.54 mAh·g - ¹ Its reversible capacity exhibits excellent rate capability.

[0069] like Figure 8 As shown, at 5A·g - ¹ Under high current density and long-term cycling tests, V3O4 / VO2-PC-VPCNF maintained a capacity retention of 79.7% after 5000 deep charge-discharge cycles; while V3O4 / VO2-VPCNF without a PANI-derived carbon shell only maintained a capacity retention of 50.4% under the same conditions. In Comparative Example 2, the sample without potassium ferricyanide showed uneven distribution of vanadium oxide on the carbon fiber surface, with obvious agglomeration. (0.2 A·g) - ¹The specific capacity is only 198.34 mAh·g - ¹, after 5000 cycles, the capacity retention rate was 62.1%, lower than 79.7% in Example 2, demonstrating the key role of the Prussian blue analog structure directing agent in the uniform dispersion of vanadium oxide.

[0070] Example 7 Performance testing of flexible zinc-ion capacitors: The flexible zinc-ion capacitors assembled in Example 5 were subjected to performance testing. Figure 11 As shown in (a), the GCD curves almost completely overlap in the three folding states of 0°, 90°, and 180°, indicating that the FZIC device has good bending stability. Figure 11 As shown in (b), the device operates at 0.5 A·g - ¹ Achieving 206.23 mAh·g at a low current density. - ¹High specific capacity, at 5 A·g - ¹The specific capacity can still reach 132.53 mAh·g under high current density. - ¹.

[0071] like Figure 2As shown, the microstructure evolution of the material is demonstrated from bare carbon nanofibers to polyaniline-derived carbon nanofiber shells, and then to vanadium-based oxide loading. The uniform distribution of C, O, N, and V elements in the composite material is also confirmed by the elemental mapping diagram.

[0072] Figure 3 Used to characterize the microstructure of carbon materials at each stage, by comparing the intensity ratio of characteristic peaks (such as the D peak characterizing defects and the G peak characterizing graphitization, $I_D / I_G$), the structural changes in the degree of defects in the carbon skeleton after the material is coated with a carbon shell and loaded with metal oxides are explained, which helps to prove the establishment of the conductive network.

[0073] Figure 4 By comparing with standard diffraction cards, the phase composition of each intermediate and the final composite material was confirmed from a crystallographic perspective. In particular, it directly proved the successful coexistence of the two crystal phases V3O4 and VO2 in the final product.

[0074] Figure 5 The chemical composition and elemental valence states of the electrode material surface were revealed, such as verifying the successful doping of nitrogen and the presence of mixed valence states of vanadium (V(III) and V(IV)), which were used to confirm the formation of chemical bonds such as VNC.

[0075] Figure 7 By plotting the relationship curve between energy density and power density, the comprehensive electrochemical output capabilities of VPCNF, PC-VPCNF, V3O4 / VO2-VPCNF and the final product of this invention can be intuitively compared, highlighting the significant advantages of the composite structure of this invention in balancing high energy density and high power density.

[0076] Figure 9 The positive effects of homogeneous heterojunctions and carbon superstructure shells on improving zinc ion diffusion dynamics were quantitatively analyzed from three dimensions: the magnitude of charge transfer impedance, solid-phase ion diffusion resistance, and the specific diffusion rate of zinc ions within the lattice.

[0077] Figure 10 The pseudocapacitive energy storage contribution of the self-supporting electrode during the charge and discharge process was stripped and quantified, demonstrating its intrinsic reaction mechanism with excellent rate performance.

[0078] In existing technologies, the composite of vanadium-based oxides and carbon materials typically employs a single crystalline phase (such as V₂O₃, VO₂, V₂O₅, etc.). For example, the V₂O₃@NHCNFs composite material reported in the literature contains only a single V₂O₃ crystalline phase, which transforms into hydrated vanadium oxide (VOH) after electrochemical oxidation, remaining a single-phase system. This invention, through a two-stage vanadium source supply strategy involving pre-embedded and exogenous sources, combined with the confinement effect of the PANI-derived carbon shell and the guiding effect of the Prussian blue analog template, achieves for the first time the controllable coexistence and nanoscale uniform distribution of V₃O₄ and VO₂ phases on a carbon framework. The V₃O₄ phase, with its metallic properties (resistivity approximately ~10⁻⁶), exhibits this characteristic. - The VO2 phase (³Ω·cm) provides excellent electronic conductivity and a rigid three-dimensional framework. Its unique tunnel structure (a one-dimensional channel along the c-axis) provides a rapid insertion / extraction pathway for zinc ions. The homogeneous-heterogeneous junction formed at the two-phase interface significantly reduces the interfacial charge transfer resistance and enhances the adsorption capacity for zinc ions by utilizing the local strain field generated by the lattice mismatch between the two phases. This homogeneous-heterogeneous symbiotic structure design has not been reported in cathode materials for zinc-ion energy storage devices.

[0079] Existing technologies typically introduce vanadium sources in a single stage, either by pre-embedding the vanadium source in the electrospinning precursor or by introducing it externally through subsequent hydrothermal / solvothermal processes. For example, the preparation of V2O3@NHCNFs uses only ammonium metavanadate as the single vanadium source, obtaining V2O3 through pre-embedding via electrospinning followed by thermal reduction; VOx@GC similarly uses only ammonium metavanadate as the single vanadium source, yielding amorphous VOx. This invention creatively employs a two-stage "pre-embedding-external source" strategy: In the first stage, vanadium source "anchors" are pre-placed inside the carbon fiber using vanadium acetylacetonate, forming VN_x or VO_x-C bonding sites through carbonization, providing abundant active nucleation sites for the subsequent in-situ uniform growth of VO_x; in the second stage, vanadium source is directionally deposited on the carbon shell surface through in-situ growth of a vanadium-based Prussian blue analogue (V-PBA) with potassium ferricyanide as a structure directing agent. This two-stage supply mechanism allows for independent control of the vanadium source concentration both inside and on the surface of the carbon fiber, thereby achieving precise control of the V3O4 and VO2 two-phase ratio (adjustable within the range of 1:0.3 to 1:3). Furthermore, the method of constructing V-PBA intermediates using potassium ferricyanide as a structure directing agent has not been reported in the preparation of vanadium-based flexible electrodes.

[0080] Multiple confinement effects of polyaniline-derived carbon superstructure shell: Unlike conventional carbon coatings, this invention grows polyaniline nano-spiky arrays in situ on the fiber surface through low-temperature (-4℃) oxidative polymerization, and forms a carbon superstructure shell with nano-spiky morphology after high-temperature carbonization. Unlike the porous carbon layers formed by PTFE templates in V2O3@NHCNFs reported in the literature, the carbon superstructure shell constructed by the PANI nanospike array in this invention has the following unique advantages: (i) The nanospike structure increases the contact area between the carbon shell and vanadium oxide, forming a continuous three-dimensional conductive network and significantly reducing the charge transfer resistance; (ii) The nitrogen atoms doped in the carbon shell (derived from PANI) form VNC chemical bonds with the vanadium oxide, enhancing the interfacial bonding force and effectively inhibiting the dissolution and loss of vanadium active materials; (iii) The physical confinement space formed by the nanospike array restricts the growth size of vanadium oxide nanoparticles (controlled within 10-30 nm), avoiding the volume expansion problem caused by large-sized particles; (iv) It forms a dual-confined network with the V-PBA-derived carbon skeleton, in which V-PBA is transformed into a nitrogen-doped carbon skeleton during high-temperature carbonization, and together with the PANI-derived carbon shell, it constructs a shell and skeleton dual-locking structure.

[0081] Compared with existing technologies, the V3O4 / VO2-PC-VPCNF electrode prepared in this invention achieves comprehensive superiority in electrochemical performance. In contrast, the V2O3@NHCNFs electrode (0.5 A·g) exhibits significantly better performance. - ¹443.8mAh·g - ¹, 20A·g - ¹The electrode of this invention retains 76% of its performance after 4000 cycles, and it operates at higher current densities (5 A·g). - ¹) Achieving a 79.7% retention rate after 5000 cycles demonstrates significant advantages in cycle stability; compared to the VOx@GC modified zinc anode system (full cell 219.6 mAh·g) - ¹@2A·g - ¹), the specific capacity of the electrode of this invention as a positive electrode material (270.13 mAh·g) - ¹@0.2A·g - ¹) Significantly higher. When the electrodes of this invention are assembled into a flexible zinc-ion capacitor, the GCD curves almost completely overlap in the folded states of 0°, 90° and 180°, exhibiting excellent bending stability.

[0082] The sequence numbers of the embodiments in this application are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0083] In the above embodiments of this application, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0084] The above description is only a preferred embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

[0085] It should be understood that the above description is for illustrative purposes and not for limitation. Many embodiments and applications beyond the provided examples will be apparent to those skilled in the art upon reading the above description. Therefore, the scope of this patent should not be determined by reference to the above description, but rather by reference to the foregoing claims and the full scope of their equivalents. For purposes of completeness, all articles and references, including patent applications and publications, are incorporated herein by reference. The omission of any aspect of the subject matter disclosed herein in the foregoing claims is not intended as a waiver of that subject matter, nor should it be construed as an indication that the applicant has not considered that subject matter as part of the disclosed inventive subject matter.

Claims

1. A method for preparing a V3O4 / VO2 homogeneous heterogeneous composite carbon superstructured porous carbon nanofiber self-supporting electrode, characterized in that, The process includes the following: After dissolving polyacrylonitrile, polytetrafluoroethylene nanoparticles and a first vanadium source in N,N-dimethylformamide and mixing them, a precursor fiber membrane was prepared by electrospinning. The precursor fiber membrane was pre-oxidized in an air atmosphere and then annealed in an inert atmosphere to obtain vanadium-containing porous carbon nanofibers. Vanadium-containing porous carbon nanofibers were immersed in an acidic solution containing aniline monomer and ammonium persulfate to carry out an oxidative polymerization reaction. After washing and drying, they were annealed in an inert atmosphere to obtain porous vanadium-containing carbon nanofibers coated with a polyaniline-derived carbon superstructure shell. Porous vanadium-containing carbon nanofibers coated with a polyaniline-derived carbon superstructure shell were placed in a mixed solution containing a second vanadium source, oxalic acid, and potassium ferricyanide for hydrothermal reaction. After washing and drying, the nanofibers were annealed in an inert atmosphere to obtain a V3O4 / VO2 homogeneous heterogeneous composite carbon superstructure shell porous carbon nanofiber self-supporting electrode.

2. The method for preparing the V3O4 / VO2 homogeneous heterogeneous composite carbon superstructured porous carbon nanofiber self-supporting electrode according to claim 1, characterized in that, The mass ratio of polyacrylonitrile, polytetrafluoroethylene nanoparticles to the first vanadium source is 0.5:0.5:0.5~1.5; the average particle size of the polytetrafluoroethylene nanoparticles is 30~100nm; the spinning voltage in the electrospinning technology is 10~20kV, and the receiving distance is 15~25cm.

3. The method for preparing the V3O4 / VO2 homogeneous heterogeneous composite carbon superstructured porous carbon nanofiber self-supporting electrode according to claim 1, characterized in that, The pre-oxidation temperature of the precursor fiber membrane in air is 230~270℃, and the pre-oxidation time is 1.5~2.5 hours. The annealing temperature of the precursor fiber membrane, vanadium-containing porous carbon nanofibers, and the washed and dried products after hydrothermal reaction in an inert atmosphere is 700~900℃, and the annealing time is 1.5~3 hours.

4. The method for preparing the V3O4 / VO2 homogeneous heterogeneous composite carbon superstructured porous carbon nanofiber self-supporting electrode according to claim 1, characterized in that, The concentration of aniline monomer in the acidic solution is 0.3~0.8M; the amount of ammonium persulfate added per 25 mL of acidic solution is 0.05~0.2g; the acidic solution is a sulfuric acid solution with a concentration of 0.5~2M; the temperature of the oxidative polymerization reaction is -10~0℃, and the time of the oxidative polymerization reaction is 18~30 hours.

5. The method for preparing the V3O4 / VO2 homogeneous heterogeneous composite carbon superstructured porous carbon nanofiber self-supporting electrode according to claim 1, characterized in that, The molar ratio of the second vanadium source, oxalic acid and potassium ferricyanide in the mixed solution is 1:0.5~1.5:1; the volume ratio of N,N-dimethylformamide to deionized water in the mixed solution is 0.5~2:1; the hydrothermal reaction temperature is 140~180℃, and the hydrothermal reaction time is 6~12 hours.

6. The method for preparing the V3O4 / VO2 homogeneous heterogeneous composite carbon superstructured porous carbon nanofiber self-supporting electrode according to claim 1, characterized in that, The first vanadium source is selected from at least one of vanadium acetylacetonate, ammonium metavanadate, or vanadium oxalate; the second vanadium source is selected from at least one of vanadium acetylacetonate, ammonium metavanadate, or vanadium oxalate; the mass ratio of the first vanadium source to the second vanadium source is 1:0.5~2.

7. The method for preparing the V3O4 / VO2 homogeneous heterogeneous composite carbon superstructured porous carbon nanofiber self-supporting electrode according to claim 1, characterized in that, The inert atmosphere is selected from at least one of nitrogen, argon or helium.

8. A V3O4 / VO2 homogeneous heterogeneous composite carbon superstructured porous carbon nanofiber self-supporting electrode prepared by the preparation method according to any one of claims 1-7, characterized in that, Including vanadium-containing porous carbon nanofibers; The outer surface of the vanadium-containing porous carbon nanofibers is covered with a polyaniline-derived carbon shell, and the surface of the polyaniline-derived carbon shell is attached with V3O4 / VO2 homogeneous heterogeneous junctions; the interior of the vanadium-containing porous carbon nanofibers contains vanadium-based anchor points formed by pre-embedded carbonization; the outer side of the polyaniline-derived carbon shell has a nano-spiky array structure; V3O4 phase and VO2 phase are co-distributed within the V3O4 / VO2 homogeneous heterogeneous junctions.

9. The V3O4 / VO2 homogeneous heterogeneous composite carbon superstructure shell porous carbon nanofiber self-supporting electrode according to claim 8, characterized in that, The mass ratio of V3O4 phase to VO2 phase in the V3O4 / VO2 homogeneous junction is 1:0.3 to 1:3; the polyaniline-derived carbon shell is doped with nitrogen atoms derived from polyaniline, and the nitrogen atoms are connected to the V3O4 / VO2 homogeneous junction by VNC chemical bonds.

10. The application of a self-supporting carbon nanofiber porous shell porous carbon superstructure electrode based on any one of claims 8 or 9 as a positive electrode in a zinc-ion battery or a flexible zinc-ion capacitor.

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