Current collector active material and preparation method and application thereof

Abstract

The invention discloses a current collector active material and a preparation method and application thereof, and relates to the technical field of electrochemical energy storage. Comprising the following steps: dissolving acid, a niobium precursor and aniline in water to form a solution A; dissolving ammonium persulfate in water to form a solution B, adding the solution B into the solution A, uniformly mixing, standing for reaction, carrying out suction filtration and drying to obtain niobium-doped polyaniline carbon nanotubes, and carrying out heat treatment on the niobium-doped polyaniline carbon nanotubes in a protective atmosphere to obtain amorphous carbon nanotubes embedded with niobium pentoxide nanoparticles. The method can be used for preparing a negative-electrode-free sodium metal battery current collector and a negative-electrode-free sodium metal battery. According to the method, hectogram or even kilogram-level superfine amorphous carbon nanotubes embedded with niobium pentoxide nanoparticles can be prepared in a single batch in a macroscopic manner, and Nb2O5 nanoparticles anchored in the carbon tubes are subjected to reversible intercalation pseudocapacitance reaction, so that the sodium ion migration rate is remarkably increased, sodium ions are preferentially adsorbed, the nucleation overpotential is greatly reduced, and the performance of the carbon nanotubes is improved. And the assembled negative-electrode-free sodium metal total battery shows an extremely high capacity retention ratio.

Description

Technical Field

[0001] The present invention relates to the technical field of electrochemical energy storage, and particularly to a current collector active material, a preparation method thereof, and an application thereof. Background Art

[0002] Sodium metal batteries are considered to be ideal alternatives to lithium metal batteries due to their high theoretical specific capacity (1166 mAh g -1 ), low reduction potential (-2.71 V vs SHE), and abundant sodium resources. However, the high activity of sodium metal and the growth of sodium dendrites lead to unstable interfaces, irreversible loss of sodium, and rapid degradation of battery performance, severely limiting its cycle life and Coulomb efficiency.

[0003] The sodium metal-free anode battery avoids the use of excessive sodium metal by depositing metallic sodium on the current collector during the first charging process, thus significantly improving the energy density and reducing costs. However, due to the uneven distribution of the electric field on the surface of the current collector and the kinetic limitations of sodium ion transport, the sodium deposition process is prone to uneven distribution, which in turn leads to the growth of sodium dendrites and the formation of "dead sodium", seriously affecting the cycle stability, sodium utilization rate, and long-term reversibility of the battery.

[0004] Currently, there are various modification schemes for the negative electrode current collector to solve such problems. One solution is to introduce sodium-philic materials (such as gold, silver, tin, zinc oxide, etc.) into a three-dimensional conductive framework, which can effectively reduce the nucleation barrier of sodium and promote the uniform deposition of sodium. However, the existing sodium-philic materials often face the following problems: on the one hand, many sodium-philic materials will undergo alloying reactions or irreversible phase changes accompanied by volume expansion during the reaction with sodium, resulting in interface loss and capacity decay; on the other hand, the preparation processes of these materials are complex and difficult for large-scale production, making it difficult to meet the actual application requirements. Therefore, how to achieve the large-scale preparation of materials while improving the sodium-philicity and sodium utilization rate of the negative electrode current collector is an urgent problem to be solved for the large-scale application of sodium metal-free anode batteries. Summary of the Invention

[0005] The purpose of the present invention is to solve the above problems in the prior art and provide a current collector active material, a preparation method thereof, and an application thereof. This method uses amorphous carbon nanotubes embedded with niobium pentoxide nanoparticles (Nb 2 O 5 @aCNT) as the main material, with a simple, environmentally friendly preparation process that is suitable for large-scale production and has good industrialization potential. Applying the modified current collector to a sodium metal-free anode battery, on the one hand, the ultrafine Nb 2 O 5The nanoparticles endow the material with excellent sodium affinity through the intercalation pseudocapacitance effect, which can reduce the nucleation overpotential of sodium metal, promote the uniform deposition of sodium metal and inhibit the growth of sodium dendrites, thereby improving the Coulomb efficiency and cycle stability. On the other hand, the amorphous carbon nanotubes construct a three-dimensional framework structure with high electrical conductivity and high mechanical stability, effectively improving the electron transport efficiency and alleviating the volume change problem of sodium metal during cycling.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A preparation method of a current collector active material, comprising the following steps:

[0008] 1) Dissolve an acid, a niobium precursor and aniline in deionized water to form solution A; dissolve ammonium persulfate in deionized water to form solution B, add solution B to solution A, mix evenly, then let stand for reaction, and then filter and dry to obtain niobium-doped polyaniline carbon nanotubes;

[0009] 2) Heat-treat the niobium-doped polyaniline carbon nanotubes in a protective atmosphere to obtain amorphous carbon nanotubes embedded with niobium pentoxide nanoparticles. The protective atmosphere is at least one of argon and nitrogen.

[0010] The niobium precursor is at least one of niobium oxalate, niobium chloride, and ammonium niobium oxalate hydrate; the acid is at least one of hydrochloric acid, phytic acid, pyromellitic acid, and naphthalenetetracarboxylic acid.

[0011] In step 1), the molar ratio of the acid to aniline is 0.1-0.5:1, the molar ratio of aniline to ammonium persulfate is 1, and the molar ratio of the acid to the niobium precursor is 5-30:1.

[0012] In step 1), the concentration of the niobium precursor aqueous solution is 0.5-4 mmol L -1 , the concentration of the acid aqueous solution is 0.01-0.03 mol L -1 , the concentration of the aniline aqueous solution is 0.07-0.1 mol L -1 , and the concentration of the ammonium persulfate aqueous solution is 0.5-1 mol L -1 .

[0013] In step 1), the temperature of the standing reaction is 0-25 °C, and the reaction time is 6-48 h.

[0014] In step 2), the heat treatment temperature is 500-900 °C, and the heat preservation time is 2-6 h.

[0015] A current collector active material is prepared by the above preparation method, and the yield is 30% - 50%. The current collector active material is composed of hollow and through amorphous carbon nanotubes and niobium pentoxide nanoparticles dispersed in the tube wall. The diameter of the amorphous carbon nanotubes is 100 - 500 nm, the length is 1 - 10 μm, and the size of the niobium pentoxide nanoparticles is 1 - 10 nm.

[0016] The application of the current collector active material is used to prepare a current collector for a sodium metal battery without a negative electrode. The amorphous carbon nanotubes embedded with niobium pentoxide nanoparticles, a conductive agent, a binder, and a solvent are mixed to form a slurry, and then coated on the surface of the current collector to form a coating, and finally dried to obtain a current collector for a sodium metal battery without a negative electrode. Among them, the current collector is copper foil, carbon-coated copper foil, aluminum foil, or carbon-coated aluminum foil. The thickness of the coating of the current collector is 10 - 30 μm, and the loading amount of the active material in each current collector is 0.3 - 0.7 mg cm -2 .

[0017] A sodium metal battery without a negative electrode includes the current collector for a sodium metal battery without a negative electrode, a positive electrode, an electrolyte, and a separator. The positive electrode includes a current collector and a positive electrode material loaded on its surface. The positive electrode material includes a positive electrode active substance, a binder, and a conductive agent.

[0018] The positive electrode active material is any one of sodium vanadium phosphate (Na 3 V 2 (PO 4 ) 3 ), sodium iron phosphate (Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 ), and sodium vanadium fluorophosphate (Na 3 V 2 (PO 4 ) 2 O 2 F).

[0019] The conductive agent is one or more of Super P conductive carbon, single-walled carbon nanotubes, and Ketjen black. The binder is at least one of sodium carboxymethyl cellulose (CMC), sodium alginate (SA), polytetrafluoroethylene (PTFE), and polyvinylidene fluoride. The solvent is at least one of deionized water and N-methylpyrrolidone (NMP).

[0020] The preparation process of the sodium metal battery without a negative electrode includes the following:

[0021] 1) Assemble the negative current collector with a sodium sheet, an electrolyte, and a separator into a sodium metal half-cell;

[0022] 2) Deposit sodium metal on the negative current collector at a certain depth of discharge (DOD), and assemble it with the electrolyte and separator into a fully symmetric battery;

[0023] 3) Use the negative current collector as the negative electrode, and assemble it with the positive electrode, electrolyte and separator to obtain the sodium metal-free battery.

[0024] The depth of discharge for depositing sodium metal is 50% - 100%; the separator is a glass fiber separator, PP or PE separator; the sodium sheet is a commercially available sodium sheet of Kejing brand with a diameter of 15.4 mm; the electrolyte contains sodium salt and ether solvent; the sodium salt is any one of sodium hexafluorophosphate (NaPF 6 ) and sodium perchlorate (NaClO 4 ); the ether solvent is one or a combination of ethylene glycol dimethyl ether (DME) and diethylene glycol dimethyl ether (DIGLYME); the preferred electrolyte is 1M NaPF 6 in DME.

[0025] The negative current collector described in the present invention is particularly suitable for high-areal-loading positive electrodes that are difficult to adapt in the prior art. The high-areal-loading positive electrode refers to a positive electrode in which the loading of the positive electrode active material is above 10 mg cm -2 (further 10 - 20 mg cm -2 ).

[0026] Compared with the prior art, the beneficial effects achieved by the technical solution of the present invention are:

[0027] 1. The one-step macroscale preparation process is efficient and stable, meeting the requirements of industrial production: The present invention adopts a one-step in-situ self-assembly process (without template etching), which can macroscale prepare amorphous carbon nanotube negative current collectors of hundreds of grams or even kilograms of ultrafine niobium pentoxide nanoparticles in a single batch, and can fundamentally solve the industrialization bottleneck of difficult preparation and high cost of traditional modified current collectors.

[0028] 2. The sodiophilicity regulation dominated by the intercalation pseudocapacitance effect realizes efficient dendrite-free deposition: The Nb 2 O 5 nanoparticles anchored inside the carbon nanotubes significantly enhance the sodium ion migration rate through reversible intercalation pseudocapacitance reactions, enabling sodium ions to be preferentially adsorbed and greatly reducing the nucleation overpotential. Through the synergistic mechanism of "pseudocapacitance intercalation pre-adsorption - lumen confinement deposition", three-dimensional uniform nucleation of sodium is achieved, and dendrite-free characteristics are maintained even under high current density and high areal capacity conditions.

[0029] 3. The performance of the full battery is adapted to the high-areal-loading system: The ultra-high structural consistency and pseudocapacitance-induced sodium flux balance characteristics of the current collector enable it to be adapted to 15 mg cm -2Stringent requirements for high-loading cathodes. The assembled sodium metal full cell without a cathode (N / P = 0) shows extremely high capacity retention, breaking through the technical limitations of out-of-control sodium deposition in high-loading systems, and providing core material support for practical high-energy-density sodium metal batteries. Brief Description of the Drawings

[0030] Figure 1 Schematic diagram of the preparation process of amorphous carbon nanotubes embedded with ultrafine niobium pentoxide nanoparticles (Nb 2 O 5 @aCNT) of the present invention;

[0031] Figure 2 SEM and TEM images of Nb 2 O 5 @aCNT prepared in Example 1; among them, Figure 2 a is the SEM image, showing the overall morphology of the nanotubular structure of Nb 2 O 5 @aCNT; Figure 2 b is the TEM image, showing the uniform distribution of Nb 2 O 5 nanoparticles inside the amorphous carbon nanotubes. The high-resolution transmission electron microscope (HRTEM) image marks the (001) crystal plane of Nb 2 O 5 with a lattice spacing of 3.90 Å and the (180) crystal plane with a lattice spacing of 3.15 Å, further proving the existence of orthorhombic Nb 2 O 5 ;

[0032] Figure 3 XRD pattern of Nb 2 O 5 @aCNT prepared in Example 1;

[0033] Figure 4 XPS spectrum, thermogravimetric curve, nitrogen adsorption-desorption curve and pore size distribution diagram of Nb 2 O 5 @aCNT prepared in Example 1; among them, Figure 4 a is the XPS spectrum, b is the thermogravimetric curve, and c is the nitrogen adsorption-desorption curve and pore size distribution diagram;

[0034] Figure 5 HAADF-STEM and EDS images of Nb 2 O 5 @aCNT prepared in Example 1;

[0035] Figure 6 Cyclic voltammetry curves and pseudocapacitance contribution diagrams of the half-cell assembled for Example 1 at different scan rates; among them, Figure 6 a in it is the cyclic voltammetry curve of the half-cell at different scan rates (2, 4, 6, 8, 10 mV s -1 ), and b is the pseudocapacitance contribution diagram of the half-cell;

[0036] Figure 7 In-situ electron microscopy experimental diagrams of Nb 2 O 5 @aCNT prepared in Example 1 as the sodium metal anode; among them, Figure 7 a in it 1 is the initial state of the sample, a 2 ~a 3 is the sodiation and deposition process of the sample, a 4 ~a 5 is the stripping process of the sample;

[0037] Figure 8 In-situ scanning electron microscopy diagrams of Nb 2 O 5 @aCNT prepared in Example 1 as the sodium metal anode at different deposition capacities; among them, Figure 8 a in it 1 is the initial state of the electrode sheet, a 2 ~a 4 is the sodium metal deposition process, a 5 is the complete stripping of the sodium metal;

[0038] Figure 9 Scanning electron microscopy and transmission electron microscopy diagrams of the amorphous carbon nanotubes without embedded niobium pentoxide prepared in Comparative Example 1; among them, Figure 9 a in it is the scanning electron microscopy diagram, and b is the transmission electron microscopy diagram;

[0039] Figure 10 Cyclic voltammetry curves and pseudocapacitance contribution diagrams of the half-cell assembled in Comparative Example 1 at different scan rates; among them, Figure 10 a in it is the cyclic voltammetry curve of the half-cell at different scan rates (2, 4, 6, 8, 10 mV s -1 ), and b is the pseudocapacitance contribution diagram of the half-cell;

[0040] Figure 11 In-situ electron microscopy experimental diagrams of aCNT prepared in Comparative Example 1 as the sodium metal anode; among them, Figure 11 a in it 1 is the initial state of the sample, a 2 ~a 3 is the sodiation and deposition process of the sample;

[0041] Figure 12 Non-in-situ scanning electron microscopy images of aCNT prepared in Comparative Example 1 as the sodium metal anode at different deposition capacities; among them, Figure 12 a in 1 is the initial state of the sample, a 2 ~a 3 is the sodiation and deposition process of the sample, a 4 ~a 5 is the stripping process of the sample;

[0042] Figure 13 Are the nucleation overpotential curve graphs of the half-cells assembled in Example 1 and Comparative Example 1;

[0043] Figure 14 Are the Coulombic efficiency cycling performance graphs of the half-cells and the voltage-time graphs of the all-symmetric cells in Example 1 and Comparative Example 1; among them, Figure 14 a in is the Coulombic efficiency cycling performance graph of the half-cell, and b is the voltage-time graph of the all-symmetric cell;

[0044] Figure 15 Are the long cycling performance graphs of the NVP-free anode sodium metal full cells in Example 1 and Comparative Example 1 at a current density of 100 mA g -1 Current density. Detailed implementation manners

[0045] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0046] Among them, the reagents or raw materials used in the following embodiments are all commercially available or self-made.

[0047] Example 1

[0048] Refer to Figure 1 , Example 1 of the present invention provides a method for macroscopically preparing a current collector for a sodium metal battery without an anode, and the method includes the following steps:

[0049] S1: Dissolve 0.1375 mol of pyromellitic acid, 5 mmol of ammonium niobium oxalate hydrate, and 0.55 mol of aniline in 7.5 L of deionized water, and stir at room temperature for 1 h to form solution A. Take 0.55 mol of ammonium persulfate and dissolve it in 750 mL of deionized water to form solution B, slowly add solution B dropwise to solution A and mix evenly, let the mixed solution stand and react at 0 °C for 24 h, then filter by suction and dry in vacuum at 100 °C for 12 h to obtain niobium-doped polyaniline carbon nanotubes, that is, Nb-PANI;

[0050] S2: Place the niobium-doped polyaniline carbon nanotubes in a corundum boat, introduce nitrogen, and adjust the gas flow rate to 100 mL min -1 , and after holding at 750 °C for 3 h, 26 g of amorphous carbon nanotubes embedded with niobium pentoxide nanoparticles (Nb 2 O 5 @aCNT) are obtained, with a yield of 30%;

[0051] S3: Mix Nb 2 O 5 @aCNT, conductive agent Super P conductive carbon, and binder sodium carboxymethyl cellulose (CMC) evenly according to a mass ratio of 8:1:1. Add deionized water to the powder to make a slurry and stir evenly. Use a spatula to evenly spread the slurry on the surface of the copper foil to form a coating, and dry it in a vacuum oven at 80 °C for 12 h to obtain a current collector for a sodium metal battery without a negative electrode. The loading amount of the active substance in each current collector is 0.5 mg cm -2 , and the coating thickness of the current collector is 25 μm.

[0052] The morphological characterization results of the Nb 2 O 5 @aCNT material prepared in this example are as Figure 2 shown. Among them, Figure 2 a in is the SEM image of Nb 2 O 5 @aCNT, indicating that the diameter and length of this material are uniform, about 100 - 500 nm, and the length is 1 - 10 μm. Figure 2 b in is the TEM image of Nb 2 O 5 @aCNT, showing that a large number of Nb 2 O 5 nanoparticles are evenly distributed in the carbon layer of aCNT. The size of the Nb 2 O 5 nanoparticles is about 3 - 10 nm, forming ultrafine particles. In addition, the high-resolution transmission electron microscopy (HRTEM) image further confirms that the lattice constants of Nb 2 O 5 are 0.315 nm and 0.390 nm respectively, which perfectly match the (180) and (001) crystal planes of T-Nb 2 O 5 , verifying that Nb 2 O 5 exists as an orthorhombic phase inside the carbon nanotubes. The Nb 2 O 5@aCNT exhibits excellent reproducibility in large-scale preparation, maintaining a unique tubular hybrid structure and uniformly distributed ultrafine Nb 2 O 5 nanoparticles.

[0053] The X-ray diffraction (XRD) pattern of the Nb 2 O 5 @aCNT prepared in this example is as Figure 3 shown. The Nb 2 O 5 @aCNT shows only two broad peaks, located at 24° and 43° respectively, corresponding to the characteristic diffraction peaks of amorphous carbon. However, due to the low loading and extremely fine particle size of the Nb 2 O 5 particles, the diffraction peaks of Nb 2 O 5 could not be effectively identified in the XRD pattern. Therefore, at a heat treatment temperature of 750 °C, the same heat treatment was carried out on the precursor salt ammonium niobium oxalate hydrate, which was finally transformed into orthorhombic Nb 2 O 5 (JCPDS No. 30-0873, T-Nb 2 O 5 ), thus providing evidence to support the embedding of T-Nb 2 O 5 into the carbon nanotubes.

[0054] The surface chemical composition and structural characteristics of the Nb 2 O 5 @aCNT prepared in this example were characterized by X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA) and nitrogen adsorption / desorption isotherm analysis (BET), as Figure 4 shown. The XPS spectrum ( Figure 4 a in) shows that there are mainly three characteristic peaks on the surface of Nb 2 O 5 @aCNT, located at 285.08 eV (C 1s), 532 eV (O1s) and 400.08 eV (N 1s) respectively, and there is also a peak at 206.43 eV, attributed to Nb 3d, proving that niobium elements are successfully embedded in the carbon nanotube structure and the content of niobium is 0.39 wt%. The results of thermogravimetric analysis ( Figure 4 b in) show that the mass fraction of Nb 2 O 5 is about 11.63 wt%, verifying the loading of niobium oxide in the carbon nanotubes. In addition, the nitrogen adsorption / desorption isotherm test ( Figure 4 c in) shows that Nb 2 O 5The specific surface area of Nb@aCNT is 324 m 2 g -1 , and the pore size distribution ranges from 0.5 to 1.5 nm, indicating that Nb 2 O 5 is successfully anchored inside the carbon nanotubes, and this material has a good pore structure.

[0055] The HAADF-STEM image of Nb 2 O 5 @aCNT prepared in this example is as shown in Figure 5 . Small and bright particles are evenly distributed inside the carbon shell of the carbon nanotubes, and these particles confirm the existence of Nb 2 O 5 without obvious aggregation. In addition, the energy-dispersive spectroscopy (EDS) elemental distribution map further verifies the uniform distribution of Nb, C, O, and N elements in Nb 2 O 5 @aCNT, indicating that niobium elements coexist uniformly with carbon, oxygen, and nitrogen elements, confirming that Nb 2 O 5 is successfully embedded into the carbon nanotubes and its distribution is uniform.

[0056] The Nb 2 O 5 @aCNT prepared in this example is studied for its pseudocapacitance effect by cyclic voltammetry (CV) with variable scan rates, as shown in Figure 6 . Referring to Figure 6 a, within the voltage range of 0.01 V to 1 V (vs. Na / Na + ), the Nb 2 O 5 @aCNT electrode exhibits relatively sharp oxidation / reduction peaks, indicating that the intercalation / deintercalation process of sodium ions in the Nb 2 O 5 lattice is relatively fast and reversible. As the scan rate increases, the reduction peak of Nb 2 O 5 @aCNT gradually broadens, showing typical pseudocapacitance behavior, indicating that Nb 2 O 5 plays an important role in the rapid intercalation process of sodium ions and is not limited by solid-state diffusion. Figure 6 b shows that Nb 2 O 5 @aCNT has a high pseudocapacitance contribution at all scan rates, which helps to improve the sodium ion transfer rate and sodium storage capacity.

[0057] The Nb 2 O 5@aCNT is used as the negative electrode, and its dynamic changes during the sodium metal deposition / deposition process are observed by in-situ transmission electron microscopy (TEM) ( Figure 7 ). Figure 7 in a 1 shows the initial state, where Na adhered to the Cu electrode is at the bottom, and sodium oxide formed due to short-term exposure to air can act as a solid electrolyte; Nb adhered to the Mo electrode is at the top 2 O 5 @aCNT, and an external power supply is connected to form a closed circuit. Move the sodium / sodium oxide to make it in firm contact with Nb 2 O 5 @aCNT. After applying a -3 V bias voltage, the carbon layer thickness of Nb 2 O 5 @aCNT slightly increases, indicating that sodium ions are rapidly sodiated within 2 seconds ( Figure 7 in a 2 ). During the subsequent sodium metal deposition process, sodium metal starts to rapidly fill the carbon nanotube cavity from the interface where Nb 2 O 5 @aCNT contacts the sodium surface. The deposition is completed in only 45 seconds, and the deposition process presents a morphology similar to liquid flow, and sodium remains in a single crystal state ( Figure 7 in a 3 ). Subsequently, a +3 V reverse bias voltage is applied for dissolution, and sodium metal is removed from the carbon nanotubes, and the desodiated outer shell almost returns to its original thickness ( Figure 7 in a 4 and a 5 ). This process indicates that Nb 2 O 5 @aCNT exhibits excellent performance in sodium ion kinetics, effectively reducing the ion diffusion barrier.

[0058] The prepared Nb 2 O 5 @aCNT in this example is used as the negative electrode, and the morphological changes during the sodium metal deposition / stripping process are observed by ex-situ scanning electron microscopy (Ex-situ SEM) ( Figure 8 ). Figure 8 in a 1 shows that before the sodium metal deposition, Nb 2 O 5 @aCNT forms a cross-linked network, which serves as a framework for accommodating sodium metal and maintains its hollow tubular structure. This structure helps to alleviate the influence of sodium volume expansion. At a deposition capacity of 0.5 mAh cm -2 , the sodiumophilic sites of Nb 2 O 5 @aCNT effectively guide the nucleation and uniform expansion of metallic sodium, and metallic sodium uniformly covers Nb2 O 5 on the surface of Nb 2 @aCNT, and the tubular structure remains intact ( Figure 8 a in 2 ). As the deposition capacity increases to 2 mAh cm -2 and 4 mAh cm -2 , sodium metal deposits on the surface of Nb 2 O 5 @aCNT and forms a compact granular structure, and the surface remains smooth and uniform ( Figure 8 a in 3 and a 4 ). After complete stripping of sodium, the tubular morphology of Nb 2 O 5 @aCNT remains clearly visible, without residual dead sodium, which benefits from the guiding effect of sodiumophilic sites on the surface of Nb 2 O 5 @aCNT, making the sodium deposition / stripping process reversible ( Figure 8 a in 5 ).

[0059] Comparative Example 1

[0060] Compared with Example 1, the difference in Comparative Example 1 is that niobium pentoxide nanoparticles (aCNT) are not embedded in the amorphous carbon nanotubes. This method includes the following steps:

[0061] S1: Dissolve 0.1375 mol of pyromellitic acid and 0.55 mol of aniline in 7.5 L of deionized water, and stir at room temperature for 1 h to form solution A. Take 0.55 mol of ammonium persulfate and dissolve it in 750 mL of deionized water to form solution B. Slowly add solution B dropwise to solution A and mix evenly. The mixed solution is left to react at 0 °C for 24 h, then filtered by suction and dried in vacuo at 100 °C for 12 h to obtain polyaniline carbon nanotubes, namely PANI;

[0062] S2: Place the polyaniline carbon nanotubes in a corundum boat, introduce nitrogen, adjust the gas flow rate to 100 mL min -1 , and the heating / cooling rate is 5 °C min -1 . After holding at 750 °C for 3 h, amorphous carbon nanotubes (aCNT) are obtained;

[0063] S3: Mix aCNT, conductive agent and binder evenly according to the mass ratio of 8:1:1. Add a solvent to the powder to make a slurry and stir evenly. Use a spatula to evenly spread the slurry on the surface of the current collector to form a coating, and dry it in a vacuum oven at 80 °C for 12 h to obtain a current collector for a sodium metal battery without a negative electrode. The loading amount of the active material in each current collector is 0.5 mg cm -2 .

[0064] The morphological characterization results of the aCNT prepared in this comparative example are as follows Figure 9 shown. Among them, Figure 9 a in is the SEM image of aCNT, indicating that the diameter and length of this material are uniform. Figure 9 b in is the TEM image of Nb 2 O 5 @aCNT. It can be seen that there is a carbon layer with uniform thickness, and there are no any other particles inside the carbon layer. The diameter of the carbon nanotube is about 200 nm, and the length is about 5 μm.

[0065] The aCNT prepared in this comparative example was used as the negative electrode, and its pseudocapacitance effect was studied by cyclic voltammetry (CV) with variable scan rates, as shown in Figure 10 shown. Figure 10 a in shows that at a scan rate of 2 mV s -1 , the aCNT electrode exhibits broad reduction / oxidation peaks, located at 0.1 V and 0.01 V respectively, indicating the adsorption and desorption of sodium ions on the amorphous carbon layer. Figure 10 b in shows that among all the tested scan rates, the aCNT electrode exhibits low capacitance control, the reduction peak is significantly inhibited, and the voltage polarization between the reduction / oxidation peaks increases. This indicates that the diffusion behavior of sodium ions is restricted, mainly controlled by the adsorption / desorption process, resulting in poor capacitance effect and limiting the rapid migration and effective storage of sodium ions in the electrode material.

[0066] The aCNT prepared in this comparative example was used as the negative electrode, and the dynamic changes of the material during the sodium metal deposition / stripping process were observed by in-situ transmission electron microscopy (TEM), as shown in Figure 11 shown. Figure 11 a in 1 and a 2 show that compared with the Nb 2 O 5 @aCNT prepared in Example 1, the sodium deposition / stripping kinetics of the aCNT electrode are significantly slower, and the sodiation process takes about 178 seconds. In addition, referring to Figure 11 a in 3 , aCNT fails to effectively deposit sodium metal inside the tube. The sodium deposition is mainly manifested as severe dendritic growth on the outside, which leads to restricted transfer of sodium ions and aggregation of sodium metal on the electrode surface. This phenomenon indicates that the carbon wall of aCNT fails to effectively encapsulate sodium metal, and sodium ions can only diffuse between the carbon wall layers and in the pores, with a slow diffusion rate, resulting in the formation of external dendrites and hindering the deposition of sodium metal and the internal sodium transport.

[0067] The aCNT prepared in this comparative example was used as the negative electrode, and the morphological changes during the sodium metal deposition / stripping process were observed by ex-situ scanning electron microscopy (Ex-situ SEM) ( Figure 12). Figure 12 in a 1 and a 2 showed that, compared with the Nb prepared in Example 1 2 O 5 @aCNT, when the deposition capacity was 0.5 mAh cm -2 , a large number of dispersed sodium nucleation deposits and randomly oriented sodium growth were observed on the aCNT electrode, indicating a lack of effective nucleation guidance and slow sodium ion transport kinetics, resulting in a concentrated local sodium ion flux density. This dispersion phenomenon may significantly increase the risk of dead sodium formation, which may lead to sodium layer fragmentation and discontinuous sodium deposition. See Figure 12 in a 3 and a 4 , when the deposition capacity increased to 2 mAh cm -2 and 4 mAh cm -2 , dendritic sodium deposition began to appear on the surface of the aCNT electrode, accompanied by multiple sodium protrusions and discontinuous cracks. Figure 12 in a 5 showed that when stripping sodium metal from the aCNT electrode, uneven blocky dead sodium remained on the electrode, resulting in low sodium utilization and decreased cycle stability.

[0068] Example 2

[0069] In this Example 2, the electrochemical performance of the Nb 2 O 5 @aCNT without a negative electrode sodium metal current collector prepared in Example 1 of the present invention and the aCNT without a negative electrode sodium metal current collector prepared in Comparative Example 1 was tested.

[0070] The Nb 2 O 5 @aCNT prepared in Example 1 of the present invention as a negative electrode current collector provides a sodium metal-free battery, including a negative electrode current collector, a positive electrode, an electrolyte, and a separator; the preparation process of the sodium metal-free battery includes the following steps: assembling the negative electrode current collector with a sodium sheet, an electrolyte, and a separator into a sodium metal half-cell; depositing sodium metal on the negative electrode current collector at a discharge depth (DOD) of 71% (pre-deposited as 14 mAh cm -2 , and the actual deposition capacity used is 10 mAh cm -2 ), and assembling it with an electrolyte and a separator into a fully symmetric cell; using the negative electrode current collector as the negative electrode, and assembling it with a positive electrode, an electrolyte, and a separator to obtain the sodium metal-free battery, the positive electrode is sodium vanadium phosphate (Na 3 V 2 (PO 4 ) 3 ), and the loading is 15 mg cm -2 . The electrolyte is 1M NaPF6 In DME, the separator is a polypropylene (PP) separator.

[0071] The aCNT prepared in Comparative Example 1 of the present invention is used as a negative current collector to provide a sodium metal battery without a negative electrode, including a negative current collector, a positive electrode, an electrolyte, and a separator; the preparation process of the sodium metal battery without a negative electrode includes the following steps: assembling the negative current collector with a sodium sheet, an electrolyte, and a separator into a sodium metal half-cell; depositing sodium metal on the negative current collector according to a discharge depth (DOD) of 71% (pre-deposited to be 14 mAh cm -2 , and the actual deposited capacity used is 10 mAh cm -2 ), and assembling it with an electrolyte and a separator into a fully symmetric cell; using the negative current collector as the negative electrode, and assembling it with a positive electrode, an electrolyte, and a separator to obtain the sodium metal battery without a negative electrode, the positive electrode is sodium vanadium phosphate (Na 3 V 2 (PO 4 ) 3 ), and the loading is 15 mg cm -2 . The electrolyte is 1M NaPF 6 in DME, and the separator is a polypropylene (PP) separator.

[0072] The electrochemical performance of the above sodium metal battery without a negative electrode is tested, including the sodium metal nucleation overpotential test, Coulomb efficiency test, long cycle test of the fully symmetric cell, and constant current charge and discharge test of the sodium metal battery without a negative electrode.

[0073] As Figure 13 shown, the sodium metal nucleation overpotential test is carried out at a current density of 1 mA cm -2 . The experimental results show that the nucleation overpotential of Nb 2 O 5 @aCNT prepared in Example 1 of the present invention is only 7.8 mV, which is much lower than 16.7 mV of aCNT prepared in Comparative Example 1. This indicates that under the guidance of the pseudocapacitance effect, Nb 2 O 5 @aCNT can more effectively promote the uniform growth of sodium metal and significantly improve the nucleation efficiency of sodium.

[0074] The Coulomb efficiency test results are as shown in Figure 14 a. The results show that compared with Comparative Example 1, Nb 2 O 5The sodium metal half-cell with @aCNT maintained a stable Coulombic efficiency of 99.996% after 850 cycles. In Comparative Example 1, the sodium metal half-cell with aCNT had significant fluctuations in Coulombic efficiency during cycling and a significantly shortened cycle life, indicating the presence of irreversible reactions such as the formation and dissolution of sodium dendrites. In addition, the sodium metal deposition process with aCNT showed poor uniformity, resulting in poor cycling performance. In all tests, the Nb 2 O 5 sodium metal half-cell with @aCNT electrode of Example 1 of the present invention exhibited more excellent Coulombic efficiency and longer cycle stability.

[0075] The long-cycle test results of the all-symmetric cell are as shown in Figure 14 b. The results show that the all-symmetric cell with Nb 2 O 5 @aCNT provided in Example 1 of the present invention could maintain a low voltage polarization and exhibited a long cycle performance of more than 820 hours under the severe test conditions of a current density of 10 mA cm -2 and an areal capacity of 10 mAh cm -2 . Moreover, under the condition of a depth of discharge exceeding 71%, the battery performance remained stable. In contrast, for the all-symmetric cell with aCNT in Comparative Example 1, during long-term cycling, the voltage polarization increased significantly, showing obvious unstable voltage fluctuations, indicating that the battery interface gradually degraded and dendrite growth occurred. Further, under more stringent deep-cycle conditions, the interface stability of the Na-aCNT electrode was poor, with less sodium metal deposition and larger voltage fluctuations, further confirming its performance degradation during long-term cycling. This result shows that, compared with Comparative Example 1, the all-symmetric cell in Example 1 exhibited smaller voltage polarization and longer cycle life.

[0076] The constant current charge-discharge test results of the sodium metal battery without a negative electrode are as shown in Figure 15 . The results show that the sodium metal battery without a negative electrode with Nb 2 O 5 @aCNT provided in Example 1 of the present invention could maintain an extremely high average Coulombic efficiency and exhibited excellent long-cycle performance at a discharge rate of 100 mA g -1 , and still maintained a capacity retention rate of 90% after 100 cycles. In contrast, for the all-symmetric cell with aCNT in Comparative Example 1, during cycling, obvious capacity decay occurred, and the capacity decreased rapidly after 25 cycles, indicating continuous sodium loss during cycling.

[0077] The sodium affinity induced by the pseudocapacitance effect of Nb 2 O 5 in improving Nb 2 O 5@aCNT plays a crucial role in the cycling stability of the sodium metal battery without a cathode. Therefore, based on Nb 2 O 5 @aCNT, the full battery provides a feasible strategy for high-energy and practically sustainable sodium metal batteries without a cathode.

[0078] In summary, the method of the present invention uses amorphous carbon nanotubes embedded with niobium pentoxide nanoparticles (Nb 2 O 5 @aCNT) as the main material and realizes large-scale production through a simple and environmentally friendly process. The current collector exhibits excellent performance in the sodium metal battery without a cathode: the ultrafine niobium pentoxide nanoparticles significantly reduce the nucleation overpotential of sodium metal through the intercalation pseudocapacitance effect, promote the uniform deposition of sodium metal and inhibit the growth of sodium dendrites, improving the Coulombic efficiency and cycling stability; the three-dimensional framework structure with high electrical conductivity and high mechanical stability constructed by amorphous carbon nanotubes effectively improves the electron transport efficiency and alleviates the volume change problem of sodium metal during cycling. The method of the present invention has the potential for industrialization, solves the industrial bottleneck of the difficult preparation and high cost of traditional modified current collectors, and provides core material support for practical high-energy-density sodium metal batteries.

[0079] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a current collector active material, characterized in that: The following steps are involved: 1) dissolving acid, niobium precursor and aniline in deionized water to form solution A; Ammonium persulfate is dissolved in deionized water to form solution B, solution B is added to solution A, mixed evenly and then allowed to stand for reaction, then filtered and dried to obtain niobium-doped polyaniline carbon nanotubes; 2) heat treating the niobium-doped polyaniline carbon nanotubes in a protective atmosphere to obtain amorphous carbon nanotubes embedded with niobium pentoxide nanoparticles.

2. A method for preparing a current collector active material according to claim 1, characterized in that: The niobium precursor is at least one of niobium oxalate, niobium chloride, and ammonium niobate oxalate hydrate; and the acid is at least one of hydrochloric acid, phytic acid, pyromellitic acid, and naphthalenetetracarboxylic acid.

3. The method for preparing a current collector active material according to claim 1, characterized in that: In step 1), the molar ratio of the acid to aniline is 0.1-0.5:1, the molar ratio of aniline to ammonium persulfate is 1, and the molar ratio of the acid to the niobium precursor is 5-30:

1.

4. A method for preparing a current collector active material according to claim 1, characterized in that: In step 1), the concentration of the niobium precursor aqueous solution is 0.5~4 mmol L -1 The concentration of the acid solution is 0.01~0.03 mol L -1 The concentration of aniline aqueous solution is 0.07~0.1 mol L -1 The concentration of ammonium persulfate aqueous solution is 0.5~1 mol L -1 .

5. The method for preparing a current collector active material according to claim 1, characterized in that: In step 1), the temperature of the static reaction is 0-25°C, and the reaction time is 6-48 h.

6. The method for preparing a current collector active material according to claim 1, characterized in that: In step 2), the heat treatment temperature is 500~900°C and the holding time is 2~6 h.

7. A current collector active material, characterized in that: Prepared by the preparation method according to any one of claims 1 to 6.

8. A current collector active material according to claim 7, characterized in that: It is composed of hollow amorphous carbon nanotubes and niobium pentoxide nanoparticles dispersed in the tube wall. The diameter of the amorphous carbon nanotubes is 100~500 nm, the length is 1~10 μm, and the size of the niobium pentoxide nanoparticles is 1~10 nm.

9. The use of a current collector active material according to claim 7 or 8, characterized in that: For the preparation of negative electrode-free sodium metal battery current collector, amorphous carbon nanotubes embedded with niobium pentoxide nanoparticles, a conductive agent, a binder and a solvent are mixed into a slurry, which is then applied on the surface of the current collector to form a coating, and finally dried to obtain a negative electrode-free sodium metal battery current collector.

10. A negative electrode-free sodium metal battery, characterized in that: It comprises the negative electrode-free sodium metal battery current collector, positive electrode, electrolyte and separator as described in claim 9.

Images