Self-supporting electrode, preparation method therefor, and sodium ion battery

Abstract

The present application relates to a self-supporting electrode, a preparation method therefor, and a sodium ion battery. The self-supporting electrode comprises a conductive substrate and an active material particle layer arranged on the conductive substrate. A molecular general formula of active material particles in the active material particle layer is: Na4-xFeV1-yMy(PO4)3, and the active material particles further comprise a conductive shell layer, where M is selected from a transition metal element and / or Al, 0≤x<0.1, and 0<y<0.1. The self-supporting electrode of the present application has high average working voltage, specific capacity, and energy density.

Description

Self-supporting electrode, preparation method thereof and sodium ion battery

[0001] This application claims priority to the Chinese patent application No. 202410420040.5, filed on April 9, 2024, entitled "Self-supporting electrode, preparation method thereof and sodium ion battery", the entire content of which is incorporated herein by reference. TECHNICAL FIELD

[0002] The present application relates to the field of sodium ion batteries, in particular to a self-supporting electrode, a preparation method thereof and a sodium ion battery. BACKGROUND

[0003] For the past three decades, lithium ion batteries have dominated the electronic device market with high energy density and significant cycle life advantages. However, the limited lithium ore resources have not been able to meet the needs of social development. Compared with lithium ore resources, sodium resources are abundant, and sodium ion batteries have similar reaction principles to lithium ion batteries and have wide temperature characteristics. Therefore, sodium ion batteries are considered to be the most promising new energy storage technology.

[0004] Among the positive electrode materials of sodium ion batteries, olivine-type sodium iron phosphate (NaFePO4) as an analogue of lithium ion battery positive electrode material LiFePO4 has been widely concerned due to its high specific capacity and good cycle performance. However, olivine-type NaFePO4 material cannot be prepared by simple traditional solid-phase method, but needs to be prepared by complex Li + , Na + ion exchange.

[0005] In order to obtain a sodium ion battery positive electrode material with low cost and environmental friendliness, the prior art uses metallic iron as the central ion to prepare Na3Fe2(PO4)3 material with NASICON (sodium fast ion conductor) structure, and the Na3Fe2(PO4)3 material can be prepared by a simple solid-phase method. However, the Na3Fe2(PO4)3 material has problems such as low intrinsic electronic conductivity, low Fe 2+ / Fe 3+ redox potential, etc., which results in the material having a low average working voltage (2.5V vs. Na + / Na), specific capacity (less than 61mAh / g) and energy density.

[0006] At the same time, the existing Na3Fe2(PO4)3 material needs to introduce programmed and tedious conductive carbon black and electrically insulating binder (polyvinylidene fluoride or polytetrafluoroethylene) when preparing the electrode, wherein the conductive carbon black and the binder will reduce the content of active substances, and the binder will also reduce the electronic conductivity of the material, thereby making the overall energy density of the electrode very low. SUMMARY

[0007] Therefore, it is necessary to provide a self-supporting electrode, a preparation method thereof and a sodium ion battery, which have a high average working voltage, specific capacity and energy density.

[0008] A self-supporting electrode comprises an electrically conductive substrate and an active material particle layer disposed on the electrically conductive substrate, wherein the active material particle layer comprises active material particles with a molecular formula of Na 4-x FeV 1-y M y (PO4)3, and the active material particles further comprise an electrically conductive shell layer, wherein M is selected from transition metal elements and / or Al elements, 0≤x<0.1, and 0<y<0.1.

[0009] In one embodiment, the transition metal elements are selected from at least one of Cu, Ag or Co.

[0010] In one embodiment, the thickness of the active material particle layer is 100 μm-400 μm.

[0011] In one embodiment, the particle size of the active material particles is 50 nm-300 nm.

[0012] In one embodiment, the electrically conductive substrate is selected from at least one of foamed nickel, foamed copper, foamed aluminum, steel sheet or titanium sheet.

[0013] In one embodiment, the electrically conductive shell layer is selected from a carbon coating layer, and the mass fraction of the carbon coating layer in the active material particles is 2%-8%.

[0014] The self-supporting electrode of the present application does not need a binder and an additional conductive agent, greatly improves the content of active material particles in the electrode, thereby improving the overall energy density of the electrode and having good mechanical properties; meanwhile, the active material particles in the self-supporting electrode, on one hand, by introducing vanadium with multiple valence states and a high redox potential and a specific content of non-active cation M with good electronic conductivity to cooperatively replace one trivalent iron ion, can improve the average working voltage, specific capacity and electronic conductivity of the active material particles; on the other hand, by disposing the electrically conductive shell layer, can cooperatively cooperate with the non-active cation M with good electronic conductivity, effectively improve the electronic conductivity of the active material particles, so that the self-supporting electrode of the present application can have a high average working voltage, specific capacity and energy density.

[0015] A preparation method of the self-supporting electrode described above, comprising:

[0016] with a molecular formula of Na4-x FeV 1-y M y (PO4)3, 0≤x<0.1, 0

[0017] The active material precursor solution is deposited on a conductive substrate by electrostatic spray deposition technology, and then sintered in a protective atmosphere to form an active material particle layer, thereby obtaining a self-supporting electrode, wherein the temperature of the conductive substrate is greater than the boiling point temperature of the active material precursor solution.

[0018] In one embodiment, in the step of mixing the vanadium source, the iron source, the M source, the complexing agent, the phosphorus source, the sodium source, the shell precursor material, and water to obtain a mixed solution, at least one of the following conditions is met:

[0019] (1) the ratio of the sum of the molar amounts of the vanadium source, the iron source, and the M source to the molar amount of the complexing agent is 1:1-1:3;

[0020] (2) the mass fraction of the shell precursor material in the mixed solution is 3%-20%, and the shell precursor material is selected from at least one of a carbon source selected from citric acid, glucose, fructose, sucrose, graphene, polyethylene glycol, polyvinylpyrrolidone, starch, dopamine, phenolic resin, or carbon nanotubes;

[0021] (3) the vanadium source is selected from at least one of ammonium metavanadate, di vanadium pentoxide, di vanadium trioxide, vanadium dioxide, or sodium metavanadate;

[0022] (4) the iron source is selected from at least one of iron nitrate nonahydrate, iron acetate, ferrous acetate, ferrous oxalate, di iron trioxide, iron powder, iron citrate, iron tartrate, iron formate, or iron lactate;

[0023] (5) the M source is selected from at least one of copper acetate, copper nitrate, or copper oxide;

[0024] (6) the complexing agent is selected from at least one of oxalic acid dihydrate, lactic acid, tartaric acid, succinic acid, or ethylenediaminetetraacetic acid;

[0025] (7) the phosphorus source is selected from at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphoric acid, sodium phosphate, or sodium dihydrogen phosphate;

[0026] (8) the sodium source is selected from at least one of sodium acetate, sodium carbonate, sodium hydroxide, sodium oxalate, sodium stearate, sodium tartrate, sodium alginate, or sodium lactate.

[0027] In one embodiment, in the step of adjusting the viscosity of the mixed solution to obtain the active material precursor solution, at least one of the following conditions is met:

[0028] (1) The viscosity of the active material precursor solution is 0.3 MPa·s-2.0 MPa·s;

[0029] (2) adjusting the viscosity of the mixed solution by adding an organic solvent to the mixed solution, wherein the mass ratio of the mixed solution to the organic solvent is 100:50-100:95, and the organic solvent is selected from at least one of N,N-dimethylformamide, nitrogen methyl pyrrolidone, ethylene glycol, butyl carbitol, anhydrous ethanol, glycerol or acetone.

[0030] In one embodiment, in the step of placing the active material precursor solution on a conductive substrate using an electrostatic spraying technique and then sintering in a protective gas atmosphere to form an active material particle layer, at least one of the following conditions is met:

[0031] (1) Electrostatic spray deposition process parameters include: voltage of 4kv-12kv, needle inner diameter of 0.6mm-1.0mm, solution flow rate of 1mLh -1 -5mLh -1 , the distance between the needle and the conductive substrate is 2cm-8cm;

[0032] (2) The protective gas atmosphere is selected from an inert gas atmosphere and / or a hydrogen atmosphere;

[0033] (3) The sintering temperature is 500-800°C and the sintering time is 6-10 hours;

[0034] (4) The temperature of the conductive substrate is 130°C-200°C;

[0035] (5) The curvature radius of the conductive substrate is 0.06m-0.6m;

[0036] (6) The roughness Ra of the conductive substrate is 20 μm ≤ Ra ≤ 720 μm;

[0037] (7) The conductive substrate is selected from at least one of foamed nickel, foamed copper, steel sheet, foamed aluminum or titanium sheet.

[0038] In the preparation method of the present application, the active material particle layer is formed on the conductive substrate by using electrostatic spray deposition technology, which is simple, avoids the programmed and tedious electrode preparation process, and at the same time, since the shell precursor material, the conductive substrate and the active material are integrated and sintered into a whole in the method, there is no need to use a binder and an additional conductive agent, which simplifies the process and avoids the problem of the decline of the electrochemical performance of the electrode caused by the addition of the binder and the additional conductive agent, thereby improving the overall energy density of the electrode.

[0039] A sodium ion battery comprising the self-supporting electrode as described above. BRIEF DESCRIPTION OF DRAWINGS

[0040] Fig. 1 is an X-ray diffraction pattern of the active material particle layer in the self-supporting electrode of Example 1 of the present application;

[0041] Fig. 2 is an electron microscope image of the active material precursor deposited on the foam nickel by electrostatic spray deposition without high-temperature sintering in Example 1 and Example 12 of the present application, wherein (a) is Example 1 and (b) is Example 12;

[0042] Fig. 3 is an electron microscope image of the active material particle layer in the self-supporting electrode of Example 1, Example 5 and Example 6 of the present application, wherein (a) is Example 1, (b) is Example 5 and (c) is Example 6;

[0043] Fig. 4 is an X-ray diffraction pattern of the active material particle layer in the self-supporting electrode of Example 5, Example 6 and Comparative Example 7 of the present application;

[0044] Fig. 5 is a graph of the first three circle charge-discharge curves of the self-supporting electrode of Example 1 of the present application at a 0.2C rate;

[0045] Fig. 6 is a comparison graph of the cycle performance of Example 1, Example 5, Example 6 and Comparative Example 6 of the present application at a 0.2C rate;

[0046] Fig. 7 is a comparison graph of the rate performance of Example 1, Comparative Example 6 and Comparative Example 7 of the present application. DETAILED DESCRIPTION

[0047] In order to facilitate the understanding of the present application, the present application will be described in more detail below. However, it should be understood that the present application can be realized in many different forms and is not limited to the embodiments or examples described herein. On the contrary, the purpose of providing these embodiments or examples is to make the disclosure of the present application more thorough and comprehensive.

[0048] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description herein is for describing specific embodiments or examples only and is not intended to be limiting of the application.

[0049] The self-supporting electrode provided by the application comprises a conductive substrate and a layer of active material particles arranged on the conductive substrate, and the molecular formula of the active material particles in the layer of active material particles is Na 4-x FeV 1-y M y (PO4)3, and the active material particles further comprise a conductive shell layer, wherein M is selected from transition metal elements and / or Al elements, 0≤x<0.1, and 0<y<0.1.

[0050] In the application, since the electrode is a self-supporting electrode, no binder and additional conductive agent are needed, which greatly improves the content of active material in the electrode and thus improves the overall energy density of the electrode. At the same time, since no binder and additional conductive agent are needed, the electrode has good mechanical properties, thereby improving the electrochemical performance of the electrode.

[0051] Compared with the traditional Na3Fe2(PO4)3 material, in the electrode active material particles of the application, by introducing vanadium with multiple valence states and a high redox potential and non-active cation M with good electronic conductivity to cooperatively replace one trivalent iron ion, the electronic conductivity, average working voltage and specific capacity of the active material particles can be improved. At the same time, considering the problem of low intrinsic electronic conductivity of phosphate materials, the active material particles in the application are provided with a conductive shell layer, which can cooperatively work with the non-active cation M with good electronic conductivity to effectively improve the electronic conductivity of the active material particles, thereby improving the discharge specific capacity of the active material.

[0052] However, since the non-active cation M does not undergo redox reaction in the charging and discharging process, it does not contribute to the capacity. In addition, a certain proportion of cation M will occupy the transition metal site, thereby affecting the discharge specific capacity of the material. Therefore, in the application, the parameter y of the non-active cation M is further limited to the range of 0<y<0.1. In this way, the electronic conductivity of the active material particles can be improved while the loss of the capacity of the active material particles is reduced to the minimum. Moreover, due to the doping of the non-active cation M, the content of the conductive shell layer in the active material particles can also be reduced, thereby reducing the diffusion path of ions and improving the electrochemical performance of the active material particles, so that the electrode has good rate performance.

[0053] Therefore, the self-supporting electrode of the application can have a high average working voltage, specific capacity and energy density.

[0054] In addition, since vanadium has multiple valence states (e.g., tetravalent, trivalent, divalent), when vanadium with trivalent ions is introduced into the active material particles, the active material particles have a two-electron reaction, and thus have a higher discharge specific capacity. However, in the charging and discharging process, V 3+ , V 4+ oxidation and reduction reactions, and V 3+ / 4+ has a higher redox potential (3.4 V vs. Na + / Na), and thus the active material particles have a higher average working voltage. At this time, the self-supporting electrode is applied as a positive electrode in a sodium ion battery. When vanadium with divalent ions is present in the active material particles, the active material particles have a higher reversible specific capacity and a lower average working voltage, and at this time, the self-supporting electrode can be applied as a negative electrode in a sodium ion battery. Therefore, the self-supporting electrode of the present application can be applied as a negative electrode or a positive electrode in a sodium ion battery by adjusting the valence state of vanadium ions.

[0055] Optionally, the transition metal element is selected from at least one of Cu, Ag, or Co. In this way, the electronic conductivity of the active material particles can be further improved.

[0056] Optionally, the thickness of the active material particle layer is 100 μm-400 μm, preferably 150 μm-300 μm. In this way, the structural strength of the self-supporting electrode can be further improved, and the mechanical properties of the self-supporting electrode can be improved.

[0057] Optionally, the particle size of the active material particles is 50 nm-300 nm. In this way, by controlling the particle size of the active material particles, the diffusion path of sodium ions can be further controlled, and the rate performance of the electrode can be improved.

[0058] Optionally, the conductive substrate is selected from at least one of foamed nickel, foamed copper, a steel sheet, foamed aluminum, or a titanium sheet.

[0059] Optionally, the conductive shell layer is selected from a carbon coating layer, and the mass fraction of the carbon coating layer in the active material particles is 1%-9%, preferably 2%-8%. In this way, the agglomeration and growth of the active material particles at high temperatures can be inhibited, and a conductive network can be better constructed, which is conducive to the transmission of electrons, improves the electronic conductivity of the active material particles, and thus further improves the specific capacity of the active material particles and the specific capacity of the electrode.

[0060] It should be noted that the conductive shell layer in the present application can be coated on at least part of the surface of the active material particles.

[0061] Preferably, the conductive shell completely covers the particle surface of the active material particles, which can effectively prevent the particle from agglomerating and growing during high-temperature calcination, shorten the diffusion path of ions, and further improve the reversible capacity of the active material particles.

[0062] Meanwhile, the application also provides a preparation method of the self-supporting electrode, comprising:

[0063] S1, mixing a vanadium source, an iron source, an M source, a complexing agent, a phosphorus source, a sodium source, a shell precursor material, and water to obtain a mixed solution, and adjusting the viscosity of the mixed solution to obtain an active material precursor solution, wherein the M source is selected from a compound containing a transition metal element and / or an Al element; 4-x FeV 1-y M y (PO4)3, 0≤x<0.1, 0<y<0.1, mixing a vanadium source, an iron source, an M source, a complexing agent, a phosphorus source, a sodium source, a shell precursor material, and water to obtain a mixed solution, and adjusting the viscosity of the mixed solution to obtain an active material precursor solution, wherein the M source is selected from a compound containing a transition metal element and / or an Al element;

[0064] S2, depositing the active material precursor solution on a conductive substrate by electrostatic spraying deposition technology, and then sintering in a protective atmosphere to form an active material particle layer to obtain a self-supporting electrode, wherein the temperature of the conductive substrate is greater than the boiling point temperature of the active material precursor solution.

[0065] In step S1, the ratio of the sum of the molar amounts of the vanadium source, the iron source, and the M source to the molar amount of the complexing agent is 1:1-1:3. In this way, the vanadium ions in the vanadium source, the iron ions in the iron source, and the non-active cations in the M source can be further complexed with the complexing agent, so that the vanadium source, the iron source, the M source, the sodium source, the phosphorus source, and the shell precursor material form a solution state, realizing a mixed solution of ion states of various elements, and facilitating the formation of an active material particle layer with uniform distribution of each element.

[0066] Optionally, the mass fraction of the shell precursor material in the mixed solution is 3%-20%, and the shell precursor material is selected from titanium boride and / or a carbon source, preferably a carbon source, and the carbon source is selected from at least one of citric acid, glucose, fructose, sucrose, graphene, polyethylene glycol, polyvinylpyrrolidone, starch, dopamine, phenolic resin, or carbon nanotubes. In this way, it is beneficial to form a carbon coating layer to better construct a conductive network for the active material particles, further improve the electronic conductivity of the active material particles, and further control the content of the carbon coating layer in the active material particles, further shorten the diffusion path of sodium ions, improve the specific capacity, and further improve the cycle stability and rate performance of the electrode.

[0067] It should be noted that the carbon source in the application will be coated on at least part of the surface of the particles to form a carbon coating layer during caramelization.

[0068] Optionally, the vanadium source is selected from at least one of ammonium metavanadate, vanadium pentoxide, vanadium trioxide, vanadium dioxide or sodium metavanadate, the iron source is selected from at least one of iron nitrate nonahydrate, iron acetate, ferrous acetate, ferrous oxalate, iron sesquioxide, iron powder, iron citrate, iron tartrate, iron formate or iron lactate, and the M source is selected from at least one of copper acetate, copper nitrate or copper oxide.

[0069] Optionally, the complexing agent is selected from at least one of oxalic acid dihydrate, lactic acid, tartaric acid, succinic acid or ethylenediaminetetraacetic acid.

[0070] Optionally, the phosphorus source is selected from at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphoric acid, sodium phosphate or sodium dihydrogen phosphate.

[0071] Optionally, the sodium source is selected from at least one of sodium acetate, sodium carbonate, sodium hydroxide, sodium oxalate, sodium stearate, sodium tartrate, sodium alginate or sodium lactate.

[0072] Optionally, the viscosity of the active material precursor solution is 0.3 MPa·s-2.0 MPa·s, preferably 0.6 MPa·s-1.0 MPa·s. In this way, by controlling the viscosity of the active material precursor solution, the diffusion rate of the active material precursor solution on the conductive substrate in the subsequent process can be further controlled, thereby affecting the uniformity in the subsequent electrostatic spraying deposition process, and facilitating the formation of a uniform active material particle layer on the conductive substrate.

[0073] Optionally, the viscosity of the mixed solution is adjusted by adding an organic solvent to the mixed solution, and the mass ratio of the mixed solution to the organic solvent is 100:50-100:95. In this way, the viscosity of the active material precursor solution can be better controlled to be 0.6 MPa·s-1.0 MPa·s, thereby improving the uniformity of the active material particle layer.

[0074] Further, the organic solvent is selected from at least one of N,N-dimethylformamide, azomethylnitrone, ethylene glycol, butyl carbitol, anhydrous ethanol, glycerol or acetone.

[0075] In step S2, the electrostatic spraying deposition process parameters include: the voltage is 4-12 kv, the inner diameter of the needle is 0.6-1.0 mm, the solution flow rate is 1-5 mL h -1 -5 mL h -1 , and the distance between the needle and the conductive substrate is 2-8 cm. In this way, by adjusting the process parameters of the electrostatic spraying, a uniform active material particle layer can be formed on the conductive substrate, and the active material particle layer has excellent electrochemical performance.

[0076] Optionally, the protective gas atmosphere is selected from an inert gas atmosphere and / or a hydrogen gas atmosphere, the inert gas atmosphere is selected from at least one of a nitrogen gas atmosphere, an argon gas atmosphere or a helium gas atmosphere, and preferably, the nitrogen gas atmosphere and the hydrogen gas atmosphere, and when the protective gas atmosphere is a mixed atmosphere of argon and hydrogen, the volume ratio of argon to hydrogen is 90:10-98:2, preferably 95:5.

[0077] Optionally, the sintering temperature is 500-800℃, and the sintering time is 6-10h. In this way, by controlling the sintering temperature and time, the active material particle layer with uniform mixing and high crystallinity is formed on the conductive substrate, and the conductive substrate and the active material particle layer are integrally sintered and formed, without the use of a binder and an additional conductive agent, thereby simplifying the process, avoiding the problem of the decline of the electrochemical performance of the electrode caused by the addition of the binder and the additional conductive agent, and further improving the overall energy density of the electrode.

[0078] Optionally, the temperature of the conductive substrate is 130-200℃. In this way, the uniformity of the active material particle layer can be further improved.

[0079] Optionally, the radius of curvature of the conductive substrate is 0.06-0.6m, which can further improve the uniformity of the active material particle layer.

[0080] Optionally, the roughness Ra of the conductive substrate is 20-720μm. In this way, the bonding force between the active material particle layer and the conductive substrate can be further improved, and the mechanical performance of the electrode is further improved.

[0081] It should be noted that the roughness of the conductive substrate in the present application can be the roughness of the conductive substrate itself, and if the roughness of the conductive substrate itself does not meet the requirement of the roughness, the surface of the conductive substrate can be treated by a surface treatment method to obtain a conductive substrate with appropriate roughness. The surface treatment method can be sandpaper polishing, acid etching or laser treatment.

[0082] Further, the conductive substrate is selected from at least one of foamed nickel, foamed copper, a steel sheet, foamed aluminum or a titanium sheet.

[0083] As can be seen, in the preparation method of the present application, the electrostatic spray deposition technology is used to form the active material particle layer on the conductive substrate, which is simple and avoids the programmed and tedious electrode preparation process. At the same time, in the method, the shell precursor material, the conductive substrate and the active material are integrally sintered and formed, without the use of a binder and an additional conductive agent, thereby simplifying the process, avoiding the problem of the decline of the electrochemical performance of the electrode caused by the addition of the binder and the additional conductive agent, and further improving the overall energy density of the electrode.

[0084] In addition, the active material particles prepared by the electrostatic spray deposition technology have high purity, small and uniform particle size.

[0085] In addition, the application further provides a sodium ion battery comprising the self-supporting electrode as described above. The sodium ion battery has high specific capacity, energy density, excellent rate and cycle performance, and the like due to containing the self-supporting electrode.

[0086] In an embodiment, the self-supporting electrode is applied to the sodium ion battery as a positive electrode.

[0087] In another embodiment, the self-supporting electrode is applied to the sodium ion battery as a negative electrode.

[0088] Hereinafter, the self-supporting electrode, the preparation method thereof and the sodium ion battery will be further described through the following specific examples.

[0089] Meanwhile, it should be noted that the reagent raw materials involved in the examples and comparative examples of the application can be purchased from the market.

[0090] Example 1

[0091] The stoichiometric ratio of Na 3.95 FeV 0.95 Cu 0.05 The stoichiometric ratio of Na

[0092] The active material precursor solution obtained above is loaded into a 100 mL syringe with a stainless steel needle, taking foamed nickel (curvature radius 0.06 m, roughness Ra 300 μm) as a collector, wherein the inner diameter of the needle is 0.7 mm, the distance between the needle and the foamed nickel is 4 cm, the temperature of the foamed nickel is 155 ℃, then the voltage is controlled to be 6.5 kv, the solution flow rate is 2 mLh -1 The electrostatic spray deposition is performed, and then sintering is performed in a tube furnace filled with argon / hydrogen (volume ratio of Ar / H2 95:5) to form an active material particle layer, wherein the sintering temperature is 650 ℃ and the sintering time is 8 h, to obtain a self-supporting electrode, wherein the active material particles in the active material particle layer have a carbon coating layer, i.e., Na 3.95 FeV 0.95 Cu0.05 The thickness of the active material particle layer is 200 μm, the mass fraction of the carbon coating layer in the active material particle is 4.5%, and the particle size of the active material particle is 150 nm.

[0093] As can be seen from FIG. 1, the active material particle in the self-supporting electrode of the embodiment has no other impurity diffraction peak; as can be seen from FIG. 2(a), no particle is precipitated on the surface of the foam nickel, indicating that the active material precursor is uniformly deposited on the surface of the foam nickel; as can be seen from FIG. 3(a), after high-temperature calcination, the active material is still uniformly deposited on the surface of the foam nickel to form an active material particle layer; as can be seen from FIG. 5, the self-supporting electrode of the embodiment has a relatively high specific discharge capacity, and after one discharge, Fe 3+ in the material is reduced to Fe 2+ , and in the second circle of the charge-discharge curve, the redox platform of Fe 2+ / Fe 3+ can be clearly seen.

[0094] Meanwhile, the inductively coupled plasma atomic emission spectrometer is used to test the molar ratio of sodium, iron, vanadium and copper elements in the active material particle of the self-supporting electrode of the embodiment 1, which is about 3.94:1:0.95:0.05, and the carbon-sulfur analyzer is used to test the mass fraction of the carbon content in the active material particle of the embodiment 1, which is about 4.5%, indicating that the active material particle Na 3.95 FeV 0.95 Cu 0.05 (PO4)3 / C of the embodiment has been successfully obtained.

[0095] Embodiment 2

[0096] Compared with the embodiment 1, the embodiment 2 only differs in that the stoichiometric ratio of Na4FeV 0.98 Ag 0.02 (PO4)3 is used as the reference, vanadium pentoxide, iron nitrate, silver acetate, glucose, diammonium hydrogen phosphate, sodium tartrate, tartaric acid and water are mixed to obtain a mixed solution, and acetone is added to the mixed solution to obtain an active material precursor solution with a viscosity of 0.4 MPa·s, wherein the ratio of the sum of the molar amounts of vanadium pentoxide, iron nitrate and silver acetate to the molar amount of tartaric acid is 1:3, the mass fraction of glucose in the mixed solution is 3%, the mass ratio of the mixed solution to acetone is 100:90, and the remaining conditions are the same, to obtain a self-supporting electrode, wherein the active material particle in the active material particle layer has a carbon coating layer, i.e., Na4FeV 0.98 Ag 0.02NaV (PO4) 3 / C, wherein the thickness of the active material particle layer is 200 μm, the mass fraction of the carbon coating layer in the active material particle is 1.1%, and the particle size of the active material particle is 280 nm.

[0097] Example 3

[0098] Example 3 differs from Example 1 only in that Na 3.92 FeV 0.92 Co 0.08 On the basis of the stoichiometric ratio of NaV (PO4) 3, ammonium metavanadate, iron citrate, copper nitrate, aluminum nitrate nonahydrate, anhydrous citric acid, ammonium dihydrogen phosphate, sodium alginate, oxalic acid dihydrate, and water are mixed to obtain a mixed solution, and acetone is added to the mixed solution to obtain an active material precursor solution with a viscosity of 0.5 MPa s, wherein the ratio of the sum of the molar amounts of ammonium metavanadate, iron citrate, copper acetate, and aluminum nitrate nonahydrate to the molar amount of oxalic acid dihydrate is 1:2, the mass fraction of anhydrous citric acid in the mixed solution is 15%, and the mass ratio of the mixed solution to acetone is 100:95, and the remaining conditions are the same, to obtain a self-supporting electrode, wherein the active material particles in the active material particle layer have a carbon coating layer, i.e., Na 3.92 FeV 0.92 Co 0.08 NaV (PO4) 3 / C, wherein the thickness of the active material particle layer is 195 μm, the mass fraction of the carbon coating layer in the active material particle is 8.7%, and the particle size of the active material particle is 70 nm.

[0099] Example 4

[0100] Example 4 differs from Example 1 only in that Na 3.95 FeV 0.95 Cu 0.03 Al 0.02 On the basis of the stoichiometric ratio of NaV (PO4) 3, ammonium metavanadate, iron citrate, copper nitrate, aluminum nitrate nonahydrate, anhydrous citric acid, ammonium dihydrogen phosphate, sodium alginate, oxalic acid dihydrate, and water are mixed to obtain a mixed solution, and acetone is added to the mixed solution to obtain an active material precursor solution with a viscosity of 0.5 MPa s, wherein the ratio of the sum of the molar amounts of ammonium metavanadate, iron citrate, copper acetate, and aluminum nitrate nonahydrate to the molar amount of oxalic acid dihydrate is 1:2, the mass fraction of anhydrous citric acid in the mixed solution is 15%, and the mass ratio of the mixed solution to acetone is 100:95, and the remaining conditions are the same, to obtain a self-supporting electrode, wherein the active material particles in the active material particle layer have a carbon coating layer, i.e., Na 3.95 FeV 0.95 Cu 0.03 Al 0.02NaV2(PO4)3 / C, wherein the thickness of the active material particle layer is 190 μm, the mass fraction of the carbon coating layer in the active material particle is 6.6%, and the particle size of the active material particle is 100 nm.

[0101] Example 5

[0102] Example 5 is compared with Example 1, the only difference is that the mass fraction of anhydrous citric acid in the mixed solution is 25%, and the rest of the conditions are the same, to obtain a self-supporting electrode, wherein the active material particles in the active material particle layer have a carbon coating layer, i.e., Na 3.95 FeV 0.95 Cu 0.05 NaV2(PO4)3 / C, wherein the thickness of the active material particle layer is 220 μm, the mass fraction of the carbon coating layer in the active material particle is 10.1%, and the particle size of the active material particle is 50 nm.

[0103] As can be seen from (b) of FIG. 3, compared with Example 1, this example is broken into irregular blocks due to the release of a large amount of gas during high-temperature sintering because of the high carbon content, thereby breaking the continuous active material particle layer; as can be seen from FIG. 4, the active material particles in the self-supporting electrode of this example have no other impurity diffraction peaks; as can be seen from FIG. 6, the self-supporting electrode of Example 1 has the best rate performance, and the discharge specific capacity thereof can reach 91.9 mAhg -1 .

[0104] Example 6

[0105] Example 6 is compared with Example 1, the only difference is that the mass fraction of anhydrous citric acid in the mixed solution is 1%, and the rest of the conditions are the same, to obtain a self-supporting electrode, wherein the active material particles in the active material particle layer have a carbon coating layer, i.e., Na 3.95 FeV 0.95 Cu 0.05 NaV2(PO4)3 / C, wherein the thickness of the active material particle layer is 180 μm, the mass fraction of the carbon coating layer in the active material particle is 0.4%, and the particle size of the active material particle is 500 nm.

[0106] As can be seen from (c) of FIG. 3, compared with Example 1, the active material particles in the self-supporting electrode of this example appear on the surface of the foamed nickel, because the carbon content is less, so that the conductive network cannot well coat the active material particles, and then agglomerate and grow to appear on the surface of the foamed nickel; as can be seen from FIG. 4, the active material particles in the self-supporting electrode of this example have no other impurity diffraction peaks; as can be seen from FIG. 6, compared with Example 1, the cycle stability of the self-supporting electrode of this example is poor.

[0107] Example 7

[0108] Example 7 differs from Example 1 only in that titanium boride is used instead of anhydrous citric acid, and the rest of the conditions are the same, to obtain a self-supporting electrode, wherein the active material particles in the active material particle layer have a titanium boride coating layer, i.e., Na 3.95 FeV 0.95 Cu 0.05 (PO4)3 / TiB2, wherein the thickness of the active material particle layer is 180 μm, the mass fraction of the titanium boride coating layer in the active material particles is 4.4%, and the particle size of the active material particles is 160 nm.

[0109] Example 8

[0110] Example 8 differs from Example 1 only in that N,N-dimethylformamide is added to the mixed solution to obtain an active material precursor solution with a viscosity of 0.2 MPa·s, wherein the mass ratio of the mixed solution to N,N-dimethylformamide is 100:95, and the rest of the conditions are the same, to obtain a self-supporting electrode, wherein the active material particles in the active material particle layer have a carbon coating layer, i.e., Na 3.95 FeV 0.95 Cu 0.05 (PO4)3 / C, wherein the thickness of the active material particle layer is 220 μm, the mass fraction of the carbon coating layer in the active material particles is 4.5%, and the particle size of the active material particles is 150 nm.

[0111] Example 9

[0112] Example 9 differs from Example 1 only in that N,N-dimethylformamide is added to the mixed solution to obtain an active material precursor solution with a viscosity of 2.5 MPa·s, wherein the mass ratio of the mixed solution to N,N-dimethylformamide is 100:80, and the rest of the conditions are the same, to obtain a self-supporting electrode, wherein the active material particles in the active material particle layer have a carbon coating layer, i.e., Na 3.95 FeV 0.95 Cu 0.05 (PO4)3 / C, wherein the thickness of the active material particle layer is 180 μm, the mass fraction of the carbon coating layer in the active material particles is 4.4%, and the particle size of the active material particles is 160 nm.

[0113] Example 10

[0114] Example 10 differs from Example 1 only in that the inner diameter of the needle is 0.6 mm, the distance between the needle and the foamed nickel is 2 cm, the temperature of the foamed nickel is 130°C, the control voltage is 4 kv, and the solution flow rate is 1 mLh -1 The rest of the conditions are the same, to obtain a self-supporting electrode, wherein the active material particles in the active material particle layer have a carbon coating layer, i.e., Na3.95 FeV 0.95 Cu 0.05 (PO4)3 / C, wherein the thickness of the active material particle layer is 110 μm, the mass fraction of the carbon coating layer in the active material particle is 4.3%, and the particle size of the active material particle is 200 nm.

[0115] Example 11

[0116] Example 11 differs from Example 1 only in that the inner diameter of the needle is 1.0 mm, the distance between the needle and the foam nickel is 8 cm, the temperature of the foam nickel is 200 °C, the control voltage is 6.5 kv, and the solution flow rate is 5 mL h -1 The rest of the conditions are the same, and a self-supporting electrode is obtained, wherein the active material particles in the active material particle layer have a carbon coating layer, that is, Na 3.95 FeV 0.95 Cu 0.05 (PO4)3 / C, wherein the thickness of the active material particle layer is 450 μm, the mass fraction of the carbon coating layer in the active material particle is 4.4%, and the particle size of the active material particle is 170 nm.

[0117] Example 12

[0118] Example 12 differs from Example 1 only in that the control voltage is 13 kv, and the rest of the conditions are the same, and a self-supporting electrode is obtained, wherein the active material particles in the active material particle layer have a carbon coating layer, that is, Na 3.95 FeV 0.95 Cu 0.05 (PO4)3 / C, wherein the thickness of the active material particle layer is 180 μm, the mass fraction of the carbon coating layer in the active material particle is 4.3%, and the particle size of the active material particle is 140 nm.

[0119] As can be seen from (b) of FIG. 2, compared with Example 1, the active material particle layer of this example is in a granular shape on the surface of the foam nickel, because the voltage is higher, which causes the shape of the sprayed droplets to be narrow and concentrated when electrostatic spraying is deposited, so that the deposited active material particles are accumulated in one area of the foam nickel, and then in a granular shape.

[0120] Example 13

[0121] Example 13 differs from Example 1 only in that the control voltage is 3 kv, and the rest of the conditions are the same, and a self-supporting electrode is obtained, wherein the active material particles in the active material particle layer have a carbon coating layer, that is, Na 3.95 FeV 0.95 Cu 0.05Na3V2(PO4)3 / C, wherein the thickness of the active material particle layer is 220 μm, the mass fraction of the carbon coating layer in the active material particle is 4.4%, and the particle size of the active material particle is 200 nm.

[0122] Example 14

[0123] Example 14 differs from Example 1 only in that a steel sheet (radius of curvature is 0.4 m, roughness Ra is 20 μm) is used instead of the foamed nickel, and the rest of the conditions are the same, to obtain a self-supporting electrode, wherein the active material particles in the active material particle layer have a carbon coating layer, that is, Na 3.95 FeV 0.95 Cu 0.05 Na3V2(PO4)3 / C, wherein the thickness of the active material particle layer is 100 μm, the mass fraction of the carbon coating layer in the active material particle is 4.2%, and the particle size of the active material particle is 160 nm.

[0124] Example 15

[0125] Example 15 differs from Example 1 only in that a foamed copper with a polished surface (radius of curvature is 0.1 m, roughness Ra is 560 μm) is used instead of the foamed nickel, and the rest of the conditions are the same, to obtain a self-supporting electrode, wherein the active material particles in the active material particle layer have a carbon coating layer, that is, Na 3.95 FeV 0.95 Cu 0.05 Na3V2(PO4)3 / C, wherein the thickness of the active material particle layer is 200 μm, the mass fraction of the carbon coating layer in the active material particle is 4.3%, and the particle size of the active material particle is 140 nm.

[0126] Example 16

[0127] Example 16 differs from Example 1 only in that the roughness Ra of the foamed nickel is 750 μm, and the rest of the conditions are the same, to obtain a self-supporting electrode, wherein the active material particles in the active material particle layer have a carbon coating layer, that is, Na 3.95 FeV 0.95 Cu 0.05 Na3V2(PO4)3 / C, wherein the thickness of the active material particle layer is 190 μm, the mass fraction of the carbon coating layer in the active material particle is 4.4%, and the particle size of the active material particle is 150 nm.

[0128] Example 17

[0129] Example 17 differs from Example 1 only in that the sintering temperature is 500 ℃, the sintering time is 6 h, and the rest of the conditions are the same, to obtain a self-supporting electrode, wherein the active material particles in the active material particle layer have a carbon coating layer, that is, Na3.95 FeV 0.95 Cu 0.05 (PO4)3 / C, the thickness of the active material particle layer is 200 μm, the mass fraction of the carbon coating layer in the active material particle is 3.8%, and the particle size of the active material particle is 140 nm.

[0130] Example 18

[0131] Example 18 differs from Example 1 only in that the sintering temperature is 800°C, the sintering time is 10 h, and the rest of the conditions are the same, to obtain a self-supporting electrode, wherein the active material particles in the active material particle layer have a carbon coating layer, i.e., Na 3.95 FeV 0.95 Cu 0.05 (PO4)3 / C, the thickness of the active material particle layer is 185 μm, the mass fraction of the carbon coating layer in the active material particle is 4.0%, and the particle size of the active material particle is 260 nm.

[0132] Comparative Example 1

[0133] Comparative Example 1 differs from Example 3 only in that Na 3.92 FeCo(PO4)3, wherein the ratio of the sum of the molar amounts of the iron nitrate nonahydrate and the cobalt acetate to the molar amount of the oxalic acid dihydrate is 1:1.5, and the rest of the conditions are the same, to obtain a self-supporting electrode, wherein the active material particles in the active material particle layer have a carbon coating layer, i.e., Na 3.92 FeCo(PO4)3 / C, the thickness of the active material particle layer is 200 μm, the mass fraction of the carbon coating layer in the active material particle is 4.3%, and the particle size of the active material particle is 150 nm.

[0134] Comparative Example 2

[0135] Comparative Example 2 differs from Example 1 only in that Na 3.95 FeV(PO4)3, wherein the ratio of the sum of the molar amounts of the copper acetate, the ammonium vanadate, and the iron nitrate nonahydrate to the molar amount of the oxalic acid dihydrate is 1:1.5, and the rest of the conditions are the same, to obtain a self-supporting electrode, wherein the active material particles in the active material particle layer have a carbon coating layer, i.e., Na 3.95 FeV(PO4)3 / C, the thickness of the active material particle layer is 200 μm, the mass fraction of the carbon coating layer in the active material particle is 4.5%, and the particle size of the active material particle is 160 nm.

[0136] Comparative Example 3

[0137] Comparative Example 3 differs from Example 1 only in that Na3.95 FeV 0.9 Cu 0.1 The stoichiometric ratio of (PO4)3 is taken as a reference, wherein the ratio of the sum of the molar amounts of ammonium vanadate, iron nitrate nonahydrate and copper acetate to the molar amount of oxalic acid dihydrate is 1:1.5, and the remaining conditions are the same, to obtain a self-supporting electrode, wherein the active material particles in the active material particle layer have a carbon coating layer, i.e., Na 3.95 FeV 0.9 Cu 0.1 (PO4)3 / C, the thickness of the active material particle layer is 200 μm, the mass fraction of the carbon coating layer in the active material particles is 4.3%, and the particle size of the active material particles is 150 nm.

[0138] Comparative Example 4

[0139] Comparative Example 4 differs from Example 1 only in that no anhydrous citric acid is added, and the remaining conditions are the same, to obtain a self-supporting electrode, wherein the active material particles in the active material particle layer do not have a carbon coating layer, i.e., Na 3.95 FeV 0.95 Cu 0.05 (PO4)3, the thickness of the active material particle layer is 180 μm, and the particle size of the active material particles is 350 nm.

[0140] Comparative Example 5

[0141] Comparative Example 5 differs from Example 1 only in that the temperature of the foamed nickel is 120°C, and the remaining conditions are the same, to obtain a self-supporting electrode, wherein the active material particles in the active material particle layer have a carbon coating layer, i.e., Na 3.95 FeV 0.95 Cu 0.05 (PO4)3 / C, the thickness of the active material particle layer is 210 μm, the mass fraction of the carbon coating layer in the active material particles is 4.1%, and the particle size of the active material particles is 280 nm.

[0142] Comparative Example 6

[0143] Na 3.95 FeV 0.95 Cu 0.05 The stoichiometric ratio of (PO4)3 is taken as a reference, wherein the ratio of the sum of the molar amounts of ammonium vanadate, iron nitrate nonahydrate and copper acetate to the molar amount of oxalic acid dihydrate is 1:1.5, and the remaining conditions are the same, to obtain a self-supporting electrode, wherein the active material particles in the active material particle layer have a carbon coating layer, i.e., Na

[0144] The active material precursor is used as an electrospinning solution, the electrospinning solution is loaded into a 100 mL syringe with a stainless steel needle, and an aluminum foil is placed as a collector at a distance of 15 cm from the needle, and then electrospinning is carried out at a voltage of 11 kV to obtain an electrospun film, and the electrospun film is placed in a tube furnace filled with argon / hydrogen (Ar / H2 volume ratio 95:5) for sintering, wherein the sintering temperature is 650°C and the sintering time is 8h, to obtain a self-supporting electrode, wherein the active material particles in the active material particle layer have a carbon coating layer, i.e., Na 3.95 FeV 0.95 Cu 0.05 (PO4)3 / C, wherein the thickness of the active material particle layer is 200μm, the mass fraction of the carbon coating layer in the active material particles is 13.7%, and the particle size of the active material particles is 50nm.

[0145] As can be seen from FIGS. 6-7, the comparative example has a relatively thick carbon coating layer, resulting in a longer ion diffusion path, and the cycle stability life and rate performance are not as good as those of the material of Example 1.

[0146] Comparative Example 7

[0147] Na 3.95 FeV 0.95 Cu 0.05 The stoichiometric ratio of NaVO3, Fe(NO3)3·9H2O, Cu(CH3COO)2·2H2O, C6H5O7H2O, (NH4)3PO4, NaCH3COO, C2H2O4·2H2O and H2O is used as a reference, and the above-mentioned substances are mixed to obtain a mixed solution, and stirred until a sol is formed, and then placed in a 120°C air drying oven for 12h to obtain a dry gel; the dry gel is crushed and placed in a tube furnace filled with argon / hydrogen (Ar / H2 volume ratio 95:5) for sintering, wherein the sintering temperature is 650°C and the sintering time is 8h, to obtain active material particles with a carbon coating layer, i.e., Na 3.95 FeV 0.95 Cu 0.05 (PO4)3 / C, and finally the active material particles are mixed with acetylene black, polyvinylidene fluoride and N-methyl pyrrolidone to obtain a uniform slurry, wherein the mass ratio of the active material particles to acetylene black, polyvinylidene fluoride and N-methyl pyrrolidone is 70:20:10:30, and the obtained slurry is coated on the surface of a carbon-coated aluminum foil and dried in a vacuum drying oven, with a drying temperature of 100°C and a drying time of 8h, to obtain a non-self-supporting electrode.

[0148] As can be seen from FIG. 4, the active material particles in the non-self-supporting electrode of the comparative example have no other impurity diffraction peaks; as can be seen from FIG. 7, the active material of Comparative Example 7 has poorer electrochemical performance than the active material of Example 1 due to the addition of additional conductive agent (acetylene black) and electronic insulator polyvinylidene fluoride solution during preparation.

[0149] Comparative Example 8

[0150] Comparative Example 8 is compared with Example 1, the only difference is that Na 3.9 FeV 0.95 Cu 0.05 The stoichiometric ratio of (PO4)3is used as a reference, ammonium metavanadate, ferric nitrate nonahydrate, copper acetate, anhydrous citric acid, ammonium dihydrogen phosphate, sodium acetate, oxalic acid dihydrate and water are mixed to obtain a mixed solution, and N,N-dimethylformamide is added to the mixed solution to obtain an active material precursor solution with a viscosity of 0.75 MPa·s, and the remaining conditions are the same to obtain a self-supporting electrode, wherein the active material particles in the active material particle layer have a carbon coating layer, i.e., Na 3.9 FeV 0.95 Cu 0.05 (PO4)3 / C, the thickness of the active material particle layer is 195 μm, the mass fraction of the carbon coating layer in the active material particles is 4.4%, and the particle size of the active material particles is 145 nm.

[0151] The self-supporting electrodes prepared by using Examples 1 to 18, Comparative Examples 1 to 6 and Comparative Example 8 and the non-self-supporting electrode prepared by using Comparative Example 7 are assembled into CR2032 type batteries as positive electrode sheets. Among them, the method for assembling the above CR2032 type batteries is as follows: taking the positive electrode and the metal sodium as the counter electrode, 1 molL -1 NaClO4as the electrolyte, and glass fiber as the separator, the CR2032 type batteries are assembled in a glove box (the water and oxygen contents are both less than 0.1 ppm).

[0152] Subsequently, the constant current charge-discharge test of each CR2032 type battery at 25°C is carried out on a blue electric multi-channel test system, the voltage window is between 2.0 V and 3.8 V, and the electrical performance test of each CR2032 type battery at different rates is carried out, and the test results are shown in Table 1.

[0153] Table 1

[0154] Referring to the data in Table 1, it can be seen from Comparative Example 1, Example 5 and Example 6 that the content of the carbon coating layer in the active material particles is too high or too low, which will affect the cycle stability and rate performance of the electrode, because too high carbon content will increase the ion diffusion path of the active material carbon coating layer, and too low carbon content will cause serious particle agglomeration and incomplete construction of the conductive network, thereby affecting the release of the electrochemical performance of the electrode.

[0155] As can be seen from Comparative Example 1, Example 8 and Example 9, the viscosity of the active material precursor solution is too high or too low, which affects the specific discharge capacity of the active material, because the ion diffusion rate is low due to the high viscosity, which affects the coating efficiency and causes the active material particles to accumulate, and the low viscosity affects the atomization state of the spray, which causes the active material film to be in a state.

[0156] As can be seen from Comparative Example 1, Example 12 and Example 13, the voltage in the electrostatic spray deposition process parameter is too high or too low, which affects the rate performance of the material, because when the voltage is too high, the droplet shape becomes narrow and is deposited on the surface of the foamed nickel, and when the voltage is too low, the droplet shape becomes wide, which affects the solvent evaporation and causes the active material particles to agglomerate.

[0157] As can be seen from Comparative Example 1, Examples 14 to 16, the roughness of the conductive substrate affects the adhesion of the material on the particle surface, and when the roughness is small, the adhesion between the precursor solution and the conductive substrate is small, which easily causes the loss of active material, and when the roughness is large, the precursor solution cannot form a continuous and flat film on the conductive substrate, which easily causes the capacity to rapidly decay when the battery is organized.

[0158] As can be seen from Comparative Example 1, Example 3, Comparative Examples 1 to 4, by introducing vanadium with multiple valence states and a high redox potential and a specific content of non-active cation M with good electronic conductivity to replace one trivalent iron ion, the average working voltage, specific capacity and electronic conductivity of the active material can be improved, and by setting a conductive shell layer, the electronic conductivity of the active material can be effectively improved in cooperation with the non-active cation M with good electronic conductivity, so that the self-supporting electrode of the present application can have a high average working voltage, specific capacity and energy density.

[0159] In combination with Table 1 and FIG. 7, as can be seen from Comparative Example 1, Comparative Examples 6 to 7, the battery prepared in Example 1 has a simple process and excellent electrochemical performance, because the electrode prepared by the electrostatic spray deposition method in Example 1 has a self-supporting structure, a small carbon coating layer thickness and good electronic conductivity, which shortens the diffusion path of sodium ions and improves the conductivity of the electrode.

[0160] The technical features of the above examples can be combined in any way, and to make the description concise, not all possible combinations of the technical features in the above examples are described, but as long as the combinations of the technical features do not exist, they should be considered as the scope of the present application.

[0161] The above embodiments only express several implementation ways of the present application, and the description is specific and detailed, but it should not be understood as a limitation to the patent scope of the present application. It should be pointed out that, for ordinary skilled in the art, several modifications and improvements can be made without departing from the concept of the present application, and these are all within the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

[0162] The above is the preferred embodiment of the present application, but it should not be understood as a limitation to the scope of the present application. It should be pointed out that, for ordinary skilled in the art, several modifications and improvements can be made without departing from the concept of the present application, and these are all within the protection scope of the present application.

Claims

1. A self-supporting electrode, wherein: The self-supporting electrode comprises a conductive substrate and an active material particle layer disposed on the conductive substrate, wherein the active material particles in the active material particle layer have a molecular formula of Na 4-x FeV 1-y M y (PO4)3, and the active material particles further include a conductive shell layer, wherein M is selected from transition metal elements and / or Al elements, 0≤x<0.1, 0<y<0.

1.

2. The self-supporting electrode according to claim 1, wherein The transition metal element is selected from at least one of Cu, Ag and Co.

3. The self-supporting electrode according to claim 1 or 2, wherein: The thickness of the active material particle layer is 100 μm to 400 μm.

4. The self-supporting electrode according to any one of claims 1 to 3, wherein: The particle size of the active material particles is 50nm-300nm.

5. The self-supporting electrode according to any one of claims 1 to 4, wherein: The conductive substrate is selected from at least one of foamed nickel, foamed copper, steel sheet, foamed aluminum or titanium sheet.

6. The self-supporting electrode according to any one of claims 1 to 5, wherein: The conductive shell layer is selected from a carbon coating layer, and the mass fraction of the carbon coating layer in the active material particles is 2%-8%.

7. A method for preparing a self-supporting electrode according to any one of claims 1 to 6, wherein: include: Take Na 4-x FeV 1-y M y (PO4)3, 0≤x<0.1, 0<y<0.1 is used as a benchmark, a vanadium source, an iron source, an M source, a complexing agent, a phosphorus source, a sodium source, a shell precursor material and water are mixed to obtain a mixed solution, and the viscosity of the mixed solution is adjusted to obtain an active material precursor solution, wherein the M source is selected from a compound containing a transition metal element and / or an Al element; The active material precursor solution is placed on a conductive substrate using electrostatic spray deposition technology, and then sintered in a protective atmosphere to form an active material particle layer to obtain a self-supporting electrode, wherein the temperature of the conductive substrate is greater than the boiling point of the active material precursor solution.

8. The method for preparing a self-supporting electrode according to claim 7, wherein: In the step of mixing the vanadium source, the iron source, the M source, the complexing agent, the phosphorus source, the sodium source, the shell precursor material, and water to obtain a mixed solution, at least one of the following conditions is met: (1) The ratio of the sum of the molar amounts of the vanadium source, the iron source, and the M source to the molar amount of the complexing agent is 1:1-1:3; (2) The mass fraction of the shell precursor material in the mixed solution is 3%-20%, and the shell precursor material is selected from a carbon source, and the carbon source is selected from at least one of citric acid, glucose, fructose, sucrose, graphene, polyethylene glycol, polyvinyl pyrrolidone, starch, dopamine, phenolic resin or carbon nanotubes; (3) The vanadium source is selected from at least one of ammonium metavanadate, vanadium pentoxide, vanadium trioxide, vanadium dioxide or sodium metavanadate; (4) The iron source is selected from at least one of ferric nitrate nonahydrate, ferric acetate, ferrous acetate, ferrous oxalate, ferrous oxide, iron powder, ferric citrate, ferric tartrate, ferric formate, or ferric lactate; (5) The M source is selected from at least one of copper acetate, copper nitrate or copper oxide; (6) The complexing agent is selected from at least one of oxalic acid dihydrate, lactic acid, tartaric acid, succinic acid or ethylenediaminetetraacetic acid; (7) The phosphorus source is selected from at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphoric acid, sodium phosphate, or sodium dihydrogen phosphate; (8) The sodium source is selected from at least one of sodium acetate, sodium carbonate, sodium hydroxide, sodium oxalate, sodium stearate, sodium tartrate, sodium alginate or sodium lactate.

9. The method for preparing a self-supporting electrode according to claim 7 or 8, wherein: In the step of adjusting the viscosity of the mixed solution to obtain an active material precursor solution, at least one of the following conditions is met: (1) The viscosity of the active material precursor solution is 0.3 MPa·s-2.0 MPa·s; (2) adjusting the viscosity of the mixed solution by adding an organic solvent to the mixed solution, wherein the mass ratio of the mixed solution to the organic solvent is 100:50-100:95, and the organic solvent is selected from at least one of N,N-dimethylformamide, nitrogen methyl pyrrolidone, ethylene glycol, butyl carbitol, anhydrous ethanol, glycerol or acetone.

10. The method for preparing a self-supporting electrode according to any one of claims 7 to 9, wherein: In the step of placing the active material precursor solution on the conductive substrate using electrostatic spraying technology and then sintering in a protective gas atmosphere to form an active material particle layer, at least one of the following conditions is met: (1) Electrostatic spray deposition process parameters include: voltage of 4.0kV-12.0kV, needle inner diameter of 0.6mm-1.0mm, solution flow rate of 1mLh -1 -5mLh -1 , the distance between the needle and the conductive substrate is 2cm-8cm; (2) The protective gas atmosphere is selected from an inert gas atmosphere and / or a hydrogen atmosphere; (3) The sintering temperature is 500-800°C and the sintering time is 6-10 hours; (4) The temperature of the conductive substrate is 130°C-200°C; (5) The curvature radius of the conductive substrate is 0.06m-0.6m; (6) The roughness Ra of the conductive substrate is 20 μm ≤ Ra ≤ 720 μm; (7) The conductive substrate is selected from at least one of foamed nickel, foamed copper, foamed aluminum, steel sheet or titanium sheet.

11. A sodium ion battery, wherein: The self-supporting electrode comprises the self-supporting electrode according to any one of claims 1 to 6.

Images