Self-supporting electrode material and preparation method thereof, self-supporting electrode and lithium battery

Abstract

The invention provides a self-supporting electrode material and a preparation method thereof, a self-supporting electrode and a lithium battery, the self-supporting electrode material comprises a carbon nanofiber with a three-dimensional conductive network structure and carbon-coated lithium vanadium phosphate anchored on the carbon nanofiber, the carbon-coated lithium vanadium phosphate comprises lithium vanadium phosphate, and the carbon-coated lithium vanadium phosphate comprises lithium vanadium phosphate. And the carbon coating layer is coated outside the lithium vanadium phosphate. The self-supporting electrode material with the structure provided by the invention can be directly used as a working electrode, and the use of a current collector and a binder is avoided, so that the overall energy density of the battery can be effectively improved; in addition, the self-supporting electrode material also has good rate capability and cycling stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries and relates to a self-supporting electrode material, and in particular to a self-supporting electrode material and a preparation method thereof, a self-supporting electrode and a lithium battery. Background Art

[0002] The abundant consumer electronics, electric vehicles, and renewable energy storage markets have led to a growing demand for high energy density electrochemical storage systems. Lithium-ion batteries are the best in today's energy storage systems due to their light weight, high energy density, and good cycling stability. However, in order to meet the growing demand for large-scale power sources (electric vehicles and smart grids), there is still an urgent need to improve safety, comprehensive electrochemical performance, and lifespan. To achieve these goals, one of the most promising strategies is to develop new electrode materials with superior performance and acceptable cost and replace the currently used materials. So far, a variety of cathode materials have been synthesized and show great commercial potential.

[0003] As a typical vanadium-based cathode material, Li3V2(PO4)3 (LVP) has the advantages of high operating voltage, large capacity and long cycle life, and is considered to be one of the most promising cathode materials for lithium-ion batteries. However, due to its inherent low electronic conductivity (2×10 -8 S cm -1 ) and ionic conductivity (10 -9 -10 -10 cm 2 ·S -1 ), resulting in poor kinetic performance and hindering its commercial application.

[0004] It is well known that surface coating of electronic or ion conductive materials can promote the movement of electrons or lithium ions within the active material, ultimately achieving a significant improvement in electrochemical performance. In addition, electrospinning technology is a general technology for preparing various one-dimensional carbon composites and flexible membranes. The materials prepared by electrospinning usually present a one-dimensional or porous hierarchical nanostructure and have the advantages of short lithium ion diffusion distance, continuous electron transport path, easy strain relaxation, and significantly increased contact area between electrode and electrolyte. Therefore, implanting electrochemically active materials into flexible composite nanofibers and rationally designing excellent electrode materials have broad application prospects.

[0005] There are also reports on the preparation of lithium vanadium phosphate positive electrode materials by electrospinning. However, in the prior art, the lithium vanadium phosphate precursor and polyvinyl pyrrolidone are generally mixed together in an aqueous solution to prepare a lithium vanadium phosphate positive electrode composite material; or lithium vanadium phosphate particles are first prepared, and then mixed with polyacrylonitrile and prepared through a multi-step method. The lithium vanadium phosphate positive electrode composite material prepared by the former has a low carbon content, poor conductivity and flexibility, and the fiber morphology is completely destroyed. It cannot be used directly as an electrode and can only be re-prepared by the traditional coating method; and although the latter has a high carbon content, the preparation process is cumbersome and costly, the rate performance and cycle performance are not ideal, and the energy density of the prepared electrode is poor, so it is not conducive to expansion into practical applications.

[0006] CN117936760A discloses an in-situ prepared flexible self-supporting electrode material and its preparation method and application. The in-situ prepared flexible self-supporting electrode material includes: carbon nanofiber, nanosilicon and carbon shell; wherein the nanosilicon is dispersed on the surface of the carbon nanofiber, and the carbon shell is coated on the outer surface of the carbon nanofiber; the carbon nanofiber is obtained by electrostatic spinning organic polyacrylonitrile and then carbonizing it at high temperature; the cross-sectional diameter of the carbon nanofiber is 50 to 2000 nm; the mass percentage of the carbon nanofiber in the flexible self-supporting electrode material is 30 to 70%; the nanosilicon is obtained by uniformly dispersing silica sol on the surface of the carbon nanofiber and then reducing it; the mass percentage of the nanosilicon in the flexible self-supporting electrode material is 20 to 70%; the carbon shell accounts for 1 to 20% of the total mass of the in-situ prepared flexible self-supporting electrode material.

[0007] CN118136801A discloses a lithium-containing phosphate positive electrode material and its preparation method and application. The lithium-containing phosphate positive electrode material comprises a plurality of composite particles, wherein the composite particles comprise a lithium-containing phosphate core and a carbon shell layer coated on the outer surface of the core, wherein the carbon shell layer is doped with heteroatoms, wherein the heteroatoms comprise at least one of phosphorus atoms, nitrogen atoms and sulfur atoms; and a three-dimensional network structure of carbon nanomaterials is formed between the plurality of the composite particles.

[0008] The electrode materials disclosed in the prior art have certain defects, such as poor conductivity and flexibility, and are difficult to be directly used as electrodes. There are also problems such as unsatisfactory rate performance and cycle performance and low energy density of the prepared battery. Therefore, it is very important to develop and design a new type of self-supporting electrode material and its preparation method, self-supporting electrode and lithium battery. Summary of the invention

[0009] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a self-supporting electrode material and a preparation method thereof, a self-supporting electrode and a lithium battery. The self-supporting electrode material of this structure provided by the present invention can be directly used as a working electrode, and avoids the use of a current collector and a binder, thereby effectively improving the overall energy density of the battery; in addition, the self-supporting electrode material also has good rate performance and cycle stability.

[0010] To achieve this object, the present invention adopts the following technical solutions:

[0011] In a first aspect, the present invention provides a self-supporting electrode material, which includes carbon nanofibers having a three-dimensional conductive network structure, and carbon-coated lithium vanadium phosphate anchored on the carbon nanofibers, wherein the carbon-coated lithium vanadium phosphate includes lithium vanadium phosphate and a carbon coating layer coated on the outside of the lithium vanadium phosphate.

[0012] In the present invention, the lithium vanadium phosphate coated with the carbon coating layer is anchored on the one-dimensional carbon nanofibers, and the one-dimensional carbon nanofibers are interwoven into a three-dimensional conductive network, thereby improving the overall electronic conductivity of the self-supporting electrode material and providing Li + The transport introduces additional active sites, thereby improving the performance of the self-supporting electrode material in three aspects: first, the carbon nanofibers have good stability and flexibility after being interwoven into a three-dimensional conductive network, so the self-supporting electrode material can be directly used as a working electrode; second, the one-dimensional carbon nanofibers are interconnected to form a unique three-dimensional network structure, and the pores in the three-dimensional conductive network structure are conducive to the penetration of electrolytes, thereby enhancing the electrolyte infiltration properties of the self-supporting electrode material; third, the three-dimensional porous carbon network structure can effectively improve the ion and electron transport in the material, and avoid the crushing and aggregation of lithium vanadium phosphate particles during the de- / intercalation process, thereby improving the electronic conductivity, ionic conductivity and cycle stability of the self-supporting electrode material.

[0013] Therefore, the self-supporting electrode material of this structure provided by the present invention can be directly used as a working electrode, and avoids the use of a current collector and a binder, thereby effectively improving the overall energy density of the battery; in addition, the self-supporting electrode material also has good rate performance and cycle stability.

[0014] Preferably, the three-dimensional conductive network structure is formed by interconnected one-dimensional nanofibers.

[0015] Preferably, the chemical formula of the lithium vanadium phosphate includes Li3V2(PO4)3.

[0016] Preferably, the carbon coating layer is a nitrogen-containing carbon coating layer.

[0017] The carbon coating layer of the present invention contains nitrogen, which further enhances the conductivity of the self-supporting electrode material, thereby enhancing the electrochemical performance of the self-supporting electrode material.

[0018] Preferably, based on the mass of the self-supporting electrode material, the mass fraction of carbon in the self-supporting electrode material is 20-30wt%, for example, it can be 20wt%, 21wt%, 22wt%, 23wt%, 24wt%, 25wt%, 26wt%, 27wt%, 28wt%, 29wt% or 30wt%, but it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0019] The amount of polyacrylonitrile added in the present invention, that is, the mass fraction of carbon in the self-supporting electrode material, will affect the morphology of the self-supporting electrode material. If the amount of polyacrylonitrile added is too small, it will cause beading, resulting in the final self-supporting electrode material losing flexibility; and if the amount of polyacrylonitrile added is too large, it will cause nozzle clogging, spinning difficulties, and excessive carbon content; therefore, the present application defines that the mass fraction of carbon in the self-supporting electrode material is 20 to 30wt%, based on the mass of the self-supporting electrode material as 100%.

[0020] In a second aspect, the present invention provides a method for preparing the self-supporting electrode material according to the first aspect, the preparation method comprising:

[0021] (1) mixing a vanadium source, a lithium source, a phosphorus source, polyacrylonitrile and a solvent to obtain a precursor solution; electrospinning the obtained precursor solution by an electrostatic spinning method to obtain a fiber precursor spinning membrane;

[0022] (2) Pre-oxidizing the fiber precursor spinning membrane obtained in step (1) in an oxygen-containing atmosphere, and then heat-treating it in a protective atmosphere to obtain a self-supporting electrode material of carbon-coated lithium vanadium phosphate-carbon nanofibers.

[0023] The carbon source in the present invention is polyacrylonitrile; on the one hand, when the carbon source is polyacrylonitrile, carbon nanofibers with a three-dimensional conductive network structure and carbon-coated lithium vanadium phosphate anchored on the carbon nanofibers can be formed; on the other hand, polyacrylonitrile contains nitrogen, so that the formed carbon coating layer contains nitrogen, thereby improving the electrochemical performance of the prepared self-supporting electrode material.

[0024] In the present invention, a flexible carbon-coated lithium vanadium phosphate-carbon nanofiber self-supporting electrode material is prepared by electrospinning and heat treatment processes. In the preparation method, reduction is performed by heat treatment, thereby preparing a three-dimensional conductive network structure formed by one-dimensional carbon nanofibers with high electrochemical activity, and a carbon coating layer similar to a graphite phase structure is in situ formed on the surface of the lithium vanadium phosphate, and the lithium vanadium phosphate coated with the carbon coating layer is anchored on the one-dimensional carbon nanofibers.

[0025] The preparation method provided by the invention has simple process and low preparation cost, and is conducive to large-scale promotion and use.

[0026] Preferably, the mixing in step (1) comprises: first mixing a vanadium source and a solvent to obtain a first mixed solution; second mixing a lithium source, a phosphorus source and the first mixed solution to obtain a second mixed solution; and third mixing polyacrylonitrile and the second mixed solution to obtain a precursor solution.

[0027] Preferably, the first mixing method includes stirring and first oil bath stirring performed sequentially, and the first mixing is stopped after the vanadium source in the first mixed liquid is completely dissolved.

[0028] Preferably, the stirring temperature of the first oil bath is 50-70°C, for example, it can be 50°C, 52°C, 55°C, 57°C, 60°C, 62°C, 65°C, 67°C or 70°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0029] Preferably, the second mixing method includes stirring in a second oil bath, and the second mixing is stopped after the lithium source and the phosphorus source are completely dissolved.

[0030] Preferably, the stirring temperature of the second oil bath is 50-70°C, for example, it can be 50°C, 52°C, 55°C, 57°C, 60°C, 62°C, 65°C, 67°C or 70°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0031] Preferably, the third mixing method includes third oil bath stirring, and the third mixing is stopped until the polyacrylonitrile is completely dissolved.

[0032] Preferably, the stirring temperature of the third oil bath is 50-70°C, for example, it can be 50°C, 52°C, 55°C, 57°C, 60°C, 62°C, 65°C, 67°C or 70°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0033] Preferably, the molar ratio of the vanadium source, the lithium source and the phosphorus source in the mixture of step (1) is (1.5-2.5):(2.5-3.5):(2.5-3.5).

[0034] The molar ratio of the vanadium source to the lithium source in the mixture of step (1) of the present invention is (1.5-2.5):(2.5-3.5), for example, it can be 1.5:2.5, 1.5:2.6, 1.5:2.8, 1.5:3.1, 1.5:3.4, 3.5:2.5, 2.5:2.5, 2.5:2.6, 2.5:2.8 or 2.5:3.1, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0035] The molar ratio of the vanadium source to the phosphorus source in the mixture of step (1) of the present invention is (1.5-2.5):(2.5-3.5), for example, it can be 1.5:2.5, 1.5:2.6, 1.5:2.8, 1.5:3.1, 1.5:3.4, 3.5:2.5, 2.5:2.5, 2.5:2.6, 2.5:2.8 or 2.5:3.1, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0036] When the phosphorus source in the present invention exists in the form of a phosphorus source solution, the molar ratio of the vanadium source to the phosphorus source is the molar ratio of the vanadium source to the phosphorus source in the phosphorus source solution.

[0037] Preferably, the mass concentration of the precursor in the precursor solution of step (1) is 0.1-0.5 g / mL, for example, it can be 0.1 g / mL, 0.15 g / mL, 0.2 g / mL, 0.25 g / mL, 0.3 g / mL, 0.35 g / mL, 0.4 g / mL, 0.45 g / mL or 0.5 g / mL, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0038] Preferably, the vanadium source in step (1) comprises any one of ammonium metavanadate, vanadium pentoxide, vanadyl sulfate, vanadium acetylacetonate, vanadium acetylacetonate or vanadium oxalate, or a combination of at least two thereof. Typical but non-limiting combinations include a combination of ammonium metavanadate and vanadium pentoxide, a combination of vanadium pentoxide and vanadium acetylacetonate, a combination of vanadium acetylacetonate and vanadium acetylacetonate, a combination of vanadium acetylacetonate and vanadium oxalate, or a combination of ammonium metavanadate, vanadium pentoxide and vanadium sulfate.

[0039] When the vanadium source in the present invention is any one of ammonium metavanadate, vanadium pentoxide, and vanadyl sulfate, or a combination of at least two thereof, a complexing agent needs to be added to the first mixture, and the molar ratio of the vanadium source to the complexing agent is (1.5-2.5):(4.5-7.5), for example, 1.5:4.5, 1.5:4.9, 1.5:5.3, 1.5:5.7, 1.5:5.9, 1.5:6.1, 1.5:6. .4, 1.5:6.7, 1.5:7.1, 1.5:7.3, 1.5:7.5, 2.5:4.5, 2.5:4.9, 2.5:5.3, 2.5:5.7, 5.5:5.9, 2.5:6.1, 2.5:6.4, 2.5:6.7, 2.5:7.1 or 2.5:7.3, but are not limited to the listed values, other values ​​not listed within the numerical range are also applicable.

[0040] Preferably, the lithium source includes any one of lithium nitrate, lithium acetate, lithium oxalate, lithium hydroxide or lithium formate, or a combination of at least two of them. Typical but non-limiting combinations include a combination of lithium nitrate and lithium acetate, a combination of lithium oxalate and lithium hydroxide, a combination of lithium hydroxide and lithium formate, or a combination of lithium nitrate, lithium acetate and lithium oxalate.

[0041] Preferably, the phosphorus source includes any one of phosphoric acid solution, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate, 1-ethyl-3-methylimidazole dihydrogen phosphate, 1-butyl-3-methylimidazole dihydrogen phosphate or 1,3-dimethylimidazole dihydrogen phosphate, or a combination of at least two thereof. Typical but non-limiting combinations include a combination of phosphoric acid solution and ammonium dihydrogen phosphate, a combination of ammonium dihydrogen phosphate and diammonium hydrogen phosphate, a combination of 1-ethyl-3-methylimidazole dihydrogen phosphate and 1-butyl-3-methylimidazole dihydrogen phosphate, or a combination of 1-ethyl-3-methylimidazole dihydrogen phosphate, 1-butyl-3-methylimidazole dihydrogen phosphate and 1,3-dimethylimidazole dihydrogen phosphate.

[0042] Preferably, the mass fraction of phosphoric acid in the phosphoric acid solution is 60-85wt%, for example, it can be 60wt%, 62wt%, 65wt%, 67wt%, 70wt%, 72wt%, 75wt%, 77wt%, 80wt%, 82wt% or 85wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0043] Preferably, the complexing agent comprises anhydrous oxalic acid and / or citric acid.

[0044] Preferably, the molecular weight of the polyacrylonitrile is 80,000-150,000, for example, 80,000, 90,000, 100,000, 110,000, 120,000, 130,000, 140,000 or 150,000, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0045] Preferably, the solvent comprises N,N-dimethylformamide.

[0046] Preferably, after the electrospinning in step (1), the electrospinning process also includes drying the electrospinning apparatus in a vacuum drying oven.

[0047] Preferably, the pre-oxidation in step (2) comprises: sequentially performing a first heating and a first heat preservation on the fiber precursor spinning membrane obtained in step (1).

[0048] Preferably, the first heating rate is 1-2°C·min -1 The end temperature is 200-220°C, and the first insulation time is 1.5-2.5h.

[0049] The first heating rate in the present invention is 1-2°C·min -1 , for example, it can be 1℃·min -1 、1.1℃·min -1 、1.2℃·min -1 、1.3℃·min -1 、1.4℃·min -1 、1.5℃·min -1 、1.6℃·min -1 、1.7℃·min -1 、1.8℃·min -1 、1.9℃·min -1 or 2℃·min -1 , but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0050] In the present invention, the endpoint temperature of the first heating is 200-220°C, for example, it can be 200°C, 202°C, 205°C, 210°C, 212°C, 215°C, 218°C or 220°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0051] In the present invention, the first insulation time is 1.5 to 2.5 hours, for example, it can be 1.5 hours, 1.7 hours, 1.9 hours, 2 hours, 2.1 hours, 2.3 hours or 2.5 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0052] Preferably, the oxygen-containing atmosphere comprises an air atmosphere.

[0053] Preferably, the pre-oxidation is carried out in a muffle furnace.

[0054] Preferably, the heat treatment in step (2) includes a second heating and a second heat preservation performed sequentially.

[0055] Preferably, the second heating rate is 1-5°C·min -1 The final temperature is 700-900°C, and the second insulation time is 2-6h.

[0056] The second heating rate in the present invention is 1-5°C·min -1 , for example, it can be 1℃·min -1 、1.5℃·min -1 、2℃·min -1 、2.5℃·min -1 、3℃·min -1 、3.5℃·min -1 、4℃·min -1 、4.5℃·min -1 or 5℃·min -1 , but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0057] The terminal temperature of the second heating in the present invention is 700-900°C, for example, it can be 700°C, 720°C, 740°C, 760°C, 780°C, 800°C, 820°C, 840°C, 860°C, 880°C or 900°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0058] The terminal temperature of heating in the protective atmosphere in step (2) of the method for preparing the self-supporting electrode material of the present invention, i.e., the insulation temperature, will affect the performance of the self-supporting electrode material, thereby affecting the performance of the obtained lithium ion battery; when the insulation temperature is 700-900°C, the lithium ion battery shows better performance, because as the temperature of the heat treatment increases, the diffraction peak of lithium vanadium phosphate can be detected, and the peak gradually becomes more obvious and the peak shape becomes sharper, indicating that as the calcination temperature increases, the crystallinity of lithium vanadium phosphate becomes stronger and the particle size becomes larger, which is beneficial to the performance of the self-supporting electrode material; however, too high a temperature will lead to a sharp increase in the preparation cost and will cause the particle size of the self-supporting electrode material to be too large, thereby causing the performance of the self-supporting electrode material to decrease.

[0059] The second insulation time in the present invention is 2 to 6 hours, for example, it can be 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours or 6 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0060] In the present invention, a second insulation temperature time that is too high will lead to an increase in preparation cost, a decrease in preparation efficiency, and will also cause the particle size of the self-supporting electrode material to be too large, thereby affecting the performance of the self-supporting electrode material. Therefore, this application limits the second insulation time during the heat treatment process to 2 to 6 hours.

[0061] Preferably, the protective atmosphere comprises nitrogen and / or an inert gas.

[0062] Preferably, step (2) further comprises cooling after the heat treatment;

[0063] As a preferred technical solution of the technical method of the present invention, the preparation method comprises:

[0064] (1) mixing a vanadium source, a complexing agent and a solvent by stirring in sequence and stirring in a first oil bath at a temperature of 50 to 70° C. until the vanadium source and the complexing agent in the first mixed solution are completely dissolved, and then the stirring is stopped to obtain a first mixed solution; then mixing a lithium source and a phosphorus source with the first mixed solution obtained by stirring in a second oil bath at a temperature of 50 to 70° C. until the lithium source and the phosphorus source are completely dissolved, and then the stirring is stopped to obtain a second mixed solution, wherein the molar ratio of the vanadium source, the lithium source, the phosphorus source and the complexing agent is (1.5 to 2.5):(2.5 to 3.5):(2.5 to 3.5):(4.5 to 7.5); then mixing polyacrylonitrile with the second mixed solution obtained by stirring in a third oil bath at a temperature of 50 to 70° C. until the polyacrylonitrile is completely dissolved, and then the stirring is stopped to obtain a precursor solution with a mass concentration of the precursor of 0.1 to 0.5 g / mL; electrospinning the obtained precursor solution by an electrospinning method, and drying the electrospinning arrangement in a vacuum drying oven after electrospinning to obtain a fiber precursor spinning membrane;

[0065] (2) spinning the fiber precursor membrane obtained in step (1) in an air atmosphere at 1 to 2 °C min -1 The temperature is raised to 200-220℃ at a rate of 1.5-2.5h and then kept at that temperature for 1.5-2.5h to achieve pre-oxidation. Then, the temperature is heated at 1-5℃·min in a protective atmosphere. -1 The temperature is raised to 700-900° C. at a rate of 100° C., maintained at that temperature for 2-6 hours, and cooled to obtain a self-supporting electrode material of carbon-coated lithium vanadium phosphate-carbon nanofibers.

[0066] In a third aspect, the present invention provides a self-supporting electrode, wherein the self-supporting electrode comprises the self-supporting electrode material described in the first aspect.

[0067] In a fourth aspect, the present invention provides a lithium battery, wherein the positive electrode of the lithium battery is the self-supporting electrode described in the third aspect.

[0068] The numerical range described in the present invention not only includes the point values ​​listed above, but also includes any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0069] Compared with the prior art, the present invention has the following beneficial effects:

[0070] (1) In the present invention, the carbon-coated lithium vanadium phosphate is anchored on the one-dimensional carbon nanofibers, and the one-dimensional carbon nanofibers are interwoven into a three-dimensional conductive network, thereby improving the overall electronic conductivity of the self-supporting electrode material and providing Li + The transmission introduces additional active sites, thereby improving the performance of the self-supporting electrode material from three aspects: first, the carbon nanofibers have good stability and flexibility after being interwoven into a three-dimensional conductive network, so the self-supporting electrode material can be directly used as a working electrode; second, the one-dimensional carbon nanofibers are interconnected to form a unique three-dimensional network structure, and the pores in the three-dimensional conductive network structure are conducive to the penetration of electrolytes, thereby enhancing the electrolyte infiltration performance of the self-supporting electrode material; third, the three-dimensional porous carbon network structure can effectively improve the ion and electron transmission in the material, and avoid the crushing and aggregation of lithium vanadium phosphate particles during the lithium extraction / insertion process, thereby improving the electronic conductivity, ionic conductivity and cycle stability of the self-supporting electrode material; therefore, the self-supporting electrode material of this structure provided by the present invention can be directly used as a working electrode, and avoids the use of current collectors and binders, thereby effectively improving the overall energy density of the battery; in addition, the self-supporting electrode material also has good rate performance and cycle stability;

[0071] (2) The carbon coating layer of the present invention contains nitrogen, which further enhances the conductivity of the self-supporting electrode material, thereby enhancing the electrochemical performance of the self-supporting electrode material;

[0072] (3) In the present invention, a flexible carbon-coated lithium vanadium phosphate-carbon nanofiber self-supporting electrode material is prepared by electrospinning and heat treatment process. In the preparation method, reduction is performed by heat treatment, thereby preparing a three-dimensional conductive network structure formed by one-dimensional carbon nanofibers with high electrochemical activity, and a carbon coating layer similar to a graphite phase structure is formed in situ on the surface of the lithium vanadium phosphate, and the lithium vanadium phosphate coated with the carbon coating layer is anchored on the one-dimensional carbon nanofibers;

[0073] (4) The preparation method provided by the present invention has a simple process and low preparation cost, which is conducive to large-scale promotion and use. BRIEF DESCRIPTION OF THE DRAWINGS

[0074] Figure 1 is a SEM image of the self-supporting electrode material provided in Example 1.

[0075] Figure 2 : is the XRD diagram of the self-supporting electrode material provided in Example 1.

[0076] Figure 3 The cyclic voltammetry curve of the self-supporting electrode material provided in Example 1 as a self-supporting electrode.

[0077] Figure 4 This is the charge and discharge curve of the lithium-ion battery prepared using the self-supporting electrode material provided in Example 1.

[0078] Figure 5 This is a rate performance curve of a lithium-ion battery prepared using the self-supporting electrode material provided in Example 1.

[0079] Figure 6 The graph is a graph showing the capacity retention rate of a lithium-ion battery prepared using the self-supporting electrode material provided in Example 1 as a function of the number of cycles. DETAILED DESCRIPTION

[0080] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0081] Example 1

[0082] The present embodiment provides a self-supporting electrode material, which includes carbon nanofibers having a three-dimensional conductive network structure formed by interconnected one-dimensional nanofibers, and carbon-coated lithium vanadium phosphate anchored on the carbon nanofibers, wherein the carbon-coated lithium vanadium phosphate includes lithium vanadium phosphate and a nitrogen-containing carbon coating layer coated on the outside of the lithium vanadium phosphate.

[0083] Based on the mass of the self-supporting electrode material as 100%, the mass fraction of carbon in the self-supporting electrode material is 25wt%.

[0084] The preparation method of the self-supporting electrode material is:

[0085] (1) mixing ammonium metavanadate, anhydrous oxalic acid and N,N-dimethylformamide by stirring in sequence and stirring in a first oil bath at a temperature of 60° C. until the ammonium metavanadate and anhydrous oxalic acid in the first mixed solution are completely dissolved, and then the stirring is stopped to obtain a first mixed solution; then mixing lithium nitrate and a phosphoric acid solution (the mass fraction of phosphoric acid is 85 wt %) with the first mixed solution by stirring in a second oil bath at a temperature of 60° C. until the lithium nitrate and the phosphoric acid solution are completely dissolved, and then the stirring is stopped to obtain a second mixed solution, wherein the molar ratio of phosphoric acid to anhydrous oxalic acid in the ammonium metavanadate, lithium nitrate and phosphoric acid solution is 2:3:3.1:6; then stirring in a second oil bath at a temperature of 60° C. until the lithium nitrate and the phosphoric acid solution are completely dissolved, and then the stirring is stopped to obtain a second mixed solution. The polyacrylonitrile and the obtained second mixed solution are mixed by stirring in a third oil bath at a temperature of 60° C. until the polyacrylonitrile is completely dissolved, and then the mixture is stopped to obtain a precursor solution with a mass concentration of 0.3 g / mL of the precursor; the obtained precursor solution is electrospun by an electrospinning method (the precursor solution is transferred to a 10 mL syringe, connected to a 22-gauge needle, so that the distance between it and the metal roller is 15 cm, connected to a 20 kV power supply, and the flow rate of the syringe is set to 0.4 mL / h), and after electrospinning, the electrospinning arrangement is placed in a 60° C. vacuum drying oven for 24 hours to remove the solvent, and a fiber precursor spinning membrane is obtained;

[0086] (2) spinning the fiber precursor membrane obtained in step (1) in an air atmosphere at 1°C min -1 The temperature was raised to 200 °C at a rate of 1.5 °C / min and then kept at that temperature for 2 h to achieve pre-oxidation. -1 The temperature was raised to 800°C at a rate of 1000 °C and kept at that temperature for 4 hours. After cooling, a self-supporting electrode material of carbon-coated lithium vanadium phosphate-carbon nanofibers was obtained.

[0087] Example 2

[0088] The present embodiment provides a self-supporting electrode material, which includes carbon nanofibers having a three-dimensional conductive network structure formed by interconnected one-dimensional nanofibers, and carbon-coated lithium vanadium phosphate anchored on the carbon nanofibers, wherein the carbon-coated lithium vanadium phosphate includes lithium vanadium phosphate and a nitrogen-containing carbon coating layer coated on the outside of the lithium vanadium phosphate.

[0089] Based on the mass of the self-supporting electrode material as 100%, the mass fraction of carbon in the self-supporting electrode material is 20wt%.

[0090] The preparation method of the self-supporting electrode material is:

[0091] (1) mixing vanadium pentoxide, citric acid and N,N-dimethylformamide by stirring in sequence and stirring in a first oil bath at a temperature of 50° C. until the vanadium pentoxide and citric acid in the first mixed solution are completely dissolved, and then the stirring is stopped to obtain a first mixed solution; then mixing lithium hydroxide and ammonium dihydrogen phosphate with the obtained first mixed solution by stirring in a second oil bath at a temperature of 50° C. until the lithium hydroxide and the ammonium dihydrogen phosphate are completely dissolved, and then the stirring is stopped to obtain a second mixed solution, wherein the molar ratio of vanadium pentoxide, lithium hydroxide, ammonium dihydrogen phosphate and citric acid is 1.5:3.5:2.5:6; then mixing polyacrylonitrile with the obtained second mixed solution by stirring in a third oil bath at a temperature of 50° C. until the polyacrylonitrile is completely dissolved, and then the stirring is stopped to obtain a precursor solution with a mass concentration of 0.5 g / mL of the precursor; electrospinning the obtained precursor solution by an electrospinning method, and after electrospinning, the electrospinning arrangement is dried in a vacuum drying oven to obtain a fiber precursor spinning membrane;

[0092] (2) spinning the fiber precursor membrane obtained in step (1) in an air atmosphere at 1°C min -1 The temperature was raised to 200 °C at a rate of 1.5 °C and then kept at that temperature for 2.5 h to achieve pre-oxidation. -1 The temperature was raised to 800°C at a rate of 1000 °C and kept at that temperature for 2 h. After cooling, a self-supporting electrode material of carbon-coated lithium vanadium phosphate-carbon nanofibers was obtained.

[0093] Example 3

[0094] The present embodiment provides a self-supporting electrode material, which includes carbon nanofibers having a three-dimensional conductive network structure formed by interconnected one-dimensional nanofibers, and carbon-coated lithium vanadium phosphate anchored on the carbon nanofibers, wherein the carbon-coated lithium vanadium phosphate includes lithium vanadium phosphate and a nitrogen-containing carbon coating layer coated on the outside of the lithium vanadium phosphate.

[0095] Based on the mass of the self-supporting electrode material as 100%, the mass fraction of carbon in the self-supporting electrode material is 30wt%.

[0096] The preparation method of the self-supporting electrode material is:

[0097] (1) mixing vanadium acetylacetonate and N,N-dimethylformamide by stirring in sequence and stirring in a first oil bath at a temperature of 70° C. until the vanadium acetylacetonate in the first mixed solution is completely dissolved, and then the stirring is stopped to obtain a first mixed solution; then mixing lithium oxalate, 1-ethyl-3-methylimidazole dihydrogen phosphate and the obtained first mixed solution by stirring in a second oil bath at a temperature of 70° C. until the lithium oxalate and 1-ethyl-3-methylimidazole dihydrogen phosphate are completely dissolved, and then the stirring is stopped to obtain a second mixed solution, wherein the molar ratio of vanadium acetylacetonate, lithium oxalate and 1-ethyl-3-methylimidazole dihydrogen phosphate is 2.5:2.5:3.5; then mixing polyacrylonitrile and the obtained second mixed solution by stirring in a third oil bath at a temperature of 70° C. until the polyacrylonitrile is completely dissolved, and then the stirring is stopped to obtain a precursor solution with a mass concentration of 0.1 g / mL of the precursor; electrospinning the obtained precursor solution by an electrospinning method, and drying the electrospinning arrangement in a vacuum drying oven after electrospinning to obtain a fiber precursor spinning membrane;

[0098] (2) spinning the fiber precursor membrane obtained in step (1) in an air atmosphere at 2°C min -1 The temperature was raised to 220°C at a rate of 1.5 h and then kept at that temperature for 1.5 h to achieve pre-oxidation. -1 The temperature was raised to 800°C at a rate of 100 °C and kept at that temperature for 6 h. After cooling, a self-supporting electrode material of carbon-coated lithium vanadium phosphate-carbon nanofibers was obtained.

[0099] Example 4

[0100] This embodiment provides a self-supporting electrode material, which is the same as that of Embodiment 1 except that the mass fraction of carbon in the self-supporting electrode material is 22 wt %.

[0101] Example 5

[0102] This embodiment provides a self-supporting electrode material, which is the same as that of Embodiment 1 except that the mass fraction of carbon in the self-supporting electrode material is 28 wt %.

[0103] Example 6

[0104] This embodiment provides a self-supporting electrode material, which is the same as that of Embodiment 1 except that the terminal temperature of heating in a nitrogen atmosphere in step (2) of the method for preparing the self-supporting electrode material, i.e., the holding temperature is 700°C.

[0105] Example 7

[0106] This embodiment provides a self-supporting electrode material, which is the same as that of Embodiment 1 except that the time of keeping warm in a nitrogen atmosphere in step (2) of the method for preparing the self-supporting electrode material is 2 hours.

[0107] Example 8

[0108] This embodiment provides a self-supporting electrode material, which is the same as that of Embodiment 1 except that the time of keeping the material warm in a nitrogen atmosphere in step (2) of the method for preparing the self-supporting electrode material is 6 hours.

[0109] Example 9

[0110] This embodiment provides a self-supporting electrode material, which is the same as that of Embodiment 1 except that the mass fraction of carbon in the self-supporting electrode material is 15 wt %.

[0111] Example 10

[0112] This embodiment provides a self-supporting electrode material, which is the same as that of Embodiment 1 except that the mass fraction of carbon in the self-supporting electrode material is 35 wt %.

[0113] Embodiment 11

[0114] This embodiment provides a self-supporting electrode material, which is the same as that of Embodiment 1 except that the terminal temperature of heating in a nitrogen atmosphere in step (2) of the method for preparing the self-supporting electrode material, i.e., the holding temperature is 900°C.

[0115] Example 12

[0116] This embodiment provides a self-supporting electrode material, which is the same as that of Embodiment 1 except that the time of keeping warm in a nitrogen atmosphere in step (2) of the method for preparing the self-supporting electrode material is 1 hour.

[0117] Example 13

[0118] This embodiment provides a self-supporting electrode material, which is the same as that of Embodiment 1 except that the time of keeping the material warm in a nitrogen atmosphere in step (2) of the method for preparing the self-supporting electrode material is 10 hours.

[0119] Comparative Example 1

[0120] This comparative example provides a self-supporting electrode material, the self-supporting electrode material comprising:

[0121] The preparation method of the self-supporting electrode material is:

[0122] (1) 15 mmol of LiOH·H2O, 10 mmol of NH4VO3 and 15 mmol of NH4H2PO4 were dissolved in 50 mL of distilled water respectively to prepare NH4VO3 solution, LiOH solution and NH4H2PO4 solution; the NH4VO3 solution, LiOH solution and NH4H2PO4 solution were added dropwise to 50 mL of 0.20 mol / L citric acid solution in sequence, and stirred at 25°C for 12 h to obtain a mixed solution; the obtained mixed solution was continuously stirred in a constant temperature oil bath at 80°C for 6 h to evaporate excess water until a blue gel was formed; the obtained blue gel was dried in a vacuum oven at 80°C for 12 h, and then annealed at 300°C for 6 h in an argon atmosphere to obtain a powdery LVP material;

[0123] (2) The LVP material (0.66 g) obtained in step (1) is added to a PAN / DMF solution of equal weight and mass fraction of 12 wt%, and then ultrasonically treated at 25°C for 12 h to obtain a precursor solution; the obtained precursor solution is electrospun by an electrospinning method, and the electrospinning arrangement is placed in a vacuum drying oven for drying to obtain a fiber precursor spinning membrane; the fiber precursor spinning membrane is then heated to 800°C at a heating rate of 2°C / min at room temperature and then kept warm for 4 h to obtain the self-supporting electrode material.

[0124] In this comparative example, lithium vanadium phosphate particles are first prepared and then electrospinning is performed. During the spinning process, a large amount of particles settle, and the self-supporting electrode material obtained after electrospinning is severely agglomerated, and carbon nanofibers with a three-dimensional conductive network structure cannot be formed.

[0125] Comparative Example 2

[0126] This comparative example provides an electrode material prepared by an electrospinning method;

[0127] The preparation method of the electrode material is:

[0128] (1) Dissolve NH4VO3 and oxalic acid in a stoichiometric ratio of 1:3 in deionized water, stir at 80°C to obtain a primary mixed solution; then add NH4H2PO4 and Li2CO3 in a stoichiometric ratio to the primary mixed solution, stir at 80°C for 10 min to obtain a mixed solution. Slowly evaporate the obtained mixed solution for several hours to remove part of the water until a gel is formed; then drop the obtained gel into a solution consisting of 1.0 g of polypyrrolidone (Mw=1300000) dissolved in 4.0 g of deionized water to obtain a remixed solution; stir the obtained remixed solution for 4 hours to obtain a uniform viscous solution to obtain a precursor solution; then electrospin the obtained precursor solution by an electrospinning method, and after electrospinning, dry the electrospinning arrangement in a vacuum drying oven to obtain a fiber precursor spinning membrane;

[0129] (2) The fiber precursor spinning membrane obtained in step (1) is heated to 200°C in an air atmosphere at a heating rate of 1°C / min and then kept warm for 2.5 hours to achieve pre-oxidation, and then heated to 800°C in an argon atmosphere at a rate of 5°C / min and kept warm for 2 hours. After cooling, a carbon-coated lithium vanadium phosphate-carbon nanofiber electrode material is obtained.

[0130] In this comparative example, PVP is used as the carbon source and the electrospinning method is adopted to prepare the electrode material. The fiber spinning membrane finally obtained is fragile, and the complete fiber spinning membrane cannot be directly used as a self-supporting electrode. The electrode material needs to be prepared into a slurry first, and then the slurry is coated to prepare it into an electrode.

[0131] Comparative Example 3

[0132] This comparative example provides an electrode material prepared by a sol-gel method;

[0133] The preparation method of the electrode material is:

[0134] First, prepare 100 mL of a polyvinyl alcohol (PVA) solution with a mass fraction of 10 wt %; then weigh lithium acetate (CH3COOLi) and ammonium metavanadate (NH4VO3), oxalic acid (H2C2O4) and a phosphoric acid solution (mass fraction of 85 wt %) in a molar ratio of 3:2:6:3, add them to the polyvinyl alcohol solution, and stir at 100°C until the solvent evaporates to obtain a precursor; grind the obtained precursor into powder and place it in a tubular furnace, heat it to 800°C at a heating rate of 5°C / min under a nitrogen atmosphere, keep it warm for 6 hours, and naturally cool it to room temperature to obtain the electrode material.

[0135] The embodiment 1 was tested by scanning electron microscopy, and the SEM image of the self-supporting electrode material provided in the embodiment 1 was obtained as follows: Figure 1 shown by Figure 1 It can be seen that the average particle size of the carbon-coated lithium vanadium phosphate anchored on the carbon nanofibers is about 200 nm.

[0136] The XRD pattern of the self-supporting electrode material provided in Example 1 is obtained by testing the embodiment 1 using an X-ray diffractometer. Figure 2 shown by Figure 2 It can be seen that the diffraction peak of lithium vanadium phosphate was detected.

[0137] The self-supporting electrode materials obtained in Examples 1 to 13 and Comparative Example 1 are directly used as self-supporting electrodes to assemble lithium ion batteries. The assembly method is as follows: lithium ion half-cell: the self-supporting LVP-CNF composite film is cut into 12 mm pole pieces as the working electrode in the battery system, the lithium sheet is used as the counter electrode, and the microporous polypropylene membrane (Celgard 2400) is used as the diaphragm. The solute of the electrolyte is 1M LiPF6, the solvent is EC:DEC:EMC=1:1:1Vol%, and the electrolyte also includes 1% VC solution. CR2032 button batteries are used for assembly in a glove box, and a hydraulic packaging machine is used for packaging to obtain a lithium ion battery;

[0138] The electrode materials obtained in Comparative Examples 2 and 3 are used to prepare electrodes. The preparation method is as follows: the electrode materials obtained in Comparative Examples 2 and 3 are respectively mixed with conductive carbon black Super P, binder PVDF and an appropriate amount of NMP solvent to prepare positive electrode slurry; according to the mass ratio of electrode material: Super P: PVDF = 8: 1: 1 is added to a vacuum mixer for mixing, and then a solvent NMP is added to the mixed slurry, and the mixed slurry is stirred until it is uniform under the action of the vacuum mixer, thereby obtaining a positive electrode slurry; the above-mentioned positive electrode slurry is evenly coated on the surface of the positive electrode collector aluminum foil, and after drying at room temperature, it is transferred to an oven for further drying, and after drying in the oven, a positive electrode sheet semi-finished product is obtained, and then the positive electrode sheet semi-finished product is cold pressed and cut to obtain a positive electrode sheet to be assembled; the prepared positive electrode sheet to be assembled is used as a working electrode, a lithium sheet is used as a counter electrode, a microporous polypropylene film (Celgard2400) is used as a diaphragm, the solute of the electrolyte is 1M LiPF6, the solvent is EC: DEC: EMC = 1: 1: 1Vol%, and the electrolyte also includes 1% VC solution, and CR2032 button batteries are used for assembly in a glove box, and a hydraulic packaging machine is used for packaging to obtain a lithium-ion battery;

[0139] The self-supporting electrode obtained in Example 1 was tested using the LAND test system and the electrochemical workstation; the test included a cyclic voltammetry test, and the method of the cyclic voltammetry test was as follows: the cyclic voltammetry curve (CV) was tested on an electrochemical workstation (CHI660E, Chenhua Instrument Co., Ltd., Shanghai, China), and the voltage window of the half-cell was 3-4.3V (vs Li / Li + ), the CV scan rate is 0.1mV / s; the cyclic voltammetry curve of the self-supporting electrode material provided in Example 1 as the self-supporting electrode is as follows Figure 3 As shown by Figure 3 It can be seen that there are three pairs of redox peaks in the self-supporting electrode.

[0140] The test includes a charge and discharge curve test of a lithium-ion battery. The charge and discharge curve test method is as follows: the voltage range is set to 3-4.3V at 25°C, and the prepared battery is charged at 1C / 1C (1C = 133mAg -1 3.0-4.3V vsLi / Li + ) current charge / discharge, the charge / discharge curve of the lithium ion battery prepared by the self-supporting electrode material provided in Example 1 is as follows Figure 4 As shown by Figure 4 It can be seen that the first discharge specific capacity is 129.5 mAh / g, and three pairs of charge and discharge platforms appear at around 3.6 V, 3.7 V and 4.1 V, corresponding to the step-by-step extraction / embedding of three lithium ions in lithium vanadium phosphate.

[0141] The test includes a rate performance test of a lithium ion battery. The method of the rate performance test is as follows: the voltage range is set to 3-4.3V at 25°C, and the prepared battery is charged / discharged at 0.2C, 1C, 2C, 5C, 10C, 20C and 30C currents in the range of 3-4.3V. The discharge specific capacity of the lithium ion battery obtained by the test is shown in Table 1; wherein the rate performance curve of the lithium ion battery prepared by the self-supporting electrode material provided in Example 1 is as shown in Figure 5 As shown, it indicates that the self-supporting electrode material still retains an extremely high discharge specific capacity at a current density of 30C.

[0142] The test includes a cycle performance test of a lithium-ion battery. The method of the cycle performance test is: the voltage range is set to 3-4.3V at 25°C, and the prepared battery is charged / discharged at a current of 5C / 5C in the range of 3-4.3V. When the battery cycles 2000 times, the capacity retention rate is recorded. The capacity retention rate of the lithium-ion battery after 2000 cycles of charge and discharge is shown in Table 1. Among them, the capacity retention rate of the lithium-ion battery prepared by the self-supporting electrode material provided in Example 1 varies with the number of cycles. Figure 6 shown.

[0143] Table 1

[0144]

[0145]

[0146] From Table 1, we can get:

[0147] (1) The self-supporting electrode material prepared in Examples 1 to 8 and 11 of the present invention is directly used as a self-supporting electrode without a binder and a current collector, thereby effectively improving the overall energy density of the battery; in addition, after the lithium-ion battery is prepared from the self-supporting battery, the obtained lithium-ion battery exhibits a higher first discharge specific capacity, better 30C rate performance and excellent cycle stability;

[0148] (2) By comparing Example 1 with Examples 9 and 10, it can be seen that the mass fraction of carbon in the self-supporting electrode material of the present invention affects the performance of the self-supporting electrode material, thereby affecting the performance of the obtained lithium ion battery; when the mass fraction of carbon in the self-supporting electrode material is 20-30wt% based on the mass of the self-supporting electrode material, the lithium ion battery shows better performance. This is because if the content of polyacrylonitrile is too small, it will cause beading phenomenon, causing the final self-supporting electrode material to lose flexibility; and when the content of polyacrylonitrile is too large, the amount of polyacrylonitrile added is too large, and too much polyacrylonitrile will cause nozzle clogging and spinning difficulties, and excessive carbon content will also lead to a decrease in the overall energy density of the battery prepared with the self-supporting electrode material;

[0149] (3) By comparing Example 1 with Examples 12 and 13, it can be seen that the insulation time in the protective atmosphere in step (2) of the method for preparing the self-supporting electrode material of the present invention will affect the performance of the self-supporting electrode material, thereby affecting the performance of the obtained lithium ion battery; when the insulation time is 2 to 6 hours, the lithium ion battery shows better performance. This is because the longer the insulation time, the stronger the diffraction peak intensity and the sharper the peak shape, which is beneficial to the performance of the self-supporting electrode material; however, too high an insulation time will lead to an increase in preparation cost and a decrease in preparation efficiency, and will also lead to an excessively large particle size of the self-supporting electrode material, thereby affecting the performance of the self-supporting electrode material;

[0150] (4) By comparing Example 1 with Comparative Examples 1 to 3, it can be seen that in the present invention, the lithium vanadium phosphate coated with the carbon coating layer is anchored on the one-dimensional carbon nanofibers, and the one-dimensional carbon nanofibers are interwoven into a three-dimensional conductive network, which improves the overall electronic conductivity of the self-supporting electrode material and provides Li +The transport introduces additional active sites, thereby improving the performance of the self-supporting electrode material in three aspects: first, the carbon nanofibers have good stability and flexibility after being interwoven into a three-dimensional conductive network, so the self-supporting electrode material can be directly used as a working electrode; second, the one-dimensional carbon nanofibers are interconnected to form a unique three-dimensional network structure, and the pores in the three-dimensional conductive network structure are conducive to the penetration of electrolytes, thereby enhancing the electrolyte infiltration performance of the self-supporting electrode material; third, the three-dimensional porous carbon network structure can effectively improve the ion and electron transport in the material, and avoid the crushing and aggregation of lithium vanadium phosphate particles during the lithium extraction / insertion process, thereby improving the electronic conductivity, ionic conductivity and cycle stability of the self-supporting electrode material; therefore, the self-supporting electrode material of this structure provided by the present invention can be directly used as a working electrode, and avoids the use of current collectors and binders, thereby effectively improving the overall energy density of the battery; in addition, the self-supporting electrode material also has good rate performance and cycle stability.

[0151] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention are within the protection scope and disclosure scope of the present invention.

Claims

1. A self-supporting electrode material, characterized in that: The self-supporting electrode material includes carbon nanofibers with a three-dimensional conductive network structure and carbon-coated lithium vanadium phosphate anchored on the carbon nanofibers. The carbon-coated lithium vanadium phosphate includes lithium vanadium phosphate and a carbon coating layer coated on the outside of the lithium vanadium phosphate.

2. The self-supporting electrode material according to claim 1, characterized in that The three-dimensional conductive network structure is formed by interconnecting one-dimensional nanofibers; Preferably, the carbon coating layer is a nitrogen-containing carbon coating layer; Preferably, based on the mass of the self-supporting electrode material as 100%, the mass fraction of carbon in the self-supporting electrode material is 20-30 wt%.

3. A method for preparing the self-supporting electrode material according to claim 1 or 2, characterized in that: The preparation method comprises: (1) mixing a vanadium source, a lithium source, a phosphorus source, polyacrylonitrile and a solvent to obtain a precursor solution; electrospinning the obtained precursor solution by an electrostatic spinning method to obtain a fiber precursor spinning membrane; (2) Pre-oxidizing the fiber precursor spinning membrane obtained in step (1) in an oxygen-containing atmosphere, and then heat-treating it in a protective atmosphere to obtain a self-supporting electrode material of carbon-coated lithium vanadium phosphate-carbon nanofibers.

4. The preparation method according to claim 3, characterized in that: The mixing in step (1) includes: first mixing a vanadium source and a solvent to obtain a first mixed solution; second mixing a lithium source, a phosphorus source and the first mixed solution to obtain a second mixed solution; and third mixing polyacrylonitrile and the second mixed solution to obtain a precursor solution; Preferably, the first mixing method includes stirring and first oil bath stirring performed sequentially, and the first mixing is stopped until the vanadium source is completely dissolved; Preferably, the second mixing method includes stirring in a second oil bath, and the second mixing is stopped until the lithium source and the phosphorus source are completely dissolved; Preferably, the third mixing method includes third oil bath stirring, and the third mixing is stopped until the polyacrylonitrile is completely dissolved.

5. The preparation method according to claim 3 or 4, characterized in that: The molar ratio of the vanadium source, the lithium source and the phosphorus source in the mixture of step (1) is (1.5-2.5):(2.5-3.5):(2.5-3.5); Preferably, the mass concentration of the precursor in the precursor solution in step (1) is 0.1 to 0.5 g / mL.

6. The preparation method according to any one of claims 3 to 5, characterized in that: The vanadium source in step (1) includes any one of ammonium metavanadate, vanadium pentoxide, vanadyl sulfate, vanadyl acetylacetonate, vanadium acetylacetonate or vanadyl oxalate, or a combination of at least two thereof; Preferably, the lithium source includes any one of lithium nitrate, lithium acetate, lithium oxalate, lithium hydroxide or lithium formate, or a combination of at least two thereof; Preferably, the phosphorus source comprises any one or a combination of at least two of phosphoric acid solution, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate, 1-ethyl-3-methylimidazole dihydrogen phosphate, 1-butyl-3-methylimidazole dihydrogen phosphate or 1,3-dimethylimidazole dihydrogen phosphate; Preferably, the mass fraction of phosphoric acid in the phosphoric acid solution is 60 to 85 wt %; Preferably, the molecular weight of the polyacrylonitrile is 80,000 to 150,000; Preferably, the solvent comprises N,N-dimethylformamide; Preferably, after the electrospinning in step (1), the electrospinning process also includes drying the electrospinning apparatus in a vacuum drying oven.

7. The preparation method according to any one of claims 3 to 6, characterized in that: The pre-oxidation in step (2) comprises: sequentially performing a first heating and a first heat preservation on the fiber precursor spinning membrane obtained in step (1); Preferably, the first heating rate is 1-2°C·min -1 , the end temperature is 200-220°C, and the first insulation time is 1.5-2.5h; Preferably, the heat treatment in step (2) comprises a second heating and a second heat preservation performed sequentially; Preferably, the second heating rate is 1-5°C·min -1 The final temperature is 700-900°C, and the second insulation time is 2-6h.

8. The preparation method according to any one of claims 3 to 7, characterized in that: The preparation method comprises: (1) mixing a vanadium source, a complexing agent and a solvent by stirring in sequence and stirring in a first oil bath at a temperature of 50 to 70° C. until the vanadium source and the complexing agent are completely dissolved, and then stopping to obtain a first mixed solution; then mixing a lithium source and a phosphorus source with the first mixed solution obtained by stirring in a second oil bath at a temperature of 50 to 70° C. until the lithium source and the phosphorus source are completely dissolved, and then stopping to obtain a second mixed solution, wherein the molar ratio of the vanadium source, the lithium source, the phosphorus source and the complexing agent is (1.5 to 2.5):(2.5 to 3.5):(2.5 to 3.5):(4.5 to 7.5); then mixing polyacrylonitrile with the second mixed solution by stirring in a third oil bath at a temperature of 50 to 70° C. until the polyacrylonitrile is completely dissolved, and then stopping to obtain a precursor solution with a mass concentration of the precursor of 0.1 to 0.5 g / mL; electrospinning the obtained precursor solution by an electrospinning method, and drying the electrospinning arrangement in a vacuum drying oven after electrospinning to obtain a fiber precursor spinning membrane; (2) spinning the fiber precursor membrane obtained in step (1) in an air atmosphere at 1 to 2 °C min -1 The temperature is raised to 200-220℃ at a rate of 1.5-2.5h and then kept at that temperature for 1.5-2.5h to achieve pre-oxidation. Then, the temperature is heated at 1-5℃·min in a protective atmosphere. -1 The temperature is raised to 700-900° C. at a rate of 100° C., maintained at that temperature for 2-6 hours, and cooled to obtain a self-supporting electrode material of carbon-coated lithium vanadium phosphate-carbon nanofibers.

9. A self-supporting electrode, characterized in that: The self-supporting electrode comprises the self-supporting electrode material according to claim 1 or 2.

10. A lithium battery, characterized in that: The positive electrode of the lithium battery is the self-supporting electrode according to claim 9.

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