A sodium vanadium phosphate positive electrode material, a positive electrode sheet and a preparation method and application thereof

Abstract

The application discloses a kind of sodium vanadium phosphate positive electrode material, positive electrode sheet and preparation method, application thereof.The preparation method of the sodium vanadium phosphate positive electrode material mainly includes the following steps: (1) vanadium source, organic alkaline substance and ethanol are mixed, precursor is prepared by microwave method;(2) the mixture of precursor and sodium source, phosphorus source is calcined, and the sodium vanadium phosphate positive electrode material prepared by the application has one-dimensional nanowire structure, which is beneficial to optimize ion conductivity, when it is applied to battery, the battery has low internal resistance, high energy density, good rate performance and cycle performance.The raw materials used in the application are relatively cheap and easy to obtain, and the production time is significantly shortened, easy to realize, and has industrial application prospect.

Description

Technical Field

[0001] This invention relates to a sodium vanadium phosphate cathode material, a cathode sheet, its preparation method, and its application. Background Technology

[0002] In recent years, my country's energy transition has become increasingly urgent, and local governments have attached great importance to research on energy storage technologies. Among the numerous energy storage technologies currently under research, electrochemical energy storage has unique advantages, such as high energy density, high energy conversion efficiency, and fast response speed, and has broad application prospects in the energy field. Currently, four types of secondary batteries have energy storage demonstration projects: lead-acid batteries, sodium-sulfur batteries, vanadium redox flow batteries, and lithium-ion batteries. However, all of these batteries have their own limitations, which require further improvement by relevant researchers. Sodium-ion batteries share the same working principle as lithium-ion batteries, are abundant in resources, and have excellent low-temperature performance, thus attracting widespread attention from research teams worldwide.

[0003] Sodium-ion cathode materials are one of the key materials in sodium-ion batteries. Existing cathode materials are mainly classified into layered oxides, polyanionic cathodes, and Prussian blue cathodes. Sodium vanadium phosphate is a nasicon-structured polyanionic cathode material with a theoretical specific capacity of 117 mAh / g and a high operating voltage (3.4V vs Na / Na). + These materials exhibit excellent cycle stability. However, their electrical conductivity is poor, requiring optimization of ionic and electronic conductivity through nanoscale reduction and surface carbon coating. Simply reducing particle size, however, leads to an increase in the specific surface area of ​​the prepared material, thus reducing its tap density and electrode loading. Increased specific surface area also increases the contact resistance of the electrode particles, resulting in greater polarization during charge and discharge. Furthermore, in conventional wet electrode techniques, increased specific surface area can increase side reactions with the electrolyte.

[0004] Current methods for preparing sodium-ion battery cathode sheets typically involve using organic solvents. The binder is first dissolved, then active and conductive materials are added, followed by a coating and drying process, after which the organic solvent is recovered. This coating process limits the maximum loading of active materials, and the organic solvents pollute the environment, requiring large space for recovery equipment, resulting in significant resource waste. Furthermore, because sodium-ion battery cathode materials are somewhat alkaline, the electrode slurry tends to form a jelly-like consistency during wet coating, which is detrimental to coating and reduces the adhesion of the active materials.

[0005] Compared to wet electrode technology, dry electrode fabrication eliminates the need for solvents, coating, ovens, and organic solvent recovery equipment, reducing investment, lowering electrode fabrication costs, saving energy, and being environmentally friendly. Furthermore, dry electrode fabrication can achieve higher active material loading, increasing battery energy density. In recent years, the industry has placed high hopes on dry electrode technology; however, it is currently still in the exploratory stage, with materials and processes remaining imperfect and requiring urgent development, accumulation, and testing. Summary of the Invention

[0006] The technical problem this invention aims to solve is to overcome the shortcomings of existing technologies, such as the large specific surface area and low tap density of sodium vanadium phosphate granular cathode materials, which result in low electrode loading and further reduced rate and cycle performance. This invention provides a sodium vanadium phosphate cathode material, cathode sheet, its preparation method, and applications. The sodium vanadium phosphate cathode material prepared by this invention has a one-dimensional nanowire structure, which is beneficial for optimizing ionic conductivity. When applied to batteries, it results in low internal resistance, high energy density, and good rate and cycle performance. The raw materials used in this invention are relatively inexpensive and readily available, and the production time is significantly shortened, making it easy to implement and promising for industrial application.

[0007] The present invention solves the above-mentioned technical problems through the following technical solutions.

[0008] This invention provides a method for preparing sodium vanadium phosphate cathode material, which mainly includes the following steps:

[0009] (1) A precursor was prepared by mixing a vanadium source, an organic alkaline substance and ethanol and using a microwave method.

[0010] (2) The precursor is calcined with the mixture of sodium source and phosphorus source.

[0011] In step (1), the vanadium source may be selected from vanadium oxide and / or vanadium salt.

[0012] The vanadium oxide can be vanadium pentoxide (V₂O₅) or vanadium dioxide (VO₂).

[0013] The vanadium salt can be ammonium metavanadate (NH4VO3).

[0014] Preferably, the vanadium source is ammonium metavanadate (NH4VO3) or vanadium pentoxide (V2O5).

[0015] In step (1), the organic alkaline substance may be selected from one or more of dodecylamine, tetradecylamine, hexadecylamine and octadecylamine, such as dodecylamine, tetradecylamine, hexadecylamine or octadecylamine.

[0016] In step (1), the ethanol may be anhydrous ethanol, which is common in the art.

[0017] In step (1), the mass ratio of the vanadium source to the organic alkaline substance can be 1:(0.5-1.5), for example 1:1, 1:1.1, 1:1.2, 1:1.3 or 1:1.5.

[0018] In step (1), the mass-to-volume ratio of the vanadium source and the ethanol can be 1g:(8-14)mL, for example 1g:8.5mL, 1g:8.9mL, 1g:10.6mL, 1g:11.0mL, 1g:11.8mL or 1g:13.9mL.

[0019] In step (1), the mixed raw materials may also include water. The water is preferably deionized water.

[0020] The mass-to-volume ratio of the vanadium source to the water can be 1g:(40-70)mL, for example, 1g:42.7mL, 1g:50mL, 1g:53.2mL, 1g:54.9mL, 1g:58.8mL or 1g:69.4mL.

[0021] Preferably, the vanadium source is first dissolved in water, and then mixed sequentially with the organic alkaline substance and the ethanol.

[0022] In step (1), the reaction temperature in the microwave method can be 150-180℃, for example, 150℃ or 180℃.

[0023] In step (1), the reaction time in the microwave method can be 60-120 min, for example 90 min.

[0024] In step (1), the heating rate to the reaction temperature in the microwave method can be 3-7℃ / min, for example 5℃ / min.

[0025] In step (1), the microwave method can employ a multi-stage heating approach:

[0026] First stage of heating: Increase the temperature by 3-7℃ / min to 150-180℃, hold the temperature for 20-40min, and stop heating for 20-40min;

[0027] Second stage of heating: Increase the temperature by 3-7℃ / min to 150-180℃, hold the temperature for 20-40min, and stop heating for 20-40min;

[0028] The third stage of heating: heat up to 150-180℃ at a rate of 3-7℃ / min, and hold the temperature for 20-40 minutes.

[0029] Preferably, the multi-stage heating method is as follows:

[0030] First stage of heating: Increase the temperature to 150-180℃ at a rate of 5℃ / min, hold the temperature for 30min, and then stop heating for 30min;

[0031] Second stage of heating: Increase the temperature to 150-180℃ at 5℃ / min, hold the temperature for 30min, and stop heating for 30min;

[0032] The third stage of heating: heat up to 150-180℃ at a rate of 5℃ / min, and hold the temperature for 30 minutes.

[0033] In a preferred embodiment, the multi-stage heating method is as follows:

[0034] First stage of heating: Heat to 180℃ at 5℃ / min, hold the temperature for 30min, and stop heating for 30min;

[0035] Second stage of heating: Heat to 180℃ at 5℃ / min, hold the temperature for 30min, and stop heating for 30min;

[0036] The third stage of heating: heating up to 180℃ at a rate of 5℃ / min, and holding at that temperature for 30 minutes.

[0037] In step (1), after the microwave treatment, a cooling operation may also be included. Preferably, the temperature is cooled to room temperature. The room temperature can be 15-30°C as commonly understood.

[0038] In step (1), preferably, after the microwave treatment, the precipitate is further washed and dried.

[0039] The drying temperature can be 60°C.

[0040] The drying process can be vacuum drying.

[0041] In step (2), the sodium source may be one or more of sodium carbonate, sodium nitrate, sodium oxalate and sodium dihydrogen phosphate, such as sodium dihydrogen phosphate.

[0042] In step (2), the phosphorus source may be one or more of sodium phosphate, sodium dihydrogen phosphate, sodium monohydrogen phosphate, ammonium phosphate, ammonium dihydrogen phosphate and ammonium monohydrogen phosphate, such as sodium dihydrogen phosphate.

[0043] In step (2), the amount of raw materials can be added according to the stoichiometric ratio of sodium vanadium phosphate [Na3V2(PO4)3].

[0044] Preferably, the stoichiometric ratio of sodium in the raw materials is 2-5% excess.

[0045] In step (2), the calcination can be carried out in a tube furnace.

[0046] In step (2), the calcination can be carried out in an Ar / H2 mixed gas.

[0047] In step (2), the calcination can be carried out in a multi-stage heat treatment manner; preferably, the calcination is carried out in a two-stage heat treatment manner.

[0048] The temperature of the first stage of heat treatment can be 300-450℃, for example, 350℃.

[0049] The first stage of heat treatment can last for 1-2 hours, for example, 1 hour.

[0050] The temperature of the second heat treatment stage can be 700-850℃, for example, 800℃.

[0051] The second heat treatment can last for 6-10 hours, for example, 8 hours.

[0052] The heating rate for the first or second heat treatment stage can be 2-10℃ / min, for example, 5℃ / min.

[0053] Step (2) may further include a cooling operation after calcination. Preferably, cooling to room temperature. The room temperature may be conventionally understood as 15-30°C.

[0054] The cooling can be carried out in an inert atmosphere or an inert atmosphere containing H2 for reducing purposes. The inert atmosphere is preferably one or more of argon, nitrogen, and helium.

[0055] This invention provides a sodium vanadium phosphate cathode material, which is prepared by the above-described method.

[0056] In this invention, the sodium vanadium phosphate cathode material is a one-dimensional nanowire material. Compared with nanoparticle materials, nanowire materials retain the advantages of nanoscale size, improve the ionic conductivity of the material, and provide a one-dimensional diffusion path for electron transfer, effectively reducing contact resistance and polarization; in addition, nanowire structures have a smaller specific surface area than nanoparticle materials, thus exhibiting fewer side reactions.

[0057] In this invention, the length of the sodium vanadium phosphate cathode material can be 1-50 μm, for example 20 μm.

[0058] The present invention also provides a positive electrode sheet comprising the above-mentioned sodium vanadium phosphate positive electrode material.

[0059] The present invention also provides a method for preparing the above-mentioned positive electrode sheet, which mainly includes the following steps: forming a self-supporting film by mixing the sodium vanadium phosphate positive electrode material, binder and conductive agent, and bonding it with a current collector to obtain the positive electrode material.

[0060] In this invention, the sodium vanadium phosphate cathode material is used as the active material.

[0061] In this invention, the binder may be one or more of PTFE, PVDF, and tetrafluoroethylene-vinylidene fluoride copolymer. The binders selected in this invention are all polymers with fibrous properties. These binders, after fiberization, form one-dimensional filaments.

[0062] When the binder is PTFE and PVDF, the mass ratio of PTFE to PVDF can be 1:(0.5-2), for example 1:1.

[0063] The PTFE is preferably purchased from DuPont PTFE / FEP perfluoropropylene copolymer (PTFE / PFA / FEP / ETFE, fiber grade); the PVDF is preferably purchased from Arkema Kynar Flex2801; and the tetrafluoroethylene-vinylidene fluoride copolymer is preferably purchased from Teflon PTFE 62N X DuPont Fluoropolymers, a copolymer of vinylidene fluoride and tetrafluoroethylene (ФOomph, F2 4).

[0064] In this invention, the conductive agent may be carbon nanotubes. As those skilled in the art will know, carbon nanotubes are one-dimensional materials.

[0065] The length of the carbon nanotubes can be 1-30 μm. Preferably, the carbon nanotubes are purchased from LG Chem CP1002M and have a length of 1-30 μm.

[0066] In this invention, the mass ratio of the sodium vanadium phosphate cathode material, the binder, and the conductive agent can be (80-99):(0.5-10):(0.5-10), for example, 85:7:8.

[0067] In this invention, the self-supporting membrane can be prepared by the following steps: dispersing the stirred mixture and performing a first hot rolling press.

[0068] The stirring temperature can be -15 to 10°C, for example -10°C.

[0069] The stirring time can be 30-90 minutes, for example, 60 minutes.

[0070] The dispersion can be carried out in a fiberizing mixer.

[0071] The dispersion temperature can be 60-120℃, for example 80℃.

[0072] The dispersion can be performed twice. The preferred rotation speed for the first dispersion is 500-2000 rpm, for example, 500 rpm. The preferred dispersion time for the first dispersion is 30-90 minutes, for example, 60 minutes. The preferred rotation speed for the second dispersion is 1500-3000 rpm, for example, 2000 rpm. The preferred dispersion time for the second dispersion is 30-90 minutes, for example, 60 minutes.

[0073] The first hot rolling process can be repeated twice.

[0074] In this invention, the thickness of the self-supporting membrane can be 1-3 mm, for example 1 mm.

[0075] In this invention, the self-supporting film may undergo a second hot rolling process before being bonded to the current collector. Preferably, after the second hot rolling process, the thickness of the self-supporting film is 200-500 μm, for example, 300 μm.

[0076] In this invention, the bonding method with the current collector can be hot rolling.

[0077] In this invention, the bonding process may further include a cutting operation. Preferably, an electrode disc with a diameter of 10 mm is obtained by cutting.

[0078] The present invention also provides an application of the above-mentioned sodium vanadium phosphate cathode material or the above-mentioned cathode sheet in a sodium-ion battery.

[0079] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0080] The reagents and raw materials used in this invention are all commercially available.

[0081] The positive and progressive effects of this invention are as follows:

[0082] This invention employs a microwave method to prepare a precursor material in an alkaline medium, which is then mixed with a sodium source and a phosphorus source and calcined to obtain a sodium vanadium phosphate cathode material Na3V2(PO4)3@C with a one-dimensional nanowire structure. This method inhibits vanadium dissolution, involves relatively inexpensive and readily available raw materials, significantly shortens production time, is easy to implement, and has promising prospects for industrial application.

[0083] The sodium vanadium phosphate cathode material prepared by this invention has a one-dimensional nanowire structure with a length of approximately 20 μm, which is beneficial for optimizing ionic conductivity and overcomes the poor conductivity of traditional cathode materials. Furthermore, it overcomes the defects of traditional cathode materials after nanoparticle formation, such as increased specific surface area, decreased tap density, increased contact resistance, and increased side reactions. When applied to batteries, it results in low internal resistance, high energy density, and good rate performance and cycle performance.

[0084] Furthermore, when the sodium vanadium phosphate cathode material of the present invention is used to prepare the cathode sheet, and both the conductive agent and the binder are one-dimensional materials, a uniform network structure can be formed after mixing, reducing agglomeration; and the dry electrode sheet without any solvent is prepared by extrusion molding, overcoming the problem of slurry gelation during the electrode preparation process by coating, further improving electrochemical performance; at the same time, it saves energy and protects the environment. Attached Figure Description

[0085] Figure 1 This is a SEM image of the sodium vanadium phosphate cathode material prepared in Example 1. Detailed Implementation

[0086] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0087] In the embodiments and comparative examples of this invention, PTFE was purchased from DuPont PTFE / FEP perfluoropropylene copolymer (PTFE / PFA / FEP / ETFE, fiber grade); PVDF was purchased from Arkema Kynar Flex 2801; carbon nanotubes were purchased from LG Chem CP1002M, with a length of 1-30 μm; and tetrafluoroethylene-vinylidene fluoride copolymer was purchased from Teflon PTFE 62N X DuPont Fluoropolymers, a copolymer of vinylidene fluoride and tetrafluoroethylene (ФOomph, F2 4).

[0088] Example 1

[0089] 1. Take 0.47g of ammonium metavanadate, 0.52g of hexadecylamine, 5mL of anhydrous ethanol, and 25mL of deionized water, and put them into a 50mL polytetrafluoroethylene inner tube. Stir the above solution thoroughly until it is completely dissolved. Then, install the polytetrafluoroethylene inner tube into a special ceramic container for microwave heaters and connect it to a microwave heater for microwave treatment.

[0090] 2. The microwave treatment heating regime is as follows: heat to 180℃ at 5℃ / min, hold at that temperature for 30 minutes, stop heating for 30 minutes, heat to 180℃ again at 5℃ / min, hold at that temperature for 30 minutes, stop heating for 30 minutes, heat to 180℃ again at 5℃ / min, hold at that temperature for 30 minutes, stop heating for 30 minutes, and then heat to 180℃ again at 5℃ / min, hold at that temperature for 30 minutes. Then stop heating and allow to cool naturally to room temperature.

[0091] 3. Remove and open the microwave-treated reaction vessel. A flocculent black precipitate forms in the inner PTFE tube. Collect the precipitate by filtration, wash it several times with deionized water, and then vacuum dry it at 60°C to obtain the precursor.

[0092] 4. Weigh 0.571 g of sodium dihydrogen phosphate according to the stoichiometric ratio [Na3V2(PO4)3], mix it with the above precipitate, transfer it to a corundum crucible, cover it, and then place it in a tube furnace.

[0093] 5. A mixture of Ar / H2 gas is introduced into the tubular furnace, and the temperature is increased to 350℃ at a rate of 5℃ / min and held for 1 hour to ensure complete carbonization of hexadecylamine. Then, the temperature is increased to 800℃ at a rate of 5℃ / min and held for 8 hours. After natural cooling under an inert atmosphere, the product (sodium vanadium phosphate cathode material) is removed and stored in a desiccator for later use.

[0094] Example 2

[0095] 1. Take 0.36g of V2O5, 0.48g of hexadecylamine, 5mL of anhydrous ethanol, and 25mL of deionized water, and put them into a 50mL polytetrafluoroethylene inner tube. Stir the above solution thoroughly until it is completely dissolved. Then, install the polytetrafluoroethylene inner tube into a special ceramic container for microwave heaters and connect it to the microwave heater for microwave treatment.

[0096] 2. The microwave treatment heating regime is as follows: heat to 180℃ at 5℃ / min, hold at that temperature for 30 minutes, stop heating for 30 minutes, heat to 180℃ again at 5℃ / min, hold at that temperature for 30 minutes, stop heating for 30 minutes, heat to 180℃ again at 5℃ / min, hold at that temperature for 30 minutes, stop heating for 30 minutes, and then heat to 180℃ again at 5℃ / min, hold at that temperature for 30 minutes. Then stop heating and allow to cool naturally to room temperature.

[0097] 3. Remove and open the microwave-treated reaction vessel. A flocculent black precipitate forms in the inner PTFE tube. Collect the precipitate by filtration, wash it several times with deionized water, and then vacuum dry it at 60°C to obtain the precursor.

[0098] 4. Weigh 0.733 g of sodium dihydrogen phosphate according to the stoichiometric ratio [Na3V2(PO4)3], mix it with the above precipitate, transfer it to a corundum crucible, cover it and place it in a tube furnace.

[0099] 5. A mixture of Ar / H2 gas is introduced into the tubular furnace, and the temperature is increased to 350℃ at a rate of 5℃ / min and held for 1 hour to ensure complete carbonization of hexadecylamine. Then, the temperature is increased to 800℃ at a rate of 5℃ / min and held for 8 hours. After natural cooling under an inert atmosphere, the product (sodium vanadium phosphate cathode material) is removed and stored in a desiccator for later use.

[0100] Example 3

[0101] 1. Take 0.90g of V2O5, 0.92g of dodecylamine, 8mL of anhydrous ethanol, and 45mL of deionized water, and put them into a 100mL polytetrafluoroethylene inner tube. Stir the above solution thoroughly, install the polytetrafluoroethylene inner tube into a special ceramic container for microwave heaters, and connect it to a microwave heater for microwave treatment.

[0102] 2. The microwave treatment heating regime is as follows: heat to 180℃ at 5℃ / min, hold at that temperature for 30 minutes, stop heating for 30 minutes, heat to 180℃ again at 5℃ / min, hold at that temperature for 30 minutes, stop heating for 30 minutes, heat to 180℃ again at 5℃ / min, hold at that temperature for 30 minutes, stop heating for 30 minutes, and then heat to 180℃ again at 5℃ / min, hold at that temperature for 30 minutes. Then stop heating and allow to cool naturally to room temperature.

[0103] 3. Remove and open the microwave-treated reaction vessel. A flocculent black precipitate forms in the inner PTFE tube. Collect the precipitate by filtration, wash it several times with deionized water, and then vacuum dry it at 60°C to obtain the precursor.

[0104] 4. Weigh 1.833 g of sodium dihydrogen phosphate according to the stoichiometric ratio [Na3V2(PO4)3], mix it with the above precipitate, transfer it to a corundum crucible, cover it and place it in a tube furnace.

[0105] 5. A mixture of Ar / H2 gas is introduced into the tubular furnace, and the temperature is increased to 350℃ at a rate of 5℃ / min and held for 1 hour to ensure complete carbonization of the dodecylamine. Then, the temperature is increased to 800℃ at a rate of 5℃ / min and held for 8 hours. After natural cooling under an inert atmosphere, the product (sodium vanadium phosphate cathode material) is removed and stored in a desiccator for later use.

[0106] Example 4

[0107] 1. Take 0.702g of ammonium metavanadate (NH4VO3), 0.808g of octadecylamine, 6mL of anhydrous ethanol, and 30mL of deionized water, and put them into a 100mL polytetrafluoroethylene inner tube. Stir the solution thoroughly, install the polytetrafluoroethylene inner tube into a special ceramic container for microwave heaters, and connect it to a microwave heater for microwave treatment.

[0108] 2. The microwave treatment heating regime is as follows: heat to 180℃ at 5℃ / min, hold at that temperature for 30 minutes, stop heating for 30 minutes, heat to 180℃ again at 5℃ / min, hold at that temperature for 30 minutes, stop heating for 30 minutes, heat to 180℃ again at 5℃ / min, hold at that temperature for 30 minutes, stop heating for 30 minutes, and then heat to 180℃ again at 5℃ / min, hold at that temperature for 30 minutes. Then stop heating and allow to cool naturally to room temperature.

[0109] 3. Remove and open the microwave-treated reaction vessel. A flocculent black precipitate forms in the inner PTFE tube. Collect the precipitate by filtration, wash it several times with deionized water, and then vacuum dry it at 60°C to obtain the precursor.

[0110] 4. Weigh 1.112 g of sodium dihydrogen phosphate according to the stoichiometric ratio [Na3V2(PO4)3], mix it with the above precipitate, transfer it to a corundum crucible, cover it and place it in a tube furnace.

[0111] 5. A mixture of Ar / H2 gas is introduced into the tubular furnace, and the temperature is increased to 350℃ at a rate of 5℃ / min and held for 1 hour to ensure complete carbonization of the octadecylamine. Then, the temperature is increased to 800℃ at a rate of 5℃ / min and held for 8 hours. After natural cooling under an inert atmosphere, the product (sodium vanadium phosphate cathode material) is removed and stored in a desiccator for later use.

[0112] Example 5

[0113] 1. Take 0.546g of V2O5, 0.808g of octadecylamine, 6mL of anhydrous ethanol, and 30mL of deionized water, and put them into a 100mL polytetrafluoroethylene inner tube. Stir the above solution thoroughly, install the polytetrafluoroethylene inner tube into a special ceramic container for microwave heaters, and connect it to a microwave heater for microwave treatment.

[0114] 2. The microwave treatment heating regime is as follows: heat to 180℃ at 5℃ / min, hold at that temperature for 30 minutes, stop heating for 30 minutes, heat to 180℃ again at 5℃ / min, hold at that temperature for 30 minutes, stop heating for 30 minutes, heat to 180℃ again at 5℃ / min, hold at that temperature for 30 minutes, stop heating for 30 minutes, and then heat to 180℃ again at 5℃ / min, hold at that temperature for 30 minutes. Then stop heating and allow to cool naturally to room temperature.

[0115] 3. Remove and open the microwave-treated reaction vessel. A flocculent black precipitate forms in the inner PTFE tube. Collect the precipitate by filtration, wash it several times with deionized water, and then vacuum dry it at 60°C to obtain the precursor.

[0116] 4. Weigh 1.112 g of sodium dihydrogen phosphate according to the stoichiometric ratio [Na3V2(PO4)3], mix it with the above precipitate, transfer it to a corundum crucible, cover it and place it in a tube furnace.

[0117] 5. A mixture of Ar / H2 gas is introduced into the tubular furnace, and the temperature is increased to 350℃ at a rate of 5℃ / min and held for 1 hour to ensure complete carbonization of the octadecylamine. Then, the temperature is increased to 800℃ at a rate of 5℃ / min and held for 8 hours. After natural cooling under an inert atmosphere, the product (sodium vanadium phosphate cathode material) is removed and stored in a desiccator for later use.

[0118] Example 6

[0119] 1. Take 0.51g of V2O5, 0.596g of tetradecylamine, 6mL of anhydrous ethanol, and 30mL of deionized water, and put them into a 100mL polytetrafluoroethylene inner tube. Stir the above solution thoroughly, install the polytetrafluoroethylene inner tube into a special ceramic container for microwave heaters, and connect it to a microwave heater for microwave treatment.

[0120] 2. The microwave treatment heating regime is as follows: heat to 180℃ at 5℃ / min, hold at that temperature for 30 minutes, stop heating for 30 minutes, heat to 180℃ again at 5℃ / min, hold at that temperature for 30 minutes, stop heating for 30 minutes, heat to 180℃ again at 5℃ / min, hold at that temperature for 30 minutes, stop heating for 30 minutes, and then heat to 180℃ again at 5℃ / min, hold at that temperature for 30 minutes. Then stop heating and allow to cool naturally to room temperature.

[0121] 3. Remove and open the microwave-treated reaction vessel. A flocculent black precipitate forms in the inner PTFE tube. Collect the precipitate by filtration, wash it several times with deionized water, and then vacuum dry it at 60°C to obtain the precursor.

[0122] 4. Weigh 1.030 g of sodium dihydrogen phosphate according to the stoichiometric ratio [Na3V2(PO4)3], mix it thoroughly with the above precipitate, transfer it to a corundum crucible, cover it and place it in a tube furnace.

[0123] 5. A mixture of Ar / H2 gas is introduced into the tubular furnace, and the temperature is increased to 350℃ at a rate of 5℃ / min and held for 1 hour to ensure complete carbonization of the octadecylamine. Then, the temperature is increased to 800℃ at a rate of 5℃ / min and held for 8 hours. After natural cooling under an inert atmosphere, the product (sodium vanadium phosphate cathode material) is removed and stored in a desiccator for later use.

[0124] Examples 7-8

[0125] 1. Using the sodium vanadium phosphate cathode materials prepared in Examples 1 and 2 as active materials, carbon nanotubes as conductive agents, and PTFE as binders, dry-process electrodes were prepared. The materials were weighed according to a mass ratio of active material: conductive agent: binder of 85:7:8.

[0126] 2. Stir the mixed powder at a low temperature (-10℃) for 60 minutes to ensure the materials are evenly mixed.

[0127] 3. Place the material in a fiberizing mixer, set the heating temperature to 80℃, disperse at 500 rpm for 60 min, then disperse at 2000 rpm for 60 min. Perform two hot rolling processes on the uniformly mixed powder to press it into a 1 mm thick self-supporting film. Perform another hot rolling process on the self-supporting film to press the electrode film to a thickness of 300 μm. Then, laminate it with carbon-coated aluminum foil. Finally, perform another hot rolling process on both materials to adhere the electrode film to the aluminum foil, thus preparing an electrode sheet. Cut the electrode sheet into 10 mm diameter electrode discs, vacuum dry them, weigh them, and transfer them to a glove box for use as working electrode sheets.

[0128] Examples 9-10

[0129] 1. Using the sodium vanadium phosphate cathode materials obtained in Examples 3 and 4 as active materials, carbon nanotubes as conductive agents, and PTFE and PVDF (50% by mass each) as binders, dry-process electrodes were prepared. The materials were weighed according to a mass ratio of active material: conductive agent: binder of 85:7:8.

[0130] 2. Stir the mixed powder at a low temperature (-10℃) for 60 minutes to ensure the materials are evenly mixed.

[0131] 3. Place the material in a fiberizing mixer, set the heating temperature to 80℃, disperse at 500 rpm for 60 min, then disperse at 2000 rpm for 60 min. Perform two hot rolling processes on the uniformly mixed powder to press it into a 1 mm thick self-supporting film. Perform another hot rolling process on the self-supporting film to press the electrode film to a thickness of 300 μm. Then, laminate it with carbon-coated aluminum foil. Finally, perform another hot rolling process on both materials to adhere the electrode film to the aluminum foil, thus preparing an electrode sheet. Cut the electrode sheet into 10 mm diameter electrode discs, vacuum dry them, weigh them, and transfer them to a glove box for use as working electrode sheets.

[0132] Examples 11-12

[0133] 1. Using the sodium vanadium phosphate cathode materials obtained in Examples 5 and 6 as active materials, carbon nanotubes as conductive agents, and tetrafluoroethylene-vinylidene fluoride copolymer (a copolymer prepared from tetrafluoroethylene and vinylidene fluoride in a molar ratio of 1:1) as binders, dry electrodes were prepared. The above materials were weighed according to a mass ratio of active material: conductive agent: binder of 85:7:8.

[0134] 2. Stir the mixed powder at a low temperature (-10℃) for 60 minutes to ensure the materials are evenly mixed.

[0135] 3. Place the material in a fiberizing mixer, set the heating temperature to 80℃, disperse at 500 rpm for 60 min, then disperse at 2000 rpm for 60 min. Perform two hot rolling processes on the uniformly mixed powder to press it into a 1 mm thick self-supporting film. Perform another hot rolling process on the self-supporting film to press the electrode film to a thickness of 300 μm. Then, laminate it with carbon-coated aluminum foil. Finally, perform another hot rolling process on both materials to adhere the electrode film to the aluminum foil, thus preparing an electrode sheet. Cut the electrode sheet into 10 mm diameter electrode discs, vacuum dry them, weigh them, and transfer them to a glove box for use as working electrode sheets.

[0136] Comparative Example 1

[0137] 1. Solid-state preparation of Na3V2(PO4)3: Weigh 0.182g V2O5 and 0.36g NaH2PO4, grind and mix them thoroughly, then transfer them to an argon atmosphere tube furnace and calcine them at 800℃ for 8h to obtain Na3V2(PO4)3 powder.

[0138] Comparative Example 2

[0139] 1. Preparation of surface-coated Na3V2(PO4)3 / C using the sol-gel method. First, 0.182 g of V2O5 and 0.378 g of H2C2O4·2H2O were weighed and added to 25 mL of deionized water. The solution was heated in an 80°C water bath and magnetically stirred until it turned blue. Then, 0.36 g of NaH2PO4 was added and stirring was continued for 15 min. Next, 0.18 g of glucose was added to the above solution, and stirring was continued vigorously until the solution was evaporated to dryness to form a gel. The resulting gel was transferred to a constant temperature oven at 120°C for thorough drying and then ground. The gel was then heated to 400°C for 4 h in a tube furnace with an Ar / H2 mixed gas, and then heated to 800°C for 8 h to obtain Na3V2(PO4)3 / C nanoparticle materials.

[0140] Comparative Examples 3-4

[0141] The sodium vanadium phosphate particles obtained in Comparative Examples 1 and 2 were used as active materials to prepare electrode pastes according to a mass ratio of active material: conductive carbon black: binder of 80:12:8. These pastes were then coated onto aluminum foil using a doctor blade coating method. The aluminum foil was dried in an oven at 80°C for 2 hours, then transferred to a vacuum drying oven and dried at 105°C for 12 hours. After being compacted with a rolling mill, the foil was cut into electrode discs with a diameter of 10 mm, weighed, and transferred to a glove box for use as working electrode sheets.

[0142] Comparative Examples 5-6

[0143] 1. Using sodium vanadium phosphate particles prepared in Comparative Example 1 and Comparative Example 2 as active materials, carbon nanotubes as conductive agents, and PTFE as binders, dry electrodes were prepared. The materials were weighed according to a mass ratio of active material: conductive agent: binder of 85:7:8.

[0144] 3. Stir the mixed powder at a low temperature (-10℃) for 60 minutes to ensure the materials are evenly mixed.

[0145] 4. Place the material in a fiberizing mixer, set the heating temperature to 80℃, disperse at 500 rpm for 60 min, then disperse at 2000 rpm for 60 min. Perform two hot rolling processes on the uniformly mixed powder to press it into a 1 mm thick self-supporting film. Perform another hot rolling process on the self-supporting film to press the electrode film to a thickness of 300 μm. Then, laminate it with carbon-coated aluminum foil. Finally, perform another hot rolling process on both materials to adhere the electrode film to the aluminum foil, thus preparing an electrode sheet. Cut the electrode sheet into 10 mm diameter electrode discs, vacuum dry them, weigh them, and transfer them to a glove box for use as working electrode sheets.

[0146] Example 1: Appearance Structure

[0147] The SEM image of the sodium vanadium phosphate cathode material prepared in Example 1 is shown below. Figure 1 As shown, the sodium vanadium phosphate cathode material prepared by this invention exhibits a one-dimensional nanowire structure with a length of up to approximately 20 μm.

[0148] Example 2: Electrochemical Performance

[0149] Button half-cells were assembled in a glove box, and the electrochemical performance of the positive electrode materials and positive electrode prepared in the above examples and comparative examples was tested and evaluated. CR 2032 button cells were assembled in the order of positive electrode, separator, and negative electrode, with a sodium metal sheet as the negative electrode, Whatman glass fiber as the separator, and a commercially available sodium-ion electrolyte with a main component of 1M NaPF6 / (EC:DEC=1:1). The assembled button cells were connected to a battery testing system, and the electrochemical performance of the materials was tested by charge-discharge testing in the range of 2.5-4V.

[0150] The test results are shown in Table 1.

[0151] Table 1

[0152]

[0153]

[0154] As shown in the table above, Examples 7-12 of the present invention can all achieve excellent rate performance (capacity greater than 110 mAh / g at 0.5C, greater than 106 mAh / g at 1C, greater than 85 mAh / g at 5C, and greater than 66 mAh / g at 10C) and cycle performance (capacity retention rate greater than 91% after 500 cycles at 1C).

[0155] Comparative Examples 1 and 2 used solid-state and sol-gel methods to prepare cathode materials, respectively. Comparative Examples 3 and 4 show that, based on Comparative Examples 1 and 2, the cathode materials prepared using traditional methods exhibited low rate performance and capacity retention. Comparative Examples 5 and 6 show that, based on Comparative Examples 1 and 2, the dry electrode preparation process slightly improved the rate performance and capacity retention compared to Comparative Examples 3 and 4, but still significantly worse than Examples 7-12 of this application.

Claims

1. A method for preparing a sodium vanadium phosphate cathode material, characterized in that, It mainly includes the following steps: (1) A precursor was prepared by mixing a vanadium source, an organic alkaline substance and ethanol using a microwave method; (2) The precursor is calcined with a mixture of sodium and phosphorus sources; The sodium vanadium phosphate cathode material has a one-dimensional nanowire structure. The organic basic substance is selected from one or more of dodecylamine, tetradecylamine, hexadecylamine and octadecylamine.

2. The method for preparing sodium vanadium phosphate cathode material as described in claim 1, characterized in that, In step (1), the reaction temperature in the microwave method is 150-180℃; And / or, in step (1), the reaction time in the microwave method is 60-120 min; And / or, in step (1), in the microwave method, the heating rate to the reaction temperature is 3-7℃ / min; And / or, in step (1), the microwave method adopts a multi-stage heating method: the first stage heating: heating at 3-7℃ / min to 150-180℃, holding the temperature for 20-40min, and stopping heating for 20-40min; the second stage heating: heating at 3-7℃ / min to 150-180℃, holding the temperature for 20-40min, and stopping heating for 20-40min; the third stage heating: heating at 3-7℃ / min to 150-180℃, holding the temperature for 20-40min; And / or, in step (1), after the microwave treatment, a cooling operation is also included; And / or, in step (1), after the microwave treatment, the precipitate is further washed and dried.

3. The method for preparing sodium vanadium phosphate cathode material as described in claim 2, characterized in that, In step (1), the reaction temperature in the microwave method is 150°C or 180°C; And / or, in step (1), the reaction time in the microwave method is 90 min.

4. The method for preparing sodium vanadium phosphate cathode material as described in claim 2, characterized in that, The multi-stage heating method is as follows: First stage of heating: Increase the temperature to 150-180℃ at a rate of 5℃ / min, hold the temperature for 30min, and then stop heating for 30min; Second stage of heating: Increase the temperature to 150-180℃ at 5℃ / min, hold the temperature for 30min, and stop heating for 30min; The third stage of heating: heat up to 150-180℃ at a rate of 5℃ / min, and hold the temperature for 30 minutes.

5. The method for preparing sodium vanadium phosphate cathode material as described in claim 4, characterized in that, The multi-stage heating method is as follows: First stage of heating: Heat to 180℃ at 5℃ / min, hold the temperature for 30min, and stop heating for 30min; Second stage of heating: Increase the temperature to 180℃ at a rate of 5℃ / min, hold the temperature for 30min, and then stop heating for 30min; The third stage of heating: heating up to 180℃ at a rate of 5℃ / min, and holding at that temperature for 30 minutes.

6. The method for preparing sodium vanadium phosphate cathode material as described in claim 1, characterized in that, In step (1), the vanadium source is selected from vanadium oxide and / or vanadium salts; And / or, in step (1), the organic basic substance is dodecylamine, tetradecylamine, hexadecylamine or octadecylamine; And / or, in step (1), the mass ratio of the vanadium source to the organic alkaline substance is 1:(0.5-1.5). And / or, in step (1), the mass-to-volume ratio of the vanadium source to the ethanol is 1 g: (8-14) mL; And / or, in step (1), the mixed raw materials also include water.

7. The method for preparing sodium vanadium phosphate cathode material as described in claim 6, characterized in that, In step (1), the vanadium oxide is vanadium pentoxide (V₂O₅) or vanadium dioxide (VO₂). And / or, the vanadium salt is ammonium metavanadate NH4VO3; And / or, in step (1), the mass-to-volume ratio of the vanadium source to the water is 1 g: (40-70) mL.

8. The method for preparing sodium vanadium phosphate cathode material as described in claim 6, characterized in that, In step (1), the vanadium source is ammonium metavanadate NH4VO3 or vanadium pentoxide V2O5; And / or, in step (1), the vanadium source is first dissolved in water, and then mixed sequentially with the organic alkaline substance and the ethanol.

9. The method for preparing sodium vanadium phosphate cathode material as described in claim 1, characterized in that, In step (2), the sodium source is one or more of sodium carbonate, sodium nitrate, sodium oxalate, and sodium dihydrogen phosphate; And / or, in step (2), the phosphorus source is one or more of sodium phosphate, sodium dihydrogen phosphate, sodium monohydrogen phosphate, ammonium phosphate, ammonium dihydrogen phosphate and ammonium monohydrogen phosphate; And / or, in step (2), the amount of raw material is added according to the stoichiometric ratio of sodium vanadium phosphate [Na3V2(PO4)3]; And / or, in step (2), the calcination is carried out in an Ar / H2 mixed gas; And / or, in step (2), the calcination is carried out using a multi-stage heat treatment method; And / or, in step (2), the calcination process also includes a cooling operation.

10. The method for preparing the sodium vanadium phosphate cathode material as described in claim 9, characterized in that, In step (2), the sodium source is sodium dihydrogen phosphate; And / or, in step (2), the phosphorus source is sodium dihydrogen phosphate; And / or, in step (2), the calcination is performed using a two-stage heat treatment method; And / or, in step (2), the cooling is carried out in an inert atmosphere or an inert atmosphere containing H2 for reduction.

11. The method for preparing sodium vanadium phosphate cathode material as described in claim 10, characterized in that, In step (2), the calcination adopts a two-stage heat treatment, and the temperature of the first stage of heat treatment is 300-450℃; And / or, in step (2), the calcination adopts a two-stage heat treatment in which the first stage of heat treatment lasts for 1-2 hours; And / or, in step (2), the calcination adopts a two-stage heat treatment in which the temperature of the second stage heat treatment is 700-850℃; And / or, in step (2), the calcination adopts a two-stage heat treatment in which the second stage heat treatment time is 6-10h; And / or, in step (2), the inert atmosphere is one or more of argon, nitrogen and helium.

12. The method for preparing sodium vanadium phosphate cathode material as described in claim 11, characterized in that, In step (2), the heating rate to the first stage of heat treatment or the second stage of heat treatment is 2-10℃ / min.

13. A sodium vanadium phosphate cathode material, characterized in that, It is prepared by any one of the preparation methods as described in claims 1-12.

14. The sodium vanadium phosphate cathode material as described in claim 13, characterized in that, The length of the sodium vanadium phosphate cathode material is 1-50 μm.

15. A positive electrode plate, characterized in that, It includes the sodium vanadium phosphate cathode material as described in claim 13 or 14.

16. A method for preparing a positive electrode sheet as described in claim 15, characterized in that, The main steps include: forming a self-supporting film from a mixture of sodium vanadium phosphate cathode material, binder, and conductive agent, and bonding it with a current collector to obtain the cathode material.

17. The method for preparing the positive electrode sheet as described in claim 16, characterized in that, The binder is one or more of PTFE, PVDF, and tetrafluoroethylene-vinylidene fluoride copolymer; And / or, the conductive agent is carbon nanotubes; And / or, the mass ratio of the sodium vanadium phosphate cathode material, the binder, and the conductive agent is (80-99):(0.5-10):(0.5-10); And / or, the self-supporting membrane is prepared by the following steps: dispersing the stirred mixture and performing a first hot rolling process; And / or, the thickness of the self-supporting membrane is 1-3 mm; And / or, before bonding with the current collector, the self-supporting membrane is also subjected to a second hot roll pressing; And / or, the bonding method with the current collector is hot rolling; And / or, the bonding process may also include a cutting operation.

18. The method for preparing the positive electrode sheet as described in claim 17, characterized in that, When the binder is PTFE and PVDF, the mass ratio of PTFE to PVDF is 1:(0.5-2). And / or, the length of the carbon nanotubes is 1-30 μm; And / or, the stirring temperature is -15 to 10°C; And / or, the stirring time is 30-90 min; And / or, the dispersion temperature is 60-120°C; And / or, the dispersion is performed twice; And / or, the first hot roller pressing is repeated twice; And / or, after the second hot rolling, the thickness of the self-supporting film is 200-500 μm.

19. The method for preparing the positive electrode sheet as described in claim 18, characterized in that, The dispersion process involves two dispersions, with the first dispersion occurring at a rotation speed of 500-2000 rpm. And / or, the dispersion is carried out in two stages, with the first dispersion taking 30-90 minutes; And / or, the rotation speed of the second dispersion in the two dispersions is 1500-3000 rpm; And / or, the second dispersion in the two dispersions takes 30-90 minutes.

20. The application of a sodium vanadium phosphate cathode material as described in claim 13 or 14, or a cathode sheet as described in claim 15, in a sodium-ion battery.

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