High-entropy fluorophosphate-doped sodium vanadium oxide positive electrode material and preparation method

Abstract

The application discloses a high-entropy doped sodium vanadium fluorophosphate positive electrode material and a preparation method thereof. The sodium source, the vanadium source, the phosphorus source, the fluorine source, the doped metal A source, the doped metal B source, the doped metal C source, the doped metal D source, the doped metal E source, the doped metal G source and the carbon source are respectively dissolved in deionized water or ethanol, then the solutions are mixed together, stirred and heated to obtain a transparent sol; the transparent sol is dried to obtain a gel, and the gel is ground to obtain a precursor powder; and the precursor powder is sintered in an inert atmosphere to obtain the high-entropy doped sodium vanadium fluorophosphate positive electrode material. The application controls the structure of the sodium vanadium fluorophosphate through six different valence doped elements, maximally cooperates the four core effects of high-entropy value, lattice distortion, delayed diffusion and cocktail effect caused by high-entropy doping, so that the high-entropy doped sodium vanadium fluorophosphate positive electrode material has excellent discharge specific capacity; the disorder degree of atomic arrangement in the material structure is increased, and the electrochemical performance and stability are improved.

Description

Technical Field

[0001] This invention belongs to the technical field of electrochemical principles, electrochemical energy storage applications, and preparation of secondary battery electrode materials, specifically relating to a high-entropy doped sodium vanadium fluorophosphate cathode material and its preparation method. Background Technology

[0002] In recent years, due to the relatively mature development technology of lithium-ion batteries and the continuous decrease in the supply of lithium resources leading to a rapid rise in the price of lithium-ion batteries, in order to seek market balance and social development, the research on sodium-ion batteries has gradually become a research hotspot in the field of energy storage at home and abroad. Sodium-ion batteries have received widespread attention from all sectors of society due to their huge advantages: (1) Sodium is widely distributed in nature, has a huge content, and is inexpensive, thus having a very strong market competitiveness; (2) Sodium compounds are easy to mine and of high quality; (3) The redox potential of sodium ions is about 300mV higher than that of lithium ions, so it can be used to decompose electrolyte solvents, electrolyte salts, and aluminum current collectors with lower potentials; (4) Sodium-ion batteries are more green and environmentally friendly and conform to the principle of sustainable development; (5) Sodium and lithium are in the same group and have similar physicochemical properties, so sodium-ion batteries and lithium-ion batteries have similar working principles. The mature development of lithium-ion batteries has paved the way for the development of sodium-ion batteries. Therefore, sodium-ion batteries are expected to become the mainstream battery device for large-scale energy storage in the future.

[0003] Currently, sodium-ion battery cathode materials that have attracted attention include transition metal oxides, polyanionic materials, Prussian blue materials, and organic cathode materials. Among existing research on sodium-ion battery cathode materials, Na3V2(PO4)2F3 (NVPF), as a polyanionic material, exhibits high thermal stability, an average discharge potential as high as 3.95 V, and a theoretical specific capacity of 128 mAh / g, resulting in a high theoretical energy density of 500 Wh / kg. It is a fast sodium-ion conductor with three-dimensional ion channels and high ionic conductivity. Therefore, NVPF has become one of the most promising sodium-ion battery cathode materials for commercial application in the eyes of researchers.

[0004] However, as a member of the NASICON family, NVPF inevitably possesses inherently poor electron conductivity, posing significant challenges to its practical applications. Furthermore, previously reported NVPF cathodes typically exhibit a low discharge plateau of Na3V2(PO4)3 around 3.4V, further reducing the average operating voltage and corresponding energy density. In short, NVPF still faces two major obstacles: poor electron conductivity and uncontrollable discharge behavior in the low-voltage region. Establishing a highly conductive network could certainly improve electron conductivity, but excessive carbon addition would simultaneously reduce energy density and cost-effectiveness. To date, effective strategies remain lacking to regulate the rise in average discharge voltage of a fixed lattice with a constant active transition metal center, which would facilitate an adjustable voltage region and simultaneously extend the discharge interval behavior. Therefore, the urgent task is to develop a synergistic strategy to improve the low-voltage discharge plateau and adequately store sodium ions at higher voltages. Summary of the Invention

[0005] To address the problems in the prior art, the purpose of this invention is to provide a high-entropy doped sodium vanadium fluorophosphate cathode material and its preparation method. This method can improve the low-voltage discharge platform, fully store sodium ions at higher voltages, and increase the degree of disorder in the atomic arrangement of the material structure, thereby improving electrochemical performance and stability.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A high-entropy doped sodium vanadium fluorophosphate cathode material includes a cathode material layer and a carbon coating layer disposed on the surface of the cathode material layer. The general structural formula of the cathode material layer is Na3V. 1.9 (VABCDEG) 0.1 / 7 (PO4)2F3 / C, where V is V 3+ A is Li + Na + With K + One or more of them, where B is Mg 2+ Ca 2+ Fe 2+ With Cu 2+ One or more of them, where C is Al 3+ Cr 3+ with Fe 3+ One or more of them, where D is Ti 4+ With Zr 4+ One or two of them, E is Nb 5+ With Ta 5+ One or two of them, G is W 6+ with Mo 6+ One or two of them.

[0007] Furthermore, the thickness of the carbon coating is 5 nm.

[0008] Furthermore, A, B, C, D, E and G are doped in equal proportions.

[0009] A method for preparing a high-entropy doped sodium vanadium fluorophosphate cathode material as described above includes the following steps: (1) Dissolve sodium source, vanadium source, phosphorus source, fluorine source, doped metal A source, doped metal B source, doped metal C source, doped metal D source, doped metal E source, doped metal G source and carbon source in deionized water or ethanol respectively, then mix the solutions together and stir under heating to obtain a transparent sol. (2) The transparent sol was dried to obtain a gel, which was then ground to obtain a precursor powder; (3) The precursor powder was sintered in an inert atmosphere to obtain a high-entropy doped sodium vanadium fluorophosphate cathode material.

[0010] Furthermore, the dopant metal A source is a lithium source, a sodium source, or a potassium source; The doping metal B source can be a magnesium source, a calcium source, an iron source, a copper source, or a zinc source; The C source for doping can be aluminum, chromium, iron, or cobalt. The doped metal D source is a titanium source or a zirconium source; The doped metal source (E) is a niobium source or a tantalum source; The doping metal G source is a tungsten source or a molybdenum source; The carbon source is one or more of citric acid monohydrate, anhydrous citric acid, diammonium citrate, diammonium hydrogen citrate, and triammonium citrate.

[0011] Furthermore, the lithium source is one or more of lithium fluoride, lithium acetate, lithium carbonate, and lithium nitrate; The sodium source is one or more of sodium fluoride, sodium acetate, sodium carbonate, and sodium nitrate; The potassium source is one or more of potassium fluoride, potassium acetate, potassium carbonate and potassium nitrate; The vanadium source is one or more of vanadium pentoxide, ammonium metavanadate and vanadium oxalate; The phosphorus source is one or more of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and ammonium phosphate; The fluorine source is one or more of ammonium fluoride and sodium fluoride; The magnesium source is one or more of magnesium nitrate, magnesium carbonate, and magnesium acetate; the calcium source is one or more of calcium nitrate, calcium carbonate, and calcium acetate; the iron source is ferrous oxalate; and the copper source is one or two of copper nitrate and copper oxide. The aluminum source is one or both of aluminum nitrate nonahydrate and basic aluminum acetate; the chromium source is one or both of chromium nitrate and chromium trioxide; the iron source is one or both of ferric nitrate and ferric trioxide. The titanium source is one or both of tetrabutyl titanate and titanium dioxide; the molybdenum source in the doped metal D source is zirconium dioxide; The niobium source is one or both of niobium oxalate and niobium pentoxide; the tantalum source is tantalum pentoxide. The tungsten source is tungsten trioxide; the molybdenum source in the doped metal G source is one or more of ammonium molybdate and molybdenum trioxide.

[0012] Furthermore, the mass of the carbon source is 1%-30% of the mass of the high-entropy sodium vanadium fluorophosphate cathode material.

[0013] Furthermore, the heating temperature is 60℃-120℃, and the time is 5-12h; the inert atmosphere is nitrogen or argon, and the gas flow rate is 30-80 mL / min.

[0014] Furthermore, the drying temperature is 60℃-120℃, and the time is 10h-20h.

[0015] Furthermore, the sintering temperature is 500℃-800℃, and the time is 2-12h.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention utilizes six different valence-state doping elements to regulate the structure of sodium vanadium fluorophosphate, maximizing the synergistic effect of four core properties: high entropy value, lattice distortion, hysteretic diffusion, and the cocktail effect induced by high entropy doping. Specifically: (1) From the perspective of charge balance, doping with low-valence ions introduces cation vacancies, while doping with high-valence ions introduces anion vacancies. This defect has been proven to increase the conductivity of electrode materials and reduce the migration barrier of charge carriers. The six different valence states introduce various defects at different positions in the lattice, which can be utilized to the maximum extent to improve conductivity.

[0017] (2) From the perspective of crystal structure, different elements have different ionic radii and different numbers of outer electrons in ions with different valence states. These factors will cause lattice distortion after the introduction of six elements with different valence states. The chemical bonds and coordination of different ions in the lattice will change. These factors will bring about changes in electrochemical performance. Taking the substitution at the V site in sodium vanadium fluorophosphate as an example, the substitution of K, Na and other elements with large ionic radii can increase the lattice spacing and improve the conductivity. The introduction of transition metal ions such as Fe and Mn will increase the types of active ions, increase the working voltage, and thus increase the specific capacity.

[0018] (3) From the perspective of high entropy, the more elements introduced, the higher the disorder in the system and the higher the entropy. The entropy reaches its maximum when introduced in equal proportions. This is one of the reasons why this work chose to dope with six elements. The doping entropy can reach 1.95R. However, after more than six elements, although the entropy can continue to increase, the synthesis cost will increase, and the slight improvement in performance cannot match the increase in cost.

[0019] (4) From a thermodynamic perspective, the introduction of multiple elements will interfere with the formation of impurity phases and increase the purity of the synthesized material. This suppresses the low-voltage discharge defect of sodium vanadium fluorophosphate and further increases the discharge specific capacity.

[0020] This invention employs a sol-gel method for preparation, utilizing readily available raw materials. The process is simple, low-cost, and reproducible, yielding a high-entropy doped sodium vanadium fluorophosphate cathode material with excellent discharge specific capacity. The sodium vanadium fluorophosphate cathode material prepared using this method exhibits stable structure and suppresses common vanadium phosphate impurities. The assembled sodium-ion battery demonstrates high specific capacity and weak polarization, along with good rate capability and cycle performance. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments of the present invention will be briefly described below. However, the drawings described below are only some embodiments of the present invention, and those skilled in the art can obtain other drawings based on these drawings without creative effort.

[0022] Figure 1 This is the XRD pattern of the high-entropy doped sodium vanadium fluorophosphate cathode material prepared in Example 1 of this invention.

[0023] Figure 2 This is the CV curve of a sodium-ion battery assembled from the high-entropy doped sodium vanadium fluorophosphate cathode material prepared in Example 1 of this invention.

[0024] Figure 3 This is the first charge-discharge curve of a sodium-ion battery assembled from the high-entropy doped sodium vanadium fluorophosphate cathode material prepared in Example 1 of this invention.

[0025] Figure 4 This is the CV curve of a sodium-ion battery assembled from the high-entropy doped sodium vanadium fluorophosphate cathode material prepared in Example 2 of this invention.

[0026] Figure 5 This is the CV curve of a sodium-ion battery assembled from the high-entropy doped sodium vanadium fluorophosphate cathode material prepared in Example 3 of this invention. Detailed Implementation

[0027] The following is a detailed description of the technical solution of the present invention in conjunction with the accompanying drawings and specific preferred embodiments, but it should not be considered as a limitation of the present invention.

[0028] In this invention, high entropy refers to the degree of disorder in a material system. When the entropy value in the system is greater than 1.5R, it is considered high entropy.

[0029] The high-entropy doped sodium vanadium fluorophosphate cathode material of the present invention includes a cathode material layer and a carbon coating layer disposed on the surface of the cathode material layer. The thickness of the carbon coating layer is approximately 5 nm, and the cathode material layer has the general formula Na3V. 1.9 (VABCDEG) 0.1 / 7 (PO4)2F3 / C, where V is V 3+ A is Li + Na + With K + One or more of them, where B is Mg 2+ Ca 2+ Fe 2+ With Cu 2+ One or more of them, where C is Al 3+ Cr 3+ with Fe 3+ One or more of them, where D is Ti 4+ With Zr 4+ One or two of them, E is Nb 5+ With Ta 5+ One or two of them, G is W 6+ with Mo 6+ One or two of them.

[0030] Six different valence state doping elements (A, B, C, D, E, and G) are used as V substitution sites in equal proportions.

[0031] By controlling the structure of sodium vanadium fluorophosphate with six doping elements, the disorder of atomic arrangement in the material structure is increased, resulting in a high-entropy doped sodium vanadium fluorophosphate cathode material with high conductivity and high-voltage stability.

[0032] The preparation method of the high-entropy doped sodium vanadium fluorophosphate cathode material described above employs the sol-gel method, and the specific steps are as follows: (1) According to the stoichiometric ratio, sodium source, vanadium source, phosphorus source, fluorine source, doped metal A source, doped metal B source, doped metal C source, doped metal D source, doped metal E source, doped metal G source and carbon source are dissolved in appropriate amounts of deionized water or organic ethanol, stirred at room temperature to dissolve, and then mixed evenly. The mixture is stirred in a water bath or oil bath at 60℃-120℃ for 5-12 hours to obtain a transparent sol. The sodium source is one or more of sodium fluoride, sodium acetate, sodium carbonate, and sodium nitrate. The potassium source is one or more of potassium fluoride, potassium acetate, potassium carbonate and potassium nitrate; The vanadium source is one or more of vanadium pentoxide, ammonium metavanadate and vanadium oxalate; The phosphorus source is one or more of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and ammonium phosphate; The fluorine source is one or more of ammonium fluoride and sodium fluoride; The doping metal A source is a lithium source, a sodium source, or a potassium source, wherein the lithium source is one or more of lithium fluoride, lithium acetate, lithium carbonate, and lithium nitrate.

[0033] The doping metal B source is a magnesium source, a calcium source, an iron source, a copper source, or a zinc source, wherein the magnesium source is one or more of magnesium nitrate, magnesium carbonate, and magnesium acetate; the calcium source is one or more of calcium nitrate, calcium carbonate, and calcium acetate; the iron source is ferrous oxalate; and the copper source is one or two of copper nitrate and copper oxide.

[0034] The doping metal C source is an aluminum source, a chromium source, an iron source, or a cobalt source, wherein the aluminum source is one or two of aluminum nitrate nonahydrate and basic aluminum acetate; the chromium source is one or two of chromium nitrate and chromium trioxide; and the iron source is one or two of ferric nitrate and ferric trioxide.

[0035] The doped metal D source is a titanium source or a molybdenum source, wherein the titanium source is one or both of tetrabutyl titanate and titanium dioxide; the zirconium source is zirconium dioxide.

[0036] The doping metal E source is a niobium source or a tantalum source, wherein the niobium source is one or both of niobium oxalate and niobium pentoxide; and the tantalum source is tantalum pentoxide.

[0037] The doping metal G source is a tungsten source or a molybdenum source, wherein the tungsten source is tungsten trioxide; and the molybdenum source is one or more of ammonium molybdate and molybdenum trioxide.

[0038] The carbon source is one or more of the following: organic acids such as citric acid monohydrate and anhydrous citric acid, or ammonium salts such as diammonium citrate, diammonium hydrogen citrate and triammonium citrate. The carbon source accounts for 1%-30% of the mass of the high-entropy sodium vanadium fluorophosphate cathode material.

[0039] (2) Transfer the transparent sol obtained in step (1) to a high temperature oven and dry it at 60℃-120℃ for 10h-20h to obtain a gel. Grind it for 1h to obtain the precursor powder. (3) The precursor powder obtained in step (2) is sintered at 500℃-800℃ for 2-12h under an inert atmosphere to obtain high-entropy doped sodium vanadium fluorophosphate cathode material. The inert atmosphere is nitrogen or argon, and the gas flow rate is 30-80 mL / min.

[0040] As mentioned above, high-entropy sodium vanadium fluorophosphate cathode materials can be used as active materials to prepare electrode materials for sodium-ion or potassium-ion batteries.

[0041] This invention optimizes the structure through multi-element doping, resulting in a high-entropy doped material that suppresses phosphate impurities in sodium vanadium fluorophosphate cathode material. Furthermore, the defects and lattice distortion introduced by multi-element doping improve conductivity, thereby reducing polarization of the material during cycling. It exhibits a reversible capacity of 100.4 mAh / g at a rate of 0.2C and a voltage of 2.5V-4.3V.

[0042] Example 1 This embodiment uses the sol-gel method to prepare high-entropy doped sodium vanadium fluorophosphate cathode material, with the chemical formula Na3V. 1.9 (VKMgAlTiFeNb) 0.1 / 7 (PO4)2F3 / C.

[0043] According to the stoichiometric ratio, 0.01 mol ammonium dihydrogen phosphate, 0.015 mol sodium fluoride, 0.0067 mol citric acid monohydrate, 0.0096 mol ammonium metavanadate, and 0.00007 mol each of potassium nitrate, magnesium nitrate, aluminum nitrate, tetrabutyl titanate, niobium oxalate, and ammonium molybdate were weighed and dissolved or dispersed in an appropriate amount of deionized water. After dissolving by stirring at room temperature, the mixture was stirred and transferred to an 80℃ water bath for 6 hours to obtain a transparent sol. The transparent sol was then transferred to a high-temperature oven at 120℃ and dried for 10 hours to obtain a gel. The gel was then ground for 1 hour to obtain a precursor powder. The precursor powder was then sintered at 600℃ for 6 hours under an argon atmosphere (50 mL / min) to obtain a high-entropy doped sodium vanadium fluorophosphate cathode material. A coin cell was assembled using metallic sodium as the negative electrode.

[0044] The mass of citric acid monohydrate is approximately 15% of the total mass of the high-entropy doped sodium vanadium fluorophosphate cathode material.

[0045] See Figure 1 XRD analysis showed that the high-entropy sodium vanadium fluorophosphate cathode material prepared in this embodiment exhibited clear structural characteristic peaks of sodium vanadium fluorophosphate, and no characteristic peaks of sodium vanadium phosphate were found, indicating that the prepared high-entropy sodium vanadium fluorophosphate cathode material has high purity and good crystallinity.

[0046] See Figure 2 As can be seen from the CV test analysis, the high-entropy sodium vanadium fluorophosphate cathode material prepared in this embodiment exhibits two pairs of clear redox peaks of sodium vanadium fluorophosphate, but no redox peak of sodium vanadium phosphate is observed. This indicates that multi-component doping can suppress the generation of impurities, and at the same time, multi-component doping improves the conductivity, thereby weakening the polarization of sodium vanadium fluorophosphate material.

[0047] See Figure 3As can be seen from the charge-discharge test analysis, the high-entropy doped sodium vanadium fluorophosphate cathode material prepared in this embodiment has an initial charge-discharge efficiency of about 85% and a discharge specific capacity of about 100mAh / g in a voltage range of 2.5-4.3V and a rate of 0.2C.

[0048] Example 2 This embodiment uses the sol-gel method to prepare high-entropy doped sodium vanadium fluorophosphate cathode material, with the chemical formula Na3V. 1.9 (VNaMgFeZrNbW) 0.1 / 7 (PO4)2F3 / C.

[0049] According to the stoichiometric ratio, 0.01 mol ammonium dihydrogen phosphate, 0.015 mol sodium fluoride, 0.0067 mol citric acid monohydrate, 0.0096 mol ammonium metavanadate, and 0.00007 mol each of sodium acetate, magnesium nitrate, ferric nitrate, zirconium dioxide, niobium pentoxide, and tungsten trioxide were weighed and dissolved or dispersed in an appropriate amount of deionized water. After dissolving by stirring at room temperature, the mixture was transferred to an 80°C water bath and stirred for 6 hours to obtain a transparent sol. The transparent sol was then transferred to a high-temperature oven and dried at 120°C for 10 hours to obtain a gel. The gel was then ground for 1 hour to obtain a precursor powder. The precursor powder was then sintered at 600°C for 6 hours under an argon atmosphere (50 mL / min) to obtain a high-entropy doped sodium vanadium fluorophosphate cathode material. A coin cell was assembled using metallic sodium as the negative electrode.

[0050] The mass of citric acid monohydrate is approximately 15% of the total mass of the high-entropy doped sodium vanadium fluorophosphate cathode material.

[0051] See Figure 4 As can be seen from the CV test analysis, the high-entropy sodium vanadium fluorophosphate cathode material prepared in this embodiment still shows two pairs of clear redox peaks of sodium vanadium fluorophosphate, but no redox peak of sodium vanadium phosphate is present, indicating that multi-element doping can suppress the generation of impurities.

[0052] Example 3 This embodiment uses the sol-gel method to prepare high-entropy sodium vanadium fluorophosphate cathode material, with the chemical formula Na3V. 1.9 (VLiFeAlTiTaMo) 0.1 / 7 (PO4)2F3 / C.

[0053] According to the stoichiometric ratio, 0.01 mol ammonium dihydrogen phosphate, 0.015 mol sodium fluoride, 0.0067 mol citric acid monohydrate, 0.0096 mol ammonium metavanadate, and 0.00007 mol each of lithium nitrate, ferrous oxalate, aluminum nitrate, tetrabutyl titanate, tantalum pentoxide, and molybdenum trioxide were weighed and dissolved or dispersed in an appropriate amount of deionized water. After dissolving at room temperature, the mixture was stirred and then transferred to an 80°C water bath and stirred for 6 hours to obtain a transparent sol. The transparent sol was transferred to a high-temperature oven and dried at 120°C for 10 hours to obtain a gel. The gel was then ground for 1 hour to obtain a precursor powder. The precursor powder was then sintered at 600°C for 6 hours under an argon atmosphere (50 mL / min) to obtain a high-entropy doped sodium vanadium fluorophosphate cathode material. A coin cell was assembled using metallic sodium as the negative electrode.

[0054] The mass of citric acid monohydrate is approximately 15% of the total mass of the high-entropy doped sodium vanadium fluorophosphate cathode material.

[0055] See Figure 5 As can be seen from the CV test analysis, the high-entropy doped sodium vanadium fluorophosphate cathode material prepared in this embodiment still exhibits two pairs of clear redox peaks of sodium vanadium fluorophosphate, but no redox peak of sodium vanadium phosphate appears. This further indicates that multi-element doping can suppress the generation of impurities, which is also one of the conditions for increasing the discharge specific capacity.

[0056] Example 4 This embodiment uses the sol-gel method to prepare high-entropy doped sodium vanadium fluorophosphate cathode material, with the chemical formula Na3V. 1.9 (VNaFeFeTiTaMo) 0.1 / 7 (PO4)2F3 / C.

[0057] According to the stoichiometric ratio, 0.01 mol ammonium dihydrogen phosphate, 0.015 mol sodium fluoride, 0.0067 mol citric acid monohydrate, 0.0096 mol ammonium metavanadate, and 0.00007 mol each of sodium citrate, ferrous oxalate, ferric nitrate, tetrabutyl titanate, tantalum pentoxide, and molybdenum trioxide were weighed and dissolved or dispersed in an appropriate amount of deionized water. After dissolving at room temperature, the mixture was stirred and then transferred to an 80°C water bath and stirred for 6 hours to obtain a transparent sol. The transparent sol was then transferred to a high-temperature oven and dried at 120°C for 10 hours to obtain a gel. The gel was then ground for 1 hour to obtain a precursor powder. The precursor powder was then sintered at 600°C for 6 hours under an argon atmosphere (50 mL / min) to obtain a high-entropy doped sodium vanadium fluorophosphate cathode material. A coin cell was assembled using metallic sodium as the negative electrode.

[0058] The mass of citric acid monohydrate is approximately 15% of the total mass of the high-entropy doped sodium vanadium fluorophosphate cathode material.

[0059] CV testing analysis showed that the high-entropy doped sodium vanadium fluorophosphate cathode material prepared in this embodiment still exhibited two pairs of clear redox peaks of sodium vanadium fluorophosphate, but no redox peak of sodium vanadium phosphate appeared. This further indicates that multi-element doping can suppress the generation of impurities, which is also one of the conditions for increasing the discharge specific capacity.

[0060] Example 5 This embodiment uses the sol-gel method to prepare high-entropy doped sodium vanadium fluorophosphate cathode material, with the chemical formula Na3V. 1.9 (VNaFeFeZrTaMo) 0.1 / 7 (PO4)2F3 / C.

[0061] According to the stoichiometric ratio, 0.01 mol ammonium dihydrogen phosphate, 0.015 mol sodium fluoride, 0.0067 mol citric acid monohydrate, 0.0096 mol ammonium metavanadate, and 0.00007 mol each of sodium nitrate, ferrous oxalate, ferric nitrate, zirconium dioxide, tantalum pentoxide, and molybdenum trioxide were weighed and dissolved or dispersed in an appropriate amount of deionized water. After dissolving at room temperature, the mixture was stirred and then transferred to an 80°C water bath and stirred for 6 hours to obtain a transparent sol. The transparent sol was then transferred to a high-temperature oven and dried at 120°C for 10 hours to obtain a gel. The gel was then ground for 1 hour to obtain a precursor powder. The precursor powder was then sintered at 600°C for 6 hours under an argon atmosphere (50 mL / min) to obtain a high-entropy doped sodium vanadium fluorophosphate cathode material. A coin cell was assembled using metallic sodium as the negative electrode.

[0062] The mass of citric acid monohydrate is approximately 15% of the total mass of the high-entropy doped sodium vanadium fluorophosphate cathode material.

[0063] CV testing analysis showed that the high-entropy doped sodium vanadium fluorophosphate cathode material prepared in this embodiment still exhibited two pairs of clear redox peaks of sodium vanadium fluorophosphate, but no redox peak of sodium vanadium phosphate appeared. This further indicates that multi-element doping can suppress the generation of impurities, which is also one of the conditions for increasing the discharge specific capacity.

[0064] Example 6 This embodiment uses the sol-gel method to prepare high-entropy doped sodium vanadium fluorophosphate cathode material, with the chemical formula Na3V. 1.9 (VKCuCrZrTaMo) 0.1 / 7 (PO4)2F3 / C.

[0065] According to the stoichiometric ratio, 0.01 mol ammonium dihydrogen phosphate, 0.015 mol sodium fluoride, 0.0067 mol citric acid monohydrate, 0.0096 mol ammonium metavanadate, and 0.00007 mol each of potassium nitrate, copper nitrate, chromium nitrate, zirconium dioxide, tantalum pentoxide, and molybdenum trioxide were weighed and dissolved or dispersed in an appropriate amount of deionized water. After dissolving at room temperature, the mixture was stirred and then transferred to an 80°C water bath and stirred for 6 hours to obtain a transparent sol. The transparent sol was then transferred to a high-temperature oven and dried at 120°C for 10 hours to obtain a gel. The gel was then ground for 1 hour to obtain a precursor powder. The precursor powder was then sintered at 600°C for 6 hours under an argon atmosphere (50 mL / min) to obtain a high-entropy doped sodium vanadium fluorophosphate cathode material. A coin cell was assembled using metallic sodium as the negative electrode.

[0066] The mass of citric acid monohydrate is approximately 15% of the total mass of the high-entropy doped sodium vanadium fluorophosphate cathode material.

[0067] CV testing analysis showed that the high-entropy doped sodium vanadium fluorophosphate cathode material prepared in this embodiment still exhibited two pairs of clear redox peaks of sodium vanadium fluorophosphate, but no redox peak of sodium vanadium phosphate appeared. This further indicates that multi-element doping can suppress the generation of impurities, which is also one of the conditions for increasing the discharge specific capacity.

[0068] Example 7 This embodiment uses the sol-gel method to prepare high-entropy doped sodium vanadium fluorophosphate cathode material, with the chemical formula Na3V. 1.9 (VKMgAlTiFeNb) 0.1 / 7 (PO4)2F3 / C.

[0069] According to stoichiometric ratios, weigh out 0.01 mol phosphoric acid (45% by mass), 0.01 mol sodium fluoride, 0.005 mol sodium acetate, anhydrous citric acid, 0.0096 mol vanadium pentoxide, 0.00007 mol potassium fluoride, 0.005 mol ammonium fluoride, 0.00007 mol calcium nitrate, 0.00007 mol basic aluminum acetate, 0.00007 mol titanium dioxide, 0.00007 mol ferric oxide, and 0.00007 mol tetrabutyl titanate. Dissolve or disperse each ingredient separately in an appropriate amount of deionized water. After dissolving by stirring at room temperature, mix the solutions together and transfer them to an 80°C water bath for 6 hours to obtain a transparent sol. Transfer the transparent sol to a high-temperature oven at 120°C and dry for 10 hours to obtain a gel. Then grind the gel for 1 hour to obtain a precursor powder. Finally, place the powder under an argon atmosphere (50°C). High-entropy doped sodium vanadium fluorophosphate cathode material was obtained by high-temperature sintering at 600℃ for 6 hours at a flow rate of mL / min; coin cells were assembled using metallic sodium as the negative electrode.

[0070] The mass of anhydrous citric acid is 1% of the total mass of the high-entropy doped sodium vanadium fluorophosphate cathode material.

[0071] Example 8 This embodiment uses the sol-gel method to prepare high-entropy doped sodium vanadium fluorophosphate cathode material, with the chemical formula Na3V. 1.9 (VKMgAlTiFeNb) 0.1 / 7 (PO4)2F3 / C.

[0072] According to the stoichiometric ratio, weigh out 0.01 mol diammonium hydrogen phosphate, 0.015 mol sodium carbonate, 0.015 mol ammonium fluoride, diammonium citrate, diammonium hydrogen citrate, 0.0096 mol vanadium oxalate, 0.00007 mol potassium carbonate, 0.00007 mol magnesium carbonate, 0.00005 mol aluminum nitrate, 0.00002 mol basic aluminum acetate, 0.00004 mol tetrabutyl titanate, and 0.00003 mol diammonium phosphate. Titanium oxide, 0.00001 mol ferric nitrate, 0.00006 mol ferric oxide, and 0.00007 mol tantalum pentoxide were dissolved or dispersed in an appropriate amount of deionized water, stirred at room temperature, and then mixed together. The mixture was then transferred to a 60°C water bath and stirred for 12 h to obtain a transparent sol. The transparent sol was then transferred to a high-temperature oven and dried at 100°C for 13 h to obtain a gel. The gel was then ground for 1 h to obtain a precursor powder. The precursor powder was then sintered at 500°C for 12 h under an argon atmosphere (60 mL / min) to obtain a high-entropy doped sodium vanadium fluorophosphate cathode material. A coin cell was assembled using metallic sodium as the anode.

[0073] The total mass of ammonium dihydrogen citrate and diammonium hydrogen citrate is 30% of the total mass of the high-entropy doped sodium vanadium fluorophosphate cathode material. The mass ratio of ammonium dihydrogen citrate to diammonium hydrogen citrate is 1:1.

[0074] Example 9 This embodiment uses the sol-gel method to prepare high-entropy doped sodium vanadium fluorophosphate cathode material, with the chemical formula Na3V. 1.9 (VKMgAlTiFeNb) 0.1 / 7 (PO4)2F3 / C.

[0075] According to stoichiometric ratios, weigh out 0.01 mol ammonium phosphate, 0.015 mol sodium nitrate, 0.015 mol ammonium fluoride, triammonium citrate, 0.0046 mol ammonium metavanadate, 0.0056 mol vanadyl oxalate, 0.00007 mol sodium fluoride, 0.00003 mol magnesium acetate, 0.00004 mol potassium acetate, 0.00007 mol aluminum nitrate, 0.00007 mol tetrabutyl titanate, 0.00007 mol niobium oxalate, and 0.00007 mol tungsten trioxide. Dissolve or disperse them separately in appropriate amounts of deionized water, stir at room temperature until dissolved, mix together, transfer to a 120℃ water bath and stir for 5 hours to obtain a transparent sol. Transfer the transparent sol to a high-temperature oven at 70℃ and dry for 15 hours to obtain a gel. Then grind the gel for 1 hour to obtain a precursor powder. Then place it in an argon atmosphere (50 High-entropy doped sodium vanadium fluorophosphate cathode material was obtained by high-temperature sintering at 700℃ for 5 h at a flow rate of mL / min; coin cells were assembled using metallic sodium as the negative electrode.

[0076] The mass of triammonium citrate is 10% of the total mass of the high-entropy doped sodium vanadium fluorophosphate cathode material.

[0077] Example 10 This embodiment uses the sol-gel method to prepare high-entropy doped sodium vanadium fluorophosphate cathode material, with the chemical formula Na3V. 1.9 (VKMgAlTiFeNb) 0.1 / 7 (PO4)2F3 / C.

[0078] According to stoichiometric ratios, weigh out 0.005 mol ammonium dihydrogen phosphate, 0.005 mol ammonium phosphate, 0.015 mol sodium fluoride, citric acid monohydrate, 0.0096 mol ammonium metavanadate, 0.00003 mol lithium carbonate, 0.00004 mol lithium nitrate, 0.00002 mol magnesium nitrate, 0.00005 mol magnesium carbonate, 0.00007 mol aluminum nitrate, 0.00007 mol tetrabutyl titanate, 0.00007 mol ferric nitrate, 0.00007 mol niobium pentoxide, and 0.00007 mol molybdenum trioxide. Dissolve or disperse them separately in appropriate amounts of deionized water, stir at room temperature until dissolved, mix together, transfer to a 100℃ oil bath and stir for 8 hours to obtain a transparent sol; transfer the transparent sol to a high-temperature oven at 60℃ and dry for 20 hours to obtain a gel, then grind the gel for 1 hour to obtain a precursor powder; then place it under a nitrogen atmosphere (80℃). High-entropy doped sodium vanadium fluorophosphate cathode material was obtained by high-temperature sintering at 600℃ for 6 hours at a flow rate of mL / min; coin cells were assembled using metallic sodium as the negative electrode.

[0079] The mass of citric acid monohydrate accounts for 20% of the total mass of the high-entropy doped sodium vanadium fluorophosphate cathode material.

[0080] Example 11 This embodiment uses the sol-gel method to prepare high-entropy doped sodium vanadium fluorophosphate cathode material, with the chemical formula Na3V. 1.9 (VKMgAlTiFeNb) 0.1 / 7 (PO4)2F3 / C.

[0081] According to the stoichiometric ratio, 0.01 mol ammonium dihydrogen phosphate, 0.015 mol sodium fluoride, citric acid monohydrate, 0.0096 mol ammonium metavanadate, and 0.00007 mol each of potassium nitrate, magnesium nitrate, aluminum nitrate, tetrabutyl titanate, ferric nitrate, and tungsten trioxide were weighed and dissolved or dispersed in an appropriate amount of deionized water. After dissolving by stirring at room temperature, the mixture was transferred to a 90℃ water bath and stirred for 10 h to obtain a transparent sol. The transparent sol was then transferred to a high-temperature oven and dried at 120℃ for 10 h to obtain a gel. The gel was then ground for 1 h to obtain a precursor powder. The precursor powder was then sintered at 800℃ for 2 h under an argon atmosphere (30 mL / min) to obtain a high-entropy doped sodium vanadium fluorophosphate cathode material. A coin cell was assembled using metallic sodium as the negative electrode.

[0082] The mass of citric acid monohydrate accounts for 25% of the total mass of the high-entropy doped sodium vanadium fluorophosphate cathode material.

[0083] The above description is only of the preferred embodiment of the present invention and should not be construed as limiting the scope of the claims. The present invention is not limited to the above embodiments, and variations in its specific structure are permitted. All variations made within the scope of the independent claims of the present invention are also within the scope of protection of the present invention.

[0084] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

Claims

1. A high-entropy doped sodium vanadium fluorophosphate cathode material, characterized in that, It includes a positive electrode material layer and a carbon coating layer disposed on the surface of the positive electrode material layer. The general structural formula of the positive electrode material layer is Na3V. 1.9 (VABCDEG) 0.1 / 7 (PO4)2F3 / C, where V is V 3+ A is Li + Na + With K + One or more of them, where B is Mg 2+ Ca 2+ Fe 2+ With Cu 2+ One or more of them, where C is Al 3+ Cr 3+ with Fe 3+ One or more of them, where D is Ti 4+ With Zr 4+ One or two of them, E is Nb 5+ With Ta 5+ One or two of them, G is W 6+ with Mo 6+ One or two of them.

2. The high-entropy doped sodium vanadium fluorophosphate cathode material according to claim 1, characterized in that, The thickness of the carbon coating is 5 nm.

3. The high-entropy doped sodium vanadium fluorophosphate cathode material according to claim 1, characterized in that, A, B, C, D, E and G are doped in equal proportions.

4. A method for preparing a high-entropy doped sodium vanadium fluorophosphate cathode material as described in any one of claims 1-3, characterized in that, Includes the following steps: (1) Dissolve sodium source, vanadium source, phosphorus source, fluorine source, doped metal A source, doped metal B source, doped metal C source, doped metal D source, doped metal E source, doped metal G source and carbon source in deionized water or ethanol respectively, then mix the solutions together and stir under heating to obtain a transparent sol. (2) The transparent sol was dried to obtain a gel, which was then ground to obtain a precursor powder; (3) The precursor powder was sintered in an inert atmosphere to obtain a high-entropy doped sodium vanadium fluorophosphate cathode material.

5. The method for preparing the high-entropy doped sodium vanadium fluorophosphate cathode material according to claim 4, characterized in that, The doping metal A source is a lithium source, a sodium source, or a potassium source; The doping metal B source can be a magnesium source, a calcium source, an iron source, a copper source, or a zinc source; The C source for doping can be aluminum, chromium, iron, or cobalt. The doped metal D source is a titanium source or a zirconium source; The doped metal source (E) is a niobium source or a tantalum source; The doping metal G source is a tungsten source or a molybdenum source; The carbon source is one or more of citric acid monohydrate, anhydrous citric acid, diammonium citrate, diammonium hydrogen citrate, and triammonium citrate.

6. The method for preparing the high-entropy doped sodium vanadium fluorophosphate cathode material according to claim 5, characterized in that, The lithium source is one or more of lithium fluoride, lithium acetate, lithium carbonate and lithium nitrate; The sodium source is one or more of sodium fluoride, sodium acetate, sodium carbonate, and sodium nitrate; The potassium source is one or more of potassium fluoride, potassium acetate, potassium carbonate and potassium nitrate; The vanadium source is one or more of vanadium pentoxide, ammonium metavanadate and vanadium oxalate; The phosphorus source is one or more of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and ammonium phosphate; The fluorine source is one or more of ammonium fluoride and sodium fluoride; The magnesium source is one or more of magnesium nitrate, magnesium carbonate, and magnesium acetate; the calcium source is one or more of calcium nitrate, calcium carbonate, and calcium acetate; the iron source is ferrous oxalate; and the copper source is one or two of copper nitrate and copper oxide. The aluminum source is one or both of aluminum nitrate nonahydrate and basic aluminum acetate; the chromium source is one or both of chromium nitrate and chromium trioxide; the iron source is one or both of ferric nitrate and ferric trioxide. The titanium source is one or both of tetrabutyl titanate and titanium dioxide; the zirconium source in the doped metal D source is zirconium dioxide; The niobium source is one or both of niobium oxalate and niobium pentoxide; the tantalum source is tantalum pentoxide. The tungsten source is tungsten trioxide; the molybdenum source in the doped metal G source is one or more of ammonium molybdate and molybdenum trioxide.

7. The method for preparing the high-entropy doped sodium vanadium fluorophosphate cathode material according to claim 4, characterized in that, The mass of the carbon source is 1%-30% of the mass of the high-entropy sodium vanadium fluorophosphate cathode material.

8. The method for preparing the high-entropy doped sodium vanadium fluorophosphate cathode material according to claim 4, characterized in that, The heating temperature is 60℃-120℃, and the time is 5-12h; the inert atmosphere is nitrogen or argon, and the gas flow rate is 30-80 mL / min.

9. The method for preparing the high-entropy doped sodium vanadium fluorophosphate cathode material according to claim 4, characterized in that, The drying temperature is 60℃-120℃, and the time is 10h-20h.

10. The method for preparing the high-entropy doped sodium vanadium fluorophosphate cathode material according to claim 4, characterized in that, The sintering temperature is 500℃-800℃, and the time is 2-12h.

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