Double-layer coated sodium vanadium phosphate positive electrode material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of battery materials, and relates to a double-layer coated sodium vanadium phosphate positive electrode material as well as a preparation method and application thereof. The invention provides the double-layer coated sodium vanadium phosphate positive electrode material, the innovative design of the double-layer coated sodium vanadium phosphate positive electrode material remarkably improves the performance of the existing aqueous battery, and particularly provides an effective solution for the problems of short cycle life and low capacity of the traditional aqueous battery. The novel positive electrode material is composed of a sodium vanadium phosphate inner core, an aluminum oxide coating layer and a carbon coating layer, the electrochemical performance of the sodium vanadium phosphate inner core is further optimized by doping metal, so that the material not only has higher structural stability, but also can effectively improve the charge-discharge efficiency and capacity.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery materials, and relates to a double-layer coated sodium vanadium phosphate positive electrode material and a preparation method and application thereof. BACKGROUND

[0002] Water-based Na-Zn hybrid ion batteries have attracted extensive attention due to their potential application in the energy storage field due to their high voltage and large capacity. This type of battery combines the advantages of sodium ions and zinc ions, has high safety, environmental friendliness and low cost, and is therefore considered as an important candidate for the next generation of green energy storage technology.

[0003] However, due to the decomposition voltage limit of water (<1.23V), the traditional aqueous electrolyte system cannot support the stable operation of high-potential positive electrode materials and low-potential negative electrode materials, resulting in that the working voltage of the aqueous battery is generally lower than 1.5V, which seriously restricts the improvement of the energy density and the development of the practical application. To break this bottleneck, researchers have begun to explore new positive electrode materials with higher redox potential and excellent structural stability. Among them, polyanion compound Na3V2(PO4)3(NVP) has attracted much attention due to its unique three-dimensional channel framework structure and rich vacancies in the lattice. This structure not only endows the material with good ion diffusion dynamics, but also enables it to maintain high structural stability and safety during repeated charge and discharge. In addition, the induction effect of polyanions helps to improve the redox potential of transition metal ions, which is expected to improve the overall working voltage of the battery. Based on these advantages, the NVP / Zn battery system has gradually become a research hotspot in the field of aqueous hybrid ion batteries.

[0004] However, although NVP exhibits many excellent properties, the system still faces the problem of insufficient cycle stability, which is mainly limited by the structural degradation of the positive electrode material during long-term operation. Studies have shown that the main reasons for the capacity decay of NVP positive electrode include: first, the oxidation reaction of the electrolyte on the surface of the positive electrode induces the dissolution of transition metal ions (such as V), which in turn induces the structural reorganization of the material surface, hindering the normal diffusion of Na + ; second, during the charge and discharge process, oxygen in the NVP lattice may be released, causing further oxidation of the electrolyte and reduction of transition metals, affecting the coulombic efficiency; finally, the transition metal oxides on the surface of the NVP crystal may peel off, exacerbating the occurrence of interface side reactions, ultimately leading to material failure.

[0005] The existence of these problems seriously affects the cycle life and practical application prospect of NVP / Zn batteries. Therefore, how to enhance the stability of NVP positive electrode through material design, surface modification or electrolyte optimization, and inhibit the above-mentioned adverse reactions, has become a key issue for promoting the practical application of water-based Na-Zn hybrid ion batteries. SUMMARY

[0006] The present application aims at the above-mentioned problems existing in the prior art, and provides a double-layer coated sodium vanadium phosphate positive electrode material suitable for aqueous electrolyte, which realizes a water-based hybrid ion battery with excellent cycle performance, rate performance and high capacity.

[0007] The object of the present application can be achieved by the following technical solutions.

[0008] A double-layer coated sodium vanadium phosphate positive electrode material, comprising: a sodium vanadium phosphate core, an aluminum oxide coating layer coated on the sodium vanadium phosphate core, and a carbon coating layer coated on the aluminum oxide coating layer, wherein the chemical formula of the sodium vanadium phosphate core is Na3V 2-x M x (PO4)3, M is at least one of doped metals including K, Mg, Cu, Zn, Al and Zr, and x=0.01-0.5.

[0009] The Al2O3 coating layer adopted in the present application is rigid, which can effectively prevent the corrosion of the positive electrode material and stabilize the material structure, and the carbon coating layer can improve the electrical conductivity of the material and provide a stable chemical and electrochemical reaction interface. However, Al2O3 is intrinsically non-conductive, which is not conducive to the high rate performance of the battery. Therefore, the double-layer coated positive electrode material with the inner Al2O3 coating and the outer carbon coating can realize the structural stability and high conductivity of the NVP material.

[0010] In the above-mentioned double-layer coated sodium vanadium phosphate positive electrode material, the thickness ratio of the carbon coating layer to the aluminum oxide coating layer is 1:(0.3-2), wherein the thickness of the aluminum oxide coating layer is 2-6 nm, and the thickness of the carbon coating layer is 2-4 nm.

[0011] The thickness of the coating layer needs to be controlled. If the thickness of the aluminum oxide and carbon coating layer is too thick, the capacity of the positive electrode material will be reduced, the impedance of the ion transmission process will be increased, and the rate performance of the battery will be reduced. If the thickness of the coating layer is too thin, it is difficult to form uniform coating in the process, and it is difficult to inhibit the side reaction at the NVP / electrolyte interface, which leads to the dissolution of transition metals, which is not conducive to the structural stability and cycle stability.

[0012] The present application also provides a preparation method of the above-mentioned double-layer coated sodium vanadium phosphate positive electrode material, which comprises the following steps:

[0013] S1. Dissolving vanadium salt, sodium salt, phosphate salt, doped metal salt and carbon source in a solvent for spray drying to obtain a powder precursor;

[0014] S2. Dispersing the powder precursor in an ammonium bicarbonate aqueous solution, then adding a carbon source to obtain a mixed solution, and then adding an Al(NO3)3 solution for stirring, and then washing, drying and calcining to obtain an Al2O3-coated positive electrode material;

[0015] S3. The Al2O3-coated cathode material and carbon source are mixed and then sintered to obtain a double-layer coated sodium vanadium phosphate cathode material.

[0016] In the above-mentioned method for preparing a double-layer coated sodium vanadium phosphate cathode material

[0017] The vanadium salt is at least one of ammonium metavanadate, vanadium pentoxide, vanadium hydroxide, and vanadium oxalate;

[0018] And / or, the sodium salt is at least one of sodium carbonate, sodium dihydrogen phosphate, sodium bicarbonate, sodium hydroxide, sodium acetate, sodium oxalate, and sodium phosphate;

[0019] And / or, the phosphate is at least one of the following: ammonium dihydrogen phosphate, diammonium hydrogen phosphate, dipotassium hydrogen phosphate, disodium hydrogen phosphate, ammonium phosphate, phosphoric acid, sodium phosphate, and potassium phosphate;

[0020] And / or, the doped metal salt includes at least one of potassium carbonate, potassium oxalate, magnesium nitrate, copper nitrate, zinc acetate, aluminum nitrate, and zirconium hydroxide;

[0021] And / or, the carbon source includes at least one of glucose, citric acid, acrylic acid, isopropanol, tartaric acid, polyethylene glycol, polyaniline, methylurea, and thiourea. In the above-described method for preparing a double-layer coated sodium vanadium phosphate cathode material, the spray drying inlet air temperature is 120-150℃, and the outlet air temperature is 80-100℃.

[0022] In the above-mentioned method for preparing a double-layer coated sodium vanadium phosphate cathode material, the concentration of Al(NO3)3 solution in step S2 is 1-5wt%, the mass ratio of Al(NO3)3 solution to powder precursor is 10-200:1, and the temperature of the mixed solution is 55-65℃ when Al(NO3)3 solution is added.

[0023] This invention requires controlling the amount of Al(NO3)3 added, because the amount of Al(NO3)3 added directly affects the coating thickness and uniformity. Too much addition leads to an excessively thick coating, which reduces the battery rate performance. If the coating layer is too thin, it is difficult to form a uniform coating in the process, which is not conducive to structural stability and cycle stability.

[0024] In the above-mentioned method for preparing a double-layer coated sodium vanadium phosphate cathode material, the calcination temperature in step S2 is 700-800℃, and the time is 1-5 hours. This invention employs a high-temperature treatment method of calcination at 700-800℃ for 1-5 hours. Simultaneously, the precursor undergoes a solid-phase reaction to form NVP, while the aluminum salt adsorbed on the precursor surface is fully decomposed and an alumina (Al2O3) coating layer is generated in situ. This calcination process can form a uniformly coated NVP material with Al2O3 in a single calcination, and also effectively removes residual organic matter and volatile impurities, improving the density and stability of the coating layer. Heat treatment within this temperature range can enhance the interfacial bonding force between Al2O3 and the NVP matrix, thereby improving the material's corrosion resistance in the electrolyte, inhibiting the dissolution of transition metal ions, and reducing the occurrence of interfacial side reactions. Furthermore, an appropriate calcination time helps to form a stable Al2O3-coated NVP material with excellent ion transport characteristics, thereby improving the material's cycle life and coulombic efficiency, and further enhancing the chemical and electrochemical stability of the cathode material.

[0025] In the above-mentioned method for preparing a double-layer coated sodium vanadium phosphate cathode material, the mass ratio of the Al2O3 coated cathode material to the carbon source in step S3 is 1-16:1.

[0026] This invention ensures a suitable outer carbon coating thickness by strictly controlling the mass ratio of Al2O3-coated cathode material to carbon source to be 1-16:1. If the carbon source ratio is too high, the carbon coating layer will be too thick, hindering the absorption of Na+. + Ion diffusion within electrode materials reduces their actual capacity; conversely, an insufficient carbon source ratio prevents the formation of a continuous and dense conductive network, affecting electronic conductivity and leading to decreased rate performance and deteriorated cycle stability. Therefore, appropriately controlling the amount of carbon source added can not only maintain high specific capacity while ensuring good conductivity, but also effectively mitigate structural damage caused by volume changes during charge and discharge, thereby enhancing the long-term cycle stability of the material.

[0027] In the above-mentioned method for preparing a double-layer coated sodium vanadium phosphate cathode material, the sintering temperature in step S3 is 550-650℃, and the time is 1-5 hours. In this invention, the sintering temperature is controlled at 550-650℃ for 1-5 hours. Within this temperature range, the carbon source undergoes an ordered carbonization process, forming a well-structured carbon layer with excellent conductivity, which tightly covers the Al2O3 coating layer, constructing a stable double-layer protective structure. Appropriate sintering temperature can avoid the adverse effects of incomplete carbon coking or excessive graphitization, thereby obtaining a carbon coating layer with high conductivity and good adhesion, while reducing the impact of secondary calcination on the activity of the cathode material. This uniform and dense carbon layer not only effectively improves the electronic conductivity of the material and promotes rapid charge transport, but also further isolates the active material from direct contact with the electrolyte, reduces interfacial side reactions, and improves the overall electrochemical performance and safety of the battery.

[0028] The present invention also provides an application of the above-mentioned double-layer coated sodium vanadium phosphate cathode material in an aqueous energy storage battery.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1. This invention provides a double-layer coated sodium vanadium phosphate cathode material, whose innovative design significantly improves the performance of existing aqueous batteries, particularly offering an effective solution to the problems of short cycle life and low capacity in traditional aqueous batteries. This novel cathode material consists of a sodium vanadium phosphate core, an alumina coating layer, and a carbon coating layer. The sodium vanadium phosphate core is further optimized for electrochemical performance through metal doping, resulting in material with not only higher structural stability but also effectively improved charge / discharge efficiency and capacity.

[0031] 2. This invention utilizes an alumina coating layer as the inner layer, with a thickness controlled between 2-6 nm, providing rigid support and helping to maintain the structural integrity of the entire material during multiple charge-discharge cycles, thereby greatly improving the cycle stability and lifespan of the battery. Simultaneously, the outer carbon coating layer, with a thickness of 2-4 nm, significantly enhances the electronic conductivity of sodium vanadium phosphate (NVP) due to its excellent electrical properties, allowing the battery to maintain good performance output even under high-rate conditions. Furthermore, the thickness ratio between the carbon coating layer and the alumina coating layer is precisely controlled at 1:(0.3-2), ensuring that the material possesses both sufficient mechanical strength and an efficient electronic transport path.

[0032] 3. This invention employs spray drying technology to prepare the precursor and completes the double-layer coating through two calcination processes. This method not only simplifies the production process but also ensures the uniformity and consistency of the coating layer, further guaranteeing the stability of material performance. Compared to traditional single-layer coated or uncoated cathode materials, the double-layer coating strategy provided by this invention effectively solves the structural degradation problem that easily occurs in NVP materials during long-term cycling in electrolytes, reduces the occurrence of interfacial side reactions, and improves the coulombic efficiency and safety of the battery. Especially for aqueous hybrid-ion batteries, this improvement significantly enhances the overall performance of the battery, achieving the goals of long cycle life, excellent rate performance, and high capacity.

[0033] 4. This invention cleverly combines the advantages of alumina and carbon to effectively modify sodium vanadium phosphate cathode material through double-layer coating. This not only overcomes the main shortcomings of traditional aqueous batteries, but also significantly improves the energy density and application potential of the battery, providing strong technical support for future efficient and environmentally friendly energy storage devices. Attached Figure Description

[0034] Figure 1 Comparison of rate performance of aqueous sodium-zinc hybrid ion batteries between Example 1 and Comparative Example 3;

[0035] Figure 2 Comparison of cycle performance of aqueous sodium-zinc hybrid ion batteries between Example 1 and Comparative Example 2;

[0036] Figure 3 Comparison of AC impedance of aqueous sodium-zinc hybrid ion batteries between Example 2 and Comparative Example 1;

[0037] Figure 4 The present invention provides a schematic diagram of the energy storage principle of an aqueous sodium-zinc hybrid ion battery. Detailed Implementation

[0038] The following are specific embodiments of the present invention, which further describe the technical solution of the present invention, but the present invention is not limited to these embodiments.

[0039] Example 1:

[0040] This embodiment provides a method for preparing a double-layer coated sodium vanadium phosphate cathode material:

[0041] S1. Dissolve sodium carbonate, ammonium metavanadate, and ammonium dihydrogen phosphate in an aqueous solution containing 50 wt% ethanol, wherein the solid content is 7% (W / W). Then add magnesium nitrate and citric acid to obtain a mixed solution, wherein the molar ratio of sodium in sodium carbonate, vanadium in ammonium metavanadate, phosphorus in ammonium dihydrogen phosphate, magnesium in magnesium nitrate, and citric acid is 2.95:2:3:0.02:0.5.

[0042] S2. The mixed solution was spray-dried using a spray drying method with an inlet temperature of 130℃ and an outlet temperature of 90℃. After sieving, the NVP precursor was obtained.

[0043] S3. Disperse 2g of NVP precursor into 20mL of 0.1M ammonium bicarbonate aqueous solution, add 0.3g of polyacrylic acid, stir and heat to 60℃, add 20mL of Al(NO3)3 solution (concentration 3wt%) and continue stirring for 4h, filter, wash, dry and calcine in a tube furnace at 750℃ for 3h under nitrogen atmosphere to obtain Al2O3 coated cathode material sample;

[0044] S4. Disperse 2g of Al2O3-coated cathode material sample into 20ml of 5wt% citric acid aqueous solution, add 2g of polyethylene glycol and stir. After filtration, sinter at 600℃ for 2 hours in an inert atmosphere to obtain a double-layer coated sodium vanadium phosphate cathode material, wherein the thickness of the alumina coating layer is about 2.5nm and the thickness of the carbon coating layer is about 3.8nm.

[0045] Example 2:

[0046] S1. Dissolve sodium carbonate, ammonium metavanadate, and ammonium dihydrogen phosphate in an aqueous solution containing 60 wt% ethanol, then add copper nitrate and citric acid to obtain a mixed solution with a solid content of 9% (w / w). The molar ratio of sodium in sodium carbonate, vanadium in ammonium metavanadate, phosphorus in ammonium dihydrogen phosphate, copper in copper nitrate, and citric acid is 2.96:2:3:0.03:1.

[0047] S2. The mixed solution was spray-dried using a spray drying method with an inlet temperature of 130℃ and an outlet temperature of 90℃. After sieving, the NVP precursor was obtained.

[0048] S3. Disperse 1g of NVP precursor into 20ml of 0.2M ammonium bicarbonate aqueous solution, add 1g of polyacrylic acid, stir and heat to 70℃, add 20ml of Al(NO3)3 solution (4wt%) and continue stirring for 4h, filter, wash, dry and calcine in a tube furnace at 750℃ for 3h under nitrogen atmosphere to obtain Al2O3 coated cathode material sample;

[0049] S4. Disperse 1g of Al2O3-coated cathode material sample into 20ml of 1wt% citric acid aqueous solution, add 0.5g of polyethylene glycol and stir. After filtration, sinter at 600℃ for 2 hours in an inert atmosphere to obtain a double-layer coated sodium vanadium phosphate cathode material, wherein the thickness of the alumina coating layer is about 3nm and the thickness of the carbon coating layer is about 3nm.

[0050] Example 3:

[0051] S1. Dissolve sodium carbonate, ammonium metavanadate, and ammonium dihydrogen phosphate in an aqueous solution containing 50 wt% ethanol, then add zinc acetate and glucose to obtain a mixed solution, wherein the molar ratio of sodium in sodium carbonate, vanadium in ammonium metavanadate, phosphorus in ammonium dihydrogen phosphate, zinc in zinc acetate, and glucose is 2.96:2:3:0.025:0.8;

[0052] S2. The mixed solution was spray-dried using a spray drying method with an inlet temperature of 130℃ and an outlet temperature of 90℃. After sieving, the NVP precursor was obtained.

[0053] S3. Disperse 1g of NVP precursor into 20ml of 0.2M ammonium bicarbonate aqueous solution, add 0.5g of polyacrylic acid, stir and heat to 60℃, add 20ml of Al(NO3)3 solution (5wt%) and continue stirring for 6h, filter, wash, dry and calcine in a tube furnace at 750℃ for 3h under nitrogen atmosphere to obtain Al2O3 coated cathode material sample;

[0054] S4. Disperse 1g of Al2O3-coated cathode material sample into 20ml of 1wt% citric acid aqueous solution, add 1.5g of polyethylene glycol and stir. After filtration, sinter at 600℃ for 2 hours in an inert atmosphere to obtain a double-layer coated sodium vanadium phosphate cathode material, wherein the thickness of the alumina coating layer is about 6nm and the thickness of the carbon coating layer is about 7nm.

[0055] Example 4:

[0056] The only difference from Example 1 is that the carbon coating thickness is 10 nm.

[0057] Example 5:

[0058] The only difference from Example 1 is that the carbon coating thickness is 0.5 nm.

[0059] Example 6:

[0060] The only difference from Example 1 is that the thickness of the alumina coating is 8 nm.

[0061] Example 7:

[0062] The only difference from Example 1 is that the thickness of the alumina coating is 0.5 nm.

[0063] Example 8:

[0064] The only difference from Example 1 is that the polyacrylic acid was not heated to 60°C after being added in step S3.

[0065] Example 9:

[0066] The only difference from Example 1 is that the calcination temperature in step S3 is 650°C.

[0067] Example 10:

[0068] The only difference from Example 1 is that the calcination temperature in step S3 is 900°C.

[0069] Example 11:

[0070] The only difference from Example 1 is that step S3 does not involve calcination, but only drying.

[0071] Example 12:

[0072] The only difference from Example 1 is that the sintering temperature in step S4 is 300°C.

[0073] Example 13:

[0074] The only difference from Example 1 is that the sintering temperature in step S4 is 800°C.

[0075] Comparative Example 1:

[0076] The only difference from Example 1 is that the coating layer is only an alumina coating layer.

[0077] Comparative Example 2:

[0078] The only difference from Example 1 is that the coating layer is only a carbon coating layer.

[0079] Comparative Example 3:

[0080] The difference from Example 1 is that the outer coating layer is an alumina coating layer and the inner coating layer is a carbon coating layer. The specific preparation includes the following steps:

[0081] Oxalic acid (11.3459 g), sodium fluoride (2.5193 g), vanadium pentoxide (4.6010 g), and ammonium dihydrogen phosphate (3.6376 g) were dissolved in deionized water and stirred at 60 °C to form a gel. After drying, the gel was pre-calcined at 350 °C for 6 hours under a nitrogen atmosphere to obtain a precursor. 0.45 g of glucose was added to 5 g of the precursor, ball-milled for 2 hours, dried in an oven at 50 °C, and sintered at 700 °C for 10 hours under a nitrogen atmosphere. The resulting material was then ground and sieved to obtain the NVPF / C cathode material. Take 1g of NVPF / C and add it to 50ml of deionized water. Sonicate for 40 minutes and stir to form a black suspension. Then add 0.01g of aluminum nitrate nonahydrate Al(NO3)3·9H2O. At 60℃, add ammonia water NH3·H2O and stir for 1.5 hours. After filtration, washing, and drying, sinter in a tube furnace at 600℃ for 2 hours. After sieving, obtain alumina and carbon composite coated sodium vanadium fluorophosphate cathode material.

[0082] The positive electrode materials prepared in Examples 1-13 and Comparative Examples 1-3 were mixed with acetylene black and polyvinylidene fluoride (PVDF) at a mass ratio of 75:15:10 to form a slurry, which was then coated onto a stainless steel mesh and dried to obtain the positive electrode sheet for an aqueous Na-Zn mixed-ion battery. Then, using a three-electrode system, the charge-discharge curves of the mixed-ion battery, positive electrode, and negative electrode were tested using the positive electrode material, zinc sheet, and silver chloride as a reference. Using a two-electrode system, the cycle stability of the aqueous battery was tested by assembling a full cell with the positive electrode material, zinc sheet, and sodium-zinc mixed-ion electrolyte.

[0083] The preparation method of the aqueous sodium-zinc mixed ion electrolyte is as follows:

[0084] 1. Prepare a zinc ion electrolyte according to the ratio of zinc perchlorate hexahydrate to urea = 1:3; prepare a sodium ion electrolyte according to the ratio of sodium perchlorate monohydrate to urea to water = 1:1:3; mix the zinc ion electrolyte to sodium ion electrolyte in a ratio of 1:30 to obtain an aqueous sodium-zinc mixed ion electrolyte (NZU).

[0085] 2. Prepare a zinc ion electrolyte according to the ratio of zinc perchlorate hexahydrate: dimethyl sulfone = 1:3; prepare a sodium ion electrolyte according to the ratio of sodium perchlorate monohydrate: dimethyl sulfone: water = 1:1:2; mix the zinc ion electrolyte and sodium ion electrolyte according to the ratio of 1:25 to obtain an aqueous sodium-zinc mixed ion electrolyte (NZM).

[0086] 3. Prepare a 2M zinc sulfate solution; prepare a 2M sodium sulfate electrolyte; mix them according to the ratio of zinc ions: sodium ions = 1:20 to obtain an aqueous sodium-zinc mixed ion electrolyte (NZS).

[0087] The above-mentioned positive electrode material, zinc negative electrode and electrolyte were assembled into a coin cell. The whole cell was charged and discharged at a rate of 1.5C within a voltage range of 0.8V-1.8V.

[0088] Table 1: Electrochemical performance of aqueous sodium-zinc hybrid ion batteries prepared using the cathode materials of Examples 1-13 and Comparative Examples 1-3

[0089]

[0090] Figure 1 Comparison of rate performance of aqueous sodium-zinc hybrid ion batteries in Example 1 and Comparative Example 3; As can be seen from the figure, the order of alumina and carbon coating directly affects the rate performance of the material, and the aqueous battery in Example 1 with rigid alumina coating on the inner layer and carbon coating on the outer layer has higher stability than the aqueous battery in Comparative Example 3 with carbon coating on the inner layer and alumina coating on the outer layer constructed from NVP / Zn.

[0091] Figure 2Comparison of cycle performance of aqueous sodium-zinc hybrid ion batteries in Example 1 and Comparative Example 2; As can be seen from the figure, the stability of the double-layer coated NVP cathode material in Example 1 is higher than that of the carbon-coated material in Comparative Example 2.

[0092] Figure 3 Comparison of AC impedance of aqueous sodium-zinc hybrid ion batteries in Example 2 and Comparative Example 1; As can be seen from the figure, the outer carbon coating can effectively reduce the interfacial impedance of alumina-coated NVP.

[0093] Figure 4 Example 1 of the present invention: Schematic diagram of the energy storage principle of an aqueous sodium-zinc hybrid ion battery; As can be seen from the figure, zinc dissolution and deposition occur at the negative electrode, and sodium-zinc hybrid ion deintercalation reaction occurs at the positive electrode. In the NZM electrolyte, sodium ion deintercalation is more likely.

[0094] In summary, this invention employs spray drying technology to prepare the precursor and completes the double-layer coating through two calcination processes. This method not only simplifies the production process but also ensures the uniformity and consistency of the coating layer, further guaranteeing the stability of material performance. Compared to traditional single-layer coated or uncoated cathode materials, the double-layer coating strategy provided by this invention effectively solves the structural degradation problem that easily occurs in NVP materials during long-term cycling in electrolytes, reduces the occurrence of interfacial side reactions, and improves the coulombic efficiency and safety of the battery. Especially for aqueous hybrid-ion batteries, this improvement significantly enhances the overall performance of the battery, achieving the goals of long cycle life, excellent rate performance, and high capacity.

[0095] The embodiments described herein cover any points not exhaustively within the scope of the technical claims of this invention, as well as new technical solutions formed by equivalent substitutions of one or more technical features in the embodiments. These are all within the scope of the claims of this invention. Furthermore, in all listed or unlisted embodiments of this invention, each parameter in the same embodiment merely represents an instance (i.e., a feasible solution) of its technical solution, and there is no strict coordination or limitation relationship between the parameters. The parameters can be substituted for each other without violating axioms and the claims of this invention, unless otherwise stated.

[0096] The technical means disclosed in this invention are not limited to those described above, but also include technical solutions composed of any combination of the above technical features. The above descriptions are specific embodiments of this invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications are also considered within the scope of protection of this invention.

[0097] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A double-layer coated sodium vanadium phosphate cathode material, characterized in that, The cathode material comprises: a sodium vanadium phosphate core, an alumina coating layer covering the sodium vanadium phosphate core, and a carbon coating layer covering the alumina coating layer, wherein the general chemical formula of the sodium vanadium phosphate core is Na3V. 2-x M x (PO4)3, M is a doped metal including at least one of K, Mg, Cu, Zn, Al, and Zr, and x = 0.01-0.

5.

2. The double-layer coated sodium vanadium phosphate cathode material according to claim 1, characterized in that, The thickness ratio of the carbon coating layer to the alumina coating layer is 1:(0.3-2), wherein the thickness of the alumina coating layer is 2-6 nm and the thickness of the carbon coating layer is 2-4 nm.

3. A method for preparing the double-layer coated sodium vanadium phosphate cathode material as described in any one of claims 1-2, characterized in that, The method includes the following steps: S1. Vanadium salt, sodium salt, phosphate, doped metal salt and carbon source are dissolved in a solvent and spray-dried to obtain a powder precursor; S2. The powdered precursor is dispersed in an ammonium bicarbonate aqueous solution, then a carbon source is added to obtain a mixture, and then an Al(NO3)3 solution is added and stirred. After washing and drying, the mixture is calcined to obtain an Al2O3-coated cathode material. S3. The Al2O3-coated cathode material and carbon source are mixed and then sintered to obtain a double-layer coated sodium vanadium phosphate cathode material.

4. The method for preparing a double-layer coated sodium vanadium phosphate cathode material according to claim 3, characterized in that, The vanadium salt is at least one of ammonium metavanadate, vanadium pentoxide, vanadium hydroxide, and vanadium oxalate; And / or, the sodium salt is at least one of sodium carbonate, sodium dihydrogen phosphate, sodium bicarbonate, sodium hydroxide, sodium acetate, sodium oxalate, and sodium phosphate; And / or, the phosphate is at least one of the following: ammonium dihydrogen phosphate, diammonium hydrogen phosphate, dipotassium hydrogen phosphate, disodium hydrogen phosphate, ammonium phosphate, phosphoric acid, sodium phosphate, and potassium phosphate; And / or, the doped metal salt includes at least one of potassium carbonate, potassium oxalate, magnesium nitrate, copper nitrate, zinc acetate, aluminum nitrate, and zirconium hydroxide; And / or, the carbon source includes at least one of glucose, citric acid, acrylic acid, isopropanol, tartaric acid, polyethylene glycol, polyaniline, methylurea, and thiourea.

5. The method for preparing a double-layer coated sodium vanadium phosphate cathode material according to claim 3, characterized in that, The inlet air temperature for spray drying is 120-150℃, and the outlet air temperature is 80-100℃.

6. The method for preparing a double-layer coated sodium vanadium phosphate cathode material according to claim 3, characterized in that, In step S2, the concentration of Al(NO3)3 solution is 1-5wt%, the mass ratio of Al(NO3)3 solution to powder precursor is 10-200:1, and the temperature of the mixture is 55-65℃ when Al(NO3)3 solution is added.

7. The method for preparing a double-layer coated sodium vanadium phosphate cathode material according to claim 3, characterized in that, The calcination temperature in step S2 is 700-800℃, and the time is 1-5h.

8. The method for preparing a double-layer coated sodium vanadium phosphate cathode material according to claim 3, characterized in that, In step S3, the mass ratio of the Al2O3-coated cathode material to the carbon source is 1-16:

1.

9. A method for preparing a double-layer coated sodium vanadium phosphate cathode material according to claim 3, characterized in that, The sintering temperature in step S3 is 550-650℃, and the time is 1-5h.

10. The application of the double-layer coated sodium vanadium phosphate cathode material as described in claim 1 in an aqueous energy storage battery.

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