CN115207347A - A kind of titanium-doped vanadium manganese phosphate sodium sodium ion battery cathode material and preparation method thereof - Google Patents

Abstract

The invention discloses a titanium-doped vanadium manganese sodium phosphate sodium ion battery positive electrode material, the chemical formula is Na _3+x MnTi _1-x V _x (PO ₄ ) ₃ , wherein the value range of x is 0.6≤x≤1 , belonging to the rhombus NASICON type structure, the space group is R-3c; the preparation process includes adding sodium source, manganese source, titanium source, vanadium source, ammonium dihydrogen phosphate and citric acid monohydrate into distilled water to obtain a mixed solution; The mixed solution is subjected to magnetic stirring in a constant temperature water bath to form a precursor wet gel; the wet gel is pre-fired after drying, and then fired to obtain a titanium with a chemical formula of Na _3+x MnTi _1-x V _x (PO ₄ ) ₃ Doped vanadium manganese sodium phosphate sodium ion battery positive electrode material; the present invention partially replaces vanadium by titanium in the vanadium manganese sodium phosphate positive electrode material, so that it can maintain a high specific capacity while showing excellent cycle performance and rate performance , extending the service life of the battery, while reducing the amount of toxic and expensive vanadium element, bringing good environmental and economic benefits.

Description

A kind of titanium-doped vanadium manganese phosphate sodium sodium ion battery cathode material and preparation method thereof

technical field

The invention belongs to the technical field of sodium ion batteries, and in particular relates to a positive electrode material of a titanium-doped vanadium manganese sodium phosphate sodium ion battery and a preparation method thereof.

Background technique

At present, my country's energy consumption is serious. In addition to energy conversion, energy storage is another effective way to solve energy consumption. In the development of energy storage devices, lithium-ion batteries are the most widely used energy storage technology. Due to their high energy density and long cycle life, they have been widely used in various portable electronic devices and electric vehicles. However, the limited resources of lithium lead to its high production cost, which cannot meet the growing demand for industrial production, limiting its further application in the field of large-scale energy storage.

Compared with lithium-ion batteries, sodium-ion batteries are rich in sodium resources, low in cost, and high in safety. At the same time, sodium and lithium are in the same main group. The chemical properties of the two are similar, and the working principles are similar, which is convenient for actual production and use. And the reduction potential of sodium is lower than that of lithium, which will bring higher input voltage and energy density, while improving the safety of the battery. In summary, Na-ion batteries can be used as the most promising energy storage compensation materials for Li-ion batteries.

Among them, the performance of cathode materials seriously affects the electrochemical performance of Na-ion batteries. Cathode materials for Na-ion batteries mainly include transition metal layered oxides, Prussian blue analogs, organic compounds and polymers, and polyanionic compounds. However, most of the cathode materials have the disadvantages of low specific capacity, low energy density, short cycle life, poor rate performance, and high cost, which will hinder commercial development and practical application. Therefore, there is an urgent need to develop cathode materials for Na-ion batteries with excellent electrochemical performance to meet commercial development and practical applications.

Among the polyanionic compounds, NASICON-type phosphate compounds have the advantages of stable structure, high ionic conductivity and high voltage platform, and have become a hot research material in the field of sodium-ion batteries. Among them, the sodium vanadium manganese phosphate cathode material has attracted wide attention due to its high specific capacity, but during the charging and discharging process, with the insertion and extraction of sodium ions, the material will undergo an irreversible phase transition, resulting in a rapid decrease in capacity, resulting in its The cycle stability is poor, the rate performance is not ideal, and the vanadium content in the material is high, and the vanadium resources on the earth are not abundant, which will lead to increased production costs, and at the same time, vanadium is also toxic and not friendly to the environment.

Studies have shown that ion doping can effectively improve the electrochemical performance of cathode materials. Therefore, it is urgent to find a suitable ion for doping and modifying the sodium vanadium manganese phosphate cathode material, so that the material has excellent cycle performance and rate performance while maintaining high specific capacity.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a titanium-doped vanadium manganese sodium phosphate sodium ion battery positive electrode material and a preparation method thereof, in which vanadium manganese sodium phosphate positive electrode material is partially replaced by titanium, so that while maintaining a high specific capacity, It exhibits excellent cycle performance and rate performance, prolongs the service life of the battery, reduces the amount of toxic and expensive vanadium elements, and brings good environmental and economic benefits.

In order to achieve the above purpose, the technical solutions are as follows:

A titanium-doped vanadium manganese sodium phosphate sodium ion battery cathode material, the chemical formula is Na _3+x MnTi _1-x V _x (PO ₄ ) ₃ , wherein the value range of x is 0.6≤x≤1, belonging to a rhombus The NASICON-type structure of , the space group is R-3c.

The preparation method of the above-mentioned sodium ion battery cathode material, comprising the following steps:

1) adding sodium source, manganese source, titanium source, vanadium source, ammonium dihydrogen phosphate and citric acid monohydrate into distilled water to obtain a mixed solution;

2) subjecting the mixed solution to magnetic stirring in a constant temperature water bath to form a precursor wet gel;

3) pre-firing the wet gel after drying, and then firing again to obtain a titanium-doped vanadium manganese sodium phosphate sodium ion battery cathode material with a chemical formula of Na _3+x MnTi _1-x V _x (PO ₄ ) ₃ , The value range of x is 0.6≤x≤1.

According to the above scheme, in step 1), the sodium source is anhydrous sodium acetate or sodium carbonate.

According to the above scheme, in step 1), the manganese source is manganese acetate tetrahydrate.

According to the above scheme, in step 1), the titanium source is dihydroxybis(ammonium lactate) titanium or tetrabutyl titanate.

According to the above scheme, in step 1), the vanadium source is ammonium metavanadate or vanadium acetylacetonate.

According to the above scheme, in step 1), the ratio of the amount of the citric acid monohydrate to the sum of the moles of the three elements of manganese, titanium and vanadium in the chemical formula of the obtained target product is 3:2.

According to the above scheme, in step 2), the temperature of magnetic stirring in a constant temperature water bath is 60-90° C., and the stirring time is 2-5h.

According to the above scheme, in step 3), the drying temperature of the wet gel is 100-150° C., and the drying time is 3-6 h.

According to the above scheme, in step 3), the temperature of calcination is 350-400° C., the time of calcination is 3-5h, and the atmosphere of calcination is argon or hydrogen-argon mixture.

According to the above scheme, in step 3), the firing temperature is 600-750° C., the firing time is 10-12 h, and the firing atmosphere is argon or a hydrogen-argon mixture.

Compared with the prior art, the beneficial effects of the present invention are as follows:

The titanium-doped vanadium manganese sodium phosphate sodium ion battery cathode material prepared by the invention belongs to the phosphate polyanion type compound, has a rhombus NASICON type structure, and the space group is R-3c. The material has a stable three-dimensional framework structure and a large ion migration gap that allows the rapid diffusion of large-radius sodium ions, which is conducive to the insertion and extraction of sodium ions during the charging and discharging process, making the volume of the material smaller and increasing the ion diffusion speed. Its diffusion coefficient during discharge is as high as 7.29×10 ^-10 cm ² /s. This enables the material to exhibit excellent cycling performance and rate capability, thus making it a promising cathode material for Na-ion batteries.

In the present invention, vanadium is partially replaced by titanium in sodium vanadium manganese phosphate. In terms of electrochemical performance, the participation of titanium is beneficial to improve the cycle stability of the material. The presence of vanadium maintains the high specific capacity of the sodium vanadium manganese phosphate cathode material. Considering the capacity and stability, the obtained titanium-doped vanadium manganese phosphate The electrochemical performance of the cathode material for Na-Na-ion batteries is good. In terms of cost, the content of titanium on the earth is more than that of vanadium, so the price of titanium is lower than that of vanadium, the industrial production cost is low, and the economic benefit is good. In terms of the environment, titanium is non-toxic, while vanadium is toxic, so adding titanium into sodium vanadium manganese phosphate has good environmental benefits. In conclusion, the prepared titanium-doped sodium vanadium manganese phosphate cathode material has broad prospects for industrial application.

The titanium-doped Na _3.7 MnTi _0.3 V _0.7 (PO ₄ ) ₃ sodium ion battery cathode material prepared by the present invention has most of the particles in irregular shape, and a small part of the particles in approximate spherical shape. The specific surface area of these spherical particles is relatively high. Large, the contact area with the electrolyte is large, which is conducive to the infiltration of the electrolyte and further improves the electrochemical performance of the material.

The sodium ion battery assembled by using the titanium-doped Na _3.7 MnTi _0.3 V _0.7 (PO ₄ ) ₃ sodium ion battery cathode material prepared by the invention has a discharge specific capacity of 79.71mAh/g in the first cycle at a rate of 0.5C, and the cycle is 100 After the cycle, the discharge specific capacity is still 69.19mAh/g, and the capacity retention rate is as high as 86.80%. At high rates of 5C and 10C, the discharge specific capacities are as high as 64.11mAh/g and 56.02mAh/g, respectively. The cathode material exhibits high specific capacity, excellent cycling performance and outstanding rate capability.

The experimental method of the invention is simple, the operability is strong, the raw materials are abundant and easy to obtain, the cost is low, the invention is environmentally friendly, and has a huge commercial application prospect.

Description of drawings

Figure 1: X-ray diffraction pattern of the positive electrode material Na _3.7 MnTi _0.3 V _0.7 (PO ₄ ) ₃ obtained in Example 1.

Figure 2: Scanning electron microscope image of the positive electrode material Na _3.7 MnTi _0.3 V _0.7 (PO ₄ ) ₃ obtained in Example 1.

Fig. 3: The cycle performance diagram of the cathode material Na _3.7 MnTi _0.3 V _0.7 (PO ₄ ) ₃ obtained in Example 1 at a rate of 0.5C.

Figure 4: The rate performance diagram of the cathode material Na _3.7 MnTi _0.3 V _0.7 (PO ₄ ) ₃ obtained in Example 1 at a rate of 0.1C-10C.

Detailed ways

In order to make those skilled in the art fully understand the technical solutions and beneficial effects of the present invention, further description is given below in conjunction with specific embodiments. The following embodiments are only used to explain the present invention, and the protection scope of the present invention is not limited thereto.

Unless otherwise stated, all the technical terms used in the following embodiments have the same meaning as those generally understood by those skilled in the art, and the technical terms used in the present invention are only for the purpose of clearly describing the embodiments, rather than the protection scope of the present invention. limit.

Unless otherwise specified, all raw materials, chemical reagents, instruments, equipment, etc. used in the present invention can be purchased through conventional commercial channels.

In the specific embodiment, a titanium-doped vanadium manganese sodium phosphate sodium ion battery cathode material is provided, and its chemical formula is Na _3+x MnTi _1-x V _x (PO ₄ ) ₃ , wherein the value range of x is 0.6≤ x≤1, belonging to the rhombus NASICON type structure, the space group is R-3c.

In the specific embodiment, the preparation method of the above-mentioned sodium-ion battery cathode material is provided:

1) adding sodium source, manganese source, titanium source, vanadium source, ammonium dihydrogen phosphate and citric acid monohydrate into distilled water to obtain a mixed solution;

2) subjecting the mixed solution to magnetic stirring in a constant temperature water bath to form a precursor wet gel;

3) drying the wet gel and pre-firing, and then firing again to obtain a titanium-doped vanadium manganese sodium phosphate sodium ion battery cathode material with a chemical formula of Na _3+x MnTi _1-x V _x (PO ₄ ) ₃ .

Specifically, the sodium source described in step 1) is anhydrous sodium acetate or sodium carbonate.

Specifically, the manganese source described in step 1) is manganese acetate tetrahydrate.

Specifically, the titanium source in step 1) is dihydroxybis(ammonium lactate) titanium or tetrabutyl titanate.

Specifically, the vanadium source described in step 1) is ammonium metavanadate or vanadium acetylacetonate.

Specifically, the ratio of the amount of citric acid monohydrate described in step 1) to the sum of the moles of the three elements of manganese, titanium and vanadium in the chemical formula of the target product is 3:2.

Specifically, in step 2), the temperature of magnetic stirring in a constant temperature water bath is 60-90° C., and the stirring time is 2-5 h.

Specifically, in step 3), the drying temperature of the wet gel is 100-150° C., and the drying time is 3-6 h.

Specifically, in step 3), the calcination temperature is 350-400° C., the calcination time is 3-5 h, and the calcination atmosphere is argon or a hydrogen-argon mixture.

Specifically, in step 3), the firing temperature is 600-750° C., the firing time is 10-12 h, and the firing atmosphere is argon or a hydrogen-argon mixture.

The specific embodiment also provides a sodium ion battery, the sodium ion battery uses the above-mentioned titanium-doped vanadium manganese phosphate sodium sodium ion battery cathode material, and its electrochemical performance is tested by the LAND test system. The prepared sodium ion battery positive electrode material is uniformly mixed with a conductive agent and a binder according to an appropriate mass ratio, coated on an aluminum foil, and dried to obtain a sodium ion battery positive electrode sheet. The conductive agent and the binder can be materials commonly used by those skilled in the art, and the method used for assembling the sodium ion battery adopts the methods commonly used by those skilled in the art.

Specifically, the prepared sodium-ion battery positive electrode material, acetylene black conductive agent, and polyvinylidene fluoride binder are ground and mixed in a mass ratio of 7:2:1, and then N methyl pyrrolidone solvent is added thereto to obtain a uniform The slurry is coated on aluminum foil, and after drying, it is cut out by a punching machine to obtain a positive electrode sheet. The metal sodium sheet was used as the counter electrode, 1M NaClO ₄ (EC: PC=1: 1 Vol%, the additive was 5% FEC) was used as the electrolyte, and the CR2032 battery shell was used to assemble a button half-cell for electrochemical performance testing. The voltage range is 2.5-3.8V.

Example 1

A method for preparing a positive electrode material for a titanium-doped vanadium manganese sodium phosphate sodium ion battery. According to the stoichiometric ratio of Na:Mn:Ti:V=3.7:1:0.3:0.7, CH ₃ COONa, (CH ₃ COO) ₂ Mn·4H ₂ O, C ₁₆ H ₃₆ O ₄ Ti, NH ₄ VO ₃ are for standby use, and the specific steps are as follows:

1) Mix the weighed CH ₃ COONa, (CH ₃ COO) ₂ Mn·4H ₂ O, C ₁₆ H ₃₆ O ₄ Ti, NH ₄ VO ₃ , NH ₄ H ₂ PO ₄ and C ₆ H ₈ O ₇ · H ₂ O was added to 80 mL of distilled water to obtain a mixed solution;

2) magnetically stir the mixed solution obtained in step 1) in a constant temperature water bath at 80°C for 3 hours to obtain a precursor wet gel;

3) Dry the wet gel obtained in step 2) in a drying oven at a drying temperature of 120° C. and a drying time of 5 hours to obtain a dry gel, grind it into powder, and place it in a muffle furnace for pre-burning and pre-heating. The firing temperature is 350 °C, the pre-firing time is 5 h, and the pre-firing atmosphere is a mixture of hydrogen and argon. Then, the pre-firing materials are placed in a muffle furnace for firing. The firing temperature is 650 ° C and the firing time is 12 hours. , the firing atmosphere is a mixture of hydrogen and argon, and finally a cathode material for a sodium ion battery with a chemical formula of Na _3.7 MnTi _0.3 V _0.7 (PO ₄ ) ₃ is obtained.

Fig. 1 is the X-ray diffraction pattern of the prepared Na _3.7 MnTi _0.3 V _0.7 (PO ₄ ) ₃ sodium ion battery positive electrode material. It can be seen from Fig. 1 that the obtained material is indeed Na _3.7 MnTi _0.3 V _0.7 (PO ₄ ) ₃ sodium The positive electrode material of ion battery belongs to the rhombic NASICON type structure, and the space group is R-3c. The prepared material has few impurities and high purity. At the same time, its diffraction peak intensity is high, and its half-peak width is small, indicating that its crystallinity is good.

Fig. 2 is a scanning electron microscope image of the positive electrode material of Na _3.7 MnTi _0.3 V _0.7 (PO ₄ ) ₃ sodium ion battery. It can be seen from Fig. 2 that the particle size of the obtained positive electrode material is between 1-10 μm, and the shape of most of the particles is between 1 and 10 μm. Irregular, a small part of the particles are approximately spherical in shape. These spherical particles have a larger specific surface area and a larger contact area with the electrolyte, which is conducive to the infiltration of the electrolyte, which is beneficial to improve the electrochemical performance of the material.

The Na _3.7 MnTi _0.3 V _0.7 (PO ₄ ) ₃ sodium-ion battery positive electrode material prepared in this example was used to make an electrode sheet, and the metal sodium sheet was used as a counter electrode to assemble a button battery, and passed the LAND test system with 0.5C. The cycle performance of the button battery was tested at the rate. The test results are shown in Figure 3. According to Figure 3, at a rate of 0.5C, the discharge specific capacity in the first cycle reached 79.71mAh/g, and after 100 cycles, the discharge specific capacity was still as high as 69.19 mAh/g, the capacity retention rate is 86.80%, and the cycle performance of the material is excellent.

Figure 4 shows the rate performance test results of a button battery assembled with Na _3.7 MnTi _0.3 V _0.7 (PO ₄ ) ₃ sodium ion battery cathode material. It can be seen from Figure 4 that the discharge specific capacity is as high as 64.11mAh/g at a rate of 5C , Under the rate of 10C, the discharge specific capacity can still reach 56.02mAh/g, and the rate performance of the material is excellent.

Example 2

A method for preparing a positive electrode material for a titanium-doped vanadium manganese sodium phosphate sodium ion battery. According to the stoichiometric ratio of Na:Mn:Ti:V=3.6:1:0.4:0.6, CH ₃ COONa, (CH ₃ COO) ₂ Mn·4H ₂ O, C ₁₆ H ₃₆ O ₄ Ti, NH ₄ VO ₃ are for standby use, and the specific steps are as follows:

1) Mix the weighed CH ₃ COONa, (CH ₃ COO) ₂ Mn·4H ₂ O, C ₁₆ H ₃₆ O ₄ Ti, NH ₄ VO ₃ , NH ₄ H ₂ PO ₄ and C ₆ H ₈ O ₇ · H ₂ O was added to 80 mL of distilled water to obtain a mixed solution;

2) The mixed solution obtained in step 1) is placed in a constant temperature water bath at 60°C for 5h with magnetic stirring to obtain a precursor wet gel;

3) Dry the wet gel obtained in step 2) in a drying oven at a drying temperature of 100° C. and a drying time of 6 hours to obtain a dry gel, grind it into powder, and place it in a muffle furnace to pre-fire it. The firing temperature is 350°C, the pre-firing time is 5h, the pre-firing atmosphere is a mixture of hydrogen and argon, and then the pre-fired material is placed in a muffle furnace for firing, the firing temperature is 600°C, and the firing time is 12h , the firing atmosphere is a mixture of hydrogen and argon, and finally a sodium-ion battery cathode material with a chemical formula of Na _3.6 MnTi _0.4 V _0.6 (PO ₄ ) ₃ is obtained.

The Na _3.6 MnTi _0.4 V _0.6 (PO ₄ ) ₃ sodium ion battery positive electrode material prepared in this example was made into an electrode sheet, and the metal sodium sheet was used as a counter electrode to assemble a button battery, and its electrochemical performance was tested by the LAND test system. , the test results show that at the rate of 0.5C, the material has a discharge specific capacity of 62.34mAh/g in the first cycle, and after 100 cycles, the discharge specific capacity still reaches 56.63mAh/g, and the capacity retention rate reaches 90.84%; at 5C and 10C At the high rate of , the discharge specific capacity reaches 49.74mAh/g and 41.63mAh/g, respectively. The cathode material exhibits high specific capacity and good cycle performance and rate performance.

Example 3

A method for preparing a positive electrode material for a titanium-doped vanadium manganese sodium phosphate sodium ion battery. According to the stoichiometric ratio of Na:Mn:Ti:V=3.9:1:0.1:0.9, CH ₃ COONa, (CH ₃ COO) ₂ Mn·4H ₂ O, C ₁₆ H ₃₆ O ₄ Ti, NH ₄ VO ₃ are for standby use, and the specific steps are as follows:

1) Mix the weighed CH ₃ COONa, (CH ₃ COO) ₂ Mn·4H ₂ O, C ₁₆ H ₃₆ O ₄ Ti, NH ₄ VO ₃ , NH ₄ H ₂ PO ₄ and C ₆ H ₈ O ₇ · H ₂ O was added to 80 mL of distilled water to obtain a mixed solution;

2) The mixed solution obtained in step 1) was placed in a constant temperature water bath at 70°C and magnetically stirred for 4 hours to obtain a precursor wet gel;

3) Dry the wet gel obtained in step 2) in a drying oven at a drying temperature of 130° C. and a drying time of 4 hours to obtain a dry gel, grind it into powder, and place it in a muffle furnace for pre-burning. The firing temperature is 400 °C, the pre-firing time is 3 hours, and the pre-firing atmosphere is a mixture of hydrogen and argon. After that, the pre-fired material is placed in a muffle furnace for firing. The firing temperature is 700 ° C and the firing time is 10 hours. , the firing atmosphere is a mixture of hydrogen and argon, and finally a sodium-ion battery cathode material with a chemical formula of Na _3.9 MnTi _0.1 V _0.9 (PO ₄ ) ₃ is obtained.

The Na _3.9 MnTi _0.1 V _0.9 (PO ₄ ) ₃ sodium ion battery cathode material prepared in this example was used to make an electrode sheet, and the metal sodium sheet was used as a counter electrode to assemble a button battery, and its electrochemical performance was tested by the LAND test system. , the test results show that at the rate of 0.5C, the material has a discharge specific capacity of 92.76mAh/g in the first cycle, and after 100 cycles, the discharge specific capacity still reaches 68.42mAh/g, and the capacity retention rate reaches 73.76%; at 5C and 10C Under the high rate of , the discharge specific capacity reaches 51.53mAh/g and 43.69mAh/g, respectively. The cathode material exhibits high specific capacity and good cycle performance and rate performance.

Example 4

A method for preparing a positive electrode material for a titanium-doped vanadium manganese sodium phosphate sodium ion battery. According to the stoichiometric ratio of Na:Mn:V=4:1:1, CH ₃ COONa and (CH ₃ COO) ₂ Mn are weighed. · 4H ₂ O, NH ₄ VO ₃ are reserved, the specific steps are as follows:

1) Add the weighed CH ₃ COONa, (CH ₃ COO) ₂ Mn·4H ₂ O, NH ₄ VO ₃ , NH ₄ H ₂ PO ₄ and C ₆ H ₈ O ₇ ·H ₂ O to 80 mL of distilled water , to obtain a mixed solution;

2) The mixed solution obtained in step 1) is placed in a 90°C constant temperature water bath for magnetic stirring for 2h to obtain a precursor wet gel;

3) Dry the wet gel obtained in step 2) in a drying oven at a drying temperature of 150° C. and a drying time of 3 hours to obtain a dry gel, grind it into powder, and place it in a muffle furnace for pre-burning and pre-heating. The firing temperature is 400 °C, the pre-firing time is 3 h, and the pre-firing atmosphere is a mixture of hydrogen and argon. After that, the pre-firing material is placed in a muffle furnace for firing. The firing temperature is 750 ° C and the firing time is 10 hours. , the firing atmosphere is a mixture of hydrogen and argon, and finally a positive electrode material for a sodium ion battery with a chemical formula of Na ₄ MnV(PO ₄ ) ₃ is obtained.

The Na ₄ MnV(PO ₄ ) ₃ sodium ion battery positive electrode material prepared in this example was made into an electrode sheet, and the metal sodium sheet was used as the counter electrode to assemble a button battery, and its electrochemical performance was tested by the LAND test system. The test results It is shown that at the rate of 0.5C, the material has a discharge specific capacity of 94.64mAh/g in the first cycle, and after 100 cycles, the discharge specific capacity still reaches 81.06mAh/g, and the capacity retention rate reaches 85.65%; at high rates of 5C and 10C , the discharge specific capacities reached 70.58mAh/g and 49.67mAh/g, respectively. The cathode material exhibits high specific capacity and good cycle performance and rate performance.

The above are only the preferred embodiments of the present invention. It should be pointed out that for those skilled in the art, various changes and improvements can be made without departing from the principles of the present invention. It should be regarded as the protection scope of the present invention.

Claims (10)

1. The titanium-doped sodium vanadium manganese phosphate positive electrode material for the ion battery is characterized by having a chemical formula of Na _3+x MnTi _1-x V _x (PO ₄ ) ₃ Wherein x is more than or equal to 0.6 and less than or equal to 1, belongs to a rhombus NASICON type structure, and has a space group of R-3c.

2. The method for preparing the positive electrode material of the sodium-ion battery according to claim 1, which is characterized by comprising the following steps:

1) Adding a sodium source, a manganese source, a titanium source, a vanadium source, ammonium dihydrogen phosphate and citric acid monohydrate into distilled water to obtain a mixed solution;

2) Performing magnetic stirring on the mixed solution in a constant-temperature water bath to form precursor wet gel;

3) Drying the wet gel, pre-sintering, and then sintering to obtain the chemical formula of Na _3+x MnTi _1-x V _x (PO ₄ ) ₃ The positive electrode material for sodium ion batteries.

3. The method for preparing the positive electrode material for the sodium-ion battery according to claim 2, wherein the sodium source in the step 1) is anhydrous sodium acetate or sodium carbonate.

4. The method for preparing the positive electrode material of the sodium-ion battery according to claim 2, wherein the manganese source in the step 1) is manganese acetate tetrahydrate.

5. The method for preparing the positive electrode material for the sodium-ion battery according to claim 2, wherein the titanium source in the step 1) is dihydroxy bis (ammonium lactate) titanium or tetrabutyl titanate.

6. The method for preparing the positive electrode material of the sodium-ion battery according to claim 2, wherein the vanadium source in the step 1) is ammonium metavanadate or vanadium acetylacetonate.

7. The method for preparing the positive electrode material of the sodium-ion battery according to claim 2The method is characterized in that the citric acid monohydrate in the step 1) is used in combination with the chemical formula Na _3+x MnTi _1-x V _x (PO ₄ ) ₃ The ratio of the sum of the mole numbers of the three elements of medium manganese, titanium and vanadium is 3:2.

8. the method for preparing the positive electrode material of the sodium-ion battery according to claim 2, wherein the temperature of the thermostatic waterbath magnetic stirring in the step 2) is 60-90 ℃, and the stirring time is 2-5h.

9. The method for preparing the positive electrode material of the sodium-ion battery according to claim 2, wherein the drying temperature of the wet gel in the step 3) is 100-150 ℃, and the drying time is 3-6h.

10. The preparation method of the sodium-ion battery cathode material as claimed in claim 2, wherein the pre-sintering temperature in the step 3) is 350-400 ℃, the pre-sintering time is 3-5h, and the pre-sintering atmosphere is argon or hydrogen-argon mixed gas; the sintering temperature is 600-750 ℃, the sintering time is 10-12h, and the sintering atmosphere is argon or a hydrogen-argon mixed gas.

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