Preparation method and application of high-capacity modified sodium manganese pyrophosphate positive electrode material for sodium-ion battery

Abstract

The invention relates to a high-capacity modified sodium manganese pyrophosphate positive electrode material of a sodium ion battery and a preparation method and application thereof, the preparation method comprises the following steps: adding sodium acetate trihydrate, manganese acetate tetrahydrate, ammonium dihydrogen phosphate and boric acid or silicon dioxide into deionized water to prepare a mixed solution, adding citric acid monohydrate, and uniformly stirring to obtain a precursor solution; sending the precursor solution to a spray dryer by using a peristaltic pump, and carrying out spray drying under the pressure of 2Bar to obtain a boron or silicon modified sodium manganese pyrophosphate precursor material; and placing the precursor material in an alumina crucible, placing the alumina crucible in a box-type furnace or a tube furnace, and carrying out heat treatment at 600 DEG C in an argon atmosphere to obtain the boron or silicon modified sodium manganese pyrophosphate material. The sodium manganese pyrophosphate-rich positive electrode material obtained through boron or silicon modification has the electrochemical sodium storage capacity superior to that of most sodium manganese pyrophosphate, and the use performance and effect of a sodium ion battery are improved.

Description

Technical Field

[0001] The present invention relates to the field of cathode materials for sodium-ion batteries, and specifically to a preparation method and application of a high-capacity modified sodium manganese pyrophosphate cathode material for sodium-ion batteries. Background Art

[0002] Sodium-ion batteries, as a monovalent battery technology similar to lithium-ion batteries, are gradually becoming strong competitors to lithium-ion batteries due to their rich sodium resource reserves and significant cost advantages. Currently, the application fields of sodium-ion batteries mainly focus on small and medium-sized electric vehicles in cities, short-distance transportation vehicles, and large-scale energy storage systems, etc. These fields have relatively low requirements for energy density, but have higher requirements for cost-effectiveness and practical application needs.

[0003] Sodium manganese pyrophosphate, as a polyanionic cathode material, exhibits great application potential. Its unique variable valence ability of transition metal Mn ions enables the material to achieve the intercalation and deintercalation process of two sodium ions, thus having theoretical advantages of high specific capacity and energy density and structural stability. Sodium manganese pyrophosphate has significant advantages as a cathode material for sodium-ion batteries.

[0004] However, the redox reaction of the Na 2 MnP 2 O 7 cathode material is restricted by its high thermodynamic stability and poor kinetics. The Na 2 MnP 2 O 7 has a large band gap, located in the insulating region (5 eV), resulting in poor electronic conductivity; although it has a three-dimensional sodium ion diffusion path, the diffusion coefficient is low; due to the induction of the polyanion group in the structure, its redox reaction potential is high. These factors greatly affect the electrochemical performance of the material, especially the specific capacity. Currently, the actually reported capacity of the Na 2 MnP 2 O 7 cathode material is far lower than its theoretical specific capacity (195 mAh / g). For example, after the research team of Professor Jiao Lifang from Nankai University improved its electronic conductivity by compounding graphene, the discharge specific capacity was 93 mAh / g (Energy Storage Mater., 16(2019)383–390); the Korea Institute of Science and Technology pointed out that the corner-sharing characteristics in the triclinic crystal structure had an initial discharge specific capacity of about 90 mAh / g at 0.05C (J.Am.Chem.Soc.135,(2013),2787-2792). Currently, the publicly disclosed Na 2 MnP 2 O 7The discharge specific capacity of the cathode material is also relatively low. Sodium manganese pyrophosphate 201711118657.8 discloses that after component modification, Na 6.24 Mn 4.88 (P 2 O 7 ) 4 The initial discharge specific capacity of the cathode material is only 96.8 mAh / g. It can be seen from this that although the electron conductivity and ionic conductivity have been greatly improved by means such as doping and carbon coating, the specific capacity is still relatively low. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a high-capacity modified sodium manganese pyrophosphate cathode material for sodium-ion batteries prepared by modifying sodium manganese pyrophosphate with silicon or boron, and its preparation method.

[0006] The present invention synthesizes a high-capacity sodium manganese pyrophosphate cathode material suitable for sodium-ion batteries through a simple process suitable for industrial production. According to the crystal structure analysis results, the material has a triclinic crystal structure p-1. The material has a relatively high actual specific capacity (>140 mAh / g). There is no literature reporting the existence of this type of material and its application in sodium-ion battery cathode materials; the synthesis method and application of the sodium manganese pyrophosphate cathode material suitable for industrial production provided by the present invention are very meaningful works.

[0007] The technical solution of the present invention is as follows:

[0008] A preparation method of a high-capacity sodium manganese pyrophosphate cathode material for sodium-ion batteries, and the specific preparation process is as follows:

[0009] (1) Prepare a precursor solution

[0010] Sodium acetate trihydrate, manganese acetate tetrahydrate, ammonium dihydrogen phosphate and boric acid or silicon dioxide are added to deionized water as raw materials according to a molar ratio of 2:1:(1-x):x to prepare a mixed solution, and then citric acid monohydrate is added according to a molar ratio of 1:1 to manganese acetate tetrahydrate, and stirred evenly to obtain a precursor solution;

[0011] (2) Prepare a precursor material

[0012] The precursor solution is sent to a spray dryer by a peristaltic pump. The temperature at the inlet of the spray dryer is 200°C to 300°C, the outlet temperature is 100°C, and spray drying is carried out under a pressure of 2 Bar to obtain a boron- or silicon-modified sodium manganese pyrophosphate precursor material;

[0013] (3) Preparation of boron- or silicon-modified sodium manganese pyrophosphate material

[0014] Place the precursor material in an alumina crucible, place the alumina crucible in a box furnace or a tube furnace, and heat-treat it at 600 °C for 2 h to 6 h under an argon atmosphere to obtain a boron- or silicon-modified sodium manganese pyrophosphate material.

[0015] Furthermore, the molar ratio of sodium acetate trihydrate, manganese acetate tetrahydrate, ammonium dihydrogen phosphate, and boric acid or silicon dioxide is 2:1:0.98:0.02.

[0016] Furthermore, the raw materials are sodium acetate trihydrate, manganese acetate tetrahydrate, ammonium dihydrogen phosphate, and boric acid.

[0017] Furthermore, the molar volume ratio of manganese acetate tetrahydrate to deionized water is 0.15 mol / L.

[0018] Furthermore, the heating rate of the heat treatment is 3 °C / min, and the heat treatment time is 3 h.

[0019] Furthermore, the stirring time in step (2) is 2 h.

[0020] Furthermore, the inlet temperature of the spray dryer is 200 °C.

[0021] Another object of the present invention is to provide the application of the high-capacity sodium manganese pyrophosphate cathode material prepared by the above preparation method as a cathode material for a sodium-ion battery.

[0022] The beneficial effects of the present invention:

[0023] The synthesis method is simple. By using boron or silicon element with an electronegativity lower than that of phosphorus element, through a one-step spray drying method combined with heat treatment, the uniform reaction of metal salts, phosphates, and sodium ions is quickly carried out, and a composite material in which a boron- or silicon-modified sodium manganese pyrophosphate material powder is in-situ coated with conductive carbon is formed, with good dispersibility and a particle size of 50 nm. Secondly, after introducing B or Si into the sodium manganese pyrophosphate structure, not only the unit cell parameter is increased, the (0-22) crystal plane grows preferentially, and the diffusion of sodium ions is promoted, but also it is beneficial to reduce the thermodynamic induction effect, lower the redox potential, and further promote the realization of a multi-electron transfer reaction, realizing the high specific capacity.

[0024] The sodium-ion battery prepared from the boron-modified sodium manganese pyrophosphate material in the present invention has a specific capacity as high as 166.37 mAh / g at a current density of 0.02C. The sodium manganese pyrophosphate-rich cathode material obtained by boron or silicon modification in the present invention has better electrochemical sodium storage capacity than most sodium manganese pyrophosphates, improving the performance and effect of the sodium-ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is the XRD pattern of the sodium manganese pyrophosphate cathode material prepared by the present invention (corresponding to the comparative example, Example 1, and Example 2);

[0026] Figure 2 It is the TG-DSC diagram of the boron-modified sodium manganese pyrophosphate cathode material prepared in the present invention (corresponding to Example 1);

[0027] Figure 3 It is the XPS diagram of the boron-modified sodium manganese pyrophosphate cathode material and the silicon-modified sodium manganese pyrophosphate cathode material prepared in the present invention (corresponding to Example 1 and Example 2);

[0028] Figure 4 It is the C1s XPS diagram of the sodium manganese pyrophosphate cathode material prepared in the present invention (corresponding to the comparative example, Example 1 and Example 2);

[0029] Figure 5 It is the SEM diagram of the sodium manganese pyrophosphate cathode material prepared in the present invention (corresponding to the comparative example, Example 1 and Example 2);

[0030] Figure 6 It is the TEM diagram of the boron-modified sodium manganese pyrophosphate cathode material and the silicon-modified sodium manganese pyrophosphate cathode material prepared in the present invention (corresponding to Example 1 and Example 2);

[0031] Figure 7 It is the EDS element distribution diagram of the boron-modified sodium manganese pyrophosphate cathode material prepared in the present invention (corresponding to Example 1);

[0032] Figure 8 It is the EDS element distribution diagram of the silicon-modified sodium manganese pyrophosphate cathode material prepared in the present invention (corresponding to Example 2);

[0033] Figure 9 It is the charge-discharge curve diagram of the sodium manganese pyrophosphate cathode material prepared in the present invention (corresponding to the comparative example, Example 1 and Example 2). Detailed implementation mode

[0034] The principles and features of the present invention will be described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention. For those conditions not specified in the examples, they shall be carried out according to the conventional conditions or the conditions recommended by the manufacturer. For those reagents or instruments whose manufacturers are not indicated, they are all conventional products that can be obtained through commercial purchase.

[0035] Example 1

[0036] (1) According to sodium manganese pyrophosphate as Na 2 Mn(P 2 O 7 )0.98(BO 3 ) 0.02Ingredients are prepared according to the stoichiometric ratio, with sodium in excess by 5% to compensate for sodium loss during high-temperature sintering. Weigh 42.8652 g of sodium acetate trihydrate, 36.7635 g of manganese acetate tetrahydrate, 33.81 g of ammonium dihydrogen phosphate, and 0.1854 g of boric acid. Dissolve them in 1 L of deionized water, and add 31.52 g of citric acid monohydrate. Mechanically stir for 2 hours at room temperature to obtain a boron-containing precursor solution;

[0037] (2) Use a peristaltic pump to send the precursor solution to a spray dryer. The inlet temperature of the spray dryer is 200 °C, the outlet temperature is 100 °C, and spray drying is carried out under a pressure of 2 Bar to obtain a precursor material;

[0038] (3) Place the precursor material in an alumina crucible with a diameter of 50 mm and a length of 100 mm. Place the alumina crucible in a tube furnace, fill it with argon as a protective gas, and heat it at a heating rate of 3 °C·min -1 Heat up, and heat-treat for 3 h at 600 °C in an argon atmosphere to obtain a boron-modified sodium manganese pyrophosphate cathode material.

[0039] Example 2

[0040] (1) According to sodium manganese pyrophosphate as Na 2 Mn(P 2 O 7 ) 0.98 (SiO 4 ) 0.02 Ingredients are prepared according to the stoichiometric ratio, with sodium in excess by 5% to compensate for sodium loss during high-temperature sintering. Weigh 42.8652 g of sodium acetate trihydrate, 36.7635 g of manganese acetate tetrahydrate, 33.81 g of ammonium dihydrogen phosphate, and 0.1802 g of silicon dioxide. Dissolve them in 1 L of deionized water, and add 31.52 g of citric acid monohydrate. Mechanically stir for 2 hours at room temperature to obtain a silicon-containing precursor solution;

[0041] (2) Use a peristaltic pump to send the precursor solution to a spray dryer. The inlet temperature of the spray dryer is 200 °C, the outlet temperature is 100 °C, and spray drying is carried out under a pressure of 2 Bar to obtain a precursor material;

[0042] (3) Place the precursor material in an alumina crucible with a diameter of 50 mm and a length of 100 mm. Place the alumina crucible in a tube furnace, fill it with argon as a protective gas, and heat it at a heating rate of 3 °C·min -1 Heat up, and heat-treat for 3 h at 600 °C in an argon atmosphere to obtain a silicon-modified sodium manganese pyrophosphate cathode material.

[0043] Comparative Example

[0044] (1) According to sodium manganese pyrophosphate as Na 2Mn(P 2 O 7 ) 0.98 The ingredients were prepared according to the stoichiometric ratio, wherein the sodium content was 5% in excess to compensate for the sodium loss during the high-temperature sintering process. 42.8652 g of sodium acetate trihydrate, 36.7635 g of manganese acetate tetrahydrate and 34.509 g of ammonium dihydrogen phosphate were weighed and dissolved in 1 L of deionized water, and 31.52 g of citric acid monohydrate was added; the mixture was mechanically stirred at room temperature for 2 hours to obtain a precursor solution;

[0045] (2) using a peristaltic pump to deliver the precursor solution to a spray dryer, the inlet temperature of the spray dryer is 200° C., the outlet temperature is 100° C., and the precursor solution is spray dried at a pressure of 2 Bar to obtain a precursor material;

[0046] (3) The precursor material is placed in an alumina crucible with a diameter of 50 mm and a length of 100 mm. The alumina crucible is placed in a tube furnace and filled with argon as a protective gas at 3 °C min -1 The temperature was increased at a heating rate and heat treated at 600°C for 3 h in an argon atmosphere to obtain a sodium manganese pyrophosphate positive electrode material.

[0047] 1. XRD test of Example 1, Example 2 and Comparative Example of the present invention

[0048] XRD test was performed on the sodium manganese pyrophosphate positive electrode material, boron-modified sodium manganese pyrophosphate positive electrode material and silicon-modified sodium manganese pyrophosphate positive electrode material prepared in the comparative example, Example 1 and Example 2 of the present invention, and the average structure of the sodium manganese pyrophosphate positive electrode material of the comparative example, the boron-modified sodium manganese pyrophosphate positive electrode material of Example 1 and the silicon-modified sodium manganese pyrophosphate positive electrode material of Example 2 was tested. The results are as follows Figure 1 As shown, the positions and relative intensities of the X-ray diffraction peaks are similar to those of Na 2 MnP 2 O 7 The standard card 019-089-8448 is consistent with that of the standard card 019-089-8448, proving that high-purity triclinic system P-1 space group with good crystallinity Na 2 MnP 2 O 7 It is worth noting that after the introduction of B or Si, no species containing these elements were detected, proving that B / Si elements enter Na 2 MnP 2 O 7 In the crystal structure. From the local map, it can be seen that after the introduction of B or Si elements, the peak shifts slightly to the left, the unit cell parameters increase, and the (-120) peak intensity decreases, while the (0-22) peak intensity increases, resulting in preferential growth, which is beneficial to the diffusion dynamics of sodium ions.

[0049] 2. TG-DSC test of Example 1 of the present invention

[0050] The TG-DSC test was carried out on the boron-modified sodium pyrophosphate manganese cathode material prepared in Example 1 to observe the content of in-situ composite conductive carbon in the sodium pyrophosphate manganese cathode material. The results are as Figure 2 shown. In an air atmosphere, during the TG-DSC test with a heating rate of 10 °C / min to 600 °C, it was found that 11.57 wt% of the weight loss corresponded to the process of carbon material decomposing into carbon dioxide, indicating that the citric acid monohydrate added during the preparation of this cathode material was in-situ converted into conductive carbon during the heat treatment in an argon atmosphere, and the weight ratio was 11.57 wt%, which was beneficial to the electron transfer of the material during the electrochemical process.

[0051] III. XPS test of Example 1, Example 2 and Comparative Example of the present invention

[0052] The XPS test was carried out on the sodium pyrophosphate manganese cathode materials prepared in Example 1 and Example 2 of the present invention to test the modified element B1s, Si 2p and C1s spectra of the sodium pyrophosphate manganese cathode material. The results are as Figure 3 shown. From Figure 3 it can be seen that Figure 3 (a) and Figure 3 (b) provided the XPS signal peaks of B and Si elements detected in the sodium pyrophosphate manganese cathode material. Combining with the XRD test that no species containing these elements were detected, it was further proved that B and Si elements could enter the crystal structure of the sodium pyrophosphate manganese cathode material, and thus played a role in changing the thermodynamics and kinetics of the material.

[0053] Figure 4 In the middle is the XPS spectrum of C element of Example 1, Example 2 and Comparative Example of the present invention; from Figure 4 it can be seen that there are three obvious diffraction peaks in the figure, representing C-C, C-O and C═O chemical bonds respectively. Compared with the sodium pyrophosphate manganese material, the boron-modified sodium pyrophosphate manganese material or the silicon-modified sodium pyrophosphate manganese material has more C-O bonds, indicating that the in-situ composite conductive carbon binds stronger to the sodium pyrophosphate manganese.

[0054] IV. SEM test of Example 1, Example 2 and Comparative Example of the present invention

[0055] The SEM test was carried out on the sodium pyrophosphate manganese cathode materials prepared in Comparative Example, Example 1 and Example 2 of the present invention to observe the morphology and size of the sodium pyrophosphate manganese cathode material. The results are as Figure 5 shown; from Figure 5 it can be seen that the boron-modified sodium pyrophosphate manganese cathode material of Example 1 and the silicon-modified sodium pyrophosphate manganese cathode material of Example 2 of the present invention have smooth surfaces and uniform sizes.

[0056] V. TEM Tests on the Boron-Modified Sodium Manganese Pyrophosphate Cathode Material of Example 1 and the Silicon-Modified Sodium Manganese Pyrophosphate Cathode Material of Example 2 of the Present Invention

[0057] TEM tests were carried out on the boron-modified sodium manganese pyrophosphate cathode material of Example 1 and the silicon-modified sodium manganese pyrophosphate cathode material of Example 2 of the present invention to observe the morphology and size of the sodium manganese pyrophosphate cathode material. The results are as Figure 6 shown; from Figure 6 it can be seen that the boron-modified sodium manganese pyrophosphate cathode material of Example 1 and the silicon-modified sodium manganese pyrophosphate cathode material of Example 2 of the present invention have smooth surfaces and uniform sizes, about 50 nm.

[0058] VI. TEM Tests on the Boron-Modified Sodium Manganese Pyrophosphate Cathode Material of Example 1 and the Silicon-Modified Sodium Manganese Pyrophosphate Cathode Material of Example 2 of the Present Invention

[0059] EDS tests were carried out on the boron-modified sodium manganese pyrophosphate cathode material of Example 1 and the silicon-modified sodium manganese pyrophosphate cathode material of Example 2 of the present invention to observe the elemental distribution of the sodium manganese pyrophosphate cathode material. The results are as Figure 7 and 8 shown; from Figure 7 and Figure 8 it can be seen that the elements Na, Mn, P, and O in the boron-modified sodium manganese pyrophosphate cathode material of Example 1 and the silicon-modified sodium manganese pyrophosphate cathode material of Example 2 of the present invention are evenly distributed. The B element in the boron-modified sodium manganese pyrophosphate cathode material of Example 1 of the present invention also shows a uniform distribution. Combining with the generation of B-containing heterophase in XRD, it shows that it evenly enters the structure of the material. Similarly, the Si element in the silicon-modified sodium manganese pyrophosphate cathode material of Example 2 also shows a uniform distribution. Combining with the fact that no Si heterophase is detected in XRD, it shows that it evenly enters the structure of the material.

[0060] VII. Electrochemical Performance Tests on Example 1, Example 2, and Comparative Example of the Present Invention

[0061] (I) Assembly of CR2025 Stainless Steel Button Sodium-Ion Batteries

[0062] (1) Preparation of the Positive Electrode Sheet

[0063] Weigh the cathode material (prepared in the comparative example or Example 1 or Example 2), Super P, and CMC according to a mass ratio of 70:20:10 and place them in a ball milling jar (where CMC is added in the form of an aqueous CMC solution). The mass concentration of the aqueous CMC solution is 1.2 wt%. Add tungsten carbide ball milling beads, and the mass ratio of balls to materials in the ball milling jar is 20:1. After ball milling for 6 h, coat it on an aluminum foil using a 0.1 μm doctor blade, place it in a vacuum drying oven and dry at 110 °C for 20 h, then cut it into a pole piece with a diameter of 10 mm. Subsequently, transfer the cut pole piece to a vacuum oven at 115 °C and dry for 10 h to obtain the positive electrode pole piece;

[0064] (2) Assemble a CR2025 stainless steel button cell

[0065] Use a sodium metal sheet as the negative electrode, drop 200 μL of commercial electrolyte, and complete the assembly of the CR2025 stainless steel button cell in a glove box filled with argon and with a water content lower than 0.01 ppm. After standing at 45 °C for 40 h, test its charge-discharge performance.

[0066] (II) Electrochemical performance test of the CR2025 stainless steel sodium-ion battery

[0067] Adopt the constant current charge-discharge method to test the cycle performance of the prepared battery. The test temperature is 25 °C, the voltage window is 1.5 - 4.6 V, and the test current densities are 0.02 C respectively, where 1 C = 200 mA / g.

[0068] As Figure 9 shown, with the introduction of B or Si element, the specific capacity of the sodium manganese pyrophosphate cathode material increases significantly. The sodium-ion battery prepared from the boron element-modified sodium manganese pyrophosphate cathode material in the present invention has a first discharge specific capacity of 166.37 mAh / g at a current density of 0.02 C. The sodium-ion battery prepared from the silicon element-modified sodium manganese pyrophosphate cathode material has a first discharge specific capacity of 140.28 mAh / g at a current density of 0.02 C, both of which are significantly higher than the sodium storage capacity of the unmodified sodium manganese pyrophosphate cathode material.

[0069] In summary, the present invention relates to a high-capacity sodium manganese pyrophosphate cathode material, its preparation method and application. By introducing silicon or boron elements with an electronegativity lower than that of phosphorus element, not only the unit cell parameter is increased, the (0 - 22) crystal plane grows preferentially, and the diffusion of sodium ions is promoted, but also it is beneficial to reduce the thermodynamic induction effect, lower the redox potential, and further promote the multi-electron transfer reaction to achieve a high specific capacity.

[0070] The above are only specific embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a high-capacity sodium manganese pyrophosphate positive electrode material for a sodium ion battery, characterized in that: The specific preparation process is as follows: (1) Preparation of precursor solution Sodium acetate trihydrate, manganese acetate tetrahydrate, ammonium dihydrogen phosphate and boric acid or silicon dioxide are added as raw materials in a molar ratio of 2:1:(1-x):x into deionized water to prepare a mixed solution, and then citric acid monohydrate is added in a molar ratio of citric acid monohydrate to manganese acetate tetrahydrate of 1:1, and stirred evenly to obtain a precursor solution; (2) Preparation of precursor materials The precursor solution is sent to a spray dryer by a peristaltic pump. The inlet temperature of the spray dryer is 200°C to 300°C and the outlet temperature is 100°C. The solution is spray dried at a pressure of 2 Bar to obtain a boron or silicon modified sodium manganese pyrophosphate precursor material. (3) Preparation of boron or silicon modified sodium manganese pyrophosphate materials The precursor material is placed in an alumina crucible, the alumina crucible is placed in a box furnace or a tube furnace, and heat treated at 600° C. for 2 h to 6 h in an argon atmosphere to obtain a boron or silicon modified sodium manganese pyrophosphate material.

2. The method for preparing the high-capacity sodium manganese pyrophosphate positive electrode material for sodium ion batteries according to claim 1 is characterized in that: The sodium acetate trihydrate, manganese acetate tetrahydrate, ammonium dihydrogen phosphate and boric acid or silicon dioxide are in a molar ratio of 2:1:0.98:0.

02.

3. The method for preparing the high-capacity sodium manganese pyrophosphate positive electrode material for sodium ion batteries according to claim 1 is characterized in that: The raw materials are sodium acetate trihydrate, manganese acetate tetrahydrate, ammonium dihydrogen phosphate and boric acid.

4. The method for preparing the high-capacity sodium manganese pyrophosphate positive electrode material for sodium ion batteries according to claim 1 is characterized in that: The molar volume ratio of manganese acetate tetrahydrate to deionized water is 0.15 mol / L.

5. The method for preparing the high-capacity sodium manganese pyrophosphate positive electrode material for sodium ion batteries according to claim 1 is characterized in that: The heating rate of the heat treatment is 3°C / min and the heat treatment time is 3h.

6. The method for preparing the high-capacity sodium manganese pyrophosphate positive electrode material for sodium ion batteries according to claim 1 is characterized in that: The stirring time in step (2) is 2 h.

7. The method for preparing the high-capacity sodium manganese pyrophosphate positive electrode material for sodium ion batteries according to claim 1 is characterized in that: The inlet temperature of the spray dryer was 200 °C.

8. Use of a high-capacity sodium manganese pyrophosphate positive electrode material prepared by the preparation method of claim 1 as a positive electrode material for a sodium ion battery.

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