Manganese-doped Prussian white material as well as preparation method and application thereof

Abstract

The invention provides a doped manganese-based Prussian white material and a preparation method and application thereof, and belongs to the technical field of electrode materials, the general formula of the doped manganese-based Prussian white material is Nan-zAzMn < 1-x > Mx [Fe (CN) 6] y, in the formula, M is selected from at least one of Fe, Ni, Cu, Zn and Co, A is selected from K and Mg, 1.7 lt; nlt; 2, 0.4 < = x < = 0.6, 0.9 lt; yt; Yt; 1, 0.02 < = z < = 0.1, and the doped manganese-based Prussian white material is of a rhombohedral phase structure. Sodium sulfate and sodium citrate are used as synthesis additives, the proportion of the sodium sulfate and the sodium citrate is optimized, the sodium content is increased, crystal defects and crystal water are reduced, structural stability in the charging and discharging process is maintained through Na-site and Mn-site element doping, and removal of the crystal water is promoted through Joule heat treatment, so that the service life of the lithium ion battery is prolonged. Therefore, the optimal balance of the capacity, the rate capability and the cycle performance is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrode materials, and particularly relates to a doped manganese-based Prussian white material, a preparation method and an application thereof. Background Art

[0002] In the field of cathode materials for sodium-ion batteries, manganese-based Prussian white materials have been widely studied due to their open framework structure, high working voltage and high specific capacity. However, in the process of electrochemical cycling of existing manganese-based Prussian white materials, the manganese ions in the materials will undergo valence changes, and the generated trivalent manganese ions Mn 3+ exhibit the Jahn-Teller effect, which will cause lattice distortion of Mn 3+ during charge and discharge, leading to the collapse of the crystal framework, resulting in a sharp decline in the capacity of the electrode material and a shortening of the cycle life. In addition, manganese-based Prussian white materials are usually synthesized in an aqueous phase environment, and crystal water will be generated in this environment. The presence of this crystal water will hinder the rapid transmission of sodium ions, and this crystal water needs to be removed by high-temperature and long-time heat treatment. However, high-temperature and long-time baking is likely to cause material decomposition and generate toxic HCN, and further reduce the structural stability.

[0003] Therefore, there is an urgent need for a manganese-based Prussian white material that can achieve high structural stability, low crystal water content and high sodium ion conductivity. Summary of the Invention

[0004] Based on the above technical problems, the object of the present invention is to provide a doped manganese-based Prussian white material, a preparation method and an application thereof. By using sodium sulfate and sodium citrate as synthesis additives and optimizing their proportions, the sodium content is increased, the crystal defects and crystal water are reduced, the structural stability during charge and discharge is maintained by doping elements at the Na site and Mn site, and the removal of crystal water is promoted by Joule heat treatment, so as to achieve an optimized balance of capacity, rate performance and cycle performance.

[0005] The specific technical solution is as follows: A doped manganese-based Prussian white material, the general formula of the doped manganese-based Prussian white material is Na n-z A z Mn 1-x M x [Fe(CN)6] y , where M is selected from at least one of Fe, Ni, Cu, Zn, Co, and A is selected from K and Mg. Among them, 1.7 < n < 2, 0.4 ≤ x ≤ 0.6, 0.9 < y < 1, 0.02 ≤ z ≤ 0.1, and the doped manganese-based Prussian white material is a rhombohedral phase structure.

[0006] In addition, a doped manganese-based Prussian white material in the above technical solution provided by the present invention may also have the following additional technical features: In the above technical solution, the molar ratio of Mg to K in the manganese-doped Prussian white material is 1.5~2.5:1.

[0007] A method for preparing a manganese-doped Prussian white material includes the following steps: S1: Sodium ferrocyanide is mixed with deionized water to obtain solution I; S2: Mix soluble divalent manganese salt and soluble divalent M salt with deionized water, then add sodium sulfate, sodium citrate, potassium salt and magnesium salt to obtain solution II; S3: Mix solution I and solution II, and obtain a suspension through co-precipitation reaction. Then, after aging, separation and drying, obtain manganese-doped Prussian white material. S4: Manganese-doped Prussian white material was subjected to Joule heat treatment and vacuum heat treatment to obtain rhombohedral phase structured manganese-doped Prussian white material.

[0008] In the above technical solution, in step S1, the concentration of solution I is 0.1~0.5 mol / L.

[0009] In the above technical solution, in step S2, the divalent manganese salt in solution II is manganese nitrate, manganese sulfate, or manganese chloride; the divalent M salt is nitrate, sulfate, or chloride; and the total concentration of the divalent manganese salt and the divalent M salt is 0.1-0.5 mol / L.

[0010] In the above technical solution, in step S2, the molar ratio of sodium sulfate to sodium ferrocyanide is 2~3:1; the molar ratio of sodium citrate to sodium ferrocyanide is 4~6:1; the potassium salt is potassium nitrate, potassium sulfate, or potassium chloride, and the potassium salt, based on the molar amount of potassium ions, is 0.05~0.3:1 of the molar amount of sodium ferrocyanide; the magnesium salt is magnesium nitrate, magnesium sulfate, or magnesium chloride, and the magnesium salt, based on the molar amount of magnesium ions, is 0.1~0.4:1 of the molar amount of sodium ferrocyanide.

[0011] In the above technical solution, in step S3, the co-precipitation reaction temperature is 40-80℃; the aging temperature is 40-80℃, and the aging time is 2-20 hours. The aged product still needs to be separated and dried.

[0012] Application of a manganese-doped Prussian white material in sodium-ion batteries.

[0013] The present invention discloses a manganese-doped Prussian white material, its preparation method, and its application. Compared with the prior art, the advantages are as follows: 1. This invention uses sodium sulfate and sodium citrate as additives and optimizes their ratio to increase the sodium content in the material during the synthesis stage, significantly reducing crystal defects and the formation of water of crystallization; through the synergistic effect of Na-site Mg / K co-doping and Mn-site transition metal element doping, it effectively suppresses the formation of Mn-related crystals during charge and discharge processes. 3+ The Jahn-Teller lattice distortion caused by the dehydration process maintains the stability of the material skeleton; in particular, the "pillar effect" formed by the co-doping of Mg / K at Na sites significantly improves the structural integrity of the material during long cycles, thereby greatly improving the cycle life.

[0014] 2. By employing Joule heat treatment and vacuum heat treatment, rapid and deep removal of crystal water can be achieved at lower temperatures and shorter times, avoiding the material decomposition and release of toxic HCN problems caused by traditional high-temperature, long-term heat treatment. This process is mild, energy-efficient, and helps maintain the high crystallinity and structural stability of the material.

[0015] 3. The preparation method of the present invention has the characteristics of simple process, low cost, short cycle, low energy consumption and suitability for industrial production. Attached Figure Description

[0016] Figure 1 X-ray diffraction (XRD) pattern of manganese-doped Prussian white prepared in Example 1; Figure 2 Charge-discharge curves of manganese-doped Prussian white prepared in Example 1; Figure 3 Rate performance of manganese-doped Prussian white prepared in Example 1; Figure 4 Cycle lifetime of the manganese-doped Prussian white prepared in Example 1; Figure 5 Charge-discharge curves of manganese-based Prussian white prepared in Comparative Example 1; Figure 6 Rate performance of manganese-based Prussian white prepared in Comparative Example 1; Figure 7 Cycle life of manganese-based Prussian white prepared in Comparative Example 1. Detailed Implementation

[0017] The following are specific implementation cases and appendices. Figure 1-7 The present invention will be further described, but the present invention is not limited to these embodiments.

[0018] A manganese-doped Prussian white material, the general formula of which is Na n-z A z Mn 1-x M x [Fe(CN)6]y , where M is selected from at least one of Fe, Ni, Cu, Zn, and Co, A is selected from K and Mg, where 1.7 < n < 2, 0.4 ≤ x ≤ 0.6, 0.9 < y < 1, 0.02 ≤ z ≤ 0.1, and the doped manganese-based Prussian white material has a rhombohedral phase structure.

[0019] Mg and K are co-doped at the Na site in the doped manganese-based Prussian white, where Mg is located at the 24d position of the lattice and K is located at the 8c position of the lattice; the doping amount is 0.02 ≤ z ≤ 0.1, and the molar ratio of Mg to K is 1.5 - 2.5:1.

[0020] From the comparison test, it can be seen from the capacity retention rate of the product of Comparative Example 1 with doped K and Mg and undoped that, relative to Na and N, K and Mg can form a larger Coulomb interaction with N. Therefore, through Mg / K co-doping, the lattice distortion during charge and discharge can be slowed down, and the lattice can be stabilized, so there is an improvement in high-rate and cycling performance. Analyzing theoretically, in the manganese-based Prussian white lattice, the migration energy barriers of Mg and K are much larger than that of Na. During the Na deintercalation process, Mg and K can be fixed in the lattice, thus playing a "supporting" role to stabilize the lattice.

[0021] It can also be analyzed from the test results of Comparative Example 6 and Comparative Examples 4 and 5 that when too much Mg / K is co-doped, Mg and K will deviate from the original lattice positions, thereby inhibiting the diffusion of Na+, reducing the capacity and rate performance, and when too little Mg / K co-doping fails to achieve the effect of stabilizing the lattice; the test also proves that Mg / K co-doping is beneficial to the dehydration of the product and, through the Coulomb interaction with N, slows down the lattice distortion during dehydration. It can also be seen from the test results of Comparative Examples 2 and 3 that single Mg or K doping cannot achieve the above effects.

[0022] M element doping is carried out at the Mn site in the doped manganese-based Prussian white, M is selected from at least one of Fe, Ni, Cu, Zn, and Co, and M contains Fe. Preferably, 0.4 ≤ x ≤ 0.6. The test proves that under the above conditions, the Jahn-Teller effect of Mn 3+ can be effectively inhibited, and an optimized balance of capacity, rate performance, and cycling performance can be achieved; the experiment proves that Mn site doping can also inhibit the lattice distortion during dehydration and is beneficial to dehydration.

[0023] It can be proved from the test results of the examples and comparative examples that Mn site and Na site doping can produce a synergistic effect, stabilize the crystal structure during charge and discharge, and promote the transport of sodium ions, thereby achieving an optimized balance of capacity, rate performance, and cycling performance.

[0024] A preparation method of a doped manganese-based Prussian white material includes the following steps: S1: Mix sodium ferrocyanide with deionized water to obtain solution I; S2: Mix soluble divalent manganese salt and soluble divalent M salt with deionized water, then add sodium sulfate, sodium citrate, potassium salt and magnesium salt to obtain solution II; S3: Mix solution I and solution II, and obtain a suspension through co-precipitation reaction. Then, after aging, separation and drying, obtain manganese-doped Prussian white material. S4: Manganese-doped Prussian white material was subjected to Joule heat treatment and vacuum heat treatment to obtain rhombohedral phase structured manganese-doped Prussian white material.

[0025] In step S1, the concentration of solution I is 0.1~0.5 mol / L. Under these conditions, the crystallinity of the product can be improved, and defects and the content of water of crystallization can be reduced.

[0026] In step S2, the divalent manganese salt in solution II is manganese nitrate, manganese sulfate, or manganese chloride; the divalent M salt is nitrate, sulfate, or chloride; and the total concentration of the divalent manganese salt and the divalent M salt is 0.1-0.5 mol / L.

[0027] In step S2, the molar ratio of sodium sulfate to sodium ferrocyanide is 2-3:1; the molar ratio of sodium citrate to sodium ferrocyanide is 4-6:1; the potassium salt is potassium nitrate, potassium sulfate, or potassium chloride, and the ratio of potassium salt to sodium ferrocyanide is 0.05-0.3:1 based on the molar weight of potassium ions; the magnesium salt is magnesium nitrate, magnesium sulfate, or magnesium chloride, and the ratio of magnesium salt to sodium ferrocyanide is 0.1-0.4:1 based on the molar weight of magnesium ions. Under these conditions, the crystallinity of the product can be improved, defects and water of crystallization content can be reduced, and controllable doping of Mg / K at Na sites and M elements at Mn sites can be achieved.

[0028] In step S3, the coprecipitation reaction temperature is 40-80℃; the aging temperature is 40-80℃, and the aging time is 2-20 hours; the aged product still needs to be separated and dried.

[0029] Under these conditions, the crystallinity of the product can be improved, and the defects and water of crystallization content can be reduced. After aging, the product still needs to be separated and dried.

[0030] Specifically, the separation process includes centrifugal separation or pressure filtration, and the drying process includes spray drying, flash drying or forced air drying.

[0031] In step S4, during Joule heat treatment, the reaction temperature is controlled by adjusting the voltage and current. The reaction temperature is 200-400℃ and the reaction time is 0.1-10s. Under these conditions, some of the water of crystallization can be effectively removed, and the bonding force between the water of crystallization and the transition metal ions can be weakened.

[0032] Vacuum heat treatment is performed at temperatures of 120-160℃ for 5-15 hours, with a vacuum level of 100-200 Pa. Under these conditions, the water of crystallization can be completely removed. Combining Joule heat treatment and vacuum heat treatment allows for the removal of water of crystallization in a short time under lower vacuum levels.

[0033] In this invention, manganese-based Prussian white material was prepared by co-precipitation. The material was then dehydrated through Joule heating and vacuum heat treatment. XRD and elemental analysis were performed on the dehydrated material using a Rigaku D / Max-2550pc XRD diffractometer and an Agilent 720ES elemental analyzer, respectively. Electrochemical testing was conducted on the obtained manganese-based Prussian white material. The test used manganese-based Prussian white as the positive electrode, metallic sodium as the negative electrode, glass fiber as the separator, and a 1 M NaPF6 solution of ethylene carbonate / diethyl carbonate as the electrolyte. 4% fluoroethylene carbonate was added. Button batteries were assembled in a glove box for charge-discharge testing using a Newway battery tester. The current density was defined as 1C = 150 mA / g, and the voltage range was 2–4 V.

[0034] Application of a manganese-doped Prussian white material in sodium-ion batteries.

[0035] Example 1: Sodium ferrocyanide was dissolved in deionized water and stirred thoroughly to obtain solution I with a concentration of 0.1 mol / L. Manganese sulfate, ferrous sulfate, and zinc sulfate were dissolved in deionized water. Sodium citrate, sodium sulfate, magnesium chloride, and potassium chloride were then added to this solution and stirred to obtain solution II. The concentrations of manganese sulfate, ferrous sulfate, and zinc sulfate were 0.05 mol / L, 0.04 mol / L, and 0.01 mol / L, respectively. The molar ratio of sodium citrate to sodium ferrocyanide was 5:1, the molar ratio of sodium sulfate to sodium ferrocyanide was 2:1, the molar ratio of potassium chloride to sodium ferrocyanide was 0.08:1, and the molar ratio of magnesium chloride to sodium ferrocyanide was 0.12:1. Solution I was added to solution II and stirred at 60°C. o The co-precipitation reaction at C yielded a suspension, which was then subjected to 60 °C. o The monoclinic manganese-based Prussian white containing crystal water was obtained by aging at C for 10 hours and subsequent treatment. Then, it was further processed at 300°C. o C Joule heating for 5 seconds and 140 o Anhydrous manganese-based Prussian white was obtained by vacuum heat treatment at C for 10 hours. Elemental analysis revealed that the molecular formula of the obtained material was Na. 1.75 Mg 0.014 K 0.008 Mn 0.51 Fe 0.38 Zn 0.11 [Fe(CN)6] 0.94 XRD analysis showed it to be a rhombohedral phase. Figure 1 .

[0036] Electrochemical testing showed that the initial discharge capacity of the product at 0.1C was 135.2 mAh / g. (See attached image) Figure 2 Rate testing showed that the capacity retention rate at 20°C was 85.1% compared to 0.1°C. Figure 3 After 200 cycles at 5C, the capacity retention was 92.8%. Figure 4 .

[0037] Comparative Example 1: The synthesis process of manganese-based Prussian white is as described in Example 1, except that potassium chloride and magnesium chloride were not added to solution II during synthesis, i.e., Mg and K were not doped at the sodium sites. Electrochemical testing of the product showed an initial discharge capacity of 126.7 mAh / g at 0.1C. (See [link to example 1]). Figure 5 At 20°C, the capacity retention was 72.2% compared to 0.1°C. (See [reference]). Figure 6 After 200 cycles at 5C, the capacity retention was 82.6%. Figure 7 .

[0038] Comparative Example 2: The synthesis process of manganese-based Prussian white is as described in Example 1, except that potassium chloride was not added to solution II during synthesis, i.e., no K was added at the sodium site. Electrochemical testing of the product showed that the capacity retention rate at 20°C was 76.5% compared to 0.1°C, and after 200 cycles at 5°C, the capacity retention rate was 84.8%.

[0039] Comparative Example 3: The synthesis process of manganese-based Prussian white is as described in Example 1, except that magnesium chloride was not added to solution II during synthesis, i.e., Mg was not added at the sodium sites. Electrochemical testing of the product showed that the capacity retention rate at 20°C was 74.1% compared to 0.1°C, and after 200 cycles at 5°C, the capacity retention rate was 83.3%.

[0040] Comparative Example 4: The synthesis process of manganese-based Prussian white is as described in Example 1, except that the molar ratio of magnesium chloride to sodium ferrocyanide in solution II is 0.05:1, and the molar ratio of Mg to K is 1.2:1. Electrochemical testing of the product showed that at 20°C, the capacity retention was 78.4% compared to 0.1°C, and after 200 cycles at 5°C, the capacity retention was 84.3%.

[0041] Comparative Example 5: The synthesis process of manganese-based Prussian white is as described in Example 1, except that the molar ratio of potassium chloride to sodium ferrocyanide in solution II is 0.03:1, and the molar ratio of Mg to K is 2.8:1. Electrochemical testing of the product showed that at 20°C, the capacity retention was 80.3% compared to 0.1°C, and after 200 cycles at 5°C, the capacity retention was 85.2%.

[0042] Comparative Example 6: The synthesis process of manganese-based Prussian white is as described in Example 1, except that the molar ratio of potassium chloride to sodium ferrocyanide in solution II is 0.35:1, and the molar ratio of magnesium chloride to sodium ferrocyanide is 0.45:1. Electrochemical testing of the product showed that at 20°C, the capacity retention was 73.7% compared to 0.1°C, and after 200 cycles at 5°C, the capacity retention was 82.9%.

[0043] Comparative Example 7: The synthesis process of manganese-based Prussian white is the same as in Example 1, except that ferrous sulfate and zinc sulfate were not added to solution II during synthesis. Electrochemical testing of the product showed that at 20°C, the capacity retention was 73.2% compared to 0.1°C, and after 200 cycles at 5°C, the capacity retention was 83.1%.

[0044] Comparative Example 8: The synthesis process of manganese-based Prussian white is the same as in Example 1, except that ferrous sulfate and zinc sulfate, as well as magnesium chloride and potassium chloride, were not added to solution II during the synthesis. Electrochemical testing of the product showed that the capacity retention rate at 20°C was 67.7% compared to 0.1°C, and after 200 cycles at 5°C, the capacity retention rate was 75.9%.

[0045] Comparative Example 9: The synthesis process of manganese-based Prussian white is the same as in Example 1, except that it does not involve Joule heat treatment; instead, it is heated at 140°C. o After heat treatment at C for 10 hours, the product is still a monoclinic phase.

[0046] Example 2: Sodium ferrocyanide was dissolved in deionized water and stirred thoroughly to obtain solution I with a concentration of 0.2 mol / L. Manganese sulfate and ferrous sulfate were dissolved in deionized water, and sodium citrate, sodium sulfate, magnesium nitrate, and potassium chloride were added to this solution. After stirring, solution II was obtained, wherein the concentrations of manganese sulfate and ferrous sulfate were 0.1 mol / L and 0.1 mol / L, respectively; the molar ratio of sodium citrate to sodium ferrocyanide was 4:1; the molar ratio of sodium sulfate to sodium ferrocyanide was 3:1; the molar ratio of potassium chloride to sodium ferrocyanide was 0.12:1; and the molar ratio of magnesium nitrate to sodium ferrocyanide was 0.15:1. Solution I was added to solution II and stirred at 60°C.o The co-precipitation reaction at C yielded a suspension, which was then subjected to 60 °C. o The monoclinic manganese-based Prussian white containing crystal water was obtained by aging at C for 10 hours and subsequent treatment. Then, it was further processed at 300°C. o Anhydrous manganese-based Prussian white was obtained by Joule heating for 5 seconds and vacuum drying at 140℃ for 10 hours. Elemental analysis showed that the molecular formula of the obtained material was Na. 1.73 Mg 0.035 K 0.018 Mn 0.53 Fe 0.47 [Fe(CN)6] 0.95 XRD analysis revealed it to be a rhombohedral phase.

[0047] Electrochemical testing showed that the initial discharge capacity of the product was 141.2 mAh / g at 0.1C. Rate testing showed that the capacity retention rate was 84.2% at 20C compared to 0.1C, and the capacity retention rate was 91.1% after 200 cycles at 5C.

[0048] Example 3: Sodium ferrocyanide was dissolved in deionized water and stirred thoroughly to obtain solution I with a concentration of 0.5 mol / L. Manganese sulfate, ferrous sulfate, and nickel sulfate were dissolved in deionized water. Sodium citrate, sodium sulfate, magnesium chloride, and potassium sulfate were then added to this solution and stirred to obtain solution II. The concentrations of manganese sulfate, ferrous sulfate, and nickel sulfate were 0.3 mol / L, 0.15 mol / L, and 0.05 mol / L, respectively. The molar ratio of sodium citrate to sodium ferrocyanide was 6:1, the molar ratio of sodium sulfate to sodium ferrocyanide was 2.4:1, the molar ratio of potassium sulfate to sodium ferrocyanide was 0.11:1, and the molar ratio of magnesium chloride to sodium ferrocyanide was 0.32:1. Solution I was added to solution II and stirred for 60 minutes. o The co-precipitation reaction at C yielded a suspension, which was then subjected to 60 °C. o The monoclinic manganese-based Prussian white containing crystal water was obtained by aging at C for 10 hours and subsequent treatment. Then, it was further processed at 300°C. o C Joule heating for 5 seconds and 140 o Anhydrous manganese-based Prussian white was obtained by vacuum drying at C for 10 hours. Elemental analysis showed that the molecular formula of the obtained material was Na. 1.71 Mg 0.061 K 0.028 Mn 0.60 Fe 0.29 Ni 0.11 [Fe(CN)6] 0.96 XRD analysis revealed it to be a rhombohedral phase.

[0049] Electrochemical testing showed that the initial discharge capacity of the product was 138.3 mAh / g at 0.1C. Rate testing showed that the capacity retention rate was 86.3% at 20C compared to 0.1C, and the capacity retention rate was 93.3% after 200 cycles at 5C.

[0050] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A manganese-doped Prussian white material, characterized in that, The general formula of the doped manganese-based Prussian white material is Na n-z A z Mn 1-x M x [Fe(CN)6] y , where M is selected from at least one of Fe, Ni, Cu, Zn, and Co, A is selected from K and Mg, where 1.7 < n < 2, 0.4 ≤ x ≤ 0.6, 0.9 < y < 1, 0.02 ≤ z ≤ 0.1, and the doped manganese-based Prussian white material has a rhombohedral phase structure.

2. The manganese-doped Prussian white material according to claim 1, characterized in that, In the doped manganese-based Prussian white material, the molar ratio of Mg to K is 1.5~2.5:

1.

3. A method for preparing a manganese-doped Prussian white material, based on the manganese-doped Prussian white material according to any one of claims 1-2, characterized in that, Includes the following steps: S1: Sodium ferrocyanide is mixed with deionized water to obtain solution I; S2: Mix soluble divalent manganese salt and soluble divalent M salt with deionized water, then add sodium sulfate, sodium citrate, potassium salt and magnesium salt to obtain solution II; S3: Mix solution I and solution II, and obtain a suspension through co-precipitation reaction. Then, after aging, separation and drying, obtain manganese-doped Prussian white material. S4: Manganese-doped Prussian white material was subjected to Joule heat treatment and vacuum heat treatment to obtain rhombohedral phase structured manganese-doped Prussian white material.

4. The method for preparing a manganese-doped Prussian white material according to claim 3, characterized in that, In step S1, the concentration of solution I is 0.1~0.5 mol / L.

5. The method for preparing a manganese-doped Prussian white material according to claim 3, characterized in that, In step S2, the divalent manganese salt in solution II is manganese nitrate, manganese sulfate, or manganese chloride; the divalent M salt is nitrate, sulfate, or chloride; and the total concentration of the divalent manganese salt and the divalent M salt is 0.1-0.5 mol / L.

6. The method for preparing a manganese-doped Prussian white material according to claim 3, characterized in that, In step S2, the molar ratio of sodium sulfate to sodium ferrocyanide is 2-3:1; the molar ratio of sodium citrate to sodium ferrocyanide is 4-6:1; the potassium salt is potassium nitrate, potassium sulfate, or potassium chloride, and the potassium salt, based on the molar amount of potassium ions, is 0.05-0.3:1 of the molar amount of sodium ferrocyanide; the magnesium salt is magnesium nitrate, magnesium sulfate, or magnesium chloride, and the magnesium salt, based on the molar amount of magnesium ions, is 0.1-0.4:1 of the molar amount of sodium ferrocyanide.

7. The method for preparing a manganese-doped Prussian white material according to claim 3, characterized in that, In step S3, the coprecipitation reaction temperature is 40-80℃; the aging temperature is 40-80℃, and the aging time is 2-20 hours; the aged product still needs to be separated and dried.

8. The application of a manganese-doped Prussian white material according to any one of claims 1-2 in a sodium-ion battery.

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