A preparation method of a manganese-based Prussian white material and its products and applications

Abstract

The invention discloses a method for preparing a manganese-based Prussian white material, comprising: 1) mixing sodium ferrocyanide with deionized water to obtain solution A; mixing a soluble divalent manganese salt, a soluble divalent iron salt, a soluble divalent nickel salt, an organic acid sodium, an inorganic acid sodium and deionized water to obtain solution B; blending solution A and solution B, and obtaining a suspension through a coprecipitation reaction; 2) subjecting the suspension to a first aging to obtain an aging liquid; 3) mixing the aging liquid with a sodium salt and a nickel salt for a second aging to obtain a manganese-based Prussian white material. The product prepared by the invention contains three metal elements, Mn, Fe and Ni, and the distribution of the three metal elements in the inner and outer layers of the product presents different rules, and the surface presents a nickel-rich gradient structure. The above characteristics enable the manganese-based Prussian material to have excellent cycle stability performance while ensuring a higher voltage and capacity, and can also improve the electronic conductivity and rate performance of the material.

Description

Technical Field

[0001] The invention relates to the field of sodium ion batteries, and in particular to a method for preparing a manganese-based Prussian white material, a product thereof, and an application of the material in sodium ion batteries. Background Art

[0002] As energy and environmental issues become increasingly serious worldwide, the development of sustainable clean energy, such as wind power, solar energy, and tidal energy, has attracted widespread attention. However, this type of clean energy has the disadvantage of instability, that is, it is variable with weather, climate, and environment. Therefore, long-life, sustainable, cheap, and environmentally friendly energy storage batteries are needed.

[0003] At present, among many candidate batteries, lithium-ion batteries have become the mainstream of energy storage batteries due to their excellent comprehensive performance, but they also face problems such as resources and safety. In contrast, sodium-ion batteries have comprehensive advantages such as good safety, low cost, abundant resources, and environmental friendliness, making them very suitable for large-scale energy storage.

[0004] Similar to lithium-ion batteries, for sodium-ion batteries, the development of suitable positive electrode materials is the key. Prussian white materials have an open framework structure, which is conducive to the rapid extraction and insertion of large-sized sodium ions. Therefore, they have the advantages of high capacity, good rate performance, and long cycle life, making them very suitable as positive electrode materials for sodium-ion batteries. Among various Prussian white materials, manganese-based materials have high voltage and capacity, but their conductivity and rate performance are poor, and trivalent manganese ions can cause the Jahn-Teller effect, and Mn 2+ It is easily soluble in the electrolyte, resulting in unsatisfactory cycle performance. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention discloses a method for preparing a manganese-based Prussian white material. The prepared product contains three metal elements, Mn, Fe and Ni. The distribution of the three metal elements in the inner layer and the outer layer of the product presents different rules, and the surface presents a nickel-rich gradient structure. Through the synergistic effect of Fe and Ni co-doping and the different but controllable distribution of Mn, Fe and Ni elements, Mn can be suppressed. 2+ The dissolution and Jahn-Teller effect enable the manganese-based Prussian material to have excellent cycle stability while ensuring high voltage and capacity, and at the same time improve the electronic conductivity and rate performance of the material.

[0006] The specific technical solutions are as follows:

[0007] A method for preparing a manganese-based Prussian white material comprises the following steps:

[0008] 1) mixing sodium ferrocyanide with deionized water to obtain solution A; mixing a soluble divalent manganese salt, a soluble divalent iron salt, a soluble divalent nickel salt, an organic sodium acid, an inorganic sodium acid and deionized water to obtain solution B; blending solution A and solution B, and obtaining a suspension through a coprecipitation reaction;

[0009] 2) subjecting the suspension to a first aging to obtain an aged liquid;

[0010] 3) The aging liquid is mixed with sodium salt and nickel salt, and aged for a second time, followed by post-treatment to obtain the manganese-based Prussian white material.

[0011] The preparation method disclosed by the invention adds two aging processes on the basis of the original coprecipitation preparation process. The first aging process is used to increase the sodium content, reduce crystal defects and crystal water content, increase the grain size, and make the Ni, Fe and Mn elements evenly distributed in the inner core; the second aging process is to redistribute the Ni, Fe and Mn elements on the surface of the product after the aging treatment in the previous step, so that the manganese-based Prussian white material finally prepared has the following special structure: the Fe, Mn and Ni elements are evenly distributed inside; the Fe, Mn and Ni elements are distributed in a gradient in the outer layer, the contents of the Fe and Mn elements gradually decrease from the inside to the outside, and the content of the Ni element gradually increases from the inside to the outside.

[0012] It can be seen that the effects of the two aging processes are different; experiments have found that if the aging process is changed to one time, that is, sodium salt and nickel salt are added for blending during the first aging, the cycle stability and capacity of the battery assembled with the final prepared product are significantly lower than those of the battery assembled with the manganese-based Prussian white material prepared by the present invention.

[0013] In step 1):

[0014] The sodium ferrocyanide is selected from sodium ferrocyanide or a hydrate of sodium ferrocyanide.

[0015] Preferably, the concentration of solution A is 0.2-0.6 mol / L; under this condition, the product can have a high sodium content, a complete crystal structure, a low crystal water content and a large grain size; more preferably, it is 0.3-0.5 mol / L.

[0016] The soluble divalent manganese salt includes but is not limited to chloride, sulfate, nitrate, acetate of divalent manganese, and hydrates of the above salts;

[0017] The soluble divalent iron salt includes but is not limited to chloride, sulfate, nitrate, acetate of divalent manganese, and hydrates of the above salts;

[0018] The soluble divalent nickel salt includes but is not limited to chloride, sulfate, nitrate, acetate of divalent manganese, and hydrates of the above salts;

[0019] Preferably, in the solution B, the total concentration of soluble divalent salts is 0.2 to 0.6 mol / L;

[0020] The total concentration of the soluble divalent salts refers to the sum of the molar concentrations of the soluble divalent manganese salts, the soluble divalent iron salts and the soluble divalent nickel salts.

[0021] The molar ratio of the soluble divalent manganese salt, the soluble divalent iron salt and the soluble divalent nickel salt is 1:0.1-0.6:0.1-0.4; more preferably 1:0.2-0.6:0.2-0.4.

[0022] The organic acid sodium, the anion is selected from one or more of citrate, gluconate, malate, lactate, ethylenediaminetetraacetate, and oxalate;

[0023] The inorganic acid sodium, anion is selected from Cl - 、NO3 - 、SO4 2- One or more of;

[0024] Preferably, in the solution B:

[0025] The concentration of organic acid sodium is 0.6~1.8mol / L;

[0026] The concentration of inorganic acid sodium is 0.5-1.0 mol / L.

[0027] Under the joint action of organic sodium acid and inorganic sodium acid, the product can have high sodium content, low crystal water content, complete crystal structure and larger grain size, thereby improving the cyclic stability of the material.

[0028] Preferably, the organic sodium acid is selected from sodium citrate or its hydrate, and the inorganic sodium acid is selected from sodium sulfate or its hydrate.

[0029] In step 1):

[0030] Preferably, the temperature of the coprecipitation reaction is 50-90° C. Under this condition, the sodium content can be increased, the crystal defects and the crystal water content can be reduced, and the grain size can be increased.

[0031] In step 2):

[0032] The first aging and the second aging refer to static aging, or aging under stirring or ultrasonic conditions.

[0033] Preferably, the temperature of the first aging is 50-90° C. and the time is 2-4 hours.

[0034] More preferably, the temperature of the first aging is 60°C.

[0035] In step 3):

[0036] Preferably, the temperature of the second aging is 50-90°C and the time is 4-8h;

[0037] More preferably, the temperature of the second aging is 60°C.

[0038] During the second aging process, an ion exchange reaction occurs, that is, part of the Mn and Fe elements in the surface grains of the product are replaced by the Ni element. This aging step is the key to preparing the manganese-based Prussian white material of the present invention with a special distribution of metal elements. Experiments have shown that the above special structure is conducive to inhibiting the Mn 3+ The Jahn-Teller distortion of Mn 2+ The dissolution of the nickel salt can further improve the cycle life. The experiment also shows that the addition of sodium salt and nickel salt has a synergistic effect, which can balance the cycle life and capacity. It should be pointed out that the above-mentioned synthesis conditions, the first aging conditions and the second aging conditions are interrelated, and any deviation from the above conditions will not result in an ideal specific structure.

[0039] Preferably, the sodium salt is selected from sodium thiosulfate and / or sodium iodide; experiments have found that if the sodium salt added during the second aging is other common sodium salts in the art, such as sodium sulfate, the cycle stability of the battery assembled from the prepared product is lower than that of the battery assembled from the manganese-based Prussian white material prepared by the present invention.

[0040] It has been found through experiments that if the nickel salt added during the second aging is replaced by other metal salts, such as zinc salts, chromium salts, and copper salts, the above-mentioned replaced metal salts also have the ability to undergo ion exchange reactions with Mn and Fe elements, but the zinc-rich, chromium-rich, or copper-rich layer on the surface of the prepared product is compared with the nickel-rich layer obtained by using nickel salts, which inhibits the Mn 2+ The dissolution effect is not obvious, and the effect of improving the product circulation performance is not obvious. Some even lead to the deterioration of the product circulation performance.

[0041] The experiment also found that if sodium salt and nickel salt are not added at the same time, it will not be possible to achieve both high capacity and high cycle stability.

[0042] Preferably, the sodium salt is selected from sodium thiosulfate; and the nickel salt is selected from nickel sulfate.

[0043] Preferred:

[0044] The molar ratio of the sodium salt to the sodium ferrocyanide in step (1) is 1 to 3:1, and more preferably 1.0 to 1.8:1.

[0045] The molar ratio of the nickel salt to the sodium ferrocyanide in step (1) is 1:1.5-10.

[0046] The post-treatment includes one or more of cooling, washing, separation and drying.

[0047] The present invention also discloses a manganese-based Prussian white material prepared according to the above method, the general structural formula of which is Na n Mn 1-x- y Fe x Ni y [Fe(CN)6] 1-z mH2O;

[0048] Where, 1.6<n≤2, 0<m≤3, 0.1≤x≤0.4, 0.05≤y≤0.3, 0 <z≤0.1。

[0049] The manganese-based Prussian white material prepared by the present invention has a cyano framework structure (–C≡N–), wherein the N atom is connected to high-spin Mn, Fe, and Ni, and the C atom is connected to the low-spin Fe in the [Fe(CN)6] structure. In the manganese-based Prussian white structure, both Mn and Fe can provide capacity through divalent / trivalent valence changes, while Ni does not provide capacity but can stabilize the structure and improve cycle stability. Ni and Fe co-doping can also reduce the band gap to below 2eV, thereby improving the electronic conductivity of the material and the corresponding rate performance.

[0050] The contents of Fe, Mn and Ni elements are evenly distributed in the lattice of the manganese-based Prussian white material, and the co-doping of Fe and Ni can effectively inhibit the 3+ Jahn-Teller distortion is reduced, thereby improving the cycle life; the outer layer of the manganese-based Prussian white material has a gradient distribution of Fe, Mn and Ni elements, the content of Fe and Mn elements gradually decreases from the inside to the outside of the lattice, and the content of Ni element gradually increases from the inside to the outside of the lattice. This element gradient distribution is beneficial to inhibiting the Mn 2+ dissolution, further improving the cycle life.

[0051] Preferably, in the outer layer of the manganese-based Prussian white material, the contents of Fe, Mn and Ni elements are gradiently distributed with a thickness of 5 to 10 nm.

[0052] The experiment found that within this thickness range, Mn 2+ dissolution, thereby improving the cycle life without affecting the capacity of the material and the lattice distortion of the outer layer.

[0053] Preferably, the manganese-based Prussian white material has a monoclinic phase structure, a secondary particle size of 0.5 to 2 μm, and is agglomerated from primary particles of 200 to 300 nm.

[0054] The manganese-based Prussian white material with this structure and size has better chemical / electrochemical stability, improves the coating performance of the electrode, increases the tap density of the electrode, and reduces the amount of electrolyte used.

[0055] The invention also discloses application of the prepared manganese-based Prussian white material in a sodium ion battery.

[0056] Compared with the prior art, the present invention has the following beneficial effects:

[0057] The invention discloses a method for preparing a manganese-based Prussian white material. A product with a special structure is prepared by adopting two aging processes based on a coprecipitation process and simultaneously adding sodium salt and nickel salt in the second aging process.

[0058] The manganese-based Prussian white material prepared by the special process in the present invention contains three metal elements, Fe, Mn and Ni, but the three elements in the inner and outer layers of the material show different distribution characteristics. In the inner layer of the material, the contents of Fe, Mn and Ni are evenly distributed in the lattice; in the outer layer of the material, the contents of Fe, Mn and Ni show a gradient distribution, the contents of Fe and Mn gradually decrease from the inside to the outside of the lattice, and the content of Ni gradually increases from the inside to the outside of the lattice; the synergistic effect of Fe and Ni co-doping and the special structure can inhibit the accumulation of Mn. 2+ The dissolution and Jahn-Teller effect enable the manganese-based Prussian material to have excellent cycle stability while ensuring high voltage and capacity, and at the same time improve the electronic conductivity and rate performance of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 This is the XRD pattern of the manganese-based Prussian white material prepared in Example 1;

[0060] Figure 2 This is a SEM photograph of the manganese-based Prussian white material prepared in Example 1;

[0061] Figure 3 The charge and discharge curves of a sodium ion battery assembled with the manganese-based Prussian white material prepared in Example 1 as the positive electrode;

[0062] Figure 4 The cycle stability curve of the sodium ion battery assembled with the manganese-based Prussian white material prepared in Example 1 as the positive electrode;

[0063] Figure 5The cyclic stability curve of the sodium ion battery assembled with the product prepared in Comparative Example 1 as the positive electrode;

[0064] Figure 6 The figure shows the charge and discharge curve of a sodium ion battery assembled with the product prepared in Comparative Example 3 as the positive electrode. DETAILED DESCRIPTION

[0065] The present invention is further described in detail below in conjunction with examples and comparative examples, but the embodiments of the present invention are not limited thereto.

[0066] Example 1

[0067] 0.03 mol of sodium ferrocyanide is dissolved in 100 mL of deionized water to obtain solution A; 0.018 mol of manganese sulfate, 0.006 mol of ferrous sulfate, and 0.006 mol of nickel sulfate are dissolved in 100 mL of deionized water to obtain solution B, and 0.07 mol of sodium sulfate and 0.12 mol of sodium citrate are added to solution B; solution A is dripped into solution B, and a suspension is obtained by coprecipitation reaction at 60° C., and then stirred and aged at 60° C. for 3 hours; then 0.01 mol of nickel sulfate and 0.05 mol of sodium thiosulfate are added, and then stirred and aged at 60° C. for 6 hours; finally, a manganese-based Prussian white material is obtained after cooling, washing, separation and drying.

[0068] The structural formula of the manganese-based Prussian white material prepared in this embodiment is Na 1.78 Mn 0.57 Fe 0.18 Ni 0.25 [Fe(CN)6] 0.95 ·2.23H2O.

[0069] XRD characterization showed that the product was a monoclinic phase. Figure 1 ; SEM characterization shows that the secondary particles are 1 μm in size and are agglomerated from primary particles of 200 nm. Figure 2 .

[0070] Inside the manganese-based Prussian white material prepared in this embodiment, the contents of Fe, Mn and Ni elements are uniformly distributed in the lattice; in the outer layer, the contents of Fe, Mn and Ni elements are gradient distributed, and the contents of Fe and Mn elements gradually decrease from the inside to the outside of the lattice, and the content of Ni element gradually increases from the inside to the outside of the lattice; in the outer layer, the contents of Fe, Mn and Ni elements are gradient distributed with a thickness of 6 to 7 nm.

[0071] The manganese-based Prussian white material prepared in this embodiment was used as the positive electrode, metallic sodium was used as the negative electrode, glass fiber was used as the separator, and NaPF6 propylene carbonate (PC) / ethyl methyl carbonate (EMC) solution was used as the electrolyte (the content of NaPF6 in the electrolyte was 1 mol / L, the volume ratio of PC to EMC was 1:1; 4 wt% (based on the total mass of the electrolyte) of fluorinated ethylene carbonate (FEC) additive was added), and a charge and discharge cycle test was carried out with a voltage range of 2 to 4 V.

[0072] When the current density is 0.1C (1C = 150mAh / g), the charge and discharge curve is as follows Figure 3 As shown in Figure 2, the initial charge and discharge capacities can reach 131 mAh / g and 128 mAh / g respectively; after 500 cycles at 5C current, the capacity retention rate is 89.1%. Figure 4 ; At 10C, the capacity can reach 85% of that at 1C.

[0073] Comparative Example 1

[0074] The preparation process is basically the same as that of Example 1, except that nickel sulfate and sodium thiosulfate are not added during the second aging process.

[0075] The battery was assembled in exactly the same manner as in Example 1 and subjected to electrochemical testing under the same conditions. At a current of 5C, the capacity retention rate after 500 cycles was 85.9%. Figure 5 .

[0076] By comparing the capacity retention rate data of Example 1 and Comparative Example 1, it can be seen that the cycle stability of Comparative Example 1 is significantly reduced. The reason may be that the metal elements are evenly distributed in the product and there is no gradient distribution in the outer layer.

[0077] Comparative Example 2

[0078] The preparation process is basically the same as that of Example 1, except that:

[0079] 0.01 mol of nickel sulfate and 0.05 mol of sodium thiosulfate were directly added to the suspension obtained by the coprecipitation reaction, and the mixture was stirred and aged at 60° C. for 9 h.

[0080] The battery was assembled in exactly the same manner as in Example 1 and electrochemically tested under the same conditions. At a current of 0.1C, the initial charge and discharge capacities were 121 mAh / g and 117 mAh / g, respectively. At a current of 5C, the capacity retention rate after 500 cycles was 80.2%.

[0081] By comparing Example 1 with Comparative Example 2, it can be found that the capacity retention rate of the battery assembled by the product prepared by one-step aging and simultaneous replacement reaction is significantly lower than that of the battery assembled by the product prepared by two agings in Example 1.

[0082] Comparative Example 3

[0083] The preparation process is basically the same as that of Example 1, except that sodium thiosulfate is not added during the second aging process.

[0084] The battery was assembled in exactly the same manner as in Example 1 and electrochemically tested under the same conditions. At a current of 0.1C, the initial charge and discharge capacities were 126 mAh / g and 125 mAh / g, respectively. Figure 6 ; After 500 cycles at 5C current, the capacity retention rate is 87.4%.

[0085] Comparative Example 4

[0086] The preparation process is basically the same as that of Example 1, except that the sodium salt added during the second aging process is sodium sulfate.

[0087] The battery was assembled in exactly the same manner as in Example 1 and subjected to electrochemical testing under the same conditions. At a current of 0.1C, the initial charge and discharge capacities were 124 mAh / g and 123 mAh / g, respectively. After 500 cycles at a current of 5C, the capacity retention rate was 87.2%.

[0088] By comparing Example 1 with Comparative Example 4, it can be found that if the sodium salt added during the secondary aging is replaced with sodium sulfate, the capacity retention rate of the battery assembled with the final product is lower than that of the battery assembled with the product prepared in Example 1.

[0089] Comparative Example 5

[0090] The preparation process is basically the same as that of Example 1, except that nickel sulfate is not added during the second aging process.

[0091] The battery was assembled in exactly the same manner as in Example 1 and electrochemically tested under the same conditions. At a current of 0.1C, the initial charge and discharge capacities were 133 mAh / g and 129 mAh / g, respectively; after 500 cycles at a current of 5C, the capacity retention rate was 78.5%.

[0092] By comparing Example 1 with Comparative Examples 1, 3 and 5, it can be found that if sodium salt and nickel salt are not added during the secondary aging, or the two are not added at the same time, the capacity retention rate of the battery assembled with the prepared product is lower than that of the battery assembled with the product prepared in Example 1.

[0093] Comparative Example 6

[0094] The preparation process is basically the same as that of Example 1, except that the aging time in the first aging process is 1 h.

[0095] The battery was assembled in exactly the same manner as in Example 1 and electrochemically tested under the same conditions. At a current of 5C, the capacity retention rate after 500 cycles was 84.4%.

[0096] By comparing the capacity retention rate data of Example 1 with that of Comparative Example 6, it can be seen that the cycle stability of Comparative Example 6 is significantly reduced. The reason may be that the first aging time is too short, the Mn, Fe, and Ni elements in the material are unevenly distributed, and the Mn can not be effectively inhibited. 3+ The Jahn-Teller effect.

[0097] Comparative Example 7

[0098] The preparation process is basically the same as that of Example 1, except that the aging time in the second aging process is 3 hours.

[0099] The battery was assembled in exactly the same manner as in Example 1 and electrochemically tested under the same conditions. At a current of 5C, the capacity retention rate after 500 cycles was 86.1%.

[0100] By comparing the capacity retention rate data of Example 1 and Comparative Example 7, it can be seen that the cycle stability of Comparative Example 7 is significantly reduced. The reason may be that the second aging time is too short, and the thickness of the gradient distribution of Fe, Mn and Ni elements in the outer layer of the manganese-based Prussian white material is less than 5nm.

[0101] Comparative Example 8

[0102] The preparation process is basically the same as that of Example 1, except that the aging time in the second aging process is 9 hours.

[0103] The battery was assembled in exactly the same manner as in Example 1 and subjected to electrochemical testing under the same conditions. The initial charge and discharge capacities were 124 mAh / g and 121 mAh / g, respectively.

[0104] By comparing the initial charge and discharge capacity data of Example 1 and Comparative Example 8, it can be seen that the initial capacity of Comparative Example 8 is significantly reduced. The reason may be that the second aging time is too long, and the content of Fe, Mn, and Ni elements in the outer layer of the manganese-based Prussian white material presents a gradient distribution with a thickness of more than 10nm. At this time, the inactive Ni content is relatively high, resulting in a low capacity.

[0105] Comparative Example 9

[0106] The preparation process is substantially the same as that of Example 1, except that the nickel sulfate in the second aging process is replaced by an equimolar amount of zinc sulfate.

[0107] The battery was assembled in exactly the same manner as in Example 1 and subjected to electrochemical testing under the same conditions. At a current of 5C, the capacity retention rate after 500 cycles was 85.5%.

[0108] Comparative Example 10

[0109] The preparation process is basically the same as that of Example 1, except that the nickel sulfate in the second aging process is replaced by an equimolar amount of copper sulfate.

[0110] The battery was assembled in exactly the same manner as in Example 1 and electrochemically tested under the same conditions. At a current of 5C, the capacity retention rate after 500 cycles was 84.3%.

[0111] Comparative Example 11

[0112] The preparation process is basically the same as that of Example 1, except that the nickel sulfate in the second aging process is replaced by an equal molar amount of chromium nitrate.

[0113] The battery was assembled in exactly the same manner as in Example 1 and electrochemically tested under the same conditions. At a current of 5C, the capacity retention rate after 500 cycles was 84.8%.

[0114] By comparing Example 1 with Comparative Examples 9 to 11, it can be found that when the Ni, Fe, and Mn on the surface of the Prussian white lattice are replaced by Zn, Cu, or Cr, the Zn-rich, Cu-rich, or Cr-rich lattices formed cannot effectively inhibit the Mn 2+ The dissolution will destroy the surface structure of the particles and lead to the degradation of the cycle performance.

[0115] Example 2

[0116] 0.03 mol of sodium ferrocyanide was dissolved in 100 mL of deionized water to obtain solution A; 0.015 mol of manganese sulfate, 0.009 mol of ferrous sulfate, and 0.006 mol of nickel sulfate were dissolved in 100 mL of deionized water to obtain solution B, and then 0.05 mol of sodium sulfate and 0.06 mol of sodium citrate were added to obtain a solution; solution A was dropped into solution B, and a precipitate was obtained by coprecipitation reaction at 60°C, and then aged at 60°C for 3 hours; then 0.003 mol of nickel sulfate and 0.03 mol of sodium thiosulfate were added, and then aged at 60°C for 8 hours; finally, post-treatment was performed.

[0117] The product prepared in this example is Na 1.75 Mn 0.51 Fe 0.31 Ni 0.18 [Fe(CN)6] 0.96·2.41H2O. XRD analysis showed that the product was a monoclinic phase, and SEM analysis showed that the secondary particles were 1 μm in size and were agglomerated from primary particles of 200 nm.

[0118] The battery was assembled in exactly the same manner as in Example 1 and subjected to electrochemical testing under the same conditions. The initial charge and discharge capacities were 130 mAh / g and 127 mAh / g, respectively. After 500 cycles at a current of 5 C, the capacity retention rate was 90.1%.

[0119] Example 3

[0120] 0.05 mol of sodium ferrocyanide was dissolved in 100 mL of deionized water to obtain solution A; 0.035 mol of manganese sulfate, 0.0075 mol of ferrous sulfate, and 0.0075 mol of nickel sulfate were dissolved in 100 mL of deionized water to obtain solution B, and then 0.1 mol of sodium sulfate and 0.18 mol of sodium citrate were added to obtain a solution; solution A was dropped into solution B, and a precipitate was obtained by coprecipitation reaction at 60°C, and then aged at 60°C for 3 hours; then 0.03 mol of nickel sulfate and 0.09 mol of sodium thiosulfate were added, and then aged at 60°C for 4 hours; finally, the product was obtained by post-treatment.

[0121] The product prepared in this example is Na 1.77 Mn 0.71 Fe 0.15 Ni 0.14 [Fe(CN)6] 0.93 ·2.19H2O. XRD analysis showed that the product was a monoclinic phase, and SEM analysis showed that the secondary particles were about 1 μm in size and were agglomerated from primary particles of 200 nm.

[0122] The battery was assembled in exactly the same manner as in Example 1 and subjected to electrochemical testing under the same conditions. The initial charge and discharge capacities were 133 mAh / g and 130 mAh / g. After 500 cycles at 5 C current, the capacity retention rate was 88.7%.

[0123] The applicant declares that the present invention illustrates the detailed method of the present invention through the above embodiments, but the present invention is not limited to the above detailed method.

Claims

1. A method for preparing a manganese-based Prussian white material, characterized in that: The steps include: 1) mixing sodium ferrocyanide with deionized water to obtain solution A; mixing a soluble divalent manganese salt, a soluble divalent iron salt, a soluble divalent nickel salt, an organic sodium acid, an inorganic sodium acid and deionized water to obtain solution B; blending solution A and solution B, and obtaining a suspension through a coprecipitation reaction; 2) subjecting the suspension to a first aging to obtain an aged liquid; 3) mixing the aging liquid with sodium salt and nickel salt, performing a second aging, and then performing post-treatment to obtain the manganese-based Prussian white material; The second aging temperature is 50-90°C and the time is 4-8h; The manganese-based Prussian white material has a general structural formula of Na n Mn 1-x-y Fe x Ni y [Fe(CN)6] 1-z mH2O; Where, 1.6<n≤2, 0<m≤3, 0.1≤x≤0.4, 0.05≤y≤0.3, 0 <z≤0.1; The contents of Fe, Mn and Ni elements are uniformly distributed in the crystal lattice inside the manganese-based Prussian white material; the contents of Fe, Mn and Ni elements are distributed in a gradient in the outer layer of the manganese-based Prussian white material, and the contents of Fe and Mn elements gradually decrease from the inside to the outside of the crystal lattice, and the content of Ni element gradually increases from the inside to the outside of the crystal lattice; The manganese-based Prussian white material has a secondary particle size of 0.5 to 2 μm and is agglomerated from primary particles of 200 to 300 nm; In the outer layer of the manganese-based Prussian white material, the contents of Fe, Mn and Ni elements are gradiently distributed with a thickness of 5 to 10 nm.

2. The method for preparing the manganese-based Prussian white material according to claim 1, characterized in that: In step 1): The concentration of solution A is 0.2-0.6 mol / L; The organic acid sodium, the anion is selected from one or more of citrate, gluconate, malate, lactate, ethylenediaminetetraacetate, and oxalate; The inorganic acid sodium, anion is selected from Cl - 、NO3 - 、SO4 2- One or more of; In the solution B: The total concentration of soluble divalent salts is 0.2-0.6 mol / L; The concentration of organic acid sodium is 0.6~1.8mol / L; The concentration of inorganic acid sodium is 0.5-1.0 mol / L.

3. The method for preparing the manganese-based Prussian white material according to claim 1, characterized in that: In step 1): The temperature of the coprecipitation reaction is 50-90°C.

4. The method for preparing the manganese-based Prussian white material according to claim 1, characterized in that: In step 2): The temperature of the first aging is 50-90° C. and the time is 2-4 hours.

5. The method for preparing the manganese-based Prussian white material according to claim 1, characterized in that: In step 3): The sodium salt is selected from sodium thiosulfate and / or sodium iodide.

6. The method for preparing the manganese-based Prussian white material according to claim 1, characterized in that: In step 3): The molar ratio of the sodium salt to the sodium ferrocyanide in step (1) is 1 to 3:1; The molar ratio of the nickel salt to the sodium ferrocyanide in step (1) is 1:1.5-10.

7. The method for preparing the manganese-based Prussian white material according to claim 1, characterized in that: In step 3): The post-treatment includes one or more of cooling, washing, separation and drying.

8. The method for preparing the manganese-based Prussian white material according to claim 1, characterized in that: The manganese-based Prussian white material has a monoclinic phase structure.

9. Use of the manganese-based Prussian white material prepared by the method according to any one of claims 1 to 8 in sodium ion batteries.

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