Preparation method of KxNayMn [Mn (CN) 6] nH2O based on potassium sulfate

Abstract

The invention discloses a potassium sulfate-based KxNayMn [Mn (CN) 6]. NH2O preparation method, which is characterized in that a manganese sulfate aqueous solution is used as a first solution, a sodium cyanide aqueous solution containing sodium sulfite is used as a second solution, and potassium sulfate is introduced into the first solution and / or the second solution as a potassium source; and dropwise adding the second solution into the first solution in an inert environment, carrying out a co-precipitation reaction to obtain a suspension, and carrying out aging treatment to obtain a final product. Cheap sodium cyanide is used for replacing potassium cyanide to serve as a cyano source, potassium ions are introduced in combination with potassium sulfate, the production cost is remarkably reduced, and efficient recovery of raw materials and emission reduction of cyanide-containing wastewater are achieved by cooling, crystallizing and recycling reaction mother liquor. The Prussian blue compound prepared by the invention has a regular crystal structure and excellent electrochemical performance, and is suitable for being used as a sodium ion battery negative electrode material.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology and relates to a manganese-based Prussian blue analog that can be used as an electrode material for sodium-ion batteries, particularly a method for preparing potassium sodium manganese-based Prussian blue compounds using potassium sulfate as a potassium source. Background Technology

[0002] Against the backdrop of global energy structure transformation, the increasing depletion of traditional fossil fuels and the resulting environmental problems have accelerated the large-scale development of renewable energy. However, renewable energy sources such as wind and solar power exhibit significant intermittency and instability, necessitating efficient and reliable energy storage technologies to support their large-scale grid-connected applications. Among various energy storage technologies, electrochemical energy storage, with its high energy conversion efficiency, flexible deployment capabilities, and environmentally friendly characteristics, has become a key component in building a new energy system.

[0003] Lithium-ion batteries, as a relatively mature technology in the field of electrochemical energy storage, dominate the secondary battery market due to their high energy density, long cycle life, and well-established industrial chain. However, the further development of lithium-ion batteries faces dual constraints: on the one hand, the uneven geographical distribution of global lithium resources and the limited abundance in the Earth's crust lead to structural risks in raw material supply; on the other hand, they pose a risk of thermal runaway under extreme operating conditions, and safety issues limit their widespread application in scenarios such as large-scale energy storage power stations.

[0004] Against this backdrop, sodium-ion batteries are considered a highly promising alternative for large-scale energy storage due to their similar working principle to lithium-ion batteries, as well as the advantages of abundant and widely distributed sodium resources and low cost. Although sodium-ion batteries do not yet match the energy density of lithium-ion batteries and the overall technology is still in the early stages of commercialization, they have demonstrated unique advantages in low-temperature performance, safety performance, and cycle stability, showing promising application prospects.

[0005] After decades of development, the core material system for sodium-ion batteries has gradually matured. Currently, the mainstream cathode materials include transition metal oxides, polyanionic compounds, and Prussian blue analogues (PBAs). Among these, transition metal oxides exhibit outstanding specific capacity, while polyanionic compounds possess superior structural stability and cycle performance.

[0006] Prussian blue analogues have the properties of being composed of cyanide (CN) - The bridging bimetallic coordination framework forms an open three-dimensional macroporous structure, which is particularly conducive to the reversible and rapid migration of larger sodium ions, thus showing significant potential in terms of theoretical specific capacity and rate performance. Its general chemical formula is A. x M1[M2(CN)6] 1-y □ y ·n H2O, where A is Na + Li + K + Equivalent mobile cations; M1 is an N-coordinated transition metal ion; M2 is a C-coordinated transition metal ion; □ represents a [M2(CN)6] vacancy; 0 ≤ x ≤2; 0≤ y＜ 1. This type of material has a wide range of raw material sources, a simple synthesis process, and is environmentally friendly. It exhibits significant advantages whether used as a positive or negative electrode material in sodium-ion batteries.

[0007] CN 118248879A discloses a sodium-ion battery, which uses K... a Na b Cu c M d [Fe(CN)6]·mH2O is the positive electrode active material, K x Na y Mn z [Mn(CN)6]·nH2O is used as the negative electrode active material in an organic sodium-ion battery system. Both the positive and negative electrode active materials of this sodium-ion battery utilize Prussian blue analogues containing a mixture of sodium and potassium ions. By introducing an appropriate amount of potassium ions, the lattice volume is effectively expanded, enhancing the unobstructed flow of sodium ion insertion / extraction channels and structural stability, thereby achieving extremely high ion diffusion rates and rate performance. Experiments show that after 10,000 cycles at a high rate of 5C, the battery retains over 99% of its capacity, demonstrating excellent long-term cycle stability.

[0008] However, its negative electrode material K x Na y Mn z The synthesis of [Mn(CN)6]·nH2O still follows the traditional salt solution co-precipitation method. A mixed solution of sodium cyanide and potassium cyanide is added dropwise to a manganese sulfate solution, reacting to form a precipitate. After filtration, washing, and drying, the target product is obtained. Although this method is simple, cost-effective, and suitable for the synthesis of nanoscale Prussian blue analogs, it has the following problems in practical industrial applications:

[0009] 1. High cost of potassium source: The potassium source used in the synthesis process is potassium cyanide, which is expensive and not conducive to controlling the overall cost of materials;

[0010] 2. Byproducts are difficult to recover: The reaction produces a mixed salt of sodium sulfate and potassium sulfate, which is difficult to separate and purify, has poor economic recovery, and the purity of the byproducts is low, making it difficult to achieve resource utilization.

[0011] 3. Insufficient environmental friendliness of the process: The use of cyanide-containing reagents and the generation of complex salt byproducts increase the burden of wastewater treatment and environmental compliance.

[0012] Currently, the synthesis of potassium-doped Prussian blue analogues generally employs potassium cyanide-containing sources, such as Her et al. (Anomalous Non-Prussian Blue Structures and Magnetic Ordering of K2Mn). II [Mn II (CN)6] andRb2Mn II [Mn II (CN)6]. Inorg. Chem (2010, 49, 1524-1534.) reported on K2Mn II [Mn II The synthesis of (CN)6 involves reacting potassium cyanide as the potassium source with a soluble manganese salt (manganese chloride or manganese acetate) in an aqueous phase. While this method is feasible on a laboratory scale, it faces the dual challenges of raw material costs and byproduct disposal in large-scale production.

[0013] Therefore, developing a method for synthesizing potassium-doped Prussian blue analogues that has lower raw material costs, greener processes, and easier separation and resource utilization of byproducts is of great significance for promoting the industrialization of sodium-ion battery materials. Summary of the Invention

[0014] The purpose of this invention is to provide a potassium sulfate-based K x Na y The method for preparing Mn[Mn(CN)6]·nH2O uses sodium cyanide as the cyanide source and potassium sulfate as the potassium source to prepare the potassium sodium manganese-based Prussian blue compound.

[0015] To achieve the above-mentioned objectives, the present invention provides a potassium sulfate-based K... x Na y The preparation method of Mn[Mn(CN)6]·nH2O involves preparing an aqueous solution of manganese sulfate as the first solution, an aqueous solution of sodium cyanide containing sodium sulfite as the second solution, and introducing potassium sulfate as a potassium source into the first and / or second solutions. Under an inert environment, the second solution is added dropwise to the first solution to carry out a co-precipitation reaction to obtain a suspension, which is then aged to obtain K. x Na y Mn[Mn(CN)6]·nH2O.

[0016] The potassium sulfate can be completely dissolved in the first solution, completely dissolved in the second solution, or distributed in any proportion and dissolved in the first and second solutions respectively.

[0017] In the preparation method of the present invention, the molar ratio of sodium cyanide, sodium sulfite and manganese sulfate is 3-5:0.1-0.2:1.

[0018] Furthermore, in the preparation method of the present invention, the molar ratio of potassium sulfate to sodium cyanide is 0.05 to 0.2:1.

[0019] As a preferred technical solution, the pH value of the first solution is further adjusted to 1-3.

[0020] As a preferred technical solution, the rate at which the second solution is added to the first solution is 10-200 mL / min.

[0021] As a preferred technical solution, the aging time of the suspension is 0.5 to 6 hours.

[0022] As a preferred technical solution, the suspension is aged, the precipitate is collected, washed, and then vacuum dried at 70–90°C for 12–24 hours to obtain K. x Na y Mn[Mn(CN)6]·nH2O products.

[0023] Furthermore, the preparation method of the present invention also includes aging the suspension and then filtering and recycling the mother liquor for reuse.

[0024] More specifically, the mother liquor is recycled by cooling the filtered mother liquor at -10 to 0°C to crystallize it, separating the precipitated sodium sulfate solid, and then using the remaining crystallized mother liquor as a solvent to prepare the second solution.

[0025] Furthermore, when preparing the second solution using the mother liquor after crystallization, the insufficient amounts of sodium cyanide, sodium sulfite, and potassium sulfate are supplemented according to the component content in the mother liquor after crystallization to meet the molar ratio requirements of the raw materials.

[0026] Furthermore, when preparing the second solution using the mother liquor after crystallization, all the additional potassium sulfate that needs to be added can be added to the first solution to simplify the operation and precisely control the composition of the final product.

[0027] When the mother liquor after crystallization described in this invention is recycled, although it still contains a small amount of sodium sulfate, it does not affect the coprecipitation reaction. Moreover, the small amount of sodium sulfate can also play a role in enriching sodium, thereby improving the vacancy defects in the prepared potassium-sodium-manganese-based Prussian blue compounds.

[0028] This invention innovatively proposes a preparation method that uses sodium cyanide, which is much cheaper than potassium cyanide, as the source of the cyanide group, and combines it with potassium sulfate to introduce potassium ions, significantly reducing production costs and successfully preparing potassium-sodium-manganese-based Prussian blue compound materials with excellent electrochemical performance. The material has a regular crystal structure and, as a negative electrode in sodium-ion batteries, exhibits high reversible specific capacity, excellent cycle stability, and outstanding rate performance.

[0029] The preparation method of this invention also achieves efficient recovery and utilization of valuable components such as sodium cyanide, sodium sulfite and potassium sulfate through the establishment of a mother liquor cooling crystallization and recycling process, which greatly reduces the discharge and subsequent treatment of cyanide-containing wastewater and meets the requirements of green and sustainable production.

[0030] The preparation method of this invention has mild process conditions, is simple and safe to operate, has good repeatability, and has the potential for large-scale industrial production. Attached Figure Description

[0031] Figure 1 K was prepared in Example 1. 1.655 Na 0.023 Mn[Mn(CN)6] 0.877 X-ray diffraction pattern of 0.45H2O.

[0032] Figure 2 K was prepared in Example 1. 1.655 Na 0.023 Mn[Mn(CN)6] 0.877 Scanning electron microscope image of 0.45H2O.

[0033] Figure 3 The first charge-discharge curve of the product prepared in Example 1 as the negative electrode material of the dual Prussian blue sodium-ion battery system is shown.

[0034] Figure 4 The diagram shows the 1C cycle performance of the product prepared in Example 1 as the negative electrode material in the dual Prussian blue sodium-ion battery system.

[0035] Figure 5 The rate performance of the product prepared in Example 1 as the negative electrode material of the dual Prussian blue sodium-ion battery system is shown.

[0036] Figure 6 K was prepared in Example 7. 1.618 Na 0.025 Mn[Mn(CN)6] 0.884 X-ray diffraction pattern of 0.46H2O.

[0037] Figure 7 K was prepared in Example 7. 1.618 Na 0.025 Mn[Mn(CN)6] 0.884 Scanning electron microscope image of 0.46H2O.

[0038] Figure 8 The first charge-discharge curve of the product prepared in Example 7 as the negative electrode material of the dual Prussian blue sodium-ion battery system is shown.

[0039] Figure 9The diagram shows the 1C cycle performance of the product prepared in Example 7 as the negative electrode material in the dual Prussian blue sodium-ion battery system.

[0040] Figure 10 The rate performance of the product prepared in Example 7 as the negative electrode material of the double Prussian blue sodium-ion battery system is shown. Implementation

[0041] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples. The following examples are only used to more clearly illustrate the technical solutions of the present invention, so that those skilled in the art can better understand and utilize the present invention, and are not intended to limit the scope of protection of the present invention.

[0042] Unless otherwise specified, the production processes, experimental methods, or testing methods involved in the embodiments and comparative examples of this invention are all conventional methods in the prior art, and their names and / or abbreviations are all conventional names in the art, which are very clear and distinct in the relevant application fields. Those skilled in the art can understand the conventional process steps based on the names and apply the corresponding equipment, and implement them according to conventional conditions or the conditions recommended by the manufacturer.

[0043] The various instruments, equipment, raw materials or reagents used in the embodiments of this invention are not subject to any special restrictions on their source. They are all conventional products that can be purchased through regular commercial channels and can be prepared according to conventional methods known to those skilled in the art.

[0044] The purpose of this invention is to provide a potassium sulfate-based K x Na y A method for preparing Mn[Mn(CN)6]·nH2O was developed to fully utilize mother liquor recycling and reduce costs.

[0045] The potassium sulfate-based K of the present invention x Na y The specific methods for preparing Mn[Mn(CN)6]·nH2O include:

[0046] S1. Prepare a manganese sulfate aqueous solution as the first solution, and adjust the pH of the first solution to 1-3;

[0047] S2. Prepare a sodium cyanide aqueous solution containing sodium sulfite as a second solution, with the molar amount of sodium cyanide being 3 to 5 times that of manganese sulfate. The molar amount of sodium sulfite is 10 to 20% of the molar amount of manganese sulfate.

[0048] S3. Dissolve potassium sulfate in the first solution and / or the second solution, wherein the molar amount of potassium sulfate accounts for 5-20% of the molar amount of sodium cyanide;

[0049] S4. Under an inert environment, the second solution is added dropwise to the first solution, and a precipitation reaction is carried out at room temperature to obtain a suspension;

[0050] S5. After aging and recovery of the mother liquor, the precipitate is collected to obtain K. x Na y Mn[Mn(CN)6]·nH2O;

[0051] S6. Cool the recovered mother liquor to crystallize, and filter to recover the sodium sulfate solid precipitate to obtain the crystallized mother liquor.

[0052] S7. The mother liquor after crystallization is reused to prepare a second solution. Example

[0053] Example 1

[0054] Weigh 42.25g (0.25mol) of manganese sulfate monohydrate and dissolve it in 200mL of deionized water. Adjust the pH to 2 with sulfuric acid solution to prepare the first solution.

[0055] Weigh 40.44 g (0.825 mol) sodium cyanide, 3.78 g (0.03 mol) sodium sulfite, and 25.44 g (0.146 mol) potassium sulfate and dissolve them in 200 mL of deionized water to prepare the second solution.

[0056] Under nitrogen protection, the second solution was added dropwise to the first solution, which was also under nitrogen protection, at a rate of 50 mL / min, and a precipitation reaction was carried out at room temperature to obtain a suspension.

[0057] The suspension was stirred and aged for 1 hour, the mother liquor was recovered by filtration, the solid precipitate was collected, washed 3 times with deionized water, washed once with anhydrous ethanol, and dried under vacuum at 80°C for 24 hours to obtain the target product.

[0058] The content of each metal element in the product was determined by inductively coupled plasma mass spectrometry (ICP-MS), with K content of 20.65 wt%, Na content of 0.17 wt%, and Mn content of 32.91 wt%. The moisture content of the product was determined by thermogravimetric analysis, with a weight loss of 2.58% upon heating to 200℃, and the number of water molecules of crystallization was calculated.

[0059] Therefore, the molecular formula of the target product is calculated to be K. 1.655 Na 0.023 Mn[Mn(CN)6] 0.877 0.45H2O.

[0060] The X-ray powder diffraction pattern of the product is as follows Figure 1 As shown, the product has a face-centered cubic structure and is a crystal with good crystallinity.

[0061] according to Figure 2 The scanning electron microscope image shows that the product is a particle agglomerate with a particle size of about 10µm.

[0062] Using the aforementioned target product as the negative electrode material, a double Prussian blue sodium-ion battery system was formed with manganese-based Prussian white, and its electrochemical performance was measured.

[0063] in accordance with Figure 3 The first charge-discharge curves show that the material achieved a discharge specific capacity of 63.8 mAh / g at a 0.1C rate, confirming its good initial electrochemical activity.

[0064] Figure 4 Cyclic performance test results show that the material has excellent structural stability. After 500 cycles at 1C rate, its capacity retention is still as high as 98.5%.

[0065] also, Figure 5 The rate performance test curves show that even under high rate conditions of 10C, the material can still release a considerable capacity of 55.9 mAh / g, demonstrating its excellent high rate performance.

[0066] Example 2

[0067] Weigh 42.25g (0.25mol) manganese sulfate monohydrate and 9.76g (0.056mol) potassium sulfate and dissolve them in 250mL of deionized water. Adjust the pH to 1.5 with hydrochloric acid solution to prepare the first solution.

[0068] Weigh 55.14 g (1.125 mol) of sodium cyanide and 3.15 g (0.025 mol) of sodium sulfite and dissolve them in 200 mL of deionized water to prepare a second solution.

[0069] Under nitrogen protection, the second solution was added dropwise to the first solution, which was also under nitrogen protection, at a rate of 100 mL / min, and a precipitation reaction was carried out at room temperature to obtain a suspension.

[0070] The suspension was stirred and aged for 0.5 h, the mother liquor was recovered by filtration, the solid precipitate was collected, washed three times with deionized water, and then washed once with anhydrous ethanol. The precipitate was then dried under vacuum at 80 °C for 24 h to obtain the target product.

[0071] Example 3

[0072] Weigh 42.25g (0.25mol) of manganese sulfate monohydrate and dissolve it in 150mL of deionized water. Adjust the pH to 1 with hydrochloric acid solution to prepare the first solution.

[0073] Weigh 44.11 g (0.9 mol) sodium cyanide, 3.78 g (0.03 mol) sodium sulfite, and 20.91 g (0.12 mol) potassium sulfate and dissolve them in 200 mL of deionized water to prepare a second solution.

[0074] Under nitrogen protection, the second solution was added dropwise to the first solution, which was also under nitrogen protection, at a rate of 80 mL / min, and a precipitation reaction was carried out at room temperature to obtain a suspension.

[0075] The suspension was stirred and aged for 2 hours, the mother liquor was recovered by filtration, the solid precipitate was collected, washed 3 times with deionized water, washed once with anhydrous ethanol, and dried under vacuum at 80°C for 24 hours to obtain the target product.

[0076] Example 4

[0077] Weigh 42.25g (0.25mol) manganese sulfate monohydrate and 13.07g (0.075mol) potassium sulfate and dissolve them in 170mL of deionized water. Adjust the pH to 2.5 with sulfuric acid solution to prepare the first solution.

[0078] Weigh 36.76 g (0.75 mol) sodium cyanide, 6.30 g (0.05 mol) sodium sulfite, and 13.07 g (0.075 mol) potassium sulfate and dissolve them in 200 mL of deionized water to prepare a second solution.

[0079] Under nitrogen protection, the second solution was added dropwise to the first solution, which was also under nitrogen protection, at a rate of 200 mL / min, and a precipitation reaction was carried out at room temperature to obtain a suspension.

[0080] The suspension was stirred and aged for 3 hours, the mother liquor was recovered by filtration, the solid precipitate was collected, washed 3 times with deionized water, washed once with anhydrous ethanol, and dried under vacuum at 80°C for 24 hours to obtain the target product.

[0081] Example 5

[0082] Weigh 42.25g (0.25mol) manganese sulfate monohydrate and 13.94g (0.08mol) potassium sulfate and dissolve them in 200mL of deionized water. Adjust the pH to 2 with sulfuric acid solution to prepare the first solution.

[0083] Weigh 47.78 g (0.975 mol) sodium cyanide, 3.78 g (0.03 mol) sodium sulfite, and 3.49 g (0.02 mol) potassium sulfate and dissolve them in 200 mL of deionized water to prepare a second solution.

[0084] Under nitrogen protection, the second solution was added dropwise to the first solution, which was also under nitrogen protection, at a rate of 10 mL / min, and a precipitation reaction was carried out at room temperature to obtain a suspension.

[0085] The suspension was stirred and aged for 6 hours, the mother liquor was recovered by filtration, the solid precipitate was collected, washed 3 times with deionized water, washed once with anhydrous ethanol, and dried under vacuum at 80°C for 24 hours to obtain the target product.

[0086] Example 6

[0087] Weigh 42.25g (0.25mol) manganese sulfate monohydrate and 4.18g (0.024mol) potassium sulfate and dissolve them in 200mL of deionized water. Adjust the pH to 3 with sulfuric acid solution to prepare the first solution.

[0088] Weigh 40.43 g (0.825 mol) sodium cyanide, 4.73 g (0.0375 mol) sodium sulfite, and 16.73 g (0.096 mol) potassium sulfate and dissolve them in 200 mL of deionized water to prepare a second solution.

[0089] Under nitrogen protection, the second solution was added dropwise to the first solution, which was also under nitrogen protection, at a rate of 150 mL / min, and a precipitation reaction was carried out at room temperature to obtain a suspension.

[0090] The suspension was stirred and aged for 1 hour, the mother liquor was recovered by filtration, the solid precipitate was collected, washed 3 times with deionized water, washed once with anhydrous ethanol, and dried under vacuum at 80°C for 24 hours to obtain the target product.

[0091] Example 7

[0092] The composition and content of the recovered mother liquor in Example 1 were analyzed. The content of sodium cyanide was 11.24 g / L, sodium sulfite was 6.96 g / L, sodium sulfate was 122.61 g / L, and potassium sulfate was 14.75 g / L.

[0093] The mother liquor was cooled and crystallized at -4℃, then filtered to collect the solid precipitate and the crystallized mother liquor separately.

[0094] Further analysis of the solid precipitate revealed that its main component was sodium sulfate.

[0095] Analysis of the mother liquor after crystallization revealed the following contents: sodium cyanide 12.84 g / L, sodium sulfite 6.12 g / L, sodium sulfate 29.23 g / L, and potassium sulfate 16.06 g / L.

[0096] Weigh 42.25g (0.25mol) manganese sulfate monohydrate and 22.23g (0.1276mol) potassium sulfate and dissolve them in 200mL of deionized water. Adjust the pH to 2 with sulfuric acid solution to prepare the first solution.

[0097] Weigh 37.87 g (0.7726 mol) of sodium cyanide and 2.56 g (0.02 mol) of sodium sulfite and dissolve them in 200 mL of the mother liquor after crystallization to prepare the second solution.

[0098] The second solution contains 40.44 g (0.825 mol) of sodium cyanide, 3.78 g (0.03 mol) of sodium sulfite, 5.85 g (0.0412 mol) of sodium sulfate, and 3.21 g (0.0184 mol) of potassium sulfate.

[0099] Under nitrogen protection, the second solution was added dropwise to the first solution, which was also under nitrogen protection, at a rate of 50 mL / min, and a precipitation reaction was carried out at room temperature to obtain a suspension.

[0100] The suspension was stirred and aged for 1 hour, the mother liquor was recovered by filtration, the solid precipitate was collected, washed 3 times with deionized water, washed once with anhydrous ethanol, and dried under vacuum at 80°C for 24 hours to obtain the target product.

[0101] The metal element content of the product was determined by ICP-MS, and the moisture content of the product was determined by thermogravimetric analysis to calculate the number of water molecules of crystallization.

[0102] The K content was 20.18 wt%, Na content was 0.18 wt%, and Mn content was 33.01 wt%; the weight loss upon heating to 200℃ was 2.62%. The calculated molecular formula of the target product is K. 1.618 Na 0.025 Mn[Mn(CN)6] 0.884 0.46H2O.

[0103] The X-ray powder diffraction pattern of the product is as follows Figure 6 It has a face-centered cubic structure and is a crystal with good crystallinity. Figure 7 The scanning electron microscope image shows that the product is a particulate aggregate with a particle size of about 10 µm.

[0104] The target product was used as the negative electrode material, and its electrochemical performance was measured by forming a double Prussian blue sodium-ion battery system with manganese-based Prussian white. Figure 3 The initial charge-discharge curve shows a discharge specific capacity of 63.2 mAh / g at a 0.1C rate, and the cycle performance curve is as follows: Figure 9 The capacity retention rate after 500 cycles at 1C is 98.5%. Figure 10 In the rate performance curve, the discharge specific capacity at 10C is 55.8mAh / g.

[0105] Example 8

[0106] The composition and content of the mother liquor recovered in Example 7 were analyzed. The content of sodium cyanide was 12.58 g / L, sodium sulfite was 7.34 g / L, sodium sulfate was 131.64 g / L, and potassium sulfate was 12.38 g / L.

[0107] The mother liquor was cooled and crystallized at -4℃, then filtered, and the solid precipitate and the mother liquor after crystallization were collected separately. Analysis showed that the main component of the solid precipitate was sodium sulfate. The mother liquor after crystallization contained 15.52 g / L sodium cyanide, 7.03 g / L sodium sulfite, 29.65 g / L sodium sulfate, and 16.58 g / L potassium sulfate.

[0108] Weigh 42.25g (0.25mol) manganese sulfate monohydrate and 22.12g (0.1269mol) potassium sulfate and dissolve them in 200mL of deionized water. Adjust the pH to 2 with sulfuric acid solution to prepare the first solution.

[0109] Weigh 37.33 g (0.7617 mol) of sodium cyanide and 2.38 g (0.0189 mol) of sodium sulfite and dissolve them in 200 mL of the mother liquor after crystallization to prepare the second solution.

[0110] The second solution contains 40.44 g (0.825 mol) of sodium cyanide, 3.78 g (0.03 mol) of sodium sulfite, 5.93 g (0.0417 mol) of sodium sulfate, and 3.32 g (0.0190 mol) of potassium sulfate.

[0111] Under nitrogen protection, the second solution was added dropwise to the first solution, which was also under nitrogen protection, at a rate of 50 mL / min, and a precipitation reaction was carried out at room temperature to obtain a suspension.

[0112] The suspension was stirred and aged for 1 hour, the mother liquor was recovered by filtration, the solid precipitate was collected, washed 3 times with deionized water, washed once with anhydrous ethanol, and dried under vacuum at 80°C for 24 hours to obtain the target product.

[0113] Example 9

[0114] The composition and content of the mother liquor recovered in Example 8 were analyzed. The content of sodium cyanide was 12.04 g / L, sodium sulfite was 7.34 g / L, sodium sulfate was 128.20 g / L, and potassium sulfate was 14.86 g / L.

[0115] The mother liquor was cooled and crystallized at -4℃, then filtered, and the solid precipitate and the mother liquor after crystallization were collected separately. Analysis showed that the main component of the solid precipitate was sodium sulfate. The mother liquor after crystallization contained 14.18 g / L sodium cyanide, 6.27 g / L sodium sulfite, 31.27 g / L sodium sulfate, and 16.69 g / L potassium sulfate.

[0116] Weigh 42.25g (0.25mol) manganese sulfate monohydrate and 22.10g (0.1268mol) potassium sulfate and dissolve them in 200mL of deionized water. Adjust the pH to 2 with sulfuric acid solution to prepare the first solution.

[0117] Weigh 37.60 g (0.7673 mol) of sodium cyanide and 2.53 g (0.0201 mol) of sodium sulfite and dissolve them in 200 mL of the mother liquor after crystallization to prepare the second solution.

[0118] The second solution contains 40.44 g (0.825 mol) of sodium cyanide, 3.78 g (0.03 mol) of sodium sulfite, 6.25 g (0.0440 mol) of sodium sulfate, and 3.34 g (0.0192 mol) of potassium sulfate.

[0119] Under nitrogen protection, the second solution was added dropwise to the first solution, which was also under nitrogen protection, at a rate of 50 mL / min, and a precipitation reaction was carried out at room temperature to obtain a suspension.

[0120] The suspension was stirred and aged for 1 hour, the mother liquor was recovered by filtration, the solid precipitate was collected, washed 3 times with deionized water, washed once with anhydrous ethanol, and dried under vacuum at 80°C for 24 hours to obtain the target product.

[0121] The above embodiments of the present invention do not describe all details exhaustively, nor do they limit the present invention to the embodiments described above. Various changes, modifications, substitutions, and variations made by those skilled in the art to these embodiments without departing from the principles and spirit of the present invention should be included within the scope of protection of the present invention.

Claims

1. A potassium sulfate-based K x Na y The method for preparing Mn[Mn(CN)6]·nH2O is characterized by: Prepare an aqueous solution of manganese sulfate as the first solution, an aqueous solution of sodium cyanide containing sodium sulfite as the second solution, and introduce potassium sulfate into the first solution and / or the second solution. Under inert conditions, the second solution is added dropwise to the first solution to undergo a co-precipitation reaction, resulting in a suspension. K is then obtained through aging. x Na y Mn[Mn(CN)6]·nH2O.

2. The preparation method according to claim 1, characterized in that: The potassium sulfate is either completely dissolved in the first solution, or completely dissolved in the second solution, or it is distributed in any proportion and dissolved in the first solution and the second solution respectively.

3. The preparation method according to claim 1, characterized in that: The molar ratio of sodium cyanide, sodium sulfite and manganese sulfate is 3-5:0.1-0.2:

1.

4. The preparation method according to claim 1, characterized in that: The molar ratio of potassium sulfate to sodium cyanide is 0.05 to 0.2:

1.

5. The preparation method according to claim 1, characterized in that: Adjust the pH of the first solution to 1-3.

6. The preparation method according to claim 1, characterized in that: The second solution is added dropwise to the first solution at a rate of 10-200 mL / min.

7. The preparation method according to claim 1, characterized in that: The aging time of the suspension is 0.5 to 6 hours.

8. The preparation method according to claim 1, characterized in that: After aging of the suspension, the precipitate was collected, washed, and vacuum dried at 70–90 °C for 12–24 h to obtain K. x Na y Mn[Mn(CN)6]·nH2O products.

9. The preparation method according to claim 1, characterized in that: It also includes aging the suspension and then filtering and recycling the mother liquor for reuse.

10. The preparation method according to claim 9, characterized in that: The mother liquor recovered by filtration is cooled at -10 to 0°C to crystallize, and the precipitated sodium sulfate solid is separated. The remaining mother liquor after crystallization is reused as a solvent to prepare the second solution.

11. The preparation method according to claim 10, characterized in that: Based on the composition of the mother liquor after crystallization, supplement the insufficient amounts of sodium cyanide, sodium sulfite, and potassium sulfate to meet the raw material molar ratio requirements.

12. The preparation method according to claim 11, characterized in that: Add all the potassium sulfate that needs to be added to the first solution.

13. A potassium-sodium-manganese-based Prussian blue compound K x Na y Mn[Mn(CN)6]·nH2O, prepared by any of the preparation methods described in claims 1 to 12, is used as a negative electrode material for sodium-ion batteries.

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