Preparation method of Prussian blue compound

Abstract

The invention belongs to the technical field of secondary ion batteries, and discloses a preparation method of a Prussian blue compound, which comprises the following steps: by taking sodium cyanide as a cyanide complexing agent and divalent manganese salt as a central complexing ion, carrying out coprecipitation reaction in an aqueous solution reaction system under the protection of an inert atmosphere and a reducing agent to prepare the Prussian blue compound NaxMn [Mn (CN) 6] y-1-y.nH2O. The Prussian blue compound prepared by the method can be used as an organic sodium ion battery positive electrode material or an aqueous sodium ion battery negative electrode material, and shows excellent electrochemical performance.

Description

Technical Field

[0001] The invention belongs to the technical field of secondary ion batteries, and relates to a Prussian blue analogue that can be used as an electrode material for a sodium ion battery, and in particular to a method for preparing a manganese-based Prussian blue compound containing only manganese and sodium metal elements. Background Art

[0002] The decreasing reserves of traditional fossil energy have intensified people's pursuit of finding new alternative energy sources. Secondary batteries have become the most attractive electrochemical storage technology due to their high energy efficiency and easy deployment.

[0003] At present, lithium-ion batteries occupy the main market of secondary batteries, but the uneven distribution and low abundance of lithium resources have become the main bottleneck restricting the large-scale energy storage application of lithium-ion batteries.

[0004] Similar to lithium-ion batteries, sodium-ion batteries are a new type of rechargeable battery that uses sodium ions as battery electrode materials. Although sodium-ion battery technology is still in the research and development stage and has not yet been commercialized on a large scale, based on the abundant reserves of sodium resources, low cost, and excellent low-temperature performance and safety performance of sodium-ion batteries, sodium-ion batteries have shown good prospects in the field of large-scale stationary energy storage and are expected to become a new generation of energy storage batteries.

[0005] Polyanionic compounds, transition metal oxides and Prussian blue analogs are widely used as electrode materials for sodium ion batteries. Among them, Prussian blue analogs (PBAs) have a high theoretical capacity due to their unique electronic structure of cyanide double coordination, unique open framework and three-dimensional macroporous structure, which is suitable for the rapid migration of sodium ions with a large radius, and have outstanding advantages such as non-toxicity, low price and excellent electrochemical performance, making them a very potential electrode material for sodium ion batteries.

[0006] Prussian blue compounds based on manganese-based structures Na x Mn[Mn(CN)6] y □ 1-y nH2O is a Prussian blue analogue with high electrochemical activity. The reversible specific capacity of this substance can reach 209 mAh / g, which is much higher than the theoretical specific capacity of 172 mAh / g of conventional reversible embedding of two sodium ions in PBAs. The reason is that three sodium ions are embedded in the constant current discharge process. The additional capacity comes from the insertion of the third sodium ion and the reduction of carbon-coordinated manganese to manganese (I). Based on this, the above-mentioned Prussian blue compounds with manganese-based structures have broad prospects as positive electrode materials for organic sodium-ion batteries.

[0007] In addition, the above-mentioned Prussian blue compounds based on manganese-manganese-based structure have a nominal potential of -0.7V relative to the standard hydrogen electrode, while the conventional manganese-iron-based Prussian blue compounds have a nominal potential of 0.9V relative to the standard hydrogen electrode. When these two materials are used to assemble aqueous sodium-ion batteries, their operating voltage can reach 1.6V, significantly improving the energy density of the device. Natronenergy has developed aqueous sodium-ion batteries based on the above two materials.

[0008] However, the industrial synthesis of the above-mentioned Prussian blue compounds based on the Mn-based structure is still a challenge. The conventional salt solution co-precipitation method of Prussian blue analogs is used to prepare the above-mentioned Prussian blue compounds, but the cyclic stability of the products is very poor and cannot meet the practical application requirements as electrode materials.

[0009] US 9099740 B1 points out that under the protection of nitrogen with an oxygen content of less than 0.1 ppm, manganese acetate tetrahydrate can be co-precipitated with sodium cyanide to prepare the above-mentioned Prussian blue compound based on the manganese-based structure. The product can be used as the negative electrode material of the aqueous sodium ion battery and can exhibit good electrochemical properties.

[0010] However, the preparation method of the Prussian blue compound provided in the above patent document still has the following shortcomings:

[0011] 1) In order to prevent the oxidation of manganese ions to form manganese hydroxide and ensure the quality of the prepared product, the patent document is extremely strict in controlling the synthesis reaction conditions, requiring that the entire synthesis process be carried out in an inert nitrogen atmosphere with an oxygen content of less than 0.1 ppm. Although a laboratory glove box can meet this requirement, it is almost impossible to achieve in actual large-scale industrial production.

[0012] 2) In order to obtain the claimed electrode material performance, the patent document requires that the crystal structure of the prepared product has a face-centered cubic structure or a monoclinic structure, or a combination of the two, and the grain size of the crystal structure must be greater than 200nm. However, according to the SEM image of the product provided in the patent document, it can be seen that the maximum grain size does not exceed 2µm. However, the particle size of the product is about 10µm, which is beneficial to separation, and the electrochemical performance of the product with this particle size is better when used as an electrode material. Summary of the invention

[0013] The purpose of the present invention is to overcome the problems of the prior art and provide a method for preparing a Prussian blue compound so as to realize large-scale industrial production of the Prussian blue compound under relatively low synthesis conditions.

[0014] The preparation method of the Prussian blue compound of the present invention is a technical improvement on US 9099740 B1. By adding a reducing agent and adjusting the pH value in the aqueous solution reaction system, it is ensured that the oxygen content in the synthesis reaction process only needs to be reduced to below 100 ppm, so that the formation and oxidation of manganese hydroxide can be effectively prevented, the product quality can be guaranteed, thereby reducing the synthesis conditions and costs, and realizing large-scale industrial production.

[0015] More specifically, the preparation method of the Prussian blue compound of the present invention is to add a sodium cyanide aqueous solution dropwise to a soluble divalent manganese salt aqueous solution reaction system under inert atmosphere to carry out a coprecipitation reaction to prepare a Prussian blue compound represented by the following structural formula: x Mn[Mn(CN)6] y □ 1-y ·nH2O, where □ represents a hole, 1.5≤x≤2, 0.6≤y≤1, 1≤n≤2;

[0016] Different from US 9099740 B1, the present invention controls the oxygen content in the inert atmosphere to 10-100 ppm, adds a reducing agent as a protective agent to the aqueous solution reaction system of the soluble divalent manganese salt, and adjusts the pH value of the aqueous solution reaction system to be no greater than 4.

[0017] The Prussian blue compound prepared by the method of the present invention has a face-centered cubic structure and a monoclinic structure, and the particle size of the compound ranges from 5 to 20 μm, more preferably from 5 to 10 μm.

[0018] The reducing agent described in the present invention is at least one of sodium sulfite, sodium thiosulfate, ascorbic acid, sodium borohydride and sodium bisulfite.

[0019] Furthermore, the more preferred reducing agent of the present invention is sodium sulfite.

[0020] Furthermore, the amount of the reducing agent used is preferably such that the molar ratio of the reducing agent to the soluble divalent manganese salt is 1:(5-10).

[0021] The present invention has no particular limitation on the raw materials used to adjust the pH value, and may be any inorganic acid or organic acid that can adjust the pH value of the reaction system and does not react with other raw materials in the reaction system, such as but not limited to at least one of hydrochloric acid, sulfuric acid, nitric acid, acetic acid, citric acid or ascorbic acid.

[0022] Furthermore, the soluble divalent manganese salt of the present invention may be manganese sulfate, manganese nitrate, manganese acetate or manganese chloride, and is preferably prepared into an aqueous solution with a concentration of 0.5 to 1.5 mol / L.

[0023] Furthermore, the present invention preferably prepares a sodium cyanide aqueous solution with a concentration of 1.5 to 6.0 mol / L.

[0024] The coprecipitation reaction of the present invention can be easily carried out at room temperature. Furthermore, the present invention preferably carries out the coprecipitation reaction at 0 to 40° C. for 5 to 120 minutes.

[0025] Furthermore, the molar ratio of the raw material soluble divalent manganese salt to sodium cyanide used for the coprecipitation reaction is preferably 1: (2-5).

[0026] More preferably, in the present invention, after stirring and aging the suspension obtained by the coprecipitation reaction, the solid precipitate is collected, washed and dried to obtain a Prussian blue compound.

[0027] Preferably, the present invention uses water and anhydrous ethanol to wash the solid precipitate respectively, and the washed solid precipitate is vacuum dried at room temperature to 100° C. for 10 to 24 hours to obtain a Prussian blue compound.

[0028] All solvents used in the preparation method of the present invention need to be degassed in advance.

[0029] The invention adds a certain proportion of a reducing agent and adjusts the pH value during the synthesis process, and by virtue of the fact that the reducing agent is more easily oxidized by oxygen than divalent manganese ions under acidic conditions, the formation and oxidation of manganese hydroxide can be effectively prevented, so that the quality of the product can be guaranteed by only controlling the oxygen content in the synthesis process to be below 100 ppm. Compared with the prior art, the synthesis conditions and the synthesis cost are greatly reduced, and large-scale industrial production can be easily realized.

[0030] The Prussian blue compounds prepared by the method of the present invention can be used as electrode materials for sodium ion batteries.

[0031] On the one hand, the Prussian blue compound can be used as a positive electrode material for an organic sodium ion battery.

[0032] The Prussian blue compound is used as a positive electrode material and assembled into an organic sodium ion battery with a glass fiber separator, metallic sodium and an organic electrolyte. The specific capacity under 0.1C test conditions can reach 205 mAh / g.

[0033] On the other hand, the Prussian blue compound can also be used as a negative electrode material for an aqueous sodium ion battery.

[0034] The Prussian blue compound is used as the negative electrode material, the manganese iron-based Prussian white electrode material is used as the positive electrode, and the aqueous solution containing sodium perchlorate is used as the electrolyte to assemble an aqueous sodium ion battery, and the specific capacity under 1C test conditions is 73mAh / g. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is the X-ray diffraction pattern of the Prussian blue compound prepared in Example 1.

[0036] Figure 2 This is a scanning electron microscope image of the Prussian blue compound prepared in Example 1.

[0037] Figure 3 The charge and discharge curves of the product prepared in Example 1 as the negative electrode material of an aqueous sodium ion battery.

[0038] Figure 4 The charge and discharge curves of the product prepared in Example 1 as the positive electrode material of an organic sodium ion battery.

[0039] Figure 5 This is the X-ray diffraction pattern of the Prussian blue compound prepared in Example 2.

[0040] Figure 6 This is a scanning electron microscope image of the Prussian blue compound prepared in Example 2.

[0041] Figure 7 This is a scanning electron microscope image of the product prepared in Comparative Example 1.

[0042] Figure 8 This is a scanning electron microscope image of the product prepared in Comparative Example 2.

[0043] Fig. 9 The charge and discharge curves of the product prepared in Comparative Example 2 as the negative electrode material for an aqueous sodium ion battery.

[0044] Fig.10 The charge and discharge curves of the product prepared in Comparative Example 2 as the positive electrode material of an organic sodium ion battery. Implementation

[0045] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are only used to more clearly illustrate the technical solution of the present invention so that those skilled in the art can well understand and utilize the present invention, rather than limiting the scope of protection of the present invention.

[0046] The production processes, experimental methods or detection methods involved in the embodiments and comparative examples of the present invention are all conventional methods in the prior art unless otherwise specified, and their names and / or abbreviations are all conventional names in the field and are very clear and unambiguous 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 to implement them according to conventional conditions or the conditions recommended by the manufacturer.

[0047] The various instruments, equipment, raw materials or reagents used in the embodiments of the present invention are not particularly limited in terms of their sources, and are all conventional products that can be purchased through regular commercial channels, or can be prepared according to conventional methods well known to those skilled in the art.

[0048] Unless otherwise specified, in the following examples and comparative examples of the present invention, the oxygen concentration in the nitrogen used for inert protection is controlled at 100 ppm. Example

[0049] Example 1

[0050] Weigh 42.26 g (0.25 mol) of manganese sulfate monohydrate and dissolve it in deionized water to prepare a concentration of 1.0 mol L -1 To the manganese sulfate solution, 3.78 g (0.03 mol) of sodium sulfite was added and dissolved evenly, and the pH value was adjusted to 2 with dilute hydrochloric acid to prepare solution A.

[0051] Dissolve 44.10 g (0.9 mol) of sodium cyanide in deionized water to prepare a concentration of 3.6 mol L -1 of solution B.

[0052] Under nitrogen protection, solution B was added dropwise to solution A which was also protected by nitrogen at a rate of 50 mL / min, and the coprecipitation reaction was carried out at room temperature for 1 h to obtain a suspension.

[0053] After the suspension was stirred and aged for 1 hour, the solid precipitate was collected by filtration, washed three times with deionized water, washed once with anhydrous ethanol, and vacuum dried at 80° C. for 24 hours to prepare a Prussian blue compound based on a manganese-based structure.

[0054] The structure of the prepared product was characterized. Figure 1 The X-ray diffraction pattern of the product proves that the product has a face-centered cubic structure and a monoclinic structure; Figure 2 The scanning electron microscope image shows that the product particles are a stack of cubic primary particles with obvious edges and steps, and the size of the primary particles is close to 10µm.

[0055] It was used as the negative electrode material to assemble an aqueous sodium ion battery with manganese iron-based Prussian white and sodium perchlorate aqueous solution, and tested under 1C conditions. Figure 3 From the charge and discharge curve shown, it can be seen that its specific capacity is 73mAh / g.

[0056] Using it as the positive electrode material, an organic sodium ion battery was assembled with a glass fiber separator, metallic sodium and an organic electrolyte, and tested under 0.1C conditions. Figure 4 From the charge and discharge curve shown, it can be seen that its specific capacity reaches 205mAh / g.

[0057] Example 2

[0058] Weigh 42.26 g (0.25 mol) of manganese sulfate monohydrate and dissolve it in deionized water to prepare a concentration of 1.2 mol L -1 To the manganese sulfate solution, 3.94 g (31.25 mmol) of sodium sulfite was added to dissolve evenly, and the pH value was adjusted to 3 with dilute sulfuric acid to prepare solution A.

[0059] Dissolve 44.10 g (0.9 mol) of sodium cyanide in deionized water to prepare a concentration of 4.5 mol L -1 of solution B.

[0060] Under nitrogen protection, solution B was added dropwise to solution A which was also protected by nitrogen at a rate of 50 mL / min, and coprecipitation reaction was carried out at 25°C for 1 h to obtain a suspension.

[0061] After the suspension was stirred and aged for 2 hours, the solid precipitate was collected by filtration, washed three times with deionized water, washed once with anhydrous ethanol, and vacuum dried at 80° C. for 24 hours to prepare a Prussian blue compound based on a manganese-based structure.

[0062] Figure 5 The X-ray diffraction pattern of the product proves that the product also has a face-centered cubic structure and a monoclinic structure; Figure 6 In the scanning electron microscope image, the particle size of the primary particles of the product is also close to 10µm.

[0063] Example 3

[0064] Weigh 42.26 g (0.25 mol) of manganese sulfate monohydrate and dissolve it in deionized water to prepare a concentration of 1.2 mol L -1 To the manganese sulfate solution, 3.78 g (0.03 mol) of sodium sulfite was added and dissolved evenly, and the pH value was adjusted to 2.5 with dilute sulfuric acid to prepare solution A.

[0065] Dissolve 44.10 g (0.9 mol) of sodium cyanide in deionized water to prepare a concentration of 3.5 mol L -1 of solution B.

[0066] Under nitrogen protection, solution B was added dropwise to solution A which was also protected by nitrogen at a rate of 20 mL / min, and the coprecipitation reaction was carried out at 15°C for 1.5 h to obtain a suspension.

[0067] After the suspension was stirred and aged for 1 hour, the solid precipitate was collected by filtration, washed three times with deionized water, washed once with anhydrous ethanol, and vacuum dried at 100° C. for 24 hours to prepare a Prussian blue compound based on a manganese-based structure.

[0068] Comparative Example 1

[0069] Weigh 42.26 g (0.25 mol) of manganese sulfate monohydrate and dissolve it in deionized water to prepare a concentration of 1.0 mol L -1 of manganese sulfate solution.

[0070] Dissolve 44.10 g (0.9 mol) of sodium cyanide in deionized water to prepare a concentration of 3.6 mol L -1 of sodium cyanide solution.

[0071] Under nitrogen protection, the sodium cyanide solution was added dropwise at a rate of 50 mL / min to the manganese sulfate solution also under nitrogen protection, and the coprecipitation reaction was carried out at room temperature for 1 hour to obtain a suspension.

[0072] After the suspension was stirred and aged for 1 hour, the solid precipitate was collected by filtration, washed three times with deionized water, washed once with anhydrous ethanol, and vacuum dried at 80° C. for 24 hours to prepare a Prussian blue compound based on a manganese-based structure.

[0073] Figure 7 The scanning electron microscope image of the product prepared in Comparative Example 1 is given, and the product is an irregular dense body with a rough surface and has not formed a complete crystalline structure.

[0074] Comparative Example 2

[0075] Weigh 42.26 g (0.25 mol) of manganese sulfate monohydrate and dissolve it in deionized water to prepare a concentration of 1.0 mol L -1 To the manganese sulfate solution, 3.78 g (0.03 mol) of sodium sulfite was added and dissolved evenly to prepare solution A.

[0076] Dissolve 44.10 g (0.9 mol) of sodium cyanide in deionized water to prepare a concentration of 3.6 mol L -1 of solution B.

[0077] Under nitrogen protection, solution B was added dropwise to solution A which was also protected by nitrogen at a rate of 50 mL / min, and the coprecipitation reaction was carried out at room temperature for 1 h to obtain a suspension.

[0078] After the suspension was stirred and aged for 1 hour, the solid precipitate was collected by filtration, washed three times with deionized water, washed once with anhydrous ethanol, and vacuum dried at 80° C. for 24 hours to prepare a Prussian blue compound based on a manganese-based structure.

[0079] Figure 8 This is a scanning electron microscope image of the product prepared in comparative example 2. In the image, only a small amount of cubic particles are formed in the product, but a large amount of irregular particles are attached to the surface.

[0080] The aqueous sodium ion battery was assembled with it as the negative electrode material, and the test results under 1C condition were Fig. 9The charge and discharge curve shown in FIG. 1 shows that the specific capacity is only 40 mAh / g, which is significantly less than that of Example 1. The charge and discharge curve of the organic sodium ion battery assembled as the positive electrode material is as follows: Fig.10 The specific capacity under 0.1C condition is also significantly smaller than that of Example 1, which is only 59 mAh / g.

[0081] The above embodiments of the present invention do not describe all the details in detail, nor limit the present invention to the above embodiments. Various changes, modifications, substitutions and variations made by ordinary technicians in this field without departing from the principles and purpose of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a Prussian blue compound, comprising the steps of adding a sodium cyanide aqueous solution dropwise to a soluble divalent manganese salt aqueous solution reaction system under an inert atmosphere to carry out a coprecipitation reaction to prepare a Prussian blue compound represented by the following structural formula: x Mn[Mn(CN)6] y □ 1-y ·nH2O, where □ represents a hole, 1.5≤x≤2, 0.6≤y≤1, 1≤n≤2; Its characteristics are The oxygen content in the inert atmosphere is controlled to be 10-100 ppm, a reducing agent is added to the aqueous solution reaction system of the soluble divalent manganese salt as a protective agent, and the pH value of the aqueous solution reaction system is adjusted to be no greater than 4.

2. The method for preparing a Prussian blue compound according to claim 1, wherein The particle size of the prepared Prussian blue compounds ranges from 5 to 20 μm.

3. The method for preparing a Prussian blue compound according to claim 2, wherein The particle size of the prepared Prussian blue compounds ranges from 5 to 10 μm.

4. The method for preparing a Prussian blue compound according to claim 1, wherein The soluble divalent manganese salt is manganese sulfate, manganese nitrate, manganese acetate or manganese chloride.

5. The method for preparing a Prussian blue compound according to claim 1, wherein The aqueous solution concentration of the soluble divalent manganese salt is 0.5 to 1.5 mol / L.

6. The method for preparing a Prussian blue compound according to claim 1, wherein The reducing agent is at least one of sodium sulfite, sodium thiosulfate, ascorbic acid, sodium borohydride and sodium bisulfite.

7. The method for preparing a Prussian blue compound according to claim 6, characterized in that The reducing agent is sodium sulfite.

8. The method for preparing a Prussian blue compound according to claim 1, wherein The molar ratio of the reducing agent to the soluble divalent manganese salt is 1:(5-10).

9. The method for preparing a Prussian blue compound according to claim 1, wherein The molar ratio of the soluble divalent manganese salt to sodium cyanide is 1:(2-5).

10. The method for preparing a Prussian blue compound according to claim 1, characterized in that The concentration of the sodium cyanide aqueous solution is 1.5 to 6.0 mol / L.

11. The method for preparing a Prussian blue compound according to claim 1, characterized in that The coprecipitation reaction temperature is 0-40° C., and the reaction time is 5-120 min.

12. The method for preparing a Prussian blue compound according to claim 1, characterized in that The suspension obtained by the coprecipitation reaction is stirred and aged, and the solid precipitate is collected to obtain a Prussian blue compound.

13. A Prussian blue compound prepared by the method according to any one of claims 1 to 12.

14. Use of the Prussian blue compound according to claim 13 as an electrode material.

15. The use according to claim 14, wherein the Prussian blue compound can be used as a positive electrode material for an organic sodium ion battery or a negative electrode material for an aqueous sodium ion battery.

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