A method for preparing Prussian blue positive electrode material for potassium ion battery

Abstract

A method for preparing a Prussian blue positive electrode material for a potassium ion battery comprises the following steps: (1) preparing two potassium bis(fluorosulfonyl)imide (KFSI) mother solutions with a concentration of 4 mol / L or more; (2) adding potassium ferrocyanide to one of the KFSI mother solutions to form a solution A; (3) adding an iron source to the other KFSI mother solution to form a solution B, and protecting the solution B with an inert gas; (4) dripping the solution A into the solution B and stirring, during which the solution B is protected with an inert gas; (5) after the dripping is completed, stirring is continued, and a product is obtained after the reaction is completed. The preparation method provided by the present invention is simple in operation, excellent in yield, and the synthesized Prussian blue material has excellent electrochemical performance.

Description

Technical Field

[0001] The invention relates to the technical field of new energy materials, and in particular to a method for preparing a Prussian blue positive electrode material for a potassium ion battery. Background Art

[0002] Nowadays, environmental pollution and energy crisis have become obstacles to the sustainable development of modern society to a great extent. Electrochemical devices are expected to meet the needs of low-cost and network-level energy storage at the same time, thus providing some feasible solutions to the energy crisis. Among them, the widespread use of lithium-ion batteries has significantly improved the utilization rate of renewable energy. However, with the global shortage of lithium resources and the rising price of cobalt metal and resource shortages, the production cost of lithium-ion batteries is increasing. Finding lithium-ion batteries that are both economical and practical to replace new ion batteries has become a hot topic in existing research.

[0003] Potassium-ion batteries offer broad application prospects for the next generation of low-cost, high-power-density rechargeable batteries due to their abundant reserves, smaller Stokes radius, standard redox potential only slightly lower than that of lithium, and the ability of potassium ions to be intercalated and deintercalated in commercial graphite negative electrodes. In the current research on positive electrode materials for potassium-ion batteries, the Prussian blue analog K2M[Fe(CN)6](PBAs) is a three-dimensional open framework structure with large pores, high specific capacity and operating voltage, adjustable composition structure, and low production cost, which has attracted widespread attention in potassium positive electrode materials. PBAs have a typical perovskite structure, bridged by four C≡N anions. Theoretically, it can accommodate large sizes with minimal volume change. PBAs are charged and discharged through K ion insertion and extraction, and the theoretical capacity can reach about 140mAh / g.

[0004] At present, the common preparation methods of PBs include single iron source method, liquid phase co-precipitation method, hydrothermal method and ball milling method. Prussian blue analogs synthesized by different synthesis methods have different morphologies, structures and electrochemical properties. For example, although the single iron source method can obtain PBAs with less vacancy content, the yield is low; although the hydrothermal method can obtain PBAs with excellent electrochemical properties, it is easy to produce harmful byproducts such as KCN and HCN under high temperature and high pressure.

[0005] The liquid phase co-precipitation method is simple to operate, has a controllable process, and is low in cost, making it the mainstream synthesis method for synthesizing PBAs. However, the synthesis reaction rate of the co-precipitation method is relatively fast, and the nucleation and growth processes of the crystals occur almost simultaneously, so the crystal crystallinity is low, and a large number of defects are easily present in the lattice, thereby introducing lattice water. The presence of a certain degree of lattice water and vacancy content will greatly damage the electrochemical properties of the material. The high operating voltage of PIBs will cause the decomposition of commonly used carbonate-based electrolytes, and the lattice water will further react with interstitial water, resulting in a large consumption of electrolyte and a series of safety issues. In addition, the excessively fast reaction rate will inevitably lead to crystal agglomeration, which is not conducive to the release of electrochemical properties. The agglomeration phenomenon is usually improved by reducing the concentration of the reaction solution, but the reduction in the concentration of the reaction solution will also lead to problems such as difficulty in centrifuging the product.

[0006] It should be noted that the information disclosed in the above background technology section is only used for understanding the background of the present application, and therefore may include information that does not constitute prior art known to ordinary technicians in the field. Summary of the invention

[0007] The main purpose of the present invention is to overcome the defects of the above-mentioned background technology and provide a method for preparing Prussian blue positive electrode material for potassium ion battery, so as to solve the problems of serious agglomeration, low lattice water content, rapid capacity decay and the like of Prussian blue positive electrode material in the liquid phase synthesis process.

[0008] To achieve the above object, the present invention adopts the following technical solutions:

[0009] A method for preparing a Prussian blue positive electrode material for a potassium ion battery comprises the following steps:

[0010] (1) preparing two portions of potassium bis(fluorosulfonyl)imide (KFSI) stock solutions with a concentration of 4 mol / L or more;

[0011] (2) adding potassium ferrocyanide to one of the KFSI mother solutions to form solution A;

[0012] (3) adding an iron source to another portion of KFSI mother liquor to form a solution B, and protecting the solution B with an inert gas;

[0013] (4) dropping the solution A into the solution B and stirring, while protecting with an inert gas;

[0014] (5) After the addition is completed, stirring is continued and the product is obtained after the reaction is completed.

[0015] Further:

[0016] In step (1), the two portions are two equal portions.

[0017] The iron source is one of ferrous sulfate and ferrous chloride.

[0018] The iron source is ferrous sulfate, and the molar ratio of the iron source to the potassium ferrocyanide is 1:1.

[0019] In step (4), the dripping rate of solution A is 0.1 mL / min-1 mL / min.

[0020] In steps (3) and (4), the inert gas is N2.

[0021] In step (5), stirring is continued for more than 4 h.

[0022] In step (5), the precipitate obtained by the reaction is washed three times with water and once with anhydrous ethanol. After washing, it is placed in a vacuum oven for drying to obtain the product.

[0023] In step (5), after the reaction is completed, the reaction solution is centrifuged once, and the supernatant after centrifugation is collected.

[0024] The following steps are also included:

[0025] (6) Adjust the concentration of the supernatant to make it the same as the concentration of the mother liquor in (1), repeat steps (1) to (5) to complete the recycling of the mother liquor.

[0026] The present invention has the following beneficial effects:

[0027] The invention adopts a high-concentration potassium bis(fluorosulfonyl)imide (KFSI) salt solution as the mother liquor of the reaction system, utilizes the high water absorption of the KFSI salt to provide an environment with fewer water molecules for the synthesis process of PBAs, and greatly reduces the nucleation and growth rate of PBAs crystals by changing the traditional deionized water synthesis system and adding a large amount of KFSI salt, thereby avoiding or reducing the agglomeration of Prussian blue positive electrode materials in the liquid phase synthesis process, thereby reducing the internal defects of the crystals and the lattice water content, so that the PBAs product has excellent electrochemical properties and slow capacity decay.

[0028] The preparation method provided by the invention has simple operation and excellent yield, and the synthesized Prussian blue material has excellent electrochemical performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It shows that the Prussian blue positive electrode material with good crystallinity obtained in the embodiment of the present invention has a particle size in the nanometer scale.

[0030] Figure 2 The cyclic performance of the current test of the Prussian blue positive electrode material obtained in the embodiment of the present invention is shown. DETAILED DESCRIPTION

[0031] The following is a detailed description of the embodiments of the present invention. It should be emphasized that the following description is only exemplary and is not intended to limit the scope and application of the present invention.

[0032] The embodiment of the present invention provides a method for preparing a Prussian blue positive electrode material for a potassium ion battery, comprising the following steps:

[0033] (1) preparing two portions of potassium bis(fluorosulfonyl)imide (KFSI) stock solutions with a concentration of 4 mol / L or more;

[0034] (2) adding potassium ferrocyanide to one of the KFSI mother solutions to form solution A;

[0035] (3) adding an iron source to another portion of KFSI mother liquor to form a solution B, and protecting the solution B with an inert gas;

[0036] (4) dropping the solution A into the solution B and stirring, while protecting with an inert gas;

[0037] (5) After the addition is completed, stirring is continued and the product is obtained after the reaction is completed.

[0038] In some embodiments, in the method for preparing a potassium ion battery Prussian blue positive electrode material in a high concentration salt solution of the present invention, potassium ferrocyanide and ferrous chloride powder are respectively dissolved in a high concentration potassium bis(fluorosulfonyl)imide (KFSI) salt solution, and the potassium ferrocyanide solution is added dropwise to the ferrous chloride salt solution to gradually form a dark blue Prussian blue precipitate. After stirring the reaction, the precipitate is centrifuged, washed with deionized water and anhydrous ethanol, and dried in a vacuum oven. The preparation means provided by the present invention is simple in operation, excellent in yield, and the synthesized Prussian blue material has excellent electrochemical performance.

[0039] The specific embodiments of the present invention are further described below.

[0040] In some embodiments, a method for preparing a Prussian blue positive electrode material for a potassium ion battery in a high concentration salt solution comprises the following steps:

[0041] A certain amount of high concentration (>4 mol / L) potassium bis(fluorosulfonyl)imide (KFSI) salt solution was prepared as the mother solution of the reaction system, and the solution was evenly divided into two equal parts. A certain amount of potassium ferrocyanide was added to one part, which was recorded as solution A, and an equal molar amount of ferrous chloride was added to the other part, which was recorded as solution B. Solution B was protected by N2 atmosphere to avoid Fe 2+Oxidized. After solutions A and B are fully stirred, slowly add solution A to solution B, and control the drop rate at about 0.1-1mL / min. Gradually, a blue precipitate is generated, and the color of the mixed solution changes from light to dark. Continue stirring for 12 hours. After the reaction is completed, centrifuge the mixed solution once. Collect the supernatant after centrifugation to realize the recycling of the mother liquor. Wash the precipitate three times with water and once with alcohol. Then put the collected solid into a 100℃ oven and dry it for 12 hours.

[0042] A method for preparing a Prussian blue positive electrode material for a potassium ion battery in a high-concentration salt solution according to an embodiment of the present invention comprises the following specific steps:

[0043] Step 1, weigh KFSI and dissolve it in 30 mL of deionized water, stir it thoroughly to dissolve it, to form a high concentration (>4 mol / L) potassium bis(fluorosulfonyl)imide (KFSI) salt solution, and divide the solution into two equal parts for use;

[0044] Step 2, weigh 0.3 mmol potassium ferrocyanide and 0.3 mmol ferrous chloride and dissolve them in the above two equal parts of the salt solution mother solution, respectively, and record them as solution A and solution B;

[0045] Step 3, then dripping solution A into solution B at a dripping speed of 0.8 mL / min, stirring continuously and protecting with nitrogen during the whole process, the solution gradually turns blue, indicating that a Prussian blue analogue is gradually generated;

[0046] Step 4, continue stirring the reaction for 12 hours, and after the reaction is completed, wash the product three times with deionized water at a speed of 10000 r / min and once with alcohol at a speed of 8000 r / min.

[0047] Step 5: Place the cleaned precipitate in a 100°C vacuum oven and dry it overnight.

[0048] The electrochemical performance test process of the embodiment of the present invention is as follows:

[0049] Prussian blue material, conductive agent and binder were mixed into slurry in a ratio of 7:1.5:1.5, and then coated on the carbon-sprayed aluminum foil current collector with a certain thickness. 2.5 mol / L KFSI / TEP was used as the electrolyte, K sheet was used as the negative electrode, and the diaphragm was a layer of glass fiber filter paper diaphragm GFA and two layers of Cellgard-2320 polypropylene membrane. Assemble into buckles in an argon-filled glove box Then The charge and discharge capacity and cycle life tests were carried out using the LandCT2001A battery testing system produced by Wuhan Jinnuo Electronics Co., Ltd.

[0050] like Figure 1As shown in , the embodiment of the present invention obtains a Prussian blue material with good crystallinity, the particle size is in the nanometer scale, the particle size is in the range of 150-200nm, there is no obvious agglomeration phenomenon, and the particles are evenly distributed in the form of cubic particles. Figure 2 As shown, the cycle performance is tested with a current of 50 mA / g. It can be seen that this method can provide a high initial discharge capacity, and the cycle performance is relatively stable. After 100 cycles, there is still a discharge capacity of 102 mAh / g.

[0051] The invention adopts a high-concentration potassium bis(fluorosulfonyl)imide (KFSI) salt solution as the mother liquor of the reaction system, utilizes the high water absorption of the KFSI salt to provide an environment with fewer water molecules for the synthesis process of PBAs, and greatly reduces the nucleation and growth rate of PBAs crystals by changing the traditional deionized water synthesis system and adding a large amount of KFSI salt, thereby reducing the internal defects of the crystals and the lattice water content, so that the PBAs product has excellent electrochemical properties.

[0052] The background section of the present invention may contain background information about the problem or environment of the present invention, but does not necessarily describe the prior art. Therefore, the content included in the background section is not an admission by the applicant that the prior art is available.

[0053] The above content is a further detailed description of the present invention in combination with specific / preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, without departing from the concept of the present invention, it can also make several substitutions or modifications to these described embodiments, and these substitutions or modifications should be regarded as belonging to the protection scope of the present invention. In the description of this specification, the description of reference terms "an embodiment", "some embodiments", "preferred embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in combination with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily target the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In the absence of mutual contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples. Although the embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions and modifications can be made herein without departing from the scope of protection of the patent application.

Claims

1. A method for preparing a Prussian blue positive electrode material for a potassium ion battery, characterized in that: The steps include: (1) dissolving potassium bis(fluorosulfonyl)imide (KFSI) in deionized water to prepare two portions of potassium bis(fluorosulfonyl)imide (KFSI) mother solutions with a concentration of 4 mol / L or more; (2) adding potassium ferrocyanide to one of the KFSI mother solutions to form solution A; (3) adding an iron source to another portion of KFSI mother liquor to form a solution B, and protecting the solution B with an inert gas; (4) dropping the solution A into the solution B and stirring, while protecting with an inert gas; (5) After the addition is completed, stirring is continued and the product is obtained after the reaction is completed.

2. The method according to claim 1, characterized in that In step (1), the two portions are two equal portions.

3. The method according to claim 2, characterized in that The iron source is one of ferrous sulfate and ferrous chloride.

4. The method according to claim 3, characterized in that The iron source is ferrous sulfate, and the molar ratio of the iron source to the potassium ferrocyanide is 1:

1.

5. The method according to any one of claims 1 to 4, characterized in that: In step (4), the dripping rate of solution A is 0.1 mL / min-1 mL / min.

6. The method according to any one of claims 1 to 4, characterized in that: In steps (3) and (4), the inert gas is N2.

7. The method according to any one of claims 1 to 4, characterized in that: In step (5), stirring is continued for more than 4 h.

8. The method according to any one of claims 1 to 4, characterized in that In step (5), the precipitate obtained by the reaction is washed three times with water and once with anhydrous ethanol. After washing, it is placed in a vacuum oven for drying to obtain the product.

9. The method according to any one of claims 1 to 4, characterized in that: In step (5), after the reaction is completed, the reaction solution is centrifuged once, and the supernatant after centrifugation is collected.

10. The method according to claim 9, characterized in that The following steps are also included: (6) Adjust the concentration of the supernatant to make it the same as the concentration of the mother liquor in (1), repeat steps (1) to (5) to complete the recycling of the mother liquor.

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