WO2024250134A1 - Method for preparing prussian blue material, and prussian blue material and use thereof - Google Patents

Abstract

The present disclosure belongs to the technical field of Prussian blue materials, and particularly relates to a method for preparing a Prussian blue material, and a Prussian blue material and the use thereof. The Prussian blue material is prepared according to electrochemical principles, and transition metal cations and transition metal cyanide anions are separated by means of a cation exchange membrane; and after energization, the transition metal cations can be slowly released and react with the transition metal cyanide anions, and the speed of precipitate formation can be further controlled by controlling a current, such that structure defects caused by a very fast reaction rate are avoided. The preparation method is beneficial for improving the electrochemical performance of a product when being used for preparing a positive electrode material for a sodium-ion battery.

Description

A preparation method of Prussian blue material, Prussian blue material and application thereof Technical Field

The present invention relates to the technical field of Prussian blue materials, and in particular to a preparation method of a Prussian blue material, a Prussian blue material and an application thereof.

Background Art

Currently, common energy storage batteries include sodium-sulfur batteries, lithium-ion batteries, lead-acid batteries, lead-carbon batteries, and flow batteries. Among these types of batteries, sodium-ion batteries have the advantages of good safety, low cost, abundant resources, and environmental friendliness, making them very suitable for large-scale energy storage. In sodium-ion batteries, Prussian blue materials have an open framework structure that is conducive to the insertion and extraction of large-sized sodium ions. Therefore, they have the advantages of high capacity and good rate performance, making them very suitable as positive electrode materials for sodium-ion batteries.

Prussian blue cathode materials are usually obtained by coprecipitating a transition metal cyanide anion (such as M′(CN) ₆ ^m- ) and a transition metal cation (such as Mn ⁺ ) in an aqueous solution, and the material has a three-dimensional skeleton crystal structure. Due to charge balance, M′(CN) ₆ holes are easily generated in the crystals of Prussian blue cathode materials. For example, in the Prussian blue cathode material crystals obtained by coprecipitating a +2-valent transition metal cation and a transition metal cyanide anion with four negative charges (where the valence state of the transition metal is also +2), in order to maintain charge balance, the molar ratio of the transition metal cation to the transition metal cyanide anion should be 2:1, so the proportion of M′(CN) ₆ holes is as high as 50%.

In Prussian blue cathode materials, the presence of each hole will produce six coordinated water, which greatly enhances the water absorption of the cathode material. In addition, the interstitial water in the pores of the crystal structure of Prussian blue cathode materials is easy to form hydrogen bonds with the coordinated water, which increases the difficulty of removing the interstitial water. The presence of these interstitial waters will occupy part of the space in the pores of the crystal structure of Prussian blue cathode materials, hindering the transmission of alkali metal or alkaline earth metal ions (such as Na ⁺ or Li ⁺ ). At the same time, the presence of these interstitial waters will also be freed into the electrolyte and react with the electrolyte, causing electrolyte consumption, instability of the negative electrode SEI film, and increased impedance, resulting in adverse consequences such as capacity decay and flatulence in electrochemical energy storage devices.

Therefore, how to reduce the hole ratio of synthesized Prussian blue-based positive electrode materials has become a technical problem that needs to be solved urgently.

In view of this, the present disclosure is proposed.

Summary of the invention

The purpose of the present invention is to provide a method for preparing a Prussian blue material, a Prussian blue material and an application thereof. Reduce the formation of defects in materials and improve the electrochemical properties of materials.

In order to achieve the above-mentioned purpose of the present disclosure, the following technical solutions can be adopted:

In a first aspect, the solution provided by the present disclosure includes a method for preparing a Prussian blue material, comprising: using a cation exchange membrane to separate transition metal cations and transition metal cyanide anions in two electrolytic cells of an electrochemical device, and preparing the material by an electrochemical method.

In some embodiments of the present disclosure, the method comprises: placing the first solution and the second solution in different electrolytic cells of an electrochemical device, respectively, and applying electricity;

Wherein, the first solution includes: a first solvent and a metal salt containing a transition metal cation;

The second solution includes: a second solvent and a sodium salt containing a transition metal cyanide anion.

In some embodiments of the present disclosure, the current applied is 1A-20A.

In some embodiments of the present disclosure, the current applied is 5A-15A.

In some embodiments of the present disclosure, the transition metal cation in the metal salt is a divalent transition metal cation.

In some embodiments of the present disclosure, the divalent transition metal cation is selected from at least one of a divalent iron ion and a divalent manganese ion.

In some embodiments of the present disclosure, the divalent transition metal cation is a divalent iron ion.

In some embodiments of the present disclosure, the sodium salt containing a transition metal cyanide anion is sodium ferrocyanide or a hydrate thereof.

In some embodiments of the present disclosure, the ferrocyanide is sodium ferrocyanide or a hydrate of sodium ferrocyanide.

In some embodiments of the present disclosure, the molar ratio of the divalent transition metal cation to the transition metal cyanide anion is (1.0-1.2):1.

In some embodiments of the present disclosure, the molar ratio of the divalent transition metal cation to the transition metal cyanide anion is (1.05-1.15):1.

In some embodiments of the present disclosure, the first solution further contains an antioxidant.

In some embodiments of the present disclosure, the antioxidant is selected from at least one of ascorbic acid, citric acid, glucose and sucrose.

In some embodiments of the present disclosure, the antioxidant is ascorbic acid.

In some embodiments of the present disclosure, the molar ratio of the antioxidant to the transition metal cation is (0.5-0.8):1.

In some embodiments of the present disclosure, the molar ratio of the antioxidant to the transition metal cation is (0.6-0.7):1.

In some embodiments of the present disclosure, the concentration of the transition metal cation in the first solution is 0.15 mol/L-0.30 mol/L.

In some embodiments of the present disclosure, the concentration of the transition metal cyanide anion in the second solution is 0.1 mol/L-0.3 mol/L.

In some embodiments of the present disclosure, the first solvent and the second solvent are both water.

In some embodiments of the present disclosure, the material of the cation exchange membrane is selected from at least one of a polyetheretherketone homogeneous cation exchange membrane, a perfluoroethylene sulfonic acid homogeneous cation exchange membrane and a polysulfone homogeneous cation exchange membrane.

In some embodiments of the present disclosure, the method comprises placing a first solution in an anode region of an electrochemical device, placing a second solution in a cathode region of the electrochemical device, and then applying power to obtain a suspension of Prussian blue material.

In some embodiments of the present disclosure, the method comprises: placing a first solution in the anode region of an electrochemical device, applying power so that transition metal cations are adsorbed onto an electrode plate in the cathode region, and then disconnecting the power; placing a second solution in the anode region of the electrochemical device, and then applying power in the reverse direction so that the adsorbed transition metal cations are decomposed and enter the region where the transition metal cyanide anions are located to react, thereby obtaining a suspension of Prussian blue material.

In some embodiments of the present disclosure, the method further includes aging, washing, and separating the obtained suspension of Prussian blue material to obtain a solid material, and drying the solid material.

In some embodiments of the present disclosure, the aging time is 2h-5h.

In a second aspect, the solution provided by the present disclosure also includes a Prussian blue material prepared by the preparation method in any of the above embodiments.

In some embodiments of the present disclosure, the chemical formula thereof is Na _x M[Fe(CN) ₆ ], wherein M represents divalent iron or divalent manganese, and 1.5<x<2.

In a third aspect, the solution provided by the present disclosure also includes the use of the Prussian blue material in the above-mentioned embodiment as a positive electrode material for a sodium ion battery.

In a fourth aspect, the solution provided by the present disclosure includes a sodium ion battery positive electrode plate, including a positive electrode collector and an active coating attached to the positive electrode collector, wherein the active coating contains the Prussian blue material in the above-mentioned embodiment.

In a fifth aspect, the solution provided by the present disclosure includes a sodium ion battery, including the sodium ion battery positive electrode plate in the above embodiment.

In a sixth aspect, the solution provided by the present disclosure includes an electrical device, including the sodium ion battery in the above embodiment.

The present disclosure adopts the principle of electrochemistry to prepare Prussian blue material, uses a cation exchange membrane to separate transition metal cations and transition metal cyanide anions, and after power is applied, the transition metal cations can be slowly released to react with transition metal cyanide anions. The speed of precipitation formation can be further controlled by controlling the current, thereby avoiding structural defects caused by too fast a reaction rate and reducing the occurrence of the hole ratio. When the preparation method provided by the present disclosure is used to prepare a positive electrode material for a sodium ion battery, it is beneficial to improve the electrochemical performance of the product.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the technical solution of the embodiment of the present disclosure, the following will describe the appended materials required for use in the embodiment. It should be understood that the following drawings only show certain embodiments of the present disclosure and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

FIG1 is a first schematic diagram of a method for preparing a Prussian blue material provided by the present disclosure;

FIG2 is a second schematic diagram of the method for preparing the Prussian blue material provided by the present disclosure; in the figure, (a) indicates that cations are adsorbed onto the cathode electrode plate by applying power; (b) indicates that the Prussian blue material is synthesized by applying power in the reverse direction;

FIG3 is an X-ray diffraction (XRD) pattern of the Prussian blue material prepared in Example 1;

FIG. 4 is a SEM image of the Prussian blue material prepared in Example 1.

DETAILED DESCRIPTION

The embodiments of the present disclosure will be described in detail below in conjunction with the examples, but those skilled in the art will appreciate that the following examples are only used to illustrate the present disclosure and should not be considered to limit the scope of the present disclosure. Where specific conditions are not specified in the examples, they are carried out under conventional conditions or conditions recommended by the manufacturer. Where the manufacturers of the reagents or instruments used are not specified, they are all conventional products that can be purchased commercially.

The endpoints and any values of the ranges disclosed in this disclosure are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, the endpoint values of each range and the individual point values, and the individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

The disclosed embodiment provides a method for preparing a Prussian blue material, which is prepared using the principle of electrochemistry, using a cation exchange membrane to separate transition metal cations and transition metal cyanide anions, and after power is applied, the transition metal cations are slowly released to react with transition metal cyanide anions to form a precipitate.

It should be noted that in the traditional method of preparing Prussian blue materials, when transition metal cyanide anions (M′(CN) ₆ ^m- ) are mixed with transition metal cations, precipitation is immediately generated. The precipitation rate is too fast, resulting in a high proportion of M′(CN) ₆ holes in the crystal structure of Prussian blue positive electrode materials, thereby increasing the proportion of interstitial water, and the material is very easy to form defects, which affects the actual specific capacity and electrochemical performance of the material. The present invention utilizes an electrochemical method to slowly release transition metal cations through a cation exchange membrane, react with transition metal cyanide anions and precipitate. The precipitation rate can be better controlled by controlling the current. The operation is simple and flexible, and the problem of defects in the material structure caused by too fast precipitation during material preparation is solved.

Specifically, the following steps may be included:

S1. Solution preparation

A metal salt containing a transition metal cation and a first solvent are mixed to obtain a first solution, and a sodium salt containing a transition metal cyanide anion and a second solvent are mixed to obtain a second solution. The first solution and the second solution are prepared for use.

In some embodiments, the transition metal cation in the metal salt is a divalent transition metal cation, such as at least one of a divalent iron ion and a divalent manganese ion, and may be any one or more of the above. Preferably, the divalent transition metal cation is a divalent iron ion to improve the electrochemical performance of the prepared Prussian blue material for a positive electrode material of a sodium ion battery. Specifically, the metal salt corresponding to the divalent iron ion may be ferrous sulfate, ferrous chloride, ferrous nitrate, etc.

In some embodiments, the sodium salt containing the transition metal cyanide anion can be at least one of sodium ferrocyanide or its hydrate, and can be any one or more of the above, and the sodium salt is used as a raw material to form a positive electrode material for a sodium ion battery after a one-step precipitation. Preferably, the ferrocyanide is sodium ferrocyanide or a hydrate of sodium ferrocyanide to improve the capacity and electrochemical performance of the material.

In some embodiments, by controlling the amount of ions in the first solution and the second solution, the molar ratio of the divalent transition metal cation and the transition metal cyanide anion is (1.0-1.2):1, preferably (1.05-1.15):1, such as 1.00:1, 1.05:1, 1.10:1, 1.15:1, 1.20:1, etc.

In some embodiments, the first solution further contains an antioxidant to prevent oxidation of ferrous ions. The specific type of the antioxidant is not limited, and can be selected from at least one of ascorbic acid, citric acid, glucose and sucrose, and can be any one or more of the above, preferably ascorbic acid.

Furthermore, the molar ratio of the antioxidant to the transition metal cation is (0.5-0.8):1, preferably (0.6-0.7):1, to achieve a better antioxidant effect. Specifically, the molar ratio of the antioxidant to the transition metal cation can be 0.5:1, 0.6:1, 0.7:1, 0.8:1, etc.

In some embodiments, the concentration of transition metal cations in the first solution is 0.15 mol/L-0.30 mol/L, such as 0.15 mol/L, 0.20 mol/L, 0.25 mol/L, 0.30 mol/L, etc. The concentration of transition metal cyanide anions in the second solution is 0.1 mol/L-0.3 mol/L, such as 0.10 mol/L, 0.15 mol/L, 0.20 mol/L, 0.25 mol/L, 0.30 mol/L, etc.

In some embodiments, the first solvent and the second solvent may both be water, but are not limited thereto.

S2. Electrochemical reaction

The first solution and the second solution are placed in different electrolytic cells of an electrochemical device respectively, and electricity is applied to the cells so that the transition metal cations are slowly released and react with the transition metal cyanide anions to form a precipitate.

In some embodiments, the electrochemical device includes a cathode electrolyzer, an anode electrolyzer and a cation exchange membrane, wherein the cation exchange membrane separates the cathode electrolyzer from the anode electrolyzer, and electrode plates are disposed in both the cathode electrolyzer and the anode electrolyzer, and the two electrode plates are connected through an external circuit. After power is applied, cations enter the cathode electrolyzer through the cation exchange membrane to react with anions.

To achieve the slow release of cations, there are two ways to achieve it, but not limited to:

(1) As shown in FIG1 , a first solution is placed in the anode region of an electrochemical device, and a second solution is placed in the The cathode region of the chemical device is then energized, and the transition metal cations in the anode region enter the cathode region through the cation exchange membrane, and react with the transition metal cyanide anions in the cathode region to obtain a suspension of Prussian blue material.

(2) As shown in FIG. 2 , the first solution is placed in the anode region of the electrochemical device, and after power is applied, the transition metal cations are adsorbed onto the electrode plate in the cathode region (as shown in (a)), and then the power is turned off; the second solution is placed in the anode region of the electrochemical device, and then the power is applied in the reverse direction, so that the adsorbed transition metal cations are decomposed and enter the region where the transition metal cyanide anions are located to react (as shown in (b)), thereby obtaining a suspension of Prussian blue material. Specifically, the first solution is placed in the anode region of the electrochemical device, and then power is applied, so that the cathode is embedded with metal ions, and the anode is embedded with anions (as shown in (a)); the second solution is placed in the anode region of the electrochemical device, and after power is applied in the reverse direction, the original anode becomes the cathode, and the original cathode becomes the anode, so that the transition metal cations are decomposed and enter the region where the transition metal cyanide anions are located through the cation exchange membrane to react and form a precipitate.

In some embodiments, the current is 1A-20A, and the power is turned off when no precipitation is observed; preferably, the current is 5A-15A. By further controlling the current, the cation release rate can be controlled within a better range, which not only ensures a better reaction rate, but also avoids structural defects caused by too fast a deposition rate.

In some embodiments, the electrode plates are all carbon electrode plates, but are not limited thereto.

In some embodiments, the material of the cation exchange membrane is selected from at least one of polyetheretherketone homogeneous cation exchange membrane, perfluoroethylene sulfonic acid homogeneous cation exchange membrane and polysulfone homogeneous cation exchange membrane, and can be any one or more of the above materials. The above cation exchange membranes are all commercially available materials.

S3, post-processing

The Prussian blue material is separated from the suspension obtained after the reaction is completed by post-treatment.

In some embodiments, the post-treatment process includes aging, washing, and separating the obtained suspension of Prussian blue material to obtain a solid material, and drying the solid material to remove surface moisture and residual washing solvent.

Furthermore, aging can be carried out in a general aging kettle, and the aging time can be 2h-5h, such as 2h, 3h, 4h, 5h, etc. Washing can be performed multiple times. The specific method of separation is not limited, and can be centrifugal separation, but is not limited thereto. Drying can be carried out in a general vacuum drying oven, and the drying temperature is approximately 120°C-320°C, and the drying time is approximately 12h-48h.

The present disclosure also provides a Prussian blue material, which is prepared by the above-mentioned preparation method and has a complete lattice morphology, a low proportion of crystal water, and also has a higher capacity, a longer cycle life and relatively excellent rate performance.

In some embodiments, the chemical formula is Na _x M[Fe(CN) ₆ ], wherein M represents divalent iron or divalent manganese, such as the chemical formula may be Na _x Fe[Fe(CN) ₆ ], 1.5<x<2. The value of x may be 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, etc.

The present disclosure also provides a sodium ion battery positive electrode plate, including a positive electrode collector and an active coating attached to the positive electrode collector, wherein the active coating contains the above-mentioned Prussian blue material. The improvement of the performance of the Prussian blue material can further improve the performance of the sodium ion battery positive electrode plate.

Specifically, the preparation process of the positive electrode plate of the sodium ion battery can refer to the existing technology, and the main steps include: mixing Prussian blue material, conductive agent, binder and solvent to form a slurry, coating the slurry on the positive electrode collector, and forming a coating after drying.

The present disclosure also provides a sodium ion battery, including the above-mentioned sodium ion battery positive electrode plate, and also includes a negative electrode plate, an electrolyte, a diaphragm, etc., and the specific material types are not limited.

The present disclosure also provides an electrical device, including the sodium ion battery, which is used to supply power, and the specific electrical device is not limited.

The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

It should be noted that the electrochemical devices used in the following examples all include: an anode electrolyzer, a cathode electrolyzer, a cation exchange membrane (made of a homogeneous cation exchange membrane of perfluoroethylene sulfonic acid), and a carbon-containing electrode plate (graphite electrode), wherein the cation exchange membrane separates the anode electrolyzer and the cathode electrolyzer. The test temperature is 26°C.

Example 1

This embodiment provides a method for preparing a Prussian blue material, comprising the following steps:

(1) Solution preparation

Ferrous sulfate and ascorbic acid were dissolved in 500 ml of deionized water to obtain solution I. The concentration of ferrous sulfate in solution I was 0.22 mol/L, and the concentration of ascorbic acid was 0.14 mol/L.

Sodium ferrocyanide decahydrate was dissolved in 500 ml of deionized water to obtain a solution II having a sodium ferrocyanide concentration of 0.2 mol/L.

(2) Electrochemical reaction

Solution I was added to the anode region of the electrochemical device, and solution II was added to the cathode region of the electrochemical device. The device was powered on at a current of 10A. Ferrous ions entered the cathode region through the cation exchange membrane and formed precipitation with cyanide anions (M′(CN) ₆ ^m -). When no precipitation was observed, the power was turned off to obtain a suspension of Prussian blue material.

(3) Post-processing

The suspension was aged for 3 hours, washed with water for 3 times, and centrifuged to obtain a solid material, which was then vacuum dried at 200° C. for 24 hours.

Note: In this embodiment, the molar ratio of the divalent transition metal cation to the transition metal cyanide anion is 1.1:1, and the molar ratio of the antioxidant to the transition metal cation is 0.64:1.

Example 2

This embodiment provides a method for preparing a Prussian blue material, comprising the following steps:

(1) Solution preparation

Ferrous sulfate and ascorbic acid were dissolved in 500 ml of deionized water to obtain solution I. The concentration of ferrous sulfate in solution I was 0.24 mol/L, and the concentration of ascorbic acid was 0.19 mol/L.

Sodium ferrocyanide decahydrate was dissolved in 500 ml of deionized water to obtain a solution II having a sodium ferrocyanide concentration of 0.2 mol/L.

(2) Electrochemical reaction

Solution I was added to the anode region of the electrochemical device, and the current was 20A for 550 minutes, so that the ferrous ions were completely adsorbed on the cathode electrode plate (as shown in Figure 2 (a)), and then the power was turned off; Solution II was added to the anode region of the electrochemical device, and the electrochemical device was reversely powered at a current of 15A. The ferrous ions entered the cathode region (the cathode region after reverse power-on) through the cation exchange membrane and began to form precipitation with the cyanide anion (M′(CN) ₆ ^m- ). When no precipitation was observed, the power was turned off to obtain a suspension of Prussian blue material.

(3) Post-processing

The suspension was aged for 3 hours, washed with water for 3 times, and centrifuged to obtain a solid material, which was then vacuum dried at 200° C. for 24 hours.

Example 3

The only difference from Example 1 is that the current is 5A.

Example 4

The only difference from Example 1 is that the current is 15A.

Example 5

The only difference from Example 1 is that the current is 20A.

Example 6

The only difference from Example 1 is that the current is 25A.

Example 7

The only difference from Example 1 is that the current is 1A.

Example 8

The only difference from Example 1 is that the concentration of sodium ferrocyanide in solution II is 0.24 mol/L, so that the molar ratio of the divalent transition metal cation to the transition metal cyanide anion is 1.0:1.

Example 9

The only difference from Example 1 is that the concentration of sodium ferrocyanide in solution II is 0.18 mol/L, so that the molar ratio of the divalent transition metal cation to the transition metal cyanide anion is 1.2:1.

Example 10

The only difference from Example 1 is that the concentration of sodium ferrocyanide in solution II is 0.275 mol/L, so that the molar ratio of the divalent transition metal cation to the transition metal cyanide anion is 0.8:1.

Embodiment 11

The only difference from Example 1 is that the concentration of sodium ferrocyanide in solution II is 0.147 mol/L, so that the molar ratio of the divalent transition metal cation to the transition metal cyanide anion is 1.5:1.

Example 12

The only difference from Example 1 is that in solution I, ascorbic acid is replaced by an equal molar amount of citric acid.

Example 13

The only difference from Example 1 is that in Solution I, ascorbic acid is replaced by an equimolar amount of glucose.

Embodiment 14

The only difference from Example 1 is that the concentration of ascorbic acid in solution I is 0.11 mol/L, so that the molar ratio of the antioxidant to the transition metal cation is 0.5:1.

Embodiment 15

The only difference from Example 1 is that the concentration of ascorbic acid in solution I is 0.176 mol/L, so that the molar ratio of the antioxidant to the transition metal cation is 0.8:1.

Example 16

The only difference from Example 1 is that the concentration of ascorbic acid in solution I is 0.066 mol/L, so that the molar ratio of the antioxidant to the transition metal cation is 0.3:1.

Embodiment 17

The only difference from Example 1 is that the concentration of ascorbic acid in solution I is 0.22 mol/L, so that the molar ratio of the antioxidant to the transition metal cation is 1.0:1.

Comparative Example 1

This comparative example provides a traditional method for preparing Prussian blue material, comprising the following steps:

(1) Ferrous sulfate and ascorbic acid were dissolved in 50 ml of deionized water to obtain a solution I, wherein the concentration of ferrous sulfate in the solution I was 0.22 mol/L, and the concentration of ascorbic acid was 0.14 mol/L.

Sodium ferrocyanide decahydrate was dissolved in 50 ml of deionized water to obtain a solution II having a sodium ferrocyanide concentration of 0.2 mol/L.

(2) Solution I and Solution II were simultaneously added into 100 ml of deionized water and coprecipitated at 26° C. to form a Prussian blue suspension.

(3) The suspension was aged for 3 hours, washed with water for 3 times, and centrifuged to obtain a solid material, which was then vacuum dried at 200° C. for 24 hours.

Test Example 1

The performance of the Prussian blue positive electrode materials prepared in the examples and comparative examples was tested, and the results are shown in Table 1.

Test method: (1) Assembly of button sodium ion battery: The Prussian blue positive electrode material, acetylene black and polyvinylidene fluoride (PVDF) prepared in the example are mixed in a mass ratio of 7:2:1, and the mixed slurry is coated on aluminum foil, dried and cut into discs as the positive electrode; the metal sodium sheet is used as the negative electrode, and Whatman glass fiber (GF/D) is used as the separator; the organic electrolyte is prepared by NaClO ₄ , EC (ethylene carbonate), DEC (diethyl carbonate) and FEC (fluoroethylene carbonate), the NaClO ₄ concentration is 1.0 mol/L, the volume ratio of EC to DEC is 1:1, and the mass fraction of FEC in the electrolyte is 5%; the sodium ion battery is assembled in an argon glove box;

Among them, the cycle performance was tested at 25℃ (1C/1C 2.0～4.3V); the gram capacity was tested at a current of 25mA/g.

Table 1 Electrochemical performance test results of Prussian blue cathode materials

It can be seen that compared with the conventional Prussian blue preparation method, the material prepared in this scheme has the advantage of better capacity retention rate.

It can be seen from the test results of Example 1 and Examples 3-7 that the applied current has a certain influence on the performance of the product, and Example 1, Example 3 and Example 4 have the best effects, that is, the applied current is preferably 5A-15A.

It can be seen from Example 1 and Examples 8-11 that the molar ratio of the divalent transition metal cation to the transition metal cyanide anion is 0.8-1.5:1, which can enable the product to have a good capacity retention rate.

It can be seen from Example 1 and Examples 12-17 that the type and amount of antioxidant have little effect on the performance of the product.

Test Example 2

The number of defects per molecule of the prepared Prussian blue cathode material was tested by inductively coupled plasma emission spectrometry (ICP), and the results are shown in Table 2.

Table 2 Test results of defects of Prussian blue positive electrode materials

It can be seen that the number of defects in the Prussian blue positive electrode material prepared in Example 1 is significantly smaller than that in Comparative Example 1.

It can be seen from the test results of Example 1 and Examples 3-6 that the applied current has a certain influence on the defects of the product, and Example 1, Example 3 and Example 4 have the best effects, that is, the applied current is preferably 5A-15A.

It can be seen from Example 1 and Examples 8-11 that the molar ratio of the divalent transition metal cation to the transition metal cyanide anion is 0.8-1.5:1, which can significantly reduce product defects.

It can be seen from Example 1 and Examples 12-17 that the type and amount of antioxidant have little effect on the defects of the product.

Test Example 3

The XRD pattern of the Prussian blue material prepared in Test Example 1 is shown in Figure 3. It can be seen that the prepared product is a pure-phase cubic Prussian blue positive electrode material; the sharp peak shape indicates that the prepared Prussian blue positive electrode material has a high degree of crystallinity.

The SEM image of the Prussian blue material prepared in Test Example 1 is shown in Figure 4. It can be seen that the prepared Prussian blue positive electrode material is in a cubic shape and has a smooth surface.

The preferred embodiments of the present disclosure are described in detail above, but the present disclosure is not limited thereto. Within the technical concept of the present disclosure, the technical solution of the present disclosure can be subjected to a variety of simple modifications, including combining various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present disclosure and belong to the protection scope of the present disclosure.

Industrial Applicability

The present invention adopts the principle of electrochemistry to prepare Prussian blue material, uses a cation exchange membrane to separate transition metal cations and transition metal cyanide anions, and after power is applied, the transition metal cations can be slowly released to react with transition metal cyanide anions, and the speed of forming precipitation can be further controlled by controlling the current, thereby avoiding structural defects caused by too fast a reaction rate and reducing the occurrence of the hole ratio. The reaction can be completed using a simple electrochemical device, the operation is convenient, and the reaction rate is easy to accurately control, which has very good industrial practicability.

Claims (30)

A method for preparing a Prussian blue material, characterized by comprising: using a cation exchange membrane to separate transition metal cations and transition metal cyanide anions in two electrolytic cells of an electrochemical device, and preparing the material by an electrochemical method. The preparation method according to claim 1, characterized in that it comprises: placing the first solution and the second solution in different electrolytic cells of the electrochemical device respectively and applying electricity; Wherein, the first solution comprises: a first solvent and a metal salt containing the transition metal cation; The second solution includes: a second solvent and a sodium salt containing the transition metal cyanide anion. The preparation method according to claim 2 is characterized in that the current is 1A-20A. The preparation method according to claim 3 is characterized in that the current is 5A-15A. The preparation method according to any one of claims 2 to 4, characterized in that the transition metal cation in the metal salt is a divalent transition metal cation. The preparation method according to claim 5, characterized in that the divalent transition metal cation is selected from at least one of a divalent iron ion and a divalent manganese ion. The preparation method according to claim 6, characterized in that the divalent transition metal cation is a divalent iron ion. The preparation method according to any one of claims 5 to 7, characterized in that the sodium salt containing the transition metal cyanide anion is sodium ferrocyanide or a hydrate thereof. The preparation method according to claim 8, characterized in that the sodium salt containing the transition metal cyanide anion is sodium ferrocyanide or a hydrate thereof. The preparation method according to claim 9, characterized in that the molar ratio of the divalent transition metal cation to the transition metal cyanide anion is (1.0-1.2):1. The preparation method according to claim 10, characterized in that the molar ratio of the divalent transition metal cation to the transition metal cyanide anion is (1.05-1.15):1. The preparation method according to any one of claims 2-11 is characterized in that the first solution also contains an antioxidant. The preparation method according to claim 12, characterized in that the antioxidant is selected from at least one of ascorbic acid, citric acid, glucose and sucrose. The preparation method according to claim 13, characterized in that the antioxidant is ascorbic acid. The preparation method according to any one of claims 12 to 14, characterized in that the molar ratio of the antioxidant to the transition metal cation is (0.5-0.8):1. The preparation method according to claim 15, characterized in that the antioxidant and the transition metal The molar ratio of cations is (0.6-0.7):1. The preparation method according to any one of claims 2 to 16, characterized in that the concentration of transition metal cations in the first solution is 0.15 mol/L-0.30 mol/L. The preparation method according to any one of claims 2 to 17, characterized in that the concentration of the transition metal cyanide anion in the second solution is 0.1 mol/L-0.3 mol/L. The preparation method according to any one of claims 2 to 18, characterized in that the first solvent and the second solvent are both water. The preparation method according to any one of claims 2 to 19 is characterized in that the material of the cation exchange membrane is selected from at least one of a polyetheretherketone homogeneous cation exchange membrane, a perfluoroethylene sulfonic acid homogeneous cation exchange membrane and a polysulfone homogeneous cation exchange membrane. The preparation method according to any one of claims 2-20 is characterized in that it comprises: placing the first solution in the anode region of the electrochemical device, placing the second solution in the cathode region of the electrochemical device, and then applying power to obtain a suspension of Prussian blue material. The preparation method according to any one of claims 2-20 is characterized in that it comprises: placing the first solution in the anode area of the electrochemical device, applying power so that the transition metal cations are adsorbed onto the electrode plate in the cathode area, and then turning off the power; placing the second solution in the anode area of the electrochemical device, and then applying power in the reverse direction so that the adsorbed transition metal cations are decomposed and enter the area where the transition metal cyanide anions are located to react, thereby obtaining a suspension of Prussian blue material. The preparation method according to claim 21 or 22 is characterized in that it also includes: aging, washing, and separating the obtained suspension of the Prussian blue material to obtain a solid material, and drying the solid material. The preparation method according to claim 23, characterized in that the aging time is 2h-5h. A Prussian blue material, characterized in that it is prepared by the preparation method described in any one of claims 1 to 24. The Prussian blue material according to claim 25, characterized in that its chemical formula is Na _x M[Fe(CN) ₆ ], wherein M represents divalent iron or divalent manganese, and 1.5<x<2. Use of the Prussian blue material described in claim 26 as a positive electrode material for a sodium ion battery. A positive electrode plate for a sodium ion battery, characterized in that it comprises a positive electrode current collector and an active coating attached to the positive electrode current collector, wherein the active coating contains the Prussian blue material described in claim 26. A sodium ion battery, characterized in that it comprises the sodium ion battery positive electrode sheet according to claim 28. An electrical device, characterized in that it comprises the sodium ion battery described in claim 29.