Hollow iron-based prussian blue and template-free preparation method and application thereof

Abstract

The application discloses hollow iron-based Prussian blue and a template-free preparation method and application thereof. The preparation method comprises the following steps: S1, preparing a sodium ferrocyanide solution to obtain solution A; S2, mixing a soluble divalent iron salt, sodium citrate and deionized water to obtain solution B; S3, quickly pouring solution B into solution A and mixing and stirring to obtain a Prussian blue suspension; and S4, aging and post-treating the suspension to obtain a material. The concentration of the sodium ferrocyanide in solution A is 0.02-0.04 mol / L; the molar ratio of the divalent iron salt in solution B to the sodium ferrocyanide in solution A is (1.4-1.5):1; and the molar ratio of the sodium citrate to the sodium ferrocyanide in solution A is (5-10):1. The iron-based hollow cubic Prussian blue is prepared through one-step co-precipitation without a template, has a large specific surface area, is beneficial to exposing more active sites, and has a shorter ion diffusion path.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of sodium ion battery materials, in particular to a hollow iron-based Prussian blue and a template-free preparation method and application thereof. BACKGROUND

[0002] The positive electrode material of a sodium ion battery is a key point for determining the performance and practical application of the sodium ion battery. The positive electrode material requires that sodium ions can be reversibly inserted and extracted. At present, the positive electrode material mainly includes layered transition metal oxides, polyanion compounds and Prussian blue compounds. Among them, Prussian blue and its analogues have a three-dimensional open framework structure, which is beneficial to the insertion and extraction of sodium ions, and have the advantages of high specific capacity, good rate performance, simple synthesis, low cost and environmental friendliness, so that they become one of ideal positive electrode materials.

[0003] When Prussian blue is synthesized in water by using a common co-precipitation method, the Prussian blue framework contains crystal water and a large number of defects in the rapid crystallization synthesis process in the solvent environment, which leads to a low actual specific capacity and poor cycle performance. In addition, Prussian blue particles with high crystallinity usually have a large particle size and a low specific surface area, which is not conducive to the rapid insertion of sodium ions. Hollow structure Prussian blue has a high specific surface area, can expose more active sites, and is beneficial to the diffusion and migration of sodium ions. However, the synthesis of hollow structure Prussian blue usually involves a soft template method and a hard template method. Traditional hollow Prussian blue usually needs to use a soft template or a hard template. The soft template method is difficult to control, and the hard template method usually needs to handle the sacrificial template, which is a complex and usually dangerous process. Therefore, it is of great significance to explore an efficient, simple and safe preparation method and process of hollow Prussian blue and its analogues for the research and practical application of sodium ion batteries. SUMMARY

[0004] The purpose of the present application is to provide a hollow iron-based Prussian blue and a template-free preparation method and application thereof to solve the above problems in the prior art. The hollow cubic Prussian blue particles prepared by the present application can be used as a positive electrode of a sodium ion battery and have a high specific capacity and good cycle stability.

[0005] The template-free preparation method of the hollow iron-based Prussian blue of the present application comprises the following steps:

[0006] S1: mixing sodium ferrocyanide or a hydrate of sodium ferrocyanide with deionized water to obtain solution A;

[0007] S2: mixing a soluble divalent iron salt and sodium citrate with deionized water to obtain solution B;

[0008] S3: quickly pour solution B into solution A, mix and stir for a period of time, and obtain a Prussian blue suspension through a rapid crystallization co-precipitation reaction;

[0009] S4: age and post-treat the above suspension to obtain a hollow cubic structure Prussian blue material;

[0010] The concentration of sodium ferrocyanide or sodium ferrocyanide hydrate in the solution A is 0.02-0.04 mol / L.

[0011] The molar ratio of the divalent iron salt in solution B to sodium ferrocyanide in solution A is (1.4-1.5):1, and the molar ratio of sodium citrate to sodium ferrocyanide in solution A is (5-10):1.

[0012] Further, in step S1, the mixing time is 0.5-1 h.

[0013] Further, in step S2, the mixing time is 0.5-1 h.

[0014] Further, in step S3, the mixing and stirring time is 1-3 h.

[0015] Further, in step S3, the co-precipitation reaction temperature is 15-30℃.

[0016] Further, in step S4, the aging temperature is 50-70℃.

[0017] Further, in step S4, the aging time is 12-24 h.

[0018] Further, in step S4, the post-treatment includes cooling, washing, centrifugation and vacuum drying treatment.

[0019] A hollow iron-based Prussian blue prepared by the above preparation method.

[0020] The application of the above hollow iron-based Prussian blue as a positive electrode material for a sodium ion battery.

[0021] Compared with the prior art, the present application has the following advantages:

[0022] The present application uses the required amount of sodium citrate to complex the excess sodium ferrocyanide or its compounds, and the shorter complexing time makes the Fe 2+ can be removed from the complex at an appropriate speed, and solution B is quickly poured into solution A for stirring, rapid mixing and crystallization, the defined solution concentration of solution B and solution A provides a suitable crystallization environment for the crystallization of the iron-based Prussian blue, so that the iron-based Prussian blue forms a single-walled hollow cubic state, and through subsequent control of the aging temperature and time, the Prussian blue has higher crystallinity and crystal integrity.

[0023] The iron-based Prussian blue prepared by the method has a hollow structure, a large specific surface area, is beneficial to expose more active sites, and has a shorter ion diffusion path. The iron-based Prussian blue is used as a positive electrode of a sodium ion battery and exhibits a high specific capacity and good cycle stability, thereby improving the electrochemical performance of the battery.

[0024] The application provides a simple one-step co-precipitation method for preparing iron-based hollow cubic Prussian blue without a sacrifice template. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 , 2 is a scanning electron microscope picture of the hollow cubic structure iron-based Prussian blue prepared in Example 1 of the application;

[0026] Figure 3 is a transmission electron microscope picture of the hollow cubic structure iron-based Prussian blue prepared in Example 1 of the application;

[0027] Figure 4 is an X-ray diffraction spectrum of the hollow cubic structure iron-based Prussian blue prepared in Example 1 of the application;

[0028] Figure 5 is a charge-discharge curve diagram of a sodium ion battery assembled by using the hollow cubic structure iron-based Prussian blue prepared in Example 1 of the application;

[0029] Figure 6 is a cycle performance diagram of the sodium ion battery assembled by using the hollow cubic structure iron-based Prussian blue prepared in Example 1 of the application. DETAILED DESCRIPTION

[0030] The following is a further description of the technical solutions of the application in combination with the drawings, but the application is not limited to these embodiments.

[0031] Example 1

[0032] The application provides a simple co-precipitation method for preparing iron-based hollow cubic Prussian blue. The method comprises the following steps:

[0033] Sodium ferrocyanide hydrate is dissolved in 100 milliliters of deionized water, and uniform stirring is performed for 0.5 hours to obtain a solution A with a concentration of 0.02 mol / L;

[0034] Ferrous sulfate and sodium citrate are dissolved in 100 milliliters of deionized water, and stirring is performed for 0.5 hours to obtain a uniform mixed solution of solution B with concentrations of 0.03 mol / L and 0.17 mol / L, respectively;

[0035] The solution B was quickly poured into solution A and stirred for 1 hour to mix evenly, and then aged at 70°C for 24 hours.

[0036] The precipitate was washed, centrifuged, and vacuum dried to obtain the Prussian blue material.

[0037] The iron-based Prussian blue material prepared in this example was used as a positive electrode, metal sodium was used as a negative electrode, glass fiber (brand Whatman GF / D) was used as a separator, and a NaClO4 ethylene carbonate (EC) / diethyl carbonate (DEC) solution was used as an electrolyte. A battery was assembled in a glove box under an argon atmosphere and subjected to charge and discharge tests, with a current density of 10 mA / g and a voltage range of 2-4.2 V.

[0038] Figure 1 and Figure 2 The scanning electron microscope image of the hollow cubic structure iron-based Prussian blue prepared in Example 1 of the present application is shown in Figure 1. It can be observed from the figure that the synthesized iron-based Prussian blue has a clear hollow structure. The particle size distribution is 200 nm to 1.8 μm.

[0039] Figure 3 The transmission electron microscope image of the hollow cubic structure iron-based Prussian blue prepared in Example 1 of the present application is shown in Figure 2. It can be seen that the synthesized iron-based Prussian blue has a hollow structure.

[0040] Figure 4 The X-ray diffraction pattern of the hollow cubic structure iron-based Prussian blue prepared in Example 1 of the present application is shown in Figure 3. It shows a cubic phase structure after analysis.

[0041] Figure 5 The charge and discharge curve of the sodium ion battery assembled with the hollow cubic structure iron-based Prussian blue prepared in Example 1 of the present application is shown in Figure 4.

[0042] Figure 6 The electrochemical performance graph of the sodium ion battery assembled with the hollow cubic structure iron-based Prussian blue prepared in Example 1 of the present application at a current density of 10 mA / g and cycled for 50 cycles is shown in Figure 5.

[0043] After electrochemical testing, the initial discharge capacity was 120.9 mAh / g at a current density of 10 mA / g, and the cycle performance graph after 50 cycles had a capacity retention rate of 74.5%.

[0044] Comparative Example 1

[0045] The material was prepared as in Example 1, except that sodium citrate was not added to solution B. The sample without complexation had no obvious hollow structure, and presented irregular particles with a size of about 200 nm. Electrochemical testing showed that the initial discharge capacity was 93 mAh / g at a current density of 10 mA / g.

[0046] Comparative Example 2

[0047] The material was prepared as in Example 1, except that the concentration of the added sodium ferrocyanide solution A was 0.01 mol / L. The sample had no obvious hollow structure and presented irregular cubic particles with a size of about 500 nm. Electrochemical tests showed that the initial discharge capacity was 103.6 mAh / g at a current density of 10 mA / g.

[0048] Comparative Example 3

[0049] The material was prepared as in Example 1, except that the B solution was slowly added to the A solution over a period of 2 hours, and after the addition was completed, the mixing and stirring were continued for 1 hour. Under this condition, the sample presented a uniform cubic structure with clear edges and no observable hollow cubic structure. It presented irregular cubic block structures with a size of 300-600 nm. Electrochemical tests showed that the initial discharge capacity was 112.7 mAh / g at a current density of 10 mA / g.

[0050] Example 2

[0051] The present application proposes a simple co-precipitation method for preparing iron-based hollow cubic Prussian blue. The method comprises the following steps:

[0052] (1) Dissolve sodium ferrocyanide decahydrate in 100 ml of deionized water and stir for 0.5 hours to obtain a solution A with a concentration of 0.03 mol / L;

[0053] (2) Dissolve ferrous sulfate and sodium citrate in 100 ml of deionized water and stir for 0.5 hours to obtain a uniform mixed solution of solution B with concentrations of 0.042 mol / L and 0.15 mol / L, respectively;

[0054] (3) Pour the B solution into the A solution quickly and stir for 1 hour to mix uniformly, and then age at 70°C for 24 hours.

[0055] (4) Wash, centrifuge, and vacuum dry the precipitate to obtain the Prussian blue material.

[0056] The sample is a hollow cubic Prussian blue particle. Electrochemical tests showed that the initial discharge capacity was 120.1 mAh / g at a current density of 10 mA / g.

[0057] Example 3

[0058] The present application proposes a simple co-precipitation method for preparing iron-based hollow cubic Prussian blue. The method comprises the following steps:

[0059] (1) Dissolve sodium ferrocyanide decahydrate in 100 ml of deionized water and stir for 0.5 hours to obtain a solution A with a concentration of 0.04 mol / L;

[0060] (2) Dissolve ferrous sulfate and sodium citrate in 100 ml of deionized water, stir for 0.5 hours to obtain a uniform mixed solution of solution B with concentrations of 0.056 mol / L and 0.2 mol / L, respectively;

[0061] (3) Pour the B solution into the A solution quickly and stir for 1 hour to mix uniformly, and then age at 50°C for 20 hours.

[0062] (4) Wash, centrifuge and vacuum dry the precipitate to obtain the Prussian blue material.

[0063] The sample is hollow cubic Prussian blue particles. After electrochemical testing, the initial discharge capacity is 118.7 mAh / g at a current density of 10 mA / g.

[0064] Example 4

[0065] The present application proposes a simple co-precipitation method for preparing iron-based hollow cubic Prussian blue. The method comprises the following steps:

[0066] (1) Dissolve sodium ferrocyanide hydrate in 100 ml of deionized water and stir for 1 hour to obtain solution A with a concentration of 0.04 mol / L;

[0067] (2) Dissolve ferrous sulfate and sodium citrate in 100 ml of deionized water, stir for 1 hour to obtain a uniform mixed solution of solution B with concentrations of 0.056 mol / L and 0.2 mol / L, respectively;

[0068] (3) Pour the B solution into the A solution quickly and stir for 2 hours to mix uniformly, and then age at 60°C for 12 hours.

[0069] (4) Wash, centrifuge and vacuum dry the precipitate to obtain the Prussian blue material.

[0070] After electrochemical testing, the initial discharge capacity is 120.4 mAh / g at a current density of 10 mA / g.

[0071] Example 5

[0072] The present application proposes a simple co-precipitation method for preparing iron-based hollow cubic Prussian blue. The method comprises the following steps:

[0073] (1) Dissolve sodium ferrocyanide hydrate in 100 ml of deionized water and stir for 1 hour to obtain solution A with a concentration of 0.04 mol / L;

[0074] (2) Dissolve ferrous sulfate and sodium citrate in 100 ml of deionized water, stir for 1 hour to obtain a uniform mixed solution of solution B with concentrations of 0.056 mol / L and 0.2 mol / L, respectively;

[0075] (3) Pour B solution into A solution quickly and stir for 3 hours to mix evenly, then age at 70°C for 24 hours.

[0076] (4) Wash, centrifuge and vacuum dry the precipitate to obtain the Prussian blue material.

[0077] After electrochemical test, the initial discharge capacity is 119.5 mAh / g at a current density of 10 mA / g.

[0078] The preparation method of the iron-based Prussian blue material provided in the application easily prepares a hollow cubic structure Prussian blue for a sodium ion battery positive electrode material through simple co-precipitation combined with a complexing agent solution without a template.

[0079] The above not involved, applicable to the prior art.

[0080] Although some specific embodiments of the present application have been described in detail through examples, those skilled in the art should understand that the above examples are only for illustration, not for limiting the scope of the present application, and those skilled in the art can make various modifications or supplements or use similar ways to replace the described specific embodiments, but will not deviate from the direction of the present application or exceed the scope defined by the appended claims. Those skilled in the art should understand that any modification, equivalent replacement, improvement, etc. made according to the technical essence of the present application to the above embodiments shall be included in the protection scope of the present application.

Claims

1. A template-free method for the preparation of hollow iron-based Prussian blue, characterized in that, The method comprises the following steps: S1: mixing sodium ferrocyanide or a hydrate of sodium ferrocyanide with deionized water to obtain solution A; S2: mixing a soluble divalent iron salt, sodium citrate and deionized water to obtain solution B; S3: quickly pouring solution B into solution A and mixing and stirring for a period of time to obtain a Prussian blue suspension through a rapid crystallization co-precipitation reaction; S4: aging and post-treating the suspension to obtain a hollow cubic structure Prussian blue material; The concentration of sodium ferrocyanide or the hydrate of sodium ferrocyanide in the solution A is 0.02-0.04 mol / L; The molar ratio of the divalent iron salt in the solution B to the sodium ferrocyanide in the solution A is (1.4-1.5):1, and the molar ratio of the sodium citrate to the sodium ferrocyanide in the solution A is (5-10):

1.

2. A template-free preparation method of hollow iron-based Prussian blue according to claim 1, characterized in that, In step S1, the mixing time is 0.5-1 h.

3. A template-free preparation method of hollow iron-based Prussian blue according to claim 1, characterized in that, In step S2, the mixing time is 0.5-1 h.

4. A template-free method of preparing hollow iron-based Prussian blue according to claim 1, characterized in that, In step S3, the mixing and stirring time is 1-3 h.

5. A template-free method of preparing hollow iron-based Prussian blue as claimed in claim 1, wherein, In step S3, the co-precipitation reaction temperature is 15-30 °C.

6. A template-free method of preparing hollow iron-based Prussian blue according to claim 1, characterized in that, In step S4, the aging temperature is 50-70 °C.

7. A template-free method of preparing hollow iron-based Prussian blue according to claim 1, characterized in that, In step S4, the aging time is 12-24 h.

8. A template-free method of preparing hollow iron-based Prussian blue according to claim 1, characterized in that, In step S4, the post-treatment comprises cooling, washing, centrifugation and vacuum drying treatment.

9. A hollow iron-based Prussian blue prepared by the method of any one of claims 1-8.

10. Use of the hollow iron-based Prussian blue of claim 9 as a positive electrode material for a sodium ion battery.

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