Iron-based prussian blue positive electrode material with improved stability and preparation method thereof

Abstract

The application belongs to the technical field of production of sodium ion battery positive electrode materials, and particularly relates to an iron-based Prussian blue positive electrode material with improved stability and a preparation method thereof. The method comprises the following steps: dissolving ferrous salt, perchlorate and sodium citrate in water to obtain solution A; dissolving sodium ferrocyanide and an antioxidant in water to obtain solution B; mixing the solution A and the solution B, stirring and reacting to obtain a suspension; allowing the suspension to stand and age, and then performing solid-liquid separation, washing and drying to obtain the iron-based Prussian blue positive electrode material. The iron-based Prussian blue positive electrode material prepared by the method can be applied to sodium ion batteries, and the long cycle performance of the sodium ion batteries is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of production of sodium ion battery cathode materials, and particularly relates to an iron-based Prussian blue cathode material with improved stability and a preparation method thereof. BACKGROUND

[0002] Sodium ion batteries are very similar to lithium ion batteries in working principle, and have the great advantage of low-cost and readily available raw materials, and are a very promising large-scale grid energy storage candidate battery. In order to realize the industrialization and commercialization of sodium ion battery technology, it is necessary to develop a suitable sodium ion intercalation cathode material.

[0003] Among them, Prussian blue analogs (PBAs) have an open three-dimensional framework structure, large interstitial sites and ion transport channels, which facilitate the reversible deintercalation of sodium ions, and are an ideal sodium ion battery cathode material. On the basis of comprehensively considering factors such as material cost, environmental friendliness and electrochemical performance, iron-based Prussian blue with double active sites (molecular formula: Na2Fe[Fe(CN)6]) is considered to be a very promising commercialized sodium ion battery cathode material and has been widely studied.

[0004] However, due to the presence of lattice vacancies and crystalline water, PBAs often exhibit poor rate performance and rapid capacity decay in practical applications. It is currently generally believed that crystalline water is the main factor causing the instability of PBAs material structure. Studies have shown that crystalline water not only easily reacts with electrolyte, leading to gas generation during the Na + insertion and extraction processes, but also can form (NaH2O) + units with Na + , hindering the migration of Na + , causing cumulative stress and inducing lattice distortion, and ultimately leading to capacity decay. However, in existing liquid synthesis techniques, these crystalline waters are inevitably introduced into the open framework of PBAs. Therefore, it is crucial to explore a reasonable method to regulate the content of crystalline water in the framework to obtain PBAs materials with high stability.

[0005] The prior art CN 118419950 A discloses a preparation method of high-quality Prussian blue compounds (PB) and analogs (PBA) for sodium ion battery cathodes. This synthesis method inevitably introduces crystalline water into the Prussian blue lattice. During the cycling process, part of the crystalline water exists in the form of hydrated sodium ions, hindering the migration of sodium ions, and is accompanied by cumulative distortion of the Prussian blue crystal structure. In addition, part of the crystalline water reacts with the electrolyte, producing gas and deteriorating battery performance.

[0006] The prior art CN115108566A discloses a preparation method of a long-life iron-based Prussian blue positive electrode material. The scheme is to disperse the initial iron-based Prussian blue material synthesized by a sodium citrate auxiliary co-precipitation method in a certain amount of deionized water under the protection of an inert atmosphere, and add a small amount of alcohol dispersant, so that the cycle stability of the iron-based Prussian blue positive electrode material is obviously improved, but the problem of the presence of a large amount of crystal water in the iron-based Prussian blue positive electrode material prepared by the conventional co-precipitation method is not solved. The iron-based Prussian blue obtained by the technology still contains a large amount of crystal water, which not only easily reacts with the electrolyte, but also leads to Na + Gas is generated in the embedding and stripping process. SUMMARY

[0007] In view of the defects of the prior art, the present application provides an iron-based Prussian blue positive electrode material with improved stability and a preparation method thereof, which aims to solve the technical problem of poor stability of the iron-based Prussian blue positive electrode material due to the presence of crystal water in the prior art.

[0008] In order to achieve the above-mentioned application purpose, according to the first aspect of the present application, a preparation method of an iron-based Prussian blue positive electrode material with improved stability is provided, characterized in that it comprises the following steps:

[0009] (1) Dissolve ferrous salt, perchlorate and sodium citrate in water to obtain solution A;

[0010] (2) Dissolve sodium ferrocyanide and an antioxidant in water to obtain solution B;

[0011] (3) Mix the solution A and the solution B to obtain a suspension;

[0012] (4) Age the suspension, then separate the solid and the liquid, wash and dry to obtain the iron-based Prussian blue positive electrode material.

[0013] Preferably, the ferrous salt is selected from one or more of ferrous chloride, ferrous sulfate, ferrous perchlorate, ferrous acetate and ferrous nitrate.

[0014] Preferably, the perchlorate is selected from ferrous perchlorate, sodium perchlorate, potassium perchlorate and calcium perchlorate.

[0015] Preferably, the antioxidant is selected from one or more of butylated hydroxyanisole, butylated hydroxytoluene, propyl gallate, tertiary butyl hydroquinone and ascorbic acid.

[0016] Preferably, in step (1), the concentration of ferrous ions in the solution A is 0.01-10 mol / L; the molar ratio of perchlorate ions in the solution A to ferrous ions in the solution A is (1-20):1; and the molar ratio of sodium citrate to ferrous ions in the solution A is (1-10):1.

[0017] Preferably, in step (2), the concentration of sodium ferrocyanide in the solution B is 0.01-10 mol / L; and the concentration of the antioxidant in the solution B is 0.001-0.1 mol / L.

[0018] Preferably, the volume ratio of the solution A to the solution B is (0.5-2):1.

[0019] Preferably, in step (3), the solution A and the solution B are reacted under stirring at a stirring rate of 300-1000 r / min for 2-4 h at a temperature of 25-40℃.

[0020] Preferably, in step (4), the aging is performed at a temperature of 25-40℃ for 6-30 h; and the drying is performed in a vacuum oven at a temperature of 100-120℃ for 12-24 h.

[0021] According to another aspect of the present application, there is provided a stable iron-based Prussian blue positive electrode material prepared by the above preparation method.

[0022] According to another aspect of the present application, there is provided an application of the stable iron-based Prussian blue positive electrode material, which is applied to a sodium ion battery.

[0023] In general, compared with the prior art, the above technical solution conceived by the present application mainly has the following technical advantages:

[0024] (1) The present application adds ferrous salt and perchlorate salt. First, since the binding energy between ferrous ions and perchlorate ions is lower than the binding energy between ferrous ions and water molecules, ferrous ions in the solution tend to coordinate with perchlorate ions rather than form coordination with water molecules, which can effectively reduce the content of crystal water in the process of crystal nucleation and growth of iron-based Prussian blue. Second, the adsorption energy of perchlorate ions on the surface of iron-based Prussian blue crystals is also lower than the adsorption energy of water molecules on the surface of iron-based Prussian blue crystals, and the crystal surface tends to adsorb perchlorate ions, thereby greatly hindering the entry of water molecules into the interior of iron-based Prussian blue crystals during the crystal growth and aging process, and reducing the content of crystal water. In addition, since there is a coordination effect between perchlorate ions and ferrous ions, the coordination effect competes with the coordination of ferrous ions with [Fe(CN)6]4- The combination of the above-mentioned technical solutions can reduce the occurrence of spontaneous nucleation and precipitation, slow down the crystallization rate, reduce the vacancy defects, prevent water molecules from filling the vacancies, and thus reduce the crystalline water content.

[0025] (2) The sodium citrate has strong complexing ability, can form a coordination compound with ferrous ions, and competitively inhibits the combination of ferrous ions with [Fe(CN)6] 4- The combination of the above-mentioned technical solutions can reduce the occurrence of spontaneous nucleation and precipitation, slow down the crystallization rate, reduce the vacancy defects, prevent water molecules from filling the vacancies, and thus reduce the crystalline water content.

[0026] (3) The iron-based Prussian blue positive electrode material prepared by the method has a nano structure and low interstitial water, and the method has low cost and high efficiency, and the iron-based Prussian blue positive electrode material has excellent long cycle performance and wide application prospect when used in a sodium ion battery. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 FIG. 4 is an X-ray diffraction (XRD) spectrum of the iron-based Prussian blue positive electrode material prepared in the examples and comparative examples.

[0028] Figure 2 FIG. 5 is a scanning electron microscope (SEM) image of the iron-based Prussian blue positive electrode material prepared in the examples and comparative examples; wherein a is Example 1; b is Example 2; c is Example 3; d is Comparative Example 1; and e is Comparative Example 2.

[0029] Figure 3 FIG. 6 is a cycle performance comparison chart of the iron-based Prussian blue positive electrode material prepared in the examples and comparative examples. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0031] Example 1

[0032] Preparation of an iron-based Prussian blue positive electrode material:

[0033] (1) Dissolve 5 mmol of ferrous perchlorate and 25 mmol of trisodium citrate in 100 ml of deionized water at 30℃ to obtain solution A;

[0034] (2) At 30℃, 5 mmol of sodium ferrocyanide and 0.1 g of ascorbic acid were dissolved in 100 ml of deionized water to obtain solution B;

[0035] (3) Under the condition of stirring rate of 300r / min, solution A was directly poured into solution B and stirred for 2 hours. Then, it was aged at room temperature of 25℃ for 24 hours, and then the iron-based Prussian blue cathode material was obtained by solid-liquid separation, washing and drying.

[0036] Figure 1 The XRD pattern of the cathode material prepared in this embodiment; Figure 2 Image a shows a SEM image of the cathode material prepared in this embodiment. As can be seen from the image, the material has a cubic phase structure, composed of cubic particles ranging from 200 nm to 1 μm. Electrochemical tests were then performed on it. Figure 3 It can be seen that it has 112.47 mAh g at a current density of 5C. -1 The discharge specific capacity is high, and the capacity retention rate after 1000 cycles is 80.11%.

[0037] Example 2

[0038] Preparation of an iron-based Prussian blue cathode material:

[0039] (1) At 30℃, 5 mmol ferrous chloride, 10 mmol sodium perchlorate and 25 mmol trisodium citrate were dissolved in 100 ml deionized water to obtain solution A;

[0040] (2) At 30℃, 5 mmol of sodium ferrocyanide and 0.1 g of ascorbic acid were dissolved in 100 ml of deionized water to obtain solution B;

[0041] (3) Under the condition of stirring rate of 800 r / min, solution A was directly poured into solution B and stirred for 2 hours. Then, it was aged at room temperature of 25°C for 24 hours, and then the iron-based Prussian blue cathode material was obtained by solid-liquid separation, washing and drying.

[0042] Figure 1 XRD pattern for preparing the cathode material in this embodiment. Figure 2 Image b shows a SEM image of the cathode material prepared in this embodiment. As can be seen from the image, the material has a cubic phase structure, composed of cubic particles ranging from 200 nm to 700 nm. Electrochemical tests were performed on it. Figure 3 It can be seen that it has 114.05 mAh g at a current density of 5C. -1 The discharge specific capacity is high, and the capacity retention rate after 1000 cycles is 70.25%.

[0043] Example 3

[0044] Preparation of a ferrous Prussian blue positive electrode material

[0045] (1) 5 mmol of ferrous sulfate, 10 mmol of sodium perchlorate and 25 mmol of trisodium citrate were dissolved in 100 ml of deionized water at 30°C to obtain solution A;

[0046] (2) 5 mmol of sodium ferrocyanide and 0.1 g of ascorbic acid were dissolved in 100 ml of deionized water at 30°C to obtain solution B;

[0047] (3) Solution A was directly poured into solution B under the condition of a stirring rate of 1000 r / min, and stirring reaction was carried out for 2 hours, followed by aging at room temperature 25°C for 24 hours, and then solid-liquid separation, washing and drying to obtain the ferrous Prussian blue positive electrode material.

[0048] Figure 1 The XRD of the positive electrode material prepared in this example, Figure 2 The SEM of the positive electrode material prepared in this example is shown in Figure c. It can be seen from the figure that the material has a cubic phase structure and is composed of cubic particles with a size of 200-700 nm. Electrochemical test was carried out on it, and it was found that it has a discharge specific capacity of 112.04 mAh g -1 at a current density of 5C, and the capacity retention rate after 1000 cycles is 72.12%. Figure 3

[0049] Comparative Example 1

[0050] Preparation of a ferrous Prussian blue positive electrode material

[0051] (1) 5 mmol of ferrous chloride and 25 mmol of trisodium citrate were dissolved in 100 ml of deionized water at 30°C to obtain solution A;

[0052] (2) 5 mmol of sodium ferrocyanide and 0.1 g of ascorbic acid were dissolved in 100 ml of deionized water at 30°C to obtain solution B;

[0053] (3) Solution A was directly poured into solution B under the condition of a stirring rate of 800 r / min, and stirring reaction was carried out for 2 hours, followed by aging at room temperature 25°C for 24 hours, and then solid-liquid separation, washing and drying to obtain the ferrous Prussian blue positive electrode material.

[0054] Figure 1 The XRD of the positive electrode material prepared in this example, Figure 2 The SEM of the positive electrode material prepared in this example is shown in Figure d. It can be seen from the figure that the material has a cubic phase structure and is composed of cubic particles with a size of 200-400 nm. Electrochemical test was carried out on it, and it was found that it has a discharge specific capacity of 112.04 mAh g Figure 3 ​It can be seen that the material has a discharge specific capacity of 115.76 mAh g -1 at a current density of 5C, and a capacity retention rate of 59.04% after 1000 cycles.

[0055] Comparative Example 2

[0056] Preparation of an iron-based Prussian blue positive electrode material:

[0057] (1) 5 mmol of ferrous sulfate, 25 mmol of trisodium citrate were dissolved in 100 ml of deionized water at 30°C to obtain solution A;

[0058] (2) 5 mmol of sodium ferrocyanide, 0.1 g of ascorbic acid were dissolved in 100 ml of deionized water at 30°C to obtain solution B;

[0059] (3) Solution A was directly poured into solution B under the condition of a stirring rate of 1000 r / min, and stirred for 2 hours, then aged at room temperature of 25°C for 24 hours, and then subjected to solid-liquid separation, washing, and drying to obtain the iron-based Prussian blue positive electrode material.

[0060] Figure 1 Figure 2 is an XRD pattern of the positive electrode material prepared in the present comparative example, Figure 2 Figure 3 is an SEM photograph of the positive electrode material prepared in the present comparative example. It can be seen from the figure that the material has a cubic phase structure, and is composed of cubic particles with a size of 200 nm-400 nm. Electrochemical tests were performed on the material, Figure 3 It can be seen that the material has a discharge specific capacity of 112.49 mAh g -1 at a current density of 5C, and a capacity retention rate of 66.92% after 1000 cycles.

[0061] Table 1: Cycle capacity of the iron-based Prussian blue positive electrode materials prepared in the examples and comparative examples

[0062]

[0063] It should be understood by those skilled in the art that the above description is only a preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement, and improvement within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing an iron-based Prussian blue cathode material with improved stability, characterized in that, Includes the following steps: (1) Dissolve ferrous salt, perchlorate and sodium citrate in water to obtain solution A; (2) Dissolve sodium ferrocyanide and antioxidant in water to obtain solution B; (3) Mix the solution A with the solution B and react to obtain a suspension; (4) The suspension is allowed to stand and age, then separated into solid and liquid, washed and dried to obtain iron-based Prussian blue cathode material.

2. The method for preparing a stable iron-based Prussian blue cathode material according to claim 1, characterized in that, The ferrous salt is selected from one or more of ferrous chloride, ferrous sulfate, ferrous perchlorate, ferrous acetate, and ferrous nitrate; the perchlorate is selected from ferrous perchlorate, sodium perchlorate, potassium perchlorate, and calcium perchlorate.

3. The method for preparing a stable iron-based Prussian blue cathode material according to claim 1, characterized in that, The antioxidant is selected from one or more of butylated hydroxyanisole, butylated hydroxytoluene, propyl gallate, tert-butylhydroquinone, or ascorbic acid.

4. The method for preparing a stable iron-based Prussian blue cathode material according to claim 1, characterized in that, In step (1), the concentration of ferrous ions in solution A is 0.01 to 10 mol / L; the molar ratio of perchlorate ions to ferrous ions in solution A is (1 to 20): 1; and the molar ratio of sodium citrate to ferrous ions in solution A is (1 to 10):

1.

5. The method for preparing a stable iron-based Prussian blue cathode material according to claim 4, characterized in that, In step (2), the concentration of sodium ferrocyanide in solution B is 0.01 to 10 mol / L; the concentration of the antioxidant in solution B is 0.001 to 0.1 mol / L.

6. The method for preparing a stable iron-based Prussian blue cathode material according to claim 5, characterized in that, The volume ratio of solution A to solution B is (0.5-2):

1.

7. The method for preparing a stable iron-based Prussian blue cathode material according to claim 1, characterized in that, In step (3), solution A and solution B react under stirring conditions, with a stirring rate of 300-1000 r / min, a stirring time of 2-4 h, and a reaction temperature of 25-40 °C.

8. The method for preparing a stable iron-based Prussian blue cathode material according to claim 1, characterized in that, In step (4), the aging temperature is 25-40℃ and the aging time is 6-30h; in step (4), the drying is done in a vacuum oven at a temperature of 100-120℃ for 12-24h.

9. The iron-based Prussian blue cathode material with improved stability prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the iron-based Prussian blue cathode material with improved stability according to claim 9, characterized in that, The iron-based Prussian blue cathode material is applied to sodium-ion batteries.

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