Preparation method of sodium ion battery cathode Prussian blue material

Abstract

The present invention discloses a preparation method of a sodium-ion battery cathode Prussian blue material. By dissolving ascorbic acid, sodium citrate monohydrate, sodium chloride and sodium ferrocyanide decahydrate to form a homogeneous solution, and slowly adding a solution formed by manganese salt or iron salt thereto, reacting and aging it under oil bath conditions, and finally subjecting the precipitate to a first-stage low-temperature freezing treatment and a second-stage vacuum freeze-thaw drying process in sequence, a Prussian blue material with a cubic morphology is finally formed. The preparation method is simple, the process is easy to control, and the cycle is short. The material can exhibit specific capacities of 125, 122, 119, 114, 103, 99 and 88 mAh / g at rates of 0.2, 0.5, 1, 2, 5, 10 and 15 C, showing excellent rate performance; the material can still maintain a capacity retention rate of 80% after cycling 650 times at a rate of 2 C, showing excellent long-cycle performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of new secondary batteries and relates to a preparation method of a sodium-ion battery cathode Prussian blue material. Background Art

[0002] With the accelerated promotion of the construction of electric vehicles and smart grids across the country, the development of energy storage technology has also become one of the hottest research fields. The Prussian blue cathode material for sodium-ion batteries has a stable and open framework structure and is a cathode material with great prospects for large-scale energy storage applications. However, there are still great challenges in synthesizing high-performance Prussian blue-based cathode materials. One of them is that Prussian blue analogs generally contain a relatively high content of crystal water, which greatly affects the electrochemical performance of the materials.

[0003] Crystal water has serious negative effects on both the electrode material and the electrolyte in the battery. Crystal water can be subdivided into bound water, interstitial water, and adsorbed water, which occupy the Fe(CN)6 vacancies, lattice interstices, and are adsorbed on the surface of the material in Prussian blue-based materials respectively. Among them, adsorbed water can be relatively easily removed by heating, but interstitial water and bound water are more difficult to remove. For interstitial water, although it can also be removed by increasing the temperature, it may damage the structure of the material, thereby affecting its function. And bound water can hardly be removed by heating. If forced to be removed by heating, the structure of the material is also severely damaged and can no longer be used as an electrode material. These several types of crystal water existing in Prussian blue-based materials all affect their electrochemical performance during the working process. For example, the crystal water in the material can all come out as Na(H2O) + units during the charging process of the battery and enter the electrolyte, resulting in slow decomposition and having an adverse effect on the stability of the electrolyte. For interstitial water, since it occupies the interstitial sites in Prussian blue-based materials, the migration of sodium ions is hindered during charge and discharge, affecting the sodium ion migration kinetics.

[0004] Based on this, it is urgent to overcome the problem of crystal water existing in the preparation of Prussian blue materials for sodium-ion battery cathodes and improve the electrochemical performance of this material. Summary of the Invention

[0005] The present invention aims to provide a preparation method of a Prussian blue material for a sodium-ion battery cathode. The preparation method is simple, the process is easy to control, and the cycle is short. By dissolving ascorbic acid, sodium citrate monohydrate, sodium chloride, and sodium ferrocyanide decahydrate to form a homogeneous solution, and slowly adding a solution formed by a manganese salt or an iron salt thereto, reacting and aging it under an oil bath condition, and finally performing a first-stage low-temperature freezing treatment and a second-stage vacuum freeze-thaw drying process on the precipitate in sequence, a Prussian blue material with a cubic morphology is finally formed, and this material has excellent electrochemical performance.

[0006] The technical solution of the present invention is as follows:

[0007] A preparation method of a positive electrode Prussian blue material for a sodium ion battery is carried out in the following sequential steps:

[0008] S1. Ascorbic acid, sodium citrate monohydrate, and sodium chloride are sequentially added to a solvent, and the mixture is heated and stirred in an oil bath at 80 °C until fully dissolved. After adding sodium ferrocyanide decahydrate and dissolving it, it is denoted as solution A;

[0009] S2. A manganese salt or an iron salt is added to distilled water and stirred and dissolved at room temperature, denoted as solution B;

[0010] S3. The obtained solution B is added to solution A through a peristaltic pump, and the mixture is heated and stirred in an oil bath at 80 °C for 6 h, then the heating and stirring are turned off and left to age for 6 h to obtain solution C;

[0011] S4. The solution C is filtered by suction to obtain a precipitate. The obtained precipitate is cryogenically frozen at -20 °C in a refrigerator for 2 h, and the frozen precipitate is transferred to a cold trap of a freeze dryer and vacuum-dried while gradually heating from -50 °C to 50 °C to obtain the Prussian blue positive electrode material.

[0012] As a limitation of the present invention:

[0013] (1) In step S1, the stirring rate is 600 rpm.

[0014] (2) In step S1, the molar ratio of ascorbic acid, sodium citrate monohydrate, sodium chloride, and sodium ferrocyanide decahydrate is 1:1:2:2.

[0015] In the present invention, the molar ratio of ascorbic acid, sodium citrate monohydrate, sodium chloride, and sodium ferrocyanide decahydrate affects indexes such as the product composition and water content, and further affects indexes such as the electrochemical performance and safety of the Prussian blue sodium ion battery positive electrode material.

[0016] (3) In step S1, the solvent is water or a water-ethanol equal-volume mixed solution.

[0017] (4) In step S1, the manganese salt is manganese chloride or manganese sulfate, and the iron salt is ferrous chloride or ferrous sulfate.

[0018] (5) In step S2, the molar amount of the manganese salt or the iron salt is 1.5 times the molar amount of sodium ferrocyanide.

[0019] The addition amount of the manganese salt or the iron salt affects whether the obtained product is the specified Prussian blue derivative.

[0020] (6) In step S3, the addition rate of solution B through the peristaltic pump is 10 mL / min.

[0021] The addition rate of Solution B to Solution A needs to be strictly controlled. This is mainly because during the preparation of Prussian blue materials through coprecipitation reactions, if the rate is too fast, it will lead to incomplete growth of the unit cell, resulting in more structural defects and reducing the electrochemical cycling stability of the material.

[0022] (VII) In step S4, medium-speed filter paper with a pore size of 30 - 50 μm is used for suction filtration.

[0023] (VIII) In step S4, the vacuum drying time in the cold trap of the freeze dryer is 1 h.

[0024] Another limitation of the present invention is that in step S4, the heating rate of the cold trap of the freeze dryer is 10 °C / h.

[0025] The freeze drying of the present invention is divided into two stages. In the first stage, it is frozen at -20 °C for 2 h. The main purpose of the staged cooling is to initially freeze the precipitate obtained by centrifugation, prevent the formation of ice crystal bands due to rapid cooling, and more easily form small and uniform ice crystals to reduce damage to the framework structure of the Prussian blue material and facilitate the growth of the cubic crystal morphology. In the second stage, it is gradually heated under vacuum conditions from -50 °C to 50 °C. The main purpose is to make the crystal water contained in the frozen precipitate reach the triple point of water under low temperature and low pressure conditions, so that the adsorbed water and lattice water in the prepared Prussian blue material are fully sublimated. The dissipation of water in this stage causes little damage to the material structure, effectively reducing the crystal water content of the Prussian blue cathode material during the formation process of the material and promoting the formation of a cubic morphology.

[0026] The above steps of the present invention are an organic whole, and each step is closely related and inseparable, jointly affecting the morphology structure and electrochemical performance of the final Prussian blue cathode material.

[0027] After adopting the above technical solutions, the beneficial effects obtained by the present invention are as follows:

[0028] 1. The preparation method of the present invention is simple, the process is easy to control, the cycle is short, and it is easy to industrialize production.

[0029] 2. By controlling the addition sequence of the two precursor solutions and the freeze drying process, the present invention not only effectively reduces the crystal water content during the formation of the Prussian blue cathode material, but also its unique drying process can form a cubic morphology, which further guarantees its excellent electrochemical performance.

[0030] 3. The Prussian blue cathode material prepared in the present invention was electrochemically tested and showed specific capacities of 125, 122, 119, 114, 103, 99, and 88 mAh / g at current rates of 0.2, 0.5, 1, 2, 5, 10, and 15 C, respectively, demonstrating excellent rate performance. The material still maintained a capacity retention rate of 80% after 650 cycles at a current rate of 2 C, showing excellent long-cycle performance.

[0031] The present invention is applicable to the preparation of Prussian blue materials and further applied to the cathode materials of sodium-ion batteries.

[0032] The specific embodiments of the present invention will be further described in detail below in conjunction with the accompanying drawings of the specification.

[0033] Accompanying drawings of the specification

[0034] Figure 1 is the XRD pattern of the layered material of the sodium-ion battery prepared in Example 1;

[0035] Figure 2 is the morphology diagram of the Prussian blue material of the sodium-ion battery prepared in Example 2;

[0036] Figure 3 is the thermogravimetric diagram of the Prussian blue material of the sodium-ion battery prepared in Example 2;

[0037] Figure 4 is the rate performance diagram of the Prussian blue material of the sodium-ion battery prepared in Example 3;

[0038] Figure 5 is the long-cycle performance diagram of the Prussian blue material of the sodium-ion battery prepared in Example 4. Specific embodiments

[0039] In the following examples for preparing Prussian blue cathode materials, unless otherwise specified, the reagents used are all commercially available reagents. Unless otherwise specified, the following experimental methods and detection methods are all existing experimental methods and detection methods.

[0040] Example 1

[0041] S1. 3 mmol of ascorbic acid, 6 mmol of sodium citrate monohydrate, and 6 mmol of sodium chloride were successively added to 100 mL of distilled water, and the mixture was heated and stirred in an oil bath at 80 °C until completely dissolved. After adding 3 mmol of sodium ferrocyanide decahydrate and dissolving it, it was denoted as solution A;

[0042] S2. 3 mmol of manganese sulfate tetrahydrate was added to 100 ml of distilled water and stirred to dissolve at room temperature, denoted as solution B;

[0043] S3. Add the obtained solution B to solution A through a peristaltic pump at an addition rate of 10 ml / min, heat and stir the reaction in an oil bath at 80 °C for 6 h, turn off the heating and stirring, and let it stand for aging for 6 h to obtain solution C;

[0044] S4. Filter the solution C to obtain a precipitate (the pore size of the filter paper used for filtration is 30 - 50 μm), freeze the obtained precipitate in a refrigerator at -20 °C for 2 h, transfer the frozen precipitate to a cold trap of a freeze dryer, evacuate it, and dry it by gradually heating from -50 °C to 50 °C. The heating rate of the cold trap of the freeze dryer is 10 °C / h to obtain a Prussian blue cathode material.

[0045] Figure 1 It is the synchrotron radiation XRD pattern of the sodium-ion battery layered material prepared in Example 1. All the diffraction peaks correspond to the standard XRD card (73 - 0687), indicating that the material synthesized by the process of this example is a pure phase.

[0046] Example 2

[0047] S1. Add 3 mmol of ascorbic acid, 6 mmol of sodium citrate monohydrate, and 6 mmol of sodium chloride to 100 mL of distilled water in sequence, heat and stir in an oil bath at 80 °C to dissolve them completely. After adding 3 mmol of sodium ferrocyanide decahydrate and dissolving it, it is denoted as solution A;

[0048] S2. Add 3 mmol of ferrous sulfate tetrahydrate to 100 ml of distilled water, stir and dissolve it at room temperature, and denote it as solution B;

[0049] S3. Add the obtained solution B to solution A through a peristaltic pump at an addition rate of 10 ml / min, heat and stir the reaction in an oil bath at 80 °C for 6 h, turn off the heating and stirring, and let it stand for aging for 6 h to obtain solution C;

[0050] S4. Filter the solution C to obtain a precipitate (the pore size of the filter paper used for filtration is 30 - 50 μm), freeze the obtained precipitate in a refrigerator at -20 °C for 2 h, transfer the frozen precipitate to a cold trap of a freeze dryer, evacuate it, and dry it by gradually heating from -50 °C to 50 °C. The heating rate of the cold trap of the freeze dryer is 10 °C / h to obtain a Prussian blue cathode material.

[0051] Figure 2 It is the SEM image of the sample prepared in this example. It can be seen from the figure that the sample is cubic.

[0052] Figure 4It is the rate performance graph of the sample prepared in Example 2. The material prepared in this example can deliver specific capacities of 125, 122, 119, 114, 103, 99, and 88 mAh / g at rates of 0.2, 0.5, 1, 2, 5, 10, and 15 C, demonstrating excellent rate performance.

[0053] Example 3

[0054] S1. Sequentially add 3 mmol of ascorbic acid, 6 mmol of sodium citrate monohydrate, and 6 mmol of sodium chloride into 100 mL of distilled water, heat and stir in an oil bath at 80 °C until fully dissolved. After adding 3 mmol of sodium ferrocyanide decahydrate and dissolving it, it is denoted as Solution A;

[0055] S2. Add 3 mmol of manganese sulfate tetrahydrate into 100 ml of distilled water, stir and dissolve at room temperature, and denote it as Solution B;

[0056] S3. Add the obtained Solution B into Solution A at an addition rate of 10 ml / min through a peristaltic pump, heat and stir in an oil bath at 80 °C for 6 h, turn off the heating and stirring, and let it stand for aging for 6 h to obtain Solution C;

[0057] S4. Filter Solution C to obtain a precipitate (the pore size of the filter paper used for filtration is 30 - 50 μm). Freeze the obtained precipitate in a refrigerator at -20 °C for 2 h. Transfer the frozen precipitate to a freeze dryer, evacuate the cold trap, and dry it by gradually heating from -50 °C to 50 °C. The heating rate of the cold trap of the freeze dryer is 10 °C / h to obtain a Prussian blue cathode material.

[0058] Figure 3 It is the thermogravimetric graph of the Prussian blue cathode material prepared in Example 3. It can be seen from the graph that the dark blue curve is the water removal effect of freeze drying, and the light blue is the water removal effect of ordinary vacuum drying. Thus, it can be seen that the water content of the freeze-dried sample is only 8%, while the water content of ordinary vacuum drying is 14%. Therefore, the water content of the Prussian blue cathode material prepared in the present invention is relatively low, and the content of crystal water and lattice water in the Prussian blue material is effectively reduced by this preparation method.

[0059] Example 4

[0060] S1. Sequentially add 3 mmol of ascorbic acid, 6 mmol of sodium citrate monohydrate, and 6 mmol of sodium chloride into 100 mL of distilled water, heat and stir in an oil bath at 80 °C until fully dissolved. After adding 3 mmol of sodium ferrocyanide decahydrate and dissolving it, it is denoted as Solution A;

[0061] S2. Add 3 mmol of manganese sulfate tetrahydrate into 100 ml of distilled water, stir and dissolve at room temperature, and denote it as Solution B;

[0062] S3. Add the obtained solution B to solution A through a peristaltic pump at an addition rate of 10 ml / min, heat and stir the reaction in an oil bath at 80 °C for 6 h, turn off the heating and stirring, and let it stand for aging for 6 h to obtain solution C;

[0063] S4. Filter solution C to obtain a precipitate (the pore size of the filter paper used for filtration is 30 - 50 μm), freeze the obtained precipitate in a refrigerator at -20 °C for 2 h, transfer the frozen precipitate to a cold trap of a freeze dryer, evacuate it, and dry it by gradually heating from -50 °C to 50 °C. The heating rate of the cold trap of the freeze dryer is 10 °C / h to obtain a Prussian blue cathode material.

[0064] Figure 5 It is the long-cycle performance graph of the sodium-ion battery layered material prepared in Example 4. It can still maintain a capacity retention rate of 80% after cycling 650 times at a rate of 2C, showing excellent long-cycle performance.

[0065] Comparative example

[0066] In order to explore the influence of different drying processes on the water content, morphology and performance of the Prussian blue cathode material, the following experiments were carried out. The preparation process was similar to that of Example 1, except that: the drying process in S4 was different.

[0067] Group A: The precipitate was dried in a forced-air oven at 100 °C for 12 h under air environmental conditions.

[0068] Group B: The precipitate was evacuated in the cold trap of a freeze dryer and dried by gradually heating from -50 °C to 50 °C. The heating rate of the cold trap of the freeze dryer was 10 °C / h.

[0069] Group C: The precipitate was frozen in a refrigerator at -20 °C for 2 h, and the frozen precipitate was transferred to the cold trap of a freeze dryer, evacuated, and dried at -50 °C for 1 h.

[0070] Group D: The precipitate was dried at 100 °C for 12 h under vacuum conditions.

[0071] Test the water content and electrochemical performance of the Prussian blue cathode materials prepared in the above groups, and the results are shown in the following table.

[0072] Group Water content (%) Specific capacity at 0.2 C rate (mAh / g) Capacity retention rate after 200 cycles at 2 C rate (%) Group A 14 110 70％ Group B 8 120 85％ Group C 10 120 80％ Group D 12 110 72％

[0073] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments or perform equivalent replacements on some of the technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the scope of protection of the claims of the present invention.

Claims

1. A preparation method of a sodium-ion battery cathode Prussian blue material, characterized in that, Carry out in the following step sequence in turn: S1. Add ascorbic acid, sodium citrate monohydrate and sodium chloride into the solvent in turn. The molar ratio of ascorbic acid, sodium citrate monohydrate, sodium chloride and sodium ferrocyanide decahydrate is 1:1:2:

2. Heat and stir in an oil bath at 80 °C until it is completely dissolved. After adding sodium ferrocyanide decahydrate and dissolving it, it is recorded as solution A; S2. Add manganese salt or iron salt into distilled water and stir to dissolve at room temperature, which is recorded as solution B; S3. Add the obtained solution B into solution A through a peristaltic pump at a rate of 10 mL / min, heat and stir in an oil bath at 80 °C for 6 h, turn off the heating and stirring, and let it stand for aging for 6 h to obtain solution C; S4. Filter the solution C to obtain a precipitate. Freeze the obtained precipitate in a refrigerator at -20 °C for 2 h. Transfer the frozen precipitate to the cold trap of a freeze dryer, evacuate it, and dry it by gradually heating from -50 °C to 50 °C. The evacuation drying time in the cold trap of the freeze dryer is 1 h, and the heating rate of the cold trap of the freeze dryer is 10 °C / h to obtain the Prussian blue cathode material.

2. The preparation method of a sodium ion battery cathode Prussian blue material according to claim 1, characterized in that, In step S1, the stirring rate is 600 rpm.

3. The preparation method of a sodium ion battery cathode Prussian blue material according to claim 1, characterized in that, In step S1, the solvent is water or a water-ethanol equal-volume mixed solution.

4. The preparation method of a sodium-ion battery cathode Prussian blue material according to claim 1, characterized in that, In step S1, the manganese salt is manganese chloride or manganese sulfate, and the iron salt is ferrous chloride or ferrous sulfate.

5. The preparation method of a sodium-ion battery cathode Prussian blue material according to claim 1, characterized in that, In step S2, the molar amount of the manganese salt or iron salt is 1.5 times the molar amount of sodium ferrocyanide.

6. The preparation method of a sodium ion battery cathode Prussian blue material according to claim 1, characterized in that, In step S4, medium-speed filter paper with a pore size of 30 - 50 µm is used for suction filtration.

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