Preparation of prussian blue positive electrode material and preparation method of solid-state sodium ion battery

Abstract

This invention relates to the field of solid-state sodium-ion battery technology, and in particular to the preparation of a Prussian blue cathode material and its application in solid-state sodium-ion batteries. First, chelating agent A and chelating agent B are dissolved in beakers A and B, respectively, each containing 50 mL of deionized water. Then, ferrous sulfite heptahydrate (FeSO4·7H2O) and sodium ferrocyanide (Na4Fe(CN)6·10H2O) are weighed and added to beakers A and B, dissolved, and stirred until homogeneous, yielding mixed solutions A and B. Solution A is slowly added dropwise to solution B, stirred, and centrifuged. The mixture is then washed multiple times with deionized water and ethanol to obtain the Prussian blue cathode material. The chelating group of the chelating agent is (CN). ‑ with Fe 2+ The presence of a competitive relationship between SSC and Fe slows down the nucleation and precipitation process, thus increasing the crystallinity of Prussian blue; 2+ The binding energy is weaker than that of Na2EDTA, CMC, and sodium phytate. The addition of chelating agent B effectively alleviates the SSC-assisted synthesis of Prussian blue [Fe(CN)6]. 4‑ The problem of vacancies; the high crystallinity of Prussian blue has structural defects and low water content, resulting in good cycle performance and stability of the battery.

Description

Technical Field

[0001] This invention relates to the field of solid-state sodium-ion battery technology, and in particular to the preparation of a Prussian blue cathode material and its application in solid-state sodium-ion batteries. Background Technology

[0002] Sodium is considered an alternative to lithium-ion batteries, especially in the energy storage market, due to its low cost and abundant reserves. Prussian blue is one of the mainstream cathode materials for sodium batteries. Traditional co-precipitation methods for preparing Prussian blue offer advantages such as non-toxicity, low cost, ease of operation, and high scalability. However, the rapid precipitation process results in a large number of vacancies and water of crystallization in the product. Water molecules occupy the active sites of sodium ions in the Prussian blue framework, leading to a decrease in specific capacity and, to some extent, reducing the sodium ion insertion and extraction capabilities. Furthermore, defects caused by vacancies disrupt the structure of Prussian blue, easily leading to structural collapse during repeated charge-discharge cycles, reducing battery cycle stability, and prematurely reaching the end of battery life. Therefore, it is necessary to slow down the co-precipitation rate and improve the quality of the Prussian blue.

[0003] However, traditional single chelating agents, such as those synthesized using sodium citrate, contain large amounts of Fe(CN)6. 4- Vacancies, while the product synthesized with Na2EDTA chelating agent contains a large amount of Fe. 3+ Vacancy. Therefore, there is an urgent need for a method to reduce Prussian blue vacancies and synthesize Prussian blue materials with high crystallinity. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for preparing a highly crystalline Prussian blue cathode material by using a chelating agent in combination to reduce Prussian blue vacancies and its application in a solid-state sodium-ion battery.

[0005] The technical solution adopted by this invention to solve its technical problem is: a method for preparing Prussian blue cathode material, comprising the following steps:

[0006] Step 1: Dissolve chelating agent A and chelating agent B in beakers A and B, respectively, containing 50 mL of deionized water;

[0007] Step 2: Weigh out ferrous sulfite heptahydrate (FeSO4·7H2O) and sodium ferrocyanide (Na4Fe(CN)6·10H2O) respectively, add them to beakers A and B to dissolve, stir well, and obtain mixed solutions A and B;

[0008] Step 3: Protect Fe from nitrogen gas in solutions A and B obtained in step 2. 2+ It is not oxidized;

[0009] Step 4: Slowly add solution A obtained in step 2 to solution B obtained in step 2, stir at 800 r / min for 6-8 h, let stand, centrifuge, take the precipitate and dry to obtain solid powder;

[0010] Step 5: Wash the solid powder obtained in Step 4 multiple times with deionized water and ethanol, and dry it under vacuum at 80°C to obtain powdered Prussian blue cathode material for later use.

[0011] Furthermore, chelating agents A, B, FeSO4·7H2O, and Na4Fe(CN)6·10H2O are all of analytical grade.

[0012] Furthermore, chelating agent B is one or more combinations of sodium phytate, disodium ethylenediaminetetraacetate (Na2EDTA), or sodium carboxymethyl cellulose (CMC).

[0013] Furthermore, chelating agent A is sodium citrate (SSC), with an addition amount of 1.40g of SSC in chelating agent A, and 0-5.01g of sodium phytate, 0-1.83g of Na2EDTA, and 0-1.31g of CMC in chelating agent B.

[0014] Furthermore, the molar ratio of chelating agent A to chelating agent B is 1:1.

[0015] Furthermore, solutions A and B were mixed under a nitrogen gas flow.

[0016] Furthermore, in step 5, the solid powder obtained in step 4 is washed with deionized water and ethanol more than 6 times.

[0017] A method for preparing a solid-state sodium-ion battery, using the aforementioned Prussian blue cathode material, includes the following steps:

[0018] Sa. Preparation of positive electrode sheet

[0019] Prussian blue cathode slurry is coated onto carbon-coated aluminum foil, vacuum dried, and then punched to form a cathode sheet.

[0020] Sb. Assemble the battery

[0021] The solid sodium-ion battery is assembled according to the following assembly sequence: positive electrode shell, positive electrode plate, solid electrolyte, separator, solid electrolyte, negative electrode plate, gasket, and negative electrode shell. After assembly, the battery is left to stand at room temperature for 2 hours. The battery is then polymerized in a vacuum oven at 70-80°C for 5-7 hours. The solid electrolyte is transformed into a gel electrolyte. After cooling, a solid sodium-ion battery with Prussian blue as the positive electrode is obtained.

[0022] Furthermore, the positive electrode sheet is composed of Prussian blue, conductive agent Super-P, VGCF, and binder PVDF, with a mass ratio of 8:0.5:0.5:1.

[0023] Furthermore, the solid electrolyte is a mixture of CMOF (D-UiO-66-NH2), TEGDMA, AIBN, MMA, and sodium ion liquid electrolyte.

[0024] The beneficial effects of the present invention are as follows: (1) The present invention provides a highly crystalline Prussian blue cathode material, wherein the chelating group of the chelating agent is (CN). - with Fe 2+ The presence of a competitive relationship slows down the nucleation and precipitation process, thus increasing the crystallinity of Prussian blue.

[0025] (2) SSC and Fe 2+ The binding energy is weaker than that of Na2EDTA, CMC, and sodium phytate. The addition of chelating agent B in this invention can effectively alleviate the SSC-assisted synthesis of Prussian blue [Fe(CN)6]. 4- The issue of empty spaces;

[0026] (3) Prussian blue with high crystallinity has fewer structural defects and less water content, making it suitable for use as the positive electrode in solid sodium-ion batteries, resulting in batteries with good cycle performance and stability. Detailed Implementation

[0027] The basic structure of the invention is illustrated only by way of illustration, and therefore only the components relevant to the invention are shown.

[0028] Example 1: Preparation of Prussian Blue using Sodium Phytate with Chelating Agent B and Preparation of Solid-State Batteries

[0029] First, dissolve 1.40g SSC and 5.01g sodium phytate in beakers A and B, each containing 50mL of deionized water. Then, weigh out 0.84g FeSO4•7H2O and 0.98g Na4Fe(CN)6•10H2O, respectively, and add them to beakers A and B to dissolve. Stir until homogeneous to form mixed solutions A and B. Protect Fe from nitrogen in solutions A and B. 2+ It is not oxidized. Solution A is slowly added dropwise to solution B, stirred at 800 r / min for 6.5 h, allowed to stand, centrifuged, and the precipitate is dried to obtain a solid powder. The solid powder is washed several times with deionized water and ethanol, and then dried under vacuum at 80°C to obtain powdered Prussian blue cathode material for later use.

[0030] Preparation of Battery 1:

[0031] The positive electrode sheet was prepared according to Example 1, with a mass ratio of Prussian blue, conductive agent Super-P, VGCF, and binder PVDF of 8:0.5:0.5:1.

[0032] A solid electrolyte was prepared by uniformly mixing CMOF (D-UiO-66-NH2), TEGDMA, AIBN, MMA, and sodium ion liquid electrolyte.

[0033] The solid sodium-ion battery was assembled according to the following assembly sequence: positive electrode shell, positive electrode sheet, solid electrolyte, separator, solid electrolyte, negative electrode sheet, gasket, and negative electrode shell. After assembly, the battery was left to stand at room temperature for 2 hours. The battery was then polymerized in a vacuum oven at 70-80°C for 5-7 hours. The solid electrolyte was converted into a gel electrolyte. After cooling, the solid sodium-ion battery with Prussian blue as the positive electrode as described in Example 1 was obtained.

[0034] Example 2: Preparation of Prussian Blue using disodium ethylenediaminetetraacetate as chelating agent B and the fabrication of solid-state batteries

[0035] First, dissolve 1.40g SSC and 1.83g Na2EDTA in beakers A and B, each containing 50mL of deionized water. Then, weigh out 0.84g FeSO4•7H2O and 0.98g Na4Fe(CN)6•10H2O, respectively, and add them to beakers A and B to dissolve. Stir until homogeneous to form mixed solutions A and B. Protect Fe from nitrogen in solutions A and B separately. 2+ It is not oxidized. Solution A is slowly added dropwise to solution B, stirred at 800 r / min for 6.5 h, allowed to stand, centrifuged, and the precipitate is dried to obtain a solid powder. The solid powder is washed several times with deionized water and ethanol, and then dried under vacuum at 80°C to obtain powdered Prussian blue cathode material for later use.

[0036] Preparation of Battery 2:

[0037] The positive electrode sheet was prepared according to Example 2, with a mass ratio of Prussian blue, conductive agent Super-P, VGCF, and binder PVDF of 8:0.5:0.5:1.

[0038] A solid electrolyte was prepared by uniformly mixing CMOF (D-UiO-66-NH2), TEGDMA, AIBN, MMA, and sodium ion liquid electrolyte.

[0039] The solid sodium-ion battery was assembled according to the following assembly sequence: positive electrode shell, positive electrode sheet, solid electrolyte, separator, solid electrolyte, negative electrode sheet, gasket, and negative electrode shell. After assembly, the battery was left to stand at room temperature for 2 hours. The battery was then polymerized in a vacuum oven at 70-80°C for 5-7 hours. The solid electrolyte was converted into a gel electrolyte. After cooling, the solid sodium-ion battery with Prussian blue as the positive electrode as described in Example 2 was obtained.

[0040] Example 3: Preparation of Prussian Blue using Sodium Carboxymethyl Cellulose as Chelating Agent B and Preparation of Solid-State Batteries

[0041] First, dissolve 1.40g SSC and 1.31g CMC in beakers A and B, each containing 50mL of deionized water. Then, weigh out 0.84g FeSO4•7H2O and 0.98g Na4Fe(CN)6•10H2O, respectively, and add them to beakers A and B to dissolve. Stir until homogeneous to form mixed solutions A and B. Protect Fe from nitrogen in solutions A and B separately. 2+ It is not oxidized. Solution A is slowly added dropwise to solution B, stirred at 800 r / min for 6.5 h, allowed to stand, centrifuged, and the precipitate is dried to obtain a solid powder. The solid powder is washed several times with deionized water and ethanol, and then dried under vacuum at 80°C to obtain powdered Prussian blue cathode material for later use.

[0042] Preparation of Battery 3:

[0043] The positive electrode sheet was prepared according to Example 3, with a mass ratio of Prussian blue, conductive agent Super-P, VGCF, and binder PVDF of 8:0.5:0.5:1.

[0044] A solid electrolyte was prepared by uniformly mixing CMOF (D-UiO-66-NH2), TEGDMA, AIBN, MMA, and sodium ion liquid electrolyte.

[0045] The solid sodium-ion battery was assembled according to the following assembly sequence: positive electrode shell, positive electrode sheet, solid electrolyte, separator, solid electrolyte, negative electrode sheet, gasket, and negative electrode shell. After assembly, the battery was left to stand at room temperature for 2 hours. The battery was then polymerized in a vacuum oven at 70-80°C for 5-7 hours. The solid electrolyte was converted into a gel electrolyte. After cooling, the solid sodium-ion battery with Prussian blue as the positive electrode as described in Example 3 was obtained.

[0046] Comparative Example 1: Preparation of Prussian blue using sodium citrate instead of chelating agent B

[0047] The preparation method of Comparative Example 1 is as follows: First, dissolve two portions of 1.40g SSC in beakers A and B, each containing 50mL of deionized water. Then, weigh out 0.84g FeSO4•7H2O and 0.98g Na4Fe(CN)6•10H2O, respectively, and add them to beakers A and B to dissolve. Stir until homogeneous to form mixed solutions A and B. Protect Fe from nitrogen in solutions A and B respectively. 2+ It is not oxidized. Solution A is slowly added dropwise to solution B, stirred at 800 rpm for 6.5 h, and centrifuged. It is washed several times with deionized water and ethanol, and dried under vacuum at 80°C for later use. Finally, the positive electrode is prepared and the battery is assembled. After standing, the battery is polymerized at 70-80°C and cooled to obtain a solid sodium-ion battery with Prussian blue as the positive electrode.

[0048] Preparation of the battery in Comparative Example 1:

[0049] A positive electrode sheet was prepared according to the mass ratio of Prussian blue, conductive agent Super-P, VGCF, and binder PVDF in Comparative Example 1 of 8:0.5:0.5:1.

[0050] A solid electrolyte was prepared by uniformly mixing CMOF (D-UiO-66-NH2), TEGDMA, AIBN, MMA, and sodium ion liquid electrolyte.

[0051] The solid sodium-ion battery was assembled according to the following assembly sequence: positive electrode shell, positive electrode sheet, solid electrolyte, separator, solid electrolyte, negative electrode sheet, gasket, and negative electrode shell. After assembly, the battery was left to stand at room temperature for 2 hours. The battery was then polymerized in a vacuum oven at 70-80°C for 5-7 hours. The solid electrolyte was converted into a gel electrolyte. After cooling, a solid sodium-ion battery with Prussian blue as the positive electrode was obtained (Comparative Example 1).

[0052] Performance testing comparison between the examples and comparative examples:

[0053] As shown in Table 1, the Prussian blue material prepared by this invention has fewer vacancies and higher crystallinity than Comparative Example 1 (single chelating agent). Theoretically, the presence of crystal vacancies and water molecules would kinetically hinder the formation of Na+. + The rapid migration of the molecules induces lattice distortion, resulting in poor rate performance and decreased cycle stability of the sodium-ion battery. Therefore, charge-discharge tests were conducted on the solid-state sodium-ion batteries of Examples 1-3 and Comparative Example 1 (voltage range 2-4V, 1C corresponds to 130mA / g).

[0054] The decay rate of the 1C cycle after 1000 cycles of this invention is significantly reduced compared to the comparative example, and the initial discharge specific capacity remains at 116-125 mAh / g, with a capacity retention rate of 82.72%-85.13%. This demonstrates that the Prussian blue material prepared by this invention has fewer lattice defects, and the solid-state battery prepared using it as the positive electrode exhibits good cycle performance and stability.

[0055] Table 1: Results of the Comparative Experiment

[0056]

[0057] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for preparing a Prussian blue cathode material, characterized in that: Includes the following steps: Step 1: Dissolve chelating agent A and chelating agent B in beakers A and B, respectively, containing 50 mL of deionized water; chelating agent A is sodium citrate (SSC), and chelating agent B is one or more combinations of sodium phytate, disodium ethylenediaminetetraacetate (Na2EDTA), or sodium carboxymethyl cellulose (CMC). Step 2: Weigh out ferrous sulfite heptahydrate FeSO4·7H2O and sodium ferrocyanide Na4Fe(CN)6·10H2O respectively, add them to beakers A and B to dissolve, stir evenly, and obtain mixed solutions A and B; Step 3: Protect Fe from nitrogen gas in solutions A and B obtained in step 2. 2+ It is not oxidized; Step 4: Slowly add solution A obtained in step 2 to solution B obtained in step 2, stir at 800 r / min for 6-8 h, let stand, centrifuge, take the precipitate and dry to obtain solid powder; Step 5: Wash the solid powder obtained in Step 4 multiple times with deionized water and ethanol, and dry it under vacuum at 80°C to obtain powdered Prussian blue cathode material for later use.

2. The method for preparing a Prussian blue cathode material according to claim 1, characterized in that: The chelating agents A, B, FeSO4·7H2O, and Na4Fe(CN)6·10H2O are all of analytical grade.

3. The method for preparing a Prussian blue cathode material according to claim 1, characterized in that: The amount of SSC added in chelating agent A is 1.40g, and the amount of sodium phytate added in chelating agent B is 0-5.01g, the amount of Na2EDTA added is 0-1.83g, and the amount of CMC added is 0-1.31g; the molar ratio of chelating agent A to chelating agent B is 1:

1.

4. The method for preparing a Prussian blue cathode material according to claim 1, characterized in that: In step 5, the solid powder obtained in step 4 is washed with deionized water and ethanol more than 6 times.

5. A method for preparing a solid-state sodium-ion battery, using Prussian blue cathode material prepared by the method described in claim 1, characterized in that: Includes the following steps: Sa. Preparation of positive electrode sheet The Prussian blue cathode slurry prepared from the Prussian blue cathode material is coated onto carbon-coated aluminum foil, vacuum dried, and then punched to form a cathode sheet. Sb. Assemble the battery The solid sodium-ion battery is assembled according to the following assembly sequence: positive electrode shell, positive electrode sheet, solid electrolyte, separator, solid electrolyte, negative electrode sheet, gasket, and negative electrode shell. After assembly, the battery is left to stand at room temperature for 2 hours. The battery is then polymerized at 70-80°C in a vacuum oven for 5-7 hours. The solid electrolyte is transformed into a gel electrolyte. After cooling, a solid sodium-ion battery with Prussian blue as the positive electrode is obtained.

6. The method for preparing a solid-state sodium-ion battery according to claim 5, characterized in that: The Prussian blue cathode slurry is composed of Prussian blue, conductive agent Super-P, VGCF, and binder PVDF, with a mass ratio of 8:0.5:0.5:

1.

7. The method for preparing a solid-state sodium-ion battery according to claim 5, characterized in that: The solid electrolyte is a mixture of CMOF, TEGDMA, AIBN, MMA, and sodium ion liquid electrolyte; the CMOF is D-UiO-66-NH2.

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