Base Prussian blue positive electrode and preparation method and application thereof

Abstract

The invention relates to the technical field of sodium ion batteries, in particular to a base Prussian blue positive electrode and a preparation method and application thereof. The crystal structure of the base Prussian blue positive electrode is a monoclinic phase; the chemical formula is NarMxMn [Fe (CN) 6] m.nH2O, r is 1-2, M is an alkali metal ion, x is 0.1-0.5, m is 0.5-1, and n is 1-3. According to the base Prussian blue positive electrode provided by the invention, a firm crystal framework is formed by introducing alkali metal ions such as potassium, rubidium and cesium and controlling the crystal structure to be a monoclinic phase, so that the initial capacity and the electrochemical stability of a sodium ion battery are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and particularly relates to a base prussian blue cathode and its preparation method and application. Background Art

[0002] Lithium ion batteries have always dominated the field of rechargeable batteries, but their application scope is shrinking due to scarce resources and high costs. As a promising next-generation rechargeable battery, sodium ion batteries have attracted increasing attention due to their abundant resource distribution and cost advantages.

[0003] The performance of sodium ion batteries depends to a large extent on the cathode materials used. Currently used cathode materials include transition metal oxides, polyanion compounds, and prussian blue compounds (or called prussian blue cathodes). In particular, prussian blue cathodes have become a new research and development hotspot due to their low price, simple production process, and excellent electrochemical performance. The general formula of prussian blue cathodes is A 2-x M[M’(CN)6] 1-y □ y ·nH2O, where A represents the alkali metal site, M and M’ represent the transition metal sites, corresponding to [M’(CN)6] 4- vacancies, □ represents vacancies, and H2O represents crystal water.

[0004] However, there are still deficiencies in the current prussian blue cathodes as cathode materials for sodium ion batteries. On the one hand, although prussian blue cathodes are known for their higher theoretical capacity than polyanion compound materials, with the development of sodium ion batteries towards high capacity, higher requirements are also put forward for the initial capacity of their cathode materials. On the other hand, a strong crystal framework is crucial for enhancing ionic conductivity and cycle stability. Existing prussian blue cathodes usually present a cubic stacked morphology and too small particle size, resulting in an unstable crystal framework, which is prone to degradation during cycling, leading to structural collapse and thus causing instability of electrochemical performance. In addition, it is difficult for the cathode materials of sodium ion batteries to simultaneously achieve high initial capacity and high cycle stability, affecting the application prospects of prussian blue cathodes as cathode materials for sodium ion batteries. Summary of the Invention

[0005] Aiming at the technical problems that the existing prussian blue cathodes as cathode materials for sodium ion batteries have low initial capacity or / and poor electrochemical performance stability, the present invention provides a base prussian blue cathode and its preparation method and application, and improves its electrochemical performance by introducing alkali metal ions such as potassium, rubidium, and cesium and controlling the crystal structure.

[0006] In the first aspect, the present invention provides a base prussian blue cathode, and the crystal structure of the base prussian blue cathode is monoclinic; the chemical formula is Nar M x Mn[Fe(CN)6] m ·nH2O, r is 1-2, M is an alkali metal ion, x is 0.1-0.5, m is 0.5-1, and n is 1-3.

[0007] Further, r is 1.66-1.76, M is rubidium ion, cesium ion or potassium ion, x is 0.14-0.25, m is 0.88-0.95, and n is 1.43-1.66.

[0008] In a second aspect, the present invention provides a method for preparing a basic Prussian blue positive electrode, comprising adding sodium ferrocyanide, sodium chloride and an alkali metal salt into water, adding trisodium citrate and a surfactant after sufficient mixing, and stirring evenly to obtain a solution A; adding a manganese sulfate solution dropwise into the solution A under continuous stirring, and continuing to stir to obtain a mixed solution with uniformly dispersed particles; heating the mixed solution at 120° C. for 4 hours for hydrothermal treatment, washing, and centrifugally collecting the precipitate and drying to obtain the basic Prussian blue positive electrode.

[0009] Furthermore, the alkali metal salt is rubidium chloride, cesium chloride or potassium chloride.

[0010] Furthermore, the molar ratio of sodium ferrocyanide, sodium chloride and alkali metal salt in the aqueous solution is 4.9: 0.0958-0.0987: 0.0013-0.0042.

[0011] Furthermore, the surfactant is polyvinyl pyrrolidone, sodium dodecyl sulfonate or sodium dodecylbenzene sulfonate.

[0012] Furthermore, drying is performed at 80° C. for 24 h under vacuum conditions.

[0013] In a third aspect, the present invention provides an application of an alkaline Prussian blue positive electrode in the preparation of a positive electrode material for a sodium ion battery.

[0014] The beneficial effects of the present invention are: The present invention provides a basic Prussian blue positive electrode, which introduces alkali metal ions such as potassium (K), rubidium (Rb) and cesium (Cs) into Na r In the Mn[Fe(CN)6] structure, the structural stability is enhanced by forming a monoclinic phase with a large crystal scale and a strong crystal framework. This structure can withstand the mechanical stress during battery operation and extend the service life of the sodium ion battery. Compared with the Prussian blue cathode without the introduction of alkali metal ions and the cubic phase of the basic Prussian blue cathode, the monoclinic phase of the basic Prussian blue cathode has achieved both high initial capacity and strong electrochemical stability, and can still maintain excellent capacitance stability in 500 repeated charge and discharge cycles. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0016] Figure 1 These are the XRD analysis images of Examples 2-3 and Comparative Examples 2-5; (a) is the XRD analysis image of PW-MC and PW-C, (b) is the XRD analysis image of PW-Rb-MC and PW-Rb-C, and (c) is the XRD analysis image of PW-Cs-MC and PW-Cs-C.

[0017] Figure 2 are SEM analysis images of PW-C and PW-MC; (a) is the SEM analysis image of PW-C, and (b) is the SEM analysis image of PW-MC.

[0018] Figure 3 are SEM analysis images of PW-Rb-C and PW-Rb-MC; (a) is the SEM analysis image of PW-Rb-C, and (b) is the SEM analysis image of PW-Rb-MC.

[0019] Figure 4 are SEM analysis images of PW-Cs-C and PW-Cs-MC; (a) is the SEM analysis image of PW-Cs-C, and (b) is the SEM analysis image of PW-Cs-MC.

[0020] Figure 5 These are TGA analysis images of Examples 2-3 and Comparative Examples 2-5; (a) is the TGA analysis image of PW-MC and PW-C, (b) is the TGA analysis image of PW-Rb-MC and PW-Rb-C, and (c) is the TGA analysis image of PW-Cs-MC and PW-Cs-C.

[0021] Figure 6 The figures are the test results of 500 charge-discharge cycles of Examples 2-3 and Comparative Examples 2-5; (a) is the test result of 500 charge-discharge cycles of PW-MC and PW-C, (b) is the test result of 500 charge-discharge cycles of PW-Rb-MC and PW-Rb-C, and (c) is the test result of 500 charge-discharge cycles of PW-Cs-MC and PW-Cs-C. DETAILED DESCRIPTION

[0022] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0023] Example 1 A method for preparing a basic Prussian blue positive electrode comprises the following steps: (1) Dissolve 4.9 M sodium ferrocyanide (Na4[Fe(CN)6]) in water, add 0.0958 M NaCl and 0.0042 M KCl, add 50 mL of water and mix thoroughly. After ensuring that the solute is completely dissolved, add 0.9 M trisodium citrate and 0.36 g polyvinyl pyrrolidone and stir thoroughly to obtain solution A. (2) Add 9.9 M manganese sulfate (MnSO4) to 16 mL of water and stir evenly to obtain a manganese sulfate solution; (3) While continuously stirring, add the manganese sulfate solution dropwise into solution A. After the addition is complete, continue stirring to ensure that the formed particles are evenly dispersed in the solution to obtain a mixed solution; (4) heating the mixed solution at 120°C for 4 h for hydrothermal treatment; (5) The mixed solution after the hydrothermal treatment is washed with deionized water for multiple times to remove any unreacted ions or impurities, and then the precipitate is collected by centrifugation and dried in a vacuum oven at 80 °C for 24 h to remove any residual moisture to obtain a potassium-based Prussian blue positive electrode.

[0024] Example 2 A method for preparing a basic Prussian blue positive electrode comprises the following steps: (1) Dissolve 4.9 M sodium ferrocyanide in water, add 0.0987 M NaCl and 0.0013 M RbCl, add 50 mL of water and mix thoroughly. After ensuring that the solute is completely dissolved, add 0.9 M trisodium citrate and 0.36 g polyvinyl pyrrolidone and stir thoroughly to obtain solution A. (2) Add 9.9 M manganese sulfate into 16 mL of water and stir evenly to obtain a manganese sulfate solution; (3) While continuously stirring, add the manganese sulfate solution dropwise into solution A. After the addition is complete, continue stirring to ensure that the formed particles are evenly dispersed in the solution to obtain a mixed solution; (4) heating the mixed solution at 120°C for 4 h for hydrothermal treatment; (5) The mixed solution after hydrothermal treatment was washed with deionized water for multiple times to remove any unreacted ions or impurities, and then the precipitate was collected by centrifugation and dried in a vacuum oven at 80 °C for 24 h to remove any residual moisture to obtain a rubidium-based Prussian blue cathode, denoted as PW-Rb-MC.

[0025] Example 3 A method for preparing a basic Prussian blue positive electrode comprises the following steps: (1) Dissolve 4.9 M sodium ferrocyanide in water, add 0.0984 M NaCl and 0.0016 M CsCl, add 50 mL of water and mix thoroughly. After ensuring that the solute is completely dissolved, add 0.9 M trisodium citrate and 0.36 g polyvinyl pyrrolidone and stir thoroughly to obtain solution A. (2) Add 9.9 M manganese sulfate into 16 mL of water and stir evenly to obtain a manganese sulfate solution; (3) While continuously stirring, add the manganese sulfate solution dropwise into solution A. After the addition is complete, continue stirring to ensure that the formed particles are evenly dispersed in the solution to obtain a mixed solution; (4) heating the mixed solution at 120°C for 4 h for hydrothermal treatment; (5) The mixed solution after hydrothermal treatment was washed with deionized water for multiple times to remove any unreacted ions or impurities, and then the precipitate was collected by centrifugation and dried in a vacuum oven at 80 °C for 24 h to remove any residual moisture to obtain a cesium-based Prussian blue cathode, denoted as PW-Cs-MC.

[0026] Comparative Example 1 A method for preparing a basic Prussian blue positive electrode comprises the following steps: (1)-(3) are the same as (1)-(3) of Example 1; (4) Aging the mixed solution at a temperature of ≤25°C for 24 hours; (5) The aged mixed solution is washed with deionized water for multiple times to remove any unreacted ions or impurities, and then the precipitate is collected by centrifugation and dried in a vacuum oven at 80 °C for 24 h to remove any residual moisture to obtain a potassium-based Prussian blue positive electrode.

[0027] Comparative Example 2 A method for preparing a basic Prussian blue positive electrode comprises the following steps: (1)-(3) are the same as (1)-(3) of Example 2; (4) Aging the mixed solution at a temperature of ≤25°C for 24 hours; (5) The aged mixed solution was washed with deionized water several times to remove any unreacted ions or impurities, and then the precipitate was collected by centrifugation and dried in a vacuum oven at 80 °C for 24 h to remove any residual moisture to obtain a rubidium-based Prussian blue cathode, denoted as PW-Rb-C.

[0028] Comparative Example 3 A method for preparing a basic Prussian blue positive electrode comprises the following steps: (1)-(3) are the same as (1)-(3) of Example 3; (4) Aging the mixed solution at a temperature of ≤25°C for 24 hours; (5) The aged mixed solution was washed with deionized water several times to remove any unreacted ions or impurities, and then the precipitate was collected by centrifugation and dried in a vacuum oven at 80 °C for 24 h to remove any residual moisture to obtain a cesium-based Prussian blue cathode, denoted as PW-Cs-C.

[0029] Comparative Example 4 A method for preparing a Prussian blue positive electrode comprises the following steps: (1) Dissolve 4.9 M sodium ferrocyanide in water, add 0.0992 M NaCl, and then add 50 mL of water and mix thoroughly. After ensuring that the solute is completely dissolved, add 0.9 M trisodium citrate and 0.36 g polyvinyl pyrrolidone and stir thoroughly to obtain solution A. (2) Add 9.9 M manganese sulfate into 16 mL of water and stir evenly to obtain a manganese sulfate solution; (3) While continuously stirring, add the manganese sulfate solution dropwise into solution A. After the addition is complete, continue stirring to ensure that the formed particles are evenly dispersed in the solution to obtain a mixed solution; (4) heating the mixed solution at 120°C for 4 hours for hydrothermal treatment; (5) The mixed solution after hydrothermal treatment was washed with deionized water several times to remove any unreacted ions or impurities, and then the precipitate was collected by centrifugation and dried in a vacuum oven at 80 °C for 24 h to remove any residual moisture to obtain a Prussian blue cathode, denoted as PW-MC.

[0030] Comparative Example 5 A method for preparing a Prussian blue positive electrode comprises the following steps: (1) Dissolve 4.9 M sodium ferrocyanide in water, add 0.0992 M NaCl, and then add 50 mL of water and mix thoroughly. After ensuring that the solute is completely dissolved, add 0.9 M trisodium citrate and 0.36 g polyvinyl pyrrolidone and stir thoroughly to obtain solution A. (2) Add 9.9 M manganese sulfate into 16 mL of water and stir evenly to obtain a manganese sulfate solution; (3) While continuously stirring, add the manganese sulfate solution dropwise into solution A. After the addition is complete, continue stirring to ensure that the formed particles are evenly dispersed in the solution to obtain a mixed solution; (4) Aging the mixed solution at a temperature of ≤25°C for 24 hours; (5) The aged mixed solution was washed with deionized water several times to remove any unreacted ions or impurities, and then the precipitate was collected by centrifugation and dried in a vacuum oven at 80 °C for 24 h to remove any residual moisture to obtain a Prussian blue positive electrode, denoted as PW-C.

[0031] Experimental Example 1 The obtained PW-Rb-MC, PW-Rb-C, PW-Cs-MC, PW-Cs-C, PW-MC and PW-C were sampled for IPC analysis, and their respective chemical formulas were obtained according to the chemical compositions obtained by the detection as shown in Table 1.

[0032] Table 1 Chemical formula of Examples 2-3 and Comparative Examples 2-5

[0033] Experimental Example 2 The obtained PW-Rb-MC, PW-Rb-C, PW-Cs-MC, PW-Cs-C, PW-MC and PW-C were subjected to XRD analysis. The results are as follows Figure 1 As shown. In Figure (a), a single peak was detected for PW-C between 20° and 30°, and a double peak was detected for PW-MC. Similarly, in Figures (b) and (c), a single peak was detected for PW-Rb-C and PW-Cs-C, and a double peak was detected for PW-Rb-MC and PW-Cs-MC between 20° and 30°, indicating that after the hydrothermal reaction, the Prussian blue cathode crystal changed from a cubic phase to a monoclinic phase. When large-sized alkali metal ions such as Rb and Cs were introduced, a new diffraction peak was detected at 31.6° in both Figures (b) and (c), indicating that the crystal structure was changed due to the introduction of large-sized alkali metal ions.

[0034] Experimental Example 3 The obtained PW-Rb-MC, PW-Rb-C, PW-Cs-MC, PW-Cs-C, PW-MC and PW-C were subjected to SEM analysis. The results are as follows Figure 2-Figure 4As shown. PW-C was not subjected to hydrothermal treatment, and the crystals showed a clear cubic morphology and were small in size. After hydrothermal treatment, the crystals of PW-MC underwent a significant transformation, with the cubic crystals becoming monoclinic structures, showing an elongated lamellar appearance, and the size also increased significantly, indicating that hydrothermal treatment promoted the growth of the crystals. Similarly, PW-Rb-C and PW-Rb-MC, PW-Cs-C and W-Cs-MC also showed similar situations, indicating that even if alkali metal ions were introduced, the crystals would transform from cubic phase to monoclinic phase after hydrothermal treatment, and the crystal size would increase significantly.

[0035] Experimental Example 4 The obtained PW-Rb-MC, PW-Rb-C, PW-Cs-MC, PW-Cs-C, PW-MC and PW-C were subjected to thermogravimetric analysis (TGA). The results are as follows Figure 5 shown.

[0036] Thermogravimetric analysis (TGA) data show that cubic PW-Rb-C and PW-Cs-C exhibit higher interstitial water content and lower coordinated water content after the addition of alkali metal ions. On the contrary, when the structure transforms to the monoclinic phase, the interstitial water content of PW-Rb-MC and PW-Cs-MC decreases, but the coordinated water content increases. In addition, PW-Rb-MC and PW-Cs-MC retain less crystalline water than PW-MC.

[0037] Experimental Example 5 The obtained PW-Rb-MC, PW-Rb-C, PW-Cs-MC, PW-Cs-C, PW-MC and PW-C were prepared as positive electrode materials for sodium ion batteries and subjected to 500 charge and discharge cycle tests under 1C conditions. The results are as follows Figure 6 shown.

[0038] When alkali metal ions were not introduced, the initial capacity and 500 charge-discharge cycle test results of PW-MC were inferior to those of PW-C. After the introduction of alkali metal ions, the initial capacity and 500 charge-discharge cycle test results of PW-Rb-MC and PW-Cs-MC were significantly better than those of PW-Rb-C and PW-Cs-C, respectively, showing good electrochemical performance.

[0039] Although the present invention has been described in detail with reference to the accompanying drawings and in combination with the preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, a person of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and these modifications or substitutions shall be within the scope of the present invention. Any person of ordinary skill in the art may easily think of changes or substitutions within the technical scope disclosed by the present invention, and these shall be within the scope of protection of the present invention.

Claims

1. A base Prussian blue positive electrode, characterized in that: The crystal structure of the positive electrode of the base Prussian blue is monoclinic; the chemical formula is Na r M x Mn[Fe(CN)6] m ·nH2O, r is 1-2, M is an alkali metal ion, x is 0.1-0.5, m is 0.5-1, and n is 1-3.

2. The base Prussian blue positive electrode according to claim 1, characterized in that r is 1.66-1.76, M is rubidium ion, cesium ion or potassium ion, x is 0.14-0.25, m is 0.88-0.95, and n is 1.43-1.

66.

3. A method for preparing a base Prussian blue positive electrode as claimed in claim 1, characterized in that: Sodium ferrocyanide, sodium chloride and alkali metal salt are added to water, trisodium citrate and surfactant are added after thorough mixing, and solution A is obtained by stirring evenly; manganese sulfate solution is added dropwise to solution A under continuous stirring, and stirring is continued to obtain a mixed solution with uniformly dispersed particles; the mixed solution is heated at 120° C. for 4 hours for hydrothermal treatment, and the precipitate collected by washing and centrifugation is dried to obtain a base Prussian blue positive electrode.

4. The method for preparing the base Prussian blue positive electrode according to claim 3, characterized in that: The alkali metal salt is rubidium chloride, cesium chloride or potassium chloride.

5. The method for preparing the base Prussian blue positive electrode according to claim 3, characterized in that: The molar ratio of sodium ferrocyanide, sodium chloride and alkali metal salt in the aqueous solution is 4.9: 0.0958-0.0987: 0.0013-0.0042.

6. The method for preparing the base Prussian blue positive electrode according to claim 3, characterized in that: The surfactant is polyvinyl pyrrolidone, sodium dodecyl sulfonate or sodium dodecylbenzene sulfonate.

7. The method for preparing the base Prussian blue positive electrode according to claim 3, characterized in that: Drying was carried out at 80°C under vacuum conditions for 24 h.

8. Use of the alkaline Prussian blue positive electrode as claimed in claim 1 in preparing positive electrode materials for sodium ion batteries.

Images