Preparation method and application of manganese-based Prussian white material with modified surface

Abstract

The invention discloses a method for preparing a manganese-based Prussian white material with a modified surface. The method comprises the following steps: providing a manganese-based Prussian white semi-finished raw material, adding the manganese-based Prussian white semi-finished raw material into a metal salt solution for mixing and washing, exchanging manganese ions with metal ions in the metal salt solution to form a doping layer on the surface of the manganese-based Prussian white semi-finished raw material, and obtaining a surface-modified manganese-based Prussian white material; the application utilizes different dissolution equilibrium constants in different materials, at which temperature, manganese ions in the manganese-based Prussian white are exchanged with metal ions in the metal salt solution to form a uniform doping layer on the surface, and in the raw material processed by the method, manganese ions can be highly selectively exchanged without affecting the content of alkali metals, and the charge state of the material surface is effectively improved.

Description

Technical Field

[0001] The present invention belongs to the field of preparation of Prussian white and its analog materials, and specifically relates to a preparation method and application of a manganese-based Prussian white material with a modified surface. Background Art

[0002] Prussian white compounds have the molecular formula A X M y [Fe(CN) 6 ·nH 2 O, where A is an alkali metal ion such as Li+, Na+, or K+, and M is a transition metal ion such as Co, Ni, Mn, Zn, or Cu; 0 ≤ x ≤ 2, 0 < y ≤ 1; 0 ≤ z < 1, 0 ≤ n ≤ 3.5; its structure is a three-dimensional network structure, and its oxidation state and reduction state can exhibit different colors. Because of its good electrochemical reversibility, high stability, and low preparation cost, and it can quickly interact with alkali metal ions in solution, Prussian white compounds are widely used in the battery field;

[0003] Among them, taking manganese-based Prussian white as an example, because of its high specific capacity, it has become a very potential cathode material for sodium-ion batteries and is widely used; however, during the cyclic discharge process, there is a phenomenon of manganese dissolution in manganese-based Prussian white, which affects the cycling performance of the material, resulting in a decrease in the conductivity of the material and a deterioration of the rate performance;

[0004] Therefore, it is often necessary to dope manganese-based Prussian white with various metal elements to improve its cycling performance. Generally, for example, doping elements are introduced during the synthesis of Prussian white. However, during the precipitation process, it is easy to form Prussian blue-like compounds, and it is difficult to coordinate the precipitation rate of this compound with that of manganese, resulting in phase separation and unsatisfactory doping effects;

[0005] For Chinese patent with the application number 202011519530.9 and the invention title: Surface-modified sodium manganese Prussian blue material and its preparation method and application, a coating layer is formed on the Prussian material through surface modification, thereby improving the cycling stability of the sodium manganese Prussian material. However, in this scheme, it is necessary to introduce a sodium-containing complexing agent and sodium salt to reduce the content of raw material sodium, and it is impossible to avoid the oxidation of sodium by acid radicals and the resulting loss phenomenon. Moreover, the reduction of the sodium ion content will seriously affect the capacity attenuation during application. For manganese-based Prussian white raw materials with a large amount of sodium ions or other monovalent metals, if the above scheme is directly used for modification, it will cause a counterproductive effect. There is an urgent need for a preparation method of a manganese-based Prussian white material with a modified surface to enhance the cycling performance of the material, which is urgently needed for social development. Summary of the Invention

[0006] A solution is provided to solve the problem that the manganese-based Prussian white doping effect in the above technology is not ideal, resulting in poor cycle performance;

[0007] To achieve the above objectives, the following solutions are adopted:

[0008] A method for preparing a manganese-based Prussian white material with a modified surface comprises the following steps:

[0009] Provide manganese-based Prussian white semi-finished raw materials;

[0010] The manganese-based Prussian white semi-finished raw material is added to a metal salt solution for mixed washing, and the manganese ions on the surface of the raw material are exchanged with the metal ions in the metal salt solution. The mixed washing temperature is 45-80°C and the time is 1-24 hours, and a surface-modified manganese-based Prussian white material is obtained.

[0011] Preferably, the concentration of the metal salt solution is 0.01-0.1M.

[0012] Preferably, the metal ion of the metal salt solution is Fe 2+ 、Co 2+ 、Ni 2+ , Cu 2+ and Zn 2+ The salt solution is one or more of chloride, sulfate, nitrate or acetate solution.

[0013] As a preferred method, the preparation method of manganese-based Prussian white semi-finished raw material is:

[0014] S1: Provide the general formula A 4 Fe(CN) 6 Ferrocyanide salts;

[0015] S2: mixing ferrocyanide salt and a soluble salt containing manganese ions, and aging to obtain a first reactant;

[0016] S3: filtering and washing the first reactant to obtain a manganese Prussian white semi-finished raw material.

[0017] Preferably, in step S1, in the general formula, A is one of Li, Na and K.

[0018] Preferably, in step S1, the concentration of ferrocyanide is 0.1-0.6M.

[0019] Preferably, in step S2, the soluble salt containing manganese ions is one or more of chloride, nitrate, sulfate and acetate.

[0020] Preferably, in step S2, ferrocyanide and a soluble salt containing manganese ions are slowly added dropwise to a reaction kettle at the same time, and the reaction is stirred at a temperature of 30-100°C.

[0021] Preferably, in step S2, the aging time is 4-72 hours.

[0022] The present invention also provides a battery positive electrode material using the above-mentioned surface modified manganese-based Prussian white material.

[0023] The beneficial effects of the present invention are as follows: compared with the prior art, the present invention provides a method for preparing a manganese-based Prussian white material with a modified surface, comprising the following steps: adding a manganese-based Prussian white semi-finished raw material to a metal salt solution for mixing, exchanging manganese ions on the surface of the raw material with metal ions in the metal salt solution, reacting at a temperature of 45-80°C for 1-24 hours, and obtaining a surface-modified manganese-based Prussian white material; the present application utilizes different dissolution equilibrium constants in different materials, at which temperature, manganese ions in the manganese-based Prussian white are exchanged with metal ions in the metal salt solution to form a uniform doping layer on the surface, and manganese ions in the raw material processed by the method can be highly selectively exchanged without affecting the content of alkali metals, and the charge state of the material surface is effectively improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is the overall flow chart of the present invention;

[0025] Figure 2 The electron microscope photographs of Example 1, Example 2 and Comparative Example of the present invention are shown in FIG.

[0026] Figure 3 It is the charge and discharge curve diagram of Example 1 of the present invention and the comparative example. DETAILED DESCRIPTION

[0027] In order to more clearly illustrate the present invention, the present invention is further described below in conjunction with the accompanying drawings.

[0028] In the following description, general election example details are given to provide a deeper understanding of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all embodiments. It should be understood that the specific embodiments are only used to explain the present invention and are not used to limit the present invention.

[0029] It should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the existence of features, integers, steps, operations, elements or components, but do not exclude the existence or addition of one or more other features, integers, steps, operations, elements, components or combinations thereof.

[0030] In the field of batteries, the selection of negative and positive electrode materials has been explored for a long time. As the progress of resource development has gradually slowed down, people have gradually shifted the exploration of new materials to the optimization of existing materials. Among positive electrode materials, Prussian materials have attracted much attention because of their good electrochemical reversibility, high stability, low preparation cost, and ability to rapidly interact with alkali metal ions in solution.

[0031] Among Prussian materials, manganese-based Prussian white is the most representative. It has become a highly potential positive electrode material for sodium-ion batteries and is widely used because of its high gram capacity. However, during the cyclic discharge process, manganese dissolves in manganese-based Prussian white, which affects the material's cyclic performance, causing the material's conductivity to decrease and its rate performance to deteriorate. This performance is particularly critical in the subsequent production of batteries and is an important indicator for determining the quality of batteries.

[0032] Therefore, it is often necessary to dope manganese-based Prussian white with a variety of metal elements to improve its cycle performance. It is generally known that, for example, doping elements are introduced in the process of synthesizing Prussian white. However, Prussian blue-like compounds are likely to appear during the precipitation process. The precipitation rate of this compound and manganese is difficult to coordinate, resulting in phase separation and unsatisfactory doping effect, which leads to the cycle performance failing to meet expectations. Although surface modification can effectively improve the cycle period, there is a risk of large-scale loss of major alkali metal ions such as sodium and lithium during the modification stage. It can be seen that there should be a method for preparing a manganese-based Prussian white material with a modified surface, so that the surface of the manganese-based Prussian white material is modified to enhance the material's cycle performance, which is an urgent need for social development.

[0033] In order to solve the above-mentioned technical problems, the present invention provides a method for preparing a manganese-based Prussian white material with a modified surface, comprising the following steps:

[0034] Step A: providing manganese-based Prussian white semi-finished product raw material;

[0035] Step B: adding a manganese-based Prussian white raw material to a metal salt solution for mixed washing, wherein the manganese ions on the surface of the raw material are exchanged with the metal ions in the metal salt solution, the reaction temperature of the mixed washing is 45-80° C., and the time is 1-24 hours. After the mixed washing is completed, filtering, washing and drying are performed in sequence to obtain a surface-modified manganese-based Prussian white material;

[0036] The present application utilizes the different dissolution equilibrium constants in different materials and selects the ion exchange temperature. It is worth noting that within the temperature parameter range and the time parameter range, the manganese ions in the manganese-based Prussian white raw material are highly selectively exchanged with the metal ions, which will not reduce the alkali metal ion content. In subsequent applications as a battery, it will not cause capacity decay problems and will not affect the performance when used as a positive electrode material. After surface modification treatment, the manganese ion content on the surface of the material is reduced, thereby reducing the probability of dissolution during the cycle, making the cycle period longer.

[0037] After testing, the concentration of the metal salt solution is 0.01-0.1M; the metal ion of the metal salt solution is Fe 2+ 、Co 2+ 、Ni 2+ , Cu 2+ and Zn 2+ The salt solution is one or more of chloride, sulfate, nitrate or acetate solution;

[0038] The method for obtaining the above-mentioned manganese-based Prussian white raw material is:

[0039] S1: Provide the general formula A 4 Fe(CN) 6 Ferrocyanide salts;

[0040] S2: mixing ferrocyanide salt and a soluble salt containing manganese ions, and obtaining a first reactant after aging;

[0041] S3: filtering and washing the first reactant to obtain a manganese Prussian white semi-finished raw material.

[0042] In step S1, in the general formula, A is one of Li, Na and K; in step S1, the concentration of ferrocyanide is 0.1-0.6M; the soluble salt containing manganese ions is one or more of chloride, nitrate, sulfate and acetate;

[0043] In step S2, ferrocyanide and a soluble salt containing manganese ions are slowly added dropwise to a reaction kettle at the same time, and stirred to react at a temperature of 30-100° C.; the aging time is 4-72 hours.

[0044] In order to further explain the present invention, the modified manganese-based Prussian material is used as the positive electrode material and prepared into an electrolyte system battery:

[0045] Embodiment 1:

[0046] S1: Provide A with a general formula of 0.6M concentration 4 Fe(CN) 6 ferrocyanide, A is Na ion;

[0047] S2: Slowly drop ferrocyanide and metal manganese ion sulfate solution into the reaction kettle at the same time, stir, and control the temperature at 40° C. After the dropwise addition, age for 30 hours to obtain the first reactant;

[0048] S3: filtering and washing the first reactant to obtain a manganese Prussian white semi-finished raw material;

[0049] S4: adding 0.1M cobalt sulfate solution to the manganese-based Prussian white semi-finished raw material, stirring, controlling the temperature at 45°C, and controlling the reaction time at 4h. After the reaction is completed, a surface-modified manganese-based Prussian white material 1 is obtained, which is filtered, washed, dried, crushed, sieved, and then used for later use;

[0050] S5: Mix the manganese-based Prussian white material 1, conductive carbon, and a binder, add N-methylpyrrolidone (NMP) as a dispersant, stir and mix evenly, use a scraper fineness meter to measure the slurry fineness to be 25 μm, prepare a battery positive electrode material and assemble it into an organic electrolyte system sodium ion half-cell.

[0051] Embodiment 2:

[0052] S1: Provide A with a general formula of 0.6M concentration 4 Fe(CN) 6 ferrocyanide, A is Na ion;

[0053] S2: Slowly drop ferrocyanide and metal manganese ion sulfate solution into the reaction kettle at the same time, stir, and control the temperature at 40° C. After the dropwise addition, age for 30 hours to obtain the first reactant;

[0054] S3: filtering and washing the first reactant to obtain a manganese Prussian white semi-finished raw material;

[0055] S4: adding 0.1M nickel sulfate solution to the manganese-based Prussian white semi-finished raw material, stirring, controlling the temperature at 45°C, and controlling the reaction time at 4h. After the reaction is completed, a surface-modified manganese-based Prussian white material 1 is obtained, which is filtered, washed, dried, crushed, sieved, and then used for later use;

[0056] S5: Mix the manganese-based Prussian white material 2, conductive carbon, and a binder, add N-methylpyrrolidone (NMP) as a dispersant, stir and mix evenly, use a scraper fineness meter to measure the slurry fineness to be 25 μm, prepare a battery positive electrode material and assemble it into an organic electrolyte system sodium ion half-cell.

[0057] Comparative Example 1:

[0058] S1: Provide A with a general formula of 0.6M concentration 4 Fe(CN)6 ferrocyanide, A is Na ion;

[0059] S2: Slowly drop ferrocyanide and metal manganese ion sulfate solution into the reaction kettle at the same time, stir, and control the temperature at 40° C. After the dropwise addition, age for 30 hours to obtain the first reactant;

[0060] S3: filtering, washing, crushing and sieving the first reactant to obtain a manganese Prussian white raw material;

[0061] S4: Mix the manganese-based Prussian white raw material, conductive carbon, and adhesive, add N-methylpyrrolidone (NMP) as a dispersant, stir and mix evenly, use a scraper fineness meter to measure the slurry fineness to be 45μm, prepare the battery positive electrode material and assemble it into an organic electrolyte system sodium ion half-cell.

[0062] First, the surface-modified manganese-based Prussian white material 1 and the manganese-based Prussian white material 2 in the example and the manganese-based Prussian white raw material 2 in the comparative example were tested by EDS. The test results are shown in Table 1:

[0063] Table 1

[0064]

[0065] It is not difficult to know from Table 1 that there is no obvious difference in the content of Na element in the comparative example and the embodiment, and it is believed that when Na ions are used as alkaline metal ions, at a concentration of 0.1M and a temperature of 45°C, the manganese ions in the manganese-based Prussian white raw material are highly selectively exchanged with Co or Ni ions. Compared with the existing ones, the need for sodium-containing complexing agents or sodium salt solutions to supplement sodium ions in the process of modifying the surface of the manganese-based Prussian white material is eliminated, and the preparation process is simpler; and the reduction in the content of Mn element proves that Mn ions are exchanged with Co ions and Ni ions, reducing the risk of Mn ions dissolving in the cycle; and since K, Li and other elements belong to the same main group as Na in the periodic table and have similar chemical properties, it is believed that in the preparation of manganese-based Prussian white material, the alkali metal A can be K, Li and other elements in addition to Na clearly selected in the above embodiment.

[0066] The manganese-based Prussian white material 1, the manganese-based Prussian white material 2 and the manganese-based Prussian white raw material in the comparative example were analyzed by electron microscopy. The manganese-based Prussian white raw material in the comparative example was marked as PW, the manganese-based Prussian white material 1 was marked as Co-DPW, and the manganese-based Prussian white material 2 was marked as Ni-DPW. The obtained electron microscopy images are shown in FIG. Figure 2 ;from Figure 2It can be seen that the particle morphology, grain size and material structure of Example 1 and Example 2 are basically the same. It can be seen that the present application only modifies the surface of the manganese-based Prussian white raw material and does not change the structure of the raw material.

[0067] The sodium-based lithium batteries obtained in Example 1 and the comparative example were subjected to electrical tests. The results obtained are shown in Figure 3 ;exist Figure 3 It is not difficult to know that according to the charge and discharge curve, the gram capacity of the sodium lithium battery of Example 1 is 109.80mAh / g, while the gram capacity of the comparative example without surface treatment is 101.51mAh / g. It can be seen that after surface modification, elements such as Co and Ni are effectively doped on the surface of the manganese-based Prussian white material, the gram capacity is improved, and the voltage difference between the charge and discharge curves is smaller, indicating that polarization is reduced; and the sodium batteries in Example 1 and the comparative example are tested for cycle periods at 1C current density and 2.0-3.8V voltage parameters. Please refer to the results. Figure 3 It is not difficult to know that in the comparative example, the gram capacity decays to less than 80% after the battery cycle is about 20 weeks, while in Example 1, the gram capacity of Example 1 has basically no obvious decay after 20 cycles, and when it continues to cycle to 40 weeks, the gram capacity decays by 2%; it can be seen that the surface modified manganese-based Prussian material obtained in Example 1 is used as a positive electrode material in sodium-based batteries and has good cycle stability.

[0068] The advantages of the present invention are:

[0069] The manganese ions in the manganese-based Prussian white semi-finished raw materials undergo highly selective exchange with metal ions, which will not reduce the alkali metal ion content. In subsequent applications as batteries, the problem of capacity decay due to the reduction of alkali metal ions is avoided, and it is better used in batteries. After surface modification treatment, the manganese ion content on the surface of the material is reduced, thereby reducing the probability of dissolution during the cycle and making the cycle period longer.

[0070] The above disclosures are only several specific embodiments of the present invention, but the present invention is not limited thereto, and any changes that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A method for preparing a manganese-based Prussian white material with a modified surface, characterized in that: Provide manganese-based Prussian white semi-finished raw materials; The manganese-based Prussian white semi-finished raw material is added to a metal salt solution for mixed washing, and the manganese ions on the surface of the raw material are exchanged with the metal ions in the metal salt solution, the mixed washing temperature is 45-80° C., the time is 1-24 hours, and a surface-modified manganese-based Prussian white material is obtained; The concentration of metal ions in the metal salt solution is 0.1 M; Na ions are used as alkaline metal ions, and when the temperature is 45° C., manganese ions in the manganese-based Prussian white raw material are selectively exchanged with Co or Ni ions.

2. The method for preparing the manganese-based Prussian white material with a modified surface according to claim 1, characterized in that: The metal ion of the metal salt solution is Fe 2+ 、Co 2+ 、Ni 2+ , Cu 2+ and Zn 2+ The salt solution is one or more of chloride, sulfate, nitrate or acetate solutions.

3. The method for preparing the manganese-based Prussian white material with a modified surface according to claim 1, characterized in that: The method for preparing the manganese-based Prussian white semi-finished raw material is as follows: S1: providing a ferrocyanide salt of the general formula A4Fe(CN)6; S2: mixing the ferrocyanide salt and the soluble salt containing manganese ions, and aging to obtain a first reactant; S3: filtering and washing the first reactant to obtain a manganese Prussian white semi-finished raw material.

4. The method for preparing the manganese-based Prussian white material with a modified surface according to claim 3, characterized in that: In step S1, the ferrocyanide salt is one of Na4Fe(CN)6, Li4Fe(CN)6 and K4Fe(CN)6.

5. The method for preparing the manganese-based Prussian white material with a modified surface according to claim 3, characterized in that: In step S1, the concentration of ferrocyanide salt is 0.1-0.6M.

6. The method for preparing the manganese-based Prussian white material with a modified surface according to claim 3, characterized in that: In step S2, the soluble salt containing manganese ions is one or more of chloride, nitrate, sulfate and acetate.

7. The method for preparing the manganese-based Prussian white material with a modified surface according to claim 3, characterized in that: In step S2, the ferrocyanide and the soluble salt containing manganese ions are slowly added dropwise to a reaction kettle at the same time, and stirred for reaction at a temperature of 30-100°C.

8. The method for preparing the manganese-based Prussian white material with a modified surface according to claim 3, characterized in that: In step S2, the aging time is 4-72 hours.

9. Use of the surface-modified manganese-based Prussian white material according to any one of claims 1 to 8 in the preparation of battery positive electrode materials.

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