Low-hygroscopic Prussian blue electrode material, preparation method and application

Abstract

The present invention discloses a low-hygroscopic Prussian blue electrode material, a preparation method and an application thereof, wherein the low-hygroscopic Prussian blue electrode material comprises a core and an outer shell, wherein the inner core is a sodium-rich Prussian blue material, and the outer layer is a sodium-poor Prussian blue material having a sodium content lower than that of the inner layer or having no sodium. The present application reduces the content of sodium ions in the outer shell of the material and even avoids the presence of sodium ions in the outer shell of the material, thereby improving the ability of the material to isolate moisture while maintaining a high sodium content, significantly reducing the moisture absorption capacity, and facilitating the subsequent production of electrodes. At the same time, the outer layer formed is dense and not easy to fall off. Compared with directly coating an isolation layer to isolate moisture, the present application reduces the hygroscopicity of Prussian blue while having better sodium storage electrochemical performance, and the cycle stability at room temperature and pressure is also greatly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of energy materials, and in particular, to a low-moisture-absorbing Prussian blue electrode material, a preparation method thereof, and an application thereof. Background Art

[0002] With the entry of lithium-ion batteries into the fields of electric vehicles and large-scale energy storage, lithium-ion batteries have seen a sharp increase in market share due to their advantages such as high energy density, long service life, high charging efficiency, and good safety. However, the rapid growth in the demand for lithium-ion batteries has led to consistently high costs of lithium resources. Sodium-ion batteries, on the other hand, have a working principle similar to that of lithium-ion batteries. The crustal abundance of sodium reaches 2.74%, while the proportion of lithium in the earth's crust is only about 0.0065%. Compared with lithium-ion batteries, sodium-ion batteries have more cost advantages and broad application prospects.

[0003] Currently, the most studied sodium-ion cathode materials mainly include three categories: polyanion compounds, layered oxides, and Prussian blue analogs. Transition metal oxides and polyanion compounds have relatively large chemical binding energies for Na w due to the presence of oxygen- and fluorine-containing lattices, making the insertion and extraction relatively difficult. In the structure of Prussian blue cathode materials, two types of transition metal octahedrons alternate with each other and are bridged by C≡N to form an open cubic framework, which can be used for sodium storage. Its unique three-dimensional MOF structure has a high theoretical capacity and cycle stability. The entire framework structure has spacious three-dimensional diffusion channels, and the inserted ions are less chemically bound, making it easy to achieve rapid ion insertion and extraction. Therefore, it is considered to be one of the sodium-ion battery cathode materials with great application potential.

[0004] However, Prussian blue materials are extremely prone to moisture absorption, which is not conducive to the subsequent fabrication of electrodes. Therefore, how to reduce the moisture absorption performance of Prussian blue materials has become a problem to be solved for battery cathode materials.

[0005] In view of this, the present invention is specifically proposed. Summary of the Invention

[0006] The purpose of the present invention is to provide a low-moisture-absorbing Prussian blue electrode material, a preparation method thereof, and an application thereof. <00000​​​​​​​​​​​[Fe(CN)6], and 0≦z<1, 4 / b≦w<3 / b, wherein b is the valence state of M2; and both M1 and M2 are metal elements.

[0009] In an optional embodiment, the M1 is at least one of a transition metal and a rare earth metal; and the M2 is at least one of a transition metal and a rare earth metal.

[0010] In an optional embodiment, along the direction from the core to the shell, the sodium ion concentration gradient in at least a portion of the core and / or the shell decreases or gradually decreases.

[0011] In an optional embodiment, the molar ratio of M2 to M1 is 1:(1-10).

[0012] In a second aspect, the present invention provides a method for preparing the low-hygroscopic Prussian blue electrode material according to any one of the aforementioned embodiments, comprising:

[0013] Preparation of the core: gradually adding a soluble salt of M1 to a solution containing ferrocyanide and sodium ions to obtain a reaction solution containing the core and ferrocyanide;

[0014] The outer shell is prepared by gradually adding a soluble salt of M2 to the reaction solution containing the core and ferrocyanide to generate a low-hygroscopic Prussian blue electrode material.

[0015] In an optional embodiment, the preparation of the core satisfies at least one of the following ①-③:

[0016] ① In a solution containing ferrocyanide and sodium ions, the molar ratio of ferrocyanide to sodium ions is 1:(4-40);

[0017] ② The concentration of the ferrocyanide is 0.1 to 2 mol / L;

[0018] ③ The molar ratio of the ferrocyanide to M1 is 1 to 5:1.

[0019] In an optional embodiment, the core preparation step is performed at a temperature of 30-80° C., a reaction time of 3-5 h, and a stirring speed of 100-1200 r / min.

[0020] In an optional embodiment, the shell preparation step is performed at a temperature of 30-80° C., a reaction time of 3-5 h, and a stirring speed of 100-1200 r / min.

[0021] In an optional embodiment, after the low-hygroscopic Prussian blue electrode material is generated, the reaction product is sequentially aged, separated, washed and dried to obtain the shell sodium-poor Prussian blue material or the shell sodium-free Prussian blue material.

[0022] Thirdly, the present invention provides a battery using the low-moisture-absorbing Prussian blue electrode material described in any one of the foregoing embodiments.

[0023] The present invention has the following beneficial effects:

[0024] This application reduces the content of sodium ions in the material shell or even avoids the presence of sodium ions in the material shell, thereby improving the ability of the material to isolate moisture while maintaining a high sodium content, significantly reducing the moisture absorption capacity, which is beneficial to the subsequent production of electrodes. Compared with directly coating an isolation layer to isolate moisture, this application not only reduces the moisture absorption of Prussian blue but also has better sodium storage electrochemical performance and greatly improved cycle stability under normal temperature and pressure.

[0025] In this application, the thickness and sodium content of the shell can be adjusted by adjusting the amount of the soluble salt of M2. The operation is simple and easy to implement industrially, and the quality of the prepared positive electrode material is controllable. Specific Embodiments

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Those not specified in the embodiments are carried out under conventional conditions or conditions recommended by the manufacturer. Those reagents or instruments not specified by the manufacturer can be obtained as conventional products through commercial purchase.

[0027] This embodiment provides a low-moisture-absorbing Prussian blue electrode material, including a core and a shell. The core structure is Na x M1 y [Fe(CN)6], where 1 < x ≦ 4 and 0 < y < 3 / a, and a is the valence state of M1; the shell structure is Na z M2 w [Fe(CN)6], where 0 ≦ z < 1 and 4 / b ≦ w < 3 / b, and b is the valence state of M2; both M1 and M2 are metal elements.

[0028] The present invention reduces the content of sodium ions in the material shell or even avoids the presence of sodium ions in the material shell, thereby improving the ability of the material to isolate moisture while maintaining a high sodium content, significantly reducing the moisture absorption capacity, which is beneficial to the subsequent production of electrodes. Compared with directly coating an isolation layer to isolate moisture, this application not only reduces the moisture absorption of Prussian blue but also has better sodium storage electrochemical performance and greatly improved cycle stability under normal temperature and pressure.

[0029] In some embodiments of the present application, M1 is at least one of a transition metal and a rare earth metal; M2 is at least one of a transition metal and a rare earth metal. Specifically, M1 and M2 in the embodiments of the present application can be selected from transition elements such as iron, manganese, nickel, cobalt, vanadium, titanium, chromium, copper, or rare earth elements such as scandium and yttrium as needed, and M1 can be selected from only one of a transition metal and a rare earth metal, or two or more. Similarly, M2 can be selected from only one of a transition metal and a rare earth metal, or two or more.

[0030] In some preferred embodiments, M1 and M2 are the same element, the outer layer and the core matrix material elements and structure are consistent, the outer shell is less likely to fall off, and can be tightly combined with the core to form a dense outer layer. At the same time, the obtained material has a smaller resistance and better rate performance.

[0031] In some embodiments of the present application, along the direction from the core to the shell, the sodium ion concentration gradient in at least a portion of the core and / or the shell decreases or gradually decreases.

[0032] In the present invention, gradient reduction or gradual reduction means that the molar ratio of the material Na and M2 transition metal is not fixed. With the core as the center, in the process of spherical extension outward, the ratio of the M2 element can gradually increase, the Na element gradually decreases, and the molar ratio of Na and M2 changes in an arithmetic progression. This gradient reduction or gradual reduction can be a section of the core, a section of the shell, or even the entire particle from the center to the surface with a sodium ion concentration gradient reduction or gradual reduction. The gradient reduction refers to a discontinuous decrease in the sodium ion concentration, for example, a sudden decrease of x from 2.5 to 2; the gradual reduction refers to a continuous decrease in the sodium ion concentration, for example, a gradual decrease of x from 2.5 to 2.

[0033] In some embodiments of the present application, the molar ratio of M2 to M1 is 1:(1-10), so that the shell has a certain thickness, which can alleviate the large amount of sodium ions on the surface of the Prussian blue positive electrode material, but the shell is too thick, which is not conducive to the transmission of sodium ions.

[0034] Another embodiment of the present application provides a method for preparing the low-hygroscopic Prussian blue electrode material according to any one of the aforementioned embodiments, comprising:

[0035] Preparation of the core: gradually adding a soluble salt of M1 to a solution containing ferrocyanide and sodium ions to obtain a reaction solution containing the core and ferrocyanide;

[0036] Preparation of the shell: gradually add a soluble salt of M2 to the reaction solution containing the core and ferrocyanide to generate a low-hygroscopic Prussian blue electrode material.

[0037] The core preparation steps are as follows:

[0038] Na4Fe(CN)6+M1 a+ +Na + →Na x M1 y [Fe(CN)6]

[0039] The steps for preparing the shell are as follows:

[0040] Na4Fe(CN)6+M2 b+ →Na w M2 z [Fe(CN)6]

[0041] Among them, sodium salt is not required to be added. The addition of sodium salt can convert the Prussian blue of the inner core layer into a high-sodium Prussian blue analogue. When no sodium salt is added, the inner core layer is regular Prussian blue. It should be noted that in this embodiment, if some sodium ions are still in the solution after the core is prepared and have not participated in the preparation of the core, then when M2 is added, the sodium ions can continue to react with M2. At this time, adding M2 facilitates the regulation of the sodium content in the outer layer to be lower than the sodium content in the core, resulting in a low-sodium outer layer structure.

[0042] The preparation method of the low-hygroscopic Prussian blue electrode material in the present application is simple to operate and easy to implement industrially. The quality of the prepared positive electrode material is controllable, and the thickness and sodium content of the shell can be easily adjusted by adjusting the amount of soluble salt of M2, and the application range is wide.

[0043] In some embodiments of the present application, in a solution containing ferrocyanide and sodium ions, the molar ratio of ferrocyanide to sodium ions is 1:(4-40), to obtain a reaction solution containing a core;

[0044] In some embodiments of the present application, the concentration of ferrocyanide is 0.1 to 2 mol / L;

[0045] In some embodiments of the present application, the molar ratio of ferrocyanide to M1 is 1 to 5:1;

[0046] In some embodiments of the present application, the M1 soluble salt is added while stirring, and the stirring speed is 100 to 1200 r / min.

[0047] Too high a concentration of sodium ferrocyanide will lead to a waste of resources, while too low a concentration will lead to more vacancy defects, thereby reducing the structural stability and conductivity of the Prussian blue electrode material.

[0048] In some embodiments of the present application, the temperature of the core preparation step is 30-80°C, the reaction time is 3-5h, and the stirring speed is 100-1200r / min; and / or the temperature of the shell preparation step is 30-80°C, the reaction time is 3-5h, and the stirring speed is 100-1200r / min. Too high a temperature will accelerate the reaction speed, resulting in more vacancies in the material and affecting the material properties. Too low a temperature will reduce production efficiency and increase production costs.

[0049] In some embodiments of the present application, after generating the low-hygroscopic Prussian blue electrode material, the reaction product is sequentially aged, separated, washed and dried to obtain the shell sodium-poor Prussian blue material or the shell sodium-free Prussian blue material.

[0050] In a third aspect, the present invention provides a battery using the low-hygroscopic Prussian blue electrode material described in any one of the aforementioned embodiments.

[0051] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0052] Example 1

[0053] (1) Weigh 9.86 g of sodium ferrocyanide decahydrate and 11.68 g of sodium chloride, dissolve them in 200 mL of deionized water to obtain a sodium-containing solution with a concentration of 0.1 mol / L of sodium ferrocyanide decahydrate and sodium chloride; add 100 mL of 0.1 mol / L MnCl2 solution dropwise to the sodium-containing solution at a rate of 10 mL / min, and react at a speed of 800 r / min and a temperature of 30°C for 4 h to obtain a high-sodium Prussian blue core;

[0054] (2) 200 mL of 0.05 mol / L FeCl3 aqueous solution was slowly added to the solution of step 1, and the mixture was reacted at a speed of 800 r / min and a temperature of 30°C for 4 h, and then aged at 30°C for 12 h. The mixture was then separated, washed, and dried at 140°C for 24 h to obtain a Prussian blue material with a sodium-rich core layer and a sodium-poor outer layer.

[0055] Example 2:

[0056] The only difference from Example 1 is that no sodium chloride is added in step 1, and a conventional sodium-poor Prussian blue material with a core layer is obtained.

[0057] Example 3:

[0058] (1) The same as step (1) in Example 2;

[0059] (2) 200 mL of 0.1 mol / L FeCl3 aqueous solution was slowly added to the solution of step 1, and the mixture was reacted at a speed of 800 r / min and a temperature of 30°C for 4 h, and then aged at 30°C for 12 h. After separation, washing and drying at 140°C for 24 h, a Prussian blue sodium ion positive electrode material with a sodium ion concentration gradient from conventional, sodium-poor to sodium-free from the inside to the outside was obtained.

[0060] Example 4:

[0061] (1) The same as step (1) in Example 2;

[0062] (2) 200 mL of 0.01 mol / L FeCl3 aqueous solution was slowly added to the solution of step 1, and the mixture was reacted at a speed of 800 r / min and a temperature of 30°C for 4 h, and then aged at 30°C for 12 h. The mixture was then separated, washed, and dried at 140°C for 24 h to obtain a Prussian blue material with a common inner layer and a sodium-poor outer layer.

[0063] Example 5:

[0064] The only difference from Example 2 is that the concentration of sodium ferrocyanide is 2 mol / L.

[0065] Example 6:

[0066] The only difference from Example 2 is that the addition of Mn 2+ The amount of sodium ferrocyanide and Mn 2+ The molar ratio is 1:1.

[0067] Example 7:

[0068] The only difference from Example 2 is that the Mn 2+ The amount used is such that the molar ratio of sodium ferrocyanide to Mn is 5:1.

[0069] Example 8:

[0070] The only difference from Example 2 is that the temperature of the core preparation step and the shell preparation step are both 80°C.

[0071] Comparative Example 1

[0072] 19.72 g of sodium ferrocyanide decahydrate was dissolved in 200 mL of deionized water to obtain a solution with a concentration of 0.2 mol / L; 200 mL of 0.1 mol / L MnCl2 solution was added dropwise to the sodium ferrocyanide solution at a rate of 10 mL / min, and the mixture was reacted at a speed of 800 r / min and a temperature of 30°C for 4 h, and then aged at 30°C for 12 h. After separation, washing, and drying at 140°C for 24 h, a conventional Prussian blue material was obtained.

[0073] Comparative Example 2

[0074] 9.86 g of sodium ferrocyanide decahydrate and 11.68 g of sodium chloride were weighed and dissolved in 200 mL of deionized water to obtain a sodium-containing solution with a concentration of 0.1 mol / L of sodium ferrocyanide decahydrate; 100 mL of a 0.1 mol / L MnCl2 solution was added dropwise to the sodium-containing solution at a rate of 10 mL / min, and the mixture was reacted at a speed of 800 r / min and a temperature of 30°C for 4 h to obtain a high-sodium Prussian blue material;

[0075] Comparative Example 3:

[0076] The only difference from Example 2 is that the concentration of sodium ferrocyanide is 0.09 mol / L.

[0077] Comparative Example 4:

[0078] The only difference from Example 2 is that the Mn 2+ The amount of sodium ferrocyanide and Mn 2+ The molar ratio is 1:0.9.

[0079] Comparative Example 5:

[0080] The only difference from Example 2 is that the Mn 2+ The amount of sodium ferrocyanide and Mn 2+ The molar ratio is 5.1:1.

[0081] Comparative Example 6:

[0082] The only difference from Example 2 is that the temperature of the core preparation step and the shell preparation step are both 81°C.

[0083] Test Example 1

[0084] Two groups of positive electrode materials prepared from Examples 1-3 and Comparative Examples 1-2 were collected. The first group was removed from the sample in a dry environment and tested for moisture content. The second group was exposed to air (temperature 20°C, humidity 40%) for 1 hour and tested for moisture content. The third group, after drying, was also sampled and tested in a dry environment. Moisture content was tested using a Karl-Fischer titrator with a cutoff temperature of 200°C. The results of the moisture content tests are shown in the table below.

[0085] The obtained powder material was homogenized in a ratio of active component: PVDF: conductive agent = 7:1:2 to prepare a 2025 button battery, and the battery cycle performance test was carried out under 4.0-2.5V and 0.1C conditions.

[0086]

[0087]

[0088]

[0089] It can be seen from the test results of the experimental examples of the present invention that the water content of the positive electrode material provided by the present invention is significantly reduced, indicating that the Prussian blue sodium ion positive electrode material with a sodium ion concentration gradient from sodium-rich, sodium-poor to sodium-free from the inside to the outside reduces the moisture absorption capacity of the dried Prussian blue material. The positive electrode material prepared by the present invention is used to prepare a sodium ion battery, which can make the battery have better cycle stability and significantly reduce gas production.

[0090] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A low-hygroscopic Prussian blue electrode material, characterized in that: It includes a core and a shell. The core structure is Na x M1 y [Fe(CN)6], where 1 < x ≦ 4 and 0 < y < 3 / a, with a being the valence state of M1; the shell structure is Na z M2 w [Fe(CN)6], where 0 < z < 1 and 4 / b ≦ w < 3 / b, with b being the valence state of M2; M1 is manganese element, M2 is iron element, and the molar ratio of M2 to M1 is 1∶(1 - 5); along the direction from the core to the shell, the sodium ion concentration gradient in at least a part of the core and / or the shell decreases or gradually decreases.

2. A method for preparing the low-hygroscopic Prussian blue electrode material according to claim 1, characterized in that: include: Preparation of the core: gradually adding a soluble salt of M1 to a solution containing ferrocyanide and sodium ions to obtain a reaction solution containing the core and ferrocyanide; Preparation of the shell: gradually add a soluble salt of M2 to the reaction solution containing the core and ferrocyanide to generate a low-hygroscopic Prussian blue electrode material.

3. The method for preparing the low-hygroscopic Prussian blue electrode material according to claim 2, characterized in that: The preparation of the core satisfies at least one of the following ①-③: ① In a solution containing ferrocyanide and sodium ions, the molar ratio of ferrocyanide to sodium ions is 1:(4~40); ② The concentration of ferrocyanide is 0.1~2 mol / L; ③ The molar ratio of the ferrocyanide to M1 is 1~5:

1.

4. The method for preparing the low-hygroscopic Prussian blue electrode material according to claim 2, characterized in that: The core preparation step has a temperature of 30-80° C., a reaction time of 3-5 h, and a stirring speed of 100-1200 r / min.

5. The method for preparing the low-hygroscopic Prussian blue electrode material according to claim 2, characterized in that: The shell preparation step has a temperature of 30-80° C., a reaction time of 3-5 hours, and a stirring speed of 100-1200 r / min.

6. The method for preparing the low-hygroscopic Prussian blue electrode material according to claim 2, characterized in that: After the low-hygroscopic Prussian blue electrode material is generated, the reaction product is sequentially aged, separated, washed and dried to obtain a shell sodium-poor type Prussian blue material or a shell sodium-free type Prussian blue material.

7. A battery using the low-hygroscopic Prussian blue electrode material according to claim 1.

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