A positive electrode material and its preparation method and application

Abstract

The present invention provides a cathode material, a preparation method thereof, and an application. The cathode material includes a core and a coating layer. The core is Na 2‑x M(FeCN6) 1‑y having a rhombic phase structure, and the coating layer is metal boride A z B, where 0 ≤ x ≤ 0.5, 0 ≤ y ≤ 0.2, and M is selected from at least one of Mn 2+ , Fe 2+ , Co 2+ , Ni 2+ , A is selected from any one of Co, Ni, Mn, Al, Zr, La, Fe, Cu, Mg, Ca, Ti, V, Cr, Y, Mo, or W, and 0

Description

Technical Field

[0001] The present invention belongs to the field of sodium ion batteries, and in particular relates to a positive electrode material and a preparation method and application thereof. Background Art

[0002] In recent years, with the increasingly severe energy crisis and environmental pollution, clean energy (such as solar energy, wind energy and tidal energy, etc.) has achieved unprecedented development. The development of these new forms of energy will involve the issue of how to store energy. As a storage device, secondary rechargeable lithium-ion batteries have been widely studied because of their high conversion efficiency and energy density. However, the scarcity and uneven distribution of lithium resources have limited its future development. With the rise of large-scale energy storage, and considering the high abundance of sodium resources in the earth's crust and their low price, sodium-ion batteries will become an important supplement to lithium-ion batteries.

[0003] In sodium-ion batteries, Prussian white analogs have attracted widespread attention due to their high theoretical energy density, simple preparation, low raw material prices, and environmental friendliness. However, Prussian white analogs with a rhombohedral phase structure have poor stability in the air and are easy to absorb water, thereby forming a monoclinic or cubic phase structure, which greatly affects their performance in the full battery. In addition, the electronic conductivity of the Prussian white analog positive electrode is poor, and the volume of the material particles changes greatly during the charge and discharge process, resulting in poor electrochemical performance. However, Prussian white analog positive electrodes are usually synthesized at room temperature and cannot be coated with carbon materials or other conductive metal oxides during high-temperature sintering like other positive electrode materials.

[0004] CN113830792A discloses a method for preparing an anhydrous Prussian white material, first obtaining a potassium-based Prussian white cathode with low crystal water content in an aqueous phase, and then obtaining an anhydrous or low-water sodium-based Prussian white material in an organic phase by ion exchange, thereby improving capacity and cycle stability. Although a Prussian white cathode with low water content can be obtained by the above method, the moisture sensitivity of the Prussian white cathode is not solved. This material may absorb water when placed in the air, which deteriorates the electrochemical performance of the material.

[0005] CN115196653A discloses a method for preparing a coated Prussian white. After the Prussian white positive electrode is prepared by a coprecipitation method, it is washed with a potassium salt solution, so that potassium ions partially replace the sodium ions on the surface to form potassium-based Prussian white on the surface. Although the coated potassium-based Prussian white can effectively inhibit the core Prussian white from absorbing moisture in the air, the potassium-based Prussian white itself is still not conducive to electronic conduction, and the electrochemical performance is still not ideal.

[0006] The Prussian white cathode material prepared by the above method still has disadvantages such as poor air stability, poor intrinsic conductivity, and large volume strain, and the electrochemical performance of the material is still not ideal enough. Therefore, it is necessary to develop a Prussian white cathode material with good air stability, electron conduction, and electrochemical performance to further promote the practical application of cathode materials such as sodium-based Prussian white analogs. Summary of the Invention

[0007] The purpose of the present invention is to provide a cathode material, a preparation method thereof, and an application thereof, which simultaneously have good air stability, electron conduction, and electrochemical performance.

[0008] To achieve the purpose of this invention, the following technical solutions are adopted:

[0009] One of the purposes of the present invention is to provide a cathode material, the cathode material includes a core and a coating layer, the core is Na 2-x M(FeCN 6 ) 1-y with a rhombic phase structure, and the coating layer is metal boride A z B, where 0 ≤ x ≤ 0.5, 0 ≤ y ≤ 0.2, M is selected from at least one of Mn 2+ , Fe 2+ , Co 2+ , Ni 2+ , A is selected from any one of Co, Ni, Mn, Al, Zr, La, Fe, Cu, Mg, Ca, Ti, V, Cr, Y, Mo or W, 0 < z ≤ 2. Among them, the value of x can be 0, 0.1, 0.2, 0.3, 0.4 or 0.5, the value of y can be 0, 0.1 or 0.2, and the value of z can be 0.1, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8 or 2, etc., but not limited to the listed values. Other unlisted values within the above numerical ranges are equally applicable.

[0010] The present invention sets a metal boride coating layer on the surface of the rhombic phase Na 2-x M(FeCN 6 ) 1-y particles to prevent the Prussian white analog from contacting with moisture and oxygen in the air, maintain the crystal structure of the rhombic phase, and exhibit a high specific capacity and a high voltage platform; the metal boride has good conductivity, and introducing the metal boride coating layer can improve the overall electron conductivity of the material and enhance the rate performance of the material; the metal boride has good mechanical toughness, provides a buffering effect for the large volume change during the charge and discharge process of the Prussian white analog cathode material, effectively inhibits the generation of cracks in the Prussian white analog cathode particles, and improves the cycling performance of the material.

[0011] A second object of the present invention is to provide a method for preparing the positive electrode material as claimed in claim 1, wherein the method comprises the following steps:

[0012] (1) mixing a sodium ferrocyanide solution, a divalent metal salt solution and a complexing agent, and then aging the mixture to obtain a Prussian white analog precursor;

[0013] (2) Adding a boron source and a metal salt solution to the Prussian white analog precursor of step (1) for a second mixing, and then drying to obtain the positive electrode material.

[0014] The present invention utilizes the interaction between boride metallic glass and the positive electrode to uniformly coat the surface of the Prussian white analog particles. The whole process is short in process flow and simple in operation, and is suitable for large-scale production. The purpose of the first mixing and aging in step (1) of the present invention is to make the Prussian white particles form a relatively perfect crystal form and morphology.

[0015] As a preferred technical solution of the present invention, the concentration of the sodium ferrocyanide solution in step (1) is 0.1-2 mol / L, wherein the concentration can be 0.1 mol / L, 0.2 mol / L, 0.4 mol / L, 0.6 mol / L, 0.8 mol / L, 1.0 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, 1.8 mol / L or 2 mol / L, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0016] Preferably, the concentration of the divalent metal salt solution in step (1) is 0.1 to 2 mol / L, wherein the concentration may be 0.1 mol / L, 0.2 mol / L, 0.4 mol / L, 0.6 mol / L, 0.8 mol / L, 1.0 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, 1.8 mol / L or 2 mol / L, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0017] Preferably, the divalent metal salt solution in step (1) comprises any one of a Mn salt, a Ni salt, a Fe salt or a Co salt, or a combination of at least two of them, wherein typical but non-limiting examples of the combination include: a combination of a Mn salt and a Ni salt, a combination of a Ni salt and a Fe salt, a combination of a Fe salt and a Co salt, or a combination of a Mn salt and a Co salt, etc.

[0018] Preferably, the Mn salt comprises any one of manganese acetate, manganese nitrate, manganese sulfate or manganese chloride, or a combination of at least two thereof, wherein typical but non-limiting examples of the combination include: a combination of manganese acetate and manganese nitrate, a combination of manganese nitrate and manganese sulfate, a combination of manganese sulfate and manganese chloride, or a combination of manganese acetate and manganese chloride, etc.

[0019] Preferably, the Ni salt comprises any one of nickel acetate, nickel nitrate, nickel sulfate or nickel chloride, or a combination of at least two thereof, wherein typical but non-limiting examples of the combination include: a combination of nickel acetate and nickel nitrate, a combination of nickel nitrate and nickel sulfate, a combination of nickel sulfate and nickel chloride, or a combination of nickel acetate and nickel chloride, etc.

[0020] Preferably, the Fe salt comprises any one of ferric acetate, ferric nitrate, ferric sulfate or ferric chloride, or a combination of at least two thereof, wherein typical but non-limiting examples of the combination include: a combination of ferric acetate and ferric nitrate, a combination of ferric nitrate and ferric sulfate, a combination of ferric sulfate and ferric chloride, or a combination of ferric acetate and ferric chloride.

[0021] Preferably, the Co salt comprises any one of cobalt acetate, cobalt nitrate, cobalt sulfate or cobalt chloride, or a combination of at least two of them, wherein typical but non-limiting examples of the combination include: a combination of cobalt acetate and cobalt nitrate, a combination of cobalt nitrate and cobalt sulfate, or a combination of cobalt sulfate and cobalt chloride, etc.

[0022] Preferably, the complexing agent comprises any one of sodium citrate, potassium citrate, ammonium citrate, ammonia water, sodium ethylenediaminetetraacetate, potassium ethylenediaminetetraacetate, ammonium ethylenediaminetetraacetate or nitrogen methyl pyrrolidone, or a combination of at least two thereof, wherein typical but non-limiting examples of the combination include: a combination of sodium citrate and potassium citrate, a combination of potassium citrate and ammonium citrate, a combination of ammonium citrate and ammonia water, a combination of ammonia water and sodium ethylenediaminetetraacetate, a combination of sodium ethylenediaminetetraacetate and potassium ethylenediaminetetraacetate, a combination of potassium ethylenediaminetetraacetate and ammonium ethylenediaminetetraacetate, or a combination of ammonium ethylenediaminetetraacetate and nitrogen methyl pyrrolidone, etc.

[0023] As a preferred technical solution of the present invention, the molar ratio of the complexing agent to the divalent metal salt solution in step (2) is 0.2 to 5:1, wherein the molar ratio can be 0.2:1, 0.5:1, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1 or 5:1, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0024] In the present invention, if the molar ratio of the complexing agent to the divalent metal salt solution is too low, the complexing effect cannot be achieved, and the precipitation rate cannot be effectively reduced, so it is not conducive to the formation of perfect crystal form and morphology of the precipitated particles; if the molar ratio of the complexing agent to the divalent metal salt solution is too high, the precipitation rate is too slow, and it is possible that no precipitation will be formed. The degree of perfection of the crystal form of the particles will affect the Na content and water content of the material.

[0025] Preferably, the mass ratio of the sodium ferrocyanide solution to the divalent metal salt solution in step (2) is 1:(0.5-1), wherein the mass ratio can be 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9 or 1:1, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0026] As a preferred technical solution of the present invention, the first mixing is carried out in a reaction kettle.

[0027] Preferably, the first mixed atmosphere is a protective gas.

[0028] Preferably, the protective gas is selected from any one of nitrogen, argon, neon or hydrogen, or a combination of at least two of them, wherein typical but non-limiting examples of the combination include: a combination of nitrogen and argon, a combination of argon and neon, or a combination of neon and hydrogen, etc.

[0029] Preferably, the temperature of the first mixing is 40-100°C, wherein the temperature may be 40°C, 50°C, 60°C, 70°C, 80°C, 90°C or 100°C, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0030] Preferably, the first mixing time is 2 to 24 hours, wherein the time can be 2 hours, 4 hours, 6 hours, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours or 24 hours, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0031] Preferably, the first mixing rate is 50-1600r / min, wherein the rate can be 50r / min, 100r / min, 200r / min, 300r / min, 400r / min, 500r / min, 600r / min, 700r / min, 800r / min, 900r / min, 1000r / min, 1100r / min, 1200r / min, 1300r / min, 1400r / min, 1500r / min or 1600r / min, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0032] Preferably, the pH value of the first mixture is 6.0-10.0, wherein the pH value may be 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5 or 10.0, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0033] As a preferred technical solution of the present invention, the aging time is 2 to 48 hours, wherein the time can be 2h, 4h, 5h, 10h, 15h, 20h, 25h, 30h, 35h, 40h, 45h or 48h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0034] Preferably, the Prussian white analog precursor is obtained by washing after aging.

[0035] As a preferred technical solution of the present invention, the boron source in step (2) is selected from any one of sodium borohydride, potassium borohydride, ammonium borohydride, sodium borate, potassium borate or ammonium borate, or a combination of at least two of them, wherein typical but non-limiting examples of the combination include: a combination of sodium borohydride and potassium borohydride, a combination of potassium borohydride and ammonium borohydride, a combination of ammonium borohydride and sodium borate, a combination of sodium borate and potassium borate, or a combination of potassium borate and ammonium borate, etc.

[0036] Preferably, the metal salt solution in step (2) is a soluble metal salt solution that forms metal borides.

[0037] Preferably, the metal type in the metal salt solution is selected from any one of Co, Ni, Mn, Al, Zr, La, Fe, Cu, Mg, Ca, Ti, V, Cr, Y, Mo or W.

[0038] Preferably, the metal salt solution comprises any one of sulfate, nitrate, chloride, acetate or oxide, or a combination of at least two thereof, wherein typical but non-limiting examples of the combination include: a combination of sulfate and nitrate, a combination of nitrate and chloride, a combination of chloride and acetate, or a combination of acetate and oxide, etc.

[0039] Preferably, the molar ratio of the metal boride formed by the metal salt solution and the boron source to the Prussian white analog precursor is 0.1-10%:1, wherein the molar ratio can be 0.1%:1, 1%:1, 2%:1, 3%:1, 4%:1, 5%:1, 6%:1, 7%:1, 8%:1, 9%:1 or 10%:1, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0040] In the present invention, if the molar ratio of the metal boride formed by the metal salt solution and the boron source to the Prussian white analog precursor is too high, the coating layer will be too thick, because the boride in the coating layer is inactive and will seriously affect the electrochemical capacity of the material; if the molar ratio is too low, the coating layer will be too thin and will not achieve the coating effect.

[0041] As a preferred technical solution of the present invention, the temperature of the second mixing in step (2) is 0-100°C, wherein the temperature can be 0°C, 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C or 100°C, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0042] Preferably, the time for the second mixing in step (2) is 0.5 to 24 h, wherein the time can be 0.5 h, 2 h, 4 h, 6 h, 8 h, 10 h, 12 h, 14 h, 16 h, 18 h, 20 h, 22 h or 24 h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0043] Preferably, the rate of the second mixing in step (2) is 50-1600 r / min, wherein the rate can be 50 r / min, 100 r / min, 200 r / min, 300 r / min, 400 r / min, 500 r / min, 600 r / min, 700 r / min, 800 r / min, 900 r / min, 1000 r / min, 1100 r / min, 1200 r / min, 1300 r / min, 1400 r / min, 1500 r / min or 1600 r / min, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0044] Preferably, the drying equipment in step (2) includes any one of a blast oven, a vacuum oven, a muffle furnace, a tube furnace or a microwave oven.

[0045] Preferably, the drying temperature in step (2) is 150-250°C, wherein the temperature can be 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C or 250°C, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0046] Preferably, the drying time in step (2) is 1 to 30 hours, wherein the time can be 1 hour, 5 hours, 10 hours, 15 hours, 20 hours, 25 hours or 30 hours, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0047] As a preferred technical solution of the present invention, the preparation method comprises the following steps:

[0048] (1) mixing a sodium ferrocyanide solution, a divalent metal salt solution and a complexing agent solution for the first time, and then aging to obtain a Prussian white analog precursor, wherein the first mixing temperature is 40 to 100° C., the time is 2 to 24 hours, the speed is 50 to 1600 r / min and the pH value is 6.0 to 10.0;

[0049] (2) Adding a boron source and a metal salt solution to the Prussian white analog precursor of step (1) for a second mixing, and then drying to obtain the positive electrode material, wherein the second mixing temperature is 0 to 100° C., the time is 0.5 to 24 h, and the rate is 50 to 1600 r / min, and the drying temperature is 150 to 250° C. and the time is 1 to 30 h.

[0050] The third object of the present invention is to provide an application of the positive electrode material as described in the first object, wherein the positive electrode material is applied in the field of sodium ion batteries.

[0051] Compared with the prior art, the present invention has the following beneficial effects:

[0052] (1) The positive electrode material prepared by the present invention has excellent electrochemical properties. When assembled into a button cell and subjected to charge and discharge tests at 0.2C, the first discharge specific capacity can reach more than 140 mAh / g of its theoretical capacity, the average discharge voltage is above 3.2V, the specific capacity at 10C is above 120 mAh / g, and the capacity retention rate can reach more than 70% after 2500 cycles at 10C.

[0053] (2) The preparation process of the positive electrode material of the present invention has a short process flow and simple operation, and is suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 This is an X-ray instrument test image of the positive electrode material in Example 1 of the present invention.

[0055] Figure 2 1 is a scanning electron microscope image of the positive electrode material in Example 1 of the present invention.

[0056] Figure 3 It is the charge and discharge curve of the positive electrode material at 0.2C in Example 1 of the present invention.

[0057] Figure 4 It is the charge and discharge curve of the positive electrode material in Example 1 of the present invention at 10C.

[0058] Figure 5 It is the cycle performance of the positive electrode material in Example 1 of the present invention at 10C. DETAILED DESCRIPTION

[0059] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only used to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0060] Example 1

[0061] This embodiment provides a positive electrode material, which includes a core and a coating layer, wherein the core is Na with a rhombohedral phase structure. 2 MnFeCN 6 The coating layer is boride metal Co 1.45 B.

[0062] This embodiment also provides a method for preparing the above-mentioned positive electrode material, and the preparation method comprises the following steps:

[0063] (1) 1M sodium ferrocyanide solution, 1M manganese sulfate solution and sodium ethylenediaminetetraacetate solution were added to a reaction kettle at a ratio of 1:1:1, and nitrogen was introduced to prevent oxidation. The temperature was raised to 70°C, stirred for 12 hours, the speed was 600 r / min, and the pH value of the reaction was maintained at 6.5. After the reaction was completed, the slurry was aged for 12 hours and washed with clean water to obtain the Prussian white analog precursor.

[0064] (2) The obtained Prussian white analog precursor is placed in a reaction container, and sodium borohydride and cobalt nitrate solution are slowly added at the same time. The molar ratio of cobalt boride and Prussian white analog precursor is 3%:1. The reaction temperature is room temperature, stirred for 5 hours, and the stirring paddle speed is 600r / min. Finally, the coated Prussian white precursor is dried in a vacuum drying oven at 200°C for 12 hours to obtain the desired rhombohedral phase Prussian white analog positive electrode material.

[0065] In this example, an X-ray machine was used to irradiate the prepared Na 2 MnFeCN 6 @Co 1.45 B positive electrode material is subjected to XRD analysis, and the test results are as follows Figure 1 As shown in the figure, it can be seen that the diffraction peaks of the prepared material correspond one to one with the standard spectrum, and the crystallinity is good, indicating that the obtained Prussian white positive electrode material has a rhombohedral phase structure.

[0066] The prepared Na 2 MnFeCN 6 @Co 1.45 The surface morphology of the positive electrode B was analyzed, and the test results were as follows Figure 2 As shown in the figure, it can be seen that the prepared material has a cubic morphology, the particle size is about 500nm, and amorphous Co 1.45 B coating layer.

[0067] Example 2

[0068] This embodiment provides a positive electrode material, which includes a core and a coating layer, wherein the core is Na with a rhombohedral phase structure. 2 FeFeCN 6 The coating layer is a boride metal La 0.17 B.

[0069] This embodiment also provides a method for preparing the above-mentioned positive electrode material, and the preparation method comprises the following steps:

[0070] (1) 0.5M sodium ferrocyanide solution, 0.5M ferrous sulfate solution and sodium citrate solution were added to a reaction kettle at a ratio of 1:1:2, and argon was introduced to prevent oxidation. The temperature was raised to 60°C, stirred for 24 hours, the rotation speed was 1000 r / min, and the pH value of the reaction was maintained at 8. After the reaction was completed, the slurry was aged for 24 hours and washed with clean water to obtain the Prussian white analog precursor.

[0071] (2) The obtained Prussian white analog precursor is placed in a reaction container, and sodium borohydride and lanthanum nitrate solution are slowly added at the same time. The molar ratio of lanthanum borohydride and Prussian white analog precursor is 5%:1. The reaction temperature is room temperature, stirred for 1 hour, the stirring paddle speed is 1000r / min, and finally washed clean. Finally, the above-mentioned coated Prussian white precursor is dried at 200°C in a tube furnace filled with argon for 24 hours to obtain the desired rhombohedral phase Prussian white analog positive electrode material.

[0072] Example 3

[0073] This embodiment provides a positive electrode material, which includes a core and a coating layer, wherein the core is Na with a rhombohedral phase structure. 2 CoFeCN 6 , the coating layer is metal boride NiB.

[0074] This embodiment also provides a method for preparing the above-mentioned positive electrode material, the preparation method comprising:

[0075] (1) 2M sodium ferrocyanide solution, 2M cobalt nitrate solution and ammonia solution were added to a reaction kettle at a ratio of 1:1:0.5, and argon was introduced to prevent oxidation. The temperature was raised to 80°C, stirred for 24 hours, the rotation speed was 800 r / min, and the pH value of the reaction was maintained at 7. After the reaction was completed, the slurry was aged for 48 hours and washed with clean water to obtain the Prussian white analog precursor.

[0076] (2) The obtained Prussian white analog precursor is placed in a reaction container, and boric acid and nickel nitrate solution are slowly added at the same time. The molar ratio of nickel boride and Prussian white analog precursor is 1%:1. The reaction temperature is room temperature, stirred for 0.5h, the stirring paddle speed is 800r / min, and finally washed clean. Finally, the above-mentioned coated Prussian white precursor is dried at 160°C in a muffle furnace filled with argon for 15h to obtain the desired rhombohedral phase Prussian white analog positive electrode material.

[0077] Example 4

[0078] This embodiment provides a positive electrode material, which includes a core and a coating layer, wherein the core is Na with a rhombohedral phase structure. 2 MnFeCN 6 The coating layer is boride metal Zr 0.5 B.

[0079] This embodiment also provides a method for preparing the above-mentioned positive electrode material, the preparation method comprising:

[0080] (1) 2M sodium ferrocyanide solution, 2M manganese sulfate solution and nitrogen methyl pyrrolidone were added to a reaction kettle at a ratio of 1:1:1, and nitrogen was introduced to prevent oxidation. The temperature was raised to 80°C, stirred for 24 hours, the rotation speed was 1000 r / min, and the pH value of the reaction was maintained at 8. After the reaction was completed, the slurry was aged for 12 hours and washed with clean water to obtain the Prussian white analog precursor.

[0081] (2) The obtained Prussian white analog precursor is placed in a reaction container, and sodium borohydride and zirconium nitrate solution are slowly added at the same time. The molar ratio of zirconium boride and Prussian white analog precursor is 7%:1. The reaction temperature is room temperature, stirred for 10 hours, the stirring paddle speed is 600r / min, and finally washed clean. Finally, the above-mentioned coated Prussian white precursor is dried at 180°C in a vacuum drying oven for 12 hours to obtain the desired rhombohedral phase Prussian white analog positive electrode material.

[0082] Example 5

[0083] This embodiment provides a positive electrode material, which includes a core and a coating layer, wherein the core is Na with a rhombohedral phase structure. 2 FeFeCN 6 The coating layer is boride metal Mn 1.1 B.

[0084] This embodiment also provides a method for preparing the above-mentioned positive electrode material, the preparation method comprising:

[0085] (1) 2M sodium ferrocyanide solution, 2M ferrous chloride solution and citric acid solution were added to a reaction kettle at a ratio of 1:1:1, and argon was introduced to prevent oxidation. The temperature was raised to 60°C, stirred for 24 hours, the rotation speed was 1200 r / min, and the pH value of the reaction was maintained at 7. After the reaction was completed, the slurry was aged for 24 hours and washed with clean water to obtain the Prussian white analog precursor.

[0086] (2) The obtained Prussian white analog precursor is placed in a reaction container, and sodium borohydride and manganese nitrate solution are slowly added at the same time. The molar ratio of manganese boride and the Prussian white analog precursor is 5%:1. The reaction temperature is room temperature, stirred for 20 hours, and the stirring paddle speed is 1200r / min. Finally, the coated Prussian white precursor is dried in a vacuum drying oven at 200°C for 20 hours to obtain the desired rhombohedral phase Prussian white analog positive electrode material.

[0087] Comparative Example 1

[0088] This comparative example provides a positive electrode material, wherein the positive electrode material is Na 2 MnFeCN 6 .

[0089] In this comparative example, 1M sodium ferrocyanide solution, 1M manganese sulfate solution and sodium ethylenediaminetetraacetate solution were added to the reactor at a ratio of 1:1:1, and nitrogen was introduced to prevent oxidation. The temperature was raised to 70°C, stirred for 12 hours, the speed was 800r / min, and the pH value of the reaction was maintained at 6.5. After the reaction was completed, the slurry was aged for 12 hours, and washed with clean water to obtain the precursor of the Prussian white analog. Finally, the uncoated Prussian white precursor was dried at 200°C in a vacuum drying oven for 12 hours to obtain the rhombohedral phase Prussian white analog positive electrode material for comparison.

[0090] Comparative Example 2

[0091] This comparative example provides a positive electrode material, wherein the positive electrode material is Na 2 MnFeCN 6 @AlPO 4 .

[0092] (1) In this embodiment, 1M sodium ferrocyanide solution, 1M manganese sulfate solution and sodium ethylenediaminetetraacetate solution were added to the reaction kettle at a ratio of 1:1:1, and nitrogen was introduced to prevent oxidation. The temperature was raised to 70°C, stirred for 12 hours, the rotation speed was 600 r / min, and the pH value of the reaction was maintained at 6.5. After the reaction was completed, the slurry was aged for 12 hours and washed with clean water to obtain the Prussian white analog precursor.

[0093] (2) The obtained Prussian white analog precursor is placed in a reaction container, and aluminum nitrate and ammonium dihydrogen phosphate solution are slowly added at the same time. The molar ratio of aluminum phosphate to the Prussian white analog precursor is 3%:1. The reaction temperature is room temperature, stirred for 1 hour, the stirring paddle speed is 600r / min, and finally washed clean. Finally, the above-mentioned coated Prussian white precursor is dried in a vacuum drying oven at 200°C for 12 hours to obtain an aluminum phosphate-coated rhombohedral phase Prussian white analog positive electrode material.

[0094] Comparative Example 3

[0095] This comparative example provides a positive electrode material, wherein the positive electrode material is Na 1.5 Mn(FeCN 6 ) 0.94 2.11H 2 O.

[0096] In this comparative example, 1M sodium ferrocyanide solution, 1M manganese sulfate solution and sodium ethylenediaminetetraacetate solution were added to the reactor at a ratio of 1:1:1, and nitrogen was introduced to prevent oxidation. The temperature was raised to 70°C, stirred for 12 hours, the speed was 600r / min, and the pH value of the reaction was maintained at 6.5. After the reaction was completed, the slurry was aged for 12 hours, and washed with clean water to obtain the precursor of the Prussian white analog. Finally, the above-mentioned Prussian white precursor was dried in an ordinary oven at 120°C for 12 hours to obtain a monoclinic or cubic Prussian white analog positive electrode material.

[0097] The positive electrode materials prepared in the above Examples 1-5 and Comparative Examples 1-3 were assembled into batteries to test the electrochemical performance:

[0098] Battery preparation method:

[0099] (1) Preparation of battery positive electrode sheet: The prepared Prussian white analog positive electrode material, Ketjen black, and polytetrafluoroethylene binder were ground and mixed in a mass ratio of 7:2:1, and then fully rolled with a double roller mill to form a film of uniform thickness. After drying in a vacuum drying oven at 120°C for 5 hours, the obtained positive electrode film was cut into square electrode sheets with a side length of about 6 mm. After accurately weighing its mass, the mass of the active material in the positive electrode sheet was calculated according to the formula composition.

[0100] (2) Battery assembly:

[0101] The above-obtained square positive electrode sheet, a 16 mm diameter separator, a 15 mm diameter sodium sheet, a spring and a gasket were assembled into a 2032-type testable button cell in a glove box (oxygen content less than 0.01 ppm, water content less than 0.01 ppm).

[0102] Electrochemical performance test:

[0103] The assembled batteries of Examples 1-5 and Comparative Examples 1-3 were subjected to charge and discharge tests at various rates using a BlueDian battery testing system.

[0104] Using Na prepared in Example 1 of the present invention 2 MnFeCN 6 @Co 1.45 The positive electrode B is assembled into a button cell, and its first discharge capacity is 160mAh / g, and the discharge medium voltage is 3.5V ( Figure 3 ), the specific capacity of 10C is 130mAh / g( Figure 4 ), the retention rate is 86% (compared to 0.2C), and the capacity retention rate can reach 74% ( Figure 5 ). It can be seen that the prepared Na 2 MnFeCN 6 @Co x B cathode material has excellent electrochemical properties.

[0105] Table 1

[0106]

[0107]

[0108] It can be seen from the above table that: By comparing Examples 1 to 5, it can be seen that the Prussian white analogue positive electrode materials obtained by the preparation method provided by the present invention all show good electrochemical performance (half-electric), and their first discharge specific capacity can reach 140 mA hg -1 Above, the specific capacity of 10C exceeds 120mA hg -1 , the retention rate exceeds 70% after 2500 cycles.

[0109] By comparing Example 1 with Comparative Example 1, it can be seen that without the metal boride coating, the rate performance and cycle performance of the material are significantly deteriorated.

[0110] By comparing Example 1, Comparative Example 1 and Comparative Example 2, it can be seen that the metal boride has obvious advantages over the coating without a coating layer and the electronic insulator aluminum phosphate coating layer, so the rate performance and cycle performance are the best.

[0111] Comparing Comparative Example 1 and Comparative Example 3, it can be seen that since the crystal water in Comparative Example 3 was not fully removed, only a monoclinic or cubic phase of Prussian blue material was obtained, and its discharge capacity and voltage were worse than those of the rhombic structured Prussian white analog positive electrode.

[0112] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a positive electrode material, It is characterized in that The positive electrode material comprises a core and a coating layer, wherein the core is Na with a rhombohedral phase structure. 2-x M(FeCN 6 ) 1-y The coating layer is a boride metal A z B, where 0≤x≤0.5, 0≤y≤0.2, and M is selected from Mn 2+ , Fe 2+ 、Co 2+ 、Ni 2+ At least one of the following, A is selected from any one of Co, Ni, Mn, Al, Zr, La, Fe, Cu, Mg, Ca, Ti, V, Cr, Y, Mo or W, 0 <z≤2; The preparation method comprises the following steps: (1) first mixing a sodium ferrocyanide solution, a divalent metal salt solution and a complexing agent, and then aging the mixture to obtain a Prussian white analog precursor; (2) Adding a boron source and a metal salt solution to the Prussian white analog precursor of step (1) for a second mixing, and then drying to obtain the positive electrode material.

2. The preparation method according to claim 1, It is characterized in that The concentration of the sodium ferrocyanide solution in step (1) is 0.1-2 mol / L.

3. The preparation method according to claim 1, It is characterized in that The concentration of the divalent metal salt solution in step (1) is 0.1-2 mol / L.

4. The preparation method according to claim 1, It is characterized in that The divalent metal salt solution in step (1) includes any one of Mn salt, Ni salt, Fe salt or Co salt, or a combination of at least two of them.

5. The preparation method according to claim 4, It is characterized in that The Mn salt includes any one of manganese acetate, manganese nitrate, manganese sulfate or manganese chloride, or a combination of at least two thereof.

6. The preparation method according to claim 4, It is characterized in that The Ni salt includes any one of nickel acetate, nickel nitrate, nickel sulfate or nickel chloride, or a combination of at least two thereof.

7. The preparation method according to claim 4, It is characterized in that The Fe salt includes any one of ferric acetate, ferric nitrate, ferric sulfate or ferric chloride, or a combination of at least two thereof.

8. The preparation method according to claim 4, It is characterized in that The Co salt includes any one of cobalt acetate, cobalt nitrate, cobalt sulfate or cobalt chloride, or a combination of at least two thereof.

9. The preparation method according to claim 1, It is characterized in that The complexing agent includes any one of sodium citrate, potassium citrate, ammonium citrate, ammonia water, sodium ethylenediaminetetraacetate, potassium ethylenediaminetetraacetate, ammonium ethylenediaminetetraacetate or nitrogen methyl pyrrolidone, or a combination of at least two thereof.

10. The preparation method according to claim 1, It is characterized in that The molar ratio of the complexing agent to the divalent metal salt solution in step (2) is 0.2-5:

1.

11. The preparation method according to claim 1, It is characterized in that The molar ratio of the sodium ferrocyanide solution to the divalent metal salt solution in step (2) is 1:(0.5-1).

12. The preparation method according to claim 1, It is characterized in that The first mixing is performed in a reaction vessel.

13. The preparation method according to claim 1, It is characterized in that The first mixed atmosphere is a protective gas.

14. The preparation method according to claim 13, It is characterized in that The protective gas is selected from any one of nitrogen, argon, neon or hydrogen, or a combination of at least two of them.

15. The preparation method according to claim 1, It is characterized in that The temperature of the first mixing is 40-100°C.

16. The preparation method according to claim 1, It is characterized in that The first mixing time is 2 to 24 hours.

17. The preparation method according to claim 1, It is characterized in that The first mixing rate is 50-1600 r / min.

18. The preparation method according to claim 1, It is characterized in that The pH value of the first mixture is 6.0-10.

0.

19. The preparation method according to claim 1, It is characterized in that The aging time is 2 to 48 hours.

20. The preparation method according to claim 1, It is characterized in that The aging and washing process is performed to obtain the Prussian white analog precursor.

21. The preparation method according to claim 1, It is characterized in that The boron source in step (2) is selected from any one of sodium borohydride, potassium borohydride, ammonium borohydride, sodium borate, potassium borate or ammonium borate, or a combination of at least two thereof.

22. The preparation method according to claim 1, It is characterized in that The metal salt solution in step (2) is a soluble metal salt solution that forms metal borides.

23. The preparation method according to claim 1, It is characterized in that The metal type in the metal salt solution is selected from any one of Co, Ni, Mn, Al, Zr, La, Fe, Cu, Mg, Ca, Ti, V, Cr, Y, Mo or W.

24. The preparation method according to claim 1, It is characterized in that The metal salt solution includes any one of sulfate, nitrate, chloride or acetate, or a combination of at least two of them.

25. The preparation method according to claim 1, It is characterized in that The molar ratio of the metal boride formed by the metal salt solution and the boron source to the Prussian white analog precursor is 0.1-10%:

1.

26. The preparation method according to claim 1, It is characterized in that The temperature of the second mixing in step (2) is 0-100°C.

27. The preparation method according to claim 1, It is characterized in that The second mixing time in step (2) is 0.5 to 24 hours.

28. The preparation method according to claim 1, It is characterized in that The second mixing rate in step (2) is 50-1600 r / min.

29. The preparation method according to claim 1, It is characterized in that The drying equipment in step (2) includes any one of a blast oven, a vacuum oven, a muffle furnace, a tube furnace or a microwave oven.

30. The preparation method according to claim 1, It is characterized in that The drying temperature in step (2) is 150-250°C.

31. The preparation method according to claim 1, It is characterized in that The drying time in step (2) is 1 to 30 hours.

32. The preparation method according to claim 1, It is characterized in that The preparation method comprises the following steps: (1) mixing a sodium ferrocyanide solution, a divalent metal salt solution and a complexing agent solution for the first time, and then aging to obtain a Prussian white analog precursor, wherein the first mixing temperature is 40-100° C., the time is 2-24 h, the speed is 50-1600 r / min and the pH value is 6.0-10.0; (2) Adding a boron source and a metal salt solution to the Prussian white analog precursor of step (1) for a second mixing, and then drying to obtain the positive electrode material, wherein the second mixing temperature is 0-100° C., the time is 0.5-24 h, and the rate is 50-1600 r / min, and the drying temperature is 150-250° C. and the time is 1-30 h.

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