Core-shell-type sodium-ion battery positive electrode material, and preparation method therefor and use thereof

Abstract

A core-shell-type sodium-ion battery positive electrode material, and a preparation method therefor and the use thereof. The positive electrode material comprises a nickel-iron-manganese inner core and a zinc-magnesium co-doped outer shell. The preparation method comprises: (1) mixing a nickel salt, a ferric salt, a manganese salt and deionized water, so as to obtain a first metal salt solution; (2) mixing a zinc salt, a magnesium salt and deionized water, so as to obtain a second metal salt solution; (3) adding the first metal salt solution, a precipitant solution and a complexing agent solution into a base solution in a parallel flow manner to perform a co-precipitation reaction, so as to obtain a nickel-iron-manganese inner core precursor; (4) replacing the first metal salt solution with a second metal salt solution, and continuously performing a co-precipitation reaction, so as to obtain a precursor; and (5) mixing the core-shell-type sodium-ion battery precursor and a sodium source, and sintering the mixture, so as to obtain a positive electrode material, wherein microwave-assisted heating is used for both the co-precipitation reactions. The preparation method simplifies the synthesis process, improves the production efficiency, and further improves the electrochemical performance of the material.

Description

A core-shell sodium-ion battery cathode material, its preparation method and application Technical Field

[0001] This application belongs to the field of battery manufacturing technology, and relates to a sodium-ion battery cathode material, and more particularly to a core-shell sodium-ion battery cathode material and its preparation method and application. Background Technology

[0002] Core-shell structured sodium-ion battery cathode materials have been extensively studied and developed due to their unique advantages. The core-shell structure can enhance the structural stability of the material. In particular, during the charging and discharging process, the shell layer can suppress the volume expansion and structural degradation of the core material. At the same time, the core-shell structure helps to improve the conductivity and ion diffusion rate of the material, thereby improving the charging and discharging efficiency and rate performance of sodium-ion batteries.

[0003] The development of core-shell sodium-ion battery cathode materials requires comprehensive consideration of material composition, structure, preparation process, and electrochemical performance to achieve a comprehensive improvement in sodium-ion battery performance. For example, CN117727938A discloses a sodium-ion battery cathode material and its preparation method that can be used for fast charging. This material is a core-shell composite cathode material, with the core layer being a nickel-manganese-based layered oxide cathode material (Na). 0.67 Ni x Mn y Mg z O2, with BNT as the shell material; firstly, a cathode material precursor is prepared using a co-precipitation method, and then the surface of the obtained precursor is coated with BNT using wet ball milling. This effectively suppresses the volume expansion and structural stress of the cathode material during charge and discharge, thereby improving structural stability and extending cycle life. However, the additional coating step makes the entire synthesis process more complex, leading to low production efficiency. Furthermore, the wet ball milling process makes it difficult to achieve uniform coating of BNT on the precursor surface, thus affecting the performance of the final product. The ball milling process also causes some mechanical damage to the precursor, which in turn affects its crystal structure and electrochemical performance.

[0004] Therefore, how to provide a core-shell sodium-ion battery cathode material and its preparation method, simplify the synthesis process, improve production efficiency, and further improve the electrochemical performance of the material has become an urgent problem to be solved by those skilled in the art.

[0005] Summary of the Invention

[0006] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of the claims.

[0007] This application provides a core-shell sodium-ion battery cathode material, its preparation method, and its application. By co-doping the outer shell with zinc and magnesium and using microwave-assisted heating for co-precipitation reaction, the synthesis process is simplified, production efficiency is improved, and the electrochemical performance of the material is enhanced, which is conducive to large-scale application.

[0008] In a first aspect, this application provides a core-shell sodium-ion battery cathode material, the core-shell sodium-ion battery cathode material comprising a nickel-iron-manganese core and a zinc-magnesium co-doped shell.

[0009] The molar ratio of all metal elements in the nickel-iron-manganese core to all metal elements in the zinc-magnesium co-doped shell is (95-99.7):(0.3-5), for example, it can be 95:5, 95.5:4.5, 96:4, 96.5:3.5, 97:3, 97.5:2.5, 98:2, 98.5:1.5, 99:1, 99.5:0.5 or 99.7:0.3, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0010] In this application, all metal elements in the nickel-iron-manganese core specifically refer to the sum of nickel, iron, and manganese elements, and all metal elements in the zinc-magnesium co-doped shell specifically refer to the sum of zinc and magnesium elements.

[0011] The core-shell sodium-ion battery cathode material provided in this application uses nickel-iron-manganese as the core and zinc-magnesium co-doping on the shell. The zinc and magnesium elements in the shell help optimize the crystal structure in the cathode material, improve the energy density, power density and cycle stability of the material, and enable the battery to have a longer service life and higher energy output.

[0012] In addition, the nickel-iron-manganese core has a high operating voltage platform, which helps to improve the energy density of the battery. The zinc-magnesium co-doped shell improves the stability of the overall structure and alleviates the volume expansion and structural degradation during charging and discharging, thereby reducing the performance degradation caused by structural changes during charging and discharging. At the same time, the zinc-magnesium co-doped shell alleviates the dissolution of the nickel-iron-manganese core in the electrolyte, further improving the long-term stability of the battery and enhancing its competitiveness in the market.

[0013] In one embodiment, the molar ratio of nickel, iron and manganese in the nickel-iron-manganese core is (0.8-1.2):(0.8-1.2):1, for example, it can be 0.8:1.2:1, 0.9:1.1:1, 1:1:1, 1.1:0.9:1 or 1.2:0.8:1, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0014] In one embodiment, the molar ratio of zinc to magnesium in the zinc-magnesium co-doped shell is (0.8-1.2):1, for example, it can be 0.8:1, 0.9:1, 1:1, 1.1:1 or 1.2:1, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0015] Secondly, this application provides a method for preparing a core-shell sodium-ion battery cathode material as described in the first aspect, the method comprising the following steps:

[0016] (1) Mix nickel salt, iron salt, manganese salt and deionized water to obtain a first metal salt solution;

[0017] (2) Mix zinc salt, magnesium salt and deionized water to obtain a second metal salt solution;

[0018] (3) The first metal salt solution, precipitant solution and complexing agent solution were added to the bottom liquid in parallel to carry out a co-precipitation reaction to obtain the nickel-iron-manganese core precursor.

[0019] (4) Replace the first metal salt solution in step (3) with the second metal salt solution, and keep all other conditions unchanged, and continue the co-precipitation reaction to obtain the core-shell sodium-ion battery precursor.

[0020] (5) The core-shell sodium-ion battery precursor and sodium source are sintered to obtain the core-shell sodium-ion battery cathode material.

[0021] In this process, steps (1) and (2) are not in any particular order; the coprecipitation reactions described in steps (3) and (4) are both performed using microwave-assisted heating.

[0022] This application employs microwave-assisted heating for co-precipitation reaction, which can achieve rapid heating by controlling the temperature rise program. This allows for the preparation of core-shell sodium-ion battery cathode materials in a short time, simplifying the synthesis process and improving production efficiency.

[0023] In addition, microwave radiation can penetrate materials and generate heat inside them, which helps to achieve more uniform heating and reaction. It effectively avoids defects such as intracrystalline segregation, vacancies, and compositional inhomogeneity caused by local overheating of the precursor during co-precipitation. The resulting precursor has a more complete crystal structure, which significantly improves the particle size uniformity and tap density of the material, and further improves the electrochemical performance of the material.

[0024] In one embodiment, the nickel salt, iron salt and manganese salt in step (1) are any one or at least two of the sulfate, nitrate or chloride salts of the corresponding metal ions. Typical but non-limiting combinations include combinations of sulfate and nitrate, nitrate and chloride, sulfate and chloride, or sulfate, nitrate and chloride.

[0025] In one embodiment, the total concentration of metal ions in the first metal salt solution in step (1) is 0.5-10 mol / L, for example, it can be 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, 5 mol / L, 5.5 mol / L, 6 mol / L, 6.5 mol / L, 7 mol / L, 7.5 mol / L, 8 mol / L, 8.5 mol / L, 9 mol / L, 9.5 mol / L or 10 mol / L, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0026] In one embodiment, the zinc salt and magnesium salt in step (2) are any one or at least two of the sulfate, nitrate or chloride salts of the corresponding metal ions. Typical but non-limiting combinations include combinations of sulfate and nitrate, nitrate and chloride, sulfate and chloride, or sulfate, nitrate and chloride.

[0027] In one embodiment, the total concentration of metal ions in the second metal salt solution in step (2) is 0.5-10 mol / L, for example, it can be 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, 5 mol / L, 5.5 mol / L, 6 mol / L, 6.5 mol / L, 7 mol / L, 7.5 mol / L, 8 mol / L, 8.5 mol / L, 9 mol / L, 9.5 mol / L or 10 mol / L, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0028] In one embodiment, the precipitant solution in step (3) comprises a sodium hydroxide solution and / or a sodium carbonate solution.

[0029] In one embodiment, the concentration of the precipitant solution in step (3) is 7-12 mol / L, for example, it can be 7 mol / L, 7.5 mol / L, 8 mol / L, 8.5 mol / L, 9 mol / L, 9.5 mol / L, 10 mol / L, 10.5 mol / L, 11 mol / L, 11.5 mol / L or 12 mol / L, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0030] In one embodiment, the complexing agent solution in step (3) comprises ammonia.

[0031] In one embodiment, the concentration of the complexing agent solution in step (3) is 4-8 mol / L, for example, it can be 4 mol / L, 4.5 mol / L, 5 mol / L, 5.5 mol / L, 6 mol / L, 6.5 mol / L, 7 mol / L, 7.5 mol / L or 8 mol / L, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0032] In one embodiment, the base liquid in step (3) is a mixture of a precipitant solution and a complexing agent solution.

[0033] In one embodiment, the pH value of the base solution in step (3) is 8.0-12.0, for example, it can be 8.0, 8.5, 9.0, 9.5, 10.0, 10.5, 11.0, 11.5 or 12.0, and the ammonia concentration is 1-100 g / L, for example, it can be 1 g / L, 5 g / L, 10 g / L, 15 g / L, 20 g / L, 25 g / L, 30 g / L, 35 g / L, 40 g / L, 45 g / L, 50 g / L, 55 g / L, 60 g / L, 65 g / L, 70 g / L, 75 g / L, 80 g / L, 85 g / L, 90 g / L, 95 g / L or 100 g / L, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0034] In one embodiment, the feed rate of the first metal salt solution in step (3) is 2-500 L / h, for example, it can be 2 L / h, 10 L / h, 50 L / h, 100 L / h, 150 L / h, 200 L / h, 250 L / h, 300 L / h, 350 L / h, 400 L / h, 450 L / h or 500 L / h, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0035] In one embodiment, the feed rate of the precipitant solution in step (3) is 1-500 L / h, for example, it can be 1 L / h, 5 L / h, 10 L / h, 15 L / h, 20 L / h, 25 L / h, 30 L / h, 35 L / h, 40 L / h, 45 L / h, 50 L / h, 60 L / h, 70 L / h, 80 L / h, 90 L / h, 100 L / h, 200 L / h, 300 L / h, 400 L / h or 500 L / h, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0036] In one embodiment, the feed rate of the complexing agent solution in step (3) is 0.01-500 L / h, for example, it can be 0.01 L / h, 0.1 L / h, 1 L / h, 10 L / h, 50 L / h, 100 L / h, 150 L / h, 200 L / h, 250 L / h, 300 L / h, 350 L / h, 400 L / h, 450 L / h or 500 L / h, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0037] In one embodiment, the coprecipitation reaction described in step (3) is carried out for a total of 0.2-30 hours before step (4) is performed. For example, the coprecipitation reaction can be 0.2 hours, 2 hours, 4 hours, 6 hours, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, 24 hours, 26 hours, 28 hours, or 30 hours, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0038] In one embodiment, the feed rate of the second metal salt solution in step (4) is 0.02-100 L / h, for example, it can be 0.02 L / h, 0.5 L / h, 5 L / h, 10 L / h, 15 L / h, 20 L / h, 25 L / h, 30 L / h, 35 L / h, 40 L / h, 45 L / h, 50 L / h, 55 L / h, 60 L / h, 65 L / h, 70 L / h, 75 L / h, 80 L / h, 85 L / h, 90 L / h, 95 L / h or 100 L / h, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0039] In one embodiment, the coprecipitation reactions in steps (3) and (4) are carried out in a protective gas atmosphere, and the protective gas includes any one or at least two of nitrogen, helium or argon. Typical but non-limiting combinations include combinations of nitrogen and helium, helium and argon, nitrogen and argon, or nitrogen, helium and argon.

[0040] In one embodiment, the temperature of the coprecipitation reaction in steps (3) and (4) is 15-70°C, for example, it can be 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C or 70°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0041] In one embodiment, the coprecipitation reactions in steps (3) and (4) are both performed using microwave-assisted heating. The microwave-assisted heating is pulsed heating, which includes controlling the power, heating time and heating interval of the microwave-assisted heating using a heating program.

[0042] In one embodiment, the power is 300-1000W, for example, it can be 300W, 350W, 400W, 450W, 500W, 550W, 600W, 650W, 700W, 750W, 800W, 850W, 900W, 950W or 1000W, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0043] In one embodiment, the heating time is 0.5-100 min, for example, it can be 0.5 min, 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min, 65 min, 70 min, 75 min, 80 min, 85 min, 90 min, 95 min or 100 min, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0044] In one embodiment, the heating interval is 0.1-100 min, for example, it can be 0.1 min, 0.5 min, 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min, 65 min, 70 min, 75 min, 80 min, 85 min, 90 min, 95 min or 100 min, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0045] In one embodiment, the average particle size of the core-shell sodium-ion battery precursor in step (4) is 5-16 μm, for example, it can be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm or 16 μm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0046] In one embodiment, the core-shell sodium-ion battery precursor described in step (5) is subjected to aging, centrifugal washing and drying in sequence before sintering.

[0047] In one embodiment, the washing solution used in the centrifugal washing includes deionized water.

[0048] In one embodiment, the drying temperature is 100-200°C, for example, it can be 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C or 200°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0049] In one embodiment, the sodium source in step (5) includes sodium carbonate.

[0050] In one embodiment, the mixing molar ratio of the core-shell sodium-ion battery precursor and the sodium source in step (5) is 1:(0.8-1.2), for example, it can be 1:0.8, 1:0.9, 1:1, 1:1.02, 1:1.04, 1:1.06, 1:1.08, 1:1.1, 1:1.12, 1:1.14, 1:1.16, 1:1.18 or 1:1.2, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0051] In one embodiment, the sintering process described in step (5) is carried out in a tube furnace in an oxygen atmosphere.

[0052] In one embodiment, the sintering temperature in step (5) is 400-1000℃, for example, it can be 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, 950℃ or 1000℃, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0053] In one embodiment, the sintering time in step (5) is 4-30h, for example, it can be 4h, 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h, 24h, 26h, 28h or 30h, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0054] In one embodiment, the sintering process described in step (5) is followed by grinding and sieving.

[0055] As an optional technical solution in the second aspect of this application, the preparation method includes the following steps:

[0056] (1) Mix nickel salt, iron salt, manganese salt and deionized water to obtain a first metal salt solution with a total metal ion concentration of 0.5-10 mol / L; wherein the nickel salt, iron salt and manganese salt are any one or a combination of at least two of the sulfate, nitrate or chloride salts of the corresponding metal ions;

[0057] (2) Mix zinc salt, magnesium salt and deionized water to obtain a second metal salt solution with a total metal ion concentration of 0.5-10 mol / L; wherein the zinc salt and magnesium salt are any one or a combination of at least two of the sulfate, nitrate or chloride salts of the corresponding metal ions;

[0058] (3) A protective gas is introduced into the reactor, and the first metal salt solution, precipitant solution, and complexing agent solution are added to the bottom liquid in a co-precipitation reaction at 15-70℃. The feed rate of the first metal salt solution is controlled at 2-500 L / h, the feed rate of the precipitant solution is 1-500 L / h, and the feed rate of the complexing agent solution is 0.01-500 L / h to obtain a nickel-iron-manganese core precursor. The protective gas includes any one or a combination of at least two of nitrogen, helium, or argon. The precipitant solution includes sodium hydroxide solution and / or sodium carbonate solution with a concentration of 7-12 mol / L. The complexing agent solution includes ammonia water with a concentration of 4-8 mol / L. The bottom liquid is a mixed solution of precipitant solution and complexing agent solution with a pH value of 8.0-12.0 and an ammonia concentration of 1-100 g / L.

[0059] (4) After the co-precipitation reaction has been carried out for 0.2-30h, the first metal salt solution in step (3) is replaced with the second metal salt solution. The feed rate of the second metal salt solution is controlled at 0.2-100L / h, and the other conditions remain unchanged. The co-precipitation reaction is continued to obtain a core-shell sodium-ion battery precursor with an average particle size of 5-16μm.

[0060] (5) The core-shell sodium-ion battery precursor is successively aged, centrifuged and washed and dried. The washing liquid used for centrifugation includes deionized water. The drying temperature is 100-200℃. Then, the core-shell sodium-ion battery precursor and sodium carbonate are mixed at a molar ratio of 1:(0.8-1.2). The mixture is sintered in a tube furnace under an oxygen atmosphere at 400-1000℃ for 4-30 hours. After grinding and sieving, the core-shell sodium-ion battery cathode material is obtained.

[0061] In this process, steps (1) and (2) are not in any particular order; the coprecipitation reactions in steps (3) and (4) are all performed using microwave-assisted heating, which is pulse heating, including: using a heating program to control the power of microwave-assisted heating to 300-1000W, the heating time to 0.5-100min, and the heating interval to 0.1-100min respectively.

[0062] Thirdly, this application provides a sodium-ion battery, wherein the sodium-ion battery includes the core-shell type sodium-ion battery positive electrode material as described in the first aspect.

[0063] The numerical range described in this application includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of brevity, this application will not exhaustively list the specific point values ​​included in the range.

[0064] Compared with related technologies, the beneficial effects of this application are as follows:

[0065] (1) The core-shell sodium-ion battery cathode material provided in this application uses nickel-iron-manganese as the core and zinc-magnesium co-doping on the shell. The zinc and magnesium elements in the shell help to optimize the crystal structure in the cathode material, improve the energy density, power density and cycle stability of the material, and make the battery have a longer service life and higher energy output.

[0066] (2) The nickel-iron-manganese core has a high working voltage platform, which helps to improve the energy density of the battery. The zinc-magnesium co-doped shell improves the stability of the overall structure and alleviates the volume expansion and structural degradation during the charging and discharging process, thereby reducing the performance degradation caused by structural changes during the charging and discharging process. At the same time, the zinc-magnesium co-doped shell alleviates the dissolution of the nickel-iron-manganese core in the electrolyte, further improving the long-term stability of the battery and enhancing its competitiveness in the market.

[0067] (3) This application uses microwave-assisted heating for co-precipitation reaction, which can achieve rapid heating by controlling the temperature rise program. The preparation of core-shell sodium-ion battery cathode material can be achieved in a short time, which simplifies the synthesis process and improves production efficiency.

[0068] (4) Microwave radiation can penetrate the material and generate heat inside the material, which helps to achieve more uniform heating and reaction. It effectively avoids defects such as intracrystalline segregation, vacancies and uneven composition caused by local overheating of the precursor during the co-precipitation process. The resulting precursor has a more complete crystal structure, which significantly improves the particle size uniformity and tap density of the material and further improves the electrochemical performance of the material.

[0069] After reading and understanding the detailed description, other aspects can be understood. Detailed Implementation

[0070] The technical solution of this application will be further described below through specific implementation methods.

[0071] Example 1

[0072] This embodiment provides a core-shell sodium-ion battery cathode material and its preparation method. The core-shell sodium-ion battery cathode material includes a nickel-iron-manganese core and a zinc-magnesium co-doped shell. The molar ratio of all metal elements in the nickel-iron-manganese core to all metal elements in the zinc-magnesium co-doped shell is 97.5:2.5. The molar ratio of nickel, iron and manganese in the nickel-iron-manganese core is 1:1:1. The molar ratio of zinc to magnesium in the zinc-magnesium co-doped shell is 1:1.

[0073] In this embodiment, the preparation method of the above-mentioned core-shell sodium-ion battery cathode material includes the following steps:

[0074] (1) Mix nickel sulfate, ferric sulfate, manganese sulfate and deionized water to obtain a first metal salt solution with a total metal ion concentration of 8 mol / L;

[0075] (2) Mix zinc sulfate, magnesium sulfate and deionized water to obtain a second metal salt solution with a total metal ion concentration of 2 mol / L.

[0076] (3) Nitrogen gas is introduced into the reactor. The first metal salt solution, a 9 mol / L sodium hydroxide solution, and a 6 mol / L ammonia solution are added to the bottom liquid in parallel flow. The co-precipitation reaction is carried out at 50°C. The feed rate of the first metal salt solution is controlled at 100 L / h, the initial feed rate of the sodium hydroxide solution is 200 L / h, and the initial feed rate of the ammonia solution is 120 L / h. By adjusting the feed rates of the sodium hydroxide solution and the ammonia solution in a timely manner, the pH value of the reaction system is controlled at 11.0±0.2 and the ammonia concentration is 7±2 g / L to obtain the nickel-iron-manganese core precursor. The bottom liquid is a mixed solution of sodium hydroxide solution and ammonia solution with an initial pH value of 11.0±1 and an initial ammonia concentration of 7±5 g / L.

[0077] (4) After the co-precipitation reaction has been carried out for 10 hours, the first metal salt solution in step (3) is replaced with the second metal salt solution. The feed rate of the second metal salt solution is controlled at 50 L / h, and the other conditions remain unchanged. The co-precipitation reaction is continued to obtain a core-shell sodium-ion battery precursor with an average particle size of 16 μm.

[0078] (5) The core-shell sodium-ion battery precursor was successively aged, centrifuged and washed and dried. The washing liquid used for centrifugation was deionized water and the drying temperature was 150°C. Then, the core-shell sodium-ion battery precursor and sodium carbonate were mixed at a molar ratio of 1:1.18 and sintered at 800°C for 17 hours in a tube furnace under an oxygen atmosphere. After grinding and sieving, the core-shell sodium-ion battery cathode material was obtained.

[0079] In both steps (3) and (4), the coprecipitation reaction is carried out using microwave-assisted heating. The microwave-assisted heating is pulsed heating, which includes controlling the power of microwave-assisted heating to 600W, the heating time to 50min, and the heating interval to 30min using a temperature rise program.

[0080] Example 2

[0081] This embodiment provides a core-shell sodium-ion battery cathode material and its preparation method. The core-shell sodium-ion battery cathode material includes a nickel-iron-manganese core and a zinc-magnesium co-doped shell. The molar ratio of all metal elements in the nickel-iron-manganese core to all metal elements in the zinc-magnesium co-doped shell is 95:5. The molar ratio of nickel, iron and manganese in the nickel-iron-manganese core is 0.8:1.2:1. The molar ratio of zinc to magnesium in the zinc-magnesium co-doped shell is 0.8:1.

[0082] In this embodiment, the preparation method of the above-mentioned core-shell sodium-ion battery cathode material includes the following steps:

[0083] (1) Mix nickel nitrate, ferric nitrate, manganese nitrate and deionized water to obtain a first metal salt solution with a total metal ion concentration of 5 mol / L;

[0084] (2) Mix zinc nitrate, magnesium nitrate and deionized water to obtain a second metal salt solution with a total metal ion concentration of 10 mol / L.

[0085] (3) Argon gas is introduced into the reactor. The first metal salt solution, a sodium hydroxide solution with a concentration of 7 mol / L, and ammonia water with a concentration of 4 mol / L are added to the bottom liquid in parallel. The co-precipitation reaction is carried out at 70°C. The feed rate of the first metal salt solution is controlled at 500 L / h, the initial feed rate of the sodium hydroxide solution is 350 L / h, and the initial feed rate of the ammonia water is 50 L / h. By adjusting the feed rates of the sodium hydroxide solution and the ammonia water in a timely manner, the pH value of the reaction system is controlled at 11.0±0.2 and the ammonia concentration is 7±2 g / L to obtain the nickel-iron-manganese core precursor. The bottom liquid is a mixed solution of sodium hydroxide solution and ammonia water with an initial pH value of 11.0±1 and an initial ammonia concentration of 7±5 g / L.

[0086] (4) After the co-precipitation reaction has been carried out for 2 hours, the first metal salt solution in step (3) is replaced with the second metal salt solution. The feed rate of the second metal salt solution is controlled at 100 L / h, and the other conditions remain unchanged. The co-precipitation reaction is continued to obtain a core-shell sodium-ion battery precursor with an average particle size of 10 μm.

[0087] (5) The core-shell sodium-ion battery precursor is successively aged, centrifuged and washed and dried. The washing liquid used for centrifugation is deionized water and the drying temperature is 100℃. Then, the core-shell sodium-ion battery precursor and sodium carbonate are mixed in a molar ratio of 1:1 and sintered in a tube furnace in an oxygen atmosphere at 400℃ for 30 hours. After grinding and sieving, the core-shell sodium-ion battery cathode material is obtained.

[0088] In both steps (3) and (4), the coprecipitation reaction is carried out using microwave-assisted heating. The microwave-assisted heating is pulsed heating, which includes controlling the power of microwave-assisted heating to 1000W, the heating time to 0.5min, and the heating interval to 30min using a temperature rise program.

[0089] Example 3

[0090] This embodiment provides a core-shell sodium-ion battery cathode material and its preparation method. The core-shell sodium-ion battery cathode material includes a nickel-iron-manganese core and a zinc-magnesium co-doped shell. The molar ratio of all metal elements in the nickel-iron-manganese core to all metal elements in the zinc-magnesium co-doped shell is 99.7:0.3. The molar ratio of nickel, iron and manganese in the nickel-iron-manganese core is 1.2:0.8:1. The molar ratio of zinc to magnesium in the zinc-magnesium co-doped shell is 1.2:1.

[0091] In this embodiment, the preparation method of the above-mentioned core-shell sodium-ion battery cathode material includes the following steps:

[0092] (1) Mix nickel chloride, ferric chloride, manganese chloride and deionized water to obtain a first metal salt solution with a total metal ion concentration of 10 mol / L;

[0093] (2) Mix zinc chloride, magnesium chloride and deionized water to obtain a second metal salt solution with a total metal ion concentration of 0.5 mol / L;

[0094] (3) Helium gas is introduced into the reactor. The first metal salt solution, a sodium hydroxide solution with a concentration of 12 mol / L, and an ammonia solution with a concentration of 8 mol / L are added to the bottom liquid in parallel. The co-precipitation reaction is carried out at 60°C. The feed rate of the first metal salt solution is controlled at 2 L / h, the initial feed rate of the sodium hydroxide solution is 0.1 L / h, and the initial feed rate of the ammonia solution is 0.01 L / h. By adjusting the feed rates of the sodium hydroxide solution and the ammonia solution in a timely manner, the pH value of the reaction system is controlled at 11.0±0.2 and the ammonia concentration is 7±2 g / L to obtain the nickel-iron-manganese core precursor. The bottom liquid is a mixed solution of sodium hydroxide solution and ammonia solution with an initial pH value of 11.0±1 and an initial ammonia concentration of 7±5 g / L.

[0095] (4) After the co-precipitation reaction has been carried out for 10 hours, the first metal salt solution in step (3) is replaced with the second metal salt solution. The feed rate of the second metal salt solution is controlled at 0.02 L / h, and the other conditions remain unchanged. The co-precipitation reaction is continued to obtain a core-shell sodium-ion battery precursor with an average particle size of 5 μm.

[0096] (5) The core-shell sodium-ion battery precursor was successively aged, centrifuged and washed and dried. The washing liquid used for centrifugation was deionized water and the drying temperature was 200℃. Then, the core-shell sodium-ion battery precursor and sodium carbonate were mixed at a molar ratio of 1:1.2 and sintered at 1000℃ for 4 hours in a tube furnace under an oxygen atmosphere. After grinding and sieving, the core-shell sodium-ion battery cathode material was obtained.

[0097] In both steps (3) and (4), the coprecipitation reaction is carried out using microwave-assisted heating. The microwave-assisted heating is pulsed heating, which includes controlling the power of microwave-assisted heating to 300W, the heating time to 100min, and the heating interval to 100min using a temperature rise program.

[0098] Example 4

[0099] This embodiment provides a core-shell sodium-ion battery cathode material and its preparation method. Except for adjusting the material ratio to change the molar ratio of nickel, iron and manganese in the nickel-iron-manganese core to 0.6:1.4:1, the other steps and conditions are the same as in Example 1, so they will not be described in detail here.

[0100] Example 5

[0101] This embodiment provides a core-shell sodium-ion battery cathode material and its preparation method. Except for adjusting the material ratio to change the molar ratio of nickel, iron and manganese in the nickel-iron-manganese core to 1.4:0.6:1, the other steps and conditions are the same as in Example 1, so they will not be described in detail here.

[0102] Example 6

[0103] This embodiment provides a core-shell sodium-ion battery cathode material and its preparation method. Except for adjusting the material ratio to change the molar ratio of zinc to magnesium in the zinc-magnesium co-doped shell to 0.01:1, the other steps and conditions are the same as in Example 1, so they will not be described in detail here.

[0104] Example 7

[0105] This embodiment provides a core-shell sodium-ion battery cathode material and its preparation method. Except for adjusting the material ratio to change the molar ratio of zinc to magnesium in the zinc-magnesium co-doped shell to 140:1, the other steps and conditions are the same as in Example 1, so they will not be described in detail here.

[0106] Comparative Example 1

[0107] This comparative example provides a core-shell sodium-ion battery cathode material and its preparation method. Except for adjusting the material ratio to change the molar ratio of all metal elements in the nickel-iron-manganese core to all metal elements in the zinc-magnesium co-doped shell to 90:10, the other steps and conditions are the same as in Example 1, so they will not be described in detail here.

[0108] Comparative Example 2

[0109] This comparative example provides a core-shell sodium-ion battery cathode material and its preparation method. Except for adjusting the material ratio to change the molar ratio of all metal elements in the nickel-iron-manganese core to all metal elements in the zinc-magnesium co-doped shell to 99.99:0.01, the other steps and conditions are the same as in Example 1, so they will not be described in detail here.

[0110] Comparative Example 3

[0111] This comparative example provides a sodium-ion battery cathode material and its preparation method. Except for step (4), which is not performed, the nickel-iron-manganese core precursor obtained in step (3) is directly used as the sodium-ion battery precursor. All other steps and conditions are the same as in Example 1, so they will not be described in detail here.

[0112] Comparative Example 4

[0113] This comparative example provides a sodium-ion battery cathode material and its preparation method. Except for replacing the microwave-assisted heating used in steps (3) and (4) of the co-precipitation reaction with traditional resistance wire heating, the other steps and conditions are the same as in Example 1, so they will not be repeated here.

[0114] Comparative Example 5

[0115] This comparative example provides a sodium-ion battery cathode material and its preparation method. The microwave-assisted heating used in the co-precipitation reaction in step (3) is replaced with traditional resistance wire heating, and step (4) is not performed. That is, the nickel-iron-manganese core precursor obtained in step (3) is directly used as the sodium-ion battery precursor. The remaining steps and conditions are the same as in Example 1, so they will not be described in detail here.

[0116] Performance testing

[0117] At 25°C, the positive electrode materials obtained in Examples 1-8 and Comparative Examples 1-5 were used as the main positive electrode material, and sodium metal sheets were used as the negative electrode to assemble CR2032 coin cells. Charge-discharge tests were then conducted within a voltage range of 1.0-4.5V, followed by 500 cycles at 1C / 5C. The relevant test results are shown in Table 1 below.

[0118] Table 1

[0119] As shown in Table 1, the batteries obtained by rapidly preparing core-shell sodium-ion battery cathode materials using microwave-assisted heating in Examples 1-3 have an initial discharge specific capacity of over 161.5 mAh / g, a 1C rate capability of over 153.2 mAh / g, a capacity retention rate of over 94.9% after 500 1C cycles, a 5C rate capability of over 132.8 mAh / g, and a capacity retention rate of over 84.6% after 500 5C cycles. In the preparation process of the core-shell cathode material described in this application, by coating its surface with Zn / Mg, not only is the rate capability of the material effectively increased, but it also has a good capacity retention rate after 500 cycles.

[0120] A comparison of Examples 1-3 with Examples 4 and 5 shows that the ratio of Ni, Fe, and Mn affects the diffusion rate of ions in the cathode material, thereby affecting the material's conductivity and tap density. With increasing Ni content, the capacity gradually increases, while the capacity retention and thermal performance deteriorate. Conversely, when the Fe content increases, although the resulting capacity decreases slightly, the electrode still exhibits stable capacity retention and thermal stability.

[0121] A comparison of Examples 1-3 with Examples 6 and 7 and Comparative Examples 1-3 shows that: if the Zn / Mg overfeed is too large during surface coating, the coating layer thickness will increase, which will not only prevent the rapid diffusion of sodium ions but also reduce electron conductivity; if the Zn / Mg overfeed is too small, it will not be able to protect the coated cathode material and prevent it from contacting the electrolyte, nor will it improve the cycle performance, rate performance, and stability of the cobalt bromide co-coated cathode material.

[0122] A comparison of Examples 1-3 with Comparative Examples 4 and 5 shows that, compared to microwave heating, traditional heating is slower and requires a longer time to reach the desired temperature. Microwave heating, on the other hand, causes the molecules inside the material to vibrate rapidly, generating heat. The heating speed is typically faster than traditional resistance heating, and the prepared materials usually have a higher tap density. Therefore, the prepared cathode materials exhibit better cycle and rate performance.

[0123] Therefore, the core-shell sodium-ion battery cathode material provided in this application uses nickel-iron-manganese as the core and zinc-magnesium co-doped in the shell. The zinc and magnesium elements in the shell help optimize the crystal structure of the cathode material, improve the energy density, power density and cycle stability of the material, and enable the battery to have a longer service life and higher energy output. The nickel-iron-manganese core has a high operating voltage platform, which helps to improve the energy density of the battery. The zinc-magnesium co-doped shell improves the stability of the overall structure, alleviates the volume expansion and structural degradation during charging and discharging, and thus reduces the performance degradation caused by structural changes during charging and discharging. At the same time, the zinc-magnesium co-doped shell alleviates the dissolution of the nickel-iron-manganese core in the electrolyte, further improving the long-term stability of the battery and enhancing its competitiveness in the market.

[0124] Furthermore, this application employs microwave-assisted heating for the co-precipitation reaction, which allows for rapid heating through controlled temperature control. This enables the preparation of core-shell sodium-ion battery cathode materials in a short time, simplifying the synthesis process and improving production efficiency. Microwave radiation can penetrate the material and generate heat within it, facilitating more uniform heating and reaction. This effectively avoids defects such as intracrystalline segregation, vacancies, and compositional inhomogeneity caused by localized overheating of the precursor during co-precipitation. The resulting precursor has a more complete crystal structure, significantly improving the particle size uniformity and tap density of the material, and further enhancing its electrochemical performance.

[0125] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of this application. It should be understood that the above descriptions are merely specific embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A core-shell type sodium-ion battery cathode material, comprising a nickel-iron-manganese core and a zinc-magnesium co-doped shell; The molar ratio of all metal elements in the nickel-iron-manganese core to all metal elements in the zinc-magnesium co-doped shell is (95-99.7):(0.3-5).

2. The core-shell sodium-ion battery cathode material according to claim 1, wherein, The molar ratio of nickel, iron and manganese in the nickel-iron-manganese core is (0.8-1.2):(0.8-1.2):

1.

3. The core-shell sodium-ion battery cathode material according to claim 1 or 2, wherein, The molar ratio of zinc to magnesium in the zinc-magnesium co-doped shell is (0.8-1.2):

1.

4. A method for preparing a core-shell sodium-ion battery cathode material as described in any one of claims 1-3, comprising the following steps: (1) Mix nickel salt, iron salt, manganese salt and deionized water to obtain a first metal salt solution; (2) Mix zinc salt, magnesium salt and deionized water to obtain a second metal salt solution; (3) The first metal salt solution, precipitant solution and complexing agent solution were added to the bottom liquid in parallel to carry out a co-precipitation reaction to obtain the nickel-iron-manganese core precursor. (4) Replace the first metal salt solution in step (3) with the second metal salt solution, and keep all other conditions unchanged, and continue the co-precipitation reaction to obtain the core-shell sodium-ion battery precursor. (5) The core-shell sodium-ion battery precursor and sodium source are sintered to obtain the core-shell sodium-ion battery cathode material. In this process, steps (1) and (2) are not in any particular order; the coprecipitation reactions described in steps (3) and (4) are both performed using microwave-assisted heating.

5. The preparation method according to claim 4, wherein, The nickel salt, iron salt, and manganese salt mentioned in step (1) are any one or a combination of at least two of the sulfate, nitrate, or chloride salts of the corresponding metal ions; Optionally, in step (1), the total concentration of metal ions in the first metal salt solution is 0.5-10 mol / L.

6. The preparation method according to claim 4 or 5, wherein, The zinc salt and magnesium salt mentioned in step (2) are any one or a combination of at least two of the sulfate, nitrate or chloride salts of the corresponding metal ions; Optionally, in step (2), the total concentration of metal ions in the second metal salt solution is 0.5-10 mol / L.

7. The preparation method according to any one of claims 4-6, wherein, The precipitant solution in step (3) includes sodium hydroxide solution and / or sodium carbonate solution; Optionally, the concentration of the precipitant solution in step (3) is 7-12 mol / L.

8. The preparation method according to any one of claims 4-7, wherein, The complexing agent solution in step (3) includes ammonia; Optionally, the concentration of the complexing agent solution in step (3) is 4-8 mol / L.

9. The preparation method according to any one of claims 4-8, wherein, The bottom solution in step (3) is a mixture of precipitant solution and complexing agent solution; Optionally, the pH value of the bottom solution in step (3) is 8.0-12.0, and the ammonia concentration is 1-100 g / L; Optionally, in step (3), the feed rate of the first metal salt solution is 2-500 L / h; Optionally, the feed rate of the precipitant solution in step (3) is 1-500 L / h; Optionally, the feed rate of the complexing agent solution in step (3) is 0.01-500 L / h.

10. The preparation method according to any one of claims 4-9, wherein, After the coprecipitation reaction described in step (3) lasts for a total of 0.2-30 hours, step (4) is then carried out. Optionally, in step (4), the feed rate of the second metal salt solution is 0.02-100 L / h; Optionally, the coprecipitation reactions in steps (3) and (4) are carried out in a protective gas atmosphere, and the protective gas includes any one or a combination of at least two of nitrogen, helium or argon.

11. The preparation method according to any one of claims 4-10, wherein, The temperatures for the coprecipitation reactions in steps (3) and (4) are 15-70℃, respectively; Optionally, the coprecipitation reactions described in steps (3) and (4) are both performed using microwave-assisted heating. The microwave-assisted heating is pulsed heating, which includes controlling the power, heating time and heating interval of the microwave-assisted heating using a heating program. Optionally, the power is 300-1000W; Optionally, the heating time is 0.5-100 min; Optionally, the heating interval is 0.1-100 min; Optionally, the average particle size of the core-shell sodium-ion battery precursor in step (4) is 5-16 μm.

12. The preparation method according to any one of claims 4-11, wherein, The core-shell sodium-ion battery precursor described in step (5) is subjected to aging, centrifugal washing and drying in sequence before sintering. Optionally, the washing solution used in the centrifugal washing includes deionized water; Optionally, the drying temperature is 100-200℃; Optionally, the sodium source in step (5) includes sodium carbonate; Optionally, the mixing molar ratio of the core-shell sodium-ion battery precursor and the sodium source in step (5) is 1:(0.8-1.2).

13. The preparation method according to any one of claims 4-12, wherein, The sintering process described in step (5) is carried out in a tube furnace under an oxygen atmosphere; Optionally, the sintering temperature in step (5) is 400-1000℃; Optionally, the sintering process in step (5) takes 4-30 hours; Optionally, after the sintering process described in step (5), the material is successively ground and sieved.

14. The preparation method according to any one of claims 4-13, comprising the following steps: (1) A first metal salt solution with a total metal ion concentration of 0.5-10 mol / L is obtained by mixing nickel salt, iron salt, manganese salt and deionized water; wherein the nickel salt, iron salt and manganese salt are sulfates, nitrates and nitrates of the corresponding metal ions, respectively. Any one or a combination of at least two of the salts or chlorides; (2) Mix zinc salt, magnesium salt and deionized water to obtain a second metal salt solution with a total metal ion concentration of 0.5-10 mol / L; wherein the zinc salt and magnesium salt are any one or a combination of at least two of the sulfate, nitrate or chloride salts of the corresponding metal ions; (3) A protective gas is introduced into the reactor, and the first metal salt solution, precipitant solution, and complexing agent solution are added to the bottom liquid in a co-precipitation reaction at 15-70℃. The feed rate of the first metal salt solution is controlled at 2-500 L / h, the feed rate of the precipitant solution is 1-500 L / h, and the feed rate of the complexing agent solution is 0.01-500 L / h to obtain a nickel-iron-manganese core precursor. The protective gas includes any one or a combination of at least two of nitrogen, helium, or argon. The precipitant solution includes sodium hydroxide solution and / or sodium carbonate solution with a concentration of 7-12 mol / L. The complexing agent solution includes ammonia water with a concentration of 4-8 mol / L. The bottom liquid is a mixed solution of precipitant solution and complexing agent solution with a pH value of 8.0-12.0 and an ammonia concentration of 1-100 g / L. (4) After the co-precipitation reaction has been carried out for 0.2-30h, the first metal salt solution in step (3) is replaced with the second metal salt solution. The feed rate of the second metal salt solution is controlled at 0.2-100L / h, and the other conditions remain unchanged. The co-precipitation reaction is continued to obtain a core-shell sodium-ion battery precursor with an average particle size of 5-16μm. (5) The core-shell sodium-ion battery precursor is successively aged, centrifuged and washed and dried. The washing liquid used for centrifugation includes deionized water. The drying temperature is 100-200℃. Then, the core-shell sodium-ion battery precursor and sodium carbonate are mixed at a molar ratio of 1:(0.8-1.2). The mixture is sintered in a tube furnace under an oxygen atmosphere at 400-1000℃ for 4-30 hours. After grinding and sieving, the core-shell sodium-ion battery cathode material is obtained. In this process, steps (1) and (2) are not sequential; the coprecipitation reactions described in steps (3) and (4) are both performed using microwave-assisted heating, which is pulsed heating, including: The heating program controls the microwave-assisted heating power to be 300-1000W, the heating time to be 0.5-100min, and the heating interval to be 0.1-100min.

15. A sodium-ion battery, wherein, The sodium-ion battery contains the core-shell sodium-ion battery cathode material as described in any one of claims 1-3.

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