Sodium-ion battery positive electrode material of core-shell structure, and preparation method therefor and use thereof

Abstract

Provided are a sodium-ion battery positive electrode material of a core-shell structure, and a preparation method therefor and a use thereof. The sodium-ion battery positive electrode material is of a core-shell structure, and comprises a nickel-manganese-zinc inner core, an iron-based intermediate layer and a copper-based shell which are stacked. The preparation method comprises: (1) mixing a nickel salt, a manganese salt, a zinc salt and deionized water to obtain a ternary salt solution; (2) carrying out first spray pyrolysis on the ternary salt solution to obtain a first precursor; (3) mixing an iron salt solution and the first precursor for second spray pyrolysis to obtain a second precursor; (4) mixing a copper salt solution and the second precursor for third spray pyrolysis to obtain a third precursor; and (5) mixing a sodium salt and the third precursor for calcination to obtain a sodium-ion battery positive electrode material of a core-shell structure. A sodium-ion battery positive electrode material of a core-shell structure is prepared by means of a spray pyrolysis method, improving the sphericity and the particle size uniformity of particles while simplifying the preparation process, improving the electrochemical performance of the material, and facilitating large-scale popularization and application.

Description

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

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

[0002] In recent years, significant progress has been made in the research of sodium-ion batteries, which use sodium ions as charge carriers moving between the negative and positive electrodes. Sodium-ion batteries are similar in working principle to lithium-ion batteries, the main difference being the use of sodium instead of lithium. Since sodium is one of the most abundant elements in the Earth's crust, it is more widely distributed and less expensive than lithium.

[0003] Sodium-ion battery cathode materials are one of the key factors determining the performance of sodium-ion batteries, affecting energy density, cycle stability, rate performance, and cost-effectiveness. Co-precipitation is a widely used technique in the preparation of sodium-ion battery cathode materials. However, this method suffers from long reaction times, requires control of a series of parameters such as pH, complexing agent, liquid alkali, and solid content, and the resulting precursors have poor sphericity and difficult-to-adjust particle size, especially when preparing core-shell structured sodium-ion battery precursors. This, to some extent, negatively impacts the electrochemical performance of the cathode material.

[0004] CN114988481A discloses a sodium-ion battery cathode material precursor and its preparation method, comprising: preparing a first mixed solution of Cu salt and Mn salt; preparing a sodium hydroxide or potassium hydroxide solution as a precipitant; preparing a first complexing agent solution; preparing a second mixed solution of Fe salt and a second complexing agent; preparing an additive solution; adding pure water, precipitant, and the first complexing agent solution to a reactor to form a base liquid; introducing a protective gas, and adding the first mixed solution, the second mixed solution, the precipitant, the first complexing agent solution, and the additive solution to the reactor for co-precipitation; and filtering, washing, and drying the product to obtain a loose and porous sodium-ion battery cathode material precursor. Although the sodium ions in the precursor material diffuse rapidly, which can improve electrical performance, the production efficiency is low, and the sphericity and particle size uniformity of the obtained precursor still have considerable room for improvement.

[0005] Therefore, how to provide a sodium-ion cathode material and its preparation method that simplifies the preparation process while improving particle sphericity and particle size uniformity, and thus improving the electrochemical performance of the material, has become an urgent problem that needs to be solved by those skilled in the art.

[0006] Summary of the Invention

[0007] 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.

[0008] This application provides a core-shell structured sodium-ion cathode material, its preparation method, and its application. The core-shell structured sodium-ion cathode material is prepared by spray pyrolysis, which simplifies the preparation process while improving the sphericity and uniformity of the particles, thus improving the electrochemical performance of the material and facilitating its large-scale application.

[0009] In a first aspect, this application provides a core-shell structured sodium-ion cathode material, wherein the sodium-ion cathode material has a core-shell structure, comprising a nickel-manganese-zinc core, an iron-based intermediate layer, and a copper-based outer shell stacked together.

[0010] The molar ratio of nickel, manganese and zinc in the nickel-manganese-zinc core is 1:(1-2):(1-4), for example, it can be 1:1:1, 1:1.2:1.5, 1:1.4:2, 1:1.6:2.5, 1:1.8:3 or 1:2:4, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0011] The sodium-ion cathode material provided in this application has a highly chemically active nickel-manganese-zinc core surface with a sequentially disposed iron-based intermediate layer and a copper-based outer shell, which are both highly conductive and structurally stable. This structure and composition help maintain the overall stability of the electrode during charging and discharging, and reduce the volume expansion and structural degradation of the active material.

[0012] Furthermore, this application uses an iron-based intermediate layer as a buffer layer, which helps alleviate the stress of sodium ions during charging and discharging. Meanwhile, iron, as an abundant and inexpensive element, can improve the battery's economics. The copper-based outer shell, due to its excellent electronic conductivity, provides a fast electron transport channel, thereby improving the rate performance of the cathode material, i.e., maintaining a high discharge capacity even at high current densities. This core-shell structure, by limiting direct contact between the core material and the electrolyte, reduces potential side reactions, thereby further improving the battery's cycle stability and lifespan.

[0013] In one embodiment, the average particle size of the nickel-manganese-zinc core is 4-5 μm, for example, it can be 4 μm, 4.1 μm, 4.2 μm, 4.3 μm, 4.4 μm, 4.5 μm, 4.6 μm, 4.7 μm, 4.8 μm, 4.9 μm or 5 μm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0014] In one embodiment, the average thickness of the iron-based intermediate layer and the copper-based outer shell are independently 0.5-2 μm, for example, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm or 2 μm, but are not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0015] In one embodiment, the average particle size of the sodium-ion cathode material is 6-9 μm, for example, it can be 6 μm, 6.2 μm, 6.4 μm, 6.6 μm, 6.8 μm, 7 μm, 7.2 μm, 7.4 μm, 7.6 μm, 7.8 μm, 8 μm, 8.2 μm, 8.4 μm, 8.6 μm, 8.8 μm or 9 μm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0016] Secondly, this application provides a method for preparing a sodium-ion cathode material as described in the first aspect, the method comprising the following steps:

[0017] (1) Mix nickel salt, manganese salt, zinc salt and deionized water to obtain a ternary salt solution;

[0018] (2) The ternary salt solution obtained in step (1) is subjected to a first spray pyrolysis to obtain a first precursor;

[0019] (3) Mix the iron salt solution and the first precursor obtained in step (2), and perform a second spray pyrolysis on the resulting mixed solution to obtain the second precursor;

[0020] (4) Mix the copper salt solution and the second precursor obtained in step (3), and perform a third spray pyrolysis on the resulting mixed solution to obtain the third precursor;

[0021] (5) The sodium salt and the third precursor obtained in step (4) are calcined to obtain a core-shell structured sodium cathode material.

[0022] This application uses a spray pyrolysis method to prepare core-shell structured sodium cathode materials, replacing the traditional co-precipitation method. This simplifies the preparation process while improving particle sphericity and particle size uniformity, thus enhancing the electrochemical performance of the material and facilitating large-scale application.

[0023] In one embodiment, the nickel salt, manganese salt and zinc salt in step (1) are any one or at least two combinations of acetate, nitrate, sulfate or chloride salts of the corresponding metal ions. Typical but non-limiting combinations include combinations of acetate and nitrate, nitrate and sulfate, sulfate and chloride, acetate, nitrate and sulfate, or nitrate, sulfate and chloride.

[0024] In one embodiment, the total concentration of the metal salt in the ternary salt solution in step (1) is 1-4 mol / L, for example, it can be 1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, 1.8 mol / L, 2 mol / L, 2.2 mol / L, 2.4 mol / L, 2.6 mol / L, 2.8 mol / L, 3 mol / L, 3.2 mol / L, 3.4 mol / L, 3.6 mol / L, 3.8 mol / L or 4 mol / L, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0025] In one embodiment, step (2) the first spray pyrolysis includes sequential ultrasonic spraying and pyrolysis treatment.

[0026] In one embodiment, the frequency of the ultrasonic spray is 0.1-20MHz, for example, it can be 0.1MHz, 1MHz, 2MHz, 4MHz, 6MHz, 8MHz, 10MHz, 12MHz, 14MHz, 16MHz, 18MHz or 20MHz, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0027] In one embodiment, the temperature of the pyrolysis treatment is 400-1200°C, for example, it can be 400°C, 500°C, 600°C, 700°C, 800°C, 900°C, 1000°C, 1100°C or 1200°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0028] In one embodiment, the solute in the iron salt solution of step (3) includes any one or a combination of at least two of ferric acetate, ferric nitrate, ferric sulfate, or ferric chloride. Typical but non-limiting combinations include combinations of ferric acetate and ferric nitrate, ferric nitrate and ferric sulfate, ferric sulfate and ferric chloride, ferric acetate, ferric nitrate and ferric sulfate, or ferric nitrate, ferric sulfate and ferric chloride.

[0029] In one embodiment, the concentration of the iron salt solution in step (3) is 0.1-4 mol / L, for example, it can be 1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, 1.8 mol / L, 2 mol / L, 2.2 mol / L, 2.4 mol / L, 2.6 mol / L, 2.8 mol / L, 3 mol / L, 3.2 mol / L, 3.4 mol / L, 3.6 mol / L, 3.8 mol / L or 4 mol / L, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0030] In one embodiment, step (3) the second spray pyrolysis includes sequential ultrasonic spraying and pyrolysis treatment.

[0031] In one embodiment, the frequency of the ultrasonic spray is 0.1-20MHz, for example, it can be 0.1MHz, 1MHz, 2MHz, 4MHz, 6MHz, 8MHz, 10MHz, 12MHz, 14MHz, 16MHz, 18MHz or 20MHz, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0032] In one embodiment, the temperature of the pyrolysis treatment is 400-1200°C, for example, it can be 400°C, 500°C, 600°C, 700°C, 800°C, 900°C, 1000°C, 1100°C or 1200°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0033] In one embodiment, the solute in the copper salt solution of step (4) includes any one or a combination of at least two of copper acetate, copper nitrate, copper sulfate or copper chloride. Typical but non-limiting combinations include a combination of copper acetate and copper nitrate, a combination of copper nitrate and copper sulfate, a combination of copper sulfate and copper chloride, a combination of copper acetate, copper nitrate and copper sulfate, or a combination of copper nitrate, copper sulfate and copper chloride.

[0034] In one embodiment, the concentration of the copper salt solution in step (4) is 0.1-4 mol / L, for example, it can be 1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, 1.8 mol / L, 2 mol / L, 2.2 mol / L, 2.4 mol / L, 2.6 mol / L, 2.8 mol / L, 3 mol / L, 3.2 mol / L, 3.4 mol / L, 3.6 mol / L, 3.8 mol / L or 4 mol / L, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0035] In one embodiment, the third spray pyrolysis in step (4) includes sequential ultrasonic spraying and pyrolysis treatment.

[0036] In one embodiment, the frequency of the ultrasonic spray is 0.1-20MHz, for example, it can be 0.1MHz, 1MHz, 2MHz, 4MHz, 6MHz, 8MHz, 10MHz, 12MHz, 14MHz, 16MHz, 18MHz or 20MHz, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0037] In one embodiment, the temperature of the pyrolysis treatment is 400-1200°C, for example, it can be 400°C, 500°C, 600°C, 700°C, 800°C, 900°C, 1000°C, 1100°C or 1200°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0038] In one embodiment, the sodium salt in step (5) includes any one or a combination of at least two of sodium acetate, sodium carbonate, or sodium bicarbonate. Typical but non-limiting combinations include a combination of sodium acetate and sodium carbonate, a combination of sodium carbonate and sodium bicarbonate, a combination of sodium acetate and sodium bicarbonate, or a combination of sodium acetate, sodium carbonate, and sodium bicarbonate.

[0039] In one embodiment, the mass ratio of the sodium salt to the third precursor in step (5) is (1-1.2):1, for example, it can be 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, 1.18:1 or 1.2:1, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0040] In one embodiment, the calcination process in step (5) is carried out in a nitrogen atmosphere and the calcination temperature is 900-1100℃, for example, it can be 900℃, 920℃, 940℃, 960℃, 980℃, 1000℃, 1020℃, 1040℃, 1060℃, 1080℃ or 1100℃, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0041] As an optional technical solution in the second aspect of this application, the preparation method includes the following steps:

[0042] (1) Mix nickel salt, manganese salt, zinc salt and deionized water to obtain a ternary salt solution with a total metal salt concentration of 1-4 mol / L; wherein the nickel salt, manganese salt and zinc salt are any one or a combination of at least two of the acetate, nitrate, sulfate or chloride salts of the corresponding metal ions;

[0043] (2) The ternary salt solution obtained in step (1) is subjected to a first spray pyrolysis, including sequential ultrasonic spraying and pyrolysis treatment, wherein the frequency of ultrasonic spraying is 0.1-20MHz and the temperature of pyrolysis treatment is 400-1200℃, to obtain the first precursor;

[0044] (3) A ferric salt solution with a concentration of 0.1-4 mol / L and the first precursor obtained in step (2) are mixed, and the resulting mixed solution is subjected to a second spray pyrolysis, including sequential ultrasonic spraying and pyrolysis treatment, wherein the frequency of ultrasonic spraying is 0.1-20 MHz and the temperature of pyrolysis treatment is 400-1200 °C, to obtain the second precursor; the solute in the ferric salt solution includes any one or a combination of at least two of ferric acetate, ferric nitrate, ferric sulfate or ferric chloride;

[0045] (4) A copper salt solution with a concentration of 0.1-4 mol / L and the second precursor obtained in step (3) are mixed, and the resulting mixed solution is subjected to a third spray pyrolysis, including sequential ultrasonic spraying and pyrolysis treatment, wherein the frequency of ultrasonic spraying is 0.1-20 MHz and the temperature of pyrolysis treatment is 400-1200 °C, to obtain the third precursor; the solute in the copper salt solution includes any one or a combination of at least two of copper acetate, copper nitrate, copper sulfate or copper chloride;

[0046] (5) Mix sodium salt and the third precursor obtained in step (4) at a mass ratio of (1-1.2):1, wherein the sodium salt includes any one or a combination of at least two of sodium acetate, sodium carbonate or sodium bicarbonate, and calcine in a nitrogen atmosphere at a calcine temperature of 900-1100℃ to obtain a core-shell structured sodium electrode material.

[0047] Thirdly, this application provides an application of the sodium-ion battery cathode material as described in the first aspect, wherein the sodium-ion battery cathode material is used to prepare a sodium-ion battery.

[0048] The numerical range described in this application includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this application will not exhaustively list the specific point values ​​included in the range.

[0049] Compared with related technologies, this application has the following advantages:

[0050] (1) The sodium electrode material provided in this application has a highly chemically active nickel-manganese-zinc core surface with a highly conductive and structurally stable iron-based intermediate layer and a copper-based outer shell. This structure and composition help maintain the overall stability of the electrode during charging and discharging, and reduce the volume expansion and structural degradation of the active material.

[0051] (2) This application uses an iron-based intermediate layer as a buffer layer, which helps to alleviate the stress of sodium ions during the charging and discharging process. At the same time, iron, as an element that is abundant in resources and low in cost, can improve the economy of the battery. The copper-based shell has excellent electronic conductivity and can provide a fast electron transport channel, thereby improving the rate performance of the positive electrode material, that is, it can still maintain a high discharge capacity under high current density. This core-shell structure reduces possible side reactions by limiting the direct contact between the core material and the electrolyte, thereby further improving the cycle stability and service life of the battery.

[0052] (3) This application uses spray pyrolysis to prepare core-shell structured sodium cathode material, replacing the traditional co-precipitation method. This simplifies the preparation process while improving particle sphericity and particle size uniformity, thus improving the electrochemical performance of the material and facilitating large-scale application.

[0053] After reading and understanding the accompanying diagrams and detailed descriptions, the other aspects can be understood. Attached Figure Description

[0054] The accompanying drawings are used to provide a further understanding of the technical solutions in this paper and form part of the specification. They are used together with the embodiments of this application to explain the technical solutions in this paper and do not constitute a limitation on the technical solutions in this paper.

[0055] Figure 1 is a SEM image of the sodium-ion cathode material provided in Example 1. Detailed Implementation

[0056] The technical solution of this application will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely to help understand this application and should not be regarded as specific limitations on this application.

[0057] Example 1

[0058] This embodiment provides a core-shell structured sodium-ion battery cathode material and its preparation method. The sodium-ion battery cathode material has a core-shell structure, comprising a stacked nickel-manganese-zinc core, an iron-based intermediate layer, and a copper-based outer shell. The molar ratio of nickel, manganese, and zinc in the nickel-manganese-zinc core is 1:1:1. The average particle size of the nickel-manganese-zinc core is 4 μm, the average thickness of the iron-based intermediate layer and the copper-based outer shell is 1 μm, and the average particle size of the sodium-ion battery cathode material is 8 μm.

[0059] In this embodiment, the preparation method of the above-mentioned sodium-ion cathode material includes the following steps:

[0060] (1) Mix nickel acetate, manganese acetate, zinc acetate and deionized water to obtain a ternary salt solution with a total metal salt concentration of 2 mol / L.

[0061] (2) The ternary salt solution obtained in step (1) is subjected to a first spray pyrolysis, including sequential ultrasonic spraying and pyrolysis treatment, wherein the frequency of ultrasonic spraying is 10MHz and the temperature of pyrolysis treatment is 800℃, to obtain the first precursor.

[0062] (3) Mix ferric acetate solution with a concentration of 2 mol / L and the first precursor obtained in step (2), and perform a second spray pyrolysis on the resulting mixed solution, including sequential ultrasonic spraying and pyrolysis treatment, wherein the frequency of ultrasonic spraying is 10 MHz and the temperature of pyrolysis treatment is 800 °C, to obtain the second precursor;

[0063] (4) Mix a copper acetate solution with a concentration of 2 mol / L and the second precursor obtained in step (3), and subject the resulting mixed solution to a third spray pyrolysis, including sequential ultrasonic spraying and pyrolysis treatment, wherein the frequency of ultrasonic spraying is 10 MHz and the temperature of pyrolysis treatment is 800 °C, to obtain the third precursor.

[0064] (5) Sodium acetate and the third precursor obtained in step (4) are mixed in a mass ratio of 1.1:1 and calcined in a nitrogen atmosphere at a calcination temperature of 1000℃ to obtain a core-shell structured sodium cathode material.

[0065] Figure 1 is a SEM image of the sodium-ion cathode material obtained in this embodiment. It can be seen that the sodium-ion cathode material obtained in this embodiment has good particle sphericity and high particle size uniformity.

[0066] Example 2

[0067] This embodiment provides a core-shell structured sodium-ion battery cathode material and its preparation method. The sodium-ion battery cathode material has a core-shell structure, comprising a stacked nickel-manganese-zinc core, an iron-based intermediate layer, and a copper-based outer shell. The molar ratio of nickel, manganese, and zinc in the nickel-manganese-zinc core is 1:2:3. The average particle size of the nickel-manganese-zinc core is 5 μm, the average thickness of the iron-based intermediate layer and the copper-based outer shell is 1 μm, and the average particle size of the sodium-ion battery cathode material is 9 μm.

[0068] In this embodiment, the preparation method of the above-mentioned sodium-ion cathode material includes the following steps:

[0069] (1) Mix nickel nitrate, manganese nitrate, zinc nitrate and deionized water to obtain a ternary salt solution with a total metal salt concentration of 4 mol / L;

[0070] (2) The ternary salt solution obtained in step (1) is subjected to a first spray pyrolysis, including sequential ultrasonic spraying and pyrolysis treatment, wherein the frequency of ultrasonic spraying is 0.1MHz and the temperature of pyrolysis treatment is 1200℃, to obtain the first precursor;

[0071] (3) Mix a 0.1 mol / L ferric nitrate solution with the first precursor obtained in step (2), and subject the resulting mixed solution to a second spray pyrolysis, including sequential ultrasonic spraying and pyrolysis treatment, wherein the frequency of ultrasonic spraying is 0.1 MHz and the temperature of pyrolysis treatment is 1200 °C, to obtain the second precursor;

[0072] (4) Mix a copper nitrate solution with a concentration of 0.1 mol / L and the second precursor obtained in step (3), and subject the resulting mixed solution to a third spray pyrolysis, including sequential ultrasonic spraying and pyrolysis treatment, wherein the frequency of ultrasonic spraying is 0.1 MHz and the temperature of pyrolysis treatment is 1200 °C, to obtain the third precursor;

[0073] (5) Sodium carbonate and the third precursor obtained in step (4) are mixed in a mass ratio of 1:1 and calcined in a nitrogen atmosphere at a calcination temperature of 1100℃ to obtain a core-shell structured sodium cathode material.

[0074] The particle sphericity and particle size uniformity of the sodium-ion cathode material obtained in this embodiment are similar to those in Example 1, so they will not be described again here.

[0075] Example 3

[0076] This embodiment provides a core-shell structured sodium-ion battery cathode material and its preparation method. The sodium-ion battery cathode material has a core-shell structure, comprising a stacked nickel-manganese-zinc core, an iron-based intermediate layer, and a copper-based outer shell. The molar ratio of nickel, manganese, and zinc in the nickel-manganese-zinc core is 1:2:4. The average particle size of the nickel-manganese-zinc core is 4 μm, the average thickness of the iron-based intermediate layer and the copper-based outer shell is 0.5 μm, and the average particle size of the sodium-ion battery cathode material is 6 μm.

[0077] In this embodiment, the preparation method of the above-mentioned sodium-ion cathode material includes the following steps:

[0078] (1) Mix nickel sulfate, manganese sulfate, zinc sulfate and deionized water to obtain a ternary salt solution with a total metal salt concentration of 1 mol / L;

[0079] (2) The ternary salt solution obtained in step (1) is subjected to a first spray pyrolysis, including sequential ultrasonic spraying and pyrolysis treatment, wherein the frequency of ultrasonic spraying is 20MHz and the temperature of pyrolysis treatment is 400℃, to obtain the first precursor.

[0080] (3) Mix a ferric sulfate solution with a concentration of 4 mol / L and the first precursor obtained in step (2), and subject the resulting mixed solution to a second spray pyrolysis, including sequential ultrasonic spraying and pyrolysis treatment, wherein the frequency of ultrasonic spraying is 20 MHz and the temperature of pyrolysis treatment is 400 °C, to obtain the second precursor.

[0081] (4) Mix a copper sulfate solution with a concentration of 4 mol / L and the second precursor obtained in step (3), and subject the resulting mixed solution to a third spray pyrolysis, including sequential ultrasonic spraying and pyrolysis treatment, wherein the frequency of ultrasonic spraying is 20 MHz and the temperature of pyrolysis treatment is 400 °C, to obtain the third precursor.

[0082] (5) Sodium bicarbonate and the third precursor obtained in step (4) are mixed in a mass ratio of 1.2:1 and calcined in a nitrogen atmosphere at a calcination temperature of 900°C to obtain a core-shell structured sodium cathode material.

[0083] The particle sphericity and particle size uniformity of the sodium-ion cathode material obtained in this embodiment are similar to those in Example 1, so they will not be described again here.

[0084] Example 4

[0085] This embodiment provides a core-shell structured sodium-ion cathode material and its preparation method. Except that the ternary salt in step (1) is replaced with nickel chloride, manganese chloride and zinc chloride respectively, the iron salt in step (3) is replaced with ferric chloride, and the copper salt in step (4) is replaced with copper chloride, the other steps and conditions are the same as in Example 1, so they will not be repeated here.

[0086] Example 5

[0087] This embodiment provides a core-shell structured sodium cathode material and its preparation method. Except for reducing the calcination temperature in step (5) to 800°C, the other steps and conditions are the same as in Example 1, so they will not be described in detail here.

[0088] Comparative Example 1

[0089] This comparative example provides a core-shell structured sodium-ion cathode material and its preparation method. Except for step (3), which removes the iron-based intermediate layer and directly coats the surface of the nickel-manganese-zinc core with a copper-based outer shell, the other steps and conditions are the same as in Example 1, so they will not be described in detail here.

[0090] Comparative Example 2

[0091] This comparative example provides a core-shell structured sodium-ion cathode material and its preparation method. Except for step (4), which removes the copper-based outer shell and coats the surface of the nickel-manganese-zinc core with an iron-based intermediate layer, the other steps and conditions are the same as in Example 1, so they will not be described in detail here.

[0092] Comparative Example 3

[0093] This comparative example provides a sodium-ion battery cathode material and its preparation method. Except for the deletion of steps (3) and (4), i.e., directly mixing sodium salt and the first precursor and calcining to obtain a nickel-manganese-zinc core as a sodium-ion battery cathode material, the remaining steps and conditions are the same as in Example 1, so they will not be repeated here.

[0094] Comparative Example 4

[0095] This comparative example provides a core-shell structured sodium-ion cathode material and its preparation method. Except for changing the order of steps (3) and (4), i.e., coating the surface of the nickel-manganese-zinc core with a copper-based intermediate layer and an iron-based outer shell in sequence, the other steps and conditions are the same as in Example 1, so they will not be repeated here.

[0096] Performance testing

[0097] At 25°C, sodium-ion battery cathode materials obtained in Examples 1-5 and Comparative Examples 1-4 were used as the main cathode material, and sodium metal sheets were used as the anode material. They were assembled into CR2032 coin cells. Electrochemical performance tests were then conducted in the voltage range of 2.0-4.0V and the discharge current density was 10mA / g. The test results are shown in Table 1 below.

[0098] Table 1

[0099] As can be seen, the sodium electrode material provided in this application has a highly chemically active nickel-manganese-zinc core with a sequentially disposed iron-based intermediate layer and a copper-based outer shell, which have good conductivity and stable structure. This structure and composition help maintain the overall stability of the electrode during charging and discharging, and reduce the volume expansion and structural degradation of the active material.

[0100] Furthermore, this application uses an iron-based intermediate layer as a buffer layer, which helps to alleviate the stress of sodium ions during charging and discharging. At the same time, iron, as an abundant and inexpensive element, can improve the economics of the battery. The copper-based shell, due to its excellent electronic conductivity, can provide a fast electron transport channel, thereby improving the rate performance of the cathode material, that is, maintaining a high discharge capacity even at high current densities. This core-shell structure reduces possible side reactions by limiting the direct contact between the core material and the electrolyte, thereby further improving the cycle stability and lifespan of the battery.

[0101] Furthermore, this application uses a spray pyrolysis method to prepare core-shell structured sodium cathode materials, replacing the traditional co-precipitation method. This simplifies the preparation process while improving particle sphericity and particle size uniformity, thus enhancing the electrochemical performance of the material and facilitating large-scale application.

[0102] The applicant declares that the above description is only a specific implementation of this application, but the protection scope of this application is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application fall within the protection and disclosure scope of this application.

Claims

1. A core-shell structured sodium battery cathode material, wherein, The sodium electric positive electrode material is a core-shell structure, comprising a nickel-manganese-zinc inner core, an iron-based intermediate layer and a copper-based outer shell arranged in layers. The molar ratio of nickel element, manganese element and zinc element in the nickel-manganese-zinc inner core is 1:(1-2):(1-4).

2. The sodium electric cathode material of claim 1, wherein, The average particle size of the nickel-manganese-zinc inner core is 4-5 μm.

3. The sodium electro-positive cathode material of claim 1 or 2, wherein, The average thickness of the iron-based intermediate layer and the copper-based outer shell is independently 0.5-2 μm.

4. The sodium electro-positive cathode material of any one of claims 1-3, wherein, The average particle size of the sodium electric positive electrode material is 6-9 μm.

5. A preparation method of the sodium electric positive electrode material according to any one of claims 1-4, comprising the following steps: (1) mixing nickel salt, manganese salt, zinc salt and deionized water to obtain a ternary salt solution; (2) performing first spray pyrolysis on the ternary salt solution obtained in step (1) to obtain a first precursor; (3) mixing an iron salt solution and the first precursor obtained in step (2), and performing second spray pyrolysis on the obtained mixed solution to obtain a second precursor; (4) mixing a copper salt solution and the second precursor obtained in step (3), and performing third spray pyrolysis on the obtained mixed solution to obtain a third precursor; (5) mixing sodium salt and the third precursor obtained in step (4) for calcination treatment to obtain a sodium electric positive electrode material with a core-shell structure.

6. The production method according to claim 5, wherein The nickel salt, manganese salt and zinc salt in step (1) are any one or a combination of at least two of the corresponding metal ion acetate, nitrate, sulfate or chloride.

7. The production method according to claim 5 or 6, wherein The total concentration of metal salt in the ternary salt solution in step (1) is 1-4 mol / L.

8. The method of making according to any one of claims 5-7, wherein, The first spray pyrolysis in step (2) comprises ultrasonic spraying and pyrolysis treatment in sequence; Optionally, the frequency of the ultrasonic spraying is 0.1-20 MHz; Optionally, the temperature of the pyrolysis treatment is 400-1200℃.

9. The method of making according to any one of claims 5-8, wherein, The solute in the iron salt solution in step (3) comprises any one or a combination of at least two of iron acetate, iron nitrate, iron sulfate or iron chloride; Optionally, the concentration of the iron salt solution in step (3) is 0.1-4 mol / L.

10. The method of making according to any one of claims 5-9, wherein, The second spray pyrolysis in step (3) comprises ultrasonic spraying and pyrolysis treatment in sequence; Optionally, the frequency of the ultrasonic spraying is 0.1-20 MHz; Optionally, the temperature of the pyrolysis treatment is 400-1200℃.

11. The method of making according to any one of claims 5-10, wherein, The solute in the copper salt solution in step (4) comprises any one or a combination of at least two of copper acetate, copper nitrate, copper sulfate or copper chloride; Optionally, the concentration of the copper salt solution in step (4) is 0.1-4 mol / L.

12. The method of making according to any one of claims 5-11, wherein, The third spray pyrolysis in step (4) comprises ultrasonic spraying and pyrolysis treatment in sequence; Optionally, the frequency of the ultrasonic spraying is 0.1-20 MHz; Optionally, the temperature of the pyrolysis treatment is 400-1200℃.

13. The method of making according to any one of claims 5-12, wherein, The sodium salt in step (5) comprises any one or a combination of at least two of sodium acetate, sodium carbonate or sodium bicarbonate; Optionally, the mixing mass ratio of the sodium salt to the third precursor in step (5) is (1-1.2):1; Optionally, the calcination treatment in step (5) is performed in a nitrogen atmosphere, and the calcination temperature is 900-1100℃.

14. The preparation method according to any one of claims 5-13, comprising the following steps: (1) mixing a nickel salt, a manganese salt, a zinc salt and deionized water to obtain a ternary salt solution with a total concentration of metal salts of 1-4 mol / L; the nickel salt, the manganese salt and the zinc salt are each any one or a combination of at least two of acetate, nitrate, sulfate or chloride of the corresponding metal ion; (2) performing first spray pyrolysis on the ternary salt solution obtained in step (1), including sequentially performing ultrasonic spraying and pyrolysis treatment, and the frequency of ultrasonic spraying is 0.1-20 MHz, and the temperature of pyrolysis treatment is 400-1200℃, to obtain a first precursor; (3) mixing an iron salt solution with a concentration of 0.1-4 mol / L and the first precursor obtained in step (2), and performing second spray pyrolysis on the obtained mixed solution, including sequentially performing ultrasonic spraying and pyrolysis treatment, and the frequency of ultrasonic spraying is 0.1-20 MHz, and the temperature of pyrolysis treatment is 400-1200℃, to obtain a second precursor; the solute in the iron salt solution includes any one or a combination of at least two of iron acetate, iron nitrate, iron sulfate or iron chloride; (4) mixing a copper salt solution with a concentration of 0.1-4 mol / L and the second precursor obtained in step (3), and performing third spray pyrolysis on the obtained mixed solution, including sequentially performing ultrasonic spraying and pyrolysis treatment, and the frequency of ultrasonic spraying is 0.1-20 MHz, and the temperature of pyrolysis treatment is 400-1200℃, to obtain a third precursor; the solute in the copper salt solution includes any one or a combination of at least two of copper acetate, copper nitrate, copper sulfate or copper chloride; (5) mixing a sodium salt and the third precursor obtained in step (4) according to a mass ratio of (1-1.2):1, the sodium salt includes any one or a combination of at least two of sodium acetate, sodium carbonate or sodium bicarbonate, and performing calcination treatment in a nitrogen atmosphere, and the calcination temperature is 900-1100℃, to obtain a sodium electric positive electrode material with a core-shell structure.

15. Use of a sodium electro-positive cathode material as claimed in any one of claims 1 to 4, wherein, The sodium electric positive electrode material is used for preparing a sodium ion battery.

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