A nickel-manganese-based sodium-ion battery positive electrode material, a preparation method and application thereof

Abstract

The application belongs to the technical field of sodium-ion positive electrode materials, and specifically discloses a nickel-manganese-based sodium-ion battery positive electrode material and a preparation method and application thereof. 0.67 Ni 0.25‑x M1 x Mn 0.75‑y M2 y O2, wherein M1 is one or more of Zn, Li or Cu, M2 is one or more of Ti or Sn, 0.05

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion cathode material technology, specifically relating to a nickel-manganese-based sodium-ion battery cathode material, its preparation method, and its application. Background Technology

[0002] Next-generation electrochemical energy storage technologies can effectively alleviate the problem of non-renewable energy consumption, such as the application of lithium-ion batteries. However, in recent years, due to fluctuations in the price of lithium carbonate and the increasing demand for lithium in electronic devices, attention has shifted to sodium-ion batteries, and research on sodium-ion batteries is gradually ushering in new opportunities. Sodium and lithium belong to the same main group, but sodium ions... The radius is much larger than that of lithium ions. During the insertion / extraction process in the bulk structure, more severe structural distortions inevitably occur, ultimately affecting the battery's cycle performance. Furthermore, due to their larger radii, sodium atoms in the transition metal layer typically exhibit octahedral coordination, while lithium atoms can be both octahedral and tetrahedral. This makes it difficult to directly apply some electrode materials suitable for lithium-ion batteries to sodium-ion batteries, necessitating further research into the development of sodium-ion battery electrode materials.

[0003] In sodium-ion batteries, the cathode material determines the overall energy density of the battery system. Layered oxides, typically composed of electrochemically active elements, are low-cost and show excellent application prospects. Among them, P2-type cathode materials have a relatively stable structure and fast sodium ion migration. Typically, when the voltage exceeds 4.2V, the material undergoes a significant phase transition, inducing structural changes, which become more pronounced at 4.3V. Element substitution is an effective strategy to suppress unfavorable phase transition behavior, but it reduces the specific capacity of the material to some extent. Therefore, developing a cathode material with excellent cycle performance and high specific capacity is of significant importance for the application of sodium-ion batteries. Summary of the Invention

[0004] To address the aforementioned issues, this invention provides a nickel-manganese-based sodium-ion battery cathode material. Through a specific element substitution strategy, different metal ions are substituted at transition metal sites, resulting in a material with high specific capacity and excellent cycle stability. The initial discharge capacity at 1C current density is approximately 90-100 mAh / g, and the capacity retention rate after cycling is over 80%.

[0005] The technical solution of the present invention is as follows:

[0006] This invention discloses a nickel-manganese-based sodium-ion battery cathode material, wherein the cathode material is a P2-type layered oxide material with the general chemical formula Na. 0.67 Ni 0.25-x M1 x Mn 0.75-yM2 y O2, where M1 is one or more of Zn, Li, or Cu, M2 is one or more of Ti or Sn, 0.05 < x ≤ 0.2, 0.05 < y ≤ 0.2, and zinc ions, lithium ions, or copper ions replace some nickel ions, and titanium ions or tin ions replace some manganese ions.

[0007] The present invention also discloses a preparation method of the above-mentioned positive electrode material, which includes the following steps:

[0008] (1) According to the stoichiometric ratio of the chemical general formula, take a sodium salt that is 1 - 1.05 times the stoichiometry of the required sodium element and mix it with the remaining metal salts of the required stoichiometry;

[0009] (2) After drying, sinter at 500 - 800 °C for 6 - 18 h, and cool to room temperature to obtain the above-mentioned positive electrode material.

[0010] In an embodiment of the present invention, the sodium salt in step (1) is a carbonate or acetate, and the remaining metal salts are one or two of oxides, oxalates, carbonates, or acetates.

[0011] In an embodiment of the present invention, step (2) includes placing the dried metal salts in a muffle furnace and heating to the set temperature for sintering at a rate of 3 - 5 °C / min.

[0012] In an embodiment of the present invention, before preparing the above-mentioned positive electrode material, it also includes verifying its feasibility: taking sodium salt, nickel salt, and manganese salt in accordance with the stoichiometry shown by the chemical formula Na 0.67 Ni 0.25 Mn 0.75 [[ID=二十六]]O2, mixing them evenly, collecting the powder and drying it after mixing, transferring it to a muffle furnace, and sintering at 500 - 800 °C for 6 - 18 h to obtain the Na 0.67 Ni 0.25 Mn 0.75 O2 material.

[0013] In an embodiment of the present invention, it also includes placing the cooled above-mentioned positive electrode material in a mortar, grinding it into powder, then transferring it to a centrifuge tube for sealing, and storing it in an argon glove box for later use.

[0014] The present invention also discloses a positive electrode sheet for a sodium-ion battery, and the positive electrode sheet includes the above-mentioned positive electrode material.

[0015] The present invention also discloses a sodium-ion secondary battery including the above-mentioned positive electrode sheet.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0017] This invention discloses a nickel-manganese-based sodium-ion battery cathode material. Through a specific element substitution strategy, a cathode material suitable for sodium-ion batteries is obtained. This cathode material exhibits excellent performance in half-cells, with an initial discharge capacity of approximately 90-100 mAh / g at a 1C current density and a capacity retention rate of over 80% after cycling. Furthermore, the raw materials used are inexpensive and readily available, demonstrating a significant advantage in large-scale cathode material preparation; it is also environmentally friendly, causing no pollution and aligning with the concept of green energy. Compared to liquid-phase methods, this invention employs a fully solid-phase method, which is simpler to operate and reduces the number of preparation steps to some extent. Generally, P2-type layered oxide materials are typically prepared at temperatures above 900°C, while the cathode material prepared in this invention requires a maximum temperature of only 800°C, further saving energy to some extent. Attached Figure Description

[0018] Figure 1 This invention relates to a nickel-manganese-based sodium-ion battery cathode material, Na. 0.67 Ni 0.25 Mn 0.75 Figure showing the half-cell charge-discharge performance of O2 at a current density of 0.2C;

[0019] Figure 2 This is a nickel-manganese-based sodium-ion battery cathode material Na as described in Example 2 of the present invention. 0.67 Ni 0.15 Cu 0.1 Mn 0.65 Ti 0.1 Half-cell cycle performance of O2 at 1C current density;

[0020] Figure 3 Na is a nickel-manganese-based sodium-ion battery cathode material according to Example 4 of the present invention. 0.67 Ni 0.15 Li 0.1 Mn 0.55 Ti 0.2 Half-cell cycle performance of O2 at 1C current density;

[0021] Figure 4 Na is a nickel-manganese-based sodium-ion battery cathode material according to Example 5 of the present invention. 0.67 Ni 0.2 Zn 0.05 Mn 0.55 Ti 0.2 SEM image of O2;

[0022] Figure 5 Na is a nickel-manganese-based sodium-ion battery cathode material according to Example 5 of the present invention. 0.67 Ni 0.2 Zn 0.05 Mn 0.55Ti 0.2 XRD pattern of O2;

[0023] Figure 6 A nickel-manganese-based sodium-ion battery cathode material of Example 5 of the present invention is Na 0.67 Ni 0.2 Zn 0.05 Mn 0.55 Ti 0.2 Half-cell rate performance diagram of O2;

[0024] Figure 7 A nickel-manganese-based sodium-ion battery cathode material of Example 5 of the present invention is Na 0.67 Ni 0.2 Zn 0.05 Mn 0.55 Ti 0.2 Half-cell cycle performance diagram of O2 at a current density of 1C;

[0025] Figure 8 A nickel-manganese-based sodium-ion battery cathode material of Example 5 of the present invention is Na 0.67 Ni 0.2 Zn 0.05 Mn 0.55 Ti 0.2 Full-cell cycle performance diagram of O2 at a current density of 0.5C. Specific embodiments

[0026] To make the above objects, features and advantages of the present invention more obvious and understandable, the following detailed description of the specific embodiments of the present invention will be made with reference to the accompanying drawings.

[0027] Many specific details are set forth in the following description in order to provide a thorough understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar generalizations without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0028] A nickel-manganese-based sodium-ion battery cathode material according to an embodiment of the present invention, wherein the cathode material is a P2-type layered oxide material, and its chemical general formula is Na 0.67 Ni 0.25-x M1 x Mn 0.75-y M2 y O2, wherein M1 is one or more of Zn, Li or Cu, M2 is one or more of Ti or Sn, 0.05 < x ≤ 0.2, 0.05 < y ≤ 0.2, zinc ions, lithium ions or copper ions replace part of the nickel ions, and titanium ions or tin ions replace part of the manganese ions. The preparation method thereof includes the following steps:

[0029] (1) According to the stoichiometric ratio of the above general chemical formula, take 1-1.05 times the required sodium element stoichiometry of sodium salt and mix it with the required amount of other metal salts; the sodium salt is a carbonate or acetate, and the other metal salts are one or two of oxides, oxalates, carbonates or acetates.

[0030] (2) After drying, the metal salt is placed in a muffle furnace and sintered at 500-800℃ for 6-18 hours at a temperature of 3-5℃ / min. Then it is cooled to room temperature to obtain the cathode material.

[0031] (3) The cooled positive electrode material is ground into powder in a mortar, then transferred to a centrifuge tube, sealed, and stored in an argon glove box for later use.

[0032] Before preparing the aforementioned cathode material, the feasibility of the cathode material is verified, specifically whether it can be used as a cathode material for sodium-ion batteries. At a minimum, it must possess a high specific capacity, including: [the specific capacity is determined by the chemical formula Na]. 0.67 Ni 0.25 Mn 0.75 The stoichiometry of sodium carbonate, nickel acetate, and manganese carbonate shown in O2 is as follows: sodium carbonate, nickel acetate, and manganese carbonate are mixed thoroughly, the powder is collected and dried, then transferred to a muffle furnace and sintered at 500-800℃ for 6-18 hours to obtain Na. 0.67 Ni 0.25 Mn 0.75 O2 material.

[0033] To verify Na 0.67 Ni 0.25 Mn 0.75 Electrochemical performance of O2. Taking a 2032-type button cell as an example, assembly is performed in an argon glove box. Before assembling the battery, positive electrode, negative electrode, and separator need to be prepared. The preparation process of the positive electrode involves obtaining Na... 0.67 Ni 0.25 Mn 0.75 80mg of O2 material, 10mg of conductive carbon black, and 10mg of PVDF binder were uniformly mixed in a mortar, then NMP was added and coated onto the surface of aluminum foil. After being stored in a vacuum drying oven for a period of time, the mixture was cut into 12mm electrodes to serve as the positive electrode, and assembled with a sodium electrode as the negative electrode to form a half-cell. After standing for several hours, the mixture was connected to a Xinwei testing system for constant current charge-discharge testing, with a test voltage range of 2-4.3V. Figure 1 As shown, at a current density of 0.2C, its initial capacity is as high as 152.6 mAh / g. Due to the instability of the crystal structure, the capacity decays rapidly during subsequent cycles.

[0034] Example 1

[0035] Example 1 of the present invention provides a nickel-manganese-based sodium-ion battery cathode material Na.0.67 Ni 0.2 Zn 0.05 Mn 0.65 Ti 0.1 O2, which includes the following preparation steps:

[0036] (1) Zinc / titanium co-substituted Na 0.67 Ni 0.25-x Zn x Mn 0.75-y Ti y O2 electrode material, where x = 0.05, y = 0.1; with a total mass of approximately 2g, according to Na... 0.67 Ni 0.2 Zn 0.05 Mn 0.65 Ti 0.1 The stoichiometry indicated by O2 is as follows: Sodium carbonate, nickel acetate, zinc acetate, manganese carbonate, and titanium dioxide are mixed, the powder is collected after thorough mixing, and then dried.

[0037] (2) After drying, the powder is placed in a circular alumina crucible and sintered at high temperature in a muffle furnace. The temperature is increased to 700°C at a rate of 3°C / min and maintained for 6 hours. After cooling to room temperature, the cathode material Na is obtained. 0.67 Ni 0.2 Zn 0.05 Mn 0.65 Ti 0.1 O2;

[0038] (4) After cooling, the positive electrode material is placed in a mortar and ground for a period of time until it is completely powdered. Then, it is sealed in a regular centrifuge tube and stored in an argon glove box for later use.

[0039] The assembly method for the 2032 button cell is the same as above. It can exhibit a discharge specific capacity of 90 mAh / g at a 1C current density and achieve an efficiency of 80% after 30 stable cycles.

[0040] Example 2

[0041] Example 2 of the present invention provides a nickel-manganese-based sodium-ion battery cathode material Na. 0.67 Ni 0.15 Cu 0.1 Mn 0.65 Ti 0.1 O2, which includes the following preparation steps:

[0042] (1) Copper / titanium co-substituted Na 0.67 Ni 0.25-x Cu x Mn 0.75-y Ti y O2 electrode material, where x = 0.1, y = 0.1; with a total mass of approximately 2g, according to Na...0.67 Ni 0.15 Cu 0.1 Mn 0.65 Ti 0.1 The stoichiometry indicated by O2 is as follows: sodium carbonate, nickel acetate, copper acetate, manganese carbonate, and titanium dioxide are mixed, the powder is collected after uniform mixing, and then dried.

[0043] (2) After drying, the powder is placed in a circular alumina crucible and sintered at high temperature in a muffle furnace. The temperature is increased to 800°C at a rate of 3°C / min and maintained for 12 hours. After cooling to room temperature, the cathode material Na is obtained. 0.67 Ni 0.15 Cu 0.1 Mn 0.65 Ti 0.1 O2;

[0044] (3) After cooling, the positive electrode material is placed in a mortar and ground for a period of time until it is completely powdered. Then, it is sealed in a regular centrifuge tube and stored in an argon glove box for later use.

[0045] The assembly method for the 2032 coin cell is the same as above, and its cycle performance at a 1C current density is measured as follows. Figure 2 As shown, it exhibits a discharge specific capacity of 94.7 mAh / g, and after 50 cycles, it obtains a discharge specific capacity of 88.1 mAh / g, with a capacity retention of 93.0%.

[0046] Example 3

[0047] Example 3 of the present invention provides a nickel-manganese-based sodium-ion battery cathode material Na. 0.67 Ni 0.15 Cu 0.1 Mn 0.6 Sn 0.15 O2, which includes the following preparation steps:

[0048] (1) Copper / tin co-substituted Na 0.67 Ni 0.25-x Cu x Mn 0.75-y Sn y O2 electrode material, where x = 0.1, y = 0.15; with a total mass of approximately 2g, according to Na... 0.67 Ni 0.15 Cu 0.1 Mn 0.6 Sn 0.15 The stoichiometry indicated by O2 is achieved by mixing sodium carbonate, nickel acetate, copper acetate, manganese carbonate, and tin oxalate, collecting the powder after thorough mixing, and then drying it.

[0049] (2) After drying, the powder is placed in a circular alumina crucible and sintered at high temperature in a muffle furnace. The temperature is increased to 800℃ at 3℃ / min and maintained for 8h. After cooling to room temperature, the cathode material Na is obtained. 0.67 Ni 0.15 Cu 0.1 Mn 0.6 Sn 0.15 O2;

[0050] (3) After cooling, the positive electrode material is placed in a mortar and ground for a period of time until it is completely powdered. Then, it is sealed in a regular centrifuge tube and stored in an argon glove box for later use.

[0051] The assembly method for the 2032 button cell is the same as above. It can exhibit a discharge specific capacity of 95 mAh / g at a 1C current density and achieve an efficiency of 80% after 60 stable cycles.

[0052] Example 4

[0053] Example 4 of this invention provides a nickel-manganese-based sodium-ion battery cathode material, Na. 0.67 Ni 0.15 Li 0.1 Mn 0.55 Ti 0.2 O2, which includes the following preparation steps:

[0054] (1) Lithium / titanium co-substituted Na 0.67 Ni 0.25-x Li x Mn 0.75-y Ti y O2 electrode material, where x = 0.1, y = 0.2; with a total mass of approximately 2g, according to Na... 0.67 Ni 0.1 Li 0.1 Mn 0.6 Ti 0.2 The stoichiometry indicated by O2 is as follows: sodium carbonate, nickel acetate, lithium acetate, manganese carbonate, and titanium dioxide are mixed, the powder is collected after uniform mixing, and then dried.

[0055] (2) After drying, the powder is placed in a circular alumina crucible and sintered at high temperature in a muffle furnace. The temperature is increased to 800℃ at 3℃ / min and maintained for 12h. After cooling to room temperature, the cathode material Na is obtained. 0.67 Ni 0.15 Li 0.1 Mn 0.55 Ti 0.2 O2;

[0056] (3) After cooling, the positive electrode material is placed in a mortar and ground for a period of time until it is completely powdered. Then, it is sealed in a regular centrifuge tube and stored in an argon glove box for later use.

[0057] The assembly method for the 2032 coin cell is the same as above, and its cycle performance at a 1C current density is measured as follows. Figure 3 As shown, it exhibits a discharge specific capacity of 90.0 mAh / g, and after 100 cycles, it achieves a discharge specific capacity of 89.6 mAh / g, with a capacity retention rate of 99.5%.

[0058] Example 5

[0059] Example 5 of the present invention provides a nickel-manganese-based sodium-ion battery cathode material, Na. 0.67 Ni 0.2 Zn 0.05 Mn 0.55 Ti 0.2 O2, which includes the following preparation steps:

[0060] (1) Zinc / titanium co-substituted Na 0.67 Ni 0.25-x Zn x Mn 0.75-y Ti y O2 electrode material, where x = 0.05, y = 0.2; with a total mass of approximately 2g, according to Na... 0.67 Ni 0.2 Zn 0.05 Mn 0.55 Ti 0.2 The stoichiometry indicated by O2 is as follows: Sodium carbonate, nickel acetate, zinc acetate, manganese carbonate, and titanium dioxide are mixed, the powder is collected after thorough mixing, and then dried.

[0061] (2) After drying, the powder is placed in a circular alumina crucible and sintered at high temperature in a muffle furnace. The temperature is increased to 800℃ at 3℃ / min and maintained for 12h. After cooling to room temperature, the cathode material Na is obtained. 0.67 Ni 0.2 Zn 0.05 Mn 0.55 Ti 0.2 O 2, Its SEM image is as follows Figure 4 As shown, the particle size is concentrated in the micrometer or submicrometer range, which is beneficial for increasing the contact area with the electrolyte; its XRD pattern is shown below. Figure 5 As shown, it exhibits the characteristics of a P2 structure throughout the entire 2θ angle range, and no obvious impurity phase formation was observed, indicating that zinc / titanium substitution occurs at the corresponding transition metal sites.

[0062] (3) After cooling, the positive electrode material is placed in a mortar and ground for a period of time until it is completely powdered. Then, it is sealed in a regular centrifuge tube and stored in an argon glove box for later use.

[0063] To verify Na0.67 Ni 0.2 Zn 0.05 Mn 0.55 Ti 0.2 Electrochemical performance of O2. The rate performance of the assembled 2032 coin cell is as follows: Figure 6 As shown, the current densities in the range of 0.2C, 0.5C, 1C, 2C, and 5C exhibit 122.9, 108.5, 99.6, 92.0, and 79.1 mAh g⁻¹, respectively. -1 The discharge specific capacity. When the tested current density returns to 0.2C, Na 0.67 Ni 0.2 Zn 0.05 Mn 0.55 Ti 0.2 The current density of O2 recovered to 118.4 mAh g. -1 This demonstrates its excellent rate performance; its cycle performance is as follows: Figure 7 As shown, during the first cycle, Na 0.67 Ni 0.2 Zn 0.05 Mn 0.55 Ti 0.2 O2 exhibits approximately 100.0 mAh g -1 The discharge specific capacity showed a capacity retention of 79.3% after 200 cycles.

[0064] To verify Na 0.67 Ni 0.2 Zn 0.05 Mn 0.55 Ti 0.2 The electrochemical performance of O2 in full cells. Taking a 2032 coin cell as an example, the preparation process of a full cell is similar to that of a half cell, except that hard carbon is used as the negative electrode instead of a sodium sheet. Furthermore, a capacity matching process is required before assembling the full cell. Its cycle performance is as follows... Figure 8 As shown, at a current density of 0.5C, it still exhibits a capacity retention of 70.8% after 100 cycles.

[0065] Example 6

[0066] Example 6 of this invention provides a nickel-manganese-based sodium-ion battery cathode material, Na. 0.67 Ni 0.1 Zn 0.15 Mn 0.6 Sn 0.15 O2, which includes the following preparation steps:

[0067] (1) Zinc / tin co-substituted Na 0.67 Ni 0.25-x Zn x Mn 0.75-ySn y O₂ electrode material, where x = 0.15 and y = 0.15; with a total mass of about 2 g, according to the stoichiometry shown by Na 0.67 Ni 0.1 Zn 0.15 Mn 0.6 Sn 0.15 Mix sodium carbonate, nickel acetate, zinc acetate, manganese carbonate, and tin oxalate according to the stoichiometry of O₂ shown. After mixing evenly, collect the powder and dry it;

[0068] (2) After drying, place the powder in a circular alumina crucible and perform high-temperature sintering in a muffle furnace. Heat it to 800 °C at a rate of 3 °C / min and maintain for 8 h, then cool to room temperature to obtain the positive electrode material Na 0.67 Ni 0.1 Zn 0.15 Mn 0.6 Sn 0.15 O₂.

[0069] (3) Grind the cooled positive electrode material in a mortar for a period of time. After it completely becomes powder, seal it in a common centrifuge tube and store it in an argon glove box for later use.

[0070] The assembled 2032-type button battery can exhibit a discharge specific capacity of 93 mAh / g at a current density of 1 C and reach an efficiency of 90% after 50 stable cycles.

[0071] Therefore, a positive electrode material for a nickel-manganese-based sodium-ion battery according to the present invention, the positive electrode material is a P2-type layered oxide material, and its chemical general formula is Na 0.67 Ni 0.25-x M1 x Mn 0.75-y M2 y O₂, where M1 is one or more of Zn, Li, or Cu, M2 is one or more of Ti or Sn, 0.05 < x ≤ 0.2, 0.05 < y ≤ 0.2, zinc ions, lithium ions, or copper ions replace part of the nickel ions, and titanium ions or tin ions replace part of the manganese ions. It has the characteristics of accurate structure, excellent performance, low-cost synthesis, environmental protection, and energy conservation, and is suitable for use as a positive electrode material in sodium-ion batteries.

[0072] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific embodiments described. Obviously, many modifications and changes can be made according to the content of this specification. These embodiments are selected and specifically described in this specification to better explain the principle and practical application of the present invention, so that those skilled in the art can understand and utilize the present invention well. The present invention is only limited by the claims and their full scope and equivalents.

Claims

1. A nickel-manganese-based sodium-ion battery cathode material, characterized in that, The positive electrode material described is a P2-type layered oxide material with a chemical general formula of Na 0.67 Ni 0.25-x M1 x Mn 0.75-y M2 y O2, where M1 is one or more of Zn, Li, or Cu, M2 is Ti and Sn, or Sn, 0.05 < x ≤ 0.2, 0.05 < y ≤ 0.2, and zinc ions, lithium ions, and copper ions replace part of the nickel ions, and titanium ions and tin ions replace part of the manganese ions.

2. A method for preparing the cathode material as described in claim 1, characterized in that, Includes the following steps: (1) According to the stoichiometric ratio of the general chemical formula, take 1-1.05 times the required stoichiometric amount of sodium salt and mix it with the required amount of other metal salts; (2) After drying, the cathode material is sintered at 500-800℃ for 6-18h and then cooled to room temperature to obtain the cathode material.

3. The method for preparing the cathode material according to claim 2, characterized in that, The sodium salt mentioned in step (1) is a carbonate or acetate, and the remaining metal salt is one or two of oxides, oxalates, carbonates or acetates.

4. The method for preparing the cathode material according to claim 2, characterized in that, Step (2) involves placing the dried metal salt in a muffle furnace and sintering it at a set temperature by heating it up to 3-5℃ / min.

5. The method for preparing the cathode material according to claim 2, characterized in that, Before preparing the aforementioned cathode material, the feasibility of its preparation is verified: using the chemical formula Na... 0.67 Ni 0.25 Mn 0.75 The stoichiometric amounts of sodium, nickel, and manganese salts, as indicated by O2, were mixed thoroughly. The resulting powder was collected, dried, and transferred to a muffle furnace for sintering at 500-800℃ for 6-18 hours to obtain Na. 0.67 Ni 0.25 Mn 0.75 O2 material.

6. The method for preparing the cathode material according to claim 2, characterized in that, It also includes grinding the cooled positive electrode material into powder in a mortar, transferring it to a centrifuge tube, sealing it, and storing it in an argon glove box for later use.

7. A positive electrode sheet for a sodium-ion battery, characterized in that, The positive electrode sheet includes the positive electrode material as described in claim 1.

8. A sodium-ion secondary battery comprising the positive electrode as described in claim 7.

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