Sodium-ion battery positive electrode material and preparation method therefor, and sodium-ion battery

Abstract

Disclosed in the present application are a sodium-ion positive electrode material and a preparation method therefor, and a sodium-ion battery. The chemical formula of the sodium-ion positive electrode material is NaiNixFeyMnzM1mM2nO2, wherein M1 is a tetravalent metal element doped and substituted at the Mn site, and M2 is a low-valence metal element doped and substituted at the transition metal site, with the low-valence metal element being one or more of a monovalent metal element and a divalent metal element.

Description

A sodium-ion battery cathode material, its preparation method, and a sodium-ion battery.

[0001] Related applications

[0002] This application claims priority to Chinese patent application filed on May 31, 2024, application number 202410699233.9, entitled "A sodium-ion battery cathode material and its preparation method and sodium-ion battery", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application belongs to the field of sodium-ion battery technology, and particularly relates to a sodium-ion battery cathode material, its preparation method, and a sodium-ion battery. Background Technology

[0004] With the large-scale application of lithium-ion batteries, their manufacturing costs are gradually increasing. Sodium-ion batteries, on the other hand, have a significant price advantage due to the abundant and inexpensive availability of sodium as a raw material. Furthermore, their working principle is very similar to that of traditional lithium-ion batteries. Therefore, the research and development of sodium-ion batteries has received high attention from enterprises and the scientific community.

[0005] Cathode materials are one of the most important factors affecting the performance of sodium-ion batteries, and their performance has become a focus of attention. Currently, the main cathode materials under research are polyanionic compounds, layered oxides, and Prussian blue analogues. Among them, O3-type layered oxides are considered one of the most commercially promising cathode materials for sodium-ion batteries due to their simple production methods and high specific capacity. The cathode material with the fastest industrialization progress is currently NaNi. 0.33 Fe 0.33 Mn 0.34 O2 is used in sodium-ion batteries, but Ni, a precious metal, is expensive, hindering its application in cost-sensitive energy storage and low-end electric vehicles. Therefore, there is a need to further develop low-cost sodium-ion battery cathode materials with lower Ni content. However, the Fe content should not exceed 0.33%, as excessive Fe migration enhances performance. Therefore, reducing Ni content is accompanied by increasing Mn content, which in turn raises the valence state of the transition metal, further reducing the number of sodium ions that can enter the bulk phase, resulting in a significant decrease in battery capacity.

[0006] Chinese patent CN116544408A addresses the aforementioned issues to some extent by introducing low-valence element doping technology. The product successfully achieved a specific capacity of 130 mAh / g and an average discharge voltage of 3.24 V, corresponding to an energy density of approximately 417 Wh / kg. This provides new ideas and possible solutions for the development of low-cost, high-performance sodium-ion battery cathode materials.

[0007] While the above techniques can reduce the cost of raw materials, they still lag behind NFM111 (typical capacity ~140mAh / g, average discharge voltage ~3.13V, energy density ~438Wh / kg) in terms of capacity and energy density. This means that their application in fields with high battery performance requirements, such as electric vehicles, will be somewhat limited. Therefore, finding a technical path that can improve the specific capacity and extend the cycle life of sodium-ion battery cathode materials while maintaining the low-cost advantage, in order to truly promote the practical application and large-scale application of sodium-ion battery technology, is an urgent problem to be solved. Summary of the Invention

[0008] This application addresses the limitations of existing sodium-ion battery cathode materials in terms of cost, capacity, and cycle stability by providing a sodium-ion battery cathode material, its preparation method, and a sodium-ion battery. It utilizes the strong binding effect of M1 with oxygen to stabilize the bulk structure and improve the material's cycle performance. Furthermore, the use of the low-valence element M2 for doping effectively reduces the valence state of the transition metal element. To maintain electroneutrality, more Na enters the bulk phase, reducing the sodium salt content remaining on the surface and improving the cathode material's processing performance, discharge specific capacity, and energy density.

[0009] To solve the above-mentioned technical problems, the technical solution proposed in this application is as follows:

[0010] A sodium-ion battery cathode material, wherein the sodium-ion battery cathode material is a layered oxide, and the general chemical formula of the layered oxide is Na. i Ni x Fe y Mn z M1 m M2 n O2, M1 is a tetravalent metal element that is doped and substituted at the Mn site, and M2 is a low-valent metal element that is doped and substituted at the transition metal site. The low-valent metal element is one or more of a monovalent metal element and a divalent metal element.

[0011] Where, 0.90≤i≤1.05, 0.1≤x≤0.3, 0.1≤y≤0.4, 0.1≤z≤0.6, 0.03<m≤0.15, 0.03<n≤0.10, x+y+z+m+n=1.

[0012] In some embodiments, in the sodium-ion battery cathode material, M1 is one or more of Ti, Zr, Si, and Ce, and M2 is one or more of Li, Mg, Cu, and Zn.

[0013] In some embodiments, the positive electrode material of the sodium-ion battery has the following properties: 0.22≤x≤0.24, 0.29≤y≤0.31, 0.28≤z≤0.30, 0.09≤m≤0.10, 0.07≤n<0.10, M1 is one or both of Ti and Zr, and M2 is one or more of Mg, Cu, and Zn.

[0014] In some embodiments, in the sodium-ion battery cathode material, the Na2CO3 and NaOH on the surface of the sodium-ion battery cathode material have a mass percentage of 0.20-0.30% and a mass percentage of 0.01-0.15% based on the total mass of the cathode material.

[0015] The test method for residual sodium on the surface is as follows: using glycerol as the test solvent for residual alkali, taking advantage of the difference in solubility of strong and weak bases in glycerol, an acid solution is added for acid-base neutralization, and the content of residual Na2CO3 and NaOH in the sample is tested by potentiometric titration.

[0016] The calculation formula is as follows:

[0017] V1 is the volume of acid standard solution consumed at the first equivalence point, V2 is the volume of acid standard solution consumed at the second equivalence point (including the first equivalence point), and V is the volume of the sample after dilution. All units are mL.

[0018] In some embodiments, the sodium-ion battery cathode material is XRD-tested to be a pure O3 phase with cell parameters 2.97≤a≤2.98 and 16.05≤c≤16.08.

[0019] In some embodiments, the sodium-ion battery cathode material is placed in 10 times its weight of water, stirred for 5 minutes, and allowed to stand for 30 minutes. The resulting solution has a pH ≤ 12.3. The lower the residual sodium and pH of the sodium-ion battery cathode material, the better its processing performance.

[0020] As a general inventive concept, this application provides a method for preparing a sodium-ion battery cathode material, comprising the following steps:

[0021] (1) After preparing a salt solution containing Ni, Fe, Mn and M1 in proportion, a co-precipitation reaction was carried out to prepare hydroxide precursor materials;

[0022] (2) The precursor material, sodium carbonate and compound containing M2 element are mixed and sintered, then cooled to room temperature and crushed and sieved to obtain sodium-ion battery cathode material.

[0023] In some embodiments, the preparation method of sodium-ion battery cathode material includes the following steps in step (1): preparing a salt solution containing Ni, Fe, Mn and M1, and then adding it to the reaction vessel in parallel with NaOH solution and ammonia water, heating and stirring to carry out a co-precipitation reaction, aging and standing after the reaction is completed, and then performing solid-liquid separation, water washing and drying on the slurry to prepare hydroxide precursor material.

[0024] In some embodiments, in the method for preparing the positive electrode material of a sodium-ion battery, in step (2), the sintering atmosphere is compressed air, the dew point of the compressed air is <-30°C, and the humidity is <1%.

[0025] In some embodiments, in the preparation method of sodium-ion battery cathode material, step (2) involves a two-step sintering process, which includes sintering at 700–850°C for 3–8 hours and then sintering at 860–1000°C for 10–15 hours. The heating rate during the sintering process is 2–5°C / min, and the cooling rate during the cooling process is 0.5–1.0°C / min. This application adds an isothermal sintering stage, which pre-oxidizes the precursor while raising the sintering temperature to near the melting point of sodium carbonate. The presence of molten sodium carbonate can provide a quasi-liquid environment, promoting continuous particle growth and improving the uniformity of particles after sintering.

[0026] As a general inventive concept, this application also provides a sodium-ion battery, wherein the positive electrode material is the sodium-ion battery positive electrode material described above or the sodium-ion battery positive electrode material prepared by the above preparation method.

[0027] Compared with the prior art, the beneficial effects of this application are as follows:

[0028] (1) This application targets sodium-ion batteries with a low-nickel and high-manganese system. The cathode material of the sodium-ion battery is doped with bimetallic elements by replacing part of Mn with an inactive tetravalent element M1. 4+ The strong binding of M1 with oxygen stabilizes the overall bulk structure, enhances the thermodynamic and cycling stability of the material, and mitigates structural degradation during charge and discharge processes. Simultaneously, a low-valence metal element M2 doping strategy is employed to effectively reduce the valence state of the transition metal, promoting the production of more Na to maintain electroneutrality. + It can be stably stored in the bulk structure, which helps to reduce the sodium salt content remaining on the surface of the cathode material, significantly improve the specific capacity of the material, improve the processing performance of the material, and make the resulting sodium-ion battery cathode material have a high energy density.

[0029] (2) The sodium-ion battery cathode material of this application has low residual alkali and good processing performance; it has high capacity and good cycle performance, with a discharge specific capacity of up to 141.2 mAh / g at 0.1C, an average voltage of up to 3.2V, an energy density of up to 452Wh / kg, and a capacity retention rate of up to 94.4% after 100 cycles of 1C charge and discharge.

[0030] (3) The method for preparing sodium-ion battery cathode material in this application is simple and easy to implement, convenient to operate, and low in cost. It ultimately yields a high-performance sodium-ion battery cathode material that balances capacity, cycle performance, energy density, low cost, and good processing performance. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of this application or the conventional technology, the drawings used in the description of the embodiments or the conventional technology will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on the disclosed drawings without creative effort.

[0032] Figure 1 shows the XRD patterns of the layered oxide materials in Examples 1, 5, 6 and Comparative Example 1.

[0033] Figure 2 is a charge-discharge curve of the layered oxide material in Example 1 and Comparative Example 4.

[0034] Figure 3 is a 100-cycle curve of the layered oxide material in Example 1 and Comparative Example 4. Detailed Implementation

[0035] To facilitate understanding of this application, a more comprehensive and detailed description of the application will be provided below in conjunction with the accompanying drawings and preferred embodiments. However, the scope of protection of this application is not limited to the specific embodiments described below. Clearly, the embodiments described below are merely some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application.

[0036] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of this application.

[0037] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application are available on the market or can be prepared by existing methods.

[0038] Example 1:

[0039] A sodium-ion battery cathode material is a layered oxide with the general chemical formula Na. 0.96 Ni 0.232 Fe 0.307 Mn 0.298 Ti 0.093 Zn 0.07 O2 and Ti are used to dop and substitute Mn sites, while Zn is used to dop and substitute transition metal sites.

[0040] The preparation method of the sodium-ion battery cathode material in this embodiment includes the following steps:

[0041] (1) Preparation of the quaternary precursor: A salt solution containing nickel nitrate, iron nitrate, manganese nitrate, and titanium nitrate with a total metal ion concentration of 1.0 mol / L was prepared (metal molar ratio Ni:Fe:Mn:Ti = 25:33:32:10); the salt solution, 5.0 mol / L NaOH solution, and 4.0 mol / L ammonia solution were added to the reactor in a co-current flow. The flow rate of the salt solution was 10 L / h, the flow rate of the NaOH solution was 4 L / h, and the flow rate of the ammonia solution was 0.05 L / h. The mixture was heated and stirred to carry out a co-precipitation reaction at a temperature of 60℃; after the reaction was completed, the mixture was aged and allowed to stand for 10 h. Then, the slurry was subjected to solid-liquid separation. The solid after separation was washed with deionized water and dried in an oven to obtain the quaternary precursor Ni. 0.25 Fe 0.33 Mn 0.32 Ti 0.10 (OH)2.

[0042] (2) The above quaternary precursor Ni 0.25 Fe 0.33 Mn 0.32 Ti 0.10 (OH)2, Na2CO3, and ZnO were dry-mixed according to the elemental molar ratio of (Ni+Fe+Mn+Ti):Na:Zn = 0.93:1.03:0.07. After uniform mixing, the mixture was heated to 750℃ in a compressed air atmosphere (dew point < -30℃, humidity < 1%) at a heating rate of 3℃ / min and sintered for 5 hours. Then, it was heated to 980℃ at a heating rate of 3℃ / min and sintered for 12 hours. Finally, it was cooled to room temperature at a cooling rate of 0.7℃ / min, crushed, and sieved to obtain a layered oxide material, which is the cathode material for sodium-ion batteries.

[0043] Example 2:

[0044] A sodium-ion battery cathode material is a layered oxide with the general chemical formula Na. 0.96 Ni 0.232 Fe 0.307 Mn 0.298 Zr 0.093 Zn0.07 O2 and Zr are used to dop and substitute Mn sites, while Zn is used to dop and substitute transition metal sites.

[0045] The preparation method of the sodium-ion battery cathode material in this embodiment includes the following steps:

[0046] (1) Preparation of the quaternary precursor: A salt solution containing nickel nitrate, iron nitrate, manganese nitrate, and zirconium nitrate with a total metal ion concentration of 1.0 mol / L was prepared (metal molar ratio of Ni:Fe:Mn:Zr = 25:33:32:10); the salt solution, 5.0 mol / L NaOH solution, and 4.0 mol / L ammonia solution were added to the reactor in parallel flow. The flow rate of the salt solution was 10 L / h, the flow rate of the NaOH solution was 4 L / h, and the flow rate of the ammonia solution was 0.05 L / h. The mixture was heated and stirred to carry out a co-precipitation reaction at a reaction temperature of 60℃; after the reaction was completed, the mixture was aged and allowed to stand for 10 h. Then, the slurry was subjected to solid-liquid separation. The solid after separation was washed with deionized water and dried in an oven to obtain the quaternary precursor Ni. 0.25 Fe 0.33 Mn 0.32 Ti 0.10 (OH)2.

[0047] (2) The above quaternary precursor Ni 0.25 Fe 0.33 Mn 0.32 Zr 0.10 (OH)2, Na2CO3, and ZnO were dry-mixed according to the elemental molar ratio of (Ni+Fe+Mn+Zr):Na:Zn = 0.93:1.03:0.07. After uniform mixing, the mixture was heated to 750℃ in a compressed air atmosphere (dew point < -30℃, humidity < 1%) at a heating rate of 3℃ / min and sintered for 5h. Then, it was heated to 980℃ at a heating rate of 3℃ / min and sintered for 12h. Finally, it was cooled to room temperature at a cooling rate of 0.7℃ / min, crushed, and sieved to obtain a layered oxide material.

[0048] Example 3:

[0049] A sodium-ion battery cathode material is a layered oxide with the general chemical formula Na. 0.96 Ni 0.232 Fe 0.307 Mn 0.298 Ti 0.093 Mg 0.07 O2 and Ti are used to dop and substitute Mn sites, while Mg is used to dop and substitute transition metal sites.

[0050] The difference between the preparation method of the sodium-ion battery cathode material in this embodiment and the preparation method in Example 1 is that the quaternary precursor Ni 0.25 Fe0.33 Mn 0.32 Ti 0.10 (OH)2, Na2CO3, and MgO were dry-mixed according to the elemental molar ratio of (Ni+Fe+Mn+Ti):Na:Mg = 0.93:1.03:0.07. Other processes and parameters remained the same as in Example 1.

[0051] Example 4:

[0052] A sodium-ion battery cathode material is a layered oxide with the general chemical formula Na. 0.96 Ni 0.232 Fe 0.307 Mn 0.298 Ti 0.093 Cu 0.07 O2 and Ti are used to dop and substitute Mn sites, while Cu is used to dop and substitute transition metal sites.

[0053] The difference between the preparation method of the sodium-ion battery cathode material in this embodiment and the preparation method in Example 1 is that the quaternary precursor Ni 0.25 Fe 0.33 Mn 0.32 Ti 0.10 (OH)2, Na2CO3, and CuO were dry-mixed according to the elemental molar ratio of (Ni+Fe+Mn+Ti):Na:Cu = 0.93:1.03:0.07, while other processes and parameters remained the same as in Example 1.

[0054] Example 5:

[0055] A sodium-ion battery cathode material is a layered oxide with the general chemical formula Na. 0.96 Ni 0.237 Fe 0.314 Mn 0.304 Ti 0.095 Zn 0.05 O2 and Ti are used to dop and substitute Mn sites, while Zn is used to dop and substitute transition metal sites.

[0056] The difference between the preparation method of the sodium-ion battery cathode material in this embodiment and the preparation method in Example 1 is that the quaternary precursor Ni 0.25 Fe 0.33 Mn 0.32 Ti 0.10 (OH)2, Na2CO3, and ZnO were dry-mixed according to the elemental molar ratio of (Ni+Fe+Mn+Ti):Na:Zn = 0.95:1.03:0.05, while other processes and parameters remained the same as in Example 1.

[0057] Example 6:

[0058] A sodium-ion battery cathode material is a layered oxide with the general chemical formula Na. 0.96 Ni 0.225 Fe 0.297 Mn 0.288 Ti 0.090 Zn 0.10 O2 and Ti are used to dop and substitute Mn sites, while Zn is used to dop and substitute transition metal sites.

[0059] The difference between the preparation method of the sodium-ion battery cathode material in this embodiment and the preparation method in Example 1 is that the quaternary precursor Ni... 0.25 Fe 0.33 Mn 0.32 Ti 0.10 (OH)2, Na2CO3, and ZnO were dry-mixed according to the elemental molar ratio of (Ni+Fe+Mn+Ti):Na:Zn = 0.93:1.03:0.10, while other processes and parameters remained the same as in Example 1.

[0060] Comparative Example 1:

[0061] The layered oxide material in this comparative example has the chemical formula Na. 0.96 Ni 0.25 Fe 0.33 Mn 0.42 O2.

[0062] The preparation method of the comparative layered oxide material includes the following steps:

[0063] (1) Preparation of ternary precursor: A salt solution containing nickel nitrate, iron nitrate, and manganese nitrate with a total metal ion concentration of 1.0 mol / L was prepared (metal molar ratio of Ni:Fe:Mn = 25:33:42); the salt solution, 5.0 mol / L NaOH solution, and 4.0 mol / L ammonia solution were added to the reactor in parallel flow. The flow rate of the salt solution was 10 L / h, the flow rate of the NaOH solution was 4 L / h, and the flow rate of the ammonia solution was 0.05 L / h. The reaction was carried out by heating and stirring at a temperature of 60℃. After the reaction was completed, the mixture was aged and allowed to stand for 10 h. Then, the slurry was separated into solid and liquid components. The solid was washed with deionized water and dried in an oven to obtain the ternary precursor Ni. 0.25 Fe 0.33 Mn 0.42 (OH)2.

[0064] (2) The above ternary precursor Ni 0.25 Fe 0.33 Mn 0.42(OH)2 and Na2CO3 were dry-mixed according to the elemental molar ratio of (Ni+Fe+Mn):Na = 1.0:1.03. After uniform mixing, the mixture was heated to 750℃ in a compressed air atmosphere (dew point < -30℃, humidity < 1%) at a heating rate of 3℃ / min and sintered for 5h. Then, it was heated to 980℃ at a heating rate of 3℃ / min and sintered for 12h. Finally, it was cooled to room temperature at a cooling rate of 0.7℃ / min and sieved to obtain a layered oxide material.

[0065] Comparative Example 2:

[0066] The layered oxide material in this comparative example has the chemical formula Na. 0.96 Ni 0.209 Fe 0.276 Mn 0.352 Ti 0.093 Zn 0.07 O2, Ti, and Zn are all obtained by doping and substituting the transition metal sites.

[0067] The preparation method of the comparative layered oxide material includes the following steps:

[0068] (1) Preparation of ternary precursor: A salt solution containing nickel nitrate, iron nitrate, and manganese nitrate with a total metal ion concentration of 1.0 mol / L was prepared (metal molar ratio of Ni:Fe:Mn = 25:33:42); the salt solution, 5.0 mol / L NaOH solution, and 4.0 mol / L ammonia solution were added to the reactor in parallel flow. The flow rate of the salt solution was 10 L / h, the flow rate of the NaOH solution was 4 L / h, and the flow rate of the ammonia solution was 0.05 L / h. The reaction was carried out by heating and stirring at a temperature of 60℃. After the reaction was completed, the mixture was aged and allowed to stand for 10 h. Then, the slurry was separated into solid and liquid components. The solid was washed with deionized water and dried in an oven to obtain the ternary precursor Ni. 0.25 Fe 0.33 Mn 0.42 (OH)2.

[0069] (2) The above ternary precursor Ni 0.25 Fe 0.33 Mn 0.42 (OH)2, Na2CO3, TiO2, and ZnO were dry-mixed according to the elemental molar ratio of (Ni+Fe+Mn):Na:TiO2:ZnO = 0.837:1.03:0.093:0.07. After uniform mixing, the mixture was heated to 750℃ in a compressed air atmosphere (dew point < -30℃, humidity < 1%) at a heating rate of 3℃ / min and sintered for 5h. Then, it was heated to 980℃ at a heating rate of 3℃ / min and sintered for 12h. Finally, it was cooled to room temperature at a cooling rate of 0.7℃ / min and sieved to obtain a layered oxide material.

[0070] Comparative Example 3:

[0071] The layered oxide material in this comparative example has the chemical formula Na. 0.96 Ni 0.25 Fe 0.33 Mn 0.37 Ti 0.05 O2.

[0072] The preparation method of the comparative layered oxide material includes the following steps:

[0073] (1) Preparation of the quaternary precursor: A salt solution containing nickel nitrate, iron nitrate, manganese nitrate, and titanium nitrate with a total metal ion concentration of 1.0 mol / L was prepared (metal molar ratio of Ni:Fe:Mn:Ti = 25:33:37:5); the salt solution, 5.0 mol / L NaOH solution, and 4.0 mol / L ammonia solution were added to the reactor in a parallel flow. The flow rate of the salt solution was 10 L / h, the flow rate of the NaOH solution was 4 L / h, and the flow rate of the ammonia solution was 0.05 L / h. The mixture was heated and stirred to carry out a co-precipitation reaction at a reaction temperature of 60℃; after the reaction was completed, the mixture was aged and allowed to stand for 10 h. Then, the slurry was subjected to solid-liquid separation. The solid after separation was washed with deionized water and dried in an oven to obtain the quaternary precursor Ni. 0.25 Fe 0.33 Mn 0.37 Ti 0.05 (OH)2.

[0074] (2) The above quaternary precursor Ni 0.25 Fe 0.33 Mn 0.37 Ti 0.05 (OH)2 and Na2CO3 were dry-mixed at an elemental molar ratio of 1.0:1.03. After uniform mixing, the mixture was heated to 750°C in a compressed air atmosphere (dew point < -30°C, humidity < 1%) at a heating rate of 3°C / min and sintered for 5 hours. Then, it was heated to 980°C at a heating rate of 3°C / min and sintered for 12 hours. Finally, it was cooled to room temperature at a cooling rate of 0.7°C / min and sieved to obtain a layered oxide material.

[0075] Comparative Example 4:

[0076] The layered oxide material in this comparative example has the chemical formula Na. 0.96 Ni 0.25 Fe 0.33 Mn 0.32 Ti 0.10 O2.

[0077] The preparation method of the comparative layered oxide material includes the following steps:

[0078] (1) Preparation of the quaternary precursor: A salt solution containing nickel nitrate, iron nitrate, manganese nitrate, and titanium nitrate with a total metal ion concentration of 1.0 mol / L was prepared (metal molar ratio of Ni:Fe:Mn:Ti = 25:33:32:10); the salt solution, 5.0 mol / L NaOH solution, and 4.0 mol / L ammonia solution were added to the reactor in parallel flow. The flow rate of the salt solution was 10 L / h, the flow rate of the NaOH solution was 4 L / h, and the flow rate of the ammonia solution was 0.05 L / h. The mixture was heated and stirred to carry out a co-precipitation reaction at a reaction temperature of 60℃; after the reaction was completed, the mixture was aged and allowed to stand for 10 h. Then, the slurry was subjected to solid-liquid separation. The solid after separation was washed with deionized water and dried in an oven to obtain the quaternary precursor Ni. 0.25 Fe 0.33 Mn 0.32 Ti 0.10 (OH)2.

[0079] (2) The above quaternary precursor Ni 0.25 Fe 0.33 Mn 0.32 Ti 0.10 (OH)2 and Na2CO3 were dry-mixed according to the elemental molar ratio of (Ni+Fe+Mn+Ti):Na = 1.0:1.03. After uniform mixing, the mixture was heated to 750℃ in a compressed air atmosphere (dew point < -30℃, humidity < 1%) at a heating rate of 3℃ / min and sintered for 5h. Then, it was heated to 980℃ at a heating rate of 3℃ / min and sintered for 12h. Finally, it was cooled to room temperature at a cooling rate of 0.7℃ / min and sieved to obtain a layered oxide material.

[0080] Comparative Example 5:

[0081] The layered oxide material in this comparative example has the chemical formula Na. 0.96 Ni 0.25 Fe 0.33 Mn 0.27 Ti 0.15 O2.

[0082] The preparation method of the comparative layered oxide material includes the following steps:

[0083] (1) Preparation of the quaternary precursor: A salt solution containing nickel nitrate, iron nitrate, manganese nitrate, and titanium nitrate with a total metal ion concentration of 1.0 mol / L was prepared (metal molar ratio of Ni:Fe:Mn:Ti = 25:33:27:15); the salt solution, 5.0 mol / L NaOH solution, and 4.0 mol / L ammonia solution were added to the reactor in a parallel flow. The flow rate of the salt solution was 10 L / h, the flow rate of the NaOH solution was 4 L / h, and the flow rate of the ammonia solution was 0.05 L / h. The mixture was heated and stirred to carry out a co-precipitation reaction at a temperature of 60℃; after the reaction was completed, the mixture was aged and allowed to stand for 10 h. Then, the slurry was subjected to solid-liquid separation. The solid after separation was washed with deionized water and dried in an oven to obtain the quaternary precursor Ni. 0.25 Fe 0.33 Mn 0.27 Ti 0.15 (OH)2.

[0084] (2) The above quaternary precursor Ni 0.25 Fe 0.33 Mn 0.27 Ti 0.15 (OH)2 and Na2CO3 were dry-mixed according to the elemental molar ratio of (Ni+Fe+Mn+Ti):Na = 1.0:1.03. After uniform mixing, the mixture was heated to 750℃ in a compressed air atmosphere (dew point < -30℃, humidity < 1%) at a heating rate of 3℃ / min and sintered for 5h. Then, it was heated to 980℃ at a heating rate of 3℃ / min and sintered for 12h. Finally, it was cooled to room temperature at a cooling rate of 0.7℃ / min and sieved to obtain a layered oxide material.

[0085] The layered oxide materials prepared in Examples 1-6 and Comparative Examples 1-5 were tested for particle size, BET, pH, and residual sodium content. The specific method for pH testing was as follows: the sodium-ion battery cathode material was placed in water with a mass equal to its weight, stirred for 5 minutes, and allowed to stand for 30 minutes before testing the pH of the solution. The specific method for residual sodium testing was as follows: 10g of sample was dissolved in 100mL of glycerol solution, stirred for 10-30 minutes, filtered, and a 0.1mol / L HCl solution was prepared. The solution was placed in an automatic potentiometric titrator and titrated using the equivalence point method. The volume of HCl consumed at the jump point was recorded, and the residual sodium content of the sample was calculated using the aforementioned formula. The test was repeated 3 times, and the average value was taken.

[0086] The layered oxide materials obtained in Examples 1-6 and Comparative Examples 1-5 were mixed uniformly with conductive agents and binders in a specific ratio to form a slurry, which was then coated onto aluminum foil to prepare a positive electrode sheet. In a glove box under an argon atmosphere, a half-cell was assembled using metallic sodium as the negative electrode and glass fiber as the separator. The half-cell was subjected to two 0.1C constant current charge-discharge cycles at room temperature (25°C) within a voltage range of 2.0-4.0V, followed by 100 cycles at 1C. The test results are shown in Table 1.

[0087] Table 1 Characteristic physicochemical properties and tack charge data of layered oxide materials

[0088] In Examples 1-6 of this application, the sodium-ion battery cathode material is doped with two metal elements. The strong binding energy of M1 with oxygen is used to stabilize the bulk structure and improve the cycle performance of the material. Then, the low-valence element M2 is used for doping, which effectively reduces the valence state of the transition metal element. In order to maintain electrical neutrality, more Na enters the bulk phase, reducing the sodium salt content remaining on the surface, improving the processing performance and discharge specific capacity of the cathode material, and also having a high energy density.

[0089] Figure 1 shows the XRD patterns of the layered oxide materials in Examples 1, 5, 6, and Comparative Example 1, all of which are pure O3 phase. Combined with the cell parameters a and c after refining the XRD patterns using TOPAS in Table 1, a comparison between Examples 1 and 5 shows that as the Zn content increases, the (003) peak continuously shifts to the right, the a value gradually increases, the c value gradually decreases, the Na content in the bulk phase continuously increases, the attraction between the sodium layer and the oxygen layer continuously strengthens, and the interlayer spacing continuously decreases. Furthermore, as the Zn content increases, the residual sodium content decreases, and the capacity and cycling performance increase. However, a comparison between Examples 1 and 6 shows that when the Zn content reaches 0.10, a ZnO impurity phase appears, and the capacity and cycling performance also decline, indicating that the doping amount of M2 element should not be too high.

[0090] Figure 2 shows the charge-discharge curves of the layered oxide materials in Example 1 and Comparative Example 4, and Figure 3 shows the 100-cycle curves of the layered oxide materials in Example 1 and Comparative Example 4. As can be seen from Comparative Example 1 and Comparative Example 4, by utilizing the synergistic effect of M1 and M2, excellent cycling performance can be achieved while ensuring low residual alkali and high capacity.

[0091] As can be seen from the performance data of Comparative Example 1 and Comparative Example 2 in Table 1, when M1 and M2 are added simultaneously by dry method, there are too many high-valence elements. Even if the contents of M1 and M2 added are the same, although the cycle performance can be improved to a certain extent, it cannot play the role of reducing residual alkali and increasing capacity as M1 and M2 are added separately in Example 1.

[0092] Based on the pH, residual sodium content, and truncation voltage test results of Comparative Examples 1 and 3-5, it is evident that when the Mn content is too high, the valence state of the transition metal element is too high, preventing the added sodium from entering the bulk phase and causing it to deposit on the surface, resulting in low capacity and poor cycle performance. Replacing Mn with a non-electrochemically active tetravalent element, utilizing M1... 4+ The strong binding energy of M1 with O and its pillaring effect stabilize the structure and improve the cycling performance of the material. However, since M1 does not participate in redox reactions, the capacity decreases continuously as the M1 content increases. Furthermore, M1 maintains a +4 valence in the system, which leads to higher valence states of transition metal elements and further increases the residual sodium content on the material surface. Therefore, it is necessary to control the M1 doping amount at an appropriate ratio to improve cycling performance while minimizing the impact on processing performance and capacity.

[0093] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0094] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A sodium-ion battery cathode material, the sodium-ion battery cathode material is a layered oxide, the chemical general formula of the layered oxide is Na i Ni x Fe y Mn z M1 m M2 n O2, M1 is a tetravalent metal element doped and substituted at the Mn site, M2 is a low-valence metal element doped and substituted at the transition metal site, the low-valence metal element is one or more of monovalent metal elements and divalent metal elements. wherein 0.90≤i≤1.05, 0.1≤x≤0.3, 0.1≤y≤0.4, 0.1≤z≤0.6, 0.03 2. The sodium-ion battery cathode material of claim 1, wherein, M1 is one or more of Ti, Zr, Si, Ce, and M2 is one or more of Li, Mg, Cu, Zn.

3. The sodium-ion battery cathode material of any one of claims 1-2, wherein, 0.22≤x≤0.24, 0.29≤y≤0.31, 0.28≤z≤0.30, 0.09≤m≤0.10, 0.07≤n≤0.10, M1 is one or both of Ti and Zr, and M2 is one or more of Mg, Cu, and Zn.

4. The sodium-ion battery cathode material of any one of claims 1-3, wherein, The mass percentage of Na2CO3 on the surface of the sodium-ion battery cathode material is 0.01-0.30% based on the total mass of the cathode material, and the mass percentage of NaOH is 0.01-0.15%.

5. The sodium-ion battery cathode material of any one of claims 1-4, wherein, The sodium-ion battery cathode material is a pure O3 phase as determined by XRD, and the cell parameters are 2.97≤a≤2.98 and 16.05≤c≤16.

08.

6. The sodium-ion battery cathode material of any one of claims 1-5, wherein, After the sodium-ion battery cathode material is placed in water 10 times its mass, stirred for 5 min, and left to stand for 30 min, the pH of the resulting solution is ≤12.

3.

7. A method for preparing the sodium-ion battery cathode material according to any one of claims 1-6, comprising the following steps: (1) preparing a hydroxide precursor material by proportionally preparing a salt solution containing Ni, Fe, Mn, and M1 and then performing a co-precipitation reaction; (2) mixing the precursor material, sodium carbonate, and a compound containing M2 elements and then sintering, cooling to room temperature, crushing, and sieving to obtain a sodium-ion battery cathode material.

8. The production method according to claim 7, wherein Step (1) specifically comprises the following steps: preparing a salt solution containing Ni, Fe, Mn, and M1, then adding the solution into a reaction kettle together with a NaOH solution and an ammonia solution in a concurrent manner, heating and stirring to perform a co-precipitation reaction, allowing the reaction to complete and then standing, and then performing solid-liquid separation, water washing, and drying on the slurry to prepare a hydroxide precursor material.

9. The method of making according to any one of claims 7-8, wherein, In step (2), the sintering atmosphere is compressed air with a dew point < -30°C and a humidity < 1%.

10. The method of making according to any one of claims 7 to 9, wherein, In step (2), the sintering is two-step sintering, which comprises first sintering at 700-850°C for 3-8 h and then sintering at 860-1000°C for 10-15 h; the heating rate during the sintering process is 2-5°C / min, and the cooling rate during the cooling process is 0.5-1.0°C / min.

11. A sodium-ion battery, the cathode material of which is the sodium-ion battery cathode material according to any one of claims 1-6 or prepared by the method according to any one of claims 7-10.

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