A layered oxide cathode material for sodium-ion batteries with a hollow core structure, its preparation method and application

Abstract

This invention discloses a layered oxide cathode material for sodium-ion batteries with a hollow core structure and its preparation method, belonging to the technical field of sodium-ion cathode materials. Addressing the shortcomings of existing hollow-structure cathode materials, such as complex preparation, high cost, and insufficient strength, the cathode material prepared in this invention consists of secondary particles formed from primary particle agglomeration, with a hollow core structure. The hollow region area accounts for 0.05 ≤ R < 0.8, and its chemical formula is Na. x Ni a Fe b Mn c M d O 2±δ Where 0.67≤x≤1.0, 0.1≤a<1, 0.01≤b≤0.4, 0.01≤c≤0.4, 0≤d≤0.3 and a+b+c+d=1; δ is the oxygen vacancy concentration, with a value range of 0≤δ≤0.1, possessing an O3-type layered structure. This invention features a simple process and low cost, yielding a material with both high mechanical strength and excellent electrochemical performance, suitable for large-scale energy storage and power battery applications.

Description

Technical Field

[0001] This invention belongs to the field of sodium ion cathode material technology, and specifically relates to a method for preparing a hollow structure cathode material and its application. Background Technology

[0002] With the rapid development of energy storage and power battery fields, the problem of limited lithium-ion battery resources has become increasingly prominent. Sodium-ion batteries, due to their abundant sodium resources, low cost, compatibility with lithium-ion battery processes, and good low-temperature performance, have become an ideal alternative system for large-scale energy storage. The overall performance of sodium-ion batteries mainly depends on their cathode materials. Among them, O3 phase layered oxide polycrystalline cathodes have advantages such as high specific capacity and fast sodium-ion transport rate, and are considered one of the most promising cathode materials for sodium-ion batteries.

[0003] During the charging and discharging process, layered oxide cathode materials undergo lattice volume changes due to repeated insertion and extraction of sodium ions, leading to internal stress accumulation, microcracks, and hindering sodium ion transport and charge transfer. This results in a gradual decrease in the material's discharge specific capacity, as well as problems such as intensified side reactions, particle pulverization, and structural collapse, which seriously affect the battery's cycle life.

[0004] O3-phase cathodes exhibit a typical α-NaFeO2-type layered structure, belonging to the hexagonal crystal system and R-3m space group. Traditional layered oxide cathode materials are often secondary particles with micron-sized aggregates formed from primary particles. The morphology and structure of these particles directly affect battery performance, including ion transport rate, surface reactivity, and mechanical stability. Therefore, optimizing the shape, size, and structure of these particles to improve energy density and cycle stability has become a crucial strategy for optimizing sodium-ion battery performance.

[0005] Currently, the optimization of particle morphology in layered oxide cathode materials for sodium-ion batteries is mainly implemented at two levels: primary particles and secondary particles. At the primary particle level, adjusting the particle morphology, size, and arrangement can improve the material's mechanical strength and reduce microcrack formation, but the performance improvement effect is significantly limited. At the secondary particle level, controlling the agglomeration behavior of primary particles allows for the design of core-shell, hollow, internally porous, and sheet-like structures; however, such morphology designs place stringent requirements on the synthesis process, significantly increasing the material preparation cost.

[0006] Currently, there is no mature hollow structure cathode material preparation technology in the sodium-ion battery field. The hollow structure design in the lithium-ion battery field can provide important reference for it. This structure is an effective way to alleviate the volume change of cathode material during charging and discharging and dissipate lattice stress. However, the synthesis of existing hollow structure cathode particles for lithium batteries requires complex preparation methods, such as template method and solvothermal method. The preparation process requires the use of template agent, etchant, etc., which is complicated, costly and difficult to scale up. For example, patent CN111916726A prepared a hollow structure high nickel cathode material. The preparation process uses sulfonated polyethylene spheres as template agent and requires the introduction of MOF material. The preparation process is complicated and the raw material cost is high, which is not suitable for large-scale industrial production.

[0007] Currently, several patents have proposed new methods for preparing hollow-structured cathode particles. Patent CN111613788A reacts a mixture of nickel source, manganese source, and solvent with a carbonate solution to generate a precursor. The precursor suspension is then mixed with oxalic acid and sequentially dried, ground, and sintered to obtain hollow spherical lithium nickel manganese oxide cathode material. However, the hollow-structured cathode material particles prepared by this method have a high proportion of hollow regions within the entire secondary particle, making them prone to breakage under significant mechanical pressure. Patent CN119118225A utilizes the process differences of a continuous two-step co-precipitation method to control the porosity and growth mode of the corresponding precursor, thereby preparing cathode particles with a hollow structure. Compared to the hollow spherical lithium nickel manganese oxide cathode material in patent CN111613788A, these cathode particles have a moderate proportion of hollow regions and exhibit better mechanical strength. However, this method requires the synthesis of new precursors and cannot be effectively compatible with existing precursor systems. Although it greatly reduces the preparation cost and complexity compared to past methods, it still increases the cost to some extent compared to traditional cathode material preparation processes.

[0008] In summary, existing hollow-structure cathode material preparation technologies still suffer from drawbacks such as complex processes, high costs, and insufficient mechanical strength. The sodium-ion battery field urgently needs a hollow-structure layered oxide cathode material that is simple to process, low in cost, structurally controllable, and possesses high stability and strength. Developing such materials is of great significance for overcoming the performance bottlenecks of sodium-ion batteries and promoting industrialization. Summary of the Invention

[0009] This invention addresses the technical problems of existing hollow structure cathode material preparation technologies, such as complex processes, high costs, and insufficient mechanical strength, by proposing a layered oxide cathode material for sodium-ion batteries with a core hollow structure, its preparation method, and its applications.

[0010] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0011] In a first aspect, the present invention provides a layered oxide cathode material for sodium-ion batteries with a hollow core structure, wherein the layered oxide cathode material is a secondary particle formed by primary particle agglomeration, and has the general chemical formula Na. x Ni a Fe b Mn c M d O 2±δ x, a, b, c, d, and 2±δ represent the molar percentages of the corresponding elements, where 0.67≤x≤1.0, 0.1≤a<1, 0.01≤b≤0.4, 0.01≤c≤0.4, 0≤d≤0.3, and a+b+c+d=1; δ is the oxygen vacancy concentration, with a value ranging from 0≤δ≤0.1; M is selected from Li. + Mg 2+ Ca 2+ Cu 2+ Zn 2+ Al 3+ B 3+ Co 3+ V 3+ Y 3+ Ti 4+ Zr 4+ Sn 4+ Mo 4+ Si 4+ Ru 4+ Nb 5+ Sb 5+ Mo 5+ Mo 6+ and W 6+ At least one of them.

[0012] The secondary particles of the sodium-ion battery layered oxide cathode material have a diameter of 2-20 μm and are hollow at the core. The ratio of the area of ​​the hollow region to the cross-sectional area of ​​the secondary particles is R, where 0.05 ≤ R < 0.8.

[0013] The hollow structure of the layered oxide cathode material for sodium-ion batteries provides spatial redundancy, effectively alleviating stress accumulation during charging and discharging, reducing the generation of microcracks, and effectively improving cycle stability.

[0014] This invention provides a method for preparing the aforementioned layered oxide cathode material for sodium-ion batteries with a hollow core structure, comprising the following steps:

[0015] (1) Dissolve the transition metal salt in ultrapure water and stir until homogeneous to obtain a transition metal salt solution; then dissolve NaOH in NH3·H2O and mix until homogeneous to obtain a mixed solution, which serves as a pH adjuster and precipitant;

[0016] (2) The transition metal salt solution was continuously stirred under inert gas protection, and then the mixed solution was added and heated to carry out the reaction. After the reaction was completed, the precursor powder was obtained by filtration, washing and drying, with a particle size of 2-20 μm.

[0017] (3) Mix the precursor powder and sodium source evenly and calcine in two steps to obtain a sodium-ion battery layered oxide cathode material with a hollow core structure.

[0018] In step (1), the transition metal salt is a soluble salt of Ni, a soluble salt of Fe, a soluble salt of Mn, and a soluble salt of M, wherein M is selected from at least one of Li, Mg, Ca, Cu, Zn, Al, B, Co, V, Y, Ti, Zr, Sn, Mo, Si, Ru, Nb, Sb, Mo, Mo and W; the total concentration of metal ions in the transition metal salt solution is 1-4 mol / L.

[0019] The concentration of NH3·H2O in the mixed solution is 1-4 mol / L, preferably 3 mol / L, and the concentration of NaOH is 2-5 mol / L, preferably 4 mol / L.

[0020] In step (2), the inert gas is nitrogen or argon; the reaction temperature is 25-80℃, preferably 50-80℃, the pH is 10-12, preferably 11-12, the rotation speed is 200-1000 r / min, preferably 550-800 r / min; the drying is vacuum drying, the temperature is 60-130℃, preferably 100-110℃, and the time is 6-24h, preferably 10-12h.

[0021] In step (3), the sodium source is selected from at least one of sodium nitrate, sodium peroxide, sodium superoxide, sodium carbonate, sodium hydroxide and sodium oxalate, and the molar ratio of metal ions to sodium ions in the precursor powder is 1:0.67-1.05, preferably 1:1-1.05.

[0022] In the two-step calcination method, the first step involves low-temperature sintering at a temperature of 400-500℃, preferably 450-500℃, for 4-7 hours, preferably 5 hours. This decomposes and removes volatile components such as water of crystallization, hydroxyl groups, and carbonate ions from the precursor and sodium source, promoting preliminary solid-phase diffusion and reaction between sodium ions and transition metal ions. The second step involves high-temperature sintering at a temperature of 700-900℃, preferably 900℃, for 10-20 hours. The entire calcination process is carried out in an air atmosphere with a heating rate of 1-20℃ / min. At higher energy levels, the material undergoes sufficient diffusion, completing the transformation from an intermediate to a highly ordered layered crystal structure. The high-temperature stage in the second step primarily promotes grain boundary migration and densification through grain growth via grain boundary diffusion and bulk diffusion.

[0023] This invention employs a commercial precursor preparation method and a specific two-step sintering process. By controlling the sintering parameters during the sintering process, diffusion kinetics are controlled, thereby regulating the growth process and agglomeration mode of the primary grains to ensure the formation of a hollow core structure and a dense outer wall. Compared with traditional preparation methods, this invention can more precisely control the particle morphology, reduce the formation of microcracks, and thus improve the cycle stability of sodium-ion batteries.

[0024] This invention optimizes the heating rate, sodium supplementation amount, sintering temperature, and sintering time during the sintering stage to regulate crystal growth kinetics and sodium ion diffusion kinetics. By utilizing the difference in shrinkage behavior between layered phases and rock salt phases during sintering, a hollow structure is formed in the cathode particles. At the same time, a balance is achieved between densification and grain growth, so that during the densification process, the pores diffuse in the reverse direction to the polycrystalline core and are annihilated, without causing excessive growth of primary grains to fill the hollow structure at the core. This results in a structure with a hollow core and a dense outer wall, ultimately achieving material densification and microstructure stabilization, thereby producing the sodium-ion battery layered oxide cathode material with a hollow core structure.

[0025] The present invention also provides the application of the aforementioned layered oxide cathode material with a hollow core structure in sodium-ion batteries.

[0026] Secondly, the present invention provides a sodium-ion battery, wherein the positive electrode material of the sodium-ion battery includes the sodium-ion battery layered oxide positive electrode material with a hollow core structure as described above, or the sodium-ion battery layered oxide positive electrode material with a hollow core structure prepared by the above preparation method.

[0027] The sodium-ion battery has a sodium metal sheet as the battery cell, a double-layer glass fiber membrane as the separator, and a 1M NaClO4 propylene carbonate (PC) / ethylene carbonate (EC) / dimethyl carbonate (DMC) electrolyte (PC / EC / DMC in a 1:1:1 ratio). The amount of fluoroethylene carbonate (FEC) added accounts for 2% of the total volume of the solvent.

[0028] The beneficial effects of this invention are:

[0029] 1. The sodium-ion battery layered oxide cathode material prepared by this invention has a hollow core structure, which can effectively alleviate the internal stress accumulation of the cathode material during cycling, reduce the occurrence of microcracks, and improve the cycling stability of the cathode material. The hollow core structure provides a larger specific surface area, which helps to improve the reactivity of the electrode, accelerate ion and electron transport, and improve the electrochemical performance of the battery. It also helps to dissipate the heat generated during cycling more quickly, reduce heat accumulation, and effectively improve the thermal stability and safety of the battery.

[0030] 2. The method for preparing the sodium-ion battery layered oxide cathode material of the present invention, compared with the template method, solvothermal method, etc., does not require template agents, etchants, etc., and can prepare the sodium-ion battery layered oxide cathode material simply by controlling parameters such as sintering temperature and holding time. It has lower energy consumption, simpler operation, lower equipment requirements, and does not introduce additional reagents, greatly reducing the preparation cost. The prepared sodium-ion battery layered oxide cathode material has a core hollow structure with a moderate proportion and a dense outer peripheral wall. Compared with the hollow structure formed by the template method, solvothermal method, or modified precursor, it has better mechanical strength and is not easily broken under high pressure conditions, thus balancing structural stability and mechanical reliability. Attached Figure Description

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

[0032] Figure 1 The X-ray diffraction patterns are of the layered oxide cathode materials for sodium-ion batteries prepared in Examples 1-3.

[0033] Figure 2 The images show X-ray diffraction patterns of the layered oxide cathode materials for sodium-ion batteries prepared in Examples 4-6.

[0034] Figure 3 This is a scanning electron microscope image of the layered oxide cathode material for sodium-ion batteries prepared in Example 1.

[0035] Figure 4 This is a scanning electron microscope image of the cross-section of the layered oxide cathode material for sodium-ion batteries prepared in Example 2.

[0036] Figure 5 This is a scanning electron microscope image of the cross-section of the layered oxide positive electrode sheet for a sodium-ion battery prepared in Example 3.

[0037] Figure 6 Scanning electron micrograph of the cross-section of the layered oxide positive electrode sheet of the sodium-ion battery prepared for Comparative Example 1.

[0038] Figure 7 This is a graph showing the cycling performance of the sodium-ion battery layered oxide cathode material prepared in Example 3 for the first 3 weeks.

[0039] Figure 8The first charge-discharge performance diagrams are for the sodium-ion battery layered oxide cathode materials prepared in Example 5 and Comparative Example 1.

[0040] Figure 9 The graph shows the 100-cycle performance of the sodium-ion battery layered oxide cathode materials prepared in Example 5 and Comparative Example 1.

[0041] Figure 10 The graph shows the first charge-discharge performance of the sodium-ion battery layered oxide cathode materials prepared in Example 6 and Comparative Example 2.

[0042] Figure 11 The graph shows the 100-cycle performance of the sodium-ion battery layered oxide cathode materials prepared in Example 6 and Comparative Example 2. Detailed Implementation

[0043] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] Example 1

[0045] NaNi, a layered oxide cathode material for sodium-ion batteries with a hollow core structure 0.3 Fe 0.3 Mn 0.4 The specific steps for preparing O2 are as follows:

[0046] (1) 6.3084g NiSO4·6H2O, 6.6725g FeSO4·7H2O and 5.4086g MnSO4·H2O were dissolved in 40mL of ultrapure water at a molar ratio of Ni:Fe:Mn = 3:3:4 and stirred until homogeneous to obtain a 2 mol / L transition metal salt solution; then 8g NaOH was dissolved in 50mL of 3 mol / L NH3·H2O and mixed until homogeneous to obtain a mixed solution, which was used as a pH adjuster and precipitant. The concentration of NH3·H2O in the mixed solution was 3 mol / L and the concentration of NaOH was 4 mol / L.

[0047] (2) Under the protection of inert argon gas, the transition metal salt solution obtained in step (1) was added to the reaction vessel and stirred continuously at a speed of 800 r / min. Then, a mixed solution was added, and the pH was controlled at 11. The reaction vessel was placed in a water bath and the temperature was controlled at 60℃ for the reaction. After the reaction was completed, the positive electrode material precursor was obtained by filtration. After washing with ultrapure water several times, it was placed in a vacuum oven and dried at 100℃ for 12 h to obtain the chemical composition Ni. 0.3 Fe 0.3 Mn 0.4 (OH)2, precursor powder with a particle size of 6 μm;

[0048] (3) Take 2.1124g of the precursor powder Ni obtained in step (2) 0.3 Fe 0.3 Mn 0.4 (OH)₂ and 1.3012 g Na₂CO₃ were mixed uniformly at a molar ratio of 1:0.525. The resulting mixture was subjected to a two-step sintering process in air atmosphere. In the first step, the temperature was increased from room temperature to 500°C at a heating rate of 5°C / min and held at this temperature for 5 h. In the second step, the temperature was increased from 500°C to 900°C at a heating rate of 5°C / min and held at this temperature for 15 h. Afterward, the mixture was allowed to cool naturally to room temperature, thus obtaining NaNi, a layered oxide cathode material for sodium-ion batteries with a hollow core structure. 0.3 Fe 0.3 Mn 0.4 O2.

[0049] The layered oxide cathode material for sodium-ion batteries prepared in this embodiment was characterized, and the XRD results are as follows: Figure 1 As shown, the results indicate that the obtained material has an α-NaFeO2 type structure, belongs to the O3 type layered structure, and has the R-3m space group; Figure 3 The scanning electron microscope (SEM) characterization results show that the sodium-ion battery layered oxide cathode material prepared in this embodiment maintains a spherical distribution with a particle size between 3 and 5 μm, mostly 5 μm. The primary particles are clearly visible, with a size of approximately 500 nm. The hollow portion has a diameter of 1.5 μm, and R≈0.09.

[0050] Example 2

[0051] NaNi, a layered oxide cathode material for sodium-ion batteries with a hollow core structure 0.6 Fe 0.1 Mn 0.2 Ti 0.1 The specific steps for preparing O2 are as follows:

[0052] (1) 12.6168g NiSO4·6H2O, 2.2242g FeSO4·7H2O, 2.7043g MnSO4·H2O and 1.9199g Ti(SO4)2 were dissolved in 40mL of ultrapure water at a molar ratio of Ni:Fe:Mn:Ti = 6:1:2:1 and stirred until homogeneous to obtain a 2 mol / L transition metal salt solution; then 8g NaOH was dissolved in 50mL of 3 mol / L NH3·H2O and mixed until homogeneous to obtain a mixed solution, which was used as a pH adjuster and precipitant. The concentration of NH3·H2O in the mixed solution was 3 mol / L and the concentration of NaOH was 4 mol / L.

[0053] (2) Under the protection of inert gas N2, the transition metal salt solution obtained in step (1) was added to the reaction vessel and stirred continuously at a speed of 700 r / min. Then, a mixed solution was added, and the pH was controlled at 11.5. The reaction vessel was placed in a water bath and the temperature was controlled at 60℃ for the reaction. After the reaction was completed, the positive electrode material precursor was obtained by filtration. After washing with ultrapure water several times, it was placed in a vacuum oven and dried at 100℃ for 12 h to obtain the chemical composition Ni. 0.6 Fe 0.1 Mn 0.2 Ti 0.1 (OH)2, precursor powder with a particle size of 5 μm;

[0054] (3) Take 2.7826g of the precursor powder Ni obtained in step (2) 0.6 Fe 0.1 Mn 0.2 Ti 0.1 (OH)₂ and 1.6278 g Na₂CO₃ were mixed uniformly at a molar ratio of 1:0.5. The resulting mixture was then subjected to a two-step sintering process in air. In the first step, the temperature was increased from room temperature to 500°C at a rate of 10°C / min and held at this temperature for 5 hours. In the second step, the temperature was increased from 500°C to 900°C at a rate of 10°C / min and held at this temperature for 10 hours. The mixture was then allowed to cool naturally to room temperature, yielding NaNi, a layered oxide cathode material for sodium-ion batteries with a hollow core structure. 0.6 Fe 0.1 Mn 0.2 Ti 0.1 O2.

[0055] The layered oxide cathode material for sodium-ion batteries prepared in this embodiment was characterized, and the XRD results are as follows: Figure 1 As shown, the results indicate that the obtained material has an α-NaFeO2 type structure, belongs to the O3 type layered structure, and has the R-3m space group; Figure 4The cross-sectional scanning electron microscope characterization results confirm that a layered oxide cathode material with a hollow core and a dense outer periphery was successfully prepared, with a hollow portion diameter of 2 μm and R≈0.16.

[0056] Example 3

[0057] NaNi, a layered oxide cathode material for sodium-ion batteries with a hollow core structure 0.7 Fe 0.2 Mn 0.1 The specific steps for preparing O2 are as follows:

[0058] (1) 14.7196g NiSO4·6H2O, 4.4483g FeSO4·7H2O and 1.3522g MnSO4·H2O were dissolved in 40mL of ultrapure water at a molar ratio of Ni:Fe:Mn = 7:2:1 and stirred until homogeneous to obtain a 2 mol / L transition metal salt solution; then 8g NaOH was dissolved in 50mL of 3 mol / L NH3·H2O and mixed until homogeneous to obtain a mixed solution, which was used as a pH adjuster and precipitant. The concentration of NH3·H2O in the mixed solution was 3 mol / L and the concentration of NaOH was 4 mol / L.

[0059] (2) Under the protection of inert gas N2, the transition metal salt solution obtained in step (1) was added to the reaction vessel and stirred continuously at a speed of 800 r / min. Then, a mixed solution was added, and the pH was controlled at 12. The reaction vessel was placed in a water bath and the temperature was controlled at 60℃ for the reaction. After the reaction was completed, the positive electrode material precursor was obtained by filtration. After washing with ultrapure water several times, it was placed in a vacuum oven and dried at 100℃ for 12 h to obtain the chemical composition Ni. 0.7 Fe 0.2 Mn 0.1 (OH)2, precursor powder with a particle size of 7 μm;

[0060] (3) Take 2.7518g of the precursor powder Ni obtained in step (2) 0.7 Fe 0.2 Mn 0.1 (OH)₂ and 1.6236 g of Na₂CO₃ were mixed uniformly at a molar ratio of 1:0.5. The resulting mixture was then subjected to a two-step sintering process in air. In the first step, the temperature was increased from room temperature to 450°C at a heating rate of 5°C / min and held at this temperature for 5 h. In the second step, the temperature was increased from 450°C to 900°C at a heating rate of 5°C / min and held at this temperature for 15 h. Afterward, the mixture was allowed to cool naturally to room temperature, yielding NaNi, a layered oxide cathode material for sodium-ion batteries with a hollow core structure. 0.7 Fe 0.2 Mn0.1 O2.

[0061] The layered oxide cathode material for sodium-ion batteries obtained in this embodiment was characterized using XRD, such as... Figure 1 As shown, the results indicate that the obtained material has an α-NaFeO2 type structure, belonging to the O3 type layered structure, and the R-3m space group. The diameter of the hollow part is 2.2 μm, and R≈0.18. Figure 5 The results are from scanning electron microscopy characterization of the cross-section of the positive electrode sheet. The results show that there are a large number of hollow structure particles in the electrode sheet, accounting for about 80%.

[0062] Example 4

[0063] NaNi, a layered oxide cathode material for sodium-ion batteries with a hollow core structure 0.3 Fe 0.2 Mn 0.4 Cu 0.1 The specific steps for preparing O2 are as follows:

[0064] (1) 6.3084g NiSO4·6H2O, 4.4483g FeSO4·7H2O, 5.4086g MnSO4·H2O and 1.9974g CuSO4·5H2O were dissolved in 40mL of ultrapure water at a molar ratio of Ni:Fe:Mn:Cu =3:2:4:1 and stirred until homogeneous to obtain a 2 mol / L transition metal salt solution; then 8g NaOH was dissolved in 50mL of 3 mol / L NH3·H2O and mixed until homogeneous to obtain a mixed solution, which was used as a pH adjuster and precipitant. The concentration of NH3·H2O in the mixed solution was 3 mol / L and the concentration of NaOH was 4 mol / L.

[0065] (2) Under the protection of inert gas N2, the transition metal salt solution obtained in step (1) was added to the reaction vessel and stirred continuously at a speed of 550 r / min. Then, a mixed solution was added, and the pH was controlled at 11.5. The reaction vessel was placed in a water bath and the temperature was controlled at 50℃ for the reaction. After the reaction was completed, the positive electrode material precursor was obtained by filtration. After washing with ultrapure water several times, it was placed in a vacuum oven and dried at 110℃ for 10 h to obtain the chemical composition Ni. 0.3 Fe 0.2 Mn 0.4 Cu 0.1 (OH)2, precursor powder with a particle size of 5 μm;

[0066] (3) Take 2.3228g of the precursor powder Ni obtained in step (2) 0.3 Fe 0.2 Mn 0.4 Cu0.1 (OH)₂ and 1.3774 g Na₂CO₃ were mixed uniformly at a molar ratio of 1:0.51. The resulting mixture was subjected to a two-step sintering process in an air atmosphere. In the first step, the temperature was increased from room temperature to 500°C at a heating rate of 1°C / min and held at this temperature for 5 h. In the second step, the temperature was increased from 500°C to 900°C at a heating rate of 1°C / min and held at this temperature for 10 h. Afterward, the mixture was allowed to cool naturally to room temperature, thus obtaining NaNi, a layered oxide cathode material for sodium-ion batteries with a hollow core structure. 0.3 Fe 0.2 Mn 0.4 Cu 0.1 O2.

[0067] The layered oxide cathode material for sodium-ion batteries prepared in this embodiment was characterized, and the XRD results are as follows: Figure 2 As shown, the results indicate that the obtained material has an α-NaFeO2 type structure, belonging to the O3 type layered structure, and the R-3m space group. The diameter of the hollow part is 1.6 μm, and R≈0.1.

[0068] Example 5

[0069] NaNi, a layered oxide cathode material for sodium-ion batteries with a hollow core structure 1 / 3 Fe 1 / 3 Mn 1 / 3 The specific steps for preparing O2 are as follows:

[0070] (1) 7.0023g NiSO4·6H2O, 7.4065g FeSO4·7H2O and 4.5027g MnSO4·H2O were dissolved in 40mL of ultrapure water at a molar ratio of Ni:Fe:Mn = 1:1:1 and stirred until homogeneous to obtain a 2 mol / L transition metal salt solution; then 8g NaOH was dissolved in 50mL of 3 mol / L NH3·H2O and mixed until homogeneous to obtain a mixed solution, which was used as a pH adjuster and precipitant. The concentration of NH3·H2O in the mixed solution was 3 mol / L and the concentration of NaOH was 4 mol / L.

[0071] (2) Under the protection of inert gas N2, the transition metal salt solution obtained in step (1) was added to the reaction vessel and stirred continuously at a speed of 600 r / min. Then, a mixed solution was added, and the pH was controlled at 11.5. The reaction vessel was placed in a water bath and the temperature was controlled at 70℃ for the reaction. After the reaction was completed, the positive electrode material precursor was obtained by filtration. After washing with ultrapure water several times, it was placed in a vacuum oven and dried at 100℃ for 12 h to obtain the chemical composition Ni. 1 / 3 Fe 1 / 3 Mn 1 / 3(OH)2, precursor powder with a particle size of 8 μm;

[0072] (3) Take 2.1323g of the precursor powder Ni obtained in step (2) 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)₂ and 1.3306 g of Na₂CO₃ were mixed uniformly at a molar ratio of 1:0.5. The resulting mixture was then subjected to a two-step sintering process in an air atmosphere. In the first step, the temperature was increased from room temperature to 500°C at a heating rate of 5°C / min and held at this temperature for 5 h. In the second step, the temperature was increased from 500°C to 900°C at a heating rate of 5°C / min and held at this temperature for 15 h. Afterward, the mixture was allowed to cool naturally to room temperature, yielding NaNi, a layered oxide cathode material for sodium-ion batteries with a hollow core structure. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2.

[0073] The layered oxide cathode material for sodium-ion batteries prepared in this embodiment was characterized, and the XRD results are as follows: Figure 2 As shown, the results indicate that the obtained material has an α-NaFeO2 type structure, belonging to the O3 type layered structure, and the R-3m space group. The diameter of the hollow part is 2.4 μm, and R≈0.09.

[0074] Example 6

[0075] NaNi, a layered oxide cathode material for sodium-ion batteries with a hollow core structure 0.4 Fe 0.2 Mn 0.4 The specific steps for preparing O2 are as follows:

[0076] (1) 8.4112g NiSO4·6H2O, 4.4483g FeSO4·7H2O and 5.4086g MnSO4·H2O were dissolved in 40mL of ultrapure water at a molar ratio of Ni:Fe:Mn = 2:1:2 and stirred until homogeneous to obtain a 2 mol / L transition metal salt solution; then 8g NaOH was dissolved in 50mL of 3 mol / L NH3·H2O and mixed until homogeneous to obtain a mixed solution, which was used as a pH adjuster and precipitant. The concentration of NH3·H2O in the mixed solution was 3 mol / L and the concentration of NaOH was 4 mol / L.

[0077] (2) Under the protection of inert gas N2, the transition metal salt solution obtained in step (1) was added to the reaction vessel and stirred continuously at a speed of 550 r / min. Then, a mixed solution was added, and the pH was controlled at 11.5. The reaction vessel was placed in a water bath and the temperature was controlled at 80℃ for the reaction. After the reaction was completed, the positive electrode material precursor was obtained by filtration. After washing with ultrapure water several times, it was placed in a vacuum oven and dried at 110℃ for 10 h to obtain the chemical composition Ni. 0.4 Fe 0.2 Mn 0.4 (OH)2, precursor powder with a particle size of 6 μm;

[0078] (3) Take 2.3567g of the precursor powder Ni obtained in step (2) 0.4 Fe 0.2 Mn 0.4 (OH)₂ and 1.3787 g of Na₂CO₃ were mixed uniformly at a molar ratio of 1:0.5. The resulting mixture was subjected to a two-step sintering process in an air atmosphere. In the first step, the temperature was increased from room temperature to 450°C at a heating rate of 20°C / min and held at this temperature for 5 h. In the second step, the temperature was increased from 450°C to 900°C at a heating rate of 20°C / min and held at this temperature for 20 h. Afterward, the mixture was allowed to cool naturally to room temperature, thus obtaining NaNi, a layered oxide cathode material for sodium-ion batteries with a hollow core structure. 0.4 Fe 0.2 Mn 0.4 O2.

[0079] The layered oxide cathode material for sodium-ion batteries prepared in this embodiment was characterized, and the XRD results are as follows: Figure 2 As shown, the results indicate that the obtained material has an α-NaFeO2 type structure, belonging to the O3 type layered structure, and the R-3m space group. The diameter of the hollow part is 2.1 μm, and R≈0.12.

[0080] Comparative Example 1

[0081] NaNi, a layered oxide cathode material for sodium-ion batteries without a core hollow structure 1 / 3 Fe 1 / 3 Mn 1 / 3 The specific steps for preparing O2 are as follows:

[0082] (1) 7.0023g NiSO4·6H2O, 7.4065g FeSO4·7H2O and 4.5027g MnSO4·H2O were dissolved in 40mL of ultrapure water at a molar ratio of Ni:Fe:Mn = 1:1:1 and stirred until homogeneous to obtain a 2 mol / L transition metal salt solution; then 8g NaOH was dissolved in 50mL of 3 mol / L NH3·H2O and mixed until homogeneous to obtain a mixed solution, which was used as a pH adjuster and precipitant. The concentration of NH3·H2O in the mixed solution was 3 mol / L and the concentration of NaOH was 4 mol / L.

[0083] (2) Under the protection of inert gas N2, the transition metal salt solution obtained in step (1) was added to the reaction vessel and stirred continuously at a speed of 500 r / min. Then, a mixed solution was added, and the pH was controlled at 11.5. The reaction vessel was placed in a water bath and the temperature was controlled at 40℃ for the reaction. After the reaction was completed, the positive electrode material precursor was obtained by filtration. After washing with ultrapure water several times, it was placed in a vacuum oven and dried at 110℃ for 10 h to obtain the chemical composition Ni. 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2, precursor powder with a particle size of 7 μm;

[0084] (3) Take 2.3589g of the precursor powder Ni obtained in step (2) 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)₂ and 1.4720 g Na₂CO₃ were mixed uniformly at a molar ratio of 1:0.5. The resulting mixture was then subjected to a two-step sintering process in an air atmosphere. In the first step, the temperature was increased from room temperature to 450°C at a heating rate of 1°C / min and held at this temperature for 5 hours. In the second step, the temperature was increased from 450°C to 950°C at a heating rate of 1°C / min and held at this temperature for 20 hours. Afterward, the mixture was allowed to cool naturally to room temperature, yielding the desired layered oxide cathode material NaNi for sodium-ion batteries. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2.

[0085] The layered oxide cathode material for sodium-ion batteries prepared in this comparative example was characterized. Figure 6 The results show the cross-sectional scanning electron microscope characterization of the positive electrode sheet. The results indicate that there are no hollow particles in the electrode sheet, and all of them are solid positive electrode particles.

[0086] Comparative Example 2

[0087] NaNi, a layered oxide cathode material for sodium-ion batteries without a core hollow structure 0.4 Fe 0.2 Mn0.4 The specific steps for preparing O2 are as follows:

[0088] (1) 8.4112g NiSO4·6H2O, 4.4483g FeSO4·7H2O and 5.4086g MnSO4·H2O were dissolved in 40mL of ultrapure water at a molar ratio of Ni:Fe:Mn = 2:1:2 and stirred until homogeneous to obtain a 2 mol / L transition metal salt solution; then 8g NaOH was dissolved in 50mL of 3 mol / L NH3·H2O and mixed until homogeneous to obtain a mixed solution, which was used as a pH adjuster and precipitant. The concentration of NH3·H2O in the mixed solution was 3 mol / L and the concentration of NaOH was 4 mol / L.

[0089] (2) Under the protection of inert gas N2, the transition metal salt solution obtained in step (1) was added to the reaction vessel and stirred continuously at a speed of 500 r / min. Then, a mixed solution was added, and the pH was controlled at 11. The reaction vessel was placed in a water bath and the temperature was controlled at 60℃ for the reaction. After the reaction was completed, the positive electrode material precursor was obtained by filtration. After washing with ultrapure water several times, it was placed in a vacuum oven and dried at 110℃ for 10 h to obtain the chemical composition Ni. 0.4 Fe 0.2 Mn 0.4 (OH)2, precursor powder with a particle size of 10 μm;

[0090] (3) Take 2.6587g of the precursor powder Ni obtained in step (2) 0.4 Fe 0.2 Mn 0.4 (OH)₂ and 1.5553 g of Na₂CO₃ were mixed uniformly at a molar ratio of 1:0.5. The resulting mixture was then subjected to a two-step sintering process in air. In the first step, the temperature was increased from room temperature to 500°C at a heating rate of 1°C / min and held at this temperature for 5 hours. In the second step, the temperature was increased from 500°C to 950°C at a heating rate of 1°C / min and held at this temperature for 20 hours. Afterward, the mixture was allowed to cool naturally to room temperature, yielding the desired layered oxide cathode material NaNi for sodium-ion batteries. 0.4 Fe 0.2 Mn 0.4 O2.

[0091] Example of implementation effect 1

[0092] The performance of the cathode materials prepared in Examples 1-6 and Comparative Examples 1-2 was tested, as follows:

[0093] First, the electrode sheets were prepared: In an argon glove box (with water and oxygen content below 0.1 ppm), the positive electrode materials, carbon nanotube (CNT) conductive agents, and polytetrafluoroethylene (PTFE) binders prepared in Examples 1-6 and Comparative Examples 1-2 were weighed at a mass ratio of 80:15:5, and then ground and mixed evenly in a mortar. The mixture was rolled into thin sheets and then cut into 8×8 mm or 10 mm diameter electrode sheets. Then, coin cells were assembled. This process was also carried out in an argon glove box. A CR2032 coin cell case was selected, with a fresh sodium metal sheet as the counter electrode and a double-layer glass fiber separator (Whatman, D). The electrolyte was a 1M NaClO4 propylene carbonate (PC) / ethylene carbonate (EC): dimethyl carbonate (DMC) electrolyte (PC / EC / DMC = 1:1:1), and the volume of fluoroethylene carbonate (FEC) added was 2% of the total solvent volume. The battery testing equipment was the Land BT2000 testing system (Wuhan). Charge-discharge tests were performed on the assembled batteries, with a charge-discharge cutoff voltage of 2.0-4.0V (1C=140 mAh / g).

[0094] The charge-discharge curves of the sodium-ion battery assembled from the cathode material prepared in Example 3 are shown in the first three cycles. Figure 7 As shown. The electrochemical performance results of sodium-ion batteries assembled with the cathode materials prepared in Examples 5-6 and Comparative Examples 1-2 are as follows. Figure 8-11 As shown in the figure; the specific data of the electrochemical performance of sodium-ion batteries assembled with the layered oxide cathode materials prepared in Examples 1-6 and Comparative Examples 1-2 are shown in Table 1:

[0095] Table 1. Electrochemical performance data of sodium-ion batteries assembled from the cathode materials prepared in Examples 1-6 and Comparative Examples 1-2.

[0096]

[0097] As shown in Table 1, the sodium-ion battery layered oxide cathode material obtained in Example 1 exhibits an activation capacity of 146.74 mAh / g and a coulombic efficiency of 96.56% at the first 0.1C rate. Cycling performance tests show that the initial capacity at 1C rate is 140.36 mAh / g, and the capacity retention rate after 100 cycles is 96.72%. The experimental results indicate that adjusting sintering parameters and controlling secondary particle densification significantly enhances the structural stability of the sodium-ion battery layered oxide cathode material with a hollow core structure formed by primary grain growth and agglomeration. This effectively mitigates microcrack formation and contributes to improving the battery's cycle stability.

[0098] Electrochemical performance tests were conducted on the sodium-ion battery layered oxide cathode material obtained in Example 2. At 0.1C rate in the first cycle, the activation capacity was 148.52 mAh / g, and the coulombic efficiency was 95.97%. Cycling performance tests showed that the initial capacity at 1C rate was 141.39 mAh / g, and the capacity retention rate after 100 cycles was 96.75%. The experimental results indicate that by controlling the sintering process parameters to achieve controllable densification of secondary particles and synergistically optimizing the growth behavior and agglomeration morphology of primary grains, the prepared sodium-ion battery layered oxide cathode material with a hollow core structure exhibits significantly enhanced structural stability. This effectively suppresses the initiation and propagation of microcracks during charge and discharge, thereby significantly improving the cycle stability of sodium-ion batteries.

[0099] Electrochemical performance tests were conducted on the sodium-ion battery layered oxide cathode material obtained in Example 3. At 0.1C rate in the first cycle, the activation capacity was 149.53 mAh / g, and the coulombic efficiency was 96.36%. Cycling performance tests showed that the initial capacity at 1C rate was 143.53 mAh / g, and the capacity retention rate after 100 cycles was 94.77%. The experimental results indicate that adjusting sintering parameters and controlling secondary particle densification, along with the core hollow structure formed by primary grain growth and agglomeration, effectively improved the structural stability of the sodium-ion battery layered oxide cathode material. This reduced stress concentration and microcrack formation during cycling, significantly suppressing surface side reactions and contributing to improved battery cycle stability.

[0100] Electrochemical performance tests were conducted on the sodium-ion battery layered oxide cathode material obtained in Example 4. At the first cycle at 0.1C rate, the activation capacity was 147.74 mAh / g and the coulombic efficiency was 96.87%. Cycling performance test results showed that the initial capacity at 1C rate was 141.51 mAh / g and the capacity retention rate was 95.52% after 100 cycles.

[0101] Electrochemical performance tests were conducted on the sodium-ion battery layered oxide cathode material obtained in Example 5. At the first cycle at 0.1C rate, the activation capacity was 146.46 mAh / g and the coulombic efficiency was 96.55%. Cycling performance test results showed that the initial capacity at 1C rate was 140.26 mAh / g and the capacity retention rate was 95.08% after 100 cycles.

[0102] Electrochemical performance tests were conducted on the sodium-ion battery layered oxide cathode material obtained in Example 6. At the first cycle at 0.1C rate, the activation capacity was 147.08 mAh / g and the coulombic efficiency was 97.32%. Cycling performance test results showed that the initial capacity at 1C rate was 141.77 mAh / g and the capacity retention rate was 95.31% after 100 cycles.

[0103] Electrochemical performance tests were conducted on the sodium-ion battery layered oxide cathode material obtained in Comparative Example 1. At the first cycle at 0.1C rate, the activation capacity was 147.63 mAh / g and the coulombic efficiency was 93.19%. Cycling performance test results showed that the initial capacity at 1C rate was 141.30 mAh / g, and the capacity retention rate was 85.21% after 100 cycles.

[0104] Electrochemical performance tests were conducted on the sodium-ion battery layered oxide cathode material obtained in Comparative Example 2. At the first cycle at 0.1C rate, the activation capacity was 146.16 mAh / g and the coulombic efficiency was 96.34%. Cycling performance test results showed that the initial capacity at 1C rate was 139.62 mAh / g, and the capacity retention rate was 86.84% after 100 cycles.

[0105] It can be observed that all embodiments exhibit 0.1C capacity, first-cycle coulombic efficiency, and 1C capacity that are similar to Comparative Examples 1 and 2, indicating that the cathode material prepared by this method does not cause negative capacity decay compared to cathode materials prepared by traditional processes. Furthermore, all embodiments show higher capacity retention rates after 100 cycles compared to Comparative Examples 1 and 2, demonstrating that the hollow-structured layered oxide cathode material for sodium-ion batteries prepared in these embodiments provides spatial redundancy through its hollow structure, effectively mitigating stress accumulation and microcrack formation during cycling. This cathode material exhibits significant structural and cycling stability.

[0106] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A layered oxide cathode material for sodium-ion batteries with a hollow core structure, characterized in that: The sodium-ion battery layered oxide cathode material is a secondary particle formed by primary particle agglomeration, with the general chemical formula Na. x Ni a Fe b Mn c M d O 2±δ x, a, b, c, d, and 2±δ represent the molar percentages of the corresponding elements. In the general chemical formula, each component satisfies charge conservation and stoichiometry, where 0.67≤x≤1.0, 0.1≤a<1, 0.01≤b≤0.4, 0.01≤c≤0.4, 0≤d≤0.3, and a+b+c+d=1; δ is the oxygen vacancy concentration, with a value ranging from 0≤δ≤0.1; M is selected from Li. + Mg 2+ Ca 2+ Cu 2+ Zn 2+ Al 3+ B 3+ Co 3+ V 3+ Y 3+ Ti 4+ Zr 4+ Sn 4+ Mo 4+ Si 4+ Ru 4+ Nb 5+ Sb 5+ Mo 5+ Mo 6+ and W 6+ At least one of them.

2. The sodium-ion battery layered oxide cathode material with a hollow core structure according to claim 1, characterized in that: The secondary particles of the sodium-ion battery layered oxide cathode material have a diameter of 2-20 μm and are hollow at the core. The ratio of the area of ​​the hollow region to the cross-sectional area of ​​the secondary particles is R, where 0.05 ≤ R < 0.

8.

3. The method for preparing the sodium-ion battery layered oxide cathode material with a hollow core structure as described in claim 1 or 2, characterized in that, Includes the following steps: (1) Dissolve the transition metal salt in ultrapure water and stir until homogeneous to obtain a transition metal salt solution; then dissolve NaOH in NH3·H2O and mix until homogeneous to obtain a mixed solution; (2) The transition metal salt solution was continuously stirred under inert gas protection, and then a mixed solution was added and heated to carry out the reaction. After the reaction was completed, the precursor powder was obtained by filtration, washing and drying. (3) Mix the precursor powder and sodium source evenly and calcine in two steps to obtain a sodium-ion battery layered oxide cathode material with a hollow core structure.

4. The preparation method according to claim 3, characterized in that: In step (1), the transition metal salt is a soluble salt of Ni, a soluble salt of Fe, a soluble salt of Mn, and a soluble salt of M, wherein M is selected from at least one of Li, Mg, Ca, Cu, Zn, Al, B, Co, V, Y, Ti, Zr, Sn, Mo, Si, Ru, Nb, Sb, Mo, Mo and W; the total concentration of metal ions in the transition metal salt solution is 1-4 mol / L.

5. The preparation method according to claim 4, characterized in that: In step (1), the concentration of NH3·H2O in the mixed solution is 1-4 mol / L, and the concentration of NaOH is 2-5 mol / L.

6. The preparation method according to claim 5, characterized in that: In step (2), the inert gas is nitrogen or argon; the reaction temperature is 25-80℃, the pH is 10-12, and the rotation speed is 200-1000 r / min; the drying is vacuum drying, the temperature is 60-130℃, and the time is 6-24h.

7. The preparation method according to claim 6, characterized in that: In step (3), the sodium source is selected from at least one of sodium nitrate, sodium peroxide, sodium superoxide, sodium carbonate, sodium hydroxide and sodium oxalate, and the molar ratio of metal ions to sodium ions in the precursor powder is 1:0.67-1.

05.

8. The preparation method according to claim 7, characterized in that: In step (3), the first stage of calcination in the two-stage process is 400-500℃ for 4-7 h, and the second stage is 700-900℃ for 10-20 h. The calcination process is carried out in an air atmosphere throughout, with a heating rate of 1-20℃ / min.

9. The application of the sodium-ion battery layered oxide cathode material with a hollow core structure as described in claim 1 or 2 in sodium-ion batteries.

10. A sodium-ion battery, characterized in that: The cathode material of the sodium-ion battery includes the layered oxide cathode material with a hollow core structure as described in claim 1 or 2, or the layered oxide cathode material with a hollow core structure prepared by the preparation method described in any one of claims 3-8.

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