Fe-doped modified p2-type sodium-ion layered oxide positive electrode material and application thereof in high-pressure environment

Abstract

The application discloses a Fe-doped modified P2-type sodium-ion layered oxide positive electrode material and application thereof in a high-pressure environment, and belongs to the technical field of sodium-ion battery positive electrode materials. 0.72 Li 0.2 Mn 0.68 Fe x O2, 0.1

Description

Technical Field

[0001] This invention belongs to the technical field of sodium-ion battery cathode materials, specifically relating to an Fe-doped modified P2-type sodium-ion layered oxide cathode material and its application in high-voltage environments. Background Technology

[0002] Layered transition metal oxides possess suitable operating potentials and two-dimensional Na+. + Advantages such as diffusion channels and low cost have made it one of the most promising systems for cathode materials in sodium-ion batteries. Among numerous candidate materials, layered transition metal oxides with oxygen anion redox (ARR) activity stand out due to their >200 mAh g⁻¹. -1 Its high capacity and low cost characteristics make it stand out. In the anionic oxygen redox reaction, the electrons involved in charge compensation originate from the π bond formed by the hybridization of TM-3d and O-2p orbitals, and the π-stable ARR has a certain degree of reversibility. When Li is introduced... + Mg 2+ When using low electronegativity doped ions, such as Li + For example, after it is doped into the transition metal layer, it can move along... c The axis forms a typical "Na-O-Li" configuration, in which there are unbonded oxygen ARR orbitals, which can endow the material with highly reversible lattice oxygen redox activity.

[0003] Currently, increasing the charging voltage can effectively activate the anion redox reaction in the cathode material, thereby significantly improving the specific capacity and developing high-voltage Na x TMO2 cathodes have become a key approach to further improve the energy density of sodium-ion batteries. Mn and Fe, due to their abundant reserves and low cost, are transition metal components with great application potential. Notably, Fe doping in the transition metal layer is more effective than Mn in suppressing Li loss from the TM layer, and is considered a key factor in achieving excellent capacity retention.

[0004] For example, the invention patent with publication number CN120709352A discloses a P2 phase sodium ion cathode material with a superlattice ordered structure and its preparation method, the chemical formula of which is: Na x M 1ab A a B bO2; where M is a transition metal element Mn or / and Ni; A is a transition metal vacancy, and / or a doping metal element Mg and / or a doping metal element Li; B is a doping transition metal element Fe or Cu or a doping transition metal element Zn; 0.8≤x≤0.9, 0.25≤a, 0.04≤b≤0.09. For example, invention patent CN113921809A discloses a P2 type layered sodium-ion battery cathode material and its preparation method, modified by co-doping with Na sites and transition metal sites. The chemical formula of the sodium-ion battery cathode material is Na. 0.67-x M x Mn 1-y N y O2, where M=Zn, Al, Mg, K, Ca, Li; N=Fe, Cr, V, Ni, Ti, Cu, Nb, Co.

[0005] However, the activation of anion redox reactions at 4.5 V high voltage easily induces lattice distortion, accompanied by excessive oxidation and release of lattice oxygen, leading to structural rearrangement or even structural collapse. Fe-containing layered oxide cathodes typically suffer from Jahn-Teller (JT) distortion and Fe migration, which disrupt the stability of the layered structure, resulting in capacity decay and reduced cycle life. Therefore, effectively suppressing irreversible anion oxygen reactions and excessive migration of transition metal cations under high voltage conditions, inhibiting the capacity and voltage decay mechanisms of layered oxide cathodes, and proposing targeted modification strategies are crucial for designing high-voltage, high-energy-density sodium-ion batteries. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides an Fe-doped modified P2-type sodium-ion layered oxide cathode material. This sodium-ion battery cathode material exhibits structural stability at a high voltage of 4.5 V, suppresses voltage decay and irreversible loss of lattice oxygen (no O2 / CO2 release), and achieves excellent rate performance (high Na2+) over a wide voltage range of 1.5-4.5 V. + It features high diffusion coefficient, high capacity retention (82.4% @1C), and stable long cycle life.

[0007] The technical solution adopted by this application to solve the above problems is as follows: This invention provides an Fe-doped modified P2-type sodium-ion layered oxide cathode material, the chemical formula of which is Na. 0.72 Li 0.2 Mn 0.68 Fe x O2, 0.1 <x<0.15。

[0008] To effectively address the problem of lattice distortion easily induced by anion redox activation under 4.5 V high voltage, accompanied by excessive oxidation and release of lattice oxygen, leading to structural rearrangement or even structural collapse, this invention optimizes the crystal configuration of the cation Fe and anion O in the P2 layered oxide cathode material by micro-tuning the Fe element, maintaining a stable transition metal (TM)-oxygen (O) structure, and constructing a stable coordination environment for lattice oxygen. The invention involves the charge transfer process from π-type ligands with TM-3d and O-2p orbitals to the metal (i.e., the reduction coupling process), suppressing cation TM migration and excessive reaction of anion O, achieving synergistic charge compensation between cations and anions, thereby activating a reversible π-type oxygen redox reaction. This effectively suppresses transition metal-oxygen bond dissociation and layered structure collapse, significantly alleviating capacity decay and voltage hysteresis, and improving the reversibility and kinetic performance of the anion redox reaction in the sodium layered cathode without losing capacity. Furthermore, refining the grain size reduces volume changes during cycling and suppresses voltage hysteresis and irreversible oxygen release.

[0009] Preferably, the chemical formula of the positive electrode material is Na. 0.72 Li 0.2 Mn 0.68 Fe 0.12 O2.

[0010] Preferably, the method for preparing the positive electrode material includes the following steps: (1) Disperse sodium source, manganese source, iron source and lithium source in solvent to obtain solid-liquid mixture; (2) The solid-liquid mixture is ball-milled to obtain a precursor slurry, and then the solvent is removed to obtain a precursor powder; (3) The precursor powder is calcined to obtain the sodium-ion battery layered oxide cathode material.

[0011] Preferably, the sodium source in step (1) is selected from at least one of sodium carbonate, sodium bicarbonate, and sodium acetate; The manganese source is selected from at least one of manganese dioxide and manganese oxide; The iron source is selected from at least one of iron oxide and iron(III) oxide; The lithium source is selected from at least one of lithium hydroxide, lithium acetate, and lithium carbonate.

[0012] Preferably, the molar ratio of sodium source, manganese source, iron source and lithium source is 0.36:0.1:0.34:n:1, 0.05 <n<0.075。

[0013] More preferably, the molar ratio of sodium source, manganese source, iron source and lithium source is 0.36:0.1:0.34:0.06:1.

[0014] Preferably, in step (2), the solvent is at least one of anhydrous ethanol, acetone and methanol.

[0015] Furthermore, in step (2), the ball-to-material ratio during ball milling is 10:1, the rotation speed is 300 rpm, and the ball milling time is 5 h.

[0016] Furthermore, the precursor slurry is dried at 60℃-80℃ for 8-12 h and then sieved through a 400-mesh grading sieve to obtain precursor powder.

[0017] Preferably, before the calcination treatment in step (3), solid-state sintering is performed at a temperature of 200°C for 2 hours. The precursor powder is then subjected to solid-state sintering to remove water of crystallization before the calcination treatment.

[0018] The heating and cooling rate during calcination is 2-5 ℃ / min, the calcination temperature is 900℃-1000℃, the calcination holding time is 10-16 h, and after the holding time is completed, the temperature is required to be reduced to 300℃ at a rate of 2 ℃ / min, followed by natural cooling.

[0019] The present invention also provides the application of the Fe-doped modified P2-type sodium-ion layered oxide cathode material in the preparation of high-voltage sodium-ion batteries.

[0020] Preferably, the charging voltage of the prepared high-voltage sodium-ion battery is 4.5 V.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention prepares Na by micro-controlling the Fe element. 0.72 Li 0.2 Mn 0.68 Fe x As a cathode material for sodium-ion batteries, O2 can effectively improve the structural stability of P2 layered oxide cathode materials, effectively suppress the dissociation of transition metal-oxygen bonds and the collapse of layered structures, significantly alleviate capacity decay and voltage hysteresis, and improve the reversibility and kinetic performance of anion redox reactions in sodium layered cathodes without losing capacity; it also refines the grain size, which can reduce the volume change of the structure during cycling, and suppress voltage hysteresis and irreversible oxygen release.

[0022] (2) The Fe-doped modified cathode material provided by the present invention has a simple preparation method.

[0023] (3) When the cathode material prepared by this invention is used in sodium-ion batteries, it effectively avoids the problem of lattice distortion easily induced by the activation of anion redox at 4.5 V high voltage, accompanied by excessive oxidation and release of lattice oxygen, which in turn leads to structural rearrangement or even structural collapse. It has structural stability at 4.5 V high voltage, suppresses voltage decay and irreversible loss of lattice oxygen (no O2 / CO2 release), and achieves excellent rate performance (high Na) within a wide voltage range of 1.5-4.5 V. + It features high diffusion coefficient, high capacity retention (82.4%@1 C), and stable long cycle life. Attached Figure Description

[0024] Figure 1 Scanning electron microscope (SEM) images of Fe-doped modified P2-type sodium ion layered oxide cathode materials prepared in the examples and comparative examples.

[0025] Figure 2 The X-ray diffraction (XRD) patterns of the Fe-doped modified P2-type sodium ion layered oxide cathode materials prepared in the examples and comparative examples are shown.

[0026] Figure 3 The images are high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) images of Fe-doped modified P2-type sodium ion layered oxide cathode materials prepared in the examples and comparative examples.

[0027] Figure 4 The Fe-doped modified P2-type sodium-ion layered oxide cathode materials prepared for the examples and comparative examples, at a current density of 0.2 C (1 C = 120 mAh g⁻¹), showed performance at a current density of 0.2 C (1 C = 120 mAh g⁻¹). -1 First charge / discharge curve.

[0028] Figure 5 The rate performance diagrams show the Fe-doped modified P2-type sodium ion layered oxide cathode materials prepared in the examples and comparative examples.

[0029] Figure 6 The graph shows the 0.2 C cycle performance of Fe-doped modified P2-type sodium ion layered oxide cathode materials prepared in the examples and comparative examples.

[0030] Figure 7 The images show in-situ XRD patterns of Fe-doped modified P2-type sodium-ion layered oxide cathode materials prepared in the examples and comparative examples. Detailed Implementation

[0031] To make the objectives, features, and advantages of the present invention more apparent and understandable, the following provides a detailed description through specific embodiments. A number of 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 improvements without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below. The technical features in various embodiments of the present invention can be combined correspondingly without conflict.

[0032] For the operation methods without specific conditions noted in the following embodiments, they are generally carried out under conventional conditions or according to the conditions recommended by the manufacturers. The content not described in detail in this specification belongs to the prior art well-known to those skilled in the art. The experimental materials used in the following embodiments, unless otherwise specified, can be obtained from conventional biochemical reagent companies.

[0033] In view of the problem that the existing P2-type sodium ion layered oxide cathode material is prone to induce lattice distortion by activating anion redox in a high-voltage environment, accompanied by excessive oxidation and release of lattice oxygen, and then causing structural rearrangement or even structural collapse, the present invention prepares a cathode material Na 0.72 Li 0.2 Mn 0.68 Fe x O2, 0.1 < x < 0.15, effectively inhibits the dissociation of transition metal–oxygen bonds and the collapse of the layered structure, significantly alleviates the capacity decay and voltage hysteresis phenomena, and improves the reversibility and kinetic performance of the anion redox reaction in the sodium layered cathode without sacrificing capacity.

[0034] Example 1 Preparation method of sodium ion battery cathode material Na 0.72 Li 0.2 Mn 0.68 Fe 0.12 O2 (NLMF0.12), using the solid-state sintering method to synthesize the P2-type sodium ion battery layered oxide cathode material, includes the following steps: (1) Weigh 0.36 mol of sodium carbonate (Na2CO3), 0.1 mol of lithium carbonate (Li2CO3), 0.68 mol of manganese dioxide (MnO2), and 0.06 mol of iron oxide (Fe2O3) in a 50 mL zirconia ball milling jar according to the stoichiometric ratio, where Na2CO3 and Li2CO3 are respectively 5 mol% and 2 mol% in excess, to obtain a solid-liquid mixture.

[0035] (2) The solid-liquid mixture was dispersed in 30 mL of acetone solvent and ball-milled using a ball mill with a ball-to-material ratio of 10:1, a rotation speed of 300 rpm, and an effective ball milling time of 5 h to obtain a precursor slurry. The precursor slurry was placed in an oven and dried at 60℃-80℃ to remove acetone. Then, it was fully crushed and ground in a mortar and sieved through a 400-mesh grading sieve to obtain precursor powder.

[0036] (3) Before calcination, the precursor powder is sintered in a solid state to remove the water of crystallization. The solid sintering temperature is 200℃ and the solid sintering time is 2 h.

[0037] (4) The precursor powder after solid sintering was further placed in a tube furnace for calcination. Under air atmosphere, the tube furnace was heated from room temperature to 960°C at a rate of 5°C / min and held for 960 min. Then it was cooled to 300°C at a rate of 2°C / min and naturally cooled to room temperature. It was named NLMF0.12.

[0038] Battery Assembly: The NLMF0.12 cathode material prepared in Example 1 was weighed and mixed with Super-P and polyvinylidene fluoride (PVDF) at a mass ratio of 7:2:1. Simultaneously, an appropriate amount of the cathode solvent N-methylpyrrolidone (NMP) was added to prepare a cathode slurry. The cathode slurry was then heated at a concentration of 1.5-3.0 mg / cm³. 2 The electrode sheet was coated onto an aluminum foil current collector and dried in an oven at 110°C for 12 hours. Using a 12 mm diameter electrode sheet as the positive electrode, metallic sodium as the negative electrode, and glass fiber as the separator, a button half-cell was prepared in an argon glove box using 1 mol / L NaClO4 EC / PC + 5% FEC as the electrolyte.

[0039] Comparative Example 1 The preparation process of Comparative Example 1 is the same as that of Example 1, except that the cathode material NLMF0.1 is obtained by using stoichiometric amounts of 0.35 mol Na2CO3, 0.1 mol Li2CO3, 0.7 mol MnO2 and 0.05 mol Fe2O3.

[0040] Comparative Example 2 The process of Comparative Example 2 is the same as that of Example 1, except that the cathode material NLMF0.15 is obtained by using stoichiometric amounts of 0.375 mol Na2CO3, 0.1 mol Li2CO3, 0.65 mol MnO2 and 0.075 mol Fe2O3.

[0041] Detection Example 1 The microstructure of the cathode material NLMF0.12 prepared in Example 1 and the cathode materials NLMF0.1 and NLMF0.15 prepared in Comparative Examples 1 and 2 were characterized by scanning electron microscopy. Figure 1 As shown.

[0042] As can be seen from the figure, the obtained cathode material NLMF0.1 ( Figure 1 (Figures a and d in the diagram), the cathode material NLMF0.12 ( Figure 1 (Figures b and e in the diagram) and the cathode material NLMF0.15 ( Figure 1 Figures c and f show well-crystallized hexagonal particles with diameters of approximately 2-6 μm. Compared to NLMF0.1 and NLMF0.12, the particle size of NLMF0.15 is significantly larger. Theoretically, particle coarsening may be due to a decrease in surface area-to-volume ratio and the size effect of defect-free energy, leading to slight voltage decay, stress concentration and particle fracture within the larger particles, and more interfacial side reactions.

[0043] Detection Example 2 The phase structures of the cathode material NLMF0.12 prepared in Example 1 and the cathode materials NLMF0.1 and NLMF0.15 prepared in Comparative Examples 1 and 2 were characterized by X-ray diffraction. Figure 2 As shown, the XRD results all exhibit typical P2 phase diffraction peaks, and the corresponding SEM results show that the hexagonal particles have more pronounced edges.

[0044] Detection Example 3 To further characterize the layered structure changes of the cathode material, high-angle annular dark-field (HAADF) and annular light-field (ABF) spherical aberration scanning transmission electron microscopy (STEM) techniques were used to determine the detailed atomic-scale structural information of the samples. The intralayer and interlayer cation arrangement was characterized for the cathode material NLMF0.12 prepared in Example 1 and the cathode materials NLMF0.1 and NLMF0.15 prepared in Comparative Examples 1 and 2.

[0045] Figure 3 Figure a in the image corresponds to the NLMF0.12 material, with the structure observed in the

[010] direction. The interplanar spacing of NLMF0.12 is 0.58 nm. The image intensity shown reflects a pattern of two bright spots followed by a relatively dark spot observed within the TM layer, indicating that the cations within the TM layer are arranged in a honeycomb-like ordered manner, mainly due to the local ordering of Li / transition metal ions in the TM layer.

[0046] Further simulation analysis was conducted using geometric phase analysis (GPA). Figure 3 Figure b in the middle - Figure 3The d-plot in the figure shows the c-axis strain distribution of cathode materials NLMF0.12, NLMF0.1, and NLMF0.15 in their pristine state. Below each plot, the microscopic region of the sample and its strain distribution are shown; the red area represents tensile stress, and the green area corresponds to regions with significantly reduced stress. In contrast, the strain values ​​in the green region of the pristine NLMF0.12 sample are significant, while the strain in the red region of NLMF0.1 exhibits fluctuating changes. The degree of redox activity aggregation of anionic oxygen ions reflects lattice stress; higher activity inevitably leads to increased lattice stress, resulting in O2 formation. Therefore, constructing a stable lattice framework of cationic transition metal and anionic oxygen promotes the stability of the layered structure.

[0047] Detection Example 4 The coin half-cells assembled in Example 1 and Comparative Examples 1-2 were subjected to relevant electrochemical tests on the Blue Electricity Test System at a test temperature of 25 °C.

[0048] Figure 4 The first-cycle galvanostatic charge-discharge curves are shown for the NLMF0.12 material at 0.2 C and a voltage range of 1.5–4.5 V. The initial specific charge-discharge capacity of NLMF0.12 material at a 0.2 C rate is approximately 182.9 mAh g⁻¹. -1 191.0 mAh g -1 The initial coulombic efficiency (CE) reached 104.43%. The specific capacities of the NLMF0.1 and NLMF0.15 cathodes were 169.2 mAh g⁻¹. -1 202.8 mAh g -1 and 135.1 mAh g -1 174.7 mAh g -1 When charged to voltages above 4.0 V, the typical long plateau period reflects the oxidation process of oxygen anions. Although the three materials exhibit similar electrochemical behavior, NLMF0.15 shows greater polarization during cycling, indicating that its capacity cannot be fully released during sodium removal. In contrast, NLMF0.1 provides a higher specific capacity during sodium removal, and exhibits a longer plateau period at high voltages, where oxygen participates in more redox reactions, achieving a CE value of 119.83%. Energy density is primarily determined by the reduction steps of lattice oxygen during discharge, rather than the oxidation process during charging. Therefore, the high activity of lattice oxygen does not directly equate to high capacity and excellent performance.

[0049] Case 5 like Figure 5 The results show the rate performance. The rate performance results indicate that the half-cell of Comparative Example 1 (cathode material NLMF0.12) has a discharge specific capacity of 76.32 mAh g⁻¹ at 5 C.-1 The average discharge capacities of the NLMF0.1 and NLMF0.15 cathode materials under 5 C conditions are approximately 72.44 mAh g⁻¹. -1 and 49.32 mAh g -1 .

[0050] Case 6 like Figure 6 As shown, within a wide voltage range of 1.5-4.5 V, under 0.2 C conditions, Comparative Example 1 (cathode material NLMF0.12) maintained a capacity retention rate of less than 80.2% at the 82nd cycle. Figure 6 (See Figure a in the diagram), which is far superior to NLMF0.1 and NLMF0.15. A high cutoff voltage exacerbates capacity decay and voltage fading; therefore, we further controlled the voltage within a narrow range of 1.9-4.9V to improve its cycle stability. Under 0.2C conditions, NLMF0.12 retained 90.6% of its capacity after 100 cycles (…). Figure 6 (Figure b in the text).

[0051] Case 7 like Figure 7 As shown, in-situ XRD was used to investigate the relationship between the electrochemical behavior and phase structure evolution of the cathode material. In contrast, Example 1 (cathode material NLMF0.12) only showed a peak shift during the charge-discharge process. Figure 7 As shown in Figure b), no phase transition occurred; its structural evolution was reversed, demonstrating the highly reversible nature of its sodium insertion / extraction behavior. For charging (oxidation), when Na… + When Fe is extracted from the lattice, interlayer expansion occurs due to increased repulsive forces within the structure, leading to an increase in the c-axis parameter and a slight shift of the (002) and (004) diffraction peaks to lower angles. Due to the oxidation of Fe, Na is extracted from the interlayer structure. + To compensate for oxidation and reduce the a-axis parameter, the (100) and (102) peaks shift to higher angles. This is due to the Mn... 4+ During the initial charge cycle, it does not participate in the reaction. When the voltage reaches 4.5 V, the only active element is oxygen, which can participate in the oxidation process to provide charge compensation. Throughout the entire charge-discharge process, the calculated change in the c-axis parameter of NLMF0.12 is only 0.81%, while the volume change is 0.62%, far less than that of the similarly behaving NLMF0.1 material (c-axis parameter change of only 2.51%, and volume change of 2.36%). Figure 7 As shown in Figure a). However, the NLMF0.15 material exhibits a broad, amorphous, low-crystallinity peak near the (002) diffraction peak (circled in red), making it impossible to calculate the corresponding lattice parameters ( Figure 7(As shown in Figure c). This phase transition with different orders causes stacking faults and leads to the appearance of the "Z" phase, which is caused by the migration of transition metal Fe into the tetrahedral coordination environment of Na, disrupting the long-range order in the MO2 layer. Excessive migration of transition metal Fe leads to a decrease in the structural order and loss of crystallinity of the material, thereby affecting subsequent structural stability and cycling performance. Therefore, the high crystallinity and low c-axis change rate of the NLMF0.12 cathode material indicate better structural reversibility. Reasonable cation optimization can effectively suppress Fe migration, maintain structural integrity, and improve the long-range order in the Na2 layer. + The excellent electrochemical performance of sodium ion cathode materials is enhanced during insertion / extraction.

[0052] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A Fe-doped modified P2-type sodium-ion layered oxide cathode material, characterized in that, The chemical formula of the positive electrode material is Na 0.72 Li 0.2 Mn 0.68 Fe x O2, 0.1 <x<0.15。 2. The Fe-doped modified P2-type sodium-ion layered oxide cathode material according to claim 1, characterized in that, The chemical formula of the positive electrode material is Na 0.72 Li 0.2 Mn 0.68 Fe 0.12 O2.

3. The Fe-doped modified P2-type sodium-ion layered oxide cathode material according to claim 1 or 2, characterized in that, The preparation method of the positive electrode material includes the following steps: (1) Disperse sodium source, manganese source, iron source and lithium source in solvent according to stoichiometric ratio to obtain solid-liquid mixture; (2) The solid-liquid mixture is ball-milled to obtain a precursor slurry, and then the solvent is removed to obtain a precursor powder; (3) The precursor powder is calcined to obtain the cathode material.

4. The Fe-doped modified P2-type sodium-ion layered oxide cathode material according to claim 3, characterized in that, The sodium source in step (1) is selected from at least one of sodium carbonate, sodium bicarbonate, and sodium acetate; The manganese source is selected from at least one of manganese dioxide and manganese oxide; The iron source is selected from at least one of iron oxide and iron(III) oxide; The lithium source is selected from at least one of lithium hydroxide, lithium acetate, and lithium carbonate.

5. The Fe-doped modified P2-type sodium-ion layered oxide cathode material according to claim 3, characterized in that, The molar ratio of sodium, manganese, iron, and lithium sources is 0.36:0.1:0.34:n:1, 0.

05. <n<0.075。 6. The Fe-doped modified P2-type sodium-ion layered oxide cathode material according to claim 5, characterized in that, The molar ratio of sodium, manganese, iron and lithium sources is 0.36:0.1:0.34:0.06:

1.

7. The Fe-doped modified P2-type sodium-ion layered oxide cathode material according to claim 3, characterized in that, In step (2), the solvent is at least one of anhydrous ethanol, acetone and methanol.

8. The Fe-doped modified P2-type sodium-ion layered oxide cathode material according to claim 3, characterized in that, Before calcination, step (3) involves solid-state sintering at a temperature of 200°C for 2 hours. The heating and cooling rate during calcination is 2-5 ℃ / min, the calcination temperature is 900℃-1000℃, the calcination holding time is 10-16h, and after the holding time is completed, the temperature is required to be reduced to 300℃ at a rate of 2 ℃ / min, followed by natural cooling.

9. The application of the Fe-doped modified P2-type sodium-ion layered oxide cathode material according to any one of claims 1-8 in the preparation of high-voltage sodium-ion batteries.

10. The application according to claim 9, characterized in that, The high-voltage sodium-ion battery prepared has a charging voltage of 4.5 V.

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