O3-type sodium-ion battery cathode material induced by reduction method for conversion of residual alkali

Abstract

The application is a kind of O3 type sodium ion battery positive electrode material of reducing method induced residual base conversion. The chemical formula of the positive electrode material is Na 1+x Ni 0.33 Fe 0.33 Mn 0.33 P x O 2+2x In the preparation, the selected reducing acid salt, including but not limited to hypophosphite or bisulfite, is used as a residual base eliminator and a reducing agent, and through grinding and calcination, the mechanism of acid-base neutralization reaction and redox reaction is used to realize the functions of residual base conversion coating and surface coordination environment adjustment. The first coulombic efficiency of the battery obtained by the application is as high as 94%, the voltage hysteresis is greatly reduced, the capacity retention rate after 300 cycles at 1C is increased from 38% to 84%, and a new generation of coating scheme with great potential for scaling is provided for layered positive electrode materials.

Description

Technical Field

[0001] This invention belongs to the technical field of sodium-ion battery cathode materials, specifically relating to a coating-coated layered cathode material for 03 type sodium-ion batteries and its preparation method. Background Technology

[0002] Benefiting from abundant sodium resources and cost advantages, sodium-ion batteries (SIBs) have become a highly promising next-generation energy storage solution. Among them, layered transition metal oxides (SMOs) show great promise for large-scale applications due to their high theoretical capacity and ease of synthesis. However, their sodium storage process requires a stable electrode interface, and practical applications are often constrained by triple interfacial instability: surface residual alkali, electrolyte corrosion, and irreversible phase transition. These problems easily lead to vicious coupling: the open structure of the layered cathode readily reacts with H2O / CO2 to generate residual alkali, which not only accelerates the dissolution of transition metals but also triggers serious side reactions that damage the cathode-electrolyte interphase (CEI). At the same time, the internal structure of the cathode is fragile, and lattice mutations and irreversible multiphase evolution generated during cycling expose fresh surfaces, exacerbating electrolyte erosion. Surface chemical degradation and structural collapse thus fall into a vicious cycle, severely limiting the cycle performance of the battery.

[0003] Therefore, surface coating has become a major interfacial stabilization strategy. While traditional inert coatings (such as Al₂O₃) can provide physical isolation, they cannot solve the surface chemical instability caused by residual alkali and structural fatigue. In recent years, researchers have developed a "waste-to-treasure" strategy, converting surface residues into Na₂O. 0.44 MnO2 tunnel-type protective layers (DOI: 10.1021 / jacs.4c04766.) or in-situ conversion of residual alkali on the surface into a stable polymer coating via NH4F treatment (DOI:10.1002 / adma.202417540.) can be used. However, these methods do not adequately protect the interface and typically lack the ability to modulate the bulk or near-surface electronic structure, leaving destructive phase transition problems unresolved. Summary of the Invention

[0004] The purpose of this invention is to overcome the challenges of coating strategies in effectively controlling electronic structure and suppressing phase transitions, and to provide an O3-type sodium-ion battery cathode material that induces residual alkali conversion through a reduction method. This material utilizes a reducing acidic salt as a residual alkali eliminator and reducing agent, leveraging acid-base neutralization and redox reactions to achieve residual alkali conversion coating and regulate the surface coordination environment. The battery obtained by this invention achieves an initial coulombic efficiency of up to 94%, significantly reduced voltage hysteresis, and a capacity retention rate that jumps from 38% to 84% after 300 cycles at 1 C. This strategy cleverly combines residual alkali conversion with directional electronic control, successfully decoupling the vicious chain reaction between residual alkali, irreversible phase transitions, and electrolyte erosion, providing a new generation of coating solutions with great potential for scalability for layered cathode materials.

[0005] The technical solution adopted by the present invention to solve the above technical problems is as follows: A cathode material for an O3-type sodium-ion battery induced by a reduction method to convert residual alkali, and the chemical formula of the cathode material is Na 1+x Ni 0.33 Fe 0.33 Mn 0.33 P x O 2+2x , 0.001 < x ≤ 0.0010; the subscripts are the theoretical atomic ratios between the elements.

[0006] Preferably, x is 0.005.

[0007] A preparation method of the cathode material for an O3-type sodium-ion battery induced by a reduction method to convert residual alkali, and the method includes the following steps: (1) According to the material ratio in the chemical formula, mix the finished matrix material and the reducing acid salt, grind them dry for 10 - 20 min, and then grind them wet for 30 - 60 min to obtain a precursor; Among them, the molar ratio of the finished matrix material to the reducing acid salt is 1:0.001~0.0010; The reducing acid salt includes but is not limited to sodium hypophosphite NaH2PO2 or sodium bisulfite NaHSO3; (2) Heat the precursor mixture in a glove box (argon atmosphere) at a temperature of 50 - 60 °C and a rotation speed of 360 - 400 r / min for 3 - 5 h to obtain a mixed material; (3) Put the mixed material into a tubular furnace, heat it to 200 - 220 °C in an air atmosphere and keep it warm for 1 - 3 h, naturally cool it to 50 - 60 °C, and then take it out and put it into a glove box to obtain the cathode material for an O3-type sodium-ion battery induced by a reduction method to convert residual alkali.

[0008] The finished product in step (1) is NaNi 0.33 Fe 0.33 Mn 0.33 O2; The grinding agent used in the grinding in step (1) is ethylene glycol dimethyl ether (DME).

[0009] The heating rate in step (3) is 5 - 8 °C / min.

[0010] The application of the cathode material for an O3-type sodium-ion battery induced by a reduction method to convert residual alkali is used as a cathode material in a sodium-ion battery.

[0011] The O3-type sodium-ion battery cathode material induced by reduction method to convert residual alkali was mixed with conductive carbon black (Super P) and binder (PVDF) at a mass ratio of 8:1:1 to obtain a mixture; then N-methylpyrrolidone (NMP) was added, and the stirred slurry was coated onto aluminum foil using a coating device to a thickness of 100-200 µm. After drying in a glove box for 8-12 h, the working electrode was obtained, which served as the cathode. The negative electrode is metallic sodium, the electrolyte is commercial 1 mol / L NaClO4 in PC + 5% FEC, and the diaphragm is a glass fiber membrane GF-A diaphragm.

[0012] The essential features of this invention are: This invention addresses the destructive effects of a chain reaction (residual alkali, phase transition, and electrolyte erosion) on the O3 phase NFM111 cathode. It utilizes acidic salts with both high reactivity and strong reducing properties, taking hypophosphite NaH2PO2 and bisulfite NaHSO3 as examples. By precisely controlling the interfacial coordination environment through electron transfer effects, a triple modification of the electrode interface is achieved simultaneously. 1. Utilizing the reaction characteristics of NaH2PO2 or NaHSO3 with alkaline substances, residual alkali on the surface is converted into a highly conductive coating layer in situ; 2. Highly conductive phosphate or sulfate coatings significantly promote Na+ absorption. + Diffusion kinetics prevents the electrolyte from corroding the positive electrode and inhibits the dissolution of transition metals; 3. Utilizing the strong reducing properties of NaH₂PO₂ or NaHSO₃ to induce Ni 3+ Become Ni 2 (This modulates the electronic state of Ni on the surface, effectively suppressing the harmful O'3 phase transition.) The following are the reaction equations showing the specific roles of NaH2PO2 and NaHSO3: H2PO2 - + 6OH - + 4Ni 3+ → PO4 3- + 4Ni 2+ + 4H2O (1) HSO3 - + 3OH - + 2Ni 3+ → SO4 2- + 2Ni 2+ + 2H2O (2) The beneficial effects of this invention are as follows: A reductive surface reconstruction strategy based on residual alkali conversion has been successfully developed, effectively mitigating the harmful interface-bulk phase coupling instability within cathode materials. Unlike exogenous passive modification through coating and doping, this invention utilizes the strong reducing properties of additives to alter the chemical environment of the bulk phase without introducing other atoms; this is an endogenous, directional control method. This method constructs a protective surface coating layer that not only efficiently consumes harmful residual alkali but also inhibits electrolyte corrosion. High concentrations of Ni... 3+ This will trigger the Jahn-Teller effect, causing axial Ni-O bond stretching, thereby driving an irreversible phase transition. This invention addresses this by using Ni... 3+ Reduced to Ni 2+ Strategically modulating the near-surface electronic coordination environment enhances the reversibility of the phase transition. Taking hypophosphite NaH2PO2 as an example, the material in Example 1 exhibits superior electrochemical performance, with lower voltage hysteresis, stronger cycling stability, and optimized Na... + Diffusion kinetics. In-situ XRD analysis clearly confirmed the stabilizing effect of the coating layer on the bulk structure evolution, effectively preventing the formation of harmful O′3 phase. After 300 cycles at 1 C, the capacity retention remained at 84%. Furthermore, the modified material exhibited excellent air stability and was successfully assembled into a highly stable sodium-ion full cell, maintaining a capacity retention of 91.2% after 200 cycles, highlighting its significant practical application potential. By simultaneously addressing the issues of interfacial chemical degradation and bulk structure evolution, this study provides a novel and feasible approach for designing next-generation surface coating strategies. Attached Figure Description

[0013] To more clearly illustrate the optimization results in this invention, the accompanying drawings used in the prior art will be described below.

[0014] Figure 1 This is a scanning electron microscope image of the cathode material obtained in Comparative Example 1 of this invention.

[0015] Figure 2 These are scanning electron microscope (SEM) images of the cathode material obtained in Example 1.

[0016] Figure 3 This is the XPS Ni 2p spectrum obtained in Comparative Example 1.

[0017] Figure 4 This is the XPS Ni 2p spectrum obtained in Example 1.

[0018] Figure 5 These are the voltage drop curves of the half-cells assembled from Example 1 and Comparative Example 1, respectively. 3.15 V was selected as the uniform voltage standard for measuring the voltage drop.

[0019] Figure 6The long cycle life curves of the half-cells assembled in Example 1 and Comparative Example 1 at a 1 C rate and a voltage range of 2.0-4.0 V are shown.

[0020] Figure 7 The graphs are of the half-cells assembled in Example 1 and Comparative Example 1 at voltage ranges of 2.0-4.0 V and at different rates.

[0021] Figure 8 This is a diagram showing the long cycle life of a full cell assembled using the positive electrode material of Example 1 as the positive electrode and hard carbon (HC) as the negative electrode. Detailed Implementation

[0022] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0023] Unless otherwise specified in the following implementation plan, the test conditions are generally as per standard test conditions or the test conditions recommended by the reagent company. Unless otherwise specified, all materials and reagents used are commercially available.

[0024] Comparative Example 1: (1) Using finished NaNi 0.33 Fe 0.33 Mn 0.33 O2 (Shenzhen Kejingxing Technology Co., Ltd., the following comparative and example examples are the same). Figure 1 The image shows a scanning electron microscope (SEM) image of the cathode material obtained in Comparative Example 1. It consists of particles of varying sizes, with many white particulate impurities distributed on its surface.

[0025] (2) Sodium-ion battery preparation: Weigh 80 mg of the positive electrode material prepared above, 10 mg of conductive carbon black (SuperP) and 10 mg of binder (PVDF), and add 10 drops of N-methylpyrrolidone (NMP) to mix them evenly. Coat the evenly stirred slurry onto aluminum foil with a coating thickness of 100 µm. Dry to obtain the working electrode as the positive electrode. The selected negative electrode is metallic sodium. The battery model is CR2032 button cell. The electrolyte is commercial 1 mol / L NaClO4 in PC + 5% FEC. The separator is a glass fiber membrane GF-A separator.

[0026] Comparative Example 2: The other steps are the same as in Comparative Example 1, except that the finished NaNi is... 0.33 Fe 0.33 Mn 0.33 O2 was left to stand in outdoor air for 7 days.

[0027] Comparative Example 3: The other steps are the same as in Comparative Example 1, except that the finished NaNi is... 0.33 Fe0.33 Mn 0.33 O2 was left to stand in outdoor air for 14 days.

[0028] Comparative Example 4: The other steps are the same as in Comparative Example 1, except that the finished NaNi is... 0.33 Fe 0.33 Mn 0.33 O2 was left to stand in outdoor air for 21 days.

[0029] Example 1: (1) Mixing and grinding: 1 mmol NaNi 0.33 Fe 0.33 Mn 0.33 O2 and 0.005 mmol NaH2PO2 were added to an agate mortar and ground dry for 10 min. Then, 10 ml of DME was added and the grinding continued for 30 min. The mixture was poured into a heated stirrer and heated in a glove box at 50 °C and 360 r / min for 3 h to obtain a mixed material. The slurry was dried to obtain a powdered precursor. (2) Sintering reaction: The powdered precursor was placed in a tube furnace and heated to 200 °C in air atmosphere and held for 1 hour to achieve coating. The heating rate was 5 °C / min. After naturally cooling to 50 °C, it was taken out and placed in a glove box to obtain the positive electrode material Na. 1.005 Ni 0.33 Fe 0.33 Mn 0.33 P 0.005 O 2.01 . Figure 2 The image shows a scanning electron microscope (SEM) image of the cathode material obtained in Example 1. It consists of particles of varying sizes, with a smooth and uniform surface, and no white particles or impurities.

[0030] (3) Sodium-ion battery preparation: Weigh 80 mg of the positive electrode material prepared above, 10 mg of conductive carbon black (SuperP) and 10 mg of binder (PVDF), and add 10 drops of N-methylpyrrolidone (NMP) to mix them evenly. Coat the evenly stirred slurry onto aluminum foil with a coating thickness of 100 µm. Dry to obtain the working electrode as the positive electrode. The selected negative electrode is metallic sodium. The battery model is CR2032 button cell. The electrolyte is commercial 1 mol / L NaClO4 in PC + 5% FEC. The separator is a glass fiber membrane GF-A separator.

[0031] Example 2: (1) Mixing and grinding: 1 mmol NaNi 0.33 Fe 0.33 Mn 0.33O2 and 0.001 mmol NaH2PO2 were added to an agate mortar and ground dry for 10 min. Then 10 ml of DME was added and the grinding continued for 30 min. The mixture was poured into a heated stirrer and heated in a glove box at 50 °C and 360 r / min for 3 h to obtain a mixed material. The slurry was dried to obtain a powdered precursor. (2) Sintering reaction: The powdered precursor is placed in a tube furnace and heated to 200 ℃ in air atmosphere and held for 1 h. The heating rate is 5 ℃ / min. After naturally cooling to 50 ℃, it is taken out and placed in a glove box to obtain the positive electrode material.

[0032] (3) Sodium-ion battery preparation: Weigh 80 mg of the positive electrode material prepared above, 10 mg of conductive carbon black (SuperP) and 10 mg of binder (PVDF), and add 10 drops of N-methylpyrrolidone (NMP) to mix them evenly. Coat the evenly stirred slurry onto aluminum foil with a coating thickness of 100 µm. Dry to obtain the working electrode as the positive electrode. The selected negative electrode is metallic sodium. The electrolyte is commercial 1 mol / L NaClO4 in PC + 5% FEC. The separator is a glass fiber membrane GF-A separator.

[0033] Example 3: (1) Mixing and grinding: 1 mmol NaNi 0.33 Fe 0.33 Mn 0.33 O2 and 0.003 mmol NaH2PO2 were added to an agate mortar and ground dry for 10 min. Then, 10 ml of DME was added and the grinding continued for 30 min. The mixture was poured into a heated stirrer and heated in a glove box at 50 °C and 360 r / min for 3 h to obtain a mixed material. The slurry was dried to obtain a powdered precursor. (2) Sintering reaction: The powdered precursor is placed in a tube furnace and heated to 200 ℃ in air atmosphere and held for 1 h. The heating rate is 5 ℃ / min. After naturally cooling to 50 ℃, it is taken out and placed in a glove box to obtain the positive electrode material.

[0034] (3) Sodium-ion battery preparation: Weigh 80 mg of the positive electrode material prepared above, 10 mg of conductive carbon black (SuperP) and 10 mg of binder (PVDF), and add 10 drops of N-methylpyrrolidone (NMP) to mix them evenly. Coat the evenly stirred slurry onto aluminum foil with a coating thickness of 100 µm. Dry to obtain the working electrode as the positive electrode. The selected negative electrode is metallic sodium. The electrolyte is commercial 1 mol / L NaClO4 in PC + 5% FEC. The separator is a glass fiber membrane GF-A separator.

[0035] Example 4: (1) Mixing and grinding: 1 mmol NaNi 0.33 Fe 0.33 Mn 0.33 O2 and 0.007 mmol NaH2PO2 were added to an agate mortar and ground dry for 10 min. Then, 10 ml of DME was added and the grinding continued for 30 min. The mixture was poured into a heated stirrer and heated in a glove box at 50 °C and 360 r / min for 3 h to obtain a mixed material. The slurry was dried to obtain a powdered precursor. (2) Sintering reaction: The powdered precursor is placed in a tube furnace and heated to 200 ℃ in air atmosphere and held for 1 h. The heating rate is 5 ℃ / min. After naturally cooling to 50 ℃, it is taken out and placed in a glove box to obtain the positive electrode material.

[0036] (3) Sodium-ion battery preparation: Weigh 80 mg of the positive electrode material prepared above, 10 mg of conductive carbon black (SuperP) and 10 mg of binder (PVDF), and add 10 drops of N-methylpyrrolidone (NMP) to mix them evenly. Coat the evenly stirred slurry onto aluminum foil with a coating thickness of 100 µm. Dry to obtain the working electrode as the positive electrode. The selected negative electrode is metallic sodium. The electrolyte is commercial 1 mol / L NaClO4 in PC + 5% FEC. The separator is a glass fiber membrane GF-A separator.

[0037] Example 5: (1) Mixing and grinding: 1 mmol NaNi was left to stand in outdoor air for 21 days 0.33 Fe 0.33 Mn 0.33 O2 and 0.005 mmol NaH2PO2 were added to an agate mortar and ground dry for 10 min. Then 10 ml of DME was added and the grinding continued for 30 min. The mixture was poured into a heated stirrer and heated in a glove box at 50 °C and 360 r / min for 3 h to obtain a mixed material. The slurry was dried to obtain a powdered precursor. (2) Sintering reaction: The powdered precursor is placed in a tube furnace and heated to 200 ℃ in air atmosphere and held for 1 h. The heating rate is 5 ℃ / min. After naturally cooling to 50 ℃, it is taken out and placed in a glove box to obtain the positive electrode material.

[0038] (3) Sodium-ion battery preparation: Weigh 80 mg of the positive electrode material prepared above, 10 mg of conductive carbon black (SuperP) and 10 mg of binder (PVDF), and add 10 drops of N-methylpyrrolidone (NMP) to mix them evenly. Coat the evenly stirred slurry onto aluminum foil with a coating thickness of 100 µm. Dry to obtain the working electrode as the positive electrode. The selected negative electrode is metallic sodium. The electrolyte is commercial 1 mol / L NaClO4 in PC + 5% FEC. The separator is a glass fiber membrane GF-A separator.

[0039] I. XPS Test The two cathode materials of Example 1 and Comparative Example 1 were subjected to photoelectron spectroscopy (XPS) tests. Figure 3 and Figure 4 These are the Ni 2p spectra of Example 1 and Comparative Example 1. The nickel species in Example 1 consisted of 63.6% Ni. 2+ (854.1 / 871.6 eV) and 36.4% Ni 3+ The composition (855.8 / 873 eV) is mainly due to oxidation during synthesis and subsequent air exposure. Notably, Ni in NFM-NHP... 2+ The proportion increased to 68.6%, which is attributed to the strong reducing properties of NaH2PO2, which reduces Ni 3+ Reduced to Ni 2+ .

[0040] II. Performance Testing The room temperature and ambient temperature mentioned in this comparative example and embodiment refer to 25°C.

[0041] ambient temperature cycling performance test (1) Add different positive electrode materials to button half-cells, charge them to 4.0 V at a current rate of 0.1 C at room temperature of 25 ℃, and then discharge them to 2.0 V. Repeat this cycle once, record and observe the voltage difference of the charge and discharge curves at a uniform voltage of 3.15 V to monitor the voltage hysteresis phenomenon.

[0042] (2) Button half-cells with different positive electrode materials were charged to 4.0 V at a current rate of 0.1 C at room temperature (25 ℃), and then discharged to 2.0 V. This cycle was repeated twice. Then, the cells were charged to 4.0 V at a current rate of 1 C, and then discharged to 2.0 V. This cycle was repeated n times. The discharge specific capacity was recorded for each week. The capacity retention rate of the room temperature cycle was calculated using the following formula: m-week capacity retention rate = discharge specific capacity of week m / discharge specific capacity of week 3 × 100%.

[0043] (3) The button cells with different positive electrode materials were charged to 4.0 V at room temperature (25 ℃) with current rates of 0.1 C, 0.2 C, 0.5 C, 1 C, 2 C and 5 C respectively, and then discharged to 2.0 V. The discharge specific capacity was recorded for each cycle at each current rate for 5 cycles.

[0044] (4) Full battery performance test Full cells were assembled using hard carbon (HC) as the negative electrode and operated within a voltage range of 0.5–4.0 V. With a positive / negative electrode capacity ratio (N / P ratio) of 1.05:1, the cells were cycled n times, and the discharge specific capacity was recorded weekly. The capacity retention rate during room temperature cycling was calculated using the following formula: m-week capacity retention rate = discharge specific capacity in week m / discharge specific capacity in week 1 × 100%. The results of the above room temperature cycling performance tests are shown in Table 1.

[0045] Table 1

[0046] Voltage hysteresis is a common phenomenon in NFM111 cathode materials. For example... Figure 5 Comparing the first constant current charge-discharge (GCD) curves of Comparative Example 1 and Example 1 at 0.1 C rate reveals that the voltage drop of the material in Example 1 (0.08 V) is significantly lower than that of the material in Comparative Example 1 (0.27 V). During the first charge-discharge cycle, Example 1 only lost 8 mAh g⁻¹. -1 Comparative Example 1, on the other hand, lost 9.3 mAh g. -1 This clearly demonstrates that the voltage hysteresis phenomenon has been effectively alleviated.

[0047] By comparing Examples 2 and 3 with Comparative Example 1, it can be seen that after introducing NaH2PO2 into the cathode material, thanks to the strong reducing power of NaH2PO2 and the synergistic effect of its reaction with alkaline substances, the cycling stability of the half-cell at room temperature is significantly improved. Moreover, as the amount of NaH2PO2 added increases, more residual alkali is consumed, the coating structure becomes more stable, and the subsequent electrochemical stability increases significantly.

[0048] A comparison of Examples 1 and 3 shows that the electrochemical stability significantly increases with the continuous increase of NaH2PO2 content. This indicates that the formed coating has not yet reached its optimal thickness, thus stabilizing the layered cathode, reducing transition metal dissolution, and stabilizing the cathode bulk structure. Therefore, based on the stable positive and negative electrode interface, the long-term cycling stability of the half-cell is significantly improved.

[0049] A comparison of Examples 1 and 3 with Example 4 shows that when the NaH2PO2 content is increased to 0.007 mmol, the electrochemical stability of the cathode material decreases slightly. This indicates that as the addition amount increases from 0.001 mmol to 0.7 mmol, the thickness of the coating gradually increases. Excessive thickness reduces the reaction kinetics of the electrode material and hinders the reaction of Na during charging and discharging. + During normal insertion-extraction / intercalation at the electrode interface, active sites are "separated," reducing the amount of material effectively participating in the reaction. Example 1, with an addition of 0.005 mmol, exhibited the best retention rate over 300 cycles, indicating that the resulting coating thickness was optimal—sufficiently protecting the interface from electrolyte erosion without excessively hindering Na+ reaction. + The migration.

[0050] The comparison between Example 5 and Comparative Example 4 shows that after standing in outdoor air for 21 days, Example 5 still has an intentional capacity retention rate compared to Comparative Example 4, indicating that the coating can effectively protect the cathode material from the influence of air.

[0051] Figure 6 The diagram shows the long cycle life of Comparative Example 1 and Example 1 at 1 C rate. The initial discharge specific capacities of Example 1 and Comparative Example 1 are 123.2 and 127.8 mAh g, respectively. -1 Example 1 exhibits a higher initial capacity and retains 97.1% of its capacity after 100 cycles, while Comparative Example 1 only retains 77.2% after 100 cycles. This is because NaH2PO2 effectively reduces the damage to the electrode caused by residual alkali during long cycles, and the coating protects the interface from electrolyte erosion. After 300 cycles, it still retains 84% ​​of its capacity, indicating that Example 1 has superior structural stability to resist the damage caused by lattice distortion.

[0052] Table 2

[0053] Comparing the high-rate charge-discharge performance of Example 1 and Comparative Example 1, such as... Figure 7 As shown in Table S2, the discharge specific capacities of Example 1 at rates of 0.1C-5C are 133.8, 133, 129.5, 126.9, 123.1, and 114.4 mAh g⁻¹. -1 All of these values ​​were higher than the discharge specific capacity of Comparative Example 1 (128.1, 124.8, 119.6, 113.7, 103.2, 81 mAh g). -1 This indicates that Example 1 has better electrode kinetics, and the reaction of NaH2PO2 with residual alkali reduces the internal resistance of the cathode material.

[0054] like Figure 8As shown, a full-cell test was conducted on the cathode material of Example 1, with hard carbon as the anode. The assembled full cell had a capacity of 130 mAh g⁻¹. -1 The reversible discharge specific capacity, with a retention rate of 91.2% after 200 cycles, demonstrates the practical commercial application feasibility and industrialization potential of Example 1.

[0055] This invention utilizes a surface reconstruction strategy based on residual alkali conversion to directionally regulate the electronic coordination environment of Ni using the strong reducing properties of NaH₂PO₂, successfully preparing O₃-type layered oxide cathode materials with phosphate coatings for sodium-ion batteries by consuming residual alkali. Comparison with the above implementation examples shows that the proposed O₃-type layered oxide cathode material for sodium-ion batteries exhibits high reversible capacity and good cycle life. This provides new ideas and approaches for next-generation coating technologies.

[0056] The present invention has been illustrated with the above embodiments to explain the detailed method of the present invention. However, the present invention is not limited to the detailed method described above, that is, it does not mean that the present invention must rely on the detailed method described above to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0057] Matters not covered in this invention are common knowledge.

Claims

1. A sodium-ion battery cathode material of type O3 induced by reduction method for residual alkali conversion, characterized in that, The chemical formula of the cathode material is Na. 1+x Ni 0.33 Fe 0.33 Mn 0.33 P x O 2+2x , 0.001≤x≤0.0010; the subscripts represent the theoretical atomic ratios between elements.

2. The O3-type sodium-ion battery cathode material with reduction-induced residual alkali conversion as described in claim 1, characterized in that, The x value is preferably 0.

005.

3. The method for preparing O3-type sodium-ion battery cathode material by reduction-induced residual alkali conversion as described in claim 1, characterized in that, The method includes the following steps: (1) According to the material ratio in the chemical formula, the finished matrix material is mixed with the reducing acid salt and dry-ground for 10-20 min, and then wet-ground for 30-60 min to obtain the precursor. The molar ratio of the finished matrix material to the reducing acid salt is 1:0.001~0.0010; the finished product is NaNi. 0.33 Fe 0.33 Mn 0.33 O2; The reducing acid salts mentioned include, but are not limited to, NaH2PO2 or NaHSO3; (2) The precursor mixture was heated in a heated stirrer in a glove box under an argon atmosphere for 3-5 hours with stirring to obtain a mixed material. (3) The mixed material is placed in a tube furnace and heated to 200-220 ℃ in an air atmosphere and kept at that temperature for 1-3 h. After naturally cooling to 50-60 ℃, it is taken out and placed in a glove box to obtain the O3 type sodium-ion battery cathode material induced by reduction method to convert residual alkali.

4. The method for preparing O3-type sodium-ion battery cathode material by reduction-induced residual alkali conversion as described in claim 3, characterized in that, The abrasive used in step (1) is ethylene glycol dimethyl ether.

5. The method for preparing O3-type sodium-ion battery cathode material by reduction-induced residual alkali conversion as described in claim 3, characterized in that, The heating rate in step (3) is 5-8 °C / min.

6. The method for preparing O3-type sodium-ion battery cathode material by reduction-induced residual alkali conversion as described in claim 3, characterized in that, In step (2), the stirring speed is 360-400 r / min.

7. The application of the O3-type sodium-ion battery cathode material induced by reduction method for residual alkali conversion as described in claim 1, characterized in that, Used as a positive electrode material in sodium-ion batteries; The O3-type sodium-ion battery cathode material induced by reduction method to convert residual alkali was mixed with conductive carbon black and binder at a mass ratio of 8:1:1 to obtain a mixture; then N-methylpyrrolidone was added, and the stirred slurry was coated onto aluminum foil using a coating device to a thickness of 100-200 µm. After drying in a glove box for 8-12 h, the working electrode was obtained, which served as the cathode. The negative electrode is metallic sodium, the electrolyte is commercial 1 mol / L NaClO4 in PC + 5% FEC, and the diaphragm is a glass fiber membrane GF-A diaphragm.

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