A doped modified p2 phase sodium-ion battery positive electrode material and a preparation method thereof

Abstract

This invention provides a doped modified P2-phase sodium-ion battery cathode material and its preparation method. The general chemical formula of the cathode material is: [formula omitted for brevity]. This invention utilizes titanium and magnesium dual-element synergistic doping, combined with a two-stage variable oxygen partial pressure sintering process and segmented quenching cooling, to ensure that the (002) interplanar spacing change rate of the cathode material does not exceed 2.5% when charged to 4.3 V, and the P2-O2 phase transition peak intensity is less than 20% of that of the undoped material. The resulting material retains a capacity of no less than 88% after 500 cycles at 1 C, exhibiting high specific capacity, excellent rate performance, and long-cycle stability. The preparation method of this invention is simple to operate, has good consistency, and is suitable for large-scale production.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, specifically to a doped and modified P2 phase sodium-ion battery cathode material and its preparation method. Background Technology

[0002] Sodium-ion batteries, due to the abundance and low cost of sodium resources, have broad application prospects in large-scale energy storage and low-speed electric vehicles. The cathode material is one of the key factors determining the electrochemical performance of sodium-ion batteries. Among them, P2-phase layered transition metal oxides are considered one of the most promising cathode material systems due to their open prismatic sodium-ion diffusion channels and low diffusion barrier. However, during charge and discharge, especially when the charging voltage exceeds 4.0 V and more than 50% of sodium ions are released, the transition metal layer of the P2-phase material is prone to interlayer slip, inducing a structural transformation from the P2 phase to the O2 phase. This is accompanied by a sharp contraction of the crystal lattice along the c-axis, leading to the collapse of the layered structure and rapid capacity decay.

[0003] To suppress unfavorable phase transitions, elemental doping has been proven to be an effective strategy for improving the structural stability of P2-phase cathode materials. For example, Chinese patent CN120261524A discloses a boric acid-modified P2-phase ternary layered oxide cathode material. This material suppresses the P2-O2 phase transition and improves cycle stability through the synergistic effect of interstitial boron doping and the surface B2O3 coating layer. However, the boron doping only occupies tetrahedral sites in the transition metal layer and fails to provide pillar support for the sodium layer. Further, synergistic modification is achieved through dual-element doping. For example, Chinese patent CN120565664A discloses an O3-type core-shell structure sodium-ion cathode material, which introduces a first lattice control element and a second lattice control element into the core and shell, respectively. However, this scheme is aimed at the O3-type material system and adopts a step-by-step process of sintering the core first and then sintering the shell a second time, which cannot be directly applied to the lattice control of P2 phase materials. CN120784353A discloses an O3-P2 layered biphase sodium-ion battery cathode material, which transforms the impurity phase into a layered P2 phase component through metal ion doping. However, this scheme essentially uses doping to form a mixed phase rather than a stable pure P2 phase structure, which limits the cycle life and rate performance.

[0004] Therefore, there is an urgent need to provide a P2 phase sodium-ion battery cathode material with high structural stability, significantly suppressed P2-O2 phase transition under high pressure, and excellent cycle performance. Summary of the Invention

[0005] To address the problems of structural collapse and rapid capacity decay caused by the P2-O2 phase transition in P2-phase layered oxide cathode materials during high-voltage charge-discharge processes, as well as the technical deficiencies of existing doping schemes and preparation processes that struggle to balance the structural stability of the transition metal layer and the interlayer pinning effect of the sodium layer, and lack of precise oxygen partial pressure control methods, this invention provides a doped modified P2-phase sodium-ion battery cathode material and its preparation method. The aim is to obtain a P2-phase sodium-ion battery cathode material with high structural stability, significantly suppressed P2-O2 phase transition under high voltage, and excellent cycle performance.

[0006] To achieve the above objectives, the present invention provides the following technical solution.

[0007] In a first aspect, a method for preparing a doped and modified P2-phase sodium-ion battery cathode material is characterized by comprising the following steps: S1: Mix sodium source compound, nickel source compound, manganese source compound, titanium source compound and magnesium source compound evenly to obtain a mixture; S2: The mixture is added to the grinding media and ground until the median particle size of the material is 0.3 μm to 0.8 μm, and then dried to obtain precursor powder; S3: The precursor powder is subjected to first-stage sintering in an atmosphere with an oxygen partial pressure of not less than 90%. The first-stage sintering temperature is 450℃~600℃ and the holding time is 4 h~8 h. S4: After the first stage of sintering is completed, the temperature is raised to 850℃~1050℃ for the second stage of sintering, and the holding time is 12h~18h. During the second stage of sintering, the oxygen partial pressure in the atmosphere is reduced to 50%~70%. S5: After the second stage of sintering is completed, the material is first rapidly cooled to 650°C at a cooling rate of not less than 10°C / min, and then slowly cooled to room temperature at a cooling rate of 2°C / min to 5°C / min to obtain the cathode material.

[0008] Preferably, the general chemical formula of the positive electrode material is: ,in , , , , , ,and The positive electrode material, when charged to a cutoff voltage of 4.3 V, exhibits an X-ray diffraction pattern in which the (002) interplanar spacing changes by no more than 2.5%, and the peak current intensity of the P2-O2 phase transition peak in the cyclic voltammetry curve is less than 20% of that of the undoped material.

[0009] Preferably, , .

[0010] Preferably, in step S1, a crystal growth regulator is added for mixing. The crystal growth regulator is boric acid or ammonium dihydrogen phosphate, and the amount added accounts for 0.5% to 2.0% of the total mass of the starting raw materials.

[0011] Preferably, in step S2, the drying temperature is 80℃~120℃ and the drying time is 8 h~24 h.

[0012] Preferably, in step S2, the grinding is wet grinding, the grinding medium is anhydrous ethanol, the grinding time is 4 h to 12 h, and the grinding speed is 300 r / min to 600 r / min.

[0013] Preferably, in step S2, the particle size distribution of the ground material has a diameter not greater than 1.2.

[0014] Preferably, in step S3, the heating rate of the first sintering stage is 0.5℃ / min to 2℃ / min; in step S5, the heating rate of the second sintering stage is 1℃ / min to 3℃ / min. Preferably, in step S4, the second sintering and heat preservation stage achieves a step-by-step reduction of oxygen partial pressure by introducing nitrogen or argon into the atmosphere furnace; the step-by-step reduction of oxygen partial pressure is as follows: 80% oxygen partial pressure from 0h to 4h, 65% to 75% oxygen partial pressure from 4h to 10h, and 50% to 70% oxygen partial pressure from 10h to 18h.

[0015] Secondly, the present invention also provides a sodium-ion battery positive electrode sheet, comprising a current collector and a positive electrode active material layer coated on the current collector, wherein the positive electrode active material layer comprises the doped modified P2 phase sodium-ion battery positive electrode material prepared by the above preparation method, a conductive agent and a binder.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention employs titanium and magnesium to co-dope P2-phase layered oxides. Titanium occupies lattice sites in the transition metal layer, reducing the orderliness of nickel ion valence state changes during charge and discharge. Magnesium partially occupies pyramidal vacancies in the sodium layer, acting as interlayer "pillars." The synergistic effect of these two materials effectively suppresses the unfavorable P2-O2 phase transition during charge and discharge, significantly improving the structural stability of the material in high-voltage regions.

[0017] The present invention employs a two-stage variable oxygen partial pressure sintering process in its preparation method. The first stage uses a high oxygen atmosphere to promote the full oxidation and initial phase formation of the precursor. The second stage reduces the oxygen partial pressure in a stepwise manner, which is beneficial to the uniform diffusion and precise occupancy of dopants in the crystal lattice. Then, a segmented quenching and cooling process is used to effectively fix the metastable doped structure at high temperature and avoid the segregation of dopants during the cooling process.

[0018] The doped modified P2 phase cathode material prepared by this invention exhibits a (002) interplanar spacing change rate of no more than 2.5% when charged to 4.3 V, and the P2-O2 phase transition peak is suppressed to below 20% of that in undoped materials. After being assembled into a coin cell, the capacity retention rate after 500 cycles at a voltage window of 2.0 V to 4.3 V and a 1C rate is no less than 88%, demonstrating good long-term cycle stability. Attached Figure Description

[0019] To more clearly illustrate the technical solution of the present invention, the drawings used in the embodiments 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.

[0020] Figure 1 This is a scanning electron microscope image of the cathode material obtained in Example 1 of the present invention at 10 μm.

[0021] Figure 2 The images show a comparison of the X-ray diffraction patterns of the cathode materials obtained in Example 1 and Comparative Example 1 before and after charging. (a) shows the original uncharged state, and (b) shows the state after charging to 4.3 V. The arrows indicate the offset direction of the diffraction peak of the (002) crystal plane.

[0022] Figure 3 This is a comparison chart of the cyclic voltammetry curves of the cathode materials obtained in Example 1 and Comparative Example 1 of the present invention.

[0023] Figure 4 The above are rate performance curves of the cathode materials obtained in Examples 1-3 and Comparative Examples 1, 5, and 7 of this invention. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to specific examples. 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.

[0025] Unless otherwise specified, the experimental methods used in this invention are conventional methods; unless otherwise specified, the materials and reagents used are commercially available.

[0026] In this invention, the raw materials used include, but are not limited to, the following specifications: Sodium carbonate (Na2CO3): purity ≥99.8%.

[0027] Nickel oxide (NiO): purity ≥ 99.5%.

[0028] Manganese dioxide (MnO2): purity ≥ 99.5%.

[0029] Titanium dioxide (TiO2): purity ≥ 99.0%.

[0030] Magnesium oxide (MgO): purity ≥ 99.0%.

[0031] Oxygen-containing atmosphere: high-purity oxygen (purity ≥ 99.999%) or air.

[0032] Inert atmosphere: High-purity argon (purity ≥ 99.999%) or high-purity nitrogen (purity ≥ 99.999%) Example 1 I. A doped and modified P2 phase sodium-ion battery cathode material, the raw materials for which are prepared are shown in Table 1 below: Table 1 Raw Material List for Example 1 The general chemical formula of the target product in this embodiment is Na. 0.67 Ni 0.28 Mn 0.62 Ti 0.05 Mg 0.05 O2.

[0033] II. A method for preparing a doped and modified P2 phase sodium-ion battery cathode material, specifically including the following steps: 1. Weigh sodium carbonate, nickel oxide, manganese dioxide, titanium dioxide, and magnesium oxide according to the molar ratio in Table 1 as starting materials, grind and mix them in a mortar for 30 min to obtain a mixture. Add sodium carbonate in excess at 105% of the target sodium content to compensate for the loss of sodium through volatilization during high-temperature sintering.

[0034] 2. Place the mixture in a planetary ball mill, add zirconia grinding balls and anhydrous ethanol (as grinding media) for wet grinding. The grinding time is 8 h, the grinding speed is 400 r / min, and the material is ground until the median particle size is 0.5 μm and the particle size distribution is 1.0.

[0035] 3. Place the ground slurry in an oven and dry it at 100℃ for 12 h to obtain precursor powder.

[0036] 4. Place the precursor powder in an atmosphere furnace and perform the first stage of sintering in an oxygen atmosphere with an oxygen partial pressure of 95%. The temperature is increased to 500°C at a heating rate of 1.0°C / min and held for 6 hours.

[0037] 5. After the first sintering is completed, the temperature is increased to 950℃ at a heating rate of 2.0℃ / min for the second sintering, and held for 15 h. During the second sintering holding stage, the oxygen partial pressure is reduced to 60% by introducing high-purity argon into the atmosphere furnace.

[0038] The second stage of heat preservation involves a stepwise reduction in oxygen partial pressure as follows: From 0 h to 4 h, maintain an oxygen partial pressure of 80%, Ar at 200 mL / min, and O2 at 800 mL / min; from 4 h to 10 h, adjust the valves to reduce the O2 flow rate to 700 mL / min (at which point the oxygen partial pressure is approximately 70%), and increase the Ar flow rate to 300 mL / min; from 10 h to 15 h, reduce the O2 flow rate to 600 mL / min (at which point the oxygen partial pressure is approximately 60%), and increase the Ar flow rate to 400 mL / min.

[0039] 6. After the second stage of sintering, the material is first rapidly cooled to 650°C at a cooling rate of 15°C / min, and then slowly cooled to room temperature at a cooling rate of 3°C / min to obtain the doped and modified P2 phase sodium-ion battery cathode material, as shown below. Figure 1 As shown.

[0040] Example 2 I. A doped and modified P2 phase sodium-ion battery cathode material, the raw materials for which are prepared are shown in Table 2 below: Table 2 Raw Material List for Example 2 The general chemical formula of the target product in this embodiment is Na. 0.65 Ni 0.35 Mn 0.45 Ti 0.10 Mg 0.10 O2.

[0041] II. A method for preparing a doped and modified P2 phase sodium-ion battery cathode material, specifically including the following steps: S1: Weigh sodium carbonate, nickel oxide, manganese dioxide, titanium dioxide, and magnesium oxide according to the molar ratio in Table 2 as starting materials, grind and mix them in a mortar for 40 min to obtain a mixture. Add sodium carbonate in excess at 105% of the target sodium content.

[0042] S2: Place the mixture in a planetary ball mill, add zirconium oxide grinding balls and anhydrous ethanol for wet grinding. The grinding time is 12 h, the grinding speed is 300 r / min, and the material is ground until the median particle size is 0.3 μm and the particle size distribution is 1.1.

[0043] S3: Place the ground slurry in an oven and dry it at 80°C for 24 h to obtain precursor powder.

[0044] S4: The precursor powder is placed in an atmosphere furnace and sintered in the first stage under an oxygen atmosphere with an oxygen partial pressure of 98%. The temperature is increased to 450°C at a heating rate of 0.5°C / min and held for 8 hours.

[0045] S5: After the first sintering is completed, the temperature is increased to 850℃ at a rate of 1.0℃ / min for the second sintering, and held for 18 h. During the second sintering holding stage, the oxygen partial pressure is gradually reduced to 50% by introducing high-purity nitrogen into the atmosphere furnace.

[0046] The second stage of the heat preservation phase involves a stepwise reduction in oxygen partial pressure as follows: From 0 h to 4 h, maintain an oxygen partial pressure of 80%, N2 at 200 mL / min, and O2 at 800 mL / min; from 4 h to 10 h, adjust the valves to reduce the O2 flow rate to 650 mL / min (at which point the oxygen partial pressure is approximately 65%), and increase the N2 flow rate to 350 mL / min; from 10 h to 18 h, reduce the O2 flow rate to 500 mL / min (at which point the oxygen partial pressure is approximately 50%), and increase the N2 flow rate to 500 mL / min.

[0047] S6: After the second stage of sintering is completed, the material is first rapidly cooled to 650°C at a cooling rate of 12°C / min, and then slowly cooled to room temperature at a cooling rate of 2°C / min to obtain the doped modified P2 phase sodium-ion battery cathode material.

[0048] Example 3 I. A doped and modified P2 phase sodium-ion battery cathode material, the raw materials for which are prepared are shown in Table 3 below: Table 3 Raw Material List for Example 3 The general chemical formula of the target product in this embodiment is Na. 0.67 Ni 0.28 Mn 0.58 Ti 0.09 Mg 0.05 O2.

[0049] II. A method for preparing a doped and modified P2 phase sodium-ion battery cathode material, specifically including the following steps: 1. Weigh sodium carbonate, nickel oxide, manganese dioxide, titanium dioxide, and magnesium oxide according to the molar ratio in Table 3 as starting materials, and add boric acid at 1.0% of the total mass of the starting materials as a crystal growth regulator. Grind and mix in a mortar for 20 minutes to obtain a mixture. Add sodium carbonate in excess at 105% of the target sodium content.

[0050] 2. Place the mixture in a planetary ball mill, add zirconium oxide grinding balls and anhydrous ethanol for wet grinding. The grinding time is 4 h, the grinding speed is 600 r / min, and the material is ground until the median particle size is 0.8 μm and the particle size distribution is 0.9.

[0051] 3. Place the ground slurry in an oven and dry it at 120℃ for 8 hours to obtain the precursor powder.

[0052] 4. Place the precursor powder in an atmosphere furnace and perform the first stage of sintering in an oxygen atmosphere with an oxygen partial pressure of 92%. The temperature is increased to 600℃ at a heating rate of 2.0℃ / min and held for 4 hours.

[0053] 5. After the first sintering is completed, the temperature is increased to 1050℃ at a heating rate of 3.0℃ / min for the second sintering, and held for 12 h. During the second sintering holding stage, the oxygen partial pressure is reduced to 70% by introducing high-purity argon into the atmosphere furnace.

[0054] The second stage of heat preservation involves a stepwise reduction in oxygen partial pressure as follows: From 0 h to 4 h, maintain an oxygen partial pressure of 80%, Ar at 200 mL / min, and O2 at 800 mL / min; from 4 h to 10 h, adjust the valves to reduce the O2 flow rate to 750 mL / min (at which point the oxygen partial pressure is approximately 75%), and increase the Ar flow rate to 250 mL / min; from 10 h to 12 h, reduce the O2 flow rate to 700 mL / min (at which point the oxygen partial pressure is approximately 70%), and increase the Ar flow rate to 300 mL / min.

[0055] 6. After the second stage of sintering is completed, the material is first rapidly cooled to 650°C at a cooling rate of 18°C / min, and then slowly cooled to room temperature at a cooling rate of 5°C / min to obtain the doped modified P2 phase sodium-ion battery cathode material.

[0056] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 does not add titanium dioxide and magnesium oxide, but replaces them with manganese dioxide to make up for the missing 0.10 mol sites of Ti and Mg, keeping the total amount of TM at 1.0, while everything else is the same.

[0057] Specifically: 0.335 mol sodium carbonate, 0.28 mol nickel oxide, and 0.72 mol manganese dioxide. The target product has the general chemical formula Na. 0.67 Ni 0.28 Mn 0.72 O2.

[0058] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that Comparative Example 2 does not add magnesium oxide, but instead uses manganese dioxide to make up for the missing 0.05 mol sites of Mg, keeping the total amount of TM at 1.0, while everything else is the same.

[0059] Specifically, the composition is: 0.335 mol sodium carbonate, 0.28 mol nickel oxide, 0.67 mol manganese dioxide, and 0.05 mol titanium dioxide (without MgO). The target product has the general chemical formula Na. 0.67 Ni 0.28 Mn 0.67 Ti 0.05 O2.

[0060] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that Comparative Example 3 does not add titanium dioxide, but instead uses manganese dioxide to make up for the 0.05 mol sites missing in Ti, keeping the total amount of TM at 1.0, while everything else is the same.

[0061] Specifically, the composition is: 0.335 mol sodium carbonate, 0.28 mol nickel oxide, 0.67 mol manganese dioxide, and 0.05 mol magnesium oxide. The target product has the general chemical formula Na. 0.67 Ni 0.28 Mn 0.67 Ti 0.05 O2.

[0062] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that the doping amounts of titanium and magnesium are different in Comparative Example 4, but everything else is the same.

[0063] Specifically, the composition is: 0.335 mol sodium carbonate, 0.28 mol nickel oxide, 0.62 mol manganese dioxide, 0.09 mol titanium dioxide, and 0.01 mol magnesium oxide. The target product has the general chemical formula Na. 0.67 Ni 0.28 Mn 0.62 Ti 0.09 Mg 0.01 O2.

[0064] Comparative Example 5 The difference between Comparative Example 5 and Example 1 is that the sintering process of Comparative Example 5 is conventional constant oxygen one-stage sintering, while all other processes are the same.

[0065] Specifically, the precursor powder obtained in step 3 was directly heated to 950℃ at a heating rate of 2.0℃ / min and kept at that temperature for 21 h under an atmosphere with a constant oxygen partial pressure of 95%.

[0066] Comparative Example 6 The difference between Comparative Example 6 and Example 1 is that the two sintering stages of Comparative Example 6 use the same oxygen partial pressure, while everything else is the same.

[0067] Specifically: in step 4, the oxygen partial pressure in the first sintering stage is 95%; in step 5, during the second sintering heat preservation stage, no inert gas is introduced to reduce oxygen, and the oxygen partial pressure is still maintained at 95%.

[0068] Comparative Example 7 The difference between Comparative Example 7 and Example 1 is that Comparative Example 7 does not undergo segmented quenching and cooling after sintering, but instead adopts conventional natural cooling to room temperature in the furnace. Everything else is the same.

[0069] Specifically: After the second stage of sintering in step 6 is completed, turn off the heating power and allow the product to cool naturally to room temperature with the furnace.

[0070] Test Example 1 XRD tests were performed on the cathode materials prepared in Examples 1-3 and Comparative Examples 1-7, and the change rate of (002) interplanar spacing before and after charging was measured.

[0071] XRD testing method: Cu Kα rays (λ=0.15406 nm) were used, with an operating voltage of 40 kV, an operating current of 40 mA, a scanning range of 10°~80°, and a scanning speed of 2° / min. The obtained XRD patterns were compared with standard diffraction cards of P2 phase layered oxides to confirm the phase composition.

[0072] (002) Method for determining the rate of change of interplanar spacing: Assemble the material to be tested into a coin cell, charge it to 4.3 V, disassemble it, take out the positive electrode, wash it three times with dimethyl carbonate and then vacuum dry it. Perform XRD test on the charged electrode, read the 2θ value of the diffraction peak of (002) crystal plane, and calculate the interplanar spacing d of (002) according to the Bragg equation 2d·sinθ=nλ. The rate of change of interplanar spacing of (002) crystal plane is calculated according to the following formula (1): (1); Where, d 原始 d represents the (002) interplanar spacing of the uncharged material. 充电 The following is the (002) interplanar spacing of the material after charging to 4.3 V. Each sample was tested 3 times and the average value was taken.

[0073] Table 4. Variation rate of (002) interplanar spacing for different samples As shown in Table 4, the variation rate of the (002) interplanar spacing in Examples 1-3 ranged from 1.20% to 1.70%, all below the threshold of 2.5%, while the variation rate in Comparative Examples 1-7 ranged from 3.42% to 5.47%, with Comparative Example 1, which was undoped with titanium and magnesium, showing the highest variation rate. Then, as... Figure 2 As shown, the (002) diffraction peak of Example 1 only shifted slightly after charging, while the (002) diffraction peak of Comparative Example 1 shifted significantly towards higher angles. This indicates that the cathode material prepared by the present invention has good high structural stability and low strain, avoiding interlayer collapse.

[0074] Test Example 2 Cyclic voltammetry tests were performed on the cathode materials obtained in Examples 1-3 and Comparative Examples 1-7 respectively to analyze the peak current intensity of the P2-O2 phase transition peak.

[0075] Test method: The test material was mixed with conductive carbon black and polyvinylidene fluoride at a mass ratio of 80:10:10, and a slurry was prepared using N-methylpyrrolidone as a solvent. The slurry was coated onto aluminum foil, vacuum dried, and then cut into working electrodes. A sodium metal sheet was used as the counter electrode and reference electrode. A solution of 1 M NaPF6 dissolved in ethylene carbonate / diethyl carbonate (volume ratio 1:1) was used as the electrolyte. A glass fiber membrane was used as the separator. A CR2032 coin cell was assembled in an argon glove box.

[0076] Cyclic voltammetry was performed on an electrochemical workstation with a scan voltage range of 2.0 V to 4.3 V and a scan rate of 0.1 mV / s. The CV curve was recorded after the third cycle, and the peak current intensity of the P2-O2 phase transition peak was read. Using the peak current intensity of the P2-O2 phase transition peak of the undoped material in Comparative Example 1 as a baseline (set to 100%), the relative intensity percentage of the phase transition peak for each sample was calculated. Three parallel cells were assembled for each sample, and the average value was taken.

[0077] The test results are shown in Table 5 and Figure 3 .

[0078] Table 5. Relative Intensities of P2-O2 Phase Transition Peaks in Different Samples From Table 5 and Figure 3 It can be seen that the P2-O2 phase transition peak intensities of Examples 1-3 are only 12.8%-16.4% of those of the undoped material, all below the 20% threshold. The undoped sample in Comparative Example 1 shows a sharp oxidation peak near 4.15 V, while the CV curve of Example 1 only shows a very gentle hump near 4.15 V. The phase transition peak intensities of Comparative Examples 2-7 are 43.7%-60.0%, all significantly higher than those of the Examples, indicating that the cathode material prepared by this invention has good high-voltage structural stability and high rate capability.

[0079] Test Example 3 Sodium-ion coin cells were assembled using the cathode materials obtained in Examples 1-3 and Comparative Examples 1-7, and constant current charge-discharge tests were performed to evaluate their discharge specific capacity, rate performance, and cycle stability.

[0080] Battery assembly method: The test material was mixed with conductive carbon black and polyvinylidene fluoride at a mass ratio of 80:10:10, and a slurry was prepared using N-methylpyrrolidone as a solvent. This slurry was coated onto aluminum foil, vacuum dried, and then cut into positive electrode sheets with a diameter of 12 mm. A sodium metal sheet was used as the counter electrode, and a solution of 1 M NaPF6 dissolved in ethylene carbonate / diethyl carbonate (volume ratio 1:1) was used as the electrolyte. A glass fiber membrane was used as the separator. A CR2032 coin cell was assembled in an argon-filled glove box. After assembly, the battery was allowed to stand for 12 hours before testing.

[0081] Constant current charge-discharge test conditions: voltage window of 2.0 V to 4.3 V, test temperature of 25℃. First, perform 3 activation cycles at a rate of 0.1 C (1 C = 150 mA / g), and record the first discharge specific capacity and the first coulombic efficiency. The first coulombic efficiency is calculated by dividing the first discharge specific capacity by the first charge specific capacity and multiplying by 100%.

[0082] Cyclic performance test conditions: 500 constant current charge-discharge cycles were performed at a 1 C rate within a voltage window of 2.0 V to 4.3 V. The discharge specific capacity was recorded at the 1st and 500th cycles. The capacity retention rate after 500 cycles was calculated using the following formula: (2); Three parallel cells were assembled for each sample, and the average value was taken.

[0083] Rate performance test conditions: Cycle 5 times each at 0.1 C, 0.2 C, 0.5 C, 1 C, 2 C, 5 C and 10 C, and record the discharge specific capacity at each rate.

[0084] Table 6. Initial discharge specific capacity, initial coulombic efficiency, and capacity retention after 500 cycles at 1C for different samples. From Table 6 and Figure 4 It can be seen that the initial discharge specific capacity of Examples 1-3 is 138.7-146.1 mAh / g, the initial coulombic efficiency is 91.3%-92.5%, and the capacity retention rate after 500 cycles at 1 C is 90.1%-92.4%. The capacity retention rate of Comparative Examples 1-7 is 72.3%-80.2%, all lower than that of Examples 1-3.

[0085] Table 7. Rate performance test results for different samples As shown in Table 7, the 10 C / 0.2 C capacity retention rates of Examples 1-3 were 76.7%-82.9%, while those of Comparative Examples 1-7 were 49.0%-62.6%, indicating that the Examples 1-3 significantly outperformed the Comparative Examples. In summary, this invention, through a titanium-magnesium dual-element synergistic doping strategy combined with a variable oxygen partial pressure two-stage sintering process, prepared a P2-phase sodium-ion battery cathode material with excellent electrochemical performance. This effectively overcomes the technical defects of existing P2-phase cathode materials, such as poor structural stability and rapid capacity decay during high-voltage cycling, and is beneficial to the development of sodium-ion batteries.

[0086] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing a doped and modified P2-phase sodium-ion battery cathode material, characterized in that, Includes the following steps: S1: Mix sodium source compound, nickel source compound, manganese source compound, titanium source compound and magnesium source compound evenly to obtain a mixture; S2: The mixture is added to the grinding media and ground until the median particle size of the material is 0.3 μm to 0.8 μm, and then dried to obtain precursor powder; S3: The precursor powder is subjected to first-stage sintering in an atmosphere with an oxygen partial pressure of not less than 90%. The first-stage sintering temperature is 450℃~600℃ and the holding time is 4 h~8 h. S4: After the first stage of sintering is completed, the temperature is raised to 850℃~1050℃ for the second stage of sintering, and the holding time is 12 h~18 h. During the second stage of sintering, the oxygen partial pressure in the atmosphere is gradually reduced to 50%~70%. S5: After the second stage of sintering is completed, the material is first rapidly cooled to 650°C at a cooling rate of not less than 10°C / min, and then slowly cooled to room temperature at a cooling rate of 2°C / min to 5°C / min to obtain the cathode material.

2. The preparation method according to claim 1, characterized in that, The general chemical formula of the cathode material is: ,in , , , , , ,and .

3. The preparation method according to claim 2, characterized in that, ， 。 4. The preparation method according to claim 1, characterized in that, In step S1, a crystal growth regulator is added and mixed. The crystal growth regulator is boric acid or ammonium dihydrogen phosphate, and the amount added accounts for 0.5% to 2.0% of the total mass of the starting raw materials.

5. The preparation method according to claim 1, characterized in that, In step S2, the drying temperature is 80℃~120℃ and the drying time is 8 h~24 h.

6. The preparation method according to claim 1, characterized in that, In step S2, the grinding is wet grinding, the grinding medium is anhydrous ethanol, the grinding time is 4 h to 12 h, and the grinding speed is 300 r / min to 600 r / min.

7. The preparation method according to claim 1, characterized in that, In step S2, the particle size distribution of the ground material has a diameter not greater than 1.

2.

8. The preparation method according to claim 1, characterized in that, In step S3, the heating rate of the first sintering stage is 0.5℃ / min to 2℃ / min; in step S4, the heating rate of the second sintering stage is 1℃ / min to 3℃ / min.

9. The preparation method according to claim 1, characterized in that, In step S4, the second sintering and heat preservation stage achieves a step-by-step reduction of oxygen partial pressure by introducing nitrogen or argon into the atmosphere furnace; the step-by-step reduction of oxygen partial pressure is as follows: 80% oxygen partial pressure from 0h to 4h, 65% to 75% oxygen partial pressure from 4h to 10h, and 50% to 70% oxygen partial pressure from 10h to 18h.

10. A positive electrode sheet for a sodium-ion battery, characterized in that, It includes a current collector and a positive electrode active material layer coated on the current collector, wherein the positive electrode active material layer contains a doped modified P2 phase sodium-ion battery positive electrode material prepared by the preparation method according to any one of claims 1 to 9, a conductive agent, and a binder.

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