Halide-doped P2-phase layered oxide positive electrode material and preparation method thereof, positive electrode and sodium ion battery

Abstract

The invention discloses a halide-doped P2-phase layered oxide positive electrode material and a preparation method thereof, a positive electrode and a sodium ion battery, and relates to the technical field of batteries. The chemical formula of the P2-phase layered oxide positive electrode material is NaaNibMcMndOeXf, a double-ion doping strategy is adopted, the doped halogen exerts the effect of improving the working voltage in a structural body phase, so that the relatively high capacity is obtained in a relatively low voltage window, and the M element is used as a structural support column to effectively improve the structural stability. The preparation method adopts a one-step method, is simple to operate, adopts low-temperature reaction, does not need special equipment or expensive precursors, is simpler and more economical, and can realize large-scale production. The prepared battery has excellent long cycle stability, high working voltage and excellent rate capability; the preparation method is beneficial to improving initial capacity and availability of active sites, improving cycle stability, enhancing high rate capability and reaction kinetics, and endowing the material with excellent environmental stability and processing applicability.

Description

Technical Field

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

[0002] Lithium resources are limited (only 0.0017% of the Earth's crust) and unevenly distributed (>70% concentrated in South America), while sodium resources are abundant (2.3% of the Earth's crust), cost only 1 / 10 of lithium, and sodium-ion batteries (SIBs) are highly compatible with lithium-ion batteries (LIBs), making them suitable for large-scale energy storage scenarios such as power grids and low-speed electric vehicles. However, existing SIB cathode materials suffer from short cycle life and low energy density, severely restricting their commercial application. The main reason is the poor structural stability of the materials, which leads to phase transitions and capacity decay during charging and discharging.

[0003] With the rapid development of sodium-ion batteries (SIBs) in the energy storage field, P2 phase layered transition metal oxides (general formula Na) are increasingly being used. x TMO2 (where TM is a transition metal) is one of the most promising cathode materials due to its open two-dimensional ion diffusion channels and high theoretical specific capacity. However, its commercial application still faces the following core problems: structural instability (the P2→O2 / OP4 phase transition easily occurs during deep desodiuming, leading to lattice distortion and capacity decay), interfacial side reactions (electrolyte decomposition forms a thick CEI layer), high-voltage oxygen evolution (irreversible oxidation of lattice oxygen at 4.2V, accompanied by the dissolution of transition metals), and poor storage stability.

[0004] To address the aforementioned issues, Chinese patent CN116845229A discloses a double-doped P2-type layered oxide composite material, its preparation method, and its applications, utilizing alkali metal sites (K... + ) and transition metal sites (Zn 2+ / Mg 2+ Co-doping can increase interlayer spacing and delay phase transition, but the redox inertness of the dopant elements leads to capacity loss and has no inhibitory effect on oxygen evolution at high voltage.

[0005] Chinese patent CN120208313A discloses a dual-modified layered oxide cathode material for sodium-ion batteries and its preparation method. The strategy of obtaining the dual-modified layered oxide cathode material for sodium-ion batteries through the synergistic effect of surface fluoride coating and near-bulk phase doping is adopted. After forming the P2 phase by high-temperature solid-state method, the target product is obtained by mixing and high-temperature quenching. Although it can effectively improve the high-voltage cycle performance of the layered oxide cathode material for sodium-ion batteries, the essence of improving structural stability is still surface confinement rather than improving the intrinsic structural stability of the material. Moreover, the material needs to be charged to a high voltage, and the requirements for the electrolyte are relatively stringent.

[0006] How to enable doped elements to play a role in increasing the working voltage in the structural phase, obtain higher capacity within a lower voltage window, and effectively improve structural stability by using doped elements as structural pillars has become a technical problem that urgently needs to be solved in this field.

[0007] In view of this, the present invention is proposed. Summary of the Invention

[0008] The purpose of this invention is to provide a halide-doped P2 phase layered oxide cathode material and its preparation method, as well as a cathode and sodium-ion battery, to solve or improve the above-mentioned technical problems.

[0009] This invention is implemented as follows: In a first aspect, the present invention provides a halide-doped P2-phase layered oxide cathode material, the chemical formula of which is shown in (I): Na a Ni b M c Mn d O e X f (I); In formula (Ⅰ), M is selected from at least one of Li, Na, K, Mg, Ca, Sr, Ba, Al, Sn, Zn, Cu, Ti, Zr, Y and Mo; X is selected from at least one of F, Cl, Br and I; 0.65≤a≤0.85, 0.2≤b<0.27, 0<c≤0.05, 0.5≤d≤0.75, 1.8≤e<2.0, 0<f≤0.18, and 0.85≤b+c+d≤1, 1.8≤e+0.5f≤2, 0.2≤c / f≤1.

[0010] Secondly, the present invention provides a method for preparing a P2 phase layered oxide cathode material as described in any of the foregoing embodiments, comprising the following steps: Sodium source, nickel source, M source, manganese source and X source are mixed in proportion and sintered using high temperature solid-state method to obtain P2 phase layered oxide cathode material. The burning process includes the following steps: raising the temperature from room temperature to 100℃ at a rate of 3℃ / min-7℃ / min, and holding at that temperature for 100min-130min; continuing to raise the temperature to 750℃-900℃ at a rate of 2℃ / min-5℃ / min, and holding at that temperature for 1200min-1500min; and lowering the temperature to 90℃-120℃ at a rate of 3℃ / min-7℃ / min.

[0011] Thirdly, the present invention provides a positive electrode comprising a P2 phase layered oxide positive electrode material as described in any of the foregoing embodiments with a mass ratio of (7-9):(0.5-1.5):(0.5-1.5), or a P2 phase layered oxide positive electrode material prepared by the preparation method as described in any of the foregoing embodiments, a conductive agent, and a binder. The conductive agent is selected from at least one of Ketjen Black, Super P and carbon nanotubes; the binder is selected from at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, styrene-butadiene rubber / sodium carboxymethyl cellulose and polyacrylic acid.

[0012] Fourthly, the present invention provides a sodium-ion battery, including a positive electrode as described in the foregoing embodiments.

[0013] The present invention has the following beneficial effects: The halide-doped P2-phase layered oxide cathode material provided by this invention employs a dual-ion doping strategy. The doped halogens in the bulk phase can enhance the working voltage, thereby achieving higher capacity within a lower voltage window. The M element, as a structural pillar, can effectively improve structural stability.

[0014] The preparation method is a one-step process, which is simple to operate and has a low reaction temperature. It does not require special equipment or expensive precursors, making it simpler and more economical, and can be mass-produced.

[0015] The prepared battery exhibits excellent long-term cycle stability, high operating voltage, and superior rate performance. This is beneficial for improving initial capacity and the availability of active sites, enhancing cycle stability, improving high-rate performance and reaction kinetics, and endowing the material with excellent environmental stability and processing suitability. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 The morphology test results are for Example 1; Figure 2 The XRD test results are for Examples 1-2 and Comparative Example 1; Figure 3 The first charge-discharge curve of Example 1; Figure 4 The results are from the time-of-flight secondary ion mass spectrometry test in Example 1. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0019] In a first aspect, the present invention provides a halide-doped P2-phase layered oxide cathode material, the chemical formula of which is shown in (I): Na a Ni b M c Mn d O e X f (I); In formula (Ⅰ), M is selected from at least one of Li, Na, K, Mg, Ca, Sr, Ba, Al, Sn, Zn, Cu, Ti, Zr, Y and Mo; X is selected from at least one of F, Cl, Br and I; 0.65≤a≤0.85, 0.2≤b<0.27, 0<c≤0.05, 0.5≤d≤0.75, 1.8≤e<2.0, 0<f≤0.18, and 0.85≤b+c+d≤1, 1.8≤e+0.5f≤2, 0.2≤c / f≤1.

[0020] It should be noted that halogen doping can simultaneously suppress bulk oxygen loss and interfacial side reactions. Halogen elements, due to their high electronegativity and strong bond energy, can significantly improve the performance of P2 phase materials. Furthermore, halogens in the bulk structure can enhance the operating voltage, thereby achieving higher capacity within a lower voltage window. M elements, acting as structural pillars, can effectively improve structural stability. For example, F... - The ionic radius (133 pm) is less than that of O. 2- (140 pm), moderate doping can expand Na + Migration channels are established without inducing phase transitions; a fluorine-rich surface layer forms a protective interface, reducing electrolyte corrosion; and strong covalent bonds are formed by F replacing lattice oxygen. F (bond energy > 500 kJ·mol) -1 This increases the oxygen vacancy formation energy, thereby effectively inhibiting oxygen loss.

[0021] If the doping amount of halogen elements is insufficient, they cannot effectively play their role in lattice stabilization and expanding the sodium layer. The material properties are similar to those of undoped materials, with limited improvement in cycle stability and insignificant suppression of high-voltage phase transitions. Excessive fluorination will generate impurity phases (such as NaF and transition metal fluorides), consuming active materials, reducing reversible capacity, decreasing first-cycle efficiency, and deteriorating rate performance.

[0022] In an optional embodiment, the P2 phase layered oxide cathode material has a disk-like morphology with a lateral dimension of 0.5 μm–2 μm and a thickness of 100 nm–200 nm.

[0023] In an optional implementation, b+c+d=1, e+0.5f=2, and 0.25≤c / f≤1; And / or, 0.7≤a≤0.82, 0.2≤b<0.25, 0.015<c≤0.045, 0.6≤d≤0.75, 1.85≤e<2.0, 0<f≤0.1.

[0024] In an optional implementation, M is selected from at least one of Ca and Zn; And / or, X is selected from at least one of F, Cl and Br.

[0025] In the optimal implementation, the halogen element selected is fluorine.

[0026] Secondly, the present invention provides a method for preparing a P2 phase layered oxide cathode material as described in any of the foregoing embodiments, comprising the following steps: Sodium source, nickel source, M source, manganese source and X source are mixed in proportion and sintered using high temperature solid-state method to obtain P2 phase layered oxide cathode material. The burning process includes the following steps: raising the temperature from room temperature to 100℃ at a rate of 3℃ / min-7℃ / min, and holding at that temperature for 100min-130min; continuing to raise the temperature to 750℃-900℃ at a rate of 2℃ / min-5℃ / min, and holding at that temperature for 1200min-1500min; and lowering the temperature to 90℃-120℃ at a rate of 3℃ / min-7℃ / min.

[0027] It should be noted that the preparation method of P2 phase layered oxide cathode material only requires two steps: grinding and sintering. No special equipment or expensive precursors are required. The preparation method of P2 phase layered oxide cathode material is simple to operate and has a low reaction temperature, making it simpler and more economical, and enabling large-scale production.

[0028] Furthermore, the preparation method of P2 phase layered oxide cathode material is a one-step doping method, but it is not a simple process adjustment. Instead, it achieves a revolutionary performance improvement by changing the intrinsic properties of the material. This is mainly reflected in its fundamental advantages in improving the intrinsic structural stability of the material and achieving long cycle and high voltage performance (results of test examples 1-2).

[0029] This invention does not impose any particular limitation on the mixing method of the raw materials, and can be reasonably selected according to actual needs. Specifically, in an optional embodiment of this invention, the sodium source, nickel source, M source, manganese source and X source are mixed in proportion, specifically by grinding and mixing in a mortar until uniformly mixed.

[0030] The uniformly mixed material is subjected to a high-temperature solid-state method and calcined in a muffle furnace to obtain a black powdery P2-phase layered oxide cathode material. The calcination equipment can be selected appropriately according to actual needs.

[0031] The sintering process of this invention employs a staged heating procedure, characterized by the following: The first stage involves slow heating and holding, allowing moisture and other substances to escape slowly and completely. Rapid heating can cause the powder to "boil," splash, or even explode, resulting in cracks. Secondly, it allows sodium salts (such as anhydrous sodium carbonate, sodium acetate, and sodium oxalate) to release carbon dioxide gas. The second stage provides sufficient reaction time and driving force, precisely controlling the degree of oxygen vacancies and cation mixing in the material. This facilitates control of the phase transition process, promotes uniform nucleation and grain growth, and through a well-designed heating / holding stage, valence state adjustment can be completed before lattice stabilization, reducing defects and improving reaction consistency and batch stability. The third stage controls cooling, avoiding thermal stress and structural defects caused by quenching, and stabilizing the crystal structure.

[0032] In an optional embodiment, the molar ratio of sodium source, nickel source, M source, manganese source and X source is (0.7-0.82):(0.2-0.25):(0.01-0.05):(0.6-0.75):(0.01-0.05).

[0033] In an optional embodiment, the sodium source is selected from at least one of anhydrous sodium carbonate, sodium acetate, sodium oxalate, and halides; And / or, the nickel source is selected from at least one of nickel oxide, nickel carbonate, nickel acetate, nickel oxalate, and halides; And / or, the source M is selected from at least one of the oxides, carbonates, acetates, oxalates and halides of M; And / or, the manganese source is selected from at least one of manganese oxides, manganese carbonate, manganese acetate, manganese oxalate, and halides.

[0034] It should be noted that the sodium source, nickel source, M source, manganese source and X source can be in the form of a halide composed of sodium source, nickel source, M source, manganese source and X source, or in the form of salt or oxide corresponding to sodium source, nickel source, M source and manganese source. The specific choice should be made according to the actual needs.

[0035] In an optional embodiment, the burning process includes the following steps: raising the temperature from room temperature to 100°C at a rate of 5°C / min and holding it for 110-125 min; continuing to raise the temperature to 800°C at a rate of 3°C / min and holding it for 1300-1450 min; and lowering the temperature to 90-110°C at a rate of 5°C / min.

[0036] Specifically, in the embodiments of the present invention, the process of heating to 100°C is to completely remove moisture from the raw materials, which is beneficial for uniform ion diffusion during the high-temperature process; the heating rate set at each stage is relatively mild, which is conducive to phase formation; if the heating is too fast, the material is prone to crystal defects, which is not conducive to electrochemical performance; if the heating is too slow, it will lead to excessive energy consumption and low efficiency. Finally, cooling to 100°C is to prevent the reaction products obtained when the furnace is cooled to room temperature from reacting with moisture and carbon dioxide in the air to produce residual alkali. Surface residual alkali is very likely to cause uneven agglomeration in the coating process.

[0037] Thirdly, the present invention provides a positive electrode comprising a P2 phase layered oxide positive electrode material as described in any of the foregoing embodiments with a mass ratio of (7-9):(0.5-1.5):(0.5-1.5), or a P2 phase layered oxide positive electrode material prepared by the preparation method as described in any of the foregoing embodiments, a conductive agent, and a binder. The conductive agent is selected from at least one of Ketjen Black, Super P and carbon nanotubes; the binder is selected from at least one of polyvinylidene fluoride (PTFE), polyvinylidene fluoride-hexafluoropropylene copolymer, styrene-butadiene rubber / sodium carboxymethyl cellulose and polyacrylic acid.

[0038] In an optional embodiment, the mass ratio of the P2 phase layered oxide cathode material, the conductive agent, and the binder is 8:1:1, the conductive agent is Ketjen Black, and the binder is PTFE; in other embodiments of the present invention, the types of materials of the conductive agent and the binder can be reasonably selected according to actual needs.

[0039] Specifically, the preparation method of the positive electrode is as follows: the obtained P2 phase layered oxide positive electrode material, conductive agent (Ketjen Black), and binder (PTFE) are thoroughly mixed and ground in a mass ratio of 8:1:1. The material is then rolled into a uniform sheet with a thickness of (100μm-0.5mm) using a rolling method, and finally cut into 0.5mm pieces. 0.5cm 2 The electrode is used as the positive electrode of the battery.

[0040] Fourthly, the present invention provides a sodium-ion battery, including a positive electrode as described in the foregoing embodiments.

[0041] Sodium-ion batteries exhibit excellent long-cycle stability, high operating voltage, and superior rate performance. For example, the battery produced, in its early cycling phase (0-100 cycles), showed an initial capacity of 130 mAh·g at a 0.1C rate. -1 After 100 cycles, the capacity retention rate was 79.12%; at a high rate of 1C, the capacity of Example 1 in the first cycle was 94 mAh·g. -1 After 1000 cycles, the capacity retention rate was 92.70%. The capacity of the battery after being submerged in water was slightly lower than that of the original material, but the capacity retention rate was basically the same.

[0042] Batteries made from halide-doped P2-phase layered oxide cathode materials are beneficial for improving initial capacity and availability of active sites, enhancing cycle stability, improving high-rate performance and reaction kinetics, and endowing the materials with excellent environmental stability and processing applicability.

[0043] Specifically, the improvement in initial capacity and availability of active sites is analyzed as follows: Appropriate fluorine doping in this invention can adjust the electronic states of the redox centers (such as Ni and Mn) in the transition metal layer, reducing charge transfer impedance and allowing for more Na to be generated during the first charge. + Fluoride ions (F₂) can efficiently and reversibly escape from the crystal lattice, thus contributing to higher reversible capacity. - The partial substitution of oxygen sites and its strong electronegativity can stabilize the transition metal-oxygen (TM-O) bond, suppress the irreversible phase transition or oxygen loss during the initial desodium removal process, and reduce the loss of active sodium ions due to structural degradation, thus exhibiting a higher initial discharge capacity.

[0044] The improvement in cycle stability is analyzed in detail below: Fluoride doping forms a dense and stable fluorine-rich cathode electrolyte interphase (CEI) in situ on the material surface. This interphase is mainly composed of NaF and organic / inorganic composite halides, which effectively prevents direct contact between the electrolyte and the highly active cathode material, thereby significantly suppressing side reactions such as electrolyte decomposition and transition metal ion dissolution. Simultaneously, the strong bond energy of the transition metal-fluorine bond (TM–F) enhances the mechanical and chemical stability of the surface crystal structure, reducing the generation of microcracks and irreversible release of lattice oxygen during phase transitions, laying the foundation for long-term cycle stability.

[0045] The specific analysis of the enhanced high-rate performance and reaction kinetics is as follows: Fluorine doping can slightly increase the interlayer spacing of sodium (Na). + (layer), and reduce the energy barrier around the sodium site, thereby accelerating the Na+ reaction. + The solid-state diffusion rate between layers. Furthermore, the aforementioned stable fluorine-rich CEI exhibits high ionic conductivity (especially for Na+). + It has good electronic insulation properties and can rapidly conduct Na+. +At the same time, it suppresses harmful electron tunneling. This makes charge exchange at the interface more efficient during high-rate charge and discharge, and the polarization voltage increases slowly. Therefore, the capacity retention capability is far superior to that of the comparative example with interface deterioration and severe polarization.

[0046] The following analysis demonstrates the material's superior environmental stability and processing suitability: The water capacity of the material after immersion is slightly lower than the original material, but the capacity retention remains essentially the same. This result reveals the environmental stability advantage brought about by fluoride doping. Fluoride doping and the fluorine-rich layer formed on the surface significantly reduce the hygroscopicity and reactivity of the material surface. It effectively prevents H2O molecules from invading the crystal lattice and undergoing irreversible H2O reactions with alkali metal ions. + / Na + The exchange reaction (a major cause of performance degradation in layered oxides in air) is a significant factor. Even after immersion in water, the crystal structure framework and active components of the material are largely preserved, thus maintaining its intrinsic electrochemical performance (capacity retention). This characteristic greatly reduces the stringent environmental (humidity) control requirements during the production, storage, and battery manufacturing of cathode materials, lowering manufacturing costs and improving the long-term consistency of battery products.

[0047] Given the material’s excellent cycle life and low cost, it can be applied to grid connection and smooth output of renewable energy (such as wind and solar power), peak and valley regulation on the grid side, energy storage units and backup power sources for smart grids.

[0048] It should be noted that the material of this invention is not only inexpensive but also has a high operating voltage and excellent rate performance, capable of meeting the high current requirements of vehicle starting, acceleration, and regenerative braking, while providing a longer driving range. It is an ideal alternative to lead-acid batteries. It is suitable for providing power to various low-speed electric vehicles, such as electric bicycles, electric tricycles, low-speed electric cars, park / scenic area sightseeing vehicles, and automated guided vehicles (AGVs).

[0049] In an optional embodiment, the sodium-ion battery is assembled into a button cell, specifically as follows: a rolled-out electrode sheet is used as the positive electrode, a sodium sheet with a diameter of φ16 mm is used as the negative electrode, and a glass fiber (GF / D) with a diameter of φ19 mm is used as the separator. NaClO4 (Duoduo reagent, NC-005) is used as the electrolyte, and the battery is assembled into a button cell. In other embodiments of the present invention, the specifications of the positive electrode, negative electrode, and separator can be reasonably cut according to actual needs.

[0050] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0051] Example 1 This embodiment provides a method for preparing a P2 phase layered oxide cathode material, including the following steps: Anhydrous sodium carbonate, nickel oxide, manganese trioxide, and zinc fluoride were mixed in a molar ratio of 0.38:0.225:0.375:0.025, ground and mixed in a mortar until homogeneous. The mixture was then poured into a quartz crucible and transferred to a muffle furnace for calcination to obtain a P2 phase layered oxide cathode material.

[0052] The calcination process employs a staged heating procedure, specifically including the following steps: a. Heating from 20°C to 100°C at a rate of 5°C / min, holding for 120 min; b. Heating further at a rate of 3°C / min to 800°C, holding for 1440 min; c. Cooling down to 100°C at a rate of 5°C / min; d. Finally, cooling to room temperature with the furnace, removing and grinding for later use to obtain the cathode material Na. 0.76 Ni 0.225 Zn 0.025 Mn 0.75 O 1.975 F 0.05 .

[0053] Example 2 This embodiment provides a method for preparing a P2 phase layered oxide cathode material. The implementation steps are the same as in Example 1, with the only difference being: Anhydrous sodium carbonate, nickel oxide, manganese trioxide, and calcium fluoride were mixed in a molar ratio of 0.38:0.225:0.375:0.025 to obtain the cathode material Na. 0.76 Ni 0.225 Ca 0.025 Mn 0.75 O 1.975 F 0.05 .

[0054] Example 3 This embodiment provides a method for preparing a P2 phase layered oxide cathode material. The implementation steps are the same as in Example 1, with the only difference being: Anhydrous sodium carbonate, nickel oxide, manganese trioxide, and zinc chloride were mixed in a molar ratio of 0.38:0.225:0.375:0.025 to obtain the cathode material Na. 0.76 Ni 0.225 Zn 0.025 Mn 0.75 O 1.975 Cl 0.05 .

[0055] Example 4 This embodiment provides a method for preparing a P2 phase layered oxide cathode material. The implementation steps are the same as in Example 1, with the only difference being: Anhydrous sodium carbonate, nickel oxide, manganese trioxide, and zinc bromide were mixed in a molar ratio of 0.38:0.225:0.375:0.025 to obtain the cathode material Na. 0.76 Ni 0.225 Zn 0.025 Mn 0.75 O 1.975 Br 0.05 .

[0056] Example 5 This embodiment provides a method for preparing a P2 phase layered oxide cathode material. The implementation steps are the same as in Example 1, with the only difference being: Anhydrous sodium carbonate, nickel oxide, manganese trioxide, and zinc fluoride were mixed in a molar ratio of 0.35:0.2:0.3875:0.025 to obtain the cathode material Na. 0.7 Ni 0.2 Zn 0.025 Mn 0.775 O 1.975 F 0.05 .

[0057] Comparative Example 1 This comparative example provides a method for preparing a P2 phase layered oxide cathode material. The implementation steps are the same as in Example 1, with the only difference being: Anhydrous sodium carbonate, nickel oxide, and manganese trioxide were mixed in a molar ratio of 0.38:0.225:0.375 to obtain the cathode material Na. 0.76 Ni 0.25 Mn 0.75 O2.

[0058] Comparative Example 2 This comparative example provides a method for preparing a P2 phase layered oxide cathode material. The implementation steps are the same as in Example 1, with the only difference being: Anhydrous sodium carbonate, nickel oxide, manganese trioxide, and zinc oxide were mixed in a molar ratio of 0.38:0.225:0.375:0.025 to obtain the cathode material Na. 0.76 Ni 0.225 Zn 0.025 Mn 0.75 O2.

[0059] Comparative Example 3 This comparative example provides a method for preparing a P2 phase layered oxide cathode material. The implementation steps are the same as in Example 1, with the only difference being: Anhydrous sodium carbonate, nickel oxide, manganese trioxide, and calcium oxide were mixed in a molar ratio of 0.38:0.225:0.375:0.025 to obtain the cathode material Na. 0.76 Ni 0.225 Ca0.025 Mn 0.75 O2.

[0060] Test Example 1 The P2 phase layered oxide cathode material prepared in Example 1 of this test case was subjected to SEM morphology testing and analysis. The relevant test results are shown below. Figure 1 .

[0061] from Figure 1 As can be seen, the sample exhibits a typical layered stacked morphology, composed of numerous nano- to submicron-sized sheet-like particles aggregated together. The layered structure is clearly visible, with a relatively smooth surface and rounded edges, resembling a disk-like morphology. The lateral dimensions of the sheet-like particles are mainly concentrated in the range of 0.5 μm–2 μm, with a thickness of approximately 100 nm–200 nm, exhibiting typical characteristics of a two-dimensional layered material, which is conducive to the rapid insertion and extraction of sodium ions. The overall morphology of the material is uniform, without obviously excessively large particles or severe agglomeration. A certain gap is maintained between the layers, which is beneficial for electrolyte wetting and ion transport. This layered morphology is consistent with the P2 phase layered crystal structure determined in the XRD analysis, further confirming that the material has good layered order and structural integrity, which is beneficial for improving its sodium storage performance and cycle stability as a cathode material for sodium-ion batteries.

[0062] Conclusion: SEM analysis shows that the halide-doped P2 phase layered oxide cathode material prepared in this invention has a regular layered morphology, suitable particle size and good structural uniformity, which provides a favorable microstructure basis for achieving efficient and stable electrochemical performance in sodium-ion batteries.

[0063] Test Example 2 This test example performs XRD tests on the P2 phase layered oxide cathode materials prepared in Examples 1-2 and Comparative Example 1, respectively. The relevant test results are shown in [link to relevant data]. Figure 2 .

[0064] from Figure 2 It can be seen that the XRD diffraction peak positions of the samples prepared in Examples 1 and 2 are consistent with the peak positions of the standard card PDF#00-054-0894, indicating that the prepared materials have a typical P2 phase layered crystal structure. Compared with Comparative Example 1 (undoped sample), some diffraction peaks in Examples 1 and 2 show slight shifts while maintaining the P2 phase structure, indicating that the introduction of halide ions has a regulatory effect on the lattice parameters, which is beneficial to improving the sodium ion mobility and structural stability of the material.

[0065] Conclusion: This invention successfully prepared a halide-doped layered oxide cathode material with high crystallinity and a single P2 phase structure. Its crystal structure is well-defined and free of impurities. The introduction of halides has a beneficial modulation on the crystal lattice structure, laying a structural foundation for further improving the electrochemical performance of sodium-ion batteries.

[0066] Test Example 3 This test example involves battery performance testing. The P2 phase layered oxide cathode materials obtained in Examples 1-2 and Comparative Examples 1-3 were used to prepare cathodes and batteries, respectively. The relevant preparation processes are as follows: The preparation method of the positive electrode is as follows: The obtained positive electrode material, conductive agent (Ketjen Black), and binder (PTFE) are thoroughly mixed and ground in a mass ratio of 8:1:1. The material is rolled into a uniform sheet with a thickness of (100μm-0.5mm) using a rolling method, and finally cut into 0.5mm pieces. 0.5cm 2 The electrode is used as the positive electrode of the battery.

[0067] The battery is prepared as follows: a button cell is assembled, specifically using rolled-out electrode sheets as the positive electrode, NaClO4 (Duoduo reagent, NC-005) as the electrolyte, a sodium sheet with a diameter of φ16 mm as the negative electrode, and glass fiber (GF / D) with a diameter of φ19 mm as the separator.

[0068] The battery testing method is as follows: The button cell battery was charged and discharged at a voltage of 2.0V-4.3V and a rate of 0.1C. The specific capacity of the first discharge cycle, the capacity after 50 cycles, and the capacity after 100 cycles were recorded. The button cell battery was pre-sodium-treated for 5 cycles at a voltage of 2.0V-4.3V and a rate of 0.1C, and then charged and discharged at a rate of 1C. The specific capacity of the first discharge cycle at 1C, the capacity after 500 cycles, and the capacity after 1000 cycles were recorded. The relevant results are shown in Table 1; the first charge and discharge curve of Example 1 is shown in Table 1. Figure 3 .

[0069] Table 1 Performance data of batteries made from P2 phase layered oxide cathode materials

[0070] Test Example 4 This test example involves a water immersion experiment on P2 phase layered oxide cathode material. The specific method is as follows: Take 0.8g of the P2 phase layered oxide cathode material prepared in Examples 1-2 and Comparative Examples 1-3, add 5mL of deionized water, soak for 24h, then transfer to a 110℃ oven and dry for 24h. Remove and roll out the electrode sheet, then assemble it into a button cell. The preparation methods of the electrode sheet and the battery are the same as in Test Example 1, and will not be repeated in this test example.

[0071] In this test example, the electrical performance of the prepared batteries was tested, and the relevant results are shown in Table 2.

[0072] Table 2 Performance data of batteries made from P2 phase layered oxide cathode materials after immersion in water.

[0073] Combining the data in Tables 1 and 2, and Figure 1 It can be seen that the initial capacity of the embodiments prepared by this invention is higher than that of the comparative example; in the early cycling (0-100 cycles), the capacity of the first cycle of the embodiment at 0.1C rate is 130 mAh·g. -1 After 100 cycles, the capacity retention rate was 79.12%, significantly higher than the comparative example; at a high rate of 1C, the capacity of Example 1 in the first cycle was 94 mAh·g. -1 After 1000 cycles, the capacity retention rate was 92.70%, while the comparative material showed accelerated capacity decay at high magnification. The capacity of the material after soaking in water was slightly lower than that of the original material, but the capacity retention rate was basically the same.

[0074] This is because the main advantage of halide doping lies in its lattice stability and suppression of phase transitions, resulting in very slow capacity decay in the early stages of cycling. At high rates, Na... + Migration speed and interface stability are key. - Doping expands Na + Because of the migration channel, the embodiment maintains good capacity retention even at high rates. In contrast, the comparative example, due to its structural instability, experiences a sharp acceleration in capacity decay at high rates.

[0075] Test Example 5 In this test example, time-of-flight secondary ion mass spectrometry (TOF-SIMS) was used to analyze the P2 phase layered oxide cathode material prepared in Example 1. The relevant test results are shown below. Figure 4 .

[0076] from Figure 4 It can be seen that the signal distributions of O, F, Na, Zn, Ni, and Mn are all continuous and uniform, with no obvious agglomeration or segregation, indicating that each element is uniformly distributed on the material surface and near the surface. The F element signal is clear and continuously distributed, confirming that halogen elements (taking F as an example) have been successfully doped into the bulk phase of the material and uniformly distributed in the layered structure, consistent with the designed material composition. The distributions of major metal elements such as Na, Mn, Ni, and Zn, as well as O, highly overlap, further confirming that the material has a uniform P2 phase layered structure without obvious impurities or compositional fluctuations. The uniform elemental distribution is beneficial for maintaining the structural integrity of the material during cycling, reducing local stress concentration and side reactions, and thus is expected to improve the electrochemical stability and cycle life of the material.

[0077] Conclusion: TOF-SIMS analysis results show that the halide-doped P2 phase layered oxide cathode material prepared in this invention has a uniform elemental distribution, especially the uniform presence of doped halogens in the material. This provides a guarantee of compositional uniformity for the material to achieve high capacity, long cycle life and good structural stability in sodium-ion batteries.

[0078] In summary, the halide-doped P2-phase layered oxide cathode material provided by this invention employs a dual-ion doping strategy. The doped halogen in the bulk phase enhances the operating voltage, thereby achieving higher capacity within a lower voltage window. The M element acts as a structural pillar, effectively improving structural stability. The preparation method is a one-step process, simple to operate and with a low reaction temperature, requiring no special equipment or expensive precursors, making it simpler, more economical, and suitable for large-scale production. The prepared battery exhibits excellent long-cycle stability, high operating voltage, and superior rate performance. It is beneficial for improving initial capacity and active site availability, enhancing cycle stability, improving high-rate performance and reaction kinetics, and endowing the material with excellent environmental stability and processing suitability.

[0079] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A halide-doped P2-phase layered oxide cathode material, characterized in that, The chemical formula of the P2 phase layered oxide cathode material is shown in (I): Na a Ni b M c Mn d O e X f (I); In formula (Ⅰ), M is selected from at least one of Li, Na, K, Mg, Ca, Sr, Ba, Al, Sn, Zn, Cu, Ti, Zr, Y and Mo; X is selected from at least one of F, Cl, Br and I; 0.65≤a≤0.85, 0.2≤b<0.27, 0<c≤0.05, 0.5≤d≤0.75, 1.8≤e<2.0, 0<f≤0.18, and 0.85≤b+c+d≤1, 1.8≤e+0.5f≤2, 0.2≤c / f≤1.

2. The P2 phase layered oxide cathode material according to claim 1, characterized in that, The P2 phase layered oxide cathode material has a disk-like morphology with a lateral dimension of 0.5μm–2μm and a thickness of 100nm–200nm.

3. The P2 phase layered oxide cathode material according to claim 1, characterized in that, b+c+d=1, e+0.5f=2, 0.25≤c / f≤1; And / or, 0.7≤a≤0.82, 0.2≤b<0.25, 0.015<c≤0.045, 0.6≤d≤0.75, 1.85≤e<2.0, 0<f≤0.

1.

4. The P2 phase layered oxide cathode material according to claim 1, characterized in that, The M is selected from at least one of Ca and Zn; And / or, the X is selected from at least one of F, Cl and Br.

5. A method for preparing the P2 phase layered oxide cathode material as described in any one of claims 1-4, characterized in that, Includes the following steps: Sodium source, nickel source, M source, manganese source and X source are mixed in proportion and sintered using high temperature solid-state method to obtain P2 phase layered oxide cathode material. The burning process includes the following steps: raising the temperature from room temperature to 100℃ at a rate of 3℃ / min-7℃ / min, and holding at that temperature for 100min-130min; continuing to raise the temperature to 750℃-900℃ at a rate of 2℃ / min-5℃ / min, and holding at that temperature for 1200min-1500min; and lowering the temperature to 90℃-120℃ at a rate of 3℃ / min-7℃ / min.

6. The preparation method according to claim 5, characterized in that, The molar ratio of sodium source, nickel source, M source, manganese source and X source is (0.7-0.82): (0.2-0.25): (0.01-0.05): (0.6-0.75): (0.01-0.05).

7. The preparation method according to claim 5, characterized in that, The sodium source is selected from at least one of anhydrous sodium carbonate, sodium acetate, sodium oxalate, and halides; And / or, the nickel source is selected from at least one of nickel oxide, nickel carbonate, nickel acetate, nickel oxalate, and halides; And / or, the M source is selected from at least one of the oxides, carbonates, acetates, oxalates and halides of M; And / or, the manganese source is selected from at least one of manganese oxides, manganese carbonate, manganese acetate, manganese oxalate, and halides.

8. The preparation method according to claim 5, characterized in that, The burning process includes the following steps: Increase the temperature from room temperature to 100℃ at a rate of 5℃ / min and hold for 110-125 minutes; continue increasing the temperature to 800℃ at a rate of 3℃ / min and hold for 1300-1450 minutes; then decrease the temperature to 90℃-110℃ at a rate of 5℃ / min.

9. A positive electrode, characterized in that, The material comprises a P2 phase layered oxide cathode material as described in any one of claims 1-4, or a P2 phase layered oxide cathode material prepared by the preparation method as described in any one of claims 5-8, a conductive agent, and a binder, wherein the mass ratio is (7-9):(0.5-1.5):(0.5-1.5). The conductive agent is selected from at least one of Ketjen Black, Super P, and carbon nanotubes; the binder is selected from at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, styrene-butadiene rubber / sodium carboxymethyl cellulose, and polyacrylic acid.

10. A sodium-ion battery, characterized in that, Includes the positive electrode as described in claim 9.

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