A P2 / O3 biphasic composite sodium-ion battery cathode material, its preparation method and application

Abstract

The present invention discloses a P2 / O3 dual-phase composite sodium-ion battery cathode material, a preparation method thereof, and an application thereof. The cathode material includes a matrix and a coating layer coated on the outer layer of the matrix. The matrix is composed of an O3-phase material with a space group of R-3m, and the coating layer is composed of a P2-phase layered material with a space group of P63 / mmc. The chemical elements contained in the P2 phase and the O3 phase are the same, and the element ratios are relatively close. The sodium-ion battery cathode material prepared by the present invention has a high capacity, excellent cycle performance, and good rate performance. At the same time, the preparation method is simple, which improves the comprehensive performance and application potential of the cathode material. The sodium-ion secondary battery prepared based on this cathode material has a high first-week efficiency, excellent cycle performance, excellent rate performance, and good safety performance, and can be used in large-scale energy storage devices for solar power generation, wind power generation, smart grid peak shaving, distributed power stations, backup power supplies, or communication base stations.

Description

Technical Field

[0001] The present invention belongs to the technical field of cathode materials for sodium-ion batteries with a P2 / O3 biphasic composite structure, and specifically relates to a P2 / O3 biphasic composite cathode material for sodium-ion batteries, a preparation method thereof, and an application thereof. Background Art

[0002] The development of industry and the consumption of fossil fuels have led to an energy crisis, ultimately driving the demand for efficient energy storage devices. The consumption of fossil fuels releases greenhouse gases such as carbon dioxide, resulting in climate change, desertification, and global warming. In addition, fossil fuel resources (coal, oil, and natural gas) are gradually decreasing. Therefore, it is urgent to develop environmentally friendly and sustainable energy storage devices using clean or renewable energy sources such as solar energy, hydropower, and wind energy, as these resources are cost-effective and sustainable. These energy sources also depend on environmental conditions such as temperature, location, and season. Therefore, it is necessary to integrate energy storage devices with superior stability and capacity. Therefore, rechargeable / secondary batteries will play a key role as the best energy storage devices due to their flexible response time, high energy density, long life cycle, pollution-free operation, high efficiency, and portability. Lithium-ion batteries (LIBs) have become an essential component of electronic and portable devices (laptops, mobile phones, tablets, cameras, etc.) due to their excellent energy density (Ed), power density (Pd), efficiency, stable capacity, low self-discharge, light weight, and long life. However, lithium resources are unevenly distributed and limited in reserves, and as the consumption increases, the cost of lithium gradually increases. Therefore, large-scale energy storage lithium-ion batteries will inevitably be restricted.

[0003] Therefore, in the field of energy storage, it is necessary to find a secondary battery system that can supplement or even replace lithium-ion batteries. Since sodium ions and lithium ions are in the same main group and have relatively similar chemical properties, and sodium is abundant in reserves on the earth and evenly distributed geographically with a low cost, developing sodium-ion secondary batteries as large-scale energy storage devices is an alternative choice.

[0004] The patent document of CN116314659A discloses a layered oxide with a mixed-phase structure, a preparation method thereof, and an application thereof. By coating a layer of P2-phase material on the surface of the O3-phase material, this coating structure combines the high-capacity core O3-phase and the structurally stable outer shell P2-phase, improving the reversibility and air stability of the cathode material, reducing the surface residual alkali, and improving the rate performance. However, in this patented technology, the O3-phase material contains Fe elements, the P2-phase material does not contain Fe elements, and the elements of the O3-phase material and the P2-phase material are quite different, which will affect the stability and electrochemical performance of the cathode material to a certain extent.

[0005] The patent document of CN117976884A discloses a core-shell structured sodium-ion battery cathode material, its preparation method and application. The core-shell structured sodium-ion battery cathode material includes an inner core, an outer shell, and a transition layer between the inner core and the outer shell; the inner core includes an O3-phase cathode material, the outer shell includes a P2-phase cathode material, and the transition layer includes a P2-O3 mixed-phase cathode material. By using the O3-phase material as the inner core and then successively coating the P2-O3 mixed-phase cathode material and the P2-phase material, through the transition of the P2-O3 mixed-phase coating layer, the material not only has the advantages of P2-phase and O3-phase materials, but also can prevent problems such as the shedding of the coating layer and the cracking of the cathode material caused by the inconsistent lattice expansion coefficients of P2 and O3 phases during charge and discharge. However, in this patented technology, the core-shell structured sodium-ion battery cathode material contains a P2-O3 mixed-phase cathode material transition layer, which makes the preparation process relatively complex. Summary of the Invention

[0006] The technical problem solved by the present invention is to provide a P2 / O3 dual-phase composite sodium-ion battery cathode material and its preparation method. The sodium-ion battery cathode material prepared by this method has a high capacity, excellent cycling performance, good rate performance, and at the same time, the preparation method is simple, which improves the comprehensive performance and application potential of the cathode material. The sodium-ion secondary battery based on this cathode material has a high first-cycle efficiency, excellent cycling performance, excellent rate performance, and good safety performance, and can be used in large-scale energy storage devices for solar power generation, wind power generation, intelligent power grid peak shaving, distributed power stations, backup power supplies, or communication base stations.

[0007] The present invention adopts the following technical solutions to solve the above technical problems. A P2 / O3 dual-phase composite sodium-ion battery cathode material, which includes a matrix and a coating layer coated on the outer layer of the matrix;

[0008] The matrix is composed of O3-phase Na 1+a Ni x Mn y M1 z M2 b O2 material, its space group is R-3m, where M1 is a transition metal element, specifically one or more of Ti, Fe, Co, Cu, or Zn, M2 is a doping element, specifically one or more of Mg, Zr, Nb, Mo, Sn, Sb, Be, Ta, B, W, Y, or Cr, -0.05 ≤ a ≤ 0.05, 0.1 ≤ x ≤ 0.5, 0.1 ≤ y ≤ 0.5, 0.05 ≤ z ≤ 0.4, 0 ≤ b ≤ 0.01, and x + y + z = 1;

[0009] The coating layer is composed of P2-phase Na c Ni d Mn e M1f It is composed of O2-layered materials with a space group of P63 / mmc. Among them, the transition metal element M1 in the P2-phase layered material is the same as the transition metal element M1 in the matrix, 0.5 ≤ c ≤ 0.7, d = x ± 0.2, e = y ± 0.2, and f = z ± 0.2.

[0010] Preferably, the molar percentage of the coating layer in the positive electrode material of the sodium-ion battery is 0.1% - 50% of the positive electrode material of the sodium-ion battery.

[0011] Preferably, the molar percentage of the coating layer in the positive electrode material of the sodium-ion battery is 1% - 30% of the positive electrode material of the sodium-ion battery.

[0012] In the positive electrode material of the sodium-ion battery of the present invention, the types of transition metal elements contained in the P2 phase and the O3 phase are the same, with slight differences in the element ratios. This is because the same elements can grow more closely during the coating process, and the structural change at the contact surface between the P2 phase and the O3 phase is relatively stable, which can reduce the influence on Na + transport and effectively guarantee the electrochemical performance of the sodium-ion battery.

[0013] The preparation method of the P2 / O3 biphasic composite sodium-ion battery positive electrode material of the present invention specifically comprises the following steps:

[0014] Step S1: Weigh and mix the sodium source, nickel-manganese precursor, M1 source, and M2 source according to the required stoichiometric ratio, and heat-treat them in an air atmosphere at 700 - 1000 °C for 10 - 20 h to obtain the O3-phase matrix material Na 1+a Ni x Mn y M1 z M2 b O2. The sodium source is one or more of sodium carbonate, sodium bicarbonate, sodium sulfate, sodium bisulfate, sodium oxalate, sodium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium peroxide, sodium hydroxide, sodium nitrate, sodium acetate, or sodium superoxide. The nickel-manganese precursor is nickel-manganese hydroxide or nickel-manganese carbonate. The M1 source and the M2 source are respectively one or more of the oxides, hydroxides, carbonates, chlorides, nitrates, acetates, or sulfates corresponding to M1 and M2. M1 is a transition metal element, specifically one or more of Ti, Fe, Co, Cu, or Zn. M2 is a doping element, specifically one or more of Mg, Al, Zr, Nb, Mo, Sn, Sb, Be, Ta, B, W, Y, or Cr.

[0015] Step S2: Mix the matrix material obtained in step S1 with the sodium source, nickel source, manganese source, and M1 source corresponding to the surface coating elements evenly, and heat-treat them in an oxygen-containing atmosphere at 700 - 1000 °C for 5 - 15 h to obtain the coated P2-phase Na cNi d Mn e M1 f The positive electrode material of a P2 / O3 biphasic composite sodium-ion battery for an O2 layered material, wherein the sodium source is one or more of sodium carbonate, sodium bicarbonate, sodium sulfate, sodium bisulfate, sodium oxalate, sodium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium peroxide, sodium hydroxide, sodium nitrate, sodium acetate or sodium superoxide, and the nickel source, manganese source and M1 source are one or more of the corresponding oxides, hydroxides, carbonates, chlorides, nitrates, acetates or sulfates of Ni, Mn and M1.

[0016] Preferably, the mixing method of the materials in steps S1 and S2 is dry mixing, and the method is ball milling or high mixing. The purpose is to mix the materials evenly. Regardless of the mixing conditions, as long as they can be mixed evenly.

[0017] Preferably, the particle size of the nickel-manganese precursor in step S1 is 1-15 μm.

[0018] Preferably, the morphology of the positive electrode material of the sodium-ion battery in step S2 includes any one of blocky, sheet-like, disc-shaped or spherical. The morphology of the positive electrode material of the sodium-ion battery will have certain differences due to different ratios of Na to metal or different precursors.

[0019] Preferably, the temperature selected for sintering in step S1 is 800-970 °C, the sintering time is 13-18 h, and the heating rate during the sintering process is 2-10 °C / min; the temperature selected for sintering in step S2 is 850-950 °C, the sintering time is 8-12 h, the heating rate during the sintering process is 2-10 °C / min, and the oxygen-containing atmosphere is an oxygen atmosphere or an air atmosphere excluding CO2.

[0020] Preferably, the matrix material after the first sintering in step S1 is a single crystal rather than a secondary ball, and the particle size D50 of the matrix material is 3-10 μm.

[0021] In the positive electrode material of the sodium-ion battery of the present invention, for the P2 phase of the coating layer, the types of transition metal elements in the coating layer and the matrix are the same, the stoichiometric coefficient ratio of sodium ions in the coating layer and the matrix remains between 0.45 and 0.7, and the proportion of transition metal elements in the coating layer is similar to that of the matrix, so as to ensure that the growth of the coating layer on the matrix is more fitting.

[0022] The present invention provides a sodium-ion secondary battery including the above positive electrode material.

[0023] The present invention provides a use of the above sodium-ion secondary battery, and the sodium-ion secondary battery is used for large-scale energy storage devices such as solar power generation, wind power generation, smart grid peak shaving, distributed power stations, backup power supplies or communication base stations.

[0024] The present invention has the following advantages and beneficial effects compared with the prior art:

[0025] 1. The sodium-ion battery material prepared by the present invention consists of an inner O3-phase matrix and an outer P2-phase coating layer. The chemical elements contained in the P2 phase and the O3 phase are the same, and the element ratios are relatively close. The same elements can ensure that the structural changes at the contact surface between the coating layer and the matrix are relatively stable, and the influence on Na + diffusion is small, which is beneficial to the diffusion of Na + during the charge and discharge process. At the same time, the supplementation of Na + in the O3 phase to the P2 phase can also reduce the phase transition of the P2 phase, effectively enhancing the structural stability, air stability and water stability of the cathode material, so that the sodium-ion battery prepared based on this cathode material has good rate performance and cycle stability performance.

[0026] 2. The core-shell structured sodium-ion battery cathode material prepared by the present invention is simple to prepare, has better comprehensive performance and application prospects, including high capacity, good rate performance and cycle performance, and good safety performance. It has great practical value and can be used in large-scale energy storage devices such as solar power generation, wind power generation, smart grid peak shaving, distributed power stations, backup power supplies or communication base stations. Description of the Drawings

[0027] Figure 1 SEM image of the cathode material prepared in Example 1.

[0028] Figure 2 XRD pattern of the cathode material prepared in Example 1.

[0029] Figure 3 Charge and discharge comparison curves of the matrix and the coated cathode material prepared in Example 1.

[0030] Figure 4 Capacity cycle retention comparison curves of the coin-type half-cells assembled with the cathode materials prepared in Examples 1-2 and Comparative Examples 1-2. Detailed Embodiments

[0031] The above content of the present invention will be further described in detail below through examples, but it should not be understood that the scope of the above subject matter of the present invention is limited to the following examples. Any technology implemented based on the above content of the present invention belongs to the scope of the present invention. Example 1

[0032] In this example, the core of the sodium-ion battery cathode material is O3-phase NaNi 0.4 Mn 0.4 Ti 0.1 Zn 0.1 Zr0.01 O2 material, the coating layer is P2-phase Na 0.5 Ni 0.2 Mn 0.6 Ti 0.1 Zn 0.1 O2 layered material, the molar ratio of the core to the coating layer is 8:2. The precursor is prepared by the co-precipitation method, and the cathode material is prepared by the solid-phase method.

[0033] According to the stoichiometric ratio of the above matrix, using NiSO4, MnSO4 and NH3·H2O as raw materials, a Ni mol :Mn mol =1 precursor is prepared by the co-precipitation method, and the particle size D50 of the precursor is 4μm; the precursor is weighed with Na2CO3, TiO2, ZnO, ZrO2 according to the stoichiometric ratio and then mixed and ball-milled. The ball-milling speed is 150r / min and the ball-milling time is 5h; the mixture is placed in a crucible and put into a box furnace. It is heated to 920°C at a heating rate of 3°C / min in an air atmosphere, sintered at this temperature for 14h, and then cooled to room temperature with the furnace after the reaction. After crushing and sieving, an O3-phase matrix material is obtained. The grains of this matrix material are hexagonal flakes with a particle size D50 of 6μm;

[0034] The matrix material obtained from the above reaction is mixed with Na2CO3, NiO, Mn3O4, TiO2 and ZnO according to the molar ratio of O3 phase:P2 phase, that is, the chemical formula is NaNi 0.4 Mn 0.4 Ti 0.1 Zn 0.1 Zr 0.01 O2:Na 0.5 Ni 0.4 Mn 0.4 Ti 0.1 Zn 0.1 O2, and weighed according to the stoichiometric ratio corresponding to a molar ratio of 8:2. Then it is mixed and ball-milled. The ball-milling speed is 150r / min and the ball-milling time is 5h; after the materials are mixed evenly, they are placed in a crucible and put into a box furnace. It is heated to 900°C at a heating rate of 3°C / min in a CO2-free air atmosphere, sintered at this temperature for 8h, cooled to room temperature with the furnace, and after crushing and sieving, an O3-phase material coated with P2 phase, that is, a P2 / O3 dual-phase composite sodium-ion battery cathode material, is obtained. Example 2

[0035] In this example, the core of the sodium-ion battery cathode material is O3-phase NaNi 0.3 Mn 0.5 Ti 0.1 Zn 0.1 Al 0.005 O2 material, the coating layer is P2-phase Na0.6 Ni 0.2 Mn 0.6 Ti 0.1 Zn 0.1 An O2-layered material with a molar ratio of core to coating layer of 9:1. The precursor is prepared by the co-precipitation method, and the cathode material is prepared by the solid-phase method.

[0036] According to the stoichiometric ratio of the above matrix, using NiSO4, MnSO4, and NH3·H2O as raw materials, a precursor with a Ni mol :Mn mol = 3:5 is prepared by the co-precipitation method. The particle size D50 of the precursor is 5 μm; after weighing the precursor, Na2CO3, TiO2, ZnO, and Al2O3 according to the stoichiometric ratio and mixing them by ball milling, the ball milling speed is 150 r / min, and the ball milling time is 5 h; the mixture is placed in a crucible and put into a box furnace. It is heated to 940 °C at a heating rate of 3 °C / min in an air atmosphere, sintered at this temperature for 14 h, cooled to room temperature with the furnace after the reaction, and an O3-phase matrix material is obtained after crushing and sieving. The grains of this matrix material are hexagonal flakes with a particle size D50 = 6 μm;

[0037] The matrix material obtained from the above reaction and Na2CO3, NiO, Mn3O4, TiO2, and ZnO are weighed according to the stoichiometric ratio corresponding to the molar ratio of O3 phase:P2 phase, that is, the chemical formula NaNi 0.3 Mn 0.5 Ti 0.1 Zn 0.1 Al 0.005 O2:Na 0.6 Ni 0.4 Mn 0.4 Ti 0.1 Zn 0.1 O2 of 9:1, and then mixed and ball milled. The ball milling speed is 150 r / min, and the ball milling time is 5 h; after the materials are mixed evenly, they are placed in a crucible and put into a box furnace. It is heated to 920 °C at a heating rate of 3 °C / min in a CO2-free air atmosphere, sintered at this temperature for 8 h, cooled to room temperature with the furnace, and an O3-phase material coated with P2 phase, that is, a P2 / O3 dual-phase composite sodium-ion battery cathode material, is obtained after crushing and sieving. Example 3

[0038] In this example, the core of the sodium-ion battery cathode material is an O3-phase NaNi 0.3 Mn 0.5 Fe 0.1 Zn 0.1 O2 material, and the coating layer is a P2-phase Na 0.6 Ni 0.2 Mn 0.6Fe 0.1 Zn 0.1 An O2-layered material with a molar ratio of core to coating layer of 9:1. The precursor is prepared by the co-precipitation method, and the cathode material is prepared by the solid-phase method.

[0039] According to the stoichiometric ratio of the above matrix, using NiSO4, MnSO4 and NH3·H2O as raw materials, Ni mol :Mn mol =3:5 precursor is prepared by the co-precipitation method, and the particle size D50 of the precursor is 5μm; after weighing the precursor, Na2CO3, Fe2O3, and ZnO according to the stoichiometric ratio, they are mixed and ball-milled. The ball-milling speed is 150 r / min, and the ball-milling time is 5 h; the mixture is placed in a crucible and put into a box furnace. It is heated to 940 °C at a heating rate of 3 °C / min in an air atmosphere, sintered at this temperature for 14 h, and cooled to room temperature with the furnace after the reaction. After crushing and sieving, an O3-phase matrix material is obtained. The grains of this matrix material are hexagonal flakes with a particle size D50 = 6μm;

[0040] The matrix material obtained from the above reaction and Na2CO3, NiO, Mn3O4, Fe2O3 and ZnO are weighed according to the stoichiometric ratio corresponding to the molar ratio of O3 phase:P2 phase, that is, the chemical formula NaNi 0.3 Mn 0.5 Fe 0.1 Zn 0.1 O2:Na 0.6 Ni 0.4 Mn 0.4 Fe 0.1 Zn 0.1 O2 is weighed according to the calculated mass corresponding to the molar ratio of 9:1, and then mixed and ball-milled. The ball-milling speed is 150 r / min, and the ball-milling time is 5 h; after the materials are mixed evenly, they are placed in a crucible and put into a box furnace. It is heated to 920 °C at a heating rate of 3 °C / min in a CO2-free air atmosphere, sintered at this temperature for 8 h, cooled to room temperature with the furnace, and an O3-phase material coated with a P2 phase, that is, a P2 / O3 dual-phase composite sodium-ion battery cathode material, is obtained after crushing and sieving.

[0041] Comparative Example 1

[0042] In this comparative example, the core of the sodium-ion battery cathode material is an O3-phase NaNi 0.3 Mn 0.5 Fe 0.1 Cu 0.1 O2 material, and the coating layer is a P2-phase Na 0.6 Ni 0.2 Mn 0.6 Ti 0.1 Zn 0.1O2 layered material, with a molar ratio of core to coating layer of 9:1. The precursor is prepared by coprecipitation method, and the cathode material is prepared by solid-phase method.

[0043] According to the stoichiometric ratio of the above matrix, using NiSO4, MnSO4 and NH3·H2O as raw materials, a precursor with a Ni mol :Mn mol =3:5 is prepared by coprecipitation method. The particle size D50 of the precursor is 5μm; the precursor, Na2CO3, Fe2O3 and CuO are weighed according to the stoichiometric ratio and then mixed and ball-milled. The ball-milling speed is 150r / min and the ball-milling time is 5h; the mixture is placed in a crucible and put into a box furnace. It is heated to 960℃ at a heating rate of 3℃ / min in an air atmosphere and sintered at this temperature for 14h. After the reaction is completed, it is cooled to room temperature with the furnace. After crushing and sieving, an O3-phase matrix material is obtained. The grains of this matrix material are hexagonal flakes with a particle size D50 of 7μm;

[0044] The matrix material obtained from the above reaction and Na2CO3, NiO, Mn3O4, TiO2 and ZnO are weighed according to the stoichiometric ratio corresponding to the molar ratio of O3 phase:P2 phase, that is, the chemical formula NaNi 0.3 Mn 0.5 Fe 0.1 Cu 0.1 O2:Na 0.6 Ni 0.4 Mn 0.4 Ti 0.1 Zn 0.1 O2 of 9:1, and then mixed and ball-milled. The ball-milling speed is 150r / min and the ball-milling time is 5h; after the materials are mixed evenly, they are placed in a crucible and put into a box furnace. It is heated to 940℃ at a heating rate of 3℃ / min in a CO2-free air atmosphere and sintered at this temperature for 8h. It is cooled to room temperature with the furnace. After crushing and sieving, an O3-phase material coated with P2 phase, that is, a P2 / O3 biphasic composite sodium-ion battery cathode material, is obtained.

[0045] Comparative Example 2

[0046] In this comparative example, the core of the sodium-ion battery cathode material is O3-phase NaNi 0.3 Mn 0.5 Ti 0.1 Zn 0.1 Al 0.005 O2 material, and the coating layer is P2-phase Na 0.6 Ni 0.2 Mn 0.6 Fe 0.1 Cu 0.1The O2 layered material has a molar ratio of core to coating layer of 9:1. The precursor is prepared by the coprecipitation method, and the cathode material is prepared by the solid-phase method.

[0047] According to the stoichiometric ratio of the above matrix, using NiSO4, MnSO4, and NH3·H2O as raw materials, a precursor with Ni mol :Mn mol =3:5 is prepared by the coprecipitation method. The particle size D50 of the precursor is 5 μm; after weighing the precursor, Na2CO3, TiO2, ZnO, and Al2O3 according to the stoichiometric ratio and mixing them by ball milling, the ball milling speed is 150 r / min, and the ball milling time is 5 h; the mixture is placed in a crucible, put into a box furnace, and heated to 940 °C at a heating rate of 3 °C / min in an air atmosphere, sintered at this temperature for 14 h, and after the reaction is completed, it is cooled to room temperature with the furnace. After pulverization and sieving, an O3-phase matrix material is obtained. The grains of this matrix material are hexagonal flakes, and the particle size D50 = 6 μm;

[0048] The matrix material obtained from the above reaction and Na2CO3, NiO, Mn3O4, Fe2O3, and CuO are weighed according to the stoichiometric ratio corresponding to the molar ratio of O3 phase:P2 phase, that is, the chemical formula NaNi 0.3 Mn 0.5 Ti 0.1 Zn 0.1 Al 0.005 O2:Na 0.6 Ni 0.4 Mn 0.4 Fe 0.1 Cu 0.1 O2 is 9:1, and then mixed and ball milled. The ball milling speed is 150 r / min, and the ball milling time is 5 h; after the materials are mixed evenly, they are placed in a crucible, put into a box furnace, and heated to 920 °C at a heating rate of 3 °C / min in a CO2-free air atmosphere, sintered at this temperature for 8 h, cooled to room temperature with the furnace, and after pulverization and sieving, an O3-phase material coated with a P2 phase, that is, a P2 / O3 dual-phase composite sodium-ion battery cathode material, is obtained.

[0049] Under the same conditions, the physical and chemical indexes and electrical properties of the cathode materials obtained in Examples 1 to 3 and Comparative Examples 1 to 2 are evaluated respectively.

[0050] Among them, the test results of the residual alkali content are shown in Table 1. According to the data, it can be seen that the surface residual alkali of the samples prepared in Examples 1 to 3 is relatively low, which indicates that the P2-phase coating method of the same elements in the present invention can effectively improve the surface structure and composition of the cathode material, which is beneficial to the electrochemical performance of the cathode material.

[0051] Table 1

[0052] Item Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 NaOH% 0.0453 0.0823 0.0765 0.1258 0.1433

[0053] The SEM image of the positive electrode material prepared in Example 1 is as Figure 1 shown. It can be seen from the figure that the prepared positive electrode material has a flaky morphology, and the average grain size is about 4 μm.

[0054] The XRD pattern of the positive electrode material prepared in Example 1 is as Figure 2 shown. The peak positions at 16.3°, 33.1°, 35.5°, 36.8°, 41.7°, 45.1°, 53.3°, 58.0°, 62.9°, and 65.5° represent the O3-phase matrix, and the peak positions at 15.8°, 31.7°, 34.3°, 36.1°, 39.2°, 42.8°, and 48.9° represent the peaks of the P2 phase, indicating that the P2 phase is generated during the coating process.

[0055] The coin-type half-cell electrochemical performance tests were carried out on the positive electrode materials obtained in Examples 1-2 and Comparative Examples 1-2.

[0056] All the electrochemical results in Examples 1-2 and Comparative Examples 1-2 were obtained through the tests of coin-type half-cells CR2032. The main production process includes the positive electrode material, the binder polyvinylidene fluoride (PVDF), and the conductive agent acetylene black, which are ground in a mass ratio of 90:5:5, and an appropriate amount of NMP is added to obtain a uniform slurry. The slurry is uniformly coated on the aluminum foil, and then dried in an oven at 100 °C and punched. Assembly is carried out in a vacuum glove box filled with argon, and finally formation is carried out on a Neware battery test cabinet. Subsequent electrochemical performance tests were carried out on a Neware battery test cabinet and a Zahner IM6ex electrochemical workstation.

[0057] Among them, the first charge-discharge curves of the positive electrode material prepared in Example 1 before and after coating are as Figure 3 shown. After coating, compared with the matrix, the first charge capacity decreases, the discharge specific capacity remains unchanged, and the first efficiency increases, indicating that the P2 phase after coating does not have a great impact on the capacity of the positive electrode material.

[0058] The coin cell cycle test results of the positive electrode materials prepared in Examples 1-2 and Comparative Examples 1-2 are as Figure 4 shown. It can be seen from the figure that the cycle stability performance of Examples 1-2 is better than that of Comparative Examples 1-2. Example 1 can still maintain a capacity retention rate of 93.15% after 100 cycles, the capacity retention rate of Example 2 after 100 cycles is 89.04%, while the capacity retention rate of Comparative Example 1 has dropped to 83.31% after 100 cycles, and the capacity retention rate of Comparative Example 2 has dropped to 84.62% after 100 cycles, indicating that the cycle stability performance of the sodium-ion battery positive electrode material prepared by the specific process of the present invention has been greatly improved.

[0059] The above embodiments have described the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principles of the present invention. Without departing from the scope of the principles of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of protection of the present invention.

Claims

1. A P2 / O3 dual-phase composite sodium-ion battery cathode material, characterized in that: The positive electrode material includes a matrix and a coating layer coated on the outer layer of the matrix; The matrix is composed of O3 phase Na 1+a Ni x Mn y M1 z M2 b O2 material, whose space group is R-3m, wherein M1 is a transition metal element, specifically one or more of Ti, Co, Cu or Zn, M2 is a doping element, specifically one or more of Mg, Al, Zr, Nb, Mo, Sn, Sb, Be, Ta, B, W, Y or Cr, -0.05≤a≤0.05, 0.1≤x≤0.5, 0.1≤y≤0.5, 0.05≤z≤0.4, 0≤b≤0.01, x+y+z=1; The coating layer is composed of a P2-phase Na c Ni d Mn e M1 f O2 layered material, and its space group is P63 / mmc. Among them, the transition metal element M1 in the P2-phase layered material is the same as the transition metal element M1 in the matrix, 0.5 ≤ c ≤ 0.7, d = x ± 0.2, e = y ± 0.2, f = z ± 0.2; In the positive electrode material of the sodium-ion battery, the molar percentage of the coating layer in the positive electrode material of the sodium-ion battery is 1% to 30%; The specific preparation steps of the P2 / O3 biphasic composite sodium-ion battery positive electrode material are as follows: Step S1: Weigh the sodium source, nickel-manganese precursor, M1 source, and M2 source according to the required stoichiometric ratio and mix them evenly. Then heat-treat them in an air atmosphere at 700 - 1000 °C for 10 - 20 h to obtain the O3-phase matrix material Na 1+a Ni x Mn y M1 z M2 b O2. The sodium source is one or more of sodium carbonate, sodium bicarbonate, sodium sulfate, sodium bisulfate, sodium oxalate, sodium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium peroxide, sodium hydroxide, sodium nitrate, sodium acetate, or sodium superoxide. The nickel-manganese precursor is nickel-manganese hydroxide or nickel-manganese carbonate. The M1 source and M2 source are respectively one or more of the corresponding oxides, hydroxides, carbonates, chlorides, nitrates, acetates, or sulfates of M1 and M2. M1 is a transition metal element, specifically one or more of Ti, Co, Cu, or Zn. M2 is a doping element, specifically one or more of Mg, Al, Zr, Nb, Mo, Sn, Sb, Be, Ta, B, W, Y, or Cr; Step S2: Mix the matrix material obtained in Step S1 evenly with the sodium source, nickel source, manganese source, and M1 source corresponding to the surface coating elements, and heat-treat them in an oxygen-containing atmosphere at 700-1000 °C for 5-15 h to obtain a P2-phase Na c Ni d Mn e M1 f O2-layered material of the P2 / O3 biphasic composite sodium-ion battery cathode material, where the sodium source is one or more of sodium carbonate, sodium bicarbonate, sodium sulfate, sodium bisulfate, sodium oxalate, sodium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium peroxide, sodium hydroxide, sodium nitrate, sodium acetate, or sodium superoxide, and the nickel source, manganese source, and M1 source are one or more of the oxides, hydroxides, carbonates, chlorides, nitrates, acetates, or sulfates corresponding to Ni, Mn, and M1.

2. The cathode material of the P2 / O3 dual-phase composite sodium-ion battery according to claim 1, characterized in that: In step S1, the particle size of the nickel-manganese precursor is 1 to 15 μm.

3. The cathode material of the P2 / O3 dual-phase composite sodium-ion battery according to claim 1, characterized in that: In step S2, the morphology of the positive electrode material of the sodium-ion battery includes any one of blocky, lamellar, disc-shaped or spherical.

4. The cathode material for a P2 / O3 dual-phase composite sodium-ion battery according to claim 1, characterized in that: In step S1, the selected sintering temperature is 800 to 970 °C, the sintering time is 13 to 18 h, and the heating rate during the sintering process is 2 to 10 °C / min; in step S2, the selected sintering temperature is 850 to 950 °C, the sintering time is 8 to 12 h, the heating rate during the sintering process is 2 to 10 °C / min, and the oxygen-containing atmosphere is an oxygen atmosphere or an air atmosphere except CO2.

5. The cathode material of the P2 / O3 dual-phase composite sodium-ion battery according to claim 1, characterized in that: After the first sintering in step S1, the matrix material is a single crystal, and the particle size D50 of the matrix material is 3 to 10 μm.

6. A sodium-ion secondary battery, characterized in that: The sodium-ion secondary battery includes the P2 / O3 biphasic composite sodium-ion battery positive electrode material according to any one of claims 1 to 5.

7. Application of the sodium-ion secondary battery according to claim 6 in large-scale energy storage devices for solar power generation, wind power generation, smart grid peak shaving, distributed power stations, backup power supplies or communication base stations.

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