Cathode material and sodium-ion battery

Abstract

This application relates to a cathode material and a sodium-ion battery. The cathode material has a sodium-rich structural defect, and the sodium-rich defect degree of the cathode material is X, where 0.25 ≤ X ≤ 0.7, and X = C1 / (C1 + C2); wherein, C1 is the difference in discharge specific capacity of the half-cell between Vopen and 2.5 V, where Vopen is the open-circuit voltage of the first charge curve of the half-cell; and C2 is the difference in discharge specific capacity between 2.5 V and 2.0 V. For the cathode material of this application, the cathode material has both high-voltage resistance performance, high capacity, and cycle stability, improving the comprehensive performance of the cathode material.

Description

Technical Field

[0001] The present invention belongs to the technical field of cathode materials, and particularly relates to a cathode material, a preparation method thereof, and a sodium-ion battery. Background Art

[0002] Due to the constraints of factors such as the shortage of traditional fossil energy and energy security, as well as the enhancement of people's awareness of ecological environment protection, the sustainable development, utilization, and storage of energy have been highly valued by countries around the world. Among various energy storage systems, the electrochemical energy storage system (EES) is considered an effective method to balance the cyclic characteristics of renewable energy due to its advantages such as long service life, low cost, less investment, and easy installation. Among them, secondary battery energy storage in electrochemical energy storage has great potential. Among them, lithium-ion batteries dominate the energy storage market due to their high theoretical specific capacity and specific energy density. However, due to the limited reserves and uneven distribution of lithium (Li) resources and the multi-faceted consumption of lithium, restricted by objective factors such as lithium extraction technology, geographical environment, and transportation conditions, there are still bottlenecks in lithium resources in the field of power batteries. To alleviate this problem, it is currently proposed to use elements with high abundance, such as sodium (Na), potassium (K), magnesium (Mg), aluminum (Al), calcium (Ca), etc. to replace lithium, so as to prepare a new generation of low-cost and environmentally friendly secondary ion batteries. Developing sodium-ion batteries has strategic significance at the national level, and sodium-ion batteries have received more and more attention and support from countries.

[0003] Sodium-based layered oxide cathode material is one of the most critical materials for sodium-ion batteries. Similar to lithium cobaltate and ternary structures in lithium batteries, the layered oxide structure has good ion channels, and there may be certain shortcomings in the cycle performance, but the average maturity is relatively high. Transition metal oxide NaXMeO2 is an insertion-type or intercalation-type compound, which theoretically has a high discharge specific capacity but poor cycle performance.

[0004] Among the existing sodium-ion battery layered oxide materials, the disadvantages of each type are obvious. For example, the O3-type cathode material has a high capacity, a low initial efficiency, and poor cycle performance; the P2-type cathode material has a low initial charging capacity, good cycle and rate performance; the P3-type cathode material has a low capacity, poor cycle performance, and a high working voltage. The comprehensive performance of each type of cathode material is not good. Summary of the Invention

[0005] The purpose of this application is to provide a cathode material and a sodium-ion battery. The cathode material has both high-voltage resistance performance, high capacity, and cycle stability, improving the comprehensive performance of the cathode material.

[0006] In the first aspect, a cathode material of this application, the cathode material has a sodium-rich structural defect, the sodium-rich defect degree of the cathode material is X, 0.25 ≤ X ≤ 0.7, and X = C1 / (C1 + C2);

[0007] Among them, C1 is the difference in discharge specific capacity of the half-cell between V open and 2.5 V, where V open is the open-circuit voltage of the first charging curve of the half-cell; C2 is the difference in discharge specific capacity between 2.5 V and 2.0 V.

[0008] In some embodiments, the sodium-rich defect degree X of the positive electrode material satisfies: 0.3 ≤ X ≤ 0.6.

[0009] In some embodiments, the positive electrode material includes a layered oxide having a P2-phase structure.

[0010] In some embodiments, the positive electrode material includes a matrix material, and the chemical general formula of the matrix material is N a M b Ni c Fe d Mn e O2, where 0.67 ≤ a ≤ 0.85, 0 ≤ b ≤ 0.5, 0.01 ≤ c ≤ 0.5, 0.01 ≤ d ≤ 0.3, 0.5 ≤ e < 1, and b + c + d + e = 1; M is a metal;

[0011] The crystal structure of the matrix material is a layered oxide having a P2-phase structure, and the crystal structure of the matrix material has the sodium-rich structural defect.

[0012] In some embodiments, when 0.8 ≤ a ≤ 0.85, measured by XRD rays, the positive electrode material has a diffraction peak at 41.4 ± 0.2°.

[0013] In some embodiments, measured by XRD rays, the positive electrode material has diffraction peaks at 15.80 ± 0.5°, 31.95 ± 0.5°, 35.90 ± 0.5°, 36.81 ± 0.5°, 39.45 ± 0.5°, 43.56 ± 0.5°, 48.84 ± 0.5°, 62.08 ± 0.5°, 64.56 ± 0.5°, 66.93 ± 0.5°, 73.87 ± 0.5°, 76.16 ± 0.5°, 78.35 ± 0.5°, and 84.97 ± 0.5°.

[0014] In some embodiments, the positive electrode material further includes a coating layer on the surface of the matrix material, and the coating layer includes at least one of a transition metal oxide and a phosphate.

[0015] In some embodiments, the coating layer includes a phosphate, and the phosphate includes at least one of lithium phosphate, sodium phosphate, potassium phosphate, titanium phosphate, aluminum phosphate, iron phosphate, and ammonium dihydrogen phosphate;

[0016] In some embodiments, the coating layer comprises phosphate, and the mass ratio of the phosphate in the matrix material is 0.05 wt% to 5 wt%.

[0017] In some embodiments, the coating layer comprises a transition metal oxide, and the transition metal in the transition metal oxide includes at least one of Cu, Al, Ti, Zr, Mg, Ta, W, Nb, and B.

[0018] In some embodiments, the coating layer comprises a transition metal oxide, and the mass ratio of the transition metal oxide in the matrix material is 0.05 wt% to 5 wt%.

[0019] In some embodiments, M includes at least one of a transition metal and a rare earth metal.

[0020] In some embodiments, M includes at least one of Cu, Al, Ti, Zr, W, Ta, Co, Mg, Ca, Mo, Nb, and B.

[0021] In some embodiments, the mass content of CO32- in the positive electrode material is ≤ 2 wt%, and the mass content of OH- in the positive electrode material is ≤ 2 wt%.

[0022] In some embodiments, the tap density of the positive electrode material is ≥ 1.6 g / cm3.

[0023] In some embodiments, the specific surface area of the positive electrode material is 0.2 m2 / g to 2 m2 / g.

[0024] In some embodiments, the median particle size D50 of the positive electrode material is 3 μm to 15 μm.

[0025] In some embodiments, the pH value of the positive electrode material is 11 to 13.

[0026] In some embodiments, the mass content of water in the positive electrode material is ≤ 0.05 wt%.

[0027] In some embodiments, the space group of the positive electrode material is P63 / mmc.

[0028] In a second aspect, the present application provides a sodium ion battery, which includes a positive electrode tab, and the positive electrode tab includes the positive electrode material described in the first aspect or the positive electrode material prepared by the method described in the second aspect.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] For the cathode material provided by this application, the ratio of the number of Na positions occupied by surplus Na ions to the total number of Na positions available for Na ion insertion is defined as the sodium-rich defect degree. Controlling the sodium-rich defect degree of the cathode material within an appropriate range can help maintain the crystal structure stability of the cathode material and the structural stability of the cathode material. An appropriate sodium-rich defect degree enables the cathode material to have a higher sodium ion extraction ability, a higher specific capacity, and at the same time can alleviate the irreversible phase change under high voltage caused by the massive extraction of sodium ions during charge and discharge, which is beneficial to maintaining the crystal structure stability of the cathode material and alleviating metal dissolution. As a result, the cathode material has both high-voltage resistance performance, high capacity, and cycle stability, improving the comprehensive performance of the cathode material. Description of the Drawings

[0031] To more clearly illustrate the technical solutions of the embodiments of this application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of this application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0032] Figure 1 It is a schematic flow chart of the preparation method of the cathode material provided by the embodiment of this application.

[0033] Figure 2a It is a scanning electron microscope image of the cathode material prepared in Example 1 of this application.

[0034] Figure 2b It is a charge-discharge curve graph of the battery assembled with the cathode material prepared in Example 1 of this application.

[0035] Figure 2c It is an XRD diffraction pattern of the cathode material prepared in Example 1 of this application.

[0036] Figure 3a It is a scanning electron microscope image of the cathode material prepared in Example 2 of this application.

[0037] Figure 3b It is a charge-discharge curve graph of the battery assembled with the cathode material prepared in Example 2 of this application.

[0038] Figure 4a It is a scanning electron microscope image of the cathode material prepared in Example 3 of this application.

[0039] Figure 4b It is a charge-discharge curve graph of the battery assembled with the cathode material prepared in Example 3 of this application.

[0040] Figure 5a It is a scanning electron microscope image of the cathode material prepared in Comparative Example 1 of this application.

[0041] Figure 5b This is the charge-discharge curve of the battery assembled with the cathode material prepared in Comparative Example 1 of this application. Specific embodiments

[0042] To better understand the technical solution of this application, the embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0043] It should be clear that the described embodiments are only a part of the embodiments of this application, rather than all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of this application.

[0044] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features.

[0045] For easy understanding of the present invention, specific terms are properly defined in this application. Unless otherwise defined herein, the scientific and technical terms used in the present invention have the meanings commonly understood by those skilled in the art to which the present invention pertains.

[0046] Sodium-based layered oxide cathode material is one of the most critical materials for sodium-ion batteries. Similar to lithium cobaltate and ternary structures in lithium batteries, the layered oxide structure has good ion channels, and there may be certain shortcomings in cycle performance, but the average maturity is relatively high. Transition metal oxide NaXMeO2 is an intercalation or insertion compound and theoretically has a high discharge specific capacity, but its cycle performance is poor.

[0047] In the existing sodium-ion battery layered oxide materials, the disadvantages of each type are obvious. For example, the O3-type cathode material has a high capacity, low initial efficiency, and poor cycle performance; the P2-type cathode material has a low first charging capacity, good cycle and rate performance; the P3-type cathode material has a low capacity, poor cycle performance, and a high working voltage, and the comprehensive performance of each type of cathode material is not good.

[0048] Therefore, this application provides a cathode material with a sodium-rich structural defect, and the sodium-rich defect degree of the cathode material is X, where 0.25 ≤ X ≤ 0.7, and X = C1 / (C1 + C2);

[0049] where C1 is the difference in discharge specific capacity between V open and 2.5V in the half-cell, where V open is the open-circuit voltage of the first charging curve of the half-cell; C2 is the difference in discharge specific capacity between 2.5V and 2.0V.

[0050] The cathode material provided by the present application can help maintain the crystal structure stability of the cathode material and the structural stability of the cathode material. An appropriate degree of sodium-rich defects enables the cathode material to have a higher sodium ion extraction ability, a higher specific capacity, and at the same time can alleviate the irreversible phase change under high voltage caused by the large amount of sodium ion extraction during charge and discharge, which is beneficial to maintaining the crystal structure stability of the cathode material and alleviating metal dissolution. As a result, the cathode material has both high-voltage resistance performance, high capacity and cycle stability, improving the comprehensive performance of the cathode material.

[0051] In the technical solution of the present application, the ratio of the number of Na positions occupied by surplus Na ions to the total number of Na positions available for Na ion insertion is defined as the sodium-rich defect degree X.

[0052] The degree of sodium-rich defects in the cathode material is closely related to the ability of the material to insert and extract Na ions during charge and discharge, and it can be characterized by the relative relationship of specific capacity in the measured C-V curve. The specific capacity of the measured C-V curve is directly related to the number of inserted and extracted Na ions. The most important feature of the P2-type material is that it can additionally insert sodium ions (the typical P2 material has a Na content of 0.67, and 0.33 Na ions can be additionally inserted in the half-cell). The capacity intervals corresponding to the additionally inserted Na are all reflected in the discharge curve between 2.0-V 开 interval (where 2.0-2.5V corresponds to the additional sodium insertion in the ideal P2 structure, corresponding to the redox reaction of Mn 4+ →Mn 3+ . 2.5V~V 开 corresponds to the additional sodium insertion with structural distortion, which is different from the original P2-type prism structure. The main corresponding redox reaction is Ni 3+ →Ni 2+ ). Therefore, the inventor of the present application found that the degree of sodium-rich defects can be reflected indirectly through the correlation between these two capacity intervals. In particular, the degree of sodium-rich defects represents the ratio of the lattice distortion defects caused by the additional Na ions to the total number of sodium ions that can be additionally inserted. According to the algorithm, when the sodium-rich defects in the cathode material increase, the specific capacity of the C1 segment increases, the specific capacity of the C2 segment decreases, and the value of x increases; conversely, when the sodium-rich defects decrease, C1 decreases, C2 increases, and the value of x decreases. The monotonicity of X is consistent with the monotonicity of the degree of sodium-rich defects and can be used as an index for the degree of sodium-rich defects.

[0053] In the present invention, the degree of sodium-rich and deficiency of the cathode material is calculated by testing the interval specific capacities C1 and C2 in the first-cycle discharge curve of the coin cell assembled with this cathode material. The specific coin cell manufacturing process and test conditions are known to those skilled in the art. For example, the manufacturing process of its cathode electrode sheet is the same as that of the lithium-ion cathode electrode sheet, and the mass ratio of the active material, PVDF (5130), and conductive carbon is 90:5:5; its coin cell manufacturing process is also basically the same as that of the lithium-ion coin cell, except that the electrolyte is replaced with NaPF6-DIGLYME electrolyte, the separator uses a glass fiber separator, and the negative electrode sheet is replaced with a commercial sodium sheet. The test is carried out using a Neware tester in the voltage range of 2.0 - 4.1V at a charge-discharge rate of 0.1C to obtain the required C-V curve graph.

[0054] Specifically, the cathode material, polyvinylidene fluoride, and conductive carbon are dispersed in N-methylpyrrolidone according to a mass ratio of 90:5:5 to prepare a cathode slurry with a solid content of 50%. After coating on an aluminum foil and drying, it is used as the cathode sheet. A sodium sheet is used as the negative electrode sheet, the separator is a glass fiber membrane, and the electrolyte is sodium hexafluorophosphate - diethylene glycol dimethyl ether (NaPF6 concentration is 1mol / L) to assemble a coin cell. Charge-discharge tests are carried out at 2.0V - 4.1V and a rate of 0.1C, and record the discharge specific capacity difference between V 开 to 2.5V during the first discharge process of the coin cell as C1, and the discharge specific capacity difference from 2.5V to 2.0V as C2, X = C1 / (C1 + C2).

[0055] It can be understood that the discharge specific capacity difference at different voltages can correspondingly characterize the number of sodium ions extracted and inserted within this voltage range.

[0056] The sodium-rich defect degree of the cathode material is X, 0.25 ≤ X ≤ 0.7. The specific values of X can be 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, or 0.7, etc. Of course, it can also be other values within the above range, which are not limited herein. An appropriate degree of sodium-rich defect enables the cathode material to have a higher ability to extract Na ions, a higher specific capacity, and at the same time can alleviate the irreversible phase change at high voltages caused by the large amount of Na ions extracted during charge and discharge, which is beneficial to maintaining the crystal structure stability of the cathode material and alleviating metal dissolution. When the sodium-rich defect degree is too large, excessive defects will hinder the extraction and insertion of sodium ions, resulting in deterioration of the capacity performance of the cathode material and poor cycle performance. In addition, when the sodium-rich defect degree is too large, the residual alkali on the material surface will increase, affecting the processing performance of the material.

[0057] In some embodiments, 0.3 ≤ X ≤ 0.6.

[0058] In some embodiments, the positive electrode material includes a layered oxide having a P2-phase structure.

[0059] In some embodiments, the positive electrode material includes a matrix material, and the chemical general formula of the matrix material is Na a M b Ni c Fe d Mn e O2, where 0.67 ≤ a ≤ 0.85, 0 ≤ b ≤ 0.5, 0.01 ≤ c ≤ 0.5, 0.01 ≤ d ≤ 0.3, 0.5 ≤ e < 1, and b + c + d + e = 1; M is a metal;

[0060] The crystal structure of the matrix material is a layered oxide with a P2 phase, and the crystal structure of the matrix material has a sodium-rich structural defect.

[0061] Specifically, the value of a can be, for example, 0.67, 0.69, 0.70, 0.72, 0.75, 0.79, 0.82, or 0.85, etc. When the molar content of Na in the positive electrode material is within the above range, the battery using this positive electrode material has a relatively high charge-discharge specific capacity; when the molar content of Na in the positive electrode material is relatively low, the specific capacity of the battery decreases, and the energy density drops, resulting in a significant decline in electrochemical performance. When the molar content of Na in the positive electrode material is relatively high, excess residual alkali will form on the material surface, and it is very easy to form a jelly-like state during the preparation of the slurry, affecting the coating effect; secondly, the influence of the residual alkali on the electrochemical performance is mainly reflected in increasing the irreversible capacity loss and deteriorating the cycle performance at the same time.

[0062] The value of b can be, for example, 0.01, 0.05, 0.08, 0.1, 0.15, 0.16, 0.18, 0.2, 0.3, 0.4, 0.45, or 0.5, etc., the value of c can be, for example, 0.01, 0.05, 0.08, 0.1, 0.15, 0.16, 0.18, 0.2, 0.3, 0.4, 0.45, or 0.5, etc., the value of d can be, for example, 0.01, 0.05, 0.08, 0.1, 0.15, 0.16, 0.18, 0.2, 0.28, or 0.3, etc., and are not limited here. The value of e can be, for example, 0.5, 0.6, 0.7, 0.75, 0.79, 0.83, 0.87, 0.9, or 0.95, etc.

[0063] In some embodiments, M includes at least one of transition metals and rare earth metals.

[0064] In some embodiments, M includes at least one of Cu, Al, Ti, Zr, W, Ta, Co, Mg, Ca, Mo, Nb, and B.

[0065] When the total molar content of Ni, Fe, Mn and M in the cathode material is within the above range, the battery has good electrochemical performance.

[0066] In some embodiments, the crystal structure of the matrix material is a layered oxide with a P2-phase structure, and there are sodium-rich structural defects in the crystal structure of the matrix material.

[0067] In the crystal structure of Na a M b Ni c Fe d Mn e O 2+f In the crystal structure, Ni, Fe, and Mn respectively form octahedral structures with neighboring oxygen atoms. M metals are doped between multiple octahedral structures to form a transition metal layer. Oxygen atoms and sodium ions in adjacent transition metal layers form a triangular prism structure, thereby forming a layered structure. Introducing a high sodium content into the P2-phase structure will reduce the average valence state of transition metal ions in the crystal structure, promote the transition of the transition metal with the lowest oxidation state in the crystal structure to its higher valence state, and achieve a higher specific capacity. The extra sodium ions brought by the sodium-rich defects can alleviate the tendency of the cathode to undergo a phase change in the high sodium extraction state during the large-scale extraction of sodium ions, thereby improving the structural stability of the cathode material.

[0068] In the crystal structure of the matrix material, Na ions are embedded in the Na positions. The Na positions available for Na ions to be embedded in the crystal structure are constant. Occupying the Na positions by surplus Na ions will bring lattice distortion defects, that is, the Na positions jointly occupied by surplus Na ions will cause the phenomenon of sodium-rich defects.

[0069] In some embodiments, the space group of the cathode material is P63 / mmc.

[0070] In some embodiments, the cathode material further includes a coating layer on the surface of the matrix material, and the coating layer includes at least one of transition metal oxides and phosphates.

[0071] In some embodiments, the phosphate includes at least one of lithium phosphate, sodium phosphate, potassium phosphate, titanium phosphate, aluminum phosphate, iron phosphate, and ammonium dihydrogen phosphate.

[0072] The phosphate in the coating layer not only has high sodium ion conductivity, inhibits the corrosion of the matrix material by the electrolyte, but also is conducive to the formation of a spatial sodium ion conductive network.

[0073] In some embodiments, the transition metal includes at least one of Cu, Al, Ti, Zr, Mg, Ta, W, Nb, and B;

[0074] In some embodiments, the mass percentage of the transition metal oxide in the matrix material is 0.05 wt% to 5 wt%, specifically it can be 0.05 wt%, 0.1 wt%, 0.3 wt%, 0.5 wt%, 0.7 wt%, 0.9 wt%, 1.0 wt%, 2.0 wt%, 3.0 wt%, 4.0 wt% or 5.0 wt% etc., and of course it can also be other values within the above range. Preferably, the mass percentage of the transition metal oxide in the matrix material is 0.05 wt% to 2 wt%.

[0075] In some embodiments, the mass percentage of the phosphate in the matrix material is 0.05 wt% to 5 wt%, specifically it can be 0.05 wt%, 0.1 wt%, 0.3 wt%, 0.5 wt%, 0.7 wt%, 0.9 wt%, 1.0 wt%, 2.0 wt%, 3.0 wt%, 4.0 wt% or 5.0 wt% etc., and of course it can also be other values within the above range. Preferably, the mass percentage of the phosphate in the matrix material is 0.05 wt% to 2 wt%.

[0076] In some embodiments, CO3 in the positive electrode material 2- has a mass content of ≤ 2 wt%, specifically it can be 0.1 wt%, 0.3 wt%, 0.5 wt%, 0.7 wt%, 0.9 wt%, 1.0 wt%, 1.2 wt%, 1.5 wt%, 1.8 wt% or 2 wt% etc., and of course it can also be other values within the above range. Preferably, the mass content of CO3 in the positive electrode material 2- is ≤ 1 wt%.

[0077] In some embodiments, OH in the positive electrode material - has a mass content of ≤ 2 wt%, specifically it can be 0.1 wt%, 0.3 wt%, 0.5 wt%, 0.7 wt%, 0.9 wt%, 1.0 wt%, 1.2 wt%, 1.5 wt%, 1.8 wt% or 2 wt% etc., and of course it can also be other values within the above range. Preferably, the mass content of OH in the positive electrode material - is ≤ 1 wt%.

[0078] In some embodiments, the median particle size D of the positive electrode material 50 is from 3 μm to 15 μm, specifically it can be 3 μm, 3.5 μm, 4 μm, 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm or 15 μm etc., and of course it can also be other numerical values within the above range, which are not limited herein. Controlling the particle size of the positive electrode material within the above range is beneficial to improving the structural stability, thermal stability and long cycle stability of the positive electrode material. Preferably, the median particle size D of the positive electrode material 50is from 5 μm to 10 μm.

[0079] In some embodiments, the particle size distance of the positive electrode material satisfies (D 90 -D 10 ) / D 50 ≤ 1.5, specifically it can be 1.5, 1.4, 1.3, 1.2, 1.1, 0.9, 0.8, 0.5, 0.3, 0.1, etc., which are not limited herein. Preferably, (D 90 -D 10 ) / D 50 ≤ 1.2.

[0080] It should be noted that the volume-based cumulative particle size distribution measured by the laser diffraction method is used, and D 10 represents the particle size corresponding to when the cumulative particle size distribution percentage of the powder reaches 10%, and D 50 represents the particle size corresponding to when the cumulative particle size distribution percentage reaches 50%, and D 90 represents the particle size corresponding to when the cumulative particle size distribution percentage reaches 90%.

[0081] In some embodiments, the specific surface area of the positive electrode material is 0.2 m 2 / g to 2 m 2 / g. Specifically, it can be 0.2 m 2 / g, 0.4 m 2 / g, 0.5 m 2 / g, 0.6 m 2 / g, 0.7 m 2 / g, 1.2 m 2 / g, 1.5 m 2 / g, 1.6 m 2 / g, 1.8 m 2 / g or 2.0 m 2 / g, etc. When the specific surface area of the positive electrode material is controlled within the above range, it is beneficial to improve the cycle performance of the battery made of this positive electrode material.

[0082] In some embodiments, the tap density of the positive electrode material ≥ 1.6 g / cm 3 , specifically it can be 1.6 g / cm 3 , 1.7 g / cm 3 , 1.8 g / cm 3 , 1.85 g / cm 3 , 1.9 g / cm 3 , 1.95 g / cm 3 or 2.0 g / cm 3etc. When the tap density of the positive electrode material is controlled within the above range, it is beneficial to improve the energy density of the battery made of the positive electrode material. Preferably, the tap density of the positive electrode material ≥ 1.8 g / cm 3 .

[0083] In some embodiments, the pH value of the positive electrode material is 11 - 13; specifically, it can be 11.5, 11.9, 12.1, 12.3, 12.5, 12.7, 12.9 or 13, etc. Of course, it can also be other values within the above range.

[0084] In some embodiments, the mass content of water in the positive electrode material ≤ 0.05 wt%, specifically, it can be 0.01 wt%, 0.02 wt%, 0.03 wt%, 0.04 wt% or 0.05 wt%, etc. Of course, it can also be other values within the above range. Controlling the water content of the positive electrode material is beneficial to inhibiting the content of residual alkali and improving the processing performance of the material. Preferably, the mass content of water in the positive electrode material ≤ 0.03 wt%.

[0085] In some embodiments, measured by XRD rays, the positive electrode material has diffraction peaks at 15.80 ± 0.5°, 31.95 ± 0.5°, 35.90 ± 0.5°, 36.81 ± 0.5°, 39.45 ± 0.5°, 43.56 ± 0.5°, 48.84 ± 0.5°, 62.08 ± 0.5°, 64.56 ± 0.5°, 66.93 ± 0.5°, 73.87 ± 0.5°, 76.16 ± 0.5°, 78.35 ± 0.5° and 84.97 ± 0.5°.

[0086] In some embodiments, measured by XRD rays, the positive electrode material has diffraction peaks at 15.80 ± 0.2°, 31.95 ± 0.2°, 35.90 ± 0.2°, 36.81 ± 0.2°, 39.45 ± 0.2°, 43.56 ± 0.2°, 48.84 ± 0.2°, 62.08 ± 0.2°, 64.56 ± 0.2°, 66.93 ± 0.2°, 73.87 ± 0.2°, 76.16 ± 0.2°, 78.35 ± 0.2°, 84.97 ± 0.2°.

[0087] In some embodiments, when 0.8 ≤ a ≤ 0.85, measured by XRD rays, the positive electrode material has a diffraction peak at 41.4 ± 0.2°.

[0088] The embodiment of the present application provides a preparation method of a positive electrode material, as Figure 1 shown, including the following steps:

[0089] Step S10: Mix a nickel-iron-manganese-based precursor, a sodium salt, and a dopant containing element M to obtain a mixture. Among them, the ratio of the total molar amount of Ni, Fe, and Mn to the molar amount of sodium is 1:(0.67 - 0.85), and M is a metal.

[0090] Step S20: Perform a primary sintering treatment on the mixture in an oxygen-containing atmosphere to obtain a cathode material. Among them, control the ratio of the oxygen content in the oxygen-containing atmosphere in the heating section to the oxygen content in the heat preservation section during the sintering treatment to be (0.4 - 0.65):1. The sodium-rich defect degree of the cathode material is X, and 0.25 ≤ X ≤ 0.7.

[0091] In the above technical solution, by controlling the ratio of the total molar amount of Ni, Fe, and Mn to the molar amount of sodium, and the ratio of the oxygen content in the heating section and the heat preservation section during the sintering treatment, the sodium-rich defect degree X of the cathode material is controlled to satisfy 0.25 ≤ X ≤ 0.7. Thus, the crystal structure stability of the sodium-rich cathode material can be better guaranteed. An appropriate sodium-rich defect degree can also enable the cathode material to have more ability to release sodium ions, have a higher specific capacity, and at the same time can alleviate the irreversible phase change at high voltage caused by the large amount of sodium ions released during charge and discharge, which is beneficial to maintaining the crystal structure stability of the cathode material and alleviating metal dissolution. Therefore, the cathode material has both high-voltage resistance performance, high capacity, and cycle stability, improving the comprehensive performance of the cathode material.

[0092] The following specifically introduces the preparation method of the present application in combination with embodiments:

[0093] Step S10: Mix a nickel-iron-manganese-based precursor, a sodium salt, and a dopant containing element M to obtain a mixture.

[0094] In some embodiments, the nickel-iron-manganese-based precursor includes at least one of a nickel-iron-manganese-based composite oxide and a nickel-iron-manganese-based hydroxide.

[0095] In some embodiments, the chemical general formula of the nickel-iron-manganese-based precursor is Ni c Fe d Mne(OH)2, where 0.01 ≤ c ≤ 0.5, 0.01 ≤ d ≤ 0.3, and 0.5 ≤ e < 1.

[0096] In some embodiments, the sodium salt includes at least one of anhydrous sodium carbonate, sodium carbonate monohydrate, sodium carbonate decahydrate, sodium bicarbonate, and sodium sulfate.

[0097] In some embodiments, the dopant containing element M includes at least one of an oxide of element M, a sulfide of element M, a nitride of element M, and a hydroxide of element M.

[0098] In some embodiments, the addition amount of the dopant containing element M satisfies that the molar amount of M accounts for 0 mol% to 50 mol% in the total molar amount of Ni, Fe and Mn; specifically, it can be 1 mol%, 2 mol%, 5 mol%, 10 mol%, 15 mol%, 20 mol%, 25 mol%, 30 mol%, 35 mol% or 50 mol% etc., which is not limited herein.

[0099] In some embodiments, M includes at least one of transition metals and rare earth metals.

[0100] In some embodiments, M includes at least one of Cu, Al, Ti, Zr, W, Ta, Co, Mg, Ca, Mo, Nb and B.

[0101] In some embodiments, the mixing conditions for obtaining the mixture are: dry grinding at 10°C to 50°C for 0.3 h to 2 h. The grinding temperature can specifically be 10°C, 20°C, 30°C, 40°C, 45°C or 50°C etc., and the grinding time can specifically be 0.3 h, 0.5 h, 1 h, 1.5 h, 1.8 h or 2 h.

[0102] In some embodiments, the mixing conditions for obtaining the mixture are: placing the raw materials in a mechanical mixing device.

[0103] In some embodiments, the mixing conditions for obtaining the mixture are: placing the raw materials in a high-speed mixer, controlling the linear speed of the high-speed mixer to be 5 m / s to 20 m / s, and the mixing time to be 1 min to 30 min.

[0104] In some embodiments, the mechanical mixing device is at least one of a ball mill, a three-dimensional mixer, a high-speed mixer and a VC mixer.

[0105] Step S20, performing a primary sintering treatment on the mixture in an oxygen-containing atmosphere to obtain a cathode material, wherein the ratio of the oxygen content in the oxygen-containing atmosphere in the heating section to the oxygen content in the holding section during the sintering treatment is controlled to be (0.4 to 0.65):1, and the sodium-rich defect degree of the cathode material is X, 0.25 ≤ X ≤ 0.7.

[0106] In some embodiments, the ratio of the oxygen content in the oxygen-containing atmosphere in the heating section to the oxygen content in the holding section during the sintering treatment can specifically be 0.4:1, 0.45:1, 0.48:1, 0.5:1, 0.55:1, 0.58:1, 0.61:1 or 0.65:1 etc. Of course, it can also be other values within the above range, which is not limited herein.

[0107] In some embodiments, during the primary sintering process, the oxygen content in the oxygen-containing atmosphere in the heating stage is controlled to be 40% - 60%, specifically it can be 40%, 42%, 45%, 48%, 50%, 52%, 55%, 58% or 60% etc., which is not limited herein. Preferably, the oxygen content in the oxygen-containing atmosphere in the heating stage is 50% - 60%. By controlling the oxygen content in the heating stage, it is beneficial for sodium ions to enter the lattice as much as possible. When the oxygen content is too high, the transition metal elements in the precursor tend to be in an oxidized state, the overall valence state increases, the binding ability between the transition metal and oxygen atoms in the crystal structure becomes stronger, the crystallization intensity of the P2-phase crystal structure is enhanced, and the binding ability between oxygen atoms and sodium ions becomes weaker, thereby hindering the entry of surplus sodium ions into the lattice.

[0108] In some embodiments, the heating rate in the heating stage is 3°C / min - 5°C / min, specifically it can be 3°C / min, 3.5°C / min, 4°C / min, 4.5°C / min or 5°C / min etc., which is not limited herein.

[0109] In some embodiments, during the primary sintering process, the oxygen content in the oxygen-containing atmosphere in the holding stage is controlled to be 80% - 100%, specifically it can be 80%, 82%, 85%, 88%, 90%, 92%, 95%, 98% or 100% etc., which is not limited herein. Preferably, the oxygen content in the oxygen-containing atmosphere in the holding stage is controlled to be 90% - 100%. In the holding stage, the crystal structure of the material is gradually completed and optimized. By increasing the oxygen content in the sintering atmosphere, sodium ions compete for the sodium positions in the crystal structure, resulting in a sodium-rich defect phenomenon.

[0110] In some embodiments, during the primary sintering process, the oxygen content in the oxygen-containing atmosphere in the cooling stage is controlled to be 20% - 25%. Preferably, during the primary sintering process, the cooling stage is controlled to use an air atmosphere, which can reduce costs.

[0111] In some embodiments, the temperature of the primary sintering process is 800°C - 950°C; specifically it can be 800°C, 820°C, 850°C, 870°C, 880°C, 900°C, 920°C or 950°C etc., and of course it can also be other values within the above range, which is not limited herein.

[0112] In some embodiments, the time of the primary sintering process is 12h - 24h, specifically it can be 12h, 14h, 15h, 18h, 20h, 22h or 24h etc., and of course it can also be other values within the above range, which is not limited herein.

[0113] In some embodiments, the oxygen-containing atmosphere includes at least one of air and oxygen.

[0114] In some embodiments, the method further includes:

[0115] Step S30: Mix at least one of phosphate and transition metal oxide with the primary sintering product, and subject the mixed product to secondary sintering to obtain a cathode material.

[0116] In some embodiments, during the mixing process of the primary sintering product with phosphate and transition metal oxide, the mixing time is 0.3 h to 2.0 h. For example, it can be 0.3 h, 0.4 h, 0.5 h, 0.7 h, 0.8 h, 1.0 h, 1.2 h, 1.5 h or 2.0 h, etc., but is not limited to the listed values, and other unlisted values within this range are also applicable. The mixing temperature is 10°C to 50°C, such as 10°C, 15°C, 25°C, 30°C, 35°C, 40°C, 45°C or 50°C, etc. Preferably, the mixing temperature is 10°C to 40°C. Through multiple experiments, the inventors found that under these mixing conditions, the mixture can be fully and evenly mixed, and side reactions of the mixed raw materials caused by excessive temperature can be prevented.

[0117] In some embodiments, the temperature of the secondary sintering treatment is 300°C to 850°C. Specifically, it can be 300°C, 400°C, 550°C, 600°C, 650°C, 700°C, 750°C or 850°C, etc. Of course, it can also be other values within the above range, which are not limited herein. Preferably, the temperature of the secondary sintering treatment is 350°C to 850°C. Through multiple experiments, the inventors found that within this sintering temperature range, the phosphate can be more evenly and firmly coated on the surface of the primary sintering product. At the same time, it is beneficial for the phosphate to react with the residual sodium on the surface of the primary sintered material, reduce the formation of residual alkali to form high-sodium-ion-conducting phosphate compounds, improve the processing performance and rate performance, and prevent the sintered product from decomposing and sodium from precipitating.

[0118] In some embodiments, the time of the secondary sintering treatment is 4 h to 10 h. Specifically, it can be 4 h, 5 h, 6 h, 7 h, 8 h, 9 h or 10 h, etc. Of course, it can also be other values within the above range, which are not limited herein. Preferably, the time of the secondary sintering treatment is 5 h to 8 h.

[0119] In some embodiments, the oxygen-containing atmosphere includes at least one of air, oxygen and nitrogen.

[0120] In some embodiments, the phosphate includes at least one of lithium phosphate, sodium phosphate, potassium phosphate, titanium phosphate, aluminum phosphate, iron phosphate and ammonium dihydrogen phosphate. Exemplarily, lithium phosphate can be LiH2PO4 and Li3PO4.

[0121] Among them, the average particle size of the phosphate is less than 10 μm. For example, it can be 0.01 μm, 0.1 μm, 1 μm, 2 μm, 4 μm, 5 μm, 8 μm, 9 μm, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0122] In some embodiments, the mass percentage of the phosphate in the primary sintered product is 0.05 wt% to 5 wt%.

[0123] In some embodiments, the transition metal includes at least one of Cu, Al, Ti, Zr, Mg, Ta, W, Nb, and B; specifically, it can be 0.05 wt%, 0.1 wt%, 0.3 wt%, 0.5 wt%, 0.7 wt%, 0.9 wt%, 1.0 wt%, 2.0 wt%, 3.0 wt%, 4.0 wt%, or 5.0 wt%, etc. Of course, it can also be other values within the above range. Preferably, the mass percentage of the phosphate in the matrix material is 0.05 wt% to 2 wt%.

[0124] In some embodiments, the mass percentage of the transition metal oxide in the matrix material is 0.05 wt% to 5 wt%; specifically, it can be 0.05 wt%, 0.1 wt%, 0.3 wt%, 0.5 wt%, 0.7 wt%, 0.9 wt%, 1.0 wt%, 2.0 wt%, 3.0 wt%, 4.0 wt%, or 5.0 wt%, etc. Of course, it can also be other values within the above range. Preferably, the mass percentage of the transition metal oxide in the matrix material is 0.05 wt% to 2 wt%.

[0125] In some embodiments, the secondary sintering is carried out in air and / or oxygen.

[0126] In some embodiments, the method further includes:

[0127] Shaping the product after secondary sintering, and the shaping includes at least one of crushing, grinding, ball milling, or classification air crushing.

[0128] The median particle size range of the shaped cathode material is 3 μm to 15 μm. Exemplarily, grinding the sintered product can effectively control the particle size to make it reach the expected particle size range. Within this pore size range, not only can the penetration of the electrolyte be ensured, the impedance of the cathode active material be reduced, the low-temperature performance and rate performance of the material be improved, but also the volume energy density of the battery will not be affected.

[0129] The embodiment of the present application further provides a sodium ion battery, which includes a positive electrode sheet, a negative electrode sheet, a separator, a non-aqueous electrolyte, and a housing. The positive electrode sheet includes a current collector and a positive active material coated on the current collector. The positive active material includes the positive electrode material as described above or the positive electrode material prepared by the preparation method of the positive electrode material as described above, a conductive agent, and a binder.

[0130] In some embodiments, the conductive agent is one of conductive carbon black, Ketjen black, graphite, and acetylene black.

[0131] In some embodiments, the binder is one of sodium carboxymethyl cellulose, cyclodextrin, and polyvinylidene fluoride.

[0132] In some embodiments, the solvent in the positive active material is selected from one of deionized water, N-methylpyrrolidone, and N,N-dimethylformamide.

[0133] The embodiments of the present invention will be further described in multiple embodiments below. Among them, the embodiments of the present invention are not limited to the following specific embodiments. Within the scope of the main rights unchanged, appropriate changes can be made for implementation.

[0134] Test method:

[0135] (1) Test on the sodium-rich defect degree and electrochemical performance of the positive electrode material

[0136] Disperse the positive electrode material, polyvinylidene fluoride, and conductive carbon in a mass ratio of 90:5:5 in N-methylpyrrolidone to prepare a positive electrode slurry with a solid content of 50%. Coat it on an aluminum foil and dry it to obtain a positive electrode sheet. Use a sodium sheet as the negative electrode sheet, a glass fiber membrane as the separator, and sodium hexafluorophosphate-diethylene glycol dimethyl ether (NaPF6 concentration is 1 mol / L) as the electrolyte to assemble a coin cell. Perform charge and discharge tests at 2.0V to 4.1V and a 0.1C rate, and record the difference in discharge specific capacity between V 开 to 2.5V during the first discharge process of the coin cell as C1, and the difference in discharge specific capacity between 2.5V and 2.0V as C2, X = C1 / (C1 + C2).

[0137] Use a LAND battery test system to perform discharge specific capacity, first Coulomb efficiency, and rate performance tests at 25°C, 2.0V to 4.1V, and a 0.1C rate. Set the reference capacity to 100 mA / g, and the current density corresponding to 0.1C is 10 mA / g.

[0138] (2) Test on the alkaline impurities of the positive electrode material:

[0139] The content of alkaline impurities on the surface of the cathode material is a characteristic of the material surface, which can be quantitatively measured by analyzing the reaction products between the surface and water. If the cathode material powder is immersed in water, a surface reaction occurs. During the reaction, the pH of the water increases (as the alkaline impurities dissolve), and the alkali content is quantified by pH titration. The result of the titration is the content of alkaline impurities. The content of alkaline impurities can be measured as follows: Immerse 5.0 g of the cathode material powder in 100 ml of deionized water and stir for 10 minutes in a sealed glass flask. After stirring to dissolve the alkali, filter the suspension of the powder in water to obtain a clear solution. Then, while stirring, titrate 90 ml of the clear solution by recording the pH curve during the addition of 0.1 M HCl at a rate of 0.5 ml / min until the pH reaches 3. By titrating a suitable mixture of NaOH and Na2CO3 dissolved in deionized water at a low concentration, a reference voltage curve is obtained. In almost all cases, two different plateaus are observed. The upper plateau with an end point y1 (in ml) between pH 8 and 9 is the equilibrium of OH - / H2O, followed by the equilibrium of CO3 2- / HCO3 - , and the lower plateau with an end point y2 (in ml) between pH 4 and 6 is the equilibrium of HCO3 - / H2CO3. The inflection points y1 between the first and second plateaus and y2 after the second plateau are obtained from the corresponding minimum values of the derivative dpH / dVol of the pH curve. The second inflection point is generally close to pH 4.7. Then the results are expressed as weight percentages of OH - and CO3 2- as shown in the following formulas (3) and (4):

[0140]

[0141]

[0142] (3) XRD test of the cathode material:

[0143] When performing the XRD test on the material, Cu-Kα rays are used as the ray source for the X-rays, and the test conditions are at 10 - 90° (2θ) with a scanning step of 0.05°.

[0144] (4) Test method for the specific surface area of the cathode material:

[0145] It is tested using the JW-DX dynamic specific surface area rapid determination instrument of Beijing Jingwei Gaobo Science and Technology Co., Ltd., and the unit is m 2 / g.

[0146] (5) Test method for the tap density of the cathode material:

[0147] Using a BET shaker, a certain amount of the sample was weighed and the tapped density was tested at 300 times / min for 3000 vibrations. (6) Test method for the particle size of the cathode material:

[0148] The particle size distribution range of the composite anode material was tested by a Malvern laser particle size analyzer.

[0149] (7) Test method for SEM of the cathode material:

[0150] Scanning electron microscopy characterization was carried out on a transmission electron microscope at an operating voltage of 200 kV to observe the structure of the cathode material. (8) Test method for the water content of the cathode material:

[0151] The cathode sample was heated in a furnace, and the water evaporated into water vapor, which was transferred by a dried carrier gas to the titration cup of a moisture analyzer for determination. In the titration cup, iodine ions were electrolytically generated, and water reacted with the iodine ions. The water content was measured by measuring the charge used to generate the iodine ions.

[0152] (9) Test method for the pH of the cathode material:

[0153] 10 wt% of the cathode material powder was dispersed in water, and the pH value of the supernatant was measured by a pH meter after ultrasonic treatment.

[0154] (10) Electrochemical performance test:

[0155] Using a LAND battery test system, capacity, initial Coulomb efficiency, and rate performance tests were carried out at 25 °C and 2.0 V to 4.1 V. The reference capacity was set to 200 mA / g, and 1 C corresponded to a current density of 200 mA / g.

[0156] Example 1

[0157] A method for preparing a cathode material, comprising the following steps:

[0158] (1) 3.13 kg of anhydrous sodium carbonate, 7.2 kg of a nickel-iron-manganese-based precursor prepared by a coprecipitation method (where the molar ratio of Ni:Fe:Mn is 1:1:2, and n Ni+Fe+Mn : n Na = 1:0.74), and a doping element precursor (5 mol% of copper oxide, 2.5 mol% of aluminum oxide) were mixed uniformly by a high-speed mixer to obtain a mixture.

[0159] (2) In a box-type atmosphere furnace, in an atmosphere with an oxygen content of 50%, the mixture was heated at a heating rate of 4 °C / min to 850 °C, and then the atmosphere oxygen content was adjusted to 95%. High-temperature calcination was carried out at 850 °C for 15 hours. During the cooling process, the atmosphere was adjusted to air, and after crushing and sieving, the matrix material was obtained.

[0160] (3) Place the layered matrix material, 1 wt% titanium oxide, 0.5 wt% copper oxide, and 0.5 wt% ammonium dihydrogen phosphate in a high-speed mixer and mix evenly to obtain a mixed material.

[0161] (4) Sinter the mixed material in a box-type atmosphere furnace at 700 °C for 8 h. The sintering atmosphere is air. After crushing and sieving, a positive electrode material is obtained.

[0162] Figure 2a This is the scanning electron microscope image of the positive electrode material prepared in this example, as Figure 2a shown. The positive electrode material includes a matrix material and a coating layer on the surface of the matrix material. The general formula of the matrix material is Na 0.704 M 0.1 Ni 0.2 Fe 0.2 Mn 0.5 O2, where M = Cu, Al. The coating layer includes titanium oxide, copper oxide, and ammonium dihydrogen phosphate. The positive electrode material is a secondary particle. The tap density of the positive electrode material is 1.9 g / cm 3 , the specific surface area is 0.9 m 2 / g, the median particle size D 50 is 7 μm, the pH value is 12.7, and the mass content of water in the positive electrode material is 0.016 wt%.

[0163] Figure 2b This is the charge-discharge curve of the battery assembled with the positive electrode material prepared in the example of this application, as Figure 2b shown. V 开 = 2.83 V, C1 = 16.93 mAh / g, C2 = 17.5 mAh / g, and the sodium-rich defect degree X of the positive electrode material is 0.49.

[0164] Figure 2c This is the XRD diffraction pattern of the positive electrode material prepared in Example 1 of this application, as Figure 2c shown. Measured by XRD rays, the positive electrode material has diffraction peaks at 15.80 ± 0.5°, 31.95 ± 0.5°, 35.90 ± 0.5°, 36.81 ± 0.5°, 39.45 ± 0.5°, 43.56 ± 0.5°, 48.84 ± 0.5°, 62.08 ± 0.5°, 64.56 ± 0.5°, 66.93 ± 0.5°, 73.87 ± 0.5°, 76.16 ± 0.5°, 78.35 ± 0.5°, and 84.97 ± 0.5°.

[0165] Example 2

[0166] A method for preparing a positive electrode material, comprising the following steps:

[0167] (1) Mix 2.98 kg of anhydrous sodium carbonate, 7.2 kg of nickel-iron-manganese-based precursor prepared by the coprecipitation method (where the molar ratio of Ni:Fe:Mn is 5:6:9, and n Ni+Fe+Mn : n Na = 1:0.703), and doping element precursors (5 mol% of magnesium oxide, 5 mol% of titanium oxide) uniformly through a high-speed mixer to obtain a mixture.

[0168] (2) In a box-type atmosphere furnace, under an atmosphere with an oxygen content of 40%, heat the mixture at a heating rate of 5 °C / min to 900 °C, then adjust the atmosphere oxygen content to 90%, and conduct high-temperature calcination at 900 °C for 12 hours. During the cooling process, adjust the atmosphere to air. After crushing and sieving, obtain the matrix material.

[0169] (3) Place the core-layered matrix material, 1 wt% of boron oxide, 0.5 wt% of copper oxide, and 0.5 wt% of titanium oxide in a high-speed mixer and mix them evenly to obtain a mixed material.

[0170] (4) Sinter the mixed material in a box-type atmosphere furnace at 400 °C for 6 h. The sintering atmosphere is air. After crushing and sieving, obtain the positive electrode material.

[0171] Figure 3a This is the scanning electron microscope image of the positive electrode material prepared in this example. As Figure 3a shown, the positive electrode material includes a matrix material and a coating layer located on the surface of the matrix material. The general formula of the matrix material is Na 0.67 M 0.1 Ni 0.25 Fe 0.2 Mn 0.45 O2, M = Mg, Ti. The coating layer includes boron oxide, copper oxide, and titanium oxide. The positive electrode material is a secondary particle. The tap density of the positive electrode material is 2.0 g / cm 3 , the specific surface area is 0.4 m 2 / g, the median particle size D 50 is 5 μm, the pH value is 12.5, and the mass content of water in the positive electrode material is 0.034 wt%.

[0172] Figure 3b This is the charge-discharge curve graph of the battery assembled with the positive electrode material prepared in the embodiment of this application. As Figure 3b shown, V 开 = 2.82 V, C1 = 9.81 mAh / g, C2 = 21.34 mAh / g, and the sodium-rich defect degree X of the positive electrode material is 0.315.

[0173] Example 3

[0174] A method for preparing a positive electrode material, comprising the following steps:

[0175] (1) 3.34 kg of anhydrous sodium carbonate, 7.2 kg of nickel-iron-manganese-based precursor prepared by the coprecipitation method (where the molar ratio of Ni:Fe:Mn is 1:1:2, and n Ni+Fe+Mn : n Na = 1:0.788), and dopant element precursors (5 mol% of copper oxide, 5 mol% of titanium oxide, 1.5 mol% of aluminum oxide) are mixed uniformly by a high-speed mixer to obtain a mixture.

[0176] (2) In a box-type atmosphere furnace, in an atmosphere with an oxygen content of 60%, the mixture is heated to 870 °C at a heating rate of 3 °C / min, and then the oxygen content of the atmosphere is adjusted to 98%. High-temperature calcination is carried out at 870 °C for 15 hours. During the cooling process, the atmosphere is adjusted to air. After crushing and sieving, a matrix material is obtained.

[0177] (3) The core-layered matrix material, 1 wt% of titanium oxide, 0.5 wt% of copper oxide, 0.5 wt% of ammonium dihydrogen phosphate, and 1 wt% of boron oxide are placed in a high-speed mixer and mixed uniformly to obtain a mixed material.

[0178] (4) The mixed material is sintered at 500 °C for 6 h in a box-type atmosphere furnace, and the sintering atmosphere is air. After crushing and sieving, a positive electrode material is obtained.

[0179] Figure 4a This is the scanning electron microscope image of the positive electrode material prepared in this example. As Figure 4a shown, the positive electrode material includes a matrix material and a coating layer on the surface of the matrix material. The general formula of the matrix material is Na 0.75 M 0.13 Ni 0.2 Fe 0.2 Mn 0.47 O2, M = Cu, Ti, and Al. The coating layer includes boron oxide, copper oxide, titanium oxide, and ammonium dihydrogen phosphate. The positive electrode material is a secondary particle. The tap density of the positive electrode material is 1.8 g / cm 3 , the specific surface area is 1.24 m 2 / g, the median particle size D 50 is 6 μm, the pH value is 12.85, and the mass content of water in the positive electrode material is 0.009 wt%.

[0180] Figure 4b This is the charge-discharge curve graph of the battery assembled with the positive electrode material prepared in the embodiment of this application. As Figure 4b shown, V 开 = 2.75 V, C1 = 24.85 mAh / g, C2 = 16.97 mAh / g, and the sodium-rich defect degree X of the positive electrode material is 0.594.

[0181] Example 4

[0182] A preparation method of a cathode material, comprising the following steps:

[0183] (1) Mix 3.34 kg of anhydrous sodium carbonate, 7.2 kg of a nickel-iron-manganese-based precursor prepared by a coprecipitation method (where the molar ratio of Ni:Fe:Mn is 1:1:2, and n Ni+Fe+Mn :n Na = 1:0.788), and a doping element precursor (5 mol% of copper oxide, 5 mol% of titanium oxide, 1.5 mol% of aluminum oxide) uniformly through a high-speed mixer to obtain a mixture.

[0184] (2) In a box-type atmosphere furnace, under an atmosphere with an oxygen content of 60%, heat the mixture at a heating rate of 5 °C / min to 870 °C, then adjust the atmosphere oxygen content to 100%, and perform high-temperature calcination at 870 °C for 15 hours. During the cooling process, adjust the atmosphere to air. After crushing and sieving, a matrix material is obtained.

[0185] The cathode material prepared in this example includes a matrix material. The general formula of the matrix material is Na 0.75 M 0.13 Ni 0.2 Fe 0.2 Mn 0.47 O2, where M = Cu, Ti, and Al. The cathode material is a secondary particle. The tap density of the cathode material is 1.8 g / cm 3 , the specific surface area is 1.4 m 2 / g, the median particle size D 50 is 6 μm, the pH value is 12.95, and the mass content of water in the cathode material is 0.012 wt%.

[0186] During the charge-discharge test of the battery assembled with the cathode material prepared in this application example, V 开 = 2.74 V, C1 = 24.89 mAh / g, C2 = 16.87 mAh / g, and the sodium-rich defect degree X of the cathode material is 0.596.

[0187] Example 5

[0188] The difference from Example 2 is that steps (3) and (4) are not carried out.

[0189] The cathode material prepared in this example includes a matrix material. The general formula of the matrix material is Na 0.67 M 0.1 Ni 0.25 Fe 0.2 Mn 0.45 O2, where M = Mg, Ti. The cathode material is a secondary particle. The tap density of the cathode material is 2.0 g / cm 3, with a specific surface area of 0.6 m 2 / g, a median particle size D 50 of 5 μm, a pH value of 12.7, and the mass content of water in the positive electrode material is 0.038 wt%.

[0190] During the charge-discharge test of the battery assembled with the positive electrode material prepared in the embodiment of the present application, V 开 = 2.82 V, C1 = 10.61 mAh / g, C2 = 20.64 mAh / g, and the sodium-rich defect degree X of the positive electrode material is 0.339.

[0191] Example 6

[0192] Different from Example 1: (2) In a box-type atmosphere furnace, under an atmosphere with an oxygen content of 50%, the temperature is raised to 950 °C at a heating rate of 4 °C / min, and then the atmosphere oxygen content is adjusted to 10%. High-temperature calcination is carried out at 950 °C for 12 hours. During the cooling process, the atmosphere is adjusted to air, and the matrix material is obtained after crushing and sieving.

[0193] The positive electrode material prepared in this example includes a matrix material and a coating layer on the surface of the matrix material. The general formula of the matrix material is Na 0.7 M 0.1 Ni 0.2 Fe 0.2 Mn 0.5 O2, M = Cu, Al, and the coating layer includes titanium oxide, copper oxide, and ammonium dihydrogen phosphate. The positive electrode material is a secondary particle, and the tap density of the positive electrode material is 1.95 g / cm 3 , with a specific surface area of 0.8 m 2 / g, a median particle size D 50 of 7.5 μm, a pH value of 12.85, and the mass content of water in the positive electrode material is 0.027 wt%.

[0194] During the charge-discharge test of the battery assembled with the positive electrode material prepared in the embodiment of the present application, V 开 = 2.84 V, C1 = 16.24 mAh / g, C2 = 17.91 mAh / g, and the sodium-rich defect degree X of the positive electrode material is 0.476.

[0195] Example 7

[0196] Different from Example 1: 4.193 kg of sodium sulfate, 7.2 kg of a nickel-iron-manganese-based precursor prepared by the coprecipitation method (where the molar ratio of Ni:Fe:Mn is 1:1:2, and n Ni+Fe+Mn :n Na = 1:0.74), and a doping element precursor (5 mol% of copper oxide, 2.5 mol% of aluminum oxide) are mixed evenly by a high-speed mixer to obtain a mixture.

[0197] The positive electrode material prepared in this embodiment includes a matrix material and a coating layer on the surface of the matrix material. The general formula of the matrix material is Na 0.7 M 0.1 Ni 0.2 Fe 0.2 Mn 0.5 O2, where M = Cu, Al. The coating layer includes titanium oxide, copper oxide, and ammonium dihydrogen phosphate. The positive electrode material is a secondary particle. The tap density of the positive electrode material is 1.9 g / cm 3 , the specific surface area is 0.88 m 2 / g, the median particle size D 50 is 7.1 μm, the pH value is 12.8, and the mass content of water in the positive electrode material is 0.027 wt%.

[0198] During the charge and discharge test of the battery assembled with the positive electrode material prepared in the embodiment of the present application, V 开 = 2.83 V, C1 = 16.52 mAh / g, C2 = 17.61 mAh / g, and the sodium-rich defect degree X of the positive electrode material is 0.484.

[0199] Example 8

[0200] Different from Example 1: The layered matrix material is mixed with 1 wt% of titanium oxide, 0.5 wt% of copper oxide, and 0.5 wt% of LiH2PO4 in a high-speed mixer to obtain a mixed material.

[0201] The positive electrode material prepared in this embodiment includes a matrix material and a coating layer on the surface of the matrix material. The general formula of the matrix material is Na 0.7 M 0.1 Ni 0.2 Fe 0.2 Mn 0.5 O2, where M = Cu, Al. The coating layer includes titanium oxide, copper oxide, and LiH2PO4. The positive electrode material is a secondary particle. The tap density of the positive electrode material is 1.9 g / cm 3 , the specific surface area is 0.8 m 2 / g, the median particle size D 50 is 7.0 μm, the pH value is 12.8, and the mass content of water in the positive electrode material is 0.024 wt%.

[0202] During the charge and discharge test of the battery assembled with the positive electrode material prepared in the embodiment of the present application, V 开 = 2.84 V, C1 = 16.11 mAh / g, C2 = 17.76 mAh / g, and the sodium-rich defect degree X of the positive electrode material is 0.475.

[0203] Example 9

[0204] Different from Example 2: 2.98 kg of anhydrous sodium carbonate and 7.2 kg of nickel-iron-manganese-based precursor prepared by the coprecipitation method (where the molar ratio of Ni:Fe:Mn is 1:1:2, and n Ni+Fe+Mn : n Na = 1:0.703) were mixed evenly by a high-speed mixer to obtain a mixture.

[0205] The positive electrode material prepared in this example includes a matrix material and a coating layer on the surface of the matrix material. The general formula of the matrix material is Na 0.67 Ni 0.25 Fe 0.25 Mn 0.5 O2, and the coating layer includes boron oxide, copper oxide, and titanium oxide. The positive electrode material is a secondary particle, and the tap density of the positive electrode material is 1.98 g / cm 3 , the specific surface area is 0.6 m 2 / g, the median particle size D 50 is 5 μm, the pH value is 12.6, and the mass content of water in the positive electrode material is 0.036 wt%.

[0206] During the charge-discharge test of the battery assembled with the positive electrode material prepared in this embodiment of the application, V 开 = 2.83 V, C1 = 8.41 mAh / g, C2 = 23.94 mAh / g, and the sodium-rich defect degree X of the positive electrode material is 0.259.

[0207] Example 10

[0208] Different from Example 1: 3.78 kg of anhydrous sodium carbonate, 7.2 kg of nickel-iron-manganese-based precursor prepared by the coprecipitation method (where the molar ratio of Ni:Fe:Mn is 1:1:2, and n Ni+Fe+Mn : n Na = 1:0.893), and doping element precursors (5 mol% of copper oxide, 2.5 mol% of aluminum oxide) were mixed evenly by a high-speed mixer to obtain a mixture.

[0209] The positive electrode material prepared in this example includes a matrix material and a coating layer on the surface of the matrix material. The general formula of the matrix material is Na 0.85 M 0.1 Ni 0.2 Fe 0.2 Mn 0.5 O2, M = Cu, Al, and the coating layer includes titanium oxide, copper oxide, and ammonium dihydrogen phosphate. The positive electrode material is a secondary particle, and the tap density of the positive electrode material is 1.98 g / cm 3 , the specific surface area is 0.8 m 2 / g, the median particle size D 50is 7 μm, the pH value is 12.9, and the mass content of water in the positive electrode material is 0.036 wt%.

[0210] During the charge-discharge test of the battery assembled with the positive electrode material prepared in the embodiment of the present application, V 开 = 2.82 V, C1 = 18.23 mAh / g, C2 = 8.19 mAh / g, and the sodium-rich defect degree X of the positive electrode material is 0.690.

[0211] Comparative Example 1

[0212] A method for preparing a positive electrode material includes the following steps:

[0213] (1) Mix 4.4 kg of anhydrous sodium carbonate, 7.2 kg of a nickel-iron-manganese-based precursor prepared by the coprecipitation method (where the molar ratio of Ni:Fe:Mn is 1:1:1, and n Ni+Fe+Mn :n Na = 1:1), and a doping element precursor (5 mol% of copper oxide, 5 mol% of titanium oxide, 1.5 mol% of aluminum oxide) uniformly through a three-dimensional mixer to obtain a mixture.

[0214] (2) In a box-type atmosphere furnace, under an air atmosphere, heat the mixture at a heating rate of 4 °C / min to 850 °C and calcine for 15 hours, then cool naturally, and obtain a matrix material after crushing and sieving.

[0215] Figure 4a is the scanning electron micrograph of the positive electrode material prepared in this comparative example. As Figure 4a shown, the positive electrode material prepared in this comparative example includes a matrix material, and the general formula of the matrix material is Na 0.99 M 0.13 Ni 0.23 Fe 0.3 Mn 0.34 O2. The positive electrode material is a secondary particle. The tap density of the positive electrode material is 1.9 g / cm 3 , the specific surface area is 1.0 m 2 / g, the median particle size D 50 is 7 μm, the pH value is 13.15, and the mass content of water in the positive electrode material is 0.063 wt%.

[0216] Figure 4b is the charge-discharge curve graph of the battery assembled with the positive electrode material prepared in this comparative example. As Figure 4b shown, V 开 = 2.99 V, C1 = 33.69 mAh / g, C2 = 7.32 mAh / g, and the sodium-rich defect degree X of the positive electrode material is 0.821.

[0217] Comparative Example 2

[0218] A preparation method of a cathode material, comprising the following steps:

[0219] (1) Mix 3.34 kg of anhydrous sodium carbonate, 7.2 kg of a nickel-iron-manganese-based precursor prepared by a coprecipitation method (where the molar ratio of Ni:Fe:Mn is 1:1:2, and n Ni+Fe+Mn :n Na = 1:0.788), and a doping element precursor (5 mol% of copper oxide, 5 mol% of titanium oxide, 1.5 mol% of aluminum oxide) uniformly through a high-speed mixer to obtain a mixture.

[0220] (2) In a box-type atmosphere furnace, under a pure oxygen atmosphere, heat the mixture at a heating rate of 4 °C / min to 900 °C and calcine for 12 hours, then cool naturally. After crushing and sieving, a matrix material is obtained.

[0221] (3) Place the matrix material, 1 wt% of titanium oxide, 0.5 wt% of copper oxide, 0.5 wt% of ammonium dihydrogen phosphate, and 1 wt% of boron oxide in a high-speed mixer and mix uniformly to obtain a mixed material.

[0222] (4) Sinter the mixed material in a box-type atmosphere furnace at 300 °C for 6 h, with the sintering atmosphere being air. After crushing and sieving, a cathode material is obtained.

[0223] The cathode material prepared in this comparative example includes a matrix material and a coating layer on the surface of the matrix material. The general formula of the matrix material is Na 0.75 M 0.13 Ni 0.2 Fe 0.2 Mn 0.47 O2, where M = Cu, Ti, and Al. The coating layer includes titanium oxide, copper oxide, boron oxide, and ammonium dihydrogen phosphate. The cathode material is a secondary particle. The tap density of the cathode material is 1.78 g / cm 3 , the specific surface area is 1.28 m 2 / g, the median particle size D 50 is 6.2 μm, the pH value is 12.9, and the mass content of water in the cathode material is 0.019 wt%.

[0224] During the charge-discharge test of the battery assembled with the cathode material prepared in this comparative example, V 开 = 2.77 V, C1 = 7.02 mAh / g, C2 = 21.16 mAh / g, and the sodium-rich defect degree X of the cathode material is 0.249.

[0225] Comparative Example 3

[0226] A preparation method of a cathode material, comprising the following steps:

[0227] (1) 3.34 kg of anhydrous sodium carbonate, 7.2 kg of nickel-iron-manganese-based precursor prepared by the coprecipitation method (where the molar ratio of Ni:Fe:Mn is 1:1:2, and n Ni+Fe+Mn : n Na = 1:0.788), and a doping element precursor (1 mol% of copper oxide, 1 mol% of titanium oxide, 0.5 mol% of aluminum oxide) are mixed uniformly by a high-speed mixer to obtain a mixture.

[0228] (2) In a box-type atmosphere furnace, under a pure oxygen atmosphere, the mixture is heated to 850 °C at a heating rate of 4 °C / min and calcined for 12 hours. During the cooling stage, the atmosphere is adjusted to air. After crushing and sieving, a matrix material is obtained.

[0229] The cathode material prepared in this comparative example includes a matrix material and a coating layer on the surface of the matrix material. The general formula of the matrix material is Na 0.75 M 0.13 Ni 0.2 Fe 0.2 Mn 0.47 O2, M = Cu, Ti and Al. The coating layer includes titanium oxide, copper oxide, boron oxide and ammonium dihydrogen phosphate. The cathode material is a secondary particle. The tap density of the cathode material is 1.8 g / cm 3 , the specific surface area is 1.3 m 2 / g, the median particle size D 50 is 6.1 μm, the pH value is 12.9, and the mass content of water in the cathode material is 0.033 wt%.

[0230] During the charge-discharge test of the battery assembled with the cathode material prepared in this comparative example, V 开 = 2.75 V, C1 = 8.13 mAh / g, C2 = 25.02 mAh / g, and the sodium-rich defect degree X of the cathode material is 0.245.

[0231] Comparative Example 4

[0232] The difference from Example 4 is that in (2), in a box-type atmosphere furnace, under an atmosphere with an oxygen content of 35%, the mixture is heated to 870 °C at a heating rate of 5 °C / min, and then the oxygen content of the atmosphere is adjusted to 100%. High-temperature calcination is carried out at 870 °C for 15 hours. During the cooling process, the atmosphere is adjusted to air. After crushing and sieving, a matrix material is obtained.

[0233] The cathode material prepared in this comparative example includes a matrix material. The general formula of the matrix material is Na 0.75 M 0.13 Ni 0.2 Fe 0.2 Mn 0.47O2, M = Cu, Ti and Al, the positive electrode material is secondary particles, and the tap density of the positive electrode material is 1.8 g / cm 3 , the specific surface area is 1.4 m 2 / g, the median particle size D 50 is 6 μm, the pH value is 12.95, and the mass content of water in the positive electrode material is 0.069 wt%.

[0234] During the charge and discharge test of the battery assembled with the positive electrode material prepared in this comparative example, V 开 = 2.86 V, C1 = 24.89 mAh / g, C2 = 10.56 mAh / g, and the sodium-rich defect degree X of the positive electrode material is 0.702.

[0235] Comparative Example 5

[0236] The difference from Example 4 is that (2) in a box-type atmosphere furnace, in an atmosphere with an oxygen content of 60%, the mixture is heated to 870 °C at a heating rate of 5 °C / min, and then the atmosphere oxygen content is adjusted to 75%, and high-temperature calcination is carried out at 870 °C for 15 hours. During the cooling process, the atmosphere is adjusted to air, and the matrix material is obtained after crushing and sieving.

[0237] The positive electrode material prepared in this comparative example includes a matrix material, and the general formula of the matrix material is Na 0.75 M 0.13 Ni 0.2 Fe 0.2 Mn 0.47 O2, M = Cu, Ti and Al, the positive electrode material is secondary particles, and the tap density of the positive electrode material is 1.8 g / cm 3 , the specific surface area is 1.5 m 2 / g, the median particle size D 50 is 6.5 μm, the pH value is 12.9, and the mass content of water in the positive electrode material is 0.053 wt%.

[0238] During the charge and discharge test of the battery assembled with the positive electrode material prepared in this comparative example, V 开 = 2.72 V, C1 = 7.23 mAh / g, C2 = 21.87 mAh / g, and the sodium-rich defect degree X of the positive electrode material is 0.248.

[0239] Table 1 Comparison table of electrochemical performance data of examples and comparative examples

[0240]

[0241]

[0242] As shown in Table 1, according to the test data of Examples 1 to 8, it can be seen that controlling the sodium-rich defect degree of the cathode material within a suitable range can help maintain the crystal structure stability of the cathode material and the structural stability of the cathode material. An appropriate sodium-rich defect degree enables the cathode material to have a higher sodium ion extraction ability, a higher specific capacity, and at the same time can alleviate the irreversible phase transformation at high voltages caused by the massive extraction of sodium ions during charge and discharge, which is beneficial to maintaining the crystal structure stability of the cathode material and alleviating metal dissolution. As a result, the cathode material has both high-voltage resistance performance, high capacity, and cycle stability, improving the comprehensive performance of the cathode material.

[0243] As shown in Table 1, during the preparation of Comparative Examples 1 to 3, during the primary sintering process, an air atmosphere or a pure oxygen atmosphere was used throughout, and the oxygen content remained stable. There was no difference in oxygen content between the heating section and the holding section, which was not conducive to sodium ions entering the lattice as much as possible. There were too few sodium ions in the crystal structure. When the sodium ion content in the crystal structure was low during charging, the P2-phase crystal structure would undergo a phase transformation, which was not conducive to maintaining the stability of the crystal structure and affected the cycle performance of the battery.

[0244] Similarly, during the preparation of Comparative Example 4, during the primary sintering process, the ratio of the oxygen content in the oxygen-containing atmosphere between the heating section and the holding section was too low, and the oxygen content in the heating section during sintering was too low, which was not conducive to sodium ions entering the lattice as much as possible. There were too few sodium ions in the crystal structure. When the sodium ion content in the crystal structure was low during charging, the P2-phase crystal structure would undergo a phase transformation, which was not conducive to maintaining the stability of the crystal structure and affected the cycle performance of the battery.

[0245] Similarly, during the preparation of Comparative Example 5, during the primary sintering process, the ratio of the oxygen content in the oxygen-containing atmosphere between the heating section and the holding section was too high, and the oxygen content in the holding section during sintering was too low, which was not conducive to promoting sodium ions to compete for the sodium positions in the crystal structure, resulting in a decrease in the sodium ion content in the crystal structure. When the sodium ion content in the crystal structure was low during charging, the P2-phase crystal structure would undergo a phase transformation, which was not conducive to maintaining the stability of the crystal structure and affected the cycle performance of the battery.

[0246] The above are only the preferred embodiments of the present application and are not used to limit the present application. For those skilled in the art, the present application can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A cathode material, characterized in that, The positive electrode material is prepared by the following steps: Mix a nickel-iron-manganese-based precursor, a sodium salt, and a dopant containing element M to obtain a mixture; wherein, the ratio of the total molar amount of Ni, Fe, and Mn to the molar amount of sodium is 1:(0.67 - 0.85); Perform a first sintering treatment on the mixture in an oxygen-containing atmosphere to obtain the positive electrode material, wherein, control the volume ratio of the oxygen content in the oxygen-containing atmosphere in the heating section and the heat preservation section during the sintering treatment to be (0.4 - 0.65):1; The positive electrode material includes a matrix material, and the chemical general formula of the matrix material is Na a M b Ni c Fe d Mn e O2, where 0.67 ≤ a ≤ 0.85, 0 ≤ b ≤ 0.5, 0.01 ≤ c ≤ 0.5, 0.01 ≤ d ≤ 0.3, 0.5 ≤ e < 1, and b + c + d + e = 1; M includes at least one of Cu, Al, Ti, Zr, W, Ta, Co, Mg, Ca, Mo, Nb, and B; the crystal structure of the matrix material is a layered oxide with a P2-phase structure, and the crystal structure of the matrix material has a sodium-rich structural defect; The sodium-rich defect degree of the positive electrode material is X, where 0.25 ≤ X ≤ 0.7, and X = C1 / (C1 + C2); where C1 is the difference in discharge specific capacity of the half-cell between V 开 and 2.5 V, where V 开 is the open-circuit voltage of the first charge curve of the half-cell; C2 is the difference in discharge specific capacity between 2.5 V and 2.0 V.

2. The cathode material according to claim 1, wherein The sodium-rich defect degree X of the positive electrode material satisfies: 0.3 ≤ X ≤ 0.

6.

3. The cathode material according to any one of claims 1 to 2, characterized in that, When 0.8 ≤ a ≤ 0.85, measured by XRD rays, the positive electrode material has a diffraction peak at 41.4 ± 0.2°.

4. The cathode material according to any one of claims 1 to 2, characterized in that, Measured by XRD rays, the positive electrode material has diffraction peaks at 15.80 ± 0.5°, 31.95 ± 0.5°, 35.90 ± 0.5°, 36.81 ± 0.5°, 39.45 ± 0.5°, 43.56 ± 0.5°, 48.84 ± 0.5°, 62.08 ± 0.5°, 64.56 ± 0.5°, 66.93 ± 0.5°, 73.87 ± 0.5°, 76.16 ± 0.5°, 78.35 ± 0.5°, and 84.97 ± 0.5°.

5. The cathode material according to claim 4, wherein The positive electrode material further includes a coating layer on the surface of the matrix material, the coating layer includes at least one of an oxide and a phosphate, the oxide includes an oxide of at least one of Cu, Al, Ti, Zr, Mg, Ta, W, Nb, and B, and the positive electrode material includes at least one of the following characteristics (1) - (3): (1) The coating layer includes a phosphate, and the phosphate includes at least one of lithium phosphate, sodium phosphate, potassium phosphate, titanium phosphate, aluminum phosphate, iron phosphate, and ammonium dihydrogen phosphate; (2) The coating layer includes a phosphate, and the mass proportion of the phosphate in the matrix material is 0.05wt% - 5wt%; (3) The mass proportion of the oxide in the matrix material is 0.05wt% - 5wt%.

6. The cathode material according to claim 1, wherein The positive electrode material includes at least one of the following characteristics (1) - (7): (1)The mass content of CO3 in the positive electrode material ≤ 2 wt%, and the mass content of OH in the positive electrode material ≤ 2 wt%. 2- - ​​ (2) The tap density of the positive electrode material is ≥ 1.6 g / cm 3 ; (3) The specific surface area of the positive electrode material is 0.2 m 2 / g to 2 m 2 / g; (4)The median particle size D of the positive electrode material 50 is 3 μm to 15 μm; (5) Disperse 10g of the positive electrode material in 100g of water to obtain a mixed solution, and after ultrasonic treatment, take the supernatant of the mixed solution to measure the pH value of the positive electrode material to be 11 - 13; (6) The mass content of water in the positive electrode material ≤ 0.05wt%; (7) The space group of the positive electrode material is P63 / mmc.

7. A sodium-ion battery, characterized in that, The sodium ion battery includes the positive electrode material according to any one of claims 1 - 6.

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