Layered oxide positive electrode material and preparation method therefor, positive electrode sheet, and sodium-ion battery

Abstract

A layered oxide positive electrode material and a preparation method therefor, a positive electrode sheet, and a sodium-ion battery, belonging to the technical field of sodium-ion batteries. The layered oxide positive electrode material comprises O3@P2 phase composite oxide particles, and an inert coating layer coated on the surface of the O3@P2 phase composite oxide particles. The O3@P2 phase composite oxide particles comprise O3-phase nickel-manganese-based oxide layered particles and a P2-phase metal oxide coating layer coated on the surface of the O3-phase nickel-manganese-based oxide layered particles. The inert coating layer is a carbon layer and / or an inorganic metal oxide layer. When the provided layered oxide positive electrode material provided is applied to a sodium-ion battery, the prepared sodium-ion battery has high first-cycle Coulombic efficiency, excellent rate capability, a long cycle life, and good air stability.

Description

Layered oxide cathode materials and their preparation methods, cathode sheets and sodium-ion batteries

[0001] This application is based on and claims priority to Chinese application CN application number 202410671665.9 filed on May 27, 2024, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0002] This invention relates to the field of sodium-ion battery technology, and more specifically, to a layered oxide cathode material and its preparation method, a cathode sheet, and a sodium-ion battery. Background Technology

[0003] Lithium-ion batteries are widely used in electric vehicles, consumer electronics, and energy storage, but their large-scale application is severely hampered by problems such as low lithium reserves, uneven distribution, and large price fluctuations. Compared to lithium resources, sodium resources are widely distributed and readily available in the Earth's crust, making sodium-ion batteries more cost-effective and promising for large-scale application in energy storage.

[0004] Sodium-ion batteries share a similar working principle with lithium-ion batteries. Sodium-ion batteries utilize the extraction and insertion of sodium ions between the positive and negative electrodes to store and release energy. Currently, the main cathode materials for sodium-ion batteries include layered transition metal oxides, polyanionic compounds, and Prussian blue analogues. Among these, layered transition metal oxide cathode materials exhibit the highest sodium storage capacity, attracting increasing research and attention. Based on the sodium ion coordination environment and interlayer stacking sequence, layered transition metal oxides can be primarily classified into P2 and O3 types. The letters P and O represent sodium ion coordination environments of triangular prism and octahedron, respectively, while the numbers 2 and 3 represent interlayer stacking sequences of ABBA and ABCABC, respectively. Among them, the P2 phase material is a sodium-poor phase (typically with a sodium content of less than 0.67%). When used to manufacture sodium-ion batteries, the resulting batteries have a low initial charge capacity, requiring an additional sodium replenishment process, which is not conducive to practical applications. The O3 phase material is a sodium-rich phase (typically with a sodium content close to 1.0%). When used to manufacture sodium-ion batteries, the resulting batteries have high charge and discharge capacities, thus the O3 phase material has the potential to become a commercial sodium-ion battery cathode material. However, the sodium element abundant in the O3 phase cathode material easily reacts with moisture and carbon dioxide in the air, resulting in a high residual alkali content on the material surface. The formed sodium carbonate, sodium hydroxide, sodium bicarbonate, and other poorly conductive substances can affect the initial coulombic efficiency and reversible capacity of the prepared sodium-ion batteries.

[0005] Therefore, how to eliminate or effectively utilize the residual alkali on the surface of the O3 phase layered oxide sodium-ion battery cathode material and improve the air stability of the O3 phase layered oxide sodium-ion battery cathode material are technical problems that urgently need to be solved in this field.

[0006] Summary of the Invention

[0007] The main objective of this invention is to provide a layered oxide cathode material and its preparation method, cathode sheet, and sodium-ion battery, in order to solve the problem that the sodium-ion battery cathode material in the prior art has poor electrochemical performance due to the poor stability of residual alkali and air.

[0008] To achieve the above objectives, the first aspect of the present invention provides a layered oxide cathode material comprising O3@P2 phase composite oxide particles and an inert coating layer covering the surface of the O3@P2 phase composite oxide particles. The O3@P2 phase composite oxide particles comprise O3 phase nickel-manganese-based oxide layered particles and a P2 phase metal oxide coating layer covering the surface of the O3 phase nickel-manganese-based oxide layered particles. The inert coating layer is a carbon layer and / or an inorganic metal oxide layer.

[0009] In the technical solution of this application embodiment, in view of the defects existing in the cathode materials of sodium-ion batteries, a layered oxide cathode material with a double-layer coating structure is provided. The P2 phase metal oxide coating layer reduces the residual alkali content on the surface of the O3 phase nickel manganese-based oxide layered particles and provides a good sodium ion transport channel. The inert coating layer delays the side reactions between the outer surface of the layered oxide cathode material and the air and electrolyte, thereby significantly reducing the residual alkali content on the surface of the oxide material and improving air stability.

[0010] Furthermore, the molecular formula of the O3 phase nickel-manganese-based oxide layered particles is Na. x Ni a Mn b M1 c O2, wherein 0.8≤x≤1.0, a+b+c=1.0 and a, b and c are all positive numbers, and M1 is selected from one or more of Fe, Ti, Mg, Cu, Al, Ca, Zn and Co; preferably, M1 is selected from one or more of Fe, Ti, Mg, Cu, Zn and Ca.

[0011] In this embodiment, the inventors conducted extensive experiments to select and optimize the types of O3 phase nickel manganese-based oxide layered particles. They found that when the composition of the particles is the same as the elemental composition and stoichiometric ratio in the above molecular formula, the air stability of the resulting O3 phase nickel manganese-based oxide layered particles is further improved. At the same time, the O3 phase nickel manganese-based oxide layered particles can also be better compatible and coordinated with the P2 phase metal oxide coating layer.

[0012] Furthermore, the molecular formula of the P2 phase metal oxide coating is Na. y M2O2; wherein 0.6≤y≤0.8, M2 is selected from one or more of Ni, Mn, Fe, Ti, Mg, Cu, Al, Ca and Co; preferably, M2 is selected from one or more of Fe, Mn, Mg, Cu and Ca.

[0013] In this embodiment, the inventors conducted extensive experiments to select and optimize the types of P2 phase metal oxide coatings. They found that when the composition of the coating is the same as the elemental composition and stoichiometric ratio in the above molecular formula, it can better reduce the residual alkali content on the surface of O3 phase nickel manganese-based oxide layered particles and effectively improve the air stability of the P2 phase metal oxide coating.

[0014] Furthermore, the inorganic metal oxide layer is selected from one or more of Al2O3 layer, TiO2 layer, CuO layer and MgO layer; preferably, the inorganic metal oxide layer is selected from one or more of Al2O3 layer, TiO2 layer and MgO layer.

[0015] In this embodiment, compared to inorganic metal oxide layers formed by other metals, the aforementioned inorganic metal oxide layers have a more stable structure and can better suppress side reactions between O3@P2 phase composite oxide particles and the electrolyte. Based on this, the inventors further selected one or more of Al2O3, TiO2, and MgO layers for the inorganic metal oxide layer, and found that these inorganic metal oxide layers can better synergize with the aforementioned preferred P2 phase metal oxide coating layer, while also being less expensive, effectively increasing the added value of the prepared layered oxide cathode material.

[0016] Furthermore, in the O3 phase nickel-manganese-based oxide layered particles, M1 is Ti, and in the P2 phase metal oxide coating layer, M2 is selected from one or more of Fe, Cu, and Mn; or, in the O3 phase nickel-manganese-based oxide layered particles, M1 is Cu or Ti and Cu, and in the P2 phase metal oxide coating layer, M2 is selected from one or more of Mg, Cu, and Mn.

[0017] In this embodiment, the inventors, through extensive experiments and comparisons, discovered that when M2 in the P2 phase metal oxide coating layer and M1 in the O3 phase nickel-manganese-based oxide layered particles are combined in the manner described above, the P2 phase metal oxide coating layer and the O3 phase nickel-manganese-based oxide layered particles can be better bonded together. At the same time, the residual alkali on the surface of the O3 phase nickel-manganese-based oxide can be more effectively eliminated, thereby improving the air stability of the obtained layered oxide cathode material.

[0018] Furthermore, the molecular formula of the O3 phase nickel-manganese-based oxide layered particles is NaNi. 0.5 Mn 0.4 Ti 0.1 The molecular formula of the O2,P2 phase metal oxide coating layer is Na. 9 / 7 Cu 2 / 9 Fe 1 / 9 Mn 2 / 3 O2, with an inert coating layer of Al2O3; or, the molecular formula of the O3 phase nickel-manganese-based oxide layered particles is NaNi. 0.45 Mn 0.4 Ti 0.1 Cu 0.05 The molecular formula of the O2,P2 phase metal oxide coating layer is Na. 0.6 Mg 0.15 Cu 0.15 Mn 0.7 O2, and the inert coating layer is a carbon layer.

[0019] In this embodiment, when the layered oxide cathode material is configured with the O3 phase nickel-manganese-based oxide layered particles as the core, the P2 phase metal oxide coating layer as the first coating layer, and the inert coating layer as the second coating layer in the above two ways, the resulting layered oxide cathode material not only has excellent electrochemical performance but also higher air stability, and can better meet its practical application requirements.

[0020] Furthermore, in the layered oxide cathode material, the thickness of the P2 phase metal oxide coating layer is 2 nm to 100 nm, and the thickness of the inert coating layer is 2 nm to 100 nm; preferably, based on 100% of the weight of the layered oxide cathode material, the mass fraction of the P2 phase metal oxide coating layer is 0.5% to 5%, and the mass fraction of the inert coating layer is 0.5% to 5%; preferably, the coverage rate of the P2 phase metal oxide coating layer on the surface of the O3 phase nickel-manganese-based oxide layered particles is 80% to 100%; the coverage rate of the inert coating layer on the surface of the O3@P2 phase composite oxide particles is 80% to 100%.

[0021] In this embodiment, when the thickness of the two coating layers is within the aforementioned range, a better balance can be achieved between suppressing side reactions, consuming residual alkali, and improving conductivity, thereby better enhancing the electrochemical performance of the cathode material. When the two coating layers are set according to the aforementioned weight ratios, better synergy and mass transfer can be achieved between the coating layers and between the P2 phase metal oxide coating layer and the core particles, resulting in higher electrochemical performance of the obtained cathode material. Furthermore, in several typical embodiments, the coverage rate of the P2 phase metal oxide coating layer on the surface of the O3 phase nickel-manganese-based oxide layered particles is 80%–100%; the coverage rate of the inert coating layer on the surface of the O3@P2 phase composite oxide particles is 80%–100%. In the structure of the layered oxide cathode material provided by this invention, the coverage rate of each coating layer can reach 80% or more, that is, a good, complete, and uniform coating structure is achieved, thus further improving the air stability of the obtained layered oxide cathode material.

[0022] A second aspect of the present invention provides a method for preparing the above-mentioned layered oxide cathode material, comprising: preparing O3-phase nickel-manganese-based oxide layered particles and a first metal source; mixing the O3-phase nickel-manganese-based oxide layered particles with the first metal source and performing a first ball milling to obtain first pre-coated particles; subjecting the first pre-coated particles to a first calcination treatment to obtain O3@P2 phase composite oxide particles; mixing the O3@P2 phase composite oxide particles with a carbon source and / or a second metal source and performing a second ball milling to obtain second pre-coated particles; and optionally subjecting the second pre-coated particles to a second calcination treatment to obtain the layered oxide cathode material.

[0023] In the technical solution of this application embodiment, a first metal source is first pre-coated with O3-phase nickel-manganese-based oxide layered particles to enhance the bonding strength between them. Then, through in-situ solid-state reaction, a P2-phase metal oxide coating layer is generated in-situ on the surface of the O3-phase nickel-manganese-based oxide layered particles, thereby significantly consuming the residual alkali on its surface and improving air stability. Subsequently, the O3@P2-phase composite oxide particles are ball-milled and pre-coated with a carbon source and / or a second metal source, and an inert coating layer is generated through another in-situ solid-state reaction. Compared with simple mixed coating or liquid-phase reaction, this method can better synergize the physicochemical properties of each coating layer, protect the structural integrity of the core particles and coating layers, simplify the process, and obtain layered oxide cathode materials with better performance and higher added value. Furthermore, the layered oxide cathode material preparation method provided by this invention is simple, highly compatible with existing preparation processes, and easy to scale up for industrial application.

[0024] Furthermore, the first ball mill operates at a speed of 100 rpm to 500 rpm for a time of 0.5 h to 4 h; and / or, the second ball mill operates at a speed of 100 rpm to 500 rpm for a time of 0.5 h to 4 h.

[0025] In this embodiment, by setting the experimental conditions for the two ball milling processes as described above, a more uniform coating can be achieved, thereby improving the compositional uniformity, structural continuity, and coating integrity of the obtained P2 phase metal oxide coating layer and inert coating layer.

[0026] Further, the weight ratio of O3 phase nickel-manganese-based oxide layered particles to the first metal source is 1:(0.005~0.05), and the weight ratio of O3@P2 phase composite oxide particles to the carbon source and / or the second metal source is 1:(0.005~0.05); preferably, the first metal source includes a sodium source and a coated metal source, the coated metal source being selected from one or more of the oxides, hydroxides, carbonates, sulfates, oxalates, acetates and citrates corresponding to Fe, Ti, Mg, Cu, Al, Ca and Co; the sodium source is selected from one or more of sodium carbonate, sodium hydroxide, sodium nitrate and sodium peroxide; preferably, the carbon source is selected from one or more of coal tar, coal pitch, petroleum pitch, expanded graphite, carbon black and graphene, and the second metal source is selected from one or more of the oxides, hydroxides and carbonates corresponding to Ni, Mn, Fe, Ti, Mg, Cu, Al, Ca and Co.

[0027] In this embodiment, the inventors, through extensive experiments, optimized the aforementioned weight ratio relationship, corresponding to the weight percentage and coating thickness of the P2 phase metal oxide coating layer and the inert coating layer. They discovered that material preparation under this weight ratio relationship more effectively improves the electrochemical performance and air stability of the resulting layered oxide cathode material. Through numerous comparative experiments, the inventors optimized the aforementioned coating metal sources and sodium sources, finding that when these types were selected, the solid-phase reaction proceeded more smoothly, enabling the formation of the P2 phase metal oxide coating layer and resulting in a cathode material with the desired structure. Similarly, through numerous comparative experiments, the inventors optimized the aforementioned carbon sources and second metal sources, finding that when these types were selected, the inert coating layer could be formed smoothly in a more continuous, uniform, and dense state, thereby obtaining a layered oxide cathode material with excellent performance.

[0028] Furthermore, the temperature of the first calcination treatment is 600℃~1000℃, and the calcination time is 2h~20h; the temperature of the second calcination treatment is 400℃~1000℃, and the calcination time is 0.5h~20h; preferably, the calcination atmosphere of the first calcination treatment is air and / or oxygen atmosphere.

[0029] In this embodiment, the inventors conducted numerous experiments to optimize the temperature and time conditions for the two calcinations and found that when carried out in this manner, the resulting two-layer coating structure was more stable. Specifically, the bonding between the P2 phase metal oxide coating layer and the surface of the O3 phase nickel-manganese-based oxide layered particles, as well as the bonding between the inert coating layer and the surface of the O3@P2 phase composite oxide particles, was more compact, thereby resulting in better air stability of the prepared layered oxide cathode material.

[0030] More preferably, the calcination atmosphere of the first calcination treatment is an air and / or oxygen atmosphere. The inventors prefer that the first calcination be carried out in the presence of air, so as to form the P2 phase oxide coating layer more efficiently and improve the ionic conductivity.

[0031] Furthermore, when the O3@P2 phase composite oxide particles are mixed with the second metal source, a second calcination treatment is performed. The temperature of the second calcination treatment is 700℃~1000℃, the time is 10h~20h, and the atmosphere is air and / or oxygen. At this time, the inert coating layer is an inorganic metal oxide layer. The inventors have optimized the above conditions through a large number of experiments to form a more stable and dense inert coating layer, thereby improving the air stability of the final layered oxide cathode material.

[0032] In this embodiment, when the O3@P2 phase composite oxide particles are mixed with a carbon source, and the carbon source is selected from one or more of coal tar, coal pitch, and petroleum pitch, a second calcination treatment is performed. The temperature of the second calcination treatment is 400℃~800℃, the time is 0.5h~2h, and the atmosphere is a nitrogen atmosphere and / or an argon atmosphere. At this time, the inert coating layer is a carbon layer, and the carbon source contains a variety of small-molecule organic matter. Therefore, the inventors have optimized the above conditions through a large number of experiments to remove small organic molecules from coal tar, coal pitch, and petroleum pitch, and at the same time complete carbonization to obtain a more complete and stable carbon layer, thereby improving the air stability of the final layered oxide cathode material.

[0033] When O3@P2 phase composite oxide particles are mixed with a carbon source, and the carbon source is selected from one or more of expanded graphite, carbon black and graphene, the second calcination treatment is not performed, and the layered oxide cathode material is obtained after the second ball milling. At this time, the inert coating layer is a carbon layer, and the carbon source contains only elemental carbon. Therefore, in order to simplify the process and shorten the cycle, the layered oxide cathode material is obtained directly after the second ball milling.

[0034] A third aspect of the present invention provides a positive electrode sheet comprising the above-described layered oxide positive electrode material.

[0035] In this embodiment, the positive electrode sheet contains the above-mentioned layered oxide positive electrode material, thus exhibiting high electrochemical performance and good air stability.

[0036] A fourth aspect of the present invention provides a sodium-ion battery comprising the above-described positive electrode.

[0037] Because the cathode material obtained by this invention has both good electrochemical performance and structural stability, when it is used as a cathode electrode component in sodium-ion batteries, the resulting sodium-ion batteries also have comprehensively improved electrochemical performance, including improved first-cycle coulombic efficiency, excellent rate performance, long cycle life and good air stability, thus enabling them to be well applied in multiple application scenarios.

[0038] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0039] To more clearly illustrate the technical solution of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0040] Figure 1 is a scanning electron microscope image of the layered oxide cathode material obtained in Example 1;

[0041] Figure 2 is a scanning electron microscope image of the layered oxide cathode material obtained in Comparative Example 1;

[0042] Figure 3 is the XRD pattern of the layered oxide cathode material obtained in Example 1;

[0043] Figure 4 shows the XRD pattern of the layered oxide cathode material obtained in Comparative Example 1. Detailed Implementation

[0044] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0045] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0046] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0047] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0048] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0049] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0050] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0051] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0052] As described in the background section, existing sodium-ion battery cathode materials suffer from poor electrochemical performance due to residual alkali and poor air stability. To address this problem, the first aspect of this invention provides a layered oxide cathode material comprising O3@P2 phase composite oxide particles and an inert coating layer on the surface of the O3@P2 phase composite oxide particles. The O3@P2 phase composite oxide particles comprise O3 phase nickel-manganese-based oxide layered particles and a P2 phase metal oxide coating layer on the surface of the O3 phase nickel-manganese-based oxide layered particles; the inert coating layer is a carbon layer and / or an inorganic metal oxide layer.

[0053] The layered oxide cathode material provided by this invention includes an O3-phase nickel-manganese-based oxide layered particle core, a first P2-phase metal oxide coating layer, and a second inert coating layer. The first P2-phase metal oxide coating layer reduces the residual alkali content on the surface of the O3-phase nickel-manganese-based oxide layered particles and provides a good sodium ion transport channel. The inert coating layer delays the side reactions between the outer surface of the layered oxide cathode material and the air and electrolyte, thereby enabling the layered oxide cathode material to exhibit high electrochemical performance and good air stability.

[0054] Specifically, the P2 phase metal oxide coating layer and the inert coating layer work together to synergistically improve the overall electrochemical performance of the O3 phase nickel-manganese-based oxide layered particles. The inert coating layer exhibits good stability, uniformity, and density. When it coats the outermost surface and directly contacts the electrolyte, it effectively reduces side reactions between the prepared layered oxide cathode material and the electrolyte, thereby reducing the erosion of the effective components of the cathode by HF generated from these side reactions and extending its service life. Simultaneously, the inert coating layer, possessing a certain degree of flexibility, can effectively suppress the formation of internal cracks in the cathode material particles. However, if the inert coating layer directly contacts the O3 phase nickel-manganese-based oxide layered particles, it will block the diffusion channels of metal ions in the core, affecting the electrochemical performance of the cathode material. In view of this, the present invention adopts a form in which a P2 phase metal oxide coating layer and an inert coating layer are sequentially coated. Although the P2 phase metal oxide coating layer has poor ability to resist electrolyte and side reactions, it has high ionic conductivity and can effectively reduce the charge transfer impedance on the surface of O3 phase nickel manganese-based oxide layered particles.

[0055] Taking into account the above factors and conducting extensive experimental verification, the inventors combined a P2 phase metal oxide coating layer with an inert coating layer. Specifically, a P2 phase metal oxide coating layer, which exhibits good ionic conductivity and significantly absorbs residual alkali, is applied to the surface of O3 phase nickel-manganese-based oxide layered particles. Subsequently, an inert coating layer is applied to the surface of the P2 phase metal oxide coating layer, with the inert coating layer in direct contact with the electrolyte. This invention leverages the advantages of both coating layers, thereby improving the electrochemical performance of the resulting layered oxide cathode material. Consequently, it can enhance the first-cycle coulombic efficiency, rate performance, and cycle life of sodium-ion batteries fabricated using this cathode material.

[0056] Furthermore, the molecular formula of the O3 phase nickel-manganese-based oxide layered particles is Na. x Ni a Mn b M1 c O2, where 0.8 ≤ x ≤ 1.0, a + b + c = 1.0 and a, b, and c are all positive numbers, and M1 is selected from one or more of Fe, Ti, Mg, Cu, Al, Ca, Zn, and Co. The inventors conducted extensive experiments to select and optimize the types of O3-phase nickel-manganese-based oxide layered particles, and found that when the composition and stoichiometry of its components are as described in the above molecular formula, the electrochemical performance is superior. Based on this, M1 is further selected from one or more of Fe, Ti, Mg, Cu, Zn, and Ca. When using these metal elements, the various electrochemical properties of the O3-phase nickel-manganese-based oxide layered particles are further improved, and they also exhibit better compatibility and coordination with their coating layer.

[0057] In several typical implementations, the molecular formula of the P2 phase metal oxide coating is Na. y M2O2; wherein 0.6≤y≤0.8, and M2 is selected from one or more of Ni, Mn, Fe, Ti, Mg, Cu, Al, Ca, Zn, and Co. Through extensive experiments, the inventors selected and optimized the types of P2-phase metal oxide coatings, discovering that when the composition and stoichiometry of the elements in the above molecular formula are achieved, the residual alkali content on the surface of O3-phase nickel-manganese-based oxide layered particles can be better reduced, and its ionic conductivity can be effectively improved. Based on this, the inventors further optimized M2 through extensive experiments, selecting one or more of Fe, Mn, Mg, Cu, Zn, and Ca. When using the above-mentioned metal elements, the resulting P2-phase metal oxide coating can more effectively reduce the charge transfer impedance on the surface of O3-phase nickel-manganese-based oxide layered particles, thereby significantly improving the electrochemical performance of the obtained layered oxide cathode material.

[0058] Regarding the selection of inert coating layers other than the carbon layer, the inventors, through extensive experimentation, have identified one or more of the following inorganic metal oxide layers in several preferred embodiments: Al2O3, TiO2, CuO, and MgO. Compared to inorganic metal oxide layers formed by other metals, the aforementioned inorganic metal oxide layers exhibit more stable structures and can better suppress side reactions between O3@P2 phase composite oxide particles and the electrolyte. Based on this, the inventors further selected one or more of Al2O3, TiO2, and MgO layers for the inorganic metal oxide layer, finding that these layers can better synergize with the aforementioned preferred P2 phase metal oxide coating layer, while also being more cost-effective, thus effectively increasing the added value of the resulting cathode material.

[0059] In several typical embodiments, M1 in the O3 phase nickel-manganese-based oxide layered particles is Ti, and M2 in the P2 phase metal oxide coating layer is selected from one or more of Fe, Cu, and Mn; or, M1 in the O3 phase nickel-manganese-based oxide layered particles is Cu or Ti and Cu, and M2 in the P2 phase metal oxide coating layer is selected from one or more of Mg, Cu, and Mn. Since the P2 phase metal oxide coating layer serves to connect the O3 phase nickel-manganese-based oxide layered particles and the inert coating layer, its ability to achieve good bonding with the O3 phase nickel-manganese-based oxide layered particles is a very important factor. Through extensive experiments and comparisons, the inventors discovered that when M2 in the P2 phase metal oxide coating layer and M1 in the O3 phase nickel manganese-based oxide particles are combined in the manner described above, the P2 phase metal oxide coating layer and the O3 phase nickel manganese-based oxide layered particles can bond better. At the same time, the residual alkali on the surface of the O3 phase nickel manganese-based oxide particles can be eliminated more effectively, thereby improving the electrochemical performance of the final layered oxide cathode material. This, in turn, improves the first-cycle coulombic efficiency, rate performance, and cycle life of sodium-ion batteries made using this cathode material.

[0060] Through extensive experimentation, the inventors further optimized the core oxide and the two coating layers of the layered oxide cathode material, and discovered in two of the most typical embodiments that the molecular formula of the O3 phase nickel-manganese-based oxide layered particles is NaNi. 0.5 Mn 0.4 Ti 0.1 The molecular formula of the O2,P2 phase metal oxide coating layer is Na. 9 / 7 Cu 2 / 9 Fe 1 / 9 Mn 2 / 3 O2, with an inert coating layer of Al2O3; or, the molecular formula of the O3 phase nickel-manganese-based oxide layered particles is NaNi. 0.45 Mn 0.4 Ti0.1 Cu 0.05 The molecular formula of the O2,P2 phase metal oxide coating layer is Na. 0.6 Mg 0.15 Cu 0.15 Mn 0.7 O2, and the inert coating layer is a carbon layer. When the layered oxide cathode material has O3 phase nickel-manganese-based oxide layered particles as the core, P2 phase metal oxide coating layer as the first coating layer, and inert coating layer as the second coating layer arranged in the above two ways, the resulting layered oxide cathode material not only has excellent electrochemical performance, but also higher air stability, and can better meet its practical application requirements.

[0061] In addition to the aforementioned preferred element combination schemes, the inventors also discovered during the experiments that the film thickness, mass fraction, and coating degree significantly affect the various properties of the obtained layered oxide cathode material. In a typical embodiment, the thickness of the P2 phase metal oxide coating layer in the layered oxide cathode material is 2 nm to 100 nm, and the thickness of the inert coating layer is 2 nm to 100 nm. When the thicknesses of the P2 phase metal oxide coating layer and the inert coating layer are within the above ranges, a better balance can be achieved between suppressing side reactions, consuming residual alkali, and improving conductivity, thereby better improving the electrochemical performance of the obtained layered oxide cathode material. Regarding the weight fraction of the P2 phase metal oxide coating layer and the inert coating layer, in a preferred embodiment, based on 100% of the weight of the layered oxide cathode material, the mass fraction of the P2 phase metal oxide coating layer is 0.5% to 5%, and the mass fraction of the inert coating layer is 0.5% to 5%. When the two coating layers are set according to the above-mentioned weight ratios, better synergy and mass transfer can be achieved between the P2 phase metal oxide coating layer and the inert coating layer, as well as between the P2 phase metal oxide coating layer and the core particles, resulting in higher electrochemical performance of the layered oxide cathode material. Furthermore, in several typical embodiments, the coverage rate of the P2 phase metal oxide coating layer on the surface of the O3 phase nickel-manganese-based oxide layered particles is 80%–100%; the coverage rate of the inert coating layer on the surface of the O3@P2 phase composite oxide particles is also 80%–100%. In the structure of the layered oxide cathode material provided by this invention, the coverage rate of the P2 phase metal oxide coating layer and the inert coating layer can reach 80% or more, that is, a good, complete, and uniform coating structure is achieved, thus further improving the air stability of the layered oxide cathode material.

[0062] A second aspect of the present invention provides a method for preparing the above-mentioned layered oxide cathode material, comprising: preparing O3-phase nickel-manganese-based oxide layered particles and a first metal source; mixing the O3-phase nickel-manganese-based oxide layered particles with the first metal source and performing a first ball milling to obtain first pre-coated particles; subjecting the first pre-coated particles to a first calcination treatment to obtain O3@P2 phase composite oxide particles; mixing the O3@P2 phase composite oxide particles with a carbon source and / or a second metal source and performing a second ball milling to obtain second pre-coated particles; and optionally subjecting the second pre-coated particles to a second calcination treatment to obtain the layered oxide cathode material.

[0063] The preparation method provided by this invention is simple, and the equipment and process conditions involved are readily available. It is also highly compatible with various existing methods for preparing cathode materials. Specifically, a first metal source is pre-coated with O3-phase nickel-manganese-based oxide layered particles to enhance the bonding strength between them. Then, through an in-situ solid-state reaction, a P2-phase metal oxide coating layer is generated on the surface of the O3-phase nickel-manganese-based oxide layered particles, significantly consuming residual alkali on the surface and improving air stability. Subsequently, the O3@P2-phase composite oxide particles are ball-milled and pre-coated with a carbon source and / or a second metal source, and an inert coating layer is generated through another in-situ solid-state reaction. Compared to simple mixed coating or liquid-phase reaction, this method better coordinates the physicochemical properties of each coating layer, protects the structural integrity of the core particles and coating layers, simplifies the process, and yields layered oxide cathode materials with better performance and higher added value.

[0064] To improve the effect of the two pre-coating processes, preferably, the first ball milling speed is 100 rpm to 500 rpm, and the time is 0.5 h to 4 h; and / or, the second ball milling speed is 100 rpm to 500 rpm, and the time is 0.5 h to 4 h. Setting the experimental conditions for the two ball milling processes as described above can achieve more uniform coating, thereby improving the compositional uniformity, structural continuity, and coating integrity of the obtained P2 phase metal oxide coating layer and inert coating layer.

[0065] To better control the weight ratio and thickness of the P2 phase metal oxide coating layer and the inert coating layer, the inventors preferred a weight ratio of 1:(0.005~0.05) for O3 phase nickel-manganese-based oxide layered particles to the first metal source in several typical embodiments, and a weight ratio of 1:(0.005~0.05) for O3@P2 phase composite oxide particles to the carbon source and / or the second metal source. Through extensive experiments, the inventors optimized the above weight ratios, which correspond to the weight ratio and thickness of the P2 phase metal oxide coating layer and the inert coating layer. They also found that preparing materials under these weight ratios can more effectively improve the electrochemical performance and air stability of the resulting layered oxide cathode material.

[0066] In several preferred embodiments, the first metal source includes a sodium source and a coating metal source. The coating metal source is selected from one or more of the oxides, hydroxides, carbonates, sulfates, oxalates, acetates, and citrates corresponding to Fe, Ti, Mg, Cu, Al, Ca, Zn, and Co. The sodium source is selected from one or more of sodium carbonate, sodium hydroxide, sodium nitrate, and sodium peroxide. Through extensive comparative experiments, the inventors have optimized the above-mentioned coating metal sources and sodium sources, and found that when these types are selected, the solid-phase reaction proceeds more smoothly, thereby enabling the formation of the P2 phase metal oxide coating layer and resulting in a layered oxide cathode material with the desired structure.

[0067] In several preferred embodiments, the carbon source is selected from one or more of coal tar, coal tar pitch, petroleum pitch, expanded graphite, carbon black, and graphene, and the second metal source is selected from one or more of the oxides, hydroxides, and carbonates corresponding to Ni, Mn, Fe, Ti, Mg, Cu, Al, Ca, and Co. Similarly, the inventors optimized the above-mentioned carbon sources and second metal sources through numerous comparative experiments, and found that when the above types are selected, the inert coating layer can be formed smoothly in a more continuous, uniform, and dense state, thereby obtaining a layered oxide cathode material with excellent performance.

[0068] This invention achieves the formation of a P2 phase metal oxide coating layer and an inert coating layer through calcination and solid-state reaction. In a typical embodiment, the temperature of the first calcination treatment is 600℃~1000℃, and the calcination time is 2h~20h; the temperature of the second calcination treatment is 400℃~1000℃, and the calcination time is 0.5h~20h. Through extensive experiments, the inventors optimized the temperature and time conditions for the two calcinations and found that when performed according to these conditions, the resulting two-layer coating structure is more stable. Specifically, the bonding between the P phase metal oxide coating layer and the surface of the O3 phase nickel-manganese-based oxide layered particles, and the bonding between the inert coating layer and the surface of the O3@P2 phase composite oxide particles are more compact, thereby improving the air stability of the prepared layered oxide cathode material. More preferably, the calcination atmosphere of the first calcination treatment is air and / or oxygen. The inventors prefer that the first calcination be carried out in the presence of air to more efficiently form the P2 phase oxide coating layer and improve ionic conductivity.

[0069] In several typical implementation methods:

[0070] When the O3@P2 phase composite oxide particles are mixed with the second metal source, a second calcination treatment is performed. The temperature of the second calcination treatment is 700℃~1000℃, the time is 10h~20h, and the atmosphere is air and / or oxygen. At this time, the inert coating layer is an inorganic metal oxide layer. The inventors have optimized the above conditions through a large number of experiments to form a more stable and dense inert coating layer, thereby improving the air stability of the final layered oxide cathode material.

[0071] When O3@P2 phase composite oxide particles are mixed with a carbon source, and the carbon source is selected from one or more of coal tar, coal pitch, and petroleum pitch, a second calcination treatment is performed. The temperature of the second calcination treatment is 400℃~800℃, the time is 0.5h~2h, and the atmosphere is a nitrogen atmosphere and / or an argon atmosphere. At this time, the inert coating layer is a carbon layer, and the carbon source contains a variety of small-molecule organic matter. Therefore, the inventors have optimized the above conditions through a large number of experiments to remove small organic molecules from coal tar, coal pitch, and petroleum pitch, and at the same time complete carbonization to obtain a more complete and stable inert coating layer, thereby improving the air stability of the final layered oxide cathode material.

[0072] When O3@P2 phase composite oxide particles are mixed with a carbon source, and the carbon source is selected from one or more of expanded graphite, carbon black and graphene, a second calcination treatment is not performed. The layered oxide cathode material is obtained after the second ball milling. At this time, the inert coating layer is a carbon layer, and the carbon source contains only elemental carbon. Therefore, in order to simplify the process and shorten the cycle, the layered oxide cathode material is obtained directly after the second ball milling. The carbon layer in its structure has achieved complete and stable coating.

[0073] A third aspect of the present invention provides a positive electrode sheet comprising the above-described layered oxide positive electrode material.

[0074] A fourth aspect of the present invention provides a sodium-ion battery comprising the above-described positive electrode.

[0075] Because the cathode material obtained by this invention has both good electrochemical performance and structural stability, when it is used as a cathode electrode component in sodium-ion batteries, the resulting sodium-ion batteries also have comprehensively improved electrochemical performance, including improved first-cycle coulombic efficiency, excellent rate performance, long cycle life and good air stability, thus enabling them to be well applied in multiple application scenarios.

[0076] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0077] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0078] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0079] I. Preparation Method

[0080] Example 1

[0081] Preparation method of layered oxide cathode materials:

[0082] First, prepare the O3 phase cathode material NaNi. 0.45 Mn 0.4 Ti 0.1 Cu 0.05 O2: Sodium carbonate, nickel oxide, manganese dioxide, titanium dioxide, and copper oxide were weighed according to their stoichiometric ratios and mixed with a certain amount of anhydrous ethanol in a ball mill for 3 hours at a speed of 450 r / min. The mixture was then dried in a vacuum drying oven for 12 hours to obtain a dry powder. The powder was then calcined in air at a temperature of 900℃ for 15 hours.

[0083] Secondly, sodium carbonate, magnesium oxide, copper oxide, and manganese dioxide were weighed according to the stoichiometric ratio in the P2 phase molecular formula, and thoroughly ground to obtain the first metal source. 1g of the first metal source was then mixed with 20g of O3 phase cathode material NaNi. 0.45 Mn 0.4 Ti 0.1 Cu 0.05 O2 was placed in a ball mill jar and milled for 3 hours at a speed of 450 rpm to obtain the first pre-coated particles. The ball-milled first pre-coated particle sample was placed in a muffle furnace and calcined at 900℃ for 10 hours. After cooling, it was ground to obtain O3@P2 phase composite oxide particles with a P2 phase metal oxide coating layer. The molecular formula of the P2 phase is Na. 0.6 Mg 0.15 Cu 0.15 Mn 0.7 O2;

[0084] Finally, 10g of O3@P2 phase composite oxide particles with the first coating layer and 0.2g of expanded graphite were placed in a ball mill jar and ball milled for 3 hours at a speed of 450 rpm to obtain the second pre-coated particles. After the ball-milled second pre-coated particle sample was thoroughly dried and ground, a layered oxide cathode material with a P2 phase metal oxide coating layer and an inert coating layer was obtained, labeled as G@P2@O3. The scanning electron microscope image of the obtained G@P2@O3 layered oxide cathode material is shown in Figure 1, and the XRD test spectrum is shown in Figure 3.

[0085] In the G@P2@O3 layered oxide cathode material, the thickness of the P2 phase metal oxide coating layer is 12 nm, and the thickness of the inert coating layer is 20 nm.

[0086] Example 2

[0087] Preparation method of layered oxide cathode materials:

[0088] First, prepare the O3 phase cathode material NaNi. 0.5 Mn 0.4 Ti 0.1 O2: Sodium carbonate, nickel oxide, manganese dioxide, titanium dioxide, and a certain amount of anhydrous ethanol were weighed according to the stoichiometric ratio and mixed evenly in a ball mill for 3 hours at a ball mill speed of 450 r / min. The mixture was then dried in a vacuum drying oven for 12 hours to obtain a dry powder. The powder was then calcined at high temperature in air at 900℃ for 15 hours.

[0089] Next, sodium carbonate, magnesium oxide, copper oxide, and manganese dioxide were weighed according to the stoichiometric ratio of the P2 phase molecular formula and thoroughly ground to obtain the first metal source. 1g of the first metal source was then mixed with 20g of O3 phase cathode material NaNi. 0.5 Mn 0.4 Ti 0.1 O2 was placed in a ball mill jar and milled for 3 hours at a speed of 450 rpm to obtain the first pre-coated particles. The ball-milled first pre-coated particle sample was placed in a muffle furnace and calcined at 900℃ for 10 hours. After cooling, it was ground to obtain O3@P2 phase composite oxide particles with a P2 phase metal oxide coating layer. The molecular formula of the P2 phase is Na. 9 / 7 Cu 2 / 9 Fe 1 / 9 Mn 2 / 3 O2;

[0090] Finally, 10g of O3@P2 phase composite oxide particles with the first coating layer and 0.05g of Al2O3 were placed in a ball mill jar and ball milled for 3 hours at a speed of 450 rpm to obtain the second pre-coated particles. The ball-milled second pre-coated particle sample was placed in a muffle furnace and calcined at 600℃ for 10 hours. After thorough drying and grinding, a layered oxide cathode material with a P2 phase metal oxide coating layer and an inert coating layer was obtained, labeled as Al2O3@P2@O3 layered oxide cathode material.

[0091] In the Al2O3@P2@O3 layered oxide cathode material, the thickness of the P2 phase metal oxide coating layer is 14 nm, and the thickness of the inert coating layer is 18 nm.

[0092] Example 3

[0093] Preparation method of layered oxide cathode materials:

[0094] First, prepare the O3 phase cathode material NaNi. 0.45 Mn 0.4 Ti 0.1 Fe 0.05 O2: Sodium carbonate, nickel oxide, manganese dioxide, titanium dioxide, ferric oxide, and a certain amount of anhydrous ethanol were weighed according to the stoichiometric ratio and mixed evenly in a ball mill for 3 hours at a ball mill speed of 450 r / min. The mixture was then dried in a vacuum drying oven for 12 hours to obtain a dry powder. The powder was then calcined at high temperature in air at 900℃ for 15 hours.

[0095] Next, sodium carbonate, magnesium oxide, copper oxide, and manganese dioxide were weighed according to the stoichiometric ratio of the P2 phase molecular formula, and thoroughly ground to obtain the first metal source. 1g of the first metal source was then mixed with 20g of O3 phase cathode material NaNi. 0.45 Mn 0.4 Ti 0.1 Fe 0.05 O2 was placed in a ball mill jar and milled for 3 hours at a speed of 450 rpm to obtain the first pre-coated particles. The ball-milled first pre-coated particle sample was placed in a muffle furnace and calcined at 900℃ for 10 hours. After cooling, it was ground to obtain O3@P2 phase composite oxide particles with a P2 phase metal oxide coating layer. The molecular formula of the P2 phase is Na. 0.6 Mg 0.15 Cu 0.15 Mn 0.7 O2;

[0096] Finally, 10g of O3@P2 phase composite oxide particles with the first coating layer and 0.05g of Al2O3 were placed in a ball mill jar and ball milled for 3 hours at a speed of 450 rpm to obtain the second pre-coated particles. The ball-milled second pre-coated particle sample was placed in a muffle furnace and calcined at 600℃ for 10 hours. After thorough drying and grinding, a layered oxide cathode material with a P2 phase metal oxide coating layer and an inert coating layer was obtained, labeled as Al2O3@P2@O3 layered oxide cathode material.

[0097] In the Al2O3@P2@O3 layered oxide cathode material, the thickness of the P2 phase metal oxide coating layer is 15 nm, and the thickness of the inert coating layer is 22 nm.

[0098] Example 4

[0099] Preparation method of layered oxide cathode materials:

[0100] First, prepare the O3 phase cathode material NaNi. 0.45 Mn 0.4 Ti 0.1 Zn 0.05 O2: Sodium carbonate, nickel oxide, manganese dioxide, titanium dioxide, and zinc oxide were weighed according to their stoichiometric ratios and mixed with a certain amount of anhydrous ethanol in a ball mill. The mixing time was 3 hours, and the ball mill speed was 450 r / min. The mixture was then dried in a vacuum drying oven for 12 hours to obtain a dry powder. The powder was then calcined at a high temperature in air. The calcination temperature was 900℃, and the holding time was 15 hours.

[0101] Next, sodium carbonate, magnesium oxide, copper oxide, and manganese dioxide were weighed according to the stoichiometric ratio of the P2 phase molecular formula and thoroughly ground to obtain the first metal source. 1g of the first metal source was then mixed with 20g of O3 phase cathode material NaNi. 0.45 Mn 0.4 Ti 0.1 Zn 0.05 O2 was placed in a ball mill jar and milled for 3 hours at a speed of 450 rpm to obtain the first pre-coated particles. The milled first pre-coated particle sample was then placed in a muffle furnace and calcined at 900℃ for 10 hours. After cooling, it was ground to obtain O3@P2 phase composite oxide particles with a P2 phase metal oxide coating. The molecular formula of the P2 phase is Na. 0.6 Mg 0.15 Cu 0.15 Mn 0.7 O2;

[0102] Finally, 10g of O3@P2 phase composite oxide particles with the first coating layer and 0.05g of TiO2 were placed in a ball mill jar and ball milled for 3 hours at a speed of 450 rpm to obtain the second pre-coated particles. The ball-milled second pre-coated particle sample was placed in a muffle furnace and calcined at 600℃ for 10 hours. After thorough drying and grinding, a layered oxide cathode material with a P2 phase metal oxide coating layer and an inert coating layer was obtained, which was labeled as TiO2@P2@O3 layered oxide cathode material.

[0103] In the TiO2@P2@O3 layered oxide cathode material, the thickness of the P2 phase metal oxide coating layer is 16 nm, and the thickness of the inert coating layer is 19 nm.

[0104] Example 5

[0105] Preparation method of layered oxide cathode materials:

[0106] The only difference between this embodiment and Embodiment 1 is that the amounts of the first metal source and expanded graphite (i.e., carbon source) are different. Specifically, the amounts of the first metal source and expanded graphite are changed so that the weight ratio of O3 phase nickel manganese-based oxide layered particles to the first metal source is 1:0.002, and the weight ratio of O3@P2 phase composite oxide particles to carbon source is 1:0.002.

[0107] In the obtained G@P2@O3 layered oxide cathode material, the thickness of the P2 phase metal oxide coating layer is 1.5 nm, and the thickness of the inert coating layer is 1.8 nm.

[0108] Example 6

[0109] Preparation method of layered oxide cathode materials:

[0110] The only difference between this embodiment and Embodiment 1 is that the amounts of the first metal source and expanded graphite (i.e., carbon source) are different. Specifically, the amounts of the first metal source and expanded graphite are changed so that the weight ratio of O3 phase nickel manganese-based oxide layered particles to the first metal source is 1:0.08, and the weight ratio of O3@P2 phase composite oxide particles to carbon source is 1:0.08.

[0111] In the obtained G@P2@O3 layered oxide material, the thickness of the P2 phase metal oxide coating layer is 125 nm, and the thickness of the inert coating layer is 140 nm.

[0112] Example 7

[0113] Preparation method of layered oxide cathode materials:

[0114] The only difference between this embodiment and Embodiment 1 is that the conditions involved in the two ball milling processes are different. Specifically:

[0115] The ball milling time for obtaining the first pre-coated particles was 5 hours and the rotation speed was 50 rpm; the ball milling time for obtaining the second pre-coated particles was 5 hours and the rotation speed was 50 rpm.

[0116] Example 8

[0117] Preparation method of layered oxide cathode materials:

[0118] The only difference between this embodiment and Embodiment 1 is that the conditions involved in the two ball milling processes are different. Specifically:

[0119] The ball milling time for obtaining the first pre-coated particles was 0.4 h, and the rotation speed was 600 rpm; the ball milling time for obtaining the second pre-coated particles was 0.4 h, and the rotation speed was 600 rpm.

[0120] Example 9

[0121] Preparation method of layered oxide cathode materials:

[0122] The only difference between this embodiment and Embodiment 1 is that the calcination conditions for the first pre-coated particle sample after ball milling are different; specifically, calcination at 500°C for 22 hours.

[0123] Example 10

[0124] Preparation method of layered oxide cathode materials:

[0125] The only difference between this embodiment and Embodiment 1 is that the calcination conditions for the first pre-coated particle sample after ball milling are different; specifically, it is calcined at 1100°C for 1 hour.

[0126] Example 11

[0127] Preparation method of layered oxide cathode materials:

[0128] The only difference between this embodiment and Embodiment 2 is that the calcination conditions for the second pre-coated particle sample after ball milling are different; specifically, calcination at 300°C for 22 hours.

[0129] Example 12

[0130] Preparation method of layered oxide cathode materials:

[0131] The only difference between this embodiment and Embodiment 2 is that the calcination conditions for the second pre-coated particle sample after ball milling are different, specifically: calcination at 1100℃ for 0.2h.

[0132] Comparative Example 1

[0133] Preparation method of layered oxide cathode materials:

[0134] The only difference between this comparative example and Example 1 is that the O3 phase cathode material NaNi was not compared. 0.45 Mn 0.4 Ti 0.1 Cu 0.05 Instead of coating O2, it is used directly as a positive electrode material.

[0135] The scanning electron microscope image of the O3 phase cathode material is shown in Figure 2, and the XRD pattern is shown in Figure 4.

[0136] Comparative Example 2

[0137] Preparation method of layered oxide cathode materials:

[0138] The only difference between this comparative example and Example 1 is that no inert coating layer was applied, and the O3@P2 phase composite oxide particles with P2 phase metal oxide coating layer were directly used as the positive electrode material.

[0139] Comparative Example 3

[0140] Preparation method of layered oxide cathode materials:

[0141] The only difference between this comparative example and Example 1 is that no P2 phase metal oxide coating was applied; that is, 10g of O3 phase cathode material particles NaNi were directly coated. 0.45 Mn 0.4 Ti 0.1 Cu 0.05 O2 and 0.2g of expanded graphite were placed in a ball mill jar and milled for 3 hours at a speed of 450 rpm to obtain pre-coated particles. After the pre-coated particles were thoroughly dried and ground, the cathode material was obtained.

[0142] Comparative Example 4

[0143] Preparation method of layered oxide cathode materials:

[0144] The only difference between this comparative example and Example 1 is that: in obtaining the O3 phase cathode material NaNi 0.45 Mn 0.4 Ti 0.1 Cu 0.05 Following O2, 1g of a mixture of the first metal source and expanded graphite (weight ratio 1:1) was added to 20g of O3-phase cathode material NaNi. 0.45 Mn 0.4 Ti 0.1 Cu 0.05 O2 was placed in a ball mill jar and milled for 3 hours at a speed of 450 rpm to obtain pre-coated particles. The pre-coated particle sample was placed in a muffle furnace and calcined at 900°C for 10 hours. After cooling, it was ground to obtain the cathode material.

[0145] That is, the material of the P2 phase metal oxide coating layer is mixed with the material of the inert coating layer and then used as a mixed coating layer for single-layer coating.

[0146] Battery assembly:

[0147] (1) Preparation of positive electrode sheet: The layered oxide positive electrode material, conductive carbon black and polyvinylidene fluoride (PVDF) prepared in the above embodiments and comparative examples are mixed in a mass ratio of 8:1:1. An appropriate amount of N-methylpyrrolidone (NMP) is added to form a uniform electrode slurry. The electrode slurry is then uniformly coated on aluminum foil, vacuum dried and cut into circular electrode sheets with a diameter of 15 mm. The sheets are then transferred to a glove box for later use.

[0148] (2) Battery Assembly: Using sodium metal as the counter electrode and glass fiber as the separator, the electrolyte consisted of sodium perchlorate as the solute and propylene carbonate, ethylene carbonate, and fluoroethylene carbonate as the solvents (volume ratio 1:1:0.05). The concentration of sodium perchlorate in the electrolyte was 1 mol / L. CR2032 button cells were assembled in an argon-filled glove box. After standing for 6 hours, the button cells were used for subsequent electrochemical performance testing.

[0149] II. Testing Methods

[0150] Coverage of P2 phase metal oxide coating and inert coating: The percentage of the area covered by the coating to the total surface area of ​​the electrode material, determined by infrared spectroscopy analysis.

[0151] Particle size: determined according to GB / T 19077, particle size analysis by laser diffraction method.

[0152] Compacted density: Determined according to GB / T 24533, powder compacted density.

[0153] pH value: Determined according to GB / T 9724, General Rules for pH Value Determination of Chemical Reagents.

[0154] Moisture content: determined according to GB / T 6283, Determination of moisture content in chemical products by Karl Fischer method (general method).

[0155] Specific surface area: The specific surface area of ​​solid substances is determined according to GB / T 19587, gas adsorption BET method.

[0156] Scanning electron microscope images: taken with a ZEISS MERLIN Compact microscope at a magnification of 50k, as shown in Figures 1 and 2.

[0157] Electrochemical performance testing: Using a constant current charge-discharge mode, charge-discharge tests were conducted at a current density of 0.1C, with a charging cutoff voltage of 4.2V and a discharging cutoff voltage of 2.0V. The first charge-discharge capacity and coulombic efficiency of each battery were tested.

[0158] Air stability: The cathode materials obtained in the above embodiments and comparative examples were exposed to the air environment for 24 hours, and the cathode materials exposed to air were prepared into batteries in the above manner, and their first charge-discharge capacity and coulombic efficiency were tested.

[0159] The particle size distribution and layer coverage of the cathode materials obtained in each embodiment and comparative example are shown in Table 1, the physicochemical performance test results are shown in Table 2, and the electrochemical performance test results of each battery further prepared are shown in Table 3.

[0160] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0161] Table 1

[0162] Table 2

[0163] Table 3

[0164] The results above demonstrate that the embodiments of this invention achieve excellent coating effects. The P2 phase metal oxide coating layer reduces the residual alkali content on the surface of the O3 phase nickel-manganese-based layered oxide, while the inert coating layer reduces side reactions between the material surface and the air and electrolyte. The experiments revealed that the double-layer coating of the P2 phase metal oxide and inert coating layers affects the material's particle size, specific surface area, pH value, moisture content, and compaction density. Appropriate nickel-manganese-based cathode materials, coating amounts, and ball milling conditions result in layered oxide cathode materials exhibiting high electrochemical performance and good air stability. Consequently, when applied to sodium-ion batteries, the prepared sodium-ion batteries exhibit high first-cycle coulombic efficiency, excellent rate performance, long cycle life, and good air stability. Furthermore, the preparation method of the layered oxide cathode material provided by this invention is simple and practical, suitable for large-scale production, and has broad application prospects.

[0165] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A layered oxide cathode material, characterized in that, The layered oxide cathode material includes O3@P2 phase composite oxide particles and an inert coating layer covering the surface of the O3@P2 phase composite oxide particles. The O3@P2 phase composite oxide particles include O3 phase nickel-manganese-based oxide layered particles and a P2 phase metal oxide coating layer covering the surface of the O3 phase nickel-manganese-based oxide layered particles. The inert coating layer is a carbon layer and / or an inorganic metal oxide layer.

2. The layered oxide cathode material according to claim 1, characterized in that, The molecular formula of the O3 phase nickel-manganese-based oxide layered particles is Na. x Ni a Mn b M1 c O2, where 0.8≤x≤1.0, a+b+c=1.0 and a, b and c are all positive numbers, and M1 is selected from one or more of Fe, Ti, Mg, Cu, Al, Ca, Zn and Co; Preferably, M1 is selected from one or more of Fe, Ti, Mg, Cu, Zn and Ca.

3. The layered oxide cathode material according to claim 1, characterized in that, The molecular formula of the P2 phase metal oxide coating layer is Na. y M2O2; wherein 0.6≤y≤0.8, and M2 is selected from one or more of Ni, Mn, Fe, Ti, Mg, Cu, Al, Ca and Co; Preferably, M2 is selected from one or more of Fe, Mn, Mg, Cu and Ca.

4. The layered oxide cathode material according to any one of claims 1 to 3, characterized in that, The inorganic metal oxide layer is selected from one or more of Al2O3 layer, TiO2 layer, CuO layer and MgO layer; Preferably, the inorganic metal oxide layer is selected from one or more of Al2O3 layer, TiO2 layer and MgO layer.

5. The layered oxide cathode material according to claim 4, characterized in that, In the O3 phase nickel-manganese-based oxide layered particles, M1 is Ti, and in the P2 phase metal oxide coating layer, M2 is selected from one or more of Fe, Cu, and Mn; or, In the O3 phase nickel-manganese-based oxide layered particles, M1 is Cu or Ti and Cu, and in the P2 phase metal oxide coating layer, M2 is selected from one or more of Mg, Cu and Mn.

6. The layered oxide cathode material according to claim 4, characterized in that, The molecular formula of the O3 phase nickel-manganese-based oxide layered particles is NaNi. 0.5 Mn 0.4 Ti 0.1 O2, the molecular formula of the P2 phase metal oxide coating layer is Na 9 / 7 Cu 2 / 9 Fe 1 / 9 Mn 2 / 3 O2, and the inert coating layer is the Al2O3 layer; or, The molecular formula of the O3 phase nickel-manganese-based oxide layered particles is NaNi. 0.45 Mn 0.4 Ti 0.1 Cu 0.05 O2, the molecular formula of the P2 phase metal oxide coating layer is Na 0.6 Mg 0.15 Cu 0.15 Mn 0.7 O2, and the inert coating layer is the carbon layer.

7. The layered oxide cathode material according to any one of claims 1 to 3, characterized in that, In the layered oxide cathode material, the thickness of the P2 phase metal oxide coating layer is 2nm to 100nm, and the thickness of the inert coating layer is 2nm to 100nm. Preferably, based on 100% of the weight of the layered oxide cathode material, the mass fraction of the P2 phase metal oxide coating layer is 0.5% to 5%, and the mass fraction of the inert coating layer is 0.5% to 5%. Preferably, the coverage of the P2 phase metal oxide coating layer on the surface of the O3 phase nickel manganese-based oxide layered particles is 80% to 100%, and the coverage of the inert coating layer on the surface of the O3@P2 phase composite oxide particles is 80% to 100%.

8. A method for preparing a layered oxide cathode material according to any one of claims 1 to 7, characterized in that, The preparation method includes: O3 phase nickel manganese-based oxide layered particles and a first metal source are provided. The O3 phase nickel manganese-based oxide layered particles are mixed with the first metal source and subjected to a first ball milling to obtain first pre-coated particles. The first pre-coated particles are subjected to a first calcination treatment to obtain the O3@P2 phase composite oxide particles; The O3@P2 phase composite oxide particles are mixed with a carbon source and / or a second metal source, and then subjected to a second ball milling to obtain second pre-coated particles. The second pre-coated particles are optionally subjected to a second calcination treatment to obtain the layered oxide cathode material.

9. The method for preparing the layered oxide cathode material according to claim 8, characterized in that, The first ball mill operates at a speed of 100 rpm to 500 rpm for a time of 0.5 h to 4 h; and / or the second ball mill operates at a speed of 100 rpm to 500 rpm for a time of 0.5 h to 4 h.

10. The method for preparing the layered oxide cathode material according to claim 8 or 9, characterized in that, The weight ratio of the O3 phase nickel-manganese-based oxide layered particles to the first metal source is 1:(0.005~0.05), and the weight ratio of the O3@P2 phase composite oxide particles to the carbon source and / or the second metal source is 1:(0.005~0.05). Preferably, the first metal source includes a sodium source and a coated metal source, wherein the coated metal source is selected from one or more of the oxides, hydroxides, carbonates, sulfates, oxalates, acetates, and citrates corresponding to Fe, Ti, Mg, Cu, Al, Ca, Zn, and Co; and the sodium source is selected from one or more of sodium carbonate, sodium hydroxide, sodium nitrate, and sodium peroxide. Preferably, the carbon source is selected from one or more of coal tar, coal pitch, petroleum pitch, expanded graphite, carbon black, and graphene, and the second metal source is selected from one or more of the oxides, hydroxides, and carbonates corresponding to Ni, Mn, Fe, Ti, Mg, Cu, Al, Ca, and Co.

11. The method for preparing the layered oxide cathode material according to claim 10, characterized in that, The temperature of the first calcination treatment is 600℃~1000℃, and the calcination time is 2h~20h; the temperature of the second calcination treatment is 400℃~1000℃, and the calcination time is 0.5h~20h. Preferably, the calcination atmosphere of the first calcination treatment is an air and / or oxygen atmosphere.

12. The method for preparing the layered oxide cathode material according to claim 11, characterized in that, When the O3@P2 phase composite oxide particles are mixed with the second metal source, the second calcination treatment is performed, and the temperature of the second calcination treatment is 700℃~1000℃, the time is 10h~20h, and the atmosphere is air and / or oxygen atmosphere. When the O3@P2 phase composite oxide particles are mixed with the carbon source, and the carbon source is selected from one or more of coal tar, coal pitch and petroleum pitch, the second calcination treatment is carried out, and the temperature of the second calcination treatment is 400℃~800℃, the time is 0.5h~2h, and the atmosphere is a nitrogen atmosphere and / or an argon atmosphere. When the O3@P2 phase composite oxide particles are mixed with the carbon source, and the carbon source is selected from one or more of expanded graphite, carbon black and graphene, the second calcination treatment is not performed, and the layered oxide cathode material is obtained after the second ball milling.

13. A positive electrode plate, characterized in that, The positive electrode sheet comprises the layered oxide positive electrode material according to any one of claims 1 to 7, or the layered oxide positive electrode material prepared by the method of preparing the layered oxide positive electrode material according to any one of claims 8 to 12.

14. A sodium-ion battery, characterized in that, The sodium-ion battery includes the positive electrode as described in claim 13.

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