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

Abstract

The present invention provides a layered oxide positive electrode material and a preparation method thereof, a positive electrode sheet and a sodium ion battery, belonging to the technical field of sodium ion batteries, wherein the layered oxide positive electrode material comprises O3@P2 phase composite oxide particles and an inert coating layer coated on the surface thereof, 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 layered oxide positive electrode material provided by the present invention is applied to a sodium ion battery, the prepared sodium ion battery has high first-cycle coulomb efficiency, excellent rate performance, long cycle life and good air stability.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and in particular to a layered oxide positive electrode material and a preparation method thereof, a positive electrode sheet and a sodium ion battery. Background Art

[0002] Lithium-ion batteries have been widely used in electric vehicles, consumer electronics, and energy storage, but they face problems such as low lithium reserves, uneven distribution, and large price fluctuations, which seriously restrict their large-scale application. Compared with lithium resources, sodium resources are widely distributed in the earth's crust and are easy to obtain. Therefore, sodium-ion batteries have a greater cost advantage and are expected to be widely used in the field of energy storage.

[0003] Sodium-ion batteries have similar working principles to lithium-ion batteries. Sodium-ion batteries use the extraction and embedding of sodium ions between the positive and negative electrodes to achieve energy storage and release. At present, the main cathode materials of sodium-ion batteries are layered transition metal oxides, polyanion compounds, and Prussian blue analogs. Among them, layered transition metal oxide cathode materials have the highest sodium storage capacity, which has attracted more and more research and attention. Among them, layered transition metal oxides can be mainly divided into P2 and O3 types according to the sodium ion coordination environment and interlayer stacking order. The English letters P and O represent the sodium ion coordination environment as prism and octahedron, respectively, and the numbers 2 and 3 represent the interlayer stacking order as ABBA and ABCABC, respectively. Among them, the P2 phase material is a sodium-poor phase (usually the sodium content is less than 0.67). When it is used to make sodium-ion batteries, the first-cycle charging capacity of the prepared sodium-ion batteries is low, and an additional sodium replenishment process is required, which is not conducive to practical application; the O3 phase material is a sodium-rich phase (usually the sodium content is close to 1.0). When it is used to make sodium-ion batteries, the prepared sodium-ion batteries have high charge and discharge capacities, so the O3 phase material has the potential to become a commercial sodium-ion battery positive electrode material. However, the rich sodium element in the O3 phase positive electrode material easily reacts with moisture and carbon dioxide in the air, resulting in a high residual alkali content on the surface of the material, and the formation of sodium carbonate, sodium hydroxide, sodium bicarbonate and other substances with poor conductivity will affect the first-cycle coulomb efficiency, reversible capacity and other properties of the prepared sodium-ion battery.

[0004] Based on this, how to eliminate or effectively utilize the residual alkali on the surface of the O3 phase layered oxide sodium ion battery positive electrode material and improve the air stability of the O3 phase layered oxide sodium ion battery positive electrode material are technical problems that need to be solved urgently in this field. Summary of the invention

[0005] The main purpose of the present invention is to provide a layered oxide positive electrode material and a preparation method thereof, a positive electrode plate and a sodium ion battery, so as to solve the problem that the sodium ion battery positive electrode material in the prior art has poor electrochemical performance due to residual alkali and poor air stability.

[0006] In order to achieve the above-mentioned objectives, the first aspect of the present invention provides a layered oxide positive electrode material, which layered oxide positive electrode material includes 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 include 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.

[0007] In the technical solution of the embodiment of the present application, in order to address the defects existing in the existing sodium ion battery positive electrode materials, a layered oxide positive electrode material with a double-layer coating structure is provided, wherein 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, and the inert coating layer delays the side reaction between the outer surface of the layered oxide positive electrode material and the air and the electrolyte, thereby significantly reducing the residual alkali content on the surface of the oxide material and improving the air stability.

[0008] Furthermore, the molecular formula of the O3 phase nickel-manganese-based oxide layered particles is Na x Ni a Mn b M1 c O 2 , 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.

[0009] In this embodiment, the inventors selected and optimized the types of O3-phase nickel-manganese-based oxide layered particles through a large number of experiments, and found that when its components are the elemental composition and stoichiometric ratio in the above molecular formula, the air stability of the obtained O3-phase nickel-manganese-based oxide layered particles is further improved, and 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.

[0010] Furthermore, the molecular formula of the P2 phase metal oxide coating is Na y M2O 2 ; 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.

[0011] In this embodiment, the inventors selected and optimized the type of P2 phase metal oxide coating layer through a large number of experiments, and found that when its components are the elemental composition and stoichiometric ratio in the above molecular formula, it can better reduce the residual alkali amount 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 layer.

[0012] Furthermore, the inorganic metal oxide layer is selected from Al 2 O 3 layer, TiO 2 One or more of a CuO layer and a MgO layer; preferably, the inorganic metal oxide layer is selected from Al 2 O 3 layer, TiO 2 One or more of a layer and a MgO layer.

[0013] In this embodiment, compared with the inorganic metal oxide layer formed by other metals, the structure of the above-mentioned inorganic metal oxide layers is more stable and can better inhibit the side reaction between the O3@P2 phase composite oxide particles and the electrolyte. On this basis, the inventor further prefers that the inorganic metal oxide layer is selected from Al 2 O 3 layer, TiO 2 layer and one or more of the MgO layer, and it is found that these inorganic metal oxide layers can better cooperate with the above-mentioned preferred P2 phase metal oxide coating layer, and the cost is also lower, which can effectively improve the product added value of the prepared layered oxide positive electrode material.

[0014] Further, 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.

[0015] In this embodiment, the inventors, through a large number of experiments and comparisons, found 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 above manner, the P2 phase metal oxide coating layer and the O3 phase nickel manganese-based oxide layered particles can be better combined, and 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 positive electrode material.

[0016] Furthermore, 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 is Na 9 / 7 Cu 2 / 9 Fe 1 / 9 Mn 2 / 3 O 2 , and the inert coating is Al 2 O 3 Alternatively, 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 O 2 The molecular formula of the P2 phase metal oxide coating is Na 0.6 Mg 0.15 Cu 0.15 Mn 0.7 O 2 , and the inert coating layer is a carbon layer.

[0017] In this embodiment, when the O3 phase nickel-manganese-based oxide layered particles as the inner 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 layered oxide positive electrode material are arranged in the above two ways, the obtained layered oxide positive electrode material not only has excellent electrochemical properties, but also has higher air stability and can better meet its actual application needs.

[0018] Furthermore, in the layered oxide positive electrode 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 the weight of the layered oxide positive electrode material being 100%, 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%.

[0019] In this embodiment, when the thickness of the two coating layers is within the above range, it is possible to better balance between suppressing side reactions, consuming residual alkali and improving conductivity, thereby better improving the electrochemical performance of the positive electrode material. When the two coating layers are arranged according to the above weight proportions, the coating layers and the P2 phase metal oxide coating layer and the core particles can better cooperate and transfer mass, and the electrochemical performance of the obtained positive electrode material is also higher. And, in several typical embodiments, 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%; the coverage of the inert coating layer on the surface of the O3@P2 phase composite oxide particles is 80% to 100%. In the structure of the layered oxide positive electrode material provided by the present invention, the coverage of each coating layer can reach 80% or more, that is, a good, complete and uniform coating structure is achieved, and the air stability of the obtained layered oxide positive electrode material is further improved.

[0020] The second aspect of the present invention provides a method for preparing the above-mentioned layered oxide positive electrode material, comprising: ： Prepare O3-phase nickel-manganese-based oxide layered particles and a first metal source, mix the O3-phase nickel-manganese-based oxide layered particles with the first metal source, perform a first ball milling, and obtain first pre-coated particles; perform a first calcination treatment on the first pre-coated particles to obtain O3@P2-phase composite oxide particles; mix the O3@P2-phase composite oxide particles with a carbon source and / or a second metal source, perform a second ball milling, and obtain second pre-coated particles; perform an optional second calcination treatment on the second pre-coated particles to obtain a layered oxide positive electrode material.

[0021] In the technical solution of the embodiment of the present application, the first metal source is first pre-coated with the O3-phase nickel-manganese-based oxide layered particles to improve the bonding strength between the two, and then the P2-phase metal oxide coating layer is in-situ generated on the surface of the O3-phase nickel-manganese-based oxide layered particles through an in-situ solid-phase reaction, thereby significantly consuming the residual alkali on its surface and improving the air stability. Thereafter, the O3@P2-phase composite oxide particles are pre-coated with the carbon source and / or the second metal source by ball milling, and an inert coating layer is generated by another in-situ solid-phase reaction. Compared with simple mixed coating or liquid phase reaction, it can better coordinate the physicochemical properties between the coating layers, protect the structural integrity of the core particles and the coating layer, and simplify the process to obtain a layered oxide positive electrode material with better performance and higher product added value. At the same time, the preparation method of the layered oxide positive electrode material provided by the present invention is simple, can be extremely compatible with the existing preparation process, and is easy to be applied in large-scale industry.

[0022] Further, the rotation speed of the first ball mill is 100 rpm to 500 rpm, and the time is 0.5 h to 4 h; and / or the rotation speed of the second ball mill is 100 rpm to 500 rpm, and the time is 0.5 h to 4 h.

[0023] In this embodiment, by setting the experimental conditions of the two ball millings as described above, a more uniform coating can be achieved, thereby improving the composition uniformity, structural continuity and coating integrity of the obtained P2 phase metal oxide coating layer and the inert coating layer.

[0024] Furthermore, 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, and the coated metal source is selected from one or more of 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 tar, petroleum asphalt, expanded graphite, carbon black and graphene, and the second metal source is selected from one or more of oxides, hydroxides and carbonates corresponding to Ni, Mn, Fe, Ti, Mg, Cu, Al, Ca and Co.

[0025] In this embodiment, the inventors have optimized the above-mentioned weight ratio relationship through a large number of experiments, and at the same time correspond to the weight ratio and coating thickness of the P2 phase metal oxide coating layer and the inert coating layer, and found that the material preparation under the above-mentioned weight ratio relationship can more effectively improve the various electrochemical properties and air stability of the obtained layered oxide positive electrode material. The inventors have optimized the above-mentioned several coated metal sources and sodium sources through a large number of comparative tests, and found that when the above-mentioned types are selected, the solid phase reaction can be carried out more smoothly, so that the formation of the P2 phase metal oxide coating layer can be achieved, and the positive electrode material with the expected structure can be obtained. Similarly, the inventors have optimized the above-mentioned several carbon sources and second metal sources through a large number of comparative tests, and found that when the above-mentioned types are selected, the inert coating layer can be smoothly formed in a more continuous, uniform and dense state, thereby obtaining a layered oxide positive electrode material with excellent performance.

[0026] Furthermore, the temperature of the first calcination treatment is 600°C to 1000°C, and the calcination time is 2h to 20h, and the temperature of the second calcination treatment is 400°C to 1000°C, and the calcination time is 0.5h to 20h; preferably, the calcination atmosphere of the first calcination treatment is air and / or oxygen atmosphere.

[0027] In this embodiment, the inventors have optimized the temperature and time conditions for the above-mentioned two calcinations through a large number of experiments, and found that when this is carried out, the resulting two-layer coating structure is more stable, that is, the P2 phase metal oxide coating layer is more tightly bonded to the surface of the O3 phase nickel-manganese-based oxide layered particles, and the inert coating layer is more tightly bonded to the surface of the O3@P2 phase composite oxide particles, thereby making the prepared layered oxide positive electrode material have better air stability.

[0028] More preferably, the calcination atmosphere of the first calcination treatment is air and / or oxygen atmosphere. The inventors prefer that the first calcination be performed in the presence of air, so as to more efficiently form the P2 phase oxide coating layer and improve the ionic conductivity.

[0029] Furthermore, when the O3@P2 phase composite oxide particles are mixed with the second metal source, a second calcination treatment is carried out, and the temperature of the second calcination treatment is 700°C to 1000°C, the time is 10h to 20h, and the atmosphere is air and / or oxygen atmosphere; at this time, the inert coating layer is an inorganic metal oxide layer, and the inventor has optimized the above conditions through a large number of experiments to form an inert coating layer with a more stable and dense structure, thereby improving the air stability of the finally formed layered oxide positive electrode material.

[0030] 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 tar and petroleum asphalt, a second calcination treatment is carried out, and the temperature of the second calcination treatment is 400°C to 800°C, the time is 0.5h to 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 molecular organic matter, so the inventor has optimized the above conditions through a large number of experiments to achieve the removal of organic small molecules in coal tar, coal tar and petroleum asphalt, and at the same time complete carbonization to obtain a more complete stable carbon layer, thereby improving the air stability of the finally formed layered oxide positive electrode material.

[0031] 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 expanded graphite, carbon black and graphene, the second calcination treatment is not performed, and a layered oxide positive electrode 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, so in order to simplify the process and shorten the cycle, the layered oxide positive electrode material is directly obtained after the second ball milling.

[0032] A third aspect of the present invention provides a positive electrode plate, which includes the above-mentioned layered oxide positive electrode material.

[0033] In this embodiment, the positive electrode plate includes the above-mentioned layered oxide positive electrode material, and thus has higher electrochemical performance and good air stability.

[0034] A fourth aspect of the present invention provides a sodium ion battery, which includes the above-mentioned positive electrode plate.

[0035] Because the above-mentioned positive electrode material obtained by the present invention has both good electrochemical properties and structural stability, when it is used as a positive electrode plate component in a sodium ion battery, the obtained sodium ion battery also has comprehensively improved electrochemical properties, including improved first-cycle coulombic efficiency, excellent rate performance, long cycle life and good air stability, so that it can be well applied to multiple usage scenarios.

[0036] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the technical solution of the present application, the following is a brief introduction to the drawings used in the present application. Obviously, the drawings described below are only some embodiments of the present application, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0038] Figure 1 This is a scanning electron microscope image of the layered oxide positive electrode material obtained in Example 1;

[0039] Figure 2 This is a scanning electron microscope image of the layered oxide positive electrode material obtained in Comparative Example 1;

[0040] Figure 3 This is the XRD pattern of the layered oxide positive electrode material obtained in Example 1;

[0041] Figure 4 This is the XRD pattern of the layered oxide positive electrode material obtained in Comparative Example 1. DETAILED DESCRIPTION

[0042] The following embodiments of the technical solution of the present application will be described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0044] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0045] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0046] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0047] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0048] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, which are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the embodiments of the present application.

[0049] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0050] As described in the background art, the sodium ion battery positive electrode material in the prior art has the problem of poor electrochemical performance of the sodium ion battery due to poor residual alkali and air stability. In order to solve the above technical problems, the first aspect of the present invention provides a layered oxide positive electrode material, the layered oxide positive electrode material includes 03@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 include 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.

[0051] The layered oxide positive electrode material provided by the present invention includes an O3 phase nickel-manganese-based oxide layered particle inner core, a first P2 phase metal oxide coating layer coated thereon, and a second inert coating layer; wherein 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 particle and provides a good sodium ion transport channel, and the inert coating layer delays the side reaction between the outer surface of the layered oxide positive electrode material and the air and the electrolyte, so that the layered oxide positive electrode material as a whole exhibits high electrochemical performance and good air stability.

[0052] Specifically, the P2 phase metal oxide coating layer and the inert coating layer cooperate with each other to synergistically improve the comprehensive electrochemical performance of the O3 phase nickel-manganese-based oxide layered particles, wherein: the inert coating layer is stable, uniform and dense. When it is coated on the outermost surface and directly in contact with the electrolyte, it can more effectively reduce the side reactions between the prepared layered oxide positive electrode material and the electrolyte, thereby reducing the erosion of the positive electrode effective components by the HF generated by the side reactions, and extending its service life. At the same time, the inert coating layer with a certain degree of flexibility can also effectively inhibit the generation of cracks inside the positive electrode material particles. However, if the inert coating layer is in direct contact with the O3 phase nickel-manganese-based oxide layered particles, the diffusion channel of the metal ions in its core will be blocked, affecting the electrochemical performance of the positive electrode material. Taking this into consideration, the present invention adopts a form of sequential coating of a P2 phase metal oxide coating layer and an inert coating layer. Although the P2 phase metal oxide coating layer has poor ability to inhibit side reactions in the electrolyte, it has a higher ionic conductivity and can effectively reduce the charge transfer impedance on the surface of the O3 phase nickel-manganese-based oxide layered particles.

[0053] The inventors comprehensively considered the above situation and verified through a large number of experiments that the P2 phase metal oxide coating layer is used in combination with the inert coating layer, that is, the surface of the O3 phase nickel manganese-based oxide layered particles is coated with a P2 phase metal oxide coating layer that has good ion conductivity and can significantly consume residual alkali, and then an inert coating layer is formed on the surface of the P2 phase metal oxide coating layer, and the inert coating layer is in direct contact with the electrolyte. The present invention synergizes the advantages of the two coating layers, thereby improving the electrochemical performance of the layered oxide positive electrode material finally obtained, and further can improve the first cycle coulomb efficiency, rate performance and cycle life of the sodium ion battery made using the positive electrode material.

[0054] Furthermore, the molecular formula of the O3 phase nickel-manganese-based oxide layered particles is Na x Ni a Mn b M1 c O 2 , 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. The inventors have selected and optimized the types of O3-phase nickel-manganese-based oxide layered particles through a large number of experiments, and found that when its components are the element composition and stoichiometric ratio in the above molecular formula, the electrochemical performance is better. On this basis, it is further preferred that M1 is selected from one or more of Fe, Ti, Mg, Cu, Zn and Ca. When the above-mentioned metal elements are used, the electrochemical properties of the O3-phase nickel-manganese-based oxide layered particles are further improved, and they can also be better compatible and coordinated with the coating layer thereon.

[0055] In several typical embodiments, the molecular formula of the P2 phase metal oxide coating is Na y M2O 2 ; Wherein, 0.6≤y≤0.8, M2 is selected from one or more of Ni, Mn, Fe, Ti, Mg, Cu, Al, Ca, Zn and Co. The inventors selected and optimized the type of P2 phase metal oxide coating through a large number of experiments, and found that when its components are the element composition and stoichiometric ratio in the above molecular formula, it can better reduce the residual alkali amount on the surface of O3 phase nickel-manganese-based oxide layered particles and effectively improve its ionic conductivity. On this basis, the inventors further preferred M2 to be selected from one or more of Fe, Mn, Mg, Cu, Zn and Ca through a large number of experiments. When the above-mentioned metal elements are used, 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 more significantly improving the electrochemical performance of the resulting layered oxide positive electrode material.

[0056] Regarding the selection of inert coating layers other than the carbon layer, the inventors have conducted a large number of experiments and found that in several preferred embodiments, the inorganic metal oxide layer is preferably Al 2 O 3 layer, TiO 2 One or more of a layer, a CuO layer and a MgO layer. Compared with inorganic metal oxide layers formed by other metals, the structures of the above-mentioned inorganic metal oxide layers are more stable and can better inhibit the side reactions between the O3@P2 phase composite oxide particles and the electrolyte. On this basis, the inventors further prefer that the inorganic metal oxide layer is selected from Al 2 O 3 layer, TiO 2 One or more of the layers and MgO layers are selected, and it is found that these inorganic metal oxide layers can better cooperate with the above-mentioned preferred P2 phase metal oxide coating layer, and the cost is also lower, which can effectively improve the product added value of the obtained positive electrode material.

[0057] 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 plays the role of connecting the O3-phase nickel-manganese-based oxide layered particles and the inert coating layer, whether it can achieve good bonding with the O3-phase nickel-manganese-based oxide layered particles is a very important factor. After a large number of experiments and comparisons, the inventors found 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 above manner, the P2 phase metal oxide coating layer and the O3 phase nickel-manganese-based oxide layered particles can be better combined, and at the same time, the residual alkali on the surface of the O3 phase nickel-manganese-based oxide particles can be more effectively eliminated, thereby improving the electrochemical properties of the final layered oxide positive electrode material, thereby improving the first-cycle coulombic efficiency, rate performance and cycle life of the sodium ion battery made using the positive electrode material.

[0058] After a large number of experiments, the inventors further optimized the core oxide and the two coating layers of the layered oxide positive electrode material, and found that in the two most typical embodiments: the molecular formula of the O3 phase nickel-manganese-based oxide layered particles is NaNi 0.5 Mn 0.4 Ti 0.1 O 2 The molecular formula of the P2 phase metal oxide coating is Na 9 / 7 Cu 2 / 9 Fe 1 / 9 Mn 2 / 3 O 2 , and the inert coating is Al 2 O 3 Alternatively, 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 O 2 The molecular formula of the P2 phase metal oxide coating is Na 0.6 Mg 0.15 Cu 0.15 Mn 0.7 O 2, and the inert coating layer is a carbon layer. When 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 layered oxide positive electrode material are arranged in the above two ways, the obtained layered oxide positive electrode material not only has excellent electrochemical performance, but also has higher air stability, and can better meet its actual application needs.

[0059] In addition to the above-mentioned preferred element matching scheme, during the experiment, the inventors also found that the film thickness, mass proportion and coating degree also have a significant impact on the various properties of the obtained layered oxide positive electrode material. In a typical embodiment, in the layered oxide positive electrode 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. When the thickness of the P2 phase metal oxide coating layer and the inert coating layer is in the above range, it can better balance between suppressing side reactions, consuming residual alkali and improving conductivity, thereby better improving the electrochemical properties of the obtained layered oxide positive electrode material. Regarding the weight proportion of the P2 phase metal oxide coating layer and the inert coating layer, in a preferred embodiment, based on the weight of the layered oxide positive electrode material as 100%, 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 arranged according to the above weight ratios, the P2 phase metal oxide coating layer and the inert coating layer, as well as the P2 phase metal oxide coating layer and the core particles can better cooperate and transfer mass, and the electrochemical performance of the obtained layered oxide positive electrode material is also higher. In addition, in several typical embodiments, 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%; the coverage of the inert coating layer on the surface of the O3@P2 phase composite oxide particles is 80% to 100%. In the structure of the layered oxide positive electrode material provided by the present invention, the coverage 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, and the air stability of the layered oxide positive electrode material is further improved.

[0060] The second aspect of the present invention provides a method for preparing the above-mentioned layered oxide positive electrode material, comprising: ：Prepare O3-phase nickel-manganese-based oxide layered particles and a first metal source, mix the O3-phase nickel-manganese-based oxide layered particles with the first metal source, perform a first ball milling, and obtain first pre-coated particles; perform a first calcination treatment on the first pre-coated particles to obtain O3@P2-phase composite oxide particles; mix the O3@P2-phase composite oxide particles with a carbon source and / or a second metal source, perform a second ball milling, and obtain second pre-coated particles; perform an optional second calcination treatment on the second pre-coated particles to obtain a layered oxide positive electrode material.

[0061] The above-mentioned preparation method provided by the present invention is simple, and the equipment and process conditions involved are all easily available, and at the same time, it can be well compatible with various preparation methods of existing positive electrode materials. Specifically, the first metal source and the O3-phase nickel-manganese-based oxide layered particles are pre-coated to improve the bonding strength between the two, and then the P2-phase metal oxide coating layer is in situ generated on the surface of the O3-phase nickel-manganese-based oxide layered particles through an in-situ solid-phase reaction, thereby significantly consuming the residual alkali on its surface and improving the air stability. Thereafter, the O3@P2-phase composite oxide particles are pre-coated with the carbon source and / or the second metal source by ball milling, and an inert coating layer is generated by another in-situ solid-phase reaction. Compared with simple mixed coating or liquid phase reaction, it can better coordinate the physicochemical properties between the coating layers, protect the structural integrity of the core particles and the coating layer, and simplify the process at the same time, to obtain a layered oxide positive electrode material with better performance and higher product added value.

[0062] In order to improve the effect of the two pre-coatings, preferably, the speed of the first ball milling is 100 rpm to 500 rpm, and the time is 0.5 h to 4 h; and / or, the speed of the second ball milling is 100 rpm to 500 rpm, and the time is 0.5 h to 4 h. Setting the experimental conditions of the two ball millings in the above manner can achieve a more uniform coating, thereby improving the composition uniformity, structural continuity and coating integrity of the obtained P2 phase metal oxide coating layer and the inert coating layer.

[0063] In order to better control the weight ratio and coating thickness of the P2 phase metal oxide coating layer and the inert coating layer, the inventors preferably set the weight ratio of the O3 phase nickel-manganese-based oxide layered particles to the first metal source to be 1: (0.005-0.05) in several typical embodiments, and the weight ratio of the O3@P2 phase composite oxide particles to the carbon source and / or the second metal source to be 1: (0.005-0.05). After a large number of experiments, the inventors have optimized the above weight ratio relationship, which corresponds to the weight ratio and coating thickness of the P2 phase metal oxide coating layer and the inert coating layer, and found that the material preparation under the above weight ratio relationship can more effectively improve the electrochemical performance and air stability of the obtained layered oxide positive electrode material.

[0064] 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 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. The inventors have selected the above-mentioned coating metal sources and sodium sources through a large number of comparative tests, and found that when the above-mentioned types are selected, the solid phase reaction can be carried out more smoothly, so that the formation of the P2 phase metal oxide coating layer can be achieved, and the layered oxide positive electrode material with the expected structure can be obtained.

[0065] In several preferred embodiments, 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 oxides, hydroxides and carbonates corresponding to Ni, Mn, Fe, Ti, Mg, Cu, Al, Ca and Co. Similarly, the inventors have selected the above-mentioned carbon sources and second metal sources through a large number of comparative tests, and found that when the above-mentioned types are selected, the inert coating layer can be smoothly formed in a more continuous, uniform and dense state, thereby obtaining a layered oxide positive electrode material with excellent performance.

[0066] The present invention realizes the formation of a P2 phase metal oxide coating layer and an inert coating layer by calcination and solid phase reaction. In a typical embodiment, the temperature of the first calcination treatment is 600°C to 1000°C, the calcination time is 2h to 20h, and the temperature of the second calcination treatment is 400°C to 1000°C, and the calcination time is 0.5h to 20h. After a large number of experiments, the inventors have respectively optimized the temperature conditions and time conditions of the above two calcinations, and found that when it is carried out in this way, the obtained two-layer coating structure is more stable, that is, the combination of the P phase metal oxide coating layer and the surface of the O3 phase nickel-manganese-based oxide layered particles, and the combination of the inert coating layer and the surface of the O3@P2 phase composite oxide particles is closer, thereby making the prepared layered oxide positive electrode material have better air stability. And more preferably, the calcination atmosphere of the first calcination treatment is air and / or oxygen atmosphere. The inventors prefer that the first calcination is carried out under the condition of air, so as to more efficiently form the P2 phase oxide coating layer and improve the ionic conductivity.

[0067] In several typical implementations:

[0068] When the O3@P2 phase composite oxide particles are mixed with the second metal source, a second calcination treatment is carried out, and the temperature of the second calcination treatment is 700°C to 1000°C, the time is 10h to 20h, and the atmosphere is air and / or oxygen atmosphere; at this time, the inert coating layer is an inorganic metal oxide layer, and the inventor has optimized the above conditions through a large number of experiments to form an inert coating layer with a more stable and dense structure, thereby improving the air stability of the finally formed layered oxide positive electrode material.

[0069] 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 tar and petroleum asphalt, a second calcination treatment is carried out, and the temperature of the second calcination treatment is 400°C to 800°C, the time is 0.5h to 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 molecular organic matter, so the inventor has optimized the above conditions through a large number of experiments to achieve the removal of organic small molecules in coal tar, coal tar and petroleum asphalt, and complete carbonization at the same time to obtain a more complete and stable inert coating layer, thereby improving the air stability of the finally formed layered oxide positive electrode material.

[0070] 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 expanded graphite, carbon black and graphene, the second calcination treatment is not performed, and a layered oxide positive electrode 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, a layered oxide positive electrode material is directly obtained after the second ball milling, and the carbon layer in its structure has achieved complete and stable coating.

[0071] A third aspect of the present invention provides a positive electrode plate, which includes the above-mentioned layered oxide positive electrode material.

[0072] A fourth aspect of the present invention provides a sodium ion battery, which includes the above-mentioned positive electrode plate.

[0073] Because the above-mentioned positive electrode material obtained by the present invention has both good electrochemical properties and structural stability, when it is used as a positive electrode plate component in a sodium ion battery, the obtained sodium ion battery also has comprehensively improved electrochemical properties, including improved first-cycle coulombic efficiency, excellent rate performance, long cycle life and good air stability, so that it can be well applied to multiple usage scenarios.

[0074] The present application is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in the present application.

[0075] Unless otherwise defined, all professional terms used below have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0076] Some specific embodiments are listed below. It should be noted that the embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used without specifying the manufacturer are all conventional products that can be obtained commercially.

[0077] 1. Preparation method

[0078] Example 1

[0079] Preparation method of layered oxide positive electrode material:

[0080] First, prepare the O3 phase cathode material NaNi 0.45 Mn 0.4 Ti 0.1 Cu 0.05 O 2 : Sodium carbonate, nickel oxide, manganese dioxide, titanium dioxide, copper oxide and a certain amount of anhydrous ethanol were weighed according to the molecular formula stoichiometric ratio and mixed evenly in a ball mill. The mixing time was 3 hours and the ball mill speed was 450r / min. Drying was carried out in a vacuum drying oven for 12 hours to obtain dry powder; the powder was placed in an air atmosphere and calcined at a high temperature of 900°C and the heat preservation time was 15 hours;

[0081] Secondly, sodium carbonate, magnesium oxide, copper oxide and manganese dioxide were weighed according to the stoichiometric ratio in the P2 phase molecular formula, and the first metal source was obtained by grinding thoroughly. 1 g of the first metal source was mixed with 20 g of the O3 phase positive electrode material NaNi 0.45 Mn 0.4 Ti 0.1 Cu 0.05 O 2 The first pre-coated particles were placed in a ball mill, the ball milling time was 3 hours, the rotation speed was 450 rpm, and the first pre-coated particles were obtained; the first pre-coated particle sample after ball milling was placed in a muffle furnace, calcined at 900 ° C for 10 hours, and ground after cooling to obtain O3@P2 phase composite oxide particles with a P2 phase metal oxide coating layer, and the P2 phase molecular formula was Na 0.6 Mg 0.15 Cu 0.15 Mn 0.7 O 2 ;

[0082] Finally, 10 g of O3@P2 phase composite oxide particles with a first coating layer and 0.2 g of expanded graphite were placed in a ball mill, and the ball milling time was 3 h at a rotation speed of 450 rpm to obtain second pre-coated particles; after the second pre-coated particle sample after ball milling was fully dried and ground, a layered oxide positive electrode material having a P2 phase metal oxide coating layer and an inert coating layer was obtained, marked as G@P2@O3, and the scanning electron microscope image of the obtained G@P2@O3 layered oxide positive electrode material is shown in Figure 1 , XRD test spectrum see Figure 3 .

[0083] In the G@P2@O3 layered oxide positive electrode material, the thickness of the P2 phase metal oxide coating layer is 12nm, and the thickness of the inert coating layer is 20nm.

[0084] Example 2

[0085] Preparation method of layered oxide positive electrode material:

[0086] First, prepare the O3 phase cathode material NaNi 0.5 Mn 0.4 Ti 0.1 O 2 : Sodium carbonate, nickel oxide, manganese dioxide, titanium dioxide and a certain amount of anhydrous ethanol were weighed according to the molecular formula stoichiometric ratio and mixed evenly in a ball mill. The mixing time was 3 hours and the ball mill speed was 450r / min. Drying was carried out in a vacuum drying oven for 12 hours to obtain dry powder; the powder was placed in an air atmosphere and calcined at high temperature. The calcination temperature was 900℃ and the insulation time was 15 hours;

[0087] Secondly, sodium carbonate, magnesium oxide, copper oxide and manganese dioxide were weighed according to the stoichiometric ratio of the P2 phase molecular formula, and the first metal source was obtained by grinding thoroughly. 1 g of the first metal source was mixed with 20 g of the O3 phase positive electrode material NaNi 0.5 Mn 0.4 Ti 0.1 O 2 The first pre-coated particles were placed in a ball mill, the ball milling time was 3 hours, the rotation speed was 450 rpm, and the first pre-coated particles were obtained; the first pre-coated particle sample after ball milling was placed in a muffle furnace, calcined at 900 ° C for 10 hours, and ground after cooling to obtain O3@P2 phase composite oxide particles with a P2 phase metal oxide coating layer, and the P2 phase molecular formula was Na 9 / 7 Cu 2 / 9 Fe 1 / 9 Mn 2 / 3 O 2 ;

[0088] Finally, 10 g of the O3@P2 phase composite oxide particles with the first coating layer were mixed with 0.05 g of Al 2 O3 The sample was placed in a ball mill for 3 h at a speed of 450 rpm to obtain the second pre-coated particles. The second pre-coated particle sample after ball milling was placed in a muffle furnace and calcined at 600 ° C for 10 h. After being fully dried and ground, a layered oxide positive electrode material having a P2 phase metal oxide coating layer and an inert coating layer was obtained, which was marked as Al 2 O 3 @P2@O3 layered oxide positive electrode material.

[0089] Al 2 O 3 In the @P2@O3 layered oxide positive electrode material, the thickness of the P2 phase metal oxide coating layer is 14nm, and the thickness of the inert coating layer is 18nm.

[0090] Example 3

[0091] Preparation method of layered oxide positive electrode material:

[0092] First, prepare the O3 phase cathode material NaNi 0.45 Mn 0.4 Ti 0.1 Fe 0.05 O 2 : Sodium carbonate, nickel oxide, manganese dioxide, titanium dioxide, ferric oxide and a certain amount of anhydrous ethanol were weighed according to the molecular formula stoichiometric ratio and mixed evenly in a ball mill. The mixing time was 3 hours and the ball mill speed was 450r / min. Drying was carried out in a vacuum drying oven for 12 hours to obtain dry powder; the powder was placed in an air atmosphere and calcined at high temperature. The calcination temperature was 900℃ and the insulation time was 15 hours;

[0093] Secondly, sodium carbonate, magnesium oxide, copper oxide and manganese dioxide were weighed according to the stoichiometric ratio of the P2 phase molecular formula, and the first metal source was obtained by grinding thoroughly. 1 g of the first metal source was mixed with 20 g of the O3 phase positive electrode material NaNi 0.45 Mn 0.4 Ti 0.1 Fe 0.05 O 2 The first pre-coated particles were placed in a ball mill, the ball milling time was 3 hours, the rotation speed was 450 rpm, and the first pre-coated particles were obtained; the first pre-coated particle sample after ball milling was placed in a muffle furnace, calcined at 900 ° C for 10 hours, and ground after cooling to obtain O3@P2 phase composite oxide particles with a P2 phase metal oxide coating layer, and the P2 phase molecular formula was Na 0.6 Mg 0.15 Cu 0.15 Mn 0.7 O 2 ;

[0094] Finally, 10 g of the O3@P2 phase composite oxide particles with the first coating layer were mixed with 0.05 g of Al 2 O 3 The sample was placed in a ball mill for 3 h at a speed of 450 rpm to obtain the second pre-coated particles. The second pre-coated particle sample after ball milling was placed in a muffle furnace and calcined at 600 ° C for 10 h. After being fully dried and ground, a layered oxide positive electrode material having a P2 phase metal oxide coating layer and an inert coating layer was obtained, which was marked as Al 2 O 3 @P2@O3 layered oxide positive electrode material.

[0095] Al 2 O 3 In the @P2@O3 layered oxide positive electrode material, the thickness of the P2 phase metal oxide coating layer is 15nm, and the thickness of the inert coating layer is 22nm.

[0096] Example 4

[0097] Preparation method of layered oxide positive electrode material:

[0098] First, prepare the O3 phase cathode material NaNi 0.45 Mn 0.4 Ti 0.1 Zn 0.05 O 2 : Sodium carbonate, nickel oxide, manganese dioxide, titanium dioxide, zinc oxide and a certain amount of anhydrous ethanol were weighed according to the molecular formula stoichiometric ratio and mixed evenly in a ball mill. The mixing time was 3 hours and the ball mill speed was 450r / min. Drying was carried out in a vacuum drying oven for 12 hours to obtain dry powder; the powder was placed in an air atmosphere and calcined at high temperature. The calcination temperature was 900℃ and the insulation time was 15 hours;

[0099] Secondly, sodium carbonate, magnesium oxide, copper oxide and manganese dioxide were weighed according to the stoichiometric ratio of the P2 phase molecular formula, and the first metal source was obtained by grinding thoroughly. 1 g of the first metal source was mixed with 20 g of the O3 phase positive electrode material NaNi 0.45 Mn 0.4 Ti 0.1 Zn 0.05 O 2 The first pre-coated particles were placed in a ball mill, the ball milling time was 3 hours, the rotation speed was 450 rpm, and the first pre-coated particles were obtained; the first pre-coated particle sample after ball milling was placed in a muffle furnace, calcined at 900 ° C for 10 hours, and ground after cooling to obtain O3@P2 phase composite oxide particles with a P2 phase metal oxide coating layer, and the P2 phase molecular formula was Na 0.6 Mg 0.15 Cu 0.15 Mn 0.7 O 2 ;

[0100] Finally, 10 g of the O3@P2 phase composite oxide particles with the first coating layer were mixed with 0.05 g of TiO 2 The sample was placed in a ball mill and milled for 3 h at a speed of 450 rpm to obtain the second pre-coated particles. The second pre-coated particle sample after ball milling was placed in a muffle furnace and calcined at 600 ° C for 10 h. After being fully dried and ground, a layered oxide positive electrode material having a P2 phase metal oxide coating layer and an inert coating layer was obtained, which was marked as TiO 2 @P2@O3 layered oxide positive electrode material.

[0101] TiO 2 In the @P2@O3 layered oxide positive electrode material, the thickness of the P2 phase metal oxide coating layer is 16nm, and the thickness of the inert coating layer is 19nm.

[0102] Example 5

[0103] Preparation method of layered oxide positive electrode material:

[0104] The only difference between this embodiment and embodiment 1 is that the amounts of the first metal source and the expanded graphite (i.e., the carbon source) are different. Specifically, the amounts of the first metal source and the expanded graphite are changed so that the weight ratio of the O3 phase nickel-manganese-based oxide layered particles to the first metal source is 1:0.002, and the weight ratio of the O3@P2 phase composite oxide particles to the carbon source is 1:0.002.

[0105] In the obtained G@P2@O3 layered oxide positive electrode 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.

[0106] Example 6

[0107] Preparation method of layered oxide positive electrode material:

[0108] The only difference between this embodiment and embodiment 1 is that the amounts of the first metal source and the expanded graphite (i.e., the carbon source) are different. Specifically, the amounts of the first metal source and the expanded graphite are changed so that the weight ratio of the O3 phase nickel-manganese-based oxide layered particles to the first metal source is 1:0.08, and the weight ratio of the O3@P2 phase composite oxide particles to the carbon source is 1:0.08.

[0109] 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.

[0110] Example 7

[0111] Preparation method of layered oxide positive electrode material:

[0112] The difference between this embodiment and embodiment 1 is that the conditions involved in the two ball millings are different, specifically:

[0113] 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.

[0114] Example 8

[0115] Preparation method of layered oxide positive electrode material:

[0116] The difference between this embodiment and embodiment 1 is that the conditions involved in the two ball millings are different, specifically:

[0117] 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.

[0118] Example 9

[0119] Preparation method of layered oxide positive electrode material:

[0120] The only difference between this embodiment and embodiment 1 is that the calcination conditions of the first pre-coated particle sample after ball milling are different, specifically: calcination at 500° C. for 22 h.

[0121] Example 10

[0122] Preparation method of layered oxide positive electrode material:

[0123] The only difference between this embodiment and embodiment 1 is that the calcination conditions of the first pre-coated particle sample after ball milling are different, specifically, calcination at 1100° C. for 1 hour.

[0124] Embodiment 11

[0125] Preparation method of layered oxide positive electrode material:

[0126] The only difference between this embodiment and embodiment 2 is that the calcination conditions of the second pre-coated particle sample after ball milling are different, specifically: calcination at 300° C. for 22 h.

[0127] Example 12

[0128] Preparation method of layered oxide positive electrode material:

[0129] The only difference between this embodiment and embodiment 2 is that the calcination conditions of the second pre-coated particle sample after ball milling are different, specifically: calcination at 1100° C. for 0.2 h.

[0130] Comparative Example 1

[0131] Preparation method of layered oxide positive electrode material:

[0132] The difference between this comparative example and Example 1 is that the O3 phase positive electrode material NaNi 0.45 Mn 0.4 Ti 0.1 Cu 0.05 O 2 It is used directly as a positive electrode material without any coating.

[0133] The scanning electron microscope image of the O3 phase positive electrode material is shown in Figure 2 , XRD test spectrum see Figure 4 .

[0134] Comparative Example 2

[0135] Preparation method of layered oxide positive electrode material:

[0136] The only difference between this comparative example and Example 1 is that no inert coating layer is performed, that is, the obtained O3@P2 phase composite oxide particles having a P2 phase metal oxide coating layer are directly used as the positive electrode material.

[0137] Comparative Example 3

[0138] Preparation method of layered oxide positive electrode material:

[0139] The difference between this comparative example and Example 1 is that no P2 phase metal oxide coating layer is used, that is, 10 g of O3 phase positive electrode material particles NaNi 0.45 Mn 0.4 Ti 0.1 Cu 0.05 O 2 The pre-coated particles were placed in a ball mill with 0.2 g of expanded graphite for 3 h at a rotation speed of 450 rpm to obtain pre-coated particles. The pre-coated particles were fully dried and ground to obtain the positive electrode material.

[0140] Comparative Example 4

[0141] Preparation method of layered oxide positive electrode material:

[0142] The difference between this comparative example and Example 1 is that: in obtaining the O3 phase positive electrode material NaNi 0.45 Mn 0.4 Ti 0.1 Cu 0.05 O 2 Then, 1 g of the mixture of the first metal source and expanded graphite (the weight ratio of the two is 1:1) is mixed with 20 g of the O3 phase positive electrode material NaNi 0.45 Mn 0.4 Ti 0.1 Cu 0.05O 2 The pre-coated particles were placed in a ball mill, milled for 3 h at a rotation speed of 450 rpm to obtain pre-coated particles. The pre-coated particle samples were placed in a muffle furnace, calcined at 900 °C for 10 h, and ground after cooling to obtain the positive electrode material.

[0143] That is, the material of the P2 phase metal oxide coating layer and the material of the inert coating layer are mixed and coated as a single layer as a mixed coating layer.

[0144] Battery Assembly:

[0145] (1) Preparation of positive electrode sheets: The layered oxide positive electrode materials, conductive carbon black and polyvinylidene fluoride (PVDF) prepared in the above-mentioned embodiments and comparative examples were mixed in a mass ratio of 8:1:1, and an appropriate amount of N-methylpyrrolidone (NMP) was added to form a uniform electrode slurry. The electrode slurry was then evenly coated on an aluminum foil, vacuum dried and cut into circular electrode sheets with a diameter of 15 mm, which were then transferred to a glove box for standby use.

[0146] (2) Battery assembly: Sodium metal was used as the counter electrode, glass fiber was used as the separator, the solute of the electrolyte was sodium perchlorate, the solvent of the electrolyte was propylene carbonate, ethylene carbonate and fluoroethylene carbonate (volume ratio of 1:1:0.05), the concentration of sodium perchlorate in the electrolyte was 1 mol / L, and a CR2032 button cell was assembled. The entire assembly process was carried out in a glove box filled with argon. The button cell was left to stand for 6 hours before subsequent electrochemical performance tests.

[0147] 2. Test Method

[0148] Coverage of P2 phase metal oxide coating layer and inert coating layer: The percentage of the area covered by the coating layer to the total surface area of ​​the electrode material, determined by infrared spectroscopy analysis.

[0149] Particle size: GB / T 19077 particle size analysis laser diffraction method.

[0150] Compacted density: GB / T 24533 Determination of compacted density of powders.

[0151] pH value: GB / T 9724 General rules for determination of pH value of chemical reagents.

[0152] Moisture content: GB / T 6283 Determination of moisture content in chemical products - Karl Fischer method (general method).

[0153] Specific surface area: GB / T 19587 gas adsorption BET method for determining the specific surface area of ​​solid substances.

[0154] Scanning electron microscope photo: taken with ZEISS MERLIN Compact, magnification 50k.

[0155] Electrochemical performance test: Use constant current charge and discharge mode to carry out charge and discharge tests at a current density of 0.1C, with a charge cut-off voltage of 4.2V and a discharge cut-off voltage of 2.0V to test the first cycle charge and discharge capacity and coulomb efficiency of each battery.

[0156] Air stability: The positive electrode materials obtained in the above embodiments and comparative examples were exposed to an air environment for 24 hours, and the positive electrode materials after exposure to air were prepared into batteries in the above manner to test their first cycle charge and discharge capacity and coulombic efficiency.

[0157] The particle size distribution of the positive electrode materials obtained in each embodiment and comparative example and the coverage of each layer are shown in Table 1, the physical and chemical performance test results are shown in Table 2, and the electrochemical performance test results of each battery further prepared are shown in Table 3.

[0158] III. Analysis of test results of various embodiments and comparative examples

[0159] Table 1

[0160]

[0161]

[0162] Table 2

[0163]

[0164]

[0165] Table 3

[0166]

[0167]

[0168] From the above results, it can be seen that the above embodiments of the present invention achieve a good coating effect, wherein the P2 phase metal oxide coating layer reduces the residual alkali content on the surface of the O3 phase nickel-manganese-based layered oxide, and the inert coating layer reduces the side reactions between the material surface and the air and the electrolyte. Through the above experiments, it was found that the double-layer coating of the P2 phase metal oxide coating layer and the inert coating layer affected the particle size, specific surface area, pH value, moisture and compaction density of the material. The appropriate nickel-manganese-based positive electrode material, coating amount, and ball milling conditions make the layered oxide positive electrode material exhibit higher electrochemical performance and better air stability. When the layered oxide positive electrode material is applied to a sodium ion battery, the prepared sodium ion battery has a high first-cycle coulomb efficiency, excellent rate performance, long cycle life and good air stability. In addition, the preparation method of the layered oxide positive electrode material provided by the present invention is simple and practical, suitable for large-scale production, and has broad application prospects.

[0169] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A layered oxide positive electrode material, characterized in that: 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, wherein 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; wherein 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 is Na 0.6 Mg 0.15 Cu 0.15 Mn 0.7 O2, and the inert coating layer is a carbon layer; in the layered oxide positive electrode material, the thickness of the P2 phase metal oxide coating layer is 1.5nm, and the thickness of the inert coating layer is 1.8nm; 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 72%, and the coverage rate of the inert coating layer on the surface of the O3@P2 phase composite oxide particles is 75%.

2. The layered oxide positive electrode material according to claim 1, characterized in that Based on 100% weight of the layered oxide positive electrode 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%.

3. A method for preparing the layered oxide positive electrode material according to claim 1 or 2, characterized in that: The preparation method comprises: Providing O3-phase nickel-manganese-based oxide layered particles and a first metal source, mixing the O3-phase nickel-manganese-based oxide layered particles and the first metal source, and performing a first ball milling to obtain first pre-coated particles; Performing a first calcination treatment on the first pre-coated particles to obtain the O3@P2 phase composite oxide particles; The O3@P2 phase composite oxide particles are mixed with a carbon source and subjected to a second ball milling to obtain second pre-coated particles; The second pre-coated particles are subjected to an optional second calcination treatment to obtain the layered oxide positive electrode material.

4. The method for preparing a layered oxide positive electrode material according to claim 3, characterized in that: The rotation speed of the first ball mill is 100 rpm to 500 rpm, and the time is 0.5 h to 4 h; and / or the rotation speed of the second ball mill is 100 rpm to 500 rpm, and the time is 0.5 h to 4 h.

5. The method for preparing a layered oxide positive electrode material according to claim 3 or 4, 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 is 1:(0.005-0.05).

6. The method for preparing a layered oxide positive electrode material according to claim 5, characterized in that: The first metal source includes a sodium source and a coating metal source, wherein the coating metal source is one or more of oxides, hydroxides, carbonates, sulfates, oxalates, acetates and citrates corresponding to Mg, Cu and Mn; and the sodium source is selected from one or more of sodium carbonate, sodium hydroxide, sodium nitrate and sodium peroxide.

7. The method for preparing a layered oxide positive electrode material according to claim 5, characterized in that: The carbon source is selected from one or more of coal tar, coal pitch, petroleum pitch, expanded graphite, carbon black and graphene.

8. The method for preparing a layered oxide positive electrode material according to claim 5, characterized in that: The temperature of the first calcination treatment is 600° C. to 1000° C., and the calcination time is 2 h to 20 h. The temperature of the second calcination treatment is 400° C. to 1000° C., and the calcination time is 0.5 h to 20 h.

9. The method for preparing a layered oxide positive electrode material according to claim 8, characterized in that: The calcination atmosphere of the first calcination treatment is air and / or oxygen atmosphere.

10. The method for preparing a layered oxide positive electrode material according to claim 8, characterized in that: 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 performed, and the temperature of the second calcination treatment is 400° C. to 800° C., the time is 0.5 h to 2 h, 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 positive electrode material is obtained after the second ball milling.

11. A positive electrode sheet, characterized in that: The positive electrode sheet comprises the layered oxide positive electrode material according to claim 1 or 2, or comprises the layered oxide positive electrode material prepared by the method for preparing the layered oxide positive electrode material according to any one of claims 3 to 10.

12. A sodium ion battery, characterized in that: The sodium ion battery comprises the positive electrode sheet as claimed in claim 11.

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