A sodium ion battery layered oxide positive electrode material and its preparation method and application

Abstract

The present invention discloses a sodium ion battery layered oxide positive electrode material and its preparation method and application, belonging to the technical field of electrochemical energy storage materials. The positive electrode material is obtained by mixing and calcining a P2-type material, an O3-type material, and a flux. The present invention uses physical mixing and the addition of flux to assist sintering to obtain a controllable ratio of P2 and O3 in the obtained P2 / O3 composite positive electrode material. The added flux not only firmly connects the P2 material and the O3 material together, providing a connecting layer for the P2-type material and the O3-type material, enhancing the interfacial transmission capacity of the material, but also consumes residual alkali on the surface of the material, forming a protective layer for the material, optimizing the interfacial performance of the material, and obtaining a high-capacity, long-cycle, low-residual-alkali positive electrode material, providing a new idea for the design of sodium ion layered oxide positive electrode materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrochemical energy storage materials, and in particular relates to a sodium ion battery layered oxide positive electrode material and a preparation method and application thereof. Background Art

[0002] With the continuous growth of global energy demand and the increasing prominence of environmental problems, the development of efficient, safe and low-cost energy storage technologies has become an important research direction in the current energy field. As the current mainstream energy storage technology, lithium-ion batteries are widely used in portable electronic devices, electric vehicles and energy storage systems due to their high energy density and long cycle life. However, the limited and uneven distribution of lithium resources has led to its rising cost, limiting the application of lithium-ion batteries in large-scale energy storage. Therefore, finding alternatives to lithium-ion batteries has become a research hotspot. Sodium-ion batteries are considered to be one of the ideal candidates for large-scale energy storage systems because of their similar working principles to lithium-ion batteries, abundant sodium resources and low cost.

[0003] A complete sodium-ion battery is mainly composed of positive electrode materials, negative electrode materials, electrolytes, separators, current collectors, and passivation films formed on the surface of the positive and negative electrode material particles during the battery cycle. Among them, the key characteristics of the battery, such as reversible specific capacity, cycle stability, air stability, operating voltage, etc., are mainly determined by the inherent electrochemical properties of the positive and negative electrode materials. Therefore, seeking suitable positive and negative electrode materials has become the key to the development of high-performance sodium-ion batteries, especially positive electrode materials, which largely determine the energy density and safety performance of the battery. At present, several different types of sodium-ion battery positive electrode materials have been discovered, including Prussian blue analogs, polyanion compounds, tunnel-type transition metal oxides, and layered transition metal oxide materials. Among them, layered transition metal oxide positive electrode materials have attracted widespread attention due to their advantages such as wide variety, easy synthesis, low cost, and high reversible capacity.

[0004] According to scholars' research, layered transition metal oxide materials can be divided into P2, O3, O3', P3, P3', O2, etc., among which P2 and O3 are two more common types of layered oxides. Generally speaking, when the sodium content is 0.6-0.8, the material tends to form a P2 type structure, and when the sodium content is 0.8-1.0, the material tends to form an O3 type structure. O3-type structural materials can provide higher capacity when the sodium content is sufficient, but the attenuation of phase transition and sodium ion diffusion kinetics will lead to irreversible degradation of the structure, limiting its application. Although P2-type structural materials have good sodium ion diffusivity and structural stability, the phase transition at high voltage and insufficient sodium content also cause their performance limitations.

[0005] In recent years, many researchers have improved the electrochemical performance of materials by designing P2 / O3 composite phase structures, combining the advantages of both P2-type structural materials and O3-type structural materials. However, there are too many factors that affect the phase ratio of P2 / O3 composite materials. For example, component changes and temperature control will affect the ratio of P2 and O3, making it difficult to control the P2 / O3 composite material with the optimal phase ratio.

[0006] Therefore, there is an urgent need to provide a preparation method that can flexibly control the phase ratio of P2 / O3 composite materials to break through the difficult problem of the "capacity-stability-rate" triangle contradiction of the positive electrode of sodium ion batteries. Summary of the Invention

[0007] To address the above technical issues, the present invention proposes a sodium-ion battery layered oxide cathode material, its preparation method, and its application, aiming to improve the structural stability and electrochemical performance of the sodium-ion battery cathode material.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] One of the objectives of the present invention is to provide a sodium ion battery layered oxide positive electrode material, which is obtained by physically mixing a P2 type material, an O3 type material and a flux, and the mass ratio of the P2 type material to the O3 type material is (1-5): (5-9);

[0010] The P2 type material is a P2 type sodium ion battery layered oxide with a space group of P63 / mmc and a chemical formula of Na X Ni A Mn B TM C O2; wherein, 0.6≤X≤0.8, 0≤A≤0.4, 0≤B≤0.7, 0≤C≤0.4, A+B+C=1, and A, B, and C cannot be 0 at the same time; TM is selected from at least one of Li, Ti, K, Mg, Ca, Zn, Cu, Sr, Fe, Al, Co, Y, La, and Bi;

[0011] The O3 type material is an O3 type sodium ion battery layered oxide with a space group of R-3m and a chemical formula of Na Y Ni D Fe E Mn F TN G O2; wherein, 0.8≤Y≤1, 0≤D≤0.4, 0≤E≤0.4, 0≤F≤0.4, 0≤G≤0.4, D+E+F+G=1, and D, E, F, and G cannot be 0 at the same time; TN is selected from at least one of Li, Ti, K, Mg, Ca, Zn, Cu, Sr, Fe, Al, Co, Y, La, and Bi.

[0012] Furthermore, the raw materials also include a soldering flux, and the amount of the soldering flux added is 0-10% of the total mass of the P2 type material and the O3 type material, and is not 0. The soldering flux is selected from one of KF, H3PO4 and H3BO3.

[0013] A second object of the present invention is to provide a method for preparing a layered oxide positive electrode material for a sodium ion battery, comprising the following steps:

[0014] The sodium source, nickel source, manganese source and TM source are mixed uniformly according to the stoichiometric ratio, ground, pressed into tablets, sintered at high temperature, and post-treated to prepare a powdered P2 material;

[0015] The sodium source, nickel source, iron source, manganese source and TN source are mixed uniformly according to the stoichiometric ratio, ground, pressed into tablets, sintered at high temperature, and post-treated to prepare a powdered O3 material;

[0016] The P2 type material and the O3 type material are mixed with the flux, ground, pressed into tablets, subjected to secondary high-temperature sintering, and post-processed to obtain a powdered sodium ion battery layered oxide positive electrode material.

[0017] The present invention optimizes the design of the components of the layered oxide positive electrode material for sodium ion batteries, suppresses the phase change of the P2-type material and the O3-type material by doping inert elements, and obtains the P2-type material and the O3-type material with good cycle performance. The P2-type material and the O3-type material are then physically mixed, and a flux is added to perform secondary sintering on the mixed material. The added flux can react with the residual alkali on the surface of the material to form a connecting layer of the composite material and a protective layer for improving the interface performance of the material, thereby further improving the comprehensive performance of the composite material. A novel composite material integrating the excellent rate performance of the P2-type material and the high capacity of the O3-type material can be obtained.

[0018] Furthermore, the grinding time is 25 minutes.

[0019] Grinding can improve the uniformity of raw material mixing.

[0020] Furthermore, the tableting process comprises the following steps: tableting the ground raw material under a pressure of 30-150 MPa for 10-35 minutes. Tableting under the above pressure and time can achieve the required density.

[0021] Mix the raw materials evenly before tableting. Tableting before high-temperature sintering can promote high-temperature sintering, make the material sintering more complete, and make the material elements more evenly distributed.

[0022] Furthermore, the specific operating steps of the high-temperature sintering include: first heating the temperature to 300-700°C at a heating rate of 1-10°C / min for primary sintering, keeping the temperature for 2-16 hours, and then heating the temperature to 700-1150°C at a heating rate of 1-10°C / min for secondary sintering, keeping the temperature for 8-24 hours; the sintering atmosphere is selected from at least one of air, oxygen, argon and nitrogen.

[0023] Furthermore, the specific operation steps of the post-treatment include: cooling the sample after high-temperature sintering to 100-250°C at a cooling rate of 1-10°C / min, and then grinding it into powder in an environment with a relative humidity of less than 1%, and controlling the grinding time to be 10-40 minutes.

[0024] Furthermore, the specific operation steps of the secondary high-temperature sintering include: heating to 550-900°C at a heating rate of 1-10°C / min for sintering, and keeping the temperature for 2-16 hours; the sintering atmosphere is selected from at least one of air, oxygen, argon and nitrogen.

[0025] Furthermore, the sodium source is selected from at least one of Na2CO3, Na2CO3·H2O, NaHCO3, NaOH, CH3COONa, NaNO3, Na2O2, NaO2 and Na2C2O4.

[0026] Furthermore, the nickel source is selected from at least one of NiO and Ni(OH)2.

[0027] Furthermore, the manganese source is selected from at least one of MnO2, Mn2O3, MnO, MnCO3 and Mn3O4.

[0028] Furthermore, the iron source is selected from at least one of Fe2O3 and FeO.

[0029] Furthermore, the amount of the sodium source is adjusted so that the sodium element exceeds the theoretical amount by 1-15%.

[0030] A third object of the present invention is to provide a positive electrode sheet, the raw materials of which include the sodium ion battery layered oxide positive electrode material.

[0031] A fourth object of the present invention is to provide a sodium ion battery, the raw materials of which include the positive electrode sheet.

[0032] A fifth object of the present invention is to provide an application of the sodium ion battery in the field of electrical devices.

[0033] Compared with the prior art, the present invention has the following advantages and technical effects:

[0034] The present invention achieves a controllable ratio of P2 to O3 in the obtained P2 / O3 composite positive electrode material by means of physical mixing and adding flux to assist sintering. The added flux not only firmly connects the P2 material and the O3 material together, provides a connecting layer for the P2 material and the O3 material, and enhances the interface transmission capacity of the material, but also consumes the residual alkali on the surface of the material, generates a protective layer for the material, optimizes the interface performance of the material, and obtains a high-capacity, long-cycle, and low-residual-alkali positive electrode material, providing new ideas for the design of sodium ion layered oxide positive electrode materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0036] Figure 1 X-ray diffraction patterns of the positive electrode materials prepared in Comparative Example 1, Comparative Example 2 and Example 3 of the present invention;

[0037] Figure 2 This is a scanning electron microscope image of the positive electrode material prepared in Comparative Example 1 of the present invention;

[0038] Figure 3 This is a scanning electron microscope image of the positive electrode material prepared in Comparative Example 2 of the present invention;

[0039] Figure 4 This is a scanning electron microscope image of the positive electrode material prepared in Example 3 of the present invention;

[0040] Figure 5 This is a comparison chart of the first cycle charge and discharge curves of button-type batteries tested for the positive electrode materials prepared in Comparative Example 1, Comparative Example 2, and Example 3 of the present invention;

[0041] Figure 6 This is a comparison chart of the first cycle charge and discharge curves of button-type batteries tested for the positive electrode materials prepared in Comparative Example 3, Comparative Example 4, and Example 3 of the present invention;

[0042] Figure 7 This is a comparison chart of the button battery test rate performance of the positive electrode materials prepared in Comparative Example 1, Comparative Example 2, and Example 3 of the present invention;

[0043] Figure 8 This is a comparison chart of the 1C cycle performance of button batteries tested for the positive electrode materials prepared in Comparative Example 1, Comparative Example 2 and Example 3 of the present invention. DETAILED DESCRIPTION

[0044] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0045] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0046] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0047] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be illustrative only.

[0048] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0049] The present invention is achieved in that:

[0050] The first aspect: The present invention provides a P2 type positive electrode material, the chemical formula of which is Na X Ni A Mn B TM C O2;

[0051] Wherein, 0.6≤X≤0.8, 0≤A≤0.4, 0≤B≤0.7, 0≤C≤0.4, and A+B+C=1; X can be 0.60, 0.65, 0.70, 0.75, 0.80, etc., A can be 0.0, 0.1, 0.2, 0.3, 0.4, etc., B can be 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, etc., and C can be 0.0, 0.1, 0.2, 0.3, 0.4, etc. (A+B+C)=1, and A, B, and C cannot all be 0. For example, in the following preferred embodiments of the present invention, the value of X can be 0.67, the value of A can be 0.23, the value of B can be 0.46, and the value of C can be 0.31.

[0052] TM is selected from at least one of Li, Ti, K, Mg, Ca, Zn, Cu, Sr, Fe, Al, Co, Y, La and Bi. Preferably, TM is selected from at least one of Li, Cu, Mg and Ti, more preferably Cu and Ti.

[0053] In the second aspect, the present invention provides an O3 type positive electrode material, whose chemical formula is Na Y Ni D Fe E Mn F TN G O2;

[0054] Where, 0.8 ≤ Y ≤ 1, 0 ≤ D ≤ 0.4, 0 ≤ E ≤ 0.4, 0 ≤ F ≤ 0.4, 0 ≤ G ≤ 0.4, and D + E + F + G = 1. Y can take values ​​of 0.80, 0.85, 0.90, 0.95, 1, etc.; D can take values ​​of 0.0, 0.1, 0.2, 0.3, 0.4, etc.; E can take values ​​of 0.0, 0.1, 0.2, 0.3, 0.4, etc.; F can take values ​​of 0.0, 0.1, 0.2, 0.3, 0.4, etc.; and G can take values ​​of 0.0, 0.1, 0.2, 0.3, 0.4, etc. (D + E + F + G) = 1, and D, E, F, and G cannot all be 0. For example, in the following preferred embodiments of the present invention, the value of Y is 0.9, the value of D is 0.2, the value of E is 0.3, the value of F is 0.375, and the value of G is 0.125.

[0055] TN is selected from at least one of Li, Ti, K, Mg, Ca, Zn, Cu, Sr, Fe, Al, Co, Y, La and Bi. Preferably, TN is selected from at least one of Zn, Cu, Mg and Ti, more preferably Cu, Zn and Ti.

[0056] In a third aspect, the present invention provides a method for preparing a layered oxide positive electrode material for a sodium ion battery, comprising the following steps: mixing the prepared P2-type material and O3-type material with a flux, grinding, tableting, secondary high-temperature sintering, and post-processing to obtain a powdered sodium ion battery layered oxide positive electrode material.

[0057] The mass ratio of the P2 type material to the O3 type material is (1-5): (5-9), preferably 1:9, 2:8, 3:7, 4:6, or 5:5.

[0058] The amount of the flux added is 0-10% of the total mass of the P2 type material and the O3 type material, and is not 0, preferably 2%, 5%, 10%, etc. More preferably, it is 2% or 5%.

[0059] The soldering flux is selected from one of KF, H3PO4 and H3BO3, preferably H3PO4.

[0060] In a preferred embodiment, TM is selected from Cu and Ti; TN is selected from Cu, Zn, and Ti; the mass ratio of the P2-type sodium ion battery positive electrode material to the O3-type sodium ion battery positive electrode material can be 1:9, 2:8, 3:7, 4:6, or 5:5; and the mass percentage of the flux content and the total mass percentage of the P2 and O3 mixed materials can be 2%. By regulating the mass percentages of the P2-type material and the O3-type material, the flux content, and the total mass percentage of the P2 and O3 mixed materials, the electrochemical performance of the positive electrode material can be further improved.

[0061] The physically mixed P2 / O3 composite sodium ion battery layered oxide positive electrode material provided in an embodiment of the present invention first suppresses the phase change of the P2-type material and the O3-type material by doping with inert elements to obtain P2-type material and O3-type material with good cycle performance, and then the P2-type material and the O3-type material are physically mixed, and a flux is added to perform a secondary sintering on the mixed material. The added flux can react with the residual alkali on the surface of the material to form a connecting layer of the composite material and a protective layer that improves the interface performance of the material, thereby further improving the comprehensive performance of the composite material, and can obtain a new composite material that integrates the excellent rate performance of the P2-type material and the high capacity of the O3-type material.

[0062] For example, an embodiment of the present invention provides a method for preparing a layered oxide positive electrode material for a sodium ion battery, comprising the following steps:

[0063] (1) The sodium source, nickel source, manganese source and TM source are mixed uniformly according to the stoichiometric ratio, ground, pressed into tablets, sintered at high temperature, and post-treated to prepare a powdered P2 material;

[0064] (2) The sodium source, nickel source, iron source, manganese source and TN source are mixed uniformly according to the stoichiometric ratio, ground, pressed into tablets, sintered at high temperature, and post-treated to prepare a powdered O3 type material;

[0065] (3) The P2 type material and the O3 type material are mixed with flux, ground, pressed into tablets, subjected to secondary high temperature sintering, and post-processed to obtain a powdered sodium ion battery layered oxide positive electrode material.

[0066] In some optional embodiments, in step (1):

[0067] The grinding time is 25 minutes. During the grinding of the raw materials, the grinding time is controlled to 25 minutes. Grinding time that is too short will result in uneven mixing; grinding time that is too long will increase the number of small particles and fine particles of the sintered material, affecting the material properties. During the grinding of the raw materials, an organic solvent is added to moisten the powder in the mortar. Using the organic solvent as a dispersant makes the grinding more uniform and improves the uniformity of the raw material mixing. The organic solvent is selected from at least one of anhydrous ethanol and acetone.

[0068] The specific operation steps of the tableting include: tableting the ground raw material under a pressure of 30-150MPa for 10-35 minutes. The pressure can be 30MPa, 40MPa, 50MPa, 60MPa, 70MPa, 80MPa, 90MPa, 100MPa, 110MPa, 120MPa, 130MPa, 140MPa, 150MPa, etc., preferably 80MPa. If the tableting pressure is too low, the tablets will not be compact enough; if the pressure is too high, the material will be too hard after sintering and will not be easy to grind into a fine powder, thereby affecting the material properties. The tableting time can be 10min, 15min, 20min, 25min, 30min, 35min, etc., preferably 10min. If the tableting time is too short, the edges and corners of the tablets will be broken, and if the tableting time is too long, the material particles will be broken, thereby affecting the material properties.

[0069] The specific operation steps of the high-temperature sintering include: first heating the temperature to 300-700°C at a heating rate of 1-10°C / min for primary sintering, holding the temperature for 2-16 hours, and then heating the temperature to 700-1150°C at a heating rate of 1-10°C / min for secondary sintering, holding the temperature for 8-24 hours; the sintering atmosphere is selected from at least one of air, oxygen, argon and nitrogen. High-temperature sintering can make the Na, Ni, Mn and TM elements uniformly retained in the bulk of the material, which is beneficial to improving the structural stability and electrochemical performance of the layered oxide positive electrode material of sodium ion batteries. The sintering is carried out by gradually increasing the temperature through a two-stage sintering process to prevent the high temperature from rising too quickly and affecting the structure and performance of the material. By regulating the temperature and time of the two-stage sintering, the electrochemical performance of the positive electrode material can be further improved. The temperature of the primary sintering can be 300°C, 400°C, 500°C, 600°C, 700°C, etc., preferably 550°C. The holding time of the primary sintering can be 2h, 5h, 8h, 10h, 12h, 14h, 16h, etc., preferably 6h. The temperature of the secondary sintering can be 700°C, 800°C, 900°C, 1000°C, 1100°C, 1150°C, etc., preferably 950°C. The holding time of the secondary sintering can be 8h, 10h, 13h, 15h, 18h, 20h, 24h, etc., preferably 16h. During the high-temperature sintering process, the heating rate can be 1°C / min, 3°C / min, 5°C / min, 8°C / min, 10°C / min, etc., preferably 2°C / min. The heating rates in both the primary and secondary sintering stages can be controlled at 1-10°C / min, and the heating rates of the two stages can be the same or different. The atmosphere during the high-temperature sintering process is selected from at least one of air atmosphere, oxygen atmosphere, argon atmosphere and nitrogen atmosphere, preferably air atmosphere.

[0070] The specific operating steps of the post-treatment include: cooling the sample after high-temperature sintering to 100-250°C at a cooling rate of 1-10°C / min, and then grinding it into powder in an environment with a relative humidity of less than 1%, and controlling the grinding time to be 10-40min. There may be agglomeration after high-temperature sintering, and the material can be ground into powder after high-temperature sintering. In the actual operation process, after high-temperature sintering, the temperature is cooled to 100-250°C, and then ground into powder in an environment with a relative humidity of less than 1%, and the grinding time is controlled to be 10-40min. After the cooling is completed, it can be immediately transferred to a low-humidity drying room and ground into powder using a mortar to prevent interference from moisture during the grinding process. Specifically, the temperature after cooling can be 100°C, 150°C, 200°C, 250°C, etc., preferably 200°C. The cooling rate is not limited, for example, it can be 1-10°C / min, preferably 2°C / min. The grinding time can be 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes, 35 minutes, 40 minutes, etc., preferably 15 minutes. Too short a grinding time will cause the material particles to agglomerate, affecting the material properties. Too long a grinding time will cause the material particles to break, which will also affect the material properties.

[0071] The sodium source is selected from at least one of Na2CO3, Na2CO3·H2O, NaHCO3, NaOH, CH3COONa, NaNO3, Na2O2, NaO2 and Na2C2O4, preferably Na2CO3.

[0072] The nickel source is selected from at least one of NiO and Ni(OH)2, preferably Ni(OH)2.

[0073] The manganese source is selected from at least one of MnO2, Mn2O3, MnO, MnCO3 and Mn3O4, preferably MnO.

[0074] The TM is selected from at least one of Li, K, Mg, Ca, Zn, Cu, Sr, Fe, Al, Co, Y, La, and Bi. Preferably, the TM is selected from at least one of Li, Cu, Mg, and Ti. The TM source is selected from at least one of oxides, hydroxides, and carbonates containing the TM element; preferably, CuO and TiO2.

[0075] By adjusting the amounts of the nickel, manganese, and TM sources, nickel, manganese, and TM elements are added according to their theoretical amounts. By adjusting the amount of the sodium source, the sodium element is added in an excess of 1-15% relative to the theoretical amount, such as 1%, 3%, 5%, 8%, 10%, 13%, 15%, and preferably 5%. By adjusting the amounts of the raw materials, an appropriate excess of sodium source (such as sodium carbonate) can be added to compensate for the loss of sodium carbonate during high-temperature sintering. However, excessive excess can result in residual sodium carbonate on the surface of the material, thereby affecting material properties.

[0076] In the present invention, the theoretical amount of each element refers to the molar amount of the element, and the excess of 1-15% refers to the ratio of the excess molar amount to the theoretical molar amount.

[0077] In some optional embodiments, in step (2):

[0078] The grinding time is 25 minutes. During the grinding of the raw materials, the grinding time is controlled to 25 minutes. Grinding time that is too short will result in uneven mixing; grinding time that is too long will increase the number of small particles and fine particles of the sintered material, affecting the material properties. During the grinding of the raw materials, an organic solvent is added to moisten the powder in the mortar. Using the organic solvent as a dispersant makes the grinding more uniform and improves the uniformity of the raw material mixing. The organic solvent is selected from at least one of anhydrous ethanol and acetone.

[0079] The specific operation steps of the tableting include: tableting the ground raw material under a pressure of 30-150MPa for 10-35 minutes. The pressure can be 30MPa, 40MPa, 50MPa, 60MPa, 70MPa, 80MPa, 90MPa, 100MPa, 110MPa, 120MPa, 130MPa, 140MPa, 150MPa, etc., preferably 80MPa; if the pressure of the tableting is too small, the tablets pressed out will not be compact enough; if the pressure is too large, the material will be too hard after sintering and will not be easy to grind into fine powder, thereby affecting the material properties. The tableting time can be 10min, 15min, 20min, 25min, 30min, 35min, etc., preferably 10min. If the tableting time is too short, the edges and corners of the pressed tablets will be broken. If the tableting time is too long, the material particles will be broken, thereby affecting the material properties.

[0080] The specific operation steps of the high-temperature sintering include: first heating the temperature to 300-700°C at a heating rate of 1-10°C / min for primary sintering, holding the temperature for 2-16 hours, and then heating the temperature to 700-1150°C at a heating rate of 1-10°C / min for secondary sintering, holding the temperature for 8-24 hours; the sintering atmosphere is selected from at least one of air, oxygen, argon and nitrogen. High-temperature sintering can make the Na, Ni, Mn and TM elements uniformly retained in the bulk of the material, which is beneficial to improving the structural stability and electrochemical performance of the layered oxide positive electrode material of sodium ion batteries. The sintering is carried out by gradually increasing the temperature through a two-stage sintering process to prevent the high temperature from rising too quickly and affecting the structure and performance of the material. By regulating the temperature and time of the two-stage sintering, the electrochemical performance of the positive electrode material can be further improved. The temperature of the primary sintering can be 300°C, 400°C, 500°C, 600°C, 700°C, etc., preferably 550°C. The holding time of the primary sintering can be 2h, 5h, 8h, 10h, 12h, 14h, 16h, etc., preferably 6h. The temperature of the secondary sintering can be 700°C, 800°C, 900°C, 1000°C, 1100°C, 1150°C, etc., preferably 950°C. The holding time of the secondary sintering can be 8h, 10h, 13h, 15h, 18h, 20h, 24h, etc., preferably 16h. During the high-temperature sintering process, the heating rate can be 1°C / min, 3°C / min, 5°C / min, 8°C / min, 10°C / min, etc., preferably 2°C / min. The heating rates in both the primary and secondary sintering stages can be controlled at 1-10°C / min, and the heating rates of the two stages can be the same or different. The atmosphere during the high-temperature sintering process is selected from at least one of air atmosphere, oxygen atmosphere, argon atmosphere and nitrogen atmosphere, preferably air atmosphere.

[0081] The specific operating steps of the post-treatment include: cooling the sample after high-temperature sintering to 100-250°C at a cooling rate of 1-10°C / min, and then grinding it into powder in an environment with a relative humidity of less than 1%, and controlling the grinding time to be 10-40min. There may be agglomeration after high-temperature sintering, and the material can be ground into powder after high-temperature sintering. In the actual operation process, after high-temperature sintering, the temperature is cooled to 100-250°C, and then ground into powder in an environment with a relative humidity of less than 1%, and the grinding time is controlled to be 10-40min. After the cooling is completed, it can be immediately transferred to a low-humidity drying room and ground into powder using a mortar to prevent interference from moisture during the grinding process. Specifically, the temperature after cooling can be 100°C, 150°C, 200°C, 250°C, etc., preferably 200°C. The cooling rate is not limited, for example, it can be 1-10°C / min, preferably 2°C / min. The grinding time can be 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes, 35 minutes, 40 minutes, etc., preferably 15 minutes. Too short a grinding time will cause the material particles to agglomerate, affecting the material properties. Too long a grinding time will cause the material particles to break, which will also affect the material properties.

[0082] The sodium source is selected from at least one of Na2CO3, Na2CO3·H2O, NaHCO3, NaOH, CH3COONa, NaNO3, Na2O2, NaO2 and Na2C2O4, preferably Na2CO3.

[0083] The nickel source is selected from at least one of NiO and Ni(OH)2, preferably Ni(OH)2.

[0084] The manganese source is selected from at least one of MnO2, Mn2O3, MnO, MnCO3 and Mn3O4, preferably MnO.

[0085] The iron source is selected from at least one of Fe2O3 and FeO, preferably Fe2O3.

[0086] TN is selected from at least one of Li, K, Mg, Ca, Zn, Cu, Sr, Fe, Al, Co, Y, La, and Bi. Preferably, TN is selected from at least one of Zn, Cu, Mg, and Ti. The TN source is selected from at least one of oxides, hydroxides, and carbonates containing TN elements, preferably TiO2, ZnO, and CuO.

[0087] By adjusting the amounts of the nickel source, iron source, manganese source, and TN source, nickel, iron, manganese, and TN elements are added according to the theoretical amounts. By adjusting the amount of the sodium source, the sodium element is added in an excess of 1-15 wt% relative to the theoretical amount, such as 1%, 3%, 5%, 8%, 10%, 13%, 15%, etc., preferably 5%. By adjusting the amounts of the raw materials, an appropriate excess of sodium source (such as sodium carbonate) can be added to compensate for the loss of sodium carbonate during high-temperature sintering. However, excessive excess can cause sodium carbonate residue on the surface of the material, thereby affecting material properties.

[0088] In the present invention, the theoretical amount of each element refers to the molar amount of the element, and the excess of 1-15% refers to the ratio of the excess molar amount to the theoretical molar amount.

[0089] In some optional embodiments, in step (3), the grinding time is 25 minutes. During the grinding of the raw materials, the grinding time is controlled to be 25 minutes. If the grinding time is too short, the mixing will be uneven; if the grinding time is too long, the sintered material will have more small particles and fine particles, affecting the material properties. During the grinding of the raw materials, an organic solvent is added to moisten the powder in the mortar. The organic solvent is used as a dispersant to make the grinding more uniform and improve the uniformity of the raw material mixing. The organic solvent is selected from at least one of anhydrous ethanol and acetone.

[0090] The specific operation steps of the tableting include: tableting the ground raw material under a pressure of 30-150MPa for 10-35 minutes. The pressure can be 30MPa, 40MPa, 50MPa, 60MPa, 70MPa, 80MPa, 90MPa, 100MPa, 110MPa, 120MPa, 130MPa, 140MPa, 150MPa, etc., preferably 80MPa; if the pressure of the tableting is too small, the tablets pressed out will not be compact enough; if the pressure is too large, the material will be too hard after sintering and will not be easy to grind into fine powder, thereby affecting the material properties. The tableting time can be 10min, 15min, 20min, 25min, 30min, 35min, etc., preferably 10min. If the tableting time is too short, the edges and corners of the pressed tablets will be broken. If the tableting time is too long, the material particles will be broken, thereby affecting the material properties.

[0091] The specific operation steps of the secondary high-temperature sintering include: heating to 550-900°C at a heating rate of 1-10°C / min for sintering, preferably 750°C, and keeping warm for 2-16 hours, preferably 6 hours; the sintering atmosphere is selected from at least one of air, oxygen, argon and nitrogen, preferably air atmosphere.

[0092] The specific operating steps of the post-treatment include: cooling the sample after high-temperature sintering to 100-250°C at a cooling rate of 1-10°C / min, and then grinding it into powder in an environment with a relative humidity of less than 1%, and controlling the grinding time to be 10-40min. There may be agglomeration after high-temperature sintering, and the material can be ground into powder after high-temperature sintering. In the actual operation process, after high-temperature sintering, the temperature is cooled to 100-250°C, and then ground into powder in an environment with a relative humidity of less than 1%, and the grinding time is controlled to be 10-40min. After the cooling is completed, it can be immediately transferred to a low-humidity drying room and ground into powder using a mortar to prevent interference from moisture during the grinding process. Specifically, the temperature after cooling can be 100°C, 150°C, 200°C, 250°C, preferably 200°C. The cooling rate is not limited, for example, it can be 1-10°C / min, preferably 2°C / min. The grinding time can be 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes, 35 minutes, 40 minutes, etc., preferably 15 minutes. Too short a grinding time will cause the material particles to agglomerate, affecting the material properties. Too long a grinding time will cause the material particles to break, which will also affect the material properties.

[0093] The mass ratio of the P2 type material to the O3 type material is (1-5): (5-9), preferably 1:9, 2:8, 3:7, 4:6, 5:5, etc.

[0094] The amount of the soldering flux added is 0-10% of the total mass of the P2-type material and the O3-type material, and is not 0, preferably 2%, 5%, 10%, etc. More preferably, it is 2%.

[0095] The soldering flux is selected from one of KF, H3PO4 and H3BO3, preferably H3PO4.

[0096] The present invention also provides a positive electrode sheet comprising the layered oxide positive electrode material for a sodium ion battery prepared according to the present invention. The improvement of the positive electrode material further enhances the electrochemical performance of the positive electrode sheet. The positive electrode sheet may further include a positive electrode current collector, etc., with a positive electrode active coating formed on the positive electrode current collector. The layered oxide positive electrode material for a sodium ion battery provided by the present invention is located within the positive electrode active coating.

[0097] An embodiment of the present invention further provides a sodium ion battery, comprising the above-mentioned positive electrode plate, and may further comprise a negative electrode plate, an electrolyte, a separator, etc. Due to the improvement of the electrochemical performance of the positive electrode plate, the sodium ion battery has more excellent electrochemical performance.

[0098] An embodiment of the present invention further provides an electrical device, comprising the above-mentioned sodium ion battery, and utilizing the sodium ion battery for power supply.

[0099] The raw materials used in the present invention are all purchased from the market.

[0100] The technical solution of the present invention is further illustrated by the following examples.

[0101] Example 1

[0102] A method for preparing a layered oxide cathode material for a sodium ion battery, wherein the chemical formula of the P2 type cathode material is Na 0.67 Ni 0.23 Cu 0.1 Mn 0.46 Ti 0.21 The chemical formula of O2, O3 type positive electrode material is Na 0.9 Ni 0.2 Mn 0.375 Fe 0.3 Cu 0.05 Zn 0.05 Ti 0.025 The mass ratio of O2, P2 and O3 materials is 1:9, and the amount of flux added is 2% of the total mass of P2 and O3 materials. The specific steps are as follows:

[0103] S1: Weigh 0.7342g of Na2CO3 (the sodium ratio is 1:1.05, that is, the sodium element is 5% more than the theoretical amount, the same below), 0.4157g of Ni(OH)2, 0.6361g of MnO, 0.1567g of CuO and 0.3302g of TiO2, mix them, add 1mL of anhydrous ethanol and grind for 25min; pour the ground raw materials into the mold of the tablet press, then place the mold in the tablet press, select a pressure of 80MPa, and continue 10min; put the pressed raw material disc into the crucible and place it in the muffle furnace. In the air atmosphere, the temperature was raised to 550℃ at a rate of 2℃ / min in the first sintering stage and kept warm for 6h. In the second sintering stage, the temperature was raised to 950℃ at the same rate of 2℃ / min and kept warm for 16h. Then, the temperature was lowered to 200℃ at a rate of 2℃ / min. The material was immediately transferred to a low humidity drying room (relative humidity less than 1%) and ground in a mortar for 15min to obtain powdered P2-type Na 0.67 Ni 0.23 Cu 0.1 Mn 0.46 Ti 0.21 O2 cathode material;

[0104] S2: Weigh 0.9154g of Na2CO3 (sodium ratio is 1:1.05), 0.3388g of Ni(OH)2, 0.4862g of MnO, 0.4378g of Fe2O3, 0.0364g of TiO2, 0.0744g of ZnO and 0.0726g of CuO, mix them, add 1mL of anhydrous ethanol and grind for 25min; pour the ground raw materials into the mold of the tablet press, then place the mold in the tablet press, select 80MPa pressure The pressed raw material disc was placed in a crucible and placed in a muffle furnace. In an air atmosphere, the temperature was raised to 550°C at a rate of 2°C / min in the first sintering stage and kept warm for 6 hours. In the second sintering stage, the temperature was raised to 950°C at the same rate of 2°C / min and kept warm for 16 hours. The temperature was then lowered to 200°C at a rate of 2°C / min. The material was then immediately transferred to a low humidity drying room (relative humidity less than 1%) and ground in a mortar for 15 minutes to obtain powdered O3-type Na 0.9 Ni 0.2 Mn 0.375 Fe 0.3 Cu 0.05 Zn 0.05 Ti 0.025 O2 cathode material;

[0105] S3: Weigh 0.1g of P2-type material, 0.9g of O3-type material and 0.02g of H3PO4, mix and grind for 25min, pour the evenly ground raw materials into the mold of the tablet press, then place the mold in the tablet press, select a pressure of 80MPa, and continue for 10min; put the pressed mixed material discs into a crucible, place it in a muffle furnace, and in an air atmosphere, heat it to 750℃ at a rate of 2℃ / min, keep it warm for 6h, and then cool it to 200℃ at a rate of 2℃ / min. Then immediately transfer the material to a low-humidity drying room (relative humidity less than 1%), and grind it in a mortar for 15min to obtain a powdered sodium ion battery layered oxide positive electrode material, named P1O9 material.

[0106] Example 2

[0107] The same as Example 1, except that the mass ratio of P2 type material to O3 type material is 2:8, that is, step S3 is: weigh 0.2g of P2 type material, 0.8g of O3 type material and 0.02g of H3PO4, mix and grind for 25min, pour the evenly ground raw materials into the mold of the tablet press, and then place the mold in the tablet press, select a pressure of 80MPa, and continue for 10min; put the pressed mixed material disc into a crucible, place it in a muffle furnace, and in an air atmosphere, heat to 750℃ at a rate of 2℃ / min, keep warm for 6h, and then cool to 200℃ at a rate of 2℃ / min, then immediately transfer the material to a low humidity drying room (relative humidity less than 1%), and then use a mortar to grind for 15min to obtain a powdered sodium ion battery layered oxide positive electrode material, named P2O8 material.

[0108] Example 3

[0109] The same as Example 1, except that the mass ratio of P2-type material to O3-type material is 3:7, that is, step S3 is: weigh 0.3 g of P2-type material, 0.7 g of O3-type material and 0.02 g of H3PO4, mix and grind for 25 minutes, pour the evenly ground raw materials into the mold of the tablet press, and then place the mold in the tablet press, select a pressure of 80 MPa, and continue for 10 minutes; put the pressed mixed material disc into a crucible, place it in a muffle furnace, and in an air atmosphere, heat to 750°C at a rate of 2°C / min, keep warm for 6 hours, and then cool to 200°C at a rate of 2°C / min, then immediately transfer the material to a low humidity drying room (relative humidity less than 1%), and then use a mortar to grind for 15 minutes to obtain a powdered sodium ion battery layered oxide positive electrode material, named P3O7 material.

[0110] Example 4

[0111] The same as Example 1, except that the mass ratio of P2 type material to O3 type material is 4:6, that is, step S3 is: weigh 0.4g of P2 type material, 0.6g of O3 type material and 0.02g of H3PO4, mix and grind for 25min, pour the evenly ground raw materials into the mold of the tablet press, and then place the mold in the tablet press, select a pressure of 80MPa, and continue for 10min; put the pressed mixed material disc into a crucible, place it in a muffle furnace, and in an air atmosphere, heat to 750℃ at a rate of 2℃ / min, keep warm for 6h, and then cool to 200℃ at a rate of 2℃ / min, then immediately transfer the material to a low humidity drying room (relative humidity less than 1%), and then use a mortar to grind for 15min to obtain a powdered sodium ion battery layered oxide positive electrode material, named P4O6 material.

[0112] Example 5

[0113] The same as Example 1, except that the mass ratio of P2-type material to O3-type material is 5:5, that is, step S3 is: weigh 0.5 g of P2-type material, 0.5 g of O3-type material and 0.02 g of H3PO4, mix and grind for 25 minutes, pour the evenly ground raw materials into the mold of the tablet press, and then place the mold in the tablet press, select a pressure of 80 MPa, and continue for 10 minutes; put the pressed mixed material disc into a crucible, place it in a muffle furnace, and in an air atmosphere, heat to 750°C at a rate of 2°C / min, keep warm for 6 hours, and then cool to 200°C at a rate of 2°C / min, then immediately transfer the material to a low humidity drying room (relative humidity less than 1%), and then use a mortar to grind for 15 minutes to obtain a powdered sodium ion battery layered oxide positive electrode material, named P5O5 material.

[0114] Example 6

[0115] The same as Example 3, except that the amount of flux added is 5% of the total mass of the P2 material and the O3 material, that is, step S3 is: weigh 0.3g of P2 material, 0.7g of O3 material and 0.05g of H3PO4, mix and grind for 25min, pour the evenly ground raw materials into the mold of the tablet press, and then place the mold in the tablet press, select a pressure of 80MPa, and continue for 10min; put the pressed mixed material disc into a crucible, place it in a muffle furnace, and in an air atmosphere, heat it to 750℃ at a rate of 2℃ / min, keep it warm for 6h, and then cool it to 200℃ at a rate of 2℃ / min, then immediately transfer the material to a low humidity drying room (relative humidity less than 1%), and then grind it in a mortar for 15min to obtain a powdered material.

[0116] Example 7

[0117] The same as Example 3, except that the flux is KF, that is, step S3 is: weigh 0.3 g of P2-type material, 0.7 g of O3-type material and 0.02 g of KF, mix and grind for 25 minutes, pour the evenly ground raw materials into the mold of the tablet press, and then place the mold in the tablet press, select a pressure of 80 MPa, and continue for 10 minutes; put the pressed mixed material disc into a crucible, place it in a muffle furnace, and in an air atmosphere, heat it to 750°C at a rate of 2°C / min, keep it warm for 6 hours, and then cool it to 200°C at a rate of 2°C / min, then immediately transfer the material to a low humidity drying room (relative humidity less than 1%), and then grind it in a mortar for 15 minutes to obtain a powdered material.

[0118] Example 8

[0119] The same as Example 3, except that the sintering temperature of step S3 is 550°C, that is, step S3 is: weigh 0.3g of P2-type material, 0.7g of O3-type material and 0.02g of H3PO4, mix and grind for 25min, pour the evenly ground raw materials into the mold of the tablet press, and then place the mold in the tablet press, select a pressure of 80MPa, and continue for 10min; put the pressed mixed material disc into a crucible, place it in a muffle furnace, and in an air atmosphere, heat to 550°C at a rate of 2°C / min, keep warm for 6h, and then cool to 200°C at a rate of 2°C / min, then immediately transfer the material to a low humidity drying room (relative humidity less than 1%), and then grind it in a mortar for 15min to obtain a powdered material.

[0120] Example 9

[0121] The same as Example 3, except that the sintering temperature of step S3 is 900°C, that is, step S3 is: weigh 0.3g of P2-type material, 0.7g of O3-type material and 0.02g of H3PO4, mix and grind for 25min, pour the evenly ground raw materials into the mold of the tablet press, place the mold in the tablet press, select a pressure of 80MPa, and continue for 10min; put the pressed mixed material disc into a crucible, place it in a muffle furnace, and in an air atmosphere, heat to 900°C at a rate of 2°C / min, keep warm for 6h, and then cool to 200°C at a rate of 2°C / min, then immediately transfer the material to a low humidity drying room (relative humidity less than 1%), and then grind it in a mortar for 15min to obtain a powdered material.

[0122] Example 10

[0123] The same as Example 3, except that the holding time of step S3 is 2h, that is, step S3 is: weigh 0.3g of P2-type material, 0.7g of O3-type material and 0.02g of H3PO4, mix and grind for 25min, pour the evenly ground raw material into the mold of the tablet press, and then place the mold in the tablet press, select a pressure of 80MPa, and continue for 10min; put the pressed mixed material disc into a crucible, place it in a muffle furnace, and in an air atmosphere, heat to 750℃ at a rate of 2℃ / min, keep warm for 2h, and then cool to 200℃ at a rate of 2℃ / min, then immediately transfer the material to a low humidity drying room (relative humidity less than 1%), and then grind it in a mortar for 15min to obtain a powdered material.

[0124] Example 11

[0125] The same as Example 3, except that the holding time of step S3 is 16h, that is, step S3 is: weigh 0.3g of P2-type material, 0.7g of O3-type material and 0.02g of H3PO4, mix and grind for 25min, pour the evenly ground raw materials into the mold of the tablet press, and then place the mold in the tablet press, select a pressure of 80MPa, and continue for 10min; put the pressed mixed material disc into a crucible, place it in a muffle furnace, and in an air atmosphere, heat to 750℃ at a rate of 2℃ / min, keep warm for 16h, and then cool to 200℃ at a rate of 2℃ / min, then immediately transfer the material to a low humidity drying room (relative humidity less than 1%), and then grind it in a mortar for 15min to obtain a powdered material.

[0126] Example 12

[0127] The same as Example 3, except that the sintering atmosphere of step S3 is oxygen, that is, step S3 is: weigh 0.3 g of P2 type material, 0.7 g of O3 type material and 0.02 g of H3PO4, mix and grind for 25 minutes, pour the evenly ground raw materials into the mold of the tablet press, and then place the mold in the tablet press, select a pressure of 80 MPa, and continue for 10 minutes; put the pressed mixed material disc into a crucible, place it in a muffle furnace, and in an oxygen atmosphere, heat it to 750°C at a rate of 2°C / min, keep it warm for 6 hours, and then cool it to 200°C at a rate of 2°C / min, then immediately transfer the material to a low humidity drying room (relative humidity less than 1%), and then grind it in a mortar for 15 minutes to obtain a powdered material.

[0128] Example 13

[0129] The same as Example 3, except that the sintering atmosphere of step S3 is argon, that is, step S3 is: weigh 0.3 g of P2 type material, 0.7 g of O3 type material and 0.02 g of H3PO4, mix and grind for 25 minutes, pour the evenly ground raw materials into the mold of the tablet press, and then place the mold in the tablet press, select a pressure of 80 MPa, and continue for 10 minutes; put the pressed mixed material disc into a crucible, place it in a muffle furnace, and under an argon atmosphere, heat it to 750°C at a rate of 2°C / min, keep it warm for 6 hours, and then cool it to 200°C at a rate of 2°C / min, then immediately transfer the material to a low humidity drying room (relative humidity less than 1%), and then grind it in a mortar for 15 minutes to obtain a powdered material.

[0130] Comparative Example 1

[0131] A method for preparing a P2 type positive electrode material, the chemical formula of which is Na 0.67 Ni 0.23 Cu 0.1 Mn 0.46 Ti0.21 O2, the specific steps are as follows:

[0132] Weigh 0.7342g of Na2CO3 (sodium ratio is 1:1.05), 0.4157g of Ni(OH)2, 0.6361g of MnO, 0.1567g of CuO and 0.3302g of TiO2, mix them, add 1mL of anhydrous ethanol and grind for 25min; pour the ground raw materials into the mold of the tablet press, then place the mold in the tablet press, select a pressure of 80MPa, and continue for 10min; put the pressed raw material disc into a crucible and place it in a muffle furnace. Under air atmosphere, the first sintering stage is heated to 550℃ at a rate of 2℃ / min and kept warm for 6h. In the second sintering stage, the temperature is raised to 950℃ at the same rate of 2℃ / min, kept warm for 16h, and then cooled to 200℃ at a rate of 2℃ / min. Then, the material is immediately transferred to a low humidity drying room (relative humidity less than 1%) and ground in a mortar for 15min to obtain powdered P2 type Na 0.67 Ni 0.23 Cu 0.1 Mn 0.46 Ti 0.21 O2 positive electrode material.

[0133] Comparative Example 2

[0134] A method for preparing an O3-type positive electrode material having the chemical formula Na 0.9 Ni 0.2 Mn 0.375 Fe 0.3 Cu 0.05 Zn 0.05 Ti 0.025 O2, the specific steps are as follows:

[0135] Weigh 0.9154g of Na2CO3 (sodium ratio is 1:1.05), 0.3388g of Ni(OH)2, 0.4862g of MnO, 0.4378g of Fe2O3, 0.0364g of TiO2, 0.0744g of ZnO and 0.0726g of CuO, mix them, add 1mL of anhydrous ethanol and grind for 25min; pour the ground raw materials into the mold of the tablet press, then place the mold in the tablet press, select a pressure of 80MPa, The pressed raw material discs were placed in a crucible and placed in a muffle furnace. In an air atmosphere, the temperature was raised to 550°C at a rate of 2°C / min in the first sintering stage and kept warm for 6 hours. In the second sintering stage, the temperature was raised to 950°C at the same rate of 2°C / min and kept warm for 16 hours. The temperature was then lowered to 200°C at a rate of 2°C / min. The material was then immediately transferred to a low humidity drying room (relative humidity less than 1%) and ground in a mortar for 15 minutes to obtain powdered O3-type Na 0.9Ni 0.2 Mn 0.375 Fe 0.3 Cu 0.05 Zn 0.05 Ti 0.025 O2 positive electrode material.

[0136] Comparative Example 3

[0137] The same as Example 3, except that no flux is added and no secondary high-temperature sintering is performed, that is, step S3 is: weigh 0.3g of P2 type material and 0.7g of O3 type material, mix and grind for 25min to obtain a positive electrode material.

[0138] Comparative Example 4

[0139] Same as Example 3, except that the soldering flux H3PO4 is not added.

[0140] Performance testing

[0141] Test method: The positive electrode material powders prepared in Examples 1-13 and Comparative Examples 1-4 were thoroughly mixed with polyvinylidene fluoride and conductive carbon black in a mass ratio of 8:1:1, stirred into a uniform slurry, and coated onto aluminum foil to a thickness of 180 μm. The mixture was then dried in a vacuum oven at 120°C, roll-pressed, and cut into circular positive electrode sheets with a diameter of 12 mm. The mass of the active material in the sheets was calculated and then transferred to a glove box for standby use. The cut circular positive electrode sheets, a sodium metal sheet (as the negative electrode), a Whatman Grade GF / D glass fiber membrane as a separator, 2025 positive and negative battery casings, springs, gaskets, and sodium hexafluorophosphate electrolyte were assembled into 2025 button-type half-cells in an argon-filled glove box. The cells were then placed in a battery test cabinet maintained at a constant temperature of 25°C for charge and discharge tests.

[0142] Table 1 Test results

[0143] 0.1C first cycle reversible specific capacity (mAh / g) 1C first cycle reversible specific capacity (mAh / g) 1C-100 cycles capacity retention rate (%) Example 1 138.62 102.19 80.11 Example 2 134.57 103.28 82.34 Example 3 130.24 107.5 88.79 Example 4 126.28 101.23 84.28 Example 5 120.41 100.21 85.39 Example 6 126.45 104.33 85.69 Example 7 125.58 103.28 85.23 Example 8 128.18 105.5 86.39 Example 9 126.35 104.9 85.21 Example 10 126.98 102.1 85.11 Example 11 125.12 101.5 86.29 Example 12 124.24 102.5 85.12 Example 13 125.31 103.5 85.64

[0144] Table 1 shows the electrochemical performance of Examples 1-13 of the present invention. Comparing Examples 1-5, when the flux addition amount is 2% of the total mass of the P2-type and O3-type materials, Example 3, with a mass ratio of 3:7 of P2-type and O3-type materials, exhibits the highest 1C discharge capacity and 1C capacity retention. Comparing Example 3 with Example 6, which differ only in the flux content, Example 3, with a flux addition amount of 2% of the total mass of the P2-type and O3-type materials, exhibits better electrochemical performance, indicating that a flux addition amount of 2% is more preferred. Comparing Example 3 with Example 7, which differ only in the flux type, Example 3, with H3PO4 as the flux, exhibits better electrochemical performance, indicating that H3PO4 is a more preferred flux type. Comparing Examples 3, 8, and 9, which differ only in the sintering temperature, Example 3, with a sintering temperature of 750°C, exhibits better electrochemical performance, indicating that a sintering temperature of 750°C is more preferred. Comparing Example 3, Example 10, and Example 11, the three differ only in the holding time. Example 3, with a holding time of 6 hours, exhibits better electrochemical performance, indicating that a holding time of 6 hours is more preferred. Comparing Example 3, Example 12, and Example 13, the three differ only in the sintering atmosphere. Example 3, with an air sintering atmosphere, exhibits better electrochemical performance, indicating that an air sintering atmosphere is more preferred.

[0145] Figure 1 The X-ray diffraction patterns of the positive electrode materials prepared in Comparative Example 1, Comparative Example 2 and Example 3 of the present invention are as follows; as can be seen from the patterns, the diffraction peak of the positive electrode material prepared in Comparative Example 1 is compared with the PDF standard card, which shows that it is the P63 / mmc space group, and no impurity phase is produced, and it is a pure P2 phase material; the diffraction peak of the positive electrode material prepared in Comparative Example 2 is compared with the PDF standard card, which shows that it is the R-3m space group, and no impurity phase is produced, and it is a pure O3 phase material; the diffraction peak of the positive electrode material prepared in Example 3 is compared with the PDF standard card, which shows that it has diffraction peaks of both P2 phase and O3 phase, and is a P2 / O3 composite material.

[0146] Figure 2 This is a scanning electron microscope image of the positive electrode material prepared in Comparative Example 1 of the present invention. Figure 3 This is a scanning electron microscope image of the positive electrode material prepared in Comparative Example 2 of the present invention. Figure 4This is a scanning electron microscope image of the positive electrode material prepared in Example 3 of the present invention; it can be seen that the surface of the positive electrode material prepared in Comparative Example 1 is very smooth, no residual alkali exists, and the particles are relatively rounded; the positive electrode material prepared in Comparative Example 2 has sharp-edged particles, a large number of small particles are enriched on the surface, and more residual alkali remains, which will cause the material to easily absorb water and moisture, deteriorate the processing performance, and thus affect the electrochemical properties of the material; the positive electrode material prepared in Example 3 has a relatively smooth surface, a small amount of small particles exist on the surface, and there are round particles and hexagonal particles, indicating that a P2 / O3 composite material is obtained.

[0147] Figure 5 This is a comparison chart of the first-cycle charge and discharge curves of button-type batteries tested for the positive electrode materials prepared by Comparative Example 1, Comparative Example 2 and Example 3 of the present invention; it can be seen that the first-cycle discharge specific capacity of the button-type battery of the positive electrode material prepared in Comparative Example 1 is 104.5mAh / g, the first-cycle discharge specific capacity of the button-type battery of the positive electrode material prepared in Comparative Example 2 is 143.28mAh / g, and the first-cycle discharge specific capacity of the button-type battery of the positive electrode material prepared in Example 3 is 130.24mAh / g; this indicates that the discharge specific capacity of the P2 / O3 composite material of Example 3 prepared by mixing Comparative Example 1 and Comparative Example 2 is greatly improved compared with the discharge specific capacity of the pure P2 phase material prepared in Comparative Example 1.

[0148] Figure 6 The following is a comparison chart of the first-cycle charge and discharge curves of button-type batteries tested for the positive electrode materials prepared in Comparative Example 3, Comparative Example 4 and Example 3 of the present invention; it can be seen that the first-cycle discharge specific capacity of the button-type battery of the positive electrode material prepared in Comparative Example 3 is 116.85 mAh / g, the first-cycle discharge specific capacity of the button-type battery of the positive electrode material prepared in Comparative Example 4 is 118.46 mAh / g, and the first-cycle discharge specific capacity of the button-type battery of the positive electrode material prepared in Example 3 is 130.24 mAh / g; among them, the button-type battery of the positive electrode material prepared in Example 3 shows the highest first-cycle discharge specific capacity, and Example 3 shows the highest first-cycle charge and discharge efficiency, which is attributed to the flux added in Example 3 consuming the residual alkali on the surface, thereby improving the reversible capacity of the material.

[0149] Figure 7The figure shows a comparison of the rate performance of button batteries of the positive electrode materials prepared in comparative examples 1, 2 and 3 of the present invention; it can be seen that the discharge capacity of Example 3 is 130.24 mAh / g at a rate of 0.1C, and 107.5 mAh / g at a rate of 1C, with a capacity retention rate of 1C / 0.1C of 82.54%; the discharge capacity of comparative example 2 is 143.28 mAh / g at a rate of 0.1C, and 113 mAh / g at a rate of 1C, with a capacity retention rate of 1C / 0.1C of only 78.87%, indicating that the physically mixed P2 / O3 composite material prepared in the present invention has relatively excellent rate performance.

[0150] Figure 8 The 1C cycle performance comparison chart of the button battery test of the positive electrode materials prepared from comparative examples 1, comparative example 2 and embodiment 3 of the present invention is shown; it can be seen that the cycle stability of embodiment 3 is improved compared with that of comparative example 2, and embodiment 3 still has a discharge specific capacity of 95.45 mAh / g after 100 cycles at a 1C rate, with a capacity retention rate of 88.79%; while comparative example 2 has only a discharge specific capacity of 87.39 mAh / g after 100 cycles, with a capacity retention rate of only 77.34%, which indicates that the P2 / O3 composite material prepared by the specific process of the present invention has a higher discharge specific capacity and better cycle stability.

[0151] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A layered oxide positive electrode material for a sodium ion battery, characterized in that: It is obtained by physically mixing P2 type material, O3 type material and flux, and the mass ratio of the P2 type material to the O3 type material is (1-5): (5-9); The P2 type material is a P2 type sodium ion battery layered oxide with a space group of P63 / mmc and a chemical formula of Na X Ni A Mn B TM C O2; wherein, 0.6≤X≤0.8, 0≤A≤0.4, 0≤B≤0.7, 0≤C≤0.4, A+B+C=1, and A, B, and C cannot be 0 at the same time; TM is selected from at least one of Li, Ti, K, Mg, Ca, Zn, Cu, Sr, Fe, Al, Co, Y, La, and Bi; The O3 type material is an O3 type sodium ion battery layered oxide with a space group of R-3m and a chemical formula of Na Y Ni D Fe E Mn F TN G O2; wherein, 0.8≤Y≤1, 0≤D≤0.4, 0≤E≤0.4, 0≤F≤0.4, 0≤G≤0.4, D+E+F+G=1, and D, E, F, and G cannot be 0 at the same time; TN is selected from at least one of Li, Ti, K, Mg, Ca, Zn, Cu, Sr, Fe, Al, Co, Y, La, and Bi; The soldering flux is selected from one of H3PO4 and H3BO3; The method for preparing the sodium ion battery layered oxide positive electrode material comprises the following steps: The sodium source, nickel source, manganese source and TM source are mixed uniformly according to the stoichiometric ratio, ground, pressed into tablets, sintered at high temperature, and post-treated to prepare a powdered P2 material; The sodium source, nickel source, iron source, manganese source and TN source are mixed uniformly according to the stoichiometric ratio, ground, pressed into tablets, sintered at high temperature, and post-treated to prepare a powdered O3 material; The P2 type material and the O3 type material are mixed with flux, ground, tableted, sintered at a secondary high temperature, and post-processed to obtain a powdered sodium ion battery layered oxide positive electrode material; the temperature of the secondary high temperature sintering is 550-900°C.

2. The sodium ion battery layered oxide positive electrode material according to claim 1, characterized in that The amount of the soldering flux added is 0-10% of the total mass of the P2-type material and the O3-type material, and is not 0.

3. A method for preparing the layered oxide positive electrode material for sodium ion batteries according to any one of claims 1 to 2, characterized in that: The following steps are involved: The sodium source, nickel source, manganese source and TM source are mixed uniformly according to the stoichiometric ratio, ground, pressed into tablets, sintered at high temperature, and post-treated to prepare a powdered P2 material; The sodium source, nickel source, iron source, manganese source and TN source are mixed uniformly according to the stoichiometric ratio, ground, pressed into tablets, sintered at high temperature, and post-treated to prepare a powdered O3 material; The P2 type material and the O3 type material are mixed with the flux, ground, pressed into tablets, subjected to secondary high-temperature sintering, and post-processed to obtain a powdered sodium ion battery layered oxide positive electrode material.

4. The method for preparing a layered oxide positive electrode material for sodium ion batteries according to claim 3, wherein: The grinding time is 25 minutes; and / or, The specific operation steps of tableting include: tableting the ground raw material under a pressure of 30-150 MPa for 10-35 minutes; and / or, The specific operation steps of the high-temperature sintering include: first heating the temperature to 300-700°C at a heating rate of 1-10°C / min for primary sintering, keeping the temperature for 2-16 hours, and then heating the temperature to 700-1150°C at a heating rate of 1-10°C / min for secondary sintering, keeping the temperature for 8-24 hours; the sintering atmosphere is selected from at least one of air, oxygen, argon and nitrogen; and / or, The specific operation steps of the post-treatment include: cooling the sample after high-temperature sintering to 100-250°C at a cooling rate of 1-10°C / min, and then grinding it into powder in an environment with a relative humidity of less than 1%, and controlling the grinding time to be 10-40 minutes; and / or, The specific operation steps of the secondary high-temperature sintering include: heating to 550-900°C at a heating rate of 1-10°C / min for sintering, and keeping the temperature for 2-16 hours; the sintering atmosphere is selected from at least one of air, oxygen, argon and nitrogen.

5. The method for preparing a layered oxide positive electrode material for sodium ion batteries according to claim 3, wherein: The sodium source is selected from at least one of Na2CO3, Na2CO3·H2O, NaHCO3, NaOH, CH3COONa, NaNO3, Na2O2, NaO2 and Na2C2O4; and / or, The nickel source is selected from at least one of NiO and Ni(OH)2; and / or, The manganese source is selected from at least one of MnO2, Mn2O3, MnO, MnCO3 and Mn3O4; and / or, The iron source is selected from at least one of Fe2O3 and FeO.

6. The method for preparing the layered oxide positive electrode material for sodium ion batteries according to claim 3, wherein: The amount of the sodium source is adjusted to make the sodium element excess by 1-15% compared to the theoretical amount.

7. A positive electrode plate, characterized in that: The raw materials include the sodium ion battery layered oxide positive electrode material according to any one of claims 1 to 2.

8. A sodium ion battery, characterized in that: The raw materials include the positive electrode sheet as described in claim 7.

9. Use of the sodium ion battery according to claim 8 in the field of electrical devices.

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