Sodium ion layered oxide positive electrode material and preparation method thereof

Abstract

The invention provides a sodium ion layered oxide positive electrode material and a preparation method thereof, and relates to the technical field of sodium ion batteries. The chemical formula of the sodium ion layered oxide material is Na < 0.67 > Ni < 0.33-x / 2 > Co < x > Mn < 0.67-x / 2 < 2 > O < 2-y > F < y >, wherein x is greater than 0 and less than or equal to 0.2, and y is greater than 0 and less than or equal to 0.1. A layered oxide with a pore structure is synthesized by utilizing a polymer dispersant high-temperature carbonization decomposition method, the structure can effectively shorten a sodium ion transmission path and relieve volume expansion, and the structural stability and reaction kinetics of the material are improved. Co / F double doping not only can improve the conductivity of the material, but also can inhibit the phase change in the charge-discharge process and stabilize the structure. According to the sodium ion layered oxide positive electrode material, through Co / F doping and material structure regulation and control, the structural stability of the material is improved, phase change is inhibited, Na < + > diffusion is improved, the specific capacity is increased, and the cycle life is prolonged.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of sodium ion batteries, in particular to a sodium ion layered oxide positive electrode material and a preparation method thereof. BACKGROUND

[0002] With the transformation of global energy structure and the continuous growth of clean energy demand, energy storage technology has become a key to promoting sustainable development. In recent years, battery technology, as an important energy storage method, has attracted widespread attention. Among many battery technologies, sodium ion batteries have become a promising energy storage technology due to their low cost, high safety, superior low-temperature performance and other characteristics. Compared with lithium ion batteries, sodium ion batteries not only have abundant raw materials and wide distribution, but also have relatively low prices, which are suitable for large-scale energy storage applications. However, despite these advantages, sodium ion batteries still face technical bottlenecks such as low energy density and short cycle life, which limit their promotion in some high-energy-density application scenarios.

[0003] Although P2-phase NiMn-based layered oxide materials have certain advantages, under high-voltage working conditions, the materials will undergo P2-O2 phase transition, resulting in severe volume change and thus causing powdering and cracking, which greatly reduces their cycle performance. In addition, P2-phase positive electrode materials will form an ordered arrangement of Na + / vacancies during the charging and discharging process, increasing the resistance of sodium ion diffusion and leading to a decrease in the kinetic performance of the material. During the charging and discharging process, the Mn element in the P2-phase material will undergo electron gain and loss, producing a Jahn-Teller effect, which causes distortion and instability of the crystal structure of the material, and thus affects the cycle stability of the material. Another prominent problem is the poor air stability of the material, which is easily humidified and reacts with CO2 to generate NaOH and Na2CO3, thus causing deformation and failure of the material structure. Ultimately, the energy density of sodium ion batteries is still lower than that of lithium ion batteries, limiting their application in high-energy-density energy storage fields.

[0004] Therefore, although P2-phase NiMn-based layered oxides have certain advantages as positive electrode materials for sodium ion batteries, their defects in stability, energy density and long-cycle performance are still significant. To further promote the application of sodium ion batteries, these defects need to be overcome, and a positive electrode material with higher specific capacity, more stable structure and smoother sodium ion diffusion needs to be developed to meet the growing demand for energy storage. In addition, although existing material synthesis methods such as solid-phase method and sol-gel method can prepare layered oxides, they lack the ability to control the micro-morphology. Therefore, a new synthesis method needs to be developed, which not only improves the specific surface area of the material, but also improves its structure and performance, so as to promote the application and development of sodium ion battery technology.

[0005] In view of the above, the present application is proposed. SUMMARY

[0006] The present application aims to provide a sodium-ion layered oxide positive electrode material and a preparation method thereof. + The sodium-ion layered oxide positive electrode material is doped with Co / F, thereby improving structural stability, inhibiting phase transition, improving Na

[0007] In order to achieve the above-mentioned purpose of the present application, the following technical solutions are adopted: In a first aspect, the present application provides a sodium-ion layered oxide positive electrode material, which has a chemical formula of: Na 0.67 Ni 0.33-x / 2 Co x Mn 0.67-x / 2 O 2-y F y ; wherein 0 The sodium-ion layered oxide positive electrode material has a plate-like morphology, and the material surface has pores. At least part of the Ni and Mn sites in the sodium-ion layered oxide positive electrode material are doped and replaced by Co elements; and at least part of the O sites are doped and replaced by F elements.

[0008] In a second aspect, the present application provides a preparation method of the sodium-ion layered oxide positive electrode material as described in the foregoing embodiments, which comprises: The soluble metal salt is complexed and dispersed by using a polymer dispersant, and the addition of a soluble sodium source and a soluble fluorine source is performed, so that the polymer dispersant is carbonized and thermally decomposed during the calcination process; based on the gas released by the carbonized thermal decomposition, pores are etched on the material surface to form a pore structure, and finally the sodium-ion layered oxide positive electrode material is obtained through calcination.

[0009] In a preferred embodiment, the polymer dispersant is selected from at least one of polyacrylic acid, polyethyleneimine, polyvinyl alcohol, and carboxymethyl cellulose.

[0010] In a preferred embodiment, the soluble metal salt comprises Co salt, Ni salt, and Mn salt.

[0011] Preferably, the soluble metal salt is cobalt acetate, nickel acetate, and manganese acetate; and / or, the soluble metal salt is cobalt nitrate, nickel nitrate, and manganese nitrate; and / or, the soluble metal salt is cobalt chloride, nickel chloride, and manganese chloride; and / or, the soluble sodium source is sodium carbonate and / or sodium acetate; and / or, the soluble fluorine source is NaF.

[0012] In a preferred embodiment, the mass ratio of the polymer dispersant to the soluble metal salt is (0.2-4): 1.

[0013] In a preferred embodiment, the preparation method comprises: adding the polymer dispersant into a solvent to form a mixed solution; adding the soluble metal salt, the soluble sodium source and the soluble fluorine source into the mixed solution, and mixing to form a mixed system; drying the mixed system to obtain a solid mixture; subjecting the solid mixture to a first calcination treatment to obtain a precursor material; subjecting the precursor material to a grinding and tabletting treatment, and then to a second calcination treatment to obtain the sodium-ion layered oxide positive electrode material.

[0014] In a preferred embodiment, the concentration of the mixed solution is 0.01 g / mL-0.2 g / mL; and / or, the mixing treatment is a mixing treatment with heating and stirring; and / or, the mixing treatment is a mixing treatment with heating and stirring; and the temperature of the heating and stirring is 60°C-100°C; and / or, the mixing treatment is a mixing treatment with heating and stirring; and the stirring time of the heating and stirring is 0.5 hours-2 hours; and / or, the adding mode of the soluble metal salt, the soluble sodium source and the soluble fluorine source is an adding mode with stirring; and / or, the adding mode of the soluble metal salt, the soluble sodium source and the soluble fluorine source is an adding mode of separate addition, and the interval of the adding time of different components is 2 minutes-10 minutes; and / or, the drying treatment is a vacuum drying under reduced pressure; and / or, the drying temperature of the drying treatment is 60°C-100°C; and / or, the drying time of the drying treatment is 6 hours-12 hours; and / or, the heating rate of the first calcination treatment is 1°C / min-5°C / min; and / or, the target temperature of the first calcination treatment is 350°C-500°C, and the holding sintering time at the target temperature is 1 hour-4 hours; and / or, the heating rate of the second calcination treatment is 5°C / min-10°C / min; and / or, The temperature rising target temperature of the second calcination treatment is 800-1000℃, and the holding sintering time at the temperature rising target temperature is 6-12 hours.

[0015] In a third aspect, the present application provides a battery comprising the sodium-ion layered oxide positive electrode material according to any one of the preceding embodiments.

[0016] In a fourth aspect, the present application provides an electrical equipment comprising the battery according to the preceding embodiments.

[0017] Compared with the prior art, the present application has the following beneficial effects: The sodium-ion layered oxide positive electrode material provided by the present application has significant electrochemical performance advantages. By introducing Co and F element doping, the structure of the material is effectively stabilized. Co doping not only improves the electrical conductivity, but also effectively suppresses the P2-O2 phase transition at high voltage, stabilizing the crystal structure. F doping stabilizes the transition metal oxide layer by forming strong TM-F bonds, reduces the Jahn-Teller effect, suppresses the dissolution of transition metal ions, and F doping can adjust the ratio of active centers Ni 2+ / Ni 3+ 、Mn 3+ / Mn 4+ 、Co 2+ / Co 3+ , stimulates the redox activity of the material, and further improves the electrical performance of the material. In addition, the plate-like morphology and pore structure of the material provide excellent Na + ion diffusion paths, significantly improving the kinetic performance and specific capacity of the material, making the positive electrode material exhibit higher energy density and longer cycle life in sodium-ion batteries. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the specific embodiments or prior art of the present application, the drawings needed in the specific embodiments or prior art description will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0019] Figure 1 is a micro-morphology diagram of the sodium-ion layered oxide positive electrode material prepared in Example 1 of the present application; Figure 2 is a capacity retention test result diagram of Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0020] The embodiments of the present application will be described in detail below with examples, but those skilled in the art will understand that the following examples are only for illustration of the present application and should not be regarded as limiting the scope of the present application. The specific conditions not noted in the examples are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used are not noted by the manufacturer, which are all conventional products that can be obtained by purchase.

[0021] The sodium ion layered oxide positive electrode material provided in the embodiments of the present application is in a plate-like morphology, and has pores on the surface of the material; at least part of the Ni and Mn sites in the sodium ion layered oxide positive electrode material are doped and replaced by Co elements; and at least part of the O sites are doped and replaced by F elements.

[0022] In the layered oxide, sodium ions occupy the interlayer space, and in the charging and discharging process, sodium ions reversibly migrate between the layers. Sodium ions are generally arranged in the form of octahedral sites or prismatic sites.

[0023] The layered structure is beneficial to the embedding and de-embedding of sodium ions. Based on the layered structure, sodium ions can diffuse freely between the layers. This structure provides sufficient space for the efficient embedding and de-embedding of sodium ions, so that sodium ions can quickly migrate during the charging and discharging process, thereby making the battery have better power density and rate performance.

[0024] The above-mentioned Co element doping can significantly improve the electrical conductivity of the material by replacing the Ni / Mn sites, reduce the resistance of charge transfer, and improve the electron transport capacity. This improvement makes the material exhibit better performance in high-power applications.

[0025] In the working process of the sodium ion battery, the material is often subjected to repeated cycles of charging and discharging. For materials with a layered structure, especially P2-type oxides, a phase transition occurs at high voltage, P2 phase converts to O2 phase (P2→O2), which causes a dramatic change in the volume of the material, and further causes the collapse of the structure and the generation of cracks, thereby affecting the cycle stability of the battery. Co doping can effectively inhibit this phase transition and maintain the stability of the P2 phase structure. This is because the Co doping forms a strong Co-O covalent bond, pinning the TMO6 layer to inhibit the interlayer slip caused by the electrostatic repulsion between the layers when sodium is removed, reducing the volume change of the material caused by the de-embedding of sodium ions, and thereby improving the cycle stability of the material.

[0026] The redox pair of Co element participates in electrochemical reactions, providing significant charge storage capacity for the material. During charging and discharging, the redox reaction of Co element increases the specific capacity of the material by providing additional redox pairs. In addition, the redox reaction of Co element increases the redox potential of the material, thereby increasing the operating voltage of the battery. The increase in specific capacity and operating voltage not only increases the energy density of the battery, but also makes the material perform more excellent in high-power applications.

[0027] In sodium-ion layered oxide materials, metal ions in the transition metal oxide layer are connected to oxygen ions through metal-oxygen bonds. - As an anion dopant, O 2- After replacing oxygen ions at the O site, a strong TM-F bond is formed between the transition metal (TM) and the fluorine ion. The strength of this fluorine-metal bond is much stronger than the traditional metal-oxygen bond, which can enhance the structural stability of the material. The formation of TM-F bond strengthens the bonding force between transition metal and oxygen atoms, reduces the migration and dissolution of transition metal ions and the irreversible loss of lattice oxygen during charging and discharging, helps to maintain the overall structure of the material, and avoids the failure and structural collapse of the material.

[0028] It should be noted that in the practical application of layered oxide materials, Mn 3+ The Jahn-teller distortion induced by the Mn element can lead to problems such as decreased material structural stability, stress concentration, and ultimately material structural degradation, ion / electron transport obstruction, and electrochemical performance decay. - After doping, the Jahn-Teller effect can be effectively inhibited by the formation of strong TM-F bonds, making the material maintain a more stable structure. This is crucial for improving the cycle stability of the material and can significantly improve the long-term cycle performance of the material, avoiding capacity decay due to structural changes.

[0029] Due to the F - Doping effectively reduces the structural distortion of the material and improves the stability of the layered structure, which has a positive effect on the cycle life of sodium-ion batteries. With the increase in charging and discharging times, the stability and reversibility of the material directly affect the life of the battery. - Doping of F can effectively inhibit the cycle decay caused by metal migration and dissolution and lattice oxygen loss, so that the sodium-ion cathode material maintains good electrochemical performance during long-term use, thereby significantly prolonging the service life of the sodium-ion battery.

[0030] In summary, Co doping significantly improves the performance of sodium-ion battery cathode materials by increasing conductivity, suppressing phase transition, enhancing specific capacity and operating voltage. F doping further improves the cycle stability and long life of the material by forming strong TM-F bonds, suppressing Jahn-Teller effect and enhancing structural stability. The synergistic effect of these doping effects makes the sodium-ion layered oxide cathode material have excellent performance in specific capacity, cycle stability and high rate performance.

[0031] The chemical formula of the sodium-ion layered oxide cathode material is: Na 0.67 Ni 0.33-x / 2 Co x Mn 0.67-x / 2 O 2-y F y ; wherein 0 < x ≤ 0.2 and 0 < y ≤ 0.1.

[0032] By limiting the doping ratio of cobalt and fluorine, the performance and stability of the material are optimized. The range of x is 0 < x ≤ 0.2, which means the doping amount of cobalt can vary to some extent, which helps to adjust the conductivity and stability of the battery material. The range of y is 0 < y ≤ 0.1, which means the doping ratio of fluorine is also limited to avoid the negative effects of excessive doping, such as reducing the electrical conductivity of the material or excessively increasing the destruction of the material structure.

[0033] Through the design of the above chemical formula, the specific capacity, operating voltage, cycle stability, kinetic performance, etc. can be controlled. The doping of cobalt enhances the electrochemical performance of the material, while the doping of fluorine helps to stabilize the structure and reduce the volume change, thereby improving the service life and cycle performance of the material.

[0034] In the embodiments of the present application, a preparation method of the sodium-ion layered oxide cathode material as described in the foregoing embodiments is provided, and the preparation method comprises: The soluble metal salt is complexed and dispersed by using a polymer dispersant, and the addition of a soluble sodium source and a soluble fluorine source is coordinated. The polymer dispersant is gradually carbonized and decomposed during the calcination process. The gas released by the thermal decomposition of the polymer dispersant etches the surface of the material to form a pore structure. After heat treatment, the sodium-ion layered oxide cathode material is obtained.

[0035] Firstly, the use of polymer dispersant is an important link in the preparation process. The polymer dispersant is used to complex and disperse the soluble metal salt.

[0036] These soluble metal salts include Co salt, Ni salt and Mn salt.

[0037] In some embodiments, the soluble metal salt can be at least one of the following combinations of ABC: A, cobalt acetate, nickel acetate, and manganese acetate; B, cobalt nitrate, nickel nitrate, and manganese nitrate; C, cobalt chloride, nickel chloride, and manganese chloride. The soluble sodium source is sodium carbonate and / or sodium acetate; and the soluble fluorine source is NaF.

[0038] For example, the soluble metal salt includes a nickel source (such as Ni(NO3)2), a cobalt source (such as Co(NO3)2), a manganese source (such as Mn(NO3)2), a soluble sodium source (such as Na2CO3 or NaNO3), and a soluble fluorine source (such as NaF). The polymer dispersant (which can be selected from at least one of polyacrylic acid, polyethyleneimine, polyvinyl alcohol, and carboxymethyl cellulose) prevents the metal ions from aggregating or crystallizing during the synthesis process by forming a complex with the metal ions. This ensures that the metal ions are uniformly distributed in subsequent steps, which helps to ensure the uniformity of the components in the final material and the stability of the doping.

[0039] Calcination is a key step in the synthesis process. In this process, the pre-formed mixture (including the polymer dispersant and the metal salt) is reacted by heating, and the polymer dispersant decomposes to produce gas at high temperatures. The gas etches pores on the surface of the material, forming a pore structure on the surface of the material. This pore structure can significantly increase the specific surface area of the material, providing more active sites for electrochemical reactions, while shortening the migration path of sodium ions, reducing the diffusion resistance of sodium ions, and accelerating the migration speed, significantly improving the electrochemical performance of the material.

[0040] Through the above steps, the final sodium-ion layered oxide cathode material has a plate-like morphology and a pore structure. The control of this morphology not only improves the specific capacity, but also improves the electrochemical performance of the material, especially during high-rate charging and discharging, showing lower resistance and higher charging and discharging efficiency.

[0041] The preparation method provided in this embodiment controls the ratio of the polymer dispersant, the metal salt, the sodium source, and the fluorine source accurately, and forms a sodium-ion layered oxide cathode material with a plate-like morphology and a pore structure through the calcination process. This method significantly improves the specific capacity, electrical conductivity, cycle stability, and kinetic performance of the material by controlling the microstructure of the material, making the final sodium-ion cathode material suitable for high-performance sodium-ion batteries.

[0042] In some embodiments, the mass ratio of the polymer dispersant to the soluble metal salt is (0.2-4): 1. For example, it can be 0.2:1, 0.4:1, 0.5:1, 1:1, 1.5:1, 2:1, 3:1, 4:1, etc.

[0043] In some embodiments, the preparation method comprises: Step S1, adding the polymer dispersant into the solvent to form a mixed solution.

[0044] The main purpose of the above step is to form a uniform mixed solution in the solvent using the polymer dispersant, providing a good dispersion environment for the subsequent addition of metal salt and sodium source.

[0045] The polymer dispersant (such as polyacrylic acid, polyethyleneimine, etc.) can complex and disperse the soluble metal salt, avoiding the agglomeration or precipitation of metal ions in the solution, thereby ensuring the uniformity of the material composition.

[0046] The above solvent can be water. In some embodiments, the concentration of the polymer dispersant in the mixed solution can be 0.01 g / mL to 0.2 g / mL; for example, it can be an aqueous solution of the polymer dispersant, and the concentration can be 0.01 g / mL, 0.03 g / mL, 0.05 g / mL, 0.08 g / mL, 0.09 g / mL, 0.10 g / mL, 0.12 g / mL, 0.15 g / mL, 0.18 g / mL, 0.20 g / mL, etc.

[0047] Step S2, adding the soluble metal salt, the soluble sodium source, and the soluble fluorine source to the mixed solution and mixing to form a mixed system.

[0048] The above step adds the soluble metal salt (such as Co salt, Ni salt, Mn salt), the soluble sodium source (such as sodium carbonate or sodium acetate), and the soluble fluorine source (such as NaF) to the above mixed solution.

[0049] Through mixing, metal ions and sodium ions begin to form a uniform dispersion system. At this time, cobalt (Co), nickel (Ni), manganese (Mn), sodium (Na), and fluorine (F) elements will be uniformly distributed in the solution, laying the foundation for the generation of stable sodium ion layered oxide positive electrode materials in the subsequent calcination process.

[0050] The mixing can be mixing by heating and stirring of the materials.

[0051] The temperature of the heating and stirring can be 60°C to 100°C; for example, it can be 60°C, 70°C, 80°C, 90°C, 100°C, etc.

[0052] The stirring time of the heating and stirring can be 0.5 hours to 2 hours; for example, it can be 0.5 hours, 0.8 hours, 0.9 hours, 1.0 hours, 1.1 hours, 1.2 hours, 1.3 hours, 1.4 hours, 1.5 hours, 1.7 hours, 1.8 hours, 1.9 hours, 2.0 hours, etc.

[0053] When adding the ingredients, the soluble metal salt, the soluble sodium source, and the soluble fluorine source can be added while stirring. In addition, the soluble metal salt, the soluble sodium source, and the soluble fluorine source can be added separately, and there should be a time interval when adding different components. The specific time interval can be 2-10 minutes; for example, it can be 2 minutes, 3 minutes, 4 minutes, 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes, and the like.

[0054] Step S3: drying the mixed system to obtain a solid mixture.

[0055] In this step, the solvent in the solution is removed by drying treatment to obtain a solid mixture. This process ensures the effective combination of metal salt and sodium source and begins to form a preliminary precursor material. Through appropriate drying conditions, excessive solvent residues can be avoided, thereby improving the quality and purity of the material.

[0056] The drying treatment is reduced pressure vacuum drying; the drying temperature of the drying treatment can be 60-100°C; for example, it can be 60°C, 70°C, 80°C, 90°C, 100°C, and the like.

[0057] The drying time of the drying treatment is 6-12 hours; for example, it can be 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, and the like.

[0058] Step S4: subjecting the solid mixture to a first calcination treatment to obtain a precursor material.

[0059] This step is one of the key steps in the synthesis process. Through the first calcination treatment, the metal salt in the solid mixture undergoes pyrolysis and reaction, and is finally converted into a precursor material. In this process, the polymer dispersant will gradually decompose and carbonize, and some solid-phase reactions will occur, and the sodium source and transition metal salt will further react at high temperatures to form the rudiment of layered oxides. The temperature and time of the first calcination need to be precisely controlled to ensure the correctness of the morphology and chemical composition of the precursor material.

[0060] The heating rate of the first calcination treatment is 1-5°C / min; the target temperature of the first calcination treatment is 350-500°C; for example, the heating rate can be 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, and the like; the target temperature can be 350°C, 370°C, 390°C, 400°C, 410°C, 420°C, 430°C, 450°C, 470°C, 480°C, 500°C, and the like.

[0061] The holding sintering time at the target temperature of the heating is 1 hour to 4 hours; for example, it can be 1 hour, 2 hours, 3 hours, 4 hours, and the like.

[0062] In step S5, the precursor material is subjected to a grinding and tabletting process, and then subjected to a second calcination process to obtain the sodium-ion layered oxide positive electrode material.

[0063] The tabletting process is to press the precursor material into a sheet or other required shape, so as to provide a more uniform material shape for the second calcination process. The tabletting can improve the density of the material, and ensure that the subsequent calcination process can uniformly promote the crystal growth of the material.

[0064] The second calcination process is to further convert the precursor material into the sodium-ion layered oxide positive electrode material in the calcination process (sintering). This step is performed at a high temperature of 800-1000℃, and the polymer dispersant carbonized after the first calcination process is further decomposed and generates gas, which etches pores on the surface of the material. After the heat treatment, the sodium-ion layered oxide positive electrode material is obtained.

[0065] The heating rate of the second calcination process is 5-10℃ / min; for example, it can be 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 10℃ / min, and the like.

[0066] The target temperature of the second calcination process is 800-1000℃; for example, it can be 800℃, 900℃, 1000℃, and the like. The holding sintering time at the target temperature of the heating can be 6-12 hours; for example, it can be 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, and the like.

[0067] The application provides a battery, which comprises the sodium-ion layered oxide positive electrode material according to any one of the preceding embodiments.

[0068] The battery is a sodium-ion battery, which can comprise the sodium-ion layered oxide positive electrode material, and can use hard carbon or graphite as the negative electrode material, and can use an organic solvent containing NaPF6 as the electrolyte, and the like. The battery can be applied to various application scenarios, such as electric vehicles, renewable energy storage systems, and portable energy storage devices, and has high specific capacity, long cycle life, good rate performance, and low internal resistance. The working principle of the battery is based on the reversible insertion and extraction of sodium ions between the positive electrode and the negative electrode during the charging and discharging process.

[0069] The application provides an electrical equipment, which comprises the battery according to the preceding embodiments.

[0070] The above electrical devices can include a variety of devices using sodium-ion batteries as energy storage devices. For example, the electrical devices can include, but are not limited to, electric vehicles (EVs), power tools, mobile power sources, portable energy storage devices, renewable energy storage systems (such as solar energy storage systems), home energy storage systems, drones, portable electronic devices (such as laptops, smartphones), and the like. These devices rely on high-performance battery systems to provide stable energy supply, and the batteries using the sodium-ion layered oxide positive electrode material as described in the foregoing embodiments can meet the needs of these devices in high energy density and long-term use due to their high specific capacity, long cycle life, and good high-rate performance.

[0071] The present application is further illustrated by the following specific examples, but it should be understood that these examples are merely for the purpose of illustrating in more detail and should not be construed as limiting the present application in any form.

[0072] Example 1 In this embodiment, a sodium-ion battery positive electrode material is provided, and the preparation method is as follows: (1) Preparation of a mixed solution: 2 g of polyacrylic acid was weighed and dissolved in 40 mL of deionized water to prepare a 0.05 g / mL polyacrylic acid aqueous solution, obtaining a mixed solution.

[0073] (2) Preparation of a mixed system: the mixed solution was heated and stirred in a water bath at 60°C. According to the stoichiometric ratio (Na:Ni:Co:Mn:F=0.67:0.28:0.1:0.62:0.06), nickel nitrate, cobalt nitrate, manganese nitrate, sodium fluoride, and sodium carbonate (5% excess) were weighed and added to the heated mixed solution at an interval of 5 minutes, and the mass ratio of the polymer dispersant to the soluble metal salt was controlled to be about 1:1. After the addition of the soluble metal salt was completed, the mixed system (thick solution) was obtained by heating and stirring in a water bath at 60°C for 60 minutes.

[0074] (3) Drying treatment: the mixed system was placed in a vacuum oven, and the vacuum drying conditions were 80°C for 10 hours, obtaining a solid mixture.

[0075] (4) First calcination treatment: the solid mixture was ground into a powder, and the temperature was raised to 400°C at a rate of 1°C / min, and the temperature was maintained for 2 hours, obtaining a precursor material.

[0076] (5) Tabletting and second calcination treatment: the powder of the precursor material was tabletted, and the temperature was raised to 900°C at a rate of 5°C / min after tabletting, and the temperature was maintained for 10 hours, and the sodium-ion layered oxide positive electrode material was obtained after cooling, and the chemical formula was: Na 0.67 Ni 0.28 Co 0.1 Mn 0.62 O1.94 F 0.06 The micro-morphology of the prepared sodium-ion layered oxide positive electrode material is shown in FIG. 1. Figure 1 .

[0077] Example 2 In this embodiment, a sodium-ion battery positive electrode material is provided, and the preparation method is basically the same as that in Example 1, except that the stoichiometric ratio of Na:Ni:Co:Mn:F elements is adjusted to 0.67:0.30:0.05:0.65:0.06, and a positive electrode material with the chemical formula of Na 0.67 Ni 0.3 Co 0.05 Mn 0.65 O 1.94 F 0.06 is prepared.

[0078] Example 3 In this embodiment, a sodium-ion battery positive electrode material is provided, and the preparation method is basically the same as that in Example 1, except that the stoichiometric ratio of Na:Ni:Co:Mn:F elements is adjusted to 0.67:0.26:0.15:0.59:0.06, and a positive electrode material with the chemical formula of Na 0.67 Ni 0.26 Co 0.15 Mn 0.59 O 1.94 F 0.06 is prepared.

[0079] Example 4 In this embodiment, a sodium-ion battery positive electrode material is provided, and the preparation method is basically the same as that in Example 1, except that the stoichiometric ratio of Na:Ni:Co:Mn:F elements is adjusted to 0.67:0.23:0.2:0.57:0.06, and a positive electrode material with the chemical formula of Na 0.67 Ni 0.23 Co 0.2 Mn 0.57 O 1.94 F 0.06 is prepared.

[0080] Example 5 In this embodiment, a sodium-ion battery positive electrode material is provided, and the preparation method is basically the same as that in Example 1, except that the stoichiometric ratio of Na:Ni:Co:Mn:F elements is adjusted to 0.67:0.28:0.1:0.62:0.03, and a positive electrode material with the chemical formula of Na 0.67 Ni 0.28 Co 0.1 Mn 0.62 O 1.97 F 0.03 is prepared.

[0081] Example 6 In this example, a sodium-ion battery cathode material is provided, and the preparation method is basically the same as that of Example 1, the difference is that the stoichiometric ratio of Na:Ni:Co:Mn:F elements is adjusted to 0.67:0.28:0.1:0.62:0.1, and a cathode material with the chemical formula of Na 0.67 Ni 0.28 Co 0.1 Mn 0.62 O 1.9 F 0.1 is prepared.

[0082] Comparative Example 1 In this comparative example, a sodium-ion battery cathode material is provided, and the preparation method is basically the same as that of Example 1, the difference is that Co / F elements are not doped, and the stoichiometric ratio of Na:Ni:Mn elements is 0.67:0.33:0.67, and a cathode material with the chemical formula of Na 0.67 Ni 0.33 Mn 0.67 O2 is prepared.

[0083] Comparative Example 2 In this comparative example, a sodium-ion battery cathode material is provided, and the preparation method is basically the same as that of Example 1, the difference is that Co elements are not doped, and the stoichiometric ratio of Na:Ni:Mn:F elements is 0.67:0.33:0.67:0.06, and a cathode material with the chemical formula of Na 0.67 Ni 0.33 Mn 0.67 O 1.94 F 0.06 is prepared.

[0084] Comparative Example 3 In this comparative example, a sodium-ion battery cathode material is provided, and the preparation method is basically the same as that of Example 1, the difference is that F elements are not doped, and the stoichiometric ratio of Na:Ni:Co:Mn elements is 0.67:0.28:0.1:0.62, and a cathode material with the chemical formula of Na 0.67 Ni 0.28 Co 0.1 Mn 0.62 O2 is prepared.

[0085] Test Experiment (1) Test method: The positive electrode materials in the above examples and comparative examples were uniformly mixed with polyvinylidene fluoride (PVDF) and conductive carbon black (SP) in a ratio of 8:1:1. NMP solvent was added to grind and mix until uniform, and then coated on aluminum foil and dried to obtain a positive electrode sheet. The positive electrode sheet, separator, and sodium sheet were assembled in sequence and an electrolyte was added to obtain a sodium ion battery, which was then subjected to electrochemical testing.

[0086] (2) Test results: The charge and discharge test results are shown in Table 1.

[0087] Table 1. Electrical performance test results of examples and comparative examples

[0088] (3) Analysis: Comprehensive data in Table 1, comparing Examples 1 to 6 and Comparative Examples 1 to 3, it can be seen that the positive electrode materials doped with Co / F elements have higher discharge capacity and capacity retention rate. 0.67 Ni 0.33 Mn 0.67 O2 material, 1C cycle 50 cycle capacity retention rate is only 73.2%, the positive electrode material doped with Co / F elements not only improves the discharge capacity, but also increases the cycle retention rate from 73.2% to 88.6%. The capacity retention rates of Example 1 and Comparative Example 1 are as follows: Figure 2 By comparing Examples 1, 2, 3, and 4 with Examples 1, 5, and 6, it can be concluded that excessive doping with Co or F elements will lead to a decrease in the electrical properties of the material. This is because excessive doping with these elements will lead to an imbalance in the material structure and phase separation. Therefore, appropriate doping with Co / F elements can effectively improve the electrical properties of the material.

[0089] By comparing Examples 1 to 6 with Comparative Examples 2 to 3, it can be seen that the effect of either single element doping of Co or F is not as good as that of Co / F dual element doping in terms of discharge capacity and capacity retention. This is because the complementary mechanism of Co / F co-doping is significantly better than single element doping in terms of structural stability, interface optimization and improvement of material dynamics. Therefore, the synergistic effect of Co / F element doping plays an important role in improving the structural stability of the positive electrode material and improving the electrical properties of the material.

[0090] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A sodium ion layered oxide positive electrode material, characterized in that: The chemical formula of the sodium ion layered oxide positive electrode material is: So 0.67 Ni 0.33-x / 2 Co x Mr 0.67-x / 2 O 2-y F y ; Where 0<x≤0.2, 0<y≤0.1; The sodium ion layered oxide positive electrode material has a plate-like morphology and has pores on the surface of the material; At least part of the Ni and Mn sites in the sodium ion layered oxide positive electrode material are doped and replaced by the Co element; and at least part of the O sites are doped and replaced by the F element.

2. A method for preparing the sodium ion layered oxide positive electrode material according to claim 1, characterized in that: The preparation method comprises: A polymer dispersant is used to complex and disperse a soluble metal salt, and a soluble sodium source and a soluble fluorine source are added to carbonize and thermally decompose the polymer dispersant during a calcination process. Gas released by the carbonization and thermal decomposition etches a pore structure on the surface of the material, and finally the sodium ion layered oxide positive electrode material is obtained through a calcination process.

3. The method for preparing the sodium ion layered oxide positive electrode material according to claim 2, wherein: The polymer dispersant is selected from at least one of polyacrylic acid, polyethyleneimine, polyvinyl alcohol and carboxymethyl cellulose.

4. The method for preparing the sodium ion layered oxide positive electrode material according to claim 2, wherein: The soluble metal salts include Co salts, Ni salts and Mn salts.

5. The method for preparing the ionic layered oxide positive electrode material according to claim 2, wherein: The soluble metal salts are cobalt acetate, nickel acetate and manganese acetate; and / or, The soluble metal salt is cobalt nitrate, nickel nitrate and manganese nitrate; and / or, The soluble metal salt is cobalt chloride, nickel chloride, manganese chloride; and / or, The soluble sodium source is sodium carbonate and / or sodium acetate; and / or, The soluble fluorine source is NaF.

6. The method for preparing the sodium ion layered oxide positive electrode material according to claim 2, wherein: The mass ratio of the polymer dispersant to the soluble metal salt is (0.2~4):

1.

7. The method for preparing the sodium ion layered oxide positive electrode material according to claim 2, wherein: The preparation method comprises: adding the polymer dispersant to a solvent to form a mixed solution; adding the soluble metal salt, the soluble sodium source and the soluble fluorine source to the mixed solution, and performing mixing treatment to form a mixed system; performing a drying process on the mixed system to obtain a solid mixture; performing a first calcination process on the solid mixture to obtain a precursor material; The precursor material is ground and tableted, and then subjected to a second calcination process to obtain the sodium ion layered oxide positive electrode material.

8. The method for preparing the sodium ion layered oxide positive electrode material according to claim 7, wherein: The concentration of the mixed solution is 0.01 g / mL to 0.2 g / mL; and / or, The mixing process is a mixing process with heating and stirring; and / or, The mixing process is a heating and stirring mixing process; and the heating and stirring temperature is 60° C. to 100° C.; and / or, The mixing process is a heating and stirring mixing process; and the heating and stirring time is 0.5 hours to 2 hours; and / or, The soluble metal salt, the soluble sodium source and the soluble fluorine source are added while stirring; and / or, The soluble metal salt, the soluble sodium source and the soluble fluorine source are added separately with a time interval of 2 minutes to 10 minutes between the addition of different components; and / or, The drying process is reduced pressure vacuum drying; and / or, The drying temperature of the drying treatment is 60°C to 100°C; and / or, The drying time of the drying treatment is 6 hours to 12 hours; and / or, The heating rate of the first calcination treatment is 1°C / min to 5°C / min; and / or, The target temperature of the first calcination treatment is 350° C. to 500° C., and the sintering time at the target temperature is 1 hour to 4 hours; and / or, The heating rate of the second calcination treatment is 5°C / min to 10°C / min; and / or, The target temperature of the second calcination treatment is 800° C. to 1000° C., and the sintering time at the target temperature is 6 hours to 12 hours.

9. A battery, characterized in that: The invention comprises the sodium ion layered oxide positive electrode material according to any one of claims 1 to 2.

10. An electrical equipment, characterized in that: Comprising the battery of claim 9.

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