Layered positive electrode material of sodium-ion battery and preparation method of layered positive electrode material

Abstract

The invention provides a sodium-ion battery layered positive electrode material and a preparation method thereof, and belongs to the field of sodium-ion batteries, the preparation method of the sodium-ion battery layered positive electrode material comprises the following steps: synthesizing a precursor material containing nickel and manganese; performing first calcining treatment on the precursor material to obtain an intermediate material; coating the intermediate material with a metal oxide to obtain a composite material; and mixing the composite material with a sodium source, and carrying out second calcination treatment to obtain the sodium-ion battery layered positive electrode material. The sodium-ion battery layered positive electrode material prepared by the invention has relatively high crystallinity and compactness, and is not easy to break in the cycle process, and the coated metal oxide can effectively isolate the erosion of electrolyte, so that the cycle performance of the positive electrode material is further improved, and the service life of the positive electrode material is prolonged. The technical problems of low crystallinity and poor cycle performance of the layered positive electrode material of the sodium-ion battery are effectively solved.

Description

Technical Field

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

[0002] To meet the growing demand for renewable, clean energy, the development of electrical energy storage technologies is crucial. While lithium-ion batteries have achieved unprecedented commercial success thanks to their high energy density and long cycle life, the high cost and limited reserves of lithium have significantly constrained their development. Because sodium has similar chemical properties to lithium-ion batteries and is abundant in the Earth's crust, sodium-ion batteries are considered the most promising alternative to lithium-ion batteries and are expected to be widely used in new energy vehicles, large-scale energy storage systems, and other fields.

[0003] In order to replace lithium-ion batteries, sodium-ion batteries must have a capacity and cycle life comparable to lithium-ion batteries. Since the positive electrode material is a key component that determines battery performance, researchers have made great efforts in designing and developing suitable and efficient positive electrode materials. So far, researchers have explored various sodium-ion battery positive electrode materials, including layered oxides, polyanion compounds, and Prussian blue analogs. Among them, O3-type layered oxide positive electrode materials are considered to be one of the most promising candidate positive electrode materials for the commercialization of sodium-ion batteries due to their relatively high energy density, wide range of raw material selectivity, and more synthesis processes.

[0004] However, existing O3-type layered oxide cathode materials are mostly made from precursors calcined once, resulting in poor crystallinity and easy particle breakage during cycling, which affects the cathode material's capacity and cycling performance. Developing O3-type layered oxide cathode materials with both superior capacity and cycling performance is a pressing challenge. Summary of the Invention

[0005] In view of the technical problems existing in the background technology, the present application provides a sodium ion battery layered positive electrode material and a preparation method thereof, aiming to solve the technical problems of low crystallinity and poor cycle performance of sodium ion battery layered positive electrode materials.

[0006] In a first aspect, the present invention provides a method for preparing a layered cathode material for a sodium ion battery, comprising the following steps:

[0007] synthesizing precursor materials containing nickel and manganese;

[0008] performing a first calcination treatment on the precursor material to obtain an intermediate material;

[0009] coating the intermediate material with a metal oxide to obtain a composite material;

[0010] The composite material is mixed with a sodium source and subjected to a second calcination treatment to obtain a layered positive electrode material for a sodium ion battery.

[0011] In the technical solution of the embodiment of the present application, a step-by-step calcination method is adopted to first perform a first calcination treatment on the precursor material containing nickel and manganese to fully crack it. After obtaining the intermediate material, a sodium source is introduced for a second calcination treatment. The two calcination treatments can effectively improve the crystallinity and density of the prepared sodium ion battery layered positive electrode material, so that it has better cycle performance; at the same time, before the second calcination treatment, the intermediate material is coated by introducing a metal oxide, which can effectively isolate the electrolyte from eroding the prepared sodium ion battery layered positive electrode material, greatly reduce the interfacial side reactions, and thus improve the cycle performance of the prepared sodium ion battery layered positive electrode material.

[0012] In some embodiments, synthesizing a precursor material containing nickel and manganese comprises the steps of:

[0013] Nickel salt, manganese salt, precipitant and complexing agent are mixed and a precursor material is obtained through coprecipitation reaction.

[0014] In this embodiment, a nickel salt and a manganese salt are mixed with a precipitant and a complexing agent by a coprecipitation method, so that nickel ions and manganese ions are uniformly coprecipitated under the action of the precipitant and the complexing agent, thereby synthesizing a precursor material containing nickel and manganese.

[0015] In some embodiments, the molar ratio of nickel in the nickel salt to manganese in the manganese salt is (0.1-0.9):(0.1-0.9); and / or,

[0016] The ratio of the total amount of nickel in the nickel salt and manganese in the manganese salt to the amount of sodium in the sodium source is 1:(0.7-1.1).

[0017] In this embodiment, by limiting the molar ratio of nickel, manganese, and sodium, the ratio of each element in the final synthesized positive electrode material can be regulated, so that the sodium ion battery layered positive electrode material formed based on the above ratio has good cycle stability and high energy density.

[0018] In some embodiments, the nickel salt is at least one of nickel sulfate, nickel hydrochloride, nickel nitrate, and nickel acetate; and / or,

[0019] The manganese salt is at least one of manganese sulfate, hydrochloride, nitrate, and acetate; and / or

[0020] The precipitant is at least one of sodium hydroxide, sodium carbonate, and oxalic acid; and / or,

[0021] The complexing agent is at least one of ammonia, citric acid, oxalic acid, and EDTA; and / or,

[0022] The sodium source is at least one of sodium hydroxide, sodium carbonate, sodium nitrate, sodium oxalate, sodium chloride and sodium acetate.

[0023] In this embodiment, by optimizing the types of raw materials for the nickel salt, manganese salt, precipitant, complexing agent, and sodium source, it is advantageous to smoothly synthesize a precursor material containing nickel and manganese through a coprecipitation reaction, and then react it with the sodium source to produce a highly crystalline positive electrode material. Furthermore, these raw materials are widely available and inexpensive, facilitating industrial production.

[0024] In some embodiments, the first calcination process comprises: heating to 350-500° C. and pre-calcining for 3-6 hours; then heating to 750-900° C. and calcining for 15-25 hours; and / or,

[0025] The first calcination treatment is performed in an oxidizing atmosphere.

[0026] In this embodiment, by limiting the conditions of the first calcination treatment, it is beneficial to promote the cracking of the precursor material into uniform flakes, so as to further grow and agglomerate during the subsequent second calcination treatment.

[0027] In some embodiments, the intermediate material is NiMnO 3 in the form of thin flakes with a thickness of 80-150 nm and a long side dimension of 500-1000 nm.

[0028] In this embodiment, the intermediate material NiMnO3 in the form of thin flakes can fully react with the sodium source during the second calcination treatment, and further grow and agglomerate from dispersed thin flakes with a large specific surface area into dense spherical particles with a small specific surface area, thereby forming a positive electrode material with high crystallinity and high density.

[0029] In some embodiments, the step of coating the intermediate material with a metal oxide to obtain a composite material comprises:

[0030] The intermediate material and the metal source are dispersed in a solvent, and then the solvent is removed by heating to obtain a composite material.

[0031] In this embodiment, a liquid phase environment is formed by introducing a solvent, which can enable the metal source to be uniformly coated on the surface of the intermediate material in the liquid phase environment, and is conducive to forming a uniform coating layer in the subsequent calcination process.

[0032] In some embodiments, the metal element in the metal source is at least one of aluminum, titanium, magnesium, copper, and zirconium, and the metal source is an oxide or an organic salt of the metal element; and / or,

[0033] The solvent is at least one of methanol, ethanol, and isopropanol; and / or,

[0034] The molar ratio of the intermediate material to the metal source is 100:(0-5).

[0035] In this embodiment, by optimizing the types of metal source and solvent, the metal source can be effectively dispersed in the solvent, and the coating formed by the metal source can effectively isolate the positive electrode material from electrolyte corrosion. At the same time, by adjusting the molar ratio of the intermediate material to the metal source, the thickness of the coating layer can be controlled to prevent an excessively thick coating from affecting the subsequent reaction and the performance of the positive electrode material.

[0036] In some embodiments, the second calcination process comprises: heating to 350-500° C. and pre-calcining for 3-6 hours; then heating to 650-900° C. and calcining for 15-25 hours; and / or,

[0037] The second calcination treatment is performed in an oxidizing atmosphere.

[0038] In this embodiment, by limiting the conditions of the second calcination treatment, the intermediate material in the form of flakes can be grown and agglomerated again into dense particles with a smaller specific surface area, and the crystallinity of the particles is increased, thereby obtaining a sodium ion battery layered positive electrode material with high crystallinity, small specific surface area and coated with metal oxide, so that it has better cycle performance.

[0039] In the second aspect, the embodiment of the present application provides a sodium ion battery layered positive electrode material, which is prepared by the preparation method provided in the first aspect; the sodium ion battery layered positive electrode material includes a chemical formula of Na a Ni b Mn c A layered oxide of O2 and a metal oxide coated on the surface of the layered oxide, wherein 0.7≤a≤1, 0.1≤b≤0.9, 0.1≤c≤0.9, and b+c=1.

[0040] In the technical solution of the embodiment of the present application, the layered positive electrode material of the sodium ion battery has high crystallinity and density, and the particles are not easy to break during the cycle, so that the positive electrode material has good cycle performance and can maintain a high capacity; at the same time, the metal oxide coated on the surface of the layered oxide can also effectively isolate the erosion of the electrolyte, greatly reduce the interfacial side reactions, and further improve the cycle performance of the positive electrode material.

[0041] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] To more clearly illustrate the technical solution of this application, the following is a brief introduction to the drawings used in this application. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be derived from these drawings without inventive effort.

[0043] Figure 1 This is the XRD spectrum of the intermediate material prepared in Example 1 of the present application;

[0044] Figure 2 This is a SEM morphology image of the intermediate material prepared in Example 1 of the present application;

[0045] Figure 3 This is a SEM morphology of the layered cathode material for sodium ion batteries prepared in Example 1 of the present application;

[0046] Figure 4 This is a comparison of the XRD spectra of the sodium ion battery layered positive electrode materials prepared in Example 1 and Comparative Example 1 of the present application;

[0047] Figure 5 This is a comparison chart of the discharge capacities of the sodium ion battery layered positive electrode materials prepared in Example 1 and Comparative Example 1 of the present application;

[0048] Figure 6 This is a comparison chart of the rate performance of the sodium ion battery layered positive electrode materials prepared in Example 1 and Comparative Example 1 of the present application;

[0049] Figure 7 This is a comparison chart of the cycle performance of the sodium ion battery layered cathode materials prepared in Example 1 and Comparative Example 1 of the present application;

[0050] Figure 8 This is a comparison chart of the EIS curves of the sodium ion battery layered positive electrode materials prepared in Example 1 and Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0051] The following embodiments of the technical solution of the present application will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only examples and are not intended to limit the scope of protection of the present application.

[0052] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned figure descriptions are intended to cover non-exclusive inclusions.

[0053] In the description of the embodiments of this application, the technical terms "first" and "second" are used only to distinguish different objects and should not be understood to indicate or imply relative importance or implicitly specify the quantity, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "plurality" is more than two, unless otherwise clearly and specifically defined.

[0054] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0055] In the description of the embodiments of this application, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0056] Existing layered positive electrode materials for sodium-ion batteries are generally made by calcining a precursor material containing sodium, nickel, and manganese once. They have low crystallinity and the particles are easily broken during the cycle, which in turn affects the cycle performance of the positive electrode material.

[0057] In order to solve the technical problems of low crystallinity and poor cycle performance of layered positive electrode materials for sodium ion batteries, the present application provides a layered positive electrode material for sodium ion batteries and a preparation method thereof, wherein, by adopting a step-by-step calcination method, a precursor material containing nickel and manganese is first subjected to a first calcination treatment to fully crack it, and then a sodium source is introduced for a second calcination treatment, which can effectively improve the crystallinity and density of the positive electrode material, so that it has better cycle performance; on this basis, by introducing a metal oxide for coating treatment, the erosion of the electrolyte on the positive electrode material can be effectively isolated, the interfacial side reactions are greatly reduced, and the cycle performance of the positive electrode material is further improved.

[0058] In a first aspect, the present invention provides a method for preparing a layered cathode material for a sodium ion battery, comprising the following steps:

[0059] S1. Synthesizing a precursor material containing nickel and manganese;

[0060] S2. performing a first calcination treatment on the precursor material to obtain an intermediate material;

[0061] S3, coating the intermediate material with a metal oxide to obtain a composite material;

[0062] S4. Mixing the composite material with a sodium source and performing a second calcination treatment to obtain a layered positive electrode material for a sodium ion battery.

[0063] In the technical solution of the embodiment of the present application, by first synthesizing a precursor material containing nickel and manganese, and performing a first calcination treatment on it, the precursor material is fully cracked to form a flaky intermediate material, and then it is coated with a metal oxide, and a sodium source is added for a second calcination treatment, which can make the intermediate material further grow and agglomerate during the calcination process, thereby forming a positive electrode material with high crystallinity and small specific surface area, effectively improving the crystallinity and density of the positive electrode material, so as to avoid the positive electrode material from being affected by its cycle performance due to breakage during the cycle. At the same time, on the basis of the improved density of the positive electrode material, combined with the coating treatment of the metal oxide, it is possible to more effectively isolate the electrolyte from the erosion of the positive electrode material, greatly reduce the interface side reaction, and further improve the cycle performance of the positive electrode material. Moreover, the high crystallinity sodium ion battery layered positive electrode material prepared based on the above method can be applied to positive electrode sheets and sodium ion batteries, and performs well in terms of capacity, rate, cycle, etc., which is conducive to broadening the application field of sodium ion batteries.

[0064] Furthermore, in some embodiments, synthesizing a precursor material containing nickel and manganese comprises the steps of:

[0065] Nickel salt, manganese salt, precipitant and complexing agent are mixed and a precursor material is obtained through coprecipitation reaction.

[0066] In the technical solution of the embodiment of the present application, a co-precipitation method is adopted to synthesize the precursor material. By mixing nickel salt, manganese salt with a precipitant and a complexing agent, the nickel ions in the nickel salt and the manganese ions in the manganese salt are co-precipitated under the action of the precipitant. At the same time, the complexing agent is used to promote the co-precipitation process to proceed uniformly and stably, so as to prepare a precursor material with uniform distribution of nickel and manganese.

[0067] More specifically, in some embodiments, the step of synthesizing a precursor material containing nickel and manganese includes:

[0068] (1) preparing a salt solution, a precipitant solution, and a complexing agent solution respectively; wherein the total molar concentration of nickel and manganese in the salt solution is 0.5 to 5 mol / L, the concentration of the precipitant solution is 0.5 to 10 mol / L, and the concentration of the complexing agent solution is 0.1 to 10 mol / L.

[0069] (2) Deionized water and a complexing agent are added to the reactor, and the mixture is stirred at a temperature of 45 to 65°C and a stirring rate of 300 to 800 r / min for 12 to 48 hours. During this period, nitrogen is continuously introduced to expel the air in the reactor, and the concentration of the complexing agent in the system is maintained at 0.1 to 2 mol / L and the pH value is maintained at 10 to 12.

[0070] (3) The prepared salt solution, precipitant solution, and complexing agent solution were added to the reactor respectively for reaction. The addition rate of each solution was controlled at 0.1-1 mL / min. After the reaction started, the pH value was kept stable by fine-tuning the addition rate of the precipitant solution.

[0071] (4) After the coprecipitation reaction is completed, the obtained liquid is washed and dried to obtain a precursor material containing nickel and manganese.

[0072] In the technical solution of the embodiment of the present application, by regulating the specific steps and corresponding parameters when synthesizing the precursor, the coprecipitation reaction can be ensured to proceed stably, so that nickel ions and manganese ions are coprecipitated uniformly, so as to obtain a precursor material with uniform nickel and manganese distribution, regular particle morphology, and uniform particle size.

[0073] Further, in some embodiments, the molar ratio of the nickel element in the nickel salt to the manganese element in the manganese salt is (0.1 to 0.9):(0.1 to 0.9); and / or, the molar ratio of the total molar amount of the nickel element in the nickel salt and the manganese element in the manganese salt to the molar amount of the sodium element in the sodium source is 1:(0.7 to 1.1).

[0074] In the technical solution of the embodiment of the present application, the nickel element in the nickel salt can play a certain skeleton support role in the layered positive electrode material of the sodium ion battery and improve the energy density and cycle stability of the positive electrode material, but its cost is relatively high. The manganese element can effectively reduce the cost and improve the safety and stability of the positive electrode material. By regulating the molar ratio between the nickel element and the manganese element, the positive electrode material can be guaranteed to have good electrochemical properties while controlling the cost to meet the needs of practical applications. At the same time, by limiting the molar ratio between the nickel element and the manganese element and the sodium element in the sodium source, it is possible to avoid the low energy density caused by too little sodium content and the safety hazard caused by too high sodium content, thereby further improving the safety and stability of the positive electrode material while achieving high energy density.

[0075] Specifically, the molar ratio of the nickel element in the nickel salt to the manganese element in the manganese salt is 0.1:0.1, 0.1:0.2, 0.1:0.3, 0.1:0.4, 0.1:0.5, 0.1:0.6, 0.1:0.7, 0.1:0.8, 0.1:0.9, 0.2:0.1, 0.3:0.1, 0.4:0.1, 0.5:0.1, 0.6:0.1, 0.7:0.1 or any value within the range of (0.1-0.9):(0.1-0.9).

[0076] Specifically, the ratio of the total amount of nickel element in the nickel salt and the manganese element in the manganese salt to the amount of sodium element in the sodium source is 1:0.7, 1:0.8, 1:0.9, 1:1.0, 1:1.1 or any value within the range of 1:(0.7~1.1).

[0077] Furthermore, in some embodiments, the nickel salt is at least one of nickel sulfate, nickel hydrochloride, nickel nitrate, and nickel acetate; and / or,

[0078] The manganese salt is at least one of manganese sulfate, hydrochloride, nitrate, and acetate; and / or

[0079] The precipitant is at least one of sodium hydroxide, sodium carbonate, and oxalic acid; and / or,

[0080] The complexing agent is at least one of ammonia, citric acid, oxalic acid, and EDTA; and / or,

[0081] The sodium source is at least one of sodium hydroxide, sodium carbonate, sodium nitrate, sodium oxalate, sodium chloride and sodium acetate.

[0082] In the technical solution of the embodiment of the present application, by optimizing the types of raw materials for nickel salt, manganese salt, precipitant and complexing agent, it is possible to promote the uniform coprecipitation of nickel ions in the nickel salt and manganese ions in the manganese salt under the action of the precipitant and complexing agent during the coprecipitation reaction. At the same time, by limiting the sodium source, it is beneficial to allow the sodium element in the sodium source to participate in the reaction during the second calcination treatment, thereby forming a highly crystallinity sodium ion battery layered positive electrode material. In addition, the above-mentioned raw materials are widely available and inexpensive, and the required raw materials can be selected according to actual conditions, which is conducive to industrial production.

[0083] Furthermore, in some embodiments, the first calcination treatment includes: heating to 350-500° C. and pre-calcining for 3-6 hours; thereafter, heating to 750-900° C. and calcining for 15-25 hours; and / or,

[0084] The first calcination treatment is performed in an oxidizing atmosphere.

[0085] In the technical solution of the embodiment of the present application, by performing the first calcination treatment in an oxidizing atmosphere, it is beneficial to promote the reaction of the precursor material with oxygen. At the same time, the present application is beneficial to promote the full reaction of the precursor material by first performing a short-term pre-calcination at a relatively low temperature and then raising the temperature for a long-term calcination. Among them, by calcining at a temperature of 750-900°C for 15-25h, it can be ensured that the precursor material is fully cracked into uniform flakes, so that it can further grow and agglomerate during the subsequent second calcination treatment.

[0086] Furthermore, in some embodiments, the intermediate material is NiMnO3 in the form of thin flakes, with a thickness of 80 to 150 nm and a long side dimension of 500 to 1000 nm.

[0087] In the technical solution of the present embodiment, by controlling the raw material ratio and reaction conditions, flaky NiMnO3 is prepared as an intermediate material. Furthermore, by coating the intermediate material with a metal oxide and then introducing a sodium source for a second calcination, the intermediate material and the sodium source are fully reacted, further agglomerating the dispersed, large-specific-surface-area flaky particles into dense, spherical particles with a smaller specific surface area, thereby effectively improving the crystallinity and density of the positive electrode material.

[0088] Specifically, the thickness of the intermediate material can be 80nm, 90nm, 100nm, 110nm, 120nm, 130nm, 140nm, 150nm or any value in the range of 80 to 150nm, and the long side dimension can be 500nm, 600nm, 700nm, 800nm, 900nm, 1000nm or any value in the range of 500 to 1000nm.

[0089] Furthermore, in some embodiments, the step of coating the intermediate material with a metal oxide to obtain a composite material includes:

[0090] The intermediate material and the metal source are dispersed in a solvent, and then the solvent is removed by heating to obtain a composite material.

[0091] In the technical solution of the embodiment of the present application, a liquid phase environment is formed by introducing a solvent, which can promote the full dispersion of the metal source in the liquid phase environment, and then uniformly coat the surface of the intermediate material, so as to form a uniform coating layer on the surface of the layered oxide formed after calcination, thereby reducing the occurrence of interfacial side reactions and improving the cycle performance of the positive electrode material.

[0092] Furthermore, in some embodiments, the metal element in the metal source is at least one of aluminum, titanium, magnesium, copper, and zirconium, and the metal source is an oxide or an organic salt of the metal element; and / or,

[0093] The solvent is at least one of methanol, ethanol, and isopropanol; and / or,

[0094] The molar ratio of the intermediate material to the metal source is 100:(0-5).

[0095] In the technical solution of the embodiment of the present application, by optimizing the types of metal source and solvent, it is possible to promote the effective dispersion of the metal source in the solvent so as to form a uniform coating layer and effectively isolate the electrolyte from erosion of the positive electrode material. At the same time, by adjusting the molar ratio of the intermediate material to the metal source, the thickness of the coating layer can also be regulated to prevent an excessively thick coating layer from affecting the subsequent reaction and the performance of the positive electrode material. Among them, the molar ratio of the intermediate material to the metal source does not include an endpoint value of 100:0, and at the same time, includes an endpoint value of 100:5. It can be understood that when the molar ratio of the intermediate material to the metal source is 100:0, it is equivalent to not adding a metal source.

[0096] Furthermore, the molar ratio of the intermediate material to the metal source is further preferably 100:(1-5) to ensure the formation of a relatively complete coating layer, thereby more effectively isolating the positive electrode material from the electrolyte. Specifically, the molar ratio of the intermediate material to the metal source can be 100:1, 100:2, 100:3, 100:4, 100:5, or any value within the range of 100:(1-5).

[0097] Furthermore, in some embodiments, when heating to remove the solvent, the solvent is slowly evaporated by heating and stirring in a water bath; wherein the heating temperature of the water bath is 45 to 70° C., and the stirring rate is 150 to 500 r / min.

[0098] In the technical solution of the embodiment of the present application, the slow volatilization of the solvent can make the coating effect more uniform, and the water vapor evaporated in the water bath can also promote the hydrolysis of the metal source.

[0099] Furthermore, in some embodiments, the second calcination treatment includes: heating to 350-500° C. and pre-calcining for 3-6 hours; then heating to 650-900° C. and calcining for 15-25 hours; and / or,

[0100] The second calcination treatment is performed in an oxidizing atmosphere.

[0101] In the technical solution of the embodiment of the present application, by performing a second calcination treatment under an oxidizing atmosphere, it is beneficial to promote the reaction of the intermediate material with the sodium source and oxygen. At the same time, during the second calcination treatment, by first pre-calcining at a relatively low temperature for a short time, and then raising the temperature for a long time, it is beneficial to promote the full progress of the reaction. Among them, by calcining at a temperature of 650 to 900 ° C for 15 to 25 hours, the flaky intermediate material can be grown again and agglomerated into dense particles with a smaller specific surface area, and the crystallinity of the particles is increased, thereby obtaining a sodium ion battery layered positive electrode material with high crystallinity, small specific surface area and coated with metal oxide, so that it has better cycle performance.

[0102] In the second aspect, the embodiment of the present application provides a sodium ion battery layered positive electrode material, which is prepared by the preparation method provided in the first aspect; the sodium ion battery layered positive electrode material includes a chemical formula of Na a Ni b Mn c A layered oxide of O2 and a metal oxide coated on the surface of the layered oxide, wherein 0.7≤a≤1, 0.1≤b≤0.9, 0.1≤c≤0.9, and b+c=1.

[0103] In the technical solution of the present application's embodiment, the layered cathode material for sodium-ion batteries, formed through step-by-step calcination, exhibits high crystallinity and compactness. The particles are less likely to break during cycling, resulting in excellent cycling performance and the ability to maintain a high capacity. Furthermore, the metal oxide coating the surface of the layered oxide effectively isolates the electrolyte from erosion, significantly reducing interfacial side reactions and further enhancing the cycling performance of the cathode material. Furthermore, by regulating the ratio of the various elements in the layered oxide, the safety and stability of the cathode material can be further improved while achieving high energy density.

[0104] Some specific examples are listed below. It should be noted that the examples described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. Where specific techniques or conditions are not specified in the examples, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used without manufacturer's indication are all commercially available conventional products.

[0105] 1. Preparation method

[0106] Example 1

[0107] This embodiment provides a method for preparing a layered cathode material for a sodium ion battery, comprising the following steps:

[0108] S1. Weigh 394.275 g of NiSO4·6H2O and 253.53 g of MnSO4·H2O and dissolve them evenly in 1.5 L of deionized water to prepare a 2 mol / L salt solution (Ni:Mn = 1:1) for the reaction. Weigh 240 g of NaOH and dissolve it evenly in 1.5 L of deionized water to prepare a 4 mol / L sodium hydroxide solution for the reaction. Measure 310.34 mL of concentrated ammonia water and dilute it with deionized water to prepare 1.5 L of a 3 mol / L ammonia solution.

[0109] Add 1.8L of deionized water as the base liquid to the 5L reactor, turn on the circulating water bath, set the water bath temperature to 50°C, and continuously supply nitrogen to the reactor through the gas path in the reactor to expel oxygen in the reactor. After the bottom liquid temperature rises to 50°C, measure 118mL of concentrated ammonia water and add it to the bottom liquid, adjust the total ammonia concentration of the bottom liquid to 0.9mol / L, then drop the prepared sodium hydroxide solution, adjust the pH of the bottom liquid to 11, and set the speed to 600rpm / min. The prepared salt solution, sodium hydroxide solution and ammonia solution were pumped into the reactor through peristaltic pumps for reaction, and the flow rate of each peristaltic pump was set to 0.7mL / min. During the reaction, the pH in the system was controlled to be stable at about 11 by adjusting the sodium hydroxide flow rate. The reaction time was 36h in total, so that all the prepared salt solutions participated in the reaction, and then aged for 12h. The final liquid was washed and dried to obtain the precursor material Ni. 0.5 Mn 0.5 (OH)2.

[0110] S2. The precursor material obtained in step S1 is placed in a tube furnace for a first calcination treatment. First, the temperature is raised to 500°C at a heating rate of 5°C / min and pre-calcined for 5 hours. Then, the temperature is raised to 900°C at a heating rate of 5°C / min and calcined for 20 hours. Finally, the temperature is slowly cooled to 20°C at a cooling rate of 2°C / min to obtain a uniform thin-sheet intermediate material NiMnO3 with a thickness of approximately 100 nm and a long side dimension of approximately 800 nm. This intermediate material is stored in a glove box.

[0111] S3. Dispersing the intermediate material obtained in step S2 and tetrabutyl titanate in 50 mL of anhydrous ethanol to obtain a mixed solution, wherein the molar ratio of the intermediate material to tetrabutyl titanate is 100:3. A beaker containing the mixed solution is placed in a water bath, the water bath temperature is set to 50° C., and the stirring speed is set to 200 rpm. During the experiment, water vapor evaporated from the water bath promotes the hydrolysis of the tetrabutyl titanate in the beaker. The ethanol in the beaker is further evaporated to dryness, and the powdered material in the beaker is then collected and vacuum dried to obtain a composite material.

[0112] S4. The composite material obtained in step S3 was fully ground and mixed with 120g of sodium hydroxide in a mortar, and then transferred to a tube furnace for a second calcination treatment. First, the temperature was raised to 500°C at a heating rate of 5°C / min, pre-calcined for 5h, then raised to 750°C at a heating rate of 5°C / min, calcined for 20h, and finally slowly cooled to 20°C at a cooling rate of 2°C / min. The obtained high crystallinity sodium ion battery layered positive electrode material is a titanium dioxide-coated sodium ion battery layered oxide material NaNi 0.5 Mn 0.5 O2.

[0113] Example 2

[0114] This embodiment provides a method for preparing a layered positive electrode material for a sodium ion battery. Compared to Example 1, the only difference is that the conditions for the first calcination treatment in step S2 are modified as follows: first, the temperature is raised to 350°C at a heating rate of 5°C / min, and pre-calcined for 3 hours; then, the temperature is raised to 750°C at a heating rate of 5°C / min, calcined for 15 hours, and finally, the temperature is slowly lowered to 20°C at a cooling rate of 2°C / min. The remaining steps are consistent with those in Example 1 and are not further described here.

[0115] Example 3

[0116] This embodiment provides a method for preparing a layered positive electrode material for a sodium ion battery. Compared to Example 1, the only difference is that the conditions for the first calcination treatment in step S2 are changed to: first, heating to 500°C at a heating rate of 5°C / min, pre-calcining for 6 hours, then heating to 900°C at a heating rate of 5°C / min, calcining for 25 hours, and finally slowly cooling to 20°C at a cooling rate of 2°C / min. The remaining steps are consistent with Example 1 and are not further described here.

[0117] Example 4

[0118] This embodiment provides a method for preparing a layered positive electrode material for a sodium ion battery. Compared to Example 1, the only difference is that the conditions for the second calcination treatment in step S4 are modified as follows: first, the temperature is raised to 350°C at a heating rate of 5°C / min, and pre-calcined for 3 hours; then, the temperature is raised to 650°C at a heating rate of 5°C / min, calcined for 15 hours, and finally, the temperature is slowly lowered to 20°C at a cooling rate of 2°C / min. The remaining steps are consistent with those in Example 1 and are not further described here.

[0119] Example 5

[0120] This embodiment provides a method for preparing a layered positive electrode material for a sodium ion battery. Compared to Example 1, the only difference is that the conditions for the second calcination treatment in step S4 are changed to: first, heating to 500°C at a heating rate of 5°C / min, pre-calcining for 6 hours, then heating to 900°C at a heating rate of 5°C / min, calcining for 25 hours, and finally slowly cooling to 20°C at a cooling rate of 2°C / min. The remaining steps are consistent with Example 1 and are not further described here.

[0121] Example 6

[0122] This example provides a method for preparing a layered cathode material for sodium-ion batteries. The only difference from Example 1 is the change in the amounts of NiSO4·6H2O and MnSO4·H2O used in step S1. In this example, 0.3 mol of NiSO4·6H2O and 2.7 mol of MnSO4·H2O were mixed to form a 2 mol / L salt solution (Ni:Mn = 1:9). The remaining steps were consistent with Example 1 and are not further described here.

[0123] Example 7

[0124] This example provides a method for preparing a layered cathode material for sodium-ion batteries. The only difference from Example 1 is the change in the amounts of NiSO4·6H2O and MnSO4·H2O used in step S1. In this example, 2.7 mol of NiSO4·6H2O and 0.3 mol of MnSO4·H2O are mixed to form a 2 mol / L salt solution (Ni:Mn = 9:1). The remaining steps are consistent with those in Example 1 and are not further described here.

[0125] Example 8

[0126] This example provides a method for preparing a layered cathode material for sodium ion batteries. The only difference from Example 1 is the change in the molar ratio of the intermediate material to tetrabutyl titanate in step S3. In this example, the molar ratio of the intermediate material to tetrabutyl titanate is changed to 100:1. The remaining steps are consistent with those in Example 1 and are not further described here.

[0127] Example 9

[0128] This example provides a method for preparing a layered cathode material for sodium ion batteries. The only difference from Example 1 is the change in the molar ratio of the intermediate material to tetrabutyl titanate in step S3. In this example, the molar ratio of the intermediate material to tetrabutyl titanate is changed to 100:5. The remaining steps are consistent with those in Example 1 and are not further described here.

[0129] Comparative Example 1

[0130] This comparative example provides a method for preparing a layered positive electrode material for a sodium ion battery. Compared with Example 1, the only difference is that step S2 and step S3 are not performed, that is, only one calcination is performed, and the metal oxide is not coated. The precursor material obtained in step S1 is directly mixed with a sodium source according to the method of step S4 in Example 1 and calcined. The synthesis method of the precursor material and the calcination conditions after mixing with the sodium source are the same as in Example 1 and will not be repeated here.

[0131] Comparative Example 2

[0132] This comparative example provides a method for preparing a layered positive electrode material for a sodium ion battery. Compared with Example 1, the only difference is that step S3 is not performed, that is, the metal oxide is not coated, and the intermediate material obtained in step S2 is directly mixed with a sodium source according to the method of step S4 in Example 1 and calcined. The specific process and parameters of each step are the same as those in Example 1 and are not repeated here.

[0133] Comparative Example 3

[0134] This comparative example provides a method for preparing a layered positive electrode material for a sodium ion battery. Compared with Example 1, the only difference is that step S2 is not performed and the order of steps S3 and S4 is changed. That is, the precursor material obtained in step S1 is first mixed with a sodium source for a second calcination treatment, and then the metal oxide coating treatment is performed. The specific process and parameters of each step are consistent with those in Example 1 and are not repeated here.

[0135] Comparative Example 4

[0136] This example provides a method for preparing a layered cathode material for sodium ion batteries. The only difference from Example 1 is the change in the molar ratio of the intermediate material to tetrabutyl titanate in step S3. In this example, the molar ratio of the intermediate material to tetrabutyl titanate is changed to 100:8. The remaining steps are consistent with those in Example 1 and are not further described here.

[0137] 2. Test Method

[0138] 1. XRD test

[0139] The intermediate material NiMnO3, the sodium ion battery layered positive electrode material prepared in Example 1, and the sodium ion battery layered positive electrode materials prepared in the remaining examples and comparative examples were tested using an X-ray diffractometer, and the crystallinity of the sodium ion battery layered positive electrode material was calculated based on the test results.

[0140] 2. SEM test

[0141] The intermediate material NiMnO3 and the sodium ion battery layered positive electrode material prepared in Example 1 were detected using a scanning electron microscope.

[0142] 3. Specific surface area test

[0143] The specific surface area of the sodium ion battery layered cathode material prepared in each embodiment and comparative example was determined by gas adsorption BET method, with reference to standard GB / T 19587-2017.

[0144] 4. Electrochemical performance test

[0145] The sodium ion battery layered cathode materials prepared in the examples and comparative examples were assembled into half-cells and subjected to electrochemical performance tests.

[0146] 3. Analysis of test results of various embodiments and comparative examples

[0147] Figure 1 is the XRD spectrum of the intermediate material prepared in Example 1, Figure 2 、 Figure 3 The following are SEM images of the intermediate material and the layered cathode material for sodium ion batteries prepared in Example 1. Figure 1-3 It can be seen that the intermediate material prepared in Example 1 is NiMnO3 in the form of thin flakes, and the layered positive electrode material for sodium ion batteries is spherical particles formed by the agglomeration of thin flake structures, indicating that the second calcination treatment in Example 1 achieves the growth and agglomeration of the thin flake intermediate material.

[0148] The XRD spectra, discharge capacity, rate performance, cycle performance and EIS curves of the sodium ion battery layered positive electrode materials prepared in Example 1 and Comparative Example 1 are shown in Figure 1. Figure 4-8 As shown. Figure 4 It can be seen that compared with Comparative Example 1, the split peaks at the main peaks 003 and 104 of the sodium ion battery layered positive electrode material prepared in Example 1 disappear, the peak intensity is enhanced, and the peak splitting phenomenon at other parts disappears, obtaining a positive electrode material with high crystallinity and a more complete layered structure. Figure 5-8 It can be seen that compared with Comparative Example 1, the sodium ion battery layered positive electrode material prepared in Example 1 exhibits higher discharge capacity, better rate performance and cycle performance, and faster ion transfer rate, and has more excellent electrochemical performance.

[0149] Table 1 shows the specific surface area and crystallinity of the sodium-ion battery layered cathode materials prepared in Examples 1-5 and Comparative Examples 1-3, as well as the first-cycle discharge capacity and capacity retention test results of half-cells made from the corresponding cathode materials. The first-cycle discharge capacity refers to the first-cycle discharge capacity at a voltage of 2-4 V and a rate of 0.1C, and the capacity retention refers to the retention rate of the capacity after 50 cycles at a voltage of 2-4 V and a rate of 1C compared to the initial capacity.

[0150] Table 1

[0151]

[0152] As can be seen from Table 1, based on the method provided in each embodiment of the present application, after the precursor material is subjected to a first calcination treatment, a metal oxide coating treatment, and a second calcination treatment in sequence, the obtained sodium ion battery layered positive electrode material has a crystallinity of more than 85%, and the capacity retention rate after recycling can reach more than 88%, with high crystallinity and good cycle performance.

[0153] Specifically, by comparing the data of Examples 1-5, it can be seen that when the step-by-step calcination is carried out, the calcination conditions during the first calcination treatment and the second calcination treatment have a certain influence on the crystallinity and cycle performance of the prepared sodium ion battery layered positive electrode material. The calcination temperature is too low or too high, and the calcination time is too long or too short, which is not conducive to improving the crystallinity and cycle performance. The moderate calcination temperature and calcination time in Example 1 can effectively improve the crystallinity and cycle performance of the sodium ion battery layered positive electrode material.

[0154] By comparing the data of Example 1 and Comparative Examples 1-3, it can be seen that in Comparative Example 1, neither step-by-step calcination nor metal oxide coating treatment was performed, and the crystallinity and capacity retention rate were both the lowest; in Comparative Example 2, step-by-step calcination was performed, but no metal oxide coating treatment was performed. Although it had a high crystallinity, the cycle performance was significantly reduced, resulting in a low capacity retention rate; in Comparative Example 3, metal oxide coating treatment was performed, but no step-by-step calcination was performed. Although it had a good capacity retention rate, the crystallinity and discharge capacity were both low; and in Example 1 of the present application, step-by-step calcination and metal oxide coating treatment were performed, and the prepared sodium ion battery layered positive electrode material had high crystallinity, discharge capacity and capacity retention rate, and had good application prospects.

[0155] By comparing the data of Example 1 and Examples 6-7, it can be seen that the change in the molar ratio of nickel and manganese has little effect on the performance of the sodium ion battery layered positive electrode material. The molar ratio of nickel and manganese can be adjusted between (0.1 to 0.9): (0.1 to 0.9) as needed, which can enable the prepared sodium ion battery layered positive electrode material to have higher crystallinity, discharge capacity and capacity retention rate.

[0156] By comparing the data of Example 1, Examples 8-9 and Comparative Example 4, it can be seen that when the molar ratio of the intermediate material to the metal source is in the range of 100: (1 to 5), the prepared sodium ion battery layered positive electrode material has good performance; if the molar ratio of the intermediate material to the metal source is adjusted to 100: 8, although excessive metal source is beneficial to improving the cycle performance of the sodium ion battery layered positive electrode material, it will lead to a significant decrease in crystallinity and discharge capacity, affecting the application of the sodium ion battery layered positive electrode material.

[0157] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A method for preparing a layered cathode material for a sodium ion battery, characterized in that: The steps include: synthesizing precursor materials containing nickel and manganese; performing a first calcination treatment on the precursor material to obtain an intermediate material; coating the intermediate material with a metal oxide to obtain a composite material; The composite material is mixed with a sodium source and subjected to a second calcination treatment to obtain a layered positive electrode material for a sodium ion battery.

2. The method for preparing a layered cathode material for sodium ion batteries according to claim 1, wherein: The synthesis of the precursor material containing nickel and manganese comprises the steps of: The nickel salt, the manganese salt, the precipitant and the complexing agent are mixed, and the precursor material is obtained through a coprecipitation reaction.

3. The method for preparing a layered cathode material for sodium ion batteries according to claim 2, wherein: The molar ratio of the nickel element in the nickel salt to the manganese element in the manganese salt is (0.1-0.9):(0.1-0.9); and / or, The ratio of the total amount of nickel in the nickel salt and the manganese in the manganese salt to the amount of sodium in the sodium source is 1:(0.7-1.1).

4. The method for preparing a layered cathode material for sodium ion batteries according to claim 2, wherein: The nickel salt is at least one of nickel sulfate, nickel hydrochloride, nickel nitrate, and nickel acetate; and / or, The manganese salt is at least one of manganese sulfate, hydrochloride, nitrate and acetate; and / or, The precipitant is at least one of sodium hydroxide, sodium carbonate and oxalic acid; and / or The complexing agent is at least one of ammonia, citric acid, oxalic acid, and EDTA; and / or, The sodium source is at least one of sodium hydroxide, sodium carbonate, sodium nitrate, sodium oxalate, sodium chloride and sodium acetate.

5. The method for preparing a layered cathode material for sodium ion batteries according to claim 1, wherein: The first calcination treatment comprises: heating to 350-500° C. and pre-calcining for 3-6 hours; then heating to 750-900° C. and calcining for 15-25 hours; and / or, The first calcination treatment is performed in an oxidizing atmosphere.

6. The method for preparing a layered cathode material for sodium ion batteries according to claim 1, wherein: The intermediate material is NiMnO3 in the form of thin sheets, with a thickness of 80 to 150 nm and a long side particle size of 500 to 1000 nm.

7. The method for preparing a layered cathode material for sodium ion batteries according to claim 1, wherein: The step of coating the intermediate material with a metal oxide to obtain a composite material comprises: The intermediate material and the metal source are dispersed in a solvent, and then the solvent is removed by heating to obtain the composite material.

8. The method for preparing a layered cathode material for sodium ion batteries according to claim 7, wherein: The metal element in the metal source is at least one of aluminum, titanium, magnesium, copper, and zirconium, and the metal source is an oxide or an organic salt of the metal element; and / or, The solvent is at least one of methanol, ethanol, and isopropanol; and / or, The molar ratio of the intermediate material to the metal source is 100:(0-5).

9. The method for preparing a layered cathode material for sodium ion batteries according to claim 1, wherein: The second calcination treatment includes: heating to 350-500°C and pre-calcining for 3-6 hours; then heating to 650-900°C and calcining for 15-25 hours; and / or, The second calcination treatment is performed in an oxidizing atmosphere.

10. A layered cathode material for a sodium ion battery, characterized in that: Prepared by the preparation method according to any one of claims 1 to 9; the sodium ion battery layered positive electrode material includes a chemical formula of Na a Ni b Mn c A layered oxide of O2 and a metal oxide coated on the surface of the layered oxide, wherein 0.7≤a≤1, 0.1≤b≤0.9, 0.1≤c≤0.9, and b+c=1.

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