Methods, materials and applications for improving the air stability of sodium ion layered oxides

Abstract

The present invention provides a method, material and application for improving the air stability of sodium ion layered oxides. A method for improving the air stability of sodium ion layered oxides is to use copper-based sodium ion layered oxide cathode materials, such as Na x Cu y M z Weighted average ionization potential Φ of ions other than sodium ion in O2 M By controlling the particle diameter r of the primary crystal particles, the crystal size becomes 47.5 nm. -1 ≦Φ M ≦50.5nm -1 and 1.4 μm≦r≦100 μm, thereby reducing the amount of sodium loss in the sodium ion layered oxide positive electrode material after deterioration in air and obtaining a layered oxide positive electrode material for sodium ion batteries that is stable in air, wherein M is Ni 2+ , Zn 2+ , Mg 2+ , Fe 3+ , La 3+ , Lu 3+ , Sb 3+ , Mn 4+ , Ti 4+ , Zr 4+ , Sn 4+ , Bi 5+ where 0.9≦x≦1 and y+z=1.

Description

[Technical Field]

[0001] (cross reference) This application claims priority to a Chinese patent application filed with the China Patent Office on March 2, 2023, bearing application number 202310192349.9 and entitled "Method, material and application for improving the air stability of sodium ion layered oxide."

[0002] (Technical field) The present invention relates to the technical field of sodium ion batteries, and in particular to methods, materials and applications for improving the air stability of sodium ion layered oxides. [Background technology]

[0003] Due to limited and unevenly distributed lithium resource reserves, limited lithium resources are gradually consumed, causing prices to continually rise, significantly increasing the manufacturing costs of lithium-ion batteries. Sodium is extremely abundant, widely distributed, and inexpensive on Earth, so sodium-ion batteries offer cost advantages and resource security advantages. Their unique advantages in high and low temperature performance and safety performance make them an excellent choice for large-scale energy storage, attracting attention and experiencing rapid development in recent years.

[0004] In the positive electrode material for sodium ion batteries, layered oxide Na xMO2 (where M is primarily a transition metal) is expected to become the first choice for industrialization due to its advantages, including high capacity, high compaction density, ease of preparation, and ease of scale-up. However, most layered oxide cathode materials for sodium-ion batteries are unstable in air and prone to sodium loss in humid air. After 48 hours in humid air, sodium loss exceeds 30%, significantly reducing the reversible specific capacity of the degraded material. The alkaline by-products on the surface of the degraded material cause a series of problems, including coating aggregation, increased internal resistance, and excessive gas generation. Furthermore, the storage conditions for the materials become more stringent, resulting in additional costs during manufacturing, transportation, and storage, which contradicts the development philosophy of sodium-ion batteries, which aim for high capacity, low cost, and long life. This drawback has a serious impact on the progress of large-scale industrialization of layered oxide cathode materials for sodium-ion batteries and poses a major challenge to the commercial success of sodium-ion batteries. Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention aims to provide a method, material and application for improving the air stability of sodium ion layered oxide, so that layered oxide cathode materials for sodium ion batteries based on this design principle can achieve good air stability and have extremely high potential for large-scale production. [Means for solving the problem]

[0006] To this end, in a first aspect, embodiments of the present invention provide a method for improving the air stability of a sodium-ion layered oxide cathode material, the method comprising: x Cu y M z Weighted average ionization potential Φ of ions other than sodium ion in O2 M By controlling the particle diameter r of the primary crystal particles, the crystal size becomes 47.5 nm. -1 ≦Φ M ≦50.5nm -1and 1.4 μm≦r≦100 μm, thereby reducing the amount of sodium loss in the sodium ion layered oxide positive electrode material after deterioration in air, and obtaining a layered oxide positive electrode material for sodium ion batteries that is stable in air; where M is Ni 2+ , Zn 2+ , Mg 2+ , Fe 3+ , La 3+ , Lu 3+ , Sb 3+ , Mn 4+ , Ti 4+ , Zr 4+ , Sn 4+ , Bi 5+ where 0.9≦x≦1 and y+z=1.

[0007] Preferably, the ionization potential is the ratio (Φ) of the ionic charge number (Z) of an ion to its ionic radius (r, nm), i.e., Φ=Z / r, and the weighted average ionization potential Φ M is a weighted average value where the weight is the percentage of the ionization potential of cations other than sodium ions, That is,

number

[0008] Preferably, the copper-based sodium ion layered oxide positive electrode material Na x Cu y M z Weighted average ionization potential Φ of ions other than sodium ion in O2 MSpecifically, controlling the particle diameter r of the primary particles of the crystals is Na x Cu y M z By changing the stoichiometric ratios y and z of Cu and M in O2, the weighted average ionization potential Φ of ions other than sodium ions can be calculated. M and controlling the particle size r of the primary particles of the crystals.

[0009] Preferably, the method for controlling the particle size r of the primary particles of the crystals comprises one or more of using an excess amount of sodium carbonate, adding sodium hydroxide, sodium oxide or sodium peroxide as a flux, increasing or decreasing the sintering temperature, and increasing or shortening the sintering time.

[0010] In a second aspect, embodiments of the present invention provide an air-stable layered oxide cathode material for sodium-ion batteries obtainable by the method described in the first aspect above.

[0011] In a third aspect, embodiments of the present invention provide a method for preparing the layered oxide cathode material for a sodium-ion battery according to the second aspect above, said method comprising: Proportionally mixing a sodium source in an amount of 100% to 110% of the required sodium stoichiometry, a Cu-containing precursor, and an M-containing precursor in an amount of 100% to 110% of the required sodium stoichiometry, and sintering the mixture at a high temperature of 800 to 1200°C to produce the layered oxide cathode material for sodium ion batteries; wherein the sodium source comprises one or more of sodium oxide, sodium peroxide, sodium hydroxide, sodium carbonate, and sodium nitrate; the Cu-containing precursor comprises a mixture of one or more of a metal oxide, a metal carbonate, a metal nitrate, a metal oxalate, a metal acetate, a metal sulfate, and a metal hydroxide containing Cu; The M-containing precursor includes one or a mixture of metal oxides, carbonates, nitrates, oxalates, acetates, sulfates, hydroxides, or multi-component metal hydroxides prepared by co-precipitation.

[0012] In a fourth aspect, an embodiment of the present invention provides a positive electrode for a sodium-ion secondary battery, the positive electrode comprising the layered oxide positive electrode material for a sodium-ion battery according to the second aspect above.

[0013] Preferably, the positive electrode further comprises a conductive additive and a binder, the conductive additive includes one or more of carbon black, acetylene black, graphite powder, carbon nanotubes, graphene, and nitrogen-doped carbon; The binder includes one or more of polyvinylidene fluoride (PVDF), sodium alginate, carmellose sodium (CMC), and styrene butadiene rubber (SBR).

[0014] In a fifth aspect, embodiments of the present invention provide a sodium-ion battery comprising the air-stable layered oxide cathode material for a sodium-ion battery according to the second aspect above, or the cathode according to the fourth aspect above.

[0015] In a sixth aspect, embodiments of the present invention provide an electronic device including the sodium ion battery according to the fifth aspect above. [Effects of the Invention]

[0016] Embodiments of the present invention provide a method for improving the air stability of sodium ion layered oxide cathode materials. The present invention provides a method for improving the air stability of sodium ion layered oxide cathode materials by reducing the weighted average ionization potential Φ MBy controlling the sintering temperature and adding elements favorable for crystal growth in the preparation process, the particle size of the material can be made relatively large, effectively reducing the contact area between the material and humid air and increasing the potential barrier for sodium ions in the bulk phase to desorb to the outside, thereby effectively reducing the likelihood of sodium ions desorbing. This synergistic effect allows layered oxide cathode materials for sodium-ion batteries based on this design principle to have good air stability and great potential for large-scale production.

[0017] This method effectively and significantly reduces the amount of sodium loss in the sodium-ion layered oxide cathode material after deterioration in air, and produces a layered oxide cathode material Na that is stable in air for sodium-ion batteries. x Cu y M z O2 can be obtained. Based on this design principle, this air-stable layered oxide positive electrode material for sodium ion batteries has been subjected to rigorous standard testing and has a low sodium release amount after 48 hours of aging, effectively solving the problems of the poor air stability of conventional layered oxide positive electrode materials for sodium ion batteries, and also solving problems such as coating aggregation, increased internal resistance, large amounts of gas generation, and high storage costs. It is suitable for large-scale production and has a high reversible specific capacity, which gives it wide applicability and advantages, as well as great practical value. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a diagram showing an X-ray diffraction (XRD) pattern of a material according to Example 1 of the present invention. [Figure 2] FIG. 1 is a diagram showing an XRD pattern of a material according to Comparative Example 1 of the present invention. [Figure 3]FIG. 10 is a diagram showing an XRD pattern of a material according to Example 4 of the present invention. [Figure 4] 1 is a scanning electron microscope (SEM) image of a material according to Example 8 of the present invention. [Figure 5] 1 is an SEM image of a material according to Example 11 of the present invention. [Figure 6] 10 is an SEM image of a material according to Example 12 of the present invention. [Figure 7] 10 is an SEM image of a material according to Example 13 of the present invention. [Figure 8] 1 is an SEM image of a material according to Comparative Example 1 of the present invention. [Figure 9] FIG. 1 is a graph showing the relationship between the amount of sodium desorbed after being left for 48 hours under strict standard aging conditions, and the weighted average cation ionization potential and the particle size of primary particles in all examples and comparative examples of the present invention. [Figure 10] FIG. 10 is a comparison diagram of charge-discharge curves in a half-cell test of materials before and after degradation in Example 4 of the present invention. [Figure 11] FIG. 10 is a comparison diagram of charge-discharge curves in a half-cell test of materials before and after degradation in Example 7 of the present invention. [Figure 12] FIG. 1 is a comparison diagram of charge-discharge curves in a half-cell test of materials before and after degradation in Comparative Example 1 of the present invention. [Figure 13] FIG. 10 is a comparison diagram of charge-discharge curves in a half-cell test of the material before and after degradation in Comparative Example 2 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] The technical solution of the present invention will be described in more detail below with reference to the drawings and examples.

[0020] An embodiment of the present invention provides a method for improving the air stability of a sodium ion layered oxide cathode material, the method comprising: x Cu y M z Weighted average ionization potential Φ of ions other than sodium ion in O2 MBy controlling the particle diameter r of the primary crystal particles, the crystal size becomes 47.5 nm. -1 ≦Φ M ≦50.5nm -1 and 1.4 μm≦r≦100 μm, thereby reducing the amount of sodium loss in the sodium ion layered oxide positive electrode material after deterioration in air, and obtaining a layered oxide positive electrode material for sodium ion batteries that is stable in air; where M is Ni 2+ , Zn 2+ , Mg 2+ , Fe 3+ , La 3+ , Lu 3+ , Sb 3+ , Mn 4+ , Ti 4+ , Zr 4+ , Sn 4+ , Bi 5+ where 0.9≦x≦1 and y+z=1.

[0021] The ionization potential is the ratio of the number of charges on an ion to the ionic radius, and is known to be expressed as Φ. In this application, the weighted average ionization potential Φ of ions other than sodium ions is M is the weighted average of the total ionization potential when the weight is the mole percentage of each ion other than Na, That is,

number

[0022] Based on the above design concept, the present invention provides an air-stable layered oxide cathode material for sodium ion batteries, which can be prepared by the following steps: The layered oxide positive electrode material for sodium ion batteries is produced by mixing a sodium source having a stoichiometric ratio of 100% to 130% of the required sodium content, a Cu-containing precursor, and an M-containing precursor having a stoichiometric ratio in a proportion that is required, and sintering the mixture at a high temperature of 800 to 1200°C by a solid-state method.

[0023] Here, the sodium source includes one or more of sodium oxide, sodium peroxide, sodium hydroxide, sodium carbonate, and sodium nitrate; the Cu-containing precursor includes a mixture of one or more of a metal oxide, metal carbonate, metal nitrate, metal oxalate, metal acetate, metal sulfate, and metal hydroxide containing Cu; and the M-containing precursor includes a mixture of one or more of a metal oxide, metal carbonate, metal nitrate, metal oxalate, metal acetate, metal sulfate, metal hydroxide, or a multi-component metal hydroxide prepared by a co-precipitation method containing M.

[0024] The stoichiometric ratio of the sodium source is preferably 100% to 110% of the required stoichiometric ratio of sodium.

[0025] The layered oxide positive electrode material for a sodium ion battery is used in a positive electrode, and may further include a conductive additive and a binder; the conductive additive includes one or more of carbon black, acetylene black, graphite powder, carbon nanotubes, graphene, and nitrogen-doped carbon; The binder includes one or more of polyvinylidene fluoride (PVDF), sodium alginate, carmellose sodium (CMC), and styrene butadiene rubber (SBR).

[0026] In order to better understand the technical solution of the present invention, specific examples are described below and compared with comparative examples. It should be understood that the specific materials used in the description of the examples disclosed below are only specific embodiments of the present invention and are not intended to limit the protection scope of the present invention.

[0027] In Examples 1 to 18, first, a metal ion M having a small ionization potential is selected based on the ionization potential table below (octahedral coordination environment), and the weighted average ionization potential Φ of ions other than sodium ions is calculated. M , Φ M is 47.5 nm -1 ≦Φ M ≦50.5nm -1Then, by adjusting the sintering method, layered oxide positive electrode materials with different crystal grain sizes were obtained.

[0028] [Table 1]

[0029] [Example 1] Φ M =50.076nm -1 The cathode material is NaZn 0.05 Cu 0.05 Ni 0.35 Fe 0.1 Mn 0.3 Ti 0.15 Prepare O2.

[0030] ZnO, CuO, NiO, Fe2O3, MnO2, and TiO2 were selected as precursors, and Na2CO3 and NaOH were selected as sodium sources. The corresponding proportions of precursors and sodium sources were weighed, ball milled for 6 hours, and sintered at 950°C for 15 hours to obtain the positive electrode material NaZn 0.05 Cu 0.05 Ni 0.35 Fe 0.1 Mn 0.3 Ti 0.15 O2 was obtained, and the particle size of the primary particles was 2.3 μm. Fig. 1 is a diagram showing the XRD pattern of the material according to Example 1 of the present invention.

[0031] [Example 2] Φ M =48.235nm -1 The cathode material was NaCu. 0.1 Ni 0.325 Fe 0.1 La 0.05 Mn 0.2 Ti 0.225 Prepare O2.

[0032] The precursors were selected from La2O3, CuO, NiO, Fe2O3, MnO2, and TiO2, and the sodium source was selected from Na2CO3 and NaOH. The precursors and sodium source were weighed in the corresponding proportions, and the mixture was ball milled for 6 hours and sintered at 950°C for 15 hours to obtain the cathode material NaCu. 0.1 Ni 0.325 Fe 0.1 La 0.05 Mn 0.2 Ti 0.225 O2 was obtained, and the particle size of the primary particles was 2.0 μm. Fig. 2 is a diagram showing the XRD pattern of the material according to Comparative Example 1 of the present invention.

[0033] [Example 3] Φ M =49.107nm -1 The cathode material was NaCu. 1 / 9 Ni 2 / 9 Fe 1 / 3 Mn 2 / 9 Ti 1 / 9 The precursors were CuO, NiO, Fe2O3, MnO2, and TiO2, and the sodium source was Na2CO3 and NaOH. The precursors and sodium source were weighed in the corresponding proportions, mixed uniformly, and then ball milled for 6 hours. The mixture was then sintered at 950°C for 15 hours to obtain the cathode material NaCuO. 1 / 9 Ni 2 / 9 Fe 1 / 3 Mn 2 / 9 Ti 1 / 9 O2 was obtained, and the particle size of its primary particles was 1.8 μm.

[0034] [Example 4] Φ M =49.159nm -1 The cathode material was NaCu. 0.1 Ni 0.35 Fe 0.1 Mn 0.2 Ti 0.25 Prepare O2.

[0035] CuO, NiO, Fe2O3, MnO2, and TiO2 were selected as precursors, and NaNO3 was selected as the sodium source. The precursors and sodium source were weighed in the corresponding proportions, and the precursors were first ball-milled for 6 hours. After that, the precursors were ground and mixed with NaNO3 in a mortar, and then sintered at 900°C for 15 hours to obtain the positive electrode material NaCu. 0.1 Ni 0.35 Fe 0.1 Mn 0.2 Ti 0.25 O2 was obtained, and the particle size of the primary particles was 1.5 μm. Fig. 3 is a diagram showing the XRD pattern of the material according to Example 4 of the present invention.

[0036] [Example 5] Φ M =49.238nm -1 The cathode material was NaCu. 0.05 Ni 0.4 Fe 0.1 Mn 0.2 Ti 0.25 Prepare O2.

[0037] CuO, NiO, Fe2O3, MnO2, and TiO2 were selected as precursors, and NaNO3 was selected as the sodium source. The precursors and sodium source were weighed in the corresponding proportions, and the precursors were first ball-milled for 6 hours. After that, the precursors were ground and mixed with NaNO3 in a mortar, and then sintered at 900°C for 15 hours to obtain the positive electrode material NaCu. 0.05 Ni 0.4 Fe 0.1 Mn 0.2 Ti 0.25 O2 was obtained, and the particle size of its primary particles was 1.5 μm.

[0038] [Example 6] Φ M =49.323nm -1 The cathode material is NaLi 0.05 Cu 0.05 Ni 0.3 Fe 0.1 Mn 0.2 Ti 0.25 Prepare O2.

[0039] The precursors were Li2CO3, CuO, NiO, Fe2O3, MnO2, and TiO2, and the sodium source was Na2CO3 and NaOH. The precursors and sodium source were weighed in the corresponding proportions, and the mixture was ball milled for 6 hours and sintered at 950°C for 15 hours to obtain the cathode material NaCu. 1 / 9 Ni 2 / 9 Fe 1 / 3 Mn 2 / 9 Ti 1 / 9 O2 was obtained, and the particle size of its primary particles was 1.4 μm.

[0040] [Example 7] Φ M =50.095nm -1 The cathode material was NaCu. 0.10 Ni 0.35 Fe 0.1 Mn 0.3 Ti 0.15 Prepare O2.

[0041] Li2CO3, CuO, NiO, Fe2O3, MnO2, and TiO2 were selected as precursors, and NaNO3 was selected as the sodium source. The precursors and sodium source were weighed in the corresponding proportions, and the precursors were first ball-milled for 6 hours. After that, the precursors were ground and mixed with NaNO3 in a mortar, and then sintered at 900°C for 15 hours to obtain the positive electrode material NaCu. 0.05 Ni 0.4 Fe 0.1 Mn 0.2 Ti 0.25 O2 was obtained, and the particle size of its primary particles was 1.5 μm.

[0042] [Example 8] Φ M =50.095nm -1 Designed to 0.10 Ni 0.35 Fe 0.1 Mn 0.3 Ti 0.15 Prepare the O2 cathode material.

[0043] First, a Ni-Fe-Mn hydroxide precursor is obtained by coprecipitation, which is specifically as follows:0.10 Ni 0.35 Fe 0.1 Mn 0.3 Ti 0.15 According to the ratio of Ni, Fe, and Mn in O2, deionized aqueous solutions of NiSO4·6H2O, FeSO4·7H2O, and MnSO4·H2O were prepared with a concentration of 2 mol / L. An alkaline solution was prepared using sodium hydroxide, aqueous ammonia, and deionized water, where the sodium hydroxide concentration was 4 mol / L and the ammonia concentration was 1 mol / L. An appropriate amount of deionized water was added to a reactor, nitrogen gas was introduced, and the mixture was heated to 60°C and kept at that temperature while stirring at 1000 r / min. Then, the transition metal solution and alkaline solution were added dropwise simultaneously, maintaining the pH between 11.5 and 12. After the reaction was completed, the precipitate was filtered, washed, and dried at 110°C for 12 hours to obtain a Ni-Fe-Mn hydroxide precursor with uniformly distributed transition metal elements. The precursors were selected from the Ni-Fe-Mn hydroxide obtained in the above step, CuO, and TiO2, and the sodium source was selected from Na2CO3 and NaOH. The corresponding proportions of precursor and sodium source were weighed, where the sodium source was in 10% excess. The precursor and sodium source were thoroughly mixed and ball milled for 6 hours, and then sintered at 1050°C for 24 hours to obtain the cathode material NaCu. 0.10 Ni 0.35 Fe 0.1 Mn 0.3 Ti 0.15 O2 was obtained, and the particle size of the primary particles was 6.20 μm. Figure 4 is an SEM image of the material according to Example 8 of the present invention.

[0044] [Example 9] Φ M =50.146nm -1 The cathode material was NaCu. 1 / 9 Ni 2 / 9 Fe 1 / 3 Mn 3 / 9 Prepare O2.

[0045] The precursors were CuO, NiO, Fe2O3, MnO2, and TiO2, and the sodium sources were Na2CO3 and NaOH. The corresponding proportions of precursor and sodium source were weighed, with the sodium source being 3% excess. The precursor and sodium source were uniformly mixed and ball milled for 6 hours, and then sintered at 950°C for 15 hours to obtain the cathode material NaCu. 1 / 9 Ni 2 / 9 Fe 1 / 3 Mn 2 / 9 Ti 1 / 9 O2 was obtained, and the particle size of its primary particles was 2.0 μm.

[0046] [Example 10] Φ M =50.199nm -1 The cathode material was NaCu. 0.1 Ni 0.35 Mn 0.3 Ti 0.2 Prepare O2.

[0047] Select CuO, NiO, MnO2, and TiO2 as precursors, select Na2CO3 as sodium source, weigh out the corresponding proportions of precursors and sodium source, where the sodium source is 3% excess, mix the precursors and sodium source uniformly, ball mill them for 6 hours, and sinter them at 900°C for 15 hours to obtain the positive electrode material NaCu 0.1 Ni 0.35 Mn 0.3 Ti 0.2 O2 was obtained, and the particle size of its primary particles was 1.6 μm.

[0048] [Example 11] Φ M =50.199nm -1 The cathode material was NaCu. 0.1 Ni 0.35 Mn 0.3 Ti 0.2 Prepare O2.

[0049] Select CuO, NiOH, MnO2, and TiO2 as precursors, select Na2CO3 and NaOH as sodium sources, and weigh out the precursors and sodium sources in the corresponding proportions, where the sodium source is 30% excess. The precursors and sodium sources are uniformly mixed and ball milled for 6 hours, and then sintered at 1200°C for 15 hours to obtain the positive electrode material NaCu. 0.1 Ni 0.35 Mn 0.3 Ti 0.2 O2 was obtained, and the particle size of the primary particles was 10.5 μm. Figure 5 is an SEM image of the material according to Example 11 of the present invention.

[0050] [Example 12] Φ M =50.466nm -1 The cathode material is Na 0.9 Cu 0.25 Fe 0.4 Mn 0.2 Ti 0.15 Prepare O2.

[0051] Select CuO, NiO, Fe2O3, MnO2, and TiO2 as precursors, select Na2CO3 and NaO as sodium sources, weigh out the precursors and sodium sources in the corresponding proportions, where the sodium source is in 3% excess, uniformly mix the precursors and sodium source, and then ball mill them for 6 hours, and sinter them at 950°C for 15 hours to obtain the positive electrode material Na 0.9 Cu 0.25 Fe 0.4 Mn 0.2 Ti 0.15 O2 was obtained, and the particle size of the primary particles was 5.0 μm. Figure 6 is an SEM image of the material according to Example 12 of the present invention.

[0052] [Example 13] Φ M =49.099nm -1 The cathode material was NaCu. 0.10 Ni 0.35 Fe 0.1 Mn 0.25 Ti 0.15 Zr 0.05First, Ni-Fe-Mn-Zr hydroxide precursor is obtained by coprecipitation, which is specifically as follows: 0.10 Ni 0.35 Fe 0.1 Mn 0.25 Ti 0.15 Zr 0.05 According to the ratio of Ni, Fe, Mn, and Zr in O2, deionized aqueous solutions of NiSO4·6H2O, FeSO4·7H2O, MnSO4·H2O, and Zr(SO4)2 were prepared at a concentration of 2 mol / L. An alkaline solution was prepared using sodium hydroxide, aqueous ammonia, and deionized water, where the sodium hydroxide concentration was 4 mol / L and the ammonia concentration was 1 mol / L. An appropriate amount of deionized water was added to a reactor, nitrogen gas was introduced, and the mixture was heated to 60°C and kept at that temperature while stirring at 1000 r / min. Then, the transition metal solution and alkaline solution were added dropwise simultaneously to maintain the pH at 11.5-12. After the reaction was completed, the precipitate was filtered, washed, and dried at 110°C for 12 hours to obtain a Ni-Fe-Mn-Zr hydroxide precursor with uniformly distributed transition metal elements. The precursors were selected from the Ni-Fe-Mn-Zr hydroxide obtained in the above step, CuO, and TiO2, and the sodium source was selected from Na2CO3 and NaOH. The corresponding proportions of precursor and sodium source were weighed, where the sodium source was in 4% excess. The precursor and sodium source were thoroughly mixed and ball milled for 6 hours, and then sintered at 900°C for 15 hours to obtain the cathode material NaCu. 0.10 Ni 0.35 Fe 0.1 Mn 0.25 Ti 0.15 Zr 0.05 O2 was obtained, and the particle size of the primary particles was 3.1 μm. Figure 7 is an SEM image of the material according to Example 13 of the present invention.

[0053] [Example 14] Φ M =48.731nm -1 The cathode material was NaCu. 0.10 Ni 0.35 Fe 0.1 Mn 0.25 Ti 0.15 Sn0.05 Prepare O2.

[0054] Select CuO, NiO, Fe2O3, MnO2, TiO2, and SnO2 as precursors, and select Na2CO3 as sodium source. Weigh out the corresponding proportions of precursor and sodium source, where the sodium source is in 5% excess. Mix the precursor and sodium source thoroughly, ball mill them for 6 hours, and sinter them at 950°C for 15 hours to obtain the cathode material NaCu. 0.10 Ni 0.35 Fe 0.1 Mn 0.25 Ti 0.15 Sn 0.05 O2 was obtained, and the particle size of its primary particles was 2.1 μm.

[0055] [Example 15] Φ M =49.634nm -1 The cathode material is NaMg 0.02 Cu 0.08 Ni 0.35 Fe 0.1 Mn 0.25 Ti 0.2 The precursors are CuO, MgO, NiO, Fe2O3, MnO2, TiO2, and SnO2, and the sodium source is Na2CO3 and NaOH. The precursors and sodium source are weighed in the corresponding proportions, with the sodium source being in 10% excess. The precursors and sodium source are thoroughly mixed and ball milled for 6 hours, followed by sintering at 1000°C for 15 hours to obtain the positive electrode material NaMgO. 0.02 Cu 0.008 Ni 0.35 Fe 0.1 Mn 0.25 Ti 0.2 O2 was obtained, and the particle size of its primary particles was 5.6 μm.

[0056] [Example 16] Φ M =48.637nm -1 The cathode material was NaCu. 0.1 Ni 0.335 Fe 0.1 Lu 0.03 Mn0.185 Ti 0.25 Prepare O2.

[0057] The precursors were selected as CuO, MgO, NiO, Fe2O3, MnO2, TiO2, and SnO2, and the sodium source was selected as Na2CO3 and NaOH. The precursors and sodium source were weighed in the corresponding proportions, where the sodium source was in 10% excess. The precursors and sodium source were thoroughly mixed and ball milled for 6 hours, and then sintered at 1000°C for 15 hours to obtain the cathode material NaCu. 0.1 Ni 0.335 Fe 0.1 Lu 0.03 Mn 0.185 Ti 0.25 O2 was obtained, and the particle size of its primary particles was 2.3 μm.

[0058] [Example 17] Φ M =48.649nm -1 The cathode material was NaCu. 0.10 Ni 0.33 Fe 0.1 Sb 0.04 Mn 0.18 Ti 0.25 The precursors were Li2CO3, CuO, NiO, Fe2O3, Sb2O3, MnO2, and TiO2, and the sodium source was Na2O2. The precursors were selected as Li2CO3, CuO, NiO, Fe2O3, Sb2O3, MnO2, and TiO2. The sodium source was selected as Na2O2. The precursors and sodium source were weighed in the corresponding proportions, with Na2O2 in an 8% excess. The precursors were first ball milled for 6 hours, then ground and mixed with Na2O2 in a mortar in an inert atmosphere. The mixture was compressed into a disk with a diameter of 15 mm under a pressure of 10 MPa, and then sintered at 900°C for 15 hours in a synthetic air atmosphere to obtain the cathode material NaCu. 0.10 Ni 0.33 Fe 0.1 Sb 0.04 Mn 0.18 Ti 0.25 O2 was obtained, and the particle size of its primary particles was 8.3 μm.

[0059] [Example 18] Φ M =48.637nm-1 The cathode material is NaLi 0.02 Cu 0.1 Ni 0.3 Fe 0.16 Mn 0.2 Ti 0.2 Bi 0.02 Prepare O2.

[0060] The precursors were CuO, LiOH·H2O, NiO, Fe2O3, MnO2, TiO2, and Bi2O3, and the sodium source was Na2CO3 and NaOH. The corresponding proportions of precursor and sodium source were weighed, with the sodium source being 10% excess. The precursor and sodium source were uniformly mixed and ball milled for 6 hours, followed by sintering at 1000°C for 15 hours to obtain the cathode material NaLi. 0.02 Cu 0.1 Ni 0.3 Fe 0.16 Mn 0.2 Ti 0.2 Bi 0.02 O2 was obtained, and the particle size of its primary particles was 2.0 μm.

[0061] [Example 19] Φ M =48.587nm -1 The cathode material was NaCu. 1 / 9 Ni 2 / 9 Fe 1 / 3 Mn 1 / 6 Ti 1 / 6 The precursors were CuO, NiO, Fe2O3, MnO2, and TiO2, and the sodium source was Na2CO3 and NaOH. The precursors and sodium source were weighed in the corresponding proportions, mixed uniformly, and ball milled for 6 hours. The mixture was then sintered at 950°C for 15 hours to obtain the cathode material NaCuO. 1 / 9 Ni 2 / 9 Fe 1 / 3 Mn 1 / 6 Ti 1 / 6 O2 was obtained, and the particle size of its primary particles was 1.6 μm.

[0062] [Example 20] Φ M =49.858nm-1 The cathode material was NaCu. 1 / 9 Ni 2 / 9 Fe 1 / 3 Mn 1 / 6 Ti 1 / 6 The precursors were CuO, NiO, Fe2O3, MnO2, and TiO2, and the sodium source was Na2CO3 and NaOH. The precursors and sodium source were weighed in the corresponding proportions, mixed uniformly, and ball milled for 6 hours. The mixture was then sintered at 1000°C for 15 hours to obtain the cathode material NaCuO. 1 / 9 Ni 2 / 9 Fe 1 / 3 Mn 1 / 6 Ti 1 / 6 O2 was obtained, and the particle size of its primary particles was 3.4 μm.

[0063] [Comparative Example 1] Φ M =50.323nm -1 The cathode material is NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 Prepare O2.

[0064] First, a Ni-Fe-Mn hydroxide precursor is obtained by coprecipitation, which is specifically as follows: 1 / 3 Fe 1 / 3 Mn 1 / 3According to the ratio of Ni, Fe, and Mn in O2, deionized aqueous solutions of NiSO4·6H2O, FeSO4·7H2O, and MnSO4·H2O were prepared with a concentration of 2 mol / L. An alkaline solution was prepared using sodium hydroxide, aqueous ammonia, and deionized water, where the sodium hydroxide concentration was 4 mol / L and the ammonia concentration was 1 mol / L. An appropriate amount of deionized water was added to a reactor, nitrogen gas was introduced, and the mixture was heated to 60°C and kept at that temperature while stirring at 1000 r / min. Then, the transition metal solution and alkaline solution were added dropwise simultaneously, maintaining the pH at 11.5-12. After the reaction was completed, the precipitate was filtered, washed, and dried at 110°C for 12 hours to obtain a Ni-Fe-Mn hydroxide precursor with uniformly distributed transition metal elements. The Ni-Fe-Mn hydroxide obtained in the above step is selected as the precursor, and Na2CO3 is selected as the sodium source. The precursor and the sodium source are weighed in the corresponding proportions, where the sodium source is in 2% excess. The precursor and the sodium source are thoroughly mixed in a mortar, and then sintered at 900°C for 15 hours to obtain the positive electrode material NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 was obtained, and the particle size of the primary particles was 0.5 μm. Fig. 8 is an SEM image of the material according to Comparative Example 1 of the present invention.

[0065] Comparative Example 2 Φ M =51.085nm -1 The cathode material is NaNi 0.4 Fe 0.2 Mn 0.4 Prepare O2.

[0066] First, a Ni-Fe-Mn hydroxide precursor is obtained by coprecipitation, which is specifically as follows: 0.4 Fe 0.2 Mn 0.4According to the ratio of Ni, Fe, and Mn in O2, deionized aqueous solutions of NiSO4·6H2O, FeSO4·7H2O, and MnSO4·H2O were prepared with a concentration of 2 mol / L. An alkaline solution was prepared using sodium hydroxide, aqueous ammonia, and deionized water, where the sodium hydroxide concentration was 4 mol / L and the ammonia concentration was 1 mol / L. An appropriate amount of deionized water was added to a reactor, nitrogen gas was introduced, and the mixture was heated to 60°C and kept at that temperature while stirring at 1000 r / min. Then, the transition metal solution and alkaline solution were added dropwise simultaneously, maintaining the pH at 11.5-12. After the reaction was completed, the precipitate was filtered, washed, and dried at 110°C for 12 hours to obtain a Ni-Fe-Mn hydroxide precursor with uniformly distributed transition metal elements. The Ni-Fe-Mn hydroxide obtained in the above step is selected as the precursor, and NaNO3 is selected as the sodium source. The precursor and the sodium source are weighed in the corresponding proportions, where the sodium source is in 4% excess. The precursor and the sodium source are thoroughly mixed in a mortar, and then sintered at 830°C for 15 hours to obtain the positive electrode material NaNi 0.4 Fe 0.2 Mn 0.4 O2 is obtained, and the particle size of its primary particles is 0.5 μm.

[0067] Comparative Example 3 Φ M =51.134nm -1 The cathode material was NaCu. 0.1 Ni 0.4 Mn 0.4 Ti 0.1 The precursors are CuO, NiO, MnO, and TiO, and the sodium source is NaCO. The precursors and the sodium source are weighed in the corresponding proportions, and the ball milling process is carried out for 6 hours, followed by sintering at 900°C for 15 hours to obtain the positive electrode material NaCuO. 0.1 Ni 0.4 Mn 0.4 Ti 0.1 O2 was obtained, and the particle size of its primary particles was 2.0 μm.

[0068] The size of the primary particles in the present invention is obtained by statistical analysis of SEM images using Nano Measurer 1.2 software. The SEM model is Hitachi S-4800.

[0069] The XRD collector was a Bruker-AXS D8 Advance (with Cu Kα radiation, λ=1.5405 Å).

[0070] The air-stable layered oxide cathode materials prepared in the above examples of the present invention and the comparative examples were subjected to strict standard conditions, and the amount of sodium released was then quantitatively determined. The specific steps are as follows:

[0071] 1. 1 g of cathode material was aged for 48 hours in an environment with a constant relative humidity of 60% and a carbon dioxide concentration of 600 ppm. This environment was maintained using a sealed tank with two gas passages, one for intake and one for exhaust, and a saturated salt solution, a standard gas, and a control gas passage placed at the bottom of the sealed tank. The saturated salt solution was a saturated sodium bromide (NaBr) solution, and the standard gas was a volumetric ratio of 78.9% N2 + 21.0% O2 + 0.1% CO2. The control gas passage included a pipe, a flow meter, and a pre-gas scrubber, and the flow rate was controlled at 50 ml / min.

[0072] 2. The degraded samples were removed and pre-treated to convert any possible degradation by-products to sodium carbonate. The pre-treatment included 6 hours in a vacuum environment, 6 hours of heating at 110°C in an argon-filled glove box, 3 hours of standing at room temperature in a carbon dioxide atmosphere, and then 6 hours of heating at 110°C in an argon-filled glove box.

[0073] 3. Weigh out 20 mg of the pretreated deteriorated sample and analyze the amount of sodium loss using titration gas chromatography. Specifically, the weighed deteriorated sample was sealed in an argon atmosphere, and then a 1 mol / L sulfuric acid solution was added until no more bubbles were generated. The amount of CO2 generated was analyzed using gas chromatography, and the amount of sodium loss was estimated. The gas chromatograph used was a Shimadzu Nexis GC-2030.

[0074] The above-mentioned degradation test and quantification will be explained in detail. x Sodium ions in MO2 (where M is mainly a transition metal) can be released by charge compensation due to oxidation of M or released by exchange with hydrogen ions, ultimately forming the sodium-deficient phase Na x-w H v MO2 (0.9≦x≦1, 0≦w≦1, 0≦v≦1) is produced. The mass of the hydrogen ion is relatively light and can be ignored, so Na x-w The loss can be expressed as MO2,w, where w is the amount of sodium lost. The desorbed sodium ions also form by-products on the surface, the main component of which is Na2CO3·nH2O (0≦n≦100), and may also contain NaHCO3 and NaOH·nH2O (0≦n≦100). By pretreatment, all by-products can be converted to sodium carbonate, Na2CO3. [ka] After aging and pretreatment, the material is converted into a sodium-deficient phase oxide, Na x-w It is converted into a mixture of MO2 and sodium carbonate, and the mass correspondence is [ka] Fulfilling where n0 represents the molar amount, and a0 represents the initial sample Na x represents MO2, and its relative molecular mass is

number

number

number

[0075] After degradation and pretreatment, the mass fraction of Na2CO3 in the mixture, f, is

number

number

number

[0076] The electrochemical properties before and after degradation and pretreatment of the layered oxide positive electrode materials stable in air prepared in the above examples of the present invention and the positive electrode materials of the comparative examples are compared.

[0077] To assemble the half-cells, the layered oxide cathode materials before and after degradation in each example and comparative example were slurried in N-methylpyrrolidone solution with conductive carbon black (Super P) and polyvinylidene fluoride (PVDF) in a mass ratio of 80:10:15 under an inert atmosphere. The slurry was applied to aluminum foil, vacuum dried, and cut into 10 mm diameter electrode pieces. Metallic sodium foil was used as the anode, a 1 mol / L solution of NaClO4 / propylene carbonate (PC):ethylene carbonate (EC):diethyl carbonate (DEC) (PC:EC:DEC = 1:1:1 (volume ratio)) was used as the electrolyte, and glass fiber was used as the separator. These were assembled into CR2032 button batteries in a glove box under an argon atmosphere. The electrode pieces and hard carbon anodes were combined to form full cells.

[0078] In the charge-discharge tests, the charge-discharge voltage range of the button-type half cell was 2.0 to 4.0 V, and the voltage range of the full cell was 1.0 to 4.0 V. The test rate was 0.2 C. All electrochemical property tests were performed at room temperature using a LAND CT3002A test equipment. The results are shown in Table 2.

[0079] [Table 2]

[0080] To facilitate intuitive understanding, Figure 9 shows the relationship between the amount of sodium desorption after 48 hours under strict standard aging conditions and the weighted average cation ionization potential and the primary particle size for each of the above examples and comparative examples. As can be seen from the figure, the amount of sodium loss of the material is closely related to the weighted average cation ionization potential and the primary particle size. As the weighted average cation ionization potential decreases and the primary particle size increases, the amount of sodium loss of the material decreases rapidly, effectively improving air stability. For example, when the primary particle sizes are similar, Example 2 has a low weighted average cation ionization potential and a lower sodium loss than Examples 7, 8, 9, 14, 16, and 18, and is significantly lower than Comparative Example 3. When the weighted average cation ionization potential is similar, Example 11 has a large primary particle size and a lower sodium loss than Examples 1, 8, and 7, and is significantly lower than Comparative Example 1. Example 17, which has a low average cation ionization potential and a large primary particle size, has a lower sodium loss than Example 15 and is significantly lower than Comparative Example 3. In contrast, Comparative Example 1 has a weighted average ionization potential of 51 nm -1 Although the particle size is less than 1.4 μm, the sodium loss amount is 0.532 because the particle size is too small. In Comparative Example 3, the particle size of the primary particles exceeds 1.4 μm, but the weighted average ionization potential is 51 nm. -1 The sodium loss in Comparative Example 2 was 0.632, which was significantly higher than the weighted average ionization potential and the primary particle size was too small. As can be seen from the above, the sodium loss in the sodium ion layered oxide cathode material after deterioration in air can be significantly reduced by the method of the present invention.

[0081] FIG. 10 is a comparison graph of charge-discharge curves in a half-cell test of the material before and after degradation in Example 4 of the present invention. FIG. 11 is a comparison graph of charge-discharge curves in a half-cell test of the material before and after degradation in Example 7 of the present invention. FIG. 12 is a comparison graph of charge-discharge curves in a half-cell test of the material before and after degradation in Comparative Example 1 of the present invention. FIG. 13 is a comparison graph of charge-discharge curves in a half-cell test of the material before and after degradation in Comparative Example 2 of the present invention. It can be seen that the comparative example, which does not use the method of the present invention, shows a significant decrease in specific capacity after degradation compared to the examples of the present invention, further demonstrating that the present invention can effectively solve the problem of poor air stability of conventional layered oxide positive electrode materials for sodium ion batteries and provide a higher reversible specific capacity.

[0082] The above-mentioned specific embodiments further illustrate the objectives, technical solutions and beneficial effects of the present invention, and it should be understood that the above are only specific embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

[0083] (Addendum) (Appendix 1) A method for improving the air stability of a sodium ion layered oxide cathode material, the method comprising: x Cu y M z Weighted average ionization potential Φ of ions other than sodium ion in O2 M By controlling the particle diameter r of the primary crystal particles, the crystal size becomes 47.5 nm. -1 ≦Φ M ≦50.5nm -1 and 1.4 μm≦r≦100 μm, thereby reducing the amount of sodium loss in the sodium ion layered oxide positive electrode material after deterioration in air, and obtaining a layered oxide positive electrode material for sodium ion batteries that is stable in air; where M is Ni 2+ , Zn 2+ , Mg 2+ , Fe 3+ , La3+ , Lu 3+ , Sb 3+ , Mn 4+ , Ti 4+ , Zr 4+ , Sn 4+ , Bi 5+ where 0.9≦x≦1 and y+z=1; A method characterized by:

[0084] (Appendix 2) The ionization potential is the ratio (Φ) of the ionic charge (Z) of an ion to its ionic radius (r, nm), i.e., Φ = Z / r, and the weighted average ionization potential Φ M is a weighted average value where the weight is the percentage of the ionization potential of cations other than sodium ions, That is,

number

[0085] (Appendix 3) The copper-based sodium ion layered oxide positive electrode material Na x Cu y M z Weighted average ionization potential Φ of ions other than sodium ion in O2 M Specifically, controlling the particle diameter r of the primary particles of the crystals is Na x Cu y M zBy changing the stoichiometric ratios y and z of Cu and M in O2, the weighted average ionization potential Φ of ions other than sodium ions can be calculated. M and controlling the particle size r of the primary particles of the crystals; 2. The method according to claim 1,

[0086] (Appendix 4) The method for controlling the particle size r of the primary particles of the crystals further includes one or more of the following: using an excess amount of sodium carbonate; adding sodium hydroxide, sodium oxide or sodium peroxide as a flux; increasing or decreasing the sintering temperature; and extending or shortening the sintering time. 2. The method according to claim 1,

[0087] (Appendix 5) A layered oxide positive electrode material for a sodium ion battery, which is stable in air and obtained by the method according to any one of appendices 1 to 4.

[0088] (Appendix 6) 6. A method for preparing a layered oxide positive electrode material for a sodium ion battery according to claim 5, the method comprising: Proportionally mixing a sodium source in an amount of 100% to 130% of the required sodium stoichiometry, a Cu-containing precursor, and an M-containing precursor in an amount of 100% to 130% of the required sodium stoichiometry, and sintering the mixture at a high temperature of 800 to 1200°C to produce the layered oxide cathode material for sodium ion batteries; wherein the sodium source comprises one or more of sodium oxide, sodium peroxide, sodium hydroxide, sodium carbonate, and sodium nitrate; the Cu-containing precursor comprises a mixture of one or more of a metal oxide, a metal carbonate, a metal nitrate, a metal oxalate, a metal acetate, a metal sulfate, and a metal hydroxide containing Cu; The M-containing precursor comprises one or a mixture of metal oxides, carbonates, nitrates, oxalates, acetates, sulfates, hydroxides, or multi-component metal hydroxides prepared by co-precipitation, each containing M; A preparation method characterized by:

[0089] (Appendix 7) A positive electrode for a sodium ion secondary battery, the positive electrode comprising the layered oxide positive electrode material for a sodium ion battery according to claim 5.

[0090] (Appendix 8) Further comprising a conductive aid and a binder, the conductive additive includes one or more of carbon black, acetylene black, graphite powder, carbon nanotubes, graphene, and nitrogen-doped carbon; The binder comprises one or more of polyvinylidene fluoride (PVDF), sodium alginate, carmellose sodium (CMC), and styrene butadiene rubber (SBR); 8. The positive electrode according to claim 7,

[0091] (Appendix 9) The layered oxide cathode material for a sodium-ion battery that is stable in air according to Appendix 5, or the cathode according to Appendix 7 or 8,

[0092] (Appendix 10) Included in appendix 9 is a sodium-ion battery. An electronic device characterized by:

Claims

1. A method for improving the air stability of a sodium ion layered oxide cathode material, the method comprising: ｘ Cu ｙ M ｚ O ２ Weighted average ionization potential Φ of ions other than sodium ion in Ｍ By controlling the particle diameter r of the primary particles of the crystal, 47.5 nm －１ ≦Φ Ｍ ≦50.5 nm －１ and 1.4 μm≦r≦100 μm, thereby reducing the amount of sodium loss in the sodium ion layered oxide positive electrode material after deterioration in air, and obtaining a layered oxide positive electrode material for sodium ion batteries that is stable in air; where M is Ni ２＋ , Zn ２＋ , Mg ２＋ , Fe ３＋ , La ３＋ , Lu ３＋ , Sb ３＋ , Mn ４＋ , Ti ４＋ , Zr ４＋ , Sn ４＋ , Bi ５＋ wherein 0.9≦x≦1 and y+z=1; A method characterized by:

2. The ionization potential is the ratio (Φ) of the ionic charge number (Z) of an ion to its ionic radius (r, nm), i.e., Φ = Z / r, and the weighted average ionization potential Φ Ｍ is a weighted average value where the weight is the percentage of the ionization potential of cations other than sodium ions, That is, [Equation 1] and Here, x ｉ is the percentage of ion i, and ｉ The sum of Φ ｉ is the ionization potential of an ion i, and Z ｉ is the charge number of an ion i, and r ｉ is the ionic radius of an ion i, 2. The method of claim 1 .

3. The copper-based sodium ion layered oxide positive electrode material Na ｘ Cu ｙ M ｚ O ２ Weighted average ionization potential Φ of ions other than sodium ion in Ｍ Specifically, controlling the particle diameter r of the primary particles of the crystals is Na ｘ Cu ｙ M ｚ O ２ By changing the stoichiometric ratios y and z of Cu and M in Ｍ and controlling the particle size r of the primary particles of the crystals; 2. The method of claim 1 .

4. The method for controlling the particle size r of the primary particles of the crystals further includes one or more of the following: using an excess amount of sodium carbonate; adding sodium hydroxide, sodium oxide or sodium peroxide as a flux; increasing or decreasing the sintering temperature; and extending or shortening the sintering time.

2. The method of claim 1 .

5. A layered oxide positive electrode material for a sodium ion battery, which is stable in air and obtainable by the method according to any one of claims 1 to 4.

6. 6. A method for preparing a layered oxide positive electrode material for a sodium ion battery according to claim 5, wherein the method comprises: Proportionally mixing a sodium source in an amount of 100% to 130% of the required sodium stoichiometry, a Cu-containing precursor and an M-containing precursor in the required stoichiometry, and sintering the mixture at a high temperature of 800 to 1200°C to produce the layered oxide cathode material for sodium ion batteries; wherein the sodium source comprises one or more of sodium oxide, sodium peroxide, sodium hydroxide, sodium carbonate, and sodium nitrate; the Cu-containing precursor comprises a mixture of one or more of a metal oxide, a metal carbonate, a metal nitrate, a metal oxalate, a metal acetate, a metal sulfate, and a metal hydroxide containing Cu; The M-containing precursor comprises one or a mixture of metal oxides, metal carbonates, metal nitrates, metal oxalates, metal acetates, metal sulfates, metal hydroxides, or multi-component metal hydroxides prepared by a co-precipitation method, each containing M; A preparation method characterized by:

7. A positive electrode for a sodium ion secondary battery, the positive electrode comprising the layered oxide positive electrode material for sodium ion batteries according to claim 5.

8. Further comprising a conductive aid and a binder, the conductive additive includes one or more of carbon black, acetylene black, graphite powder, carbon nanotubes, graphene, and nitrogen-doped carbon; The binder comprises one or more of polyvinylidene fluoride (PVDF), sodium alginate, carmellose sodium (CMC), and styrene butadiene rubber (SBR); The positive electrode according to claim 7 .

9. The layered oxide positive electrode material for a sodium ion battery that is stable in air according to claim 5, or the positive electrode according to claim 7 or 8, A sodium-ion battery characterized by:

10. 10. The sodium ion battery of claim 9, An electronic device characterized by:

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