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

Abstract

The embodiment of the present invention relates to a method, material and application for improving the air stability of sodium ion layered oxide. The method for improving the air stability of sodium ion layered oxide positive electrode material comprises: regulating the air stability of copper-based sodium ion layered oxide positive electrode material Na x Cu y M z The weighted average ionic potential Φ of O2 ions except sodium ions M And adjust the crystal primary particle size r, so that 47.5 nanometers ‑1 ≤Φ M ≤50.5 nm ‑1 , and 1.4 microns ≤ r ≤ 100 microns, thereby reducing the amount of sodium loss after the sodium ion layered oxide positive electrode material deteriorates in the air, and obtaining a class of air-stable sodium ion battery layered oxide positive electrode materials; wherein M is selected from Ni 2+ 、Zn 2+ Mg 2+ 、Fe 3+ 、La 3+ 、Lu 3+ 、Sb 3+ 、Mn 4+ 、Ti 4+ 、Zr 4+ 、Sn 4+ 、Bi 5+ One or more of; 0.9≤x≤1, and y+z=1.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and in particular to a method, material and application for improving the air stability of sodium ion layered oxides. Background Art

[0002] Due to the limited reserves and uneven distribution of lithium resources, the manufacturing cost of lithium-ion batteries has increased significantly with the gradual consumption of limited lithium resources and the continuous rise in prices. Sodium is extremely abundant on Earth, widely distributed, and inexpensive, so sodium-ion batteries will have cost advantages and resource security advantages. Combined with the unique advantages in high and low temperature performance and safety performance, sodium-ion batteries are a better choice for large-scale energy storage. They have attracted much attention in recent years and have developed rapidly.

[0003] In the cathode materials of sodium ion batteries, layered oxides Na x MO2 (M is mainly a transition metal) is expected to become the first choice for industrialization due to its advantages such as high capacity, high compaction density, easy preparation and easy scalability. However, most layered oxide cathode materials for sodium-ion batteries are unstable to air and easily lose sodium in humid air. The sodium loss after being placed in humid air for 48 hours is greater than 30%. The reversible specific capacity of the degraded material is greatly attenuated. The alkaline byproducts on the surface of the degraded material will further bring about a series of problems such as coating agglomeration, increased internal resistance, and severe gas production. In addition, the storage conditions of the material are also more stringent, which will bring additional cost increases during the production, transportation, and storage process, which runs counter to the vision of developing high-capacity, low-cost, and long-life sodium-ion batteries. This shortcoming has seriously affected the large-scale industrialization of layered oxide cathode materials for sodium-ion batteries and is a severe challenge to the successful commercialization of sodium-ion batteries. Summary of the Invention

[0004] The purpose of the present invention is to provide a method, material and application for improving the air stability of sodium ion layered oxides, so that the sodium ion battery layered oxide positive electrode material based on this design principle can obtain good air stability and have great potential for large-scale production.

[0005] To this end, in a first aspect, an embodiment of the present invention provides a method for improving the air stability of a sodium ion layered oxide positive electrode material, the method comprising: regulating the copper-based sodium ion layered oxide positive electrode material Na x Cu y M z The weighted average ionic potential Φ of O2 ions except sodium ions M And adjust the crystal primary particle size r, so that 47.5 nanometers -1 ≤Φ M ≤50.5 nm -1, and 1.4 microns ≤ r ≤ 100 microns, thereby reducing the amount of sodium loss after the sodium ion layered oxide positive electrode material deteriorates in the air, and obtaining a class of air-stable sodium ion battery layered oxide positive electrode materials;

[0006] Wherein, M is selected from Ni 2+ 、Zn 2+ Mg 2+ 、Fe 3+ 、La 3+ 、Lu 3+ 、Sb 3+ 、Mn 4+ 、Ti 4+ 、Zr 4+ 、Sn 4+ 、Bi 5+ One or more of; 0.9≤x≤1, and y+z=1.

[0007] Preferably, the ionic potential is the ratio (Φ) of the ionic charge number (Z) of a certain ion to its ionic radius (r, nanometers), that is, Φ = Z / r. The weighted average ionic potential Φ M is the weighted average of the ionic potentials of cations other than sodium ions, with the percentage of cations as the weight, that is, Where x i is the percentage of a certain ion i and satisfies all x i The sum of is 1; Φ i is the ionic potential of a certain ion i, Z i is the charge number of an ion i, r i is the ionic radius of a certain ion i.

[0008] Preferably, the copper-based sodium ion layered oxide positive electrode material Na x Cu y M z The weighted average ionic potential Φ of O2 ions except sodium ions M And regulating the crystal primary particle size r specifically includes:

[0009] By changing the Na x Cu y M z The stoichiometric ratios y and z of Cu and M in O2 are used to control the weighted average ionic potential Φ of ions other than sodium ions. M And the crystal primary particle size r.

[0010] Preferably, the method for regulating the size r of the primary crystal particles comprises: using excess sodium carbonate, adding sodium hydroxide, sodium oxide or sodium peroxide as a flux, increasing or decreasing the sintering temperature, extending or shortening the sintering time or more.

[0011] In a second aspect, an embodiment of the present invention provides an air-stable sodium ion battery layered oxide positive electrode material obtained according to the method described in the first aspect above.

[0012] In a third aspect, an embodiment of the present invention provides a method for preparing the sodium ion battery layered oxide positive electrode material according to the second aspect, comprising:

[0013] A sodium source having a stoichiometric amount of 100% to 110% of the required sodium, a Cu-containing precursor and an M-containing precursor having a required stoichiometric amount are mixed in proportion, and sintered at a high temperature of 800-1200° C. to produce the sodium ion battery layered oxide positive electrode material;

[0014] Wherein, the sodium source includes: one or more of sodium oxide, sodium peroxide, sodium hydroxide, sodium carbonate, and sodium nitrate;

[0015] The Cu-containing precursor includes: a mixture of one or more of Cu-containing metal oxides, metal carbonates, metal nitrates, metal oxalates, metal acetates, metal sulfates, and metal hydroxides;

[0016] The M-containing precursor includes: one or more mixtures of M-containing metal oxides, metal carbonates, metal nitrates, metal oxalates, metal acetates, metal sulfates, metal hydroxides, or multi-metal hydroxides prepared by a coprecipitation method.

[0017] In a fourth aspect, an embodiment of the present invention includes a positive electrode of a sodium ion secondary battery, wherein the positive electrode includes the sodium ion battery layered oxide positive electrode material described in the second aspect above.

[0018] Preferably, the positive electrode further comprises: a conductive additive and a binder;

[0019] The conductive additive includes one or more of carbon black, acetylene black, graphite powder, carbon nanotubes, graphene, and nitrogen-doped carbon;

[0020] The binder includes one or more of polyvinylidene fluoride PVDF, sodium alginate, sodium carboxymethyl cellulose CMC, and styrene-butadiene rubber SBR.

[0021] In a fifth aspect, an embodiment of the present invention provides a sodium ion battery, comprising: the air-stable sodium ion battery layered oxide positive electrode material described in the second aspect above, or the positive electrode described in the fourth aspect above.

[0022] In a sixth aspect, an embodiment of the present invention provides an electronic device comprising the sodium ion battery described in the fifth aspect.

[0023] The present invention provides a method for improving the air stability of sodium ion layered oxide cathode materials. The present invention adjusts the weighted average ion potential Φ M Keeping it within a relatively low value range can, on the one hand, increase the electrochemical potential of the material and prevent direct oxidation in the air from causing sodium desorption; on the other hand, it can enhance the interaction between sodium ions and lattice oxygen, reducing the possibility of sodium ions being released by exchanging with generated hydrogen ions in the presence of water vapor and carbon dioxide. By adjusting the sintering temperature in the preparation method and introducing elements that are conducive to crystal growth to keep the particle size of the material within a relatively large range, the contact area between the material and humid air can be effectively reduced, and the barrier to the escape of bulk sodium ions can be increased, thereby effectively reducing the possibility of the aforementioned sodium ions escaping. Under these combined effects, the layered oxide cathode material for sodium-ion batteries based on this design principle has good air stability and great potential for large-scale production.

[0024] This method can effectively and significantly reduce the amount of sodium lost by sodium ion layered oxide cathode materials after degradation in air, and obtain a class of air-stable sodium ion battery layered oxide cathode materials Na x Cu y M z O2. Under this design principle, this type of air-stable layered oxide positive electrode material for sodium ion batteries has low sodium removal after 48 hours of deterioration after strict standard testing. It can effectively solve the problem of poor air stability of traditional layered oxide positive electrode materials for sodium ion batteries, and further solve the problems of coating agglomeration, increased internal resistance, severe gas production and high storage cost. It is suitable for large-scale production and has high reversible specific capacity. It has broad application prospects and advantages and high practical value. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is the X-ray diffraction (XRD) pattern of the material of Example 1 of the present invention;

[0026] Figure 2 This is the XRD pattern of the material of Comparative Example 1 of the present invention;

[0027] Figure 3 This is the XRD pattern of the material of Example 4 of the present invention;

[0028] Figure 4 This is a scanning electron microscope (SEM) image of the material of Example 8 of the present invention;

[0029] Figure 5 This is an SEM image of the material of Example 11 of the present invention;

[0030] Figure 6 This is an SEM image of the material of Example 12 of the present invention;

[0031] Figure 7This is an SEM image of the material of Example 13 of the present invention;

[0032] Figure 8 This is an SEM image of the material of Comparative Example 1 of the present invention;

[0033] Figure 9 This is a graph showing the relationship between the amount of sodium removed, the weighted average cationic potential, and the primary particle size after being placed under strict standard degradation conditions for 48 hours for all embodiments and comparative examples of the present invention;

[0034] Figure 10 This is a comparison chart of charge and discharge curves of a half-cell test of the material before and after degradation in Example 4 of the present invention;

[0035] Figure 11 This is a comparison chart of charge and discharge curves of a half-cell test of the material before and after degradation in Example 7 of the present invention;

[0036] Figure 12 This is a comparison chart of the charge and discharge curves of the half-cell test of the material before and after degradation in Comparative Example 1 of the present invention;

[0037] Figure 13 This is a comparison chart of the charge and discharge curves of the half-cell test of the material before and after degradation in Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0038] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments.

[0039] The embodiment of the present invention provides a method for improving the air stability of a sodium ion layered oxide positive electrode material, comprising: regulating the air stability of a copper-based sodium ion layered oxide positive electrode material Na x Cu y M z The weighted average ionic potential Φ of O2 ions except sodium ions M And adjust the crystal primary particle size r, so that 47.5 nanometers -1 ≤Φ M ≤50.5 nm -1 , and 1.4 microns ≤ r ≤ 100 microns, thereby reducing the amount of sodium loss after the sodium ion layered oxide positive electrode material deteriorates in the air, and obtaining a class of air-stable sodium ion battery layered oxide positive electrode materials;

[0040] Wherein, M is selected from Ni 2+ 、Zn 2+ Mg 2+ 、Fe 3+ 、La 3+ 、Lu 3+ 、Sb 3+ 、Mn 4+ 、Ti 4+ 、Zr4+ 、Sn 4+ 、Bi 5+ One or more of; 0.9≤x≤1, and y+z=1.

[0041] As we all know, ionic potential refers to the ratio of the ionic charge to the ionic radius, which is expressed as Φ. The weighted average ionic potential of ions other than sodium ions in this application is Φ M , is the weighted average of the total ion potential when the molar percentage of each ion except Na is used as the weight, that is, Where x i is the percentage of a certain ion i and satisfies all x i The sum of is 1; Φ i is the ionic potential of a certain ion i, Z i is the charge number of an ion i, r i is the ionic radius of a certain ion i. The present invention changes Na x Cu y M z The stoichiometric ratios y and z of Cu and M in O2 are used to control the weighted average ionic potential Φ of ions other than sodium ions. M and the crystal primary particle size r, so that it meets 47.5 nanometers -1 ≤Φ M ≤50.5 nm -1 , and 1.4 microns ≤ r ≤ 100 microns. In addition, the method for regulating the size r of the primary crystal particles may also include: using excess sodium carbonate, adding sodium hydroxide, sodium oxide or sodium peroxide as a flux, increasing or decreasing the sintering temperature, extending or shortening the sintering time or more. For example, using excess sodium carbonate, adding sodium hydroxide, sodium oxide or sodium peroxide as a flux, increasing the sintering temperature, and extending the sintering time can increase the size r of the crystal particles. The present invention regulates the weighted average ionic potential Φ MKeeping it within a relatively low range of values, thereby limiting the material and addition ratio of the doping metal M, on the one hand, effectively reduces the exchange rate of sodium ions and hydrogen ions in the layered oxide cathode material in the presence of water vapor and carbon dioxide, thereby improving the material's electrochemical potential and preventing direct oxidation in air, which causes sodium desorption. On the other hand, it enhances the interaction between sodium ions and lattice oxygen, reducing the possibility of sodium ions being released through exchange with generated hydrogen ions in the presence of water vapor and carbon dioxide. At the same time, by adjusting the sintering conditions during the preparation process and introducing elements that promote crystal growth, such as Cu and Zn, the material particle size is kept within a relatively large range, effectively reducing the contact area between the material and humid air, increasing the barrier to the outward release of bulk sodium ions, and further effectively reducing the possibility of sodium ion release, thereby synergistically significantly reducing the amount of sodium loss from the sodium ion layered oxide cathode material after degradation in air. This method effectively solves the problem of air instability of sodium ion layered oxide cathode materials. Such air-stable sodium ion battery layered oxide cathode materials based on this design principle have low sodium desorption after rigorous standard degradation testing, showing broad application prospects and advantages. The standard strict degradation test used in the present invention is to place 1g of the positive electrode material in an environment with a constant relative humidity of 60% and a constant carbon dioxide concentration of 600ppm for 48 hours.

[0042] Based on the above ideas, the present invention provides an air-stable layered oxide positive electrode material for sodium ion batteries, which can be prepared by the following steps:

[0043] A sodium source with a stoichiometric amount of 100% to 130% of the required sodium, a Cu-containing precursor and an M-containing precursor with a required stoichiometric amount are mixed in proportion, and sintered at a high temperature of 800-1200° C. by a solid phase method to generate the sodium ion battery layered oxide positive electrode material.

[0044] Among them, the sodium source includes: one or more of sodium oxide, sodium peroxide, sodium hydroxide, sodium carbonate, and sodium nitrate; the Cu-containing precursor includes: one or more mixtures of Cu-containing metal oxides, metal carbonates, metal nitrates, metal oxalates, metal acetates, metal sulfates, and metal hydroxides; the M-containing precursor includes: one or more mixtures of M-containing metal oxides, metal carbonates, metal nitrates, metal oxalates, metal acetates, metal sulfates, metal hydroxides, or multi-metal hydroxides prepared by a coprecipitation method.

[0045] The stoichiometric amount of the sodium source is preferably 100% to 110% of the stoichiometric amount of sodium required.

[0046] The above sodium ion battery layered oxide positive electrode material is used for the positive electrode, and the positive electrode may further include: a conductive additive and a binder;

[0047] Conductive additives include: one or more of carbon black, acetylene black, graphite powder, carbon nanotubes, graphene, and nitrogen-doped carbon;

[0048] The binder includes one or more of polyvinylidene fluoride (PVDF), sodium alginate, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR).

[0049] In order to better understand the technical solution of the present invention, the following is described with specific examples and compared with comparative examples. It should be understood that the specific materials used in the following examples are only specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention.

[0050] In Examples 1-18, the metal ion M with the smaller ionic potential is first selected according to the lower ionic potential table (octahedral coordination environment) to control the weighted average ionic potential Φ of other ions except sodium ion. M , so that Φ M Meet 47.5nm -1 ≤Φ M ≤50.5 nm -1 , and then layered oxide positive electrode materials with different grain sizes are obtained by adjusting the sintering method.

[0051]

[0052]

[0053] Table 1

[0054] Example 1

[0055] Design M =50.076 nm -1 , prepare NaZn 0.05 Cu 0.05 Ni 0.35 Fe 0.1 Mn 0.3 Ti 0.15 O2 positive electrode material.

[0056] Select ZnO, CuO, NiO, Fe2O3, MnO2, TiO2 as precursors, select Na2CO3 and NaOH as sodium sources; weigh the corresponding proportions of precursors and sodium sources, ball mill for 6 hours, and sinter at 950℃ for 15 hours to obtain NaZn 0.05 Cu 0.05 Ni 0.35 Fe 0.1 Mn 0.3 Ti 0.15 The primary particle size of the O2 positive electrode material is 2.3 microns. Figure 1 This is the XRD pattern of the material of Example 1 of the present invention.

[0057] Example 2

[0058] Design M =48.235 nm -1 , prepare NaCu 0.1 Ni 0.325 Fe 0.1 La 0.05 Mn 0.2 Ti 0.225 O2 positive electrode material.

[0059] Select La2O3, CuO, NiO, Fe2O3, MnO2, TiO2 as precursors, select Na2CO3 and NaOH as sodium sources; weigh the corresponding proportions of precursors and sodium sources, ball mill for 6 hours, and sinter at 950℃ for 15 hours to obtain NaCu 0.1 Ni 0.325 Fe 0.1 La 0.05 Mn 0.2 Ti 0.225 The primary particle size of the O2 positive electrode material is 2.0 microns. Figure 2 This is the XRD pattern of the material of Comparative Example 1 of the present invention.

[0060] Example 3

[0061] Design M =49.107 nm -1 , prepare NaCu 1 / 9 Ni 2 / 9 Fe 1 / 3 Mn 2 / 9 Ti 1 / 9 O2 positive electrode material. Select CuO, NiO, Fe2O3, MnO2, TiO2 as precursors, select Na2CO3 and NaOH as sodium sources; weigh the corresponding proportions of the precursors and sodium sources; mix the precursors and sodium sources evenly and ball mill for 6 hours, and sinter at 950℃ for 15 hours to obtain NaCu 1 / 9 Ni 2 / 9 Fe 1 / 3 Mn 2 / 9 Ti 1 / 9O2 positive electrode material, its primary particle size is 1.8 microns.

[0062] Example 4

[0063] Design M =49.159 nm -1 , prepare NaCu 0.1 Ni 0.35 Fe 0.1 Mn 0.2 Ti 0.25O2 positive electrode material.

[0064] Select CuO, NiO, Fe2O3, MnO2, TiO2 as precursors, and select NaNO3 as sodium source; weigh the corresponding proportions of the precursors and sodium source; ball mill the precursors for 6 hours, then grind and mix with NaNO3 in a mortar, and then sinter at 900℃ for 15 hours to obtain NaCu 0.1 Ni 0.35 Fe 0.1 Mn 0.2 Ti 0.25 The primary particle size of the O2 positive electrode material is 1.5 microns. Figure 3 This is the XRD pattern of the material of Example 4 of the present invention.

[0065] Example 5

[0066] Design M =49.238 nm -1 , prepare NaCu 0.05 Ni 0.4 Fe 0.1 Mn 0.2 Ti 0.25 O2 positive electrode material.

[0067] Select CuO, NiO, Fe2O3, MnO2, TiO2 as precursors, and select NaNO3 as sodium source; weigh the corresponding proportions of the precursors and sodium source; ball mill the precursors for 6 hours, then grind and mix with NaNO3 in a mortar, and then sinter at 900℃ for 15 hours to obtain NaCu 0.05 Ni 0.4 Fe 0.1 Mn 0.2 Ti 0.25 The primary particle size of the O2 positive electrode material is 1.5 microns.

[0068] Example 6

[0069] Design M =49.323 nm -1 , preparation of NaLi 0.05 Cu 0.05 Ni 0.3 Fe 0.1 Mn 0.2 Ti 0.25 O2 positive electrode material.

[0070] Li2CO3, CuO, NiO, Fe2O3, MnO2, TiO2 were selected as precursors, and Na2CO3 and NaOH were selected as sodium sources. The precursors and sodium sources were weighed in corresponding proportions. The NaCu was obtained by ball milling for 6 hours and sintering at 950℃ for 15 hours. 1 / 9Ni 2 / 9 Fe 1 / 3 Mn 2 / 9 Ti 1 / 9O2 positive electrode material, its primary particle size is 1.4 microns.

[0071] Example 7

[0072] Design M =50.095 nm -1 , prepare NaCu 0.10 Ni 0.35 Fe 0.1 Mn 0.3 Ti 0.15 O2 positive electrode material.

[0073] Li2CO3, CuO, NiO, Fe2O3, MnO2, and TiO2 were selected as precursors, and NaNO3 was selected as the sodium source. The precursors and the sodium source were weighed in corresponding proportions. The precursors were ball-milled for 6 hours, then ground and mixed with NaNO3 in a mortar, and then sintered at 900℃ for 15 hours to obtain NaCu 0.05 Ni 0.4 Fe 0.1 Mn 0.2 Ti 0.25 The primary particle size of the O2 positive electrode material is 1.5 microns.

[0074] Example 8

[0075] Design M =50.095 nm -1 , prepare NaCu 0.10 Ni 0.35 Fe 0.1 Mn 0.3 Ti 0.15 O2 positive electrode material.

[0076] First, a Ni-Fe-Mn hydroxide precursor is obtained by a coprecipitation method. The coprecipitation method is as follows: according to the molecular formula NaCu 0.10 Ni 0.35 Fe 0.1 Mn 0.3 Ti 0.15The ratio of Ni, Fe and Mn in O2 is used to prepare deionized water solutions of NiSO4·6H2O, FeSO4·7H2O and MnSO4·H2O, with a concentration of 2 mol / L; alkali solution is prepared using sodium hydroxide, ammonia water and deionized water, wherein the concentration of sodium hydroxide is 4 mol / L and the concentration of ammonia is 1 mol / L; an appropriate amount of deionized water is added to a reactor and nitrogen is introduced, the reactor is heated to 60°C and kept warm, stirred at a speed of 1000 r / min, and then the transition metal solution and the alkali solution are added dropwise at the same time, and the pH is maintained between 11.5 and 12; after the reaction is completed, the precipitate is 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, CuO and TiO2 obtained in the above steps were selected as precursors, and Na2CO3 and NaOH were selected as sodium sources. The precursors and sodium sources were weighed in corresponding proportions, wherein the sodium source was 10% in excess. The precursors and sodium source were fully mixed and ball-milled for 6 hours, and then sintered at 1050°C for 24 hours to obtain NaCu 0.10 Ni 0.35 Fe 0.1 Mn 0.3 Ti 0.15 The primary particle size of the O2 positive electrode material is 6.20 microns. Figure 4 This is the SEM image of the material of Example 8 of the present invention.

[0077] Example 9

[0078] Design M =50.146 nm -1 , prepare NaCu 1 / 9 Ni 2 / 9 Fe 1 / 3 Mn 3 / 9 O2 positive electrode material.

[0079] CuO, NiO, Fe2O3, MnO2, and TiO2 were selected as precursors, and Na2CO3 and NaOH were selected as sodium sources. The corresponding proportions of the precursors and the sodium source were weighed, wherein the sodium source was 3% in excess. The precursors and the sodium source were evenly mixed and ball-milled for 6 hours, and sintered at 950°C for 15 hours to obtain NaCu 1 / 9 Ni 2 / 9 Fe 1 / 3 Mn 2 / 9 Ti 1 / 9 The primary particle size of the O2 positive electrode material is 2.0 microns.

[0080] Example 10

[0081] Design M =50.199 nm -1 , prepare NaCu 0.1Ni 0.35 Mn 0.3 Ti 0.2 O2 positive electrode material.

[0082] Select CuO, NiO, MnO2, TiO2 as precursors, select Na2CO3 as sodium source; weigh the corresponding proportions of the precursors and sodium source, wherein the sodium source is 3% in excess; uniformly mix the precursors and the sodium source, ball mill for 6 hours, and sinter at 900°C for 15 hours to obtain the NaCu 0.1 Ni 0.35 Mn 0.3 Ti 0.2 The primary particle size of the O2 positive electrode material is 1.6 microns.

[0083] Example 11

[0084] Design M =50.199 nm -1 , prepare NaCu 0.1 Ni 0.35 Mn 0.3 Ti 0.2 O2 positive electrode material.

[0085] CuO, NiOH, MnO2, and TiO2 were selected as precursors, and Na2CO3 and NaOH were selected as sodium sources. The precursors and sodium sources were weighed in corresponding proportions, wherein the sodium source was 30% in excess. The precursors and sodium source were uniformly mixed and ball-milled for 6 hours, and sintered at 1200°C for 15 hours to obtain the NaCu 0.1 Ni 0.35 Mn 0.3 Ti 0.2 The primary particle size of the O2 positive electrode material is 10.5 microns. Figure 5 This is the SEM image of the material of Example 11 of the present invention.

[0086] Example 12

[0087] Design M =50.466 nm -1 , prepare Na 0.9 Cu 0.25 Fe 0.4 Mn 0.2 Ti 0.15 O2 positive electrode material.

[0088] CuO, NiO, Fe2O3, MnO2, TiO2 were selected as precursors, and Na2CO3 and NaO were selected as sodium sources; the precursors and sodium sources were weighed in corresponding proportions, wherein the sodium source was 3% in excess; the precursors and sodium source were uniformly mixed and ball-milled for 6 hours, and sintered at 950°C for 15 hours to obtain the Na 0.9 Cu 0.25Fe 0.4 Mn 0.2 Ti 0.15 The primary particle size of the O2 positive electrode material is 5.0 microns. Figure 6 This is the SEM image of the material of Example 12 of the present invention.

[0089] Example 13

[0090] Design M =49.099 nm -1 , prepare NaCu 0.10 Ni 0.35 Fe 0.1 Mn 0.25 Ti 0.15 Zr 0.05 O2 positive electrode material. First, Ni-Fe-Mn-Zr hydroxide precursor is obtained by co-precipitation method. The co-precipitation method is as follows: according to the molecular formula NaCu 0.10 Ni 0.35 Fe 0.1 Mn 0.25 Ti 0.15 Zr 0.05 The ratio of Ni, Fe, Mn and Zr in O2 is used to prepare deionized water solutions of NiSO4·6H2O, FeSO4·7H2O, MnSO4·H2O and Zr(SO4)2, and the concentration is 2 mol / L; alkali solution is prepared with sodium hydroxide, ammonia water and deionized water, wherein the concentration of sodium hydroxide is 4 mol / L and the concentration of ammonia is 1 mol / L; an appropriate amount of deionized water is added to the reactor and nitrogen is introduced, the reactor is heated to 60°C and kept warm, stirred at a speed of 1000 r / min, and then the transition metal solution and the alkali solution are added dropwise at the same time, and the pH is maintained between 11.5 and 12; after the reaction is completed, the precipitate is 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 Ni-Fe-Mn-Zr hydroxide, CuO and TiO2 obtained in the above steps were selected as precursors, and Na2CO3 and NaOH were selected as sodium sources. The precursors and sodium sources were weighed in corresponding proportions, wherein the sodium source was 4% in excess. The precursors and sodium source were fully mixed and ball-milled for 6 hours, and then sintered at 900°C for 15 hours to obtain NaCu 0.10 Ni 0.35 Fe 0.1 Mn 0.25 Ti 0.15 Zr 0.05 The primary particle size of the O2 positive electrode material is 3.1 microns. Figure 7 This is the SEM image of the material of Example 13 of the present invention.

[0091] Example 14

[0092] Design M =48.731 nm -1 , prepare NaCu 0.10 Ni 0.35 Fe 0.1 Mn 0.25 Ti 0.15 Sn 0.05 O2 positive electrode material.

[0093] CuO, NiO, Fe2O3, MnO2, TiO2 and SnO2 were selected as precursors, and Na2CO3 was selected as the sodium source. The corresponding proportions of the precursors and the sodium source were weighed, wherein the sodium source was 5% in excess. The precursors and the sodium source were evenly mixed and ball-milled for 6 hours, and sintered at 950℃ for 15 hours to obtain NaCu 0.10 Ni 0.35 Fe 0.1 Mn 0.25 Ti 0.15 Sn 0.05 The primary particle size of the O2 positive electrode material is 2.1 microns.

[0094] Example 15

[0095] Design M =49.634 nm -1 , prepare NaMg 0.02 Cu 0.08 Ni 0.35 Fe 0.1 Mn 0.25 Ti 0.2 O2 positive electrode material. CuO, MgO, NiO, Fe2O3, MnO2, TiO2 and SnO2 were selected as precursors, and Na2CO3 and NaOH were selected as sodium sources. The precursors and sodium sources were weighed in corresponding proportions, with the sodium source being 10% in excess. The precursors and sodium source were evenly mixed and ball-milled for 6 hours, and sintered at 1000℃ for 15 hours to obtain NaMg 0.02 Cu 0.008 Ni 0.35 Fe 0.1 Mn 0.25 Ti 0.2 The primary particle size of the O2 positive electrode material is 5.6 microns.

[0096] Example 16

[0097] Design M =48.637 nm -1 , prepare NaCu 0.1 Ni 0.335 Fe 0.1 Lu 0.03 Mn 0.185 Ti0.25 O2 positive electrode material.

[0098] CuO, MgO, NiO, Fe2O3, MnO2, TiO2 and SnO2 were selected as precursors, and Na2CO3 and NaOH were selected as sodium sources. The precursors and sodium sources were weighed in corresponding proportions, wherein the sodium source was 10% in excess. The precursors and sodium source were evenly mixed and ball-milled for 6 hours, and sintered at 1000℃ for 15 hours to obtain NaCu 0.1 Ni 0.335 Fe 0.1 Lu 0.03 Mn 0.185 Ti 0.25 The primary particle size of the O2 positive electrode material is 2.3 microns.

[0099] Example 17

[0100] Design M =48.649 nm -1 , prepare NaCu 0.10 Ni 0.33 Fe 0.1 Sb 0.04 Mn 0.18 Ti 0.25 O2 positive electrode material. Li2CO3, CuO, NiO, Fe2O3, Sb2O3, MnO2, TiO2 are selected as precursors, and Na2O2 is selected as the sodium source; the corresponding proportions of the precursors and the sodium source are weighed, wherein Na2O2 is in excess of 8%; the precursors are first ball-milled for 6 hours, and then ground and mixed with Na2O2 in a mortar under an inert atmosphere; the mixture is pressed into a 15mm diameter disc under a pressure of 10Mpa, and then sintered at 900℃ for 15 hours in a synthetic air atmosphere to obtain NaCu 0.10 Ni 0.33 Fe 0.1 Sb 0.04 Mn 0.18 Ti 0.25 The primary particle size of the O2 positive electrode material is 8.3 microns.

[0101] Example 18

[0102] Design M =48.637 nm -1 , preparation of NaLi 0.02 Cu 0.1 Ni 0.3 Fe 0.16 Mn 0.2 Ti 0.2 Bi 0.02 O2 positive electrode material.

[0103] CuO, LiOH·H2O, NiO, Fe2O3, MnO2, TiO2 and Bi2O3 were selected as precursors, and Na2CO3 and NaOH were selected as sodium sources. The precursors and sodium sources were weighed in corresponding proportions, with the sodium source being 10% in excess. The precursors and sodium source were evenly mixed and ball-milled for 6 hours, and sintered at 1000℃ for 15 hours to obtain NaLi. 0.02 Cu 0.1 Ni 0.3 Fe 0.16 Mn 0.2 Ti 0.2 Bi 0.02 The primary particle size of the O2 positive electrode material is 2.0 microns.

[0104] Comparative Example 1

[0105] Design M =50.323 nm -1 , prepare NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 positive electrode material.

[0106] First, a Ni-Fe-Mn hydroxide precursor is obtained by coprecipitation method. The coprecipitation method is as follows: according to the molecular formula NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 The ratio of Ni, Fe and Mn in O2 is used to prepare deionized water solutions of NiSO4·6H2O, FeSO4·7H2O and MnSO4·H2O, with a concentration of 2 mol / L; alkali solution is prepared using sodium hydroxide, ammonia water and deionized water, wherein the concentration of sodium hydroxide is 4 mol / L and the concentration of ammonia is 1 mol / L; an appropriate amount of deionized water is added to a reactor and nitrogen is introduced, the reactor is heated to 60°C and kept warm, stirred at a speed of 1000 r / min, and then the transition metal solution and the alkali solution are added dropwise at the same time, and the pH is maintained between 11.5 and 12; after the reaction is completed, the precipitate is 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 steps is selected, and Na2CO3 is selected as the sodium source; the precursor and the sodium source are weighed in corresponding proportions, wherein the sodium source is 2% in excess; the precursor and the sodium source are fully mixed in a mortar, and then sintered at 900°C for 15 hours to obtain the NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, the primary particle size is 0.5 microns. Figure 8 This is the SEM image of the material of Comparative Example 1 of the present invention.

[0107] Comparative Example 2

[0108] Design M =51.085 nm -1 , prepare NaNi 0.4 Fe 0.2 Mn 0.4 O2 positive electrode material.

[0109] First, a Ni-Fe-Mn hydroxide precursor is obtained by coprecipitation method. The coprecipitation method is as follows: according to the molecular formula NaNi 0.4 Fe 0.2 Mn 0.4 The ratio of Ni, Fe and Mn in O2 is used to prepare deionized water solutions of NiSO4·6H2O, FeSO4·7H2O and MnSO4·H2O, with a concentration of 2 mol / L; alkali solution is prepared using sodium hydroxide, ammonia water and deionized water, wherein the concentration of sodium hydroxide is 4 mol / L and the concentration of ammonia is 1 mol / L; an appropriate amount of deionized water is added to a reactor and nitrogen is introduced, the reactor is heated to 60°C and kept warm, stirred at a speed of 1000 r / min, and then the transition metal solution and the alkali solution are added dropwise at the same time, and the pH is maintained between 11.5 and 12; after the reaction is completed, the precipitate is 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 steps was selected, and NaNO3 was selected as the sodium source; the precursor and the sodium source were weighed in corresponding proportions, wherein the sodium source was in excess of 4%; the precursor and the sodium source were fully mixed in a mortar, and then sintered at 830°C for 15 hours to obtain the NaNi 0.4 Fe 0.2 Mn 0.4 O2, the primary particle size is 0.5 microns.

[0110] Comparative Example 3

[0111] Design M =51.134 nm -1 , prepare NaCu 0.1 Ni 0.4 Mn 0.4 Ti 0.1 O2 positive electrode material. CuO, NiO, MnO2 and TiO2 were selected as precursors, and Na2CO3 was selected as the sodium source. The precursors and sodium source were weighed in corresponding proportions, ball milled for 6 hours, and sintered at 900℃ for 15 hours to obtain the NaCu 0.1 Ni 0.4 Mn 0.4 Ti 0.1 The primary particle size of the O2 positive electrode material is 2.0 microns.

[0112] The air-stable layered oxide cathode materials prepared in each of the above-described embodiments of the present invention and the materials in the comparative examples were degraded under strict standard conditions and then quantitatively measured for sodium loss. Specifically, 1g of the cathode material was placed in an environment with a constant relative humidity of 60% and a carbon dioxide concentration of 600 ppm for 48 hours. The material was then removed and dried in an argon-filled glove box. The resulting sodium carbonate byproduct was titrated to determine the sodium loss.

[0113] The electrochemical performance of the air-stable layered oxide cathode materials prepared in the above embodiments of the present invention and the materials in the comparative examples before and after degradation is compared:

[0114] Half-cell assembly: The layered oxide cathode materials from each example and comparative example, both before and after degradation, were slurried with conductive carbon black (Super P) and polyvinylidene fluoride (PVDF) in an N-methylpyrrolidone solution at a mass ratio of 80:10:15 under inert atmosphere. The slurry was then coated onto aluminum foil. After vacuum drying, the slurry was cut into 10 mm diameter electrode sheets. A sodium metal sheet was used as the negative electrode, and a 1 mol / L solution of NaClO₄ / propylene carbonate (PC):ethylene carbonate (EC):diethyl carbonate (DEC) (1:1:1 by volume) was used as the electrolyte. A glass fiber separator was used. CR2032 button-type cells were assembled in an argon glove box. The electrode sheets were then paired with a hard carbon negative electrode to form a full cell.

[0115] Charge and discharge tests: The voltage range for charge and discharge of button-type half-cells was 2.0-4.0V, and the voltage range for full-cells was 1.0-4.0V. The test rate was 0.2C. All electrochemical performance tests were conducted at room temperature. The results are shown in Table 2.

[0116]

[0117] Table 2

[0118] More intuitively, the relationship between the sodium removal amount of the above embodiments and comparative examples after being placed under strict standard degradation conditions for 48 hours and the weighted average cationic potential and primary particle size is shown by Figure 9It can be shown. It can be seen that the amount of sodium loss of the material is closely related to the weighted average cationic potential and the primary particle size. With the decrease of the weighted average cationic potential and the increase of the primary particle size, the amount of sodium loss of the material decreases rapidly, and the air stability is effectively improved. For example, under similar primary particle sizes, Example 2 has a lower weighted average cationic potential, and the amount of sodium loss is lower than that of Examples 7, 8, 9, 14, 16 and 18, and is much lower than that of Comparative Example 3; under similar weighted average cationic potential, Example 11 has a larger primary particle size, and the amount of sodium loss is lower than that of Examples 1, 8 and 7, and is much lower than that of Comparative Example 1; Example 17 with a low average cationic potential and a large primary particle size has a sodium loss lower than that of Example 15, and is much lower than that of Comparative Example 3. In comparison, although the weighted average ionic potential of Comparative Example 1 is lower than 51 nanometers, -1 , but the particle size is too small, the sodium loss is 0.532; although the primary particle size of Comparative Example 3 is greater than 1.4 microns, the weighted average ion potential is higher than 51 nanometers -1 , the sodium loss reached 0.401; in Comparative Example 2, the weighted average ionic potential was too high and the primary particle size was too small, resulting in a sodium loss as high as 0.632. Thus, the method of the present invention can significantly reduce the sodium loss of sodium ion layered oxide cathode materials after degradation in air.

[0119] Figure 10 This is a comparison chart of charge and discharge curves of a half-cell test of the material before and after degradation in Example 4 of the present invention; Figure 11 This is a comparison chart of charge and discharge curves of a half-cell test of the material before and after degradation in Example 7 of the present invention; Figure 12 This is a comparison chart of the charge and discharge curves of the half-cell test of the material before and after degradation in Comparative Example 1 of the present invention; Figure 13 This figure compares the charge-discharge curves of the half-cell material before and after degradation in Comparative Example 2 of the present invention. As can be seen, the comparative example, which does not employ the present invention's method, exhibits a significant decrease in specific capacity after degradation compared to the present invention's example. This further demonstrates that the present invention can effectively address the poor air stability of traditional layered oxide cathode materials for sodium-ion batteries, providing a higher reversible specific capacity.

[0120] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for improving the air stability of a sodium ion layered oxide cathode material, characterized in that: The method comprises: regulating the copper-based sodium ion layered oxide positive electrode material Na x Cu y M z The weighted average ionic potential Φ of O2 ions except sodium ions M And control the size of crystal primary particles r , making 47.5 nm -1 ≤Φ M ≤ 50.5 nm -1 , and 1.4 microns ≤ r ≤100 microns, thereby reducing the amount of sodium lost by the sodium ion layered oxide cathode material after degradation in the air, and obtaining a class of air-stable sodium ion battery layered oxide cathode materials; Wherein, M is selected from Ni 2+ 、Zn 2+ Mg 2+ 、Fe 3+ 、La 3+ 、Lu 3+ 、Sb 3+ 、Mn 4+ 、Ti 4+ 、Zr 4+ 、Sn 4+ 、Bi 5+ One or more of ; 0.9≤x≤1, and y+z=1.

2. The method according to claim 1, characterized in that The ionic potential is the ratio of the ionic charge Z of a certain ion to its ionic radius r, Φ, that is, Φ=Z / r, the unit of the ionic radius is nanometer, the weighted average ionic potential Φ M is the weighted average of the ionic potentials of cations other than sodium ions, with the percentage of cations as the weight, that is, , where x i is the percentage of a certain ion i and satisfies all x i The sum of is 1; Φ i is the ionic potential of a certain ion i, Z i is the charge number of an ion i, r i is the ionic radius of a certain ion i.

3. The method according to claim 1, characterized in that The method for regulating the copper-based sodium ion layered oxide positive electrode material Na x Cu y M z The weighted average ionic potential Φ of O2 ions except sodium ions M And control the size of crystal primary particles r tool The body includes: By changing the Na x Cu y M z The stoichiometric ratios y and z of Cu and M in O2 are used to control the weighted average ionic potential Φ of ions other than sodium ions. M and crystal primary particle size r。 4. The method according to claim 1, wherein The particle size of the primary crystal particles is regulated r The method further includes: using excess 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.

5. An air-stable layered oxide cathode material for sodium ion batteries obtained according to the method of any one of claims 1 to 4.

6. A method for preparing the layered oxide positive electrode material for sodium ion batteries according to claim 5, characterized in that: The preparation method comprises: A sodium source having a stoichiometric amount of 100% to 130% of the required sodium, a Cu-containing precursor and an M-containing precursor having a required stoichiometric amount are mixed in proportion, and sintered at a high temperature of 800-1200° C. to produce the sodium ion battery layered oxide positive electrode material; Wherein, 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 Cu-containing metal oxides, metal carbonates, metal nitrates, metal oxalates, metal acetates, metal sulfates, and metal hydroxides; The M-containing precursor includes: one or more mixtures of M-containing metal oxides, metal carbonates, metal nitrates, metal oxalates, metal acetates, metal sulfates, metal hydroxides, or multi-metal hydroxides prepared by a coprecipitation method.

7. A positive electrode for a sodium ion secondary battery, characterized in that The positive electrode comprises the sodium ion battery layered oxide positive electrode material according to claim 5.

8. The positive electrode according to claim 7, characterized in that 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, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR).

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

10. An electronic device, characterized in that: The electronic device comprises the sodium ion battery according to claim 9.

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