Layered oxide positive electrode material and sodium ion battery

Abstract

The chemical general formula of the layered oxide is Nan [AaCub] NicMndO2, Cu, Ni and Mn exist in a transition metal layer, and Na and A are metal elements in an alkali metal layer; ni and Mn are matrix elements forming the layered oxide, and Cu and A are co-doping elements; wherein the element A is selected from metal elements which are within the ion radius range and only have one valence state, and is distributed in IA and IIA main groups and IIB and IIIB subgroups in the periodic table of elements, and the configuration of a d electron orbit is d0 or d10. The invention also discloses a sodium ion battery using the layered oxide as the positive electrode material, an A element having strong interaction with oxygen is introduced into an alkali metal layer, and a small amount of Cu is supplemented to modify a transition metal layer, so that the structural stability of the layered oxide as the positive electrode material is synergistically enhanced; and the sodium ion battery shows excellent cycling stability and rate capability.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, and specifically relates to a P2-type layered oxide cathode material, its preparation method, and its application. Background Technology

[0002] With the rapid advancement of the global economy and the continuous depletion of fossil fuels, the resulting energy crisis and environmental pollution are intensifying, seriously threatening human survival. A series of global challenges to sustainable development are receiving increasing attention from all countries. Against this backdrop, developing a high-power, low-cost, long-life, and environmentally friendly energy conversion and storage system has become increasingly important. Due to the growing demand for energy density and the uneven distribution of global lithium resources, the manufacturing cost of lithium-ion batteries is constantly increasing, severely hindering the development of the new energy industry and national security. To ensure the self-sufficiency of energy storage technologies, it is necessary to accelerate the development and exploration of other new energy storage technology routes. Sodium-ion batteries, due to their widespread resource distribution and cost advantages, have become an important piece of the energy transition puzzle.

[0003] The cathode material determines the energy density and cycle life of a battery, and is therefore a key factor restricting the current development of sodium-ion batteries. Among various cathode material systems, layered oxides (general formula Na₂O₃) are the most common. x TMO2 (where TM is a transition metal, such as Mn, Ni, Co, Fe, etc.) is considered the most promising cathode material for sodium-ion batteries due to its high theoretical capacity, diverse structural chemical composition, and process compatibility. Its scalable structural design allows for customization of its electrochemical performance by introducing different elements into the matrix. The crystal structure of layered oxides mainly exhibits O3, O2, and P2 types, with different structural types directly affecting the sodium-ion coordination environment and diffusion kinetics. Its overall structure can be viewed as an alternating stack of transition metal layers (TM layers) and alkali metal layers (Na layers), forming a typical two-dimensional layered structure; where the transition metal layer consists of transition metal ions and their coordinated oxygen ions (O... 2 -) together form the [TMO6] octahedral plates, which provide the structural framework and redox active centers for the layered oxide; the alkali metal layer is composed of sodium ions (Na+). + The layered oxide occupies a two-dimensional planar layer between two adjacent transition metal-oxygen octahedral layers, serving as a channel for sodium ion storage and diffusion. However, the layered oxide undergoes an irreversible P2O2 structural phase transition, the Jan Taylor distortion effect, and Na+ during charge and discharge. + Problems such as vacancy ordering lead to rapid capacity decay and poor rate performance, making it difficult to achieve long cycle life, which is detrimental to practical commercial applications. Therefore, there is an urgent need to develop a type of structurally stable sodium-ion battery cathode material. Summary of the Invention

[0004] Therefore, the purpose of this invention is to provide a P2-type layered oxide that, through a rational design, introduces metal elements into the alkali metal layer as interlayer pillars to enhance the interaction between adjacent transition metal layers. This allows it to suppress relative slippage between adjacent layers when used as a cathode material in a deeply desodium-free state, thus mitigating adverse phase transitions to the structure and improving the structural stability of the cathode material.

[0005] Another object of the present invention is to provide a method for preparing the above-mentioned P2 type layered oxide.

[0006] Another objective of this invention is to provide the application of the above-mentioned P2-type layered oxide as a positive electrode material in sodium-ion batteries.

[0007] To achieve the above objectives, the present invention adopts the following technical solution.

[0008] This invention first provides a layered oxide with the general chemical formula Na. n [A a Cu b Ni c Mn d O2 has an overall structure that is a two-dimensional layered structure formed by alternating layers of transition metals and alkali metals. Cu, Ni, and Mn are transition metals in the transition metal layers, while Na and A are metal elements present in the alkali metal layers. Ni and Mn are the matrix elements constituting the layered oxide, and Cu and A are co-doping elements forming the layered oxide. The element A is selected from the range of ionic radii. Furthermore, it is a metallic element with only one valence state, and element A is distributed in the main groups IA and IIA and the subgroups IIB and IIIB of the periodic table. Its d electron orbital configuration is d0 or d10, and it has low electronegativity. Ni, Mn, Cu and O in the transition metal layer form a transition metal oxygen octahedron.

[0009] In the above general chemical formula, 0.6≤n≤0.8, 0.03≤a≤0.1, 0.05≤b≤0.1, 0.15≤c≤0.23, 0.65≤d≤0.69, and a+b+c+d=1.

[0010] The layered oxide has a P2-type hexagonal layered crystal structure with a P63 / mmc space group.

[0011] In the above general chemical formula, element A is preferably any one of Mg, Ca, Zn, Cu, Sr, Y, and Rb.

[0012] The layered oxide has a microstructure consisting of spherical, near-spherical, polygonal, or plate-shaped particles with an average particle size ≤2μm.

[0013] The layered oxide provided by this invention, through the above-described rational design, introduces metal element A as an interlayer support in the alkali metal layer of the layered oxide, thereby suppressing relative slippage between adjacent layers, mitigating adverse phase transitions to the structure, and improving its structural stability as a cathode material. The design concept of the layered oxide described above can be simply explained as follows.

[0014] In layered oxides, alumina (A) chooses orbital configurations d0 and d10. Considering that the electronic configurations of d0 and d10 lack orbital directionality, they are better suited to the environment of Na site distortion during charging and discharging. This electronic configuration of A results in a lack of crystal field stabilization energy (CFSE), or only zero CFSE, thus lacking the intrinsic driving force to occupy octahedral geometric sites and thus tending to occupy Na sites. This differs from elements like Ni and Mn, which, in an octahedral coordination field, can obtain significant CFSE, allowing them to exist stably in the TM layer. Alumina's low electronegativity makes it more inclined to form ionic bonds, while transition metal layers possess strong covalent bond networks, especially dp hybridization with oxygen. Therefore, it is energy-disadvantageous for A to occupy transition metal sites, so it tends to occupy alkali metal layers. Alumina typically has a stable, single, and low valence state in oxides. According to the principle of charge conservation, if A generates Na vacancies in alkali metal layers, it is more energy-efficient. The ionic radius of element A should be similar to that of Na, as a more compatible ionic radius facilitates its entry into the alkali metal layer. In summary, elements from groups IA, IIA, IIB, and IIIB are preferred for element A, as they are more likely to enter the alkali metal layer from multiple perspectives, thereby forming new interlayer pillars and enhancing the structural stability of the material. Simultaneously, entering the alkali metal sites will also break down the Na... + / Ordered distribution of vacancies, thereby reducing Na + The diffusion energy barrier improves rate performance.

[0015] By rationally designing the selection of element A and controlling parameters such as its content, element A successfully enters the alkali metal layer. The strong interaction between element A and oxygen makes it act as an interlayer support in the alkali metal layer, reinforcing the structural stability of the adjacent transition metal layer. This suppresses the unfavorable phase transition of the cathode material during deep sodium removal under high pressure, maintaining the P2 phase. Meanwhile, Ni, Cu, and Mn synergistically strengthen the structural framework in the transition metal layer. Specifically, Ni, Cu, and Mn form strong covalent bonds with oxygen in the transition metal layer, regulating charge transfer while forming a stable layered structure, maximizing electron transfer between redox pairs. On the other hand, the introduction of element A into the alkali metal layer, due to its stronger interaction than Na-O, successfully shields the electrostatic repulsion of adjacent oxygen octahedra, thus significantly suppressing the relative slippage of the transition metal layer under high pressure and enhancing structural stability. Furthermore, the presence of element A in the alkali metal layer disrupts the Na...+ The ordered arrangement of vacancies causes the charge-discharge curve to exhibit a single-phase solid solution reaction, enhancing the Na... + The diffusion ability of Cu. Furthermore, the addition of Cu as a dopant in the transition metal layer can modulate the electronic structure and charge distribution of the transition metal layer. Cu doping replaces part of the host element Ni, maintaining a +2 valence state throughout the process. x In TMO2, to maintain the average oxidation state of TM, the valence state of Mn will increase, thereby reducing the oxidation state of Mn. 3+ The easily induced Jan Taylor effect can severely compromise the stability of the structure. Therefore, the modulating effect of Cu in the transition metal layer can also enhance the stability of the structure.

[0016] The present invention also provides a method for preparing the above-mentioned layered oxide, comprising the following steps.

[0017] Step S10: Mix the various metal sources, including sodium source, A source, copper source, nickel source and manganese source, in deionized water to prepare the first solution.

[0018] Step S20: Dissolve the complexing agent in deionized water to prepare a second solution.

[0019] Step S30: The second solution is added dropwise to the first solution. During this dropwise addition, the first solution is kept in a water bath and reacts with the added second solution in a water bath to obtain a sol.

[0020] Step S40: Place the sol in an oven for drying reaction to obtain a solid.

[0021] Step S50: The solid is pre-fired at a first temperature and kept at that temperature for a first time period, then calcined at a second temperature and kept at that temperature for a second time period, and then naturally cooled to room temperature to obtain the layered oxide.

[0022] Furthermore, each metal source in step S10 is at least one of acetate, sulfate, and nitrate. Specifically, the sodium source is selected from at least one of sodium acetate, sodium sulfate, and sodium nitrate; the A source is selected from at least one of acetate A, sulfate A, and nitrate A; the nickel source is selected from at least one of nickel acetate, nickel sulfate, and nickel nitrate; the copper source is selected from at least one of copper acetate, copper sulfate, and copper nitrate; and the manganese source is selected from at least one of manganese acetate, manganese sulfate, and manganese nitrate. The metal sources can form stable complexes in the solution, maintaining a uniform distribution of each component at the molecular level, obtaining a material with uniform properties, and being low in cost, safe, and easy to operate.

[0023] Further, the complexing agent mentioned in step S20 is selected from at least one of citric acid and oxalic acid, and the stoichiometric molar ratio of the amount of complexing agent to the total amount of metal source is 1:1 to 1.5:1.

[0024] Furthermore, the water bath reaction described in step S30 refers to evaporation and concentration in a water bath at 70-90°C until the sol is obtained.

[0025] Furthermore, the drying reaction described in step S40 refers to keeping the food at 100-120°C in an oven for 3-6 hours.

[0026] Further, in step S50, the first temperature is 430-470℃, and the first time period is 5-7h; the second temperature is 890-910℃, and the second time period is 14-16h.

[0027] Furthermore, in step S10, the amounts of the A source, copper source, nickel source, and manganese source added to the first solution are equal to the molecular formula Na of the prepared layered oxide. n [A a Cu b Ni c Mn d The stoichiometric ratio of O2 is used for weighing; while the amount of Na source is considered to compensate for the sodium loss caused by high-temperature evaporation, and the sodium source is added in excess of 2% to 10%, that is, the amount of sodium source added to A source, copper source, nickel source and manganese source meets the molar ratio: (1.02n to 1.10n):a:b:c:d.

[0028] This invention also provides a sodium-ion battery positive electrode sheet, specifically the application of the aforementioned layered oxide as a positive electrode material in a sodium-ion battery. The positive electrode sheet includes a positive electrode current collector and a positive electrode active layer located on the positive electrode current collector, wherein the active material of the positive electrode active layer is the layered oxide.

[0029] The present invention also provides a sodium-ion battery, wherein the sodium-ion battery includes the above-described positive electrode sheet.

[0030] The beneficial effects of this invention include:

[0031] (1) This invention introduces metal elements as interlayer pillars in the alkali metal layer through reasonable design, which enhances the interaction between adjacent transition metal plates; thereby, when it is used as a cathode material for sodium-ion batteries, it can suppress the relative slippage between adjacent plates in the deep desodium state, alleviate the adverse phase transition on the structure, and improve the structural stability of the cathode material.

[0032] (2) The present invention controls the appropriate amount of Na in the layered oxide to make the synthesized layered oxide P2 type and avoid the appearance of other impurity phases.

[0033] (3) In this invention, a suitable metal element A is selected as a dopant element and introduced into the alkali metal layer of the layered oxide. By controlling parameters such as the doping amount of dopant element A, the dopant element A can successfully enter the alkali metal layer, and the synthesis of the layered oxide avoids the occurrence of impurity phases or segregation phenomena other than P2 type. Moreover, an OAO interlayer structure is constructed at this location, which not only achieves stronger Na-O bond interactions than elsewhere, improving the structural stability of the layered oxide as a positive electrode material for sodium-ion batteries under high voltage, but also disrupts the Na... + The orderly arrangement of vacancy enhances Na + The diffusion dynamics are optimized to achieve excellent rate performance.

[0034] (4) In the layered oxide of the present invention, Ni, Cu, Mn and oxygen in the transition metal layer form a transition metal oxygen octahedron. Cu is selected as the doping element and the doping amount of Cu is controlled within a suitable range. At the same time, the content of the main transition metals Ni and Mn is optimized. The reasonable combination of the contents of Cu, Ni and Mn in the transition metal layer is beneficial to adjusting the surrounding charge distribution. Under the premise of not reducing the redox active center as much as possible, a stable transition metal layer structure is ensured while maintaining a high specific capacity of the cathode material. In addition, a small amount of Cu is added to modify the transition metal layer, which synergistically enhances the structural stability of the layered oxide as a cathode material, so that the sodium-ion battery exhibits excellent cycle stability and rate performance.

[0035] (5) The microstructure of the layered oxide of the present invention is spherical, near-spherical, polygonal or lamellar particles with an average particle size ≤2μm. When used as a positive electrode material, the above particle size characteristics are beneficial to improving the tap density and compaction density of the electrode material, which is beneficial to the preparation of sodium-ion battery positive electrode sheets.

[0036] (6) The sodium-ion battery using the layered oxide of the present invention as the positive electrode material has high specific capacity, long cycle stability, excellent rate performance and excellent high and low temperature characteristics.

[0037] (7) The preparation method of the layered oxide cathode material provided by the present invention is simple and does not require complex process conditions during the doping process. It can significantly improve the consistency and yield of the product and reduce the production cost of the product. Attached Figure Description

[0038] Figure 1 These are scanning electron microscope (SEM) images of the layered oxides prepared in Example 1, Comparative Example 1, and Comparative Example 2 of the present invention; wherein (a) corresponds to Example 1, (b) corresponds to Comparative Example 1, and (c) corresponds to Comparative Example 2.

[0039] Figure 2The images show the X-ray diffraction (XRD) patterns of the layered oxides prepared in Examples 1, 1, and 2 of this invention.

[0040] Figure 3 The diagram shows the first-principles DFT calculation results of the P2 and O2 phases of the layered oxides in Example 1 and Comparative Example 2 of this invention.

[0041] Figure 4 The diagram shows the cycle stability test results of sodium-ion batteries using layered oxides as positive electrode materials prepared in Examples 1, 1, and 2 of this invention.

[0042] Figure 5 The figures show the first charge-discharge curves of sodium-ion batteries using layered oxides as positive electrode materials prepared in Example 1, Comparative Example 1, and Comparative Example 2 of this invention; wherein (a) corresponds to Example 1, (b) corresponds to Comparative Example 1, and (c) corresponds to Comparative Example 2.

[0043] Figure 6 The graph shows the rate performance test results of sodium-ion batteries using layered oxides as cathode materials prepared in Examples 1, 1, and 2 of this invention. Detailed Implementation

[0044] The present invention will be further described below with reference to specific embodiments.

[0045] Example 1

[0046] Na 0.67 Y 0.05 Cu 0.1 Ni 0.18 Mn 0.67 Preparation of O2 layered oxides:

[0047] CH3COONa, Y(CH3COO)3·xH2O, Cu(CH3COO)2·H2O, Ni(CH3COO)2·4H2O, and Mn(CH3COO)2·4H2O were used as metal source materials. The metal source materials were weighed according to the molar ratio of 0.67×1.05:0.05:0.1:0.18:0.67. The Na source was added in excess to prevent high temperature loss. The stoichiometric ratio was increased by 5% based on the stoichiometric ratio of 0.67, that is, 5% excess. Each metal source was dissolved in deionized water and stirred thoroughly to prepare a first solution. Citric acid was weighed and dissolved in deionized water and stirred thoroughly, with the stoichiometric ratio of citric acid to total metal sources being 1.5:1, to prepare a second solution. The second solution was slowly added dropwise to the first solution. During this process, the first solution was kept in an 80°C water bath and stirred continuously at a speed of 500 r / min for evaporation and concentration until a sol was obtained. The obtained sol was transferred to a corundum crucible and placed in an oven to dry at 120°C for 3 h to react and obtain a dry gel solid. The obtained dry gel solid was transferred to a muffle furnace and pre-calcined at 450°C for 6 h. The obtained solid was then transferred to a mortar for thorough grinding and then transferred back to a muffle furnace for calcination at 900°C for 15 h, with a heating rate of 2°C / min. After natural cooling to room temperature, the final layered oxide was obtained.

[0048] Example 2

[0049] Na 0.6 Y 0.03 Cu 0.05 Ni 0.23 Mn 0.69 Preparation of O2 layered oxides:

[0050] Using CH3COONa, Y(CH3COO)3·xH2O, Cu(CH3COO)2·H2O, Ni(CH3COO)2·4H2O, and Mn(CH3COO)2·4H2O as metal source materials, each metal source material was weighed in a molar ratio of 0.6×1.02:0.03:0.05:0.23:0.69, with Na source added in excess at 2%. The materials were dissolved in deionized water and stirred thoroughly to prepare a first solution. Citric acid was weighed and dissolved in deionized water, and stirred thoroughly. The stoichiometric ratio of citric acid to total metal source materials was 1:1 to prepare a second solution. The second solution was then slowly added dropwise... The solution was added to the first solution, which was continuously stirred in a 70°C water bath at a stirring speed of 500 r / min for evaporation and concentration until a sol was obtained. The obtained sol was transferred to a corundum crucible and placed in an oven to dry at 100°C for 3 h to react and obtain a dry gel solid. The obtained dry gel solid was transferred to a muffle furnace and pre-calcined at 430°C for 7 h. The obtained solid was then transferred to a mortar for thorough grinding and then transferred back to a muffle furnace for calcination at 890°C for 16 h with a heating rate of 2°C / min. After natural cooling to room temperature, the final layered oxide was obtained.

[0051] Example 3

[0052] Na 0.8 Y 0.1 Cu 0.1 Ni 0.15 Mn 0.65 Preparation of O2 layered oxides:

[0053] Using CH3COONa, Y(CH3COO)3·xH2O, Cu(CH3COO)2·H2O, Ni(CH3COO)2·4H2O, and Mn(CH3COO)2·4H2O as metal source materials, each metal source material was weighed in a molar ratio of 0.8×1.10:0.1:0.1:0.15:0.65, with Na source in 10% excess. The materials were dissolved in deionized water and stirred thoroughly to prepare a first solution. Citric acid was weighed and dissolved in deionized water, and stirred thoroughly. The stoichiometric ratio of citric acid to total metal source material was 1.5:1 to prepare a second solution. The second solution was slowly added dropwise to... In the first solution, during this process, the first solution was continuously stirred in a 90℃ water bath at a stirring speed of 500 r / min for evaporation and concentration until a sol was obtained. The obtained sol was transferred to a corundum crucible and placed in an oven to dry at 120℃ for 6 h to react and obtain a dry gel solid. The obtained dry gel solid was transferred to a muffle furnace and pre-calcined at 470℃ for 5 h. The obtained solid was then transferred to a mortar for thorough grinding and then transferred back to a muffle furnace for calcination at 910℃ for 14 h with a heating rate of 2℃ / min. After naturally cooling to room temperature, the final layered oxide was obtained.

[0054] Example 4

[0055] Na 0.67 Mg 0.05 Cu 0.1 Ni 0.18 Mn 0.67 Preparation of O2 layered oxides:

[0056] Using CH3COONa, Mg(CH3COO)2·4H2O, Cu(CH3COO)2·H2O, Ni(CH3COO)2·4H2O, and Mn(CH3COO)2·4H2O as metal source materials, each metal source material was weighed in a molar ratio of 0.67×1.05:0.05:0.1:0.18:0.67, with Na source in 5% excess. The materials were dissolved in deionized water and stirred thoroughly to prepare a first solution. Citric acid was weighed and dissolved in deionized water, and stirred thoroughly. The stoichiometric ratio of citric acid to total metal source material was 1.5:1 to prepare a second solution. The second solution was then slowly added dropwise... The solution was placed in an 80°C water bath and continuously stirred at a stirring speed of 500 r / min for evaporation and concentration until a sol was obtained. The obtained sol was transferred to a corundum crucible and placed in an oven to dry at 120°C for 6 h to react and obtain a dry gel solid. The obtained dry gel solid was transferred to a muffle furnace and pre-calcined at 450°C for 6 h. The obtained solid was then transferred to a mortar for thorough grinding and then transferred back to a muffle furnace for calcination at 900°C for 15 h with a heating rate of 2°C / min. After natural cooling to room temperature, the final layered oxide was obtained.

[0057] Example 5

[0058] Na 0.6 Mg 0.03 Cu 0.05 Ni 0.23 Mn 0.69 Preparation of O2 layered oxides:

[0059] Using CH3COONa, Mg(CH3COO)2·4H2O, Cu(CH3COO)2·H2O, Ni(CH3COO)2·4H2O, and Mn(CH3COO)2·4H2O as metal source materials, each metal source material was weighed in a molar ratio of 0.6×1.02:0.03:0.05:0.23:0.69, with Na source in excess at 2%. The materials were dissolved in deionized water and stirred thoroughly to prepare a first solution. Citric acid was weighed and dissolved in deionized water, and stirred thoroughly. The stoichiometric ratio of citric acid to total metal source material was 1.1:1 to prepare a second solution. The second solution was then slowly added dropwise... The solution was placed in a 70°C water bath and continuously stirred at a stirring speed of 500 r / min for evaporation and concentration until a sol was obtained. The obtained sol was transferred to a corundum crucible and placed in an oven to dry at 100°C for 3 h to react and obtain a dry gel solid. The obtained dry gel solid was transferred to a muffle furnace and pre-calcined at 430°C for 7 h. The obtained solid was then transferred to a mortar for thorough grinding and then transferred back to a muffle furnace for calcination at 890°C for 16 h with a heating rate of 2°C / min. After natural cooling to room temperature, the final layered oxide was obtained.

[0060] Example 6

[0061] Na 0.8 Mg 0.1 Cu 0.1 Ni 0.15 Mn 0.65 Preparation of O2 layered oxides:

[0062] Using CH3COONa, Mg(CH3COO)2·4H2O, Cu(CH3COO)2·H2O, Ni(CH3COO)2·4H2O, and Mn(CH3COO)2·4H2O as metal source materials, each metal source material was weighed according to a stoichiometric ratio of 0.8×1.10:0.1:0.1:0.15:0.65, with Na source in 10% excess. The materials were dissolved in deionized water and stirred thoroughly to prepare a first solution. Citric acid was weighed and dissolved in deionized water, and stirred thoroughly. The stoichiometric ratio of citric acid to total metal source material was 1.5:1 to prepare a second solution. The second solution was then slowly added dropwise... The solution was placed in a 90°C water bath and continuously stirred at a stirring speed of 500 r / min for evaporation and concentration until a sol was obtained. The obtained sol was transferred to a corundum crucible and placed in an oven to dry at 120°C for 6 h to react and obtain a dry gel solid. The obtained dry gel solid was transferred to a muffle furnace and pre-calcined at 470°C for 5 h. The obtained solid was then transferred to a mortar for thorough grinding and then transferred back to a muffle furnace for calcination at 910°C for 14 h with a heating rate of 2°C / min. After natural cooling to room temperature, the final layered oxide was obtained.

[0063] Example 7

[0064] Na 0.67 La 0.05 Cu 0.1 Ni 0.18 Mn 0.67 Preparation of O2 layered oxides:

[0065] Using CH3COONa, La(CH3COO)3·xH2O, Cu(CH3COO)2·H2O, Ni(CH3COO)2·4H2O, and Mn(CH3COO)2·4H2O as metal source materials, each metal source material was weighed in a molar ratio of 0.67×1.05:0.05:0.1:0.18:0.67, with Na source in 5% excess. The materials were dissolved in deionized water and stirred thoroughly to prepare a first solution. Citric acid was weighed and dissolved in deionized water, and stirred thoroughly. The stoichiometric ratio of citric acid to total metal source material was 1.5:1 to prepare a second solution. The second solution was then slowly added dropwise... The solution was placed in an 80°C water bath and continuously stirred at a stirring speed of 500 r / min for evaporation and concentration until a sol was obtained. The obtained sol was transferred to a corundum crucible and placed in an oven to dry at 120°C for 6 h to react and obtain a dry gel solid. The obtained dry gel solid was transferred to a muffle furnace and pre-calcined at 450°C for 6 h. The obtained solid was then transferred to a mortar for thorough grinding and then transferred back to a muffle furnace for calcination at 900°C for 15 h with a heating rate of 2°C / min. After natural cooling to room temperature, the final layered oxide was obtained.

[0066] Example 8

[0067] Na 0.6 La 0.03 Cu 0.05 Ni 0.23 Mn 0.69 Preparation of O2 layered oxides:

[0068] Using CH3COONa, La(CH3COO)3·xH2O, Cu(CH3COO)2·H2O, Ni(CH3COO)2·4H2O, and Mn(CH3COO)2·4H2O as metal source materials, each metal source material was weighed in a molar ratio of 0.6×1.02:0.03:0.05:0.23:0.69, with Na source in excess at 2%. The materials were dissolved in deionized water and stirred thoroughly to prepare a first solution. Citric acid was weighed and dissolved in deionized water, and stirred thoroughly. The stoichiometric ratio of citric acid to total metal source material was 1.1:1 to prepare a second solution. The second solution was then slowly added dropwise... The solution was placed in a 70°C water bath and continuously stirred at a stirring speed of 500 r / min for evaporation and concentration until a sol was obtained. The obtained sol was transferred to a corundum crucible and placed in an oven to dry at 100°C for 3 h to react and obtain a dry gel solid. The obtained dry gel solid was transferred to a muffle furnace and pre-calcined at 430°C for 7 h. The obtained solid was then transferred to a mortar for thorough grinding and then transferred back to a muffle furnace for calcination at 890°C for 16 h with a heating rate of 2°C / min. After natural cooling to room temperature, the final layered oxide was obtained.

[0069] Example 9

[0070] Na 0.8 La 0.1 Cu 0.1 Ni 0.15 Mn 0.65 Preparation of O2 layered oxides:

[0071] Using CH3COONa, La(CH3COO)3·xH2O, Cu(CH3COO)2·H2O, Ni(CH3COO)2·4H2O, and Mn(CH3COO)2·4H2O as metal source materials, each metal source material was weighed in a molar ratio of 0.8×1.10:0.1:0.1:0.15:0.65, with Na source in 10% excess. The materials were dissolved in deionized water and stirred thoroughly to prepare a first solution. Citric acid was weighed and dissolved in deionized water, and stirred thoroughly. The stoichiometric ratio of citric acid to total metal source material was 1.5:1 to prepare a second solution. The second solution was then slowly added dropwise to… In the first solution, during this process, the first solution was continuously stirred in a 90℃ water bath at a stirring speed of 500 r / min for evaporation and concentration until a sol was obtained. The obtained sol was transferred to a corundum crucible and placed in an oven to dry at 120℃ for 6 h to react and obtain a dry gel solid. The obtained dry gel solid was transferred to a muffle furnace and pre-calcined at 470℃ for 5 h. The obtained solid was then transferred to a mortar for thorough grinding and then transferred back to a muffle furnace for calcination at 910℃ for 14 h with a heating rate of 2℃ / min. After naturally cooling to room temperature, the final layered oxide was obtained.

[0072] Example 10

[0073] Na 0.67 Sr 0.05 Cu 0.1 Ni 0.18 Mn 0.67 Preparation of O2 layered oxides:

[0074] Using CH3COONa, Sr(CH3COO)2·xH2O, Cu(CH3COO)2·H2O, Ni(CH3COO)2·4H2O, and Mn(CH3COO)2·4H2O as metal source materials, each metal source material was weighed in a molar ratio of 0.67×1.05:0.05:0.1:0.18:0.67, with Na source in 5% excess. The materials were dissolved in deionized water and stirred thoroughly to prepare a first solution. Citric acid was weighed and dissolved in deionized water, and stirred thoroughly. The stoichiometric ratio of citric acid to total metal source material was 1.5:1 to prepare a second solution. The second solution was then slowly added dropwise... The solution was placed in an 80°C water bath and continuously stirred at a stirring speed of 500 r / min for evaporation and concentration until a sol was obtained. The obtained sol was transferred to a corundum crucible and placed in an oven to dry at 120°C for 6 h to react and obtain a dry gel solid. The obtained dry gel solid was transferred to a muffle furnace and pre-calcined at 450°C for 6 h. The obtained solid was then transferred to a mortar for thorough grinding and then transferred back to a muffle furnace for calcination at 900°C for 15 h with a heating rate of 2°C / min. After natural cooling to room temperature, the final layered oxide was obtained.

[0075] Example 11

[0076] Na 0.6 Sr 0.03 Cu 0.05 Ni 0.23 Mn 0.69 Preparation of O2 layered oxides:

[0077] Using CH3COONa, Sr(CH3COO)2·xH2O, Cu(CH3COO)2·H2O, Ni(CH3COO)2·4H2O, and Mn(CH3COO)2·4H2O as metal source materials, each metal source material was weighed in a molar ratio of 0.6×1.02:0.03:0.05:0.23:0.69, with Na source in excess at 2%. The materials were dissolved in deionized water and stirred thoroughly to prepare a first solution. Citric acid was weighed and dissolved in deionized water, and stirred thoroughly. The stoichiometric ratio of citric acid to total metal source material was 1.1:1 to prepare a second solution. The second solution was then slowly added dropwise... The solution was placed in a 90°C water bath and continuously stirred at a stirring speed of 500 r / min for evaporation and concentration until a sol was obtained. The obtained sol was transferred to a corundum crucible and placed in an oven to dry at 100°C for 3 h to react and obtain a dry gel solid. The obtained dry gel solid was transferred to a muffle furnace and pre-calcined at 430°C for 7 h. The obtained solid was then transferred to a mortar for thorough grinding and then transferred back to a muffle furnace for calcination at 890°C for 16 h with a heating rate of 2°C / min. After natural cooling to room temperature, the final layered oxide was obtained.

[0078] Example 12

[0079] Na 0.8 Sr 0.1 Cu 0.1 Ni 0.15 Mn 0.65 Preparation of O2 layered oxides:

[0080] Using CH3COONa, Sr(CH3COO)2·xH2O, Cu(CH3COO)2·H2O, Ni(CH3COO)2·4H2O, and Mn(CH3COO)2·4H2O as metal source materials, each metal source material was weighed in a molar ratio of 0.8×1.1:0.1:0.1:0.15:0.65, with Na source in 10% excess. The materials were dissolved in deionized water and stirred thoroughly to prepare a first solution. Citric acid was weighed and dissolved in deionized water, and stirred thoroughly. The stoichiometric ratio of citric acid to total metal source material was 1.5:1 to prepare a second solution. The second solution was slowly added dropwise to... In the first solution, during this process, the first solution was continuously stirred in a 70℃ water bath at a stirring speed of 500 r / min for evaporation and concentration until a sol was obtained. The obtained sol was transferred to a corundum crucible and placed in an oven to dry at 120℃ for 6 h to react and obtain a dry gel solid. The obtained dry gel solid was transferred to a muffle furnace and pre-calcined at 470℃ for 5 h. The obtained solid was then transferred to a mortar for thorough grinding and then transferred back to a muffle furnace for calcination at 910℃ for 14 h with a heating rate of 2℃ / min. After naturally cooling to room temperature, the final layered oxide was obtained.

[0081] Example 13

[0082] Na 0.67 Rb 0.05 Cu 0.1 Ni 0.18 Mn 0.67 Preparation of O2 layered oxides:

[0083] Using CH3COONa, CH3COORb·xH2O, Cu(CH3COO)2·H2O, Ni(CH3COO)2·4H2O, and Mn(CH3COO)2·4H2O as metal source materials, each metal source material was weighed in a molar ratio of 0.67×1.05:0.05:0.1:0.18:0.67, with Na source in 5% excess. The materials were dissolved in deionized water and stirred thoroughly to prepare a first solution. Citric acid was weighed and dissolved in deionized water, and stirred thoroughly. The stoichiometric ratio of citric acid to total metal source material was 1.5:1 to prepare a second solution. The second solution was slowly added dropwise to the first... In one solution, during the process, the first solution was continuously stirred in an 80℃ water bath at a stirring speed of 500 r / min for evaporation and concentration until a sol was obtained. The obtained sol was transferred to a corundum crucible and placed in an oven to dry at 120℃ for 6 h to react and obtain a dry gel solid. The obtained dry gel solid was transferred to a muffle furnace and pre-calcined at 450℃ for 6 h. The obtained solid was then transferred to a mortar for thorough grinding and then transferred back to a muffle furnace for calcination at 900℃ for 15 h with a heating rate of 2℃ / min. After natural cooling to room temperature, the final layered oxide was obtained.

[0084] Example 14

[0085] Na 0.6 Rb 0.03 Cu 0.05 Ni 0.23 Mn 0.69 Preparation of O2 layered oxides:

[0086] Using CH3COONa, CH3COORb·xH2O, Cu(CH3COO)2·H2O, Ni(CH3COO)2·4H2O, and Mn(CH3COO)2·4H2O as metal source materials, each metal source material was weighed in a molar ratio of 0.6×1.02:0.03:0.05:0.23:0.69, with Na source in excess at 2%. The materials were dissolved in deionized water and stirred thoroughly to prepare a first solution. Citric acid was weighed and dissolved in deionized water, and stirred thoroughly. The stoichiometric ratio of citric acid to total metal source material was 1.1:1 to prepare a second solution. The second solution was slowly added dropwise to the first... In a solution, the first solution was continuously stirred in a 70°C water bath at a stirring speed of 500 r / min for evaporation and concentration until a sol was obtained. The obtained sol was transferred to a corundum crucible and placed in an oven to dry at 100°C for 3 h to react and obtain a dry gel solid. The obtained dry gel solid was transferred to a muffle furnace and pre-calcined at 430°C for 7 h. The obtained solid was then transferred to a mortar for thorough grinding and then transferred back to a muffle furnace for calcination at 890°C for 16 h with a heating rate of 2°C / min. After natural cooling to room temperature, the final layered oxide was obtained.

[0087] Example 15

[0088] Na 0.8 Rb 0.1 Cu 0.1 Ni 0.15 Mn 0.65 Preparation of O2 layered oxides:

[0089] Using CH3COONa, CH3COORb·xH2O, Cu(CH3COO)2·H2O, Ni(CH3COO)2·4H2O, and Mn(CH3COO)2·4H2O as metal source materials, each metal source material was weighed in a molar ratio of 0.8×1.10:0.1:0.1:0.15:0.65, with Na source in 10% excess. The materials were dissolved in deionized water and stirred thoroughly to prepare a first solution. Citric acid was weighed and dissolved in deionized water, and stirred thoroughly. The stoichiometric ratio of citric acid to total metal source material was 1.5:1 to prepare a second solution. The second solution was slowly added dropwise to the first... In one solution, during the process, the first solution was continuously stirred in a 90℃ water bath at a stirring speed of 500 r / min for evaporation and concentration until a sol was obtained. The obtained sol was transferred to a corundum crucible and placed in an oven to dry at 120℃ for 6 h to react and obtain a dry gel solid. The obtained dry gel solid was transferred to a muffle furnace and pre-calcined at 470℃ for 5 h. The obtained solid was then transferred to a mortar for thorough grinding and then transferred back to a muffle furnace for calcination at 910℃ for 14 h with a heating rate of 2℃ / min. After natural cooling to room temperature, the final cathode material was obtained.

[0090] Comparative Example 1

[0091] Na 0.67 Ni 0.23 Cu 0.1 Mn 0.67 Preparation of O2 layered oxides

[0092] In this comparative example, the layered oxide structure Na is used. 0.67 Ni 0.23 Cu 0.1 Mn 0.67 O2 was adjusted in terms of raw materials and dosage. The raw materials used were CH3COONa, Ni(CH3COO)2·4H2O, Cu(CH3COO)2·H2O, and Mn(CH3COO)2·4H2O. The addition amounts of each material, except for Na, were adjusted to a 5% excess based on the stoichiometric ratio. The other materials were added according to the stoichiometric ratio in the structural formula, i.e., the molar ratio of the four materials was 0.67×1.05:0.23:0.1:0.67. The specific preparation method was carried out as described in Example 1.

[0093] Comparative Example 2

[0094] Na 0.67 Ni 0.33 Mn 0.67 Preparation of O2 layered oxides

[0095] In this comparative example, the layered oxide structure Na is used.0.67 Ni 0.33 Mn 0.67 O2 was used to adjust the raw materials and dosages, employing CH3COONa (5% excess), Ni(CH3COO)2·4H2O, and Mn(CH3COO)2·4H2O, with a molar ratio of 0.67×1.05:0.33:0.67. The specific preparation method is as described in Example 1.

[0096] The layered oxides prepared in the above embodiments and comparative examples were analyzed and tested:

[0097] 1) Microstructure testing: The microstructure of the layered oxides prepared in the above embodiments and comparative examples was analyzed using scanning electron microscopy (SEM). For example... Figure 1 The images show SEM images of the layered oxides prepared in Examples 1, 1, and 2 of this invention, where (a) corresponds to Example 1, (b) corresponds to 1, and (c) corresponds to 2. The images show that the microstructure of the layered oxides synthesized in Examples 1 and 1 and 2 all exhibits a predominantly polygonal or plate-shaped particle structure, but also includes spherical or near-spherical particles, with an average particle size of approximately 2 μm or slightly smaller. The SEM measurements of the other examples also show similar characteristics. Figure 1 Same characteristics. (By) Figure 1 Comparing the three figures, it can be seen that, compared with the comparative example, the addition of the two doping elements, whether Cu or A metal elements, has no significant effect on the microstructure of the layered oxides prepared in each embodiment of the present invention.

[0098] 2) XRD Analysis of Crystal Structure: XRD diffraction was used to analyze the crystal structure characteristics of the layered oxides prepared in the above embodiments and comparative examples. The XRD analysis results showed that the layered oxides prepared in all embodiments and comparative examples all had a hexagonal layered structure of the P2 type and possessed the P63 / mmc space group. However, compared to Comparative Examples 1 and 2, the XRD patterns of the layered oxides in all embodiments showed a contraction in the interlayer spacing along the c-axis. This indicates that the alkali metal layer of the layered oxides prepared in all embodiments successfully introduced doped metal element A. Metal element A, due to its strong interaction with oxygen in the alkali metal layer, makes it difficult for relative slippage to occur between adjacent layers during deep sodium removal under high pressure. When used as a positive electrode material in sodium-ion batteries, it can suppress unfavorable phase transitions in the positive electrode material, allowing it to maintain the P2 phase during charging and discharging. The irreversible P2-O2 structural phase transition is suppressed, a point supported by subsequent first-principles DFT calculations. For example, as... Figure 2The X-ray diffraction (XRD) patterns of the layered oxides prepared in Example 1, Comparative Example 1, and Comparative Example 2 of this invention are shown. As can be seen from the patterns, the crystal structures of the layered oxides prepared in Example 1 and Comparative Examples 1 and 2 are all hexagonal layered structures with the P63 / mmc space group. The (002) main peak of Example 1 is significantly shifted to the right compared to Comparative Examples 1 and 2. According to the Bragg equation, the rightward shift of this peak indicates that the interlayer spacing in the c-axis direction of the layered oxide of Example 1 has shrunk compared to Comparative Examples 1 and 2. This means that the doped metal element Y has been successfully introduced into the alkali metal layer of the layered oxide of Example 1.

[0099] 3) First-principles DFT calculation:

[0100] To theoretically verify that the layered oxides prepared in each embodiment can suppress the unfavorable P2-O2 structural phase transition of the cathode material due to the entry of metal element A into the alkali metal layer, and thus maintain the P2 phase during charge and discharge, the inventors performed first-principles DFT calculations on the layered oxides with the chemical structural formulas of each embodiment and comparative example, using the total energy of the P2 and O2 phases to explore their thermodynamic stability. Figure 3 The Na of Example 1 is given. 0.67 Y 0.05 Cu 0.1 Ni 0.18 Mn 0.67 O2 layered oxides and Na (Comparative Example 2) 0.67 Ni 0.33 Mn 0.67 The DFT calculation results of the O2 layered oxide, compared with those in the figure, show that the layered oxide of Example 1 ( Figure 3 The "With Y" in the text indicates that the total energy of the P2 phase is lower after Y doping, making it more thermodynamically stable. Therefore, in electrochemical processes, the P2 phase has better thermal stability than the O2 phase, thus suppressing the P2-O2 phase transition. In contrast, the undoped layered oxide in Comparative Example 2... Figure 3 The conclusion is that the total energy of the O2 phase (without Y) is lower and it is more stable, thus making it prone to P2-O2 phase transition during electrochemical processes. Therefore, the layered oxides modified with metal element A in the alkali metal layer exhibit strong interactions with oxygen, and their presence in the Na+ layer is significant. + During the insertion / extraction process, the crystal structure exhibits superior structural stability and is less prone to phase transitions.

[0101] In addition to the layered oxide of Comparative Example 2, the layered oxide of Example 1 contains not only the aforementioned A metal Y element doping, but also transition metal Cu element doping. The two doping elements have a certain synergistic effect: Cu, as a dopant of the transition metal layer, can regulate the electronic structure and charge distribution of the transition metal layer, and also helps to maintain the structural stability of the layered oxide; in addition, after Cu enters the alkali metal layer, it can expand the c-axis, thereby slightly increasing the distance of the alkali metal layer and thus allowing A element to enter with more space. 2+ The Ginger-Taylor distortion effect also exists, and the pillar effect of element A in alkali metals can also alleviate the local distortion of transition metal layers.

[0102] The layered oxides prepared in the above embodiments and comparative examples were applied to sodium-ion batteries: using the layered oxides prepared in the embodiments and comparative examples as positive electrode materials, positive electrode sheets were prepared for assembling sodium-ion batteries. The specific preparation process of the positive electrode sheet and the assembly process of the sodium-ion battery are as follows.

[0103] 1) Preparation of positive electrode:

[0104] Layered oxides were used as the positive electrode active material. They were mixed with conductive carbon black (SP) and binder polyvinylidene fluoride (PVDF) in a mass ratio of 7:2:1 and dissolved in the solvent N-methylpyrrolidone (NMP). After stirring, a uniform slurry was obtained. The slurry was then uniformly coated onto carbon-coated aluminum foil for current collectors and dried in air at 120°C for 3 hours. It was then further dried under vacuum at 120°C for 12 hours to remove NMP. After thorough drying, the slurry was cut into discs with a diameter of 12 mm to obtain the positive electrode sheet.

[0105] 2) Sodium-ion battery assembly:

[0106] The positive electrode sheet prepared above is assembled together with the negative electrode sheet, the electrolyte located between the positive and negative electrodes, and the separator to form a sodium-ion battery. The negative electrode sheet uses hard carbon as the negative electrode material, the electrolyte is a carbonate-based electrolyte, namely: 1M NaClO4 dissolved in PC + 5% FEC solution, and the separator is a glass fiber separator.

[0107] Sodium-ion batteries assembled using layered oxides as cathode materials prepared according to the above embodiments and comparative examples were tested and characterized. The electrochemical test voltage window for the sodium-ion batteries was 2.0–4.3 V, and the test temperature was 25 °C.

[0108] like Figure 4The graph shows the cycle stability test results of sodium-ion batteries using layered oxides as positive electrode materials prepared in Examples 1, 1, and 2 of this invention at a 1C charge-discharge rate. The graph shows that Example 1 retains 89% capacity retention after 100 cycles at a 1C current density, a significant improvement over the 32% capacity retention of Comparative Example 2, and a further improvement over the 79% capacity retention of Comparative Example 1. The improved cycle stability of these examples also demonstrates the reinforcing effect of metal element A entering the alkali metal layer in each example.

[0109] like Figure 5 The figures show the first charge-discharge curves of sodium-ion batteries using layered oxides as positive electrode materials prepared in Examples 1, 1, and 2 of this invention; wherein (a) corresponds to Example 1, (b) corresponds to Example 1, and (c) corresponds to Example 2, at 1C (1C = 150 mAg). -1 At current densities of 2.0–4.3 V, their first-cycle reversible discharge specific capacities within a voltage range of 2.0–4.3 V were 94, 123.4, and 125 mAh g, respectively. -1 Although the reversible specific capacity of the embodiment was slightly lower in the first cycle compared to the comparative example, the capacity decay problem was significantly improved and the cycle stability was significantly enhanced after a certain number of cycles. Furthermore, multiple voltage plateaus were observed in the charge-discharge curve of the comparative example, with a clear phase transition plateau at 4.2V. After the metal element entered the alkali metal layer, the voltage plateau at 4V disappeared, exhibiting a sloping and smooth state, indicating a single-phase solid solution reaction. The plateau representing the phase transition at 4.2V was significantly shortened, proving that the phase transition problem was improved and the structural stability was enhanced after doping. The disappearance of the voltage plateau at 3.5V also indicates that Na in the cathode material... + The disordered structure of vacant sites is broken, which also helps to improve Na + Diffusion in the structure.

[0110] like Figure 6 The graph shows the rate performance of sodium-ion batteries using the layered oxides prepared in Example 1, Comparative Example 1, and Comparative Example 2 as cathode materials. The graph shows that Example 1 exhibits excellent rate performance, maintaining high specific capacity even at high current densities. This indicates that the Y metal ions in the layered oxide of Example 1, after entering the alkali metal layer, break down the Na+ layer. + The ordered structure of vacant spaces improves Na + The diffusion capacity within the structure, as demonstrated in the other embodiments, also exhibits similar characteristics. The design of the layered oxide of this invention provides a new approach for fast-charging cathode materials.

[0111] The material characteristics and electrochemical performance indicators described above are given in conjunction with Example 1. Test results from other examples show that they exhibit completely similar characteristics. The electrochemical performance indicators of each example and comparative example are shown in Table 1.

[0112] Table 1 summarizes the test data of sodium-ion batteries assembled using positive electrode materials in Examples 1-15 and Comparative Examples 1-2.

[0113]

[0114]

Claims

1. A layered oxide, characterized in that: The chemical formula of the layered oxide is Na. n [A a Cu b Ni c Mn d O2 is a two-dimensional layered structure composed of alternating layers of transition metals and alkali metals; its crystal structure is a hexagonal layered structure of type P2 with the space group P63 / mmc. Cu, Ni, and Mn are present in the transition metal layer, forming a transition metal oxygen octahedron with O; Na and A are metal elements present in the alkali metal layer; Ni and Mn are matrix elements constituting the layered oxide, and Cu and A are co-doping elements forming the layered oxide. Element A is selected from the ionic radius range. It is a metallic element with only one valence state, and element A is distributed in groups IA and IIA and subgroups IIB and IIIB of the periodic table, with d electron orbital configurations of d0 or d10.

2. The layered oxide according to claim 1, characterized in that: In the general chemical formula, 0.6≤n≤0.8, 0.03≤a≤0.1, 0.05≤b≤0.1, 0.15≤c≤0.23, 0.65≤d≤0.69, and a+b+c+d=1.

3. The layered oxide according to claim 1, characterized in that: In the general chemical formula, element A is selected from any one of the elements Mg, Ca, Zn, Cu, Sr, Y, and Rb.

4. A layered oxide according to claim 1, characterized in that: The layered oxide has a microstructure consisting of spherical, near-spherical, polygonal, or plate-shaped particles with an average particle size ≤2μm.

5. A method for preparing a layered oxide according to any one of claims 1-4, characterized in that, Includes the following steps: Step S10: Mix the various metal sources, including sodium source, A source, copper source, nickel source and manganese source, in deionized water to prepare the first solution; Step S20: Dissolve the complexing agent in deionized water to prepare a second solution; Step S30: The second solution is added dropwise to the first solution. During this dropwise addition, the first solution is kept in a water bath and reacts with the added second solution in a water bath to obtain a sol. Step S40: The sol is placed in an oven for drying to obtain a solid. In step S50, the solid is pre-fired at a first temperature and kept at that temperature for a first time period; then it is calcined at a second temperature and kept at that temperature for a second time period, and then naturally cooled to room temperature to obtain the layered oxide.

6. The method for preparing a layered oxide according to claim 5, characterized in that: In step S10, each metal source is at least one of acetate, sulfate, and nitrate; in step S20, the complexing agent is selected from at least one of citric acid and oxalic acid, and the stoichiometric molar ratio of the amount of complexing agent to the total amount of each metal source is 1:1 to 1.5:

1.

7. The method for preparing a layered oxide according to claim 5, characterized in that: The water bath reaction described in step S30 refers to evaporation and concentration in a water bath at 70-90°C to obtain the sol; the drying reaction described in step S40 refers to heat treatment in an oven at 100-120°C for 3-6 hours. In step S50, the first temperature is 430–470°C and the first time period is 5–7 hours; the second temperature is 890–910°C and the second time period is 14–16 hours.

8. The method for preparing a layered oxide according to claim 5, characterized in that: In step S10, the amounts of the A source, copper source, nickel source, and manganese source added to the first solution are based on the molecular formula Na of the prepared layered oxide. n [A a Cu b Ni c Mn d The stoichiometric ratio of O2 is used for weighing; while the amount of Na source is added in excess of 2% to 10%, that is, the amount of sodium source added to A source, copper source, nickel source and manganese source meets the molar ratio: (1.02n to 1.10n): a:b:c:d.

9. A sodium-ion battery positive electrode, characterized in that: The sodium-ion battery cathode uses the layered oxide described in any one of claims 1-4 as the cathode active material.

10. A sodium-ion battery, characterized in that: The sodium-ion battery includes the positive electrode as described in claim 9.

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