Air-stabilized oxygen-laden cathode materials and their preparation methods, cathode sheets and sodium-ion batteries

Abstract

The present invention provides an air-stable layered oxygen cathode material, a preparation method thereof, a cathode sheet and a sodium-ion battery, relating to the technical field of sodium-ion batteries. The air-stable layered oxygen cathode material includes an O3-type layered metal oxide and a Li3PO4-MgO amorphous passivation layer, which is coated on the surface of the O3-type layered metal oxide. The chemical general formula of the O3-type layered metal oxide is Na 1‑2x Ca x (Ni a Cu b Fe c Mn d ) 1‑y Zn y O2, where 0 < x ≤ 0.075, 0 ≤ y ≤ 0.1, 0.2 ≤ a ≤ 0.3, 0 ≤ b ≤ 0.1, 0.3 ≤ c ≤ 0.4, 0.3 ≤ d ≤ 0.4, and a + b + c + d = 1. The air-stable layered oxygen cathode material of the present application has a stable crystal structure, a suitable layer spacing, excellent Na + diffusion channels and air stability.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, and more specifically, to an air-stabilized layered oxygen cathode material, its preparation method, cathode sheet, and sodium-ion battery. Background Technology

[0002] Sodium-ion batteries, as an emerging electrochemical energy storage technology, have attracted widespread attention from the global scientific and industrial communities due to their unique performance characteristics. Compared with lithium-ion batteries, sodium-ion batteries not only demonstrate comparable energy density but also possess significant advantages such as lower energy loss and more economical manufacturing costs. Especially in large-scale energy storage applications, the potential of sodium-ion batteries cannot be underestimated, thanks to the abundant reserves and low price of sodium on Earth. O3-type layered transition metal oxides are considered a highly attractive choice for cathode materials in sodium-ion batteries due to their high theoretical specific capacity, simple synthesis process, and low cost. However, these materials face key challenges: the inherent instability of the layered structure and the relationship between sodium and... + The limitations of ion diffusion pathways and these two factors together restrict its cycle stability and rate performance in practical applications.

[0003] A major challenge of O3-type layered transition metal oxide cathode materials stems from their surface characteristics: free sodium ions and strongly alkaline groups (such as Na-O / Na-OH) readily react chemically with water vapor and carbon dioxide when exposed to air, forming a non-conductive, inert passivation layer such as sodium carbonate. This layer not only physically blocks the transport pathway of sodium ions, affecting the Na+ ion transport process... + The efficiency of insertion and extraction can lead to distortion of the material's lattice structure, affecting its stability and electrochemical performance. More importantly, this process may trigger chemical reactions inside the battery, increasing internal resistance, reducing energy efficiency, and creating safety hazards under extreme conditions, such as thermal runaway or gas generation. Traditional solutions remove alkaline residues from the material surface using acidic solutions, but this method can easily cause over-etching of the material's bulk structure, resulting in capacity loss exceeding 15%. This structural damage further affects the material's cycle performance and lifespan. Encapsulating the material in an inert gas environment (such as argon) to isolate it from moisture and carbon dioxide in the air is also an option, but this method is expensive, costing over 150 yuan / kg, which is a heavy economic burden for large-scale production. Depositing an oxide layer (such as Al2O3 or SiO2) on the material surface can protect it from environmental corrosion. However, when the coating thickness exceeds 5nm, it significantly increases interfacial impedance, causing the battery's internal resistance to increase by more than 200%, affecting the Na+... + Transmission efficiency and overall battery performance. Summary of the Invention

[0004] The main objective of this invention is to provide an air-stable layered oxygen cathode material and its preparation method, cathode sheet, and sodium-ion battery, to solve the problems of unstable layered structure and Na+ in existing O3-type layered transition metal oxides. + The problems include poor diffusion channels and poor air stability.

[0005] To achieve the above objectives, according to one aspect of the present invention, an air-stabilized layered oxygen cathode material is provided, comprising: an O3-type layered metal oxide and a Li3PO4-MgO amorphous passivation layer coated on the surface of the O3-type layered metal oxide; the chemical formula of the O3-type layered metal oxide is Na. 1-2x Ca x (Ni a Cu b Fe c Mn d ) 1-y Zn y O2, where 0 <x≤0.075,0≤y≤0.1,0.2≤a≤0.3,0≤b≤0.1,0.3≤c≤0.4,0.3≤d≤0.4,a+b+c+d=1。

[0006] Furthermore, the thickness of the above-mentioned Li3PO4-MgO amorphous passivation layer is 1~10nm; and / or, the molar ratio of Li3PO4 to MgO in the Li3PO4-MgO amorphous passivation layer is 1:(0.3~3); and / or, the O3-type layered metal oxide is formed by stacking sheet-like particles, the average thickness of the sheet-like particles is 50~200nm, and the average sheet diameter is 1~2µm.

[0007] Furthermore, 0.025 ≤ x ≤ 0.06; and / or, 0.015 ≤ y ≤ 0.075.

[0008] Furthermore, the aforementioned O3-type layered metal oxide is Na. 0.9 Ca 0.05 (Ni 0.24 Cu 0.05 Fe 0.36 Mn 0.35 ) 0.975 Zn 0.025 O2.

[0009] Furthermore, the surface sodium ion content of the aforementioned air-stabilized laminar oxygen cathode material is 15-20%.

[0010] According to another aspect of the present invention, a method for preparing the aforementioned air-stabilized layered oxygen cathode material is provided, the method comprising: S1, mixing a sodium source and a Ni a Cu b Fec Mn d (OH)2 and the dopant source are mixed and then calcined to obtain O3-type layered metal oxide; wherein the dopant source is a calcium source, or a combination of calcium and zinc sources, and a, b, c, d are the same as a, b, c, d in any of 1 to 5; S2, the O3-type layered metal oxide, phosphorus source and LiCl-MgCl2 mixed molten salt are mixed and then sintered to form a Li3PO4-MgO amorphous passivation layer on the surface of the O3-type layered metal oxide, thereby obtaining an air-stable layered oxygen cathode material.

[0011] Further, the mass ratio of the above-mentioned O3-type layered metal oxide to the total mass of the LiCl-MgCl2 mixed molten salt and phosphorus source is (50~200):2.85; and / or, the calcination temperature is 850~925℃; and / or, the heating rate of the calcination is 1~5℃ / min; and / or, the holding time of the calcination is 10~20h; and / or, the sintering process includes a first sintering process and a second sintering process performed sequentially, the temperature of the first sintering process is 400~900℃; and / or, the time of the first sintering process is 3.5~11h; and / or, the temperature of the second sintering process is 500~800℃; and / or, the time of the second sintering process is 6~16h.

[0012] Furthermore, the aforementioned first sintering treatment includes a first stage, a second stage, a third stage, and a cooling stage performed sequentially. The atmosphere of the first stage is a hydrogen-argon mixed atmosphere, the temperature is 400~500℃, and the time is 2~4h; and / or, the atmosphere of the second stage is an oxygen atmosphere, the temperature is 600~800℃, and the time is 1~5h; and / or, the atmosphere of the third stage is an air atmosphere, the temperature is 750~900℃, and the time is 0.5~2h; and / or, the cooling rate of the cooling stage is 2~20℃ / min.

[0013] According to another aspect of the present invention, a positive electrode is provided, which contains the aforementioned air-stabilized layered oxygen positive electrode material.

[0014] According to another aspect of the present invention, a sodium-ion battery is provided, comprising a positive electrode, an electrolyte, and a negative electrode, wherein the positive electrode is the aforementioned positive electrode.

[0015] The beneficial effects of this application using the technical solution of the present invention are as follows: The presence of the Li3PO4-MgO amorphous passivation layer in this application helps to reduce the sodium ion content on the surface of the air-stable layered oxygen cathode material, thereby helping to reduce the reaction of sodium ions with water and carbon dioxide in the air to form an inert passivation layer; on the other hand, it acts as a physical barrier, blocking the penetration of water and carbon dioxide in the air and preventing the O3-type layered transition metal oxide from reacting with water and carbon dioxide in the air. The doping of Ca in the O3-type layered metal oxide helps to protect the active material from degradation during environmental electrode processing, maintaining its structural integrity and crystallinity. Furthermore, the doping of Ca helps to suppress the occurrence of side reactions. More importantly, the doping of Ca helps to stabilize the crystal structure of the O3-type layered transition metal oxide, expanding the interlayer spacing, thereby facilitating the formation of an inert passivation layer. + The embedding / de-embedding of Na helps to improve Na + The diffusion kinetics of the nanoparticles are improved, reducing volume expansion during electrochemical sodium formation and enhancing battery cycle performance. Zinc doping helps suppress side reactions and reduce volume changes during charge and discharge, further improving the cycle performance of the air-stabilized layered oxygen cathode material. Therefore, the air-stabilized layered oxygen cathode material of this application possesses a stable crystal structure, suitable interlayer spacing, and excellent Na+ diffusion kinetics. + Diffusion channels and air stability. Attached Figure Description

[0016] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0017] Figure 1 SEM images of the air-stabilized layered oxygen cathode material in Embodiment 2 of this application are shown;

[0018] Figure 2 SEM images of the air-stabilized layered oxygen cathode material in Embodiment 5 of this application are shown;

[0019] Figure 3 SEM images of the air-stabilized layered oxygen cathode material in Comparative Example 1 of this application are shown;

[0020] Figure 4 The XRD comparison diagrams of Embodiments 2, 5, Comparative Example 1 and Comparative Example 2 of this application are shown. Detailed Implementation

[0021] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0022] As analyzed in the background section of this application, in the prior art, O3-type layered transition metal oxides exhibit unstable layered structures and Na... + To address the issues of poor diffusion channels and poor air stability, this application provides an air-stable layered oxygen cathode material, its preparation method, cathode sheet, and sodium-ion battery.

[0023] In a typical embodiment of this application, an air-stabilized layered oxygen cathode material is provided, comprising: an O3-type layered metal oxide and a Li3PO4-MgO amorphous passivation layer, coated on the surface of the O3-type layered metal oxide; the general chemical formula of the O3-type layered metal oxide is Na. 1-2x Ca x (Ni a Cu b Fe c Mn d ) 1- y Zn y O2, where 0 <x≤0.075,0≤y≤0.1,0.2≤a≤0.3,0≤b≤0.1,0.3≤c≤0.4,0.3≤d≤0.4,a+b+c+d=1。

[0024] The presence of the Li3PO4-MgO amorphous passivation layer in this application helps to reduce the sodium ion content on the surface of the air-stabilized layered oxygen cathode material, thereby reducing the reaction of sodium ions with water and carbon dioxide in the air to form an inert passivation layer. On the other hand, it acts as a physical barrier, blocking the penetration of water and carbon dioxide from the air and preventing the O3-type layered transition metal oxide from reacting with water and carbon dioxide in the air. Ca doping in the O3-type layered metal oxide helps protect the active material from degradation during environmental electrode processing, maintaining its structural integrity and crystallinity. Furthermore, Ca doping helps suppress side reactions. More importantly, Ca doping helps stabilize the crystal structure of the O3-type layered transition metal oxide, increasing the interlayer spacing, which is beneficial for Na… + The embedding / de-embedding of Na helps to improve Na + The diffusion kinetics of the nanoparticles are improved, reducing volume expansion during electrochemical sodium formation and enhancing battery cycle performance. Zinc doping helps suppress side reactions and reduce volume changes during charge and discharge, further improving the cycle performance of the air-stabilized layered oxygen cathode material. Therefore, the air-stabilized layered oxygen cathode material of this application possesses a stable crystal structure, suitable interlayer spacing, and excellent Na+ diffusion kinetics. + Diffusion channels and air stability.

[0025] In one embodiment of this application, the thickness of the above-mentioned Li3PO4-MgO amorphous passivation layer is 1~10nm; and / or, the molar ratio of Li3PO4 to MgO in the Li3PO4-MgO amorphous passivation layer is 1:(0.3~3), specifically 1:0.3, 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5, 1:3 and any range between two ratios; and / or, the O3-type layered metal oxide is formed by stacking sheet-like particles, the average thickness of the sheet-like particles is 50~200nm, and the average sheet diameter is 1~2µm.

[0026] Controlling the thickness of the Li3PO4-MgO amorphous passivation layer within the aforementioned range helps to effectively isolate moisture and carbon dioxide from the air while ensuring that the air-stable layered oxygen cathode material has a low interfacial resistance, thus enabling Na… + Rapid transport between the air-stabilized layered oxygen cathode material and the electrolyte optimizes the rate and cycle performance of the battery. Controlling the molar ratio of Li3PO4 to MgO within the aforementioned range helps improve the structural stability of the Li3PO4-MgO amorphous passivation layer. Controlling the average thickness and average diameter of the lamellar particles within the aforementioned range helps increase the specific surface area of ​​the air-stabilized layered oxygen cathode material and promotes Na+ absorption. + Embedding and de-embedding.

[0027] In one embodiment of this application, 0.025≤x≤0.06, where x can specifically be 0.025, 0.03, 0.035, 0.04, 0.045, 0.05, 0.055, 0.06, or any value between two values; and / or, 0.015≤y≤0.075, where y can specifically be 0.015, 0.02, 0.025, 0.03, 0.035, 0.04, 0.045, 0.05, 0.055, 0.06, 0.065, 0.07, 0.075, or any value between two values.

[0028] Ca doping effectively stabilizes the crystal structure of O3-type layered oxide air-stabilized layered oxygen cathode materials. Ca ions have a relatively large ionic radius (approximately 0.99 Å), while Na ions have an ionic radius of approximately 0.95 Å. When Ca ions partially replace Na ions in the crystal lattice, they occupy the transition metal layer (TM layer) instead of the sodium layer. This process effectively expands the interlayer distance, promoting Na doping. +The successful insertion and extraction of Ca and Zn mitigates the volume expansion and contraction of the material during charging and discharging, thereby improving its structural stability. The addition of Zn reduces the activity of the charge compensation mechanism and decreases redox reactions during charging and discharging, thus reducing structural changes during cycling and improving the material's cycle stability. Controlling the values ​​of x and y within the aforementioned range helps enhance the synergistic effect between the two elements. Ca provides direct structural support by increasing the interlayer spacing, while Zn provides indirect support by enhancing the framework rigidity. The synergistic effect of the two elements optimizes the structure of the layered oxide air-stabilized layered oxygen cathode material, making it more stable during cycling and reducing structural degradation and performance decline.

[0029] To further enhance the synergistic effect between Ca and Zn elements, thereby improving the structural stability of air-stabilized layered oxygen cathode materials and Na... + Regarding diffusion efficiency and air stability, in one embodiment of this application, the aforementioned O3-type layered metal oxide is selected from Na. 0.9 Ca 0.05 (Ni 0.24 Cu 0.05 Fe 0.36 Mn 0.35 ) 0.975 Zn 0.025 O2, Na 0.9 Ca 0.05 (Ni 0.24 Cu 0.05 Fe 0.36 Mn 0.35 ) 0.95 Zn 0.05 O2 and Na 0.9 Ca 0.05 (Ni 0.24 Cu 0.05 Fe 0.36 Mn 0.35 ) 0.925 Zn 0.075 Any one or more of O2.

[0030] In one embodiment of this application, the aforementioned O3-type layered metal oxide is Na. 0.9 Ca 0.05 (Ni 0.24 Cu 0.05 Fe 0.36 Mn 0.35 ) 0.975 Zn 0.025 O2.

[0031] O3-type layered metal oxides with the above chemical formula have a more stable crystal structure and interlayer spacing, which helps to improve Na +This improves the diffusion kinetics performance, thereby helping to enhance the rate performance and cycle stability of sodium-ion batteries.

[0032] In one embodiment of this application, the surface sodium ion content of the air-stabilized laminar oxygen cathode material is 15-20%.

[0033] Controlling the sodium ion content on the surface of the air-stabilized layered oxygen cathode material within the above-mentioned range helps to reduce the reaction of sodium ions with water and carbon dioxide in the air to form an inert passivation layer, thereby helping to reduce the interfacial impedance of the air-stabilized layered oxygen cathode material and thus helping to improve the rate performance of the battery.

[0034] In another typical embodiment of this application, a method for preparing the aforementioned air-stabilized layered oxygen cathode material is provided, the method comprising: S1, mixing a sodium source and Ni... a Cu b Fe c Mn d (OH)2 and the dopant source are mixed and then calcined to obtain O3-type layered metal oxide; wherein the dopant source is a calcium source, or a combination of calcium and zinc sources, and a, b, c, d are the same as a, b, c, d mentioned above; S2, the O3-type layered metal oxide, phosphorus source and LiCl-MgCl2 mixed molten salt are mixed and then sintered to form a Li3PO4-MgO amorphous passivation layer on the surface of the O3-type layered metal oxide, thereby obtaining an air-stable layered oxygen cathode material.

[0035] In step S1, Ni a Cu b Fe c Mn dThe mixture of (OH)2, sodium source, and dopant source undergoes calcination, which helps to form a stable O3-type layered metal oxide. In step S2, the O3-type layered metal oxide, LiCl-MgCl2 mixed molten salt, and phosphorus source are mixed and then sintered. During sintering, the high temperature causes the LiCl-MgCl2 mixed molten salt to decompose, releasing lithium ions, magnesium ions, etc., and the phosphorus source also undergoes thermal decomposition. The surface ions of the O3-type layered metal oxide exhibit enhanced activity at high temperatures, and diffuse and migrate with ions from the molten salt decomposition and ions generated by the phosphorus source. Lithium ions combine with phosphate ions in the phosphorus source to form lithium phosphate nuclei on the material surface, which then continue to grow. Simultaneously, magnesium ions combine with oxygen to form magnesium oxide nuclei, which also continue to grow. Due to the complex reaction conditions and ion diffusion, lithium phosphate and magnesium oxide do not form regular crystals, but rather form an amorphous structure, gradually covering the surface of the O3-type layered metal oxide, ultimately forming a Li3PO4-MgO amorphous passivation layer. Furthermore, the surface ions of Li3PO4, MgO, and O3-type layered metal oxides are chemically bonded, resulting in a tight bond between the passivation layer and the substrate, stably providing passivation protection. The Li3PO4-MgO amorphous passivation layer acts as a physical barrier, preventing the penetration of water and carbon dioxide from the air and avoiding reactions between the O3-type layered transition metal oxides and water and carbon dioxide in the air. Moreover, during the sintering process, Li... + / Mg 2 + Ion replacement reduces the sodium ion content on the surface of air-stabilized layered oxygen cathode materials, thereby helping to reduce the probability of sodium ions reacting with water and carbon dioxide in the air to form an inert passivation layer. The addition of a Ca source helps stabilize the crystal structure of O3-type layered transition metal oxides and expands the interlayer spacing, which is beneficial for Na... + The embedding / de-embedding of Na helps to improve Na + The diffusion kinetics of the zinc source are improved, reducing volume expansion during electrochemical sodium formation and enhancing battery cycle performance. The addition of a zinc source helps suppress side reactions and reduce volume changes during charge and discharge, thus further improving the cycle performance of the air-stabilized layered oxygen cathode material. The above preparation method is simple, and the air-stabilized layered oxygen cathode material prepared using this method possesses a stable crystal structure, suitable interlayer spacing, and excellent Na+ diffusion kinetics. + Diffusion channels and air stability.

[0036] Including but not limited to, the sodium source is selected from sodium carbonate and / or sodium bicarbonate; the calcium source is selected from calcium carbonate and / or calcium hydroxide; the zinc source is selected from any one or more of zinc acetate, zinc oxide and zinc hydroxide; and the phosphorus source is selected from any one or more of NaH2PO4, Na2HPO4 and NH4H2PO4.

[0037] In one embodiment of this application, the mass ratio of the above-mentioned O3-type layered metal oxide to the total mass of the LiCl-MgCl2 mixed molten salt and phosphorus source is (50~200):2.85; and / or, the calcination temperature is 850~925℃; and / or, the heating rate of the calcination is 1~5℃ / min; and / or, the holding time of the calcination is 10~20h; and / or, the sintering process includes a first sintering process and a second sintering process performed sequentially, the temperature of the first sintering process is 400~900℃; and / or, the time of the first sintering process is 3.5~11h; and / or, the temperature of the second sintering process is 500~800℃; and / or, the time of the second sintering process is 6~16h.

[0038] Controlling the calcination temperature and time within the aforementioned range helps improve the crystal structure stability and purity of the O3-type layered metal oxide. Controlling the heating rate during calcination within the aforementioned range helps improve the thermal uniformity of the internal structure of the material, thereby further enhancing the crystal structure stability of the O3-type layered metal oxide. Controlling the mass ratio of O3-type layered metal oxide, LiCl-MgCl2 mixed molten salt, and phosphorus source within the aforementioned range helps control the thickness of the final Li3PO4-MgO amorphous passivation layer. This helps to effectively isolate moisture and carbon dioxide from the air while ensuring the air-stable layered oxygen cathode material has a low interfacial resistance, allowing Na... + Rapid transport between the air-stabilized layered oxygen cathode material and the electrolyte optimizes the rate performance and cycle performance of the battery. Controlling the temperature and time of the first sintering treatment within the aforementioned range helps promote the formation and purity of the Li3PO4-MgO amorphous passivation layer. Water washing removes residual molten salt from the surface of the air-stabilized layered oxygen cathode material. Controlling the temperature and time of the second sintering treatment within the aforementioned range further improves the stability of the Li3PO4-MgO amorphous passivation layer.

[0039] In one embodiment of this application, the first sintering process includes a first stage, a second stage, a third stage, and a cooling stage performed sequentially. The atmosphere of the first stage is a hydrogen-argon mixed atmosphere, the temperature is 400~500℃, and the time is 2~4h; and / or, the atmosphere of the second stage is an oxygen atmosphere, the temperature is 600~800℃, and the time is 1~5h; and / or, the atmosphere of the third stage is an air atmosphere, the temperature is 750~900℃, and the time is 0.5~2h; and / or, the cooling rate of the cooling stage is 2~20℃ / min.

[0040] Controlling the atmosphere, temperature, and time in the first stage within the aforementioned ranges helps to liquefy the LiCl-MgCl2 mixed molten salt. + / Mg2+ With surface Na + The replacement process is carried out; controlling the atmosphere, temperature, and time in the second stage within the above range helps to promote the decomposition of molten salt to generate the Li3PO4-MgO amorphous passivation layer; controlling the atmosphere, temperature, time, and cooling rate in the third stage within the above range helps to reduce the oxygen vacancy concentration of the air-stabilized layered oxygen cathode material on the one hand, and helps to repair the spinel phase of the material on the other hand, thereby helping to improve the structural stability of the air-stabilized layered oxygen cathode material.

[0041] In another typical embodiment of this application, a positive electrode is provided, which contains the aforementioned air-stabilized layered oxygen positive electrode material.

[0042] Because the above-mentioned positive electrode contains the air-stabilized layered oxygen positive electrode material of this application, the positive electrode has high rate performance and cycle stability.

[0043] In another typical embodiment of this application, a sodium-ion battery is provided, including a positive electrode, an electrolyte, and a negative electrode, wherein the positive electrode is the aforementioned positive electrode.

[0044] Because the positive electrode in the above-mentioned sodium-ion battery contains the air-stabilized layered oxygen positive electrode material of this application, the sodium-ion battery has high rate performance, cycle stability and safety.

[0045] The beneficial effects of this application will be further illustrated below with reference to the embodiments.

[0046] Example 1

[0047] Using anhydrous ethanol as a solvent, the required sodium carbonate is reacted with calcium carbonate and Ni. 0.24 Cu 0.05 Fe 0.36 Mn 0.35 (OH)₂ is composed of sodium, calcium, and Ni elements. 0.24 Cu 0.05 Fe 0.36 Mn 0.35 The molar ratio of (OH)₂ was 0.95:0.025:1, and the mixture was ground uniformly. After thorough mixing in a high-speed mixer, the sample was placed in a muffle furnace for calcination at 850℃ at a heating rate of 5℃ / min. Calcination was carried out at this temperature for 10 hours. After calcination, the muffle furnace was turned off, and the sample was allowed to cool naturally to room temperature. The sample was then crushed and sieved to obtain the molecular formula Na. 0.95 Ca 0.025 (Ni 0.24 Cu 0.05 Fe 0.36 Mn 0.35O3-type layered metal oxides of O2. O3-type layered metal oxides are mixed with a LiCl-MgCl2 molten salt and NaH2PO4. 4‌ A mixture was prepared by mixing LiCl and MgCl2 in a mass ratio of 100:1.85:1, resulting in a LiCl-MgCl2 mixed molten salt with a mass ratio of 1.35:1. The mixture underwent a first sintering treatment: sintering was performed in an Ar / H2 mixed atmosphere (5% hydrogen by volume) at 400℃ for 2 hours; followed by a second sintering in an O2 atmosphere at 600℃ for 1 hour; and then a third sintering in an air atmosphere at 750℃ for 0.5 hours. Finally, the mixture was cooled to room temperature at a rate of 20℃ / min to obtain the sintered product. The sintered product was washed with water to remove residual molten salt, dried under vacuum at 80℃ for 10 hours, and then subjected to a second sintering treatment in an air atmosphere at 500℃ for 6 hours. After sieving, Na was obtained. 0.95 Ca 0.025 (Ni 0.24 Cu 0.05 Fe 0.36 Mn 0.35 An air-stabilized layered oxygen cathode material with an O2 surface coated with an amorphous passivation layer of Li3PO4-MgO, wherein the Na content was measured using SEM. 0.95 Ca 0.025 (Ni 0.24 Cu 0.05 Fe 0.36 Mn 0.35 The average thickness of the O2 flake particles is 100 nm, and the average flake diameter is 1.3 µm. The thickness of the Li3PO4-MgO amorphous passivation layer was measured to be 3.5 nm using TEM. The molar ratio of Li3PO4 to MgO in the Li3PO4-MgO amorphous passivation layer was measured to be 1:1 using XPS.

[0048] Example 2

[0049] The difference from Example 1 is that sodium carbonate is mixed with calcium carbonate and Ni. 0.24 Cu 0.05 Fe 0.36 Mn 0.35 Sodium, calcium and Ni in (OH)2 0.24 Cu 0.05 Fe 0.36 Mn 0.35 The molar ratio of (OH)₂ is 0.9:0.05:1, ultimately yielding Na. 0.9 Ca 0.05 (Ni 0.24 Cu 0.05 Fe 0.36 Mn 0.35Air-stabilized layered oxygen cathode material with an O2 surface coated with an amorphous passivation layer of Li3PO4-MgO.

[0050] Example 3

[0051] The difference from Example 1 is that the calcination temperature was 925°C, ultimately yielding Na. 0.95 Ca 0.025 (Ni 0.24 Cu 0.05 Fe 0.36 Mn 0.35 Air-stabilized layered oxygen cathode material with an O2 surface coated with a Li3PO4-MgO amorphous passivation layer, wherein Na 0.95 Ca 0.025 (Ni 0.24 Cu 0.05 Fe 0.36 Mn 0.35 The average thickness of the O2 flake particles is 150 nm, and the average flake diameter is 1.7 µm.

[0052] Example 4

[0053] The difference from Example 1 is that sodium carbonate is mixed with calcium carbonate and Ni. 0.24 Cu 0.05 Fe 0.36 Mn 0.35 Sodium, calcium and Ni in (OH)2 0.24 Cu 0.05 Fe 0.36 Mn 0.35 The molar ratio of (OH)₂ was 0.9:0.05:1, and the calcination temperature was 925℃, ultimately yielding Na. 0.9 Ca 0.05 (Ni 0.24 Cu 0.05 Fe 0.36 Mn 0.35 Air-stabilized layered oxygen cathode material with an O2 surface coated with a Li3PO4-MgO amorphous passivation layer

[0054] Example 5

[0055] Using anhydrous ethanol as a solvent, the required sodium carbonate, calcium carbonate, and Ni are... 0.24 Cu 0.05 Fe 0.36 Mn 0.35 (OH)₂ reacts with zinc acetate according to sodium, calcium, and Ni elements. 0.24 Cu 0.05 Fe 0.36 Mn 0.35The molar ratio of (OH)₂ to zinc was 0.9:0.05:0.975:0.025. The mixture was then ground uniformly. After thorough mixing in a high-speed mixer, the sample was placed in a muffle furnace for calcination at 850℃ at a heating rate of 5℃ / min. Calcination was carried out at this temperature for 10 hours. After calcination, the muffle furnace was turned off, and the sample was allowed to cool naturally to room temperature. The sample was then crushed and sieved to obtain a sample with the molecular formula Na. 0.9 Ca 0.05 (Ni 0.24 Cu 0.05 Fe 0.36 Mn 0.35 ) 0.975 Zn 0.025 O3-type layered metal oxides of O2. O3-type layered metal oxides are mixed with a LiCl-MgCl2 molten salt and NaH2PO4. 4‌ A mixture was prepared by mixing LiCl and MgCl2 in a mass ratio of 100:1.85:1, resulting in a LiCl-MgCl2 mixed molten salt with a mass ratio of 1.35:1. The mixture was then subjected to a first-stage sintering at 400℃ for 2 hours under an Ar / H2 mixed atmosphere (5% hydrogen by volume). A second-stage sintering was then performed at 600℃ for 1 hour under an O2 atmosphere, followed by a third-stage sintering at 750℃ for 0.5 hours under an air atmosphere. Finally, the mixture was cooled to room temperature at a rate of 20℃ / min to obtain the sintered product. The sintered product was washed with water to remove residual molten salt, dried under vacuum at 80℃ for 10 hours, and then subjected to a second sintering treatment at 500℃ for 6 hours under an air atmosphere. After sieving, Na was obtained. 0.9 Ca 0.05 (Ni 0.24 Cu 0.05 Fe 0.36 Mn 0.35 ) 0.975 Zn 0.025 Air-stabilized layered oxygen cathode material with an O2 surface coated with an amorphous passivation layer of Li3PO4-MgO.

[0056] Example 6

[0057] The difference from Example 5 is that sodium carbonate, calcium carbonate, and Ni are used. 0.24 Cu 0.05 Fe 0.36 Mn 0.35 (OH)₂ reacts with sodium, calcium, and Ni elements in zinc acetate. 0.24 Cu 0.05 Fe 0.36 Mn 0.35The molar ratio of (OH)₂ to zinc is 0.9:0.05:0.95:0.05, ultimately yielding Na. 0.9 Ca 0.05 (Ni 0.24 Cu 0.05 Fe 0.36 Mn 0.35 ) 0.95 Zn 0.05 Air-stabilized layered oxygen cathode material with an O2 surface coated with an amorphous passivation layer of Li3PO4-MgO.

[0058] Example 7

[0059] The difference from Example 5 is that sodium carbonate, calcium carbonate, and Ni are used. 0.24 Cu 0.05 Fe 0.36 Mn 0.35 (OH)₂ reacts with sodium, calcium, and Ni elements in zinc acetate. 0.24 Cu 0.05 Fe 0.36 Mn 0.35 The molar ratio of (OH)₂ to zinc is 0.9:0.05:0.925:0.075, ultimately yielding Na. 0.9 Ca 0.05 (Ni 0.24 Cu 0.05 Fe 0.36 Mn 0.35 ) 0.925 Zn 0.075 Air-stabilized layered oxygen cathode material with an O2 surface coated with an amorphous passivation layer of Li3PO4-MgO.

[0060] Example 8

[0061] The difference from Example 5 is that sodium carbonate, calcium carbonate, and Ni are used. 0.24 Cu 0.05 Fe 0.36 Mn 0.35 (OH)₂ reacts with sodium, calcium, and Ni elements in zinc acetate. 0.24 Cu 0.05 Fe 0.36 Mn 0.35 The molar ratio of (OH)₂ to zinc is 0.9:0.05:0.9:0.1, ultimately yielding Na. 0.9 Ca 0.05 (Ni 0.24 Cu 0.05 Fe 0.36 Mn 0.35 ) 0.9 Zn 0.1Air-stabilized layered oxygen cathode material with an O2 surface coated with an amorphous passivation layer of Li3PO4-MgO.

[0062] Example 9

[0063] The difference from Example 1 is that sodium carbonate is mixed with calcium carbonate and Ni. 0.24 Cu 0.05 Fe 0.36 Mn 0.35 Sodium, calcium and Ni in (OH)2 0.24 Cu 0.05 Fe 0.36 Mn 0.35 The molar ratio of (OH)₂ is 0.85:0.075:1, ultimately yielding Na. 0.85 Ca 0.075 (Ni 0.24 Cu 0.05 Fe 0.36 Mn 0.35 Air-stabilized layered oxygen cathode material with an O2 surface coated with an amorphous passivation layer of Li3PO4-MgO.

[0064] Example 10

[0065] The difference from Example 1 is that the calcination temperature was 950°C, ultimately yielding Na. 0.95 Ca 0.025 (Ni 0.24 Cu 0.05 Fe 0.36 Mn 0.35 Air-stabilized layered oxygen cathode material with an O2 surface coated with an amorphous passivation layer of Li3PO4-MgO.

[0066] Example 11

[0067] The difference from Example 1 is that the heating rate of the calcination treatment was 10℃ / min, and the holding time of the calcination treatment was 30h, finally yielding Na. 0.95 Ca 0.025 (Ni 0.24 Cu 0.05 Fe 0.36 Mn 0.35 Air-stabilized layered oxygen cathode material with an O2 surface coated with a Li3PO4-MgO amorphous passivation layer, wherein Na 0.95 Ca 0.025 (Ni 0.24 Cu 0.05 Fe 0.36 Mn 0.35 The average thickness of the O2 flake particles is 233 nm, and the average flake diameter is 2.2 µm.

[0068] Example 12

[0069] The difference from Example 1 is that the O3-type layered metal oxide, the LiCl-MgCl2 mixed molten salt, and NaH2PO4 are used. 4‌ The mass ratio of LiCl to MgCl2 in the LiCl-MgCl2 mixed molten salt is 50:1.85:1, and the mass ratio of LiCl to MgCl2 in the LiCl-MgCl2 mixed molten salt is 1.35:1, ultimately yielding Na 0.95 Ca 0.025 (Ni 0.24 Cu 0.05 Fe 0.36 Mn 0.35 An air-stabilized layered oxygen cathode material with an O2 surface coated with a Li3PO4-MgO amorphous passivation layer, wherein the thickness of the Li3PO4-MgO amorphous passivation layer is 9.7 nm, and the molar ratio of Li3PO4 to MgO in the Li3PO4-MgO amorphous passivation layer is 1:1.

[0070] Example 13

[0071] The difference from Example 1 is that the O3-type layered metal oxide, the LiCl-MgCl2 mixed molten salt, and NaH2PO4 are used. 4‌ The mass ratio of LiCl to MgCl2 in the LiCl-MgCl2 mixed molten salt is 200:1.85:1, and the mass ratio of LiCl to MgCl2 in the LiCl-MgCl2 mixed molten salt is 1.35:1, ultimately yielding Na 0.95 Ca 0.025 (Ni 0.24 Cu 0.05 Fe 0.36 Mn 0.35 An air-stabilized layered oxygen cathode material with an O2 surface coated with a Li3PO4-MgO amorphous passivation layer, wherein the thickness of the Li3PO4-MgO amorphous passivation layer is 1 nm, and the molar ratio of Li3PO4 to MgO in the Li3PO4-MgO amorphous passivation layer is 1:1.

[0072] Example 14

[0073] The difference from Example 1 is that the O3-type layered metal oxide, the LiCl-MgCl2 mixed molten salt, and NaH2PO4 are used. 4‌ The mass ratio of LiCl to MgCl2 in the LiCl-MgCl2 mixed molten salt is 30:1.85:1, and the mass ratio of LiCl to MgCl2 in the LiCl-MgCl2 mixed molten salt is 1.35:1, ultimately yielding Na 0.95 Ca 0.025 (Ni 0.24 Cu 0.05 Fe 0.36 Mn 0.35An air-stabilized layered oxygen cathode material with an O2 surface coated with a Li3PO4-MgO amorphous passivation layer, wherein the thickness of the Li3PO4-MgO amorphous passivation layer is 14 nm, and the molar ratio of Li3PO4 to MgO in the Li3PO4-MgO amorphous passivation layer is 1:1.

[0074] Example 15

[0075] The difference from Example 1 is that the stage of heating for the first sintering treatment is omitted, and the temperature is directly raised to 750°C and held for 3.5 hours to finally obtain Na. 0.95 Ca 0.025 (Ni 0.24 Cu 0.05 Fe 0.36 Mn 0.35 Air-stabilized layered oxygen cathode material with an O2 surface coated with an amorphous passivation layer of Li3PO4-MgO.

[0076] Example 16

[0077] Using anhydrous ethanol as a solvent, the required sodium carbonate is reacted with calcium carbonate and Ni. 0.3 Cu 0.1 Fe 0.3 Mn 0.3 (OH)₂ is composed of sodium, calcium, and Ni elements. 0.3 Cu 0.1 Fe 0.3 Mn 0.3 The molar ratio of (OH)₂ was 0.88:0.06:1, and the mixture was ground uniformly. After thorough mixing in a high-speed mixer, the sample was placed in a muffle furnace for calcination at 850℃ at a heating rate of 1℃ / min. Calcination was carried out at this temperature for 20 hours. After calcination, the muffle furnace was turned off, and the sample was allowed to cool naturally to room temperature. The sample was then crushed and sieved to obtain the molecular formula Na. 0.88 Ca 0.06 (Ni 0.3 Cu 0.1 Fe 0.3 Mn 0.3 O3-type layered metal oxides of O2. O3-type layered metal oxides are mixed with a LiCl-MgCl2 molten salt and NaH2PO4. 4‌A mixture was prepared by mixing molten LiCl and MgCl2 in a mass ratio of 100:1.85:1, resulting in a LiCl-MgCl2 mixed molten salt with a mass ratio of 1.35:1. The mixture underwent a first sintering treatment: sintering at 500℃ for 4 hours in an Ar / H2 mixed atmosphere (5% hydrogen by volume) followed by a second sintering at 800℃ for 5 hours in an O2 atmosphere, and then a third sintering at 900℃ for 2 hours in an air atmosphere. Finally, the mixture was cooled to room temperature at a rate of 2℃ / min to obtain the sintered product. The sintered product was washed with water to remove residual molten salt, dried under vacuum at 80℃ for 10 hours, and then subjected to a second sintering treatment at 800℃ for 16 hours in an air atmosphere. After sieving, Na was obtained. 088 Ca 0.06 (Ni 0.3 Cu 0.1 Fe 0.3 Mn 0.3 Air-stabilized layered oxygen cathode material with an O2 surface coated with a Li3PO4-MgO amorphous passivation layer, wherein Na 0.88 Ca 0.06 (Ni 0.3 Cu 0.1 Fe 0.3 Mn 0.3 The average thickness of the O2 flake particles is 140 nm, the average flake diameter is 1.5 µm, the thickness of the Li3PO4-MgO amorphous passivation layer is 2.8 nm, and the molar ratio of Li3PO4 to MgO in the Li3PO4-MgO amorphous passivation layer is 1:1.

[0078] Comparative Example 1

[0079] The difference from Example 1 is that the addition of calcium carbonate was omitted, ultimately yielding NaNi. 0.24 Cu 0.05 Fe 0.36 Mn 0.35 Materials with an O2 surface coated with an amorphous passivation layer of Li3PO4-MgO.

[0080] Comparative Example 2

[0081] The difference from Example 1 is that the step of coating with the Li3PO4-MgO amorphous passivation layer is omitted, ultimately yielding NaNi. 0.24 Cu 0.05 Fe 0.36 Mn 0.35 O2 materials.

[0082] Battery manufacturing

[0083] The materials prepared in the examples and comparative examples were left in air at a temperature of 25°C and a humidity of 40% for 0 days and 7 days, respectively, before being used to prepare button batteries.

[0084] The specific preparation method of the button cell battery is as follows: The above materials, conductive agent (carbon nanotubes + Super-P + Ketjen Black), and binder polyvinylidene fluoride are weighed in a mass ratio of 94:3:3, and an appropriate amount of N-methylpyrrolidone is added. The mixture is stirred in a high-speed mixer at 2000 rpm for 5 minutes, and this process is repeated twice to obtain the positive electrode slurry. The positive electrode slurry is uniformly coated onto carbon-coated aluminum foil. The slurry is heated from room temperature (25℃) to 110℃, and after drying and rolling to obtain a dry electrode, it is punched into circular electrode sheets with a diameter of 13 mm and placed in a vacuum drying oven at 120℃ for 8 hours. After complete drying, it is transferred to an argon-filled glove box for later use (water content <0.01 ppm, oxygen content <0.01 ppm). A sodium sheet with a diameter of 15.6 mm is used as the negative electrode, glass fiber (manufacturer: Whatman) is used as the separator, and NaClO4 is used as the electrolyte. The button cell is assembled in an anhydrous and oxygen-free vacuum glove box.

[0085] Performance testing

[0086] The surface sodium ion content of the materials prepared by the examples and comparative examples was tested using XPS, and the results are shown in Table 1.

[0087] Coin cells prepared by placing the materials in an environment of 25℃ and 40% humidity for 0 days and 7 days were tested in a voltage range of 2~4.1V. The specific capacity of the first discharge at 0.1C, the specific capacity of the first discharge at 5C, and the capacity retention rate after 50 cycles at 1C were tested. The results are shown in Table 2.

[0088] Table 1

[0089]

[0090] Table 2

[0091]

[0092] As can be seen from the data of the embodiments in Table 2, the air-stable layered oxygen cathode material in the embodiments, when placed in an environment of 25°C and 40% humidity for 7 days, the assembled battery has a first discharge specific capacity of more than 100 mAh / g at 0.1C and a first discharge specific capacity of more than 60 mAh / g at 5C, with a capacity retention rate of 60%. In the industry, the material of this application belongs to the category of air-stable layered oxygen cathode materials.

[0093] Figure 1 This is a SEM image of the air-stabilized layered oxygen cathode material in Example 2 of this application. Figure 2 This is a SEM image of the air-stabilized layered oxygen cathode material in Example 5 of this application. Figure 3 The image shows a SEM image of the air-stabilized layered oxygen cathode material in Comparative Example 1 of this application. Figure 1 and Figure 3 The comparison shows that the Ca-doped and undoped samples exhibit similar particle morphology and size, indicating that Ca doping did not alter the particle shape, size, or crystal structure of the material; from Figure 2 and Figure 3 The comparison shows that the samples doped with Zn and Ca exhibit similar particle morphology and size to those without Zn and Ca doping, indicating that Zn and Ca doping did not change the particle shape, size, or crystal structure of the material.

[0094] Figure 4 These are XRD comparison images of Embodiments 2, 5, Comparative Example 1, and Comparative Example 2 of this application. Figure 4 As can be seen from the comparison of the diffraction peak positions of Examples 2, 5, Comparative Example 1 and Comparative Example 2 with the standard card of hexagonal NaCrO2 (PDF#25-0819), it can be seen that the coating of the Li3PO4-MgO amorphous passivation layer and the air-stabilized layered oxygen cathode material doped with Ca and Zn elements all maintain the α-NaFeO2 structure of R-3m space group, that is, the typical O3 phase structure, and no change in crystal structure has occurred.

[0095] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects:

[0096] The presence of the Li3PO4-MgO amorphous passivation layer in this application helps to reduce the sodium ion content on the surface of the air-stabilized layered oxygen cathode material, thereby reducing the reaction of sodium ions with water and carbon dioxide in the air to form an inert passivation layer. On the other hand, it acts as a physical barrier, blocking the penetration of water and carbon dioxide from the air and preventing the O3-type layered transition metal oxide from reacting with water and carbon dioxide in the air. Ca doping in the O3-type layered metal oxide helps protect the active material from degradation during environmental electrode processing, maintaining its structural integrity and crystallinity. Furthermore, Ca doping helps suppress side reactions. More importantly, Ca doping helps stabilize the crystal structure of the O3-type layered transition metal oxide, increasing the interlayer spacing, which is beneficial for Na… + The embedding / de-embedding of Na helps to improve Na +The diffusion kinetics of the nanoparticles are improved, reducing volume expansion during electrochemical sodium formation and enhancing battery cycle performance. Zinc doping helps suppress side reactions and reduce volume changes during charge and discharge, further improving the cycle performance of the air-stabilized layered oxygen cathode material. Therefore, the air-stabilized layered oxygen cathode material of this application possesses a stable crystal structure, suitable interlayer spacing, and excellent Na+ diffusion kinetics. + Diffusion channels and air stability.

[0097] The above are merely embodiments of the present invention and are not intended to limit the invention. Those skilled in the art will recognize that the present invention can have various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An air-stabilized layered oxygen cathode material, characterized in that, The air-stabilized oxygen-laden cathode material includes: O3-type layered metal oxides; and A Li3PO4-MgO amorphous passivation layer is coated on the surface of the O3-type layered metal oxide; The general chemical formula of the O3-type layered metal oxide is Na. 1-2x Ca x (Ni a Cu b Fe c Mn d ) 1-y Zn y O2, wherein 0.025≤x≤0.06, 0.015≤y≤0.075, 0.2≤a≤0.3, 0≤b≤0.1, 0.3≤c≤0.4, 0.3≤d≤0.4, a+b+c+d=1; the molar ratio of Li3PO4 to MgO in the Li3PO4-MgO amorphous passivation layer is 1:(0.3~3); the preparation method of the air-stabilized layered oxygen cathode material includes: S1, sodium source, Ni a Cu b Fe c Mn d (OH)2 and a dopant source are mixed and then calcined to obtain O3-type layered metal oxides; wherein the dopant source is a combination of calcium and zinc sources; S2, the O3-type layered metal oxide, phosphorus source and LiCl-MgCl2 mixed molten salt are mixed and then sintered to form a Li3PO4-MgO amorphous passivation layer on the surface of the O3-type layered metal oxide, thereby obtaining the air-stable layered oxygen cathode material. The sintering process includes a first sintering process and a second sintering process performed sequentially. The first sintering process includes a first stage, a second stage, a third stage, and a cooling stage performed sequentially. The atmosphere in the first stage is a hydrogen-argon mixed atmosphere, the temperature is 400~500℃, and the time is 2~4h. The atmosphere in the second stage is an oxygen atmosphere, the temperature is 600~800℃, and the time is 1~5h. The atmosphere in the third stage is an air atmosphere, the temperature is 750~900℃, and the time is 0.5~2h. The cooling rate in the cooling stage is 2~20℃ / min.

2. The air-stabilized layered oxygen cathode material according to claim 1, characterized in that, The thickness of the Li3PO4-MgO amorphous passivation layer is 1~10nm; And / or, the O3-type layered metal oxide is formed by stacking sheet-like particles, the average thickness of which is 50~200nm and the average sheet diameter is 1~2µm.

3. The air-stabilized layered oxygen cathode material according to claim 1, characterized in that, The O3-type layered metal oxide is Na. 0.9 Ca 0.05 (Ni 0.24 Cu 0.05 Fe 0.36 Mn 0.35 ) 0.975 Zn 0.025 O2.

4. The air-stabilized laminar oxygen cathode material according to any one of claims 1 to 3, characterized in that, The surface sodium ion content of the air-stabilized laminar oxygen cathode material is 15-20%.

5. A method for preparing an air-stabilized layered oxygen cathode material according to any one of claims 1 to 4, characterized in that, The preparation method includes: S1, sodium source, Ni a Cu b Fe c Mn d (OH)2 and the dopant source are mixed and then calcined to obtain O3-type layered metal oxide; wherein the dopant source is a combination of calcium source and zinc source, and a, b, c, d are the same as a, b, c, d in any one of claims 1 to 4; S2, the O3-type layered metal oxide, phosphorus source and LiCl-MgCl2 mixed molten salt are mixed and then sintered to form a Li3PO4-MgO amorphous passivation layer on the surface of the O3-type layered metal oxide, thereby obtaining the air-stable layered oxygen cathode material.

6. The method for preparing the air-stabilized layered oxygen cathode material according to claim 5, characterized in that, The mass ratio of the O3-type layered metal oxide to the total mass of the LiCl-MgCl2 mixed molten salt and the phosphorus source is (50~200):2.85; And / or, the calcination temperature is 850~925℃; and / or, the heating rate of the calcination is 1~5℃ / min; and / or, the holding time of the calcination is 10~20h; And / or, the temperature of the second sintering treatment is 500~800℃; and / or, the time of the second sintering treatment is 6~16h.

7. A positive electrode plate, characterized in that, The positive electrode sheet contains the air-stabilized laminar oxygen positive electrode material as described in any one of claims 1 to 4.

8. A sodium-ion battery, comprising a positive electrode, an electrolyte, and a negative electrode, characterized in that, The positive electrode is the positive electrode as described in claim 7.

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