O2-type lithium ion layered oxide having a coating layer and a method for preparing the same

Abstract

The application discloses an O2 type lithium ion layered oxide with a coating layer and a preparation method thereof. The method comprises the following steps: mixing a sodium source, a cobalt source, a nickel source and / or a manganese source according to a specific chemical formula, and preparing a sodium ion layered oxide through one-time and two-time calcination; mixing the oxide with a lithium source and a coating material, and preparing a target product through a hydrothermal reaction and heat treatment. The method realizes in-situ low-temperature coating through a hydrothermal ion exchange method, a liquid phase system provides an ion transmission medium, ion migration activation energy is reduced, efficient ion exchange is realized, a dynamic open ion channel provides a high-activity binding site for the coating material, the coating layer is densely combined with the matrix, and a homogeneous nucleation mechanism ensures that the thickness of the coating layer is controllable. The method retains the structural advantages of the O2 type material while constructing the coating layer, improves the high-temperature stability and interface ion conductivity of the material, and provides a feasible scheme for large-scale application.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery cathode material technology, and relates to an O2-type lithium-ion layered oxide with a coating layer and its preparation method. Background Technology

[0002] Lithium-ion batteries, with their outstanding advantages such as high energy density, high operating voltage, and good cycle performance, have become promising energy storage systems for various application scenarios, including portable electronic devices, electric vehicles, and distributed energy storage. As a core component of lithium-ion batteries, the performance of the cathode material directly determines the energy density of the battery; therefore, the development of high-voltage, high-specific-capacity cathode materials is crucial for increasing the energy density of lithium-ion batteries.

[0003] Layered oxide cathode materials, represented by lithium cobalt oxide (LiCoO2), have significant advantages in improving battery energy density due to their high discharge voltage and large discharge capacity. Currently, the most widely used commercially available layered oxide cathode material is the O3-type structure. However, under high cutoff voltage cycling, the capacity of O3-type layered oxide cathodes decays rapidly. The failure is mainly due to the irreversible transformation of the H1-3 / O1 phase after deep delithiation and severe interfacial reactions with the electrolyte. Specifically, the oxygen layers in O3-type layered oxides are arranged in an ABCABC pattern, with LiO6 and TMO6 octahedra sharing edges. TM ions in the shared-edge structure more easily migrate to Li vacancy sites in the Li-O octahedra to form a spinel structure. However, during lithium intercalation, they irreversibly return to the TM-O octahedra, thus enhancing the activity of oxygen in the TM-O octahedra and generating more oxygen, ultimately leading to more severe structural damage and side reactions. In contrast, the oxygen layers in the O2-type structure are arranged in an ABCBAB pattern, with the LiO6 octahedron sharing a face with the TMO6 octahedron on one side and connecting along a common edge on the other. Due to the stronger electrostatic repulsion between the cations sharing the face, the migration of TM from the central site to the adjacent Li site is suppressed, exhibiting excellent structural stability and electrochemical performance.

[0004] Although O2-type layered oxides exhibit better structural stability compared to O3-type structures, their surface oxidizability increases with increasing charging voltage, leading to severe surface structural damage. Simultaneously, high voltage intensifies interfacial side reactions between the electrode and electrolyte, further damaging the electrode surface structure and impacting battery performance. Therefore, improving the surface stability of materials is crucial. Surface coating, by constructing heterogeneous or solid solution layers on the material surface, can act as a physical barrier to protect the surface structure, while also promoting charge transfer and reaction kinetics, mitigating structural deformation, and inhibiting transition metal ion dissolution and oxygen release. Currently, conventional industrial coating processes typically involve mixing the substrate material and the coating material and then sintering at high temperatures. However, due to their thermodynamically metastable structural characteristics, O2-type layered oxides transform into the O3 phase at temperatures exceeding 280°C. This makes traditional high-temperature sintering coating processes unsuitable for O2-type layered oxides, creating an urgent need to develop low-temperature coating processes adapted to their properties. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides an O2-type lithium-ion layered oxide with a coating layer and its preparation method, thereby solving the technical problem that the high-temperature sintering coating process in the prior art cannot effectively prepare O2-type layered oxides because their thermodynamic metastable structural characteristics cause them to transform into the O3 phase at temperatures exceeding 280°C.

[0006] This invention is achieved through the following technical solution: A method for preparing an O2-type lithium-ion layered oxide with a coating layer includes the following steps: S1: According to the chemical formula Na m Co x M （1-x） O2, where M is Ni and / or Mn, 0.70 ≤ m ≤1.00, 0.60≤ x ≤1.00, sodium source, cobalt source, nickel source and / or manganese source are mixed evenly, and then subjected to a first calcination treatment and a second calcination treatment in sequence to obtain sodium ion layered oxide; the temperature of the first calcination treatment is lower than the temperature of the second calcination treatment; S2: The sodium ion layered oxide is mixed evenly with a lithium source and a coating material, and after hydrothermal reaction, the product is heat-treated to obtain the O2-type layered oxide with a coating layer.

[0007] Preferably, the temperature of the first calcination treatment is 500~600℃ and the time is 2~6h.

[0008] Preferably, the temperature of the secondary calcination treatment is 700~900℃, and the time is 6~20h.

[0009] Preferably, the hydrothermal reaction is carried out at a temperature of 150~250℃ for 5~12 hours.

[0010] Preferably, in step S2, the molar ratio of transition metal atoms in the sodium ion layered oxide to lithium atoms in the lithium source is 1:(1~3).

[0011] Preferably, the coating material accounts for 0.02% to 0.5% of the mass of lithium cobalt oxide.

[0012] Preferably, the coating is a metal oxide or a fast ion conductor.

[0013] An O2-type lithium-ion layered oxide with a coating layer is prepared by the method described above.

[0014] A positive electrode sheet comprising the above-mentioned O2-type lithium-ion layered oxide with a coating layer.

[0015] A lithium-ion battery comprising the aforementioned positive electrode.

[0016] Compared with the prior art, the present invention has the following beneficial technical effects: This invention discloses a method for preparing O2-type lithium-ion layered oxides with a coating layer. The method achieves in-situ low-temperature coating through hydrothermal ion exchange, and simultaneously completes ion exchange and coating layer construction in a liquid environment. First, the hydrothermal reaction's liquid-phase system provides a "solventization channel" for ion transport. In a closed autoclave, water acts as a solvent, forming a uniform ion transport medium that allows the coating precursor (such as a metal salt solution) to rapidly contact Li / Na ions on the substrate surface via liquid-phase diffusion. This solvation effect significantly reduces the activation energy for ion migration, enabling efficient ion exchange without high temperatures. Furthermore, during ion exchange, temporary vacancies are created in the lattice of sodium-ion layered oxides due to the migration of Li / Na ions, forming dynamically open ion channels. These channels remain stably open in the liquid-phase environment, providing highly active binding sites for the coating ions. This "instant binding" mechanism allows the coating layer to form a dense bond with the substrate at low temperatures, eliminating the need for high-temperature-driven solid-phase diffusion. Moreover, in the liquid-phase environment, the coating precursor is dispersed in ionic or colloidal form, avoiding particle agglomeration problems in solid-phase mixing. This homogeneous nucleation mechanism ensures controllable coating layer thickness and tight bonding with the substrate interface. The low-temperature in-situ coating strategy in this invention not only preserves the structural advantages of O2-type materials, but also effectively inhibits electrolyte erosion through a dense coating layer, significantly improving the high-temperature stability and interfacial ion conductivity of the materials, providing a feasible low-temperature preparation scheme for the large-scale application of O2-type layered oxides.

[0017] Furthermore, the primary calcination treatment is carried out at a temperature of 500-600℃ for 2-6 hours. These conditions allow the sodium, cobalt, nickel, and / or manganese sources to mix thoroughly and undergo preliminary chemical reactions, generating intermediate products with a specific crystal structure and chemical composition. These conditions ensure effective solid-phase reactions between the raw materials, allowing for uniform distribution of elements and the initial formation of a layered structural framework. This provides a stable and suitable crystal structure foundation for the final product, facilitating the orderly insertion and extraction of lithium ions between layers and thus improving the electrochemical performance of the material.

[0018] Furthermore, the secondary calcination treatment is carried out at a temperature of 700-900℃ for 6-20 hours, which further promotes crystal growth and increases crystallinity. Under these temperature and time conditions, the atoms in the intermediate product gain sufficient energy to rearrange themselves, eliminate crystal defects, and form a more complete and regular layered crystal structure. This optimized crystal structure facilitates the rapid conduction of lithium ions in the material, improves the ionic conductivity of the material, and thus enhances the charge-discharge performance and cycle stability of the product.

[0019] Furthermore, the hydrothermal reaction temperature is 150-250℃, and the time is 5-12 hours. Since O2-type lithium-ion layered oxides transform into the O3 phase at temperatures exceeding 280℃, the hydrothermal reaction temperature of 150-250℃ is far below the critical phase transition temperature, effectively preventing the transformation of the material structure and maintaining the unique structural advantages of O2-type layered oxides. In addition, this temperature range provides suitable conditions for the uniform dispersion and deposition of the coating in the liquid environment. Under hydrothermal conditions, the coating precursor can stably exist in the solution in ionic or colloidal form and be uniformly deposited on the surface of the sodium-ion layered oxide through diffusion and adsorption. The reaction time of 5-12 hours ensures sufficient time for the coating to nucleate and grow, forming a uniform and dense coating layer.

[0020] Furthermore, in step S2, the molar ratio of transition metal atoms in the sodium-ion layered oxide to lithium atoms in the lithium source is 1:(1~3). A suitable molar ratio ensures sufficient ion exchange between lithium atoms in the lithium source and sodium atoms in the sodium-ion layered oxide. When the molar ratio is within the range of 1:(1~3), lithium atoms can effectively enter the crystal lattice of the layered oxide, replacing sodium atoms and forming a lithium-ion layered oxide with good electrochemical performance. Simultaneously, by adjusting this molar ratio, the crystal structure and electronic structure of the material can be controlled, thereby affecting the lithium-ion insertion and extraction mechanism and optimizing the charge / discharge capacity and rate performance of the material.

[0021] Furthermore, the coating material accounts for 0.02% to 0.5% of the mass of lithium cobalt oxide. Too little coating material results in an excessively thin coating layer, which cannot effectively isolate the electrolyte from direct contact with the cathode material, thus failing to fully exert the protective function of the coating layer. Too much coating material results in an excessively thick coating layer, increasing the diffusion resistance of lithium ions on the material surface and affecting the electrochemical performance of the material. A coating material mass of 0.02% to 0.5% of the mass of lithium cobalt oxide ensures the coating effect while avoiding negative impacts on material performance, achieving a balance between coating effectiveness and material performance.

[0022] Furthermore, the coating material is a metal oxide or a fast ion conductor. Metal oxides are chosen as the coating material because they possess excellent chemical and thermal stability. They can form a dense protective layer on the material surface, effectively suppressing side reactions between the electrolyte and the cathode material, reducing the dissolution of active materials and structural damage, thereby improving the high-temperature stability and cycle life of the material, allowing the product to maintain good electrochemical performance even under harsh environments. Fast ion conductors have high ionic conductivity, and as a coating material, they can promote the rapid transport of lithium ions on the material surface. This helps reduce the diffusion resistance of lithium ions on the material surface, improves the rate performance of the material, and allows the product to maintain high capacity and efficiency during rapid charge and discharge processes. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 The image shows the XRD pattern of LiCoO2 obtained in Example 1 of this invention. Figure 2 The first charge-discharge capacity results of Mn3O4@LCO prepared in Example 2 of this invention and LCO prepared in the comparative example; Figure 3 Cycling performance of Mn3O4@LCO prepared in Example 2 of this invention and LCO prepared in the comparative example at a 1 C rate; Figure 4 The LiCo obtained in Example 3 of this invention 0.8 N i0.1 Mn 0.1 XRD pattern of O2; Figure 5 This is a SEM image of O2-type LiCoO2 with a Li3PO4 coating obtained in Example 5 of the present invention. Figure 6This is a SEM image of LCO obtained for comparison. Detailed Implementation

[0025] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0026] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0027] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0028] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0029] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0030] This invention provides a method for preparing O2-type lithium-ion layered oxides, which first synthesizes sodium-ion layered oxides Na via a high-temperature solid-state method. m Co x M （1-x） O2, where M is Ni and / or Mn, 0.70≤ m ≤1.00, 0.60≤ x ≤1.00); then, the sodium ion layered oxide is mixed evenly with lithium salt and coating material, dissolved in water, added to a hydrothermal reactor for ion exchange, and in-situ coating is completed to obtain O2-type layered oxide cathode material LiCo with coating layer. x M （1-x） O2.

[0031] Specifically, the preparation method of the above-mentioned O2-type lithium-ion layered oxide with a coating layer includes the following steps: S1: According to the chemical formula Na m Co x M （1-x） O2, where M is Ni and / or Mn, 0.70 ≤ m ≤1.00, 0.60≤ x ≤1.00, sodium source, cobalt source, nickel source and / or manganese source are mixed evenly, and then subjected to a first calcination treatment and a second calcination treatment in sequence to obtain sodium ion layered oxide; the temperature of the first calcination treatment is lower than the temperature of the second calcination treatment; here the first calcination treatment is the pre-calcination treatment.

[0032] The above steps are specific, according to the chemical formula Na m Co x M （1-x） O2 is weighed out, along with a sodium source, a cobalt source, and a compound containing element M (i.e., a nickel source and / or a manganese source). After thorough mixing, the mixture is subjected to a first calcination treatment and a second calcination treatment. After calcination, it is allowed to cool naturally to room temperature to obtain sodium ion layered oxide Na. m Co x M （1-x） O2; Preferably, the sodium source is at least one of Na2CO3 and NaOH; the cobalt source is cobalt oxalate (CoC2O4), cobalt tetroxide (Co3O4), cobalt trioxide (Co2O3), or cobalt carbonate (CoCO3); the nickel source is nickel oxide (NiO), nickel oxalate (NiC2O4), or nickel carbonate (NiCO3); and the manganese source is manganese oxalate (MnC2O4), manganese monoxide (MnO), manganese dioxide (MnO2), or manganese carbonate (MnCO3).

[0033] Preferably, the temperature for a single calcination treatment is 500~600℃ and the time is 2~6h; The temperature for the secondary calcination treatment is 700~900℃, and the time is 6~20h; The atmosphere for both the primary and secondary calcination is air.

[0034] S2: The sodium ion layered oxide is mixed evenly with a lithium source and a coating material, and the mixture is subjected to a hydrothermal reaction. The product is then heat-treated to obtain the O2-type layered oxide with a coating layer.

[0035] The above steps are specific, according to the chemical formula LiCo x M （1-x） O2, where M is Ni and / or Mn, 0.70≤ m ≤1.00, 0.60≤ x≤1.00, weigh out the sodium ion layered oxide Na obtained from S1. m Co x M （1-x） O2, an equal or slightly excess amount of lithium source and coating material are mixed evenly and then added to a hydrothermal reactor for hydrothermal reaction. After washing, drying and heat treatment, the O2-type layered oxide with coating layer is obtained.

[0036] Preferably, the lithium source is at least one of LiNO3, LiCl, and LiOH.

[0037] The coating material is not limited, but preferably, the coating material is a metal oxide or a fast ion conductor. The metal oxide includes at least one of Al2O3, MgO, Mn3O4, V2O5, ZnO, ZrO2 and TiO2, and the ion conductor includes phosphate fast ion conductors, specifically including at least one of Li3PO4, AlPO4, LiMgPO4, LiFePO4 and Zr3(PO4)4.

[0038] Fast ion conductors, also known as superionic conductors or solid electrolytes, are a class of conductors that exhibit high ionic conductivity (typically ≥10 Ω·cm) comparable to that of liquid electrolytes within a specific temperature range. -2 Solid materials with low ionic conductivity (S / cm) and low activation energy (≤0.40 eV).

[0039] More preferably, the mass of the coating material accounts for 0.02% to 0.5% of the mass of lithium cobalt oxide, that is, the coating amount is 200 to 5000 ppm.

[0040] The molar ratio of transition metal atoms in the sodium ion layered oxide to lithium atoms in the lithium source is 1:(1~3). The transition metal atoms in the sodium ion layered oxide are cobalt, nickel, and / or manganese. The temperature of the above hydrothermal reaction is 150~250℃, and the time is 5~12h.

[0041] The heat treatment is performed in an air atmosphere at a temperature of 150 ℃ for 2 to 5 hours.

[0042] This invention successfully prepares O2-type layered oxides with a coating layer using a high-temperature solid-state method combined with a hydrothermal ion exchange method. Existing surface coating techniques typically rely on high-temperature processes (usually 400°C to 800°C), requiring a high-temperature environment to enhance ion diffusion kinetics and ensure the formation of a continuous, dense coating layer that is firmly bonded to the substrate. However, high-temperature conditions can lead to material defects, including structural damage to the material itself, harmful side reactions at the coating-substrate interface, and high energy consumption. In contrast, this invention introduces a coating material during the ion exchange process. The formation of the coating material occurs simultaneously with the ion exchange reaction, directly growing a uniform coating layer in situ on the material surface, achieving in-situ low-temperature coating. On the one hand, the liquid-phase environment of the hydrothermal reaction provides ideal conditions for ion exchange. The uniform dispersion of the coating in the liquid-phase environment effectively reduces particle agglomeration. At the same time, during the ion exchange process, Li / Na ions in the layered oxide lattice migrate and exchange, and the ion channels are dynamically opened, providing easier binding sites for the coating. Without a high-temperature environment, the coating can form a tighter bond with the substrate material, constructing a dense and firmly bonded protective layer. This effectively isolates the electrolyte from direct contact with the cathode material, reducing the occurrence of side reactions. In addition, the lower temperature of the hydrothermal environment enables low-temperature coating, avoiding structural phase transitions that may occur during traditional high-temperature coating, and solving the problem that existing technologies are not suitable for O2-type layered oxide cathode materials due to high coating temperatures. On the other hand, the ion exchange and coating process is completed in situ in one step during the hydrothermal reaction, eliminating additional coating steps, simplifying the production process, and effectively reducing coating energy consumption. It has the advantages of simple process, uniform coating, and strong controllability.

[0043] Furthermore, this low-temperature coating method is adaptable to various types of coatings, allowing for flexible selection based on surface coating requirements and demonstrating excellent scalability. For example, when enhanced interfacial ion conductivity is needed, ionic conductors such as Li3PO4 can be selected, achieving uniform deposition through open ion channels; if the focus is on improving high-temperature stability, inert oxides such as Al2O3 can be used, forming a dense protective layer through channel guidance. Simultaneously, the process parameters are highly adjustable. By changing parameters such as hydrothermal temperature, reaction time, and coating material quality, the thickness (from a few nanometers to tens of nanometers) and density of the coating layer can be flexibly controlled to meet the differentiated requirements for material interfacial performance in various scenarios.

[0044] This invention provides a universal pathway for high-performance O2-type layered oxide cathode materials that balances precise structural design and large-scale production through hydrothermal ion exchange combined with low-temperature coating technology, synergistic liquid-phase control, and solid-liquid interface engineering. This pathway can be widely applied in fields such as power batteries. The O2-type layered oxide cathode material with a coating layer prepared by this method exhibits excellent cycle performance; under conditions of 3-4.65 V and 1 C, the capacity retention rate is over 92% after 50 cycles. The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0045] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0046] Comparative Example This comparative sample has no coating layer, and the chemical formula of the O2-type layered oxide cathode material is LiCoO2. Specifically, the method for preparing the uncoated O2-type LiCoO2 cathode material includes the following steps: Step 1: Weigh out Co3O4, NiCO3, and MnCO3 according to the chemical formula NaCoO2 ratio, mix them evenly using a ball mill, and calcine the mixture at 600℃ for 4 hours, followed by a second calcine treatment at 900℃ for 10 hours. After the second calcine treatment, allow it to cool naturally to room temperature to obtain sodium ion layered oxide NaCoO2. Step 2: Weigh the NaCoO2 and LiOH obtained in Step 1 according to the molar ratio of Co atoms to Li atoms of 1:1.5, mix them evenly using a ball mill, disperse them in deionized water, and place them in a closed reaction vessel. Control the reaction temperature at 250℃ and the reaction time at 5h. After the hydrothermal reaction is completed, use ultrasonic washing to remove the surface salt residue, filter, and heat treat at 150℃ for 2h. The product collected is the O2-type LiCoO2 without coating layer, labeled as LCO.

[0047] Example 1 In this embodiment, Al2O3 is selected as the coating material, with a coating amount of 200 ppm. The chemical formula of the O2-type layered oxide cathode material is LiCoO2. Specifically, the method for preparing the O2-type LiCoO2 cathode material with an Al2O3 coating layer includes the following steps: Step 1: According to the chemical formula Na 0.7 CoO2 was prepared by weighing out Co3O4 and Na2CO3, and mixing them uniformly using a ball mill. The mixture was then calcined at 500℃ for 2 hours, followed by a second calcination at 700℃ for 6 hours. After the second calcination, the mixture was allowed to cool naturally to room temperature to obtain sodium ion layered oxide Na. 0.7 CoO2; Step 2: Weigh out the Na obtained in Step 1 according to a Co atom to Li atom molar ratio of 1:1. 0.7 CoO2, LiCl and 200ppm Al2O3 were uniformly mixed using a ball mill and dispersed in deionized water. The mixture was placed in a sealed reactor and the reaction temperature was controlled at 150℃ for 5 hours. After the hydrothermal reaction was completed, the surface salt residue was removed by ultrasonic washing, filtered, and then subjected to low-temperature heat treatment at 150℃ for 2 hours. The resulting product was O2-type LiCoO2 with an Al2O3 coating.

[0048] Figure 1 The image shows the XRD pattern of LiCoO2 obtained in Example 1 of this invention. As can be seen from the image, all diffraction peaks belong to the O2 type structure, and the space group is [missing information]. P6 3 mc It belongs to the hexagonal crystal system and has good crystallinity, indicating that the low-temperature coating did not affect the O2 type structure of LiCoO2.

[0049] Example 2 In this embodiment, Mn3O4 is selected as the coating material, with a coating amount of 1000 ppm. The chemical formula of the O2-type layered oxide cathode material is LiCoO2. Specifically, the method for preparing the O2-type LiCoO2 cathode material with a Mn3O4 coating layer includes the following steps: Step 1: According to the chemical formula Na 0.8 Weigh out CoO2, Co2O3, and NaOH according to the specified ratio, and mix them evenly using a ball mill. Calcine the mixture at 500℃ for 2 hours, then calcine it again at 800℃ for 10 hours. After the second calcination, allow it to cool naturally to room temperature to obtain sodium ion layered oxide Na. 0.8 CoO2; Step 2: Weigh out the Na obtained in Step 1 according to the molar ratio of Co atoms to Li atoms of 1:1.5. 0.8CoO2, LiCl, and 1000 ppm Mn3O4 were uniformly mixed using a ball mill and dispersed in deionized water. The mixture was then placed in a sealed reactor and the reaction temperature was controlled at 180°C for 5 hours. After the hydrothermal reaction was completed, the surface salt residue was removed by ultrasonic washing, filtered, and then subjected to low-temperature heat treatment at 150°C for 4 hours. The resulting product was O2-type LiCoO2 with a Mn3O4 coating layer, labeled as Mn3O4@LCO.

[0050] The charge-discharge performance testing process of the cathode material prepared in this embodiment is as follows: Using the positive electrode material prepared in this embodiment as the active material, acetylene black as the conductive agent, and polyvinylidene fluoride as the binder, they were uniformly mixed in a mass ratio of 8:1:1. Next, 30 times the mass of the binder was added dropwise, and the mixture was stirred to form a slurry. The slurry was evenly coated onto aluminum foil, and then placed in a constant temperature drying oven at 120°C for 12 hours. After drying to constant weight, a small disc with a diameter of 12 mm was punched out using a punching machine; this is the positive electrode working electrode. Ensuring the absence of water, the small disc was placed in a glove box filled with argon gas. Lithium foil was used as both the counter and reference electrodes, and a Celgard 2400 polypropylene film (a lithium-ion battery separator made of polypropylene) was used as the separator. The electrolyte was LP30 (a commonly used lithium-ion battery electrolyte, typically 1 M LiPF6 dissolved in a 1:1 volume ratio of ethylene carbonate and dimethyl carbonate). Finally, CR2023 coin cells were assembled in a glove box. The electrochemical performance of the assembled cells was tested at 25°C, within a voltage range of 3.0–4.65 V, and at 1 C.

[0051] Figure 2 The initial charge-discharge capacity results of Mn3O4@LCO prepared in Example 2 of this invention and LCO prepared in the comparative example are shown in the figure. As can be seen, the initial charge-discharge capacities of the O2-type lithium-ion layered oxide with coating prepared in Example 2 of this invention are 249.90 mAh / g and 246.57 mAh / g, respectively. The coating material Mn3O4 in this example is an inert oxide, non-electrochemically active, and does not participate in the redox reaction during the charge-discharge process. The main function of this coating layer is to improve the cycle stability of the material, not to increase the material capacity. An excessively thick or uneven coating layer can actually reduce the material capacity. However, in this example, the capacity of the material after coating did not show a significant decrease, proving that the coating process in this invention can achieve uniform coating on the material surface.

[0052] Figure 3The cycling performance of Mn3O4@LCO prepared in Example 2 of this invention and LCO prepared in the comparative example at a 1 C rate is shown in the figure. It can be seen that after electrochemical cycling at 1 C with a voltage range of 3.0~4.65 V, the capacity retention rate after 50 cycles is 92.72%, which is significantly improved compared with the uncoated control sample.

[0053] Example 3 In this embodiment, Mn3O4 was selected as the coating material, with a coating amount of 1000 ppm. The chemical formula of the O2-type layered oxide cathode material is LiCo. 0.8 Ni 0.1 Mn 0.1 O2. Specifically, O2-type LiCo with a Mn3O4 coating layer was prepared. 0.8 Ni 0.1 Mn 0.1 The method for using O2 cathode materials includes the following steps: Step 1: According to the chemical formula Na 0.8 Co 0.8 Ni 0.1 Mn 0.1 The following O2 components were weighed out: CoCO3, NiO, MnO2, and NaOH. They were then uniformly mixed using a ball mill. The mixture was calcined at 600℃ for 6 hours, followed by a second calcination at 900℃ for 12 hours. After the second calcination, the mixture was allowed to cool naturally to room temperature to obtain sodium ion layered oxide Na. 0.8 Co 0.8 Ni 0.1 Mn 0.1 O2; Step 2: Weigh the Na obtained in Step 1 according to the (Co+Ni+Mn):Li molar ratio of 1:2. 0.8 Co0 .8 Ni0.1Mn 0.1 O2, LiNO3, and 1000 ppm Mn3O4 were uniformly mixed using a ball mill and dispersed in deionized water. The mixture was then placed in a sealed reactor at a controlled temperature of 200°C for 8 hours. After the hydrothermal reaction, surface salt residue was removed by ultrasonic washing, followed by filtration and a low-temperature heat treatment at 150°C for 4 hours. The resulting product was O2-type LiCo with a Mn3O4 coating. 0.8 Ni 0.1 Mn 0.1 O2.

[0054] Figure 4 The LiCo obtained in Example 3 of this invention 0.8 N i0.1 Mn 0.1The XRD pattern of O2 shows that all diffraction peaks belong to the O2 type structure, indicating that adjusting the proportion of transition metals within a certain range in this invention will not change the O2 type structure of the layered oxide.

[0055] Example 4 In this embodiment, Mn3O4 was selected as the coating material, with a coating amount of 5000 ppm. The chemical formula of the O2-type layered oxide cathode material is LiCo. 0.8 Ni 0.1 Mn 0.1 O2. Specifically, O2-type LiCo with a Mn3O4 coating layer was prepared. 0.8 Ni 0.1 Mn 0.1 The method for using O2 cathode materials includes the following steps: Step 1: According to the chemical formula Na 0.8 Co 0.8 Ni 0.1 Mn 0.1 The following O2 components were weighed out: Co3O4, NiO, MnO, and NaOH. They were then uniformly mixed using a ball mill. The mixture was calcined at 600℃ for 6 hours, followed by a second calcination at 900℃ for 12 hours. After the second calcination, the mixture was allowed to cool naturally to room temperature to obtain sodium ion layered oxide Na. 0.8 Co 0.8 Ni 0.1 Mn 0.1 O2; Step 2: Weigh the Na obtained in Step 1 according to the (Co+Ni+Mn):Li molar ratio of 1:3. 0.8 Co 0.8 Ni 0.1 Mn 0.1 O2, LiOH, and 5000 ppm Mn3O4 were uniformly mixed using a ball mill and dispersed in deionized water. The mixture was then placed in a sealed reactor at a controlled temperature of 250°C for 12 hours. After the hydrothermal reaction, surface salt residue was removed by ultrasonic washing, followed by filtration and a low-temperature heat treatment at 150°C for 5 hours. The resulting product was O2-type LiCo with a Mn3O4 coating. 0.8 Ni 0.1 Mn 0.1 O2.

[0056] Example 5 In this embodiment, Li3PO4 is selected as the coating material, with a coating amount of 2000 ppm. The chemical formula of the O2-type layered oxide cathode material is LiCoO2. Specifically, the method for preparing the O2-type LiCoO2 cathode material with a Li3PO4 coating layer includes the following steps: Step 1: Weigh out Co3O4 and NaOH according to the chemical formula NaCoO2 ratio, mix them evenly using a ball mill, and calcine the mixture at 600℃ for 4 hours, followed by a second calcine treatment at 900℃ for 12 hours. After the second calcine treatment, allow it to cool naturally to room temperature to obtain sodium ion layered oxide NaCoO2; Step 2: Weigh out NaCoO2, LiOH and 2000 ppm Li3PO4 obtained in Step 1 according to the molar ratio of Co atoms to Li atoms of 1:2. Mix them evenly using a ball mill and disperse them in deionized water. In a closed reaction vessel, control the reaction temperature at 220℃ and the reaction time at 12h. After the hydrothermal reaction is completed, use ultrasonic washing to remove surface salt residue, filter, and heat treat at 150℃ for 5h. The product collected is O2-type LiCoO2 with a Li3PO4 coating layer.

[0057] Figure 5 The image shows an SEM image of O2-type LiCoO2 with a Li3PO4 coating layer obtained in Example 5 of this invention. As can be seen from the image, the LiCoO2 particle size is about 5 μm and the Li3PO4 coating layer is evenly distributed.

[0058] Figure 6 The SEM image of LCO obtained for comparison is shown below. Figure 6 Compared to the comparative SEM images, Figure 5 The smoother surface of the particles after encapsulation indicates that the coating layer has been successfully constructed on the particle surface. Furthermore, the absence of obvious local protrusions or depressions on the particle surface indicates that the encapsulation process of this invention has little impact on particle size and morphology, and the coating layer thickness is uniform, resulting in a good encapsulation effect.

[0059] Example 6 In this embodiment, Li3PO4 was selected as the coating material, with a coating amount of 3000 ppm. The chemical formula of the O2-type layered oxide cathode material is LiCo. 0.8 Ni 0.1 Mn 0.1 O2. Specifically, O2-type LiCo with a Li3PO4 coating layer was prepared. 0.8 Ni 0.1 Mn 0.1 The method for using O2 cathode materials includes the following steps: Step 1: According to the chemical formula Na 0.9 Co 0.8 Ni 0.1 Mn 0.1O2 was used to weigh out Co3O4, NiCO3, and MnCO3, which were then uniformly mixed using a ball mill. The mixture was calcined at 600℃ for 4 hours, followed by a second calcination at 900℃ for 20 hours. After the second calcination, the mixture was allowed to cool naturally to room temperature to obtain sodium ion layered oxide Na. 0.9 Co 0.8 Ni 0.1 Mn 0.1 O2; Step 2: Weigh the Na obtained in Step 1 according to the (Co+Ni+Mn):Li molar ratio of 1:2. 0.9 Co 0.8 Ni 0.1 Mn 0.1 O2, LiOH, and 3000 ppm Li3PO4 were uniformly mixed using a ball mill and dispersed in deionized water. The mixture was then placed in a sealed reactor at a controlled temperature of 250°C for 12 hours. After the hydrothermal reaction, surface salt residue was removed by ultrasonic washing, followed by filtration and a low-temperature heat treatment at 150°C for 5 hours. The resulting product was O2-type LiCo with a Li3PO4 coating. 0.8 Ni 0.1 Mn 0.1 O2.

[0060] Example 7 In this embodiment, AlPO4 was selected as the coating material, with a coating amount of 3000 ppm. The chemical formula of the O2-type layered oxide cathode material is LiCo. 0.6 Ni 0.2 Mn 0.2 O2. Specifically, O2-type LiCo with an AlPO4 coating was prepared. 0.6 Ni 0.2 Mn 0.2 The method for using O2 cathode materials includes the following steps: Step 1: According to the chemical formula Na 0.9 Co 0.6 Ni 0.2 Mn 0.2 The O2 ratio was determined by weighing out CoC2O4, NiC2O4, and MnC2O4, and then uniformly mixing them using a ball mill. The mixture was then calcined at 600℃ for 4 hours, followed by a second calcination at 900℃ for 20 hours. After the second calcination, it was allowed to cool naturally to room temperature to obtain sodium ion layered oxide Na. 0.9 Co 0.6 Ni 0.2 Mn 0.2 O2; Step 2: Weigh the Na obtained in Step 1 according to the (Co+Ni+Mn):Li molar ratio of 1:3. 0.9 Co0.6 Ni 0.2 Mn 0.2 O2, LiOH, and 3000 ppm AlPO4 were uniformly mixed using a ball mill and dispersed in deionized water. The mixture was then placed in a sealed reactor at a controlled temperature of 250°C for 12 hours. After the hydrothermal reaction, surface salt residue was removed by ultrasonic washing, followed by filtration and a low-temperature heat treatment at 150°C for 5 hours. The resulting product was O2-type LiCo with an AlPO4 coating. 0.6 Ni 0.2 Mn 0.2 O2.

[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing an O2-type lithium-ion layered oxide with a coating layer, characterized in that, Includes the following steps: S1: According to the chemical formula Na m Co x M （1-x） O2, where M is Ni and / or Mn, 0.70 ≤ m ≤1.00, 0.60≤ x ≤1.00, sodium source, cobalt source, nickel source and / or manganese source are mixed evenly, and then subjected to a first calcination treatment and a second calcination treatment in sequence to obtain sodium ion layered oxide; the temperature of the first calcination treatment is lower than the temperature of the second calcination treatment; S2: The sodium-ion layered oxide is mixed uniformly with a lithium source and a coating material. After hydrothermal reaction, the product is heat-treated to obtain an O2-type lithium-ion layered oxide LiCo with a coating layer. x M （1-x） O2; The heat treatment atmosphere is air, the temperature is 150 ℃, and the time is 2~5 h; The hydrothermal reaction is carried out at a temperature of 150~250℃ for 5~12 hours. In step S2, the molar ratio of transition metal atoms in the sodium ion layered oxide to lithium atoms in the lithium source is 1:(1~3).

2. The method for preparing an O2-type lithium-ion layered oxide with a coating layer according to claim 1, characterized in that, The temperature of the first calcination treatment is 500~600℃, and the time is 2~6h.

3. The method for preparing an O2-type lithium-ion layered oxide with a coating layer according to claim 1, characterized in that, The secondary calcination treatment is carried out at a temperature of 700~900℃ for a time of 6~20h.

4. The method for preparing an O2-type lithium-ion layered oxide with a coating layer according to claim 1, characterized in that, The coating is a metal oxide or a fast ion conductor.

5. An O2-type lithium-ion layered oxide with a coating layer, characterized in that, It is prepared by the method described in any one of claims 1 to 4.

6. A positive electrode sheet, characterized in that, It includes an O2-type lithium-ion layered oxide with a coating layer as described in claim 5.

7. A lithium-ion battery comprising a positive electrode as described in claim 6.

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