Lithium nickel manganese oxide cathode material and preparation method thereof, and electrochemical device

Abstract

The application provides a lithium nickel manganese oxide positive electrode material and a preparation method thereof, and an electrochemical device. The lithium nickel manganese oxide positive electrode material comprises a base material, a first coating layer on the surface of the base material, and a second coating layer on the side of the first coating layer away from the base material, wherein the base material comprises an Nb and Al co-doped lithium nickel manganese oxide positive electrode active material, the first coating layer contains Li 1.4 W 0.2 Ti 1.6 (PO4)3, and the second coating layer contains Zr(HPO4)2. Through the three-layer structure design of the base material-LWTP-Zr(HPO4)2, the application can realize the synchronous improvement of the ion transmission rate, structural stability and electrochemical stability of the high-voltage lithium nickel manganese oxide positive electrode material.

Description

Technical Field

[0001] This application relates to the field of new energy technology, specifically to a lithium nickel manganese oxide cathode material and its preparation method, as well as an electrochemical device. Background Technology

[0002] With the rapid development of electric vehicles and portable electronic devices, the demand for high-energy-density and high-power-density lithium-ion batteries is increasing. Traditional cathode materials, such as spinel-type LiMn2O4, layered LiCoO2, and olivine-type LiFePO4, are limited by their theoretical capacity and operating voltage, making it difficult to meet the high energy density requirements. Lithium nickel manganese oxide (LNMO) cathode materials, due to their advantages such as high output voltage, high energy density, low cost, and environmental friendliness, have become an important choice for next-generation high-energy-density lithium-ion batteries.

[0003] However, in practical applications, LNMOs suffer from problems such as structural distortion, capacity decay, gas production, and decreased coulombic efficiency during use, which limits the large-scale promotion of LNMOs. Summary of the Invention

[0004] In view of this, in order to solve at least one of the above technical problems, this application provides a lithium nickel manganese oxide cathode material.

[0005] In addition, this application also provides a method for preparing lithium nickel manganese oxide cathode material and an electrochemical device using the lithium nickel manganese oxide cathode material.

[0006] In a first aspect, embodiments of this application provide a lithium nickel manganese oxide cathode material, which includes a substrate material, a first coating layer located on the surface of the substrate material, and a second coating layer located on the side of the first coating layer away from the substrate material. The substrate material includes Nb and Al co-doped lithium nickel manganese oxide cathode active material, and the first coating layer contains Li. 1.4 W 0.2 Ti 1.6 (PO4)3, the second coating layer contains Zr(HPO4)2.

[0007] Based on the first aspect, in some possible embodiments, the matrix material is a spinel structure; the Li 1.4 W 0.2 Ti 1.6 (PO4)3 has a sodium superionic conductor structure; Zr(HPO4)2 is amorphous.

[0008] Based on the first aspect, in some possible embodiments, the Li 1.4 W 0.2 Ti 1.6The mass percentage of (PO4)3 to the matrix material is 0.1wt% to 2wt%; and / or the mass percentage of Zr(HPO4)2 to the matrix material is 0.1wt% to 1.5wt%.

[0009] Based on the first aspect, in some possible embodiments, the general chemical formula of the matrix material is Li(Li) c Ni （2-a-b-c） / 4 Mn 3（2-a-b-c） / 4 Nb a Al b )O 4-δ , 0.02≤a≤0.06, 0.05≤b≤0.15, 0.02≤c≤0.1, 0≤δ≤0.2; and / or the lithium nickel manganese oxide cathode material is a single crystal material.

[0010] Secondly, this application provides a method for preparing a lithium nickel manganese oxide cathode material. The method includes: mixing a nickel manganese precursor, a lithium source, an aluminum source, and a niobium source to form a mixture; performing a first sintering on the mixture to obtain a matrix material; mixing the matrix material with a first coating agent and spray-drying it to obtain a dried material; and performing a second sintering on the dried material to react and generate a Li-containing compound on the surface of the matrix material. 1.4 W 0.2 Ti 1.6 The intermediate material is obtained by first coating layer of (PO4)3; and the intermediate material is mixed with a second coating agent and sintered for a third time to form a second coating layer containing Zr(HPO4)2 on the surface of the intermediate material, thereby obtaining the lithium nickel manganese oxide cathode material.

[0011] Based on the second aspect, in some possible embodiments, the atmosphere pressure of the first sintering is greater than atmospheric pressure by 0.01 MPa to 0.20 MPa, and the atmosphere of the first sintering is an oxygen-containing atmosphere with an oxygen concentration of 20% to 70%.

[0012] Based on the second aspect, in some possible embodiments, the first sintering is a two-stage sintering, including a first stage sintering and a second stage sintering performed sequentially. The temperature of the first stage sintering is 850℃~950℃, and the time of the first stage sintering is 6h~20h. The temperature of the second stage sintering is 550℃~750℃, and the time of the second stage sintering is 5h~10h. The temperature is reduced from the temperature of the first stage sintering to the temperature of the second stage sintering at a cooling rate of 1℃ / min~4℃ / min.

[0013] Based on the second aspect, in some possible embodiments, the moisture content of the dried material is 0~1wt%; and / or the atmosphere pressure of the second sintering is greater than atmospheric pressure by 0.01MPa~0.20MPa, the atmosphere of the second sintering is an oxygen-containing atmosphere with an oxygen concentration of 20%~70%; and / or the temperature of the second sintering is 600℃~700℃, and the time of the second sintering is 6h~12h.

[0014] Based on the second aspect, in some possible embodiments, the atmosphere pressure of the third sintering is greater than atmospheric pressure by 0.01 MPa to 0.20 MPa, the atmosphere of the third sintering is an air atmosphere; and / or the temperature of the third sintering is 300℃ to 450℃, and the time of the third sintering is 6h to 12h.

[0015] Thirdly, embodiments of this application also provide an electrochemical device, the electrochemical device including a positive electrode sheet, the positive electrode sheet including a positive electrode material, the positive electrode material being the aforementioned lithium nickel manganese oxide positive electrode material.

[0016] Compared to existing technologies, the lithium nickel manganese oxide cathode material provided in this application, firstly, by co-doping Nb and Al into the lithium nickel manganese oxide matrix material, can effectively improve the working voltage and energy density of the lithium nickel manganese oxide cathode material; secondly, by coating the surface of the matrix material with Li... 1.4 W 0.2 Ti 1.6 The first coating layer of (PO4)3 (LWTP) serves as a fast ion conductor layer, enhancing the ionic conductivity of the lithium nickel manganese oxide cathode material and thus improving its rate performance. Thirdly, by coating the surface of the first coating layer with a second coating layer containing Zr(HPO4)2 as a passivation protective layer, the chemical and structural stability of the lithium nickel manganese oxide cathode material is improved, effectively reducing manganese dissolution from the matrix material and interfacial side reactions between the lithium nickel manganese oxide cathode material and the electrolyte, thereby improving the cycle performance of the lithium nickel manganese oxide cathode material. This application achieves a simultaneous improvement in the ion transport rate, structural stability, and electrochemical stability of high-voltage lithium nickel manganese oxide cathode materials through a three-layer structure design of "matrix material-LWTP-Zr(HPO4)2". Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of a lithium nickel manganese oxide cathode material provided in an embodiment of this application.

[0018] Figure 2 This is a process flow diagram of a method for preparing lithium nickel manganese oxide cathode material according to an embodiment of this application.

[0019] Figure 3This is a scanning electron microscope image of the lithium nickel manganese oxide cathode material in Comparative Example 1 of this application. Figure 3 Figure a shows the observation results magnified 10,000 times. Figure 3 Figure b shows the observation results magnified 5000 times.

[0020] Figure 4 This is a scanning electron microscope (SEM) image of the lithium nickel manganese oxide cathode material in Example 1 of this application. Figure 4 Figure a shows the observation results magnified 10,000 times. Figure 4 Figure b shows the observation results magnified 5000 times.

[0021] Figure 5 The X-ray diffraction patterns are those of lithium nickel manganese oxide cathode materials in Examples 1-3 and Comparative Examples 1-4 of this application. Detailed Implementation

[0022] The embodiments of this application are described in detail below. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application; it should be noted that, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; where there is no conflict, the implementation methods and features of the implementation methods of this application can be combined with each other; many specific details are set forth in the following description to provide a full understanding of this application, and the described implementation methods are only a part of the implementation methods of this application, and not all of the implementation methods.

[0023] Studies have found that lithium nickel manganese oxide (LNMO) cathode materials are prone to oxygen defects during conventional high-temperature sintering processes, leading to the formation of disordered phase structures in some materials, accompanied by non-electrochemically active rock salt phase byproducts, Li. x Ni 1-xThe generation of O reduces the proportion of active material. In addition, the 4.7V high voltage platform of LNMO cathode material also brings some problems: (1) The structure of LNMO cathode material is easily damaged during charge-discharge cycles, which hinders the normal insertion / extraction of lithium ions and leads to capacity decay; (2) High voltage will cause the electrolyte to decompose violently, and the decomposition products will react with LNMO cathode material, increase the contact interface resistance, hinder lithium ion transport, consume active lithium source, and deteriorate cycle life. At the same time, the gas production will increase significantly, and the dissolution of Mn element will intensify, further damaging the structural integrity of LNMO cathode material. Moreover, the high voltage characteristics of LNMO cathode material bring both opportunities and challenges to LNMO cathode material. Thanks to the high voltage characteristics of LNMO cathode material, LNMO has great potential for application in semi-solid / all-solid battery systems. However, in all-solid batteries, the electrode-electrolyte interface changes from solid / liquid contact to solid / solid contact. Solid materials lack wettability, resulting in the interface being a point contact, forming a high interface resistance, which seriously hinders the cross-interface transport of lithium ions and weakens the battery power output and charge-discharge efficiency.

[0024] Therefore, this application provides a novel lithium nickel manganese oxide cathode material, which includes a substrate material, a first coating layer on the surface of the substrate material, and a second coating layer on the side of the first coating layer away from the substrate material. The substrate material includes Nb and Al co-doped lithium nickel manganese oxide cathode active material, and the first coating layer contains Li. 1.4 W 0.2 Ti 1.6 (PO4)3, the second coating layer contains Zr(HPO4)2. (Binding) Figure 1 The diagram shown is a possible structural schematic of the aforementioned novel lithium nickel manganese oxide cathode material 100, but it is not limited thereto. The substrate material 10 is coated with a composite coating layer 20, which includes a first coating layer 21 and a second coating layer 22.

[0025] This application selects Nb and Al to co-dope the active material of lithium nickel manganese oxide cathode, which can give the matrix material higher structural stability on the basis of the high operating voltage and energy density of the matrix material itself, thereby improving the cycle life and rate performance of lithium nickel manganese oxide cathode material.

[0026] Specifically, the general chemical formula of the matrix material is Li(Li) c Ni （2-a-b-c） / 4 Mn 3（2-a-b-c） / 4 Nb a Al b )O 4-δThe formula is defined as follows: 0.02≤a≤0.06, 0.05≤b≤0.15, 0.02≤c≤0.1, 0≤δ≤0.2. The "4-δ" in the general chemical formula indicates that the matrix material may contain oxygen vacancies. Due to the presence of these potential oxygen vacancies, LNMO contains a certain amount of trivalent Mn, leading to a disordered arrangement of transition metal ions. Although the ion diffusion rate in this disordered spinel (Fd-3m) is two orders of magnitude higher than that of the ordered spinel (P4332), and it exhibits higher capacity and rate performance, trivalent Mn can induce the Jameer-Taylor effect, causing drastic structural changes in the lithium nickel manganese oxide cathode material and accelerating its structural degradation. Limiting the value to 0≤δ≤0.2 helps to control oxygen vacancies in the matrix material and thus the content of trivalent manganese.

[0027] Among them, the matrix material is doped with Nb element: (1) Due to its large ionic radius and high charge (high ionic potential), Nb will preferentially adsorb on specific high surface energy crystal surfaces during crystal growth. The adsorption effect of Nb can weaken the difference in growth rate of each crystal surface, and the crystal growth mode changes from strong anisotropy to quasi-isotropic growth, so that the morphology of the matrix material is more like a smooth and spherical single crystal particle than a sharp polyhedron, which is conducive to the final preparation of a spherical high-capacity long-cycle lithium nickel manganese oxide cathode material. (2) The bond dissociation energy (BDE) of Nb-O bond is 726.5 kJ·mol -1 Higher than Ni-O bonds (366 kJ·mol) -1 ) and Mn-O bonds (362 kJ·mol -1 The bond dissociation energy of ) can effectively improve the structural stability of the matrix material and reduce cation mixing and manganese dissolution.

[0028] Doping Al elements in the matrix material: (1) Suppresses the formation of impurity phases and promotes the formation of pure phases: In high-temperature solid-state reactions, lithium nickel manganese oxide without Al doping is prone to forming rock salt phase Li during cooling. x Ni 1-x O impurities, due to the high Al-O bond energy, can maintain the spinel structure of lithium nickel manganese oxide at high temperatures, reducing Ni... 2+ The tendency of transition metal site migration and reduction effectively suppresses the formation of rock salt phase impurities, which is conducive to obtaining a matrix material with higher purity spinel phase and improving the structural stability and thermal stability of the matrix material. (2) Reduce cation mixing degree: cation mixing refers to Ni 2+ (Ionic radius approximately 0.69 Å) migrates to Li + The position (8a site, ionic radius approximately 0.76 Å) hinders lithium-ion diffusion, while Al... 3+ The ionic radius (approximately 0.535 Å) is similar to that of Mn. 4+ (Approximately 0.53 Å) similar, Al3+ It preferentially occupies the 16d octahedral sites (transition metal sites) in the spinel structure. Furthermore, due to Al... 3+ Stable price state and no Jahn-Teller effect, Al 3+ The presence of these elements acts as an "anchor," stabilizing the lithium nickel manganese oxide lattice and reducing the Ni content. 2+ The driving force and available sites for migration effectively reduce the degree of cation mixing in lithium nickel manganese oxide. (3) The BDE of the Al-O bond is 726.5 kJ·mol -1 The bond dissociation energy is higher than that of NO bond and Mn-O bond, which can effectively improve the structural stability of the matrix material and reduce manganese dissolution. (4) Optimize the particle morphology and growth of the matrix material: The incorporation of Al can affect the growth kinetics of grains during high-temperature sintering, which is conducive to obtaining particles with more uniform size and higher crystallinity. Although the effect of Al doping on the morphology of the matrix material is not as direct as that of Nb in promoting the spheroidization of matrix material particles, Al reduces the excessive growth of abnormal grains by stabilizing the growth environment, which lays the foundation for obtaining the microstructure of lithium nickel manganese oxide cathode material with good electrochemical performance.

[0029] The co-doping of Nb and Al in lithium nickel manganese oxide cathode materials plays a synergistic enhancing role: Al, with its high bond energy, strongly stabilizes the bulk crystal structure of the matrix material, improving the structural stability and thermal safety of the lithium nickel manganese oxide cathode material; Nb, by inducing the spheroidization of matrix material particles, optimizes particle morphology and reduces cation mixing and manganese dissolution. Therefore, through their synergistic effect, the particle morphology of the matrix material can be optimized and its structural stability improved, thereby enhancing the cycle life and rate performance of the lithium nickel manganese oxide cathode material.

[0030] To further improve the electrochemical performance and structural stability of lithium nickel manganese oxide cathode materials, a composite coating layer is provided on the surface of the substrate material. This composite coating layer includes Li... 1.4 W 0.2 Ti 1.6 The first coating layer is (PO4)3 (LWTP) and the second coating layer contains Zr(HPO4)2.

[0031] The first coating layer containing LWTP is located on the side of the overall coating layer closest to the substrate material. As a fast ion conductor layer, the first coating layer containing LWTP can improve the ionic conductivity of lithium nickel manganese oxide cathode material and accelerate the ion transport rate at the interface between lithium nickel manganese oxide cathode material and solid electrolyte, thereby improving the rate performance of lithium nickel manganese oxide cathode material.

[0032] Furthermore, LWTP exhibits a sodium superionic conductor (NASICON) structure. Compared to LATP, which also belongs to the NASICON family, LWTP has a higher valence W... 6+The introduction of lithium vacancies and wider ion migration channels results in higher bulk ionic conductivity for LWTP. Compared to fast ion conductors such as lithium tungstate, lithium niobate, and lithium molybdate, which are easily decomposed and have low conductivity, the NASICON framework structure of LWTP is more stable, exhibiting not only a wider electrochemical window but also excellent air stability and mechanical strength, resulting in a more balanced overall performance.

[0033] The second coating layer containing Zr(HPO4)2 is located on the outermost layer of the overall material. As a passivation layer, the second coating layer has high chemical stability and can effectively block the direct contact between the matrix material (especially Mn in the matrix material) and the electrolyte, significantly reducing the dissolution of manganese ions. This is beneficial to improving the structural stability of lithium nickel manganese oxide cathode material, thereby improving the cycle performance of lithium nickel manganese oxide cathode material.

[0034] Furthermore, Zr(HPO4)2 is amorphous. Compared to traditional metal oxide coatings (such as alumina) or phosphate coatings (such as aluminum phosphate), amorphous Zr(HPO4)2 possesses an amorphous structure and unique chemical properties. Specifically, amorphous Zr(HPO4)2 exhibits a dense, grain-bound second coating layer, enabling more uniform and defect-free comprehensive coating of the high-voltage substrate material. This effectively blocks electrolyte corrosion of the substrate material and reduces manganese leaching. Simultaneously, amorphous Zr(HPO4)2 itself exhibits excellent high-voltage stability and acid corrosion resistance (such as HF), avoiding the problem of localized corrosion of the substrate material caused by the presence of grain boundaries, which can lead to protective failure in crystalline coatings. Moreover, this coating synergistically works with the aforementioned LWTP to provide effective protection while increasing the lithium-ion transport rate. This, in turn, mitigates the side reactions at the interface between the lithium nickel manganese oxide cathode material and the electrolyte, ensuring excellent electrochemical kinetic performance of lithium nickel manganese oxide.

[0035] In some embodiments, Li 1.4 W 0.2 Ti 1.6 The mass percentage of (PO4)3 to the matrix material can be 0.1wt% to 2wt%, which is beneficial for effectively improving the conductivity of lithium nickel manganese oxide cathode materials while maintaining their high energy density. This mass percentage can be, for example, 0.1wt%, 0.2wt%, 0.5wt%, 0.8wt%, 1.0wt%, 1.2wt%, 1.5wt%, 1.8wt%, 2.0wt%, or any value within the range of any two of the above values. The mass percentage can further be 0.5wt% to 1.0wt%.

[0036] In some embodiments, the mass percentage of Zr(HPO4)2 to the matrix material can be 0.1wt% to 1.5wt%, which is beneficial for balancing the stability and conductivity of the lithium nickel manganese oxide cathode material. This mass percentage can, exemplarily, be 0.1wt%, 0.2wt%, 0.5wt%, 0.8wt%, 1.0wt%, 1.2wt%, 1.5wt%, or any value within the range of any two of the above values. The mass percentage can further be 0.4wt% to 0.9wt%.

[0037] Compared with existing technologies, the lithium nickel manganese oxide cathode material of this application has the following beneficial effects:

[0038] 1. The lithium nickel manganese oxide cathode material of this application has been co-doped with Nb and Al in the matrix material. The fixed combination of the two elements has optimized the particle morphology of the matrix material and improved the structural stability of the matrix material, thereby improving the cycle life and rate performance of the lithium nickel manganese oxide cathode material.

[0039] 2. The lithium nickel manganese oxide cathode material of this application adopts a unique LWTP-Zr(HPO4)2 double coating structure, which effectively improves the lithium-ion transport rate and structural stability of the lithium nickel manganese oxide cathode material, enabling the lithium-rich manganese-based material to have advantages such as high operating voltage, high energy density, excellent rate performance and long cycle life.

[0040] 3. The matrix material provided in this application embodiment is a spinel structure. The LWTP in the first coating layer is a NASICON type structure, while the Zr(HPO4)2 in the second coating layer is an amorphous structure, thus constructing a three-layer heterostructure of "spinel-NASICON-amorphous". This structural design further improves the structural stability and conductivity of lithium nickel manganese oxide cathode material.

[0041] Please see Figure 2 As shown, based on the same inventive concept, this application provides a method for preparing lithium nickel manganese oxide cathode material, specifically including the following steps:

[0042] Step S1: Mix the nickel-manganese precursor, lithium source, aluminum source and niobium source to form a mixture, and perform a first sintering and cooling heat treatment on the mixture to obtain the matrix material.

[0043] In some embodiments, the nickel-manganese precursor may include nickel-manganese hydroxide.

[0044] The median particle size Dv50 of the nickel-manganese precursor can be 3μm~8μm, which is beneficial to the dispersion of the nickel-manganese precursor and to the uniform mixing of the nickel-manganese precursor with other raw materials.

[0045] In some embodiments, the lithium source may include at least one of lithium hydroxide, lithium carbonate, and lithium nitrate.

[0046] In some embodiments, the aluminum source may include at least one of aluminum hydroxide and aluminum oxide.

[0047] In some embodiments, the niobium source may include at least one of niobium hydroxide and niobium oxide.

[0048] In this step, the raw materials can be mixed using a high-speed mixer. Furthermore, the mixing frequency can be 400Hz~2000Hz, and the mixing time can be 5min~20min, which helps to thoroughly and evenly mix the raw materials. Even further, the mixing frequency can be 1000Hz~1400Hz.

[0049] During the first sintering process, the atmosphere pressure can be 0.01 MPa to 0.20 MPa higher than atmospheric pressure. Increasing the atmosphere pressure (especially the oxygen partial pressure) helps reduce the volatilization of metal elements and helps maintain the oxidized state of metal ions in the matrix material. The atmosphere for the first sintering can be an oxygen-containing atmosphere with an oxygen concentration of 20% to 70%, which is beneficial for maintaining the oxidized state of metal ions in the matrix material. For example, the atmosphere pressure for the first sintering can be 0.01 MPa, 0.08 MPa, 0.10 MPa, 0.12 MPa, 0.14 MPa, 0.16 MPa, 0.20 MPa higher than atmospheric pressure, or any value within the range of any two of the above values. The atmosphere pressure for the first sintering can further be 0.05 MPa to 0.15 MPa higher than atmospheric pressure. The oxygen concentration of the atmosphere for the first sintering can be 20%, 30%, 40%, 50%, 60%, 70%, or any value within the range of any two of the above values.

[0050] In some embodiments, the first sintering can be a two-stage sintering, including a first stage sintering and a second stage sintering performed sequentially. Segmented sintering facilitates precise control of the sintering process.

[0051] Furthermore, the sintering temperature for the first stage can be 850℃~950℃. Performing the first stage sintering at a higher temperature can promote ion migration and increase the grain growth rate. The sintering temperature for the first stage can, for example, be 850℃, 870℃, 880℃, 890℃, 900℃, 910℃, 920℃, 930℃, 940℃, 950℃, or any value within the range of any two of the above values. The sintering temperature for the first stage can further be 880℃~920℃. The sintering time for the first stage can be 6h~20h. The sintering time can, for example, be 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, or any value within the range of any two of the above values. The sintering time for the first stage can further be 10h~14h.

[0052] The second-stage sintering temperature can be 550℃~750℃. Performing the second-stage sintering at a lower temperature allows for oxygen repair of the matrix material due to the presence of disordered crystalline phases in lithium nickel manganese oxide. This repairs surface defects and oxygen defects in the bulk phase. Furthermore, annealing allows fragments detached from the particle surface during the pulverization process to be remelted back, improving the capacity and cycle life of the lithium nickel manganese oxide cathode material. The second-stage sintering temperature can, for example, be 550℃, 600℃, 650℃, 700℃, 750℃, or any value within the range of any two of the above values. A further variation is 600℃~700℃. The second-stage sintering time can be 5h~10h, for example, 5h, 6h, 7h, 8h, 9h, 10h, or any value within the range of any two of the above values. A further variation is 7h~9h.

[0053] Furthermore, controlling the cooling rate from the first sintering temperature to the second sintering temperature to be 1℃ / min to 4℃ / min allows for sufficient oxygen repair and reduces the adverse effects of internal stress accumulation caused by rapid external temperature changes, thereby improving the rate performance and cycle life of the matrix material. This cooling rate can be further increased to 2℃ / min to 3℃ / min.

[0054] In some embodiments, the median particle size Dv50 of the matrix material can be 4 μm to 9 μm, which is beneficial for subsequent control of the particle size of the lithium nickel manganese oxide cathode material, enabling the lithium nickel manganese oxide cathode material to have suitable specific surface area and compaction density. The median particle size Dv50 of the matrix material can exemplary be 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or any value within the range of any two of the above values. The median particle size Dv50 of the matrix material can further be 5 μm to 7 μm.

[0055] Step S2: The matrix material is mixed with the first coating agent and spray-dried to obtain a dried material. The dried material is then subjected to a second sintering to react on the surface of the matrix material to generate Li-containing compounds. 1.4 W 0.2 Ti 1.6 The first coating layer of (PO4)3 yields the intermediate material.

[0056] Specifically, the matrix material and the first coating agent are mixed in a stirred tank. Alternatively, a solvent (such as water or a dispersant) can be added to the stirred tank for wet mixing to form a slurry. Then, the slurry is spray-dried and granulated using a spray dryer to obtain a dry material with relatively uniform particle size and good flowability. This improves the uniformity of the second sintering. A second sintering is then performed, and the first coating agent reacts in situ on the surface of the matrix material to form a first coating layer containing LWTP, resulting in the intermediate material.

[0057] In some embodiments, the first coating agent may include a lithium-containing compound, a tungsten-containing compound, a titanium-containing compound, and a phosphorus-containing compound, capable of reacting to generate LWTP. Specifically, the lithium-containing compound may include at least one of lithium hydroxide, lithium carbonate, and lithium nitrate; the tungsten-containing compound may include at least one of oxides, tungstic acid, ammonium metatungstate, and ammonium paratungstate; the titanium-containing compound may include at least one of titanium oxide, titanic acid, and tetrabutyl titanate; and the phosphorus-containing compound may include at least one of 85% industrial-grade phosphoric acid solution and ammonium dihydrogen phosphate.

[0058] In some embodiments, the dispersant may include at least one of ethanol, acetone, and isopropanone.

[0059] In some embodiments, the inlet air temperature of the spray dryer can be 200°C to 250°C, and the outlet air temperature can be 100°C to 180°C. This facilitates the removal of moisture from the mixture of the matrix material and the first coating agent, effectively reducing agglomeration of the dried material during the second sintering process and improving the efficiency of the second sintering. Furthermore, the moisture weight percentage of the dried material obtained after spray drying can be controlled within 0 to 1 wt%.

[0060] During the second sintering process, the atmosphere pressure can be 0.01 MPa to 0.20 MPa higher than atmospheric pressure. Increasing the atmosphere pressure (especially the oxygen partial pressure) helps to further reduce the volatilization of metal elements and maintain the metal ions in the matrix material in an oxidized state, and also improves the bonding force between LWTP and the matrix material. The atmosphere for the second sintering can be an oxygen-containing atmosphere with an oxygen concentration of 20% to 70%, which is beneficial for maintaining the oxidized state of metal ions in the matrix material. For example, the atmosphere pressure for the second sintering can be 0.01 MPa, 0.08 MPa, 0.10 MPa, 0.12 MPa, 0.14 MPa, 0.16 MPa, 0.20 MPa higher than atmospheric pressure, or any value within the range of any two of the above values. The atmosphere pressure for the second sintering can further be 0.05 MPa to 0.15 MPa higher than atmospheric pressure. The oxygen concentration of the atmosphere for the second sintering can be 20%, 30%, 40%, 50%, 60%, 70%, or any value within the range of any two of the above values.

[0061] The second sintering temperature is 600℃~700℃, which facilitates the full reaction of the first coating agent on the surface of the matrix material to generate LWTP, thereby forming a dense and uniform LWTP-containing first coating layer in situ. The second sintering temperature can, for example, be 600℃, 610℃, 620℃, 630℃, 640℃, 650℃, 660℃, 670℃, 680℃, 690℃, 700℃, or any value within the range of any two of the above values. The second sintering temperature can further be 600℃~700℃. The second sintering time is 6h~12h, which facilitates the full reaction of the first coating agent. The second sintering time can, for example, be 6h, 7h, 8h, 9h, 10h, 11h, 12h, or any value within the range of any two of the above values. The second sintering time can further be 7h~9h.

[0062] In some embodiments, the median particle size Dv50 of the intermediate material can be 4 μm to 9 μm, which is beneficial for subsequent control of the particle size of the lithium nickel manganese oxide cathode material, enabling the lithium nickel manganese oxide cathode material to have suitable specific surface area and compaction density. The median particle size Dv50 of the intermediate material can exemplary be 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or any value within the range of any two of the above values. The median particle size Dv50 of the intermediate material can further be 5 μm to 7 μm.

[0063] Step S3: Mix the intermediate material with the second coating agent and perform a third sintering to form a second coating layer containing Zr(HPO4)2 on the surface of the intermediate material, thereby obtaining lithium nickel manganese oxide cathode material.

[0064] Specifically, the intermediate material already coated with LWTP is mixed evenly with the second coating agent in a high-speed mixer, and then subjected to a third sintering. The second coating agent forms a second coating layer containing Zr(HPO4)2 on the surface of the intermediate material. After crushing, classifying and sieving, lithium nickel manganese oxide cathode material is obtained.

[0065] In some embodiments, the second coating agent may include Zr(HPO4)2, facilitating the direct formation of a second coating layer containing Zr(HPO4)2. Further, the second coating agent may be commercially available amorphous Zr(HPO4)2, which is readily available and can directly form a second coating layer containing amorphous Zr(HPO4)2.

[0066] In this step, the intermediate material and the second coating agent can be mixed using a high-speed mixer. Further, the mixing frequency is 400Hz~2000Hz, and the mixing time is 5min~20min, which helps to ensure thorough and uniform mixing of the intermediate material and the second coating agent. Even further, the mixing frequency can be 1000Hz~1400Hz.

[0067] During the third sintering process, the atmosphere pressure can be greater than atmospheric pressure by 0.01 MPa to 0.20 MPa (preferably 0.05 to 0.15 MPa). Increasing the atmosphere pressure helps to further reduce the volatilization of metal elements, maintain the metal ions in the matrix material in an oxidized state, and also improve the bonding force between Zr(HPO4)2 and the intermediate material. The atmosphere for the third sintering can be air. For example, the atmosphere pressure for the third sintering can be greater than atmospheric pressure by 0.01 MPa, 0.08 MPa, 0.10 MPa, 0.12 MPa, 0.14 MPa, 0.16 MPa, 0.20 MPa, or any value within the range of any two of the above values. The atmosphere pressure for the third sintering can further be greater than atmospheric pressure by 0.05 MPa to 0.15 MPa.

[0068] The third sintering temperature is 300℃~450℃, which is conducive to the formation of an amorphous structure of Zr(HPO4)2 on the surface of the intermediate material, thereby forming a continuous, dense and uniform second coating layer. The third sintering temperature can, for example, be 300℃, 320℃, 350℃, 380℃, 400℃, 420℃, 450℃, or any value within the range of any two of the above values. The third sintering temperature can further be 350℃~400℃. The third sintering time is 6h~12h, which is conducive to the sufficient reaction of the first coating agent. The third sintering time can, for example, be 6h, 7h, 8h, 9h, 10h, 11h, 12h, or any value within the range of any two of the above values. The third sintering time can further be 8h~10h.

[0069] In some embodiments, the median particle size Dv50 of the lithium nickel manganese oxide cathode material can be 4 μm to 9 μm, which is beneficial for the lithium nickel manganese oxide cathode material to have a suitable specific surface area and compaction density. The median particle size Dv50 of the lithium nickel manganese oxide cathode material can exemplary be 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or any value within the range of any two of the above values. The median particle size Dv50 of the lithium nickel manganese oxide cathode material can further be 5 μm to 7 μm.

[0070] Compared with existing technologies, the preparation method of lithium nickel manganese oxide cathode material in this application has the following advantages:

[0071] 1. The first coating agent reacts in situ on the surface of the matrix material to generate a first coating layer containing LWTP, which is beneficial to improving the continuity, density and uniformity of the first coating layer, and is beneficial to improving the ion transport rate of lithium nickel manganese oxide cathode material.

[0072] 2. The second coating agent forms a second coating layer containing Zr(HPO4)2 on the surface of the intermediate material, which is beneficial for passivating and protecting the matrix material, effectively isolating the matrix material from the electrolyte / electrolyte, and improving the structural and chemical stability of the lithium nickel manganese oxide cathode material.

[0073] 3. By controlling the atmospheric pressure and oxygen content of the first and second sintering, it is beneficial to maintain the oxidizing properties of the metal elements in the matrix material and to make the surfaces of the matrix material and intermediate material more compact.

[0074] This application also provides an electrochemical device (e.g., a secondary battery) that includes a positive electrode plate, the positive electrode plate including a positive electrode material, wherein the positive electrode material is the aforementioned lithium nickel manganese oxide positive electrode material.

[0075] Compared with the prior art, the electrochemical device provided in this application embodiment has higher operating voltage, conductivity and stability due to the application of the aforementioned lithium nickel manganese oxide cathode material, and can be used stably for a long time in a cyclic manner.

[0076] The present application's solution will be explained below with reference to embodiments. Those skilled in the art will understand that the following examples are for illustrative purposes only and should not be construed as limiting the scope of the application. Unless otherwise stated, reagents, software, and instruments involved in the following embodiments that are not specifically described are all conventional commercially available products or publicly disclosed.

[0077] Example 1

[0078] Step S1, according to the chemical formula Li (Li 0.04 Ni 0.4690 Mn 1.407 Nb 0.08 Al 0.004 )O 4-δ A certain amount of lithium carbonate, hydroxide precursor, niobium oxide and alumina were weighed and mixed uniformly for 15 min at a frequency of 1400 Hz using a high-speed mixer. The first sintering was carried out in an atmosphere with an atmospheric pressure greater than atmospheric pressure of 0.12 MPa and an oxygen concentration of 50%. The first sintering was a two-stage sintering, which included a first stage sintering and a second stage sintering carried out sequentially. After the first stage sintering at 880℃ for 12 h, the temperature was lowered at a rate of 3℃ / min, and then the second stage sintering at 680℃ for 10 h was carried out for annealing and oxygen repair. The sintered material was then subjected to air jet milling and classification to obtain a matrix material with a median particle size Dv50 of 5 μm to 7 μm.

[0079] Step S2: The matrix material is mixed with the first coating agent and spray-dried to obtain a dried material. The moisture content of the dried material can be less than 1 wt%. The dried material is then subjected to a second sintering at 650°C for 10 hours under an atmosphere with a pressure greater than atmospheric pressure (0.12 MPa) and an oxygen concentration of 50%, to react on the surface of the matrix material to generate Li-containing compounds. 1.4 W 0.2 Ti 1.6 The first coating layer of (PO4)3, after air jet milling and sieving, yields an intermediate material with a median particle size Dv50 of 5 μm to 7 μm. The first coating agent comprises Li according to the chemical formula... 1.4 W 0.2 Ti 1.6 The molar ratios of the elements in (PO4)3 were measured using lithium hydroxide, ammonium metatungstate, titanium oxide, and an 85% industrial-grade phosphoric acid solution. The first coating layer contained Li... 1.4 W 0.2 Ti 1.6The mass percentage of (PO4)3 to the matrix material is 0.5 wt%.

[0080] Step S3: The intermediate material and the second coating agent are mixed in a high-speed mixer at a frequency of 1400 Hz for 10 min, and then sintered for the third time at 400 °C for 8 h in an air atmosphere with an atmospheric pressure greater than atmospheric pressure by 0.12 MPa, so as to form a second coating layer containing Zr(HPO4)2 on the surface of the intermediate material. After air jet milling and sieving, a lithium nickel manganese oxide cathode material with a median particle size Dv50 of 5 μm to 7 μm is obtained. The second coating agent is amorphous Zr(HPO4)2, and the mass percentage of Zr(HPO4)2 to the matrix material in the second coating layer is 0.3 wt%.

[0081] Example 2:

[0082] The difference from Example 1 is that in step S1, the chemical formula Li (Li 0.04 Ni 0.4715 Mn 1.4145 Nb 0.07 Al 0.004 )O 4-δ Weigh the raw materials to prepare the matrix material, with 0 ≤ δ ≤ 0.2. The preparation methods for the remaining lithium nickel manganese oxide cathode materials are basically the same as in Example 1.

[0083] Example 3:

[0084] The difference from Example 1 is that in step S1, the chemical formula Li (Li 0.04 Ni 0.4685 Mn 1.4055 Nb 0.08 Al 0.006 )O 4-δ Weigh the raw materials to prepare the matrix material, with 0 ≤ δ ≤ 0.2. The preparation methods for the remaining lithium nickel manganese oxide cathode materials are basically the same as in Example 1.

[0085] Example 4:

[0086] The difference from Example 1 is that: in the first coating layer, Li 1.4 W 0.2 Ti 1.6 The mass percentage of (PO4)3 to the matrix material is 0.1 wt%. The preparation method of the remaining lithium nickel manganese oxide cathode material is basically the same as that in Example 1.

[0087] Example 5:

[0088] The difference from Example 1 is that: in the first coating layer, Li 1.4 W 0.2 Ti 1.6The mass percentage of (PO4)3 to the matrix material is 2 wt%. The preparation method of the remaining lithium nickel manganese oxide cathode material is basically the same as that in Example 1.

[0089] Example 6:

[0090] The difference from Example 1 is that the mass percentage of Zr(HPO4)2 to the matrix material in the second coating layer is 0.1 wt%. The preparation method of the remaining lithium nickel manganese oxide cathode material is basically the same as that in Example 1.

[0091] Example 7:

[0092] The difference from Example 1 is that the mass percentage of Zr(HPO4)2 to the matrix material in the second coating layer is 1.5 wt%. The preparation method of the remaining lithium nickel manganese oxide cathode material is basically the same as that in Example 1.

[0093] Comparative Example 1:

[0094] The difference from Example 1 is that in step S1, the chemical formula Li(Ni) is used. 0.5 Mn 1.5 )O 4-δ Weigh the raw materials to prepare the matrix material, 0≤δ≤0.2, without performing steps S2 and S3. The matrix material is the lithium nickel manganese oxide cathode material. The preparation methods of the remaining lithium nickel manganese oxide cathode materials are basically the same as in Example 1.

[0095] Comparative Example 2:

[0096] The difference from Example 1 is that steps S2 and S3 are omitted; the substrate material obtained in step S1 is the lithium nickel manganese oxide cathode material. The preparation methods for the remaining lithium nickel manganese oxide cathode materials are basically the same as in Example 1.

[0097] Comparative Example 3:

[0098] The difference from Example 1 is that step S3 is omitted, and only steps S1 and S2 are performed to obtain a single-coated Li-containing product. 1.4 W 0.2 Ti 1.6 The first coating layer of (PO4)3 is a lithium nickel manganese oxide cathode material. The preparation methods of the remaining lithium nickel manganese oxide cathode materials are basically the same as in Example 1.

[0099] Comparative Example 4:

[0100] The difference from Example 1 is that step S2 is omitted, and only steps S1 and S3 are performed to obtain a lithium nickel manganese oxide cathode material with a single coating containing a second coating layer of Zr(HPO4)2. The preparation methods of the remaining lithium nickel manganese oxide cathode materials are basically the same as those in Example 1.

[0101] The following tests were performed on the lithium nickel manganese oxide cathode materials obtained in Examples 1-7 and Comparative Examples 1-4.

[0102] 1. Scanning electron microscopy (SEM) test: A JCM 6000 scanning electron microscope from Japan Electronics Corporation was used. This model of instrument has high-resolution imaging capabilities and can clearly observe the microstructure and structural features of the cathode material. The magnification is 2000Kx and 500Kx.

[0103] 2. X-ray diffraction (XRD) analysis: The test step size was 0.02°, the scanning speed was 2° / min, and the scanning angle was 14~80°.

[0104] 3. Particle size test: The particle size distribution Dv50 was tested using a Malvern 3000 particle size analyzer after internal ultrasonic dispersion for 5 minutes.

[0105] 4. Electrochemical Performance Testing: Battery Preparation: Lithium nickel manganese oxide cathode material was used to fabricate cathode sheets for coin cell assembly. CR2025 coin cells were fabricated using a SP:PVDF:lithium manganese oxide cathode material ratio of 5:3:92. The compaction density of the cathode sheets was 3.0~3.2 g / cm³. 3 .

[0106] (i) Rate performance test: The test operating voltage range is 3.0V~4.9V, the temperature is 25℃, and the charging and discharging are carried out at current densities of 0.1C / 0.1C and 0.2C / 5C. The CV cutoff current of charging is 0.01C. The first discharge capacity and power of the battery made of lithium nickel manganese oxide cathode material are measured. Power = 5C discharge capacity / 0.1C discharge capacity * 100%.

[0107] (ii) Cyclic performance test: The working voltage range is 3.0V~4.9V, the temperature is 45℃, and the battery is cycled 100 times at a current density of 1C. The capacity retention rate of the battery prepared with lithium nickel manganese oxide cathode material is measured.

[0108] (iii) “Shoulder capacity ratio” is the ratio of capacity (3.0~4.3V) to capacity (3.0~4.9V) under 0.1C discharge conditions. The lower the “shoulder capacity ratio”, the lower the capacity contribution ratio of the disordered phase of lithium nickel manganese oxide.

[0109] 5. Gas Generation Test: The amount of gas generated by a 2Ah soft-pack battery made of lithium nickel manganese oxide cathode material was measured when it was stored at 45°C for 7 days in a fully charged state. The specific measurement method adopted was the immersion volume method, which is a solvent displacement method based on Archimedes' principle. This method can accurately obtain the amount of gas generated (mL) and calculate the amount of gas generated per unit mass of cathode material in the cathode sheet (mL / g).

[0110] The relevant process parameters of Examples 1-7 and Comparative Examples 1-4 are shown in Tables 1 and 2, and the corresponding test results of the obtained lithium nickel manganese oxide cathode material and the prepared battery are shown in Table 3.

[0111] Table 1

[0112]

[0113] Table 2

[0114]

[0115] Table 3

[0116]

[0117] The above results indicate that:

[0118] As can be seen from Tables 1 to 3, compared with Comparative Examples 1-4, the lithium nickel manganese oxide cathode materials in Examples 1-7 are superior to those in Comparative Examples 1-4 in terms of discharge capacity, power, cycle performance, and storage (low gas production) performance due to the doping of Nb and Al in the bulk phase of the matrix material and the coating of LWTP and Zr(HPO4)2 on the surface of the matrix material. Specifically, in Example 1, the 0.1C discharge capacity is 133.1 mAh / g, the 5C discharge capacity is 128.1 mAh / g, the power is 96.2%, and the cycle retention rate at 45℃ is 96.3%. In contrast, in Comparative Example 1, the 0.1C discharge capacity is only 130.1 mAh / g, the 5C discharge capacity is 119.3 mAh / g, the power is 91.7%, and the cycle retention rate at 45℃ is 80.2%. The synergistic effect of Nb and Al co-doping with the dual coating of LWTP and Zr(HPO4)2 simultaneously improves the ion transport rate, structural stability and electrochemical stability of high-voltage lithium nickel manganese oxide cathode materials.

[0119] A comparison of Comparative Example 2 with Comparative Example 1 shows that the synergistic composite doping of Nb and Al can improve the power, cycle performance, and storage (low gas production) performance of lithium nickel manganese oxide cathode materials. A comparison of Comparative Example 3 with Comparative Example 2, and Comparative Example 1 with Comparative Example 4, shows that the LWTP fast ion conductor coating in the first coating layer can improve the capacity, power, cycle performance, and storage (low gas production) performance of lithium nickel manganese oxide cathode materials. A comparison of Comparative Example 4 with Comparative Example 2, and Comparative Example 1 with Comparative Example 3, shows that the amorphous Zr(HPO4)2 coating in the second coating layer can improve the cycle performance and storage (low gas production) performance of lithium nickel manganese oxide cathode materials. A comparison of Examples 1-3 with Comparative Example 2 shows that the synergistic effect of the first fast ion conductor coating and the second passivation protective layer coating can significantly improve the capacity, power, cycle performance, and storage (low gas production) performance of lithium nickel manganese oxide materials.

[0120] As can be seen from the comparison of Examples 1-3, when the doping amounts of Nb and Al are slightly adjusted within the specified range, the electrochemical performance of the lithium nickel manganese oxide cathode material is at a good level. There are no significant differences in the capacity, rate performance, cycle performance and storage performance of the lithium nickel manganese oxide cathode materials in Examples 1-3.

[0121] from Figure 3 and Figure 4 It can be seen that the final morphology of lithium nickel manganese oxide cathode materials in Example 1 and Comparative Example 1 are both single crystal particles. The morphology of lithium nickel manganese oxide cathode material in Example 1 is more rounded and uniform than that in Comparative Example 1, and is closer to a sphere.

[0122] from Figure 5 As can be seen from the XRD patterns of Examples 1-3 and Comparative Examples 1-4, both Examples 1-3 and Comparative Examples 1-4 formed lithium nickel manganese oxide phases without impurity peaks.

[0123] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of the present invention, and the present invention is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A lithium nickel manganese oxide cathode material, characterized in that, The positive electrode active material comprises a base material, a first coating layer on the surface of the base material, and a second coating layer on the side of the first coating layer away from the base material, wherein the base material comprises a lithium nickel manganese oxide positive electrode active material co-doped with Nb and Al, the first coating layer contains Li 1.4 W 0.2 Ti 1.6 (PO4)3, and the second coating layer contains Zr(HPO4)2, and the chemical general formula of the base material is Li c Ni （2-a-b-c） / 4 Mn 3（2-a-b-c） / 4Nb a Al b )O 4-δ , 0.02≤a≤0.06, 0.05≤b≤0.15, 0.02≤c≤0.1, 0≤δ≤0.2, the mass percentage of the Li 1.4 W 0.2 Ti 1.6 (PO4)3 in the base material is 0.5wt%-2wt%, and the mass percentage of the Zr(HPO4)2 in the base material is 0.1wt%-1.5wt%.

2. The lithium nickel manganese oxide cathode material of claim 1, wherein, The base material is a spinel structure; The Li 1.4 W 0.2 Ti 1.6 (PO4)3 is a sodium superionic conductor type structure; The Zr(HPO4)2 is amorphous.

3. The lithium nickel manganese oxide cathode material of claim 1, wherein, The lithium nickel-manganese oxide positive electrode material is a single crystal material.

4. A method for preparing a lithium nickel manganese oxide cathode material, characterized in that, comprising: A nickel-manganese precursor, a lithium source, an aluminum source and a niobium source are mixed to form a mixture, the mixture is subjected to a first sintering to obtain a base material, the base material has a chemical general formula of Li(Li c Ni （2-a-b-c） / 4 Mn 3（2-a-b-c） / 4 Nb a Al b )O 4-δ , 0.02≤a≤0.06, 0.05≤b≤0.15, 0.02≤c≤0.1, 0≤δ≤0.2; mixing the base material with a first coating agent and spray drying to obtain a dry material, and secondly sintering the dry material to react on the surface of the base material to form a first coating layer containing Li 1.4 W 0.2 Ti 1.6 (PO4)3, the mass percentage of Li 1.4 W 0.2 Ti 1.6 (PO4)3and the base material is 0.5wt%-2wt%, to obtain an intermediate material; and mixing the intermediate material with a second coating agent and performing a third sintering to form a second coating layer containing Zr(HPO4)2 on the surface of the intermediate material, the mass percentage of the Zr(HPO4)2 to the base material being 0.1wt%-1.5wt%, to obtain the lithium nickel-manganese oxide positive electrode material.

5. The production method according to claim 4, wherein The atmosphere pressure of the first sintering is greater than 0.01MPa-0.20MPa than the atmospheric pressure, and the atmosphere of the first sintering is an oxygen-containing atmosphere with an oxygen concentration of 20%-70%.

6. The production method according to claim 4, wherein The first sintering comprises a first-stage sintering and a second-stage sintering performed in sequence, the temperature of the first-stage sintering being 850°C-950°C, and the time of the first-stage sintering being 6h-20h; The temperature of the second-stage sintering is 550°C-750°C, and the time of the second-stage sintering is 5h-10h; The temperature is decreased from the temperature of the first-stage sintering to the temperature of the second-stage sintering at a cooling rate of 1°C / min-4°C / min.

7. The production method according to claim 4, wherein The water content of the dried material is 0-1wt%; and / or The atmosphere pressure of the second sintering is greater than 0.01MPa-0.20MPa than the atmospheric pressure, and the atmosphere of the second sintering is an oxygen-containing atmosphere with an oxygen concentration of 20%-70%; and / or The temperature of the second sintering is 600°C-700°C, and the time of the second sintering is 6h-12h.

8. The production method according to claim 4, wherein The atmosphere pressure of the third sintering is greater than 0.01MPa-0.20MPa than the atmospheric pressure, and the atmosphere of the third sintering is an air atmosphere; and / or The temperature of the third sintering is 300°C-450°C, and the time of the third sintering is 6h-12h.

9. An electrochemical device, characterized by, The electrochemical device comprises a positive electrode sheet, the positive electrode sheet comprising a positive electrode material, the positive electrode material being the lithium nickel-manganese oxide positive electrode material according to any one of claims 1-3 or the lithium nickel-manganese oxide positive electrode material prepared by the preparation method according to any one of claims 4-8.

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