Lithium-rich manganese-based oxide positive electrode material with reconstructed surface and preparation method of lithium-rich manganese-based oxide positive electrode material

Abstract

The invention relates to a surface-reconstructed lithium-rich manganese-based oxide positive electrode material and a preparation method thereof. The method comprises the following steps: (1) dispersing lithium-rich manganese-based oxide powder in a heteropolyacid solution, and fully mixing, infiltrating and drying to obtain heteropolyacid-coated lithium-rich manganese-based oxide; the heteropoly acid is an inducer for surface reconstruction of the lithium-rich manganese-based oxide; and (2) carrying out heat treatment on the heteropolyacid-coated lithium-rich manganese-based oxide to induce a surface reaction so as to obtain the surface-reconstructed lithium-rich manganese-based oxide positive electrode material. According to the method, in-situ reconstruction is carried out on the surface of the lithium-rich manganese-based oxide to obtain the disordered rock salt phase heterostructure layer, and the reconstructed layer not only inhibits oxygen precipitation and stabilizes the structure of the material, but also provides rapid lithium ion conduction, so that the charge-discharge cycle performance and the rate capability of the lithium-rich manganese-based oxide are greatly improved. In addition, the method is simple in process and low in cost, and has a large-scale application prospect.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and relates to the surface modification of lithium-rich manganese-based oxides, specifically to a structural design and preparation method of a surface reconstruction layer based on a disordered rock salt phase. Background Technology

[0002] High-capacity cathode materials are one of the most critical factors in improving the energy density of lithium-ion batteries and have always been a research hotspot both domestically and internationally. Traditional cathode materials, such as lithium cobalt oxide, nickel-cobalt-manganese ternary materials, lithium manganese oxide, and lithium iron phosphate, have relatively low actual specific capacities (<220 mAhg). -1 The traditional method of using conventional cathodes (CCPs) is gradually failing to meet the market's demand for long driving ranges in electric vehicles. Among the new generation of cathodes, lithium-rich manganese-based oxide cathodes possess high specific capacity exceeding 250 mAh / g and low cost. They are derived from traditional layered oxide cathodes where lithium replaces a small amount of metal elements in the transition metal layers. Their industrialization can be modeled after the relatively mature nickel-cobalt-manganese ternary materials, making them the most promising cathode material for achieving a single-cell energy density exceeding 400 Wh / kg in lithium-ion power batteries, with significant potential for industrial application. The chemical formula of lithium-rich manganese-based oxides can be represented as xLi₂MnO₃·(1-x)LiMO₂ (M = Ni, Co, Mn) or Li 1+x M 1-x O2 (M=Ni, Co, Mn) can be viewed as a two-phase or solid solution structure composed of LiMO2 (orthorhombic hexahedral R-3m type structure) and Li2MnO3 (C2 / m type monoclinic structure) at the nanoscale.

[0003] Since Numata et al. first reported the lithium-rich manganese-based oxide cathode material LiCoO2-Li2MnO3 in 1997, its cycle stability has been a persistent issue, hindering its commercial application. The key problem lies in the fact that the activation of oxygen redox activity at high potentials in lithium-rich manganese-based oxides easily leads to oxygen evolution, causing not only the loss of active oxygen but also a series of problems such as material structure collapse and transition metal migration, resulting in voltage and capacity decay. The main methods for modifying lithium-rich manganese-based oxides include elemental doping and surface modification. Researchers hope to stabilize the material structure by elemental doping the bulk phase, thereby improving the initial charge-discharge efficiency and suppressing voltage decay. However, while stabilizing the bulk lattice oxygen, the redox activity of bulk oxygen in lithium-rich manganese-based oxides is also significantly suppressed, causing capacity loss (J. Am. Chem. Soc. 2023, 145, 15, 8700–8713). Lattice oxygen release and lattice structure disruption in lithium-rich manganese-based oxides often begin at the surface and extend to the bulk phase with cycling (Nat. Nanotechnol. 2019, 14, 602–608). Therefore, surface modification is an effective strategy to improve the stability of such materials. Researchers both domestically and internationally have mainly focused on constructing surface coatings to suppress lattice oxygen evolution and transition metal ion dissolution, thereby improving the cycling stability of lithium-rich manganese-based oxides. Common coatings include metal oxides, metal fluorides, and metal phosphates. While these coatings improve the initial coulombic efficiency and cycling stability of lithium-rich manganese-based oxide cathodes to some extent, they often exhibit low ionic and electronic conductivity, which inhibits capacity release and affects rate performance. Furthermore, achieving uniform heterogeneous coating is very challenging (Adv. Funct. Mater. 2023, 2213260). Therefore, considering the existing problems of lithium-rich manganese-based oxides and the current research status, developing an efficient surface modification method is crucial. Summary of the Invention

[0004] Therefore, this invention provides a method for in-situ construction of a disordered rock salt phase reconstruction layer on the surface of lithium-rich manganese-based oxides. This is achieved through the following technical solution: (1) Disperse lithium-rich manganese-based oxide powder in a heteropoly acid solution, and after thorough mixing, wetting and drying, obtain lithium-rich manganese-based oxide coated with heteropoly acid; heteropoly acid is an inducing agent for surface reconstruction of lithium-rich manganese-based oxide. (2) The lithium-rich manganese-based oxide coated with heteropolyacid is subjected to heat treatment to induce surface reaction, thereby obtaining a surface-reconstructed lithium-rich manganese-based oxide cathode material.

[0005] In this invention, lithium-rich manganese-based oxide powder is dispersed in a solution of heteropolyacids. Heteropolyacids are a class of oxypolyacids composed of heteroatoms (X, such as P, Si, etc.) and polyatoms (M, such as Mo, W, V, Nb, Ta, etc.) linked by oxygen atom coordination bridging in a specific structure. They are readily soluble in organic solvents such as water and ethanol. After thorough mixing, wetting, and drying, the heteropolyacid precipitate uniformly coats the primary particles of the lithium-rich manganese-based oxide. Heteropolyacids exhibit the general properties of acids; heat treatment causes H2O to form on the surface. + / Li + Exchange and H + The extracted nickel and cobalt ions from the transition metal layer readily diffuse to vacancies in the lithium layer, resulting in a disordered rock salt phase reconstruction layer. The exchanged lithium reacts with MO6 octahedra in heteropolyacids to form lithium-conducting materials (such as Li2MoO4, Li2WO4, LiNbO3, etc.). A small number of heteroatoms (such as P, Si, etc.) can be doped into the surface lattice to form polyanions with strong covalent interactions (such as PO4). 3- SiO4 4- (etc.), thereby obtaining a reconstructed layer based on a disordered rock salt phase on the surface of lithium-rich manganese-based oxide, and thus obtaining a surface-reconstructed lithium-rich manganese-based oxide cathode material.

[0006] Preferably, the lithium-rich manganese-based oxide includes polycrystalline lithium-rich manganese-based oxide and monocrystalline lithium-rich manganese-based oxide.

[0007] Preferably, the polycrystalline lithium-rich manganese-based oxide is composed of secondary lithium-rich manganese-based oxide particles with a particle size of 1 to 100 μm, which are composed of primary lithium-rich manganese-based oxide particles with a particle size of 50 to 500 nm.

[0008] Preferably, the particle size of the single-crystal lithium-rich manganese-based oxide is 50 nm to 5 μm.

[0009] Preferably, the lithium-rich manganese-based oxide has the composition xLi2MnO3·(1-x)LiMO2, 0<x≤1, and M is one or more of Ni, Co and Mn.

[0010] Preferably, the heteropolyacids include phosphomolybdic acid, phosphotungstic acid, phosphoninic acid, phosphotantalic acid, silimolybdic acid, and silimolybdic acid.

[0011] Preferably, the solvent for the heteropolyacid solution is at least one selected from distilled water, ethanol, methanol, isopropanol, n-butanol, isobutanol, and cycloethanol.

[0012] Preferably, the mass ratio of the heteropolyacid to the lithium-rich manganese-based oxide is 0.5% to 5%; the solid content of the lithium-rich manganese-based oxide in the heteropolyacid solution is 0.5 wt% to 50 wt%; the mixing and impregnation method is one or more of mechanical stirring, magnetic stirring, and ultrasonic dispersion; the drying temperature is 20 to 90°C, and the time is 0.5 to 12 h; preferably, stirring and / or ultrasonic treatment can be performed during the drying process.

[0013] Preferably, the heat treatment temperature for the surface-induced reaction is 250~800℃, the heat treatment time is 0.5~24 h, the heat treatment heating rate is 2~5 ℃ / min, and the heat treatment atmosphere is one of air, oxygen, nitrogen, and argon.

[0014] On the other hand, the present invention provides a lithium-rich manganese-based oxide cathode material with surface reconstruction prepared according to the above method.

[0015] Compared with the prior art, the present invention achieves the following technical effects: The basic principle of this invention is to utilize heteropolyacid complexes (such as phosphomolybdic acid, phosphotungstic acid, phosphoninic acid, phosphotantalic acid, silicomolybdic acid, silicotungstic acid, etc.) as inducing agents for surface reconstruction of lithium-rich manganese-based oxides, and to utilize H during the heat treatment process. + / Li + The exchange reaction causes the material surface to form a lithium-deficient state, thereby inducing nickel and cobalt ions to diffuse into the lithium layer to form a disordered rock salt phase reconstruction layer. This reconstruction layer not only inhibits oxygen evolution and stabilizes the material structure, but also provides a fast lithium-ion conduction rate, which can effectively improve the charge-discharge cycle performance and rate performance of lithium-rich manganese-based oxides.

[0016] In addition, H + / Li + The lithium produced by the exchange reaction can form lithium-conducting materials (such as Li₂MoO₄, Li₂WO₄, LiNbO₃, etc.) with the MO₆ octahedrons in heteropolyacids, providing a fast lithium-ion transport channel. A small number of heteroatoms (such as P, Si, etc.) can be doped into the surface lattice to form polyanions with strong covalent interactions (such as PO₄²⁻). 3- SiO4 4- (etc.), which can further stabilize the oxygen framework on the surface of lithium-rich manganese-based oxides. The synergistic effect of the two can further improve the cycle stability and rate performance of lithium-rich manganese-based oxides.

[0017] The surface reconstruction layer described in this invention is a disordered rock-salt phase heterostructure constructed in situ on the surface of lithium-rich manganese-based oxides. It has an atomic-level chemical bond with the material bulk, and is not a simple physical coating. Therefore, the surface modification layer will not detach due to stress generated during charging and discharging. This invention's technical solution is simple in process, low in cost, and has potential for large-scale application. Attached Figure Description

[0018] Figure 1 The image shows the X-ray diffraction (XRD) patterns of lithium-rich manganese-based oxides, including Example 1, Example 2, and Comparative Example 1 without surface reconstruction. Figures 2A-2B The image shows a scanning electron microscope (SEM) image of a lithium-rich manganese-based oxide, which is Example 1 after surface reconstruction. Figures 3A-3B The image is a high-angle annular dark-field image (HAADF-STEM) of a lithium-rich manganese-based oxide, which is Example 1 after surface reconstruction. Figure 4 The first charge-discharge curve of the lithium-rich manganese-based oxide cathode material at a rate of 0.1C is shown. The lithium-rich manganese-based oxide includes Example 1 and Example 2, which have undergone surface reconstruction, and Comparative Example 1, which has not undergone surface reconstruction. Figures 5A-5C The charge-discharge curves of lithium-rich manganese-based oxide cathode materials at different charge-discharge cycles at 0.5 C rate are shown. The lithium-rich manganese-based oxide includes Comparative Example 1 (5A) without surface reconstruction, Example 1 (5B) and Example 2 (5C) with surface reconstruction. Figure 6 The graph shows a comparison of the cycle stability of lithium-rich manganese-based oxide cathode materials, including Example 1 and Example 2 with surface reconstruction and Comparative Example 1 without surface reconstruction. Figure 7 The initial discharge specific capacity (0.1 C) and initial coulombic efficiency, specific capacity and capacity retention before and after 0.5 C cycling of different lithium-rich manganese-based oxides were summarized. The lithium-rich manganese-based oxides included Examples 1, 2, 3 and 4 with surface reconstruction, and Comparative Examples 1 and 2 without surface reconstruction. Detailed Implementation

[0019] The present invention is further illustrated by the following embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the present invention.

[0020] In this invention, heteropoly acids (such as phosphomolybdic acid, phosphotungstic acid, phosphoninic acid, phosphotantalic acid, silicomolybdic acid, silicotungstic acid, etc.) are innovatively used as inducing agents for surface reconstruction of lithium-rich manganese-based oxides, and H is generated through heat treatment. + / Li +The exchange reaction creates a lithium-deficient state on the material surface, inducing nickel and cobalt ions to diffuse into the lithium layer, forming a disordered rock-salt phase reconstruction layer. Simultaneously, lithium-conducting materials (such as Li₂MoO₄, Li₂WO₄, LiNbO₃, etc.) and a small amount of heteroatoms (such as P, Si, etc.) are formed on the material surface. This surface reconstruction layer not only suppresses oxygen evolution and stabilizes the material structure but also provides a rapid lithium-ion conduction rate, effectively improving the charge-discharge cycle performance and rate performance of lithium-rich manganese-based oxides. The surface reconstruction layer described in this invention is a heterostructure based on a disordered rock-salt phase constructed on the surface of lithium-rich manganese-based oxides through in-situ reaction. It is not a simple physical coating but has atomic-level chemical bonding with the bulk material, eliminating the risk of lattice stress causing the modification layer to detach. This invention has a novel technical principle, simple process, and low cost, facilitating large-scale application. More specifically, to better understand this invention, specific embodiments are described in further detail below.

[0021] Preparation of heteropolyacid solutions. Heteropolyacids were selected as inducing agents for surface reconstruction of lithium-rich manganese-based oxides. Heteropolyacids possess the general properties of acids and can induce H+ ionization during heat treatment. + / Li + The exchange reaction creates a lithium-deficient state on the material surface, inducing nickel and cobalt ions to diffuse into the lithium layer, forming a disordered rock salt phase reconstruction layer. Simultaneously, lithium-conducting materials (such as Li₂MoO₄, Li₂WO₄, LiNbO₃, etc.) may form. Small amounts of heteroatoms (such as P, Si, etc.) can be doped into the surface lattice to form polyanions with strong covalent interactions (such as PO₄²⁻). 3- SiO4 4- This reconstructed layer stabilizes the surface structure of the material and provides a rapid lithium-ion conductivity. The solvent used to dissolve the heteropolyacid is at least one of distilled water, ethanol, methanol, isopropanol, n-butanol, isobutanol, and cycloethanol. The mass of the heteropolyacid powder used should be calculated based on the mass ratio of the heteropolyacid to the lithium-rich manganese-based oxide (0.5%~5%). The mass fraction of the heteropolyacid solution is determined based on the solid content of the lithium-rich manganese-based oxide in the heteropolyacid solution (0.5wt%~50wt%).

[0022] Lithium-rich manganese-based oxide powder is dispersed in a solution of a heteropolyacid (at least one selected from phosphomolybdic acid, phosphotungstic acid, phosphoninic acid, phosphotantalic acid, silimolybdic acid, and silimolybdic acid) to obtain a mixed solution containing lithium-rich manganese-based oxide. After thorough mixing, wetting, and drying, heteropolyacid-coated lithium-rich manganese-based oxide is obtained. The lithium-rich manganese-based oxide includes polycrystalline lithium-rich manganese-based oxide and monocrystalline lithium-rich manganese-based oxide. The polycrystalline lithium-rich manganese-based oxide consists of primary lithium-rich manganese-based oxide particles with a particle size of 50-500 nm, followed by secondary lithium-rich manganese-based oxide particles with a particle size of 1-100 μm. The monocrystalline lithium-rich manganese-based oxide has a particle size of 50 nm to 5 μm. The composition of the lithium-rich manganese-based oxide is xLi₂MnO₃·(1-x)LiMO₂, where 0 < x ≤ 1, and M is one or more of Ni, Co, and Mn. The mixing and impregnation methods are one or more of mechanical stirring, magnetic stirring, and ultrasonic dispersion. The drying temperature is 20~90℃ and the time is 0.5~12 h. During the drying process, stirring and / or ultrasonic treatment may be performed.

[0023] Lithium-rich manganese-based oxides coated with heteropolyacids are subjected to heat treatment to induce surface reactions, thereby obtaining surface-reconstructed lithium-rich manganese-based oxide cathode materials. The heat treatment temperature for the surface reaction is 250–800 °C, the heat treatment time is 0.5–24 h, the heat treatment heating rate is 2–5 °C / min, and the heat treatment atmosphere is one of air, oxygen, nitrogen, or argon.

[0024] The following examples further illustrate the present invention in detail. It should be understood that the following examples are for illustrative purposes only and should not be construed as limiting the scope of protection of the present invention. Non-essential improvements and adjustments made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The process parameters in the following examples are also merely an example within a suitable range, and those skilled in the art can make appropriate selections based on the description herein.

[0025] Comparative Example 1 Unmodified raw lithium-rich manganese-based oxides (Li) 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2).

[0026] Electrode preparation and battery assembly: Lithium-rich manganese-based oxide cathode material, Super P, and PVDF were mixed in an 8:1:1 ratio, and N-methylpyrrolidone was added. The mixture was stirred to form a slurry and coated onto aluminum foil. The coated cathode was then dried in a vacuum drying oven. The dried cathode was cut into small circular pieces with a diameter of 12 mm. A 14 mm diameter lithium metal sheet was used as the anode, and a 16 mm diameter PE film was used as the separator. The separator and electrode sheet were wetted with high-voltage electrolyte. CR2025 button cells were assembled in an argon glove box and allowed to stand at room temperature (25°C) for 8 h before testing.

[0027] Battery Testing: The button batteries, after being left to rest, were tested using a Newway battery tester at room temperature (25°C). A constant current charge / discharge mode was used, with the current set at a rate of 1 C = 250 mAg. -1 The calculated charging and discharging voltage range is 2.0V-4.7V.

[0028] Material morphology and structural characterization: The microstructure of the lithium-rich manganese-based oxide cathode material was observed using a field emission scanning electron microscope (Nova Nano SEM-450). The phase composition of the cathode material was analyzed using X-ray diffraction (X'Pert Powder). High-resolution HAADF-STEM images of the cathode material were observed using a Hitachi HF5000 condenser lens aberration-corrected transmission electron microscope.

[0029] Comparative Example 2 Step 1): Take 2 g of lithium-rich manganese-based oxide (Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2), add 10 mL of ethanol, and ultrasonically disperse for 30 min; Step 2): Stir the mixture from Step 1) in a 50°C water bath for 1 hour, then dry it in a drying oven at 60°C for 2 hours. Collect the powder after drying. Step 3): Place the powder obtained in Step 2) into a muffle furnace, heat it to 350°C in air at a rate of 5°C / min, calcine for 2 h, and then cool it naturally to room temperature. Grind and collect the material to obtain lithium-rich manganese-based oxide cathode material.

[0030] The obtained cathode material of Comparative Example 2 was characterized in terms of microstructure and structure, and the electrode was prepared, battery was assembled and tested. The process was the same as that of Comparative Example 1.

[0031] Example 1 Step 1): Dissolve 0.028 g of phosphomolybdic acid in 10 mL of ethanol to prepare a phosphomolybdic acid solution with a mass fraction of 0.35%. Step 2): Take 2 g of lithium-rich manganese-based oxide (Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2), mixed with phosphomolybdic acid solution, and ultrasonically dispersed for 30 min; Step 3): The mixture from Step 2) is stirred in a 50°C water bath for 1 hour, then placed in a drying oven at 60°C for 2 hours. After drying, lithium-rich manganese-based oxides coated with phosphomolybdic acid are obtained. Step 4): The lithium-rich manganese-based oxide coated with phosphomolybdic acid obtained in Step 3) is placed in a muffle furnace and heated to 350°C in air at a rate of 5°C / min. It is calcined for 2 h and then naturally cooled to room temperature. The material is then ground and collected to obtain the surface-reconstructed lithium-rich manganese-based oxide cathode material.

[0032] The microstructure and structure characterization, electrode preparation, battery assembly and testing of the surface-reconstructed lithium-rich manganese-based oxide obtained in Example 1 were carried out in the same manner as in Comparative Example 1.

[0033] Example 2 Step 1): Dissolve 0.028 g of phosphomolybdic acid in 10 mL of ethanol to prepare a phosphomolybdic acid solution with a mass fraction of 0.35%. Step 2): Take 2 g of lithium-rich manganese-based oxide (Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2), mixed with phosphomolybdic acid solution, and ultrasonically dispersed for 30 min; Step 3): The mixture from Step 2) is stirred in a 50°C water bath for 1 hour, then placed in a drying oven at 60°C for 2 hours. After drying, lithium-rich manganese-based oxides coated with phosphomolybdic acid are obtained. Step 4): The lithium-rich manganese-based oxide coated with phosphomolybdic acid obtained in Step 3) is placed in a muffle furnace and heated to 600°C in air at a rate of 5°C / min. It is calcined for 2 hours and then naturally cooled to room temperature. The material is then ground and collected to obtain the surface-reconstructed lithium-rich manganese-based oxide cathode material.

[0034] The microstructure and structure characterization, electrode preparation, battery assembly and testing of the surface-reconstructed lithium-rich manganese-based oxide obtained in Example 2 were carried out in the same manner as in Comparative Example 1.

[0035] Example 3 Step 1): Dissolve 0.028 g of phosphomolybdic acid in 10 mL of ethanol to prepare a phosphomolybdic acid solution with a mass fraction of 0.35%. Step 2): Take 2 g of lithium-rich manganese-based oxide (Li 1.2 Ni0.13 Co 0.13 Mn 0.54 O2), mixed with phosphomolybdic acid solution, and ultrasonically dispersed for 30 min; Step 3): The mixture from Step 2) is stirred in a 50°C water bath for 1 hour, then placed in a drying oven at 60°C for 2 hours. After drying, lithium-rich manganese-based oxides coated with phosphomolybdic acid are obtained. Step 4): The lithium-rich manganese-based oxide coated with phosphomolybdic acid obtained in Step 3) is placed in a muffle furnace and heated to 500°C in air at a rate of 5°C / mins. It is calcined for 2 h and then naturally cooled to room temperature. The material is then ground and collected to obtain the surface-reconstructed lithium-rich manganese-based oxide cathode material.

[0036] The microstructure and structure characterization, electrode preparation, battery assembly and testing of the surface-reconstructed lithium-rich manganese-based oxide obtained in Example 3 were carried out in the same manner as in Comparative Example 1.

[0037] Example 4 Step 1): Dissolve 0.056 g of phosphomolybdic acid in 10 mL of ethanol to prepare a phosphomolybdic acid solution with a mass fraction of 0.35%. Step 2): Take 2 g of lithium-rich manganese-based oxide (Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2), mixed with phosphomolybdic acid solution, and ultrasonically dispersed for 30 min; Step 3): The mixture from Step 2) is stirred in a 50°C water bath for 1 hour, then placed in a drying oven at 60°C for 2 hours. After drying, lithium-rich manganese-based oxides coated with phosphomolybdic acid are obtained. Step 4): The lithium-rich manganese-based oxide coated with phosphomolybdic acid obtained in Step 3) is placed in a muffle furnace and heated to 350°C in air at a rate of 5°C / min. It is calcined for 2 h and then naturally cooled to room temperature. The material is then ground and collected to obtain the surface-reconstructed lithium-rich manganese-based oxide cathode material.

[0038] The microstructure and structure characterization, electrode preparation, battery assembly and testing of the surface-reconstructed lithium-rich manganese-based oxide obtained in Example 4 were carried out in the same manner as in Comparative Example 1.

[0039] Example 5 Step 1): Dissolve 0.045 g of phosphotungstic acid in 10 mL of ethanol to prepare a phosphotungstic acid solution with a mass fraction of 0.56%. Step 2): Take 2 g of lithium-rich manganese-based oxide (Li 1.2 Ni 0.13 Co 0.13 Mn0.54 O2) is mixed with phosphotungstic acid solution and ultrasonically dispersed for 30 min; Step 3): The mixture from Step 2) is stirred in a 50°C water bath for 1 hour, then placed in a drying oven at 60°C for 2 hours. After drying, lithium-rich manganese-based oxides coated with phosphotungstic acid are obtained. Step 4): The lithium-rich manganese-based oxide coated with phosphotungstic acid obtained in Step 3) is placed in a muffle furnace and heated to 350°C in air at a rate of 5°C / min. It is calcined for 2 h and then naturally cooled to room temperature. The material is then ground and collected to obtain the surface-reconstructed lithium-rich manganese-based oxide cathode material.

[0040] The microstructure and structure characterization, electrode preparation, battery assembly and testing of the surface-reconstructed lithium-rich manganese-based oxide obtained in Example 5 were carried out in the same manner as in Comparative Example 1.

[0041] Example 6 Step 1): Dissolve 0.028 g of molybdic acid in 10 mL of ethanol to prepare a 0.35% molybdic acid solution; Step 2): Take 2 g of lithium-rich manganese-based oxide (Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2), mixed with molybdic acid solution, and ultrasonically dispersed for 30 min; Step 3): The mixture from Step 2) is stirred in a 50°C water bath for 1 hour, then placed in a drying oven at 60°C for 2 hours. After drying, lithium-rich manganese-based oxides coated with molybdate are obtained. Step 4): The lithium-rich manganese-based oxide coated with molybdenum silica obtained in Step 3) is placed in a muffle furnace and heated to 350°C in air at a rate of 5°C / min. It is calcined for 2 hours and then naturally cooled to room temperature. The material is then ground and collected to obtain the surface-reconstructed lithium-rich manganese-based oxide cathode material.

[0042] The microstructure and structure characterization, electrode preparation, battery assembly and testing of the surface-reconstructed lithium-rich manganese-based oxide obtained in Example 6 were carried out in the same manner as in Comparative Example 1.

[0043] Figure 1The X-ray diffraction (XRD) patterns of lithium-rich manganese-based oxide cathode materials include Examples 1 and 2 with surface reconstruction and Comparative Example 1 without surface reconstruction. The XRD patterns show that the diffraction peaks of Examples 1 and 2 with surface reconstruction and Comparative Example 1 without surface reconstruction all match well with the layered α-NaFeO2 structure (R-3m space group), and all show diffraction peaks corresponding to the Li2MnO3 (C2 / m space group) superlattice within the diffraction angle range of 20°-25°. This demonstrates that all three materials possess a typical two-phase solid solution structure of lithium-rich manganese-based oxides, and also indicates that the chemical reaction of phosphomolybdic acid-induced surface reconstruction does not alter the bulk structure of the lithium-rich manganese-based oxide.

[0044] Figures 2A-2B This is a scanning electron microscope (SEM) image of Example 1 after surface reconstruction. Figure 2A The SEM image (20,000x magnification) shows that the diameter of the secondary particles of lithium-rich manganese-based oxide reconstructed on the surface is approximately 10 μm. Figure 2B SEM images (100,000x magnification) show that the diameter of the primary particles constituting the secondary particles of the lithium-rich manganese-based oxide is 200–500 nm. This result is the same as the morphology of the original lithium-rich manganese-based oxide, indicating that the phosphomolybdic acid-induced surface reconstruction does not change the microstructure of the lithium-rich manganese-based oxide.

[0045] Figures 3A-3B This is a high-angle annular dark-field image (HAADF-STEM) of Example 1 after surface reconstruction. Figure 3A The edge brightness of the primary particles in the medium is significantly higher than that of the bulk phase, and the thickness of the brighter portion is approximately 3 nm. (Selection) Figure 3A A magnified image of a portion of the image near the edge was taken to obtain an atomic-level HAADF-STEM image along the

[010] zone axis. Figure 3B The image shows a typical layered lattice structure of lithium-rich manganese-based oxides within the particle. The bright spots represent heavier transition metal ions, while lighter oxygen and lithium ions, which are not visualized, are distributed on either side of the transition metal and between the layers. The outer surface shows a distinct disordered rock salt phase reconstruction layer, where the original lithium layers have been occupied by the transition metal, forming a lithium-deficient phase with a thickness of approximately 3 nm. In HAADF-STEM mode, the disordered rock salt phase, with its higher concentration of heavier transition metal cations, exhibits greater brightness, indicating... Figure 3A The primary particles are encapsulated by this rock salt phase. Therefore, HAADF-STEM characterization demonstrates that phosphomolybdic acid successfully induced the formation of a surface reconstruction layer based on the disordered rock salt phase on the surface of lithium-rich manganese-based oxide particles.

[0046] Figure 4This is a comparison of the initial charge-discharge curves of lithium-rich manganese-based oxide cathode materials at 0.1 C. The materials include Example 1 and Example 2, which underwent surface reconstruction, and Comparative Example 1, which did not undergo surface reconstruction. The results show that Comparative Example 1, without surface reconstruction, has an initial discharge specific capacity of 308 mAhg. -1 The initial coulombic efficiency was 86.6%, while Example 1, which underwent surface reconstruction at 350°C, exhibited the highest initial discharge specific capacity, reaching 317 mAh g⁻¹ at 0.1 C. -1 The initial coulombic efficiency was 88.9%, both higher than that of Comparative Example 1. Furthermore, the initial discharge capacity of Example 2, after surface reconstruction at 600°C, was 297 mAh g⁻¹. -1 The initial coulombic efficiency was 86.3%, and the discharge specific capacity was slightly lower than that of Example 1 and Comparative Example 1. The discharge curve of Example 2 showed a clear discharge plateau of spinel phase at the 2.5 V voltage position, indicating that excessively high induction temperature would cause the rock salt reconstructed layer to transform into a spinel reconstructed layer, which would sacrifice some capacity.

[0047] Figures 5A-5C Charge-discharge curves of lithium-rich manganese-based oxide cathode materials at different charge-discharge cycles at 0.5 C rate (Note: the first charge-discharge was performed at 0.1 C rate for battery activation). The lithium-rich manganese-based oxide includes Comparative Example 1 (5A) without surface reconstruction, Example 1 (5B) and Example 2 (5C) with surface reconstruction. Figure 6 This is a comparison of the cycle stability of these lithium-rich manganese-based oxides. Comparative Example 1, without surface reconstruction, has a discharge specific capacity of 268.9 mAhg at 0.5 C rate. -1 After 200 cycles, the specific capacity was 201.3 mAhg. -1 The capacity retention rate was 74.8%. Meanwhile, Example 1, after surface reconstruction at 350°C, exhibited a discharge specific capacity of 275.1 mAhg at a high rate of 0.5 C. -1 After 200 cycles, the specific capacity reached 234.9 mAhg. -1 The capacity retention rate was 85.4%, which was higher than that of Comparative Example 1. Example 2, after surface reconstruction at 600°C, had a discharge specific capacity of 262.8 mAhg at a 0.5 C rate. -1 Although slightly lower than Comparative Example 1, the specific capacity still reached 225.9 mAhg after 200 cycles. -1 The capacity retention rate was 85.9%, and the cycle stability was also better than that of the comparative example 1 without surface reconstruction. Furthermore, combining the charge-discharge curves ( Figures 5A-5CAs can be seen, compared with Comparative Example 1 without surface reconstruction, Examples 1 and 2 with surface reconstruction have significantly lower voltage drops after 200 cycles, indicating that phosphomolybdic acid-induced surface reconstruction significantly improves the structural stability of lithium-rich manganese-based oxides.

[0048] Figure 7 The parameters such as initial discharge specific capacity, initial coulombic efficiency, and capacity retention during cycling of different cathode materials were summarized. It can be seen that lithium-rich manganese-based oxides with phosphomolybdic acid-induced surface reconstruction have significantly better rate performance and cycle stability.

[0049] The results of material characterization and battery testing show that the surface reconstruction induced by other heteropoly acids, such as phosphotungstic acid (Example 5) and silicomolybdic acid (Example 6), also significantly improves the structural stability of lithium-rich manganese-based oxides, thereby significantly improving the rate performance and cycle stability of the cathode material.

[0050] The above results fully demonstrate the effectiveness of the modification method of surface reconstruction of lithium-rich manganese-based oxides induced by heteropolyacids, which can significantly improve the rate performance and cycle stability of lithium-rich manganese-based oxide cathode materials.

[0051] The above embodiments are merely preferred embodiments provided to fully illustrate the present invention, and it should be understood that the scope of protection of the present invention is not limited thereto. The scope of protection of the present invention is defined by the claims. Any non-essential improvements and adjustments made by those skilled in the art based on the present invention are also within the scope of protection of the present invention.

Claims

1. A method for preparing a surface-reconstructed lithium-rich manganese-based oxide cathode material, characterized in that, The method comprises the following steps: (1) dispersing the lithium-rich manganese-based oxide powder in a solution of heteropoly acid, and obtaining a lithium-rich manganese-based oxide coated with heteropoly acid through sufficient mixing, infiltration and drying; the heteropoly acid is an inducing agent for surface reconstruction of the lithium-rich manganese-based oxide; (2) performing heat treatment on the lithium-rich manganese-based oxide coated with heteropoly acid to induce surface reaction, and obtaining a surface-reconstructed lithium-rich manganese-based oxide positive electrode material.

2. The production method according to claim 1, characterized by, The lithium-rich manganese-based oxide comprises polycrystalline lithium-rich manganese-based oxide and single-crystal lithium-rich manganese-based oxide. Preferably, the primary particle size of the polycrystalline lithium-rich manganese-based oxide is 50-500 nm, and the secondary particle size is 1-100 μm. Preferably, the particle size of the single-crystal lithium-rich manganese-based oxide is 50 nm-5 μm.

3. The preparation method according to claim 1, characterized in that, The lithium-rich manganese-based oxide has a composition of xLi2MnO3·(1-x)LiMO2, 0 4. The method of claim 1, wherein, The heteropoly acid comprises at least one of phosphomolybdic acid, phosphotungstic acid, phosphoniobic acid, phosphotantalum acid, silicomolybdic acid and silicotungstic acid.

5. The preparation method according to claim 1, characterized in that, The solvent of the heteropoly acid solution is at least one of distilled water, ethanol, methanol, isopropanol, n-butanol, isobutanol and cyclohexanol.

6. The method of claim 1, wherein, The mass ratio of the heteropoly acid to the lithium-rich manganese-based oxide is 0.5%-5%, the solid content of the lithium-rich manganese-based oxide in the heteropoly acid solution is 0.5wt%-50wt%, the mixing and infiltration mode is at least one of mechanical stirring, magnetic stirring and ultrasonic dispersion, the drying temperature is 20-90℃, and the drying time is 0.5-12 h; preferably, stirring and / or ultrasonic treatment can be performed during the drying process.

7. The preparation method according to claim 1, characterized in that, The heat treatment temperature for surface induction reaction is 250-800℃, the heat treatment time is 0.5-24 h, the heat treatment temperature rising rate is 2-5℃ / min, and the heat treatment atmosphere is one of air, oxygen, nitrogen and argon.

8. A surface-reconstructed lithium-rich manganese-based oxide positive electrode material prepared by the preparation method according to any one of claims 1-7.

Images