A multi-phase lithium manganese oxide microsphere positive electrode material and a preparation method and application thereof

Abstract

This invention provides a multiphase lithium manganese oxide microsphere cathode material, its preparation method, and its application. The chemical formula of the multiphase lithium manganese oxide microsphere cathode material is LiMn. 2‑x Sr x O4, x=0.005-0.1; the crystal structure includes a main phase, a secondary phase, and a tertiary phase. The main phase is Sr-doped spinel-type LiMn2O4, the secondary phase is perovskite-type Sr2Mn2O5, and the tertiary phase is a layered Li2MnO3-like structure. This invention constructs a composite system of Sr-doped spinel LiMn2O4 main phase, perovskite Sr2Mn2O5 secondary phase, and layered Li2MnO3 phase, achieving a triple synergy of uniform Sr doping in the crystal lattice, mechanical buffering at grain boundaries, and stable / enhanced ion diffusion of the layered phase structure. This fundamentally solves the intrinsic failure problem of LMO cathode materials and significantly improves the cycle stability, rate performance, and high-temperature tolerance of LMO cathode materials.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, specifically relating to a multiphase lithium manganese oxide microsphere cathode material, its preparation method, and its application. Background Technology

[0002] Lithium manganese oxide (LMO) cathode materials, especially spinel-structured LiMn2O4, are lithium-ion battery cathode materials with great commercial potential. They have core advantages such as low raw material cost, environmental friendliness, high thermal safety, and three-dimensional lithium-ion diffusion channels that are suitable for fast charging scenarios. They are widely used in power, energy storage and consumer lithium-ion battery fields.

[0003] However, spinel-structured LMO cathode materials suffer from severe performance degradation during charge-discharge cycles, limiting their large-scale commercial application.

[0004] Currently, the main methods for modifying lithium manganese oxide cathode materials include high-temperature solid-state methods and wet chemical methods. Among them, the high-temperature solid-state method is the mainstream process for industrial production of LMO. The core scheme is as follows: lithium source (such as lithium carbonate, lithium hydroxide), manganese source (such as electrolytic manganese dioxide), and dopant element source (such as strontium oxide / carbonate) are weighed according to stoichiometric ratio, and the powder is mixed by mechanical ball milling. Then, it is calcined at high temperature to complete the solid-state reaction and crystallization. After cooling, grinding, sieving, demagnetizing and other post-processing steps, the doped and modified LMO cathode material is finally obtained. Some schemes will also add secondary coating and secondary annealing processes after calcination to further optimize the material interface stability. This method has many drawbacks: 1) Complex process, high energy consumption, and long production cycle: It requires multiple high-temperature heat treatments, with a single batch production cycle exceeding 24 hours, resulting in high energy consumption; at the same time, it involves multiple processes such as grinding, sieving, and demagnetization, leading to high equipment and labor costs and low production efficiency; 2) Extremely poor doping uniformity: It relies on mechanical ball milling to achieve element mixing, which cannot achieve atomic-level uniform doping, easily leading to dopant element agglomeration and radial concentration gradient problems within particles, resulting in a significant reduction in modification effect and poor batch stability; 3) Weak controllability of morphology and structure: Solid-state reactions easily lead to excessive growth and uneven size of primary grains, and irregular morphology of secondary particles with poor sphericity and low tap density, limiting electrode processing performance and rate performance; 4) Inability to achieve precise control of multiphase structure: Solid-state reactions are difficult to construct in-situ grain boundary phase and layered phase composite structures, and can only achieve single lattice doping, which cannot simultaneously solve multiple failure problems of LMO such as Jahn-Teller distortion, manganese dissolution, and cyclic microcrack propagation.

[0005] Wet chemical methods, represented by co-precipitation and sol-gel methods, involve the following core steps: first, preparing manganese-based precursors (such as manganese hydroxide and manganese carbonate) with controllable morphology and particle size through liquid-phase reaction; then, mixing the precursors with lithium and dopant sources in a specific ratio, followed by spray drying, multi-step high-temperature calcination (pre-calcination + final calcination), and post-treatment to obtain modified LMO materials. The sol-gel method involves first preparing a gel containing lithium, manganese, and dopants using a complexing agent, followed by drying and high-temperature calcination to obtain the product. These methods can achieve a preliminary uniform distribution of dopants and are commonly used in the preparation of laboratory-grade high-performance modified LMOs; however, they also have several drawbacks: 1) long process flow and limited scalability. 1) High difficulty: The co-precipitation process requires precise control of parameters such as pH, temperature, and feeding rate, making process management difficult; at the same time, it still requires subsequent high-temperature calcination and post-processing, resulting in a long production cycle, high wastewater and waste liquid treatment costs, and significant environmental pressure; 2) Disconnection between doping and phase structure control: Liquid-phase precursors can only achieve element premixing, and the final doping effect and phase composition are still determined by subsequent high-temperature calcination, which easily leads to element segregation and phase separation, making it impossible to achieve in-situ precise construction of multiphase structures; 3) High production cost: The complexing agents, precipitants, and precursor raw materials required for wet chemical methods are expensive, and the process yield is lower than that of solid-phase methods, making it difficult to adapt to the needs of large-scale industrial production.

[0006] In addition, a few existing studies have reported spray pyrolysis technology for LMO. Although this type of method can achieve rapid gas-solid-liquid multiphase reaction and shorten the process flow to a certain extent, it requires high-temperature calcination and doping / coating post-treatment steps after spray pyrolysis. It cannot achieve one-step synthesis of multiphase modified LMO with good crystallinity, thus losing the process advantages of spray pyrolysis. Moreover, it can only achieve single doping modification and cannot build multiphase synergistic structures, making it difficult to solve the intrinsic failure problem of LMO at the same time.

[0007] Therefore, how to fundamentally solve the multiple failure problems inherent in spinel LMO, such as Jahn-Teller distortion, Mn disproportionation and dissolution, structural collapse and microcrack propagation during charge-discharge cycles, and high-temperature performance degradation, in order to obtain LMO cathode materials with excellent cycle stability, rate performance and high-temperature performance, is an urgent technical problem to be solved. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the present invention aims to provide a multiphase lithium manganese oxide microsphere cathode material, its preparation method, and its applications. This invention constructs a composite system consisting of an Sr-doped spinel-type LiMn₂O₄ main phase, a perovskite-type Sr₂Mn₂O₅ secondary phase, and a layered Li₂MnO₃-like structural phase. This overcomes the bottleneck of existing technologies where doping and phase regulation are disconnected, achieving a synergistic effect of three modification effects: uniform Sr doping, the mechanical buffering effect of the grain boundary second phase, and the structural stability and enhanced ion diffusion brought by the layered phase. This fundamentally solves multiple failure problems inherent in spinel LMO, such as Jahn-Teller distortion, Mn disproportionation dissolution, structural collapse and microcrack propagation during charge-discharge cycles, and high-temperature performance degradation. It significantly improves the cycle stability, rate performance, and high-temperature tolerance of LMO cathode materials, meeting the large-scale application requirements of fast-charging lithium-ion batteries and possessing strong commercial application potential.

[0009] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a multiphase lithium manganese oxide microsphere cathode material, wherein the chemical formula of the multiphase lithium manganese oxide microsphere cathode material is LiMn. 2-x Sr x O4, x=0.005-0.1; the crystal phase structure of the multiphase lithium manganese oxide microsphere cathode material includes a main phase, a secondary phase and a tertiary phase, wherein the main phase is Sr-doped spinel-type LiMn2O4, the secondary phase is perovskite-type Sr2Mn2O5 phase, and the tertiary phase is a layered Li2MnO3-like structural phase.

[0010] This invention constructs a composite system consisting of a Sr-doped spinel-type LiMn2O4 main phase, a perovskite-type Sr2Mn2O5 secondary phase, and a layered Li2MnO3-like structural phase. It breaks through the bottleneck of the disconnect between doping and phase regulation in existing technologies, and achieves the synergistic effect of three modification effects: uniform Sr doping, mechanical buffering effect of the grain boundary second phase, and structural stability and enhanced ion diffusion brought by the layered phase. This fundamentally solves multiple failure problems of intrinsic spinel LMO, such as Jahn-Teller distortion, Mn disproportionation and dissolution, structural collapse and microcrack propagation during charge-discharge cycles, and high-temperature performance degradation. It significantly improves the cycle stability, rate performance and high-temperature tolerance of LMO cathode materials, meets the needs of large-scale application of fast-charging lithium-ion batteries, and has great potential for commercial application.

[0011] This invention achieves atomically uniform Sr doping, fundamentally suppressing Jahn-Teller distortion and Mn disproportionation reactions, and stabilizing the spinel lattice framework. The perovskite-type Sr₂Mn₂O₅ secondary phase constructed in this invention achieves dual buffering of grain refinement and mechanical stress: on the one hand, it significantly suppresses excessive growth of primary particles, refines primary particle size, and improves the density of secondary particles; on the other hand, as a mechanical buffer phase, it effectively alleviates the mechanical stress caused by lattice strain and volume changes during charge-discharge cycles, suppresses the initiation and propagation of microcracks, and maintains the integrity of the electrode structure during long-term cycling. The layered Li₂MnO₃-like structural phase introduced in this invention, as a third phase, achieves synergistic improvement in structural stability and ion dynamics: on the one hand, it significantly enhances the bulk structural stability of the material, suppressing manganese dissolution and electrolyte interface side reactions; on the other hand, it can provide additional Li₂MnO₃. + Diffusion channels, reducing Li + The migration barrier resolves the inherent contradiction between "improved structural stability and decreased ion dynamics" in traditional doping modification, while simultaneously optimizing cycle life and rate performance.

[0012] In this invention, the determination of each crystal phase can be confirmed by X-ray diffraction patterns and neutron diffraction tests.

[0013] In this invention, x = 0.005-0.1, for example, it can be 0.005, 0.01, 0.05, or 0.1. A suitable Sr doping amount is beneficial for controlling the material's crystal structure, suppressing phase transitions and lattice distortions, reducing cation mixing, and improving the material's structural stability.

[0014] Preferably, the multiphase lithium manganese oxide microsphere cathode material is a spherical secondary particle, which is formed by the aggregation of nanoscale primary grains.

[0015] The multiphase lithium manganese oxide microsphere cathode material provided by this invention combines the advantages of high tap density and nanoscale primary grains, ensuring excellent electrode processing performance while achieving short Li... + Its diffusion distance perfectly matches the high-power fast charging requirements of lithium-ion batteries.

[0016] Preferably, the space group of the principal phase is Fd-3m.

[0017] The space group of the main phase constructed in this invention is Fd-3m. This space group is beneficial for constructing a stable crystal framework, providing efficient three-dimensional lithium-ion transport channels, and improving the structural stability and ion conduction rate of the material.

[0018] Preferably, based on the mass of the multiphase lithium manganese oxide microsphere cathode material, the mass percentage of the main phase is 82-97 wt%, for example, it can be 82 wt%, 83 wt%, 85 wt%, 88 wt%, 90 wt%, 92 wt%, 95 wt%, 96.5 wt%, or 97 wt%, etc.; the mass percentage of the secondary phase is 1-8 wt%, for example, it can be 1 wt%, 2 wt%, 3 wt%, 5 wt%, 6 wt%, or 8 wt%, etc.; and the mass percentage of the tertiary phase is 2-10 wt%, for example, it can be 2 wt%, 4 wt%, 6 wt%, 7 wt%, 8 wt%, or 10 wt%, etc.

[0019] In the multiphase lithium manganese oxide microsphere cathode material provided by the present invention, the main phase, secondary phase and tertiary phase satisfy the above ratio, which helps to synergistically exert the structural advantages of each phase, stabilize the overall crystal lattice framework of the material, improve ion transport efficiency, alleviate the volume effect, and improve cycle stability and rate performance.

[0020] Preferably, the space group of the third phase is C2 / m.

[0021] The space group of the third phase constructed in this invention is C2 / m. This space group can provide additional lithium-ion insertion / extraction sites, which helps to optimize the ion conduction of the layered structure, while enhancing structural adaptability and improving the cycling and rate performance of the material.

[0022] Preferably, the secondary phase is distributed at the grain boundaries of the nanoscale primary grains and on the surface of the spherical secondary particles.

[0023] In this invention, the secondary phase is distributed at the grain boundaries of the nanoscale primary grains and on the surface of the spherical secondary particles. It can suppress the excessive growth of the primary grains, refine the grain size, and improve the particle density. At the same time, as a mechanical buffer phase, it can effectively alleviate the mechanical stress caused by lattice strain and volume change during charge and discharge cycles, suppress the initiation and propagation of microcracks, and maintain the integrity of the electrode structure during long-term cycling.

[0024] Preferably, the third phase is distributed in a localized domain structure within the spherical secondary particles.

[0025] In this invention, the third phase is distributed within the spherical secondary particles in a localized domain structure, which can significantly enhance the bulk structural stability of the material and suppress manganese dissolution and electrolyte interface side reactions; at the same time, it provides additional Li + Diffusion channels, reducing Li + The migration barrier resolves the inherent contradiction between "improved structural stability and decreased ion dynamics" in traditional doping modification, while simultaneously optimizing cycle life and rate performance.

[0026] Preferably, in the multiphase lithium manganese oxide microsphere cathode material, the Sr element is uniformly distributed within the spherical secondary particles.

[0027] In this invention, the Sr element is uniformly distributed within the spherical secondary particles, with no radial concentration gradient, which is beneficial for increasing the average oxidation state of Mn and reducing unstable Mn. 3+ The proportion of [amount] can fundamentally suppress Jahn-Teller distortion and Mn disproportionation reaction, thereby stabilizing the spinel lattice framework.

[0028] It should be noted that the distribution of Sr elements can be verified through SEM and EDS mapping.

[0029] Preferably, in the multiphase lithium manganese oxide microsphere cathode material, the average oxidation state of Mn element is 3.5-3.7, for example, it can be 3.5, 3.6 or 3.7.

[0030] In this invention, the average oxidation state of Mn is 3.5-3.7, indicating that Mn 3+ With Mn 4+ When Mn coexists in an appropriate ratio, the system 3+ The content was controlled within a moderate range, avoiding high concentrations of Mn. 3+ The resulting structural instability helps to suppress Jahn-Teller distortion.

[0031] Preferably, in the multiphase lithium manganese oxide microsphere cathode material, Mn 4+ With Mn 3+ The molar ratio is 1.2-2, for example, it can be 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9 or 2, etc.

[0032] In this invention, Mn 4+ With Mn 3+ The molar ratio is 1.2-2, indicating that the high-spin Mn in the system... 3+ When the content of MnO6 is regulated to an appropriate level, the distortion tendency of the MnO6 octahedral ligand field can be effectively reduced, which is beneficial to suppressing the Jahn-Teller distortion.

[0033] It should be noted that the average oxidation state of Mn and the Mn content can be obtained through X-ray photoelectron spectroscopy (XPS). 4+ With Mn 3+ The molar ratio.

[0034] Preferably, the particle size of the spherical secondary particles is 0.5-5μm, for example, it can be 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3.0μm, 3.5μm, 4μm, 4.5μm or 5μm, and is more preferably 1-3μm.

[0035] Preferably, the particle size of the nanoscale primary grains is 50-500nm, for example, it can be 50nm, 80nm, 100nm, 200nm, 300nm, 400nm or 500nm, etc.

[0036] Preferably, the tap density of the spherical secondary particles is 1.8-2.2 g / cm³. 3 For example, it could be 1.8 g / cm³ 3 1.9g / cm 3 2g / cm 3 2.1g / cm 3 Or 2.2g / cm 3 wait.

[0037] The spherical secondary particles provided by this invention have a tap density of 1.8-2.2 g / cm³. 3 This is far superior to LMO materials prepared by traditional methods (tap density 1.2-1.6 g / cm³). 3 The electrode coating has good processability and high compaction density, which can improve the volumetric energy density of the battery.

[0038] It should be noted that the tap density can be obtained by a powder tap density tester, referring to the standard GB / T5162-2021 "Determination of Tap Density of Metal Powders".

[0039] Secondly, the present invention provides a method for preparing a multiphase lithium manganese oxide microsphere cathode material as described in the first aspect, the method comprising the following steps: A precursor solution is obtained by mixing a lithium source, a manganese source, a strontium source, and a solvent.

[0040] The precursor solution is fed into a spray pyrolysis system to carry out a single spray pyrolysis synthesis reaction, thereby obtaining the multiphase lithium manganese oxide microsphere cathode material.

[0041] This invention proposes a one-step, post-processing-free spray pyrolysis synthesis process, which integrates five core processes—droplet atomization, solvent evaporation, precursor pyrolysis, crystallization, and multiphase structure construction—into a single step. The reaction time from precursor solution to final product is only a few seconds, eliminating the need for any subsequent high-temperature calcination, doping, coating, grinding, or sieving. This significantly simplifies the process, shortens the production cycle, and substantially reduces energy consumption and production costs, demonstrating excellent potential for continuous and large-scale production.

[0042] The preparation method provided by this invention has an extremely simple process flow and achieves an order-of-magnitude improvement in production efficiency: This one-step process takes only a few seconds from raw material solution to final product, which is significantly more efficient than the production cycle of tens of hours of traditional solid phase method and coprecipitation method. It eliminates multiple steps such as high temperature calcination, grinding, sieving, and post-processing, reducing the number of production steps by more than 80% and greatly reducing equipment investment and labor costs.

[0043] The preparation method provided by this invention significantly reduces energy consumption and cost: it does not require long-term high-temperature calcination, and the total energy consumption is significantly reduced compared with the traditional solid-phase method; the raw materials do not require expensive complexing agents or precipitants, the solvent is water, and there are no organic solvents or wastewater treatment costs, and the overall production cost is significantly reduced compared with the existing wet process and solid-phase process.

[0044] The preparation method provided by this invention yields products with excellent consistency and uniformity: the microdroplet confined reaction achieves atomic-level uniform mixing of elements, with Sr elements uniformly distributed inside the particles, without doping agglomeration or concentration gradients; the continuous process ensures high consistency between batches, solving the industry pain points of large batch differences and unstable modification effects in traditional solid-state methods.

[0045] The preparation method provided by this invention has strong controllability over the morphology of the product and excellent processing performance: the prepared product is a regular spherical secondary particle with uniform particle size distribution and high tap density; the electrode coating has good processability and high compaction density, which can improve the volumetric energy density of the battery.

[0046] The entire process provided by this invention produces no wastewater or waste residue, and only generates a small amount of nitrogen oxide tail gas that can be harmlessly treated. The environmental pressure is far lower than that of the wet chemical method. The process can achieve fully continuous and automated production, and is compatible with the industrial production line transformation of existing cathode materials. The difficulty of industrialization is extremely low.

[0047] Preferably, the lithium source includes any one or a combination of at least two of lithium nitrate, lithium acetate, lithium citrate, or lithium sulfate, with lithium nitrate being the most preferred.

[0048] The reason why lithium nitrate is preferred in this formulation is that it is a water-soluble lithium salt, its thermal decomposition temperature is suitable for spray pyrolysis process, and it leaves no difficult-to-decompose impurities.

[0049] Preferably, the manganese source includes any one or a combination of at least two of manganese nitrate hexahydrate, manganese nitrate tetrahydrate, manganese acetate, manganese sulfate, or manganese chloride, with manganese nitrate hexahydrate being the most preferred.

[0050] The reason why manganese nitrate hexahydrate is preferred in this invention is that it has excellent water solubility and high matching degree with the thermal decomposition behavior of lithium source and strontium source.

[0051] Preferably, the strontium source includes any one or a combination of at least two of strontium nitrate, strontium acetate, or strontium chloride, with strontium nitrate being the most preferred.

[0052] The reason why strontium nitrate is preferred in this invention is that it is compatible with the main salt system and can achieve atomic-level uniform mixing.

[0053] Preferably, the solvent includes any one or a combination of at least two of distilled water, deionized water, or anhydrous ethanol, with distilled water being the preferred choice.

[0054] The reason why distilled water is preferred in this invention is that distilled water is low in cost, environmentally friendly, and its evaporation rate is suitable for the spray pyrolysis process.

[0055] Preferably, the total metal ion concentration of the precursor solution is 0.1-1 mol / L, for example, it can be 0.1 mol / L, 0.2 mol / L, 0.5 mol / L, 0.8 mol / L or 1.0 mol / L, and more preferably 0.3-0.6 mol / L.

[0056] This invention delivers a precursor solution with a suitable total metal ion concentration into a spray pyrolysis system. This concentration is beneficial for optimizing the pelletizing effect of spray pyrolysis, ensuring the uniformity of precursor components, and improving production efficiency and batch stability.

[0057] Preferably, the spray pyrolysis system includes a precursor feeding system, an ultrasonic atomizer, a high-temperature tubular reactor, a powder collection device, and a tail gas treatment device connected in sequence.

[0058] For example, a powder collection device may be a bag filter or a cyclone separator.

[0059] For example, the total length of the heating zone of the high-temperature tubular reactor can be 800-1500mm, such as 800mm, 900mm, 1000mm, 1100mm, 1200mm, 1300mm, 1400mm or 1500mm, etc., and the length of the constant temperature zone is ≥600mm, such as 600mm, 700mm, 800mm, 900mm, 1000mm or 1200mm, etc., with a temperature control accuracy of ±5℃.

[0060] In this invention, the exhaust gas treatment device is used to treat the exhaust gas generated during the reaction process so that it meets the emission standards; the entire process generates no wastewater or waste residue, and continuous production can be achieved.

[0061] Preferably, after the precursor solution is atomized by the ultrasonic atomizer, the resulting aerosol droplets are carried into the high-temperature tubular reactor by a carrier gas.

[0062] Preferably, the carrier gas includes any one of dry compressed air, nitrogen, or oxygen, with dry compressed air being the most preferred.

[0063] The reason why dry compressed air is preferred in this invention is that it is low in cost and can provide a stable oxidation atmosphere, ensuring that the manganese valence state is controllable.

[0064] Preferably, the flow rate of the carrier gas is 5-20 L / min, for example, it can be 5 L / min, 8 L / min, 12 L / min, 15 L / min or 20 L / min, etc., preferably 8-12 L / min.

[0065] In this invention, a suitable carrier gas flow rate can ensure the precursor is fully pyrolyzed, optimize particle morphology, and improve process stability.

[0066] Preferably, the atomization frequency of the ultrasonic atomizer is 1-2.5MHz, for example, it can be 1MHz, 1.5MHz, 2MHz or 2.5MHz, and is preferably 1.5-2MHz.

[0067] Preferably, the aerosol droplets formed after the precursor solution is atomized by the ultrasonic atomizer have a particle size of 1-10 μm, such as 1 μm, 3 μm, 5 μm, 8 μm or 10 μm.

[0068] In this invention, the aerosol droplets have a particle size of 1-10 μm, which is beneficial for optimizing the morphology and particle size uniformity of the precursor microspheres, ensuring sufficient pyrolysis and uniform composition.

[0069] Preferably, the high-temperature tubular reactor includes a constant temperature zone; wherein the temperature of the constant temperature zone is 800-1100℃, for example, it can be 800℃, 850℃, 900℃, 950℃, 1000℃, 1050℃ or 1100℃, etc., preferably 900-1050℃; the residence time in the constant temperature zone is 0.5-10s, for example, it can be 0.5s, 1s, 2s, 5s, 8s or 10s, etc., preferably 1-5s.

[0070] This invention allows for the rapid occurrence of the entire process of solvent evaporation, precursor pyrolysis, crystal crystallization, and in-situ construction of multiphase structures within a constant temperature range of 800-1100℃ for 0.5-10 seconds. This eliminates the need for any subsequent high-temperature calcination, doping, coating, grinding, or sieving, significantly simplifying the process, shortening the production cycle, reducing energy consumption and production costs, and demonstrating excellent potential for continuous and large-scale production.

[0071] Preferably, the single-stage spray pyrolysis synthesis reaction includes droplet atomization, solvent evaporation, precursor pyrolysis, crystallization, and in-situ construction of multiphase structures in sequence.

[0072] This invention requires only one spray pyrolysis synthesis reaction to complete product preparation. The confined reaction of aerosol droplets achieves atomic-level uniform mixing of elements, with Sr elements uniformly distributed inside the particles, without doping agglomeration or concentration gradients. The continuous process ensures high consistency between batches, solving the industry pain points of large batch differences and unstable modification effects in traditional solid-state methods.

[0073] Preferably, the preparation method includes the following steps: (1) Weigh the lithium source, manganese source and strontium source according to the target stoichiometric ratio to obtain solid raw materials; wherein, the ratio of the molar amount of the lithium source to the total molar amount of the manganese source and strontium source is (1-1.1):2 (for example, it can be 1:2, 1.02:2, 1.04:2, 1.06:2, 1.08:2 or 1.1:2, etc.), preferably (1.03-1.08):2; the molar ratio of the manganese source and strontium source is (1.9-1.995):(0.005-0.1) (the selection range of the manganese source "1.9-1.995" can be, for example, 1.9, 1.92, 1.94, 1.95, 1.97, 1.99 or 1.995, etc., and the selection range of the strontium source "0.005-0.1" can be, for example, 0.005, 0.01, 0.05 or 0.1, etc.).

[0074] The solid raw material is added to a solvent and stirred at 20-60°C (e.g., 20°C, 30°C, 40°C, 50°C, or 60°C) for 10-60 min (e.g., 10 min, 20 min, 30 min, 40 min, 50 min, or 60 min), and then subjected to ultrasonic treatment for 5-30 min (e.g., 5 min, 10 min, 15 min, 20 min, 25 min, or 30 min) to obtain a precursor solution with a total metal ion concentration of 0.1-1 mol / L.

[0075] (2) Provide a spray pyrolysis system, the spray pyrolysis system comprising a precursor feeding system, an ultrasonic atomizer, a high-temperature tubular reactor, a powder collection device and a tail gas treatment device connected in sequence.

[0076] The precursor solution is fed into the spray pyrolysis system, where it is first atomized into droplets. Then, it is carried by a carrier gas with a flow rate of 5-20 L / min into a high-temperature tubular reactor, where solvent evaporation, precursor pyrolysis, crystallization, and in-situ construction of multiphase structures are carried out sequentially. After completion, the precursor solution is carried by the carrier gas into the powder collection device to achieve gas-solid separation and obtain multiphase lithium manganese oxide microsphere cathode material.

[0077] The carrier gas includes any one of dry compressed air, nitrogen, or oxygen; the atomization frequency of the ultrasonic atomizer is 1-2.5MHz; the aerosol droplets formed after the precursor solution is atomized by the ultrasonic atomizer have a particle size of 1-10μm; the high-temperature tubular reactor includes a constant temperature zone with a temperature of 800-1100℃, and the residence time of the aerosol droplets in the constant temperature zone is 0.5-10s.

[0078] Thirdly, the present invention provides a lithium-ion battery, the lithium-ion battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte; wherein the active material of the positive electrode comprises the multiphase lithium manganese oxide microsphere positive electrode material as described in the first aspect.

[0079] For example, the preparation steps of the positive electrode sheet are as follows: Multiphase lithium manganese oxide microsphere positive electrode material, conductive agent (e.g., acetylene black, carbon nanotubes or conductive graphite, etc.), binder (e.g., polyvinylidene fluoride (PVDF), etc.) are mixed in a mass ratio of (80-95):(2-10):(2-10) (the selection range of multiphase lithium manganese oxide microsphere positive electrode material "80-95" can be, for example, 80, 85, 90 or 95, etc.; the selection range of conductive agent "2-10" can be, for example, 2, 4, 6, 8 or 10, etc.; the selection range of binder "2-10" can be, for example, 2, 4, 6, 8 or 10, etc.), and N-methylpyrrolidone (NMP) solvent is added to form a slurry, which is coated on an aluminum current collector, and after drying, rolling and stamping, the positive electrode sheet is obtained.

[0080] For example, the negative electrode can be a commercially available negative electrode system such as a lithium metal sheet, graphite, or silicon-based negative electrode. The separator can be a commercially available polypropylene / polyethylene microporous separator, and the electrolyte can be a commercially available lithium salt electrolyte system.

[0081] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0082] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention constructs a composite system consisting of a Sr-doped spinel-type LiMn2O4 main phase, a perovskite-type Sr2Mn2O5 secondary phase, and a layered Li2MnO3-like structural phase. It breaks through the bottleneck of the disconnect between doping and phase regulation in the existing technology, and realizes the synergistic effect of the three modification effects of uniform Sr lattice doping, mechanical buffering effect of grain boundary second phase, and structural stability and enhanced ion diffusion brought by layered phase. Thus, it fundamentally solves the multiple failure problems of intrinsic spinel LMO such as Jahn-Teller distortion, Mn disproportionation dissolution, structural collapse and microcrack propagation during charge-discharge cycle, and high-temperature performance degradation. It significantly improves the cycle stability, rate performance and high-temperature tolerance of LMO cathode material, adapts to the large-scale application requirements of fast-charging lithium-ion batteries, and has great commercial application potential.

[0083] (2) This invention proposes a one-step spray pyrolysis synthesis process without post-processing, which integrates the five core processes of droplet atomization, solvent evaporation, precursor pyrolysis, crystallization and multiphase structure construction into a single step. It only takes a few seconds of reaction time from the precursor solution to the final product, without any subsequent high-temperature calcination, doping, coating, grinding and sieving, etc. This greatly simplifies the process flow, shortens the production cycle, significantly reduces energy consumption and production costs, and has excellent potential for continuous and large-scale production. Detailed Implementation

[0084] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0085] The scope of this invention can be defined by lower and upper limits. The selected lower and upper limits define the boundaries of a specific range. The range defined in this way can be defined by the inclusion or exclusion of endpoints. Any endpoint can be independently selected for inclusion or exclusion, and all lower and upper limits can be arbitrarily combined to form new ranges. That is, any lower limit can be combined with any upper limit to form an effective range. For example, if the ranges of 60~120 and 80~110 are listed for specific parameters, it should be understood that the ranges of 60~110 and 80~120 also fall within the scope of this invention. In addition, if the minimum range values ​​1 and 2 are listed, and the maximum range values ​​3, 4 and 5 are also listed, then all ranges of 1~3, 1~4, 1~5, 2~3, 2~4 and 2~5 fall within the scope of this invention. In this invention, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0~5" means that all real numbers between 0 and 5 have been fully listed in this document, and "0~5" is only a shortened representation of this set of numerical combinations. When a parameter is expressed as an integer ≥2, it is equivalent to listing positive integers that meet the requirements, such as 2, 3, 4, 5, 6, 7, 8, 9, 10, etc. When a parameter is expressed as an integer selected from "2~10", it is equivalent to listing any integer among 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0086] In this invention, "a combination of at least two" refers to a quantity greater than or equal to 2 unless otherwise specified. For example, "any one or a combination of at least two" means that any one of the listed items can be selected, or a combination of at least two of the listed items formed in a manner that does not conflict and enables the implementation of this invention. In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" cover any one of two or more related listed items, as well as any and all combinations of the related listed items. The arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" means a set consisting of A, B, and combinations of A and B, where "containing A and / or B" can be understood, depending on the context of the statement, as containing A, containing B, or simultaneously containing both A and B. In this invention, "optional" means that the corresponding feature, component, step or solution is not necessary, that is, it is selected from either "with" or "without". If there are multiple "optional" limitations in a technical solution, unless otherwise specified and there is no technical conflict or mutual constraint, each "optional" limitation is independent and does not affect the others.

[0087] In this invention, technical features or solutions described using open-ended terms such as "comprising" or "including" do not exclude additional non-conflicting elements beyond the listed elements unless otherwise specified. They are considered to disclose both closed-ended features or solutions consisting solely of the listed elements and open-ended features or solutions that may include additional non-conflicting elements beyond the listed elements. For example, if A includes a1, a2, and a3, unless otherwise specified, this means that A can consist only of a1, a2, and a3, or it can include other non-conflicting elements based on a1, a2, and a3. This corresponds to the disclosure of technical solutions such as "A consists of a1, a2, and a3," "A is selected from a1, a2, and a3," and "A not only includes a1, a2, and a3, but may also include other non-conflicting elements." All embodiments and optional embodiments of this invention, unless otherwise specified and without technical conflict, can be combined to form new technical solutions, and such combinations fall within the scope of this invention. The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of the invention. The appearance of this phrase in various locations throughout the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will understand, explicitly and implicitly, that the embodiments described in this invention can be combined with other embodiments that do not conflict with the technology. The ordinal numbers "first," "second," "third," and "fourth," etc., used in the expressions "first aspect," "second aspect," "third aspect," and "fourth aspect" in this invention are for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly specifying the importance or quantity of the indicated technical features. They serve only as a non-exhaustive enumeration and do not constitute a closed limitation on quantity.

[0088] In this invention, the order in which the steps are written in the methods described in each embodiment does not imply a strict execution order. The actual execution order of each step should be determined based on its function and possible internal logic. Unless otherwise specified, all steps of this invention can be executed in the order they are written, or in any order without technical conflict. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) executed sequentially, or it may include steps (b) and (a) executed sequentially. If the method also includes step (c), then step (c) can be added to the method in any order without conflict, including but not limited to the execution order of steps (a), (b), and (c), steps (a), (c), and (b), steps (c), (a), and (b), etc.

[0089] Example 1 This embodiment provides a multiphase lithium manganese oxide microsphere cathode material with the chemical formula LiMn. 2-xSr x O4, x=0.05; the crystal phase structure of the multiphase lithium manganese oxide microsphere cathode material includes a main phase, a secondary phase and a tertiary phase. The main phase is Sr-doped spinel-type LiMn2O4 with space group Fd-3m; the secondary phase is perovskite-type Sr2Mn2O5; and the tertiary phase is a layered Li2MnO3-like structure with space group C2 / m.

[0090] The multiphase lithium manganese oxide microsphere cathode material is a spherical secondary particle, which is formed by the aggregation of nanoscale primary grains; the particle size of the spherical secondary particle is 2-3 μm, and the particle size of the nanoscale primary grain is 50-500 nm.

[0091] Based on the mass of the multiphase lithium manganese oxide microsphere cathode material, the mass percentage of the main phase is 90 wt%, the mass percentage of the secondary phase is 4 wt%, and the mass percentage of the tertiary phase is 6 wt%.

[0092] The secondary phase is distributed at the grain boundaries of the nanoscale primary grains and on the surface of the spherical secondary particles; the third phase is distributed in the interior of the spherical secondary particles in a localized domain structure; in the multiphase lithium manganese oxide microsphere cathode material, the Sr element is uniformly distributed within the spherical secondary particles.

[0093] This embodiment also provides a method for preparing the above-mentioned multiphase lithium manganese oxide microsphere cathode material, the method comprising the following steps: (1) Weigh lithium nitrate, manganese nitrate hexahydrate and strontium nitrate according to the target stoichiometric ratio to obtain solid raw materials; wherein, the molar ratio of the lithium nitrate to the total molar ratio of the manganese source and the strontium source is 1.05:2; and the molar ratio of the manganese nitrate hexahydrate and the strontium nitrate is 1.95:0.05.

[0094] The solid raw material was added to distilled water and magnetically stirred at 25°C for 30 min, followed by ultrasonic treatment for 15 min to obtain a precursor solution with a total metal ion concentration of 0.5 mol / L.

[0095] (2) Provide a spray pyrolysis system, the spray pyrolysis system comprising a precursor feeding system, an ultrasonic atomizer, a quartz high-temperature tubular reactor, a powder collection device and a tail gas treatment device connected in sequence; wherein, the powder collection device is a bag filter; the quartz high-temperature tubular reactor includes a constant temperature zone, the length of which is 1200 mm.

[0096] The precursor solution is fed into the spray pyrolysis system, where it is first atomized into droplets. Then, it is carried by a carrier gas with a flow rate of 10 L / min into a high-temperature tubular reactor, where solvent evaporation, precursor pyrolysis, crystallization, and in-situ construction of multiphase structures are carried out sequentially. After completion, the precursor solution is carried by the carrier gas into the powder collection device to achieve gas-solid separation and obtain multiphase lithium manganese oxide microsphere cathode material.

[0097] Wherein, the carrier gas is dry compressed air; the atomization frequency of the ultrasonic atomizer is 1.7MHz; the aerosol droplets formed after the precursor solution is atomized by the ultrasonic atomizer have a particle size of 1-10μm; the temperature of the constant temperature zone is 1000℃, and the residence time of the aerosol droplets in the constant temperature zone is 2s.

[0098] Example 2 This embodiment provides a multiphase lithium manganese oxide microsphere cathode material with the chemical formula LiMn. 2-x Sr x O4, x=0.01; the crystal phase structure of the multiphase lithium manganese oxide microsphere cathode material includes a main phase, a secondary phase and a tertiary phase. The main phase is Sr-doped spinel-type LiMn2O4 with space group Fd-3m; the secondary phase is perovskite-type Sr2Mn2O5; and the tertiary phase is a layered Li2MnO3-like structure with space group C2 / m.

[0099] The multiphase lithium manganese oxide microsphere cathode material is a spherical secondary particle, which is formed by the aggregation of nanoscale primary grains; the particle size of the spherical secondary particle is 1-2 μm, and the particle size of the nanoscale primary grain is 50-500 nm.

[0100] Based on the mass of the multiphase lithium manganese oxide microsphere cathode material, the mass percentage of the main phase is 82 wt%, the mass percentage of the secondary phase is 8 wt%, and the mass percentage of the tertiary phase is 10 wt%.

[0101] The secondary phase is distributed at the grain boundaries of the nanoscale primary grains and on the surface of the spherical secondary particles; the third phase is distributed in the interior of the spherical secondary particles in a localized domain structure; in the multiphase lithium manganese oxide microsphere cathode material, the Sr element is uniformly distributed within the spherical secondary particles.

[0102] This embodiment also provides a method for preparing the above-mentioned multiphase lithium manganese oxide microsphere cathode material, the method comprising the following steps: (1) Weigh lithium nitrate, manganese nitrate hexahydrate and strontium nitrate according to the target stoichiometric ratio to obtain solid raw materials; wherein, the molar ratio of the lithium nitrate to the total molar ratio of the manganese source and the strontium source is 1.05:2; and the molar ratio of the manganese nitrate hexahydrate and the strontium nitrate is 1.99:0.01.

[0103] The solid raw material was added to distilled water and magnetically stirred at 25°C for 30 min, followed by ultrasonic treatment for 15 min to obtain a precursor solution with a total metal ion concentration of 0.2 mol / L.

[0104] (2) Provide a spray pyrolysis system, the spray pyrolysis system comprising a precursor feeding system, an ultrasonic atomizer, a quartz high-temperature tubular reactor, a powder collection device and a tail gas treatment device connected in sequence; wherein, the powder collection device is a bag filter; the quartz high-temperature tubular reactor includes a constant temperature zone, the length of which is 1200 mm.

[0105] The precursor solution is fed into the spray pyrolysis system, where it is first atomized into droplets and then carried into a high-temperature tubular reactor by a carrier gas with a flow rate of 5 L / min. Solvent evaporation, precursor pyrolysis, crystallization, and in-situ construction of multiphase structures are carried out sequentially. After completion, the precursor solution is carried into the powder collection device by the carrier gas to achieve gas-solid separation and obtain multiphase lithium manganese oxide microsphere cathode material.

[0106] Wherein, the carrier gas is dry compressed air; the atomization frequency of the ultrasonic atomizer is 1MHz; the aerosol droplets formed after the precursor solution is atomized by the ultrasonic atomizer have a particle size of 1-10μm; the temperature of the constant temperature zone is 800℃, and the residence time of the aerosol droplets in the constant temperature zone is 10s.

[0107] Example 3 This embodiment provides a multiphase lithium manganese oxide microsphere cathode material with the chemical formula LiMn. 2-x Sr x O4, x=0.1; the crystal phase structure of the multiphase lithium manganese oxide microsphere cathode material includes a main phase, a secondary phase and a tertiary phase. The main phase is Sr-doped spinel-type LiMn2O4 with space group Fd-3m; the secondary phase is perovskite-type Sr2Mn2O5; and the tertiary phase is a layered Li2MnO3-like structure with space group C2 / m.

[0108] The multiphase lithium manganese oxide microsphere cathode material is a spherical secondary particle, which is formed by the aggregation of nanoscale primary grains; the particle size of the spherical secondary particle is 3-4 μm, and the particle size of the nanoscale primary grain is 50-500 nm.

[0109] Based on the mass of the multiphase lithium manganese oxide microsphere cathode material, the mass percentage of the main phase is 97 wt%, the mass percentage of the secondary phase is 1 wt%, and the mass percentage of the tertiary phase is 2 wt%.

[0110] The secondary phase is distributed at the grain boundaries of the nanoscale primary grains and on the surface of the spherical secondary particles; the third phase is distributed in the interior of the spherical secondary particles in a localized domain structure; in the multiphase lithium manganese oxide microsphere cathode material, the Sr element is uniformly distributed within the spherical secondary particles.

[0111] This embodiment also provides a method for preparing the above-mentioned multiphase lithium manganese oxide microsphere cathode material, the method comprising the following steps: (1) Weigh lithium nitrate, manganese nitrate hexahydrate and strontium nitrate according to the target stoichiometric ratio to obtain solid raw materials; wherein, the molar ratio of the lithium nitrate to the total molar ratio of the manganese source and the strontium source is 1.05:2; and the molar ratio of the manganese nitrate hexahydrate and the strontium nitrate is 1.9:0.1.

[0112] The solid raw material was added to distilled water and magnetically stirred at 25°C for 30 min, followed by ultrasonic treatment for 15 min to obtain a precursor solution with a total metal ion concentration of 1 mol / L.

[0113] (2) Provide a spray pyrolysis system, the spray pyrolysis system comprising a precursor feeding system, an ultrasonic atomizer, a quartz high-temperature tubular reactor, a powder collection device and a tail gas treatment device connected in sequence; wherein, the powder collection device is a bag filter; the quartz high-temperature tubular reactor includes a constant temperature zone, the length of which is 1200 mm.

[0114] The precursor solution is fed into the spray pyrolysis system, where it is first atomized into droplets. Then, it is carried by a carrier gas with a flow rate of 20 L / min into a high-temperature tubular reactor, where solvent evaporation, precursor pyrolysis, crystallization, and in-situ construction of multiphase structures are carried out sequentially. After completion, the precursor solution is carried by the carrier gas into the powder collection device to achieve gas-solid separation and obtain multiphase lithium manganese oxide microsphere cathode material.

[0115] Wherein, the carrier gas is dry compressed air; the atomization frequency of the ultrasonic atomizer is 2.5MHz; the aerosol droplets formed after the precursor solution is atomized by the ultrasonic atomizer have a particle size of 1-10μm; the temperature of the constant temperature zone is 1100℃, and the residence time of the aerosol droplets in the constant temperature zone is 1s.

[0116] Example 4 The difference between this embodiment and Embodiment 1 is that the molar ratio of manganese nitrate hexahydrate and strontium nitrate in step (1) is 1.98:0.02, making the chemical formula of the multiphase lithium manganese oxide microsphere cathode material LiMn 2-x Sr x O4, x=0.02; the particle size of the spherical secondary particles is 1-3μm.

[0117] The remaining preparation methods and parameters are consistent with those in Example 1.

[0118] Example 5 The difference between this embodiment and Embodiment 1 is that the molar ratio of manganese nitrate hexahydrate and strontium nitrate in step (1) is 1.9:0.1, making the chemical formula of the multiphase lithium manganese oxide microsphere cathode material LiMn 2-x Sr x O4, x=0.1.

[0119] The remaining preparation methods and parameters are consistent with those in Example 1.

[0120] Example 6 The difference between this embodiment and embodiment 1 is that, in step (1), the molar ratio of the lithium nitrate to the total molar ratio of the manganese source and the strontium source is 1.08:2; in step (2), the flow rate of the carrier gas is 8 L / min, the temperature of the constant temperature zone is 950 °C, and the particle size of the spherical secondary particles is 1-2 μm.

[0121] The remaining preparation methods and parameters are consistent with those in Example 1.

[0122] Example 7 The difference between this embodiment and Embodiment 1 is that the particle size of the spherical secondary particles is adjusted to 4-5 μm, and the particle size of the nanoscale primary crystals is 50-500 nm, so that in the multiphase lithium manganese oxide microsphere cathode material, the mass ratio of the main phase is 98 wt%, the mass ratio of the secondary phase is 1 wt%, and the mass ratio of the tertiary phase is 1 wt%.

[0123] The remaining preparation methods and parameters are consistent with those in Example 1.

[0124] Example 8 The difference between this embodiment and Embodiment 1 is that the particle size of the spherical secondary particles is adjusted to 0.5-1μm, and the particle size of the nanoscale primary crystals is 50-500nm, so that in the multiphase lithium manganese oxide microsphere cathode material, the mass ratio of the main phase is 80wt%, the mass ratio of the secondary phase is 9wt%, and the mass ratio of the tertiary phase is 11wt%.

[0125] The remaining preparation methods and parameters are consistent with those in Example 1.

[0126] Example 9 The difference between this embodiment and Embodiment 1 is that the flow rate of the carrier gas is 1 L / min.

[0127] The remaining preparation methods and parameters are consistent with those in Example 1.

[0128] Example 10 The difference between this embodiment and Embodiment 1 is that the flow rate of the carrier gas is 25 L / min.

[0129] The remaining preparation methods and parameters are consistent with those in Example 1.

[0130] Example 11 The difference between this embodiment and Embodiment 1 is that the temperature of the constant temperature zone is 700℃.

[0131] The remaining preparation methods and parameters are consistent with those in Example 1.

[0132] Example 12 The difference between this embodiment and Embodiment 1 is that the temperature of the constant temperature zone is 1200℃.

[0133] The remaining preparation methods and parameters are consistent with those in Example 1.

[0134] Example 13 The difference between this embodiment and Embodiment 1 is that the dwell time in the constant temperature zone is 12 seconds.

[0135] The remaining preparation methods and parameters are consistent with those in Example 1.

[0136] Comparative Example 1 This comparative example provides a method for preparing a pure-phase lithium manganese oxide cathode material, the method comprising the following steps: (1) Lithium nitrate and manganese nitrate hexahydrate were selected as raw materials, weighed according to the molar ratio of Li:Mn=1.05:2, and distilled water was used as solvent. After mixing and stirring to dissolve, the mixture was sonicated for 15 min to prepare a precursor solution with a total metal ion concentration of 0.5 mol / L.

[0137] (2) Provide a spray pyrolysis system, the spray pyrolysis system comprising a precursor feeding system, an ultrasonic atomizer, a quartz high-temperature tubular reactor, a powder collection device and a tail gas treatment device connected in sequence; wherein, the powder collection device is a bag filter; the quartz high-temperature tubular reactor includes a constant temperature zone, the length of which is 1200 mm.

[0138] The precursor solution is fed into the spray pyrolysis system, where it is first atomized into droplets. Then, it is carried by a carrier gas with a flow rate of 10 L / min into a high-temperature tubular reactor, where solvent evaporation, precursor pyrolysis, crystallization, and in-situ construction of multiphase structures are carried out sequentially. After completion, the precursor solution is carried by the carrier gas into the powder collection device to achieve gas-solid separation and obtain multiphase lithium manganese oxide microsphere cathode material.

[0139] Wherein, the carrier gas is dry compressed air; the atomization frequency of the ultrasonic atomizer is 1.7MHz; the aerosol droplets formed after the precursor solution is atomized by the ultrasonic atomizer have a particle size of 1-10μm; the temperature of the constant temperature zone is 1000℃, and the residence time of the aerosol droplets in the constant temperature zone is 2s.

[0140] Comparative Example 2 This comparative example provides a method for preparing a lithium manganese oxide cathode material, the method comprising the following steps: (1) Weigh lithium nitrate, manganese nitrate hexahydrate and strontium nitrate according to the stoichiometric ratio of Li:Mn:Sr=1.05:1.95:0.05 to obtain solid raw materials.

[0141] The solid raw material was added to a planetary ball mill and milled for 6 hours at 300 rpm using anhydrous ethanol as the milling medium. After the milling was completed, the mixture was dried to obtain a mixed powder.

[0142] (2) The mixed powder is placed in a muffle furnace with an air atmosphere and calcined at 850°C for 15 hours. After cooling with the furnace, it is ground and sieved through a 300-mesh sieve to obtain Sr-doped lithium manganese oxide cathode material.

[0143] Comparative Example 3 The difference between this comparative example and Example 1 is that in step (1), strontium nitrate is replaced with an equimolar amount of manganese nitrate hexahydrate, that is, the multiphase lithium manganese oxide microsphere cathode material does not contain Sr.

[0144] The remaining preparation methods and parameters are consistent with those in Example 1.

[0145] Comparative Example 4 The difference between this comparative example and Example 1 is that the molar ratio of manganese nitrate hexahydrate and strontium nitrate in step (1) is 1.85:0.15, resulting in the chemical formula of the multiphase lithium manganese oxide microsphere cathode material being LiMn. 2-x Sr x O4, x=0.15.

[0146] The remaining preparation methods and parameters are consistent with those in Example 1.

[0147] Performance testing (i) Using the cathode materials provided in the above embodiments and comparative examples as test objects, the tap density, average oxidation state of Mn element, and Mn content were tested. 4+ With Mn 3+ The molar ratio.

[0148] (II) Based on the positive electrode materials provided in the above embodiments and comparative examples, a CR2032 coin cell was fabricated. The steps included: weighing the positive electrode material, acetylene black, and polyvinylidene fluoride in a mass ratio of 8:1:1, adding N-methylpyrrolidone solvent, magnetically stirring to form a uniform slurry, coating the slurry onto a 12μm thick aluminum foil, vacuum drying at 120℃ for 12h, and then rolling and stamping to form a positive electrode sheet with a diameter of 14mm and a single-sided active material loading of approximately 2.0 mg / cm². 2 In an argon-atmosphere glove box (water and oxygen content <0.1ppm), a CR2032 coin cell was assembled using a lithium metal sheet as the negative electrode, a Celgard 2400 polypropylene membrane as the separator, and a 1mol / L LiPF6 EC / DMC / EMC (volume ratio 1:1:1) solution as the electrolyte.

[0149] Electrochemical performance tests were performed on the above-mentioned CR2032 coin cell, including: 1) 0.1C charge-discharge, with a charge-discharge voltage range of 3.2-4.3V (vs. Li). + / Li), test the first discharge specific capacity and first coulombic efficiency; 2) 25℃, 1C charge and discharge, charge and discharge voltage range is 3.2-4.3V (vs. Li + / Li), cycled 400 times, and tested the discharge specific capacity and capacity retention rate after 400 cycles; 3) constant current charge-discharge tests were performed at 0.1C, 0.2C, 0.5C, 1C, 2C, and 5C rates, with a charge-discharge voltage range of 3.2-4.3V (vs. Li). + / Li), test the discharge specific capacity at 5C; 4) 45℃, 1C charge and discharge, charge and discharge voltage range is 3.2-4.3V (vs. Li + / Li), cycled 150 times, and tested the capacity retention rate after 150 cycles; 5) assembled coin cells with graphite anode, and after 200 cycles at 1C, tested the amount of Mn deposited on the surface of graphite anode.

[0150] The test results are shown in Table 1.

[0151] Table 1 analyze: As shown in Table 1, this invention constructs a composite system consisting of a Sr-doped spinel-type LiMn2O4 main phase, a perovskite-type Sr2Mn2O5 secondary phase, and a layered Li2MnO3-like structural phase. This breakthrough overcomes the bottleneck of the disconnect between doping and phase regulation in existing technologies, and achieves the synergistic effect of the triple modification effects of uniform Sr lattice doping, mechanical buffering effect of the grain boundary second phase, and structural stability and enhanced ion diffusion brought by the layered phase. The multiphase lithium manganese oxide microsphere cathode material provided by this invention maintains a discharge specific capacity of 81.72 mAh / g after 400 cycles at 1C, with a capacity retention of 92.8%; at a high rate of 5C, the discharge specific capacity reaches 76.78 mAh / g, which is 70.3% of the capacity at 0.1C; and at 45℃ and 1C, the capacity retention reaches 70.4% after 150 cycles. Electrochemical impedance spectroscopy shows that after 200 cycles, the charge transfer impedance R of the multiphase lithium manganese oxide microsphere cathode material provided by this invention is [not specified in the original text]. ct It can be reduced to 56.17Ω, Li + The diffusion coefficient can reach 7.99 × 10⁻⁶. - 13 cm 2 / s; In addition, the soft-pack full battery assembled with the multiphase lithium manganese oxide microsphere cathode material of the present invention as the cathode and commercial graphite as the anode can achieve a capacity retention rate of 84.53% after 100 cycles at 1C rate, and has extremely strong commercial application potential.

[0152] A comparison of Examples 1 and 7-8 shows that if the mass proportion of the main phase in the multiphase lithium manganese oxide microsphere cathode material is too large, while the mass proportions of the secondary and tertiary phases are too small, the multiphase synergistic effect fails, the Jahn-Teller distortion cannot be effectively suppressed, and the cycle and rate performance deteriorates significantly. If the mass proportion of the main phase in the multiphase lithium manganese oxide microsphere cathode material is too small, while the mass proportions of the secondary and tertiary phases are too large, the reversible specific capacity of the material decreases significantly, ion transport is hindered, and the rate performance and energy density do not meet the standards.

[0153] A comparison of Examples 1 and 9-10 shows that if the flow rate of the carrier gas is too small, the particles will over-burn and agglomerate, the spherical morphology will collapse, and the tap density and processing performance will decrease; if the flow rate of the carrier gas is too large, the precursor pyrolysis will be incomplete, there will be more impurities, component segregation, and the electrochemical performance will deteriorate.

[0154] As can be seen from the comparison between Example 1 and Examples 11-12, if the temperature of the isothermal zone is too low, the pyrolysis and crystal phase transformation will be insufficient, resulting in many structural defects and insufficient capacity utilization; if the temperature of the isothermal zone is too high, the particle morphology will be out of control, the manganese valence state will be unbalanced, the Jahn-Teller distortion will be aggravated, and the cycle performance will drop sharply.

[0155] A comparison between Example 1 and Example 13 shows that if the residence time in the isothermal zone is too long, the grains grow abnormally, the multiphase ratio becomes unbalanced, and the tap density and electrochemical performance deteriorate simultaneously.

[0156] As can be seen from the comparison between Example 1 and Comparative Example 1, the pure phase LMO prepared by conventional spray pyrolysis has a capacity of only 17.02 mAh / g after 400 cycles at 25°C and 1C rate, with a capacity retention rate of only 19.2%, indicating poor cycle stability. The discharge specific capacity at 5C rate is only 45.2 mAh / g, which is 40.9% of the 0.1C capacity, making it unsuitable for fast charging applications. After 150 cycles at 45°C and 1C rate, the capacity retention rate is only 50.3%, indicating that structural collapse and manganese dissolution at high temperatures cannot be effectively suppressed, resulting in poor high-temperature performance. In the full cell, the Mn deposition on the negative electrode surface is as high as 0.2 wt%, the surface manganese dissolution is not suppressed, the amount of inert byproducts such as LiF is large, and the electrode interface stability is poor.

[0157] As can be seen from the comparison between Example 1 and Comparative Example 2, if Sr-doped LMO is prepared by solid-state method, the capacity retention rate is only 42.6% after 400 cycles at 25°C and 1C rate, indicating poor cycle stability. In addition, the results of high-temperature performance test and rate performance test also show that its high-temperature cycle stability and rate performance are poor.

[0158] As can be seen from the comparison between Example 1 and Comparative Examples 3-4, if there is no Sr doping in the multiphase lithium manganese oxide microsphere cathode material, the Jahn-Teller distortion cannot be effectively suppressed, the crystal structure stability is poor, the manganese dissolution is severe, and the cycle life and rate performance are significantly reduced. If the Sr doping amount in the multiphase lithium manganese oxide microsphere cathode material is too large, an impurity phase will be introduced to occupy the active site, the reversible specific capacity of the material will be greatly reduced, ion transport will be hindered, and the electrochemical performance will be degraded.

[0159] It should be noted that the present invention is illustrated through the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, additions of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A multiphase lithium manganese oxide microsphere cathode material, characterized in that, The general chemical formula of the multiphase lithium manganese oxide microsphere cathode material is LiMn. 2-x Sr x O4, x=0.005-0.1; the crystal phase structure of the multiphase lithium manganese oxide microsphere cathode material includes a main phase, a secondary phase and a tertiary phase, wherein the main phase is Sr-doped spinel-type LiMn2O4, the secondary phase is perovskite-type Sr2Mn2O5 phase, and the tertiary phase is a layered Li2MnO3-like structural phase.

2. The multiphase lithium manganese oxide microsphere cathode material according to claim 1, characterized in that, The multiphase lithium manganese oxide microsphere cathode material is a spherical secondary particle, which is formed by the aggregation of nanoscale primary grains.

3. The multiphase lithium manganese oxide microsphere cathode material according to claim 2, characterized in that, The space group of the principal phase is Fd-3m; And / or, based on the mass of the multiphase lithium manganese oxide microsphere cathode material, the mass percentage of the main phase is 82-97 wt%, the mass percentage of the secondary phase is 1-8 wt%, and the mass percentage of the tertiary phase is 2-10 wt%; And / or, the space group of the third phase is C2 / m.

4. The multiphase lithium manganese oxide microsphere cathode material according to claim 2 or 3, characterized in that, The secondary phase is distributed at the grain boundaries of the nanoscale primary grains and on the surface of the spherical secondary particles; And / or, the third phase is distributed in a localized domain structure within the spherical secondary particles; And / or, in the multiphase lithium manganese oxide microsphere cathode material, the Sr element is uniformly distributed within the spherical secondary particles; And / or, in the multiphase lithium manganese oxide microsphere cathode material, the average oxidation state of Mn element is 3.5-3.7; And / or, in the multiphase lithium manganese oxide microsphere cathode material, Mn 4+ With Mn 3+ The molar ratio is 1.2-2.

5. The multiphase lithium manganese oxide microsphere cathode material according to any one of claims 2-4, characterized in that, The spherical secondary particles have a particle size of 0.5-5 μm, preferably 1-3 μm; And / or, the particle size of the nanoscale primary grains is 50-500 nm; And / or, the tap density of the spherical secondary particles is 1.8-2.2 g / cm³. 3 .

6. A method for preparing a multiphase lithium manganese oxide microsphere cathode material as described in any one of claims 1-5, characterized in that, The preparation method includes the following steps: A precursor solution is obtained by mixing a lithium source, a manganese source, a strontium source, and a solvent. The precursor solution is fed into a spray pyrolysis system to carry out a single spray pyrolysis synthesis reaction, thereby obtaining the multiphase lithium manganese oxide microsphere cathode material.

7. The preparation method according to claim 6, characterized in that, The total metal ion concentration of the precursor solution is 0.1-1 mol / L, preferably 0.3-0.6 mol / L; And / or, the spray pyrolysis system includes a precursor feeding system, an ultrasonic atomizer, a high-temperature tubular reactor, a powder collection device, and a tail gas treatment device connected in sequence.

8. The preparation method according to claim 6 or 7, characterized in that, The atomization frequency of the ultrasonic atomizer is 1-2.5MHz, preferably 1.5-2MHz; And / or, after the precursor solution is atomized by the ultrasonic atomizer, the resulting aerosol droplets have a particle size of 1-10 μm; And / or, the high-temperature tubular reactor includes a constant temperature zone; wherein, the temperature of the constant temperature zone is 800-1100℃, preferably 900-1050℃; and the residence time in the constant temperature zone is 0.5-10s, preferably 1-5s; And / or, the primary spray pyrolysis synthesis reaction includes sequential droplet atomization, solvent evaporation, precursor pyrolysis, crystallization, and in-situ construction of multiphase structures.

9. The preparation method according to any one of claims 6-8, characterized in that, The preparation method includes the following steps: (1) Weigh lithium source, manganese source and strontium source according to the target stoichiometric ratio to obtain solid raw materials; wherein, the molar ratio of the lithium source to the total molar ratio of the manganese source and strontium source is (1-1.1):2, preferably (1.03-1.08):2; the molar ratio of the manganese source and strontium source is (1.9-1.995):(0.005-0.1); The solid raw material is added to a solvent and stirred at 20-60°C for 10-60 min, followed by ultrasonic treatment for 5-30 min to obtain a precursor solution with a total metal ion concentration of 0.1-1 mol / L. (2) Provide a spray pyrolysis system, the spray pyrolysis system comprising a precursor feeding system, an ultrasonic atomizer, a high-temperature tubular reactor, a powder collection device and a tail gas treatment device connected in sequence; The precursor solution is fed into the spray pyrolysis system, where it is first atomized into droplets and then carried into a high-temperature tubular reactor by a carrier gas with a flow rate of 5-20 L / min. Solvent evaporation, precursor pyrolysis, crystal crystallization, and in-situ construction of multiphase structure are carried out sequentially. After completion, the precursor solution is carried into the powder collection device by the carrier gas to achieve gas-solid separation and obtain multiphase lithium manganese oxide microsphere cathode material. The carrier gas includes any one of dry compressed air, nitrogen, or oxygen; the atomization frequency of the ultrasonic atomizer is 1-2.5MHz; the aerosol droplets formed after the precursor solution is atomized by the ultrasonic atomizer have a particle size of 1-10μm; the high-temperature tubular reactor includes a constant temperature zone with a temperature of 800-1100℃, and the residence time of the aerosol droplets in the constant temperature zone is 0.5-10s.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes a positive electrode, a negative electrode, a separator, and an electrolyte; wherein the active material of the positive electrode includes the multiphase lithium manganese oxide microsphere positive electrode material as described in any one of claims 1-5.

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