Phosphate positive electrode material, preparation method thereof, positive electrode plate and lithium ion battery

Abstract

The invention provides a phosphate positive electrode material, a preparation method thereof, a positive electrode plate and a lithium ion battery. The preparation method comprises the following steps: sequentially performing first drying and first sintering on first slurry containing a first lithium source, an iron source, a manganese source, a phosphorus source and a first carbon source to obtain a first precursor; second slurry containing a second lithium source, a second carbon source and the first precursor is sequentially subjected to second drying and second sintering, and a second precursor is obtained; dispersing the second precursor in an organic solvent to obtain a third precursor; and performing third drying and third sintering on third slurry containing a third lithium source, the microemulsion and a third precursor in sequence to obtain the phosphate positive electrode material. According to the method, the technical effect of remarkably improving the electrochemical performance and the energy density of the lithium manganese iron phosphate material is achieved by regulating and controlling the adding time of the lithium source and using the microemulsion dispersion system as the nano reactor.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries, and more specifically, to a phosphate cathode material, its preparation method, cathode sheet, and lithium-ion battery. Background Technology

[0002] High-compact lithium manganese iron phosphate (LMFP), as an upgraded material of lithium iron phosphate (LFP), has attracted widespread attention in recent years. Its olivine structure combines high safety and stability, and due to the introduction of manganese, the voltage plateau is increased to 4.1V, with a theoretical energy density 15%–20% higher than LFP. However, the compaction density of traditional LMFP materials is relatively low (approximately 2.1–2.4 g / cm³). 3 This limits its volumetric energy density and practical applications. Furthermore, LMFPs suffer from low electronic conductivity (10⁻⁶ Ω·cm). -13 Problems include low compaction density (S / cm), low manganese leaching leading to decreased cycle performance, etc.

[0003] To improve conductivity, LMFP is typically fabricated into nanoscale particles (~300 nm). However, small particles lead to increased specific surface area and porosity between particles, reducing compaction density. Furthermore, LMFP may exhibit uneven iron-manganese distribution, resulting in irregular particle shapes and difficulty in close packing. While carbon coating improves conductivity, excessive carbon occupies volume, reducing compaction density. To overcome these bottlenecks, the industry employs carbon coating and metal ion doping (such as Mg...) as methods. 2+ Al 3+ Methods such as improving compaction density and electrochemical performance include using novel electrolytes (e.g., manganese ion complexing agents).

[0004] Despite significant progress in the aforementioned technologies, challenges remain in the industrial production of high-compaction, high-performance lithium manganese iron phosphate materials. Traditional synthesis methods often struggle to precisely control particle size and morphology, resulting in poor consistency and reproducibility of the final product. Furthermore, multiple calcination and surface treatment processes not only increase the complexity of the preparation process but also raise production costs, limiting the feasibility of large-scale commercial applications. Therefore, finding an efficient, economical preparation method that can precisely control the material's structure and properties is crucial for promoting the application of lithium manganese iron phosphate materials.

[0005] Therefore, how to further optimize the preparation method of phosphate cathode materials so that the prepared phosphate cathode materials have ideal particle size distribution characteristics and thus exhibit higher compaction density and energy density is one of the important technical problems that need to be solved in this field. Summary of the Invention

[0006] The main objective of this invention is to provide a phosphate cathode material, its preparation method, cathode sheet, and lithium-ion battery, so as to solve the problem of poor electrochemical performance of phosphate cathode materials in the prior art due to imperfect particle size distribution.

[0007] To achieve the above objectives, a first aspect of the present invention provides a method for preparing a phosphate cathode material, comprising: step S1, wherein a first slurry comprising a first lithium source, an iron source, a manganese source, a phosphorus source, and a first carbon source is sequentially subjected to a first drying and a first sintering to obtain a first precursor; step S2, wherein a second slurry comprising a second lithium source, a second carbon source, and the first precursor is sequentially subjected to a second drying and a second sintering to obtain a second precursor; the molar ratio of the second lithium source to the first precursor is (0.2~0.4):1; step S3, wherein the second precursor is dispersed in an organic solvent to obtain a third precursor; step S4, wherein a third slurry comprising a third lithium source, a microemulsion, and the third precursor is sequentially subjected to a third drying and a third sintering to obtain a phosphate cathode material; the molar ratio of the third lithium source to the third precursor is (0.1~0.2):1; the microemulsion comprises a surfactant, a C1~C6 alcohol compound, and a C5~C12 alkane compound. This invention successfully constructed a three-tiered particle structure (large, medium, and small) by precisely controlling the multiple introductions of lithium source at stoichiometric ratios, combined with the use of a microemulsion system and a multi-stage sintering strategy, thereby significantly improving the compaction density of the resulting cathode material. Simultaneously, due to the optimized particle size, the electrochemical activity of the resulting phosphate material in the battery system is significantly enhanced, exhibiting higher energy density and cycle stability.

[0008] Further, in step S1, the molar ratio of the first lithium source, iron source, manganese source, and phosphorus source is (0.6~0.8):(0.2~0.5):(0.5~0.8):1; and / or, based on the total weight of the first lithium source, iron source, manganese source, and phosphorus source being 100%, the amount of the first carbon source added is 6%~10%; and / or, the first lithium source is selected from one or more of lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate, lithium hydrogen phosphate, lithium chloride, and lithium nitrate; and / or, the iron source is selected from one or more of ferric oxide, ferric phosphate, ferrous oxalate, and ferromanganese phosphate; and / or, the manganese source is selected from one or more of ferromanganese phosphate, manganese carbonate, and manganese tetroxide; and / or, the phosphorus source is selected from one or more of lithium dihydrogen phosphate, ammonium dihydrogen phosphate, ferric phosphate, and ferromanganese phosphate; and / or, the first carbon source is selected from one or more of glucose, polyethylene glycol, starch, polyvinyl alcohol, and citric acid. The preferred types and amounts of raw materials described above can further optimize the distribution of lithium, iron, manganese and phosphorus elements in the obtained phosphate material, resulting in better structural integrity and electrochemical activity; at the same time, it can initially form a more stable carbon coating layer, thereby stabilizing the precursor structure and ultimately obtaining a phosphate cathode material with a more uniform particle size distribution.

[0009] Further, step S1 includes: step S1-1, where an iron source, manganese source, phosphorus source, first carbon source, and first dispersant are first mixed to obtain a first dispersion; a first lithium source and the first dispersion are second mixed to obtain a first slurry; step S1-2, where the first slurry is sequentially subjected to a first grinding with a particle size D50 of 0.8 μm to 1.5 μm, a second grinding with a particle size D50 of 0.6 μm to 0.8 μm, a first drying, and a first sintering to obtain a first precursor. The above-mentioned preferred reaction conditions and parameters can more effectively control the size and morphology of the first precursor particles, thereby facilitating further material gradation in subsequent steps and more effectively improving the compaction density and electrochemical performance of the obtained phosphate cathode material. Simultaneously, it can better balance the relationship between the full development of the first precursor structure and energy consumption, improving crystallinity and optimizing electrochemical performance while better reducing excessive phase transitions.

[0010] Further, in step S2, based on the total weight of the second lithium source and the first precursor being 100%, the amount of the second carbon source added is 1.5% to 4%; and / or, the second lithium source is selected from one or more of lithium hexafluorophosphate, lithium fluoride, lithium peroxide, and lithium hydroxide; and / or, the second carbon source is polyethylene glycol and / or polyvinyl alcohol. The above-mentioned preferred types and amounts of raw materials can form a more uniform and highly graphitized conductive layer on the surface of the second precursor, significantly improving its conductivity and thus further enhancing its electrochemical activity.

[0011] Further, step S2 includes: step S2-1, mixing the second lithium source, the second carbon source, and the second dispersant to obtain a second dispersion; mixing the first precursor and the second dispersion to obtain a second slurry; step S2-2, subjecting the second slurry to a third grinding with a particle size D50 of 0.8μm~1.5μm, a fourth grinding with a particle size D50 of 0.5μm~0.6μm, a second drying, and a second sintering to obtain a second precursor. The above-mentioned preferred reaction conditions and parameters can better optimize the particle size distribution of the material, promote a more uniform distribution of lithium ions in the second precursor, better maintain the stability of the internal structure of the material particles, and reduce lattice distortion caused by over-sintering.

[0012] Further, in step S3, the organic solvent includes a first solvent, a second solvent, and a third solvent, wherein the first solvent is water, the second solvent is selected from one or more of ethanol, propanol, and acetone, and the third solvent is selected from one or more of toluene, xylene, dimethylformamide, and N-methylformamide; and / or, the dispersion treatment includes sequential stirring and ultrasonic treatment, wherein the stirring time is 2h~3h, the rotation speed is 200rpm~300rpm, and the ultrasonic treatment time is 30min~60min. The above preferred embodiment can more effectively dissolve the organic carbon source, remove impurities, regulate the wettability and charge distribution of the particle surface, promote more uniform dispersion in the organic solvent, and subsequently form a higher quality microemulsion dispersion system, ultimately obtaining a phosphate cathode material with superior performance.

[0013] Further, in step S4, the weight ratio of surfactant, alcohol compound, and alkane compound is (0.20~0.30):(0.6~0.8):(0.05~0.10); and / or, based on the total weight of the third slurry as 100%, the weight percentage of microemulsion is 2%~5%; and / or, the surfactant is selected from one or more of sodium di(2-ethylhexyl)succinate sulfonate, sorbitan monooleate, sodium alkylbenzene sulfonate, and sodium lauryl sulfate; and / or, the alcohol compound is selected from one or more of n-butanol, n-pentanol, and isopropanol; and / or, the alkane compound is selected from one or more of n-hexane, cyclohexane, and isooctane; and / or, the third lithium source is selected from one or more of lithium hexafluorophosphate, lithium fluoride, lithium peroxide, and lithium hydroxide. The preferred types and amounts of raw materials described above can provide a more ideal microreactor for the growth of particles in a controlled environment, thereby more effectively achieving the gradation of the three-stage particles and further improving the compaction density and electrochemical activity of the obtained phosphate material.

[0014] Further, step S4 includes: step S4-1, mixing the third lithium source, the third precursor, and the third dispersant to obtain a third dispersion; step S4-2, subjecting the third dispersion to a fifth grinding with a particle size D50 of 0.8μm~1.5μm and a sixth grinding with a particle size D50 of 0.4μm~0.5μm, then adding a microemulsion to obtain a third slurry; the third slurry is then subjected to a third drying and a third sintering to obtain a phosphate cathode material. The above-mentioned preferred reaction conditions and parameters can further promote the maturation of the material's internal structure, improve crystallinity, better stabilize the chemical composition of the material, remove organic residues from the obtained phosphate cathode material, and reduce structural damage caused by over-sintering, ultimately obtaining a phosphate cathode material with higher compaction density.

[0015] A second aspect of this invention provides a phosphate cathode material prepared by the aforementioned method. Because the preparation method utilizes in-situ gradation technology, combined with multi-stage sintering and a microemulsion dispersion system, it achieves a three-tiered distribution of large, medium, and small cathode material particles. The resulting phosphate cathode material maintains good chemical stability and structural integrity while exhibiting significant advantages in compaction density and excellent electrochemical performance.

[0016] Furthermore, the phosphate cathode material includes a first particle with a particle size of 0.6 μm to 0.8 μm, a second particle with a particle size of 0.3 μm to 0.5 μm, and a third particle with a particle size of 0.1 μm to 0.3 μm, and the weight ratio of the first, second, and third particles is (10~15):(15~25):(60~75). By optimizing the above-mentioned multi-level particle system, a more reasonable distribution of particles of different sizes in the phosphate cathode material can be achieved, more effectively reducing the low contact efficiency of large particles and the structural stability problem of small particles, ultimately achieving higher compaction density and higher energy density.

[0017] A third aspect of the present invention provides a positive electrode sheet comprising a positive electrode active material, wherein the positive electrode active material is the aforementioned phosphate positive electrode material; or, the positive electrode active material is prepared by the aforementioned method for preparing the phosphate positive electrode material. Because the phosphate positive electrode material synthesized using the aforementioned in-situ gradation technology provided by the present invention optimizes the microstructure of the electrode sheet through the synergistic effect of large, medium, and small particles, thereby improving its electronic and ionic conductivity, the resulting electrode sheet exhibits higher energy density and more stable cycle performance.

[0018] A fourth aspect of the present invention provides a lithium-ion battery comprising the aforementioned positive electrode. Because the particle size distribution of the phosphate positive electrode material provided by the present invention can effectively shorten the diffusion path of lithium ions and improve electron transport efficiency, the lithium-ion battery containing it exhibits higher energy density, shorter charge / discharge time, and longer cycle life.

[0019] By applying the technical solution of this invention, the synthesis and proportion of large, medium and small particles in the prepared cathode material are precisely controlled by adjusting the timing of lithium source addition and utilizing a microemulsion dispersion system as a nanoreactor. This achieves the goal of optimizing the material structure and increasing compaction density, ultimately resulting in a significant improvement in the electrochemical performance and energy density of lithium manganese iron phosphate materials. Attached Figure Description

[0020] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0021] Figure 1 The results are shown in the scanning electron microscope (SEM) characterization of the phosphate cathode material obtained in Example 1 of this invention. Detailed Implementation

[0022] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0023] As described in the background section, existing phosphate cathode materials suffer from poor electrochemical performance due to suboptimal particle size distribution. To address the aforementioned technical problems, the first aspect of this invention provides a method for preparing a phosphate cathode material, comprising: step S1, wherein a first slurry containing a first lithium source, an iron source, a manganese source, a phosphorus source, and a first carbon source is sequentially subjected to a first drying and a first sintering to obtain a first precursor; step S2, wherein a second slurry containing a second lithium source, a second carbon source, and the first precursor is sequentially subjected to a second drying and a second sintering to obtain a second precursor; the molar ratio of the second lithium source to the first precursor is (0.2~0.4):1; step S3, wherein the second precursor is dispersed in an organic solvent to obtain a third precursor; step S4, wherein a third slurry containing a third lithium source, a microemulsion, and the third precursor is sequentially subjected to a third drying and a third sintering to obtain a phosphate cathode material; the molar ratio of the third lithium source to the third precursor is (0.1~0.2):1; the microemulsion contains a surfactant, C1~C6 alcohols, and C5~C12 alkanes.

[0024] The preparation method of this invention achieves asynchronous particle growth by controlling the timing of lithium source addition in steps S1, S2, and S4: A relatively lithium-rich region and a lithium-poor region appear inside the manganese iron phosphate precursor. After high-temperature sintering, the lithium-rich region particles continue to grow, while the growth of the lithium-poor region is inhibited. A secondary lithium supplementation method allows lithium to be captured in the lithium-poor region, achieving a particle size distribution and improving the material's compaction density. A microemulsion dispersion system is used as a nanoreactor to synthesize small-sized, monodisperse particles, thus forming a tertiary particle size distribution. In step S3, an organic solvent is used to dissolve the amorphous carbon or hydrocarbons on the surface of the precursor particles, while graphitized carbon is retained, improving the material's electronic conductivity. More specifically: In step S1, a first slurry is prepared by controlling the stoichiometric ratio of the first lithium source, iron source, manganese source, phosphorus source, and first carbon source, and then subjected to a first drying and a first sintering process to obtain the first precursor. Subsequently, in step S2, a second lithium source and a second carbon source are introduced, followed by slurry preparation, drying, and sintering to form a second precursor. Particular emphasis is placed on the precise control of the molar ratio (0.2~0.4):1 of the second lithium source to the first precursor to achieve lithium ion replenishment and optimized proportions in the material. Step S3 involves dispersing the second precursor in an organic solvent, which not only helps clean the particle surface but also promotes more uniform contact between the material and the lithium source in subsequent steps. Finally, in step S4, the third precursor is prepared by adding a third lithium source (0.1~0.2):1 and a microemulsion. The surfactants, alcohols, and alkanes in the microemulsion work synergistically to regulate particle growth and promote particle dispersion, ensuring the final material's particle size distribution.

[0025] In summary, this invention successfully constructed a three-tiered particle structure of large, medium, and small particles by precisely controlling the multiple introductions of lithium source at precise stoichiometric ratios, combined with the use of a microemulsion system and a multi-stage sintering strategy, thereby significantly improving the compaction density of the resulting cathode material. Simultaneously, due to the optimized particle size, the electrochemical activity of the resulting phosphate material in the battery system is significantly enhanced, exhibiting higher energy density and cycle stability.

[0026] In step S1, the preferred molar ratio of the first lithium source, iron source, manganese source, and phosphorus source is (0.6~0.8):(0.2~0.5):(0.5~0.8):1, so as to further optimize the distribution of lithium, iron, manganese, and phosphorus elements in the obtained phosphate material, and promote its better structural integrity and electrochemical activity. Regarding the first carbon source, in order to initially form a more stable carbon coating layer, thereby stabilizing the precursor structure and ultimately obtaining a phosphate cathode material with a more uniform particle size distribution, the preferred addition amount of the first carbon source is 6%~10% based on the total weight of the first lithium source, iron source, manganese source, and phosphorus source being 100%; and / or, the first carbon source is selected from one or more of glucose, polyethylene glycol, starch, polyvinyl alcohol, and citric acid.

[0027] In several typical embodiments, the first lithium source is preferably selected from one or more of lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate, lithium hydrogen phosphate, lithium chloride, and lithium nitrate; and / or, the iron source is selected from one or more of ferric oxide, ferric phosphate, ferrous oxalate, and ferromanganese phosphate; and / or, the manganese source is selected from one or more of ferromanganese phosphate, manganese carbonate, and manganese tetroxide; and / or, the phosphorus source is selected from one or more of lithium dihydrogen phosphate, ammonium dihydrogen phosphate, ferric phosphate, and ferromanganese phosphate.

[0028] Furthermore, to achieve preliminary classification of the first precursor particles, step S1 preferably includes: step S1-1, where an iron source, manganese source, phosphorus source, first carbon source, and first dispersant are first mixed to obtain a first dispersion; a first lithium source and the first dispersion are second mixed to obtain a first slurry; step S1-2, where the first slurry is sequentially subjected to a first grinding with a particle size D50 of 0.8μm~1.5μm, a second grinding with a particle size D50 of 0.6μm~0.8μm, a first drying, and a first sintering to obtain the first precursor. In particular, by optimizing the particle size parameters obtained during the two grinding processes, the size and morphology of the first precursor particles can be more effectively controlled, thereby facilitating further material gradation in subsequent steps and more effectively improving the compaction density and electrochemical performance of the obtained phosphate cathode material. In the above process, it is preferable that both the first and second mixing are carried out with a stirring speed of 200 rpm to 300 rpm to facilitate the full dispersion of precursor particles during the mixing process, reduce the formation of large particles, and benefit subsequent grinding and gradation. Preferably, the first mixing time is 2 h to 5 h; and / or the second mixing time is 1 h to 2 h, which can promote effective reactions between the components and further promote the homogenization process of phosphate particles.

[0029] During the formation of the first precursor, the preferred holding temperature for the first sintering is 700℃~750℃ to facilitate the formation of a more stable olivine structure, while better maintaining the stability of the material framework in subsequent preparation processes, and improving crystallinity and structural integrity. A preferred holding time of 4h~6h can better balance the relationship between the full development of the first precursor structure and energy consumption, effectively reducing excessive phase transitions while improving crystallinity and optimizing electrochemical performance.

[0030] In step S2, to form a more uniform and highly graphitized conductive layer on the surface of the second precursor, and to significantly improve its conductivity, thereby further improving its electrochemical activity, the amount of the second carbon source added is preferably 1.5% to 4% based on the total weight of the second lithium source and the first precursor being 100%; and / or, the second carbon source is polyethylene glycol and / or polyvinyl alcohol. Preferably, the second lithium source is selected from one or more of lithium hexafluorophosphate, lithium fluoride, lithium peroxide, and lithium hydroxide, which allows for flexible adjustment of lithium ion replenishment, optimization of the lithium content of the material system, and further improvement of the compaction density and energy density of the final cathode material.

[0031] Furthermore, in several typical embodiments, to better optimize the particle size distribution of the material, step S2 preferably includes: step S2-1, mixing the second lithium source, the second carbon source, and the second dispersant to obtain a second dispersion; mixing the first precursor and the second dispersion to obtain a second slurry; step S2-2, sequentially subjecting the second slurry to a third grinding with a particle size D50 of 0.8μm~1.5μm, a fourth grinding with a particle size D50 of 0.5μm~0.6μm, a second drying, and a second sintering to obtain a second precursor. In particular, by optimizing the particle size results of the third and fourth grinding processes, precise adjustment of particle size is further achieved, optimizing the particle size distribution, and ultimately obtaining a phosphate cathode material with higher compaction density. In step S2, the mixing of the second lithium source, the second carbon source, and the second dispersant, as well as the mixing of the first precursor and the second dispersion, are specifically performed under the following conditions: 200rpm~300rpm for 2h~3h.

[0032] During the second sintering process, the preferred holding temperature is 600℃~700℃, and the holding time is 4h~6h. These optimized sintering conditions promote a more uniform distribution of lithium ions in the second precursor, while also better maintaining the stability of the internal structure of the material particles and reducing lattice distortion caused by over-sintering. During this sintering process, the interactions between large, medium, and small particles are further optimized, forming a preliminary particle size distribution, thereby more effectively improving the electrochemical performance of the final phosphate material.

[0033] In step S3, preferably, the organic solvent includes a first solvent, a second solvent, and a third solvent, wherein the first solvent is water, the second solvent is selected from one or more of ethanol, propanol, and acetone, and the third solvent is selected from one or more of toluene, xylene, dimethylformamide, and N-methylformamide. Water, as the first solvent, helps to dissolve and disperse the material particles, while the second and third solvents stabilize the material surface, reduce agglomeration, and improve the monodispersity of the particles. In other words, the above-mentioned organic solvent system can utilize the synergistic effect of different solvents to more effectively dissolve amorphous carbon or hydrocarbons on the surface of the precursor particles, thereby further optimizing the surface properties and dispersion state of the material particles, creating more favorable conditions for subsequent microemulsion synthesis, and ultimately obtaining a phosphate cathode material with superior particle size distribution and higher compaction density. Based on this, it is further preferred that the volume ratio of the first solvent, the second solvent, and the third solvent in the above mixed solvent is (30~40):(40~50):(10~20), so as to more effectively dissolve the organic carbon source, remove impurities, regulate the wettability and charge distribution of the particle surface, promote its more uniform dispersion in the organic solvent, and subsequently form a higher quality microemulsion dispersion system, ultimately obtaining a phosphate cathode material with superior performance.

[0034] In several typical implementations, to further break up particle agglomeration and improve the uniformity of the dispersion system, thereby more effectively optimizing the surface properties and dispersion state of the particles, the dispersion treatment preferably includes sequential stirring and ultrasonic treatment, with the stirring time being 2-3 hours and the rotation speed being 200-300 rpm, and the ultrasonic treatment time being 30-60 minutes. In practical applications, to more thoroughly remove residual organic carbon and obtain a more structurally stable phosphate material, step S3 further includes cleaning the third precursor after dispersion treatment, and the cleaning treatment includes sequential first and second cleaning. The cleaning agent used in the first cleaning is the organic solvent used in the dispersion treatment, while the cleaning agent used in the second cleaning is water. During the cleaning process, the organic solvent dissolves the amorphous carbon or hydrocarbons on the surface of the material particles, while graphitized carbon is retained, thereby significantly improving the electronic conductivity of the final phosphate cathode material.

[0035] Further, in step S4, the preferred weight ratio of surfactant, alcohol, and alkane is (0.20~0.30):(0.6~0.8):(0.05~0.10). In the microemulsion system used in this invention, the surfactant reduces the oil-water interfacial tension and forms a stable nanoreactor, providing a controlled microenvironment for particle growth. The addition of alcohol as a co-surfactant and alkane as the oil phase further stabilizes this microenvironment, ensuring the consistency and controllability of particle growth. Based on this, the inventors optimized the above weight ratio through numerous experiments, which can more effectively utilize the interfacial activity of surfactant, the stabilizing effect of alcohol, and the dispersing effect of alkane to jointly promote a more uniform distribution and growth of particles in the microemulsion, further optimizing the particle size distribution of the obtained phosphate material and improving its compaction density and energy density. Furthermore, in order to more effectively encapsulate and modify the material particles, form a more stable dispersion system, and reduce the introduction of impurities, it is preferable that the weight percentage of the microemulsion is 2% to 5% based on the total weight of the third slurry as 100%, thereby forming a more ideal particle size distribution and further improving the electrochemical activity of the resulting phosphate cathode material.

[0036] In several typical embodiments, the surfactant is preferably selected from one or more of sodium di(2-ethylhexyl)succinate sulfonate, sorbitan monooleate, sodium alkylbenzene sulfonate, and sodium lauryl sulfate, to more effectively reduce the oil-water interfacial tension and form a more stable microemulsion system. The alcohol compound is preferably selected from one or more of n-butanol, n-pentanol, and isopropanol, because these alcohols have better stability and dispersing properties, helping to more effectively maintain the dispersion state of the microemulsion. The alkane compound is preferably selected from one or more of n-hexane, cyclohexane, and isooctane, which can provide a better inert environment. In particular, the microemulsion formed by sodium di(2-ethylhexyl)succinate sulfonate, n-butanol, and isooctane is more stable and can provide a more ideal microreactor for particle growth under controlled conditions, thereby more effectively achieving the gradation of tertiary particles and further improving the compaction density and electrochemical activity of the resulting phosphate material. Furthermore, in this process, the third lithium source is preferably selected from one or more of lithium hexafluorophosphate, lithium fluoride, lithium peroxide, and lithium hydroxide.

[0037] Further, the preferred step S4 includes: step S4-1, mixing the third lithium source, the third precursor, and the third dispersant to obtain a third dispersion; step S4-2, sequentially subjecting the third dispersion to a fifth grinding with a particle size D50 of 0.8μm~1.5μm and a sixth grinding with a particle size D50 of 0.4μm~0.5μm, then adding a microemulsion to obtain a third slurry; the third slurry is then sequentially dried and sintered to obtain a phosphate cathode material. In the aforementioned preferred step S4, the particle size of the material can be further controlled, thereby forming a more ideal particle size distribution and significantly improving the compaction density and electrochemical performance of the obtained phosphate cathode material. In step S4, the mixing of the third lithium source, the third precursor, and the third dispersant, and the further addition of the microemulsion to obtain the third slurry, are specifically performed under the following conditions: 200rpm~300rpm for 2h~3h.

[0038] In the third sintering process, the preferred holding temperature is 750℃~850℃, and the holding time is 8h~10h. These optimized sintering conditions further promote the maturation of the material's internal structure, increase crystallinity, better stabilize the material's chemical composition, reduce structural damage caused by over-sintering, and ultimately obtain a phosphate cathode material with higher compaction density. Simultaneously, these sintering conditions can better remove organic residues from the obtained phosphate cathode material, optimize its surface properties, and thus further improve its electrochemical performance.

[0039] In practical applications, to better balance drying speed and material structure preservation, improve particle integrity, reduce cracks or morphological changes caused by over-drying, and provide more reliable sintering particles for subsequent high-temperature sintering, ultimately producing phosphate cathode materials with higher compaction density and better electrochemical activity, it is preferable that the first, second, and third drying processes are all spray drying, with each spray drying process having an independent outlet air temperature of 100℃~110℃. Furthermore, in practical applications, it is preferred that the first dispersant is water and / or ethanol (when using a water / ethanol mixture, the volume percentage of ethanol in water can be 5%~15%); the second and third dispersants are both water.

[0040] A second aspect of this invention provides a phosphate cathode material prepared by the aforementioned method. Because the preparation method utilizes in-situ gradation technology, combined with multi-stage sintering and a microemulsion dispersion system, it achieves a three-tiered distribution of large, medium, and small cathode material particles. The resulting phosphate cathode material maintains good chemical stability and structural integrity while exhibiting significant advantages in compaction density and excellent electrochemical performance.

[0041] It should be noted that due to the complex structural formation and compositional changes during the preparation process, and the limitations of the specific characteristics of the materials field and existing testing and characterization methods, it is difficult to perform a comprehensive quantitative characterization of the complex microstructure of the obtained phosphate cathode material. However, performance test results show that the cathode material obtained in this invention has a higher compaction density and exhibits a higher energy density in application.

[0042] Furthermore, the phosphate cathode material includes a first particle with a diameter of 0.6 μm to 0.8 μm, a second particle with a diameter of 0.3 μm to 0.5 μm, and a third particle with a diameter of 0.1 μm to 0.3 μm, with a weight ratio of (10~15):(15~25):(60~75). In the resulting phosphate cathode material, small-sized particles can effectively shorten the diffusion path of lithium ions and promote fast charge and discharge performance; medium-sized particles help to build connections between materials and improve electron transport efficiency; while large particles, while ensuring the overall structural stability of the material, further optimize the migration path of lithium ions through the porosity effect between them. Based on this, by optimizing the above-mentioned multi-level particle system, a more reasonable distribution of particles of different sizes in the phosphate cathode material can be achieved, more effectively reducing the low contact efficiency of large particles and the structural stability problem of small particles, ultimately achieving higher compaction density and higher energy density.

[0043] A third aspect of the present invention provides a positive electrode sheet comprising a positive electrode active material, wherein the positive electrode active material is the aforementioned phosphate positive electrode material; or, the positive electrode active material is prepared by the aforementioned method for preparing the phosphate positive electrode material. Because the phosphate positive electrode material synthesized using the aforementioned in-situ gradation technology provided by the present invention optimizes the microstructure of the electrode sheet through the synergistic effect of large, medium, and small particles, thereby improving its electronic and ionic conductivity, the resulting electrode sheet exhibits higher energy density and more stable cycle performance.

[0044] A fourth aspect of the present invention provides a lithium-ion battery comprising the aforementioned positive electrode. Because the particle size distribution of the phosphate positive electrode material provided by the present invention can effectively shorten the diffusion path of lithium ions and improve electron transport efficiency, the lithium-ion battery containing it exhibits higher energy density, shorter charge / discharge time, and longer cycle life.

[0045] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0046] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0047] Example 1

[0048] A method for preparing a phosphate cathode material:

[0049] (1) According to the stoichiometric ratio Li:Fe:Mn:P=0.6:0.5:0.5:1, weigh lithium carbonate, iron phosphate, manganese tetroxide, and lithium dihydrogen phosphate. Add iron source, manganese source, phosphorus source, and glucose (based on the total weight of the first lithium source, iron source, manganese source, and phosphorus source being 100%, the amount of the first carbon source added is 8%) to the solvent water. Stir at 300 rpm for 2 hours to obtain the first dispersion. Then add lithium carbonate to it and continue stirring for 2 hours to obtain the first slurry. Coarsely grind the first slurry to a D50 of 0.8 μm and ultrafine grind it to a D50 of 0.6 μm. Spray dry at an outlet temperature of 110℃ and sinter at 700℃ for 6 hours to obtain the first precursor.

[0050] (2) Weigh lithium hydroxide and the obtained first precursor according to the stoichiometric ratio of Li: first precursor = 0.4:1. Dissolve lithium hydroxide and the second carbon source PEG (the amount of the second carbon source added is 3% based on the total weight of the second lithium source and the first precursor being 100%) in water. Stir at 300 rpm for 2 h to obtain a second dispersion. Add the first precursor to the obtained second dispersion and continue stirring at 300 rpm for 2 h to obtain a second slurry. Coarsely grind the obtained second slurry to a D50 of 0.8 μm, ultrafine grind it to a D50 of 0.5 μm, spray dry it at 100℃, and sinter it at 600℃ for 6 h to obtain a graded lithium manganese iron phosphate precursor, i.e., the second precursor.

[0051] (3) Mix deionized water, ethanol, and NMP in a volume ratio of 40:40:20 to obtain a mixed organic solvent. Add the second precursor to it and stir at 300 rpm for 2 h. After sonication for 30-60 min, filter it and wash it three times with the above-mentioned composite organic solvent and three times with deionized water to obtain the third precursor.

[0052] (4) Weigh lithium hexafluorophosphate and the obtained third precursor according to the stoichiometric ratio of Li: third precursor = 0.15:1, dissolve them in deionized water, stir at 300 rpm for 2 h, and then perform coarse grinding to a D50 of 0.8 μm and ultrafine grinding to a D50 of 0.45 μm to obtain the third dispersion. Weigh sodium di(2-ethylhexyl) succinate sulfonate, co-surfactant n-butanol, and oil phase isooctane according to the mass ratio of 0.3:0.6:0.1. Dissolve sodium di(2-ethylhexyl) succinate sulfonate in oil phase isooctane and stir to disperse. Add co-surfactant n-butanol and stir to disperse to obtain a microemulsion. Add 2% of the total mass of the microemulsion to the above third slurry, continue stirring at 300 rpm for 2 h, spray dry at an outlet temperature of 100℃, and sinter at 800℃ for 8 h to obtain the in-situ graded high-pressure lithium manganese iron phosphate cathode material.

[0053] The SEM characterization results of the obtained cathode material are shown in the figure. Figure 1 It is evident from this that the large, medium, and small particles exhibit a distinct three-level distribution. Specifically, the obtained cathode material includes a first particle with a diameter of 0.6 μm to 0.8 μm, a second particle with a diameter of 0.3 μm to 0.5 μm, and a third particle with a diameter of 0.1 μm to 0.3 μm, with a weight ratio of 15:20:65 for the first, second, and third particles.

[0054] Example 2

[0055] A method for preparing a phosphate cathode material:

[0056] (1) According to the stoichiometric ratio Li:Fe:Mn:P=0.7:0.5:0.5:1, weigh lithium carbonate, iron phosphate, manganese tetroxide, and lithium dihydrogen phosphate. Add iron source, manganese source, phosphorus source, and glucose (based on the total weight of the first lithium source, iron source, manganese source, and phosphorus source being 100%, the amount of the first carbon source added is 8%) to the solvent water. Stir at 300 rpm for 2 h to obtain the first dispersion. Then add lithium carbonate to it and continue stirring for 2 h to obtain the first slurry. Coarsely grind the first slurry to a D50 of 0.8 μm and ultrafine grind it to a D50 of 0.6 μm. Spray dry at an outlet temperature of 110℃ and sinter at 700℃ for 6 h to obtain the first precursor.

[0057] (2) Weigh lithium hydroxide and the obtained first precursor according to the stoichiometric ratio of Li: first precursor = 0.3:1. Dissolve lithium hydroxide and the second carbon source PEG (the amount of the second carbon source added is 3% based on the total weight of the second lithium source and the first precursor being 100%) in water. Stir at 300 rpm for 2 h to obtain a second dispersion. Add the first precursor to the obtained second dispersion and continue stirring at 300 rpm for 2 h to obtain a second slurry. Coarsely grind the obtained second slurry to a D50 of 0.8 μm, ultrafine grind it to a D50 of 0.5 μm, spray dry it at 100℃, and sinter it at 600℃ for 6 h to obtain a graded lithium manganese iron phosphate precursor, i.e., the second precursor.

[0058] (3) Mix deionized water, ethanol, and NMP in a volume ratio of 40:40:20 to obtain a mixed organic solvent. Add the second precursor to it and stir at 300 rpm for 2 h. After sonication for 30-60 min, filter it and wash it three times with the above-mentioned composite organic solvent and three times with deionized water to obtain the third precursor.

[0059] (4) Weigh lithium hexafluorophosphate and the obtained third precursor according to the stoichiometric ratio of Li: third precursor = 0.15:1, dissolve them in deionized water, stir at 300 rpm for 2 h, and then perform coarse grinding to a D50 of 0.8 μm and ultrafine grinding to a D50 of 0.45 μm to obtain the third dispersion. Weigh sodium di(2-ethylhexyl) succinate sulfonate, co-surfactant n-butanol, and oil phase isooctane according to the mass ratio of 0.3:0.6:0.1. Dissolve sodium di(2-ethylhexyl) succinate sulfonate in oil phase isooctane and stir to disperse. Add co-surfactant n-butanol and stir to disperse to obtain a microemulsion. Add 2% of the total mass of the microemulsion to the above third slurry, continue stirring at 300 rpm for 2 h, spray dry at an outlet temperature of 100℃, and sinter at 800℃ for 8 h to obtain the in-situ graded high-pressure lithium manganese iron phosphate cathode material.

[0060] The obtained cathode material includes a first particle with a particle size of 0.6μm to 0.8μm, a second particle with a particle size of 0.3μm to 0.5μm, and a third particle with a particle size of 0.1μm to 0.3μm, and the weight ratio of the first particle, the second particle, and the third particle is 15:20:65.

[0061] Example 3

[0062] A method for preparing a phosphate cathode material:

[0063] The only difference between this embodiment and Embodiment 1 is that in step (4), the molar ratio of the third lithium source to the third precursor is changed to 0.2:1.

[0064] Example 4

[0065] A method for preparing a phosphate cathode material:

[0066] The only difference between this embodiment and Embodiment 1 is that in step (4), the third lithium source is changed to lithium hydroxide.

[0067] Example 5

[0068] A method for preparing a phosphate cathode material:

[0069] The only difference between this embodiment and embodiment 1 is that the amount of microemulsion added in step (4) is changed so that the weight ratio of microemulsion is 5% based on the total weight of the third slurry being 100%.

[0070] Example 6

[0071] A method for preparing a phosphate cathode material:

[0072] The only difference between this embodiment and embodiment 1 is that the holding temperature of the first sintering in step (1) is changed to 750°C and the holding time is changed to 4h; the holding temperature of the second sintering in step (2) is changed to 700°C and the holding time is changed to 4h; and the holding temperature of the third sintering in step (4) is changed to 750°C and the holding time is changed to 10h.

[0073] Example 7

[0074] A method for preparing a phosphate cathode material:

[0075] The only difference between this embodiment and embodiment 1 is that the holding temperature of the first sintering in step (1) is changed to 650°C and the holding time is changed to 8h.

[0076] Example 8

[0077] A method for preparing a phosphate cathode material:

[0078] The only difference between this embodiment and embodiment 1 is that the holding temperature of the first sintering in step (1) is changed to 700°C and the holding time is changed to 3h.

[0079] Example 9

[0080] A method for preparing a phosphate cathode material:

[0081] The only difference between this embodiment and embodiment 1 is that the holding temperature of the second sintering in step (2) is changed to 550°C and the holding time is changed to 8h.

[0082] Example 10

[0083] A method for preparing a phosphate cathode material:

[0084] The only difference between this embodiment and embodiment 1 is that the holding temperature of the second sintering in step (2) is changed to 750°C and the holding time is changed to 2h.

[0085] Example 11

[0086] A method for preparing a phosphate cathode material:

[0087] The only difference between this embodiment and embodiment 1 is that the amount of microemulsion added in step (4) is changed so that the weight ratio of microemulsion is 1% based on the total weight of the third slurry being 100%.

[0088] Example 12

[0089] A method for preparing a phosphate cathode material:

[0090] The only difference between this embodiment and embodiment 1 is that the amount of microemulsion added in step (4) is changed so that the weight ratio of microemulsion is 8% based on the total weight of the third slurry being 100%.

[0091] Example 13

[0092] A method for preparing a phosphate cathode material:

[0093] The only difference between this embodiment and embodiment 1 is that the holding temperature of the third sintering in step (4) is changed to 700°C and the holding time is changed to 12h.

[0094] Example 14

[0095] A method for preparing a phosphate cathode material:

[0096] The only difference between this embodiment and embodiment 1 is that the holding temperature of the third sintering in step (4) is changed to 900°C and the holding time is changed to 5h.

[0097] Comparative Example 1

[0098] A method for preparing a phosphate cathode material:

[0099] The only difference between this comparative example and Example 1 is that no microemulsion was added in step (4).

[0100] Comparative Example 2

[0101] A method for preparing a phosphate cathode material:

[0102] The only difference between this comparative example and Example 1 is that in step (1), the molar ratio of the first lithium source, iron source, manganese source and phosphorus source is changed to Li:Fe:Mn:P=0.9:0.5:0.5:1; and the molar ratio of the second lithium source to the first precursor in step (2) is changed to 0.1:1.

[0103] Comparative Example 3

[0104] A method for preparing a phosphate cathode material:

[0105] The only difference between this comparative example and Example 1 is that in step (4), the molar ratio of the third lithium source to the third precursor is changed to 0.05:1.

[0106] Comparative Example 4

[0107] A method for preparing a phosphate cathode material:

[0108] The only difference between this comparative example and Example 1 is that isooctane was not added to the microemulsion in step (4).

[0109] Battery Sample Preparation and Testing Methods

[0110] The compacted lithium manganese iron phosphate material samples prepared in each embodiment and comparative example were used as positive electrode active materials. They were prepared into slurries according to a ratio of positive electrode active material: conductive agent: binder = 90:5:5, and the slurry concentration was 130~150 g / m³. 2 The areal density of the coating is applied to carbon-coated copper foil to form the positive electrode. Graphite is used as the negative electrode, and lithium hexafluorophosphate (LiP) is used as the negative electrode. Using lithium salt as the electrolyte, various battery samples were prepared. Finally, the battery casing was sealed to isolate it from air, and the samples were left to stand for a period of time after preparation. The entire battery assembly process was carried out in a glove box filled with argon atmosphere.

[0111] Under test conditions of 2.5~4.5V, the 0.2C discharge specific capacity and 1C discharge specific capacity of each battery sample at 25℃ were tested. Simultaneously, the powder compaction of the cathode materials prepared in each example and comparative example was tested at 221MPa. The test results are listed in Table 1.

[0112] Table 1

[0113]

[0114] As can be seen from the above description, compared to the comparative examples, the embodiments of the present invention achieve the preparation of a phosphate cathode material with a three-stage particle size distribution (large, medium, and small). The resulting phosphate cathode material, while maintaining good chemical stability and structural integrity, possesses higher compaction density and energy density. When used as a cathode active material and assembled to prepare a lithium-ion battery, the resulting battery also exhibits a correspondingly higher discharge specific capacity.

[0115] In various embodiments:

[0116] Comparing Examples 7 and 8 with Example 1, it can be seen that by optimizing the conditions of the first sintering in step S1, a more stable olivine structure can be formed, while better maintaining the stability of the material framework in the subsequent preparation process, as well as improving crystallinity and structural integrity; at the same time, it can better balance the relationship between the full development of the first precursor structure and energy consumption, and better reduce excessive phase transition while improving crystallinity and optimizing electrochemical performance.

[0117] Comparing Examples 9 and 10 with Example 1, it can be seen that by optimizing the conditions of the second sintering in step S2, a more uniform distribution of lithium ions in the second precursor can be promoted, while also better maintaining the stability of the internal structure of the material particles and reducing lattice distortion caused by over-sintering.

[0118] Comparing Examples 11 and 12 with Example 1, it can be seen that in step S4, by optimizing the amount of microemulsion added, the microemulsion can more effectively encapsulate and modify the material particles, forming a more stable dispersion system while reducing the introduction of impurities, thereby forming a more ideal particle size distribution, and the electrochemical activity of the obtained phosphate cathode material is further improved.

[0119] Comparing Examples 13 and 14 with Example 1, it can be seen that by optimizing the conditions of the third sintering in step S4, the internal structure of the material can be further promoted to mature, the crystallinity can be improved, the chemical composition of the material can be better stabilized, the structural damage caused by over-sintering can be reduced, and finally a phosphate cathode material with higher compaction density can be obtained.

[0120] It should be noted that the terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such terms can be used interchangeably where appropriate so that the embodiments of this application described herein can be implemented, for example, in a sequence other than those described herein.

[0121] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a phosphate cathode material, characterized in that, include: Step S1 involves a first slurry containing a first lithium source, an iron source, a manganese source, a phosphorus source, and a first carbon source being sequentially dried and sintered to obtain a first precursor. Step S2 involves a second slurry comprising a second lithium source, a second carbon source, and the first precursor, which is then subjected to a second drying and a second sintering process to obtain a second precursor; the molar ratio of the second lithium source to the first precursor is (0.2~0.4):

1. Step S3: The second precursor is dispersed in an organic solvent to obtain the third precursor; Step S4 involves a third slurry containing a third lithium source, a microemulsion, and the third precursor, which is then subjected to a third drying and a third sintering process to obtain the phosphate cathode material. The molar ratio of the third lithium source to the third precursor is (0.1~0.2):

1. The microemulsion contains a surfactant, C1~C6 alcohols, and C5~C12 alkanes.

2. The method for preparing the phosphate cathode material according to claim 1, characterized in that, In step S1 The molar ratio of the first lithium source, the iron source, the manganese source, and the phosphorus source is (0.6~0.8):(0.2~0.5):(0.5~0.8):1; and / or, Based on the total weight of the first lithium source, the iron source, the manganese source, and the phosphorus source being 100%, the amount of the first carbon source added is 6% to 10%; and / or, The first lithium source is selected from one or more of lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate, lithium hydrogen phosphate, lithium chloride, and lithium nitrate; and / or, the iron source is selected from one or more of ferric oxide, ferric phosphate, ferrous oxalate, and ferromanganese phosphate; and / or, the manganese source is selected from one or more of ferromanganese phosphate, manganese carbonate, and manganese tetroxide; and / or, the phosphorus source is selected from one or more of lithium dihydrogen phosphate, ammonium dihydrogen phosphate, ferric phosphate, and ferromanganese phosphate; and / or, the first carbon source is selected from one or more of glucose, polyethylene glycol, starch, polyvinyl alcohol, and citric acid.

3. The method for preparing the phosphate cathode material according to claim 1 or 2, characterized in that, Step S1 includes: In step S1-1, the iron source, the manganese source, the phosphorus source, the first carbon source, and the first dispersant are mixed in a first process to obtain a first dispersion; the first lithium source and the first dispersion are mixed in a second process to obtain the first slurry. In steps S1-2, the first slurry is subjected to a first grinding process with a particle size D50 of 0.8μm to 1.5μm, a second grinding process with a particle size D50 of 0.6μm to 0.8μm, a first drying process, and a first sintering process to obtain the first precursor.

4. The method for preparing the phosphate cathode material according to any one of claims 1 to 3, characterized in that, In step S2 Based on the total weight of the second lithium source and the first precursor being 100%, the amount of the second carbon source added is 1.5% to 4%; and / or, The second lithium source is selected from one or more of lithium hexafluorophosphate, lithium fluoride, lithium peroxide and lithium hydroxide; and / or, the second carbon source is polyethylene glycol and / or polyvinyl alcohol.

5. The method for preparing the phosphate cathode material according to any one of claims 1 to 4, characterized in that, Step S2 includes: Step S2-1: The second lithium source, the second carbon source, and the second dispersant are mixed to obtain a second dispersion; the first precursor and the second dispersion are mixed to obtain a second slurry. In step S2-2, the second slurry is subjected to a third grinding process with a particle size D50 of 0.8μm to 1.5μm, a fourth grinding process with a particle size D50 of 0.5μm to 0.6μm, a second drying process, and a second sintering process to obtain the second precursor.

6. The method for preparing the phosphate cathode material according to any one of claims 1 to 5, characterized in that, In step S3 The organic solvent includes a first solvent, a second solvent, and a third solvent, wherein the first solvent is deionized water, the second solvent is selected from one or more of ethanol, propanol, and acetone, and the third solvent is selected from one or more of toluene, xylene, dimethylformamide, and N-methylformamide; and / or, The dispersion treatment includes sequential stirring and ultrasonic treatment, wherein the stirring time is 2h~3h and the rotation speed is 200rpm~300rpm, and the ultrasonic treatment time is 30min~60min.

7. The method for preparing the phosphate cathode material according to any one of claims 1 to 6, characterized in that, In step S4 The weight ratio of the surfactant, the alcohol compound, and the alkane compound is (0.20~0.30):(0.6~0.8):(0.05~0.10); and / or, Based on the total weight of the third slurry being 100%, the microemulsion accounts for 2% to 5% of the total weight; and / or, The surfactant is selected from one or more of sodium di(2-ethylhexyl)succinate sulfonate, sorbitan monooleate, sodium alkylbenzene sulfonate, and sodium lauryl sulfate; and / or, the alcohol is selected from one or more of n-butanol, n-pentanol, and isopropanol; and / or, the alkane is selected from one or more of n-hexane, cyclohexane, and isooctane; and / or, the third lithium source is selected from one or more of lithium hexafluorophosphate, lithium fluoride, lithium peroxide, and lithium hydroxide.

8. The method for preparing the phosphate cathode material according to any one of claims 1 to 7, characterized in that, Step S4 includes: Step S4-1: The third lithium source, the third precursor, and the third dispersant are mixed to obtain a third dispersion. In step S4-2, the third dispersion is subjected to a fifth grinding process with a particle size D50 of 0.8μm~1.5μm and a sixth grinding process with a particle size D50 of 0.4μm~0.5μm, and then the microemulsion is added to obtain the third slurry. The third slurry is then subjected to a third drying process and a third sintering process to obtain the phosphate cathode material.

9. A phosphate cathode material, characterized in that, The phosphate cathode material is prepared by the method for preparing phosphate cathode material according to any one of claims 1 to 8.

10. The phosphate cathode material according to claim 9, characterized in that, The phosphate cathode material includes a first particle with a particle size of 0.6 μm to 0.8 μm, a second particle with a particle size of 0.3 μm to 0.5 μm, and a third particle with a particle size of 0.1 μm to 0.3 μm, and the weight ratio of the first particle, the second particle, and the third particle is (10 to 15): (15 to 25): (60 to 75).

11. A positive electrode sheet, comprising a positive electrode active material, characterized in that, The positive electrode active material is the phosphate positive electrode material according to claim 9 or 10; or, the positive electrode active material is prepared by the method for preparing the phosphate positive electrode material according to any one of claims 1 to 8.

12. A lithium-ion battery, characterized in that, The lithium-ion battery includes the positive electrode sheet as described in claim 11.

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