Positive electrode material, preparation method thereof and lithium ion battery

Abstract

The invention provides a positive electrode material, a preparation method thereof and a lithium ion battery. The positive electrode material provided by the invention comprises micron-sized lithium manganese iron phosphate particles and nano-sized porous lithium manganese iron phosphate particles attached to the surfaces of the micron-sized lithium manganese iron phosphate particles, and the mass ratio of the micron-sized lithium manganese iron phosphate particles to the nano-sized porous lithium manganese iron phosphate particles is (3-5): 1. According to the positive electrode material provided by the invention, the nano-scale porous lithium manganese phosphate particles are attached to the surfaces of the micron-scale lithium manganese phosphate particles to form a micro-nano composite structure, and a porous structure in the nano-scale porous lithium manganese phosphate is combined, so that rich transmission channels and storage sites are provided for lithium ions, the diffusion path of the lithium ions is shortened, and the performance of the lithium ion battery is improved. The diffusion rate of lithium ions is improved, so that the lithium ion battery can be rapidly charged and discharged, and the high-power requirement in practical application is met.

Description

Technical Field

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

[0002] With the depletion of petrochemical energy, attention has gradually shifted to the development of new energy sources. Lithium-ion batteries, due to their advantages such as high voltage, high energy density, long lifespan, and environmental friendliness, have received increasing attention in recent years. Among these, the cathode material, a key material limiting performance improvement, is crucial. Currently, widely researched cathode materials include lithium cobalt oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium iron phosphate, and lithium manganese iron phosphate. While the theoretical capacity of lithium manganese iron phosphate is similar to that of lithium iron phosphate (approximately 170 mAh / g), it boasts a higher voltage platform (reaching 4.1V). When its actual capacity reaches the same level as lithium iron phosphate, its energy density can be increased by 15%–20%. Furthermore, manganese is a widely distributed element in nature, making it inexpensive and not contributing to increased battery costs. Therefore, lithium manganese iron phosphate batteries appear to be the most promising alternative to lithium iron phosphate batteries.

[0003] However, due to the introduction of manganese, lithium iron phosphate (LMFP) batteries face the problem of manganese leaching. Manganese ions in the cathode material exhibit the Jahn-Teller effect. This effect causes crystal deformation in LMFP, increasing the resistance within the crystal lattice and thus increasing electron transport resistance, which in turn reduces the electronic conductivity (approximately 10⁻¹⁴ S / cm) and ion diffusion coefficient (approximately 10⁻¹⁶ cm⁻¹). -2 ·s -1 Its extremely low efficiency results in unsatisfactory rate performance. Significant polarization occurs during charging and discharging under high current, reducing capacity and impacting power density. Furthermore, lithium manganese iron phosphate may cause manganese to dissolve during charging and discharging. Manganese severely damages the structure of the conductive liquid, reducing battery cycle performance and shortening the battery's lifespan, making it difficult to meet the required lifespan of power batteries.

[0004] Developing a lithium iron phosphate (LFP) product with excellent overall performance is of great research significance, as it aims to improve the conductivity, rate performance, and cycle performance of LFP while ensuring its high energy density. Summary of the Invention

[0005] The main objective of this application is to provide a cathode material to solve the problem that current lithium manganese iron phosphate cannot simultaneously achieve excellent energy density and cycle stability due to the dissolution of manganese.

[0006] To achieve the above objectives, according to the first aspect of this application, a cathode material is provided, comprising micron-sized lithium manganese iron phosphate particles and nano-sized porous lithium manganese iron phosphate particles attached to the surface of the micron-sized lithium manganese iron phosphate particles, wherein the mass ratio of the micron-sized lithium manganese iron phosphate particles to the nano-sized porous lithium manganese iron phosphate particles is (3~5):1.

[0007] Furthermore, the Dv50 particle size of the nano-porous lithium manganese iron phosphate is 50nm-80nm, and the porosity is 30%~80%.

[0008] Furthermore, the Dv50 particle size of the micron-sized lithium manganese iron phosphate particles is 1~3μm.

[0009] Furthermore, the nano-sized porous lithium manganese iron phosphate particles are doped with metal M, which includes at least one of titanium, ruthenium, magnesium, zirconium, niobium, cobalt, nickel, aluminum, or zinc.

[0010] Furthermore, metal M includes titanium, ruthenium, and magnesium. Based on the number of lithium moles per mol, the doping amount of titanium in the nano-porous lithium manganese iron phosphate particles is 0.04~0.06 mol, the doping amount of ruthenium is 0.01~0.03 mol, and the doping amount of magnesium is 0.02~0.04 mol.

[0011] To achieve the above objectives, according to a second aspect of this application, a method for preparing the cathode material provided in the first aspect is also provided. The method includes: mixing micron-sized lithium manganese iron phosphate particles and nano-sized porous lithium manganese iron phosphate particles, such that the nano-sized porous lithium manganese iron phosphate particles adhere to the surface of the micron-sized lithium manganese iron phosphate particles, thereby obtaining a lithium manganese iron phosphate material.

[0012] Furthermore, the preparation method of nano-sized porous lithium manganese iron phosphate particles includes: Step S1, mixing a first lithium source, a first manganese source, a first iron source, a first phosphorus source, and an optional doping metal M source and preparing lithium manganese iron phosphate gel by sol-gel method, and breaking the lithium manganese iron phosphate gel into nano-sized lithium manganese iron phosphate precursor particles; Step S2, dispersing the nano-sized lithium manganese iron phosphate precursor particles in a solution containing a template agent, and allowing the template agent molecules to arrange themselves in an orderly manner on the surface of the nano-sized lithium manganese iron phosphate precursor particles through self-assembly to form a mesoporous template, thereby obtaining nano-sized porous lithium manganese iron phosphate precursor; Step S3, subjecting the nano-sized lithium manganese iron phosphate precursor to a first calcination treatment to obtain nano-sized porous lithium manganese iron phosphate particles.

[0013] Further, in step S1, the temperature for the gelation reaction in the sol-gel method is 80~100℃, and the gelation reaction time is 1~3h.

[0014] Further, in step S2, the template agent is selected from at least one of triblock copolymer P123, triblock copolymer F127, triblock copolymer P105, or triblock copolymer F108.

[0015] Furthermore, the solvent of the solution containing the template agent is an alcohol solvent, preferably ethanol.

[0016] Further, in step S3, the temperature of the first calcination treatment is 500-700℃, and the time of the first calcination treatment is 2-5h.

[0017] Furthermore, the first calcination treatment is carried out under a first protective gas atmosphere, the first protective gas being selected from at least one of nitrogen, argon, or helium.

[0018] Furthermore, the preparation method of micron-sized lithium manganese iron phosphate includes: mixing a second lithium source, a second manganese source, a second iron source, and a second phosphorus source for a second calcination treatment, followed by crushing treatment to obtain micron-sized lithium manganese iron phosphate particles; wherein, the second calcination treatment includes a low-temperature pre-calcination treatment and a high-temperature sintering treatment; wherein, the low-temperature pre-calcination treatment includes a temperature of 300~500℃ and a time of 2~4h; the high-temperature sintering treatment includes a temperature of 600~800℃ and a time of 4~5h.

[0019] Furthermore, the second calcination treatment is carried out under a second protective gas atmosphere, the second protective gas being selected from at least one of nitrogen, argon, or helium.

[0020] Furthermore, micron-sized lithium manganese iron phosphate particles and nano-sized porous lithium manganese iron phosphate particles are mixed by ball milling at a speed of 250~400 r / min for 1~4 h.

[0021] According to a third aspect of this application, a lithium-ion battery is provided, the lithium-ion battery comprising a positive electrode active material, the positive electrode active material being the positive electrode material provided in the first aspect above or the positive electrode material obtained according to the preparation method provided in the second aspect.

[0022] By applying the technical solution of this application, the cathode material provided by this application forms a micro-nano composite structure by attaching nano-sized porous lithium manganese iron phosphate particles to the surface of micron-sized lithium manganese iron phosphate particles. Combined with the porous structure inside the nano-sized porous lithium manganese iron phosphate, it provides abundant transport channels and storage sites for lithium ions, shortens the diffusion path of lithium ions, and improves the diffusion rate of lithium ions, enabling lithium-ion batteries to achieve rapid charging and discharging, meeting the high power requirements of practical applications. At the same time, by introducing a micro-nano composite structure, this application also significantly improves the structural stability of lithium manganese iron phosphate materials, which is beneficial for suppressing manganese dissolution and thus further improves cycle stability. Detailed Implementation

[0023] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present application will now be described in detail with reference to the embodiments.

[0024] As analyzed in the background section of this application, manganese ions in lithium manganese iron phosphate (LMFP) materials exhibit the Jan Taylor effect, causing crystal deformation in LMFP and reducing its electronic conductivity (approximately 10⁻¹⁴ S / cm) and ion diffusion coefficient (approximately 10⁻¹⁶ cm⁻¹). -2 ·s -1 The conductivity of lithium manganese iron phosphate is extremely low, resulting in unsatisfactory rate performance and capacity reduction during charge and discharge, thus affecting power density. Furthermore, lithium manganese iron phosphate may cause manganese dissolution during charge and discharge, reducing battery cycle performance. To address the issues of low conductivity, poor rate performance, or poor cycle performance of lithium manganese iron phosphate materials with high energy density, this application provides a cathode material, its preparation method, and a lithium-ion battery.

[0025] In a first typical embodiment of this application, a cathode material is provided, comprising micron-sized lithium manganese iron phosphate particles and nano-sized porous lithium manganese iron phosphate particles attached to the surface of the micron-sized lithium manganese iron phosphate particles, wherein the mass ratio of the micron-sized lithium manganese iron phosphate particles to the nano-sized porous lithium manganese iron phosphate particles is (3~5):1.

[0026] The cathode material provided in this application forms a micro-nano composite structure by attaching nano-sized porous lithium manganese iron phosphate particles to the surface of micron-sized lithium manganese iron phosphate particles. Combined with the porous structure within the nano-sized porous lithium manganese iron phosphate, this provides abundant transport channels and storage sites for lithium ions, shortening the lithium ion diffusion path and increasing the lithium ion diffusion rate. This enables the lithium-ion battery to achieve rapid charge and discharge, meeting the high power requirements of practical applications. Furthermore, by introducing a micro-nano composite structure, this application combines the high reactivity of nanomaterials with the structural stability of micron-sized materials. This not only improves the electrochemical performance of the material but also ensures its processing performance and mechanical stability in practical applications, which is beneficial for suppressing manganese dissolution and thus further improving cycle stability.

[0027] In the cathode material provided in this application, the mass ratio of micron-sized lithium manganese iron phosphate particles to nano-sized porous lithium manganese iron phosphate particles is 3:1, 3.5:1, 4:1, 4.5:1, 5:1, or any range of two values.

[0028] In some embodiments of this application, the Dv50 particle size of the nano-porous lithium manganese iron phosphate particles is 50nm~80nm, and the porosity is 30%~60%. Controlling the Dv50 particle size of the nano-porous manganese phosphate particles to 50nm~80nm is more conducive to improving the stability of the micro-nano structure formed between them and the micron-sized lithium manganese iron phosphate particles, thereby improving the cycle stability of the battery and extending its service life. Controlling the porosity of the nano-porous lithium manganese iron phosphate particles to 30%~60% is more conducive to constructing efficient electron transport channels, improving the electronic conductivity of the material, thereby improving the rate performance of the battery and reducing energy loss.

[0029] Specifically, the Dv50 particle size of the nano-sized porous lithium manganese iron phosphate particles is 50nm, 55nm, 60nm, 65nm, 70nm, 80nm or any two of these values; the porosity of the nano-sized porous lithium manganese iron phosphate particles is 30%, 35%, 40%, 45%, 50%, 55%, 60% or any two of these values.

[0030] In some embodiments, the pores in the nano-porous lithium manganese iron phosphate particles are mainly mesopores (pore size 2nm~50nm), and may contain a small number of micropores (pore size <2nm) or macropores (pore size >50nm). The mesopore rate is 70%~90%, which is beneficial to increase the specific surface area of ​​the nano-porous lithium manganese iron phosphate particles, provide more lithium-ion storage sites, provide more channels for lithium-ion transport, effectively shorten the diffusion path of lithium-ions, and thus facilitate the rapid charging and discharging of the battery to meet the high power requirements of practical applications.

[0031] Specifically, the mesoporous properties of the nano-sized porous lithium manganese iron phosphate particles are 70%, 75%, 80%, 85%, 90%, or any combination of two values.

[0032] In some embodiments of this application, the Dv50 particle size of the micron-sized lithium manganese iron phosphate particles is 1~3μm, which is beneficial to further improve the stability of the micro-nano structure formed by the particles and the nano-sized porous lithium manganese iron phosphate particles, thereby improving the cycle stability of the battery. At the same time, the Dv50 particle size of the micron-sized lithium manganese iron phosphate particles is controlled to be 1~3μm, which is beneficial to improve the energy density of the battery.

[0033] Specifically, the Dv50 particle size of the micron-sized lithium manganese iron phosphate particles is 1μm, 1.5μm, 2μm, 2.5μm, 3μm, or any combination of two values.

[0034] In some embodiments of this application, nanoscale porous lithium manganese iron phosphate particles are doped with metal M. This metal M is incorporated into the lattice of the lithium manganese iron phosphate, enhancing the stability of the internal crystal structure of the nanoscale lithium manganese iron phosphate particles, further suppressing manganese dissolution and lattice distortion, and further improving the structural stability of the lithium manganese iron phosphate material and the cycle stability of the battery. The aforementioned metal M is a commonly used doping metal in the art, including but not limited to one or more of titanium, ruthenium, magnesium, zirconium, niobium, cobalt, nickel, aluminum, or zinc. Specifically, titanium doping can optimize the crystal structure, improve the crystal structure stability of the material, and effectively suppress manganese dissolution and lattice distortion; ruthenium doping can enhance ionic conductivity; and magnesium doping can effectively improve the diffusion performance of lithium ions.

[0035] In some specific embodiments of this application, metal M includes titanium, ruthenium, and magnesium. Based on 1 mol of lithium moles, the doping amount of titanium in the nano-porous lithium manganese iron phosphate particles is 0.04~0.06 mol, the doping amount of ruthenium is 0.01~0.03 mol, and the doping amount of magnesium is 0.02~0.04 mol. By selecting elements with different electronic structures and ionic radii—titanium, ruthenium, and magnesium—for synergistic doping, the doping of titanium optimizes the crystal structure, which is more conducive to improving the crystal structure stability of the material and more effectively suppressing manganese dissolution and lattice distortion. Ruthenium doping enhances ionic conductivity, and magnesium doping improves lithium-ion diffusion performance. The synergistic doping of titanium, ruthenium, and magnesium further improves the structural stability of the lithium manganese iron phosphate material, thereby improving the cycle stability of the battery and extending its lifespan.

[0036] Specifically, in the nano-sized porous lithium manganese iron phosphate particles, with 1 mol of lithium as the molar amount, the doping amount of titanium is 0.04 mol, 0.05 mol, 0.06 mol or any two of these values; the doping amount of ruthenium is 0.01 mol, 0.02 mol, 0.03 mol or any two of these values; and the doping amount of magnesium is 0.02 mol, 0.03 mol, 0.04 mol or any two of these values.

[0037] In a second typical embodiment of this application, a method for preparing the cathode material provided in the first aspect is provided. The method includes: mixing micron-sized lithium manganese iron phosphate particles and nano-sized porous lithium manganese iron phosphate particles, such that the nano-sized porous lithium manganese iron phosphate particles are attached to the surface of the micron-sized lithium manganese iron phosphate particles, thereby obtaining the lithium manganese iron phosphate material.

[0038] The method for preparing the cathode material provided in this application is simple, easy to operate, and more conducive to large-scale production, thereby further reducing the preparation cost.

[0039] In some embodiments of this application, the preparation method of nanoscale porous lithium manganese iron phosphate particles includes: step S1, mixing lithium source, manganese source, iron source, phosphorus source and optional dopant metal M and preparing lithium manganese iron phosphate gel by sol-gel method, and breaking the lithium manganese iron phosphate gel into nanoscale lithium manganese iron phosphate precursor particles; step S2, dispersing the nanoscale lithium manganese iron phosphate precursor particles in a solution containing a template agent, and allowing the template agent molecules to arrange themselves in an orderly manner on the surface of the nanoscale lithium manganese iron phosphate particles through self-assembly to form a mesoporous template, thereby obtaining nanoscale porous lithium manganese iron phosphate precursor; step S3, subjecting the nanoscale lithium manganese iron phosphate precursor to a first calcination treatment to obtain nanoscale porous lithium manganese iron phosphate particles.

[0040] The above-mentioned method for preparing nano-sized porous lithium manganese iron phosphate particles involves preparing nano-sized lithium manganese iron phosphate precursor particles via a sol-gel method. The nano-sized lithium manganese iron phosphate precursor particles are dispersed in a solution containing a template agent and then self-assembled and subsequently calcined to form a rich mesoporous structure inside and between the nano-sized lithium manganese iron phosphate particles, thus obtaining nano-sized porous lithium manganese iron phosphate particles.

[0041] In some specific embodiments, the preparation method of lithium manganese iron phosphate gel in step S1 above includes: step S11, weighing the first lithium source, the first manganese source, the first iron source, the first phosphorus source, and the optional metal M source according to the stoichiometric ratio, mixing them evenly and dispersing them in the first organic solvent, adding a complexing agent to promote the metal ions to form a stable complex with the complexing agent, and obtaining lithium manganese iron phosphate sol; step S12, subjecting the lithium manganese iron phosphate sol to a gel reaction and drying it to obtain lithium manganese iron phosphate gel (dry gel); step S13, crushing the lithium manganese iron phosphate gel into nano-sized lithium manganese iron phosphate precursor particles.

[0042] The aforementioned complexing agents are commonly used complexing agents in this field, including but not limited to any one or more of citric acid, tetraethylamine oxalate (EDTA), ammonium gluconate, and ethylenediamine.

[0043] The specific type of the first organic solvent is not limited, and any commonly used organic solvent in the art is acceptable. From the perspective of environmental protection and cost reduction, ethylene glycol is preferred as the first organic solvent.

[0044] The specific type of the first lithium source is not limited, including but not limited to one or more of lithium carbonate, lithium bicarbonate, lithium acetate, lithium chloride, lithium bromide, lithium hydroxide, lithium phosphate, dilithium hydrogen phosphate, lithium dihydrogen phosphate, lithium oxalate, or lithium sulfate.

[0045] The specific type of the first iron source is not limited, including but not limited to any one or more of ferrous phosphate, ferrous oxalate, ferrous chloride, ferrous nitrate, ferrous oxide, ferrous sulfate, ferric chloride, ferric nitrate, ferric sulfate, ferric oxide, iron tetroxide, or ferric phosphate.

[0046] The specific type of the first phosphorus source is not limited, including but not limited to any one or more of diammonium hydrogen phosphate, ammonium phosphate, phosphorus pentoxide, phosphoric acid, or phosphorous acid.

[0047] The specific type of the first manganese source is not limited, including but not limited to any one or more of manganese carbonate, manganese phosphate, manganese phosphate, manganese sulfate, manganese oxalate, manganese acetate, manganese chloride, manganese trioxide, or manganese tetroxide.

[0048] When the aforementioned metal source M is a titanium source, the specific type of titanium source is not limited, including but not limited to any one or more of tetrabutyl titanate, tetrabutyl titanate, and tetraethyl titanate; when the aforementioned metal source M is a ruthenium source, the specific type of ruthenium source is not limited, including but not limited to any one or more of ruthenium chloride, ruthenium trichloride, ruthenium dioxide, and ruthenium acetate; when the aforementioned metal source M is a magnesium source, the specific type of magnesium source is not limited, including but not limited to any one or more of magnesium nitrate, magnesium oxide, magnesium carbonate, and magnesium oxalate.

[0049] In some embodiments, to further improve the preparation efficiency of lithium manganese iron phosphate sol, the ratio of the total molar amount of the lithium source, manganese source, iron source, phosphorus source, and optional metal M source to the molar amount of the complexing agent is (3~10):1. Specifically, the ratio of the total molar amount of the lithium source, manganese source, iron source, phosphorus source, and optional metal M source to the molar amount of the complexing agent is 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, or any range of two such values.

[0050] In some embodiments, in step S12 above, the gelation reaction temperature is 80~100℃, and the gelation reaction time is 1~3h, to further promote the efficiency of the gelation reaction. Specifically, the gelation reaction temperature is 80℃, 85℃, 90℃, 100℃, or any two of these values; the gelation reaction time is 1h, 1.5h, 2h, 2.5h, 3h, or any two of these values.

[0051] In some embodiments, in step S12 above, the drying temperature is 30-60°C, and the drying time is 10-12 hours, to facilitate the drying of the wet gel formed by the gelation reaction at a low temperature, removing the first organic solvent and moisture, and forming a fluffy dry gel, i.e., lithium manganese iron phosphate gel. Specifically, the drying temperature is 30°C, 35°C, 40°C, 50°C, 60°C, or any combination of two values; the drying time is 10 hours, 10.5 hours, 11 hours, 11.5 hours, 12 hours, or any combination of two values.

[0052] In some embodiments, in step S13 above, to further improve the preparation efficiency of nano-sized lithium manganese iron phosphate precursor particles, it is preferable to break the lithium manganese iron phosphate gel into nano-sized lithium manganese iron phosphate precursor particles by ball milling; wherein, the ball milling speed is 300~400 r / min, and the ball milling time is 3~4 h. Specifically, the ball milling speed is 300 r / min, 320 r / min, 350 r / min, 380 r / min, 400 r / min or any two of these values, and the ball milling time is 3 h, 3.2 h, 3.5 h, 3.8 h, 4 h or any two of these values.

[0053] In some embodiments, in step S2 above, the template agent is selected from any one or a mixture of triblock copolymers P123 (polyoxyethylene-polyoxypropylene-polyoxyethylene triblock copolymer), polyoxypropylene-polyoxyethylene copolymer Pluronic F127 (polyoxyethylene-polyoxypropylene-polyoxyethylene triblock copolymer), triblock copolymer Pluronic P105 (polyoxyethylene-polyoxypropylene-polyoxyethylene triblock copolymer), and Pluronic F108 (polyoxyethylene-polyoxypropylene-polyoxyethylene triblock copolymer).

[0054] In some embodiments, in step S2 above, the solvent of the solution containing the template agent is an alcohol solvent to further improve the dispersion uniformity of the template agent. From the perspective of cost saving and environmental protection, the solvent of the solution containing the template agent is preferably ethanol.

[0055] In some embodiments, in step S3 above, the temperature of the first calcination treatment is 500-700℃, and the time of the first calcination treatment is 2-5 hours, in order to remove the template agent and improve the structural stability of the nano-porous lithium manganese iron phosphate material, thereby further improving the electrochemical performance of the cathode material. Specifically, the temperature of the first calcination treatment is a range of 500℃, 520℃, 550℃, 580℃, 600℃, 620℃, 650℃, 680℃, 700℃, or any two of these values, and the time of the first calcination treatment is 2 hours, 3 hours, 4 hours, 5 hours, or any two of these values.

[0056] In some embodiments, in order to further improve the electrochemical performance of nano-porous lithium manganese iron phosphate particles, the first calcination treatment is preferably carried out under a first protective gas atmosphere to avoid introducing impurities during the calcination process that may affect the performance of the nano-porous lithium manganese iron phosphate particles. The first protective gas includes, but is not limited to, any one or more of nitrogen, argon or helium to form a mixture of gases.

[0057] In some embodiments, the above-mentioned micron-sized lithium manganese iron phosphate particles are purchased commercially or prepared in-house. In some specific embodiments, the micron-sized lithium manganese iron phosphate particles are prepared according to the following steps: lithium source, manganese source, iron source and phosphorus source are weighed and mixed according to stoichiometric ratio to obtain a raw material mixture; the raw material mixture is subjected to a second calcination treatment, followed by crushing treatment to obtain micron-sized lithium manganese iron phosphate particles.

[0058] In some specific embodiments, the lithium source, manganese source, iron source and phosphoric acid are preferably mixed evenly by ball milling to obtain a raw material mixture.

[0059] In some specific embodiments, the second calcination treatment of the raw material mixture includes pre-calcination followed by sintering. The pre-calcination temperature is 300-500°C for 2-4 hours to decompose the organic components in the raw material mixture and reduce volume expansion and gas release during subsequent sintering. Afterwards, the temperature is raised to 600-800°C and sintered for 4-5 hours to form lithium manganese iron phosphate sintered products. The cooled sintered products are then crushed to obtain micron-sized lithium manganese iron phosphate particles.

[0060] Specifically, the temperature for low-temperature pre-firing is 300℃, 350℃, 400℃, 450℃, 500℃, or any two of these values; the time for low-temperature pre-firing is 2h, 2.5h, 3h, 3.5h, 4h, or any two of these values; the temperature for high-temperature sintering is 600℃, 650℃, 700℃, 750℃, 800℃, or any two of these values; and the time for high-temperature sintering is 4h, 4.2h, 4.5h, 4.8h, 5h, or any two of these values.

[0061] In some embodiments, ball milling is used to mix micron-sized lithium manganese iron phosphate particles and nano-sized porous lithium manganese iron phosphate particles, which is more conducive to improving the mixing efficiency and thus the preparation efficiency of lithium manganese iron phosphate materials. Preferably, the ball milling speed is 250~400 r / min, and the ball milling time is 1~4 h. Specifically, the ball milling speed is 250 r / min, 280 r / min, 300 r / min, 320 r / min, 350 r / min, 380 r / min, 400 r / min, or any combination of two values; the ball milling time is 1 h, 1.5 h, 2 h, 3 h, 4 h, or any combination of two values.

[0062] In a third typical embodiment of this application, a lithium-ion battery is provided, which includes a positive electrode active material, which is the lithium manganese iron phosphate material provided in the first aspect or the lithium iron phosphate material obtained by the preparation method provided in the second aspect.

[0063] The lithium-ion battery provided in this application introduces lithium manganese iron phosphate material with a micro-nano composite structure as the positive electrode active material. It combines the high reactivity of nanomaterials with the structural stability of micromaterials. This not only provides abundant transport channels and storage sites for lithium ions, shortens the diffusion path of lithium ions, and improves the diffusion rate of lithium ions, enabling the lithium-ion battery to achieve rapid charging and discharging to meet the high power requirements of practical applications, but also ensures the processing performance and mechanical stability of the material in practical applications, which is beneficial to suppressing manganese dissolution and thus further improving cycle stability.

[0064] The beneficial effects of this application will be further illustrated below with reference to embodiments and comparative examples.

[0065] Example 1

[0066] This embodiment provides a lithium manganese iron phosphate material, which includes micron-sized lithium manganese iron phosphate particles and nano-sized porous lithium manganese iron phosphate particles uniformly attached to the surface of the micron-sized lithium manganese iron phosphate particles, with a mass ratio of 3:1.

[0067] The lithium manganese iron phosphate material provided in this embodiment is prepared according to the following steps:

[0068] (1) Accurately weigh 0.1 mol lithium acetate, 0.06 mol manganese nitrate, 0.04 mol ferrous sulfate, and 0.1 mol ammonium dihydrogen phosphate. Add 0.004 mol tetrabutyl titanate, 0.001 mol ruthenium chloride, and 0.002 mol magnesium nitrate, and mix them thoroughly with the other raw materials. Add the mixture to 200 mL of ethylene glycol and stir at 600 r / min for 2 h on a magnetic stirrer to ensure complete dissolution. Then add 0.08 mol citric acid and continue stirring for 2 h to form a uniform lithium manganese iron phosphate sol.

[0069] (2) The lithium manganese iron phosphate sol was heated in a water bath at 80°C, and the solvent was slowly evaporated to carry out a gelation reaction for 2 hours to form a wet lithium manganese iron phosphate gel. The wet lithium manganese iron phosphate gel was dried in a vacuum drying oven at 60°C for 12 hours to obtain a dry lithium manganese iron phosphate gel. The lithium manganese iron phosphate gel was placed in a ball mill and ball milled at a speed of 400 r / min for 4 hours to obtain nano-sized lithium manganese iron phosphate precursor particles.

[0070] (3) Weigh 5g of the above-mentioned nano-sized lithium iron phosphate precursor particles and disperse them in 100mL of ethanol solution containing 0.25g P123. Stir at room temperature for 12h to allow P123 molecules to self-assemble on the surface of the nano-sized lithium iron phosphate precursor particles to form a mesoporous template, thus obtaining a mesoporous template solution. Filter the mesoporous template solution to obtain a solid product. Place it in a tube furnace and, under nitrogen protection, heat it from room temperature to 550℃ at a heating rate of 5℃ / min. Calcinate it at this temperature for 3h to remove the P123 template, thus obtaining nano-sized porous lithium manganese iron phosphate particles with a Dv50 particle size of 65nm and a porosity of 45% with a mesoporous structure.

[0071] (4) Accurately weigh 0.1 mol lithium acetate, 0.06 mol manganese nitrate, 0.04 mol ferrous sulfate, and 0.1 mol ammonium dihydrogen phosphate. Place the weighed raw materials into a ball mill or mortar and mill for 2 hours. Pre-calcine at 400℃ for 3 hours. Then, load the pre-calcineed powder into a high-temperature furnace purged with nitrogen and sinter at 700℃ for 5 hours. After sintering, cool the sintered product to room temperature in the furnace and then pulverize and grind it to obtain micron-sized lithium manganese iron phosphate particles with a Dv50 particle size of 2 μm.

[0072] (5) Weigh 2g of nano-sized porous lithium manganese iron phosphate particles with mesoporous structure and 6g of micron-sized lithium manganese iron phosphate particles, put them into a ball mill, and ball mill at 300r / min for 2h to make the nano-sized porous lithium manganese iron phosphate particles uniformly attached to the surface of the micron-sized lithium manganese iron phosphate particles, forming a micro-nano composite lithium manganese iron phosphate material.

[0073] Example 2

[0074] This embodiment provides a lithium manganese iron phosphate material, which includes micron-sized lithium manganese iron phosphate particles and nano-sized porous lithium manganese iron phosphate particles uniformly attached to the surface of the micron-sized lithium manganese iron phosphate particles, with a mass ratio of 4:1.

[0075] The lithium manganese iron phosphate material provided in this embodiment is prepared according to the following steps:

[0076] (1) Accurately weigh 0.1 mol lithium acetate, 0.06 mol manganese nitrate, 0.04 mol ferrous sulfate, and 0.1 mol ammonium dihydrogen phosphate. Add 0.005 mol tetrabutyl titanate, 0.002 mol ruthenium chloride, and 0.003 mol magnesium nitrate, and mix them thoroughly with the other raw materials. Add the mixture to 200 mL of ethylene glycol and stir at 600 r / min for 2 h on a magnetic stirrer to ensure complete dissolution. Then add 0.08 mol citric acid and continue stirring for 2 h to form a uniform lithium manganese iron phosphate sol.

[0077] (2) The lithium manganese iron phosphate sol was heated in a water bath at 80°C, and the solvent was slowly evaporated to carry out a gelation reaction for 2 hours to form a wet lithium manganese iron phosphate gel. The wet lithium manganese iron phosphate gel was dried in a vacuum drying oven at 60°C for 12 hours to obtain a dry lithium manganese iron phosphate gel. The lithium manganese iron phosphate gel was placed in a ball mill and ball milled at a speed of 400 r / min for 4 hours to obtain nano-sized lithium manganese iron phosphate precursor particles.

[0078] (3) Weigh 5g of the above-mentioned nano-sized lithium manganese iron phosphate precursor particles and disperse them in 100mL of ethanol solution containing 0.25g P123. Stir at room temperature for 12h to allow P123 molecules to self-assemble on the surface of the nano-sized lithium manganese iron phosphate precursor particles to form a mesoporous template, which is then attached to the mesoporous template solution. Filter the mesoporous template solution to obtain a solid product, place it in a tube furnace, and under nitrogen protection, heat it from room temperature to 550℃ at a heating rate of 5℃ / min. Calcine it at this temperature for 3h to remove the P123 template, obtaining nano-sized porous lithium manganese iron phosphate particles with a Dv50 particle size of 65nm and a porosity of 45% with a mesoporous structure.

[0079] (4) Accurately weigh 0.1 mol lithium acetate, 0.06 mol manganese nitrate, 0.04 mol ferrous sulfate, and 0.1 mol ammonium dihydrogen phosphate. Place the weighed raw materials into a ball mill or mortar and mill for 2 hours. Pre-calcine at 350℃ for 3 hours. Then, load the pre-calcineed powder into a high-temperature furnace purged with nitrogen and sinter at 750℃ for 5 hours. After sintering, cool the sintered product to room temperature in the furnace and then pulverize and grind it to obtain Dv50 micron-sized lithium manganese iron phosphate particles with a particle size of 2 μm.

[0080] (5) Weigh 2g of nano-sized porous lithium manganese iron phosphate particles with mesoporous structure and 8g of micron-sized lithium manganese iron phosphate particles, put them into a ball mill, and ball mill at 300r / min for 2h to make the nano-sized porous lithium manganese iron phosphate particles uniformly attached to the surface of the micron-sized lithium manganese iron phosphate particles, forming a micro-nano composite lithium manganese iron phosphate material.

[0081] Example 3

[0082] This embodiment provides a lithium manganese iron phosphate material comprising micron-sized lithium manganese iron phosphate particles and nano-sized porous lithium manganese iron phosphate particles uniformly attached to the surface of the micron-sized lithium manganese iron phosphate particles, with a mass ratio of 5:1.

[0083] The lithium manganese iron phosphate material provided in this embodiment is prepared according to the following steps:

[0084] (1) Accurately weigh 0.1 mol lithium acetate, 0.06 mol manganese nitrate, 0.04 mol ferrous sulfate, and 0.1 mol ammonium dihydrogen phosphate. Add 0.006 mol tetrabutyl titanate, 0.003 mol ruthenium chloride, and 0.004 mol magnesium nitrate, and mix them thoroughly with the other raw materials. Add the mixture to 200 mL of ethylene glycol and stir at 600 r / min for 2 h on a magnetic stirrer to ensure complete dissolution. Then add 0.08 mol citric acid and continue stirring for 2 h to form a uniform lithium manganese iron phosphate sol.

[0085] (2) The lithium manganese iron phosphate sol was heated in a water bath at 80°C, and the solvent was slowly evaporated to carry out a gelation reaction for 2 hours to form a wet lithium manganese iron phosphate gel. The wet lithium manganese iron phosphate gel was dried in a vacuum drying oven at 60°C for 12 hours to obtain a dry lithium manganese iron phosphate gel. The lithium manganese iron phosphate gel was placed in a ball mill and ball milled at a speed of 400 r / min for 4 hours to obtain nano-sized lithium manganese iron phosphate precursor particles.

[0086] (3) Weigh 5g of the above-mentioned nano-sized lithium iron phosphate precursor particles and disperse them in 100mL of ethanol solution containing 0.25g P123. Stir at room temperature for 12h to allow P123 molecules to self-assemble on the surface of the nano-sized lithium iron phosphate precursor particles to form a mesoporous template, thus obtaining a mesoporous template solution. Filter the mesoporous template solution to obtain a solid product. Place it in a tube furnace and, under nitrogen protection, heat it from room temperature to 550℃ at a heating rate of 5℃ / min. Calcinate it at this temperature for 3h to remove the P123 template, thus obtaining nano-sized porous lithium manganese iron phosphate particles with a Dv50 particle size of 65nm and a porosity of 45% with a mesoporous structure.

[0087] (4) Accurately weigh 0.1 mol lithium acetate, 0.06 mol manganese nitrate, 0.04 mol ferrous sulfate, and 0.1 mol ammonium dihydrogen phosphate. Place the weighed raw materials into a ball mill or mortar and mill for 2 hours. Pre-calcine at 350 degrees Celsius for 3 hours. Then, load the pre-calcined powder into a high-temperature furnace purged with nitrogen and sinter at 750 degrees Celsius for 5 hours. After sintering, cool the product to room temperature in the furnace and then pulverize and grind the first product to obtain micron-sized lithium manganese iron phosphate particles with a Dv50 particle size of 2 μm.

[0088] (5) Weigh 2g of nano-sized porous lithium manganese iron phosphate particles with mesoporous structure and 10g of micron-sized lithium manganese iron phosphate particles, put them into a ball mill, and ball mill at 300r / min for 2h to make the nano-sized porous lithium manganese iron phosphate particles uniformly attached to the surface of the micron-sized lithium manganese iron phosphate particles, forming a micro-nano composite lithium manganese iron phosphate material.

[0089] Example 4

[0090] The difference between this embodiment and Embodiment 1 is that the amount of tetrabutyl titanate in step (1) is adjusted to 0.007 mol, the amount of ruthenium chloride is adjusted to 0.004 mol, and the amount of magnesium nitrate is adjusted to 0.005 mol.

[0091] Example 5

[0092] The difference between this embodiment and Embodiment 1 is that the amount of tetrabutyl titanate in step (1) is adjusted to 0.001 mol, the amount of ruthenium chloride is adjusted to 0.002 mol, and the amount of magnesium nitrate is adjusted to 0.001 mol.

[0093] Example 6

[0094] The difference between this embodiment and Example 1 is that ruthenium chloride was not added in step (1), and the amount of tetrabutyl titanate was adjusted to 0.005 mol.

[0095] Example 7

[0096] The difference between this embodiment and Example 1 is that in step (1), magnesium nitrate was not added, and the amount of tetrabutyl titanate was adjusted to 0.005 mol.

[0097] Example 8

[0098] The difference between this embodiment and Example 1 is that tetrabutyl titanate was not added in step (1), and the amount of ruthenium chloride was adjusted to 0.003 mol and the amount of magnesium nitrate was adjusted to 0.004 mol.

[0099] Example 9

[0100] The difference between this embodiment and Embodiment 1 is that tetrabutyl titanate, ruthenium chloride and magnesium nitrate were not added in step (1), that is, no metal element doping was performed.

[0101] Example 10

[0102] The difference between this embodiment and embodiment 1 is that the ball milling speed and ball milling time in step (2) and the amount of P123 in step (3) are adjusted so that the Dv50 particle size of the nano-level porous lithium manganese iron phosphate particles obtained in step (3) is 50 nm and the porosity is 30%.

[0103] Example 11

[0104] The difference between this embodiment and embodiment 1 is that the ball milling speed and ball milling time in step (2) and the amount of P123 in step (3) are adjusted so that the Dv50 particle size of the nano-level porous lithium manganese iron phosphate particles obtained in step (3) is 80 nm and the porosity is 60%.

[0105] Example 12

[0106] The difference between this embodiment and embodiment 1 is that the ball milling speed and ball milling time in step (2) are adjusted so that the Dv50 particle size of the nano-level porous lithium manganese iron phosphate particles obtained in step (3) is 150nm.

[0107] Example 13

[0108] The difference between this embodiment and embodiment 1 is that the ball milling speed and ball milling time in step (2) are adjusted so that the Dv50 particle size of the nano-level porous lithium manganese iron phosphate particles obtained in step (3) is 30nm.

[0109] Example 14

[0110] The difference between this embodiment and embodiment 1 is that the amount of P123 in step (3) is adjusted so that the porosity of the nano-level porous lithium manganese iron phosphate particles obtained in step (3) is 80%.

[0111] Example 15

[0112] The difference between this embodiment and embodiment 1 is that the amount of P123 in step (3) is adjusted so that the porosity of the nano-level porous lithium manganese iron phosphate particles obtained in step (3) is 20%.

[0113] Example 16

[0114] The difference between this embodiment and embodiment 1 is that the ball milling speed and ball milling time in step (4) are adjusted so that the Dv50 particle size of the micron-sized lithium manganese iron phosphate particles obtained in step (4) is 5 μm.

[0115] Example 17

[0116] The difference between this embodiment and embodiment 1 is that the ball milling speed and ball milling time in step (4) are adjusted so that the Dv50 particle size of the micron-sized lithium manganese iron phosphate particles obtained in step (4) is 500 nm.

[0117] Comparative Example 1:

[0118] This comparative example provides a lithium manganese iron phosphate material, which is a nano-sized lithium manganese iron phosphate particle with a Dv50 particle size of 65nm.

[0119] It is prepared according to the following steps:

[0120] (1) Accurately weigh 0.1 mol lithium acetate, 0.06 mol manganese nitrate, 0.04 mol ferrous sulfate, and 0.1 mol ammonium dihydrogen phosphate. Mix the raw materials thoroughly and add them to 200 mL of ethylene glycol. Stir at 600 r / min for 2 h on a magnetic stirrer to ensure complete dissolution. Then add 0.08 mol citric acid and continue stirring for 2 h to form a uniform lithium manganese iron phosphate sol.

[0121] (2) The lithium manganese iron phosphate sol was heated in a water bath at 80°C to slowly evaporate the solvent and form a wet lithium manganese iron phosphate gel. The wet lithium manganese iron phosphate gel was dried in a vacuum drying oven at 60°C for 12 hours to obtain a dry lithium manganese iron phosphate gel. The lithium manganese iron phosphate gel was placed in a ball mill and ball-milled at 400 r / min for 4 hours to obtain nano-sized lithium manganese iron phosphate precursor particles.

[0122] Comparative Example 2

[0123] This comparative example provides a lithium manganese iron phosphate material, which is a nano-sized lithium manganese iron phosphate particle with a Dv50 particle size of 65nm, and is doped with titanium, ruthenium and magnesium.

[0124] It is prepared according to the following steps:

[0125] (1) Accurately weigh 0.1 mol lithium acetate, 0.06 mol manganese nitrate, 0.04 mol ferrous sulfate, and 0.1 mol ammonium dihydrogen phosphate. Add 0.005 mol tetrabutyl titanate, 0.002 mol ruthenium chloride, and 0.003 mol magnesium nitrate, and mix them thoroughly with the other raw materials. Add the mixture to 200 mL of ethylene glycol and stir at 600 r / min for 2 h on a magnetic stirrer to ensure complete dissolution. Then add 0.08 mol citric acid and continue stirring for 2 h to form a uniform lithium manganese iron phosphate sol.

[0126] (2) The lithium manganese iron phosphate sol was heated in a water bath at 80°C to slowly evaporate the solvent and form a wet lithium manganese iron phosphate gel. The wet lithium manganese iron phosphate gel was dried in a vacuum drying oven at 60°C for 12 hours to obtain a dry lithium manganese iron phosphate gel. The dry gel was placed in a ball mill and ball-milled at 400 r / min for 4 hours to obtain nano-sized lithium manganese iron phosphate precursor particles.

[0127] Comparative Example 3

[0128] The difference between this comparative example and Example 1 is that the mass ratio of micron-sized lithium manganese iron phosphate particles to nano-sized porous lithium manganese iron phosphate particles is 6:1.

[0129] Comparative Example 4

[0130] The difference between this comparative example and Example 1 is that the mass ratio of micron-sized lithium manganese iron phosphate particles to nano-sized porous lithium manganese iron phosphate particles is 1:1.

[0131] Comparative Example 5

[0132] The difference between this comparative example and Example 1 is that the amount of tetrabutyl titanate in step (1) is adjusted to 0.007 mol, the amount of ruthenium chloride is adjusted to 0.004 mol, the amount of magnesium nitrate is adjusted to 0.005 mol, and the mass ratio of micron-sized lithium manganese iron phosphate particles to nano-sized porous lithium manganese iron phosphate particles is 6:1.

[0133] Comparative Example 6

[0134] The difference between this comparative example and Example 1 is that non-porous nano-sized lithium manganese iron phosphate particles are used instead of nano-sized porous lithium manganese iron phosphate particles. The preparation method of these non-porous nano-sized lithium manganese iron phosphate particles is the same as that of the nano-sized lithium manganese iron phosphate particles provided in Comparative Example 1, and will not be described again.

[0135] (a) Electrochemical performance testing

[0136] Using the lithium manganese iron phosphate material provided in the examples and comparative examples as the positive electrode material, positive electrode sheets were prepared, and coin cells were assembled for electrochemical performance testing and analysis, as detailed below:

[0137] (1) Preparation of positive electrode sheet

[0138] Using the lithium manganese iron phosphate material provided in the comparative examples, conductive carbon (super-p) and PVDF (polyvinylidene fluoride) were dissolved in N-methylpyrrolidone (NMP) at a mass ratio of 8:1:1 and stirred to form a uniform and stable slurry. The slurry was then coated onto the surface of carbon-coated aluminum foil using a doctor blade method to a coating thickness of approximately 100 μm. After drying, the coating was cut into 14 mm diameter discs using a slicing machine to obtain the positive electrode sheet. The disc was weighed, sealed, and placed in a desiccator for later use.

[0139] (2) Assemble the battery

[0140] CR2032 coin cells were assembled in a glove box filled with high-purity argon atmosphere, using lithium metal sheets as the negative electrode and the prepared positive electrode as the positive electrode. The electrolyte was 1M LiPF6, and the solvent was a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a 1:1:1 volume ratio. A PP membrane was used as the separator. The assembled CR2032 coin cells were subjected to constant current charge / discharge tests using a LAND CT2001A battery testing system, with a charge / discharge voltage window of 2.0–4.3V. The results are shown in Table 1.

[0141] (3) The test method for the capacity retention rate after 500 cycles at 1C is as follows: Use a battery cycle tester (Blue Battery), charge and discharge cutoff voltage (charge to 4.2V, discharge to 2.5V), and charge and discharge rate (1C charge, 1C discharge). Record the initial discharge capacity C0. After completing 500 cycles, take the last stable discharge capacity as the final discharge capacity C500 after 500 cycles. Calculate the capacity retention rate after 500 cycles according to the formula: Capacity retention rate (%) = (C500 / C0) × 100%.

[0142] Table 1

[0143]

[0144] As can be seen from the above description, the embodiments of this application achieve the following technical effects:

[0145] As can be seen from the comparison between Examples 1-17 and Comparative Examples 1-6, the lithium manganese iron phosphate material provided in this application forms a micro-nano composite structure by attaching nano-sized porous lithium manganese iron phosphate particles to the surface of micron-sized lithium manganese iron phosphate particles, and combined with the porous structure inside the nano-sized porous lithium manganese iron phosphate, the structural stability of the lithium manganese iron phosphate material is improved, so that the lithium manganese iron phosphate material has both excellent capacity density and cycle stability.

[0146] A comparison of Examples 1-3, 10-11, and 4-9 shows that, in the lithium manganese iron phosphate material provided in this application, based on 1 mol of lithium, the titanium doping amount in the nano-porous lithium manganese iron phosphate particles is 0.04~0.06 mol, the ruthenium doping amount is 0.01~0.03 mol, and the magnesium doping amount is 0.02~0.04 mol. This more effectively suppresses the dissolution of manganese and lattice distortion. At the same time, the micro-nano composite structure also improves the mechanical stability of the material, which is more conducive to improving the capacity density and cycle stability of the lithium manganese iron phosphate material.

[0147] A comparison of Examples 1-3, 10-11, and 12-17 shows that in the lithium manganese iron phosphate material provided in this application, the Dv50 particle size of the nano-sized porous lithium manganese iron phosphate particles is 50nm~80nm, the porosity is 30%~60%, and the Dv50 particle size of the micron-sized lithium manganese iron phosphate particles is 1~3μm. The introduction of mesoporous structure and micro-nano composite structure provides abundant transport channels and storage sites for lithium ions, further shortens the diffusion path of lithium ions, improves the diffusion rate of lithium ions, and is more conducive to improving the capacity density and cycle stability of lithium manganese iron phosphate material.

[0148] (ii) EIS testing

[0149] The resistance of the CR2032 button cell fresh batteries was tested. After cycling the CR2032 button cell fresh batteries at 1C for 500 cycles, the resistance was tested again, and the results are shown in Table 2. The battery resistance was obtained using EIS testing by Zahner (Germany).

[0150] Table 2

[0151]

[0152] As can be seen from the above description, the embodiments of this application achieve the following technical effects:

[0153] As can be seen from the comparison between Examples 1-17 and Comparative Examples 1-6, the lithium manganese iron phosphate material provided in this application forms a micro-nano composite structure by attaching nano-sized porous lithium manganese iron phosphate particles to the surface of micron-sized lithium manganese iron phosphate particles, and combined with the porous structure inside the nano-sized porous lithium manganese iron phosphate, which not only improves the structural stability of the lithium manganese iron phosphate material, but also reduces the internal resistance of the lithium manganese iron phosphate material.

[0154] A comparison of Examples 1-3, 10-11, and 4-9 shows that, in the lithium manganese iron phosphate material provided in this application, based on 1 mol of lithium, the titanium doping amount in the nano-porous lithium manganese iron phosphate particles is 0.04~0.06 mol, the ruthenium doping amount is 0.01~0.03 mol, and the magnesium doping amount is 0.02~0.04 mol. This more effectively suppresses the dissolution of manganese and lattice distortion. At the same time, the micro-nano composite structure also improves the mechanical stability of the material, which is more conducive to reducing the internal resistance of the lithium manganese iron phosphate material and improving the cycle stability.

[0155] A comparison of Examples 1-3, 10-11, and 12-17 shows that in the lithium manganese iron phosphate material provided in this application, the Dv50 particle size of the nano-sized porous lithium manganese iron phosphate particles is 50nm~80nm, the porosity is 30%~60%, and the Dv50 particle size of the micron-sized lithium manganese iron phosphate particles is 1~3μm. The introduction of mesoporous structure and micro-nano composite structure provides abundant transport channels and storage sites for lithium ions, further shortens the diffusion path of lithium ions, improves the diffusion rate of lithium ions, and is more conducive to improving the cycle stability and reducing the internal resistance of lithium manganese iron phosphate material.

[0156] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A positive electrode material, characterized in that, The lithium manganese iron phosphate material includes micron-sized lithium manganese iron phosphate particles and nano-sized porous lithium manganese iron phosphate particles attached to the surface of the micron-sized lithium manganese iron phosphate particles, wherein the mass ratio of the micron-sized lithium manganese iron phosphate particles to the nano-sized porous lithium manganese iron phosphate particles is (3~5):

1.

2. The cathode material according to claim 1, characterized in that, The nano-porous lithium manganese iron phosphate particles have a Dv50 particle size of 50nm~80nm and a porosity of 30%~60%. And / or, the Dv50 particle size of the micron-sized lithium manganese iron phosphate particles is 1~3μm.

3. The cathode material according to claim 1, characterized in that, The nano-sized porous lithium manganese iron phosphate particles are doped with metal M, wherein metal M includes at least one of titanium, ruthenium, magnesium, zirconium, niobium, cobalt, nickel, aluminum or zinc; Preferably, the metal M includes titanium, ruthenium, and magnesium. With 1 mol of lithium moles as the basis, the nano-porous lithium manganese iron phosphate particles contain 0.04 to 0.06 mol of titanium, 0.01 to 0.03 mol of ruthenium, and 0.02 to 0.04 mol of magnesium.

4. A method for preparing a cathode material according to any one of claims 1 to 3, characterized in that, The preparation method of the lithium manganese iron phosphate material includes: The micron-sized lithium manganese iron phosphate particles and the nano-sized porous lithium manganese iron phosphate particles are mixed so that the nano-sized porous lithium manganese iron phosphate particles adhere to the surface of the micron-sized lithium manganese iron phosphate particles, thereby obtaining the lithium manganese iron phosphate material.

5. The method for preparing the cathode material according to claim 4, characterized in that, The preparation method of the nano-sized porous lithium manganese iron phosphate particles includes: Step S1: Mix the first lithium source, the first manganese source, the first iron source, the first phosphorus source and the optional doped metal M source and prepare lithium manganese iron phosphate gel by sol-gel method, and break the lithium manganese iron phosphate gel into nano-sized lithium manganese iron phosphate precursor particles. Step S2: The nano-sized lithium manganese iron phosphate precursor particles are dispersed in a solution containing a template agent. Through self-assembly, the template agent molecules are arranged in an orderly manner on the surface of the nano-sized lithium manganese iron phosphate precursor particles to form a mesoporous template, thereby obtaining a nano-sized porous lithium manganese iron phosphate precursor. Step S3: The nano-sized lithium manganese iron phosphate precursor is subjected to a first calcination treatment to obtain the nano-sized porous lithium manganese iron phosphate particles.

6. The method for preparing the cathode material according to claim 5, characterized in that, In step S1, the temperature for the gel reaction in the sol-gel method is 80~100℃, and the gel reaction time is 1~3h. And / or, in step S3, the temperature of the first calcination treatment is 500-700℃, and the time of the first calcination treatment is 2-5h; And / or, the first calcination treatment is carried out under a first protective gas atmosphere, wherein the first protective gas is selected from at least one of nitrogen, argon or helium.

7. The method for preparing the cathode material according to claim 5, characterized in that, In step S2, the template agent is selected from at least one of triblock copolymer P123, triblock copolymer F127, triblock copolymer P105, or triblock copolymer F108. And / or, the solvent of the solution containing the template agent is an alcohol solvent, preferably ethanol.

8. The method for preparing the cathode material according to claim 4, characterized in that, The method for preparing the micron-sized lithium manganese iron phosphate particles includes: mixing a second lithium source, a second manganese source, a second iron source, and a second phosphorus source and subjecting them to a second calcination treatment, followed by crushing treatment to obtain the micron-sized lithium manganese iron phosphate particles. The second calcination treatment includes a low-temperature pre-calcination treatment and a high-temperature sintering treatment. The low-temperature pre-calcination treatment is performed at a temperature of 300-500°C for 2-4 hours; the high-temperature sintering treatment is performed at a temperature of 600-800°C for 4-5 hours. And / or, the second calcination treatment is carried out in a second protective gas atmosphere, the second protective gas being selected from at least one of nitrogen, argon or helium.

9. The method for preparing the cathode material according to any one of claims 4 to 8, characterized in that, The micron-sized lithium manganese iron phosphate particles and the nano-sized porous lithium manganese iron phosphate particles are mixed by ball milling at a speed of 250-400 r / min for 1-4 h.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes a positive electrode active material, which is the positive electrode material according to any one of claims 1 to 3 or the positive electrode material obtained by the preparation method according to any one of claims 4 to 9.

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