Microcrystalline iron phosphate precursor, preparation method thereof, lithium iron phosphate positive electrode material and preparation method thereof

Abstract

The application discloses a microcrystalline iron phosphate precursor and a preparation method thereof, a lithium iron phosphate positive electrode material and a preparation method thereof. The microcrystalline iron phosphate precursor is anchored with all-inorganic perovskite quantum dots on the surface. In the process of preparing the lithium iron phosphate from the microcrystalline iron phosphate precursor, the quantum dots can provide additional electrons, which are coupled with the electrons of Fe 2+ to realize directional reduction of Fe 3+ impurities and optimization of lattice oxygen arrangement, thereby improving the electronic conductivity of the lithium iron phosphate. In addition, in the process of preparing the lithium iron phosphate, alkali metal ions such as Cs + and fourth main group metal ions such as Pb 2+ doped into the lithium iron phosphate crystal are generated by calcination and decomposition of the quantum dots, thereby widening the lithium ion diffusion channel, improving the lithium ion diffusion rate, and inhibiting the grain growth. The lithium iron phosphate positive electrode material prepared from the microcrystalline iron phosphate precursor is applied to a lithium ion battery, and the electrochemical performance such as the rate performance and the low-temperature performance of the battery can be significantly improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a microcrystalline iron phosphate precursor and its preparation method, lithium iron phosphate cathode material and its preparation method, cathode sheet, lithium-ion battery, and power-consuming device. Background Technology

[0002] Lithium iron phosphate (LiFePO4) batteries are lithium-ion batteries that use lithium iron phosphate (LiFePO4) as the positive electrode material. They offer advantages such as high operating voltage, high energy density, long cycle life, good safety performance, low self-discharge rate, and no memory effect. However, lithium iron phosphate has a low intrinsic electronic conductivity (~10⁻⁶). -9 The slow diffusion rate (S / cm) and slow lithium-ion diffusion rate result in poor electrochemical performance of lithium-ion batteries, such as rate performance and low-temperature performance.

[0003] Therefore, it is urgent to optimize and modify lithium iron phosphate cathode materials to improve the electrochemical performance of lithium-ion batteries. Summary of the Invention

[0004] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, one object of this invention is to provide a microcrystalline iron phosphate precursor, the surface of which is modified with all-inorganic perovskite quantum dots. Using this microcrystalline iron phosphate precursor to prepare lithium iron phosphate cathode materials can significantly improve the electrochemical performance of lithium-ion batteries, such as rate performance and low-temperature performance.

[0005] Specifically, the first aspect of the present invention provides a microcrystalline iron phosphate precursor, comprising a microcrystalline iron phosphate matrix and all-inorganic perovskite quantum dots modified on the surface of the microcrystalline iron phosphate matrix;

[0006] The molecular formula of the all-inorganic perovskite quantum dots is ABX3, where A includes alkali metal ions, B includes group IV metal ions, and X includes halide ions.

[0007] The microcrystalline iron phosphate (FePO4) precursor of this invention has fully inorganic perovskite quantum dots ABX3, such as CsPbX3, anchored on its surface. During the preparation of lithium iron phosphate (LiFePO4) from this precursor, the fully inorganic perovskite quantum dots can provide additional electrons (especially since the quantum dots can generate a large number of photogenerated electrons after irradiation), which interact with Fe... 2+ Electrons undergo coupling effect, directional reduction of Fe 3+ Impurities are removed and the lattice oxygen arrangement is optimized, thereby improving the electronic conductivity of lithium iron phosphate. Additionally, during the preparation of lithium iron phosphate, alkali metal ions such as Cs are generated from the calcination and decomposition of all-inorganic perovskite quantum dots. + and Group 4 metal ions such as Pb 2+Alkali metal ions such as Cs are incorporated into lithium iron phosphate crystals. + Occupying the interstitial spaces of Li sites widens the lithium-ion diffusion channels and increases the lithium-ion diffusion rate; Group IV metal ions such as Pb 2+ This method can suppress grain growth (average particle size of primary particles ≤ 200 nm). Smaller grains result in a larger specific surface area and a shorter lithium-ion diffusion path, thus significantly improving the rate performance and low-temperature performance of the material. It also helps improve particle uniformity and enhances the structural stability of the material. Applying the lithium iron phosphate cathode material prepared from the aforementioned microcrystalline iron phosphate precursor to lithium-ion batteries can significantly improve the battery's electrochemical performance, such as rate performance and low-temperature performance.

[0008] According to some embodiments of the present invention, the microcrystalline iron phosphate precursor comprises the microcrystalline iron phosphate matrix, a bifunctional ligand molecule, and the all-inorganic perovskite quantum dots; the surface of the microcrystalline iron phosphate matrix has hydroxyl groups; the bifunctional ligand molecule contains thiol and carboxyl groups, one end of the bifunctional ligand molecule binds to the hydroxyl groups on the surface of the microcrystalline iron phosphate matrix through the thiol group, and the other end of the bifunctional ligand molecule binds to the all-inorganic perovskite quantum dots through the carboxyl group.

[0009] According to some embodiments of the present invention, the all-inorganic perovskite quantum dots include CsPbX3; optionally, the CsPbX3 includes one or more of CsPbCl3, CsPbBr3, and CsPbI3, preferably CsPbBr3.

[0010] According to some embodiments of the present invention, the bifunctional ligand molecule includes one or more of 4-mercaptobenzoic acid, 3-mercaptobenzoic acid, and o-mercaptobenzoic acid, preferably 4-mercaptobenzoic acid.

[0011] According to some embodiments of the present invention, the molar ratio of the all-inorganic perovskite quantum dot to the bifunctional ligand molecule is 1:(1.02-1.05).

[0012] A second aspect of the present invention provides a method for preparing the microcrystalline iron phosphate precursor of the first aspect of the present invention, comprising the following steps:

[0013] The microcrystalline iron phosphate matrix, bifunctional ligand molecules, and all-inorganic perovskite quantum dots were ultrasonically mixed in a solvent and reacted under heating; after filtration and drying, the microcrystalline iron phosphate precursor was obtained.

[0014] The method of this invention is simple, low-cost, and suitable for large-scale industrial application. This method enables the anchoring of all-inorganic perovskite quantum dots onto a microcrystalline iron phosphate matrix.

[0015] According to some embodiments of the present invention, the reaction temperature is 0 to 100°C, preferably 50°C to 80°C; the reaction time is 1 hour to 5 hours, preferably 1 hour to 3 hours.

[0016] According to some embodiments of the present invention, after drying, the method further includes: irradiating the microcrystalline iron phosphate precursor with ultraviolet light in a protective atmosphere.

[0017] According to some embodiments of the present invention, the wavelength of the ultraviolet light is 300nm-500nm; the irradiance is 5mW / cm². 2 -15mW / cm 2 The irradiation time is 20-40 minutes.

[0018] According to some embodiments of the present invention, the solvent includes an aqueous solvent.

[0019] A third aspect of the present invention provides a lithium iron phosphate cathode material, comprising: a lithium iron phosphate core co-doped with an alkali metal element and a Group 4 metal element, and a carbon coating layer covering the surface of the lithium iron phosphate core.

[0020] The lithium iron phosphate cathode material of this invention is prepared from the microcrystalline iron phosphate precursor of the first aspect of this invention. It has a core-shell structure, with the core being lithium iron phosphate co-doped with an alkali metal and a Group IV metal, and the outer shell being a carbon coating layer. By doping with alkali metals and Group IV metals, the electronic conductivity and lithium-ion diffusion rate of lithium iron phosphate can be improved. The carbon coating layer can optimize the surface potential energy distribution of lithium iron phosphate, enabling high-speed lithium-ion transport within the material. Applying this lithium iron phosphate cathode material to lithium-ion batteries can improve the battery's electrochemical performance, such as rate performance and low-temperature performance.

[0021] According to some embodiments of the present invention, based on the weight of the lithium iron phosphate cathode material, the total doping amount of the alkali metal element and the fourth group metal element is 1100ppm-12000ppm.

[0022] According to some embodiments of the present invention, the D50 particle size of the lithium iron phosphate cathode material is 0.1 μm-1.8 μm.

[0023] A fourth aspect of the present invention provides a method for preparing the lithium iron phosphate cathode material of the third aspect of the present invention, comprising the following steps:

[0024] The microcrystalline iron phosphate precursor of the first aspect of the present invention or the microcrystalline iron phosphate precursor prepared by the method of the second aspect of the present invention is mixed with a lithium source and a carbon source, spray-dried, and calcined to obtain the lithium iron phosphate cathode material.

[0025] The method of this invention has simple process steps, low cost, and the prepared lithium iron phosphate cathode material has excellent electrochemical performance, especially rate performance and low temperature performance.

[0026] According to some embodiments of the present invention, the lithium source includes one or more of battery-grade lithium carbonate, lithium phosphate, lithium oxalate, lithium hydroxide, and lithium oxide, preferably lithium carbonate; the carbon source includes one or more of asphalt, polydopamine, resorcinol, formaldehyde, starch, activated carbon, graphene, carbon nanotubes, fullerene, sucrose, glucose, sodium carboxymethyl cellulose, polyvinylidene fluoride, polyvinylpyrrolidone, tannic acid, polyvinyl alcohol, polypyrrole, vitamin C, polyethylene glycol, anthracene, or aniline.

[0027] According to some embodiments of the present invention, the calcination temperature is 500℃-800℃, preferably 620℃-680℃; the calcination time is 5h-10h, preferably 6h-8h.

[0028] The fifth aspect of the present invention provides a positive electrode sheet, comprising the lithium iron phosphate positive electrode material of the third aspect of the present invention or the lithium iron phosphate positive electrode material obtained by the method of the fourth aspect of the present invention.

[0029] Because the above-mentioned lithium iron phosphate cathode material is used, the cathode sheet of the present invention has all the advantages of the lithium iron phosphate cathode material, which will not be repeated here.

[0030] The sixth aspect of the present invention provides a lithium-ion battery, including the positive electrode sheet of the fifth aspect of the present invention.

[0031] Because the lithium iron phosphate cathode material described above is used, the lithium-ion battery of the present invention has all the advantages of the lithium iron phosphate cathode material, which will not be repeated here.

[0032] A seventh aspect of the present invention provides an electrical device comprising a lithium-ion battery according to a sixth aspect of the present invention.

[0033] Because the above-mentioned lithium iron phosphate cathode material is used, the electrical device of the present invention has all the advantages of the lithium iron phosphate cathode material, which will not be repeated here.

[0034] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0035] Figure 1 This is a scanning electron microscope (SEM) image of the lithium iron phosphate cathode material prepared from a microcrystalline iron phosphate precursor modified with all-inorganic perovskite quantum dots according to Example 1 of the present invention.

[0036] Figure 2This is a SEM image of the lithium iron phosphate cathode material prepared from the microcrystalline iron phosphate precursor in Comparative Example 1. Detailed Implementation

[0037] The embodiments of the present invention are described in detail below. These embodiments are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0038] In the description of this invention, unless otherwise stated, "a plurality of" means two or more. "Multiple" means two or more. Throughout this document, the terms "comprising" or "including" are open-ended expressions, meaning they include the contents specified in this invention but do not exclude other aspects.

[0039] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0040] Lithium iron phosphate (LiFePO4) batteries are lithium-ion batteries that use lithium iron phosphate (LiFePO4) as the positive electrode material. They offer advantages such as high operating voltage, high energy density, long cycle life, good safety performance, low self-discharge rate, and no memory effect. However, lithium iron phosphate has a low intrinsic electronic conductivity (~10⁻⁶). -9 The slow diffusion rate (S / cm) and low lithium-ion diffusion rate of lithium-ion batteries result in poor electrochemical performance, such as rate performance and low-temperature performance. Therefore, it is urgent to optimize and modify lithium iron phosphate cathode materials to improve the electrochemical performance of lithium-ion batteries.

[0041] To address the above problems, this invention proposes a microcrystalline iron phosphate precursor. The surface of this microcrystalline iron phosphate (FePO4) precursor is anchored with all-inorganic perovskite quantum dots ABX3, such as CsPbX3. During the preparation of lithium iron phosphate (LiFePO4) from this precursor, the all-inorganic perovskite quantum dots can provide additional electrons (especially since the quantum dots can generate a large number of photogenerated electrons after irradiation). These electrons interact with Fe... 2+ Electrons undergo coupling effect, directional reduction of Fe 3+ Impurities are removed and the lattice oxygen arrangement is optimized, thereby improving the electronic conductivity of lithium iron phosphate. Additionally, during the preparation of lithium iron phosphate, alkali metal ions such as Cs are generated from the calcination and decomposition of all-inorganic perovskite quantum dots. + and Group 4 metal ions such as Pb 2+ Alkali metal ions such as Cs are incorporated into lithium iron phosphate crystals. +Occupying the interstitial spaces of Li sites widens the lithium-ion diffusion channels and increases the lithium-ion diffusion rate; Group IV metal ions such as Pb 2+ This method can suppress grain growth (average particle size of primary particles ≤ 200 nm). Smaller grains result in a larger specific surface area and a shorter lithium-ion diffusion path, thus significantly improving the rate performance and low-temperature performance of the material. It also helps improve particle uniformity and enhances the structural stability of the material. Applying the lithium iron phosphate cathode material prepared from the aforementioned microcrystalline iron phosphate precursor to lithium-ion batteries can significantly improve the battery's electrochemical performance, such as rate performance and low-temperature performance.

[0042] In some embodiments, the microcrystalline iron phosphate precursor comprises the microcrystalline iron phosphate matrix, a bifunctional ligand molecule, and the all-inorganic perovskite quantum dots; the surface of the microcrystalline iron phosphate matrix has hydroxyl groups; the bifunctional ligand molecule contains thiol and carboxyl groups, one end of the bifunctional ligand molecule binds to the hydroxyl groups on the surface of the microcrystalline iron phosphate matrix via the thiol group, and the other end of the bifunctional ligand molecule binds to the all-inorganic perovskite quantum dots via the carboxyl group. Using the bifunctional ligand molecule can firmly anchor the all-inorganic perovskite quantum dots to the surface of the microcrystalline iron phosphate matrix, preventing the quantum dots from separating from the microcrystalline iron phosphate matrix, thereby achieving effective metal ion doping.

[0043] In some embodiments, the all-inorganic perovskite quantum dots comprise CsPbX3.

[0044] In some embodiments, the CsPbX3 includes one or more of CsPbCl3, CsPbBr3, and CsPbI3, preferably CsPbBr3. Anchoring all-inorganic perovskite quantum dots CsPbX3 on the surface of a microcrystalline iron phosphate matrix can generate electron-ion synergistic transport: the quantum dots CsPbX3 act as "electron pumps" to generate photogenerated electrons during the preparation of lithium iron phosphate; and during the preparation of lithium iron phosphate, CsPbX3 undergoes high-temperature calcination decomposition to produce Cs... + Occupying the interstitial spaces of Li sites, widening the lithium-ion diffusion channels; decomposition produces Pb 2+ Inhibit grain growth (average grain size ≤200nm), thereby improving the electrochemical performance of the cathode material.

[0045] In some embodiments, based on the weight of the microcrystalline iron phosphate precursor, the loading of the all-inorganic perovskite quantum dots is less than 3 wt%, preferably 0.2 wt% to 1.5 wt%. By controlling the loading of the all-inorganic perovskite quantum dots, the amount of metal ions doped in the lithium iron phosphate cathode material can be controlled, thereby optimizing the electrochemical performance of the battery.

[0046] In some specific embodiments, the loading of the all-inorganic perovskite quantum dots is 0.2wt%, 0.4wt%, 0.6wt%, 0.8wt%, 1.0wt%, 1.2wt%, 1.4wt%, 1.6wt%, 1.8wt%, 2.0wt%, 2.2wt%, 2.4wt%, 2.6wt%, 2.8wt%, or 3wt%.

[0047] In some embodiments, the particle size of the all-inorganic perovskite quantum dots is less than 10 nm, for example, 1 nm, 2 nm, 4 nm, 6 nm, 8 nm or 10 nm, preferably 3 nm-5 nm.

[0048] In some embodiments, the particle size of the microcrystalline iron phosphate matrix is ​​less than 5 μm, for example, 1 μm, 2 μm, 3 μm, 4 μm or 5 μm, preferably 1 μm-2 μm.

[0049] In some embodiments, the bifunctional ligand molecules include one or more of 4-mercaptobenzoic acid, 3-mercaptobenzoic acid, and o-mercaptobenzoic acid, preferably 4-mercaptobenzoic acid. These bifunctional ligand molecules can act as good bridging links, anchoring all-inorganic perovskite quantum dots to the surface of a microcrystalline iron phosphate matrix.

[0050] In some embodiments, the molar ratio of the all-inorganic perovskite quantum dots to the bifunctional ligand molecules is 1:(1.02-1.05). Optimizing the molar ratio of quantum dots to ligand molecules is beneficial for connecting as many quantum dots as possible on the microcrystalline iron phosphate matrix and avoiding quantum dot loss.

[0051] In some specific embodiments, the molar ratio of the all-inorganic perovskite quantum dot to the bifunctional ligand molecule is 1:1.02, 1:1.03, 1:1.04, or 1:1.05.

[0052] Quantum technology is primarily used in perovskite solar cells or photocatalysts, but its systematic application in the synthesis of iron phosphate precursors is yet to be seen. This invention provides a quantum dot-modified microcrystalline iron phosphate precursor, wherein the precursor has a microcrystalline structure and its surface is anchored with entirely inorganic perovskite quantum dots. As mentioned above, this quantum dot material can exert multiple effects in lithium iron phosphate applications compared to other types of iron phosphate precursors.

[0053] A second aspect of the present invention provides a method for preparing the microcrystalline iron phosphate precursor of the first aspect of the present invention, comprising the following steps:

[0054] The microcrystalline iron phosphate matrix, bifunctional ligand molecules, and all-inorganic perovskite quantum dots were ultrasonically mixed in a solvent and reacted under heating; after filtration and drying, the microcrystalline iron phosphate precursor was obtained.

[0055] The method of this invention is simple, low-cost, and suitable for large-scale industrial application. This method enables the anchoring of all-inorganic perovskite quantum dots onto a microcrystalline iron phosphate matrix.

[0056] In some embodiments, the reaction temperature is 0–100°C, for example 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, or 100°C, preferably 50°C–80°C. The reaction time is 1 h–5 h, for example 1 h, 2 h, 3 h, 4 h, or 5 h, preferably 1 h–3 h.

[0057] In some embodiments, after drying, the method further includes: irradiating the microcrystalline iron phosphate precursor with ultraviolet light in a protective atmosphere. Irradiating the quantum dot-modified microcrystalline iron phosphate precursor with ultraviolet light can promote the generation of a large number of photogenerated electrons from the quantum dots. During the preparation of lithium iron phosphate from it, these photogenerated electrons can react with Fe... 2+ Electrons undergo coupling effect, directional reduction of Fe 3+ Impurities are removed and the lattice oxygen arrangement is optimized, thereby improving the electronic conductivity of lithium iron phosphate. The protective atmosphere includes argon.

[0058] In some embodiments, the wavelength of the ultraviolet light is 300 nm-500 nm, for example, 300 nm, 350 nm, 400 nm, 450 nm, or 500 nm. The irradiance is 5 mW / cm². 2 -15mW / cm 2 For example, 5mW / cm 2 7mW / cm 2 9mW / cm 2 11mW / cm 2 13mW / cm 2 Or 15mW / cm 2 The irradiation time is 20-40 minutes, for example, 20 minutes, 25 minutes, 30 minutes, 35 minutes, or 40 minutes. Optimizing the ultraviolet irradiation conditions is beneficial for promoting the generation of more photogenerated electrons in quantum dots.

[0059] In some embodiments, the solvent includes an aqueous solvent. The aqueous solvent includes water, or a mixture of water with ethanol or methanol, etc. The type of solvent can be selected according to actual needs.

[0060] In some embodiments, the microcrystalline iron phosphate matrix may be commercially available or prepared. For example, the microcrystalline iron phosphate matrix may be prepared by a hydrothermal or solvothermal method.

[0061] In some specific embodiments, the preparation method of the microcrystalline iron phosphate matrix includes the following steps:

[0062] FeSO4·7H2O and H3PO4 are mixed at a Fe / P molar ratio of 1:1 to 1:1.1, preferably 1:1.05, and a template agent (e.g., sodium citrate) is added. The mixture is then subjected to a hydrothermal reaction to obtain a microcrystalline iron phosphate matrix.

[0063] The hydrothermal reaction temperature is 100℃-200℃, preferably 150℃-200℃. The hydrothermal reaction time is 10h-15h, preferably 12h. The particle size of the prepared microcrystalline iron phosphate matrix is ​​less than 5μm, for example, 1μm, 2μm, 3μm, 4μm or 5μm, preferably 1μm-2μm.

[0064] In some embodiments, the all-inorganic perovskite quantum dots are commercially available or can be fabricated. For example, the all-inorganic perovskite quantum dots can be synthesized by a thermal injection method.

[0065] In some specific embodiments, the preparation method of the all-inorganic perovskite quantum dots includes the following steps:

[0066] A2CO3 and BX2 are dissolved in an organic solvent (e.g., octadecene), and oleic acid or oleylamine ligands are injected. The mixture is reacted at 250℃-300℃ for 5-10 minutes, and then centrifuged to obtain CsPbX3 all-inorganic perovskite quantum dots.

[0067] “A” represents an alkali metal ion. “B” represents a Group IV metal ion. “X” represents Cl, Br, or I.

[0068] In some specific embodiments, A2CO3 is Cs2CO3, and BX2 is PbX2.

[0069] The reaction time can be 250℃, 260℃, 270℃, 280℃, 290℃, or 300℃. The reaction time can be 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, or 10 minutes.

[0070] A third aspect of the present invention provides a lithium iron phosphate cathode material, comprising: a lithium iron phosphate core co-doped with an alkali metal element and a Group 4 metal element, and a carbon coating layer covering the surface of the lithium iron phosphate core.

[0071] The lithium iron phosphate cathode material of this invention is prepared from the microcrystalline iron phosphate precursor of the first aspect of this invention. It has a core-shell structure, with the core being lithium iron phosphate co-doped with an alkali metal and a Group IV metal, and the outer shell being a carbon coating layer. By doping with alkali metals and Group IV metals, the electronic conductivity and lithium-ion diffusion rate of lithium iron phosphate can be improved. The carbon coating layer can optimize the surface potential energy distribution of lithium iron phosphate, enabling high-speed lithium-ion transport within the material. Applying this lithium iron phosphate cathode material to lithium-ion batteries can improve the battery's electrochemical performance, such as rate performance and low-temperature performance.

[0072] In some embodiments, based on the weight of the lithium iron phosphate cathode material, the total doping amount of the alkali metal element and the Group IV metal element is 1100ppm-12000ppm. Optimizing the doping amount of the metal elements is beneficial to improving the electronic conductivity and lithium-ion diffusion rate of lithium iron phosphate, thereby improving the electrochemical performance of the battery, such as rate performance and low-temperature performance. As a specific example, the total doping amount of the alkali metal element and the Group IV metal element is 1100ppm, 2000ppm, 3000ppm, 4000ppm, 5000ppm, 6000ppm, 7000ppm, 8000ppm, 9000ppm, 10000ppm, 11000ppm, or 12000ppm.

[0073] In some embodiments, the D50 particle size of the lithium iron phosphate cathode material is 0.1 μm-1.8 μm, for example, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm or 1.8 μm.

[0074] In this article, D50 particle size refers to the particle size at which the cumulative particle size distribution percentage of a sample reaches 50%. Physically, it means that 50% of the particles are larger than D50, and 50% are smaller. D50 particle size is also called median particle size or median particle size.

[0075] A fourth aspect of the present invention provides a method for preparing the lithium iron phosphate cathode material of the third aspect of the present invention, comprising the following steps:

[0076] The microcrystalline iron phosphate precursor of the first aspect of the present invention or the microcrystalline iron phosphate precursor prepared by the method of the second aspect of the present invention is mixed with a lithium source and a carbon source, spray-dried, and calcined to obtain the lithium iron phosphate cathode material.

[0077] The method of this invention features simple process steps, low cost, and produces lithium iron phosphate cathode materials with excellent electrochemical performance, particularly in rate performance and low-temperature performance. Furthermore, the lithium iron phosphate prepared by this method exhibits no loss in energy density.

[0078] In some embodiments, the lithium source includes one or more of battery-grade lithium carbonate, lithium phosphate, lithium oxalate, lithium hydroxide, and lithium oxide, preferably lithium carbonate. The lithium source can react with a microcrystalline iron phosphate precursor to form lithium iron phosphate, thereby enabling the preparation of the cathode material.

[0079] In some embodiments, the carbon source includes one or more of the following: asphalt, polydopamine, resorcinol, formaldehyde, starch, activated carbon, graphene, carbon nanotubes, fullerene, sucrose, glucose, sodium carboxymethyl cellulose, polyvinylidene fluoride, polyvinylpyrrolidone, tannic acid, polyvinyl alcohol, polypyrrole, vitamin C, polyethylene glycol, anthracene, or aniline. After calcination, the carbon source can be converted into a carbon coating layer, improving the electronic conductivity of lithium iron phosphate.

[0080] In some embodiments, the calcination can be carried out in a protective atmosphere such as nitrogen. The calcination temperature is 500°C-800°C, for example, 500°C, 600°C, 700°C, or 800°C, preferably 620°C-680°C. The calcination time is 5h-10h, for example, 5h, 6h, 7h, 8h, 9h, or 10h, preferably 6h-8h. During calcination, the quantum dots decompose into Cs. + and Pb 2+ Cs + and Pb 2+ Doping is introduced into lithium iron phosphate crystals, due to Cs + and Pb 2+ Due to their different ionic radii, the Pb atoms enter the lithium iron phosphate lattice at different positions, forming a gradient doping layer. Simultaneously, the carbon source is converted to form a continuous carbon-coated network. This reduces the carbothermal reduction temperature by over 100°C, decreasing energy consumption. 2+ Inhibit grain growth (average grain size ≤200nm).

[0081] In some embodiments, the microcrystalline iron phosphate precursor and the lithium source can be fed in a molar ratio of iron, phosphorus, and lithium of 1:0.96-0.98:1.03-1.05. The molar ratio can be, for example, 1:0.96:1.03, 1:0.96:1.04, 1:0.96:1.05, 1:0.97:1.03, 1:0.97:1.04, 1:0.97:1.05, 1:0.98:1.03, 1:0.98:1.04, or 1:0.98:1.05. The carbon source accounts for 8%-13% of the mass of the microcrystalline iron phosphate matrix, for example, 8%, 9%, 10%, 11%, 12%, or 13%.

[0082] The present invention will be explained below with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0083] Example 1

[0084] (1) Preparation of microcrystalline iron phosphate matrix:

[0085] Microcrystalline iron phosphate matrix was prepared by hydrothermal method. Specifically, FeSO4·7H2O and H3PO4 were mixed at a Fe / P molar ratio of 1:1.05, sodium citrate template agent was added, and the mixture was subjected to hydrothermal reaction at 180℃ for 12 h. After filtration and drying, microcrystalline iron phosphate matrix was obtained with a particle size of 1-2 μm.

[0086] (2) Preparation of CsPbBr3 quantum dots:

[0087] Cs2CO3 and the halogenated molecule PbBr2 were dissolved in the organic solvent octadecene, oleic acid ligands were injected, and the mixture was reacted at 280 °C for 5 minutes. CsPbBr3 quantum dots were obtained by centrifugation.

[0088] (3) Preparation of quantum dot-modified microcrystalline iron phosphate precursor:

[0089] CsPbBr3 quantum dots and 4-mercaptobenzoic acid (a bifunctional ligand molecule) were dispersed in ethanol at a molar ratio of 1:1.03 and stirred for 30 min. Then, a microcrystalline iron phosphate matrix was added, with a mass ratio of microcrystalline iron phosphate matrix to quantum dots of 1:0.015. The mixture was ultrasonically composited in the ethanol system and reacted at 60 °C for 2 h. After the reaction, the mixture was filtered and dried to obtain a quantum dot-modified microcrystalline iron phosphate precursor powder.

[0090] (4) In an argon glove box, a UV-LED light source (365nm, 10mW / cm²) was used. 2 Irradiate the precursor powder obtained in step 3 for 30 minutes.

[0091] (5) Preparation of lithium iron phosphate cathode material:

[0092] Lithium iron phosphate was prepared using a carbothermal reduction method. Specifically, the precursor powder obtained in step 4 was mixed with lithium carbonate (lithium source) and glucose (carbon source) at a mass ratio of 1:0.25:0.13 by sand milling, spray drying, and calcination in a tube furnace (N2 atmosphere) at 640℃ for 8 hours with a heating rate of 3℃ / min. Afterward, it was allowed to cool naturally to obtain quantum dot-doped carbon-coated lithium iron phosphate cathode material. Its SEM image is shown below. Figure 1 As shown.

[0093] Example 2

[0094] Quantum dot-modified microcrystalline iron phosphate precursor and lithium iron phosphate cathode material were prepared according to the method described in Example 1, except that in step 3, 4-mercaptobenzoic acid was replaced with o-mercaptobenzoic acid.

[0095] Example 3

[0096] Quantum dot-modified microcrystalline iron phosphate precursor and lithium iron phosphate cathode material were prepared according to the method described in Example 1, except that the calcination temperature in step 5 was 740°C.

[0097] Example 4

[0098] Quantum dot-modified microcrystalline iron phosphate precursor and lithium iron phosphate cathode material were prepared according to the method described in Example 1, except that the calcination temperature in step 5 was 600°C.

[0099] Example 5

[0100] Quantum dot-modified microcrystalline iron phosphate precursor and lithium iron phosphate cathode material were prepared according to the method described in Example 1, except that step 4 was not performed.

[0101] Example 6

[0102] Quantum dot-modified microcrystalline iron phosphate precursor and lithium iron phosphate cathode material were prepared according to the method described in Example 1, except that in step (2) preparation of CsPbCl3 quantum dots: Cs2CO3 and halogenated molecule PbCl2 were dissolved in the organic solvent octadecene, oleic acid ligand was injected, and the reaction was carried out at 280°C for 5 minutes. CsPbCl3 quantum dots were obtained by centrifugation.

[0103] Example 7

[0104] Quantum dot-modified microcrystalline iron phosphate precursor and lithium iron phosphate cathode material were prepared according to the method described in Example 1, except that in step (2) preparation of CsPbI3 quantum dots: Cs2CO3 and halogenated molecule PbI2 were dissolved in the organic solvent octadecene, oleic acid ligand was injected, and the reaction was carried out at 280°C for 5 minutes. CsPbI3 quantum dots were obtained by centrifugation.

[0105] Example 8

[0106] Quantum dot-modified microcrystalline iron phosphate precursor and lithium iron phosphate cathode material were prepared according to the method described in Example 1, except that in step 3, the reaction temperature was 80°C and the reaction time was 1 h.

[0107] Example 9

[0108] Quantum dot-modified microcrystalline iron phosphate precursor and lithium iron phosphate cathode material were prepared according to the method described in Example 1, except that in step 3, the reaction temperature was 100°C and the reaction time was 1 h.

[0109] Example 10

[0110] Quantum dot-modified microcrystalline iron phosphate precursor and lithium iron phosphate cathode material were prepared according to the method described in Example 1, except that in step 3, the reaction temperature was 120°C and the reaction time was 1 h.

[0111] Example 11

[0112] Quantum dot-modified microcrystalline iron phosphate precursor and lithium iron phosphate cathode material were prepared according to the method described in Example 1, except that in step 4, the wavelength of ultraviolet light was 300 nm and the irradiance was 15 mW / cm². 2 The irradiation time was 20 minutes.

[0113] Example 12

[0114] Quantum dot-modified microcrystalline iron phosphate precursor and lithium iron phosphate cathode material were prepared according to the method described in Example 1, except that in step 4, the wavelength of ultraviolet light was 500 nm and the irradiance was 5 mW / cm². 2 The irradiation time was 40 minutes.

[0115] Comparative Example 1

[0116] (1) Preparation of microcrystalline iron phosphate precursor:

[0117] Microcrystalline iron phosphate precursor was prepared by hydrothermal method. Specifically, FeSO4·7H2O and H3PO4 were mixed at a Fe / P molar ratio of 1:1.05, sodium citrate template agent was added, and hydrothermal reaction was carried out at 180℃ for 12 h. After filtration and drying, microcrystalline iron phosphate precursor was obtained. The particle size of the iron phosphate precursor was 1-2 μm.

[0118] (2) Preparation of lithium iron phosphate cathode material:

[0119] Lithium iron phosphate was prepared using a carbothermal reduction method. Specifically, the iron phosphate precursor powder prepared in step 1, lithium carbonate (lithium source), and glucose (carbon source) were mixed by sand milling at a mass ratio of 1:0.25:0.13, spray-dried, and calcined in a tube furnace (N2 atmosphere) at a temperature of 640℃ for 8 hours with a heating rate of 3℃ / min. Afterward, it was allowed to cool naturally to obtain a carbon-coated lithium iron phosphate cathode material. Its SEM image is shown below. Figure 1 As shown.

[0120] Button battery assembly

[0121] The lithium iron phosphate cathode material prepared above was assembled into a CR2025 coin cell. Specifically, the following steps were included:

[0122] (1) Preparation of the positive electrode sheet:

[0123] The positive electrode slurry was prepared using N-methylpyrrolidone as a solvent, PVDF as a binder, and acetylene black as a conductive agent. The mass ratio of the various components in the slurry was: lithium iron phosphate positive electrode material: binder: conductive agent = 100:2.3:0.8. The battery slurry was uniformly coated on aluminum foil and vacuum dried. After cutting and pressing, the positive electrode sheet was obtained.

[0124] (2) Preparation of negative electrode sheet

[0125] A lithium sheet with a diameter of 14mm was used as the negative electrode.

[0126] (3) Preparation of the diaphragm

[0127] A polyethylene (PE) film with a thickness of 14 μm was used as the separator.

[0128] (4) Preparation of electrolyte

[0129] The organic solvent is a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), wherein the volume ratio of EC, EMC, and DEC is 20:20:60. In an argon-atmosphere glove box with a water content of <10 ppm, thoroughly dried lithium salt LiPF6 is dissolved in the above organic solvent, then additives are added and mixed thoroughly to obtain the electrolyte. The concentration of the lithium salt is 1 mol / L.

[0130] (5) Assembly of CR2025 button cells

[0131] In the glove box, the positive electrode, negative electrode, separator, electrolyte, and gasket spring are assembled into a CR2025 button half cell.

[0132] Performance testing of lithium iron phosphate cathode material and CR2025 coin cell

[0133] (1) Cs in lithium iron phosphate cathode materials + and Pb 2+ Total doping amount ICP test

[0134] Quantitative analysis of trace elements was performed using inductively coupled plasma optical emission spectrometry (ICP-OES). Calibration curves were established using the national standard reference material (GBW(E)080125 Lithium Iron Phosphate). The linear correlation coefficient R0 was [not specified]. 2 >0.999. The test results are shown in Table 1.

[0135] (2) D50 particle size test of lithium iron phosphate cathode material

[0136] The lithium iron phosphate cathode material was dispersed in anhydrous ethanol (refractive index 1.52), and the D50 particle size was measured using a Malvern 2000 particle size analyzer. The test results are shown in Table 1.

[0137] (3) 0.1C discharge efficiency test of CR2025 button half-cell

[0138] The installed battery was tested for electrical performance using a Blue Battery Tester. Under constant current charging and discharging conditions of 0.1C within a voltage range of 2.5V-3.8V, the initial discharge capacity and discharge efficiency were tested. The test results are shown in Table 1.

[0139] (4) 2C discharge efficiency test of CR2025 button half cell

[0140] The installed battery was tested for electrical performance using a Blue Battery Tester. Within a voltage range of 2.5V-3.8V, it was charged at a constant current of 0.5C and discharged at 2C. The discharge capacity and discharge efficiency were tested under these conditions, and the results are shown in Table 1.

[0141] (5) Low-temperature discharge efficiency test of CR2025 button half-cell

[0142] The assembled battery was placed in a low-temperature chamber to test its electrical performance, with the temperature set to -20℃. Within a voltage range of 2.5V-3.8V, it was charged and discharged at a constant current of 1C to test the discharge capacity and low-temperature discharge efficiency. The test results are shown in Table 1.

[0143] Table 1

[0144]

[0145] Note: ND indicates not detected.

[0146] Comparing Examples 1, 3, and 4, it can be seen that the calcination temperature affects the D50 particle size of lithium iron phosphate, thereby affecting the rate performance and low-temperature performance of the battery.

[0147] Comparing Examples 1 and 5, it can be seen that ultraviolet irradiation during the preparation process is beneficial to improving the rate performance of the battery.

[0148] Comparing Examples 1, 6, and 7, it can be seen that quantum dots containing different halogen elements affect the doping amounts of Cs and Pb, as well as the D50 particle size of lithium iron phosphate, thereby affecting the rate performance and low-temperature performance of the battery.

[0149] Comparing Examples 1 and 8-10, it can be seen that the temperature during the preparation of quantum dot-modified microcrystalline lithium iron phosphate precursor affects the doping amounts of Cs and Pb, as well as the D50 particle size of lithium iron phosphate, thereby affecting battery performance.

[0150] In summary, the battery of this invention maintains a capacity retention rate of over 98% at 0.1C and over 92% at 2C (compared to ≤90% for conventional materials); its low-temperature discharge efficiency at -20℃ is over 63% (compared to an industry average of approximately 50%). It is evident that the lithium iron phosphate cathode material of this invention achieves a significant improvement in electrochemical performance, particularly in rate performance and low-temperature performance.

[0151] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0152] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A microcrystalline iron phosphate precursor, characterized in that, It includes a microcrystalline iron phosphate matrix and all-inorganic perovskite quantum dots modified on the surface of the microcrystalline iron phosphate matrix; The molecular formula of the all-inorganic perovskite quantum dots is ABX3, where A includes alkali metal ions, B includes group IV metal ions, and X includes halide ions.

2. The microcrystalline iron phosphate precursor according to claim 1, characterized in that, Includes the microcrystalline iron phosphate matrix, bifunctional ligand molecules, and the all-inorganic perovskite quantum dots; The surface of the microcrystalline iron phosphate matrix has hydroxyl groups; The bifunctional ligand molecule contains thiol and carboxyl groups. One end of the bifunctional ligand molecule binds to the hydroxyl groups on the surface of the microcrystalline iron phosphate matrix via the thiol group, and the other end of the bifunctional ligand molecule binds to the all-inorganic perovskite quantum dots via the carboxyl group.

3. The microcrystalline iron phosphate precursor according to claim 1 or 2, characterized in that, The all-inorganic perovskite quantum dots include CsPbX3; Optionally, the CsPbX3 includes one or more of CsPbCl3, CsPbBr3, and CsPbI3, preferably CsPbBr3.

4. The microcrystalline iron phosphate precursor according to claim 2, characterized in that, The bifunctional ligand molecule includes one or more of 4-mercaptobenzoic acid, 3-mercaptobenzoic acid, and o-mercaptobenzoic acid, preferably 4-mercaptobenzoic acid.

5. The microcrystalline iron phosphate precursor according to claim 2, characterized in that, The molar ratio of the all-inorganic perovskite quantum dots to the bifunctional ligand molecules is 1:(1.02-1.05).

6. A method for preparing the microcrystalline iron phosphate precursor according to any one of claims 1-5, characterized in that, Includes the following steps: The microcrystalline iron phosphate matrix, bifunctional ligand molecules, and all-inorganic perovskite quantum dots were ultrasonically mixed in a solvent and reacted under heating; after filtration and drying, the microcrystalline iron phosphate precursor was obtained.

7. The method according to claim 6, characterized in that, The reaction temperature is 0-100℃, preferably 50℃-80℃; the reaction time is 1h-5h, preferably 1h-3h.

8. The method according to claim 6 or 7, characterized in that, After drying, the method further includes irradiating the microcrystalline iron phosphate precursor with ultraviolet light in a protective atmosphere.

9. The method according to claim 8, characterized in that, The wavelength of ultraviolet light is 300nm-500nm; the irradiance is 5mW / cm². 2 -15mW / cm 2 The irradiation time is 20-40 minutes.

10. The method according to claim 6, characterized in that, The solvent includes aqueous solvents.

11. A lithium iron phosphate cathode material, characterized in that, include: A lithium iron phosphate core co-doped with alkali metal elements and Group IV metal elements, and a carbon coating layer covering the surface of the lithium iron phosphate core.

12. The lithium iron phosphate cathode material according to claim 11, characterized in that, Based on the weight of the lithium iron phosphate cathode material, the total doping amount of the alkali metal element and the fourth group metal element is 1100ppm-12000ppm.

13. The lithium iron phosphate cathode material according to claim 11, characterized in that, The D50 particle size of the lithium iron phosphate cathode material is 0.1μm-1.8μm.

14. A method for preparing the lithium iron phosphate cathode material according to any one of claims 11-13, characterized in that, Includes the following steps: The microcrystalline iron phosphate precursor of any one of claims 1-5 or the microcrystalline iron phosphate precursor prepared by any one of claims 6-10 is mixed with a lithium source and a carbon source, spray-dried, and calcined to obtain the lithium iron phosphate cathode material.

15. The method for producing lithium iron phosphate cathode material according to claim 14, characterized in that, The lithium source includes one or more of battery-grade lithium carbonate, lithium phosphate, lithium oxalate, lithium hydroxide, and lithium oxide, preferably lithium carbonate; The carbon source includes one or more of the following: asphalt, polydopamine, resorcinol, formaldehyde, starch, activated carbon, graphene, carbon nanotubes, fullerene, sucrose, glucose, sodium carboxymethyl cellulose, polyvinylidene fluoride, polyvinylpyrrolidone, tannic acid, polyvinyl alcohol, polypyrrole, vitamin C, polyethylene glycol, anthracene, or aniline.

16. The method for producing lithium iron phosphate cathode material according to claim 14, characterized in that, The calcination temperature is 500℃-800℃, preferably 620℃-680℃; the calcination time is 5h-10h, preferably 6h-8h.

17. A positive electrode plate, characterized in that, The lithium iron phosphate cathode material includes any one of claims 11-13 or any one of claims 14-16.

18. A lithium-ion battery, characterized in that, Includes the positive electrode sheet as described in claim 17.

19. An electrical appliance, characterized in that, Including the lithium-ion battery as described in claim 18.

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