CN111430687B - Carbon-coated lithium iron phosphate composite material, preparation method thereof and lithium ion battery - Google Patents

Carbon-coated lithium iron phosphate composite material, preparation method thereof and lithium ion battery Download PDF

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CN111430687B
CN111430687B CN202010161316.4A CN202010161316A CN111430687B CN 111430687 B CN111430687 B CN 111430687B CN 202010161316 A CN202010161316 A CN 202010161316A CN 111430687 B CN111430687 B CN 111430687B
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iron phosphate
lithium iron
lithium
composite material
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CN111430687A (en
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邱申保
赵悠曼
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Dongguan Chuangming Battery Technology Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/364—Composites as mixtures
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

The invention belongs to the technical field of batteries, and particularly relates to a preparation method of carbon-coated lithium iron phosphate, which comprises the following steps: mixing a lithium source, iron phosphate, a carbon source and water, and then grinding and granulating to obtain first powder; obtaining an iron-based metal organic framework, mixing the iron-based metal organic framework with the first powder, and grinding to obtain a second powder; and calcining the second powder under the atmosphere of protective gas to obtain the carbon-coated lithium iron phosphate composite material. According to the preparation method provided by the invention, the lithium iron phosphate is subjected to carbon coating twice, so that the resistance among particles is reduced, the conductivity is improved, and the carbon-coated lithium iron phosphate is attached to a metal organic framework in the calcining process to form a three-dimensional conductive network, so that the electrical property of the lithium iron phosphate is improved, and the lithium ion diffusion performance and the conductivity of the composite material are improved.

Description

Carbon-coated lithium iron phosphate composite material, preparation method thereof and lithium ion battery
Technical Field
The invention belongs to the technical field of batteries, and particularly relates to a carbon-coated lithium iron phosphate composite material, a preparation method thereof and a lithium ion battery.
Background
The lithium ion battery mainly comprises three parts, namely a positive electrode, an electrolyte and a negative electrode. The lithium ion battery anode material is a key factor for determining the electrochemical performance, safety performance, energy density and price cost of the battery. Currently, there are many positive electrode materials for lithium ion batteries, such as cobalt-based positive electrode materials, nickel-based positive electrode materials, manganese-based positive electrode materials, lithium iron phosphate positive electrode materials, and the like. Olivine-type lithium iron phosphate (LiFePO)4) The lithium ion battery anode material is one of lithium ion battery anode materials with quite wide application prospect, has higher theoretical reversible specific capacity (170mAh/g), moderate charge-discharge voltage (3.4V), has the advantages of wide raw material source, low pollution, good safety, long cycle life and the like, is an ideal power-shaped and energy-storage lithium ion battery anode material at present, becomes a hotspot of lithium ion battery electrode material research in recent years, and is widely applied to the field of various movable power supplies, particularly the field of large power supplies required by electric vehicles.
However, lithium iron phosphate has a low lithium ion diffusion coefficient and low activation energy due to the fact that lithium ion diffusion in lithium iron phosphate is a one-bit channel, and electron conduction can only be performed through Fe-O-FeThe conductivity and the capacity of the lithium iron phosphate are limited, and particularly in a low-temperature environment, the charge and discharge performance of the lithium iron phosphate is greatly reduced. Due to the limitation of the self structure, the ionic conductivity and the electronic conductivity of the lithium iron phosphate are low, and the lithium iron phosphate is only suitable for charging and discharging under low current density, and the specific capacity is reduced during high-rate charging and discharging, so that the application of the material is limited. The prior art has mainly passed through the reduction of LiFePO4The electrochemical performance of the lithium iron phosphate is effectively improved by the approaches of particle size, metal ion doping, high-temperature carbon doping and the like, wherein the carbon doping is considered to be the most effective lithium iron phosphate modification method which can realize industrial application. However, the method for modifying the lithium iron phosphate by doping carbon still has the problems that the reduction process in the sagger has temperature difference, the coating is not uniform at low temperature and the like, so that the electronic conduction among material particles is influenced, and the electrical property of the lithium iron phosphate battery is further influenced.
Disclosure of Invention
The invention aims to provide a preparation method of a carbon-coated lithium iron phosphate composite material, and aims to solve the technical problems that the carbon coating is not uniform, the temperature difference exists in the reduction process, the ionic conductivity and the electronic conductivity of lithium iron phosphate cannot be effectively improved and the like in the preparation of the carbon-coated lithium iron phosphate.
Another object of the present invention is to provide a carbon-coated lithium iron phosphate composite.
Another object of the present invention is to provide a lithium ion battery.
In order to achieve the purpose of the invention, the technical scheme adopted by the invention is as follows:
a preparation method of a carbon-coated lithium iron phosphate composite material comprises the following steps:
mixing a lithium source, iron phosphate, a carbon source and water, and then grinding and granulating to obtain first powder;
obtaining an iron-based metal organic framework, mixing the iron-based metal organic framework with the first powder, and grinding to obtain a second powder;
and calcining the second powder under the atmosphere of protective gas to obtain the carbon-coated lithium iron phosphate composite material.
Preferably, the step of grinding granulation comprises: mixing a lithium source, iron phosphate, a carbon source and water, and then grinding to obtain a first mixed slurry; then, granulating the first mixed slurry to obtain a first powder material; and/or the presence of a gas in the gas,
the conditions of the calcination treatment include: calcining for 8-10 hours in a protective gas atmosphere at the temperature of 700-800 ℃.
Preferably, the molar ratio of the iron phosphate to the iron-based metal organic framework in the second powder is 1: (0.05 to 0.3); and/or the presence of a gas in the gas,
the molar ratio of the lithium source to the iron phosphate to the carbon source is (1-1.1): 1: (0.1-0.4).
Preferably, the granularity of the first powder is 5-20 mu m; and/or the presence of a gas in the gas,
the granularity of the first mixed slurry is 200-1000 nm; and/or the presence of a gas in the gas,
the granularity of the second powder is 0.5-5 mu m; and/or the presence of a gas in the gas,
the molar ratio of the lithium source, the iron phosphate and the carbon source is (1.02-1.05): 1 (0.1-0.2).
Preferably, the iron-based metal organic framework is selected from: at least one of MIL series, MOF series, and CID series; and/or the presence of a gas in the gas,
the lithium source is selected from: at least one of lithium carbonate, lithium oxalate, lithium phosphate, lithium dihydrogen phosphate and lithium hydroxide; and/or the presence of a gas in the gas,
the carbon source is selected from: at least one of glucose, sucrose, fructose, polyethylene glycol, and dopamine.
Preferably, the MIL series is selected from: at least one of MIL-53, MIL-100, MIL-101, MIL-88, and MIL-68; and/or the presence of a gas in the gas,
the MOF series is selected from: at least one of MOF-74 and MOF-235.
Preferably, the particle size of the carbon-coated lithium iron phosphate composite material is 0.5-8 microns; and/or the presence of a gas in the gas,
the total mass of the carbon-coated lithium iron phosphate composite material is 100%, wherein the carbon content is 0.4-5%.
Accordingly, a carbon-coated lithium iron phosphate composite material comprises an iron-based metal three-dimensional frame and carbon-coated lithium iron phosphate attached to the iron-based metal three-dimensional frame.
Preferably, the particle size of the carbon-coated lithium iron phosphate composite material is 0.5-8 microns; and/or the presence of a gas in the gas,
the total mass of the carbon-coated lithium iron phosphate composite material is 100%, wherein the content of carbon is 0.4-5%; the mass percentage of the iron-based metal three-dimensional frame is 1% -4.5%.
Accordingly, a lithium ion battery comprising the carbon-coated lithium iron phosphate composite material prepared by the above method, or comprising the above carbon-coated lithium iron phosphate composite material.
The preparation method of the carbon-coated lithium iron phosphate composite material comprises the steps of mixing a lithium source, iron phosphate, a carbon source and water, grinding and granulating to fully and uniformly mix the lithium source and the iron phosphate, and coating the carbon source on the surface of the mixture for the first time to form first powder. And then mixing the iron-based metal organic framework and the first powder, and grinding to ensure that the iron-based metal organic framework and the first powder are fully and uniformly mixed, thereby providing a second carbon source and an iron source for the preparation of the lithium iron phosphate. And calcining the second powder under the protective gas atmosphere to generate lithium iron phosphate, wherein a carbon source and an organic ligand in the iron-based metal organic framework respectively provide a carbon source for coating the lithium iron phosphate to form secondary carbon-coated lithium iron phosphate, and after calcination, the three-dimensional network structure of the iron-based metal organic framework can still be maintained, and the secondary carbon-coated lithium iron phosphate is attached to the three-dimensional network structure of the metal organic framework. On one hand, the lithium iron phosphate coated by the secondary carbon not only reduces the resistance among particles, but also shortens the transmission distance between electrons and particles; the carbon layer can inhibit the lithium iron phosphate crystal particles from growing continuously, and the integrity and the proper size of the particles are ensured; with CO accompanying the carbon coating process2And CO gas is produced, so that the specific surface area of the lithium iron phosphate can be improved. On the other hand, the carbon-coated lithium iron phosphate particles are mutually crosslinked and calcinedThe lithium iron phosphate is attached to a metal organic framework to form a three-dimensional conductive network, so that the electrical property of the lithium iron phosphate is improved, and the lithium ion diffusion property and the electrical conductivity of the composite material are improved.
The carbon-coated lithium iron phosphate composite material comprises an iron-based metal three-dimensional frame and carbon-coated lithium iron phosphate attached to the iron-based metal three-dimensional frame, and on one hand, the carbon-coated layer can greatly reduce the resistivity among lithium iron phosphate particles by coating the lithium iron phosphate with carbon, so that the conductivity and consistency of the lithium iron phosphate are improved. On the other hand, the iron-based metal three-dimensional frame has a larger specific surface area, and the carbon-coated lithium iron phosphate is attached to the iron-based metal three-dimensional frame, so that the porous structure of the composite material is improved, and the comparative area of the composite material is improved, so that the wettability of the material is improved, a three-dimensional conductive network structure is formed, the electrical property of the composite material is improved, and the lithium ion diffusion coefficient and the conductivity of the composite material are improved.
The lithium ion battery provided by the invention comprises the carbon-coated lithium iron phosphate composite material, the composite material comprises an iron-based metal three-dimensional frame and carbon-coated lithium iron phosphate attached to the iron-based metal three-dimensional frame, the carbon-coated lithium iron phosphate has a three-dimensional network structure and a large specific surface area, and lithium iron phosphate particles are mutually crosslinked and have higher conductivity, so that the diffusion coefficient and the conductivity of lithium ions in the lithium ion battery are improved, and the electrochemical performance of the lithium ion battery is improved.
Drawings
Fig. 1 is a schematic structural diagram of a carbon-coated lithium iron phosphate composite according to an embodiment of the present invention.
Fig. 2 is a scanning electron microscope image of a carbon-coated lithium iron phosphate composite provided in an embodiment of the present invention.
Fig. 3 is a graph showing electrical conductivity tests of the carbon-coated lithium iron phosphate composite provided in examples 1 to 5 of the present invention and the carbon-coated lithium iron phosphate composite provided in comparative example 1.
Detailed Description
In order to make the purpose, technical solution and technical effect of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention is clearly and completely described, and it is obvious that the described embodiments are a part of the embodiments of the present invention, but not all embodiments. All other embodiments obtained by a person of ordinary skill in the art without any inventive step in connection with the embodiments of the present invention shall fall within the scope of protection of the present invention.
In the description of the present invention, it is to be understood that the terms "first", "second" and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implying any number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless specifically defined otherwise.
The weight of the related components mentioned in the description of the embodiments of the present invention may not only refer to the specific content of each component, but also represent the proportional relationship of the weight among the components, and therefore, the content of the related components is scaled up or down within the scope disclosed in the description of the embodiments of the present invention as long as it is in accordance with the description of the embodiments of the present invention. Specifically, the weight described in the description of the embodiment of the present invention may be a mass unit known in the chemical industry field such as μ g, mg, g, kg, etc.
The embodiment of the invention provides a preparation method of a carbon-coated lithium iron phosphate composite material, which comprises the following steps:
s10, mixing a lithium source, iron phosphate, a carbon source and water, and grinding and granulating to obtain first powder;
s20, obtaining an iron-based metal organic frame, mixing the iron-based metal organic frame with the first powder, and grinding to obtain second powder;
and S30, calcining the second powder under the atmosphere of protective gas to obtain the carbon-coated lithium iron phosphate composite material.
The preparation method of the carbon-coated lithium iron phosphate composite material provided by the embodiment of the invention comprises the steps of mixing a lithium source, iron phosphate, a carbon source and water, grinding and granulating to obtain the lithium sourceAnd fully and uniformly mixing the carbon source and the iron phosphate, and coating the carbon source on the surface of the mixture for the first time to form first powder. And then mixing the iron-based metal organic framework and the first powder, and grinding to ensure that the iron-based metal organic framework and the first powder are fully and uniformly mixed, thereby providing a second carbon source and an iron source for the preparation of the lithium iron phosphate. And calcining the second powder under the protective gas atmosphere to generate lithium iron phosphate, wherein a carbon source and an organic ligand in the iron-based metal organic framework respectively provide a carbon source for coating the lithium iron phosphate to form secondary carbon-coated lithium iron phosphate, and after calcination, the three-dimensional network structure of the iron-based metal organic framework can still be maintained, and the secondary carbon-coated lithium iron phosphate is attached to the three-dimensional network structure of the metal organic framework. On one hand, the lithium iron phosphate coated by the secondary carbon not only reduces the resistance among particles, but also shortens the transmission distance between electrons and particles; the carbon layer can inhibit the lithium iron phosphate crystal particles from growing continuously, and the integrity and the proper size of the particles are ensured; with CO accompanying the carbon coating process2And CO gas is produced, so that the specific surface area of the lithium iron phosphate can be improved. On the other hand, the carbon-coated lithium iron phosphate particles are mutually crosslinked and attached to the metal organic framework in the calcining process to form a three-dimensional conductive network, so that the electrical property of the lithium iron phosphate is improved, and the lithium ion diffusion property and the electrical conductivity of the composite material are improved.
Specifically, in step S10, the lithium source, the iron phosphate, the carbon source, and water are mixed, and then ground and granulated to obtain the first powder. In some embodiments, after mixing a lithium source, iron phosphate, a carbon source and water, grinding to obtain a first mixed slurry; and then, granulating the first mixed slurry in a spraying mode or the like to obtain a first powder material. According to the embodiment of the invention, the lithium source, the iron phosphate, the carbon source and the water are mixed and then are ground and granulated, so that the particle size of each raw material is reduced, the specific surface area of the particles is increased, the lithium source and the iron phosphate are fully mixed, the carbon source is fully coated on the outer surface of the particles, and the carbon-coated lithium iron phosphate particles can be generated in the subsequent preparation process.
In some embodiments, the molar ratio of the lithium source, the iron phosphate, and the carbon source is (1-1.1): 1: (0.1-0.4), and the raw material components in the proportion provide sufficient raw material components for generating the carbon lithium iron phosphate. If the carbon source is excessively added, the surface area of the lithium iron phosphate is too large due to the excessively thick carbon coating layer, and the tap density is too small, so that the processability of the material is affected; if the carbon source is added too little, the carbon coating layer is too thin, and the electrical property of the lithium iron phosphate cannot be effectively improved due to the too low carbon content. In some embodiments, the molar ratio of the lithium source, the iron phosphate, and the carbon source is (1.02-1.05): 1 (0.1-0.2).
In some embodiments, the first mixed slurry has a particle size of 200 to 1000 nm. According to the embodiment of the invention, the lithium source, the iron phosphate, the carbon source and water are mixed and ground into the first mixed slurry with the granularity of 200-1000 nm, so that nano primary particles with approximate sizes are formed in the high-temperature solid-phase calcination reaction, and the nano-crystallization of the lithium iron phosphate is realized. Meanwhile, the lithium iron phosphate is fully contacted with a dissolved carbon source, the coating effect is improved, the conductivity of the lithium iron phosphate is improved, the multiplying power and the low-temperature performance are further improved, but the reduction of tap density and the increase of processing cost are also accompanied, so that the grinding of the granularity of the first mixed slurry to 200-1000 nm is proper. In some embodiments, the particle size of the first mixed slurry is 200nm, 500nm, 700nm, 900nm, or 1000 nm.
In some embodiments, the first frit has a particle size of 5 to 20 μm. In the embodiment of the invention, the first mixed slurry is granulated by spray drying and other modes, and the granularity of the formed first powder is 5-20 mu m (D50) by controlling the parameters of the slurry such as the feeding speed, the inlet and outlet temperature, the atomization frequency and the like, so that the dried particles (the first powder) are ensured to be in a spherical shape and the granularity distribution is reduced; the method is favorable for improving the generation efficiency of the carbon-coated lithium iron phosphate in the subsequent calcining process. In some embodiments, the particle size of the first powder (D50) is 5 μm, 10 μm, 15 μm, or 20 μm.
In some embodiments, the lithium source is selected from: lithium carbonate, lithium oxalate, lithium phosphate, lithium dihydrogen phosphate and lithium hydroxide. The lithium sources adopted by the embodiment of the invention can react with iron phosphate, carbon sources and the like in the calcining treatment process to generate lithium iron phosphate.
In some embodiments, the carbon source is selected from: at least one of glucose, sucrose, fructose, polyethylene glycol, and dopamine. The carbon sources adopted by the embodiment of the invention are dissolved carbon sources, and the dissolved carbon sources can be more fully contacted with iron phosphate and lithium source particles in the mixed slurry and coated on the surfaces of the particles, so that the coating effect is improved, and the formation of a carbon coating layer is facilitated.
In some embodiments, at least one lithium source selected from iron phosphate, lithium carbonate, lithium oxalate, lithium phosphate, lithium dihydrogen phosphate and lithium hydroxide, at least one carbon source selected from glucose, sucrose, fructose, polyethylene glycol and dopamine are mixed with water and then ground to obtain a first mixed slurry with the particle size of 200-1000 nm, and then spray granulation is adopted to obtain a first powder with the particle size of 5-20 μm. Wherein the molar ratio of the lithium source, the iron phosphate and the carbon source is (1-1.1): 1: (0.1-0.4).
Specifically, in step S20, an iron-based metal organic framework is obtained, and the iron-based metal organic framework is mixed with the first powder and then ground to obtain a second powder. According to the embodiment of the invention, the iron-based metal organic framework and the first powder are mixed and then ground, and the particle size of the secondary particles is controlled, so that the size of the generated carbon-coated lithium iron phosphate particles is ensured, and the electrical property of the lithium iron phosphate is improved.
In some embodiments, the molar ratio of the iron phosphate to the iron-based metal organic framework in the second powder is 1: (0.05-0.3). The molar ratio of the ferric phosphate to the iron-based metal organic framework in the second powder material is 1 (0.05-0.3), if the content of the iron-based metal organic framework is too high, the excessive carbon source amount secondarily coated by the lithium iron phosphate can be caused, so that the surface area of the lithium iron phosphate is too large, the tap density is too small, and the too low load capacity of the lithium iron phosphate on the metal organic framework in the carbon-coated lithium iron phosphate composite material can be caused, so that the content of the lithium iron phosphate in the composite material is too low, and the specific energy of the composite material is reduced; if the content of the iron-based metal organic framework is too low, the aims of improving the appearance and improving the electrical property cannot be achieved. In some embodiments, the molar ratio of the iron phosphate to the iron-based metal organic framework in the second powder may be 1: 0.05, 1: 0.1, 1: 0.15, 1: 0.2, 1: 0.25 or 1: 0.3.
in some embodiments, the second powder has a particle size of 0.5 to 5 μm. According to the embodiment of the invention, the iron-based metal organic framework and the first powder are mixed and then ground again, so that the metal organic framework and the first powder are uniformly mixed, the particle size of the mixed powder is refined again, a carbon-coated lithium iron phosphate composite material with uniform particle size, proper size and specific surface area can be formed, and the electrical property of the lithium iron phosphate is improved. If the particle size is too small, the tap density of the prepared lithium iron phosphate composite material is too low, and the application and processing performance of the composite material are affected; if the particle size is too large, the degree of nanocrystallization of the composite material is affected, and the conductivity and rate capability of the carbon-coated lithium iron phosphate composite material are affected. In some embodiments, the particle size of the second powder may be 0.5 microns, 1 micron, 2 microns, 3 microns, 4 microns, or 5 microns.
In some embodiments, the iron-based metal-organic framework is selected from: at least one of MIL series, MOF series, and CID series. In some embodiments, the MIL series is selected from: at least one of MIL-53, MIL-100, MIL-101, MIL-88, and MIL-68. In some embodiments, the MOF series is selected from: at least one of MOF-74 and MOF-235. The metal organic frames adopted in the embodiments of the invention are all iron-based frames, which can provide a secondary coated carbon source for the production of lithium iron phosphate and can also provide an iron source, and the iron-based metal organic frames have good stability, and after being calcined in time, the three-dimensional frame structure can still be maintained, so that a three-dimensional framework is provided for the formation of a carbon-coated lithium iron phosphate three-dimensional composite material. In some embodiments, the preparation of MIL-100 (Fe) comprises the steps of: mixing Fe (NO)3)3·9H2O addition to H2Adding trimesic acid (H) into the solution3BTC), reactant ratio of Fe (NO3)3·9H2O：H3BTC = 2: 3: 300, stirring at room temperature for 1h, transferring to a muffleHeating in a furnace at 160 ℃ for 12h, filtering, washing with 80 ℃ deionized water for 3h, washing with 65 ℃ hot ethanol for 3h, and drying at 80 ℃ for 12h to obtain the product.
In some embodiments, at least one MIL series of MIL-53, MIL-100, MIL-101, MIL-88, MIL-68; at least one MOF series of MOF-74, MOF-235; or mixing the CID series with the first powder, and grinding into a second powder with the granularity of 1-5 mu m. Wherein the molar ratio of the ferric phosphate to the iron-based metal organic framework in the second powder is 1: (0.05-0.3).
Specifically, in step S30, the second powder is calcined in a protective gas atmosphere to obtain a carbon-coated lithium iron phosphate composite material. In the embodiment of the invention, under the atmosphere of protective gas such as nitrogen, argon and the like, the second powder is calcined to generate the lithium iron phosphate, and meanwhile, the generated iron phosphate is coated by a carbon source and an organic ligand in a metal organic framework in a double-layer manner to form carbon-coated lithium iron phosphate. And the three-dimensional network structure frame of the metal organic frame can be reserved in the calcining process, so that the generated carbon-coated lithium iron phosphate can be attached to the three-dimensional network structure of the metal organic frame to form the composite material with the three-dimensional network structure embedded with the carbon-coated lithium iron phosphate nano particles.
In some embodiments, the conditions of the calcination treatment include: calcining for 8-10 hours in a protective gas atmosphere at the temperature of 700-800 ℃. In the embodiment of the invention, the second powder is calcined for 8-10 hours in the protective gas atmosphere at the temperature of 700-800 ℃, and all raw material components are fully reacted to form the carbon-coated lithium iron phosphate three-dimensional network composite material. If the calcining temperature is too low or the calcining time is too short, the lithium iron phosphate and carbon can be incompletely crystallized; if the calcination temperature is too high or the calcination time is too long, the prepared lithium iron phosphate crystal grains are too large, and the material performance is affected.
In some embodiments, the carbon-coated lithium iron phosphate composite has a particle size of 0.5 to 8 microns. The average particle size (D50) of the carbon-coated lithium iron phosphate composite material prepared by the embodiment of the invention is 0.5-8 microns, the particle size is uniform, the performance is stable, the crushing process can be reduced, the application is flexible and convenient, and the application cost can be reduced.
In some embodiments, the carbon-coated lithium iron phosphate composite material has a carbon content of 0.4 to 5% by mass based on 100% by mass of the total mass of the carbon-coated lithium iron phosphate composite material. The carbon content of the carbon-coated lithium iron phosphate composite material prepared by the embodiment of the invention is 0.4-5%, and the carbon component in percentage can realize a good coating effect on lithium iron phosphate, reduce the resistance among particles, shorten the transmission distance between electrons and particles and improve the conductivity of the lithium iron phosphate; but also can effectively inhibit the lithium iron phosphate crystal grains from growing continuously, and ensure the integrity and proper size of the lithium iron phosphate particles. If the carbon content is too high, the surface area of the lithium iron phosphate is too large, the tap density is too small, and the processability of the material is affected; if the carbon content is too low, the carbon content is not effective in improving electrical properties.
In some embodiments, a method of preparing a carbon-coated lithium iron phosphate composite includes the steps of:
s10, mixing and grinding iron phosphate, at least one lithium source of lithium carbonate, lithium oxalate, lithium phosphate, lithium dihydrogen phosphate and lithium hydroxide and at least one carbon source of glucose, sucrose, fructose, polyethylene glycol and dopamine with water to obtain first mixed slurry with the particle size of 200-1000 nm, and then performing spray granulation to obtain first powder with the particle size of 5-20 microns. Wherein the molar ratio of the lithium source, the iron phosphate and the carbon source is (1-1.1): 1: (0.1-0.4).
S20, mixing at least one MIL series of MIL-53, MIL-100, MIL-101, MIL-88 and MIL-68; at least one MOF series of MOF-74, MOF-235; or mixing the CID series with the first powder, and grinding into a second powder with the granularity of 0.5-5 mu m. Wherein the molar ratio of the ferric phosphate to the iron-based metal organic framework in the second powder is 1: (0.025 to 0.05).
And S30, calcining the second powder for 8-10 hours in a protective gas atmosphere at the temperature of 700-800 ℃, and fully reacting the raw material components to form a carbon-coated lithium iron phosphate three-dimensional network composite material with the particle size of 0.5-8 microns, wherein the carbon content is 0.4-5% by taking the total mass of the carbon-coated lithium iron phosphate composite material as 100%.
The preparation method of the carbon-coated lithium iron phosphate composite material provided by the embodiment of the invention can be used for preparing the following carbon-coated lithium iron phosphate composite material.
As shown in fig. 1 and 2, an embodiment of the present invention further provides a carbon-coated lithium iron phosphate composite material, which includes an iron-based metal three-dimensional frame and carbon-coated lithium iron phosphate attached to the iron-based metal three-dimensional frame.
The carbon-coated lithium iron phosphate composite material provided by the embodiment of the invention comprises an iron-based metal three-dimensional frame and carbon-coated lithium iron phosphate attached to the iron-based metal three-dimensional frame, and on one hand, the carbon-coated layer can greatly reduce the resistivity among lithium iron phosphate particles by coating the lithium iron phosphate with carbon, so that the conductivity and consistency of the lithium iron phosphate are improved. On the other hand, the iron-based metal three-dimensional frame has a larger specific surface area, and the carbon-coated lithium iron phosphate is attached to the iron-based metal three-dimensional frame, so that the porous structure of the composite material is improved, and the comparative area of the composite material is improved, so that the wettability of the material is improved, a three-dimensional conductive network structure is formed, the electrical property of the composite material is improved, and the lithium ion diffusion coefficient and the conductivity of the composite material are improved.
In some embodiments, the carbon-coated lithium iron phosphate composite has a particle size of 0.5 to 8 microns. The average particle size (D50) of the carbon-coated lithium iron phosphate composite material prepared by the embodiment of the invention is 0.5-8 microns, the particle size is uniform, the performance is stable, the crushing process can be reduced, the application is flexible and convenient, and the application cost can be reduced.
In some embodiments, the carbon-coated lithium iron phosphate composite material contains 0.4 to 5% of carbon by 100% of the total mass; the mass percentage of the iron-based metal three-dimensional frame is 1% -4.5%. The carbon-coated lithium iron phosphate composite material prepared by the embodiment of the invention has the carbon content of 0.4-5% and the mass percentage of the iron-based metal three-dimensional framework of 1-4.5%, wherein the carbon percentage can achieve a good coating effect on lithium iron phosphate, reduce the resistance between particles, shorten the transmission distance between electrons and the particles and improve the conductivity of the lithium iron phosphate; but also can effectively inhibit the lithium iron phosphate crystal grains from growing continuously, and ensure the integrity and proper size of the lithium iron phosphate particles. If the carbon content is too high, the surface area of the lithium iron phosphate is too large, the tap density is too small, and the processability of the material is affected; if the carbon content is too low, the carbon content is not effective in improving electrical properties. The mass percentage of the iron-based metal three-dimensional frame provides a sufficient framework structure for the composite material forming the three-dimensional network structure, if the content is too low, the coating of the carbon-coated lithium iron phosphate on the iron-based metal three-dimensional frame is too thick, and lithium iron phosphate particles are agglomerated, so that the particle size is too large, and the nanocrystallization of the composite material is not facilitated; if the content is too high, the content of the lithium iron phosphate in the composite material is too low, the specific capacity is low, and the overall electrochemical performance of the composite material is influenced.
Correspondingly, the embodiment of the invention also provides a lithium ion battery, and the lithium ion battery comprises the carbon-coated lithium iron phosphate composite material prepared by the method or the carbon-coated lithium iron phosphate composite material.
The lithium ion battery provided by the embodiment of the invention comprises the carbon-coated lithium iron phosphate composite material, the composite material comprises an iron-based metal three-dimensional frame and carbon-coated lithium iron phosphate attached to the iron-based metal three-dimensional frame, the carbon-coated lithium iron phosphate has a three-dimensional network structure and a large specific surface area, and lithium iron phosphate particles are mutually crosslinked and have higher conductivity, so that the diffusion coefficient and the conductivity of lithium ions in the lithium ion battery are improved, and the electrochemical performance of the lithium ion battery is improved.
In order to make the above implementation details and operations of the present invention clearly understood by those skilled in the art and to make the progress of the carbon-coated lithium iron phosphate composite material and the method for preparing the same apparent, the above technical solution is illustrated by the following examples.
Example 1
A preparation method of a carbon-coated lithium iron phosphate composite material comprises the following steps:
s10, mixing and grinding the iron phosphate, lithium carbonate, glucose and water to obtain a first mixed slurry with the particle size of 200-1000 nm, and then performing spray granulation to obtain a first powder with the particle size of 5-20 microns. Wherein the molar ratio of the lithium source, the iron phosphate and the carbon source is 1.02: 1: 0.2.
s20, mixing the MOF-74 with the first powder, and grinding into second powder with the granularity of 0.5-5 mu m. Wherein the molar ratio of the ferric phosphate to the iron-based metal organic framework in the second powder is 1: 0.05.
and S30, calcining the second powder for 10 hours in a protective gas atmosphere at the temperature of 780 ℃, and fully reacting the raw material components to form the carbon-coated lithium iron phosphate three-dimensional network composite material with the granularity of about 1 micron.
Example 2
A preparation method of a carbon-coated lithium iron phosphate composite material comprises the following steps:
s10, mixing and grinding the iron phosphate, lithium carbonate, glucose and water to obtain a first mixed slurry with the particle size of 200-1000 nm, and then performing spray granulation to obtain a first powder with the particle size of 5-20 microns. Wherein the molar ratio of the lithium source, the iron phosphate and the carbon source is 1.02: 1: 0.2.
s20, mixing the MOF-74 with the first powder, and grinding into second powder with the granularity of 0.5-5 mu m. Wherein the molar ratio of the ferric phosphate to the iron-based metal organic framework in the second powder is 1: 0.1.
and S30, calcining the second powder for 10 hours in a protective gas atmosphere at the temperature of 780 ℃, and fully reacting the raw material components to form the carbon-coated lithium iron phosphate three-dimensional network composite material with the granularity of about 1 micron.
Example 3
A preparation method of a carbon-coated lithium iron phosphate composite material comprises the following steps:
s10, mixing and grinding the iron phosphate, lithium carbonate, glucose and water to obtain a first mixed slurry with the particle size of 200-1000 nm, and then performing spray granulation to obtain a first powder with the particle size of 5-20 microns. Wherein the molar ratio of the lithium source, the iron phosphate and the carbon source is 1.02: 1: 0.2.
s20, mixing the MOF-74 with the first powder, and grinding into second powder with the granularity of 0.5-5 mu m. Wherein the molar ratio of the ferric phosphate to the iron-based metal organic framework in the second powder is 1: 0.15.
and S30, calcining the second powder for 10 hours in a protective gas atmosphere at the temperature of 780 ℃, and fully reacting the raw material components to form the carbon-coated lithium iron phosphate three-dimensional network composite material with the granularity of about 1 micron.
Example 4
A preparation method of a carbon-coated lithium iron phosphate composite material comprises the following steps:
s10, mixing and grinding the iron phosphate, lithium carbonate, glucose and water to obtain a first mixed slurry with the particle size of 200-1000 nm, and then performing spray granulation to obtain a first powder with the particle size of 5-20 microns. Wherein the molar ratio of the lithium source, the iron phosphate and the carbon source is 1.02: 1: 0.2.
s20, mixing the MOF-74 with the first powder, and grinding into second powder with the granularity of 0.5-5 mu m. Wherein the molar ratio of the ferric phosphate to the iron-based metal organic framework in the second powder is 1: 0.2.
and S30, calcining the second powder for 10 hours in a protective gas atmosphere at the temperature of 780 ℃, and fully reacting the raw material components to form the carbon-coated lithium iron phosphate three-dimensional network composite material with the granularity of about 1 micron.
Example 5
A preparation method of a carbon-coated lithium iron phosphate composite material comprises the following steps:
s10, mixing and grinding the iron phosphate, lithium carbonate, glucose and water to obtain a first mixed slurry with the particle size of 200-1000 nm, and then performing spray granulation to obtain a first powder with the particle size of 5-20 microns. Wherein the molar ratio of the lithium source, the iron phosphate and the carbon source is 1.02: 1: 0.2.
s20, mixing the MOF-74 with the first powder, and grinding into second powder with the granularity of 0.5-5 mu m. Wherein the molar ratio of the ferric phosphate to the iron-based metal organic framework in the second powder is 1: 0.25.
and S30, calcining the second powder for 10 hours in a protective gas atmosphere at the temperature of 780 ℃, and fully reacting the raw material components to form the carbon-coated lithium iron phosphate three-dimensional network composite material with the granularity of about 1 micron.
Comparative example 1
A preparation method of a carbon-coated lithium iron phosphate composite material comprises the following steps:
s10, mixing and grinding the iron phosphate, lithium carbonate, glucose and water to obtain a first mixed slurry with the particle size of 200-1000 nm, and then performing spray granulation to obtain a first powder with the particle size of 5-20 microns. Wherein the molar ratio of the lithium source, the iron phosphate and the carbon source is 1.02: 1: 0.2.
and S20, calcining the first powder for 10 hours in a protective gas atmosphere at the temperature of 780 ℃, and fully reacting the raw material components to form the carbon-coated lithium iron phosphate composite material.
Further, in order to verify the advancement of the carbon-coated lithium iron phosphate composite material prepared in the embodiment of the present invention, the embodiment of the present invention was subjected to a conductivity test.
Test example 1
The test examples of the present invention tested the electrical conductivity of the carbon-coated lithium iron phosphate three-dimensional network composite materials prepared in examples 1 to 5 and the carbon-coated lithium iron phosphate composite material prepared in comparative example 1, and the test results are shown in fig. 3 below. According to the test results, the conductivity of the carbon-coated lithium iron phosphate three-dimensional network composite material prepared by doping the lithium iron metal organic framework in the embodiments 1-5 of the present invention is obviously higher than that of the lithium iron phosphate composite material prepared by coating only a carbon source in the comparative example 1, and with the increase of the iron-based metal organic framework, the conductivity of the composite material rapidly increases and then becomes stable, which indicates that the molar ratio of the iron phosphate to the iron-based metal organic framework in the second powder material in the embodiments of the present invention is 1: (0.05-0.3), the composite material has the best effect of improving the conductivity of the composite material.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.

Claims (10)

1. A preparation method of a carbon-coated lithium iron phosphate composite material is characterized by comprising the following steps:
mixing a lithium source, iron phosphate, a carbon source and water, and then grinding and granulating to obtain first powder;
obtaining an iron-based metal organic framework, mixing the iron-based metal organic framework with the first powder, and grinding to obtain a second powder;
calcining the second powder under the atmosphere of protective gas to obtain a carbon-coated lithium iron phosphate composite material;
the carbon-coated lithium iron phosphate composite material includes: an iron-based metal three-dimensional frame and carbon-coated lithium iron phosphate attached to the iron-based metal three-dimensional frame.
2. The method of preparing a carbon-coated lithium iron phosphate composite according to claim 1, wherein the step of grinding and granulating comprises: mixing a lithium source, iron phosphate, a carbon source and water, and then grinding to obtain a first mixed slurry; then, granulating the first mixed slurry to obtain a first powder material; and/or the presence of a gas in the gas,
the conditions of the calcination treatment include: calcining for 8-10 hours in a protective gas atmosphere at the temperature of 700-800 ℃.
3. The method for preparing the carbon-coated lithium iron phosphate composite material according to claim 2, wherein the molar ratio of the lithium source, the iron phosphate, and the carbon source is (1-1.1): 1: (0.1-0.4).
4. The method of preparing the carbon-coated lithium iron phosphate composite material according to claim 3, wherein the first powder has a particle size of 5 to 20 μm; and/or the presence of a gas in the gas,
the granularity of the first mixed slurry is 200-1000 nanometers; and/or the presence of a gas in the gas,
the granularity of the second powder is 0.5-5 microns; and/or the presence of a gas in the gas,
the molar ratio of the lithium source, the iron phosphate and the carbon source is (1.02-1.05): 1 (0.1-0.2).
5. The method of preparing a carbon-coated lithium iron phosphate composite material according to any one of claims 1, 2 or 4, wherein the iron-based metal organic framework is selected from the group consisting of: at least one of the MIL series and the MOF series; and/or the presence of a gas in the gas,
the lithium source is selected from: at least one of lithium carbonate, lithium oxalate, lithium phosphate, lithium dihydrogen phosphate and lithium hydroxide; and/or the presence of a gas in the gas,
the carbon source is selected from: at least one of glucose, sucrose, fructose, and dopamine.
6. The method of preparing a carbon-coated lithium iron phosphate composite according to claim 5, wherein the MIL series is selected from the group consisting of: at least one of MIL-53, MIL-100, MIL-101, MIL-88, and MIL-68; and/or the presence of a gas in the gas,
the MOF series is selected from: at least one of MOF-74 and MOF-235.
7. The method of preparing a carbon-coated lithium iron phosphate composite according to any one of claims 1, 2, 4, or 6, wherein the particle size of the carbon-coated lithium iron phosphate composite is 0.5 to 8 μm; and/or the presence of a gas in the gas,
the total mass of the carbon-coated lithium iron phosphate composite material is 100%, wherein the carbon content is 0.4-5%.
8. A carbon-coated lithium iron phosphate composite material prepared by the method of any one of claims 1 to 7, comprising an iron-based metal three-dimensional framework and carbon-coated lithium iron phosphate attached to the iron-based metal three-dimensional framework.
9. The carbon-coated lithium iron phosphate composite of claim 8, wherein the carbon-coated lithium iron phosphate composite has a particle size of 0.5 to 8 microns; and/or the presence of a gas in the gas,
the total mass of the carbon-coated lithium iron phosphate composite material is 100%, wherein the content of carbon is 0.4-5%; the mass percentage of the iron-based metal three-dimensional frame is 1% -4.5%.
10. A lithium ion battery comprising the carbon-coated lithium iron phosphate composite material prepared by the method according to any one of claims 1 to 7, or the carbon-coated lithium iron phosphate composite material according to any one of claims 8 to 9.
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