CN115241462B - Polymer-coated lithium iron phosphate positive electrode material and preparation method and application thereof - Google Patents

Polymer-coated lithium iron phosphate positive electrode material and preparation method and application thereof Download PDF

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CN115241462B
CN115241462B CN202211169320.0A CN202211169320A CN115241462B CN 115241462 B CN115241462 B CN 115241462B CN 202211169320 A CN202211169320 A CN 202211169320A CN 115241462 B CN115241462 B CN 115241462B
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lithium
phosphate
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ferric
iron phosphate
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CN115241462A (en
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何蕊
魏爱佳
白薛
刘振法
张利辉
李晓辉
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Energy Research Institute of Hebei Academy of Sciences
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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
    • H01M4/62—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
    • 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
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • 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
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    • 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 battery materials, and particularly relates to a polymer-coated lithium iron phosphate positive electrode material and a preparation method and application thereof. Mixing ferric salt, lithium salt, phosphate and a high-molecular organic polymer in a solvent, heating to different temperatures in sequence at a specific heating speed to react, reacting with hexadecyl trimethyl ammonium halide and soluble ferric salt in an acidic aqueous solution at a low temperature for 2-4 hours after the reaction is finished, and carrying out solid-liquid separation to obtain the composite. The lithium iron phosphate anode material prepared by the method is coated by a polymer containing halogen ions, has a three-dimensional network structure formed by carbon, and has the advantages of remarkably improved electronic conductivity, greatly improved low-temperature performance and no obvious change in volume and mass specific energy compared with pure lithium iron carbonate. The lithium ion power battery prepared by using the lithium ion composite material as the anode material can improve the electrochemical performance and the low-temperature performance of the lithium ion power battery and reduce the production cost of the battery.

Description

Polymer-coated lithium iron phosphate positive electrode material and preparation method and application thereof
The present application claims priority from chinese patent application 202211100541.2, filed on 09/08/2022, which is hereby incorporated by reference in its entirety.
Technical Field
The invention belongs to the technical field of battery materials, and particularly relates to a polymer-coated lithium iron phosphate positive electrode material, and a preparation method and application thereof.
Background
The anode material is the most critical raw material of the lithium ion battery, and the total cost proportion is the highest in the lithium ion battery, so that the anode material is the main bottleneck for improving the energy density of the battery and reducing the production cost of the battery. Currently, the mainstream lithium battery anode materials in the world include four materials, namely lithium cobaltate, lithium manganate, lithium iron phosphate, ternary materials (NCM nickel cobalt manganese), and the like. Lithium cobaltate is poor in safety, cobalt is a rare nonferrous metal, and the cost is high, so that the lithium cobaltate is one of the reasons for restricting the development of ternary materials. And the lithium manganate battery has a short life. Although the lithium iron phosphate does not use rare nonferrous metal, the service life of the lithium iron phosphate is greatly prolonged compared with that of lithium manganate, and the lithium iron phosphate has the advantages of high specific capacity, stable working voltage, low cost, environmental friendliness and the like, but the energy density is low, and the low-temperature performance of the lithium iron phosphate is poor due to the reasons of impedance increase, ion diffusion rate reduction and the like at the interface of the electrode in a low-temperature environment.
At present, doping or surface coating of a conductive agent is a main method for improving the conductivity of lithium iron phosphate, and the conductive agent can effectively promote the transmission of electrons and reduce the contact resistance between electrode materials, so that the diffusion rate of ions entering and exiting the lithium iron phosphate at low temperature is improved, and the electrochemical performance of the lithium iron phosphate material is improved. The doping and coating of carbon are more researched, and the technology is mature. However, carbon is an inactive substance with a low mass density, and the tap density of the lithium iron phosphate material can be reduced by doping or coating the carbon, so that the volume and mass specific energy are reduced.
Disclosure of Invention
Aiming at the technical problems, the invention provides a polymer-coated lithium iron phosphate positive electrode material and a preparation method and application thereof. Compared with pure lithium iron phosphate, the lithium iron phosphate anode material provided by the invention has the advantages that the electron conductivity is greatly improved, and the volume and mass specific energy of the material cannot be reduced.
In order to achieve the purpose of the invention, the embodiment of the invention adopts the following technical scheme:
the invention provides a preparation method of a polymer-coated lithium iron phosphate positive electrode material, which specifically comprises the following steps:
s1, uniformly mixing iron salt, lithium salt, phosphate and a high-molecular organic polymer in a solvent, carrying out solid-liquid separation, drying and grinding the obtained solid, heating to 80-200 ℃ at a heating rate of 5-15 ℃/min, reacting for 2-4 h, heating to 300-450 ℃ at a heating rate of 3-7 ℃ for reacting for 1-3 h, heating to 600-750 ℃ at a heating rate of 5-10 ℃ for reacting for 5-10h, and naturally cooling after the reaction is finished; the molar ratio of iron element, lithium element and phosphorus element in the ferric salt, the lithium salt and the phosphate is 1 to 095 to 1.05, and the mass of the high molecular organic polymer is 1 to 8 percent of the total mass of the ferric salt, the lithium salt and the phosphate;
s2, dispersing pyrrole in an acidic aqueous solution, adding the product obtained in the step S1 and cetyltrimethylammonium halide, uniformly mixing, slowly adding a water-soluble ferric salt, reacting at 0-5 ℃ for 2-4h, then carrying out solid-liquid separation, and calcining the obtained solid at 300-400 ℃ for 2-4h to obtain the lithium iron phosphate positive electrode material; the cetyl trimethyl ammonium halide is cetyl trimethyl ammonium bromide or cetyl trimethyl ammonium chloride.
The preparation method comprises the steps of firstly carrying out reaction at a relatively low temperature to enable iron salt, phosphorus salt, lithium salt and a high-molecular organic polymer to form a precursor which is uniformly mixed, and further carrying out subsequent two-step high-temperature reaction to carbonize the high-molecular organic polymer to form a three-dimensional network structure in the process of generating lithium iron phosphate by reacting iron element, phosphorus element and lithium element, wherein lithium iron phosphate molecules are uniformly distributed in holes of the three-dimensional network structure.
And (2) in the reaction process of S2, a polypyrrole coating containing bromine or chlorine is generated on the surface of the product obtained in S1 in situ. On one hand, the polypyrrole belongs to a conductive polymer and can effectively improve the conductivity of lithium iron phosphate, and on the other hand, hexadecyl trimethyl ammonium halide not only improves the uniformity of polypyrrole coating in S2, but also enables the polypyrrole coating layer not to physically coat on the surface of the lithium iron phosphate but to be connected with a three-dimensional network structure in the lithium iron phosphate, so that the impedance at an electrode interface is further reduced and the ion diffusion rate is improved. And the polypyrrole has certain theoretical specific capacity, and bromine and chlorine elements brought into the polypyrrole coating by the hexadecyl trimethyl ammonium halide further improve the specific capacity, so that the defect of reduction of volume and mass specific energy caused by carbon doping and carbon coating in the prior art is overcome.
In combination with the first aspect, the high molecular organic polymer is at least one selected from methylcellulose, ethylcellulose, hydroxyethyl cellulose, hydroxypropyl methylcellulose, gum arabic, gelatin, polyacrylamide, polyvinyl alcohol, polyethylene glycol, polyalditol, soluble starch, polyvinylpyrrolidone, phenolic resin, epoxy resin, urea resin, furan resin, polyacrylic resin, polyvinylidene fluoride, polyvinyl chloride, and polymethacrylate.
Illustratively, the high molecular organic polymer is a combination of methylcellulose, gelatin and polyethylene glycol, a combination of ethylcellulose and polyacrylamide, a combination of hydroxyethylcellulose, polyvinyl alcohol and soluble starch, a combination of hydroxypropylcellulose, polyglycitol and polyvinylpyrrolidone, a combination of hydroxypropylmethylcellulose and polyvinylidene fluoride, a combination of gum arabic, phenol resin and polyvinyl chloride, a combination of epoxy resin and polymethacrylate, and the like, a combination of hydroxypropylmethylcellulose and furan resin, or a urea-formaldehyde resin or polyacrylic resin alone. Among them, preferred combinations are a combination of methylcellulose, gelatin and polyethylene glycol and a combination of ethylcellulose and polyacrylamide.
In combination with the first aspect, the lithium salt is selected from at least one of lithium carbonate, lithium nitrate, lithium sulfate, lithium acetate, and lithium phosphate. The above lithium salts are commercially available lithium salts, but lithium nitrate and lithium sulfate generate harmful gases such as nitrogen oxides and sulfur dioxide in the process of producing lithium iron phosphate, and therefore at least one of lithium carbonate, lithium acetate and lithium phosphate is preferably used. Optionally, the lithium salt is a combination of lithium carbonate and lithium phosphate or a combination of lithium acetate and lithium phosphate. Phosphate radicals in the lithium phosphate can participate in the reaction to generate lithium iron phosphate, and carbon atoms in lithium carbonate or lithium acetate can participate in the formation of a three-dimensional network structure in the reaction process of S1, so that the three-dimensional network structure is more uniform, the dispersion degree of the carbon atoms among lithium iron phosphate molecules is higher, and the ion diffusion is more facilitated.
In combination with the first aspect, the iron salt is selected from at least one of iron phosphate, ferrous oxalate, ferric chloride, ferrous chloride, ferric sulfate, and ferrous sulfate. The iron salt can be produced by using a by-product of the process, such as ferrous sulfate which is a by-product in the production of titanium white, to reduce the cost.
In combination with the first aspect, the phosphate is selected from at least one of iron phosphate, ferrous phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, or sodium phosphate. Because ammonium dihydrogen phosphate and diammonium hydrogen phosphate can generate ammonia gas in the reaction for preparing lithium iron phosphate, and are not beneficial to environmental protection, at least one of ferric phosphate, ferrous phosphate or sodium phosphate is preferably adopted.
With reference to the first aspect, the mass of the pyrrole in S2 is 3% to 5% of the mass of the product obtained in S1, and the molar ratio of the pyrrole to the cetyltrimethylammonium halide is 1.05 to 0.15. The thickness of a polypyrrole coating layer formed by the polypyrrole coating layer is determined by the using amount of the pyrrole, and if the using amount is too small, ideal effects of reducing impedance and improving ion diffusion rate are not easily achieved; because the structure of the polypyrrole coating layer is relatively loose, the thickness of the formed coating layer is too thick when the consumption of the polypyrrole is too high, and the tap density of the obtained lithium iron phosphate anode material can be reduced. The mol ratio of pyrrole to hexadecyl trimethyl ammonium halide determines the doping capacity of halogen elements, directly influences the specific capacity of the polypyrrole coating layer and further influences the specific capacity of the obtained lithium iron phosphate anode material. Within the range of the mass ratio and the molar ratio, the electrical property of the lithium iron phosphate anode material can be obviously improved, and the tap density of the lithium iron phosphate anode material cannot be obviously influenced.
With reference to the first aspect, the hydrogen ion concentration in the acidic aqueous solution is 0.8 to 1.5m, and optionally the acidic component is selected from hydrochloric acid, sulfuric acid, nitric acid or phosphoric acid.
In combination with the first aspect, the water-soluble iron salt is at least one selected from the group consisting of ferric chloride, ferric bromide, ferric sulfate, ferric nitrate and ferric perchlorate, and the molar ratio of iron ions in the iron salt to pyrrole is 0.01 to 0.05.
In combination with the first aspect, S2 further includes washing the solid product obtained by solid-liquid separation with water or an aqueous ethanol solution to remove unreacted materials and a small amount of free carbon generated in S1 that does not participate in forming a three-dimensional network structure.
The invention provides a polymer-coated lithium iron phosphate positive electrode material, which is prepared by the preparation method of the polymer-coated lithium iron phosphate positive electrode material.
The third aspect of the invention provides an application of the polymer-coated lithium iron phosphate cathode material in the preparation of a lithium ion battery. Compared with pure lithium iron carbonate, the polymer-coated lithium iron phosphate cathode material has the advantages that the electronic conductivity is remarkably improved, the low-temperature performance is greatly improved, meanwhile, the volume-mass ratio energy of the polymer-coated lithium iron phosphate cathode material is not obviously changed, the polymer-coated lithium iron phosphate cathode material is used as the cathode material to prepare the lithium ion power battery, the electrochemical performance and the low-temperature performance of the lithium ion power battery can be improved, the production cost of the battery is reduced, and the polymer-coated lithium iron phosphate cathode material has higher practical value and economic value.
Drawings
Fig. 1 shows the microstructure (transmission electron microscope picture) of the polymer-coated lithium iron phosphate positive electrode material obtained in example 1 of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The polymer-coated lithium iron phosphate cathode material is mainly applied to lithium ion batteries. The lithium ion battery mainly comprises a positive electrode material, a negative electrode material, a diaphragm, electrolyte and the like, wherein the positive electrode material accounts for the highest proportion of the total cost of the lithium ion battery. In the current mainstream lithium battery cathode material, the safety of lithium cobaltate is poor, and the cost of lithium cobaltate and the cobalt in ternary materials are more rare, so that the cost is increased year by year; although rare nonferrous metals are not used in lithium manganate and lithium iron phosphate, the lithium manganate and the lithium iron phosphate have short service life, and the lithium manganate and the lithium iron phosphate have low energy density and poor low-temperature performance. The conductivity of the lithium iron phosphate can be improved by doping or coating a conductive agent on the surface, wherein carbon doping and carbon coating are more researched and technically mature methods, but the mass density of carbon is lower, and the tap density of the lithium iron phosphate material can be reduced by doping or coating, so that the volume-mass specific energy is reduced.
In order to improve the electrochemical performance of the lithium iron phosphate anode material and not obviously reduce the tap density of the lithium iron phosphate anode material, the embodiment of the invention improves the existing preparation method of the lithium iron phosphate anode material, and provides a preparation method of a polymer-coated lithium iron phosphate anode material, which specifically comprises the following steps:
s1, uniformly mixing iron salt, lithium salt, phosphate and a high-molecular organic polymer in a solvent, carrying out solid-liquid separation, drying and grinding the obtained solid, heating to 80 to 200 ℃ at a heating rate of 5 to 15 ℃/min, reacting for 2 to 4h, heating to 300 to 450 ℃ at a heating rate of 3 to 7 ℃, reacting for 1 to 3h, heating to 600 to 750 ℃ at a heating rate of 5 to 10 ℃, reacting for 5 to 10h, and naturally cooling after the reaction is finished; the molar ratio of iron element, lithium element and phosphorus element in the ferric salt, the lithium salt and the phosphate is 1 to 095 to 1.05, and the mass of the high molecular organic polymer is 1 to 8 percent of the total mass of the ferric salt, the lithium salt and the phosphate;
s2, dispersing pyrrole in an acidic aqueous solution, adding the product obtained in the step S1 and cetyltrimethylammonium halide, uniformly mixing, slowly (finally removing) adding soluble ferric salt, reacting at 0 to 5 ℃ for 2 to 4 hours, carrying out solid-liquid separation, and calcining the obtained solid at 300 to 400 ℃ for 2 to 4 hours to obtain the lithium iron phosphate cathode material; the cetyl trimethyl ammonium halide is cetyl trimethyl ammonium bromide or cetyl trimethyl ammonium chloride.
In the embodiment of the present application, the high molecular organic polymer may be at least one of methylcellulose, ethylcellulose, hydroxyethyl cellulose, hydroxypropyl methylcellulose, gum arabic, gelatin, polyacrylamide, polyvinyl alcohol, polyethylene glycol, polyalditol, soluble starch, polyvinylpyrrolidone, phenolic resin, epoxy resin, urea resin, furan resin, polyacrylic resin, polyvinylidene fluoride, polyvinyl chloride, and polymethacrylate; the lithium salt may be selected from at least one of lithium carbonate, lithium nitrate, lithium sulfate, lithium acetate and lithium phosphate; the iron salt can be at least one selected from iron phosphate, ferrous oxalate, ferric chloride, ferrous chloride, ferric sulfate and ferrous sulfate; the phosphate may be at least one selected from iron phosphate, ferrous phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, or sodium phosphate.
As an illustrative example, the high molecular organic polymer may use a combination of methylcellulose, gelatin and polyethylene glycol, a combination of ethylcellulose and polyacrylamide, a combination of hydroxyethylcellulose, polyvinyl alcohol and soluble starch, a combination of hydroxypropylcellulose, polyglycitol and polyvinylpyrrolidone, a combination of hydroxypropylmethylcellulose and polyvinylidene fluoride, a combination of gum arabic, phenol resin and polyvinyl chloride, a combination of epoxy resin and polymethacrylate, or the like, or hydroxypropylmethylcellulose, epoxy resin, urea resin, furan resin or polyacrylic resin alone; the lithium salt can be a combination of lithium carbonate and lithium phosphate or a combination of lithium acetate and lithium phosphate; the iron salt is ferrous sulfate; the phosphate can be at least one of ferric phosphate, ferrous phosphate or sodium phosphate.
In order to simultaneously give consideration to the effects of reducing impedance and improving ion diffusion rate and tap density, in the embodiment of the application, the mass of pyrrole in S2 is 3% -5% of that of a product obtained in S1, and the molar ratio of pyrrole to cetyltrimethylammonium halide is 1.05-0.15.
Unreacted materials can also remain in the S1 and the S2, and very little carbon generated in the S1 can not participate in forming a three-dimensional network structure and is dissociated in a reaction system, and the S2 in the embodiment of the application also comprises a solid product obtained by cleaning solid-liquid separation with water or ethanol water solution.
The following examples are intended to further illustrate the invention in terms of several examples.
Example 1
The embodiment provides a polymer-coated lithium iron phosphate cathode material, and the preparation method comprises the following steps:
s1, uniformly mixing ferrous sulfate, lithium carbonate, lithium phosphate, iron phosphate (the molar ratio is 1; the total mass of the hydroxyethyl cellulose, the polyvinyl alcohol and the soluble starch is 4.5 percent of the total mass of the ferrous sulfate, the lithium carbonate, the lithium phosphate and the iron phosphate;
s2, dispersing 0.80g of pyrrole in 1M hydrochloric acid aqueous solution with the weight 30 times that of the pyrrole, adding 20g of the product obtained in the S1 and 0.43g of hexadecyl trimethyl ammonium bromide, uniformly mixing, slowly adding 71.5mg of ferric sulfate, reacting at 3 ℃ for 3 hours, carrying out solid-liquid separation, washing the solid product obtained by the solid-liquid separation with water, drying, and calcining at 355 ℃ for 3 hours to obtain the catalyst.
The microscopic morphology of the obtained polymer-coated lithium iron phosphate cathode material is shown in fig. 1.
Example 2
The embodiment provides a polymer-coated lithium iron phosphate cathode material, and the preparation method comprises the following steps:
s1, uniformly mixing iron phosphate, lithium acetate, lithium phosphate, ferrous phosphate (the molar ratio is 1; the total mass of the methylcellulose, the gelatin and the polyethylene glycol is 5 percent of the total mass of the ferric phosphate, the lithium acetate, the lithium phosphate and the ferrous phosphate;
s2, dispersing 0.80g of pyrrole in 1M hydrochloric acid aqueous solution with the weight 30 times that of the pyrrole, adding 20g of the product obtained in the S1 and 0.38g of hexadecyl trimethyl ammonium chloride, uniformly mixing, slowly adding 126.7mg of ferric perchlorate, reacting for 3 hours at the temperature of 3 ℃, carrying out solid-liquid separation, washing the solid product obtained by the solid-liquid separation with water, drying, and calcining for 3 hours at the temperature of 355 ℃, thus obtaining the material.
Example 3
The embodiment provides a polymer-coated lithium iron phosphate cathode material, and the preparation method comprises the following steps:
s1, uniformly mixing ferrous oxalate, lithium carbonate, lithium phosphate, sodium phosphate (the molar ratio is 5; the total mass of the ethyl cellulose and the polyacrylamide is 4 percent of the total mass of the ferrous oxalate, the lithium carbonate, the lithium phosphate and the sodium phosphate;
s2, dispersing 0.70g of pyrrole in 1M nitric acid aqueous solution with the weight being 30 times that of the pyrrole, adding 20g of S1 product and 0.33g of hexadecyl trimethyl ammonium chloride, uniformly mixing, slowly adding 62.6mg of ferric sulfate, reacting at 3 ℃ for 3.5 hours, carrying out solid-liquid separation, cleaning the solid product obtained by the solid-liquid separation with 30 v/v ethanol aqueous solution, drying, and calcining at 355 ℃ for 3 hours to obtain the material.
Example 4
The embodiment provides a polymer-coated lithium iron phosphate cathode material, and the preparation method comprises the following steps:
s1, uniformly mixing ferric chloride, lithium carbonate, lithium phosphate, iron phosphate (the molar ratio is 1; the total mass of the hydroxypropyl cellulose, the polyglycitol and the polyvinylpyrrolidone is 5.5 percent of the total mass of the ferric chloride, the lithium carbonate, the lithium phosphate and the ferric phosphate;
s2, dispersing 0.75g of pyrrole in 1M nitric acid aqueous solution with the weight being 30 times that of the pyrrole, adding 20g of the product obtained in S1 and 0.24g of hexadecyl trimethyl ammonium bromide, uniformly mixing, slowly adding 132.2mg of ferric bromide, reacting for 3.5 hours at the temperature of 3 ℃, carrying out solid-liquid separation, cleaning the solid product obtained by the solid-liquid separation by using 70 v/v ethanol aqueous solution, drying, and calcining for 3 hours at the temperature of 365 ℃, thus obtaining the pyrrole-containing catalyst.
Example 5
The embodiment provides a polymer-coated lithium iron phosphate cathode material, and the preparation method comprises the following steps:
s1, uniformly mixing ferrous chloride, lithium carbonate, lithium phosphate, sodium phosphate (the molar ratio is 5; the total mass of the hydroxypropyl methylcellulose and the polyvinylidene fluoride accounts for 6 percent of the total mass of the ferrous chloride, the lithium carbonate, the lithium phosphate and the sodium phosphate;
s2, dispersing 0.85g of pyrrole in 0.6M sulfuric acid aqueous solution with the weight 30 times that of the pyrrole, adding 20g of the product obtained in the S1 and 0.37g of hexadecyl trimethyl ammonium bromide, uniformly mixing, slowly adding 149.8mg of ferric bromide, reacting at the temperature of 3 ℃ for 2.5 hours, carrying out solid-liquid separation, washing the solid product obtained by the solid-liquid separation with water, drying, and calcining at the temperature of 345 ℃ for 3 hours to obtain the catalyst.
Example 6
The embodiment provides a polymer-coated lithium iron phosphate cathode material, and the preparation method comprises the following steps:
s1, uniformly mixing ferric sulfate, lithium acetate, lithium phosphate, iron phosphate (the molar ratio is 1; the total mass of the Arabic gum, the phenolic resin and the polyvinyl chloride is 3.5 percent of the total mass of the ferric sulfate, the lithium acetate, the lithium phosphate and the ferric phosphate;
s2, dispersing 0.9g of pyrrole in a 0.7M sulfuric acid aqueous solution with the weight being 30 times that of the pyrrole, adding 20g of the product obtained in the S1 and 0.56g of hexadecyl trimethyl ammonium chloride, uniformly mixing, slowly adding 43.5mg of ferric chloride, reacting at 3 ℃ for 3.5 hours, carrying out solid-liquid separation, cleaning the solid-liquid separation product by using 70 v/v ethanol aqueous solution, drying, and calcining at 335 ℃ for 3.5 hours to obtain the composite material.
Example 7
The embodiment provides a polymer-coated lithium iron phosphate cathode material, and the preparation method comprises the following steps:
s1, uniformly mixing iron phosphate, lithium acetate, lithium phosphate, ferrous phosphate (the molar ratio is 1; the total mass of the epoxy resin and the polymethacrylate is 3 percent of the total mass of the ferric phosphate, the lithium acetate, the lithium phosphate and the ferrous phosphate;
s2, dispersing 0.95g of pyrrole in 0.4M phosphoric acid aqueous solution with the weight 30 times that of the pyrrole, adding 20g of the product obtained in the S1 and 0.72g of hexadecyl trimethyl ammonium bromide, uniformly mixing, slowly adding 68.5mg of ferric nitrate, reacting at the temperature of 3 ℃ for 2.5 hours, carrying out solid-liquid separation, cleaning the solid-liquid separation product with 50% v/v ethanol aqueous solution to obtain a solid product, drying, and calcining at the temperature of 365 ℃ for 3.5 hours to obtain the product.
Example 8
The embodiment provides a polymer-coated lithium iron phosphate cathode material, and the preparation method comprises the following steps:
s1, uniformly mixing ferrous sulfate, lithium acetate, lithium phosphate, sodium phosphate (the molar ratio is 4; the total mass of the hydroxypropyl methylcellulose and the furan resin is 7 percent of the total mass of the ferrous sulfate, the lithium acetate, the lithium phosphate and the sodium phosphate;
s2, dispersing 0.65g of pyrrole in 0.8M hydrochloric acid aqueous solution with the weight 30 times that of the pyrrole, adding 20g of the product obtained in the S1 and 0.34g of hexadecyl trimethyl ammonium chloride, uniformly mixing, slowly adding 68.6mg of ferric perchlorate, reacting at the temperature of 3 ℃ for 2.5 hours, carrying out solid-liquid separation, washing the solid-liquid separated solid product with water, drying, and calcining at the temperature of 345 ℃ for 3.5 hours to obtain the catalyst.
Example 9
The embodiment provides a polymer-coated lithium iron phosphate cathode material, and the preparation method comprises the following steps:
s1, uniformly mixing ferrous chloride, lithium acetate, ferrous phosphate, sodium phosphate (the molar ratio is 1; the mass of the urea-formaldehyde resin is 1 percent of the total mass of the ferrous chloride, the lithium acetate, the ferrous phosphate and the sodium phosphate;
s2, dispersing 0.6g of pyrrole in 0.5M phosphoric acid aqueous solution with the weight 30 times that of the pyrrole, adding 20g of the product obtained in the S1 and 0.16g of hexadecyl trimethyl ammonium bromide, uniformly mixing, slowly adding 108.2mg of ferric nitrate, reacting at the temperature of 3 ℃ for 2 hours, carrying out solid-liquid separation, cleaning the solid product obtained by the solid-liquid separation by using 40 v/v ethanol aqueous solution, drying, and calcining at the temperature of 375 ℃ for 2 hours to obtain the product.
Example 10
The embodiment provides a polymer-coated lithium iron phosphate cathode material, and the preparation method comprises the following steps:
s1, uniformly mixing ferrous oxalate, lithium phosphate, iron phosphate (the molar ratio is 1; the mass of the polyacrylic resin is 8% of the total mass of the ferrous oxalate, the lithium phosphate and the ferric phosphate;
s2, dispersing 1.00g of pyrrole in 1.2M nitric acid aqueous solution with the weight being 30 times that of pyrrole, adding 20g of the product obtained in the S1 and 0.72g of hexadecyl trimethyl ammonium chloride, uniformly mixing, slowly adding 24.2mg of ferric chloride, reacting at the temperature of 3 ℃ for 4 hours, carrying out solid-liquid separation, washing the solid-liquid separation product with water, drying, and calcining at the temperature of 325 ℃ for 4 hours to obtain the material.
Example 11
The embodiment provides application of a polymer-coated lithium iron phosphate cathode material in preparation of a lithium ion battery.
Lithium ion batteries were prepared from the polymer-coated lithium iron phosphate positive electrode materials prepared in examples 1 to 10, and the negative electrode materials were all carbon negative electrode materials.
The obtained lithium ion battery was tested for specific discharge capacity, cycle performance, and lithium ion mobility, and the results are shown in table 1:
TABLE 1 results of specific discharge capacity, cycle performance and lithium ion mobility measurement (examples)
Figure 42180DEST_PATH_IMAGE001
Comparative example 1
The comparative example provides a polymer-coated lithium iron phosphate cathode material, and the preparation method comprises the following steps:
s1, uniformly mixing ferrous sulfate, lithium carbonate, lithium phosphate, iron phosphate (the molar ratio is 1; the total mass of the hydroxyethyl cellulose, the polyvinyl alcohol and the soluble starch is 8 percent of the total mass of the ferrous sulfate, the lithium carbonate, the lithium phosphate and the iron phosphate;
s2, dispersing 0.80g of pyrrole in 1M hydrochloric acid aqueous solution with the weight being 30 times that of pyrrole, adding 20g of S1 obtained product and 0.43g of hexadecyl trimethyl ammonium bromide, uniformly mixing, slowly adding 71.5mg of ferric sulfate, reacting at 3 ℃ for 3 hours, carrying out solid-liquid separation, washing the solid product obtained by the solid-liquid separation with water, drying, and calcining at 355 ℃ for 3 hours to obtain the material.
Comparative example 2
The comparative example provides a polymer-coated lithium iron phosphate cathode material, and the preparation method comprises the following steps:
s1, uniformly mixing ferrous sulfate, lithium carbonate, lithium phosphate, iron phosphate (the molar ratio is 1; the total mass of the hydroxyethyl cellulose, the polyvinyl alcohol and the soluble starch is 8 percent of the total mass of the ferrous sulfate, the lithium carbonate, the lithium phosphate and the iron phosphate;
s2, dispersing 0.80g of pyrrole in 1M hydrochloric acid aqueous solution with the weight being 30 times that of pyrrole, adding 20g of S1 obtained product and 0.32g of sodium dodecyl sulfate, uniformly mixing, slowly adding 71.5mg of ferric sulfate, reacting at 3 ℃ for 3 hours, carrying out solid-liquid separation, washing the solid product obtained by the solid-liquid separation with water, drying, and calcining at 355 ℃ for 3 hours to obtain the catalyst.
Comparative example 3
The comparative example provides a polymer-coated lithium iron phosphate positive electrode material, and the preparation method comprises the following steps:
s1, uniformly mixing ferrous sulfate, lithium carbonate, lithium phosphate, iron phosphate (the molar ratio is 1; the total mass of the hydroxyethyl cellulose, the polyvinyl alcohol and the soluble starch is 8 percent of the total mass of the ferrous sulfate, the lithium carbonate, the lithium phosphate and the iron phosphate;
s2, dispersing 0.80g of pyrrole in 1M hydrochloric acid aqueous solution with the weight 30 times that of the pyrrole, adding 20g of the product obtained in the S1 and 0.42g of sodium dodecyl benzene sulfonate, uniformly mixing, slowly adding 71.5mg of ferric sulfate, reacting at 3 ℃ for 3 hours, carrying out solid-liquid separation, washing the solid product obtained by the solid-liquid separation with water, drying, and calcining at 355 ℃ for 3 hours to obtain the catalyst.
The positive electrode materials obtained in comparative examples 1 to 3 were respectively prepared into lithium ion batteries by the method of example 11, and the discharge specific capacity, the cycle performance, and the lithium ion mobility were measured, and the results are shown in table 2:
TABLE 2 results of specific discharge capacity, cycle performance and lithium ion mobility measurement (comparative example)
Figure 640652DEST_PATH_IMAGE002
Therefore, the lithium ion battery made of the lithium iron phosphate cathode material prepared by the comparative example has lower discharge specific capacity, cycle performance and lithium ion mobility than the lithium ion battery made of the lithium iron phosphate cathode material prepared by the embodiment.
The above description is intended to be illustrative of the preferred embodiment of the present invention and should not be taken as limiting the invention, but rather, the invention is intended to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

Claims (10)

1. A preparation method of a polymer-coated lithium iron phosphate positive electrode material is characterized by comprising the following steps:
s1, uniformly mixing iron salt, lithium salt, phosphate and a high-molecular organic polymer in a solvent, carrying out solid-liquid separation, drying and grinding the obtained solid, heating to 80-200 ℃ at a heating rate of 5-15 ℃/min, reacting for 2-4 h, heating to 300-450 ℃ at a heating rate of 3-7 ℃ for reacting for 1-3 h, heating to 600-750 ℃ at a heating rate of 5-10 ℃ for reacting for 5-10h, and naturally cooling after the reaction is finished; the molar ratio of iron element, lithium element and phosphorus element in the ferric salt, the lithium salt and the phosphate is 1 to 095 to 1.05, and the mass of the high molecular organic polymer is 1 to 8 percent of the total mass of the ferric salt, the lithium salt and the phosphate;
and S2, dispersing pyrrole in an acidic aqueous solution, adding the product obtained in the step S1 and hexadecyl trimethyl ammonium halide, uniformly mixing, slowly adding a water-soluble ferric salt, reacting at 0 to 5 ℃ for 2 to 4 hours, carrying out solid-liquid separation, and calcining the obtained solid at 300 to 400 ℃ for 2 to 4 hours to obtain the lithium iron phosphate cathode material.
2. The method for preparing the polymer-coated lithium iron phosphate cathode material according to claim 1, wherein the high molecular organic polymer is at least one selected from the group consisting of methylcellulose, ethylcellulose, hydroxyethyl cellulose, hydroxypropyl methylcellulose, gum arabic, gelatin, polyacrylamide, polyvinyl alcohol, polyethylene glycol, polyalditol, soluble starch, polyvinylpyrrolidone, phenol resin, epoxy resin, urea resin, furan resin, polyacrylic resin, polyvinylidene fluoride, polyvinyl chloride, and polymethacrylate; and/or
The lithium salt is selected from at least one of lithium carbonate, lithium nitrate, lithium sulfate, lithium acetate and lithium phosphate; and/or
The ferric salt is at least one selected from ferric phosphate, ferrous oxalate, ferric chloride, ferrous chloride, ferric sulfate and ferrous sulfate; and/or
The phosphate is selected from at least one of ferric phosphate, ferrous phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate or sodium phosphate; and/or
The cetyl trimethyl ammonium halide is cetyl trimethyl ammonium bromide or cetyl trimethyl ammonium chloride.
3. The method for preparing the polymer-coated lithium iron phosphate cathode material according to claim 2, wherein the high molecular organic polymer is a combination of methylcellulose, gelatin and polyethylene glycol, a combination of ethylcellulose and polyacrylamide, a combination of hydroxyethylcellulose, polyvinyl alcohol and soluble starch, a combination of hydroxypropylcellulose, polyglycitol and polyvinylpyrrolidone, a combination of hydroxypropylmethylcellulose and polyvinylidene fluoride, a combination of arabic gum, phenol resin and polyvinyl chloride, a combination of epoxy resin and polymethacrylate, or the like, a combination of hydroxypropylmethylcellulose and furan resin, or a urea-formaldehyde resin or polyacrylic resin alone; and/or
The lithium salt is selected from at least one of lithium carbonate, lithium acetate and lithium phosphate; and/or
The phosphate is selected from at least one of ferric phosphate, ferrous phosphate or sodium phosphate.
4. The method for preparing the polymer-coated lithium iron phosphate cathode material according to claim 3, wherein the high molecular organic polymer is a combination of methylcellulose, gelatin and polyethylene glycol or a combination of ethylcellulose and polyacrylamide; and/or
The lithium salt is the combination of lithium carbonate and lithium phosphate or the combination of lithium acetate and lithium phosphate.
5. The preparation method of the polymer-coated lithium iron phosphate cathode material of claim 1, wherein the mass of pyrrole in S2 is 3-5% of that of a product obtained in S1, and the molar ratio of pyrrole to cetyltrimethylammonium halide is 1.05-0.15.
6. The method for preparing the polymer-coated lithium iron phosphate cathode material according to claim 1, wherein the concentration of hydrogen ions in the acidic aqueous solution is 0.8 to 1.5M.
7. The preparation method of the polymer-coated lithium iron phosphate cathode material according to claim 1, wherein the water-soluble ferric salt is at least one selected from the group consisting of ferric chloride, ferric bromide, ferric sulfate, ferric nitrate and ferric perchlorate, and a molar ratio of iron ions in the ferric salt to the pyrrole is from 0.01 to 0.05.
8. The preparation method of the polymer-coated lithium iron phosphate positive electrode material according to any one of claims 1 to 7, wherein S2 further comprises washing a solid product obtained by solid-liquid separation with water or an aqueous ethanol solution.
9. A polymer-coated lithium iron phosphate cathode material is characterized in that the polymer-coated lithium iron phosphate cathode material is prepared by the preparation method of the polymer-coated lithium iron phosphate cathode material according to any one of claims 1 to 8.
10. The use of the polymer-coated lithium iron phosphate positive electrode material of claim 9 in the preparation of a lithium ion battery.
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