RU2615697C1 - METHOD FOR PRODUCING CATHODE MATERIAL BASED ON SYSTEM Li2FeSiO4 - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: as initial component, Aerosil (SiO₂) nanoscale powder with a surface area of 350-380 m²/g is selected and dried in vacuo for 1-3 hours. Iron oxide and lithium oxide films with a thickness of 1-3 nm are coated on aerosil powder by means of the MLT method to achieve the stoichiometric composition Li₂FeSiO₄ and the diffusion mixing of the resulting composition Li₂FeSiO₄ is carried out at 300°C to 500°C for 8-15 hours.

EFFECT: invention allows to obtain a cathode material having a high specific surface area and high specific capacity, with the uniform distribution of the chemical composition in the total powder volume and the defect-free crystal structure.

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Description

The invention relates to the electrical field and can be used in storage batteries of transport and space systems with improved specific characteristics.

A known method of obtaining a composite cathode material Li ₂ FeSiO ₄ / graphene hydrothermal method. Solutions of Fe (NO ₃ ) ₃ ⋅ 9H ₂ O, tetraethylorthosilicate, and LiOH и 2H ₂ O in ethylene glycol were used as initial components, they were mixed to obtain a dark green colloidal solution, which was placed in an autoclave and kept there at a temperature of 200 ° C in within 6 days. To obtain a composite material Li ₂ FeSiO ₄ / graphene, 0.3 g of the obtained Li ₂ FeSiO ₄ powder was taken and homogeneously distributed in 30 ml of water with the addition of 0.03 g of PVP and 0.03 g of graphene. The resulting suspension was dried by freezing, and then heat treated for a certain time in an argon atmosphere [Li ₂ FeSiO ₄ nanorods connected with graphene for high-performance batteries // J. Mater. Chem. A, 2015, 3, pp. 9601-9608].

The disadvantages of the method are the multi-stage process, the difficulty in obtaining a defect-free structure and a pure chemical composition, the duration of exposure in an autoclave, low cyclic stability of the obtained material, as well as low specific surface area of the obtained powder.

A known method of producing porous microspheres of the Li ₂ FeSiO ₄ / C system using spray drying technology. As initial components, iron powder and citric acid are used, which are mixed in deionized water. After thorough mixing, a silicon source is added to the solution and sprayed in a spray dryer at a temperature of 108 ° C. The result is a green powder. The green powder is heat treated in a horizontal tubular furnace in an Ar stream at a temperature of 700 ° C for 10 h in order to obtain the final compound Li ₂ FeSiO ₄ / C [Preparation and characterization of porous microspheres of the Li ₂ FeSiO ₄ / C system using spray drying technology // Int. J. Electrochem. Sci., 10, 2015, pp. 4453-4460].

The disadvantages of the method are the multi-stage process, the difficulty in obtaining a defect-free structure and pure chemical composition, the difficulty of maintaining the desired acidity of the solution during synthesis, low specific capacity of the obtained cathode powder, low specific surface of the obtained powder.

A known method of producing a cathode material Li ₂ FeSiO ₄ / C by conducting a solid-phase reaction in vacuum, selected as the prototype [Morphology and electrical properties of the system Li ₂ FeSiO ₄ / C obtained by conducting a solid-phase reaction in vacuum // Materials Chemistry and Physics, 139, 2013, pp. 550-556]. To obtain the powder of the Li ₂ FeSiO ₄ / C system, SiO ₂ , LiCH ₃ COO⋅2H ₂ O and FeC2O4⋅2H2O were used as initial components, all components were taken in a stoichiometric ratio. Initially, all the initial components were mixed in an agate mortar, then glucose was taken as a carbon source and also intensively mixed. Then, the resulting mixture was heat treated for 10 hours at a temperature of 650 ° C in vacuum, the pressure was 0.1 MPa.

The disadvantages of the method are the difficulty in obtaining a defect-free structure and pure chemical composition, low specific capacity of the obtained cathode powder, low specific surface area of the obtained powder, as well as an uneven distribution of the chemical composition by volume.

The objective of the invention is to obtain a cathode powder material based on the Li ₂ FeSiO _{4 system} with a high specific surface and high specific capacity, uniform distribution of chemical composition throughout the volume and defect-free crystal structure.

To solve this problem, a method for producing a cathode powder material based on the compound Li ₂ FeSiO _{4 is} proposed. As the initial component, nanosized aerosil powder (SiO ₂ ) with a specific surface area of 350-380 m ² / g was selected, then the powder was placed in the installation for thin films deposition by molecular layering and drying was carried out in vacuum for 1-3 hours. After drying, thin films of iron oxide and lithium oxide were alternately applied to the powder until the stoichiometric composition of Li ₂ FeSiO _{4 was} reached; the thickness of iron oxide and lithium oxide varied from 1-3 nm. Next, diffusion mixing of the obtained composition of Li ₂ FeSiO _{4 was} carried out at a temperature of 300 ° C to 500 ° C for 8-15 hours to form a homogeneous defect-free structure of Li ₂ FeSiO ₄ .

When used as an initial component of aerosil, the finished material Li ₂ FeSiO ₄ has a specific capacity of the order of 300 m ² / g, which can significantly increase the diffusion coefficient of lithium ions from the volume of the cathode material, which in turn significantly increases the specific capacity. To achieve the stoichiometric composition of the Li ₂ FeSiO _{4 system} by applying thin films of iron oxide and lithium oxide to aerosil, molecular layering technology was used [Atomic layer deposition: from precursors to thin films // Thin solid films, 2002, 409, p. 138-146 ]. Before starting the molecular layering process, it is required to remove all moisture from the aerosil volume to ensure the best conformity of the coatings, for which drying is carried out. The molecular layering method is based on the passage of a self-controlled heterogeneous reaction, which allows one to obtain defect-free films of oxide systems uniformly on the entire surface of the aerosil, which leads to a uniform defect-free structure with a uniform distribution of chemical elements throughout the volume of the obtained cathode material. During the deposition of thin films, their thickness varied from 1-3 nm, the thicknesses of this order allow diffusion mixing of chemical elements in volume even at low temperatures from 300 to 500 ° C, as a result of which the crystal structure of the Li ₂ FeSiO _{4 system} with various lattice parameters.

As the initial component, nanosized aerosil powder (SiO ₂ ) with a specific surface area range of 350-380 m ² / g was chosen. When using aerosil with a specific surface of less than 350 m ² / g, the final cathode material, after applying lithium oxides and iron oxides, will not have a sufficient diffusion coefficient for lithium, which will lead to a deterioration in electrochemical characteristics. When using aerosil with a specific surface of more than 380 m ² / g, the final cathode material, due to its high activity, will dissolve in the electrolyte. The drying time of aerosil is from 1 to 3 hours, when the aerosil is in vacuum for less than 1 hour, all adsorbed moisture does not evaporate completely, which will lead to defects in the applied films, when drying for more than 3 hours, surface functional groups begin to fly away from the aerosil surface, which also leads to deterioration of chemisorption between aerosil and oxides of lithium and iron. The thickness of the coatings of iron oxide and lithium oxide applied to the aerosil was determined in the range of 1-3 nm, with a thickness of less than 1 nm the formation of conformal films is not provided, and thicknesses of more than 3 nm do not allow full diffusion mixing at temperatures of 300-500 ° C, which in turn, will lead to the formation of defects in the crystal structure and a decrease in electrochemical characteristics. With diffusion stirring at a temperature of at least 300 ° C and at least 8 hours, lithium and iron will not be completely introduced into the aerosil matrix, which will lead to the formation of a non-stoichiometric composition. During heat treatment for more than 15 hours at a temperature of more than 500 ° C, the growth of aerosil particles coated with lithium oxide and iron oxide will occur, which in turn will lead to a decrease in the specific surface and, therefore, to a decrease in the specific capacity of the finished cathode material.

To obtain a cathode powder material based on the Li ₂ FeSiO ₄ system, aerosil with a specific surface area of 350-380 m ² / g was selected as the initial component. After drying in vacuum for 1-3 hours, thin layers of lithium oxide and iron oxide 1 to 3 nm thick were alternately applied to aerosil by molecular layering to obtain the stoichiometric composition of Li ₂ FeSiO ₄ . Then conducted diffusion mixing at a temperature of 300-500 ° C for 8-15 hours, (table 1)

The synthesized cathode powder material based on the Li ₂ FeSiO _{4 system} has a high specific surface and high specific capacity, a uniform distribution of the chemical composition throughout the powder and a defect-free crystal structure due to the use of certain materials and the use of original technology, which is characterized by the use of the molecular layering method of lithium oxides and iron followed by diffusion mixing.

Claims (1)

A method of producing a cathode material based on the Li ₂ FeSiO _{4 system} , including the selection of a powder based on silicon oxide, characterized in that nanosized aerosil powder with a specific surface area of 350-380 m ² / g is selected as silicon oxide, dried in vacuum for 1- 3 hours, films of iron oxide and lithium oxide with a thickness of 1-3 nm are applied to the aerosil powder by molecular layering to achieve the stoichiometric composition of Li ₂ FeSiO ₄ , diffusion mixing of the obtained composition of Li ₂ FeSiO _{4 is} carried out at a temperature of 300 ° C to 500 ° C during e 8-15 hours for the formation of a defect-free structure of Li ₂ FeSiO ₄ .