LiFePO4 (lithium iron phosphate) positive electrode material with specific morphology and structure and lithium secondary battery

Abstract

The present invention relates to a lithium iron phosphate anode material with specific morphology and structure and a secondary battery using the same. The carbon-coated lithium iron phosphate anode material with specific morphology and structure of the present invention is characterized in that: the material contains spherical or spherical-like secondary particles prepared from sheet-shaped primary particles through conglomeration. A space exists among the primary particles; the average particle size of the secondary particles is 12 microns to 28 microns; the primary particles are sheet-shaped carbon-coated lithium iron phosphate particles; and the average particle size and average thickness of the primary particles in the two-dimensional plane are respectively 0.2 microns to 1 micron and 60 nanometers to 90 nanometers. The carbon layer evenly coated on the surface of the primary particles of the lithium iron phosphate anode material with specific morphology and structure of the present invention can ensure the conductive capability of the active material, maximally utilize the capacity of the active material, and improve large-current charge-discharge property of the material. In addition, the form of secondary particles performs excellently in aspects such as the active substance utilization rate, the large-current charge-discharge capability, and the capacity retention ratio of the electrode material with circulation.

Description

Technical field [0001] The invention relates to a lithium iron phosphate cathode material, in particular to a lithium iron phosphate anode material with a specific morphology structure and a secondary battery using the same. Background technique [0002] Since Goodenough's research group discovered lithium metal phosphate in 1994, and in 1997, AKPadhi first reported that olivine-type lithium iron phosphate has the function of lithium removal and lithium insertion. Lithium iron phosphate has high specific capacity, long cycle life, safety, and raw material. The advantages of abundant sources, cheapness, and environmental friendliness have been extensively studied, and have become an ideal cathode material for the production of lithium-ion batteries, especially lithium-ion power batteries. In recent years, with the strong support of governments of various countries, the commercial application of lithium iron phosphate power batteries has been increasing. [0003] With the continuous...

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Problems solved by technology

For example, CN101752564A discloses a method of synthesizing lithium iron phosphate with a one-dimensional nanostructure by hydrothermal synthesis. Under the condition that the feeding rate is suitable, the crystal morphology is controlled by adjusting the pH value of the reaction system to obtain nano crystalline, but this one-dimensional nanostructure is not conducive to the use of minimal binders during electrode preparation

[0004] CN102066241A discloses a method for preparing lithium iron phosphate with α-FeOOH. Scanning electron microscope results of the obtained lithium iron phosphate show that the powder has a spherical morphology with a medium spherical size (about 30 microns), and a single sphere contains LiFePO 4 primary particles, and there are gaps between the primary particles, but Fe 3+ (i.e. α-FeOOH) as a raw material, it is necessary to use a reducing agent (including sugar raw materials, such as sucrose) in the reaction to convert Fe 3+ reduced to Fe 2+ , the method adds sucrose to the reaction system during the synthesis of lithium iron phosphate, which leads to the following technical problems: one is that the amount of sucrose cannot be accurately calculated, including the amount of sucrose used to reduce Fe 3+ The amount used to form the carbon coating layer and the amount used to form the carbon coating layer; the second is to affect the dispersion uniformity and coating thickness of the carbon coating layer; the third is that the method adds the lithium salt solution and the iron solution to the solution and then adds phosphoric acid and Sucrose, that is, when sucrose is added, lithium iron phosphate is not produced in the reaction system, and all that exists in the system are intermediate products, and the coating of lithium iron phosphate with sucrose cannot be realized, resulting in carbon dioxide in the generated product particles. The layer covers the lithium iron phosphate particles incompletely, which affects the electrical conductivity of the active particles and the electrochemical performance of the product.

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