Lithium-ion secondary batteries

Abstract

A positive electrode active material for lithium-ion secondary batteries with high capacity and excellent charge-discharge cycle characteristics is provided. The positive electrode active material comprises lithium, cobalt, magnesium, oxygen, and fluorine. When the pattern obtained by powder X-ray diffraction using CuKα1 rays is subjected to Ritwald analysis, a crystal structure with space group R⁻³m is observed, with an a-axis lattice constant greater than 2.814 × 10⁻¹⁰ m and less than 2.817 × 10⁻¹⁰ m, and a c-axis lattice constant greater than 14.05 × 10⁻¹⁰ m and less than 14.07 × 10⁻¹⁰ m. When subjected to X-ray photoelectron spectroscopy analysis, the relative value of magnesium concentration at a cobalt concentration of 1 is greater than 1.6 and less than 6.0.

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