ACTIVE MATERIAL, NEGATIVE ELECTRODE ACTIVE MATERIAL, AND FLUORIDE ION SECONDARY BATTERY

An active material contains a composite metal fluoride containing Al, F, and Ti and can occlude and release fluoride ions. The composite metal fluoride is represented by a compositional formula: AlTiF, where x satisfies 0.01≤x≤0.9 and y satisfies, 2≤y≤4.