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

The active material includes a composite metal fluoride containing Al, F, and a metal element Me and can occlude and release fluoride ions. The metal element Me includes at least one transition metal element selected from the group consisting of Ti, Fe, Co, Ni, and Cu and/or at least one alkaline-earth metal element selected from the group consisting of Ca, Ba, and Sr.