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

The present disclosure provides a negative electrode active material for a fluoride ion secondary battery, the negative electrode active material including yttrium fluoride, where a crystallite size of the negative electrode active material is more than 7 nm and less than 27 nm. A fluoride ion secondary battery 10 of the present disclosure includes a positive electrode 2, a negative electrode 4, and an electrolyte layer 3 disposed between the positive electrode 2 and the negative electrode 4, where the negative electrode 4 includes the negative electrode active material of the present disclosure.