NEGATIVE ELECTRODE ACTIVE MATERIAL, NEGATIVE ELECTRODE, AND BATTERY

Provided is a negative electrode active material which is excellent in capacity, capacity retention ratio, and a coulombic efficiency when charging/discharging is repeated. The chemical composition of the alloy particles of the negative electrode active material of the present disclosure includes 0.50 to 3.00 mass % of oxygen, and alloy elements containing Sn: 13.0 to 40.0 at % and Si: 6.0 to 40.0 at %, with the balance being Cu and impurities. The structure of the alloy particles includes: one or more types selected from the group consisting of a phase having a D0structure, and a δ phase; one or more types selected from the group consisting of an ε phase and an η′ phase; and a SiOphase (x=0.50 to 1.70). The SiOphase (x=0.50 to 1.70) has a volume fraction of 5.0 to 60.0% and the η′ phase has a volume fraction of 0 to 60.0%.