Negative active material

摘要

PURPOSE: A negative electrode active material is provided to have high capacity performance, and to maintain battery efficiency and life time remarkably. CONSTITUTION: A negative electrode active material comprises an A phase containing active silicon, and a B phase having a metal alloy matrix containing silicon and transition metal. The negative electrode active material satisfies the general formula 1: X >= 500 Hv. In formula, X is the Vickers hardness of the metal alloy matrix measured at 100 gf. In case of ex situ XRD analysis before charging/discharging, a peak, except peaks based on the active silicon of the A phase, can be detected after charging/discharging.