Alkaline electrolyte storage battery having an anode formed of an active material composition

1-yyt-zz An active material composition for an alkaline storage battery comprises a) an alloy capable of forming a hydride, of formula RMgNiMin which R is La, optionally substituted by Nd and/or Pr, M is at least one element chosen from the group comprising Mn, Fe, Al, Co, Cu, Zr and Sn, in which 0.1≦y≦0.4, 3.2≦t≦3.5, and z≦0.5, and of which the equilibrium hydrogen pressure with the alloy, for a hydrogen insertion into the alloy of 0.5 H/Metal at 40°, is less than 0.7 bar, and b) a yttrium-based compound in a mixture with alloy a).