Structure and properties of the MlNi5 system with tin substitution

The hydriding performance, electrochemical properties and structure of MlNi5−xSnx (x=0∼0.5) and LaNi5−xSnx (x=0–0.2) hydrogen storage alloys were investigated by pressure–composition isotherms, electrochemical measurements, XRD and atomic parameters. The substitution of Ni by Sn leads to an increase of the unit cell volume and decrease of the electron concentration. The unit cell volume increase decreases the plateau pressure and improves the hydride stability and charge–discharge cycle life. The main factor which influences the standard enthalpy of the hydriding reaction is the number of the outer orbit electrons and not the atomic size factor. With a small amount of tin substitution (such as Sn=0.2), the cycle life increases by 52% (0.5C) and 42% (1.0C), but maximum discharge capacity decreases only by 3.0 and 3.5%, respectively.