Effects of Cr addition on the microstructures and electrochemical properties of as-cast and quenched La2Mg(Ni0.85Co0.15)9 electrode alloys

A trace of Cr was added in La-Mg-Ni based (PuNi3-type) electrode alloy and rapid quenching technique was used in order to improve its cycle stability. The electrode alloys La2Mg(Ni0.85Co0.15)9Crx (x = 0, 0.1, 0.2, 0.3, 0.4) were prepared by casting and rapid quenching, and the effects of Cr addition on the microstructures and electrochemical performances of the as-cast and quenched alloys were investigated in detail. The results obtained by XRD, SEM and TEM show that the as-cast and quenched alloys have a multiphase structure, including two main phases of (La, Mg)Ni3 and LaNi5, a residual phase of LaNi2. The Cr addition has an inappreciable influence on the phase compositions of the alloys, whereas it changes the phase abundance of the alloys. The results obtained by the electrochemical measurement indicate that the Cr addition obviously enhances the cycle stability of the as-cast and quenched alloys and leads to a different extent decrease of the discharge capacity of the alloys. When the amount of Cr addition changes incrementally from 0 to 0.4, the discharge capacity of the as-cast alloy decreases from 396.5 to 355.6 mAh/g, and the cycle life increases from 72 to 97 cycles. For the as-quenched (30 m/s) alloys, the discharge capacity decreases from 364.6 to 334.2 mAh/g, and the cycle life increases from 100 to 131 cycles. The Cr addition improves the discharge voltage characteristic and activation capability of the as-cast alloys, but it slightly decreases the activation capability of the as-quenched alloys.