The impact of the addition of rare earth elements to Si1-xSnx negative electrode materials for Li-ion batteries

The impact of the addition of cerium and lanthanum-rich misch metal (MM, a mixture of rare earth elements) to silicon-tin alloys was studied using combinatorial and high-throughput materials science methods. Combinatorial libraries of Si1-xSnx, Si1-xMMx, and Si1-x-ySnxMMy were prepared using the Dalhousie University combinatorial sputtering systems. The addition of MM increases the crystallization temperature of amorphous Si1-x-ySnxMMy alloys, which makes their preparation in the amorphous state more likely by rapid solidification techniques like melt-spinning. Increasing the atomic fraction of MM in both Si1-xMMx and Si1-x-ySnxMMy amorphous alloys decreases the reversible specific capacity of the alloys for lithium, but does not negatively impact capacity retention. Attractive compositions were identified in pseudoternary Si1-x-ySnxMMy system that: (1) remain amorphous during charge-discharge cycling between 0.005 and 1.5 V vs Li/Li+; (2) show excellent capacity retention; (3) have specific capacities as large as 1000 mAh/g; and (4) may be compatible with rapid solidification techniques for the production of amorphous materials. In particular, amorphous alloys containing 20-40 atom % tin and 15-20 atom % MM exhibited excellent capacity retention and reversible specific capacities near 800-1000 mAh/g. (C) 2006 The Electrochemical Society.