Simple model for the capacity of amorphous silicon-aluminum-transition metal negative electrode materials

Thin-film libraries of Si-Al-M (M = Cr, Fe, Mn, Ni) negative electrode materials were characterized using combinatorial and high-throughput techniques. Transition metal content had a large effect on capacity, such that alloys with more than ca. 20-50 atom % M did not alloy with Li during room temperature or 70 degrees C charge-discharge cycling. The 200 mA h/g contour line was used to separate those compositions that readily alloyed with Li from those that did not. This contour line also approximately connects the lowest M content equilibrium crystalline phases. We propose that all Si-Al-M crystalline equilibrium phases are inactive. The capacity of a given composition of Si-Al-M can be approximated, to first order, using only the equilibrium ternary phase diagram. These results could have a large impact on the study of other, more complex, amorphous alloy negative electrode material systems. (C) 2006 The Electrochemical Society.