Combinatorial Study of Snsub 1−xCosub x (0<x<0.6) and Sn[sub 0.55Cosub 0.45]sub 1−yCsub y (0<y<0.5) Alloy Negative Electrode Materials for Li-Ion Batteries

Using combinatorial and high-throughput materials science methods, we have studied thin-film libraries of and alloy negative electrode materials for Li-ion batteries. Over one hundred compositions have been studied carefully by X-ray diffraction and electrochemical methods. The system is found to be amorphous for . For , the amorphous phase coexists with electrochemically inactive crystalline . Amorphous materials with show a specific capacity of , but differential capacity, , vs potential is not stable vs cycling indicating irreversible atomic-scale changes in the alloy, most likely due to tin aggregation. Adding carbon to this system, for example in the library, has a number of positive effects. First, all alloys with are amorphous, with carbon directly incorporated within the amorphous phase. Second, the addition of carbon increases, not decreases, the specific capacity from about for for . Third, compositions with show differential capacity vs potential curves that do not change during charge-discharge cycling, indicating that such alloys are stable on the atomic scale and hence are extremely good candidates for long cycle life. Stability increases with carbon content up to .