Phase changes in electrochemically lithiated silicon at elevated temperature

Samples of LixSi with average compositions of Li1Si, Li2Si, and Li3Si as well as the metastable crystalline Li15Si4 alloy were prepared electrochemically. The phase changes in these samples at elevated temperature were explored using differential scanning calorimetry and X-ray diffraction. The amorphous LixSi phase present in the Li1Si and Li2Si samples transformed first, near 190 degrees C, to Li7Si3, instead of the expected Li12Si7 based on the Li-Si phase diagram. The amorphous component in the Li3Si sample apparently has a higher average lithium content and transformed to both Li15Si4 and Li7Si3 near 190 degrees C. At higher temperatures all the samples transformed into the thermodynamically stable phases expected based on their average compositions and the Li-Si phase diagram. The metastable crystalline Li15Si4 apparently transforms into thermodynamically stable phases in one step. (c) 2006 The Electrochemical Society.