Synthesis of Single-Phase LiSi by Ball-Milling: Electrochemical Behavior and Hydrogenation Properties

The Li-Si phase diagram shows the existence of four stable phases Li 12 Si 7 , Li 7 Si 3 , Li 13 Si 4 and Li 22 Si 5 . In addition, Zintl phase LiSi, usually prepared under high temperature-pressure (873 K-4 GPa), has recently been added into the diagram as LiSi is also indeed stable under ambient conditions. A novel synthesis method for single-phase LiSi by highly energetic ball-milling is detailed herein. LiSi is investigated for two different applications: a negative electrode for lithium-ion batteries and a hydrogen storage material. Up to now, the electrochemistry of LiSi has not yet been explored. In order to obtain metastable Li 15 Si 4 at deep discharge, it is crucial to first form an amorphous Li-poor silicide by oxidation. Subsequent electrochemical behavior after the first cycle follows closely to that of classical silicon with fast capacity fading. On the contrary, when LiSi is first oxidized and x is kept below 1 in Li x Si, a unique electrochemical signature is observed with an initial capacity of 870 mAh.g −1 and good retention for the first 10 cycles. Concerning the hydrogenation properties, 2.8 wt% H 2 can be absorbed by LiSi at 573 K to form LiH + Si, but the reaction is irreversible because of the slow LiSi formation kinetics.