High Rate Transfer Mechanism of Lithium Ions in Lithium-Tin and Lithium-Indium Alloys for Lithium Batteries

The lithium-tin alloy electrode, as an artificial solid-electrolyte interphase (SEI) material with outstanding electrochemical properties, is promising to realize advanced next-generation lithium batteries. Experimental explorations on Li-Sn alloy have already achieved great success, while theoretical understanding on the mechanism of lithium-ion transport is still lacking. In this work, we carried out first-principles simulations and developed a theoretical methodology to reveal how a lithium ion diffuses in different lithium-tin phases and further elaborated the origin of low diffusion barriers. The simulation results indicate that two kinds of diffusion modes, interstitial and vacancy diffusion, will compete with each other with the increase in lithium concentration. Furthermore, the underlying mechanisms of direct hopping and coordinate process are also different in different Li-Sn/In phases. It is interesting to discover that during the lithiation process of alloy phases, the high-rate transport channel will gradually transform from the interstitial direct-hopping to vacancy mechanism and finally to the interstitial knock-off mechanism. This work provides a thorough theoretical understanding on lithium-ion transportation, further opening up the possibility of synthesizing or modifying SEI materials with enhanced Li conductivity in novel Li-ion battery designs.