Comparison of Storage Mechanisms in RuO2, SnO2, and SnS2 for Lithium-Ion Battery Anode Materials

A comparison of the molecular mechanisms of lithium sorption in RuO2, SnO2, and SnS2 was conducted with first-principles calculations. The calculated discharge curves for lithium absorption qualitatively agreed with experiment for the three materials. Our computations show that high-capacity lithium sorption in RuO2 beyond the stoichiometric conversion limit is due to interfacial storage, i.e., lithium absorption in the interface between the metallic ruthenium islands and the lithium oxide produced by conversion. Lithium sorption beyond the conversion limit in SnO2 and SnS2 is due to alloying, but interfacial storage is also found to contribute beyond the alloying limit. Therefore, interfacial storage appears to be a universal high-capacity mechanism for metal oxide and metal sulfide materials, accounting at least partially for the observed capacity beyond stoichiometric limits. Among the three materials examined, SnS2 is shown to expand the least with lithium sorption, furthering its promise as an anode material for Li-ion batteries.