Molecular Mechanisms for the Lithiation of Ruthenium Oxide Nanoplates as Lithium-Ion Battery Anode Materials: An Experimentally Motivated Computational Study

Abstract

First-principles computational studies were used to calculate discharge curves for lithium in RuO2 and to understand the molecular mechanism of lithium sorption into crystalline bulk RuO2. These studies were complemented by experiments to provide new insights into the molecular mechanisms for the first and subsequent discharges of RuO2 anodes in lithium ion batteries. RuO2 nanoplates show slow fading of capacity over multiple cycles, retaining 76% of their original capacity after 20 cycles. The calculated discharge curves for lithium in RuO2 lattice show qualitative agreement with experimental discharge curves for RuO2 nanoplates. The molecular level analysis shows that an intercalation mechanism is operational until a 1:1 Li:Ru ratio is reached, which is followed by a conversion mechanism into Ru metal and Li2O. Furthermore, in agreement with experiment, the computations predict superstoichiometric capacity of RuO2, i.e., accommodation of lithium well beyond the stoichiometric limit of 4:1 Li:Ru ratio, and show that the additional lithium atoms reside at the interface of the Ru metal and Li2O. This shows that the extra capacity can be explained without invoking electrolyte or solvent–electrolyte interface effects.