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