New electrode materials are highly desired for Li-ion batteries (LiB) for increased capacity, power, lifetime, and safety. The most commonly used anode material is graphite which suffers from low Li capacity and poor rate capability. Recently, a new class of materials, two-dimensional (2D) transition metal carbides and nitrides (MXenes), have been synthesized. Recent experimen- tal results showed that these are very promising, delivering high storage capacity and rates as LiB anodes. Here, we present the study of surface structure and Li-ion storage of 2D transition metal (Sc, Ti, V, Cr, and Nb) carbides by combing theoretical investigation and experimental measure- ments. We find the surfaces of MXenes are typically covered by hydroxyl groups with some fluorine and few oxygen. We show that the Li capacity and electrode performance is strongly affected by the type of surface functional groups. Purely oxygen terminated carbides should have the highest capacity. We observe surface structure changes and reactions between Li and surface functional groups during the first lithiation cycle. Based on the correspondence between computed capacities for already synthesized MXenes, we predict the Li storage capacity for several new MXenes that have not been measured experimentally.

Understanding the surface structure and Li-ion storage of functionalized 2D transition metal carbides

247th National Meeting (2014)

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