Li-ion energy storage of two-dimensional ``MXene'' transition metal carbides

A new class of two-dimensional early transition metal carbides and carbonitrides, the so-called MXenes, has been synthesized by extracting the ``A'' element from MAX phases. Experiments have demonstrated that MXenes (Ti$_2$C, V$_2$C, Nb$_2$C, Ti$_3$C$_2$...) are promising anode materials for lithium ion batteries, delivering high storage capacity and good rate performance. However, the mechanism of Li-ion storage on MXene surfaces is not clear, with counterintuitive differences in predicted vs measured capacities, and large differences between exfoliated and delaminated samples. I will discuss how a strong collaboration between theory and a range of experimental characterization methods, including x-ray adsorption spectroscopy and inelastic neutron scattering, is able to provide a including for the highest measured Li capacities.\\[4pt] In collaboration with Yu Xie, Alexander Kolesnikov, Oak Ridge National Laboratory; Xiquan Yu, Kyung-Wan Nam, Xiao-Qing Yang, Brookhaven National Laboratory; Michael Naguib, Vadym Mochalin, Michel Barsoum, and Yury Gogotsi, Department of Materials Science and Engineering, and A.J. Drexel Nanotechnology Insititute, Drexel University.