Exploring MXenes as Cathodes for Non-Aqueous Lithium-Oxygen Batteries: Design Rules for Selectively Nucleating Li2O2

The potential of MXenes, an emerging class of layered materials, is investigated as cathode materials for rechargeable Li-O-2 battery chemistry, exploring MXenes from the primary standpoint of the key challenge of rechargeability, which translates to selectivity towards lithium peroxide, the primary discharge product. This study captures the effects of three primary electronic-structure-tuning variables: The termination group and its coverage of the surface as well as the transition metal. The trends are rationalized with regard to the thermodynamic nucleation over-potential, determined through the computed free energy of the adsorbed intermediate LiO2*. Design rules for identifying MXene cathode materials are developed based on discharge product selectivity and stability against potential decomposition products. Of all investigated MXenes, analysis suggests that Ni4N3(OH)(2) exhibits the lowest nucleation over-potential and identifies mixed-transition-metal MXenes as a promising exploration direction.