Surface Ti vacancy passivation of Ti3C2O2 MXene via transition metal atoms as high-performance potassium-ion batteries anodes

Abstract

MXene exhibits tunable interlayer spacing, excellent conductivity and high redox activity, appearing to be ideal intercalated anodes of potassium ion battery. However, defects formed in the preparation process of this material seriously decrease the initial Coulombic efficiency (ICE) and diffusion rate. Herein, transition metals (TMs) passivation is employed to solve this problem based on DFT calculations. TMs filled in Ti vacancy (vTi) is figured out to form strong bonds with surround C and O atoms, which strength is positively-related with the outer electron numbers at d + s orbits of TMs. It enlarged the K adsorption energy difference (ΔEa) between cubic closest packing (ccp)- and hexagonal closest packing (hcp)-site, suggesting larger capacity than Ti3C2O2. ΔEa is revealed negatively linear-correlated with d-band center difference between TM and Ti element, then Fe and Mn would be excellent elements of passivation due to the smallest distance of d-band center to Ti. More importantly, TMs passivation obviously decreases the interaction between vTi and K+, lowering K+ diffusion barrier. This work provides new possibility of surface engineering for MXene performance modification beyond PIBs anodes.