Polarized nucleation and efficient decomposition of Li2O2 for Ti2C MXene cathode catalyst under a mixed surface condition in lithium-oxygen batteries

MXene based materials are theoretical predicted as one of the most promising cathode materials for lithium-oxygen batteries due to their unique electronic structure, large surface area and lattice matching with Li2O2, but still be impeded by the lack of high electrocatalytic performance, inhomogeneous surface condition and poor understanding for reaction kinetics and mechanism during ORR/OER process. In the present work, we fabricated the Ti2C MXene decorated with -O and -F multifunctional groups. DFT calculations revealed that the Ti2CO2 surface provided a high efficient single electron reaction pathway for the adsorption-nucleation-decomposition process of Li2O2 acting as the main catalytic sites compared to the Ti2CF2 surface, meanwhile, the bare Ti2C surface degraded the catalytic capability of Ti2C MXene due to the strong chemical binding with Li2O2. Further, the inhomogeneous surface condition was supposed to promote the polarized nucleation and growth of discharge products to form the porous structure from spatial-direction accumulated nanoflakes, which can provide an efficient pathway for mass transfer. As a result, the T2C MXene cathode exhibited excellent performance in terms of superior capacity and long cycle stability. The present work provides intrinsic insights toward the catalytic mechanism and reaction kinetics of Ti2C MXene decorated with multifunctional groups, which contributes to the rational design of high performance MXene based materials in Li-O2 batteries.