Bulk and nanosized MAX and MXene phases are comparatively evaluated for microwave absorption and Li-ion battery anode applications.

A 3 D intermetallic anti‐perovskite carbide, Fe3SnC, is reported as a Li‐ion battery anode. Single‐phase Fe3SnC showed a reversible Li‐ion capacity of 426 mAh g−1 that increased significantly (600 mAh g−1) upon its in situ synthesis by electrospinning and pyrolysis to render a conducting carbon nanofibre (CNF) based composite. Importantly, the Fe3SnC@CNF composite showed excellent stability in up to 1000 cycles with a remarkable 96 % retention of capacity. The rate performance was equally impressive with a high capacity of 500 mAh g−1 delivered at a high current density of 2 A g−1. An estimation of Li ion diffusion from the electrochemical impedance data showed a major enhancement of the rate by a factor of 2 in the case of Fe3SnC@CNF compared to the single‐phase Fe3SnC sample. Post‐cyclic characterisation revealed that the unit cell was retained despite a volume expansion upon the inclusion of four Li atoms per unit cell, as calculated from the capacity value. The cyclic voltammogram shows four distinctive peaks that could be identified as the sequential incorporation of up to four Li atoms. First‐principles DFT calculations were performed to elucidate the favourable sites for the inclusion of 1–4 Li atoms inside the Fe3SnC unit cell along with the associated strain.

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