Fe2CS2 MXene: a promising electrode for Al-ion batteries.

Abstract

Aluminum-ion batteries are one of the most promising candidates for next-generation rechargeable batteries. However, the strong electrostatic interactions between highly ionic Al3+ and the electrode hinder the reversible intercalation and fast transport of Al ions. This study suggests a design strategy for a MXene electrode for realizing high-performance Al-ion batteries. Instead of early transition metals and oxygen, the metal M and surface termination T of general MXene (Mn+1XnTx), the use of late transition metals and sulfur can dramatically improve the capacity and rate capability, respectively. The capacity increases 2.2-fold, from 288 mA h g-1 (Ti2CO2) to 642 mA h g-1 (Fe2CS2), and the Al-ion diffusivity increases 104-fold, from 2.8 × 10-16 cm2 s-1 (Ti2CO2) to 6.0 × 10-12 cm2 s-1 (Fe2CS2). This remarkable performance enhancement is due to the charge redistribution in the M and T layers by the late transition metals and the shallowing of the potential energy surface for Al-ion intercalation by sulfur.