Fe₂CS₂ MXene: A promising electrode for Al-ion batteries

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 (M_n+1X_nT_x), 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.