Nb₂CT_x MXene Cathode for High-Capacity Rechargeable Aluminum Batteries with Prolonged Cycle Lifetime

Aluminum-ion batteries have garnered significant interest as a potentially safer and cheaper replacement for conventional lithium-ion batteries, offering a shorter charging time and denser storage capacity. Nonetheless, the progress in this field is considerably hampered by the limited availability of suitable cathode materials that can sustain the reversible intercalation of Al³⁺/[AlCl₄]^- ions, particularly after long cycles. Herein, we demonstrate that rechargeable Al batteries embedded with two-dimensional (2D) Nb₂CT_x MXene as a cathode material exhibit excellent capacity and exceptional long cyclic performance. We have successfully improved the initial electrochemical performance of Nb₂CT_x MXene after being properly delaminated to a single-layered microstructure and subjected to a post-synthesis calcining treatment. Compared to pristine Nb₂CT_x MXene, the Al battery embedded with the calcined Nb₂CT_x MXene cathode has, respectively, retained high capacities of 108 and 80 mAh g^-1 after 500 cycles at current densities of 0.2 and 0.5 A g^-1 in a wide voltage window (0.1-2.4 V). Noteworthily, the cyclic lifetime of Nb₂CT_x MXene was extended from ∼300 to >500 times after calcination. We reveal that attaining Nb₂CT_x nanosheets with a controllable d-spacing has promoted the migration of the [AlCl₄]^- and Al³⁺ ions in the MXene interlayers, leading to enhanced charge storage. Furthermore, we found out that the formation of niobium oxides and amorphous carbon after calcination probably benefits the electrochemical performance of Nb₂CT_x MXene electrode in Al batteries.