Intrinsic voltage plateau of a Nb₂CTx MXene cathode in an aqueous electrolyte induced by high-voltage scanning

Although MXene has been widely used in many energy storage systems, the absence of a high intrinsic voltage plateau results in its poor discharging feature. Herein, we report a Nb₂CTx MXene cathode with an apparent discharge voltage plateau for high-performance aqueous zinc ion batteries. Triggered by a repeated high-voltage scanning up to 2.4 V, the Nb₂CTx cathode gradually displays a stable Zn²⁺ storage dominated by a battery behavior. A high discharge voltage plateau of 1.55 V is presented, which is distinct from all reported MXene electrodes. Consequently, a record-level energy density among all aqueous MXenes electrodes of 146.7 Wh kg⁻¹ with a 63% contribution from the plateau region is obtained, which is 292% that of the capacitive Nb₂CTx electrode. The developed high-voltage scanning strategy is also effective for Ti₃C₂T_x MXene to achieve a remarkable voltage plateau.