Development of Flexible High‐Efficient Aluminum ion Supercapacitors With 2D Niobium MXene Electrode

Abstract

ABSTRACTA high‐performance aluminum‐ion supercapacitor is fabricated using 2D few‐layered Nb2CTx MXene, as an active electrode material and Al2(SO4)3 electrolyte for efficient energy storage. Nb2CTx MXene has been synthesized from Nb2AlC MAX phase using HF. Nb2CTx MXene coated on carbon cloth (Nb@CC) displays a capacitance of 307 F g−1 with 90% coulombic efficiency. The specific capacitance of Nb@CC in Al2(SO4)3 electrolyte is exceptionally high compared to those (≤32.2 F g−1) in H2SO4, Na2SO4, and MgSO4 electrolytes. Both symmetric and asymmetric aluminum ion supercapacitors are fabricated with Nb@CC electrode. The Nb@CC//Nb@CC symmetric device exhibits a capacitance of 122 F g−1 with a high energy density (Ed) of 33.2 Wh kg−1 at 1.41 kW kg−1 power density (Pd). An asymmetric supercapacitor device (ASC), Nb@CC//CNT@CC, with carbon nanotube (CNT@CC) cathode delivers a maximum Ed of 24.7 Wh kg−1 at 3.41 kW kg−1 Pd and excellent stability with 90% capacitance retention after 4000 cycles. A remarkably high Pd of 34 kW kg−1 is maintained with 13.2 Wh kg−1 Ed, and the rate capability is 53% for a 10‐fold increase in current density. These results offer the feasibility of efficient aqueous supercapacitors with Al‐ion as guest species, presenting new possibilities for supercapacitors.