Ti3C2Tx//AC dual-ions hybrid aqueous supercapacitors with high volumetric energy density

Supercapacitors with an advanced high volumetric energy density require a match of both electrodes materials and suitable electrolyte. Here, aqueous asymmetric supercapacitors are designed by employing layered Ti 3 C 2 T x as negative electrodes and highly compact activated carbon (AC) as positive electrodes. Ti 3 C 2 T x //AC asymmetric supercapacitors (Ti 3 C 2 T x //AC ASCs) with 1.7 V voltage window are designed by regulating the mass ratio of both electrodes, which results from the shift of the open circuit potential with different applied voltages. Then, dual-ion hybrid supercapacitors (Ti 3 C 2 T x //AC-KBr HSCs) are also constructed by introducing redox active (KBr) into traditional electrolyte (H 2 SO 4 ) for Ti 3 C 2 T x //AC ASCs to achieve a high volumetric energy density, in which fast hydronium ion intercalated pseudocapacitance happens at the Ti 3 C 2 T x negative electrode, while redox reaction of Br − /Br 3 − within the highly compact AC happens at the positive electrode. As a result, the Ti 3 C 2 T x //AC-KBr HSC achieves a high volumetric capacitance of 250 F cm −3 at 2 mV s −1 , a volumetric energy density of as high as 102.8 Wh L −1 at 424 W L −1 and an outstanding cycling stability with 122% capacitance retention after 6000 cycles. Furthermore, the self-discharge performance for the Ti 3 C 2 T x //AC-KBr HSC is obviously improved, which is mainly ascribed to the adsorption of oxidized species at the AC surface.