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 Ti3C2Tx as negative electrodes and highly compact activated carbon (AC) as positive electrodes. Ti3C2Tx//AC asymmetric supercapacitors (Ti3C2Tx//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 (Ti3C2Tx//AC-KBr HSCs) are also constructed by introducing redox active (KBr) into traditional electrolyte (H2SO4) for Ti3C2Tx//AC ASCs to achieve a high volumetric energy density, in which fast hydronium ion intercalated pseudocapacitance happens at the Ti3C2Tx negative electrode, while redox reaction of Br-/Br-3(-) within the highly compact AC happens at the positive electrode. As a result, the Ti3C2Tx//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 Ti3C2Tx//AC-KBr HSC is obviously improved, which is mainly ascribed to the adsorption of oxidized species at the AC surface.