All-pseudocapacitive asymmetric MXene-carbon-conducting polymer supercapacitors

With ever-increasing demands for high-energy and high-power operation of compact energy storage devices, asymmetric pseudocapacitors attract tremendous attention due to their high volumetric energy and fast charge/discharge capability. However, it is challenging to achieve compact structures with abundant ions access and fast charge transport for both positive and negative electrodes simultaneously. Herein, we designed a flexible and asymmetric pseudocapacitor using a Ti3C2Tx MXene film with wavy architecture as the negative electrode, and a graphene/carbon nanotube/polyaniline (rGO/CNT/PANI) ternary nanocomposite film resistive to anodic oxidation as the positive electrode, respectively. The wavy MXene facilitates ion transport and maintains its highly compact structure, resulting in an ultrahigh volumetric capacitance of 1277 F cm−3 and a significantly enhanced rate capability with 89% capacitance retention at 1000 mV s−1. The compatible metal-free rGO/CNT/PANI positive electrode with molecular-level integration of PANI on graphene and further insertion of CNT in between rGO/PANI sheets also sets an extremely high volumetric capacitance of 1038 F cm−3 and excellent rate performance. As a result, Ti3C2Tx//rGO/CNT/PANI asymmetric device outputs both high volumetric energy density of 70 Wh L−1 and high volumetric power density of 111 kW L−1 (per volume of active material), which surpasses most state-of-the-art aqueous asymmetric and symmetric devices.