Molecular-Level Heterostructures Assembled from Titanium Carbide MXene and Ni-Co-Al Layered Double-Hydroxide Nanosheets for All-Solid-State Flexible Asymmetric High-Energy Supercapacitors

Unique layered Ti3C2/Ni-Co-Al layered double hydroxide (LDH) heterostructures alternatively stacked with molecular-level nanosheets are for the first time synthesized by a facile liquid-phase cofeeding and electrostatic attraction hetero-assemble strategy between negatively charged Ti3C2 and positively charged Ni-Co-Al-LDH nanosheets. The molecular-level Ti3C2/ Ni-Co-Al-LDH heterostructures possessing the merits of both conductive and pseudocapacitive components can show greatly enhanced dynamic behavior in Faradaic reaction, which is significant for obtaining a high power density. Electrons penetrate in Ti3C2 layers, while ions diffuse rapidly along two-dimensional galleries, displaying the shortest diffusion pathway and highest efficiency for charge transfer. The Ti3C2/Ni-Co-Al-LDH heterostructure exhibits a specific capacitance of 748.2 F at current density of 1 A g(-1) showing an enhanced rate capacity. Importantly, a maximum energy density of 45.8 Wh kg(-1) is obtained when Ti3C2/Ni-Co-Al-LDH acts as the positive electrode for an all-solid-state flexible asymmetric supercapacitor. The results indicate that molecular-level heterotructure is a promising candidate for future high-energy supercapacitors.