Fast electrochemical redox kinetics of two-dimensional TiO2/Ti3C2T (MXene) heterostructure for high-performance lithium-ion capacitor

Li ion capacitors (LICs) are such a kind of novel energy storage systems that possess the advantage of high energy density of batteries and high power density as well as long cycle life of capacitors. Here, TiO2/Ti3C2Tx (MXene) heterostructure is prepared by a general ex situ route to the simple self-assembly of TiO2 nanoparticles on Ti3C2Tx nanosheets through van der Waals interactions. The obtained TiO2/Ti3C2Tx heterostructure demonstrates enhanced specific capacity (304 mAh·g−1 at 100 mA·g−1), outstanding rate capability (∼120 mAh·g−1 at 2 A·g−1) and excellent cyclic stability due to the morphological and functional synergy of the two building blocks. Then, a novel LIC is successfully constructed utilizing TiO2/Ti3C2Tx as anode and carrot-derived porous carbon (CPC) as cathode. The assembled TiO2/Ti3C2Tx//CPC LIC owns a wide operating voltage window of 0–4.0 V, demonstrating an exceptionally high energy density (129.4 Wh·kg−1), a high power density (10 kW·kg−1), a rather good cycling stability with a capacitance retention of 77 % after 10,000 cycles at 1 A·g−1. This strategy can be applied to controllably prepare general transition metal oxide (TMO) nanostructures on the MXene nanosheets with a fast faradaic reaction.