Nanoengineering S-Doped TiO2 Embedded Carbon Nanosheets for Pseudocapacitance-Enhanced Li-Ion Capacitors

Li-ion capacitors, comprising a battery anode and a supercapacitor cathode, have been expected to bridge the gap between batteries and supercapacitors. However, the kinetics mismatch between the anodic sluggish insertion and the cathodic capacitive process has impeded the energy-storage potential of devices. Developing pseudocapacitive anode materials is urgently needed in that pseudocapacitance can deliver energy in the same time scale as electrostatic adsorption and offer a comparable level of energy storage to that of battery-type materials. Here we demonstrate an inside and outside synergistic nanoengineering strategy to synthesize nanoporous carbon-modified S-TiO2 hybrid nanosheets, through which both the carbon layer and sulfur doping can be simultaneously generated in situ. Benefiting from the in situ S doping, the electronic and ionic conductivity of anatase TiO2 nanoparticles is enhanced. The carbon-modified S-TiO2 with dominant pseudocapacitance realizes an unprecedentedly high capacity of 550 mAh g–1 at 0.3 C and excellent rate capability, outperforming that of the ever-reported TiO2-based materials. Furthermore, a hybrid Li-ion capacitor based on the as-obtained carbon-modified S-TiO2 electrode has been assembled, delivering a high energy density of 92.7 Wh kg–1 and power density of 26 kW kg–1 with a stable cycling life (85.8% after 10 000 cycles). Our work offers a new avenue for achieving electrode materials with extrinsic pseudocapacitance that is kinetically comparable to capacitive materials.