Ultrafast Na+-storage in TiO2-coated MoS2@N-doped carbon for high-energy sodium-ion hybrid capacitors

As a hybrid battery-supercapacitor energy-storage device, Na-ion capacitors (NICs) are regarded to show both high-energy performance and low lost. However, the sluggish electrochemical kinetics and low specific capacities of most reported anode materials, severely restrict their practical applications. Herein, we report that ultrafine Mo2C nanoparticles are homogeneously embedded within an N-doped carbon matrix (Mo2C@NC) through a simple solid-phase reaction. After sulfuration, the optimal MoS2@NC electrode exhibits a high discharge capacity (535.3 mAh g(-1) at 0.1 A g(-1)) and outstanding rate capability (420.2 mAh g(-1) at 20 A g(-1) with a remarkable retention of 78% relative to 0.1 A g(-1)), but its cycle life is not satisfied. To address this issue, amorphous TiO2 coating of different thicknesses is further coated on MoS2@NC by atomic layer deposition. It is found that the electrode made of TiO2-coated MoS2@NC shows excellent cyclability with 100% capacity retention after 500 cycles at 2 A g(-1). Furthermore, a novel hybrid NIC is constructed by using TiO2/MoS2@NC as an anode and commercial activated carbon (AC) as a cathode, delivering high energy and power densities (148 Wh kg(-1)/200 W kg(-1), 64.4 Wh kg(-1)/20,000 W kg(-1)). The performance outperforms the recently reported NIC counterparts.