Enhanced Ionic/Electronic Transport in Nano-TiO2/Sheared CNT Composite Electrode for Na+ Insertion-based Hybrid Ion-Capacitors

Ion-insertion capacitors show promise to bridge the gap between supercapacitors of high power densities and batteries of high energy densities. While research efforts have primarily focused on Li + -based capacitors (LICs), Na + -based capacitors (SICs) are theoretically cheaper and more sustainable. Owing to the larger size of Na + compared to Li + , finding high-rate anode materials for SICs has been challenging. Herein, an SIC anode architecture is reported consisting of TiO 2 nanoparticles anchored on a sheared-carbon nanotubes backbone (TiO 2 /SCNT). The SCNT architecture provides advantages over other carbon architectures commonly used, such as reduced graphene oxide and CNT. In a half-cell, the TiO 2 /SCNT electrode shows a capacity of 267 mAh g −1 at a 1 C charge/discharge rate and a capacity of 136 mAh g −1 at 10 C while maintaining 87% of initial capacity over 1000 cycles. When combined with activated carbon (AC) in a full cell, an energy density and power density of 54.9 Wh kg −1 and 1410 W kg −1 , respectively, are achieved while retaining a 90% capacity retention over 5000 cycles. The favorable rate capability, energy and power density, and durability of the electrode is attributed to the enhanced electronic and Na + conductivity of the TiO 2 /SCNT architecture.