Pseudocapacitive behaviours of Na2Ti3O7@CNT coaxial nanocables for high-performance sodium-ion capacitors

Abstract

Hybrid sodium-ion capacitors (NICs) have tremendous potential in large-scale energy storage applications due to their low cost, long lifetime and high power. However, it remains a great challenge to find a desirable anode material with fast kinetics and superior cycle life. Here an applicable strategy to in situ grow Na₂Ti₃O₇ on 1D CNTs as an anode material for sodium-ion capacitors is presented. Benefiting from the unique 1D nanostructure and the presence of pseudocapacitive charge storage mechanism, the Na₂Ti₃O₇@CNT electrode exhibits excellent electrochemical performance with high rate capability and superb cycling stability. Moreover, a high performance hybrid NIC is also fabricated by using Na₂Ti₃O₇@CNTs as an anode and activated carbon derived from the outer peanut shell as a cathode, which delivers high energy density (58.5 W h kg⁻¹), high power density (3000 W kg⁻¹), and long term cycle life (retaining ca. 75% of its original capacity at 0.4 A g⁻¹ after 4000 cycles).