Free-standing β-Ta2O5/SWCNTs composite film for high-rate Li-ion storage

The rapid development of portable and wearable electronic devices is responding to the urgent demand for high-efficiency flexible energy storage devices. Flexible supercapacitors, showing long cycle life, high power density, and good safety, are considered ideal candidates. Nevertheless, the relatively low energy density restricts their practical applications. With a large dielectric constant of 18–46, Ta2O5-based materials typically exhibit excellent electron-binding ability, which is critical for enhancing the energy density of supercapacitors. In this work, the free-standing β-Ta2O5/single-walled carbon nanotubes (SWCNTs) composite film was prepared, with a high β-Ta2O5 loading of over 70%. By anchoring β-Ta2O5 nanoparticles onto the surface of SWCNTs, the system’s flexibility and conductivity were significantly enhanced, which also facilitated the intercalation electrodynamics of metal cations. As a result, the flexible β-Ta2O5/SWCNTs film exhibits excellent Li-ion storage performance, with a high volumetric specific capacitance of 392.3 F cm−3 at the scan rate of 10 mV s−1 and 198.9 F cm−3 at 500 mV s−1. In addition, the asymmetric device, assembled by the β-Ta2O5/SWCNTs and activated carbon films, shows a high energy density of 45.5 Wh kg−1 at the power density of 10.8 kW kg−1. This technique opens up a new avenue for improving the energy density and rate performance of flexible supercapacitors.