Densified Carbon Nanotubes Macrofilm with Fast Charge Transfer for Flexible Lithium-Ion Supercapacitors

Flexible lithium-ion supercapacitors have attracted extensive attention in the field of portable electronic devices. However, their development is hampered by severe capacity loss, which is mainly caused by the underperforming current collectors under various operating conditions. In this study, a densified carbon nanotubes macrofilm (d-CMF) was developed as a current collector for flexible lithium-ion supercapacitor. This optimized d-CMF is characterized by strong interaction among individual carbon nanotube units, resulting in improved electrical conductivity, enhanced electrolyte wettability, and greater mechanical strength for the d-CMF-based electrode. Moreover, the d-CMF can vest a distinct interfacial structure with fast electron/ion conversion kinetics. As a result, the lithium-ion supercapacitors assembled with this d-CMF demonstrate outstanding electrochemical properties. They exhibit a high initial specific capacitance of 100 F g–1, excellent rate performance at a current density of 12 A g–1, and remarkable cycling stability over 3500 cycles. Importantly, the lithium-ion supercapacitor can maintain stable energy storage characteristics under various extreme conditions. This work not only offers valuable insights for the design of high-performance current collectors in flexible energy devices but also broadens the scope for optimizing interface structures to facilitate fast charge conversion processes in a variety of energy conversion systems.