Ultra‐Lightweight and Flexible Current Collector Based on Freestanding Carbon Nanotube Sheets for Lithium‐Ion Capacitors

Abstract A new and simple strategy for the fabrication of an ultra‐lightweight and flexible current collector based on freestanding carbon nanotube (CNT) sheets for lithium‐ion capacitors (LICs) with excellent electrochemical performance is reported. A novel lightweight current collector is fabricated using CNT sheets (≈0.05 mg cm⁻²) which are prepared by a direct spinning method. LICs are assembled using prelithiated graphite/CNT sheets as anodes, and activated carbon/CNT sheets as cathodes. The electrochemical performances of anode and cathode are investigated through coin‐type half‐cell tests, demonstrating the high discharge capacities of about 350 and 40 mAh g⁻¹, respectively. These discharge capacities based on the total mass of electrode exhibit about 73% and 75% of capacities based on the mass of active materials. However, in the case of fabricating metallic current collector electrode, discharge capacities are reduced to about 6.5% and 20%, respectively. LICs demonstrate the maximum energy density of ≈26.4 Wh kg⁻¹ and the maximum power density of ≈672 W kg⁻¹, showing comparable energy and power densities when values are evaluated on the basis of the total mass of electrode. These features make the collector a potential candidate for the energy storage systems, which require large‐scale and lightweight power sources.