Flexible Cellulose Paper-based Asymmetrical Thin Film Supercapacitors with High-Performance for Electrochemical Energy Storage

Cellulose paper (CP)-based asymmetrical thin fi lm supercapacitors (ATFSCs) have been considered to be a novel platform for inexpensive and portable devices as the CP is low-cost, lightweight, and can be rolled or folded into 3D confi gurations. However, the low energy density and poor cycle stability are serious bottlenecks for the development of CP-based ATFSCs. Here, sandwich-structured graphite/Ni/Co2 NiO4-CP is developed as positive electrode and the graphite/Ni/AC-CP as negative electrode for fl exible and high-performance ATFSCs. The fabricated graphite/Ni/Co2NiO4-CP positive electrode shows a superior areal capacitance (734 mF/cm2 at 5 mV/s) and excellent cycling performance with similar to 97.6% C sp retention after 15 000 cycles. The fabricated graphite/Ni/AC-CP negative electrode also exhibits large areal capacitance (180 mF/cm(2) at 5 mV/s) and excellent cycling performance with approximate to 98% C-sp retention after 15 000 cycles. The assembled ATFSCs based on the sandwich-structured graphite/Ni/Co2NiO4-CP as positive electrode and graphite/Ni/AC-CP as negative electrode exhibit large volumetric C-sp (7.6 F/cm(3) at 5 mV/s), high volumetric energy density (2.48 mWh/cm(3), 80 Wh/kg), high volumetric power density (0.79 W/cm(3), 25.6 kW/kg) and excellent cycle stability (less 4% C-sp loss after 20 000 cycles). This study shows an important breakthrough in the design and fabrication of high-performance and fl exible CP-based electrodes and ATFSCs.