Natural sisal fibers derived hierarchical porous activated carbon as capacitive material in lithium ion capacitor

• Hierarchical porous activated carbon is derived from natural sisal fibers.
• Sisal fiber activated carbon (SFAC) is applied to LIC for the first time.
• Hierarchical porous structure benefits the electrochemical properties of SFAC.
• LIC displays high energy density of 41 Wh kg−1 at the power density of 5.7 kW kg−1.

Lithium-ion capacitor (LIC) is a novel advanced electrochemical energy storage (EES) system bridging gap between lithium ion battery (LIB) and electrochemical capacitor (ECC). In this work, we report that sisal fiber activated carbon (SFAC) was synthesized by hydrothermal treatment followed by KOH activation and served as capacitive material in LIC for the first time. Different particle structure, morphology, specific surface area and heteroatoms affected the electrochemical performance of as-prepared materials and corresponding LICs. When the mass ratio of KOH to char precursor was 2, hierarchical porous structured SFAC-2 was prepared and exhibited moderate specific capacitance (103 F g−1 at 0.1 A g−1), superior rate capability and cyclic stability (88% capacity retention after 5000 cycles at 1 A g−1). The corresponding assembled LIC (LIC-SC2) with optimal comprehensive electrochemical performance, displayed the energy density of 83 Wh kg−1, the power density of 5718 W kg−1 and superior cyclic stability (92% energy density retention after 1000 cycles at 0.5 A g−1). It is worthwhile that the source for activated carbon is a natural and renewable one and the synthesis method is eco-friendly, which facilitate that hierarchical porous activated carbon has potential applications in the field of LIC and other energy storage systems.