Hierarchical porous activated carbon anode for dual carbon lithium-ion capacitors: Energy storage mechanisms and electrochemical performances

Background: Utilizing the graphite anode and activated carbon cathode to construct dual carbon lithium-ion capacitors (DC-LICs) is recently attracted much attention owing to their cost-effectiveness, enlarged operating voltage, high safety, etc. Despite these merits mentioned above, the kinetic mismatch and imbalance capacity among the electrodes restricts the rate capability and energy density, respectively. Methods: Herein, the high mass-loading (9 mg/cm2) and flexible electrodes composed of hydrogel-derived hierarchical porous activated carbon (H-HPAC) are prepared by mechanically blending, repeatedly calendared, and completely dried at 130celcius. The resulting free-standing sheets were adopted as electrodes for DC-LICs. Significant findings: Benefiting from the distinctive textural properties (e.g., graphitic layers, multi-porosity, and huge specific surface area of 2,012 m2/g), the energy storage mechanisms of H-HPAC anodes simultaneously follow the intercalation and adsorption phenomena, which were confirmed by electrochemical and micro-Raman identifications. Moreover, an additional capacitive contribution (-31%) and voltage delay of 64 mV are reflected at 5 mV/sec, as evidenced using cyclic voltammetry. Consequently, the DC-LICs assembled with pre-lithiated H-HPAC anode and H-HPAC cathode exhibited outstanding rate performances (39.7 mAh/g at 0.1 mA/cm2 and 20.3 mAh/g at 10 mA/cm2) and comparable cyclability (81% of retention after 1,400 cycles at 1 mA/cm2), revealing that our H-HPAC materials are promising for serving as anode and cathode in DC-LICs.