High Performance Supercapacitors Based on Wood-Derived Thick Carbon Electrodes Synthesized Via Green Activation Process

Electrical double-layer supercapacitors are one type of electrochemical energy devices promising for next-generation energy storage, while they still suffer from great challenges of inferior energy density and poor tolerance to harsh conditions toward practical applications. Herein, by designing a thick carbon electrode with an ultrahigh mass loading (~40 mg cm-2 ) from carbonization and activation of basswood, a supercapacitor is able to operating under harsh conditions such as fast charge/discharge rates (100 mA cm-2 ), ultralong cycle life (≥ 50,000 cycles), and ultralow temperature (-40 ℃) . The carbon electrode inherited the vertical channels of basswood, which enhances the penetration and mass transport of electrolyte ions; and it also possessed rational micro/meso-sized pores and oxygen-containing functional groups induced by H2O2 activation, which improves the ion transport kinetics of electrodes. In consequence, the assembled supercapacitors achieved appreciable capacitive performance even with commercial-level mass loadings and at ultralow temperatures, that delivered a specific capacitance of 6205.7 mF cm-2 (221.6 F g-1 and 77.6 F cm-3) and 4886.4 mF cm-2 (174.5 F g-1, 61.1 F cm-3) at ambient temperature and -40 ℃, respectively. In addition, the device presented an ultralong working lifetime in harsh environments, evidenced by a capacitance retention of 90.6% even after 70,000 cycles at -40 ℃. Benefiting from the renewable precursor, green activation process, and encouraging capacitive performances, the H2O2 -activated wood-derived carbon monoliths would be promising high mass-loading electrodes for developing supercapacitors working at ultralow temperatures.