High performance supercapacitors based on wood-derived thick carbon electrodes synthesized via green activation process

Abstract

Electrical double-layer supercapacitors are a type of electrochemical energy devices that are 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 operate under harsh conditions such as fast charge/discharge rates (100 mA cm⁻²), ultralong cycle life (≥50 000 cycles), and ultralow temperature (−40 °C). The carbon electrodes inherit the vertical channels of basswood, which enhance the penetration and mass transport of electrolyte ions; they also possess rational micro/meso-sized pores and oxygen-containing functional groups induced by H₂O₂ activation, which improve the ion transport kinetics of electrodes. As a consequence, the assembled supercapacitor achieves appreciable capacitive performance even with ultrahigh mass loading and at ultralow temperatures, which delivers 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 °C, respectively. In addition, the device presents an ultralong working lifetime in harsh environments evidenced by a capacitance retention of 90.6% even after 70 000 cycles at −40 °C. Benefiting from the renewable precursor, green activation process, and encouraging capacitive performances, the H₂O₂-activated wood-derived carbon monoliths will be promising high mass-loading electrodes for developing supercapacitors working at ultralow temperatures.