Microstructure transformation of electrochemically activated alkali-treated soft carbons for energy storage applications

Abstract

Electrochemical activation (EA) is an effective method for modifying the micro-structure of the alkali-treated soft carbon (ASC), enabling the irreversible trapping of ions within carbon layers to enhance the electrochemical reversibility and specific capacitance. This study aims to elucidate the structural transformations during EA using the in-situ Raman spectroscopy, elemental mapping with an electron probe microanalyzer (EPMA), transmission electron microscopy (TEM), and other analytical methods. The phosphorus concentration increases with enlarging the applied voltages, and simultaneously, the carbon layers are expanded. The ions irreversibly trapped in the expanded carbon layers during EA originate from PF₆⁻ in the electrolyte and act as nanopillars to transform ASC into a high-performance supercapacitor material. When the electrochemically activated ASC was integrated into the lithium-ion capacitor (LIC), this EA-treated ASC exhibited a low self-discharge rate (70 % voltage retention under the open circuit state for 1000 h) and outstanding cycling stability (95 % capacitance retention after 3000 cycles). This comprehensive study not only elucidates the mechanism of the EA process but also highlights the practical applications of EA-treated ASC, paving the way for further advancements in EA-based energy storage technologies.