Unveiling Activated Carbon Degradation in Supercapacitor Using Liquid Cell Transmission Electron Microscopy

Electrode stability critically impacts energy storage device performance, and despite theoretical recognition, directly observing the evolving electrode-electrolyte interface during the charge-discharge cycle of a supercapacitor remains challenging. This work directly addresses the technical gap by employing liquid-cell-assisted in situ transmission electron microscopy. This innovative approach realizes real-time observation of the dynamic response of the activated carbon electrode during an electrical cycling of the supercapacitor cells. Driving the cell potential above a certain threshold potential during cycling leads to gas evolution that initiates a cascade of events, causing the active carbon to disintegrate. This is being manifested in the electrode’s mass loss and rapid capacity decline upon further cycling. A nanolayer oxide coating of the activated carbon electrode using atomic layer deposition effectively suppresses electrode-electrolyte reactions, stabilizing the electrode and improving the electrochemical properties. The first in situ transmission electron microscopy liquid cell design using an activated carbon substrate represents a breakthrough in understanding supercapacitor degradation, offering a working strategy for electrode dynamics investigation of various energy storage devices.