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.