Monitoring the length change of Ni@C composite electrodes during charging/discharging processes

The iterative volume change of electrode materials during electrochemical charging/discharging processes could generally result in the performance degradation of electrochemical capacitors. This work investigates the mechanical stability of the electrode material during the electrochemical charging/discharging processes, which can be monitored by means of in situ dilatometry technique with a focus on the length change of the electrode. As a simple model, the porous Ni@C composite was prepared with a core-shell structure as the electrode for electrochemical capacitor, which exhibits excellent electrochemical cycling stability in a dilute electrolyte. This stability of Ni@C electrode may benefit from the small length change during the electrochemical cycling. The experimental results exhibit that the expansion and contraction of the electrodes in response to the charge state at the surface of the electrode is weakly asymmetric. This finding of an unbalanced strained state may contribute to a better understanding of the performance degradation of electrochemical capacitors.