Real-Time Mass Change: An Intrinsic Indicator to Dynamically Probe the Electrochemical Degradation Evolution in WO3

Although tungsten trioxide (WO3) films are considered as the most popular inorganic electrochromic cathode, the irreversible accumulation of lithium ion in it leads to the degradation of cycling stability. In situ monitoring of mass change is critical to intrinsically probe the dynamical degradation evolution of the WO3 films. Based on electrochemical quartz crystal microbalance analysis, a transfer model based on the migration of three mass carriers (lithium ion, perchlorate ion and propylene carbonate) is proposed. Higher potential can boost the migration of mass carriers, benefiting from the intensive driving force. Due to moderate intercalation of mass carriers and smallest difference in molar mass, the excellent electrochemical reversibility at 40 mV s(-1) is observed. As the migration of mass carriers progresses, continuous corrosion of the WO3 films results in electrochemical degradation. It is demonstrated that electrochemical quartz crystal microbalance-based analyses provide a valuable insight for the intercalation and extraction of mass carriers, in favor of further revealing degradation evolution induced by the irreversible intercalation of conductive ions in electrochemical devices.