In Situ Monitoring of Gravimetric and Viscoelastic Changes in 2D Intercalation Electrodes

Viscoelastic properties of battery electrodes in contact with electrolyte solutions may affect the electrodes' cycling performance. However, they are not easily assessed by in situ measurements. Herein, we show that an electrochemical quartz-crystal microbalance with dissipation (EQCM-D) enables extraordinary sensitive probing of intrinsic electrodes materials' properties such as intercalation-induced gravimetric and viscoelastic changes, using Ti₃C₂(OH)₂ (MXene) as a classical 2D intercalation model material. The insertion of each Li-ion into thin electrodes comprising this MXene is accompanied by insertion of one water molecule. Solvent-dependent viscoelastic changes and periodic stiffening/softening upon fully reversible Li-ion intercalation/deintercalation into an MXene electrode correlates well with its excellent long-term cycling performance. The experimental platform based on a commercial instrument, EQCM-D monitoring, and advanced viscoelastic modeling (extended Voight-type model) can be used for in situ real time characterization of intrinsic materials' properties of practical composite battery electrodes important for a deeper understanding of the factors controlling their cycling performance.