In Situ Real-Time Mechanical and Morphological Characterization of Electrodes for Electrochemical Energy Storage and Conversion by Electrochemical Quartz Crystal Microbalance with Dissipation Monitoring
Quartz crystal microbalance with dissipation monitoring (QCM-D) generates surface-acoustic waves in" quartz crystal plates that can effectively probe the structure of films, particulate composite electrodes of complex geometry rigidly attached to quartz crystal surface on one side and contacting a gas or liquid phase on the other side. The output QCM-D characteristics consist of the resonance frequency (MHz frequency range) and resonance bandwidth measured with extra-ordinary precision of a few tenths of Hz. Depending on the electrodes stiffness/ softness, QCM-D operates either as a gravimetric or complex mechanical probe of their intrinsic structure. For at least 20 years, QCM-D has been successfully used in biochemical and environmental science and technology for its ability to probe the structure of soft solvated interfaces. Practical battery and supercapacitor electrodes appear frequently as porous solids with their stiffness changing due to interactions with electrolyte solutions or as a result of ion intercalation/adsorption and long-term electrode cycling. Unfortunately, most QCM measurements with electrochemical systems are carried out based on a single (fundamental) frequency and, as such, provided that the resonance bandwidth remains constant, are suitable for only gravimetric sensing. The multiharmonic measurements have been carried out mainly on conducting/redox polymer films rather than on typical composite battery/supercapacitor electrodes. Here, we summarize the most recent publications devoted to the development of electrochemical QCM-D (EQCM-D)-based methodology for systematic characterization of mechanical properties of operating battery/supercapacitor electrodes. By varying the electrodes' composition and structure (thin/thick layers, small/large particles, binders with different mechanical properties, etc.), nature of the electrolyte solutions and charging/cycling conditions, the method is shown to be operated in different application modes. A variety of useful electrode-material properties are assessed noninvasively, in situ, and in teal time frames of ion:intercalation into the electrodes of interest. A detailed algorithm for the mechanical characterization of battery electrodes kept in the gas phase and immersed into the electrolyte 'solutions has been developed for fast recognition of stiff and viscoelastic materials in terms of EQCM-D signatureS:treated by the hydrodynamic and viscoelastic models. Working-examples of the use of in situ hydrodynamic spectroscopy to characterize stiffrough/porous solids of complex geometry and viscoelastic characterization of soft electrodes are presented: The most demonstrative example relates to-theformation of solid electrolyte interphase on 114.T15012 electrodes in the-presence of different electrolyte solutions, and additives: only a few cycles,(an experiment during similar to 30 min) were required for screening the electrolyte systems for their ability to form high-quality surface films in experimental EQCM-D, cells as compared to 100 cycles (200: hh cycling) iii conventional,coin Thin/small-mass electrodes required for the EQCM,D analysis enable accelerated cycling tests. for ultrafast mechanical characterization of these electrodes in different electrolyte solutions. Hence, this methodology can be easily implemetfted a a highly effective in situ analytical tool' in the field of energy storage and conversion.