(Allen J. Bard Award in Electrochemical Science Address) Electroanalytical Techniques Coupled with in-Situ Structural Characterization of Electrodes in Devices for Energy Storage and Conversion
Authors: Aurbach Doron 
Published: February 2020

Inspired by the seminal work of A. J. Bard in electroanalytical chemistry during more than half of a century, we are trying to apply novel electroanalytical tools in conjunction with in-situ spectro-electrochemical techniques for the study of the most reactive electrochemical systems, related to energy storage and conversion. A variety of electroanalytical methods are widely used in advanced batteries and super-capacitors research for screening and optimization of electrode materials including their characteristic electrochemical windows, onset potentials of ions insertion and extraction, formation of protective surface-solution interphases etc. These parameters affect the electrodes stability, capacity retention, cycling efficiency and rate capability. Electroanalytical methods have their own intrinsic accessible time windows and different amplitude of electric perturbation (potential or current). Among these methods electrochemical impedance spectroscopy (EIS) has the widest time window from ca. 10-5 to 103 s and small potential amplitude which enables the probing the kinetics of a large variety of processes accompanying electrochemical insertion of Li , Na and Mg ions into battery electrodes separating them by the characteristic time constants of these processes. In contrast, cyclic voltammetry (CV) effectively probes kinetic steps in the long time window (from 102 to 105 s) close to either quasi-equilibrium intercalation or intercalation process in the form of first-order phase transition. CV is a large-amplitude technique, and attempts to apply it for a shorter time domain, e.g. corresponding to characteristic solid-state diffusion time constants inevitably results in lack of their resolution with respect to electrode potential (or intercalation level). The niche between EIS and CV is effectively bridged by intermittent titration techniques (PITT, GITT) ensuring highly resolved separation between the different sequential phase transitions in the long time domain, and potential-resolved chemical diffusion coefficients of intercalated ions. [1] The area-averaged responses of battery electrodes obtained by electroanalytical techniques depend on the local chemical or porous electrode structure: very often this information is required for correct interpretation of the electrochemical characteristics (e.g. chemical diffusion coefficients).

Recent progress in electroanalytical methods adapted for application in LIB , NIB and Mg batteries research relates to development of non-gravimetric EQCM-D (electrochemical quartz-crystal microbalance with dissipation monitoring) techniques , which in contrast to classical EQCM, tracks not only resonant frequency change DF/n (n is overtone order) but also dissipation of the oscillation energy (or equivalently, resonance peak width change, DW/n). Tracking complex frequency change, DF*/n = DF/n + iDW/n, for rigid porous battery electrodes as a function of the penetration depth of transverse oscillation wave in the electrolyte solution, d (dependent on the overtone order and liquid’s density and viscosity) over multiple harmonics ,allows the characterization of the complex electric and mechanical properties of thin electrode coatings in electrolyte solutions (using the most relevant materials for advanced rechargeable batteries and super-capacitors) under applied potential. Intercalation-induced changes of dimensional and porous electrodes’ structure can be quantified in terms of hydrodynamic admittance models by fitting well developed models for momentum transfer to the experimental RQCM-D data retrieving structural parameters in way similar to fitting experimental EIS data (e.g. Nyquist plots) by equivalent electrical circuit analogs. Validation of the extracted parameters for their internal consistency and comparison with the results from complimentary other in-situ techniques (e.g. scanning probe microscopes) is required. The methodology of hydrodynamic spectroscopy of porous solids and composite electrodes that we develop in recent years is inexpensive, noninvasive and highly useful in a broad spectrum of applications including deeper insights into the dynamic build-up and subsequent development of solid-electrolyte interfaces in Li and Na battery electrodes and stresses-volume changes-stability interrelation of ion intercalation electrodes.[3] 

References

[1] M.D. Levi and D. Aurbach, Electrochim. Acta 45 (1999) 167-185.

[2] N. Shpigel, M.D. Levi, S. Sigalov, O. Girshevitz, D. Aurbach, L. Daikhin, P. Pikma, M. Marandi, A. Janes, E. Lust, N. Jackel, V. Presser, Nat. Mater. 15 (2016) 570-575.

[3] S. Sigalov, N. Shpigel, M. D. Levi, M. Feldberg, L. Daikhin, D. Aurbach, Anal. Chem. 88, (2016) 10151–10157.