(Invited) The Use of Eqcm-D for in-Situ Characterization of Dimensional Changes in Cycled Battery Electrodes

Ions adsorption/desorption in nanoporous carbon electrodes and, especially, Li-ion insertion/extraction to/from typical battery electrodes are accompanied by significant volume changes, which complicates enormously gravimetric analysis by EQCM of the ionic fluxes involved in these processes. [1, 2] Gravimetric analysis by EQCM is based on the use of the classical Sauerbrey’s equation, which transforms ions insertion-induced resonance frequency changes into mass (or ions population) changes. Such an approach implies that additional mass onto quartz-crystal coating is of pure inertial origin, so that the dissipation factor of the oscillating crystal, and hence the related resonance width, remain constant. Figure 1 shows a drastic increase in the resonance width accompanying frequency change during Li-ion extraction from a thin LiFePO₄ electrode. A finite difference of about 20% exists between the experimentally measured frequency shift and that calculated from the Sauerbrey’s equation (based on the electrochemical data that enable calculations of mass changes).  As has been recently reported,  [3] measuring  frequency differences together with the changes in the resonance peak width can provide input parameters of the hydrodynamic admittance models of composite battery electrodes.  With such information it is possible to obtain important potential-dependent structural parameters of the composite electrodes, namely, effective thickness of the porous active mass and its permeability (linked to porosity). This new approach to characterization of composite battery materials has been recently developed in collaboration with researchers from Tel-Aviv University [1,2], and was applied successfully to describe dynamics of Li ion batteries  electrodes [3] and to understand the capacitive paradox of Ti₃C₂  MXene  phase electrodes [4] in collaboration with research teams at the Leibnitz Institute (Germany) and Drexel University (USA), respectively. The method is based on the fact that intercalation-induced changes in geometric structural parameters of electrodes, modify their hydrodynamic interactions of with the electrolyte solutions. These are nicely recorded by EQCM-D and analyzed in terms of suitable admittance models.  Until recently, we applied this approach to composite electrodes containing only rigid binders (such as PVdF in contact with aqueous solutions). Herein we are going to extend the EQCM-D based methodology for structural characterization of composite electrodes containing viscoelastic polymeric binders, developing thus a non-invasive in-situ dynamic monitoring of elastic properties of composite battery electrodes (using EQCM-D) [5]. This unique method can be adjusted for the characterization of viscoelastic behavior of polymeric binders during long-term cycling of composite electrodes used in all kinds of batteries.

References

(1)       Levi, M.D;  Sigalov S.; Aurbach, D.; Daikhin, L. J. Phys. Chem. C 2013, 117, 14876−14889.

(2)       Daikhin, L.; Levi, M.D.; Sigalov, S.; Salitra, G.; Aurbach, D. Anal. Chem., 2011, 83, 9614–9621.

(3)       Levi, M.D;  Sigalov S.; Salitra, G.; Elazari, R.; Aurbach, D.;  Daikhin, L.; Presser,  V. J. Phys. Chem. C  2013, 117, 1247−1256.

(4)       Levi, M. D.; Lukatskaya , M. R.; Sigalov, S.; Beidaghi, M.; Shpigel, N.; Daikhin, L.; Aurbach, D.; Barsoum, M. W.; Gogotsi, Y.;. Adv. Energy Mater. 2015, 1400815.

(5)       Shpigel, N.; Levi, M.D;  Sigalov, S.; Girshevitz,O.; Aurbach, D.; Daikhin, L.; Jäckel, N.;] Presser, V. Angew. Chemie, 2015 (accepted) DOI: 10.1002/anie.201501787.