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ACS Appl Mater Interfaces. 2017 Aug 23;9(33):27664-27675. doi: 10.1021/acsami.7b06243. Epub 2017 Aug 10.

In Situ Multilength-Scale Tracking of Dimensional and Viscoelastic Changes in Composite Battery Electrodes.

Author information

1
Department of Chemistry, Bar-Ilan University , Ramat-Gan 52900, Israel.
2
INM - Leibniz Institute for New Materials , 66123 Saarbrücken, Germany.
3
Department of Materials Science and Engineering, Saarland University , 66123 Saarbrücken, Germany.
4
School of Chemistry, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel-Aviv University , Ramat Aviv 69978, Israel.

Abstract

Intercalation-induced dimensional changes in a composite battery electrode (comprising a polymeric binder) are one of the major factors limiting electrode cycling performance. Since electrode performance is expressed by the quantities averaged over its entire surface area (e.g., capacity retention, Faradaic efficiency, rate capability), significant efforts have been made to develop a methodology allowing its facile mechanical diagnostics at the same areal scale. Herein we introduce such a generic methodology for a highly sensitive in situ monitoring of intrinsic mechanical properties of composite battery electrodes. The gravimetric, dimensional, viscoelastic, and adhesive changes in the composite electrodes caused by Li-ions intercalation are assessed noninvasively and in real time by electrochemical quartz-crystal microbalance with dissipation monitoring (EQCM-D). Multiharmonic acoustic waves generated by EQCM-D penetrate into thin porous electrodes comprising either rigid or a soft binder resulting in frequency and dissipation changes quantified by analytical acoustic load impedance models. As a first demonstration, we used a composite LiFePO4 (LFP) electrode containing either polyvinylidene dichloride (PVdF) or Na carboximethyl cellulose (NaCMC) as rigid and viscoelastic binders, respectively, in aqueous electrolytes. The intercalation-induced volume changes of LFP electrode were evaluated from a hydrodynamic correction to the mass effect of the intercalated ions for PVdF, and both components of the effective complex shear modulus (i.e., storage and loss moduli) in case of NaCMC binder have been extracted. The sliding friction coefficients for large particles bound at their bottom to the quartz crystal surface (a measure of the adhesion strength of binders) has also been evaluated. Tracking the mechanical properties of the composite electrodes in different environments and charging/cycling conditions in a self-consistent manner provides all necessary conditions for an optimal selection of the polymeric binders resistant to intercalation-induced volume changes of intercalation particles.

KEYWORDS:

EQCM; NaCMC; PVdF; QCM-D; composite electrodes; lithium ion battery; polymer binders

PMID:
28777536
DOI:
10.1021/acsami.7b06243

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