Dynamic interactions between electrode and electrolyte species during electrochemical cycling have an impact on the interfacial kinetics and mechanical stability of the electrode materials. In this study, we employ in-situ stress and strain measurements to investigate potential-dependent mechanical changes in lithium iron phosphate (LiFePO4) cathodes during cyclic voltammetry in LiPF6 and LiClO4-containing electrolytes. Analysis of the stress and strain derivatives in LiClO4-containing electrolytes exhibits single peaks during both lithiation and delithiation that coincide with LiFePO4 phase transformations. An additional feature in the stress and strain derivatives is observed in LiPF6-containing electrolytes at the onset of the delithiation process. The current peak splitting in LiPF6 is larger than in LiClO4, and electrochemical impedance spectroscopy measurements show higher impedances in LiPF6 versus LiClO4-containing electrolytes in lithiated LiFePO4. The larger current peak splitting and higher impedance in LiPF6 electrolytes suggest the potential-dependent growth of a thick and resistive cathode/electrolyte interface (CEI) layer on LiFePO4 cathodes. We hypothesize that kinetic limitations in Li+ transport through the CEI leads to additional stress and strain development at the electrode surface.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Materials Chemistry
- Surfaces, Coatings and Films
- Renewable Energy, Sustainability and the Environment