Probing the Aging Effects on Nanomechanical Properties of a Thin Film LiFePO4 Cathode

Abstract

Li-ion batteries offer great promise for future due to their superior gravimetric and volumetric energy density. One of the challenges is to improve the cycle life of Li-ion batteries which requires detailed understanding of the aging phenomenon. The aging mechanism of Li-ion batteries can have both chemical and mechanical origins. While the chemical degradation mechanisms have been studied extensively, mechanical degradation mechanisms have received little attention so far. In this study, we probed the changes in mechanical properties of a thin film and composite LiFePO4 cathode on pristine and aged samples. By studying both composite (active particles and binder) and thin film (active particles only) cathodes in parallel, it is possible to pinpoint the origin and magnitude of the mechanical degradation. Results showed that mechanical properties of the thin film LiFePO4 did not show as significant deterioration as in a composite LiFePO4 cathode indicating mechanical degradation in binder is more problematic than the mechanical degradation in the active material.