Heterogeneous behaviour of the lithium battery composite electrode LiFePO4

To improve the performance of the positive electrode in batteries, it is important to thoroughly characterize these materials during battery cycling, beyond just electrochemical characterization. Among the very few techniques available for operando studies, X-ray Absorption Spectroscopy (XAS) appears very powerful, with high spatial and time resolutions provided by synchrotron radiation. Moreover XAS is well known for its capabilities in charge transfer and structure determinations, both being the major changes induced by electrochemical cycling of electrode materials. By an appropriate combination of three XAS beamlines using a specially designed electrochemical cell, we have studied composite positive electrodes made with LiFePO4 as the active material. We directly observed the heterogeneity of the electrode during operation, some parts being delayed and others advanced, compared to the mean charge state of the electrode. A mapping of this heterogeneity was made at different length scales.

► Structural and electronic modifications of a battery electrode were observed operando.
► A heterogeneous behaviour of the electrode is clearly evidenced.
► The redox process is mapped at a micrometre scale.
► The heterogeneity is influenced by cycling regime, pressure, formulation.