Radiolysis study on PVDF binder - how does it affect the X-ray photoelectron spectroscopy characterisation of phospho-olivine electrodes?

The reliability of surface characterisation in battery research is often compromised by the diagnostic techniques, which can induce unintended chemical changes during measurement. This is a particular concern for polyvinylidene fluoride (PVDF), which is a standard polymer binder used to maintain the structural integrity of battery electrodes. Such degradation creates measurement artefacts that can be easily mistaken for genuine electrochemical behaviour. This study utilizes X-ray photoelectron spectroscopy and kinetic modelling to investigate the X-ray-induced radiolysis of the PVDF binder. In addition, by comparing the behaviour of pure LiMn x Fe1-x PO4 powder to electrodes cast with PVDF, we demonstrate that the presence of the active material fundamentally alters how the binder decomposes, which triggers a consistent reduction of Fe oxidation states across all electrodes post-exposure. Specifically, the degradation is PVDF-concentration-dependent. The 2 wt% PVDF electrode displays a more rapid overall formation of LiF on the surface than the 10 wt% PVDF electrode, which shows an accelerated initial fluorine loss but a stabilised LiF content after 5 hours. These findings provide essential guidelines for interpreting spectroscopic data of battery electrodes, enabling researchers to properly distinguish measurement-induced artefacts from genuine electrochemical phenomena.