Salt Effects on Li-Ion Exchange Kinetics of Na₂Mg₂P₃O₉N: Systematic in Situ Synchrotron Diffraction Studies

The kinetics and thermodynamics of solid-state ion exchange of Li⁺ into Na₂Mg₂P₃O₉N were investigated using in situ synchrotron X-ray diffraction methods for a series of Li-containing salts, allowing systematic trends with general applicability to ion exchange reactions to be elucidated. The collection of data for a wide range of reaction conditions was enabled through the use of a novel multiwell sample environment which leverages the ability of the synchrotron beamline to rapidly (∼1 s) collect high-quality data suitable for monitoring reaction progress. From these data, it was possible to resolve the influence of salt choice and salt concentration on the ion exchange reaction kinetics. Furthermore, by carrying out experiments at different temperatures, initial estimates of activation energies were obtained. It was generally found that the ion exchange reaction kinetics strongly depended on the salt chosen as the ion source rather than being primarily determined by the ion mobility of the ceramic.