Following the reaction mechanisms of materials for Li-ion batteries under in situ conditions can provide vital new clues in the development of better battery materials. A new in situ cell was developed for such a purpose which allows an almost simultaneous measurement of XRD (X-ray diffraction) and XAS (X-ray absorption spectroscopy) at energies as low as the Ti K-edge. Change from one method to the other was possible in less than a minute at the Swiss–Norwegian Beamline (SNBL). Using this cell with its flexibility in terms of windows, it was proven that the reaction mechanism of iron titanium oxyphosphate (Fe0.5TiOPO4) upon lithiation and delithiation consists of a combined insertion–conversion reaction with the mostly reversible reduction of Ti4+ to Ti2+ and Fe2+ to Fe0.

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The reaction mechanism of Cu0.5TiOPO4 upon lithiation and delithiation was elucidated by XAS, 31P-NMR, XRD, EDX, and electrochemical methods. The material reacts with a combined insertion and conversion process, forming first LiTiOPO4 + Cu. Afterwards, Ti4+ is reduced reversibly in an insertion reaction followed by a conversion reaction leading to amorphisation while titanium is reduced below 2+.