In situ and ex situ X-ray study of formation and decomposition of Li2CoPO4F under heating and cooling. Investigation of its local structure and electrochemical properties

Two synthetic processes, a single-step and a two-step one, both using preliminary mechanical activation (MA) of reagent mixtures, were investigated to prepare Li2CoPO4F. In situ and ex situ X-ray study of the formation and decomposition of Li2CoPO4F under heating and cooling was performed. It was found that Li2CoPO4F was already formed at the stage of MA of the mixture of LiCoPO4 with LiF. However, phase pure Li2CoPO4F was obtained only after heating to 600 – 650°C and quenching this mixture to room temperature via incorporation of LiF into the structure of LiCoPO4. Structural and electrochemical properties of as prepared material were analyzed by IR, NMR spectroscopy and galvanostatic cycling. According to IRS, the introduction of F- ions in the second coordination sphere of P3 + results in the rise of symmetry of PO4 tetrahedra in Li2CoPO4F. Three distinct Li positions and one P position, as well as the presence of Li defects in as prepared Li2CoPO4F were approved by NMR study.