ИСТИНА

In spite of a decade of successful commercialization, LiFePO4 and its derivatives continue to be an important part of scientific research in the field of Li-ion batteries due to their rich crystal chemistry and the number of intriguing properties1. Presence of certain amount of defects in the crystal structure of lithium iron phosphate may not only deteriorate but also to improve electrochemical performance of the olivine-type materials. The former effect is well-studied and generally acknowledged (e.g. antisite Fe/Li disorder diminishing Li+ diffusivity). The reasons and mechanisms of the latter (e.g. a small number of Li-Fe cations facilitating Li+ diffusivity), however, are still rather vague and need to be studied even more thoroughly since they could significantly improve existing technology2,3. Series of lithium-excess olivine-type cathode materials with general formula Li1+δ(Fe,M)PO4 (M = Mn, Co, Ni, Mg, Li; δ~0.05) was synthesized via solvothermal route with Li3PO4 as intermediate. Samples were investigated by X-ray powder diffraction, scanning electron microscopy and Mössbauer spectroscopy. The electrochemical properties and phase transformations were studied by means of galvanostatic cycling, potentiostatic intermittent titration, operando X-ray powder diffraction and Mössbauer spectroscopy. Dependence of high-C-rate performance, phase transformation behavior, electrode potential hysteresis on presence of one or two types of defects in the crystal structure is discussed in the work.