Identifying the Structure of the Intermediate, Li2/3CoPO4, Formed during Electrochemical Cycling of LiCoPO4.

摘要: In situ synchrotron diffraction measurements and subsequent Rietveld refinements are used to show that the high energy density cathode material LiCoPO4 (space group Pnma) undergoes two distinct two-phase reactions upon charge discharge, both occurring via an intermediate Li2/3(Co2+)2/3(Co3+)1/3PO4 phase. Two resonances observed for Li2/3CoPO4 with intensity ratios of 2:1 1:1 in 31P 7Li NMR spectra, respectively. An ordering Co2+/Co3+ oxidation states is proposed within a (a × 3b c) supercell, Li+/vacancy investigated using experimental data combination first-principles solid-state DFT calculations. lowest configuration, Co3+ ions Li vacancies found order along b-axis. other low schemes only 5 meV per formula unit higher energy. All three configurations lie below LiCoPO4–CoPO4 convex hull they may be readily interconverted by Li+ hops b-direction.