The source of first-cycle capacity loss in LiFePO4

The electrochemical extraction of lithium from solid-state synthesised LiFePO4 has been studied by neutron powder diffraction. A “coffee-bag” type cell of configuration left angle bracketLi-metal liq. el. LiFePO4right-pointing angle bracket has been charged to 4.1 V, dismantled in a glovebox, and the composite cathode powder sample scraped from the current collector. Two-phase Rietveld refinement gave a triphylite (LiFePO4) to heterosite (FePO4) phase-ratio of 18:82. In the absence of significant absorption effects, this ratio is a true representation of the conversion of LiFePO4 to FePO4. Possible mechanisms for lithium extraction/insertion during the first-cycle are discussed.