Delithiation Study of LiFePO4 Crystals Using Electron Energy-Loss Spectroscopy

There is still some controversy about the mechanisms responsible for the delithiation of LiFePO4. We studied the delithiation of both large single crystals and powder by electron energy-loss spectroscopy. It is shown that Li depletion leads to a change in the Fe valency, to an enhanced prepeak at the O K edge, and to a pronounced interband transition peak between 4 and 6 eV. Exploiting these spectral changes, the delithiation process was monitored, with the result that in the large single crystal, delithiation takes place by removal of Li from the surface-near region, whereas in small particles, Li is removed from the particle core.