Mechanistic insights of Li(+) diffusion within doped LiFePO(4) from Muon Spectroscopy

The Li(+) ion diffusion characteristics of V- and Nb-doped LiFePO(4) were examined with respect to undoped LiFePO(4) using muon spectroscopy (µSR) as a local probe. As little difference in diffusion coefficient between the pure and doped samples was observed, offering D(Li) values in the range 1.8–2.3 × 10(−10) cm(2) s(−1), this implied the improvement in electrochemical performance observed within doped LiFePO(4) was not a result of increased local Li(+) diffusion. This unexpected observation was made possible with the µSR technique, which can measure Li(+) self-diffusion within LiFePO(4), and therefore negated the effect of the LiFePO(4) two-phase delithiation mechanism, which has previously prevented accurate Li(+) diffusion comparison between the doped and undoped materials. Therefore, the authors suggest that µSR is an excellent technique for analysing materials on a local scale to elucidate the effects of dopants on solid-state diffusion behaviour.