Towards elucidating microscopic structural changes in Li-ion conductors Li1+yTi2-yAly[PO4](3) and Li1+yTi2-yAly[PO4](3-x)[MO4](x) (M = V and Nb): X-ray and Al-27 and P-31 NMR studies

摘要

A combination of X-ray powder diffraction (XRD) and nuclear magnetic resonance (NMR) studies has demonstrated that attempted substitutions of Al, V and Nb into the framework of LiTi2(PO4)(3) yield several impurity phases in addition to direct substitutions of Al into Ti and V, Nb into P sites. Direct substitutions were confirmed by changes in the unit cell dimensions as indicated by the peak shifts observed in the X-ray diffractographs and by analyses of the Al-27 and P-31 magic angle spinning (MAS) spectra. A major impurity phase was identified as AlPO4 (found in at least two polymorphs) and the amount present increases with increasing Al additions. The formation of AlPO4 appeared to be enhanced by further V but suppressed by Nh substitution. These results suggest that the presence of AlPO4, together with the non-stoichiometric modified LTP, may be the cause for the observed densification of this material upon sintering and the increased ionic conductivity. [References: 17]