Hyperfine fields at the Li site in LiFePO₄-type olivine materials for lithium rechargeable batteries: A ⁷Li MAS NMR and SQUID study

The ⁷Li NMR isotropic shift for olivine LiMPO₄ (M = Fe, Mn, Co, Ni) is assigned to hyperfine coupling between the ⁷Li nucleus and the transition metal unpaired electrons on the basis of the Curie−Weiss temperature dependence of the shift. The hyperfine shift arises from a linear combination of Li−O−M through-bond interactions wherein the unpaired A‘ electrons contribute a negative shift and the unpaired A‘ ‘ electrons contribute a positive shift. The hyperfine coupling constant is determined for each composition.