Olivine-type cathodes: Achievements and problems

The recent progress at Sony in the design of practical olivine-type cathodes is reviewed briefly. First principle calculations revealed LiFePO4 is a semiconductor with ca. 0.3 eV band gap and LiMnPO4 is an insulator with ca. 2 eV band gap, which seems the major intrinsic obstacle to a smooth redox reaction at 4 V in the Mn-rich phase. Attention is also focused on the lattice frustration induced by the strong electron (Mn3+: 3d4–egσ*)–lattice interaction (Jahn-Teller effect) in the charged state of Li(MnyFe1−y)PO4 (0≤y≤1). Dense nanocomposite formation with disordered conductive carbon as well as the choice of the appropriate synthetic precursors is highlighted as important engineering aspects, followed by some specific issues concerning tolerance to unusual conditions.