Luminescence in some lithiated transition metal oxide cathodes

Lithiated transition metal oxides such as LiNiVO4, Li2MnO3 and Li0.4WO3 used as cathode materials in high density lithium-ion batteries, show intense optical absorption followed by fluorescence in the region of 2–4 eV. These optical transitions can tentatively be assigned to either transition metal to oxygen charge transfer type or Jahn-Teller type local distortion. For fluorescing samples (LiNiVO4, Li2MnO3 and Li0.4WO4), photo-induced impedance (Bode plot) data show significant enhancement in impedance under low frequency range (not, vert, similar10 Hz). However, more important cathode materials such as LiCoO2 and LiMn2O4 do not show either fluorescence or photo-induced impedance enhancement. The presence or absence of an optical transition in the cathode system may give some clues on the tendency for electrochemical fading.