Electrical transport properties in LiMn2O4, Li0.95Mn2O4, and LiMn1.95B0.05O4 (B=Al or Ga) around room temperature

Abstract

In order to identify the carrier responsible for the electrical transport at room temperature in LiMn2O4 from the viewpoint of practical applications as a cathode material, the bulk conductivity measurements by complex-plane impedance analyses have been carried out on LiMn2O4, Li0.95Mn2O4, and LiMn1.95B0.05O4 (B=Al3+ or Ga3+) together with the measurements of four-probe dc conductivities and dielectric relaxation processes, because these are two candidates for the carrier, a Li ion or a nonadiabatic small polaron of an eg electron on Mn3+. The comparison of the ionic conductivity estimated numerically from the parameters obtained experimentally for the Li-diffusion in LiMn2O4 with the bulk conductivity indicates that the Li-diffusion seems difficult to play the primary role in the electrical conduction. Instead, a hopping-process of nonadiabatic small polarons of eg electrons is likely to dominate predominantly the electrical transport properties. The dielectric relaxation process, and the activation energies and the pre-exponential factors of the bulk conductivities in Li0.95Mn2O4 and LiMn1.95B0.05O4 are explained self-consistently in terms of the polaronic conduction.