Long-Range and Short-Range Transport Dynamics of Li Ions in LiMn2O4

Investigation of lithium ion transport between different crystallographic sites in different phase structures has been regarded as a challenging diffraction issue. In this work, isothermal dielectric spectroscopy and the electric modulus of LiMn2O4 (LMO) were adopted to reveal Li-ion transport behavior. Dielectric and electric modulus spectra show three thermally activated processes: (i) enhanced mid-frequency dielectric permittivity above 133 K contributed by the short-range migration of Li ions, (ii) high-frequency dielectric relaxation associated with hopping of small polarons, and (iii) low-frequency giant dielectric loss (dc conductivity) caused by the long-range migration of Li ions at high temperature. In addition, an obvious change of dielectric permittivity around 280 K happens at structural transition from cubic to tetragonal of LMO. Furthermore, it was found that the short-range mobility of Li ions and hopping of small polarons lead to the variation of beta in the Kohlrausch-Williams-Watts (KWW) function of the electric modulus. Thus, our work provides a revealing insight into the electrical transport mechanism and migration dynamics of Li ions in LMO.