LiMn1.5Ni0.5O4 is synthesized by a sol–gel method and the intercalation kinetics as positive electrode for lithium-ion batteries is investigated by EIS. LiMn1.5Ni0.5O4 particles prepared via sol–gel process possess spinel phase with Fd-3m space group. The charge-transfer resistance, the exchange-current density and the solid-phase diffusion are found as a function of temperature. The apparent activation energy of the exchange current, the charge transfer, and the lithium diffusion in solid phase are also determined, respectively. This result indicates that the effect of the temperature on the cell capacity and the current dependence of the capacity results mainly from the enhancement of the lithium diffusion at elevated temperatures. It can be concluded that LiMn1.5Ni0.5O4 cell has a bad rate cycling performance at elevated temperatures before any modification due to the high diffusion apparent activation energy. The relevant theoretical elucidations thus provide us some useful insights into the design of novel LiMn1.5Ni0.5O4-based positive-electrode materials.