Interfacial lithium-ion transfer at the LiMn2O4 thin film electrode/aqueous solution was investigated. The cyclic voltammograms of the film electrode conducted in the aqueous solution was similar to an adsorption-type voltammogram of reversible system, suggesting that fast charge transfer reaction proceed in the aqueous solution system. We found that the activation energy for this interfacial lithium-ion transfer reaction obtains 23-25 kJ mol(-1), which is much smaller than that in the propylene carbonate solution (50 kJ mol(-1)). This small activation energy will be responsible for the fast interfacial lithium-ion transfer reaction in the aqueous solution. These results suggest that fast lithium insertion/extraction reaction can be realized by decreasing the activation energy for interfacial lithium-ion transfer reaction. (C) 2007 Elsevier B.V. All rights reserved.