The standard Gibbs free energy of formation of LiMnO2 and LiMn2O4 at the temperatures of (680, 740 and 800) K has been determined with the help of the solid-state galvanic cells involving lithium-p-alumina electrolyte. The equilibrium electrical potentials of cathode containing LixMn2O4 spinel, in the composition ranges 0 less than or equal to x less than or equal to 1 and 1 less than or equal to x less than or equal to 2, vs. metallic lithium in the reversible intercalation galvanic cell have been calculated. The existence of two-voltage plateaus which appeared during charging and discharging processes in reversible intercalation of lithium into LixMn(2)O(4) spinel, has been discussed. (C) 2004 Elsevier Ltd. All rights reserved.