A phenomenological expression of solid-state redox potentials is proposed in order to understand anomalous voltage behaviors of the insertion materials LiCoO2, LiCo1/2Ni1/2O2, and LiNiO2. The method consists of the superposition of each redox system characterized by Eq. 4 and 5 (see text), describing both one-phase and two-phase reactions by adjusting the interaction-energy parameter z phi(i). For the reaction of square MeO2 + yLi --> Li(y)MeO2, the reversible electrode potentials, E(y), which are observable, are obtained in a self-consistent manner from the electrochemical density of states. A thus- described solid-state electrochemical reaction consists of three redox systems characterized by E-Oi = 4.50, 4.18, and 3.91 V for LiCoO2; 4.23, 3.93, and 3.63 V for LiNiO2; and 4.58, 4.05, and 3.58 V for LiCo1/2Ni1/2O2. From these results the characteristic features of solid-state redox electrodes are described and the significance of this method in materials research for advanced batteries is discussed.