Enhanced Thermal Electromotive Force in Lithiated CoPBA/NiPBA Tertiary Battery

Tertiary batteries (TBs), or thermo-rechargeable batteries, have attracted attention as an energy harvesting technology that utilizes changes in ambient temperature. Prussian blue analogues (A-MPBAs; AxM[Fe(CN)6]y, where A and M are Li+ or Na+ ions and a transition metal, respectively) are typical active materials for TBs. In this study, we investigated the lithiation effect on the temperature (α) and capacity (β) coefficients of redox potential E, which governs the thermal electromotive force (VTB) and discharge capacity (QTB) of TBs. We fabricated lithiated and non-lithiated TBs composed of A-CoPBA and A-NiPBA and investigated their performance between 20 °C and 39 °C. We found that the observed VTB (= 29–30 mV) of the lithiated TB is larger than that (= 23–25 mV) of the non-lithiated TB and interpreted the behavior in terms of the smaller ionic radius of Li+.