Current dependence of output voltage and discharge capacity of a tertiary battery

Tertiary batteries (TBs), which can be charged by a temperature change (ΔT), are prospective energy-harvesting devices. In this work, we investigated the variations in the output voltage (VTB) and discharge capacity (QTB) with current (I) of NaxCo[Fe(CN)6]0.87/NaxNi[Fe(CN)6]0.94 TBs (ΔT of 30 K) per unit weight of total active materials at 45 °C. Reflecting the battery resistance R, VTB(I) decreases with increasing I as VTBIRI=VTB0−MRI, where M is the total weight of the active material. We found that QTB(I) had values that were slightly smaller than those obtained by incorporating only the voltage-drop effect, QTBIRI=QTB(0)×VTBIR(I)VTB(0). The deviation between the observed QTB(I) and QTBIR(I) can be accurately explained in terms of the I-induced deformation of the discharge curve.