Tertiary battery is charged by the environmental heat, not by the electric energy, by using the difference (Δα) in the thermal coefficient (α=dV/dT) of redox potential (V) between the anode and cathode materials. The thermal cyclability is not good in the prototypical NaxCo[Fe(CN)6]0.71 (NCF71)/NaxCo[Fe(CN)6]0.90 (NCF90) tertiary battery. Here, we significantly improved the thermal cyclability of the tertiary battery with using Ni‐substituted NaxNi[Fe(CN)6]0.68 (NNF68). The Ni‐substituted NNF68/NCF90 tertiary battery shows good thermal cyclability: both the cell voltage and capacity essentially unchanged up to the 10th thermal cycles.

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