Abstract
The temperature coefficient (α≡∂V∂T) of the redox potential (V) is a significant physical quantity for energy conversion. A thermocell can convert heat energy into electric energy by using the difference in α between cathode and anode materials. Here, we carefully determined α of a prototypical intercalation compound, LixFePO4, against Li concentration (x). α is found to be ≈ 0.90 mV/K irrespective of x, reflecting phase separation (PS) into LiFePO4 and FePO4. We further evaluated the entropies (S) of LiFePO4 and FePO4 by means of first-principles calculations. Considering the solvent effect of ≈ 0.50 mV/K, the residual amount (≈ 0.40 mV/K) of α is well reproduced by 1eΔS between LiFePO4 and FePO4, where e is the elementary charge (> 0).
Highlights
The charged electric energy can be extracted through the discharge process at (b) T H and (d) T L
The charged electric energy can be extracted through discharge processes
Shibata et al.[4] recently fabricated a battery-type thermocell, which consists of two kinds of Prussian blue analogue (PBA) solids with different α
Summary
A thermocell can convert heat energy into electric energy by using the difference in α between cathode and anode materials. Several researchers[1,2,3,4,5] reported that a thermocell that uses the difference in the temperature coefficient of redox potential between the anode and cathode materials converts cell temperature to cell voltage. The thermocell produces electric energy from a thermal cycle, which sharply contrasts semiconductor-based thermoelectric devices This thermal cycle consists of four processes: (a) heating from low temperature (T L) to high temperature (T H), (b) discharge at T H,. Lee et al.[1] fabricated a thermocell where the anode and cathode are [Fe(CN)6]3+/[Fe(CN)6]4+6 and Prussian blue analogue (PBA) solid, and succeed in production of electric energy.
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