Confined phase transition triggering a high-performance energy storage thermo-battery†

Abstract

A thermoelectric device can directly convert heat to electricity, but its operation requires a temperature difference between the two electrodes of the thermocell. Unfortunately, the potential difference between the two electrodes disappears when there is no temperature difference, which greatly limits the practical conditions for power electronic devices. Here, we first report the utilization of thermo-responsive hydrophobic interactions to obtain a high-performance thermo-battery with a certain electrical storage capacity and achieve a thermoelectric device that can still supply power in the absence of heat input. In I⁻/I₃⁻ aqueous solution containing methyl cellulose (MC), the I₃⁻ concentration gradient caused by the hydrophobic association effect and the low/high entropy electrolyte transition caused by the confinement of bacterial cellulose (BC) not only enabled the thermo-battery to exhibit high thermoelectric performance (1.75 and −6.84 mV K⁻¹), but also, most surprisingly, the thermal voltage could be slowly self-discharged for about 312 hours (from −164.4 to −29.0 mV) when the temperatures at the hot- and cold-terminal electrodes are almost equal. This is the first discovery of rechargeable battery behavior in the field of thermoelectricity, which opens up new developments in thermocells at a deeper level.