Flow battery recharging by thermoresponsive liquid–liquid phase separation

Abstract

Thermally regenerative flow batteries have attracted attention as thermo-electrochemical conversion devices because they enable not only the utilization of low-grade heat but also energy storage. Thermally regenerative flow batteries previously reported, however, are complicated systems because the charging process generates gases and requires evaporators and condensers for solvents. In this work, we proposed a thermally rechargeable flow battery based on a new concept, which is a liquid–liquid phase separation of the electrolyte in response to temperature. The proposed flow battery achieved stable charge–discharge cycles by using a small temperature difference between 60 °C and room temperature (approximately 23 °C). The thermal efficiency of the cell was estimated to be 0.9%, which was 8.1% relative to that of the Carnot cycle (11.1%). This concept can enhance the simplicity and safety of thermally regenerative redox flow batteries. Moreover, the operation temperature and cell performance can be flexibly tuned by designing an electrolyte with a large number of candidates for solvents exhibiting phase separation in response to temperature.