Calcium-ion thermal charging cell for advanced energy conversion and storage

Converting low-grade heat into electricity improves energy efficiency, reduces thermal pollution, and contributes to sustainability. However, the low thermal voltage, thermopower, or conversion efficiency of current monovalent-ion-based thermocells severely impede their application. Herein, we propose a new multivalent-ion-based calcium-ion thermal charging cell (CTCC) by introducing the concept of calcium-ion batteries into a thermoelectric system which demonstrates an ultrahigh thermopower of 25.2 mV K−1 through the synchronous thermo-extraction effect of oleic acid-treated Ca0.24V2O5·H2O electrode and thermodiffusion effect of electrolyte. The appealing calcium-ion energy carrier, favorable aqueous Ca(CF3SO3)2 electrolyte, and facile oleic acid modification strategy can ensure potentially higher voltage, enable fast diffusion kinetics, and prevent vanadium species from dissolution. As a result, the CTCC achieves ultrahigh thermal voltage of 1.149 V and Carnot-relative efficiency of 24.42% (± 0.22%) at a temperature difference of 45 K. This work enriches the multivalent-ion-based thermocell classes for efficient heat-to-electricity conversion in sustainable energy utilization.