Principal Investigator Yang Shao-Horn
Co-investigator Carl Thompson
Technologies for the Internet of Things (IoT) are be- ing developed. An IoT network consists of large quan- tities of networked sensors that are often in remote or difficult to access locations, which drives the need for self-powered systems. Here, we come up with two types of multi-cell thermogalvanic systems that gener- ate electrical power through temperature cycles.
The dual-temperature, dual-stack, self-powered electrochemical system is depicted. This dual-temperature system uses two identical electrochemical stacks, which can be a single battery or multiple batteries connected in series; however, each electrochemical stack is held at a different temperature. On the other hand, a single-temperature system works similarly, with the electrochemical stacks having similar operating potentials but oppositely signed temperature coefficients. Its operation is illustrated. Both systems can harvest energy from temperature cycles.
We have tested both dual-temperature systems and single-temperature systems with different cathode/ anode materials, load resistances, and frequencies of temperature cycles. The largest energy conversion efficiency was obtained from the dual-temperature experiment with two homemade LiCoO2/Li coin cells in which the cathodes with composition Li0.85CoO2 were cycled between 20 °C and 50 °C. The loads were two 100Ω resistors. The current is shown in Figure 3, and the efficiency was calculated to be 0.22%. This value is comparable to the efficiency obtained using charging-free thermally regenerative electrochemical cycles (TRECs), thermocapacitive cycles and ionic thermoelectric supercapacitors, but with more flexibility of material selection. In the meantime, we have also tested two single-temperature systems with four LiV2O5/Li-Al and three LiCoO2/Li cells, and one LiMnO2/Li-Al and one LiV2O5/Li-Al cell, respectively. Although the efficiency and power were still limited, they confirmed the feasibility of this concept. These systems can be further optimized by using materials with higher temperature coefficients and decreasing internal resistance at the same time.