Rational Material Selection for Li-Ion-Based Thermogalvanic Harvesting Devices

Abstract

Harvesting devices based on thermogalvanic principles,such asthermally regenerative electrochemical cycles (TREC), hold great promisefor Internet of Things applications where autonomy is critical. Onearchitecture that is particularly interesting for TREC cells withimproved energy density, efficiency, and scalability is the thin-filmLi-ion battery. In this work, a paradigm to guide the design of thin-filmLi-ion-based TREC cells is established via three criteria for electrodeselection. These requirements were distilled by translating the TRECprinciple into measurable material properties for Li-ion electrodes.More specifically, the identified criteria included a high thermogalvaniccell coefficient preferably exceeding 0.2 mV K-1, a weak dependence of the thermogalvanic coefficient on the lithiationstate, and a favorable balance between the thermogalvanic cell coefficientand electrode kinetics as estimated from the lithiation overpotential.The material properties necessary to assess these criteria can allbe obtained via a previously developed thermogalvanic characterizationmethodology. In the present work, this methodology was applied toa catalogue of five electrode materials, namely, LiMn2O4 (LMO), Li4Ti5O12 (LTO),LiFePO4 (LFP), anatase TiO2, and Cl-doped amorphousTiO(2). The obtained results were organized into three separateblocks, each focused on a specific aspect, like electrolyte decomposition,nanoscaling effects, and kinetics, that warrants special considerationduring thermogalvanic characterization. A material selection matrixwas subsequently compiled by applying the aforementioned selectioncriteria to the characterization results. In this manner, LTO wasidentified as the most suitable candidate electrode, and recommendationsfor future investigations of thin-film Li-ion TREC devices could bedelivered.