Engineering of Novel Thermoelectric Materials and Devices for Next Generation, Long Life, 20 Efficient Space Power Systems

摘要

Proven state-of-practice "heritage" thermoelectric (TE) materials used in extremely reliable radioisotope power systems (RPS) exhibit only modest dimensionless figure of merit (ZT) values, resulting in relatively system-level conversion efficiencies of 6 to 6.5%. These heritage materials have been known since the late 1950's and 1960's, so that even the recently developed multi-mission radioisotope thermoelectric generator (MMRTG) used in the recent mission to Mars, Curiosity, builds upon 40-year old thermoelectric converter technology. However, there is great potential for large gains in performance thanks to recent advances in materials synthesis, the discovery of novel complex structure compounds, the ability to engineer with increasing precision micro- and nanostructure features coupled with improved scientific understanding of electrical and thermal transport in such engineered materials and the means to perform in-depth theoretical simulations with fast turnaround time. In the last few years, sustained NASA-funded collaborative research on high temperature TE materials has already resulted in doubling TE couple-level conversion efficiency from about 7.0 - 7.5% up to 15% at beginning of life. Current efforts are aimed at achieving even higher conversion efficiencies, in excess of 20%, in the next few years. The research areas include structurally complex refractory compounds, design engineering of composite materials to decouple and optimize electrical and thermal transport properties and compositional tuning guided by computationally intensive first principles theoretical calculations. In addition, activities have also recently focused on facilitating the infusion of these high performance materials into robust, long life converters by exploring mechanical strengthening through nanocompositing processes, developing advanced, fast throughput synthesis, compaction and metallization techniques, and evaluating approaches to modular device and converter architectures.