Device‐Level Optimization ofn‐Type Mg₃(Sb, Bi)₂‐Based Thermoelectric Modules toward Applications: A Perspective

Abstract

In recent decades, improvements in thermoelectric material performance have made it more practical to generate electricity from waste heat and to use solid‐state devices for refrigeration. However, despite the development of successful strategies to enhance the figure‐of‐merit zT, optimizing devices for large‐scale applications remains challenging. High zT values do not guarantee excellent device performance, and maintaining high zT over a wide temperature range is difficult. Thus, device‐level structural optimization is crucial for maximizing overall energy conversion efficiency. Proper interfacial and structure design strategies, including contact layer selection, multi‐stage optimization, and size matching for the n‐ and p‐type thermoelectric legs, are necessary for advancing device performance. Additionally, thermal stability issues, device assembly techniques, mechanical properties, and manufacturing costs are crucial considerations for large‐scale applications. To achieve actual applications, the thermoelectric community must look beyond simply aiming for high zT values. This article focuses on modules based on n‐type Mg3(Sb, Bi)2, one of the most promising commercially available thermoelectric materials, and discusses the influence of various parameters on the modules and on the corresponding device‐level optimization strategies.

Low-Cost Magnesium-Based Thermoelectric Materials: Progress, Challenges, and Enhancements

“…Iron demonstrated a lower contact resistance for Mg 3 Bi 1.5 Sb 0.5 in comparison with Ni. 163 It had a contact resistance of 1.18 × 10 −5 Ω• cm 2 after hot pressing, and increased to 1.76 × 10 −5 Ω•cm 2 after 2100 h aging at 573 K. Wu et al employed alloys like Fe 7 Mg 2 Cr and Fe 7 Mg 2 Ti as interfacial contact material for Mg 3 Sb 2 -based TE legs, which had a balanced high σ s (45−50 MPa) and low contact resistance of 2−3 × 10 −6 Ω•cm 2 , although it increased to 7−8 × 10 −6 Ω•cm 2 after aging at 673 K for 15 days. 134 An optimized interfacial alloy, FeCrTiMnMg, demonstrated a CTE of approximately 16 × 10 −6 K −1 at room temperature, approaching that of Mg 3 Sb 1.5 Bi 0.5 .…”

“…However, the conductivity reduced after long service time. 163 Nickel contact hot-pressed on the as-prepared Mg 3+δ Bi 1.5 Sb 0.5 had a resistance of 1.30 × 10 −5 Ω•cm 2 , which increased to 1.85 × 10 −5 Ω•cm 2 after aging for 2100 h at 573 K. 163,164 Mixtures of Ni with other metals like Fe or Cr also showed promising results, especially NiFe, which exhibited excellent thermal stability and the lowest ohmic contact resistance even after aging (1.30 × 10 −5 Ω•cm 2 ) due to the formation of metallic NiMgBi between NiFe and Mg 3+δ Bi 1.5 Sb 0.5 .…”