Enhanced Thermoelectric Properties of Bi₂Te₃‐Based Micro–Nano Fibers via Thermal Drawing and Interfacial Engineering

Abstract

High-performance thermoelectric (TE) materials with great flexibility and stability are urgently needed to efficiently convert heat energy into electrical power.Recently, intrinsically crystalline, mechanically stable, and flexible inorganic TE fibers that show TE properties comparable to their bulk counterparts are of interest to researchers. Despite remarkable progress moving TE fibers towards room-temperature TE conversion, the figure-of-merit value (ZT) and bending stability still need enhancement. Herein, we report interfacial engineering enhanced thermoelectric properties of micro-nano polycrystalline TE fibers fabricated by thermally drawing Bi2Te3-based bulks in a glass-fiber template. The interfacial engineering effect comes from generating stress-induced oriented nanocrystals to increase electrical conductivity and producing strain-distorted interfaces to decrease thermal conductivity. The resulting fibers achieve a 40% higher ZT (~1.4 at 300 K) than their 2 / 20 bulk counterparts and show a reversible bending radius of 50 µm, approaching the theoretical elastic limit. This fabrication strategy works for a wide range of inorganic TE materials and benefits the development of fiber-based micro-TE devices.

Enhanced N-Type Bismuth-Telluride-Based Thermoelectric Fibers via Thermal Drawing and Bridgman Annealing

“…The Seebeck coefficients ( S ) or the electrical conductivities ( σ ) of some fibers were measured by the four-probe method [ 20 ]. For each sample, 3-time fiber measurements were carried out under the same conditions, and we used the average values of 3-time fiber measurements as the measuring value.…”

“…In recent years, researchers have demonstrated ultralong TE fibers by the thermal drawing method to integrate crystalline TE micro/nanofibers into a glass-fiber template [ 15 , 16 , 17 , 18 , 19 ]. Although p-type Bi 2 Te 3 fibers are reported with a high ZT ~1.4 at room temperature [ 20 ], n-type Bi 2 Te 3 fibers have not been systematically studied or improved ZT values effectively by thermal drawing or post-treatment, resulting in TE fiber devices with p-n pairs cannot be widely used. The p-n pair fibers then have the potential to be applied in the field of wearable self-powered devices and temperature-sensing fabrics [ 7 , 21 , 22 , 23 ].…”

High-Performance n-Type Bi2Te3 Thermoelectric Fibers with Oriented Crystal Nanosheets

“…Theoretically, the ability of crystalline orientation is highly related to the crystal size and orientation degree of the c plane ( F ) [ 6 ]. There have been many studies on the introduction of crystalline orientation at various scales [ 7 , 8 , 9 , 10 , 11 , 12 ]; however, the artificial regulation of crystalline orientation and related mechanisms have rarely been reported.…”

“…In high-performance thermoelectric fiber devices, p-n Bi 2 Te 3 fibers are usually paired in series electrically and in parallel thermally to realize thermoelectric conversion [ 13 ]. To date, it has been found that the n-type Bi 2 Te 3 fibers (thermally drawn with glass cladding by a powder-in-tube method) could exhibit a restricted ZT < 0.5 owing to the low relative density and more texturing-related sensitivity of the carriers’ mobility than their p-type fibers ( ZT ~1.4) [ 9 ]. In the thermoelectric fibers fabricated by thermal drawing from our previous works [ 14 , 15 , 16 , 17 ], the c -plane crystalline orientation enhances the carrier mobility and electrical conductivity in Bi 2 Te 3 core fibers.…”

“…The optimized ZT values of the annealed fibers are measured to be about 1 near room temperature, which is about twice as large as that of their as-drawn fiber counterparts. The n-type Bi 2 Te 3 fibers with oriented crystal nanosheets in the core and the glass cladding protection can be connected by electroconductive paste electrically in series and thermally in parallel with the similar p-type Bi 2 Te 3 fibers to fabricate thermoelectric elements [ 6 , 9 , 13 ]. Additionally, they could be used in the field of waste heat recycling on the curved surface (e.g., hot water tubes and vehicle tailpipes), Peltier cooling, and temperature-sensing textiles (e.g., face masks and sleeveless shirts), etc.…”