Zuoqian Wang

Enhanced Performance of Dispenser Printed MA n-type Bi2Te3 Composite Thermoelectric Generators

This work presents performance advancements of dispenser printed composite thermoelectric materials and devices. Dispenser printed thick films allow for low-cost and scalable manufacturing of microscale energy harvesting devices. A maximum ZT value of 0.31 has been achieved for mechanically alloyed (MA) n-type Bi₂Te₃-epoxy composite films with 1 wt % Se cured at 350 °C. The enhancement of ZT is a result of increase in the electrical conductivity through the addition of Se, which ultimately lowers the sintering temperature (350 °C). A 62 single-leg thermoelectric generator (TEG) prototype with 5 mm ×700 μm × 120 μm printed element dimensions was fabricated on a custom designed polyimide substrate with thick metal contacts. The prototype device produced a power output of 25 μW at 0.23 mA current and 109 mV voltage for a temperature difference of 20 °C, which is sufficient for low power generation for autonomous microsystem applications.

High-Performance Dispenser Printed MA p-Type Bi0.5Sb1.5Te3 Flexible Thermoelectric Generators for Powering Wireless Sensor Networks

This work presents a novel method to synthesize p-type composite thermoelectric materials to print scalable thermoelectric generator (TEG) devices in a cost-effective way. A maximum ZT of 0.2 was achieved for mechanically alloyed (MA) p-type Bi0.5Sb1.5Te3 (8 wt % extra Te additive)-epoxy composite films cured at 250 °C. A 50% increase in Seebeck coefficient as a result of adding 8 wt % extra Te in stoichiometric Bi0.5Sb1.5Te3 contributed to the increase in ZT. To demonstrate cost-effective and scalable manufacturing, we fabricated a sixty element thermoelectric generator prototype with 5.0 mm × 600 μm × 120 μm printed dimensions on a custom designed polyimide substrate with thick metal contacts. The prototype TEG device produced a power output of 20.5 μW at 0.15 mA and 130 mV for a temperature difference of 20 K resulting in a device areal power density of 152 μW/cm(2). This power is sufficient for low power applications such as wireless sensor network (WSN) devices.

Integration of dispenser-printed ultra-low-voltage thermoelectric and energy storage devices

This paper reports on an integrated energy harvesting prototype that consists of dispenser-printed thermoelectric energy harvesting and electrochemical energy storage devices. Parallel-connected thermoelectric devices with low internal resistances were designed, fabricated and characterized. The use of a commercially available dc-to-dc converter was explored to step-up a 27.1 mV input voltage from a printed thermoelectric device to a regulated 2.34 V output at a maximum of 34% conversion efficiency. The regulated power succeeds in charging dispenser-printed, zinc-based micro-batteries with charging efficiencies of up to 67%. The prototype presented in this work demonstrates the feasibility of deploying a printable, cost-effective and perpetual power solution for practical wireless sensor network applications.

Dispenser printed circular thermoelectric devices using Bi and Bi0.5Sb1.5Te3

This work presents polymer based composite materials used in slurries form to print low cost and scalable micro-scale Thermoelectric Generator (TEG) devices. Bi-epoxy composite is chosen as n-type material and mechanical alloy p-type Bi0.5Sb1.5Te3 with 8 wt. % extra Te-epoxy composite is used as p-type material. Maximum power factor of 0.00008 W/m-K2 is achieved for Bi-epoxy and Bi0.5Sb1.5Te3 with 8 wt. % extra Te-epoxy composite dispenser printed thick films. A 10 couple dispenser printed circular TEG prototype produced 130 μW power at ΔT of 70 K resulting in a device areal power density of 1230 μW/cm2.

Mechanical fatigue as a mechanism of water tree propagation in TR-XLPE

The paper reports on an investigation of the fatigue failure of tree retardant cross-linked polyethylene (TR-XLPE) that is relevant to water tree development in underground cable insulation. Finite element calculations were used to estimate the stresses developed in cable insulation by di-electrophoretic forces; these stresses are in the low megaPascal range around inclusions (or water tree branches) that are long and thin. They are insufficient to bring about instantaneous failure of the insulation. However, these stresses might be sufficient to cause cyclic fatigue failure of the insulation, and, accordingly, fatigue measurements were carried out on samples from a commercial cable. The resulting fatigue failures, that occurred at cycle numbers achievable in practical work, suggest that fatigue might be an explanation for slow development of water trees over years of service in the ground. Cycle numbers at failure were found to be lower at higher mechanical stresses, at higher temperatures and in the presence of humic acid or ferric ions; however, the number of cycles to failure was larger in the presence of water.

Development and manufacture of printable next-generation gel polymer ionic liquid electrolyte for Zn/MnO 2 batteries

While much energy storage research focuses on the performance of individual components, such as the electrolyte or a single electrode, few investigate the electrochemical system as a whole. This research reports on the design, composition, and performance of a Zn/MnO2 battery as affected by the manufacturing method and next-generation gel polymer electrolyte composed of the ionic liquid [BMIM][Otf], ZnOtf salt, and PVDF-HFP polymer binder. Materials and manufacturing tests are discussed with a focus on water concentration, surface features as produced by printing processes, and the effect of including a gel polymer phase. Cells produced for this research generated open circuit voltages from 1.0 to 1.3 V. A dry [BMIM][Otf] electrolyte was found to have 87.3 ppm of H2O, while an electrolyte produced in ambient conditions contained 12400 ppm of H2O. Cells produced in a dry, Ar environment had an average discharge capacity of 0.0137 mAh/cm2, while one produced in an ambient environment exhibited a discharge capacity at 0.05 mAh/cm2. Surface features varied significantly by printing method, where a doctor blade produced the most consistent features. The preliminary results herein suggest that water, surface roughness, and the gel polymer play important roles in affecting the performance of printed energy storage.