Power generation of thermoelectric oxide modules

Different versions of a thermoelectric unicouple composed of p-type Ca_2.7Bi_0.3Co₄O₉ (Co-349) and n-type La_0.9Bi_0.1NiO₃ (Ni-113) bulks were constructed using Ag paste containing p- and n-type oxide powders, for connection between p- or n-legs and Ag electrodes, respectively. Open-circuit voltage V₀ of the unicouple connected using Ag paste containing 6wt% of the oxide powders reaches 100 mV at a hot-side temperature T_H of 1073 K and a temperature difference AT of 500 K in air. Internal resistance R_I of this unicouple is 26.2 mΩ at 1073 K in air and decreases with increasing temperature. Maximum output power P_max, evaluated using the formula P_max = V₀²/4R_I, is 94 mW at 1073 K (ΔT= 500 K) and increases with temperature. This value corresponds to a volume power density of 0.66 W/cm³. The incorporation of oxide powders in Ag paste is shown to be effective to reduce the contact resistance and the thermal hysteresis effect at oxide/metal junctions. High power density is a strong point of thermoelectric generation. Exploitation of this salient characteristic would make thermoelectric modules promising candidates for mobile power applications. Here we show how power can be generated using a small thermoelectric module composed of 140 pairs of oxide thermoelectric unicouples. The module weighs 19.8 g and its dimensions are 53 mm long, 32 mm wide, and 5.0 mm thick. The hot-pressed thermoelectric oxide bulk materials used were connected with an Ag paste, incorporating 6wt% of oxide powder, and Ag electrodes. The module´s V₀ increases with increasing hot-side temperature (T_H) and reaches 4.5 V at a T_H of 1072 K in air. No deterioration in output power was seen when power generation was carried out ten times at a T_H of 723 K with intermediate cooling to room temperature. The module was successfully used to charge a lithium-ion battery in a mobile phone.