Power generation of thermoelectric oxide modules

Different versions of a thermoelectric unicouple composed of p-type Ca/sub 2.7/Bi/sub 0.3/Co/sub 4/O/sub 9/ (Co-349) and n-type La/sub 0.9/Bi/sub 0.1/NiO/sub 3/ (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 V/sub 0/ of the unicouple connected using Ag paste containing 6wt% of the oxide powders reaches 100 mV at a hot-side temperature T/sub H/ of 1073 K and a temperature difference AT of 500 K in air. Internal resistance R/sub I/ of this unicouple is 26.2 m/spl Omega/ at 1073 K in air and decreases with increasing temperature. Maximum output power P/sub max/, evaluated using the formula P/sub max/ = V/sub 0//sup 2//4R/sub I/, is 94 mW at 1073 K (/spl Delta/T= 500 K) and increases with temperature. This value corresponds to a volume power density of 0.66 W/cm/sup 3/. 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 V/sub 0/ increases with increasing hot-side temperature (T/sub H/) and reaches 4.5 V at a T/sub H/ of 1072 K in air. No deterioration in output power was seen when power generation was carried out ten times at a T/sub 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.