The thermodynamic and thermoelectric properties of LixTiS2 and LixCoO2

Abstract

The partial thermodynamic functions and for LixTi1.03S2 (0.13 x 0.97) and Li0.95CoO2 were obtained from EMF-temperature measurements (T=-30−20°C). For LixTi1.03S2, the x-dependence of these quantities is discussed in relation to a semiempirical expression for the EMF-x relation. The electronic component of the thermoelectric power in LixTi1.03S2 (0 × 0.97, T = 50−200°C) and LixCoO2 (0.20 x 1.00, T = 30−400°C) was determined. From the sign of the (electronic) Seebeck coefficient it followed that LixTi1.03S2 is a n-type and LixCoO2 a p- type electronic conductor. The influence of the amount of inserted lithium and temperature dependence on the Seebeck coefficient is discussed. A new method to determine the ionic heat of transport directly from the ionic Seebeck co-efficient was developed. This method was applied to LixTi1.03S2 (0.61 x 0.97, T = -30−30°C). The heat of transport is uch smaller than the activation enthalpy for Li+-conduction, indicating a high ionic polaron binding energy. Thermogravimetric analysis indicates that LixCoO2 with x < 1 decomposes to Li1CoO2 and Co2O3 at temperatures higher than 80°C. This is sustained by the data for the electronic Seebeck coefficient. Also the thermodynamic, thermoelectric and kinetic data of LixTi1.03S2 are critically compared with those of AgxTiS2.