The thermodynamic and thermoelectric properties of LixTiS2 and LixCoO2
Abstract The partial thermodynamic functions Δ H Li and Δ S Li for Li x Ti 1.03 S 2 (0.13 ⩽ x ⩽ 0.97) and Li 0.95 CoO 2 were obtained from EMF-temperature measurements ( T =-30−20° C ). For Li x Ti 1.03 S 2 , 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 Li x Ti 1.03 S 2 (0 ⩽ × ⩽ 0.97, T = 50−200° C ) and Li x CoO 2 (0.20 ⩽ x ⩽ 1.00, T = 30−400° C ) was determined. From the sign of the (electronic) Seebeck coefficient it followed that Li x Ti 1.03 S 2 is a n -type and Li x CoO 2 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 Li x Ti 1.03 S 2 (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 Li x CoO 2 with x 1 CoO 2 and Co 2 O 3 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 Li x Ti 1.03 S 2 are critically compared with those of Ag x TiS 2 .