2-DIMENSIONAL AND QUASI-2-DIMENSIONAL ISOTHERMS FOR LI INTERCALATION AND UPD PROCESSES AT SURFACES

The possibility of electrochemically driven sorption of Li ions into layer-lattice host materials such as transition metal sulphides and oxides has led to the relatively new technology of rechargeable Li batteries employing aprotic solvents. The phenomenology of these systems is examined in terms of their discharge and recharge behaviour, and its interpretation in terms of quasi-two dimensional sorption isotherms. Special attention is directed to close analogies to the behaviour of two-dimensional underpotential deposition (upd) processes and their interpretation in terms of adsorption isotherms. The development of adsorption pseudocapacitance associated with upd processes has close parallels in Li intercalation reactions where the same types of thermodynamic equations apply. Conditions leading to phase separations in intercalation are discussed as they can determine the reversibility of intercalation and de-intercalation; again close analogies can be drawn with related upd processes where two-dimensional phase and order/disorder transitions arise giving rise to multiple state adsorption below monolayer limits of coverage by the adspecies.