Ionic conductivity of Li2O-P2O5 glasses from thermodynamic modeling of their chemical structure

Modeling the transport properties of glasses, and ionic conductivity in particular, has been a recurrent issue motivated for their high interest in the rapid developing field of energy conversion and storage devices for a wide range of applications such as in lithium rechargeable batteries. Despite the absolute conductivity of phosphate-based glasses is not among the highest, their ease of preparation and ability to host transition metals and secondary anions has contributed to foster their research from which good examples are the LiPON electrolytes or the LATP-based glass ceramics. In this work, the structure and ionic conductivity of lithium phosphate glasses with nominal composition x Li2O(1-x)P2O5, and x between 46 and 58 mol%, have been studied through the thermodynamic approach of the associated solutions model that was introduced by Shakhmatkin and Vedishcheva in glasses. The weak electrolyte model and the Anderson and Stuart model have also been employed herein in order to calculate the activation energy of the conduction of lithium ions within the glass matrix. Experimental ionic conductivity and activation energy data have been determined and were compared with the ones calculated using the models mentioned above. The structural units of the network have also been obtained by means of the thermodynamic approach and compared with those determined by P-31 nuclear magnetic resonance (NMR) spectra. All of them showed that the glass network structure can be reliably represented by a solution of chemical species and whose properties can then be derived from the respective weights in the system.