Revisiting LiClO4 as an electrolyte for Li-ion battery: Effect of aggregation behavior on ion-pairing dynamics and conductance

Abstract

A mixture of 0.5 M LiClO4 in 80% tetramethylsulfone (TMS) and 20% propylene carbonate (PC) was investigated through classical molecular dynamics simulations to understand properties that could make this a possible candidate for a better electrolyte for lithium-ion battery. The structural analysis through radial distribution function (RDF) reveals the strong interactions between Li+ and ClO4− ions, which increase with the increase in temperature. The interaction between the cation and the solvent molecules is found to be weaker than the cation-anion interactions. However, with an increase in temperature, the cation-TMS interactions decrease while the cation-PC interactions increase. There are prominent, sharp peaks in RDFs, which indicate an aggregating character of the ions in the system with pronounced effects in transport properties. The increase in temperature suggests a faster formation of these aggregates. The ions in this system show moderate ion transport and ionic conductivity. The obtained theoretical results were compared with the experimental data at the reported temperature. The value of correlated conductivity (0.24 mS cm−1) is in good agreement with the experimental (0.21 mS cm−1) results of 0.5 M LiClO4 in PC. Ionic conductivities were calculated for the various temperatures; it increases with increase in temperature. Conductivity calculated by either method shows Arrhenius behavior; the activation energy for ionic conduction is also discussed. From the dielectric calculations, it is observed that the dielectric constant of TMS decreases with an increase in temperature; this is the reason for the increased aggregating character of entities as the temperature increases. The model used in this study also provided values for the dielectric constant that was not very deviating from the experimental results. Understanding this feature, we also propose the concentration of electrolyte that shows enhanced conductivity by changing the TMS-PC proportions in the mixture.