Detailed Comparison of Lib and SIB Electrolytes Via DFT Calculations

While electrolytes for lithium-ion batteries (LIB) have been explored extensively, this is not (yet) the case for sodium-ion battery (SIB) electrolytes – especially true when it comes to detailed modelling efforts.

We have studied both LIB and SIB electrolytes using density functional theory (DFT), both to understand the dissociation ability of the salts used [1] and the solvation of the cations in the electrolyte solvents in detail [2]. By studying these properties for both LIB and SIB electrolytes, the major differences between the two systems can be outlined, and used for further rational design of new electrolytes and to explain experimental features. Here the main observations will be presented and recommendations given on areas to focus on, pertaining to the fundamental differences between LIB and SIB electrolytes. In general we find that the Na-salts have a higher tendency to dissociate into charge carrying species than Li-salts – from a pure ion-ion interaction strength point of view. A set of >50 different salts, i.e. choices of anions, were evaluated against Li⁺ and Na⁺.   However, when the coordination and solvation of the respective cation, Li⁺ or Na⁺, explicitly by carbonate solvents, is taken into account, the ion-solvent interaction is similarly lowered. These observations thus lead almost to a status quo situation, but we stress that some nuances are worthy to consider for further development of SIB electrolytes and batteries.

[1] E. Jónsson, P. Johansson, Phys. Chem. Chem. Phys., 2012, 14, 10774-10779

[2] E. Jónsson, P. Johansson, submitted