Evaluate Sulfone-Based Reduction Sensitive Electrolytes with Lithium Li4Ti5O12/Li and Symmetric Li4+XTi5O12/Li4Ti5O12 Cells

Binary mixtures of cyclic or acyclic sulfones with EMC or DMC are used in electrolytes containing LiPF6 (1M) in both Li4Ti5O12/Li half-cells and Li4+xTi5O12/Li4Ti5O12 symmetrical cells and compared with standard EC/EMC or EC/DMC mixtures. In half-cells, sulfone-based electrolytes cannot be satisfactorily cycled owing to the formation of a resistive layer at the lithium interface, which is not stable and generates species (RSO2-, RSO3-) able to migrate toward the titanate electrode interface. Potentiostatic and galvanostatic tests in Li4Ti5O12/Li half-cells show that charge transfer resistance increases drastically when sulfones are used in the electrolyte composition. Moreover, cycling ability and coulombic efficiency are low. At the opposite, when symmetrical Li4+xTi5O12/Li4Ti5O12 cells are used, it is demonstrated that MIS- (methyl isopropyl sulfone) and TMS- (tetra methyl sulfone) based electrolytes exhibit reasonable electrochemical performances compared to the EC/DMC or EC/EMC standard mixtures. Surface analysis by XPS of both the Li4+xTi5O12 (partially oxidized) and Li7Ti5O12 (reduced) electrodes taken from symmetrical cells reveals that sulfones do not participate in the formation of surface layers. Alkylcarbonates (EMC or DMC), used as co-solvents in sulfone-based binary electrolytes, ensure the formation of surface layers at the titanate interfaces.