Electrochemical Lithium Intercalation into Graphite in a Mixed Glyme–Propylene Carbonate Electrolyte

Electrolyte formulation for Li-ion batteries is never a trivial task because trade-offs usually exist among the different design considerations: ion transport efficiency in the bulk, the properties (stability, ion transfer kinetics) of its interface with the electrode materials, compatible temperature range, etc. The combinative strategy, wherein some constituents’ advantages complement the others’ deficiencies, proves to be a rapid and often effective approach to address the above dilemma. However, for certain successful combinations, the synergy might not be that obvious to clarify. We herein study a novel electrolyte system constituted by LiNO3 as the sole salt, dissolved in an uncommon selection of two solvents regarded as incompatible with the graphite anode, i.e., diethylene glycol dimethyl ether and propylene carbonate. Unexpectedly, this electrolyte is free of signs of solvent cointercalation into the graphite electrode that has plagued both solvents for decades and works even more reversibly than the superconcentrated LiNO3 electrolyte. Solvation structure evaluation of the Li+ ions and the analysis of the solid electrolyte interphase (SEI) layer’s composition have been conducted to understand the mechanisms underpinning the reversibility of the graphite electrode, in which the modification of SEI arguably has a greater impact than the change of desolvation kinetics. The SEI’s stability is demonstrated to be endowed by a marriage of inorganic and organic moieties, contributed by the respective decomposition of LiNO3 and propylene carbonate. The organic character of the SEI layer thus might not be entirely dispensable when designing a new electrolyte.