Solvation-controlled ester-based concentrated electrolyte solutions for high-voltage lithium-ion batteries

Highly concentrated electrolyte solutions exhibit high stability against oxidation, and hence have a high potential for the high voltage operation of lithium-ion batteries (LIBs). However, they are highly viscous and very costly due to an extensive use of lithium salts. These problems were solved by diluting the highly concentrated electrolyte solutions with a diluent that has a low donor number, a high miscibility, and a high stability against oxidation. The resultant electrolyte solutions suppressed the degradation of 5 V-class LiNi0.5Mn1.5O4 positive-electrodes upon repeated charge/discharge cycling, and extended the reversible capacity of LiNi0.5Co0.2Mn0.3O2 electrodes to ca. 200 mAh g−1 by charging to a high voltage of 4.6 V.