Rational Formulation of Ether‐Lactone Electrolytes for Safe and Sustainable Ni‐Rich Lithium‐Ion Batteries

This study reports the formulation of innovative electrolytes designed to improve safety, sustainability, and compatibility with LiNi$_{0.92}$Mn$_{0.04}$Co$_{0.04}$O$_2$ (NMC92) cathodes. The use of bio-based solvents (γ-valerolactone, GVL) and safe, stable, innovative co-solvents (diethylene glycol butyl ethyl ether, DEGBEE) is investigated in combination with imide- and borate-based salts, demonstrating reduced flammability and enhanced transport properties. Molecular dynamics simulations reveal their advantageous solvation characteristics, highlighting increased lithium-ion mobility in GVL-based electrolytes due to diminished ionic clustering. Overall, the investigated electrolytes exhibit outstanding electrochemical performance with NMC92 cathodes in a half-cell configuration, retaining above 80% of their initial capacity after 300 galvanostatic cycles at 1 C and an enhanced rate capability. This behavior is attributed to the inorganic nature of the resulting cathode-electrolyte interphase, as confirmed by ex situ x-ray photoelectron spectroscopy. Finally, the suitability of this novel formulation for real-scale application is evaluated at the pouch-cell level, demonstrating similar performance to benchmark formulations while enhancing overall device safety and sustainability.