Entropy‐Driven 60 mol% Li Electrolyte for Li Metal‐Free Batteries

Abstract Highly Li‐concentrated electrolytes are acknowledged for their compatibility with Li metal negative electrodes and high voltage positive electrodes to achieve high‐energy Li metal batteries, showcasing stable and facile interfaces for Li deposition/dissolution and high anodic stability. This study aims to explore a highly concentrated electrolyte by adopting entropy‐driven chemistry for Li metal‐free (so‐called anode‐free) batteries. The combination of lithium bis(fluorosulfonyl)amide (LiFSA) and lithium trifluoromethanesulfonate (LiOTf) salts in a pyrrolidinium‐based ionic liquid is found to significantly modify the coordination structure, resulting in an unprecedented 60 mol% Li concentration and a low solvent‐to‐salt ratio of 0.67:1 in the electrolyte system. This novel 60 mol% Li electrolyte demonstrates unique coordination stricture, featuring a high ratio of monodentate‐anion structures and aggregates, which facilitates an enhanced Li + transference number and improved anodic stability. Moreover, the developed electrolyte provides a facile de‐coordination process and leads to the formation of an anion‐based solid electrolyte interface, which enables stable Li deposition/dissolution properties and demonstrates excellent cycling stability in the Li metal‐free full cell with a Li[Ni 0.8 Co 0.1 Mn 0.1 ]O 2 (NCM811) positive electrode.