A Green Asymmetric Bicyclic Co-Solvent Molecule for High-Voltage Aqueous Lithium-Ion Batteries.

Hybridizing aqueous electrolytes with organic co-solvents is regarded as an effective strategy that can expand the stable voltage window of aqueous electrolytes while reducing salt usage and enhancing wettability, but reported organic co-solvents are usually flammable and toxic, hardly achieving compatibility between safety and electrochemical performance. Here, we report a new non-flammable and non-toxic low-salt-concentration (1.85 m) aqueous electrolyte via hybridizing with a green and sustainable organic co-solvent of isosorbide dimethyl ether (IDE) with a special asymmetric bicyclic molecular structure. Owing to the unique three-dimensional (3D) spatial molecular structure of IDE, a five-membered ring structure can be formed by binding the Li ion with the O atoms of the endo-OCH 3 and opposite cyclic ether in the same plane of IDE. Meanwhile, the steric hindrance effect induced by the 3D spatial bicyclic molecular structure of IDE weakens its solvation ability with Li ions, allowing more anions to participate in the primary solvation sheath of Li ion and thus generating a robust and uniform LiF-rich SEI layer while containing elastic IDE-derived organics. Moreover, the asymmetric bicyclic IDE molecules with multiple O atoms can effectively regulate the intermolecular hydrogen bonding networks, thus reducing H 2 O molecule activity and expanding the electrochemical window. Such unique solvation structures and optimized hydrogen bonding networks enabled by the asymmetric bicyclic molecular structure of IDE effectively suppress electrode/electrolyte interfacial side reactions, thus achieving a 4.3 V voltage window. The as-developed Li 4 Ti 5 O 12 (LTO)||LiMn 2 O 4 (LMO) full cell delivers outstanding cycling performance with an average Coulombic efficiency of 99.35% over 450 cycles at 2 C. This article is protected by copyright. All rights reserved.