A Hybrid Ultrastrong Coordinating Solvent and an Ion-Conductive Diluent for High-Voltage Ether-Based Li-Metal Batteries

The Li⁺ solvation structure and the electrode-electrolyte interface critically determine the cell performance. Here, we systematically compare the effects of the coordination ability of ether with Li⁺ on cell performance, from ultrastrong coordinating solvents (crown ethers) to a moderate coordinating solvent (dimethoxyethane) and weak coordinating solvents (diol dimethyl ethers). Compared with the moderate coordinating ether, both weak and strong coordinating ethers show improved antioxidation capability, while weak coordinating ethers facilitate faster Li⁺ desolvation and enable better performance with the Li-metal anode. Dimethoxypropane shows a relatively better electrochemical performance owing to the coexistence of strong chelating and weak monodentate coordination with Li⁺. Furthermore, introducing interfacial passivators of lithium bis(fluorosulfonyl)imide and fluoroethylene carbonate further improves the cell performance and narrows the gap among solvents. Based on their respective benefits of solvents, we propose a hybrid electrolyte combining strongly coordinating 12-crown-4 (12-C-4) for Li⁺ capture and weakly coordinating hexanediol dimethyl ether (HDE) as an ion-conductive diluent. The strong coordination of 12-C-4 with Li⁺ and the dual anions in axial coordination facilitate the construction of an inorganic-rich cathode/electrolyte interphase, while the HDE diluent buffers the energy barrier during Li⁺ desolvation and uniforms Li-plating. This hybrid electrolyte exhibits higher ionic conductivity and better interfacial stability with both the anode and cathode than single ether, significantly improving the cycling stability of Li//LiNi_0.85Mn_0.075Co_0.075O₂ cells and bringing a new electrolyte design paradigm for high-voltage ether electrolytes.