Reduction‐Resistant Chlorinated Ether‐based Diluent in Locally Concentrated Ionic Liquid Electrolytes for Highly Stable Lithium Metal Batteries

Abstract Locally concentrated ionic liquid electrolytes (LCILEs) are promising electrolyte systems for lithium metal batteries (LMBs) due to their robust anion‐derived solid electrolyte interphase (SEI) and compatibility with Ni‐rich cathodes. Low‐halogen‐content chlorides, with low price and weakly coordinating ability to Li ⁺ , emerge as exceptional candidates for diluents in LCILEs. Here, it is demonstrated that the anti‐reduction capability of chloride‐based diluent in LCILEs significantly affects the stability of the Li anode. Typically, 1,4‐dichlorobutane (DCB14) and 1,5‐dichloropentane (DCP15) possess high electrophilicity, making them susceptible to electron attack and prone to severe side reactions with Li metal anode. In contrast, 2,2‐dichlorodiethyl ether (DCDEE), where an oxygen atom replaces the central carbon atom in DCP15, demonstrates excellent reduction stability as it constitutes an electron‐rich system with low electrophilicity. In LCILE with DCDEE diluent, the weak coordination interaction of DCDEE facilitates Li ⁺ ion transport, while the resulting dual‐halide LiF/LiCl hybrid electrode‐electrolyte interphases (EEIs) effectively enhance the stability of electrodes. Consequently, Li||Cu cells sustain up to 740 cycles with a high coulombic efficiency (CE) of 99%. Furthermore, 1.2 Ah Li||LiNi _0.9 Co _0.05 Mn _0.05 O ₂ (NCM90) pouch cells are assembled to assess practical applicability, which exhibit impressive cycling stability with a high CE of 99.8%.