Reduction-Resistant Chlorinated Ether-based Diluent in Locally Concentrated Ionic Liquid Electrolytes for Highly...

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_0.9Co_0.05Mn_0.05O₂ (NCM90) pouch cells are assembled to assess practical applicability, which exhibit impressive cycling stability with a high CE of 99.8%.