Active lithium loss, which is caused by parasitic reactions due to the instability of solid electrolyte interphase (SEI) on the anodes, results in fast capacity fade of batteries. Constructing robust SEI layer is an effective way to reduce active lithium loss. Herein, we propose a AgF-coated separator (AgF-CS) to facilitate robust LiF-rich SEI on the anode during initial cycle. Electrochemical analysis and microstructure investigations confirm the formation of the LiF-rich SEI on the anode induced by the fluoride-containing coating layer. The fluoride-containing interfacial layer not only effectively enhances the reversible capacity of the SiO anode even under lean electrolyte (14 μL mAh −1 ) condition, but also prolongs the cycling life of lithium metal batteries by reducing the consumption of electrolyte and active lithium. The initial Coulombic efficiency (ICE) of LiFePO 4 ||SiO full cell is increased from 43.68 % to 84.18 % with pretreatment by AgF-CS. As a result, the reversible capacity of LiFePO 4 ||SiO full cell is increased by ∼124 % in contrast with that of the unmodified one. The strategy proposed here, benefiting from the simple manufacture, provides a feasible way to alleviate active lithium loss and elevate energy density of rechargeable lithium batteries.
Passivation by the inorganic-rich solid electrolyte interphase (SEI), especially the LiF-rich SEI, is highly desirable to guarantee the durable lifespan of Li metal batteries (LMBs). Here, we report a diluent with the capability to facilitate the formation of LiF-rich SEI while avoiding the excess consumption of Li salts. Dissimilar to most of reported inert diluents, heptafluoro-1-methoxypropane (HM) is firstly demonstrated to cooperate with the decomposition of anions to generate LiF-rich SEI via releasing F-containing species near Li surface. The designed electrolyte consisting of 1.8 M LiFSI in the mixture of 1,2-dimethoxyethane (DME)/HM (2:1 by vol.) achieves excellent compatibility with both Li metal anodes (Coulombic efficiency ∼ 99.8%) and high-voltage cathodes (4.4 V LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811) and 4.5 V LiCoO 2 (LCO) vs Li + /Li). The 4.4 V Li (20 μm)||NMC811 (2.5 mA h cm −2 ) and 4.5 V Li (20 μm)||LCO (2.5 mA h cm −2 ) cells achieve capacity retentions of 80% over 560 cycles and 80% over 505 cycles, respectively. Meanwhile, the anode-free pouch cell delivers an energy density of ∼293 W h kg −1 initially and retains 70% of capacity after 100 deep cycles. This work highlights the critical impact of diluent on the SEI formation, and opens up a new direction for designing desirable interfacial chemistries to enable high-performance LMBs.
Fluorinated amide electrolytes represent a promising solution for high-energy density lithium metal batteries, yet their application in Ni-rich layered oxide cathodes is hindered by interfacial instability. This study develops a non-flammable fluorinated amide-based deep eutectic electrolyte modified with fluoroethylene carbonate, which simultaneously enhances ionic conductivity (1.5 × 10 −4 S cm −1 ) and anodic stability (>4.4 V vs Li + /Li). Applied in Li/NCM811 batteries, the fluoroethylene carbonate-based electrolyte enables 83.2% capacity retention after 200 cycles at 0.5 C, significantly outperforming conventional counterparts. ToF-SMIS and XPS tests reveal that fluoroethylene carbonate facilitates the formation of a LiF-rich cathode-electrolyte interphase, suppressing parasitic reactions and improving Li + transport kinetics. Furthermore, the electrolyte demonstrates superior lithium metal compatibility, inhibiting dendrite growth while enhancing thermal safety. These findings underscore the critical role of fluorinated amide electrolytes in stabilizing Ni-rich cathodes and highlight their potential for next-generation high-voltage lithium metal batteries.
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