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The specific energy of Li metal batteries (LMBs) can be improved by using high‐voltage cathode materials; however, achieving long‐term stable cycling performance in the corresponding system is particularly challenging for the liquid electrolyte. Herein, a novel pseudo‐oversaturated electrolyte (POSE) is prepared by introducing 1,1,2,2‐tetrafluoroethyl‐2,2,3,3‐tetrafluoropropyl ether (TTE) to adjust the coordination structure between diglyme (G2) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). Surprisingly, although TTE shows little solubility to LiTFSI, the molar ratio between LiTFSI and G2 in the POSE can be increased to 1:1, which is much higher than that of the saturation state, 1:2.8. Simulation and experimental results prove that TTE promotes closer contact of the G2 molecular with Li+ in the POSE. Moreover, it also participates in the formation of electrolyte/electrode interphases. The electrolyte shows outstanding compatibility with both the Li metal anode and typical high‐voltage cathodes. Li||Li symmetric cells show a long life of more than 2000 h at 1 mA cm−2, 1 mAh cm−2. In the meantime, Li||LiNi0.8Co0.1Mn0.1O2 (NCM811) cell with the POSE shows a high reversible capacity of 134.8 mAh g−1 after 900 cycles at 4.5 V, 1 C rate. The concept of POSE can provide new insight into the Li+ solvation structure and in the design of advanced electrolytes for LMBs. [ABSTRACT FROM AUTHOR]

Rechargeable aluminum ion batteries (AIBs) are one of the most promising battery technologies for future large‐scale energy storage due to their high theoretical volumetric capacity, low‐cost, and high safety. However, the low capacity of the intercalation‐type cathode materials reduces the competitiveness of AIBs in practical applications. Herein, a conversion‐type FeF3‐expanded graphite (EG) composite is synthesized as a novel cathode material for AIBs with good conductivity and cycle stability. Combined with the introduction of a single‐wall carbon nanotube modified separator, the shuttle effect of the intermediate product, FeCl2, is significantly restrained. Moreover, enhanced coulombic efficiency and reversible capacity are achieved. The AIB exhibits a satisfying reversible specific capacity of 266 mAh g−1 at 60 mA g−1 after 200 cycles, and good Coulombic efficiency of nearly 100% after 400 cycles at a current density of 100 mA g−1. Ex situ X‐ray diffraction and X‐ray photoelectron spectroscopy are applied to explore the energy storage mechanism of FeF3 in AIBs. The results reveal that the intercalation of Al3+ species and the reduction of Fe3+ species occurrs in the discharge process. These findings are meaningful for the fundamental understanding of the FeF3 cathode for AIBs and provide unprecedented insight into novel conversion type cathode materials for AIBs. [ABSTRACT FROM AUTHOR]