Lithium–metal batteries (LMBs) are the focus of upcoming energy storage systems with extremely high-energy density. However, the leakage of liquid electrolyte and the uncontrollable dendritic Li growth on the surface of the Li anode lead to their low reversibility and safety risks. Herein, we propose a stable quasi-solid LMB with in situ gelation of liquid electrolyte and an in-built fluorinated solid electrolyte interface (SEI) on the Li anode. The gel polymer electrolyte (GPE) is readily constructed via cationic polymerization between lithium hexafluorophosphate and ether electrolyte. The fluorine-containing additive, fluoroethylene carbonate (FEC), plays a crucial role in the building of a dense SEI with fast interfacial charge transport. The ex situ spectroscopic characterizations suggest that the enhanced LiF species in the SEI with the addition of FEC and the in situ optical microscopy reveal the inhibited dendritic Li growth. Moreover, GPE@FEC exhibits a high oxidative stability beyond 5.0 V (vs Li/Li+). The significantly improved Li plating/stripping efficiency (400 cycles, 98.7%) is presented for the Li∥Cu cells equipped with GPE@FEC. Decent cycling stability is also available for the cells with the LiFePO4 cathode, reflecting the feasibility of GPE@FEC for practical LMBs with enhanced stability and safety.

No abstract

Lithium (Li) metal is a competitive anode material for rechargeable high energy density batteries due to its high specific capacity and low reduction potential. However, great challenges remain in addressing uncontrollable Li dendrite growth and unstable interface. Herein, we report a quasi‐solid electrolyte enabled by in situ polymerization of polyethylene glycol methyl ether acrylate. Meanwhile, a LiF‐enriched solid electrolyte interphase (SEI) is built on Li‐metal surface by function of the fluoroethylene carbonate additive. The SEI with a good mechanical stability prompts the dense and uniform Li deposition behavior. The in situ polymerized gel polymer electrolyte exhibits an ionic conductivity of 1.71×10−4 S cm−1 at 30 °C, and a considerable oxidative stability up to 4.5 V (vs. Li/Li+). The Li||Li symmetric cells delivers a long‐term cycle life over 1400 h and a low voltage hysteresis at 0.5 mA cm−2, 1 mAh cm−2. To be paired with a LiFePO4 positive electrode, the cell shows a high discharge capacity of 135.6 mAh g−1 and capacity retention of 92.7 % after 300 cycles. This work provides a reference for the practical development of quasi‐solid electrolyte for lithium‐metal battery.