Single-phase local-high-concentration solid polymer electrolytes for lithium-metal batteries

Solid polymers are promising electrolytes for Li-metal batteries, but they have limitations: they cannot simultaneously achieve high ionic conductivity, good mechanical strength and compatibility with high-voltage cathodes while suppressing Li dendrites. Here, we design a class of locally high-concentration solid polymer electrolytes based on polymer blends, which are termed Li-polymer in F diluter (LPIFD). The Li-polymer (polymer-in-salt) ensures continuous Li-ion conduction channels and contributes to the solid electrolyte interphase (SEI), and the F diluter (inert fluorinated polymer) adds mechanical strength. Studies reveal that a single-phase LPIFD, which is based on a miscible polymer blend, lacks phase boundaries and forms an organic-less and LiF-rich SEI, effectively suppressing lithium dendrites. The single-phase LPIFD delivers ionic conductivity of 3.0 × 10−4 S cm−1, and enables the Li anode to reach a high coulombic efficiency of 99.1% and a critical current density of 3.7 mA cm−2. Furthermore, the ability to form an F-rich cathode electrolyte interphase allows LiNi0.8Co0.1Mn0.1O2||Li cells to achieve a cycle life of 450 cycles at a high operating voltage of 4.5 V. This design will inspire efforts to commercialize polymer electrolytes for high-energy Li-metal batteries.