Li2S6‐Integrated PEO‐Based Polymer Electrolytes for All‐Solid‐State Lithium‐Metal Batteries

The integration of Li2S6 within a poly(ethylene oxide) (PEO)‐based polymer electrolyte is demonstrated to improve the polymer electrolyte's ionic conductivity because the strong interplay between O2−(PEO) and Li+ from Li2S6 reduces the crystalline volume within the PEO. The Li/electrolyte interface is stabilized by the in situ formation of an ultra‐thin Li2S/Li2S2 layer via the reaction between Li2S6 and lithium metal, which increases the ionic transport at the interface and suppresses lithium dendrite growth. A symmetric Li/Li cell with the Li2S6‐integrated composite electrolyte has excellent cyclability and a high critical current density of 0.9 mA cm−2 at 40 °C. Impressive electrochemical performance is demonstrated with all‐solid‐state Li/LiFePO4 and high‐voltage Li/LiNi0.8Mn0.1Co0.1O2 cells at 40 °C. Li2S6 is used as an additive for a PEO‐LiTFSI polymer electrolyte and serves to improve the Li+‐ion conductivity of the electrolyte by reducing the crystalline volume in the PEO as well as aiding in the formation of a thin stable layer that stabilizes the interface with lithium metal. This leads to an impressive electrochemical performance at 40 °C in all‐solid‐state full cells with a lithium metal anode and an LiFePO4 or LiNi0.8Mn0.1Co0.1O2 cathode.