Balanced Anion‐Cation‐EO Interaction Enables Ultrahigh Lithium‐Ion Transport in 4.5 V‐Class PEO‐Based All‐Solid‐State Lithium Batteries

Abstract The sluggish lithium‐ion transport in high‐concentration polyethylene oxide (hc‐PEO) solid electrolytes (SEs) and across the electrode/hc‐PEO SE interface causes failure of high‐voltage PEO‐based all‐solid‐state lithium batteries (ASSLBs). Here, bi‐salt hc‐PEO SEs with TFSI − and PO 2 F 2 − are creatively fabricated, where PO 2 F 2 − possesses higher Li + ─PO 2 F 2 − bonding energy, balancing anion‐Li + ‐EO interactions by weakening Li + ‐EO interaction while strengthening Li + ‐anion interaction, and decomposes at electrode/SE interfaces, enabling facilitated lithium‐ion transport in the SE and across interfaces. Li + interactions in anion‐Li + ‐EO aggregations are counterintuitively optimized when two anions reach an approximate molar ratio. Consequently, the ionic conductivity at 60 °C is enhanced by ≈20 times to 1.2 × 10 −4 S cm −1 , compared to hc‐PEO SE with LiTFSI (5.8 × 10 −6 S cm −1 ) or dominated LiPO 2 F 2 (5.2 × 10 −6 S cm −1 ). Using the bi‐salt hc‐PEO SE, Li//Li cells deliver an ultrahigh critical current density of 2 mA cm −2 with 20 times enhanced exchange current, and 4.5 V Li//LiCoO 2 ASSLBs exhibit a capacity retention of 80% after 200 cycles, superior to reported results. The synergistic anion decomposition, yielding pure lithium‐ion conductive electrode/SE interfaces containing Li 3 PO 4 and Li x POF y , depresses adverse side reactions and breaks sluggish ionic transport. This work explicitly demonstrates the utility of coordination regulations in achieving enhanced lithium‐ion transport for long‐lifespan high‐voltage ASSLBs.