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

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 PO₂F₂ ^- are creatively fabricated, where PO₂F₂ ^- possesses higher Li⁺─PO₂F₂ ^- 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 LiPO₂F₂ (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//LiCoO₂ 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 Li₃PO₄ and Li_xPOF_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.