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 LixPOFy, 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.