Monoanion-regulated high-voltage nitrile-based solid electrolyte with compatible lithium inertness

High-voltage plastic solid electrolytes (PSEs) have emerged as appealing candidates for energy-dense Li-metal batteries, but their inherent instabilities toward reductive Li anodes pose a hurdle to practical application. Herein, we report the monoanion-regulated design of a lithium-inert, high-voltage PSEs, demonstrated with a nitrile-decorative PSEs (CN-PSEs) driven by BF₂C₂O₄⁻ monoanion. The monoanion-induced shielding layer helps to smooth lithium deposition, suppress the plastic matrix depletion, and thus retain robust Li/CN-PSEs interface even after cycling up to 1600 h in Li/Li cell, while the high-polarity nitrile group can support ion conduction and high-voltage tolerance up to 5.25 V. Benefit from the synergy, all-solid-state batteries with CN-PSEs show the superior cycling (300 cycles at 25 °C). This effective strategy provides a novel design principle for high-voltage PSEs to address the poor reductive stability.