High-Voltage Single-Ion Covalent Organic Framework Electrolytes Enabled by Nitrile Migration Ladders for Lithium...

The poor electrochemical stability window and low ionic conductivity in solid-state electrolytes hinder the development of safe, high-voltage, and energy-dense lithium metal batteries. Herein, taking advantage of the unique electronic effect of nitrile groups, we designed a novel azanide-based single-ion covalent organic framework (CN-iCOF) structure that possesses effective Li⁺ transport and high-voltage stability in lithium metal batteries. Density functional theory (DFT) calculations and molecular dynamics (MD) revealed that electron-withdrawing nitrile groups not only resulted in an ultralow HOMO energy orbital but also enhanced Li⁺ dissociation through charge delocalization, leading to a high t_Li+ of 0.93 and remarkable oxidative stability up to 5.6 V (vs. Li⁺/Li) simultaneously. Moreover, cyanation leveraging Strecker reaction transformed reversible imine-linkage to a stable sp³-carbon-containing azanide anion, which facilitated contorted alignment of transport "ladders" along the one-dimensional anionic channels and the ionic conductivity could reach 1.33×10^-5 S cm^-1 at ambient temperature without any additives. As a result, CN-iCOF allowed operation of solid-state lithium metal batteries with high-voltage cathodes such as LiNi_0.8Mn_0.1Co_0.1O₂ (NCM811), demonstrating stable lithium deposition up to 1,100 h and reversible battery cycling at ambient temperature up to 4.5 V, shedding light on the importance of discovering new functionality for forthcoming high-performance batteries.