Water Clusters Act as a Nano-Steam Engine in Covalent Organic Framework Nanochannels for Boosting Solid-State Li-Ion Conduction and Electrochemical Stability.

The development of solid-state electrolytes (SSE) that combine high ionic conductivity with a wide electrochemical window remains a significant challenge. This work presents a novel "nano-steam engine" concept within the one-dimensional nanochannels of urea-linked covalent organic frameworks (COFs) to address this challenge. By leveraging the strong anchoring effect of urea groups on water clusters, a fast lithium-ion conductor was developed by using the hydrophilicity of lithium salts. This design strategy promotes the dissociation of lithium salts and establishes a low-energy pathway for ion migration, achieving exceptional room-temperature ionic conductivity of 1.5 × 10-3 S cm-1. Meanwhile, the strong anchoring effect of the urea group on water clusters effectively suppressed the hydrogen evolution reaction, enabling the electrochemical window of the hydrated SSE to exceed 4.8 V. The assembled solid-state LiMn2O4//Li4Ti5O12 battery demonstrated a stable charge/discharge over 100 cycles. This study provides a groundbreaking strategy for designing high-performance solid-state lithium-ion batteries by turning water into a promoter of lithium-ion conduction.