Insight into Multiple Intermolecular Coordination of Composite Solid Electrolytes via Cryo-Electron Microscopy for High-Voltage All-Solid-State Lithium Metal Batteries

Polymer/ceramic-based composite solid electrolytes (CSE) are promising candidates for all-solid-state lithium metal batteries (SLBs), benefiting from the combined mechanical robustness of polymeric electrolytes and the high ionic conductivity of ceramic electrolytes. However, the interfacial instability and poorly understood interphases of CSE hinder their application in high-voltage SLBs. Herein, a simple but effective CSE that stabilizes high-voltage SLBs by forming multiple intermolecular coordination interactions between polyester and ceramic electrolytes is discovered. The multiple coordination between the carbonyl groups in poly(ε-caprolactone) and the fluorosulfonyl groups in anions with Li_6.5La₃Zr_1.5Ta_0.5O₁₂ nanoparticles is directly visualized by cryogenic transmission electron microscopy and further confirmed by theoretical calculation. Importantly, the multiple coordination in CSE not only prevents the continuous decomposition of polymer skeleton by shielding the vulnerable carbonyl sites but also establishes stable inorganic-rich interphases through preferential decomposition of anions. The stable CSE and its inorganic-rich interphases enable Li||Li symmetric cells with an exceptional lifespan of over 4800 h without dendritic shorting at 0.1 mA cm⁻². Moreover, the high-voltage SLB with LiNi_0.5Co_0.2Mn_0.3O₂ cathode displays excellent cycling stability over 1100 cycles at a 1C charge/discharge rate. This work reveals the underlying mechanism behind the excellent stability of coordinating composite electrolytes and interfaces in high-voltage SLBs.