Covalent Organic Framework Mediated Solvation Regulation Reinforces Anion-Derived Interface in Quasi-Solid-State...

The pursuit of high-energy-density and intrinsically safe lithium-ion batteries (LIBs) has intensified interest in quasi-solid-state electrolytes (QSSEs) coupled with silicon (Si) anodes. However, most in situ-formed polymer electrolytes suffer from low ionic conductivity and limited Li⁺ transference numbers, primarily arising from high polymer crystallinity and sluggish segmental dynamics. Herein, a 1,3,5-trioxane (TXE)-derived QSSE is engineered by incorporating fluoroethylene carbonate (FEC) and methyl propionate (MP) as plasticizers, together with a lithiated covalent organic framework (COFLi) as a functional filler to suppress crystallization, enhance Li⁺ transport, and improve interfacial stability. Consequently, the optimized COFLi-modified TXE-based electrolyte enables the Si anode to deliver a high reversible capacity of 1814.6 mAh g^-1 at 2 A g^-1 after 200 cycles and to retain 1530 mAh g^-1 at 0.5 A g^-1 even at -20°C. Moreover, a molecular-level interfacial model is proposed to elucidate the role of COFLi in regulating the Li⁺ solvation structure, reducing desolvation energy, and promoting the formation of a LiF-rich inorganic solid-electrolyte interphase), thereby suppressing electrolyte decomposition and mitigating Si pulverization. This work provides fundamental insights into solvation chemistry and interfacial evolution in TXE-based QSSEs and offers a rational design strategy for high-performance, Si-compatible quasi-solid-state LIBs.