Engineering Molecule‐Designed In Situ Polymerization on Al‐Doped Molecular‐Sieve Framework Enables Robust Quasi‐Solid‐State Lithium Batteries

Abstract Achieving fast Li + transport kinetics and stable electrode/electrolyte interfaces is of paramount importance, yet extremely challenging for the practical success of solid‐state lithium metal batteries, which requires the rational design of the structure and composition of solid‐state electrolytes. Herein, a composite quasi‐solid‐state electrolyte is fabricated through in situ polymerization of a molecule‐designed polymer chain within the functionalized molecular sieve framework (Al‐MCM41). In this design, the robust Brønsted/Lewis acid–base interactions between Al‐MCM41 and TFSI − facilitate the dissociation of lithium salt, leading to a Li + transference number as high as 0.81. Meanwhile, the well‐ordered mesopores of Al‐MCM41 act as the “reservoir” of the polymer chain, creating continuous ionic migration pathways to offer an excellent Li + conductivity of 1.09 × 10 −3 S cm −1 at 30 °C. Furthermore, the polymer with fluorinated and nitrided functional groups guarantees a dual‐reinforced anode and cathode interface. Such an integrated electrolyte with simultaneous unimpeded Li + transport and robust interfaces delivers extraordinary capacity retention of 84.6% over 600 cycles at 5 C when coupled with LiFePO 4 cathode and remarkable reversible capacity of 129.0 mAh g −1 after 200 cycles with high‐voltage NCM622 cathode. This work provides a significant avenue for enhancing the practical feasibility of solid‐state lithium metal batteries.