Engineering Functionalized 2D Metal‐Organic Frameworks Nanosheets with Fast Li⁺ Conduction for Advanced Solid Li Batteries

Abstract Solid‐state batteries can ensure high energy density and safety in lithium metal batteries, while polymer electrolytes are plagued by slow ion kinetics and low selective transport of Li⁺. Metal‐organic frameworks (MOFs) are proposed as emerging fillers for solid‐state poly(ethylene oxide)(PEO) electrolytes, however, developing functionalized MOFs and understanding their roles on ion transfer has proven challenging. Herein, combining computational and experimental results, the functional group regulation in MOFs can effectively change surficial charge distribution and limit anion movement is revealed, providing a potential solution to these issues. Specifically, functionalized 2D MOF sheets are designed through molecular engineering to construct high‐performance composite electrolytes, where the electron‐donating effect of substituents in 2D‐MOFs effectively limits the movement of ClO₄⁻ and promotes mechanical properties and ion migration numbers (0.36 up to 0.64) of PEO. As a result, Li/Li cells with composite electrolyte exhibit superior cyclability for 1000 h at a current density of 0.2 mA cm⁻². Meanwhile, the solid LiFePO₄/Li battery delivers highly reversible capacities of 148.8 mAh g⁻¹ after 200 cycles. These findings highlight a new approach for anion confinement through the use of functional group electronic effects, leading to enhanced ionic conductivity, and a feasible direction for high‐performance solid‐state batteries.