Ion‐Sieving Calixarene Fillers Boost Li ⁺ Transport in Quasi‐Solid Electrolytes for High‐Loading Lithium Metal Batteries

ABSTRACT Calixarenes (CAs), featuring unique cavity architectures and exceptional host–guest capabilities, provide an attractive molecular platform for tailoring ion coordination and transport behaviors in solid‐state electrolytes (SSEs). Despite these structural advantages, their potential in SSEs has been rarely explored. Herein, we design a calix[6]arene‐functionalized (C6A) polymer quasi‐solid electrolyte (PECQSE) via in situ polymerization, in which a cross‐linked matrix is formed between urethane‐functionalized poly(ethylene oxide) (PEG‐IEM) and ethoxylated trimethylolpropane triacrylate (ETPTA). The incorporation of C6A establishes a size‐selective, interaction‐dominated ion‐regulation framework, in which bulky TFSI − exhibit restricted mobility, while Li + transport is facilitated along conduction pathways, resulting in Li + transference number of 0.76. Meanwhile, hydrogen‐bonding interactions between C6A phenolic hydroxyl groups and urethane segments suppress PEG crystallinity and promote LiTFSI dissociation. These interactions facilitate interfacial LiTFSI reduction and support the formation of a LiF/Li 2 O‐rich SEI, which guides uniform lithium deposition and suppresses dendrite growth. Consequently, Li|Li symmetric cells exhibit ultralong cycling stability exceeding 7000 h with low polarization and high‐loading LiFePO 4 |Li full cells retain 80.6% capacity after 700 cycles at 2 C. The assembled 1 Ah pouch cell delivers excellent safety and durability with 91.8% retention after 240 cycles, demonstrating an effective interfacial engineering strategy for next‐generation lithium metal batteries.