Thiol‐Branched Solid Polymer Electrolyte Featuring High Strength, Toughness, and Lithium Ionic Conductivity for Lithium‐Metal Batteries

Abstract Lithium‐metal batteries (LMBs) with high energy densities are highly desirable for energy storage, but generally suffer from dendrite growth and side reactions in liquid electrolytes; thus the need for solid electrolytes with high mechanical strength, ionic conductivity, and compatible interface arises. Herein, a thiol‐branched solid polymer electrolyte (SPE) is introduced featuring high Li + conductivity (2.26 × 10 −4 S cm −1 at room temperature) and good mechanical strength (9.4 MPa)/toughness (≈500%), thus unblocking the tradeoff between ionic conductivity and mechanical robustness in polymer electrolytes. The SPE (denoted as M‐S‐PEGDA) is fabricated by covalently cross‐linking metal–organic frameworks (MOFs), tetrakis (3‐mercaptopropionic acid) pentaerythritol (PETMP), and poly(ethylene glycol) diacrylate (PEGDA) via multiple CSC bonds. The SPE also exhibits a high electrochemical window (>5.4 V), low interfacial impedance (<550 Ω), and impressive Li + transference number ( t Li+ = 0.44). As a result, Li||Li symmetrical cells with the thiol‐branched SPE displayed a high stability in a >1300 h cycling test. Moreover, a Li|M‐S‐PEGDA|LiFePO 4 full cell demonstrates discharge capacity of 143.7 mAh g −1 and maintains 85.6% after 500 cycles at 0.5 C, displaying one of the most outstanding performances for SPEs to date.