A Healable Quasi‐Solid Polymer Electrolyte with Balanced Toughness and Ionic Conductivity

Abstract Solid polymer electrolytes (SPEs) have garnered extensive attention as potential alternatives to traditional liquid electrolytes, primarily due to their prowess in curbing lithium dendrite formation and preventing electrolyte leaks. The quest for SPEs that are both mechanically robust and exhibit superior ionic conductivity has been vigorous. However, achieving a harmonious balance between these two attributes remains a significant challenge. In this study, we introduce a novel quasi‐solid electrolyte, ingeniously crafted from a poly(urethane‐urea) network, enriched with lithium salts and plasticizers. This innovative composition not only boasts remarkable toughness but also ensures commendable ionic conductivity. Our post‐gelation method yields gel polymer electrolytes that undergo rigorous evaluation, leading to an optimized version that stands out with its exceptional room‐temperature ionic conductivity (2.94×10 −4 S cm −1 ) and outstanding toughness (11.9 MJ m −3 ). Moreover, it demonstrates a broad electrochemical window (4.73 V), remarkable stability across a 600‐hour cycle test, a high capacity retention exceeding 80 % after 100 cycles at 0.2 C, and a noteworthy self‐healing capability. This quasi‐solid polymer electrolyte emerges as a promising contender to replace current liquid electrolyte solutions.