Extending The Calendar Life of Fiber Lithium‐Ion Batteries to 200 Days with Ultra‐High Barrier Polymer Tubes

. This innovation enabled an ultra-long calendar life of 200 days and cycle life of 870 cycles for FLIBs, with over 80% capacity retention in ambient air. Additionally, 2%OMMT-PCTFE-FLIBs exhibited excellent flexibility, retaining an impressive 85.31% capacity after 10 000 bending cycles. This research presents a simple yet effective approach to enhance the lifetime and practicality of FLIBs through building a high-performance polymer-based encapsulation layer.