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

Abstract Scalable fiber lithium‐ion batteries (FLIBs) have garnered significant attention due to huge potential applications in wearable technology. However, their widespread applications have been limited by inadequate cycle and calendar life, primarily due to the high permeability of the encapsulation layer to water vapor in ambient air. To address this challenge, an ultra‐high barrier composite tube is developed by blending polytrifluorochloroethylene (PCTFE) with organically modified montmorillonite (OMMT) for the continuous packaging of FLIBs. Due to the high crystallinity (≈40.21%) and small free volume (103.443 Å 3 ), the PCTFE tube exhibited a low water vapor transmission rate (WVTR) of 0.123 mg day −1 pkg −1 . Furthermore, through the melt extrusion, OMMT with its plate‐like morphology are fully exfoliated and dispersed within the PCTFE matrix. This created more complex pathways for water, increasing the diffusion path length and thereby reducing WVTR to 0.006 mg day −1 pkg −1 . 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.