Polymer Molecular Engineering Enables Rapid Electron/Ion Transport in Ultra‐Thick Electrode for High‐Energy‐Density Flexible Lithium‐Ion Battery

Abstract Flexible lithium‐ion batteries (LIBs) with high energy density are of urgent need for the ever‐increasing flexible and wearable electronic equipments, but limited by the low areal loading of active materials in traditional electrodes with lamellar structure. It is still a great challenge to solve the sluggish electron/ion transport problem caused by increasing the areal loading of active materials. Herein, a kind of ethylene vinyl acetate copolymer (EVA) is proposed to provide flexible supports and ion channels for ultra‐thick flexible LFP/CNT/EVA cathode and LTO/CNT/EVA anode, thereby achieving high energy density and all flexible LIBs. LFP/CNT/EVA shows a ternary homogeneous structure formed by the entanglement of EVA chains and CNT on LFP, which attributes to LFP content up to 80wt% and adjustable thickness from 20 to 460 µm. In sharp contrast to previous studies LFP/CNT/EVA delivers basically the constant specific capacity of ≈160 mAh g −1 at a 0.1 C rate with the thickness increasing, thus achieving ultrahigh areal capacity up to 4.56 mAh cm −2 . A flexible full LIBs based on LFP/CNT/EVA and LTO/CNT/EVA is demonstrated and exhibits favorable cycle performance under an alternant flat and bending state. Those findings are supposed to open new avenues for designing high‐energy‐density flexible LIBs for future wearable energy storage devices.