Highly Flexible Electrodes Based on Nano/Micro-Fiber for Flexible Lithium Metal Batteries

Abstract

Although Li metal batteries (LMBs) with high flexibility are attractive energy storage systems for wearable devices due to their high energy density, there exist critical challenges such as limited loading density, poor dimensional stability, and thus mechanical instability under repeated mechanical deformations including bending, twisting, and folding. In this work, extremely flexible nano/microfiber composite electrodes are developed for LMBs. The highly flexible and mechanically durable electrode is composed of oxidized polyethylene terephthalate (O-PET) microfiber (MF) substrates covered by single-walled carbon nanotube (CNT) nanofibers (NF), prepared by mass-producible O2 plasma treatment and spray-coating. CNT nanofibers provided an electrical intertangled network to integrate the active materials (i.e., either NCM or passivated Li powder (PLP)) and anchored to a flexible O-PET MF substrate, which permits high mass loading of active materials, improved electrochemical performance while maintaining mechanical durability. Resultantly, the flexible LMBs based on nano/micro fibrous electrodes have excellent energy density (300.1 Wh kg-1 electrode; nominal voltage of 3.7 V) and stable capacity retention (97.1%) without mechanical failure over 500 folding cycles. Highly flexible microfiber (MF) and nanofiber (NF) composite electrodes showed high mechanical durability (almost 100% retention of electrical conductivity) under structural deformation of folding state (folded 1000 times). Remarkably, the battery performance of pouch-cell with MF@NF electrode revealed that 97.1% of capacity retention is observed after 500 folding cycles. image