Wet spinning of fiber-shaped flexible Zn-ion batteries toward wearable energy storage

High-performance flexible one-dimensional (1D) electrochemical energy storage devices are crucial for the applications of wearable electronics. Although much progress on various 1D energy storage devices has been made, challenges involving fabrication cost, scalability, and efficiency remain. Herein, a high-performance flexible all-fiber zinc-ion battery (ZIB) is fabricated using a low-cost, scalable, and efficient continuous wet-spinning method. Viscous composite inks containing cellulose nanofibers/carbon nanotubes (CNFs/CNTs) binary composite network and either manganese dioxide nanowires (MnO2 NWs) or commercial Zn powders are utilized to spinning fiber cathodes and anodes, respectively. MnO2 NWs and Zn powders are uniformly dispersed in the interpenetrated CNFs/CNTs fibrous network, leading to homogenous composite inks with an ideal shear-thinning property. The obtained fiber electrodes demonstrate favorable uniformity and flexibility. Benefiting from the well-designed electrodes, the assembled flexible fiber-shaped ZIB delivers a high specific capacity of 281.5 mAh g−1 at 0.25 A g−1 and displays excellent cycling stability over 400 cycles. Moreover, the wet-spun fiber-shaped ZIBs achieve ultrahigh gravimetric and volumetric energy densities of 47.3 Wh kg−1 and 131.3 mWh cm−3, respectively, based on both cathode and anode and maintain favorable stability even after 4000 bending cycles. This work offers a new concept design of 1D flexible ZIBs that can be potentially incorporated into commercial textiles for wearable and portable electronics.