Dendrite‐Free Flexible Fiber‐Shaped Zn Battery with Long Cycle Life in Water and Air

Fiber‐shaped aqueous rechargeable Zn batteries (FARZBs) show flexibility, good reliability, cost‐effectiveness, high energy/power densities, and high safety that have attracted increasing attention as promising energy storage devices for future wearable applications. However, the development of FARZB is limited by its poor cycling life and inferior charge–discharge performance, mainly suffering from zinc dendrite growth and increasing electrode irreversibility. In this work, dendrite‐free fiber‐shaped Zn//Co3O4 rechargeable batteries with a long cycle life tested in water and air, are obtained via tuning the surface binding energy of Zn on the anode using the zincophilic N,O‐functional carbon fiber, as well as engineering the Co3O4 cathode with a nanowire array structure. The fiber‐shaped Zn//Co3O4 full battery demonstrates remarkable long cycle life in water and air with high energy density, impressive flexibility, and excellent waterproof ability (fully immersed and charged/discharged under water for more than 33 h for 3000 cycles with capacity retention of ≈80%). The reversible electrochemical mechanisms of the FARZBs, without obvious zinc dendrite deposits and structural change of Co3O4 nanowires, are confirmed by a series of characterizations. These results demonstrate that the FARZBs are promising power sources for emerging wearable electronics. Dendrite‐free fiber‐shaped Zn//Co3O4 rechargeable batteries are fabricated by assembling a shell‐like zinc flake on N,O‐functionalized carbon fibers as anodes and a Co3O4 nanowire array as cathodes. The resulting batteries show outstanding cycle life in water (above 33 h under water for 3000 cycles with capacity retention of ≈80%) and air, impressive flexibility and high energy density.