In Situ Encapsulating Metal Oxides into Core-Shell Hierarchical Hybrid Fibers for Flexible Zinc-Ion Batteries toward High Durability and Ultrafast Capability for Wearable Applications.

Rechargeable aqueous Zn-ion batteries are promising power sources for the advanced electronics because of their low cost, high safety, environmental friendliness, etc. However, their practical applications are severely restricted by the low energy density, poor rate capability, and low mass loading. In this work, a new type of the core-shell hierarchical structured hybrid fiber with encapsulated metal oxide nanoparticles is reported, which is used as a flexible cathode for aqueous Zn-ion batteries. The hierarchical hybrid fibers, consisting of one-dimensional (1D) central hollow shell and inside carbon network, build bicontinuous conductive pathways and highly porous networks for the in situ formed metal oxide nanoparticles. The core-shell hierarchical structure facilitates fast electron/ion transport and high mass loading; moreover, the 1D structure ensures good pliability and high flexibility. Two transition metal oxides, i.e., ZnVO and VO, are employed to construct the hybrid fibers. Both hybrid fibers exhibit excellent electrochemical properties and superior high rate capabilities. They achieve the capacities of 162 mAh g (for ZnVO) and 409 mAh g (for VO) even at a high current density of 8 A g. Moreover, the flexible Zn-ion batteries are fabricated on the basis of the hybrid fibers. The superior energy/power density and good long-term cycling stability demonstrate their good energy storage capability and fast charge/discharge capability. Especially, the well-retained performance under high degree of outside deformations further promotes their applications in wearable electronics.