Flexible one-dimensional yarn-like Ni-Zn battery: micron-nano hierarchical-structure array, high energy density and excellent capacity retention

Abstract

Many researches are devoted to design the wearable fibrous energy storage devices with miniaturization in order to satisfy the large demand of power for portable wearable electronics. As a kind of flexible battery, one-dimensional yarn-like nickel-zinc (Ni-Zn) battery has a lot of disadvantages such as low energy density and poor power density. Significantly, metal–organic framework (MOF) material provides an opportunity to solve the preceding shortcomings due to its porous structure, excellent specific surface area and multi-functionalization. In this study, the nickel cobalt layered double hydroxides (NiCo LDHs) with triangular micro sheet array and nano sheet structure is designed and prepared on silver coated nylon fibers (SCNF) as the flexibly fibrous Ni-Zn battery cathodes (SCNF@Ni@MOF@NiCo LDHs yarn electrode), which have high specific surface area and super structure stability even during bending of the yarn. Therefore, the cathodes have abundant active sites, excellent electron conduction and fast ion diffusion. The assembled aqueous Ni-Zn battery is featured with suitable capacitance (342 mAh/g at 7.6 A/g), appropriate energy density (572.5 Wh/g at 2.59 W g−1) and superior stability (55 % after 5000 cycles). In addition, the obtained one-dimensional yarn-like Ni-Zn battery has excellent flexibility and high capacity retention (90 % after 1000 bends and over 80 % after different deformation ways such as bend, squeeze and twist). These fascinating results demonstrate that the SCNF@Ni@MOF@NiCo LDHs yarn electrode have great application potential in wearable energy storage devices.