A battery–capacitor hybrid yarn device with excellent flexibility and high electrochemical performance

Abstract

Novel battery–capacitor hybrid devices combine the advantages of batteries and supercapacitors to achieve higher energy densities, larger operating voltage windows, and superior cycle life. However, battery–capacitor hybrid yarn devices have been very little investigated because the synthesis of high-performance battery-type and capacitor-type yarn electrodes is still a challenge. Herein, we report the in situ growth of NiCo-layered double hydroxides (CoNi-LDHs) nanosheets on carbon-based yarn (CoNi-LDHs@CBY) to prepare battery-type yarn electrodes. This unique electrode structure provides a large specific surface area (655 m² g⁻¹) and abundant active sites, which are conducive to promoting the electrochemical performance. Meanwhile, by uniformly anchoring S-doped carbon nanoparticles on the carbon-based yarn (S-CNPs@CBY), capacitor-type yarn electrodes with abundant porosity were successfully prepared, which is conducive to rapid ion transport. Furthermore, a novel battery–capacitor hybrid yarn device was assembled based on the CoNi-LDHs@CBY battery-type yarn electrode as the cathode and the S-CNPs@CBY capacitor-type yarn electrode as the anode with PVA/KOH gel electrolyte. The assembled yarn device shows a wider voltage operating window (1.4 V), larger area capacitance (227 mF cm⁻² at 1.8 mW cm⁻²), higher energy density (62 μW h cm⁻²), and excellent cycle life (5000 cycles). Additionally, the assembled yarn device still achieves stable electrochemical output under bending and winding conditions, which indicates its good flexibility. Thus, this work provides a novel solution for the development of next-generation flexible yarn energy storage devices.