Conducting Polymer and Zinc-Ion Co-Intercalated Vanadium Oxide Nanofibers for High-Performance Stretchable Zinc-Ion Micro-Battery

The form of next-generation digital electronic devices has been changed to a wearable design that can be worn or attached to the human body to provide super-connection between people and devices using wireless systems. The wearable electronic device is designed in a stretchable form without shape restriction to secure functionality and wearability. In addition, it is necessary to develop a stretchable battery that can be integrated into a stretchable electronic device to drive a wearable electronic device. Lithium-ion batteries, which are currently the most commonly used batteries, are not suitable as stretchable batteries for wearable electronics due to their flammability and toxicity, which may pose a potential risk to human health. Furthermore, since lithium-ion batteries are manufactured under inert conditions, it is difficult to apply manufacturing processes for stretchable batteries. Recently, aqueous zinc-ion batteries, which have excellent capacity, low price, high safety, and are harmless to the human body, have attracted attention as energy supply devices for wearable electronics. In addition, the aqueous zinc-ion battery has the advantage of being manufactured under ambient conditions where various methods are easily applied, unlike a non-aqueous lithium-ion battery. A wavy-structure strategy has been known as one of the methods for imparting elasticity to objects, and in this strategy, the flexibility of the battery component is inevitably required. However, metal oxides, generally used as the active material for battery electrodes, lack elasticity and flexibility and break easily. As a result, it is difficult to maintain the intrinsic electrochemical performance of the device under repeated deformation. In this study, we developed a stretchable zinc-ion micro-battery with excellent mechanical properties and battery performance. Various strategies such as synthesis of cathode material with improved elasticity and flexibility, pre-zincification, wavy structural design, and assembly technique were applied together to achieve excellent electrochemical performance and mechanical properties of the stretchable zinc-ion micro-battery. Vanadium oxide nanofiber, which is co-intercalated with Zn²⁺ ions and poly 3,4-ethylene dioxythiophene (PEDOT), was synthesized as an active material of the cathode using a facile sonochemical method. The vanadium oxide nanofiber co-intercalated with Zn²⁺ ions and PEDOT showed improved mechanical properties, electrical conductivity, and specific capacity than the vanadium oxide intercalated with only Zn²⁺ ions. In addition, the pre-zincification of the cathode extended the cyclic stability of the stretchable zinc-ion micro-battery. As a result, the stretchable zinc-ion micro-battery exhibited a high areal capacity of 0.15 mAh cm^-2 and maximum energy density of 0.12 mWh cm^-2 at a power density of 0.12 mW cm^-2 and retained 83% of initial capacity over 500 cycles. In addition, the excellent mechanical performance of the stretchable zinc-ion micro-battery was demonstrated while maintaining a capacity of 78.9% during 7000 simultaneous stretching and bending tests. The strategy proposed in this study for fabricating stretchable zinc-ion batteries is expected to contribute to the development of wearable energy storage devices.