Automated Silver-Zinc Fiber Battery Fabrication

Abstract

Flexible electronics play host to a wide array of applications, ranging from wearable devices to large scale systems. Improvements in battery energy density while maintaining safe and stable operation under mechanical deformation is key in advancing the success of these flexible electronic systems. Currently, the majority of flexible batteries are fabricated as planar devices in which the electrodes and separator are stacked in sheets. These devices are limited due to their ability to only bend biaxially and the fact that repeated biaxial bending stresses often result in delamination or cracking of the battery components which is impractical for wearable devices. Batteries in a cable configuration have been proposed as an alternative to planar architectures; this form factor offers the ability for multi-directional bending and promises applications in woven textiles and washable electronics. The current process for fabricating such batteries as described in literature involves separate manual stages of plating the anode on a wire substrate, synthesizing an electrolyte and coating it around the anode, wrapping the cathode and packaging the final device with shrink tubing. This handmade approach to fabrication can vary between research groups and is not suitable for scaling to meet industry production levels; accordingly, such a process would be greatly benefitted by high throughput automation. In the current work, we demonstrate a modular automated system for the fabrication of a secondary Ag/Zn wire battery; such automation enables rapid prototyping in a roll to roll compatible process for the testing and fabrication of new chemistries for flexible battery systems. Moreover, pipeline fabrication ensures repeatability of fabricated devices and offers a more streamlined approach to manufacturing. In our work, 3D printed parts are used with low-cost Arduino microcontrollers to feed a carbon fiber wire through a sequence of dip coating baths in order to synthesize the Zn anode and coat it in a polymer electrolyte which is safer for wearable applications than organic electrolyte alternatives. The next stage encases the cable with the Ag cathode before the device is packaged in chemically resistive tubing and passed through the final dip coating bath of a liquid electrolyte. The desired length of cable is then cut and sealed. Characterization of the wire batteries is reported based on SEM analysis, strain cycling, charge cycling, cyclic voltammetry, and electrochemical impedance spectroscopy in order to demonstrate the successful realization of a fiber battery based on our automated process. Performance metrics from these analyses such as discharge capacity and capacity retention is also compared to performance reported in literature for similar cable architectures.