Flexible Electrical Energy Storage Structure with Variable Stiffness for Soft Robotics and Wearable Electronics

Based on the analysis of the structures of robots and electronics developed so far, it should be noted that a majority of them need a reservoir for electrical energy storage. Unfortunately, most off-the-shelf devices commercially available nowadays are based on rigid parts that heavily limit the possibilities of incorporating such products into soft robots and wearable electronics. To address these issues, a new type of flexible structure for electrical energy storage, which consists of small battery cells connected by liquid metal paths, was proposed. It can achieve a low value of Young's modulus (about 0.13 MPa) while maintaining electrochemical stability for large stretches (max. capacity reduction-2%). We proposed an individual layer structure as well as a sandwich structure with a granular core, which by way of granular jamming phenomena can change the stiffness (almost 300%). This article describes the concept and working principle of the proposed flexible electrical energy storage structure, followed by the mechanical and electrical characterization, electrochemical impedance spectroscopy, and galvanostatic battery cell cycling. Scanning electron microscopy and energy-dispersive X-ray spectroscopy were used to characterize the electrodes. The article also includes numerical simulations and potential applications of the studied structure.