Electrode Design Concepts for Intrinsically Stretchable and Sustainable Batteries

High-capacity stretchable batteries are crucial for next-generation wearables to enable long-term operation and mechanical conformability with human users. However, in existing stretchable battery electrode designs, increasing the active material loading to yield higher capacity often leads to thicker and stiffer electrodes with poor mechanical properties.¹ Here, we will present a concept that decouples the electrochemical (redox-active material) and mechanical properties of the battery electrode by 1) designing an energy storage process that relies of <i>diffusion</i> of the redox active species within a porous conductive scaffold,² and 2) by engineering conductive redox-active fluids as electrodes for stretchable batteries.³ The key innovation of the concept is that the mass loading of the active material and their resulting battery capacity is independent from the overall stiffness of the cell. Such a design enables thicker battery electrodes with higher capacities without a trade-off in mechanical properties. Considering the exponential growth of the internet-of-things devices by 2035, of which many will be wearables, adopting sustainable practices to mitigate the environmental impact of traditional energy storage solutions while advancing their mechanical functions and battery performance is urgently needed to meet the United Nations Sustainable development goals. Currently, majority of reported stretchable batteries predominantly use unsustainable battery chemistries (Li-ion and toxic organic electrolytes), expensive and finite metal current collectors, and non-biodegradable petroleum-based polymers such as fluorinated polymers, and elastomers such as silicones and styrene block co-polymers as either binders and/or encapsulation layers. To demonstrate the decoupled stretchable battery concept and address the environmental sustainability challenges, biomass-derived materials were utilised to construct the battery from plant-based redox-active biomolecules (e.g., lignin), cellulose nanofibers as mechanical scaffolds and biodegradable elastomers as encapsulation layers. Ultimately, we hope that the work would inspire future stretchable battery designs that simultaneously addresses the mechanical, electrochemical, and sustainability considerations.<br/><br/>[1] A. Rahmanudin,* et al., J. Mater. Chem. A, <b>2023</b>, 11, 22718-22736.<br/>[2] A. Rahmanudin, * et al., Mater. Horizon, <b>2024</b>. In press.<br/>[3] M. Mohammadi, et al., Manuscript under review, <b>2024</b>.