Nanocellulose-Based Flexible Electrodes for Safe and Sustainable Energy Storage

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The intensive use of battery-powered electronic devices, in addition to the challenging recycling requirements, have contributed to the accumulation of e-waste, one of the most alarming environmental issues of the modern world. This urges the importance of developing advanced energy storage systems by using non-toxic and more sustainable materials1. Nanocellulose as the most abundant bio-polymer, can tackle current ecological and safety concerns but also keep up with contemporary resilience requisites in powering flexible electronics. Herein, we present the development of organic nanocellulose-based battery electrodes, that can be used in applications with relatively low energy storage demands, such as medical systems, wearables and bendable Internet of Things (IoT) devices. We investigate hybrid electrodes composed of nanocellulose fibres and carbon-based battery active materials, by implementing a safer, aqueous fabrication processing and with a focus on understanding the underlying charge storage mechanisms2. The main constituent of the electrodes is a porous nanocellulose network that maintains structural integrity acting as a binder but also transports ions from an organic electrolyte to the active battery material with reduced diffusion limitations. The overall battery structure is flexible and mechanically robust, minimizing any volume changes during charge/discharge, which translates to cycling stability3. The nanocellulose-based electrodes were manufactured by using different techniques including vacuum filtration and blade coating, and yielded free-standing and current-collector-integrated electrodes. Structural properties and surface morphology were examined via atomic force microscopy (tapping mode and conductive-AFM), and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), while electrochemical atomic force microscopy (EC-AFM) was used for in operando visualization and elucidation of molecular level charge transfer mechanisms occurring at the electrode-electrolyte interface. Electrochemical performance was assessed by variable-rate cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronopotentiometry (CP). Furthermore, bending stress tests were conducted where the bending radius and charge/discharge profile of the electrode are correlated. The proposed battery concept paves the way for safe, non-toxic, mechanically flexible and sustainable energy storage technologies that aim to fulfil the growing need for low-power commercial devices. References Leung, O. M., Schoetz, T., Prodromakis, T. & Ponce de Leon, C. Review—Progress in Electrolytes for Rechargeable Aluminium Batteries. Journal of The Electrochemical Society 168, 056509 (2021). Schoetz, T., Gordon, L., Ivanov, S., Bund, A., Mandler, D. & Messinger, R. Disentangling faradaic, pseudocapacitive, and capacitive charge storage: A tutorial for the characterization of batteries, supercapacitors, and hybrid systems. Electrochimica Acta 412, 140072 (2022). Kim, J.-H., Lee, D., Lee, Y.-H., Chen, W. & Lee, S.-Y. Nanocellulose for Energy Storage Systems: Beyond the Limits of Synthetic Materials. Advanced Materials 31, 1804826 (2019).

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