Form factor-free, flexible paper power sources

Abstract

Forthcoming smart ubiquitous era, which will involve widespread use of electric vehicles, stationary energy storage systems, and flexible/wearable electronics, is in relentless pursuit of advanced rechargeable power sources. Here, we demonstrate a new class of form factor-free, flexible power sources based on cellulose nanofibrils (CNFs) as an environmentally-friendly multifunctional 1D building block. Our first approach is focused on development of CNF-based flexible all-paper lithium-ion batteries. The all-paper lithium-ion batteries consist of CNFs/multiwall carbon nanotubes (MWNTs)-intermingled heteronets embracing electrode active powders and CNF separator membranes. The CNF/MWNT heteronet-based material/structural uniqueness enables the construction of three-dimensional bicontinuous electron/ion transport pathways in the electrodes, eventually facilitating electrochemical reaction kinetics. Driven by the 1D structure and chemical versatility of the CNFs, the resultant paper batteries provide unprecedented advances in the electrochemical performance and shape flexibility, which lie far beyond those achievable with conventional battery technologies. Next, a new class of solid-state flexible supercapacitors are fabricated directly on conventional A4 paper using a commercial desktop inkjet printer. A salient feature of the inkjet-printed power sources is their monolithic integration with paper, i.e., they look like inkjet-printed letters or figures that are commonly found in office documents. Cellulose nanofibrils-mediated nanoporous mats are inkjet-printed on top of paper as a primer layer to enable high-resolution images. We envision that the CNFs presented herein hold a great deal of promise as a reliable and versatile 1D building block strategy to open a new route toward high-performance/flexible power sources.