Enhanced electrical and mechanical properties of nanographite electrodes for supercapacitors by addition of nanofibrillated cellulose

Abstract

Graphene and porous carbon materials are widely used as electrodes in supercapacitors. In order to form mechanically stable electrodes, binders can be added to the conducting electrode material. However, most binders degrade the electrical performance of the electrodes. Here we show that by using nanofibrillated cellulose (NFC) as a binder the electrical properties, such as capacitance, were enhanced. The highest capacitance was measured at an NFC content of approximately 10 % in ratio to the total amount of active material. The NFC improved the ion transport in the electrodes. Thus, electrodes made of a mixture of nanographite and NFC achieved larger capacitances in supercapacitors than electrodes with nanographite only. In addition to electrical properties, NFC enhanced the mechanical stability and wet strength of the electrodes significantly. Furthermore, NFC stabilized the aqueous nanographite dispersions, which improved the processability. Galvanostatic cycling was performed and an initial transient behaviour of the supercapacitors during the first cycles was observed. However, stabilized supercapacitors showed efficiencies of 98–100%.

Nanofibrillated cellulose/nanographite composite films

“…Graphene has been recognised as a promising material that will revolutionise science and engineering. Nanographite (NG), in contrast, is a heterogeneous carbon material comprising a mixture of graphene, a few multi-layer graphene flakes, and graphite (Blomquist et al 2016;Andres et al 2014). It can be recognised as a highly functional conductive carbon nanoparticles that can be tailored for specific applications such as batteries, supercapacitors, graphite-based composites, printed electronics, sensors, energy applications, and life-science applications (Blomquist et al 2016).…”

“…Andres et al (2014) showed that a 10 % addition of nanofibrillated cellulose (NFC) to the NG improved both wet and dry strength while maintaining the capacitance. Malho et al (2012) reported that NFC could be used in aerogels, composites, and other hybrid materials; they used NFC together with multi-layer graphene (1.25 wt%) to improve the mechanical properties of the nanocomposite, with the resulting material having a Young's modulus 16.9 GPa, ultimate strength of 351 MPa, and work of fracture of 22.3 MJm -3 .…”

Flexible and Cellulose-based Organic Electronics

“…Andres et al demonstrated how the introduction of NFC in graphite-based supercapacitors not only enhanced the capacitance of the devices but also improved their lifetime by acting as a mechanically supporting matrix which prevented cracking of the graphite during cycling measurements. [72] There are also many reports of paper-based batteries which have the same advantages as supercapacitors. [82][83] The flexibility of such paper devices has resulted in a completely new battery device concept: origami batteries.…”

“…Nanofibrillated cellulose (NFC) water suspensions have been shown to have excellent colloidal stabilizing properties for both graphite particles and CNT, making it possible to produce high quality conductive papers. [71][72] Conductive polymers can be composited with paper either by adding it in the form of a liquid suspension or by direct polymerization onto the cellulose fibers in solution or on paper. [73][74][75][76] It has been demonstrated that the type of cellulose and the surface charge of the fibers have a strong influence on the quality of the polymer coating on paper and hence the conductivity.…”

“…This makes paper, with its intrinsic porous structure, an interesting candidate for building charge storage devices with the added advantage of flexibility. [69] Paper-based supercapacitors have been constructed by functionalizing cellulose with carbon [72] , conductive polymers [74,79] or metal oxides [80] . Both Gui et al [81] and Chen et al [80] investigated the role of mesoporosity in cellulose on the performance of electrochemical energy storage.…”