Carbons from all-cellulose composites for energy storage

Sustainable energy storage is a key to challenge issues connected to climate change. There are manifold options to address this grand challenge, e.g. pumped hydro, flywheels, batteries or supercapacitors. These technologies have their strength and weaknesses, which depend on the application areas. For instance, they feature different charge/discharge times, require some access to resources and some of them have limitations regarding scalability. In supercapacitors, the energy is stored in the form of charges on the surface of electrically conductive materials. Commercial applications employ highly porous activated carbons , whose main feature is a high surface area easily exceeding 1500 m2/g. The second crucial parameter, which has a direct impact on supercapacitor performance, is pore size (distribution). Nowadays, highly porous activated carbons are produced in large scale from coconut shells. The procedure involves a two step thermal treatment of the biomass. The first step is char formation, i.e. incineration of the coconut shells is prevented to achieve a high yield of a carbon rich material. The second step is the activation, which introduces pores down to the nanometer level into the activated carbons, ideally yielding a hierarchically structured material. In literature, the chemical processes taking place during these two steps are well known. However, the influence of the starting material in terms of e.g. morphology, composition, hierarchy, has not been systematically researched so far, with a majority of studies dealing with empiric approaches. The lack of systematics, however, impedes a better understanding of the influence of biomass starting materials on final supercapacitor performance, slowing down progress in the field. CellStor explores the basic correlations between morphology, chemical composition and hierarchical structure of biomass on the properties of activated carbons. For this purpose, Cellstor employs a defined set of materials, which are prepared by mixing a variety of cellulosic materials in different ratios. The materials consist of pulp fibers, nanocellulose (fiber diameter nanometer) and cellulose beads (sphere diameter micrometer range). This allows to synthesize materials with defined properties, allowing for a systematic evaluation of parameters coming from the starting materials and to study their effect on the performance of supercapacitors.