Natural Cellulose Materials for Supercapacitors

Supercapacitors are becoming important energy storage devices in efficient electrical systems and they are typically fabricated from high surface area carbon materials which are manufactured using complex, eco-destructive processes. An alternative approach is based on the conversion of biomass materials which we explore in this paper. Cellulose from cotton pulp is subject to a two-step carbonisation process at a range of elevated temperatures up 1900 °C. The resultant materials are characterized using a range of physical methods, along with cyclic voltammetry and galvanostatic discharge techniques to measure the specific capacitance of the materials formed. It is shown that the optimum processing temperature is around 1000 °C; at lower processing temperatures, the materials are insufficiently conductive whilst at high carbonization temperatures low capacitance is seen due to a loss of surface area. This arises from the inaccessibility of nanometre size pores which are present in abundance after the lower temperature carbonization steps. Cotton pulp carbonised at 1000 °C showed the highest value of capacitance of 107 F g−1 with excellent stability for 2000 cycles. The electrochemical performance of this material is very competitive to other reported carbon materials and indicates the two-stage carbonisation method described is suitable for converting biomass into high quality carbon-based materials for supercapacitor applications.