Graphitic carbon-based composite materials derived from catalytic graphitization of biomass wastes as cost-effective anode materials in lithium-ion batteries

Abstract

The development of lithium-ion batteries has become an important aspect of advanced technology and innovations. Although this type of batteries has already exceeded other rechargeable batteries in terms of energy density, specific capacity, and shelf life, the material cost as well as sustainability still need to be improved. And most importantly, the current commercial anode, graphite, has lower theoretical capacity compared to other novel anode materials. In the meantime, graphite provides stable performance and could be produced from various carbon sources by graphitization. Hence, the objective of this study is to develop graphitic carbon-based anode materials from sustainable carbon sources, biomass wastes. Banana and water hyacinth stem were used as precursors due to their xylem-like structure and large surface area, which could promote both graphitization rate and lithium reaction rate. In addition, catalytic graphitization with the assistance of transition metal yields both graphitic carbon and metal oxides, which are known to possess higher theoretical capacity than graphite. Both biomass wastes were converted to composite materials by simple processes. Firstly, the precursors were washed and blended with various concentrations of iron catalyst solution (Fe(NO3)3.H2O). The mixture was graphitized by heat treatment at 800oC to obtain C/FeOx composite materials. From X-ray diffraction patterns, it was shown that the materials were composed of mainly carbon and iron oxide species. In case of the products from acid-treated precursor, iron metal was also commonly detected. The morphology was revealed by microscopic methods to be rough carbon sheets with nanoparticles and nanocrystals scattered on the surface. The percentages of carbon in composite materials were measured by thermogravimetric analysis to be around 40-70%. Carbon structure was also studied by Raman spectroscopy, which revealed that the composite materials possessed more organized structure than the precursors. Furthermore, electrochemical tests revealed that the materials with the best performance from each biomass waste still could not overcome the stability of pure graphite at the slow charge-discharge rate (100 mA/g). However, at the fast charge-discharge rate (2A/g), they could provide much higher capacity, displaying the reversible capacity at the 1000th cycle at 172.8 mAh/g for banana and 171.1 mAh/g for water hyacinth stem, compared to 63.4 mAh/g provided by graphite. Hence, these newly developed materials were suitable to be used as anode for lithium-ion batteries at faster charge-discharge rates.