Effect of Nitrogen Dopant Agents in the Performance of Graphene-Based Cathodes for Li-S Batteries

Lithium-sulphur (Li-S) batteries offer high energy density compared to lithium-ion batteries, emerging as a promising technology for the next generation of energy storage systems. The ongoing challenge is to improve their electrochemical performance, extend their useful life and mitigate some problems that persist in this technology, by the investigation in materials with diverse properties. This work seeks to elucidate the importance and repercussions associated with functionalisation of graphene-based materials through nitrogen incorporation (more than 9 wt.% N), employing different chemical agents such as ethylenediamine and ammonia. Herein, differences in both the textural properties and the chemical environment of nitrogen within the carbonaceous network are identified, resulting in distinct electrochemical behaviours. The electrochemical performance of electrodes prepared from ammonia-functionalised samples surpasses that of ethylenediamine-functionalised samples in terms of both efficiency and rate performance. Conversely, the ethylenediamine-functionalised samples excel in stability, showing exceptional values in capacity retention per cycle. The outcomes exceeded expectations in energy performance, allowing the Li-S cells to be subjected to ultra-high rate cycling while maintaining appropriate capacity values.