Investigations into Improved Electrochemical Performance of Sn Doped Hard Carbons as Negatives for Sodium-Ion Batteries

Hard carbons are the most suitable anode materials for practical sodium-ion batteries (NIBs). Despite various studies, there is still significant scope for improvement in the understanding of the (de)sodiation mechanisms. Here, we study Sn incorporation in waste derived commercial and model sucrose derived hard carbons and its effect on the electrochemical performance. Sn incorporation leads to improved first cycle coulombic efficiency and capacity, specifically increase in the plateau capacity. An improvement from 220 mAh/g to 285 mAh/g and 325 mAh/g is respectively obtained for 7 % and 15 % Sn in hard carbon-Sn composites (HC/Sn). Sn incorporation in both hard carbons has been shown to improve the electrochemical performance, notably achieving a synergy with capacities in excess of that expected from simple addition. For example, 7 % Sn additions tend to increase capacity by 25 %, twice that predicted from simple addition. X-ray diffraction (XRD) studies show that the number of graphene layers in nano-graphitic domains is reduced after Sn incorporation with no change in interlayer spacing. Full cells with commercial benchmark cathodes are also presented along with cost analysis of the Sn doping routes in this study to demonstrate the commercial viability of the strategy. Cost effective anode: Improvements in hard carbon negatives achieved through Sn doping with improvement in electrochemical performance. Specifically, improvement in plateau region of hard carbon is observed with no compromise on initial coulombic efficiency.image