The Non-Ignorable Impact of Surface Oxygen Groups on the Electrochemical Performance of N/O Dual-Doped Carbon Anodes for Sodium Ion Batteries

Oxygen functional groups universally exist in most nitrogen-containing carbon materials, but the influences on structure and sodium storage performance are usually not been well considered. In this work, the carbon nanospheres material with 6.92 at. % of nitrogen and 16.01 at. % of oxygen exhibits high capacity (325 mAh g(-1) at 50 mA g(-1)) and excellent rate performance (114 mAh g(-1) at 5 A g(-1)) as an anode material for sodium-ion batteries. By hydrogen reduction treatment with different time, N/O dual-doped carbon nanospheres with different oxygen content are obtained. According to integrated analysis of structural characterizations and electrochemical performance of these carbon nanospheres, we propose that C-O- will lead to more irreversible capacity and relatively poor cycling performance in long-term cycle due to the irreversible reaction with Na+. However, surface oxygen in C-OH phenol groups, C-O-C ether groups and COOH carboxylic groups can effectively improve capacity by enlarging interlayer distance, increasing active sites, and thus enhancing reaction activity. Our work provides a deep insight about the impact of oxygen functional groups on sodium storage performance and is significant to design advanced carbon anode materials for sodium ion batteries. (C) 2018 The Electrochemical Society.