Origin of additional capacities in selenium-based ZnSe@C nanocomposite Li-ion battery electrodes

•Mesoporous nanospheres consisting of ZnSe@C core-shell nanoparticles are prepared.•This composite delivers a high reversible 960 mA h g− 1 at 0.2 A g− 1 after 400 cycles.•The Se element is firstly proved to be generated and activated during the charging processes.

Metal sulfides/selenides (MSx/MSex) are used as promising alternative electrode materials for Li-ion batteries. However, the performance of MSx/MSex electrodes is often accompanied by rising and additional reversible capacities beyond their theoretical capacities during cycling, the mechanisms of which are still poorly understood. This study employs ex situ X-ray photoelectron spectroscopy, along with cyclic voltammetry to control the electrochemical charge/discharge process, to explore the origin of the additional capacities in ZnSe@C composite electrodes. Such ZnSe@C composites exhibit a rising reversible capacity of 960 mAh g− 1 (approximately 2 times its theoretical capacity) at 0.2 A g− 1 after 400 cycles at 0.01–3 V. The analysis shows that a major contribution to the extra rising capacity in this system is due to the generation and activation of Se during the electrochemical process.

Graphical abstractThe mesoporous ZnSe@C nanospheres exhibit a high rising reversible capacity. The major contribution to this extra rising capacity in this system is due to the generation and activation of Se during the electrochemical charging process.Figure optionsDownload full-size imageDownload as PowerPoint slide