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 960mAhg−1 (approximately 2 times its theoretical capacity) at 0.2Ag−1 after 400cycles at 0.01–3V. 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.