Study of the Lithium Storage Mechanism of N-Doped Carbon-Modified Cu2 S Electrodes for Lithium-Ion Batteries.

Owing to their high specific capacity and abundant reserve, Cux S compounds are promising electrode materials for lithium-ion batteries (LIBs). Carbon compositing could stabilize the Cux S structure and repress capacity fading during the electrochemical cycling, but the corresponding Li+ storage mechanism and stabilization effect should be further clarified. In this study, nanoscale Cu2 S was synthesized by CuS co-precipitation and thermal reduction with polyelectrolytes. High-temperature synchrotron radiation diffraction was used to monitor the thermal reduction process. During the first cycle, the conversion mechanism upon lithium storage in the Cu2 S/carbon was elucidated by operando synchrotron radiation diffraction and in situ X-ray absorption spectroscopy. The N-doped carbon-composited Cu2 S (Cu2 S/C) exhibits an initial discharge capacity of 425 mAh g-1 at 0.1 A g-1 , with a higher, long-term capacity of 523 mAh g-1 at 0.1 A g-1 after 200 cycles; in contrast, the bare CuS electrode exhibits 123 mAh g-1 after 200 cycles. Multiple-scan cyclic voltammetry proves that extra Li+ storage can mainly be ascribed to the contribution of the capacitive storage.