Study of the Lithium Storage Mechanism of N‐Doped Carbon‐Modified Cu2S Electrodes for Lithium‐Ion Batteries

Owing to their high specific capacity and abundant reserve, CuxS compounds are promising electrode materials for lithium‐ion batteries (LIBs). Carbon compositing could stabilize the CuxS 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 Cu2S 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 Cu2S/carbon was elucidated by operando synchrotron radiation diffraction and in situ X‐ray absorption spectroscopy. The N‐doped carbon‐composited Cu2S (Cu2S/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. Ad LIB: In this study, thermal carbon reduction of CuS into Cu2S was monitored by high‐temperature synchrotron radiation diffraction (SRD). As LIB electrode material, Li+ storage intermediate Cu1.8S is confirmed by operando methods. The result shows that some original Cu2S remains unreacted after the first cycle, and carbon modification can improve the cycling stability of Cu2S for LIBs in the long‐term cycle.