CuFeS2 Quantum Dots Anchored in Carbon Frame: Superior Lithium Storage Performance and the Study of Electrochemical Mechanism.

Herein, we report a simple and quick synthetic route to prepare the pure CuFeS2 quantum dots (QDs) @C composites with the unique structure of CuFeS2 QDs encapsulated in the carbon frame. When tested as anode materials for the lithium ion battery, the CuFeS2 QDs @C composites based electrodes exhibit excellent electrochemical performances. When charge-discharge occurred with a current density of 0.5 A g-1, the electrodes exhibit a high reversible capacity (760 mA h g-1) for as long as 700 cycles, which indicates the superior cycling life. Detailed investigations of the morphological and structural changes of CuFeS2 QDs by ex situ XRD, ex situ Raman, and ex situ TEM reveal an interesting electrochemical reaction mechanism, a hybrid of a lithium-copper iron sulfide battery and lithium-sulfur battery. The direct observation of orthorhombic FeS2 by HRTEM and the existence of Li2FeS2 detected by Raman support our assertion. We believe such an electrochemical mechanism would attract more attention to the CuFeS2 nanomaterials as lithium ion battery anode materials. The excellent electrochemical properties would be derived from the unique structure, which include CuFeS2 QDs encapsulated in the carbon frame.