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.