Ultra-small ZnS quantum dots embedded in N-doped carbon matrix for high-performance Li-ion battery anode

We report zinc sulfide (ZnS) quantum dots composed of three different polymorphs (pure zinc blende, pure wurtzite, and poly-type (zinc blende/wurtzite)) uniformly embedded in an N-doped carbon matrix as a potential electrode material for anode applications in lithium-ion batteries (LIBs), for the first time. The ZnS polymorph quantum dots with cubic and hexagonal lattices anchored onto a N-doped carbon matrix (ZnS-QD@NC) electrode is prepared by a polyol-assisted pyro-synthesis technique. A combined operando XRD and ex-situ XAS analyses revealed that the electrochemical reaction mechanism in ZnS-QD@NC was reversible and comprised of an insertion reaction followed by a conversion-cum-alloying reaction. Due to the structural property of the composite and its unique electrochemical behavior, the ZnS-QD@NC electrode registers a reversible specific capacity as high as 800 mAhg- 1 with a high initial energy round-trip efficiency of 83%, and better cycling stability and power. The results from this study can help in the production of high-performance electrode materials with unique structural and morphological composition using an efficient pyro-synthetic reaction for rechargeable battery applications.