Rational Engineering of p-n Heterogeneous ZnS/SnO2 Quantum Dots with Fast Ion Kinetics for Superior Li/Na-Ion Battery.

Constructing heterogeneous nanostructures is an efficient strategy to improve the electrical and ionic conductivity of metal chalcogenide-based anodes. Herein, ZnS/SnO2 quantum dots (QDs) as p-n heterojunctions that are uniformly anchored to reduced graphene oxides (ZnS-SnO2 @rGO) are designed and engineered. Combining the merits of fast electron transport via the internal electric field and a greatly shortened Li/Na ion diffusion pathway in the ZnS/SnO2 QDs (3-5 nm), along with the excellent electrical conductivity and good structural stability provided by the rGO matrix, the ZnS-SnO2 @rGO anode exhibits enhanced electronic and ionic conductivity, which can be proved by both experiments and theoretical calculations. Consequently, the ZnS-SnO2 @rGO anode shows a significantly improved rate performance that simple counterpart composite anodes cannot achieve. Specifically, high reversible specific capacities are achieved for both lithium-ion battery (551 mA h g-1 at 5.0 A g-1 , 670 mA h g-1 at 3.0 A g-1 after 1400 cycles) and sodium-ion battery (334 mA h g-1 at 5.0 A g-1 , 313 mA h g-1 at 1.0 A g-1 after 400 cycles). Thus, this strategy to build semiconductor metal sulfides/metal oxide heterostructures at the atomic scale may inspire the rational design of metal compounds for high-performance battery applications.

Preparation of ZnS@N-doped-carbon composites via a ZnS-amine precursor vacuum pyrolysis route.

ZnS/carbon nanocomposites have potential electrochemical applications due to their improved conductivity and more active sites through modification of the carbon materials. Herein, we report a facile method to synthesize the nanocomposites comprising ZnS nanoparticles and nitrogen-doped carbon (ZnS@NC). The inorganic-organic hybrid ZnS-amine material ZnS(ba) (ba = n-butylamine) is synthesized on a large scale by a reflux method, which effectively shortens the reaction time while maintaining the high yield compared with the solvothermal method. Then ZnS(ba) is used as precursor for obtaining ZnS@NC nanocomposites via a vacuum pyrolysis route, in which the content of carbon and nitrogen can be controlled by adjusting the pyrolysis temperature. Further, a series of ZnS-amine hybrid materials ZnS(ha), ZnS(en)0.5 and ZnS(pda)0.5 (ha = n-hexylamine; en = ethylenediamine; pda = 1,3-propanediamine) are synthesized and used as precursors for the preparation of ZnS@NC materials, indicating the universality of this method. Moreover, the as-synthesized ZnS@NC materials exhibit remarkable lithium storage performance with outstanding cycling stability, high-rate capability and remarkable pseudo-capacitance characteristics.