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.