Engineering of Yolk-Double Shell Cube-like SnS@N-S Codoped Carbon as a High-Performance Anode for Li- and Na-Ion Batteries.

ABSTRACT

A yolk-double shell cube-like SnS@N-S codoped carbon (YDSC-SnS@NSC) was delicately tailored by a self-templated and selective etching method as well as a self-assembly strategy. Herein, the ZnSn(OH)6 (ZHS) solid nanocubes were used as templates for the formation of a thin carbon shell that encapsulated the active material, thereby preventing the aggregation and maintaining the uniformity. ZHS is then converted into an intermediate ZnS-SnS2 hybrid by a facile thermal sulfidation process. Because SnS2 is insoluble in acidic condition, it is easy to create a yolk-shell architecture by selectively removing the ZnS component. Further heat treatment promoted the melting of SnS2 and resulted in the decomposition of SnS2 into SnS, which is simultaneously accompanied with a heat- and capillary-driven self-assembly to form a SnS inner core and SnS/C double shell. Such nanostructures with an inner void space and robust double shells are useful in buffering the volume expansion of SnS during lithiation and sodiation. Furthermore, N and S atoms doped into the carbon shell can enhance the electrical conductivity, which is beneficial to the fast charge-transfer kinetics. Because of these advantages, YDSC-SnS@NSC as the anode for Li-ion batteries exhibits improved electrochemical properties. Especially, the YDSC-SnS@NSC anode for Na-ion batteries shows an outstanding rate capability of 257 mA h g-1 at 8 A g-1 and an ultrastable long-term cyclic performance at a current density of 1 A g-1 with a capacity retention of 83.5% (340 mA h g-1 at the first cycle and ultimately reached 284 mA h g-1) and only 0.012% capacity decay per cycle for over 1500 cycles. Such superior electrochemical performance demonstrated that this rationally designed anode is promising for application in both Li- and Na-ion storages.