Controllable synthesis of hierarchical core-shell NiS2/CoS2@N,S-C nanospheres for lithium storage

Abstract

Transition metal sulfides (TMSs) present high theoretical capacity as anode materials for Lithium-ion batteries, and structural design of TMSs is proved to be an effective strategy to acquire satisfactory electrochemical performances. Herein, the hierarchical NiS 2 /CoS 2 @N,S-C nanospheres consisting of NiS 2 /CoS 2 matrixes and N,S-codoped carbon outer layer (N,S-C) are fabricated. Additionally, NiS 2 /CoS 2 @N,S-C nanospheres with different core-shell structures appear in this study when the amount of nickle and cobalt is precisely controlled, which further confirms the different abilities of nickle and cobalt in tailoring and modulating structure. In particular, the NiS 2 /CoS 2 @N,S-C(Ni:Co=1:2) with yolk-shell property presents sufficient internal void space, which is conductive to the transport of Li + and electron. Moreover, the protective N,S-codoped carbon layer and the porous sheet arrays provide the enhanced structural stability and increased active sites. Benefitting from the unique structure, the NiS 2 /CoS 2 @N,S-C(Ni:Co=1:2) anode with binary metal sulfide composition presents good cycling performance (795 mAh g −1 at 0.2 A g −1 after 100 cycles) and rate capability (469 mAh g −1 at 5 A g −1 ). This study provides a reference for the design and preparation of novel TMSs-based materials with different morphologies in the field of energy storage. • NiS 2 /CoS 2 nanosphere encapsulated in the N,S-codoped carbon layer to synthesize the hierarchical NiS 2 /CoS 2 @N,S-C. • The regulation of core-shell structure of NiS 2 /CoS 2 nanospheres by changing the molar ratio of Ni/Co. • The N,S-codoped carbon layer improves the structural stability and conductivity of the final composites. • The NiS 2 /CoS 2 @N,S-C(Ni:Co=1:2) delivers the improved lithium storage performance than other vulcanized composites.