Spherical NiCo2S4 wrapped with nitrogen-doped carbon as ultra-fast/high lithium storage materials.

The objective of this paper is to prepare a series of spherical NiCo 2 S 4 materials coated with N-doped C (NiCo 2 S 4 /NC-400 °C, NiCo 2 S 4 /NC-450 °C and NiCo 2 S 4 /NC-500 °C) by calcining the precursor of NiCo-MOF (metal organic framework) at different temperatures, and to explore the applications as anode materials for lithium-ion batteries. The results showed that the electrochemical reaction mechanism of the three materials is conversion reaction. Compared with NiCo 2 S 4 /NC-400 °C and NiCo 2 S 4 /NC-450 °C, NiCo 2 S 4 /NC-500 °C exhibited excellent cycle performance and rate performance at different current densities. NiCo 2 S 4 /NC-500 °C has a minimum charge transfer resistance. In addition, the pseudocapacitance contribution rate was 67.1 % at the scanning speed of 0.5 mV s−1, as well as relatively good structural characteristics and small particle size. The results of this study provide a reference for the application of NiCo 2 S 4 /NC materials in lithium-ion batteries. • Spherical NiCo 2 S 4 coated with N-doped C is prepared by calcining the precursor of NiCo-MOF. • N-doped C leads to good structural characteristics, small particle size and increases the intrinsic conductivity. • NiCo 2 S 4 /NC-500 °C demonstrates the best specific discharge/charge capacities and rate performance. • The conversion reaction mechanism of NiCo 2 S 4 /NC is revealed. [ABSTRACT FROM AUTHOR]