Three-dimensional porous N-doped graphite carbon with embedded CoS2 nanoparticles as advanced anode for sodium-ion batteries

To achieve both high capacity and long cycling stability in sodium-ion batteries (SIBs), the structural optimizations of anode materials should take into considerations of the reaction kinetics, the insertion/extraction processes of Na+, and the structural stability of anodes. In this study, the growth of CoS2 nanoparticles on N-doped graphite carbon three-dimensional nano-skeleton (CoS2/NGC) is designed to increase the active sites for sodium storage, to provide high ionic/electrical conductivity, and to alleviate the volume swelling and reduce Na+ diffusion energy barrier. As employed as anode materials of SIB, CoS2/NGC shows a great rate capability, affording an initial capacity of 660 mAh g(-1), and maintaining a coulombic efficiency of 99.7% even after 1000 cycles at 1.0 A g(-1). The cyclic voltammetry experiments demonstrate that the main contribution of the capacity is from the capacitive charge-storage. Density functional theory calculations reveal that the advantageous Na+ storage kinetics of the CoS2/NGC electrode is attributed to its low Na+ adsorption energy of-2.21 eV and low Na+ diffusion barrier of 0.113 eV. This systematic study paves a way for the efficient design of metal sulfides anodes for SIB, which is conducive to develop battery systems with remarkable electrochemical performance.