Chinese knot-like bimetallic NiCo2S4 grew on 3D graphene foam as high-performance electrode for Na+ storage

Abstract Bimetallic NixCo3−xS4 (x = 1 or 2) with synergistic effect is a promising candidate material for sodium-ion battery (SIB) anodes because of its higher electrical conductivity than monometallic sulfides owing to its lower bandgap. In this study, samples of bimetallic sulfide NixCo3−xS4 with tunable chemical Ni/Co components are successfully grown on graphene foam (GF), forming free-standing Chinese knot-like nanowires (NiCo2S4 NWs/GF) and Chinese lantern-like nanoarrays (CoNi2S4 NAs/GF). When evaluate as anodes for SIBs at 0.3–3.0 V in ether-based electrolytes, the NiCo2S4 NWs/GF electrodes offer superior rate performance and cycling stability than the CoNi2S4 NAs/GF electrodes. More specifically, the NiCo2S4 NWs/GF electrode has a high capacity of 650–556 mAh g−1 at 0.1–2.0 A g−1 and 457 mAh g−1 after 200 cycles at 0.5 A g−1 with a high initial coulombic efficiency (ICE) of 95.6%. And its rate performance outperforms most existing electrodes those contain NiSx, CoSx, or NiCo2S4. The excellent electrochemical performance of the NiCo2S4 NWs/GF electrode is attributed to its unique composition, smaller size, and porous nanowires that can reduce the diffusion length of e- and Na+, and enhance reaction kinetics.