Insights into the phase transformation of NiCo2S4@rGO for sodium-ion battery electrode

A promising hybrid anode material for sodium ion batteries (SIBs) is designed and synthesized by coating reduced graphene oxide onto NiCo2S4 nanoparticles (denoted as NCS@rGO). An intrinsic 3D micro-mesoporous network is obtained, which can shorten and fasten the access of Na+ diffusion and electron transport, provide sufficient reaction active sites, and enhance structural stability to suppress volume expansion. As a result, as an anode for SIBs, the NCS@rGO electrode delivers reversible capacity of 621 and 532 mAh g(-1) at 0.1 and 0.5 A g(-1), respectively. A high capacity retention of 95% is obtained at 0.1 A g(-1) after 100 cycles. The reaction mechanism of NCS@rGO during charge and discharge has been investigated. The results reveal that the conversion products of NiS2 and CoS2 from the phase transformation of NiCo2S4 are successfully confined with the rGO coating. Furthermore, the NCS@rGO hybrid exhibits a pseudo-capacitive dominated behaviour, which contributes to the measured superior rate capability. This work provides valuable insight into how the phase transformation of NCS@rGO during the charge/discharge process affecting the performance of sodium ion batteries, and this hybrid can be applied as a promising anode for SIBs. (C) 2020 Elsevier Ltd. All rights reserved.