Highly stable rGO-wrapped Ni₃S₂ nanobowls: Structure fabrication and superior long-life electrochemical performance in LIBs

Uniform Ni₃S₂ nanobowls with an average size of 250nm and shell thickness of ~30nm wrapped by rGO sheets were firstly synthesized by a simple wet chemical method. The Ni₃S₂-rGO hybrid composite with spatial three-dimensional (3D) structure showed enhanced electrochemical properties in lithium-ion batteries, compared with Ni₃S₂ hollow chains. Its specific capacity could be up to 443mAhg^-1 at 0.5C after 500 cycles (theoretical capacity of Ni₃S₂ is 462mAhg^-1), while Ni₃S₂ hollow chains faded dramatically to 147mAhg^-1 after 100 cycles. The improved cycle stability of the composite could be ascribed to the bowl structure with both exposed interior and exterior arch surfaces which could stand much more lithiation-delithiation than quasi-1D hollow chains. The novel stable bowl-like structure, the wrapped flexible rGO sheets served as buffers for the expansion of Ni₃S₂ bowls, the attachment sites provided by bowls keeping rGO from aggregation, and the improved electron transfer rate by rGO sheets, all synergetic effects made the composite a superior anode material. Furthermore, an efficient simple method was proposed to check componential transform during cycles by comparing the peak ratio in S2p spectrum when sulfides were used as electrode materials in LIBs.