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

• Uniform Ni3S2 nanobowls wrapped by rGO sheets are synthesized by a simple wet chemical method.
• The specific capacity of Ni3S2 nanobowls–rGO composite is 443 mA h g−1 at 0.5 C after 500 cycles.
• The composite has good componential and structural reversibility during long-term cycles.
• The study gives a suggestion on designing optimal structures for electrode materials with superior electrochemical performance.

Uniform Ni3S2 nanobowls with an average size of 250 nm and shell thickness of ~30 nm 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 443 mA h g−1 at 0.5 C after 500 cycles (theoretical capacity of Ni3S2 is 462 mA h g−1), while Ni3S2 hollow chains faded dramatically to 147 mA h g−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.

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