Pseudocapacitance-tuned high-rate and long-term cyclability of NiCo2S4 hexagonal nanosheets prepared by vapor transformation for lithium storage

Abstract

Well-defined NiCo ₂S ₄ hexagonal nanosheets with a large aspect ratio of ∼45 show pseudocapacitance-tuned high-rate and long-term cyclability for lithium storage.

Abstract

The high conductivity of bimetallic thiospinel NiCo ₂S ₄ endows energy storage devices with very fascinating performance. However, the unsatisfactory rate capability and long-term cyclability of this material series significantly limit their large-scale practical applications such as in electric vehicles and hybrid electric vehicles. Herein, we successfully synthesized NiCo ₂S ₄ hexagonal nanosheets with a large lateral dimension of ∼1.35 μm and a thickness of ∼30 nm through a vapor transformation method. The dynamic transformation process of the NiCo ₂S ₄ polycrystalline nanosheets from NiCo-hydroxide has been revealed in detail. Originating from their two-dimensional thin-sheet structure with a high aspect ratio, the induced extrinsic capacitive contribution as high as 91% makes them an ideal candidate for high-capacity and high-rate lithium-ion anodes. The NiCo ₂S ₄ nanosheets deliver a reversible capacity of 607 mA h g ⁻¹ upon 800 cycles at a current density of 2 A g ⁻¹. This outstanding long cycle performance sheds light on the structural design of electrode materials for high-rate lithium-ion batteries.