Synthesis and lithium storage performance of nickel oxide octahedra

Abstract

The present work was devoted to the construction of nickel oxide (NiO) polyhedral structures through a simple, efficient and environmentally friendly one-step process. Initially, a series of intimate mixtures of nickel chloride (NiCl₂) and β-cyclodextrin (β-CD) with different initial molar ratios were used as precursors. By simply sintering the precursors, we successfully obtained NiO octahedra with smooth surfaces and uniform size distribution. Control experiments showed that the formation, morphologies and grain sizes of NiO octahedra can be finely modulated by changing two parameters: the initial molar ratio of NiCl₂ to β-CD and the sintering time. The former is a decisive factor for creating the NiO octahedra, while the latter is a key factor for regulating their size and shape evolution. Moreover, we found that the role of β-CD can be played by other carbon sources such as active carbon and glucose, but not as well as β-CD. Several independent experiments (FTIR spectroscopy, conductivity and thermogravimetric analyses) were performed to understand the mechanism of this role. Our data suggested that β-CD has a stronger interaction with NiCl₂ than the other two carbon sources, leading to an earlier transformation from NiCl₂ to NiO. Further, this octahedral material exhibited a very small hysteresis loop below 1000 Oe at 300 K, indicating ferromagnetic behaviour, which is different from the antiferromagnetic behaviour of bulk NiO materials. Electrochemical tests demonstrated that the octahedral structure as well as the agglomerate structure has high lithium storage capacity. Also, the agglomerate structure presented very low irreversible capacity loss and good cyclability. Therefore, the results give the impression that they are promising anode materials for rechargeable lithium-ion batteries and for high-power applications, in particular. We believe that these results will increase our understanding of the relationship between structures, properties and functions of transition metal oxide materials.