In situ transmission electron microscopy graphene liquid cell on chemical sodiation of nickel oxide nanoparticles

Abstract

Nickel oxide (NiO) is one of the transition metal oxide been studied as effective electrode material for sodium ion batteries with response to it is high theoretical specific capacity, good rate capability and excellent cycling performance for sodium storage. However, to date out of $718mAhg^{-1}$ the sodiation theoretical capacity of NiO, only $480mAhg^{-1}$ was practically achieved. Almost 34% of this capacity is not usable. For efficiently utilizing this electrode material via suitable structure design, this study attempted to understand in deeply the chemical sodiation mechanism on NiO nanoparticles (NPs) through advanced in situ transmission electron microscopy approach using graphene liquid cell, a liquid film of sodium electrolyte consisting of NiO NPs has been encapsulated between two layers of graphene transferred on the 200 mesh Au grid. Relatively to others in situ techniques, graphene liquid cell testified to offers clear insight with high atomic resolution for morphological evolutions during real time observation of the sodiation in actual liquid electrolyte. During chemical sodiation the conversion reaction between NiO NPs and Na-ion to form crystalline $Na_2O$ and Ni NPs was investigated. Likewise, high resolution images revealed the sodiation mechanisms to be accompanied with the formation of incoherent interphase boundaries between Ni and $Na_2O$ phases.