Anion De/Intercalation in Nickel Hydroxychloride Microspheres: A Mechanistic Study of Structural Impact on Energy Storage Performance of Multianion-Containing Layered Materials

Electrochemical cation de/intercalation has long been investigated for energy-relevant applications, while anion de/intercalation is comparatively highly challenging, although promising for promoting the performance of materials. Herein, layered nickel hydroxychloride was selected as a model multianion-containing inorganic functional material to study. Hierarchical flower-like microspheres self-assembled from nanosheets were synthesized via a solvothermal method. The as-prepared nickel hydroxychloride was built up from neutral layers of [Ni(OH)3/3Cl3/3] octahedra, showing an expanded interlayer spacing of 0.57 nm. With this unique microstructure, Cl– deintercalation and OH– intercalation were accomplished through an effective nonelectrochemical process. The nickel hydroxychloride Ni(OH)0.99Cl1.01 with a maximum Cl– ion content was found to possess the largest interlayer spacing, which when first employed as electrode materials for supercapacitor, delivered an ultrahigh specific capacitance of 3831 F/g at a current density of 1 A/g. For the latter case, Ni(OH)2.18(H3O)0.18 with a maximum OH– content showed a specific capacitance of 1489 F/g at 1 A/g. Expanded interlayer spacing associated with the anion de/intercalation is the key that enhances ion diffusion kinetics between layers. The methodology of anion de/intercalation reported in this work would provide hints of exploring novel multianion-containing materials with anion de/intercalation necessary for high-performance energy applications.