Tuning Na2Ti3O7 Nanostructures for Tailoring High-Performance Na-Ion Supercapacitors

Abstract

The slow kinetic nature and poor cycling performance of bulk Na2Ti3O7 (NTO) can be addressed by fabricating hierarchical nanostructures, such as 1D interconnected nanotubes, 2D flakes, and 3D pillar-like structures. The morphology-dependent pseudocapacitance behavior of NTO, in an aqueous Na-ion based electrolyte, is discussed. In comparison to 2D flakes or 3D pillar-like morphologies, the interconnected 1D nanotubular particles show a much higher electrochemical performance. This is attributed to its higher intercalation pseudocapacitive contribution owing to the facilitated intercalation of Na+ through the layered structure. Finally, high-performance Na-ion supercapacitors could be fabricated using these materials. The asymmetric device, fabricated using the NTO nanotube as the negative electrode and NaFePO4 as the positive electrode, is found to deliver the maximum energy density of ∼16 W h kg–1 at a specific power of ∼1.77 kW kg–1. The carbon footprint of each particle morphology is also discussed using life cycle assessment studies. This study further proves the importance of the nanotubular morphology.