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

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.