A novel KTP-type NaTiPO4F electrode material for high-performance Na-ion batteries

Abstract

Titanium-based polyanionic phosphate should theoretically be a promising electrode material for Na-ion batteries (NIBs) due to its low cost, robust structure framework and high safety. However, the currently reported titanium-based materials either have low reversible capacity or low average voltage, which makes them unable to serve as a cathode for practical NIBs due to undesirable energy density. Herein, by combining the inductive effect of F^- anions with strong electronegativity and the KTiOPO₄ (KTP)-type framework, we develop a novel titanium-based NaTiPO₄F material, which demonstrates a reversible capacity of ∼137 mA h g^-1 and energy density of ∼355 W h kg^-1 for NIBs. Various in situ characterizations combined with theoretical calculations have revealed favorable Na⁺ ion diffusion kinetics, reversible Ti³⁺/Ti⁴⁺ redox and quasi solid solution reaction mechanisms in NaTiPO₄F electrodes. Our current work shed light on the design and application of low-cost titanium-based phosphate electrodes for high-performance NIBs.