Development of a macroporous-spherical polyanionic compound (TiO)2P2O7 as a novel anode material for sodium ion batteries

Abstract

The phosphate-based polyanionic compound with the formula (TiO)₂P₂O₇ was synthesized by a simple precipitation method with a soft template as a novel anode material for sodium ion batteries for the first time. The polyanionic compound (TiO)₂P₂O₇ with a macroporous-spherical structure exhibited an initial specific capacity of 293.0 mA h g⁻¹ at 0.1C in the voltage range of 0.01–2.5 V vs. Na⁺/Na. The reversible capacity remained at 200.9 mA h g⁻¹ after 100 cycles. It is attractive that the macroporous-spherical (TiO)₂P₂O₇ delivered an extremely stable cycling performance at a high charge rate of 2.5C. A high capacity retention of 85.1% was obtained after 1100 cycles with an initial specific capacity of 112.7 mA h g⁻¹. The ex situ XRD and XPS analysis indicates that the excellent cycle stability and high rate capability are attributed to the intrinsic 3D framework structure and well-connected macroporous-spherical morphology of (TiO)₂P₂O₇. The macroporous-spherical (TiO)₂P₂O₇ is a promising anode for sodium ion batteries.