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

The phosphate-based polyanionic compound with the formula (TiO)(2)P2O7 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)(2)P2O7 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)(2)P2O7 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)(2)P2O7. The macroporous-spherical (TiO)(2)P2O7 is a promising anode for sodium ion batteries.