Layered-Structure SbPO4/Reduced Graphene Oxide: An Advanced Anode Material for Sodium Ion Batteries.

Sodium ion batteries are one of most promising alternatives to lithium ion batteries for large-scale energy storage, due to the high abundance and low cost of sodium in the earth. However, the lack of advanced electrode materials greatly affects their applications. Here, layered-structure SbPO4 is explored as an anode material for sodium ion batteries in terms of SbPO4 nanorods on reduced graphene oxide (SbPO4/rGO). In situ transmission electron microscopy images reveal the preferential expansion along the transverse direction of the nanorods upon the first discharging, which arises from the reduction of SbPO4 to Sb and the subsequent alloying of Sb as supported by in situ X-ray diffraction and selected area electron diffraction patterns. SbPO4/rGO exhibits a capacity retention of 99% after 100 cycles at 0.5 A g-1 both in half cells and in full cells. Its specific capacity at 5 A g-1 is 214 mA h g-1 in half cells or 134 mA h g-1 in full cells. Moreover, the energy density of the full cells at 1.2 kW kg-1total is still 99.8 W h kg-1total, very promising as an advanced electrode material.