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^-1_total is still 99.8 W h kg^-1_total, very promising as an advanced electrode material.