Watermelon-like multicore-shell Fe(PO₃)₂@carbon nanocapsule anode to construct an all iron phosphate-based sodium ion battery

Rechargeable sodium ion battery (SIB) has attracted much attention recently. However, the deficiency of high-performance electrode materials limits its commercial development. Exploring new cost-effective, high safe electrode materials and full battery matching technology is an important direction of future research. In this work, a novel watermelon-like multicore-shell Fe(PO₃)₂@C nanocapsule anode material is designed via a facile and eco-friendly process for high performance SIB. Fe(PO₃)₂@C composite anode exhibits remarkable electrochemical performances for SIB, showing high sodium storage capacity (452 mAh·g^–1 at 0.2 A·g^–1), good rate (235 mAh·g^–1 at 10 A·g^–1), stable long-term cycling life (210 mAh·g^–1 over 2,000 cycles under 5 A·g^–1), and superior high-low temperature performance. Furthermore, a new type all iron-based phosphate full battery with high specific capacity is constructed, which can output initial capacity of 309 mAh·g^–1 and a high energy density of 254, 107, and 82 Wh·kg^–1 at the power density of 186, 917, and 1,640 W·kg^–1 at room temperature. The exceptional performance of multicore-shell Fe(PO₃)₂@C nanocapsule structure can be ascribed to the large specific surface, good structure stability, high conductivity, as well as the multiple layer protection for superior electron/ion transportation.