Rational design of red phosphorus/reduced graphene oxide composites for stable sodium ion storage

Elemental phosphorus, one of the most promising high-capacity anode materials for sodium-ion batteries (SIB), suffers from the low practical capacity and severe cycling degradation, due to its low conductivity and significant volume change (>300%) upon electrochemical sodiation/desodiation. Here, we report a ball-milled phosphorus/reduced graphene oxide (rGO) nanocomposite for high-performance anode in SIBs. The reduction level of the rGO is tuned to simultaneously achieve highly conductive pathways and tight chemical bonding between P and rGO in the composite electrode. Allotrope transformation from red to black phosphorus nanocrystalline is observed in the milled nanocomposites. The optimized P/rGO1000 composite, containing rGO reduced by hydrothermal reaction and heat-treatment, achieves high specific capacity (2032.4 mAh g⁻¹ at 100 mA g⁻¹), excellent rate capability (1306.6 mAh g⁻¹ at 1C rate), and stable cyclability (98.7% capacity retention after 300 cycles at 780 mA g⁻¹). These excellent electrochemical performances are ascribed to the synergistic effects of nanostructuring by ball milling, existence of black phosphorus nanocrystallines, and tight chemical bonding at interfaces between P and rGO. Considering the facile synthesis of ball milling process, our approach can be highly promising for high-capacity anode in practical SIB.