Hierarchically porous carbon/red phosphorus composite for high-capacity sodium-ion battery anode.

Red phosphorus has received remarkable attention as a promising anode material for sodium ion batteries (NIBs) due to its high theoretical capacity. However, its practical application has been impeded by its intrinsic low electronic conductivity and large volume variations during sodiation/desodiation process. Here, we design a composite to confine nanosized red phosphorus into the hierarchically porous carbon (HPC) walls by a vaporization-condensation strategy. The mass loading of P in the HPC/P composite is optimized to deliver a reversible specific capacity of 2,202 mAh/g based on the mass of red P (836 mAh/g based on the total composite mass), a high capacity retention over 77% after 100 cycles, and excellent rate performance of 929 mAh/g at 2 C. The hierarchical porous carbon serves as the conductive networks, downsize the red phosphorus to nanoscale, and provide free space to accommodate the large volume expansions. The suppressed mechanical failure of the red phosphorus also enhances the stability of solid-electrolyte interface (SEI) layer, which is confirmed by the microscopy and impedance spectroscopy after the cycling tests. Our studies provide a feasible approach for potentially viable high-capacity NIB anode.