Encapsulation of Red Phosphorus in Carbon Nanocages with Ultrahigh Content for High-Capacity and Long Cycle Life Sodium-Ion Batteries.

Red phosphorus (RP) has attracted great attention as a potential candidate for anode materials of high-energy density sodium-ion batteries (NIBs) due to its high theoretical capacity, appropriate working voltage, and natural abundance. However, the low electrical conductance and huge volumetric variation during the sodiation-desodiation process, causing poor rate performance and cyclability, have limited the practical application of RP in NIBs. Herein, we report a rational strategy to resolve these issues by encapsulating nanoscaled RP into conductive and networked carbon nanocages (denoted as RP@CNCs) using a combination of a phosphorus-amine based method and evacuation-filling process. The large interior cavities volume of CNCs and controllable solution-based method enable the ultrahigh RP loading amount (85.3 wt %) in the RP@CNC composite. Benefiting from the synergic effects of the interior cavities and conductive network, which afford high structure stability and rapid electron transport, the RP@CNC composite presents a high systematic capacity of 1363 mA h g at a current density of 100 mA g after 150 cycles, favorable high-rate capability, and splendid long-cycling performance with capacity retention over 80% after 1300 cycles at 5000 mA g. This prototypical design promises an efficient solution to maximize RP loading as well as to boost the electrochemical performance of RP-based anodes.