Air-stable red phosphorus anode for potassium/sodium-ion batteries enabled through dual-protection design

Red phosphorus (P) anodes possesses the highest theoretical capacities for both potassium-ion and sodium-ion batteries (PIBs/SIBs). An optimal strategy to play out its electrochemical performance is to confine nanoscale red P within a porous carbon structure. Nevertheless, the practical application of these P/carbon nanocomposites is challenged by their high air-sensitivity and poor cyclability associated with inevitable P deposition onto the external surface of carbon matrices, especially with high P content in the P/carbon composite. Herein, a dual-protection red P material was designed and fabricated by simple surface coating of a polypyrrole (PPy) layer onto a red P-activated carbon (P@AC) composite. The conducting PPy coating plays a multifunctional role including, promoting the structural stability by isolating the direct contact of active material from the electrolyte, improving electrical conductivity, and enhancing the air oxidation resistance by the PPy barrier layer. The PPy-coated P@AC with a relatively high P content of similar to 52 wt% demonstrates excellent air stability while exhibiting high reversible capacities (similar to 800 mAh g(-1) at 0.05 A g(-1) for SIBs; similar to 400 mAh g(-1) at 0.02 A g(-1) for PIBs) and long cycle life. This study sheds light on the rational design of advanced P-based anodes for alkali metal-ion batteries.