A Strain-Relaxation Red Phosphorus Freestanding Anode for Non-Aqueous Potassium Ion Batteries

Red phosphorus (RP), as a promising anode for potassium-ion batteries (KIBs), and has attracted extensive attention due to its high theoretical capacity, low redox potential, and abundant natural sources. However, RP shows dramatic capacity decay and rapid structure degradation caused by huge volume expansion and poor electronic conductivity. Here, a volume strain-relaxation electrode structure is reported, by encapsulating well-confined amorphous RP in 3D interconnected sulfur, nitrogen co-doped carbon nanofibers (denoted as RP@S-N-CNFs). In situ transmission electron microscopy and the corresponding chemo-mechanical simulation reveal the excellent structural integrity and robustness of the N, S carbon matrix. As a freestanding anode for KIBs, the RP@S-N-CNFs electrode exhibits high reversible capacities (566.7 mAh g(-1) after 100 cycles at 0.1 A g(-1)) and extraordinary durability (282 mAh g(-1) after 2000 cycles at 2 A g(-1)). The highly reversible one-electron transfer mechanism with a final discharge product of KP and faster kinetics are demonstrated through in situ characterizations and density functional theory calculations. This work sheds light on the rational design of large-volume-vibration type anodes for next-generation high-performance KIBs.