Solid‐State Nuclear Magnetic Resonance Investigations of the Lithium‐ and Sodium‐Storage Mechanisms of Pyrolytic Phosphorus‐Carbon Composites

Phosphorus-doped carbons provide a balance between the electrochemical stability of graphitic lattices and the high energy density of phosphorus materials when used in lithium and sodium-ion batteries. Herein, a comprehensive ex situ ³¹P, ⁷Li, and ²³Na solid-state nuclear magnetic resonance analysis of the intercalation mechanism of novel, stable, dual-phase phosphorus-doped, and phosphorus-encapsulated turbostratic graphite microspheres is presented. Results indicate that lithium intercalation occurs through the formation of Li₃P from white phosphorus trapped within the graphitic layers, with the involvement of lithiated phosphorus atoms within the graphitic lattice. A dual-lithiated carbon doped-phosphorus environment is tentatively proposed at low voltages. Sodiation occurs through a similar mechanism; however, no evidence of a dual-sodiated doped-phosphorus environment is observed. Upon removal of ions, carbon-encapsulated phosphorus with a local structure similar to red phosphorus forms, which subsequently allows effective reversible ion storage.