States of thermochemically or electrochemically synthesized NaxPy compounds analyzed by solid state 23Na and 31P nuclear magnetic resonance with theoretical calculation

Phosphorus is a promising material for the electrode in sodium ion batteries (NIBs). In this study, the states of NaxPy compounds synthesized by thermochemical reaction and electrochemical sodiation were compared using solid state 23Na magic angle spinning (MAS) NMR, 23Na multiple quantum (MQ) MAS NMR, and 31P MAS NMR. The NMR signals in thermochemically synthesized NaxPy compounds (Na3P, NaP, Na3P7, Na3P11, NaP7) are assigned in reference to theoretical chemical shifts, based on first-principles calculations. Furthermore, the NMR signals in electrochemically prepared NaxPy compounds after two sodiation/desodiation cycles are ascribed to Na3P compounds and three amorphous compositions. The amorphous compounds ascribed to Na1−αP (0