Insights into Structural Transformations in the Local Structure of Li2VO2F Using Operando X-ray Diffraction and Total Scattering: Amorphization and Recrystallization.

Disordered rock salt Li2VO2F cathode material for lithium-ion batteries was investigated using operando X-ray diffraction and total scattering to gain insight into the structural changes of the short-range and long-range orders during electrochemical cycling. The X-ray powder diffraction data show the well-known pattern of the disordered rock salt cubic structure, whereas the pair distribution function (PDF) analysis reveals significant deviations from the ideal cubic structure. During battery operation, a reversible rock salt-to-amorphous phase transformation is observed, upon Li extraction and reinsertion. The X-ray total scattering data show strong indications of the formation of tetrahedrally coordinated V in a nondisordered rock salt phase of the charged electrode material. The results show that the disordered rock salt Li2VO2F material undergoes a hidden structural rearrangement during battery operation.