Magnetic Compton scattering study of Li_xMn₂O₄ battery material at the Verwey transition

We discuss magnetic Compton scattering spectra and parallel calculations for interpreting these spectra from the Spinel Li_xMn₂O₄ (LMO). Due to its high redox voltage (~ 4.5 V) and lower cost compared to lithiated Co and Ni oxides, LMO is one of the leading candidates for next generation Li-ion battery cathodes. LMO has a mixed-valence Mn³⁺/Mn⁴⁺ state with a strong magnetic Jahn-Teller (J-T) effect. The high temperature phase is cubic with a random distribution of Mn³⁺/ Mn⁴⁺ ions. However, because of J-T distortion, LMO undergoes a structural transition from cubic to orthorhombic around 280K with charge and orbital ordering of Mn³⁺/ Mn⁴⁺ ions. This structural transition known as the Verwey transition plays an important role in the functioning of the LMO cathode. Our x-ray magnetic Compton spectra allow a faithful reconstruction of the redox orbitals at the Verwey transition, and our analysis gives insight into the interplay between effects of J-T distortion, charge and spin ordering, and the mechanism of LMO cathode degradation at the Verwey transition.