Li-Rich Li1+xMn2-xO4 Spinel Electrode Materials: An Operando Neutron Diffraction Study during Li+ Extraction/Insertion

In situ neutron diffraction (ND) during battery operation is becoming a promising technique for the study of electrode materials in Li-ion batteries. We recently designed an electrochemical cell for operando ND studies and demonstrated that it can deliver powder patterns of good quality for Rietveld structural refinements. Herein we used such a cell to study the deintercalation process occurring in manganese spinels of general formula Li1+xMn2xO4. Three samples with increasing Li/Mn ratio (x = 0, x = 0.05, and x = 0.10) were synthesized and measured on the D20 high-flux powder diffractometer at ILL. We found fundamental differences between the phase diagrams of the three samples, intimately related to their electrochemical features. Upon charge, the study revealed a sequence of two biphasic reactions for LiMn2O4 (with an intermediate phase of composition close to Li0.6Mn2O4), a solid solution followed by a biphasic reaction for Li1.05Mn1.95O4, and a full solid solution for Li1.10Mn1.90O4. Moreover, Rietveld refinement led to key parameters such as cell parameters, oxygens fractional atomic coordinates, and more importantly, lithiums site occupancy factors, whose rate of variation is found to be related to the state of charge of the electrode.