In-situ neutron diffraction study of the simultaneous structural evolution of a LiNi0.5Mn1.5O4 cathode and a Li4Ti5O12 anode in a LiNi0.5Mn1.5O4∥Li4Ti5O12 full cell

In this study, the application of neutron powder diffraction on studying the time-resolved structural evolution of a cell comprised with LiNi 0.5Mn1.5O4 cathode and Li4Ti 5O12 anode during charge-discharge cycling is demonstrated. As expected, the lattices of the LiNi0.5Mn 1.5O4 cathode and the Li4Ti5O 12 anode in the cell are found to simultaneously contract during charging and expand during discharging. It is found that for the LiNi 0.5Mn1.5O4 cathode a solid-solution reaction is associated with the lattice change and the Ni2+/Ni3+ redox couple between 3.06 and 3.16 V (vs. Li4Ti5O 12), and a two-phase reaction between LixNi 0.5Mn1.5O4 and Ni0.25Mn 0.75O2 is corresponding to the Ni3+/Ni 4+ redox couple at voltage higher than 3.22 V (vs. Li 4Ti5O12) without a corresponding change in lattice. The oxidation states of the metals in the electrodes are determined by tracking the associated change in the oxygen position. In addition, the Ti oxidation state is correlated to the intensity of the Li4Ti 5O12 222 reflection at the anode, and the determined oxidation state of the Ni is correlated to the lithium occupancy within the cathode. Furthermore, the small volume changes of the cathode and the anode upon cycling suggest that the cell chemistry is favorable for practical applications.