In situ X-ray diffraction patterns were collected using a laboratory X-ray diffractometer during the first electrochemical charge/discharge cycle of the layered lithium excess compound Li[Li0.2Ni0.2Mn0.6]O-2 in the family of Li[NixLi1/3-2x/3Mn2/3-x/3]O-2 (x=1/5). Dynamic changes in peak positions, lattice parameters, and microstrain help to explain the lithium de-intercalation mechanism in this class of materials. Strong anisotropy is observed in the shifts of the lattice parameters during the first cycle. The in situ electrochemical measurement shows dynamically changing strain during the first electrochemical cycle that is explained by known lithium and transition metal (TM) migration mechanisms. Published by Elsevier B.V.