Crystal Structure Changes of LiNi0.5Co0.2Mn0.3O2Cathode Materials During the First Charge Investigated by in situ XRD

The structural changes of Li 1-x Ni 0.5 Co 0.2 Mn 0.3 O 2 cathode material for lithium ion battery during the first charge was investigated in comparison with Li 1-x Ni 0.8 Co 0.15 Al 0.05 O 2 using a synchrotron based in situ X-ray diffraction technique.The structural changes of these two cathode materials show similar trend during first charge: an expansion along the c-axis of the unit cell with contractions along the a-and b-axis during the early stage of charge and a major contraction along the c-axis with slight expansions along the a-and b-axis near the end of charge at high voltage limit.In Li 1-x Ni 0.5 Co 0.2 Mn 0.3 O 2 cathode, however, the initial unit cell volume of H2 phase is bigger than that of H1 phase since the c-axis undergo large expansion while a-and b-axis shrink slightly.The change in the unit cell volume for Li 1-x Ni 0.5 Co 0.2 Mn 0.3 O 2 during charge is smaller than that of Li 1-x Ni 0.8 Co 0.15 Al 0.05 O 2 .This smaller change in unit cell volume may give the Li 1-x Ni 0.5 Co 0.2 Mn 0.3 O 2 cathode material a better structural reversibility for a long cycling life.