Phase transitions in Li1-delta Ni0.5Mn1.5O4 during cycling at 5 v

Structural change of LiNi0.5Mn1.5O4 with two different crystallographic structures of Fd (3) over barm and P4(3)32 was studied during Li extraction. Ex situ X-ray diffraction and transmission electron microscopy studies on partially delithiated Li1-deltaNi0.5Mn1.5O4 revealed that LiNi0.5Mn1.5O4 (Fd (3) over barm) structure lost its characteristic diagonal glide symmetry, suggesting a structural transition arising from the possible migration of cations during oxidation from Ni2+ to Ni4+. For the Li1-deltaNi0.5Mn1.5O4 (P4(3)32), ordering of cations was destroyed by random migration of cations during Li extraction, resulting in the formation of intermediate phase with the Fd (3) over barm structure. The phase transitions were reversible, meaning that migration of cations is highly reversible during lithiation/delithiation. (C) 2004 The Electrochemical Society.