Phase Transitions in Li[sub 1−δ]Ni[sub 0.5]Mn[sub 1.5]O[sub 4] during Cycling at 5 V

Structural change of with two different crystallographic structures of and was studied during Li extraction. Ex situ X-ray diffraction and transmission electron microscopy studies on partially delithiated revealed that structure lost its characteristic diagonal glide symmetry, suggesting a structural transition arising from the possible migration of cations during oxidation from to For the ordering of cations was destroyed by random migration of cations during Li extraction, resulting in the formation of intermediate phase with the structure. The phase transitions were reversible, meaning that migration of cations is highly reversible during lithiation/delithiation. © 2004 The Electrochemical Society. All rights reserved.