Comparative study of different crystallographic structure of LiNi0.5Mn1.5O4-δ cathodes with wide operation voltage (2.0-5.0 V)

LiNi0.5Mn1.5O4-delta cathode materials with two different structures (Fd (3) over barm and P4(3)32) were synthesized by ultrasonic spray pyrolysis method. The X-ray diffraction (XRD) data was confirmed that face-centered spinel (Fd (3) over barm) transformed into primitive simple cubic (P4(3)32) structure by annealing process at 700 degrees C. In spite of two electrons operated cut-off voltage range between 2.0 and 5.0 V, LiNi0.5Mn1.5O4 with P4(3)32 structure has better electrochemical behaviors than the cathode with simple cubic (3) over bar structure. Ex situ XRD study of the electrode revealed that LiNi0.5Mn1.5O4 (P4(3)32) has reversible crystal transformation between fully lithiated state (2.0 V) and delithiated state (5.0 V) whereas LiNi0.5Mn1.5O4-delta (Fd (3) over barm) showed irreversible phase transformed at two voltage region. The LiNi0.5Mn1.5O4-delta (Fd (3) over barm) has voltage drop was occurred after 20th cycled compared without any voltage drop of the P4(3)32 structure. (C) 2007 Elsevier Ltd. All rights reserved.