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

LiNi0.5Mn1.5O4−δ cathode materials with two different structures (Fd3¯m and P4332) were synthesized by ultrasonic spray pyrolysis method. The X-ray diffraction (XRD) data was confirmed that face-centered spinel (Fd3¯m) transformed into primitive simple cubic (P4332) structure by annealing process at 700 °C. In spite of two electrons operated cut-off voltage range between 2.0 and 5.0 V, LiNi0.5Mn1.5O4 with P4332 structure has better electrochemical behaviors than the cathode with simple cubic Fd3¯m structure. Ex situ XRD study of the electrode revealed that LiNi0.5Mn1.5O4 (P4332) has reversible crystal transformation between fully lithiated state (2.0 V) and delithiated state (5.0 V) whereas LiNi0.5Mn1.5O4−δ (Fd3¯m) showed irreversible phase transformed at two voltage region. The LiNi0.5Mn1.5O4−δ (Fd3¯m) has voltage drop was occurred after 20th cycled compared without any voltage drop of the P4332 structure.