Abstract
Layered solid solution materials Li1.2Ni0.2Mn0.6O2 were synthesized with one sample heat treated and three other coated with ZnAl2O4 with varying amounts (0.5, 1 and 2.5 wt%) at high temperature. The materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The effect of ZnAl2O4 coatings on the electrochemical performance of the pristine material was evaluated from charge/discharge cycles, rate performance, and electrochemical impedance spectroscopy (EIS). The results from TEM and selected area electron diffraction (SAED) indicate that the ZnAl2O4 coating assumes a spinel structure on the Li1.2Ni0.2Mn0.6O2. The discharge capacities and coulombic efficiencies of the Li1.2Ni0.2Mn0.6O2 materials in the first cycle are improved with the addition of ZnAl2O4. Li1.2Ni0.2Mn0.6O2 coated with 1 wt% ZnAl2O4 shows the highest discharge capacity (254.3 mAhg−1), highest capacity retention (98.6% for 50 cycles), and best rate capability (84 mAhg−1 at 10 C). EIS indicates that the resistance of Li1.2Ni0.2Mn0.6O2 electrodes decrease with the addition of ZnAl2O4 consistent with the excellent rate capability.
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