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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 35, Number 12
BKCSDE 35(12)
December 20, 2014 

Synthesis and Electrochemical Performance of Reduced Graphene Oxide/AlPO4-coated LiMn1.5Ni0.5O4 for Lithium-ion Batteries
Jaehyun Hur, Il Tae Kim*
Reduced graphene oxide, Aluminum phosphate, 5 V Spinel, Lithium-ion batteries
The reduced graphene oxide(rGO)/aluminum phosphate(AlPO4)-coated LiMn1.5Ni0.5O4 (LMNO) cathode material has been developed by hydroxide precursor method for LMNO and by a facile solution based process for the coating with GO/AlPO4 on the surface of LMNO, followed by annealing process. The amount of AlPO4 has been varied from 0.5 wt % to 1.0 wt %, while the amount of rGO is maintained at 1.0 wt %. The samples have been characterized by X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy. The rGO/AlPO4-coated LMNO electrodes exhibit better cyclic performance compared to that of pristine LMNO electrode. Specifically, rGO(1%)/AlPO4(0.5%)- and rGO(1%)/AlPO4(1%)-coated electrodes deliver a discharge capacity of, respectively, 123 mAh g−1 and 122 mAh g−1 at C/6 rate, with a capacity retention of, respectively, 96% and 98% at 100 cycles. Furthermore, the surface-modified LMNO electrodes demonstrate higher-rate capability. The rGO(1%)/AlPO4(0.5%)-coated LMNO electrode shows the highest rate performance demonstrating a capacity retention of 91% at 10 C rate. The enhanced electrochemical performance can be attributed to (1) the suppression of the direct contact of electrode surface with the electrolyte, resulting in side reactions with the electrolyte due to the high cut-off voltage, and (2) smaller surface resistance and charge transfer resistance, which is confirmed by total polarization resistance and electrochemical impedance spectroscopy.
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