Synthesis and Electrochemical Performance of Reduced Graphene Oxide/AlPO4-coated LiMn1.5Ni0.5O4 for Lithium-ion Batteries

Abstract

The reduced graphene oxide(rG0)/aluminum phosphate(AlPO4)-coated LiMni.5Ni0.504 (LMNO) cathode material has been developed by hydroxide precursor method for LMNO and by a facile solution based process for the coating with GO/A1PO4 on the surface of LMNO, followed by annealing process. The amount of A1PO4 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/A1PO4-coated LMNO electrodes exhibit better cyclic performance compared to that of pristine LMNO electrode. Specifically, rG0(1%)/A1PO4(0.5%)- and rG0(1%)/A1PO4(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 rG0(1%)/A1PO4(0.5%)-coated LMNO electrode shows the highest rate performance demonstrating a capacity retention of 91% at 10 degrees 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.