Synthesis and Electrochemical Performance of Reduced Graphene Oxide/AlPO₄-coated LiMn_1.5Ni_0.5O₄for Lithium-ion Batteries

Abstract

The reduced graphene oxide(rGO)/aluminum phosphate(AlPO 4 )-coated LiMn 1.5 Ni 0.5 O 4 (LMNO) cathode material has been developed by hydroxide precursor method for LMNO and by a facile solution based process for the coating with GO/AlPO 4 on the surface of LMNO, followed by annealing process. The amount of AlPO 4 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/AlPO 4 -coated LMNO electrodes exhibit better cyclic performance compared to that of pristine LMNO electrode. Specifically, rGO(1%)/AlPO 4 (0.5%)-and rGO(1%)/AlPO 4 (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%)/AlPO 4 (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.

Origin of Enhanced Cyclability in Covalently Modified LiMn1.5Ni0.5O4 Cathodes

“…Figure 3c presents the capacity retentions and Coulombic efficiencies of LMNO electrodes over 100 charge/discharge cycles. The high Coulombic efficiencies (greater than 99%) exhibited by all electrodes are consistent with the previous work on LMNO cathodes 35 and indicate that, regardless of surface modification, highly reversible electrochemistry is maintained. Further, all coated electrodes exhibit improved capacity retention relative to unmodified LMNO, suggesting that surface modification imparts additional stability to the oxide cathode.…”

Synthesis and characterization of aryl substituted functionalized graphene sheets and their electrochemical behavior

“…Additionally, graphene is prone to restacking during electrode preparation and even upon electrochemical cycling [12,13]. These phenomena can cause polarization, impedance growth, and capacity loss of cathode of lithium-ion batteries, especially at high operating voltage [14]. A potential approach to overcome the aforementioned issues involves the covalent modification of graphene with organic moieties via diazonium chemistry [15,16].…”