Enhanced electrochemical performances of Li-rich layered oxides by surface modification with reduced graphene oxide/AlPO4 hybrid coating

Abstract

The electrochemical performance of lithium-rich layered oxide cathode materials coated with reduced graphene oxide (rGO)/AlPO₄ hybrid coatings has been investigated. The amount of graphene was varied from 0.5 to 4.0 wt%, while AlPO₄ was maintained at 2.0 wt%. The structure and morphology of the samples have been investigated using X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. Compared to the pristine cathode, the rGO/AlPO₄-coated cathodes exhibit higher discharge capacity with lower irreversible capacity loss, better cyclability, and higher rate capability. Specifically, the rGO (0.5 wt%)/AlPO₄ (2.0 wt%)- and rGO (1.0 wt%)/AlPO₄ (2.0 wt%)-coated samples exhibit high discharge capacities of 235 mA h g⁻¹ and 240 mA h g⁻¹, respectively, at C/10 rate with capacity retentions of 94% and 95%, respectively, at 100 cycles. Moreover, the rGO/AlPO₄-coated cathodes show better cyclability than the pristine cathode at an elevated temperature (55 °C). The superior electrochemical performances of the rGO/AlPO₄-coated electrodes could be attributed to the decrease in the Li content in the solid-electrolyte interphase (SEI) layer and facilitation of faster charge transfer as suggested by XPS and electrochemical impedance spectroscopy (EIS).