LaPO4-coated Li1.2Mn0.56Ni0.16Co0.08O2 as a cathode material with enhanced coulombic efficiency and rate capability for lithium ion batteries

Abstract

In this paper, pristine Li-rich layered oxide Li[Li_0.2Mn_0.56Ni_0.16Co_0.08]O₂ porous microspheres have been successfully synthesized by a urea combustion method, and then coated with 1.0%, 2.0%, and 3.0 wt% LaPO₄ via a facile chemical precipitation route. The structures and morphologies of both pristine and LaPO₄ coated Li_1.2Mn_0.54Ni_0.16Co_0.08O₂ were investigated by X-ray diffractometry (XRD), field-emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HR-TEM). XPS data and FESEM demonstrate that the LaPO₄ was successfully coated on the surface of the Li[Li_0.2Mn_0.56Ni_0.16Co_0.08]O₂ porous microspheres. Especially, the 2 wt% LaPO₄ coated-Li[Li_0.2Mn_0.56Ni_0.16Co_0.08]O₂ demonstrates the best electrochemical performance. As lithium ion battery cathodes, the 2 wt% LaPO₄ coated sample, compared with the pristine one, has shown significantly improved electrochemical performances: the initial coulumbic efficiency improves from 78.81% to 84.76% at 0.1C and the rate compatibility increased from 70 mA h g⁻¹ to a high capacity of 112.73 mA h g⁻¹ at a current density of 5C. The analysis of dQ/dV plots and electrochemical impedance spectroscopy (EIS) demonstrate that the enhanced electrochemical performance is mainly attributed to the fact that the LaPO₄ coating layer can not only stabilize the cathode structure by reducing the loss of oxygen, but also protect the Li-rich cathodes by decreasing the side reactions of Li[Li_0.2Mn_0.56Ni_0.16Co_0.08]O₂ with the electrolyte and lower the charge transfer resistance of the sample.