Dual modification of LiNi0.6Co0.2Mn0.2O2 with MgHPO4 as a high-performance cathode material for Li-ion batteries

Abstract

MgHPO₄ has been introduced as a reactant that interacts with LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622) to achieve the dual modification of Mg²⁺ gradient doping and Li₃PO₄ surface coating. The structure, morphology, elemental distribution, and electrochemical properties of the materials are elaborately explored using X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), and electrochemical measurements. On the one hand, Mg²⁺ gradient doping stabilizes the crystal structure of the Li⁺/Ni²⁺ cation and minimizes its disorder. On the other hand, the coating of the fast lithium-ion conductor Li₃PO₄ not only increases the rate of lithium-ion diffusion at the electrode–electrolyte interface but also protects the cathodic material and mitigates electrolyte corrosion. The dual-modified NCM622 cathode exhibits remarkable cycling performance, retaining 89.57% of its capacity after 200 cycles at 1C from 2.8 to 4.3 V and 79.03% after 100 cycles at 3C from 2.8 to 4.5 V. Additionally, the dual-modified cathode exhibits better electrode kinetics and a reversible capacity of 119.4 mA h g⁻¹ at 10C. This straightforward dual modification technique improves the lithium-ion diffusion kinetics at the interface while also stabilizing the internal crystal structure of Ni-rich cathode materials.