Understanding the Improvement in the Electrochemical Properties of Surface Modified 5 V LiMn1.42Ni0.42Co0.16O4 Spinel Cathodes in Lithium-ion Cells

The 5 V spinel cathode LiMn1.42Ni0.42Co0.16O4 with cation disorder in the 16d octahedral sites has been surface modified with 2 wt % nanosize Al2O3, ZnO, Bi2O3, and AlPO4 by an electrostatic self-assembly method. The bare and surface-modified samples have been characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), high-resolution transmission electron microscopy (TEM), charge-discharge measurements in lithium cells, electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (XPS). The surface-modified samples exhibit better cycling performance, better rate capability, and better rate capability retention during cycling compared to the bare sample. EIS and XPS studies show that the inferior electrochemical performances of the bare LiMn1.42Ni0.42Co0.16O4 are closely related to the formation of thick solid-electrolyte interfacial (SEI) layer at the high operating voltages of similar to 5 V. Surface modifications with nanosize Al2O3, ZnO, Bi2O3, and AlPO4 suppress the formation of thick SEI layers on LiMn1.42Ni0.42Co0.16O4 and thereby improve the electrochemical performances significantly. Moreover, the differences in the surface compositions formed during the annealing or electrochemical cycling processes also influence the electrochemical properties.