High performance LiNi0.5Mn1.5O4 cathode material with a bi-functional coating for lithium ion batteries

Abstract

LiPO₃, one of the compounds from the Li₂O–P₂O₅ binary phase diagram, is successfully coated on LiNi_0.5Mn_1.5O₄ particles as a bifunctional layer with respect to its good ionic conductivity and chemical passivation properties. The coating layer with a thickness of 1 nm is identified by X-ray diffraction (XRD) and high resolution transition electron microscopy (TEM). Fourier transform-infrared spectrometer (FT-IR) and Raman spectra reveal that LiPO₃ coated LiNi_0.5Mn_1.5O₄ (LiPO₃/LiNi_0.5Mn_1.5O₄) possesses a cubic spinel structure with a space group of Fdm. The electrochemical properties of synthesized materials are evaluated in both Li ion half cells and full cells. LiPO₃/LiNi_0.5Mn_1.5O₄ exhibits significantly enhanced rate performance and superior cyclability compared with non-coated LiNi_0.5Mn_1.5O₄. Impedance analysis indicates that the LiPO₃ coating dramatically reduces the LiPO₃/LiNi_0.5Mn_1.5O₄ cell impedance, especially the resistances of the lithium ion migration compared with non-coated LiNi_0.5Mn_1.5O₄. In addition, the LiPO₃ coating can effectively act as a passivation layer to minimize electrolyte–electrode interface side reactions and thus improve the long-term cyclability.