title: Polyimide encapsulated lithium-rich cathode material for high voltage lithium-ion battery.
abstract: Lithium-rich materials represented by xLi2MnO3·(1 - x)LiMO2 (M = Mn, Co, Ni) are attractive cathode materials for lithium-ion battery due to their high specific energy and low cost. However, some drawbacks of these materials such as poor cycle and rate capability remain to be addressed before applications. In this study, a thin polyimide (PI) layer is coated on the surface of Li1.2Ni0.13Mn0.54Co0.13O2 (LNMCO) by a polyamic acid (PAA) precursor with subsequently thermal imidization process. X-ray diffraction (XRD), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HR-TEM) results confirm the successful formation of a PI layer (∼3 nm) on the surface of LNMCO without destruction of its main structure. X-ray photoelectron spectroscopy (XPS) spectra show a slight shift of the Mn valence state from Mn(IV) to Mn(III) in the PI-LNMCO treated at 450 °C, elucidating that charge transfer takes place between the PI layer and LNMCO surface. Electrochemical performances of LNMCO including cyclic stability and rate capability are evidently improved by coating a PI nanolayer, which effectively separates the cathode material from the electrolyte and stabilizes their interface at high voltage.
authors.affiliation: School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University , 800 Dongchuan Road, Shanghai 200240, China.
authors.forename: Jie
authors.initials: J
authors.lastname: Zhang
authors.forename: Qingwen
authors.initials: Q
authors.lastname: Lu
authors.forename: Jianhua
authors.initials: J
authors.lastname: Fang
authors.forename: Jiulin
authors.initials: J
authors.lastname: Wang
authors.forename: Jun
authors.initials: J
authors.lastname: Yang
authors.forename: Yanna
authors.initials: Y
authors.lastname: NuLi
keywords: interfacial reaction; lithium-ion battery; lithium-rich material; polyimide; surface coating