Electrochemical performance of SrF2-coated LiNi1/3Co1/3Mn1/3O2 cathode materials for Li-ion batteries

SrF2-coated LiNi1/3Co1/3Mn1/3O2 cathode materials with improved cycling performance over 2.5-4.6V were investigated. The structural and electrochemical properties of the materials were Studied using Xray diffraction (XRD), scanning electron microscope (SEM), charge-discharge tests and electrochemical impedance spectra (EIS). The results showed that the crystalline SrF2 with about 10-50 nm particle size is uniformly coated on the surface of LiNi1/3Co1/3Mn1/3O2 particles. As the coating amount increased from 0.0 to 2.0 mol%, the initial capacity and rate capability of the coated LiNi1/3Co1/3Mn1/3O2 decreased slightly owing to the increase of the charge-transfer resistance: however, the cycling stability was improved by suppressing the increase of the resistance during cycling. 4.0 mol% SrF2-coated LiNi1/3Co1/3Mn1/3O2 showed remarkable decrease of the initial capacity. 2.0 mol% coated sample exhibited the best electrochemical performance. It presented an initial discharge capacity of 165.7 mAh g(-1), and a capacity retention of 86.9% after 50 cycles at 4.6 V cut-off cycling. (C) 2008 Elsevier B.V. All rights reserved.