Increased cycling stability of Li_4Ti_5O_(12)-coated LiMn_(1.5)Ni_(0.5)O_4 as cathode material for lithium-ion batteries

摘要

Li_4Ti_5O_(12) (LTO)-coated 5 V spinel LiMn_(1.5)Ni_(0.5)O_4 as cathode was prepared by the sol -gel method followed by high-temperature calcinations. The structural and electrochemical properties of these cathodes were investigated using differential thermal analysis (DTA) and thermogravimetery (TG), X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV), and charge discharge studies. TG-DTA shows that LiMn_(1.5)Ni_(0.5)O_4 spinel forms at about 400 °C. XRD reveals that a substitutional compound LiMn_(2-x-y)Ni_xTi_yO_4 can be formed when the coated content of LTO exceeds 3 wt%. SEM exhibits that the coated LiMn1.5Nio.5O4 is covered with small particles that consist mainly of LTO. CV and dQ/dV versus voltage curves demonstrate that the modified material exhibits remarkably enhanced electrochemical reversibility and stability. The charge-discharge test indicates that 3 wt% LTO-coated LiMn_(1.5)Ni_(0.5)O_4 has excellent fast charge-discharge performances. These results reveal that LTO-coated layer protects the surface of the active materials from HF in the electrolyte during electrochemical cycling. As a result, the surface-modification of LiMn_(1.5)Ni_(0.5)O_4 with LTO should be an effective way to improve the fast charge-discharge properties.