Abstract:

Spinel LiMn_1-xNi_xTiO₄(x=0, 0.1, 0.2, 0.3) cathode materials were prepared by Sol-Gel method. The surface morphology and phase structure of LiMn_1-xNi_xTiO₄ (x=0, 0.1, 0.2, 0.3) were characterized by FESEM and XRD. FESEM analysis indicated all the samples consisted of irregular particles and XRD patterns showed that all the materials had impurity TiO₂, but there were no impurities related to Ni element. Electrochemical studies of doped and undoped spinels were carried out by cyclic voltammetry (CV) and constant current charge-discharge. CV results showed that LiMnTiO₄ had two couples of sharp redox peaks corresponding to Mn³⁺/Mn⁴⁺, Mn²⁺/Mn³⁺ redox reactions. However, after Ni substitution, there appeared the third redox coupled, which was related to the Ni³⁺/Ni⁴⁺ redox reaction. LiMn_1-xNi_xTiO₄ (x=0.1, 0.2, 0.3) exhibited improved electrochemical properties compared with LiMnTiO₄. When the Ni substitution was 0.1, the first discharge capacity of LiMn_0.9Ni_0.1TiO₄ was 171.6 mAh/g at current density of 30 mA/g, and after 48 charge-discharge cycles, the discharge capacity was 162.8 mAh/g, with the capacity retention of 82.7%. The Ex XRD pattern of LiMn_0.9Ni_0.1TiO₄ showed that the material structure had no changes after the first cycle, and there was no transition between cubic phase and tetragonal phase.

Key words: lithium ion batteries, LiMnTiO4, Ni substitution, Sol-Gel