Influence of Al Substitution on the Electrochemical Performance of Spinel LiMi0.5-xMn1.5AlxO4 Cathode

Al-doped LiMi_0.5-xMn_1.5Al_xO₄ cathodes materials were synthesized by a simple sol-gel method. The structure and electrochemical properties have been investigated systematically by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectra, cyclic voltamogram (CV), charge-discharge tests and Ac impedance spectroscopy. XRD patterns reveal that trace of Li_xNi_1-xO-like impurity phase exists in the pristine LiNi_0.5Mn_1.5O₄ and is suppressed by substituting of Ni²⁺ with Al³⁺. With Al³⁺-substitution, the electrochemical performance of spinel cathodes are enhanced, which is ascribed to the improvement of structural stability and electronic conductivity as well as the suppression of impurity phase. However, the discharge capacity deteriorates in the case of LiNi_0.40Mn_1.5Al_0.10O₄ spinel, which might result from the blocking of migration pathway of electrons in octahedral site.