Effect of Al-substitution on the stability of LiMn2O4 spinel, synthesized by citric acid sol–gel method

Spinel LiMn2O4 and LiAlxMn2−xO4 (x=0.05, 0.15) are synthesized by a sol–gel method using citric acid as a chelating agent. The effect of calcination temperature on the purity of the Al-substituted spinel is examined by X-ray diffraction measurements which suggests that pure material is obtained by calcination at 800°C. Cyclic voltammetry is employed to characterize the reactions of lithium insertion into and extraction from the spinel materials. Surface morphology changes are observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicate that Al-substitution enhances sintering of the spinel LiMn2O4. Charge–discharge cycling studies show that Al-substitution improves substantially the capacity retention of the spinel LiMn2O4.