Crystal structure and multicomponent effects in Li1+xMn2−x−yAlyO4 cathode materials for Li-ion batteries

Abstract

Li, Al co-doped LiMn2O4 (Li1+xMn2−x−yAlyO4, 0 ≤ x ≤ 0.12, 0 ≤ y ≤ 0.1) cathode has been synthesized via a solid-state reaction designedly using industrial raw materials in bulk scale (>20 kg). The multicomponent substitution effects on the crystal structures are examined systematically by Rietveld refinement of X-ray diffraction, and the resultant electrochemical properties for Li-ion batteries are also evaluated by galvanostatic charge–discharge and electrochemical impedance spectroscopy measurements. As a result, Li, Al co-doping significantly changes the unit cell parameter and atomic arrangement. With the increasing of doping levels, a cell dimension contracts with concomitant changes in bond length, whereby the MO6 octahedron (M = Mn/Li/Al) shrinks to provide structural integrity and the LiO4 tetrahedron expands to facilitate a fast electrochemical process. The strong spinel-framework contributes to a better structure-stabilization, resulting in a superior capacity retention ratio of 90% after 200 cycles at 0.5 C at 55 °C for the optimized composition (Li1.06Mn1.86Al0.08O4), which possesses an initial value of 102 mAh g−1. Meanwhile, the expansion of LiO4 tetrahedron leads to better high-rate performance, bringing about a capacity of 88 mAh g−1 upon cycling at 10 C at 55 °C. Further, Li1.06Mn1.86Al0.08O4 displays lower impedance than that of the pristine LiMn2O4.