Synthesis and electrochemical performance evaluations of polyhedra spinel LiAlxMn2-xO4 (x≦0.20) cathode materials prepared by a solution combustion technique

Abstract

A series of single-crystal polyhedra spinel LiAlxMn2-xO4 (x = 0, 0.05, 0.10, 0.15 and 0.20) cathode materials have been rapidly prepared by a solution combustion technique using HNO3 solution as an auxiliary oxidant. The crystal structure and phase identification of as-prepared samples were characterized through X-ray diffraction (XRD), which shows that all samples present the characteristic diffraction peaks of spinel LiMn2O4. The morphology and particle size of as-prepared samples were observed by field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM), which indicate that all samples have single-crystal polyhedra morphology and good crystallinity. The cycling performances of as-prepared samples were evaluated by galvanostatic charge/discharge cycling performance tests, which demonstrate that LiAl0.10Mn1.90O4 exhibits the optimal cycling and rate properties. It delivers a capacity retention rate of 60.7% after 2000 cycles with an initial discharge specific capacity of 99.5 mAh g−1 at 10 C (1 C = 148 mAh g−1) and 25 °C, while the capacity retention rate of pristine LiMn2O4 is only 9.6% with an initial discharge specific capacity of 81 mAh g−1 at the same conditions. The Al-doped samples show better elevated temperature cycling stability than pristine LiMn2O4. LiAl0.10Mn1.90O4 sample shows a capacity retention rate of 81.5% with a discharge specific capacity of 91.3 mAh g−1 after 500 cycles at 1 C and 55 °C, which is much superior compared with the capacity retention rate of 18.5% for pristine LiMn2O4. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) tests certify that LiAl0.10Mn1.90O4 presents the better electrode reversibility, more rapidly charge-transfer and Li+ diffusion kinetics processes.