Preparation and characterization of LiAl_xMn_2-xO₄ for a supercapacitor in aqueous electrolyte

LiAl_xMn_2-xO₄ (0≤x≤0.5) was synthesized by high temperature solid-state reaction. The structure and morphology of LiAl_xMn_2-xO₄ were investigated by X-ray diffraction and scanning electron microscopy (SEM). The results indicate that all samples show spinel phase. The polyhedral particles turn to club-shaped, then change to small spherical, and finally become agglomerates with increasing Al content. The supercapacitive performances of LiAl_xMn_2-xO₄ were studied by means of galvanostatic charge-discharge, cyclic voltammetry, and alternating current (AC) impedance in 2 mol·L^-1 (NH₄)₂SO₄ aqueous solution. The results show that LiAl_xMn_2-xO₄ represents rectangular shape performance in the potential range of 0-1 V. The capacity and cycle performance can be improved by doping Al. The composition of x=0.1 has the maximum special capacitance of 160 F·g^-1, which is 1.37 times that of LiMn₂O₄ electrode. The capacitance loss of LiAl_xMn_2-xO₄ with x=0.1 is only about 14% after 100 cycles.