Studies on chromium/aluminium-doped manganese spinel as cathode materials for lithium-ion batteries-A novel chelated sol-gel synthesis

Nanoparticles of LiMn₂O₄, LiCr_xMn_2-xO₄ and LiAl_xMn_2-xO₄ (x = 0.0-0.4) have been synthesized using either phthalic acid or fumaric acid as chelating agents, for the first time, through sol-gel method. These materials were characterized by thermo gravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Electrochemical performance of these materials was assessed to use as cathode material for lithium-ion batteries. XRD patterns ascertain the formation of the phase pure compounds. SEM images indicate the nanosized nature of the particles with uniform morphology and texture. Doping of Cr/Al with the spinel resulted to increased agglomeration. Cr-doped spinel delivers 138 mAh/g while Al-doped spinel exhibit 139 mAh/g at the first cycle reversible capacity. Doping of 0.1 Al spinel cells shows superior performance over the tested 10 cycles in terms of low capacity fading. Co-doped Li_3-xCo_xN (x = 0.40) has also been synthesized by solid-state method to use as anode material for lithium-ion batteries. Cells were assembled with the synthesized spinel cathodes and these cells delivered stable specific capacity with high columbic efficiency. Cyclic voltammograms of both spinels exhibit good oxidation and reduction peaks for Mn³⁺/Mn⁴⁺, Cr³⁺/Cr⁴⁺ and Al⁺/Al³⁺.