Synthesis and electrochemical properties of spherical spinel Li1.05M0.05Mn1.9O4 (M=Ni, Mg, Al) as a cathode material for lithium ion batteries by co-precipitation method

Abstract

Introduction A commercial lithium-ion batteries employ layered LiCoO2 as a cathode material. But it has still some limits such as high cost, environmental problems and limited sources of cobalt ore. Recently, the spinel LiMn2O4 and its derivatives are considered as one of the most attractive cathode materials for lithium secondary batteries because of their low cost, abundance, and non-toxicity. And the spinel cathodes are very attractive for Hybrid Electric Vehicle (HEV) power. But Mn spinel has problem for application. It is the capacity fading on cycling under severe condition (above 40℃). To overcome capacity fading, the manganese site was replaced by some of transition metals to enhance structural stability [1,2]. In this study, we report the preparation of (M-Mn)3O4 precursor by a hydroxide co-precipitation method and characterization of electrochemical properties for Li1.05M0.05Mn1.9O4 (M = Ni, Mg, Al). We study the effect of M (M = Ni, Mg, Al) substitution in the manganese sites.

Experimental The spherical (M-Mn)3O4 was prepared as follows; An aqueous solution of MnSO4·H2O and M (M = NiSO4·6H2O, MgSO4, Al2(SO4)3) with a concentration of 2.0 mol/L was pumped into continuous stirred tank reactor (CSTR, capacity 4L) under Air. At the same time, NaOH solution (aq) of 4.0 mol/L and desired amount of NH4OH solution (aq) as a chelating agent were also separately fed into the reactor. The concentration of the solution, pH, temperature, and stirring speed of the mixture in the reactor were controlled with care. The Mn(OH)2 is easily changed to metal oxide. To promote this reaction, we precipitate manganese sulfate and sodium hydroxide under Air. At the initial stage of the co-precipitation reaction, the irregular secondary particles from the agglomeration of the acicular primary structure were formed and the irregular particles changed gradually into spherical particles by vigorous stirring at 50℃ for 12 h. Then, the spherical (M-Mn)3O4 particles were filtered, washed, and dried. The obtained spherical particles dried at 110˚C to remove adsorbed water. The as-prepared powder was simply mixed with lithium sources, and then the prepared powders were calcined at 800 ℃ in a box furnace.

Results and discussion The morphology of precursor and Li1.05M0.05Mn1.9O4 (M = Ni, Mg, Al) was examined by SEM. Figure 1 shows that the powders consist of a spherical morphology with an average particle size of approximately 8 ㎛. The X-ray diffraction (XRD) patterns of Li1.05M0.05Mn1.9O4 (M = Ni, Mg, Al) are in Figure 2. The spectra show that all the samples have a typical spinel phase.