The mechanism of Sol-Gel synthesis of normal spinel LiMn₂O₄ with chelation of citric acid

Abstract

The sol-gel process of citric acid chelating with metal cations for the synthesis of normal spinel LiMn₂O₄ and the reaction mechanism were investigated by means of XRD, IR, TG-DTA and SEM. The results show that at the beginning lithium citrate and chelate compound of citric acid with manganese ions formed, and then with heating the esterification and condensation reactions occured between them and glycol. The products obtained are polymers in which metal cations are distributed homogenously on atomic scale that ensure high reactivity to cations of Li⁺ and Mn²⁺. Firing the gel prepared by this process, the lattice diffusions of solid reactant ions caused by non-homogeneity of reactants are eliminated and avoided. At 400°C phase-pure LiMn₂O₄ with nanometer scale crystallization having precise stoichiometry and perfect crystallization can be obtained. The model of chelate coordinate of double-molecule between citric acid and Mn²⁺ in the gel network is proposed. It is important for explaining the dispersion state of Mn²⁺ and the formation process of gel by this model.

Keywords

sol-gel process / chelation of citric acid / LiMn₂O₄ / mechanism of reaction

References

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