Synthesis of Lithium-Manganese Oxide Spinel in Hydrothermal Conditions.

Danchevskaya M., Ivakin Yu., Panasyuk G., Voroshilov I., Boudova G., Azarova L, Privalov V., Minin V., Skundin A., Kanevsky L., Kulova T.

High Pressure Research (in the press)

Abstract. In the recent paper spinel LiMn2O4 and the phase Li2MnO3 were prepared by hydrothermal treatment of MnO2 with solutions of LiOH at 170 C under autogenic pressure after 24 days. In the present work were studied the products of solid state reaction of powdered mixture of gamma-MnO2 or beta-MnO2 and LiOH or Li2CO3 with a molar ratio Li:Mn (0.85-1.60):2 during thermovaporous treatment at 400 C, P H2O = 20 MPa, 1-2 days. The following methods were used: lazer dispersion analysis, X-ray phase analysis, microscopy, thermogravimetry, NMR, EPR and IR spectroscopy. At a ratio Li:Mn 1:2 spinel LiMn2O4, sp. gr. Fd3m (ASTM, inorg. 18-736) was a single crystal phase with the size of crystal grains 1-70 mkm. At change of this ratio in the charge from 1:2 up to 1.6:2 the lattice constant a(c) grew from 0.817 till 0.820 nm. At a ratio Li:Mn < 1:2 in the charge a prevailling phase in a product was spinel with a(c) =0.814-0.815 nm, and besides the impurity of beta-MnO2 and beta-Mn2O3 were present. On the heating curve up to 1400 C the endothermic peaks at 130 and 530 C were present, peculiar to hydrothermal spinels, and also additional endothermic peak at 230 C was present. Besides, endothermic peaks at 990 and 1100 C were present, peculiar to spinels, obtained by solid-state high temperature reaction. In NMR (7)Li spectra of spinels two lines with chemical shift 500 - 1400 ppm and 100 -350 ppm are observed. Two signals also there are in EPR spectra: a symmetric one without thin structure and nonsymmetric one with thin structure. The conclusion was made, that the parameters of the spectrum are determined by size and sign of pseudo-contact and dipol-dipol interaction (7)Li: - e- and that they depend on the magnitude of electronic conductivity. The spinel, obtained in the conditions of monophase synthesis, have been used for manufacturing a cathodes in scale models of the rechargeable lithium cells Li/1M LiClO4-propilene carbonate dimethoxyethan (7:3)/LixMn2O4. The cells discharged in the potential range 2.8-3.5V. The specific capacity was 100-140 mAh/g. The charge-discharge curves are high stable during the cycling, and the specific characteristics of cathode have a slight dependence on the load in sufficiently wide interval of current densities.

Laboratory of Catalysis and Gas Electrochemistry