ИСТИНА

The silicates of lithium and 3d-elements Li2MSiO4∙(M = Mn, Co, Ni) are considered as promising cathode materials for lithium-ion rechargeable batteries [1]. The sol-gel process, included sol formation, gelation and subsequent gel decomposition under heating, allows obtaining the compounds at relatively low temperatures [2]. The study of main chemical processes under heating of dried silica gel, contained acetates of 3d-element and lithium acetate, is the main goal of this study. The acetates of transition elements and lithium acetate were used as water solution, silicon was introduced into reaction in the tetraethylorthosilicate (TEOS) form. The obtained mixture was heated at 60°C for gelation, than dried at 100°C for several days. In order to reveal the main stage of interaction in Li2MSiO4∙forming, the reaction of M2SiO4 and Li4SiO4 synthesis were studied additionally. For identification the basic chemical processes occurring during the heating of silica gels with included acetates of 3d-element and lithium acetate the TG-DSC technique NETZSCH STA 409 PC/PG and STA 449 C (alumina crucibles) with the mass-analyzer (MS) QMS 403 C Aëolos was used. The experiments were carried out in He-flow at heating rate 10°/min. The MS analyses of vapor composition in addition to TG-DSC allow understanding the main particularities of the interaction. The phase composition of start compounds and products of reaction were controlled by X-ray analysis (Huber G670 diffractometer). Maxima in the derivative weight correlated with thermal maxima and maxima of gassing. The main gaseous products, found in mass-spectra were water vapour (18), carbon dioxide (44), CH3CO (43) and CH3 (15) particles. Carbon dioxide, CH3CO (43) and CH3 (15) were identified as the products of thermal decomposition of acetates of 3d-elements and lithium acetates. Two main effects of acetates decomposition were found: near 310 and 400°C. Low temperature effect corresponded to decomposition of 3d-element acetates, while high temperature effect – to lithium acetate. The decomposition of lithium acetate accompanied, likely, according MS spectra, its partial carbonization, that, the formed lithium carbonate reacts with silica at the higher temperatures. This reaction is accompanied by escaping of carbon dioxide. The emission of carbon dioxide continues up to 800°C, it may indirectly indicate the kinetic difficulty of such solid state reaction. According to TG-DSC-MS study we can conclude that the decomposition of 3d-elements acetates take place at the first stage, then - lithium acetate, followed by interaction with silica gel.