ИСТИНА

The chemical reactions of LiMPO4 (M = Mn, Fe, Co, Ni) cathode materials syntheses from phosphates and lithium carbonate were studied by the TG-DSC technique with simultaneous mass-spectroscopic analyzing (MS) of gaseous products of reaction, using NETZSCH STA 409 PC/PG and STA 449 C (alumina crucibles) technique with the mass-analyzer QMS 403 C Aëolos. The phase composition of start compounds and products of reaction were confirmed by X-ray analysis (Huber G670 diffractometer). The ammonia phosphates NH4MPO4•xH2O, hydrophosphates MHPO4∙xH2O and pyrophosphates M2P2O7∙xH2O were used as the start phosphate substances. The MS analyses of vapor composition in addition of TG-DSC allow understanding the main particularities of the interaction. The ions with m/e = 15 (NH+), 18 (H2O+) and 44 (CO2+) were taken into consideration for the unique determination of the vapor composition. The NH4MPO4•xH2O are thermally unstable and decomposed in two stages with formation hydrophosphates and subsequent transportation in pyrophosphate [1, 2]. A complicated mechanism of Co-contained ammonia phosphates decomposition was revealed due to MS results. The ammonia loss was detected at the second stage of reaction, coursed, probably, by the higher stability of cobalt-ammonia complexes in comparison with water one. A two-step mechanism of interaction was revealed under heating of NH4MPO4•xH2O and Li2CO3 mixture. At the first stage, the decomposition of NH4MPO4•H2O with escaping of ammonia and crystalhydrate water with formation of hydrophosphates was mainly observed, as in the case of individual substance decomposition. A small elimination of carbon dioxide at this stage may be coursed, likely, as a result of the side interaction of lithium carbonate with escaping water vapor. At the second stage, the hydrophosphate reacts with lithium carbonate for LiMPO4 formation with escaping of carbon dioxide. The obtained results are compared with the data of interaction of hydrophosphates and pyrophosphates with lithium carbonate. The reaction of Li2CO3 with cobalt hydrophosphates repeats mainly the result, obtained for ammonia-cobalt phosphate, but in case of interaction with cobalt pyrophosphates higher temperature is required. The obtained results are discussed in supposition of increasing reaction activity at phosphates restructuring under decomposition with elimination of gaseous components.