Quantification of hydroxide in co-precipitated nickel, manganese, cobalt carbonate precursor via TG-MS analyses

A significant obstacle associated with the synthesis of carbonate precursors for lithium nickel manganese cobalt oxides (NMC) is the concurrent precipitation of nickel hydroxide. Depending on the synthesis conditions and on the desired transition metals stoichiometric ratio, nickel may precipitate solely in its hydroxide form, even with excess carbonate present in the synthesis medium. The present work investigates the use of thermogravimetry-mass spectrometry (TG-MS) technique to quantify the dehydration, dehydroxylation and decarbonation of such mixed precursors. A calibration curve built for the dehydroxylation of nickel hydroxide with a copper sulfate internal standard allowed for the differentiation of sample weight loss associated to either hydrates or hydroxides. Thereafter, the numerical deconvolution of derivative TG and MS peaks obtained for NMC precursors enabled the calculation of atomic percentages of metal hydroxides and carbonates. Various commonly cited mathematical models for deconvolution are examined to investigate the quality of fitted data. According to this research, asymmetric double sigmoidal functions best represented the TG-MS data obtained for NMC carbonate precursors.