Chemistry evolution of LiNi1/3Co1/3Mn1/3O2-NaHSO4·H2O system during roasting

Abstract

LiNi1/3Co1/3Mn1/3O2 is one of the key materials used in power lithium-ion batteries. At present, much attention is put on the study of chemical properties of LiNi1/3Co1/3Mn1/3O2 in acidic aqueous solutions. Different from the acidic aqueous solutions reaction system, this paper presents a study on the chemistry evolution of LiNi1/3Co1/3Mn1/3O2-NaHSO4·H2O system with stoichiometric mass ratio of 1:4.30 during roasting process, which is studied by thermogravimetry-differential scanning calorimetry, in-situ X-ray diffraction, X-ray diffraction and X-ray photoelectron spectroscopy. The experimental results show that the quondam phase composition of the mixture is disappeared and transformed to its corresponding sulfates (LiNaSO4 and Na2Ni(SO4)2 etc.). In the temperature range under 425 °C, the original structure of LiNi1/3Co1/3Mn1/3O2 is completely destroyed due to the lack of Li in the α-NaFeO2 layered structure, and the bimetallic sulfates were transformed and existed in the form of Na2M(SO4)2 (M = Ni, Co, Mn) from 425 °C to 550 °C. The occurrence of Li, Ni, Co, and Mn elements evolves as follows: LiNi1/3Co1/3Mn1/3O2 → Li2SO4 → LiNaSO4, LiNi1/3Co1/3Mn1/3O2 → NiSO4 → Na6Ni(SO4)4 → Na2Ni(SO4)2, LiNi1/3Co1/3Mn1/3O2 → CoSO4 → Na6Co(SO4)4 → Na2Co(SO4)2, LiNi1/3Co1/3Mn1/3O2 → MnO2 → Mn2O3 → MnSO4 → Na2Mn(SO4)2, and the change of valence state of Co and Mn is +3 → +2 and + 4 → +3 → +2, respectively. The chemistry reaction mechanism of this roasting process might be reactions as follows: 12LiNi1/3Co1/3Mn1/3O2 + 36NaHSO4·H2O → 18Na2SO4 + 6Li2SO4 + 4NiSO4 + 4CoSO4 + 4MnSO4 + 54H2O + 3O2, Li2SO4 + Na2SO4 → 2LiNaSO4, MeSO4 + 3Na2SO4 → Na6Me(SO4)4 (Me = Ni, Co), Na6Me(SO4)4 → Na2Me(SO4)2 + 2Na2SO4, MnSO4 + Na2SO4 = Na2Mn(SO4)2.