Chemistry evolution of LiNi_1/3Co_1/3Mn_1/3O₂-NaHSO₄·H₂O system during roasting

LiNi_1/3Co_1/3Mn_1/3O₂ 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 LiNi_1/3Co_1/3Mn_1/3O₂ in acidic aqueous solutions. Different from the acidic aqueous solutions reaction system, this paper presents a study on the chemistry evolution of LiNi_1/3Co_1/3Mn_1/3O₂-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 LiNi_1/3Co_1/3Mn_1/3O₂ 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: LiNi_1/3Co_1/3Mn_1/3O₂ → Li₂SO₄ → LiNaSO₄, LiNi_1/3Co_1/3Mn_1/3O₂ → NiSO₄ → Na₆Ni(SO₄)₄ → Na₂Ni(SO₄)₂, LiNi_1/3Co_1/3Mn_1/3O₂ → CoSO₄ → Na₆Co(SO₄)₄ → Na₂Co(SO₄)₂, LiNi_1/3Co_1/3Mn_1/3O₂ → 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: 12LiNi_1/3Co_1/3Mn_1/3O₂ + 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.