Characteristic Features of Layered Li[M_xNi_(1−x)/2Mn_(1−x)/2]O₂ (M = Co and Ni) Positive Electrode Materials and Their Li-ion Batteries

Abstract

Layered lithium nickel manganese oxides described as Li[M_xNi_(1−x)/2Mn_(1−x)/2]O₂ (M = Ni and Co, 0≦x≦1/3) were induced from superlattice layered Li[Ni_1/2Mn_1/2]O₂. XAS results suggested that Li[Ni_xNi_(1−x)/2Mn_(1−x)/2]O₂ compounds contained Ni^2,3+ and Mn⁴⁺, and that Li[Co_xNi_(1−x)/2Mn_(1−x)/2]O₂ contained Co³⁺, Ni²⁺ and Mn⁴⁺. Li[Co_1/3Ni_1/3Mn_1/3]O₂ showed almost the same reversible capacity as LiCoO₂. From results on DSC of the electrode charged by 4.3 V versus Li metal, Li[Co_1/3Ni_1/3Mn_1/3]O₂ exhibited higher thermal stability than LiCoO₂. ARC measurements of the full-charged Li-ion batteries were carried out. The battery with Li[Co_1/3Ni_1/3Mn_1/3]O₂ exhibited lower self-heat rate for thermal runaway than that with LiCoO₂, suggesting that the battery with Li[Co_1/3Ni_1/3Mn_1/3]O₂ was superior to that with LiCoO₂ in terms of thermal stability at full-charged state.