High-capacity lithium insertion materials of lithium nickel manganese oxides for advanced lithium-ion batteries: toward rechargeable capacity more than 300 mA h g−1

Abstract

Lithium nickel manganese oxides Li[Ni_xLi_{(1/ 3−2}x/3)Mn_{(2/ 3−}x/3)]O₂ (x = 1/2, 2/7, and 1/5) are prepared and characterized by XRD and FT-IR, and the samples are examined in non-aqueous lithium cells at room temperature and 55 °C. Among these materials LiNi_{1 / 2}Mn_{1 / 2}O₂ (x = 1/2) shows the highest operating voltage and the smallest polarization with a rechargeable capacity of ca. 230 mA h g⁻¹ and Li[Li_{1/ 5}Ni_{1 / 5}Mn_{3 /5}]O₂ (x = 1/5) shows the lowest operating voltage and the largest polarization with a rechargeable capacity more than 300 mA h g⁻¹. Extraordinarily large rechargeable capacity of Li[Li_{1/ 5}Ni_{1 / 5}Mn_{3 /5}]O₂ together with an anomalously long voltage plateau at 4.5 V only observed at first charging process is examined by window-opening charge and discharge, continuous charge and discharge combined with differential chronopotentiometry at room temperature and at 55 °C, and possible mechanisms are discussed in terms of lithium insertion scheme.