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

Lithium nickel manganese oxides LiNixLi(1/3−2x/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 LiNi1/2Mn1/2O2 (x = 1/2) shows the highest operating voltage and the smallest polarization with a rechargeable capacity of ca. 230 mA h g−1 and LiLi1/5Ni1/5Mn3/5O2 (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 LiLi1/5Ni1/5Mn3/5O2 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.