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 Li[NixLi(1/3-2x/3)Mn(2/3-x/3)]O-2 (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 degrees 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 Li[Li1/5Ni1/5Mn3/5]O-2 (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[Li1/5Ni1/5Mn3/5]O-2 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 degrees C, and possible mechanisms are discussed in terms of lithium insertion scheme.