Synthesis, characterization, and electrochemical behavior of improved Li[NixCo1-2xMnx]O2 (0.1 ≤ x ≤ 0.5)

In recent papers, our laboratory has reported new cathode materials based on the Li[NixCo1-2xMnx] O-2 series. These materials show good performance and appear to be much less reactive with electrolyte at high temperatures than LiCoO2 at the same potential; however, the tap density and resulting electrode density of samples reported previously is lower than required for many industrial applications in Li-ion batteries. This paper focuses on changes to the synthesis procedure to increase the tap and pellet densities. Denser samples (pellet density between 3.7 and 4.1 g/cm(3)) can be obtained using an improved coprecipitation method, followed by heating at 1100 degreesC. Different cell performance is obtained depending on the cooling conditions and on the stoichiometry, x, in Li[NixCo1-2xMnx] O-2. The best capacity retention for cycling to 4.4 V is obtained for Li[Ni0.25Co0.5Mn0.25] O-2 heated to 1100 degreesC followed by slow cooling in oxygen. The volumetric energy density of electrodes (not including the current collector! of this material is 2110 Wh/L compared to 2270 Wh/L for optimized LiCoO2 cycled under the same conditions (40 mA/g, 2.5 to 4.4 V). The volumetric energy density of Li[Ni0.25Co0.5Mn0.25] O-2 would exceed that of LiCoO2 if the irreversible capacity (about 20 mAh/g) could be eliminated, and that will be the focus of future work. (C) 2003 The Electrochemical Society.