Synthesis, Characterization, and Electrochemical Behavior of Improved Li[Ni[sub x]Co[sub 1−2x]Mn[sub x]]O[sub 2] (0.1≤x≤0.5)

Abstract

In recent papers, our laboratory has reported new cathode materials based on the Li[NixCo1−2xMnx]O2Li[NixCo1−2xMnx]O2 series. These materials show good performance and appear to be much less reactive with electrolyte at high temperatures than LiCoO2LiCoO2 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/cm3)4.1 g/cm3) can be obtained using an improved coprecipitation method, followed by heating at 1100°C. Different cell performance is obtained depending on the cooling conditions and on the stoichiometry, x,x, in Li[NixCo1−2xMnx]O2.Li[NixCo1−2xMnx]O2. The best capacity retention for cycling to 4.4 V is obtained for Li[Ni0.25Co0.5Mn0.25]O2Li[Ni0.25Co0.5Mn0.25]O2 heated to 1100°C 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 LiCoO2LiCoO2 cycled under the same conditions (40 mA/g, 2.5 to 4.4 V). The volumetric energy density of Li[Ni0.25Co0.5Mn0.25]O2Li[Ni0.25Co0.5Mn0.25]O2 would exceed that of LiCoO2LiCoO2 if the irreversible capacity (about 20 mAh/g) could be eliminated, and that will be the focus of future work. © 2003 The Electrochemical Society. All rights reserved.