Li[NixCo1-2xMnx]O-2 electrode materials prepared at 900degreesC show good performance and are less reactive with electrolyte at elevated temperatures than LiCoO2 when charged to 4.2 V (vs. Li) and above. However, the tap density and the resulting electrode density of samples reported previously are lower than required for some industrial applications in Li-ion batteries. One way to increase the density while preserving a 900degreesC heating temperature is to use a sintering agent. A few weight percent of B2O3 was added during the synthesis of Li[NixCo1-2xMnx]O-2 as a sintering agent. The preparation, structure, morphology, density, and electrochemical behavior of the resulting materials, for several compositions, including x = 0 (i.e., LiCoO2), are presented as a function of B2O3 content. We found that denser Li[NixCo1-2xMnx]O-2 (x > 0) could be obtained using B2O3 as a sintering agent. The presence of a lithium borate impurity in LiCoO2 samples and an increase in the amount of Ni in the Li layer for Li[NixCo1-2xMnx]O-2 with x > 0 are induced by B2O3 additions. For x = 0.1, and for up to 1 wt % added B2O3, the electrochemical behavior remains quite good while the sintering significantly improves the density of the powder. (C) 2004 The Electrochemical Society.