The formation of LiOH and Li2CO3 impurities on high Ni content LiNi0.83Co0.15Al0.02O2 powders due to H2O and CO2 absorption from the air can be reduced without structural degradation by washing in water. Although the as- synthesized sample had a moisture content of 570 ppm immediately after firing, this level increased rapidly to 1270 ppm in air with a relative humidity of 50%. However, its content was decreased to 210 ppm after washing twice in water, followed by heat- treatment at 700 degrees C. It is believed that this improvement was due to the decreased level of Li2CO3 and LiOH impurities on the particles. This was highlighted by the decreasing swelling of the Li- ion cell at 90 degrees C, and the thickness of the cell containing the washed samples was decreased by 50% compared with the bare sample. (c) 2005 The Electrochemical Society.