The electrochemical cycling and storage characteristics of LiCo0.96M0.04O2 and M-3(PO4)(2) nanoparticle-coated LiCoO2 cathodematerials (M = Zn and Mg) were compared at room temperature and 90 degrees C between 3 and 4.5 V. The doped cathodes showed degraded electrochemical performance at room temperature compared to the uncoated cathode. The first discharge capacities of the uncoated and the doped cathodes were 186 and 175 mAh/g, respectively. The doped cathodes showed 30 mAh/g after 30 cycles, while the uncoated cathode showed 100 mAh/g after 50 cycles at a 1 C rate. Mg-3(PO4)(2) and Zn-3(PO4)(2)-coated LiCoO2 showed discharge capacities of 179 and 187 mAh/g, respectively, and hadsignificantly improved capacity retention, showing 133 and 153 mAh/g, respectively, after 50 cycles. After storage at 90 degrees C, in the electrolytes using 4.5 V charged electrodes, the doped cathodes showed both greatly decreased side reactions with the electrolytes and formation of Co3O4 and CoO phases from Li and Co dissolution. However, the coated cathodes did not show either structural transformation into the Co3O4 and CoO phases or side reactions with the electrolytes. (C) 2008 The Electrochemical Society.