M[sub 3](PO[sub 4])[sub 2]-Nanoparticle-Coated LiCoO[sub 2] vs LiCo[sub 0.96]M[sub 0.04]O[sub 2](M=Mg and Zn) on Electrochemical and Storage Characteristics

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Abstract
The electrochemical cycling and storage characteristics of LiCo0.96M0.04O2LiCo0.96M0.04O2 and M3(PO4)2M3(PO4)2 nanoparticle-coated LiCoO2LiCoO2 cathode materials (M=ZnandMg)(M=ZnandMg) were compared at room temperature and 90°C90°C between 3 and 4.5V4.5V . 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 175mAh∕g175mAh∕g , respectively. The doped cathodes showed 30mAh∕g30mAh∕g after 30 cycles, while the uncoated cathode showed 100mAh∕g100mAh∕g after 50 cycles at a 1C1C rate. Mg3(PO4)2Mg3(PO4)2 and Zn3(PO4)2Zn3(PO4)2 -coated LiCoO2LiCoO2 showed discharge capacities of 179 and 187mAh∕g187mAh∕g , respectively, and hadsignificantly improved capacity retention, showing 133 and 153mAh∕g153mAh∕g , respectively, after 50 cycles. After storage at 90°C90°C , in the electrolytes using 4.5V4.5V charged electrodes, the doped cathodes showed both greatly decreased side reactions with the electrolytes and formation of Co3O4Co3O4 and CoOCoO phases from Li and Co dissolution. However, the coated cathodes did not show either structural transformation into the Co3O4Co3O4 and CoOCoO phases or side reactions with the electrolytes.

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