M-3(PO4)(2)-nanoparticle-coated LiCoO2 vs LiCo0.96M0.04O2 (M = Mg and Zn) on electrochemical and storage characteristics

Abstract

The electrochemical cycling and storage characteristics of LiCo0.96 M0.04 O2 and M3 (PO4)2 nanoparticle-coated LiCoO2 cathode materials (M=Zn and Mg) were compared at room temperature and 90°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 mAhg, respectively. The doped cathodes showed 30 mAhg after 30 cycles, while the uncoated cathode showed 100 mAhg after 50 cycles at a 1 C rate. Mg3 (PO4)2 and Zn3 (PO4)2 -coated LiCoO2 showed discharge capacities of 179 and 187 mAhg, respectively, and hadsignificantly improved capacity retention, showing 133 and 153 mAhg, respectively, after 50 cycles. After storage at 90°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 Co3 O4 and CoO phases from Li and Co dissolution. However, the coated cathodes did not show either structural transformation into the Co3 O4 and CoO phases or side reactions with the electrolytes.