Joon-Gon Lee

Effect of AlPO4-Nanoparticle Coating Concentration on High-Cutoff-Voltage Electrochemical Performances in LiCoO2

AlPO 4 coating thickness on LiCoO 2 cathodes was controlled in the range on the order of 10-100 nm by changing the AlPO 4 -nanoparticle concentration in the coating solution. The specific capacity and cycle-life performance of the coated cathodes had a strong correlation with the AlPO 4 coating concentration (thickness). The cycle-life performance of the 1.0 wt % AlPO 4 -coated cathodes had the best cycling stability, showing 149 mAh/g capacity retention with 4.8 V charge cutoff by 50 cycles at 1 C (=140 mA/g) rate after precycles. However, the bare cathode showed zero capacity retention at the same condition after only 20 cycles. As the coating concentration was increased to 3.2 wt %, the amount of Co dissolution into the electrolyte decreased. In contrast, the 1.0 wt % AlPO 4 -coated cathode showed the best cycling stability, possibly due to the suppression of Li diffusivity decay and the appropriate electronic conduction.

Annealing-Temperature Effect on Various Cutoff-Voltage Electrochemical Performances in AlPO4-Nanoparticle-Coated LiCoO2

The electrochemical properties of AlPO 4 -coated LiCoO 2 cathodes were found to be superior to those of bare cathodes at various charge-cutoff voltages (4.3, 4.6, and 4.8 V), and depended on the annealing temperature. The AlPO 4 -coated cathodes annealed at 600 and 700°C retained a discharge capacity of ∼150 mAh/g even with a 4.8 V charge-cutoff voltage (after 46 cycles at I C = 140 mA/g). The bare cathode showed zero capacity retention at the same condition after only 20 cycles. The enhanced electrochemical performance and rate capability in the coated cathodes were attributed to the inhibition of structural degradation during cycling. The AlPO 4 -nanoparticle coating layer on the LiCoO 2 effectively suppressed cobalt dissolution and a nonuniform distribution of local strain in the cathode.