Comparison of Overcharge Behavior of AlPO[sub 4]-Coated LiCoO[sub 2] and LiNi[sub 0.8]Co[sub 0.1]Mn[sub 0.1]O[sub 2] Cathode Materials in Li-Ion Cells

The overcharge behavior of -coated cathodes was compared to that of -coated cathodes in Li-ion cells. The former exhibited less heat generation than the latter as the charge voltage increased. Moreover, the coated cathode showed two distinct sets of exothermic peaks beginning at ∼75 and ∼200°C, respectively, while the coated exhibited relatively continuously increasing exothermic peak beginning at ∼150°C. The results were consistent with the 12 V overcharge tests using Li-ion full cells. As the C rate increased from 1 to 3 C, the cell-surface temperature with the -coated cathode did not exceed ∼125°C, and that of the coated exceeded ∼170°C. However, the Li-ion cells containing either cathode with the -nanoparticle coating did not exhibit thermal runaway, although short-circuits occurred at 12 V during a 3 C overcharging rate. It is evident that the -coating layer on the powder drastically reduced the violent exothermic reaction between the electrolyte and cathode, controlling the overall safety of the Li-ion cells. © 2004 The Electrochemical Society. All rights reserved.