Comparison of Overcharge Behavior of AlPO4-Coated LiCoO2 and LiNi0.8Co0.1Mn0.1 O 2 Cathode Materials in Li-Ion Cells

The overcharge behavior of AlPO 4 -coated Li x Ni 0.8 Co 0.1 Mn 0.1 O 2 cathodes was compared to that of AlPO 4 -coated Li x CoO 2 cathodes in Li-ion cells. The former exhibited less heat generation than the latter as the charge voltage increased. Moreover, the coated Li x Ni 0.8 Co 0.1 Mn 0.1 O 2 cathode showed two distinct sets of exothermic peaks beginning at ∼75 and ∼200°C, respectively, while the coated Li x CoO 2 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 AlPO 4 -coated Li x Ni 0.8 Co 0.1 Mn 0.1 O 2 cathode did not exceed ∼125°C, and that of the coated Li x CoO 2 exceeded ∼170°C. However, the Li-ion cells containing either cathode with the AlPO 4 -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 AlPC 4 -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.

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