Comparison of Overcharge Behavior of AlPOsub 4-Coated LiCoOsub 2 and LiNisub 0.8Cosub 0.1Mnsub 0.1Osub 2 Cathode Materials in Li-Ion Cells

The overcharge behavior of AlPO4x0.80.10.12-coated LiNiCoMnO (cathodes was compared to that of AlPO)(-coated Li)(CoO)(4)(x)(2) (cathodes in Li-ion cells. The former exhibited less heat generation than the latter as the charge voltage increased. Moreover, the coated Li)(Ni)(Co)(Mn)(O)(x)(0.8)(0.1)(0.1)(2) (cathode showed two distinct sets of exothermic peaks beginning at 75 and 200C, respectively, while the coated Li)(CoO)(x)(2) (exhibited relatively continuously increasing exothermic peak beginning at 150C. 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)(-coated Li)(Ni)(Co)(Mn)(O)(4)(x)(0.8)(0.1)(0.1)(2) (cathode did not exceed 125C, and that of the coated Li)(CoO)(x)(2) (exceeded 170C. However, the Li-ion cells containing either cathode with the AlPO)(-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 AlPO)(4)(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.