Failure mechanism of LiCoO2-based pouch-type full cells during 1C/10 V overcharge and the countermeasure

Abstract

Overcharge is one of the most common causes that triggers thermal runaway of lithium-ion batteries, which leads to personal injury and property loss. Therefore, it is momentous to penetrate into the mechanism of overcharge and enhance the overcharge safety from the essence of battery materials. Herein, the combined Al doping and Al2O3 coating strategies are applied to the LiCoO2 cathode materials, which are employed to enhance the overcharge performance of 950 mAh LiCoO2-based pouch-type full cells. The results show that only the pouch-type full cells using LiCoO2 with both Al doping and Al2O3 coating as cathode pass the 1C/10 V overcharge test successfully. In-situ X-ray diffraction (XRD) and differential electrochemical mass spectrometry (DEMS) results illustrate that the critical factors leading to thermal runaway lie in the structural instability of LiCoO2 and the violent interfacial reaction rooted in electrolyte decomposition. Further post analysis of pouch-type full cells demonstrate that the enhanced overcharge safety depends on the synergetic effect of Al doping and Al2O3 coating of LiCoO2. That is the Al doping can enhance the structural robustness of LiCoO2 significantly, while the coated Al2O3 works as a passive film to cut off the further reaction between the cathode and the electrolyte during overcharge.