Unraveling the effect of short-term high-temperature storage on the performance and thermal stability of LiNi0.5Co0.2Mn0.3O2/graphite battery

In practical applications, the batteries are usually subjecting to short-term high-temperature storage (e.g., 80 degrees C for several days), which is quite different from long-term storage with temperature lower than 60 degrees C. Herein, the effect of such a short-term high-temperature storage on the performance of LiNi0.5Co0.2Mn0.3O2/graphite battery under normal cycling (under 1C at 25 degrees C) is studied by electrochemical characterizations and post-mortem analysis. Due to the thickened Solid-Electrolyte-Interface (SEI) film on the stored anode, the loss of active lithium significantly increases after cycling and leads to increased cathode state of charge (SOC) offset. On the other hand, the thickened Cathode-Electrolyte-Interface (CEI) layer on stored cathode consists of more organic contents due to particle cracking. Such interface degradations hinder lithium ion diffusion, causing increased polarization, SOC offset, and reduced inherent performance of the electrodes. By quantificationally analyzing the degradation factors, it is revealed that the polarization related to interfaces is the dominating factors for battery degradation, and the cathode decay rate is distinctly expedited after short-term high-temperature storage. Additionally, the decreased thermal stability of electrode materials is observed by differential scanning calorimeter (DSC) measurements. In all, the short-term high-temperature storage accelerates the battery aging during normal cycling and reduces the battery safety.