LiNi0.5Co0.2Mn0.3O2/graphite batteries storing at high temperature: Capacity fading and raveling of aging mechanisms

The effects of storage on the aging mechanisms of the battery have attracted a lot of attention. In practice, the battery for electric vehicles (EVs) can undergo short periods of higher temperature storage. Therefore, the widely-used LiNi0.5Co0.2Mn0.3O2/graphite batteries are stored at different temperatures (25 °C, 60 °C, and 70 °C) for 15 days, and then cycled under normal ambient environment. The aging mechanisms are analyzed by electrochemical characterizations and post-mortem analysis. The aging rate and mechanisms of batteries stored at a lower temperature (e.g. 25 °C and 60 °C) almost remain unchanged. According to the results of quantitative analysis, although the aging of batteries stored at a higher temperature (e.g. 70 °C) is attributed to the increased polarization, the underlying reasons might be different. Increased polarization at higher temperature is primarily ascribed to cathode decay in addition to the anode decay. The thickened cathode surface layer and increased cation disorder hinder the lithium ion diffusion, contributing to the cathode decay. Based on these test results, it is proposed that batteries subjecting to lower storage temperature for short time can have a second life while those at higher storage temperature should be discarded.