Revealing the correlation between structural evolution and long-term cyclability of the LiNi0.5Co0.2Mn0.3O2/artificial graphite pouch cells at various rates

Abstract

In recent years, researches on improving high-voltage performance of lithium-ion batteries incorporating LiNi0.5Co0.2Mn0.3O2 (NCM523) and artificial graphite (AG) have been widely reported. However, limited attentions have been paid to understand the effects and influence mechanisms of charge and discharge rates and charge limit currents on cyclability of NCM523/AG cells. Herein, a ∼1.9 Ah NCM523/AG pouch cell is employed, whose electrochemical and structural evolutions after 800 cycles at various rates are comprehensively investigated. We find that cycling performances are strongly influenced by charge rate, followed by limit current and discharge rate. The cell charged at a high rate and cell charged until reaching a low limit current both exhibit low capacity retentions compared to the cell discharged at a high rate. Possible failure reasons are analyzed by advanced characterizations. Results reveal that NCM523 cathodes of the cells deteriorated early experience severe transition metal dissolution, lattice distortion, and partial phase transformation. Meanwhile, the deposited transition metals on AG anodes catalyze the electrolyte consumption, lithium plating and active area loss. Finally, these side reactions notably increase cell impedance and electrochemical polarization. Undoubtedly, these findings clearly outline the challenges and optimization direction for high-rate NCM523/AG cells.