Failure analysis of LiNi0·83Co0·12Mn0·05O2/graphite–SiOx pouch batteries cycled at high temperature

The combination of Ni-rich layered oxide and graphite–SiOx is regarded as a high-energy-density system for the lithium-ion power batteries. It is significant to elaborate the failure mechanism of the two materials in full batteries, especially at high temperature. In this study, the failure behavior of LiNi0·83Co0·12Mn0·05O2/graphite–SiOx pouch batteries (≥50 Ah) cycled at 45 °C has been studied by using the non-destructive electrochemical methods and physico-chemical methods for the cathode and anode materials. Compared with the failure mechanism of lithium-ion batteries cycled at room temperature, it is more inclined to occur at high temperature that transition metal ions dissolve out from cathode and deposit on the anode, electrolyte decomposes, and solid electrolyte interphase grows. The resulting phenomena show that the cathode deterioration is slight, and the anode degradation is the main factor of pouch battery degradation. After failure analysis, the concentration-gradient NCM cathode and nitrile-containing electrolyte additive are assembled into the pouch batteries, and the capacity retention increases from 75.24% (pristine batteries at 280 cycles) to 83.44% (improved batteries at 1500 cycles). Therefore, we suggest that power batteries operating at high temperature should be with minimized transition metal dissolution of cathode materials and stable solid electrolyte interphase.