Quantitative Analysis of Origin of Lithium Inventory Loss and Interface Evolution over Extended Fast Charge Aging in Li Ion Batteries

During the extreme fast charging (XFC) of lithium-ionbatteries,lithium inventory loss (LLI) and reaction mechanisms at the anode/electrolyteinterface are crucial factors in performance and safety. Determiningthe causes of LLI and quantifying them remain an essential challenge.We present mechanistic research on the evolution and interactionsof aging mechanisms at the anode/electrolyte interface. We used NMC532/graphitepouch cells charged at rates of 1, 6, and 9 C up to 1000 cycles forour investigation. The cell components were characterized after cyclingusing electrochemical measurements, inductively coupled plasma opticalemission spectroscopy, Li-7 solid-state nuclear magneticresonance spectroscopy, and high-performance liquid chromatography/massspectrometry. The results indicate that cells charged at 1 C exhibitno Li plating, and the increase of SEI thickness is the dominant sourceof the Li loss. In contrast, Li loss in cells charged at 9 C is relatedto the formation of the metallic plating layers (42%) the SEI layer(38.1%) and irreversible intercalation into the bulk graphite (19%).XPS analysis suggests that the charging rate has little influenceon the evolution of SEI composition. The interactions between competingaging mechanisms were evaluated by a correlation analysis. The quantitativemethod established in this work provides a comprehensive analyticalframework for understanding the synergistic coupling of anodic degradationmechanisms, forecasting SEI failure scenarios, and assessing the XFClithium-ion battery capacity fade.