Effect of transition metal ions on solid electrolyte interphase layer on the graphite electrode in lithium ion battery

In lithium-ion batteries, dissolved transition-metal ions from the cathode deposit as a solid– electrolyte interphase (SEI) layer on the graphite electrode and degrade the battery performance. This study develops a physics-based electrochemical modeling framework with coupled side reactions to predict the cell performance of graphite/lithium half-cells, including the effect of transition-metal ions on SEI layers. The side reactions and graphite anode degradation considered in this study include 1) loss of cyclable lithium due to SEI layer formation, 2) loss of cyclable lithium and formation of additional decomposition layers due to transition metal deposition, 3) increases in film and charge-transfer resistances, and 4) decrease in the diffusion coefficient due to side reactions. This study reveals that lithium loss and capacity fading due to SEI formation were dominant initially, but side reactions and degradation induced by Mn deposition become significant as cycling progressed. Moreover, Mn ions degrade graphite mostly by increasing the electrode resistances rather than by lithium loss due to side reactions. This integrated study reveals several key mechanisms related to transition-metal deposition and SEI layer formation at the particle level and quantitatively connects the side reactions and cell-level performance. This modeling framework provides valuable guidance for battery design and management.