Understanding Degradation in Earth-Abundant Cathode Particles through Cryo-STEM Electron Energy Loss Spectroscopy (EELS)

Currently, cobalt-containing lithium-ion batteries (LIBs) are the commercial standard, but due to scarcity and high cost, there is a need for batteries that use more earth-abundant cathode materials. Understanding the degradation pathways in earth-abundant alternative cathode (EACaM) materials due to cycling is key to ensure that similar performance and stability to current standard cathodes are achieved. This work evaluates the effects of electrolyte additives on the cathode electrolyte interface (CEI) formed on EACaM particles during cycling using cryogenic electron microscopy techniques. Additives predicted by machine learning (ML) models to have optimal performance are selected and experimentally validated, demonstrating a significant improvement over the baseline. The use of cryogenic scanning transmission electron microscopy (cryo-STEM) with electron energy loss spectroscopy (EELS) preserves the beam-sensitive CEI providing atomic- to nanoscale information on the surface chemistry of the EACaM particles. Cycled cathodes with the ML additive combination were seen to have less variation in Mn valence state at the CEI layer compared to the bulk and the oxygen pre-edge peak associated with transition metal bonding was retained. This suggests a stabilized surface chemistry of the EACaM particles making them less prone to Mn dissolution, contributing to the observed improvements of LIB performance with these ML electrolyte additives.