Transition metal dissolution from a high-voltage Li-ion battery cathode accelerates capacity fade leading to unacceptably short battery lifetimes. After dissolution, metals like Mn, Ni, and Co deposit at the carbon anode and disrupt the formation and performance of the solid-electrolyte interphase (SEI), a vital battery interface responsible for protecting the electrolyte from the highly reductive anode. SEI contamination by metals results in continual Li loss and uncontrolled SEI growth, culminating in severe capacity decay. Fundamental understanding of the role of each metal in undermining SEI passivation is necessary to mitigate this degradation and to enable commercialization of high-voltage Li-ion cathodes.

In this work we interrogate the effects of three transition metals (Mn, Ni, and Co) on charge-transfer through the SEI via in-situ electrochemical characterization. Our approach is to grow an SEI in metal-contaminated electrolyte and then characterize the film via rotating disk electrode voltammetry. Redox mediators deconvolute through-film transport and reaction kinetics to determine physical charge-transfer mechanisms. We find that each metal disrupts the electronic properties of the SEI far more than the morphological properties, and that Mn-contamination is the most detrimental of the three metals. We compare charge-transfer mechanisms based on electron tunneling across the SEI and electrocatalytic metal cycling between redox states and compare experiments to microkinetic models of each mechanism. Our results indicate that reaction thermodynamics and kinetics do not fully capture why Mn facilitates faster through-film charge-transfer than Ni or Co. This suggests that differences in coordination environment between transition metals embedded in the SEI are responsible for the more aggressive disruption by Mn, offering insight into mitigation approaches to inhibit accelerated capacity fade.