Delineating the Impact of Transition‐Metal Crossover on Solid‐Electrolyte Interphase Formation with Ion Mass Spectrometry

Lithium-metal batteries (LMB) employing cobalt-free layered-oxide cathodes are a sustainable path forward to achieving high energy densities, but these cathodes exhibit substantial transition-metal dissolution during high-voltage cycling. While transition-metal crossover is recognized to disrupt solid-electrolyte interphase (SEI) formation on graphite anodes, experimental evidence is necessary to demonstrate this for lithium-metal anodes. In this work, advanced high-resolution 3D chemical analysis is conducted with time-of-flight secondary-ion mass spectrometry (TOF-SIMS) to establish spatial correlations between the transition metals and electrolyte decomposition products found on cycled lithium-metal anodes. Insights into the localization of various chemistries linked to crucial processes that define LMB performance, such as lithium deposition, SEI growth, and transition-metal deposition are deduced from a precise elemental and spatial analysis of the SEI. Heterogenous transition-metal deposition is found to perpetuate both heterogeneous SEI growth and lithium deposition on lithium-metal anodes. These correlations are confirmed across various lithium-metal anodes that are cycled with different cobalt-free cathodes and electrolytes. An advanced electrolyte that is stable to higher voltages is shown to minimize transition-metal crossover and its effects on lithium-metal anodes. Overall, these results highlight the importance of maintaining uniform SEI coverage on lithium-metal anodes, which is disrupted by transition-metal crossover during operation at high voltages.