Engineering battery corrosion films by tuning electrical double layer composition

Battery performance is strongly influenced by the solid electrolyte interphase (SEI) that forms from electrolyte decomposition and remains a key target for engineering design. Whereas traditional approaches to tune the SEI have focused on electrolyte chemistry, we show that manipulating the electric field offers a novel approach. Here, we change the electrical double layer (EDL) composition by either applying or removing the local electric field, which directly controls SEI formation. Surprisingly, the solvent-derived SEI known to form in a conventional electrolyte exhibits anion-enhanced chemistry when the electric field is removed, which is attributed to the Coulombic interaction between the electric field and free anions. With the electric field control, we produce an anion-enhanced SEI in conventional electrolytes that demonstrates improved battery cycling and corrosion resistance. Together, our findings highlight the importance of EDL composition and demonstrate electric field strength as a new parameter to tune SEI structure and chemistry. [Display omitted] •The EDL composition and resulting SEI features can be tuned by the electric field•Chemical SEI formed without the electric field exhibits more inorganic components•Coulombic interaction with free anions strongly influences the EDL composition•Turning the electric field offers a robust strategy to engineer the SEI chemistry The solid electrolyte interphase (SEI) is a critical battery passivation film that forms on the lithium (Li) metal surface and dictates battery performance. While conventional design principles for improving Li metal batteries all attempt to form more passivating SEI films, there are few approaches beyond changing the electrolyte chemistry to modify the SEI properties. We introduce a new approach to engineering battery SEI films: leveraging the local electric field to tune the nanoscale electrical double-layer (EDL) composition. We discover that the SEI properties can vary dramatically in the same electrolyte when an electric field is applied or removed, which is the direct result of the electric field’s influence on the EDL composition. Our surprising findings have direct implications on improving the corrosion resistance of Li metal batteries and provide a new perspective into how spatial variations in the electric field can lead to non-uniform SEI films and battery failure. The solid electrolyte interphase (SEI) forms from electrolyte decomposition during battery operation,