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.