The
composition of the solid electrolyte interphase (SEI) plays
an important role in controlling Li–electrolyte reactions,
but the underlying cause of SEI composition differences between electrolytes
remains unclear. Many studies correlate SEI composition with the bulk
solvation of Li ions in the electrolyte, but this correlation does
not fully capture the interfacial phenomenon of SEI formation. Here,
we provide a direct connection between SEI composition and Li-ion
solvation by forming SEIs using polar substrates that modify interfacial
solvation structures. We circumvent the deposition of Li metal by
forming the SEI above Li+/Li redox potential. Using theory,
we show that an increase in the probability density of anions near
a polar substrate increases anion incorporation within the SEI, providing
a direct correlation between interfacial solvation and SEI composition.
Finally, we use this concept to form stable anion-rich SEIs, resulting
in high performance lithium metal batteries.