The solid electrolyte interphase (SEI), a passivation layer formed on the battery electrode-electrolyte interface [1], defines fundamental battery properties - its capacity, cycle stability, and safety. While understanding the SEI formation holds keys to these, such studies are complicated by the diversity of interlinked surface reactions and complex nanoarchitecture of the anode active material and electrical double layer (EDL) [2]. Such nanoarchitecture predetermines the electrolyte supramolecular interactions, electrical charge, and ion transport, therefore, dominating the initial SEI formation. To date, the real space molecular arrangements of electrolyte solvents/anions inside the EDL and their effects on the SEI formation remain elusive [3].



In this work, we resolve this complex puzzle, using a novel solid-liquid interface characterization tool with a nanoscale spatial resolution for accessing the whole evolution process from initial molecular-scale EDL structures, toward nanoscale 3D SEI structures. We introduce in-situ electrochemical 3D nanorheology microscopy (3D-NRM) [4] combined with magnetic excitation molecular-level solvation force spectroscopy and molecular dynamics simulations to explore a matrix of two morphologically dissimilar but chemically identical surfaces of typical carbon electrode material (basal and edge graphene planes) and different solvent-electrolyte systems (strong and weakly solvating electrolytes, as well as ionic liquid electrolyte). These approaches allowed us to get direct insight into the atomistic pictures for the underlying influence of cation’s intercalation and solvation structures on the initial SEI formation.