Operando Electro‐Rheology: Unraveling Decoupled Ion Transport‐Mechanical‐Morphological Properties in Nanostructured Block Copolymer Electrolytes

Block copolymer electrolytes exhibit a complex interplay between self‐assembled morphology, ion transport, and mechanical properties under galvanostatic battery cycling. Here, we propose a novel operando methodology combining concurrent rheology and electrochemical measurements upon dc polarization for a lithium bis (trifluoromethanesulfonyl) imide (LiTFSI) doped polystyrene‐ block ‐poly (ethylene oxide) diblock copolymer electrolyte. Time‐resolved measurements of the viscoelastic and electrochemical responses to the galvanostatic stimulus permit to uncover the effective response of the block copolymer electrolyte, tracking ion transport‐mechanical‐morphological properties simultaneously. Corroborated by scanning transmission electron microscopy (STEM) imaging, we observe the block copolymer transitioning from unperturbed, increasingly aligned lamellae to reorganized self‐assembled nanostructures as the applied current density approaches the limiting current and, beyond its onset, the nanomorphology evolves toward gyroid and hexagonal phases. The diffusion coefficients decrease as current density increases, which is attributed to concentration polarization phenomena. Lastly, this methodology identifies a direct coupling between interfacial electrochemical processes and mechanical properties, highlighting the intimate interplay between interfacial phenomena and rubbery plateau modulus upon current densities.