Piezoelectric COFs Function as Dynamic “Ion Pumps” to Facilitate Li ⁺ Transport in Solid‐State Batteries

Abstract

ABSTRACT The development of solid‐state electrolytes is restricted by sluggish ion transport and unstable electrode‐electrolyte interfaces. To address this issue, we introduce a paradigm‐shifting approach that actively converts cycling‐induced mechanical stress into an electrochemical driving force for ion migration. Through strategically structural engineering of a covalent organic framework (COF), we create a piezoelectric COF (CityU‐57) with a broken structural symmetry, enabling a built‐in electric field under mechanical stress (piezoelectric field). This structural modification not only decreases the HOMO energy level to improve oxidative stability but also enhances Li + affinity and reduces migration barriers, especially under a piezoelectric field. When implemented as a solid electrolyte, CityU‐57 achieves exceptional performance, including a high Li + transference number (0.539), low interfacial resistance, and unprecedented cycling stability exceeding 5000 h in symmetric cells. Comprehensive characterization through piezo‐response force microscopy, electrochemical analysis, and theoretical calculations, we verify a “mechano‐electric coupling” mechanism where mechanically induced piezoelectric fields function as a dynamic “ion pump” to facilitate Li + transport and homogenize the deposition.