Design of Self-Healing Epoxy-Based Solid Polymer Electrolytes for Li-ion Structural Batteries

Abstract

Structural batteries impose coupled requirements on electrolytes because ionic transport, mechanical load transfer, and tolerance to damage must coexist in a single material system. This thesis develops and evaluates three polymer-based structural electrolyte architectures under a unified design framework. The first architecture employs a self-healable epoxy (SHEP) network blended with polyethylene glycol and LiTFSI, which introduces a polymer-rich conducting phase within a load-bearing matrix. The second architecture employs a self-healable epoxy network blended with poly(ionic liquid) and LiTFSI to form an ionically conducting domain within a crosslinked structural framework. The third architecture employs porous, self-healable epoxy scaffolds with controlled porosity and a fixed pore-former size, followed by electrolyte infiltration to establish continuous conducting pathways within a mechanically supportive scaffold.

The three architectures were characterized with respect to thermal behavior, mechanical performance, ionic transport, and post-damage functional recovery in terms of mechanical and ionic conductivity. The SHEP-polyethylene glycol blend provides high ionic conductivity (2.58 × 10−3 S/cm at 100 ∘C) and ionic conductivity healing in solid polymer electrolytes and offers straightforward processing; however, mechanical performance and mechanical healing remain limited under the present conditions. The SHEP-poly(ionic liquid) blend exhibits low conductivity, underscoring the shortcomings of blend structures and informing the development of porous structures. The porous scaffold and infiltration architecture decouples ionic transport from the load-bearing phase and improves mechanical performance without an apparent loss in ionic conductivity (1.56 × 10−3 S/cm at 100 ∘C) relative to the first architecture. The same architecture shows effective recovery of ionic transport after damage, whereas the healing of macroscopic mechanical properties remains limited.

This work provides a comparative map of the practical trade-offs among load bearing, ionic transport, and post-damage functional recovery across three structural electrolyte architectures. It shows that achieving both mechanical support and ion transport in polymer structural electrolytes depends not only on the choice of conducting component, but also on how the conducting phase is arranged within the load-bearing network. Simple bulk blending can define an achievable property window, yet it may fail when the mixing restricts segmental motion and disrupts the formation of continuous ion-conduction pathways. In contrast, an architecture that separates the structural framework from the conducting phase can improve the balance between stiffness and conductivity and enable partial recovery of ionic transport after damage. These results provide practical guidelines for designing self-healing structural polymer electrolytes for future structural battery systems.