Microstructure and multifunctional properties of liquid + polymer bicomponent structural electrolytes: Epoxy gels and porous monoliths

Abstract

Multifunctional structural batteries and supercapacitors have the potential to improve performance and efficiency in advanced lightweight systems. A critical requirement is a structural electrolyte with superior multifunctional performance. We present here structural electrolytes prepared by the integration of liquid electrolytes with structural epoxy networks. Two distinct approaches were investigated: direct blending of an epoxy resin with a poly(ethylene-glycol) (PEG)-or propylene carbonate (PC)-based liquid electrolyte followed by in-situ cure of the resin; and formation of a porous neat epoxy sample followed by backfill with a PC-based electrolyte. The results show that in situ cure of the electrolytes within the epoxy network does not lead to good multifunctional performance due to a combination of plasticization of the structural network and limited percolation of the liquid network. In contrast, addition of a liquid electrolyte to a porous monolith results in both good stiffness and high ionic conductivity that approach multifunctional goals.

Structural lithium ion battery electrolytesviareaction induced phase-separation

“…This approach has been demonstrated via several routes using either vinyl ester or epoxy systems combined with either traditional electrolyte solvents or ionic liquids. [25][26][27][28][29][30] Lodge et al developed the concept of polymerization induced phase separation (PIPS) to form membranes with two bis-continuous phases allowing for both high ionic conductivity and mechanical strength. 31,32 A wide range of combinations of ionic liquids, lithium salts, PEG segments, crosslinked polystyrene, and solid plasticizers has been used to demonstrate the versatility of this approach.…”

Optimized microstructures for multifunctional structural electrolytes

“…These results demonstrated the superiority of the optimized microstructures obtained from this work compared to the Schwarz-P. In addition, the latest experimental results of mechanical stiffness and ionic conductivity in the literature were presented and compared [28,29,63,64] (figure 7). This comparison clearly shows that the multifunctional performance of the optimized microstructures obtained in this study is superior to that of previous studies.…”

Structural Batteries: A Review

“…Starting from the consideration demonstrated by Torquato et al [ 88 ], that the optimal microstructure for multi-modal transport is the one with segregated phases, Gienger et al [ 83 ] tried to improve the structural battery electrolytes (SBEs) multifunctionality via a complete separation of the two phases, creating a robust solid microstructure and backfilling it with high conductivity ionic liquid. Three different solid electrolytes were manufactured and compared.…”

“…The concept of phase separation introduced by Gienger et al [ 83 ] was recently reinterpreted by Beringer et al [ 91 ] and Lee and coworkers [ 26 ], who designed and 3D-printed optimized polymeric microstructures with enhanced multifunctional performance. Based on the know-how developed during prior studies, Beringer et al [ 91 ] investigated the definition of an engineered structural electrolyte solution in which the involved phases were distinctly segregated to reduce at the minimum the risk to compromise their properties, and the microstructure was geometrically optimized to maximize the properties of interest in the multi-phase system.…”

“… Microstructure for EPON 828/PACM-based multifunctional polymers at 65% of electrolyte content from Gienger et al [ 83 ]. ( a ) 1 M LiTFSI in PC.…”