Engineering Solid Polymer Electrolytes for Structural Batteries with Enhanced Mechanical and Electrochemical Performances

Lithium-ion batteries are widely used today due to their longevity and efficiency. They are, however, highly flammable and possess steep volumetric requirements. Structural battery composites are an emerging alternative that integrates battery and structural functions in a single multifunctional component, reducing weight and increasing safety and energy density. These composites harness carbon fibers for structural reinforcement and as electrodes, with a solid polymer electrolyte (SPE) serving as the separator and matrix. Traditionally, in SPEs mechanical and electrochemical properties are mutually exclusive. Here, we explored a bi-continuous SPE with polymer-reach and solvent-reach domains, synthesized through polymerization-induced phase separation, to decouple ionic conductivity and mechanical properties. We investigated the impact of monomer/solvent+Li salt ratio, film thickness, and the addition of glass fibers (GF) on the synthesized SPEs performance. Characterization through thermal analysis, mechanical testing, SEM and electrochemical impedance spectroscopy demonstrated that a 40/60 and 50/50 weight ratio of monomer/solvent+Li salt results in a polymer film with a bi-continuous structure leading to improved ionic conductivity. Furthermore, the incorporation of GFs in polymer film improved its mechanical strength, as confirmed by tensile testing. Surprisingly, adding GFs to the polymer films also significantly increased the ionic conductivity of the composite SPEs. SEM images revealed the formation of void spaces at the polymer/GF interface, which can potentially contribute to improved ionic conductivity via enhancing ions mobility and permeability. Developing lightweight, and compact SPEs with enhanced ionic conductivity, mechanical strength, safety and efficiency
can facilitate further advancement of structural batteries.