Electrochemical Impedance Spectroscopy of PolyHIPE Separators for a New Generation of Stretchable Batteries

A truly conformal soft energy storage is crucial for engineering stand-alone soft electronics, including wearables, soft robots, or biomedical applications. Although, there are several ways to power those assemblies, such as photovoltaic cells, supercapacitors, or near field technology, a battery represents the gold-standard of energy storage systems. Where flexible technologies are already available on the market, introducing stretchability, in particular intrinsically stretchable batteries, is challenging and comes with great performance cost. Herein, I present a new separator material, so-called PolyHIPEs, being intrinsically stretchable and an excellent ion conductor. Their open-cellular structure, allowing ions to travel easily when filled with a liquid, is shown by scanning electron microscopy. I investigate the tunability of porosity and its effect on both mechanical and electrical properties. Tensile strain measurements show typical foam-like behaviour, with low Youngs moduli and rapidly increasing stress at high strain levels. More specifically, for polyHIPEs with 85 % porosity a maximum elongation before rupture of 40 % is achieved. Electrical performance is characterized in terms of conductivity, resulting in 90 mS=cm for 85 % porosity polyHIPEs. This also is the highest achievable porosity value, exhibiting MacMullin numbers as low as 1:65. These separators are successfully incorporated in intrinsically stretchable batteries showing a total capacity of 38 mAh. By combining the excellent ion conductivity of the separator material with an optimized geometry, I demonstrate devices with internal resistances lower than 3 , being a major improvement to previous designs. With the demonstrated approach, engineering soft electronic devices that function completely on their own, without any rigid component becomes feasible.eingereicht von Doris DanningerUniversität Linz, Masterarbeit, 2019(VLID)376845