Stretchable Polymerized High Internal Phase Emulsion Separators for High Performance Soft Batteries

Abstract

large areas available on the skin or within the body. [3] Intrinsically stretchable batteries effectively make use of available space while perfectly complying to deformations and maintaining comfort for the wearer. [4][5][6] Recent developments exploit high-energydensity materials, such as Zn and Li-ion based batteries, [7][8][9][10] to enhance battery capacity and close the gap to rigid-island designs. [11] Despite the progress in capacity and rechargeability, the principle design of planar intrinsically stretchable batteries has largely remained unchanged. The interplay of electrodes, efficient current collectors, highly ionically conductive separators/gelelectrolytes, and their conformal orientation must collectively be optimized to boost battery performance. Promising solutions for single components, including multilayer current collectors, [12] tough electrodes, [13] and self-healing gel-electrolytes [14] were demonstrated recently. However, many prototypes still use the coplanar orientation of electrodes [4,12,[15][16][17] as proposed for the first soft batteries. [18] This design sacrifices performance due to increased ionic pathways in the gel electrolytes. Introducing a sandwich design of stacked battery components (Figure 1a), greatly reduces ionic pathways and therefore the internal resistance of the battery. [19] Soft (sandwich-design) batteries require electron-insulating separators, which have to meet high ion conductivity, extensibility, and chemical inertness. Hydrogels are often used in water-based systems, serving as gel Powering soft embodiments of robots, machines and electronics is a key issue that impacts emerging human friendly forms of technologies. Batteries as energy source enable their untethered operation at high power density but must be rendered elastic to fully comply with (soft) robots and human beings. Current intrinsically stretchable batteries typically show decreased performance when deformed due to design limitations, mainly imposed by the separator material. High quality stretchable separators such as gel electrolytes represent a key component of soft batteries that affects power, internal resistance, and capacity independently of battery chemistry. Here, polymerized high internal phase emulsions (polyHIPEs) are introduced as highly ionically conductive separators in stretchable (rechargeable) batteries. Highly porous (>80%) separators result in electrolyte to polyHIPE conductivity ratios of below 2, while maintaining stretchability of ≈50% strain. The high stretchability, tunable porosity, and fast ion transport enable stretchable batteries with internal resistance below 3 Ω and 16.8 mAh cm −2 capacity that power on-skin processing and communication electronics. The battery/separator architecture is universally applicable to boost battery performance and represents a step towards autonomous operation of conformable electronic skins for healthcare, robotics, and consumers.

Wet‐spun porous fibers from high internal phase emulsions: Continuous preparation and high stretchability

“…Surprisingly, the WF‐ X s were stretchable. Cyclic tensile stress–strain curves in Figure 5(A) showed that the WF‐ X s exhibited high tensile strains, with WF‐17 to be the largest at 155% and WF‐14 to be the least at 125%, which are much higher than the ultimate failure strain of 36% for elastic polyHIPEs from trimethylolpropane tris (3‐mercaptopropionate) and divinylbenzene 27 and of 40% for stretchable polyHIPEs from urethane diacrylate and 2‐ethylhexylacrylate 28 . WF‐17 showed the largest stress at 306 kPa while WF‐18 had the lowest stress at around 200 kPa.…”

“…Cyclic tensile stress-strain curves in Figure 5(A) showed that the WF-Xs exhibited high tensile strains, with WF-17 to be the largest at 155% and WF-14 to be the least at 125%, which are much higher than the ultimate failure strain of 36% for elastic polyHIPEs from trimethylolpropane tris (3-mercaptopropionate) and divinylbenzene 27 and of 40% for stretchable polyHIPEs from urethane diacrylate and 2-ethylhexylacrylate. 28 WF-17 showed the largest stress at 306 kPa while WF-18 had the lowest stress at around 200 kPa. An obvious hysteresis was observed to all the WF-Xs for the first cycle, while compared to the second loading cycle, the loading-unloading curves of the further cycles were mostly overlapped, showing their relatively high stability in tensile after the first cycle.…”

Skin‐Like Stretchable Fuel Cell Based on Gold‐Nanowire‐Impregnated Porous Polymer Scaffolds

“…Ultrathin gold nanowires have proved to be a good candidate for wearable sensors, [4,35] stretchable/transparent electrodes, [37] and supercapacitors. [38] Here, we further extended their applications as stretchable fuel cells for the electro-oxidation of ethanol upon mechanical deformation.…”

“…[ 34–36 ] It has not been used for deigning soft wearable energy devices until very recent report as a new type of ionically conductive separators in stretchable batteries. [ 37 ]…”

“…[34][35][36] It has not been used for deigning soft wearable energy devices until very recent report as a new type of ionically conductive separators in stretchable batteries. [37] Here, we use ultrathin gold nanowires (AuNWs) as conductive filler and trimethylolpropane triacrylate (TMPTA) polyHIPEs as the 3D soft skeleton for the fabrication of stretchable skin-like fuel cell. For biomedical applications, gold is frequently used as a biosensing electrode due to its unique attributes such as biocompatibility, chemical inertness, facile surface functionalization, broad electrochemical window, and recently demonstrated stretchability.…”