All Solid State Supercapacitors Based on Ionic Liquid/Crosslinked PEO-PPO Tetrablock Copolymer Electrolytes

Tuesday, October 13, 2015
West Hall 1 (Phoenix Convention Center)
J. H. Han (Korea Research Institute of Chemical Technology, Hanyang University), T. H. Kim (Korea Research Institute of Chemical Technology), and Y. T. Hong (Korea Research Institute of Chemical Technology)
Supercapacitors are widely recognized as an important class of energy storage devices, because they can provide a high specific power, long cycle life. Compared with the conventional supercapacitors using liquid electrolyte, all-solid state supercapacitors have many advantages such as lightweight, high flexibility, high safety and environmentally benign nature, which are suitable for flexible and portable electronics. The realization of high performance all solid state supercapacitors strongly depends on the electrical properties and mechanical integrity of constitutive materials and their controlled assembly of electrode and solid electrolyte. 
In this work, we designed and prepared novel ionic liquid (IL)-doped crosslinked PEO-PPO tetrablock copolymer electrolytes. Triethoxysilane-endcapped precursors were first prepared by reacting the terminal hydroxyl groups of the corresponding Tetronic® (BASF) copolymers with 3-isocyanatopropyl triethoxysilane. Then, the IL-doped and crosslinked electrolytes were fabricated via in situ sol-gel reactions of the triethoxysilane end groups of the precursors and subsequent solution casting process in the presence of IL. Despite large IL doping up to 200 wt%, solid and transparent film could be obtained mainly due to the crosslinked structure. The resulting electrolytes were denoted as cTPL-TPE-A-B, where A and B indicate the codename of Tetronic® and the content of IL doped, respectively. It was confirmed that cTPL-TPE-A-Bs possessed completely amorphous structure and non-fusible property from the XRD and DSC experiments. The Ionic conductivity of a cTPL-TPE-90R4-200 with 200 wt% BMIM-BF4 reached 3.65×10-3 S/cm at room temperature and 2.73×10-2 S/cm at 80 °C (see Figure 1). These values were more than 10 times higher than those of the PEO electrolyte with the same range of BMIM-BF4 content thanks to the entirely amorphous structure of cTPL-TPE-A-Bs.
 All-solid-state supercapacitors were fabricated assembling cTPL-TPE-A-Bs as electrolytes with graphene sheets (prepared from a kneading method) as electrodes. Consequently, the device exhibited high electrochemical performance such as high operating voltage of 3.7 V, high specific capacitance of 157.4 F/g, and an energy density of 55.3 Wh/kg (@ 10 mA/g).