Engineering porous polymer electrolyte for high-performance quasi solid-state supercapacitor

Abstract

Quasi-solid-state supercapacitors based on polymer electrolytes (PEs) have drawn recent attention in promising high-power density, durability, and flexibility for various applications such as wearable devices, micropower systems, and unmanned lightweight vehicles. However, understanding the underlying fundamentals among the properties, structures, and overall cell performance of porous PEs still remained a challenge limiting the actual realization of a high-performance supercapacitor. This dissertation addresses the aforementioned knowledge gaps by investigating the relationships between various properties of PEs and cell performance, specifically with respect to the physical and chemical control of PEs. In this context, the structure of PEs is engineered using various additives to understand property changes like morphology, chemical structure, thermal stability, mechanical strength, and electrochemical properties. For experiments, poly(vinyl alcohol) (PVA) is used as base PEs due to their simple structure of PVA chains allowing simple polymerization with the freeze/thaw method, which leads to the ease of chemical structure modification and property control with additives. This dissertation focuses on the effect of these controlled properties of PEs applied to the electrochemical properties of supercapacitors. This dissertation discovers that the additives in PEs change their chemical structure and control many other properties such as morphology, crystallinity, thermal stability, and degree of swelling. It successfully determines the positive linear relationship between crystallinity and various other properties such as degree of swelling, thermal stability, and electrode capacitance. Meanwhile, it discovers that pore size, pore area fraction, and compressive modulus are inversely proportional with crystallinity. With the novel findings, the performance of supercapacitors can achieve high capacitance, low electrolyte and internal resistance, and high power and energy density by optimizing their PE properties. Also, this dissertation successfully develops methods in integrating electrodes and electrolytes and exchanging liquid electrolytes in PEs to further increase cell performance.--Author's abstract