Author ORCID Identifier

https://orcid.org/0000-0002-4234-2397

Date Available

10-4-2023

Year of Publication

2021

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Engineering

Department/School/Program

Chemical and Materials Engineering

First Advisor

Dr. Fuqian Yang

Abstract

Supercapacitors are important energy storage device of high-power density, fast charge/discharge rate, environmental friendliness and long service life. Currently, flexible supercapacitors have attracted widespread interest in academia and industry. Supercapacitors under the action of external force will inevitably cause structural changes, performance degradation and even loss of energy storage and supply functionalities. As the most abundant renewable resource so far, biomass is an important energy source for human survival and development. Most electrode materials for supercapacitors are porous activated carbons, which can be derived from abundant renewable biomass, contributing to the sustainable development of society and environmental protection. This thesis is focused on the mechanical behavior of porous carbons derived from biomass and the stress effect on the symmetric supercapacitors made from the biomass-derived porous carbons. The specific research content is summarized as follows.

First, we used the high fructose corn syrup as the precursor to prepare porous carbon microspheres through hydrothermal treatment. Impression tests were applied to investigate the mechanical response the carbon-microsphere-based electrode with dry surface. The experimental results are analyzed using a three parameter Weibull distribution. The results suggest that increasing impression force and holding time increases the contact modulus, maximum impression depth and energy dissipation. A model was formulated to describe the relation between the effective contact modulus and the ratio of the maximum impression depth to the electrode thickness. Considering the effect of electrolyte on the porous electrode, we also studied the mechanical responses of wetted electrode surface with the same carbon material by controlling the water droplet placing time. The experimental results suggested that the elastic modulus of the wetted electrode is larger than that of dry electrode due to the capillary force between the space of carbon microsphere. However, increasing the droplet placing time reduced the elastic modulus of the wetted electrode. A power law model was proposed to describe the relationship between the compressive stress and the maximum strain.

Secondly, the electrochemical behavior of the supercapacitors made from potato-derived electrodes was studied under compressive stress. The electrode materials were prepared from the potato mash through hydrothermal treatment followed by an activation process. We studied the electrochemical performance of the supercapacitors with the electrodes from the H2O-steam activated carbon. The experimental results indicate that the specific capacitance and diffusion coefficient increase with the increase of compressive stress and decrease with the increase of electrode mass. A power law correlation between specific-areal capacitance and compressive stress and a linear correlation between IR drop and compressive stress were formulated, respectively. We also constructed supercapacitors with electrodes from the KOH-activated carbon, which had larger specific areas than the H2O-steam activated carbon. Following the same compression process, we observed that the supercapacitors with the KOH-activated carbon possessed relatively higher specific capacitance and diffusivity than those from the H2O-steam activated carbon under the same compression condition. Both the power and energy densities of the supercapacitor with the KOH-activated carbon increase with the increase of compressive stress.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2021.382

Funding Information

This study was supported by the National Science Foundation (CMMI-1634540) in 2018.

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