Multifunctional Energy and Power Materials for Batteries and Supercapacitors

Abstract

Multifunctional energy and power systems can simultaneously store energy and accomplish a second function. Typically, the other function is structural or safety related. Both of these rely on robust mechanical properties along with good electrochemical properties for storing energy. However, there is an inherent tradeoff between mechanical and electrochemical properties. This presents a unique challenge in fabricating materials with both high energy storage (specific energy, specific power, rate capability, cycle stability, and etc.) and high mechanical properties (Young’s modulus, ultimate strength, ultimate strain, toughness, etc.). This dissertation focuses on the use of high performance nanomaterials (reduced graphene oxide, carbon nanotubes, and/or aramid nanofibers) for use in multiple energy storage device components. Namely, aramid nanofibers are used to fabricate thermally stable and mechanically robust battery separators while reduced graphene oxide, carbon nanotubes, and aramid nanofibers are used in a composite electrode to fabricate structural supercapacitor electrodes.

Aramid nanofiber separators were fabricated using vacuum-assisted filtration. The separators possessed excellent thermal stability with a high 5 wt% decomposition temperature of 447 °C. In addition, the aramid nanofiber separator was able to self-extinguish when exposed to flames. The separator also possessed excellent mechanical properties such as a Young’s modulus of 8.8 GPa. Finally, the separator possessed a reduced capacity of 123.4 mA h g⁻¹ in a lithium nickel manganese cobalt oxide vs lithium battery setup. Holistically, the separator possessed a good combination of thermal, mechanical, and electrochemical properties for safer lithium ion batteries.

Reduced graphene oxide/aramid nanofiber/carbon nanotube composite electrodes for supercapacitors were fabricated using vacuum-assisted filtration and studied using both an informatics and experimental approach. The informatics study focused on using data science to minimize the number of experiments required to find the optimal combination of the three components in the composite. An optimal composition was found that performed better than the initial experimental dataset by 5.5 % (using a unique multifunctional metric). The experimental study focused on systematically varying the carbon nanotube content to better understand how carbon nanotubes affect the electrode. This work found that the carbon nanotubes can increase the mechanical and electrochemical response of the electrode.