Synthesis and Characterization of Polymeric Sensing Materials for Detection of Gases in Energy Storage Devices

Abstract

The increasing popularity of portable electronic devices, electric vehicles, and smart grids has created a need for energy storage systems including battery technology with lithium-ion batteries (LIBs) being one of the most common battery types. However, enhancing the safety of these LIBs remains a prominent aspect that requires advancements in battery technology as it has been shown that gas evolution occurs in LIBs. The identification and detection of these gases (which can be hazardous in different ways) are critical to protecting human and environmental health. Hence, there is an urgent need for gas-sensing devices (i.e., gas sensors) to minimize concerns regarding health, safety, and the environment.

This thesis presents an investigation on the design, evaluation, and characterization of polymeric gas sensing materials for the room-temperature detection of harmful gases (in ppm levels) generated in energy storage devices (e.g., lithium-ion batteries). The importance of gas sensing materials is well recognized as the sensing material is the ‘heart’ of a sensor that interacts with the target analyte, leading to a detection signal generated by the sensor. Four gases, namely, hydrogen (H2), ethylene (C2H4), carbon monoxide (CO), and carbon dioxide (CO2), were found to be the main gases released in LIBs and identified as target gases for detection.

Polymers modified/doped with metal oxides have displayed reasonable sensing behavior making them promising sensing materials in gas sensor applications. Polyaniline (PANI) doped with various concentrations of different metal oxide nanoparticles were synthesized and evaluated as sensing materials for target analytes, along with other polymeric materials like polypyrrole (PPy), polythiophene (PTh), and polyvinylpyrrolidone (PVP). Gas sorption characteristics were evaluated using formaldehyde as a "simulant" or "surrogate" due to safety concerns associated with testing target analytes in an academic environment.

The doped PANI materials, in particular, exhibited enhanced gas sorption properties, attributed to the synergistic effects of the dopants, which improved the interaction between the polymer matrix and gas molecules.

The effect of environmental factors (e.g., ageing), on the sensing performance, related to the sensing material stability, was also evaluated for selected sensing materials. Other property characteristics of the sensing materials were also determined using different techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-rays (EDX), dynamic light scattering (DLS), and Brunauer-Emmett-Teller (BET) tests, to provide a more detailed explanation and additional confirmation of the sorption trends.

In the final step, optimal sensing materials were deposited on a MEMS (micro-electro-mechanical system) sensor, which is efficient, inexpensive, and of small size. The sensor as a whole was then evaluated for its sensing performance towards 50 ppm ethylene.