| Despite significant efforts in improving the performance of Li-ion batteries, their low power densities coupled with high costs and safety concerns have kept them from many applications. As a result, supercapacitors have emerged in recent years as promising energy storage technology. Supercapacitors, also known as ultracapacitors or electrochemical capacitors, store energy as electrical charge on highly porous materials. Among electrochemical energy storage devices, supercapacitors offer the advantage of high power densities coupled with long cycle life. Despite the obvious benefits, supercapacitors have their drawbacks that limit their competitiveness, such as high self-discharge and low energy density. In the quest for improving the performance of supercapacitors many studies have been done in developing electrode materials as well as the electrolyte with a particular focus on univalent ions. On the other hand, the literature on the use of multivalent ions, such as, Mg2+, Be2+ , Ca2+, Al3+, and La3+, etc, is very limited. Said multivalent ions, offer the advantage of transferring more than one electron. In this work, the first part of the project demonstrates that multivalent ions increase the capacitance in aqueous electrochemical double layer capacitors (EDLCs), especially when the mobility of multivalent ions was higher. However, above an optimum electrolyte concentration, capacitance and impedance were negatively affected. The second part of the project explored the intercalation of the Be2+ ion into alpha-MoO3. The study demonstrated that the small size of the Be2+ ion coupled with its higher charge, compared to most univalent ions(e.g. Li + and H+), and decent diffusion rates in MoO3 crystals potentially contributed to increasing the capacitance as well as cyclability. Finally we compared the performance of two bivalent ions of different size (Be2+ and Mg2+) for their performance in alpha-MoO3. This part of the project allowed us to determine that diffusion paths are highly dependent on the covalent nature of ions as well as preferred coordination number. |
