Emerging Molten Salts Based Electrochemical Energy Technologies

Abstract

Molten salts of inorganic nature are excellent reaction media for various research and industrial uses. Their applications in energy technologies are also wide, including, but not limited to, thermal, nuclear, and electrochemical processes and their combinations. This review aims to capture and analyze selected innovations and developments in recent past, with a specific focus on electrochemical energy storage (EES) technologies. Additionally, it seeks to clarify some fundamental concepts in EES and address prevalent misconceptions, such as those related to Faradaic capacitive/Nernstian processes, battery-like/capacitive cyclic voltammograms (CVs) and galvanostatic charge-discharge curves (GCDs), as well as the calculation of specific energy. The application of molten salts in an emerging EES technology, known as supercapattery, is also explored in this review. This includes the design principle, fundamental calculations, and recent noteworthy demonstrations. Functioning as a hybrid technology, supercapattery combines the merits of both supercapacitor and battery and potentially outperforms each. Drawing insights from advancements in molten salt batteries and molten salt supercapacitors, this review delves into the prospects of developing a sodium-activated carbon (Na-AC) molten salt supercapattery. Through thermodynamic calculations, a specific energy of 445 W h kg−1-AM (where AM denotes the total active mass on both electrodes) is projected, which surpasses the specific energy of 250 W h kg−1-cell achieved by the best commercial lithium-ion battery.

Keywords

• molten salt
• electrochemical energy storage
• supercapattery
• thermodynamic calculation