Betaine–based natural deep eutectic solvents as sustainable electrolytes for the electrochemical energy storage devices

The research project titled: "Betaine–based natural deep eutectic solvents as sustainable electrolytes for the electrochemical energy storage devices" focused on developing new, environmentally friendly liquid electrolytes for use in devices such as batteries, accumulators, and capacitors. The researchers concentrated on the development of so-called Natural Deep Eutectic Solvents (NADES) based on betaine and its derivatives, which have the potential to replace traditional, less eco-friendly electrolytes.

Betaine is a natural chemical compound in plants like sugar beets, making it a fully renewable resource. Chemically, betaine is a derivative of the amino acid glycine, meaning it possesses a positive functional group at one end of the molecule and a negative charge at the opposite end. This gives betaine the characteristics of an ionic compound known as a zwitterion, which can be successfully used as an electrolyte additive.

During the research, three different NADESs were synthesized, and betaine hydrochloride served as the hydrogen bond acceptor (HBA). At the same time, glycerol, ethylene glycol, and glycolic acid acted as hydrogen bond donors (HBD). The researchers then examined their physical properties, such as density, viscosity, pH, and conductivity, and assessed these substances' electrochemical stability.

Among the studied NADES, the one based on betaine hydrochloride as the HBA and ethylene glycol as the HBD proved to be the most suitable electrolyte for supercapacitors due to its low viscosity and high ionic conductivity. Tests involving this substance demonstrated that devices using this electrolyte exhibited high specific capacitance and stability during prolonged use.

The results confirm that NADES based on betaine can serve as a more sustainable alternative to conventional electrolytes, which is a step toward creating more environmentally friendly energy storage systems in the future.

This research was founded on the whole by the National Science Centre, Poland (grant No. 2023/07/X/ST5/00629). For the purpose of Open Access, the author has applied a CC-BY public copyright to any Author Accepted Manuscript (AAM) version arising from this submission.