Designing new halogen free borate anions for functional applications

Abstract

Ionic liquids (ILs) have attracted considerable attention since the discovery of the protic ionic liquid [EtNH3][NO3] by Walden in 1914. They have been explored for a range of applications as solvents, in electrochemistry, and in catalysis. However, concerns over their synthesis, purification, toxicity, and environmental impact have limited their widespread industrial use. While the development of new cations for ILs has been extensive, less attention has been given to the development of anions. Common anions include halides, nitrate, and tetrafluoroborate. However, the lack of cheap, safe, and environmentally friendly anions has hindered adoption.This work explores new halogen-free N-O coordinated borate anions building on thebis(oxalato)borate structure - an area that is underexplored in anion development. ILs based on nine new borate anions were synthesised, and characterised using NMR, thermal analysis, density/viscosity measurements, and electrochemical tests, including conductivity and cyclic voltammetry. The O/N- and N-coordinated borate anions demonstrated superior stability in water compared to O/O-orthoborates. This suggests that the incorporation of B-N bonds can address previous stability limitations while offering good thermal stability. The O/N- orthoborates also showed excellent performance as electrolytes for sodium-ion batteries, exhibiting high conductivity, improved ion diffusion, and strong electrochemical stability.

Date of Award	Dec 2024
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	Northern Ireland Department for the Economy
Supervisor	Gosia Swadzba-Kwasny (Supervisor) & John Holbrey (Supervisor)