The designer nature of ionic liquids makes them a promising material for applications spanning disciplines from material processing to energy generation. While a great deal of interest has been directed towards dialkylimidazolium-based ionic liquids, there are many understudied classes of cations with favorable properties for energy related applications, such as disubstituted boroniums. To date only a handful of boronium cation-based ionic liquids have been thoroughly characterized despite exhibiting electrochemical stabilities (> 5.0 V) far surpassing what is seen with their alkylimidazolium and alkylpyrrolidinium counterparts. This work investigates a series of novel boronium-bistriflimide [TFSI^-] ionic liquids using electrochemical and physical characterization techniques such as cyclic voltammetry, broadband dielectric spectroscopy, oscillatory shear rheology, and thermogravimetric analysis. Systematic variations in boronium cation structure were employed to help identify the structural motifs that lead to optimal electrochemical and physical properties. The best performing boronium-based ionic liquids were then tested for initial lithium stability to further probe their potential for use in battery applications.