Influence of LiBOB as an Electrolyte Additive on the Performance of BiF3/C for Fluoride Shuttle Batteries

The potential effects of using lithium bis(oxalato)borate (LiBOB) as an electrolyte additive on the redox reactions of the positive bismuth fluoride (BiF3) electrode were investigated in tetraglyme (G4) containing the anion acceptor (AA) triphenylboroxin (TPhBX). The electrolyte system, containing 0.06 M LiBOB, 0.5 M TPhBX, and saturated cesium fluoride (CsF) was prepared. The study also included a comparison with previously studied systems based on G4, which did not contain LiBOB but AA. The tolerances to reduction and oxidation were enhanced after introducing LiBOB to the system. The capacity of BiF3 improved at C/10 rate. Defluorination of BiF3 was demonstrated to proceed through a direct desorption-insertion mechanism, whereas the contribution of the dissolution-deposition mechanism was known to be predominant in the G4-based systems. Addition of only 1 w/w% LiBOB to the G4 system resulted in an interesting change in the mechanism and an improvement in the capacity at high C rate. This improvement was associated with the increasing electrochemical stability of the electrolyte due to the interaction between BOB− and Cs+, reducing the possibilities of electrolyte degradation and loss of active material owing to a direct desorption-insertion mechanism.