Revisiting Amides as Cosolvents for Flame Resistant Sodium Bis(oxalato)borate in Triethyl Phosphate Electrolyte

In selecting electrolytes for Na-ion batteries, simply importing the analogue of common lithium-ion battery electrolytes to sodium-ion batteries does not address safety concerns like toxicity and flammability. Electrolytes based on sodium bis(oxalato)borate (NaBOB) in organophosphates like triethyl phosphate (TEP) largely alleviate these specific safety concerns. However, it may be beneficial to obtain solutions with higher ionic conductivities than NaBOB in TEP, and compare the performance in Na-ion batteries with high mass loading electrodes. Here, we have shown that N,N-dimethyl formamide (DMF), N,N-dimethyl acetamide (DMAc), and N-methyl pyrrolidone (NMP) cosolvents almost double the ionic conductivity (from similar to 3.5 mS/cm to similar to 7 mS/cm) without sacrificing the flame-retarding properties of the base NaBOB in TEP electrolyte. The physical properties of these cosolvent electrolyte mixtures are investigated, along with the electrochemical performance of these electrolytes full-cells based on hard carbon anodes and Prussian white cathodes with near-commercial areal capacity (similar to 2 mAh/cm(2)).

Automated summary

In this study, the addition of N,N-dimethyl formamide (DMF), N,N-dimethyl acetamide (DMAc), and N-methyl pyrrolidone (NMP) cosolvents significantly increased the ionic conductivity of Na-ion battery electrolytes to around 7 mS/cm without compromising their flame-retarding properties.