Corrosion inhibition of aluminum in lithium imide electrolyte by lithium borate addition

Abstract

Lithium bis(fluorosulfonyl)imide (LiFSI) is a promising imide group salt due to its comparable ionic conductivity and superior thermal stability to common Lithium hexafluorophosphate (LiPF6), but aluminum (Al) corrosion issue is a bottleneck for its wide use. The Al corrosion becomes much severe in higher ionic conductive imide-based electrolytes while no trends are observed in non-corrosive electrolytes. This study demonstrates that Al corrosion in LiFSI electrolyte is clearly suppressed by the addition of Li borates salts. For anodic corrosion of Al in LiFSI ethylene carbonate (EC)/diethyl carbonate (DEC), inhibition ability of borate additives is remarkable while fluoride and phosphate additives do not help inhibit the corrosion. The corrosion resistance of Al in 0.8 M LiFSI + 0.2 M lithium difluoro(oxalato)borate (LiDFOB) is comparable to that in 1 M LiPF6. Moreover, borates also suppress the corrosion of Al in LiTFSI solutions. Suppression of corrosion by borates is ascribed to the passive organic layer. Unfortunately, LiDFOB-added electrolytes suffer from severe Mn dissolution. This study provides a way to improve energy density of LIBs without compromising reliability. The discovery of this study enables the use of LiFSI electrolyte for various cathode materials in addition to LiFePO4, and provides huge implication in developing highly reliable LIBs without compromising energy and power densities. ⓒ 2014 DGIST