Comparative study on lithium borates as corrosion inhibitors of aluminum current collector in. lithium bis(fluorosulfonyl)imide electrolytes

Abstract

Abstract Lithium bis(fluorosulfonyl)imide (LiFSI) is a promising salt that can possibly overcome the limitations of lithium hexafluorophosphate (LiPF<inf>6</inf>) in current Li-ion batteries (LIBs). Aluminum (Al) corrosion issue, however, is a major bottleneck for the wide use of LiFSI. This study investigates lithium borate salts as Al corrosion inhibitors in LiFSI electrolytes. Through a systematic comparison among lithium tetrafluoroborate (LiBF<inf>4</inf>), lithium bis(oxalato)borate (LiBOB), and lithium difluoro(oxalato)borate (LiDFOB), and LiPF<inf>6</inf>, the inhibition ability of the additives is revealed to be in the following order: LiDFOB > LiBF<inf>4</inf> ≈ LiPF<inf>6</inf> > LiBOB. In particular, the inhibition effect of LiDFOB is outstanding; the anodic behavior of Al in 0.8 M LiFSI + 0.2 M LiDFOB ethylene carbonate (EC)-based electrolyte is comparable to that of corrosion-free 1 M LiPF<inf>6</inf> solution. The superior inhibition ability of LiDFOB is attributed to the formation of a passive layer composed of Al-F, Al<inf>2</inf>O<inf>3</inf>, and B-O species, as evidenced by X-ray photoelectron spectroscopy (XPS) measurements. A LiCoO<inf>2</inf>/graphite cell with 0.8 M LiFSI + 0.2 M LiDFOB electrolyte exhibits a rate capability comparable to a cell with 1 M LiPF<inf>6</inf> solution, whereas a cell with 0.8 M LiFSI solution without LiDFOB suffers from poor power performance resulting from severe Al corrosion. © 2015 Elsevier B.V.