Nanoconfinement of Water-in-Salt Electrolytes in Nanometer-wide Boron-Nitride Nanotube for Potential Application in Aqueous Li-ion Batteries.

Aqueous Li-ion battery performance has been recently identified to be enhanced by using highly concentrated water-in-salt electrolyte (WISE) systems due to the formation of solid electrolyte interphase (SEI) at the negative electrode. The localization of the cation-anion pair near the negative electrode in the absence of free water plays an important role in SEI formation. In this study, atomistic simulations are conducted to show that a LiTFSI aqueous electrolyte solution of a much lower concentration is enough to ensure such water-free TFSI- anion localization at the negative electrode surface. Such a scenario is made possible by confining the LiTFSI electrolyte solution in a 1-nm-diameter boron nitride nanotube (BNNT). Our findings indicate that the interplay of the greater affinity of the TFSI- ion to enter the empty 1nm-wide BNNT before other electrolyte molecules and the nano-confinement, which results in the molecular ordering of the TFSI- ions and water molecules, allow such water-free localization of the TFSI- ion at the negative electrode.