Water-free Localization of Anion at Anode for Small-Concentration Water-in-Salt Electrolytes Confined in Boron-Nitride Nanotube

Water-in-salt electrolyte (WISE) systems have been recently identified to significantly enhance the performance of aqueous Li-ion batteries owing to the formation of solid electrolyte interphase (SEI) due to localization of the cation-anion pair near the negative electrode in the absence of free water. Such localization occurs for an extremely large concentration of the electrolyte salt that enhances the interionic attraction between the salt cation and anion, thereby ensuring that the cation “carries” the anion with itself to the anode. Here, we use atomistic simulations to establish that for a LiTFSI electrolyte solution (LiTFSI is a salt that is widely known to form WISE systems) confined in a 1-nm-diameter boron nitride nanotube (BNNT), such water-free TFSI− anion localization at the anode surface is possible at a LiTFSI concentration that is several times smaller than that needed for such localization in a non-nanoconfined LiTFSI WISE system.