Direct evidences for bis(fluorosulfonyl)imide anion hydrolysis in industrial production: Pathways based on thermodynamics analysis and theoretical simulation.

LiFSI (lithium bis(fluorosulfonyl)imide) is a promising lithium salt for electrolytes in Li-ion batteries. However, the accumulation of harmful gases and heat during LiFSI hydrolysis could lead to serious safety accidents. Here we systematically investigate LiFSI hydrolysis processes under comprehensive conditions: higher temperature/acidity/basicity and lower water content can accelerate the hydrolysis, whereas the presence of DEC (diethyl carbonate) solvent, and other alkali metals (Na+, K+) can stabilize FSI−. Unexpectedly, under alkaline conditions, temperature/water content could not affect the hydrolysis greatly. By monitoring the hydrolysis intermediates and products using time-dependent ion chromatography, infrared spectra, and nuclear magnetic resonance, the hydrolysis routes are proposed and validated by accelerating rate calorimetry, differential scanning calorimetry measurements, and theoretical calculations. Under neutral/acidic conditions, electrophilic attack on the S–N bond generates FSO 2 NH 2 and FSO 3 −, while nucleophilic attack on the S–F bond produces FSO 2 NSO 3 2− and SO 3 NHSO 3 2− under alkaline conditions. As indicated by DFT calculation, the weaker S–N bond and larger S–N–S angle facilitate the electrophilic attack under acid conditions. Furthermore, very unstable intermediates (FSO 2 NH 2 and CH 3 CH 2 OSO 3 H) are determined for the first time. Based on these hydrolysis mechanisms, strategies for inhibiting LiFSI hydrolysis are provided, which is significant for the high-efficiency production and safe storage/transportation of LiFSI. [Display omitted] • LiFSI hydrolysis in comprehensive conditions has been investigated. • Hydrolysis routes are proposed by monitoring intermediates and products. • Two very unstable intermediates in LiFSI hydrolysis have been firstly determined. • The weaker S–N bond and larger S–N–S angle facilitate electrophilic attack. [ABSTRACT FROM AUTHOR]