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 FSO2NH2 and FSO3 �, while nucleophilic attack on the S-F bond produces FSO2NSO32 � and SO3NHSO32 � 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 (FSO2NH2 and CH3CH2OSO3H) are determined for the first time. Based on these hydrolysis mechanisms, stra-tegies for inhibiting LiFSI hydrolysis are provided, which is significant for the high-efficiency production and safe storage/transportation of LiFSI.