On the moisture tolerance of LiFSI based lithium-ion batteries: A systematic study on NMC622/graphite full cells

• A systematic study on the effect of moisture in LiFSI based NMC622/graphite cells. • Intentionally added H 2 O (∼1000 ppm) improved NMC622/lithium half-cell performance • Moisture negatively affected graphite/lithium half and NMC622/graphite full cells. Lithium-ion battery (LIB) technology is state-of-the-art energy storage technology for portable electronics and electric vehicles (EVs). In this incumbent LIB technology, lithium hexafluorophosphate (LiPF 6 ) is the most widely used electrolyte salt to date. However, the challenges related to its chemical/thermal stability, sensitivity to moisture and the consequent formation of strong acids such as hydrogen fluoride (HF) need to be resolved with alternative salts. Due to its better chemical/thermal stability, resistance to moisture and HF formation, and better ionic conductivity, lithium bis(fluorosulfonyl)imide (LiFSI) has been considered as a promising alternative electrolyte salt to LiPF 6 . In this study, the effect of addition of 1000 ppm water on LiFSI based electrolytes was systematically investigated by testing NMC622/lithium and artificial graphite/lithium half and NMC622/graphite full cells in four LiFSI based electrolytes; plain LiFSI, LiFSI + 1000 ppm H 2 O, LiFSI + 10 wt% FEC, and LiFSI + 1000 ppm H 2 O + 10 wt% FEC. Post mortem characterization of selected electrodes was also conducted with SEM imaging and XPS to study the surface chemistry and morphology of cycled electrodes. Overall, this study shows that 1000 ppm water can slightly improve the electrochemical performance of NMC622/lithium half cells; however, the same amount of moisture severly degrades the graphite half and NMC622/graphite full cells.