(Digital Presentation) Free Solvent Molecules in the Electrolyte Leading to Severe Safety Concern of Ni-Rich Li-Ion Batteries

Abstract

The safety of Li-ion batteries is one of the most important factors, if not the most, determining their practical applications. We have found that free carbonate-based solvent molecules in the hybrid electrolyte system can cause severe safety concerns. The 18650 battery cells using the 50% varied-alkyl chain piperidinium-based TFSI result in an immediate and aggressive explosion after applying the impact test (UN38.3) compared with the cell using the conventional electrolyte, having a mild explosion after applying the impact force with 16 s-delayed time. Furthermore, the greater concentration of gases especially C2H4 and CO in the hybrid electrolyte system compared with the conventional electrolyte system was observed by online in situ DEMS, which is evidence for the aggressive explosion of the cell using the hybrid electrolyte. In additionally, the classical MD investigation is suggested that hybrid electrolytes have a high AGG concentration of Li+ and TFSI−, producing a high concentration of the isolated EC or free solvent, which could generate more gases in the fully charged battery cell. Mixing ionic liquids with a carbonate-based solvent as the co-solvent at a fixed salt concentration of 1 M LiPF6 can lead to free carbonate-based molecules causing poor charge storage performance and safety concerns. Keywords: Ni-rich Li-ion bateriesIonic liquids; Safety; Battery explosion; Mismatch electronic properties; 1865 cylindrical cells