Ionic Liquid-Type Additive for Lithium Metal Batteries Operated in LiPF 6 Based-Electrolyte Containing 2500 ppm H 2 O.

The presence of trace amounts of moisture in the electrolyte can cause hydrolysis of LiPF 6 and deteriorate the stability of lithium metal batteries. Herein, we propose a multifunctional ionic liquid-type additive constituting a 1-methyl-1-butyl pyrrolidium cation (Py 14 + ) and an acetate anion (CH 3 COO - ) (denoted as IL-AC in this study), which can effectively adsorb the trace moisture and thus prevent the hydrolysis of LiPF 6 via intermolecular interactions. The prepared IL-AC can also remove HF to suppress the dissolution of transition metal ions from cathode materials through the reaction CH 3 COO - + HF → CH 3 COOH + F - . Compared with the baseline electrolyte, the contents of HF and transition metal ions are significantly lower in the electrolyte with 0.5% IL-AC. Upon the addition of 0.5% IL-AC additive and 2500 ppm H 2 O, the Li||NCM811 battery shows a capacity of 153.7 mAh g -1 after 300 cycles, while the Li||LNMO battery possesses stable capacity retention of 93.22% after 500 cycles at 1C and a Coulombic efficiency greater than 99%. Thus, this work provides a convenient and effective method to absorb trace amounts of water and remove HF in the electrolyte and provides a new path for the expensive and tedious process of water removal from the electrolyte in industry.