π‐Electron‐driven ionic liquids to enhance lithium recovery from spent batteries: Experimental and mechanistic insights

Abstract A novel strategy is proposed to enhance Li + extraction from spent lithium‐ion batteries (LIBs) by ionic liquid (IL)‐based extractants with π‐electron regulation. N ‐butyl‐4‐methylpyridinium bis(trifluoromethylsulfonyl)imide ([BMPy][Tf 2 N]) + tributyl phosphate (TBP) was designed as an optimal extractant resulting in extraction efficiency of Li + up to 98.4%, separation selectivities of Li + over other ions β Li + /Co 2+ , β Li + /Ni 2+ , and β Li + /Mn 2+ up to 705, 740, and 663, respectively, and Li 2 CO 3 product with 93.2 wt.% purity. The molecular‐level mechanism for enhancing Li + extraction was unraveled by quantum chemical calculations and molecular dynamics simulations. It is found that the [BMPy][Tf 2 N] + TBP system with moderate π‐electron density is not able to disrupt the strong hydration of divalent metal ions Co 2+ , Ni 2+ and Mn 2+ , but it can disrupt Li + hydration by so‐called the “π‐electron density matching effect.” This work provides theoretical guidance for rational design of specific IL‐based extractants to selective extraction of target metal ions from spent LIBs.