Origin of Unusual Acidity and Li+ Diffusivity in a Series of Water-in-Salt Electrolytes

• DOI: 10.1021/acs.jpcb.0c02483
• Publication Date: 2020-06-02T19:27:33Z
• Authors: Kee Sung Han; Zhou Yu; Hui Wang; Paul C. Redfern; Lin Ma; Lei Cheng; Ying Chen; Jian Zhi Hu; Larry A. Curtiss; Kang Xu; Vijayakumar Murug...; Karl T. Mueller
• Keywords: Pulsed field gradient; Solvation shell

Superconcentrated aqueous electrolytes ("water-in-salt" electrolytes, or WiSEs) enable various battery chemistries beyond the voltage limits imposed by Pourbaix diagram of water. However, their detailed structural and transport properties remain unexplored could be better understood through added studies. Here, we report on our observations strong acidity (pH 2.4) induced lithium bis(trifluoromethane sulfonyl)imide (LiTFSI) at superconcentration (at 20 mol/kg). Multiple nuclear magnetic resonance (NMR) pulsed-field gradient (PFG) diffusion NMR experiments, density functional theory (DFT) calculations, molecular dynamics (MD) simulations reveal that such originates from formation nanometric ion-rich structures. The experimental simulation results indicate separation water-rich domains salt concentrations ≥5 m arising therefrom is due to deprotonation water molecules in domains. As such, domain composed hydrophobic −CF3 (of TFSI–) hydrophilic hydroxyl (OH–) groups. At concentration, tortuosity radius channels are estimated ∼10 ∼1 nm, respectively, which close values obtained hydrated Nafion membranes also have polytetrafluoroethylene (PTFE) backbones consisting SO3– ion cluster networks providing for ions Thus, discovered similarity between WiSE nanometer scale.