Stabilizing the Solid-Electrolyte Interphase with Polyacrylamide for High-Voltage Aqueous Lithium-Ion Batteries.

The introduction of "water-in-salt" electrolyte (WiSE) concept opens a new horizon to aqueous electrochemistry that is benefited from the formation of a solid-electrolyte interphase (SEI). However, such SEI still faces multiple challenges, including dissolution, mechanical damaging, and incessant reforming, which result in poor cycling stability. Here, we report a polymeric additive, polyacrylamide (PAM) that effectively stabilizes the interphase in WiSE. With the addition of 5 molar % PAM to 21 mol kg-1 LiTFSI electrolyte, a LiMn2 O4 ∥L-TiO2 full cell exhibits enhanced cycling stability with 86 % capacity retention after 100 cycles at 1 C. The formation mechanism and evolution of PAM-assisted SEI was investigated using operando small angle neutron scattering and density functional theory (DFT) calculations, which reveal that PAM minimizes the presence of free water molecules at the anode/electrolyte interface, accelerates the TFSI- anion decomposition, and densifies the SEI.