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 LiMn${}_2$O${}_4$$\parallel$L-TiO${}_2$ 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. (© 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH)