Solid-Electrolyte Interphase of Molecular Crowding Electrolytes

Abstract

Molecular crowding electrolyte was proposed to improve the stability of water at a low concentration of Li salt (2 m LiTFSI )1. Low-cost and safe poly (ethylene glycol) (PEG, Mn=400) is adopted as a crowding agent to confine water molecules through hydrogen bonding and strengthen the covalent bond of H-O (H2O), leading to effective suppression of water decomposition (especially HER). However, the mechanism behind the improved cathodic stability of molecular crowding electrolyte is not yet fully understood. Specifically, the composition of the SEI and the impact of salt on the electrochemical stability of PEG-based electrolyte are still unknown. To gain a deeper insight into the stability mechanism in molecular crowding electrolytes, we investigated the cathodic stability of PEG-based molecular crowding electrolytes with LiTFSI and LiClO4 as the electrolyte salt. We characterized the composition and structure of SEI on Li4Ti5O12 electrode (LTO) derived from LiTFSI- and LiClO4-containing electrolytes, and correlated cathodic stability to the composition of the SEI. Comprehensive characterizations including linear sweep voltammetry (LSV), online electrochemical mass spectroscopy (OEMS), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) are used to study the cathodic stability of water. The enhance mechanism will be discussed.[1] Xie, J., Liang, Z. & Lu, Y. C. Molecular crowding electrolytes for high-voltage aqueous batteries. Nat. Mater. 2020, 19, 9, 1006-1011[2] Xie, J., Guan, Y., Huang, Y., & Lu, Y. C. Solid–electrolyte interphase of molecular crowding electrolytes. Chem. Mater. 2022, 34, 11, 5176–5183AcknowledgementThis work is supported by a grant from the Research Grant Council of Hong Kong Special Administrative Region, China (Project No. RFS2223-4S03) and a grant from the Innovation and Technology Commission of the Hong Kong Special Administrative Region, China (Project No. ITS/219/21FP).