Bifunctional Fluorocarbon Electrode Additive Lowers the Salt Dependence of Aqueous Electrolytes

• Published in: Advanced materials (Weinheim) 2024-12, Vol.36 (50), p.e2413573-n/a
• Main Authors: Liu, Binghang, Ma, Jintao, Feng, Jingnan, Lin, Ting, Suo, Liumin
• Format: Article
• Language: English
• Subjects: Anions; Aqueous electrolytes; aqueous Li ion battery; battery polarization reduction; bifunctional electrode additive; Charge transfer; Efficiency; Electric energy storage; Electrode polarization; Electrodes; Electrolytes; fluorocarbon; Graphite; Hydrogen evolution; Mass transfer; Molten salt electrolytes; Perfluorocarbons; SEI construction; Solid electrolytes
• ISSN: 0935-9648; 1521-4095; 1521-4095
• DOI: 10.1002/adma.202413573

The solid electrolyte interphase (SEI) plays a crucial role in extending the life of aqueous batteries. The traditional anion‐derived SEI formation in aqueous electrolytes highly depends on high‐concentrated organic fluorinating salts, resulting in low forming efficiency and long‐term consumption. In response, this study proposes a bifunctional fluorocarbon electrode additive (BFEA) that enables electrochemical pre‐reduction instead of TFSI anion to form the LiF‐rich SEI and in situ produce conductive graphite inside the anode before the lithiation. The BFEA lowers the salt dependence of aqueous electrolytes, enabling the inorganic LiCl electrolyte to work first, but also successfully achieves a high SEI formation efficiency in the relatively low 10 m LiTFSI without mass transfer concerns, suppressing the parasitic hydrogen evolution from 11.24 to 4.35 nmol min−1. Besides, BFEA strengthens the intrinsic superiority of Li storage reaction by lowering battery polarization resulting from the in situ production of graphite, promoting charge transfer of electrode kinetics. Compared with the control group, the demonstrated Ah‐level pouch cell employing BFEA exhibits better cycle stability above 300 cycles with higher capacity retention of 78.2% and the lower decay of the round‐trip efficiency (△RTE = 2%), benefiting for maintaining the high efficiency and reducing heat accumulation in large‐scale electric energy storage. A bifunctional fluorocarbon electrode additive (BFEA) is proposed to construct solid electrolyte interphase independent of aqueous electrolyte. The LiF from reduction of BFEA suppresses hydrogen evolution, increasing coulombic efficiency while the carbon byproduct lowers battery polarization, improving round‐trip efficiency. The unique advantages of BFEA make it highly compatible with aqueous batteries and promising for large‐scale energy storage applications.