Rational Design of Electrolyte Additives for Improved Solid Electrolyte Interphase Formation on Graphite Anodes : A Study of 1,3,6-Hexanetrinitrile

The construction of a thin, uniform, and robust solid electrolyte interphase (SEI) film on the surface of active materials is pivotal for enhancing the overall performance of lithium-ion batteries (LiBs). However, conventional electrolytes often fail to achieve the desired SEI characteristics. In this work, we introduced 1,3,6-hexanetrinitrile (HTCN) in the baseline electrolyte (BE) of 1.0 M LiPF6 in Ethylene Carbonate/Dimethyl Carbonate (EC/DMC) (3:7 by volume) with 5 wt.% fluoroethylene carbonate (FEC), denoted as BE-FH. By systematically investigating the influence of FEC: HTCN weight ratios on the electrochemical performance of graphite anodes, we identified an optimal composition (FEC:HTCN = 5:4 by weight, denoted as BE-FH54) that demonstrated greatly improved initial Coulombic efficiency, rate capability, and cycling stability compared with the baseline electrolyte. Deviations from the optimal FEC:HTCN ratio resulted in the formation of either small cracks or excessively thick SEI layers. The enhanced performance of BE-FH54-based LiB is mainly ascribed to the synergistic effect of FEC and HTCN in forming a robust, thin, homogeneous, and ion-conducting SEI. This research highlights the importance of rational electrolyte design in enhancing the electrochemical performance of graphite anodes in LiBs and provides insights into the role of nitrile-based additives in modulating the SEI properties.