Weakly Solvated and Interfacially Compatible Fluorinated Nitrile Based Electrolyte for High-Energy-Density Li/CFx Batteries

Lithium/fluorinated carbon (Li/CFx) batteries have attracted much attention due to the highest theoretical energy density (2180 Wh·kg–1) compared to other primary batteries, yet they still suffer from large polarization and slow kinetics at high current density. Herein, a fluorinated nitrile compound, 3-(2,2,3,3,3-pentafluoropropoxy) propanenitrile (F5EON), was first reported as an electrolyte cosolvent for Li/CFx batteries, offering advantages such as weak solvation and interfacial compatibility. With the optimized electrolyte of 1.0 M LiBF4 in F5EON/DME (1:1, by vol.), the Li/CFx batteries delivered a superior energy density of 1703 Wh·kg–1 at the current density of 1000 mA·g–1, while the baseline electrolyte of 1.0 M LiBF4 in PC/DME (1:1, by vol.) only provided 1348 Wh·kg–1. Through theoretical calculations and experimental analysis, it has been found that the fluorinated nitrile based electrolyte not only formed a weakly solvated structure via molecular interactions between F5EON and DME but also exhibited good compatibility with the Li metal anode and excellent wettability with the CFx cathode. Correspondingly, the results of accelerating the desolvation and diffusion kinetic process of Li+, reducing the charge-transfer resistance, and forming LiF with a smaller partical size are beneficial for the high-current-density performance of Li/CFx batteries. The fluorinated nitrile based electrolyte demonstrates considerable promise as a viable electrolyte system for high-energy-density Li/CFx batteries.