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

Lithium/fluorinated carbon (Li/CF x ) 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/CF x batteries, offering advantages such as weak solvation and interfacial compatibility. With the optimized electrolyte of 1.0 M LiBF 4 in F5EON/DME (1:1, by vol.), the Li/CF x 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 LiBF 4 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 CF x 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/CF x batteries. The fluorinated nitrile based electrolyte demonstrates considerable promise as a viable electrolyte system for high-energy-density Li/CF x batteries.