The Functions and Applications of Fluorinated Interface Engineering in Li-Based Secondary Batteries

Li-based secondary batteries are now attracting soaring research attention as a promising energy storage system with high energy density for commercial applications. However, the high-energy systems meanwhile are causing serious concerns on safety issues due to unstable interfaces on both cathodes and anodes. To improve interphase stability upon extended cycles, surface fluorinated treatment becomes highly desirable due to its unique capability in modulating the chemistry of electrode/electrolyte interface to ensure a stable electrochemical performance. Accordingly, it is essential that a deeper understanding on the solid electrolyte interphase (SEI), especially the role of fluorine-containing components, is demanded to guide the interface design. This review begins with an introduction to the fundamental knowledge on the structure of SEI with focus on the unique physiochemical properties of fluorides. Detailed discussions are then taken on the control strategies for a reliable construction of fluoride-based interfaces, which typically includes the surface coating of metal fluorides on cathodes and ex situ/in situ fluorination on lithium, based on which the structure-performance relationship is elaborated to inspire a rational interface engineering. Finally, perspectives are provided to give insights into the possible research directions of fluorinated SEI for further development of rechargeable Li batteries.