Advanced fluorine chemistry in >4.2 V high-voltage lithium metal batteries

Lithium metal batteries (LMBs), operating at high voltage (>4.2 V), exhibit unprecedented energy density (>400 Wh kg^-1), but are restricted by uncontrollable Li dendrites, enigmatic interfacial chemistries, and unstable solid electrolyte interfaces (SEIs). Fluorine, with its high stability, non-flammability, and low cost, is playing an increasingly vital role in high-voltage LMBs and is expected to resolve the above obstacles. Unfortunately, there are few reviews that comprehensively summarise the exquisite design of fluorine engineering in high-voltage LMBs, especially in-depth analysis of its action mechanism in LMBs. In this review, we start with the fundamentals of SEI formation and Li nucleation and deposition, systematically dissecting the exquisite engineering of fluorine chemistry in high-voltage LMBs, including fluorinated electrolyte systems (salts, solvents, additives, etc.), fluorinated polymer-based SEIs, fluorinated collectors and separators. Meanwhile, several targeted and sophisticated cases are handpicked to be portrayed in conjunction with the proposed ideas, aiming to clarify the functionality of fluorine engineering in inhibiting dendrite growth, stabilising SEIs, and minimising safety hazards. Additionally, we highlight the obstacles faced by fluorine chemistry in LMBs and point out its future perspectives. This review provides guidance for the engineering of fluorine chemistry in high-voltage LMBs.