Unlocking high fluorination efficiency of anode interphase via electrostatic interaction for ultra-stable lithium metal batteries.

Constructing a fluorine (F)-enriched solid electrolyte interphase (SEI) is a well-established approach for stabilizing lithium (Li) metal batteries, yet achieving an SEI with the desired high fluorination efficiency (FE) remains challenging. Herein, we address this by proposing an electrostatic-interaction strategy that employs a fluorinated ionic additive, 4-fluoro-phenylammonium tetrafluoroborate (FPT). Leveraging electrostatic attraction, FP+ cations preferentially adsorb onto the negatively charged Li anode surface within the inner Helmholtz plane (IHP), as supported by systematic theoretical analysis, multiple microscopy characterizations and electrochemical measurements. This unique interfacial configuration effectively suppresses the accumulation of solvent molecules, attracts fluorinated anions and promotes the prior decomposition of FP+, leading to high fluorination efficiency and the formation of a LiF-enriched SEI. Consequently, the Li//Li symmetric cell achieves exceptional cycling stability over 3000 h even at an ultra-high current density of 10 mA cm-2. Furthermore, the derived BF4- anions concurrently construct a protective cathode interphase, which inhibits Al corrosion and electrolyte oxidative decomposition, thus allowing the pure ether-based electrolytes to enable not only stable Li//LiFePO4 but also high-voltage Li//LiNi0.8Co0.1Mn0.1O2 full cells. This work demonstrates a design paradigm centered on targeted molecular attraction to construct a highly fluorinated SEI without requiring high-concentration F-containing species.