Strontium Trifluoroacetate Additive Enables a Fluorine-Rich Interphase for Highly Stable Lithium Metal Anodes

Tuning the chemical composition and mechanical properties of the solid electrolyte interphase (SEI) is an effective approach to enhancing the interfacial stability of lithium metal anodes. Among various strategies, the incorporation of functional electrolyte additives that directly react with lithium metal to modulate SEI formation offers a simple yet powerful solution to the suppression of dendritic growth. In this work, strontium trifluoroacetate (Sr(TFA)2) is introduced as an electrolyte additive to regulate the interfacial chemistry of lithium metal. Upon an in situ reaction with lithium, Sr(TFA)2 generates a fluorine-rich interface comprising metallic Sr, LiF, and SrF2. Metallic Sr alloying with lithium enhances the interfacial conductivity and promotes Li+ transport, while the outer LiF and SrF2 components stabilize the SEI and protect the underlying alloy phase. Consequently, the Sr(TFA)2-modified electrolyte enables the stable Li deposition/stripping for over 450 cycles in Li–Cu asymmetric cells at 0.5 mA·cm–2, with the significantly improved average Coulombic efficiency and extended Sand’s time. Moreover, Li–Li symmetric cells exhibit the prolonged cycling stability over 1800 h at 0.5 mA·cm–2 and maintain over 400 h even under the high capacity condition (6 mAh·cm–2). In full-cell configurations with Li-LiNi0.8Co0.1Mn0.1O2, the Sr(TFA)2 additive delivers synergistic interfacial stabilization at both electrodes, leading to remarkable improvements in cycling stability and rate performance.