Lithium metal batteries hold great promise for high performance energy storage due to their high theoretical energy density. However, practical implementation is hindered by interfacial side reactions and dendrite growth at the Li metal anode, particularly in carbonate-based electrolytes. Hereby, we introduce a novel multifunctional group additive strategy using 2-fluorobenzenesulfonamide (2-FBSA) to address these challenges. The 2-FBSA additive plays a crucial role in modulating the solvation structure of the electrolyte, facilitating Li⁺ transport kinetics by lowering the desolvation energy barrier. Additionally, the preferential decomposition of 2-FBSA at the anode interface leads to the formation of a robust solid electrolyte interphase (SEI) enriched with inorganic Li salts, including LiF, Li₃N, and ROSO₂Li. This SEI layer effectively suppresses Li dendrite growth and mitigates parasitic side reactions, resulting in significantly improved cycling stability and rate performance of Li||Li symmetric cells and Li||LiFePO₄ full cells. The Li||Li symmetric cell achieves a remarkable lifespan exceeding 2400 h at 0.5 mA·cm⁻²/1 mAh·cm⁻², while the Li||LiFePO₄ full cell demonstrates a capacity retention of 72% after 400 cycles at 1 C. This study highlights the potential of multifunctional group molecular additive 2-FBSA in interfacial optimization and provides new insights into additive design principles for high performance battery systems.