Cation-Anion Synergy: CsF Additive for Dendrite Suppression and Interface Reinforcement in Lithium Metal Batteries

The extremely high theoretical capacity of lithium metal anode positions it as an ideal candidate for next-generation high-energy-density energy storage systems. However, its practical application is hindered by uncontrollable lithium dendrite growth and the instability of the solid electrolyte interphase (SEI) layer. This study proposes an electrolyte modification strategy based on the synergetic effect of Cs⁺ and F^–, employing low-concentration CsF additives to simultaneously achieve uniform lithium deposition and optimized the composition of SEI. The results reveal that Cs⁺ preferentially adsorbs at the tip regions of the lithium metal surface via an electrostatic shielding mechanism, forcing Li⁺ to nucleate uniformly on flat regions, thereby effectively suppressing dendrite formation. Meanwhile, F^– promotes the formation of LiF within the SEI layer, significantly enhancing interfacial stability. Electrochemical tests revealed that the addition of 0.05 M CsF enhanced the average Coulombic efficiency of Li||Cu cells from 58.9% to 70.9% after 100 cycles at 0.5 mA/cm², while significantly extending the cycling lifespan of Li||Li symmetric cells from 100 h to over 250 h under 1 mA/cm² current density. In NCM622||Li cells, the capacity retention after 100 cycles at 1C improves from 38.6% to 80.6%. X-ray photoelectron spectroscopy and scanning electron microscopy characterization confirm that the LiF-enriched SEI layer induced by CsF effectively reduces interfacial impedance and inhibits dead lithium accumulation. This work provides innovative insights into developing high-performance lithium metal batteries through cation-anion synergetic regulation of electrolyte interfaces.