A gradient solid electrolyte interphase with high Li⁺ conductivity induced by bisfluoroacetamide additive for stable lithium metal batteries

Stable Li metal anodes have become the driving factor for high-energy-density battery systems. However, uncontrolled growth of Li dendrite hinders the application of rechargeable Li metal batteries (LMBs). Here, a multifunctional electrolyte additive bisfluoroacetamide (BFA) was proposed to facilitate high-performance LMBs. The uniform and dense deposition of Li⁺ was achieved due to the reduced nucleation and plateau overpotential by the addition of BFA. Moreover, X-ray photoelectron spectroscopy (XPS) tests reveal a gradient solid electrolyte interface (SEI) structure on the Li metal surface. Cyclic voltammetry (CV) curves at different sweep speeds prove the formation of pseudocapacitance at the electrode–electrolyte interface, which accelerates the Li⁺ transport rate and protects the electrode structure. The low activation energy also indicates the ability of rapid Li⁺ transportation in electrolyte bulk. Therefore, the Li||Li symmetric cells with 1.0 wt.% BFA electrolyte exhibit good cycling performance at 0.5 mA·cm⁻² for over 2000 h, and Li||LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622) full cells maintain a high capacity for 200 cycles at 1 C rate.