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. [Figure not available: see fulltext.]