Electrode Interface Engineering in Lithium–Sulfur Batteries Enabled by a Trifluoroacetamide-Based Electrolyte

The passivation caused by the deposition of the insulating discharge final product, lithium sulfide (Li₂S), leads to the instability of the cycle and the rapid capacity fading of lithium-sulfur batteries (LSBs), which restricts the development of LSBs. This paper proposes the employment of trifluoroacetamide (TFA) as an electrolyte additive to alleviate the passivation by increasing the solubility of Li₂S. The solubilization effect of TFA on Li₂S is attributed to intermolecular hydrogen bonds and O-Li bonds. Li₂S in the TFA-based electrolyte exhibits a flower-like 3D deposition behavior, which further alleviates the surface passivation of the electrode and impels conversion kinetics. In addition, the LiF-rich solid electrolyte interface layer can effectively defend the Li metal anode and suppress the growth of Li dendrites. Accordingly, the discharge capacity of the TFA-based battery remains at an excellent 681.2 mA h g^-1 after 400 cycles with a Coulombic efficiency of 99% at 0.5 C. After the battery stabilizes, the capacity decay is only 0.036% per cycle. Under harsh conditions, such as high rates (2 C) and high sulfur loadings (5.2 mg cm^-2) with lean electrolytes and elevated temperatures (60 °C), TFA-containing batteries exhibited more durable and stable cycling. This paper provides new insights into solving practical problems and gives an impetus in cycle stability for LSBs.