Design of an LiF-rich interface layer using high-concentration fluoroethylene carbonate and lithium bis(fluorosulfonyl)imide (LiFSI) to stabilize Li metal batteries

The development of high-energy-density Li metal batteries is limited by the uncontrollable growth of Li dendrites and an unstable Li/electrolyte interface during long-term Li plating/stripping. In this work, using high-concentration fluoroethylene carbonate (FEC) electrolyte, an LiF-rich interface layer was generated on the Li metal surface. This LiF-rich interface layer could effectively inactivate the high reactivity of the Li metal surface and suppress lithium dendrite growth, forming a uniform and dense structure at the Li/electrolyte interface to stabilize Li metal batteries. Owing to the enhanced interface stability offered by the high-concentration FEC electrolyte with LiFSI additive, the Li‖LiFePO₄ cell presented high capacity retention (89.1%) after 200 cycles at 1C (165 mA g⁻¹) and retained over 133.7 mA h g⁻¹ at 10C rate, whereas only 115.0 mA h g⁻¹ was achieved in the traditional carbonate ester electrolyte. The results show an obvious improvement in the cycle performance and rate capability of Li metal batteries containing a high-concentration FEC electrolyte with LiFSI as an additive.