Assessing LiF as coating material for Li metal electrodes

Li metal electrodes have the potential to increase the energy density of conventional lithium-ion batteries by up to 60%. However, challenges regarding the cycling efficiency and safety of these electrodes still remain. Effective surface treatments seem to be a promising approach for resolving issues such as dendrite formation or excessive reaction with the electrolyte. LiF has been reported to exhibit most of the properties required of a coating material in this context, offering high electro-/chemical stability, mechanical strength, high surface energies, etc. Nevertheless, contradicting reports on the effectiveness of LiF coatings to improve the cycling efficiency of Li metal electrodes raise doubts on its effectiveness to protect the Li metal surface. The mechanism of protection for this material is also not well understood. Thus, a comparative study was conducted, selecting three different approaches for the synthesis of a LiF coating on Li metal and following with detailed electrochemical analysis. Using the same experimental setup for all samples enabled direct comparison between the selected coatings, and subsequently, a reliable evaluation on the effectiveness of LiF as protective coating. Graphic abstract