Ultra-low concentration and flame-retardant electrolyte for next-generation lithium metal batteries

Lithium metal batteries (LMBs) are regarded as the next generation of electrochemical energy storage devices with high energy density that hold great promise in the applications of electric vehicles (EVs) and portable electronic devices. However, the commercial carbonate electrolytes are limited by their flammability, lithium dendrite growth and poor cycle stability. In this work, an ultra-low concentration and flame-retardant electrolyte with 0.2 M lithium hexafluorophosphorate (LiPF₆) solventated in fluoroethylene carbonate (FEC), dimethyl carbonate (DMC) and 1,1,2,2-tetrafluoroethylene-2,2,3,3-tetrafluoropropyl ether (TTE) was prepared for lithium metal batteries. The results demonstrate that the introduction of a large amount of fluorine-containing solvent formed a uniform, strong and thin electrolyte/electrode interface layer both on the cathode and anode. That efficiently suppressed dendrite formation on the lithium metal anode, and greatly reduced the appearance of undesirable decomposition products, ensuring the cycling stability of electrolyte and electrode materials. Notably, the ultra-low concentration electrolyte has excellent flame retardancy, and significantly improves the electrochemical characteristics of Li||Li symmetrical batteries and Li||LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) batteries. The work presents a promising non-flammable, low-concentration electrolyte for next-generation LMBs and new insights into innovations in the formulation of advanced electrolytes for electrochemical energy storage technologies.