Engineering an Inorganic-Rich Interphase with Versatile Nonflammable Electrolytes toward Stable Alkali Metal Batteries

Alkali metal-based anodes are considered key to increasing the energy density of batteries thanks to the low redox potential and high capacity. Nevertheless, their practical application has been hampered by safety issues caused by the high reactivity of alkali metals, as well as the flammability of conventional organic electrolytes. In this study, we report a type of intrinsically nonflammable, cost-effective, and high-performance electrolytes. Such a novel flame-retardant electrolyte consists of heptafluoro-1-methoxypropane and fluoroethylene carbonate. In the proof-of-concept demonstration, the LiCoO₂-based battery achieves the capacity of 182.6 mAh g^–1 at a rate of 5C, with 81.2% capacity retention after 300 cycles even at a high upper cutoff voltage of 4.6 V. The Na ion battery can reach a capacity retention of 90.6% at an ultrahigh rate of 30C, and the K ion battery retains 84.2% of its initial capacity after 200 cycles.