In Situ Designing a Gradient Li⁺ Capture and Quasi-Spontaneous Diffusion Anode Protection Layer toward Long-Life Li-O₂ Batteries.

Abstract

Lithium metal is the only anode material that can enable the Li-O₂ battery to realize its high theoretical energy density (≈3500 Wh kg^-1 ). However, the inherent uncontrolled dendrite growth and serious corrosion limitations of lithium metal anodes make it experience fast degradation and impede the practical application of Li-O₂ batteries. Herein, a multifunctional complementary LiF/F-doped carbon gradient protection layer on a lithium metal anode by one-step in situ reaction of molten Li with poly(tetrafluoroethylene) (PTFE) is developed. The abundant strong polar C-F bonds in the upper carbon can not only act as Li⁺ capture site to pre-uniform Li⁺ flux but also regulate the electron configuration of LiF to make Li⁺ quasi-spontaneously diffuse from carbon to LiF surface, avoiding the strong Li⁺ -adhesion-induced Li aggregation. For LiF, it can behave as fast Li⁺ conductor and homogenize the nucleation sites on lithium, as well as ensure firm connection with lithium. As a result, this well-designed protection layer endows the Li metal anode with dendrite-free plating/stripping and anticorrosion behavior both in ether-based and carbonate ester-based electrolytes. Even applied protected Li anodes in Li-O₂ batteries, its superiority can still be maintained, making the cell achieve stable cycling performance (180 cycles).