Reversing nitride/fluoride distribution in the solid electrolyte interphase enables a highly reversible lithium metal anode

A robust solid electrolyte interphase (SEI) is essential for constructing high-performance lithium-metal battery (LMB). Here, we designed a unique layered SEI film with a reverse gradient distribution of nitride and fluoride compounds using a dual-salt electrolyte. Notably, the solvation structures, especially aggregates (AGG) are influenced by both the concentration effect and the binding energy differences between different anions and lithium ions. Through finely adjusting AGG, the anion decomposition processes can be controlled, thereby optimizing the component ratio of SEI film. As a result, the optimized electrolyte achieves a high CE of 99.50 % and ensures dendrite-free lithium deposition. The LMB (50 μm Li|| LiFePO₄, N/P ratio is 3) achieves high capacity retention rate of 90 % after 300 cycles. This work not only develops a novel and excellent electrolyte for stable LMBs, but also reveals the internal mechanisms between solvation structure and SEI component/structure.