In Situ Formed Continuous and Dense Inorganic Borate-Based SEI for High-Performance Li-Metal Batteries

The practical application of lithium metal batteries (LMBs) is largely hindered by the notorious lithium dendrite growth, low cycle efficiency associated with insufficient electrode-electrolyte interphase dynamics, and electrolyte combustion. Here, an advanced electrolyte using a combination of three kinds of salts dissolved in carbonate-based solvents is developed. The salt anions dominate a primary solvation sheath, resulting in weak interaction between Li⁺ and the solvents, as well as the in situ formation of an inorganic-rich bilayer solid electrolyte interface (SEI). The designed electrolyte enables high cycle stability in LMBs with a high-loading NMC cathode (approximately 20 mg cm^-2), exhibiting 89.89% capacity retention after 200 cycles with the cutoff voltage of 4.5 V. Cryo-TEM characterization and density-functional theory (DFT) calculations reveal that the borate-based bilayer SEI, characterized by an exceptional dense structure, effectively suppresses lithium dendrite growth, and certify the crucial role of inorganic component continuity and density within the SEI, which surpasses the absorption and migration energy barrier in terms of significance. This profound understanding of SEI structure holds great potential for advancing the development of high-stable LMBs and can be expanded to other battery system.