Elevating operation voltage of LiTFSI-electrolyte via a universal passivation strategy for high-voltage lithium-metal batteries

Lithium bis((trifluoromethyl)sulfonyl)azanide (LiTFSI) based electrolytes have become the preferred electrolytes for lithium metal batteries (LMBs) due to their exceptional anode stability and ionic conductivity. However, challenges including unstable cathode electrolyte interface (CEI) formation and aluminum current collector (AlCC) corrosion have hindered the application of LiTFSI-based electrolyte in high-voltage LMBs. In this work, a universal passivation strategy is proposed and achieved with additive 8-hydroxyquinoline (8-HQ) in LiTFSI based electrolyte (ED-HQ). The 8-HQ additive preferentially decomposes on the cathode surface to generate Li₃N, inducing the formation of inorganic-rich CEI with a uniform thickness of only 10 nm. The dense and homogeneous inorganic-rich CEI enables the cycling stability of the cathode. Meanwhile, the 8-HQ additive shows strong adsorption on the AlCC surface, which promotes the formation of a composite passivation layer consisting of an Aluminum-8-hydroxyquinoline (Alq₃) chelate layer and an AlF₃/LiF inorganic layer, increasing the stable operating voltage of AlCC to 4.9 V and reducing the corrosion current density to one tenth. As a result, the joint effects enable Li||LiFePO₄ cells with ED-HQ electrolyte to achieve 89.8% capacity retention after 500 cycles at an elevated cutoff voltage of 4.5 V, demonstrating a viable pathway toward stable high-voltage LMB operation.