Tailoring Electrode‐Electrolyte Interfaces via Electrolyte Additive Engineering for Reliable 5 V‐Class 500 Wh Kg ⁻¹ Lithium Metal Batteries

The inherent incompatibility of nonaqueous electrolytes with highly reactive cathodes, along with their high flammability, severely impedes the development of high-voltage lithium metal batteries (LMBs). Herein, functional carbonate-based electrolytes are designed by incorporating 1,2-bis(bromoacetoxy)ethane (BBAE) additive, demonstrating the intrinsic nonflammability and remarkable operation of 5.0 V cells. Experimental results and theoretical simulations uncover that the addition of BBAE induces a self-absorption plane and modifies the solvation structure, leading to the in situ formation of reinforced hybrid halide electrode-electrolyte interphases (EEIs), which suppress surface parasitic reactions under high-voltage conditions above 4.5 V while inhibiting lithium dendrite growth on the lithium metal anode. Moreover, the optimized electrolytes exhibit enhanced fire retardancy thanks to the contribution from the bromine functionality within BBAE and the effective combination with nonflammable triethyl phosphate. Consequently, LMBs equipped with typical cathodes including LiNi_0.9Co_0.05Mn_0.05O₂ (NCM90), high-voltage LiCoO₂, etc., exhibit exceptional deep cycling stability and wide-temperature-tolerant capability over a broad voltage window of 4.1 - 5.0 V. Additionally, 520 Wh kg^-1 NCM90||Li pouch cells surprisingly pass the nail penetration tests, highlighting the prominent safety. This straightforward and cost-effective approach provides an inspirational strategy for the safe application of LMBs by reinforcing the interface stability and reconciling the electrolyte flame retardancy.