Enhancing High‐Voltage LNMO Cathode Performance in Li‐Metal Batteries Via Anionic Electrolyte Additive‐Integrated CEI Engineering

Abstract An anionic‐additive electrolyte system is introduced by incorporating Lithium tetrafluoroborate (LiBF 4 ) into a conventional base electrolyte for high‐voltage LiNi₀.₅Mn₁.₅O₄ (LNMO) cathodes in lithium‐metal batteries. At high voltages, the sacrificial oxidation of LiBF 4 mitigates electrolyte degradation and forms a robust cathode electrolyte interface (CEI) enriched with boron and fluorine‐based components, which protects against active material corrosion. Density Functional Theory (DFT) studies reveal that BF₄⁻ is more readily oxidized, while MD simulations validate the CEI's inorganic composition. Initial cycling with a specialized charge‐discharge protocol ensures optimal use of the additive, resulting in a uniform, thin (4–6 nm) CEI on the LNMO cathode. The CEI formed in anionic‐additive electrolyte system effectively suppresses transition metal dissolution and surface degradation, enhancing long‐term cycling performance. The LiBF 4 ‐enhanced electrolyte also lowers overpotential and promotes more uniform Li deposition compared to the base electrolyte. At a 1 C‐rate, the LNMO cathode with a Li metal anode and optimized electrolyte achieves a discharge capacity of 115 mA h g⁻¹ and an energy density of 540 Wh kg⁻¹ over 500 cycles. These findings underscore LiBF 4 ’s dual role in protecting LNMO cathodes and Li metal anodes, highlighting the critical role of additives in CEI development for advanced lithium‐metal batteries.