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

An anionic-additive electrolyte system is introduced by incorporating Lithium tetrafluoroborate (LiBF₄) into a conventional base electrolyte for high-voltage LiNi₀.₅Mn₁.₅O₄ (LNMO) cathodes in lithium-metal batteries. At high voltages, the sacrificial oxidation of LiBF₄ 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 LiBF₄-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 LiBF₄’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.