Dual‐Anion Electrolyte Additives Regulating Solvation Structure Toward Stable High‐Voltage Lithium Metal Batteries with NCM90 Cathodes

Lithium metal batteries (LMBs) with high‐voltage high‐Ni cathodes (LiNi x Co y Mn z O 2 , x ≥ 0.8) are highly promising for next‐generation high‐energy‐density storage systems. However, the combination of reactive Li anodes, ultrahigh‐Ni‐content cathodes (NCM90, x ≥ 0.9), and elevated charging voltages leads to severe interfacial side reactions, capacity degradation, and safety hazards, necessitating functional electrolytes for mitigation. This work introduces a dual‐additive strategy using bis(trifluoromethanesulfonyl)imide (TFSI − ) and bis(oxalato)borate (BOB − ) anions to regulate electrolyte solvation structure and enhance electrode–electrolyte interphase (EEI) stability. Theoretical simulations and experimental results demonstrate that the modified electrolytes form anion‐rich solvation sheaths, which preferentially decompose to create thin and robust EEIs rich in inorganic components. These EEIs effectively suppress electrolyte oxidation and transition metal dissolution on NCM90 cathodes while promoting uniform Li deposition with a high Coulombic efficiency (≈99%) on anodes. Consequently, Li||NCM90 batteries exhibit superior electrochemical performance under 4.6 V operation, including 84.8% capacity retention after 200 cycles at 1C and a reversible capacity of 153.8 mAh g −1 at 5C. This dual‐anion approach offers critical insights into EEI engineering via solvation chemistry tailoring, providing a viable pathway for developing stable high‐voltage high‐Ni LMBs.