Robust Surface-Engineered Li ₅ FeO ₄ with Enhanced Air Tolerance and Powerful Prelithiation Capability for Lithium-Ion Battery Cathodes

The formation of solid electrolyte interphase (SEI) on lithium-free anodes consumes the cathode’s precious lithium up to 30%. As one of the cathode prelithiation additives, Li5FeO4 (LFO) offers a high capability of compensation for cathode’s lithium loss and moderate working voltage but suffers from extremely low air tolerance due to its fast parasitic reactions with moisture and CO2. This presents significant engineering challenges for storage of LFO material and cathode processing, including slurry preparation, coating, and drying. To address the issue, we propose a robust and scalable dopamine-assisted dry coating method to synthesize carbon-coated Li5FeO4 (LFO@C), which utilizes the catechol moiety of dopamine hydrochloride to provide strong adsorption capability on the LFO surface. The carbon coating helps LFO to construct SEI with more uniform thickness and less side products on the graphite anode and simultaneously to improve the cathode stability. As a result, the powerful lithium release capability and high air tolerance of LFO@C can be achieved. After 6 h of air exposure (relative humidity ∼60%), LFO@C still retains a high lithium compensation capacity of 418.7 mAh g–1 and simultaneously exhibits an improved Li+ diffusion coefficient of 4.56 × 10–14 cm2 s–1 (vs 1.93 × 10–14 cm2 s–1 for pristine LFO after 6 h air exposure). When integrated into NCM9055 cathodes, the LFO@C additive improves the initial Coulombic efficiency of full batteries by 7.4% and enhances the capacity retention by 4.9% after 300 cycles at 0.5 C. In addition, the solid-state battery based on the LFO@C-incorporated NCM cathode demonstrates excellent resilience to mechanical abuses. This work offers a practical and scalable strategy for engineering air-tolerant prelithiation additives for LIB cathodes, advancing the manufacturability and performance of next-generation batteries.