Unlocking Ultra-stable Li5FeO4 in Air: Key Advances and Practical Demonstrations

Li₅FeO₄ (LFO) holds great promise as a cathode pre-lithiation additive for enhancing the energy density of lithium-ion batteries. However, its significant air instability poses a formidable barrier to commercialization. In this study, we have developed an exceptionally effective “pitch-enabled carbon encapsulation” strategy to engineer ultra-stable LFO. By leveraging the meltability of pitch, a compact carbon coating can be formed on LFO (LFO@C), enabling it to retain a substantial capacity of 745.1 mAh/g even after 72 hours of exposure to air with 20% relative humidity (RH). Notably, this retained capacity after 72 hours constitutes 92.6% of its initial capacity and 85.9% of its theoretical maximum, representing the best air stability reported for LFO to date. In contrast, pure LFO rapidly declines to just 14.3% of its initial capacity within 4 hours under the same conditions. Beyond enhancing air stability, the carbon coating also improves LFO's specific capacity, rate capability, and cycling stability. To demonstrate its practical application, we assembled a pouch-type full cell on an industrial pilot line, accompanied by comprehensive failure analyses. The results indicate that the incorporation of LFO@C boosts the pouch cell's energy density by 13.7%. We believe that this work will significantly accelerate the real-world implementation of LFO.