Interfacial engineering enables air-stable Li₅FeO₄ prelithiation additives for long-Life LiFePO₄|graphite batteries

Lithium iron phosphate (LiFePO₄, LFP)|graphite (Gr) full cells are widely used in large-scale energy storage owing to their safety and long cycling stability. However, irreversible lithium consumption during solid electrolyte interphase (SEI) formation depletes the limited lithium inventory, causing initial capacity loss and compromising the cycling stability of full cells. Lithium-rich lithium ferrite (Li₅FeO₄, LFO) has emerged as a promising cathode prelithiation additive for compensating lithium loss, but its poor air stability and moisture sensitivity restrict practical application. Herein, we introduce a TiO₂ interfacial coating strategy to stabilize LFO by constructing a nanoscale protective layer on particle surfaces. The TiO₂ coating preserves the antifluorite structure of LFO while suppressing surface degradation and improving electrode processing compatibility. The optimized 1.5% TiO₂@LFO maintains structural integrity after air exposure for 2 h and effectively mitigates slurry gelation. In LFP|Gr full cells, TiO₂@LFO delivers an irreversible delithiation plateau at 3.5–4.0 V, compensating for SEI-related lithium consumption and increasing the initial discharge capacity from 160 to 175 mAh g⁻¹. Moreover, TiO₂@LFO enables stable cycling over 500 cycles at 1C, while LFP|Gr pouch cells achieve 60% capacity retention after 2000 cycles and remain capable of powering an LED lamp. This work provides an effective interfacial engineering approach for developing air-stable LFO prelithiation additives toward practical high-energy-density lithium-ion batteries.