Abstract:

Lithium ferrate Li₅FeO₄ is a promising cathode prelithiation additive for lithium-ion batteries, boasting a high theoretical capacity of 867 mAh g⁻¹, which compensates for lithium loss due to solid electrolyte interphase (SEI) formation during the initial cycle. However, its practical application faces significant challenges due to inherent chemical instability. The material is extremely sensitive to air, readily undergoing deleterious side reactions with atmospheric carbon dioxide and moisture to form electrochemically inert Li₂CO₃ surface layers. This degradation in the atmosphere presents several major issues. It not only substantially reduces active lithium content but also induces severe slurry gelation during electrode manufacturing. In addition, it promotes continuous gas generation and electrolyte decomposition during battery operation, and leads to a significant increase in electrochemical impedance. Previous stabilization attempts via carbon coating or metal doping have shown limited success, often introducing new problems such as capacity reduction or inadequate protection, highlighting the urgent need for a more comprehensive and effective modification method. To address these challenges, this study proposes an efficient Lewis acid-induced regeneration strategy through thermal modification with PF₅. This approach effectively removes surface inert impurities and facilitates the in-situ construction of a composite layer of Li₃PO₄ and LiF on the Li₅FeO₄ particles. The regenerated Li₅FeO₄ exhibits excellent dispersion, air stability, and electrolyte interfacial compatibility, effectively suppressing slurry gelation and interfacial side reactions. In comparison with the bare counterpart, the regenerated Li₅FeO₄ shows a significantly reduced viscosity upon slurry processing and gas generation during high-temperature storage. When 1.5% (wt) regenerated Li₅FeO₄ is introduced to the LiFePO₄ cathode in the full cells, the cathode maintains a high capacity of 135.0 mAh g⁻¹ and a retention rate of 95.3% after 200 cycles. In contrast, the control LiFePO₄ cathode without Li₅FeO₄ only retains 113.7 mAh g⁻¹ with a capacity retention of 92.2%. This approach integrates impurity removal, interfacial stabilization, and performance enhancement of Li₅FeO₄ into one strategy, which will find extensive applications in long-cycle lithium-ion batteries.

Key words: Lithium-ion battery, Cathode prelithiation, Li₅FeO₄, Lewis acid, Regeneration