Air-stable Li₅FeO₄ additive enabled by carbon coating for energy-dense lithium-ion batteries

Li₅FeO₄ is a promising pre-lithiation additive for the positive electrode in lithium-ion batteries, offering the potential to enhance energy density. However, its susceptibility to air degradation presents a significant challenge for commercialization. In this study, we develop an effective carbon coating strategy utilizing pitch to improve the air stability of Li₅FeO₄. The coating process results in the formation of a compact carbon layer on the surface of Li₅FeO₄ particles, enabling the coated Li₅FeO₄ to retain a high specific capacity of 743.4 mAh g^-1 after 72 h of exposure to air with 20% relative humidity. This retention represents 92.3% of its initial capacity and 85.7% of its theoretical maximum capacity. In contrast, uncoated Li₅FeO₄ undergoes rapid degradation, losing most of its electrochemical activity within just 4 h under identical conditions. Beyond improving air stability, the carbon coating enhances Li₅FeO₄'s specific capacity, rate capability, and cycling stability. To substantiate the practical application of carbon-coated Li₅FeO₄, we construct a pouch-type cell, which exhibits a 13.7% increase in energy density compared to the cell without the prelithiation additive. These findings collectively suggest that the carbon-coated Li₅FeO₄ represents a viable strategy for advancing the commercial deployment of this material in lithium-ion batteries.