Crystal structure modification enhances air stability and suppresses O2 evolution in Li5FeO4: insights from experiments and DFT calculations†

The usage of Li₅FeO₄ (LFO) as a prelithiation additive in cathodes to improve battery energy density stands out as an excellent option, boasting a remarkable theoretical specific capacity and the additional advantages of cost-effectiveness in raw materials and low preparation cost. However, the problem of stabilization in humid atmospheres and oxygen release during cycles has seriously impeded its further application. In this work, a series of Co-doped Li_5+xFe_1−xCo_xO₄ compounds were prepared at varying ratios, revealing notable structural transformations at 12.5% Co and significant improvements in air stability at 25% Co in humid environments. These advancements led to the formulation of Li_5.25Fe_0.75Co_0.25O₄ (LF6C2O), which demonstrates a higher prelithiated capacity and achieves over 200 mA h g⁻¹ in the first cycle of prelithiated LiFePO₄ batteries, all while maintaining enhanced cycle stability at a 1C high rate. Additionally, LF6C2O exhibits reduced O₂ release during prelithiation compared to LFO, a finding supported by first-principles calculations. These results highlight LF6C2O's potential as an effective cathode additive.