Oxygen-Incorporated Lithium-Rich Iron Sulfide Cathodes for Li-Ion Batteries with Boosted Material Stability and Electrochemical Performance

Affordable and environmentally friendly electrode materials with multielectron redox reactions are imperative for the advancement of next-generation Li-ion batteries. In this context, the Li-rich layered iron sulfide cathode material (i.e., Li₂FeS₂) stands out as a promising candidate due to its unique multielectron cationic and anionic redox features. However, its practical application is hampered by inherent limitations in terms of poor structural stability and cycling performance. Herein, we conduct a systematic investigation into the impact of anionic substitution, where sulfur is partially replaced with oxygen, on the structural stability, intrinsic conductivity, and electrochemical properties of the Li₂FeS₂ cathode. First-principle calculations confirm that an optimum amount of oxygen incorporation is beneficial to stabilize the crystal structure and improve Li ion diffusion. Furthermore, cathodes with oxygen incorporation exhibit significant structural stability even when exposed to air for 24 h, demonstrating resistance against moisture. The Li₂FeS_1.8O_0.2 cathode achieves a higher Coulombic efficiency of ∼100%, charge-discharge capacity of 310 mA h g^-1 after 100 cycles, and a remarkable capacity recovery of around 94% following rate capability tests spanning 75 cycles. These findings introduce an innovative anion substitution approach for the development of Li-rich layered sulfide cathode materials, effectively mitigating structural deterioration.