Anionic Substitution as A Pathway to Enhanced Charge-Transfer Kinetics and Cyclability of Lithium-Rich Sulfide-Based Cathodes

Rechargeable batteries with cost-effective and environmentally friendly electrode materials are essential for the development of next-generation Li-ion batteries. In this regard, low-cost, and safe positive electrode materials such as Li₂FeS₂ are good candidates due to their multi-electron redox behavior. In this study, we aim to investigate the impact of anion(O) substitution on the properties of the Li₂FeS_2-xO_x cathode material via two-step solid-state method. In-situ and ex-situ Techniques have been utilized to establish a correlation between material properties and the redox behavior of the cathode materials. We examined the electron density distribution of both pristine and Li₂FeS_2-xO_x using X-ray absorption spectroscopy (XANES). The surface morphology and microstructure of the cathode material were studied using a Scanning electron microscope (SEM) and Transmission electron microscopy (TEM), while Galvanostatic charge-discharge (GCD), CV, and galvanostatic intermittent titration technique GITT measurements were conducted to evaluate the electrochemical performance and charge transfer mechanisms. DFT calculations were employed to support our experimental findings on Li⁺ diffusivity and material stability. This study revealed that oxygen-incorporation improved the air stability of the material, long-term cyclability, and enhanced the charge transfer kinetics of the cathode material. As a result, Li₂FeS_1.8O_0.2 achieved a capacity of 310 mA h g⁻¹ after long-term cycles. The charge transfer has been greatly improved by the partial substitution of oxygen (70 Ω) as compared to that of the bare sample with 110 Ω. This improvement is due to the improved interfacial stability of the oxygen-substituted sample (Li₂FeS_1.8O_0.2). In conclusion, the comprehensive characterization and experimental results highlight the potential of Li₂FeS_2-xO_x as a promising cathode material for advanced lithium-ion battery applications. The study's detailed insights and experimental outcomes will be presented, along with reflections on future directions in the field.