Improving the Performance of LiFePO4 Cathodes with a Sulfur-Modified Carbon Layer

LiFePO₄ (LFP) cathodes are popular due to their safety and cyclic performance, despite limitations in lithium-ion diffusion and conductivity. These can be improved with carbon coating, but further advancements are possible despite commercial success. In this study, we modified the carbon coating layer using sulfur to enhance the electronic conductivity and stabilize the carbon surface layer via two methods: 1-step and 2-step processes. In the 1-step process, sulfur powder was mixed with cellulose followed by heat treatment to form a coating layer; in the 2-step process, an additional coating layer was applied on top of the carbon coating layer. Electrochemical measurements demonstrated that the 1-step sulfur-modified LFP significantly improved the discharge capacity (~152 mAh·g−1 at 0.5 C rate) and rate capability compared to pristine LFP. Raman analyses indicated that sulfur mixed with a carbon source increases the graphitization of the carbon layer. Although the 2-step sulfur modification did not exceed the 1-step process in enhancing rate capability, it improved the storage characteristics of LFP at high temperatures. The residual sulfur elements apparently protected the surface. These findings confirm that sulfur modification of the carbon layer is effective for improving LFP cathode properties, offering a promising approach to enhance the performance and stability of LFP-based lithium-ion batteries.