Understanding the Electrochemical Performance of FeS2 Conversion Cathodes

Conversion cathodes represent a viable route to improve rechargeable Li+ battery energy densities, but their poor electrochemical stability and power density have impeded their practical implementation. Here, we explore the impact cell fabrication, electrolyte interaction, and current density have on the electrochemical performance of FeS2/Li cells by deconvoluting the contributions of the various conversion and intercalation reactions to the overall capacity. By varying the slurry composition and applied pressure, we determine that the capacity loss is primarily due to the large volume changes during (de)lithiation, leading to a degradation of the conductive matrix. Through the application of an external pressure, the loss is minimized by maintaining the conductive matrix. We further determine that polysulfide loss can be minimized by increasing the current density (>C/10), thus reducing the sulfur formation period. Analysis of the kinetics determines that the conversion reactions are rate-limiting, specifically the formation of metallic iron at rates above C/8. While focused on FeS2, our findings on the influence of pressure, electrolyte interaction, and kinetics are broadly applicable to other conversion cathode systems.

Automated summary

Conversion cathodes have the potential to improve energy densities in rechargeable Li+ batteries, but their limited electrochemical stability and power density have hindered their practical use. In this study, we investigate the effects of cell fabrication, electrolyte interaction, and current density on the electrochemical performance of FeS2/Li batteries. The capacity loss is primarily attributed to the large volume changes during (de)lithiation, leading to the degradation of the conductive matrix. However, by applying external pressure and increasing current density, the capacity loss and polysulfide loss can be minimized.