Advantageous Li3PO4 Coating on Conductive Agents for Sulfide-Based All-Solid-State-Batteries

Sulfide-based all-solid-state-batteries (ASSBs) are garnering attentions as a next-generation battery system due to their high ionic conductivity and the ductility-derived processability. However, it is imperative to address the issue of side reactions between carbon additive-based conductive agents and solid electrolytes. Irreversible reactions of solid electrolytes, stemming from narrow electrochemical stability window, lead to capacity fading of ASSBs. Previous research has explored conductive agents in the form of fibers with a smaller specific surface area or reducing the proportion of conductive agents. Nevertheless, these approaches have not provided a fundamental solution. Herein, we apply an oxide coating to the surface of carbon nanofiber conductive agents to prevent interfacial side reactions between the electrolyte and the conductive agent. Through computational screening among various oxide-based coating candidates, Li3PO4 is identified as possessing the highest chemical interfacial stability and superior ionic conductivity when interfaced with cathode active materials and solid electrolytes. This approach not only preserves the electronic percolation pathway essential for high-rate capability but also effectively suppress the decomposition of solid electrolytes through a stable ceramic layer. The efficacy of the Li3PO4 coating is demonstrated through enhanced ionic conductivity by up to 150% and improved rate capability and cycle performance in ASSBs, without significant loss of electronic conductivity in the composite cathode. This work introduces a novel concept in conductive agent modification, offering significant advantages in both ionic and electronic conductivity aspects.