Impact of Conductive Agents in Sulfide Electrolyte Coating on Cathode Active Materials for Composite Electrodes in All-Solid-State Batteries

All-solid-state batteries (ASSBs) with sulfide-based solid electrolytes (SEs) are promising next-generation lithium-ion batteries owing to their high energy density and safety. The composite electrode is crucial in electrochemical performance, and SE coating on the cathode active material (CAM) is an effective strategy for improving the composite electrode structure. However, despite the importance of conducting agents (CAs) in composite electrodes, their impact on the SE coating process has not been thoroughly investigated. Here, the effect of CA incorporation during the SE coating process on the morphology of the coating layer, composite electrode structure, and resulting electrochemical performance of ASSBs were examined. When the SE coating excluded CA (SE@CAM), a dense SE layer was formed on the CAM surface. By contrast, incorporating carbon black (Super P) during SE coating (SE–SP@CAM) resulted in a Super P-rich SE coating layer, reducing the active surface area and electrical conductivity of electrode and resulting in poor electrochemical performance. Meanwhile, incorporating vapor-grown carbon fibers (VGCF, 1D CA) during the SE coating process (SE–VGCF@CAM) resulted in the formation of VGCF-embedded SE coating layer. This enlarged the active surface area and facilitated electron conduction, yielding an electrochemical performance higher than that of SE–SP@CAM and comparable to that of SE@CAM. This study revealed the impact of CA incorporation during the SE coating process on the morphology of the coating layer and composite electrode structure. Furthermore, it emphasizes the importance of the mixing protocol and CA selection in electrode fabrication, offering valuable insights into developing high-performance ASSBs.