High-Packing-Density Electrodes by Self-forming Ion Conduction Pathway During Charge Process for All-Solid-State Lithium Ion Batteries

The Li2S–V2S3–LiI cathode materials doped with different LiI amounts developed in this study presented a high charge/discharge capacity without solid electrolyte and carbon in the composite electrode. The reaction mechanism of the cathode materials was elucidated using a combination of analytical methods. Potential step measurements revealed that LiI doping amounts above 10 mol % largely increased the ionic conductivity of the Li2S–V2S3–LiI cathodes during charging. The X-ray computed tomography and cross-sectional SEM–EDX mapping results demonstrated that the LiI-rich domain formed from the Li2S–V2S3–LiI cathode during charging because the lithium content of the cathode material changed. These results indicated that the self-forming LiI-rich domain served as an ionic conduction pathway in the cathode matrix during the first charge cycle and improved the electrochemical performance of the cathode materials. This material design strategy for composite electrodes with self-formed ionic conduction pathways is useful for designing high packing density electrodes for all-solid-state batteries, because the capacity per composite electrode is larger than that of conventional composite electrodes consisting of solid electrolyte and electrode active material.