## 5 Conclusions  
In this study, the tortuosity in all-solid-state battery electrodes was systematically analyzed in relation to electrode design factors (i.e., the active material shape and size) and a process factor (pressing pressure). The experimental results are summarized as follows. 1. In the electrodes with a high active material ratio, the tortuosity values increased in the order of spherical, plate-shaped, and fibrous active materials. Because the porosity values of the electrodes using the spherical and plate-shaped active materials were almost the same, the difference in tortuosity between the two shapes was due to the difference in the complexity of the solid electrolyte path resulting from a simple shape difference. The porosity of the electrode using the active fibrous material was approximately twice that of the others because the solid electrolyte did not sufficiently fill in the micropores formed by the aggregation of the material particles. In an all-solid-state battery electrode, when a high proportion of active fibrous material is used, special attention should be paid to the low filling factor of the solid electrolyte resulting from particle aggregation. 2. As the particle size of the spherical active material increased, the degree of tortuosity also increased. When the particle sizes were 10 \(\upmu\)m and 70 \(\upmu\)m, the electrode porosity values were similar, suggesting that the 70 \(\upmu\)m active material electrode had higher tortuosity due to the poor connectivity of the solid electrolyte in the large particle gaps. The electrode with the 100 \(\upmu\)m active material showed a significant increase in porosity, implying that the increase in unfilled pores, along with the low solid electrolyte connectivity in the large particle gaps, additionally contributed to the increase in tortuosity. In other words, even if the particle size of the active material increases and the particle gaps increase under a high active material ratio, the connectivity between electrolyte particles may deteriorate as a result of the limited amount of solid electrolyte. 3. Regardless of the material shape, the tortuosity decreased with pressing pressure, and the fibrous material showed a different porosity change pattern to the others. In the electrodes containing the spherical and plate-shaped materials, the porosity change was insignificant as the pressing pressure increased, suggesting that the tortuosity decrease with the pressing pressure was simply due to the improvement in the contact characteristics between the electrolyte particles. In the case of the fibrous material, the porosity considerably changed in the low-pressure region, but there was little change in the high-pressure region. It was conjectured that the electrolyte penetrated the fibrous aggregate and filled the micropores at low pressure, while the tortuosity further decreased at high pressure as the contact characteristics between the electrolyte particles were improved. **Author Contributions:** Data curation, S.-Y.P. and J.J.; Formal analysis, S.-Y.P. ; Funding acquisition, H.-C.S. ; Investigation, S.-Y.P. and J.J.; Methodology, S.-Y.P. ; Supervision, H.-C.S. ; Validation, S.-Y.P., J.J. and H.-C.S. ; Writing--original draft, S.-Y.P. ; Writing--review and editing, H.-C.S. All authors have read and agreed to the published version of the manuscript. **Funding:** This work was supported by the National Research Foundation (NRF-2018R1A5A1025594) of the Ministry of Science and ICT and \"the Competency Development Program for Industry Specialists\" of Korean Ministry of Trade, Industry, and Energy (MOTIE), operated by the Korea Institute for Advancement of Technology (KIAT) (Grant No. P0002019, HRD Program for High Value-Added Metallic Material Expert), and was supported by the Materials Technology Institute at Pusan National University. **Institutional Review Board Statement:** Not applicable. **Informed Consent Statement:** Not applicable.