Polymer-based solid-state batteries (SSBs) have received increasing attentions due to the absence of interfacial problems in sulfide/oxide-type SSBs, but the lower oxidation potential of polymer-based electrolytes greatly limits the application of conventional high-voltage cathode such as LiNiCoMnO (NCM) and lithium-rich NCM. Herein, this study reports on a lithium-free VO cathode that enables the applications of polymer-based solid-state electrolyte (SSE) with high energy density due to the microstructured transport channels and suitable operational voltage. Using a synergistic combination of structural inspection and non-destructive X-ray computed tomography (X-CT), it interprets the chemo–mechanical behavior that determines the electrochemical performance of the VO cathode. Through detailed kinetic analyses such as differential capacity and galvanostatic intermittent titration technique (GITT), it is elucidated that the hierarchical VO constructed through microstructural engineering exhibits smaller electrochemical polarization and faster Li-ion diffusion rates in polymer-based SSBs than those in the liquid lithium batteries (LLBs). By the hierarchical ion transport channels created by the nanoparticles against each other, superior cycling stability (≈91.7% capacity retention after 100 cycles at 1 C) is achieved at 60 in polyoxyethylene (PEO)-based SSBs. The results highlight the crucial role of microstructure engineering in designing Li-free cathodes for polymer-based SSBs.