Garnet-type Li7La3Zr2O12 (LLZO) solid electrolytes are synthesized with interconnected and larger rounded particle morphologies using a cellulose template method and conventional solid-state reaction, respectively. The synthesized LLZOs are optimized and used as a solid electrolyte in a natural graphite (NG)-based composite anode in an all-solid-state lithium battery. For the LLZO with the interconnected particle morphology, the optimum heat-treatment temperature (900 °C) and LLZO content (30 wt%) are determined to result in higher ionic conductivity. That is, higher dispersion or good distribution of the interconnected LLZO (width of 1 μm or less) within the composite anode enables easier ionic conduction of the interconnected LLZO. The NG-based composite anode filled with interconnected LLZO shows effective improvement due to a well-controlled inner percolation structure, resulting in improved cycle stability and enhanced high-rate capability, compared with the composite anode embedded with conventional spherical-type LLZO particles.