<p>Oxygen-deficient crystalline LiSiO_2−x materials for the anode of all-solid-state lithium batteries (ASLBs) were prepared using a sol-gel and reduction process. The resulting powder exhibited a lithium-rich, oxygen-deficient composition, which was approximated as Li_1.2Si₁O_1.86 by combining the bulk Li/Si ratio obtained from ICP–OES with the surface O/Si ratio derived from XPS analysis. The change in oxygen content on the particle surface was examined by X-ray photoelectron spectroscopy, indicating that oxygen deficiency was optimized when heat-treated at 700&#xa0;°C after silicon addition. The powder was then mixed with graphite (Gr), Li_6.25Al_0.25La₃Zr₂O₁₂ (LLZO), polyethylene oxide (PEO), and Super-P in specific ratios to form a composite anode. To investigate the effect of silicon oxide on the anode, the LiSiO_2−x:graphite ratio was varied across three compositions (10:0, 5:5, and 2:8). ASLBs were fabricated using a half-cell configuration with 2032-coin cells, consisting of a working electrode made of LiSiO_2−x composite anode, a solid electrolyte composed of LLZO-PEO composite film, and a lithium metal counter electrode. No liquid electrolyte was used, and LiClO₄ salt was incorporated into both the anode and electrolyte. Electrochemical testing revealed that the cell with a Si: Gr ratio of 2:8 exhibited an initial capacity of 360 mAh g^− 1, confirming reduced irreversible capacity loss during cycling.</p>