Lithium-ion batteries have become central to the battery industry due to their eco-friendliness and excellent performance, resulting in a sharp increase in demand. However, this rising demand is leading to supply challenges for lithium and other minerals, while there is still no established method for the disposal of spent lithium-ion batteries, which raises environmental concerns. To address these issues, research is being conducted on recycling spent lithium-ion batteries, with direct recycling of spent cathode materials receiving particular attention. However, spent cathode materials often experience structural degradation due to prolonged charge/discharge cycles, and to be reused in new lithium-ion batteries, these materials must recover their original layered structure. In this study, we analyzed the temperatures at which spent cathode materials (LiNi0.6C0.2Mn0.2O2) thermodynamically form a layered structure through XRD structural analysis in the range of 700 °C, 800 °C, and 900 °C. The spent cathode materials exhibited the highest I003/I104 value of 1.44 when heat-treated at 800 °C, compared to 700 °C and 900 °C. Additionally, the specific capacity at 0.1 C was highest at 171.3 mAh/g for the material heat-treated at 800 °C. Through this, we identified 800 °C as the optimal temperature for thermodynamically forming the layered structure, successfully restoring the structure of the spent cathode material.