With the evolution of energy storage, Thermal Runaway (TR) stands out as the most critical safety concern for Lithium-Ion Batteries (LIBs). This study employs a prismatic lithium battery with a nominal capacity of 40Ah, featuring Li(Ni0.6Co0.2Mn0.2)O2 as the cathode material. The investigation delves into the thermal runaway characteristics of the battery at 25%, 50%, 75%, and 100% State of Charge (SOC) in a nitrogen environment. The findings indicate: 1) an ascending trend in the highest temperatures at various points within the battery as SOC increases, accompanied by a declining trend in normalized gas production and a non-linear relationship between the heat released during TR and the stored electrochemical energy; 2) the highest temperature point withinthe battery consistently resides at the surface, offering insights for the temperature monitoring of the Battery Thermal Management System (BTMS); 3) a direct correlation between higher SOC and increased material ejection, with a mass loss rate of 25.8% at 100% SOC, a static total gas production of 2.45 mol, and a maximum explosion index of 0.2886 kPa⋅m⋅s⁻¹.