During thermal runaway, high-capacity lithium iron phosphate (LFP) batteries can release substantial amounts of flammable thermal runaway gas (TRG), significantly increasing the explosion risk in battery energy storage systems (BESS). This study investigates the explosion characteristics of TRG from a 280 Ah LFP battery and compares the suppression effects of premixed 2H-Heptafluoropropane (HFC-227ea) and CO2. Laminar burning velocities were calculated using experimentally measured pressure history data to validate a chemical kinetic model, facilitating the analysis of key parameters such as adiabatic flame temperature, adiabatic combustion pressure, heat release rate, and radical mole fractions. Results indicate that the explosion intensity is highest when the TRG-air equivalence ratio is 1.1, with a maximum explosion pressure (Pmax) of 0.475 MPa. 5% HFC-227ea can completely suppress the explosion, while CO2 requires an addition of 25%. Under fuel-lean and stoichiometric conditions, HFC-227ea exhibits a combustion enhancement effect, increasing Pmax by up to 23.65%, with the effect becoming more pronounced as fuel-lean degree increase. Compared with CO2, HFC-227ea significantly reduces the thermal diffusivity of TRG-air, increases heat loss during flame propagation, and removes many chain reaction radicals. Its combustion enhancement effect is tied to its suppression mechanism, here the removal of chain reaction radicals releases significant heat, while producing flammable substances such as H2 and CO, which sustain the chain reaction. These findings offer valuable insights for mitigating TRG explosion risks in BESS.