With the application and promotion of new energy vehicles in China, the study of aging and thermal safety performance of lithium-ion batteries in low temperature environments in winter is of great significance for the safe application of batteries. This paper selects 30 Ah prismatic LiFePO₄ batteries as experimental samples to explore the effects of ambient temperature (25 ℃, 10 ℃ and 0 ℃) on the aging and thermal safety performance of lithium-ion batteries. The results show that low-temperature aging can lead to a significant degradation in battery capacity. The electrochemical characterization, X-ray CT and SEM-EDS results show that lithium plating, electrode material damage and gas production are the main factors causing the degradation of battery cycle performance. In terms of thermal safety performance, low-temperature aging will aggravate the thermal runaway behavior of the battery, and its safety valve opening time and thermal runaway triggering time will be significantly advanced. Furthermore, by analyzing the changing trend of multi-point temperature on the battery surface during thermal runaway, it is proved that the surface temperature monitoring at the bottom of the battery (T_bot) is more suitable for accurate assessment of battery thermal runaway status. This work can provide theoretical reference and data support for the construction of safety assessment and early warning models for lithium-ion batteries under different ambient temperatures.