Lithium iron phosphate (LiFePO4) batteries, known for their high safety and long lifespan, are widely used in crucial fields such as energy storage systems and electric vehicles. During the cyclic use of batteries under various operating conditions, non-uniform deposition of lithium metal on the anode can occur. To elucidate the mechanism by which lithium plating affects the electrothermal stability of batteries and to enhance battery performance, this study designed low-temperature cycling charge-discharge experiments to induce lithium plating. Overcharging and heating experiments were then conducted on both new batteries and those with lithium plating, followed by comparative analysis. The experimental results show that, compared to new batteries, the internal resistance of batteries with lithium plating increases more rapidly with overcharge capacity. Furthermore, the thermal stability of batteries with lithium plating is significantly correlated with the degree of lithium plating; as the degree of lithium plating increases, the thermal stability deteriorates, potentially leading to thermal runaway. These findings provide important guidance for subsequent battery design optimization, charging management strategy design, battery failure prevention, and thermal runaway warning systems.