软包磷酸铁锂电池高电压浮充后热安全研究

Research on thermal safety of soft-pack LiFePO4 battery after high-voltage float charge

磷酸铁锂电池以其较好的安全性在储能领域得到了广泛应用。本工作以额定容量21 Ah的软包磷酸铁锂电池为实验对象,在25℃下以4.05 V、4.25 V、4.50 V和5.0 V高电压下浮充电24 h。研究单体高温热失控和材料热稳定性。结果表明,在4.25 V、4.50 V和5.0 V电压下均出现鼓胀,电压升高鼓胀加剧。在5.0 V电池破裂,负极活性材料溶解,铜集流体裸露,同时出现大量锂沉积。在4.05 V、4.25 V和4.50 V下浮充后的高温热失控试验中发现,随电压升高电池破裂温度下降,热失控触发温度由249.86℃升至278.65℃,提前破裂释放能量使得热失控触发温度升高,但并不具有较好的安全性,热失控最高温度由484.67℃升至516.08℃,最大温升速率也明显升高,且热失控触发到最高温度时间缩短,高电压浮充后电池热稳定性变差,热失控更加剧烈。隔膜在120.63℃开始发生相变,在367.06℃开始分解。而正、负极未出现明显分解,其自身热稳定性较好。因此应避免高电压使用,保持电池安全使用和稳定运行。

LiFePO_(4) batteries are widely used in the field of energy storage because of their safety.The test object was a soft-pack LiFePO_(4) LFP battery with a rated capacity of 21 Ah that was float-charged at high voltages of 4.05 V,4.25 V,4.50 V,and 5.0 V for 24 h at 25℃.The high-temperature thermal runaway and battery material thermal stability were investigated.The results show that bulging occurs at voltages of 4.25 V,4.50 V,and 5.0 V,and the bulging increases as the voltage increases.At the 5.0 V battery rupture,the anode active material was dissolved,the copper current collector was exposed,and a substantial amount of lithium was deposited simultaneously.In the high-temperature thermal runaway test after float charging at 4.05 V,4.25 V,and 4.50 V,the battery's rupture temperature decreased as the voltage increased.The thermal runaway-triggering temperature increased from 249.86℃to 278.65℃,and the early rupture-released energy raised the thermal runaway trigger temperature;however,the system was unsafe.The maximum temperature of the thermal runaway increased from 484.67℃to 516.08℃,the maximum temperature rise rate also increased significantly,and the time of thermal runaway to the maximum temperature decreased.The battery's thermal stability deteriorated after high-voltage float-charging,and the thermal runaway became more severe.The separator begins to undergo a phase transition at 120.63℃and begins to decompose at 367.06℃.However,the positive and negative electrodes did not decompose and had good thermal stability.Therefore,the float voltage must be precisely controlled to make the battery safe and stable to use.