过充截止电压对NCM523电池热安全的影响

Influence of overcharge cut-off voltage on thermal safety of NCM523 battery

分别以4.40 V、4.60 V和4.80 V为截止电压,对LiNi_(0.5)Co_(0.2)Mn_(0.3)O_(2)(NCM523)软包装锂离子电池进行过充实验,并通过外部热源辐射进行热失控触发。分析电池热失控的火焰现象、起始时间、峰值温度及热释放速率,探究热失控火灾危害性;结合电化学原理对过充老化电池热失控内部反应机制进行深入分析。截止电压由4.40 V升至4.80 V,锂离子电池的火焰峰值温度由336.2℃增加到482.9℃,热释放速率峰值由3.425 kW增加到8.588 kW,热失控起始时间由397 s提前到263 s;热失控火焰喷射更剧烈。这表明,高截止电压过充造成电池热稳定性下降,且电池具有更加强烈的热失控火灾危害性。容量损失、dQ/dU及电化学阻抗分析表明,电解质氧化分解、电解质与锂的反应、锂枝晶的生成、正负极活性材料的损失以及可燃气体的积累,是导致热安全性下降的主要原因。

The overcharge experiments were carried out with LiNi_(0.5)Co_(0.2)Mn_(0.3)O_(2)(NCM523) pouch Li-ion battery at the cut-off voltages of 4.40 V,4.60 V and 4.80 V,respectively.The thermal runaway triggering was carried out by external heat source radiation.By analyzing the flame phenomenon,onset time,peak temperature and heat release rate of battery thermal runaway,the fire hazards of thermal runaway were explored,the internal reaction mechanism of thermal runaway of overcharged aging battery was further analyzed combined with electrochemical principle.When the cut-off voltage increased from 4.40 V to 4.80 V,the flame temperature of the Li-ion battery increased from 336.2℃to 482.9℃,the peak heat release rate increased from 3.425 kW to 8.588 kW,the onset time of thermal runaway decreased from 397 s to 263 s.The thermal runaway jet fire became more intense,which indicated the lower thermal stability and the more serious flame hazard at high overcharge cut-off voltage.The analysis of capacity loss,dQ/dU and electrochemical impedance analysis showed that the electrolyte oxidative decomposition,the reaction between electrolyte and lithium,the formation of lithium dendrites,the loss of cathode and anode active materials and the accumulation of combustible gas were the main reasons for the decrease of thermal safety.