The Influence Of Thermal Safety Performance For Overcharged Lithium Ion Battery Under Low Pressure In Aviation

As a new energy storage devices,lithium ion batteries(LIBs)have been applied in the field of new energy vehicles and energy storage power station widely.However,the thermal runaway(TR)phenomenon of fire and burn will be happened due to the abuse behavior.The overcharge is one of the most dangerous abuse behaviors.For LIBs thermal safety in electric aircraft field,especially for the different of thermal hazard and electrochemical reaction mechanism,the overcharge aging and TR experiment of LIBs at atmospheric(95 k Pa)and low pressure(30 k Pa)environments are conducted.Combined with the principle of electrochemistry,the TR behaviors are further investigated,which can provide the theoretical basis of use,protection,monitoring and early warning for LIBs at aeronautical environment.The NCM 523 pouch LIBs as experimental samples were used to conducted TR experiment of overcharged aging battery at 95 k Pa and 30 k Pa.The research is mainly to explore the influence of different overcharge rates,cut-off voltages,and cycles on the TR characteristics of LIBs under low pressure.The experimental results show that the internal side reaction mechanisms of batteries with different rates of overcharge are different.The main reasons for the performance degradation of the 0.5 C rate overcharged battery are the loss of the negative electrode material and the thickening of the SEI layer,while the 1 C and 2C overcharged batteries are mainly due to the oxidative decomposition of the electrolyte near the positive electrode and the formation of lithium dendrites near the negative electrode.Under the atmospheric pressure,as the overcharge rate increases from 0.5 C to 2 C,the TR time of the battery is advanced by about 141 s.Under the low pressure,the TR time of the battery lags and the TR intensity decreases.The low pressure environment does not significantly inhibit the TR intensity of the 1 C and 2 C batteries.The internal mechanism of the battery overcharge with different cut-off voltages is different.Only the 4.4 V overcharged battery has serious performance degradation,mainly due to the accumulation of lithium dendrites near the negative electrode.For the 4.6 V and 4.8 V overcharged batteries,the large consumption of electrolyte and the accumulation of dead lithium are the main reasons.With the increase of the cut-off voltage,the thermal stability of the battery decreases,and the TR intensity increases,and the 4.8 V overcharged battery has a high fire hazard.In a low pressure environment,although the thermal stability of the battery is increased,the 4.8 V overcharged battery still has a high flame temperature,which needs to be guarded against.The effects of different overcharge cycles on battery performance are different.The performance of the battery with one overcharge cycle is less attenuated,while the performance of the battery with10 cycles and 20 cycles is more attenuated due to the continuous consumption of electrolyte and the increase of irreversible lithium.At the same time,with the increase of the number of cycles,the thermal stability of the battery decreases,the fire hazard increases,and the low pressure environment has no obvious effect on the TR of the battery treated by the number of overcharge cycles.Comparing the three overcharge conditions,the low pressure environment has a lower inhibitory effect on the overcharged battery with a higher cut-off voltage and a higher rate,which the TR fire hazard is still high.