Study On Internal Thermal Strain Characteristics Of Lithium Batteries At High C Rates Under Low Temperature

Lithium batteries on aircraft generally experience the low temperature environment in the high altitude.However,current research on lithium batteries has not focused on lowtemperature internal characteristics.Therefore,it is necessary to understand the internal temperature and thermal strain generation rules and mechanism of the lithium battery during charging and discharging in a low temperature environment.In this experiment,the embedded sensor lithium battery is designed for the special structure of the soft pack lithium battery,which can collect the internal state parameters of the lithium battery in real-time and accurately.It can reduce the experimental error and ensure the accuracy of the data.The experiments were performed in a low-temperature experimental chamber.High C rates(1C,2C,3C)charge and discharge experiments were performed at normal temperature(25 ?)and low temperature(10 ?,0 ?,-10 ?,-20 ?).From the aspects of charge and discharge time,capacity,internal maximum temperature,internal maximum strain,and electrochemical reaction of lithium batteries,the internal state changes of lithium batteries under low temperature environment are studied.The experimental results show that the charge and discharge time and capacity of the lithium iron phosphate battery decrease as the ambient temperature decreases,and the internal temperature and internal strain increase with the decrease of the ambient temperature.When the ambient temperature decreases by about 10 ?,the charge and discharge time also decreases.The corresponding reduction is about 10%.At 25 ?,10 ? and 0 ?,the battery shows a flat and long voltage plateau,but when the temperature is-10 ?,-20 ?,the voltage will rebound during the initial charge and discharge.In this paper,the experimental results are verified by theoretical calculation.Referring to previous analytical solution of temperature field and thermal stress field of lithium battery.The maximum internal temperature of the lithium battery at 25 ? is calculated to be 39.8 ?,which is 1.9 ? lower than the maximum temperature of 41.7 ? obtained from the experiment.Therefore,in addition to excluding experimental errors and calculation errors,the experimental results are considered accurate.According to the experimental data,the temperature coefficients of the Bernardi heat generation model at low temperature are calculated,which are 0.279 mV/K at 25 ?,0.355 mV/K and 0.362 mV/K at 10 ? and 0 ?,and-10 ? 0.482 mV/K and 0.511 mV/K at-20 ?.This article provides a certain theoretical support for the future research on the safety of on-board lithium batteries and the airworthiness verification of China's civil aviation full-electric and multi-electric aircraft.