| The performance of lithium-ion battery is the focus of battery use,in this paper,18650ncm811 new battery and aged battery with 2750 m Ah provided by a battery manufacturer are taken as the research object.After 1500 charge-discharge cycles,the actual capacity of aging battery is 1870 m Ah,The discharge performance,heat generation law,internal resistance and entropy heat coefficient of the battery were studied by experiments.The electrochemical thermal coupling model was established to simulate the change of temperature field during battery discharge.The influence of particle radius of positive and negative electrodes on battery discharge voltage and heat generation power was also studied.After the pre-test,the new battery was discharged at 0.5c rate at different ambient temperatures(-20?,0?,25?,40?)and 25? at different rates(0.2C,0.5C,1C,2C).The discharge voltage curve,discharge capacity and the temperature change curve of the surface during the discharge process were obtained.The discharge voltage and discharge capacity increase with the increase of ambient temperature,the variation of the surface temperature of the battery decreases with the increase of the ambient temperature.The results show that the discharge capacity of new battery is 95.6% of 0.2C discharge capacity,and the discharge capacity of aged battery is 82% of 0.2C discharge capacity at 2C discharge rate at 25?,and the temperature rise of aged battery is greater than that of new battery under the same test conditions.The battery was tested by hybrid pulse capability,entropy heat coefficient and isothermal calorimetry.The charge resistance and discharge resistance of the battery under different state of charge(SOC)were obtained by the hybrid power pulse capability characteristic test.Under the same test conditions,the overall internal resistance curve of the aged battery is about 38m? higher than that of the new battery,and the internal resistance curve of the new battery is between 42 and 62m?.The internal resistance is related to the irreversible heat generation of the battery.Therefore,under the same charge and discharge conditions,the irreversible heat generation of the aged battery is much greater than that of the new battery.The reversible heat of the battery is related to the entropy heat coefficient.The entropy heat coefficient corresponding to SOC is calculated by recording the voltage temperature curves of the battery at different SOC.The entropy heat coefficient curves of the aged battery and the new battery are similar,which are positive in the range of 100% ?40% SOC,and decrease from positive to negative in the range of 30%SOC,and continue to decrease in the range of 30%? 0SOC.The entropy heat coefficient of the aged battery at 0 SOC is higher than that of the new battery,the thermal coefficient is less than that of the new battery.The thermal power curve and heat production of new and aged batteries during charging and discharging were measured by isothermal adiabatic calorimeter.At low rate of charge and discharge,the irreversible heat and reversible heat have great influence on the heat generation of the battery,while at high rate of charge and discharge,the irreversible heat has great influence on the heat generation power of the battery.After verifying the accuracy of the electrochemical-thermal coupling model,simulate the temperature field during discharge at 0.5C at 25? to obtain the transient temperature field distribution of the battery and the surrounding environment during the discharge process;change the radius of the positive and negative particles to study the particles The diameter of the battery affects the heat generation and discharge voltage of the battery.It is found that the increase in the radius of the negative electrode particles significantly increases the heat generation power.The increase in the radius of the positive electrode particles only slightly increases the heat generation power in the middle of the discharge.Increases all reduce the voltage slightly. |
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