Study On Life Attenuation Mechanism And Thermal Behavior Simulation Of Lithium-ion Power Batteries

With the increasing application of lithium-ion batteries,their safety performance has become more prominent.However,only utilizing experimental methods shows some limitations to fully explain the internal micro-mechanism of lithium-ion batteries.In this thesis,based on the aforementioned point,a finite element simulation is utilized to systematically study the three key issues of capacity degradation,SEI film growth,and lithium electrodeposition:（1）Via the finite element theory,an electrochemical-thermal coupling model is established.During charging and discharging processes at low temperatures or high rates,it causes the increase of the lithium concentration gradients inside the electrode particles,which in turn leads to the degradation of the batteries capacity.It is revealed that polarization heat and ohmic heat are the dominant factors upon cycling at low and high rates,respectively.（2）On the basis of（1）,a growth kinetic model of the anode electrodes SEI films is established.Moreover,the simulation results are totally supported by some experimental results.In the initial 300 cycles of the batteries,the SEI films are quickly formed with a thickness of 8 nm.After the later cycles,the films thickness continues to increase,eventually up to 35 nm.More importantly,the formation of the SEI films result in capacity fade of 14%in lithium ion batteries.（3）Based on the phase field theory,the influence on the Li+mass transfer process on the microstructure of lithium deposition is studied.Some factors,such as,low temperatures and low-concentration electrolyte,result in aggravating the Li+concentration gradients around the electrodes,which in turn leads to uneven lithium deposition.