Study On Parameters Identification Of Electrochemical Model For Lithium Ion Battery

Battery model is mainly divided into equivalent circuit model and electrochemical model,the equivalent circuit model mechanism is to use the RC circuit to fit the external characteristic curve of the battery.The parameters have no actual physical meaning,and the model has fast simulation speed and lower precision;The electrochemical model is based on the internal reaction mechanism of the battery.By identifying the internal parameters,it reflects the external characteristics of the battery,and the simulation accuracy is high,which has practical physical meaning.It's a bridge connecting the external characteristics and the internal electrochemical reaction mechanism of the battery.However,the electrochemical model includes many parameters,each formulas are coupled to each other.The calculation amount is large and complicated,it's difficult to balance the accuracy and speed of the operation,and it cannot be widely applied.In this thesis,the contradiction between electrochemical model complexity and calculation accuracy is studied,based on a large number of model comparison and analysis,a new electrochemical simplified model is proposed,which can reduce the calculation amount to some extent under the premise of ensuring accuracy.By disassembling the battery,the actual parameters were obtained,combining with the experimental data for verification analysis.By the internal electrochemical parameters' variation,the external characteristics of the battery were analyzed.The thesis studied on following research around the modeling and simulation of the new electrochemical models and external characteristics analysis:Firstly,pseudo-two-dimensional model were introduced detailedly,it includes solid phase and electrolytic phase diffusion,solid phase and electrolytic phase Ohm' law,Butler-Volmer electrochemical reaction equation.Replace the variation of the volume current density along the thickness of the electrode by the average volume current density,three-parameter parabolic approximation equations is used to simplify solid phase lithium diffusion partial differential equations into ordinary differential equations.Based on single particle model,a new electrochemical model was established by adding the influence of the electrolytic phase concentration and electrolytic phase potential and the overpotential caused by SEI impedance on the voltage.Secondly,taking Samsung 18650 ternary battery as the research object,by disassembling the battery to obtain the structural parameters,the positive open circuit voltage expression was obtained by experiment and simulation.The parameters sensitivity analysis of the electrochemical parameters was carried out to analysis each parameter sensitivity.Through the adaptive chaotic particle swarm algorithm to identify the parameters,and the accuracy of the parameters was verified by experiment and simulations.At last,in order to study the influence of the electrochemical parameters on the external characteristics of the battery.Firstly,the cycle test of the battery was carried out,and the performance test was interspersed in two consecutive cycle life experiment.Thus the parameters of different aging stages of the battery were obtained.By identifying the electrochemical parameters at different stages of the battery,the relationship between the electrochemical parameters and external characteristics during the aging process of the battery is obtained.