Study On Mechanism Modeling And Impact Factors For The Cycling Process Of Lithium-ion Batteries

Lithium-ion batteries(LIBs)have become the preferred technology for portable devices,electric vehicles and energy storage systems benefited from its high energy density,long cycle life and low self-discharge rate,which is regarded as the key technology to solve the environmental pollution and energy shortage issue.The further industrial application and development of lithium batteries require high requirements for battery charging speed,endurance capability,and capacity retention during long-term operation.These macroscopic performances of lithium-ion batteries are strongly related to the microscopic structure inside the electrode.Meanwhile,there are intricate and irregular electrode morphology interacting with reaction-diffusion processes at various length scales.There is no confirmed concusion on the mechanism of how the internal microstructure affects the long-term performance of the battery yet.Establishing a mechanism model that accurately describes the physicochemical processes within the electrode can reveal the structureperformance relationship by visualizing the dynamic evolution of unobservable variables inside the battery.And the combination of mechanism model and optimal algorithm enables the design of battery microstructure and delving deeper into unlocking the performance potential of batteries.However,existing electrochemical models are primarily described by partial differential equations(PDEs),which are difficult to be solved with the consideration of irregular solidliquid phase boundaries.Therefore,the computation efficiency of existing electrochemical models is hard to meet the requirement of predicting long-term battery performance and optimizing multiple parameters.In this paper,cellular automata(CA)technology is applied to reconstruct the irregular solid-liquid phase boundary conditions,and a multiscale model is established by combining CA and PDEs,in which the macroscopic performance is contacted with the microscopic structure while the computational efficiency is ensuring.On this basis,the impact of different electrode structures on the short-term operational performance and long-term aging processes of batteries are investigated,furthermore,the key structural parameters of the electrode are optimized to improve the life-cycle performance of the battery,and further to guide intelligent design of the electrode structure.The research work is detailed in the following four parts:Preliminary investigations of the CA technology are first conducted to address the issue that traditional electrochemical models struggle to accurately simulate long-term cycle processes and perform multi-parameter optimizations when considering irregular electrode morphologies.The perspective of CA modeling brings the possibility of efficient simulation of reaction-diffusion process under irregular phase interface,in which the material evolution rules are extracted from phenomena.The CA framework is used to simulate the lithium-ion evolution process of diffusion,reaction and phase transition,and the simulation results are compared with those obtained by traditional PDE model.It is proved that CA can provide high computational efficiency and well visualization effect when dealing with irregular solid-liquid boundary and moving phase interface,which lays a foundation for the simulation of complex multi-scale processes with lower computational cost.Further,the physical-chemical processes inside the battery are divided in order to introduce CA into traditional electrochemical model.Irregular phase boundaries or moving phase interfaces are described by CA,while aspects involving mass and energy conservation in physical fields are described by PDEs.Then the multi-scale model is established by setting the information interaction between the models.Through the established model,the evolution process of unmeasurable variables such as concentration and potential within different electrode structures during a single charge cycle can be obtained.So that the microscopic process mechanisms of how electrode morphology influences battery performance can be revealed,and the dominant mass transfer resistances at various positions within the electrode can be analyzed,then the targeted adjustments and design of electrode structures can be realized to enhance battery performance.Then,next aim is to solve the issue that the battery aging curve,including linear decay stage and nonlinear decay stage,is difficult to predict,and the internal mechanism is not clear.Based on the established model,two aging side reactions i.e.the growth of solid electrolyte layer(SEI)and lithium deposition,are considered on the surface of electrode particles.The battery aging process during long-term cycle operation are simulated,and the competition mechanism of the two aging factors under different electrode internal structures are explored.Theoretical basis is provided for the accurate identification of the inflection point between the linear aging stage and the nonlinear aging stage.Finally,the single charge efficiency performance during short-term operation and the capacity retention performance during long-term operation are considered comprehensively in electrode structure design.Considering the design of electrode structure is difficult to consider various battery performance and impact factors,a Bayesian optimization method is combined with the established electrochemical model,and the optimal electrode structure can be found with high optimization efficiency.In addition,the electrode structure can be improved and designed by setting the weight of each performance index in the objective function.In summary,a systematic research framework,from multi-scale electrochemical modeling to electrode structure – battery performance relation investigation and to electrode structure optimization,is established.This framework could pave the way for the development of an efficient battery design-to-use lifecycle performance optimization system,and the potential of battery performance can be exploited through the internal microscopic mechanism,further to promote the development of lithium battery industry.