Phase-field Studies On Electrochemo-mechanical Behaviors Of Lithium Dendrite

With the irreversible environmental damage caused by the fossil fuels,researchers began to seek efficient ways to store energy.Lithium batteries technology is becoming more and more mature after more than 40 years’ development.As an environmental protected technology with high energy density,it has been widely used in the fields of automobile,consumer electronic products,medical devices and energy storage devices.In the future,lithium batteries will have clear applications because of the tremendous potential in energy storage.The spread of dendrites is becoming the most important problem in lithium metal batteries.In order to realize the efficient utilization of energy,the growth of lithium dendrites has become an urgent mission to finish.The generation of dendrite belongs to uneven electrodeposition in the battery system,which directly leads to the problems such as lower columbic efficiency and shorter cycle life,and is more likely to cause serious safety accidents,which greatly limits the application and development of lithium batteries.Most of the researches has only focused on the theoretical study of dendrites in pure liquid electrolyte lithium batteries.Although the mechanism of dendrites has not completed clearly,there are reliable theories to explain this phenomenon.In this paper,we started from the mechanism of lithium dendrite generation,and chose the phase field method to model the dendrite growth in lithium batteries.At present,this method can accurately explain lithium ion diffusion,potential change and phase interface migration.On this basis,the deposition behaviors of lithium dendrites are studied as follows:Through the research and results we projected,a phase-field model is proposed to simulate the growth process of dendrites and predict their morphology in battery systems,which provides a new idea for improving the structural design of lithium batteries.Our main works are as follows:(1)Based on the basic theories of interface diffusion theory,free energy theory,electrochemical theory and finite element method,the phase field method is developed to work on the basic calculation of order parameters,lithium ion concentration,potential and stress field.The morphology of dendrite in lithium battery was predicted by numerical simulation.The effects of electrochemical parameters such as potential,cumulative coefficient and anisotropic strength on dendrite morphology were discussed,and the dendrite deposition was quantitatively characterized.(2)Combining with temperature diffusion equation and stress equilibrium equation,the PFM model under the coupling of physical fields of temperature field and stress field is modified.The influence of different physical effects on dendrite morphology is discussed.The phase field model with coupling of electricity,heat and stress is established.The influence of temperature and stress on dendrite evolution morphology is simulated.Through the simulation results,it is proved that temperature has an important influence on dendrite evolution,and the mechanism of soft substrate regulating dendrite morphology through stress release is revealed.(3)The diffusion model of dendrite propagation along the crystal in solid-state lithium battery is constructed by multiphase simulation.Compared with the experimental results,the method of controlling dendrite evolution in solid electrolyte is studied by using the constructed model.The growth rate of dendrite along grain boundary was calculated,and the influence of material properties,elastic modulus,and stress on dendrite deposition was developed to find ways to suppress dendrite growth.