Study On Dendrite Growth Mechanism Of Lithium Battery By Phase Field Method

Lithium metal is one of the cathode materials with great application prospect in the next generation energy storage system.However,the existence and growth of lithium dendrite can lead to thermal runaway in the battery,which seriously limits its sustainable development in the battery field.In conventional liquid electrolytes,lithium dendrites can cause a short circuit inside the battery,leading to thermal runaway problems.Even in solid electrolytes with high mechanical strength,the high mechanical strength of lithium dendrites can still cause electrolyte damage.Aiming at the problem of lithium dendrite to batteries and other problems,this paper established the phase field model of lithium dendrite growth in solid/liquid electrolyte under the multi-field coupling of force,electricity and chemistry,explored the influencing factors of dendrite growth,and provided theoretical guidance for the subsequent optimization of the performance and structure design of solid electrolyte.The research content of this paper mainly includes the following three aspects:(1)Phase-field simulation of lithium dendrite growth by liquid electrolytationelectromultiphysical field coupling.Firstly,phase field sequence variables were introduced to describe the interfacial states of dendrites.Based on the basic Gibbs free energy and interfacial energy,the phase field model of dendrite growth in liquid electrolyte was established.The accuracy of the model is verified by the comparing between the one-dimensional simulation results with the experiments.On this basis,the morphology evolution of single dendrite and multi-dendrite was simulated,and the effects of anisotropic strength,initial angle and modulus on the morphology of dendrite were analyzed.The results show that polydendrites tend to grow longitudinally and form short circuit more easily.In addition,the anisotropic strength and initial angle have great influence on the dendrite morphology,that is the anisotropy intensity is large and the initial angle is small,the primary dendrite growth is accelerated and the secondary dendrite is inhibited.(2)Phase field simulation of lithium dendrite growth in solid electrolyte with force-electrochemical multifield coupling.Considering the interaction between dendrites and the surrounding solid electrolyte during the growth process,the elastic potential energy is introduced.The phase field model of dendrite growth in solid electrolyte was established based on Gibbs free energy,interfacial energy and elastic energy.The evolution of single and multi-dendrite morphology and the evolution of stress and lithium concentration were simulated.The effects of mechanical properties,anisotropic strength,interfacial mobility coefficient and electrode surface conductivity on the morphology and stress distribution of lithium dendrite were analyzed.The results show that from the point of view of the stress distribution,the destruction degree of multiple dendrites to the electrolyte is greater,and the inhibition effect of neighboring dendrites is more obvious.In addition,the simulation results show that the growth of single/polydendrite is inhibited by the higher mechanical strength,higher anisotropy strength,higher interfacial mobility coefficient and lower electrode conductivity,but the stress of single/polydendrite increases.(3)Phase-field simulation of crack growth in solid electrolyte.The phase field variables were introduced to simulate the crack growth at the interface between electrode and electrolyte in solid electrolyte under force-electric multi-field coupling to further explore the failure mechanism of interface defects on solid electrolyte.The results show that in the early stage of crack initiation,there is stress accumulation,and the crack growth laterally first,and then tend to grow longitudinally at the later stage,which is more humful the electrolyte.At the same time,the relationship between the crack,overpotential and current density is qualitatively studied.It is found that the current density around the crack is high and there is certain overpotential.