| Due to the booming development of the industry of electric vehicles(EVs),the demand for traction batteries is increasing rapidly.However,driving mileage is still the main challenge restricting the development of EVs because of the low theoretical energy density of the graphite anode(～372mAh/g).Li metal is one of the most potential candidates for anode materials for EVs,owing to its high theoretical energy density(～3860mAh/g).However,during cycling,the formation and propagation of Li dendrites cause the rupture and failure of solid-electrolyte interphase(SEI),internal short-circuit,etc.,thus,resulting in the battery capacity attenuation and Coulombic efficiency reduction,and even leading to safety problems such as thermal runaway or fire propagation.Therefore,Li dendrites impede the commercialization of high-energy Li metalbased batteries.Furthermore,interfacial contact loss generated in Li stripping will cause uncontrolled Li dendrite nucleation and growth and the degradation of cycling performance or even battery failure.As a result,to effectively suppress Li dendrites and achieve the practical applications of Li-metal batteries,the interfacial contact and the related multi-physical interaction mechanisms during Li dendrite growth should be systematically investigated,which includes mechanical,thermal,electrochemical,etc.Unfortunately,the real-time characterization and quantification of interfacial contact,Li dendrite growth,propagation,and interactions with SEI/solid electrolyte is hindered by the enclosed packaging and complex working conditions.The finite element method and phase-field model,which can bridge the microstructure and macroproperties of materials,are powerful in exploring Li dendrites and Li stress.However,the published Li dendrite models either assume a pseudo-SEI layer that ignores the mechanical interaction with Li dendrites or deformation,or does not include the Li stress(especially Li creep stress),or are not bridged the Li dendrite growth and the macroscopic cell performance and its underlying mechanisms.Additionally,the mechanism of Li/solid electrolyte interfacial contact loss is still unclear.To solve these problems and construct efficient fullfield models to investigate the Li dendrite and Li stress,this work focuses on forming finite-element-based or phase-field-based models that can explore the moving and deformation of SEI layer,the failure of solid electrolyte,the internal short-circuit,Li creep stress,and deciphering the related mechanisms.The developed models are then applied to accelerate the designing and strategies of the suppression of Li dendrite as well as the commercialization of Li-metal batteries.The details of the work include:(1)A general creep/contact electro-chemo-mechanical model is developed to reveal the mechanisms of void formation during stripping.The creep stress evolution of Li metal is calculated by introducing a novel FSI theory where the strain-rate-dependent creep deformation is analogous to the incompressible viscous fluid flow.Based on the present model,the dominant mechanism that impedes void formation is the creep-induced flux enhancement of vacancies,which are transported into Li metal for a non-ideal Li/SE interface with preexisting interfacial defects.This contrasts with the previous simulations on an ideal flat Li/SE interface in which the vacancy diffusion away from the interface was shown to govern whether voids are formed.(2)A phase-field Li dendrite-creep stress mechano-electro-chemical model is developed.The influence of mechanical stress on the microstructure evolution of lithium dendrites is introduced to an electrochemical-mechanical phase-field Li dendrite model based on the modified Butler-Volmer equation.Additionally,the model establishes a link between the deposition rate of Li dendrite and the creep deformation rate of Li metal,capturing the creep stress during electrodeposition.Based on the present model,the effects of operation conditions,grain boundary,and contact losses at the Li/SE interface on the evolution of the Li dendrite microstructure and the corresponding Li creep stress are revealed.The results show that maintaining a low roughness at the Li/SE interface can alleviate the pulverization of the Li anode due to lithium dendrite growth.(3)A general continuum mechano-electro-chemical phase-field Li dendriteSEI model is developed.The coupling between the diffusion interface in the phase-field model and the sharp interface in the SEI model is achieved by the bidirectional transmission of the Li dendrite growth rate and SEI mechanical stress.Thus,an electro-chemo-mechanical full-filed model(which combing the SEI mechanical model and phase-field Li dendrite model)is established,including the dynamical SEI moving,stress/strain distribution,interfacial overpotential,and morphology evolution of Li dendrite are captured selfconsistently.The results are well consistent with the experimental observations,and show the potential of this model in exploring the mechanical interaction between Li dendrite and SEI as well as the design of artificial SEI.Based on the presented model,the effects of Li/SEI morphology,SEI heterogeneity,and SEI electrochemical/mechanical properties on the moving and deformation of SEI and Li deposition were investigated.The results show that the combination of soft and hard SEI layers is a suitable choice for designing SEI.(4)A Li dendrite-full cell phase-field multiscale framework is formulated to reveal the interplay between the microstructure evolution and macro-level battery performance,and fill the gap that the multi-physical and multi-scale models with spatiotemporal resolved Li dendrite growth behavior cannot be directly used to analyze and predict the macroscopic performance of full battery cells.A bridge between the phase-field Li dendrite model and battery model is built through the phase-field order parameter and short-circuit model,which can be used to connect the microstructure evolution of Li dendrite(micro-level)and the battery voltage and internal short-circuit(macro-level).Thus,a multiscale Li dendrite-full cell model is developed for predicting and resolving the Li dendrite penetration induced internal short-circuit behavior.Based on the presented model,the relationship between Li dendrite growth and the voltage change is deeply investigated,and a theoretical model that elucidates Li penetrate depth-related battery voltage drop is established.Furthermore,the effect of the microstructure,electrochemical/mechanical properties,and operating conditions on the internal short-circuit are carefully investigated.The map of internal short-circuit risk is produced based on the charging rate and ionic conductivity(or stack pressure and GB Young’s modulus)and charging time,which can provide a safe operating workspace for batteries. |
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