Electrochemo-Mechanical Modeling Of Porous Electrode In Lithium-Ion Batteries And Its Application In Design

The porous electrodes in the lithium-ion batteries are the core parts for energy storage,whose porous structure strongly influence the battery performance.To further improve the energy density of batteries,the silicon-based material,which owns large energy density,is a competitive candidate as electroactive materials for lithium-ion batteries to substitute the conventional graphite material.Due to the large expansion ratio of the silicon-based material,the electrochemo-mechanical coupling effect becomes more significant.Thus,for the structural design and mechanism anaylsis of the porous electrode made by silicon-based material,developing the electrode model which can describe the interaction of electrode structure and multiphysical processes is important for the further commercialization of silicon-based materials.In this work,taking the silicon monoxide(Si O)as the investigated material,the electrochemo-mechanical electrode model for silicon-based material is derived.Then,the model is verified through the results of multiscale electrochemical characterization tests.Finally,the design problems in material,electrode and cell scales respectively are analyzed using the electrode model,and the advices for battery design of silicon-based materials are proposed.Firstly,the Si O single particle microelectrode is fabricated using the micro-nano manufacturing system and the material is characterized through electrochemical experiments.The data in this part is the basics for the following modeling work.Secondly,the single particle electrochemo-mechanical impedance model is derived.Considering a single electroactive particle in the electrode,the electrochemo-mechanical impedance model for a single particle,which considers the influence of the coupling between the ionic diffusion and surface reaction with the diffusion-induced stress,is derived.Through numerical simulation and analysis,the 45° line in the low frequency range of the Nyquist plot is transformed into a semicircle,which is induced by the diffusion stress and the reason for the formation of the semicircle and under which circumstance it can be visualized are analyzed.Through fitting the impedance model to the EIS data of the Si O single particle electrode,the kinetical properties of the Si O are measured.Based on the single-particle impedance model,the electrochemo-mechanical impedance model for the porous electrode is derived.The contact stress is found to weaken the effect of the diffusion stress.Then,the effective Young’s modulus of the electrode and the binding effect of the substrate to the electrode layer is analyzed.In addition,considering that the stress effect and ionic diffusion in the electrolyte can both influence the impedance in the low frequency range,their interaction is analyzed using the impedance model.Thirdly,based on the single-particle impedance model,the time-domain electrochemo-mechanical model for a single particle is derived using the finite deformation theory.The model is validated through the experimental results of the Si O single-particle electrode.Then,the time-domain electrochemo-mechanical model for the porous electrode is derived based on the time-domain electrochemo-mechanical model for a single particle.The delithiation process of the electrode at high C rates is analyzed,the results shows that the severe reaction concentration phenomenon in the center part of the electrode occurs at high C rates.Additionally,through comparing the full model with different simplified model,neglecting the diffusion stress and the variation of pore structure can lead to a bias up to 30% compared with the full model,indicating that the two factors are found to be the two predominant factors which influences the model accuracy.For silicon-based batteries,the influence of mechanical properties on the electrochemical processes needs to be considered and the electrochemo-mechanical model is necessary for the analysis of the silicon-based batteries.Finally,using the time-domain electrochemo-mechanical model for porous electrode,the design factors at the material,electrode,and cell scales,which are the Young’s modulus of the binder,electrode porosity,and clamping pressure respectively,were analyzed and discussed.The corresponding design opinions for silicon-based materials are given.