Review on electrode-level fracture in lithium-ion batteries

Fracture occurred in electrodes of the lithium-ion battery compromises the integrity of the electrode structure and would exert bad influence on the cell performance and cell safety.Mechanisms of the electrode-level fracture and how this fracture would affect the electrochemical performance of the battery are of great importance for comprehending and preventing its occurrence.Fracture occurring at the electrode level is complex,since it may involve fractures in or between different components of the electrode.In this review,three typical types of electrode-level fractures are discussed:the fracture of the active layer,the interfacial delamination,and the fracture of metallic foils(including the current collector and the lithium metal electrode).The crack in the active layer can serve as an effective indicator of degradation of the electrochemical performance.Interfacial delamination usually follows the fracture of the active layer and is detrimental to the cell capacity.Fracture of the current collector impacts cell safety directly.Experimental methods and modeling results of these three types of fractures are concluded.Reasonable explanations on how these electrode-level fractures affect the electrochemical performance are sorted out.Challenges and unsettled issues of investigating these fracture problems are brought up.It is noted that the state-of-the-art studies included in this review mainly focus on experimental observations and theoretical modeling of the typical mechanical damages.However,quantitative investigations on the relationship between the electrochemical performance and the electrode-level fracture are insufficient.To further understand fractures in a multiscale and multi-physical way,advancing development of the cross discipline between mechanics and electrochemistry is badly needed.

Stress-Induced Uphill Diffusion with Interfacial Contact Loss in Solid-State Electrodes

We simulate the mechanical-chemical coupling during delithiation and relaxation of a cathode in a solid-state lithium-ion battery.Contact loss at the interface between the active particle and the solid electrolyte is considered.Uphill diffusion is observed during delithiation and relaxation.This phenomenon is explained by analyzing the total chemical potential and its two components.Contact loss at the interface greatly influences the stress and stress gradient in the active particle.As delithiation continues,the stress and stress gradient grow considerably,and the mechanical part of the total chemical potential becomes dominant over the chemical part of it.In the latter stage of delithiation,the influence of the incomplete interfacial constraint on the stress becomes dominant,while the effect of the concentration gradient becomes negligible.After relaxation,the concentration and stress gradients increase in a particle with contact loss.The influence of the degree of contact loss on the mechanical-chemical coupling is investigated.The overall tensile stress in the active particle increases with decreasing contact loss,causing a sharp decrease in local concentration.We also check the effect of the elastic modulus of the solid electrolyte on the coupling of the active material.A rigid solid electrolyte with a higher elastic modulus more strongly restricts the active particle,leading to a higher tensile stress,a larger stress gradient,and a greater concentration gradient.