The crucial role of mechanical stress in voltage hysteresis of lithium ion batteries in charge–discharge cycles is investigated theoretically and experimentally.

Analytical solutions of diffusion induced stress in a cylindrical multilayer electrode during lithiation are obtained. Design insights are provided by analyzing the diffusion induced stress as a function of geometrical parameters, material properties and charging procedure. It is found that the stress is induced not only by the Li-ion concentration inhomogeneity in the active layer materials, but also by the restriction of the lithiated active layer by the current collector. Curvature and thickness of electrode, as well as rigidity of current collector, have great impacts on the stresses. The maximum stress during charging can be minimized by reducing the thickness of electrode, employing soft material for the current collector and decreasing the thickness of current collector. It is also found that the ratio of maximum stress to minimum stress in the active layers can be reduced from 2.1 to 1.1 if the radius-to-thickness ratio of electrode is increased from 1 to 10. Employing this radius-to-thickness ratio provides that the maximum stresses are quite uniform in the two active layers attached on current collector, independently of lithiation or delithiation. Finally, an optimized charging procedure is suggested based on the diffusion induced stresses, i.e. galvanostatic first followed by potentiostatic.

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 multi-scale and multi-physical way, advancing development of the cross discipline between mechanics and electrochemistry is badly needed.