Mechanical Failure Modes and Effect on Electrochemical Performance for Conventional LiCoO₂ Electrodes for Flexible Li-Ion Batteries

As the demand for flexible electronic devices like wearables and foldable gadgets increases, it becomes necessary to develop appropriate components such as flexible batteries. While there has been progress in flexing entire battery cells during electrochemical cycling, further research is needed to understand how mechanical failure affects individual battery components, especially the electrodes, after flexing. In this study, we intend to highlight how characteristics of various lithium cobalt oxide (LCO) electrodes, such as particle size and mass loading differences, impact mechanical failure during flexing. This will entail an analysis of bending diameters corresponding to curvature angles and flexing duration, as well as studying the electrochemical performance of the electrodes after repeated bending (up to 3000 times) at diameters of 100, 50, and 25 mm. The mechanical strength (cohesion and adhesion properties) of the bent electrodes was evaluated through peel and scratch tests after undergoing flexing under different bending conditions. Optical and scanning electron microscopy were used to observe the mechanical failures on the surface and cross-section of the peeled and scratched electrodes after bending. The findings reveal that using a smaller LCO particle size can improve the durability of flexible electrodes, while high mass loadings cause formation of distinctive pore distribution with microcracks that propagate across the cross-sectional microstructure. Additionally, certain electrode microstructures can allow for mitigation of the deleterious effect of bending on the discharge capacity obtained at different C-rates.