Mechanics in Li-Ion Batteries

High-energy density Li-ion batteries have attracted significant attention for applications in portable electronics, electric vehicles, stationary electricity storage at power stations, and load leveling of renewable sources. A Li-ion battery is a system that dynamically couples electrochemistry and mechanics. During charge and discharge of a Li-ion battery, the amount of Li in the electrodes varies substantially, causing the host electrodes to deform. The deformation induces a field of stress, which may lead to fracture or morphological change. The lithiation reactions in batteries lead to rich phenomena of mechanics in the electrodes, such as large deformation, plasticity, fracture, and fatigue. Likewise, mechanics can influence the chemistry of lithiation in a significant manner. Stress affects reactions at the interface between the electrode and electrolyte, diffusion of Li in the electrode particles, and phase transformations of the electrode materials. This chapter highlights the intimate relation between mechanics and electrochemistry in Li-ion batteries. Theories of diffusion-induced stresses, coupled Li diffusion and large elastic-plastic deformation, concurrent reactions and deformation, and fracture of electrodes are reviewed. Complementary atomistic simulations and experimental measurements that emphasize the mechanisms of chemical reactions and deformation are also described.