Peter Stein's blog

Investigations on the fast capacity loss of Lithium-ion batteries (LIBs) have highlighted a rich field of mechanical phenomena occurring during charging/discharging cycles, to name only a few, large deformations coupled with nonlinear elasticity, plastification, fracture, anisotropy, structural instability, and phase separation phenomena. In the last decade, numerous experimental and theoretical studies have been conducted to investigate and model these phenomena.

The demand for higher specific capacity and rate capability has led to the adoption of nanostructured electrodes for lithium-ion batteries. At these length scales, surface effects gain an appreciable impact not only on the electrochemical and mechanical behavior of the electrode material, but also on defect thermodynamics. The focus of this study is the distribution of surface-induced bulk stresses in a LiCoO2 nanoparticle and their impact on the migration of Li vacancies. LiCoO2 is a prototypical cathode material, where the diffusion of Li is mediated by the vacancy mechanism.

The size- and shape-dependency of the chemo-mechanical behavior of spherical and ellipsoidal nanoparticles in Li-ion battery electrodes are investigated by a stress-assisted diffusion model and 3D finite element simulations. The model features surface tension, a direct coupling between diffusion and elasticity, concentration-dependent diffusivity, and a Butler-Volmer relation for the description of electrochemical reactions that is modified to account for mechanical effects.