Chemo-Mechanical Coupled Behaviors of Nanosized Electrode Particles in Li-Based Batteries: The Effects of Surface Stress and External Pressure

Due to close contact between various components, the volume change of active materials during lithiation or delithiation leads to inevitable constraint-induced stresses. This is particularly prominent in all-solid-state batteries, which impose relatively high external pressure on electrode particles. To date, the effects of this additional external pressure on chemo-mechanical coupled behaviors are not fully understood. To address these issues, this study develops a chemo-mechanical coupled model of electrode particles in Li-based batteries that incorporates the effects of surface stress and external pressure. The theoretical results indicate that lithiation kinetics and stress evolution within electrode particles are size-dependent, varying from bulk to nanoscale sizes. As particle size decreases, Li ions increasingly tend to accumulate near-surface storage sites, which is aggravated by external pressure due to the growing compressive stress and a resultant reduction in stress-dependent diffusivity. Moreover, the low-porosity surrounding matrix can exacerbate this tendency by amplifying the external pressure. The work enhances our understanding of capacitor-like behaviors of some nanosized electrode materials, which may arise from the combined effects of surface stress and external pressure. It also emphasizes the importance of interactions between neighboring components in chemo-mechanical coupled performance.