Understanding of degradation mechanisms in batteries is essential for the widespread use of eco-friendly vehicles. Degradation mechanisms affect battery performance not only individually but also in a coupled manner. Solid electrolyte interface (SEI) formation deteriorates battery capacity through consuming available lithium ions. On the other hand, as the SEI layer grows over multiple cycles, the level of mechanical constraints is changed, which can affect the fracture behavior of the active particles. We investigate the effect of the SEI layer growth on the fracture probability of the electrode particles. The simulations show that as the SEI layer grows, tensile stress inside the active particles turns into compressive stress, reducing the probability of particle fracture. Once the SEI layer is fractured, the particle fracture is sequentially more likely to happen because the SEI constraint is removed. The study emphasizes that the stability of SEI layers is important because it helps in alleviating electrochemical performance fade as well as mechanical failure probability. In addition, the SEI layer on small particles tends to be more fractured than that on large particles, suggesting that the particle size uniformity is essential for reducing the fracture probability of the SEI layers at the electrode.

In this study, stress generation at the electrode in Li-ion batteries was studied using a two-dimensional cell-scale model that includes multiple active particles during galvanostatic discharge. Numerical simulations were performed using an electrochemical-mechanical coupled model to elucidate the simultaneous effects of particle size and location, lithium intercalation kinetics and binder constraints on the stress. The simulation results showed that when different sizes of particle are considered in the electrode, the small particles were discharged more than the large particles, resulting in higher level of stress in the smaller particles. In addition, the closer the particles were located to the separator, the larger the stresses that were developed in those particles. Therefore, a layered structure, where the particle size gradually increases as the distance from the particles to the separator decreases, can alleviate stress on the electrode. When binder constraints were considered for the electrode particles, the stress was increased at the anode and alleviated at the cathode upon discharge. This indicates that the effect of mechanical constraints on stress generation in the particles differs in the lithiation and delithiation process.

The mechanical failure of electrodes is one of the main mechanisms of degradation in Li-ion batteries. Many studies have been carried out on the fracture inside a single particle; however, studies on particles with binders are limited. In this study, we investigated stress development under the anisotropic lithium flux in a graphite particle partially attached to an ionically non-conductive polyvinylidene difluoride (PVDF) binder. The study reveals that the location of the maximum stress depends on the particle sizes and C-rates due to the anisotropic lithium intercalation and the mechanical failure can initiate with high probability either at the particle center or at the binder interface according to different sizes and C-rates. The simulations showed that small particles under low charging rates tend to produce high stress at the edge of the particle/binder interface, while large particles under high charging rates tend to generate high stress inside the particle. The possible fracture locations are determined by competition of the interface fracture due to expansion and at the inner fracture due to the gradients of lithium concentration. We also studied the effect of binder geometries on the level of stress and found that the stress concentration near the binder edges increases the possibility of the binder debonding as the binder size increases and the angle between the binder and particle decreases. The study will expand to crack propagation in the cluster of particles, eventually linking to the capacity fade issue due to mechanical failures.

The active particle at the electrode of Li-ion batteries is surrounded by other particles and binders. During the lithiation/delithiation process, these surrounding materials mechanically constrain expansion and contraction of the particle. Since electrochemical and mechanical responses mutually influence each other, the constraining condition can finally affect cell performance. In this paper, we investigate the mechanical and electrochemical responses at the particle and cell levels with consideration of the coupling effect of electrochemistry and mechanics. To study the effect of mechanical constraints on cell

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