Effects of Diffusion-Induced Nonlinear Local Volume Change on the Structural Stability of NMC Cathode Materials of Lithium-Ion Batteries

Abstract

Electrochemical stress induced by the charging/discharging of electrode materials strongly affects the lifetime of lithium-ion batteries (LIBs) by regulating mechanical failures. Electrochemical stress is caused by a change in the local volume of the active materials associated with the lithium-ion concentration. The local volume change of certain active materials, such as nickel-rich LiNixMnyCozO2 (NMC), varies nonlinearly with the lithium content, which has not been considered in the stress calculations in previous studies. In this paper, the influence of nonlinear local volume change on the mechanical response of NMC-active materials is investigated numerically. The goal is achieved by using a concentration-dependent partial molar volume calculated from the previously obtained local volume change experimental results. A two-dimensional axisymmetric model was developed to perform finite element simulations by fully coupling lithium diffusion and stress generation at a single particle level. The numerical results demonstrate that (1) the global volume change of the particle evolves nonlinearly, (2) the stress response correlates with the rate of change of the active particle’s volume, and (3) stress–concentration coupling strongly affects the concentration levels inside the particle. We believe this is the first simulation study that highlights the effect of a concentration-dependent partial molar volume on diffusion-induced stresses in NMC materials. The proposed model provides insight into the design of next-generation NMC electrode materials to achieve better structural stability by reducing mechanical cracking issues.

Electro-Chemo-Mechanical Evolution at the Garnet Solid Electrolyte–Cathode Interface

“…For example, Bai et al have shown that, in polycrystalline cathode, chemical inhomogeneity from Li concentration profile within the cathode can cause stress and cracking . Due to this limitation, the model used in this work does not explain the onset of intergranular crack formation, though it is evident from the cross-sectional images from our work (Figure ), as well as in previous studies. − More rigorous mechanical modeling of layered oxide cathodes considering both their polycrystalline and anisotropic properties can be found in other studies. − Furthermore, a more thorough chemo-mechanical modeling of the intergranular cracks and interface delamination is worthwhile to resolve whether these two are related (as assumed and analyzed here) or form independently upon strains in the cathode layer.…”

“…The intergranular cracks observed in our work (Figure b–f) are consistent with this process. Formation of intergranular cracks and separations between grains for layered oxide cathodes due to cycling have also been reported by both experimental and theoretical works. − …”

A Review of the Synthesis of Biopolymer Hydrogel Electrolytes for Improved Electrode–Electrolyte Interfaces in Zinc-Ion Batteries

“…Simulations using the cohesive zone model showed that interfacial debonding between the active material particles and binder starts from the edge of the interface, propagating rapidly to the inner zone, and that it leads to a larger extent of the average state of charges in the particles because of the increased flux of ions through the new, debonded zones [92]. The state of charge and diffusion-induced stress evolution is significantly impacted by concentration-dependent local volume changes of the active material [93]. Moreover, this interfacial debonding is more probable in an electrode with a higher number of binder connections due to an increased amount of stress concentration locations [94].…”