Multiphysics Coupling in Lithium-Ion Batteries with Reconstructed Porous Microstructures

Abstract

For an energy storage application such as electrical vehicles (EVs), lithium-ion batteries must overcome limited lifetime and performance degradation under specific conditions. Particularly, lithium-ion batteries show significant capacity loss at higher discharging rates (C-rates). In this work, we develop computational models incorporating coupled electrochemical–mechanical–thermal factors in order to reveal the relationship between the experimentally observed capacity loss and predicted mechanical stresses during electrochemical (dis)­charging. Specifically, a multiphysics finite element model consisting of electrochemistry, heat generation, mass transport, and solid mechanics is developed to investigate thermal- and diffusion-induced stresses with the reconstructed porous microstructures of commercial LiFePO4 batteries. It has been suggested that porous microstructures in electrodes could mitigate the electrolyte reactivity for an improved battery life and safety. Therefore, the reconstructed porous microstructures from focused ion beam–scanning electron microscopy (FIB-SEM) images are adopted. The integrated experimental measurements and computational simulations show that: (1) Lithium-ion cells electrochemically tested at 3.6C have 30% capacity loss versus cells tested at 1.2C; a corresponding stress increase of 150% is observed from the multiphysic simulations. (2) The thermal models verified by in operando temperature measurement via the fiber Bragg grating (FBG) sensor demonstrate that increasing temperature results in larger thermal stresses during (dis)­charging. However, increases in thermal stress due to higher temperature played a lesser role at higher C-rates. (3) Lithium-ion concentration distribution is location dependent; that is, at any time and at any given C-rate, the outer layer of the particle exhibits a higher concentration than that inside the particle. (4) Higher diffusion-induced stresses are observed at the connecting areas between particles, suggesting that the higher stresses may result from higher concentration variations in the connecting area. This study presents results that include evolutions of lithium-ion concentration and mechanical stresses and could help to provide insight into the decreasing electrochemical performance of lithium-ion batteries at higher C-rates.

Heterogeneous aging of large‐scale flexible lithium‐ion batteries based on micro‐heterostructures and simulation

“…The von Mises stress is the maximum at the site where two particles make contact, which is caused by interaction and constraints between particles. 40 This also explains why the lithium-ion concentration at the contact site between two particles is low (Section 3.2, Concentation Distribution): this is because the very large stress at this site weakens the capacity of lithium ions to penetrate the cathode materials, leading to the low lithium-ion concentration at the site, which is consistent with experimental observations. 41 Only considering the homogeneous spherical morphology imposes limitations on the stress analysis, while the reconstruction of the microstructure of electrode particles can better reflect the interaction between the electrode particles contained in the electrode materials.…”

“…Figure 8B displays stress development in the whole range of SOC at a rate of 1C: with the increase of SOC, particles expand and the resulting stress rises. The von Mises stress is the maximum at the site where two particles make contact, which is caused by interaction and constraints between particles 40 . This also explains why the lithium‐ion concentration at the contact site between two particles is low (Section 3.2, Concentation Distribution): this is because the very large stress at this site weakens the capacity of lithium ions to penetrate the cathode materials, leading to the low lithium‐ion concentration at the site, which is consistent with experimental observations 41 .…”

Progress in 3D electrode microstructure modelling for fuel cells and batteries: transport and electrochemical performance

“…Especially in LIBs, more physics are simulated, such as Li diffusion and structural mechanics in electrode particles, to take into account the stress generated by Li intercalation and, in turn, the effect of mechanical stress on Li diffusivity [33,107,141,143]. Similarly, heat balance is sometimes coupled with the electrochemical model [32,140], so that the temperature field is solved on the same computational mesh used to solve for species concentrations and electric potentials. This normally means that, in the same domain, the mesh requirements are dictated by the physics which requires a finer mesh to resolve stronger gradients, leading to an unnecessary increase in degrees of freedom for the processes which do not need accurate spatial discretisation.…”

“…The exchange current density i0 is evaluated as a function of the local species concentration in Li-ion battery modelling [32,33,[109][110][111], such as:…”

Guiding the Design of Heterogeneous Electrode Microstructures for Li‐Ion Batteries: Microscopic Imaging, Predictive Modeling, and Machine Learning

“…Microstructure-resolved models enable the quantification of the contributions of these effects for different electrode materials and thus make it possible to go beyond homogenized electrode models and to simplify the electrochemo-mechanical theories accordingly, along with in situ and operando characterization tools which provide a quantitative insight that can be used to validate emerging models. [86,90,94] Kim et al [216] demonstrated on a 2D reconstructed section of a LFP cathode that the thermal strain is negligible compared to diffusion-induced strain during normal charge-discharge and that the experimental capacity fade of the battery cell and the averaged stress in the particles have a positive correlation. In the NMC622 model developed by Xu et al, [101] the plastic deformation was treated as a trivial term based on the author's serial experimental investigations on single particles and electrodes, [217][218][219] which show brittle fracture of the material before large plastic deformation could accumulate.…”