Computational Modeling of Heterogeneity of Stress, Charge, and Cyclic Damage in Composite Electrodes of Li-Ion Batteries

Abstract

Charge heterogeneity is a prevalent feature in many electrochemical systems. In a commercial cathode of Li-ion batteries, the composite is hierarchically structured across multiple length scales including the sub-micron single-crystal primary-particle domains up to the macroscopic particle ensembles. The redox kinetics of charge transfer and mass transport strongly couples with mechanical stresses. This interplay catalyzes substantial heterogeneity in the charge (re)distribution, stresses, and mechanical damage in the composite electrode during charging and discharging. We assess the heterogeneous electrochemistry and mechanics in a LiNixMnyCozO2 (NMC) cathode using a fully coupled electro-chemo-mechanics model at the cell level. A microstructure-resolved model is constructed based on the synchrotron X-ray tomography data. We calculate the stress field in the composite and then quantitatively evaluate the kinetics of surface charge transfer and Li transport biased by mechanical stresses. We further model the cyclic behavior of the cell. The repetitive deformation of the active particles and the weakening of the interfacial strength cause gradual increase of the interfacial debonding. The mechanical damage impedes electron transfer, incurs more charge heterogeneity, and results in the capacity degradation in batteries over cycles.

Kinetic Limitations in Single‐Crystal High‐Nickel Cathodes

“…To evaluate the impact of local mass transport and charge transfer on the redox kinetics in S and P electrodes, we performed finite element analysis (FEA) simulations on the electrochemical process by using the measured values from GITT/EIS measurements (Figure 2 d). [31] Specifically, the simulation involves two particles (A and B) being charged simultaneously at constant current rate (as illustrated in the Supporting Information, Figure S12). Figures 4 a–c plot the Ni 4+ concentration distribution inside particles at different charge states as indicated by the dots showing in the simulated voltage profile in Figure 4 d.…”

Kinetic Limitations in Single‐Crystal High‐Nickel Cathodes

“…[30] To evaluate the impact of local mass transport and charge transfer on the redox kinetics in S and P electrodes, we performed finite element analysis (FEA) simulations on the electrochemical process by using the measured values from GITT/EIS measurements (Figure 2 d). [31] Specifically, the simulation involves two particles (A and B) being charged simultaneously at constant current rate (as illustrated in the Supporting Information, Figure S12). Figures 4 a-c voltage-dependent values extracted from GITT); 2) both A and B have fast Li diffusion rates as in P electrodes (D A = D B = 10 À9 cm 2 s À1 , [22] also check details in the Supporting Information): 3) a mixture of slow Li diffusion (A, D A = value extracted from GITT) and fast Li diffusion (B, D B = 10 À9 cm 2 s À1 ), representing S and P particles, respectively in the mixed electrodes.…”

Synchrotron X‐Ray Tomography for Rechargeable Battery Research: Fundamentals, Setups and Applications

“…Furthermore, by jointly employing the representative volume element (RVE) model and the 3D synchrotron X‐ray tomography imaging, lithium‐ion migration dynamics within active materials during battery operation can be studied. [ 97 ] For example, Kashkooli et al [ 98 ] revealed the lithium‐ion distribution inside the LiFePO 4 electrode at different state‐of‐charge (SOC), as shown in Figure 7c. They pointed out that lithium ions are mainly concentrated in the surface area exposed to the electrolyte.…”