Porous Electrode Model with Particle Stress Effects for Li(Ni_1/3Co_1/3Mn_1/3)O₂Electrode

Abstract

A porous electrode model, incorporating particle stress effects, is developed for the electrode kinetic processes in the positive Li(Ni 1/3 Mn 1/3 Co 1/3)O 2 or NMC111 electrode. The model is used to analyze experimental data from galvanostatic intermittent titration technique (GITT) during charging at the beginning of life. The equilibrium potential accounts for the influence of mechanical stress in the electrode particles. While the standard Newman-based model proves unable to capture the dynamic performance of NMC111, the extended model with stress allows good fits of the GITT responses for NMC half cells for a voltage range from 3.7-4.1 V vs Li/Li + at 10°C, 25°C and 40°C. Four physical parameters are extracted to analyze the underlying diffusive, kinetic, thermodynamic and stress phenomena from polarization to relaxation during a GITT transient. Strong dependencies of the kinetic rate constant k, slope of the open-circuit potential curve dE conc /dx pos and stress proportionality factor ϒ stress with lithium concentration are found. The effective diffusion coefficients D s,eff are ∼10 −14-10 −13 cm 2 /s across voltages and temperatures. Diffusion limitation and particle surface stress are more profound at higher voltages and at higher temperatures. This leads to large lithium concentration gradient near particle surface, requiring longer relaxation time during GITT.

Asynchronous-to-Synchronous Transition of Li Reactions in Solid-Solution Cathodes

“…After losing a fraction of the capacity at the end of the first cycle, the system stays at higher values of Li diffusivity for subsequent cycles, thus preventing further capacity loss in subsequent cycles. A similar trend holds for the reaction rate constant of NMC for the surface charge transfer . A prior study showed that the variation of the reaction rate could result in the autocatalytic effect and fictitious phase separation in layered oxide cathode …”

“…A similar trend holds for the reaction rate constant of NMC for the surface charge transfer. 37 A prior study showed that the variation of the reaction rate could result in the autocatalytic effect and fictitious phase separation in layered oxide cathode. 9 Figure 4b shows literature reports 30,38−41 of the electrical conductivity of NMC materials (symbols) and the curve adopted in our computational model (continuous black line).…”

Review of parameterisation and a novel database (LiionDB) for continuum Li-ion battery models

“…Real electrodes contain a distribution of particle sizes and shapes that confounds the determination of a single representative radius for each electrode, as is required by the basic DFN model [60]. For polycrystalline materials, the choice of a characteristic length based on primary or secondary agglomerated structures can change the radius parameter by a factor of 20 [61]. Particle radii tend to fall below 20 µm according to figure 5.…”

Intercalation in Li-ion batteries: thermodynamics and its relation to non-ideal solid-state diffusion

“…For this analysis, a selection of specific cathode materials is considered, including NMC111 [59,75,76], NMC532 [60], NMC622 [62,77], NMC811 [16,61], NCA [63,78], and LCO [64,79,80], which are commonly used in commercial Li-ion batteries [81,82]. For a more comprehensive analysis, section 3.1 includes also graphite [56,69] and LFP [7,54], as they are representative of a class of active materials that undergo phase separation during lithiation [50].…”