Performance benchmarks for open source porous electrode theory models.

The electrochemical response characteristics of existing and emerging porous electrode theory (PET) models was benchmarked to establish a common basis to assess their physical reaches, limitations, and accuracy. Three open source PET models: dualfoil, MPET, and LIONSIMBA were compared to simulate the discharge of a LiMnO-graphite cell against experimental data. For C-rates below 2C, the simulated discharge voltage curves matched the experimental data within 4% deviation for dualfoil, MPET, and LIONSIMBA, while for C-rates above 3C, dualfoil and MPET show smaller deviations, within 5%, against experiments.

Toward Reservoir-on-a-Chip: Rapid Performance Evaluation of Enhanced Oil Recovery Surfactants for Carbonate Reservoirs Using a Calcite-Coated Micromodel.

Enhanced oil recovery (EOR) plays a significant role in improving oil production. Tertiary EOR, including surfactant flooding, can potentially mobilize residual oil after water flooding. Prior to the field deployment, the surfactant performance must be evaluated using site-specific crude oil at reservoir conditions.

Origin and hysteresis of lithium compositional spatiodynamics within battery primary particles.

The kinetics and uniformity of ion insertion reactions at the solid-liquid interface govern the rate capability and lifetime, respectively, of electrochemical devices such as Li-ion batteries. Using an operando x-ray microscopy platform that maps the dynamics of the Li composition and insertion rate in Li(x)FePO4, we found that nanoscale spatial variations in rate and in composition control the lithiation pathway at the subparticle length scale. Specifically, spatial variations in the insertion rate constant lead to the formation of nonuniform domains, and the composition dependence of the rate constant amplifies nonuniformities during delithiation but suppresses them during lithiation, and moreover stabilizes the solid solution during lithiation.

The formation mechanism of eutectic microstructures in NiAl-Cr composites.

NiAl-based eutectic alloys, consisting of an ordered bcc matrix (B2) and disordered bcc fibers (A2), have been a subject of intensive efforts aimed at tailoring the properties of many of the currently used nickel-based superalloys. A thermodynamic phase field model was developed on a thermodynamic foundation and fully integrated with a thermo-kinetic database of the Ni-Al-Cr ternary system to elucidate the resulting peculiar eutectic microstructure. Invoking a variation of the liquid/solid interfacial thickness with temperature, we simulated the characteristic sunflower-like eutectic microstructures in the NiAl-Cr composites, consistent with experimental observations.

Quantitative phase-field modeling of dendritic electrodeposition.

A thin-interface phase-field model of electrochemical interfaces is developed based on Marcus kinetics for concentrated solutions, and used to simulate dendrite growth during electrodeposition of metals. The model is derived in the grand electrochemical potential to permit the interface to be widened to reach experimental length and time scales, and electroneutrality is formulated to eliminate the Debye length. Quantitative agreement is achieved with zinc Faradaic reaction kinetics, fractal growth dimension, tip velocity, and radius of curvature.

Current-induced transition from particle-by-particle to concurrent intercalation in phase-separating battery electrodes.

Many battery electrodes contain ensembles of nanoparticles that phase-separate on (de)intercalation. In such electrodes, the fraction of actively intercalating particles directly impacts cycle life: a vanishing population concentrates the current in a small number of particles, leading to current hotspots. Reports of the active particle population in the phase-separating electrode lithium iron phosphate (LiFePO4; LFP) vary widely, ranging from near 0% (particle-by-particle) to 100% (concurrent intercalation).

Theory of coherent nucleation in phase-separating nanoparticles.

The basic physics of nucleation in solid single-crystal nanoparticles is revealed by a phase-field theory that includes surface energy, chemical reactions, and coherency strain. In contrast to binary fluids, which form arbitrary contact angles at surfaces, complete "wetting" by one phase is favored at binary solid surfaces. Nucleation occurs when surface wetting becomes unstable, as the chemical energy gain (scaling with area) overcomes the elastic energy penalty (scaling with volume).

Coherency strain and the kinetics of phase separation in LiFePO4 nanoparticles.

A theoretical investigation of the effects of elastic coherency strain on the thermodynamics, kinetics, and morphology of intercalation in single LiFePO(4) nanoparticles yields new insights into this important battery material. Anisotropic elastic stiffness and misfit strains lead to the unexpected prediction that low-energy phase boundaries occur along {101} planes, while conflicting reports of phase boundary orientations are resolved by a partial loss of coherency in the [001] direction. Elastic relaxation near surfaces leads to the formation of a striped morphology with a characteristic length scale predicted by the model, yielding an estimate of the interfacial energy.

Suppression of phase separation in LiFePO₄ nanoparticles during battery discharge.

Using a novel electrochemical phase-field model, we question the common belief that Li(X)FePO(4) nanoparticles always separate into Li-rich and Li-poor phases during battery discharge. For small currents, spinodal decomposition or nucleation leads to moving phase boundaries. Above a critical current density (in the Tafel regime), the spinodal disappears, and particles fill homogeneously, which may explain the superior rate capability and long cycle life of nano-LiFePO(4) cathodes.

Thermodynamic phase-field model for microstructure with multiple components and phases: the possibility of metastable phases.

A diffuse-interface model for microstructure with an arbitrary number of components and phases was developed from basic thermodynamic and kinetic principles and formalized within a variational framework. The model includes a composition gradient energy to capture solute trapping and is therefore suited for studying phenomena where the width of the interface plays an important role. Derivation of the inhomogeneous free energy functional from a Taylor expansion of homogeneous free energy reveals how the interfacial properties of each component and phase may be specified under a mass constraint.