arXiv subjects

Bernardo Orvananos

Publications and source records attributed to Bernardo Orvananos.

3 recordsLinked to original sources

arXiv2026

Smoothed Boundary Method Framework for Electrochemical Simulation of Li-ion Battery Cathode with Complex Microstructure: Model, Formulation and Parameterization

Rechargeable battery electrodes have highly complex microstructures, consisting of nonuniform electrode particles, tortuous electrolyte channels, and irregular particle-electrolyte interfaces. Moreover, the electrochemical processes involve several coupled physical mechanisms, including mass transport in the electrode particles and electrolyte, current continuity in the solid and liquid, and electrochemical surface reactions. These geometric and mechanistic complexities create a challenging barrier of electrochemical simulations at the microstructural level using conventional methods. In this paper, we introduce a smoothed-boundary method (SBM) electrochemical simulation framework for modeling the electrochemical dynamics of complex battery electrode microstructures. The conventional governing equations are reformulated into SBM versions, and are solved using uniform Cartesian grids. The simulations utilize an image-based, experimentally reconstructed 3D microstructure as the input geometry, and the physical parameters acquired from experimental measurements. Two models of lithiation mechanisms, solid-solution and two-phase, are examined under potentiostatic discharging of a Li$_x$CoO$_2$ composite cathode. Detailed dynamics of the complex cathode microstructure are revealed through the simulations. The comparison between the two models indicates that modeling two-phase lithiation with Fick's diffusion will overestimate the electrode's performance. The presented simulation framework provides an innovative avenue in exploring the electrochemical dynamics at the microstructural level.

cond-mat.mtrl-sci↗

arXiv2016

Synthesis of a mixed-valent tin nitride and considerations of its possible crystal structures

Recent advances in theoretical structure prediction methods and high-throughput computational techniques are revolutionizing experimental discovery of the thermodynamically stable inorganic materials. Metastable materials represent a new frontier for studies, since even simple binary non ground state compounds of common elements may be awaiting discovery. However, there are significant research challenges related to non-equilibrium thin film synthesis and crystal structure predictions, such as small strained crystals in the experimental samples and energy minimization based theoretical algorithms. Here we report on experimental synthesis and characterization, as well as theoretical first-principles calculations of a previously unreported mixed-valent binary tin nitride. Thin film experiments indicate that this novel material is N-deficient SnN with tin in the mixed II/IV valence state and a small low-symmetry unit cell. Theoretical calculations suggest that the most likely crystal structure has the space group 2 (SG2) related to the distorted delafossite (SG166), which is nearly 0.1 eV/atom above the ground state SnN polymorph. This observation is rationalized by the structural similarity of the SnN distorted delafossite to the chemically related Sn3N4 spinel compound, which provides a fresh scientific insight into the reasons for growth of polymorphs of the metastable material. In addition to reporting on the discovery of the simple binary SnN compound, this paper illustrates a possible way of combining a wide range of advanced characterization techniques with the first-principle property calculation methods, to elucidate the most likely crystal structure of the previously unreported metastable materials.

cond-mat.mtrl-sci↗

arXiv2013

Particle-Level Modeling of the Charge-Discharge Behavior of Nanoparticulate Phase-Separating Li-Ion Battery Electrodes

In nanoparticulate phase-separating electrodes, phase separation inside the particles can be hindered during their charge/discharge cycles even when a thermodynamic driving force for phase separation exists. In such cases, particles may (de)lithiate discretely in a process referred to as mosaic instability. This instability could be the key to elucidating the complex charge/discharge dynamics in nanoparticulate phase-separating electrodes. In this paper, the dynamics of the mosaic instability is studied using Smoothed Boundary Method simulations at the particle level, where the concentration and electrostatic potential fields are spatially resolved around individual particles. Two sets of configurations consisting of spherical particles with an identical radius are employed to study the instability in detail. The effect of an activity-dependent exchange current density on the mosaic instability, which leads to asymmetric charge/discharge, is also studied. While we show that our model reproduces the results of a porous-electrode model for the simple setup studied here, it is a powerful framework with the capability to predict the detailed dynamics in three-dimensional complex electrodes and provides further insights into the complex dynamics that result from the coupling of electrochemistry, thermodynamics, and transport kinetics.

cond-mat.mtrl-sci↗