Electrochemical impedance spectroscopy (EIS) is a powerful and non-destructive characterization technique widely used in the electrochemical research field. It can measure many macroscopic properties such as internal resistance, capacitance, and diffusivity by fitting the obtained impedance with equivalent circuits. Each of the acquired quantities reflects an electrochemical mechanism, e.g, charge-transfer reaction, double layer formation, and mass transport, taking place in the electrode. However, the obtained quantity is a total value for the whole electrode. The underlying connections between the macroscopic properties, intrinsic material parameters, and electrode microstructures are not well understood. This dissertation focuses on building a modeling framework to simulate EIS processes with given electrode microstructures and intrinsic material parameters. With this simulation tool, we provide a digital bridge between battery electrode material properties, electrode microstructures, and their corresponding EIS impedance. Capacitance of an electrochemical device originates from double layer formation in the electrolyte. However, there is a huge spatial discrepancy between the dimensions of double layer and electrode particles (or interparticle space). Thus, smoothed boundary method and adaptive mesh refinement are used to handle the scale discrepancy and the complex geometries of electrode particles in solving the Nernst-Planck-Poisson equations in simulating the double layer formation under voltage loading.The obtained double-layer capacitance is incorporated into multiphysics electrochemical simulations. Cathode electrode made of Nickel-Manganese-Cobalt (NMC111) oxide, is examined with this simulation tool. As a solid solution material, lithium transport in the NMC111 electrode particles is described by Fick's law. EIS curves for various conditions, including different states of charge, electrolyte salt concentration, electrode microstructures, are extracted from the simulations and analyzed. The simulations properly reflect the relationships between particle exchange current density, reactive surface area, and the total resistance of the electrode.Anodes made of graphite, a phase-transforming material upon lithiation/delithiation, are also examined using the simulation tool. The Cahn-Hilliard equation is employed to model the phase transformation processes in the particles. EIS simulations are conducted on single-phase and multi-phase graphite. For single-phase or core-shell phase-distributed graphite particles, the simulated EIS curves exhibit a typical semicircle with a Warburg part. Interestingly, if phase boundaries intersect particle surfaces, a low frequency inductive loop appears on the EIS curve. Lastly, the simulation tool is applied to simulate EIS processes of a full-cell battery of both cathode and anode microstructures. On each electrode, the total current is comprised of capacitance and reaction currents. It is observed that, depending on the loading frequency, the ratio of capacitance-to-reaction current on the two electrodes can be significantly different. The simulation tool allows us to examine the details of electrochemical processes during EIS measurements.

In this book, a new procedure to analyze lithium-ion cells is introduced. The cells are disassembled to analyze their components in experimental cell housings. Then, Electrochemical Impedance Spectroscopy, time domain measurements and the Distribution function of Relaxation Times are applied to obtain a deep understanding of the relevant loss processes. This procedure yields a notable surplus of information about the electrode contributions to the overall internal resistance of the cell.

In this book, a new procedure to analyze lithium-ion cells is introduced. The cells are disassembled to analyze their components in experimental cell housings. Then, Electrochemical Impedance Spectroscopy, time domain measurements and the Distribution function of Relaxation Times are applied to obtain a deep understanding of the relevant loss processes. This procedure yields a notable surplus of information about the electrode contributions to the overall internal resistance of the cell. This work was published by Saint Philip Street Press pursuant to a Creative Commons license permitting commercial use. All rights not granted by the work's license are retained by the author or authors.

The Essential Reference for the Field, Featuring Protocols, Analysis, Fundamentals, and the Latest Advances Impedance Spectroscopy: Theory, Experiment, and Applications provides a comprehensive reference for graduate students, researchers, and engineers working in electrochemistry, physical chemistry, and physics. Covering both fundamentals concepts and practical applications, this unique reference provides a level of understanding that allows immediate use of impedance spectroscopy methods. Step-by-step experiment protocols with analysis guidance lend immediate relevance to general principles, while extensive figures and equations aid in the understanding of complex concepts. Detailed discussion includes the best measurement methods and identifying sources of error, and theoretical considerations for modeling, equivalent circuits, and equations in the complex domain are provided for most subjects under investigation. Written by a team of expert contributors, this book provides a clear understanding of impedance spectroscopy in general as well as the essential skills needed to use it in specific applications. Extensively updated to reflect the field’s latest advances, this new Third Edition: Incorporates the latest research, and provides coverage of new areas in which impedance spectroscopy is gaining importance Discusses the application of impedance spectroscopy to viscoelastic rubbery materials and biological systems Explores impedance spectroscopy applications in electrochemistry, semiconductors, solid electrolytes, corrosion, solid state devices, and electrochemical power sources Examines both the theoretical and practical aspects, and discusses when impedance spectroscopy is and is not the appropriate solution to an analysis problem Researchers and engineers will find value in the immediate practicality, while students will appreciate the hands-on approach to impedance spectroscopy methods. Retaining the reputation it has gained over years as a primary reference, Impedance Spectroscopy: Theory, Experiment, and Applications once again present a comprehensive reference reflecting the current state of the field.

Lithium-ion batteries are commonly modeled using a volume-averaged formulation (porous electrode theory) in order to simulate battery behavior on a large scale. These methods utilize effective material properties and assume a simplified spherical geometry of the electrode particles. In contrast, a particle-scale (non-porous electrode) simulation applied to resolved electrode geometries predicts localized phenomena. Complete simulations of batteries require a coupling of the two scales to resolve the relevant physics. A central focus of this thesis is to develop a fully-coupled finite volume methodology for the simulation of the electrochemical equations in a lithium-ion battery cell at both the particle scale and using volume-averaged formulations. Due to highly complex electrode geometries at the particle scale, the formulation employs an unstructured computational mesh and is implemented within the MEMOSA software framework of Purdue’s PRISM (Prediction of Reliability, Integrity and Survivability of Microsystems) center. Stable and efficient algorithms are developed for full coupling of the nonlinear species transport equations, electrostatics, and Butler-Volmer kinetics. The model is applied to synthetic electrode particle beds for comparison with porous electrode theory simulations and to evaluate numerical performance capabilities. The model is also applied to a half-cell mesh created from a real cathode particle bed reconstruction to demonstrate the feasibility of such simulations. The second focus of the thesis is to investigate 3D battery electrode architectures that offer potential energy density and power density improvements over traditional particle bed battery geometries. A singular feature of these geometries is their interpenetrating nature, which significantly reduces diffusion distance. Advancement of micro-scale additive manufacturing techniques has made it possible to fabricate these electrode microarchitectures. A fully-coupled finite volume methodology for the transport equations coupled to the relevant electrochemistry is implemented in the PETSc (Portable, Extensible Toolkit for Scientific Computation) software framework which allows for a straightforward scalable simulation on orthogonal hexahedral meshes. Such scalability becomes important when performing simulations on fully resolved microstructures with many parameter sweeps across multiple variables. Using the computational model, a variety of 3D battery electrode geometries are simulated and compared across various battery discharge rates and length scales in order to quantify performance trends and investigate geometrical factors that improve battery performance. The energy density and power density of the 3D battery microstructures are compared in several ways, including a uniform surface area to volume ratio comparison as well as a comparison requiring a minimum manufacturable feature size. Significant performance improvements over traditional particle bed electrode designs are observed, and electrode microarchitectures derived from minimal surfaces are shown to be superior under a minimum feature size constraint. An average Thiele modulus formulation is presented to predict the performance trends of 3D microbattery electrode geometries. As a natural extension of the 3D battery particle-scale modeling, the third and final focus of the thesis is the development and evaluation of a volume-averaged porous electrode theory formulation for these unique 3D interpenetrating geometries. It is necessary to average all three material domains (anode, cathode, and electrolyte) together, in contrast to traditional two material volume-averaging formulations for particle bed geometries. This model is discretized and implemented in the PETSc software framework in a manner similar to the particle-scale implementation and enables battery-level simulations of interpenetrating 3D battery electrode architectures. Electrode concentration gradients are modeled using a characteristic diffusion length, and results for plate and cylinder electrode geometries are compared to particle-scale simulation results. Additionally, effective diffusion lengths that minimize error with respect to particle-scale results for gyroid and Schwarz P electrode microstructures are determined, since a theoretical single diffusion length is not easily calculated. Using these models, the porous electrode formulation for these 3D interpenetrating geometries is shown to match the results of particle-scale models very well.