Dean R. Wheeler

Brigham Young University - Provo Main Campus | BYU · Department of Chemical Engineering

To improve power and cycling performance of lithium-ion batteries, dual-layer or porosity-gradient electrodes have been proposed. By using a higher porosity close to the separator, the intention is to improve ion transport where it is most needed. Here, MacMullin numbers of two dual-layer anode samples are tested using an impedance measurement tech...

In this work, we present a combination of experiments and modeling of a two-layer anode structure designed by EnPower Inc. for high-energy and fast-charge capabilities. The anode consists of lower porosity near the current collector and higher porosity near the separator with comparable active materials in both regions. A pseudo-two-dimensional ele...

The microstructure determines transport properties in lithium-ion battery electrodes. There is generally a tradeoff between electronic and ionic transport when adjusting the microstructure. One way of adjusting the microstructure is through calendering, where the electrode is compressed following drying. Understanding how calendering affects not on...

Binder is a crucial component of high-capacity silicon anodes. It allows the active material to cohere to itself and surrounding materials. In the past few years, there have been divergent conclusions on the cell performance of anodes using water-based PAA vs. LiOH-PAA binder [1-3]. While there is agreement that LiOH-PAA facilitates the coating pro...

The drying process of electrodes might seem to be a simple operation, but it has profound effects on the microstructure. Some unexpected changes can happen depending on the drying conditions. In prior work, we developed the multiphase-smoothed-particle (MPSP) model, which predicted a relative increase in the carbon additive and binder adjacent to t...

Electrodes can suffer from inconsistencies in performance due to heterogeneity in particle arrangements. Manufacturing processes such as drying and calendering significantly alter the microstructure and introduce randomness, making it difficult to predict the final structure of the film, given process inputs. This has a crucial impact on the electr...

Contact resistance between the battery film and its current collector should be minimized in order to fully optimize battery electrodes. Increased resistance results from any factor limiting electrons from transitioning between the current collector and porous electrode materials, such as increased pockets of void space, depletion of conductive add...

Currently, Li-ion battery electrodes are produced by coating onto the current collector a slurry composed of active particles, carbon black (CB), binder, and solvent. Coating is followed by drying, and calendering steps. This method creates a quasi-random distribution of CB particles throughout the battery electrode. The CB particles are intended t...

Electrical conductivity is a key metric in the performance of lithium-ion batteries. However, accurately measuring the electronic conductivity nondestructively is difficult. We have developed a micro-four-line probe that has been used to make this measurement and to demonstrate the heterogeneity of electrical conductivity of lithium-ion electrodes...

Due to the nature of how porous battery electrodes are fabricated, their microstructure is not uniform. For instance, there are variations in composition, effective electronic transport, and effective ionic transport. Such heterogeneity has been associated with several battery application issues. For example, variability in transport of ions can le...

Newman-type or macrohomogeneous cell models have had a significant contribution toward designing and optimizing Li-ion batteries. In order to lower the computational cost and accommodate limited experimental information, this model assumes that battery electrodes are functionally homogenous. However, this assumption can be far from reality even for...

Lithium-ion battery electrodes are known to have irregularities in their microstructure. When electrodes are not uniform in terms of conductivity, such inhomogeneities can lead to localized variability in current flow, potential, and species concentrations, which are associated with cell degradation [1]. Understanding and quantifying heterogeneity...

During cycling or other aging processes, the capacity of lithium-ion batteries decreases and it is also observed that cell impedance increases. In order to better understand these processes, we are investigating the electronic conductivity and ionic conductivity of electrodes harvested from 18650 cells that have been cycled by different amounts. Ef...

The mechanical properties of thin-film Li-ion battery electrodes are controlled by the microstructure of the constituent materials. In this work, a noncontact and nondestructive measurement of the mechanical properties of electrode films is performed by measurement of zero-group velocity (ZGV) resonances. Theoretical models are used to quantify the...

Substantial heterogeneity and defects in lithium-ion battery films can be a cause of material and battery failure. Although non-uniformity has been observed previously, the physical origin of electronic impedance non-uniformities in cathode materials has not been well-studied. We show that the local microscopic structure of materials strongly affec...

Local variations of mechanical, structural, transport, and kinetic properties, referred to as heterogeneity can detrimentally affect battery life and performance. Local heterogeneity results in non-uniform current, temperature, state of charge (SOC), and aging. In this work, we introduce a model that combines Newman-type and equivalent circuit subm...

Measuring the mechanical properties of lithium-ion battery films, such as thickness and elasticity, is important for predicting and improving homogeneity of the films and subsequent performance of the battery. Problems with film heterogeneity could be identified and addressed early on through accurate, non-destructive inspection of the electrode as...

Battery performance in part relies on the microstructure of each electrode, which is determined by the electrode composition and fabrication process. Accurate and direct experimental measurement of electrode properties is challenging due to the thickness of electrode films (30-80 µm), yet those properties are needed to generate cell-level performan...

Lithium-Ion battery success can be defined by a series of measureable characteristics. Two important characteristics that have been difficult to fully explore are the ionic [1] and electronic tortuosity. Micro-N-line probes were previously developed [2][3] in order to accurately measure electronic thin-film conductivity on a micro-scale. Multiple i...

In addition to the characteristics of the materials that make up the electrode (such as active material and additives) and the ratios in which the materials are combined, the electrode fabrication process itself plays an important role in the cell performance. This is because the fabrication process is a contributing factor in determining the distr...

Local variations of mechanical, structural, transport, and kinetic properties, referred to as heterogeneity (generated by a non-optimized manufacturing process [1]), can detrimentally affect battery life and performance, especially at high cycling rates and low temperatures, in a number of manners. The distribution of current density across an elec...

Measurements of the mechanical properties of lithium-ion battery electrode films can be used to quantify and improve manufacturing processes and to predict the mechanical and electrochemical performance of the battery. This paper demonstrates the use of acoustic resonances to distinguish among commercial-grade battery films with different active el...

The role of carbon additives in improving the electronic conductivity of composite porous electrodes is well understood. However, there has been little work studying the effect of various carbon additives on effective ionic transport in porous electrodes. This work determines effective ionic conductivities and associated tortuosities of composite c...

In principle a wide range of organic materials can store energy in the form of reversible redox conversions of stable radicals. Such chemistry holds great promise for energy storage applications due to high theoretical capacities, high rate capabilities, intrinsic structural tunability, and the possibility of low-cost “green” syntheses from renewab...

The electrical conductivity of battery films is an important characteristic in how battery cells perform but is not very well understood on a µm scale. Although the macroscopic electrical conductivity of battery films has been explored, small-scale variations in the film have been shown to exist [1]. Factors that may affect this heterogeneity inclu...

Tortuosity is a geometric parameter of porous electrodes that quantifies the tortuous path ions take to meet electrons in order for the chemical reaction to take place on the surface of the active material. Ionic resistance in the electrodes, which is directly related to the tortuosity, is a key factor that influences battery performance, and must...

Li-ion battery performance is greatly affected by how well ions travel through the electrodes, which in turn depends on the microstructure of the porous pathways through the electrodes. During cell formation and cycling, changes in the microstructure therefore lead to changes in ionic transport. Currently what causes these changes and their magnitu...

Electrical conductivity is a fundamental characteristic determining the performance of lithium-ion batteries. However, methods to measure the conductivity nondestructively have proven difficult. This is due to the presence of a metallic conductive current collector as well as dominating effect of the contact resistance between the film and the prob...

Measuring the mechanical properties of lithium-ion battery films, such as thickness and elasticity, is important for predicting and improving homogeneity of the film and performance of the battery. Problems with film heterogeneity could be identified and addressed early on through accurate, non-destructive inspection of the electrode as it is being...

The microstructure of commercially made lithium-ion battery electrodes is not necessarily optimal for cell performance. In an attempt to optimize the performance, detailed understanding of the microstructure is necessary. Factors that influence electrode microstructure include high-level variables such as composition and porosity; as well as detail...

Electron transport in lithium-ion battery structures is a key factor in overall battery performance, but the cause of localized high and low electron transport values, or conductivity, has not been well-studied or understood. Factors that may affect such heterogeneity include high-level variables such as film composition and porosity, as well as ma...

The fabrication process of Li-ion battery electrodes plays a prominent role in the microstructure and corresponding cell performance. Here, a mesoscale particle dynamics simulation is developed to relate the manufacturing process of a cathode containing Toda NCM-523 active material to physical and structural properties of the dried film. Particle i...

We introduce here the Fourier correlation (FC) method for obtaining bulk diffusion coefficients in simulations of condensed, nonideal mixtures. The method in particular allows a Fickian mutual diffusion coefficient to be calculated directly in a molecular dynamics simulation and provides for a correction of errors due to finite system sizes. It is...

FIB-SEM tomography is used to reconstruct the carbon-binder domain (CBD) of a LiCoO2 battery cathode (3.9 × 5 × 2.3 μm3) with contrast enhancement by ZnO infiltration via atomic layer deposition. We calculate the porosity inside the CBD (57.6%), the cluster-size distribution with a peak at 54 nm, and the pore-size distribution with a peak at 64 nm....

Measurement of the electronic conductivity of porous thin-film battery electrodes poses significant challenges, particularly when the film is attached to a metallic current collector.We have developed a micro-four-line probe and testing procedure that overcomes many of these difficulties while relying on principles similar to commonly used four-poi...

Accurately determining electronic conductivity of thin-film battery electrodes is not trivial, especially with the metallic current conductor still attached. A fast and reliable method would be of use for quality control and optimization purposes in battery manufacture, and would provide insight into the effects of changes in the fabrication proces...

The microstructure of commercially made lithium-ion battery electrodes is not necessarily optimal for cell performance. In an attempt to optimize the performance, detailed understanding of the microstructure is necessary. Factors that influence electrode microstructure include high-level variables such as composition and porosity; as well as detail...

Yearly demand for primary alkaline batteries is around US$5 billion. Even though it is a mature technology, continued performance improvement is still possible. In common with other types of batteries, the performance of alkaline batteries is strongly affected by the composition and microstructure of the electrodes, especially the cathode. Naturall...

The original regression hypothesis of Onsager contains more physics than the fluctuation-dissipation theorem. A discrepancy in a prior derivation of the reciprocal relation for Stefan-Maxwell coefficients through fluctuation theory is resolved. Along with a demonstration of the correct reciprocal relation, it is shown how to use the regression hypo...

Electronic conductivity of battery electrodes and the interfacial resistance at the current collector are key metrics affecting cell performance. However, in many cases they have not been properly quantified because of the lack of a suitably accurate and convenient non-destructive measurement method. There are also indications that conductivity acr...

LiCoO2 electrodes contain three phases, or domains, each having specific-intended functions: ion-conducting pore space, lithium-ion-reacting active material, and electron conducting carbon-binder domain (CBD). Transport processes take place in all domains on different characteristic length scales: from the micrometer scale in the active material gr...

An accurate assessment of the electronic conductivity of electrodes is necessary for understanding and optimizing battery performance. The bulk electronic conductivity of porous LiCoO2-based cathodes was measured as a function of porosity, pressure, carbon fraction, and the presence of an electrolyte. The measurements were performed by delamination...

This paper describes-research to understand the relationships between materials, microstructure, and performance for primary alkaline battery cathodes composed primarily of electrolytic manganese dioxide (EMD). Specifically, the effect of various carbon additives on electronic transport within cathodes was investigated. Of the various carbon additi...

X-ray tomography allows the active-material domain (LiCoO2) of Li-ion battery cathodes to be imaged, but it is unable to resolve the carbon-binder domain (CBD). Here, a new method for creating a complete 3D representation (virtual design) of all three phases of a cathode is provided; this includes the active-material domain, the CBD, and the electr...

The objective of this work is to build an accurate 3D model to provide understanding of the effect of microstructure electrode performance, specifically on both electronic and ionic conductivity. The investigated system, the widely used primary alkaline battery, uses electrolytic manganese dioxide (EMD) active material in the cathode. An accurate a...

Monoliths are considered to be a low pressure alternative to particle packed columns for liquid chromatography (LC). However, the chromatographic performance of organic monoliths, in particular, has still not reached the level of particle packed columns. Since chromatographic performance can be attributed to morphological features of the monoliths,...

A new polarizable water model is developed for molecular dynamics (MD) simulations of the proton transport process. The interatomic potential model has three important submodels corresponding to electrostatic interactions, making and breaking of covalent bonds, and treatment of electron exchange and correlation through a van der Waals potential. A...

A non-microbial fuel cell utilizing an organic fuel containing a hydroxyl group and a non-metallic catalyst is disclosed. Compositions for use in and methods for generating electric energy from chemical energy using fuel cells are also disclosed. Compositions for use in and methods of storing energy using fuel cells are also disclosed.

Viologen, organic catalyst, must be immobilized on the anode of a direct-carbohydrate fuel cell to achieve a recyclable and efficient fuel cell. Novel viologen monomers, called 1-(3-acrylamidopropyl)-(4,4′-bipyridin)-1- ium (AAPB), are synthesized and immobilized on a gold electrode surface by electroreductive polymerizaiton. The polymeric viologen...

We present a new method to quantify tortuosity in the porous, LiCoO 2 cathode of a Li-ion battery. The starting point is a previously published 3D reconstruction from FIB/SEM images with three phases, the active material domain, carbon-binder domain and pore space. Based on this geometrical configuration, we com-pute effective diffusivities, from w...

Detailed battery models require mass-transport resistance parameters such as ionic conductivity and salt diffusivity. Effective transport properties can be related to the tortuosities of the porous layers containing the electrolyte. Nevertheless, relatively few direct tortuosity measurements have been performed for cathodes and for anodes. Tortuosi...

In molecular simulations, Coulombic interactions are frequently treated using a lattice sum because the interactions decay very slowly and simple truncation can lead to artifacts. Traditional lattice sum methods such as Ewald and particle-particle particle-mesh (P3M) give total (volume-averaged) energy and virial stress, as well as particle forces,...

Dialkyl viologens are known to be effective catalysts in the oxidation of carbohydrates under alkaline conditions and are being investigated for use in direct-carbohydrate fuel cells (DCFCs). However, dialkyl viologens hydrolyze to more stable monoalkyl viologens under alkaline conditions. It has been reported that monoalkyl viologens also act as c...

This paper examines the use of amine-functionalized templates to create nanopatterned metal features. A key aspect of the work is the use of an additive to increase the plating density and enable continuous metallization of nanoscale features. Specifically, MPS (3-mercapto-1-propane sulfonate) was found to increase the plating density of copper on...

The goal of this work is to deposit nanoscale metal features on a nonconductive substrate in a specific and controlled manner in order to make nanoscale devices. To this end we studied the effects of several plating additives on electroless plating of nanoscale-thin layers in a model system, namely palladium metal on plain and chemically modified s...

The recently developed chemical potential perturbation (CPP) method [S. G. Moore and D. R. Wheeler, J. Chem. Phys. 134, 114514 (2011)] is extended to the lattice (Ewald) sum treatment of intermolecular potentials. The CPP method predicts chemical potentials for a range of composition points using the local (position-dependent) pressure tensor of an...

Dialkyl viologens are known to be effective catalysts for carbohydrate oxidation by O2 under the mild conditions of room temperature and pH 9–12 and have been used to construct a simple carbohydrate fuel cell. The mechanism of carbohydrate oxidation proceeds by a stepwise, dialkyl viologen-mediated, sequential oxidation starting at the anomeric car...

Monoalkyl viologens are N-alkyl-4,4'-bipyridine salts that are being considered as catalysts for oxidation of carbohydrates in alkaline media. Cyclic voltammograms of these viologens have been run and the results are reported here. Simple-fuel-cell tests were also run, with homogeneous viologens as catalysts and primarily fructose as fuel, and it w...

This work combines experiments and computer models in order to understand the relationships between electrode microstructure and ionic transport resistances so that one may predict cell performance from fundamental principles. A scanning electron microscope (SEM) with focused ion beam (FIB) was used to image sections of commercially made porous ele...

of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.

Catalytic oxidation of carbohydrates by oxygen using various viologens under mild conditions was recently shown to occur at high efficiency with formate and carbonate formed as products. However, high efficiency was only achieved at viologen/carbohydrate ratios >10. The use of such high catalyst ratios is undesirable and a mechanistic study was ini...

For non-inhibitory irradiances, the rate of algal biomass synthesis was modeled as the product of the algal autotrophic yield Φ(DW) and the flux of photons absorbed by the culture, as described using Beer-Lambert law. As a contrast to earlier attempts, the use of scatter-corrected extinction coefficients enabled the validation of such approach, whi...

A new method, called chemical potential perturbation (CPP), has been developed to predict the chemical potential as a function of density in periodic molecular simulations. The CPP method applies a spatially varying external force field to the simulation, causing the density to depend upon position in the simulation cell. Following equilibration th...

This work encompasses modeling and experimental work to improve understanding of transport and other resistances for LiFePO4 composite cathodes used in Li-ion batteries. Modeling LiFePO4 active material requires consideration of the carbon coating around the particle, phase-change behavior, and diffusion in only one of the lattice dimensions of the...

The Ewald sum method is commonly used in equilibrium simulations of polar fluids to enhance convergence of long-range Coulombic forces within modest-sized cubic simulation cells. In this work, we derive a form of the standard Ewald sum technique for use with non-equilibrium molecular dynamics (NEMD) simulations of viscosity that make use of the Lee...

Non-equilibrium molecular dynamics (NEMD) with isobaric and isokinetic controls were used to simulate the shear viscosity for binary mixtures of water, methanol and acetone, and for ternary mixtures. In all, 22 different liquid composition points were simulated at 298.15 K and 0.1 MPa. A new set of acetone potential parameters was developed, while...

An improved understanding of proton-transport mechanisms in aqueous and hydrophilic systems such as low-temperature fuel cells can be helpful in optimizing such systems. In hydrogen-bonded networks, protons transport by both vehicular and structural diffusion. In particular, structural diffusion which involves the making and breaking of covalent bo...

As has been recognized for several decades, molecular dynamics simulations can be an elegant way to calculate and predict transport properties, including diffusion coefficients. The active development in the field over the years has led to a number of simulation techniques for diffusivity, most notably the Green-Kubo relation for equilibrium molecu...

The chemical potential is a very useful and important property. It can be related to many different phenomena such as phase equilibria, including solubility and osmosis; transport processes such as diffusion; as well as chemical reaction rates. These phenomena are important in many industrial applications. A new method of simulating differences in...

Kirkwood-Buff (KB) solution theory is a means to obtain certain thermodynamic derivatives from knowledge of molecular distributions. In actual practice the required integrals over radial distribution functions suffer inaccuracies due to finite-distance truncation effects and their use in closed systems. In this work we discuss how best to minimize...

Deriving electrical energy from glucose and other carbohydrates under mild conditions is an important research objective because these biomolecules are abundant, renewable, have high energy density, and are convenient as fuels. This rich promise has not been realized because stable, inexpensive, and efficient catalysts are not available to oxidize...

Li-ion battery electrodes are ion-milled and prepared for three-dimensional reconstruction imaging using a focused ion beam and a method of automated serial sectioning. This tool is being developed as a means to gain additional information not typically obtained with traditional microscopy in order to improve models and further understand the struc...

An accurate assessment of liquid-phase mass transport resistances is necessary for understanding and optimizing battery performance using mathematical models. This work combines modeling and experiments to quantify tortuosity in electrolyte-filled porous battery structures (separator and active-material film). Tortuosities of separators were measur...

Dielectrophoresis has been used to place nanotubes, nanorods, nanowires, and other nanostructures between surface patterned metal electrodes. This technique can deposit a varying number of structures between each set of electrodes. We have developed a method to control the number of deposited singled-walled carbon nanotubes by tuning the impedance...

Investigation of viologen-based organic catalysts has shown them to be capable of directly oxidizing various sugars. Methyl viologen has been studied using oxygen uptake vial experiments, NMR analysis, and electrochemical methods. We have found that under appropriate conditions this catalyst is capable of completely oxidizing glucose to form carbon...