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Papers by Martin Bazant

Lithium-ion batteries are powering a revolution in electrification, but the underlying intercalat... more Lithium-ion batteries are powering a revolution in electrification, but the underlying intercalation 25

Physical Review E, Nov 10, 2010

We provide some general theoretical results to guide the optimization of transverse hydrodynamic ... more We provide some general theoretical results to guide the optimization of transverse hydrodynamic phenomena in superhydrophobic channels. Our focus is on the canonical micro-and nanofluidic geometry of a parallel-plate channel with an arbitrary two-component (low-slip and high-slip) coarse texture, varying on scales larger than the channel thickness. By analyzing rigorous bounds on the permeability, over all possible patterns, we optimize the area fractions, slip lengths, geometry and orientation of the surface texture to maximize transverse flow. In the case of two aligned striped surfaces, very strong transverse flows are possible. Optimized superhydrophobic surfaces may find applications in passive microfluidic mixing and amplification of transverse electrokinetic phenomena.

APS March Meeting Abstracts, Nov 1, 2003

Motivated by recent work on AC electro-osmosis, a general theory of ``induced-charge electro-osmo... more Motivated by recent work on AC electro-osmosis, a general theory of ``induced-charge electro-osmosis'' (ICEO) has been developed, and a variety of new microfluidic pumping and mixing strategies have been proposed using weak DC and AC applied voltages [physics/0304090, physics/0306100]. ICEO slip of a liquid electrolyte generally occurs at polarizable (metal or dielectric) surfaces in response to applied electric fields. Due

Journal of Physical Chemistry B, Mar 31, 2005

We present the application of a mathematical method reported earlier 1 by which the van der Waals... more We present the application of a mathematical method reported earlier 1 by which the van der Waals-Platteeuw statistical mechanical model with the Lennard-Jones and Devonshire approximation can be posed as an integral equation with the unknown function being the intermolecular potential between the guest molecules and the host molecules. This method allows us to solve for the potential directly for hydrates for which the Langmuir constants are computed, either from experimental data or from ab initio data. Given the assumptions made in the van der Waals-Platteeuw model with the spherical-cell approximation, there are an infinite number of solutions; however, the only solution without cusps is a unique central-well solution in which the potential is at a finite minimum at the center to the cage. From this central-well solution, we have found the potential well depths and volumes of negative energy for 16 single-component hydrate systems: ethane (C 2 H 6), cyclopropane (C 3 H 6), methane (CH 4), argon (Ar), and chlorodifluoromethane (R-22) in structure I; and ethane (C 2 H 6), cyclopropane (C 3 H 6), propane (C 3 H 8), isobutane (C 4 H 10), methane (CH 4), argon (Ar), trichlorofluoromethane (R-11), dichlorodifluoromethane (R-12), bromotrifluoromethane (R-13B1), chloroform (CHCl 3), and 1,1,1,2-tetrafluoroethane (R-134a) in structure II. This method and the calculated cell potentials were validated by predicting existing mixed hydrate phase equilibrium data without any fitting parameters and calculating mixture phase diagrams for methane, ethane, isobutane, and cyclopropane mixtures. Several structural transitions that have been determined experimentally as well as some structural transitions that have not been examined experimentally were also predicted. In the methane-cyclopropane hydrate system, a structural transition from structure I to structure II and back to structure I is predicted to occur outside of the known structure II range for the cyclopropane hydrate. Quintuple (L w-sI-sII-L hc-V) points have been predicted for the ethane-propane-water (277.3 K, 12.28 bar, and x eth,waterfree) 0.676) and ethane-isobutanewater (274.7 K, 7.18 bar, and x eth,waterfree) 0.81) systems.

Journal of Physical Chemistry Letters, Oct 4, 2018

One challenge in developing the next generation of lithium-ion batteries is the replacement of or... more One challenge in developing the next generation of lithium-ion batteries is the replacement of organic electrolytes, which are flammable and most often contain toxic and thermally unstable lithium salts, with safer, environmentally friendly alternatives. Recently developed Water-in-Salt Electrolytes (WiSEs) were found to be a promising alternative, having also enhanced electrochemical stability. In this work, we develop a simple modified Poisson-Fermi theory, which demonstrates the fine interplay between electrosorption, solvation, and ion correlations. The phenomenological parameters are extracted from molecular simulations, also performed here. The theory reproduces the electrical double layer structure of WiSEs with remarkable accuracy.

Meeting abstracts, May 1, 2020

Growth of the solid electrolyte interphase (SEI) is a major driver of capacity fade in LIBs. Desp... more Growth of the solid electrolyte interphase (SEI) is a major driver of capacity fade in LIBs. Despite its importance, the fundamental mechanisms remain unclear, primarily because of the complicated reaction pathways involved[1–3]. SEI growth can be both electrochemical and chemical in nature[4], and thus, it is a strong function of the potential and degree of lithiation of the electrode. We model the early-stage and long-term growth of SEI by accurately capturing the potential dependence of its formation kinetics as well as long term rate limiting steps, and validating it against the world’s largest open source battery cycling data, generated in-house[5]. This is done using the Multiphase Porous Electrode Theory (MPET) framework[6] on graphite (phase separating) and carbon black (non phase separating) particles. Lithium plating is another key degradation phenomenon that has been elusive, and it becomes important while trying to fast-charge batteries, i.e., 0% - 80% state-of-charge in 30 mins. We show that lithium plating is a key function of electrode morphology, phase-separation dynamics and potential. Phase-separation in graphite is modeled in the electrode using the Cahn-Hilliard Reaction framework described by Bazant[7]. We understand the electrochemistry of the onset of lithium plating with in-situ measurements connected to real time cell potential in a phase-separating electrode for the first time[8]. Results indicate that the peak SEI-forming currents are higher for higher driving currents. Also, we find that SEI only grows during electrode lithiation, i.e. the battery only degrades while being charged. We also find that onset of lithium plating is correctly captured only when phase separation in active material is accounted for. Further, the onset of plating is delayed on electrodes with a thick SEI layer – understanding SEI/plating coupling is integral to predicting fast charging manufacturing protocols for LIBs. This work holds promise for the predictive design of procedures[9] for manufacture and formation of LIBs. [1] Cohen, Y. S.; Cohen, Y.; Aurbach, D. Micromorphological Studies of Lithium Electrodes in Alkyl Carbonate Solutions Using in Situ Atomic Force Microscopy. J. Phys. Chem. B 2000, 104, 12282–12291. https://doi.org/10.1021/jp002526b. [2] Horstmann, B.; Single, F.; Latz, A. Review on Multi-Scale Models of Solid-Electrolyte Interphase Formation, Current Opinion in Electrochemistry 13, 62-69 2019. [3] Nie, M.; Abraham, D. P.; Seo, D. M.; Chen, Y.; Bose, A.; Lucht, B. L. Role of Solution Structure in Solid Electrolyte Interphase Formation on Graphite with LiPF6 in Propylene Carbonate. J. Phys. Chem. C 2013, 117 (48), 25381–25389, https://doi.org/10.1021/jp409765w. [4] Das, S.; Attia, P. M.; Chueh, W. C.; Bazant, M. Z. Electrochemical Kinetics of SEI Growth on Carbon Black: Part II. Modeling. J. Electrochem. Soc. 2019, 166 (4), E107– E118. https://doi.org/10.1149/2.0241904jes. [5] Attia, P. M.; Das, S.; Harris, S. J.; Bazant, M. Z.; Chueh, W. C. Electrochemical Kinetics of SEI Growth on Carbon Black: Part I. Experiments. J. Electrochem. Soc. 2019, 166 (4), E97–E106. https://doi.org/10.1149/2.0231904jes. [6] Smith, R. B.; Bazant, M. Z. Multiphase Porous Electrode Theory, J. Electrochem. Soc. 2017, 164 (11). https://doi.org/10.1149/2.0171711jes. [7] Bazant, M. Z., Theory of chemical kinetics and charge transfer based on nonequilibrium thermodynamics, Accounts of Chemical Research, 46(5), 1144–1160. https://doi.org/10.1021/ar300145c [8] T. Gao, Y. Han, S. Das, T. Zhou, D. Fraggedakis, N. Nadkarni, C. N. Yeh, W. Chueh, J. Li, M.Z. Bazant, Interplay of lithium intercalation and plating on graphite using in-situ optical measurements, submitted. [9] Huang, W.; Attia, P. M.; Wang, H.; Renfrew, S. E.; Jin, N.; Das, S.; Zhang, Z.; Boyle, D. T.; Li, Y.; Bazant, M. Z.; McCloskey, B. D.; Chueh, W. C. and Cui, Y.; Nano Letters 2019 19 (8), 5140-5148. DOI: 10.1021/acs.nanolett.9b01515

arXiv (Cornell University), Jul 21, 2014

The Marcus-Hush-Chidsey (MHC) model is well known in electro-analytical chemistry as a successful... more The Marcus-Hush-Chidsey (MHC) model is well known in electro-analytical chemistry as a successful microscopic theory of outer-sphere electron transfer at metal electrodes, but it is unfamiliar and rarely used in electrochemical engineering. One reason may be the difficulty of evaluating the MHC reaction rate, which is defined as an improper integral of the Marcus rate over the Fermi distribution of electron energies. Here, we report a simple analytical approximation of the MHC integral that interpolates between exact asymptotic limits for large overpotentials, as well as for large or small reorganization energies, and exhibits less than 5% relative error for all reasonable parameter values. This result enables the MHC model to be considered as a practical alternative to the ubiquitous Butler-Volmer equation for improved understanding and engineering of electrochemical systems.

EPL, Dec 1, 2010

In multiphase flow in confined geometries an elementary event concerns the interaction of a dropl... more In multiphase flow in confined geometries an elementary event concerns the interaction of a droplet with an obstacle. As a model of this configuration we study the collision of a droplet with a circular post that spans a significant fraction of the cross section of a microfluidic channel. We demonstrate that there exist conditions for which a drop moves completely around the obstacle without breaking, while for the same geometry but higher speeds the drop breaks. Therefore, we identify a critical value of the capillary number above which a drop will break. We explain the results with a one-dimensional model characterizing the flow in the narrow gaps on either side of the obstacle, which identifies a surface-tension-driven instability associated with a variation in the permeability in the flow direction. The model captures the major features of the experimental observations.

Science, Aug 5, 2016

The kinetics and uniformity of ion insertion reactions at the solid-liquid interface govern the r... more 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 FePO 4 , 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. This coupling of lithium composition and surface reaction rates controls the kinetics and uniformity during electrochemical ion insertion.

Journal of The Electrochemical Society, 2013

A mathematical theory is presented for the charging and discharging behavior of membraneless elec... more A mathematical theory is presented for the charging and discharging behavior of membraneless electrochemical cells that rely on slow diffusion in laminar flow to separate the half reactions. Ion transport is described by the Nernst-Planck equations for a flowing quasi-neutral electrolyte with heterogeneous Butler-Volmer kinetics. Analytical approximations for the current-voltage relation and the concentration and potential profiles are derived by boundary layer analysis (in the relevant limit of large Peclet numbers) and validated against finite-element numerical solutions. Both Poiseuille and plug flows are considered to describe channels of various geometries, with and without porous flow channels. The tradeoff between power density and reactant crossover and utilization is predicted analytically. The theory is applied to the membrane-less Hydrogen Bromine Laminar Flow Battery and found to accurately predict the experimental and simulated current-voltage data for different flow rates and reactant concentrations, during both charging and discharging. This establishes the utility of the theory to understand and optimize the performance of membrane-less electrochemical flow cells, which could also be extended to other fluidic architectures.

Physical Review Letters, Feb 4, 2008

The application of AC electric fields in aqueous suspensions of anisotropic particles leads to un... more The application of AC electric fields in aqueous suspensions of anisotropic particles leads to unbalanced liquid flows and nonlinear, induced-charge electrophoretic (ICEP) motion. We report experimental observations of the motion of "Janus" microparticles with one dielectric and one metal-coated hemisphere induced by uniform fields of frequency 100 Hz-10 kHz in NaCl solutions. The motion is perpendicular to the field axis and persists after particles are attracted to a glass wall. This phenomenon may find applications in microactuators, microsensors, and microfluidic devices.

Meeting abstracts, Jul 7, 2022

This talk will describe the physics of driven nucleation and growth in battery materials. The res... more This talk will describe the physics of driven nucleation and growth in battery materials. The resulting nonequilibrium pattern formation may be either reaction-limited or transport limited. Examples of the former include driven phase separation in Li-ion batteries, electrodeposition in Li-air batteries, and Li plating in Li-ion batteries, controlled by electro-autocatalysis and competing electrochemical reactions. Examples of the latter include stable electrodeposition in Li-metal batteries with charged porous separators, controlled by deionization shock waves.

Meeting abstracts, May 1, 2020

Potential safety hazard of lithium ion batteries, their long recharging time and performance degr... more Potential safety hazard of lithium ion batteries, their long recharging time and performance degradation during usage are the major obstacles that prevent the wide adoption of electric vehicles in our society. Lithium plating on graphite anode is considered the leading cause of thermal runaway, degradation and the barrier for fast charging. However, the onset of lithium plating on graphite anodes is not well understood. For the first time, we resolved the spatial dynamics of lithiation of a single graphite particle using in-situ optical microscopy, and shed light on the interplay between lithium intercalation and plating. Enabled by simultaneously monitoring of the voltage, phase transformation and lithium plating, we are able to elucidate the energetics and kinetics of the two competing reactions, and establish a comprehensive mechanistic picture of Li plating mechanism on graphite anode. The proposed mechanism was further validated by simulation using a 1-D phase field model. This work is therefore providing insights on guidelines of designing graphite anode and operating LiB for reducing the risk of lithium plating.

Applied Physics Letters, Oct 2, 2006

This letter demonstrates dramatic improvements in flow rate and frequency range over conventional... more This letter demonstrates dramatic improvements in flow rate and frequency range over conventional planar AC electro-osmotic (ACEO) pumps by exploiting three-dimensional (3D) stepped electrodes. A 3D ACEO pump was fabricated by electroplating steps on a symmetric electrode array and tested against a state-of-the-art asymmetric planar ACEO pump in a microfluidic loop. For all frequencies (0.1-100 kHz), the 3D pump had a faster flow rate, in some cases by an order of magnitude. Our experimental results suggest that, after some optimization, mm/sec velocities will be attainable with alternating battery voltages, which presents an exciting opportunity for microfluidics. Manuscript Microfluidics is a growing area of science and technology with important applications in biomedical devices and portable electronics. Traditional pressure-driven flows do not scale well with miniaturization, due to large viscous stresses, so other pumping techniques have been explored 1. An attractive alternative is electro-osmosis, the effective slip of a liquid electrolyte past a solid surface in

Meeting abstracts, Nov 23, 2020

Growth of the solid electrolyte interphase (SEI) is a major driver of capacity fade in LIBs. Desp... more Growth of the solid electrolyte interphase (SEI) is a major driver of capacity fade in LIBs. Despite its importance, the fundamental mechanisms remain unclear, primarily because of the complicated reaction pathways involved [1–3]. SEI growth can be both electrochemical and chemical in nature [4,5], and thus, it is a strong function of the potential and degree of lithiation of the electrode. We model the early-stage and long-term growth of SEI by accurately capturing the potential dependence of its formation kinetics as well as long term rate limiting steps. Battery degradation involves a complex interplay of multiple phenomena, most of which are unknown. Our model captures some of the essential trends that we see while cycling hundreds of commercial cells [6]. This is done using the Multiphase Porous Electrode Theory (MPET) framework [7] on graphite (phase separating) and carbon black (non phase separating) particles. Lithium plating is another key degradation phenomenon that has been elusive, and it becomes important while trying to fast-charge batteries, i.e., 0% - 80% state-of-charge in 30 mins. We show that lithium plating is a key function of electrode morphology, phase-separation dynamics and potential. Phase-separation in graphite is modeled in the electrode using the Cahn-Hilliard Reaction framework described by Bazant [8]. We understand the electrochemistry of the onset of lithium plating with in-situ measurements connected to real time cell potential in a phase-separating electrode [9]. Results indicate that the peak SEI-forming currents are higher for higher driving currents and that SEI only grows during electrode lithiation, i.e. the battery only degrades while being charged. Additionally we capture a transition in the time-dependence of capacity fade from a steep initial drop to a more gradual ‘square-root-of-time’ trend by modeling the SEI as a bilayer with different rate-limiting steps for each type of SEI. We also find that onset of lithium plating is correctly captured only when phase separation in active material is accounted for. Further, the onset of plating is delayed on electrodes with a thick SEI layer – understanding SEI/plating coupling is integral to predicting fast charging manufacturing protocols for LIBs. This work holds promise for the predictive design of procedures [10] for manufacture and formation of LIBs. [1] Cohen, Y. S.; Cohen, Y.; Aurbach, D. Micromorphological Studies of Lithium Electrodes in Alkyl Carbonate Solutions Using in Situ Atomic Force Microscopy. J. Phys. Chem. B 2000, 104, 12282–12291. https://doi.org/10.1021/jp002526b. [2] Horstmann, B.; Single, F.; Latz, A. Review on Multi-Scale Models of Solid-Electrolyte Interphase Formation, Current Opinion in Electrochemistry 13, 62-69 2019. [3] Nie, M.; Abraham, D. P.; Seo, D. M.; Chen, Y.; Bose, A.; Lucht, B. L. Role of Solution Structure in Solid Electrolyte Interphase Formation on Graphite with LiPF6 in Propylene Carbonate. J. Phys. Chem. C 2013, 117 (48), 25381–25389, https://doi.org/10.1021/jp409765w. [4] Das, S.; Attia, P. M.; Chueh, W. C.; Bazant, M. Z. Electrochemical Kinetics of SEI Growth on Carbon Black: Part II. Modeling. J. Electrochem. Soc. 2019, 166 (4), E107– E118. https://doi.org/10.1149/2.0241904jes. [5] Attia, P. M.; Das, S.; Harris, S. J.; Bazant, M. Z.; Chueh, W. C. Electrochemical Kinetics of SEI Growth on Carbon Black: Part I. Experiments. J. Electrochem. Soc. 2019, 166 (4), E97–E106. https://doi.org/10.1149/2.0231904jes. [6] Severson, K. A., Attia, P. M., Jin, N., Perkins, N., Jiang, B., Yang, Z., ... & Bazant, M. Z. (2019). Data-driven prediction of battery cycle life before capacity degradation. Nature Energy, 4(5), 383-391. [7] Smith, R. B.; Bazant, M. Z. Multiphase Porous Electrode Theory, J. Electrochem. Soc. 2017, 164 (11). https://doi.org/10.1149/2.0171711jes. [8] Bazant, M. Z., Theory of chemical kinetics and charge transfer based on nonequilibrium thermodynamics, Accounts of Chemical Research, 46(5), 1144–1160. https://doi.org/10.1021/ar300145c [9] T. Gao, Y. Han, S. Das, T. Zhou, D. Fraggedakis, N. Nadkarni, C. N. Yeh, W. Chueh, J. Li, M.Z. Bazant, Interplay of lithium intercalation and plating on graphite using in-situ optical measurements, submitted. [10] Huang, W.; Attia, P. M.; Wang, H.; Renfrew, S. E.; Jin, N.; Das, S.; Zhang, Z.; Boyle, D. T.; Li, Y.; Bazant, M. Z.; McCloskey, B. D.; Chueh, W. C. and Cui, Y.; Nano Letters 2019 19 (8), 5140-5148. DOI: 10.1021/acs.nanolett.9b01515

Electrochimica Acta, Jun 1, 2014

Electrochemical impedance spectra for battery electrodes are usually interpreted using models tha... more Electrochemical impedance spectra for battery electrodes are usually interpreted using models that assume isotropic active particles, having uniform current density and symmetric diffusivities. While this can be reasonable for amorphous or polycrystalline materials with randomly oriented grains, modern electrode materials increasingly consist of highly anisotropic, single-crystalline, nanoparticles, with different impedance characteristics. In this paper, analytical expressions are derived for the impedance of anisotropic particles with tensorial diffusivities and orientation-dependent surface reaction rates and capacitances. The resulting impedance spectrum contains clear signatures of the anisotropic material properties and aspect ratio, as well as statistical variations in any of these parameters.

Nano Letters, Oct 20, 2011

Using a novel electrochemical phase-field model, we question the common belief that Li x FePO 4 n... more Using a novel electrochemical phase-field model, we question the common belief that Li x FePO 4 nanoparticles 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.

Physical Review Letters, Feb 10, 2004

We give a general, physical description of "induced-charge electro-osmosis" (ICEO), the nonlinear... more We give a general, physical description of "induced-charge electro-osmosis" (ICEO), the nonlinear electrokinetic slip at a polarizable surface, in the context of some new techniques for microfluidic pumping and mixing. ICEO generalizes "AC electro-osmosis" at micro-electrode arrays to various dielectric and conducting structures in weak DC or AC electric fields. The basic effect produces micro-vortices to enhance mixing in microfluidic devices, while various broken symmetries-controlled potential, irregular shape, non-uniform surface properties, and field gradients-can be exploited to produce streaming flows. Although we emphasize the qualitative picture of ICEO, we also briefly describe the mathematical theory (for thin double layers and weak fields) and apply it to a metal cylinder with a dielectric coating in a suddenly applied DC field.

Journal of Colloid and Interface Science, May 1, 2007

Recent numerical and experimental studies have investigated the increase in efficiency of microfl... more Recent numerical and experimental studies have investigated the increase in efficiency of microfluidic ac electro-osmotic pumps by introducing nonplanar geometries with raised steps on the electrodes. In this study, we analyze the effect of the step height on ac electro-osmotic pump performance. AC electro-osmotic pumps with three-dimensional electroplated steps are fabricated on glass substrates and pumping velocities of low ionic strength electrolyte solutions are measured systematically using a custom microfluidic device. Numerical simulations predict an improvement in pump performance with increasing step height, at a given frequency and voltage, up to an optimal step height, which qualitatively matches the trend observed in experiment. For a broad range of step heights near the optimum, the observed flow is much faster than with existing planar pumps (at the same voltage and minimum feature size) and in the theoretically predicted direction of the "fluid conveyor belt" mechanism. For small step heights, the experiments also exhibit significant flow reversal at the optimal frequency, which cannot be explained by the theory, although the simulations predict weak flow reversal at higher frequencies due to incomplete charging. These results provide insight to an important parameter for the design of nonplanar electro-osmotic pumps and clues to improve the fundamental theory of ACEO.

In this paper, the development of a novel low power (mW), low current (mA) AC microfluidic pump i... more In this paper, the development of a novel low power (mW), low current (mA) AC microfluidic pump is described that is capable of generating kPa head pressures.

Lithium-ion batteries are powering a revolution in electrification, but the underlying intercalat... more Lithium-ion batteries are powering a revolution in electrification, but the underlying intercalation 25

Physical Review E, Nov 10, 2010

We provide some general theoretical results to guide the optimization of transverse hydrodynamic ... more We provide some general theoretical results to guide the optimization of transverse hydrodynamic phenomena in superhydrophobic channels. Our focus is on the canonical micro-and nanofluidic geometry of a parallel-plate channel with an arbitrary two-component (low-slip and high-slip) coarse texture, varying on scales larger than the channel thickness. By analyzing rigorous bounds on the permeability, over all possible patterns, we optimize the area fractions, slip lengths, geometry and orientation of the surface texture to maximize transverse flow. In the case of two aligned striped surfaces, very strong transverse flows are possible. Optimized superhydrophobic surfaces may find applications in passive microfluidic mixing and amplification of transverse electrokinetic phenomena.

APS March Meeting Abstracts, Nov 1, 2003

Motivated by recent work on AC electro-osmosis, a general theory of ``induced-charge electro-osmo... more Motivated by recent work on AC electro-osmosis, a general theory of ``induced-charge electro-osmosis'' (ICEO) has been developed, and a variety of new microfluidic pumping and mixing strategies have been proposed using weak DC and AC applied voltages [physics/0304090, physics/0306100]. ICEO slip of a liquid electrolyte generally occurs at polarizable (metal or dielectric) surfaces in response to applied electric fields. Due

Journal of Physical Chemistry B, Mar 31, 2005

We present the application of a mathematical method reported earlier 1 by which the van der Waals... more We present the application of a mathematical method reported earlier 1 by which the van der Waals-Platteeuw statistical mechanical model with the Lennard-Jones and Devonshire approximation can be posed as an integral equation with the unknown function being the intermolecular potential between the guest molecules and the host molecules. This method allows us to solve for the potential directly for hydrates for which the Langmuir constants are computed, either from experimental data or from ab initio data. Given the assumptions made in the van der Waals-Platteeuw model with the spherical-cell approximation, there are an infinite number of solutions; however, the only solution without cusps is a unique central-well solution in which the potential is at a finite minimum at the center to the cage. From this central-well solution, we have found the potential well depths and volumes of negative energy for 16 single-component hydrate systems: ethane (C 2 H 6), cyclopropane (C 3 H 6), methane (CH 4), argon (Ar), and chlorodifluoromethane (R-22) in structure I; and ethane (C 2 H 6), cyclopropane (C 3 H 6), propane (C 3 H 8), isobutane (C 4 H 10), methane (CH 4), argon (Ar), trichlorofluoromethane (R-11), dichlorodifluoromethane (R-12), bromotrifluoromethane (R-13B1), chloroform (CHCl 3), and 1,1,1,2-tetrafluoroethane (R-134a) in structure II. This method and the calculated cell potentials were validated by predicting existing mixed hydrate phase equilibrium data without any fitting parameters and calculating mixture phase diagrams for methane, ethane, isobutane, and cyclopropane mixtures. Several structural transitions that have been determined experimentally as well as some structural transitions that have not been examined experimentally were also predicted. In the methane-cyclopropane hydrate system, a structural transition from structure I to structure II and back to structure I is predicted to occur outside of the known structure II range for the cyclopropane hydrate. Quintuple (L w-sI-sII-L hc-V) points have been predicted for the ethane-propane-water (277.3 K, 12.28 bar, and x eth,waterfree) 0.676) and ethane-isobutanewater (274.7 K, 7.18 bar, and x eth,waterfree) 0.81) systems.

Journal of Physical Chemistry Letters, Oct 4, 2018

One challenge in developing the next generation of lithium-ion batteries is the replacement of or... more One challenge in developing the next generation of lithium-ion batteries is the replacement of organic electrolytes, which are flammable and most often contain toxic and thermally unstable lithium salts, with safer, environmentally friendly alternatives. Recently developed Water-in-Salt Electrolytes (WiSEs) were found to be a promising alternative, having also enhanced electrochemical stability. In this work, we develop a simple modified Poisson-Fermi theory, which demonstrates the fine interplay between electrosorption, solvation, and ion correlations. The phenomenological parameters are extracted from molecular simulations, also performed here. The theory reproduces the electrical double layer structure of WiSEs with remarkable accuracy.

Meeting abstracts, May 1, 2020

Growth of the solid electrolyte interphase (SEI) is a major driver of capacity fade in LIBs. Desp... more Growth of the solid electrolyte interphase (SEI) is a major driver of capacity fade in LIBs. Despite its importance, the fundamental mechanisms remain unclear, primarily because of the complicated reaction pathways involved[1–3]. SEI growth can be both electrochemical and chemical in nature[4], and thus, it is a strong function of the potential and degree of lithiation of the electrode. We model the early-stage and long-term growth of SEI by accurately capturing the potential dependence of its formation kinetics as well as long term rate limiting steps, and validating it against the world’s largest open source battery cycling data, generated in-house[5]. This is done using the Multiphase Porous Electrode Theory (MPET) framework[6] on graphite (phase separating) and carbon black (non phase separating) particles. Lithium plating is another key degradation phenomenon that has been elusive, and it becomes important while trying to fast-charge batteries, i.e., 0% - 80% state-of-charge in 30 mins. We show that lithium plating is a key function of electrode morphology, phase-separation dynamics and potential. Phase-separation in graphite is modeled in the electrode using the Cahn-Hilliard Reaction framework described by Bazant[7]. We understand the electrochemistry of the onset of lithium plating with in-situ measurements connected to real time cell potential in a phase-separating electrode for the first time[8]. Results indicate that the peak SEI-forming currents are higher for higher driving currents. Also, we find that SEI only grows during electrode lithiation, i.e. the battery only degrades while being charged. We also find that onset of lithium plating is correctly captured only when phase separation in active material is accounted for. Further, the onset of plating is delayed on electrodes with a thick SEI layer – understanding SEI/plating coupling is integral to predicting fast charging manufacturing protocols for LIBs. This work holds promise for the predictive design of procedures[9] for manufacture and formation of LIBs. [1] Cohen, Y. S.; Cohen, Y.; Aurbach, D. Micromorphological Studies of Lithium Electrodes in Alkyl Carbonate Solutions Using in Situ Atomic Force Microscopy. J. Phys. Chem. B 2000, 104, 12282–12291. https://doi.org/10.1021/jp002526b. [2] Horstmann, B.; Single, F.; Latz, A. Review on Multi-Scale Models of Solid-Electrolyte Interphase Formation, Current Opinion in Electrochemistry 13, 62-69 2019. [3] Nie, M.; Abraham, D. P.; Seo, D. M.; Chen, Y.; Bose, A.; Lucht, B. L. Role of Solution Structure in Solid Electrolyte Interphase Formation on Graphite with LiPF6 in Propylene Carbonate. J. Phys. Chem. C 2013, 117 (48), 25381–25389, https://doi.org/10.1021/jp409765w. [4] Das, S.; Attia, P. M.; Chueh, W. C.; Bazant, M. Z. Electrochemical Kinetics of SEI Growth on Carbon Black: Part II. Modeling. J. Electrochem. Soc. 2019, 166 (4), E107– E118. https://doi.org/10.1149/2.0241904jes. [5] Attia, P. M.; Das, S.; Harris, S. J.; Bazant, M. Z.; Chueh, W. C. Electrochemical Kinetics of SEI Growth on Carbon Black: Part I. Experiments. J. Electrochem. Soc. 2019, 166 (4), E97–E106. https://doi.org/10.1149/2.0231904jes. [6] Smith, R. B.; Bazant, M. Z. Multiphase Porous Electrode Theory, J. Electrochem. Soc. 2017, 164 (11). https://doi.org/10.1149/2.0171711jes. [7] Bazant, M. Z., Theory of chemical kinetics and charge transfer based on nonequilibrium thermodynamics, Accounts of Chemical Research, 46(5), 1144–1160. https://doi.org/10.1021/ar300145c [8] T. Gao, Y. Han, S. Das, T. Zhou, D. Fraggedakis, N. Nadkarni, C. N. Yeh, W. Chueh, J. Li, M.Z. Bazant, Interplay of lithium intercalation and plating on graphite using in-situ optical measurements, submitted. [9] Huang, W.; Attia, P. M.; Wang, H.; Renfrew, S. E.; Jin, N.; Das, S.; Zhang, Z.; Boyle, D. T.; Li, Y.; Bazant, M. Z.; McCloskey, B. D.; Chueh, W. C. and Cui, Y.; Nano Letters 2019 19 (8), 5140-5148. DOI: 10.1021/acs.nanolett.9b01515

arXiv (Cornell University), Jul 21, 2014

The Marcus-Hush-Chidsey (MHC) model is well known in electro-analytical chemistry as a successful... more The Marcus-Hush-Chidsey (MHC) model is well known in electro-analytical chemistry as a successful microscopic theory of outer-sphere electron transfer at metal electrodes, but it is unfamiliar and rarely used in electrochemical engineering. One reason may be the difficulty of evaluating the MHC reaction rate, which is defined as an improper integral of the Marcus rate over the Fermi distribution of electron energies. Here, we report a simple analytical approximation of the MHC integral that interpolates between exact asymptotic limits for large overpotentials, as well as for large or small reorganization energies, and exhibits less than 5% relative error for all reasonable parameter values. This result enables the MHC model to be considered as a practical alternative to the ubiquitous Butler-Volmer equation for improved understanding and engineering of electrochemical systems.

EPL, Dec 1, 2010

In multiphase flow in confined geometries an elementary event concerns the interaction of a dropl... more In multiphase flow in confined geometries an elementary event concerns the interaction of a droplet with an obstacle. As a model of this configuration we study the collision of a droplet with a circular post that spans a significant fraction of the cross section of a microfluidic channel. We demonstrate that there exist conditions for which a drop moves completely around the obstacle without breaking, while for the same geometry but higher speeds the drop breaks. Therefore, we identify a critical value of the capillary number above which a drop will break. We explain the results with a one-dimensional model characterizing the flow in the narrow gaps on either side of the obstacle, which identifies a surface-tension-driven instability associated with a variation in the permeability in the flow direction. The model captures the major features of the experimental observations.

Science, Aug 5, 2016

The kinetics and uniformity of ion insertion reactions at the solid-liquid interface govern the r... more 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 FePO 4 , 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. This coupling of lithium composition and surface reaction rates controls the kinetics and uniformity during electrochemical ion insertion.

Journal of The Electrochemical Society, 2013

A mathematical theory is presented for the charging and discharging behavior of membraneless elec... more A mathematical theory is presented for the charging and discharging behavior of membraneless electrochemical cells that rely on slow diffusion in laminar flow to separate the half reactions. Ion transport is described by the Nernst-Planck equations for a flowing quasi-neutral electrolyte with heterogeneous Butler-Volmer kinetics. Analytical approximations for the current-voltage relation and the concentration and potential profiles are derived by boundary layer analysis (in the relevant limit of large Peclet numbers) and validated against finite-element numerical solutions. Both Poiseuille and plug flows are considered to describe channels of various geometries, with and without porous flow channels. The tradeoff between power density and reactant crossover and utilization is predicted analytically. The theory is applied to the membrane-less Hydrogen Bromine Laminar Flow Battery and found to accurately predict the experimental and simulated current-voltage data for different flow rates and reactant concentrations, during both charging and discharging. This establishes the utility of the theory to understand and optimize the performance of membrane-less electrochemical flow cells, which could also be extended to other fluidic architectures.

Physical Review Letters, Feb 4, 2008

The application of AC electric fields in aqueous suspensions of anisotropic particles leads to un... more The application of AC electric fields in aqueous suspensions of anisotropic particles leads to unbalanced liquid flows and nonlinear, induced-charge electrophoretic (ICEP) motion. We report experimental observations of the motion of "Janus" microparticles with one dielectric and one metal-coated hemisphere induced by uniform fields of frequency 100 Hz-10 kHz in NaCl solutions. The motion is perpendicular to the field axis and persists after particles are attracted to a glass wall. This phenomenon may find applications in microactuators, microsensors, and microfluidic devices.

Meeting abstracts, Jul 7, 2022

This talk will describe the physics of driven nucleation and growth in battery materials. The res... more This talk will describe the physics of driven nucleation and growth in battery materials. The resulting nonequilibrium pattern formation may be either reaction-limited or transport limited. Examples of the former include driven phase separation in Li-ion batteries, electrodeposition in Li-air batteries, and Li plating in Li-ion batteries, controlled by electro-autocatalysis and competing electrochemical reactions. Examples of the latter include stable electrodeposition in Li-metal batteries with charged porous separators, controlled by deionization shock waves.

Meeting abstracts, May 1, 2020

Potential safety hazard of lithium ion batteries, their long recharging time and performance degr... more Potential safety hazard of lithium ion batteries, their long recharging time and performance degradation during usage are the major obstacles that prevent the wide adoption of electric vehicles in our society. Lithium plating on graphite anode is considered the leading cause of thermal runaway, degradation and the barrier for fast charging. However, the onset of lithium plating on graphite anodes is not well understood. For the first time, we resolved the spatial dynamics of lithiation of a single graphite particle using in-situ optical microscopy, and shed light on the interplay between lithium intercalation and plating. Enabled by simultaneously monitoring of the voltage, phase transformation and lithium plating, we are able to elucidate the energetics and kinetics of the two competing reactions, and establish a comprehensive mechanistic picture of Li plating mechanism on graphite anode. The proposed mechanism was further validated by simulation using a 1-D phase field model. This work is therefore providing insights on guidelines of designing graphite anode and operating LiB for reducing the risk of lithium plating.

Applied Physics Letters, Oct 2, 2006

This letter demonstrates dramatic improvements in flow rate and frequency range over conventional... more This letter demonstrates dramatic improvements in flow rate and frequency range over conventional planar AC electro-osmotic (ACEO) pumps by exploiting three-dimensional (3D) stepped electrodes. A 3D ACEO pump was fabricated by electroplating steps on a symmetric electrode array and tested against a state-of-the-art asymmetric planar ACEO pump in a microfluidic loop. For all frequencies (0.1-100 kHz), the 3D pump had a faster flow rate, in some cases by an order of magnitude. Our experimental results suggest that, after some optimization, mm/sec velocities will be attainable with alternating battery voltages, which presents an exciting opportunity for microfluidics. Manuscript Microfluidics is a growing area of science and technology with important applications in biomedical devices and portable electronics. Traditional pressure-driven flows do not scale well with miniaturization, due to large viscous stresses, so other pumping techniques have been explored 1. An attractive alternative is electro-osmosis, the effective slip of a liquid electrolyte past a solid surface in

Meeting abstracts, Nov 23, 2020

Growth of the solid electrolyte interphase (SEI) is a major driver of capacity fade in LIBs. Desp... more Growth of the solid electrolyte interphase (SEI) is a major driver of capacity fade in LIBs. Despite its importance, the fundamental mechanisms remain unclear, primarily because of the complicated reaction pathways involved [1–3]. SEI growth can be both electrochemical and chemical in nature [4,5], and thus, it is a strong function of the potential and degree of lithiation of the electrode. We model the early-stage and long-term growth of SEI by accurately capturing the potential dependence of its formation kinetics as well as long term rate limiting steps. Battery degradation involves a complex interplay of multiple phenomena, most of which are unknown. Our model captures some of the essential trends that we see while cycling hundreds of commercial cells [6]. This is done using the Multiphase Porous Electrode Theory (MPET) framework [7] on graphite (phase separating) and carbon black (non phase separating) particles. Lithium plating is another key degradation phenomenon that has been elusive, and it becomes important while trying to fast-charge batteries, i.e., 0% - 80% state-of-charge in 30 mins. We show that lithium plating is a key function of electrode morphology, phase-separation dynamics and potential. Phase-separation in graphite is modeled in the electrode using the Cahn-Hilliard Reaction framework described by Bazant [8]. We understand the electrochemistry of the onset of lithium plating with in-situ measurements connected to real time cell potential in a phase-separating electrode [9]. Results indicate that the peak SEI-forming currents are higher for higher driving currents and that SEI only grows during electrode lithiation, i.e. the battery only degrades while being charged. Additionally we capture a transition in the time-dependence of capacity fade from a steep initial drop to a more gradual ‘square-root-of-time’ trend by modeling the SEI as a bilayer with different rate-limiting steps for each type of SEI. We also find that onset of lithium plating is correctly captured only when phase separation in active material is accounted for. Further, the onset of plating is delayed on electrodes with a thick SEI layer – understanding SEI/plating coupling is integral to predicting fast charging manufacturing protocols for LIBs. This work holds promise for the predictive design of procedures [10] for manufacture and formation of LIBs. [1] Cohen, Y. S.; Cohen, Y.; Aurbach, D. Micromorphological Studies of Lithium Electrodes in Alkyl Carbonate Solutions Using in Situ Atomic Force Microscopy. J. Phys. Chem. B 2000, 104, 12282–12291. https://doi.org/10.1021/jp002526b. [2] Horstmann, B.; Single, F.; Latz, A. Review on Multi-Scale Models of Solid-Electrolyte Interphase Formation, Current Opinion in Electrochemistry 13, 62-69 2019. [3] Nie, M.; Abraham, D. P.; Seo, D. M.; Chen, Y.; Bose, A.; Lucht, B. L. Role of Solution Structure in Solid Electrolyte Interphase Formation on Graphite with LiPF6 in Propylene Carbonate. J. Phys. Chem. C 2013, 117 (48), 25381–25389, https://doi.org/10.1021/jp409765w. [4] Das, S.; Attia, P. M.; Chueh, W. C.; Bazant, M. Z. Electrochemical Kinetics of SEI Growth on Carbon Black: Part II. Modeling. J. Electrochem. Soc. 2019, 166 (4), E107– E118. https://doi.org/10.1149/2.0241904jes. [5] Attia, P. M.; Das, S.; Harris, S. J.; Bazant, M. Z.; Chueh, W. C. Electrochemical Kinetics of SEI Growth on Carbon Black: Part I. Experiments. J. Electrochem. Soc. 2019, 166 (4), E97–E106. https://doi.org/10.1149/2.0231904jes. [6] Severson, K. A., Attia, P. M., Jin, N., Perkins, N., Jiang, B., Yang, Z., ... & Bazant, M. Z. (2019). Data-driven prediction of battery cycle life before capacity degradation. Nature Energy, 4(5), 383-391. [7] Smith, R. B.; Bazant, M. Z. Multiphase Porous Electrode Theory, J. Electrochem. Soc. 2017, 164 (11). https://doi.org/10.1149/2.0171711jes. [8] Bazant, M. Z., Theory of chemical kinetics and charge transfer based on nonequilibrium thermodynamics, Accounts of Chemical Research, 46(5), 1144–1160. https://doi.org/10.1021/ar300145c [9] T. Gao, Y. Han, S. Das, T. Zhou, D. Fraggedakis, N. Nadkarni, C. N. Yeh, W. Chueh, J. Li, M.Z. Bazant, Interplay of lithium intercalation and plating on graphite using in-situ optical measurements, submitted. [10] Huang, W.; Attia, P. M.; Wang, H.; Renfrew, S. E.; Jin, N.; Das, S.; Zhang, Z.; Boyle, D. T.; Li, Y.; Bazant, M. Z.; McCloskey, B. D.; Chueh, W. C. and Cui, Y.; Nano Letters 2019 19 (8), 5140-5148. DOI: 10.1021/acs.nanolett.9b01515

Electrochimica Acta, Jun 1, 2014

Electrochemical impedance spectra for battery electrodes are usually interpreted using models tha... more Electrochemical impedance spectra for battery electrodes are usually interpreted using models that assume isotropic active particles, having uniform current density and symmetric diffusivities. While this can be reasonable for amorphous or polycrystalline materials with randomly oriented grains, modern electrode materials increasingly consist of highly anisotropic, single-crystalline, nanoparticles, with different impedance characteristics. In this paper, analytical expressions are derived for the impedance of anisotropic particles with tensorial diffusivities and orientation-dependent surface reaction rates and capacitances. The resulting impedance spectrum contains clear signatures of the anisotropic material properties and aspect ratio, as well as statistical variations in any of these parameters.

Nano Letters, Oct 20, 2011

Using a novel electrochemical phase-field model, we question the common belief that Li x FePO 4 n... more Using a novel electrochemical phase-field model, we question the common belief that Li x FePO 4 nanoparticles 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.

Physical Review Letters, Feb 10, 2004

We give a general, physical description of "induced-charge electro-osmosis" (ICEO), the nonlinear... more We give a general, physical description of "induced-charge electro-osmosis" (ICEO), the nonlinear electrokinetic slip at a polarizable surface, in the context of some new techniques for microfluidic pumping and mixing. ICEO generalizes "AC electro-osmosis" at micro-electrode arrays to various dielectric and conducting structures in weak DC or AC electric fields. The basic effect produces micro-vortices to enhance mixing in microfluidic devices, while various broken symmetries-controlled potential, irregular shape, non-uniform surface properties, and field gradients-can be exploited to produce streaming flows. Although we emphasize the qualitative picture of ICEO, we also briefly describe the mathematical theory (for thin double layers and weak fields) and apply it to a metal cylinder with a dielectric coating in a suddenly applied DC field.

Journal of Colloid and Interface Science, May 1, 2007

Recent numerical and experimental studies have investigated the increase in efficiency of microfl... more Recent numerical and experimental studies have investigated the increase in efficiency of microfluidic ac electro-osmotic pumps by introducing nonplanar geometries with raised steps on the electrodes. In this study, we analyze the effect of the step height on ac electro-osmotic pump performance. AC electro-osmotic pumps with three-dimensional electroplated steps are fabricated on glass substrates and pumping velocities of low ionic strength electrolyte solutions are measured systematically using a custom microfluidic device. Numerical simulations predict an improvement in pump performance with increasing step height, at a given frequency and voltage, up to an optimal step height, which qualitatively matches the trend observed in experiment. For a broad range of step heights near the optimum, the observed flow is much faster than with existing planar pumps (at the same voltage and minimum feature size) and in the theoretically predicted direction of the "fluid conveyor belt" mechanism. For small step heights, the experiments also exhibit significant flow reversal at the optimal frequency, which cannot be explained by the theory, although the simulations predict weak flow reversal at higher frequencies due to incomplete charging. These results provide insight to an important parameter for the design of nonplanar electro-osmotic pumps and clues to improve the fundamental theory of ACEO.

In this paper, the development of a novel low power (mW), low current (mA) AC microfluidic pump i... more In this paper, the development of a novel low power (mW), low current (mA) AC microfluidic pump is described that is capable of generating kPa head pressures.