Investigation and Optimization of Electrochemical Systems via Simulation and Theory

Electrochemical systems are ubiquitous in our modern lives in many forms, including energy storage and conversion devices like batteries and fuel cells, which enable our modern consumer electronics and underpin our shift away from fossil fuels, and corrosion, which affects many metallic structures. However, the physical phenomena that underlie the working of such systems often involve several mechanisms spanning multiple length scales. Due to this complexity, the research and development (R&D) of electrochemical systems has been challenging. The goal of this Ph.D. dissertation is to accelerate the R&D of electrochemical systems by adopting a Materials Genome Initiative (MGI)-based approach, which integrates modern computational tools and data-driven methods with experiments. The approach is employed to achieve four goals. The first is to implement modeling and simulation techniques that incorporate the relevant physics and solve the resulting mathematical model in complex geometries. This aspect also includes a machine-learning-based automated parameterization algorithm developed to determine unknown model parameters. The second is to generate insights into the behavior of the system, especially into the characteristics like the reaction current density distribution that cannot be easily obtained via experiments. The third is to optimize the system design for superior performance by exploiting these insights. The last goal is to reduce the computational cost associated with the approach by developing analytical and semi-analytical frameworks. These goals are achieved to varying extents for Li-ion batteries, Mg alloys undergoing microgalvanic corrosion, and solid oxide fuel cells. For Li-ion batteries, the tradeoff between the energy density and fast-charging capability in conventional electrodes is overcome by employing a novel-electrode architecture and studying its effect on the fast-charging performance using electrode-level simulations parameterized by machine learning. The novel architecture is formed by ablating vertical channels along the thickness of the electrodes with laser, and it is referred to as the Highly Ordered Laser-Patterned Electrode architecture. Simulations and theoretical analyses resulted in scientific understanding and an approach to optimizing such an architecture. For Mg alloys, an open-source software application in PRISMS-PF has been developed to simulate the microgalvanic corrosion behavior. Using the application, the effect of the electrochemical properties and the spatial distribution of second phases on the corrosion behavior is elucidated, and design strategies are devised for the alloy microstructure to minimize the corrosion rate. Finally, for solid-oxide fuel cells, the impedance behavior of a mixed ion-electron conducting cathode with an experimentally determined microstructure is simulated, and the effect of material properties on the impedance behavior is studied. Furthermore, the Adler-Lane-Steele model, a widely used analytical model for determining the impedance response, is extended to account for the spatial variation of the vacancy-concentration amplitude due to the reaction at the pore/solid interface.PhDMaterials Science and EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/177738/1/vishwasg_1.pd

Enabling 6C Fast Charging of Li- Ion Batteries with Graphite/Hard Carbon Hybrid Anodes

Li- ion batteries that can simultaneously achieve high- energy density and fast charging are essential for electric vehicles. Graphite anodes enable a high- energy density, but suffer from an inhomogeneous reaction current and irreversible Li plating during fast charging. In contrast, hard carbon exhibits superior rate performance but lower energy density owing to its lower initial coulombic efficiency and higher average voltage. In this work, these tradeoffs are overcome by fabricating hybrid anodes with uniform mixtures of graphite and hard carbon, using industrially- relevant multi- layer pouch cells (>1 Ah) and electrode loadings (3 mAh cm- 2). By controlling the graphite/hard carbon ratio, this study shows that battery performance can be systematically tuned to achieve both high- energy density and efficient fast charging. Pouch cells with optimized hybrid anodes retain 87% and 82% of their initial specific energy after 500 cycles of 4C and 6C fast- charge cycling, respectively. This is significantly higher than the 61% and 48% specific energy retention with graphite anodes under the same conditions. The enhanced performance is attributed to improved homogeneity of the reaction current throughout the hybrid anode, which is supported by continuum- scale modeling. This process is directly compatible with existing roll- to- roll battery manufacturing, representing a scalable pathway to fast charging.Hybrid anodes fabricated by mixing graphite and hard carbon are shown to achieve fast charging Li- ion batteries with high- energy densities, using industrially relevant multi- layer pouch cells (>1 Ah). By tuning the blend ratio of graphite/hard carbon, pouch cells with 180 Wh kg- 1 energy density and 87%/82% energy retention after 500 cycles of 4C/6C fast- charge cycling are achieved.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/166373/1/aenm202003336.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/166373/2/aenm202003336-sup-0001-SuppMat.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/166373/3/aenm202003336_am.pd

Enabling 6C Fast Charging of Li‐Ion Batteries with Graphite/Hard Carbon Hybrid Anodes

Li- ion batteries that can simultaneously achieve high- energy density and fast charging are essential for electric vehicles. Graphite anodes enable a high- energy density, but suffer from an inhomogeneous reaction current and irreversible Li plating during fast charging. In contrast, hard carbon exhibits superior rate performance but lower energy density owing to its lower initial coulombic efficiency and higher average voltage. In this work, these tradeoffs are overcome by fabricating hybrid anodes with uniform mixtures of graphite and hard carbon, using industrially- relevant multi- layer pouch cells (>1 Ah) and electrode loadings (3 mAh cm- 2). By controlling the graphite/hard carbon ratio, this study shows that battery performance can be systematically tuned to achieve both high- energy density and efficient fast charging. Pouch cells with optimized hybrid anodes retain 87% and 82% of their initial specific energy after 500 cycles of 4C and 6C fast- charge cycling, respectively. This is significantly higher than the 61% and 48% specific energy retention with graphite anodes under the same conditions. The enhanced performance is attributed to improved homogeneity of the reaction current throughout the hybrid anode, which is supported by continuum- scale modeling. This process is directly compatible with existing roll- to- roll battery manufacturing, representing a scalable pathway to fast charging.Hybrid anodes fabricated by mixing graphite and hard carbon are shown to achieve fast charging Li- ion batteries with high- energy densities, using industrially relevant multi- layer pouch cells (>1 Ah). By tuning the blend ratio of graphite/hard carbon, pouch cells with 180 Wh kg- 1 energy density and 87%/82% energy retention after 500 cycles of 4C/6C fast- charge cycling are achieved.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/166373/1/aenm202003336.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/166373/2/aenm202003336-sup-0001-SuppMat.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/166373/3/aenm202003336_am.pd

Origin of Rapid Delithiation In Secondary Particles Of LiNi0.8Co0.15Al0.05O2 and LiNiyMnzCo(1-y-z)O2 Cathodes

Most research on the electrochemical dynamics in materials for high-energy Li-ion batteries has focused on the global behavior of the electrode. This approach is susceptible to misleading analyses resulting from idiosyncratic kinetic conditions, such as surface impurities inducing an apparent two-phase transformation within LiNi 0.8Co0.15Al0.05O2 . Here, we use nano-focused X-ray probes to measure delithiation operando at the scale of secondary particle agglomerates in layered cathode materials during charge. After an initial latent phase, individual secondary particles undergo rapid, stochastic, and largely uniform delithiation, which is in contrast with the gradual increase in cell potential. This behavior reproduces across several layered oxides. Operando X-ray microdiffraction (µ-XRD) leverages the relationship between Li content and lattice parameter to further reveal that rate acceleration occurs between Li-site fraction (xLi) ~0.9 and ~0.4 for LiNi0.8Co0.15Al0.05O2 . Physics-based modeling shows that, to reproduce the experimental results, the exchange current density (i0) must depend on xLi , and that i0 should increase rapidly over three orders of magnitude at the transition point. The specifics and implications of this jump in i0 are crucial to understanding the charge-storage reaction of Li-ion battery cathodes

Origin of Rapid Delithiation In Secondary Particles Of LiNi0.8Co0.15Al0.05O2 and LiNiyMnzCo1−y−zO2 Cathodes

Most research on the electrochemical dynamics in materials for high-energy Li-ion batteries has focused on the global behavior of the electrode. This approach is susceptible to misleading analyses resulting from idiosyncratic kinetic conditions, such as surface impurities inducing an apparent two-phase transformation within LiNi0.8Co0.15Al0.05O2. Here, nano-focused X-ray probes are used to measure delithiation operando at the scale of secondary particle agglomerates in layered cathode materials during charge. After an initial latent phase, individual secondary particles undergo rapid, stochastic, and largely uniform delithiation, which is in contrast with the gradual increase in cell potential. This behavior reproduces across several layered oxides. Operando X-ray microdiffraction ((Formula presented.) -XRD) leverages the relationship between Li content and lattice parameter to further reveal that rate acceleration occurs between Li-site fraction (xLi) ≈0.9 and ≈0.5 for LiNi0.8Co0.15Al0.05O2. Physics-based modeling shows that, to reproduce the experimental results, the exchange current density (i0) must depend on xLi, and that i0 should increase rapidly over three orders of magnitude at the transition point. The specifics and implications of this jump in i0 are crucial to understanding the charge-storage reaction of Li-ion battery cathodes