Ryan Jacobs

Origins of Large Voltage Hysteresis in High-Energy-Density Metal Fluoride Lithium-Ion Battery Conversion Electrodes

Metal fluorides and oxides can store multiple lithium ions through conversion chemistry to enable high-energy-density lithium-ion batteries. However, their practical applications have been hindered by an unusually large voltage hysteresis between charge and discharge voltage profiles and the consequent low-energy efficiency (<80%). The physical origins of such hysteresis are rarely studied and poorly understood. Here we employ in situ X-ray absorption spectroscopy, transmission electron microscopy, density functional theory calculations, and galvanostatic intermittent titration technique to first correlate the voltage profile of iron fluoride (FeF3), a representative conversion electrode material, with evolution and spatial distribution of intermediate phases in the electrode. The results reveal that, contrary to conventional belief, the phase evolution in the electrode is symmetrical during discharge and charge. However, the spatial evolution of the electrochemically active phases, which is controlled by reaction kinetics, is different. We further propose that the voltage hysteresis in the FeF3 electrode is kinetic in nature. It is the result of ohmic voltage drop, reaction overpotential, and different spatial distributions of electrochemically active phases (i.e., compositional inhomogeneity). Therefore, the large hysteresis can be expected to be mitigated by rational design and optimization of material microstructure and electrode architecture to improve the energy efficiency of lithium-ion batteries based on conversion chemistry.

Lithium transport through lithium-ion battery cathode coatings

The surface coating of cathodes using insulator films has proven to be a promising method for high-voltage cathode stabilization in Li-ion batteries, but there is still substantial uncertainty about how these films function. More specifically, there is limited knowledge of lithium solubility and transport through the films, which is important for coating design and development. This study uses first-principles calculations based on density functional theory to examine the diffusivity of interstitial lithium in the crystals of α-AlF3, α-Al2O3, m-ZrO2, c-MgO, and α-quartz SiO2, which provide benchmark cases for further understanding of insulator coatings in general. In addition, we propose an ohmic electrolyte model to predict resistivities and overpotential contributions under battery operating conditions. For the crystalline materials considered we predict that Li+ diffuses quite slowly, with a migration barrier larger than 0.9 eV in all crystalline materials except α-quartz SiO2, which is predicted to have a migration barrier of 0.276 eV along 〈001〉. These results suggest that the stable crystalline forms of these insulator materials, except for oriented α-quartz SiO2, are not practical for conformal cathode coatings. Amorphous Al2O3 and AlF3 have higher Li+ diffusivities than their crystalline counterparts. Our predicted amorphous Al2O3 resistivity (1789 MΩ m) is close to the top of the range of the fitted resistivities extracted from previous experiments on nominal Al2O3 coatings (7.8 to 913 MΩ m) while our predicted amorphous AlF3 resistivity (114 MΩ m) is very close to the middle of the range. These comparisons support our framework for modeling and understanding the impact on overpotential of conformal coatings in terms of their fundamental thermodynamic and kinetic properties, and support that these materials can provide practical conformal coatings in their amorphous form.

Understanding and Controlling the Work Function of Perovskite Oxides Using Density Functional Theory

Perovskite oxides containing transition metals are promising materials in a wide range of electronic and electrochemical applications. However, neither their work function values nor an understanding of their work function physics have been established. Here, we predict the work function trends of a series of perovskite (

Intrinsic defects and conduction characteristics of Sc2O3in thermionic cathode systems

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Ab Initio Modeling of Electrolyte Molecule Ethylene Carbonate Decomposition Reaction on Li(Ni,Mn,Co)O2 Cathode Surface

formula) materials using Density Functional Theory, and show that the work functions of (001)-terminated AO- and

Work function and surface stability of tungsten-based thermionic electron emission cathodes

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Predicting the thermodynamic stability of perovskite oxides using machine learning models

-oriented surfaces can be described using concepts of electronic band filling, bond hybridization, and surface dipoles. The calculated range of AO (

Strain control of oxygen kinetics in the Ruddlesden-Popper oxide La1.85Sr0.15CuO4

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Data and Supplemental information for predicting the thermodynamic stability of perovskite oxides using machine learning models

) work functions are 1.60-3.57 eV (2.99-6.87 eV). We find an approximately linear correlation (

Doped strontium vanadate: Computational design of a stable, low work function material

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