Ramez Ahmed Elgammal

Classical secondary-current theory predicts a directionally neutral through-thickness reaction distribution when a porous electrode’s effective electronic and ionic conductivities are equal. In a working concentrated electrolyte, the salt-concentration gradient adds a thermodynamic contribution to electrolyte current that shifts this balance. A convention-consistent reduction of the porous-electrode equations shows that, in the quasi-steady weak-depletion onset limit, reaction skew vanishes when the electronic-to-ionic conductivity ratio equals 1/(1+ρe), or 0.390 for the reference electrolyte. Separator-favored reaction therefore persists well below the classical equal-conductivity condition. Full Doyle–Fuller–Newman (DFN) calculations reproduce ∼93% of the predicted boundary displacement across a 2.7-fold change in ρe, although the reduced theory overpredicts skew amplitude away from the boundary; the zero location is the more robust reduced-order result. The boundary does not prescribe the finite-time trajectory: across a 36-condition rate–thickness study, 8 of 17 evaluable trajectories show collector-ward centroid motion followed by separator-ward recovery, and nearly matched cutoff capacities conceal different internal histories. Finally, differencing two depth-resolved stored-lithium profiles at matched delivered capacities recovers the capacity-window-averaged reaction distribution from two states, with predicted through-thickness contrasts reaching ∼33% in 150 µm electrodes.

Peukert exponents are widely used to summarize battery rate capability, yet they obscure the transition from nearly uniform intercalation across a porous cathode to strongly nonuniform through-plane current distribution. Here we derive an analytical Wagner-number criterion for this transition from a one-dimensional conduction-kinetics model. The ionic Wagner number governs the spatial current distribution, yielding a closed-form second-moment utilization factor and a mechanistic relation between Peukert response and cathode utilization. In its predictive form, the criterion is evaluated before field-resolved simulation from applied areal current density, cathode thickness, effective ionic conductivity, and the Tafel slope parameter; the specific interfacial area cancels from the mean-field expression. The framework establishes a single-mechanism conduction-Tafel ceiling of 1.5 for the Peukert exponent. Isothermal Doyle–Fuller–Newman simulations of a 75.6 µ m NMC811 cathode show nearly uniform utilization through 2 C discharge, with 93.5% capacity retention, followed by entry into reaction-zone localization as the predicted Wagner number approaches unity near 3 C, where electrolyte depletion drives retention down to 45.5%. Balanced thickness scaling and literature data support the predicted Wagner number as an onset criterion for rate-dependent cathode underutilization.

Calcium, magnesium, and zinc metal batteries offer attractive combinations of low cost and high specific energy, yet progress is limited by sluggish and poorly quantified interfacial kinetics. Atomistic calculations frequently predict large desolvation and interphase crossing barriers for multivalent cations, but there is still no simple rule that allows a cell designer to translate those barriers into an allowable C rate at 25 °C for a given voltage window. In this work we develop and validate a compact “voltage tax” framework that connects an effective desolvation barrier, extracted from experiments, to whole-cell performance in porous electrodes.

By using an air electrode, metal-air batteries achieve impressive energy density based on the materials used. However, these ‘open’ systems typically require a ‘balance of plant’ that significantly impacts the total system energy density that is achieved in practice. For any open system, the power density or current density must be maximized to allow the energy conversion unit (typically a stack) to minimize the parts cost associated with increments in the total number of cells required for a given power output.

Peukert exponents are widely used to summarize battery rate capability, yet they obscure the transition from nearly uniform intercalation across a porous cathode to strongly nonuniform through-plane current distribution. Here we derive an analytical Wagner-number criterion for this transition from a one-dimensional conduction-kinetics model. The ionic Wagner number governs the spatial current distribution, yielding a closed-form second-moment utilization factor and a mechanistic relation between Peukert response and cathode utilization. In its predictive form, the criterion is evaluated before field-resolved simulation from applied areal current density, cathode thickness, effective ionic conductivity, and the Tafel slope parameter; the specific interfacial area cancels from the mean-field expression. The framework establishes a single-mechanism conduction-Tafel ceiling of 1.5 for the Peukert exponent. Isothermal Doyle-Fuller-Newman simulations of a 75.6 µm NMC811 cathode show nearly uniform utilization through 2C discharge, with 93.5% capacity retention, followed by entry into reaction-zone localization as the predicted Wagner number approaches unity near 3C, where electrolyte depletion drives retention down to 45.5%. Balanced thickness scaling and literature data support the predicted Wagner number as an onset criterion for rate-dependent cathode underutilization.

Deep eutectic solvents (DESs) have emerged as an alternative to both common organic solvents and ionic liquids (ILs). DESs share physicochemical properties with ILs such as low vapor pressure, high thermal stability, while offering advantages such as low toxicity, lower cost, and ease of preparation. Moreover, DESs are attractive candidates for electrochemical applications due to their large voltage windows and solubility properties. DESs as a solvent class share a general composition of a hydrogen bond donor (HBD), typically a polyol, amide, or acid, and a hydrogen bond acceptor (HBA), usually a quaternary ammonium or phosphonium salt. At a specific molar composition of a HBD and HBA, the DES forms a eutectic mixture resulting in a large melting point depression. Despite being widely studied, the microscopic structures of DESs have remained largely uncharacterized. Herein, we present a multitechnique NMR study of ethaline (ethylene glycol + choline chloride). Pulsed field gradient diffusion, nuclear Overhauser effect spectroscopy (NOESY), ¹³C NMR relaxation experiments are deployed to sample a range of frequencies and modes of motion of the polyol and choline components of the DES. Generally, translational and rotational diffusion of polyols are more rapid than those of choline while short-range rotational motions observed from ¹³C relaxation indicate slow local motion of ethylene glycol at low choline chloride (ChCl) content. Additionally, we have investigated the solubility properties of several lithium salts (LiTFSI, LiFSI, LiBF₄, and LiOAc) in these DESs and utilized the same suite of NMR techniques to understand how they act as solvents. One interesting observation is that the Li⁺ diffusivity exceeds that of the counterion for TFSI^-, but not for FSI^-. Finally, large changes in the structural organization of DESs that result from the presence of lithium salts may serve as a guide to the design of a new class of electrolytes for lithium-ion batteries.

Deep eutectic solvents (DESs) have emerged as an alternative to both common organic solvents and ionic liquids (ILs). DESs share physicochemical properties with ILs such as low vapor pressure, high thermal stability, high viscosity while offering advantages such as low toxicity, lower cost, and ease of preparation. Moreover, DESs are attractive candidates for electrochemical applications due to their large voltage windows and solubility properties. DESs as a solvent class share a general composition of a hydrogen bond donor (HBD), typically a polyol, amide, or acid, and a hydrogen box acceptor (HBA), usually a quaternary ammonium or phosphonium salt. At a specific molar composition of a HBD and HBD, the DES forms a eutectic mixture resulting in a large melting point depression due to extensive hydrogen bonding between the components. Despite being widely studied, the microscopic structures of DESs have remained largely uncharacterized. Herein, we present a multitechnique NMR study of two DESs: glyceline (glycerol + choline chloride) and ethaline (ethylene glycol + choline chloride). Fast-field cycling ¹H relaxometry, pulsed field gradient diffusion, nuclear Overhauser effect spectroscopy (NOESY), ¹³C NMR relaxation, and pressure-dependent NMR experiments are deployed to sample a range of frequencies and modes of motion of the polyol and choline components of the DES. Generally, translational and rotational diffusion of polyols are more rapid than those of choline while short-range rotational motions observed from ¹³C relaxation indicate slow local motion of glycerol at low choline chloride (ChCl) content. We show how the additional hydroxyl group present in glycerol contributes to not only higher viscosities, but a larger perturbation of the hydrogen bonding network by the addition of ChCl. Additionally, we have investigated the solubility properties of several lithium salts (LiTFSI, LiFSI, LiPF₆, LiBF₄, and LiOAc) in these DESs and utilized the same suite of NMR techniques to understand how they act as solvents. We observe that due to anion effects, the heterogeneities present in DES result in differential solvation for some species where there is a distinction of lithium salts co-existing in these holes as well as the bulk. The large changes in the structural organization of DESs that result from the presence of lithium salts will serve as a guide to the design of a new class of electrolytes for lithium-ion batteries.

Deep eutectic solvents (DESs) have emerged as an alternative to both common organic solvents and ionic liquids (ILs). DESs share physicochemical properties with ILs such as low vapor pressure, high thermal stability, high viscosity while offering advantages such as low toxicity, lower cost, and ease of preparation. Moreover, DESs are attractive candidates for electrochemical applications due to their large voltage windows and solubility properties. DESs as a solvent class share a general composition of a hydrogen bond donor (HBD), typically a polyol, amide, or acid, and a hydrogen box acceptor (HBA), usually a quaternary ammonium or phosphonium salt. At a specific molar composition of a HBD and HBD, the DES forms a eutectic mixture resulting in a large melting point depression due to extensive hydrogen bonding between the components. Despite being widely studied, the use and subsequent characterization of DESs as solvents for aromatic phenols and related aromatics has only recently received attention. In this study we have investigated the solubility of a broad class of aromatic solutes as a function of DES composition and solute concentration using ¹H, ¹³C, pulsed field gradient (PFG), and nuclear Overhauser effect (NOE) NMR. The degree to which homogenous mixtures versus heterogeneous and/or multi-phase systems are formed as a function of solute, temperature, and DES composition is examined. Two classes of DESs glyceline (glycerol + choline chloride) and ethaline (ethylene glycol + choline chloride) were investigated. As many as three distinct phases depending on the nature of the aromatic solute are observed by NMR. {¹H-¹H}-NOESY measurements show strong correlations between the choline chloride ammonium cation and the aryl protons with cation-pi interactions disrupting the hydrogen bonding network of the DES. We will discuss the implications for these systems as green solvents and comment on how clustering of solutes on the nanoscale may find use in catalysis and self-assembly.

A newly developed "liquid silicon" precursor will be discussed. Cyclohexasilane (CHS; Si6H12) has been used to make silicon-based films (such as polysilicon, silicon nitride, silicon carbide and others), as well as silicon nanowires and quantum dots. CHS offers a more versatile, lower-cost and safer pathway to a variety of silicon based products being considered for flexible and printable electronics. One particularly interesting deposition method for CHS that has recently received interest is ALD. There is a need for a silicon precursor that is not only cost effective, but one that can be readily chemically functionalized to develop advanced materials. CHS is one such silicon precursor that is a liquid at room temperature allowing for easier storage and handling. Cyclohexasilane has a moderate boiling point, 80 °C at 15 torr. It has long been considered to be the preeminent silicon precursor for a variety of applications including silicon anodes, solid state lighting, and a wide variety of semiconductor devices. CHS may also be used to create thin films of β-SiC on a variety of substrates under mild conditions. Aside from those advantages, CHS allows for facile p-doping of materials and due to the methods of deposition and the deposition conditions amenable to a reagent such as CHS, continuous growth with the suppression of unintentional secondary deposits may be readily achieved. Moreover, it may be possible to use CHS to achieve solution growth to deliver high structural quality materials with significantly decreased capital and operational costs. The use of CHS across a wide range of industries and applications will be discussed as will the advantages of this material over incumbent technologies.