Gerardine G. Botte

Mathematical Modeling of Secondary Lithium Batteries

Modeling of secondary lithium batteries is reviewed in this paper. The models available to simulate the electrochemical and thermal behavior of secondary lithium batteries are discussed considering not only their electrochemical representation (transport phenomena and thermodynamics of the system), but also the mathematical techniques that have been used for solving the equations. A brief review of the governing equations for porous electrodes, and methods for solving these equations is also given.

Influence of Some Design Variables on the Thermal Behavior of a Lithium‐Ion Cell

A mathematical model that includes an anode (carbon) decomposition reaction has been used to predict the temperature of a lithium-ion cell during medium- and high-rate discharge conditions. This work describes how various design parameters and the activation energy for the decomposition reaction of the anode (carbon) affect the predicted temperature of a Li{sub x}C{sub 6}/Li{sub y}NiO{sub 2} cell. The predicted results show that the particle size in the negative electrode (assumed here to be petroleum coke) is an important parameter for predicting the temperature of the cell.

Thermal stability of LiPF6–EC:EMC electrolyte for lithium ion batteries

Abstract A differential scanning calorimeter (DSC) was used to perform a thermal stability study of the LiPF6–EC:EMC electrolyte. The effect of different variables on its thermal stability was evaluated: salt (LiPF6) concentration effect, solvents, EC:EMC ratios, and heating rates. Hermetically sealed and crimped DSC pans were used during the experiments. The results indicate that the salt concentration, solvent concentration, and heating rates play an important role in the thermal stability of the LiPF6–EC:EMC electrolyte.

Hydrogen Production from the Electro-oxidation of Ammonia Catalyzed by Platinum and Rhodium on Raney Nickel Substrate

The optimization of a novel anode for the production of hydrogen via an ammonia alkaline electrolytic cell is presented. The novel anode was prepared by electrodeposition and contains Raney nickel, platinum, and rhodium in its catalytic layer. The platinum and rhodium layers were optimized by considering their influences on reaction kinetics and characterization by scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. It was demonstrated through electrochemical analysis that platinum and rhodium realized a synergistic catalytic effect on the oxidation of ammonia, showing higher activity than Pt-only electrodes with comparable catalyst loading. Hydrogen was successfully produced from a 1 M NH 3 /5 M KOH solution at 14.54 Wh/g H 2 at a current density of 2.5 mA/cm 2 by an anode containing 1 mg/cm 2 Rh and 10 mg/cm 2 Pt at ambient temperature and pressure.

Dissociation Rates of Urea in the Presence of NiOOH Catalyst: A DFT Analysis

Single molecule reactions have been studied between nickel oxyhydroxide, urea, and the hydroxide ion to understand the process of urea dissociation into ammonia, isocyanic acid, cyanate ion, carbon dioxide, and nitrogen. In the absence of hydroxide ions, nickel oxyhydroxide will catalyze urea to form ammonia and isocyanic acid with the rate-limiting step being the formation of ammonia with a rate constant of 1.5 × 10⁻⁶ s⁻¹. In the presence of hydroxide, the evolution of ammonia was also the rate-limiting step with a rate constant of 1.4 × 10⁻²⁶ s⁻¹. In addition, desorption of the cyanate ion presented an energy barrier of 6190 kJ mol⁻¹ suggesting that the cyanate ion cannot be separated from NiOOH unless further reactions occurred. Finally, elementary dissociation reactions with hydroxide ions deprotonating urea to produce nitrogen and carbon dioxide were analyzed. These elementary reactions were investigated along three paths differing in the order that protons were removed and the nitrogen atoms were rotated. The rate-limiting step was found to be the removal of carbon dioxide with a rate constant of 4.3 × 10⁻⁶⁵ s⁻¹. Therefore, the catalyst could be deactivated by the surface blockage caused by carbon dioxide adsorption.

Modeling Lithium Intercalation in a Porous Carbon Electrode

Two different approaches were used to model the insertion of lithium ions into a carbon particle. In the first approach, a concentration gradient was considered as the driving force (DFM) for diffusion while in the second approach chemical potential driving force was used (CPM). Lithium ion-lithium ion interactions are included in the CPM model but not in the DFM model These approaches were used to model a lithium foil/1 M LiClO 4 -propylene carbonate/carbon fiber cell. The model predictions indicate that the lithium ion-lithium ion interactions inside the particle play a significant role in predicting the electrochemical and thermal performance of the cell.

Comparison of finite difference and control volume methods for solving differential equations

Abstract Comparisons are made between the finite difference method (FDM) and the control volume formulation (CVF). An analysis of truncation errors for the two methods is presented. Some rules-of-thumb related to the accuracy of the methods are included. It is shown that the truncation error is the same for both methods when the boundary conditions are of the Dirichlet type, the system equations are linear and represented in Cartesian coordinates. A technique to analyze the accuracy of the methods is presented. Two examples representing different physical situations are solved using the methods. The FDM failed to conserve mass for a small number of nodes when both boundary conditions include a derivative term (i.e. either a Robin or Neumann type boundary condition) whereas the CVF method did conserve mass for these cases. The FDM is more accurate than the CVF for problems with interfaces between adjacent regions. The CVF is (ΔX) order of accuracy for a Neumann type boundary condition whereas the FDM is (ΔX) 2 order.

Theoretical Investigations of NiYSZ in the Presence of H2S

Quantum chemistry and molecular dynamics were used to evaluate the performance of solid oxide fuel cell anode materials in the presence of H 2 and H 2 S. The most common anode material Ni-yttria-stabilized zirconia (Ni-YSZ) was used for the study. It was found that the presence of H 2 S has an important effect on the oxidation of H 2 . Thermodynamics and transport limitations favor the oxidation of H 2 instead of H 2 S. Furthermore it is predicted that the presence of H 2 S slows down the oxidation of the hydrogen due to transport limitations (the H 2 S molecules tend to be surrounded by H 2 molecules in the media).

Recycling of graphite anodes for the next generation of lithium ion batteries

Graphite is currently the state-of-the-art anode material for most of the commercial lithium ion batteries. Among different types of natural graphite, flake graphite has been recently recognized as one of the critical materials due to the predicted future market growth of lithium ion batteries for vehicular applications. Current status and future demand of flake graphite in the market are discussed. It was found that flake graphite could become a critical material in the near future for countries such as the United States and members of the European Union with no graphite production. Recycling of flake graphite from its different waste resources is proposed as a potential solution to meet the future demand of graphite. The current status of graphite anodes in the present recycling technologies of spent lithium ion batteries was reviewed. The limitation of current technologies and a new perspective towards the future concept of “battery recycling” were also pointed out. Challenges in recycling battery grade flake graphite from spent lithium ion batteries and possible research opportunities in this regard were introduced.Graphical Abstract

Density Functional Theory Analysis of Raman Frequency Modes of Monoclinic Zirconium Oxide Using Gaussian Basis Sets and Isotopic Substitution

Geometry and vibration properties for monoclinic zirconium oxide were studied using Gaussian basis sets and LDA, GGA, and B3LYP functionals. Bond angles, bond lengths, lattice parameters, and Raman frequencies were calculated and compared to experimental values. Bond angles and lengths were found to agree within experimental standard deviations. The B3LYP gave the best performance of all three functionals with a percent error of 1.35% for the lattice parameters while the average difference between experimental and calculated Raman frequency values was -3 cm(-1). The B3LYP functional was then used to assign the atomic vibrations causing each frequency mode using isotopic substitution of (93.40)Zr for (91.22)Zr and (18.00)O for (16.00)O. This resulted in seven modes assigned to the Zr atom, ten modes to the O atom, and one mode being a mixture of both.