21 research outputs found
Modeling the Effect of Cell Variation on the Performance of a Lithium-Ion Battery Module
No full textOwing to the variation between lithium-ion battery (LIB) cells, early discharge termination and overdischarge can occur when cells are coupled in series or parallel, thereby triggering a decrease in LIB module performance and safety. This study provides a modeling approach that considers the effect of cell variation on the performance of LIB modules in energy storage applications for improving the reliability of the power quality of energy storage devices and efficiency of the energy system. Ohm’s law and the law of conservation of charge were employed as the governing equations to estimate the discharge behavior of a single strand composing of two LIB cells connected in parallel based on the polarization properties of the electrode. Using the modeling parameters of a single strand, the particle swarm optimization algorithm was adopted to predict the discharge capacity and internal resistance distribution of 14 strands connected in series. Based on the model of the LIB strand to predict the discharge behavior, the effect of cell variation on the deviation of the discharge termination voltage and depth of discharge imbalance was modeled. The validity of the model was confirmed by comparing the experimental data with the modeling results
Three-Dimensional Modeling of the Thermal Behavior of a Lithium-Ion Battery Module for Hybrid Electric Vehicle Applications
No full textThis paper reports a modeling methodology to predict the effects of operating conditions on the thermal behavior of a lithium-ion battery (LIB) module. The potential and current density distributions on the electrodes of an LIB cell are predicted as a function of discharge time based on the principle of charge conservation. By using the modeling results of the potential and current density distributions of the LIB cell, the non-uniform distribution of the heat generation rate in a single LIB cell within the module is calculated. Based on the heat generation rate in the single LIB cell determined as a function of the position on the electrode and time, a three-dimensional thermal modeling of an LIB module is performed to calculate the three-dimensional velocity, pressure, and temperature distributions within the LIB module as a function of time at various operating conditions. Thermal modeling of an LIB module is validated by the comparison between the experimental measurements and the modeling results. The effect of the cooling condition of the LIB module on the temperature rise of the LIB cells within the module and the uniformity of the distribution of the cell temperatures are analyzed quantitatively based on the modeling results
A Main Factor Determining the Uniform Step Coverage in Chemical Vapor Deposition
No full textABSTRACTProfile evolution simulations during chemical vapor deposition based on a 2-D continuum model reveal that the type of surface kinetics plays an important role as a measure of determining step coverage of films deposited in a high aspect ratio trench or via. The linear surface kinetics, resulting from adsorption rate limitation, is found to be difficult to bring about conformal step coverage in a deep narrow trench without reducing the growth rate considerably; that is, under such a condition void free filling can not be achievable with holding an appropriate growth rate. High tendency of the precursor for chemical equilibrium on a surface, tending to cause the non-linear surface kinetics by surface reaction limitation, is mainly responsible for the significant improvement of step coverage in TEOS-based depositions.</jats:p
Dissociative Adsorption of H2 on the H/Si(100) Surface: The Effect of Intradimer pi-Bonding Disruption
No full textWe have studied dissociative H2 adsorption on the H/Si(100) surface by means of pseudopotential density functional theory calculations. This work is directly motivated by the observations of Biederman et al. [Phys. Rev. Lett., 83, 1810 (1999)]: "H2 adsorption is significantly promoted in an interdimer configuration of two adjacent singly occupied dimers." We find that there is no adsorption barrier on the local site where two quasi-free dangling bonds are available; the adsorption energy is estimated to be 2.6 eV per H2 within the local density approximation. We present maximally localized Wannier functions that clearly illustrate the behavior of dangling orbitals upon the approach of H2. The results suggest that intradimer pi-bonding disruption is crucial for the significant promotion of H2 adsorption on Si(100)
Simulation of Film Growth Contour in a Narrow Deep Trench and Film Crystallinity in LPCVD Process
No full textABSTRACTDeposition of a thin film in the LPCVD process has been simulated by a Monte–Carlo method based on a simple model taking into account the desorption, the surface reaction, and the surface migration of the film precursor. The model has been used for the simulation of the film profile obtained in a narrow and deep trench and of the film crystallinity on a flat surface. The simulation results describe successfully those obtained by experiments under various process conditions.</jats:p
Modeling the Effects of the Cathode Composition of a Lithium Iron Phosphate Battery on the Discharge Behavior
No full textThis paper reports a modeling methodology to predict the effects on the discharge behavior of the cathode composition of a lithium iron phosphate (LFP) battery cell comprising a LFP cathode, a lithium metal anode, and an organic electrolyte. A one-dimensional model based on a finite element method is presented to calculate the cell voltage change of a LFP battery cell during galvanostatic discharge. To test the validity of the modeling approach, the modeling results for the variations of the cell voltage of the LFP battery as a function of time are compared with the experimental measurements during galvanostatic discharge at various discharge rates of 0.1C, 0.5C, 1.0C, and 2.0C for three different compositions of the LFP cathode. The discharge curves obtained from the model are in good agreement with the experimental measurements. On the basis of the validated modeling approach, the effects of the cathode composition on the discharge behavior of a LFP battery cell are estimated. The modeling results exhibit highly nonlinear dependencies of the discharge behavior of a LFP battery cell on the discharge C-rate and cathode composition
