Publications

A particle filter (PF) is shown to be more accurate than non-linear least squares (NLLS) and an unscented Kalman filter (UKF) for predicting the remaining useful life (RUL) and time until end of discharge voltage (EODV) of a Lithium-ion battery. The three algorithms, i.e. PF, UKF, and NLLS track four states with correct initial estimates of the states and 5% variation on the initial state estimates. The four states are data-driven, equivalent circuit properties or Lithium concentrations and electroactive surface areas depending on the model. The more accurate prediction performance of PF over NLLS and UKF is reported for three Lithium-ion battery models: a data-driven empirical model, an equivalent circuit model, and a physics-based single particle model.

© The Electrochemical Society © The Author(s) 2015. In this computational study, we demonstrate the use of a high-fidelity multiphysics model to predict the effects of operational parameters and the performance of a new Solid Oxide Iron-Air Redox Battery (SOIARB) operated at 800.C. The results show explicitly that the operating current density has the most pronounced effect on the H \textless inf \textgreater 2 \textless /inf \textgreater concentration distribution, Nernst potential, specific energy and round-trip efficiency. The initial porosity in the Redox Cycle Unit (RCU) must be \textgreater 0.50 at high current density in order to avoid significant diffusion limitation. Also, the distance between the RSOFC (reversible Solid Oxide Fuel Cell) and the RCU has little effect on the performance of the SOIARB, but has an appreciable effect on the chamber pressure. The simulations indicate that a high round-trip efficiency (RTE) can be achieved at the expense of useful capacity. Enhancement of the electrolysis electro-kinetics of RSOFC and FeO-reduction kinetics of RCU is a key to achieving high capacity with high efficiency.

An ASPEN Plus based model is presented for an intermediate-temperature solid oxide iron-air redox battery (IT-SOIARB) system. The model shows that the energy efficiency of the system can be as high as 83%. Furthermore, the model is used to determine the factors that affect the energy efficiency of the battery. With air as the working fluid, a heat exchanger and thermal storage unit are included in the battery system to utilize effectively the heat generated from the discharge cycle in the charge cycle. The results show that air utilization (or air mass flow rate) plays a key role in regulating heat flow between the battery components.

A new computational method is proposed that can be used to reduce the numerical difficulties in modeling the electrical and thermal behavior of a spirally wound Li-ion cell. By analyzing the winding locus of the electrodes, some important geometric relationships of the spiral surfaces are identified, and algorithms for coordinate transform and variable extrusion between 2-D and 3-D domains are derived. Our method reduces the computation time and memory requirements needed to simulate the cell performance. The accuracy of our method was validated by model-to-model comparisons. © 2013 Published by Elsevier B.V.

Stress generation due to Li ion insertion into/extraction from LiMn 2O4 particles is studied with a mathematical model for a lithium ion battery with pure LiMn2O4 or mixed LiMn 2O4 and LiNi0.8Co0.15Al 0.05O2 cathode. The simulated stress profile in a pure LiMn2O4 electrode shows nonuniformity across the positive electrode. The cathode blended model predicts that the stress generated in the LiMn2O4 particles is reduced at the end of discharge due to adding LiNi0.8Co0.15Al0.05O2 to the cathode. The effect of the variation in the blend ratio on the stress generation is also investigated. © 2013 Elsevier B.V. All rights reserved.

Three-dimensional transient thermal analyses of an air-cooled module that contains prismatic lithium-ion cells operating under an aggressive driving profile were performed using a commercial computational fluid dynamics code. The existing module utilized air cooling through evenly-spaced channels on both sides of each cell. It was found that lowering the gap spacing and/or higher flow rate of the fan lead to a decrease of the maximum temperature rise. To achieve improved temperature uniformity over the module, the gap spacing should be of a moderate size. For the given module, operating with a uniform gap spacing of 3 mm and an air flow rate of 40.8 m3 h-1 appears to be the best choice that satisfies the trade-off requirements of the fan power, maximum temperature rise and temperature uniformity. Using the same gap spacing and air flow rate, a proposed design of one-side cooling is less effective than two-side cooling. Uneven gap spacing affects the temperature distributions, but it does not impact the maximum temperature rise markedly. Considering the variety of the design change options and their combinations, it is concluded that the temperature gradients along the air flow direction can be affected but are generally unavoidable. © 2013 Elsevier B.V. All rights reserved.

A mathematical model for the capacity fade of a LiMn2O4 (LMO) electrode is developed in this paper by including the acid attack on the active material and the solid electrolyte interphase (SEI) film formation on the LMO particle surface. The acid generated by the LiPF6 and the solvent decompositions are coupled to the manganese (Mn) dissolution. The decrease of the Li ion diffusion coefficient is involved as another contribution to the capacity fade, which is caused by the passive film formation on the active material surface. The effects of cell practical operation/fabrication conditions and kinetics of side reactions on battery life are also investigated by utilizing the developed mathematical model.

A life model is developed for a lithium ion cell with a spinel-based cathode. It is assumed in the proposed model that the Mn(III) disproportionation reaction causes the degradation of the spinel cathode. The Mn(III) disproportionation reaction leads to the Mn(II) dissolving into the electrolyte and the formation of an inactive material layer which causes a resistance increase in the cathode. The proposed model is used to investigate the effects of ambient temperature and voltage range of cycling on the loss of the cell capacity and the changes in the volume fraction of the cathode active material, the radius of the cathode particle and the resistance of the cathode. © 2012 Elsevier B.V. All rights reserved.

An isothermal reduced order physics-based Li ion battery model is developed by incorporating solution phase charge and material balances into single particle (SP) model. Li ion concentration and potential profiles in electrolyte phase are approximated by polynomial functions. A cubic polynomial is used for electrolyte concentration and potential inside electrodes, while separator liquid phase potential and concentration are estimated by parabolas. Diffusion inside solid particles is also simplified using an approximate solution based on analytical solution for the solid concentration. Applying the aforementioned reduction techniques decreases the degree of freedom of full order model by more than 100, while the cell voltage relative error of proposed model is less than 1% at different charge-discharge rates up to 5C. © 2012 Elsevier B.V. All rights reserved.

This paper presents a distributed thermal model for a lithium-ion electrode plate pair used to predict the distributed electrical and thermal behavior of the electrode pair including tabs. Our model was developed by coupling the heat equation with a pseudo two dimensional (P2D) physics-based electrochemical model. The local heat generation rate is predicted by the P2D model at every node point in the 2D electrode pair. To reduce significantly the computation load of the model, a linear approximation method is introduced to decouple the electrochemical model from the heat equation with a very slight loss in accuracy. © 2012 Elsevier B.V. All rights reserved.