Publications

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This manual defines a complete body of abuse tests intended to simulate actual use and abuse conditions that may be beyond the normal safe operating limits experienced by electrical energy storage systems used in electric and hybrid electric vehicles. The tests are designed to provide a common framework for abuse testing various electrical energy storage systems used in both electric and hybrid electric vehicle applications. The manual incorporates improvements and refinements to test descriptions presented in the Society of Automotive Engineers Recommended Practice SAE J2464 ''Electric Vehicle Battery Abuse Testing'' including adaptations to abuse tests to address hybrid electric vehicle applications and other energy storage technologies (i.e., capacitors). These (possibly destructive) tests may be used as needed to determine the response of a given electrical energy storage system design under specifically defined abuse conditions. This manual does not provide acceptance criteria as a result of the testing, but rather provides results that are accurate and fair and, consequently, comparable to results from abuse tests on other similar systems. The tests described are intended for abuse testing any electrical energy storage system designed for use in electric or hybrid electric vehicle applications whether it is composed of batteries, capacitors, or a combination of the two.

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Two 100 kW min-1 (1.67 kW h-1) Li-ion battery energy storage systems (BESS) are described. The systems include a high-power Li-ion battery and a 100 kW power conditioning system (PCS). The battery consists of 12 modules of 12 series-connected Saft Li-ion VL30P cells. The stored energy of the battery ranges from 1.67 to 14 kW h-1 and has an operating voltage window of 515-405 V (dc). Two complete systems were designed, built and successfully passed factory acceptance testing after which each was deployed in a field demonstration. The first demonstration used the system to supplement distributed microturbine generation and to provide load following capability. The system was run at its rated power level for 3 min, which exceeded the battery design goal by a factor of 3. The second demonstration used another system as a stand-alone uninterrupted power supply (UPS). The system was available (online) for 1146 h and ran for over 2 min. © 2005 Elsevier B.V. All rights reserved.

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At Sandia National Laboratories, we have built 18650 Li-ion cells with Li reference electrode for in situ characterization of electrodes including impedance and other electrochemical properties. At a 200 mA ({approx}C/5 rate) discharge, the cell gave {approx}900 mAh. Impedance measurements indicate that the anode dominates the cell impedance. For example, at 0 C, the anode and cathode impedances at 10 mHz were around 149 and 53 m{Omega}, respectively, and the total cell impedance at 10 mHz was {approx}203 m{Omega}. The three-electrode configuration also permits measurement of individual electrode voltages during charge and discharge. During discharge, while the cell voltage drops from 4.1 to 3 V, the cathode and the anode voltages change from 4.1 to 3.7 and from {approx}0 to 0.7 V, respectively. During charge, the cathode and anode voltages trace back to their initial values before discharging. The voltage swing for the anode is higher than that for the cathode. This also indicates that the impedance for the anode is higher than for the cathode. Pulse measurements on the cells indicate the voltage drop of the full-cell is equal to the sum of the anode and cathode voltage drops for a 2 A discharge pulse.

Battery life is an important, yet technically challenging, issue for battery development and application. Adequately estimating battery life requires a significant amount of testing and modeling effort to validate the results. Integrated battery testing and modeling is quite feasible today to simulate battery performance, and therefore applicable to predict its life. A relatively simple equivalent-circuit model (ECM) is used in this work to show that such an integrated approach can actually lead to a high-fidelity simulation of a lithium-ion cell's performance and life. The methodology to model the cell's capacity fade during thermal aging is described to illustrate its applicability to battery calendar life prediction. © 2004 Elsevier B. V. All rights reserved.

High-power 18650 Li-ion cells have been developed for hybrid electric vehicle applications as part of the DOE FreedomCAR Advanced Technology Development (ATD) program. Cells have been developed for high-power, long-life, low-cost and abuse tolerance conditions. The thermal abuse response of advanced materials and cells were measured and compared. Cells were constructed for determination of abuse tolerance to determine the thermal runaway response and flammability of evolved gas products during venting. Advanced cathode and anode materials were evaluated for improved tolerance under abusive conditions. Calorimetric methods were used to measure the thermal response and properties of the cells and cell materials up to 450 °C. Improvements in thermal runaway response have been shown using combinations of these materials.

Sandia National Laboratories has been conducting studies on performance of laboratory and commercial lithium-ion and other types of electrochemical cells using inductive models [1]. The objectives of these investigations are: (1) To develop procedures and techniques to rapidly determine performance degradation rates while these cells undergo life tests; (2) To model cell voltage and capacity in order to simulate cell performance characteristics under variable load and temperature conditions; (3) To model rechargeable battery degradation under charge/discharge cycles and many other conditions. The inductive model and methodology are particularly useful when complicated cell performance behaviors are involved, which are often difficult to be interpreted from simple empirical approaches. We find that the inductive model can be used effectively: (1) To enable efficient predictions of battery life; (2) To characterize system behavior. Inductive models provide convenient tools to characterize system behavior using experimentally or analytically derived data in an efficient and robust framework. The approach does not require detailed phenomenological development. There are certain advantages unique to this approach. Among these advantages is the ability to avoid making measurements of hard to determine physical parameters or having to understand cell processes sufficiently to write mathematical functions describing their behavior. We used artificial neural network for inductive modeling, along with ancillary mathematical tools to improve their accuracy. This paper summarizes efforts to use inductive tools for cell and battery modeling. Examples of numerical results will be presented. One of them is related to high power lithium-ion batteries tested under the U.S. Department of Energy Advanced Technology Development Program for hybrid vehicle applications. Sandia National Laboratories is involved in the development of accelerated life testing and thermal abuse tests to enhance the understanding of power and capacity fade issues and predict life of the battery under a nominal use condition. This paper will use power and capacity fade behaviors of a Ni-oxide-based lithium-ion battery system to illustrate how effective the inductive model can interpret the cell behavior and provide predictions of life. We will discuss the analysis of the fading behavior associated with the cell performance and explain how the model can predict cell performance.

High-power 18650 Li-ion cells have been developed for hybrid electric vehicle applications as part of the DOE Advanced Technology Development (ATD) program. The thermal abuse response of two advanced chemistries (Gen1 and Gen2) were measured and compared with commercial Sony 18650 cells. Gen1 cells consisted of an MCMB graphite based anode and a LiNi0.85Co 0.15O2 cathode material while the Gen2 cells consisted of a MAG10 anode graphite and a LiNi0.80Co0.15 Al 0.05O2 cathode. Accelerating rate calorimetry (ARC) and differential scanning calorimetry (DSC) were used to measure the thermal response and properties of the cells and cell materials up to 400°C. The MCMB graphite was found to result in increased thermal stability of the cells due to more effective solid electrolyte interface (SEI) formation. The Al stabilized cathodes were seen to have higher peak reaction temperatures that also gave improved cell thermal response. The effects of accelerated aging on cell properties were also determined. Aging resulted in improved cell thermal stability with the anodes showing a rapid reduction in exothermic reactions while the cathodes only showed reduced reactions after more extended aging. Published by Elsevier B.V.

Li-ion cells are being developed for high-power applications in hybrid electric vehicles currently being designed for the FreedomCAR (Freedom Cooperative Automotive Research) program. These cells offer superior performance in terms of power and energy density over current cell chemistries. Cells using this chemistry are the basis of battery systems for both gasoline and fuel cell based hybrids. However, the safety of these cells needs to be understood and improved for eventual widespread commercial application in hybrid electric vehicles. The thermal behavior of commercial and prototype cells has been measured under varying conditions of cell composition, age and state-of-charge (SOC). The thermal runaway behavior of full cells has been measured along with the thermal properties of the cell components. We have also measured gas generation and gas composition over the temperature range corresponding to the thermal runaway regime. These studies have allowed characterization of cell thermal abuse tolerance and an understanding of the mechanisms that result in cell thermal runaway.

This document describes a general protocol (involving both experimental and data analytic aspects) that is designed to be a roadmap for rapidly obtaining a useful assessment of the average lifetime (at some specified use conditions) that might be expected from cells of a particular design. The proposed experimental protocol involves a series of accelerated degradation experiments. Through the acquisition of degradation data over time specified by the experimental protocol, an unambiguous assessment of the effects of accelerating factors (e.g., temperature and state of charge) on various measures of the health of a cell (e.g., power fade and capacity fade) will result. In order to assess cell lifetime, it is necessary to develop a model that accurately predicts degradation over a range of the experimental factors. In general, it is difficult to specify an appropriate model form without some preliminary analysis of the data. Nevertheless, assuming that the aging phenomenon relates to a chemical reaction with simple first-order rate kinetics, a data analysis protocol is also provided to construct a useful model that relates performance degradation to the levels of the accelerating factors. This model can then be used to make an accurate assessment of the average cell lifetime. The proposed experimental and data analysis protocols are illustrated with a case study involving the effects of accelerated aging on the power output from Gen-2 cells. For this case study, inadequacies of the simple first-order kinetics model were observed. However, a more complex model allowing for the effects of two concurrent mechanisms provided an accurate representation of the experimental data.

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