Cycle-life testing of 100-Ah class lithium-ion battery in a simulated geosynchronous-Earth-orbit satellite operation

In this paper, we review our work on cycle-life testing of a 100-Ah class lithium-ion battery in a simulated geosynchronous-Earth-orbit (GEO) satellite operation. The battery consists of ten 100-Ah lithium-ion (10) cells in a series, with a high energy density exceeding 100 Wh kg⁻¹ at the battery level. We simulate the eclipse period in real-time testing with five depth-of-discharge (DOD) patterns at an ambient temperature of 15 °C. We also simulate a sun-shine period in 8-day thermally accelerated full-charge storage at an ambient temperature of 25 °C, which in our experience corresponds to full-charge storage of a half-year operation at 0 °C. Eighteen eclipse seasons have presently been completed, corresponding to 9 years of GEO operation. The battery maintained a high voltage near 3.4 V at the end of the discharge, even when the DOD was set at 70%. The voltage dispersion of 10 cells was also sufficiently small in the range of 48 mV. The cell temperature reached a maximum of 29 °C and maintained minimal dispersion smaller than 4 °C even when the battery was discharged at a high DOD of 70%.     

Electrode structure analysis and surface characterization for lithium-ion cells simulated low-Earth-orbit satellite operation: I. Electrochemical behavior and structure analysis

Lithium-ion cells for satellite applications operate under a special condition, and are expected to behave differently from those for commercial purposes. To understand the performance-degradation mechanism of lithium-ion cells experienced cycle-life testing in a simulated low-Earth-orbit (LEO) satellite operation, we conducted the structure analysis and surface characterization of the aged LiCoO₂ cathode and graphite anode obtained from a lithium-ion cell with 4350-cycle LEO simulation experience. The analysis results were compared with a fresh cell which served as control. This paper provides a review of testing results on electrochemical and structure analysis. The capacity-verification and impedance measure results indicated that the LiCoO₂ cathode, rather than graphite anode, was responsible for the performance degradation of the aged cell. This conclusion was confirmed by the structure analysis. The qualitative analysis of the XRD spectra disclosed that the aged cathode exhibited a much larger structure change than the aged anode. We also detected the lithium ions that were irreversibly reserved in graphite anode in XRD and ⁷Li nuclear magnetic resonance (NMR) analysis of aged graphite anode. These results lead us to deduce that the serious structure change in LiCoO₂ cathode was primarily responsible for the performance degradation of the aged cell.     

Simulated low-earth-orbit cycle-life testing of commercial laminated lithium-ion cells in a vacuum

We tested the life cycle of commercial laminated lithium-ion cells with both liquid (LE cells) and polymer (PE cells) electrolytes by simulating a satellite's low earth orbit (LEO) operation under various environmental conditions to develop a power storage system for microsatellites. We completed 4000 cycles, corresponding to about 8 months of LEO satellite operation. The LE cell initially exhibited better performance than the PE cell in a normal atmosphere. However, the LE cell began to expand in a vacuum (about 20 Pa), accompanied by capacity loss and voltage decline at the end of the discharge. In contrast, the PE cell exhibited excellent endurance in a vacuum and maintained high capacity and voltage at the end of the discharge. The reliable cycling of the PE cell in a vacuum was attributed to the adhesive properties of the gel electrolyte that held the laminate film package and active electrode materials together. A comparison of cell performance at various ambient temperatures demonstrated that the proper ambient temperature range for a PE cell is from 10 to 30 °C.     

Development and on-orbit operation of lithium-ion pouch battery for small scientific satellite “REIMEI”

A lithium-ion battery was developed using off-the-shelf pouch cells and launched with a small scientific satellite “REIMEI.” The cells were potted with polyurethane or epoxy resin to protect the battery from vacuum in space. Preliminary experimental test results of pouch cells potted in a soft aluminum cap suggested that the cells tended to swell in vacuum, although they had been reinforced with the resins. Bread board models (BBMs), in which pouch cells were potted with resins in a hard aluminum case, were fabricated for cycle life performance tests in the laboratory. The test results indicated that the performance of epoxy-potted BBM was superior to that of the polyurethane-potted BBM. The measured cell resistance implied that the electrolyte solution leaked through the polyurethane resin, resulting in premature deterioration. The epoxy resin was used for the flight battery. The end-of-discharge-voltage (EoDV) trend of the flight battery on orbit was compared with the laboratory test results corrected based on a post-launch cycle test using a fresh cell. The corrected EoDV trend in the laboratory was in good agreement with the on-orbit trend for the early cycle period, indicating that the on-orbit battery was not inadvertently affected by conditions in space.     

Experimental study on fire extinguishing of large-capacity lithium-ion batteries by various fire extinguishing agents

为研究不同灭火介质对大容量动力锂离子电池火灾的有效性,搭建了适用于多种灭火介质的灭火测试平台。在灭火测试平台上以功率为300 W的电热管作为外热源引发单电池热失控,通过改变灭火介质,研究了不同灭火介质的灭火行为及灭火效率。研究结果表明,对于38 A·h单体动力电池火灾,ABC干粉、七氟丙烷（HFC）、水、全氟己酮和CO₂灭火剂均能快速熄灭电池明火,但CO₂灭火剂灭火后电池出现了复燃;电池灭火过程中,不同的灭火剂在抑制电池温度上升表现出明显差异,其中,抑制温升效果优劣依次为水、全氟己酮、HFC、ABC干粉和CO₂。本研究的结果可为工程应用及电池灭火规范制定提供实验支撑。     

Statistical methodology for predicting the life of lithium-ion cells via accelerated degradation testing

Statistical models based on data from accelerated aging experiments are used to predict cell life. In this article, we discuss a methodology for estimating the mean cell life with uncertainty bounds that uses both a degradation model (reflecting average cell performance) and an error model (reflecting the measured cell-to-cell variability in performance). Specific forms for the degradation and error models are presented and illustrated with experimental data that were acquired from calendar-life testing of high-power lithium-ion cells as part of the U.S. Department of Energy's (DOEs) Advanced Technology Development program. Monte Carlo simulations, based on the developed models, are used to assess lack-of-fit and develop uncertainty limits for the average cell life. In addition, we discuss the issue of assessing the applicability of degradation models (based on data acquired from cells aged under static conditions) to the degradation of cells aged under more realistic dynamic conditions (e.g., varying temperature).     

Graft copolymer-based lithium-ion battery for high-temperature operation

The use of conventional lithium-ion batteries in high temperature applications (>50 °C) is currently inhibited by the high reactivity and volatility of liquid electrolytes. Solvent-free, solid-state polymer electrolytes allow for safe and stable operation of lithium-ion batteries, even at elevated temperatures. Recent advances in polymer synthesis have led to the development of novel materials that exhibit solid-like mechanical behavior while providing the ionic conductivities approaching that of liquid electrolytes. Here we report the successful charge and discharge cycling of a graft copolymer electrolyte (GCE)-based lithium-ion battery at temperatures up to 120 °C. The GCE consists of poly(oxyethylene) methacrylate-g-poly(dimethyl siloxane) (POEM-g-PDMS) doped with lithium triflate. Using electrochemical impedance spectroscopy (EIS), we analyze the temperature stability and cycling behavior of GCE-based lithium-ion batteries comprised of a LiFePO₄ cathode, a metallic lithium anode, and an electrolyte consisting of a 20-μm-thick layer of lithium triflate-doped POEM-g-PDMS. Our results demonstrate the great potential of GCE-based Li-ion batteries for high-temperature applications.     

Electrode structure analysis and surface characterization for lithium-ion cells simulated low-Earth-orbit satellite operation: II: Electrode surface characterization

As a sequence work to investigate the performance-degradation mechanism of an aged commercial laminated lithium-ion cell experiencing 4350-cycle charge–discharge in a simulated low-Earth-orbit (LEO) satellite operation, we performed the surface characterization of LiCoO₂ cathode and graphite anode by Fourier transform infrared-Attenuated total reflection (FTIR-ATR) and X-ray photoelectron spectroscopy (XPS) analysis in this work. Overall, the graphite anode had a larger change in surface chemistry than that of the LiCoO₂ cathode. Except the common surface components, we detected Co metal at the aged graphite surface in the first time. This Co metal deposition was believed to originate from Co²⁺ dissolution from LiCoO₂ cathode during prolonged cycling, and detrimental to structure stability of LiCoO₂ cathode which was a main cause of cell capacity loss. The amount of surface-film component was also estimated by FTIR analysis. Though the total amount of surface film increased, the organic (inorganic) surface film decreased (increased) with prolonged cycling.     

全氟己酮及细水雾灭火装置对大容量三元锂离子电池的灭火实验

本工作搭建了锂电池燃烧-抑制实验平台,以额定容量为150 A·h的三元铝壳动力锂离子电池单体为研究对象,采用电加热方法诱导其发生热失控,研究全氟己酮及细水雾灭火装置对热失控锂离子电池的灭火降温效果,测试了不同工况下的灭火时间、最高温度、质量损失、灭火效率.实验结果表明:标准设计下的全氟己酮灭火装置能够快速灭火,最大降温...     

Inductive modeling of lithium-ion cells

Sandia National Laboratories has conducted a sequence of studies on the performance of lithium ion and other types of electrochemical cells using inductive models. The objectives of some of these investigations are: (1) to develop procedures to rapidly determine performance degradation rates while these cells undergo life tests; (2) to model cell voltage and capacity in order to simulate cell output under variable load and temperature conditions; (3) to model rechargeable battery degradation under conditions of cyclic charge/discharge, and many others. Among the uses for the models are: (1) to enable efficient predictions of battery life; (2) to characterize system behavior.

Inductive models seek to characterize system behavior using experimentally or analytically obtained data in an efficient and robust framework that does not require phenomenological development. There are certain advantages to this. 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 have used artificial neural networks (ANNs) 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 are presented.     

Modeling capacity fade in lithium-ion cells

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.     

Long-term operation of solid oxide fuel cells and preliminary findings on accelerated testing

Stationary applications of Solid Oxide Fuel Cell systems require operating times of 40,000 to 80,000 h for market introduction. Therefore, extended lifetime tests are essential for learning about the long-term behavior and various degradation mechanisms and to foster ideas about accelerated stack testing. The Forschungszentrum Jülich has been gradually extending the testing time, resulting in successful short-stack operating times of between 20,000 and 40,000 h. This work highlights the results of these long-term tests and compares the observations for different material combinations, operating temperatures of 700 and 800 °C, including different fuel utilizations and gas compositions. An increase of temperature from 700 to 800 °C leads to an acceleration of the degradation rate by a factor of 1.5–2. Meanwhile, an increase in fuel utilization from 40 to 80% did not result in increased degradation. The same was found for higher current densities of up to 1 Acm⁻².     

Calendar life performance of pouch lithium-ion cells

An accelerated method was used to determine the effect of temperature, end-of-charge voltage and the type of storage condition over the performance pouch lithium-ion cells. The cells were studied for 4.0 V and 4.2 V end-of-charge voltages (EOCV) both at 5 °C and 35 °C. The irreversible capacity loss of the cell was analyzed every month using a capacity measurement protocol. The results indicated that higher temperature and voltage accelerates the degradation of the cells. The open circuit voltage (OCV) decay of the cells stored under open circuit conditions was also analyzed. The reasons for the irreversible capacity loss, energy loss, OCV decay and the increase in the internal resistance of the cell are discussed in detail. The most detrimental storage condition and the most mild storage condition are identified and discussed in detail.     

Overview and preliminary in orbit behaviour of the lithium-ion batteries used onboard TX-2 satellite

通信技术卫星二号锂离子蓄电池组是我所自主研制的锂离子蓄电池组首次在GEO卫星上应用。卫星对蓄电池组提出了长寿命和高可靠性的技术要求,通过研究分析提出了合理的在轨管理策略和故障隔离技术以满足总体技术要求。同时介绍了通信技术卫星二号锂离子蓄电池组的设计、地面性能测试与考核以及在轨运行验证情况。在轨运行期间,锂离子蓄电池组性能优异,各单体电池之间保持良好的一致性;在轨管理策略合理。遥测数据表明：锂离子蓄电池组在轨运行良好,充分验证了地面设计,为锂离子蓄电池组后续在GEO卫星上的大量应用打下了良好的基础。     

Cycle life performance of lithium-ion pouch cells

Cycle life studies have been done on lithium-ion pouch cell with LiCoO₂ as cathode and meso-carbon micro-beads (MCMB) as anode at five different temperatures. By using the rate capability tests done at the same temperature as that of cycling and the half cell studies done on the fresh and cycled individual electrodes, the stoichiometric windows of individual electrodes at the beginning and at the end of cycling have been estimated. By analyzing these estimates along with the X-ray diffraction studies and half cell studies on cycled cathodes, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and half cell studies on cycled anodes, possible causes of increased capacity fade with increasing temperature were found to be the anode active material loss, probably due to a solvent/salt reduction reaction on the anode. Lithium deposition on the anode also has been identified as a possible side reaction during later stages of cycling at 35 and 45 °C.     

Comparison of the surface changes on cathode during long term storage testing of high energy density cylindrical lithium-ion cells

Nickel-based oxide cathode material taking out from lithium-ion cell after storage for 2 years at 45 °C is analyzed by electron energy-loss spectroscopy in a scanning transmission electron microscope (STEM-EELS) and the result of STEM-EELS is compared with cobalt-based oxide cathode material which is treated as same manor as nickel-based oxide cathode material. The Ni-L_2,3 energy-loss near-edge structure (ELNES) spectra of nickel-based oxide cathode material show peak positions similar to original material before storage. This result indicates that nickel-based oxide material has no significant change in the surface structure. On the other hand, a remarkable shift to low energy is observed in the Co-L_2,3 ELNES spectra of the cobalt-based oxide cathode material after storage. The cycle test at 60 °C under the conditions of aggressive driving cycle (US06) mode for the nickel-based oxide cathode/graphite cell is also carried out. It is clear that cycle performance of the nickel-based oxide cathode/graphite cell is dependent on the depth of discharge (DOD).     

Mechanisms of impedance rise in high-power,lithium-ion cells

Cells were life-cycled cells using profiles with a 3, 6, or 9% change in state of charge (ΔSOC) at 40, 50, 60, and 70 °C. From the voltage response of the cells to the life-cycle profile at each temperature, we separated the overall impedance rise into two simpler terms, R_o (ohmic) and R_p (polarization), using an equivalent circuit model. The R_o data tend to follow the expected trends (40>50>60>70 °C). Although the R_p data trends show that R_p can either decrease or increase asymptotically with time, the overall temperature-dependent behavior is similar to that of R_o. We illustrate the types of processes that can occur in one lithium-ion cell chemistry. Based on the initial rates, the processes are complex. The R_o term dominates the observable cell impedance, but R_p adds a non-trivial contribution.     

Diagnostic examination of thermally abused high-power lithium-ion cells

The inherent thermal instability of lithium-ion cells is a significant impediment to their widespread commercialization for hybrid-electric vehicle applications. Cells containing conventional organic electrolyte-based chemistries are prone to thermal runaway at temperatures around 180 °C. We conducted accelerating rate calorimetry measurements on high-power 18650-type lithium-ion cells in an effort to decipher the sequence of events leading to thermal runaway. In addition, electrode and separator samples harvested from a cell that was heated to 150 °C then air-quenched to room temperature were examined by microscopy, spectroscopy, and diffraction techniques. Self-heating of the cell began at 84 °C. The gases generated in the cell included CO₂ and CO, and smaller quantities of H₂, C₂H₄, CH₄, and C₂H₆. The main changes on cell heating to 150 °C were observed on the anode surface, which was covered by a thick layer of surface deposits that included LiF and inorganic and organo-phosphate compounds. The sources of gas generation and the mechanisms leading to the formation of compounds observed on the electrode surfaces are discussed.     

Experimental triggers for internal short circuits in lithium-ion cells

Lithium-ion cell field failures due to internal short circuits are a significant concern to the entire lithium-ion cell market from consumer electronics to electric vehicles. While the probability of these failure events occurring is estimated to be very low (1 in 5-10 million), the consequences of a cell failure due to an internal short in a high energy battery system have the potential to be catastrophic. The statistical probability of one of these events is very low and they are difficult to predict and simulate in a laboratory using some external test; which makes cell failure due to an internal short circuit a unique challenge to overcome. Several of the experiments designed to simulate internal shorts have been adopted as testing protocols across the industry; in general, they do not accurately simulate an internal short. This work highlights our efforts to experimentally trigger an internal short circuit in a lithium-ion cell.     

Overcharge studies of carbon fiber composite-based lithium-ion cells

Prototype lithium-ion pouch cells of 5.5 Ah have been fabricated with carbon fiber composite anodes, LiCoO₂ cathodes, and LiPF₆ electrolyte to investigate the overcharge characteristics of these cells at the 1C rate. The cells were made with anode to cathode capacity (A/C) ratios of 1.0 and 1.1. The cells were first examined for charge–discharge characteristics at different rates in order to determine the delivered capacity, specific energy and energy density and rate capability, and to ensure that the cells are suitable for overcharge studies. The current, voltage, and temperature responses during overcharge to 12 V were recorded. Maximum temperatures of 65 and 85 °C were observed with the cells with A/C equal to 1.1 and 1.0, respectively. The overcharged cells were dissected in an inert atmosphere and their components were analyzed using scanning electron microscopy and x-ray fluorescence spectroscopy. It is believed that a relatively low amount of heat is generated with carbon fiber composite-based lithium-ion cells and a separator shutdown mechanism is operative in the cell system which prevents fire or explosion during overcharge.