Larry Whitcanack

Effect of Electrolyte Type upon the High-Temperature Resilience of Lithium-Ion Cells

The effect of electrolyte type upon the resilience of lithium-ion cells to high-temperature storage has been investigated in experimental mesocarbon microbead carbon-Li x Ni y Co 1 - y O 2 three-electrode cells. Specifically, electrolytes have been studied where the solvent mixtures have been varied, with the intention of determining the impact of ethylene carbonate (EC) content upon performance. In addition to determining the reversible and irreversible capacity losses sustained as a result of high-temperature storage (55 to 70°C), a number of electrochemical measurements (ac impedance, Tafel polarization, and linear polarization) have been performed to determine the impact of the high-temperature exposure upon the electrode kinetics and the nature of the electrode surface films. It was observed that cells containing electrolytes with high EC content (i.e., 70% EC by volume) displayed superior resilience to high-temperature storage, in contrast to cells containing low EC content electrolytes (i.e., 30% EC by volume), which displayed much larger irreversible capacity losses and poorer lithium intercalation/deintercalation kinetics after exposure to high temperatures. Solid-state 7 Li nuclear magnetic resonance measurements were used to determine quantitatively the fraction of Li in the irreversible solid electrolyte interphase (SEI) as compared to Li in the active electrode (both anode and cathode) material. In addition, the electrodes were characterized using a scanning electron microscope equipped with an X-ray energy-dispersive spectrometer to examine the film morphology and composition. The results indicate that the nature of the SEI formed on the anode in low EC content cells correlates with the poor electrochemical performance observed after being subjected to high temperatures.

Performance characteristics of lithium-ion cells for NASA's Mars 2001 Lander application

NASA requires lightweight rechargeable batteries for future missions to Mars and the outer planets that are capable of operating over a wide range of temperatures, with high specific energy and energy densities. Due to the attractive performance characteristics, lithium-ion batteries have been identified as the battery chemistry of choice for a number of future applications, including Mars rovers and landers. The Mars 2001 Lander (Mars Surveyor Program MSP 01) will be one of the first missions which will utilize lithium-ion technology. This application will require two lithium-ion batteries, each being 28 V (eight cells), 25 Ah and 8 kg. In addition to the requirement of being able to supply at least 200 cycles and 90 days of operation on the surface of Mars, the battery must be capable of operation (both charge and discharge) at temperatures as low as -20/spl deg/C. To assess the viability of lithium-ion cells for these applications, a number of performance characterization tests have been performed, including: assessing the room temperature cycle life, low temperature cycle life (-20/spl deg/C), rate capability as a function of temperature, pulse capability, self-discharge and storage characteristics, as well as mission profile capability. This paper describes the Mars 2001 Lander mission battery requirements and contains results of the cell testing conducted to-date in support of the mission,.

Performance characteristics of lithium ion cells at low temperatures

The low temperature charge and discharge characteristics of experimental MCMB-Li/sub x/Ni/sub y/Co/sub 1-y/O/sub 2/ cells containing different electrolytes were investigated. The use of low ethylene carbonate (EC)-content electrolyte formulations has resulted in good discharge performance to temperatures as low as -40/spl deg/C. The effect of charge voltage and charge current upon the individual electrode potentials at low temperature was investigated using the three electrode cells (containing lithium reference electrodes). In some cases, lithium plating was observed to occur upon low temperature charge, and found to be facilitated by high charge voltages, high charge currents, and poor anode kinetics. Electrochemical characterization of the cells has helped to establish the conditions under which lithium plating can occur by providing information regarding the polarization effects present at each electrode.

Behavior of Li ion cells in high-intensity radiation environments

Planetary exploration missions to Jupiter and its moons require that the power system components, including batteries, be tolerant to high intensities, about 4 Mrad, of γ-radiation. In view of the several polymeric materials used as separators and binders and the use of organic electrolyte solutions in Li-ion cells, it is difficult to predict their response to such radiation environments. Therefore, a detailed experimental evaluation was undertaken to determine the performance of Li-ion cells after exposure to various levels of cumulative radiation levels up to 25 Mrad, at different levels of intensities. Prototype cells, obtained from two domestic sources for aerospace lithium-ion batteries and consisting of two different chemistries, were used as test articles. Discharge performances, at ambient and low temperatures, as well as, electrical impedance spectroscopy responses were determined after each exposure, and analyses were made for the impedance characteristics and their changes upon irradiation. Postradiation cycling tests were carried out on these cells to assess their cyclability subsequent to radiation exposure. Although control measurements were not made on cells without radiation, these studies reveal that the lithium-ion cells display good tolerance to radiation, with only marginal decline in their capacity, and with no significant change in capacity fade rate during subsequent cycling.

Lithium-ion batteries for aerospace

Under the Mars Surveyor Program (MSP01), lithium-ion batteries were developed by Lithion Inc. (Yardney Technical Products Inc.), each being 28 V, 25 Ah, 8-cells, 9 kg and fully qualified prior to mission cancellation. In addition to the requirement of being able to supply at least 90 cycles on the surface of Mars, the battery was demonstrated to be capable of operation (both charge and discharge) over a large temperature range (-20/spl deg/ to +40/spl deg/C), with tolerance to non-operational excursions to -30/spl deg/ and +50/spl deg/C. After mission cancellation, the batteries delivered to JPL were subjected to generic performance tests to demonstrate the applicability of the technology to meet future NASA aerospace applications. One of the two batteries currently being tested at JPL is undergoing testing according to anticipated performance requirements of future Mars Lander applications. The primary goal of this activity is to determine the performance capability to power surface operation on Mars for a prolonged period (> 3 years) after being subjected to a long cruise period. The second 25 AHr battery is being tested to determine the viability of using lithium-ion technology for future planetary orbiter applications. The test implemented consists of cycling the battery continuously under LEO conditions (30% DOD), while periodically checking the battery impedance and full capacity (100% DOD). Prior to initiating these tests, a number of characterization tests were performed to determine general performance attributes and battery health. In addition to presenting battery data, results obtained with individual cells will also be presented to further describe the capabilities of the technology to meet future applications.

Double-Layer Capacitor Electrolytes Using 1,3-Dioxolane for Low Temperature Operation

Double-layer capacitor electrolytes employing 1,3-dioxolane as a cosolvent with acetonitrile have been evaluated in coin cells using electrochemical impedance spectroscopy and dc charging and discharging tests. Addition of the lower-melting-point 1,3-dioxolane to the standard acetonitrile solvent was found to extend the low-temperature operational range of test cells beyond that of commercially available cells. By adjusting the concentration of the tetraethylammonium tetrafluoroborate salt used, the equivalent series resistance can be minimized to enable optimal power delivery at a given temperature.

An Update on the Performance of Li -Ion Rechargeable Batteries on Mars Rovers

NASA’s Mars Rovers, Spirit and Opportunity have been exploring the surface of Mars for the last thirty months, far exceeding the primary mission life of three months, performing astounding geological studies to examine the habitability of Mars. Such an extended mission life may be attributed to impressive performances of several subsystems, including power subsystem components, i.e., solar array and batteries. The novelty and challenge for this mission in terms of energy storage is the use of lithium-ion batteries, for the first time in a major NASA mission, for keeping the rover electronics warm, and supporting nighttime experimentation and communications. The use of Li-ion batteries has considerably enhanced or even enabled these rovers, by providing greater mass and volume allocations for the payload and wider range of operating temperatures for the power subsystem and thus reduced thermal management. After about 800 days of exploration, there is only marginal change in the end-of discharge (EOD) voltages of the batteries or in their capacities, as estimated from in-flight voltage data and corroborated by ground testing of prototype batteries. Enabled by such impressive durability from the Li-ion batteries, both from a cycling and calendar life stand point, these rovers are poised to extend their exploration well beyond 1000 sols, though other components have started showing signs of decay. In this paper, we will update the performance characteristics of these batteries on both Spirit and Opportunity.

Lithium-ion cell technology demonstration for future NASA applications

NASA requires lightweight rechargeable batteries for future missions to Mars and the outer planets that are capable of operating over a wide range of temperatures, with high specific energy and energy densities. Due to their attractive performance characteristics, lithium-ion (Li-ion) batteries have been identified as the battery chemistry of choice for a number of future applications, including planetary orbiters, rovers and landers. For example, under the Mars Surveyor Program M5P 01 lithium-ion batteries were developed by Lithion (each being 28 V, 25 Ah, 8-cells, and 9 kg) and fully qualified prior to mission cancellation. In addition to the requirement of being able to supply at least 90 cycles on the surface of Mars, the battery demonstrated operational capability (both charge and discharge) over a large temperature range (-20/spl deg/C to +40/spl deg/C), with tolerance to nonoperational excursions to -30/spl deg/C and 50/spl deg/C. Currently, JPL is implementing lithium-ion technology on the 2003 Mars Exploration Rover (MER), which will be coupled with a solar array. This mission has similar performance requirements to that of the 2001 Lander in that high energy density and a wide operating temperature range are necessitated. In addition to planetary rover and lander applications, we are also engaged in determining the viability of using lithium-ion technology for orbiter applications that require exceptionally long life (/spl deg/20,000 cycles at partial depth of discharge). To assess the viability of lithium-ion cells for these applications, a number of performance characterization tests have been performed (at the cell and battery level) on state-of-art prototype lithium-ion cells, including: assessing the cycle life performance (at varying DODs), life characteristics at extreme temperatures (+40/spl deg/C), rate capability as a function of temperature (-30/spl deg/C to 40/spl deg/C), pulse capability, self-discharge and storage characteristics, as well as, mission profile capability. This paper will describe the current and future NASA missions that are considering lithium (Li) ion batteries and will contain results of the cell testing conducted to-date to validate the technology for these missions.

Li-Ion Electrolytes Containing Ester Co-Solvents for Wide Operating Temperature Range

As part of our continuing efforts to develop advanced electrolytes to improve the performance of lithium-ion cells, especially at low temperatures, we have identified a number of electrolyte co-solvents that can be incorporated into multi-component electrolyte formulations for enhanced performance, especially at very low temperatures (down to -70oC). In the current work, we investigated a number of ester co-solvents, namely methyl propionate (MP), ethyl propionate (EP), methyl butyrate (MB), ethyl butyrate (EB), propyl butyrate (PB), and butyl butyrate (BB), in multi-component electrolytes of the following composition: 1.0 M LiPF6 in ethylene carbonate (EC) + ethyl methyl carbonate (EMC) + X (20:60:20 v/v %) [where X = ester co-solvent]. These electrolytes have been optimized to provide good low temperature performance (down to -60oC) while still offering reasonable high temperature resilience to produce the desired wide operating temperature systems (-60 to +60oC). This has primarily been achieved by fixing the EC-content at 20% and the ester co-solvent at 20%, in contrast to the previously developed systems.

Potentiostatic Depassivation of Lithium-Sulfur Dioxide Batteries on Mars Exploration Rovers

NASAs 2003 Mars Exploration Rovers, Spirit and Opportunity, have been performing exciting surface exploration studies for the past 3 years, providing conclusive evidence for the presence of past water on Mars. Although the rovers are being powered by Li-ion batteries and solar arrays, their critical entry, descent, and landing (EDL) maneuvers were successfully supported by primary lithium-sulfur dioxide batteries. These batteries exhibited voltage delay at the end of cruise, which necessitated a depassivation of these batteries prior to EDL. In the absence of conventional depassivation across a specified load, a new method of depassivation via potentiostatic discharge was employed for the mission. Several simulation tests were performed on cells, cell strings, and battery assemblies, at different potentiostatic voltages and durations to characterize the depassivation process. Effects of repassivation of the lithium anode subsequent to depassivation were also studied, mainly to establish the timeline necessary for depassivation prior to use during the EDL process. Finally, a phenomenological model was developed for the potentiostatic depassivation of Li-SO 2 cells, based on dielectric properties of the surface film on Li, which gave voltage predictions in quantitative agreement with the experimental data. The laboratory results obtained were subsequently corroborated by the in-flight data received from the spacecraft.