Workshop coordinator Jeff Brewer has kept this event, now in its 18th year, free to delegates.

The NASA Aerospace Battery Workshop is an annual event hosted by the NASA Marshall Space Flight Center. The workshop is quite a bargain since attendance is free! It is sponsored by the NASA Aerospace Flight Battery Systems Program and has been held in Huntsville, Alabama, for 18 years. Jeff Brewer has been the coordinator for 17 years. Over 120 government and industry scientists and engineers from several countries participated in this year’s workshop.

Michelle Manzo, from NASA Glenn Research Center, was the opening speaker. She gave an introduction to the work being performed by the NASA Engineering and Safety Center’s (NESC) Battery Working Group. The NESC mission is to perform value-added independent testing, analysis, and assessments of NASA’s high-risk projects to ensure safety and mission success. The NESC engages proactively to help NASA avoid future problems.

Gopalakrishna M. Rao, from NASA Goddard Space Flight Center, reported on the wet life of Ni-H2 batteries. Presently, three to five years of wet-life storage is recommended. However, the replacement cells for the Hubble space telescope will have more than eight years of wet-life storage at launch. Final recommendations on the use of these cells will be made shortly.

Hari Vaidyanathan of COMSAT-Lockheed Martin reported that better definition is needed for activation procedures, cell balancing, cell design, charge-discharge rates, and operating temperatures of batteries. In the future, battery guidelines will become part of sub-system procurement documents. According to Barbara McKissock of NASA Glenn, a preliminary draft of a guideline document has been prepared for program managers, payload managers, and technologists. This document is publically available but is not Internet- accessible.

John Weintritt, NASA/ESCG, reported on black spots and corrosion on Li-ion pouch cells. LG and SKC cells did not exhibit spots due to a thicker tab seal and layers of separator outside the stack. Kokam and Saehan and Electrovaya cells had spots after storage. Generally, cells with less than 10kohm insulation resistance show black spots containing P (from LiPF6) and Al.

Judy Jeevarajan, NASA Johnson Space Center, discussed voltage thresholds in Commercial Off The Shelf (COTS) 18650 cells. She said that internal protective devices have limitations. The maximum voltage tolerance varied by manufacturer. The PTC breakdown voltage occurs during a 15A charge. In a battery string, single cell open circuits always activate CID’s. As a general rule, both voltage and current must be specified for safe operations. Eric Darcy added when a PTC is reset, its resistance will double, and its size will expand 5%. Untripped PTC resistance varies for different manufacturers’ cells. PTC activation can damage seals causing shorting and leakage. Moli and Panasonic cells withstand high voltages. Sony and Sanyo cells have unstable AC resistance after their PTC’s are tripped.

Kumar Bugga, Jet Propulsion Laboratory (JPL), gave a report on low-temperature electrolytes. LG-Compact Power cells, using spinel cathodes and ester-based electrolytes, perform well at -50°C. He also said that kinetics are hindered when anode potentials go below Li plating potentials. This occurs during high-rate or low-temperature charge and poor interfacial conditions. The electrolyte, the electrodes, and cathode to anode ratios affect lithium-ion intercalation. Cells were more susceptible to Li plating at -40°C than at -20°C, and plating was strongly associated with C/A ratios greater than one.

Hiroshi Nakahara discussed characterization tests for Quallion’s 15Ah and 72Ah aerospace cells. The program goal was 60,000 cycles at 40% depth of discharge (DOD), low earth orbit (LEO) cycles. These cells are prismatic with specific energy of 150Wh/kg and energy density of 350Wh/L. Their cathode is LiNixCoyAl2O2, and the anode is graphite. A 170mAh cell has reached 18,275 cycles to 90% capacity retention, and they predict 77% capacity retention after 60,000 cycles. Cycling on the 72Ah cell has reached 9,500 cycles, and 75% capacity retention is expected at 60,000 cycles. Batteries -- eight series cells and no balancing circuit -- have reached 11,000 cycles at 24% DOD. After discharge, voltage and temperature of individual cells were within 0.015mV and 2.39°C.

David Carmen gave an update on A123 space batteries that use doped nanophosphate cathodes and graphite anodes in their Li-ion cells. Cells range from 1.1 to 8.8Ah capacity. There is little oxygen evolution or excess lithium. Therefore, these cells are safer during overcharge and can be discharged at 60°C. A123 manufactures in China and Colorado and has a Pack and Systems Group designing electronics for aviation, small trucks, and lead-acid replacements. A 200kW battery for a hybrid bus has been developed for BAE systems and another battery is being developed for Chevrolet.

David Gallup presented battery trends at Yardney/Lithion. which has delivered Li-ion batteries for Mars applications and is continuing development for NASA. Process changes have resulted in beginning-of-life capacity improvements. In 20% LEO cycles, cell lives are projected at over 50,000 cycles. This is above mission requirements. Yardney is developing modular electronics that are external to the battery. They claim rapid field replacement, no depot-level service, and simplified EMI protection. Yardney and BASF have a strategic partnership for materials, with BASF guaranteeing a 10-year supply of cathode material.

Yannick Borthomieu, from Poitiers, France, discussed SAFT’s batteries. Their geosynchronous orbit (GEO), real-time life test has reached 14 seasons. More than 20 cells have had destructive physical analysis (DPA) after LEO and GEO testing. On-orbit data are also being analyzed by SAFT. To date, 19 satellites have been launched with SAFT Li-ion batteries, and the company has more than 1,300 Li-ion cells on orbit. SAFT is researching new materials, including a LiFePO4 cathode, a lithium titanate anode, and an optimized LEO technology with Ni-based oxides.

Tami Max discussed ABSL’s program for qualifying commercial off the shelf (COTS) cells for space. ABSL batteries have powered 32 spacecraft. They have the longest serving LEO battery (six years and 35,000 cycles), and contracts for 80 new applications. ABSL is an outgrowth of COMDEV and AEA in the UK, but it has a US affiliate in Colorado. COTS cells are screened and tested for consistency and are stockpiled in 10,000-cell rolling stocks. Cells are given a final screening prior to use. Their suppliers provide last-time-buy agreements, and there is an ongoing effort to qualify new cells.

On Tuesday evening, a complimentary mixer-reception was held for all attendees. This allowed delegates to discuss the day’s proceedings, to enjoy hors d’oeuvres and dessert, and to socialize with old friends and new acquaintances. Several companies had displays.

Dr. Boris Tsenter opened Wednesday’s sessions with a talk on GEM Power’s intelligent battery management. He was followed by George Altemose of Aeroflex who presented the Aeroflex 8627 Battery Electronics Unit (BEU). This unit is built to meet a Boeing design. Cell balancing is the most important function of the BEU. Cell voltages are equalized within 0.020mV over the 20-year life of the unit.

Jeremy Neubauer, of ABSL Space Products, spoke about the effects of end of charge voltage (EOCV) on COTS 18650 battery management. This test was performed by NAVSEA Crane. EOCVs studied were 4.05V, 3.95V, and 3.85V. Test results show that the lowest EOCV retained the highest capacity. Compared to 4.20V EOCV, fade rates are two times lower at 4.05 and three times lower at 3.85V. In other results, increasing the temperature of discharge to 30°C reduces the life of the battery. During the comment period, Scott Verzwyvelt, of the U.S. Government, commented that the lower EOCV minimizes the reserve on the battery, which is a concern because it can jeopardize the mission.

Vincent Visco of Quallion gave details of the launcher battery pack for the Delta IV rocket. It uses COTS Li-ion cells, in a 9S × 2P array. It is a 32V, 5.4Ah unit. Laser welds are used for cell connections. Cell arrays are packaged in polymer casings with dampening materials and packed within a hermetically sealed housing with temperature sensors and individual cell monitors. The overall weight is 11 pounds with 5 pounds attributed to the cells. Visco claimed that Quallion can design and qualify a new launcher-pack in six months. Dr. Margot Wasz of The Aerospace Corp. commented that the six-month estimate is only for mechanical qualification; full flight qualification will take much longer.

According to Yosuke Osako, Mitsubishi Electric Corp. has developed carbon fiber reinforced plastic (CFRP) modules, which are as strong as and lighter than aluminum. In a thermal vacuum test, the thermal conductivity was 19% better than aluminum, and the thermal conductivity was calculated to be 214W/m°K. However, flatness must be improved.

Walter Tracinski, of Applied Power International (API), reported on tests of the AN-PRC battery pack, which powers a crew survival radio. The 12V battery is a BA-5312/U. It contains 2/3A, Li/MnO2 cells in a 4S × 3P array. The cell string that powers the board is lower in voltage than the other two strings. An inadvertent charge test (2A, 12V limit) resulted in a 65°C temperature increase without fire or flame. The test was repeated to a 48V limit, and some cells vented without flame. A string overdischarge test resulted in reversal to -10V with only one cell venting. An internal short circuit test resulted in venting with flame and peak temperatures of 270 to 290°C. Heat-to-vent tests on single cells resulted in a temperature increase to 145°C followed by venting. Pre mortems showed poor welds that might not survive vibration.

Dr. Margot Wasz, of The Aerospace Corp., discussed the Teflon® emulsions used in the manufacture of hydrogen electrodes for Ni-H2 cells. These emulsions will not be available after 2013. Originally, the electrode processing parameters were optimized for fuel cells. Therefore, little is known about the critical attributes as they relate to Ni-H2 cells. Electrodes containing T30 and TE3859 emulsions were made for Aerospace by Eagle Picher, and these are now being studied. It has been difficult to interpret the data since the normal variation of these parameters was unknown. Tyler Mahy, of the U.S. Government, commented that he has seen poorer performance with the TE3859 material in primary cells at high-rate applications.

Roger Hollandsworth, of Lockheed Martin Missiles and Space, gave an update on the replacement batteries for Hubble. The original batteries have been operating for 17.6 years. The replacement batteries were made from cells produced in 1996. The service mission for battery replacement is scheduled for August 2008. Waivers are needed to use the replacement cells because of extended wet and dry stands. The six batteries in orbit are each delivering an average of 50Ah. Based on trends, the minimum capacity allowed (45Ah/cell) will be reached in 2009. NAVSEA Crane is running stress tests of representative cells. The results are not in agreement. In addition, the voltages of the replacement flight batteries in cold storage are dropping. This is not understood, and it is a concern for Lockheed Martin.

Dr. Margot Wasz also reported on non-destructive evaluation of Li-ion cells. Various Model 18650 cells were tested. Nyquist plots on 1996 vintage Sony cells show the greatest impedance increases from 3.1 to 2.8V. Stored cells show a large increase in impedance in the mid-range frequencies associated with electrochemical behavior. Cycled cells display a shift in high-frequency behavior, and Moli cells show differences from Sony cells.

Judith A. Jeevarajan, of NASA Johnson, presented test results for A123, 2.3Ah, high-rate LiFePO4 cells. The cells were cycled at 60A. Margot Wasz interjected that the cells self-heat after discharge. Dr. Jeevarajan confirmed this observation. The cells were fast-charged to 2Ah at 10°C for 15 minutes, and could be pulsed (130A) at -20°C, but not at -30°C. Continuous discharges below 0°C were poor. In the vent and burst test, the cells vented at 320 to 340psig and burst at 425psig. NASA Johnson requires a larger ratio of burst to vent pressures. During the heat-to-vent test, venting occurred between 130 and 140°C. External short circuit tests resulted in bulging, leakage, and blown vents. The cells vented without fire during overcharge tests. The maximum temperature during overcharge was 300°C.

Dr. Hartley gave an impromptu talk on a four-year student challenge to convert a 2005 Chevrolet Equinox into a hybrid electric vehicle (HEV). Professor Hartley was the faculty advisor for the University of Akron team. Seventeen schools participated in this challenge. The high-voltage DC bus uses ultracapacitors (Nesscap 3500P) and a lead-acid battery pack. The University of Akron did not win the competition, but their submission performed well.

Delegates were treated on Wednesday evening to a reception hosted by Aeroflex. There was a complimentary bar and a light dinner buffet. Aeroflex also held three drawings for two iPods and a digital camera.

Takefumi Inoue, of GS Yuasa Technology, opened Thursday’s session. JSB merged with Yuasa to form GS Yuasa, which produces 50Ah, 100Ah, and 175Ah cells for aerospace applications. Three Li-ion batteries have already been launched, and eight GEO and four LEO batteries will soon be launched. A semi-accelerated GEO test at a maximum DOD of 80% was discussed. Each accelerated season was composed of 42 eclipse days (at 1 cycle per day “real time”) followed by eight days at solstice storage. After 37 seasons, capacity has declined from 108Ah to 75Ah. Thirty-five seasons is equivalent to eight years on orbit. A second test has achieved 29 seasons at a maximum DOD of 70%. The capacity of that cell has dropped from 110 to 88Ah. A real-time LEO test has reached 40,000 cycles at 25% DOD with a capacity drop from 80Ah to 40Ah. A completed LEO test achieved 28,000 cycles at 40% DOD. A float-charge storage test at 15°C and 100% SOC lost 15% of capacity after 80 months of storage. At 5% SOC, the capacity loss was 9%.

Geoff Dudley, of ESA/ESTEC, gave information on a LEO life test of ABSL batteries using Sony 18650HC cells. This test was started in 1999. The battery is an 18Ah, 6S × 12P array. Individual cells can be monitored, one string at a time, and 75,000 cycles have been reached with no string or cell failures. The test is exceeding predictions for fade and impedance growth, but the reasons are not understood. Capacity was measured only at the start of the test. After 73,335 cycles, strings were isolated and capacities ranged from 51.9% to 71.0% of initial capacity. It was concluded that the battery is very robust. In a string, stresses are reduced in the weak cells and increase in stronger cells. Cell balancing may not have improved performance. Finally, ESA is confident that the ABSL, Sony, hard-carbon-cell batteries can support long-range satellite missions.

William R. Bennett, of NASA Glenn, reported on a Li-ion battery demonstration for the 2007 NASA Desert Research and Technology Studies Program. The Quallion test batteries used pouch cells with JPL electrolytes. One of the pouches burned during a crush test due to a hard short. Preliminary and final trials were completed in September 2007. The batteries with the JPL-5 electrolyte performed best, but all electrolytes were good at low-temperatures.

A presentation by Tami Max stated that ABSL has safely built and delivered batteries in excess of 300V for high-voltage, underwater vehicle batteries and space ion thrusters. A 250V to 350V system has been delivered to the Korea Aerospace Research Institute (KARI) using high-power cells. This battery has been fully space-qualified and will be launched in 2008.

Hisashi Tsukamoto, the president of Quallion, shared company news with the delegates. Quallion is expanding their capacity to 1,000 aerospace cells per year. Quallion has a zero-volt storage technology, which prevents capacity loss when cells are stored at 0V. They have a SaFE-LYTE™ flame-retardant additive, a heat absorption material (HAM), and an electron beam treatment that enhances crystallinity of microporous separators.