Battery Developments at the 3rd International Energy Conversion Engineering Conference

Battery technology and use were among the key topics of the 79 papers presented at the 3rd International Energy Conversion Engineering Conference (IECEC) that was held in San Francisco, California, on August 15 to 18. Other topics ranged from results of research in aerospace energy conversion technology to efficient travel in the rising petroleum-cost era. The American Institute of Aeronautics and Astronautics conducts the IECEC, and the IEEE Aerospace and Electronic Systems Society is a participant in this conference.

Our world’s growing consumption has raised the price of energy in gasoline to a level that is higher than the price of the electric energy delivered by many electric utilities. Furthermore, the efficiency of most gasoline engines is less than 30%. The efficiency of an electric-vehicle’s propulsion motor is over 80%. These new energy costs have motivated intense development of battery-powered portable-power systems that were topics of 25 of the 192 technical papers presented at the 3rd IECEC.

The retail price of gasoline, which reached $3.00 a gallon in the United States, has signaled the start of a new era in energy sources and uses. For example, the user of the 33.85 kilowatt-hour of energy in a $3.00-per-gallon gasoline pays 7.09 cents per kWh of energy that he uses in his inefficient car’s engine. The homeowner in the Puget Sound area of the state of Washington pays 6.81 cents a kWh for his electric energy. Electric energy stored in lithium-ion batteries propelled the two-passenger tZero electric car. It traveled 100 miles at a speed of 50 miles per hour and delivered the equivalent of 150 miles per gallon of gasoline.

Speakers from all over the world came to describe new technology for alternatives that can replace the high-cost petroleum products for powering personal and commercial transportation. For example, if the families in China adopted the petroleum-product-consuming lifestyle in the United States, then that nation’s petroleum consumption would exceed today’s output of all the oil wells in the world. China is solving its energy problem by building the 18 gigawatt Yangtze River hydro plant and nuclear power plants, and the nation’s fast-growing production of battery-powered electric bicycles is well over a million per year.

One key motivation for developing new power generation technology is President Bush’s decision to build an inhabited colony on our Moon’s dust-covered surface, where there is low gravity, no air for breathing, no water for use in a power plant, and nighttime lasts two weeks. Dr. Kathie L. Olsen came from the President’s Office of Science and Technologic Policy to describe program plans for getting this base into inhabited operation within 12 years (1). In a morning session M. Piszczor and R. Shaltens from NASA described the basic problems that need to be solved. During this period a new-design nuclear power plant needs to be built and tested to prove its reliability in the Moon’s unique environment. New spacecraft are also being planned for traveling outside of the solar system into interstellar space. Power for their propulsion, control, and communication with earth will not be available from sunlight.

In the text that follows we review battery applications for the coming aerospace missions, like building a colony on the Moon, and exploring the space beyond the outermost solar-system planets. We cite new energy production and use developments that can improve energy efficiency in earth-surface travel.

Restoring Oxygen for Breathing by Lunar Pioneers

Human beings need to breath oxygen which is conveniently available from the our atmosphere. The carbon dioxide (CO2) we breathe out drifts to plant leaves where the carbon is extracted for making carbohydrates, and the oxygen is released for re-use. On the Moon’s surface there are no green-leaf plants, and any released carbon dioxide quickly disappears into deep space. Replacing the lost oxygen from the Earth would require burning fuel by rocket-launching a heavy freight-carrying spacecraft, then decelerating this vehicle for a lunar landing, and again accelerating the empty spacecraft for its return to Earth.

A. Nishimura described work in reforming CO2 into CH4, C2H4 and C2H6 that was done at the Mie University, Tsu, Japan (2). The report indicated that with a TiO2 film the carbon and oxygen could be separated using electrical energy from the lunar colony’s nuclear power plant.

Many developments are required for the lunar colony. The residence for the personnel needs to be equipped with apparatus for extracting oxygen from the carbon dioxide produced by breathing in the living space. Also, water in the sewage will need to be recovered and purified. Suitable electric-propelled vehicles with sealed personnel compartments must be equipped for travel over deep layers of dust. Sites must be constructed for the landing of freight and passenger-carrying vehicles arriving from the Earth. These vehicles would need to be refueled with propellant and oxidizer for their return to Earth.

Power Generation for Lunar Colony

The surface of our Moon has a unique environment for power generation. There is no atmosphere that can supply cooling gasses, so all power losses must be radiated into deep space. During lunar daylight the solar intensity is 135 watts per square foot, and is zero during the half-month nighttime in all regions except near the poles of rotation. During night the surface temperature, when not facing the Earth, is near 0°K. No streams or lakes are available for cooling a power plant’s condensers, so the power plant’s losses must be radiated into space. The surface of the Moon is covered with varying thicknesses of dust.

Continuously available electric power is essential in a lunar colony where nights can be a half-month long. Traditional fuel-burning power plants are not practical because there is no oxygen-containing atmosphere. Huge storage batteries would be needed to store solar-cell generated power for the two-week nighttimes. A conventional nuclear power plant has a water-cooled heat exchanger that condenses the steam turbine’s exhaust. High power-plant efficiency is required to minimize the mass of components that must be accelerated and decelerated in rocket-powered spacecraft during transportation from the Earth to the Moon.

Radioisotope heated thermoelectric generators have produced power for planet orbiting spacecraft and Mars Landers. The power for the Lunar Lander that previously carried astronauts to the Moon’s surface was generated by fuel cells, and batteries propelled the vehicle on which an astronaut traveled briefly on the Moon’s surface. However, fuel cells for a long-duration colony would need a continuing delivery of fuel and oxidizer from the Earth with rocket-propelled spacecraft, so a Moon-surface nuclear power plant appears to be the only practical source of power for the lunar colony.

Lithium-ion Battery’s Mars Success Starts New Battery Development for Space Programs

In the NASA Mars Surveyor Program two paralleled 30 volt, 10 ampere-hour lithium-ion batteries are propelling each of NASA’s Mars Exploration Rovers, “Spirit” and “Opportunity.” They are capturing impressive images and analyzing drillings from Martian rocks. R. Bugga described how these batteries had performed exceptionally well, showing minimal degradation in end-of-discharge voltage, energy efficiency, and low-temperature performance (3). These Rovers have been enabled for the first time by advanced rechargeable lithium-ion batteries and solar-energy recharging systems that operate in a near vacuum at low temperatures. These batteries appear to be capable of extending their Rovers’ data-gathering operation for a second year on Mars.

The success of the Mars Surveyor program has motivated new programs for evaluating lithium-ion batteries for other new space programs. C. Reid described the life-testing at low temperature in a low-Earth-orbit profile to assess a lithium-ion battery’s capability to provide long-term energy storage for aerospace missions (4). Being tested at 0°C is a 28V, 25Ah battery, which is subjected to 9000 charge/discharge cycles that corresponds to 18 months in low-earth-orbit. Capacity, impedance, energy efficiency, end-of-discharge voltage, and voltage dispersions at 1000-cycle intervals were reported.

Li-ion Batteries for Geo-Synchronous Orbit Satellites

In analyzing the applicability of lithium-ion batteries for satellites in geo-synchronous orbits, A. Schoen observed that in most satellites the battery is its heaviest component that can weigh up to 500kg on unmanned satellites (5). The battery also can add significant thermal and power overhead to the satellite. These features increase the cost of the satellite, which can correspond to $40,000 per kilogram and $1,000 per watt. Consequently, in the last 10 years satellite manufacturers have been evaluating the problems that must be solved in replacing conventional satellite batteries with lithium batteries. Pertinent requirements of lithium batteries include battery-charge balancing, overcharge protection, battery reconditioning, and adapting the satellite to a lithium battery. During the last three years these problems have been solved, so several spacecraft now carry lithium batteries and others are in the pipeline.

At Boeing the life qualification process and pack qualification of a lithium-ion battery pack for a long-life geostationary satellite will be completed this year. Qualification of battery electronics will be completed in 2006. This status has led to lithium-ion battery systems being baselined on the Boeing 702 for a 100V bus. Future development aims to improve the power-to-mass ratio, and raise peak-power capability.

In Japan life-testing is already under way on a 100Ah lithium-ion battery for geo-synchronous satellite service. X. Wang reported that their 10-cell battery had an energy density of over 100Wh/kg at the battery level (6). The battery temperature would fall to 15°C during an eclipse, and in the following eight days of sunshine full charge would be reached and stored in the battery that would be at a temperature of 25°C. So far in the testing 18 eclipse seasons have been completed. This corresponds to nine years in geosynchronous orbit. The battery maintained a high voltage of 3.4 volts per cell at the end of discharge, even after a 70% depth of discharge. The voltage dispersion in the cells was within 48 millivolts. The maximum cell temperature was 29°C and the cell-temperature variations were within 4°C during a 70% depth of discharge.

Potential Fuel-Cost Saving in Local Travel

The tZero two-passenger sports car illustrates the possibilities for reducing the energy consumption in personal travel. This car was entered, along with 48 other contestants, in the year-2003 Michelin Challenge Bibendum race’s fuel economy event. Every entrant was required to travel 100 miles at a speed of 45 miles per hour. After crossing the finish line each entrant’s battery was completely discharged to measure the energy that was consumed in this travel. The tZero won the event by traveling the 100 miles in just two hours at an average speed of 50 miles per hour. It consumed 21.7kWh of energy in the process. At eight cents per kWh this electric energy would cost $1.74. This energy consumption corresponds to 153 miles of travel with the energy contained in one gallon of gasoline. The tZero’s energy was carried in a battery pack that contained 8,600 stretched AA-size lithium-ion cells that have lifetimes of over 30,000 charge/discharge cycles. A small on-board power-generating free-piston Stirling engine could increase the tZero’s travel range.

References

The following technical papers are published in the Proceedings of the 3rd International Energy Engineering Conference which was held in San Francisco August 15 - 18, 2005. These Proceedings are published by the American Institute of Aeronautics and Astronautics, 1801

Alexander Bell Drive, Reston, VA 20191-4344.

1. Kathie L. Olsen, U.S. Executive Office of Science and Technology, “Keynote Address on the Administration’s Energy Policy,” at Awards Luncheon.

2. A. Nishimura and Associates, “Influence of Photocatalyst Film Forming Conditions on CO2 Reforming,” (2005-5536).

3. R. Bugga, “An Update on the Performance of Lithium-Ion Rechargeable Batteries on Mars Rovers,” Jet Propulsion Laboratory, Pasadena, CA, 2005-5602.

4. C. Reid, “Low Temperature Low-Earth-Orbit Testing of Mars Surveyor Program Lander Lithium-ion Battery,” NASA Glenn Research Center, Cleveland, OH, 2005-5562.

5. A. Schoen, A. Powers, A. Arastu, S. Canter, and J. Hall, “High Performance Lithium Ion Battery Systems Development for Long Life Geostationary Satellites,” Boeing Satellite Systems, Torrance, CA, 2005-5864.

6. X. Wang, H. Naito, C. Yamada, G. Segami, and K. Kibe, “Cycle-Life Testing of 100-Ah Class Lithium-Ion Batteries in a Simulated GEO Operation,” Japan Aerospace Exploration Agency, Tskuba City, Japan.