Portable utility pallet houses regenerative fuel cells to provide power during eclipse periods on planetary surfaces.

Lithium-Ion Battery used in Extravechicular Suit Demonstration

These technologies provide the opportunity to demonstrate dual-use technologies for clean and renewable energy for terrestrial applications as advances envisioned for space use are also expected to provide benefits for homes, cars and other Earth-based applications.

Lithium Ion Batteries

Advanced batteries with high specific energy and long cycle life can extend the range of planetary robots and mobility systems and reduce the mass of landing systems (increasing available payload mass) while adding functionality by providing more power.  For crew excursions, compact spacesuit batteries with even greater specific energy are critical for extending mission durations and therefore scientific return.

Batteries used in automobiles and trucks contain a number of individual cells. Many batteries, such as those found in flashlights (D-cells) and TV remotes (AA-cells), are comprised of just one electrochemical cell. This project is developing advanced cell components (electrode materials, electrolytes and safety devices) for space-rated lithium ion cells with the following enhancements:

• High specific energy - amount of energy per unit mass
• High energy density - amount of energy stored per unit volume
• Cell-level safety – tolerance to electrical and thermal abuse

Fabricating advanced electrodes at Glenn Research Center.  The electrodes are then assembled into cells for further testing.

Cathodes (positive plates), anodes (negative plates) and separators are stacked to form a prismatic cell.  Electrolyte fills the voids and safety components include electrode coatings and electrolyte additives.

To reach our performance goals, we are developing:

• Silicon-composite anodes to significantly improve capacity by developing elastomeric binders and nanostructures to extend cycle life;
• Novel layered-oxide cathodes with lithium-excess compositions to improve capacity; and
• Electrolytes that are stable at high voltages.

To reach our safety goals we are developing:

• Nano-particle circuit breakers to reversibly shut-down the cell in a hazardous situation;
• Flame-retardant electrolytes to prevent fire and flame without degrading battery performance; and
• Cathode coatings to increase the thermal stability of the cell.

These components are being developed individually at a variety of companies and universities, and screened for performance and compatibility at Glenn.  Manufacturability advice is given by an industrial partner, who also scales up the material and builds cells from the components.

	Testing lithium-ion cells to determine the performance of advanced components in a representative system.

Fuel Cells

Shuttle Flight Unit

Fuel cells are enabling technologies for many aspects of lunar surface operations. In applications where electrical power is needed for an extended period of time, fuel cells are a viable option. The total amount of energy available from a fuel cell is dependent on the size of the hydrogen and oxygen reactant tanks. The reactants feed into a fuel cell to produce electricity with drinkable water as a by-product.

Regenerative Fuel Cell (RFC) System.

There are two types of fuel cells. Primary fuel cells convert oxygen and hydrogen into electrical energy and water, but stop producing electricity once the reactant supply is depleted. Regenerative fuel cells produce electrical energy in the same way as primary fuel cells. However, they are also capable of recovering the reactants by using electricity to split the product water molecules into hydrogen and oxygen in a process called electrolysis. For this process, electricity could be provided by solar arrays or a fission power system.

Glenn is currently developing Proton Exchange Membrane (PEM) fuel cell technology in collaboration with the Johnson Space Center, Kennedy Space Center, and Jet Propulsion Laboratory. This fuel cell chemistry is smaller and more efficient than previous types such as the alkaline fuel cells used on the Space Shuttle. Its compact size helps reduce the overall mass and volume of the spacecraft’s power system.

“Non-Flow-Through” Proton Exchange Membrane Fuel Cell System Model

Commercial fuel cells use air as the oxidizer reactant, which has an oxygen content of only 21%. The PEM fuel cells that NASA is developing operate with an oxidizer reactant that is 100% oxygen. This means that the reactant tank only stores pure oxygen, so all of its contents can produce electrical energy (rather than only 21%). Without nitrogen in the tank, the tank can be smaller and more lightweight.

To reduce system mass, volume and parasitic power, and increase system lifetimes even further for both primary and regenerative PEM fuel cells, we are developing “non-flow-through” technology, in which product water generated at the electrode surface wicks across the adjacent gas cavity by capillary action across a screen and through a hydrophilic membrane into a water coolant cavity within each cell of the stack.  There are no recirculating reactants, and hence no requirement for providing either recirculation or external product water separation from two-phase reactant streams.  Therefore, there is no need for the major components that provide these functions, and no resulting weight, volume, parasitic power, reliability, life, or cost penalties.  These major flow-through PEM fuel cell components can comprise 25-35% of total system mass, so their elimination offers a major advantage for non-flow-through systems.

“Flow-through” PEM fuel cell technology is the more conventional approach as it is widely used in terrestrial applications.  This is because terrestrial air supplies must be purged of everything except oxygen, and this purge system can therefore carry away the product water.  Because the reliability of regenerative fuel cells is such a high risk for lunar surface systems,  we have elected to pursue non-flow-through technology based on data indicating that non-flow-through technology should both reduce mass by ~40% and eliminate the life-limiting balance-of-plant components.

Testing hydrogen/oxygen fuel cell system at Glenn Research Center.

Although non-flow-through technology will eliminate ancillary components associated with reactant flow management, the thermal management system for the primary fuel cell and electrolyzer also requires ancillary components. To increase their lifetimes, we have developed passive thermal management technologies to replace current active pumped liquid coolant loops.  These technologies include pyrolytic graphite plates and flat-plate heat pipes for direct insertion into fuel cell and electrolysis stacks, replacing individual cell coolant cavities.
 
The materials from which fuel cells are made must be very durable since pure oxygen is more corrosive than air. The proton exchange membrane, fuel cell channels and other materials wetted by the reactant oxygen must all be corrosion resistant to achieve a fuel cell with long operational life. Catalyst formulations, a critical material in fuel cells, take part in the oxygen-hydrogen reaction to make electricity, but are not consumed during the process. The catalysts must also be resistant to corrosion by the flow of oxygen through the fuel cell.

Summary

Through lithium ion battery and fuel cell technology development efforts, Glenn is addressing critical energy storage requirements for spaceflight applications. Reducing weight and improving overall performance, reliability and safety are critical to the successful deployment of fuel cells and batteries in NASA’s long-term exploration missions

Advanced rechargeable lithium-ion batteries add operational capability for a lunar lander ascent stage. Advanced fuel cell technology provides power to the descent stage and initial power on the lunar surface.

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Contact at NASA Glenn Research Center
Acting Chief,  Advanced Capabilities Project Office: John K. Lytle
Space Flight Systems  Directorate / Advanced Flight Projects Office
216-433-3213