FEATURE

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A government-industry partnership between Goddard Space Flight Center and Boundless Corporation of Boulder, Colorado, has resulted in a space- and weight-saving battery concept for small satellites (smallsat). In this structural battery concept, battery cells replace "inert" spacecraft structure, accomplishing multiple purposes with one item -- the hallmark of many smallsat innovations.

Batteries Replace "Inert" Structure

The structural battery decreases total mass and volume of the combined battery and structure assemblies because rigid, load-bearing lithium-ion cells form the core of a lightweight sandwich panel that provides structure. Because inert structure is traded away — the dual-function structural battery occupies space normally allocated to single-function structure materials — battery volume effectively becomes very small and both energy density and power density effectively becomes very high. This battery structure, once fully developed, could be used flexibly to replace all or part of a satellite's structure, as required. For example, depending on the requirements for strength and battery performance (capacity and power), active structural battery cells could be interspersed with inert carbon composite. Of course, weight savings is limited by the mass of the inert core structure replaced with useful structural battery.
The key component of the structural battery technology is a partially-saturated carbon fabric composite anode with the dual functionality of strength and lithium-ion intercalation.
Anode development required careful consideration of the matrix resin for stability in the battery, and the carbon fabric for optimum lithium intercalation capacity, strength and electrolyte seal. Details about the selection, methods, and testing of component materials is available from the technologists involved in the project.

Performance

Weight savings is limited by the mass of the replaced inert core structure. As a simple example, if the inert structural mass replaced was one quarter of the battery mass, then the effective specific energy (ESE) would be increased by 20 percent.

In initial tests, the fabric selected demonstrated a charge capacity of 285 mAh/g and an irreversible capacity of seven percent. This approaches the electrochemical performance of the particulate carbon (MCMB) popularly used in lithium-Ion battery anodes, while offering structural performance.

Technology Readiness Level

The structural battery is currently at Technology Readiness Level (TRL) 3. The plan to advance this technology to a TRL of 6 includes:

Application-specific bicells

• Specify size, energy storage, strength

Integrate bicells into structural panel or member

• Parallel/series connections, insulations, cable routing, tie points

Electrical and thermal management

• Algorithms/voltage limits for charging/discharging
• Temperature limits: 20+/- 20 deg C, to be established based on application specifics

Battery testing

• Cycle life testing with application-specific duty cycle and anticipated temperature conditions

Environmental qualification for space

• Launch, thermal vacuum, radiation

Other activities include planning for manufacturability and scale-up of fabrication activities.

Contacts/Credits

Work in the structural battery partnership was shared by engineers at Goddard, including Bob Beaman and Gopal Rao of the Power Systems Branch (563), and personnel at Boundless Corporation including John Olson, Tim Feaver, and Phil Lyman.
Boundless was awarded a Phase I SBIR contract for its work with GSFC on this project and the work was also funded in part by the CrossEnterprise/IRAD program.

Want more? Contact Bob Beaman or Gopal Rao for more details or read the Structural Battery IRAD proposal paper.