Tuesday, April 27, 2010

EaglePicher Teams with PNNL to Transform Large-scale Energy Storage

Thin beta-alumina electrolyte membrane used in a new, planar sodium-beta battery design being developed by EPT and PNNL
 Image credit: Pacific Northwest National Laboratory

Renewable energy sources, such as wind and solar power, have the potential to drastically reduce greenhouse gas emissions. But currently the power they produce is too intermittent for utilities to predict when the power will be available. A team of researchers at Pacific Northwest National Laboratory and EaglePicher Technologies, LLC, is developing a next generation large-scale battery that could enable the widespread use of renewable energy sources by providing grid-scale energy storage. Grid-scale storage has the potential to make renewable energy more predictable.

This work is part of an Advanced Research Projects Agency for Energy (ARPA-E), grant awarded to EaglePicher Technologies (EPT), a leading battery developer. The joint EPT- PNNL effort leverages PNNL's extensive experience in fundamental materials science and planar solid-oxide fuel cells with EPT's years of experience in battery systems design and manufacture.

Why it matters:
One of the most promising technologies for large-scale energy storage is the sodium-beta battery; however, current sodium-beta batteries are limited by reliability issues and excessive cost. The next generation of sodium-beta battery being developed by EPT and PNNL incorporates a unique planar design that will greatly simplify manufacturing and enable production of more reliable, scalable, modular batteries at half the cost of today's tubular sodium-beta batteries.

PNNL estimates that the development of reliable and affordable renewable energy storage using the improved sodium-beta battery could reduce carbon dioxide emissions by 150 million tons per year in the United States. An effective large-scale energy storage solution may also enable intermittent renewable energy sources, such as wind and solar, to become base-load generators.

Sodium-beta batteries are electrochemical devices that store energy via sodium (Na+) transport through conductive solid-oxide membranes, or electrolytes. Current sodium-beta batteries are constructed using approximately 3-mm-thick tubular electrolyte elements that require operating temperatures of about 350 degrees C to attain sufficiently rapid Na+ transport and adequate power characteristics in the battery. The high operating temperatures complicate thermal management and create materials stability issues that limit the overall cycle life, resulting in increased costs.

The key to the EPT-PNNL approach is using a planar, stacked, modular battery design that employs thinner electrolyte materials. Fundamental research is being conducted by PNNL to design materials, from the molecular level up, with the desired properties. These materials will enable an estimated 30 percent reduction in operating temperature. Lower operating temperatures lessen the cost of battery construction materials and reduce thermal stress, thus extending battery operating lifetimes and reducing life cycle costs.

The proposed planar batteries have increased active area per volume and decreased diffusion distances, which greatly improve the power characteristics over existing tubular designs. Planar designs also allow greater stacking efficiency, resulting in a 30 percent increase in energy density. Manufacturing processes are simplified and process yields are improved when fabricating planar, rather than tubular, ceramic components, leading to the reduction of fabrication costs by a factor of 10 over current tubular batteries.

What's next
The EPT-PNNL team expects to develop a prototype battery over the next three years. During this time, researchers at PNNL will focus on developing thin ceramic electrolyte materials, planar cell design and fabrication and advanced sealing technology. EPT has the lead responsibility for battery design, systems controls, testing and, eventually, full-scale manufacturing of battery modules.

Acknowledgements: This work is being funded by an award from the Advanced Research Projects Agency for Energy (ARPA-E), led by EaglePicher Technologies.

References: The PNNL team is led by Dr. Gary Yang, Dr. Vincent Sprenkle, Dr. John Lemmon and Dr. Jun Liu. Members of the EPT team include R. David Lucero, Robert Higgins, and James DeGruson.

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