LabNotes - November 2013

High-Performance Rechargeable Batteries May Help Keep the Lights On

Unlike many commodity-based industries, the energy industry must match with reasonable accuracy the electricity they supply with consumer demand. If supply exceeds demand, the excess electricity is undoubtedly wasted. Demand in excess of supply leads to brown-outs or blackouts when producers cannot send enough electricity through the grid. This has happened during regional heat waves, for instance, when millions of people use their air-conditioning more than anticipated.

Large power plants aren’t very flexible when it comes to changing the rate at which they produce electricity, either. These plants are most efficient when they are operated at a constant rate. Changing the number of megawatts they produce takes time and results in consuming more fuel per megawatt; if they burn fossil fuels, they also emit more carbon dioxide – an environmental pollutant.

Add to these factors the growing desire to reduce carbon dioxide emissions by using renewable resources such as solar and wind energy – which only produce electricity when the sun shines or the wind blows – and it becomes increasingly difficult to provide the level load of electricity that consumers pay for and expect.

To overcome this dilemma, NETL and its Regional University Alliance (RUA) partners have been researching improved battery technologies in order to address these large-scale supply and demand problems, and have made advances that could someday reach the goal of storing large amounts of electricity for use when needed.

Photograph of an NETL-RUA-developed metal chalcogenide cathode. Chalcogenides are chemical compounds containing sulfur, selenium, or tellurium. This cathode was synthesized using a low-cost chemical method developed by this research team. Each of the cubes in the photo is less than one-half of one-millionth of a meter in size.
Photograph of an NETL-RUA-developed metal chalcogenide cathode. Chalcogenides are chemical compounds containing sulfur, selenium, or tellurium. This cathode was synthesized using a low-cost chemical method developed by this research team. Each of the cubes in the photo is less than one-half of one-millionth of a meter in size.

Along with researchers from the University of Pittsburgh and Pennsylvania State University, NETL scientists have embarked on an integrated approach to designing rechargeable magnesium (Mg) batteries for grid-scale electrical storage under the Innovative Process Technologies (IPT) project. Magnesium is an attractive candidate for rechargeable batteries: it is lightweight, abundant, cheap, non-toxic, biodegradable, and offers substantially higher theoretical energy density than lithium (Li). A key ingredient in the rechargeable Li-ion batteries that power consumer electronics, electric and hybrid vehicles, lithium cycles one electron; a Li atom loses one electron at the battery’s anode and gains one electron at the cathode. Magnesium cycles two electrons instead, increasing the current that can travel through the current collectors into the electrodes to provide reversible power.

Despite the advantages of Mg, there are tough technological barriers to overcome. The components of the battery – anode, cathode, electrolyte, and current collector – are made of different materials that react chemically with one another in very specific ways to allow ions and electrons to flow. These reactions must be reversible to regenerate the electrodes during recharging, and the battery must be able to be recharged many times (cycling). Undesirable reactions – such as those that cause corrosion – must be controlled for the battery to continue working over long time periods. Unfortunately, Mg has a tendency to react strongly with many substances, so a major technical challenge is to find compatible materials for the anode/cathode/electrode system.

Electrochemical performance of the NETL-RUA developed cathode. The graph shows that it continues to perform well after many recharging cycles.
Electrochemical performance of the NETL-RUA developed cathode. The graph shows that it continues to perform well after many recharging cycles.

Researchers from Penn State, Pitt, and NETL used an integrated approach to identify and develop compatible components for Mg-ion batteries. To find good materials for current collectors, one studytested several metals (copper, nickel, stainless steel, aluminum, titanium) in a Mg-based electrolyte. Most of these metals corroded quickly, but nickel and titanium showed very high stability and efficiency and would potentially be good choices for manufacturing current collectors for Mg batteries.

Researchers from Pitt and NETL developed several new electrolytes, cathodes, and current collectors that perform better in Mg batteries than others documented in scientific papers, but they also wanted to improve tedious and inefficient synthesis and manufacturing methods. They successfully developed less expensive chemical and mechanical milling methods that have higher yields than current manufacturing methods. These new methods are also scalable – that is, they can be used not only to make small amounts of material to test in a lab, but with suitable larger equipment, they could cost-effectively produce enough material to supply a battery manufacturing operation.

Though the research project has ended, the research team continues to develop patents and reports documenting the significant improvements made in cathodes, current collectors, and electrolytes, adding to the knowledge base about rechargeable magnesium batteries, which may someday play a key role in making our electrical grid smarter.

Contact: David Alman, 541-967-5885


Rocks Demystified in Geomechanical Properties Lab

Someday, should regulation and technology make it attractive, carbon dioxide (CO2) will be captured from power plants and injected deep beneath the surface of the earth. The ability to do this is now much closer to reality than it is to science fiction; and scientists working in the Geological Sequestration Core Flow Lab (GSCFL) at NETL are making it possible to predict how Earth’s rocks will behave when the CO2 is placed in deep storage.

NETL scientist Igor Haljasmaa at work in the Core lab.
NETL scientist Igor Haljasmaa at work in the Core lab.

Contrary to the old adage “solid as a rock,” rocks contain holes that are naturally filled with fluids like air, water, oil, or natural gas. To remove fluids, as we do when recovering oil and natural gas resources, the fluid has to be able to move through the rock. The percent of the rock that is made up of holes – or pores – is its porosity, and the ease with which fluid flows through a rock is its permeability. Under normal geologic conditions, porosity in rocks is less than 20%, and an attractive permeability for recovering fluids is more than 100 millidarcies (a darcy is the unit of measure for permeability). The higher the permeability and porosity, the more appealing the formation is for CO2 storage as well.

Equipment in the GSCFL has recently been significantly upgraded to measure broader ranges of porosity and permeability, as well as other geomechanical characteristics such as sonic velocity, Young’s modulus, and Poisson’s ratio. These measurements can help NETL scientists determine which fluids are in the pores and how the rock reacts to the stress of injecting or withdrawing fluids from the earth, as happens with gas and oil production, hydraulic fracturing of reservoirs, sequestration of carbon dioxide, and in geothermal projects.

Coal seams, brine aquifers, and depleted oil and gas reservoirs have all been suggested as potential storage locations for CO2. Experiments in the lab have shown that most gases, including CO2, combine with coal when injected into pores; this causes the coal to swell – decreasing both porosity and permeability. Reducing these values can decrease the ability to inject CO2 into the formation. Injection into a brine aquifer or depleted reservoir of sandstone, in contrast, would be easy in the short term, but over time the CO2 can affect the minerals cementing the sand grains together. Testing the rocks periodically or in different locations could help determine how far the CO2 has traveled from its injection point, and whether the rock characteristics are changing.

In addition to good porosity and permeability of the rock formation where the CO2 is injected, a primary consideration is that the rock above the injection formation has to provide a barrier or seal that prevents the CO2moving into higher rocks. The GSCFL also tests the “seal” rock to ensure it can withstand the swelling caused by injection of CO2.

The lab’s capabilities are important, says researcher Bob McLendon, “...because information necessary to efficiently and successfully complete fluid injection/extraction projects can be determined.” Samples tested in the lab are cores (cylinders) taken from drilling into the formation where the injection or oil and gas recovery are taking place, or from places where the rocks appear at the earth’s surface. When this information is combined with analyses done in the field at a drilling site, a better understanding of these deep rocks is possible, helping us produce fossil fuel resources responsibly, reduce our carbon footprint, and protect the environment for future generations.

Contact: Robert McLendon, 412-386-5749

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