Editorial Feature

Carbon Nanotubes for Energy Storage Applications

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With a diameter range from 0.7 - 50 nanometers and often comprised of a single sheet of pure graphite forming its cylindrical structure, carbon nanotubes (CNTs) exhibit extraordinary properties of strength, thermal and electrical power that have been applied in various fields.

The hexagonal lattice of carbon found in graphite allows the atoms within CNTs to move and vibrate freely, effectively producing electrical charges and thermal energy throughout the tube.

In addition to their high electric conductivity, CNTs have a large surface area, enabling increased electrochemical accessibility, and mechanical, chemical and electrochemical stability. These unique properties create the potential for CNTs to be used as a supplemental material for energy conversion and storage devices.

Lithium-ion Batteries

The lithium-ion battery, which was originally pioneered in 1912 by G.N. Lewis but not made commercially available until the 1970s, is the fastest growing and most promising battery available today. With the greatest electrochemical potential and largest energy density in weight compared to all other metals, lithium-ion is a safe and low maintenance battery option for most electronics on the market today.

Lithium-ion batteries can be separated into three basic components: the two electrodes; the anode (negative electrode), the cathode (positive electrode) and an electrolyte allowing charged ions to flow between the electrodes enabling charge or discharge.

While lithium-ion has several advantages over most other chemistries available for energy storage, it is a fragile chemistry, requiring a protection circuit in order to maintain its safe operation.

Researchers are becoming increasingly interested in developing high-capacity lithium-ion batteries, particularly those with advanced flexibility to allow thin batteries to be incorporated into wearable devices.

Companies, such as Texas based Black Diamond Structures, are looking to incorporate current research on this topic into real-world topics. Through the application of groundbreaking nanotechnology, Black Diamond Structures has integrated nanomaterials into both lead acid and lithium-ion batteries, enabling enhanced energy storage, increased strength, and higher performance.

These batteries are both part of the MOLECULAR REBAR ® technology created by Black Diamond Structures, and they both specifically address the tendency of carbon nanotubes to become entangled, which is a plague of this powerful agent.

Through MOLECULAR REBAR ® products, carbon nanotubes are untangled into discrete individual tubes of a uniform size, allowing their successful incorporation into lead acid and lithium-ion batteries, creating significantly stronger and conductive energy storage products.

The lead acid batteries exhibit a 50% improved cycle life compared to its preceding products, improved cold temperature performance, a 25% improved charge-acceptance, and a stronger resistance to both physical and thermal misuse.

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Hydrogen Storage

Of particular interest for the automotive industry is the storage of hydrogen. Hydrogen is an element with the highest energy per mass of any other fuel, and it has become a key enabling technology.

With its ability to be stored physically either as a gas or a liquid, the storage of hydrogen is particularly difficult due to its low ambient temperature density, often resulting in a low energy per unit volume.

Organizations such as the U.S. Department of Energy’s Fuel Cell Technologies Office conducts research and development activities in an effort to advance hydrogen storage system technology and develop advanced storage materials for this element.

Recent research performed by Woon-Ming Lau and Ka-Wai Wong have achieved successful hydrogen storage and release inside nanocontainers made from single-walled nanotubes.

As a liquid, hydrogen is typically stored in highly pressurized metal tanks, where the tank can account for more than 90% of the total weight of the fuel, neutralizing the high-energy storage capability of hydrogen. With the incorporation of nanotubes, which were used as tiny high-pressure tanks whose ends were sealed with ice, a pressure of 5.0 MPa was successfully stored without any significant leakage.

As nanotechnology continues to spark interest with the scientists of the world, its advances for energy storage purposes are showing extraordinary promise. From its applications in traditional lithium-batteries, to its ability to transform the already revolutionary use of hydrogen energy, the future possibilities of carbon nanotubes for energy storage appear endless.

Sources and Further Reading

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