Carbon Nanotubes for Batteries

Carbon Nanotubes for Batteries

Groundbreaking battery technology holds potential to revolutionize powering vehicles.

Spectroscopic image of clusters of rod-shaped particles interspersed with short strands of hair-like materials. Enlarge image

This color-enhanced cross sectional image shows the Fe3O4 nanorods (yellow/blue) and 5 wt % carbon nanotubes (white).
Source: NREL

At about one ten-thousandth the size of a human hair, carbon nanotubes may be miniscule, but they are also mighty. Corral a few billion of them, and their powerful energy-related applications can impact solar cells, wind turbine blades, and batteries.

Materials used for capturing solar and wind energy have long and successful research histories at NREL. Now that success also applies to materials used in batteries.

This happened recently when NREL scientists revealed their groundbreaking findings on metal oxide nanoparticles as high-capacity anode materials. They expanded on that research by employing carbon nanotubes to enhance the performance of batteries. Senior Scientist Anne Dillon leads this effort, which began about 4 years ago.

The goal of the nanotube research was to use carbon nanotubes as the "conductive additive" in electrodes for lithium-ion batteries designed for next-generation vehicles. It was essential that the component materials be inexpensive, nontoxic, and durable—and that the electrode have a high charge/discharge rate and a high reversible capacity. The NREL team accomplished just that by using the properties of long carbon nanotubes with a highly crystalline structure in a two-step process that synthesized nanoparticles of an oxide of iron (Fe3O4) embedded in a "nanotube net." The net can maintain electrical conductivity without a polymer binder, an improvement that enhances the space for active materials in this new electrode to 95% (compared to about 80% for typical electrodes). Better yet, the binder-free electrode is both stable and has a high reversible capacity.

Having achieved this, the scientists moved on to researching the cathode—with equally successful results. They demonstrated that the nanotube net improves conductivity and stabilizes the surface with an astonishing 6-minute charge/discharge rate. This study included the collaboration of Professor M. Stanley Whittingham of the State University of New York at Binghamton, who is widely recognized as the inventor of lithium-ion batteries.

So far, this research has produced one patent and two high-impact articles in Advanced Energy Materials. The two articles were highlighted in "Materials Views" and one made the publication's cover. The NREL research team also made the strategic move of hiring Chunmei Ban, a gifted young scientist. She was a graduate student in the Whittingham group when she came to NREL for a 2-year postdoctoral position. Such was the value of her contribution to this project that she was hired on staff.

Dillon credits the rapid achievements to many things. One is NREL's Laboratory Directed Research and Development (LDRD) program, which backed the first year of research based on the project's innovative concept and considerable upside potential. LDRD projects provide an important mechanism to establish proof of principle of new, innovative concepts.

Another key to advancement is NREL's core expertise in related technologies such as electrochromic windows, which are similar to batteries. Perhaps even more important is NREL's ambience. "We have the facilities we need, a collaborative environment, and a mindset to accomplish things," says Dillon.

This groundbreaking battery technology is currently available for licensing. Potential investors may be concerned that it is too costly based on the necessity of using lasers to produce the nanotubes, but Dillon points out cost advantages related to longer lifetimes and savings on materials. "Our back-of-the-envelope calculations indicate that it may cheaper in the end," she says.

—Susan Moon

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