Nanostructured MnO2-based cathodes for Li-ion/polymer electrochemical cells have been investigated in a continuing effort to develop safe, highenergy-density, reliable, low-toxicity, rechargeable batteries for a variety of applications in NASA programs and in mass-produced commercial electronic equipment. Whereas the energy densities of state-of-the-art lithium-ion/polymer batteries range from 150 to 175 W·h/kg, the goal of this effort is to increase the typical energy density to about 250 W·h/kg. It is also expected that an incidental benefit of this effort will be increases in power densities because the distances over which Li ions must diffuse through nanostructured cathode materials are smaller than those through solid bulk cathode materials.
The developmental MnO2-based cathode nanostructures are, more specifically, layered structures that have compositions of Li x Mn1– y M y O2 (where 0 ≤ x, 0 ≤ y ≤1, and M denotes a dopant metal other than Mn or Li). The average size of crystallites in cathodes made from nanolayered Li x Mn1– y M y O2 was observed to be about 50 nm. The energy densities of these cathodes were found to be approximately 440 W·h/kg. The charge/discharge curves of these cathodes were observed to lie in the potential range of 4.2 to 2 V and to be continuous. The nanostructures were found to be stable and the charge/discharge capacities of the cathodes were found not to fade after multiple charge/discharge cycles (see figure).
The experiments performed thus far have involved small laboratory cells. Further research will be needed to demonstrate practical cells. The tailoring of nanostructures and compositions is likely to be an important topic of research because the electrochemical properties of Li x Mn1– y M y O2 from which the cathodes are made depend on the sizes of the crystallites, and the type and the amounts of dopants.
This work was done by Ganesh Skandan and Amit Singhal of Nanopowder Enterprises Inc. for Johnson Space Center. In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:
Dr. Ganesh Skandan
Nanopowder Enterprises Inc.
120 Centennial Avenue
Piscataway, NJ 08854-3908
Phone: (732) 885-1088
Refer to MSC-23368, volume and number of this NASA Tech Briefs issue, and the page number.