Scientists have developed a type of composite graphite anode that will benefit the U.S. space program and private industry by increasing the rechargeability of lithium-ion batteries. Rechargeable lithium-ion batteries, which are used on the space shuttle and Space Station, are also used in laptop computers, portable telephones, and other portable electronic devices.
The chemistry of lithium-ion batteries differs from the chemistries of other types of batteries. The development of the present composite graphite anode addresses one aspect of this chemistry: In a typical lithium-ion cell, a graphite anode is part of a composite that also includes a solid polymer electrolyte of composition [polyacrylonitrile (PAN)-ethylene carbonate (EC)]/[propylene carbonate (PC)-LiPF6]. Reduction of PC on graphite occurs at a potential of about 0.8 V versus Li+/Li, whereas intercalation of Li into graphite takes place at potentials between 0.1 and 0.0 V versus Li+/Li. When, as a result, the PC becomes extensively reduced, there remains little reversible capacity for intercalation of lithium; in other words, the cell loses capacity for recharging.
The scientists found that by adding cyclic ethers to graphite-electrode/[(PAN-EC)/(PC-LiPF6) solid electrolyte] composites, they were able to mitigate the reduction of PC, thereby preserving high capacities for reversible intercalation of lithium into the graphite electrodes. Through their design of the composite graphite anode, these scientists achieved a reversible capacity of close to 1 mole of lithium per six moles of carbon — a remarkable degree of reversibility.
Reversible composite graphite anodes based on this concept can be expected to prove beneficial to the U.S. space program and, indeed, to any commercial venture in which rechargeable lithium-ion batteries are used. While rechargeable batteries based on other chemistries are already available, rechargeable lithium-ion batteries fill a unique niche and are highly marketable. The development of highly rechargeable composite graphite anodes could contribute significantly to success in the future development of portable electronic devices and of systems in which those devices are used.
This work was done by Zhiping Jiang, Kuzhikalail Abraham, and Mohamed Alamgir of EIC Laboratories, Inc., for Johnson Space Center. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp under the Materials category.
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
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Refer to MSC-22789, volume and number of this NASA Tech Briefs issue, and the page number.