Rechargeable, thin-film, lithium-based microbatteries of the proposed type would be manufactured in the discharged condition, and lithium anodes would be formed in situ during subsequent charging. In contrast, state-of-the-art rechargeable, thin-film, lithium-based microbatteries are fabricated in the charged condition, with metallic lithium anodes. As explained below, the proposed batteries would offer advantages of safety and manufacturability over the state-of-the-art batteries.
Rechargeable, thin-film, lithium-based microbatteries are potentially useful as power sources on integrated-circuit chips. For example, they could provide standby power for complementary oxide/semiconductor memory chips. The advantages of lithium-based microbatteries over typical power sources include the following:
- They can be fabricated in a variety of shapes;
- Because they are all-solid-state, there is no worry about gaseous components generated during operation;
- They feature high energy and power densities; and
- They can endure large numbers of charge/discharge cycles.
The figure schematically illustrates the structures of cells in alternative versions of the state-of-the-art and the proposed rechargeable, thin-film, lithium-based batteries. In fabricating a state-of-the-art battery, the metallic lithium anodes are formed by chemical vapor deposition (CVD) or sputtering of lithium. The cathodes are made of TiS2 or V2O5. The metallic lithium in the newly formed anodes is very chemically reactive with moisture and air; this poses a danger and can cause loss of usable lithium during later stages of fabrication. The fabrication process is complicated by the requirements of the deposition process and the need to take extreme care for safety and for preservation of the newly deposited lithium.
The difficulty, danger, and complexity by deposition of metallic lithium would not be present in the fabrication of a battery of the proposed type because lithium would not be used in metallic form during the fabrication process. Instead, the usable lithium stock in each cell would be intercalated into a metal oxide to make a cathode of lithiated metal oxide (for example, LiCoO2, LiNiO2, or LiMn2O4). The anode in each cell would be fabricated as either (1) a metallic Cu, Ni, or Ag current-collecting electrode formed by sputtering or CVD; or else (2) an electrode layer of composite material made by mixing a current-collector metal (Cu, Ag, or Ni) with a fully lithiated oxide (e.g., tungsten oxide). During subsequent charging, lithium ions would be deintercalated from the cathode, and metallic lithium would be plated onto the anode; this plating process would constitute the in situ formation of lithium mentioned above.
The solid electrolyte in the proposed cells could be Li3.3PO3.8N0.22, which is used in the state-of-the-art cells. Alternatively, the solid electrolyte could be Li5SiP3or Li8SiP4. If necessary, the proposed microbatteries could be encapsulated with electrically insulating materials. Another option would be the use of carbon as an anode material, though at the present state of development, it appears that the lithiated metal oxides would offer superior performance.
This work was done by Chen-Kuo Huang and Shiao-Ping Yen of Caltech and Jeff Wolfenstine of UC Irvine for NASA's Jet Propulsion Laboratory. For further information,access the Technical Support Package (TSP) free on-line at www.techbriefs.com under the Electronic Components and Circuits category, or circle no. 127 on the TSP Order Card in this issue to receive a copy by mail ($5 charge).
This invention is owned by NASA, and a patent application has been filed. Inquiries concerning nonexclusive or exclusive license for its commercial development should be addressed to
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Refer to NPO-19778.