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IMPERMEABLE SEALING FOR AIR-TIGHT ENERGY CONVERSION DEVICES

IP.com Disclosure Number: IPCOM000007055D
Original Publication Date: 1993-Oct-01
Included in the Prior Art Database: 2002-Feb-21
Document File: 2 page(s) / 117K

Publishing Venue

Motorola

Related People

Frank R. Denton: AUTHOR

Abstract

Methods for sealing energy conversion cells such as batteries and capacitors have proved critical to their consumer use, particularly for portable batter- ies. Liquid electrolytes typically require stringent sealing (with provisions for venting) to prevent evap- oration and leakage that might endanger consum- ers. If the cell operates at high voltages or employs neat alkali metals, the sealant must not only retain the solvent-salt solution but also exclude moisture, since the presence of water in the cell would result in self-discharge and hydrogen generation through electrolysis of the water.

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MOTOROLA INC. Technical Developments Volume 20 October 1993

IMPERMEABLE SEALING FOR AIR-TIGHT ENERGY CONVERSION DEVICES

by Frank R. Denton

  Methods for sealing energy conversion cells such as batteries and capacitors have proved critical to their consumer use, particularly for portable batter- ies. Liquid electrolytes typically require stringent sealing (with provisions for venting) to prevent evap- oration and leakage that might endanger consum- ers. If the cell operates at high voltages or employs neat alkali metals, the sealant must not only retain the solvent-salt solution but also exclude moisture, since the presence of water in the cell would result in self-discharge and hydrogen generation through electrolysis of the water.

  Developments in solid-state electrolysis have in several instances made it unnecessary to use a can as a container, since leakage will not occur. How- ever, impermeable barrier packaging is still needed to protect the cell from moisture in the ambient atmo- sphere. Lightweight plastic films may serve as sim- ple moisture barriers; using these instead ofa metal can dramatically improve the overall gravimetric energy density~ofthe packaged cell.

  So-called "potato chip bags" are an example of this technology. These are laminates comprised ofa metal foil sandwiched between two plastic films; the laminar sheet may be folded around a cell and heat- sealed to yield a solid-state cell inside an air-filled impermeable envelope. Although these laminar envelopes represent a substantial advance in the tech- nology, the packaging is essentially a balloon: it employs an excess of packaging substance and the trapped air lowers the volumetric energy density of the cells.

  One improvement would be to use shrink-wrap plastic moisture barriers to seal the cell since this minimizes trapped volume. This has at least two disadvantages: (1) the mass of the packaging mate- rial may still approach that of the very light "potato chip bags:' and (2) assembly is complicated because of awkward handling and the vulnerability of the cell to the kind ofheating required to shrink or melt

the plastic wrap.

  Arguably, the ideal way to package solid-state devices with environmental sensitivity is to spray individual cells with a solution that can polymerize instantly on contact to form a tough, impermeable, insoluble thin film, and for which film neither the liquid mist nor the resultant film would react with the battery c...