Gas Generation in Carbon Double-Layer Capacitors
presented at the International Seminar on Double-Layer Capacitors and Similar Energy Storage Devices, December 9-11, 1991
David A. Evans

Introduction

Applications for carbon double-layer capacitors (DLC's) have increased in recent years. The popu larity of these devices is derived from their high energy density relative to conventional capacitors and their long life and high power density rela tive to batteries. Attractive alternatives to batter ies in power back-up circuits, DLCs exhibit vir tually unlimited cyde life and maintenance free operations.

One life-limiting medhanism of commercially available DLG with aqueous electrolytes is electrolyte loss through evaporation, particualrly at elevated operating temperature. One design approadh to extend life and increase temperature range of DLCs is to prevent electrolyte loss by housing the device within a hermetic case (1). Hermetic components of all types are well known in high-reliability designs and for military and aerospace applications.

DLCs fabricated with commercially pure acti vated carbon electrodes generate small quantities of carbon dioxide gas during normal operation, posing a significant problem for hermetic case designs. This paper presents a unique design approach to extending the life of carbon double layer capacitors.

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