Development of a new separator for silver-zinc cells of improved life and energy density

摘要

One of the most serious obstacles to the development of high energy density, long-life, rechargeable silver-zinc cells is the use of cellulosic separators (plain or treated cellophane or sausage casing) which have been employed since thedevelopment of this system. The major disadvantages of the cellulosics are excessive thickness and limited resistance to attack by the alkaline electrolyte, which restrict energy density and wet life, respectively.A separator that promises to overcome those disadvantages was developed by Yardney, in conjunction with the Naval Surface Warfare Center, Carderock Division, and designated at Type 4-B. This material is much thinner than cellophane (approximately 1.5 mils wet vs 3.2 mils) and is not attacked by KOH solutions. It consists of Celgard 3401, to which a Yardney proprietary coating is applied.This separator was first tried on 13 Ah silver-zinc cells, with excellent results. Furthermore, methods were developed for machine coating the Celgard, a necessary step for the large scale manufacture of the 4-B separator. Additional tests are scheduledon larger, 200 Ah cells.Data will be presented showing that the use of 4-B separator allows for increases of 30% in the energy density (Wh/L) and 18% in the specific energy (Wh/kg) of medium rate silver-zinc cells, such as the 200 Ah used in the MK30 MOD 2 torpedo target. The4-B, used in conjunction with Bi{sub}2O{sub}3 additive inthe negative electrodes, is expected to provided 2-3 times the cycle life and twice the wet life of existing cells for the same application.