Evaluation of cellulose-based separators in cycle and wet life testing of alkaline rechargeable cells

A study has been established to determine the dependence of cell cycle and wet life on the source material and composition of cellulose-based separator materials in alkaline rechargeable cells. Silver-zinc rechargeable cells of 28 Ahr capacity, identical in every respect except for the separator composition, are being tested in statistically significant numbers under identical temperature and relative humidity conditions, with 45% KOH as the electrolyte. The cycle life test regime is C/5 discharge to 1.30 V and C/15 charge to 2.03 V continuous cycling, while the wet life test regime includes a 30-day wet stand at full charge between cycles. The purpose of the study is to obtain cycle and wet life data as a function of separator composition and to relate these data to material analysis data on separator properties including degree of polymerization, crystallinity, wet tensile strength, silver penetration rates, etc. The results will be transitioned to manufacture of silver-zinc rechargeable cells in order to obtain assets of optimum life for US Naval Fleet use. Eight separator compositions, all cellulose-based, are being evaluated. This paper discusses the data available to date on cycle and wet life and their relationship to separator properties before and after cycling.