NASA LEWIS ADVANCED INDIVIDUAL PRESSURE-VESSEL (IPV) NICKEL-HYDROGEN TECHNOLOGY

Individual pressure vessel (IPV) nickel/hydrogen technology was advanc ed at NASA Lewis and under Lewis contracts. Some of the advancements a re as follows: (i) to use 26% KOH electrolyte to improve cycle life an d performance; (ii) to modify the state-of-the-art cell design to elim inate identified failure modes and further improve cycle life, and (ii i) to develop a lightweight nickel electrode to reduce battery mass, h ence reduce launch and/or increase satellite payload. A breakthrough i n the Low-Earth-Orbit (LEO) cycle life of individual pressure vessel n ickel/hydrogen battery cells was reported. The cycle life of boiler pl ate cells containing 26% KOH electrolyte was about 40 000 accelerated LEO cycles at 80% depth-of-discharge (DOD) compared with 3500 cycles f or cells containing 31% KGH. Results of the boiler plate cell tests ha ve been validated at Naval Weapons Support Center, Crane, IN. Forty-ei ght Ah flight cells containing 26 and 31% KOH have undergone real time LEO cycle life testing at an 80% DOD, 10 degrees C. The three cells c ontaining 26% KOH failed on the average at cycle 19 500. The three cel ls containing 31% KOH failed on the average at cycle 6400. Validation testing of NASA Lewis 125 Ah advanced design IPV nickel/hydrogen fligh t cells is also being conducted at Naval Weapons Support Center, Crane , IN under a NASA Lewis contract. This consists of characterization, s torage, and cycle-life testing. There was no capacity degradation afte r 52 days of storage with the cells in the discharged state, on open c ircuit, 0 degrees C, and a hydrogen pressure of 14.5 psia (1 atm). The catalyzed wall wick cells have been cycled for over 22 694 cycles wit h no cell failures in the continuing test. All three of the noncatalyz ed wall wick cells failed (cycles 9588, 13 900 and 20 575). Cycle-life test results of the Fibrex nickel electrode has demonstrated the feas ibility of an improved nickel electrode giving a higher specific energ y nickel/hydrogen cell. A nickel/hydrogen boiler plate cell using an 8 0 mil (2 mm) thick, 90% porous Fibrex nickel electrode has been cycled for 10 000 cycles at 40% DOD.