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Exploration missions to the moons of the outer planets (such as Europa) pose unique challenges regarding the design of the spacecraft power source. Current aerospace qualified primary battery technologies cannot adequately meet the mass and volume requirements of proposed missions. Although they have not been used in prior deep space landed missions, lithium carbon-fluoride (Li/CFx) technologies were identified as a potentially viable option, both with and without blends of manganese dioxide (MnO2). To meet the performance requirements over the intended operating conditions of future NASA missions requires further development of this technology, in particular in the delivery of a high specific energy at moderate to low temperatures, and low discharge rates. A cell development effort was therefore pursued with an industrial battery cell manufacturer. Low (50 mA) and medium (250 mA) discharge rates were used to assess the performance of D-size cells under mission relevant conditions, between 0degC and [?]40degC. Select AA-size and C-size cells were also evaluated using similar rates scaled to the lower cell capacities. Developmental Li/CFx-MnO2 D-size cells designed for higher specific energy over these conditions were fabricated and tested, targeting operation between 0 and [?]40degC and a 50 mA constant discharge current, as the baseline operating condition.

Lithium-carbon monofluoride (Li/CFx) D-sized battery cells discharged at very low rates (C/1800) were found to deliver inconsistent capacities. These effects were found to be absent as the discharge rate was increased to C/600. Destructive physical analysis of the cells discharged at C/1800 confirmed the effects of corrosion, manifesting as preferential utilization of the Li anode around the copper current collector, discoloration of the remaining excess Li, and more crucially loss of adhesion to the copper current collector, resulting in a premature completion of discharge. This anomalous behavior may be attributed to the competing corrosion reaction at the Li anode during discharge, whereby Li+is lost to the electrolyte at a rate that is similar to the competing current-producing charge transfer process. At higher rates, this corrosion process is masked by the more significant discharge current generated by the full cell, which occurs at a much higher rate. The inconsistent capacity delivery may relate to the uneven breakdown of the surface film at these very low rates, where the current density is very low. Experimental data from both D-sized and three-electrode cells describing this effect are presented, as well as possible remedies for cells where very low discharge rates are desired.

Rechargeable lithium metal anodes are contenders to supplant carbon anodes, but because of their thermodynamic instability the kinetic stability afforded by solid electrolyte interphase (SEI) layer formed in situ is crucial. Unlike graphite, a stable SEI that facilitates charge transfer is rarely formed on Li in any electrolyte, and requires an “engineered” interface. The interfacial stability of Li can be improved in both liquid and solid electrolytes by thin coatings of AlF3using atomic layer deposition. Its method of deposition and its efficacy to protect Li in acetonitrile, and improve specific capacity and cycle life of lithium-sulfur cells are described.

Exploration missions to the moons of the outer planets (such as Europa) pose unique challenges regarding the design of the spacecraft power source. Current aerospace qualified primary battery technologies cannot adequately meet the mass and volume requirements of proposed missions. Although they have not been used in prior deep space landed missions, lithium carbon-fluoride (Li/CFx) technologies were identified as a potentially viable option, both with and without blends of manganese dioxide (MnO2). To meet the performance requirements over the intended operating conditions of future NASA missions requires further development of this technology, in particular in the delivery of a high specific energy at moderate to low temperatures, and low discharge rates. A cell development effort was therefore pursued with an industrial battery cell manufacturer. Low (50 mA) and medium (250 mA) discharge rates were used to assess the performance of D-size cells under mission relevant conditions, between 0°C and −40°C. Select AA-size and C-size cells were also evaluated using similar rates scaled to the lower cell capacities. Developmental Li/CFx-MnO2D-size cells designed for higher specific energy over these conditions were fabricated and tested, targeting operation between 0 and −40°C and a 50 mA constant discharge current, as the baseline operating condition.

Hydrogen-oxygen fuel cell technology is a critical component for crewed space exploration mission beyond low earth orbit. While lowering platinum loading is of paramount importance for automotive fuel cells, it is not a significant constraint for MEAs used for space applications. As such, support-less platinum black catalysts is a viable choice. Historically, surfactant-stabilized polytetrafluoroethylene (PTFE) emulsion is used as the binder for platinum black electrode. High temperature treatment steps needed for the PTFE emulsion prevents the direct deposition of the electrocatalysts onto the Nafion® membrane. In this study, two alternative materials have been used to replace PTFE emulsion. These include surfactant-free PTFE fine particles and functionalized carbon nanotube with Nafion®. An ultrasonic spray deposition technique was applied to directly deposit support-less Pt black catalyst ink onto the Nafion® membrane. The fabrication process was optimized to produce high performance membrane electrode assemblies that approaching NASA performance target.

The performances of ruthenium oxide-based oxygen evolution catalysts fabricated by various techniques have been studied. A thermal processing technique has been identified that can produce viable iridium and lead-doped ruthenium oxide catalyst. The best oxygen evolution performance was obtained with an iridium-doped ruthenium oxide catalyst with nine molar percent iridium. The cell voltage of the Ir(9)-d-RuO2 catalyst at an applied current density of 200 mA/cm2 was 1.45 volts at 70 oC. The oxygen evolution Tafel slope for doped ruthenium oxide catalysts are in the range of 40 to 55 mV/decade, a minimum of 10 mV/decade lower than what was found for ruthenium oxide.