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Completed TRL 3 (started at 1, targeting 3)
Project Objective
The development of a custom 3D printable solid polymer electrolyte (SPE) for sodium-ion batteries that contains a polymer matrix, a sodium salt, a photoinitiator and optional oxide nanofillers to be used once printed as SPE component (with an ionic conductivity >10-4 S/cm at 90°C) in a classical sodium-ion battery.
Project Description
Constructed more than 20 years ago, the International Space Station’s primary power system originally used nickel-hydrogen batteries with a lifetime of 6.5 years, until NASA began the process of replacing them in 2016 with lithium-ion batteries with a lifetime of 10 years. Besides utilization in the ISS, rechargeable batteries are present in many space applications: they are installed in exploration robots, life support systems and in portable communication devices, to mention some. In this context, this project is focused on the in-space manufacturing of shape-conformable batteries using in-situ resources and aims to address the NASA’s gaps related to the development of next generation of energy storage devices, as well as in-space manufacturing and in-situ resource utilization. The work also tackled the Human Exploration and Operations Mission Directorate (HEOMD) objectives targeting the in-space additive manufacturing (AM) from Lunar/Martian materials (regolith as AM feedstock) to reinvigorate America’s Human Space Exploration Program. This project is specifically dedicated to batteries; it lends itself towards the maturation of in-space manufacturing via 3D printing using in-situ resources, stated in HEOMD and Space Technology Mission Directorate (STMD) goals.
This project paves the way towards in-space/on-surface development of free-form energy storage devices that will better fill unique volumes and save dead space for applications like small spacecraft, portable power devices, robots, and large-scale power systems for Lunar/Martian habitats. These novel complex geometries have the potential to improve their performance and rival traditionally manufactured batteries despite the usual losses associated with additively manufactured materials and 3D printing.
Project Results and Conclusions
Impedance spectroscopy testing of the samples containing a titanium dioxide (TiO2) quantity ranging from 1 - 5% was performed to deduce the percentage exhibiting the highest ionic conductivity. The graphs provided are the result of the testing at 25°C (left) or 80°C (right). One graph represents the summary of the results after taking into account thickness and area of each sample in the ionic conductivity formula. The results indicate that the ideal composition exhibiting the highest ionic conductivity is 1% TiO2. Testing at temperatures between 30°C and 80°C was also performed to samples containing 1% TiO2 that were manufactured either through tape casting or 3D printing with the PRUSA SL1S. The results indicate that 3D printing induces a fractional loss of ionic conductivity, but in general a 3D printed sample and tape casted sample are comparable in performance. Moreover, with increasing temperature, it can be observed that the ionic conductivity increases, which is expected because the components in the mixture become more liquid and movement of sodium ions is more favorable.
Samples were found to be flexible after printing. This feature accommodates the tortuosity of the electrodes with which they may be paired with. However, the interfacial compatibility between these samples and electrodes was not evaluated. After aging in air for one month, the samples did not crumble or lose flexibility but shrank by no more than 5%.
Thermogravimetric Analysis (TGA) under a flow of N2 was performed on tape casted samples containing 1% of TiO2 and repeated three times. The objective was to deduce the temperature that the samples can withstand before losing part of the components as gas within a furnace. It was found that at 150°C approximately 5% of weight is lost, and by 200°C approximately, 20% of weight is lost. Within a battery, we do not expect these results to be identical, given that the battery is a completely closed system. Mechanical testing in the form of tensile tests was performed to 3D printed dogbones obtained with the 1% TiO2 composition with an average ultimate tensile strength (UTS) of 0.54 MPa.
Development of functional solid polymer electrolyte will allow to open operational temperatures for sodium ion batteries. For other type of batteries the process and methodology of manufacturing and binder materials can open the possibility to reduce flammability and the use of aqueous solvents hard to manage in space due to safety concerns when exposed to vacuum. The photopolymerization additive manufacturing technique will open to printability of multilaterals, including ceramics for the generation of complex geometries at fine resolution, although sintering and annealing post-processing will still required for this type of manufacturing technique.
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