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Thermal batteries are important power sources in applications requiring a long shelf life, fast activation, and reliable power delivery. They operate at high temperatures and utilize molten salt electrolytes, typically eutectic mixtures, which are inert solids at ambient temperatures and provide fast ionic conductivity above the melting point of the salt. The size, energy density, and mechanical properties of thermal batteries are limited by the current manufacturing processes, which are slow and labor-intensive. The development of printable, coated-film electrodes and components will lead to batteries with increased energy density, a more efficient production process, and form factor flexibility. The electrolyte salt (LiCl-KCl eutectic) and MgO separator materials are combined in a single ‘electrolyte binder’ mixture (EB). Slurries were prepared with the EB using DMSO as the carrier solvent and additional dissolved LiCl as a binder for the printed film. The slurries show a large change in viscosity as a portion of the electrolyte dissolves during the mixing process. The initial coarse slurry mixture quickly increases in apparent viscosity before smoothing out into highly shear-thinning suspension with a small overall particle size ( Thermal analysis data indicates that neither the modified salt content nor the dissolution and re-crystallization process significantly alter the melting behavior of the electrolyte salts and separator coatings when compared to the standard thermal battery separator mixtures. Thermogravimetric analysis (TGA) indicates that the solvent is sufficiently removed from the printed films during the drying process, and differential scanning calorimetry (DSC) measurements show that the melting point of the electrolyte in the coated separator film shifts by less than 5ºC, in comparison to the standard LiCl-KCl eutectic mixture. Single-cell electrochemical tests using the combined multi-layer separator/cathode films yielded voltages of >1.9 V delivering a capacity >100 mAh/g and with a lower internal resistance than standard thermal battery cells. Figure 1. Cross-sectional micro-CT image of printed multi-layer electrode, consisting of carbon fiber support with cathode film and separator/electrolyte overcoat. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.This paper describes objective technical results and analysis. Any subjective views or opinions that might be expressed in the paper do not necessarily represent the views of the U.S. Department of Energy or the United States Government. SAND No. SAND2020-5349 A Figure 1

The additive manufacturing of electro-ceramics is a major technological challenge with many possible applications. The technology can prototype and produce in small volume production, custom dielectric, piezoelectric and solid state ionic devices. Sandia National Laboratories was the birthplace of modern, 3-D ceramic additive manufacturing. The newly developed manufacturing methods are considered to be the foundation of 3-D printing via particulate slurries and our spin off company Robocasting Enterprises, is commercially producing dense ceramic and composite parts. These parts are used in various applications including complex geometry catalyst supports and casting filters. This technique is based on the layer-by-layer deposition of highly loaded colloidal slurries that are extruded through a small nozzle. The rheology of the slurry is crucial in order to maintain the structural integrity of the part being built, as Robocasting does not rely on polymerization reactions or solidification to retain shape after extrusion. Since this process is essentially binderless, a dense ceramic part can typically be freeformed, dried, and sintered in less than 24 hours. Although Robocasting is a highly useful technique, it has been optimized for ceramic and composite materials. More recently there has been some work on expanding this technology for use in printing electrode materials. Printing conductors and other structures for electrochemical and electronics using direct write technology gives the potential to reduce production time and reduce waste of expensive material. We have demonstrated that this direct write manufacturing technique can produce Multi-Chip Modules (MCM) by depositing silver and gold on Low Temperature Co-fired Ceramics (LTCC). We have also applied this additive manufacturing technique to our unique design of electrochemical gas sensors. These multi-component mixed potential sensors consist of solid electrodes and a porous electrolyte. In order to expand the versatility of this manufacturing method to be used in solid state ionic devices, slurries of solid electrolytes and electrode materials with specific rheological properties were developed. Another challenge was controlling the residual stress and shrinkage through the material properties of various components. These devices are capable of detecting NOx, hydrocarbons, and NH3 at concentrations on the order of parts per million. The additive manufacturing technique allows for the rapid prototyping of these devices and low volume production of custom devices optimized for specific applications. Figure 1

The fabrication of solid state ionic devices requires customization of size, shape, geometry, and composition for various components. Traditionally used fabrication methods are tape casting and screen printing. Although these methods are well developed they are difficult, time consuming, and costly to adjust to fit particular device requirements. Sandia National Laboratory has recently developed Robocasting, an additive manufacturing technique that was developed as a method that allows for the adaptation needed to rapidly prototype specialty ceramics in a more economically efficient way. Robocasting is currently used commercially to produce complex ceramic parts that are used in various applications including catalyst supports and casting filters. The technology has not been developed for the fabrication of ceramic electrochemical devices. While this has worked well for these limited specific needs, this technology has been optimized primarily for alumina based ceramic materials. In order to expand the versatility of this method for solid state ionic devices, powder precursors of solid electrolytes and electrode materials with specific properties must be developed. Tailoring the rheology of the pastes and slurries used in this extrusion method is an important aspect that determines the resolution of the resulting ceramic components. Another challenge is controlling the residual stress and shrinkage through the material properties of various components. We have applied this additive manufacturing technique to our unique design of gas sensors. These multi-component sensors consist of a yttria-stabilized zirconia substrate onto which a set of three solid electrodes and a porous YSZ electrolyte are deposited. The production method employed involves the direct printing of a suspended powder of the electrode and electrolyte components using Robocasting technology. This allows for the rapid prototyping of these devices. The key to this process is the use of high temperature co-fired ceramics which enables all components to be fired together. The electrodes consist of a platinum counter electrode and lanthanum-strontium-chromite and gold-palladium working electrodes. By taking advantage of the dissimilar electrochemical catalytic activity of these materials, the difference in mixed potential between two electrodes can be used to quantify the concentration and discriminate the type of gas present. These devices are capable of detecting NOx, hydrocarbons, H2, and NH3 at concentrations on the order of parts per million. Figure 1