Solid-State Ultracapacitor for Improved Energy Storage

NASAs solid-state ultracapacitor technology is based on the novel materials design and processes used to make the IBLC-type ultracapacitor. The IBLC concept is known to provide outstanding capacitance behavior but has been difficult to reproduce. NASA has developed a careful process to produce dielectric materials to be used in printed electronic applications with reproducibility. An individual cell is created by building electrodes on each side of the dielectric layer, and complete modules can be constructed by stacking multiple cells. Closely related NASA innovations on dielectric and conductive ink (electrode) formulations are key to the ultracapacitor construct, and are included in the technology package. Target performance criteria of this technology include the following: &#8226 Use of standard materials and processing methods &#8226 Robust, solid-state device with no liquid electrolytes &#8226 High-energy densitytarget energy densities of 60 J/cc at a minimum operating voltage of 50 V &#8226 High dielectric breakdown strength (> 25 MV/m) &#8226 Excellent pulse-power performance; rapid discharge and charge &#8226 Reliable performance under repeated cycling (> 500,000 cycles) Additional development work is underway to build and test complete capacitor modules and further improve material properties and performance.

NASA's technology is a dielectric materials formulation comprising polymers, organic binders, solvents, and surfactants, formulated together with a ceramic perovskite nanopowder. The ceramic nanopowder can be optimized for the required dielectric properties of capacitance, voltage breakdown, and leakage. This involves the addition of dopants or the use of advanced coatings on the powder particulates, and subsequent thermal treatments. The rheology of the formulation can be adjusted to work with a variety of coating or printing methods, from conventional thick-film methods to advanced inkjet or direct-write 3D printing methods used for printed electronics. 3D printing provides the ease of printed manufacturing along with the deposition of thinner layers (e.g., 5 microns in thickness vs. 50-100 micron layer via thick-film methods). Individual devices can then be formed in multilayer arrangements, or stacked and packaged as required for the given device application. The ultracapacitor described in MFS-TOPs-75 uses this dielectric material in its assembly. The ink composition is a careful blend of polyimide or polyvinylidene fluoride (PVDF) polymers, solvents, surfactants, and barium titanate nanopowders. Proper ratios are needed for viscosity and processability (e.g., nanopowder wetting and dispersion), along with the optimal ultracapacitor device performance.

The subject technology is an extension of closely related, solid-state ultracapacitor innovations by the same team of inventors. The primary distinction for this specific technology is the addition of co-dopants to affect the dielectric behavior of the barium titanatebased perovskite materials. These co-dopants include lanthanum and other rare earths as well as hydroxyl ions. The materials are processed at the nano scale, and are subjected to carefully designed thermal treatments as well. The presence of the hydroxyl ions has been shown to provide several orders of magnitude increase in the capacitance of the dielectric material. Additionally, these high capacitance values are obtained at relatively low voltages found in current consumer and industrial electronics. The capacitors tested to date are simple, single-layer devices. Ultimately, a range of manufacturing methods are possible for making commercial devices. Features of the technology enable manufacturing via traditional thick-film processing methods widely used in the capacitor industry, or via advanced printing methods for state-of-the-art printed electronics. Future efforts will be made to advance the manufacturing and packaging processes to increase device energy density, including multilayer devices and packages

The NASA technology is based on a perovskite ceramic developed at MSFC, reduced lanthanum barium titanate (rLBT). rLBT is comprised of reduced barium titanate (BaTiO3) doped with lanthanum (La) and co-doped with potassium hydroxide (KOH). rLBT was developed while exploring the suitability of sintered perovskites to produce screen-printed ultracapacitors; the prototypes unexpectedly demonstrated an extreme sensitivity to moisture, prompting exploration of the material for use as a vapor-sensitive dielectric ink. To eliminate inconvenient high temperature firing necessary to produce capacitors, the inventors developed rLBT-loaded polymer composites capable of curing under low heat (110 degrees C) for epoxy or under ultraviolet (UV) light for UV-sensitive resin. At suitable ceramic particle loading concentrations, thin ink layers (30 micrometers) demonstrate RH sensitivity, instantaneously detecting breath vapor (RH change from 30% to 93%) with a recovery time of only 1s. Prototypes demonstrated near log-linear response curves over three orders of magnitude of capacitance with minimal drift (see Figures 1 and 2). NASA’s low temperature dielectric ink for humidity sensing is at technology readiness level (TRL) 4 (component performance has been validated in a lab setting) and the related patent is now available to license. Please note that NASA does not manufacture products itself for commercial sale.

NASA&#8217s conductive ink system is based on a unique combination of commercially available components, including nano-silver/silver alloys suspended in a high-performance co-polymer formulated as an ink vehicle, and combined with various solvent systems, surfactants, and other additives. The formulation can be readily tailored to meet the needs of various printing methods, from high-viscosity, conventional, thick-film screen printing to state-of-the-art, low-viscosity, high-resolution aerosol inkjet and direct-write 3D printing methods. This new, high-performance conductor ink has very advantageous performance characteristics of high conductivity, good surface adhesion to various substrate materials, and good solder coverage and component wetting with common electronics solder materials. These characteristics make the ink a highly desirable and commercially viable material for the development of high-density, high-performance microelectronics with 3D printing and other additive manufacturing processes. The conductor ink formulation exhibits conductivity equivalent to commercially available, conventional, silver thick-film inks. Adhesion to various substrate materials and solderability using lead-tin and silver-bearing electronic solders has been tested and verified.