Deposition of functional materials on nonplanar surfaces remains a challenge for various applications, including three-dimensional (3D) all-solid-state Li-ion batteries. In this Letter we present a new process to deposit functional oxide materials on high aspect ratio microstructures without the use of vacuum-based deposition methods. Using ultrasonic spray deposition in combination with metal citrate chemistry, we were able to deposit high-quality coatings on Si microcylinders with an aspect ratio of 10. These results were achieved by controlling the precursor chemistry, wetting properties, gel mobility, and precursor decomposition. The versatility of the process was shown by depositing titanium oxide (TiO2), lithium lanthanum titanate (Li0.35La0.55TiO3), and tungsten oxide (WO3) on Si microcylinders of 50 μm length with an intercylinder distance of 5 μm. Finally, a proof of the 3D battery concept was achieved by coating of TiN/Si microcylinders with WO3 using a minimized thermal budget to preserve the (oxidative) TiN current collector. This led to an almost 3-fold electrode capacity enhancement per footprint area, due to the high surface-to-bulk ratio of the 3D coating. Therefore, these results represent a breakthrough in the field of solution-processing of nonplanar microstructures. In addition, the flexibility, low cost, and high scale-up potential of this approach are very promising for various applications requiring coated 3D microstructures.
Integration of electronic circuit components onto flexible materials such as plastic foils, paper and textiles is a key challenge for the development of future smart applications. Therefore, conductive metal features need to be deposited on temperature sensitive substrates in a fast and straightforward way. The feasibility of these emerging (nano-) electronic technologies depends on the availability of well-designed deposition techniques and on novel functional metal inks. As ultrasonic spray coating (USSC) is one of the most promising techniques to meet the above requirements, innovative metal organic decomposition (MOD) inks are designed to deposit silver features on plastic foils. Various amine ligands were screened and their influence on the ink stability and the characteristics of the resulting metal depositions were evaluated to determine the optimal formulation. Eventually, silver layers with excellent performance in terms of conductivity (15% bulk silver conductivity), stability, morphology and adhesion could be obtained, while operating in a very low temperature window of 70 °C-120 °C. Moreover, the optimal deposition conditions were determined via an in-depth analysis of the ultrasonically sprayed silver layers. Applying these tailored MOD inks, the USSC technique enabled smooth, semi-transparent silver layers with a tunable thickness on large areas without time-consuming additional sintering steps after deposition. Therefore, this novel combination of nanoparticle-free Ag-inks and the USSC process holds promise for high throughput deposition of highly conductive silver features on heat sensitive substrates and even 3D objects.
By ultrasonic spray deposition of precursors, conformal deposition on 3D surfaces of tungsten oxide (WO 3 ) negative electrode and amorphous lithium lanthanum titanium oxide (LLT) solid-electrolyte has been achieved as well as an all-solid-state half-cell. Electrochemical activity was achieved of the WO 3 layers, annealed at temperatures of 500 • C. Galvanostatic measurements show a volumetric capacity (415 mAh·cm −3 ) of the deposited electrode material. In addition, electrochemical activity was shown for half-cells, created by coating WO 3 with LLT as the solid-state electrolyte. The electron blocking properties of the LLT solid-electrolyte was shown by ferrocene reduction. 3D depositions were done on various micro-sized Si template structures, showing fully covering coatings of both WO 3 and LLT. Finally, the thermal budget required for WO 3 layer deposition was minimized, which enabled attaining active WO 3 on 3D TiN/Si micro-cylinders. A 2.6-fold capacity increase for the 3D-structured WO 3 was shown, with the same current density per coated area.
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