As sensors, wireless communication devices, personal health monitoring systems, and autonomous microelectromechanical systems (MEMS) become distributed and smaller, there is an increasing demand for miniaturized integrated power sources. Although thinfilm batteries are well-suited for on-chip integration, their energy and power per unit area are limited. Three-dimensional electrode designs have potential to offer much greater power and energy per unit area; however, efforts to date to realize 3D microbatteries have led to prototypes with solid electrodes (and therefore low power) or mesostructured electrodes not compatible with manufacturing or on-chip integration. Here, we demonstrate an on-chip compatible method to fabricate high energy density (6.5 μWh cm −2 ·μm −1 ) 3D mesostructured Li-ion microbatteries based on LiMnO 2 cathodes, and NiSn anodes that possess supercapacitor-like power (3,600 μW cm −2 ·μm −1 peak). The mesostructured electrodes are fabricated by combining 3D holographic lithography with conventional photolithography, enabling deterministic control of both the internal electrode mesostructure and the spatial distribution of the electrodes on the substrate. The resultant full cells exhibit impressive performances, for example a conventional light-emitting diode (LED) is driven with a 500-μA peak current (600-C discharge) from a 10-μm-thick microbattery with an area of 4 mm 2 for 200 cycles with only 12% capacity fade. A combined experimental and modeling study where the structural parameters of the battery are modulated illustrates the unique design flexibility enabled by 3D holographic lithography and provides guidance for optimization for a given application.energy storage | microelectronics | miniature batteries | lithium-ion batteries | interference lithography M icroscale devices typically use power supplied off-chip because of difficulties in miniaturizing energy storage technologies (1, 2). However, a miniaturized on-chip battery would be highly desirable for applications including autonomous microelectromechanical systems (MEMS)-based actuators, microscale wireless sensors, distributed monitors, and portable and implantable medical devices (3-8). For many of the applications, high energy density, high power density (charge and/or discharge), or some combination of high energy and power densities is required, all characteristics which can be difficult to achieve in a microbattery due to size and footprint restrictions, and process compatibilities with the other steps required for device fabrication. Although 2D thin-film microbatteries (typical thickness of a few micrometers) can deliver high power, they require large (often cm 2 ) footprints to provide reasonable energies (9). Making the electrodes thicker boosts the theoretical areal energy density but the resultant increases in electron and ion diffusion lengths reduce the effective power and energy densities. Efforts to improve microbattery performance have focused on increasing the electrode surface area and active material loading...

Formation of thick, high energy density, flexible solid supercapacitors is challenging because of difficulties infilling gel electrolytes into porous electrodes. Incomplete infilling results in a low capacitance and poor mechanical properties. Here we report a bottom-up infilling method to overcome these challenges. Electrodes up to 500 μm thick, formed from multi-walled carbon nanotubes and a composite of poly(3,4-ethylenedioxythiophene), polystyrene sulfonate and multi-walled carbon nanotubes are successfully infilled with a polyvinyl alcohol/phosphoric acid gel electrolyte. The exceptional mechanical properties of the multi-walled carbon nanotube-based electrode enable it to be rolled into a radius of curvature as small as 0.5 mm without cracking and retain 95% of its initial capacitance after 5000 bending cycles. The areal capacitance of our 500 μm thick poly(3,4-ethylenedioxythiophene), polystyrene sulfonate, multi-walled carbon nanotube-based flexible solid supercapacitor is 2662 mF cm–2 at 2 mV s–1, at least five times greater than current flexible supercapacitors.

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Water vapor condensation is a ubiquitous process in nature and industry. Over the past century, methods achieving dropwise condensation using a thin (<1 µm) hydrophobic 'promoter' layer have been developed, which increases the condensation heat transfer by 10 times compared to filmwise condensation. Unfortunately, implementations of dropwise condensation have been limited due to poor durability of the promoter coatings. Here, we develop thin film condensation which utilizes a promoter layer not as a condensation surface, but rather to confine the condensate within a porous biphilic nanostructure, nickel inverse opals (NIO) with a thin (<20 nm) hydrophobic top-layer of decomposed polyimide. We demonstrate filmwise condensation confined to thicknesses <10 µm. To test the stability of thin film condensation, we performed condensation experiments to show that at higher supersaturations (0.975 < S < 2.05), droplets coalescing on top of the hydrophobic layer are absorbed into the superhydrophilic layer through coalescence induced transitions. Through detailed This article is protected by copyright. All rights reserved.3 thermal-hydrodynamic modeling, we show that thin film condensation has the potential to achieve heat transfer coefficients approaching ≈100 kW m -2 while avoiding durability issues by significantly reducing nucleation on the hydrophobic surface. The work presented here develops an approach to potentially ensure durable and high performance condensation comparable to dropwise condensation.

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This paper describes a nickel-based cellular material, which has the strength of titanium and the density of water. The material’s strength arises from size-dependent strengthening of load-bearing nickel struts whose diameter is as small as 17 nm and whose 8 GPa yield strength exceeds that of bulk nickel by up to 4X. The mechanical properties of this material can be controlled by varying the nanometer-scale geometry, with strength varying over the range 90–880 MPa, modulus varying over the range 14–116 GPa, and density varying over the range 880–14500 kg/m3. We refer to this material as a “metallic wood,” because it has the high mechanical strength and chemical stability of metal, as well as a density close to that of natural materials such as wood.

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This paper considers a distributed reinforcement learning problem for decentralized linear quadratic control with partial state observations and local costs. We propose the Zero-Order Distributed Policy Optimization algorithm (ZODPO) that learns linear local controllers in a distributed fashion, leveraging the ideas of policy gradient, zero-order optimization and consensus algorithms. In ZODPO, each agent estimates the global cost by consensus, and then conducts local policy gradient in parallel based on zero-order gradient estimation. ZODPO only requires limited communication and storage even in large-scale systems. Further, we investigate the nonasymptotic performance of ZODPO and show that the sample complexity to approach a stationary point is polynomial with the error tolerance's inverse and the problem dimensions, demonstrating the scalability of ZODPO. We also show that the controllers generated by ZODPO are stabilizing with high probability. Lastly, we numerically test ZODPO on a multi-zone HVAC system.