Conformal atomic layer deposition of RuOxon highly porous current collectors for micro-supercapacitor applications.

3D porous electrodes have been considered as a new paradigm shift for increasing the energy storage of pseudocapacitive micro-supercapacitors for on-chip electronics. However, the conformal deposition of active materials is still challenging when highly porous structures are involved. In this work, we have investigated the atomic layer deposition (ALD) of ruthenium dioxide RuO2on porous Au and Pt architectures prepared by hydrogen bubble templated electrodeposition, with area enlargement factors ranging from 400 to 10 000 cm2/cm2. Using proper ALD conditions, a uniform RuO2coverage has been successfully obtained on porous Au, with a specific electrode capacitance of 8.1 mF cm-2and a specific power of 160 mW cm-2for a minute amount of active material. This study also shows the importance of the chemical composition and reactivity of the porous substrate for achieving conformal deposition of a ruthenium oxide layer.

Low Temperature Deposition of Highly Cyclable Porous Prussian Blue Cathode for Lithium-Ion Microbattery.

Small dimension Li-ion microbatteries are of great interest for embedded microsystems and on-chip electronics. However, the deposition of fully crystallized cathode thin film generally requires high temperature synthesis or annealing, incompatible with microfabrication processes of integrated Si devices. In this work, a low temperature deposition process of a porous Prussian blue-based cathode on Si wafers is reported. The active material is electrodeposited under aqueous conditions using a pulsed deposition protocol on a porous dendritic metallic current collector that ensures good electronic conductivity of the composite. The high voltage cathodes exhibit a huge areal capacity of ≈650 µAh cm-2 and are able to withstand more than 2000 cycles at 0.25 mA cm-2 rate. The application of these electrode composites with porous Sn based alloying anodes is also demonstrated for the first time in full cell configuration, with high areal energy of 3.1 J cm-2 and more than 95% reversible capacity. This outstanding performance can be attributed to uniform deposition of Prussian blue materials on conductive matrix, which maintains electronic conductivity while simultaneously providing mechanical integrity to the electrode. This finding opens new horizons in the monolithic integration of energy storage components compatible with the semiconductor industry for self-powered microsystems.

High Areal Capacity Porous Sn-Au Alloys with Long Cycle Life for Li-ion Microbatteries.

Long-term stability is one of the most desired functionalities of energy storage microdevices for wearable electronics, wireless sensor networks and the upcoming Internet of Things. Although Li-ion microbatteries have become the dominant energy-storage technology for on-chip electronics, the extension of lifetime of these components remains a fundamental hurdle to overcome. Here, we develop an ultra-stable porous anode based on SnAu alloys able to withstand a high specific capacity exceeding 100 µAh cm-2 at 3 C rate for more than 6000 cycles of charge/discharge. Also, this new anode material exhibits low potential (0.2 V versus lithium) and one of the highest specific capacity ever reported at low C-rates (7.3 mAh cm-2 at 0.1 C). We show that the outstanding cyclability is the result of a combination of many factors, including limited volume expansion, as supported by density functional theory calculations. This finding opens new opportunities in design of long-lasting integrated energy storage for self-powered microsystems.

3D Interdigitated Microsupercapacitors with Record Areal Cell Capacitance.

Due to their high-power density and long lifetime, microsupercapacitors have been considered as an efficient energy supply/storage solution for the operation of small electronic devices. However, their fabrication remains confined to 2D thin-film microdevices with limited areal energy. In this study, the integration of all-solid-state 3D interdigitated microsupercapacitors on 4 in. silicon wafers with record energy density is demonstrated. The device electrodes are composed of a pseudocapacitive hydrated ruthenium dioxide RuO2 deposited onto highly porous current collectors. The encapsulated devices exhibit cell capacitance of 812 mF cm-2 per footprint area at an energy density of 329 mJ cm-2 , which is the highest value ever reported for planar configuration. These components achieve one of the highest surface energy/power density trade-offs and address the issue of electrical energy storage of modern electronics.

Microsupercapacitors as miniaturized energy-storage components for on-chip electronics.

The push towards miniaturized electronics calls for the development of miniaturized energy-storage components that can enable sustained, autonomous operation of electronic devices for applications such as wearable gadgets and wireless sensor networks. Microsupercapacitors have been targeted as a viable route for this purpose, because, though storing less energy than microbatteries, they can be charged and discharged much more rapidly and have an almost unlimited lifetime. In this Review, we discuss the progress and the prospects of integrated miniaturized supercapacitors. In particular, we discuss their power performances and emphasize the need of a three-dimensional design to boost their energy-storage capacity. This is obtainable, for example, through self-supported nanostructured electrodes. We also critically evaluate the performance metrics currently used in the literature to characterize microsupercapacitors and offer general guidelines to benchmark performances towards prospective applications.

3D RuO2 Microsupercapacitors with Remarkable Areal Energy.

Large areal capacitance electrodes made of ruthenium oxide on highly porous gold current collectors are realized by an attractive approach. The hybrid structure exhibits a capacitance in excess of 3 F cm(-2) and an areal energy density for all-solid-state microsupercapacitors that is comparable to those of microbatteries.

Ultrahigh-power micrometre-sized supercapacitors based on onion-like carbon.

Electrochemical capacitors, also called supercapacitors, store energy in two closely spaced layers with opposing charges, and are used to power hybrid electric vehicles, portable electronic equipment and other devices. By offering fast charging and discharging rates, and the ability to sustain millions of cycles, electrochemical capacitors bridge the gap between batteries, which offer high energy densities but are slow, and conventional electrolytic capacitors, which are fast but have low energy densities. Here, we demonstrate microsupercapacitors with powers per volume that are comparable to electrolytic capacitors, capacitances that are four orders of magnitude higher, and energies per volume that are an order of magnitude higher. We also measured discharge rates of up to 200 V s(-1), which is three orders of magnitude higher than conventional supercapacitors. The microsupercapacitors are produced by the electrophoretic deposition of a several-micrometre-thick layer of nanostructured carbon onions with diameters of 6-7 nm. Integration of these nanoparticles in a microdevice with a high surface-to-volume ratio, without the use of organic binders and polymer separators, improves performance because of the ease with which ions can access the active material. Increasing the energy density and discharge rates of supercapacitors will enable them to compete with batteries and conventional electrolytic capacitors in a number of applications.